Effects of Fructose and Stress on Rat Renal Copper Metabolism and Antioxidant Enzymes Function

Abstract

The effects of a fructose-rich diet and chronic stress on copper metabolism in the kidneys are still understudied. We investigated whether fructose and/or chronic unpredictable stress modulate copper metabolism in a way that affects redox homeostasis, thus contributing to progression of metabolic disturbances in the kidney. We determined protein level of copper transporters, chaperones, and cuproenzymes including cytochrome c oxidase, as well as antioxidant enzymes function in the kidneys of male Wistar rats subjected to 20% liquid fructose supplementation and/or chronic stress. Liquid fructose supplementation increased level of copper chaperone of superoxide dismutase and decreased metallothionein level, while rendering the level of copper importer and copper chaperones involved in copper delivery to mitochondria and trans Golgi network unaffected. Stress had no effect on renal copper metabolism. The activity and expression of renal antioxidant enzymes remained unaltered in all experimental groups. In conclusion, fructose, independently of stress, decreased renal copper level, and modulated renal copper metabolism as to preserve vital cellular function including mitochondrial energy production and antioxidative defense, at the expense of intracellular copper storage.

Keywords: copper chaperone of superoxide dismutase; copper transporter; fructose-fed rat; kidney; oxidative stress.

Figure 1

Effects of liquid fructose supplementation and/or stress on copper concentration and proteins involved in copper import (CTR1 and DMT1), storage (MT), and transport to Golgi network (ATOX1). Groups: control (C), fructose-fed (F), stress (S) and fructose + stress (FS). Renal copper concentrations (a), representative Western blots (b) and protein level of CTR1 (c), DMT1 (d) MT (e) and ATOX1 (f) in renal whole cell extracts. Scatter plot with bar graphs represent the means ± SEMs for each protein normalized to β-actin and expressed relative to controls (n = 6 animals/group). Two-way ANOVA was used to evaluate the effects of fructose and stress, and their interaction. Asterisk denotes statistically significant main effect of fructose. p < 0.05.

Figure 2

Effects of liquid fructose supplementation and/or stress on COX17 and COX2 protein level. Groups: control (C), fructose-fed (F), stress (S) and fructose + stress (FS). Protein level of COX17 (a) and COX2 (b) in renal whole cell extracts was measured by Western blot. Scatter plot with bar graphs represent the means ± SEMs for each protein normalized to β-actin and expressed relative to controls (n = 6 animals/group). Two-way ANOVA was used to evaluate the effects of fructose and stress, and their interaction.

Figure 3

Effects of liquid fructose supplementation and/or stress on the level of copper chaperone CCS and antioxidant enzymes. Groups: control (C), fructose-fed (F), stress (S) and fructose + stress (FS). Protein level of CCS (a), SOD1 (b) and SOD2 (c), CAT (d), GPX (e) and GR (f) in renal whole cell extracts, was measured by Western blot. Scatter plot with bar graphs represent the means ± SEMs for each protein normalized to β-actin and expressed relative to controls (n = 6 animals/group). Two-way ANOVA was used to evaluate the effects of fructose and stress, and their interaction. Asterisk denotes statistically significant main effect of fructose. p < 0.05.