Virucidal and Immunostimulating Activities of Monogalactosyl Diacylglyceride from Coccomyxa sp. KJ, a Green Microalga, against Murine Norovirus and Feline Calicivirus

Abstract

Human noroviruses are the most common pathogens causing acute gastroenteritis and may lead to more severe illnesses among immunosuppressed people, including elderly and organ transplant recipients. To date, there are no safe and effective vaccines or antiviral agents for norovirus infections. In the present study, we aimed to demonstrate the antiviral activity of monogalactosyl diacylglyceride (MGDG) isolated from a microalga, Coccomyxa sp. KJ, against murine norovirus (MNV) and feline calicivirus (FCV), the surrogates for human norovirus. MGDG showed virucidal activities against these viruses in a dose- and time-dependent manner—MGDG at 100 μg/mL reduced the infectivity of MNV and FCV to approximately 10% after 60 min incubation. In the animal experiments of MNV infection, intraoral administration of MGDG (1 mg/day) exerted a therapeutic effect by suppressing viral shedding in the feces and produced high neutralizing antibody titers in sera and feces. When MGDG was orally administered to immunocompromised mice treated with 5-fluorouracil, the compound exhibited earlier stopping of viral shedding and higher neutralizing antibody titers of sera than those in the control mice administered with distilled water. Thus, MGDG may offer a new therapeutic and prophylactic alternative against norovirus infections.

Therapeutic Effects of a Dry Powder Prepared from the Green Microalga Coccomyxa sp. KJ in Mice Infected with Influenza A Virus

“…We recently reported that MGDG, a component of Coccomyxa sp. KJ, exerts virucidal effects against herpes simplex virus type 2, SARS-CoV-2, murine norovirus, and feline calicivirus [10][11][12]. As shown in Figure 6, 1 mg/day of MGDG exerted therapeutic effects in IFV-infected mice.…”

“…Recently, we investigated its antiviral component(s) using a bioactivity-guided assay. Among these components, monogalactosyl diacylglyceride (MGDG) exerted virucidal effects against herpes simplex virus type 2, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and norovirus [10][11][12]. In vivo studies of norovirus have shown that MGDG suppresses viral replication and induces the production of virus-specific antibodies [10].…”

“…Among these components, monogalactosyl diacylglyceride (MGDG) exerted virucidal effects against herpes simplex virus type 2, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and norovirus [10][11][12]. In vivo studies of norovirus have shown that MGDG suppresses viral replication and induces the production of virus-specific antibodies [10]. However, because MGDG constitutes only 4-5% of microalgal dry weight, it is expensive to use.…”

Phenol Derivatives Obtained from Grape Seed Extract Show Virucidal Activity against Murine Norovirus

“…Antiviral activity was estimated using selectivity indices (SIs), calculated as the ratio of 50% cytotoxic concentration (CC 50 ) to 50% effective concentration (EC 50 ) (SI = CC 50 /EC 50 ) [27]. To evaluate the cytotoxicity of GSE in Vero, MDCK, HeLa, and RAW 264.7 cells, uninfected subconfluent cells were cultured at 37 • C in a CO 2 incubator in the presence of increasing concentrations of GSE.…”

Drug screening identified that handelin inhibits feline calicivirus infection by inhibiting HSP70 expression in vitro

“…These drugs show favourable antiviral activity in vitro. Moreover, some compounds, such as lemon essential oil, theaflavins-enriched tea leaf extract TY-1 and monogalactosyldiacylglyceride, exert virucidal effects [1,24,25]. Currently, few antiviral drugs are approved for the clinical treatment of FCV [26].…”