Phytanic Acid Metabolism
Diet has played a major role in the evolution of human and non-human primate digestive systems. Phytanic acid is a potentially toxic branched chain fatty acid that can be acquired in humans by ingesting plant and/or animal products. In ruminants, the fermentation of ingested plant materials by gut microbes can liberate phytol, a constituent of chlorophyll, which can be rapidly metabolized to phytanic acid and stored in fats. Members of the marine food chain can accumulate phytanic acid by ingesting zooplankton and/or krill, sources of phytol and chlorophyll-related precursors. Although humans can convert free phytol into phytanic acid, they do not derive appreciable amounts of phytanic acid from chlorophyll in plant materials. Humans with impaired phytanic acid metabolism can accumulate toxic stores of phytanic acid that have deleterious effects on multiple organ systems. Although it was established that humans cannot derive phytanic acid from chlorophyll and instead normally obtain it only from meat, dairy, and fish products, less was known about the capacity of non-human primate with proportionally larger hindguts to obtain phytanic acid from plant materials. We discuss studies profiling phytanic acid levels in red blood cells obtained from humans and captive non-human primates all on low phytanic acid diets. Therein, captive apes and Old World and New World monkeys displayed significantly higher red blood cell phytanic acid levels relative to humans. Furthermore, a small-scale gene expression profiling study indicated that genes relevant to phytanic acid metabolism were more highly expressed in the liver, heart, and testes of humans relative to chimpanzees. The favored hypothesis is that, unlike humans, the non-human primates surveyed can derive significant amounts of phytanic acid from the degradation of ingested chlorophyll through gut fermentation. This raises the possibility that red blood cell phytanic acid levels could serve as a biomarker for evaluating the digestive health of captive NHPs.