|Posted on December 11, 2020 at 1:40 PM|
Some free fatty acids derived from milk and vegetable oils are known to have potent antiviral and antibacterial properties. However, therapeutic applications of short to medium chain fatty acids are limited by physical characteristics such as immiscibility in aqueous solutions. We evaluated a novel proprietary formulation based on an emulsion of short chain caprylic acid, ViroSAL, for its ability to inhibit a range of viral infections in vitro and in vivo. In vitro, ViroSAL inhibited the enveloped viruses Epstein-Barr, measles, herpes simplex, Zika and orf parapoxvirus, together with Ebola, Lassa, vesicular stomatitis and SARS-CoV-1 pseudoviruses, in a concentration- and time-dependent manner. Evaluation of the components of ViroSAL revealed that caprylic acid was the main antiviral component; however, the ViroSAL formulation significantly inhibited viral entry compared with caprylic acid alone. In vivo, ViroSAL significantly inhibited Zika and Semliki Forest Virus replication in mice following the inoculation of these viruses into mosquito bite sites. In agreement with studies investigating other free fatty acids, ViroSAL had no effect on norovirus, a non-enveloped virus, indicating that its mechanism of action may be via surfactant disruption of the viral envelope. We have identified a novel antiviral formulation that is of great interest for prevention and/or treatment of a broad range of enveloped viruses.
The antimicrobial properties of fatty acids have been extensively reported in the literature (for review, see Thormar et al. (Thormar and Hilmarsson, 2007) and (Churchward et al., 2018). Previously, (Thormar et al., 1987) demonstrated the antiviral effects of 14 different free fatty acids and lipid extracts from human milk against vesicular stomatitis virus (VSV), herpes simplex virus (HSV) and visna virus revealed that short chain saturated fatty acids (butyric, caproic and caprylic) together with long chain saturated fatty acids (palmitic and stearic) had no or very little antiviral activity, whereas medium chain saturated entities including capric, lauric, myristic and long chain unsaturated oleic, linoleic and linolenic acids were anti-viral, albeit at different concentrations. Another study (Hilmarsson et al., 2005) reported similar trends in the antiviral activity of six medium chain fatty acids together with their alcohol and mono-glyceride derivatives against herpes simplex viruses 1 and 2. In contrast, Dichtelmuller et al (2002) reported that caprylic acid had antiviral activity against enveloped viruses including human immunodeficiency virus, bovine viral diarrhoea virus, Sindbis virus and pseudorabies virus (Dichtelmuller et al., 2002, Pingen et al., 2016). Studies investigating the antiviral properties of whole milk reported no antiviral properties of fresh human milk, whereas milk that had been stored at 4°C possessed potent antiviral activity against several viruses in vitro. Refrigeration disrupts the milk fat globule membrane allowing ingress of milk serum lipase which results in hydrolysis of milk fat triglyceride (Thormar et al., 1987, Isaacs et al., 1990). It was concluded that release of fatty acids from milk triglycerides in stored milk, and that recovered from neonatal (achlorhydric) stomachs, was responsible for generating antiviral factor(s) (Thormar et al., 1987).
We investigated the effect of a specifically formulated emulsion of free fatty acids, ViroSAL, on infectivity of enveloped and non-enveloped viruses. Caprylic acid delivered in the ViroSAL emulsion exhibited significant anti-viral effects. A range of enveloped viral infection systems was utilized, and complete inhibition of viral infection was observed without any evidence of cytotoxicity. ViroSAL had no effect on the infectivity of a non-enveloped virus, norovirus, which is in agreement with previous studies demonstrating that free fatty acids are ineffective against non-enveloped viruses (Thormar et al., 1987, Kohn et al., 1980). Furthermore, ViroSAL inactivated the enveloped mosquito-borne viruses Semliki Forest virus (SFV) and Zika virus (ZIKV) in vitro. Prophylactic topical treatment of viral infection in mosquito bites with ViroSAL inhibited local replication and dissemination of SFV and plasma levels of ZIKV in mice. Transmission electron microscopy analysis indicated that ViroSAL disrupts orf parapoxvirus envelope integrity, with higher concentrations completely disrupting virion morphology. These data indicate that ViroSAL has antiviral activity against a range of enveloped viruses in vitro and in vivo.