Orally Administered Salacia reticulata Extract Reduces H1N1 Influenza Clinical Symptoms in Murine Lung Tissues Putatively Due to Enhanced Natural Killer Cell Activity

Abstract

Influenza is a major cause of respiratory tract infection. Although most cases do not require further hospitalization, influenza periodically causes epidemics in humans that can potentially infect and kill millions of people. To countermeasure this threat, new vaccines need to be developed annually to match emerging influenza viral strains with increased resistance to existing vaccines. Thus, there is a need for finding and developing new anti-influenza viral agents as alternatives to current treatments. Here, we tested the antiviral effects of an extract from the stems and roots of Salacia reticulata (SSRE), a plant rich in phytochemicals, such as salacinol, kotalanol, and catechins, on H1N1 influenza virus-infected mice. Following oral administration of 0.6 mg/day of SSRE, the incidence of coughing decreased in 80% of mice, and only one case of severe pulmonary inflammation was detected. Moreover, when compared with mice given Lactobacillus casei JCM1134, a strain previously shown to help increase in vitro natural killer (NK) cell activity, SSRE-administered mice showed greater and equal NK cell activity in splenocytes and pulmonary cells, respectively, at high effector cell:target cell ratios. Next, to test whether or not SSRE would exert protective effects against influenza in the absence of gut microbiota, mice were given antibiotics before being inoculated influenza virus and subsequently administered SSRE. SSRE administration induced an increase in NK cell activity in splenocytes and pulmonary cells at levels similar to those detected in mice not treated with antibiotics. Based on our results, it can be concluded that phytochemicals in the SSRE exerted protective effects against influenza infection putatively via modulation of the immune response, including enhancement of NK cell activity, although some protective effects were not necessarily through modulation of gut microbiota. Further investigation is necessary to elucidate the molecular mechanisms underlying the protective effects of SSRE against influenza infection.

Antiviral effect of phytochemicals from medicinal plants: Applications and drug delivery strategies

“…The main findings related to antiviral plant extracts are collected in Table 1. Included extracts were tested in cell culture, and some extracts were also studied in vivo [11,23,31,39].…”

Protective Effect of Panax notoginseng Root Water Extract against Influenza A Virus Infection by Enhancing Antiviral Interferon-Mediated Immune Responses and Natural Killer Cell Activity

“…For this reason, much attention has been devoted to identifying natural compounds with activity against influenza. For example, extracts from plants such as Salacia reticulata ( 15 ), Ribes nigrum folium ( 16 ), Cryptoporus volvatus ( 17 ), and Psoraleae semen ( 18 ) displayed potent antiviral activity against influenza A virus.…”

“…The innate immune system consists of a range of components including type-I interferon (IFN) and pro-inflammatory cytokines, and is the first line of defense against viral infection ( 29 ). Another component of the innate immune system, natural killer (NK) cells, as well as the adaptive immune system cells macrophages, have been reported to inhibit virus replication and protect against cancer ( 15 , 18 ). NK cells are known to provide the first line of early defense against viral infections ( 30 – 32 ).…”

Effect of Daily Intake of Heat-Killed Lactobacillus plantarum HOKKAIDO on Immunocompetence: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study

“…Natural killer (NK) cells are the key factors of the innate immunity and various factors, such as mental stress [5,6] and smoking [7,8], can decrease NK cell activity. Several reports have suggested that the promotion of NK cell activity was related to the inhibition of influenza infection [9][10][11].…”