|Mein, Jonathan R.|
|Russel, Robert M.|
Submitted to: Archives Of Biochemistry and Biophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2010
Publication Date: 2/1/2011
Citation: Mein, J., Dolnikowski, G., Hansgeorg, E., Russel, R., Wang, X. 2011. Enzymatic formation of apo-carotenoids from the xanthophyll carotenoids lutein, zeaxanthin and b-cryptoxanthin by ferret carotene-9, 10-monooxygenase. Archives Of Biochemistry and Biophysics. 506:109-121 PMID 21081106. Interpretive Summary: Accumulating evidence strongly suggests that xanthophylls, which include the oxygenated carotenoids lutein, zeaxanthin, and beta-cryptoxanthin, may provide potential health benefits against several chronic and degenerative diseases in humans. However, there remains a substantial gap in knowledge regarding the vertebrate metabolic pathways of these carotenoids. The work of our lab and others has substantiated the excentric carotenoid cleavage pathway through the biochemical characterization of the endogenous carotenoid cleaving enzyme carotene-9,10-monooxygenase (CMO2). In the present study, we demonstrate for the first time that ferret CMO2 catalyzes the excentric cleavage of xanthophylls, including the non-provitamin A carotenoids zeaxanthin and lutein and the provitamin A carotenoid beta-cryptoxanthin. Importantly, we showed the xanthophylls zeaxanthin and lutein are preferentially cleaved over the mono-hydroxy beta-cryptoxanthin, providing strong biochemical evidence that accumulation of the xanthophylls lutein and zeaxanthin in adipose tissue and skin are due to mutations in the CMO2 gene. Considering the significant interest in and potential beneficial effects of lutein, zeaxanthin and beta-cryptoxanthin in human health, enzymatic cleavage of xanthophylls by CMO2 represents a new avenue of research regarding vertebrate carotenoid metabolism and biological function.
Technical Abstract: Xanthophyll carotenoids, such as lutein, zeaxanthin and b-cryptoxanthin, may provide potential health benefits against chronic and degenerative diseases. Investigating pathways of xanthophyll metabolism are important to understanding their biological functions. Carotene-15,150-monooxygenase (CMO1) has been shown to be involved in vitamin A formation, while recent studies suggest that carotene-90,100-monooxygenase(CMO2) may have a broader substrate specificity than previously recognized. In this in vitro study, we investigated baculovirus-generated recombinant ferret CMO2 cleavage activity towards the carotenoid substrates zeaxanthin, lutein and b-cryptoxanthin. Utilizing HPLC, LC–MS and GC–MS, we identified both volatile and non-volatile apo-carotenoid products including 3-OH-b-ionone,3-OH-a-ionone, b-ionone, 3-OH-a-apo-100-carotenal, 3-OH-b-apo-100-carotenal, and b-apo-100-carotenal,indicating cleavage at both the 9,10 and 90,100 carbon–carbon double bond. Enzyme kinetic analysis indicated the xanthophylls zeaxanthin and lutein are preferentially cleaved over b-cryptoxanthin, indicating a key role of CMO2 in non-provitamin A carotenoid metabolism. Furthermore, incubation of 3-OH-b-apo-100-carotenal with CMO2 lysate resulted in the formation of 3-OH-b-ionone. In the presence of NAD+, in vitro incubation of 3-OH-b-apo-100-carotenal with ferret hepatic homogenates formed 3-OHb-apo-100-carotenoic acid. Since apo-carotenoids serve as important signaling molecules in a variety of biological processes, enzymatic cleavage of xanthophylls by mammalian CMO2 represents a new avenue of research regarding vertebrate carotenoid metabolism and biological function.