EFFECTS OF OXO AND DIHYDRO METABOLITES OF 12-HYDROXY-5,8,10,14-EICOSATETRAENOIC ACID ON CHEMOTAXIS AND CYTOSOLIC CALCIUM LEVELS IN HUMAN NEUTROPHILS

One of the pathways of metabolism of leukotriene B-4 (LTB(4)) and 12-h ydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) in leukocytes is oxid ation of the 12-hydroxyl group, followed by reduction of the 10,11-dou ble bond. In the case of 12R-HETE and 12S-HETE, this results in the fo rmation of 12-oxo-ETE, 10,11-dihydro-12-oxo-ETE, and the 12R and 12S i somers of 10,11-dihydro-12-HETE (i.e., 12R-HETrE and 12S-HETrE). We in vestigated the effects of metabolites of 12-HETE formed by this pathwa y on cytosolic calcium levels and chemotaxis in human neutrophils. Of the above series of metabolites, 12S-HETrE (which has the same absolut e stereochemistry at C-12 as 12R-HETE) was the most potent in stimulat ing both cytosolic calcium levels and chemotaxis. It was slightly less potent than 12R-HETE, consistent with the concept that reduction of t he 10,11-double bond results in a loss of biological activity on neutr ophils. The effect of 12S-HETrE on calcium levels was blocked by prein cubation of these cells with LTB(4), suggesting that it acted by stimu lating the LTB(4) receptor. 12R-HETrE was about 20 times less potent t han its 12S isomer in stimulating cytosolic calcium in neutrophils and was also less active as a chemotactic agent. Oxidation of the 12-hydr oxyl group to an oxo group resulted in a further loss of biological ac tivity. 12-Oxo-ETE, 8-trans-12-oxo-ETE, and 12-oxo-ETrE had only modes t effects on cytosolic calcium levels at concentrations as high as 10 mu M and did not display detectable chemotactic activity. However, 12- oxo-ETE and its 8-trans isomer inhibited calcium responses to LTB(4) b y about 40%. It is concluded that reduction of the 10,11-double bond o f 12-HETE results in a slight loss of biological activity on neutrophi ls, whereas oxidation of the 12-hydroxyl group results in a considerab ly greater loss of activity.