Liver function in protein-energy malnutrition measured by cinnamic acid tolerance and benzoic acid tolerance: effect of carnitine supplementation

Rats with Long-Term Cholestasis Have a Decreased Cytosolic but Maintained Mitochondrial Hepatic CoA Pool

Previous studies showed that rats with long-term bile duct ligation have reduced coenzyme A stores per g of liver but maintained mitochondrial CoA stores. Based on these observations, we determined the CoA pool in the liver homogenate, liver mitochondria, and liver cytosol of rats with bile duct ligation for 4 weeks (BDL rats, n = 9) and sham-operated control rats (CON rats, n = 5). In addition, we tested the cytosolic and mitochondrial CoA pools by assessing the metabolism of sulfamethoxazole and benzoate in vivo and of palmitate in vitro. The hepatic total CoA content was lower in BDL than CON rats (mean ± SEM; 128 ± 5 vs. 210 ± 9 nmol/g), affecting all subfractions equally (free CoA (CoASH), short- and long-chain acyl-CoA). In BDL rats, the hepatic mitochondrial CoA pool was maintained, and the cytosolic pool was reduced (23.0 ± 0.9 vs. 84.6 ± 3.7 nmol/g liver; CoA subfractions were affected equally). The urinary excretion of hippurate after i.p. benzoate administration (measuring mitochondrial benzoate activation) was reduced in BDL rats (23.0 ± 0.9 vs. 48.6 ± 3.7% of dose/24 h), whereas the urinary elimination of N-acetylsulfamethoxazole after i.p. sulfamethoxazole administration (measuring the cytosolic acetyl-CoA pool) was maintained (36.6 ± 3.0 vs. 35.1 ± 2.5% of dose/24 h BDL vs. CON rats). Palmitate activation was impaired in the liver homogenate of BDL rats but the cytosolic CoASH concentration was not limiting. In conclusion, BDL rats have reduced hepatocellular cytosolic CoA stores, but this reduction does not limit sulfamethoxazole N-acetylation or palmitate activation. The hepatocellular mitochondrial CoA pool is maintained in BDL rats. Impaired hippurate formation in BDL rats is explained best by mitochondrial dysfunction.

Inhibition of mTOR improves malnutrition induced hepatic metabolic dysfunction

Severe malnutrition accounts for half-a-million deaths annually in children under the age of five. Despite improved WHO guidelines, inpatient mortality remains high and is associated with metabolic dysfunction. Previous studies suggest a correlation between hepatic metabolic dysfunction and impaired autophagy. We aimed to determine the role of mTORC1 inhibition in a murine model of malnutrition-induced hepatic dysfunction. Wild type weanling C57/B6 mice were fed a 18 or 1% protein diet for two weeks. A third low-protein group received daily rapamycin injections, an mTORC1 inhibitor. Hepatic metabolic function was assessed by histology, immunofluorescence, gene expression, metabolomics and protein levels. Low protein-fed mice manifested characteristics of severe malnutrition, including weight loss, hypoalbuminemia, hypoglycemia, hepatic steatosis and cholestasis. Low protein-fed mice had fewer mitochondria and showed signs of impaired mitochondrial function. Rapamycin prevented hepatic steatosis, restored ATP levels and fasted plasma glucose levels compared to untreated mice. This correlated with increased content of LC3-II, and decreased content mitochondrial damage marker, PINK1. We demonstrate that hepatic steatosis and disturbed mitochondrial function in a murine model of severe malnutrition can be partially prevented through inhibition of mTORC1. These findings suggest that stimulation of autophagy could be a novel approach to improve metabolic function in severely malnourished children.

Carnitine dynamics and their effects on hyperammonemia in cirrhotic Japanese patients

AIM

Supplementation with levocarnitine preparations has been reported to improve hepatic encephalopathy, but no detailed investigations have addressed the dynamics of carnitine or its supplementation indication in cirrhosis patients. We studied carnitine dynamics in cirrhotic patients by measuring serum and liver tissue carnitine levels and tested the effects of levocarnitine supplementation on concurrent hyperammonemia.

METHODS

In a pilot cohort of seven patients with liver cirrhosis and five patients without cirrhosis, the serum and liver carnitine concentrations were measured. Then the serum carnitine fractions were analyzed in 70 liver cirrhosis patients. Among them, a levocarnitine preparation (1800 mg/day) was supplemented orally for 3 months in 27 patients with refractory hyperammonemia, and the effects were evaluated.

RESULTS

A significant correlation was observed between serum and liver tissue carnitine concentrations (r = 0.69, P < 0.05). The serum total carnitine concentration was 68.4 ± 4.7 μmol/L, the free carnitine concentration was 53.2 ± 2.6 μmol/L, and the acylcarnitine concentration was 13.2 ± 1.1 μmol/L in 70 cirrhotic patients (reference values are 45-91, 36-74, 6-23 μmol/L, respectively). There was no correlation between blood ammonia and serum carnitine concentrations. The serum carnitine concentration rose with levocarnitine supplementation, reaching steady state after 1 month and, in parallel, refractory hyperammonemia was significantly improved. The cut-off level for a 20% decrease in blood ammonia was identified as 62.0 μmol/L total carnitine concentration by receiver-operating characteristic curve analysis, with an area under the curve of 0.69.

CONCLUSION

Serum carnitine concentrations were within standard levels in the majority of liver cirrhosis patients. In patients with concurrent hyperammonemia, the levocarnitine supplementation reduced blood ammonia levels.

Dietary Egg Yolk Supplementation Improves Low-Protein-Diet-Induced Fatty Liver in Rats

Egg yolk is an important source of nutrients and contains different bioactive substances. In the present study, we studied the benefits of egg yolk in preventing low-protein-diet-induced fatty liver in rats. Rats were fed the following diets, which were based on the AIN-76 formula, for 2 wk: an adequate-protein diet containing 20% casein (C), a low-protein diet containing 5% casein (LP-C), a low-protein diet supplemented with 12.5% egg yolk (LP-EY), and a low-protein diet supplemented with 4.1% egg yolk oil (LP-EYO). The low-protein diets were adjusted to contain 4.13% protein and 4.7% lipids. The LP-C diet resulted in a greater increase in the liver trigriceride (TG) and the vacuolation and a greater decrease in the serum TG and free fatty acid (FFA) than did the C diet. These deviations in the serum and liver TG, serum FFA levels and the liver histopathology were corrected in rats fed the LP-EY diet but not in those fed the LP-EYO diet. Compared to rats fed the LP-C diet, although the activities of lipogenesis-related enzymes (fatty acid synthase, glucose-6-phosphate dehydrogenase, and malic enzyme) decreased in rats fed both of the LP-EY and LP-EYO diets, the level of the microsomal TG transfer protein (MTP) increased only in rats fed the LP-EY diet. Collectively, these results suggest that dietary egg yolk supplementation decreases the LP diet-induced accumulation of TG in the liver by increasing transport of TG in the liver, and egg yolk oil alone is not sufficient enough to bring about these benefits.

L-carnitine supplementation to diet: a new tool in treatment of nonalcoholic steatohepatitis--a randomized and controlled clinical trial

OBJECTIVES

Nonalcoholic steatohepatitis (NASH) is a known metabolic disorder of the liver. No treatment has been conclusively shown to improve NASH or prevent disease progression. The function of L-carnitine to modulate lipid profile, glucose metabolism, oxidative stress, and inflammatory responses has been shown. The aim of this study was to evaluate the effects of L-carnitine's supplementation on regression of NASH.

METHODS

In patients with NASH and control subjects, we randomly dispensed one 1-g L-carnitine tablet after breakfast plus diet and one 1 g tablet after dinner plus diet for 24 weeks or diet alone at the same dosage and regimen. We evaluated liver enzymes, lipid profile, fasting plasma glucose, C-reactive protein (CRP), tumor necrosis factor (TNF)-alpha, homeostasis model assessment (HOMA)-IR, body mass index, and histological scores.

RESULTS

At the end of the study, L-carnitine-treated patients showed significant improvements in the following parameters: aspartate aminotransferase (P=0.000), alanine aminotransferase (ALT) (P=0.000), gamma-glutamyl-transpeptidase (gamma-GT) (P=0.000), total cholesterol (P=0.000), low-density lipoprotein (LDL) (P=0.000), high-density lipoprotein (HDL) (P=0.000), triglycerides (P=0.000), glucose (P=0.000), HOMA-IR (P=0.000), CRP (P=0.000), TNF-alpha (P=0.000), and histological scores (P=0.000).

CONCLUSIONS

L-carnitine supplementation to diet is useful for reducing TNF-alpha and CRP, and for improving liver function, glucose plasma level, lipid profile, HOMA-IR, and histological manifestations of NASH.

Failure of carnitine in improving hepatic nitrogen content in alcoholic and non-alcoholic malnourished rats

AIMS

To investigate the effect of carnitine supplementation on alcoholic malnourished rats' hepatic nitrogen content.

METHODS

Malnourished rats, on 50% protein-calorie restriction with free access to water (malnutrition group) and malnourished rats under the same conditions with free access to a 20% alcohol/water solution (alcohol group) were studied. After the undernourishment period (4 weeks with or without alcohol), both groups were randomly divided into two subgroups, one of them nutritionally recovered for 28 days with free access to a normal diet and water (recovery groups) and the other re-fed with free access to diet and water plus carnitine (0.1 g/g body weight/day by gavage) (carnitine groups). No alcohol intake was allowed during the recovery period.

RESULTS

The results showed: i) no difference between the alcohol/no alcohol groups, with or without carnitine, regarding body weight gain, diet consumption, urinary nitrogen excretion, plasma free fatty acids, lysine, methionine, and glycine. ii) Liver nitrogen content was highest in the carnitine recovery non-alcoholic group (from 1.7 to 3.3 g/100 g, P<0·05) and lowest in alcoholic animals (about 1.5 g/100g). iii) Hepatic fat content (~10 g/100 g, P>·05) was highest in the alcoholic animals.

CONCLUSION

Carnitine supplementation did not induce better nutritional recovery.

Parenteral nutrition related hepato-biliary disease in adults

Parenteral nutrition is a life-saving therapy in patients with intestinal failure. One of the major causes of morbidity and mortality in patients receiving long-term total parenteral nutrition (TPN) is liver disease. Early on, there is steatosis, which can evolve to steatohepatitis and eventually to cholestasis of varying severity. The etiology of parenteral nutrition related liver disease is multifactorial. Provision of excess calories in the TPN solution, along with lipids administered >1 g/kg are thought to increase the risk of parenteral nutrition related liver disease. Other factors such as nutrient deficiencies and nutrient toxicities may also play a role in the pathogenesis of liver disease, along with sepsis and the lack of enteral stimulation. Non-pharmacological management strategies for TPN-related liver disease include enteral stimulation, optimal TPN composition, and avoidance of excess carbohydrate and lipid calories. Pharmacological therapy with ursodeoxycholic acid and antibiotic therapy to reduce the risk of bacterial translocation and sepsis should be considered. Early referral for transplantation should be considered in patients with evidence of portal hypertension. This review focuses on the clinical aspects, pathogenesis, and management strategies of parenteral nutrition-related liver disease in adult patients.

Effects of L-acetylcarnitine on cirrhotic patients with hepatic coma: randomized double-blind, placebo-controlled trial

Multiple therapeutic modalities have been used to treat hepatic encephalopathy. L: -Acetylcarnitine (LAC) is a physiologically active substance that improves both the energetic and the neurotransmission profiles. LAC is able to cross the hematoencephalic barrier and reach the cerebral regions, where the acetylic group may be utilized. The aim of this work was to evaluate the efficacy of LAC in the treatment of hepatic coma in cirrhotic patients. Twenty-four suitably selected patients were enrolled in the study and, following randomization, received either LAC (n=13) or placebo (n=11). Statistically significant differences in neurological findings, as evaluated by the Glasgow Scale, as well as in ammonia serum levels and BUN were found following LAC treatment. In the placebo group we observed two cases of improved neurological findings as well as one case of improved EEG grading. In the other group we observed an improvement of neurological findings and of EEG grade in 10 and 8 subjects, respectively. Noteworthily, seven (54%) patients went from grade 4 down to grade 3, and one from grade 4 down to grade 1. The improvement in the neurological picture was evident at between 1 and 4 hr after the end of treatment, remaining until 24 hr after. No side effects were observed in our study series. Our study demonstrates that LAC administration improved neurological and biohumoral symptoms in selective cirrhotic patients with hepatic coma.

Carnitine depletion in rat pups from mothers given mildronate: a model of carnitine deficiency in late fetal and neonatal life

Mildronate (3-(2,2,2,-trimethylhydrazinium)propionate), is a butyrobetaine analogue that is known to inhibit gamma-butyrobetaine hydroxylase, the enzyme catalyzing the last step of carnitine biosynthesis. When administered to adult rats it determines a systemic carnitine deficiency and may therefore serve as an animal model for human carnitine depletion. The aim of this study was to evaluate the effect of mildronate administration to pregnant and lactating rats on tissue carnitine concentrations in 4- and 13-day-old rat pups. At 14 days of gestation female rats began to receive mildronate in the diet (200 mg/kg/d) and this continued for entire lactation period. Mildronate treatment determined a large reduction of carnitine levels in the milk of lactating dams. Because organ carnitine concentrations in neonatal rats are directly related to dietary supply, pups from mildronate group had significantly depleted levels of total carnitine in serum, heart, liver, muscle, brain and pancreas relative to controls, at 4 and 13 days of age. Correspondingly, an increase in triglyceride levels was observed in liver, heart and muscle of mildronate pups. This is in agreement with a reduction of basal rate of oxidation of [U-(14)C]-palmitate to (14)CO(2) and (14)C-acid-soluble products observed in liver homogenates from carnitine-deficient pups. All functional and biochemical modifications were compatible with a carnitine deficiency status. In conclusion our results describe a model of carnitine depletion in pups, suitable for the investigation of carnitine deficiency in fetal-neonatal nutrition, without any concomitant mildronate-mediated metabolic alterations.

Review article: breath testing for human liver function assessment

Carbon-labelled breath tests were proposed as tools for the evaluation of human liver function 30 years ago, but have never become part of clinical routine. One reason for this is the complex role of the liver in metabolic regulation, making it difficult to provide essential information for the management of patients with liver disease with a single test and to satisfy the hepatology community. As a result, a battery of breath tests have been developed. Depending on the test compound administered, different metabolic pathways (microsomal, cytosolic, mitochondrial) can be examined. Most available data come from microsomal function tests, whilst information about cytosolic and mitochondrial liver function is more limited. However, breath tests have shown promise in some studies, in particular to predict the outcome of patients with chronic liver disease or to monitor hepatic function after treatment. Whilst we await new substrates that can be used to measure liver function in a more valid manner, and large prospective studies to assess the usefulness of available test compounds, the aim of this review is to describe how far we have come in this controversial and unresolved issue.

Other disease associations with non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is usually seen in middle-aged women with obesity, non-insulin-dependent diabetes mellitus and/or hyperlipidaemia. NAFLD has also been associated with other conditions. Surgical procedures to treat obesity such as jejunoileal bypass and gastroplasty as well as massive small bowel resection have been associated with NAFLD. Mechanisms such as rapid weight loss, certain nutritional deficiencies and bacterial overgrowth have been proposed. Other nutritional conditions such as extreme malnutrition and total parenteral nutrition can also cause NASH. This can be due to abnormal glucose and fat metabolism, deficiencies like carnitine, essential fatty acid and choline or, in the case of parenteral nutrition, excess of calories, glucose or lipids. Several drugs have also been implicated as well as some inborn errors of metabolism and, more rarely, other diseases.

Relationship between hepatic mitochondrial functions in vivo and in vitro in rats with carbon tetrachloride-induced liver cirrhosis

BACKGROUND/AIMS

The metabolic capacity of liver mitochondria is impaired in rats with carbon tetrachloride (CCl4)-induced cirrhosis. These studies were performed to find out whether benzoate and/or palmitate are suitable substrates for assessing hepatic mitochondrial function in vivo.

METHODS

In vivo metabolism of benzoate and 1-14C-palmitate was assessed by monitoring urinary excretion of hippurate and exhalation of 14CO2, respectively, in cirrhotic and control rats (n=8 for each group). Isolation of liver mitochondria, and in vitro benzoate and palmitate metabolism were performed by methods published previously. The hepatic content of mitochondria was assessed by stereological analysis of the volume of hepatocytes and by biochemical determination, using the activity of citrate synthase.

RESULTS

Renal excretion of hippurate following i.p. administration of benzoate was reduced in cirrhotic rats (64+/-15 vs. 85+/-14% of administered dose over 24 h), and showed a linear correlation with hippurate formation by isolated mitochondria. The activities of benzoyl-CoA synthase and benzoyl-CoA:glycine N-acyltransferase were reduced by approximately 60%, and the coenzyme A content by 50% in hepatic mitochondria from cirrhotic rats, explaining impaired hippurate formation. Peak exhalation of 14CO2 after i.p. administration of 1-14C-palmitate was reduced by 44% and the area under the 14CO2 exhalation-time curve by 34% in cirrhotic rats. Peak 14CO2 exhalation revealed a linear correlation with oxidative metabolism of palmitoylcarnitine in isolated mitochondria. Both in vivo benzoate and palmitate metabolism showed a linear correlation with the volume fraction of hepatocytes. The mitochondrial protein content was reduced in cirrhotic rats per g liver and per liver but equal to control rats per volume of hepatocytes.

CONCLUSIONS

In vivo metabolism of both palmitate and benzoate reflects hepatic mitochondrial function in rats with CCl4-induced cirrhosis. Hepatic mitochondrial function is impaired in rats with CCl4-induced cirrhosis due to both reduced mitochondrial volume per liver and impaired metabolism of the remaining mitochondria. In contrast to rats with secondary biliary cirrhosis, rats with CCl4-induced cirrhosis showed no hepatic mitochondrial proliferation to counteract reduced mitochondrial function.

Carnitine metabolism in chronic liver disease

The liver is a central organ for carnitine metabolism and for the distribution of carnitine to the body. It is therefore not surprising that carnitine metabolism is impaired in patients and experimental animals with certain types of chronic liver disease. In this review, the changes in carnitine metabolism associated with chronic liver disease and the role of carnitine as a therapeutic agent in some of these conditions are discussed.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.