Alpha-glutathione S-transferase in the assessment of hepatotoxicity--its diagnostic utility in comparison with other recognized markers in the Wistar Han rat

New biomarkers for liver involvement by dengue infection in adult Vietnamese patients: a case-control study

Liver injury with marked elevation of aspartate aminotransferase enzyme (AST) is commonly observed in dengue infection. To understand the pathogenesis of this liver damage, we compared the plasma levels of hepatic specific, centrilobular predominant enzymes (glutamate dehydrogenase, GLDH; glutathione S transferase-α, αGST), periportal enriched 4-hydroxyphenylpyruvate dioxygenase (HPPD), periportal predominant arginase-1 (ARG-1), and other non-specific biomarkers (paraoxonase-1, PON-1) in patients with different outcomes of dengue infection. This hospital-based study enrolled 87 adult dengue patients, stratified into three groups based on plasma AST levels (< 80, 80-400, > 400 U/L) in a 1:1:1 ratio (n = 40, n = 40, n = 40, respectively. The new liver enzymes in the blood samples from the 4th to 6th days of their illness were measured by commercial enzyme-linked immunosorbent assay (ELISA) or colorimetric kits. Based on the diagnosis at discharge days, our patients were classified as 40 (46%) dengue without warning signs (D), 35 (40.2%) dengue with warning signs (DWS), and 11 (12.6%) severe dengue (SD) with either shock (two patients) or AST level over 1000 U/L (nine patients), using the 2009 WHO classification. The group of high AST (> 400 U/L) also had higher ALT, GLDH, ARG-1, and HPPD than the other groups, while the high (> 400 U/L) and moderate (80-400 U/L) AST groups had higher ALT, αGST, ARG-1, and HPPD than the low AST group (< 80 U/L). There was a good correlation between AST, alanine aminotransferase enzyme (ALT), and the new liver biomarkers such as GLDH, αGST, ARG-1, and HPPD. Our findings suggest that dengue-induced liver damage initiates predominantly in the centrilobular area toward the portal area during the dengue progression. Moreover, these new biomarkers should be investigated further to explain the pathogenesis of dengue and to validate their prognostic utility.

Biomarkers of Hepatic Toxicity: An Overview

Background

Hepatotoxicity is the foremost issue for clinicians and the primary reason for pharmaceutical product recalls. A biomarker is a measurable and quantifiable attribute used to evaluate the efficacy of a treatment or to diagnose a disease. There are various biomarkers which are used for the detection of liver disease and the intent of liver damage.

Objective

This review aims to investigate the current state of hepatotoxicity biomarkers and their utility in clinical settings. Using hepatic biomarkers, the presence of liver injury, its severity, prognosis, causative agent, and type of hepatotoxicity can all be determined.

Methods

Relevant published articles up to 2022 were systematically retrieved from MEDLINE/PubMed, SCOPUS, EMBASE, and WOS databases using keywords such as drug toxicity, hepatotoxicity biomarkers, biochemical parameters, and nonalcoholic fatty liver disease.

Results

In clinical trials and everyday practice, biomarkers of drug-induced liver injury are essential for spotting the most severe cases of hepatotoxicity. Hence, developing novel biomarker approaches to enhance hepatotoxicity diagnosis will increase specificity and/or identify the person at risk. Importantly, early clinical studies on patients with liver illness have proved that some biomarkers such as aminotransferase, bilirubin, albumin, and bile acids are even therapeutically beneficial.

Conclusions

By assessing the unique signs of liver injury, health care professionals can rapidly and accurately detect liver damage and evaluate its severity. These measures contribute to ensuring prompt and effective medical intervention, hence reducing the risk of long-term liver damage and other major health concerns.

Short term biodistribution and in vivo toxicity assessment of intravenously injected pristine graphene oxide nanoflakes in SD rats

The present study aimed to elucidate the short term biodistribution of nano sized graphene oxide (GO) along with the toxicological assessment under in-vivo condition with an intent to analyse the toxic effects of sudden accidental exposure of GO The synthesised GO was characterized using UV-Visible spectroscopy, XRD, FTIR, Raman spectroscopy, TGA and DLS. The morphological imaging was performed using SEM, TEM and AFM. With a lateral size of less than 300 nm, these nanoparticles exhibit significant organ barrier permeability of up to 20%. Upon acute exposure to 10 mg/kg dose of ICG-tagged GO nanoflakes through intravenous route, various organs such as kidney, spleen and liver were observed, and the nanoparticles predominantly accumulated in the liver upon 24 h of exposure. Upon confirming the accumulation of these particles in liver through IVIS imaging, our next attempt was to analyse various biochemical and serum parameters. An elevation in various serum parameters such as ALT, AST, Creatinine and Bilirubin was observed. Similarly, in the case of biochemical parameters tested in liver homogenates, an increase in NO, Catalase, GSH, SOD, ROS, LPO, GR, GPx, and GST was observed. This study highlights the potential toxicological risk associated with GO exposure which must be taken into account for any risk analysis associated with GO based consumer products and the occupational hazards.

Are changes in olanzapine-induced liver enzyme levels associated with GSTT1, GSTM1, GSTP1, and OGG1 gene polymorphisms?

Olanzapine treatment sometimes produces transient liver biochemistry abnormalities, and such drug-induced liver injuries are mainly monitored by measuring blood levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), whereas alpha-glutathione-S-transferase (α-GST) is not routinely measured in clinics, even though it can serve as an earlier and more specific biomarker of liver damage. Susceptibility to drug-induced liver injury can much depend on the gene polymorphisms regulating the activity of DNA detoxification and repair enzymes. The aim of this study was to evaluate which of the three liver enzymes - α-GST, ALT, and AST - is the most sensitive biomarker of olanzapine-induced liver injury and how their blood levels are affected by the GSTT1, GSTM1, GSTP1, and OGG1 gene polymorphisms in 30 olanzapine-treated patients. Contrary to our hypothesis, the increase in serum α-GST levels was not significantly greater than that of the transaminases. ALT turned out to be an earlier biomarker of liver injury than the other two enzymes. No significant association was found between gene polymorphisms and liver enzyme levels, save for GSTP1 Ile/Val + Val/Val and ALT, which points to this genotype as a risk factor for drug-induced liver injury. Future studies might help to identify the underlying mechanisms of transient liver enzyme increase associated with this genotype.

Factors predicting 30-day mortality after pancreaticoduodenectomy-the impact of elevated aspartate aminotransferase

PURPOSE

High preoperative bilirubin levels and cholangitis are associated with poor peri-operative outcomes following pancreaticoduodenectomy (PD). However, the impact of deranged preoperative aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels on immediate postoperative outcomes is relatively unexplored. We hypothesized that deranged AST and ALT lead to worse postoperative outcomes after PD. The aim of this study was to assess the factors contributing to postoperative mortality (POM) following PD, and to study the impact of deranged aminotransferases.

METHODS

This is a retrospective analysis of 562 patients. Risk factors for POM were computed using a multivariate logistic regression model.

RESULTS

The rate of POM was 3.9%. On univariate analysis, the American Society of Anaesthesiologists grades, diabetes mellitus, cardiac comorbidity, preoperative biliary stenting, elevated serum bilirubin, AST, elevated serum creatinine, clinically relevant pancreatic fistula (CRPF), and grade B+C post-pancreatectomy hemorrhage (PPH) were associated with 30-day mortality. On multivariate analysis, preoperative elevated AST was independently predictive of 30-day POM (OR = 6.141, 95%CI 2.060-18.305, p = 0.001). Other factors independently predictive of POM were elevated serum creatinine, preoperative biliary stenting, CRPF and grade B and C PPH. The ratio of AST/ALT > 0.89 was associated with 8 times increased odds of POM.

CONCLUSION

Elevated preoperative AST emerged as a predictor of 30-day POM after PD, with an 8-times increased odds of death with an AST/ALT ratio > 0.89.

Biomarkers of drug-induced liver injury: a mechanistic perspective through acetaminophen hepatotoxicity

Introduction: Liver injury induced by drugs is a serious clinical problem. Many circulating biomarkers for identifying and predicting drug-induced liver injury (DILI) have been proposed.Areas covered: Biomarkers are mainly predicated on the mechanistic understanding of the underlying DILI, often in the context of acetaminophen overdose. New panels of biomarkers have emerged that are related to recovery/regeneration rather than injury following DILI. We explore the clinical relevance and limitations of these new biomarkers including recent controversies. Extracellular vesicles have also emerged as a promising vector of biomarkers, although the biological role for EVs may limit their clinical usefulness. New technological approaches for biomarker discovery are also explored.Expert opinion: Recent clinical studies have validated the efficacy of some of these new biomarkers, cytokeratin-18, macrophage colony-stimulating factor receptor, and osteopontin for DILI prognosis. Low prevalence of DILI is an inherent limitation to DILI biomarker development. Furthering mechanistic understanding of DILI and leveraging technological advances (e.g. machine learning/omics) is necessary to improve upon the newest generation of biomarkers. The integration of omics approaches with machine learning has led to novel insights in cancer research and DILI research is poised to leverage these technologies for biomarker discovery and development.

Serum glutamate dehydrogenase activity enables early detection of liver injury in subjects with underlying muscle impairments

Serum activities of alanine and aspartate aminotransferases (ALT and AST) are used as gold standard biomarkers for the diagnosis of hepatocellular injury. Since ALT and AST lack liver specificity, the diagnosis of the onset of hepatocellular injury in patients with underlying muscle impairments is severely limited. Thus, we evaluated the potential of glutamate dehydrogenase (GLDH) as a liver specific alternative biomarker of hepatocellular injury. In our study, serum GLDH in subjects with Duchene muscular dystrophy (DMD) was equivalent to serum GLDH in age matched healthy subjects, while serum ALT was increased 20-fold in DMD subjects. Furthermore, serum GLDH in 131 subjects with variety of muscle impairments was similar to serum GLDH of healthy subjects while serum ALT corelated with serum creatine kinase, a widely accepted biomarker of muscle impairment. In addition, significant elevations of ALT, AST, and CK were observed in a case of a patient with rhabdomyolysis, while serum GLDH stayed within the normal range until the onset of hypoxia-induced liver injury. In a mouse model of DMD (DMD^mdx), serum GLDH but not serum ALT clearly correlated with the degree of acetaminophen-induced liver injury. Taken together, our data support the utility of serum GLDH as a liver-specific biomarker of liver injury that has a potential to improve diagnosis of hepatocellular injury in patients with underlying muscle impairments. In drug development, GLDH may have utility as a biomarker of drug induced liver injury in clinical trials of new therapies to treat muscle diseases such as DMD.

Molecular Biomarkers in Drug-Induced Liver Injury: Challenges and Future Perspectives

Drug-induced liver injury (DILI) is one among the common adverse drug reactions and the leading causes of drug development attritions, black box warnings, and post-marketing withdrawals. Despite having relatively low clinical incidence, its potentially severe adverse events should be considered in the individual patients due to the high risk of acute liver failure. Although traditional liver parameters have been applied to the diagnosis of DILI, the lack of specific and sensitive biomarkers poses a major limitation, and thus accurate prediction of the subsequent clinical course remains a significant challenge. These drawbacks prompt the investigation and discovery of more effective biomarkers, which could lead to early detection of DILI, and improve its diagnosis and prognosis. Novel promising biomarkers include glutamate dehydrogenase, keratin 18, sorbitol dehydrogenase, glutathione S-transferase, bile acids, cytochrome P450, osteopontin, high mobility group box-1 protein, fatty acid binding protein 1, cadherin 5, miR-122, genetic testing, and omics technologies, among others. Furthermore, several clinical scoring systems have gradually emerged for the diagnosis of DILI including the Roussel Uclaf Causality Assessment Method (RUCAM), Clinical Diagnostic Scale (CDS), and Digestive Disease Week Japan (DDW-J) systems. However, currently their predictive value is limited with certain inherent deficiencies. Thus, perhaps the greatest benefit would be achieved by simultaneously combining the scoring systems and those biomarkers. Herein, we summarized the recent research progress on molecular biomarkers for DILI to improved approaches for its diagnosis and clinical management.

MicroRNA-mediated regulation of glutathione and methionine metabolism and its relevance for liver disease

The discovery of the microRNA (miRNA) family of small RNAs as fundamental regulators of post-transcriptional gene expression has fostered research on their importance in every area of biology and clinical medicine. In the particular area of liver metabolism and disease, miRNAs are gaining increasing importance. By focusing on two fundamental hepatic biosynthetic pathways, glutathione and methionine, we review recent advances on the comprehension of the role of miRNAs in liver pathophysiology and more specifically of models of hepatic cholestasis/fibrosis and hepatocellular carcinoma.

The Genetic Architecture of Murine Glutathione Transferases

Glutathione S-transferase (GST) genes play a protective role against oxidative stress and may influence disease risk and drug pharmacokinetics. In this study, massive multiscalar trait profiling across a large population of mice derived from a cross between C57BL/6J (B6) and DBA2/J (D2)—the BXD family—was combined with linkage and bioinformatic analyses to characterize mechanisms controlling GST expression and to identify downstream consequences of this variation. Similar to humans, mice show a wide range in expression of GST family members. Variation in the expression of Gsta4, Gstt2, Gstz1, Gsto1, and Mgst3 is modulated by local expression QTLs (eQTLs) in several tissues. Higher expression of Gsto1 in brain and liver of BXD strains is strongly associated (P < 0.01) with inheritance of the B6 parental allele whereas higher expression of Gsta4 and Mgst3 in brain and liver, and Gstt2 and Gstz1 in brain is strongly associated with inheritance of the D2 parental allele. Allele-specific assays confirmed that expression of Gsto1, Gsta4, and Mgst3 are modulated by sequence variants within or near each gene locus. We exploited this endogenous variation to identify coexpression networks and downstream targets in mouse and human. Through a combined systems genetics approach, we provide new insight into the biological role of naturally occurring variants in GST genes.

Mitochondrial dysfunction and oxidative damage in the liver and kidney of rats following exposure to copper nanoparticles for five consecutive days

Mitochondrial dysfunction and oxidative damage may be the initial events of copper nanoparticle (CuNP)-induced hepato and nephrotoxicity.

The Predictive Safety Testing Consortium: A synthesis of the goals, challenges and accomplishments of the Critical Path

The qualification of biomarkers of drug safety requires data on many compounds and nonclinical and clinical studies. The cost and effort associated with these qualifications cannot be easily covered by a single pharmaceutical company. Intellectual property associated with safety biomarkers is also held by many different companies. Consortia between different pharmaceutical companies can overcome cost and intellectual property hurdles to biomarker qualification. The Predictive Safety Testing Consortium (PSTC) is a collaborative effort between 16 different pharmaceutical companies to generate data supporting biomarker qualification. This Consortium is coordinated through the C-Path Institute, and currently has five biomarker qualification working groups engaged in this collaboration: nephrotoxicity, hepatotoxicity, vascular injury, myopathy, and non-genotoxic carcinogenicity. These working groups are aided by a data management team and a translational strategy team. Qualification studies of promising biomarkers are already progressing in several of the working groups, and results in the nephrotoxicity working group warranted a data submission to the FDA and EMEA for regulatory qualification of new nephrotoxicity biomarkers.:

Current challenges and controversies in drug-induced liver injury

Current key challenges and controversies encountered in the identification of potentially hepatotoxic drugs and the assessment of drug-induced liver injury (DILI) are covered in this article. There is substantial debate over the classification of DILI itself, including the definition and validity of terms such as 'intrinsic' and 'idiosyncratic'. So-called idiosyncratic DILI is typically rare and requires one or more susceptibility factors in individuals. Consequently, it has been difficult to reproduce in animal models, which has limited the understanding of its underlying mechanisms despite numerous hypotheses. Advances in predictive models would also help to enable preclinical elimination of drug candidates and development of novel biomarkers. A small number of liver laboratory tests have been routinely used to help identify DILI, but their interpretation can be limited and confounded by multiple factors. Improved preclinical and clinical biomarkers are therefore needed to accurately detect early signals of liver injury, distinguish drug hepatotoxicity from other forms of liver injury, and differentiate mild from clinically important liver injury. A range of potentially useful biomarkers are emerging, although so far most have only been used preclinically, with only a few validated and used in the clinic for specific circumstances. Advances in the development of genomic biomarkers will improve the prediction and detection of hepatic injury in future. Establishing a definitive clinical diagnosis of DILI can be difficult, since it is based on circumstantial evidence by excluding other aetiologies and, when possible, identifying a drug-specific signature. DILI signals based on standard liver test abnormalities may be affected by underlying diseases such as hepatitis B and C, HIV and cancer, as well as the concomitant use of hepatotoxic drugs to treat some of these conditions. Therefore, a modified approach to DILI assessment is justified in these special populations and a suggested framework is presented that takes into account underlying disease when evaluating DILI signals in individuals. Detection of idiosyncratic DILI should, in some respects, be easier in the postmarketing setting compared with the clinical development programme, since there is a much larger and more varied patient population exposure over longer timeframes. However, postmarketing safety surveillance is currently limited by the quantity and quality of information available to make an accurate diagnosis, the lack of a control group and the rarity of cases. The pooling of multiple healthcare databases, which could potentially contain different types of patient data, is advised to address some of these deficiencies.

Identification of novel liver-specific mRNAs in plasma for biomarkers of drug-induced liver injury and quantitative evaluation in rats treated with various hepatotoxic compounds

Circulating liver-specific mRNAs such as albumin (Alb) and α-1-microglobulin/bikunin precursor (Ambp) have been reported to be potential biomarkers for drug-induced liver injury (DILI). We identified novel circulating liver-specific mRNAs and quantified them, together with the two previously reported mRNAs, in plasma from rats treated with various hepatotoxicants to validate circulating liver-specific mRNAs as biomarkers for DILI. Among six genes selected from the database, high liver specificity of apolipoprotein h (Apoh) and group-specific component (Gc) mRNAs were confirmed by reverse transcription (RT)-PCR and the copy numbers of these mRNAs elevated in plasma from rats treated with thioacetamide. Liver-specific mRNAs (Alb, Ambp, Apoh, and Gc) were quantified by real-time RT-PCR in plasma from rats with single dosing of seven hepatotoxicants. There were noticeable interindividual and intercompound variabilities in the severity of liver injury. The levels of four mRNAs increased almost in parallel and correlated with changes in the alanine aminotransferase (ALT) values and the hepatocellular necrosis scores at 24h after dosing. It was noteworthy that the magnitude of the increases in mRNA levels was greater than that in the ALT value. Time course analysis within 24h after dosing revealed that the timing of the increase was different among mRNA species, and the plasma levels of Alb and Gc mRNAs increased substantially earlier than the ALT values, suggesting that patterns of changes in circulating liver-specific mRNAs indicate the progression of liver injury. These results strongly support the reliability and usefulness of the four circulating liver-specific mRNAs as biomarkers for DILI.

ASS and SULT2A1 are Novel and Sensitive Biomarkers of Acute Hepatic Injury-A Comparative Study in Animal Models

Liver and kidney damage associated with polytrauma, endotoxic shock/sepsis, and organ transplantation, are among the leading causes of the multiple organ failure. Development of novel sensitive biomarkers that detect early stages of liver and kidney injury is vital for the effective diagnostics and treatment of these life-threatening conditions. Previously, we identified several hepatic proteins, including Argininosuccinate Synthase (ASS) and sulfotransferases which were degraded in the liver and rapidly released into circulation during Ischemia/Reperfusion (I/R) injury. Here we compared sensitivity and specificity of the newly developed sandwich ELISA assays for ASS and the sulfotransferase isoform SULT2A1 with the standard clinical liver and kidney tests Alanine Aminotransferase (ALT) and Aspartate Transaminase (AST) in various pre-clinical models of acute injury. Our data suggest that ASS and SULT2A1 have superior characteristics for liver and kidney health assessment in endotoxemia, Ischemia/Reperfusion (I/R), chemical and drug-induced liver injury and may be of high potential value for clinical applications.

Metabolic adaptive ALT isoenzyme response in livers of C57/BL6 mice treated with dexamethasone

Alanine aminotransferase (ALT) is used as an indicator of hepatocellular injury. Since ALT consists of two isoenzymes, a better understanding of ALT isoenzyme biology in response to compounds that cause metabolic adaptive versus hepatotoxic responses will allow for a more accurate assessment of the significance of an ALT increase. The purpose of this study was to characterize the ALT isoenzyme response in mice treated with 25 or 75 mg/kg of dexamethasone, which is known to induce a progluconeogenic state, for 24 or 72 hr. Those mice treated with 75 mg/kg for 72 hr showed an increase in total liver ALT activity. Western blot showed that there was an increase in ALT2 at both doses and time points and there was a concurrent increase in ALT2 ribonucleic acid at 24 and 72 hr. The ALT isoenzyme response assessed by an activity assay showed an increase in ALT2. The increases in liver ALT were associated with an increase in liver glycogen and there was no hepatocellular necrosis. There was an increase in total serum ALT activity, although serum isoenzymes were not evaluated. Thus, the authors demonstrated that dexamethasone induced increases in hepatic and serum ALT, which reflect a hepatocellular progluconeogenic metabolic adaptive response.

Glutathione transferases, regulators of cellular metabolism and physiology

BACKGROUND

The cytosolic glutathione transferases (GSTs) comprise a super family of proteins that can be categorized into multiple classes with a mixture of highly specific and overlapping functions.

SCOPE OF REVIEW

The review covers the genetics, structure and function of the human cytosolic GSTs with particular attention to their emerging roles in cellular metabolism.

MAJOR CONCLUSIONS

All the catalytically active GSTs contribute to the glutathione conjugation or glutathione dependant-biotransformation of xenobiotics and many catalyze glutathione peroxidase or thiol transferase reactions. GSTs also catalyze glutathione dependent isomerization reactions required for the synthesis of several prostaglandins and steroid hormones and the catabolism of tyrosine. An increasing body of work has implicated several GSTs in the regulation of cell signaling pathways mediated by stress-activated kinases like Jun N-terminal kinase. In addition, some members of the cytosolic GST family have been shown to form ion channels in intracellular membranes and to modulate ryanodine receptor Ca(2+) channels in skeletal and cardiac muscle.

GENERAL SIGNIFICANCE

In addition to their well established roles in the conjugation and biotransformation of xenobiotics, GSTs have emerged as significant regulators of pathways determining cell proliferation and survival and as regulators of ryanodine receptors that are essential for muscle function. This article is part of a Special Issue entitled Cellular functions of glutathione.

Evaluation of miR-122 and other biomarkers in distinct acute liver injury in rats

The detection of drug-induced hepatotoxicity remains an important safety issue in drug development. A liver-specific microRNA species, microRNA-122 (miR-122), has recently shown potential for predicting liver injury in addition to the standard hepatic injury biomarkers. The objective of this study was to measure miR-122 together with several other liver markers in distinct settings of acute liver toxicity in rats to determine the value of miR-122 as a biomarker for liver injury in this species. Rats were exposed to 3 well-established liver toxicants (acetaminophen, allyl alcohol, and α-naphthyl isothiocyanate), a liver-enzyme inducer (phenobarbital), or a cardiotoxicant (doxorubicin). There was a clear increase in plasma miR-122 following administration of acetaminophen, allyl alcohol, and α-naphthyl isothiocyanate. The response of miR-122 paralleled that of other markers and was consistent with liver injury as indicated by histopathological evaluation. Furthermore, the changes in miR-122 were detected earlier than standard liver injury markers and exhibited a wide dynamic range. In contrast, miR-122 responses to phenobarbital and doxorubicin were low. Based on these findings, miR-122 shows significant promise and may provide added value for assessing liver toxicity in drug development.

Hepatocurative activity of biosynthesized silver nanoparticles fabricated using Andrographis paniculata

The current investigation was aimed to determine the hepatocurative role of silver nanoparticles (AgNPs) synthesized rapidly using Andrographis paniculata. The nanoparticles fabricated at varying temperatures were characterized by UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), fourier transform infra-red spectroscopy (FTIR), energy dispersive X-ray (EDX) and inductively coupled plasma optical emission spectroscopy (ICP-OES) alongside zeta potential measurement. UV-vis spectroscopic readings indicated a prominent peak at 423 nm. TEM analysis indicated that the biosynthesized nanospheres were in the size range of 13-27 nm. EDX spectrum indicated strong signal for AgNPs with 90.1% purity. The total concentration of AgNps was 216.7 mg/L after synthesis as by ICP-OES. Zeta potential was -34.3 mV indicating stable AgNPs. In vitro radical scavenging assay proved strong antioxidant effect of the AgNPs compared to 5% aqueous leaf extract. CCl(4) was used to induce hepatic injury in mice model. The biosynthesized AgNPs at three different doses (25, 50, 100mg/kg BW of the animal) were used for treatment. Silymarin was used as a standard. Low dose (25mg/kg BW) was effective in revival of all biological parameters to near normal in all intoxicated groups indicating the curing effects on CCl(4) induced liver injury.

Liver hypertrophy: a review of adaptive (adverse and non-adverse) changes--conclusions from the 3rd International ESTP Expert Workshop

Preclinical toxicity studies have demonstrated that exposure of laboratory animals to liver enzyme inducers during preclinical safety assessment results in a signature of toxicological changes characterized by an increase in liver weight, hepatocellular hypertrophy, cell proliferation, and, frequently in long-term (life-time) studies, hepatocarcinogenesis. Recent advances over the last decade have revealed that for many xenobiotics, these changes may be induced through a common mechanism of action involving activation of the nuclear hormone receptors CAR, PXR, or PPARα. The generation of genetically engineered mice that express altered versions of these nuclear hormone receptors, together with other avenues of investigation, have now demonstrated that sensitivity to many of these effects is rodent-specific. These data are consistent with the available epidemiological and empirical human evidence and lend support to the scientific opinion that these changes have little relevance to man. The ESTP therefore convened an international panel of experts to debate the evidence in order to more clearly define for toxicologic pathologists what is considered adverse in the context of hepatocellular hypertrophy. The results of this workshop concluded that hepatomegaly as a consequence of hepatocellular hypertrophy without histologic or clinical pathology alterations indicative of liver toxicity was considered an adaptive and a non-adverse reaction. This conclusion should normally be reached by an integrative weight of evidence approach.

Preclinical safety assessment: current gaps, challenges, and approaches in identifying translatable biomarkers of drug-induced liver injury

Currently, no serum biomarkers, including the biochemical gold standard alanine aminotransferase, can differentiate drug-induced from non-drug-related liver injury, can differentiate liver injury mediated by a specific drug or mechanism, or can accurately predict the progression and outcome of hepatic injury. Efforts have been made by veterinary clinical pathologists, toxicologists, and other scientists to address the gaps in hepatic biomarkers faced during drug development; although there have been no breakthroughs, several novel biomarker candidates have been identified. Efforts to address the gaps in translatable hepatic biomarkers and the challenges and hurdles faced during this process are highlighted in this review.

Effects of Hepatic Drug-metabolizing Enzyme Induction on Clinical Pathology Parameters in Animals and Man

Hepatic drug-metabolizing enzyme (DME) induction is an adaptive response associated with changes in preclinical species; this response can include increases in liver weight, hepatocellular hyperplasia and hypertrophy, and upregulated tissue expression of DMEs. Effects of DME induction on clinical pathology markers of hepatobiliary injury and function in animals as well as humans are not well established. This component of a multipart review of the comparative pathology of xenobiotically mediated induction of hepatic metabolizing enzymes reviews pertinent data from retrospective and prospective preclinical and clinical studies. Particular attention is given to studies with confirmation of DME induction and concurrent evaluation of liver and/or serum hepatobiliary marker enzyme activities and histopathology. These results collectively indicate that in the rat, when histologic findings are limited to hepatocellular hypertrophy, DME induction is not expected to be associated with consistent or substantive changes in serum or plasma activity of hepatobiliary marker enzymes such as alanine aminotransferase, alkaline phosphatase, and gamma glutamyltransferase. In the dog and the monkey, published studies also do not demonstrate a consistent relationship across DME-inducing agents and changes in these clinical pathology parameters. However, increased liver alkaline phosphatase or gamma glutamyltransferase activity in dogs treated with phenobarbital or corticosteroids suggests that direct or indirect induction of select hepatobiliary injury markers can occur both in the absence of liver injury and independently of induction of DME activity. Although correlations between tissue and serum levels of these hepatobiliary markers are limited and inconsistent, increases in serum/plasma activities that are substantial or involve changes in other markers generally reflect hepatobiliary insult rather than DME induction. Extrahepatic effects, including disruption of the hypothalamic-pituitary-thyroid axis, can also occur as a direct outcome of hepatic DME induction in humans and animals. Importantly, hepatic DME induction and associated changes in preclinical species are not necessarily predictive of the occurrence, magnitude, or enzyme induction profile in humans.

Impact of biomarker development on drug safety assessment

Drug safety has always been a key aspect of drug development. Recently, the Vioxx case and several cases of serious adverse events being linked to high-profile products have increased the importance of drug safety, especially in the eyes of drug development companies and global regulatory agencies. Safety biomarkers are increasingly being seen as helping to provide the clarity, predictability, and certainty needed to gain confidence in decision making: early-stage projects can be stopped quicker, late-stage projects become less risky. Public and private organizations are investing heavily in terms of time, money and manpower on safety biomarker development. An illustrative and "door opening" safety biomarker success story is the recent recognition of kidney safety biomarkers for pre-clinical and limited translational contexts by FDA and EMEA. This milestone achieved for kidney biomarkers and the "know how" acquired is being transferred to other organ toxicities, namely liver, heart, vascular system. New technologies and molecular-based approaches, i.e., molecular pathology as a complement to the classical toolbox, allow promising discoveries in the safety biomarker field. This review will focus on the utility and use of safety biomarkers all along drug development, highlighting the present gaps and opportunities identified in organ toxicity monitoring. A last part will be dedicated to safety biomarker development in general, from identification to diagnostic tests, using the kidney safety biomarkers success as an illustrative example.

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.

Histologically defined biomarkers in toxicology

Histopathology is the gold standard when defining toxicological effects, but it is invasive, time consuming and expensive. Using biomarkers linked to distinct, defined cell types and tissues may provide a direct link to histopathology without its drawbacks and it also provides increased sensitivity and specificity. Furthermore, as histological testing is often impractical in human subjects, using biomarkers with a known histological distribution may fill the need of localising toxic injury to distinct organs or tissues. This paper discusses how, by using biomarkers with a known cellular origin (histologically defined biomarkers), toxic effects may be found earlier and at lower doses of compound, leading to potential savings in drug development.

Effect of Enalpril on acute liver injury induced by CCl4 in rats and its anti-oxidative function

AIM: To investigate the effect of Enalpril on acute liver injury induced by carbon tetrachloride (CCl₄) in rats and its anti-oxidative function.

METHODS: Fifty normal male SD rats were randomly divided into five groups (10 rats/group): Enalpril interventional groups A, B, and C (10, 5, and 2.5 mg/kg, respectively), injury-model group, and control group. Rats in interventional and model groups were given hypodermic CCl₄ (diluted with an equal volume of olive oil). Rats in control group received normal saline injection. Rats with liver injury induced by CCl₄ were then treated with Enalpril (10, 5, 2.5; ig). The activities of serum aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP) and total bile acid (TBA) were detected using full automatic biochemical analyzer. Superoxide dismutase (SOD), xanthine oxidase (XOD), glutathione perioxidase (GSH-PX), and malondialdehyde (MDA) were determined using colorimetric method.

RESULTS: Enalpril significantly reduced serum ALT (685 ± 63, 1 241 ± 168, 1 705 ± 83, 2 302 ± 174 nkat/L vs> 3 531 ± 776 nkat/L in control, A, B, C versus model group respectively; P < 0.01), AST (1 240 ± 158, 2 430 ± 386 nkat/L vs> 3 372 ± 138 nkat/L in control, A versus model group; P < 0.01, P < 0.05 respectively), ALP (2 659 ± 248, 2 567 ± 159 nkat/L vs> 3 609 ± 346 nkat/L in control, A versus model group; P < 0.01) and TBA (8.48 ± 0.49, 16.35 ± 5.43, 16.92 ± 2.68 μmol/L vs> 24.16 ± 9.27 μmol/L in control, A, B versus model group; P < 0.01, P < 0.05, P < 0.05 respectively) in acute liver injury induced by CCl₄. The level of XOD in model group was significantly higher than that in control, A, B and C groups (1 042 ± 188 nkat/L vs> 571 ± 28, 724 ± 18, 821 ± 28, 868 ± 58 nkat/L; P < 0.01). SOD level in model group was significantly higher than that in control and A group (8 579 ± 861 nkat/L vs> 6 006± 639, 7 135 ± 1 560 nkat/L; P < 0.01, P < 0.05). MDA level in interventional group was obviously lower than that in model group and GSH-PX level was obviously higher than that in model group.

CONCLUSION: Enalpril has protective effects for rats with acute hepatic injury induced by carbon tetrachloride and the mechanism closely relates to its anti-oxidative function.

Studies on liver-protection of Sorbaria sorbifolia aqueous extract

AIM

To study the liver-protection effects of Sorbaria sorbifolia aqueous extract.

METHODS

Sorbaria sorbifolia was perfused into stomach of the rats with liver injury induced by carbon tetrachloride and D-galactosamine. The activities of serum aspartate transaminase (AST), alanine transaminase (ALT), superoxide dismutase (SOD), glutathione perioxidase (GSH-PX), and malondialdehyde (MDA) were investigated by using colorimetric method.

RESULTS

The aqueous extract of Sorbaria sorbifolia significantly reduced serum ALT and AST in acute liver-injury induced by carbon tetrachloride and D-galactosamine, the activities of SOD and GSH-PX were signficantly higher in treated group than that in model group, and the MDA content in treated group was lower than that in model group.

CONCLUSION

The aqueous extract of Sorbaria sorbifolia has protecting effects for rats with acute hepatic injury induced by carbon tetrachloride and D-galactosamine.