Carnitine and type 2 diabetes

Integrated plasma metabolomic and cytokine analysis reveals a distinct immunometabolic signature in atopic dermatitis

Importance

Disease models for atopic dermatitis (AD) have primarily focused on understanding underlying environmental, immunologic, and genetic etiologies. However, the role of metabolic mechanisms in AD remains understudied.

Objective

To investigate the circulating blood metabolomic and cytokine profile of AD as compared to healthy control patients.

Design

This study collected plasma from 20 atopic dermatitis with moderate-to-severe itch (score of ≥5 on the itch Numeric Rating Scale and IGA score ≥3) and 24 healthy control patients. Mass-spectrometry based metabolite data were compared between AD and healthy controls. Unsupervised and supervised machine learning algorithms and univariate analysis analyzed metabolic concentrations. Metabolite enrichment and pathway analyses were performed on metabolites with significant fold change between AD and healthy control patients. To investigate the correlation between metabolites levels and cytokines, Spearman's rank correlation coefficients were calculated between metabolites and cytokines.

Setting

Patients were recruited from the Johns Hopkins Itch Center and dermatology outpatient clinics in the Johns Hopkins Outpatient Center.

Participants

The study included 20 atopic dermatitis patients and 24 healthy control patients.

Main outcomes and measures

Fold changes of metabolites in AD vs healthy control plasma.

Results

In patients with AD, amino acids isoleucine, tyrosine, threonine, tryptophan, valine, methionine, and phenylalanine, the amino acid derivatives creatinine, indole-3-acrylic acid, acetyl-L-carnitine, L-carnitine, 2-hydroxycinnamic acid, N-acetylaspartic acid, and the fatty amide oleamide had greater than 2-fold decrease (all P-values<0.0001) compared to healthy controls. Enriched metabolites were involved in branched-chain amino acid (valine, leucine, and isoleucine) degradation, catecholamine biosynthesis, thyroid hormone synthesis, threonine metabolism, and branched and long-chain fatty acid metabolism. Dysregulated metabolites in AD were positively correlated cytokines TARC and MCP-4 and negatively correlated with IL-1a and CCL20.

Conclusions and relevance

Our study characterized novel dysregulated circulating plasma metabolites and metabolic pathways that may be involved in the pathogenesis of AD. These metabolic pathways serve as potential future biomarkers and therapeutic targets in the treatment of AD.

Molecular pathways and nutrigenomic review of insulin resistance development in gestational diabetes mellitus

Gestational diabetes mellitus is a condition marked by raised blood sugar levels and insulin resistance that usually occurs during the second or third trimester of pregnancy. According to the World Health Organization, hyperglycemia affects 16.9% of pregnancies worldwide. Dietary changes are the primarily alternative treatment for gestational diabetes mellitus. This paper aims to perform an exhaustive overview of the interaction between diet, gene expression, and the metabolic pathways related to insulin resistance. The intake of foods rich in carbohydrates can influence the gene expression of glycolysis, as well as foods rich in fat, can disrupt the beta-oxidation and ketogenesis pathways. Furthermore, vitamins and minerals are related to inflammatory processes regulated by the TLR4/NF-κB and one carbon metabolic pathways. We indicate that diet regulated gene expression of PPARα, NOS, CREB3L3, IRS, and CPT I, altering cellular physiological mechanisms and thus increasing or decreasing the risk of gestational diabetes. The alteration of gene expression can cause inflammation, inhibition of fatty acid transport, or on the contrary help in the modulation of ketogenesis, improve insulin sensitivity, attenuate the effects of glucotoxicity, and others. Therefore, it is critical to comprehend the metabolic changes of pregnant women with gestational diabetes mellitus, to determine nutrients that help in the prevention and treatment of insulin resistance and its long-term consequences.

Heterogeneity in Early Postpartum Metabolic Profiles Among Women with GDM Who Progressed to Type 2 Diabetes During 10-Year Follow-Up: The SWIFT Study

GDM is a strong risk factor for progression to T2D after pregnancy. Although both GDM and T2D exhibit heterogeneity, the link between the distinct heterogeneity of GDM and incident T2D has not been established. Herein, we evaluate early postpartum profiles of women with recent GDM who later developed incident T2D using a soft clustering method, followed by the integration of both clinical phenotypic variables and metabolomics to characterize these heterogeneous clusters/groups clinically and their molecular mechanisms. We identified three clusters based on two indices of glucose homeostasis at 6-9 weeks postpartum - HOMA-IR and HOMA-B among women who developed incident T2D during the 12-year follow-up. The clusters were classified as follows: pancreatic beta-cell dysfunction group (cluster-1), insulin resistant group (cluster-3), and a combination of both phenomena (cluster-2) comprising the majority of T2D. We also identified postnatal blood test parameters to distinguish the three clusters for clinical testing. Moreover, we compared these three clusters in their metabolomics profiles at the early stage of the disease to identify the mechanistic insights. A significantly higher concentration of a metabolite at the early stage of a T2D cluster than other clusters indicates its essentiality for the particular disease character. As such, the early-stage characters of T2D cluster-1 pathology include a higher concentration of sphingolipids, acyl-alkyl phosphatidylcholines, lysophosphatidylcholines, and glycine, indicating their essentiality for pancreatic beta-cell function. In contrast, the early-stage characteristics of T2D cluster-3 pathology include a higher concentration of diacyl phosphatidylcholines, acyl-carnitines, isoleucine, and glutamate, indicating their essentiality for insulin actions. Notably, all these biomolecules are found in the T2D cluster-2 with mediocre concentrations, indicating a true nature of a mixed group. In conclusion, we have deconstructed incident T2D heterogeneity and identified three clusters with their clinical testing procedures and molecular mechanisms. This information will aid in adopting proper interventions using a precision medicine approach.

Differential metabolic host response to pathogens associated with community-acquired pneumonia

Background

Metabolic changes induced by the host immune response to pathogens found in patients with community-acquired pneumonia (CAP) may provide insight into its pathogenesis. In this study, we characterized differences in the host metabolic response to common CAP-associated pathogens.

Method

Targeted metabolomic profiling was performed on serum samples obtained from hospitalized CAP patients (n = 119) at admission. We quantified 347 unique metabolites across multiple biochemical classes, including amines, acylcarnitines, and signaling lipids. We evaluated if unique associations between metabolite levels and specific CAP-associated pathogens could be identified.

Results

Several acylcarnitines were found to be elevated in C. burnetii and herpes simplex virus and lowered in M. pneumoniae as compared to other pathogens. Phenylalanine and kynurenine were found elevated in L. pneumophila as compared to other pathogens. S-methylcysteine was elevated in patients with M. pneumoniae, and these patients also showed lowered cortisol levels in comparison to almost all other pathogens. For the herpes simplex virus, we observed a unique elevation of eicosanoids and several amines. Many lysophosphatidylcholines showed an altered profile in C. burnetii versus S. pneumoniae, L. pneumophila, and respiratory syncytial virus. Finally, phosphatidylcholines were negatively affected by the influenza virus in comparison to S. pneumoniae.

Conclusions

In this exploratory analysis, metabolites from different biochemical classes were found to be altered in serum samples from patients with different CAP-associated pathogens, which may be used for hypothesis generation in studies on differences in pathogen host response and pathogenesis of CAP.

Effects of L-carnitine supplementation on glucolipid metabolism: a systematic review and meta-analysis

Background: L-carnitine supplementation has been utilized against glucolipid metabolism disruption. However, to the best of our knowledge, no meta-analysis process has analyzed the effects of L-carnitine supplementation on insulin resistance, fasting blood glucose, lipid metabolism, and liver enzyme levels in adults. Methods: Through the analysis and screening of 12 221 studies, 15 studies were selected from eligible trials for meta-analysis. Meta-analysis was performed in a random effect model with heterogeneity determined by I², and subgroup analyses were used to further identify the source of heterogeneity. Result: The results showed significant effects of L-carnitine on FBG (MD = -4.94 mg dL^-1, 95% CI: -7.07 to -2.82), insulin (MD = -0.99 μU mL^-1, 95% CI: -1.41 to -0.56), HOMA-IR (MD = -0.58, 95% CI: -0.77 to -0.38), TG (MD = -11.22 mg dL^-1, 95% CI: -19.21 to -3.22), TC (MD = -6.45 mg dL^-1, 95% CI: -9.95 to -2.95, LDLc (MD = -8.28 mg dL^-1, 95% CI: -11.08 to -5.47), and ALT (MD = -19.71 IU L^-1, 95% CI: -36.45 to -2.96). However, no significant effect of L-carnitine supplementation was observed in HDLc (MD = -0.77 mg dL^-1, 95% CI: -0.10 to -1.63) or AST (MD = -11.05 IU L^-1, 95% CI: -23.08 to 0.99). The duration of carnitine supplementation was negatively associated with mean differences in FBG, as assessed by meta-regression. Conclusion: The current meta-analysis revealed that L-carnitine may have favorable effects on glucolipid profile, especially insulin, FBG, HOMA-IR, TG, TC, LDLc, and ALT levels.

A Study of the Metabolic Pathways Affected by Gestational Diabetes Mellitus: Comparison with Type 2 Diabetes

BACKGROUND

Gestational diabetes mellitus (GDM) remains incompletely understood and increases the risk of developing Diabetes mellitus type 2 (DM2). Metabolomics provides insights etiology and pathogenesis of disease and discovery biomarkers for accurate detection. Nuclear magnetic resonance (NMR) spectroscopy is a key platform defining metabolic signatures in intact serum/plasma. In the present study, we used NMR-based analysis of macromolecules free-serum to accurately characterize the altered metabolic pathways of GDM and assessing their similarities to DM2. Our findings could contribute to the understanding of the pathophysiology of GDM and help in the identification of metabolomic markers of the disease.

METHODS

Sixty-two women with GDM matched with seventy-seven women without GDM (control group). ¹H NMR serum spectra were acquired on an 11.7 T Bruker Avance DRX NMR spectrometer.

RESULTS

We identified 55 metabolites in both groups, 25 of which were significantly altered in the GDM group. GDM group showed elevated levels of ketone bodies, 2-hydroxybutyrate and of some metabolic intermediates of branched-chain amino acids (BCAAs) and significantly lower levels of metabolites of one-carbon metabolism, energy production, purine metabolism, certain amino acids, 3-methyl-2-oxovalerate, ornithine, 2-aminobutyrate, taurine and trimethylamine N-oxide.

CONCLUSION

Metabolic pathways affected in GDM were beta-oxidation, ketone bodies metabolism, one-carbon metabolism, arginine and ornithine metabolism likewise in DM2, whereas BCAAs catabolism and aromatic amino acids metabolism were affected, but otherwise than in DM2.

The Role of l-Carnitine in Mitochondria, Prevention of Metabolic Inflexibility and Disease Initiation

Mitochondria control cellular fate by various mechanisms and are key drivers of cellular metabolism. Although the main function of mitochondria is energy production, they are also involved in cellular detoxification, cellular stabilization, as well as control of ketogenesis and glucogenesis. Conditions like neurodegenerative disease, insulin resistance, endocrine imbalances, liver and kidney disease are intimately linked to metabolic disorders or inflexibility and to mitochondrial dysfunction. Mitochondrial dysfunction due to a relative lack of micronutrients and substrates is implicated in the development of many chronic diseases. l-carnitine is one of the key nutrients for proper mitochondrial function and is notable for its role in fatty acid oxidation. l-carnitine also plays a major part in protecting cellular membranes, preventing fatty acid accumulation, modulating ketogenesis and glucogenesis and in the elimination of toxic metabolites. l-carnitine deficiency has been observed in many diseases including organic acidurias, inborn errors of metabolism, endocrine imbalances, liver and kidney disease. The protective effects of micronutrients targeting mitochondria hold considerable promise for the management of age and metabolic related diseases. Preventing nutrient deficiencies like l-carnitine can be beneficial in maintaining metabolic flexibility via the optimization of mitochondrial function. This paper reviews the critical role of l-carnitine in mitochondrial function, metabolic flexibility and in other pathophysiological cellular mechanisms.

Role of carnitine in regulation of blood pressure (MAP/SBP) and gene expression of cardiac hypertrophy markers (α/β-MHC) during insulin-induced hypoglycaemia: Role of oxidative stress

Cardiovascular disease is a leading cause of death in diabetic patients. Hyperglycaemia and iatrogenic hypoglycaemia exacerbate several pathogenic mechanisms underlying hypertension and heart diseases. Carnitine is a potent endogenous antioxidant and cellular fatty acid transporter for antioxidative stress and energy production in the cardiovascular system. The current study aimed to find the role of carnitine in the regulation of hypoglycaemia-induced hypertension and cardiac hypertrophy. Male rats received insulin glargine (InG) to induce hypoglycaemia followed by D-carnitine or acetyl-L-carnitine for carnitine depletion or carnitine supplementation, respectively. The obtained results showed that carnitine deficiency provoked hypoglycaemia-induced hypertension. Mean arterial pressure was elevated from 78.16 ± 11.4 to 100 ± 5.11 mm Hg in InG treated group, and from 78.2 ± 8.5 to 123.4 ± 28.2 mm Hg in InG + D-carnitine treated group. Acetyl-L-carnitine resisted the elevation in blood pressure in all hypoglycaemic animals and kept it within the normal values (68.33 ± 6.7 mm Hg). Acetyl-L-carnitine increased myocardial carnitine content leading to the attenuation of hypoglycaemia-induced oxidative stress, which was evaluated through measurement of the oxidative stress biomarkers such as inducible nitric oxide synthase, NAD(P)H quinone dehydrogenase-1, heme oxygenase-I, and glutathione S-transferase. Moreover, acetyl-L-carnitine prevented induction of gene expression of cardiac hypertrophy markers during hypoglycaemic conditions, which was assessed via the evaluation of mRNA expression of α-myosin heavy chain and β-myosin heavy chain. These findings demonstrate that carnitine might play an essential role in prevention of hypoglycaemia-induced hypertension and cardiac hypertrophy through providing energy and antioxidants to the cardiovascular system.

15 N-carnitine, a novel endogenous hyperpolarized MRI probe with long signal lifetime

PURPOSE

The purpose of this study was to investigate hyperpolarization and in vivo imaging of [¹⁵ N]carnitine, a novel endogenous MRI probe with long signal lifetime.

METHODS

L-[¹⁵ N]carnitine-d₉ was hyperpolarized by the method of dynamic nuclear polarization followed by rapid dissolution. The T₁ signal lifetimes were estimated in aqueous solution and in vivo following intravenous injection in rats, using a custom-built dual-tuned ¹⁵ N/¹ H RF coil at 4.7 T. ¹⁵ N chemical shift imaging and ¹⁵ N fast spin-echo images of rat abdomen were acquired 3 minutes after [¹⁵ N]carnitine injection.

RESULTS

Estimated T₁ times of [¹⁵ N]carnitine at 4.7 T were 210 seconds (in H₂ O) and 160 seconds (in vivo), with an estimated polarization level of 10%. Remarkably, the [¹⁵ N]carnitine coherence was detectable in rat abdomen for 5 minutes after injection for the nonlocalized acquisition. No downstream metabolites were detected on localized or nonlocalized ¹⁵ N spectra. Diffuse liver enhancement was detected on ¹⁵ N fast spin-echo imaging 3 minutes after injection, with mean hepatic SNR of 18 ± 5 at a spatial resolution of 4 × 4 mm.

CONCLUSION

This study showed the feasibility of hyperpolarizing and imaging the biodistribution of HP [¹⁵ N]carnitine.

Pre-diagnostic biomarkers of type 2 diabetes identified in the UAE's obese national population using targeted metabolomics

Currently, type 2 diabetes mellitus (T2DM) and obesity are major global public health issues, and their prevalence in the United Arab Emirates (UAE) are among the highest in the world. In 2019, The UAE diabetes national prevalence was 15.4%. In recent years there has been a considerable investigation of predictive biomarkers associated with these conditions. This study analysed fasting (8 h) blood samples from an obese, normoglycemic cohort and an obese, T2DM cohort of UAE nationals, employing clinical chemistry analysis, 1D ¹H NMR and mass spectroscopy (FIA-MS/MS and LC-MS/MS) techniques. The novel findings reported for the first time in a UAE population revealed significant differences in a number of metabolites in the T2DM cohort. Metabolic fingerprints identified by NMR included BCAAs, trimethylamine N-oxide, β-hydroxybutyrate, trimethyl uric acid, and alanine. A targeted MS approach showed significant differences in lysophosphatidylcholines, phosphatidylcholines, acylcarnitine, amino acids and sphingomyelins; Lyso.PC.a.C18.0, PC.ae.C34.2, C3.DC..C4.OH, glutamine and SM.C16.1, being the most significant metabolites. Pearson's correlation studies showed associations between these metabolites and the clinical chemistry parameters across both cohorts. This report identified differences in metabolites in response to T2DM in agreement with many published population studies. This contributes to the global search for a bank of metabolite biomarkers that can predict the advent of T2DM and give insight to its pathogenic mechanisms.

The osmo-metabolic approach: a novel and tantalizing glucose-sparing strategy in peritoneal dialysis

Peritoneal dialysis (PD) is a viable but under-prescribed treatment for uremic patients. Concerns about its use include the bio-incompatibility of PD fluids, due to their potential for altering the functional and anatomical integrity of the peritoneal membrane. Many of these effects are thought to be due to the high glucose content of these solutions, with attendant issues of products generated during heat treatment of glucose-containing solutions. Moreover, excessive intraperitoneal absorption of glucose from the dialysate has many potential systemic metabolic effects. This article reviews the efforts to develop alternative PD solutions that obviate some of these side effects, through the replacement of part of their glucose content with other osmolytes which are at least as efficient in removing fluids as glucose, but less impactful on patient metabolism. In particular, we will summarize clinical studies on the use of alternative osmotic ingredients that are commercially available (icodextrin and amino acids) and preclinical studies on alternative solutions under development (taurine, polyglycerol, carnitine and xylitol). In addition to the expected benefit of a glucose-sparing approach, we describe an ‘osmo-metabolic’ approach in formulating novel PD solutions, in which there is the possibility of exploiting the pharmaco-metabolic properties of some of the osmolytes to attenuate the systemic side effects due to glucose. This approach has the potential to ameliorate pre-existing co-morbidities, including insulin resistance and type-2 diabetes, which have a high prevalence in the dialysis population, including in PD patients.

Potential roles of carnitine in patients with polycystic ovary syndrome: a systematic review

Polycystic ovary syndrome (PCOS) is recognized as the most prevalent endocrinopathy in reproductive-aged women. This systematic review was performed with focus on the current knowledge on carnitine concerning metabolic variables in PCOS. PubMed, Scopus, Embase, ClinicalTrials.gov and Google Scholar databases were searched from inception until May 2018. All clinical trials and observational studies published in English-language journals were eligible. Studies that provided insufficient outcomes, animal and in vitro studies were excluded. Out of 451 articles identified in our search, only six articles were eligible for analysis. Two observational studies evaluated the association of serum carnitine levels with metabolic variables, and four clinical trials examined the effect of carnitine supplementation in patients with PCOS. Serum carnitine levels had inverse relationship with glycemic status, body mass index (BMI) and waist circumference. Also, carnitine supplementation resulted in improved weight loss, glycemic status, oxidative stress, follicles and size of ovarian cells; no significant effects were reported on sex hormones and lipid profile. According to the current evidence, carnitine might improve weight loss, glycemic status and oxidative stress. However, to explore the exact mechanisms of carnitine role in patients with PCOS, further studies are recommended.

Role of carnitine and its derivatives in the development and management of type 2 diabetes

Type 2 diabetes is a highly prevalent chronic metabolic disorder characterized by hyperglycemia and associated with several complications such as retinopathy, hyperlipidemia and polyneuropathy. The dysregulated fatty acid metabolism along with tissue lipid accumulation is generally assumed to be associated in the development of insulin resistance and T2D. Moreover, several studies suggest a central role for oxidative stress in the pathogenesis of the disease. Since L-carnitine (LC) has an indispensable role in lipid metabolism via its involvement in the β-oxidation of long-chain fatty acids and it has antioxidant properties as well, carnitine supplementation may prove to be an effective tool in the management of the clinical course of T2D. In this review we summarize the results from animal and clinical studies demonstrating the effects of supplementation with LC or LC derivatives (acetyl-LC, propionyl-LC) on various metabolic and clinical parameters associated with T2D.

Carnitine acetyltransferase: A new player in skeletal muscle insulin resistance?

Carnitine acetyltransferase (CRAT) deficiency has previously been shown to result in muscle insulin resistance due to accumulation of long-chain acylcarnitines. However, differences in the acylcarnitine profile and/or changes in gene expression and protein abundance of CRAT in myotubes obtained from obese patients with type 2 diabetes mellitus (T2DM) and glucose-tolerant obese and lean controls remain unclear. The objective of the study was to examine whether myotubes from obese patients with T2DM express differences in gene expression and protein abundance of CRAT and in acylcarnitine species pre-cultured under glucose and insulin concentrations similar to those observed in healthy individuals in the over-night fasted, resting state. Primary myotubes obtained from obese persons with or without T2DM and lean controls (n=9 in each group) were cultivated and harvested for LC-MS-based profiling of acylcarnitines. The mRNA expression and protein abundance of CRAT were determined by qPCR and Western Blotting, respectively. Our results suggest that the mRNA levels and protein abundance of CRAT were similar between groups. Of the 14 different acylcarnitine species measured by LC-MS, the levels of palmitoylcarnitine (C16) and octadecanoylcarnitine (C18) were slightly reduced in myotubes derived from T2DM patients (p<0.05) compared to glucose-tolerant obese and lean controls. This suggests that the CRAT function is not the major contributor to primary insulin resistance in cultured myotubes obtained from obese T2DM patients.

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Gene expression and protein abundance of CRAT are not altered in myotubes derived from T2D patients.

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Palmitoylcarnitine (16:0) and octadecanoylcarnitine (C18) are reduced in myotubes derived from T2D patients.

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CRAT function is not the major contributor to primary insulin resistance.

Plasma L-carnitine levels of obese and non-obese polycystic ovary syndrome patients

It is well-known that plasma L-carnitine concentrations are significantly decreased in obese individuals. A study showed that L-carnitine concentrations are significantly lower in lean PCOS patients than in lean healthy women. Thus, it has been suggested that lowered L-carnitine is associated with PCOS. This study also showed that the women with PCOS had significantly lower L-carnitine levels than those of the healthy controls. In addition, this study hypothesised that low L-carnitine levels in PCOS patients were associated with obesity and/or insulin resistance. Moreover, plasma L-carnitine concentrations were found to be statistically similar in PCOS patients and healthy controls, when controlled for obesity. This study implied that L-carnitine could be used as an adjunctive therapy in the management of insulin resistance or obesity in women who have PCOS. Further research might be planned to clarify the clinical effects of L-carnitine administration in PCOS patients with insulin resistance and/or obesity.

Mitochondrial involvement in skeletal muscle insulin resistance: A case of imbalanced bioenergetics

Skeletal muscle insulin resistance in obesity associates with mitochondrial dysfunction, but the causality of this association is controversial. This review evaluates mitochondrial models of nutrient-induced muscle insulin resistance. It transpires that all models predict that insulin resistance arises as a result of imbalanced cellular bioenergetics. The nature and precise origin of the proposed insulin-numbing molecules differ between models but all species only accumulate when metabolic fuel supply outweighs energy demand. This observation suggests that mitochondrial deficiency in muscle insulin resistance is not merely owing to intrinsic functional defects, but could instead be an adaptation to nutrient-induced changes in energy expenditure. Such adaptive effects are likely because muscle ATP supply is fully driven by energy demand. This market-economic control of myocellular bioenergetics offers a mechanism by which insulin-signalling deficiency can cause apparent mitochondrial dysfunction, as insulin resistance lowers skeletal muscle anabolism and thus dampens ATP demand and, consequently, oxidative ATP synthesis.

Effects of a New Metabolic Conditioning Supplement on Perioperative Metabolic Stress and Clinical Outcomes: A Randomized, Placebo-Controlled Trial

BACKGROUND

Insulin resistance is a measure of metabolic stress in the perioperative period. Before now, no clinical trial has determined the summative effects of glutamine, L-carnitine, and antioxidants as metabolic conditioning supplements in the perioperative period.

OBJECTIVES

The purpose of this study was to determine the effects of a new conditioning supplement on perioperative metabolic stress and clinical outcomes in non-diabetic patients.

PATIENTS AND METHODS

In this randomized controlled trial, 89 non-diabetic patients scheduled for coronary artery bypass grafting, with ejection fractions above 30%, were selected. Using the balanced block randomization method, the patients were allocated to one of four study arms: 1) SP (supplement/placebo): supplement seven days before and placebo 30 days after the surgery; 2) PS: placebo before and supplement after the surgery; 3) SS: supplement before and after the surgery; and 4) PP: placebo before and after the surgery. The supplement was composed of glutamine, L-carnitine, vitamin C, vitamin E, and selenium, which was manufactured for the first time by this research team. Five blood samples were drawn: seven days preoperatively, at the entrance to the operating room, while leaving the operating room, seven days postoperatively, and 30 days postoperatively. Levels of glucose, insulin, and HbA1c were measured in blood samples. Insulin resistance and sensitivity were calculated using a formula. Surgical complications were assessed 30 days postoperatively. Data analysis was done using one-way ANOVA, the Chi-square test, and a general linear model repeated-measures analysis with Bonferroni adjustment.

RESULTS

Blood glucose levels were increased postoperatively in the four groups (< 0.001), but a significantly higher increase occurred in the PP group compared to the SP (0.027), PS (0.026), and SS (0.004) groups. The superficial wound infection rate was significantly different between the four groups (0.021): 26.08% in PP, 9.09% in SP, 4.54% in PS, and 0% in SS.

CONCLUSIONS

Our new metabolic conditioning supplement, whether given pre- or postoperatively, led to better perioperative glycemic control and decreased postsurgical wound infections in non-diabetic patients.

Carnitine supplementation in high-fat diet-fed rats does not ameliorate lipid-induced skeletal muscle mitochondrial dysfunction in vivo

Muscle lipid overload and the associated accumulation of lipid intermediates play an important role in the development of insulin resistance. Carnitine insufficiency is a common feature of insulin-resistant states and might lead to incomplete fatty acid oxidation and impaired export of lipid intermediates out of the mitochondria. The aim of the present study was to test the hypothesis that carnitine supplementation reduces high-fat diet-induced lipotoxicity, improves muscle mitochondrial function, and ameliorates insulin resistance. Wistar rats were fed either normal chow or a high-fat diet for 15 wk. One group of high-fat diet-fed rats was supplemented with 300 mg·kg(-1)·day(-1) L-carnitine during the last 8 wk. Muscle mitochondrial function was measured in vivo by (31)P magnetic resonance spectroscopy (MRS) and ex vivo by high-resolution respirometry. Muscle lipid status was determined by (1)H MRS (intramyocellular lipids) and tandem mass spectrometry (acylcarnitines). High-fat diet feeding induced insulin resistance and was associated with decreases in muscle and blood free carnitine, elevated levels of muscle lipids and acylcarnitines, and an increased number of muscle mitochondria that showed an improved capacity to oxidize fat-derived substrates when tested ex vivo. This was, however, not accompanied by an increase in muscle oxidative capacity in vivo, indicating that in vivo mitochondrial function was compromised. Despite partial normalization of muscle and blood free carnitine content, carnitine supplementation did not induce improvements in muscle lipid status, in vivo mitochondrial function, or insulin sensitivity. Carnitine insufficiency, therefore, does not play a major role in high-fat diet-induced muscle mitochondrial dysfunction in vivo.

Listening to Our Gut: Contribution of Gut Microbiota and Cardiovascular Risk in Diabetes Pathogenesis

What we understand about diabetes from decades of genetics research is now being supplemented with exciting new evidence based on a better understanding of how one of the biggest "environmental" factors the body is exposed to is influencing the pathogenesis of disease. The recent discovery that certain dietary nutrients possessing a trimethylamine (TMA) moiety (namely choline/phosphatidylcholine and L-carnitine) participate in the development of atherosclerotic heart disease has renewed attention towards the contributions of gut microbiota in the development of cardiovascular diseases. Collectively, animal and human studies reveal that conversion of these nutrient precursors to trimethylamine N-oxide (TMAO) depends on both microbial composition and host factors, and can be induced by dietary exposures. In addition, circulating TMAO levels are strongly linked to cardiovascular disease risks and various adverse cardio-renal consequences. Our group and others have further demonstrated that circulating TMAO levels are elevated in patients with type 2 diabetes mellitus compared to healthy controls and gut microbiota-dependent phosphatidylcholine metabolism has been implicated in metabolic dysregulation and insulin resistance in animal models. Therefore, preventive strategies to minimize adverse consequences associated with TMAO generation in the diabetic population are warranted.

Effect of carnitine-orotate complex on glucose metabolism and fatty liver: a double-blind, placebo-controlled study

BACKGROUND AND AIM

Effective medicines have not been introduced for insulin resistance-related fatty liver. The efficacy and safety of treatment between a combination of metformin and carnitine-orotate complex and metformin alone in a 12-week, double-blind, randomized, placebo-controlled study on drug-naïve patients with impaired glucose metabolism and fatty liver were compared.

METHODS

Fifty-two patients with fasting glucose 100-240 mg/dL or glycosylated hemoglobin (HbA1c) ≥ 6.0% and alanine aminotransferase (ALT) 40-250 IU/L were randomized to receive metformin (250 mg t.i.d.), or metformin (250 mg t.i.d.) and carnitine-orotate complex (300 mg t.i.d.) for 12 weeks (n = 26 per group). The primary end-point was a change from baseline ALT level. Secondary end-points were changes in fasting glucose, HbA1c, aspartate aminotransferase levels, mitochondrial DNA (mtDNA) copy number in the peripheral blood, and urinary output of 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress.

RESULTS

The combined treatment reduced ALT level significantly more than metformin alone (-51.5 ± 33.2 IU/L vs -16.7 ± 31.3 IU/L, P = 0.001). The HbA1c levels also decreased significantly in both groups but there was no significant difference between them (-0.9% ± 1.0% vs -0.7% ± 0.9%). Treatment with the complex decreased the urinary 8-hydroxy-2'-deoxyguanosine level and increased mtDNA copy number significantly compared with metformin alone (both P < 0.05). No severe adverse events were observed.

CONCLUSION

A 12-week treatment with metformin and carnitine-orotate complex significantly improved liver function enzyme levels. This was associated with changes in oxidative stress and mtDNA copy number compared with metformin alone in patients with impaired glucose metabolism and fatty liver (clinical trial number: KCT0000193).

Human serum acylcarnitine profiles in different glucose tolerance states

AIMS

To understand the relationship between serum acylcarnitine profiles and glucose tolerance status.

METHODS

We analyzed 61 subjects who were divided into three groups based on their glucose tolerance status: normal glucose tolerance (NGT; n=20,M/F=9/11, mean age 48 years), pre-diabetes (Pre-DM; n=20,M/F=11/9, mean age 51 years), or newly diagnosed type 2 diabetes mellitus (T2DM; n=21,M/F=8/13, mean age 49 years). Fasting serum free carnitine and acylcarnitine concentrations were determined using isotope dilution electrospray ionization mass spectrometry coupled with high performance liquid chromatography.

RESULTS

In comparison with NGT subjects, Pre-DM and type 2 diabetes subjects showed serum metabonomic changes highlighted by dysregulation of mitochondrial fatty acid combustion. Of the long-chain carnitine esters, significantly higher palmitoylcarnitine (C16), 3-OH-hexadecanoylcarnitine (C16-OH), carnitine C20, carnitine C22, and carnitine C24 concentrations (all P<0.05) were noted in the newly diagnosed type 2 diabetes group, and even the pre-diabetes group.

CONCLUSIONS

This research provides further evidence of alterations in serum acylcarnitine profiles being associated with worse glucoseintolerance. The findings may suggest different degrees of involvement of dysregulated mitochondrial function and incomplete long-chain fatty acid oxidation pathways in the natural course of type 2 diabetes.

High L-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients

Increased intake of L-carnitine, a cofactor in cellular energy metabolism, is recommended for diabetic patients with late complications. However, its clinical benefits remain controversial. We hypothesized that patients with low L-carnitine levels would have an increased rate of diabetic complications. To test this hypothesis, we evaluated the relationship of L-carnitine concentrations in blood with the prevalence and severity of late diabetic complications in type 1 and 2 diabetic patients. Human blood samples were collected from 93 and 87 patients diagnosed as having type 1 or type 2 diabetes, respectively, and 122 nondiabetic individuals. The determination of free L-carnitine concentrations in whole blood lysates was performed using ultra-performance liquid chromatography with tandem mass spectrometry. In diabetic patients, diabetic complications such as neuropathy, retinopathy, nephropathy, or hypertension were recorded. The average L-carnitine concentration in the blood of control subjects was 33 ± 8 nmol/mL, which was not significantly different from subgroups of patients with type 1 (32 ± 10 nmol/mL) or type 2 diabetes (36 ± 11 nmol/mL). Patients with low (<20 nmol/mL) l-carnitine levels did not have increased occurrences of late diabetic complications. In addition, patient subgroups with higher L-carnitine concentrations did not have decreased prevalence of late diabetic complications. Our results provide evidence that higher L-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients.

Propionyl-L-carnitine corrects metabolic and cardiovascular alterations in diet-induced obese mice and improves liver respiratory chain activity

AIMS

Obesity is a primary contributor to acquired insulin resistance leading to the development of type 2 diabetes and cardiovascular alterations. The carnitine derivate, propionyl-L-carnitine (PLC), plays a key role in energy control. Our aim was to evaluate metabolic and cardiovascular effects of PLC in diet-induced obese mice.

METHODS

C57BL/6 mice were fed a high-fat diet for 9 weeks and then divided into two groups, receiving either free- (vehicle-HF) or PLC-supplemented water (200 mg/kg/day) during 4 additional weeks. Standard diet-fed animals were used as lean controls (vehicle-ST). Body weight and food intake were monitored. Glucose and insulin tolerance tests were assessed, as well as the HOMA(IR), the serum lipid profile, the hepatic and muscular mitochondrial activity and the tissue nitric oxide (NO) liberation. Systolic blood pressure, cardiac and endothelial functions were also evaluated.

RESULTS

Vehicle-HF displayed a greater increase of body weight compared to vehicle-ST that was completely reversed by PLC treatment without affecting food intake. PLC improved the insulin-resistant state and reversed the increased total cholesterol but not the increase in free fatty acid, triglyceride and HDL/LDL ratio induced by high-fat diet. Vehicle-HF exhibited a reduced cardiac output/body weight ratio, endothelial dysfunction and tissue decrease of NO production, all of them being improved by PLC treatment. Finally, the decrease of hepatic mitochondrial activity by high-fat diet was reversed by PLC.

CONCLUSIONS

Oral administration of PLC improves the insulin-resistant state developed by obese animals and decreases the cardiovascular risk associated to this metabolic alteration probably via correction of mitochondrial function.

Effect of L-carnitine on the hepatic transcript profile in piglets as animal model

Background

Carnitine has attracted scientific interest due to several health-related effects, like protection against neurodegeneration, mitochondrial decay, and oxidative stress as well as improvement of glucose tolerance and insulin sensitivity. The mechanisms underlying most of the health-related effects of carnitine are largely unknown.

Methods

To gain insight into mechanisms through which carnitine exerts its beneficial metabolic effects, we fed piglets either a control or a carnitine supplemented diet, and analysed the transcriptome in the liver.

Results

Transcript profiling revealed 563 genes to be differentially expressed in liver by carnitine supplementation. Clustering analysis of the identified genes revealed that most of the top-ranked annotation term clusters were dealing with metabolic processes. Representative genes of these clusters which were significantly up-regulated by carnitine were involved in cellular fatty acid uptake, fatty acid activation, fatty acid β-oxidation, glucose uptake, and glycolysis. In contrast, genes involved in gluconeogenesis were down-regulated by carnitine. Moreover, clustering analysis identified genes involved in the insulin signaling cascade to be significantly associated with carnitine supplementation. Furthermore, clustering analysis revealed that biological processes dealing with posttranscriptional RNA processing were significantly associated with carnitine supplementation.

Conclusion

The data suggest that carnitine supplementation has beneficial effects on lipid and glucose homeostasis by inducing genes involved in fatty acid catabolism and glycolysis and repressing genes involved in gluconeogenesis.

Chronic effects of palmitate overload on nutrient-induced insulin secretion and autocrine signalling in pancreatic MIN6 beta cells

BACKGROUND

Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling.

PRINCIPAL FINDINGS

GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (~75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate.

CONCLUSIONS

Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.

Tetradecylthioacetic acid increases hepatic mitochondrial β-oxidation and alters fatty acid composition in a mouse model of chronic inflammation

The administration of tetradecylthioacetic acid (TTA), a hypolipidemic and anti-inflammatory modified bioactive fatty acid, has in several experiments based on high fat diets been shown to improve lipid transport and utilization. It was suggested that increased mitochondrial and peroxisomal fatty acid oxidation in the liver of Wistar rats results in reduced plasma triacylglycerol (TAG) levels. Here we assessed the potential of TTA to prevent tumor necrosis factor (TNF) α-induced lipid modifications in human TNFα (hTNFα) transgenic mice. These mice are characterized by reduced β-oxidation and changed fatty acid composition in the liver. The effect of dietary treatment with TTA on persistent, low-grade hTNFα overexpression in mice showed a beneficial effect through decreasing TAG plasma concentrations and positively affecting saturated and monounsaturated fatty acid proportions in the liver, leading to an increased anti-inflammatory fatty acid index in this group. We also observed an increase of mitochondrial β-oxidation in the livers of TTA treated mice. Concomitantly, there were enhanced plasma levels of carnitine, acetyl carnitine, propionyl carnitine, and octanoyl carnitine, no changed levels in trimethyllysine and palmitoyl carnitine, and a decreased level of the precursor for carnitine, called γ-butyrobetaine. Nevertheless, TTA administration led to increased hepatic TAG levels that warrant further investigations to ascertain that TTA may be a promising candidate for use in the amelioration of inflammatory disorders characterized by changed lipid metabolism due to raised TNFα levels.

Mildronate treatment improves functional recovery following middle cerebral artery occlusion in rats

Mildronate (3-(2,2,2-trimethylhydrazinium) propionate) is an inhibitor of l-carnitine biosynthesis and an anti-ischemic drug. In the present study, we investigated the effects of mildronate in rats following focal cerebral ischemia. Male Wistar rats were subjected to transient occlusion of the middle cerebral artery (MCAO) for 90min, followed by the intraperitoneal administration of mildronate at doses of 100 and 200mg/kg 2h after reperfusion and then daily for an additional 14days. The beam-walking, rota-rod and cylinder tests were used to assess sensorimotor function, and vibrissae-evoked forelimb-placing and limb-placing tests examined responses to tactile and proprioceptive stimulation. Following behavioural testing, the infarct volume was measured. The cerebellar concentrations of l-carnitine, γ-butyrobetaine (GBB) and mildronate were also measured. The results showed that saline-treated MCAO rats had minor or no spontaneous recovery in sensorimotor and proprioceptive function up to 14days post-stroke. Treatment with mildronate at a dose of 200mg/kg was found to accelerate recovery of motor and proprioceptive deficits in limb-placing, cylinder and beam-walking tests. Analysis of rat cerebellar tissue extracts revealed that l-carnitine and GBB concentrations changed with mildronate treatment; the concentration of l-carnitine was significantly decreased by mildronate treatment, whereas the concentration of GBB was significantly increased. Cerebellar concentrations of mildronate also increased in a dose-dependent manner following systemic administration. Infarct size did not differ among the experimental groups on post-stroke day 14. The present study suggests that mildronate treatment improves the functional outcome in MCAO rats without influencing infarct size.

A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation

Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose-fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment.