Tenofovir/Emtricitabine Metabolites and Endogenous Nucleotide Exposures are associated with p16^INK4a Expression in Subjects on Combination Therapy

Abstract

Background HIV may amplify immunologic, physiologic, and functional changes of aging. We determined associations of frailty phenotype, a T-cell senescence marker (p16INK4a expression), age, and demographics with exposures of the intracellular metabolites (IM) and endogenous nucleotides (EN) of tenofovir/emtricitabine (TFV/FTC), efavirenz (EFV), atazanavir (ATV), and ritonavir (RTV). Materials and Methods Plasma and PBMC samples for drug, IM, and EN concentrations were collected at 4 time points in HIV+ adults receiving TFV/FTC with EFV or ATV/RTV. Subjects underwent frailty phenotyping and p16INK4a expression analysis. Noncompartmental analysis generated an area under the curve (AUC) for each analyte. Spearman rank correlation and Kruskal-Wallis tests were used to assess associations between AUC, demographics, and aging markers, adjusting for multiple comparisons with the Holm procedure. Results Subjects (n=79) ranged in age from 22–73yr (median 48yr). Forty-eight were African-American, 24 were female, 54 received EFV. Three subjects (range 51–60yr) demonstrated frailty, with 17 subjects (range 26–60yr) demonstrating pre-frailty. Negative associations were observed between p16INK4a expression and each of FTC-triphosphate (r= −0.45), deoxyadenosine triphosphate (dATP) (r= −0.47), and deoxycytidine triphosphate (dCTP) (r= −0.57) AUCs (p-values<0.02). TFV and FTC AUCs were larger among subjects with lower renal function or higher chronologic age (p-values ≤0.05). No associations were observed for EFV, ATV, or RTV AUCs. Conclusions Associations of IM/EN exposure and p16INK4a expression observed here suggest that senescence may alter drug phosphorylation, metabolism, or transport. This finding warrants further mechanistic study to ensure optimal treatment in the aging HIV+ population.

Population Pharmacokinetics Modeling of Unbound Efavirenz, Atazanavir, and Ritonavir in HIV‐Infected Subjects With Aging Biomarkers

“…This is consistent with a previous analysis of associations of exposures with age, frailty phenotype, and p16 INK4a expression 36. In a study evaluating trough concentrations measured during therapeutic drug monitoring, their analysis suggested no changes in EFV concentrations with age, with increased concentrations of protease inhibitors, such as ATV and RTV, although only 16.5% of these participants were 50 years old or older 37.…”

p16INK4a, a Senescence Marker, Influences Tenofovir/Emtricitabine Metabolite Disposition in HIV‐Infected Subjects

“…The covariate relationship between TFV‐dp and FTC‐tp CL and p16 INK4a expression is novel, and is also associated with lower TFV‐dp and FTC‐tp exposures in these participants,27 as PBMC CL increases with higher expression of p16 INK4a . This observation is consistent with our hypothesis that increased cellular activation, which may be associated with senescence, increases the kinase activity responsible for the metabolism of the intracellular species.…”

“…Analytical methods have been previously described 27. All drug concentrations were determined in the UNC Center for AIDS Research Clinical Pharmacology and Analytical Chemistry Laboratory.…”

Concentrations of Pro-Inflammatory Cytokines Are Not Associated with Senescence Marker p16INK4a or Predictive of Intracellular Emtricitabine/Tenofovir Metabolite and Endogenous Nucleotide Exposures in Adults with HIV Infection

“…TFV-dp, FTC-tp, dATP, and dCTP concentrations in peripheral blood mononuclear cells (PBMCs) were measured using LC-MS/MS in the UNC Center for AIDS Research Clinical Pharmacology and Analytical Chemistry Laboratory [12]. Drug exposure was measured as area under the curve (AUC) using non-compartmental analysis in Phoenix WinNonlin 6.3 (Pharsight, A Certara Company, St. Louis, MO); the linear up/log down trapezoidal method [22] was used to calculate AUC over the dosing interval.…”

“…In order to exert their antiviral effect, they must cross the cellular membrane and undergo phosphorylation to their respective metabolites, tenofovir diphosphate (TFV-dp) and emtricitabine triphosphate (FTC-tp). We previously demonstrated that higher expression of p16 INK4a is associated with lower exposures of FTC-tp, dATP, and dCTP in HIV-infected participants [12]. Inflammation may contribute to this relationship, as it has been shown to regulate drug transporters, such as breast cancer resistance protein (BCRP) and P-glycoprotein 1(P-gp), on cell membranes [13] capable of effluxing NRTIs and their metabolites [14, 15].…”