Biochemical mechanisms underlying endocannabinoid dysregulation in the pancreas and adipose tissue of high fat diet-fed mice

Isabel Matias1, Katarzyna Starowicz1, Luigia Cristino2, Alessandro Racioppi1, Vincenzo Di Marzo1. 1Endocannabinoid Research Group, Institute of Biomolecular Chemistry, Consiglio Nazionale delle Ricerche, Pozzuoli (NA), Italy, 2Endocannabinoid Research Group, Institute of Cybernetics, Consiglio Nazionale delle Ricerche, Pozzuoli (NA), Italy.

The endocannabinoid (EC) system (comprising the EC ligands, anandamide and 2-arachidonoyl-glycerol, the cannabinoid CB1 and CB2 receptors, and EC biosynthesising and degrading enzymes) is involved in the control of energy homeostasis (Matias and Di Marzo, 2007). There is increasing evidence for peripherally elevated EC levels during conditions of unbalanced energy homeostasis such as abdominal obesity, dyslipidemia and hyperglycemia, but the biochemical mechanisms underlying these alterations are not understood (Cota et al., 2003; Matias et al., 2006; Matias and Di Marzo, 2007).

Here, we assessed in mice fed for up to 14 weeks with a standard or high fat (HFD) diet: 1) the expression of cannabinoid receptors and EC biosynthesising enzymes (NAPE-PLD and DAGLα) and degrading enzymes (FAAH and MAGL) in pancreatic and adipose tissue sections by immunohistochemistry; 2) the amounts, measured by liquid chromatography-mass spectrometry, of the ECs, 2-AG and anandamide, and of palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), whose levels are regulated by the same enzymes as anandamide. Seven-week old C57Bl/6J male mice were fed a diet containing 25.5% fat (49% of calories), 22% protein and 38.4% carbohydrate (TD97366, Harlan) for up to 14 weeks. Control mice received a standard diet. At the beginning of the treatments (time 0), the weight of the mice was 22.44±0.15 g. At the end of the treatment (14 weeks), HFD-fed mice weighed 41.5% more than age-matched animal fed with standard diet. Four mice per condition (HFD and controls) at each time point (3, 8 and 14 weeks) were tested.

Whereas CB1 receptors and biosynthetic enzymes were found mostly in α-cells, degrading enzymes were identified in β-cells. Following HFD, a strong upregulation of biosynthetic enzymes in β-cells, and a decrease of FAAH levels, were observed together with an increase of pancreatic levels of anandamide (48.0±2.8 vs. 85.7±12.1 pmol g-1 after HFD), but not PEA and OEA. In the visceral fat, we observed no changes in the levels of EC metabolic enzymes, while in the subcutaneous fat a decrease in EC levels (63.3±4.4 vs. 13.7±5.31 pmol g-1 for anandamide and 1.41±0.24 vs. 0.22±0.05 pmol g-1 for 2-AG), OEA and PEA concentrations was accompanied by down- and up-regulation of biosynthesising enzymes and FAAH, respectively. No significant change in cannabinoid receptor levels was observed in any tissue following HFD.

These data provide novel information on the distribution of EC metabolic enzymes in the pancreas and adipose organ, where their aberrant expression during hyperglycemia and obesity in part determines dysregulated EC levels.

Cota et al. (2003) J Clin Invest 112:423-431

Matias et al. (2006) J Clin Endocrinol Metab 91:3171-80

Matias and Di Marzo (2007) Trends Endocrinol Metab 18:27-37

Supported by a Research Grant from Sanofi-Aventis.