Flavonoids: A Functional Food With Anticancer Properties

Introduction

Flavonoids are a class of non-nutrient bioactive polyphenolic compounds that are found naturally in plants as a secondary metabolite. They are present in abundance as a constituent of different parts of flowering plants like bark, rhizomes, leaves, flowers and fruits of almost every plant. Although a large number of different flavonoid compounds are predicted to exist, there may be over 1000 flavonoid compounds in different plants, some of them exclusively found in dietary plants that are eaten daily and thus appears as an integral part of dietary foods (Pérez-Jiménez et. al., 2010). To date about 9000 flavonoids have been isolated from different plant sources (Xiao et. al., 2011). The flavonoids are synthesized from its precursor phenylalanine via the phenylpropanoid pathway in which phenylalanine is first converted into 4-coumaroyl-CoA with the help of phenylalanine ammonia lyase (PAL), which finally enters the flavonoid biosynthesis pathway in which 4-coumaroyl-CoA combines with 3-malonyl-CoA to form chalcones by the enzyme chalcone synthase. The basic structure formed in general phenylpropanoid pathway undergoes various modifications through enzymes to form different flavonoids in plants (Zhu et. al., 2015). There is no harm in this, although in recent times it has been suggested that dietary intake of natural flavonoids is able to protect humans from various diseases, such as infections and cancers (Swanson, 2015). It has been found to be protective against redox-mediated oxidative damage and in several degenerative diseases like cardiovascular diseases and other age-related diseases (Rice-Evans et. al., 1995; Kumar et. al., 2013; Khan et. al., 2021). Flavonoids as dietary supplements have also been found to protect the body from harmful side effects of therapeutic intervention carried out against many diseases, such as cancer and bacterial as well as viral infections. Thus it has been found to play an important role in the rehabilitation of chronic patients who have been undergone therapeutic treatment. However directional studies related to the role of flavonoids in different pathological conditions and in rehabilitation medicine as well is severely lacking; it has been considered that its major protective effects are due to its possession of anti-oxidant properties capable of acting in both in vitro and in vivo system (Rice-Evans et. al., 1995; Andreu et. al., 2017). Recently, it has been found that flavonoids are capable of showing an adaptogenic property on mice stress model (Habbu et. al., 2010) which is indicative of flavonoids being very effective in managing different pathophysiological conditions in different ways (Figure 1). Although it has already been established that it acts as a secondary antioxidant defense system in plant tissues exposed to various abiotic and biotic stresses (Kumar & Pandey, 2013) and thus naturally it is present in the nucleus as well as the location of mesophyll cells where generation of ROS takes place. Thus it appears to be a bioactive molecule that occurs naturally occurring in the natural system to protect it from the harmful insult of free radicals. However, detailed studies regarding the role of these dietary flavonoids in various pathophysiological conditions are severely lacking. Therefore, the present chapter is an attempt to discuss the role of dietary flavonoids in health and diseases and its future prospects in the management of various chronic health problems.