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Neomycin Has No Persistent Sparing Effect on Vitamin B-12 Status in Pectin-Fed Rats^{1 ,2 ,3}

Department of Nutritional Sciences, University of California, Berkeley, CA 94720

In the present study, rats were depleted of vitamin B-12 with fiber-free or 5% pectin diets, with or without neomycin. Through use of this intestinal antibiotic reported to "spare" vitamin B-12, we sought to determine if bacterial fermentation of pectin might explain our previous observations of negative effects of pectin on vitamin B-12 status. However, neomycin did not lessen interference by pectin with vitamin B-12 metabolism. Pectin increased urinary methylmalonate and decreased propionate oxidation to a greater extent in the presence than in the absence of neomycin. Also, regardless of the presence of neomycin, the biologic half-life of injected [⁵⁷Co]vitamin B-12 was 58 d for rats fed the fiber-free diets and only 38 d for rats fed 5% pectin diets. Neomycin delayed early fecal excretion of ⁵⁷Co but had no persistent effect. Thus, neomycin-sensitive bacteria do not mediate the negative effects of pectin on vitamin B-12 status. Pectin may interfere directly with vitamin B-12 absorption or may stimulate vitamin B-12 uptake or propionate production by microbial species that have adapted to neomycin.

KEY WORDS: • [⁵⁷Co]vitamin B-12 • intestinal flora • antibiotics • male rats • propionate • dietary fiber • methylmalonate • pectin

¹ Supported in part by National Institutes of Health Grant AM-19970.

² A preliminary report was presented at the 64th Annual Meeting of the Federation of American Societies for Experimental Biology, Anaheim, CA, April 1980. [Cullen, R. W. & Oace, S. M. (1980) Impact on vitamin B-12 status of pectin and six dietary fibers in rats. Fed. Proc. 39: 785 (abs.)].

³ Data are taken from the dissertation submitted by R. W. Cullen to the Graduate Division, University of California, Berkeley, in partial fulfillment of the requirements for the Ph.D. in Nutrition.

⁴ Present address: Department of Human Nutrition and Food Systems Management, Winthrop College, Rock Hill, SC 29733.

⁵ To whom reprint requests should be addressed.

Manuscript received 27 February 1989. Revision accepted 30 May 1989.