title: Long-chain acylcarnitines activate cell stress and myokine release in C2C12 myotubes: calcium-dependent and -independent effects.
abstract: Acylcarnitines, important lipid biomarkers reflective of acyl-CoA status, are metabolites that possess bioactive and inflammatory properties. This study examined the potential for long-chain acylcarnitines to activate cellular inflammatory, stress, and death pathways in a skeletal muscle model. Differentiated C2C12 myotubes treated with l-C14, C16, C18, and C18:1 carnitine displayed dose-dependent increases in IL-6 production with a concomitant rise in markers of cell permeability and death, which was not observed for shorter chain lengths. l-C16 carnitine, used as a representative long-chain acylcarnitine at initial extracellular concentrations ≥25 μM, increased IL-6 production 4.1-, 14.9-, and 31.4-fold over vehicle at 25, 50, and 100 μM. Additionally, l-C16 carnitine activated c-Jun NH2-terminal kinase, extracellular signal-regulated kinase, and p38 mitogen-activated protein kinase between 2.5- and 11-fold and induced cell injury and death within 6 h with modest activation of the apoptotic caspase-3 protein. l-C16 carnitine rapidly increased intracellular calcium, most clearly by 10 μM, implicating calcium as a potential mechanism for some activities of long-chain acylcarnitines. The intracellular calcium chelator BAPTA-AM blunted l-C16 carnitine-mediated IL-6 production by >65%. However, BAPTA-AM did not attenuate cell permeability and death responses, indicating that these outcomes are calcium independent. The 16-carbon zwitterionic compound amidosulfobetaine-16 qualitatively mimicked the l-C16 carnitine-associated cell stress outcomes, suggesting that the effects of high experimental concentrations of long-chain acylcarnitines are through membrane disruption. Herein, a model is proposed in which acylcarnitine cell membrane interactions take place along a spectrum of cellular concentrations encountered in physiological-to-pathophysiological conditions, thus regulating function of membrane-based systems and impacting cell biology.
authors: Molecular, Cellular and Integrative Physiology Graduate Group, University of California, Davis, California;
authors: Colin S
authors: CS
authors: McCoin
authors: Obesity & Metabolism Research Unit, United States Department of Agriculture-Agricultural Research Service Western Human Nutrition Research Center, Davis, CA; Department of Nutrition, University of California, Davis, Davis, California; and.
authors: Trina A
authors: TA
authors: Knotts
authors: Obesity & Metabolism Research Unit, United States Department of Agriculture-Agricultural Research Service Western Human Nutrition Research Center, Davis, CA;
authors: Kikumi D
authors: KD
authors: Ono-Moore
authors: Obesity & Metabolism Research Unit, United States Department of Agriculture-Agricultural Research Service Western Human Nutrition Research Center, Davis, CA;
authors: Pieter J
authors: PJ
authors: Oort
authors: Molecular, Cellular and Integrative Physiology Graduate Group, University of California, Davis, California; Department of Nutrition, University of California, Davis, Davis, California; and Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas SHAdams@uams.edu.
authors: Sean H
authors: SH
authors: Adams
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002331:Carnitine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D015850:Interleukin-6 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects*; D013329:Structure-Activity Relationship
chemical_list: D015850:Interleukin-6; C116917:acylcarnitine; D002331:Carnitine; D002118:Calcium
keywords: cell death; interleukin-6; skeletal muscle