Investigation of monoclonal antibody dimers in a final formulated drug by separation techniques coupled to native mass spectrometry

Therapeutic monoclonal antibodies (mAbs) are highly complex proteins that must be exhaustively characterized according to the regulatory authorities' recommendations. MAbs display micro-heterogeneity mainly due to their post-translational modifications, but also to their susceptibility to chemical and physical degradations. Among these degradations, aggregation is quite frequent, initiated by protein denaturation and then dimer formation. Here, we investigated the nature and structure of the high molecular weight species (HMW) present at less than 1% in an unstressed formulated roledumab biopharmaceutical, as a model of high purity mAb. HMW species were first purified through preparative size-exclusion chromatography (SEC) and then analyzed by a combination of chromatographic methods (ion-exchange chromatography (IEX), SEC) coupled to native mass spectrometry (MS), as well as sodium dodecyl sulfate–polyacrylamide gel electrophoresis and capillary gel electrophoresis under non-reducing conditions. Both covalently and non-covalently bound dimers were identified at a proportion of 50/50. In-depth characterization of the HMW fraction by SEC and IEX hyphenated to native MS revealed the presence of three mAb dimer forms having the same mass, but differing by their charge and size. They were attributed to different compact and elongated dimers. Finally, high-resolution middle-up approaches using different enzymes (IdeS and IgdE) were performed to determine the mAb domains implicated in the dimerization. Our results revealed that the roledumab dimers were associated mainly by a single Fab-to-Fab arm-bound association.

Development and validation of the mental health professional culture inventory

AIMS

No instrument has been developed to explicitly assess the professional culture of mental health workers interacting with severely mentally ill people in publicly or privately run mental health care services. Because of theoretical and methodological concerns, we designed a self-administered questionnaire to assess the professional culture of mental health services workers. The study aims to validate this tool, named the Mental Health Professional Culture Inventory (MHPCI). The MHPCI adopts the notion of 'professional culture' as a hybrid construct between the individual and the organisational level that could be directly associated with the professional practices of mental health workers.

METHODS

The MHPCI takes into consideration a multidimensional definition of professional culture and a discrete number of psychometrically derived dimensions related to meaningful professional behaviour. The questionnaire was created and developed by a conjoint Italian-Canadian research team with the purpose of obtaining a fully cross-cultural questionnaire and was pretested in a pilot study. Subsequently, a validation survey was conducted in northern Italy and in Canada (Montreal area, Quebec). Data analysis was conducted in different steps designed to maximise the cross-cultural adaptation of the questionnaire through a recursive procedure consisting of performing a principal component analysis (PCA) on the Italian sample (N = 221) and then testing the resulting factorial model on the Canadian sample (N = 237). Reliability was also assessed with a test-retest design.

RESULTS

Four dimensions emerged in the PCA and were verified in the confirmatory factor analysis: family involvement, users' sexuality, therapeutic framework and management of aggression risk. All the scales displayed good internal consistency and reliability.

CONCLUSIONS

This study suggests the MHPCI could be a valid and reliable instrument to measure the professional behaviour of mental health services workers. The content of the four scales is consistent with the literature on psychosocial rehabilitation, suggesting that the instrument could be used to evaluate staff behaviour regarding four crucial dimensions of mental health care.

Biochemical characterization of LR769, a new recombinant factor VIIa bypassing agent produced in the milk of transgenic rabbits

BACKGROUND

The bypassing agent factor VII (FVIIa) is a first-line therapy for the treatment of acute bleeding episodes in patients with haemophilia and high-titre inhibitors. FVIIa is a highly post-translationally modified protein that requires eukaryotic expression systems to produce a fully active molecule. A recombinant FVIIa was produced in the milk of transgenic rabbits to increase expression and provide an efficient, safe and affordable product after purification to homogeneity (LR769).

AIM

To present the biochemical and functional in vitro characteristics of LR769.

RESULTS

Mass spectrometric analyses of the intact protein and of heavy and light chains revealed a fully activated, mature and properly post-translationally modified protein notably regarding N/O-glycosylations and γ-carboxylation. Primary structure analysis, performed by peptide mapping, confirmed 100% of the sequence and the low level or absence of product-derived impurities such as oxidized, deamidated and glycated forms. Low levels of aggregates and fragments were observed by different chromatographic methods. Higher order structure investigated by circular dichroism showed appropriate secondary/tertiary structures and conformational change in the presence of Ca²⁺ ions. Finally, activated partial thromboplastin time and thrombin generation assays showed the ability of LR769 to decrease coagulation time and to generate thrombin in haemophiliac-A-plasmas, even in the presence of inhibitors.

CONCLUSION

The innovative expression system used to produce LR769 yields a new safe and effective rhFVIIa for the treatment of haemophilia A or B patients with inhibitors.

Voyager planetary radio astronomy at neptune

Detection of very intense short radio bursts from Neptune was possible as early as 30 days before closest approach and at least 22 days after closest approach. The bursts lay at frequencies in the range 100 to 1300 kilohertz, were narrowband and strongly polarized, and presumably originated in southern polar regions ofthe planet. Episodes of smooth emissions in the frequency range from 20 to 865 kilohertz were detected during an interval of at least 10 days around closest approach. The bursts and the smooth emissions can be described in terms of rotation in a period of 16.11 +/- 0.05 hours. The bursts came at regular intervals throughout the encounter, including episodes both before and after closest approach. The smooth emissions showed a half-cycle phase shift between the five episodes before and after closest approach. This experiment detected the foreshock of Neptune's magnetosphere and the impacts of dust at the times of ring-plane crossings and also near the time of closest approach. Finally, there is no evidence for Neptunian electrostatic discharges.

Voyager 2 radio observations of uranus

Within distances to Uranus of about 6 x 10(6) kilometers (inbound) and 35 x 10(6) kilometers (outbound), the planetary radio astronomy experiment aboard Voyager 2 detected a wide variety of radio emissions. The emission was modulated in a period of 17.24 +/- 0.01 hours, which is identified as the rotation period of Uranus' magnetic field. Of the two poles where the axis of the off-center magnetic dipole (measured by the magnetometer experiment aboard Voyager 2) meets the planetary surface, the one closer to dipole center is now located on the nightside of the planet. The radio emission generally had maximum power and bandwidth when this pole was tipped toward the spacecraft. When the spacecraft entered the nightside hemisphere, which contains the stronger surface magnetic pole, the bandwidth increased dramatically and thereafter remained large. Dynamically evolving radio events of various kinds embedded in these emissions suggest a Uranian magnetosphere rich in magnetohydrodynamic phenomena.

Ultra-relativistic electrons in Jupiter's radiation belts

Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20[?]MeV. Although most radiation belt models predict electrons at higher energies, adiabatic diffusion theory can account only for energies up to around 20[?]MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8[?]GHz synchrotron emission that confirm the presence of electrons with energies up to 50[?]MeV; the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20[?]MeV are more numerous than previously believed.

Application of rat hepatocyte culture to predict in vivo metabolic auto-induction: studies with DFP, a cyclooxygenase-2 inhibitor

The drug candidate DFP [5,5-dimethyl-3-(2-isopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone] is a selective cyclooxygenase-2 inhibitor under evaluation for analgesic and anti-inflammatory therapy. The in vitro metabolic pathways (rat microsomes) involve hydroxylation of the isopropyl side chain at either of two positions, the methyl or the methine, thus producing a hydroxylated metabolite (DFHP) or a dealkylated metabolite (DFH). DFH formation was the major pathway. Using hepatic microsomes from rats treated with agents that induce specific CYP isozymes, it was shown that the dexamethasone-inducible rat CYP3A isozyme(s) play a major role in DFH formation. The roles of CYP3A1 and -3A2 were confirmed with genetically engineered rat CYP enzymes. The potential for induction of rat CYP3A by DFP was evaluated by incubating DFP in rat hepatocyte cultures and measuring the CYP3A levels. Both CYP3A immunoreactive protein and enzyme activity were induced in a dose-dependent manner. The induction was confirmed in vivo by dosing rats with DFP at 100 mg/kg for 4 days. Microsomes prepared from the excised livers showed that DFP gave approximately 55% of the induction observed with dexamethasone, as determined by Western blot. In vitro metabolic auto-induction of DFP was assessed by measuring the metabolism of DFP in hepatocytes treated with DFP. DFH formation was significantly enhanced in the DFP-treated cells. In vivo, treating rats with DFP at doses of 10 to 100 mg/(kg.day) for 13 weeks indicated that DFP induced its own metabolism. The C(max) and plasma drug area under the curve values during the thirteenth week were significantly lower than that on the first day, and the effect was dose-dependent.

SAR in the alkoxy lactone series: the discovery of DFP, a potent and orally active COX-2 inhibitor

Extensive SAR has been established in the alkoxy lactone series and this has lead to the discovery of DFP (5,5-dimethyl-3-(2-propoxy)-4-methanesulfonylphenyl)-2(5H)-furanon e), a potent COX-2 inhibitor exhibiting in vivo efficacy in all models studied.

Rofecoxib [Vioxx, MK-0966; 4-(4'-methylsulfonylphenyl)-3-phenyl-2-(5H)-furanone]: a potent and orally active cyclooxygenase-2 inhibitor. Pharmacological and biochemical profiles

The discoveries that cyclooxygenase (COX)-2 is an inducible form of COX involved in inflammation and that COX-1 is the major isoform responsible for the production of prostaglandins (PGs) in the gastrointestinal tract have provided a rationale for the development of specific COX-2 inhibitors as a new class of anti-inflammatory agents with improved gastrointestinal tolerability. In the present study, the preclinical pharmacological and biochemical profiles of rofecoxib [Vioxx, also known as MK-0966, 4-(4'-methylsulfonylphenyl)-3-phenyl-2-(5H)-furanone], an orally active COX-2 inhibitor, are described. Rofecoxib is a potent inhibitor of the COX-2-dependent production of PGE(2) in human osteosarcoma cells (IC(50) = 26 +/- 10 nM) and Chinese hamster ovary cells expressing human COX-2 (IC(50) = 18 +/- 7 nM) with a 1000-fold selectivity for the inhibition of COX-2 compared with the inhibition of COX-1 activity (IC(50) > 50 microM in U937 cells and IC(50) > 15 microM in Chinese hamster ovary cells expressing human COX-1). Rofecoxib is a time-dependent inhibitor of purified human recombinant COX-2 (IC(50) = 0.34 microM) but caused inhibition of purified human COX-1 in a non-time-dependent manner that could only be observed at a very low substrate concentration (IC(50) = 26 microM at 0.1 microM arachidonic acid concentration). In an in vitro human whole blood assay, rofecoxib selectively inhibited lipopolysaccharide-induced, COX-2-derived PGE(2) synthesis with an IC(50) value of 0.53 +/- 0.02 microM compared with an IC(50) value of 18.8 +/- 0.9 microM for the inhibition of COX-1-derived thromboxane B(2) synthesis after blood coagulation. Using the ratio of the COX-1 IC(50) values over the COX-2 IC(50) values in the human whole blood assay, selectivity ratios for the inhibition of COX-2 of 36, 6.6, 2, 3, and 0.4 were obtained for rofecoxib, celecoxib, meloxicam, diclofenac, and indomethacin, respectively. In several in vivo rodent models, rofecoxib is a potent inhibitor of carrageenan-induced paw edema (ID(50) = 1.5 mg/kg), carrageenan-induced paw hyperalgesia (ID(50) = 1.0 mg/kg), lipopolysaccharide-induced pyresis (ID(50) = 0.24 mg/kg), and adjuvant-induced arthritis (ID(50) = 0.74 mg/kg/day). Rofecoxib also has a protective effect on adjuvant-induced destruction of cartilage and bone structures in rats. In a (51)Cr excretion assay for detection of gastrointestinal integrity in either rats or squirrel monkeys, rofecoxib has no effect at doses up to 200 mg/kg/day for 5 days. Rofecoxib is a novel COX-2 inhibitor with a biochemical and pharmacological profile clearly distinct from that of current nonsteroidal anti-inflammatory drugs and represents a new therapeutic class of anti-inflammatory agents for the treatment of the symptoms of osteoarthritis and rheumatoid arthritis with improved gastrointestinal tolerability.

The discovery of rofecoxib, [MK 966, Vioxx, 4-(4'-methylsulfonylphenyl)-3-phenyl-2(5H)-furanone], an orally active cyclooxygenase-2-inhibitor

The development of a COX-2 inhibitor rofecoxib (MK 966, Vioxx) is described. It is essentially equipotent to indomethacin both in vitro and in vivo but without the ulcerogenic side effect due to COX-1 inhibition.

2,3-Diarylcyclopentenones as orally active, highly selective cyclooxygenase-2 inhibitors

Cyclopentenones containing a 4-(methylsulfonyl)phenyl group in the 3-position and a phenyl ring in the 2-position are selective inhibitors of cyclooxygenase-2 (COX-2). The selectivity for COX-2 over COX-1 is dramatically improved by substituting the 2-phenyl group with halogens in the meta position or by replacing the phenyl ring with a 2- or 3-pyridyl ring. Thus the 3,5-difluorophenyl derivative 7 (L-776,967) and the 3-pyridyl derivative 13 (L-784,506) are particularly interesting as potential antiinflammatory agents with reduced side-effect profiles. Both exhibit good oral bioavailability and are potent in standard models of pain, fever, and inflammation yet have a much reduced effect on the GI integrity of rats compared to standard nonsteroidal antiflammatory drugs.

Outburst of Jupiter's synchrotron radiation after the impact of comet Shoemaker-Levy 9

Jupiter's nonthermal microwave emission, as measured by a global network of 11 radio telescopes, increased dramatically during the Shoemaker-Levy 9 impacts. The increase was wavelength-dependent, varying from approximately 10 percent at 70 to 90 centimeters to approximately 45 percent at 6 and 36 centimeters. The radio spectrum hardened (flattened toward shorter wavelengths) considerably during the week of impacts and continued to harden afterward. After the week of cometary impacts, the flux density began to subside at all wavelengths and was still declining 3 months later. Very Large Array and Australia Telescope images of the brightness distribution showed the enhancement to be localized in longitude and concentrated near the magnetic equator. The evidence therefore suggests that the increase in flux density was caused by a change in the resident particle population, for example, through an energization or spatial redistribution of the emitting particles.

Calcium mobilization and right-angle light scatter responses to 12-oxo-derivatives of arachidonic acid in neutrophils: evidence for the involvement of the leukotriene B4 receptor

The biological activities of two carbonyl compounds derived from arachidonic acid, (5Z,8Z,10E,14Z)-12-keto-5,8,10,14-eicosatetraeno ic acid (12-OxoETE) and (5Z,8Z,10E)-12-oxo-5,8,10-dodecatrienoic acid (12-OxoDTrE) were investigated. The ability of these compounds to induce a mobilization of calcium and to trigger a right-angle scatter response in isolated peripheral blood human neutrophils was determined. The two compounds induced a rapid and dose-dependent increase in the concentration of cytoplasmic free calcium; these effects were clearly detectable at concentrations greater than or equal to 10(-8) M. Pre-exposure of neutrophils to leukotriene B4 completely abolished the calcium mobilization induced by 12-OxoDTre and 12-OxoETE, while pre-exposure of the cells to the carbonyl compounds only slightly reduced the response to subsequent stimulation of neutrophils by leukotriene B4. The carbonyl compounds also induced a decrease in right-angle light scatter and these effects were abolished by pretreatment of neutrophils with leukotriene B4. These data demonstrate that 12-OxoETE and 12-OxoDTrE show significant agonist activities towards human neutrophils and strongly suggest that their mechanisms of action involve the leukotriene B4 binding sites or a common activation sequence.

Stereoselective carbonyl reductases from rat skin and leukocyte microsomes converting 12-ketoeicosatetraenoic acid to 12(S)-HETE

Cell-free preparations from rat polymorphonuclear leukocytes and skin were found to catalyze the reduction of 12-keto-5,8,10,14-eicosatetraenoic acid (12-KETE) to 12-hydroxyeicosatetraenoic acid (12-HETE). The reductase activity was associated with the microsomal fraction and showed a marked preference for NADH over NADPH as reducing cofactor. Characterization of the reaction product by chiral phase HPLC of the methyl ester derivative indicated that 12-KETE reduction generated almost exclusively 12(S)-HETE. The results demonstrate that rat skin and leukocyte microsomes possess an NADH-dependent 12-KETE reductase activity that forms 12(S)-HETE as a major product. The identification of stereoselective 12-KETE reductases provides a basis for further defining the role these enzymes may play in the regulation of 12-KETE levels and in the protection against degradation of 12-KETE to the pro-inflammatory 12(R)-HETE by selectively generating 12-HETE of the S configuration.

NAD(P)H-dependent reduction of 12-ketoeicosatetraenoic acid to 12(R)- and 12(S)-hydroxyeicosatetraenoic acid by rat liver microsomes

The possibility that 12-keto-5,8,10,14 eicosatetraenoic acid (12-KETE) could be used as substrate by reductase(s) to generate 12-hydroxyeicosatetraenoic acid (12-HETE) was investigated using rat liver microsomes as a source of enzyme activity. Microsomes catalyzed the time-dependent reduction of 12-KETE to 12-HETE in a reaction that required NAD(P)H. The maximal specific activity of 12-HETE formation was 1.7 nmol/min/mg of protein in the presence of NADH. The reaction could not be detected in the absence of cofactor or by using heat inactivated microsomes. The identity of the 12-HETE product was established by U.V. spectroscopy and co-elution with 12-HETE in two different systems of RP-HPLC. Resolution of the methyl esters of reaction products by chromatography on chiral columns also indicated that the reduction of 12-KETE with either NADPH or NADH generated a mixture of 12(S)- and 12(R)-HETE in a ratio of about 2:1. The results demonstrate the presence of a 12-KETE reductase activity in rat liver microsomes which can form both the R and S isomers of 12-HETE.

Analogs of leukotriene B4: effects of modification of the hydroxyl groups on leukocyte aggregation and binding to leukocyte leukotriene B4 receptors

The syntheses and agonist and binding activities of 5(S)-hydroxy- 6(Z), 8(E), 10(E), 14(Z)-eicosatetraenoic acid (12-deoxy LTB4), 5(S), 12(S)-dihydroxy-6(Z), 8(E), 10(E), 14(Z)-eicosatetraenoic acid (12-epi LTB4), 12(R)-hydroxy-6(Z), 8(E), 10(E), 14(Z)-eicosatetraenoic acid (5-deoxy LTB4), 5(R), 12(S)-dihydroxy-6(Z), 8(E), 10(E), 14(Z)-eicosatetraenoic acid (5-epi LTB4), 6(Z), 8(E), 10(E), 14(Z)-eicosatetraenoic acid (5, 12-deoxy LTB4) are described. These leukotriene B4 analogs were all able to aggregate rat leukocytes and compete with [3H]-leukotriene B4 for binding to rat and human leukocyte leukotriene B4 receptors with varying efficacy. The analog in which the 12-hydroxyl group was removed was severely reduced both in agonist action (aggregation) and binding. The epimeric 12-hydroxyl analog demonstrated better agonist and binding properties than the analog without a hydroxyl at this position. In contrast, in the case of the 5-hydroxyl the epimeric hydroxyl analog had greatly reduced agonist and binding activities while the 5-deoxy analog demonstrated potency only several fold less than leukotriene B4 itself. The dideoxy leukotriene B4 analog was more than a thousand fold less active than leukotriene B4 as an agonist and in binding to the leukotriene B4 receptor. These results show that binding to the leukocyte leukotriene B4 receptor requires a hydroxyl group at the 12 position in either stereochemical orientation but that the presence of a hydroxyl at the 5 position is less important. However, the epimeric C5 leukotriene B4 analog clearly interacts unfavourably with the binding site of the leukotriene B4 receptor.

Activation of leukocyte movement and displacement of [3H]leukotriene B4 from leukocyte membrane preparations by (12R)- and (12S)-hydroxyeicosatetraenoic acid

Both (12R)- and (12S)-hydroxyeicosatetraenoic acid were demonstrated to produce aggregation of rat leukocytes and enhance human leukocyte chemokinesis. (12R)-Hydroxyeicosatetraenoic acid was 10-20-fold more potent than (12S)-hydroxyeicosatetraenoic acid but at least 500-fold less potent than leukotriene B4 in these assays. These relative potencies are correlated with the potencies of (12R)- and (12S)-hydroxyeicosatetraenoic acid for competition of [3H]leukotriene B4 binding to rat and human leukocyte membrane preparations.

Modulation of rat polymorphonuclear leukocyte 5-lipoxygenase activity by 5-HPETE and NADH-dependent flavin inhibition

The effect of nicotinamide and flavin coenzymes on the 5-lipoxygenase activity has been determined in cell-free extracts from rat polymorphonuclear leukocytes. 5-lipoxygenase was assayed in the presence of 5-hydroperoxyeicosatetraenoic acid (5-HPETE), which caused a 3 to 4-fold stimulation in the maximal conversion of radiolabeled arachidonic acid to 5-hydroxyeicosatetraenoic acid (5-HETE) and 5,12-dihydroxyeicosatetraenoic acid (5,12-di-HETE). Addition of FMN or FAD to the assay mixture had little effect on the 5-lipoxygenase activity and caused inhibition only at high concentrations (IC50 greater than 100 microM). NADH markedly potentiated the inhibition of lipoxygenase by flavins with a 100-fold decrease in the FMN concentration required to inhibit the enzyme (IC50 approximately equal to 2 microM). Similar effects were observed for FAD although this flavin derivative was slightly less potent than FMN (IC50 congruent to 10 microM). NADH could be substituted by NADPH but not by NAD or NADP, indicating that the inhibition was not due to the production of the oxidized forms of these co-factors. These results show that the 5-lipoxygenase activity is stimulated by 5-HPETE and inhibited by flavin-dependent redox transformations.

Leukotriene B3, leukotriene B4 and leukotriene B5; binding to leukotriene B4 receptors on rat and human leukocyte membranes

Specific high-affinity binding sites for [3H]-leukotriene B4 have been identified on membrane preparations from rat and human leukocytes. The rat and human leukocyte membrane preparations show linearity of binding with increasing protein concentration, saturable binding and rapid dissociation of binding by excess unlabelled leukotriene B4. Dissociation constants of 0.5 to 2.5 nM and maximum binding of 5000 fmoles/mg protein were obtained for [3H] leukotriene B4 binding to these preparations. Displacement of [3H]-leukotriene B4 by leukotriene B4 was compared with displacement by leukotriene B3 and leukotriene B5 which differ from leukotriene B4 only by the absence of a double bond at carbon 14 or the presence of an additional double bond at carbon 17, respectively. Leukotriene B3 was shown to be equipotent to leukotriene B4 in ability to displace [3H]-leukotriene B4 from both rat and human leukocyte membranes while leukotriene B5 was 20-50 fold less potent. The relative potencies for the displacement of [3H]-leukotriene B4 by leukotrienes B3, B4 and B5 on rat and human leukocyte membranes were shown to correlate well with their potencies for the induction of the aggregation of rat leukocytes and the chemokinesis of human leukocytes.

The lipoxins: determination of their biosynthesis

The stereochemistry and double bond geometry of a novel series of leukocyte derived arachidonic acid metabolites, the lipoxins, was determined by comparison to pure unambiguous synthetic standards. The lipoxins were found to be a mixture of four lipoxin A isomers and two lipoxin B isomers. In determining the biosynthesis of these compounds, they were shown to be formed via a tetraene epoxide. In addition, it was shown that all of the lipoxin isomers formed by the incubation of 15-HPETE with human leukocytes were also formed by non enzymatic hydrolysis of this tetraene epoxide.

Neutrophil LTA4 hydrolases and leukotriene B4 receptors: effects of leukotriene epoxides and their enzymatic products

A selection of inhibitors of rat and human neutrophil LTA4 hydrolases have been studied in vitro using partially purified enzymes. 5(S)trans 5,6 oxido-7,9-trans-11-cis-eicosatrienoic acid (LTA3) and 5(S)trans 5,6 oxido, 7,9-trans, 11,14,17-cis-eicosapentaenoic acid (LTA5) have been shown to inhibit neutrophil LTA4 hydrolases in a time-dependent manner. The products of hydrolysis of LTA3, LTA4 and LTA5 by human and rat neutrophil LTA4 hydrolase have been shown to displace [3H] LTB4 binding to human and rat neutrophil membranes. The order of displacement of [3H] LTB4 is LTB4 = LTB3 greater than LTB5 and this correlated well with their biological potencies for enhancement of neutrophil aggregation and chemokinesis.