Influence of calcium channel blocker treatment on the mechanical properties of diabetic rat myocardium

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

The effects of telmisartan on mechanical responses of left ventricular papillary muscle in rats with streptozotocin-induced diabetes mellitus

The purpose of this study was to investigate the effects of telmisartan (5 × 10(-5) M) on the mechanical response of left ventricular papillary muscle in rats with streptozotocin-induced diabetes mellitus. We studied 32 rats; 16 were rendered diabetic by a single intravenous injection of streptozotocin (45 mg kg(-1) i.v.) and 16 formed a non-diabetic control group. Diabetic animals were divided into two groups: diabetic-telmisartan group and the diabetic-control group. Non-diabetic controls were further divided into the non-diabetic-telmisartan group and the non-diabetic-control group. We found: (1) Muscle twitch tension (P (0)) and contraction and relaxation rates were significantly lower in diabetic controls than in the other groups. (2) Telmisartan significantly increased P (0) in both diabetic and non-diabetic rats. (3) Times to peak tension and half-relaxation were significantly greater in groups DC and DT than in the non-diabetics. In conclusion, our data suggest that telmisartan attenuates diabetes-induced impairment of diabetic rat papillary muscles, and may thus be able to reduce cardiac complications in diabetes.

Effect of successful hypertension control by manidipine or lisinopril on albuminuria and left ventricular mass in diabetic hypertensive patients with microalbuminuria

OBJECTIVE

The aim of this open-labelled, randomised, parallel-group study was to evaluate the effect of long-term monotherapy with manidipine or lisinopril on albumin excretion rate (AER) and left ventricular mass index (LVMI) in hypertensive patients with type-2 diabetes and microalbuminuria.

METHODS

After a 4-week wash-out period, 174 patients with essential hypertension [diastolic blood pressure (DBP) >80 mmHg and <100 mmHg], type-2 diabetes and microalbuminuria were randomised to manidipine 10 mg o.d. or lisinopril 10 mg o.d.; after 8 weeks, the dose was doubled in non-responders (DBP >80 mmHg); after 3 months, treatment was discontinued in the non-responder patients and in those complaining of side effects; the remaining 121 patients continued their therapy with manidipine or lisinopril, and 99 completed the 2-year study. At the end of the wash-out period, of the titration period and after 6, 12, 18 and 24 months of treatment, BP was measured, AER, creatinine clearance, glycosylated haemoglobin (HbA1c) and body mass index (BMI) were evaluated and an echocardiographic evaluation was performed.

RESULTS

The 99 patients who completed the study were statistically analysed according to a per-protocol evaluation. Manidipine and lisinopril significantly reduced systolic blood pressure (SBP) and DBP levels (at 24 months, --22.3/15.5 mmHg, P<0.001 versus baseline and --21.4/15.7 mmHg, P<0.01 versus baseline, respectively). Both drugs provided a significant decrease in AER, but it was significantly more pronounced with lisinopril (at 24 weeks, --37.2 mg/24 h, P<0.001 versus baseline) than with manidipine (--29.9 mg/24 h, P<0.05 versus baseline) and became evident earlier in the lisinopril group (after 3 months versus 6 months of treatment). Manidipine produced a greater reduction of LVMI than lisinopril (--14.9 g/m(2) versus --10.8 g/m(2) at 24 months). The effect was more pronounced in patients with left ventricular hypertrophy at baseline (--19.8 g/m(2) versus --12.8 g/m(2), P<0.05).

CONCLUSION

These data suggest that, despite similar BP lowering, non-haemodynamic factors play an important role in the pharmacological reduction of AER and LVMI in diabetic hypertensive patients.