Evaluating toxin-induced hepatic injury in rats by laboratory results and discriminant analysis

Anthocyanins Protect Hepatocytes against CCl4-Induced Acute Liver Injury in Rats by Inhibiting Pro-inflammatory mediators, Polyamine Catabolism, Lipocalin-2, and Excessive Proliferation of Kupffer Cells

: This study examined the hepatoprotective and anti-inflammatory effects of anthocyanins from Vaccinim myrtillus (bilberry) fruit extract on the acute liver failure caused by carbon tetrachloride-CCl₄ (3 mL/kg, i.p.). The preventive treatment of the bilberry extract (200 mg anthocyanins/kg, orally, 7 days) prior to the exposure to the CCl₄ resulted in an evident decrease in markers of liver damage (glutamate dehydrogenase, sorbitol dehydrogenase, malate dehydrogenase), and reduced pro-oxidative (conjugated dienes, lipid hydroperoxide, thiobarbituric acid reactive substances, advanced oxidation protein products, NADPH oxidase, hydrogen peroxide, oxidized glutathione), and pro-inflammatory markers (tumor necrosis factor-alpha, interleukin-6, nitrite, myeloperoxidase, inducible nitric oxide synthase, cyclooxygenase-2, CD68, lipocalin-2), and also caused a significant decrease in the dissipation of the liver antioxidative defence capacities (reduced glutathione, glutathione S-transferase, and quinone reductase) in comparison to the results detected in the animals treated with CCl₄ exclusively. The administration of the anthocyanins prevented the arginine metabolism's diversion towards the citrulline, decreased the catabolism of polyamines (the activity of putrescine oxidase and spermine oxidase), and significantly reduced the excessive activation and hyperplasia of the Kupffer cells. There was also an absence of necrosis, in regard to the toxic effect of CCl₄ alone. The hepatoprotective mechanisms of bilberry extract are based on the inhibition of pro-oxidative mediators, strong anti-inflammatory properties, inducing of hepatic phase II antioxidant enzymes (glutathione S-transferase, quinone reductase) and reduced glutathione, hypoplasia of Kupffer cells, and a decrease in the catabolism of polyamines.

Liver biomarker and in vitro assessment confirm the hepatic origin of aminotransferase elevations lacking histopathological correlate in beagle dogs treated with GABAA receptor antagonist NP260

NP260 was designed as a first-in-class selective antagonist of α4-subtype GABAA receptors that had promising efficacy in animal models of pain, epilepsy, psychosis, and anxiety. However, development of NP260 was complicated following a 28-day safety study in dogs in which pronounced elevations of serum aminotransferase levels were observed, although there was no accompanying histopathological indication of hepatocellular injury. To further investigate the liver effects of NP260, we assayed stored serum samples from the 28-day dog study for liver specific miRNA (miR-122) as well as enzymatic biomarkers glutamate dehydrogenase and sorbitol dehydrogenase, which indicate liver necrosis. Cytotoxicity assessments were conducted in hepatocytes derived from dog, rat, and human liver samples to address the species specificity of the liver response to NP260. All biomarkers, except ALT, returned toward baseline by Day 29 despite continued drug treatment, suggesting adaptation to the initial injury. In vitro analysis of the toxicity potential of NP260 to primary hepatocytes indicated a relative sensitivity of dog>human>rat, which may explain, in part, why the liver effects were not evident in the rodent safety studies. Taken together, the data indicate that a diagnostic biomarker approach, coupled with sensitive in vitro screening strategies, may facilitate interpretation of toxicity potential when an adaptive event masks the underlying toxicity.

Clinical Biochemistry and Hematology

This chapter discusses the clinical biochemistry and hematology of the rabbit (Oryctolagus cuniculus), guinea pig (Cavia porcellus), hamster (Mesocricetus auratus), and other rodents, including the gerbil (Meriones unguiculatus), chinchilla (Chinchilla laniger), degu (Octodon degus), deer mouse (Peromyscus maniculatus), dormouse (Gliridae family), kangaroo rat (Dipodomys spp.), cotton rat (Sigmodon hispidus), and sand rat (Psammomys obesus). The chapter begins with a review of sample collection and preparation, and a description of commonly measured parameters and analytical techniques. The reference values, sources of variation, and unique characteristics are then presented for each species, as available. Many variables affect the parameters of clinical biochemistry and hematology including methods of sample collection and preparation, equipment, reagents, and methods of analysis, as well as the age, sex, breed, and environment of the animals being sampled. Values obtained from a clinical case are usually compared with reference values that are either produced in the same laboratory or in a similar group of animals, or cited in the literature. Optimal sites for blood collection vary between laboratory animals and are described in this chapter for each species for which information is available. Total blood volume of the rabbit is discussed in the Hematology section of the chapter. The rabbit is recognized as a valuable model for human disturbances in lipid metabolism, such as the metabolic syndrome and hypercholesterolemia leading to atherosclerosis. Hematology is the study of blood and blood-forming organs, including the diagnosis, treatment, and prevention of diseases of the blood, bone marrow, and immunologic, hemostatic, and vascular systems. Hematologic analysis is often used for the diagnosis and treatment of animal diseases.

Mechanism-based bioanalysis and biomarkers for hepatic chemical stress

Adverse drug reactions, in particular drug-induced hepatotoxicity, represent a major challenge for clinicians and an impediment to safe drug development. Novel blood or urinary biomarkers of chemically-induced hepatic stress also hold great potential to provide information about pathways leading to cell death within tissues. The earlier pre-clinical identification of potential hepatotoxins and non-invasive diagnosis of susceptible patients, prior to overt liver disease is an important goal. Moreover, the identification, validation and qualification of biomarkers that have in vitro, in vivo and clinical transferability can assist bridging studies and accelerate the pace of drug development. Drug-induced chemical stress is a multi-factorial process, the kinetics of the interaction between the hepatotoxin and the cellular macromolecules are crucially important as different biomarkers will appear over time. The sensitivity of the bioanalytical techniques used to detect biological and chemical biomarkers underpins the usefulness of the marker in question. An integrated analysis of the biochemical, molecular and cellular events provides an understanding of biological (host) factors which ultimately determine the balance between xenobiotic detoxification, adaptation and liver injury. The aim of this review is to summarise the potential of novel mechanism-based biomarkers of hepatic stress which provide information to connect the intracellular events (drug metabolism, organelle, cell and whole organ) ultimately leading to tissue damage (apoptosis, necrosis and inflammation). These biomarkers can provide both the means to inform the pharmacologist and chemist with respect to safe drug design, and provide clinicians with valuable tools for patient monitoring.

The current state of serum biomarkers of hepatotoxicity

The level of serum alanine aminotransferase (ALT) activity reflects damage to hepatocytes and is considered to be a highly sensitive and fairly specific preclinical and clinical biomarker of hepatotoxicity. However, an increase in serum ALT activity level has also been associated with other organ toxicities, thus, indicating that the enzyme has specificity beyond liver in the absence of correlative histomorphologic alteration in liver. Thus, unidentified non-hepatic sources of serum ALT activity may inadvertently influence the decision of whether to continue development of a novel pharmaceutical compound. To assess the risk of false positives due to extraneous sources of serum ALT activity, additional biomarkers are sought with improved specificity for liver function compared to serum ALT activity alone. Current published biomarker candidates are reviewed herein and compared with ALT performance in preclinical and on occasion, clinical studies. An examination of the current state of hepatotoxic biomarkers indicates that serum F protein, arginase I, and glutathione-S-transferase alpha (GSTalpha) levels, all measured by ELISA, may show utility, however, antibody availability and high cost per run may present limitations to widespread applicability in preclinical safety studies. In contrast, the enzymatic markers sorbitol dehydrogenase, glutamate dehydrogenase, paraxonase, malate dehydrogenase, and purine nucleoside phosphorylase are all readily measured by photometric methods and use reagents that work across preclinical species and humans and are commercially available. The published literature suggests that these markers, once examined collectively in a large qualification study, could provide additional information relative to serum ALT and aspartate aminotransferase (AST) values. Since these biomarkers are found in the serum/plasma of treated humans and rats, they have potential to be utilized as bridging markers to monitor acute drug-induced liver injury in early clinical trials.

Advantage of serum type-I arginase and ornithine carbamoyltransferase in the evaluation of acute and chronic liver damage induced by thioacetamide in rats

BACKGROUND

We evaluated the usefulness of serum type-I arginase (ARG) and ornithine carbamoyltransferase (OCT) in thioacetamide (TAA)-induced acute and chronic liver injury in rats.

METHODS

In an acute injury model, we measured the time-courses of serum concentrations of ARG and OCT using ELISA, together with AST and ALT using biochemical enzymatic assays after a single administration of TAA (200 mg/kg, i.p.). In the chronic model, TAA was repeatedly administered (20 mg/kg/day, p.o.) for 16 weeks and serum concentrations of the enzymes were evaluated.

RESULTS

In the acute model, the concentrations of the enzymes were increased in a similar manner, peaking 24 h after the administration, and ARG showed the earliest and greatest increase among the enzymes tested. In the chronic model, the serum concentration of OCT was significantly increased only 1 week after oral treatment, while concentrations of the other enzymes were increased at 8 to 12 weeks. In the histological analysis, TAA treatment damaged hepatocytes in both the acute and chronic model.

CONCLUSIONS

These results clearly show the usefulness of ARG and OCT for the evaluation of acute and chronic liver injury, respectively.

Serum 5'nucleotidase activity in rats: a method for automated analysis and criteria for interpretation

A manual kit for determining serum 5'nucleotidase (5'NT, EC 3.1.3.5) activity was adapted for use with rat samples on a large discrete clinical chemistry analyzer. The precision of the method was good (within-run C.V. = 2.14%; between-run C.V. = 5.5%). A comparison of the new automated method with a manual and semi-automated method gave regression statistics of y = 1.18X -3.66 (Sy. x = 4.54), and y = 0.733X + 1.97 (Sy. x = 1.69), respectively. Temperature conversion factors provided by the kit manufacturer for human samples were determined to be inaccurate for converting results from rat samples. Analysis of components contributing to normal variation in rat serum 5'NT activity showed age and sex to be major factors. Increased serum 5'NT activity was observed in female rats when compared to male rats beginning at about 5 to 6 weeks of age. An analysis of variance of serum 5'NT, alkaline phosphatase, and GGT activities observed over a 9-week period in normal rats suggests several advantages for 5'NT as a predictor of biliary lesions in rats.

Retrospective evaluation of serum ornithine carbamyltransferase activity as an index of hepatotoxicity in toxicological studies with rats

The sensitivity of elevated serum ornithine carbamyltransferase (OCT) as an index of hepatotoxicity in rats was assessed in different studies conducted over a number of years and originally designed to examine the toxicity or carcinogenicity of a variety of test chemicals and diets. Changes in serum OCT activities were compared with the more widely used clinical endpoints, alanine aminotranserase (ALT) and aspartate aminotransferase (AST). In the first study, rats received a single oral dose of the hepatotoxic and hepatocarcinogenic fungal toxin aflatoxin B(1) (AFB(1)). The increase in enzyme levels between control and AFB(1)-treated rats was greater for serum OCT than for ALT or AST. This response was similar to the changes in serum enzyme levels in studies where rats ingested a hepatotoxic and hepatocarcinogenic choline deficient (CD) diet. When rats were exposed to the hepatotoxic and nephrotoxic fungal toxin fumonisin B(1) (FB(1)) by intraperitoneal injection for 6 days, serum AST and ALT were significantly elevated above control levels while OCT was unaffected. The peroxisome proliferator ciprofibrate caused elevated ALT and AST but not OCT at week 52 of dietary exposure, after the development of liver nodules and tumours. Of the two liver-specific enzymes examined in all of the studies, ALT was more consistently predictive of hepatotoxicity than OCT.

A multidisciplinary approach to toxicological screening: I. Systemic toxicity

The toxicity of 10 chemicals, including pesticides (carbaryl, chlordane, heptachlor, and triadimefon), solvents (carbon tetrachloride, dichloromethane, tetrachloroethylene, and trichloroethylene), and industrial chemicals [diethylhexylphthalate (DEHP) and phenol] was examined in the liver, kidneys, spleen, thymus, and adrenals of female F344 rats after 1 or 14 d of oral dosing. For each chemical, 4 doses were based on fractions of the acute LD50, which was estimated using an abbreviated (up-and-down) method. A multivariate analysis (MANOVA) was conducted for each organ using selected measures of toxicity. A post hoc contrast analysis was also conducted for significant MANOVA results in order to determine effective and ineffective doses. A single dose of heptachlor resulted in necrotic lymphocytes in the spleen and thymus at doses > or = 23 mg/kg. Triadimefon altered liver and spleen weights; this effect has not been described previously. Dichloromethane (> or = 337 mg/kg/d for 14 d) increased the incidence of necrosis of individual centrilobular hepatocytes. Trichloroethylene-induced hepatotoxicity was obtained at doses an order of magnitude lower than those reported in the literature. Acute DEHP (150 mg/kg) increased mitotic figures in hepatocytes, which were replaced by hepatocellular cytomegaly after 14 d of dosing at the same level. Following phenol exposure, there was an increased incidence in hepatocellular necrosis at 1 d, and an increased incidence of kidney lesions at 1 and 14 d; these findings were considered to be the result of vascular stasis. Overall, the algorithm used to select doses was effective for both 1- or 14-d dosing regimens. For all chemicals except carbon tetrachloride, the lowest effective dose for systemic toxicity was within the range of 3-56% of the LD50 for acute dosing, and 1-30% of the LD50 for repeated administration.

Clinical pathology testing recommendations for nonclinical toxicity and safety studies. AACC-DACC/ASVCP Joint Task Force

Clinical pathology testing in nonclinical toxicity and safety studies is an important part of safety assessment. In recent years, clinical laboratory testing has rapidly expanded and improved. Some government regulatory agencies provide guidelines for clinical pathology testing in nonclinical toxicity and safety studies. To improve these testing guidelines and the resultant safety assessments, the American Association for Clinical Chemistry's Division of Animal Clinical Chemistry and the American Society for Veterinary Clinical Pathology formed a joint committee to provide expert recommendations for clinical pathology testing of laboratory species involved in subchronic and chronic nonclinical toxicity and safety studies. These recommendations include technical recommendations on blood collection techniques and hematology, serum chemistry, and urinalysis tests.

The diagnostic usefulness of isocitrate dehydrogenase (ICDH) in the marmoset (Callithrix jacchus)

Marmosets were given either a hepatotoxin, carbon tetrachloride, orally or an i.m. injection of a mytoxin, chlorpromazine. Although muscle damage alone caused small increases in the plasma levels of lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase and isocitrate dehydrogenase (ICDH), only the isoenzyme analysis of ICDH can differentiate definitely between liver and muscle damage. Only very severe muscle damage can increase the plasma concentration of this enzyme but, in this case, the elevation of plasma creatinine kinase levels helps differentiation. It is recommended that the elevation of ICDH is the most specific indicator of hepatic damage in the marmoset.