Structural And Functional Interaction Of Delta(9)-Tetrahydrocannabinol With Liver Fatty Acid Binding Protein (Fabp1)

Although serum (Delta)9-tetrahydrocannabinol (Delta(9)-THC) undergoes rapid hepatic clearance and metabolism, almost nothing is known regarding the mechanism(s) whereby this highly lipophilic phytocannabinoid is transported for metabolism/excretion. A novel NBD-arachidonoylethanolamide (NBD-AEA) fluorescence displacement assay showed that liver fatty acid binding protein (FABP1), the major hepatic endocannabinoid (EC) binding protein, binds the first major metabolite of Delta(9)-THC (Delta(9)-THC OH) as well as Delta(9)-THC itself. Circular dichroism (CD) confirmed that not only Delta(9)-THC and Delta(9)-THC OH but also downstream metabolites Delta(9)-THC COOH and Delta(9)-THC CO-glucuronide directly interact with FABP1. Delta(9)-THC and metabolite interaction differentially altered the FABP1 secondary structure, increasing total a-helix (all), decreasing total beta-sheet (Delta(9)-THC-COOH, Delta(9)-THC-CO-glucuronide), increasing turns (Delta(9)-THC-OH, Delta(9)-THC-COOH, Delta(9)-THC CO-glucuronide), and decreasing unordered structure (Delta(9)-THC, Delta(9)-THC-OH). Cultured primary hepatocytes from wild-type (WT) mice took up and converted Delta(9)-THC to the above metabolites. Fabpl gene ablation (LKO) dramatically increased hepatocyte accumulation of Delta(9)-THC and even more so its primary metabolites Delta(9)-THC-OH and Delta(9)-THC-COOH. Concomitantly, rtPCR and Western blotting indicated that LKO significantly increased Delta(9)-THC's ability to regulate downstream nuclear receptor transcription of genes important in both EC (Napepld > Daglb > Dagla, Naaa, Cnr1) and lipid (CptlA > Fasn, FATP4) metabolism. Taken together, the data indicated that FABP1 may play important roles in Delta(9)-THC uptake and elimination as well as Delta(9)-THC induction of genes regulating hepatic EC levels and downstream targets in lipid metabolism.