Fatty acid amide hydrolase and monoacylglycerol lipase activities in adipocytes taken from obese surgical patients

Jemma Cable1, Garry Tan1, Stephen Alexander1,2, Saoirse O'Sullivan1. 1University of Nottingham, Division of Vascular Medicine, DE22 3DT, Derby, United Kingdom, 2University of Nottingham, School of Biomedical Sciences, NG7 2UH, Nottingham, United Kingdom.

The role of the endocannabinoid system (ECS) in metabolism is gradually emerging, and there is evidence that the peripheral ECS is dysregulated in obesity. Blood concentrations of the endocannabinoids anandamide and 2-arachidonoyl glycerol (2-AG) are increased in obese humans (Blüher et al. 2006). Gene expression of the enzymes involved in endocannabinoid catabolism, fatty acid amide hydrolase (FAAH) for anandamide and monoacylglycerol lipase (MGL) for 2-AG, have been investigated in the subcutaneous and omental adipose tissue of lean and obese subjects, but the reported results are highly contradictory. In some studies, expression does not differ between visceral and subcutaneous adipose depots (Pagano et al 2007), whilst in others, significant differences have been found (Blüher et al. 2006). These studies are based on mRNA expression. The aim of the present study was to investigate whether FAAH and MGL activities differ between omental and subcutaneous adipocytes in obese subjects. Additionally, the relationship between metabolic health or co-morbidities and enzyme activity was analysed.

Ethical approval for the study was granted by Derbyshire Research Ethics Committee and Research and Development at Derby City General Hospital Trust. Patients undergoing laparascopic bariatric surgery or cholecystectomy were recruited to the study and anthropometric measurements and fasting venous blood samples were taken prior to surgery. Subcutaneous adipose biopsies were taken during surgery from all patients (age range was 20-48 years, with a mean of 31±8.7 years; n = 28) and omental adipose samples were taken from 14 of these. Blood samples were analysed in the hospital pathology department for standard metabolic markers, including lipid profile, glucose and insulin. The adipose tissue samples were stored at -80°C until digestion with collagenase and subsequent homogenisation of the isolated mature adipocytes. The particulate and cytosolic cell fractions were separated using centrifugation and stored at -80°C. FAAH activity in the cell membrane fraction was assayed using 2 μM N-arachidonoyl-[3H]-ethanolamine as substrate, and 100 μM 2-oleoyl-[3H]-glycerol was used to measure MGL activity in the cytosolic fraction.

The activities of FAAH and MGL were not found to be significantly different between adipocytes isolated from omental (FAAH 70.3±25.1 pmol/min/mg protein; MGL 12.7±1.9 nmol/min/mg protein) versus subcutaneous (FAAH 69.3±14.5 pmol/min/mg protein; MGL 9.0±2.3 nmol/min/mg protein) adipose depots (paired t-test, n = 14). In subcutaneous adipocytes, FAAH and MGL activities were not different between subgroups of metabolically healthy (FAAH 59.6±21.9 pmol/min/mg protein; MGL 7.3±2.4 nmol/min/mg protein), metabolic syndrome (FAAH 50.4±9.4 pmol/min/mg protein; MGL 7.8±1.7 nmol/min/mg protein) or diabetic patients (FAAH 74.4±26.2 pmol/min/mg protein; MGL 6.2±1.5 nmol/min/mg protein). FAAH and MGL activity in subcutaneous mature adipocytes showed no correlation with BMI (FAAH r2 = 0.03, P = 0.41; MGL r2<0.01, P = 0.95) or any of the anthropometric or metabolic parameters measured in this study. The results of this study indicate that the activities of two major ECS enzymes are not altered with increasing adiposity or metabolic disease in the obese population.

Blüher, M et al. (2006). Diabetes 55: 3053-3060.

Pagano, C et al. (2007). J Clin Endocrinolog Metab 92: 4810-4819.