Polyunsaturated fatty acid oxidation in Alzheimer’s disease.

Alzheimer’s disease is a neurodegenerative disorder which has been characterised with genetic (apolipoproteins), protein (ß-amyloid and tau) and lipid oxidation/metabolism alterations in its pathogenesis. In conjunction with the Dementia Research Group, Bristol University, investigation into genetic, protein and lipid oxidation in Alzheimer’s disease was conducted. A large sample cohort using the double-blind criteria, along with various clinical and chemical data sets were used to improve the statistical analysis and therefore the strength of this particular study. Bristol University completed genetic and protein analysis with lipid oxidation assays performed at Aston University. Lipid oxidation is a complex process that creates various biomarkers, from transient intermediates, to short carbon chain products and cyclic ring structures. Quantification of these products was performed on lipid extracts of donated clinical diseased and non-diseased frontal and temporal brain regions, from the Brain Bank within Frenchay Hospital. The initial unoxidised fatty acids, first transient oxidation intermediates the conjugated dienes and lipid hydroperoxides, the endpoint aldehyde biomarkers and finally the cyclic isoprostanes and neuroprostanes were determined to investigate lipid oxidation in Alzheimer’s. Antioxidant levels were also investigated to observe the effect of oxidation on the defence pathways. Assays utilised in this analysis included; fatty acid composition by GC-FID, conjugated diene levels by HPLC-UV and UV-spec, lipid hydroperoxide levels by FOX, aldehyde content by TBARs, antioxidant status by TEAC and finally isoprostane and neuroprostane quantification using a newly developed EI-MS method. This method involved the SIM of specific ions from F-ring isoprostane and neuroprostane fragmentation, which enabled EI-MS to be used for their quantification. Analyses demonstrated that there was no significant difference between control and Alzheimer samples across all the oxidation biomarkers for both brain regions. Antioxidants were the only marker that showed a clear variance; with Alzheimer samples having higher levels than the age matched controls. This unique finding is supported with the observed lower levels of lipid oxidation biomarkers in Alzheimer brain region samples. The increased antioxidant levels indicate protection against oxidation which may be a host response to counteract the oxidative pathways, but this requires further investigation. In terms of lipid oxidation, no definitive markers or target site for therapeutic intervention have been revealed. This study concludes that dietary supplementation of omega-3 fatty acids or antioxidants would most likely be ineffective against Alzheimer disease, although it may support improvement in other areas of general health.

Free radical reaction products and antioxidant capacity in beating heart coronary artery surgery compared to conventional bypass

Oxygen-derived free radicals are important agents of tissue injury during ischemia and reperfusion. The aim of this study was to investigate changes in protein and lipid oxidation and antioxidant status in beating heart coronary artery surgery and conventional bypass and to compare oxidative stress parameters between the two bypass methods. Serum lipid hydroperoxide, nitric oxide, protein carbonyl, nitrotyrosine, vitamin E, and β-carotene levels and total antioxidant capacity were measured in blood of 30 patients undergoing beating heart coronary artery surgery (OPCAB, off-pump coronary artery bypass grafting) and 12 patients undergoing conventional bypass (CABG, on-pump coronary artery bypass grafting). In the OPCAB group, nitric oxide and nitrotyrosine levels decreased after reperfusion. Similarly, β-carotene level and total antioxidant capacity also decreased after anesthesia and reperfusion. In the CABG group, nitric oxide and nitrotyrosine levels decreased after ischemia and reperfusion. However, protein carbonyl levels elevated after ischemia and reperfusion. Vitamin E, β-carotene, and total antioxidant capacity decreased after ischemia and reperfusion. Significantly decreased nitration and impaired antioxidant status were seen after reperfusion in both groups. Moreover, elevated protein carbonyls were found in the CABG group. The off-pump procedure is associated with lower degree of oxidative stress than on-pump coronary surgery. © 2011 Pleiades Publishing, Ltd.

The selective protection afforded by ebselen against lipid peroxidation in an ROS-dependent model of inflammation

The effects of an experimental model of hydrogen-peroxide-induced foot pad oedema on indices of oxidative damage to biomolecules have been investigated. We have demonstrated increased levels of fluorescent protein and lipid peroxides occurring in plasma at 24 and 48 h post-injection. In addition, a decrease in the degree of galactosylation of IgG was observed which kinetically related the degree of inflammation and to the increase in protein autofluorescence (a specific index of oxidative damage). The effects of ebselen, a novel organoselenium compound which protects against oxidative tissue injury in a glutathione-peroxidase-like manner, have also been examined in this model. Pretreatment of animals with a dose of 50 mg/kg ebselen afforded significant and selective protection against lipid peroxidation only. This effect may contribute to the anti-inflammatory effect of this agent in hydroperoxide-linked tissue damage.

Phagocyte oxidation of phospholipids: comparison of hydroperoxide, chlorohydrin and epoxyisoprostane formation by LC-MS

Phagocytic cells produce a variety of oxidants as part of the immune defence, which react readily both with proteins and lipids, and could contribute to the oxidation of low density lipoprotein in atherosclerosis. We have investigated the oxidation of phospholipid vesicles by isolated human polymorphonuclear and mononuclear leukocytes, to provide a model of lipid oxidation in the absence of competing protein. PMA-stimulated cells were incubated with phospholipid vesicles contammg dipalmitoyl phosphatidylcholine (DPPC), palmitoyl-arachidonoyl phosphatidylcholine (PAPC), and stearoyl-oleoyl phosphatidylcholine (SOPC), before extraction of the lipids for analysis by HPLC coupled to electrospray mass spectrometry. In this system, oxidized phosphatidylcholines elute earlier than the native lipids owing to their decreased hydrophobicity, and can be identified according to their molecular mass. The formation of monohydroperoxides of P APC was observed routinely, together with low levels of hydroxides, but no chlorohydrin derivatives of P APC or SOPC were detected. However, the major oxidized product occurred at 828 m/z, and was identified as I-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphocholine. These results show that phagocytes triggered by PMA cause oxidative damage to lipids predominantly by free radical mechanisms, and that electrophilic addition involving HOCl is not a major mechanism of attack. The contribution of myeloperoxidase and metal ions to the oxidation process is currently being investigated, and preliminary data suggest that myeloperoxidase-derived oxidants are responsible for the epoxyisoprostane phospholipid formation. The identification of an epoxyisoprostane phospholipid as the major product following phagocyte-induced phospholipid oxidation is novel and has implications for phagocyte involvement in atherogenesis.