Pulsed blue light, saliva and curcumin significantly inactivate human coronavirus

In a recent study, we showed that pulsed blue light (PBL) inactivates as much as 52.3% of human beta coronavirus HCoV-OC43, a surrogate of SARS-CoV-2, and one of the major strains of viruses responsible for the annual epidemic of the common cold. Since curcumin and saliva are similarly antiviral and curcumin acts as blue light photosensitizer, we used Qubit fluorometry and WarmStart RT-LAMP assays to study the effect of combining 405 nm, 410 nm, 425 nm or 450 nm wavelengths of PBL with curcumin, saliva or a combination of curcumin and saliva against human beta coronavirus HCoV-OC43. The results showed that PBL, curcumin and saliva independently and collectively inactivate HCoV-OC43. Without saliva or curcumin supplementation 21.6 J/cm² PBL reduced HCoV-OC43 RNA concentration a maximum of 32.8% (log₁₀ = 2.13). Saliva supplementation alone inactivated the virus, reducing its RNA concentration by 61% (log₁₀ = 2.23); with irradiation the reduction was as much as 79.1%. Curcumin supplementation alone decreased viral RNA 71.1%, and a maximum of 87.8% with irradiation. The combination of saliva and curcumin reduced viral RNA to 83.1% and decreased the RNA up to 90.2% with irradiation. The reduced levels could not be detected with qPCR. These findings show that PBL in the range of 405 nm to 450 nm wavelength is antiviral against human coronavirus HCoV-OC43, a surrogate of the COVID-19 virus. Further, it shows that with curcumin as a photosensitizer, it is possible to photodynamically inactivate the virus beyond qPCR detectable level using PBL. Since HCoV-OC43 is of the same beta coronavirus family as SARS-CoV-2, has the same genomic size, and is often used as its surrogate, these findings heighten the prospect of similarly inactivating novel coronavirus SARS-CoV-2, the virus responsible for COVID-19 pandemic.