Curcumin, Alone or in Combination with Aminoguanidine, Increases Antioxidant Defenses and Glycation Product Detoxification in Streptozotocin-Diabetic Rats: A Therapeutic Strategy to Mitigate Glycoxidative Stress

Abstract

Both oxidative stress and the exacerbated generation of advanced glycation end products (AGEs) have crucial roles in the onset and progression of diabetic complications. Curcumin has antioxidant and antidiabetic properties; its combination with compounds capable of preventing the advanced glycation events, such as aminoguanidine, is an interesting therapeutic option to counteract diabetic complications. This study is aimed at investigating the effects of treatments with curcumin or aminoguanidine, alone or in combination, on metabolic alterations in streptozotocin-diabetic rats; the focus was mainly on the potential of these bioactive compounds to oppose the glycoxidative stress. Curcumin (90 mg/kg) or aminoguanidine (50 and 100 mg/kg), alone or in combination, slightly decreased glycemia and the biomarkers of early protein glycation, but markedly decreased AGE levels (biomarkers of advanced glycation) and oxidative damage biomarkers in the plasma, liver, and kidney of diabetic rats. Some novel insights about the in vivo effects of these bioactive compounds are centered on the triggering of cytoprotective machinery. The treatments with curcumin and/or aminoguanidine increased the activities of the antioxidant enzymes (paraoxonase 1, superoxide dismutase, and catalase) and the levels of AGE detoxification system components (AGE-R1 receptor and glyoxalase 1). In addition, combination therapy between curcumin and aminoguanidine effectively prevented dyslipidemia in diabetic rats. These findings demonstrate the combination of curcumin (natural antioxidant) and aminoguanidine (prototype therapeutic agent with anti-AGE activity) as a potential complementary therapeutic option for use with antihyperglycemic agents, which may aggregate beneficial effects against diabetic complications.

Figure 1

Body weight (a) and glycemia levels (b) of streptozotocin-induced diabetic rats treated for 45 days with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. Differences in the same group relative to day 0 were analyzed using paired Student's t-test. ^#Different compared to day 0 (p < 0.05). Here and in Figures 2to 8—NYOG: normal rats treated with yoghurt; DYOG: diabetic rats treated with yoghurt; DINS: diabetic rats treated with 4 U/day insulin; DC: diabetic rats treated with 90 mg/kg curcumin in yoghurt; DA-50: diabetic rats treated with 50 mg/kg aminoguanidine in yoghurt; DCA-50: diabetic rats treated with 90 mg/kg curcumin+50 mg/kg aminoguanidine in yoghurt; DA-100: diabetic rats treated with 100 mg/kg aminoguanidine in yoghurt; DCA-100: diabetic rats treated with 90 mg/kg curcumin+100 mg/kg aminoguanidine in yoghurt.

Figure 2

Antioxidant defenses and glycoxidative stress biomarkers in the plasma of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Activity of PON 1 (a) and levels of fluorescent AGEs (b), PCO (c), TBARS (d), and NO_x (e). Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG. ^CDifferences to DINS. ^DDifferences to DC. ^EDifferences to DA-50.

Figure 3

Antioxidant system biomarkers in the liver of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Activities of the enzymes SOD (a), CAT (b), GSH-Px (c), and GSH-Rd (d) and levels of NPSH groups (e). Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG.

Figure 4

Antioxidant system biomarkers in the kidney of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Activities of SOD (a), CAT (b), GSH-Px (c), and GSH-Rd (d) and levels of NPSH groups (e). Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG.

Figure 5

AGE detoxification biomarkers in the liver of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Representative lanes of protein levels as detected by western blot analysis for AGE-R1, GLO 1, and β-actin (a); densitometric analysis of western blot results for AGE-R1 (b) and GLO 1 (c). Values are expressed as the mean ± standard error of the mean (SEM) (n = 6). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG.

Figure 6

AGE detoxification biomarkers in the kidney of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Representative lanes of protein levels as detected by western blot analysis for AGE-R1, GLO 1, and β-actin (a); densitometric analysis of western blot results for AGE-R1 (b) and GLO 1 (c). Values are expressed as the mean ± standard error of the mean (SEM) (n = 6). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG. ^CDifferences to DINS. ^DDifferences to DC. ^EDifferences to DA-50. ^FDifferences to DCA-50.

Figure 7

Glycoxidative stress biomarkers in the liver of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Levels of fluorescent AGEs (a), PCO (b), and TBARS (c). Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG.

Figure 8

Glycoxidative stress biomarkers in the kidney of streptozotocin-induced diabetic rats after 45 days of treatment with yoghurt enriched with curcumin, alone or in combination with aminoguanidine. Levels of fluorescent AGEs (a), PCO (b), and TBARS (c). Values are expressed as the mean ± standard error of the mean (SEM) (n = 10). Differences between groups were considered significant at p < 0.05 and were analyzed using one-way ANOVA followed by the Student-Newman-Keuls test. ^ADifferences to NYOG. ^BDifferences to DYOG.