Different regulation of human delta-opioid receptors by SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide] and endogenous enkephalins.

Among the different mechanisms underlying opioid tolerance, receptor desensitization would represent a major cellular adaptation process in which the role of receptor internalization is still a matter of debate. In the present study, we examined desensitization of the human delta-opioid receptor (hDOR) produced by endogenous opioid peptides Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) and Met-enkephalin (Tyr-Gly-Gly-Phe-Met), and the contribution of internalization in this process. Results obtained with natural peptides were compared with those produced by a synthetic opioid agonist, SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide). After a 30-min treatment, we observed a different regulation of hDOR between agonists. SNC-80 produced a stronger and faster desensitization and was associated with a loss of opioid binding sites by 50%. SNC-80 also caused a marked hDOR down-regulation by 30% as observed by Western blot. Immunocytochemistry revealed that SNC-80 induced a complete redistribution of hDOR from cell surface into intracellular compartments, whereas a partial internalization was visualized upon enkephalin exposure. In contrast, a stronger hDOR recycling and resensitization were measured after enkephalin treatment compared with SNC-80. These data strongly suggested a differential sorting of the internalized receptors caused by enkephalins and SNC-80 that was further confirmed by chloroquine as a lysosomal degradation blocker and monensin as a recycling endosome inhibitor. Finally, by preventing hDOR internalization with 0.5 M sucrose, we demonstrated that hDOR internalization contributes partially to desensitization. In conclusion, hDOR desensitization depends both on its internalization and its sorting either to the recycling pathway or to lysosomes.

Relationship between polymorphisms in the renin-angiotensin system and nephropathy in type 2 diabetic patients.

BACKGROUND: Renin Angiotensin system is involved in renal function and its polymorphisms may influence diabetic nephropathy. ID ACE polymorphism modulates ACE level whereas M235T AGT polymorphism is involved in arterial hypertension. The A1166C AT1R polymorphism is involved in arterial hypertension and in diabetic retinopathy. METHODS: Two hundred thirty five type 2 diabetic patients were enrolled in this transversal study. Data were documented for clinical characteristics of the population, HbA(1c), urinary albumin excretion, presence of retinopathy or antihypertensive treatment. Polymorphisms were analyzed by PCR techniques. The patients were divided into 3 groups: group 1, without nephropathy (n=118), group 2, microalbuminuria (n=78), group 3, macroalbuminuria (n=39). RESULTS: Diabetes duration was longer (p<0.001), retinopathy (p<0.001) and antihypertensive treatment (p<0.02) were more frequent in group 3 compared to group 1 and 2. The I/D ACE and M235T AGT polymorphisms were not differently distributed between the three groups. In contrast, the CC genotype of the AT1R polymorphism was overrepresented in group 2 (p=0.021). The presence of the CC AT1R genotype considerably increased the incidence of albuminuria after 10 years of diabetes (AA vs CC p=0.01), particurlarly in men. No effect was seen with I/D ACE and M235T AGT polymorphisms. CONCLUSION: In conclusion, we observed an interaction of A1166C AT1R polymorphism with diabetes in men but not of I/D ACE and M235T AGT polymorphisms.