Association between 4-year all-cause mortality and carnitine profile in maintenance hemodialysis patients

Metabolic Biomarkers of Liver Failure in Cell Models and Patient Sera: Toward Liver Damage Evaluation In Vitro

Recent research has concentrated on the development of suitable in vitro cell models for the early identification of hepatotoxicity during drug development in order to reduce the number of animal models and to obtain a better predictability for hepatotoxic reactions in humans. The aim of the presented study was to identify translational biomarkers for acute liver injury in human patients that can serve as biomarkers for hepatocellular injury in vivo and in vitro in simple cell models. Therefore, 188 different metabolites from patients with acute-on-chronic liver failure before and after liver transplantation were analyzed with mass spectrometry. The identified potential metabolic biomarker set, including acylcarnitines, phosphatidylcholines and sphingomyelins, was used to screen primary and permanent hepatocyte culture models for their ability to model hepatotoxic responses caused by different drugs with known and unknown hepatotoxic potential. The results obtained suggest that simple in vitro cell models have the capability to display metabolic responses in biomarkers for liver cell damage in course of the treatment with different drugs and therefore can serve as a basis for in vitro models for metabolic analysis in drug toxicity testing. The identified metabolites should further be evaluated for their potential to serve as a metabolic biomarker set indicating hepatocellular injury in vitro as well as in vivo.

Fatty Acid β-Oxidation May Be Associated with the Erythropoietin Resistance Index in Stable Patients Undergoing Haemodialysis

BACKGROUND/OBJECTIVES

Lipid metabolism and adiponectin modulate erythropoiesis in vitro and in general population studies and may also affect responsiveness to erythropoietin in patients undergoing haemodialysis (HD). However, little is known about the impact of lipid-associated biomarkers on reticulocyte production and erythropoietin resistance index (ERI) in patients undergoing HD. Therefore, we aimed to investigate their impacts in 167 stable patients undergoing HD.

METHODS

Pre-dialysis blood samples were collected and analysed for reticulocyte counts and serum lipid profiles by routine analyses and serum carnitine profiles (C0-C18) by LC-MS/MS. ERI was calculated as erythropoietin dose/kg/week normalized for haemoglobin levels.

RESULTS

The independent positive determinants of reticulocyte count were log [Triglyceride (TG)] and logC18:1. A large proportion of longer-chain acylcarnitines was positively correlated with reticulocyte counts, possibly resulting from the accumulation of acylcarnitines in mitochondria undergoing fateful exocytosis from reticulocytes. These results indicate a possible association between reticulocyte formation and reduced β-oxidation, which occurs during the peripheral phase of erythroblast enucleation. Total cholesterol (TC) and log [C2/(C16 + C18:1)] as a putative marker of β-oxidation efficiency were negative independent determinants of ERI. Moreover, acyl chain length had a significantly positive impact on the correlation coefficients of individual acylcarnitines with ERI, suggesting that enhanced β-oxidation may be associated with reduced ERI. Finally, adiponectin had no independent association with reticulocyte counts or ERI despite its negative association with HDL-C levels.

CONCLUSIONS

Enhanced fatty acid β-oxidation and higher TC levels may be associated with lower ERI, whereas higher TG levels and longer acylcarnitines may be related to the latest production of reticulocytes in stable patients undergoing HD.

Abnormal carnitine metabolism in hemodialysis patients on different anticoagulants

INTRODUCTION

We aimed to determine whether unfractionated heparin (UH) and low molecular weight heparin (LH) contribute to aberrant carnitine metabolism in patients receiving hemodialysis.

METHODS

The rate of increase in serum free fatty acids (FFAs) and the ratio of acylcarnitine to free carnitine (AC/FC) from before to after hemodialysis were determined in patients receiving UH and LH. Additionally, the effect of switching patients to UH from LH was examined.

RESULTS

AC/FC was significantly higher in the UH group. In addition, serum FFAs in that group increased to 0.825 ± 0.270 after dialysis from 0.172 ± 0.160 before dialysis, showing a positive correlation with AC/FC. Furthermore, AC/FC was observed to be significantly higher in patients who were switched to UH from LH at 3 months after the change.

CONCLUSION

Compared with UH, LH has a lesser effect on lipid metabolism, suggesting that it also has a lesser effect on carnitine metabolism.

Plasma Cholesterol- and Body Fat-Lowering Effects of Chicken Protein Hydrolysate and Oil in High-Fat Fed Male Wistar Rats

Rest raw materials provide a new source of bioactive dietary ingredients, and this study aimed to determine the health effects of diets with chicken protein hydrolysate (CPH) and chicken oil (CO) generated from deboned chicken meat. Male Wistar rats (n = 56) were divided into seven groups in three predefined sub-experiments to study the effects of protein source (casein, chicken fillet, pork fillet, and CPH), the dose-effect of CPH (50% and 100% CPH), and the effects of combining CPH and CO. Rats were fed high-fat diets for 12 weeks, and casein and chicken fillet were used as controls in all sub-experiments. While casein, chicken-, or pork fillet diets resulted in similar weight gain and plasma lipid levels, the CPH diet reduced plasma total cholesterol. This effect was dose dependent and accompanied with the reduced hepatic activities of acetyl-CoA carboxylase and fatty acid synthase. Further, rats fed combined CPH and CO showed lower weight gain, and higher hepatic mitochondrial fatty acid oxidation, plasma L-carnitine, short-chain acylcarnitines, TMAO, and acetylcarnitine/palmitoylcarnitine. Thus, in male Wistar rats, CPH and CO lowered plasma cholesterol and increased hepatic fatty acid oxidation compared to whole protein diets, pointing to potential health-beneficial bioactive properties of these processed chicken rest raw materials.

Stereoselective effects of fungicide difenoconazole and its four stereoisomers on gut barrier, microbiota, and glucolipid metabolism in male mice

Difenoconazole is a commonly used triazole fungicide that consists of four stereoisomers [(2S,4S)-, (2S,4R)-, (2R,4R)-, and (2R,4S)-isomers] with different bioactivity. For example, the toxicity of the (2R,4S)-isomer to fish is approximately seven times higher than that of the (2S,4S)-isomer. However, the stereoselective toxic effects of difenoconazole stereoisomers on mammals have received little attention. In the present study, adult male mice were orally treated with a mixture of the four stereoisomers or each stereoisomer individually (0, 30, or 100 mg/kg/d) by gavage for 28 days. Pathological staining of the liver sections showed that the (2R,4R)-isomer caused lipid droplet accumulation. The mixture or each individual stereoisomers decreased the levels of amino acids and acyl-carnitine in serum. Moreover, the (2S,4R)-, (2R,4R)-, and (2R,4S)-isomers affected intestinal permeability, causing decreases in mucus secretion and tight junction protein expression in colon. Analysis of the gut microbiota composition showed that the stereoisomers caused decreases of OTU numbers and observed species at different levels. Interestingly, difenoconazole and its four stereoisomers reduced the relative abundance of Bacteroidetes at the phylum level and some short-chain fatty acid (SCFA)-producing bacteria. Taking the findings together, 2R-difenoconazole with strong bioactivity against pathogenic fungi also had significant effects in mammals, disrupting hepatic lipid metabolism, intestinal permeability, and gut microbiota. It is concluded that the health risks of the four difenoconazole stereoisomers to mammals should not be overlooked.

Enhancement of Acylcarnitine Levels in Small Intestine of Abdominal Irradiation Rats Might Relate to Fatty Acid β-Oxidation Pathway Disequilibration

Objective

This study aims to analyze the alteration of carnitine profile in the small intestine of abdominal irradiation-induced intestinal injury rats and explore the possible reason for the altered carnitine profile.

Methods

The abdomens of 15 male Sprague Dawley (SD) rats were irradiated with 0, 10, and 15 Gy of ⁶⁰Co gamma rays. The carnitine profile in the small intestine and plasma samples of SD rats at 72 h after abdominal irradiated with 0 Gy or 10 Gy of ⁶⁰Co gamma rays were measured by targeted metabolomics. The changes of fatty acid β-oxidation (FAO), including the expression of carnitine palmitoyltransferase 1 (CPT1) and acyl-CoA dehydrogenases, were analyzed in the small intestine samples of SD rats after exposed to 0, 10, and 15 Gy groups.

Results

There were eleven acylcarnitines in the small intestine and fourteen acylcarnitines in the plasma of the rat model significantly enhanced, respectively (P < .05). The expression level and activity of CPT1 in the small intestine were remarkably increased (P < .05), and the activity of acyl-CoA dehydrogenase in the small intestine was noticeably reduced (P < .01) after abdominal irradiation.

Conclusion

The enhanced acylcarnitine levels in the small intestine of abdominal irradiation rats might relate to the FAO pathway disequilibration.

Lipidomic approaches to dissect dysregulated lipid metabolism in kidney disease

Dyslipidaemia is a hallmark of chronic kidney disease (CKD). The severity of dyslipidaemia not only correlates with CKD stage but is also associated with CKD-associated cardiovascular disease and mortality. Understanding how lipids are dysregulated in CKD is, however, challenging owing to the incredible diversity of lipid structures. CKD-associated dyslipidaemia occurs as a consequence of complex interactions between genetic, environmental and kidney-specific factors, which to understand, requires an appreciation of perturbations in the underlying network of genes, proteins and lipids. Modern lipidomic technologies attempt to systematically identify and quantify lipid species from biological systems. The rapid development of a variety of analytical platforms based on mass spectrometry has enabled the identification of complex lipids at great precision and depth. Insights from lipidomics studies to date suggest that the overall architecture of free fatty acid partitioning between fatty acid oxidation and complex lipid fatty acid composition is an important driver of CKD progression. Available evidence suggests that CKD progression is associated with metabolic inflexibility, reflecting a diminished capacity to utilize free fatty acids through β-oxidation, and resulting in the diversion of accumulating fatty acids to complex lipids such as triglycerides. This effect is reversed with interventions that improve kidney health, suggesting that targeting of lipid abnormalities could be beneficial in preventing CKD progression.

The role of carnitine in maintenance dialysis therapy

Carnitine metabolism and homeostasis is significantly altered in patients receiving maintenance dialysis. Current literature in the adult and pediatric dialysis populations suggest a high prevalence of carnitine deficiency, which may lead to erythropoietin-resistant anemia, cardiomyopathy, and muscle weakness. However, the results of pediatric dialysis studies are limited and have not provided the evidence necessary to support strong recommendations or guidelines pertaining to carnitine management. The characteristics and function of carnitine, the definition and consequences of deficiency, a brief overview of recent adult studies, and current studies on carnitine supplementation in pediatric hemodialysis (HD) and peritoneal dialysis (PD) populations are discussed in this review.

Significance of Levocarnitine Treatment in Dialysis Patients

Carnitine is a naturally occurring amino acid derivative that is involved in the transport of long-chain fatty acids to the mitochondrial matrix. There, these substrates undergo β-oxidation, producing energy. The major sources of carnitine are dietary intake, although carnitine is also endogenously synthesized in the liver and kidney. However, in patients on dialysis, serum carnitine levels progressively fall due to restricted dietary intake and deprivation of endogenous synthesis in the kidney. Furthermore, serum-free carnitine is removed by hemodialysis treatment because the molecular weight of carnitine is small (161 Da) and its protein binding rates are very low. Therefore, the dialysis procedure is a major cause of carnitine deficiency in patients undergoing hemodialysis. This deficiency may contribute to several clinical disorders in such patients. Symptoms of dialysis-related carnitine deficiency include erythropoiesis-stimulating agent-resistant anemia, myopathy, muscle weakness, and intradialytic muscle cramps and hypotension. However, levocarnitine administration might replenish the free carnitine and help to increase carnitine levels in muscle. This article reviews the previous research into levocarnitine therapy in patients on maintenance dialysis for the treatment of renal anemia, cardiac dysfunction, dyslipidemia, and muscle and dialytic symptoms, and it examines the efficacy of the therapeutic approach and related issues.

Blood carnitine profiling on tandem mass spectrometry in liver cirrhotic patients

BACKGROUND

The level and profiles of blood free carnitine and acylcarnitines, obtained by acylcarnitine analysis using tandem mass spectrometry, reflect various metabolic conditions. We aimed to examine the level of free carnitine and acylcarnitines in liver cirrhosis patients by acylcarnitine analysis and determine the clinical and subjective factors associated with blood carnitine fraction levels in liver cirrhosis.

METHODS

We compared blood carnitine fractions in 54 liver cirrhotic patients to other laboratory test results and questionnaire answers.

RESULTS

In almost all patients, the blood levels of free carnitine (C0) and acetylcarnitine (C2) were within the normal reference range. However, in some patients, the levels of long-chain acylcarnitines, such as C16 and C18:1-acylcarnitine, were higher than the normal reference range. Liver function, assessed by Child-Pugh score, was significantly correlated with the blood level of each carnitine fraction measured (C0, C2, C3, C4, C6, C10, C12, C12:1, C14:1, C16, C18:1, and C18:2-acylcarnitine). Cirrhotic symptom score was significantly correlated with C0, C2, C3, C16, and C18-1-acylcarnitine blood levels. Among the 36-item short-form health survey (SF-36) items, the physical component summary was significantly associated with C0, C2, and C18-1-acylcarnitine blood levels.

CONCLUSIONS

Carnitine fraction levels were positively correlated with liver cirrhosis stage, particularly, long-chain acylcarnitines. Moreover, carnitine fraction levels were associated with various subjective physical symptoms in liver cirrhosis patients.

Mass Spectrometric Analysis of L-carnitine and its Esters: Potential Biomarkers of Disturbances in Carnitine Homeostasis

PURPOSE

After a golden age of classic carnitine research three decades ago, the spread of mass spectrometry opened new perspectives and a much better understanding of the carnitine system is available nowadays. In the classic period, several human and animal studies were focused on various distinct physiological functions of this molecule and these revealed different aspects of carnitine homeostasis in normal and pathological conditions. Initially, the laboratory analyses were based on the classic or radioenzymatic assays, enabling only the determination of free and total carnitine levels and calculation of total carnitine esters' amount without any information on the composition of the acyl groups. The introduction of mass spectrometry allowed the measurement of free carnitine along with the specific and sensitive determination of different carnitine esters. Beyond basic research, mass spectrometry study of carnitine esters was introduced into the newborn screening program because of being capable to detect more than 30 metabolic disorders simultaneously. Furthermore, mass spectrometry measurements were performed to investigate different disease states affecting carnitine homeostasis, such as diabetes, chronic renal failure, celiac disease, cardiovascular diseases, autism spectrum disorder or inflammatory bowel diseases.

RESULTS

This article will review the recent advances in the field of carnitine research with respect to mass spectrometric analyses of acyl-carnitines in normal and various pathological states.

CONCLUSION

The growing number of publications using mass spectrometry as a tool to investigate normal physiological conditions or reveal potential biomarkers of primary and secondary carnitine deficiencies shows that this tool brought a new perspective to carnitine research.