SAT-299 CD38 INHIBITION DECREASE RENAL OXIDATIVE STRESS IN DIABETIC KIDNEY DISEASE BY RESTORING OF SIRT3 ACTIVATION.

Abstract

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease worldwide. Aging is recognized as one of the risk factors for the development of end-stage renal failure due to chronic kidney disease including DKD. Therefore, investigation of aging-related mechanisms would be needed to discover a novel therapeutic target to treat DKD. Nicotinamide adenine dinucleotide (NAD) levels decrease during aging and are involved in age-related metabolic decline. Previous report demonstrated that expression and activity of the NADase CD38 increase with aging and that CD38 is required for the age-related NAD decline and mitochondrial dysfunction via a pathway mediated at least in part by regulation of sirt3 activity. We already discovered that the expression of CD38 was significantly increased in diabetic kidney and reduction in Sirt3 activity contributes to mitochondrial oxidative stress by decreasing the activation of anti-oxidative enzymes in the kidney of diabetic model rats. So, we investigated whether the inhibition of CD38 suppress mitochondrial oxidative stress through restoring of Sirt3 activity in diabetic rats and high glucose-incubated human renal tubular epithelial cells (HK2 cells). We used Male non-diabetic Zucker Lean (ZL) and type2 diabetes model rats, Zucker Diabetic Fatty rats (ZDFRs). CD38 inhibitor, apigenin or saline were prepared for oral gavage at 20mg/kg/day for 5 times by a week ,continued 4weeks and sacrificed at 28 weeks of age. In vitro study, HK2 cells were cultured in standard or high glucose condition and were treated for 48 hours with 10 μM apigenin or DMSO. At 28 weeks of age, compared to ZL, ZDFRs exhibited elevated HbA1c levels, heavier kidney weight, increased urinary albumin, liver type fatty acid binding protein (L-FABP), and 8-hydroxy-2’ -deoxyguanosine (8-OHdG), excretion, histological tubulo-interstitial fibrosis. In the immunostaining, increased CD38 positive cell in the kidney, particularly tubulo-interstitial area. Expression of mRNA and protein of CD38 were all significantly elevated in renal cortex. Administration of apigenin inhibited mRNA and protein expression of CD38, decreased albumin/L-FABP/8-OHdG excretion and ameliorated tubulo-interstitial fibrosis. Apigenin suppressed overexpression of CD38 in diabetic kidney and may ameliorated tubular cell damage. In addition, ZDFRs showed abnormal mitochondrial morphology, such as swelling and loss of cristae in primal tubular cell. In renal mitochondria, the NAD+/NADH ratio was reduced, and acetylation levels of mitochondrial antioxidant enzymes such as isocitrate dehydrogenase 2 (IDH2) and superoxide dismutase (SOD2), regulated by sirt3 were increased in ZDFRs. While apigenin restored abnormal mitochondrial morphology, increased NAD+/NADH ratio and reduced the acetylation of IDH2 and SOD2. Similarly, high glucose medium incubation in HK2 cell elevated CD38 levels associated with the reduction in NAD+/NADH ratio and increasing acetylation levels of SOD2 and IDH2. Administration of apigenin increased NAD+/NADH ratio, decreased SOD2 and IDH2 acetylation. Administration of the CD38 inhibitor, apigenin restored the NAD+/NADH ratio, decreased the levels of IDH2 and SOD2 acetylation and renal oxidative stress. Therefore, inhibition of CD38 may be a therapeutic target for the suppression of DKD.