Chimeric mice with humanized liver as a model for testing organophosphate and carbamate pesticide exposure

Humanized mouse models: A valuable platform for preclinical evaluation of human cancer

Animal models are routinely employed to assess the treatments for human cancer. However, due to significant differences in genetic backgrounds, traditional animal models are unable to meet bioresearch needs. To overcome this restriction, researchers have generated and optimized immunodeficient mice, and then engrafted human genes, cells, tissues, or organs in mice so that the responses in the model mice could provide a more reliable reference for treatments. As a bridge connecting clinical application and basic research, humanized mice are increasingly used in the preclinical evaluation of cancer treatments, particularly after gene interleukin 2 receptor gamma mutant mice were generated. Human cancer models established in humanized mice support exploration of the mechanism of cancer occurrence and provide an efficient platform for drug screening. However, it is undeniable that the further application of humanized mice still faces multiple challenges. This review summarizes the construction approaches for humanized mice and their existing limitations. We also report the latest applications of humanized mice in preclinical evaluation for the treatment of cancer and point out directions for future optimization of these models.

SGX523 causes renal toxicity through aldehyde oxidase-mediated less-soluble metabolite formation in chimeric mice with humanized livers

SGX523 is a c-Met tyrosine kinase inhibitor that failed in clinical trials because of renal toxicity caused by crystal deposits in renal tubules. SGX523 is metabolized by aldehyde oxidase (AOX) in a species-dependent manner to the considerably less soluble 2-quinolinone-SGX523, which is likely involved in the clinically observed obstructive nephropathy. This study investigated the metabolism and renal toxicity of SGX523 in chimeric mice with humanized livers (humanized-liver mice). The 2-quinolinone-SGX523 formation activity was higher in humanized-liver mouse and human hepatocytes than in mouse hepatocytes. Additionally, this activity in the liver cytosolic fraction from humanized-liver mice was inhibited by the AOX inhibitors raloxifene and hydralazine. After oral SGX523 administration, higher maximum concentrations, larger areas under the plasma concentration versus time curves, and higher urinary concentrations of 2-quinolinone-SGX523 were observed in humanized-liver mice than in non-humanized mice. Serum creatinine and blood urea nitrogen levels were elevated in humanized-liver mice following repeated oral SGX523 administration. The accumulation of amorphous material in the tubules and infiltration of inflammatory cells around tubules were observed in the kidneys of humanized-liver mice after repeated oral SGX523 administration. These findings demonstrate that humanized-liver mice are useful for understanding the metabolism and toxicity of SGX523.

HepaSH cells: Experimental human hepatocytes with lesser inter-individual variation and more sustainable availability than primary human hepatocytes

Primary human hepatocytes (PHHs) have been commonly used as the gold standard in many drug metabolism studies, regardless of having large inter-individual variation. These inter-individual variations in PHHs arise primarily from genetic polymorphisms, as well as from donor health conditions and storage conditions prior to cell processing. To equalize the effects of the latter two factors, PHHs were transplanted to quality-controlled mice providing human hepatocyte proliferation niches, and engrafted livers were generated. Cells that were harvested from engrafted livers, call this as experimental human hepatocytes (EHH; termed HepaSH cells), were stably and reproducibly produced from 1014 chimeric mice produced by using 17 different PHHs. Expression levels of acute phase reactant (APR) genes as indicators of a systemic reaction to the environmental/inflammatory insults of liver donors varied widely among PHHs. In contrast to PHHs, the expression of APR genes in HepaSH cells was found to converge within a narrower range than in donor PHHs. Further, large individual differences in the expression levels of drug metabolism-related genes (28 genes) observed in PHHs were greatly reduced among HepaSH cells produced in a unified in vivo environment, and none deviated from the range of gene expression levels in the PHHs. The HepaSH cells displayed a similar level of drug-metabolizing enzyme activity and gene expression as the average PHHs but retained their characteristics for drug-metabolizing enzyme gene polymorphisms. Furthermore, long-term 2D culture was possible and HBV infection was confirmed. These results suggest that the stably and reproducibly providable HepaSH cells with lesser inter-individual differences in drug-metabolizing properties, may have a potential to substitution for PHH as practical standardized human hepatocytes in drug discovery research.

Humanized liver TK-NOG mice with functional deletion of hepatic murine cytochrome P450s as a model for studying human drug metabolism

Chimeric TK-NOG mice with a humanized liver (normal Hu-liver) are a unique animal model for predicting drug metabolism in humans. However, residual mouse hepatocytes occasionally prevent the precise evaluation of human drug metabolism. Herein, we developed a novel humanized liver TK-NOG mouse with a conditional knockout of liver-specific cytochrome P450 oxidoreductase (POR cKO Hu-liver). Immunohistochemical analysis revealed only a few POR-expressing cells around the portal vein in POR cKO mouse livers. NADPH-cytochrome c reductase and cytochrome P450 (P450)-mediated drug oxidation activity in liver microsomes from POR cKO mice was negligible. After the intravenous administration of S-warfarin, high circulating and urinary levels of S-7-hydroxywarfarin (a major human metabolite) were observed in POR cKO Hu-liver mice. Notably, the circulating and urinary levels of S-4′-hydroxywarfarin (a major warfarin metabolite in mice) were much lower in POR cKO Hu-liver mice than in normal Hu-liver mice. POR cKO Hu-liver mice with minimal interference from mouse hepatic P450 oxidation activity are a valuable model for predicting human drug metabolism.

Occupational exposure of rural workers to pesticides in a vegetable-producing region in Brazil

The health of family farmers is at risk due to occupational exposure to pesticides. The aims of the current study were to investigate the level of farmers' perception of risks associated with pesticide use and to assess their health condition based on biochemical and immunological tests. Family farmers living in a vegetable-producing region in Southern Brazil were selected to participate in the study. More than 70% of the family farmers were often exposed to more than one type of pesticides; 41.2% were intensively using several pesticides for more than one decade and 74.4% were not using personal protective equipment (PPE) at the time of pesticide handling due to low perception of the risks posed by these chemicals. Enzymatic analysis performed in participants' blood samples showed changes in catalase (CAT) and glutathione reductase (GR) activity, in lipid peroxidation (TBARS) and carbonylated protein levels, as well as in chemoattractant (IL-8) and anti-inflammatory (IL-10) interleukin expression. Low perception of health-related risks posed by pesticides can be attributed to factors such as low schooling and lack of information, which put farmers' health at risk, as evidenced by blood biochemical and immunological changes.

Methyl-hydroxylation and subsequent oxidation to produce carboxylic acid is the major metabolic pathway of tolbutamide in chimeric TK-NOG mice transplanted with human hepatocytes

Tolbutamide is an oral anti-hyperglycaemic agent used to treat non-insulin-dependent diabetes mellitus with species-dependent metabolic profiles. In this study, we investigated tolbutamide metabolism in chimeric TK-NOG mice transplanted with human hepatocytes (humanised-liver mice).Substantial 4-hydroxytolbutamide and 4-carboxytolbutamide production was observed in hepatocytes from humanised-liver mice (Hu-Liver cells) and humans, whereas 4-carboxytolbutamide production was not detected in mouse hepatocytes. In Hu-Liver cells, 4-hydroxytolbutamide formation was inhibited by sulfaphenazole (CYP2C9 inhibitor), whereas 4-carboxytolbutamide formation was inhibited by raloxifene/ethinyloestradiol (aldehyde oxidase inhibitor) and disulfiram (aldehyde dehydrogenase inhibitor).After a single oral dose of tolbutamide (10 mg/kg), the plasma levels of 4-carboxytolbutamide and p-tolylsulfonylurea were higher in humanised-liver mice than in TK-NOG mice. Urinary excretion was the predominant route (>99% of unchanged drug and metabolites detected in excreta) of elimination in both groups. 4-Carboxytolbutamide was the most abundant metabolite in humanised-liver mouse urine, as similarly reported for humans, whereas 4-hydroxytolbutamide was predominantly excreted in TK-NOG mouse urine.These results suggest that humanised-liver mice might represent a suitable animal model for studying the successive oxidative metabolism of tolbutamide by multiple drug-metabolising enzymes. Future work is warranted to study the general nature of primary alcohol metabolism using humanised-liver mice.

Pharmacokinetics of primary oxidative metabolites of thalidomide in rats and in chimeric mice humanized with different human hepatocytes

The approved drug thalidomide is teratogenic in humans, nonhuman primates, and rabbits but not in rodents. The extensive biotransformation of 5'-hydroxythalidomide after oral administration of thalidomide (250 mg/kg) in rats was investigated in detail using liquid chromatography-tandem mass spectrometry. Probable metabolites 5'-hydroxythalidomide sulfate and glucuronide were extensively formed, with approximately tenfold and onefold peak areas, respectively, to the primary 5'-hydroxythalidomide measured using authentic standards. As a minor metabolite, 5-hydroxythalidomide was also detected. The output of simplified physiologically based pharmacokinetic rat models was consistent with the observed in vivo data under a metabolic ratio of 0.05 for the hepatic intrinsic clearance of thalidomide to unconjugated 5'-hydroxythalidomide. The aggregate of unconjugated and sulfate/glucuronide conjugated 5'-hydroxythalidomide forms appear to be the predominant metabolites in rats. Two hours after oral administration of thalidomide (100 mg/kg) to chimeric mice humanized with four different batches of genotyped human hepatocytes, the plasma concentration ratios of 5-hydroxythalidomide to 5'-hydroxythalidomide were correlated with replacement indexes of human liver cells previously transplanted in immunodeficient mice. These results indicate that rodent livers mediate thalidomide primary oxidation, leading to extensive deactivation in vivo to unconjugated/conjugated 5'-hydroxythalidomide and suggest that thalidomide activation might be dependent on the humanized livers in mice transplanted with human hepatocytes.

Discovery of treatment for nerve agents targeting a new metabolic pathway

The inhibition of acetylcholinesterase is regarded as the primary toxic mechanism of action for chemical warfare agents. Recently, there have been numerous reports suggesting that metabolic processes could significantly contribute to toxicity. As such, we applied a multi-omics pipeline to generate a detailed cascade of molecular events temporally occurring in guinea pigs exposed to VX. Proteomic and metabolomic profiling resulted in the identification of several enzymes and metabolic precursors involved in glycolysis and the TCA cycle. All lines of experimental evidence indicated that there was a blockade of the TCA cycle at isocitrate dehydrogenase 2, which converts isocitrate to α-ketoglutarate. Using a primary beating cardiomyocyte cell model, we were able to determine that the supplementation of α-ketoglutarate subsequently rescued cells from the acute effects of VX poisoning. This study highlights the broad impacts that VX has and how understanding these mechanisms could result in new therapeutics such as α-ketoglutarate.

Combination of Patulin and Chlorpyrifos Synergistically Induces Hepatotoxicity via Inhibition of Catalase Activity and Generation of Reactive Oxygen Species

Patulin (PAT) is the most common food-borne mycotoxin found in fruits and fruit-derived products, while chlorpyrifos (CPF) is a widely used pesticide on fruit and other crops. On the basis of the residue data, certain types of fruits can be contaminated simultaneously by patulin and chlorpyrifos. However, there are no available data about the combined toxicity. Since liver is a possible toxic target of both patulin and chlorpyrifos, we tested whether the combination exposure can cause enhanced hepatotoxicity using both cell culture and animal models. Results showed that the combination resulted in synergistic cytotoxicity in vitro and significantly enhanced liver toxicity in vivo. Mechanistically, PAT inhibited catalase activity via PIG3 induction, while CPF decreased catalase expression. These two mechanisms were converged in response to the combination, leading to enhanced inactivating catalase and boosted reactive oxygen species generation. The finding implicated that it is necessary to consider the combined toxicity in safety assessment of these food-borne contaminants.

Predictability of human pharmacokinetics of diisononyl phthalate (DINP) using chimeric mice with humanized liver

1. In order to investigate the pharmacokinetics of diisononyl phthalate (DINP) in humans, we administered [phenyl-U-¹⁴C]DINP at a dose of 50.0 mg/kg orally to chimeric mice (humanized-liver mice) in which the liver of TK-NOG mice (control mice) was replaced with human hepatocytes. 2. The plasma radioactivity concentrations peaked (18.0 and 59.9 µg equivalent of DINP/mL, respectively) at 2 h after administration in control and humanized-liver mice. Concentrations rose again at 8 h in controls, but not in humanized-liver mice. 3. The cumulative excretion rates in urine and feces, respectively, were 58.1% and 37.3% of the doses in controls up to 48 h, but were 86.0% and 7.7% in humanized-liver mice. 4. The main circulating metabolites in control and humanized-liver mice were monoisononyl phthalate (MINP) and the glucuronide of oxidized MINP, respectively. The urinary excretion ratio of the glucuronide of oxidized MINP in control mice was one-third of that in humanized-liver mice. 5. The present results suggested that the oxidation rates of the primary metabolite of DINP and their excretion routes to urine/feces were different for control and humanized-liver mice. Species differences in liver activities could be a determinant factor in the in vivo metabolism and disposition of diallyl phthalates such as DINP.

Expression and inducibility of cytochrome P450s in human hepatocytes isolated from chimeric mice with humanised livers

The evaluation of drug-mediated cytochrome P450 (P450) induction using human hepatocytes is important for predicting drug interactions. In this study, we prepared hepatocytes from chimeric mice with humanised livers (Hu-Liver mice) and evaluated the expression and inducibility of P450s in these hepatocytes. Up to 95% of the Hu-Liver cells stained positive for human leukocyte antigen and the mean viability exceeded 85% (n = 10). Monolayer-cultured Hu-Liver cells displayed a similar morphology to cultures of the corresponding human hepatocytes used as transplantation donors. The mRNA expression levels in Hu-Liver cells of 16 P450 forms belonging to P450 subfamilies 1-4 correlated well with the expression levels of the same enzymes in human hepatocytes. The variations in individual P450 mRNA levels between Hu-Liver cells and the corresponding human hepatocytes were within five-fold for 13 P450 forms. The production of 6β-hydroxytestosterone in Hu-Liver cells was significantly increased (p < .05) following treatment with the CYP3A inducer, rifampicin. Hu-Liver cells have characteristics similar to those of human hepatocytes in terms of mRNA expression levels and the inducibility of the various P450 forms. Thus, Hu-Liver cells can potentially be used for in vitro drug-mediated induction assays of human hepatic P450s.

Evidence of risks of renal function reduction due to occupational exposure to agrochemicals: A systematic review

Agriculture accountsfor an important economic activity worldwide and the search for the increased productivity incorporated the use of pesticides in this practice. Such compounds have significant environmental and human health effects, especially for workers exposed to them. Among the main health problems caused by pesticides are the renal alterations, which in more advanced stages comprise an important public health problem. For this reason, this systematic review aimed at gathering evidence of the risk of renal changes induced by occupational exposure to pesticides. The search was made in PubMed, Scopus, Lilacs and Scielo in December 2017, using keywords as pesticides, poisoning, kidney, renal insufficiency. After the application of inclusion criteria, 11 studies were selected. It was possible to gather evidence on the prevalence and risk (3.12-6.71) of renal injury from the occupational exposure of agricultural workers and its association with the exposure to agrichemicals, as organophosphates and herbicides.