Isoform-specific alanine aminotransferase measurement can distinguish hepatic from extrahepatic injury in humans

John N, Zaidi F, Doyle F, Fasullo M. High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

The Evolution of Circulating Biomarkers for Use in Acetaminophen/Paracetamol-Induced Liver Injury in Humans: A Scoping Review

Acetaminophen (APAP) is a widely used drug, but overdose can cause severe acute liver injury. The first reports of APAP hepatotoxicity in humans were published in 1966, shortly after the development of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) as the first biomarkers of liver injury as opposed to liver function. Thus, the field of liver injury biomarkers has evolved alongside the growth in APAP hepatotoxicity incidence. Numerous biomarkers have been proposed for use in the management of APAP overdose patients in the intervening years. Here, we comprehensively review the development of these markers from the 1960s to the present day and briefly discuss possible future directions.

Hepatic pyruvate and alanine metabolism are critical and complementary for maintenance of antioxidant capacity and resistance to oxidative insult

OBJECTIVE

Mitochondrial pyruvate is a critical intermediary metabolite in gluconeogenesis, lipogenesis, and NADH production. As a result, the mitochondrial pyruvate carrier (MPC) complex has emerged as a promising therapeutic target in metabolic diseases. Clinical trials are currently underway. However, recent in vitro data indicate that MPC inhibition diverts glutamine/glutamate away from glutathione synthesis and toward glutaminolysis to compensate for loss of pyruvate oxidation, possibly sensitizing cells to oxidative insult. Here, we explored this in vivo using the clinically relevant acetaminophen (APAP) overdose model of acute liver injury, which is driven by oxidative stress.

METHODS

We used pharmacological and genetic approaches to inhibit MPC2 and alanine aminotransferase 2 (ALT2), individually and concomitantly, in mice and cell culture models and determined the effects on APAP hepatotoxicity.

RESULTS

We found that MPC inhibition sensitizes the liver to APAP-induced injury in vivo only with concomitant loss of alanine aminotransferase 2 (ALT2). Pharmacological and genetic manipulation of neither MPC2 nor ALT2 alone affected APAP toxicity, but liver-specific double knockout (DKO) significantly worsened APAP-induced liver damage. Further investigation indicated that DKO impaired glutathione synthesis and increased urea cycle flux, consistent with increased glutaminolysis, and these results were reproducible in vitro. Finally, induction of ALT2 and post-treatment with dichloroacetate both reduced APAP-induced liver injury, suggesting new therapeutic avenues.

CONCLUSIONS

Increased susceptibility to APAP toxicity requires loss of both the MPC and ALT2 in vivo, indicating that MPC inhibition alone is insufficient to disrupt redox balance. Furthermore, the results from ALT2 induction and dichloroacetate in the APAP model suggest new metabolic approaches to the treatment of liver damage.

Validation of a novel point-of-care test for alanine aminotransferase measurement: A pilot cohort study

BACKGROUND

Alanine aminotransferase (ALT) measurement is essential for evaluation of liver disease. We validated a novel rapid point-of-care (POC) test for ALT1 against laboratory ALT.

METHODS

Stored plasma samples from adults with chronic liver disease (Test cohort n = 240; Validation cohort n = 491) were analysed using the BioPoint® antigen immunoassay POC ALT1 lateral flow test, which provides quantitative ALT results (Axxin handheld reader) or semi-quantitative results (visual read, cut off 40 IU/ml). The accuracy of POC ALT1 to detect ALT > 40 IU/L was determined by ROC analysis. In patients with chronic hepatitis B, treatment eligibility (EASL criteria) was determined using POC ALT1 and compared to laboratory ALT.

RESULTS

POC ALT1 test had good accuracy for laboratory ALT > 40 IU/L: AUROC 0.93 (95% CI: 0.89-0.96) in the Test cohort and AUROC 0.92 (95% CI: 0.88-0.95) in the Validation cohort. POC ALT1 cut off of 0.8 for ALT > 40 IU/L maximised sensitivity (97%) and specificity (71%) in the Test cohort (42% laboratory ALT > 40 IU/L) and yielded PPV 84% and NPV 91% in the Validation cohort (19% laboratory ALT > 40 IU/L). Semi-quantitative POC ALT1 had good accuracy for laboratory ALT in the Validation cohort (AUROC 0.85, 95% CI: 0.81-0.99; sensitivity 77% and specificity 93%). Combined with HBV DNA and transient elastography, both quantitative and semi-quantitative POC ALT1 tests had good accuracy for excluding hepatitis B treatment needs (sensitivity 96%, specificity 78% and NPV 99%).

CONCLUSION

The POC ALT1 test had good accuracy for elevated ALT levels and for determining treatment eligibility among people with chronic hepatitis B.

Amaryllidaceae, Lycopodiaceae Alkaloids and Coumarins—A Comparative Assessment of Safety and Pharmacological Activity

The study aimed to evaluate the safety and pharmacological activity Amaryllidaceae, Lycopodiaceae alkaloids and coumarins obtained from Narcissus triandrus L., Lycopodium clavatum L., Lycopodium annotinum L., Huperzia selago L. and Angelica dahurica (Hoffm.) Benth. & Hook.f. ex Franch. & Sav. In the in vivo studies. The influence of the tested compounds on the central nervous system of rats was assessed in behavioral tests (locomotor activity, Y-maze, passive avoidance). In order to investigate the mechanisms of action, biochemical determinations were performed (AChE activity, BChE activity, IL-1β, IL-6 concentration). In order to assess safety, the concentrations of AST, ALT, GGT and urea and creatinine were determined. The results of the conducted studies indicate a high safety profile of the tested compounds. Behavioral tests showed that they significantly improved rodent memory in a passive avoidance test. The results of biochemical studies showed that by reducing the activity of AChE and BChE and lowering the concentration of IL-1β and IL-6, the coumarin-rich Angelica dahurica extract shows the most promising potential for future therapeutic AD strategies.

Specificity of transaminase activities in the prediction of drug-induced hepatotoxicity

The activities of the transaminases (aminotransferases) alanine aminotransferase and aspartate aminotransferase in the blood (serum or plasma) are widely used as sensitive markers of possible tissue damage and, in particular for liver toxicity. On the other hand, an increase in transaminase activities is not always accompanied by findings suggestive of hepatotoxicity. Transaminases are some of the key enzymes in the gluconeogenesis and glycolysis pathways and exist in many organs and tissues which have high activities of the gluconeogenesis and glycolysis. The activities of transaminases are altered not only in the liver but also in other organs by modification of gluconeogenesis by nutritional or hormonal factors and this phenomenon leads to alteration of transaminase activity in the blood. Drugs, which are considered to directly or secondarily modify gluconeogenesis through lowering blood glucose levels or activating lipid metabolism, such as α-glucosidase inhibitors and fibrates, slightly increase transaminase activities in the blood but there is little evidence that the phenomenon is related to drug-induced liver injury (DILI). This type of elevations can be called pharmacology-related elevation. The pharmacology-related elevation of transaminase activities sometimes makes it difficult to assess precisely the potential hepatotoxicity of new investigational drugs. Considering the characteristic of transaminases, concomitant use of new biomarkers more specific to hepatic injury is needed in the assessment of DILI both in non-clinical and clinical studies. In this review, we will discuss the specificity of transaminases to DILI and future perspectives for transaminases in the estimation of risk of DILI.

Elevated levels of circulating CDH5 and FABP1 in association with human drug-induced liver injury

BACKGROUND & AIMS

The occurrence of drug-induced liver injury (DILI) is a major issue in all phases of drug development. To identify novel biomarker candidates associated with DILI, we utilised an affinity proteomics strategy, where antibody suspension bead arrays were applied to profile plasma and serum samples from human DILI cases and controls.

METHODS

An initial screening was performed using 4594 randomly selected antibodies, representing 3450 human proteins. Resulting candidate proteins together with proposed DILI biomarker candidates generated a DILI array of 251 proteins for subsequent target analysis and verifications. In total, 1196 samples from 241 individuals across four independent cohorts were profiled: healthy volunteers receiving acetaminophen, patients with human immunodeficiency virus and/or tuberculosis receiving treatment, DILI cases originating from a wide spectrum of drugs, and healthy volunteers receiving heparins.

RESULTS

We observed elevated levels of cadherin 5, type 2 (CDH5) and fatty acid-binding protein 1 (FABP1) in DILI cases. In the two longitudinal cohorts, CDH5 was elevated already at baseline. FABP1 was elevated after treatment initiation and seemed to respond more rapidly than alanine aminotransferase (ALT). The elevations were verified in the DILI cases treated with various drugs. In the heparin cohort, CDH5 was stable over time whereas FABP1 was elevated.

CONCLUSIONS

These results suggest that CDH5 may have value as a susceptibility marker for DILI. FABP1 was identified as a biomarker candidate with superior characteristics regarding tissue distribution and kinetics compared to ALT but likely with limited predictive value for the development of severe DILI. Further studies are needed to determine the clinical utility of the proposed markers.

A longitudinal assessment of miR-122 and GLDH as biomarkers of drug-induced liver injury in the rat

CONTEXT

There is an ongoing search for specific and translational biomarkers of drug-induced liver injury (DILI). MicroRNA-122 (miR-122) has previously shown potential as a sensitive, specific, and translational biomarker of DILI in both rodent, and human studies.

OBJECTIVE

To build on previous work within the field, we examined biomarker kinetics in a rat model of acetaminophen (APAP)-induced liver injury to confirm the sensitivity, and specificity of miR-122 and glutamate dehydrogenase (GLDH).

MATERIALS AND METHODS

qRT-PCR and a standard enzymatic assay were used for biomarker analysis.

RESULTS

Both miR-122 and GLDH were demonstrated to be more readily-detectable biomarkers of APAP-DILI than alanine aminotransferase (ALT). Peak levels for all biomarkers were detected at 2 days after APAP. At day 3, miR-122 had returned to baseline; however, other biomarkers remained elevated between 3 and 4 days. We were also able to demonstrate that, although miR-122 is present in greater quantities in exosome-free form, both exosome-bound and non-vesicle bound miR-122 are released in a similar profile throughout the course of DILI.

DISCUSSION AND CONCLUSIONS

Together, this study demonstrates that both GLDH and miR-122 could be used during preclinical drug-development as complementary biomarkers to ALT to increase the chance of early detection of hepatotoxicity.

Biomarkers in DILI: One More Step Forward

Despite being relatively rare, drug-induced liver injury (DILI) is a serious condition, both for the individual patient due to the risk of acute liver failure, and for the drug development industry and regulatory agencies due to associations with drug development attritions, black box warnings, and postmarketing withdrawals. A major limitation in DILI diagnosis and prediction is the current lack of specific biomarkers. Despite refined usage of traditional liver biomarkers in DILI, reliable disease outcome predictions are still difficult to make. These limitations have driven the growing interest in developing new more sensitive and specific DILI biomarkers, which can improve early DILI prediction, diagnosis, and course of action. Several promising DILI biomarker candidates have been discovered to date, including mechanistic-based biomarker candidates such as glutamate dehydrogenase, high-mobility group box 1 protein and keratin-18, which can also provide information on the injury mechanism of different causative agents. Furthermore, microRNAs have received much attention lately as potential non-invasive DILI biomarker candidates, in particular miR-122. Advances in “omics” technologies offer a new approach for biomarker exploration studies. The ability to screen a large number of molecules (e.g., metabolites, proteins, or DNA) simultaneously enables the identification of ‘toxicity signatures,’ which may be used to enhance preclinical safety assessments and disease diagnostics. Omics-based studies can also provide information on the underlying mechanisms of distinct forms of DILI that may further facilitate the identification of early diagnostic biomarkers and safer implementation of personalized medicine. In this review, we summarize recent advances in the area of DILI biomarker studies.

Intrahepatic and extrahepatic aminotransferase elevation associated with clinical‐therapeutic events in a schizophrenic patient

A schizophrenic patient showed rhabdomyolysis with idiopathic transaminitis. The intermixed pattern of intrahepatic and extrahepatic alanine aminotransferase (ALT) elevation is associated with respective clinical‐therapeutic events. Aminotransferases play a role as surrogate biomarkers of “liver metabolic functioning” beyond the obsolete classical concept associating ALT elevation only with liver cellular damage.

Liver enzymes, metabolomics and genome-wide association studies: From systems biology to the personalized medicine

For several decades, serum levels of alanine (ALT) and aspartate (AST) aminotransferases have been regarded as markers of liver injury, including a wide range of etiologies from viral hepatitis to fatty liver. The increasing worldwide prevalence of metabolic syndrome and cardiovascular disease revealed that transaminases are strong predictors of type 2 diabetes, coronary heart disease, atherothrombotic risk profile, and overall risk of metabolic disease. Therefore, it is plausible to suggest that aminotransferases are surrogate biomarkers of “liver metabolic functioning” beyond the classical concept of liver cellular damage, as their enzymatic activity might actually reflect key aspects of the physiology and pathophysiology of the liver function. In this study, we summarize the background information and recent findings on the biological role of ALT and AST, and review the knowledge gained from the application of genome-wide approaches and “omics” technologies that uncovered new concepts on the role of aminotransferases in human diseases and systemic regulation of metabolic functions. Prediction of biomolecular interactions between the candidate genes recently discovered to be associated with plasma concentrations of liver enzymes showed interesting interconnectivity nodes, which suggest that regulation of aminotransferase activity is a complex and highly regulated trait. Finally, links between aminotransferase genes and metabolites are explored to understand the genetic contributions to the metabolic diversity.

Circulating mitochondrial biomarkers for drug-induced liver injury

Liver mitochondria affected by drugs can be released into circulation and serve as biomarkers for drug-induced liver injury (DILI). The tissue specificity of ALT was improved by differentiating cytosolic ALT1 and mitochondrial ALT2 isoforms released in circulation. Prior to ALT elevation, mitochondrial cytochrome c, OCT, GLDH, CPS1 and DNA were increased in circulation following DILI. The baseline expression of mt-Nd6 was predictive of individual DILI susceptibility in animals. As mitochondrial DILI biomarkers appeared to be drug or species dependent, they might have value in clinical scenarios when culprit drugs are established, but may not be ideal tools to assess DILI potentials of new drugs.

Keratin-18 and microRNA-122 complement alanine aminotransferase as novel safety biomarkers for drug-induced liver injury in two human cohorts

BACKGROUND & AIMS

There is a demand for more sensitive, specific and predictive biomarkers for drug-induced liver injury (DILI) than the gold standard used today, alanine aminotransferase (ALT). The aim of this study was to qualify novel DILI biomarkers (keratin-18 markers M65/M30, microRNA-122, glutamate dehydrogenase and alpha-foetoprotein) in human DILI.

METHODS

Levels of the novel biomarkers were measured by enzyme-linked immunosorbent assay or real-time quantitative reverse-transcription PCR (qRT-PCR) in two human DILI cohorts: a human volunteer study with acetaminophen and a human immunodeficiency virus (HIV)/tuberculosis (TB) study.

RESULTS

In the acetaminophen study, serum M65 and microRNA-122 levels were significantly increased at an earlier time point than ALT. Furthermore, the maximal elevation of M65 and microRNA-122 exceeded the increase in ALT. In the HIV/TB study, all the analysed novel biomarkers increased after 1 week of treatment. In contrast to ALT, the novel biomarkers remained stable in a human cohort with exercise-induced muscular injury.

CONCLUSIONS

M65 and microRNA-122 are potential biomarkers of DILI superior to ALT with respect to sensitivity and specificity.

Activating transcription factor 4 mediates up-regulation of alanine aminotransferase 2 gene expression under metabolic stress

Alanine aminotransferase (ALT) provides a molecular link between carbohydrate and amino acid metabolism. In humans, two ALT isoforms have been characterized: ALT1, cytosolic, and ALT2, mitochondrial. To gain insight into the transcriptional regulation of the ALT2 gene, we cloned and characterized the human ALT2 promoter. 5'-deletion analysis of ALT2 promoter in transiently transfected HepG2 cells and site-directed mutagenesis allowed us to identify ATF4 as a new factor involved in the transcriptional regulation of ALT2 expression. Quantitative RT-PCR assays showed that the metabolic stressors histidinol and tunicamycin increased ATF4 levels and up-regulated ALT2 in HepG2 and Huh7 cells. Consistently, knock-down of ATF4 decreased ALT2 mRNA levels in HepG2 and Huh-7 cells. Moreover, ATF4 silencing prevented the activating effect of histidinol and tunicamycin on ATF4 and ALT2 expression. Our findings point to ALT2 as an enzyme involved in the metabolic adaptation of the cell to stress.

Regulation of pyruvate metabolism and human disease

Pyruvate is a keystone molecule critical for numerous aspects of eukaryotic and human metabolism. Pyruvate is the end-product of glycolysis, is derived from additional sources in the cellular cytoplasm, and is ultimately destined for transport into mitochondria as a master fuel input undergirding citric acid cycle carbon flux. In mitochondria, pyruvate drives ATP production by oxidative phosphorylation and multiple biosynthetic pathways intersecting the citric acid cycle. Mitochondrial pyruvate metabolism is regulated by many enzymes, including the recently discovered mitochondria pyruvate carrier, pyruvate dehydrogenase, and pyruvate carboxylase, to modulate overall pyruvate carbon flux. Mutations in any of the genes encoding for proteins regulating pyruvate metabolism may lead to disease. Numerous cases have been described. Aberrant pyruvate metabolism plays an especially prominent role in cancer, heart failure, and neurodegeneration. Because most major diseases involve aberrant metabolism, understanding and exploiting pyruvate carbon flux may yield novel treatments that enhance human health.