Reaction Cycles of Halogen Species in the Immune Defense: Implications for Human Health and Diseases and the Pathology and Treatment of Covid19

Lu, Qing-Bin

There is no vaccine or specific antiviral treatment for COVID19 that is causing a global pandemic. One current focus is drug repurposing research, but those drugs have limited therapeutic efficacies and known adverse effects. The pathology of COVID19 is essentially unknow. Without this understanding, it is challenging to discover a successful treatment to be approved for clinical use. This paper addresses several key biological processes of reactive oxygen, halogen and nitrogen species (ROS, RHS and RNS) that play crucial physiological roles in organisms from plants to humans. It includes why superoxide dismutases, the enzymes to catalyze the formation of H2O2, are required for protecting ROS-induced injury in cell metabolism, why the amount of ROS/RNS produced by ionizing radiation at clinically relevant doses is ~1000 fold lower than the endogenous ROS/RNS level routinely produced in the cell, and why a low level of endogenous RHS plays a crucial role in the innate immune defense. Here we propose a striking yet plausible amplification mechanism in the immune defense: ozone-depleting-like halogen cyclic reactions enhancing RHS effects are responsible for all the mentioned physiological functions, which are activated by H2O2 and deactivated by NO signaling molecule. Our calculated results show that the reaction cycles can be repeated thousands of times and amplify the RHS pathogen-killing (defense) effects by 100000 folds, resembling the cyclic O3-depleting reactions in the stratosphere. It is unraveled that H2O2 is a required protective signaling molecule (angel) in the defense system for human health and its dysfunction can cause many diseases such as autoimmune disorders, aging and cancer. We also identify a class of potent drugs for effective treatment of invading pathogens (COVID19), cancer and other diseases, and provide a molecular mechanism of action of the drugs or candidates.