Neutrophil:lymphocyte ratio and cell-free DNA dynamics during excessive heat stress in occupational and experimental settings

Abstract

Introduction

Systemic inflammation is postulated to mediate heat stroke and heat-related organ injury, yet acute inflammatory responses among heat-stressed workers remains poorly understood. We aimed to describe neutrophil mobilisation and potential release of DNA during heat stress in multiple hot occupational settings and a controlled experimental setting.

Methods

Neutrophil:lymphocyte ratio (NLR) was investigated in six sugarcane worker groups: Nicaraguan cohorts consisting of 1a) workers undergoing pre-employment screening (N = 5257), 1b) workers with acute kidney injury (AKI, N = 470); 2) Salvadoran cane cutters (N = 45) sampled pre/post-shift before and during a rest-shade-hydration intervention; 3) Mexican cane workers performing 3a) heavy (N = 148) and 3b) light-moderate (N = 24) work, sampled pre/post shift; and 4) Honduran cane cutters sampled pre/post-shift (N = 72). Cell-free DNA (cf-DNA) was measured in two cross-shift sugarcane worker groups (N = 26, El Salvador and N = 20, Nicaragua). NLR and cf-DNA was also measured in research participants (N = 10) exercising in temperate and hot conditions.

Results

NLR was elevated in sugarcane workers with AKI and increased during work shifts. Large positive NLR changes were associated with not having rest-shade-hydration, heavy workload, high environmental heat and high core body temperatures. cf-DNA increased across work-shifts in both cane cutter groups and after exercise in heat.

Conclusion

Neutrophil mobilisation was common among workers with AKI, and NLR and cf-DNA increased during and after field-based occupational and experimental heat stress. The findings indicate that acute systemic inflammation with neutrophil activation and destruction is common during excessive exertional heat stress.