Trans-isomers, of lycopene

STAHL w, SCHWARZ w, SUNDQUIST A R and SIES H (1992) Cis-trans isomers of lycopene and beta-carotene in human serum and tissues. Arch Biochem Biophys 294(1) 173-7. 

Figure F2.4.1 Liquid chromatography/mass spectrometry (LC/MS) analysis of isomeric carotenes in a hexane extract from 0.5 ml human serum. Positive ion electrospray ionization MS was used on a quadrupole mass spectrometer with selected ion monitoring to record the molecular ions of lycopene, p-carotene, and a-carotene at m/z (mass-to-charge ratio) 536. A C30 HPLC column was used for separation with a gradient from methanol to methyl-ferf-butyl ether. The a -trans isomer of lycopene was detected at a retention time of 38.1 min and various c/ s isomers of lycopene eluted between 27 and 39 min. The all-frans isomers of a-carotene and P-carotene were detected at 17.3 and 19.3 min, respectively.

Figure F2.4.3 Flow-injection positive ion atmospheric pressure chemical ionization (APCI) mass spectrum of -1 pmol lycopene. The carrier solvent for flow injection analysis consisted of metha-nol/methyl-ferf-butyl ether (50 50 v/v) at a flow rate of 200 ul/min. The lycopene standard was isolated from tomatoes. The a -trans isomer of lycopene is shown, which is the most abundant isomer found in the tomato. This carotene is the familiar red pigment of the tomato.

Stahl, W., Schwarz, W., Sundquist, A.R., and Sies, H., cis-trans Isomers of lycopene and beta-carotene in human serum and tissues,Hrcfr Biochem. Biophys., 294,173-177,1992. 

Freeze-dried tomato powders obtained from whole tomato fruits and from their pulp after centrifugation, containing 474 and 5399 pg/g dry weight, respectively, were developed for use as additives for food fortification. Cis isomers of lycopene were determined in only a few smdies. The 5-cis-, 9-cis-, and 13-d5 --El5-d5 -lycopene were the isomers found in commercial tomato products. The structures of lycopene cis isomers are shown in Figure 4.2.1 and the structure of the dll-trans isomer is displayed in Figure 6.2.1 in Chapter 6. 

A second enzyme, BC02, was identified that cleaves carotenoids asymmetrically at the 9,10-double bond to produce the 10-apocarotenal (C27) and (3-ionone (C13), in a reaction similar to the Arabidopsis CCD7. Examples of BC02 have been cloned from mouse, zebra fish, ferret, and human (Kiefer et al. 2001, von Lintig et al. 2005, Hu et al. 2006). Substrate studies with different BC02s showed that these enzymes prefer acyclic carotenoids such as lycopene over cyclic carotenoids (Kiefer et al. 2001, von Lintig et al. 2005, Hu et al. 2006). These enzymes also seem to be selective for different carotenoid isomers. BC02 from ferret for example cleaves d,v-isomers of lycopene but not all-trans-lycopene (Hu et al. 2006). 

All-trans lycopene is rapidly isomerized to an equilibrium mixture with its cis isomers both in cell culture medium (Liu et al. 2006) and in vivo in prostate tissue (Clinton et al. 1996, van Breemen et al. 2002). The cis isomers of lycopene are absorbed better than the all -trans isomers when fed to humans (Unlu et al. 2007). The 5 -cis isomer predominates in plasma (Gustin et al. 2004). Since lycopene absorption by prostate cells might be due to facilitated diffusion (Liu et al. 2006), it is likely that the cis isomers of lycopene form a significant proportion of intracellular lycopene in the experiments that are reviewed later. 

Lycopene is the most predominant carotenoid in human plasma with a half-life of about 2-3 days (Stahl and Sies, 1996). Although the most prominent geometric isomers of lycopene in plants are the all-trans, in human plasma, lycopene is present as an isomeric mixture containing 50% of the... 

The 5-cis, 9-cis and 15-di-isomers of lycopene have been assayed in various foods and in human tissues using nuclear magnetic resonance (NMR) spectroscopy (Zumbrunn et al., 1985). In the various tomato-based foods surveyed by Schierle et al. (1996), the all-trans isomer represented between 35% to 96% of the total lycopene. In their survey, the proportion of 5-di-isomer in tomato products ranged from 4% to 27%, with considerably lower amounts of the other di-isomers. In human serum and tissues, the di-isomers of lycopene were found to contribute more than 50% of total lycopene (Krinsky et al., 1990). 

In human plasma, lycopene occurs as a 50/50 mixture of cis- and trans-isomers. This is the case in human and animal tissues, because this mixture corresponds to an equilibrium between the trans- and di-isomers (Boileau et al., 1999). Among the different geometrical isomers of lycopene, the dv-isomers (5-cis, 9-cis, 13-cis and 15-di) are better absorbed by the human body than the naturally occurring all-trans form (Stahl and Sies, 1992 Boileau et al., 1999). The m-isomers of lycopene are better absorbed than the all-trans isomer (Sakamoto et al., 1994 Britton, 1995 Stahl and Sies, 1996 Boileau et al., 1999). This may be due to the greater solubility of m-isomers in mixed micelles, possibly to the preferential incorporation into chylomicrons, and a lower tendency of di-isomers to aggregate, f/.v-isomcrs are less likely to crystallize, are more efficiently solubilized in lipophilic solutions and are more readily transported within cells or tissue matrix. 

Hengartner U, Bernhard K and Meyer K (1992) Synthesis, isolation, and NMR-spectroscopic characterization of fourteen (Z)-isomers of lycopene and of some acetylenic didehydro-and tetrahydrolycopenes. Helv Chim Acta 75 1848-1865 Hu Y, Hashimoto H, Moine G, Hengartner U and Koyama Y (1997) Unique properties of the 11 -cis and 11,11 -di-cis isomers of )3-carotene as revealed by electronic absorption, resonance Raman and H and NMR spectroscopy and by HPLC analysis of their thermal isomerization. J Chem Soc Perkin Trans 2 2699-2710... 

Boileau TW, Boileau AC, Erdman JW. Bioavailability of all-trans and cis-isomers of lycopene. Exp Biol Med (Maywood) 2002 227 914-919. 

Upon exposure to thermal energy, absorption of light, or involvement in specific chemical reactions, interconversion of lycopene isomers is known to take place. The cis isomers of lycopene, formed by rotation around any of its conjugated double bonds, have chemical and physical characteristics distinctly different from their all-frans counterparts. Some of the differences resulting from trans-to-cis isomerization include lower melting point, decreased color intensity, a shift in the lambda max, smaller extinction coefficients, and the appearance of a new maximum in the ultraviolet spectrum. ... 

Other Human Tissues. Details of extraction procedures and isocratic as well as RP-HPLC analysis of carotenoids present in various human tissues have been summarized by Parker (218) and by Schmitz et al. (219). Cis and trans isomers of carotenoids may have different biological activities. Thus the isomeric composition of lycopene and P-carotene was determined in the serum of healthy volunteers and in seven human tissues obtained by autopsy soon after death, using RP-HPLC on a Merck 5-p.m C18 end-capped column with a solvent mixture of CH3OH/CH3CN/CH2CI2/H2O) (7/7/2/0.16) and a photodiode array detector (220). 

The presence of other carotenoids can affect the absorption of carotenoids into intestinal mucosal cells, since carotenoids can compete for absorption or facilitate the absorption of another. Data on carotenoid interactions are not clear. Human studies show that /3-carotene decreases lutein absorption, while lutein has either no effect or a lowering effect on /3-carotene absorption. Although not confirmed in humans, the inhibitory effect of lutein on /3-carotene absorption might be partly attributed to the inhibition of the /3-carotene cleavage enzyme by lutein shown in rats. Beta-carotene also seemed to lower absorption of canthaxanthin, whereas canthaxanthin did not inhibit /3-carotene absorption. Studies showed that /3-carotene increased lycopene absorption, although lycopene had no effect on /3-carotene. Alpha-carotene and cryptoxanthin show high serum responses to dietary intake compared to lutein. In addition, cis isomers of lycopene seem to be more bioavailable than the -trans, and selective intestinal absorption of a)X-trans /3-carotene occurs, as well as conversion of the 9-cis isomer to sW-trans /3-carotene. It is clear, then, that selective absorption of carotenoids takes place into the intestinal mucosal cell. 

Besides the capacity of CRTI to introduce all four double bonds in the conversion of phytoene to lycopene, the enzyme produces different geometric isomers than does PDS/ZDS (see graphic, side-by-side comparison in Fraser and Bramley ). CRTI produces all-trans isomers. Studies that have examined the function of the paired plant desaturases acting together, from Arabidopsis, and from maize and from... 

Similar results were obtained during hot-break processing of tomato juice and even of tomato paste, the amounts of trans- and cis- lycopene isomers remained almost unchanged, whereas increased levels of ris-P-carotene were found during these processes (Abushita et al. 2000). 

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