Despite the known risk of diabetes-induced cardiac fibrosis, less is known about whether diabetes causes an altered cardiac phenotype independent of coronary atherosclerosis. Peroxisome proliferator-activated receptor δ (PPARδ), a versatile regulator of metabolic homeostasis, may be a potential therapeutic target. Herein we investigated the effectiveness of telmisartan, a unique angiotensin receptor blocker that increases PPARδ expression, in improving left ventricular remodeling in diabetic humans and rats. In this longitudinal, prospective study, we enrolled 15 diabetic patients receiving telmisartan (20 mg/day) for 12 weeks. After treatment, strain was measured and compared with the baseline value. Using streptozotocin to induce type 1 diabetes rat model, we measured PPARδ expression and downstream targets. After treatment with telmisartan, both longitudinal and circumferential strains improved in diabetic patients. Compared with that of controls, the diabetic rat heart developed significant fibrosis, which markedly decreased after treatment with telmisartan (30 mg/kg/day, orally) for 7 days. After incubation with 30 mM glucose, rat cardiomyocytes showed a significant down-regulation of PPARδ. Interestingly, the increased expression of fibrosis-associated proteins, including signal transducer and activator of transcription 3 (STAT3) was attenuated by the co-incubation of GW0742, a PPARδ agonist. By knockdown or inhibition of STAT3, the hyperglycemia related high expression of fibrosis associated targets was reversed. Independent from the hyperglycemic incubation, STAT3 over-expression led to similar results. Conversely, in the presence of GSK0660, a PPARδ inhibitor, the protective effects of telmisartan were diminished. Telmisartan improved the hyperglycemia-induced cardiac fibrosis through the PPARδ/STAT3 pathway.

Despite no significant differences of growth differentiation factor‐15 expressions in peripheral, right atrial, and right ventricular blood, in the pulmonary arterial blood, there was a significantly high level of growth differentiation factor‐15 in Group I pulmonary arterial hypertension patients subsequently developing heart failure. During right heart catheterization, collecting pulmonary blood samples is suggested to measure growth differentiation factor‐15.