Some patients with diabetes develop a serious condition known as diabetic cardiomyopathy, which is slow and cannot be directly attributed to hypertension or other cardiovascular disorders. This often under-diagnosed heart function impairment is one of the leading causes of death in diabetic patients and it affects both type 1 and type 2 diabetes. There is no current specific drug treatment or clinical protocol approved to address this disease.
A study published in the journal Pharmacological Research describes a potential target that could spur the design of new therapeutic strategies to specifically treat diabetic cardiomyopathy. The paper describes the beneficial effects — on the disease — of activating a protein the nuclear receptor PPARβ/δ present in all body cells and especially abundant in organs and tissues with more active metabolism (skeletal muscle, heart, liver or adipose tissue).
Manuel Vázquez-Carrera and Xavier Palomer, from the UB’s Faculty of Pharmacy and Food Sciences, the UB Institute of Biomedicine (IBUB) and the Sant Joan de Déu Research Institute (IRSJD), lead the study as experts from the Centre for Biomedical Research Network (CIBER) on Diabetes and Associated Metabolic Diseases (CIBERDEM).
Other researchers signing this paper are Fátima Crispi, from the UB’s Faculty of Medicine and Health Sciences, BCNatal (IRSJD and Hospital Clínic - IDIBAPS) and the Centre for Biomedical Research Network on Rare Diseases (CIBERER); Francisco Nistal, from the University of Cantabria and the Marqués de Valdecilla University Hospital and the Centre for Biomedical Research Network on Cardiovascular Diseases (CIBERCV), and Walter Wahli, from the University of Lausanne (Switzerland), among other experts.
A protein involved in cardiac pathologies
Alterations in metabolism, inflammation, fibrosis and cardiac cell death by apoptosis are some of the causes for the development of diabetic cardiomyopathy. The study reveals that activation of the PPARβ/δ receptor can help to slow down the processes of inflammation and fibrosis in laboratory animal models and human cardiac cells under hyperglycaemic conditions.
The PPARβ/δ factor is the most abundant member of the peroxisome proliferator-activated receptor (PPAR) family in the heart. However, Manuel Vázquez-Carrera notes that “the energy reservoir it contains is barely sufficient to maintain cardiac function for more than ten seconds, a constant supply of energy obtained through the oxidation of fatty acids (70%) and, to a lesser extent, other substrates such as glucose or lactate, supplied through the blood”.
“Many of the PPARβ/δ-regulated genes are involved in lipid and glucose metabolism. This protein is linked to metabolic diseases with an inflammatory background: for example, insulin resistance induced by obesity or diabetes, dyslipidaemia or metabolic fatty liver disease (MASLD)”, the expert Manuel Vázquez-Carrera says.
“Most of these pathologies are associated with a decrease in the transcriptional activity of PPARβ/δ and, in fact, it has been suggested that its activation could be useful to treat them. A reduction in the activity of this protein is also implicated in the development of several cardiac disorders”, says Vázquez-Carrera. “It also plays an important role in the regulation of inflammation and tissue remodelling”, he adds.
Inflammation, fibrosis and diabetic cardiomyopathy
In diabetes or obesity, insulin resistance in the myocardium causes the heart to derive energy almost exclusively from mitochondrial oxidation of fatty acids. This causes lipid accumulation in the myocardium and leads to lipotoxicity, which results in the heart muscle demanding more oxygen. Diabetic hyperglycaemia and lipotoxicity trigger cardiac inflammation and fibrosis through the activation of proinflammatory and profibrotic transcription factors (NF-қB and AP-1). Once activated, these factors drive the process of cardiac remodelling, which increases myocardial stiffness and impairs cardiac relaxation (diastole) after contraction (systole).
The activation of NF-қB and AP-1, together with mitogen-activated protein kinase (MAPK) activity, induces cardiomyocyte cell death, which also contributes to contractile dysfunction in diabetic cardiomyopathy. Professor Xavier Palomer points out that “together, all these processes lead to extracellular cardiac remodelling, contractile dysfunction, left ventricular hypertrophy and dilated cardiomyopathy, ultimately leading to heart failure”.
How does the PPARβ/δ protein act in diabetic cardiomyopathy?
To date, it was known that activation of PPARβ/δ in the heart could prevent metabolic dysregulation during diabetes and obesity. This would help prevent heart failure, the inability of the heart to pump blood efficiently to all organs and tissues in the body.
The study reveals that the beneficial effect of the PPARβ/δ protein in diabetic cardiomyopathy is explained by its ability to inhibit the MAPK pathway, according to the results obtained in cultured human cardiac cells.
Oxidative stress, hyperglycaemia and lipotoxicity were also known to accelerate cardiomyocyte inflammation, fibrosis and apoptosis in diabetic cardiomyopathy through the activation of mitogen-activated protein kinases (MAPKs), which also affects tissue remodelling after myocardial infarction.
Vázquez-Carrera points out that “it is not surprising, therefore, that the inhibition of these MAPKs can prevent inflammation and fibrosis not only in the heart, but also in other organs and tissues such as the liver, lung, kidney or even skeletal muscle, in various pathological conditions”.
