ABSTRACT
Colon carcinogenesis is a multistep process resulting in the genetic alterations of a variety of oncogenes and tumour suppressor genes that transforms normal epithelial cell into an invasive carcinoma. Recent data from the cancer registry of the University College Hospital Ibadan, Nigeria revealed an increase in malignant colorectal disease relative to what was recorded 10-20 years ago. Several epidemiology studies suggest that diet is a major factor closely linked with the upsurge in colorectal cancer incidence. This study examined the phytochemical constituents of Arachis hypogaea seeds and its possible anticarcinogenic potential against 1, 2- dimethylhydrazine-induced colon carcinogenesis.
Eighty-four (84) rats of both sexes were used for this study. They were divided into seven groups of 6 male rats and another seven groups of 6 female rats each. 1, 2- dimethylhydrazine was administered subcutaneously at a dose of 25 mg/kg body weight. Group A (control) rats of both sexes were maintained on normal rat feed. The group B rats were maintained on normal feed and administered DMH once weekly for 12 weeks. The group C rats were provided normal feed and administered DMH weekly for 24 weeks. Group D rats were administered DMH and normal feed for 12 weeks followed by supplementation with peanut diet for the next 12 weeks without further DMH administration. The group E rats received DMH weekly and supplemented with peanut diet concomitantly for 24 weeks while group F rats had peanut diet for 12 weeks before the administration of DMH for 12 weeks. Group G rats were maintained on peanut diet only for 24 weeks. After the treatment period, which lasted for 24 weeks, each rat was sacrificed under mild anaesthesia. While under anaesthesia, blood was obtained by heart puncture, and the colon and liver were excised. Sera and colon and liver homogenates were prepared for biochemical assays. Portion of the colon were preserved by fixation for histopathological examination.
Phytochemical analyses revealed the presence of tannins, saponins, flavonoids, alkaloids and coumarins. High performance liquid chromatogragphy, HPLC analyses showed the presence of resveratrol, quercetin, rutin and gallic acid. The total tannin, phenol, proanthocyanidin and flavonoid content of the seed were 35.38 ± 0.58 mg TAE/g, 28.37 ± 0.69 mg GAE/g, 993 ± 23.09 mg AAE/g and 17 ± 0.47 mg QE/g extract respectively. In vitro antioxidant capacity revealed that peanut extract had a better DPPH scavenging capacity relative to standard vitamin C as evidenced by its lower IC50 value of 3.04 x10-4 ± 0.11 µg mL-1 as against 8.01 x10-4 ± 0.42 µg mL-1 obtained for vitamin C. 1, 2- dimethylhydrazine (DMH) significantly (p ≤ 0.05) increased malondialdehyde level in the colon and liver as evidenced from the supernatants of their homogenates. This increase was reversed by the incorporation of peanut in the diet. There was also significant (p ≤ 0.05) decline in colon, liver and serum antioxidant enzyme activities (catalase, superoxide dismutase and glutathione peroxidase) and reduced glutathione level in the groups that received DMH alone. Consumption of peanut diet ameliorated the decline in these parameters occasioned by DMH administration. There were also significant (p ≤ 0.05) increases in the activities of lactate and glucose-6-phospate dehydrogenases in the colon of rats exposed to DMH alone and a corresponding reduction in the activities of both enzymes in the groups that were fed peanut diet. Colon histology revealed that DMH caused ultrastructural changes, notably crypt cell and epithelial lining dysplasia and carcinoma-in situ. Supplementation with peanut ameliorated the DMH-induced ultrastructural changes in the colon. Immunohistochemistry of the colon showed that rats exposed to DMH for 24 weeks were positive for cytokeratin 20, indicative of the presence of cancerous cells. The results therefore suggest that Arachis hypogaea seeds could prevent or ameliorate 1, 2-dimethyhyrazine-induced colon carcinogenesis in rat.
