Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters.

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D3 or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for ß-amyloid peptide efflux and influx, the sodium phosphate transporters (NaPi), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTß) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aß) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Host microbiota dictates the proinflammatory impact of LPS in the murine liver.

Gut microbiota can impact liver disease development via the gut-liver axis. Liver inflammation is a shared pathological event in various liver diseases and gut microbiota might influence this pathological process. In this study, we studied the influence of gut microbiota on the inflammatory response of the liver to lipopolysaccharide (LPS). The inflammatory response to LPS (1-10 µg/ml) of livers of specific-pathogen-free (SPF) or germ-free (GF) mice was evaluated ex vivo, using precision-cut liver slices (PCLS). LPS induced a more pronounced inflammatory response in GF PCLS than in SPF PCLS. Baseline TNF-α gene expression was significantly higher in GF slices as compared to SPF slices. LPS treatment induced TNF-α, IL-1ß, IL-6 and iNOS expression in both SPF and GF PCLS, but the increase was more intense in GF slices. The anti-inflammatory markers SOCS3 and IRAK-M gene expression was significantly higher in GF PCLS than SPF PCLS at 24h with 1 µg/ml LPS treatment, and IL-10 was not differently expressed in GF PCLS than SPF PCLS. In addition, TLR-4 mRNA, but not protein, at basal level was higher in GF slices than in SPF slices. Taken together, this study shows that, in mice, the host microbiota attenuates the pro-inflammatory impact of LPS in the liver, indicating a positive role of the gut microbiota on the immune homeostasis of the liver.

Targeted imaging of integrins in cancer tissues using photocleavable Ru(ii) polypyridine complexes as mass-tags.

Targeted epitope-based mass spectrometry imaging (MSI) utilizes laser cleavable mass-tags bound to targeting moieties for detecting proteins in tissue sections. Our work constitutes the first proof-of-concept of a novel laser desorption ionization (LDI)-MSI strategy using photocleavable Ru(ii) polypyridine complexes as mass-tags for imaging of integrins αvß3 in human cancer tissues.

Ex vivo toxicological evaluation of experimental anticancer gold(i) complexes with lansoprazole-type ligands.

Gold-based compounds are of great interest in the field of medicinal chemistry as novel therapeutic (anticancer) agents due to their peculiar reactivity and mechanisms of action with respect to organic drugs. Despite their promising pharmacological properties, the possible toxic effects of gold compounds need to be carefully evaluated in order to optimize their design and applicability. This study reports on the potential toxicity of three experimental gold-based anticancer compounds featuring lansoprazole ligands (1-3) studied in an ex vivo model, using rat precision cut kidney and liver slices (PCKS and PCLS, respectively). The results showed a different toxicity profile for the tested compounds, with the neutral complex 2 being the least toxic, even less toxic than cisplatin, followed by the cationic complex 1. The dinuclear cationic gold complex 3 was the most toxic in both liver and kidney slices. This result correlated with the metal uptake of the different compounds assessed by ICP-MS, where complex 3 showed the highest accumulation of gold in liver and kidney slices. Interestingly compound 1 showed the highest selectivity towards cancer cells compared to the healthy tissues. Histomorphology evaluation showed a similar pattern for all three Au(i) complexes, where the distal tubular cells suffered the most extensive damage, in contrast to the damage in the proximal tubules induced by cisplatin. The binding of representative gold compounds with the model ubiquitin was also studied by ESI-MS, showing that after 24 h incubation only 'naked' Au ions were bound to the protein following ligands' loss. The mRNA expression of stress response genes appeared to be similar for both evaluated organs, suggesting oxidative stress as the possible mechanism of toxicity. The obtained results open new perspectives towards the design and testing of bifunctional gold complexes with chemotherapeutic applications.

Bioconjugation of Supramolecular Metallacages to Integrin Ligands for Targeted Delivery of Cisplatin.

Cisplatin occupies a crucial role in the treatment of various malignant tumors. However, its efficacy and applicability are heavily restricted by severe systemic toxicities and drug resistance. Our study exploits the active targeting of supramolecular metallacages to enhance the activity of cisplatin in cancer cells while reducing its toxicity. Thus, Pd2L4 cages (L = ligand) have been conjugated to four integrin ligands with different binding affinity and selectivity. Cage formation and encapsulation of cisplatin was proven by NMR spectroscopy. Upon encapsulation, cisplatin showed increased cytotoxicity in vitro, in melanoma A375 cells overexpressing αvß3 integrins. Moreover, ex vivo studies in tissue slices indicated reduced toxicity toward healthy liver and kidney tissues for cage-encapsulated cisplatin. Analysis of metal content by ICP-MS demonstrated that the encapsulated drug is less accumulated in these organs compared to the "free" cisplatin.

Targeting Oxidative Stress for the Treatment of Liver Fibrosis.

Oxidative stress is a reflection of the imbalance between the production of reactive oxygen species (ROS) and the scavenging capacity of the antioxidant system. Excessive ROS, generated from various endogenous oxidative biochemical enzymes, interferes with the normal function of liver-specific cells and presumably plays a role in the pathogenesis of liver fibrosis. Once exposed to harmful stimuli, Kupffer cells (KC) are the main effectors responsible for the generation of ROS, which consequently affect hepatic stellate cells (HSC) and hepatocytes. ROS-activated HSC undergo a phenotypic switch and deposit an excessive amount of extracellular matrix that alters the normal liver architecture and negatively affects liver function. Additionally, ROS stimulate necrosis and apoptosis of hepatocytes, which causes liver injury and leads to the progression of end-stage liver disease. In this review, we overview the role of ROS in liver fibrosis and discuss the promising therapeutic interventions related to oxidative stress. Most importantly, novel drugs that directly target the molecular pathways responsible for ROS generation, namely, mitochondrial dysfunction inhibitors, endoplasmic reticulum stress inhibitors, NADPH oxidase (NOX) inhibitors, and Toll-like receptor (TLR)-affecting agents, are reviewed in detail. In addition, challenges for targeting oxidative stress in the management of liver fibrosis are discussed.

Development of a mechanistic biokinetic model for hepatic bile acid handling to predict possible cholestatic effects of drugs.

Drug-induced liver injury (DILI) is a common reason for drug withdrawal from the market. An important cause of DILI is drug-induced cholestasis. One of the major players involved in drug-induced cholestasis is the bile salt efflux pump (BSEP; ABCB11). Inhibition of BSEP by drugs potentially leads to cholestasis due to increased (toxic) intrahepatic concentrations of bile acids with subsequent cell injury. In order to investigate the possibilities for in silico prediction of cholestatic effects of drugs, we developed a mechanistic biokinetic model for human liver bile acid handling populated with human in vitro data. For this purpose we considered nine groups of bile acids in the human bile acid pool, i.e. chenodeoxycholic acid, deoxycholic acid, the remaining unconjugated bile acids and the glycine and taurine conjugates of each of the three groups. Michaelis-Menten kinetics of the human uptake transporter Na+-taurocholate cotransporting polypeptide (NTCP; SLC10A1) and BSEP were measured using NTCP-transduced HEK293 cells and membrane vesicles from BSEP-overexpressing HEK293 cells. For in vitro-in vivo scaling, transporter abundance was determined by LC-MS/MS in these HEK293 cells and vesicles as well as in human liver tissue. Other relevant human kinetic parameters were collected from literature, such as portal bile acid levels and composition, bile acid synthesis and amidation rate. Additional empirical scaling was applied by increasing the excretion rate with a factor 2.4 to reach near physiological steady-state intracellular bile acid concentrations (80µM) after exposure to portal vein bile acid levels. Simulations showed that intracellular bile acid concentrations increase 1.7 fold in the presence of the BSEP inhibitors and cholestatic drugs cyclosporin A or glibenclamide, at intrahepatic concentrations of 6.6 and 20µM, respectively. This simplified model provides a tool for a first indication whether drugs at therapeutic concentrations might cause cholestasis by inhibiting BSEP.

Cleavable Crosslinkers as Tissue Fixation Reagents for Proteomic Analysis.

Formaldehyde fixation is widely used for long-term maintenance of tissue. However, due to formaldehyde-induced crosslinks, fixed tissue proteins are difficult to extract, which hampers mass spectrometry (MS) proteomic analyses. Recent years have seen the use of different combinations of high temperature and solubilizing agents (usually derived from antigen retrieval techniques) to unravel formaldehyde-fixed paraffin-embedded tissue proteomes. However, to achieve protein extraction yields similar to those of fresh-frozen tissue, high-temperature heating is necessary. Such harsh extraction conditions can affect sensitive amino acids and post-translational modifications, resulting in the loss of important information, while still not resulting in protein yields comparable to those of fresh-frozen tissue. Herein, the objective is to evaluate cleavable protein crosslinkers as fixatives that allow tissue preservation and efficient protein extraction from fixed tissue for MS proteomics under mild conditions. With this goal in mind, disuccinimidyl tartrate (DST) and dithiobis(succinimidylpropionate) (DSP) are investigated as cleavable fixating reagents. These compounds crosslink proteins by reacting with amino groups, leading to amide bond formation, and can be cleaved with sodium metaperiodate (cis-diols, DST) or reducing agents (disulfide bonds, DSP), respectively. Results show that cleavable protein crosslinking with DST and DSP allows tissue fixation with morphology preservation comparable to that of formaldehyde. In addition, cleavage of DSP improves protein recovery from fixed tissue by a factor of 18 and increases the number of identified proteins by approximately 20 % under mild extraction conditions compared with those of formaldehyde-fixed paraffin-embedded tissue. A major advantage of DSP is the introduction of well-defined protein modifications that can be taken into account during database searching. In contrast to DSP fixation, DST fixation followed by cleavage with sodium metaperiodate, although effective, results in side reactions that prevent effective protein extraction and interfere with protein identification. Protein crosslinkers that can be cleaved under mild conditions and result in defined modifications, such as DSP, are thus viable alternatives to formaldehyde as tissue fixatives to facilitate protein analysis from paraffin-embedded, fixed tissue.

Challenges on the road to a multicellular bioartificial liver.

Over recent years, the progress in the development of a bioartificial liver (BAL) as an extracorporeal device or as a tissue engineered transplantable organ has been immense. However, many important BAL characteristics that are necessary to meet clinical demands have not been sufficiently addressed. This review describes the existing challenges in the development of a BAL for clinical applications, highlighting multicellularity and sinusoidal microarchitecture as crucial BAL characteristics to fulfil various liver functions. Currently available sources of nonparenchymal liver cells, such as endothelial cells, cholangiocytes and macrophages, used in BAL development are defined. Also, we discuss the recent studies on the reconstruction of the complex liver sinusoid microarchitecture using various liver cell types. Moreover, we highlight some other aspects of a BAL, such as liver zonation and formation of a vascular as well as biliary network for an adequate delivery, biotransformation and removal of substrates and waste products. Finally, the benefits of a multicellular BAL for the pharmaceutical industry are briefly described. Copyright © 2016 John Wiley & Sons, Ltd.

Alterations in gene expression in vitamin D-deficiency: Down-regulation of liver Cyp7a1 and renal Oat3 in mice.

The vitamin D-deficient model, established in the C57BL/6 mouse after 8 weeks of feeding vitamin D-deficient diets in the absence or presence of added calcium, was found associated with elevated levels of plasma parathyroid hormone (PTH) and plasma and liver cholesterol, and a reduction in cholesterol 7α-hydroxylase (Cyp7a1, rate-limiting enzyme for cholesterol metabolism) and renal Oat3 mRNA/protein expression levels. However, there was no change in plasma calcium and phosphate levels. Appraisal of the liver revealed an up-regulation of mRNA expressions of the small heterodimer partner (Shp) and attenuation of Cyp7a1, which contributed to hypercholesterolemia in vitamin D-deficiency. When vitamin D-sufficient or D-deficient mice were further rendered hypercholesterolemic with 3 weeks of feeding the respective, high fat/high cholesterol (HF/HC) diets, treatment with 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ], active vitamin D receptor (VDR) ligand, or vitamin D (cholecalciferol) to HF/HC vitamin D-deficient mice lowered the cholesterol back to baseline levels. Cholecalciferol treatment partially restored renal Oat3 mRNA/protein expression back to that of vitamin D-sufficient mice. When the protein expression of protein kinase C (PKC), a known, negative regulator of Oat3, was examined in murine kidney, no difference in PKC expression was observed for any of the diets with/without 1,25(OH)2 D3 /cholecalciferol treatment, inferring that VDR regulation of renal Oat3 did not involve PKC in mice. As expected, plasma calcium levels were not elevated by cholecalciferol treatment of vitamin D-deficient mice, while 1,25(OH)2 D3 treatment led to hypercalcemia. In conclusion, vitamin D-deficiency resulted in down-regulation of liver Cyp7a1 and renal Oat3, conditions that are alleviated upon replenishment of cholecalciferol.

On the toxicity and transport mechanisms of cisplatin in kidney tissues in comparison to a gold-based cytotoxic agent.

Mechanisms of toxicity and cellular transport of anticancer metallodrugs, including platinum-based agents, have not yet been fully elucidated. Here, we studied the toxic effects and accumulation mechanisms of cisplatin in healthy rat kidneys ex vivo, using the Precision Cut Tissue Slices (PCTS) method. In addition, for the first time, we investigated the nephrotoxic effects of an experimental anticancer cyclometallated complex [Au(pyb-H)(PTA)Cl]PF6 (PTA = 1,3,5-triazaphosphaadamantane). The viability of the kidney slices after metallodrug treatment was evaluated by ATP content determination and histomorphology analysis. A concentration dependent decrease in viability of PCKS was observed after exposure to cisplatin or the Au(iii) complex, which correlated with the increase in slice content of Pt and Au, respectively. Metal accumulation in kidney slices was analysed by ICP-MS. The involvement of OCTs and MATE transporters in the accumulation of both metal compounds in kidneys was evaluated co-incubating the tissues with cimitedine, inhibitor of OCT and MATE. Studies of mRNA expression of the markers KIM-1, villin, p53 and Bax showed that cisplatin damages proximal tubules, whereas the Au(iii) complex preferentially affects the distal tubules. However, no effect of cimetidine on the toxicity or accumulation of cisplatin and the Au(iii) complex was observed. The effect of temperature on metallodrug accumulation in kidneys suggests the involvement of a carrier-mediated uptake process, other than OCT2, for cisplatin; while carrier-mediated excretion was suggested in the cases of the Au(iii) complex.

Anticancer Gold N-Heterocyclic Carbene Complexes: A Comparative in†vitro and ex†vivo Study.

A series of organometallic AuI N-heterocyclic carbene (NHC) complexes was synthesized and characterized for anticancer activity in four human cancer cell lines. The compounds' toxicity in healthy tissue was determined using precision-cut kidney slices (PCKS) as a tool to determine the potential selectivity of the gold complexes ex vivo. All evaluated compounds presented cytotoxic activity toward the cancer cells in the nano- or low micromolar range. The mixed AuI NHC complex, (tert-butylethynyl)-1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I), bearing an alkynyl moiety as ancillary ligand, showed high cytotoxicity in cancer cells in vitro, while being barely toxic in healthy rat kidney tissues. The obtained results open new perspectives toward the design of mixed NHC-alkynyl gold complexes for cancer therapy.

Rat precision-cut liver slices predict drug-induced cholestatic injury.

Drug-induced cholestasis (DIC) is one of the leading manifestations of drug-induced liver injury (DILI). As the underlying mechanisms for DIC are not fully known and specific and predictive biomarkers and pre-clinical models are lacking, the occurrence of DIC is often only reported when the drug has been approved for registration. Therefore, appropriate models that predict the cholestatic potential of drug candidates and/or provide insight into the mechanism of DIC are highly needed. We investigated the application of rat precision-cut liver slices (PCLS) to predict DIC, using several biomarkers of cholestasis: hepatocyte viability, intracellular accumulation of total as well as individual bile acids and changes in the expression of genes known to play a role in cholestasis. Rat PCLS exposed to the cholestatic drugs chlorpromazine, cyclosporine A and glibenclamide for 48 h in the presence of a 60 µM physiological bile acid (BA) mix reflected various changes associated with cholestasis, such as decrease in hepatocyte viability, accumulation and changes in the composition of BA and changes in the gene expression of Fxr, Bsep and Ntcp. The toxicity of the drugs was correlated with the accumulation of BA, and especially DCA and CDCA and their conjugates, but to a different extent for different drugs, indicating that BA toxicity is not the only cause for the toxicity of cholestatic drugs. Moreover, our study supports the use of several biomarkers to test drugs for DIC. In conclusion, our results indicate that PCLS may represent a physiological and valuable model to identify cholestatic drugs and provide insight into the mechanisms underlying DIC.

Validation of precision-cut liver slices to study drug-induced cholestasis: a transcriptomics approach.

Hepatotoxicity is one of the major reasons for withdrawal of drugs from the market. Therefore, there is a need to screen new drugs for hepatotoxicity in humans at an earlier stage. The aim of this study was to validate human precision-cut liver slices (PCLS) as an ex vivo model to predict drug-induced cholestasis and identify the possible mechanisms of cholestasis-induced toxicity using gene expression profiles. Five hepatotoxicants, which are known to induce cholestasis (alpha-naphthyl isothiocyanate, chlorpromazine, cyclosporine, ethinyl estradiol and methyl testosterone) were used at concentrations inducing low (<30 %) and medium (30-50 %) toxicity, based on ATP content. Human PCLS were incubated with the drugs in the presence of a non-toxic concentration (60 µM) of a bile acid mixture (portal vein concentration and composition) as model for bile acid-induced cholestasis. Regulated genes include bile acid transporters and cholesterol transporters. Pathway analysis revealed that hepatic cholestasis was among the top ten regulated pathways, and signaling pathways such as farnesoid X receptor- and liver X receptor-mediated responses, which are known to play a role in cholestasis, were significantly affected by all cholestatic compounds. Other significantly affected pathways include unfolded protein response and protein ubiquitination implicating the role of endoplasmic reticulum stress. This study shows that human PCLS incubated in the presence of a physiological bile acid mixture correctly reflect the pathways affected in drug-induced cholestasis in the human liver. In the future, this human PCLS model can be used to identify cholestatic adverse drug reactions of new chemical entities.

The consequence of regional gradients of P-gp and CYP3A4 for drug-drug interactions by P-gp inhibitors and the P-gp/CYP3A4 interplay in the human intestine ex vivo.

Intestinal P-gp and CYP3A4 work coordinately to reduce the intracellular concentration of drugs, and drug-drug interactions (DDIs) based on this interplay are of clinical importance and require pre-clinical investigation. Using precision-cut intestinal slices (PCIS) of human jejunum, ileum and colon, we investigated the P-gp/CYP3A4 interplay and related DDIs with P-gp inhibitors at the different regions of the human intestine with quinidine (Qi), dual substrate of P-gp and CYP3A4, as probe. All the P-gp inhibitors increased the intracellular concentrations of Qi by 2.1-2.6 fold in jejunum, 2.6-3.8 fold in ileum but only 1.2-1.3 fold in colon, in line with the different P-gp expression in these intestinal regions. The selective P-gp inhibitors (CP100356 and PSC833) enhanced 3-hydroxy-quinidine (3OH-Qi) in jejunum and ileum, while dual inhibitors of P-gp and CYP3A4 (verapamil and ketoconazole) decreased the 3OH-Qi production, despite of the increased intracellular Qi concentration, due to inhibition of CYP3A4. The outcome of DDIs based on P-gp/CYP3A4 interplay, shown as remarkable changes in the intracellular concentration of both the parent drug and the metabolite, varied among the intestinal regions, probably due to the different expression of P-gp and CYP3A4, and were different from those found in rat PCIS, which may have important implications for the disposition and toxicity of drugs and their metabolites.

Maintenance of drug metabolism and transport functions in human precision-cut liver slices during prolonged incubation for 5 days.

Human precision-cut liver slices (hPCLS) are a valuable ex vivo model that can be used in acute toxicity studies. However, a rapid decline in metabolic enzyme activity limits their use in studies that require a prolonged xenobiotic exposure. The aim of the study was to extend the viability and function of hPCLS to 5 days of incubation. hPCLS were incubated in two media developed for long-term culture of hepatocytes, RegeneMed®, and Cellartis®, and in the standard medium WME. Maintenance of phase I and II metabolism was studied both on gene expression as well as functional level using a mixture of CYP isoform-specific substrates. Albumin synthesis, morphological integrity, and glycogen storage was assessed, and gene expression was studied by transcriptomic analysis using microarrays with a focus on genes involved in drug metabolism, transport and toxicity. The data show that hPCLS retain their viability and functionality during 5 days of incubation in Cellartis® medium. Albumin synthesis as well as the activity and gene expression of phase I and II metabolic enzymes did not decline during 120-h incubation in Cellartis® medium, with CYP2C9 activity as the only exception. Glycogen storage and morphological integrity were maintained. Moreover, gene expression changes in hPCLS during incubation were limited and mostly related to cytoskeleton remodeling, fibrosis, and moderate oxidative stress. The expression of genes involved in drug transport, which is an important factor in determining the intracellular xenobiotic exposure, was also unchanged. Therefore, we conclude that hPCLS cultured in Cellartis® medium are a valuable human ex vivo model for toxicological and pharmacological studies that require prolonged xenobiotic exposure.