Effect of silymarin on kidneys of rats suffering from alloxan-induced diabetes mellitus
Introduction
Oxidative stress is increased in diabetes mellitus and plays an important role in the development and progression of diabetic vascular complications, including nephropathy. Kidneys are especially prone to oxidant damage (Ha and Kim 1995), which may be generated by several pathways in diabetes mellitus, such as NADPH oxidase (Inoguchi et al. 2000), protein kinase C (Ha and Endou 1992), mitochondrial metabolism and glucose auto-oxidation (Hunt and Dean 1998). These oxidants or reactive oxygen species (ROS) may impair or activate pathways, like in mesangial cells (Lee et al. 2003), to cause structural and functional tissue damage and produce chronic renal insufficiency. ROS are inactivated by endogenous cellular defense mechanisms, including the glutathione system and the antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GSHPx) and catalase (CAT).
Alloxan is commonly used to induce diabetes mellitus in laboratory animals. This compound causes necrosis of β-pancreatic cells and therefore reduces insulin secretion (Dunn et al. 1943). Alloxan induces the production of ROS such as H2O2, O2 and OH (Szkudelski 2001), which damage pancreatic, renal and other tissues (Sha et al., 2007, Soto et al., 2004), providing a useful model to study the effectiveness of antioxidant compounds.
Silymarin, a free radical scavenger, is a flavonoid mixture obtained from the milk thistle Silybum marianum that protects against oxidative peroxidation in experimental models and in human hepatic damage. This drug was approved in Germany (Leng-Peschlow 1994) and Belgium (Laekeman et al. 2003) to treat liver damage due to cirrhosis as well as other liver pathologies. It is actually widely used in many other countries (Wellington and Harvis, 2001, Luper, 1998, Valenzuela and Garrido, 1994). It has an oral absorption about 23–47% reaching maximum plasmatic concentrations at 4–6 h (Wellington and Harvis 2001). Silymarin increases levels of reduced glutathione (GSH). We previously reported that silymarin could protect pancreatic tissue by preventing the rise in both plasma glucose and pancreatic lipid peroxidation in alloxan-treated rats, increasing pancreatic and plasma GSH (Soto et al. 1998), and increasing the activity of pancreatic antioxidant enzymes (Soto et al. 2003). Additionally we reported that silymarin restored endocrine pancreatic function by improving insulin and glucagon expression to achieve normoglycemia after alloxan damage (Soto et al. 2004). Here, we tested whether silymarin improved renal tissue damage and restored expression of superoxide dismutase, glutathione peroxidase and catalase.
Section snippets
Materials and methods
Silymarin and all reagents were of analytical grade and obtained from Sigma Chemical Co. (St. Louis, MO, USA) or from local suppliers (Merck and J.T. Baker, Mexico).
The experiments in this study were performed following the guidelines stated in “Principles of Laboratory Animal Care” (NIH publication #85-23, revised 1985) and Mexican regulations “Norma Oficial Mexicana NOM-062-ZOO-1999, Especificaciones técnicas para la producción, cuidado y uso de animales de laboratorio” (published in December
Silymarin effect on serum glucose levels
Serum glucose in normal rats was 6.18 ± 0.212 mmol/l. Chronic (20 days) of alloxan treatment increased glucose levels (23.28 ± 1.89 mmol/l). Daily silymarin treatment for 9 weeks after the 20-day alloxan treatment decreased serum glucose from initial levels (23.28 ± 1.89 mmol/l) at the end of alloxan treatment to near normal levels (8.70 ± 1.58 mmol/l) (Table 1). Silymarin alone or vehicle treatment did not change serum glucose levels (Table 1).
Chronic silymarin effect on SOD, GSHPx and CAT activities in diabetic rats
SOD and GSHPx, but not CAT, were significantly decreased in
Discussion
We previously showed that silymarin increased the pancreatic activity of SOD, GSHPx and CAT in diabetic rats, which may mediate its protective effects (Soto et al., 1998, Soto et al., 2003). Here we showed that silymarin blocked alloxan-induced decreases in the activity and changes in expression levels of these renal antioxidant enzymes. Silymarin also restores normal renal histology in diabetic rats.
Alloxan directly generates ROS (Szkudelski 2001) and the hyperglycemia induced by this compound
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