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Zamani M, Pahlavani N, Nikbaf-Shandiz M, Rasaei N, Ghaffarian-Ensaf R, Asbaghi O, Shiraseb F, Rastgoo S. The effects of L-carnitine supplementation on glycemic markers in adults: A systematic review and dose-response meta-analysis. Front Nutr 2023; 9:1082097. [PMID: 36704801 PMCID: PMC9871499 DOI: 10.3389/fnut.2022.1082097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Accepted: 12/21/2022] [Indexed: 01/11/2023] Open
Abstract
Background and aims Hyperglycemia and insulin resistance are concerns today worldwide. Recently, L-carnitine supplementation has been suggested as an effective adjunctive therapy in glycemic control. Therefore, it seems important to investigate its effect on glycemic markers. Methods PubMed, Scopus, Web of Science, and the Cochrane databases were searched in October 2022 for prospective studies on the effects of L-carnitine supplementation on glycemic markers. Inclusion criteria included adult participants and taking oral L-carnitine supplements for at least seven days. The pooled weighted mean difference (WMD) was calculated using a random-effects model. Results We included the 41 randomized controlled trials (RCTs) (n = 2900) with 44 effect sizes in this study. In the pooled analysis; L-carnitine supplementation had a significant effect on fasting blood glucose (FBG) (mg/dl) [WMD = -3.22 mg/dl; 95% CI, -5.21 to -1.23; p = 0.002; I 2 = 88.6%, p < 0.001], hemoglobin A1c (HbA1c) (%) [WMD = -0.27%; 95% CI, -0.47 to -0.07; p = 0.007; I 2 = 90.1%, p < 0.001] and homeostasis model assessment-estimate insulin resistance (HOMA-IR) [WMD = -0.73; 95% CI, -1.21 to -0.25; p = 0.003; I 2 = 98.2%, p < 0.001] in the intervention compared to the control group. L-carnitine supplementation had a reducing effect on baseline FBG ≥100 mg/dl, trial duration ≥12 weeks, intervention dose ≥2 g/day, participants with overweight and obesity (baseline BMI 25-29.9 and >30 kg/m2), and diabetic patients. Also, L-carnitine significantly affected insulin (pmol/l), HOMA-IR (%), and HbA1c (%) in trial duration ≥12 weeks, intervention dose ≥2 g/day, and participants with obesity (baseline BMI >30 kg/m2). It also had a reducing effect on HOMA-IR in diabetic patients, non-diabetic patients, and just diabetic patients for insulin, and HbA1c. There was a significant nonlinear relationship between the duration of intervention and changes in FBG, HbA1c, and HOMA-IR. In addition, there was a significant nonlinear relationship between dose (≥2 g/day) and changes in insulin, as well as a significant linear relationship between the duration (weeks) (coefficients = -16.45, p = 0.004) of intervention and changes in HbA1C. Conclusions L-carnitine could reduce the levels of FBG, HbA1c, and HOMA-IR. Systematic review registration https://www.crd.york.ac.uk/prospero/, identifier: CRD42022358692.
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Affiliation(s)
- Mohammad Zamani
- Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran
| | - Naseh Pahlavani
- Health Sciences Research Center, Torbat Heydariyeh University of Medical Sciences, Torbat-e Heydariyeh, Iran,Behbahan Faculty of Medical Sciences, Behbahan, Iran
| | | | - Niloufar Rasaei
- Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences (TUMS), Tehran, Iran
| | | | - Omid Asbaghi
- Cancer Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran,Student Research Committee, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Farideh Shiraseb
- Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences (TUMS), Tehran, Iran,*Correspondence: Farideh Shiraseb ✉
| | - Samira Rastgoo
- Student Research Committee, Shahid Beheshti University of Medical Sciences, Tehran, Iran,Department of Cellular and Molecular Nutrition, Faculty of Nutrition Science and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran,Samira Rastgoo ✉
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2
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Sahebnasagh A, Avan R, Monajati M, Hashemi J, Habtemariam S, Negintaji S, Saghafi F. L-carnitine: Searching for New Therapeutic Strategy for Sepsis Management. Curr Med Chem 2021; 29:3300-3323. [PMID: 34789120 DOI: 10.2174/0929867328666211117092345] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 08/19/2021] [Accepted: 08/21/2021] [Indexed: 11/22/2022]
Abstract
In this review, we discussed the biological targets of carnitine, its effects on immune function, and how L-carnitine supplementation may help critically ill patients. L-carnitine is a potent antioxidant. L-carnitine depletion has been observed in prolonged intensive care unit (ICU) stays, while L-carnitine supplementation has beneficial effects in health promotion and regulation of immunity. It is essential for the uptake of fatty acids into mitochondria. By inhibiting the ubiquitin-proteasome system, down-regulation of apelin receptor in cardiac tissue, and reducing β-oxidation of fatty acid, carnitine may decrease vasopressor requirement in septic shock and improve clinical outcomes of this group of patients. We also have an overview of animal and clinical studies that have been recruited for evaluating the beneficial effects of L-carnitine in the management of sepsis/ septic shock. Additional clinical data are required to evaluate the optimal daily dose and duration of L-carnitine supplementation.
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Affiliation(s)
- Adeleh Sahebnasagh
- Clinical Research Center, Department of Internal Medicine, North Khorasan University of Medical Sciences, Bojnurd. Iran
| | - Razieh Avan
- Department of Clinical Pharmacy, Medical Toxicology and Drug Abuse Research Center (MTDRC), Faculty of Pharmacy, Birjand University of Medical Sciences, Birjand. Iran
| | - Mahila Monajati
- Department of Internal Medicine, Golestan University of Medical Sciences, Gorgan. Iran
| | - Javad Hashemi
- Department of Pathobiology and Laboratory Sciences, School of Medicine, North Khorasan University of Medical Sciences, Bojnurd. Iran
| | - Solomon Habtemariam
- Pharmacognosy Research Laboratories and Herbal Analysis Services, School of Science, University of Greenwich, Central Avenue, Chatham-Maritime, Kent ME4 4TB. United Kingdom
| | - Sina Negintaji
- Student Research Committee, School of Pharmacy, Shahid Sadoughi University of Medical Sciences, Yazd. Iran
| | - Fatemeh Saghafi
- Department of Clinical Pharmacy, Faculty of Pharmacy and Pharmaceutical Sciences Research Center, Shahid Sadoughi University of Medical Sciences, Yazd. Iran
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3
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Mohammad S, Al Zoubi S, Collotta D, Krieg N, Wissuwa B, Ferreira Alves G, Purvis GSD, Norata GD, Baragetti A, Catapano AL, Solito E, Zechendorf E, Schürholz T, Correa-Vargas W, Brandenburg K, Coldewey SM, Collino M, Yaqoob MM, Martin L, Thiemermann C. A Synthetic Peptide Designed to Neutralize Lipopolysaccharides Attenuates Metaflammation and Diet-Induced Metabolic Derangements in Mice. Front Immunol 2021; 12:701275. [PMID: 34349763 PMCID: PMC8328475 DOI: 10.3389/fimmu.2021.701275] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 06/29/2021] [Indexed: 12/17/2022] Open
Abstract
Metabolic endotoxemia has been suggested to play a role in the pathophysiology of metaflammation, insulin-resistance and ultimately type-2 diabetes mellitus (T2DM). The role of endogenous antimicrobial peptides (AMPs), such as the cathelicidin LL-37, in T2DM is unknown. We report here for the first time that patients with T2DM compared to healthy volunteers have elevated plasma levels of LL-37. In a reverse-translational approach, we have investigated the effects of the AMP, peptide 19-2.5, in a murine model of high-fat diet (HFD)-induced insulin-resistance, steatohepatitis and T2DM. HFD-fed mice for 12 weeks caused obesity, an impairment in glycemic regulations, hypercholesterolemia, microalbuminuria and steatohepatitis, all of which were attenuated by Peptide 19-2.5. The liver steatosis caused by feeding mice a HFD resulted in the activation of nuclear factor kappa light chain enhancer of activated B cells (NF-ĸB) (phosphorylation of inhibitor of kappa beta kinase (IKK)α/β, IκBα, translocation of p65 to the nucleus), expression of NF-ĸB-dependent protein inducible nitric oxide synthase (iNOS) and activation of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome, all of which were reduced by Peptide 19-2.5. Feeding mice, a HFD also resulted in an enhanced expression of the lipid scavenger receptor cluster of differentiation 36 (CD36) secondary to activation of extracellular signal-regulated kinases (ERK)1/2, both of which were abolished by Peptide 19-2.5. Taken together, these results demonstrate that the AMP, Peptide 19-2.5 reduces insulin-resistance, steatohepatitis and proteinuria. These effects are, at least in part, due to prevention of the expression of CD36 and may provide further evidence for a role of metabolic endotoxemia in the pathogenesis of metaflammation and ultimately T2DM. The observed increase in the levels of the endogenous AMP LL-37 in patients with T2DM may serve to limit the severity of the disease.
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Affiliation(s)
- Shireen Mohammad
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | - Sura Al Zoubi
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom.,Department of Basic Medical Sciences, School of Medicine, Al-Balqa Applied University, As-Salt, Jordan
| | - Debora Collotta
- Department of Drug Science and Technology, University of Turin, Turin, Italy
| | - Nadine Krieg
- Department of Anesthesiology and Intensive Care Medicine, Jena University Hospital, Jena, Germany.,Septomics Research Center, Jena University Hospital, Jena, Germany
| | - Bianka Wissuwa
- Department of Anesthesiology and Intensive Care Medicine, Jena University Hospital, Jena, Germany.,Septomics Research Center, Jena University Hospital, Jena, Germany
| | | | - Gareth S D Purvis
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom.,Sir William Dunn School Pathology, University of Oxford, Oxford, United Kingdom
| | - Giuseppe Danilo Norata
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, Italy.,IRCCS Multimedica, Sesto San Giovanni, Milan, Italy.,Società Italiana per lo Studio della Aterosclerosi (S.I.S.A.) Centre for the Study of Atherosclerosis, Bassini Hospital, Milan, Italy
| | - Andrea Baragetti
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, Italy.,IRCCS Multimedica, Sesto San Giovanni, Milan, Italy
| | - Alberico Luigi Catapano
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, Italy.,IRCCS Multimedica, Sesto San Giovanni, Milan, Italy.,Società Italiana per lo Studio della Aterosclerosi (S.I.S.A.) Centre for the Study of Atherosclerosis, Bassini Hospital, Milan, Italy
| | - Egle Solito
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom.,Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Universitá degli Studi di Napoli "Federico II", Napoli, Italy
| | - Elisabeth Zechendorf
- Department of Intensive Care and Intermediate Care, University Hospital RWTH Aachen, Aachen, Germany
| | - Tobias Schürholz
- Department of Intensive Care and Intermediate Care, University Hospital RWTH Aachen, Aachen, Germany
| | | | - Klaus Brandenburg
- Brandenburg Antiinfektiva GmbH, c/o Forschungszentrum Borstel, Borstel, Germany
| | - Sina M Coldewey
- Department of Anesthesiology and Intensive Care Medicine, Jena University Hospital, Jena, Germany.,Septomics Research Center, Jena University Hospital, Jena, Germany
| | - Massimo Collino
- Department of Neurosciences "Rita Levi Montalcini", University of Turin, Turin, Italy
| | - Muhammad M Yaqoob
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | - Lukas Martin
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom.,Department of Intensive Care and Intermediate Care, University Hospital RWTH Aachen, Aachen, Germany
| | - Christoph Thiemermann
- William Harvey Research Institute, Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
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Sepandar F, Daneshpazhooh M, Djalali M, Mohammadi H, Yaghubi E, Fakhri Z, Tavakoli H, Ghaedi E, Keshavarz A, Zarei M, Shahrbaf MA, Ghandi N, Darand M, Javanbakht MH. The effect of
l
‐carnitine supplementation on serum levels of omentin‐1, visfatin and SFRP5 and glycemic indices in patients with pemphigus vulgaris: A randomized, double‐blind, placebo‐controlled clinical trial. Phytother Res 2019; 34:859-866. [DOI: 10.1002/ptr.6568] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 11/03/2019] [Accepted: 11/12/2019] [Indexed: 02/05/2023]
Affiliation(s)
- Farnaz Sepandar
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Maryam Daneshpazhooh
- Autoimmune Bullous Diseases Research Center, Department of DermatologyTehran University of Medical Sciences Tehran Iran
| | - Mahmoud Djalali
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Hamed Mohammadi
- Department of Clinical Nutrition, School of Nutrition and Food Science, Food Security Research CenterIsfahan University of Medical Sciences Isfahan Iran
| | - Elham Yaghubi
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Zahra Fakhri
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Hajar Tavakoli
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Ehsan Ghaedi
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Ali Keshavarz
- Department of Clinical Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | - Mahnaz Zarei
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
| | | | - Narges Ghandi
- Autoimmune Bullous Diseases Research Center, Department of DermatologyTehran University of Medical Sciences Tehran Iran
| | - Mina Darand
- Student Research Committee, National Nutrition and Food Technology Research Institute, Faculty of Nutrition Sciences and Food TechnologyShahid Beheshti University of Medical Sciences Tehran Iran
| | - Mohamad Hassan Javanbakht
- Department of Cellular and Molecular Nutrition, School of Nutritional Sciences and DieteticsTehran University of Medical Sciences Tehran Iran
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5
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Urfalı S, Koyuncu O, Hakimoğlu S, Özbakış Akkurt Ç, Polat S. Oral L-Carnitine Kullanan Hastada Tedavi Yaklaşımımız. MUSTAFA KEMAL ÜNIVERSITESI TIP DERGISI 2019. [DOI: 10.17944/mkutfd.511773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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6
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Bruls YM, de Ligt M, Lindeboom L, Phielix E, Havekes B, Schaart G, Kornips E, Wildberger JE, Hesselink MK, Muoio D, Schrauwen P, Schrauwen-Hinderling VB. Carnitine supplementation improves metabolic flexibility and skeletal muscle acetylcarnitine formation in volunteers with impaired glucose tolerance: A randomised controlled trial. EBioMedicine 2019; 49:318-330. [PMID: 31676389 PMCID: PMC6945245 DOI: 10.1016/j.ebiom.2019.10.017] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Revised: 10/10/2019] [Accepted: 10/10/2019] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Type 2 diabetes patients and individuals at risk of developing diabetes are characterized by metabolic inflexibility and disturbed glucose homeostasis. Low carnitine availability may contribute to metabolic inflexibility and impaired glucose tolerance. Here, we investigated whether carnitine supplementation improves metabolic flexibility and insulin sensitivity in impaired glucose tolerant (IGT) volunteers. METHODS Eleven IGT- volunteers followed a 36-day placebo- and L-carnitine treatment (2 g/day) in a randomised, placebo-controlled, double blind crossover design. A hyperinsulinemic-euglycemic clamp (40 mU/m2/min), combined with indirect calorimetry (ventilated hood) was performed to determine insulin sensitivity and metabolic flexibility. Furthermore, metabolic flexibility was assessed in response to a high-energy meal. Skeletal muscle acetylcarnitine concentrations were measured in vivo using long echo time proton magnetic resonance spectroscopy (1H-MRS, TE=500 ms) in the resting state (7:00AM and 5:00PM) and after a 30-min cycling exercise. Twelve normal glucose tolerant (NGT) volunteers were included without any intervention as control group. RESULTS Metabolic flexibility of IGT-subjects completely restored towards NGT control values upon carnitine supplementation, measured during a hyperinsulinemic-euglycemic clamp and meal test. In muscle, carnitine supplementation enhanced the increase in resting acetylcarnitine concentrations over the day (delta 7:00 AM versus 5:00 PM) in IGT-subjects. Furthermore, carnitine supplementation increased post-exercise acetylcarnitine concentrations and reduced long-chain acylcarnitine species in IGT-subjects, suggesting the stimulation of a more complete fat oxidation in muscle. Whole-body insulin sensitivity was not affected. CONCLUSION Carnitine supplementation improves acetylcarnitine formation and rescues metabolic flexibility in IGT-subjects. Future research should investigate the potential of carnitine in prevention/treatment of type 2 diabetes.
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Affiliation(s)
- Yvonne Mh Bruls
- Department of Radiology and Nuclear Medicine, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands; Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Marlies de Ligt
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Lucas Lindeboom
- Department of Radiology and Nuclear Medicine, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands; Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Esther Phielix
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Bas Havekes
- Department of Internal Medicine, Division of Endocrinology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Gert Schaart
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Esther Kornips
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Joachim E Wildberger
- Department of Radiology and Nuclear Medicine, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Matthijs Kc Hesselink
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Deborah Muoio
- Department of Medicine, Duke University Medical Center, Durham, NC NC22704, United States of America
| | - Patrick Schrauwen
- Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands
| | - Vera B Schrauwen-Hinderling
- Department of Radiology and Nuclear Medicine, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands; Department of Nutrition and Movement Sciences, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, 6200 MD Maastricht, the Netherlands.
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7
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Radfar S, Ghoreishi SM. Experimental extraction of L-Carnitine from oyster mushroom with supercritical carbon dioxide and methanol as co-solvent: Modeling and optimization. J Supercrit Fluids 2018. [DOI: 10.1016/j.supflu.2018.06.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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8
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Shaw A, Jeromson S, Watterson KR, Pediani JD, Gallagher IJ, Whalley T, Dreczkowski G, Brooks N, Galloway SD, Hamilton DL. Multiple AMPK activators inhibit l-carnitine uptake in C2C12 skeletal muscle myotubes. Am J Physiol Cell Physiol 2017; 312:C689-C696. [PMID: 28298333 DOI: 10.1152/ajpcell.00026.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Revised: 02/21/2017] [Accepted: 03/14/2017] [Indexed: 12/29/2022]
Abstract
Mutations in the gene that encodes the principal l-carnitine transporter, OCTN2, can lead to a reduced intracellular l-carnitine pool and the disease Primary Carnitine Deficiency. l-Carnitine supplementation is used therapeutically to increase intracellular l-carnitine. As AMPK and insulin regulate fat metabolism and substrate uptake, we hypothesized that AMPK-activating compounds and insulin would increase l-carnitine uptake in C2C12 myotubes. The cells express all three OCTN transporters at the mRNA level, and immunohistochemistry confirmed expression at the protein level. Contrary to our hypothesis, despite significant activation of PKB and 2DG uptake, insulin did not increase l-carnitine uptake at 100 nM. However, l-carnitine uptake was modestly increased at a dose of 150 nM insulin. A range of AMPK activators that increase intracellular calcium content [caffeine (10 mM, 5 mM, 1 mM, 0.5 mM), A23187 (10 μM)], inhibit mitochondrial function [sodium azide (75 μM), rotenone (1 μM), berberine (100 μM), DNP (500 μM)], or directly activate AMPK [AICAR (250 μM)] were assessed for their ability to regulate l-carnitine uptake. All compounds tested significantly inhibited l-carnitine uptake. Inhibition by caffeine was not dantrolene (10 μM) sensitive despite dantrolene inhibiting caffeine-mediated calcium release. Saturation curve analysis suggested that caffeine did not competitively inhibit l-carnitine transport. To assess the potential role of AMPK in this process, we assessed the ability of the AMPK inhibitor Compound C (10 μM) to rescue the effect of caffeine. Compound C offered a partial rescue of l-carnitine uptake with 0.5 mM caffeine, suggesting that AMPK may play a role in the inhibitory effects of caffeine. However, caffeine likely inhibits l-carnitine uptake by alternative mechanisms independently of calcium release. PKA activation or direct interference with transporter function may play a role.
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Affiliation(s)
- Andy Shaw
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - Stewart Jeromson
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - Kenneth R Watterson
- Molecular Pharmacology Group, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom; and
| | - John D Pediani
- Molecular Pharmacology Group, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom; and
| | - Iain J Gallagher
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - Tim Whalley
- Biological and Environmental Sciences, School of Natural Sciences, University of Stirling, Stirling, United Kingdom
| | - Gillian Dreczkowski
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - Naomi Brooks
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - Stuart D Galloway
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom
| | - D Lee Hamilton
- Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom;
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9
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Malinowska AM, Szwengiel A, Chmurzynska A. Dietary, anthropometric, and biochemical factors influencing plasma choline, carnitine, trimethylamine, and trimethylamine-N-oxide concentrations. Int J Food Sci Nutr 2016; 68:488-495. [PMID: 27855528 DOI: 10.1080/09637486.2016.1256379] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The objective of the study was to evaluate the nutritional, anthropometric, and biochemical factors that influence choline, l-carnitine, trimethylamine (TMA), and trimethylamine-N-oxide (TMAO) metabolism in elderly women. The volunteers' diet was assessed using a food frequency questionnaire. Dietary patterns were estimated using a self-established score method. Body mass index (BMI), serum glucose, total, HDL, LDL cholesterol, triacylglycerol, homocysteine (tHcy), free choline (fchol), L-carnitine, TMA, and TMAO were assessed. Higher concentrations of l-carnitine, fchol, and TMAO were found in those women who had more western-style dietary patterns. Nor choline or betaine intake affected plasma fchol, TMA, or TMAO. BMI was positively correlated with fchol and TMA. tHcy was positively correlated with fchol, TMA, and TMAO, while fchol was also positively correlated with TMA and TMAO. Dietary patterns and plasma tHcy concentration influence fchol, TMA, and TMAO plasma concentration. Plasma TMA and fchol may be associated with BMI.
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Affiliation(s)
- Anna M Malinowska
- a Department of Human Nutrition and Hygiene , Poznań University of Life Sciences , Poznań , Poland
| | - Artur Szwengiel
- b Department of Fermentation and Biosynthesis, Institute of Food Technology of Plant Origin , Poznań University of Life Sciences , Poznań , Poland
| | - Agata Chmurzynska
- a Department of Human Nutrition and Hygiene , Poznań University of Life Sciences , Poznań , Poland
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10
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Park HJ, Lee HS. The influence of obesity on the effects of spirulina supplementation in the human metabolic response of Korean elderly. Nutr Res Pract 2016; 10:418-23. [PMID: 27478549 PMCID: PMC4958645 DOI: 10.4162/nrp.2016.10.4.418] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 01/05/2016] [Accepted: 02/19/2016] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND/OBJECTIVES Spirulina, a blue-green alga, is widely produced and commercialized as a dietary supplement with bio- and immune-modulatory functions. We have previously shown that spirulina had favorable effects on lipid profiles, immune functions, and antioxidant capacity in healthy Korean elderly. Despite favorable effect of spirulina supplementation, some sub-populations have shown a poor response to supplementation. Obesity is a factor related to poor-response. Therefore, the purpose of this study was to determine the immuno-modulation, antioxidant capacity, and lipid-lowering effect of spirulina in obese and non-obese Korean elderly. SUBJECTS/METHODS The subjects were 78 elderly aged 60-87 years. In a randomized double blind, placebo-controlled study, subjects were fed either placebo or spirulina daily, at 8 g for 12 weeks. Subjects were divided into the non-obese group and the obese group based on body mass index (BMI) criteria for Asians suggested by the International Obesity Task Force: BMI < 25 kg/m2 (non-obese) and BMI ≥ 25 kg/m2 (obese). RESULTS In the non-obese group, spirulina supplementation showed a significant lowering effect on plasma concentration of total cholesterol and LDL-cholesterol, a significant increase in interleukin (IL)-2 concentration (P < 0.01) and a significant increment (P < 0.05) in IL-2/IL-6 ratio, and a significant increase in total antioxidant status level and a significant decrease in thiobarbituric acid reactive substances level. However, these effects were not observed in the obese group. CONCLUSIONS These results demonstrated that blood lipid lowering and immune and antioxidant improving response for spirulina supplement was affected by obesity in Korean elderly.
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Affiliation(s)
- Hee-Jung Park
- Food and Nutrition, Kookmin University, Seoul 02707, Korea
| | - Hyun-Sook Lee
- Food Science and Nutrition, Dongseo University, 47 Jurye-ro, Sasang-gu, Busan 47011, Korea
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11
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Deusing DJ, Beyrer M, Fitzenberger E, Wenzel U. Carnitine protects the nematode Caenorhabditis elegans from glucose-induced reduction of survival depending on the nuclear hormone receptor DAF-12. Biochem Biophys Res Commun 2015; 460:747-52. [PMID: 25817784 DOI: 10.1016/j.bbrc.2015.03.101] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Accepted: 03/18/2015] [Indexed: 11/17/2022]
Abstract
Besides its function in transport of fatty acids into mitochondria in order to provide substrates for β-oxidation, carnitine has been shown to affect also glucose metabolism and to inhibit several mechanisms associated with diabetic complications. In the present study we used the mev-1 mutant of the nematode Caenorhabditis elegans fed on a high glucose concentration in liquid media as a diabetes model and tested the effects of carnitine supplementation on their survival under heat-stress. Carnitine at 100 μM completely prevented the survival reduction that was caused by the application of 10 mM glucose. RNA-interference for sir-2.1, a candidate genes mediating the effects of carnitine revealed no contribution of the sirtuin for the rescue of survival. Under daf-12 RNAi rescue of survival by carnitine was abolished. RNA-interference for γ-butyrobetaine hydroxylase 2, encoding the key enzyme for carnitine biosynthesis did neither increase glucose toxicity nor prevent the rescue of survival by carnitine, suggesting that the effects of carnitine supplementation on carnitine levels were significant. Finally, it was demonstrated that neither the amount of lysosomes nor the proteasomal activity were increased by carnitine, excluding that protein degradation pathways, such as autophagy or proteasomal degradation, are involved in the protective carnitine effects. In conclusion, carnitine supplementation prevents the reduction of survival caused by glucose in C. elegans in dependence on a nuclear hormone receptor which displays high homologies to the vertebrate peroxisomal proliferator activated receptors.
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Affiliation(s)
- Dorothé Jenni Deusing
- Molecular Nutrition Research, Interdisciplinary Research Center, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.
| | - Melanie Beyrer
- Molecular Nutrition Research, Interdisciplinary Research Center, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.
| | - Elena Fitzenberger
- Molecular Nutrition Research, Interdisciplinary Research Center, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.
| | - Uwe Wenzel
- Molecular Nutrition Research, Interdisciplinary Research Center, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.
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12
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Guarnieri G. Carnitine in Maintenance Hemodialysis Patients. J Ren Nutr 2015; 25:169-75. [DOI: 10.1053/j.jrn.2014.10.025] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Accepted: 10/29/2014] [Indexed: 11/11/2022] Open
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13
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Cahova M, Chrastina P, Hansikova H, Drahota Z, Trnovska J, Skop V, Spacilova J, Malinska H, Oliyarnyk O, Papackova Z, Palenickova E, Kazdova L. Carnitine supplementation alleviates lipid metabolism derangements and protects against oxidative stress in non-obese hereditary hypertriglyceridemic rats. Appl Physiol Nutr Metab 2015; 40:280-91. [DOI: 10.1139/apnm-2014-0163] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The aim of this study was to estimate the effect of carnitine supplementation on lipid disorders and peripheral tissue insulin sensitivity in a non-obese animal model of insulin resistance, the hereditary hypertriglyceridemic (HHTg) rat. Male HHTg rats were fed a standard diet, and half of them received daily doses of carnitine (500 mg·kg−1body weight) for 8 weeks. Rats of the original Wistar strain were used for comparison. HHTg rats exhibited increased urinary excretion of free carnitine and reduced carnitine content in the liver and blood. Carnitine supplementation compensated for this shortage and promoted urinary excretion of acetylcarnitine without any signs of (acyl)carnitine accumulation in skeletal muscle. Compared with their untreated littermates, carnitine-treated HHTg rats exhibited lower weight gain, reduced liver steatosis, lower fasting triglyceridemia, and greater reduction of serum free fatty acid content after glucose load. Carnitine treatment was associated with increased mitochondrial biogenesis and oxidative capacity for fatty acids, amelioration of oxidative stress, and restored substrate switching in the liver. In skeletal muscle (diaphragm), carnitine supplementation was associated with significantly higher palmitate oxidation and a more favorable complete to incomplete oxidation products ratio. Carnitine supplementation further enhanced insulin sensitivity ex vivo. No effects on whole-body glucose tolerance were observed. Our data suggest that some metabolic syndrome-related disorders, particularly fatty acid oxidation, steatosis, and oxidative stress in the liver, could be attenuated by carnitine supplementation. The effect of carnitine could be explained, at least partly, by enhanced substrate oxidation and increased fatty acid transport from tissues in the form of short-chain acylcarnitines.
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Affiliation(s)
- Monika Cahova
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
| | - Petr Chrastina
- Institute of Inherited Metabolic Disorders, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Prague 2, Czech Republic
| | - Hana Hansikova
- Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Prague 2, Czech Republic
| | - Zdenek Drahota
- Institute of Physiology, Czech Academy of Sciences, Prague 4, Czech Republic
| | - Jaroslava Trnovska
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
| | - Vojtech Skop
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
- Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague 6, Czech Republic
| | - Jana Spacilova
- Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Prague 2, Czech Republic
| | - Hana Malinska
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
| | - Olena Oliyarnyk
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
| | - Zuzana Papackova
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
| | - Eliska Palenickova
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
- Department of Cell Biology, Faculty of Science, Charles University in Prague, Prague 2, Czech Republic
| | - Ludmila Kazdova
- Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Videnska 1958/9, Prague 4, Czech Republic
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14
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Liu L, Zhang DM, Wang MX, Fan CY, Zhou F, Wang SJ, Kong LD. The adverse effects of long-term l-carnitine supplementation on liver and kidney function in rats. Hum Exp Toxicol 2015; 34:1148-61. [DOI: 10.1177/0960327115571767] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Levo-Carnitine (l-carnitine) is widely used in health and food. This study was to focus on the adverse effects of 8-week oral supplementation of l-carnitine (0.3 and 0.6 g/kg) in female and male Sprague Dawley rats. l-carnitine reduced body and fat weights, as well as serum, liver, and kidney lipid levels in rats. Simultaneously, hepatic fatty acid β-oxidation and lipid synthesis were disturbed in l-carnitine-fed rats. Moreover, l-carnitine accelerated reactive oxygen species production in serum and liver, thereby triggering hepatic NOD-like receptor 3 (NLRP3) inflammasome activation to elevate serum interleukin (IL)-1β and IL-18 levels in rats. Alteration of serum alkaline phosphatase levels further confirmed liver dysfunction in l-carnitine-fed rats. Additionally, l-carnitine may potentially disturb kidney function by altering renal protein levels of rat organic ion transporters. These observations may provide the caution information for the safety of long-term l-carnitine supplementation.
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Affiliation(s)
- L Liu
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - D-M Zhang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - M-X Wang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - C-Y Fan
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - F Zhou
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - S-J Wang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
| | - L-D Kong
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, People’s Republic of China
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15
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Wang X, Liu H, Chen J, Li Y, Qu S. Multiple Factors Related to the Secretion of Glucagon-Like Peptide-1. Int J Endocrinol 2015; 2015:651757. [PMID: 26366173 PMCID: PMC4558455 DOI: 10.1155/2015/651757] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 08/02/2015] [Accepted: 08/03/2015] [Indexed: 12/15/2022] Open
Abstract
The glucagon-like peptide-1 is secreted by intestinal L cells in response to nutrient ingestion. It regulates the secretion and sensitivity of insulin while suppressing glucagon secretion and decreasing postprandial glucose levels. It also improves beta-cell proliferation and prevents beta-cell apoptosis induced by cytotoxic agents. Additionally, glucagon-like peptide-1 delays gastric emptying and suppresses appetite. The impaired secretion of glucagon-like peptide-1 has negative influence on diabetes, hyperlipidemia, and insulin resistance related diseases. Thus, glucagon-like peptide-1-based therapies (glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors) are now well accepted in the management of type 2 diabetes. The levels of glucagon-like peptide-1 are influenced by multiple factors including a variety of nutrients. The component of a meal acts as potent stimulants of glucagon-like peptide-1 secretion. The levels of its secretion change with the intake of different nutrients. Some drugs also have influence on GLP-1 secretion. Bariatric surgery may improve metabolism through the action on GLP-1 levels. In recent years, there has been a great interest in developing effective methods to regulate glucagon-like peptide-1 secretion. This review summarizes the literature on glucagon-like peptide-1 and related factors affecting its levels.
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Affiliation(s)
- XingChun Wang
- Department of Endocrinology and Metabolism, Shanghai 10th People's Hospital, Tongji University, Shanghai 200072, China
| | - Huan Liu
- Department of Urology, Zhenjiang First People's Hospital, Zhenjiang, Jiangsu 212002, China
| | - Jiaqi Chen
- Department of Endocrinology and Metabolism, Shanghai 10th People's Hospital, Tongji University, Shanghai 200072, China
- Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Yan Li
- Department of Endocrinology and Metabolism, Shanghai 10th People's Hospital, Tongji University, Shanghai 200072, China
- Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Shen Qu
- Department of Endocrinology and Metabolism, Shanghai 10th People's Hospital, Tongji University, Shanghai 200072, China
- Nanjing Medical University, Nanjing, Jiangsu 210029, China
- *Shen Qu:
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16
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A need to reconsider the definition of 'healthy participants' in epidemiological studies and clinical trials. Eur J Clin Nutr 2014; 68:724-5. [PMID: 24713623 DOI: 10.1038/ejcn.2014.57] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Revised: 02/21/2014] [Accepted: 02/27/2014] [Indexed: 11/09/2022]
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17
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Ringseis R, Keller J, Eder K. Mechanisms underlying the anti-wasting effect of l-carnitine supplementation under pathologic conditions: evidence from experimental and clinical studies. Eur J Nutr 2013; 52:1421-42. [DOI: 10.1007/s00394-013-0511-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 03/03/2013] [Indexed: 01/17/2023]
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Mansour A, Hosseini S, Larijani B, Pajouhi M, Mohajeri-Tehrani MR. Nutrients related to GLP1 secretory responses. Nutrition 2013; 29:813-20. [PMID: 23415393 DOI: 10.1016/j.nut.2012.11.015] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Revised: 11/04/2012] [Accepted: 11/23/2012] [Indexed: 12/25/2022]
Abstract
The hormone glucagon-like peptide (GLP-1) is secreted from gut endocrine L cells in response to ingested nutrients. The activities of GLP-1 include stimulating insulin gene expression and biosynthesis, improving β-cell proliferation, exogenesis, and survival. Additionally, it prevents β-cell apoptosis induced by a variety of cytotoxic agents. In extrapancreatic tissues, GLP-1 suppresses hunger, delays gastric emptying, acts as an ileal brake, and increases glucose uptake. The pleiotropic actions of GLP-1, especially its glucose-lowering effect, gave rise to the suggestion that it is a novel approach to insulin resistance treatment. Hormones secreted from the gut including GLP-1, which are involved in the regulation of insulin sensitivity and secretions, have been found to be affected by nutrient intake. In recent years, there has been a growing interest in the effect nutrients may have on GLP-1 secretion; some frequently studied dietary constituents include monounsaturated fatty acids, fructooligosaccharides, and glutamine. This review focuses on the influence that the carbohydrate, fat, and protein components of a meal may have on the GLP-1 postprandial responses.
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Affiliation(s)
- Asieh Mansour
- Endocrinology and Metabolism Research Center, Tehran University of Medical Sciences, Tehran, Iran
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Role of carnitine in the regulation of glucose homeostasis and insulin sensitivity: evidence from in vivo and in vitro studies with carnitine supplementation and carnitine deficiency. Eur J Nutr 2011; 51:1-18. [PMID: 22134503 DOI: 10.1007/s00394-011-0284-2] [Citation(s) in RCA: 111] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 11/17/2011] [Indexed: 10/15/2022]
Abstract
BACKGROUND Although carnitine is best known for its role in the import of long-chain fatty acids (acyl groups) into the mitochondrial matrix for subsequent β-oxidation, carnitine is also necessary for the efflux of acyl groups out of the mitochondria. Since intracellular accumulation of acyl-CoA derivatives has been implicated in the development of insulin resistance, carnitine supplementation has gained attention as a tool for the treatment of insulin resistance. More recent studies even point toward a causative role for carnitine insufficiency in developing insulin resistance during states of chronic metabolic stress, such as obesity, which can be reversed by carnitine supplementation. METHODS The present review provides an overview about data from both animal and human studies reporting effects of either carnitine supplementation or carnitine deficiency on parameters of glucose homeostasis and insulin sensitivity in order to establish the less well-recognized role of carnitine in regulating glucose homeostasis. RESULTS Carnitine supplementation studies in both humans and animals demonstrate an improvement of glucose tolerance, in particular during insulin-resistant states. In contrast, less consistent results are available from animal studies investigating the association between carnitine deficiency and glucose intolerance. The majority of studies dealing with this question could either find no association or even reported that carnitine deficiency lowers blood glucose and improves insulin sensitivity. CONCLUSIONS In view of the abovementioned beneficial effect of carnitine supplementation on glucose tolerance during insulin-resistant states, carnitine supplementation might be an effective tool for improvement of glucose utilization in obese type 2 diabetic patients. However, further studies are necessary to explain the conflicting observations from studies dealing with carnitine deficiency.
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