Transcriptional regulation of multidrug resistance-1 gene by interleukin-2 in lymphocytes

Mechanism of tacrolimus in the treatment of lupus nephritis

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder, with more than half of the patients developing lupus nephritis (LN), which significantly contributes to chronic kidney disease (CKD) and end-stage renal disease (ESRD). The treatment of lupus nephritis has always been challenging. Tacrolimus (TAC), an effective immunosuppressant, has been increasingly used in the treatment of LN in recent years. This review aims to explore the mechanisms of action of tacrolimus in treating LN. Firstly, we briefly introduce the pharmacological properties of tacrolimus, including its role as a calcineurin (CaN) inhibitor, exerting immunosuppressive effects by inhibiting T cell activation and cytokine production. Subsequently, we focus on various other immunomodulatory mechanisms of tacrolimus in LN therapy, including its effects on T cells, B cells, and immune cells in kidney. Particularly, we emphasize tacrolimus' regulatory effect on inflammatory mediators and its importance in modulating the Th1/Th2 and Th17/Treg balance. Additionally, we review its effects on actin cytoskeleton, angiotensin II (Ang II)-specific vascular contraction, and P-glycoprotein activity, summarizing its impacts on non-immune mechanisms. Finally, we summarize the efficacy and safety of tacrolimus in clinical studies and trials. Although some studies have shown significant efficacy of tacrolimus in treating LN, its safety remains a challenge. We outline the potential adverse reactions of long-term tacrolimus use and provide suggestions on effectively monitoring and managing these adverse reactions in clinical practice. In general, tacrolimus, as a novel immunosuppressant, holds promising prospects for treating LN. Of course, further research is needed to better understand its therapeutic mechanisms and ensure its safety and efficacy in clinical practice.

Inhibition of ZEB1-AS1 confers cisplatin sensitivity in breast cancer by promoting microRNA-129-5p-dependent ZEB1 downregulation

Background

Breast cancer is the leading cause of cancer-related mortality in women worldwide. Long non-coding RNAs (lncRNAs) are of critical importance in tumor drug resistance. Herein, this study aims to determine the roles of lncRNA ZEB1-AS1 in drug resistance of breast cancer involving microRNA-129-5p (miR-129-5p) and ZEB1.

Methods

Microarray-based gene expression profiling of breast cancer was conducted to identify the differentially expressed lncRNAs. ZEB1 expression was measured in adjacent and cancerous tissues. Next, MCF-7 and MDA-MB-231 cells were treated with a series of inhibitor, mimic or siRNA to clarify the roles of lncRNA ZEB1-AS1 and miR-129-5p in drug resistance of breast cancer. Then the target relationship of miR-129-5p with lncRNA ZEB1-AS1 and ZEB1 was verified. The expression patterns of miR-129-5p, lncRNA ZEB1-AS1, Bcl-2, MDR-1, ZEB1 and corresponding proteins were evaluated. Moreover, the apoptosis and drug resistance of MCF-7 cell were detected by CCK-8 and flow cytometry respectively.

Results

LncRNA ZEB1-AS1 was observed to be an upregulated lncRNA in breast cancer, and ZEB1 overexpression was noted in breast cancerous tissues. MiR-129-5p was revealed to specifically bind to both ZEB1 and lncRNA ZEB1-AS1. Moreover, the expression levels of ZEB1-AS1, ZEB1, Bcl-2, MDR-1, and corresponding proteins were decreased, but the expression of miR-129-5p was increased with transfection of miR-129-5p mimic and lncRNA ZEB1-AS1 siRNA. Besides, drug resistance to cisplatin was inhibited, and cell apoptosis was promoted in breast cancer after transfection of miR-129-5p mimic, lncRNA ZEB1-AS1 siRNA, and ZEB1 siRNA.

Conclusion

In conclusion, the study provides evidence that lncRNA ZEB1-AS1 silencing protects against drug resistance in breast cancer by promoting miR-129-5p-dependent ZEB1 downregulation. It may serve as a novel therapeutic target in breast cancer treatment.

Peripheral Lymphocyte Multidrug Resistance Activity as a Predictive Tool of Biological Therapeutic Response in Rheumatoid Arthritis

Objective.

Multidrug resistance (MDR) transporters may be used as biomarkers to monitor disease progression in RA and as a predictive tool to establish responsiveness to biological therapy. In this multicenter clinical trial, we aimed to assess the predictive value of activity measurement of transporters MDR1, MD resistance protein (MRP)1, and breast cancer resistance protein (BCRP) for biological therapeutic response in RA before the initiation of biological therapy as well as 4 to 6 and 12 weeks after.

Methods.

Peripheral blood samples were collected from 27 responders and 12 nonresponders to biological disease-modifying antirheumatic drugs (bDMARD) at the indicated timepoints as well as from 35 healthy controls. MDR activity factor (MAF) of MDR1, MRP1, and BCRP was measured in CD3+ and CD19+ cells using the Solvo MDQ Kit and cell surface staining by flow cytometry following peripheral blood mononuclear cells isolation.

Results.

At the start of therapy, MAFC (composite MAF of MRP1 and MDR1) and MAFMDR values, and at 4 to 6 weeks of treatment, MAFC, MAFMRP, and MAFMDR values of CD3 cells were higher in nonresponders compared to responders. Receiver-operation characteristic curve analysis revealed that RA patients with MAFC values above 21.3 in CD3 cells at the start of bDMARD therapy are likely to be nonresponders. At 4 to 6 weeks of treatment, these also predict unfavorable response: MAFC values above 20.3, MAFMRP values above 6.0, and MAFMDR values above 13.9 in CD3 cells.

Conclusion.

Our results indicate that the determination of MAFC values in CD3 cells of patients with RA may be of predictive value prior to the initiation of biological therapy, to establish whether the patient will demonstrate sufficient therapeutic response.

Treatment with Methotrexate and Intravenous Cyclophosphamide Pulse Therapy Regulates the P-gp+CD4+ Cell-related Pathogenesis in a Representative Patient with Refractory Proliferative Lupus Nephritis

Diffuse proliferative lupus nephritis (DPLN) is a serious organ complication. Drug resistance correlates with P-glycoprotein (P-gp) expression on activated lymphocytes. We encountered a refractory DPLN patient with expansion of peripheral CD69/CXCR3-co-expressing P-gp⁺CD4⁺ cells producing IL-2 and IL-6. Treatment with high-dose corticosteroid combined with biweekly intravenous cyclophosphamide pulse therapy (IVCY) failed to reduce the population of activated P-gp⁺CD4⁺ cells or control the disease activity. Methotrexate (MTX) with monthly IVCY reduced activated P-gp⁺CD4⁺ cells and improved the clinical symptoms, resulting in long-term remission and tapering of corticosteroids. MTX-IVCY combination therapy, which down-regulates the activated P-gp⁺CD4⁺ cell-mediated disease activity, may be useful for the treatment of refractory DPLN.

MDR1 in immunity: friend or foe?

MDR1 is an ATP-dependent transmembrane transporter primarily studied for its role in the detoxification of tissues and for its implication in resistance of tumor cells to chemotherapy treatment. Several studies also report on its expression on immune cells where it plays a protective role from xenobiotics and toxins. This review provides an overview of what is known on MDR1 expression in immune cells in human, and its implications in different pathologies and their treatment options.

Role of P-glycoprotein on CD69+CD4+ cells in the pathogenesis of proliferative lupus nephritis and non-responsiveness to immunosuppressive therapy

Introduction

P-glycoprotein (P-gp) expression on activated lymphocytes in systemic lupus erythematosus (SLE) plays a role in active efflux of intracellular drugs, resulting in drug resistance. The role of P-gp-expressing lymphocytes in the pathogenesis of SLE remains unclear. The aim of this study was to determine the importance of P-gp⁺CD4⁺ cells in organ manifestations in refractory SLE.

Methods

The proportion of P-gp⁺CD4⁺ cells was determined by flow cytometry in peripheral blood of patients with SLE (n=116) and healthy adults (n=10). Renal biopsy specimens were examined by immunohistochemistry for P-gp expression.

Results

CD69 is a marker of CD4 cell activation. The proportion of both P-gp-expressing CD4⁺ cells and CD69-expressing CD4⁺ cells in peripheral blood was higher in SLE than control. The proportion of P-gp⁺CD69⁺CD4⁺ cells correlated with Systemic Lupus Erythematosus Disease Activity Index and was higher in poor responders to corticosteroids. Furthermore, the proportion of P-gp⁺CD69⁺CD4⁺ cells was significantly higher in proliferative lupus nephritis (LN) with poor response to corticosteroids. The efficacy of immunosuppressive therapy depended on the regulation of the proportion of P-gp⁺CD69⁺CD4⁺ cells. Marked accumulation of P-gp⁺CD4⁺ cells in renal interstitial tissue and high proportion of peripheral P-gp⁺CD69⁺CD4⁺ cells were noted in patients with proliferative LN.

Conclusions

The results showed high proportion of P-gp⁺CD69⁺CD4⁺ cells in peripheral blood and their accumulation in renal tissue in patients with proliferative LN refractory to CS therapy, suggesting that P-gp expression on activated CD4⁺ T cells is a potentially useful marker for refractoriness to treatment and a novel target for treatment.

Relevance of P-glycoprotein on CXCR4+ B cells to organ manifestation in highly active rheumatoid arthritis

INTRODUCTION

In rheumatoid arthritis (RA), P-glycoprotein (P-gp) expression on activated B cells is associated with active efflux of intracellular drugs, resulting in drug resistance. CXCR4 is associated with migration of B cells. This study was designed to elucidate the relevance of P-gp expression on CXCR4⁺ B cells to clinical manifestations in refractory RA.

METHODS

CD19⁺ B cells were analyzed using flow cytometry and immunohistochemistry.

RESULTS

P-gp was highly expressed especially on CXCR4⁺CD19⁺ B cells in RA. The proportion of P-gp-expressing CXCR4⁺ B cells correlated with disease activity, estimated by Simplified Disease Activity Index (SDAI), and showed marked expansion in RA patients with high SDAI and extra-articular involvement. In highly active RA, massive infiltration of P-gp⁺CXCR4⁺CD19⁺ B cells was noted in CXCL12-expressing inflammatory lesions of RA synovitis and RA-associated interstitial pneumonitis. In RA patient with active extra-articular involvement, intracellular dexamethasone level (IDL) in lymphocytes diminished with expansion of P-gp⁺CXCR4⁺ CD19⁺ B cells. Adalimumab reduced P-gp⁺CXCR4⁺ CD19⁺ B cells, increased IDL in lymphocytes, and improved the clinical manifestation and allowed tapering of concomitant medications.

CONCLUSIONS

Expansion of P-gp⁺CXCR4⁺ B cells seems to be associated with drug resistance, disease activity and progressive destructive arthritis with extra-articular involvement in RA.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

Serum levels of P-glycoprotein and persistence of disease activity despite treatment in patients with systemic lupus erythematosus

Around 25% of patients with systemic lupus erythematosus (SLE) could be refractory to conventional therapies. P-glycoprotein expression on cell surface has been implied on drug resistance, however, to date, it is unknown if P-gp serum levels are associated with SLE disease activity. Evaluate the association of serum P-gp levels and SLE with disease activity despite treatment. A cross-sectional study was conducted on 93 female SLE patients, all receiving glucocorticoids at stable doses for the previous 6 months before to baseline. SLE patients were classified into two groups: (a) patients with active disease [SLE disease activity index (SLEDAI) ≥ 3] despite treatment, and (b) patients with inactive disease (SLEDAI < 3) after treatment. Forty-three healthy females comprised the control group. Serum P-gp, anti-DNA, and both anti-nucleosome antibody levels were measured using ELISA. Active-SLE patients despite treatment had higher P-gp levels compared with inactive-SLE after treatment (78.02 ng/mL ± 114.11 vs. 33.75 ng/mL ± 41.11; p = 0.018) or versus reference group subjects (30.56 ng/mL ± 28.92; p = 0.011). P-gp levels correlated with the scores of SLEDAI (r = 0.26; p = 0.01), Mexican-SLEDAI (MEX-SLEDAI) (r = 0.32; p = 0.002), SLICC/ACR damage index (r = 0.47; p < 0.001), and with prednisone doses (r = 0.33; p = 0.001). In the multivariate model, the high P-gp levels were associated with SLICC/ACR score (p = 0.001), and SLEDAI score (p = 0.014). Our findings support a relationship between serum P-gp levels and SLE with disease activity despite treatment, but it requires further validation in longitudinal studies.

Changes in ABCB1 mRNA Expression in Peripheral Blood Cells before and after Renal Transplantation

Cyclosporine (CSA), which is one of the substrates of ATP binding cassette subfamily B member 1 (ABCB1), is widely used as an immunosuppressant in patients undergoing transplantation. The expression level of P-glycoprotein on lymphocytes that is encoded by ABCB1 gene is considered to be one of the major causes of differences in intracellular CSA concentration. The clinical relevance of ABCB1 mRNA expression in peripheral blood was analyzed. We examined (i) the relationship between ABCB1 mRNA and the intracellular concentration of CSA in vitro, (ii) the change in long-term ABCB1 mRNA expression levels, and (iii) its association with acute rejection (AR) or cytomegalovirus (CMV) reactivation in living-donor renal transplantation. A significantly negative correlation between ABCB1 mRNA expression and intracellular CSA concentration in vitro was obtained (p<0.05). ABCB1 mRNA expression was significantly reduced (55%) 1 week after transplantation (p<0.001) and returned to the pre-transplantation level after 1 year. Although the sample size may be too small to obtain a definitive conclusion, no association was observed between ABCB1 mRNA expression levels and AR or CMV reactivation.

ΔNp63α controls YB-1 protein stability: evidence on YB-1 as a new player in keratinocyte differentiation

Y-box binding protein 1 (YBX-1 or YB-1) is an oncoprotein that promotes replicative immortality, tumor cell invasion and metastasis. The increase in the abundance of YB-1 in the cell or YB-1 translocation from the cytoplasm to the nucleus is characteristic of malignant cell growth. We have previously reported that ΔNp63α, a transcription factor that is known to play a pivotal role in keratinocyte proliferation and differentiation, promotes YB-1 nuclear accumulation. Here, we show that YB-1 is highly expressed in proliferating keratinocytes and is down-regulated during keratinocyte differentiation. ΔNp63α reduces YB-1 protein turnover and leads to accumulation of ubiquitin-conjugated YB-1 into the nucleus. Reduction of YB-1 protein level, following treatment with a DNA-damaging agent, is inhibited by ΔNp63α suggesting that YB-1 and ΔNp63α interplay can support keratinocyte proliferation and protect cells from apoptosis under genotoxic stress.

Disease control by regulation of P-glycoprotein on lymphocytes in patients with rheumatoid arthritis

The main purpose of treatment of rheumatoid arthritis (RA) with disease modifying antirheumatic drugs (DMARDs) is to control activation of lymphocytes, although some patients do not respond adequately to such treatment. Among various mechanisms of multidrug resistance, P-glycoprotein (P-gp), a member of ATP-binding cassette transporters, causes drug-resistance by efflux of intracellular drugs. Certain stimuli, such as tumor necrosis factor-α, activate lymphocytes and induce P-gp expression on lymphocytes, as evident in active RA. Studies from our laboratories showed spontaneous nuclear accumulation of human Y-box-binding protein-1, a multidrug resistance 1 transcription factor, in unstimulated lymphocytes, and surface overexpression of P-gp on peripheral lymphocytes of RA patients with high disease activity. The significant correlation between P-gp expression level and RA disease activity is associated with active efflux of drugs from the lymphocyte cytoplasm and in drug-resistance. However, the use of biological agents that reduce P-gp expression as well as P-gp antagonists (e.g., cyclosporine) can successfully reduce the efflux of corticosteroids from lymphocytes in vitro, suggesting that both types of drugs can be used to overcome drug-resistance and improve clinical outcome. We conclude that lymphocytes activated by various stimuli in RA patients with highly active disease acquire P-gp-mediated multidrug resistance against corticosteroids and probably some DMARDs, which are substrates of P-gp. Inhibition/reduction of P-gp could overcome such drug resistance. Expression of P-gp on lymphocytes is a promising marker of drug resistance and a suitable therapeutic target to prevent drug resistance in patients with active RA.

Persistent expression and function of P-glycoprotein on peripheral blood lymphocytes identifies corticosteroid resistance in patients with systemic lupus erythematosus

Corticosteroids (CS) are the mainstay of treatment in systemic lupus erythematosus (SLE) patients. However, some patients have poor response to CS treatment. Among the multiple mechanisms of CS resistance, overexpression of P-glycoprotein (P-gp) on peripheral blood lymphocytes (PBL) may be one of them as this result in efflux of CS from lymphocytes. Thus, we evaluated the role of P-gp protein on PBLs in patients with SLE in its response to CS therapy. SLE patients (n = 42) (fulfilling ACR revised criteria) who were naïve to CS and immunosuppressive drugs were enrolled. Disease activity was assessed using SLE disease activity index (SLEDAI) and expression, and function of P-gp was evaluated by flow cytometry at baseline and after 3 months of therapy with CS. At 3 months, patients with SLEDAI >4 and SLEDAI ≤4 were grouped as nonresponders and responders, respectively. P-gp expression was significantly increased on PBLs of SLE patients as compared to healthy controls (p < 0.001). P-gp expression and function correlated with SLEDAI (r = 0.49, p = 0.005; and r = 0.49, p = 0.001, respectively). P-gp expression and function were not different in responders and nonresponders at baseline. However, at 3 months of CS therapy, P-gp expression and function decreased in responders (p < 0.001 and p < 0.005, respectively), whereas in nonresponders, it remained unchanged. Persistent overexpression and activity of P-gp are associated with poor response to CS in CS naïve patients of SLE.

Chronic inflammation up-regulates P-gp in peripheral mononuclear blood cells via the STAT3/Nf-κb pathway in 2,4,6-trinitrobenzene sulfonic acid-induced colitis mice

Patients with inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis, often suffer drug intolerance. This resistance can be divided into intrinsic resistance and acquired resistance. Although there is agreement on acquired resistance, studies regarding intrinsic resistance have demonstrated inconsistencies, especially for Crohn’s disease. For this reason, an animal model of Crohn’s disease was induced with 2,4,6-trinitrobenzene sulfonic acid solution (TNBS), and intrinsic resistance was analyzed by measuring the function and expression of P-glycoprotein (P-gp) in peripheral mononuclear blood cells (PMBC), followed by mechanistic studies. The results revealed reduced retention of cyclosporine A in PMBC over-expressing P-gp in a TNBS-treated group and enhanced secretion of the cytokines IL-1β, IL-6, IL-17, and TNF-α as well as LPS in plasma. These cytokines and LPS can induce P-gp expression through the STAT3/Nf-κb pathway, contributing to a decrease of cyclosporine A retention, which can be reversed by the application of a P-gp inhibitor. Our results demonstrated that the sustained chronic inflammation could induce the intrinsic resistance presented as P-gp over-expression in PBMC in Crohn’s disease through STAT3/Nf-κb pathway and this resistance might be reversed by combinational usage of P-gp inhibitors.

Basiliximab treatment for steroid-resistant rejection in pediatric patients following liver transplantation for acute liver failure

An IL-2 receptor antagonist, basiliximab, decreases the frequency of ACR in liver transplant (LT) recipients as induction therapy. The aim of this study was to evaluate the effectiveness of basiliximab against SRR as rescue therapy in pediatric LT patients with ALF. Forty pediatric ALF patients underwent LT between November 2005 and July 2013. Among them, seven patients suffering from SRR were enrolled in this study. The median age at LT was 10 months (6-12 months). SRR was defined as the occurrence of refractory rejection after more than two courses of steroid pulse therapy. Basiliximab was administered to all patients. The withdrawal of steroids without deterioration of the liver function was achieved in six patients treated with basiliximab therapy without patient mortality, although one patient developed graft loss and required retransplantation for veno-occlusive disease. The pathological examinations of liver biopsies in the patients suffering from SRR revealed severe centrilobular injuries, particularly fibrosis within one month after LT. We demonstrated the effectiveness and safety of rescue therapy consisting of basiliximab for SRR in pediatric LT recipients with ALF.

Interference of flavonoids with fluorescent intracellular probes: methodological implications in the evaluation of the oxidative burst by flow cytometry

The evaluation of oxidative burst is particularly relevant in many pathological and subclinical conditions. Flow cytometry provides quick and accurate measures of the reactive oxygen species production by leukocytes in most situations. However, spurious results, related to probes' efflux may be observed in several instances. Many factors affect the evaluation of the oxidative burst with fluorescent probes that require intracellular deacetylation and could be substrate of the multidrug resistance proteins (MDR). After discussing the implications of the efflux of fluorophores in the normalization strategies in flow cytometry assays, we have pointed out the possible interference of flavonoids with fluorescet probes' staining and signal. We have also reviewed the results from human intervention studies regarding the evaluation of oxidative burst with these probes. In vitro, at concentrations close to post-ingestion circulating levels, some flavonoids and their metabolites could interfere with probes' staining and fluorescence signal through different mechanisms, such as the inhibition of esterases, the modulation of the MDR-mediate efflux of probe and the inhibition of the oxidation of probe. These effects may explain the contrasting results obtained by human intervention studies. Finally, also inflammatory state or the use of drugs substrate of MDR proteins could affect the evaluation of the oxidative burst with intracellular probes.

Multi-drug resistance-1 gene polymorphisms in nephrotic syndrome: impact on susceptibility and response to steroids

BACKGROUND

Role of multidrug resistance-1 (MDR-1) gene polymorphisms has not been clarified in nephrotic syndrome (NS). Additionally, researchers studied several genetic polymorphisms to explain their influence on different patients' responses to steroid; however the data were inconsistent. Therefore, we aimed to investigate the association of MDR-1 gene polymorphisms [C1236T, G2677T/A, C3435T] and haplotypes with susceptibility to childhood nephrotic syndrome, and whether they influence steroid response.

METHODS

We detected MDR-1 gene polymorphisms using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) in 138 NS patients and 140 age and sex matched healthy children.

RESULTS

The frequencies of MDR1 G2677T/A GT, GA, TT+AA genotypes or T allele, MDR1 C3435T TT genotype, and T allele genotype frequencies were significantly increased in NS group. While no significant differences were observed in distributions of C1236T genotypes or allele between NS patients and healthy children. Moreover, steroid non-responder NS patients had significantly higher frequencies of MDR1 G2677T/A GT, GA, and TT+AA genotypes than steroid responsive NS patients. We observed also that NS patients with age less than 6 years old had increased frequencies of MDR1 G2677T/A GT, GA, TT+AA genotypes or T allele MDR1 C3435T CT, TT genotypes and T allele. Interestingly the frequency of the TGC haplotype of MDR1 was lower in the initial steroid responders than in non-responders NS patients. On the contrary, there were no any association between the MDR1 haplotypes with NS susceptibility and they did not influence renal pathological findings.

CONCLUSION

Our data suggested that MDR1 C3435T or G2677T/A gene polymorphisms are risk factors of increased susceptibility, earlier onset of NS, and steroid resistance.

Cold shock Y-box protein-1 proteolysis autoregulates its transcriptional activities

BACKGROUND

The Y-box protein-1 (YB-1) fulfills pleiotropic functions relating to gene transcription, mRNA processing, and translation. It remains elusive how YB-1 shuttling into the nuclear and cytoplasmic compartments is regulated and whether limited proteolysis by the 20S proteasome releases fragments with distinct function(s) and subcellular distribution(s).

RESULTS

To address these questions, mapping of domains responsible for subcellular targeting was performed. Three nuclear localization signals (NLS) were identified. NLS-1 (aa 149-156) and NLS-2 (aa 185-194) correspond to residues with unknown function(s), whereas NLS-3 (aa 276-292) matches with a designated multimerization domain. Nuclear export signal(s) were not identified. Endoproteolytic processing by the 20S proteasome before glycine 220 releases a carboxy-terminal fragment (CTF), which localized to the nucleus, indicating that NLS-3 is operative. Genotoxic stress induced proteolytic cleavage and nuclear translocation of the CTF. Co-expression of the CTF and full-length YB-1 resulted in an abrogated transcriptional activation of the MMP-2 promoter, indicating an autoregulatory inhibitory loop, whereas it fulfilled similar trans-repressive effects on the collagen type I promoter.

CONCLUSION

Compartmentalization of YB-1 protein derivatives is controlled by distinct NLS, one of which targets a proteolytic cleavage product to the nucleus. We propose a model for an autoregulatory negative feedback loop that halts unlimited transcriptional activation.

Depression is improved when low-dose tacrolimus is given to rheumatoid arthritis patients showing an inadequate response to biologic agents

PURPOSE

Depression in rheumatoid arthritis (RA) patients is more severe than in healthy people. Herein, we report improved depression in RA patients using biologic agents. We examined whether depression was improved by tacrolimus combination therapy when biologic agents were ineffective.

METHOD

The study included 13 RA patients who used biologic agents. The following methods were used before the initiation of tacrolimus combination therapy and at 14 and 30 weeks after treatment initiation: the Zung self-rating depression scale (SDS) to evaluate depression state, disease activity score 28/erythrocyte sedimentation rate (DAS28), tender joint counts, swollen joint counts, a patient global assessment to evaluate RA disease activity, and the modified health assessment questionnaire (mHAQ) to evaluate quality of life.

RESULTS

The SDS scores before the initiation of tacrolimus combination therapy and at 14 and 30 weeks after treatment initiation were 45.2 ± 10.6, 44.8 ± 12.8, and 41.6 ± 11.2 (p = 0.047), respectively, indicating significant improvement. The DAS28 was 5.0 ± 1.3 prior to treatment, 3.8 ± 1.3 at 14 weeks, and 3.5 ± 0.9 at 30 weeks, demonstrating significant improvement at both 14 and 30 weeks (p < 0.001). The mHAQ score changed from 0.60 ± 0.45 at baseline to 0.54 ± 0.52 and 0.38 ± 0.43 at 14 and 30 weeks, respectively. The mHAQ score was significantly lower at 30 weeks when compared to baseline (p = 0.013).

CONCLUSION

Tacrolimus combination therapy does not directly improve depression in RA patients, but it is possible that the observed improvement in depression accompanies the improvement in the secondary failure of RA.

Immunological response as a source to variability in drug metabolism and transport

Through the last decades it has become increasingly evident that disease-states involving cytokines affect the pharmacokinetics of drugs through regulation of expression and activity of drug metabolizing enzymes, and more recently also drug transporters. The clinical implication is however difficult to predict, since these effects are dependent on the degree of inflammation and may be changed when the diseases are treated. This article will give an overview of the present understanding of the effects of cytokines on cytochrome P450 enzymes and drug transporters, and highlight the importance of considering these issues in regard to increasing use of the relatively new class of drugs, namely therapeutic proteins.

Midterm clinico-radiologic findings of an open label observation study of add-on tacrolimus with biologics or non-biologic DMARDs

Tacrolimus (TAC) suppresses immune-inflammation by an intermediary inhibition of calcineurin activation in the treatment of rheumatoid arthritis (RA). Various combination therapies for RA have been reported to be superior to monotherapies. The aim was therefore to study add-on TAC in a combination with biologics (BIO) and/or non-BIO disease-modifying anti-rheumatic drugs (DMARDs) in treatment-resistant patients. In eight RA patients, TAC was added on to BIO (TAC/BIO group) and in forty-one to non-BIO DMARDs (TAC/non-BIO group). The mean C-reactive protein (CRP) decreased from 33 mg/l at the baseline to 16 mg/l at first year in the TAC/BIO group (P < 0.05), from 41 to 14 mg/l in the TAC/non-BIO group (P < 0.05); the mean DAS28-CRP (28 joint count) disease activity score decreased from 5.3 to 4.4 in the TAC/BIO group (P < 0.05) and from 5.0 to 3.9 in the TAC/non-BIO group (P < 0.05). The median of Δ modified total Sharp score decreased from 43 during the year preceding the baseline to 3 during the first year of the follow-up in the TAC/BIO group (P < 0.05) and from 22 to 0 during the second year in the TAC/non-BIO group (P < 0.05). Twenty-six adverse events occurred in this study in 26 patients (53% in all); however, the only severe adverse event was one case of an atypical mycobacterial disease (2%). The combination therapy of TAC with BIO or non-BIO DMARDs represents an effective and relatively safe mode of therapy in treatment-resistant RA.

Treatment strategy based on targeting P-glycoprotein on peripheral lymphocytes in patients with systemic autoimmune disease

Although corticosteroids, immunosuppressants and disease-modifying antirheumatic drugs (DMARDs) are widely used in the treatment of various systemic autoimmune diseases such as systemic lupus erythematosus (SLE), we often experience patients with systemic autoimmune diseases who are resistant to these treatments. P-glycoprotein (P-gp) of membrane transporters, a product of the multiple drug resistance (MDR)-1 gene, is known to play a pivotal role in the acquisition of drug resistance to chemotherapy in malignancy. However, the relevance of MDR-1 and P-gp to resting and activated lymphocytes, which are the major target in the treatment of systemic autoimmune diseases, remains unclear. Studies from our laboratories found surface expression of P-gp on peripheral lymphocytes in patients with SLE and a significant correlation between the expression level and disease activity. Such expression is induced not only by genotoxic stresses but also by various stimuli including cytokines, resulting in active efflux of drugs from the cytoplasm of lymphocytes, resulting in drug-resistance and high disease activity. However, the use of both P-gp antagonists (e.g., cyclosporine) and inhibition of P-gp synthesis with intensive immunosuppressive therapy successfully reduces the efflux of corticosteroids from lymphocytes in vitro, suggesting that P-gp antagonists and P-gp synthesis inhibitors could be used to overcome drug-resistance in vivo and improve outcome. In conclusion, lymphocytes activated by various stimuli in patients with highly active disease apparently acquire MDR-1-mediated multidrug resistance against corticosteroids and probably some DMARDs, which are substrates of P-gp. Inhibition/reduction of P-gp could overcome such drug resistance. The expression of P-gp on lymphocytes is a promising marker of drug resistance and a suitable target to combat drug resistance in patients with active systemic autoimmune diseases.

MDR1a/1b gene silencing enhances drug sensitivity in rat fibroblast-like synoviocytes

BACKGROUND

Drug resistance mediated by P-glycoprotein (P-gp) is one of the major reasons for the failure of rheumatoid arthritis (RA) therapy with disease modifying anti-rheumatic drugs and glucocorticoids. In the present study, we aimed to investigate the in vitro effectiveness of small interfering RNA (siRNA) to render rat fibroblast-like synoviocytes (FLS) susceptible to drugs. We also attempted the electroporation-mediated transfer of siRNA against multidrug resistance (MDR) genes into rat knee joints.

METHODS

FLS were transfected with siRNAs corresponding to MDR1a and MDR1b genes. FLS were treated with dexamethasone (DEX) and lipopolysaccharide. The mRNA and protein levels of tumor necrosis factor-alpha, interleukin (IL)-6 and IL-1beta were measured. Both siRNAs were co-transduced into rat knee joints by an electroporation method and evaluated the target gene expressions in the synovium.

RESULTS

Each siRNA could sequence-specifically reduce the target gene expression by over 70% and effectively suppressed P-gp expression and function in the FLS. Both gene expression and protein production of the inflammatory cytokines in the cells transfected with siRNA were reduced by a greater amount compared to in control cells. The in vivo electroporation-mediated transduction of siRNA could significantly inhibit the target gene expressions.

CONCLUSIONS

MDR1a/1b gene silencing by siRNA could effectively inhibit P-gp in rat FLS, resulting in a significant enhancement of the anti-inflammatory effects of DEX. The in vivo siRNA transduction could successfully silence MDR gene expression in the rat synovium. These findings indicate that the siRNA targeting MDR gene could be a useful tool for treating refractory arthritis in RA.

Tacrolimus, a calcineurin inhibitor, overcomes treatment unresponsiveness mediated by P-glycoprotein on lymphocytes in refractory rheumatoid arthritis

OBJECTIVE

Tacrolimus, a calcineurin inhibitor, is used for treatment of rheumatoid arthritis (RA). It also inhibits functions of P-glycoprotein, which is involved in drug resistance. We examined the mechanisms of early response to 2-week tacrolimus treatment in patients with RA.

METHODS

One hundred thirteen patients with refractory RA despite at least 3 antirheumatic agents, including methotrexate, were treated with tacrolimus (1.5-3 mg/day) and the response was assessed at 2 weeks. Expression of the multidrug resistance (MDR-1) gene and P-glycoprotein was assessed in peripheral blood mononuclear cells (PBMC) collected from 113 patients and 40 healthy subjects. The drug exclusion function by the P-glycoprotein was measured by the residual amount of intracellular tritium-labeled dexamethasone cell/medium ratio (C/M ratio).

RESULTS

The disease activity of enrolled patients was 5.8 +/- 1.2 (mean +/- SD) by DAS28 erythrocyte sedimentation rate. A good response to tacrolimus was noted at 2 weeks in 22 of 113 patients. At baseline, PBMC of patients with RA showed upregulated expression of MDR-1 gene and P-glycoprotein and low C/M ratio. The response to tacrolimus correlated with P-glycoprotein expression and C/M ratio. A significant improvement in C/M ratio was noted after 2 weeks of treatment. The C/M ratio correlated significantly with P-glycoprotein expression on CD4+ lymphocytes.

CONCLUSION

Early efficacy of tacrolimus treatment depended on its inhibitory effect on the drug exclusion function of P-glycoprotein, leading to restoration of intracellular therapeutic levels of corticosteroids and clinical improvement. Evaluation of P-glycoprotein expression on lymphocytes is potentially useful for predicting the response to RA treatment.

Etanercept overcomes P-glycoprotein-induced drug resistance in lymphocytes of patients with intractable rheumatoid arthritis

P-glycoprotein (P-gp) on activated lymphocytes is an adenosine triphosphate (ATP)-binding cassette transporter that causes drug resistance by exclusion of intracellular drugs in patients with active rheumatoid arthritis (RA). However, infliximab with methotrexate (MTX) can overcome P-gp-mediated drug resistance. We encounter patients who cannot continue infliximab or MTX. Here we tested how etanercept affected P-gp-mediated drug resistance in such intractable RA patients. Peripheral lymphocytes of 11 RA patients (3 switched from infliximab and 8 who could not be treated with MTX) were analyzed for P-gp expression by flow cytometry and for drug exclusion using radioisotope-labeled dexamethasone. Activated lymphocytes of RA patients overexpressed P-gp and coexpressed CD69. Incubation of these lymphocytes with dexamethasone in vitro reduced intracellular dexamethasone levels. Two-week etanercept therapy significantly reduced P-gp expression and eliminated such P-gp- and CD69-high-expressing subgroup. The reduction in P-gp resulted in recovery of intracellular dexamethasone levels in lymphocytes and improvement of disease activity, thus allowing tapering of corticosteroids. None of the patients experienced any severe adverse effects. Etanercept is useful for overcoming P-gp-mediated treatment resistance in intractable RA patients who have to discontinue infliximab or are intolerant to MTX.

Etanercept overcomes P-glycoprotein-induced drug resistance in lymphocytes of patients with intractable rheumatoid arthritis

P-glycoprotein (P-gp) on activated lymphocytes is an adenosine triphosphate (ATP)-binding cassette transporter that causes drug resistance by exclusion of intracellular drugs in patients with active rheumatoid arthritis (RA). However, infliximab with methotrexate (MTX) can overcome P-gp-mediated drug resistance. We encounter patients who cannot continue infliximab or MTX. Here we tested how etanercept affected P-gp-mediated drug resistance in such intractable RA patients. Peripheral lymphocytes of 11 RA patients (3 switched from infliximab and 8 who could not be treated with MTX) were analyzed for P-gp expression by flow cytometry and for drug exclusion using radioisotope-labeled dexamethasone. Activated lymphocytes of RA patients overexpressed P-gp and coexpressed CD69. Incubation of these lymphocytes with dexamethasone in vitro reduced intracellular dexamethasone levels. Two-week etanercept therapy significantly reduced P-gp expression and eliminated such P-gp- and CD69-high-expressing subgroup. The reduction in P-gp resulted in recovery of intracellular dexamethasone levels in lymphocytes and improvement of disease activity, thus allowing tapering of corticosteroids. None of the patients experienced any severe adverse effects. Etanercept is useful for overcoming P-gp-mediated treatment resistance in intractable RA patients who have to discontinue infliximab or are intolerant to MTX.

P-glycoprotein function in peripheral T lymphocyte subsets of myasthenia gravis patients: clinical implications and influence of glucocorticoid administration

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder with a chronic clinical course that requires long-term glucocorticoid (GC) therapy. A drug efflux pump, P-glycoprotein (P-gp), actively transports GC out of target cells, thereby reducing its efficacy. We evaluated the P-gp function of peripheral-blood mononuclear cells in 59 MG patients. P-gp function was estimated from a decrease in fluorescent P-gp substrate Rhodamine 123 and its inhibition by the conformation-sensitive UIC2 monoclonal antibody. P-gp function on CD8(+) T cells in 21 MG patients having experienced GC therapy was higher than that in 19 MG patients having no history of GC therapy (p=0.026). There was a significant correlation between P-gp function in CD3(+) (r=0.55, p=0.014) or CD4(+) (r=0.48, p=0.034) T cells and the total dose of prednisolone for treatment. P-gp function on CD4(+) T cells in MG patients who showed low responses to prednisolone therapy (n=8) was higher than that in patients who showed relatively high responses to prednisolone therapy (n=10) (p=0.045). These results suggest that higher P-glycoprotein activity on CD3(+) or CD4(+) cells necessitated treatment with higher steroid doses in order to achieve a clinical response. The measurement of P-gp function on CD4(+) T cells is useful in the assessment of clinical response to GC therapy.

Multiple drug-resistant gene 1 in children with steroid-sensitive nephrotic syndrome

BACKGROUND

A full dose of corticosteroid is required to induce complete remission (CR) in steroid-sensitive nephrotic syndrome (SSNS), unless it is possible to taper and discontinue along with the course after CR. But the mechanism of this change in steroid sensitivity remains unknown. P-glycoprotein (PGP) can eliminate given corticosteroids from cytoplasm, which results in corticosteroid resistance. Therefore, drug delivery was analyzed using real-time polymerase chain reaction (PCR) of multiple drug-resistant gene 1 (MDR1; encoding PGP) mRNA expression.

METHODS

Fourteen patients with SSNS (male/female: 14/0; age: 1-23 years; mean 10.4 years) were enrolled in the study. MDR1 mRNA gene expression of peripheral blood nucleated cells (PBNC), before and after CR (19 sets of blood samples), was quantified using real-time PCR.

RESULTS

The MDR1 mRNA levels before CR were variable in each patient, but there was an apparent decrease in the MDR1 gene expression of PBNC after CR (P < 0.003).

CONCLUSION

PGP may play a role in the tapering of corticosteroids after CR in SSNS.

Expression of multidrug resistance P-glycoprotein on lymphocytes from nephrotic children treated with cyclosporine A and ACE-inhibitor

The aim of this work was to determine the expression of P-glycoprotein (P-gp) on peripheral lymphocytes (CD3) in children with steroid-dependent nephrotic syndrome (SDNS) during cyclosporine A (CyA) and ACE-inhibitor (ACE-I) treatment. The study group (I) consisted of 20 children with SDNS aged 5-18 years, with a subsequent proteinuria relapse at the time of prednisone dose reduction. All nephrotic syndrome (NS) children were examined three times: A--at proteinuria relapse, before CyA treatment; B--after 3 months; C--after 12 months of CyA administration. The control group (II) consisted of 20 healthy children. CD3/P-gp was measured using a flow cytometry assay. The serum CyA level was assessed by means of the immunofluorescence method. The expression of CD3/P-gp in NS relapse, prior to CyA+ACE-I administration, was much higher (median 9.15%, range 1.50-13.50%) when compared to healthy controls (median 1.20%, range 0.30-5.70%). The absolute number of CD3/P-gp in this examination was almost five times higher when compared to healthy controls (p<0.01). After 3 months of CyA+ACE-I therapy, the expression of CD3/P-gp decreased dramatically and was similar to the controls. Similar results were obtained after 12 months of treatment. A strong negative correlation was found between CD3/P-gp and serum CyA concentration in both examinations (r=-0.624, p<0.01; r=-0.464, p<0.01). We conclude that the results of our studies indicate that CyA+ACE-I in SDNS inhibits the expression of P-gp. CyA is an alternative therapy that may lead to the optimization of glucocorticoid (GC) doses, thus, reducing the risk that is associated with the treatment.

Differential regulation of the serotonin transporter gene by lithium is mediated by transcription factors, CCCTC binding protein and Y-box binding protein 1, through the polymorphic intron 2 variable number tandem repeat

The serotoninergic pathways are possible targets for the action of lithium, a therapeutic agent for treatment of bipolar affective disorders. This study aimed to investigate the molecular mechanisms regulating human serotonin transporter gene (SLC6A4) expression by lithium and, specifically, the role of the variable number tandem repeat (VNTR) polymorphic region in intron 2, which is potentially a predisposing genetic factor for bipolar affective disorders. We demonstrated that addition of lithium to human JAr cells led to changes in the levels of SLC6A4 mRNA and protein. Additional investigations revealed that the intron 2 VNTR domain was a potential target for mediation of a transcriptional response to lithium. Properties of two transcription factors, CCCTC binding protein (CTCF) and Y-box binding protein 1 (YB-1), previously shown to be involved in the regulation of SLC6A4 VNTR, were found to be modulated by LiCl. Thus, levels of CTCF and YB-1 mRNA and protein were altered in vivo in response to LiCl. Furthermore, CTCF and YB-1 showed differential binding to the polymorphic alleles of the VNTR on exposure to LiCl. Our data suggest a model in which differential binding of CTCF and YB-1 to the allelic variants of the intron 2 VNTR can be regulated by lithium and in part result in differential and even aberrant expression of SLC6A4. Our study of the regulation of the SLC6A4 VNTR by lithium may improve the understanding of psychiatric disorders and enable the development of novel therapies for conditions such as bipolar affective disorder to target only the at-risk allele.

[Multi-drug resistance in the treatments of autoimmune diseases]

Although corticosteroids and immunosuppressants are widely used for the treatments of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), we often experience patients who are resistant to these treatments. P-glycoprotein (P-gp) of membrane transporters, a product of the multiple drug resistance (MDR)-1 gene, plays a pivotal role in the acquisition of drug resistance. However, the relevance of MDR-1 and P-gp to resting and activated lymphocyte, major targets of the treatments in autoimmune diseases, remains unclear. We found that peripheral lymphocytes in patients with SLE and RA express P-gp on the surface and its expression is highly correlated with disease activity. P-gp on lymphocytes is induced by activation with cytokines such as IL-2, IL-4 and TNF-alpha, resulting in active efflux of corticosteroids from cytoplasm of lymphocytes, which mechanisms could lead to drug-resistance and high disease activity. However, the addition of P-gp antagonists such as ciclosporin A and inhibitors of P-gp synthesis successfully reduce efflux of corticosteroids from lymphocytes in vitro and these results imply that P-gp antagonists and P-gp synthesis inhibitors could work in order to overcome drug-resistance in vivo. Therefore, we propose that measurement of P-gp on lymphocytes is useful marker to indicate drug resistance and requirement of antagonists and/or intensive treatments to overcome drug resistance in active SLE and RA patients.

MDR-1 gene polymorphisms and clinical course of steroid-responsive nephrotic syndrome in children

The study was aimed at investigating the association between MDR-1 genetic polymorphisms [C1236T, G2677T(A), C3435T] and parameters describing the clinical course and treatment response of childhood steroid-responsive nephrotic syndrome (SRNS). Three MDR-1 genetic markers were analyzed in 108 children diagnosed with SRNS and in 135 healthy controls with neither allergic nor renal disease. All subjects were genotyped by PCR-restriction fragment length polymorphism (RFLP) analysis, and an EM algorithm-based analysis was utilized to estimate haplotype frequencies. As expected, there was no difference in genotypic and allelic distribution between and among SRNS patients and healthy children. However, all individual polymorphisms were strongly associated with time to response to initial prednisone therapy. The frequencies of the mutated alleles were higher in late responders (time to remission: >7 days) to oral prednisone (0.53, 0.52,0.66) than in early responders (time to remission: <7 days; 0.24, 0.19, 0.32), with all p values <0.001 for positions 1236, 2677 and 3435, respectively). Odds ratios (ORs) reflecting the strength of the associations were as follows: 6.79 (95% CI:1.96- 23.54) for 1236 T/T, 13.7 (95% CI:2.78-67) for 2677 T/T and 9.92 (95% CI: 3.01-32.71) for 3435 T/T as compared to the respective-wild type homozygotes. The TTT haplotype was similarly found to be significantly associated with late oral steroid response (0.49 vs. 0.19, p=0.0003). Variants 1236T, 2677TA and 3435T identify patients that respond slower to oral prednisone. Although the functional properties of the substitutions investigated here are still to be determined, our findings may be a small step toward the optimization of immunosuppressive therapy in SRNS children.

Fragmented hyaluronan induces transcriptional up-regulation of the multidrug resistance-1 gene in CD4+ T cells

P-glycoprotein, encoded by the multidrug resistance (MDR)-1 gene, expels various drugs from cells resulting in multidrug resistance. We found previously that interleukin-2, a lymphocyte-activation cytokine, induces P-glycoprotein expression on lymphocytes. Lymphocyte activation involves adhesion with the extracellular matrix, such as hyaluronan, through adhesion molecules on lymphocytes. We investigated the transcriptional regulation of MDR-1 in lymphocytes by fragmented hyaluronan. Fragmented hyaluronan (especially the 6.9-kDa form), not native high molecular hyaluronan, induced translocation of YB-1, a specific transcriptional factor for MDR-1, from the cytoplasm into the nucleus and resulted in the transcription of MDR-1 and the expression of P-glycoprotein on lymphocytes in a dose-dependent manner. Transfection of YB-1 antisense oligonucleotides inhibited P-glycoprotein expression induced by fragmented hyaluronan. The fragmented hyaluronan induced significant P-glycoprotein expression on only activated CD4+ T cells, which highly expressed CD69, and resulted in excretion of intracellular dexamethasone added in vitro. Cyclosporin A, a competitive P-glycoprotein inhibitor, restored intracellular dexamethasone levels in CD4+ T cells. Anti-CD44 monoclonal antibody (Hermes-1) inhibited fragmented hyaluronan-induced YB-1 activation and P-glycoprotein expression in CD4+ T cells. We provide the first evidence that binding of fragmented hyaluronan to CD44 induces YB-1 activation followed by P-glycoprotein expression in accordance with activation of CD4+ T cells. Our findings imply that CD4+ T cell activation by fragmented hyaluronan, induced by characteristic extracellular matrix changes in inflammation, tumors, and other conditions, results in P-glycoprotein-mediated multidrug resistance.

Expression of P-glycoprotein in lymphocytes from children with nephrotic syndrome, depending on their steroid response

The aim of this study was to examine the expression of P-glycoprotein (P-gp) in CD3 lymphocytes of children with nephrotic syndrome (NS) in relation to their clinical response to glucocorticoid (GC) treatment. The examinations were performed on two groups. The study group (I) consisted of 88 children aged 2.0-20.0 years with NS, divided according to their clinical response to GC: NFR-non-frequent relapse NS; FR-frequent relapse NS; SD-steroid-dependent NS. The control group (II) consisted of 18 healthy children never treated with GC. We measured P-gp expression on CD3 lymphocytes of patients with NS using a flow cytometry assay. The CD3/P-gp was significantly higher than in controls. The difference was higher in SD (P=0.0001) and FR - (P=0.0002) group. The difference in NFR was smaller. Mean CD3/P-gp (in percent) was twice as high in SD children than in NFR, and the difference, as between FR and NFR, was statistically significant (P<0.01). Worse response to GC or dependency may be due to overexpression of P-gp. Further examinations are necessary to establish whether increased P-gp activity is a result of MDR-1 polymorphism and to determine GC response, or to ascertain if such activity is only a result of GC therapy.

Clinical relevance of the expression of P-glycoprotein on peripheral blood lymphocytes to steroid resistance in patients with systemic lupus erythematosus

OBJECTIVE

P-glycoprotein (P-gp) of membrane transporters leads to drug resistance by the exclusion of intracellular drugs, including corticosteroids. Some patients with highly active systemic lupus erythematosus (SLE) show poor response to corticosteroids; however, the mechanisms of steroid resistance remain unclear. The aim of this study was to elucidate the clinical relevance of P-gp expression on lymphocytes to steroid resistance in patients with active SLE.

METHODS

Flow cytometric analyses of the expression of P-gp on peripheral blood lymphocytes from 20 normal volunteers and 80 SLE patients were performed. Steroid-exclusion analysis of peripheral blood mononuclear cells (PBMCs) was conducted by using radioisotope-labeled dexamethasone.

RESULTS

P-gp was expressed at significantly high levels on most of the peripheral blood lymphocytes from SLE patients, whereas normal lymphocytes had only marginal expression. The quantity of P-gp on SLE lymphocytes correlated with the disease activity in each patient, as estimated by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). Furthermore, in SLE patients whose SLEDAI scores were >12 despite taking >0.5 mg/kg/day of prednisolone, P-gp expression on lymphocytes was markedly increased, and intracellular dexamethasone in their PBMCs was significantly decreased. However, intensive immunosuppressive treatment in these SLE patients resulted in successful control of disease activity, which occurred in parallel with a marked reduction of P-gp on lymphocytes.

CONCLUSION

The overexpression of P-gp on lymphocytes might lead to exclusion of corticosteroids from lymphocytes, resulting in steroid resistance in patients with highly active SLE. Reduction of P-gp expression achieved by intensive immunosuppressive treatment overcame the steroid resistance. We therefore propose that measurement of P-gp expression on lymphocytes is useful in the assessment of steroid resistance and is a good marker for indicating the need for intensive immunosuppressive treatment in patients with highly active SLE.