Inhibition by Chlorella of N-Methylnitrosourea-induced Aberrant Crypt Foci in Rat Colon

An inhibitory effect of heterotrophically grown Chlorella regularis (green algae) against the formation of aberrant crypt foci (ACFs), putative precursors of colon cancer, was evaluated in rats. Six Sprague-Dawley rats in each group received three intrarectal doses of 2 mg N-methylnitrosourea in week 1 for inducing ACFs, and were killed at week 6 for quantifying ACFs. Treatment with a daily intragastric dose of 10 mg chlorella powder during weeks 1–5 and weeks 2–5, but not during week 1, resulted in a significant reduction of ACF formation, whereas treatments with a daily dose of 50 mg or 2 mg chlorella, or with 25 mg, 2.5 mg, or 0.25 mg sodium copper chlorophyllin during week 1–5, were less effective. The results support a protective effect for an optimum dose of chlorella against ACF formation and carcinogenesis in the colon, by the potent inhibition of the promotion phase rather than the initiation phase. The inhibition is presumably due to the combined effect of the large amounts of chlorophyll (2.4%) and caro-tenoids (0.6%) in the chlorella used.