In its December 2013 issue the scientific journal Environmental Health Perspectives published a letter to Gayrard et al., authors of a June 2013 study, which had questioned the validity of toxicological studies using gavage (reported on by the FPF). Gayrard and colleagues showed that BPA is absorbed orally when present in food, through the mucosa under the tongue. They argued that these findings may explain the detection of free, unconjugated BPA in human blood samples—an issue that had previously been discounted as a measurement artifact.
In their letter, Teeguarden, Fisher and Doerge, scientists at the Pacific Northwest National Laboratory and the National Center for Toxicological Research, both U.S., criticized Gayrard’s hypothesis that sublingual adsorption may explain human serum bisphenol A (BPA) levels. They argue that according to pharmacokinetic modeling sublingual exposure cannot be higher than that resulting from bolus intravenous administration. They therefore conclude that BPA serum levels cannot become higher than 0.07 ng/ml. Further, Teeguarden and colleagues criticize that Gayrard et al. evaluated jugular vein blood, rather than blood representative for systemic exposure (f.e. the leg vein). Consequently, they consider sample contamination a more likely explanation for the discrepancy between measured levels in humans and levels in pharmacokinetic studies.
In their response, Gayrard et al. point out that sublingual BPA exposure may lead to much higher local BPA serum levels (f.e. the internal jugular vein) than in other systemically representative blood vessels. Further, short-lived compounds like BPA may occur in significantly higher levels in arterial blood than in peripheral venal vessels (Chiou 1989). In addition, Gayrard et al. stress that in sensitive subpopulations, such as children, BPA levels may be 6 times higher than in adults (reaching 0.6 ng/ml) due to higher per kilogram exposure levels. Based on their findings Gayrard et al. conclude that bioavailability of BPA may be 100 %, rather than the 1% expected following oral gavage.
Teeguarden, J. et al. (2013). “Exposure Conditions and Pharmacokinetic Principles: Interpreting Bisphenol A Absorption in the Canine Oral Cavity.” Environmental Health Perspectives 121, 11-12, A323.
Gayrard, V. et al. (2013). “Interpreting Bisphenol A Absorption in the Canine Oral Cavity: Gayrard et al. Respond.” Environmental Health Perspectives 121, 11-12, A323-A324.