Decreased carnitine biosynthesis in rats with secondary biliary cirrhosis

A New Murine Liver Fibrosis Model Induced by Polyhexamethylene Guanidine-Phosphate

Liver fibrosis is part of the wound healing process to help the liver recover from the injuries caused by various liver-damaging insults. However, liver fibrosis often progresses to life-threatening cirrhosis and hepatocellular carcinoma. To overcome the limitations of current in vivo liver fibrosis models for studying the pathophysiology of liver fibrosis and establishing effective treatment strategies, we developed a new mouse model of liver fibrosis using polyhexamethylene guanidine phosphate (PHMG-p), a humidifier sterilizer known to induce lung fibrosis in humans. Male C57/BL6 mice were intraperitoneally injected with PHMG-p (0.03% and 0.1%) twice a week for 5 weeks. Subsequently, liver tissues were examined histologically and RNA-sequencing was performed to evaluate the expression of key genes and pathways affected by PHMG-p. PHMG-p injection resulted in body weight loss of ~15% and worsening of physical condition. Necropsy revealed diffuse fibrotic lesions in the liver with no effect on the lungs. Histology, collagen staining, immunohistochemistry for smooth muscle actin and collagen, and polymerase chain reaction analysis of fibrotic genes revealed that PHMG-p induced liver fibrosis in the peri-central, peri-portal, and capsule regions. RNA-sequencing revealed that PHMG-p affected several pathways associated with human liver fibrosis, especially with upregulation of lumican and IRAK3, and downregulation of GSTp1 and GSTp2, which are closely involved in liver fibrosis pathogenesis. Collectively we demonstrated that the PHMG-p-induced liver fibrosis model can be employed to study human liver fibrosis.

Untargeted liquid chromatography-mass spectrometry metabolomics to assess drug-induced cholestatic features in HepaRG® cells

Cholestasis is a liver disease associated with retention of bile in the liver, which leads to local hepatic inflammation and severe liver damage. In order to investigate the mode of action of drug-induced cholestasis, in vitro models have shown to be able to recapitulate important elements of this disease. In this study, we applied untargeted metabolomics to investigate the metabolic perturbances in HepaRG® cells exposed for 24 h and 72 h to bosentan, a cholestatic reference toxicant. Intracellular profiles were extracted and analysed with liquid chromatography and accurate-mass spectrometry. Metabolites of interest were selected using partial least-squares discriminant analysis and random forest classifier models. The observed metabolic patterns associated with cholestasis in vitro were complex. Acute (24 h) exposure revealed metabolites related to apoptosis, such as ceramide and triglyceride accumulation, in combination with phosphatidylethanolamine, choline and carnitine depletion. Metabolomic alterations during exposure to lower dosages and a prolonged exposure (72 h) included carnitine upregulation and changes in the polyamine metabolism. These metabolites were linked to changes in phospholipid metabolism, mitochondrial pathways and energy homeostasis. The metabolic changes confirmed the mitotoxic effects of bosentan and revealed the potential involvement of phospholipid metabolism as part of the mode of action of drug-induced cholestasis.

L-carnitine prevents ammonia-induced cytotoxicity and disturbances in intracellular amino acid levels in human astrocytes

BACKGROUND AND AIM

L-carnitine (L-CA) has been used therapeutically to treat hepatic encephalopathy with hyperammonemia, but the mechanism by which L-CA contributes to ammonia detoxification in the brain is still unclear. Thus, the cytotoxicity and changes in intracellular amino acids (AAs) in astrocytes with hyperammonemia following L-CA administration were studied.

METHODS

Human astrocytes were treated with ammonium chloride (NH₄ Cl), L-CA or a mixture of NH₄ Cl, and L-CA under defined conditions. Total intracellular reactive oxygen species and lactate dehydrogenase leakage were measured following different treatment periods. The intracellular levels of AAs in astrocytes were determined using metabolomic analysis.

RESULTS

Intracellular total reactive oxygen species and lactate dehydrogenase leakage were significantly increased after treatment with NH₄ Cl. In contrast, co-treatment with L-CA significantly inhibited the cytotoxic effects of NH₄ Cl. The intracellular levels of almost all AAs involving glutamine and branched-chain AAs (BCAAs) were significantly increased in the NH₄ Cl-treated cells compared with in the control cells; these changes in BCAA levels were reduced with L-CA co-treatment. Additionally, the level of 3-methyl-2-oxovaleric acid, which is a metabolite from isoleucine and plays a critical role in neurological damage, was significantly increased in the NH₄ Cl-treated cells, but this metabolite was significantly decreased with L-CA co-treatment.

CONCLUSION

L-CA protects human astrocytes from ammonia-induced acute cytotoxic effects and the increased intracellular levels of glutamine and BCAAs.

Efficacy and safety of rifaximin in Japanese patients with hepatic encephalopathy: A phase II/III, multicenter, randomized, evaluator-blinded, active-controlled trial and a phase III, multicenter, open trial

AIM

The efficacy and safety of rifaximin in the treatment of hepatic encephalopathy (HE) are widely known, but they have not been confirmed in Japanese patients with HE. Thus, two prospective, randomized studies (a phase II/III study and a phase III study) were carried out.

METHODS

Subjects with grade I or II HE and hyperammonemia were enrolled. The phase II/III study, which was a randomized, evaluator-blinded, active-comparator, parallel-group study, was undertaken at 37 institutions in Japan. Treatment periods were 14 days. Eligible patients were randomized to the rifaximin group (1200 mg/day) or the lactitol group (18-36 g/day). The phase III study was carried out in the same patients previously enrolled in the phase II/III study, and they were all treated with rifaximin (1200 mg/day) for 10 weeks.

RESULTS

In the phase II/III study, 172 patients were enrolled. Blood ammonia (B-NH₃ ) concentration was significantly improved in the rifaximin group, but the difference between the two groups was not significant. The portal systemic encephalopathy index (PSE index), including HE grade, was significantly improved in both groups. In the phase III study, 87.3% of enrolled patients completed the treatment. The improved B-NH₃ concentration and PSE index were well maintained from the phase II/III study during the treatment period of the phase III study. Adverse drug reactions (ADRs) were seen in 13.4% of patients who received rifaximin, but there were no severe ADRs leading to death.

CONCLUSION

The efficacy of rifaximin is sufficient and treatment is well tolerated in Japanese patients with HE and hyperammonemia.

Impaired Exercise Performance and Skeletal Muscle Mitochondrial Function in Rats with Secondary Carnitine Deficiency

Purpose: The effects of carnitine depletion upon exercise performance and skeletal muscle mitochondrial function remain largely unexplored. We therefore investigated the effect of N-trimethyl-hydrazine-3-propionate (THP), a carnitine analog inhibiting carnitine biosynthesis and renal carnitine reabsorption, on physical performance and skeletal muscle mitochondrial function in rats.

Methods: Male Sprague Dawley rats were treated daily with water (control rats; n = 12) or with 20 mg/100 g body weight THP (n = 12) via oral gavage for 3 weeks. Following treatment, half of the animals of each group performed an exercise test until exhaustion.

Results: Distance covered and exercise performance were lower in THP-treated compared to control rats. In the oxidative soleus muscle, carnitine depletion caused atrophy (–24%) and impaired function of complex II and IV of the mitochondrial electron transport chain. The free radical leak (ROS production relative to oxygen consumption) was increased and the cellular glutathione pool decreased. Moreover, mRNA expression of markers of mitochondrial biogenesis and mitochondrial DNA were decreased in THP-treated compared to control rats. In comparison, in the glycolytic gastrocnemius muscle, carnitine depletion was associated with impaired function of complex IV and increased free radical leak, whilst muscle weight and cellular glutathione pool were maintained. Markers of mitochondrial proliferation and mitochondrial DNA were unaffected.

Conclusions: Carnitine deficiency is associated with impaired exercise capacity in rats treated with THP. THP-induced carnitine deficiency is associated with impaired function of the electron transport chain in oxidative and glycolytic muscle as well as with atrophy and decreased mitochondrial DNA in oxidative muscle.

Identification of the plasma metabolomics as early diagnostic markers between biliary atresia and neonatal hepatitis syndrome

Early detection is the most effective way to improve the clinical outcome of biliary atresia (BA). Emerging metabolomics provides a powerful platform for discovering novel biomarkers and biochemical pathways to improve early diagnosis. The aim of this study is to find the potential biomarkers to distinguish BA from neonatal hepatitis syndrome (NHS) by using a metabolomics method. We comprehensively analyzed the serum metabolites in a total of 124 blood samples from patients with BA or neonatal hepatitis syndrome (NHS) and from normal individuals using advanced metabolomic approaches, and found that the levels of glutarylcarnitine (C5DC) significantly increased in the BA group while the levels of threonine (Thr) significantly rose in the NHS group comparing with the other groups. The levels of glutamic acid (Glu) in the BA group were significantly elevated compared to those in the NHS group, but still lower than the hyperbilirubinemia and normal controls. The levels of propionyl carnitine (C3), isovaleryl carnitine (C5) and glutamine (Gln) were reduced in the BA group compared to those in the NHS group, but still higher than the hyperbilirubinemia and normal controls. This study demonstrates the possibility of metabolomics as non-invasive biomarkers for the early detection of BA and also provides new insight into pathophysiologic mechanisms for BA.

Effect of carnitine, acetyl-, and propionylcarnitine supplementation on the body carnitine pool, skeletal muscle composition, and physical performance in mice

PURPOSE

Pharmacokinetics and effects on skeletal muscle and physical performance of oral acetylcarnitine and propionylcarnitine are not well characterized. We therefore investigated the influence of oral acetylcarnitine, propionylcarnitine, and carnitine on body carnitine homeostasis, energy metabolism, and physical performance in mice and compared the findings to non-supplemented control animals.

METHODS

Mice were supplemented orally with 2 mmol/kg/day carnitine, acetylcarnitine, or propionylcarnitine for 4 weeks and studied either at rest or after exhaustive exercise.

RESULTS

In the supplemented groups, total plasma and urine carnitine concentrations were significantly higher than in the control group receiving no carnitine, whereas the skeletal muscle carnitine content remained unchanged. The supplemented acylcarnitines were hydrolyzed in intestine and liver and reached the systemic circulation as carnitine. Bioavailability of carnitine and acylcarnitines, determined as the urinary excretion of total carnitine, was in the range of 19 %. Skeletal muscle morphology, including fiber-type composition, was not affected, and oxygen consumption by soleus or gastrocnemius fibers was not different between the groups. Supplementation with carnitine or acylcarnitines had no significant impact on the running capacity, but was associated with lower plasma lactate levels and a higher glycogen content in white skeletal muscle after exhaustive exercise.

CONCLUSIONS

Oral supplementation of carnitine, acetylcarnitine, or propionylcarnitine in mice is associated with increased plasma and urine total carnitine concentrations, but does not affect the skeletal muscle carnitine content. Despite better preservation of skeletal muscle glycogen and lower plasma lactate levels, physical performance was not improved by carnitine or acylcarnitine supplementation.

Progression of diethylnitrosamine-induced hepatic carcinogenesis in carnitine-depleted rats

AIM: To investigate whether carnitine deficiency is a risk factor during the development of diethylnitrosamine (DENA)-induced hepatic carcinogenesis.

METHODS: A total of 60 male Wistar albino rats were divided into six groups with 10 animals in each group. Rats in group 1 (control group) received a single intraperitoneal (i.p.) injection of normal saline. Animals in group 2 (carnitine-supplemented group) were given L-carnitine (200 mg/kg per day) in drinking water for 8 wk. Animals in group 3 (carnitine-depleted group) were given D-carnitine (200 mg/kg per day) and mildronate (200 mg/kg per day) in drinking water for 8 wk. Rats in group 4 (DENA group) were injected with a single dose of DENA (200 mg/kg, i.p.) and 2 wk later received a single dose of carbon tetrachloride (2 mL/kg) by gavage as 1:1 dilution in corn oil. Animals in group 5 (DENA-carnitine depleted group) received the same treatment as group 3 and group 4. Rats in group 6 (DENA-carnitine supplemented group) received the same treatment as group 2 and group 4.

RESULTS: Administration of DENA resulted in a significant increase in alanine transaminase (ALT), gamma-glutamyl transferase (G-GT), alkaline phosphatase (ALP), total bilirubin, thiobarbituric acid reactive substances (TBARS) and total nitrate/nitrite (NOx) and a significant decrease in reduced glutathione (GSH), glutathione peroxidase (GSHPx), catalase (CAT) and total carnitine content in liver tissues. In the carnitine-depleted rat model, DENA induced a dramatic increase in serum ALT, G-GT, ALP and total bilirubin, as well as a progressive reduction in total carnitine content in liver tissues. Interestingly, L-carnitine supplementation resulted in a complete reversal of the increase in liver enzymes, TBARS and NOx, and a decrease in total carnitine, GSH, GSHPx, and CAT induced by DENA, compared with the control values. Histopathological examination of liver tissues confirmed the biochemical data, where L-carnitine prevented DENA-induced hepatic carcinogenesis while D-carnitine-mildronate aggravated DENA-induced hepatic damage.

CONCLUSION: Data from this study suggest for the first time that: (1) carnitine deficiency is a risk factor and should be viewed as a mechanism in DENA-induced hepatic carcinogenesis; (2) oxidative stress plays an important role but is not the only cause of DENA-induced hepatic carcinogenesis; and (3) long-term L-carnitine supplementation prevents the development of DENA-induced liver cancer.

Effect of carnitine deprivation on carnitine homeostasis and energy metabolism in mice with systemic carnitine deficiency

BACKGROUND/AIMS

Juvenile visceral steatosis (jvs-/-) mice lack the activity of the carnitine transporter OCTN2 and are dependent on carnitine substitution. The effects of carnitine deprivation on carnitine homeostasis and energy metabolism are not known in jvs-/- mice.

METHODS

jvs-/- mice were studied 3, 6 and 10 days after carnitine deprivation, and compared to jvs-/- mice substituted with carnitine, wild-type (jvs+/+) and jvs+/- mice. Carnitine concentrations were assessed radioenzymatically.

RESULTS

Compared to wild-type mice, carnitine-treated jvs-/- mice had decreased plasma beta-hydroxybutyrate levels and showed hepatic fat accumulation. The carnitine levels in plasma, liver and skeletal muscle were decreased by 58, 16 and 17%, respectively. After ten days of carnitine deprivation, the plasma carnitine concentration had fallen by 87% (to 2.3 mumol/l) and the tissue carnitine levels by approximately 50% compared to carnitine-treated jvs-/- mice. Carnitine deprivation was associated with a further drop in plasma beta-hydroxybutyrate and increased hepatic fat. Skeletal muscle glycogen stores decreased and lactate levels increased with carnitine deprivation, whereas tissue ATP levels were maintained.

CONCLUSIONS

In jvs-/- mice, tissue carnitine stores are more resistant than carnitine plasma concentrations to carnitine deprivation. Metabolic changes (liver steatosis and loss of muscle glycogen stores) appear also early after carnitine deprivation.

L-carnitine inhibits hepatocarcinogenesis via protection of mitochondria

Hepatocellular carcinoma is usually preceded by chronic inflammation. However, the molecular mechanism in hepatocarcinogenesis is not well known. Recently, we reported that mitochondrial dysfunction plays an important role in hepatocarcinogenesis via the production of free radicals. Furthermore, we proved that L-carnitine effectively protects mitochondrial function in vivo. Therefore, we investigated whether long-term administration of L-carnitine could prevent hepatitis and subsequent hepatocellular carcinoma in Long-Evans Cinnamon rats that are often analyzed as a model of hepatocarcinogenesis. The results indicated that oxidative stress elicited from abnormally accumulated copper increased the amount of free fatty acids, thereby inducing mitochondrial dysfunction, resulting in cell death and enhanced secondary generation of reactive oxygen species, which were significantly inhibited by carnitine treatment. Finally, the occurrence of placental glutathione S-transferase-positive foci as a marker for preneoplastic lesions and hepatocarcinogenesis were significantly inhibited by L-carnitine. These facts suggest that mitochondrial injury plays an essential role in the development of hepatocarcinogenesis and that the clinical use of carnitine has excellent therapeutic potential in individuals with chronic hepatitis.

Selective Na+/H+ exchange inhibition by cariporide reduces liver fibrosis in the rat

The aim of this study was to evaluate the effect of cariporide, a selective Na(+)/H(+) exchange inhibitor, on isolated and cultured hepatic stellate cells (HSCs) and in 2 in vivo models of rat liver fibrosis. Platelet-derived growth factor (PDGF)-induced HSC proliferation, evaluated by measuring the percentage of bromodeoxyuridine-positive cells, was significantly inhibited by cariporide, with a maximal effect at 10 micromol/L. Incubation with cariporide did not inhibit PDGF-induced extracellular-regulated kinase 1/2 (ERK1/2), Akt (a downstream component of the phosphatidylinositol [PI]-3 kinase pathway), and protein kinase C (PKC) activation but reduced PDGF-induced activation of the Na(+)/H(+) exchanger, with a maximal effect at 10 micromol/L. Rats treated with dimethylnitrosamine (DMN; 10 mg/kg) for 1 and 5 weeks received a diet with or without 6 ppm cariporide. Treatment with cariporide reduced the degree of liver injury, as determined by alanine aminotransferase (ALT) values, also when administered after the induction of hepatic damage. This was associated with reduced HSC activation and proliferation and reduced collagen deposition, as determined by morphometric evaluation of alpha-smooth muscle actin (SMA)/proliferating cell nuclear antigen-positive cells and percentage of Sirius red-positive parenchyma, respectively. Moreover, cariporide was also able to reduce alpha(1)I procollagen messenger RNA (mRNA) expression. Similar effects were observed in bile duct-ligated (BDL) rats. In conclusion, selective inhibition of the Na(+)/H(+) exchanger by cariporide may represent an effective therapeutic strategy in the treatment of hepatic fibrosis.

S-Adenosylmethionine revisited: its essential role in the regulation of liver function

Dietary methionine is mainly metabolized in the liver where it is converted into S-adenosylmethionine (AdoMet), the main biologic methyl donor. This reaction is catalyzed by methionine adenosyltransferase I/III (MAT I/III), the product of MAT1A gene, which is exclusively expressed in this organ. It was first observed that serum methionine levels were elevated in experimental models of liver damage and in liver cirrhosis in human beings. Results of further studies showed that this pathological alteration was due to reduced MAT1A gene expression and MAT I/III enzyme inactivation associated with liver injury. Synthesis of AdoMet is essential to all cells in the organism, but it is in the liver where most of the methylation reactions take place. The central role played by AdoMet in cellular function, together with the observation that AdoMet administration reduces liver damage caused by different agents and improves survival of alcohol-dependent patients with cirrhosis, led us to propose that alterations in methionine metabolism could play a role in the onset of liver disease and not just be a consequence of it. In the present work, we review the recent findings that support this hypothesis and highlight the mechanisms behind the hepatoprotective role of AdoMet.