A proper NADH/NAD + balance allows for the flow of metabolic and catabolic activities determining cellular growth. In Escherichia coli, more than 80 NAD + dependent enzymes are involved in all major metabolic pathways, including the post-transcriptional build-up of thiazole and oxazole rings from small linear peptides, which is a critical step for the antibiotic activity of some microcins. In recent years, NAD metabolism boosting drugs have been explored, mostly precursors of NAD + synthesis in human cells, with beneficial effects on the aging process and in preventing oncological and neurological diseases. These compounds also enhance NAD + metabolism in the human microbiota, which contributes to these beneficial effects. On the other hand, inhibition of NAD + metabolism has been proposed as a therapeutic approach to reduce the growth and propagation of tumor cells and mitigating inflammatory bowel diseases; in this case, the activity of the microbiota might mitigate therapeutic efficacy. Antibiotics, which reduce the effect of microbiota, should synergize with NAD + metabolism inhibitors, but these drugs might increase the proportion of antibiotic persistent populations. Conversely, antibiotics might have a stronger killing effect on bacteria with active NAD + production and reduce the cooperation of NAD + producing bacteria with tumoral cells. The use of NADH/NAD + modulators should take into consideration the use of antibiotics and the population structure of the microbiota.
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