Apolipoprotein E (apoE), an anti-atherogenic apolipoprotein, plays a significant role in the metabolism of lipoproteins. It lowers plasma lipid levels by acting as a ligand for low-density lipoprotein receptor (LDLr) family of proteins, in addition to playing a role in promoting macrophage cholesterol efflux in atherosclerotic lesions. The objective of this study is to examine the effect of acrolein modification on the structure and function of rat apoE and to determine sites and nature of modification by mass spectrometry. Acrolein is a highly reactive aldehyde, which is generated endogenously as one of the products of lipid peroxidation and is present in the environment in pollutants such as tobacco smoke and heated oils. In initial studies, acrolein-modified apoE was identified by immunoprecipitation using an acrolein-lysine specific antibody, in the plasma of ten-week old male rats that were exposed to filtered air (FA) or low doses of environmental tobacco smoke (ETS). While both groups displayed acrolein-modified apoE in the lipoprotein fraction, the ETS group had higher levels in lipid-free fraction compared to the FA group. This observation provided the rationale to further investigate the effect of acrolein modification on rat apoE at a molecular level. Treatment of recombinant rat apoE with a 10-fold molar excess of acrolein resulted in: (i) a significant decrease in lipid-binding and cholesterol efflux abilities, (ii) impairment in the LDLr- and heparin-binding capabilities, and (iii) significant alterations in the overall stability of the protein. The disruption in the functional abilities is attributed directly or indirectly to acrolein modification yielding: an aldimine adduct at K149 and K155 (+38); a propanal adduct at K135 and K138 (+56); an Nε-(3-methylpyridinium)lysine (MP-lysine) at K64, K67 and K254 (+76), and Nε-(3-formyl-3,4-dehydropiperidino)lysine (FDP-lysine) derivative at position K68 (+94), as determined by Matrix-Assisted Laser Desorption/Ionization-Time of Flight/Time of Flight Mass Spectrometry (MALDI-TOF/TOF MS). The loss of function may also be attributed to alterations in the overall fold of the protein as noted by changes in the guanidine HCl-induced unfolding pattern and to protein cross-linking. Overall, disruption of the structural and functional integrity of apoE by oxidative modification of essential lysine residues by acrolein is expected to affect its role in maintaining plasma cholesterol homeostasis and lead to lipid dysregulation.

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This study was carried out to evaluate the phytochemical, antioxidant potentials, and proximate composition of extracts of Citrullus lanatus rind (CLR) in different solvents. Chloroform, n-hexane, ethyl acetate, ethanol, and aqueous extracts of CLR were prepared after which they were subjected to phytochemical, antioxidants, and proximate analysis using standard methods. The ethanol and aqueous extracts of Citrullus lanatus rind were rich in alkaloids, saponins, and terpenoids, while the chloroform and ethanol extract were rich in flavonoids. It was observed that the ethyl acetate, chloroform and ethanol extracts of Citrullus lanatus rind had the highest concentration of total phenolic substances when compared with other extracts considered. The DPPH antioxidant scavenging activity was significantly higher in the ethyl acetate, hexane, and chloroform extracts. The aqueous extract Citrullus lanatus rind was richer in moisture content, but chloroform and hexane extracts were richer in calorie or carbohydrate a relatively high percentage of crude protein in the ethanol extract. With prescence of alkaloids, saponins, terpenoids, and phenolic compounds in ethanol and aqueous extracts of CLR. They may be beneficial in reducing cardiovascular diseases. Also, with improvement in quality of Citrullus lanatus rind, it may be of high medicinal value to man and livestock.

The objective of our study was to assess if second hand smoke exposure predisposes subjects towards developing heart disease. We monitored the effect of reactive aldehydes in tobacco smoke on the status of plasma apolipoprotein E (apoE). ApoE plays a critical role in regulating plasma cholesterol homeostasis, since it serves as a ligand for the low density lipoprotein family of receptors. ELISA indicated that rats exposed to low doses of tobacco smoke had lower plasma apoE levels compared to the control group. Immunoprecipitation analysis revealed that the smoke‐exposed group also had higher levels of modified apoE in their lipid‐free fractions. There were no differences between the two groups in lipid peroxidation products levels or in the susceptibility of the lipoproteins to lipid peroxidation. In vitro analysis using recombinant apoE provided further support for modification of essential lysines. Our results suggest that the occurrence of oxidatively modified apoE in a lipid‐free state can result in decreased clearance of plasma lipoproteins. We propose that sustained second hand smoke exposure can potentially lead to a proatherogenic profile. Source of research support: Tobacco Related Disease Research Program, American Heart Association, NIH R25 HL096365‐01, CSULB funding and SCAC award.