Bioactivity and Therapeutic Potential of Kaempferol and Quercetin: New Insights for Plant and Human Health

Abstract

Plant secondary metabolites, especially flavonoids, are major metabolites widely found in plants that play several key roles in plant defence and signalling in response to stress conditions. The most studied among these flavonoids are kaempferol and quercetin due to their anti-oxidative potential and their key roles in the defence system, making them more critical for plant adaptation in stress environments. Kaempferol and quercetin in plants have great therapeutic potential for human health. Despite being well-studied, some of their functional aspects regarding plants and human health need further evaluation. This review summarizes the emerging potential of kaempferol and quercetin in terms of antimicrobial activity, bioavailability and bioactivity in the human body as well as in the regulation of plant defence in response to stresses and as a signalling molecule in terms of hormonal modulation under stress conditions. We also evaluated the safe use of both metabolites in the pharmaceutical industry.

Keywords: antioxidant; bioactivity; bioavailability; kaempferol; quercetin; therapeutic.

Figure 3

Proposed model indicate schematic representation of plant responses to abiotic stresses mediated via ABA and flavonoid signalling. Mostly, abiotic stress reduces water availability and consequently plant close the stomata and release ABA hormone. Flavonoids (kaempferol, quercetin) act as ROS scavenger and interact with ABA and auxin in leaf and root respectively. Stomatal opening in leaves is permitted by ABA binding to the membrane receptors resulting in ions and water efflux leading to stomata closure. ABA induces R2R3-MYB gene and stimulating flavonoids biosynthesis, which also triggers a signalling cascade which leading to ROS generation. In root, flavonoids reduce auxin transport resulting to auxin accumulation and root development. This model is adopted from Justine Laoué et al. [69].

Figure 1

Chemical structure of 3-hydroxyflavone, kaempferol and quercetin. (A) shows flavonol skeleton, (B) shows kaempferol and (C) shows quercetin structure.

Figure 2

Proposed flow chart of the regulation of plant defence system mediated via kaempferol and quercetin under stress condition. The figure is adopted from our previously published article [50]. DHK (dihydrokaempferol), DHQ (dihydroquercetin), DFR (dihydroflavonol 4-reductase), FLS (flavonol synthase), F3H (flavanone 3-hydroxylase), KMP (kaempferol), QUR (quercetin), QGR (quercetin 3-O-glucoside 7-O-rhamnoside), QRR (quercetin 3-O-rhamnoside 7-O-rhamnoside), QRGR (quercetin 3-O-[6″-O-(rhamnosyl) glucoside] 7-O-rhamnoside), SLR (slender rice mutant), GA (gibberellic acid), JA (jasmonic acid), Col-1 (collagen type I), JA-l1e (Jasmonic Acid-Isoleucine), PR (pathogenesis related), NPR (nonexpressor pathogenesis-related), KGR (kaempferol 3-O glucoside 7-O rhamnoside), KRR (kaempferol-3,7-dirhamnoside), KRGR (kaempferol 3-O-[6″-O-(rhamnosyl) glucoside] 7-O rhamnoside), SA (salicylic acid), and ROS (reactive oxygen specie).