4-hydroxy-2-nonenal and cariporide

Evidence for an important role for Na(+)/H(+) exchangers in diabetic complications is emerging. The aim of this study was to evaluate whether Na(+)/H(+) exchanger 1 inhibition reverses experimental peripheral diabetic neuropathy. Control and streptozotocin-diabetic rats were treated with the specific Na(+)/H(+) exchanger 1 inhibitor cariporide for 4 wk after 12 wk without treatment. Neuropathy end points included sciatic motor and sensory nerve conduction velocities, endoneurial nutritive blood flow, vascular reactivity of epineurial arterioles, thermal nociception, tactile allodynia, and intraepidermal nerve fiber density. Advanced glycation end product and markers of oxidative stress, including nitrated protein levels in sciatic nerve, were evaluated by Western blot. Rats with 12-wk duration of diabetes developed motor and sensory nerve conduction deficits, thermal hypoalgesia, tactile allodynia, and intraepidermal nerve fiber loss. All these changes, including impairment of nerve blood flow and vascular reactivity of epineurial arterioles, were partially reversed by 4 wk of cariporide treatment. Na(+)/H(+) exchanger 1 inhibition was also associated with reduction of diabetes-induced accumulation of advanced glycation endproduct, oxidative stress, and nitrated proteins in sciatic nerve. In conclusion, these findings support an important role for Na(+)/H(+) exchanger 1 in functional, structural, and biochemical manifestations of peripheral diabetic neuropathy and provide the rationale for development of Na(+)/H(+) exchanger 1 inhibitors for treatment of diabetic vascular and neural complications.

Topics: Aldehydes; Animals; Arterioles; Behavior, Animal; Blood Glucose; Blotting, Western; Body Weight; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetic Neuropathies; Glycation End Products, Advanced; Guanidines; Male; Nerve Fibers; Nitrates; Pain Measurement; Pyruvaldehyde; Rats; Rats, Wistar; Reduced Folate Carrier Protein; Sciatic Nerve; Skin; Sulfones; Superoxides; Tyrosine

The Na⁺-H⁺-exchanger-1 (NHE-1) controls intracellular pH and glycolytic enzyme activities, and its expression and activity are increased by diabetes and high glucose. NHE-1-dependent upregulation of the upper part of glycolysis, under conditions of inhibition (lens) or insufficient activation (retina) of glyceraldehyde 3-phosphate dehydrogenase, underlies diversion of the excessive glycolytic flux towards several pathways contributing to oxidative stress, a causative factor in diabetic cataractogenesis and retinopathy. This study evaluated the role for NHE-1 in diabetic cataract formation and retinal oxidative stress and apoptosis. Control and streptozotocin-diabetic rats were maintained with or without treatment with the NHE-1 inhibitor cariporide (Sanofi-Aventis, 10 mgkg-1d-1) for 3.5 months. In in vitro studies, bovine retinal pericytes and endothelial cells were cultured in 5 or 30 mM glucose, with or without 10 µM cariporide, for 7 days. A several-fold increase of the by-product of glycolysis, α-glycerophosphate, indicative of activation of the upper part of glycolysis, was present in both rat lens and retina at an early (1-month) stage of streptozotocin-diabetes. Cariporide did not affect diabetic hyperglycemia and counteracted lens oxidative-nitrative stress and p38 MAPK activation, without affecting glucose or sorbitol pathway intermediate accumulation. Cataract formation (indirect ophthalmoscopy and slit-lamp examination) was delayed, but not prevented. The number of TUNEL-positive cells per flat-mounted retina was increased 4.4-fold in diabetic rats (101 ± 17 vs. 23 ± 8 in controls , P<0.01), and this increase was attenuated by cariporide (45 ± 12, P<0.01). Nitrotyrosine and poly(ADP-ribose) fluorescence and percentage of TUNEL-positive cells were increased in pericytes and endothelial cells cultured in 30 mM glucose, and these changes were at least partially prevented by cariporide. In conclusion, NHE-1 contributes to diabetic cataract formation, and retinal oxidative-nitrative stress and apoptosis. The findings identify a new therapeutic target for diabetic ocular complications.

Topics: Aldehydes; Animals; Apoptosis; Blood Glucose; Blotting, Western; Cataract; Cattle; Diabetes Complications; Extracellular Signal-Regulated MAP Kinases; Fasting; Guanidines; In Situ Nick-End Labeling; Lens, Crystalline; Male; Nitrosation; Oxidative Stress; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Poly(ADP-ribose) Polymerases; Rats; Rats, Wistar; Retina; Sodium-Hydrogen Exchangers; Sulfones; Tyrosine