420
20.4 Biosynthesis of Carotenoids
Carotenoids are members of the tetraterpenoids containing 40 carbon atoms built by
the arrangements of terpene units joined together through their head and tail (Bonnie
and Choo 1999; Mattea et al. 2009). They are synthesized by plants, some algae,
bacteria and fungi (Okada et al. 2008). The biosynthetic pathway were elucidated
between the years 1950 to 1960 through classical biochemical approaches by the
use of specific inhibitors and certain mutants blockers at different steps in the carotenoid synthesis pathway (Fraser and Bramley 2004). The biosynthesis in plant starts
from the initiation step, where mevalonic acid is converted to isopentenyl pyrophosphate (IPP) and condensed with dimethylallyl pyrophosphate (DMAPP) by a head
to tail fashion to generate geranyl pyrophosphate (GPP). Addition of two more molecule of IPP in two steps to GPP produces farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) through IPP isomerase and GGPP synthase
respectively (Fig. 20.3). GGPP is the immediate precursor for the biosynthesis of
carotenoids. Two molecules GGPP when condensed together head to head produce
pre-phytoene pyrophosphate, which produces phytoene through the reductive
dimerization of by the action of the enzyme phytoene synthase. Synthesis of phytoene is followed by dehydrogenation, desaturation, cyclization, hydroxylation,
epoxidation and oxidation (Yano et al. 2005).
20.5 Pharmacological Activities of Carotenoids
20.5.1 Anti-aging Activity
The development and progression of atherosclerosis is regarded as one of the major
manifestations of aging. It has been documented that the production of reactive
oxygen species (ROS) by the inflammatory milieu of atherosclerotic plaque is one
of the causes of atherosclerosis (Tavakoli and Asmis 2012). The level of ROS in
aging blood arteries leads to endothelial damage and dysfunction, and this stimulates the progression of atherosclerosis (Selvaraju et al. 2012). Also, the combination of atherosclerosis and aging by ROS is a result of reduction of nitric oxide (NO)
in the vascular tissue. Nevertheless, in normal vascular tissue, the concentration or
bioavailability of NO is usually high. The atherosclerotic vascular aging is inhibited
by NO produced in the endothelium by several mechanisms including maintenance
of normal flow of blood in organs via flow/shear stress mediated vasodilation. The
preserved vasodilation mediating blood flow in organs is one of the main mechanism of preventing anti-vascular aging (Celermajer et al. 1994). Also, NO stimulates the suppression of inflammation and thrombosis (Ungvari et al. 2010).
Carotenoids like lutein, lycopene and others inhibits vascular aging as a result of
their anti-oxidant activity, which elevates the bioavailability of NO in the vascular
system (Fig. 20.4). Consistently, tomato extract of β-carotene and lycopene decrease
A. Olatunde et al.
20.4 Biosynthesis of Carotenoids
Carotenoids are members of the tetraterpenoids containing 40 carbon atoms built by
the arrangements of terpene units joined together through their head and tail (Bonnie
and Choo 1999; Mattea et al. 2009). They are synthesized by plants, some algae,
bacteria and fungi (Okada et al. 2008). The biosynthetic pathway were elucidated
between the years 1950 to 1960 through classical biochemical approaches by the
use of specific inhibitors and certain mutants blockers at different steps in the carotenoid synthesis pathway (Fraser and Bramley 2004). The biosynthesis in plant starts
from the initiation step, where mevalonic acid is converted to isopentenyl pyrophosphate (IPP) and condensed with dimethylallyl pyrophosphate (DMAPP) by a head
to tail fashion to generate geranyl pyrophosphate (GPP). Addition of two more molecule of IPP in two steps to GPP produces farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) through IPP isomerase and GGPP synthase
respectively (Fig. 20.3). GGPP is the immediate precursor for the biosynthesis of
carotenoids. Two molecules GGPP when condensed together head to head produce
pre-phytoene pyrophosphate, which produces phytoene through the reductive
dimerization of by the action of the enzyme phytoene synthase. Synthesis of phytoene is followed by dehydrogenation, desaturation, cyclization, hydroxylation,
epoxidation and oxidation (Yano et al. 2005).
20.5 Pharmacological Activities of Carotenoids
20.5.1 Anti-aging Activity
The development and progression of atherosclerosis is regarded as one of the major
manifestations of aging. It has been documented that the production of reactive
oxygen species (ROS) by the inflammatory milieu of atherosclerotic plaque is one
of the causes of atherosclerosis (Tavakoli and Asmis 2012). The level of ROS in
aging blood arteries leads to endothelial damage and dysfunction, and this stimulates the progression of atherosclerosis (Selvaraju et al. 2012). Also, the combination of atherosclerosis and aging by ROS is a result of reduction of nitric oxide (NO)
in the vascular tissue. Nevertheless, in normal vascular tissue, the concentration or
bioavailability of NO is usually high. The atherosclerotic vascular aging is inhibited
by NO produced in the endothelium by several mechanisms including maintenance
of normal flow of blood in organs via flow/shear stress mediated vasodilation. The
preserved vasodilation mediating blood flow in organs is one of the main mechanism of preventing anti-vascular aging (Celermajer et al. 1994). Also, NO stimulates the suppression of inflammation and thrombosis (Ungvari et al. 2010).
Carotenoids like lutein, lycopene and others inhibits vascular aging as a result of
their anti-oxidant activity, which elevates the bioavailability of NO in the vascular
system (Fig. 20.4). Consistently, tomato extract of β-carotene and lycopene decrease
A. Olatunde et al.