Reductive stress-a common metabolic feature of obesity and cancer

Reductive stress, characterized by rising level of NADH (nicotinamide adenine dinucleotide) for a status of NADH/NAD⁺ ratio elevation, has been reported in obesity and cancer. However, the mechanism and significance of reductive stress remain to be established in obesity. This perspective is prepared to address the issue with new insights published recently. NADH is used in production of NADPH, glutathione, ATP and heat in the classical biochemistry. In obesity, elevation of NADH/NAD⁺ ratio, likely from overproduction due to substrate overloading, has been found in the liver for insulin resistance and gluconeogenesis. New evidence demonstrates that the elevation may induce lipogenesis, purine biosynthesis and gluconeogenesis through activation of transcription factors of ChREBP and NRF2. In cancer cells, NADH/NAD⁺ elevation under the Warburg effect is primarily derived from decreased NADH consumption in the mitochondrial respiration. Alternatively, NRF2 overactivation from gene mutation represents another mechanism of NADH/NAD⁺ elevation from NADH production in the cancer cells. The elevation is required for quick proliferation of cancer cells through induction of biosynthesis of the essential molecules. It appears that the causes of reductive stress are different between obesity and cancer, while its impact in anabolism is similar in the two conditions.