Nicotinamide adenine dinucleotide biosynthetic and tryptophan metabolic pathways (NAD and Trp pathways)

The Nicotinamide adenine dinucleotide (NAD) synthesis and tryptophan metabolic pathways represent a complex biochemical network essential for cellular energy homeostasis, DNA repair, and immune modulation. In humans, tryptophan is an essential amino acid primarily metabolized via the kynurenine pathway, which serves as the de novo route for NAD+ production (Canto et al., 2015, Cell Metabolism). This pathway is a major therapeutic focus in oncology, where enzymes like Indoleamine 2,3-dioxygenase 1 (IDO1) and Tryptophan 2,3-dioxygenase (TDO) are often overexpressed by tumors to create an immunosuppressive environment by depleting tryptophan and accumulating kynurenine (Prendergast et al., 2017, Cancer Research). Additionally, the NAD salvage pathway, particularly the rate-limiting enzyme Nicotinamide phosphoribosyltransferase (NAMPT), is critical for maintaining the high NAD+ requirements of rapidly proliferating cancer cells (Galli et al., 2013, Cancer Research). Drugs targeting this system include IDO1 inhibitors designed to restore T-cell function and NAMPT inhibitors intended to deplete cellular ATP. Conversely, the pathway is also targeted for longevity and metabolic health through the use of NAD+ precursors like nicotinamide riboside to counteract age-related NAD+ decline (Yoshino et al., 2018, Cell Metabolism).

Other names

Kynurenine pathwayNAD+ biosynthetic pathwaysTryptophan-kynurenine-NAD axisDe novo NAD+ synthesis pathway

Inhibition of rate-limiting enzymes such as Indoleamine 2,3-dioxygenase 1 (IDO1) to prevent immune evasion, or inhibition of Nicotinamide phosphoribosyltransferase (NAMPT) to deplete cellular energy in cancer cells; alternatively, supplementation with precursors like Nicotinamide riboside to increase NAD+ levels.