Immunomodulatory Effects of Herbal Compounds Quercetin and Curcumin on Cellular and Molecular Functions of Bovine-Milk-Isolated Neutrophils toward Streptococcus agalactiae Infection

SIMPLE SUMMARY: Many herbal remedies contain quercetin or curcumin as one of the active ingredients. The broad pharmacologic effects of these herbal compounds have received significant attention in recent years for their roles in the modulation of the innate immune response in humans and animals. The use of quercetin and curcumin in dairy cattle may be the most promising alternative to control S. agalactiae, which are prominent pathogens involved in bovine mastitis. However, the mechanisms by which quercetin and curcumin facilitate the elimination of invading pathogens is not yet fully understood. This study examined the cellular and molecular levels of the innate immune activities induced by quercetin and curcumin, separately, in milk-isolated bovine neutrophils during S. agalactiae stimulation. Our results demonstrate that quercetin and curcumin present beneficial effects, including increasing cell migration and antioxidant activities, enhancing phagocytosis and bacterial killing, increasing NET release, altered patterns of gene expression, and manipulating cell death. Our results regarding these two herbal compounds indicate that they may alleviate inflammation due to the innate immune cell dynamic in bacterial mastitis. Further investigations are needed to confirm our observations and examine the underlying mechanisms. ABSTRACT: Herbal phytochemicals featuring active ingredients including quercetin and curcumin have shown potential in treating human and animal diseases. The current study investigated their potential function in vitro for host immunomodulation associated with Streptococcus agalactiae subclinical bovine mastitis via milk-isolated neutrophils. Our results showed a positive influence on cellular migration, reactive oxygen species (ROS) generation, phagocytosis, and bacterial killing as well as neutrophil extracellular traps (NETs) release. This study also highlighted several important molecular aspects of quercetin and curcumin in milk-isolated neutrophils. Gene expression analyses by RT-PCR revealed significant changes in the expression of proinflammatory cytokines (IL1B, IL6, and TNF), ROS (CYBA), phagocytosis (LAMP1), and migration (RAC). The expression levels of apoptotic genes or proteins in either pro-apoptosis (CASP3 and FAS) or anti-apoptosis (BCL2, BCL2L1, and CFLAR) were significantly manipulated by the effects of either quercetin or curcumin. A principal component analysis (PCA) identified the superior benefit of quercetin supplementation for increasing both cellular and molecular functions in combating bacterial mastitis. Altogether, this study showed the existing and potential benefits of these test compounds; however, they should be explored further via in vivo studies.