Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

Joshua W Gatson,Ahamed H Idris,Joseph P Minei,James W Simpkins,Jane G Wigginton,David L Maass

doi:10.1186/1742-2094-6-30

Abstract

BackgroundPatients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.MethodsIn this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.ResultsIn burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).ConclusionFollowing severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Highlights

Patients with severe burn injury experience a rapid elevation in multiple circulating proinflammatory cytokines, with the levels correlating with both injury severity and outcome
We found that in those animals receiving SQ estradiol, there was a time-dependent increase in the levels of circulating 17 β-estradiol concentrations ranging from approximately 1 ng/ml to approximately 10 ng/ml
With respect to inflammatory cytokines measured in the rat brain tissue, at all evaluated time-points there was a significant reduction in TNF-α levels in the 17 β-estradiol group compared to the placebo group (*p < 0.05 at 4, 8, 12, 18, and 24 hours post-injury, and **p < 0.01 at 0.5, 1, 2, and 6 hours post-injury)

Summary

Introduction

Patients with severe burn injury experience a rapid elevation in multiple circulating proinflammatory cytokines, with the levels correlating with both injury severity and outcome. A significant incidence of multiple organ (liver, thymus, spleen, skeletal muscle, lung, heart, and brain) dysfunction and failure has been noted in both animals and humans, surviving the initial insult of severe burn injury. This failure of different organ systems is thought to be, at least in part, due to increased apoptotic cell death and enhanced production of inflammatory cytokines such as interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), interleukin 1beta (IL-1β), and prostaglandins [2,3,4]. In behavioral studies such animals appear to have long-term cognitive deficits associated with a disruption in the blood-brain barrier [17,18,19], increased inflammation [13], and/or altered metabolism in the brain [10,16]

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