Expression of mRNA for the gap‐junctional protein connexin43 in human colonic tissue is variable in response to β‐carotene supplementation

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Abstract
Increased expression of the gap‐junctional protein connexin43 (Cx43) is reported to be increased in mouse and human dermal fibroblasts in vitro in response to β‐carotene treatment. In the present study, we determined the level of Cx43 mRNA expression in colonic mucosa from normal subjects and subjects with a prior history of colonic polyps or cancer before and after three months of administration of a placebo or β‐carotene. RNA was reverse transcribed and used in a polymerase chain reaction assay employing primers selected from the human Cx43 gene sequence. Cx43 mRNA expression was normalized on the basis of β2‐microglobulin mRNA expression. The β‐carotene concentration in colonic mucosa, as well as serum and diet, was also determined to establish a correlation between Cx43 expression and β‐carotene concentration. In an initial analysis of samples collected from 10 subjects before supplementation, the quantity of Cx43 mRNA was variable and did not correlate with β‐carotene intake or the concentration of β‐carotene in tissue or serum. In samples collected at zero and three months from eight subjects who were controls or received a placebo, there was no correlation between Cx43 mRNA level and tissue or serum β‐carotene concentration. In samples collected from subjects before and after three months of β‐carotene supplementation, there was a significant increase in tissue and serum β‐carotene concentration in all subjects and an increase in Cx43 mRNA expression after supplementation relative to baseline in four of six samples. The high variability in Cx43 expression indicates that induction of Cx43 mRNA expression is not solely dependent on the concentration of β‐carotene in diet, serum, or tissue. However, the results from subjects supplemented with β‐carotene suggest that induced expression may occur in colonic tissue of some individuals.

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