Carnitine deficiency: a possible risk factor in paracetamol hepatotoxicity

Experimental Models for Studying Structural and Functional State of the Pathological Liver (Review)

Liver pathologies remain one of the leading causes of mortality worldwide. Despite a high prevalence of liver diseases, the possibilities of diagnosing, prognosing, and treating non-alcoholic and alcoholic liver diseases still have a number of limitations and require the development of new methods and approaches. In laboratory studies, various models are used to reconstitute the pathological conditions of the liver, including cell cultures, spheroids, organoids, microfluidic systems, tissue slices. We reviewed the most commonly used in vivo, in vitro, and ex vivo models for studying non-alcoholic fatty liver disease and alcoholic liver disease, toxic liver injury, and fibrosis, described their advantages, limitations, and prospects for use. Great emphasis was placed on the mechanisms of development of pathological conditions in each model, as well as the assessment of the possibility of reconstructing various key aspects of pathogenesis for all these pathologies. There is currently no consensus on the choice of the most adequate model for studying liver pathology. The choice of a certain effective research model is determined by the specific purpose and objectives of the experiment.

Functional differences between l- and d-carnitine in metabolic regulation evaluated using a low-carnitine Nile tilapia model

l-Carnitine is essential for mitochondrial β-oxidation and has been used as a lipid-lowering feed additive in humans and farmed animals. d-Carnitine is an optical isomer of l-carnitine and dl-carnitine has been widely used in animal feeds. However, the functional differences between l- and d-carnitine are difficult to study because of the endogenous l-carnitine background. In the present study, we developed a low-carnitine Nile tilapia model by treating fish with a carnitine synthesis inhibitor, and used this model to investigate the functional differences between l- and d-carnitine in nutrient metabolism in fish. l- or d-carnitine (0·4 g/kg diet) was fed to the low-carnitine tilapia for 6 weeks. l-Carnitine feeding increased the acyl-carnitine concentration from 3522 to 10 822 ng/g and alleviated the lipid deposition from 15·89 to 11·97 % in the liver of low-carnitine tilapia. However, as compared with l-carnitine group, d-carnitine feeding reduced the acyl-carnitine concentration from 10 822 to 5482 ng/g, and increased lipid deposition from 11·97 to 20·21 % and the mRNA expression of the genes involved in β-oxidation and detoxification in the liver. d-Carnitine feeding also induced hepatic inflammation, oxidative stress and apoptosis. A metabolomic investigation further showed that d-carnitine feeding increased glycolysis, protein metabolism and activity of the tricarboxylic acid cycle and oxidative phosphorylation. Thus, l-carnitine can be physiologically utilised in fish, whereas d-carnitine is metabolised as a xenobiotic and induces lipotoxicity. d-Carnitine-fed fish demonstrates increases in peroxisomal β-oxidation, glycolysis and amino acid degradation to maintain energy homeostasis. Therefore, d-carnitine is not recommended for use in farmed animals.

The effects of colostrum on some biochemical parameters in the experimental intoxication of rats with paracetamol

In the current study, the possible prophylactic and therapeutic effects of colostrum (COL) on acute organ injury caused by paracetamol (PAR) in rats were evaluated. Within the scope of this study, a 2-month-old male (150-200 g) 70 Wistar Albino rat was used and a total of seven groups were designed. The first group (CNT) was maintained for control purposes. The second group (COL-1) was given COL for 1 day, at a dose of 500 mg/kg at 6-h intervals, and blood and tissue sampling was performed at 24 h. The third group (COL-7) received COL for 7 days, at a dose of 500 mg/kg at 6-h intervals on day 1 and at a daily dose of 500 mg/kg on the following days, and blood and tissue samples were taken at the end of seventh day. The fourth group (PAR-1) was administered with PAR at a dose of 1.0 g/kg bw and was blood and tissue sampled at 24 h. The fifth group (PAR-7) received PAR at a dose of 1.0 g/kg bw on day 1 and was blood and tissue was removed at the end of day 7. The sixth group (PAR+COL-1) was administered with a combination of PAR (1 g/kg bw) and COL (500 mg/kg at 6-h intervals), and blood and tissue samples were collected at 24 h. The seventh group (PAR+COL-7) received 1.0 g/kg bw of PAR on day 1 and was given COL throughout the 7-day study period (at a dose of 500 mg/kg at 6-h intervals on day 1 and at a daily dose of 500 mg/kg on the following days). In the seventh group, blood and tissue samples were taken at the end of seventh day. Alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), glucose, creatinine, triglyceride, total bilirubin, total protein and albumin levels/activities were analysed in the serum samples. The malondialdehyde (MDA), nitric oxide (NO), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) levels/activities, known as oxidative stress parameters, were assayed for tissue homogenates and blood (erythrocytes/plasma); in addition, enzyme activities of GSH S-transferase (GST), cytochrome P4502E1 (CYP2E1), NADH-cytochrome b5 reductase (CYTB5), glucose-6-phosphate dehydrogenase (G6PD), NADPH-cytochrome P450 C reductase (CYTC) and glutathione (GSH) levels/activities defined as drug metabolising parameters were measured in liver homogenates. In result, it was determined that PAR caused significant alterations in some biochemical and lipid peroxidation parameters and the activities/levels of drug metabolising parameters in the liver and that COL normalised some of these parameters and reduced PAR-induced tissue damage.

Paracetamol: overdose-induced oxidative stress toxicity, metabolism, and protective effects of various compounds in vivo and in vitro

Paracetamol (APAP) is one of the most widely used and popular over-the-counter analgesic and antipyretic drugs in the world when used at therapeutic doses. APAP overdose can cause severe liver injury, liver necrosis and kidney damage in human beings and animals. Many studies indicate that oxidative stress is involved in the various toxicities associated with APAP, and various antioxidants were evaluated to investigate their protective roles against APAP-induced liver and kidney toxicities. To date, almost no review has addressed the APAP toxicity in relation to oxidative stress. This review updates the research conducted over the past decades into the production of reactive oxygen species (ROS), reactive nitrogen species (RNS), and oxidative stress as a result of APAP treatments, and ultimately their correlation with the toxicity and metabolism of APAP. The metabolism of APAP involves various CYP450 enzymes, through which oxidative stress might occur, and such metabolic factors are reviewed within. The therapeutics of a variety of compounds against APAP-induced organ damage based on their anti-oxidative effects is also discussed, in order to further understand the role of oxidative stress in APAP-induced toxicity. This review will throw new light on the critical roles of oxidative stress in APAP-induced toxicity, as well as on the contradictions and blind spots that still exist in the understanding of APAP toxicity, the cellular effects in terms of organ injury and cell signaling pathways, and finally strategies to help remedy such against oxidative damage.

Mechanistic Modelling of Drug-Induced Liver Injury: Investigating the Role of Innate Immune Responses

Drug-induced liver injury (DILI) remains an adverse event of significant concern for drug development and marketed drugs, and the field would benefit from better tools to identify liver liabilities early in development and/or to mitigate potential DILI risk in otherwise promising drugs. DILIsym software takes a quantitative systems toxicology approach to represent DILI in pre-clinical species and in humans for the mechanistic investigation of liver toxicity. In addition to multiple intrinsic mechanisms of hepatocyte toxicity (ie, oxidative stress, bile acid accumulation, mitochondrial dysfunction), DILIsym includes the interaction between hepatocytes and cells of the innate immune response in the amplification of liver injury and in liver regeneration. The representation of innate immune responses, detailed here, consolidates much of the available data on the innate immune response in DILI within a single framework and affords the opportunity to systematically investigate the contribution of the innate response to DILI.

Acute liver failure in a term neonate after repeated paracetamol administration

Objective:

Severe hepatotoxicity caused by paracetamol is rare in neonates. We report a case of paracetamol-induced acute liver failure in a term neonate.

Case description:

A 26-day-old boy was admitted with intestinal bleeding, shock signs, slight liver enlargement, coagulopathy, metabolic acidosis (pH=7.21; bicarbonate: 7.1mEq/L), hypoglycemia (18mg/dL), increased serum aminotransferase activity (AST=4,039IU/L; ALT=1,087IU/L) and hyperbilirubinemia (total: 9.57mg/dL; direct: 6.18mg/dL) after receiving oral paracetamol (10mg/kg/dose every 4 hours) for three consecutive days (total dose around 180mg/kg; serum concentration 36-48 hours after the last dose of 77µg/ mL). Apart from supportive measures, the patient was successfully treated with intravenous N-acetylcysteine infusion during 11 consecutive days, and was discharged on day 34. The follow-up revealed full recovery of clinical and of laboratory findings of hepatic function.

Comments:

The paracetamol pharmacokinetics and pharmacodynamics in neonates and infants differ substantially from those in older children and adults. Despite the reduced rates of metabolism by the P-450 CYP2E1 enzyme system and the increased ability to synthesize glutathione - which provides greater resistance after overdoses -, it is possible to produce hepatotoxic metabolites (N-acetyl-p-benzoquinone) that cause hepatocellular damage, if glutathione sources are depleted. Paracetamol clearance is reduced and the half-life of elimination is prolonged. Therefore, a particular dosing regimen should be followed due to the toxicity risk of cumulative doses. This report highlights the risk for severe hepatotoxicity in neonates after paracetamol multiple doses for more than two to three days.

In HepG2 cells, coexisting carnitine deficiency masks important indicators of marginal biotin deficiency

BACKGROUND

A large number of birth defects are related to nutrient deficiencies; concern that biotin deficiency is teratogenic in humans is reasonable. Surprisingly, studies indicate that increased urinary 3-hydroxyisovalerylcarnitine (3HIAc), a previously validated marker of biotin deficiency, is not a valid biomarker in pregnancy.

OBJECTIVE

In this study we hypothesized that coexisting carnitine deficiency can prevent the increase in 3HIAc due to biotin deficiency.

METHODS

We used a 2-factor nutrient depletion design to induce isolated and combined biotin and carnitine deficiency in HepG2 cells and then repleted cells with carnitine. To elucidate the metabolic pathogenesis, we quantitated intracellular and extracellular free carnitine, acylcarnitines, and acylcarnitine ratios using liquid chromatography-tandem mass spectrometry.

RESULTS

Relative to biotin-sufficient, carnitine-sufficient cells, intracellular acetylcarnitine increased by 90%, propionylcarnitine more than doubled, and 3HIAc increased by >10-fold in biotin-deficient, carnitine-sufficient (BDCS) cells, consistent with a defensive mechanism in which biotin-deficient cells transesterify the acyl-coenzyme A (acyl-CoA) substrates of the biotin-dependent carboxylases to the related acylcarnitines. Likewise, in BDCS cells, the ratio of acetylcarnitine to malonylcarnitine and the ratio of propionylcarnitine to methylmalonylcarnitine both more than tripled, and the ratio of 3HIAc to 3-methylglutarylcarnitine (MGc) increased by >10-fold. In biotin-deficient, carnitine-deficient (BDCD) cells, the 3 substrate-derived acylcarnitines changed little, but the substrate:product ratios were masked to a lesser extent. Moreover, carnitine repletion unmasked biotin deficiency in BDCD cells as shown by increases in acetylcarnitine, propionylcarnitine, and 3HIAc (each increased by >50-fold). Likewise, ratios of acetylcarnitine:malonylcarnitine, propionylcarnitine:methylmalonylcarnitine, and 3HIAc:MGc all increased by >8-fold.

CONCLUSIONS

Our findings provide strong evidence that coexisting carnitine deficiency masks some indicators of biotin deficiency and support the potential importance of the ratios of acylcarnitines arising from the acyl-CoA substrates and products for biotin-dependent carboxylases in detecting the biotin deficiency that is masked by coexisting carnitine deficiency.

Serum carnitine level and its associated factors in patients with chronic viral hepatitis

ABSTRACT: 

Aim: Serum carnitine level and its associated factors have been evaluated in patients with chronic viral hepatitis. Methods: Patients with confirmed chronic viral hepatitis based on the serological markers and liver biopsy were included. In total, 86 volunteers and 86 patients with chronic viral hepatitis completed the study. Demographic data, type of treatment regimen and nutritional status of the patients were recorded and one blood sample was collected from each patient after an overnight fasting. A double antibody sandwich ELISA kit was used to measure carnitine serum level. Results: Mean ± standard deviation of serum carnitine level in the case and control groups were 34.3 ± 15.3 and 55.7 ± 28.4 μmol/l, respectively (p = 0.001). Regarding carnitine deficiency definition, 64 out of 86 patients (74.4%) and 21 out of 86 (24.5%) healthy individuals suffered from carnitine deficiency (p < 0.001). Carnitine dietary intake was significantly lower (p < 0.001). Compared with patients with chronic hepatitis C infection, a more severe form of carnitine deficiency was detected in patients with chronic hepatitis B infection (18.39 ± 15.68 μmol/l vs 42.30 ± 32.92 μmol/l; p = 0.03). In addition, serum carnitine level (41.1 ± 14.8 μmol/l) was significantly higher in the cirrhotic than noncirrhotic patients (31.60 ± 13.2 μmol/l; p = 0.04). Conclusion: Although the cirrhotic patients had higher serum carnitine level compared with noncirrhotic patients, serum carnitine level in the patients with chronic hepatitis was significantly lower than the healthy individuals. Also compared with the defined cut-off point for normal carnitine serum level, carnitine deficiency was common in Iranian patients with chronic hepatitis.

Acylcarnitine profiles in acetaminophen toxicity in the mouse: comparison to toxicity, metabolism and hepatocyte regeneration

High doses of acetaminophen (APAP) result in hepatotoxicity that involves metabolic activation of the parent compound, covalent binding of the reactive intermediate N-acetyl-p-benzoquinone imine (NAPQI) to liver proteins, and depletion of hepatic glutathione. Impaired fatty acid β-oxidation has been implicated in previous studies of APAP-induced hepatotoxicity. To better understand relationships between toxicity and fatty acid β-oxidation in the liver in APAP toxicity, metabolomic assays for long chain acylcarnitines were examined in relationship to established markers of liver toxicity, oxidative metabolism, and liver regeneration in a time course study in mice. Male B6C3F1 mice were treated with APAP (200 mg/kg IP) or saline and sacrificed at 1, 2, 4, 8, 24 or 48 h after APAP. At 1 h, hepatic glutathione was depleted and APAP protein adducts were markedly increased. Alanine aminotransferase (ALT) levels were elevated at 4 and 8 h, while proliferating cell nuclear antigen (PCNA) expression, indicative of hepatocyte regeneration, was apparent at 24 h and 48 h. Elevations of palmitoyl, oleoyl and myristoyl carnitine were apparent by 2–4 h, concurrent with the onset of Oil Red O staining in liver sections. By 8 h, acylcarnitine levels were below baseline levels and remained low at 24 and 48 h. A partial least squares (PLS) model suggested a direct association of acylcarnitine accumulation in serum to APAP protein adduct and hepatic glutathione levels in mice. Overall, the kinetics of serum acylcarnitines in APAP toxicity in mice followed a biphasic pattern involving early elevation after the metabolism phases of toxicity and later depletion of acylcarnitines.

Acetyl-L-carnitine ameliorates caerulein-induced acute pancreatitis in rats

In the present study, we have addressed the possible protective role of acetyl-L-carnitine in caerulein-induced acute pancreatitis in male Swiss albino rats. Acute pancreatitis paradigm was developed by challenging animals with a supramaximal dose of caerulein (20 microg/kg, SC) four times at hourly intervals. Caerulein induced acute pancreatitis that was well-characterized morphologically and biochemically. Severe oedema with marked increased relative pancreatic weight, marked atrophy of acini with increased interacinar spaces, vacuolization, and extensive leucocytic infiltration were diagnostic fingerprints of the pancreatitis phenotype. A biochemical test battery that confirmed the model comprised increased plasma amylase and lipase activities, calcium levels as well as increased pancreatic enzymatic myeloperoxidase and glutathione-S-transferase activities, beside increased pancreatic contents of nitric oxide and malondialdehyde and reduced pancreatic glutathione level. Prior administration of acetyl-L-carnitine (200 mg/kg, IP) for seven consecutive days ahead of caerulein challenge alleviated all the histological and biochemical manifestations of acute pancreatitis. These results suggest a possible protective role of the carnitine ester in such a murine acute pancreatitis model probably via regulation of the oxidant/antioxidant balance, beside modulation of the myeloperoxidase and nitric oxide systems, which are involved in the inflammatory cascade that most often associate the disease.

Carnitine deficiency aggravates carboplatin nephropathy through deterioration of energy status, oxidant/anti-oxidant balance, and inflammatory endocoids

We have recently shown that carnitine deficiency could represent a risk factor in paracetamol hepatotoxicity. By the same token, d-carnitine-induced carnitine deficiency aggravated carboplatin nephropathy following challenge with a single dose (35mg/kg, IP) of the platinum drug in male Swiss albino rats. The combination modality induced marked degenerative changes and severe inflammation in kidney tissues that surpassed either carboplatin or d-carnitine given alone. The combined regimen synergistically increased the serum levels of creatinine, blood urea nitrogen (BUN), tumor necrosis factor alpha (TNF-alpha), palmitate, and kidney malondialdehyde (MDA), adenosine triphosphate (ATP), nitric oxide (NO) contents as well as kidney myeloperoxidase (MPO) activity. The only parameter that has been notably decreased was the kidney reduced glutathione (GSH) level. Exaggeration by carnitine deficit of the deleterious effects of carboplatin is most probably ascribed to energy starvation. The reduction in kidney content of ATP parcels was associated with elevation of serum palmitate level that reflected debilitated fatty acid oxidation, and this further deteriorated energy resources in kidney tissues. Compromising the oxidant/anti-oxidant balance and modulating the release of some inflammatory endocoids namely, TNF-alpha and NO could also possibly account for such combinatorial detrimental toxicity. The current study was further extended to elucidate any possible nephroprotective effects of l-carnitine. Interestingly, carnitine supplementation ahead of carboplatin challenge ameliorated and almost normalized all the biochemical parameters and also mitigated the injurious effects of the cytotoxic drug. Thus, one could conclude that carnitine deficiency, whether being a causative clue or a sequela, might represent a risk factor in carboplatin nephropathy.