Polymorphisms in human organic anion-transporting polypeptide 1A2 (OATP1A2): implications for altered drug disposition and central nervous system drug entry

Organic anion-transporting polypeptide 1A2 (OATP1A2) is a drug uptake transporter known for broad substrate specificity, including many drugs in clinical use. Therefore, genetic variation in SLCO1A2 may have important implications to the disposition and tissue penetration of substrate drugs. In the present study, we demonstrate OATP1A2 protein expression in human brain capillary and renal distal nephron using immunohistochemistry. We also determined the extent of single nucleotide polymorphisms in SLCO1A2 upon analyses of ethnically defined genomic DNA samples (n = 95 each for African-, Chinese-, European-, and Hispanic-Americans). We identified six nonsynonymous polymorphisms within the coding region of SLCO1A2 (T38C (I13T), A516C (E172D), G559A (A187T), A382T (N128Y), A404T (N135I), and C2003G (T668S)), the allelic frequencies of which appeared to be ethnicity-dependent. In vitro functional assessment revealed that the A516C and A404T variants had markedly reduced capacity for mediating the cellular uptake of OATP1A2 substrates, estrone 3-sulfate and two delta-opioid receptor agonists, deltorphin II, and [D-penicillamine(2,5)]-enkephalin. On the other hand, the G559A and C2003G variants appeared to have substrate-dependent changes in transport activity. Cell surface biotinylation and immunofluorescence confocal microscopy suggested that altered plasma membrane expression of the transporter may contribute to reduced transport activity associated with the A516C, A404T, and C2003G variants. The A404T (N135I) variant also showed a shift in the apparent molecular size, indicative of alterations in glycosylation status. Taken together, these data suggest that SLCO1A2 polymorphisms may be an important yet unrecognized contributor to inter-individual variability in drug disposition and central nervous system entry of substrate drugs.     

Monitoring the acetohydroxy acid synthase reaction and related carboligations by circular dichroism spectroscopy

Acetohydroxy acid synthase (AHAS) and related enzymes catalyze the production of chiral compounds [(S)-acetolactate, (S)-acetohydroxybutyrate, or (R)-phenylacetylcarbinol] from achiral substrates (pyruvate, 2-ketobutyrate, or benzaldehyde). The common methods for the determination of AHAS activity have shortcomings. The colorimetric method for detection of acyloins formed from the products is tedious and does not allow time-resolved measurements. The continuous assay for consumption of pyruvate based on its absorbance at 333 nm, though convenient, is limited by the extremely small extinction coefficient of pyruvate, which results in a low signal-to-noise ratio and sensitivity to interfering absorbing compounds. Here, we report the use of circular dichroism spectroscopy for monitoring AHAS activity. This method, which exploits the optical activity of reaction products, displays a high signal-to-noise ratio and is easy to perform both in time-resolved and in commercial modes. In addition to AHAS, we examined the determination of activity of glyoxylate carboligase. This enzyme catalyzes the condensation of two molecules of glyoxylate to chiral tartronic acid semialdehyde. The use of circular dichroism also identifies the product of glyoxylate carboligase as being in the (R) configuration.     

Specific transport of S-nitrosocysteine in human red blood cells: Implications for formation of S-nitrosothiols and transport of NO bioactivity within the vasculature

The transport of various S-nitrosothiols, NO and NO donors in human red blood cells (RBC) and the formation of erythrocytic S-nitrosoglutathione were investigated. Of the NO species tested only S-nitrosocysteine was found to form S-nitrosoglutathione in the RBC cytosol. L-Serine, L-cysteine and L-lysine inhibited formation of S-nitrosoglutathione. Incubation of RBC pre-incubated with S-[15N]nitroso-L-cysteine with native plasma or platelet-rich plasma led to formation of S-[15N]nitrosoalbumin and inhibited platelet aggregation, respectively. The specific transporter system of S-nitroso-L-cysteine in the RBC membrane may have implications for formation of S-nitrosoalbumin and S-nitrosohemoglobin and for transport of NO bioactivity within the vasculature.     

Mannose 6-phosphate receptors, Niemann-Pick C2 protein, and lysosomal cholesterol accumulation

Niemann-Pick disease type C (NPC), caused by mutations in the NPC1 gene or the NPC2 gene, is characterized by the accumulation of unesterified cholesterol and other lipids in endo/lysosomal compartments. NPC2 is a small, soluble, lysosomal protein that is targeted to this compartment via a mannose 6-phosphate-inhibitable pathway. To obtain insight into the roles of mannose 6-phosphate receptors (MPRs) in NPC2 targeting, we here examine the trafficking and function of NPC2 in fibroblast lines deficient in one or both of the two MPRs, MPR46 and MPR300. We demonstrate that either MPR alone is sufficient to transport NPC2 to the endo/lysosomal compartment, although MPR300 seems to be more efficient than MPR46. In the absence of both MPRs, NPC2 is secreted into the culture medium, and only a small amount of intracellular NPC2 can be detected, mainly in the endoplasmic reticulum. This leads to massive accumulation of unesterified cholesterol in the endo/lysosomal compartment of the MPR46/300-deficient fibroblasts, a phenotype similar to that of the NPC patient fibroblasts. In addition, we observed an upregulation of NPC1 protein and mRNA in the MPR-double-deficient cells. Taken together, our results suggest that the lysosomal targeting of NPC2 is strictly dependent on MPRs in fibroblasts.     

A novel convenient procedure for extractive work-up of whole-cell biotransformations using de-emulsifying hydrolases

Extractive work-up of whole-cell biotransformations generally suffers from the formation of stable gels and slimes upon addition of the organic solvent to the cell suspension and the cell-free solution, respectively. This problem has been overcome by enzymatic lysis of emulsifying agents present in the medium through addition of hydrolases. Of these agents, proteases have exhibited the most powerful de-emulsifying activity. Enzyme treatment of cell-free culture media of Saccharomyces cerevisiae with pronase E drastically reduced phase separation time (t(p)) from 1 week to 30 min without significantly affecting product integrity. Yeast cell suspensions were de-emulsified best with protease N-01, where phase separation was complete after 1 h. As was exemplified with cell-free culture media of Lactobacillus kefir, wherein addition of pronase E or protease N-01 reduced t(p) from 1 week to 2 h each, this practical, ready-to-use method is appropriate for both fungal and bacterial biocatalysts.     

Nongenomic inhibition of oxytocin binding by progesterone in the ovine uterus

Progesterone (P4) has been reported to inhibit oxytocin (OT) binding to its receptor in isolated murine endometrial membranes. The purpose of the present research was to 1). examine the in vivo and in vitro effect of P4 on the binding of OT to its receptor in the ovine endometrium and 2). determine whether the endometrial plasma membranes have high-affinity binding sites for P4. Ovariectomized ewes were pretreated with a sequence of estradiol-17beta (2 days) and P4 (5 days) before being treated with estradiol-17beta plus either vehicle (corn oil), P4, or P4 + mifepristone (RU 486) for 3 consecutive days. Treatment of ewes with 10 mg P4/day for 3 days suppressed binding of OT (P < 0.01) compared with that of controls, whereas concomitant treatment with the progestin antagonist RU 486 (10 mg/day) blocked the effect of P4. Similarly, incubation of endometrial plasma membranes with P4 (5 ng/ml) inhibited binding of OT (P < 0.05), whereas this effect of P4 was blocked by the presence of RU 486 (10 ng/ml). By radioreceptor assay, the endometrial plasma membranes were found to contain a high-affinity binding site for P4 and the progestin agonist promegestone (Kd 1.2 x 10-9 and 1.74 x 10-10M, respectively). Incubation of endometrial plasma membranes with P4 (5 ng/ml) significantly increased the concentration of progestin binding sites. Binding of labeled promegestone (R 5020) was competitively inhibited by excess unlabeled R 5020, P4, RU 486, and OT but not by estradiol-17beta, cortisol, testosterone, and arginine vasopressin. These data suggest a direct suppressive action of P4 on the binding of OT to OT receptors in the ovine endometrial plasma membrane.     

SOCS-1 and SOCS-3 inhibit IFN-alpha-induced expression of the antiviral proteins 2,5-OAS and MxA

Although the use of IFN-alpha in combination with ribavirin has improved the treatment efficacy of chronic hepatitis C virus (HCV) infection, 20-50% of patients still fail to eradicate the virus depending on the HCV genotype. Recently, overexpression of HCV core protein has been shown to inhibit IFN signaling and induce SOCS-3 expression. Aim of this study was to examine the putative role of SOCS proteins in IFN resistance. By Western blot analysis, a 4-fold induction of STAT-1/3 phosphorylation by IFN-alpha was observed in mock-transfected HepG2 clones. In contrast, IFN-induced STAT-1/3 phosphorylation was considerably downregulated by SOCS-1/3 overexpression. In mock-transfected cells, IFN-alpha induced 2',5'-OAS and myxovirus resistance A (MxA) promoter activity 40- to 80-fold and 10- to 35-fold, respectively, and this effect was abrogated in SOCS-1/3 overexpressing cells. As detected by Northern blot technique, IFN-alpha potently induced 2',5'-OAS and MxA mRNA expression in the control clones. Overexpression of SOCS-1 completely abolished both 2',5'-OAS and MxA mRNA expression, whereas SOCS-3 mainly inhibited 2',5'-OAS mRNA expression. Our results demonstrate that SOCS-1 and SOCS-3 proteins inhibit IFN-alpha-induced activation of the Jak-STAT pathway and expression of the antiviral proteins 2',5'-OAS and MxA. These data suggest a potential role of SOCS proteins in IFN resistance during antiviral treatment.     

Rac1 and Toll-IL-1 receptor domain-containing adapter protein mediate Toll-like receptor 4 induction of HIV-long terminal repeat

Opportunistic infections, common in HIV-1-infected patients, increase HIV replication; however, the intracellular signaling mechanisms involved are not clearly known. We have shown that Toll-like receptor 2 (TLR2), TLR4, and TLR9 mediate microbial Ag-induced HIV-long terminal repeat (HIV-LTR) trans-activation and HIV-1 replication, and that LPS-induced HIV-LTR trans-activation is mediated through myeloid differentiation adapter protein. Recently, Toll-IL-1R domain-containing adapter protein (TIRAP) has been identified as an adapter molecule that mediates responses to TLR2 and TLR4 ligands, and TIRAP was suggested to provide signaling specificity for different TLRs. Rac1, a small GTP-binding protein that is activated upon LPS stimulation of macrophages, activates phosphatidylinositol 3-kinase and Akt and leads to NF-kappaB activation. The roles of Rac1 and TIRAP in LPS activation of HIV replication is not known. In the present study we show that LPS stimulation of human microvessel endothelial cells leads to Rac1 activation. Constitutively active Rac1 (Rac1V12) simulated the effect of LPS to activate HIV-LTR, whereas the expression of dominant negative Rac1 (Rac1N17) partially blocked LPS-induced HIV-LTR trans-activation. Rac1V12-induced HIV-LTR activation was independent of myeloid differentiation adapter protein, and dominant negative TIRAP blocked Rac1V12-induced HIV-LTR trans-activation. In this study we show for the first time that activation of Rac1 leads to HIV-LTR trans-activation, and this is mediated through TIRAP. Together these results underscore the importance of Rac1 and TIRAP in TLR4 activation of HIV replication and help delineate the signaling pathways induced by TLRs to mediate microbial Ag-induced HIV replication and HIV pathogenesis.