PAF-2-Thio is a synthetic substrate for lysophospholipase II and for PAF-Acetyl hydrolase. In the Ellman reaction (the free thiol product of reaction is detected colorimetrically with the DTNB reagent)
A wealth of evidence suggests that Lipoprotein-associated phospholipase A2 (Lp-PLA2) plays a relevant role in atherogenesis and inflammation, which in turn are associated with the risk of developing dementia. The aim of this study was to evaluate whether serum Lp-PLA2 activity might be an early and/or late biomarker for different forms of dementia. Serum Lp-PLA2 activity was assessed in older patients with mild cognitive impairment (MCI, n = 166; median clinical follow-up = 29 months), Late-Onset Alzheimer's disease (LOAD, n = 176), vascular dementia (VAD, n = 43), dementia characterized by an overlap between LOAD and VAD (AD-VAD MIXED dementia) (n = 136), other dementia subtypes (n = 45), and cognitively normal controls (n = 151). We found a significant trend towards higher levels of Lp-PLA2 activity in VAD compared with the other groups (ANOVA, p = 0.028). Similarly, Lp-PLA2 activity was greater in MCI converting to VAD compared with those that did not or did convert to the other types of dementia (ANOVA, p = 0.011). After adjusting for potential confounders, high levels of Lp-PLA2 activity were associated with the diagnosis of VAD (O.R. = 2.38, 95% C.I. = 1.06-5.10), but not with other types of dementia. Our data suggest that increased serum Lp-PLA2 activity may represent a potential biomarker for the diagnosis of VAD.
Title: Catabolism of platelet-activating factor and its acyl analog. Differentiation of the activities of lysophospholipase and platelet- activating-factor acetylhydrolase Aarsman AJ, Neys FW, Van den Bosch H Ref: European Journal of Biochemistry, 200:187, 1991 : PubMed
Recent investigations have shown the presence of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine, i.e. the acyl analog of platelet-activating factor (PAF), in unstimulated tissues as well as its formation along with platelet-activating factor upon stimulation of a variety of cells. We demonstrate here that this acyl analog of PAF can be catabolized by purified lysophospholipases I and II from bovine liver with near stoichiometric formation of 2-acetyl-sn-glycero-3-phosphocholine. Lysophospholipase II also deacetylated PAF to lysoPAF and evidence is presented to show that this is an intrinsic activity of this enzyme. This suggested that some lysophospholipases may contribute to intracellular inactivation of PAF by deacetylation. Anion-exchange chromatography of rat liver cytosol confirmed this possibility. However, similar experiments with rat kidney cytosol and rat and human platelet cytosol clearly separated lysophospholipase activities without PAF acetylhydrolase activity from specific PAF acetylhydrolases not having lysophospholipase activity. Thus, lysophospholipases are clearly involved in the metabolism of the acyl analog of PAF and in some tissues, such as liver, may even contribute to abolishing the biological activity of PAF through deacetylation.
Title: Structure-activity relationships for platelet-activating factor (PAF) and analogues reveal differences between PAF receptors on platelets and macrophages Stewart AG, Grigoriadis G Ref: J Lipid Mediat, 4:299, 1991 : PubMed
Analogues of PAF were examined for their potency in stimulating either platelet aggregation or macrophage superoxide anion generation. Modification of either the alkyl side-chain or the acetyl side-chain increased the relative potency of PAF analogues in macrophages, but all these compounds were more active in platelets. However, an analogue of PAF with an increased inter-ionic distance in the polar head group, hexanolamine PAF, showed a greater potency in macrophages than platelets. The latter compound also appeared to act as a partial agonist in both rabbit platelets and guinea-pig macrophages, but not in guinea-pig platelets. Differences in the rank order of potency of the PAF analogues in stimulating these cell elements suggest that platelet and macrophage PAF receptors differ.
