Expression of P-glycoprotein and multidrug resistance-associated protein in healthy volunteers and HIV-infected patients

Expression of CYP2B6 Enzyme in Human Liver Tissue of HIV and HCV Patients

Background and Objectives: Hepatitis C virus (HCV) and human immunodeficiency virus (HIV) infections present significant public health challenges worldwide. The management of these infections is complicated by the need for antiviral and antiretroviral therapies, which are influenced by drug metabolism mediated by metabolic enzymes and transporters. This study focuses on the gene expression of CYP2B6, CYP3A4, and ABCB1 transporters in patients with HIV, HCV, and HIV/HCV co-infection, aiming to assess their potential association with the choice of therapy, patohistological and clinical parameters of liver damage such as the stage of liver fibrosis, serum levels of ALT and AST, as well as the grade of liver inflammation and other available biochemical parameters. Materials and Methods: The study included 54 patients who underwent liver biopsy, divided into HIV-infected, HCV-infected, and co-infected groups. The mRNA levels of CYP2B6, CYP3A4, and ABCB1 was quantified and compared between the groups, along with the analysis of liver fibrosis and inflammation levels. Results: The results indicated a significant increase in CYP2B6 mRNA levels in co-infected patients, a significant association with the presence of HIV infection with an increase in CYP3A4 mRNA levels. A trend towards downregulation of ABCB1 expression was observed in patients using lamivudine. Conclusions: This study provides insight into gene expression of CYP2B6 CYP3A4, and ABCB1 in HIV, HCV, and HIV/HCV co-infected patients. The absence of correlation with liver damage, inflammation, and specific treatment interventions emphasises the need for additional research to elucidate the complex interplay between gene expression, viral co-infection, liver pathology, and therapeutic responses in these particular patients population.

Impact of endotoxin on the expression of drug transporters in the placenta of HIV-1 transgenic (HIV-Tg) rats

BACKGROUND

Inflammatory responses in HIV (+) patients may be exacerbated due to reports of subclinical endotoxemia and existing immune dysregulation. As inflammation has been reported to mediate changes in the expression of transporters, this could be potentiated in pregnant HIV (+) women. Similar to humans, the HIV-Tg rat model develops immune dysregulation and chronic AIDS-like conditions. Our objective was to examine the expression of placental drug transporters in HIV-Tg rats in response to low-dose endotoxin.

METHODS

Pregnant HIV-Tg rats or wild-type littermates (WT) were treated with low dose bacterial endotoxin 0.1mg/kg (n=8) or 0.25mg/kg (n=4-6) on GD18 and placentas were harvested 18h later. Placental and hepatic expression of transporters and cytokines were examined using qRT-PCR and Western blotting.

RESULTS

As compared to WT, endotoxin administration increased the hepatic and placental expression of IL-6 and TNF-α to a greater extent in HIV-Tg rats (p<0.05). The placental mRNA and protein expression of Abcb1a and Slco2b1 was significantly decreased in endotoxin-treated HIV-Tg but not WT rats and downregulation of Slco4a1 mRNA was more pronounced in the HIV-Tg group (p<0.05). These changes significantly correlated with the placental expression of pro-inflammatory cytokines. Abcc3 mRNA expression was increased in the placenta of endotoxin treated WT rats only, while placental expression of Abcc1, Abcc2 and Abcc4 was not significantly affected in both WT and HIV rats. Endotoxin imposed a pronounced downregulation in the hepatic expression of Abcb1a, Abcc2, Abcc4, Abcg2, Slco1a1, Slco1b2 and Slc29a1 in both HIV-Tg and WT rats; however, Abcb1b expression was increased in HIV but not WT rats.

CONCLUSION

Our results indicate that low-dose endotoxin resulted in an augmented inflammatory response in HIV-Tg rats accompanied with significant changes in the placental expression of several drug transporters. Our data suggests that subclinical endotoxemia and other co-existing infections may alter the placental transfer of drugs in the HIV population.

Role and modulation of drug transporters in HIV-1 therapy

Current treatment of human immunodeficiency virus type-1 (HIV-1) infection involves a combination of antiretroviral drugs (ARVs) that target different stages of the HIV-1 life cycle. This strategy is commonly referred to as highly active antiretroviral therapy (HAART) or combined antiretroviral therapy (cART). Membrane-associated drug transporters expressed ubiquitously in mammalian systems play a crucial role in modulating ARV disposition during HIV-1 infection. Members of the ATP-binding cassette (ABC) and solute carrier (SLC) transporter superfamilies have been shown to interact with ARVs, including those that are used as part of first-line treatment regimens. As a result, the functional expression of drug transporters can influence the distribution of ARVs at specific sites of infection. In addition, pathological factors related to HIV-1 infection and/or ARV therapy itself can alter transporter expression and activity, thus further contributing to changes in ARV disposition and the effectiveness of HAART. This review summarizes current knowledge on the role of drug transporters in regulating ARV transport in the context of HIV-1 infection.

P-glycoprotein (ABCB1) activity decreases raltegravir disposition in primary CD4+P-gphigh cells and correlates with HIV-1 viral load

Objectives

To evaluate the role of P-glycoprotein (P-gp) and multidrug-resistant-protein 1 (MRP1) on raltegravir intracellular drug disposition in CD4+ T cells, investigate the effect of HIV-1 infection on P-gp expression and correlate HIV-1 viraemia with P-gp activity in primary CD4+ T cell subsets.

Methods

The cellular accumulation ratio of [³H]raltegravir was quantified in CD4+ T cell lines overexpressing either P-gp (CEM-P-gp) or MRP1 (CEM-MRP1) and in primary CD3+CD4+ T cells with high (P-gp^high) and low P-gp activity (P-gp^low); inhibition of efflux transporters was confirmed by the intracellular retention of calcein-AM. The correlation of P-gp activity with HIV-1 viraemia was assessed in naive and memory T cell subsets from 21 HIV-1-infected treatment-naive subjects.

Results

[³H]Raltegravir cellular accumulation ratio decreased in CEM-P-gp cells (P < 0.0001). XR9051 (a P-gp inhibitor) and HIV-1 PIs reversed this phenomenon. Primary CD4+P-gp^high cells accumulated less raltegravir (38.4% ± 9.6%) than P-gp^low cells, whereas XR9051 also reversed this effect. In vitro HIV-1 infection of PBMCs and stimulation of CD4+ T cells increased P-gp mRNA and P-gp activity, respectively, while primary CD4+P-gp^high T cells sustained a higher HIV-1 replication than P-gp^low cells. A significant correlation between HIV-1 viraemia and P-gp activity was found in different CD4+ T cell subsets, particularly memory CD4+ T cells (r = 0.792, P < 0.0001).

Conclusions

Raltegravir is a substrate of P-gp in CD4+ T cells. Primary CD4+P-gp^high T cells eliminate intracellular raltegravir more readily than P-gp^low cells and HIV-1 viraemia correlates with P-gp overall activity. Specific CD4+P-gp^high T cell subsets could facilitate the persistence of viral replication in vivo and ultimately promote the appearance of drug resistance.

Expression of breast cancer resistance protein in peripheral T cell subsets from HIV‑1‑infected patients with antiretroviral therapy

The aim of the present study was to investigate the expression of breast cancer resistance protein (BCRP) in peripheral T cell subsets of human immunodeficiency virus 1 (HIV‑1)‑infected patients, and to analyze the association between the levels of BCRP expression and disease progression in HIV‑1 infection. Peripheral blood mononuclear cells (PBMCs) were obtained from HIV‑1‑infected patients (n=118), including 92 patients with antiretroviral therapy (ART) and 26 patients without a history of ART. Control samples from 30 healthy donors were also analyzed. The expression levels of BCRP in T cells were evaluated by flow cytometry. A high inter‑individual variability was observed in CD4+ and CD8+ T cells in the HIV‑1‑infected patients and healthy donors; however, the analyzed expression levels of BCRP were significantly higher in the HIV‑1‑infected group with ART than those in the group with no history of ART (P<0.01). Furthermore, the frequency of BCRP‑expressing T cells was inversely correlated with CD4+ and CD8+ T cell counts in HIV‑1‑infected patients with ART. The results suggested that BCRP expression varied among HIV‑1‑infected patients and healthy donors but was significantly higher in HIV‑1 patients undergoing ART. In conclusion, the present study suggested that overexpression of BCRP may be involved in disease progression of the HIV‑1 infection and may participate in drug resistance to ART, thus contributing to the failure of highly active ART in HIV‑1 therapeutics.

Expression of membrane drug efflux transporters in the sigmoid colon of HIV-infected and uninfected men

The use of antiretroviral therapy (ART) as pre-exposure prophylaxis (PrEP) has gained global attention as a promising HIV prevention strategy in men who have sex with men. Permeability of these agents in the rectal mucosa may be partially regulated by interactions with drug efflux transporters, P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs) and/or breast cancer resistance protein (BCRP). The objective of this work was to investigate the expression of drug efflux transporters in recto-sigmoid colon tissues of HIV-infected and uninfected men, and evaluate the association of ART and/or HIV infection with drug transporter expression. MDR1/P-gp, MRPs (1-4) and BCRP mRNA and protein expression were detected in sigmoid colon biopsies of HIV-uninfected individuals. Biopsies from HIV-infected, ART-naïve participants revealed a significant downregulation of P-gp and MRP2 protein levels compared to HIV-uninfected individuals. Biopsies from HIV-infected ART-treated patients showed 1.9-fold higher P-gp protein expression and 1.5-fold higher MRP2 protein expression compared to the ones obtained from the HIV-infected ART-naïve patients. This is a first report demonstrating that HIV infection or ART could alter expression of drug efflux transporters in gut mucosa which in turn could affect the permeability of PrEP antiretroviral agents across this barrier, a highly vulnerable site of HIV transmission.

Influence of drug transport proteins on the pharmacokinetics and drug interactions of HIV protease inhibitors

Protease inhibitors, a class of antiretroviral agents frequently used in the treatment of HIV infection, interact with numerous transport proteins resulting in clinically significant drug-drug interactions (DDIs). This review focuses on the proteins that transport protease inhibitors and directly influence the pharmacokinetics of these drugs, as well as the transport proteins that are inhibited or induced by protease inhibitors. Clinically relevant DDIs involving drug transporters and protease inhibitors, either as "victim" drugs or as "perpetrator" drugs, and the pharmacokinetic consequences of such interactions are highlighted. A summary of transporter-mediated processes underlying the toxicity of protease inhibitors is provided. Finally, the effect of HIV infection or co-infection on drug transport proteins, and the implications for protease inhibitor pharmacokinetics is discussed. Transport proteins significantly influence the pharmacokinetics, efficacy and toxicity profiles of this important class of drugs.

ABC transporters in human lymphocytes: expression, activity and role, modulating factors and consequences for antiretroviral therapies

IMPORTANCE OF THE FIELD

ATP-binding cassette (ABC) transporters are a superfamily of efflux pumps that transport numerous compounds across cell membranes. These transporters are located in various human tissues including peripheral blood cells, in particular lymphocytes, and present a high variability of expression and activity. This variability may affect the intracellular concentrations and efficacy of drugs acting within lymphocytes, such as antiretroviral drugs.

AREAS COVERED IN THIS REVIEW

This review focuses on the current knowledge about the expression, activity, roles and variability of ABC drug transporters in human lymphocytes. The identified modulating factors and their impact on the intracellular pharmacokinetics and efficacy of antiretroviral drugs are also detailed.

WHAT THE READER WILL GAIN

Controversial data regarding the expression, activity and sources of variability of ABC transporters in lymphocytes are discussed. The modulating factors and their pharmacological consequences regarding antiretroviral therapies are also provided.

TAKE HOME MESSAGE

Numerous studies have reported conflicting results regarding the expression and activity of ABC drug transporters in lymphocytes. Despite these discrepancies, which may partly result from heterogeneous analytical methods, ABCC1 appears to have the highest expression in lymphocytes and may thus play a predominant role in the resistance to antiretroviral drugs, particularly to protease inhibitors.

Identification of a potential pharmacological sanctuary for HIV type 1 in a fraction of CD4(+) primary cells

We have identified a subset of HIV-susceptible CD4(+)CCR5(+) cells in human PBMCs that can efficiently exclude protease inhibitors (PI) due to high P-glycoprotein (P-gp) efflux activity. Phenotypically these cells are heterogeneous, include both T and non-T cells, and some display markers of memory cells. Cells with high P-gp represent 16-56% (median = 37.3) of all CD4(+)CCR5(+) cells in healthy donors, and are selectively depleted in HIV-1-infected individuals (4.1-33%, median = 10.1). A fraction of primary cells productively infected by HIV-1, in vitro, have high P-gp pump activity, demonstrating that infection does not inhibit P-gp function. In agreement with these data, HIV-susceptible cells expressing high levels of P-gp require higher levels of PI for complete inhibition of virus spread. We conclude that the PI concentrations achieved in plasma could be suboptimal for full inhibition of virus spread in high P-gp cells, indicating that they may represent a pharmacological sanctuary for HIV-1.

Flow cytometric evaluation of multidrug resistance proteins

There are several ways to detect proteins on cells. One quite frequently used method is flow cytometry. This method needs fluorescently labeled antibodies that can attach selectively to the protein to be investigated for flow cytometric detection. Flow cytometry scans individual cells, virtually without their surrounding liquid, and can scan many cells in a very short time. Because of this advantage of flow cytometry, it was adapted to investigate transport proteins on normal and cancerous human cells and cell lines. These transport proteins play important roles in human metabolism. Absorption in the intestine, excretion at the kidney, protection of the CNS compartment and the fetus from xenobiotics, and other vital functions depend on these transporters. However, several transporters are overexpressed in cancer cells. These overexpressed transporters pump out anticancer drugs from the cells and prevent their curative effects. The detection and quantitation of these types of transporters in cancer cells is important for this reason. Here, we review literature on flow cytometric detection of the three most studied transporters: P-glycoprotein, multidrug resistance-associated proteins, and breast cancer resistance protein.

Comparative description of haplotype structure and genetic diversity of MDR1 (ABCB1) in HIV-positive and HIV-negative populations

Human P-glycoprotein (P-gp), encoded by MDR1 (ABCB1), is an efflux transporter with a wide specificity for substrates/drugs, including HIV protease inhibitors which are commonly used in HIV/AIDS treatment. Three single nucleotide polymorphisms (SNPs) in MDR1 have been shown to affect P-gp expression and function, and may affect HIV/AIDS treatment outcome: 1236C>T [G412G, exon-12], 2677G>T/A [A893S/T, exon-21] and 3435C>T [I1145I, exon-26]. In the present study, our aims were (i) to compare the 3-SNP MDR1 haplotype structure and genetic diversity between North American HIV-positive and HIV-negative individuals belonging to four major ethnic groups and (ii) to determine whether the haplotype structure and genetic diversity observed in these ethnically admixed populations differ from that in ethnically non-admixed populations. For these aims, we analyzed a cohort of 447 HIV/AIDS patients (White [n=193], Black [n=235], Hispanic [n=17], and Asian [n=2]). Results obtained for these patients were compared with the results for (i) HIV-negative individuals (n=356) and (ii) various HapMap and Environmental Genome Project populations. We observed that the genetic characteristics of MDR1 were largely consistent between HIV-positive and HIV-negative populations, but there were striking interethnic differences in the genetic characteristics of MDR1 in both populations. Although it appeared that the genetic characteristics of MDR1 were largely consistent between ethnically admixed and non-admixed populations, genetic characterization of the admixed populations remains to be done. Thus, our results provide useful comparative insights about the genetic characteristics of MDR1 that could be extrapolated across population groups worldwide. For a meaningful interpretation of these results regarding HIV/AIDS treatment outcome, MDR1 haplotype/diplotype structure data, genetic characterization of population admixture, and polymorphisms in other relevant drug transporter and/or metabolizing enzyme genes should be considered in future clinical studies.

Expression levels of MDR1, MRP1, MRP4, and MRP5 in peripheral blood mononuclear cells from HIV infected patients failing antiretroviral therapy

The aim of the study was to evaluate the mRNA expression of four relevant ABC-transporter genes [MDR1 (P-glycoprotein; Pgp), MRP1, MRP4, and MRP5] in HIV-positive individuals failing treatment and analyze the association between the levels of their expression and viral load, CD4 cell count, and therapeutic history. Ninety-eight HIV-positive samples and 20 samples from healthy donors were analyzed, retrospectively. Peripheral blood mononuclear cells (PBMCs) from HIV1-positive individuals were collected at the time of virological failure. Expression of mRNA of Pgp, MRP1, MRP4, and MRP5 in PBMCs was evaluated by real-time PCR. A high inter-individual variability was observed in both HIV-positive individuals and healthy donors but the expression levels of all mRNA analyzed were significantly higher in the HIV-infected group (P < 0.05). A weak but significant inverse correlation was observed between CD4 cell counts and expression levels of MRP4 and MRP5. Comparison of mRNA expression between individuals with different therapeutic histories showed that expression of MRP4 and MRP5 genes in patients who were both protease inhibitor (PI) and non-nucleoside reverse transcriptase inhibitor (NNRTI)-experienced was significantly higher than in patients who were PI experienced but NNRTI-naïve. In conclusion, the mRNA expression of Pgp, MRP1, MRP4, and MRP5 varies among HIV-infected patients and healthy donors but is significantly higher in HIV-positive patients than in donors. The expression of MRP4 and MRP5 seems to correlate with CD4 cell counts. The same protein seems to be overexpressed in patients receiving NNRTIs.

Interindividual variability in the effect of atazanavir and saquinavir on the expression of lymphocyte P-glycoprotein

OBJECTIVES

ABCB1 encodes the efflux transporter P-glycoprotein (P-gp), which regulates the intracellular concentration of many xenobiotics, including several HIV protease inhibitors (PIs). Exposure to some xenobiotics, such as the antibiotic rifampicin, increases P-gp expression. In the present study, we investigated the effect of the HIV PIs saquinavir and atazanavir on the expression and function of ABCB1 and P-gp in primary and cultured lymphocytes, as well as the molecular interactions between these drugs and P-gp. ABCB1 and P-gp expression and function were examined in lymphocyte samples from healthy subjects before and after atazanavir-boosted saquinavir treatment. Expression and function were also studied in CEM cells following exposure to atazanavir and saquinavir. The inhibitory effects of these drugs were investigated in ABCB1-transfected HEK293T cells.

METHODS

P-gp expression and function were measured by flow cytometry. ABCB1 mRNA expression was evaluated using quantitative RT-PCR.

RESULTS

There were no overall changes in ABCB1 or P-gp expression or function after saquinavir-atazanavir treatment in primary lymphocyte samples. However, there was considerable interindividual variability in baseline lymphocyte ABCB1 expression, as well as in the degree of change in ABCB1 expression after saquinavir-atazanavir administration. In cell culture, 5 microM saquinavir increased ABCB1 levels, although it did not affect P-gp expression. Atazanavir inhibited P-gp function at concentrations above therapeutic levels.

CONCLUSIONS

Differences in lymphocyte ABCB1 expression, which may be caused by genetic polymorphisms in ABCB1 or its regulatory partners, are a likely cause of interindividual variation in the disposition and efficacy of clinically relevant P-gp substrates, including HIV PIs.

Lack of sex-related differences in saquinavir pharmacokinetics in an HIV-seronegative cohort

AIMS

To examine the influence of sex on steady-state saquinavir pharmacokinetics in HIV-seronegative volunteers administered saquinavir without a concomitant protease inhibitor.

METHODS

Thirty-eight healthy volunteers (14 female) received saquinavir soft-gel capsules 1200 mg three times daily for 3 days to achieve steady-state conditions. Following administration of the 10th dose, blood was collected serially over 8 h for measurement of saquinavir plasma concentrations. Saquinavir pharmacokinetic parameter values were determined using noncompartmental methods and compared between males and females. CYP3A phenotype (using oral midazolam) and MDR-1 genotypes at positions 3435 and 2677 were determined for all subjects in order to characterize possible mechanisms for any observed sex-related differences.

RESULTS

There was no significant difference in saquinavir AUC(0-8) or any other pharmacokinetic parameter value between the sexes. These findings persisted after mathematically correcting for total body weight. The mean weight-normalized AUC(0-8) was 29.9 (95% confidence interval 15.5, 44.3) and 29.8 (18.6, 40.9) ng h(-1) ml(-1) kg(-1) for males and females, respectively. No significant difference in CYP3A phenotype was observed between the groups; likewise, the distribution of MDR-1 genotypes was similar for males and females.

CONCLUSION

In contrast to previous study findings, results from this investigation showed no difference in saquinavir pharmacokinetics between males and females. The discrepancy between our findings and those previously reported may be explained by the fact that we evaluated HIV-seronegative volunteers and administered saquinavir in the absence of concomitant protease inhibitors such as ritonavir. Caution must be exercised when extrapolating pharmacokinetic data from healthy volunteer studies (including sex-based pharmacokinetic differences) to HIV-infected populations or to patients receiving additional concurrent medications.

Multidrug Resistance-Associated Proteins: Expression and Function in the Central Nervous System

Drug delivery to the brain is highly restricted, since compounds must cross a series of structural and metabolic barriers to reach their final destination, often a cellular compartment such as neurons, microglia, or astrocytes. The primary barriers to the central nervous system are the blood-brain and blood-cerebrospinal fluid barriers. Through structural modifications, including the presence of tight junctions that greatly limit paracellular transport, the cells that make up these barriers restrict diffusion of many pharmaceutically active compounds. In addition, the cells that comprise the blood-brain and blood-cerebrospinal fluid barriers express multiple ATP-dependent, membrane-bound, efflux transporters, such as members of the multidrug resistance-associated protein (MRP) family, which contribute to lowered drug accumulation. A relatively new concept in brain drug distribution just beginning to be explored is the possibility that cellular components of the brain parenchyma could act as a "second" barrier to brain permeation of pharmacological agents via expression of many of the same transporters. Indeed, efflux transporters expressed in brain parenchyma may facilitate the overall export of xenobiotics from the central nervous system, essentially handing them off to the barrier tissues. We propose that these primary and secondary barriers work in tandem to limit overall accumulation and distribution of xenobiotics in the central nervous system. The present review summarizes recent knowledge in this area and emphasizes the clinical significance of MRP transporter expression in a variety of neurological disorders.

Role of Lymphocyte Multidrug Resistance Protein 1 in HIV Infection

The multidrug resistance protein 1 (MRP1) is a drug transporter that protects cells from oxidative stress, which increases HIV-1 replication. The aim of this study was to characterize the expression, function, and role of lymphocyte MRP1 in HIV-1 infection and its modulation by antiretroviral drugs such as the protease inhibitors (PIs). Peripheral blood mononuclear cells (PBMCs) from HIV-positive individuals do not show significant alterations of MRP1 expression despite highly active antiretroviral therapy and HIV plasma viral load levels; however, they exhibit different intracellular MRP1 expression as compared with healthy subjects. By contrast, MRP efflux function is increased in subjects with primary HIV infection and becomes defective in later stages of the infection. PI- and probenecid (PBCD)-mediated inhibition of MRP lowers the in vitro stress-induced response of lymphoid cells by reducing the level of the specific reactive oxygen species superoxide anion and hydrogen peroxide. Finally, the blockade of MRP by PBCD and PIs down-modulates HIV-1 replication by a mechanism independent of inhibition of the HIV-1 protease. Our results are consistent with a model wherein HIV replication is favored by the MRP1-related oxidative stress and inhibition of MRP1 may contribute to the antiviral activity of PIs.

The implications of P-glycoprotein in HIV: friend or foe?

P-glycoprotein (P-gp), coded by the ABCB1 gene, has a wide tissue distribution. The drug transporter is known to limit the bioavailability of a plethora of drugs and xenobiotics including the human immunodeficiency virus (HIV) protease inhibitors. There remains a considerable degree of debate in the literature with respect to the role of ABCB1 polymorphisms in HIV-treatment outcome and some studies have also implicated antiretroviral drugs as inducers of P-gp. Recent evidence indicates a role for P-gp in the inhibition of viral infectivity and/or release and cellular relationships with other infection-related proteins (and cholesterol). It is becoming increasingly clear that future studies on P-gp in HIV should consider both pharmacological and virological issues.

Altered P-glycoprotein expression in AIDS patients with HIV encephalitis

Penetrance of anti-retroviral drugs into the CNS depends partly on the activity of P-glycoprotein (P-gp), an ATP-dependent efflux pump involved in restricting entry of lipophilic drugs into the brain. The present study characterizes the patterns of P-gp expression in the brains of AIDS patients and examines its relationship with clinical and neuropathological indicators of HIV encephalitis (HIVE). For this purpose, brain tissue collected at autopsy from 26 subjects with a history of HIV (9 without HIVE; 17 with HIVE) was analyzed. Immunocytochemical staining and Western blot analyses for regional P-gp expression were performed and levels were correlated with neuropathological indicators and with HIV RNA. Double labeling experiments were performed with antibodies against astroglial (GFAP), endothelial (CD31), microglial (CD45) and neuronal (MAP2) cell markers. In the HIVE-negative cases, P-gp immunoreactivity was associated primarily with endothelial cells. HIVE-positive cases showed extensive immunolabeling of astroglial and microglial cells, but relatively less endothelial cell immunolabeling. No neuronal P-gp immunostaining was detected in brain tissue from any cases in the study. In the HIVE-positive cases with extensive astroglial labeling, the most intense immunoreactivity was detected in white matter. A subset of HIVE-positive cases displayed intense P-gp immunostaining of astrocytes closely associated with blood vessels in the cortex. Both the immunocytochemical and Western blot analyses showed a significant correlation between P-gp expression and HIV RNA levels. In conclusion, P-gp immunoreactivity was detected largely in glial cells in tissue from HIVE-positive patients. Furthermore, in HIVE-positive patients, brain viral burden and P-gp levels were significantly higher than those in HIVE-negative patients. Taken together, our data suggest that P-gp may be part of a central pathway mediating viral compartmentalization in the brains of HIV-infected individuals and may play a significant part in HIV disease progression in the brain.

Intestinal P glycoprotein acts as a natural defense mechanism against Listeria monocytogenes

Mechanisms by which the intestinal epithelium resists invasion by food-borne pathogens such as Listeria monocytogenes are an evolving area of research. Intestinal P glycoprotein is well known to limit the absorption of xenobiotics and is believed to act as a cytotoxic defense mechanism. The aim of this study was to determine if intestinal P glycoprotein is involved in host defense against L. monocytogenes. Caco-2 cells and a P-glycoprotein-overexpressing subclone (Caco-2/MDR) were employed in addition to mdr1a(-/-) mice and wild-type controls. In vitro invasion assays and in vivo experiments were employed to measure bacterial invasion and dissemination. In addition, L. monocytogenes proteins were labeled with [(35)S]methionine, and the transepithelial transport across Caco-2 monolayers was characterized in both directions. Overexpression of P glycoprotein in Caco-2/MDR cells led to increased resistance to L. monocytogenes invasion, whereas P-glycoprotein inhibition led to increased invasion. Flux of [(35)S]methionine-labeled L. monocytogenes proteins was significantly greater in the basolateral-to-apical direction than in the apical-to-basolateral direction, indicating dependence on an apically located efflux transporter. Moreover, inhibiting P glycoprotein reduced the basolateral-to-apical flux of the proteins. Early dissemination of L. monocytogenes from the gastrointestinal tract was significantly greater in the mdr1a(-/-) mice than in wild-type controls. Expression and function of intestinal P glycoprotein is an important determinant in resistance to early invasion of L. monocytogenes.

Differential expression levels of MRP1, MRP4, and MRP5 in response to human immunodeficiency virus infection in human macrophages

Multidrug resistance proteins (MRPs) have been reported to be involved in the efflux of some anti-human immunodeficiency virus (HIV) drugs. We show here that MRP1, MRP4, and MRP5 are expressed at the mRNA level in human monocyte-derived macrophages. HIV infection caused increased transcription of these MRPs; however, temporal differences in stimulation are reported.

The expression of P-glycoprotein and cellular kinases is modulated at the transcriptional level by infection and highly active antiretroviral therapy in a primate model of AIDS

The beneficial effects of highly active antiretroviral therapy (HAART) in HIV-infected patients may be limited by inadequate compliance and viral resistance, but also by host cell factors, such as P-glycoprotein (P-gp) and intracellular kinases involved in the phosphorylation of nucleoside reverse transcriptase inhibitors. We investigated the effects of infection and HAART (zidovudine [AZT], lamivudine [3TC], and indinavir [IDV] on the expression of P-gp and cell kinases involved in the phosphorylation of AZT and 3TC in SHIV89.6P-infected cynomolgus macaques. Under unstimulated conditions, we observed a decrease in P-gp mRNA levels in the peripheral blood and lymph node mononuclear cells of infected macaques, which was accentuated by HAART. SHIV infection also resulted in the overexpression of thymidine kinase mRNA, which was abolished by HAART. In conclusion, retroviral infection and HAART modulate in vivo at the transcriptional level the expression of host cell factors that may affect the efficacy of HAART.

The role of pharmacological enhancement in protease inhibitor-based highly active antiretroviral therapy

Having changed the landscape in the treatment of HIV infection, the functional efficacy of current protease inhibitors (PIs) remains limited by their pharmacokinetic and pharmacodynamic profiles. Complex metabolism by the cytochrome P450 system (particularly the 3A4 isoenzyme), action of membrane drug transporter elements (such as P-glycoprotein and multi-drug resistance-associated proteins) and activation of the nuclear receptor steroid xenobiotic receptor may alter exposures and compromise the antiretroviral activity of these drugs. These factors, as well as inadequate adherence, can facilitate the emergence of PI resistance and lead to regimen failure. Coadministration of ritonavir can enhance exposures of a primary PI by inhibiting CYP3A4 metabolism, P-glycoprotein activity and multi-drug resistance protein-1-mediated efflux. Adding ritonavir, however, is not without cost. Dyslipidaemia (possibly increasing the risk of cardiovascular events), gastrointestinal intolerance, multiple drug-to-drug interactions and activation of steroid xenobiotic receptor can all result and must be balanced against the pharmacokinetic improvement rendered by the addition of ritonavir. Understanding the pharmacological origins for the variations in exposures of PIs, both between and within patients, is important for the successful use of these agents.

A simplified approach to determining P-glycoprotein expression in peripheral blood mononuclear cell subsets

P-glycoprotein (P-gp), encoded by the MDR-1 (multidrug resistance) gene mediates the cellular efflux of several therapeutic agents with the potential of treatment failure. The differential expression of P-gp in many localised tissues and cells of the hematopoietic system implies diverse physiological and pharmacological roles. The exact function of P-gp involved in multidrug resistance remains unclear owing to the numerous discrepancies between different laboratories. The ability to characterise accurately P-gp expression has important clinical implications. However, a complete consensus recommendation regarding methods of P-gp detection has been difficult to reach. With the advancement in immune technology and new commercially available antibodies, we describe a simplified direct immunofluorescent assay capable of detecting surface P-gp expression in peripheral blood mononuclear cells (PBMCs) and subpopulations of lymphocytes in vivo by dual colour flow cytometry. Results were expressed as mean increase in fluorescence (MI) compared to isotypically matched controls. Using this assay, differential basal P-gp expression was found to exist in the following significant hierarchy CD56+ (MI=0.684+/-0.273; n=15)>CD8+ (MI=0.312+/-0.117; n=15)>CD4+ (MI=0.194+/-0.086; n=15). This method is rapid and reproducible and has potential use for in vitro and in vivo application.

In vitro and in vivo modulation of MDR1/P-glycoprotein in HIV-infected patients administered highly active antiretroviral therapy and liposomal doxorubicin

P-glycoprotein (P-gp) transports a wide range of structurally unrelated drugs, such as HIV protease inhibitors (PIs) and cytotoxic compounds such as anthracyclines. Because modification of P-gp phenotype and function is an important underlying mechanism of drug interactions, the current study was conducted in order to evaluate whether highly active antiretroviral therapy (HAART), HIV plasma viral load (VL), or cancer chemotherapy may induce in vivo changes of P-gp phenotype in peripheral blood mononuclear cells (PBMCs) from HIV-infected treatment-naive and -experienced subjects at different stages of HIV infection and/or disease, including patients with HIV-associated Kaposi sarcoma (KS). Our results show that neither HAART nor HIV VL, nor the stage of HIV infection and/or disease, significantly alter P-gp expression on PBMCs. In particular, surface P-gp expression is expressed at low levels by T-cell subsets, B cells, and NK cells, whereas almost all monocytes are double positive and these results are not modified by HIV PI-containing regimens. By contrast, a significant phenotype modification is detected in PBMCs from AIDS/KS patients after challenge with the liposomal formulation of the anthracycline doxorubicin (L-DOX) with the higher expression reached 24 hours after the end of the drug infusion. In addition, accumulation of L-DOX is unaffected by P-gp-mediated drug efflux as documented by in vitro experiments, in sharp contrast to the kinetic of free DOX, based on HIV PI blockade experiments. Finally, P-gp expression was found in KS spindle cells from HIV-infected treatment-naive AIDS/KS patients. We conclude that P-gp phenotype in PBMCs and specific subsets is not altered by HAART and/or HIV, whereas a significant increase is induced by specific anticancer drugs such as L-DOX. Moreover, HIV PIs possess an inhibitory effect on P-gp function that may improve DOX sensitivity in KS spindle cells.

Intracellular pharmacology of nucleoside analogues and protease inhibitors: role of transporter molecules

Antiretroviral agents target HIV replication within infected cells. It is therefore important to focus on the pharmacology of these drugs at their site of action rather than just in plasma. Activation of nucleoside analogues to a triphosphate is essential for antiretroviral activity. Following activation, by intracellular kinases, drug triphosphates compete with endogenous triphosphates for HIV reverse transcriptase. Methodologies to measure triphosphates in peripheral blood mononuclear cells from HIV patients have been described. This has allowed investigation of once-daily dosing regimens, drug interactions, modulation of intracellular activation and the bypassing of initial phosphorylation steps. Drug accumulation within a cell is a balance between influx and efflux. There is a growing body of evidence indicating that transport proteins are vitally important in regulating intracellular concentrations of antiretroviral drugs. Allelic variants, inhibition (or induction) are all potentially critical determinants of active drug present in the cell. It is hoped that understanding the intracellular pharmacology will improve long-term therapy and reduce the likelihood of cellular resistance in therapeutic failure.