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Dietary Aluminum Chloride Reduces the Amount of Intestinal Calbindin D-28K in Chicks Fed Low Calcium or Low Phosphorus Diets^{1, 2, 3, 4,}

Department of Food Science and Human Nutrition ^* Department of Animal Sciences, University of Hawaii, Honolulu, HI 96822

The mechanism of aluminum (Al) toxicity may involve disturbances in calcium (Ca) metabolism. Aluminum compounds have been reported to reduce vitamin D-dependent Ca absorption in chicks, rats and humans. To investigate the mechanism by which Al reduces Ca absorption, we studied the effect of dietary aluminum chloride (AlCl₃) on the relative amounts of intestinal calbindin D-28K in chicks fed diets varying in Ca and phosphorus concentration. AlCl₃ was added so that Al constituted 0, 0.15 or 0.3 g/100 g of diets that were either adequate, low in Ca, low in P, or contained supplemental P. Diets were fed for 2 wk. Intestinal calbindin D-28K levels were assayed using SDS-PAGE and ⁴⁵Ca binding to Western blots. Added dietary Al greatly reduced the amount of intestinal calbindin in chicks fed adequate diets, low Ca diets, or low P diets. When diets with supplemental P were fed, little calbindin was evident with or without added Al. Tibia ash, body weight and food intake were also reduced (P < 0.05) by added Al. These results indicate that dietary AlCl₃ inhibits vitamin D-dependent Ca absorption by reducing the amount of intestinal calbindin D-28K. Aluminum, therefore, may interfere with the body's ability to regulate intestinal calbindin D-28K levels. This could have implications for other tissues that contain substantial levels of calbindin D-28K.

KEY WORDS: • aluminum chloride • phosphorus • intestinal calbindin D-28K • chicks • calcium

¹ Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, April 1992, Anaheim, CA [Dunn, M. A., Johnson, N. E., Zierold, C. & Liew, M.Y.B. (1992) Dietary aluminum reduces the amount of a 24 kilodalton protein in chick intestine. FASEB J. 6: A1946 (abs. 5850)].

² Supported in part by the U.S. Department of Agriculture under CSRS Special Grant no. 91-34135-6166, managed by Pacific Basin Administrative Group (PBAG).

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ Journal Series no. 3834, the Hawaii Institute of Tropical Agriculture and Human Resources, University of Hawaii, Honolulu, HI 96822.

⁵ To whom correspondence should be addressed.

Manuscript received 8 December 1992. Revision accepted 29 June 1993.