FIGURE 1.

Changes that can occur in the glycolytic pathway in COVID-19. When immune cells are resting, glucose is metabolised via the glycolytic pathway, yielding pyruvate as a product. This substrate is subsequently used in the tricarboxylic acid cycle (TCA) to form intermediates that will be processed by oxidative phosphorylation to produce 32 molecules of ATP, for each molecule of glucose. When immune cells are activated or hypoxic, glucose metabolism is reprogrammed. There is an increase in the type 1 alpha hypoxia-inducing factor (HIFa), which inhibits pyruvate dehydrogenase enzyme complex (PDH). Pyruvate is thus transformed into lactate by the action of lactate dehydrogenase (LDH). But this mechanism motivates the capture of more glucose for the synthesis of further ATP molecules. There is also activation of the pentose phosphate (PPP) pathway that produces ribose and NADPH. The latter can be used by immune cells through the actions of NADPH oxidase to produce reactive oxygen species (ROS).