Augmented cardiac formation of oxidatively-induced carbonylated proteins accompanies the increased functional severity of post-myocardial infarction heart failure in the setting of type 1 diabetes mellitus

Abstract

Summary: Heart failure (HF) is a dominant cause for the higher mortality of diabetics after myocardial infarction (MI). In the present investigation, we have discovered that higher levels of oxidative stress (OS)-induced carbonylated proteins accompany worsening post-MI HF in the presence of type 1 diabetes. These findings provide a mechanistic link between amplified OS and exacerbation of post-infarction HF in diabetes.

Background: Type 1 diabetes mellitus (DM) patients surviving myocardial infarction (MI) manifest an increased incidence of subsequent heart failure (HF). We have previously shown that after MI, type 1 DM is associated with accentuated myocardial oxidative stress (OS) and concomitant worsening of left ventricular (LV) function. However, the precise mechanisms whereby type 1 DM-enhanced OS adversely affects HF after MI remain obscure. As carbonylation of proteins is an irreversible post-translational modification induced only by OS that often leads to the loss of function, we analyzed protein-bound carbonyls in the surviving LV myocardium of MI and DM+MI rats in relation to residual LV function.

Methods: Type 1 DM was induced in rats via administration of streptozotocin. Two weeks after induction of type 1 DM, MI was produced in DM and non-DM rats by coronary artery ligation. Residual LV function and remodeling was assessed at 4 weeks post-MI by echocardiography. Myocardial carbonylated proteins were detected through OxyBlot analysis, and identified by mass spectrometry.

Results: Compared with MI rats, DM+MI rats exhibited significantly poorer residual LV systolic function and elevated wet to dry weight ratios of the lungs. Protein carbonyl content in cardiac tissue and isolated heart mitochondria of DM+MI rats was 20% and 48% higher, respectively, versus MI rats. Anti-oxidative enzymes and fatty acid utilization proteins were among the carbonylated protein candidates identified.

Conclusions: These findings implicate myocardial protein carbonylation as part of the molecular pathophysiology of aggravated HF in the type 1 diabetic post-infarction heart.

Keywords: Carbonylation; Heart failure; Myocardial infarction; Oxidative stress; Type 1 diabetes mellitus.

Figure 1

Representative echocardiographic images consisting of 2-dimensional echocardiography at parasternal short-axis plane (top) and M-mode short axis of LV (bottom) of type 1 diabetic and non-diabetic rat hearts at 4 weeks post-MI. (A): Sham MI; (B): MI; (C): DM + MI.

Figure 2

Levels of carbonylated proteins in the surviving LV myocardial tissue of MI and DM + MI groups of rats at 4 weeks post-MI. (A): Representative OxyBlot. DV, derivatized molecular weight markers; DC, derivatization-control (negative control); K, Kaleidoscope protein standard markers. (B): Densitometric analysis of DNP-immunoreactivity for CV, DM, sham MI, MI and DM + MI groups of rats. In all samples, the densitometric measurements of DNP-immunoreactivity were normalized to total protein. OxyBlots were performed in duplicate.

Figure 3

Levels of carbonylated proteins in mitochondria isolated from the surviving LV myocardial tissue of MI and DM + MI groups of rats at 4 weeks post-MI. Densitometric analysis of DNP-immunoreactivity is shown for CV, DM, sham MI, MI and DM + MI groups of rats. In all samples, the densitometric measurements of DNP-immunoreactivity were normalized to total protein. OxyBlots were performed in duplicate.

Figure 4

Molecular functions of the proteins found to be more highly carbonylated in the failing type 1 diabetic post-MI rat myocardium.

Figure 5

Biological processes that are carried out by the proteins found to be more highly carbonylated in the failing type 1 diabetic post-MI rat myocardium.