Katrin Wlcek

Organic anion transporting polypeptides (OATPs): regulation of expression and function.

Eleven members of the human organic anion transporter (OATP) family (grouped into six families) facilitate the Na(+)- independent transmembrane transport of various endo- and xenobiotics (bile acids, bilirubin, steroid hormone conjugates, thyroid hormones, prostaglandins, clinically used drugs, and toxins). OATPs are 12-transmembrane glycoproteins (643-722 amino acids) and contain many conserved structural features, for example, eleven cysteines in the large extracellular loop 5. They are important for proper transport, for which translocation of substrates through a central, positively-charged pore in a rocker-switch-type mechanism has been proposed. Although OATPs are expressed in various cells and tissues, some members show a more restricted pattern (well-studied OATP1B1/OATP1B3 in liver, OATP4C1 in kidney, and OATP6A1 in testis). In cancer, the distribution pattern is no longer maintained, and OATPs, like OATP1B3, become upregulated in malignant tissues (colon, breast, prostate). Studies in cell lines and animal models further revealed that the expression of OATPs is regulated in a cell- and tissue-specific way by cytokines and activation of nuclear receptors (LXR, FXR, PXR, CAR, HNF4). Also epigenetic mechanisms and postranslational modifications influence their expression and function. Therefore, changes in the expression of OATPs under pathological conditions will influence transport processes causing an altered accumulation of OATP substrates in cells of excretory organs (intestine, liver, kidney) and on various blood/organ barriers (such as brain, testis, placenta). For drugs, this may result in increased toxicity and adverse drug reactions. Therefore, it is important to improve the knowledge on the regulation and function of individual OATPs, and to apply it for therapeutic considerations.

Tumor-specific expression of organic anion-transporting polypeptides: transporters as novel targets for cancer therapy.

Members of the organic anion transporter family (OATP) mediate the transmembrane uptake of clinical important drugs and hormones thereby affecting drug disposition and tissue penetration. Particularly OATP subfamily 1 is known to mediate the cellular uptake of anticancer drugs (e.g., methotrexate, derivatives of taxol and camptothecin, flavopiridol, and imatinib). Tissue-specific expression was shown for OATP1B1/OATP1B3 in liver, OATP4C1 in kidney, and OATP6A1 in testis, while other OATPs, for example, OATP4A1, are expressed in multiple cells and organs. Many different tumor entities show an altered expression of OATPs. OATP1B1/OATP1B3 are downregulated in liver tumors, but highly expressed in cancers in the gastrointestinal tract, breast, prostate, and lung. Similarly, testis-specific OATP6A1 is expressed in cancers in the lung, brain, and bladder. Due to their presence in various cancer tissues and their limited expression in normal tissues, OATP1B1, OATP1B3, and OATP6A1 could be a target for tumor immunotherapy. Otherwise, high levels of ubiquitous expressed OATP4A1 are found in colorectal cancers and their metastases. Therefore, this OATP might serve as biomarkers for these tumors. Expression of OATP is regulated by nuclear receptors, inflammatory cytokines, tissue factors, and also posttranslational modifications of the proteins. Through these processes, the distribution of the transporter in the tissue will be altered, and a shift from the plasma membrane to cytoplasmic compartments is possible. It will modify OATP uptake properties and, subsequently, change intracellular concentrations of drugs, hormones, and various other OATP substrates. Therefore, screening tumors for OATP expression before therapy should lead to an OATP-targeted therapy with higher efficacy and decreased side effects.

Altered expression of organic anion transporter polypeptide (OATP) genes in human breast carcinoma

Organic anion transporter polypeptides (OATPs) mediate the transmembrane uptake of endogenous compounds and clinically important drugs in various tissues thereby effecting drug disposition and tissue penetration. OATPs have also been identified in gastric, pancreatic, and colon carcinomas but little is known about their expression in breast carcinoma. We therefore analyzed the expression pattern of all 11 known OATPs in three breast cancer cell lines (MCF-7, ZR-75-1, MDA-MB-231) and one immortalized breast epithelial cell line (MCF-10A) using quantitative real-time RT-PCR. Transcripts of 7/11 OATP genes with heterogeneity in their expression profile were detected in control and/or cancer cell lines. Of these seven OATPs, five were also expressed in breast tumor and adjacent non-tumorous specimens from 13 patients. OATP2B1, not found in the analyzed cell lines, was verified in the tissue samples. Interestingly, mRNA expression of OATP2B1, OPATP3A1, and OATP4A1 was significantly higher (p

The analysis of organic anion transporting polypeptide (OATP) mRNA and protein patterns in primary and metastatic liver cancer.

Organic anion transporting polypeptides (OATP, SLCO genes) mediate the uptake of endobiotics and drugs. Thus, their expression levels and pattern could be of relevance for cancer therapy. This prompted us to investigate the expression of poorly characterized OATPs, namely OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in hepatic cancer of different origin. First, mRNA levels of all eleven OATPs were determined in paired (cancerous and adjacent non-cancerous) specimens from 43 patients with primary liver cancer (hepatocellular carcinoma, HCC; cholangiocellular carcinoma, CCC) and liver metastases from colon tumors (MLT). Real-time RT-PCR analysis revealed that all OATPs, except OATP1C1 and OATP6A1, are extensively expressed in nearly all samples. In contrast to downregulated OATP1B1, OATP1B3, OATP1A2 and OATP2B1 in cancerous vs. non-cancerous samples, an increase in OATP2A1, OATP3A1, OATP4A1 and OATP5A1 mRNA levels was seen in tumors (up to 40-fold for OATP5A1 in the MLT group). Therefore, OATP2A1, OATP3A1, OATP4A1 and OATP5A1 were further investigated by immunofluorescence microscopy on paraffin-embedded cancerous and non-cancerous sections (seven per group). OATP-derived immunoreactivity was observed in plasma membranes and cytosol of hepatic tumor cells, and additionally, in various cytokeratin 19 positive bile ducts. An increased percentage of immunoreactive cells and a higher staining intensity in cancerous vs. non-cancerous paraffin sections paralleled higher mRNA levels of OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in cancerous tissues of HCC, CCC and MLT patients. The extensive expression of OATP2A1, OATP3A1, OATP4A1 and OATP5A1 in hepatic tumors of different origin suggests that these transporters might be further exploited for the discovery of novel anticancer agents.

Antifungal Activity of Eugenol and Various Eugenol-Containing Essential Oils against 38 Clinical Isolates of Candida albicans

Abstract The antifungal activity of eugenol containing essential oils - pimento oil (Pimenta dioica (L.) Merr), bay oil (Pimenta racemosa (Mill.) J. W. Moore), clove oil (Szygium aromaticum (L.) Merr. & M. Perry), and cinnamon oil (Cinnamomum zeylanicum Blume) was investigated against 38 clinical isolates of Candida albicans (12 oropharyngeal, 16 vaginal and 10 skin damaging strains). The strains isolated from skin infections were more susceptible to all of the investigated essential oils whereas the oropharyngeal strains were more resistible. The strongest antifungal activity against clinical isolates of oropharyngeal, vagina and skin strains of Candida albicans possesses clove oil, followed by cinnamon oil, pimento oil and bay oil. Anticandidial action of the investigated oils is significantly due to its major component eugenol, but also minor constituents of the essential oils, such as methyleugenol, chavicol and linalool, must have additional and/or synergistic effects to explain the obtained anticandidal data of each essential oil sample.

Hepatocellular Organic Anion–Transporting Polypeptides (OATPs) and Multidrug Resistance–Associated Protein 2 (MRP2) Are Inhibited by Silibinin

Silibinin has been reported to be a promising compound for hepatitis C treatment of nonresponders to standard treatment. Although administered silibinin is well tolerated, increased serum bilirubin levels have been observed during high-dose i.v. silibinin therapy. The mechanism of silibinin-induced hyperbilirubinemia in humans, however, has not been identified so far. The aim of this study was to investigate the effect of silibinin on hepatocellular uptake and efflux transport systems for organic anions to elucidate the cause of silibinin-induced hyperbilirubinemia. Therefore, the effect of silibinin on transport activity of the hepatocellular uptake transporters organic anion–transporting polypeptides (OATPs) OATP1B1, OATP1B3, and OATP2B1, as well as Na+-taurocholate cotransporting polypeptide (NTCP) and of the efflux transporters multidrug resistance–associated protein 2 (MRP2) and bile-salt export pump (BSEP) was studied. The effect of silibinin on OATPs and NTCP function was studied in stable transfected Chinese hamster ovary cells using the radiolabeled model substrates estrone-3-sulfate and dehydroepiandrosteronesulfate for OATPs and taurocholate for NTCP. Interaction of silibinin with MRP2 and BSEP was measured in vesicles isolated from Sf21 or Sf9 insect cells expressing these transporters using either estradiol-17β-glucuronide or taurocholate as substrates. OATP1B1, OATP1B3, and OATP2B1 were inhibited by silibinin, with OATP1B1 being inhibited by (a) complex mechanism(s). An inhibitory effect was also seen for MRP2. In contrast, the bile acid transporters NTCP and BSEP were not affected by silibinin. We concluded that silibinin-induced hyperbilirubinemia may be caused by an inhibition of the bilirubin-transporting OATPs and the efflux-transporter MRP2.

Antifungal Activities of Essential Oils of Salvia lavandulifolia, Salvia officinalis and Salvia sclarea against Various Pathogenic Candida species

Abstract Antifungal activities of essential oils of Salvia lavandulifolia, Salvia officinalis and Salvia sclarea against various pathogenic Candida species were investigated. It was shown that antifungal activity of sage essential oils depends on their Chemical composition. The strongest anti-fungal activity possesses the essential oil of S. lavandulifolia, followed by essential oils of S. sclarea and S. officinalis. The Candida albicans strain responsible for oropharyngeal infections was found to be the most resistible, whereas C. albicans ATCC 10231 and C.albicans strains responsible for skin infections were assessed as the most susceptible ones.

ATP‐binding cassette transporters in liver

The human ATP‐binding cassette (ABC) superfamily consists of 48 members with 14 of them identified in normal human liver at the protein level. Most of the ABC members act as ATP dependent efflux transport systems. In the liver, ABC transporters are involved in diverse physiological processes including export of cholesterol, bile salts, and metabolic endproducts. Consequently, impaired ABC transporter function is involved in inherited diseases like sitosterolemia, hyperbilirubinemia, or cholestasis. Furthermore, altered expression of some of the hepatic ABCs have been associated with primary liver tumors. This review gives a short overview about the function of hepatic ABCs. Special focus is addressed on the localization and ontogenesis of ABC transporters in the human liver. In addition, their expression pattern in primary liver tumors is discussed.

Flagging Drugs That Inhibit the Bile Salt Export Pump

The bile salt export pump (BSEP) is an ABC-transporter expressed at the canalicular membrane of hepatocytes. Its physiological role is to expel bile salts into the canaliculi from where they drain into the bile duct. Inhibition of this transporter may lead to intrahepatic cholestasis. Predictive computational models of BSEP inhibition may allow for fast identification of potentially harmful compounds in large databases. This article presents a predictive in silico model based on physicochemical descriptors that is able to flag compounds as potential BSEP inhibitors. This model was built using a training set of 670 compounds with available BSEP inhibition potencies. It successfully predicted BSEP inhibition for two independent test sets and was in a further step used for a virtual screening experiment. After in vitro testing of selected candidates, a marketed drug, bromocriptin, was identified for the first time as BSEP inhibitor. This demonstrates the usefulness of the model to identify new BSEP inhibitors and therefore potential cholestasis perpetrators.

Transport of estradiol-17β-glucuronide, estrone-3-sulfate and taurocholate across the endoplasmic reticulum membrane: evidence for different transport systems

Graphical abstract