Effects of L-ascorbic acid on two cycles of cisplatin-induced DNA double-strand breaks and phosphorylation of p53 in the liver.

Cisplatin, a commonly used anticancer drug, was studied to investigate its effects on structure, DNA damage and p53 along with the possible protective effects of L-ascorbic acid in the liver. Adult male BALB/c mice were treated with 0, 10 mg/kg L-ascorbic acid and two cycles of cisplatin 1 mg/kg/2.5 mg/kg with or without L-ascorbic acid (17 days recovery period between the cycles) and the livers were collected at 72 h after the last exposure. Structural damage was analyzed in Masson's trichrome and Hortega's silver stained liver tissues. The DNA double-strand breaks with duplex 3' overhangs and 5' P-blunt ends were labeled by in situ oligo ligation by using hairpin oligonucleotide probes. The expression of p53 and phosphorylated p53 (p-p53) was detected by immunohistochemistry. Structural changes such as vacuolization of hepatocytes, pyknosis, infiltration of leukocytes and pericentral fibrosis were observed without any protection from L-ascorbic acid. The reticular fibrous framework was affected and the incidence of Kupffer cells was decreased. Cisplatin induced the DNA double-strand breaks (p<0.001); however, the latter appeared in a p53-independent, but p-p53-dependent manner. L-ascorbic acid showed significant protective effect on cisplatin-induced DNA damage (p<0.001). Cisplatin also enhanced p53 phosphorylation in a dose-dependent manner and L-ascorbic acid reduced this biochemical change only in 1 mg/kg group. In conclusion, cisplatin-induced structural changes are not, but the DNA damage and phosphorylation of p53 are, significantly, but not completely, alleviated by L-ascorbic acid.