Expression of NG,NG-dimethylarginine dimethylaminohydrolase and protein arginine N-methyltransferase isoforms in diabetic rat kidney: effects of angiotensin II receptor blockers

• Objective: The nitric oxide (NO) synthase inhibitor, asymmetric dimethylarginine (ADMA) is generated by protein arginine N-methyltransferase (PRMT)-1 and is metabolized by NG, NG-dimethylarginine dimethylaminohydrolase (DDAH). We tested the hypothesis that increased serum ADMA (SADMA) in the streptozotocin (STZ)-induced rat model of diabetes mellitus (DM) is mediated by an angiotensin receptor blocker– sensitive change in DDAH or PRMT expression.Research design and Methods: Data were compared from 4 groups of rats: sham injected controls; untreated STZ- DM at 4 weeks; STZ-DM rats administered the angiotensin II receptor blocker telmisartan for 2 weeks; control rats administered telmisartan for 2 weeks.Results: Immunostaining and Western blotting of microdissected nephron segments localized DDAH I in the proximal tubules and DDAH II in the glomeruli, afferent arterioles, macula densa and distal nephron. Renal angiotensin II and SADMA increased with DM but were normalized by 2 weeks of telmisartan. DDAH I expression was decreased in DM kidneys while DDAH II expression was increased. These changes were reversed by telmisartan which also reduced expression of PRMT-1 and -5. Telmisartan increased expressions of DDAH I but decreased DDAH II in Ang II-stimulated kidney slices ex-vivo.Conclusion: Renal angiotensin II and SADMA are increased in insulinopenic DM. They are normalized by an angiotensin II receptor blocker which increases the renal expression of DDAH I, decreases PRMT-1 and increases renal NO metabolites.

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