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.
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands; and.
Bart
B
Wessels
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands; and.
Nicole M A
NM
van den Broek
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands; and.
Jolita
J
Ciapaite
Laboratory Genetic Metabolic Diseases, Departments of Pediatrics and Clinical Chemistry, Academic Medical Center, Amsterdam, the Netherlands.
Sander M
SM
Houten
Laboratory Genetic Metabolic Diseases, Departments of Pediatrics and Clinical Chemistry, Academic Medical Center, Amsterdam, the Netherlands.
Ronald J A
RJ
Wanders
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands; and.
Klaas
K
Nicolay
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands; and j.j.prompers@tue.nl.
Jeanine J
JJ
Prompers
D000818:Animals; D002331:Carnitine / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D059305:Diet, High-Fat; D019587:Dietary Supplements; D050356:Lipid Metabolism / Q000187:drug effects; D008055:Lipids / Q000009:adverse effects*; D008297:Male; D008931:Mitochondria, Muscle / Q000187:drug effects* / Q000378:metabolism; D028361:Mitochondrial Diseases / Q000178:diet therapy* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D008055:Lipids; C116917:acylcarnitine; D002331:Carnitine
carnitine supplementation; fatty acid oxidation; insulin resistance; lipid accumulation; mitochondrial function