Dietary fibers reduce the urinary excretion of 1-hydroxypyrene following intravenous administration of pyrene.

Abstract

During biological monitoring of exposure to a chemical, a possible source of interindividual variability in the measurement of a urinary metabolite that undergoes enterohepatic cycling is the presence of dietary fiber in the gastrointestinal tract. This study examined the effect of diets containing either the insoluble fiber Alphacel (nonnutritive bulk cellulose) or the soluble pectin (from citrus fruit, MW 20,000-40,000). Five groups of male Sprague-Dawley rats received one of the following diets: poor (5% w/w) or rich (15% w/w) in Alphacel, poor (5% w/w) or rich (15% w/w) in pectin, or no fiber (NF). Five micromol/kg of pyrene was administered by iv injection immediately after feeding the animals with their respective diet, and urine and feces collections started for the determination of 1-hydroxypyrene (1-OHP), a metabolite of pyrene. The type of fiber had no influence on the results. The rats receiving diets both poor and rich in fiber excreted less 1-OHP (18 +/- 8 and 15 +/- 7 pmol per g of rat, respectively) in the 24-h urine samples than the NF group (28 +/- 6 pmol/g). There was a nonstatistically significant trend towards increased fecal and total (urinary + fecal) 1-OHP excretion with increasing amount of fiber in the diet. An in vitro experiment showed an inverse correlation (r(2) = 0.98) between the amount of Alphacel in suspension in a 1-OHP aqueous solution and the recovery of 1-OHP from the soluble fraction. The reduction in urinary output of the metabolite due to fiber reaching approximately 40% may contribute to its interindividual variability observed in occupational and environmental studies.