Anti-inflammatory activity of citrus pectin on chicken monocytes' immune response

Highlights

• CP did not affect chicken monocytes’ apoptosis and viability.

• CP inhibited the chemotactic activity of chicken monocytes.

• CP reduced the phagocytic activity of chicken monocytes.

• CP exerts in vitro immunomodulatory effects in poultry.

Abstract

Pectin is a dietary fibre composed of galacturonic acid, primarily found in the citrus fruits' cell walls. Citrus pectin (CP) has demonstrated antioxidative, anticancer, and anti-inflammatory properties in humans and animals. In broilers, CP supplementation improves energy utilization and nutrient digestibility, but limited information on its effects on chicken immunity is available so far. This study aimed to assess the in vitro impact of CP on chicken monocytes' immune response. Cells were purified from whole blood of healthy chickens and incubated with increasing concentrations (0, 0.25, 0.5, 0.75, 1 mg/mL) of CP to determine CP working concentration. The effects of different CP concentrations on cells' apoptosis and viability were assessed by measuring caspase-3 and -7 and the cells' metabolic activity (MTT assay), respectively. CP had no dose-dependent effect on monocyte apoptosis and viability.Then, the effects of CP (0.5 mg/mL) on chicken monocytes' chemotaxis and phagocytosis were assessed by measuring transwell migration and fluorescein-labelled E. coli incorporation, respectively. CP inhibited both monocytes' chemotaxis and phagocytosis.These data demonstrate that CP exerts an immunomodulatory role in chicken monocytes, supporting its integration in nutrition strategies that might be beneficial for the animal's immunity and health.

Introduction

Pectin is a family of complex polysaccharides, primarily composed of repeating units of galacturonic acid, joined by $\alpha 1$ → 4 glycosidic linkages, creating a linear polymer (Ridley et al., 2001). Different degrees of methyl esterification (DM) of the pectin carboxyl groups can be observed, often associated with structural and functional differences of the pectin (Chen et al., 2006; Salman et al., 2008).

Pectin is found in all plants' cell walls, but it is most abundant in citrus fruits (Sahasrabudhe et al., 2018). Citrus pectin (CP) is widely used as dietary fibre in both human and animal nutrition (Langhout and Schutte, 1996; Leclere et al., 2013). Previous in vitro and in vivo studies demonstrated CP's antioxidative (Sanders et al., 2004), anti-diabetic (Liu et al., 2016), anticancer (Glinsky and Raz, 2009; Salehi et al., 2018), anti-inflammatory (Sahasrabudhe et al., 2018; Salman et al., 2008) and other immunomodulatory activities (Chen et al., 2006). In vitro studies performed in human PBMC demonstrated that CP with higher esterification degrees (60 and 90 %) inhibits in a dose-dependent manner the production of the proinflammatory cytokine IL-1β, while increases the secretion of anti-inflammatory cytokines IL-1ra and IL-10 (Salman et al., 2008). Low DM citrus pectin blocked immune receptors in human dendritic cells and murine macrophages by inhibiting the Toll-like receptor 1 (TLR1) and Toll-like receptor 2 (TLR2) proinflammatory pathways. The production of IL-6 and IL-10 was also reduced in human dendritic cells, and only of IL-6 in murine macrophages (Sahasrabudhe et al., 2018). Lemon pectin can also activate human THP-1 monocytic cell line, in a TLR and DM dependent manner, and exert a protective effect on the human epithelial barrier (Vogt et al., 2016). The immunomodulatory effects observed in these studies were all dependent on the DM of the citrus pectin used, in which generally the higher the DM (> 50 %), the stronger the effects observed.

Although CP supplementation of broilers' diet improves the energy utilization and nutrient digestibility, increasing productive performance (Silva et al., 2013), limited information of CP effects on chicken immunity is available so far. The impact of CP on immune functions of chicken mononuclear cells have not been assessed yet either. The present investigation aims to cover this gap by evaluating the in vitro impact of CP (55–70 % DM) on chicken monocytes' immune response, including its effects on spontaneous apoptosis, viability, chemotaxis and phagocytosis.