Mast cell degranulation contributes to neutrophil migration failure and susceptibility of diabetic mice to polymicrobial sepsis

Introduction

The major cause of mortality and morbidity of patients and experimental animals with diabetes mellitus is sepsis due to their high susceptibility to microbial infections. However, the mechanisms involved in this increased susceptibility are unclear.

Objective

In the present study we investigated the effect of the mast cell degranulation in neutrophil migration failure observed in diabetic mice after polymicrobial sepsis induced by cecal ligation and puncture (CLP).

Methods

On the fifth day after Balb/c mice became diabetic through intravenous administration of alloxan (40 mg/kg), they were pretreated for 4 days with the mast cell degranulator (compound 48/80; 0.6 mg/kg on day 1; 1.0 mg/kg on day 2; 1.2 mg/kg on day 3; and 2.4 mg/kg on day 4, twice a day, i.p.). Mild sepsis (MS) was performed 24 hours after the last dose and the experiments were conducted 6 hours later.

Results

Nondiabetic mice subjected to MS showed 100% survival during 7 days, whereas all diabetic mice died within 24 hours of observation. The diabetic mice were highly susceptible to sepsis due to an incapacity to promote neutrophil migration to the peritoneal cavity accompanied by bacteremia and overexpression of the inflammatory response, determined by high levels of circulating TNFα and MIP-2 and lung neutrophil sequestration. The reduction of the neutrophil migration correlated with decreased CXCR2 receptor expression on the neutrophil membrane. However, diabetic mice submitted to MS and daily pretreatment with compound 48/80 did not display failure of neutrophil migration to infectious focus. As a consequence, these animals exhibited low bacteremia and a high survival rate. In addition, the pretreatment of diabetic mice with compound 48/80 significantly blocked the increase of serum TNFα and MIP-2 levels after septic stimulus. Accordingly, the reduction of the membrane expression of CXCR2 in neutrophils observed in diabetic mice after MS was significantly re-established in diabetic mice pretreated with compound 48/80.

Conclusion

These results suggest that in diabetic mice undergoing polymicrobial infection, mast cells play a key role in the neutrophil migration failure due to reduction of the CXCR2 expression, resulting in bacterial spreading and systemic release of mediators, and as a consequence augmented susceptibility to sepsis development.