John T. Landrum, Professor
Department of Chemistry and Biochemistry and 

Director of the FIU Office of Pre-Health Professions Advising 
Florida International University
Miami, Florida  33199

phone: (305)-348-3091
FAX: (305)-348-3772
Email: landrumj@fiu.edu 
  
 

     Carotenoids: Physical, Chemical, and Biological Functions and Properties. Editor: 2010 John T. Landrum (ed), CRC Press, Boca Raton, Fl 

Carotenoids are brightly colored natural products that are synthesized by plants, algae and bacteria. More than 750 naturally occurring carotenoids have been extracted and identified from a wide variety of biological sources. The majority of carotenoids are tetraterpenes and contain eight isoprene units. These tetraterpene carotenoids have a C40 carbon skeleton and are typified by a conjugated polyene chain containing 9 or 10 double bonds. It is this linear conjugated polyene that is responsible for the characteristic intense colors of carotenoids. Carotenoids are natural dietary components of higher animals which are unable to synthesize these compounds. They serve a variety of functional roles in higher animals which absorb these lipophylic components from the diet and deposit them in many different tissues. In virtually all higher animals the provitamin A carotenoids are a source of vitamin A (retinol) which is essential for normal growth and health in addition to its function as a visual pigment. In birds yellow, orange, and red plumage are due to a variety of carotenoid compounds.

 

Eschscholzia mexicana (eschscholtzxanthin), golden finch (lutein), Lobelia cardineli (lycopene?), Calthus palustrus (epilutein)

beta-carotene has been identified as an anti-oxidant and its accumulation in many tissues is believed to protect against free radical processes which degrade and damage cellular structures leading to carcinogenisis, apoptosis, mutations, and structural damage associated with aging. Similarly, other carotenoids are found in a variety of tissues and may serve an anti-oxidant role. The possibility that metabolism of non-provitamin A carotenoids occurs producing essential or non-essential compounds that are biologically active cannot be neglected.

Our research which has largely been devoted to an elucidation of the composition and function of the macular pigment now includes the broader goal to understand the nature of the metabolism of the non-provitamin A dihydroxy-carotenoids, particularly lutein and zeaxanthin. The presence of meso-zeaxanthin (3R,3'S-beta,beta-carotene-3,3'-diol) in the human retina requires a complex transformation which is thought to be enzyme mediated. We are working toward a basic understanding of the oxidation and degradation reactions of lutein and zeaxanthin. Understanding the role of non-provitamin A carotenoids in human health will necessitate a complete clarification of the metabolism of these compounds, their metabolic products, and their fate.

 

Research Interests:

Macular pigment:  Identification of the components of the macular pigment, their absorption, transport, uptake, function, and metabolism are the major activities of our research group.  We have in demonstrated that lutein, zeaxanthin, meso-zeaxanthin are all major components of the macular pigment present in the human macula.  Meso-zeaxanthin is a rare dietary component and is produced by metabolic processes within the central macular region of the retina.  We have been able to demonstrate that dietary lutein and zeaxanthin supplementation will produce increases in the level of macular pigmentation.  The functions of the macular pigment include the absorption of blue light by the highly concentrated  pigment found in the inner layers of the retina and action as an antioxidant within the retinal pigment epithelium and photoreceptors themselves.  Our recent comparison of the amounts of macular pigment found in the retinas of control eyes and those diagnosed with age-related macular degeneration (AMD) show that individuals having the highest levels of macular pigment (as measured in the peripheral retina) have a ~75% lower risk of AMD than individuals in having the lowest levels.

 

Macular pigment of the macaque retina and the cross-section of the retina showing the macular pigment concentrated in the inner neural layers.  The fundus view of the macaque reint  on the left from a paper by Malinow et al IOVS, 1980. Martha Neuringer shared this photo with us.  The cross-seciontal color photograph of the macular of the macaque retina was published by Max Snodderly in his landmark paper in IOVS; Snodderly DM, Auran JD, and Delori FC (1984) IOVS 25, 674-685.

Our research has demonstrate that the concentration of the macular pigment approaches 1mM concentration in the central regions of the macula more than a 10,000 times more concentrated than that in the blood.  The profile of the macular pigment concentration across the retina varies dramatically, > 100times, from the peripheral retina to the central retina as is seen in the graph above on the right.  The cyan points illustrate how the relative proportions of lutein and zeaxanthin vary within the retina and how carefully the retina controls the composition of the pigments in different area of the retina.  Landrum JT and Bone RA, Carotenoids in Health and Disease, 2004.

The distribuiont of the macular pigments is influenced by the conversion of lutein into meso-zeaxanthin within the central retina. The distribution of meso-zeaxanthin is shown in the graph below.  The concentration of meso-zeaxanthin is very low in the peripheral retina and increases reaching a maximum in the center of the fovea where the approximate ratios of L : Z : MZ is 1 : 1 : 1 within the central 3 mm.

 

We have modeled the topological mobility of the carotenoids by studying the ability of the ionone ring end-groups to rotate relative to the polyene chain.  Our studies demonstrate that end-groups can provide a very sensitive means for the carotenoid to be identified by the proteins which must be responsible for binding and transporting them within the retina.  The carotenoid zeaxanthin has two beta-ionone rings and is symmetrical whereas lutein possess one beta-ionone ring and one epsilon-ionone ring, below.  The preferred conformational geometries of these two ionone rings is different.  The beta-ionone ring adopts a 'co-planar' geometry with the polyene chain whereas the epsilon-ionone ring flexes and the plane of the ring is nearly perpendicular to the polyene chain.  The end-groups in zeaxanthin are therefor 'spade-like' with the ring geometry similar to that of the shovel blade relative to the long-chain polyene.  In lutein, the epsilon ring assumes a more 'hoe-like' geometry; these are very distinct and it would require a large amount of energy to make one of these rings adopt the geometry preferred by the other.  The graph below comes from our recent paper describing calculations detailing the geometries of these rings versus energy.

Landrum JT et al. Archives of Biochemistry and Biophysics 493 (2010) 169174

 

There are a number of animal models that are being studied to understand more effectively the mechanisms by which carotenoids, particularly lutein and zeaxanthin, are transported in biological systems.  We have been looking at the Monarch butterfly whose larvae exhibit a characteristic 'tiger-stripe' pattern with black, white and yellow regions.  Our analysis of the carotenoid content of these regions demonstrates that the yellow regions typically 15 times as much lutein in them as the black or white regions. The transport of lutein in the Monarch butterfly, like that in the human macula, depends on proteins capable of specifically recognizing and mobilizing these molecules to the appropriate tissue.

 

 

in   Carotenoids: Physical, Chemical, and Biological Functions and Properties Editor: 2010 John T. Landrum (ed), CRC Press, Boca Raton, Fl  p568. 

Vita

Recent Publications
 

Courses:

Freshman Exp, SLS 1501 -  Rope Course a Go For Fri. Oct 21 , Ropes Photos

General Chemistry I,     CHM1045 - syllabus, assignments
General Chemistry II,    CHM1046 - syllabus, assignments
Organic Chemistry I,     CHM2210 - syllabus, assignments

Organic Chemistry II,    CHM 2211 - syllabus, assignments

Survey of Organic Chemistry,  CHM 2200 - syllabus, assignments

 

Advanced Inorganic Chemistry, CHM 4610 - syllabus, assignments