J W Horton

Burn trauma and tumor necrosis factor alpha alter calcium handling by cardiomyocytes.

ABSTRACT It is well recognized that bum trauma induces an inflammatory cascade and the release of cytokines including tumor necrosis factor (TNF)-±. The negative inotropic effects of TNF-± on the heart are well recognized, but the cellular mechanisms remain unclear. To examine one aspect of cellular function, we exposed cardiac myocytes isolated from NZW rabbits (collagenase digestion) to either TNF-± (200, 400, or 1000 U/mL) or sham or burn plasma (10% by volume) for 3 to 4 h and measured calcium transient ratios in the isolated, contracting myocytes using the fluorescent indicator Fura-2-acetoxymethyl (1.2 ±M); myocytes treated with media alone served as controls. Cells were placed in a perfusion chamber on the stage of an inverted Nikon microscope and superfused with buffer at 37±C and stimulated at 1 Hz. A Tracor Northern Fluoroplex 1000 microspectrofluorometer and camera system, set to provide excitation of 340 and 380 nm with emission at 450–580 nm, was used to measure Ca2+ transients during systole-diastole. [Ca2+]i was reported as a fluorescence ratio (F340/F380) to minimize effects of different cell thickness and motion artifacts. After recording diastolic/systolic [Ca2+]i, cells were stimulated with isoproterenol, and [Ca2+]i, was again measured. TNF-± produced diastolic and systolic [Ca2+]i, values (1.067 ± .023/1.301 ± .017) that were similar to values seen after myocyte exposure to burn plasma (1.099 ± .024/1.307 ± .028) and significantly greater than values measured in controls (.857 ± .017/1.077 ± .015, p < .05). Our data confirm that burn trauma and TNF-± alter calcium handling by cardiomyocytes. The possible contribution of altered intracellular calcium dynamics to cardiac contractile abnormalities after burn trauma and TNF-± administration warrants further study.

Heart rate variability as a predictor of death in burn patients

Heart rate variability (HRV), a noninvasive technique used to quantify fluctuations in the interval between normal heart beats (NN), is a predictor of mortality in some patient groups. The aim of this study was to assess HRV in burn trauma patients as a predictor of mortality. The authors prospectively performed 24-hour Holter monitoring on burn patients and collected demographic information, burn injury details, and in-hospital clinical events. Analysis of HRV in the time and frequency domains was performed. A total of 40 burn patients with a mean age of 44 ± 15 years were enrolled. Mean %TBSA burn was 27 ± 22% for the overall population and was significantly higher in those who died compared with those who survived (55 ± 23% vs 19 ± 13%; P < .0001). There was a statistically significant inverse linear correlation between SD of NN intervals and %TBSA (r = −.337, R2 = 0.113, 95% CI = −0.587 to −0.028, two-tailed P = .034), as well as with ultra low frequency power and %TBSA burn (r = −0.351, R2 = 0.123, 95% CI = −0.152 to −0.009; P = .027). The receiver–operator characteristic showed the area under the curve for %TBSA as a predictor of death was 0.82 (P < .001), for SDANN was 0.94 (P < .0001), and for ultra low frequency power was 0.96 (P < .0001). Deranged HRV in the early postburn period is a strong predictor of death.

BURN PLASMA MEDIATES CARDIAC MYOCYTE APOPTOSIS VIA ENDOTOXIN: 96

Thermal trauma is associated with cardiac myocyte apoptosis in vivo. To determine whether cardiac myocyte apoptosis could be secondary to burn-induced cytokines or inflammatory mediators, we investigated the effects of tumor necrosis factor-alpha (TNF-alpha) and burn plasma on a murine cardiac myocyte cell line and primary culture myocytes. HL-1 cells were exposed to plasma isolated from burned or sham rats. Burn, but not sham plasma, induced significant increases in caspase-3 activity and DNA fragmentation. Similar results were obtained in primary culture rat myocytes. A dose-dependent increase in caspase-3 activity was observed when HL-1 cells were incubated with increasing concentrations of TNF-alpha. Even though TNF-alpha increased apoptosis, enzyme-linked immunosorbent assay detected no TNF-alpha in burn plasma. Burn plasma also failed to induce TNF-alpha mRNA, eliminating an autocrine mechanism of TNF-alpha secretion and binding. Also, treatment of burn plasma containing rhuTNFR:Fc failed to inhibit apoptosis. To examine the possibility that endotoxin within burn plasma might account for the apoptotic effect, burn plasma was preincubated with rBPI(21). Caspase-3 activity was reduced to control levels. These data indicate that burn plasma induces apoptosis in cardiac myocytes via an endotoxin-dependent mechanism and suggest that systemic inhibition of endotoxin may provide a therapeutic approach for treatment of burn-associated cardiac dysfunction.