A newly described plant-derived flavonoid, hypolaetin-8-glucoside, which has anti-inflammatory and gastroprotective actions in-vivo, and its corresponding aglycone, hypolaetin, have been compared with 14 other flavonoids for inhibition of eicosanoid generation via the 5-lipoxygenase and cyclo-oxygenase pathways in elicited rat peritoneal leukocytes stimulated with calcium ionophore. Comparable results for the inhibitory profiles of the compounds were obtained using either radioimmunoassay of released eicosanoids or radio-TLC of metabolites formed from labelled arachidonate, but there were differences in absolute potency of the inhibitors. Hypolaetin-8-glucoside was a weak but selective inhibitor of 5-lipoxygenase (IC50 56 microM vs 5-lipoxygenase; greater than 1000 microM vs cyclo-oxygenase), whereas the aglycone hypolaetin was a more potent and selective 5-lipoxygenase inhibitor (IC50 4.5 microM vs 70 microM). Results with three other glycoside/aglycone pairs confirmed that addition of sugar residues greatly reduces inhibitory potency whilst retaining selectivity against 5-lipoxygenase. Analysis of 12 aglycone flavonoids showed that inhibitory potency and selectivity against 5-lipoxygenase is conferred by the presence of 3'4'-vicinal diol (catechol) in ring B as part of a 3,4-dihydroxycinnamoyl structure as proposed by others and by incorporation of additional hydroxyl substituents. In contrast, "cross-over" of inhibitory selectivity is observed in compounds containing few hydroxyl substituents (with none in ring B) which are selective against cyclo-oxygenase. These results are discussed in relation to possible mechanisms of hypolaetin-8-glucoside's protective actions and the concept that these inhibitory effects of flavonoids cannot be ascribed to a unitary free radical scavenging action.

In press .). We now report that intracerebroventricular administration of lipocortin-1 fragment causes marked inhibition of infarct size (60%) and cerebral edema (46%) measured 2 h after cerebral ischemia (middle cerebral artery occlusion) in the rat in vivo. The lipocortin-1 fragment was effective when administered 10 min after induction of ischemia. Ischemia caused increased expression of lipocortin-1 around the area of infarction as demonstrated by immunocytochemistry. Intracerebroventricular injection of neutralizing antilipocortin-1 fragment antiserum increased the size of infarct (53%) and the development of edema (29%) . These findings indicate that lipocortin-1 is an endogenous inhibitor of cerebral ischemia with considerable therapeutic potential .

Lipocortins form a group of proteins that have been proposed as mediators of the anti-inflammatory actions of glucocorticoids. Intracerebroventricular injection of a recombinant fragment of lipocortin 1 (NH2-terminal 1-188) caused dose-dependent (0.4-1.2 micrograms) reductions in the acute increases in colonic temperature and oxygen consumption, which occurred in response to central injections of recombinant interleukin 1 beta and gamma-interferon in conscious rats. In contrast the lipocortin fragment did not affect the response to prostaglandin E2, and its activity was prevented by heat treatment or by pretreatment of animals with polyclonal antiserum raised to the fragment. Central injection of antiserum significantly enhanced the thermogenic responses to interleukin 1 beta in rats treated with dexamethasone without affecting the responses in normal animals. These results support a physiological role for lipocortin in the central effects of glucocorticoids.

Lipocortin‐1 and its N‐terminal derivatives exert potent inhibitory actions in various models of acute inflammation. The present study examined the ability of lipocortin (LC)‐1 to suppress the release of the acute pro‐inflammatory mediators, tumour necrosis factor (TNFα) and prostaglandin E2 (PGE2) from human peripheral blood mononuclear cells (PBMC) stimulated with lipopolysaccharide (LPS) or recombinant human interleukin‐1β (rhIL‐1β). LPS (10 μg ml−1)‐stimulated release of TNFα and PGE2 from PBMC was significantly inhibited by (4 h) co‐incubation of the cells with 10−6 m dexamethasone (Dex), but not with 10−9 m to 10−7 m of a N‐terminal fragment (amino acids 1–188) of recombinant human LC‐1 (LC‐1 fragment). However, Dex suppression of LPS‐stimulated TNFα and PGE2 secretion from PBMC was reversed when polyclonal antibody to LC‐1 fragment (1:10,000 dilution) was included in the medium. rhIL‐1β (5times10−8 m)‐stimulated release of TNFα and PGE2 from PBMC (after 18 h) was abolished by co‐incubation of the cells with 10−7 m LC‐1 fragment. After incubation with Dex (4 h), cellular proteins from PBMC were immunoblotted using anti‐LC‐1 fragment antibody (which showed no cross‐reactivity with human annexins 2 to 6). Dex caused no increase in immunoreactive (ir)LC‐1 content of PBMC, although there was a three fold increase in the amount of a lower mass species with LC‐1‐like immunoreactivity. This was accompanied by the appearance of irLC‐1 in the extracellular medium. The results of the present study implicate endogenous LC‐1 in glucocorticoid suppression of TNFα and PGE2 release from human PBMC and suggest an extracellular site of action for LC‐1. LC‐1 may also inhibit rhIL‐1β‐stimulated TNFα and PGE2 secretion from PBMC.