JP2019099521A - Method for producing 8-prenylnaringenin, antiviral food composition, and antiviral agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method for producing 8-prenylnaringenin. A watermelon preparation step of preparing a watermelon, an extraction step of obtaining a watermelon extract from the watermelon, and a separation step of separating 8-prenylnaringenin from the watermelon extract obtained in the extraction step are performed. It is a method for producing 8-prenylnaringenin, which is characterized by the above. [Selection diagram] FIG. 4

Description

  The present invention provides a novel method for producing 8-prenylnaringenin, an antiviral food composition and an antiviral agent, in particular, a method for producing 8-prenylnaringenin from watermelon as a raw material, and an anti-viral drug for preventing or treating a viral infection. The present invention relates to a food composition for virus and an antiviral agent.

Viral infection is an infectious disease caused by the virus, which is a pathogen present in the environment (air, water, soil, animals, etc.), invading the human body, and it ends in a local epidemic. In some cases, the movement of animals (especially humans) can spread the infection on a global scale and can be a public health problem.
Viruses are tiny parasites, generally of about 0.02 to 0.3 μm in size, mainly composed of the protein shell (capsid) and the nucleic acid (RNA or DNA) inside the shell. There is.
The virus is completely cell dependent for its replication and first adsorbs to the host cell and invades the cell. Then, they are released (unshelled) and replicated in cells and DNA, but in the process, specific enzymes are required. Host cells infected with a virus can not function normally and usually die, and new virus is released from the host cell to further infect other host cells.
Viruses are roughly divided into DNA viruses that have DNA as their genome and RNA viruses that have RNA. Among the RNA viruses, influenza viruses that cause respiratory disease as a representative virus and rota that causes digestive disease Viruses and noroviruses are known.

Influenza virus causes influenza, which is an acute respiratory infection, and millions of influenza patients are reported each winter in Japan, and influenza is associated with high morbidity and mortality. In particular, it is an important disease for infants and the elderly, and the elderly has a high complication rate of pneumonia, and the majority of deaths due to influenza are accounted for by the elderly.
Influenza viruses belong to the Orthomyxoviridae family and are classified into A-type, B-type and C-type according to the difference in antigenicity of nucleoprotein. Among them, glycoproteins on the surface of A- and B-type viruses are highly mutated, which is a cause of many types of influenza. In particular, influenza A virus causes influenza virus infection every year because antigenicity is easily mutated.

In order to prevent influenza virus infection, influenza vaccine is used, and it is common practice to establish immunity against influenza virus beforehand in the body by subcutaneous injection or intramuscular injection of vaccine and to prevent infection. .
In addition, as a therapeutic agent for influenza, for example, amantadine (trade name: Symmetrel), which suppresses virus growth by inhibiting M2 protein necessary for releasing RNA in cells during virus shedding process, is used. There is. In addition, oseltamivir (trade name: Tamiflu) and zanamivir (trade name: Relenza), which suppress virus growth by inhibiting neuraminidase required for virus release from infected host cells in the process of virus release, are used. .

However, in addition to the fact that antigenicity is prone to mutation, it is difficult to predict epidemic antigen types, particularly for influenza A virus, because of the vaccine production time, so an effective vaccine is sufficient. Difficult to manufacture and supply.
In addition, while the efficacy of influenza therapeutic agents has been recognized, there are problems such as side effects and the appearance of resistant strains. In addition, amantadine has the effect of inhibiting M2 protein of A-type virus, but can not bind to protein of B-type virus and has no effect, so the effect is different depending on the type of virus even with the same active ingredient (see Non-patent document 1) .
Influenza is a contagious disease that continues to be a major epidemic today due to its strong transmission power, and is causing enormous damage to society. There are few drugs that are effective and safe for influenza virus, and the appearance of resistant virus is also considered as a problem, so there is a strong demand for development of anti-influenza virus agents with new mechanisms.

Rotavirus is a virus that causes infectious gastroenteritis, which is a digestive disease, and is generally known as a cause of infantile diarrhea and vomiting diarrhea. In particular, infant diarrhea, which occurs in winter, is a severe diarrheal disease that causes fever, vomiting, diarrhea and dehydration mainly for infants younger than 2 years of age.
In Japan, the annual number of patients with rotavirus gastroenteritis is estimated to be about 800,000 and the number of hospitalizations is about 7 to 80,000, and several deaths are reported each year. Rotavirus is highly contagious, and even in a well-developed industrialized country, it is believed that by the age of five almost 100% of humans will be infected with rotavirus once. In the United States, more than 500,000 people visit the hospital with diarrhea mainly annually, and especially children are prone to severe diarrhea, and about 10% of affected patients are said to be hospitalized. It is thought that there are regional differences, but it is believed that about 700,000 people die each year worldwide.
According to epidemiological surveys in developed countries, improvement in hygiene can not reduce the prevalence of rotavirus. In addition, although a vaccine for rotavirus has been developed for the time being, there are ineffective types and recombinant forms of the vaccine, and so countermeasures are required. Therefore, development of a novel mechanism of rotavirus therapeutic agent is expected.

Norovirus is a virus that causes infectious gastroenteritis, which is a digestive disease, and causes food poisoning due to the feeding of shellfish such as oysters, feces and feces of infected human beings, or they become dry. Oral infection via dust from things. Mass infection with Norovirus spp. Occurs sporadically in schools, infants' facilities and facilities for the elderly around the world, and there are cases of severe death from dehydration.
Norovirus infections tend to increase in recent years, and noroviruses may be repeatedly mutated to cause human-to-human transmission, and are often prevalent because they do not have antibodies against new types of norovirus. However, some vaccines against norovirus are still effective and are still in development, and development of norovirus vaccines and development of novel mechanisms of norovirus therapeutic agents are expected.

On the other hand, in recent years, a wild-type watermelon (Citrus lanatus: Citrullus lanatus) containing a high concentration of citrulline, which is a kind of free amino acid, has attracted attention.
As a representative of wild watermelons, Botswana native watermelons that are native to the Kalahari desert of Africa are known, and unlike watermelons adapted to the relatively mild environment in Japan, to survive severe desert environments It has an environmental stress tolerance ability (see Non-Patent Document 1).
Wild watermelon accumulates high levels of citrulline and is superior in its ability to protect itself from strong ultraviolet light and its ability to retain water, so elucidation of the mechanisms of various functions and functional expression and thus this substance Development of the usage of

For example, Patent Document 1 discloses an active oxygen scavenging agent and a moisturizing agent, each containing a flesh extract of wild type watermelon as an active ingredient. And, using the extract of wild type watermelon itself as an active oxygen scavenging agent is about 10 times higher in active oxygen scavenging activity than using citrulline contained in the flesh of wild type watermelon alone. It has been revealed that the extract of flesh of the seed watermelon has a high moisturizing effect.
Moreover, the melanin production inhibitor which uses the extract of a wild type watermelon as an active ingredient is mentioned to patent document 2. FIG. And it has also become clear that the leaf extract has a superior active oxygen scavenging action and a tyrosinase inhibitory action than the flesh extract of wild type watermelon.

  The functionality of the wild watermelon extract is believed to be due in part to the accumulation of high concentrations of citrulline, but for the most part to unidentified substances. Then, only a part of the functionality of the extract of wild watermelon has been clarified, and elucidation of functions other than the above-mentioned functions and development of usage of this substance are expected.

Patent No. 4887499 JP 2007-197360 A

Yokota et al .: Annals of botany 89: 825-832 (2002)

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a novel 8-prenylnaringenin.
Another object of the present invention is to provide an antiviral food composition and an antiviral agent which are novel methods of using 8-prenylnaringenin.

  As a result of intensive studies, the inventors of the present invention have shown that watermelon, particularly wild watermelon extract, contains 8-prenylnaringenin, and 8-prenylnaringenin is a virus, in particular, the growth of influenza virus, rotavirus and norovirus, which are RNA viruses. Have been found to have the effect of inhibiting

Therefore, according to the method for producing 8-prenylnaringenin according to the present invention, the subject is a watermelon preparation step of preparing watermelon, an extraction step of obtaining a watermelon extract from the watermelon, and the watermelon obtained in the extraction step And a separation step to separate 8-prenylnaringenin from the extract.
At this time, it is preferable that the watermelon is Citrullus lanatus.
At this time, the Citrullatus lanatus may be a wild watermelon derived from the Kalahari Desert, Africa.
At this time, it is preferable that the watermelon extract is a fruit juice obtained from the fruit of Citrullus lanatus.
At this time, the fruit may include the flesh, peel and seeds of the fruit.

Moreover, according to the food composition for antivirals of the present invention, the above-mentioned subject is solved by containing 8- prenylnaringenin as an active ingredient, and using for prevention or amelioration of a virus infection.
According to the above configuration, for example, when 8-prenylnaringenin is administered to a human, particularly a virus-infected patient, 8-prenylnaringenin acts to inhibit viral growth in vivo, so the present invention is used as a preventive or therapeutic agent for viral infection. It can be used as
And, by administering 8-prenylnaringenin, the inhibitory effect on virus growth is improved.
And it can be suitably used as an agent for preventing or treating influenza virus infection, rotavirus infection or norovirus infection, which causes serious damage to society by the strong transmission power among virus infections.

  In addition, an antiviral food composition containing 8-prenylnaringenin as an active ingredient and used for the prevention or treatment of infectious gastroenteritis, and an antiviral food composition used for the prevention or amelioration of viral infections are also provided. can do.

According to the present invention, it is possible to provide a process for producing novel 8-prenylnaringenin.
In addition, it is possible to provide an antiviral food composition and an antiviral agent which are novel methods of using 8-prenylnaringenin.

It is a flowchart which shows the manufacturing method of 8- prenyl naringenin of this embodiment. It is a graph which shows the result of the fractionation test of the anti-influenza component examined in the test 1. It is a chromatogram of 8- prenylnaringenin standard solution (0.1 ng / mL) which measured in test 3. It is a chromatogram of the test solution which measured in test 3. It is data which show the result of influenza virus growth inhibition rate by 8-prenylnaringenin (8-PN) which measured in test 4. FIG. 16 is data showing the results of MTT assay of 8-prenylnaringenin, which was measured in Test 5. FIG. Data showing the results of growth inhibition test at adsorption period, culture period, adsorption period and culture period of influenza virus by 8-prenylnaringenin, which were measured in Test 6, and in different periods during culture of influenza virus infected cells, 8 -Data showing results of influenza virus growth inhibition test when prenylnaringenin is added.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6.
The present embodiment relates to a method of producing 8-prenylnaringenin from watermelon.
In addition, this embodiment is an antiviral characterized in that 8-prenylnaringenin is used as an active ingredient, and administration to a human inhibits growth of a virus in the human body to be used for the prevention or treatment of a viral infection. The invention relates to a food composition and an antiviral agent.

<8- Prenylnaringenin>
8-Prenylnaringenin (CAS Registry Number: 53846-50-7) has a structure in which a prenyl group is bound to the 8-position of the flavonoid (flavanone) naringenin as shown in the following structural formula (Formula 1) ing. Here, the prenyl group is a generic term for a structural unit composed of an isoprene unit having 5 carbon atoms, and one having 5 carbon atoms (C5) is called a dimethylallyl group.

  8-prenylnaringenin (8-PN) is also referred to as flavaprelin, (S) -8-dimethylallynalingenin ((S) -8-dimethylallylnaringenin), hopane (hopein), sophoraflavanone B, etc. .

Watermelon
In the method for producing 8-prenylnaringenin according to the present invention, "watermelon" as a raw material of 8-prenylnaringenin is a perennial herb classified as a Cucurbitaceae watermelon genus, and mainly uses fruits as edible. Plants grown for
Among watermelons, "wild watermelon" is, in particular, native to Botswana naturally grown in the Kalahari desert of Africa, and includes cultivated products. In addition, it also includes watermelons of other wild species that are native to arid and desert areas.
Watermelon also includes those obtained by genetic methods such as recombination, transduction, transformation and the like.

The flesh portion of watermelon contains about 90% of water, and its juice contains about 6% of carbohydrate and a small amount of citrulline, malic acid, arginine, potassium, and the pigments include lycopene and carotene. It is included. In addition, the seeds contain about 20% fat and about 50% or more protein, and also contain phytosterose, urease and the like.
Focusing on citrulline among them, wild watermelon contains about 20 to 200 mg of citrulline per 100 g.
In addition to the ingredients contained in normal watermelon, wild watermelon has an action and effect that is completely different from that of ordinary watermelon, which is produced by highly concentrated citrulline and unidentified active ingredients.

Also, focusing on the sugar content of the flesh portion of watermelon, the sugar content of ordinary watermelon is about 5.03% for fructose, 1.57% for glucose, and 0.98% for sucrose. (Watermelon ingredients and effects: Sugawara Farm Co., Ltd.), the sugar content of wild watermelon is about 0.50 to 1.00% fructose, about 0.30 to 0.60% glucose, and about 0 sucrose .05% or less.
As described above, since wild watermelons have low sugar concentration and low sweetness, the available range is very wide compared to normal watermelons.

<Method for producing 8-prenylnaringenin>
In the method for producing 8-prenylnaringenin according to the present embodiment, a step of preparing a watermelon, an extraction step of obtaining a watermelon extract from the watermelon, and 8-prenylnaringenin from the watermelon extract obtained in the extraction step And separating.
Hereinafter, each process will be described in detail with reference to FIG.

(Watermelon preparation process)
At a watermelon preparation process, the watermelon used as the raw material of 8- prenylnaringenin is prepared (step S1).
The raw material watermelon is preferably Citrullus lanatus, especially wild watermelon from the Kalahari Desert of Africa.

(Extraction process)
In the extraction step, a watermelon extract containing 8-prenylnaringenin is obtained from the watermelon prepared in the watermelon preparation step (step S2).

  "Watermelon extract" refers to those extracted from watermelon, and includes watermelon fruit, mashed fruit, fruit juice obtained by squeezing fruit, residue remaining after squeezing fruit, these fruit It contains the mash and juice, and the filtrate obtained by filtering the residue or the supernatant obtained by centrifugation.

Moreover, the extract extracted with a polar solvent or a nonpolar solvent etc. is also included. When a polar solvent is used as an extraction solvent, for example, water, a hydrophilic organic solvent and the like can be mentioned, and it is preferable to use these alone or in combination of two or more at room temperature or at a temperature below the boiling point of the solvent.
Examples of hydrophilic organic solvents include lower aliphatic alcohols having 1 to 5 carbon atoms such as methanol, ethanol, propyl alcohol and isopropyl alcohol; lower aliphatic ketones such as acetone and methyl ethyl ketone; 1,3-butylene glycol, propylene glycol, glycerin And C.sub.2-C.sub.5 polyhydric alcohols and the like.
The extraction solvent and the extraction means are not particularly limited as long as they can extract 8-prenylnaringenin, and any solvent and means may be used.

  The watermelon extract may be used after concentration or drying, but may be used as it is, or may be used after dissolving or suspending the concentrate or the dried product in a suitable solvent. In addition, the obtained extract may be used by obtaining a fraction having an antiviral activity, using known purification methods such as liquid chromatography, and purifying it.

  Here, in the method for producing 8-prenylnaringenin according to the present embodiment, it is preferable to use watermelon fruit as an extract of watermelon, more preferably squeezed in a state including fruit skin, peel and seeds as well as fruit. It is good to use (squeezed) as juice. More preferably, the juice is ultrafiltered and used as an extract. Alternatively, a residue (other than fruit juice) remaining after squeezing the fruit may be used, and in that case, it is preferable to use a residue obtained by drying the residue (powder of the residue). Alternatively, fruit, fruit juice or extract may be used as a commercially available watermelon extract, in which case it is preferable to use a concentrated watermelon extract.

(Separation process)
In the separation step, 8-prenylnaringenin is separated from the watermelon extract obtained in the extraction step (step S3).
The method of separation (fractionation) is not particularly limited as long as 8-prenylnaringenin can be separated, but, for example, suitable separation means (eg, partition extraction, gel filtration, silica gel chromatography, reverse phase) Or a method of obtaining a fraction having a high 8-prenylnaringenin fraction by normal phase high performance liquid chromatography (HPLC etc.) or the like, or a watermelon extract is filtered to separate into an extract and a residue, and an extract Are concentrated and fractionated by liquid chromatography.
In the separation step, 8-prenylnaringenin may be purified. Although the method of purification is not particularly limited, for example, a method of purifying 8-prenylnaringenin by an appropriate separation column or recrystallization can be mentioned.

<Overview of virus>
Viruses are roughly classified into DNA viruses and RNA viruses, depending on whether the genome is DNA or RNA.
DNA viruses can be classified mainly into two depending on whether the DNA is single-stranded or double-stranded.
Specifically, parvoviridae, etc. exist as single-stranded DNA viruses, and herpesviruses, poxviridae, hepadnaviridae, etc. as double-stranded DNA viruses having an envelope. There exist viruses such as Adenovirus and Papillomavirus as those which do not have an envelope.
Examples of viral diseases caused by single-stranded DNA virus include human parvo B19 (infectious erythematosus) and the like, and viral diseases caused by double-stranded DNA virus include herpes simplex (gingival stomatitis , Herpes zoster, genital herpes virus infection), chickenpox / zoster, sputum, hepatitis B, adeno (pharyngeal conjunctival fever, acute hemorrhagic conjunctivitis, epidemic keratoconjunctivitis), human papilloma and the like.

In the RNA virus, is the RNA single-stranded or double-stranded, or in the case of a single-stranded RNA virus, is the sense of the genome be plus strand (+ strand) or minus strand (-strand)? Can be divided into three main categories.
Specifically, first, as a single-stranded-strand RNA virus (having an envelope), viruses such as Orthomyxoviridae, Rhabdoviridae, Paramyxoviridae, Philoviridae, Bunyaviridae and Arenaviridae are included. Exists. The influenza virus belongs to the orthomyxoviridae family.
Viral diseases caused by these single-strand RNA viruses include influenza, bird flu, rabies, measles, mumps (mumps), RS (respiratory tract infection), Ebola (hemorrhagic fever) Marburg (hemorrhagic fever), Crimea and Congo hemorrhagic fever, SFTS, Lassa (hemorrhagic fever), funin / sabier / ganarito / machupo (hemorrhagic fever) and the like.

Next, among the single-stranded positive-strand RNA viruses, there are Flaviviridae, Coronaviridae, Togaviridae, Retroviridae, etc. as having an envelope, and the Caliciviridae and Pico as those without an envelope. There is a virus such as Lunaviridae. Norovirus belongs to the calicivirus family.
Viral diseases caused by these single-stranded positive-strand RNA viruses include dengue, West Nile, Japanese encephalitis, hepatitis C, yellow fever, SARS corona, MERS corona, rubella, human immunodeficiency (AIDS), human T Lymphophilic (adult T-cell leukemia), hepatitis E, noro (infectious gastroenteritis), polio (acute gray myelitis), hepatitis A, coxsackie (hand and foot disease, herpangina), rhino (common cold) etc. Be

Finally, as a double-stranded RNA virus (without an envelope), reoviridae and the like exist.
Rotavirus belongs to Reoviridae.
Examples of viral diseases caused by double-stranded RNA virus include rota (sensitive gastroenteritis) and the like.

Influenza virus is an RNA virus belonging to the Orthomyxoviridae family, which induces inflammation in the respiratory tract and is directly transmitted into the air by cough and saliva of infected persons or indirectly by contact with influenza patients etc. Is a highly contagious virus that can be transmitted to humans.
Influenza virus adsorbs to host cells by the activities of hemagglutinin (HA) and neuraminidase (Neuraminidase: NA), which are antigenic glycoproteins present on the virus surface, and invades into host cells by the activity of neuraminidase. Can.
Influenza viruses are classified into A-type, B-type and C-type according to the difference in these antigenic glycoproteins. In particular, influenza A virus is divided into 144 subtypes according to the type of 16 hemagglutinin and 9 types of neuraminidase. Then, it is known that these combinations change frequently, which results in the emergence of new subtypes of viruses of different antigenicity.

Influenza virus causes acute respiratory infections, and its clinical symptoms include general symptoms such as sudden fever, headache, joint pain, general fatigue, various respiratory symptoms seen in cold such as nasal discharge and cough, and It is characterized by high heat of 38 ° C or more.
Healthy individuals usually develop with a latency period of about 24 to 48 hours and cure in about 1 to 2 weeks, but infants, elderly people and patients with chronic diseases of the respiratory system, circulatory system, kidney, diabetes etc. In patients with metabolic disease or impaired immune function, secondary infections caused by bacteria etc. and pneumonia often result in death. In addition, not only local respiratory infections but also extremely severe cases such as severe nervous system complications represented by influenza encephalitis and encephalopathy have been reported. In addition, digestive tract symptoms such as abdominal pain, nausea and vomiting, and diarrhea may be seen.

Rotavirus is an RNA virus that belongs to the Rotavirus genus of Reoviridae.
Rotavirus particles are composed of double-shell particles composed of three layers, a core, an inner shell and an outer shell, and have RNA polymerase and a cap synthesis related enzyme in the virus particle. The core consists of the proteins VP1, VP2 and VP3 and is covered by the inner shell protein VP6 to form a single shell particle, and further covered with the outer shell proteins VP4 and VP7 to form a double shell particle or infectious virus particle .
Rotaviruses are classified into eight types of groups A to H according to the antigenicity of the inner shell protein VP6. Rotaviruses that have been reported to be transmitted to humans are mainly groups A to C.
Rotavirus infects intestinal epithelial cells of human small intestine and causes changes in tissue lesions such as disordered or missing microvilli arrangement. This inhibits the absorption of water from the intestine and causes diarrhea. The onset usually occurs after an incubation period of about 48 hours and causes acute gastroenteritis mainly in infants and children.
The main symptoms are diarrhea (without blood or mucous blood), nausea, vomiting, fever, abdominal pain, which usually heals spontaneously in about 1 to 2 weeks, but if dehydration is severe, shock, electrolyte abnormality, sometimes death may occur. There is also.

The process of propagation of RNA virus including influenza virus and rotavirus in cells can be explained as follows: “adsorption time” when the virus adsorbs to the host cell, “invasion time” when the adsorbed virus invades the cell, the invaded virus Through the "de-shelling period" of releasing (de-shelling) RNA in cells, the "replication period" of replication of new virus from the shed-out RNA, and the "release period" of replicated virus being released from cells Go.
Viruses do not have the materials necessary for the synthesis of nucleic acids and proteins, and necessarily require living cells. It parasitizes in living cells, proliferates using cell metabolism, and synthesizes self components using materials, metabolic enzymes of host cells, and host cell ribosomes for protein synthesis.
For example, while bacteria basically grow by two divisions, viruses increase rapidly in number in host cells infected with one particle.

In the "adsorption period", the binding protein (ligand) of the envelope or capsid present on the surface of the virus binds to a receptor (receptor) on the surface of the host cell. The infectivity to a virus depends on whether the host cell has a receptor for the virus.
In the case of influenza virus, hemagglutinin on the virus surface binds to the cell side sialic acid receptor.
In the case of rotavirus, binding proteins (outer coat proteins VP4, VP7) on the virus surface bind to receptors on the cell side.

In the “invasion stage”, the virus is generally taken up into intracellular endosomes by endocytosis of cells. Then, acidification in the endosome fuses the envelope of the virus surface with the cell membrane of the host cell.
In the fusion of influenza virus, cleavage of a peptide bond at a specific sequence site of hemagglutinin by host cell-derived endoprotease is essential. This cleavage exposes the membrane fusion domain of hemagglutinin and causes fusion with the endosomal membrane.
In the case of rotavirus, the coat protein VP4 needs to be cleaved into the proteins VP5 and VP8 by the host cell-derived protease (trypsin). After this cleavage, protein VP8 first contacts with a molecule containing sialic acid (first receptor), and then protein VP5 and coat protein VP7 bind to integrin (second receptor) for direct entry or endocytosis. It is thought to enter the cell by tosis.

In the "de-shelling period", the virus capsid that has entered the cell is degraded and RNA is released in the host cell (de-shelling). The period from uncoating to reconstitution of virus particles apparently causes virus particles to disappear, and this period is also called dark period.
On the surface of influenza A virus, a membrane protein called M2 protein is present, and the M2 protein forms an ion channel that allows H ⁺ to pass through. As the endosome is further acidified (lowered pH), the gate of this ion channel opens and H ⁺ is taken into the virus. Triggered by this, virus uncoating occurs and RNA is released into cells.
In the case of rotavirus, the coat protein VP4, VP7 is removed upon cell entry. Disengagement of the coat proteins VP4 and VP7 causes rearrangement of the coat protein VP6 released into the cell to initiate RNA transcription.

  In the "replication stage", the unshelled RNA is taken into the nucleus of the host cell, and a large amount of new RNA is replicated, and at the same time the transcription of the RNA (the synthesis of mRNA) leads to the synthesis of a large amount of virus-specific proteins. Ru. During RNA replication, an RNA-dependent RNA polymerase that functions as an RNA replication enzyme functions. In addition, at the time of synthesis from mRNA to protein, protein synthesis systems such as ribosomes possessed by host cells function. The replicated RNA and the synthesized protein assemble in the cell, and a new virus is assembled (replicated).

In the “release stage”, the virus is released from the host cell by attaching it to the cell membrane or nuclear membrane of the host cell and sprouting it or killing the host cell.
In the case of influenza virus, cleavage of hemagglutinin and sialic acid receptor by virus-derived neuraminidase is essential when the virus is propagated in cells and then released from infected host cells.

Here, to explain the existing anti-influenza virus agents, amantadine can inhibit the ion channel action of M2 protein of influenza virus and can suppress the detachment of influenza virus after entering the target cell, but M2 protein There is no effect on type B and C viruses, and there are also problems with strong side effects and the expression of resistant bacteria.
In addition, oseltamivir and zanamivir inhibit the action of neuraminidase, which is one of the spike proteins present in the influenza virus envelope, to allow replicated influenza virus to sprout from the host cell and spread the infection to other host cells. Although it can be suppressed, in recent years, side effects on young people have become a problem.

  Also, at present, there is no general antiviral agent effective for rotavirus, and hydration treatment to prevent dehydration and nutritional supplementation to prevent physical exhaustion are at the center of treatment .

Norovirus is an RNA virus belonging to the Caliciviridae family, which has not yet succeeded in infecting cultured cells and experimental animals, and it is said that humans are the only susceptible animals.
Since norovirus causes acute gastrointestinal inflammatory conditions such as vomiting and diarrhea in humans, and it is excreted in the patient's stool for about 3 to 7 days after disappearance of symptoms, it is necessary to be careful about secondary infection .
Norovirus is thought to infect the epithelial cells of the jejunum of humans, causing atrophy and flattening of the cilia, and exfoliation and shedding resulting in diarrhea.
The incubation period is considered to be about 24 to 48 hours, and nausea, vomiting and diarrhea are the main symptoms, but may be accompanied by abdominal pain, headache, fever, chills, myalgia, sore throat, fatigue, etc. Although it relieves without the need for special treatment, it is necessary to be careful about vomiting, dehydration and asphyxiation due to diarrhea in infants, the elderly and others who are physically weak.
At present, there is no general antiviral agent effective against norovirus, and symptomatic treatment is usually performed, and it is possible to rehydrate to prevent dehydration and to supply nutrition to prevent physical exhaustion. It is central to the treatment. It is also difficult to identify norovirus infection from clinical symptoms alone.

<Viral growth inhibitory action>
The antiviral agent of the present embodiment exerts an antiviral effect through the inhibitory action of the virus growth possessed by 8-prenylnaringenin, in particular, the inhibitory action of the RNA viral growth.
The specific action mechanism is as follows.
(1) 8-Prenylnaringenin is a virus in which the binding protein (ligand) on the surface of the virus binds to a receptor on the surface of the host cell during the "adsorption period" of the growth process of RNA virus. Act to inhibit the adsorption of
Specifically, when the RNA virus is an influenza virus, 8-prenylnaringenin acts to inhibit the activity of glycoproteins (such as hemagglutinin) required for the time of adsorption of the virus.
When the RNA virus is rotavirus, 8-prenylnaringenin acts to inhibit the activity of binding proteins (outer coat proteins VP4 and VP7) involved in the adsorption period of the virus and specific enzymes.

(2) In addition, 8-prenylnaringenin is an RNA virus that is generated during the replication process of RNA virus during the replication process, and the synthesized protein assembles, and when a new virus is assembled, the virus It acts to inhibit replication in the host cell.
In particular, when the RNA virus is influenza virus, 8-prenylnaringenin acts to inhibit the activity of a specific enzyme required for replication of the virus.
When the RNA virus is rotavirus or norovirus, 8-prenylnaringenin acts to inhibit the activity of binding proteins or specific enzymes involved in the replication period of these viruses.

Therefore, 8-prenylnaringenin, which is an effective main component of antiviral agent, inhibits the virus growth at least in the "adsorption time" and "replication time" of the virus growth process, as an effect which conventional antiviral agents do not have. Act to
Therefore, if it is this antiviral agent, even if it is the adsorption time of the first half of the virus growth process compared with the conventional antiviral agent which exhibits antiviral activity only at a specific time in the growth process of the virus. Also, even in the latter half of replication time, it is possible to exert antiviral activity.
In addition, the present antiviral agent is, for example, A-type, B-type, in comparison with an antiviral agent such as amantadine which does not have an effect on B-type and C-type, although it exerts an effect on influenza A virus. It exerts antiviral activity against all influenza viruses, regardless of type C.
Therefore, there is a possibility of clinical application as a new antiviral agent next to amantadine, oseltamivir and zanamivir, which are approved for use as conventional antiviral agents.

<Use>
The antiviral agent containing 8-prenylnaringenin of the present embodiment as an active ingredient can be administered to a patient with a viral infection or a nonhuman animal suffering from a viral infection as a therapeutic agent for viral infection, It can be used as a therapeutic agent for viral diseases.
In addition, it can also be used as a preventive agent for viral infections in humans, in a virus infection preparatory human, and nonhuman animals before suffering from a viral infection, and as a preventive agent for viral diseases.
Moreover, the antiviral agent of this embodiment can also be used as a preventive agent or a therapeutic agent of infectious gastroenteritis which makes a virus a pathogen.

Among the viruses, the antiviral agent of the present embodiment is preferably administered to patients infected with influenza virus, rotavirus and norovirus.
In the case of influenza virus, administration to a patient infected with influenza A virus is desirable, and it is further desirable that the subtype of the virus is H1N1.
In the case of rotavirus, it is desirable to be administered to a patient infected with group A rotavirus, and it is further desirable that the virus is group A rotavirus Wa strain (G1 P [8]).

  The antiviral agent of the present embodiment is used as a composition such as a pharmaceutical composition, a food composition, etc. containing an antiviral agent that exerts the above-mentioned effects on influenza virus, rotavirus and norovirus among viruses. can do.

(Pharmaceutical composition)
In the field of medicine, it is pharmaceutically effective to inhibit viral growth, that is, to inhibit adsorption of the virus to the host cell or release of the virus from the host cell. The pharmaceutical composition having the effect is provided by incorporating an acceptable carrier or additive therein. The pharmaceutical composition may be a pharmaceutical or quasi-drug.
The pharmaceutical composition may be applied internally or externally. Therefore, the pharmaceutical composition is used in the form of an internal preparation, intravenous injection, subcutaneous injection, intradermal injection, injection such as intramuscular injection and / or intraperitoneal injection, transmucosal application, transdermal application and the like. be able to.
The dosage form of the pharmaceutical composition can be appropriately set depending on the form of application, for example, solid preparations such as tablets, granules, capsules, powders, powders, etc., liquid preparations such as solutions, suspensions, etc. Semisolid agents such as ointments or gels are included.

(Food composition)
In the field of food, it is possible to provide a food composition having the above-mentioned action by blending an effective amount of 8-prenylnaringenin capable of exerting the action of inhibiting virus growth in vivo in various foods.
That is, the present invention can provide a food composition labeled as antiviral, for inhibiting viral growth, and the like in the field of food. Examples of the food composition include, in addition to general foods, food for specified health use, nutritive function food, functional display food, food for hospital patients, supplement and the like. It can also be used as a food additive.
Examples of the food composition include seasonings, processed meat products, processed agricultural products, beverages (soft drinks, alcoholic drinks, alcoholic drinks, carbonated drinks, milk drinks, fruit drinks, tea, coffee, nutritional drinks, etc.), powdered drinks (powders) Juices, powdered soups, etc., concentrated beverages, confectionery (candy (nodice), cookies, biscuits, gums, gummi, chocolate, etc.), bread, cereals, etc. can be mentioned. Further, in the case of food for specified health use, nutritive function food, functional display food and the like, it may be in the form of capsules, troches, syrups, granules, powders and the like.

Here, the food for specified health use is a food containing a health functional ingredient that affects physiological functions etc., and can be displayed as being suitable for a specific use of health with the permission of the Commissioner of the Consumer Agency. is there. In the present invention, it is a food marketed and labeled as prevention of viral infection, treatment, inhibition of viral growth, prevention of infectious gastroenteritis, treatment, etc. as a specific health use.
Also, the nutritive function food is a food used for supplementation of nutritional components (vitamins, minerals), and displays the function of the nutritional components. In order to sell it as a nutritionally functional food, it is necessary for the amount of nutritional component contained in the daily intake standard amount to be within the defined upper limit value and lower limit value, and not only the display of nutritional function but also alert display etc. You also need to
In addition, the functional labeling food is a food which displays scientific basis-based functionality at the responsibility of the business operator. Information on the basis of safety and functionality etc. was sent to the Secretary General of the Consumer Agency before sales.

In the above, the present invention contains 8-prenylnaringenin as an active ingredient, and is a food for specified health food for antiviral agents for viral infection patients, nonhuman animals suffering from viral infections, and antiviral agent nutrition function It can be used as a food, an antiviral agent functional indication food.
Further, the present invention comprises 8-prenylnaringenin as an active ingredient, and is specific for an organism, for example, a human before suffering from a viral infection, a human of a virus infection preparatory army, and an antiviral agent for non-human animals. It can be used as health food, nutritive function food for antiviral agent, and functional display food for antiviral agent.

<Usage and dose>
As the usage of the antiviral agent of the present embodiment, for example, in the case of influenza virus, it is easy to be infected in the upper respiratory tract (nasal cavity or pharynx) of a human, so for example, spraying directly into the nasal cavity or oral cavity by a spray, inhalation It may be introduced into the nasal cavity or the oral cavity by a vessel. In addition, it is good to introduce into the oral cavity with a mouthwash. In addition, nasal administration may be used, nasal administration, oral administration with throat, troche, gum, etc., or may be used as a mask or disinfecting hand.
Further, for example, rotavirus and norovirus are easily infected in the human intestine, so it is preferable to formulate the antiviral agent so that it dissolves in the intestine (not in the stomach). For example, it may be orally administered by capsule, tablet, granule, syrup or the like.

Example 1
An extract of wild watermelon was prepared by the following procedure.
Fruits of wild watermelon (Citrus lanatus: Citrullus lanatus) derived from the Kalahari Desert of Africa, including the peel and the seeds, were squeezed using a known squeezer to obtain fruit juice. The fruit juice was subjected to ultrafiltration for the purpose of preventing the formation of a precipitate, etc. to remove components having a molecular weight of 3,000 or more, thereby obtaining an extract extract of wild watermelon.
The extract was used as a watermelon extract as a raw material of 8-prenylnaringenin.

<Test 1 Fractional test of anti-influenza component>
(Test method of Test 1)
(1) 20 g of the ODSC 18 was dissolved in 200 ml of methanol, degassed, and packed in a column.
(2) 50 ml of acetonitrile was substituted and left overnight.
(3) After flowing 50 ml × 2 times of ultrapure water, 4 ml of a sample (without concentration) was allowed to penetrate the gel.
(4) The solvent shown in the following Table 1 was poured to carry out fractionation. Fractional sample (50 ml of each fraction (Fr)) was collected in 25 ml × 2.
(5) The obtained fraction (after Fr2) was evaporated with an evaporator, lyophilized, and dissolved in 1 ml of ultrapure water.
(6) Sterilized with a 0.45 μm filter for addition experiment.
(7) Add the lysate of each fraction to MDCK cells infected with influenza virus strain (P / R / 8/34) in a 24-well plate to 10% of 500 μl / well of culture medium for 24 hours The supernatant was collected later, and the virus was quantified by the focus method.

(Result of test 1)
After 24 hours, the 24 well plate was observed with a microscope. The results are shown in FIG. 2 and Table 2.

(Discussion of Test 1)
From the above results, it was found that a part of the active ingredient in the Kalahari watermelon filtered juice is adsorbed to the ODSC 18. From the results of the addition experiment and the focusing method, Fr1,1 '(non-adsorbed fraction) and Fr3 (adsorbed fraction) showed antiviral activity, and particularly, strong activity was observed in Fr3.

<Test 2 Qualification of active fraction and identification of active ingredient by LC / MS, LC-MS / MS>
The anti-influenza virus component contained in the active fraction obtained in Test 1 is searched.
(Test method of Test 2)
The active fraction and the non-active fraction obtained in Test 1 were collected multiple times each under the same conditions, and were collected until the freeze-dried weight required for MS measurement was obtained. After collection, measurement was performed by LC-MS and LC-MS / MS to analyze the active ingredient. The molecular weight was measured by LC-MS, and the molecular weight and molecular formula were measured by LC-MS / MS. The analysis was performed comparing the molecular weight in both measuring devices and the peak of the active fraction and the nonactive fraction.

(Analysis conditions)
・ LC-MS
LC device: Agilent 1260
Column: synergi Hydro-RP-100A (100 mm x 3 mm, 2.5 2.5 μm)
Temperature: 40 ° C
Mobile phase: A liquid-2% acetic acid solution, B liquid-(0.5% acetic acid solution: acetonitrile 1: 1 (v / v)), mobile phase gradients are shown in Table 3 below.
Flow rate: 0.4 ml / min
Injection volume: 5.0 μl

MS device: Agilent LCM 6430
Dry nitrogen gas: 350 ° C (12 L / min)
Nebulizer pressure: 60 psi
Capillary voltage: 2500V
Fragmenter voltage: 100V
The ionization method measures ESI's Positive / Negative simultaneously, Qualitative Abalysis Ver. B 0 6.00 It analyzed by Buird 6.0.3 33 SP.

・ LC-MS / MS
LC device: Shimadzu LC20A
Column: synergi Hydro-RP-100A (100 mm x 3 mm, 2.5 2.5 μm)
Temperature: 40 ° C
Mobile phase: A liquid-2% acetic acid solution, B liquid-(0.5% acetic acid solution: acetonitrile 1: 1 (v / v))
Flow rate: 0.4 ml / min
Injection volume: 5.0 μl

  The conditions of LC-MS / MS were performed on the same mobile phase gradient conditions as Table 3 above.

  MS instrument: Agilent LCM6430, dry nitrogen gas: 200 ° C (8 L / min), nebulizer pressure: 1.6 bar, capillary voltage: -4500 V / 2800 V, ionization method: ESI (Positive / Negative measurement), Auto MSMS simultaneously It measured and analyzed by Data Analysis Ver4.0 SP2 (Build27.4).

(Result of trial 2)
The lyophilized weight was 0.334 g for Fr1, 0.04 g for Fr1 ′, 0.011 g for Fr2, 0.073 g for Fr3, and 0.011 g for Fr4.

  As a result of analysis, 8-prenylnaringenin was listed as a candidate of the active ingredient. In the following tests, 8-prenylnaringenin was examined focusing on.

<Test 3 Quantitative Test of 8-Prenylnaringenin in Watermelon Extract>
In test 3, quantification of 8-prenylnaringenin contained in the watermelon extract (watermelon juice) of Example 1 was performed.

(Test method of Test 3)
(1. Overview)
One mL of the watermelon extract was taken out, and a test solution was prepared in 10 mL volume with a mixture of water and methanol (1/1). The test solution was subjected to liquid chromatography-tandem mass spectrometry (LC-MS / MS) to quantify 8-prenylnaringenin in the sample. As a standard product of 8-prenylnaringenin, a product provided by a client (purity 98%) was used.

(2. Equipment conditions)
-Measurement condition device for LC-MS / MS: [LC] Nexera XR (manufactured by Shimadzu Corporation)
[MS / MS] QTRAP 5500 (manufactured by AB Siex)
Column: L-column 2 ODS 150 mm × 2.0 mm, 3 μm (manufactured by Chemical Substance Evaluation Research Organization)
Column temperature: 40 ° C
Mobile phase: Mobile phase (A) 0.1% aqueous solution of formic acid Mobile phase (B) 0.1% solution of formic acid in methanol B 30% (0 min) → 10 min → B 90% (5 min)
Flow rate: 0.2mL / min
Injection volume: 5 μL
Ionization method: ESI (Negative)
Measurement mode: Selective reaction detection method (SRM)
Measurement ion: quantitative ion m / z 339.8> 219.9
Confirmation ion m / z 339.8> 176.0

(Result of trial 3)
Chromatograms of the 8-prenylnaringenin standard solution (0.1 ng / mL) and the test solution are shown in FIGS. 3A and 3B.
The results of quantitative analysis of 8-prenylnaringenin in samples are shown in Table 4.

<Test 4 Growth inhibition test of influenza virus>
Using 8-prenylnaringenin, tests were conducted to confirm its action to inhibit influenza virus growth. Using MDCK (Madin-Darby canine kidney) cells as host cells, using influenza virus type A / PR / 8/34 (H1N1) strain as virus, and containing 10% FBS (Fetal Bovine Serum) as medium DMEM (Dulbecco's Modified Eagle Medium) medium was used.

First, MDCK cells were each seeded on a 24-well plate at 1.0 × 10 ⁴ cells / well, and monolayer culture was performed at 37 ° C. and 5% CO ₂ for 24 hours.
Then, the cultured MDCK cells were infected with influenza virus at 0.001 moi (multiplicity of infection) and left at 37 ° C. for 1 hour (adsorbed).
Thereafter, 8-prenylnaringenin was added to the liquid medium so as to contain a predetermined concentration, and cultured in a CO ₂ incubator for 24 hours.
Thereafter, the supernatant containing the virus released from the infected cells was collected, and the virus titer (FFU / ml) of the cells was measured using the focus method to calculate the virus growth inhibition rate (%). In addition, the concentration of 8-prenylnaringenin (IC50) that inhibits viral infection of cells by 50% was calculated.

(Result of Test 4)
The results of analysis of the above test are shown in FIG. 4 which is a graph comparing the rate of inhibition of viral growth at each concentration by 8-prenylnaringenin.
The virus growth inhibition rate further increased as the extract concentration increased.
Here, "concentration 1 μg / ml" indicates that 1 μg of 8-prenylnaringenin is contained in 1 ml of the liquid medium.

(Discussion of Test 4)
From the results of Test 4, 8-prenylnaringenin was confirmed to have the effect of inhibiting influenza virus growth at all concentrations. In addition, the effect of inhibiting virus growth was increased depending on concentration.
From this, it was found that among the components contained in watermelon, 8-prenylnaringenin was more effective in inhibiting influenza virus growth.
In addition, it was found that the preferred concentration (IC50) of 8-prenylnaringenin in the action of inhibiting influenza virus growth is 0.087 μg / ml.
The IC50 value of the aglycone naringenin was 70 μg / ml, and 8-prenylnaringenin showed very high influenza virus inhibitory activity. In terms of the number of moles, it is 0.26 × 10 ^-3 M for naringenin (molecular weight: 272), 0.26 × 10 ^-6 M for 8-prenylnaringenin (molecular weight: 340), and 8-prenylnaringenin together with naringenin In comparison, it showed 10 ³ times higher activity.

<Test 5 MTT assay of 8-prenylnaringenin>
A test was conducted to examine the presence or absence of cytotoxicity of 8-prenylnaringenin using 8-prenylnaringenin. A mixture of 8-prenylnaringenin and a serum-free DMEM medium containing a final concentration of 4 μg / ml acetyltrypsin was added to the monolayer-cultured MDCK cells in a microplate, and the mixture was cultured at 37 ° C. for 1 day. The MTT labeling reagent was added and further cultured at 37 ° C. for 4 hours, and the solubilization solution was added and cultured overnight at 37 ° C. The absorbance was measured at 575 nm using a microplate reader at a reference wavelength of 650 nm.

(Result of Test 5)
The above test results are analyzed, and a graph plotting absorbance at each concentration by 8-prenylnaringenin is shown in FIG.
No decrease in absorbance was observed as compared to the control.

(Discussion of Test 5)
The results of Test 5 suggested that 8-Prenylnaringenin had no cytotoxicity in the range of 0-25 μg / ml.

<Test 6 Infection inhibition test in the growth process of influenza virus>
Using 8-prenylnaringenin, a test was conducted to confirm which growth process of the processes necessary for influenza virus growth is inhibited. MDCK cells were used as host cells, influenza virus type A / PR / 8/34 strain was used as virus, and DMEM medium containing 10% FBS was used as medium.
First, MDCK cells cultured in monolayer as in Test 1 were infected (added) with influenza virus at 0.01 moi (multiplicity of infection) and left at 37 ° C. for 1 hour (adsorbed).

Then, DMEM medium supplemented with 10 μg / ml of 8-prenylnaringenin was added to the virus-infected MDCK cells at a predetermined timing.
DMSO (dimethyl sulfoxide) was added as a control.
After 8 hours from virus adsorption, freezing and thawing at −80 ° C. to 37 ° C. was repeated twice, and the intracellular virus titer was measured using the focus method to calculate the virus growth inhibition rate.

  As the timing for adding 8-prenylnaringenin, (0) only at the time of pretreatment (1) at the time of adsorption (the timing corresponding to the "adsorption time" in the virus growth process, up to one hour after virus infection), (2) At the time of virus culture (from 0 hours to 8 hours of culture), (3) Both at the time of adsorption and at time of culture, (4) From 0 hours to 4 hours of culture Timing, up to 4 hours after virus adsorption), (5) 4 to 8 hours of culture (time corresponding to “replication / release timing” in the virus growth process, from 4 to 8 hours after virus adsorption ), (6) culture 0 hour to 2 hours, (7) culture 2 hours to 4 hours, (8) culture 4 hours to 6 hours, (9) culture 6 hours to 8 hours.

  Specifically, in (0), 8-prenylnaringenin was added only at the time of pretreatment, and the medium was replaced with a medium to which 8-prenylnaringenin was not added. In (1), 8-prenylnaringenin was added simultaneously with virus infection, and it replaced | exchanged for the culture medium which did not add 8- prenylnaringenin 1 hour after virus infection. In (2), 8-prenylnaringenin was added at the start of virus culture, and cultivation was performed in the presence of 8-prenylnaringenin until 8 hours later. In (3), 8-prenylnaringenin was added simultaneously with virus infection, 8-prenylnaringenin was added also at the start of virus culture, and culture was performed in the presence of 8-prenylnaringenin until 8 hours later. In (4), 8-prenylnaringenin was added simultaneously with virus adsorption, and after 4 hours of virus adsorption, the medium was replaced with a medium to which 8-prenylnaringenin was not added. In (5), 4-prenylnaringenin was added 4 hours after virus adsorption and replaced with a medium to which 8-prenylnaringenin was not added 8 hours after virus adsorption. In (6), 8-prenylnaringenin was added simultaneously with virus adsorption, and after 2 hours of virus adsorption, the medium was replaced with a medium to which 8-prenylnaringenin was not added. In (7), 2-prenylnaringenin was added 2 hours after virus adsorption and replaced with a medium to which 8-prenylnaringenin was not added 4 hours after virus adsorption. In (8), 4-prenylnaringenin was added 4 hours after virus adsorption, and it replaced | exchanged for the culture medium which did not add 8- prenylnaringenin 6 hours after virus adsorption. In (9), 8-prenylnaringenin was added 6 hours after virus adsorption and replaced with a medium to which 8-prenylnaringenin was not added 8 hours after virus adsorption.

(Result of Test 6)
The results of the above test are analyzed, and a graph is shown in FIG. 6 which compares the growth inhibitory activity at the time of adsorption of virus, at the time of culture of virus, and at the time of adsorption and culture only during pretreatment with 8-prenylnaringenin.
At the time of pretreatment only, the rate of inhibition of growth was 57%, 96%, 51%, and 96% in order of adsorption of virus, culture, adsorption and culture, respectively.
The extract was added at 0 to 4 hours of culture, 4 to 8 hours of culture, 0 to 2 hours of culture, 2 to 4 hours of culture, 4 to 6 hours of culture, and 6 to 8 hours of culture. The inhibition rates were 9%, 59%, -4%, -13%, 13%, and 29%, respectively.

(Discussion of Test 6)
From the results of Test 6, it was found that the addition of 8-prenylnaringenin inhibited the growth of the virus both at the time of adsorption of the virus to the cells and at the time of the intracellular growth of the virus. In addition, "at the time of adsorption to cells" had a higher effect of inhibiting viral growth than "at the time of growth in cells".

Claims (11)

Watermelon preparation process of preparing watermelon,
Extracting the watermelon extract from the watermelon;
Separating the 8-prenylnaringenin from the watermelon extract obtained in the extraction step;
A method of producing 8-prenylnaringenin, characterized in that   The method for producing 8-prenylnaringenin according to claim 1, wherein the watermelon is Citrullus lanatus.   The method for producing 8-prenylnaringenin according to claim 2, wherein said Citrullus lanatus is a wild watermelon derived from the Kalahari Desert of Africa.   The method for producing 8-prenylnaringenin according to claim 2 or 3, wherein the watermelon extract is a fruit juice obtained from the fruit of Citrullus lanatus.   The method for producing 8-prenylnaringenin according to claim 4, wherein the fruit comprises flesh, peel and seeds of the fruit. It contains 8-prenylnaringenin as an active ingredient,
An antiviral food composition, which is used for the prevention or amelioration of viral infection.   7. The antiviral food composition according to claim 6, wherein the viral infection is an infection of at least one virus selected from the group consisting of influenza virus, norovirus and rotavirus.   The antiviral food composition according to claim 7, wherein the viral infection is an influenza virus infection. It contains 8-prenylnaringenin as an active ingredient,
An antiviral agent which is used for the prevention or treatment of a viral infection.   The antiviral agent according to claim 9, wherein the viral infection is an infection of at least one virus selected from the group consisting of influenza virus, norovirus and rotavirus.   The antiviral agent according to claim 10, wherein the viral infection is an influenza virus infection.