Carotenoid transformation

Repeta D.J., Gagosian R.B.(1982) Carotenoid transformation in coastal marine waters. Nature 295, 51-4. 

Pathways. Studies of carotenoid transformations that take place when a mutant strain, PGl, of the green alga Scenedesmus obliquus is transferred from dark to light conditions have indicated that the transformations 15-cw-phytoene (180) 15-c/5-phytofluene (181) - 15-cis- -carotene (182) -> trans-C-caro-tene (183) (Scheme 7) take place in the biosynthesis of the normal cyclic carotenoids. The results were also in agreement with the formation of the xanthophylls lutein (16) and zeaxanthin (174) from the corresponding carotenes. 

Table 13.6 Higher plants transformed with carotenoid genes...

A single gene transformation crtB from Erwinia) was sufficient to increase carotenoid levels some 50-fold in seeds of canola (Brassica napus), which already contains low levels of carotenoids (Shewmaker et ah, 1999). This is the most spectacular increase in carotenoid levels of any plant to date. 

Both intact carotenoids and their apolar metabolites (retinyl esters) are secreted into the lymphatic system associated with CMs. In the blood circulation, CM particles undergo lipolysis, catalyzed by a lipoprotein lipase, resulting in the formation of CM remnants that are quickly taken up by the liver. In the liver, the remnant-associated carotenoid can be either (1) metabolized into vitamin A and other metabolites, (2) stored, (3) secreted with the bile, or (4) repackaged and released with VLDL particles. In the bloodstream, VLDLs are transformed to LDLs, and then HDLs by delipidation and the carotenoids associated with the lipoprotein particles are finally distributed to extrahepatic tissues (Figure 3.2.2). Time-course studies focusing on carotenoid appearances in different lipoprotein fractions after ingestion showed that CM carotenoid levels peak early (4 to 8 hr) whereas LDL and HDL carotenoid levels reach peaks later (16 to 24 hr). 

Carotenoid chemical structure is usually not affected by the physical quenching. Another mechanism can occur in which a carotenoid chemically quenches singlet oxygen and is thus transformed in derived products. ... 

Studies on carotenoid autoxidation have been performed with metals. Gao and Kispert proposed a mechanism by which P-carotene is transformed into 5,8-per-oxide-P Carotene, identified by LC-MS and H NMR, when it is in presence of ferric iron (0.2 eq) and air in methylene chloride. The P-carotene disappeared after 10 min of reaction and the mechanism implies oxidation of the carotenoid with ferric iron to produce the carotenoid radical cation and ferrous iron followed by the reaction of molecular oxygen on the carotenoid radical cation. Radical-initiated autoxidations of carotenoids have also been studied using either radical generators like or NBS.35... 

Aside from isomerization, transformation of the 5,6-epoxy to the 5,8-furanoid group is a common alteration during heating treatments of carotenoids. Violaxanthin was found to be the major carotenoid in mangoes however, in commercially processed mango juice, violaxanthin was not detected while auroxanthin, not present in the... 

FIGURE 5.3.5 Enhancement of lycopene accumulation in . coZi by over-expression of DXS. Lycopene accumulation (left) is enhanced (right) when E. coli cells carrying a carotenoid pathway gene cassette (+EIB) are further transformed with a dxs gene on a multicopy plasmid (+E1B +dxs). Lycopene hyperaccumulation was demonstrated by Matthews and Wurtzel. ... 

Sandmann, G., Carotenoid analysis in mutants from Escherichia coli transformed with carotenogenic gene cluster and Scenedesmus obliquus mutant C-6D, Meth. Enzymol. 214, 341, 1993. 

The late emergence of hydrophilic, synthetically modified carotenoids is probably the result of a too well-respected principle by traditional carotenoid chemists synthesize carotenoids—don t synthesize with carotenoids Indeed, except for some early reported functional group transformations... 

The spontaneous isomerization of all-trans- carotenoids at room temperature is a slow process, and its rate depends on the solvent and the pigment structure. For example, the initial solutions of P-carotene in a mixture of tetrahydrofuran (THF), methanol, and acetonitrile containing ca. 95% of all -trans- and 5% of 9-cis- plus 13-co-isomers was transformed to 90% all-fra ns- p -ca rot ene and 9% of 9-cis- plus 13-cA-carotene after 24h of spontaneous isomerization at 25°C (Pesek et al. 

In general, the major consequences of food thermal processing, either at laboratory or commercial scales, on carotenoids are the transformation of the 5,6-epoxy to the 5,8-furanoid rings, trans- to cis- isomerization and oxidation. In addition, independently of the food matrix or thermal... 

The photosensitized transformation of carotenoids has been studied using several sensitizer molecules, such as chlorophylls, iodine, rose bengal (RB), and methylene blue (MB) and in general terms isomerization is the major pathway of reaction. 

FIGURE 15.3 Hypothetical pathways responsible for carotenoid uptake, metabolic transformations, tran-scytosis to the neural retin, or secretion to the blood. 

Khachik, F, de Moura, FF, Zhao, DY, Aebischer, CP, and Bernstein, PS, 2002. Transformations of selected carotenoids in plasma, liver, and ocular tissues of humans and in nonprimate animal models. Invest Ophthalmol Vis Sci 43, 3383-3392. 

Bertram, J. S., A. Pung, M. Churley et al. 1991. Diverse carotenoids protect against chemically induced neoplastic transformation. Carcinogenesis 12(4) 671-678. 

It has been shown that the expression of connexin 43 (Cx43) is upregulated by cancer-preventive retinoids and carotenoids, which correlate with the suppression of carcinogen-induced transformation in 10T1/2 cells. Recently, it has been reported that Cx43 induction by astaxanthin, but not by a RAR-specific retinoid, was inhibited by GW9662, a PPARy antagonist (Bertram et al., 2005). 

---