Effect of inhibition of glycosphingolipid synthesis on vascular and cardiac function: a novel therapeutic strategy

Background. Vascular dysfunction of conduit arteries is manifest as atherosclerosis and vascular stiffness, which are significant contributors to cardiovascular disease. Vascular dysfunction is characterized by thickening and stiffening of the vessel walls, and is accelerated by a sedentary lifestyle and advancing age. Despite the heavy public health burden of vascular dysfunction, no cure has been found. A recent study by Chatterjee et al., using a dietary model of atherosclerosis in rabbits, showed that atherogenesis was inhibited by D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), a glycosphingolipid synthesis inhibitor. The work presented in this thesis focusses on determining the molecular mechanism by which D-PDMP affects vascular and cardiac function through modification of wall properties, by inhibition of atherosclerosis and associated pathological cardiac hypertrophy (LVH), in murine models of atherosclerosis. Novel imaging methods of assessing atherosclerosis are explored, as well as drug delivery systems of D-PDMP with the aim of improving therapeutic efficacy. Methods. Experiments were performed in ApoE (-/-) mice fed a high cholesterol and high fat diet, with and without D-PDMP, from 12 to 36 weeks, during the prevention phase and treated from 20 to 36 weeks for the intervention phase. Plaque area, intima-media wall thickness, cardiac hypertrophy and contractility were assessed using high-resolution ultrasound. Blood pressure (tail cuff) and aortic pulse wave velocity (PWV, measure of arterial stiffness) were measured. Tissues were harvested for further molecular and histopathological studies. In separate cohorts of mice, molecular imaging of inflammation was conducted using the radiotracer Iodo-DPA-713 and SPECT. Drug delivery of D-PDMP was explored using biodegradable polymer encapsulation. Results. Apo E(-/-) mice fed a hyperlipidemic diet showed marked accumulation of atherosclerotic plaque, increased PWV independent of blood pressure, decreased cardiac contractility, and increased LVH and fibrosis, compared to control and treated mice These effects were largely attenuated during the prevention phase, and reversed during the intervention phase of D-PDMP. Measurement of glycolipid glycotransferases showed that a hyperlipidemic diet increased the activity of glucosylceramide synthase and lactosylceramide synthase in the aortic wall and myocardium of Apo E (-/-) mice. Treatment with D-PDMP prevented these changes. Novel molecular imaging showed that IodoDPA is a promising, new imaging agent for assessing atherosclerosis, with specificity for the macrophage component of the lesions. Delivery of D-PDMP via biodegradable polymer encapsulation resulted in improved efficacy of glycolipid synthase inhibition, through increases in gastro-intestinal absorption and residence time, compared to non-encapsulated D-PDMP treatment method. Conclusion: D-PDMP is therapeutically an anti-atherogenic and cardio-protective treatment, with concomitant reduction of arterial stiffness. The work presented in this thesis has elucidated a mechanism of action through inhibition of glucosylceramide and lactosylceramide synthase. This work, and related studies, will enhance our understanding of the pathophysiological, molecular, and genetic mechanisms underlying the progression, prevention and intervention of cardiovascular diseases, using novel therapeutic and methodic strategies.