Association of cannabinoid receptor expression with anandamide concentrations in endometrial cancer

Abstract

BackgroundThe incidence of endometrial cancer is increasing worldwide. Despite improved overall survival rates, its aetiopathogenesis remains complicated, although oestrogens are known causal factors. Among other factors thought to be implicated are the endocannabinoids. Anandamide (AEA), the prototypical endocannabinoid, has emerged as a possible factor in the pathogenesis of endometrial cancer because oestrogen regulates AEA concentrations and the expression of the cannabinoid receptors in other tissues. Furthermore, the endocannabinoid system is protective against the growth and spread of different malignancies. We aimed to investigate and quantify anandamide and its receptors in endometrial cancer. MethodsIn this single-centre study conducted at a UK teaching hospital, 31 patients with endometrial carcinomas (27 type 1, four type 2) and seven healthy age-matched controls with atrophic endometria were recruited. Biopsy samples were taken and divided into two—one for this study and the other for histological confirmation of diagnosis (graded according to the FIGO system). The biopsy sample for this study was further divided into two—one for AEA measurement and the other for quantitative RT-PCR. CB1 and CB2 transcript levels were measured in triplicate and normalised against the housekeeping genes PPIA, MRPL19, and IPO8. 15 of 31 cancer patients (12 type 1, three type 2) and all seven of the control group, volunteered blood for plasma collection. At hysterectomy, 31 endometrial cancer samples (27 type 1, four type 2) and seven age-matched atrophic control endometrial biopsy samples were obtained for tissue AEA measurement. Extracts from the plasma and endometrial homogenates were assessed for the presence of AEA with UHPLC-tandem mass spectrometry. FindingsIn the endometrial cancer tissues, both CB1 and CB2 transcript levels were significantly decreased by 90% (p<0·0004) and 80% (p< 0·0001), respectively, compared with atrophic tissues. Plasma AEA concentrations were significantly higher in patients with endometrial cancer than in the control group (mean 1·95 nM [SE 0·59] vs 1·06 [0·08], p=0·037). Plasma AEA concentrations in patients with type 1 disease were significantly higher than in control patients (2·17 [0·72] vs 1·06 [0·08], p<0·05), but in patients with type 2 disease there was no difference (1·08 [0·05]). Similarly, tissue AEA in patients with endometrial cancer was significantly higher than in the control group (5·45 nmol/g [SE 0·91] vs 1·77 [0·66], p=0·046). Tissue AEA was significantly higher in type 1 endometrial cancer than in atrophic samples (6·12 [0·98] vs 1·77 [0·66], p<0·05), but type 2 samples did not differ (0·90 [0·16]). Furthermore, in samples available for comparison (15 endometrial cancer, seven atrophic) there was a statistically significant correlation between plasma and tissue AEA concentrations (r=0·55, p=0·008). InterpretationThe results from this study suggest that downregulation of CB1 and CB2 receptor transcript levels and raised tissue and plasma AEA concentrations are linked in some way. We speculate that the endocannabinoid system is implicated in the aetiopathogenesis of endometrial cancer, but further work is warranted. The correlation between plasma and tissue AEA concentrations suggests that plasma AEA could be used as a biomarker for some forms of endometrial malignant disease, especially type 1 endometrioid adenocarcinoma. The endocannabinoid system thus presents an attractive novel target for pharmacological intervention in some endometrial malignancies. FundingUniversity Hospitals of Leicester NHS Trust.