Changes in plasma amino acids during sobriety in alcoholic patients with and without liver disease

Plasma tryptophan and kynurenine pathway metabolites in abstinent patients with alcohol use disorder and high prevalence of psychiatric comorbidity

BACKGROUND

Alterations in tryptophan (TRP) metabolism has been linked to drug exposure and mental disorders. However, most of studies have been performed without considering the co-occurrence of both disorders in the context of addiction. This cross-sectional study examines TRP metabolism through the serotonin (5-HT) and kynurenine (KYN) pathways in subjects with alcohol use disorders (AUD) and high prevalence of psychiatric comorbidity.

METHODS

For this purpose, male and female abstinent AUD patients (N = 130) and healthy controls (N = 80) were clinically evaluated for substance use and mental disorders, and blood samples were collected to determine plasma concentrations of TRP, 5-HT, KYN and kynurenic acid (KA) using high performance liquid chromatography. Clinical and biochemical variables were analyzed for potential associations considering AUD, psychiatric comorbidity and sex.

RESULTS

TRP concentrations were significantly associated with an interaction effect between AUD diagnosis and sex (p < .01): TRP concentrations were lower in male AUD patients but higher in female AUD patients compared with their controls. KYN and KA concentrations were significantly associated with AUD diagnosis (p < .01 and p < .05, respectively). Thus, AUD patients showed significantly higher KYN concentrations and lower KA concentrations than controls. Regarding 5-HT concentrations, there were sex differences in the alcohol group (p < .05) and female AUD patients showed lower 5-HT concentrations than male AUD patients. Moreover, there was a significant interaction effect between psychiatric comorbidity and sex on TRP concentrations in the alcohol group (p < .01). Whereas male patients with both comorbid substance use and mental disorders showed lower TRP concentrations than male non-comorbid patients, female patients with comorbid mental disorders showed higher TRP concentrations than female non-comorbid patients.

CONCLUSION

While alterations in the KYN pathway appear to be directly associated with a history of AUD, altered TRP concentrations are associated with the presence of comorbid psychiatric disorders. Finally, sex differences in TRP metabolism must be considered in future studies.

Essential Amino Acid Supplement Lowers Intrahepatic Lipid despite Excess Alcohol Consumption

Excess alcohol consumption is a top risk factor for death and disability. Fatty liver will likely develop and the risk of liver disease increases. We have previously demonstrated that an essential amino acid supplement (EAAS) improved protein synthesis and reduced intrahepatic lipid in the elderly. The purpose of this exploratory pilot study was to initiate the evaluation of EAAS on intrahepatic lipid (IHL), body composition, and blood lipids in individuals with mild to moderate alcohol use disorder (AUD). Following consent, determination of eligibility, and medical screening, 25 participants (18 males at 38 ± 15 years/age and 7 females at 34 ± 18 years/age) were enrolled and randomly assigned to one of two dosages: a low dose (LD: 8 g of EAAS twice/day (BID)) or high dose (HD: 13 g of EAAS BID). Five of the twenty-five enrolled participants dropped out of the intervention. Both groups consumed the supplement BID for 4 weeks. Pre- and post-EAAS administration, IHL was determined using magnetic resonance imaging/spectroscopy, body composition was analyzed using dual-energy X-ray absorptiometry, and blood parameters were measured by LabCorp. T-tests were used for statistical analysis and considered significant at p < 0.05. While there was no significant change in IHL in the LD group, there was a significant 23% reduction in IHL in the HD group (p = 0.02). Fat mass, lean tissue mass, bone mineral content, and blood lipids were not altered. Post-EAAS phosphatidylethanol was elevated and remained unchanged in LD at 407 ± 141 ng/mL and HD at 429 ± 196 ng/mL, indicating chronic and excess alcohol consumption. The HD of the proprietary EAAS formulation consumed BID seemed to lower IHL in individuals with mild to moderate AUD. We suggest that further studies in a larger cohort be conducted to more completely address this important area of investigation.

Tryptophan metabolism in alcoholism

Acute and chronic alcohol (ethanol) intake and subsequent withdrawal exert major effects on tryptophan (Trp) metabolism and disposition in human subjects and experimental animals. In rats, activity of the rate-limiting enzyme of Trp degradation, liver Trp pyrrolase (TP), is enhanced by acute, but inhibited after chronic, ethanol administration, then enhanced during withdrawal. These changes lead to alterations in brain serotonin synthesis and turnover mediated by corresponding changes in circulating Trp availability to the brain. A low brain-serotonin concentration characterizes the alcohol-preferring C57BL/6J mouse strain and many alcohol-preferring rat lines. In this mouse strain, liver TP enhancement causes the serotonin decrease. In man, acute ethanol intake inhibits brain serotonin synthesis by activating liver TP. This may explain alcohol-induced depression, aggression and loss of control in susceptible individuals. Chronic alcohol intake in dependent subjects may be associated with liver TP inhibition and a consequent enhancement of brain serotonin synthesis, whereas subsequent withdrawal may induce the opposite effects. The excitotoxic Trp metabolite quinolinate may play a role in the behavioural disturbances of the alcohol-withdrawal syndrome. Some abstinent alcoholics may have a central serotonin deficiency, which they correct by liver TP inhibition through drinking. Further studies of the Trp and serotonin metabolic status in long-term abstinence in general and in relation to personality characteristics, alcoholism typology and genetic factors in particular may yield important information which should facilitate the development of more effective screening, and preventative and therapeutic strategies in this area of mental health.

Serotonin and alcohol intake, abuse, and dependence: clinical evidence

A large body of literature has emerged concerning the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake and the development of alcoholism. Despite the wealth of information, the functional significance of this neurotransmitter remains to be fully elucidated. This paper, part one of a two-part review, summarizes the available clinical research along two lines: the effects of alcohol on serotonergic functioning and the effects of pharmacological manipulation of serotonergic functioning on alcohol intake in normal (nonalcohol dependent) and alcohol-dependent individuals. It is concluded that considerable evidence exists to support the notion that some alcoholic individuals may have lowered central serotonin neurotransmission.

Nutrition and alcoholic liver disease

While the rate of malnutrition is relatively modest in alcoholic patients without alcoholic liver disease, the rate of malnutrition is virtually 100% in patients with alcoholic hepatitis and/or alcoholic cirrhosis. The reasons for malnutrition in the alcoholic hepatitis patient include various factors such as anorexia, poor diet, malabsorption, and altered metabolic state. When the patient is hospitalized, the malnutrition frequently worsens because of fasting for tests, continued anorexia, and complications such as gastrointestinal bleeding. Patients with severe acute hepatitis appear to be both hypermetabolic and hypercatabolic, whereas data are much more conflicting concerning patients with more stable liver disease. Most studies suggest that patients with alcoholic liver disease require at least 60 g of protein per day to maintain positive nitrogen balance. Consistent alterations in plasma amino acid profiles occur in alcoholic liver disease, and specialized nutritional formulations have been devised to correct this amino acid profile with the intent of improving overall nutritional status, hepatic encephalopathy, and mortality. The effects of nutritional support (including use of specialized products) on outcome, on acute hepatic encephalopathy, and on chronic or latent portal systemic encephalopathy are reviewed.

Alcoholic liver disease

Liver injury may develop in some people who consume alcohol. The pathogenesis of liver damage in such subjects remains obscure. Major histopathologic features of alcohol-associated liver injury include steatosis, steatonecrosis, and cirrhosis. The clinical manifestations of alcoholic liver disease are nonspecific and range from asymptomatic hepatomegaly to stigmata of portal hypertension with advanced parenchymal failure. The severity of the clinical presentation and the degree of aminotransferase elevation correlate poorly with the liver histopathology, particularly in patients who continue to drink alcohol. Short-term mortality of such patients is best predicted by a composite of clinical and laboratory parameters that are influenced by alcohol consumption as well as by liver disease. Long-term prognosis is determined by residual damage to vital organs (that is, whether or not cirrhosis has developed) and whether or not the patient continues to drink. Current therapy of alcoholic liver disease includes abstinence and correction of nutritional deficiencies. Other therapies are experimental and are best utilized in the setting of controlled clinical trials.

Blood cell superoxide dismutase and enolase activities as markers of alcoholic and nonalcoholic liver diseases

Monitoring of chronic alcoholism would be facilitated by using sensitive biochemical markers in blood cells, mainly to detect differences between alcoholic subjects with or without liver injury. We propose two types of markers: the first one is superoxide dismutase (SOD) activity involved in the conversion of superoxide radicals (O2-.) formed during acetaldehyde oxidation by xanthine oxidase after chronic alcohol consumption; the second one is enolase activity with both isoenzyme forms: nonneuronal enolase (NNE) and neuron specific enolase (NSE) which has been shown to be modified in many injuries related to the glycolytic pathways. For SOD activity we found a significant increase in alcoholic patients with liver injury and mainly in cirrhotic patients with ascitis. Both enolase activities were also found to be significantly increased in alcoholic patients with liver injury but NNE activity was also increased in alcoholics without apparent liver disease. Our results suggest that increased activity of SOD and NSE in blood cells may be related to liver injury mainly in alcoholism while increased NNE activity may also be a marker of alcohol abuse without liver injury.

Pyridoxine deficiency and ethanol-induced liver injury

It has been suggested that pyridoxine deficiency may potentiate ethanol-induced liver injury. Our purpose was to clarify the effect of pyridoxine deficiency on ethanol-associated liver injury by comparing liver histology, serum liver enzymes, and the viability of cultured hepatocytes from pyridoxine-deficient and pyridoxine-sufficient rats that had been chronically fed ethanol-enriched diets. Our data fail to substantiate that pyridoxine-deficient animals are more susceptible to the hepatotoxic effects of ethanol than pair-fed pyridoxine-sufficient controls. Furthermore, the addition of pyridoxine to hepatocyte cultures fails to prevent in vitro cytotoxicity of added ethanol. Pyridoxine deficiency may augment ethanol-induced enhancement of hepatic urea synthesis. These data suggest that pyridoxine deficiency may contribute to the abnormal plasma amino acid profiles and nitrogen balance of chronic alcoholics, but that it does not potentiate ethanol-induced liver injury.