Short Communication: Specimen Processing Impacts Tissue Tenofovir Pharmacokinetic Measurements

Abstract

Antiretroviral drug concentrations at sites of HIV exposure are important drivers that influence the development of HIV pre-exposure chemoprophylaxis strategies and regimens. We assessed the effect of collection method-in the presence or absence of tissue culture medium-on tenofovir (TFV) and tenofovir diphosphate (TFV-DP) concentrations in colonic biopsies. We find significant baseline interbiopsy variation in TFV (38% CV) and TFV-DP (33% CV) concentrations. Incubation in medium leads to a fluid absorption-driven twofold increase in tissue weight with a concomitant 75% decrease in weight-adjusted tissue TFV concentrations 120 min post-incubation. In contrast, adjusted TFV-DP concentrations decrease by only 25% during the same period, with this difference not achieving statistical significance. Although colonic biopsies should be collected in the absence of medium for accurate TFV concentrations, the presence of medium does not significantly impact TFV-DP-dependent pharmacokinetic or pharmacodynamic assays. Appropriate assessment of tissue drug concentrations should account for biopsy collection method and drug mechanism of action.

Keywords: PK/PD; antiretroviral; biopsy; tenofovir; tissue.

FIG. 1.

Effect of incubation upon biopsies. (A) Biopsy weights increase upon submergence in medium. Increase occurred within 10 min and weights stabilized by 60 min. Six biopsies measured per time point. Data labels indicate fold-change in average cohort weight. Average weight at all time points was significantly (p < .005, Student's t-test) higher than weight of nonincubated control group. (B) Tissue TFV concentrations decrease rapidly upon incubation. Directly measured concentrations (filled circles) reduced ∼85% after 10 min of incubation and were stable thereafter. Adjusted concentrations (average concentration multiplied by fold-change in cohort weight, open circles) revealed a loss of ∼75% upon incubation. % loss = (difference in concentration between time 0 and time of interest/concentration at time 0) × 100. (C) Tissue TFV-DP concentrations also reduce when tissues are incubated in medium. Directly measured concentrations (filled circles) reduced ∼70% within 30 min and then stayed stable up to 120 min. One value in the 10 min group and one in the nonincubated group were judged as outliers by Chauvenet's rule and excluded from analysis. Adjusted TFV-DP concentrations (average concentration multiplied by fold-change in cohort weight, open circles) revealed a loss of ∼25% upon incubation. Adjusted TFV-DP concentrations at 30, 60, and 120 min are not significantly different from concentrations at 0 min (all p > .1). Gain in adjusted TFV-DP concentration at 10 min is likely an artifact of large interbiopsy variation in TFV-DP concentrations. % loss = (difference in concentration between time 0 and time of interest/concentration at time 0) × 100. TFV, tenofovir; TFV-DP, tenofovir diphosphate.