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Martin Lipkin

Publications and source records attributed to Martin Lipkin.

22 records · Page 2Linked to original sources
PubMed2002

Colonic epithelial cell proliferation decreases with increasing levels of serum 25-hydroxy vitamin D.

Epidemiological evidence suggests a potential role for vitamin D in colon cancer prevention. Vitamin D, absorbed from the intestine or derived from solar ultraviolet light, is metabolized in the liver to 25-hydroxyvitamin D (25-OH D(3)). Previous studies examining effects of vitamin D upon carcinogenesis have focused upon the active metabolite 1,25-dihydroxyvitamin D [1,25-(OH)(2) D(3)], which interacts with nuclear vitamin D receptors in several organs. Until recently, the metabolism of 25-OH D(3) to 1,25-(OH)(2) D(3) was believed to occur only in the kidney, but more recent studies have shown that 25-OH D(3) conversion to 1,25-(OH)(2) D(3) can occur in other tissues. We examined the association between fasting levels of 25-OH D(3), 1,25-(OH)(2) D(3), and BsmI polymorphism of the vitamin D receptor (VDR) gene with indices of colonic epithelial cell proliferation and differentiation in a chemoprevention study, after giving vitamin D or calcium and taking rectal biopsies that were incubated with bromodeoxyuridine. Vitamin D receptor polymorphism was determined by genotyping of the 3' BsmI polymorphism in intron eight of the VDR gene. No significant changes in cell proliferation or in differentiation were found in subjects between study start and end. However, fasting serum levels of 25-OH D(3) showed a highly significant decrease with whole crypt labeling index and the size of the proliferative compartment (phi h). There was no correlation between serum levels of 1,25-(OH)(2) D(3) and the proliferative parameters. Calcium supplementation induced a significant effect upon the relationship between serum 25-OH D(3) and rectal epithelial cell labeling index and phi h when studied by covariance analysis without a relationship with 1,25-(OH)(2) D(3) levels. VDR genotype did not influence the effects of serum 25-OH D(3) or serum 1,25-(OH)(2) D(3) levels upon proliferation. These data suggest that there might be a local effect of 25-OH D(3) on colonic epithelial cells through conversion of 25-OH D(3) to 1,25-(OH)(2) D(3). Subsequent studies have demonstrated the presence of 1alpha-hydroxylase mRNA in normal colorectal epithelium and in colorectal cancer. Thus, vitamin D may have an important role in determining the effects of calcium on colorectal epithelial proliferation and may explain some of the discrepancies found previously in studies that examine the direct role of calcium on the colorectal epithelium.

Adult↗
PubMed2002

Early development of cancer chemoprevention clinical trials: studies of dietary calcium as a chemopreventive agent for human subjects.

Early cancer chemoprevention clinical trials in human subjects had to be carried out with large numbers of subjects studied for long durations, measuring cancer as an end point. However new findings on abnormal epithelial cell growth and development during the multistage evolution of colonic tumors made it possible to carry out chemoprevention clinical trials in several stages, with fewer subjects studied for shorter durations, thus enabling investigators to analyze increasing numbers of chemopreventive agents and nutritional regimens in clinical trials. Supplemental dietary calcium was the first candidate chemopreventive agent studied in this multistage approach in human subjects, as a putative agent for colon cancer prevention. Early- and late-stage intermediate biomarker studies in humans have strongly suggested utility for supplemental dietary calcium to inhibit the development of benign and subsequent malignant colonic neoplasms. Preclinical experimental studies have further demonstrated the ability of increased dietary calcium to inhibit the evolution of colonic tumors when they were induced by targeted mutations, dietary factors, and particularly when given over a long duration of lifespan.

Anticarcinogenic Agents↗
PubMedDate not supplied

Cyclin D1 expression in the intestinal mucosa and tumors of Apc1638N mice.

Altered expression of cyclin D1 contributes to the development of several types of cancer, including colorectal cancer. This study examined cyclin D1 expression in 32 intestinal tumors in different stages of tumorigenesis in Apc1638N mice, a mouse model for human familial adenomatous polyposis (FAP). Three morphological patterns of expression of cyclin D1 in intestinal epithelial cells were found: nuclear, punctate-cytoplasmic and fine granular cytoplasmic. The nuclear pattern of cyclin D1 was detected in all of the tumors, including adenomas (n = 18) and adenocarcinomas (n = 14); this pattern was found predominantly in the tubular region of the tumors and in flat mucosa adjacent to a subset of the tumors (67% of adenomas and 57% of carcinomas). The punctate-cytoplasmic pattern of cyclin D1 expression was found in all adenocarcinomas and a majority of adenomas (80%), mainly in invasive and villous areas of the tumors; it was not found in normal flat adjacent mucosa suggesting that this pattern and altered cytoplasmic/nuclear expression were associated with tumor progression. Fine cytoplasmic granules were located in normal duodenum in the basal portion of the crypts and in colon in epithelial cells at the surface of the colonic crypts; in both duodenum and colon the number of cells with fine cytoplasmic granules significantly increased after feeding a Western-style diet. These altered patterns of expression of cyclin D1 may provide useful biomarkers of abnormal cell development for studies of tumorigenesis and the effects of chemopreventive agents.

Adenomatous Polyposis Coli↗