Therapeutic concentrations of cyclosporine A, but not FK506, increase P-glycoprotein expression in endothelial and renal tubule cells

The Effect of Platelet Activity, ABCB1 Genetic Polymorphism, and Renal Function on the Development of Ticagrelor-Related Dyspnea in Patients with Acute Coronary Syndrome

Purpose

The aim of this study was to determine the effect of ABCB1 genetic polymorphism and renal function on the occurrence of ticagrelor-related dyspnea.

Patients and Methods

A total of 299 patients with acute with type 1, 2, or 3 myocardial infarction (with and without ST-segment elevation), who underwent coronary angiography and PTCA with stent implantation and were treated with antiplatelet drugs (ticagrelor and aspirin), were enrolled in this prospective study. For all enrolled patient's platelet aggregation (induction with high-sensitivity adenosine diphosphate, ADP HS) testing was performed using a MULTIPLATE® analyzer. Venous blood was also collected for genotyping.

Results

Patients experiencing ticagrelor-related dyspnea had lower ADP HS value (ADP HS ≤ 19.5 U; OR = 2.254; P = 0.009), higher creatinine concentration (>90 µmol/l; OR = 3.414; P = 0.019), and lower GFR value (<60 mL/min/1.73 m2; OR = 2.211; P = 0.035). ABCB1 T allele was associated with ticagrelor-related dyspnea (OR = 2.550; P = 0.04).

Conclusion

Ticagrelor-related dyspnea was found to be related to low platelet aggregation, increased plasma creatinine concentration, decreased GFR, and ABCB1 T allele. Carriers of the ABCB1 T allele had a higher plasma creatinine concentration that could be associated with an inhibitory effect of ticagrelor on P-glycoprotein function.

Role of cyclosporin A in the treatment of kidney disease and nephrotoxicity

The clinical use of cyclosporin A (CsA) has led to significant advances and achievements in the field of transplantation and immune diseases. However, the nephrotoxicity of CsA is a major concern in current immunosuppression regimens. CsA causes abnormal kidney function while treating kidney disease, causing problems for clinicians and patients. Evidence of CsA nephrotoxicity is almost always present in transplant recipients after long-term CsA administration (up to 10 years), and similar phenomena occur with other calcineurin inhibitors. In this review, we summarize the mechanisms and influencing factors of CsA for the treatment of primary nephrotic syndrome. The mechanisms of CsA nephrotoxicity, clinical-pathological features, diagnosis, prevention strategies, and risk factors are summarized. We discuss the correlates and mechanisms of the switch between kidney disease prevention and nephrotoxicity of CsA to better understand the function of CsA in the kidney and to provide a basis for the prevention and treatment of CsA nephrotoxicity.

P-glycoprotein: new insights into structure, physiological function, regulation and alterations in disease

The multidrug resistance phenomenon presents a major threat to the pharmaceutical industry. This resistance is a common occurrence in several diseases and is mediated by multidrug transporters that actively pump substances out of the cell and away from their target regions. The most well-known multidrug transporter is the P-glycoprotein transporter. The binding sites within P-glycoprotein can accommodate a variety of compounds with diverse structures. Hence, numerous drugs are P-glycoprotein substrates, with new ones being identified every day. For many years, the mechanisms of action of P-glycoprotein have been shrouded in mystery, and scientists have only recently been able to elucidate certain structural and functional aspects of this protein. Although P-glycoprotein is highly implicated in multidrug resistant diseases, this transporter also performs various physiological roles in the human body and is expressed in several tissues, including the brain, kidneys, liver, gastrointestinal tract, testis, and placenta. The expression levels of P-glycoprotein are regulated by different enzymes, inflammatory mediators and transcription factors; alterations in which can result in the generation of a disease phenotype. This review details the discovery, the recently proposed structure and the regulatory functions of P-glycoprotein, as well as the crucial role it plays in health and disease.

Therapeutic concentrations of calcineurin inhibitors do not deregulate glutathione redox balance in human renal proximal tubule cells

The calcineurin inhibitors (CNI) cyclosporine A and tacrolimus comprise the basis of immunosuppressive regimes in all solid organ transplantation. However, long-term or high exposure to CNI leads to histological and functional renal damage (CNI-associated nephrotoxicity). In the kidney, proximal tubule cells are the only cells that metabolize CNI and these cells are believed to play a central role in the origin of the toxicity for this class of drugs, although the underlying mechanisms are not clear. Several studies have reported oxidative stress as an important mediator of CNI-associated nephrotoxicity in response to CNI exposure in different available proximal tubule cell models. However, former models often made use of supra-therapeutic levels of tissue drug exposure. In addition, they were not shown to express the relevant enzymes (e.g., CYP3A5) and transporters (e.g., P-glycoprotein) for the metabolism of CNI in human proximal tubule cells. Moreover, the used methods for detecting ROS were potentially prone to false positive results. In this study, we used a novel proximal tubule cell model established from human allograft biopsies that demonstrated functional expression of relevant enzymes and transporters for the disposition of CNI. We exposed these cells to CNI concentrations as found in tissue of stable solid organ transplant recipients with therapeutic blood concentrations. We measured the glutathione redox balance in this cell model by using organelle-targeted variants of roGFP2, a highly sensitive green fluorescent reporter protein that dynamically equilibrates with the glutathione redox couple through the action of endogenous glutaredoxins. Our findings provide evidence that CNI, at concentrations commonly found in allograft biopsies, do not alter the glutathione redox balance in mitochondria, peroxisomes, and the cytosol. However, at supra-therapeutic concentrations, cyclosporine A but not tacrolimus increases the ratio of oxidized/reduced glutathione in the mitochondria, suggestive of imbalances in the redox environment.

Human structural proteome-wide characterization of Cyclosporine A targets

MOTIVATION

Off-target interactions of a popular immunosuppressant Cyclosporine A (CSA) with several proteins besides its molecular target, cyclophilin A, are implicated in the activation of signaling pathways that lead to numerous side effects of this drug.

RESULTS

Using structural human proteome and a novel algorithm for inverse ligand binding prediction, ILbind, we determined a comprehensive set of 100+ putative partners of CSA. We empirically show that predictive quality of ILbind is better compared with other available predictors for this compound. We linked the putative target proteins, which include many new partners of CSA, with cellular functions, canonical pathways and toxicities that are typical for patients who take this drug. We used complementary approaches (molecular docking, molecular dynamics, surface plasmon resonance binding analysis and enzymatic assays) to validate and characterize three novel CSA targets: calpain 2, caspase 3 and p38 MAP kinase 14. The three targets are involved in the apoptotic pathways, are interconnected and are implicated in nephrotoxicity.

Long-term effects of ABCB1 and SXR SNPs on the systemic exposure to cyclosporine in pediatric kidney transplant patients

Aim: Cyclosporine is characterized by a wide interindividual variability in its pharmacokinetics. The objective of this study was to evaluate the effects of ABCB1 and SXR SNPs on cyclosporine exposure in a group of kidney transplant patients followed up from childhood to adulthood. Patients & methods: Recipients were genotyped for ABCB1 C1236T, G2677T/A and C3435T, and for SXR RS3842689 and A7635G. Dose-adjusted trough levels and weight-adjusted daily doses were compared among patients according to allelic status by a generalized estimation equation approach that allows longitudinal data analyses. Results: A genotype-dependent effect was found in all ABCB1 genotypes and in one of the SXR SNPs. This effect was particularly evident for the TT genotype of the ABCB1 G2677T/A SNP, the TT genotype of the ABCB1 C3435T SNP and for heterozygotes of the deletion of 6 bp in the promoter region of SXR. Conclusion: The presence of specific ABCB1 and SXR SNPs could significantly affect cyclosporine exposure during a kidney transplant patient’s development from childhood to adulthood in a time-dependent fashion.

Original submitted 3 May 2013; Revision submitted 25 July 2013

Evaluation of stability and sensitivity of cell fluorescent labels when used for cell migration

The directed migration of mammalian cells is a foundation of development and growth. A variety of processes such as tissue development, wound healing, pathogen recognition/destruction as well as cancer metastasis are the result of regulated or dysregulated cell migration. While the ability to measure a cell's propensity to migrate has clinical relevance in several settings, no universal protocol has been established to measure cell migration. A variety of techniques are currently used to measure migration including manual counting, flow cytometry or Coulter counting, microfluidic devices, computerized spectroscopic methods, or the use of various tracking dyes interfaced with fluorescent or non-fluorescent plate readers. In order to expedite the measurement of migration, we compared several common cytoplasmic and lipophilic cell tracking dyes to determine the best dye for determining migration of rare population of cells. CellVue® Burgundy was found to be superior over calcein AM, Cell Tracker Green CMFDA (chloromethyl fluorescein diacetate), Vybrant CFDA (carboxy fluorescein diacetate succinimidyl ester) in its retention within cells, superior to CellVue® NIR 815, PKH67, and CM DiI with regard to signal to noise ratio, and superior to PKH26 with regard to instrument versatility.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

Top Three Pharmacogenomics and Personalized Medicine Applications at the Nexus of Renal Pathophysiology and Cardiovascular Medicine

Pharmacogenomics is a field with origins in the study of monogenic variations in drug metabolism in the 1950s. Perhaps because of these historical underpinnings, there has been an intensive investigation of 'hepatic pharmacogenes' such as CYP450s and liver drug metabolism using pharmacogenomics approaches over the past five decades. Surprisingly, kidney pathophysiology, attendant diseases and treatment outcomes have been vastly under-studied and under-theorized despite their central importance in maintenance of health, susceptibility to disease and rational personalized therapeutics. Indeed, chronic kidney disease (CKD) represents an increasing public health burden worldwide, both in developed and developing countries. Patients with CKD suffer from high cardiovascular morbidity and mortality, which is mainly attributable to cardiovascular events before reaching end-stage renal disease. In this paper, we focus our analyses on renal function before end-stage renal disease, as seen through the lens of pharmacogenomics and human genomic variation. We herein synthesize the recent evidence linking selected Very Important Pharmacogenes (VIP) to renal function, blood pressure and salt-sensitivity in humans, and ways in which these insights might inform rational personalized therapeutics. Notably, we highlight and present the rationale for three applications that we consider as important and actionable therapeutic and preventive focus areas in renal pharmacogenomics: 1) ACE inhibitors, as a confirmed application, 2) VDR agonists, as a promising application, and 3) moderate dietary salt intake, as a suggested novel application. Additionally, we emphasize the putative contributions of gene-environment interactions, discuss the implications of these findings to treat and prevent hypertension and CKD. Finally, we conclude with a strategic agenda and vision required to accelerate advances in this under-studied field of renal pharmacogenomics with vast significance for global public health.

The pharmacogenetics of calcineurin inhibitor-related nephrotoxicity

Chronic calcineurin inhibitor (CNI)-induced nephrotoxicity is associated with prolonged use of cyclosporine and tacrolimus and has been observed after all types of transplantation, as well as during treatment of autoimmune disease. Extensive alterations in the renal architecture including glomerular sclerosis, tubular atrophy and interstitial fibrosis may lead to end-stage renal failure. Increasing evidence shows that pharmacogenetic factors explain part of the between-patient differences in susceptibility to developing CNI-induced nephrotoxicity. In this paper this evidence is reviewed, with special emphasis on the role of genetic factors influencing metabolism and transportation of CNIs in both acceptor and donor.

Individualized monitoring of nuclear factor of activated T cells-regulated gene expression in FK506-treated kidney transplant recipients

BACKGROUND

The suggested key mechanism of both cyclosporine A (CsA) and FK506 is the inhibition of calcineurin phosphatase activity, preventing nuclear factor of activated T cells (NFAT)-translocation into the nucleus of T cells, with a subsequent transcriptional block of crucial cytokine genes. However, the two drugs exert different clinical activities as exemplified by the ability of FK506 to treat acute rejections. Inhibition of calcineurin activity by FK506 occurs in vitro at the same or even higher dose as for CsA; however, the magnitude of clinical and experimental immunosuppression is higher, indicating that FK506 may act in a calcineurin-independent way.

METHODS

To test this hypothesis, we measured the inhibition of NFAT-regulated gene expression in 262 stable kidney transplanted patients after FK506 intake.

RESULTS

Previously, we showed that the optimal degree of NFAT inhibition in patients treated with CsA is between 15% and 30% residual gene expression. A considerable number of patients treated with FK506 do not achieve this level of immunosuppression despite therapeutic drug concentrations. Importantly, FK506 does inhibit protein translation. This insufficient degree of NFAT inhibition was associated with a higher rate of biopsy-proven acute rejection but also with a lower incidence of recurrent infections. Conversion of CsA to FK506 causes immediately reduced inhibition of NFAT-regulated gene expression.

CONCLUSION

We could demonstrate that a considerable number of FK506-treated patients benefit from the drug, irrespective of the potency of NFAT inhibition in T cells by a yet unknown mechanism. Nevertheless, residual expression of NFAT-regulated genes seems to be a useful pharmacodynamic method to monitor FK506 therapy in renal transplant patients.

CYP3A5 and ABCB1 genes and hypertension

Hypertension is the first single modifiable cause of disease burden worldwide. Genes encoding proteins that are involved in the metabolism (CYP3A5) and transport (ABCB1) of drugs and hormones might contribute to blood pressure control in humans. Indeed, recent data have suggested that CYP3A5 and ABCB1 gene polymorphisms are associated with blood pressure in the rat as well as in humans. Interestingly, the effects of these genes on blood pressure appear to be modified by dietary salt intake. This review summarizes what is known regarding the relationships of the ABCB1 and CYP3A5 genes with blood pressure, and discusses the potential underlying mechanisms of the association. If the role of these genes in blood pressure control is confirmed in other populations and other ethnic groups, these findings would point toward a new pathway for blood pressure control in humans.

MRP (ABCC) transporters-mediated efflux of anti-HIV drugs, saquinavir and zidovudine, from human endothelial cells

The constituents of highly active anti-retroviral therapy (HAART) include HIV-1 protease inhibitors (HPIs) and nucleoside reverse transcriptase inhibitors (NRTIs). Endothelial cell (EC) barriers, especially the blood-brain-barrier (BBB) suppresses the entry of HAART drugs to subendothelial HIV-1 reservoirs. The ATP binding cassette (ABC) transporter family members, multidrug resistant-1 (MDR-1) and multidrug resistance-associated proteins (MRPs) can efflux both HPIs and NRTIs from intracellular compartments. Using brain derived ECs from non-human sources, previous studies suggested a dominant role for MDR-1 in HAART efflux from the BBB. However, due to species variations in ABC-transporter expression, drug-efflux functions using human brain ECs need to be investigated. Furthermore, roles of ABC-transporters in drug-efflux from systemic EC barriers need to be studied. We monitored the expression of ABC-transporters in primary human ECs obtained from brain (HBMVECs), aorta (HAECs), pulmonary-artery (HPAECs), dermal-microvessel (HDMVECs) and umbilical vein (HUVECs). Gene expression for MDR-1 and MRPs (MRP-1 to MRP-5) were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). Drug efflux functions were determined by calcein retention assays. Intracellular accumulation of both 3H-saquinavir (an HPI) and 3H-zidovudine (an NRTI) were also monitored in HAECs and HBMVECs. Both assays were carried out in presence of verapamil (20-60 microM) or MK-571 (12.5-50 microM) inhibitors of MDR-1 and MRPs, respectively in presence of verapamil or MK-571. The HBMVECs expressed higher levels of MRPs than MDR-1 and only MK-571 significantly (P<0.01) suppressed calcein efflux from these cells. However, both HAECs and HPAECs showed MDR-1 and MRP expression and calcein efflux was inhibited by both verapamil and MK-571. Both inhibitors suppressed 3H-saqubinavir efflux from HAECs, but only MK-571 suppressed saquinavir efflux from HBMVECs. In both ECs, 3H-zidovudine efflux was only suppressed by MK-571. Thus, primary human ECs, especially brain derived ECs, predominantly express MRPs and their specific inhibition may enhance HAART efficacy in subendothelial HIV-1 reservoirs.

Association of ABCB1 genetic variants with renal function in Africans and in Caucasians

BACKGROUND

The P-glycoprotein, encoded by the ABCB1 gene, is expressed in human endothelial and mesangial cells, which contribute to control renal plasma flow and glomerular filtration rate. We investigated the association of ABCB1 variants with renal function in African and Caucasian subjects.

METHODS

In Africans (290 subjects from 62 pedigrees), we genotyped the 2677G>T and 3435 C>T ABCB1 polymorphisms. Glomerular filtration rate (GFR) was measured using inulin clearance and effective renal plasma flow (ERPF) using para-aminohippurate clearance. In Caucasians (5382 unrelated subjects), we analyzed 30 SNPs located within and around ABCB1, using data from the Affymetrix 500 K chip. GFR was estimated using the simplified Modification of the Diet in Renal Disease (MDRD) and Cockcroft-Gault equations.

RESULTS

In Africans, compared to the reference genotype (GG or CC), each copy of the 2677T and 3435T allele was associated, respectively, with: GFR higher by 10.6 +/- 2.9 (P < 0.001) and 4.4 +/- 2.3 (P = 0.06) mL/min; ERPF higher by 47.5 +/- 11.6 (P < 0.001) and 28.1 +/- 10.5 (P = 0.007) mL/min; and renal resistances lower by 0.016 +/- 0.004 (P < 0.001) and 0.011 +/- 0.004 (P = 0.004) mm Hg/mL/min. In Caucasians, we identified 3 polymorphisms in the ABCB1 gene that were strongly associated with all estimates of GFR (smallest P value = 0.0006, overall P = 0.014 after multiple testing correction).

CONCLUSION

Variants of the ABCB1 gene were associated with renal function in both Africans and Caucasians and may therefore confer susceptibility to nephropathy in humans. If confirmed in other studies, these results point toward a new candidate gene for nephropathy in humans.

Different renal toxicity profiles in the association of cyclosporine and tacrolimus with sirolimus in rats

BACKGROUND

The association of calcineurin inhibitors (CNIs) with mTOR inhibitors (mTORi) is still a problem in clinical practice and there is substantial interest in better understanding the impact of these associations on kidney toxicity. We aimed to analyse the functional and histological profiles of damage and to define the contribution of inflammatory and pro-fibrotic mediators in the association of cyclosporine (CsA) and/or tacrolimus (Tac) with sirolimus (SRL).

METHODS

A well-defined model of nephrotoxicity in salt-depleted male rats was used. Monotherapy groups were distributed as a non-treated control group with saline solution (n = 12), the Tac group (n = 16) (tacrolimus 6 mg/kg/day) and the CsA group (n = 13) (CsA 15 mg/kg/day). The groups with different associations were scattered as the Tac + SRL group (n = 14) (tacrolimus 6 mg/kg/day and rapamycin 3 mg/kg/day) and the CsA + SRL group (n = 7) (CsA 15 mg/kg/day and rapamycin 3 mg/kg/day). Groups were divided into 30 and 70 days of follow-up, but the CsA + SRL group was only studied for 30 days because animals became sick.

RESULTS

Rats with the CsA + SRL association were the only ones which showed a significant reduction in body weight, impairment of renal function and severe and diffuse tubular vacuolization and tubular atrophy following a striped distribution, and scarce areas of the kidney were still preserved. The Tac + SRL association did not produce renal function impairment, and mild histological damage including enhanced periglomerular tubular atrophy was observed. This local damage affected the distal convoluted tubule involving macula densa and juxtaglomerular apparatus. Pro-inflammatory mediators paralleled functional and structural data. ED-1 and TNF-alpha were noticeably higher in the CsA + SRL than in the Tac + SRL association. Only in the CsA + SRL association an important increase in alpha-SMA+ cells was seen, mainly found in the areas with tubular atrophy. TGF-beta1 was also markedly enhanced in the CsA + SRL association whilst monotherapy or Tac + SRL groups at 30 days TGF-beta1 did not show any changes. However, at 70 days of treatment TGF-beta1 was significantly increased in the Tac + SRL group. Animals receiving SRL showed a decrease in renal vascular endothelial growth factor (VEGF) expression. This growth factor was significantly down-regulated in both CNI associations than in SRL monotherapy. P-glycoprotein (Pgp) was overexpressed in CsA and CsA + SRL therapy whilst Tac and TAC + SRL showed a middle increase Pgp expression but higher than the control and SRL group.

CONCLUSION

We conclude that the association of SRL with high doses of CsA or Tac produces a different functional, histological, inflammatory and pro-fibrogenic pattern. Thus, the addition of SRL to high doses of CsA leads to severe renal injury. Combination with high doses of Tac is clearly less deleterious in the short term. However, there is a low grade of pro-fibrotic inflammatory expression when this association is prolonged.

Role of P-glycoprotein in cyclosporine cytotoxicity in the cyclosporine-sirolimus interaction

Cyclosporine nephrotoxicity remains a major side effect in solid organ transplantation, and can be exacerbated by concomitant administration of sirolimus. Cyclosporine and sirolimus are P-glycoprotein (Pgp) substrates. We hypothesized that the Pgp activity level may affect cyclosporine cytotoxicity by interfering with the ability of Pgp to remove cyclosporine from within tubular cells, and that an interaction between cyclosporine and sirolimus on Pgp function may explain the enhancement of cyclosporine nephrotoxicity by sirolimus. Cyclosporine cytotoxicity was evaluated in primary cultures of normal human renal epithelial cells (HRECs) by cell viability and cytotoxicity assays. Verapamil, quinine, PSC833, and PGP-4008 were used as Pgp inhibitors. Rhodamine-123 (R-123), a fluorescent substrate of Pgp, was used to assess Pgp-mediated transport. Cellular cyclosporine concentration was measured by high-performance liquid chromatography coupled to tandem mass spectrometry. Pgp expression and function were confirmed in HRECs and cyclosporine and sirolimus were shown to be Pgp inhibitors in this model. Verapamil-induced inhibition of Pgp led to a significant increase in cellular concentration of cyclosporine (P<0.05). Cyclosporine exerted a concentration-dependent cytotoxic effect on HRECs that was significantly increased by inhibition of Pgp activity. Sirolimus exerted an inhibitory effect on R-123 efflux in HRECs and increased cellular cyclosporine concentrations in a dose-dependent manner. These data demonstrate that Pgp plays a critical role in protecting renal epithelial cells from cyclosporine toxicity. The inhibitory effect of sirolimus on Pgp-mediated efflux and the cellular concentration of cyclosporine could explain the exacerbation of cyclosporine nephrotoxicity observed clinically.

Modulation of P-glycoprotein activity by cannabinoid molecules in HK-2 renal cells

1. Endogenous and synthetic cannabinoid molecules have been investigated as possible MDR-1/P-glycoprotein (P-gp) modulators in HK-2-immortalized renal cells, using calcein acetoxymethylester (calcein-AM) as a P-gp substrate. 2. Among the endocannabinoid molecules tested, anandamide (AEA), but not 2-arachidonoyl-glycerol (2-AG) or palmitoyl-ethanolamide (PEA), increased the intracellular fluorescence emitted by calcein, a metabolic derivative of the P-gp substrate calcein-AM, indicative of a reduction in transport capacity. 3. All the three synthetic cannabimimetics tested, that is, R-(+)-methanandamide (R(+)-MET), AM 251 and CP55,940 significantly increased calcein accumulation in the cytosol. 4. RT-PCR demonstrated that HK-2 cells do not express CB1 or CB2 cannabinoid receptors. 5. R(+)-MET, AM251 and CP55,940 were also evaluated as modulators of P-gp expression, by Western blot analysis. Only AM251 weakly enhanced the protein levels (by 1.2-fold) after a 4-day-long incubation with the noncytotoxic drug concentration 2 microM. 6. The present data provide the first evidence that the endocannabinoid AEA and different synthetic cannabinoids may inhibit the P-gp activity in vitro via a cannabinoid receptor-independent mechanism.

Does pharmacogenetics have the potential to allow the individualisation of immunosuppressive drug dosing in organ transplantation?

The immunosuppressive drugs used in organ transplantation have a narrow therapeutic index, with rejection occurring as a consequence of underdosing and infection, malignancy and a number of drug-specific side effects with excessive dosing. Significant heterogeneity in the dose of drug required to achieve therapeutic blood concentrations adds to the complexity of the problem, which has been partly resolved by therapeutic drug monitoring. Single nucleotide polymorphisms have been identified in genes encoding metabolic enzymes, drug efflux pumps and drug targets for most of the drugs in widespread use. A pharmacogenetic approach to immunosuppressive drug prescribing remains to be tested. Based on current evidence, the most promising strategy would be use of the cytochrome P450 3A5 expressor genotype to guide initial dosing with tacrolimus.

Effect of nonylphenol ethoxylates (NPEs) on barrier functions of epithelial cell membranes: Opening of tight junctions and competitive inhibition of P-gp-mediated efflux

The effect of nonylphenol ethoxylates (NPEs) on selected barrier functions of biological membranes, such as tight junction and P-gp efflux pump of epithelial membranes, against the transport of xenobiotics was examined. The Caco-2 cell line was used to evaluate the transport of mannitol and daunomycin across the cell monolayer as well as the cellular uptake of daunomycin. In the presence of NPEs, the transport of mannitol was increased, with NP-9 showing a maximal effect, and the transepithelial electrical resistance (TEER) was reduced. The onset of this effect of NP-9 was fairly rapid and reversible for a short term (e.g., 2 h) treatment, while irreversible for a long term (e.g., 72 h) treatment. In the presence of NP-9, the apical uptake of daunomycin was increased, suggesting competitive inhibition between NP-9 and daunomycin in the efflux via the P-gp system. However, a 72 h pretreatment of the cells with NP-9 (up to 1000 nM) did not affect the apparent cellular uptake of daunomycin, suggesting no significant effect of NPEs on the expression of P-gp. In conclusion, NPEs appear to rapidly open the tight junction of epithelial cell membranes and to competitively inhibit the efflux of P-gp substrates, thereby reducing the self-protection ability of the organism against xenobiotics or hazardous environmental compounds that are transported via the paracellular pathway (i.e., uptake) or the P-gp system (i.e., efflux).

Increased functional expression of P-glycoprotein in Caco-2 TC7 cells exposed long-term to cadmium

The objective of this study was to investigate whether P-glycoprotein (P-gp) functional expression in intestinal cells is modified after long-term exposure to the food contaminant cadmium (Cd). The Caco-2 cell line, clone TC7, was first validated as a cellular model for long-term exposure to cadmium. Cytotoxicity tests after acute exposure of 24 h showed a significant concentration-dependent decrease in cellular viability at cadmium levels higher than 10 microM and led us to select the cadmium ranges for long-term exposure: 1, 5, and 10 microM. Intestinal cells were exposed to these cadmium concentrations for four consecutive weeks without inducing DNA condensation or fragmentation. In the second part of this work, we studied the functional expression of the drug efflux pump multidrug resistance P-glycoprotein after long-term exposure to cadmium by immunoblotting with the monoclonal antibody F4 and measurement of calcein-AM+/-the P-gp inhibitor verapamil. Western blot analysis with the F4 antibody detected a single band of 170 to 180 kDa which is the size previously reported for P-gp. Calcein-AM assay showed that four weeks exposure of intestinal cells to 1, 5, and 10 microM Cd increased P-gp functional expression in proportion to the Cd concentration.

Calcineurin Inhibitor–Induced Nephrotoxicity and Renal Expression of P-glycoprotein

STUDY OBJECTIVE

To evaluate immunohistochemistry staining patterns for P-glycoprotein (P-gp) and a marker of early apoptosis (active caspase-3) in renal biopsy specimens obtained from solid organ transplant recipients with nephrotoxicity and those from a control group.

DESIGN

Retrospective analysis of pathology specimens and medical records.

SETTING

Medical university.

SUBJECTS

Twenty-nine solid organ transplant recipients with nephrotoxicity and 32 control patients.

MEASUREMENTS AND MAIN RESULTS

Medical records were reviewed for patient demographics, clinical laboratory results, and prescribed drugs. Immunohistochemistry techniques using primary antibodies to P-gp and active caspase-3 were performed to evaluate staining patterns of these proteins in the kidney specimens. Differences in measures of interest between groups were compared with the Fisher exact test for categoric data and Wilcoxon rank sum test for continuous data. Logistic and linear modeling were used to evaluate difference in measures of P-gp and active caspase-3 between groups while controlling for confounders. Immunohistochemistry confirmed the presence of P-gp in the renal tubules (apical and basal membranes and cytoplasm). Intensity of P-gp staining (score range 0-4) was reduced in renal specimens of transplant recipients with nephrotoxicity compared with the control specimens (mean +/- SD intensity scores 3.2 +/- 0.7 vs 3.8 +/- 0.4, p=0.0002). Neither P-gp-inducing nor P-gp-inhibiting drugs predicted expression of P-gp in the renal specimens of either group. The extent of tubular staining (score range 1-4) for the apoptosis marker, active caspase-3, was less in the nephrotoxicity group than in the control group (mean +/- SD extent scores 1.7 +/- 0.6 vs 2.8 +/- 0.5, p=0.0003).

CONCLUSION

P-glycoprotein expression was less pronounced in renal biopsy specimens with calcineurin inhibitor-induced nephrotoxicity compared with the nonnephrotoxic control specimens. Reduced P-gp expression was evident even when the analysis controlled for factors such as renal function, age, sex, race, diabetes mellitus, level of proteinuria, or prescribed therapy with P-gp inducers or inhibitors. Interpretation of the results from active caspase-3 staining requires further study.

ABCB1 genotype of the donor but not of the recipient is a major risk factor for cyclosporine-related nephrotoxicity after renal transplantation

Cyclosporine (CsA) nephrotoxicity is a severe complication in organ transplantation because it leads to impaired renal function and chronic allograft nephropathy, which is a major predictor of graft loss. Animal models and in vivo studies indicate that the transmembrane efflux pump P-glycoprotein contributes substantially to CsA nephrotoxicity. It was hypothesized that the TT genotype at the ABCB1 3435C-->T polymorphism, which is associated with decreased expression of P-glycoprotein in renal tissue, is a risk factor for developing CsA nephrotoxicity. In a case-control study, 18 of 97 patients developed CsA nephrotoxicity and showed complete recovery of renal function in all cases when switched to a calcineurin inhibitor-free regimen. Both recipients and donors were genotyped for ABCB1 polymorphisms at the positions 3435C-->T and 2677G-->T/A. For controlling for population stratification, two additional polymorphisms, CYP2D6*4 and CYP3A5*3, with intermediate allelic frequencies were studied. The P-glycoprotein low expressor genotype 3435TT only of renal organ donors but not of the recipients was overrepresented in patients with CsA nephrotoxicity as compared with patients without toxicity (chi2 = 10.5; P = 0.005). CsA dosage, trough levels, and the concentration per dose ratio were not different between the patient groups. In a multivariate model that included several other nongenetic covariates, only the donor's ABCB1 3435TT genotype was strongly associated with CsA nephrotoxicity (odds ratio, 13.4; 95% confidence interval, 1.2 to 148; P = 0.034). A dominant role of the donor's ABCB1 genotype was identified for development of CsA nephrotoxicity. This suggests that P-glycoprotein is an important factor in CsA nephrotoxicity.

Overview of tacrolimus-based immunosuppression after heart or lung transplantation

Transplantation has evolved into an accepted treatment for end-stage heart or lung disease. Acute rejection, complications related to immunosuppressive protocols, and the development of chronic rejection continue to challenge the long-term success of heart and lung transplantations. Wide acceptance of tacrolimus as an important immunosuppressant in renal and hepatic transplantations has led subsequently to its investigation as primary immunosuppression in heart and lung transplant recipients, either combined with azathioprine or with the newer agents mycophenolate mofetil or rapamycin. Studies have shown that tacrolimus is an effective therapeutic alternative to cyclosporine for primary immunosuppression in heart or lung transplantation and demonstrates equivalent if not improved prophylaxis of acute rejection, and more recently demonstrates a potential influence on chronic rejection, particularly in lung transplant recipients. Of importance, the enhanced immunosuppressive activity of tacrolimus is achieved without increased risk of infection or malignancy. Differences in tolerability profiles and side effects between tacrolimus and cyclosporine may be used in selecting the optimal immunotherapy after thoracic transplantation. In particular, the lesser propensity of tacrolimus to cause hypertension and hyperlipidemia potentially offers decreased cardiovascular risk for heart and lung transplant recipients.

Comparative Study on the Effects of Cyclosporin A in Renal Cells in Culture

BACKGROUND

Although cyclosporin A (CSA) inhibits P-glycoprotein (ABCB1), the relationship between this inhibition and CSA-induced nephrotoxicity is not established.

METHODS

Three renal cell lines were used to investigate the effects of CSA in cellular viability and accumulation of rhodamine 123 (Rho123): LLC-PK1, which does not express ABCB1 substantially; MDCK, expressing moderate amounts of this protein, and Ma104 cells, which express high amounts of ABCB1.

RESULTS

The viability was significantly reduced in the three cell lines after treatment with CSA concentrations >10 microM. Ma104 was the more resistant and LLC-PK1 the more sensitive. CSA increased Rho123 accumulation in the three cell lines when incubated simultaneously, MDCK presenting the higher increase. However, different results were achieved when the periods of incubation with Rho123 and CSA were disconnected: a post-incubation with CSA was more effective in Ma104 cells, while MDCK and LLC-PK1 showed no difference between pre-, co- and post-incubation with CSA.

CONCLUSIONS

Our results suggest that the effects of CSA may be divided into two groups: ABCB1-independent (direct injury), and ABCB1-dependent toxicity, due to modulation of its activity. This could result in increased accumulation of noxious ABCB1 substrates, contributing to CSA-induced nephrotoxicity. Furthermore, the mechanisms of ABCB1 modulation by CSA may be different for different cell lines.

MDR1 mRNA expressions in peripheral blood mononuclear cells of patients with ulcerative colitis in relation to glucocorticoid administration

Overexpression of multidrug resistance (MDR) protein, P-glycoprotein (P-gp), on lymphocytes has been suggested to be implicated in the failure of glucocorticoid (GC) therapy in patients with ulcerative colitis (UC). However, whether the overexpression of P-gp in a class of patients with inflammatory bowel disease (IBD) is intrinsic or related to the administration of GC is unknown. Relative amounts of MDR1 mRNA expressed in peripheral blood mononuclear cells (PBMCs) were measured using the reverse-transcriptase polymerase chain reaction (RT-PCR) technique in 25 UC patients having no history of GC administration, 25 UC patients having experienced GC therapy, 19 patients with Crohn's disease (CD) with no history of GC therapy, and 27 healthy subjects. Relative amounts of MDR1 mRNA expressed in PBMCs were compared among the groups. The relationship between the amounts of MDR1 mRNA expressed, as well as the total dose of GC administered or the period of GC therapy in UC patients, was examined. The relative amounts of MDR1 mRNA expressed in PBMCs were not significantly different between the healthy subjects and CD patients or UC patients having no history of GC therapy. However, the mean MDR1 mRNA amount in PBMCs of UC patients having experienced GC therapy was significantly greater than that in PBMCs of UC patients with no history of GC administration (p = 0.0375). The amounts of MDR1 mRNA in PBMCs of UC patients having experienced GC therapy significantly correlated with the total dose of GCs administered (p = 0.0175). Overexpression of MDR1 mRNA in PBMCs of IBD patients is not intrinsic. However, high-dose administration of GCs for the treatment of UC may result in an increased expression of MDR1 mRNA, which may impair successful GC therapy in these patients.

Cyclosporin A but not estradiol can protect endothelial cells against etoposide-induced apoptosis

This study was undertaken to examine the possibilities of endothelial protection toward toxicity of anticancer drugs. To test the hypothesis that estradiol (E2) and cyclosporin A (CsA) can interfere within programmed cell death in human umbilical vein endothelial cells (HUVECs), apoptosis was induced by etoposide with and without E2 or CsA. All the concentrations of E2 tested (from 10(-9) to 10(-5) M) failed to protect HUVECs. For CsA a dual effect was observed: used at 1 or 10 microg/mL in coincubation with etoposide, CsA significantly reduced etoposide-induced apoptosis but complete inhibition was not reached, whereas used at 50 microg/mL CsA did not protect HUVECs anymore and even had deleterious effects. Furthermore, a 24-h pretreatment of HUVECs by CsA at 10 microg/mL significantly protected the cells by preventing both bcl-2 level decrease and caspase-3 activation related to etoposide-induced apoptosis. Protective effects of CsA toward endothelial cells were concentration dependent; in pretreatment at 10 microg/mL, CsA was an effective protector and might contribute in vivo to inhibit obvious toxic effects caused by anticancer drugs.

Whole-blood cultures from renal-transplant patients stimulated ex vivo show that the effects of cyclosporine on lymphocyte proliferation are related to P-glycoprotein expression

BACKGROUND

Cyclosporine (CsA) is a substrate for the MDR-1 gene product P-glycoprotein (P-gp). CsA efficacy may be modulated by lymphocyte P-gp expression levels. In this study, CsA inhibition of lymphocyte proliferation in whole-blood cultures ex vivo has been related to (1) lymphocyte P-gp expression and (2) the C3435T polymorphism in the MDR-1 gene, which has been reported to alter P-gp function.

METHODS

In 30 renal-transplant recipients taking CsA monotherapy, P-gp expression was measured by flow cytometry. Whole-blood samples were stimulated with purified protein derivative (PPD) and phytohemagglutinin (PHA). CsA resistance ex vivo was defined as less than 10% reduction in proliferation with either PPD or PHA at 2 hours compared with 0 hours.

RESULTS

CsA resistance was associated with greater P-gp expression using either PPD (median expression, resistant 1.89 vs. sensitive 0.96, P =0.02) or PHA (1.66 vs. 0.96, respectively, P =0.02). Whole-blood CsA levels in resistant and sensitive patients were similar. The C3435T polymorphism did not affect inhibition of proliferation by CsA (P >0.05 for all between genotype group comparisons).

CONCLUSIONS

Our results indicate that lymphocyte P-gp expression determines the degree of inhibition of proliferation by CsA ex vivo; whether this also affects CsA effectiveness in vivo and therefore graft survival requires further study.

The pharmacogenetics of immunosuppression for organ transplantation: a route to individualization of drug administration

Transplantation has transformed the treatment of patients with organ failure in a number of clinical settings, and immunosuppressive drug therapy is fundamental to its success. However, all the drugs in current use have a narrow therapeutic index. Under-dosing can lead to rejection, while over-dosing increases the risks of infection, malignant disease, and serious drug-specific adverse effects, including diabetes mellitus, nephrotoxicity, hypertension, and hyperlipidemia. Heterogeneity in the pharmacokinetics of these drugs makes initial dose determination difficult, as there is a poor correlation between dose and blood concentration. This results in difficulties in achieving target blood concentrations early after transplantation, which are important for reducing the rate of immunological rejection. This problem is compounded by the observation that neither drug dose nor drug blood concentration accurately predict clinical efficacy or toxicity. The main determinant of heterogeneity in dose requirements is intestinal absorption of the active drug. The oxidative enzymes, cytochrome P450 (CYP) 3A4 and CYP3A5, and the drug efflux pump P-glycoprotein (P-gp) in enterocytes regulate this process. Most substrates for the P-gp pump are also substrates for the CYP3A enzymes. An efficient barrier to xenobiotic absorption is formed by the CYP enzymes and P-gp, and by the two systems working synergistically. Genetic polymorphisms have been reported for the genes associated with the expression of the CYP3A enzymes and P-gp. Genotyping patients for CYP3A genes has the potential to aid the establishment of optimal dosage regimens for transplant patients. Genetic polymorphism of the multiple drug resistance gene-1 (MDR1, also known as ABCB1) [3435C/T] and the CYP3A5 genes (CYP3A5*1, CYP3AP1*1) have the greatest potential to influence the pharmacokinetics of immunosuppressants. Homozygosity of the T allele of the MDR1 3435C/T polymorphism has been associated with reduced enterocyte expression of P-gp resulting in increased drug absorption. The presence of the CYP3A5*1 allele is necessary for the production of a fully catalytic CYP3A5 protein, and also influences the ratio of CYP3A4 : CYP3A5 as well as the overall CYP3A catalytic activity. The CYP3A4 : CYP3A5 ratio may, in turn, influence the pattern of drug metabolites formed. Heterogeneity in the production of active and inactive metabolites has implications for both the pharmacokinetics and pharmacodynamics of these drugs.Gene frequencies and drug dose requirements differ between ethnic groups. Ethnic differences in dose requirements for immunosuppressants have been discussed widely. However, ethnicity is a rather crude marker for genotype. Pharmacogenetic typing offers the possibility of significant improvement in the individualization of immunosuppressive drug prescribing with reduced rates of rejection and toxicity.

Structure-activity relationship: analyses of p-glycoprotein substrates and inhibitors

OBJECTIVE

A large number of structurally and functionally diverse compounds act as substrates or modulators of p-glycoprotein (p-gp). Some of them possess multiple drug resistance (MDR)-reversing activity, but only a small number of them have entered clinical study. In order to uncover the factors which exert a significant impact on the interaction between substrates/modulators and p-gp, we have performed structure-activity relationship (SAR) analyses, including molecular modelling, two-dimensional (2D) and three-dimensional (3D) parameter-frame-setting analysis, quantitative structure activity relationship (QSAR) analysis among substrates/modulators, as well as clinically promising MDR-reversing agents.

METHODS

The physicochemical parameters C log P, CMR and all regression equations were derived by using C log P version 4.0 and the latest CQSAR software, respectively. Molecular modelling and all other parameter calculations were performed by using HyperChem version 5.0 program, after geometry optimization and energy minimization using the AM1 semiempirical method.

RESULTS

SAR analyses indicate that MDR reversal activity is correlated with the lipophilicity (C log P), molecular weight (log Mw), longest chain (Nlc) of the molecule and the energy of the highest occupied orbital (Ehomo). In addition, the presence of a basic tertiary nitrogen atom in the structure is also an important contributor to p-gp inhibitory activity. Some separation in space is achieved for different subsets of p-gp substrates and inhibitors using Nlc, C log P and Ehomo as three independent parameters in the 3D-parameter-frame setting.

CONCLUSION

A highly effective p-gp modulator candidate should possess a log P value of 2.92 or higher, 18-atom-long or longer molecular axis, and a high Ehomo value, as well as at least one tertiary basic nitrogen atom. The results obtained may be useful in explaining drug-p-gp interactions for different compounds, including drug interactions and the development of new MDR chemosensitizers.

Evaluation of the role of P-glycoprotein in inflammation induced blood-brain barrier damage

In this study we evaluated the role of the multi-drug transporter p-glycoprotein (Pgp) in the process of activated T lymphocyte-mediated blood-brain barrier dysfunction as described previously. Lymphocyte exposure induced significant endothelial cell death and there was an elevation of the expression of Pgp in the surviving cells. Inhibition of Pgp function using the antibody MRK16 and verapamil displayed a dose-dependent prevention of T cell mediated endothelial cell death and barrier breakdown. These data suggest that the activity of Pgp at the blood-brain barrier may play a role in lymphocyte induced barrier cell damage and a role as a possible survival mechanism to prevent further endothelial cell death in later stages of inflammation.

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

Expression of multidrug resistance P-glycoprotein in kidney allografts from cyclosporine A-treated patients

BACKGROUND

The multidrug resistance (MDR) gene product P-glycoprotein (P-gp) is a transmembrane efflux pump for hydrophobic, potentially toxic compounds, including the immunosuppressant cyclosporine A (CsA). We have previously shown that CsA increases P-gp expression in proximal tubule and endothelial cells in vitro. The aim of the present study was to investigate the in vivo relevance of these observations in renal allograft biopsies from CsA-treated patients.

METHODS

P-gp expression was determined by immunohistochemistry of paraffin sections using two different monoclonal antibodies (UIC2 and MRK16). Biopsies were taken from CsA-treated renal transplant patients with different histopathological diagnoses (N = 79) and were compared with biopsies from normal human kidneys (N = 13) or with allograft biopsies from patients under a CsA-free immunosuppression (N = 15). Moreover, biopsies from 10 donor kidneys before implantation and during rejection episodes ("zero biopsies") were investigated.

RESULTS

P-gp expression in biopsies with acute tubular necrosis (ATN; N = 10) after CsA treatment was significantly higher in arterial endothelia, proximal tubules, and epithelial cells of Bowman's capsule (BC), whereas P-gp was sparsely induced in CsA nephrotoxicity (N = 19) compared with controls. Acute cellular (N = 30) and vascular rejection (N = 10) or chronic allograft nephropathy (N = 10) after CsA was associated with strong P-gp expression in infiltrating leukocytes and increased P-gp expression in arterial endothelia, proximal tubules, and BC. In contrast, biopsies of patients treated with a CsA-free immunosuppression regimen did not show increases in P-gp expression compared with controls. Zero biopsies showed a weak, homogeneous, nonpolarized expression of P-gp in tubules and an increased expression of P-gp after CsA therapy in the brush border, arterial endothelia, and BC.

CONCLUSIONS

CsA treatment was associated with increased P-gp expression in parenchymal cells of kidney transplants with ATN, acute or chronic transplant rejection, but P-gp was not increased in patients with CsA nephrotoxicity. This indicates that CsA induces its own detoxification by P-gp and that inadequate up-regulation of P-gp in renal parenchymal cells contributes to CsA nephrotoxicity. Increased expression of P-gp in infiltrating leukocytes correlated with the severity of allograft rejection, suggesting that P-gp may decrease the immunosuppressive efficacy of CsA. Thus, individual differences in the P-gp induction response of CsA-exposed renal parenchymal cells and/or infiltrating leukocytes may predispose to either CsA nephrotoxicity or rejection, respectively.

Pharmacokinetic and pharmacodynamic implications of P-glycoprotein modulation

P-glycoprotein (P-gp) is a cell membrane-associated protein that transports a variety of drug substrates. Although P-gp has been studied extensively as a mediator of multidrug resistance in cancer, only recently has the role of P-gp expressed in normal tissues as a determinant of drug pharmacokinetics and pharmacodynamics been examined. P-glycoprotein is present in organ systems that influence drug absorption (intestine), distribution to site of action (central nervous system and leukocytes), and elimination (liver and kidney), as well as several other tissues. Many marketed drugs inhibit P-gp function, and several compounds are under development as P-gp inhibitors. Similarly, numerous drugs can induce P-gp expression. While P-gp induction does not have a therapeutic role, P-gp inhibition is an attractive therapeutic approach to reverse multidrug resistance. Clinicians should recognize that P-gp induction or inhibition may have a substantial effect on the pharmacokinetics and pharmacodynamics of concomitantly administered drugs that are substrates for this transporter.

Increased glomerular cell heparan sulfates in vitro by ciclosporin A: a Possible explanation of Its beneficial effect in idiopathic nephrotic syndrome

BACKGROUND/AIM

In idiopathic nephrotic syndrome (INS), ciclosporin A (CsA) was shown to decrease proteinuria, an effect explained by its immunologic and hemodynamic actions. In order to determine whether CsA could have a direct action on glomerular cells, we studied the effect of CsA on glomerular cells in vitro, particularly on glycosaminoglcycans (GAG) and heparan sulfates (HS) which are decreased in INS patients.

METHODS

Human glomerular epithelial cells and rat mesangial cells were cultured at various concentrations of CsA. HS were quantified using a cationic membrane after metabolic labeling.

RESULTS

Mesangial cell GAG and HS and epithelial cell HS increased significantly when cells were cultured with CsA. For both cell types this increase was prevailing on the secreted fraction of HS in comparison with the cellular fraction. CsA induced also an increase in cellular cAMP levels, but the effect of CsA was not transduced via a cAMP pathway.

CONCLUSIONS

CsA is able to increase glomerular GAG and HS in vitro. As this effect of CsA was the opposite effect on glomerular cells to the effect of plasma from INS patients, we conclude that this direct action of CsA on glomerular cells could explain in part the effect of this drug in decreasing proteinuria in INS.

P-glycoprotein in HK-2 proximal tubule cell line

P-glycoprotein (PGP) is an efflux pump physiologically expressed in the apical membrane of the proximal tubular cells. PGP may play a role in the elimination of exogenous substances such as chemotherapeutic drugs, calcium channel blockers and immunosuppressors. The involvement of renal PGP in the transport of endogenous substrates is under investigation. HK-2 is an immortalized proximal tubule cell line from normal adult human kidney, reported to retain a phenotype indicative of a well-differentiated state. No data regarding expression and/or activity of PGP in this cell line are available. The aim of this study was to ascertain the usefulness of HK-2 cell line to investigate the properties and roles of PGP in proximal tubular cells. PGP expression in HK-2 cells was determined by immunoblotting analysis using the monoclonal antibody C219. The activity of PGP was assessed by measuring the transport of the fluorescent probe Rhodamine 123 (R-123) in intact cell monostrates. The interactions of putative PGP modulators, including verapamil and cyclosporin A were also evaluated. Western blot revealed a C219 immunoreactive band of about 150 kDa consistent with the presence of PGP. HK-2 cells preloaded with R-123 rapidly effluxed the dye, the efflux being inhibited by verapamil. Verapamil and, to a major extent cyclosporin A, significantly increased R-123 intracellular accumulation. PGP immunoblottable amount was increased when cells were cultured in the presence of either cyclosporin A or dexamethasone. The results suggest that the HK-2 cells, among the various differentiation features of proximal tubules, retain also the expression of a functional PGP in their membranes and that both PGP activity and expression may be modulated by drugs. Therefore, HK-2 line appears a suitable and promising tool for the study in vitro of renal transport processes dependent on PGP.

Chronic cyclosporine administration induces renal P-glycoprotein in rats

The effect of cyclosporine doses on renal P-glycoprotein expression was examined. Rats were given cyclosporine orally at 2, 10, 30 mg/kg/day or subcutaneously at 1, 5, 15 mg/kg/day for 28 days with or without 14 days of additional vehicle dosing. Following cyclosporine dosing, renal function and P-glycoprotein expression were measured. Renal function was reduced in rats receiving oral cyclosporine and the highest subcutaneous dose, 15 mg/kg/day. Western blot analysis showed that cyclosporine administered orally at 10 and 30 mg/kg/day and subcutaneously at 15 mg/kg/day induced significantly renal P-glycoprotein expression. After discontinuation of cyclosporine, renal P-glycoprotein returned to pre-dosing levels in oral groups, whereas the return was incomplete in subcutaneous groups. These results indicate that cyclosporine induces renal P-glycoprotein overexpression a dose-dependent manner.

SEX AND ETHNICITY MAY CHIEFLY INFLUENCE THE INTERACTION OF FLUCONAZOLE WITH CALCINEURIN INHIBITORS12

BACKGROUND

Calcineurin inhibitors (CNI) and azole antifungal agents have been reported to interact in a disparate manner. The azole dose and route and the level of involvement of the liver and intestines have been implicated, although data are limited. A significant interaction may result in CNI toxicity, and withdrawal of the azole may result in subtherapeutic CNI concentrations. Fluconazole, available in both intravenous and oral formulations, is commonly used in transplant recipients and is ideal for determining the presence of a disparate effect on CNI concentrations. We retrospectively investigated the interaction of CNIs with fluconazole, evaluating CNI blood troughs corrected for daily CNI dose, the factors influencing the interaction, and the effect on clinical outcomes in renal and simultaneous pancreas kidney transplant recipients.

METHODS

Twenty-eight patients received a CNI and fluconazole during the calendar year 1999, but only 19 patients had documented CNI blood troughs and outpatient follow-up. There were 25 episodes of use in the 19 included patients. CNI blood troughs were evaluated for changes induced by fluconazole, given by both routes, and clinical outcomes were tracked.

RESULTS

Data demonstrated both intravenous and oral fluconazole alter CNI blood concentrations. Two metabolic patterns were observed, and we termed these convergent and divergent. Divergent metabolizers did not have significant interaction (n=5), and convergent metabolizers did have a significant interaction (n=15). One patient had a divergent episode after a previous convergent episode. The main contributors to the lack of interaction appeared to be female sex and African American ethnicity. Additionally, tacrolimus levels were significantly more affected than cyclosporine, during and after fluconazole administration. No patient experienced nephrotoxicity or cellular rejection related to antifungal therapy.

CONCLUSIONS

Oral and intravenous fluconazole appear to increase oral CNI trough concentrations to a similar extent even after adjusting for daily calcineurin dose. These interactions appear to be chiefly influenced by sex and ethnicity. Further prospective study is necessary to clarify this issue.

Characterization of multidrug transporters in a normal renal tubular cell line resistant to doxorubicin. Multidrug transporters in the LLC-PK(1) cell line and its resistant counterpart

LLC-PK(1) is a proximal tubular cell line derived from normal pig kidney which has a structure and function similar to those of renal proximal tubular cells and which expresses baseline levels of P-glycoprotein. We isolated by drug selection a doxorubicin-resistant cell line (LLC-PK(1)/ADR) that exhibited a multidrug-resistant phenotype; this cell line was characterized by reduced intracellular drug concentrations, an increased drug extrusion, and increased expression of a 170-kDa P-glycoprotein detected by Western blot analysis with monoclonal antibody C219. In addition, an increased expression of MDR1 mRNA was seen by reverse transcriptase-polymerase chain reaction. These results suggest that it is possible to induce the overexpression of P-glycoprotein by chronic treatment with doxorubicin in a normal cell line that physiologically expresses low levels of this protein. This multi-resistant cell line could provide an interesting model for studying the role of P-glycoprotein and the consequence of its induction in a normal tissue.