The effects of platelet activating factor (PAF) and its cell analogs 1-O-alk-1;-enyl-2-acetyl-sn-glycero-3-phosphocholine (1-alkenyl-PAF) and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-PAF) on chemotaxis of human leukocytes in vitro and their inflammatory and antiinflammatory activities in vivo were studied. Both analogs stimulated chemotaxis of human leukocytes in agarose gel. PAF and 1-alkenyl-PAF induced rat paw edema in the range of doses 0.1-10 and 10-100 micro g per paw, respectively. Paw edema induced by 1-acyl-PAF (10-100 micro g per paw) was more pronounced than that induced by PAF or 1-alkenyl-PAF. The latter also exhibited significant antiinflammatory effect by inhibiting PAF- or carrageenan-induced rat paw edema, and this effect exceeded that of dexamethasone. In these models of inflammation 1-acyl-PAF did not exhibit any antiinflammatory activity. The data suggest that PAF is not the only cell phospholipid mediating inflammation--its cell analogs, 1-acyl-PAF and 1-alkenyl-PAF, may also be involved into the inflammatory response. Possible interrelationships between cellular synthesis of 1-acyl-PAF, its formation in oxidized LDL, biological effects of lysolecithin, and penetration of LDL into the arterial wall are discussed.

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The influence of acetyl salicylic acid (ASA) derivatives with platelet-activating factor (PAF) lipid analogs on PAF-induced human platelet aggregation has been studied. It was found that the ASA amide with an ethanolamine plasmalogen PAF analog (1-0-alk-1'-enyl-2-acetyl-sn-glycero-3-phospho-(N-2'-acetoxybenzoyl)ethanolamine) and the ASA ester with a choline plasmalogen PAF analog (1-0-alk-1'-enyl-2-(2'-acetoxybenzoyl)-sn-glycero-3-phosphocholine) at concentrations of 10-7-10-6 M effectively inhibit PAF-induced aggregation of human platelets. In contrast to these compounds, the ASA amide with an alkyl PAF analog (1-0-alkyl-2-acetyl-sn-glycero-3-phospho-(N-2'-acetoxybenzoyl)ethanolamine) did not inhibit PAF-induced platelet aggregation. As possible mechanisms of action of the studied compounds, the blockade of PAF-receptor and cyclooxygenase inhibition are proposed.

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