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Calcium Reduces the Increased Fecal 1,2-sn-Diacylglycerol Content in Intestinal Bypass Patients: A Possible Mechanism for Altering Colonic Hyperproliferation¹

Department of Medicine, St. Luke's/Roosevelt Hospital Center and Columbia University, New York, New York 10025 [G. S., P. R. H.]; the Comprehensive Cancer Center and Institute of Cancer Research, College of Physicians & Surgeons of Columbia University, New York, New York 10032 [M. M., K. N., I. B. W.]; and Section of Human Nutrition, Texas A & M University, College Station, Texas 77843 [J. L.]

Diacylglycerol (DAG) is a second messenger for protein kinase C, an enzyme with a key role in cellular signal transduction and growth control. In previous studies, it was demonstrated that DAG is produced by intestinal microflora. Bacterial DAG production is increased by bile acids and phospholipids, both of which may be precipitated by calcium. We have demonstrated that fecal total lipids, bile acids, and rectal epithelial proliferation are increased in intestinal bypass (IB) patients. Calcium was shown to alter fecal lipid composition and to reduce cell proliferation. In the present study, fecal DAG content and ¹⁴C-labeled DAG, ¹⁴C-phosphatidylcholine, and ¹⁴C-phosphatidylinositol metabolism were measured in 24-h stool collections in 15 stable IB patients before and after 3-month therapy with oral elemental calcium, 2.4 or 3.6 g/day. Fecal DAG concentration and output in IB patients were >25- and >200-fold greater than in normal controls. Oral calcium markedly reduced fecal DAG concentration and output and increased DAG, phosphatidylcholine, and phosphatidylinositol metabolism without enhancing DAG production. We conclude that fecal DAG content is markedly elevated post-IB and that calcium supplementation in these patients reduces fecal DAG and accelerates bacterial metabolism of DAG and its precursors. In separate studies, we have found that calcium supplementation also decreases rectal hyperproliferation in IB patients. Taken together, these findings suggest that a high luminal level of DAG enhances colonic cell proliferation and that calcium reduces cell proliferation in part by decreasing the level of DAG.

¹ This work was supported in part by NIH Grant AG00124, the Overseas Maritime Corporation, and awards from the Aaron Diamond Foundation and the Yakult-Honsha Company, Tokyo. This work was presented in part at the American Gastroenterological Association meeting, May 1992, and published as an abstract (31).

² To whom requests for reprints should be addressed, at the Department of Gastrointestinal Medical Oncology and Digestive Diseases, Box 78, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030.

Received 6/14/93. Accepted 12/30/93.