Sexual dimorphism in myocardial acylcarnitine and triglyceride metabolism

Devanathan et al. Biology of Sex Differences (2016) 7:25 DOI 10.1186/s13293-016-0077-7 RESEARCH Open Access Sexual dimorphism in myocardial acylcarnitine and triglyceride metabolism Sriram Devanathan1†, Timothy D. Whitehead1†, Nicole Fettig1, Robert J. Gropler1,2, Samuel Nemanich1 and Kooresh I. Shoghi1,3,4* Abstract Background: Cardiovascular disease is the leading cause of death among diabetic patients. Importantly, recent data highlight the apparent sexual dimorphism in the pathogenesis of cardiovascular disease in diabetics with respect to both frequency- and age-related risk factors. The disposition to cardiovascular disease among diabetic patients has been attributed, at least in part, to excess lipid supply to the heart culminating in lipotoxicity of the heart and downstream derangements. A confounding factor in obese animal models of diabetes is that increased peripheral lipid availability to the heart can induce cardio-metabolic remodeling independent of the underlying pathophysiology of diabetes, thus masking the diabetic phenotype. To that end, we hypothesized that the use of non-obese diabetic (NOD) animal models will reveal metabolic signatures of diabetes in a sex-specific manner. Methods: To test this hypothesis, male and female NOD Goto-Kakizaki (GK) rats were used to assess the expression profile of 84 genes involved in lipid metabolism. In parallel, targeted lipidomics analysis was performed to characterize sex differences in homeostasis of non-esterified fatty acids (NEFA), acylcarnitines (AC), and triglycerides (TG). Results: Our analysis revealed significant sex differences in the expression of a broad range of genes involved in transport, activation, and utilization of lipids. Furthermore, NOD male rats exhibited enhanced oxidative metabolism and accumulation of TG, whereas female NOD rats exhibited reduced TG content coupled with accumulation of AC species. Multi-dimensional statistical analysis identified saturated AC16:0, AC18:0, and AC20:0 as dominant metabolites in mediating sex differences in AC metabolism. Confocal microscopy of rat cardiomyocytes exposed to AC14:0, AC16:0, and AC18:0 confirmed induction of ROS with AC18:0 being more potent followed by AC14:0. Conclusion: Overall, we demonstrate sex differences in myocardial AC and TG metabolism with implications for therapy and diagnosis of diabetic cardiovascular disease. Keywords: Sex differences, Lipid metabolism, Acylcarnitines, Triglycerides, NEFA, Type 2 diabetes, Non-obese, Lipidomics, Genomics, Cardiac metabolism, Biomarker, ROS Background Heart disease is the leading cause of death among diabetic patients, independent of macro- and micro- vascular diseases [1–3]. While diabetes increases the risk of cardiovascular disease in both males and females, recent data suggests that heart disease is fivefold more common in diabetic women compared with twofold in men [4]. * Correspondence: † Equal contributors 1 Department of Radiology, Washington University in St. Louis, 510 South Kingshighway Blvd., Campus Box 8225, Saint Louis, MO 63110, USA 3 Department of Biomedical Engineering, Washington University in St. Louis, 510 South Kingshighway Blvd., Campus Box 8225, Saint Louis, MO 63110, USA Full list of author information is available at the end of the article For example, in the setting of myocardial infarction, diabetic women have a greater progression to heart failure and poorer outcome compared with diabetic males [5]. This “sexual dimorphism” is in contrast to the established notion of a “female advantage” in that premenopausal women in general are better protected from most common forms of cardiovascular disease compared to men [4, 6–9]. Thus, T2DM nullifies the female advantage in the prevalence of cardiovascular disease [4, 10]. Multiple lines of evidence suggest that the predisposition to heart failure among diabetic patients is a consequence of severe alterations in myocardial substrate metabolism [11, 12]. In particular, insulin resistance shifts the balance of substrate utilization such that the © 2016 Devanathan et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Devanathan et al. Biology of Sex Differences (2016) 7:25 diabetic heart relies almost exclusively on fatty acids (FAs) for its energy needs [13]. The increased reliance on FA oxidation competes with glucose oxidation further exacerbating deficiencies in insulin signaling [14]. Excess lipid supply beyond the oxidative capacity of the heart results in accumulation of triglycerides (TG) and lipid intermediates, leading to lipotoxicity of the heart and downstream derangements, including generation of reactive oxygen species (ROS), inflammation, and cell death [15–20]. On the one hand, the observed sexual dimorphism may be explained by the higher systemic availability of lipids [21, 22] resulting in increased myocardial FA metabolism. Indeed, it is well established that females have higher distribution of visceral fat with higher levels of circulating FA and TGs [22]. As an omnivore, the heart will necessarily utilize circulating substrates in proportion to their availability in blood. To that end, in vivo metabolic imaging studies in diabetic humans have demonstrated that, in fact, female hearts exhibit higher flux of FAs compared to age-matched males [23, 24], attributed to higher systemic availability of FA. On the other hand, however, there may be intrinsic sex differences in cardiac lipid metabolism beyond increased peripheral supply of lipids to the heart that may account for the sexual dimorphism. One confounding factor in obese and dietary animal models of diabetes is that increased peripheral lipid availability to the heart can induce cardio-metabolic remodeling independent of the underlying pathophysiology of diabetes, thus masking the diabetic phenotype. In this regard, it is worth noting that, in fact, 20 % of the population is non-obese diabetic (NOD) [25, 26]. This suggests that studies utilizing NOD humans and/or non-obese animal models of diabetes may unmask mechanisms relevant to pathophysiology of diabetes. In this work, we sought to determine whether there are intrinsic sex differences in myocardial FA metabolism in the setting of diabetes, independent of systemic effects seen in obesity or dietary animal models of diabetes. We previously demonstrated that NOD Goto-Kakizaki (GK) rats exhibit a genomic disposition to increased FA metabolism [27]. We hypothesized (...truncated)