Comparative studies on immunologically and non-immunologically produced slow-reacting substances from man, guinea-pig and rat

Slow-reacting substances and their structural elucidation

For more than forty years since their discovery, the structure of a group of closely related materials known collectively as slow-reacting substances has been unknown. These substances are released from a variety of tissues in response to immunological or non-immunological stimulation. A slow-reacting substance is believed to be implicated in hypersensitivity reactions such as asthma; in order to fully understand its bronchoconstrictor role, the structural elucidation of these materials has been a necessary (albeit difficult) task. Studies on both immunologically generated slow-reacting substance of anaphylaxis (SRS-A) and other slow-reacting substances (SRSs) have indicated a precursor role for arachidonic acid in their biosynthesis; this, coupled with enzymic and chemical activity destruction data, gave an insight into the structure of these moieties. In order to define the structure of these materials homogeneous SRS-A was required; a purification scheme was developed relying on the high resolution separative capability of reverse-phase high pressure liquid chromatography, resulting in extensively purified SRS-A. It was then possible to demonstrate that SRS-A possessed a characteristic ultraviolet spectrum, allowing us for the first time to define a major structural moiety in the molecule (conjugated triene). To complement studies on, and to act as a model for the more pathologically relevant SRS-A, a slow-reacting substance was produced from rat basophilic leukaemia (RBL-1) cells. The structure of this biologically active species has been determined by mass spectrometric examination of the intact molecule as a derivative, together with analytical protein chemical studies, and shown to be the novel peptidolipid 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid.

Ionophore-dependent generation of eicosanoids in human dispersed lung cells. Modulation by 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1 (U-60,257)

6,9-Deepoxy-6-9-(phenylimino)-delta 6,8-prostaglandin I1, a prostacyclin analogue reported to inhibit sulphidopeptide leukotriene formation in animals, was evaluated for its pharmacological activity against eicosanoid and histamine release from human dispersed lung cells (HDLC). In the absence of drug, challenge of HDLC with A23187 (2.5 microM) increased immunoreactive eicosanoid generation by factors of 7.6 for prostaglandin (PG) D2, 9.1 for TXB2, 3.2 for PGF2 alpha, 2.0 for 5-HETE, 6.3 for LTC4, in association with a twofold increase in histamine release. When exogenous [14C]-arachidonic acid was added to HDLC simultaneously with A23187 challenge, radiolabelled eicosanoids were recovered in the supernatant, but on separating the products by radio-thin layer chromatography the proportions of individual eicosanoids were not significantly different from unchallenged cells. With endogenous arachidonate, U-60,257 was a potent inhibitor of i-LTC4 generation at 1 microM, but between 3 and 300 microM there was a concentration-related reversal of this inhibition. The effects of U-60,257 on the metabolism of exogenous [14C]-arachidonic acid were also studied. Under these circumstances the drug was a potent inhibitor of both 5-HETE and 5,12-diHETE formation, without significantly affecting the formation of other mono-HETES. In agreement with previous endogenous substrate experiments there was a concentration-dependent inhibition of TxB2 formation from exogenous arachidonic acid. These findings highlight the complex pharmacological actions of U-60,257 which appear dependent on the source of arachidonic acid substrate.

Oxidative transformations of arachidonic acid in human dispersed lung cells: disparity between the utilization of endogenous and exogenous substrate

Eicosanoid release from human dispersed lung cells (HDLC) containing ca 5% mast cells was studied before and after cell activation with ionophore A23187 or anti-IgE. Basal release of eicosanoids synthesized from endogenous arachidonate was measured by radioimmunoassay. In descending order of abundance the products were: 5-hydroxyeicosatetraenoic acid (5-HETE) greater than thromboxane B2 (TXB2) greater than prostaglandin F2 alpha (PGF2 alpha) approximately immunoreactive (i)-PGE2 greater than PGD2 greater than 6-keto-PGF1 alpha approximately i-LTC4. Stimulation of HDLC with ionophore A23187 or, after passive sensitization, with anti-IgE resulted in 2-10 fold increases in the generation of individual eicosanoids. In terms of net generation the most abundant products were PGD2 and TXB2 with either stimulus. Activation with A23187 caused net release of i-LTC4 and 5-HETE, but these products were not measured after immunological activation. A more complete profile of lipoxygenase products released from HDLC dispersed from one lung was obtained after separation by high performance liquid chromatography combined with ultra violet spectroscopy and bioassay. The major products released from the cells from this lung with ionophore stimulation were 13-hydroxylinoleic acid greater than LTB4 greater than 5-HETE greater than 12-HETE greater than LTC4 greater than 15-HETE greater than 11-HETE approximately 9-HETE. When the utilization of exogenous [14C]-arachidonic acid for prostanoid biosynthesis was compared to that of endogenous unlabelled arachidonate the formation of TXB2 was consistently underestimated. These results imply compartmentalization of arachidonic acid utilization in Ca2+-activated HDLC. In unstimulated cells the proportional formation of PGD2 was overestimated when exogenous arachidonic acid was substrate. After activation with A23187 the proportions of PGD2 were similar with both substrate sources. The large proportions of PGD2 and TXB2 generated by HDLC further supports the view that these eicosanoids may be important inflammatory mediators in lung tissue.

Measurement of immunoreactive leukotriene C4 in blood of asthmatic children

Peptide leukotriene (LT) such as LTC4, LTD4, LTE4 have been considered to be major mediators of immediate type hypersensitivity reaction such as asthma. We have developed a rapid and simple extraction method using a Sep-Pak C18 cartridge for the measurement of LTC4 by radioimmunoassay (i-LTC4). In this extraction method, 91% LTC4 was recovered in a final methanol fraction. The identity was confirmed by the recovery test and by the dilution method. The amount of i-LTC4 in plasma from asthmatic patients was determined by radioimmunoassay after the extraction. The order of the plasma level of i-LTC4 was; severe asthma greater than slight or moderate asthma greater than asthmatic patient without attack greater than healthy adult. The highest level of LTC4 was 0.27 +/- 0.11 pmol/ml in severe asthmatic plasma.

Comparative effects of inhaled leukotriene C4, leukotriene D4, and histamine in normal human subjects

The comparative actions of inhaled leukotriene C4 (LTC4), leukotriene D4 (LTD4), and histamine were studied in six normal subjects. LTC4 and LTD4 were shown to be more potent bronchoconstrictors than histamine, with a more sustained action. LTC4 and LTD4 caused wheezing without cough or throat irritation and were shown to act on large and small airways.

Release of slow reacting substance from the guinea-pig lung by phospholipases A2 of Vipera russelli snake venom

Phospholipases A2 (PLA2) of Vipera russelli venom were isolated by column chromatography. The ability of PLA2 fractions to release slow reacting substance (SRS) was studied in the guinea-pig lung perfused with Krebs' solution. The relationship between the perfusion pressure change produced by PLA2 and SRS release was also studied. Two PLA2 fractions (II-5 and III-3; 3-100 micrograms), injected into the lung increased the perfusion pressure and released SRS. Pretreatment of the lung with indomethacin (10 micrograms) reduced the pressure response induced by the PLA2 fractions. The SRS released in the lung effluent by PLA2 was identified by bioassay as a mixture of thromboxane A2 (TXA2), prostacyclin (PGI2) and leukotrienes. TXA2 and PGI2 release was also quantitated by radioimmunoassay of the degradation products TXB2 and 6-keto-PGF1 alpha, respectively. There was a positive linear correlation between the pressure increases and the ratios of TXB2 to 6-keto-PGF1 alpha (r = 0.87). It appears that the relative amounts of TXA2 and PGI2 released determine the effects of PLA2 fractions on the guinea-pig lung. The release of arachidonic acid metabolites, prostaglandins and leukotrienes may account for part of the hypotensive action of PLA2.

The extraction of leukotrienes (LTC4, LTD4, and LTE4) from tissue fluids: the metabolism of these mediators during IgE-dependent hypersensitivity reactions in lung

The metabolites of arachidonic acid known as the leukotrienes are a class of lipid mediators which have potent and diverse biological effects in pulmonary tissue. Leukotrienes C, D, and E (LTC4, LTD4, and LTE4) are known to be principal mediators of immunoglobulin E (IgE)-mediated hypersensitivity reactions in lung tissue. It is therefore important to develop reliable and quantitative isolation techniques for estimating levels of these mediators in tissue. In this study, LTC4, LTD4, and LTE4 were separated from other arachidonate metabolites by organic extraction procedures. 5-Hydroxyeicosatetraeonic acid and leukotriene B4 extract efficiently into the organic layer of aqueous:ether or aqueous:chloroform extractions, whereas arachidonate metabolites containing conjugated peptides (e.g., LTC4, LTD4, and LTE4) failed to extract into these organic solvents. An extraction step was therefore developed that affords quantitative extraction of LTC4, LTD4, and LTE4 into the organic phase of an isopropanol:ether:H2O mixture. This step is the key for a two-step extraction method that isolates histamine, LTC4, LTD4, and LTE4 with a recovery of 100, 85, 75, and 57%, respectively. One advantage of this separation procedure for obtaining these mediators by organic extraction is an ability to expediently process many samples. Furthermore, the leukotriene content of extracted samples can be analyzed using the guinea pig ileum bioassay without interference from vasoamines or platelet-activating factor. These later substances are eliminated from leukotriene-enriched fractions by this extraction process. When histamine and LTC4 were added to supernatant fluids recovered from isolated lung tissue, they were quantitatively recovered using this extraction method.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation, purification, and structure elucidation of slow-reacting substance of anaphylaxis from guinea pig lung

The work that we have described had originally three main aims: (a) to design a new purification system for SRS-A from which we would obtain pure material for the structural analysis: (b) to define the functional groups in the pure material by spectrophotometric, chemical, and enzymic inactivation methods; and (c) to deduce the complete covalent structure by an accepted spectroscopic method capable of defining structure in atomic detail. These aims have been achieved. The structure of SRS-A, the physiologically more relevant example of the SRSs that were studied, because it was derived immunologically from an animal model of an acute hypersensitivity reaction, has been rigorously defined. Of paramount importance in the determination of this structure was the mass spectrometric analysis of the intact molecule. Degradative and comparative studies are not capable of unequivocally defining structure. For example, the mass spectrum clearly showed the absence of an amide or similar C-terminal blocking groups or, as has been suggested, a sulfone in the molecule; such conclusions could not be drawn from comparative chromatographic data even on multiple systems. Mass spectrometric analysis of the intact molecule could overcome these problems by allowing the complete covalent structure to be collated from the information obtained from each fragmentation. The use of stable isotopes and accurate mass measurement removed possible ambiguities in the interpretation, and the sensitivity and specificity of mass spectrometry made it the method of choice for the structural analysis.

Pharmacologic characterization of immune complex induced bronchoconstriction in guinea pigs

Intravenous injections of soluble immune complexes to anesthetized guinea pigs resulted in bronchoconstriction that was inhibited by FPL 55712, indomethacin, oxarbazole, soybean trypsin inhibitor, and cobra venom factor. Immune complex induced bronchoconstriction was not inhibited by atropine, imidazole, mepyramine, ketotifen, methysergide, and the anti-anaphylactic compound DPP (Diethyl [2-(4-pyridyl)-4-pyrimidinyl]aminoethylene malonate). Immune complex induced bronchoconstriction in guinea pigs appears to involve activation of complement and formation of anaphylatoxins. In addition, products of cyclo-oxygenase metabolism of arachidonic acid and kinins may be involved.

Some physical and chemical properties of the smooth muscle inhibitory factor in extracts of the bovine retractor penis muscle

1. A method of extracting and partially purifying a smooth muscle inhibitory factor from the bovine retractor penis is described. This consists of extraction in methanol followed by adsorption on an anion exchange resin, elution from the resin with 500 mM-sodium chloride solution and, if necessary, removal of adenine nucleotides by adsorption on alumina. 2. The inhibitory factor exists in a stable pharmacologically inactive form and an unstable pharmacologically active form. Conversion to the active form is by a brief exposure to acid at pH 2.0. 3. The inhibitory factor is insoluble in ether or acetone but soluble in methanol. Anhydrous methanol, however, irreversibly destroys pharmacological activity especially if the inhibitory factor is in the active form. This effect of methanol is prevented by the presence of 20-30-% water. 4. The inhibitory factor binds to an anion exchange resin but not to a cation exchange resin. It can be eluted from the resin by 500 mM-sodium chloride solution. 5. The molecular weight of the inhibitory factor, as judged by the ability to pass ultrafiltration membranes, is about 500. 6. Inhibitory activity is unaffected by the proteases trypsin, subtilisin or pepsin or by leucine aminopeptidase, pyroglutamate aminopeptidase or carboxypeptidase. The inhibitory effect of the extract and the inhibitory response to stimulation of the non-adrenergic, non-cholinergic nerves are also unaffected by the protease inhibitor, aprotinin. The active material, therefore, is unlikely to be a peptide. 7. Inhibitory activity is abolished by exposure of the extracts to periodic acid or sodium periodate. Acetic anhydride in pyridine also abolishes activity but the vehicle pyridine is also effective. 8. Sodium borohydride but not borate abolishes inhibitory activity when added to the acid-activated material at pH 2.0 but has no effect or may even potentiate activity if added to the stable inactive form at pH 9.0. When added to the acid-activated but neutralized material at pH 6.8 it usually abolishes inhibitory activity but occasionally has no effect. 9. These results suggest the smooth muscle inhibitory factor in these extracts is potent and probably novel. It does not appear to be a peptide or a lipid but may contain a carbohydrate as part of the molecule. Its possible physiological role is discussed.

A smooth muscle inhibitory material from the bovine retractor penis and rat anococcygeus muscles

1. A material that powerfully inhibits the bovine retractor penis and rat anococcygeus muscles has been extracted from these muscles. The inhibitory activity is unaffected by atropine 10(-6) M, phentolamine 5 x 10(-6) M or propranolol 5 x 10(-6) M. 2. This inhibitory material exists in two forms, a stable but inactive form and an unstable inhibitory form. As isolated the material is in the stable, inactive form and is converted into the active form by a brief exposure to acid. The optimum for conversion is pH 2.0 and the active form, after neutralization, reverts with time to the inactive but can be reactivated by a further exposure to acid. The reversion to the inactive form is temperature sensitive, and is rapid at 37 degrees C. 3. The inhibitory material, both active and inactive, is irreversibly destroyed by 2 min in a boiling water bath or by exposure to U.V. irradiation. 4. The inhibitory material is not confined to tissues known to possess a non-adrenergic non-cholinergic innervation. Similar activity has been detected in extracts os skeletal and cardiac muscle and of the liver. The poorly innervated rat uterus and the non-innervated human umbilical artery, however, gave only small and variable amounts. The possible relationship of this material to non-adrenergic non-cholinergic nerves is discussed.

Slow-reacting substances and their formation by a lipoxygenase pathway

Slow-reacting substances are formed from arachidonic acid by the action of a lipoxygenase, which leads to the formation of 5-hydroperoxy, 6, 8, 11, 14 eicosatetraenoic acid. The covalent structures of SRS-A from guinea-pig lung and SRS from RBL-1 cells have been determined by protein chemical analysis and electron impact mass spectrometry of a derivative of the intact molecules. The structures of SRS-A and SRS are identical, being 5-hydroxy-6-cysteinyl-glycinyl-7, 9, 11, 14-eicosatetraenoic acid. SRSs may be formed by a combination of the metabolism of arachidonic acid by the lipoxygenase pathway and the glutathione detoxification pathway involving nucleophilic attack on 5,6-oxidoeicosatetraenoic acid.

Characterization of slow reacting substances (SRSs) of rat basophilic leukemia (RBL-1) cells: effect of cysteine on SRS profile

When RBL-1 cells were incubated with L-cysteine (7.5 mM) and the ionophore A23187, the slow reacting substances SRS-GSH and SRS-Cys-Gly were formed. When L-cysteine was omitted in the incubation, SRS-GSH and SRS-Cys were isolated but only a trace amount of SRS-Cys-Gly was detectable. Each of the characterized SRSs was accompanied by an as yet uncharacterized structural isomer showing UV absorption at 278 nm. L-Cysteine and other thiols inhibited an aminopeptidase that transforms the highly bioactive SRS of anaphylaxis (SRS-Cys-Gly) into the less bioactive SRS-Cys. SRS-GSH, SRS-Cys-Gly, and SRS-Cys may be readily distinguished from each other by means of their bioactivities, antagonism by FPL 55712, and relative susceptibilities to the actions of soybean lipoxygenase, microsome-bound leucine aminopeptidase, and gamma-glutamyl transpeptidase.

Slow reacting substance of anaphylaxis, SRS-A; assignment of the stereochemistry

We have recently described the structure elucidation of slow reacting substance of anaphylaxis S(SRS-A) from lung and of a slow reacting substance (SRS) from basophilic leukaemia cells as 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid. The stereochemistry of this molecule has now been shown to be 5(S)-hydroxy- 6(R)-cysteinylghlycinyl-7,9-trans-11,14-ciseicosatetraenoic acid by comparison of the synthetic and natural products and their derivatives using mass spectrometric and HPLC chromatographic techniques. The synthetic and natural compounds are also indistinguishable by their pharmacological properties, their conversion by soybean lipoxygenase, and their UV spectra.

Biomolecular structure determination by mass spectrometry

Mass spectometry, conventionally used with smallish molecules (less than 1,000 daltons), has suprisingly emerged as a powerful technique for the determination of the amino acid sequences of proteins and the structure of glycopeptides as well as for the characterization of biologically active materials of unusual structure such as the peptidolipids. Further applications to biomedical problems are foreseen.

Slow reacting substances (SRSs): the structure identification of SRSs from rat basophil leukaemia (RBL-1) cells

Slow Reacting Substances have been produced from RBL-l cells by calcium ionophore A23187 and purified to homogeneity by high pressure liquid chromatography (HPLC). The structure of the major biologically active species has been determined by mass spectrometric examination of the intact molecule as a derivative, together with amino-acid analysis and sequence determination. The characteristic triene chromophore which we originally identified in immunologically generated SRS-A is present in RBL-l SRS, and we determine the structure of this SRS as the thio-substituted dipeptide, 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid.

The distribution of adrenoceptors and other drug receptors between the two ends of the rat vas deferens as revealed by selective agonists and antagonists

1. The effects of adrenoceptor agonists and other agonists on the contractile responses of the prostatic and epididymal portions of the rat isolated vas deferens to single pulse field stimulation were investigated. 2. alpha-Adrenoceptor agonists produced prejunctional alpha 2-mediated inhibition and post-junctional alpha 1-mediated potentiation of the nerve-induced responses. Guanabenz and xylazine produced mainly inhibitory effects, xylazine being 10 times less potent. Clonidine and oxymetazoline produced inhibition with similar potency to guanabenz but at higher concentrations excitatory effects were present, particularly in the epididymal portion. Phenylephrine produced only potentiation of the nerve-induced response in both portions. Potentiation of nerve-induced responses was a more sensitive and quantitative index of excitation than was direct contraction of the tissue. 3. Isoprenaline and salbutamol both gave beta 2-mediated inhibition of the nerve-induced responses in both portions of tissue. At least part of the effect was post-junctional since phenylephrine contractions were inhibited. Isoprenaline also produced a post-junctional alpha 1-mediated excitation. 4. Noradrenaline produced effects qualitatively similar to those of the other alpha-adrenoceptor agonists, inhibition and excitation predominating in the prostatic and epididymal ends respectively. 5. Morphine produced inhibition in the mouse but not in the rat vas deferens. In rat vas, however, enkephalin analogues produced pre-junctional inhibition of responses in both portions which could be partly reversed by naloxone; restoration of the adrenergic component was more complete. Rat anococcygeus showed no equivalent effect. 6. Adenosine 5'-triphosphate (ATP) inhibited nerve-induced responses in each portion with a greater effect on the prostatic portion.