Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo

Meeting Abstracts: Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo Clearwater Beach, FL, USA. 9-11 June 201

Cardiovascular Dysfunction Following Burn Injury: What We Have Learned from Rat and Mouse Models

Severe burn profoundly affects organs both proximal and distal to the actual burn site. Cardiovascular dysfunction is a well-documented phenomenon that increases morbidity and mortality following a massive thermal trauma. Beginning immediately post-burn, during the ebb phase, cardiac function is severely depressed. By 48 h post-injury, cardiac function rebounds and the post-burn myocardium becomes tachycardic and hyperinflammatory. While current clinical trials are investigating a variety of drugs targeted at reducing aspects of the post-burn hypermetabolic response such as heart rate and cardiac work, there is still a paucity of knowledge regarding the underlying mechanisms that induce cardiac dysfunction in the severely burned. There are many animal models of burn injury, from rodents, to sheep or swine, but the majority of burn related cardiovascular investigations have occurred in rat and mouse models. This literature review consolidates the data supporting the prevalent role that β-adrenergic receptors play in mediating post-burn cardiac dysfunction and the idea that pharmacological modulation of this receptor family is a viable therapeutic target for resolving burn-induced cardiac deficits

Biventricular differences in β-adrenergic receptor signaling following burn injury.

Burn injury detrimentally affects the myocardium, primarily due to over-activation of β-adrenergic receptors (β-AR). Autopsy reports from our institution reveal that patients often suffer from right ventricle (RV) failure. Since burn injury affects β-AR signaling in the left ventricle (LV), we proposed that β-AR signaling may also be altered in the RV. A rodent model with a scald burn of 60% of the total body surface area was used to test this hypothesis. Ventricles were isolated 7 days post-burn. We examined the expression of β-ARs via Western blotting and the mRNA expression of downstream signaling proteins via qRT-PCR. Cyclic adenosine monophosphate (cAMP) production and protein kinase A (PKA) activity were measured in membrane and cytosolic fractions, respectively, using enzyme immunoassay kits. β1-AR protein expression was significantly increased in the RV following burn injury compared to non-burned RV but not in the LV (p = 0.0022). In contrast, β2-AR expression was unaltered among the groups while Gαi expression was significantly higher in the LV post-burn (p = 0.023). B-arrestin-1 and G-protein coupled receptor kinase-2 mRNA expression were significantly increased in the left ventricle post-burn (p = 0.001, p<0.0001, respectively). cAMP production and PKA activity were significantly lower in the LV post-burn (p = 0.0063, 0.0042, respectively). These data indicate that burn injury affects the β-AR signaling pathway in the RV independently of the LV. Additionally, non-canonical β-AR signaling may be activated in the RV as cAMP production and PKA activity were unchanged despite changes in β1-AR protein expression

cAMP production and PKA activity post-burn.

<p>(A) cAMP production in membrane fractions isolated from right and left ventricles and (B) PKA activity in cytosolic fractions from right and left ventricles, seven days post-burn. Data are expressed as the mean ±SEM. Statistical analysis was performed using a one-way ANOVA. n = 6–9; p = 0.006 for cAMP; p = 0.004 for PKA; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; cAMP, cyclic adenosine monophosphate; PKA, protein kinase A; *, p<0.05 vs LV C; †, p<0.05 vs RV C; ‡, p<0.05 vs RV B.</p

β₂-AR and G_i protein expression post-burn.

<p>Representative Western blots of β₂-AR (A, B) and G_i (A, C) protein expression in right and left ventricles seven days post-burn. Controls were nonburned animals. The <i>bar</i> graphs show the ratio of protein to GAPDH. Data are expressed as the mean ± SEM. Statistical analysis was performed using a one-way ANOVA. n = 9–12; p<0.0001 for β₂-AR; p = 0.011 for G_i; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; β-AR, beta adrenergic receptor; †, p<0.05 vs RV C; ‡, p<0.05 vs RV B.</p

β₃-AR protein expression post-burn.

<p>Representative Western blots of β3-AR protein expression in right and left ventricles seven days post-burn. Controls were nonburned animals. The <i>bar</i> graphs show the ratio of protein to GAPDH. Data are expressed as the mean ± SEM. Statistical analysis was performed using a one-way ANOVA. n = 6; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; β-AR; beta adrenergic receptor.</p

Gene expression of β-AR desensitization proteins post-burn.

<p>(A) β-arrestin 1 mRNA expression from right and left ventricles and (B) GRK2 mRNA gene from right and left ventricles at seven days post-burn. Data are expressed as the mean ±SEM. Statistical analysis was performed using a one-way ANOVA. n = 7–9; p = 0.001, <0.0001 respectively; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; GRK2, G-protein coupled receptor kinase 2; *, p<0.05 vs LV C; †, p<0.05 vs RV C; ‡, p<0.05 vs RV B.</p

Primers for qRT-PCR.

<p>Primers for qRT-PCR.</p

VEGF and IGF-1 gene expression post-burn.

<p>PCR measurement of VEGF-A (A), VEGF-B (B), and IGF1 (C) mRNA expression in right and left ventricles, seven days post-burn. Controls were nonburned animals. Data are expressed as the mean ± SEM. Statistical analysis was performed using a one-way ANOVA. n = 6–9; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; VEGF, vascular endothelial growth factor; IGF1, insulin-like growth factor 1; *, p<0.05 vs LV C; †, p<0.05 vs RV C; ‡, p<0.05 vs RV B.</p

β₁-AR and G_s protein expression post-burn.

<p>Representative Western blots of β₁-AR (A, B) and G_s (A, C) protein expression in right and left ventricles seven days post-burn. Controls were nonburned animals. The <i>bar</i> graphs show the ratio of protein to GAPDH. Data are expressed as the mean ± SEM. Statistical analysis was performed using a one-way ANOVA. n = 9–12; p<0.00001 for β₁-AR; RV C: right ventricle control; RV B: right ventricle burned; LV C: left ventricle control; LV B: left ventricle burned; †, p<0.05 vs RV C.</p