Induction of PKC causes multiple deleterious effects, including but not limited to blood flow abnormalities, capillary occlusion and pro-inflammatory gene expression. Finally, glucose, as well as other intermediates such as fructose and glyceraldehyde-3-phosphate, when present in high concentrations, promote the formation of advanced glycation endproducts (AGEs). These, in turn, can irreversibly cross link to proteins and cause intracellular aggregates that cannot be degraded by proteases and thereby, alter intracellular signalling. Also, AGEs can be exported to the intercellular space where they can bind AGE receptors (RAGE). This AGE/RAGE interaction activates
inflammatory pathways such as NF-κB, in the host cells in an autocrine fashion, or in macrophages in a paracrine fashion. Neutrophil activation can also lead to NAD(P)H oxidase production of free radicals further damaging the surrounding cells. Finally, exported glycation products bind extracellular proteins and alter the matrix, cell-matrix interactions and promote fibrosis. A major source of increased myocardial stiffness is crosslinking between AGEs and collagen. In fact, a hallmark of uncontrolled diabetes is glycated products in the serum and can be used as a marker for diabetic microangiopathy. Autonomic neuropathy
While the heart can function without help from the nervous system, it is highly innervated with autonomic nerves, regulating the heart beat according to demand in a fast manner, prior to hormonal release. The autonomic innervations of the myocardium in diabetic cardiomyopathy are altered and contribute to myocardial dysfunction. Unlike the brain, the peripheral nervous system does not benefit from a barrier protecting it from the circulating levels of glucose.
Later in the progression, a prolonged QT interval may be indicative of fibrosis. Given that diabetic cardiomyopathys definition excludes concomitant atherosclerosis or hypertension, there are no changes in perfusion or in atrial natriuretic peptide levels up until the very late stages of the disease, when the hypertrophy and fibrosis become very pronounced. Pathophysiology
Defects in cellular processes such as autophagy and mitophagy are thought to contribute to the development of diabetic cardiomyopathy. Diabetic cardiomyopathy is characterized functionally by ventricular dilation, enlargement of heart cells, prominent interstitial fibrosis and decreased or preserved systolic function in the presence of a diastolic dysfunction.While it has been evident for a long time that the complications seen in diabetes are related to the hyperglycemia associated to it, several factors have been implicated in the pathogenesis of the disease. Etiologically, four main causes are responsible for the development of heart failure in diabetic cardiomyopathy: microangiopathy and related endothelial dysfunction, autonomic neuropathy, metabolic alterations that include abnormal glucose use and increased fatty acid oxidation, generation and accumulation of free radicals, and alterations in ion homeostasis, especially calcium transients. Additional effects include inflammation and upregulation of local angiotensin systems. Diabetic cardiomyopathy may be associated with restrictive (HFPEF) and dilated phenotypes (HFREF). HFPEF results predominantly from hyperinsulinemia, hyperglycemia, lipotoxicity, AGEs and microvascular rarefication. HFREF is associated with autoimmunity, hyperglycemia, lipotoxicity, microvascular rarefication and AGE formation. Microangiopathy
Microangiopathy can be characterized as subendothelial and endothelial fibrosis in the coronary microvasculature of the heart. This endothelial dysfunction leads to impaired myocardial blood flow reserve as evidence by echocardiography.