Glutamate Dehydrogenase as a Marker of Alcohol Dependence

Serum glutamate dehydrogenase activity enables sensitive and specific diagnosis of hepatocellular injury in humans

Serum activities of alanine- and aspartate aminotransferases (ALT and AST) are considered the "gold standard" biomarkers of hepatocyte injury in clinical practice and drug development. However, due to the expression of ALT and AST in myocytes, the diagnosis of hepatocellular injury in patients with underlying muscle diseases, including drug-induced muscle injury, is severely limited. Thus, we proposed glutamate dehydrogenase (GLDH) as a liver-specific alternative to serum ALT and AST. In fact, our exploratory studies showed that GLDH has comparable performance to ALT for detecting hepatocyte injury without interference from concomitant muscle injury. Here, we report the results of studies confirming the reference intervals in a healthy human population and the sensitivity and specificity of GLDH for the detection of hepatocyte injury in human subjects. In human subjects, we could not perform liver biopsies due to ethical reasons; we also confirmed the relationship of GLDH and histopathologic lesions using 32 model toxicants in rats. Furthermore, we have shown that injury to tissues that are known to express appreciable levels of GLDH does not affect serum GLDH measurements, indicating excellent liver specificity of serum GLDH. Finally, we observed faster elimination of GLDH than ALT in humans, indicating that decreasing GLDH values could be considered an early sign of recovery. This study provides comprehensive evidence of excellent sensitivity and liver specificity of GLDH for diagnosis of hepatocellular injury, including evaluation of reference intervals, which is essential for the interpretation of serum GLDH in human subjects.

Advanced Biomarkers of Hepatotoxicity in Psychiatry: A Narrative Review and Recommendations for New Psychoactive Substances

One of the factors that increase the effectiveness of the pharmacotherapy used in patients abusing various types of new psychoactive substances (NPSs) is the proper functioning of the liver. However, the articles published to date on NPS hepatotoxicity only address non-specific hepatic parameters. The aim of this manuscript was to review three advanced markers of hepatotoxicity in psychiatry, namely, osteopontin (OPN), high-mobility group box 1 protein (HMGB1) and glutathione dehydrogenase (GDH, GLDH), and, on this basis, to identify recommendations that should be included in future studies in patients abusing NPSs. This will make it possible to determine whether NPSs do indeed have a hepatotoxic effect or whether other factors, such as additional substances taken or hepatitis C virus (HCV) infection, are responsible. NPS abusers are at particular risk of HCV infection, and for this reason, it is all the more important to determine what factors actually show a hepatotoxic effect in them.

Classical blood biomarkers identify patients with higher risk for relapse 6 months after alcohol withdrawal treatment

This naturalistic study among patients with alcohol dependence examined whether routine blood biomarkers could help to identify patients with high risk for relapse after withdrawal treatment. In a longitudinal study with 6-month follow-up among 133 patients with alcohol dependence who received inpatient alcohol withdrawal treatment, we investigated the usefulness of routine blood biomarkers and clinical and sociodemographic factors for potential outcome prediction and risk stratification. Baseline routine blood biomarkers (gamma-glutamyl transferase [GGT], alanine aminotransferase [ALT/GPT], aspartate aminotransferase [AST/GOT], mean cell volume of erythrocytes [MCV]), and clinical and sociodemographic characteristics were recorded at admission. Standardized 6 months' follow-up assessed outcome variables continuous abstinence, days of continuous abstinence, daily alcohol consumption and current abstinence. The combined threshold criterion of an AST:ALT ratio > 1.00 and MCV > 90.0 fl helped to identify high-risk patients. They had lower abstinence rates (P = 0.001), higher rates of daily alcohol consumption (P < 0.001) and shorter periods of continuous abstinence (P = 0.027) compared with low-risk patients who did not meet the threshold criterion. Regression analysis confirmed our hypothesis that the combination criterion is an individual baseline variable that significantly predicted parts of the respective outcome variances. Routinely assessed indirect alcohol biomarkers help to identify patients with high risk for relapse after alcohol withdrawal treatment. Clinical decision algorithms to identify patients with high risk for relapse after alcohol withdrawal treatment could include classical blood biomarkers in addition to clinical and sociodemographic items.

Relation of plasma carnitine and aminotransferases to alcohol dose and time of dependence

BACKGROUND

Serum aspartate, alanine aminotransferases (AST, ALT), and plasma carnitine are all indirect biomarkers of alcohol abuse. Carnitine transfers long-chain fatty acids from cytoplasm to mitochondria for β-oxidation. The aim of the study was to determine the relationship between daily alcohol intake, time of alcohol dependence, plasma carnitine, and serum aminotransferases.

PATIENTS

We studied 26 men who were addicted for 2-30 years, consuming ethanol from 75 to 700 g/day (alcoholic group), as well as 17 healthy men (control group).

RESULTS

In alcoholics, compared to the controls, we found: a significant increase in serum: AST (p = 0.0014), ALT (p = 0.0071), AST/ALT ratio (p < 0.000); significantly lower plasma free carnitine (FC) (p = 0.0316) and total carnitine (TC) (p = 0.0349); and a significant negative correlation between FC (r = -0.6200; R² = 0.3844; p = 0.0007), TC (r = -0.4365; R² = 0.1905; p = 0.0258), and time of alcohol dependence, suggesting carnitine as an indirect marker of alcohol abuse. We did not find any significant correlation between FC, TC, and levels of alcohol or aminotransferase activity.

CONCLUSION

In the alcoholic group, there was an increase in serum activity of AST, ALT, and AST/ALT ratio that confirms liver injury. In addition, we found low plasma FC and TC, which may indicate damage to mitochondrial β-oxidation caused by alcohol metabolites. The significantly higher plasma FC and TC in patients consuming the most, compared to patients consuming smaller doses of alcohol, may be caused by a lower carnitine demand of injured liver cells, decreased urinary carnitine excretion by impaired renal tubules, and leakage of carnitine into the blood from damaged muscles by the higher quantities of alcohol. The negative correlation between carnitine concentration and time of alcohol dependence may suggest the potential use of carnitine for treatment of alcohol abuse.

Structural Insights into l-Tryptophan Dehydrogenase from a Photoautotrophic Cyanobacterium, Nostoc punctiforme

l-Tryptophan dehydrogenase from Nostoc punctiforme NIES-2108 (NpTrpDH), despite exhibiting high amino acid sequence identity (>30%)/homology (>50%) with NAD(P)⁺-dependent l-Glu/l-Leu/l-Phe/l-Val dehydrogenases, exclusively catalyzes reversible oxidative deamination of l-Trp to 3-indolepyruvate in the presence of NAD⁺ Here, we determined the crystal structure of the apo form of NpTrpDH. The structure of the NpTrpDH monomer, which exhibited high similarity to that of l-Glu/l-Leu/l-Phe dehydrogenases, consisted of a substrate-binding domain (domain I, residues 3 to 133 and 328 to 343) and an NAD⁺/NADH-binding domain (domain II, residues 142 to 327) separated by a deep cleft. The apo-NpTrpDH existed in an open conformation, where domains I and II were apart from each other. The subunits dimerized themselves mainly through interactions between amino acid residues around the β-1 strand of each subunit, as was observed in the case of l-Phe dehydrogenase. The binding site for the substrate l-Trp was predicted by a molecular docking simulation and validated by site-directed mutagenesis. Several hydrophobic residues, which were located in the active site of NpTrpDH and possibly interacted with the side chain of the substrate l-Trp, were arranged similarly to that found in l-Leu/l-Phe dehydrogenases but fairly different from that of an l-Glu dehydrogenase. Our crystal structure revealed that Met-40, Ala-69, Ile-74, Ile-110, Leu-288, Ile-289, and Tyr-292 formed a hydrophobic cluster around the active site. The results of the site-directed mutagenesis experiments suggested that the hydrophobic cluster plays critical roles in protein folding, l-Trp recognition, and catalysis. Our results provide critical information for further characterization and engineering of this enzyme.

IMPORTANCE

In this study, we determined the three-dimensional structure of l-Trp dehydrogenase, analyzed its various site-directed substitution mutants at residues located in the active site, and obtained the following informative results. Several residues in the active site form a hydrophobic cluster, which may be a part of the hydrophobic core essential for protein folding. To our knowledge, there is no previous report demonstrating that a hydrophobic cluster in the active site of any l-amino acid dehydrogenase may have a critical impact on protein folding. Furthermore, our results suggest that this hydrophobic cluster could strictly accommodate l-Trp. These studies show the structural characteristics of l-Trp dehydrogenase and hence would facilitate novel applications of l-Trp dehydrogenase.

The Measurement of Ammonia in Human Breath and its Potential in Clinical Diagnostics

Ammonia is an important component of metabolism and is involved in many physiological processes. During normal physiology, levels of blood ammonia are between 11 and 50 µM. Elevated blood ammonia levels are associated with a variety of pathological conditions such as liver and kidney dysfunction, Reye's syndrome and a variety of inborn errors of metabolism including urea cycle disorders (UCD), organic acidaemias and hyperinsulinism/hyperammonaemia syndrome in which ammonia may reach levels in excess of 1 mM. It is highly neurotoxic and so effective measurement is critical for assessing and monitoring disease severity and treatment. Ammonia is also a potential biomarker in exercise physiology and studies of drug metabolism. Current ammonia testing is based on blood sampling, which is inconvenient and can be subject to significant analytical errors due to the quality of the sample draw, its handling and preparation for analysis. Blood ammonia is in gaseous equilibrium with the lungs. Recent research has demonstrated the potential use of breath ammonia as a non-invasive means of measuring systemic ammonia. This requires measurement of ammonia in real breath samples with associated temperature, humidity and gas characteristics at concentrations between 50 and several thousand parts per billion. This review explores the diagnostic applications of ammonia measurement and the impact that the move from blood to breath analysis could have on how these processes and diseases are studied and managed.

Elevated baseline serum glutamate as a pharmacometabolomic biomarker for acamprosate treatment outcome in alcohol-dependent subjects

Acamprosate has been widely used since the Food and Drug Administration approved the medication for treatment of alcohol use disorders (AUDs) in 2004. Although the detailed molecular mechanism of acamprosate remains unclear, it has been largely known that acamprosate inhibits glutamate action in the brain. However, AUD is a complex and heterogeneous disorder. Thus, biomarkers are required to prescribe this medication to patients who will have the highest likelihood of responding positively. To identify pharmacometabolomic biomarkers of acamprosate response, we utilized serum samples from 120 alcohol-dependent subjects, including 71 responders (maintained continuous abstinence) and 49 non-responders (any alcohol use) during 12 weeks of acamprosate treatment. Notably, baseline serum glutamate levels were significantly higher in responders compared with non-responders. Importantly, serum glutamate levels of responders are normalized after acamprosate treatment, whereas there was no significant glutamate change in non-responders. Subsequent functional studies in animal models revealed that, in the absence of alcohol, acamprosate activates glutamine synthetase, which synthesizes glutamine from glutamate and ammonia. These results suggest that acamprosate reduces serum glutamate levels for those who have elevated baseline serum glutamate levels among responders. Taken together, our findings demonstrate that elevated baseline serum glutamate levels are a potential biomarker associated with positive acamprosate response, which is an important step towards development of a personalized approach to treatment for AUD.

Biochemical characterization of an L-tryptophan dehydrogenase from the photoautotrophic cyanobacterium Nostoc punctiforme

An NAD(+)-dependent l-tryptophan dehydrogenase from Nostoc punctiforme NIES-2108 (NpTrpDH) was cloned and overexpressed in Escherichia coli. The recombinant NpTrpDH with a C-terminal His6-tag was purified to homogeneity using a Ni-NTA agarose column, and was found to be a homodimer with a molecular mass of 76.1kDa. The enzyme required NAD(+) and NADH as cofactors for oxidative deamination and reductive amination, respectively, but not NADP(+) or NADPH. l-Trp was the preferred substrate for deamination, though l-Phe was deaminated at a much lower rate. The enzyme exclusively aminated 3-indolepyruvate; phenylpyruvate was inert. The pH optima for the deamination of l-Trp and amination of 3-indolpyruvate were 11.0 and 7.5, respectively. For deamination of l-Trp, maximum enzymatic activity was observed at 45°C. NpTrpDH retained more than 80% of its activity after incubation for 30min at pHs ranging from 5.0 to 11.5 or incubation for 10min at temperatures up to 40°C. Unlike l-Trp dehydrogenases from higher plants, NpTrpDH activity was not activated by metal ions. Typical Michaelis-Menten kinetics were observed for NAD(+) and l-Trp for oxidative deamination, but with reductive amination there was marked substrate inhibition by 3-indolepyruvate. NMR analysis of the hydrogen transfer from the C4 position of the nicotinamide moiety of NADH showed that NpTrpDH has a pro-S (B-type) stereospecificity similar to the Glu/Leu/Phe/Val dehydrogenase family.

Intelligent data analysis for the diagnosis of alcohol dependence syndrome

Alcohol dependence syndrome is hard to diagnose because none of the existing laboratory markers alone has sufficient specificity and sensitivity. This study investigated whether combinations of markers would improve the identification of patients with alcohol dependence syndrome. Intelligent data analysis was carried out using the decision tree induction method with training and test data from 244 healthy volunteers and 238 patients with alcohol dependence syndrome. The results showed that a combination of two or three laboratory markers can identify alcohol dependence syndrome with almost 85% accuracy. It must be noted that induced decision trees offer a qualitatively different diagnostic evaluation of laboratory findings that varies from common practice, because they set up their own new borders and criteria that are different to generally accepted or set reference values. Tests for all of the selected laboratory markers are widely available, inexpensive to perform and usually form part of a routine laboratory examination.

Psoriasis and unreported excessive alcohol intake--a simple screening approach

Psoriasis is a chronic immune-mediated skin disease of complex aetiology. Alcohol overuse has long been suspected to contribute to psoriasis pathology, and the knowledge of individual's drinking pattern may be of substantial importance for managing the disease. Unfortunately, a number of patients fail to admit to their true alcohol consumption and there is no single sign, symptom or laboratory parameter adequate for alcohol abuse diagnosis. However, there are some laboratory findings that, when present, should raise physician's suspicion that alcohol may be a problem. The aim of this article was to present simple, widely available and relatively reliable laboratory markers that might effectively assist physicians in establishing patient's drinking status. A possible screening approach is illustrated by two distinct reports of psoriatic patients who initially concealed having the problem with alcohol.

Glycoconjugates in the detection of alcohol abuse

Up to 30% of all hospital admissions and health-care costs may be attributable to alcohol abuse. Ethanol, its oxidative metabolites, acetaldehyde and ROS (reactive oxygen species), non-oxidative metabolites of alcohol [e.g. FAEEs (fatty acid ethyl esters)] and the ethanol-water competition mechanism are all involved in the deregulation of glycoconjugate (glycoprotein, glycolipid and proteoglycan) metabolic processes including biosynthesis, modification, transport, secretion, elimination and catabolism. An increasing number of new alcohol biomarkers that are the result of alcohol-induced glycoconjugate metabolic errors have appeared in the literature. Glycoconjugate-related alcohol markers are involved in, or are a product of, altered glycoconjugate metabolism, e.g. CDT (carbohydrate-deficient transferrin), SA (sialic acid), plasma SIJ (SA index of apolipoprotein J), CETP (cholesteryl ester transfer protein), β-HEX (β-hexosaminidase), dolichol, EtG (ethyl glucuronide) etc. Laboratory tests based on changes in glycoconjugate metabolism are useful in settings where the co-operativeness of the patient is impaired (e.g. driving while intoxicated) or when a history of alcohol use is not available (e.g. after trauma). In clinical practice, glycoconjugate markers of alcohol use/abuse let us distinguish alcoholic from non-alcoholic tissue damage, having important implications for the treatment and management of diseases.