Fig. 3.

Molecular mechanisms of chemoprevention by dietary phytochemicals.

Polyphenols like curcumin, resveratrol and noscapine regulate autophagic cell death via inhibition of mTORC1 signalling. Similarly, curcumin, resveratrol, noscapine, allicin, and excisanin activate the PI3K signalling for elongation of extending phagophore. Kaempferol, curcumin and resveratrol enhance the LC3 lipidation in the extending autophagosomes. Resveratrol enhances the expression of ATG-5 and ATG-12. Similarly, kaempferol and resveratrol also regulate the ATG-16 formation from ATG-5 and ATG-12. Curcumin, resveratrol and kaempferol enhance the Bax/Bcl-2 expression to regulate apoptosis. In addition to this, kaempferol, oridonin and curcumin upregulate the caspase cascades responsible for the onset of apoptosis. Oridonin regulates the expression of caspase 3 and caspase 9 while cucurbitacin B and allicin regulate the Bcl-2 expression for induction of apoptotic cell death. Sulforaphane also alters the apoptotic signal through upregulation of Bax and downregulation of Bcl-2. β-carotene enhances the release of cytochrome C to mediate mitochondrial apoptosis. Resveratrol enhances the expression of caspase 8 during the onset of extrinsic apoptosis while kaempferol elicits the death receptors that are responsible for extrinsic apoptosis.