Potential Implications of Citrulline and Quercetin on Gut Functioning of Monogastric Animals and Humans: A Comprehensive Review

Abstract

The importance of gut health in animal welfare and wellbeing is undisputable. The intestinal microbiota plays an essential role in the metabolic, nutritional, physiological, and immunological processes of animals. Therefore, the rapid development of dietary supplements to improve gut functions and homeostasis is imminent. Recent studies have uncovered the beneficial effects of dietary supplements on the immune response, microbiota, gut homeostasis, and intestinal health. The application of citrulline (a functional gut biomarker) and quercetin (a known potent flavonoid) to promote gut functions has gained considerable interest as both bioactive substances possess anti-inflammatory, anti-oxidative, and immunomodulatory properties. Research has demonstrated that both citrulline and quercetin can mediate gut activities by combating disruptions to the intestinal integrity and alterations to the gut microbiota. In addition, citrulline and quercetin play crucial roles in maintaining intestinal immune tolerance and gut health. However, the synergistic benefits which these dietary supplements (citrulline and quercetin) may afford to simultaneously promote gut functions remain to be explored. Therefore, this review summarizes the modulatory effects of citrulline and quercetin on the intestinal integrity and gut microbiota, and further expounds on their potential synergistic roles to attenuate intestinal inflammation and promote gut health.

Supplementation of Dietary Quercetin and Vitamin E Promotes the Intestinal Structure and Immune Barrier Integrity in Aged Breeder Hens

“…In this study, the antioxidant capacity was improved by the combination of quercetin and vitamin E in the intestinal mucosa and serum of aged breeder hens. Similar studies have shown that individual quercetin and vitamin E supplementation prevented the production and accumulation of ROS induced by proinflammatory cytokines; thereby, alleviating oxidative stress and apoptosis in animals ( 25 , 43 , 54 , 67 , 68 ).…”

“…The benefits of the intestinal health in animal wellbeing and welfare is unmeasurable. The importance of gut health in animal welfare and wellbeing is undisputable because of its important physiological functions ( 25 ). The current study elucidated the synergistic effects of dietary supplementation of quercetin and vitamin E on the intestinal structure and barrier integrity of aged breeder hens to promote immune response, gut homeostasis, and intestinal health.…”

“…The intestinal mucosa is the first line of defense against oxidative stress, because it is composed of an extensive enzyme and non-enzymatic antioxidant system. However, in aged animals, due to imbalances in the antioxidant system, the intestinal mucosa experiences oxidative stress ( 25 , 54 ). Previous studies have shown that aged animals fed without dietary antioxidant supplements experience oxidative stress responses ( 26 , 54 ).…”

“…Therefore, a rapid development of dietary supplements to improve gut function and homeostasis in aged animals is imminent ( 25 , 26 ). Vitamin E (VE) is a powerful dietary supplement characterized with a strong antioxidant property that attenuates the production and accumulation of reactive oxygen species (ROS) to prevent tissue damage caused by oxidative stress in chickens ( 27 , 28 ).…”

“…( 34 ) reported that quercetin has a strong synergistic effect with other dietary supplements such as rutin and α -tocopherol without any detrimental effects ( 34 ). Moreover, quercetin has also been found to have interactive effects with dietary supplements including catechin ( 55 ), citrulline ( 25 ), and resveratrol ( 40 ) to promote physiological functions in animals.…”