Endotoxemia-induced lymphocyte apoptosis is augmented by a hyperinsulinemic-euglycemic clamp

BACKGROUND: Sepsis and endotoxemia are associated with lymphocyte apoptosis. This has been regarded as harmful, contributing to further immune suppression in already immune-compromised patients. Because normalization of blood glucose improves outcome in critically ill patients, the authors hypothesized that one of the effects of insulin and normoglycemia would be inhibition of lymphocyte apoptosis. Therefore, in this experimental study in pigs, the authors examined the separate and combined effects of acute endotoxemia and a hyperinsulinemic-euglycemic clamp (HEC) on lymphocyte apoptosis.

METHODS: After 60 min of stabilization, 38 anesthetized and mechanically ventilated pigs (weight, 35-40 kg) were divided (by randomization performed before the experiment) into four groups and were then studied for 570 min. Group 1 received no intervention. Group 2 received a HEC (5 mm p-glucose, insulin infusion rate of 0.6 mU . kg (-1). min(-1)) for 570 min. Group 3 received a lipopolysaccharide infusion for 180 min. Group 4 was given a combination of a HEC and a lipopolysaccharide infusion. After the 570-min study period, the pigs were killed, and tissue was sampled from the spleen and frozen. In four sections of each sample, the apoptosis of B and T lymphocytes were analyzed using stereologic methods: The number of apoptotic B and T cells was estimated by fluorescence immunohistochemistry with anti-active caspase-3 and either anti-CD21 (B lymphocytes) or anti-CD3epsilon (T lymphocytes). The number of apoptotic B and T lymphocytes was then compared using two-way analysis of variance, and the interaction between endotoxemia and the clamp (hyperinsulinemia and euglycemia) was investigated.

RESULTS: Endotoxemia induced apoptosis of B (P < 0.001) and T lymphocytes (P = 0.016) in the spleen, and this effect was independent of the clamp. The ratios of apoptotic cells in the spleen tissue of pigs with and without endotoxemia were 2.4 (confidence interval, 1.7-3.4) and 1.6 (confidence interval, 1.1-2.2) for B and T lymphocytes, respectively. Independent of endotoxin infusion, HEC increased the number of apoptotic lymphocytes (P = 0.029 and P = 0.038 for B and T lymphocytes, respectively). The ratios of the number of apoptotic spleen cells in pigs treated and not treated with HEC were 1.5 (confidence interval, 1.0-2.1) and 1.5 (confidence interval, 1.0-2.1) for B and T lymphocytes, respectively.

CONCLUSION: In this porcine model, both endotoxemia and a HEC increased the number of apoptotic B and T lymphocytes in the spleen. Contrary to our hypothesis, lymphocyte apoptosis during acute endotoxemia was augmented by a HEC.