Phytenic acid: identification of five isomers in chemical and biological products of phytol

Phytol metabolites are circulating dietary factors that activate the nuclear receptor RXR

RXR is a nuclear receptor that plays a central role in cell signaling by pairing with a host of other receptors. Previously, 9-cis-retinoic acid (9cRA) was defined as a potent RXR activator. Here we describe a unique RXR effector identified from organic extracts of bovine serum by following RXR-dependent transcriptional activity. Structural analyses of material in active fractions pointed to the saturated diterpenoid phytanic acid, which induced RXR-dependent transcription at concentrations between 4 and 64 microM. Although 200 times more potent than phytanic acid, 9cRA was undetectable in equivalent amounts of extract and cannot be present at a concentration that could account for the activity. Phytanic acid, another phytol metabolite, was synthesized and stimulated RXR with a potency and efficacy similar to phytanic acid. These metabolites specifically displaced [3H]-9cRA from RXR with Ki values of 4 microM, indicating that their transcriptional effects are mediated by direct receptor interactions. Phytol metabolites are compelling candidates for physiological effectors, because their RXR binding affinities and activation potencies match their micromolar circulating concentrations. Given their exclusive dietary origin, these chlorophyll metabolites may represent essential nutrients that coordinate cellular metabolism through RXR-dependent signaling pathways.

Occurrence of novel branched-chain fatty acids in Refsum's disease

Two novel branched-chain fatty acids, which appear to be unsaturated analogs of phytanic acid, have been observed in sera and urine of patients with Refsum's disease. They occur in both phospholipids and neutral lipids, and have been isolated and characterized.

Synthesis and analysis of phytyl and phytenoyl wax esters

An efficient procedure for preparing phytenic acid methyl ester, free of isomers, from phytol is reported. Phytyl phytenate and other isoprenoid wax esters were synthesized. Gas liquid chromatography of these wax esters and other compounds related to phytol and phytenic acid is described. The alkyl constituents of isoprenoid wax esters can be analyzed after alkaline methanolysis and the acyl constituents after acidic methanolysis. The applicability of these methods to natural mixtures was demonstrated with wax esters from mosses which contained both types of isoprenoids and with wax esters from healthy and frost damaged grass which contained phytol, but not phytenic acid.

Occurrence of 7-methyl-7-hexadecenoic acid, the corresponding alcohol, 7-methyl-6-hexadecenoic acid, and 5-methyl-4hexadecenoic acid in sperm whale oils

Two sperm whale oils from the northern hemisphere and two from the southern hemisphere were fractionated. Triglyceride and wax esters were examined for fatty acids and alcohols with monoethylenic unsaturation bearing a methyl branch on an ethylenic carbon. The 7-methyl-7-hexadecenoic acid (0.37-1.37%) was accompanied by the corresponding alcohol (0.28-0.72%), but these materials were not accompanied by shorter chain homologues. The 7-methyl-6-hexadecenoic acid was relatively less important (0.23-0.68%), but was accompanied by 5-methyl-4-hexadecenoic acid (0.10-0.39%), and a partially identified C13 compound. Chromatographic properties on silver nitrate impregnated silicic acid TLC and on three GLC liquid phases are reported.

Metabolism of long-chain isoprenoid alcohols. Incorporation of phytol and dihydrophytol into the lipids of rat brain

[U-14-C]Phytol (3,7,11,15-tetramethylhexadec-2-en-1-ol) and [U-14-C]dihydrophytol (3,7,11,15-tetramethylhexadecanol) were administered intracerebrally to 18-day-old rats and incorporation of radioactivity into brain lipids was determined after 6 and 24 h. Radioactivity from [U-14-C]phytol was found in free phytenic (3,7,11,15-tetramethylhexadec-2-enoic), phytanic (3,7,11,15-tetramethylhexadecanoic) and pristanic (2,6,10,14-tetramethylpentadecanoic) acids, in phytanic and pristanic acid moieties of neutral and polar lipids, and in esters of phytol. In addition, evidence is presented for the utilization of phytol to form 1-O-phytenyl-2-acyl glycerophosphatides. Radioactivity from [U-14-C]dihydrophytol was found in free phytanic and pristanic acids, the corresponding acyl groups of neutral and polar lipids, esters of dihydrophytol and 1-O-phytanyl-2-acyl glycerophosphatides. Incorporation of either substrate into O-alkylglycerols was very low, and labeled branched-chain alk-1-enylglycerols could not be detected.