Juice of Citrullus lanatus var. citroides (wild watermelon) inhibits the entry and propagation of influenza viruses in vitro and in vivo

Abstract

Vaccines and various anti‐influenza drugs are clinically used to prevent and treat influenza infections. However, with the antigenic mismatch of vaccines and the emergence of drug‐resistant viral strains, new approaches for treating influenza are warranted. This study focused on natural foods as potential candidates for the development of new treatment options for influenza infections. The screening of plants from the Cucurbitaceae family revealed that the juice of Citrullus lanatus var. citroides (wild watermelon) had the strongest ability to inhibit the replication of influenza virus in Madin–Darby canine kidney cells. The results of a time‐of‐addition assay indicated that wild watermelon juice (WWMJ) inhibits the adsorption and late stages of viral replication, suggesting that WWMJ contains multiple constituents with effective anti‐influenza activity. A viral adsorption analysis showed that WWMJ reduces the amount of viral RNA in the cells at 37°C but not at 4°C, confirming that WWMJ inhibits viral entry into the host cells at 37°C. These results suggest that a mechanism other than the inhibition of viral attachment is involved in the anti‐influenza action of WWMJ, which is perhaps responsible for a reduction in internalization of the virus. Administration of WWMJ into the nasal mucosa of BALB/c mice infected with the A/PR/8/34 mouse‐adapted influenza virus was seen to significantly improve the survival rate. The findings of this study, therefore, demonstrate the anti‐influenza potential of WWMJ in vitro and in vivo, thereby suggesting the candidature of WWMJ as a functional food product that can be used to develop anti‐influenza agents and drugs.

Influenza virus entry and replication inhibited by 8‐prenylnaringenin from Citrullus lanatus var. citroides (wild watermelon)

“…Focus‐forming reduction assay (FFRA) was performed as previously described (Morimoto et al., 2021 ; Nagai et al., 2018 ). In brief, infected cells were visualized by adding murine monoclonal anti‐HA antibody (C179 for H1, F49 for H3, and 7B11 for B; Morimoto et al., 2021 ) and a goat anti‐mouse IgG antibody conjugated to horseradish peroxidase (Merck KGaA).…”

“…In the current study, (±)-naringenin was used instead of (S)-naringenin, considering the cost. Morimoto et al (2021). Briefly, the virus culture was diluted in serum-free MEM containing 0.04% bovine serum albumin (BSA, fraction V; Sigma-Aldrich) and then incubated with the cells to infect them at a multiplicity of infection (MOI) of 0.001 for 1 h at 37°C.…”

“…We conducted a time-of-addition experiment using a previously described procedure (Morimoto et al, 2021) with slight modifications.…”

“…Although there have been several reports on the usefulness of WWM, its food functionality remains a relatively new area of research. In a previous study, we reported an anti-influenza activity of WWM juice, but the effective components remained unknown (Morimoto et al, 2021). In the current study, we aimed to investigate the flavonoid-based components present in WWM juice and due to the large amount of polyphenols detected, we focused on phytoestrogens, in which daidzein, acacetin, kaempferol, naringenin, and resveratrol have been reported to have anti-influenza virus effects (Dong et al, 2014;Kim et al, 2001;Nagai et al, 2019;Palamara et al, 2005).…”

“…Recently, functional foods showing antiviral activity have been reported (Chen et al., 2016 ; Morimoto et al., 2021 ; Nagai et al., 2018 ), and ingredients of functional foods have received increased attention. Some foods have been reported to have various ingredients with anti‐INF activity, including tea polyphenols such as catechins, theaflavins, and procyanidins (Yang et al., 2014 ).…”