Original articleSulforaphane prevents the development of cardiomyopathy in type 2 diabetic mice probably by reversing oxidative stress-induced inhibition of LKB1/AMPK pathway
Graphical abstract
Introduction
Type 2 diabetes mellitus (T2DM) is the most widespread metabolic disease in the world. It is estimated that 347 million people worldwide have diabetes [1], of which 90–95% is T2DM [2]. Cardiovascular disease is the major cause of mortality in diabetic patients [3]. Although coronary atherosclerosis likely contributes to the onset of heart failure in diabetic patients [4], diabetes-related cardiomyopathy appears to be a major initiating factor [4]. As first reported by Rubler et al. in 1972 [5], diabetic cardiomyopathy is characterized by cardiac dysfunction without underlying coronary artery disease and/or hypertension. A number of mechanisms for the development of diabetic cardiomyopathy have been proposed, including oxidative stress, inflammation and extracellular fibrosis [6], all of which may be related to cardiac lipotoxicity [7], [8]. However, the involvement of intramyocardial lipid accumulation in the pathogenesis of diabetic cardiomyopathy remains incompletely understood.
AMP-activated protein kinase (AMPK), which is an α,β,γ-heterotrimer complex, is an important sensor that regulates lipid metabolism [9]. Liver kinase B1 (LKB1), the major upstream kinase of AMPK, phosphorylates Thr-172 and activates AMPK [10]. Activation of AMPK in the heart stimulates lipid oxidation to produce energy through its downstream targets. First, activated AMPK upregulates autophagy [11]. Reportedly lipid droplets (LDs) can be selectively degraded by the lysosomal pathway of macroautophagy, which is termed lipophagy [12]. In T2DM, elevated myocardial lipids stored as triglycerides (TGs) in LDs were observed [13], [14]. Lipophagy contributes to myocardial TGs catabolizing into fatty acids via the induction of lysosomal acid lipase [15]. Second, AMPK phosphorylates and inactivates acetyl-CoA carboxylase (ACC), resulting in the down-regulation of malonyl-CoA levels. The product of ACC, malonyl-CoA, is an inhibitor of carnitine palmitoyl transferase-1 (CPT-1), which is a key protein involved in mitochondrial uptake of fatty acids. Therefore, AMPK activation will increase mitochondrial fatty acid uptake [16]. Third, AMPK enhances NAD+-dependent type III deacetylase sirtuin 1 (Sirt1) activity [17]. Activation of AMPK and Sirt1 increases the expression of peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α) [17], [18]. PGC-1α is a key regulator of fatty acid oxidation, ATP synthesis and lipid homeostasis in mitochondria.
Sulforaphane (SFN), a naturally occurring isothiocyanate compound, is isolated from cruciferous vegetables such as broccoli and cabbage. Several studies indicate that SFN prevents diabetes-induced cardiac [19] and aortic damage [20] and testicular apoptotic cell death [21]. It was found that SFN activates nuclear factor erythroid 2 related factor 2 (Nrf2) to upregulate cellular antioxidants against oxidative stress and damage [19]. Recently, it was reported that SFN can attenuate high fat diet (HFD)-induced visceral adiposity, adipocyte hypertrophy and lipid accumulation in the liver [22]. SFN inhibition of adipogenesis through suppressing lipogenesis is mediated by activating AMPK to inhibit ACC in the adipose tissue of HFD-fed mice. However, the mechanism of AMPK activity by SFN is still unclear.
There are several key pathogenic abnormalities, including hyperglycemia, hyperlipidemia, insulin resistance, and abnormal insulin secretion caused by impaired β-cell function in patients with T2DM [23]. However, there is no genetic animal model of T2DM that includes all above features [24], [25], [26]. Several approaches to make T2DM animal models have been explored [21], [27], [28], one of which is the non-genetic model of T2DM [HFD feeding with a single dose of streptozotocin (STZ) treatment], which mimics the metabolic abnormalities seen in human T2DM [21], [29]. We have also used this model of T2DM to investigate diabetic complications including diabetic cardiomyopathy [27] and male germ cell death [21].
In the present study, therefore, we used our previously reported animal model of T2DM [21] to determine (a) whether HFD feeding induces cardiac lipotoxicity; (b) whether T2DM further worsens cardiac lipotoxicity compared to HFD-induced obesity alone; and (c) whether and how SFN prevents T2DM-induced cardiac lipotoxicity and the development of cardiomyopathy by activation of the AMPK pathway.
Section snippets
Animals
C57BL/6J male mice, 8–10 weeks of age, were purchased from The Jackson Laboratory (Bar Harbor, Maine). The mice were housed at the University of Louisville Research Resources Center at 22 °C with a 12 h light/dark cycle with free access to food and tap water.
Generation of diabetic mouse model and treatment with SFN
Experimental procedures, animal treatment and tissue collection information have been described in a recent study [21]. All experimental procedures were approved by the Institutional Animal Care and Use Committee of the University of
T2DM general features and the effect of SFN on heart weight of DM mice
Mice fed with HFD exhibited all of the features of insulin resistance compared with control mice [21], characterized by an increased area under the curve of the glucose tolerance test, hyperinsulinemia, mild hyperglycemia, hypertriglyceridemia, and hypercholesterolemia (Table 1). DM mice further increased insulin resistance, along with elevations in the levels of fasting blood glucose, triglyceride, and cholesterol. SFN treatment for 4 months did not change these diabetes-induced increases
Discussion
In our present study, we observed that HFD feeding induced cardiac hypertrophy but not cardiac dysfunction. We have successfully established a non-genetic rodent model of T2DM, the HFD + STZ induced diabetic mouse [20], [21]. In this animal model, diabetic mice exhibited significant insulin resistance along with increased levels of fasting blood glucose, insulin, triglyceride, and cholesterol. We demonstrated here that DM mice showed a decrease of cardiac wall thickness, EF and FS along with an
Disclosures
None.
Acknowledgements
This study was supported in part by grants from the American Diabetes Association (1-14-IN-38, to N.M. & L.C.; 7-14-BS-018, to L.C.) and the National Natural Science Foundation of China (No. 81370318, to Y.Z.).
Author contribution
Z.Z., S.W., S.Z., X.Y., Y.W., J.C., J.G., N.M., and Y.T. researched data. Z.Z., J.C., M.K. and Y.T. analyzed the data and reviewed the article. N.M., Y.Z., and L.C. contributed initial discussion of the project and reviewed the article. N.M. and L.C. wrote and edited
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2022, Trends in Food Science and TechnologyCitation Excerpt :SFN can also reduce the expressions of fibrogenic mediators (CTGF and TGF-β1) and prevent the fibrosis of the aortic induced by DM(Bai & Cui et al., 2013; Miao & Bai et al., 2012). Inflammation and oxidative damage are two of the main pathogenic factors of myocardial fibrosis, while SFN could significantly reduce the accumulation of 4-HNE and 3-NT in aortic (Miao & Bai et al., 2012; Zhang & Wang et al., 2014), and prevent inflammation (TNF- α and PAI-1) caused by DM(Bai & Cui et al., 2013). The prevalence of hypertension in T2DM patients increased significantly with age.
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