Investigation of the effects of silymarin and vitamin c on renal damage and aquaporin-2 dovnregulation in lithium-induced nephrogenic diabetes insipidus in male rats

Lithium (LIT), which is currently preferred in the treatment of bipolar disease and mania, is one of the most common causes of Acquired Nephrogenic Diabetes Insipidus and downregulation of Aquaporin 2 (AQP2). Long-term use of LIT is known to cause oxidative damage. It was aimed to investigate the protective effects of SIL, Vit C, and the combination of both, on damaged kidney tissues of rats with experimental Nephrogenic Diabetes Insipidus (NDI), by light microscopic and biochemical methods in this study. The 16-week-old male rats used in the study were divided into eight groups. Control group (CNT), Silymarin (SIL), Vitamin C (Vit C), and Silymarin+Vitamin C (SİL+Vit C) groups were fed with an additive-free standard feed for 28 days. Lithium (LIT), Lithium+Silymarin (LIT+SIL), Lithium+Vitamin C (LIT+Vit C), and Lithium+Silymarin+Vitamin C (LIT+SIL+Vit C) groups were fed with added 80 mmol LiCl/kg feed for 28 days. Physiological saline at a daily dose of 1 ml/kg was given to the CNT and LIT groups by oral gavage. SIL at a daily dose of 100 mg/kg was given to the SIL and LIT+SIL groups by oral gavage. Vit C at a daily dose of 200 mg/kg was given to Vit C and LIT+Vit C groups by oral gavage. SIL at a daily dose of 100 mg/kg and Vit C at a daily dose of 200 mg/kg was given to SIL+Vit C and LIT+SIL+Vit C groups by oral gavage. From the urine samples taken from all groups on the first and last day of the experiment; osmolality, sodium, potassium, urea, urea nitrogen (BUN), and creatinine values were measured. In blood serum samples taken from all groups; osmolality, sodium, potassium, urea, urea nitrogen, creatinine, and LIT levels were measured. The right kidney was used to determine the AQP2, ROS, GSH, SOD, MDA levels. Left kidneys; were subjected to histopathological and immunohistochemical evaluation. Glomerulus diameter measurement and damage level scoring of the groups were performed. When the kidney tissues belonging to the LIT group are examined histologically, in the cortex; shrinkage of the glomerulus, lymphocytic cell infiltrations in the peritubular and interstitial areas, thickening of the glomerular basement membrane and interstitial fibrosis, in the medulla; Dilatation in the loop of Henle and local desquamation in collective, proximal and distal tubules epithelium and thickening of the tubular membranes were the most important findings. While the histological findings of the LIT+Vit C group were similar to the LIT group; It was noted that these findings were significantly reduced in LIT+SIL and LIT+SIL+Vit C groups. AQP2 data, the amount of which was determined by ELISA method in kidney tissues and immune positivity was revealed by immunohistochemical method, were parallel to each other. AQP2 amount and immunopositivity were significantly decreased in the LIT group compared to CNT, SIL, Vit C, and SIL+Vit C groups. LIT+Vit C findings were similar to the LIT group. AQP2 amount and immunopositivity were observed to be increased in LIT+SIL and LIT+SIL+Vit C groups compared to the LIT group. When the osmolality, sodium, potassium, urea, BUN, and creatinine values in the urine samples taken on the first and last day in all groups were compared, it was determined that the values in all groups given LIT showed a significant decrease compared to the CNT, SIL, Vit C, and SIL+Vit C groups. When the intergroup osmolality, sodium, potassium, urea, BUN, and creatinine values in urine samples taken on the last day were compared, it was determined that the values in the LIT and LIT+Vit C groups were significantly lower than the other groups. When the serum osmolality values between the groups were compared, LIT and LIT+Vit C groups were found to be significantly lower than all other groups. There was no significant difference between the groups in terms of serum potassium, sodium, BUN, urea, and creatinine. When serum LIT levels were examined, it was determined that the values of all groups given LIT were significantly higher than the CNT, SIL, Vit C, and SIL+Vit C groups. It was determined that GSH and SOD levels decreased, ROS and MDA levels increased in all LIT groups compared to CNT, SIL, Vit C, and SIL+Vit C groups. GSH and SOD levels were higher in LIT+SIL and LIT+SIL+Vit C groups, and ROS and MDA were less in the LIT group. As a result, it is thought that SIL application significantly eliminates the negative effects of LIT-induced NDI on the kidney and may contribute to the treatment of NDI and that Vit C does not have any protective effect in LIT-induced NDI. Keywords: Lithium, Nephrogenic Diabetes Insipidus, AQP2, Silymarin, Vitamin C