**4.1 Anticancer activity**

Cancer is a major health problem that can be defined as impaired cell cycle and uncontrolled proliferation, which results in the growth of abnormal cells. Increased exposure to stress, pollution, radiation, ultraviolet rays, smoking, oxidative stress, genetic mutation, and lack of apoptotic function are the major causes of cancer. Anthocyanins, flavones, flavones, flavonols, and chalcones are major flavonoids having anticancer activities. The mixed mechanism of action of flavonoids as anticancer action includes down-regulation of mutant p53 protein, inhibition of expression of Ras proteins, estrogen receptor binding capacity, tyrosine kinase inhibition and cell cycle arrest. Quercetin was reported to exert a growth inhibitory effect on various tumor cells also cell cycle arrest in proliferating lymphoid cells. *Dryopteris erythrosora Erythrina suberosa, Phaseolus vulgaris* L., *Medicago truncatula* Gaertn, *Ceratonia siliqua* L., *Butea monosperma, Glycyrrhiza glabra* L. and many more plants reported as anticancer due to presence of flavonoids [12–14].

#### **4.2 Antioxidant activity**

Plants, animals, and human protection against the effect of reacting oxygen species by suppressing reacting oxygen species with chelation of the trace elements involved in the free radical generation and enzyme inhibition. They are found in the chloroplast having scavenging activity of singlet oxygen and stabilizers of the chloroplast outer envelope membrane [15].

The enzymatic and non-enzymatic systems involve detoxification and removal of oxidant species of glutathione [GSH], GSH peroxidase, GSH reductase, and GSH S-transferase. The prooxidant activity of flavonoids becomes cytotoxic that undergoes transition metal reactions resulting in the formation of highly reactive oxygen species that damages protein and DNA [1].

#### **4.3 Antimicrobial activity**

According to World Health Organization, multidrug-resistant pathogenic microorganisms are major global health complications, which involve various natural products. As one of the class of secondary metabolites of the natural class, flavonoids play a vast and crucial role to handle multidrug-resistant pathogenic microorganisms strains with their versatile pharmacological activities. Prenylation or geranylation at C6; and hydroxylation of C5, C7, C3', and C4' have reported to enhance bacterial inhibition of flavonoids, whereas methoxylation at C3' and C5 has been studied to decrease antibacterial action of flavonoid. It is reported that the cell membrane is found at the major site of flavonoid action, which help in the inhibition of the respiratory chain and the ATP synthesis that also involves damage to phospholipid bilayers. Flavanone is acting as potent antibacterial activity by synthesizing a compound with halogenations of the B ring, as well as lavandulyl or geranyl substitution of the A ring [16–18].

#### **4.4 Cardioprotective activity**

More than 4000 flavonoids, which include chalcones, flavonols, dihyroflavonols, catechins, isoflavones, and catechins have the capacity for cardioprotective activity against myocardial ischemia or reperfusion as antihypertensive, anti-atherosclerotic, and anti-platelet. The significant role of flavonoids by preventing cardiovascular diseases, which may be due to antioxidant, antithrombotic, and antiatherogenic activity. For example, red wine consumption will protect against thrombosis and atherosclerosis by inhibition of platelet aggregation and LDL oxidation. The literature revealed that a daily diet of 100 mg of flavonoid helps in the reduction and possibility of cardiovascular diseases by inhibition of low-density lipoprotein oxidation and reduced platelet aggregability [19–22].

### **5. Conclusion**

For thousands of years, flavonoids in plants are utilized as traditional medicine. They are polyphenolic compounds that are biosynthesized by the polypropanoid pathway and have potential as cosmeceutical, nutraceutical, and pharmaceutical applications. They work in the multi-mechanism of action, such as protecting endothelial cell, inhibiting foam cell formation, regulating lipid metabolism, anti-inflammatory, and underlying molecular mechanism. In future prospective, flavonoids as nutraceutical, cosmeceutical, and pharmaceutical aspects would help to reduce the burden in urban and rural populations of developed and developing countries by elevation of its pharmacokinetic, metabolic, and pharmacodynamic characteristics and using in novel drug delivery system technology.

*Importance of Flavonoid as Secondary Metabolites DOI: http://dx.doi.org/10.5772/intechopen.107462*
