Cellular issues relating to the resistance of HIV to antiretroviral agents

Role of MRP transporters in regulating antimicrobial drug inefficacy and oxidative stress-induced pathogenesis during HIV-1 and TB infections

Multi-Drug Resistance Proteins (MRPs) are members of the ATP binding cassette (ABC) drug-efflux transporter superfamily. MRPs are known to regulate the efficacy of a broad range of anti-retroviral drugs (ARV) used in highly active antiretroviral therapy (HAART) and antibacterial agents used in Tuberculus Bacilli (TB) therapy. Due to their role in efflux of glutathione (GSH) conjugated drugs, MRPs can also regulate cellular oxidative stress, which may contribute to both HIV and/or TB pathogenesis. This review focuses on the characteristics, functional expression, and modulation of known members of the MRP family in HIV infected cells exposed to ARV drugs and discusses their known role in drug-inefficacy in HIV/TB-induced dysfunctions. Currently, nine members of the MRP family (MRP1-MRP9) have been identified, with MRP1 and MRP2 being the most extensively studied. Details of the other members of this family have not been known until recently, but differential expression has been documented in inflammatory tissues. Researchers have found that the distribution, function, and reactivity of members of MRP family vary in different types of lymphocytes and macrophages, and are differentially expressed at the basal and apical surfaces of both endothelial and epithelial cells. Therefore, the prime objective of this review is to delineate the role of MRP transporters in HAART and TB therapy and their potential in precipitating cellular dysfunctions manifested in these chronic infectious diseases. We also provide an overview of different available options and novel experimental strategies that are being utilized to overcome the drug resistance and disease pathogenesis mediated by these membrane transporters.

Host determinants of antiretroviral drug activity

PURPOSE OF REVIEW

As physicians are confronted with a diversity of adverse events and variability in response to medication among patients, this review will focus on the available evidence regarding the impact of genetic variation on drug response. Specifically, variation in drug metabolizing enzymes such as the cytochrome P450s, drug transporters and human leucocyte antigen (for idiosyncratic drug reactions). The potential role of pharmacogenetics in the management of HIV-1 infected individuals and drug discovery will be discussed.

RECENT FINDINGS

Wide inter-individual variability of antiretroviral therapy efficacy and toxicity in HIV-infected patients has been extensively reported in the literature. Since treatment involves multiple drugs and drug classes with the potential for significant variability in drug-host as well as drug-drug interactions, antiretroviral drug therapy represents a significant challenge. Despite this inherent complexity, considerable recent advances have led to a greater understanding of interactions between genetic and host factors that influence the efficacy and toxicity of these agents.

SUMMARY

The goal of pharmacogenetics in antiretroviral therapy is to outline differences within a given population that influence drug efficacy and toxicity. Although to date, despite the numerous studies available in the literature, conclusions on how the analysis of the relationship between single nucleotide polymorphisms and drug efficacy may not always be clinically useful. Further studies are warranted to clarify the role of pharmacogenetics and antiretroviral drug management.

HIV-Tat protein induces P-glycoprotein expression in brain microvascular endothelial cells

Among the different factors which can contribute to CNS alterations associated with HIV infection, Tat protein is considered to play a critical role. Evidence indicates that Tat can contribute to brain vascular pathology through induction of endothelial cell activation. In the present study, we hypothesized that Tat can affect expression of P-glycoprotein (P-gp) in brain microvascular endothelial cells (BMEC). P-gp is an ATP-dependent cellular efflux transporter which is involved in the removal of specific non-polar molecules, including drugs used for highly active antiretroviral therapy (HAART). Treatment of BMEC with Tat(1-72) resulted in P-gp overexpression both at mRNA and protein levels. These alterations were confirmed in vivo in brain vessels of mice injected with Tat(1-72) into the hippocampus. Furthermore, pre-treatment of BMEC with SN50, a specific NF-kappaB inhibitor, protected against Tat(1-72)-stimulated expression of mdr1a gene, i.e. the gene which encodes for P-gp in rodents. Tat(1-72)-mediated changes in P-gp expression were correlated with increased rhodamine 123 efflux, indicating the up-regulation of transporter functions of P-gp. These results suggest that Tat-induced overexpression of P-gp in brain microvessels may have significant implications for the development of resistance to HAART and may be a contributing factor for low efficacy of HAART in the CNS.