Adrenaline Induces Oxidative Stress-Mediated Perturbation in Cardiac Riboflavin Metabolism Through Direct Interaction with Flavin Coenzymes: Protection by Melatonin-a Mechanistic Insight.

Riboflavin metabolism governs a myriad of redox-driven biochemical processes fundamental to energy production, cellular signaling, and biosynthesis. Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) act as obligatory prosthetic groups for a plethora of regulatory enzymes of key metabolic pathways, correlating riboflavin status directly to cellular energy flux and redox balance. Oxidative stress may disturb physiological activities of riboflavin metabolizing machineries. Chronic stress induces surge in levels of circulatory catecholamines including adrenaline which subsequently undergo auto-oxidation generating free radicals. Cardio-protective efficacy of melatonin is well-documented against cardiovascular diseases. In this study, subcutaneous administration of adrenaline in rats for 10 consecutive days induces an oxidative stress milieu in heart, mimicking a chronic stress model. Adrenaline precipitates antioxidant imbalance, tissue-morphological alterations and disruption of mitochondrial membrane potential accompanied by alterations in tissue riboflavin, FMN and FAD levels and prominent reductions in the activities of riboflavin metabolizing enzymes. Altered levels of these co-factors also disrupt cardiac energy metabolism. However, melatonin protects against these deleterious repercussions of adrenaline. Melatonin safeguards cardiac tissue from inflammation by restraining the surge in interleukin-1 beta, tumor necrosis factor-alpha and interleukin-10 and also from apoptosis by suppression of Caspase-8 and Caspase-3 levels. Intriguingly, isothermal titration calorimetric study revealed spontaneous binding of adrenaline with FAD and FMN. Melatonin also exhibits strong binding affinity for adrenaline. 1H-NMR spectroscopic studies unveiled fascinating findings concerning the site of interactions of adrenaline with FAD, FMN, and melatonin. Findings suggest that melatonin may impede binding of adrenaline with flavin co-enzymes plausibly by potential encounter and sequestration of adrenaline, FMN or FAD by melatonin.