Identification and quantitative analysis of hydroxy-eicosatetraenoic acids in rat brains exposed to regional ischemia.

Abstract

To clarify possible roles in the pathogenesis of ischemic brain edema, identification and quantitative analysis of hydroxy-ekosatetraenoic acids (HETEs) in rat brains exposed to middle cerebral artery occlusion were carried out using high-performance liquid chromatography. Rat brain sampling was done by in situ freezing 24 and 72 hours after occlusion. Only a small amount of 15-HETE was found in control rat brains. Twenty-four hours after ischemia, 11-HETE appeared, and the amount of 15-HETE tended to increase. Seventy-two hours after ischemia, when brain edema reached its maximum, 5-, 8-, 9-, 11-, 12-, and 15-HETEs were identified, and the amounts of all HETEs except 8-and 12-HETE were significantly increased. The detection of 5-HETE in ischemic rat brain indicates the simultaneous production of leukotrienes in the same brain area. The above results support the view that lipoxygenase products may play significant roles in the formation of ischemic brain edema. ISCHEMIC cerebral edema is a serious and sometimes fatal complication of stroke, but the precise mechanism of edema formation is not fully understood yet. In recent study of the arachidonate cascade, the possible roles of potent bioactive eicosanoids in various pathologic conditions have been attracting more attention. In the brain, membrane-bound fatty acids were released following ischemic insult or seizure activity.1 " 4 Among these fatty acids, arachidonic acid was shown to cause brain edema and destruction of capillary ehdothelial membranes when injected directly into the brain.5 " 8 Arachidonic acid is a substrate for two oxygenases, and its conversion to various eicosanoids seems to be responsible for these pathologic states. The administration of the cyclooxygenase inhibitor indomethacin did not alleviate ischemic brain edema, or rather aggravated it, 79 " 12 which led us to speculate that lipoxygenase metabolites rather than cyclooxygenase products might play key roles in the pathogenesis of ischemic brain edema, if eicosanoids were involved at all. However, little is known about lipoxygenase metabolism and the pathophysiology of its metabolites in the brain. The following experiments were undertaken to identify the lipoxygenase metabolites and to clarify their relation to ischemic brain edema. Materials and Methods Occlusion Model and Method of Brain SamplingEight male Sprague-Dawley rats weighing about 200 g were anesthetized with 2% halothane, and ac- Received June 17, 1986; accepted November 27, 1986. cording to the method reported elsewhere, 13 they underwent left subtemporal craniectomy. After dural opening, the left middle cerebral artery (MCA) was electrocauterized and severed at the proximal portion just medial to the olfactory tract. In 4 sham-operated rats, the surgical procedure was done in a similar manner except for the MCA occlusion. After surgery, the rats were returned to their cages and fed ad libitum. These rats were anesthetized again with 2% halothane 24 and 72 hours after MCA occlusion. After tracheostomy was performed, ...

Linoleic acid participates in the response to ischemic brain injury through oxidized metabolites that regulate neurotransmission

“…The present study confirmed previous reports of increased AA-derived prostaglandins (in particular PGE 2 and PGD 2 ), thromboxane B2 and lipoxygenase products (HETE, oxo-ETE and leukotrienes) 41, 46, 47, 56, 70 , and increased DHA-derived 17-HDoHE 41, 49 in hippocampus or whole brain of rodents subjected to hypoxic or ischemic brain injury. By incorporating an expanded AA and DHA oxylipin panel in our LC-MS/MS platform, we also found an increase in epoxidized metabolites of AA and DHA following ischemia in cortex, hippocampus, cerebellum and brainstem.…”

“…The majority of unesterified AA and DHA are re-esterified into the phospholipid membrane 44 , whereas a small portion (~3%) is converted via non-enzymatic or enzymatic pathways into oxylipins 41, 45–47 that regulate the brain’s response to injury 2–4 . This response involves oxylipins that acutely down-regulate neuronal hyperexcitability 48 and enhance vasodilation 49 as a protective mechanism.…”

Effect of indomethacin and a free radical scavenger on cerebral blood flow and edema after cerebral artery occlusion in cats.

“…This difference may be ascribed to the absence of cydooxygenase inhibition. Further, following permanent MCA occlusion in rats, 38 we have shown an enhanced lipoxygenase activity of brain microvessels, which may be triggered by an increase in the ambient level of lipid hydroperoxides. 39 - 41 The possible roles of hydroperoxides and lipoxygenase products in the pathogenesis of edema formation merits further investigation.…”

Molecular mechanisms in differentiated thyroid cancer

“…The free fatty acids contribute to neuronal damage by serving as substrates for the formation of lipid peroxides that have detrimental effects on cellular metabolism and oxygen utilization (314–316). Other fatty acids released during ischemia, such as AA, are converted to HETEs, leukotrienes and eicosanoids (317–319) that compromise collateral flow, increase the production of free radicals (208) and recruit leukocytes in the ischemic area. The recruitment of leukocytes and swelling of the brain may also reduce flow to the injured tissue at the margins of the infarct.…”