Expression and function of P-glycoprotein and absence of multidrug resistancerelated protein in rat and beige mouse peritoneal mast cells, Histochem

Summary To clarify the function of the multidrug transporter P-glycoprotein in mast cells we used the green fluorescent compound Bodipy-FL-verapamil, which is a substrate of P-glycoprotein. This compound is also transported by Multidrug Resistancerelated Protein (MRP), another membrane transport protein expressed in many tumour resistant cells as well as in normal cells. When rat peritoneal mast cells were incubated with Bodipy-verapamil, a rapid uptake of this compound was observed. Pretreatment with modulators of P-glycoprotein activity, such as verapamil and vinblastine, increased Bodipy-verapamil intracellular concentrations. In addition, Bodipy-verapamil efflux from these cells was rapid and also inhibited by verapamil and vinblastine. In contrast, no effect was observed when cells were treated with agents, such as probenecid and indomethacin, that are known inhibitors of MRP. Methylamine and monensin, substances that modify the pH values in the granules, were able to lower the concentrations of Bodipy-verapamil. Microscopical observations, conducted in both rat and beige mouse mast cells, demonstrated that the fluorochrome accumulated in the cytoplasmic secretory granules. RT-PCR performed on rat peritoneal mast cells revealed the presence of MDR1a and MDR1b mRNAs; on the contrary, MRP mRNA was not expressed. Mast cells were further treated with the fluorescent probe LysoSensor Blue, a weak base that becomes fluorescent when inside acidic organelles. This substance accumulated in mast cell granular structures and its fluorescence was reduced either by treatment with P-glycoprotein modulators or with agents that disrupt pH gradients. In conclusion, these data further confirm the presence of an active P-glycoprotein, but not of MRP, in rat peritoneal mast cells. These findings, coupled with previous ultrastructural data, lend further support to the assumption that this protein is located on the mast cell perigranular membrane. The functional role of P-glycoprotein in these cells is at present unclear, but a possible involvement in the transport of molecules from the granules to the cytosol can be hypothesized. Alternatively, this protein might be indirectly implicated in changes of pH values inside secretory granules

Bodipy-FL-verapamil: A fluorescent probe for the study of multidrug resistance proteins

Abstract. Most of the substances used as fluorescent probes to study drug transport and the effect of efflux blockers in multidrug resistant cells have many drawbacks, such as toxicity, unspecific background, accumulation in mitochondria. New fluorescent compounds, among which Bodipy-FL-verapamil (BV), have been therefore proposed as more useful tools. The uptake of BV has been evaluated by cytofluorimetry and fluorescence microscopy using cell lines that overexpress P-glycoprotein (P388/ADR and LLC-PK 1 /ADR) or MRP (multidrug resistance-related protein) (PANC-1) and clinical specimens from patients. The effect of specific inhibitors for P-glycoprotein (verapamil and vinblastine) or MRP (MK571 and probenecid) has been also studied. BV intracellular concentrations were significantly lower in the two P-glycoprotein overexpressing cell lines in comparison with the parental lines. In addition, verapamil and vinblastine increased the intracellular concentrations of the dye; MK571 and probenecid, two MRP inhibitors, increased BV levels in PANC-1 cells, that express this protein. These findings were confirmed in clinical specimens from patients. Fluorescence microscopy revealed a faint fluorescence emission in P-glycoprotein or MRP expressing cell lines; however, treatment with specific inhibitors significantly increased the fluorescence. BV is a useful tool for studying multidrug resistance proteins with different techniques such as cytofluorimetry and fluorescence microscopy, but does not discriminate between P-glycoprotein and MRP. In comparison with other classic fluorescent probes, the assay with this dye is extremely rapid, simple, not toxic for cells, devoid of fluorescent background, and can be useful in the clinical settings

Carbamazepine hypersensitivity syndrome triggered by a human herpes virus reactivation in a genetically predisposed patient

A case of severe hypersensitivity syndrome, triggered by carbamazepine in the presence of a concomitant active human herpes virus (HHV) 6 and 7 infection is described. To further understand the molecular mechanism of this adverse reaction, analyses of the genetic variants of human leukocyte antigen (HLA) and of the epoxide hydrolase gene (EPHX1), previously associated with carbamazepine hypersensitivity, were performed. A lymphocyte transformation test (LTT) was conducted in order to detect drug-specific lymphocytes. In the hypersensitive patient, 2 genetic factors previously associated with intolerance to carbamazepine were detected: the allele HLA-A*3101 and homozygosity for the variant allele of SNP rs1051740 in EPHX1. Drug-specific lymphocytes could be detected by LTT when the HHV was active (positive PCR for viral DNA and increased anti-HHV 6 IgG titer), but not when it was no longer active. In conclusion, we document a case of severe carbamazepine hypersensitivity triggered by viral reactivation in a patient presenting the interaction of 2 unfavorable genetic factor

Glutathione-S-transferase-P1 I105V polymorphism and response to antenatal betamethasone in the prevention of respiratory distress syndrome

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