Within Our Skin.

From "beauty is only skin deep" to "it takes a thick skin," there are a countless number of skin-related aphorisms that serve as social commentaries on the beauty and resilience of skin. The skin as an interface to society may have diverse psychological implications, but its physiological importance to health is undeniable. As the largest organ in the body, the skin presents a formidable barrier that serves to protect our internal physiology from potentially harmful stimuli of the external environment.

The Bugs Within Our Body: The Human Microbiota.

The human microbiota is the ecological community of microorganisms that live within our bodies. Emerging evidence has revealed that dysregulation of the host-microbe symbiotic relationship contributes to the pathogenesis of a vast number of human diseases and impacts the efficacy and toxicity of therapeutic drugs. Therefore, a deeper understanding of the human microbiota is crucial to the development of therapeutic interventions that target the microbiota and also provides fundamental insights towards understanding intersubject variability in therapeutic outcomes.

Blood-brain barrier: an impediment to neuropharmaceuticals.

The blood-brain barrier (BBB) serves as a highly selective barrier separating the central nervous system from the systemic circulation. Although contributing to neurological health, the BBB restricts the ability of drugs to reach their site of action and thus presents a major challenge to the treatment of neurological disorders. Advances in our understanding of the complexity of the BBB have fostered development of novel pharmacometric models and drug delivery strategies to better predict and improve therapeutic access.

Inflammation: the dynamic force of health and disease.

Replacing "happiness" with "inflammation" in Thomas Merton's quotation holds true for the processes that govern our immune response and health. The balance between pro- and anti-inflammatory signals regulates inflammatory responses, leading to either restoration of health or the development and progression of disease, depending on whether it creates equilibrium or dysfunction. This issue of Clinical Pharmacology & Therapeutics highlights emerging research and concepts related to inflammation and its underlying role in chronic disease and variable drug response.

Network medicine: finding the links to personalized therapy.

Network medicine is a new approach that focuses on applying systems biology to pharmacology by "understanding the molecular system [and its perturbations] as a whole" so as to unravel the complex relationships among disease processes, genes, drugs, therapeutic indicators, and adverse effects.(1,2.)

Epigenetics: a new link toward understanding human disease and drug response.

Molecular medicine is moving beyond genomics to encompass the new scientific field of epigenetics. First described as a conceptual model of how genes might interact with their surroundings to produce a phenotype, epigenomic research currently investigates mechanisms of nongenetic modification contributing to gene regulation and examines the impact of these changes on human health and behavior.

Efficacy assessment of sustained intraperitoneal paclitaxel therapy in a murine model of ovarian cancer using bioluminescent imaging.

We evaluated the pre-clinical efficacy of a novel intraperitoneal (i.p.) sustained-release paclitaxel formulation (PTX(ePC)) using bioluminescent imaging (BLI) in the treatment of ovarian cancer. Human ovarian carcinoma cells stably expressing the firefly luciferase gene (SKOV3(Luc)) were injected i.p. into SCID mice. Tumour growth was evaluated during sustained or intermittent courses of i.p. treatment with paclitaxel (PTX). In vitro bioluminescence strongly correlated with cell survival and cytotoxicity. Bioluminescent imaging detected tumours before their macroscopic appearance and strongly correlated with tumour weight and survival. As compared with intermittent therapy with Taxol, sustained PTX(ePC) therapy resulted in significant reduction of tumour proliferation, weight and BLI signal intensity, enhanced apoptosis and increased survival times. Our results demonstrate that BLI is a useful tool in the pre-clinical evaluation of therapeutic interventions for ovarian cancer. Moreover, these results provide evidence of enhanced therapeutic efficacy with the sustained PTX(ePC) implant system, which could potentially translate into successful clinical outcomes.

Breast cancer resistance protein: mediating the trans-placental transfer of glyburide across the human placenta.

Members of the ATP-binding cassette (ABC) efflux transporter family, including P-glycoprotein (PGP), the multidrug resistance-associated proteins (MRPs) and the breast cancer resistance protein (BCRP) have been shown to be highly expressed in the human placenta. Recent studies documented that the oral hypoglycemic glyburide does not cross the human placenta to an appreciable extent. Furthermore, the trans-placental transfer of glyburide has been shown not to be affected by either the presence of PGP inhibitor, verapamil or MRP inhibitor, indomethacin. Therefore, our objective was to identify other human placental ABC transporters potentially involved in limiting the trans-placental transfer of glyburide to the fetus. [(3)H]-glyburide transport was examined in brush border human placental vesicles in the presence or absence of specific inhibitors. Prepared vesicles were 70% oriented right-side-out and demonstrated 25-27 fold enrichment as compared to whole placenta. Functional studies demonstrated significant increases in the intra-vesicular accumulation of [(3)H]-glyburide in vesicles treated with the BCRP inhibitor, novobiocin. In contrast, PGP inhibition as well as MRP inhibition did not affect [(3)H]-glyburide accumulation. This is the first evidence to clearly indicate that glyburide is preferentially transported by BCRP, in the brush border of the human placenta. Our study also indicates that BCRP likely effluxes substrates in the fetal to maternal direction in the human placenta.

Pharmacokinetic studies in pregnant women.

Prescription and over-the-counter drug use during pregnancy is necessary for many women today. A study of US and Canadian women found that, on average, 2.3 drugs were used during pregnancy; however, 28% reported using more than 4. For some women, this is because they become pregnant with preexisting conditions that require ongoing or intermittent pharmacotherapy. For others, this is because pregnancy itself can give rise to new medical conditions such as gestational diabetes and preeclampsia. The principal concern of prescribing physicians is whether or not agents will harm the fetus (i.e., have teratogenic effects). This concern rose to prominence primarily as a result of the thalidomide disaster. Marketed for use in morning sickness, thalidomide was found to be a potent teratogen capable of producing a variety of birth defects relating to development. Consequently, determining the teratogenicity of new drugs currently dominates the objectives of pregnancy-relevant experiments conducted throughout drug development. This often comes at the expense of valuable pharmacokinetic (PK) studies, which are seldom performed pre-market. Sex differences in PK parameters have been demonstrated in animals and humans since the 1930s. It is, therefore, not surprising that differences also arise in pregnancy. A wide array of physiological and hormonal changes occur during pregnancy; most begin early in the first trimester and increase linearly until parturition. Physicians lacking adequate PK information typically prescribe the standard adult dose in pregnancy, and this can be either inadequate or excessive depending on a variety of factors. The purpose of this report is to highlight this issue and illustrate how current methods used to obtain PK data in pregnancy are insufficient. The steps that are being taken to address this issue will also be discussed.

Hepatoprotective role of PXR activation and MRP3 in cholic acid-induced cholestasis.

BACKGROUND AND PURPOSE: Activation of the pregnane X receptor (PXR) has been shown to protect against cholestatic hepatotoxicity. As PXR alters the expression of numerous hepatic bile acid transporters, we sought to delineate their potential role in hepatoprotection. EXPERIMENTAL APPROACH: Wild-type (PXR+/+) and PXR-null (PXR-/-) mice were fed a 1% cholic acid (CA) diet with or without the PXR activator, PCN. Liver function was assessed along with the corresponding changes in hepatic gene expression. KEY RESULTS: CA administration caused significant hepatotoxicity in PXR+/+ mice and was associated with induction of several FXR and PXR regulated genes, which encode for bile acid transport and metabolizing proteins. Compared to CA alone, co-administration of PCN to CA-fed PXR+/+ mice significantly decreased hepatotoxicity and was associated with induction of MRP3 mRNA as well as CYP3A11 mRNA and functional activity. Unexpectedly, PXR-/- mice, which expressed significantly higher basal and CA-induced levels of MRP2, MRP3, OSTalpha, OSTbeta, OATP2 and CYP3A11, were dramatically less sensitive to CA hepatotoxicity than PXR+/+ mice. CONCLUSIONS: Protection of PXR+/+ mice against CA-induced hepatotoxicity by PCN is associated with the induction of MRP3 and CYP3A11 expression. Resistance against CA-induced hepatotoxicity in PXR-/- mice may result from higher basal and induced expression of bile acid transporters, particularly MRP3. These findings emphasize the importance of transport by MRP3 and metabolism as major protective pathways against cholestatic liver injury.

Transport of glyburide by placental ABC transporters: implications in fetal drug exposure.

Much evidence has demonstrated that a number of ATP-binding cassette (ABC) efflux transporters including P-glycoprotein (PGP), the multidrug resistance-associated proteins (MRPs) and the breast cancer resistance protein (BCRP) are highly expressed in placental tissues and are believed to profoundly limit the passage of therapeutic or toxic xenobiotics to the fetus. Recent studies indicate that the oral hypoglycemic glyburide does not cross the human placenta to an appreciable extent. Our objective was to identify placental transporters potentially involved in limiting the transplacental transfer of glyburide to the fetus. Thus, [(3)H]-glyburide transport was examined in BCRP, PGP, MRP1, MRP2 and MRP3 over-expressing cell lines in the presence or absence of specific inhibitors. Our results demonstrated significant increases in the intracellular accumulation of [(3)H]-glyburide in BCRP and MRP3 over-expressing cells in the presence of the inhibitors novobiocin and indomethacin, respectively. PGP inhibition with verapamil or MRP inhibition with indomethacin did not affect [(3)H]-glyburide accumulation in the PGP or MRP2 over-expressing cell lines and only limited changes were seen in the MRP1 over-expressing cell line. On the other hand, glyburide was found to significantly inhibit MRP1-, MRP2- and MRP3-mediated efflux of 5-carboxyfluorescein diacetate and PGP-mediated transport of rhodamine 123. Our evidence is the first to clearly indicate that glyburide is preferentially transported by BCRP and MRP3.

Hybrid films from blends of chitosan and egg phosphatidylcholine for localized delivery of paclitaxel.

Chitosan and egg phosphatidylcholine (ePC) were used as a unique combination to prepare composite films for localized drug delivery. In comparison to other phospholipids analyzed, ePC was found to produce chitosan-based films with minimal swelling and a high degree of stability. The properties of the chitosan-ePC films were characterized and found to be dependent on the ratio of chitosan:ePC present. FTIR analysis of chitosan-ePC films revealed that their high stability may be attributed to interactions present between these two biomaterials. In vitro evaluation of the cytotoxicity and protein adsorption properties of the films were used to provide a preliminary indication of their biocompatibility. The chitosan-ePC film was also evaluated as a matrix for the localized delivery of the anti-cancer agent, paclitaxel. Nanoparticles containing paclitaxel were dispersed throughout the chitosan-ePC film to result in a drug:material ratio of 1:8 (wt/wt). The film was found to provide a sustained release of paclitaxel over a 4-month period in biologically relevant media. The biological activity of paclitaxel loaded in the chitosan-ePC film was confirmed in SKOV-3 human ovarian cancer cells.

Suppression of drug-metabolizing enzymes and efflux transporters in the intestine of endotoxin-treated rats.

Infection and inflammation impose a suppression in the expression and activity of several drug transporters and drug-metabolizing enzymes in liver. In the intestine, cytochrome P450 3A (CYP3A), P-glycoprotein (PGP/mdr1), and the multidrug resistance-associated protein 2 (MRP2) are important barriers to the absorption of many clinically important drugs; thus, the expression and activity of these proteins were examined in inflammation. Transport and metabolism were determined in jejunum segments isolated at 24 h from endotoxin-treated or control rats (n = 8) mounted in Ussing chambers. Transport and metabolism of (3)H-digoxin, 5-carboxyfluorescein (5-CF), amiodarone (AM), and 7-benzyloxyquinoline (7-BQ) were measured for 90 min in the presence and absence of inhibitors. Reverse transcription-polymerase chain reaction was used to measure mRNA levels. As compared with controls, levels of mdr1a and mrp2 mRNA were significantly decreased by approximately 50% in the jejunum of LPS-treated rats. Corresponding reductions in the basolateral-->apical efflux of digoxin, AM, and 5-CF were observed, resulting in significant increases in the apical-->basolateral absorption of these compounds. Intestinal CYP3A mRNA levels and CYP3A-mediated metabolism of 7-BQ and AM were also decreased by approximately 50 to 70% (p < 0.05) in the LPS group. Mannitol permeability and lactate dehydrogenase release were not altered. These studies indicate that endotoxin-induced inflammation imposes a reduction in the intestinal expression and activity of PGP, mrp2, and CYP3A in rats, which elicits corresponding changes in the intestinal transport and metabolism of their substrates. Hence, infection and inflammatory diseases may impose variability in drug bioavailability through alterations in the intestinal expression and activity of drug transporters and metabolic enzymes.

Cellular uptake and metabolism of DNA frayed wires.

DNA frayed wires are a novel, multistranded form of DNA that arises from interactions between single-stranded oligodeoxyribonucleotides with the general sequence d(N(x)G(y)) or d(G(y)N(x)), where y > 10 and x > 5. Frayed wires exhibit greater stability with respect to thermal and chemical denaturation than single- or double-stranded DNA molecules and, thus, may have potential usefulness for DNA drug delivery. However, the stability and uptake of frayed wires have not been investigated in biological systems. Our objective was to examine the cellular uptake and stability of frayed wires in cultured hepatic cells. In these studies, the parent oligonucleotide d(A(15)G(15)) was used to form DNA frayed wires (DNA(FW)) while a random 30-mer oligonucleotide was used as the control nonaggregated DNA (DNA(SS)). Uptake and metabolism studies of DNA(FW) were performed in cultured human hepatoma, HepG2 cells and compared to DNA(SS). Our results indicate that DNA(FW) are not cytotoxic and that their intracellular uptake in HepG2 cells is 2-3.5-fold greater than that of DNA(SS) within the first 2 h (p < 0.05). Similarly, nuclear localization of DNA(FW) is 10-13-fold higher than that of DNA(SS) (p < 0.05). As both internalized and extracellular DNA(FW) appear to be more stable in vitro than DNA(SS), the enhanced uptake may be due to either increased stability or enhanced intracellular transport. These studies also indicate that uptake of DNA(FW) likely occurs via active processes such as receptor-mediated endocytosis similar to mechanisms which have been proposed for DNA(SS). The internalization pathways of DNA(FW) may differ somewhat from that of DNA(SS) insofar as chloroquine does not appear to alter DNA(FW) uptake and degradation, as is the case with DNA(SS).

Influence of IL-6 on MDR and MRP-mediated multidrug resistance in human hepatoma cells.

The objective of this study was to examine effects of interleukin-6 (IL-6) on the expression and activity of the drug resistance transporters (MDR1 and MRP) in human hepatoma cell lines. Expression and activity of MDR1 and MRP transporters were examined in IL-6-treated and control HuH 7 and HepG2 cells using semi-quantitative RT-PCR analysis and by rhodamine 123 and 5-carboxyfluorescin efflux assays. Results from RT-PCR demonstrated expression of MRP3, MRP6, and MDR1 in HuH 7 cells and expression of MRP1, MRP2, MRP3, MRP6, and MDR1 in HepG2 cells. Compared with controls, treatment of HuH 7 cells with IL-6 (10 ng/mL, 24 h) resulted in a 1.8-fold increase in MRP-mediated efflux of 5-CF with a corresponding 1.5-fold induction of MRP3 mRNA levels (p < 0.05). Similarly, in HepG2 cells, a 2-fold increase in MRP functional activity and a 1.8-fold induction of MRP1 mRNA levels were seen in the IL-6 treated cells (p < 0.05). Treatment of cells with IL-6 was also found to cause significant reductions in the expression and activity of MDR1 in HuH 7 cells, but not in HepG2 cells. Our data suggest that IL-6 induces MRP expression and activity in human hepatoma cell lines. Suppressive effects of IL-6 on MDR1 expression and activity were also observed in HuH 7 cells. This underscores the importance of examining the regulation of multiple drug resistance proteins as these proteins may have opposing regulatory mechanisms in malignant cells.