Determinants of Individual Variation in Intracellular Accumulation of Anti-HIV Nucleoside Analog Metabolites

Abstract

Individual variation in response to antiretroviral therapy is well-known, but it is not clear if demographic characteristics such as gender, age, and ethnicity are responsible for the variation. To optimize anti-HIV therapy and guide antiretroviral drug discovery, determinants that cause variable responses to therapy need to be evaluated. We investigated the determinants of intracellular concentrations of nucleoside analogs using peripheral blood mononuclear cells from 40 healthy donors. We observed individual differences in the concentrations of the intracellular nucleoside analogs; the mean concentrations of the triphosphate metabolite of ethynylstavudine (4-Ed4T), zidovudine (AZT), and lamivudine (3TC) were 0.71 pmol/10 6 cells (minimum and maximum, 0.10 and 3.00 pmol/10 6 cells, respectively), 0.88 pmol/10 6 cells (minimum and maximum, 0.10 and 15.18 pmol/10 6 cells, respectively), and 1.70 pmol/10 6 cells (minimum and maximum, 0.20 and 7.73 pmol/10 6 cells, respectively). Gender and ethnicity had no effect on the concentration of 4-Ed4T and 3TC metabolites. There was a trend for moderation of the concentrations of AZT metabolites by gender (P ‫؍‬ 0.17 for gender ⅐ metabolite concentration). We observed variability in the activity and expression of cellular kinases. There was no statistically significant correlation between thymidine kinase 1 (TK-1) activity or expression and thymidine analog metabolite concentrations. The correlation between the activity of deoxycytidine kinase (dCK) and the 3TC monophosphate metabolite concentration showed a trend toward significance (P ‫؍‬ 0.1). We observed an inverse correlation between the multidrug-resistant protein 2 (MRP2) expression index and the concentrations of AZT monophosphate, AZT triphosphate, and total AZT metabolites. Our findings suggest that the observed variation in clinical response to nucleoside analogs may be due partly to the individual differences in the intracellular concentrations, which in turn may be affected by the cellular kinases involved in the phosphorylation pathway and ATP-binding cassette (ABC) transport proteins.Individual variation in response, such as viral suppression and adverse effects, to antiretroviral therapy is a well-described phenomenon (19, 49). Epidemiological and limited clinical studies suggest that demographic characteristics (e.g., gender, age, and ethnicity) and the HIV disease state of an individual may be partly responsible for the variation in efficacy and toxicity observed with treatment by nucleoside analog reverse transcriptase inhibitors (NRTIs). For example, published studies show that women experienced a 4-fold lower rate of disease progression than did men while they were on zidovudine (AZT) monotherapy; however, women experienced exaggerated toxicities during NRTI therapy compared to those of men (15-17, 20, 37). Gender and ethnicity have been suggested to be possible variables that explain the observed differences in treatment response to NRTIs (1,16,43).In a cohort of 4 HIV-1-infected women and 29 HIV-1-in...

Influence of gender on ABCC2 expression in peripheral blood mononuclear cells

“…Similar finding was observed in a study on white blood cells extracted from 9 healthy volunteers (5 females, 4 males) using GAPDH as an endogenous control (Paintsil et al, 2011). The study also observed that ABCC2 expression was not correlated with metabolite levels of ethynylstavudine and lamivudine, but was tentatively to be correlated with zidovudine (P > 0.05) (Paintsil et al, 2011).…”

“…The study also observed that ABCC2 expression was not correlated with metabolite levels of ethynylstavudine and lamivudine, but was tentatively to be correlated with zidovudine (P > 0.05) (Paintsil et al, 2011). However, this study was conducted on a small number of subjects with limited statistical power (Paintsil et al, 2011). In contrast, the present study found that gender may potentially influence ABCC2 expression in PBMCs, where males showed greater levels of ABCC2 expression compared to females.…”

“…Similarly, a previous study found that males had greater variability of protein ABCC2 expression in liver than females (MacLean et al, 2008). On the other hand, another study found that females had greater variability in PBMC ABCC2 expression than males (Paintsil et al, 2011).…”

“…On the other hand, expression of ABCC2 protein in renal cells was significantly higher in males as compared to females (Wang et al, 2012). Other studies examining ABCC2 protein expression in human liver cells (Deo et al, 2012) and PBMCs (Paintsil et al, 2011) found no effect of gender on its expression. These studies suggested that expression of ABCC2 may be dependent on the tissue/organ in which it is expressed.…”

Modulation of the pentose phosphate pathway alters phase I metabolism of testosterone and dextromethorphan in HepG2 cells

“…It has been recognized for some time that individual parameters, such as gender, age, body weight, and nutrition as well as lifestyle factors, such as alcohol, tobacco, physical exercise, and food preference, contribute to individual variations in drug metabolism [28][29][30][31] . However, it is unknown how these external factors (epi-factors) affect the intrinsic function of drug metabolism.…”