Effect of adipokine priming upon neutrophil oxygen radical and extracellular trap release in response to stimulation by periodontal bacteria

Abstract

Obesity is a major public health problem worldwide of increasing prevalence. It is characterised by a low grade chronic inflammatory state, which contributes to obesity-associated morbidity. A body of evidence suggests that obesity is associated with periodontitis, and is second only to smoking as a risk factor for periodontal tissue destruction, but underlying biological mechanisms for this association remain unclear. Adipose tissue functions as an endocrine organ, secreting cytokines (adipokines) that are reported to be associated with dysregulated/inflammatory immune responses to bacterial challenge. Adipokines include tumour necrosis factor alpha (TNF\(\alpha\)), adiponectin, resistin, leptin and interleukin-6 (IL-6), all of which have been shown to prime/affect neutrophils for a secondary stimulus. Neutrophils are the major cell type involved in periodontal immunity to infectious agents. This study therefore aimed to elucidate neutrophil reactive oxygen species (ROS) and neutrophil extracellular trap (NET) responses to bacterial stimulation in an adipokine rich (obese) verses an adipokine normal (lean) environment. Blood was isolated from healthy male volunteers, with no history of diabetes and with normal body mass indices (BMI’s) (range 20-25). Peripheral blood neutrophils were isolated by Percoll\(^{TM}\) discontinuous gradient centrifugation, primed with TNF\(\alpha\), adiponectin, resistin, leptin or IL-6, alongside control two control stimuli GM-CSF and IL-8, at concentrations reflective of lean and obese individuals. Neutrophils were subsequently stimulated with Fusobacterium nucleatum (ATCC 10953) for Toll-Like receptor (TLR)-4 activation, opsonised Staphyloccocus aureus (NCTC 6571) for Fc\( \gamma\)RII activation or phorbol 12-myristate 13-acetate (PMA) for direct activation via protein kinase C (PKC). Neutrophil ROS were measured by luminol enhanced and chemiluminsecence and NET release was by fluorometric assay of DNA and fluorescence microscopy. Adipokine concentrations representative of those found in obese individuals have been shown in this pilot study to enhance neutrophil ROS and NET generation after exposure to bacterial stimulus. The effects are however stimulus dependent and require longer studies to validate any significant results.