Excess lipid accumulation in non-adipose tissues is associated with insulin resistance, pancreatic ␤-cell apoptosis and heart failure. Here, we demonstrate in cultured cells that the relative toxicity of two common dietary long chain fatty acids is related to channeling of these lipids to distinct cellular metabolic fates. Oleic acid supplementation leads to triglyceride accumulation and is well tolerated, whereas excess palmitic acid is poorly incorporated into triglyceride and causes apoptosis. Unsaturated fatty acids rescue palmitate-induced apoptosis by channeling palmitate into triglyceride pools and away from pathways leading to apoptosis. Moreover, in the setting of impaired triglyceride synthesis, oleate induces lipotoxicity. Our findings support a model of cellular lipid metabolism in which unsaturated fatty acids serve a protective function against lipotoxicity though promotion of triglyceride accumulation.

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Recent studies provide clues regarding the cellular mechanisms that determine whether excess lipid accumulation is well tolerated or cytotoxic. Critical in this process are physiologic mechanisms for directing excess free fatty acids to specific tissues as well as cellular mechanisms for channeling excess fatty acid to particular metabolic fates. Insight into these mechanisms may contribute to the development of more effective therapies for common human disorders in which lipotoxicity contributes to pathogenesis.

Inherited and acquired cardiomyopathies are associated with marked intracellular lipid accumulation in the heart. To test the hypothesis that mismatch between myocardial fatty acid uptake and utilization leads to the accumulation of cardiotoxic lipid species, and to establish a mouse model of metabolic cardiomyopathy, we generated transgenic mouse lines that overexpress long-chain acylCoA synthetase in the heart (MHC-ACS). This protein plays an important role in vectorial fatty acid transport across the plasma membrane. MHC-ACS mice demonstrate cardiac-restricted expression of the transgene and marked cardiac myocyte triglyceride accumulation. Lipid accumulation is associated with initial cardiac hypertrophy, followed by the development of left-ventricular dysfunction and premature death. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and cytochrome c release in transgenic hearts suggest that cardiac myocyte death occurs, in part, by lipid-induced programmed cell death. Taken together, our data demonstrate that fatty acid uptake/utilization mismatch in the heart leads to accumulation of lipid species toxic to cardiac myocytes. This novel mouse model will provide insight into the role of perturbations in myocardial lipid metabolism in the pathogenesis of inherited and acquired forms of heart failure.

Cell dysfunction and death induced by lipid accumulation in nonadipose tissues, or lipotoxicity, may contribute to the pathogenesis of obesity and type 2 diabetes. However, the mechanisms leading to lipotoxic cell death are poorly understood. We recently reported that, in Chinese hamster ovary (CHO) cells and in H9c2 cardiomyoblasts, lipid overload induced by incubation with 500 mM palmitate leads to intracellular accumulation of reactive oxygen species, which subsequently induce endoplasmic reticulum (ER) stress and cell death. Here, we show that palmitate also impairs ER function through a more direct mechanism. Palmitate was rapidly incorporated into saturated phospholipid and triglyceride species in microsomal membranes of CHO cells. The resulting membrane remodeling was associated with dramatic dilatation of the ER and redistribution of protein-folding chaperones to the cytosol within 5 h, indicating compromised ER membrane integrity. Increasing b-oxidation, through the activation of AMP-activated protein kinase, decreased palmitate incorporation into microsomes, decreased the escape of chaperones to the cytosol, and decreased subsequent caspase activation and cell death. Thus, palmitate rapidly increases the saturated lipid content of the ER, leading to compromised ER morphology and integrity, suggesting that impairment of the structure and function of this organelle is involved in the cellular response to fatty acid overload.-

Cytotoxic accumulation of long chain fatty acids has been proposed to play an important role in the pathogenesis of diabetes mellitus and heart disease. To explore the mechanism of cellular lipotoxicity, we cultured Chinese hamster ovary cells in the presence of media supplemented with fatty acid. The saturated fatty acid palmitate, but not the monounsaturated fatty acid oleate, induced programmed cell death as determined by annexin V positivity, caspase 3 activity, and DNA laddering. De novo ceramide synthesis increased 2.4-fold with palmitate supplementation; however, this was not required for palmitate-induced apoptosis. Neither biochemical nor genetic inhibition of de novo ceramide synthesis arrested apoptosis in Chinese hamster ovary cells in response to palmitate supplementation. Rather, our data suggest that palmitate-induced apoptosis occurs through the generation of reactive oxygen species. Fluorescence of an oxidant-sensitive probe was increased 3.5-fold with palmitate supplementation indicating that production of reactive intermediates increased. In addition, palmitate-induced apoptosis was blocked by pyrrolidine dithiocarbamate and 4,5-dihydroxy-1,3-benzene-disulfonic acid, two compounds that scavenge reactive intermediates. These studies suggest that generation of reactive oxygen species, independent of ceramide synthesis, is important for the lipotoxic response and may contribute to the pathogenesis of diseases involving intracellular lipid accumulation.

Abstract-Evidence is emerging that systemic metabolic disturbances contribute to cardiac myocyte dysfunction and clinically apparent heart failure, independent of associated coronary artery disease. To test the hypothesis that perturbation of lipid homeostasis in cardiomyocytes contributes to cardiac dysfunction, we engineered transgenic mice with cardiac-specific overexpression of fatty acid transport protein 1 (FATP1) using the ␣-myosin heavy chain gene promoter. Two independent transgenic lines demonstrate 4-fold increased myocardial free fatty acid (FFA) uptake that is consistent with the known function of FATP1. Increased FFA uptake in this model likely contributes to early cardiomyocyte FFA accumulation (2-fold increased) and subsequent increased cardiac FFA metabolism (2-fold). By 3 months of age, transgenic mice have echocardiographic evidence of impaired left ventricular filling and biatrial enlargement, but preserved systolic function. Doppler tissue imaging and hemodynamic studies confirm that these mice have predominantly diastolic dysfunction. Furthermore, ambulatory ECG monitoring reveals prolonged QT c intervals, reflecting reductions in the densities of repolarizing, voltage-gated K ϩ currents in ventricular myocytes. Our results show that in the absence of systemic metabolic disturbances, such as diabetes or hyperlipidemia, perturbation of cardiomyocyte lipid homeostasis leads to cardiac dysfunction with pathophysiological findings similar to those in diabetic cardiomyopathy. Moreover, the MHC-FATP model supports a role for FATPs in FFA import into the heart in vivo. Key Words: lipids Ⅲ metabolism Ⅲ cardiomyopathy C ardiomyopathy has been observed in a variety of metabolic disorders. In inherited disorders of ␤-oxidation, accumulation of unmetabolized lipid in cardiac myocytes is associated with ventricular systolic dysfunction. 1 In obesity, increased myocardial oxygen consumption and decreased efficiency may contribute to diastolic and systolic dysfunction. 2,3 In diabetes mellitus, heart failure in the absence of valvular or congenital heart disease, alcoholism, hypertension, or significant epicardial coronary atherosclerosis is defined as diabetic cardiomyopathy and accounts for significant morbidity and mortality in people with type 1 and type 2 diabetes. 4 Echocardiographic and hemodynamic studies suggest left ventricular (LV) diastolic impairment represents an early preclinical manifestation of diabetic cardiomyopathy that may progress over an extended period of time to both diastolic and systolic dysfunction. 5,6 In these metabolic disorders, systemic metabolic perturbations lead to myocyte dysfunction and/or loss. Glucotoxicity, 7 ATP depletion, 8 and maladaptive changes in metabolic substrate utilization 9 are mechanisms proposed to contribute to cardiac dysfunction. It has also been hypothesized that mismatch between tissue free fatty acid (FFA) import and utilization leads to lipid accumulation and results in lipotoxicity. In diabetes, this imbalance results from high-serum F...

Niemann-Pick type C1 (NPC1) disease is a rare progressive neurodegenerative disorder characterized by endolysosomal cholesterol accumulation. Previous studies implicating oxidative stress in NPC1 disease pathogenesis raised the possibility that non-enzymatic formation of cholesterol oxidation products could serve as disease biomarkers. We measured these metabolites in the plasma and tissues of the Npc1−/− mouse model and found several cholesterol oxidation products that were elevated in Npc1−/− mice, were detectable prior to the onset of symptoms, and were associated with disease progression. Non-enzymatically formed cholesterol oxidation products were similarly increased in the plasma of all human NPC1 subjects studied and delineated an oxysterol profile specific for NPC1 disease. This oxysterol profile also correlated with age of disease onset and disease severity. We further show that the plasma oxysterol markers decreased in response to an established therapeutic intervention in the NPC1 feline model. These cholesterol oxidation products are robust blood-based biochemical markers for NPC1 disease that may prove transformative for diagnosis and treatment of this disorder, and as outcome measures to monitor response to therapy.