Raman studies of structural rearrangements induced in human plasma lipoprotein carotenoids by malondialdehyde

Abstract

Raman and resonance Raman spectra of plasma lipoproteins +/- malondialdehyde were studied at concentrations which block the normal receptor-mediated uptake by cells. The strong resonance Raman bands at about 1010, 1162 and 1530 cm-1, due to the presence of carotenoids in the lipoproteins, are envisaged as structural probes. High resolution resonance Raman spectra of the 1500-1600 cm-1 region reveal multiple features suggesting the coexistence of several structural populations of beta-carotene whose precise assignment is complex. When plasma lipoproteins are reacted with malondialdehyde, a complex change occurs in the resonance Raman banding of beta-carotene in the 1500-1600 cm-1 region. Malonaldehyde (MDA) also modifies the acoustical region (70-200 cm-1 of low density lipoprotein (LDL) lipids. We suggest that malondialdehyde association with plasma lipoproteins alters the lipid structure via apoprotein or apoprotein/lipid associations.

Structural Abnormality in LDL From Diabetic Patients as Revealed by Resonance Raman Spectroscopy

“…The latter phenomenon, in turn, may influence the organization of acyl chain and hence could affect the thermal transition. We provided direct proof that cross-linking of apoB with malondialdehyde substantially alters the lipid organization (19). Our data support the possibility that nonenzymatic binding of glucose to the lysine residues may alter the lipid structure via apoprotein or apoprotein-lipid associations.…”

“…Considering the model of Laggner et al (26) for CE arrangement in the core of human LDL and the results in Verma et al (19) and Verma and Wallach (23), we suggest that carotenoid molecules may be located away from cholesterol moities, perhaps associated with an ester part in the core, phospholipids, and apoprotein. That carotenoids could be associated with apolipoprotein is supported by our previous RR data (19) and studies on apoB-carotenoid complex (unpublished observations).…”

“…Our studies on various solvents (hexane, chloroform, methanol, and sodium dodecyl sulfate) for delipidation of LDL, followed by high-resolution RR and chemical analyses of carotenoids and apoB in each isolated component, suggest the existence of at least 0.1 mol carotenoid/mol protein in the solvent residue and ~5 mol in the solvent extract (19).…”

“…Carotenoids are considered to be localized in the lipid core, although their precise assignment is not yet established. RR studies on native and modified LDL (6,19), serum albumin-p-carotene complex (6), erythrocyte ghost (23), iso- lated platelets (7), carotenoproteins of lobster shell (24), and studies on the kinetics of carotenoid transfer between model and native lipoproteins (25) provide clues that suggest that carotenoid molecules may bind with both lipids and proteins. The association of carotenoids with apoB in LDL could be possible either directly or via adjacent lipids (boundary lipids).…”

“…No significant lipid oxidation was observed by thiobarbituric acid test (17). Proteins were measured according to the method of Lowry et al (18), and carotenoids were measured as previously described (19).…”