Increased glutathione levels and activity of PON1 (phenyl acetate esterase) in the liver of rats after a single dose of cyclophosphamide: a defense mechanism?

The clinical utility of cyclophosphamide (CYP) as an anticancer drug is limited by its urotoxicity and nephrotoxicity and to a lesser extent by its hepatotoxicity. The present study was undertaken in order to find out the reason why liver is least susceptible of the three organs to CYP-induced damage although it is the major site for drug activation and metabolism. Adult female Wistar rats weighing 200-250 g were administered single intraperitoneal injection of CYP at the dose of 150 mg/kg body weight and sacrificed at various time intervals 6, 16 or 24h after the dose of CYP. The control rats were administered saline alone. Hepatotoxicity was assessed by measuring plasma alanine aminotransferase (ALT) activity and histopathology of the liver. Liver was used for the assay of reduced glutathione; activity of paraoxonase (PON1) malondialdehyde - marker of lipid peroxidation. Serum was used for the assay of ALT activity and PON1 activity. The level of reduced glutathione in the liver CYP treated rat was increased by 22% and 57% at 16 and 24h, respectively. Interestingly, a marked increase in the activity of PON1 (122%) was observed in the livers of CYP treated rats 24h after treatment. This was accompanied by significant increase in PON1 activity (23%) in the serum. No significant alteration in hepatic malondialdehyde level was observed at any time period after treatment. Serum ALT activity was increased slightly 24h after treatment with CYP. Mild liver damage was observed histologically only 24h after treatment with the drug. The present investigation shows for the first time that an increase in antioxidant levels in the liver may be a defense mechanism to prevent/minimize CYP-induced liver damage.

Enhanced PON1 activity in the kidneys of cyclophosphamide treated rats may play a protective role as an antioxidant against cyclophosphamide induced oxidative stress.

Recent studies have shown that paraoxanase (PON1) has protective effect against oxidative stress and hence can act as an antioxidant. A time course study was carried out in order to find out alterations in PON1 activity in cyclophosphamide (CYP) induced renal injury. Eight to ten weeks old female rats were administered CYP at the dose of 150 mg/kg body wt. (i.p.) and sacrificed at 6, 16, or 24 h after treatment. Saline treated rats served as control. CYP exposure for 6 h caused a dramatic increase in PON1 activity (83%), which escalated to 160% at 16 h. The renal PON1 activity reached control values 24 h after treatment with CYP. The renal malondialdehyde level was unaltered 6 h after treatment with CYP and an increase by 35% was observed 16 h after treatment with CYP. The present investigation shows for the first time that an increase in renal PON1 activity is an early biochemical event in cyclophosphamide induced renal damage. It is suggested that this enzyme may have a role within the antioxidant systems of the kidney.

Effect of cyclophosphamide treatment on selected lysosomal enzymes in the kidney of rats.

The anti-cancer drug cyclophosphamide (CYP) is nephrotoxic besides being urotoxic thereby limiting its clinical utility. Since the nephrotoxicity of CYP is less common compared to its urotoxicity, not much importance has been given for the study of mechanism of CYP-induced nephrotoxicity. The aim of the present study is to investigate the possible role of lysosomal enzymes in CYP-induced renal damage. Adult female Wistar rats weighing 200-250 g were used for the study. The rats were administered single-intraperitoneal injection of CYP at the dose of 150 mg/kg body wt and sacrificed at various time intervals 6, 16 or 24 h after the dose of CYP. The control rats were administered saline alone. Nephrotoxicity was assessed by measuring plasma creatinine and urea and histopathology of the kidney. The kidney was weighed and used for the assay of lysosomal enzymes namely acid phosphatase, beta-glucuronidase and N-acetylglucosaminidase and total protein content. Histologically, the CYP-treated rat kidneys showed progressive renal damage with increase in time after treatment. Glomerular nephritis, cortical tubular vacuolization and interstitial edema were observed in the CYP-treated rats. Surprisingly, a significant drastic decrease (instead of an increase) in the activities of lysosomal enzymes was observed in the kidneys of CYP-treated rats at 16 and 24 h as compared with the control. A highly significant increase (270%) in protein content was observed in the kidneys of the CYP-treated rats as compared with the control. Decrease in the activities of lysosomal protein digestive enzymes may contribute to CYP-induced renal damage. The accumulation of abnormal amounts of the protein in the kidney may be due at least in part to defect in lysosomal enzyme activity and contribute to renal damage.