The Protective Effects of Melatonin on Aluminum-Induced Hepatotoxicity and Nephrotoxicity in Rats

Abstract

Aluminum (Al) is a ubiquitous element with known toxicity for both humans and animals. Herein, we aimed to investigate the potential role of melatonin (MEL) in hepatotoxicity and nephrotoxicity following aluminum chloride (AlCl₃) treatment in rats. Adult male rats were treated with AlCl₃ (34 mg/kg bwt) for eight weeks. Exposure to AlCl₃ enhanced the serum activities of the liver transaminases (alanine aminotransferase and aspartate aminotransferase) and increased the level of bilirubin, in addition to the serum kidney function markers urea and creatinine. AlCl₃ intoxication boosted oxidative stress, as evidenced by increases in the levels of lipid peroxidation (LPO) and nitric oxide (NO) along with simultaneous decreases in the levels of glutathione (GSH), various antioxidant enzymes, and Nrf2 mRNA expression. MEL (5 mg/kg bwt) treatment repressed LPO and NO levels, whereas it augmented GSH content. The activities of the antioxidant enzymes GPx, SOD, CAT, and GR were also restored concomitantly when MEL was administered before AlCl₃. MEL also suppressed the apoptotic effect of AlCl₃ by enhancing Bcl-2 protein expression in the liver and kidney and decreasing the expression levels of proinflammatory cytokines. Histopathological findings in the liver and kidney tissues confirmed the beneficial effect of MEL against AlCl₃ toxicity. These findings indicate that MEL prevents AlCl₃ toxicity by enhancing the antioxidant defense system.

Figure 1

Protective effects of melatonin on the aluminum accumulation in liver and kidney tissues of rats exposed to aluminum chloride (AlCl₃). Data are expressed as mean ± SD values (n = 7). ^ap < 0.05 vs. the control group; ^bp < 0.05 vs. the AlCl₃-intoxicated group, using Tukey's post hoc test.

Figure 2

Protective effects of melatonin on aluminum chloride (AlCl₃-) induced oxidative stress markers (LPO, NO, and GSH) in the liver and kidney tissues of rats. Data are expressed as mean ± SD values (n = 7). ^ap < 0.05 vs. the control group; ^bp < 0.05 vs. the AlCl₃-intoxicated group, using Tukey's post hoc test.

Figure 3

Protective effects of melatonin on aluminum chloride (AlCl₃-) induced inhibition in the antioxidant enzyme activities (SOD, CAT, GPx, and GR) in the liver and kidney tissues of rats. Data are expressed as mean ± SD values (n = 7). ^ap < 0.05 vs. the control group; ^bp < 0.05 vs. the AlCl₃-intoxicated group, using Tukey's post hoc test.

Figure 4

Protective effects of melatonin on aluminum chloride (AlCl₃-) induced downregulation in (a) Nrf2 mRNA expression in the liver and kidney tissues of rats and (b) western blot analysis of Nrf2 protein in the liver and kidney tissues of rats, and (c) quantification of the density of expression level of Nrf2. mRNA data were normalized with β-actin and represented as fold change (log2 scale) as compared to mRNA levels from the control rats, and western blot data were normalized with histone H1 and represented as fold change as compared to protein levels from the control rats. Data are expressed as mean ± SD values (n = 5). ^Ap < 0.05 vs. the control group; ^Bp < 0.05 vs. the AlCl₃-intoxicated group, using Tukey's post hoc test.

Figure 5

Protective effects of melatonin on aluminum chloride (AlCl₃-) induced inflammation in the liver and kidney tissues of rats. Data are expressed as mean ± SD values (n = 7). ^ap < 0.05 vs. the control group; ^bp < 0.05 vs. the AlCl₃-intoxicated group, using Tukey's post hoc test.

Figure 6

Effects of melatonin on pathological changes in liver tissues of rats exposed to aluminum chloride (AlCl₃): (a) control, (b) MEL, (c) AlCl₃, and (d) MEL+AlCl₃. Magnification at 400x. The red arrow indicated apoptotic hepatocytes, the blue arrow indicates inflammatory cells infiltrated, and the black arrow indicates degenerated hepatocytes.

Figure 7

Effects of melatonin on pathological changes in the kidney tissues of rats exposed to aluminum chloride (AlCl₃): (a) control, (b) MEL, (c) AlCl₃, and (d) MEL+AlCl₃. Magnification at 400x. The red star indicates congested glomerulus, the white star indicates degenerated glomerulus, the blue arrow indicates inflammatory cells infiltrated, and the black arrow indicates degenerated renal tubules.

Figure 8

Effects of MEL on Bcl-2 immunostaining of the liver tissues of rats exposed to aluminum chloride (AlCl₃): (a) control, (b) MEL, (c) AlCl₃, and (d) MEL+AlCl₃. Magnification at 400x.

Figure 9

Effects of MEL on the Bcl-2 immunostaining of the kidney tissues of rats exposed to aluminum chloride (AlCl₃): (a) control, (b) MEL, (c) AlCl₃, and (d) MEL+AlCl₃. Magnification at 400x.