Carotenoids (like alpha carotene, beta carotene, beta -cryptoxanthin, lutein, lycopene, and zeaxanthin) are also known as dietary antioxidants due to many factors:
1. Anti-oxidant activity hence may protect from chronic diseases
2. Pro-vitamin A activity
3. Protect the cell membrane from oxidative radicals either during the metabolism or maybe due to environmental stress
Carotenoids as precursor of vitamin A
Vitamin A is vital for the human beings by playing crucial role in immune function, vision, reproduction, and cellular communication. Humans are not capable of de novo synthesis of vitamins; hence they required it either through food or supplements. Carotenoids are structurally very similar to the Vitamin A [26]. Some carotenoids like alpha carotene, beta-carotene, and beta-cryptoxanthin can act as precursor of vitamin A while others like lycopene, zeaxanthin can't [27]. Provitamin A carotenoids are transformed to retinoic acid through intermediary steps of conversions into retinol and retinal. Retinoic acid acts as the precursor of 11-cis-retinal-dehyde and thus is essential component of rhodopsin required for development and functioning of the conjunctival membranes and cornea. Deficiency of vitamin A may lead to xerophthalmia (dry eye) and ultimately to night blindness or total blindness [1-13]. Vitamin A and its active compound retinol, is widely known to influence the innate immune system. It also known to regulate the antibody response hence resists the infections. Vitamin A also modulates pro-inflammatory and anti-inflammatory immune responses in the gastrointestinal tract [14-19]. It also supports cell growth. More specifically, Vitamin A plays a critical role in development and maintenance of the heart, lungs, and kidneys. Furthermore, Vitamin A has been shown to play an important role in maintenance of healthy skin, teeth, skeletal and soft tissue, and mucus membranes. It is also known for the differentiation and proliferation of epithelial tissues [20-23]. Vitamin A also plays crucial role in males through maintenance of genital tracts and spermatogenesis while in case of females, Vitamin A plays a signal role for the initiation of meiosis in female gonads and helps in pregnancy i.e. fertilization, implantation, development of embryo as well as placenta [20,24].
Beta-carotene: It is known to quench efficiently singlet molecular oxygen, peroxides, peroxide radicals esp during lipid metabolism, due to presence of conjugated alternate carbon-carbon single double bonds. Beta carotene known for its 100% conversion from pro-vitamin A to vitamin A which later converted into retinoid compounds in the intestine and liver by the enzyme 15-15'-beta-carotenoid dioxygenase and by alcohol dehydrogenases respectively. Conversion may be enhanced by alpha-tocopherol & zinc [8,25].
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ProCarDB