Uptake and elimination of methylsiloxanes in hens after oral exposure: Implication for risk estimation

Methylsiloxanes are accumulated easily in aquatic organisms and may pose potential risks. However, available information on their uptake and accumulation in terrestrial species remains scarce. This study investigated the uptake, elimination and accumulation of eight typical methylsiloxanes in hens after a single oral exposure. At 1440 min after oral exposure, methylsiloxanes were mainly accumulated in kidney, liver and ovary, representing for 29.5 %, 20.4 % and 17.4 % of the summed methylsiloxanes in all tissues, respectively; all investigated chemicals were also detected in brains and unformed yolks. We found much higher mass uptake fractions (MUFs) of cyclic (27.5-66.5 %) than linear chemicals (9.9-17.3 %) by hens via this exposure, and the observed MUFs of individual cyclic congeners were comparable to the higher values of those reported for rats or fish previously. However, the metabolic half-life (t1/2) of these chemicals in hen tissues were in the range of 1.04-57.5 h based on kinetic analyses, indicating higher clearances in comparison with those reported for fish and rats. More research is needed on the metabolic mechanism of these chemicals in hens. Our findings provide important information for further understanding of transportation and transformation of these chemicals in terrestrial organisms and the associated potential risks.

Metabolic Pathway of Cyclosporine A and Its Correlation with Nephrotoxicity

Background:

Cyclosporine A (CsA) is widely used for organ transplantation and autoimmune disorders. However, CsA nephrotoxicity is a serious side effect that limits the clinical use of CsA. The metabolism of CsA has a close relationship with this disease in renal-transplant patients. However, the metabolic pathways of CsA and its metabolizing enzymes have rarely been comprehensively reviewed. In this review, we have summarized the specific metabolic profiles of CsA in humans, especially renal-transplant patients. Moreover, the specific metabolizing enzymes and the potential roles that CsA metabolism plays in CsA nephrotoxicity were summarized and discussed.

Methods:

Electronic databases including PubMed, Web of Science, and Scifinder were searched with the keywords "Cyclosporine A and metabolism", and "Cyclosporine A and nephrotoxicity", "Cyclosporine A metabolism and nephrotoxicity". All these studies published until 2018 were included in this review.

Results:

The major metabolic pathways of CsA in humans are hydroxylation and N-demethylation. Normally, these metabolites are relatively less toxic than CsA. However, the metabolism of CsA in the kidneys is much weaker than that in the liver, which explains why CsA is so toxic to the kidneys. CYP3A families, especially CYP3A4 and CYP3A5, play an important role in the biotransformation of CsA. Moreover, increased lines of evidence show that some metabolites (including AM19) associate directly with nephrotoxicity in CsA-treated organ-transplant patients.

Conclusion:

The findings of this review help to further understand the metabolic activities of CsA in renal-transplant patients and cast some light on the mechanisms of CsA nephrotoxicity.

Causes and Consequences of Variability in Drug Transporter Activity in Pediatric Drug Therapy

Drug transporters play a key role in mediating the uptake of endo- and exogenous substances into cells as well as their efflux. Therefore, variability in drug transporter activity can influence pharmaco- and toxicokinetics and be a determinant of drug safety and efficacy. In children, particularly in neonates and young infants, the contribution of tissue-specific drug transporters to drug absorption, distribution, and excretion may differ from that in adults. In this review 5 major factors and their interdependence that may influence drug transporter activity in children are discussed: developmental differences, genetic polymorphisms, pediatric comorbidities, interacting comedication, and environmental factors. Even if data are sparse, altered drug transporter activity due to those factors have been associated with clinically relevant differences in drug disposition, efficacy, and safety in pediatric patients. Single nucleotide polymorphisms in drug transporter-encoding genes were the most studied source of drug transporter variability in children. However, in the age group where drug transporter activity has been reported to differ from that in adults, namely neonates and young infants, hardly any studies have been performed. Longitudinal studies in this young population are required to investigate the age- and disease-dependent genotype-phenotype relationships and relevance of drug transporter drug-drug interactions. Physiologically based pharmacokinetic modeling approaches can integrate drug- and patient-specific parameters, including drug transporter ontogeny, and may further improve in silico predictions of pediatric-specific pharmacokinetics.

Pharmacokinetics, pharmacodynamics and pharmacogenetics associated with nonsteroidal anti-inflammatory drugs and opioids in pediatric cancer patients

INTRODUCTION

Advancing appropriate and adequate analgesic pharmacotherapy in pediatric patients with cancer is an area of clinical need. Few studies have been performed to evaluate the selection of an analgesic and appropriate dosing corresponding to analgesic effect among pediatric cancer patients. This review describes information related to pharmacokinetic, pharmacodynamic, and pharmacogenomic (when applicable) considerations for analgesics that are commonly used to manage pain experienced by pediatric patients with cancer. Areas covered: Analgesics commonly used to treat pediatric patients with malignancy patterned after the World Health Organization's 'analgesic ladder' for cancer pain management. Expert opinion: Addressing pain management safely and effectively in pediatric patients with cancer will require advances in both drug development, to increase the armament of analgesics available for children, and our pharmacologic understanding of those analgesics in current use. However, performing the necessary types of studies to develop new analgesics, or gain knowledge of existing therapy, within a population that is relatively small, diverse, and who experience pain originating from a variety of sources, is a tremendous challenge.

Tissue distribution, metabolism and hepatic tissue injury in Chinese lizards (Eremias argus) after a single oral administration of lambda-cyhalothrin

Lambda-cyhalothrin (LCT) is a widely used pyrethroid with neurotoxicity. However, little is known about the toxicokinetics of LCT in reptiles. In this study, the absorption, distribution, metabolism and excretion of LCT in Chinese lizards (Eremias Argus) were determined following a single dose (10 mg kg^-1) treatment. In the liver, brain, gonads and skin, LCT levels peaked within several hours and then decreased rapidly. However, the concentration of LCT gradually increased in the fat tissue. More than 90% of the LCT dose was excreted in the faeces. One LCT metabolite, 3-phenoxybenzoic acid (PBA), was detected in lizard plasma and tissues. PBA preferentially accumulates in the brain and plasma. The half-life of PBA in the brain was 3.2 days, which was 35.4-fold greater than that of LCT. In the plasma, the concentration of PBA was significantly higher than that of LCT. The bioaccumulation of LCT in tissues was enantioselective, and the enantiomeric fractions (EF) ranged from 0.72 to 0.26. The preferential accumulation of enantiomers changed according to exposure time, but the reasons behind this phenomenon were not clear. For pathological analysis, vacuolation of the cytoplasm and large areas of necrosis were observed in the liver sections after 168 h of dosing. The liver tissues exhibited both decreases in the hepatosomatic index and histopathological lesions during the exposure period. In this study, the effect concentration of LCT in lizards was 200-fold lower than its LD₅₀ value used in risk assessments for birds. These results may provide additional information for the risk assessment of LCT for reptiles and indicate that birds may not be an ideal surrogate for reptile toxicity evaluation.

[Molecular Biological Analysis of Factors Influencing Pharmacokinetics to Achieve Personalized Pharmacotherapy]

Large individual variations in drug efficacy and safety could be explained in part by pharmacokinetics regulated by drug transporters and drug-metabolizing enzymes. However, expression and/or function of these proteins often fluctuate in pathological conditions, causing individual pharmacokinetic variability. To achieve a personalized pharmacotherapy after liver transplantation, our group has been investigating the pharmacokinetics of drugs and factors causing its variation based on molecular biological analysis using rats with liver ischemia-reperfusion (I/R) injury as a model for injuries immediately after liver transplantation. The first finding is that the oral bioavailability of cyclosporine A (CsA), which is an immunosuppressant, was decreased by increased first-pass metabolism due to elevated CYP3A and P-glycoprotein (P-gp) specifically in the upper small intestine after liver I/R. Expression of CYP3A in the small intestine was also elevated through transcriptional regulation by endogenous bile acids, whereas expression and function of intestinal P-gp were increased by post-transcriptional regulation via microRNA-145. Next, the pharmacokinetics of a cationic drug, cimetidine, which is eliminated from the kidney, and the expressional variation of drug transporters in the kidney after liver I/R were examined. Liver I/R decreased tubular secretion of cimetidine, mainly because of decreased expression of rat organic cation transporter 2 in the kidney. These findings provide useful information on the etiology of liver I/R injury and appropriate use of immunosuppressants and drugs eliminated from the kidney after liver transplantation.

Effects of Pringle maneuver and partial hepatectomy on the pharmacokinetics and blood-brain barrier permeability of sodium fluorescein in rats

Liver diseases are known to affect the function of remote organs. The aim of the present study was to investigate the effects of Pringle maneuver, which results in hepatic ischemia-reperfusion (IR) injury, and partial hepatectomy (Hx) on the pharmacokinetics and brain distribution of sodium fluorescein (FL), which is a widely used marker of blood-brain barrier (BBB) permeability. Rats were subjected to Pringle maneuver (total hepatic ischemia) for 20 min with (HxIR) or without (IR) 70% hepatectomy. Sham-operated animals underwent laparotomy only. After 15 min or 8h of reperfusion, a single 25-mg/kg dose of FL was injected intravenously and serial (0-30 min) blood and bile and terminal brain samples were collected. Total and free (ultrafiltration) plasma, total brain homogenate, and bile concentrations of FL and/or its glucuronidated metabolite (FL-Glu) were determined by HPLC. Both IR and HxIR caused significant reductions in the biliary excretions of FL and FL-Glu, resulting in significant increases in the plasma AUC of the marker. Additionally, the free fraction of FL in plasma was significantly increased by HxIR. Although the brain concentrations of FL were increased by almost twofold in both IR and HxIR animals, the brain concentrations corrected by the free FL AUC (and not the total AUC) were similar in both groups at either time points. It is concluded that Pringle maneuver and/or partial hepatectomy substantially alters the hepatobiliary disposition, plasma AUC, plasma free fraction, and brain accumulation of FL without altering the BBB permeability to the marker.

[Effect of repeated oral treatment with etoposide on the expression of intestinal P-glycoprotein and oral morphine analgesia]

Currently, the World Health Organization recommends oral administration of opioid analgesics for patients with cancer to treat cancer-related pain from the initial stage of treatment. Furthermore, many anticancer drugs have been newly-developed and approved as oral form. Because of this trend, the chances of drug-drug interactions between anticancer drugs and opioid analgesics during absorption process from the intestine are likely to increase. To investigate these possible drug-drug interactions, we have focused on intestinal P-glycoprotein (P-gp) which regulates the absorption of various substrate drugs administered orally. Previously, we have found that repeated oral treatment with etoposide (ETP), an anticancer drug, attenuates analgesia of oral morphine, a substrate drug for P-gp, by increasing the expression and activity of intestinal P-gp. However, the mechanism by which ETP treatment increases the intestinal P-gp expression and decreases oral morphine analgesia remains unclear. RhoA, a small G-protein, and ROCK, an effector of RhoA, pathway has been attracted attention with regard to their involvement in the regulatory mechanism of the expression and activity of P-gp. Interestingly, this pathway is activated in response to various signaling induced by some anticancer drugs. Furthermore, it has been reported that ezrin/radixin/moesin (ERM) play a key role in the plasma membrane localization of P-gp, and that RhoA/ROCK pathway regulates the activation process of ERM. This review article introduces the result of our previous research as well as recent findings on the involvement of ERM via activation of RhoA/ROCK in the increased expression of intestinal P-gp and decreased oral morphine analgesia induced by repeated oral treatment with ETP.

Evaluating the enantioselective degradation and novel metabolites following a single oral dose of metalaxyl in mice

Metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D,L-alaninemethylester] is a systemic fungicide widely used in agriculture. In this study, the enantioselective distribution, degradation and excretion of metalaxyl were investigated after oral gavage administration of rac-metalaxyl to mice. Concentration of metalaxyl and its enantiomers was determined by HPLC-MS/MS. The results showed that R-metalaxyl was much higher than S-metalaxyl in heart, liver, lung, urine and feces. As for the strong first pass effect, concentrations of metalaxyl in liver were much higher than those in other tissues. The total body clearance (CL) of metalaxyl in mice was 1.77 L h(-1 )kg(-1) and degradation half-lives of (t1/2) of S-metalaxyl and R-metalaxyl in liver were 2.2 h and 3.0 h, respectively. Such results indicated the enantioselectivity of metalaxyl lies in distribution, degradation and excretion processes in mice. Main metabolites were also determined and biotransformation reactions were hydroxylation, demethylation and didemethylation. Furthermore, metabolite concentrations in urine and feces were much higher than those in tissues. These results may have potential implications to predict toxicity and provide additional information associated with adverse health effects for risk assessment of metalaxyl.

MicroRNAs as regulators of drug transporters, drug-metabolizing enzymes, and tight junctions: implication for intestinal barrier function

Drug transporters, drug-metabolizing enzymes, and tight junctions in the small intestine function as an absorption barrier and sometimes as a facilitator of orally administered drugs. The expression of these proteins often fluctuates and thereby causes individual pharmacokinetic variability. MicroRNAs (miRNAs), which are small non-coding RNAs, have recently emerged as a new class of gene regulator. MiRNAs post-transcriptionally regulate gene expression by binding to target mRNA to suppress its translation or regulate its degradation. They have been shown to be key regulators of proteins associated with pharmacokinetics. Moreover, the role of miRNAs on the expression of some proteins expressed in the small intestine has recently been clarified. In this review, we summarize current knowledge regarding the role of miRNAs in the regulation of drug transporters, drug-metabolizing enzymes, and tight junctions as well as its implication for intestinal barrier function. MiRNAs play vital roles in the differentiation, architecture, and barrier function of intestinal epithelial cells, and directly and/or indirectly regulate the expression and function of proteins associated with drug absorption in intestinal epithelial cells. Moreover, the variation of miRNA expression caused by pathological and physiological conditions as well as genetic factors should affect the expression of these proteins. Therefore, miRNAs could be significant factors affecting inter- and intra-individual variations in the pharmacokinetics and intestinal absorption of drugs. Overall, miRNAs could be promising targets for personalized pharmacotherapy or other attractive therapies through intestinal absorption of drugs.

Altered pharmacokinetics of cimetidine caused by down-regulation of renal rat organic cation transporter 2 (rOCT2) after liver ischemia-reperfusion injury

The renal tubular secretion of cationic drugs is dominated by basolateral organic cation transporter 2 (rOCT2/SLC22A2) and luminal multidrug and toxin extrusion 1 (rMATE1/SLC47A1). Little is known about the variation in the expression of these renal transporters after liver ischemia-reperfusion (I/R) injury. Here, we examined the pharmacokinetics of a cationic drug, cimetidine, and renal rOCT2 and rMATE1 levels as well as their regulation after liver I/R. Rats were subjected to 60 min of liver ischemia followed by 12 h of reperfusion. The antioxidant Trolox was administered intravenously 5 min before reperfusion. The systemic and tubular secretory clearances of cimetidine (78% and 55%) as well as renal rOCT2 and rMATE1 levels (67% and 61%) in I/R rats were decreased compared with those in sham-operated rats, respectively. However, the renal tissue-to-plasma concentration ratio but not the renal tissue-to-urine clearance ratio of cimetidine was decreased after liver I/R. Moreover, Trolox prevented the decreases in renal rOCT2 levels and systemic clearance of cimetidine after liver I/R. These results demonstrate that liver I/R decreases the tubular secretion of cimetidine, mainly because of the decreased rOCT2 level in the kidney, and that oxidative stress should be responsible in part for decreased renal rOCT2 after liver I/R injury.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

MicroRNA-145 post-transcriptionally regulates the expression and function of P-glycoprotein in intestinal epithelial cells

P-glycoprotein (P-gp/MDR1) is a multispecific efflux transporter regulating the pharmacokinetics of various drugs. Although P-gp expression in the small intestine is elevated after liver ischemia-reperfusion (I/R) injury, the regulatory mechanism remains to be clarified. MicroRNAs (miRNAs) play an important role in the post-transcriptional regulation of the expression of drug transporters. Here, we investigated the intestinal expression profile of miRNAs after liver I/R and the role of miRNAs in the post-transcriptional regulation of P-gp in intestinal epithelial cells. Microarray analysis showed that microRNA-145 (miR-145) level was decreased in the small intestine of I/R rats. This downregulation of miR-145 was further confirmed by real-time polymerase chain reaction. In silico analysis revealed that 3'-untranslated regions (UTRs) of rat Mdr1a, mouse Mdr1a, and human MDR1 mRNA retain binding sites for miR-145. Luciferase assays using MDR1 3'-UTR reporter plasmid in HEK293 cells showed that luciferase activity was decreased by the overexpression of miR-145, and the deletion of miR-145 binding site within MDR1 3'-UTR abolished this decreased luciferase activity. The downregulation of miR-145 in Caco-2 cells, an epithelial cell line derived from human colon, increased P-gp expression and efflux activity of rhodamine 123, but not MDR1 mRNA level. These findings demonstrated that miR-145 negatively regulates the expression and function of P-gp through the repression of mRNA by direct interaction on the 3'-UTR of MDR1 mRNA. In addition, the downregulation of miR-145 should significantly contribute to the elevated intestinal P-gp expression after liver I/R. Our results provide new insight into the post-transcriptional regulation of intestinal P-gp.

Isolation of gentiopicroside from Gentianae Radix and its pharmacokinetics on liver ischemia/reperfusion rats

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiopicroside (GPS) is a secoiridoid glucoside isolated from the ethanol extract of Gentianae Radix with a content of 13%, which has been used for centuries in Chinese as a digestive aid.

AIM OF THE STUDY

This study investigates the pharmacokinetics of GPS and its metabolic pathway for the liver ischemia/reperfusion (I/R) in rats.

MATERIALS AND METHODS

The experimental animals were anesthetized intraperitoneally (i.p.) with a mixture of urethane (1.0 g/kg) and α-chloralose (0.1 g/kg). A midline laparatomy was performed and the liver hilum was gently exposed. All structures in the portal triad (hepatic artery, portal vein, and bile duct) to the left and median liver lobes were occluded with silk thread for 30 min. Ischemia was followed by a sudden reperfusion after removing the occluding threads. After 60 min reperfusion, the rats received a single intravenous 5 mg/kg dose of GPS.

RESULTS

The area under concentration curve (AUC) was significantly increased; however, the clearance (Cl) was significantly decreased in the liver I/R rats. Furthermore, after pretreated with SKF-525A (50 mg/kg, i.p.), a cytochrome P450 (CYP) inhibitor, AUC, elimination half-life (t(1/2)) and the mean residence time (MRT) of GPS in rat blood were significantly increased, suggesting that CYP was involved in the metabolism of GPS. For the group without liver I/R, GPS was administered at doses of 5 mg/kg and 100 mg/kg intravenously and orally, respectively. The pharmacokinetic results indicated that the AUC was 565±95.1 and 1163±273 min μg/mL and the t(1/2) of GPS was 71±9 and 106±17 min after intravenous and oral administration, respectively. The oral bioavailability of GPS was 10.3±2.4% in the rats.

CONCLUSIONS

The status of I/R might prolong the disposition of GPS, and the plasma concentration of GPS in the liver I/R injury rats was significantly increased. The increased body exposure of GPS in the treatment of liver I/R may result from the decreased metabolism of GPS mediated by CYP in the liver.

In vitro and in vivo small intestinal metabolism of CYP3A and UGT substrates in preclinical animals species and humans: species differences

Intestinal first-pass metabolism has a great impact on the bioavailability of cytochrome P450 3A4 (CYP3A) and/or uridine 5'-diphosphate (UDP)-glucoronosyltranferase (UGT) substrates in humans. In vitro and in vivo intestinal metabolism studies are essential for clarifying pharmacokinetics in animal species and for predicting the effects of human intestinal metabolism. We review species differences in intestinal metabolism both in vitro and in vivo. Based on mRNA expression levels, the major intestinal CYP3A isoform is CYP3A4 for humans, CYP3A4 (3A8) for monkeys, CYP3A9 for rats, cyp3a13 for mice, and CYP3A12 for dogs. Additionally, the intestinal-specific UGT would be UGT1A10 for humans, UGT1A8 for monkeys, and UGT1A7 for rats. In vitro and in vivo intestinal metabolism of CYP3A substrates were larger in monkeys than in humans, although a correlation in intestinal availability between monkeys and humans has been reported. Little information is available regarding species differences in in vitro and in vivo UGT activities; however, UGT-mediated in vivo intestinal metabolism has been demonstrated for raloxifene in humans and for baicalein in rats. Further assessment of intestinal metabolism, particularly for UGT substrates, is required to clarify the entire picture of species differences.