Yonsei Med J.  2016 May;57(3):664-673. 10.3349/ymj.2016.57.3.664.

Protective Effects of Curcumin on Renal Oxidative Stress and Lipid Metabolism in a Rat Model of Type 2 Diabetic Nephropathy

• Kim BH
• Lee ES
• Choi R
• Nawaboot J
• Lee MY
• Lee EY
• Kim HS
• Chung CH

• KMID: 2374087
• DOI: http://doi.org/10.3349/ymj.2016.57.3.664

Abstract

PURPOSE
Diabetic nephropathy is a serious complication of type 2 diabetes mellitus, and delaying the development of diabetic nephropathy in patients with diabetes mellitus is very important. In this study, we investigated inflammation, oxidative stress, and lipid metabolism to assess whether curcumin ameliorates diabetic nephropathy.
MATERIALS AND METHODS
Animals were divided into three groups: Long-Evans-Tokushima-Otsuka rats for normal controls, Otsuka-Long-Evans-Tokushima Fatty (OLETF) rats for the diabetic group, and curcumin-treated (100 mg/kg/day) OLETF rats. We measured body and epididymal fat weights, and examined plasma glucose, adiponectin, and lipid profiles at 45 weeks. To confirm renal damage, we measured albumin-creatinine ratio, superoxide dismutase (SOD), and malondialdehyde (MDA) in urine samples. Glomerular basement membrane thickness and slit pore density were evaluated in the renal cortex tissue of rats. Furthermore, we conducted adenosine monophosphate-activated protein kinase (AMPK) signaling and oxidative stress-related nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling to investigate mechanisms of lipotoxicity in kidneys.
RESULTS
Curcumin ameliorated albuminuria, pathophysiologic changes on the glomerulus, urinary MDA, and urinary SOD related with elevated Nrf2 signaling, as well as serum lipid-related index and ectopic lipid accumulation through activation of AMPK signaling.
CONCLUSION
Collectively, these findings indicate that curcumin exerts renoprotective effects by inhibiting renal lipid accumulation and oxidative stress through AMPK and Nrf2 signaling pathway.

Keyword

Curcumin; diabetic nephropathy; oxidative stress; lipid metabolism

MeSH Terms

Albuminuria
Animals
Anti-Inflammatory Agents, Non-Steroidal/*therapeutic use
Curcumin/*pharmacology
Diabetes Mellitus, Type 2/*metabolism/urine
Diabetic Nephropathies/complications/*drug therapy/metabolism/pathology
Gene Expression/drug effects
Inflammation
Kidney/drug effects/metabolism/physiopathology
Kidney Glomerulus/metabolism/physiopathology
Lipid Metabolism/*drug effects
Male
Malondialdehyde/metabolism/urine
Oxidative Stress/*drug effects
Rats
Rats, Inbred OLETF
Rats, Long-Evans
Superoxide Dismutase/metabolism
Anti-Inflammatory Agents, Non-Steroidal
Curcumin
Malondialdehyde
Superoxide Dismutase

Figure

• 

  Fig. 1 Effect of curcumin on insulin tolerance and glucose tolerance tests. (A) At 45 weeks of age, the plasma glucose level of the DM group was significantly increased, compared to the CON group, using the intravenous insulin tolerance test, while glucose levels of the CUR group were not significant, compared to the DM group. (B) Using the intraperitoneal glucose tolerance test, the plasma glucose level of the DM group was found to be significantly decreased, compared to the CON group; however, such changes in glucose levels were not shown in the CUR group, compared to the DM group. Data expressed as mean±SD. *p<0.05 vs. CON. CON (•), control group; DM (▪), diabetic group; CUR (▴), curcumin-treated (100 mg/kg, p.o.) diabetic group.

• 

  Fig. 2 Effect of curcumin on urine albumin levels and 24-hour albumin/creatinine ratio (ACR). (A) At 45 weeks of age, urinary albumin levels of the CUR group in 24-hour urine samples were significantly decreased, compared to the DM group. (B) 24-hour ACR was also significantly decreased, compared to the DM group. Data expressed as mean±SD. *p<0.05 vs. CON, †p<0.05 vs. DM. CON, control group; DM, diabetic group; CUR, curcumin-treated (100 mg/kg, p.o.) diabetic group.

• 

  Fig. 3 Effect of curcumin on kidney histological morphology changes. (A) Representative image of glomerular hematoxylin and eosin (H&E)-stained sections. (B) Representative electron photomicrographs show glomerular basement membrane (GBM) thickness and open slit pores (arrows). (C) Glomerular volume. Differences in glomerular volume were not significant among these three groups. (D) GBM thickness. DM group shows significant glomerular thickening, compared with the CON group, while the CUR group shows significant reductions in diabetic alterations in kidneys at 45 weeks of age. (E) The number of open slit pores between podocyte foot processes. Glomerular injury decreased after treatment with curcumin, compared to the DM group. Data express mean±SD. *p<0.05 vs. CON, †p<0.05 vs. DM. H&E staining scale bar, 100 µm, ×400. EM scale bar, 100 µm, ×30000. CON, control group; DM, diabetic group; CUR, curcumin-treated (100 mg/kg, p.o.) diabetic group.

• 

  Fig. 4 Effect of curcumin on urine SOD and MDA, Nrf2/Keap1, and HO-1 protein expression in the urine or renal cortex. (A) Urinary SOD was significantly increased in the CUR group, compared to the DM group, at 45 weeks of age. (B) Urinary MDA significantly decreased in the CUR group, compared with the DM group. (C) Representative pictures of Nrf2/Keap1 protein ratio and HO-1 expression in renal kidney cortex of 45 weeks of age. (D) Reduced Nrf2/Keap1 protein ratio and HO-1 protein expression related to renal oxidative stress, which were significantly increased in the CUR group. Data expressed as mean±SD. *p<0.05 vs. CON, †p<0.05 vs. DM. CON, control group; DM, diabetic group; CUR, curcumin-treated (100 mg/kg, p.o.) diabetic group; SOD, superoxide dismutase; MDA, malondialdehyde; Nrf2, nuclear factor (erythroid-derived 2)-like 2; HO-1, heme oxygenase-1.

• 

  Fig. 5 Effect of curcumin on FFA, renal triglyceride (TG), AMPK, ACC, SREBP-1, SREBP-2, and ADRP protein expressions in renal cortex. (A) Serum FFA level. It was significantly increased in the DM group at 45 weeks of age, but it was significantly decreased by curcumin treatment. (B) Renal TG level. It tended to increase in the DM group (p=0.055), and curcumin significantly reduced renal TG. (C) Representative Western blots depicting protein abundance of the phosphorylated AMPK and ACC in the renal cortex. (D) The DM group showed significantly decreased phosphorylated AMPK and ACC expression in the renal cortex. These changes were reversed upon treatment with curcumin. (E) Representative Western blots depicting protein abundance of SREBP-1, SREBP-2, and ADRP in the renal tissues. (F) The DM group showed significantly increased SREBP-1, SREBP-2, and ADRP expressions in renal cortex. These changes were reversed upon treatment with curcumin. Data expressed as mean±SD. *p<0.05 vs. CON, †p<0.05 vs. DM. CON, control group; DM, diabetic group; CUR, curcumin-treated (100 mg/kg, p.o.) diabetic group; FFA, free fatty acid; AMPK, adenosine monophosphate-activated protein kinase; ACC, acetyl-CoA carboxylase; ADRP, adipose differentiation related protein.

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