Phytochemical Antioxidants as Immunomodulators: Benefits, Limitations, and Safety Concerns

Abstract

In their ability to control the immune response and the inhibition of oxidative stress, phytochemical antioxidants have received significant scientific interest. These compounds which are derived out of fruits, vegetables, herbs, spices, teas and medicinal plants influence a variety of molecular pathways and regulate the immune cell differentiation, cytokine production and redox homeostasis. An extensive body of preclinical evidence shows that phytochemical antioxidants have the potential to strengthen host defense, alleviate chronic inflammation and modulate innate and adaptive immunity by actions that are associated with NF-kB inhibition, Nrf2 activation, MAPK signaling, episodetic regulation, and microbiota remodeling. Nevertheless, the promised benefits still have serious limitations. These are variable bioavailability, reliance on gastrointestinal metabolism, lack of standardization, possibilities of drug interactions and dose-dependent toxicity. There is clinical evidence inconsistency, which is mainly caused by heterogeneity in the formulations, inadequate dosing, and poor control of confounding dietary factors. The hepatotoxicity of concentrated extracts, immunosuppression of high doses, and the possible pro-oxidative effect of such extracts in certain circumstances are also safety concerns. This literature review provides a synthesis of existing information regarding the immunomodulatory effects of phytochemical antioxidants, mechanisms, therapeutic potential, limitations, and safety of these antioxidants. It sums up on the necessity of strict clinical trials, standardization of extract characterization and mechanistic research to explain long term efficacy and safety of human populations. Keywords: phytochemicals, antioxidants, immunomodulation, oxidative stress, safety.