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.

Generation of a small cell lung cancer variant resistant to lymphokine-activated killer (LAK) cells: association with resistance to a LAK cell-derived, cytostatic factor

Cells of OS2-RA, a human small cell lung cancer line sensitive to lymphokine-activated killer (LAK) cells, were repeatedly cocultured with human LAK cells. Fourteen cycles of the coculture produced a variant, termed OS2-RA-R, capable of growing successfully in the presence of LAK cells. OS2-RA-R showed a moderate resistance to lysis by LAK cells in 4-h 51Cr release assays. OS2-RA-R acted positively as a cold target for lysis of OS2-RA by LAK cells, suggesting no loss of the binding site for LAK cells on the cell surface of the variant. On the other hand, LAK cells were shown to produce a factor capable of suppressing the proliferation of OS2-RA and certain other cell lines but not lymphocytes. Interestingly, OS2-RA-R exhibited a substantial resistance to the cytostatic activity of LAK cell supernatants. The cytostatic factor, eluted at the 57-kDa fraction in gel filtration, showed no activity of interleukin 1, gamma-interferon, transforming growth factor beta, or tumor necrosis factor. These results suggest that LAK cells exhibit antitumor activity through not only rapid cytolysis but also slow-acting cytokine production, and the successful growth of OS2-RA-R in a coculture with LAK cells is the result of acquiring resistance to these two different LAK cell phenomena.

The anti-oedematogenic effect of SRS as an additional factor in the mode of action of non-steroid anti-inflammatory drugs

A partially purified preparation of SRS was obtained from peritoneal exudates induced by a non-anaphylactic immediate hypersensitivity reaction. This preparation injected in the rat skin caused vasoconstriction and when administered together with carrageenin reduced oedema formation. Injection of carrageenin into the peritoneal cavity progressively increased exudate formation. Pretreatment of the animals with anti-inflammatory doses of aspirin, indomethacin and salicylate significantly reduced exudate formation and this inhibition was correlated with the appearance of SRS in the exudates. It is suggested that, in some inflammatory exudates, stimulation of the synthesis of vasoconstrictor SRS might be an additional factor to the inhibition of prostaglandin synthesis induced by non-steroid anti-inflammatory drugs.

Lipid-mediator synthesis in peritoneal macrophages from mice injected with immunostimulants

The metabolism of bioreactive lipid mediators was studied in two types of activated macrophages (M phi). We compared the capacity of resident and activated M phi to release, upon a zymosan challenge, cyclooxygenase and lipoxygenase products as well as PAF-acether (platelet-activating factor) and its 2-lyso precursor. Activated M phi were obtained from mice injected intraperitoneally either with nonviable C74 streptococci (St-M phi) or with trehalose dimycolate, a defined immunostimulant isolated from Mycobacterium tuberculosis (TDM-M phi). Both activated populations exhibited common features: conversion of endogenous [14C]arachidonic acid into prostaglandin E2 and thromboxane A2 rather than into prostaglandin I2 and low biosynthesis of PAF-acether, probably due to an impairment of the acetylation step. However, contrary to St-M phi, TDM-M phi did not display a marked overall reduction of arachidonate metabolism. In addition, as compared to resident M phi, TDM-M phi presented a ratio of thromboxane B2/6-ketoprostaglandin F1 alpha 30-fold higher, a better conversion of leukotriene C to leukotriene D and a higher capacity to release the PAF-acether they synthesize. These macrophages thus seem to be valuable tools for studying the formation of mediators and for determining specific markers of an activated state.

Identification of the slow reacting substances from cat paws

Perfusion of cat paws with compound 48/80 released two slow reacting substances (SRSs) which were isolated and characterized as 5-hydroxy-6-S-cysteinylglycyl-7,9,11,14-icosatetraenoic acid (SRS I) and 5-hydroxy-6-S-cysteinyl-7,9,11,14-icosatetraeonic acid (SRS II) on the basis of chemical degradations, amino acid analyses, spectroscopic and enzymic experiments, and comparison with synthetic samples. The smooth muscle-contractile activities of synthetic 5-hydroxy-6-gamma-glutamylcysteinylglycyl-7,9,11,14-icosatetraenoic acid, synthetic 5-hydroxy-6-S-cysteinyl-7,9,11,14-icosatetraenoic acid, and SRS II were not inactivated by arylsulfatase. On the other hand, the spasmogenic activities produced by synthetic 5-hydroxy-6-S-cysteinylglycyl-7,9,11,14-icosatetraenoic acid and SRS I were destroyed at the same rate by the arylsulfatase. This mode of inactivation was attributed to an aminopeptidase activity in the arylsulfatase preparation because 5-hydroxyl-6-S-cysteinyl-7,9,11,14-icosatetraenoic acid was isolated and identified as the reaction end product. Because the properties of SRS from cat paws closely resemble those of SRS generated by immunological stimulation of human tissues (SRS-A) and because all known SRS-A are inactivated by arylsulfatases, we contend that 5-hydroxy-6-S-cysteinylglycyl-7,9,11-14-icosatetraenoic acid (SRS I) corresponds to SRS-A.

Identification of leukotriene C-1 as a major component of slow-reacting substance from rat mononuclear cells

Slow-reacting substance (SRS) was produced by rat peritoneal mononuclear cells after stimulation with the ionophore A23187. The SRS consisted of two main components as judged by high-pressure liquid chromatography (HPLC) on Florisil. The larger and more polar component consisted mainly of leukotriene (LT) C-1 as judged by ultraviolet spectroscopy, mass spectrometry (after desulfurization), amino acid analysis, and conversion by soybean lipoxygenase. Comparisons with authentic LTC-1 showed identity on reverse phase HPLC and guinea pig ileum bioassay. The latter methods are known to distinguish between LTC-1 and stereoisomers of LTC-1.

Slow reacting substances of anaphylaxis: identification of leukotrienes C-1 and D from human and rat sources

Slow reacting substance(s) of anaphylaxis (SRS-A) was isolated from both human (lung) and rat sources and compared with three synthetic SRS-As of known structure-leukotrienes (LTs) C-1, C-2, and D. Reversed-phase liquid chromatography was used both as a final purification step and a means of comparison of biologically derived and synthetic substances. Two major peaks of SRS-A activity of both rat and human origin corresponded chromatographically with LTC-1 and LTD, respectively, and had equivalent specific activities on the guinea pig ileum. With guinea pig ileum, the specific activities (units/pmol) for synthetic leukotrienes and anaphylactic peaks were (mean +/- SEM): synthetic LTC-1, 1.93 +/- 0.13; SRS-A(rat) peak I, 1.69 +/- 0.43; synthetic LTD, 6.10 +/- 1.15; SRS-A(rat) peak II, 7.14 +/- 0.51; and SRS-A(hu) peak II, 1.90. Both synthetic LTC-1 and LTD and their SRS-A natural counterparts had a preferential contractile activity on guinea pig peripheral airway compared to central airways and were at least 200 times more active than histamine on peripheral airways on a molar basis. Leukotriene D is the major SRS-A of human lung and accounts for almost all of the biological activity. It likely is formed from leukotriene C-1 in vivo by an enzymic process of the well-known gamma-glutamyltransferase type.

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.

Slow reacting substance (SRS) from ionophore A23187-stimulated human leukemic basophils. I. Evidence for a precursor role of arachidonic acid and initial purification

SRS was generated from human leukemic basophils upon stimulation with ionophore A23187. Radiolabel from [14C]-AA was incorporated into SRS with continued comigration of radioactivity and bioactivity through several chromatographic systems including DEAE-cellulose, silicic acid, and RP-HPLC. Human basophilic leukemia SRS displayed physiochemical properties similar to those of rat basophilic leukemia cell SRS.

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

1 Slow-reacting substance of anaphylaxis (SRS-A) was produced by antigen challenge of passively sensitized human lung and actively sensitized guinea-pig lung. 2 A slow-reacting substance (SRS) was prepared from the peritoneal fluid of rats treated with calcium ionophore A23187. 3 These substances were extensively purified by charcoal adsorption, Sephadex G-15 gel filtration, ether extraction and reverse phase high pressure liquid chromatography. 4 The three substances are pharmacologically, chemically and chromatographically indistinguishable. 5 Our data suggest that the same SRS entities are released from a variety of tissues and that these acidic lipids may have a wider physiological significance than just anaphylaxis.