Spirogyra neglecta, freshwater green alga, modulates the early stages of 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

Spirogyra neglecta (Hassall) Kützing is an edible freshwater green macroalga found in northern Thailand. Our studies found that the hot water extract of S. neglecta showed antimutagenic effects against several environmental mutagens in Salmonella mutation assay and anticarcinogenicity in diethylnitrosamine-induced hepatocarcinogenesis in rats. This study focused on the chemopreventive effects of the hot water extract of S. neglecta (SNE) and dried S. neglecta mix diet (SND) on 1,2-dimethylhydrazine (DMH)-induced preneoplastic lesion of colorectal carcinogenesis. Male Wistar rats were divided into 8 groups. Groups 1 – 5 were subcutaneously injected by 40 mg/kg bw of DMH, while Groups 6 – 8 were injected by 0.9% NaCl instead. Groups 1 and 6 were a positive control and a negative control, respectively. Groups 2 and 4 were fed with low dose of SNE and SND, respectively. Groups 3 and 7 were given by high dose of SNE, while Groups 4 and 8 were fed with high dose of SND. To study their effects on the initiation stage, SNE and SND were fed a week before DMH injection. The 5 week treatment of SNE significantly decreased number of aberrant crypt foci (ACF) in the colon of DMH treated rats. The extract also modulated the activities of some hepatic detoxifying and antioxidant enzymes including UDP-glucuronyl transferase, glutathione-S-transferase and glutathione peroxidase when compared to a DMH alone group. To study the effect on the post-initiation stage, SNE and SND were administered for 10 weeks after DMH injection. The SNE significantly declined number of colonic ACF in DMH-treated rats. It also significantly reduced number of proliferating cell nuclear antigen (PCNA) positive cells and increased number of apoptotic cells in colonic crypts of DMH-treated rats. In conclusion, S. neglecta modulated the early stages of DMH-induced colon carcinogenesis in rats via modulation of xenobiotic metabolizing enzymes and inhibition of cell proliferation as well as induction of apoptosis.