**4. Lipid peroxidation products: A possible biomarker of HIV disease progression**

Lipid peroxidation is a free radical reaction. Any species that has sufficient reactivity to abstract a hydrogen atom from a polyunsaturated fatty acid side chain in membrane lipids may initiate this process [38]. This occurs when hydroxyl radicals and possibly oxygen react with the unsaturated lipids of bio-membrane, resulting in the generation of lipid peroxide radical (R000 ), lipid hydroperoxide (R00H) and fragmentation products such as hydroxyoctadecadie‐ noic acid from linoleates, F2-isoprostanes from arachidonates and neuroprostanes from docosahexaenoates [39], 4-hydroxy-hexanal, 4-hydroxy-2-nonenal and malondialdehyde (MDA) [40] that gives the OS condition. MDA seems to be the most potent biomarker of lipid peroxidation although 4-hydroxy-hexanal and 4-hydroxy-2-nonenal are also specific, sensitive and quantifiable markers (noninvasive) measurable in urine for OS overview [41]. Lipid peroxidation in biological membranes generally proceeds through a complex process involv‐ ing rearrangement and destruction of the double bonds in polyunsaturated fatty acid. This occurs in three steps, viz. initiation, propagation and termination phases. Peroxidation of membrane lipids can have several outcomes, such as increased membrane rigidity, decreased activity of membrane–bound enzymes, altered activity of membrane receptors (e.g. sodium pumps), altered permeability (increased permissibility), formation of hydrophobic centres that approaches the external phase, alteration of protein structure, mutagenicity (resulting from DNA/RNA damage or binding) and inhibition of growth and protein synthesis [24]. This is caused by the high nucleophilic properties of decomposed aldehyde products formed during lipid peroxidation, which enables them to react with electrophilic sites such as amino and thiol groups [42]. Biomarkers are characteristics that are specific, reliable and can be measured objectively upon evaluation as indicators of normal biological processes, pathogenic processes or pharmacologic responses to a therapeutic intervention.

It is now established that HIV infection is associated with formation of lipid peroxidation products. The importance of evaluating these products is to determine or rather to have a fair idea of the degree of damage the infection has caused the cell. Numerous research works have implicated lipid peroxides as a marker of disease prognosis, drug development and evaluation of efficiency of drugs [43, 44]. A number of scientists have suggested the use of OS marker MDA as a potent additional tool for the assessment and surveillance of HIV/AIDS disease [25,39] and a possible predicator of HIV/AIDS disease progression [45].This is not unlikely knowing that different levels of OS measures as MDA is associated with stages of HIV/AIDS infection classification (Fig. 1).
