Structure-activity relationship of biaryl acylsulfonamide analogues on the human EP(3) prostanoid receptor

Potent and selective ligands for the human EP3 prostanoid receptor are described. Biaryl compounds bearing a tethered ortho substituted acidic moiety were identified as potent EP3 antagonists based on the SAR described herein. The binding affinity of key compounds on all eight human prostanoid receptors is reported.

Placental anomalies in a viable cloned calf

Placental anomalies are associated with a high mortality rate in mammalian cloning programs. In this report, we detail the very unusual occurrence of a grossly abnormal placenta that supported a viable cloned calf to term. The placenta was recovered intact 3 h following birth, and its weight was within normal limits (4.3 kg). The chorioallantois of the cloned transgenic female Holstein calf contained only 26 cotyledons. Twelve of these were enlarged and functional. Six were poorly developed, and eight were degenerating. The 12 functional cotyledons ranged in diameter from 8 to 20 cm. The nongravid horn had six rudimentary (<5 cm in diameter) cotyledons and eight cotyledons that remained as oval, mineralized plaques. Despite the reduction in number of placentomes, there was no adventitial placentation. Although this report documents observations from a single case, it does show that a morphologically deficient placenta was able to support development to term and resulted in a viable calf.

Selective modulation of chemokinesis, degranulation, and apoptosis in eosinophils through the PGD2 receptors CRTH2 and DP

BACKGROUND

PGD(2) is the major prostanoid released by mast cells during an allergic response. Its role in the allergic response, however, remains unclear.

OBJECTIVE

Because the accumulation of eosinophils is a feature of allergic reactions, we investigated the role of PGD(2) in the modulation of eosinophil function.

METHODS

Circulating human eosinophils were isolated and challenged with PGD(2). The effects of PGD(2) on various eosinophil functions were then analyzed.

RESULTS

PGD(2) binds with high affinity preferentially to 2 receptors, DP and chemoattractant receptor-homologous molecule expressed on T(H)2 cells (CRTH2). We show that both DP and CRTH2 are detectable on circulating eosinophils. We demonstrate that PGD(2) (1-10 nmol/L) induces a rapid change in human eosinophil morphology and an increase in chemokinesis and promotes eosinophil degranulation. These effects are induced by the CRTH2-selective agonist 13-14-dihydro-15-keto-PGD(2) (DK-PGD(2)) but not by the DP-selective agonist BW245C. These results suggest a role for CRTH2 in the modulation of eosinophil movement and in triggering the release of cytotoxic proteins. Finally, we demonstrate that BW245C, but not DK-PGD(2), can delay the onset of apoptosis in cultured eosinophils, presumably through interaction with DP.

CONCLUSION

These data support the hypothesis that PGD(2) controls eosinophil functions through 2 pharmacologically distinct receptors with independent functions. Blockade of PGD(2)-mediated effects on human eosinophils may reduce the damage caused by these cells during an allergic response, but inhibition of both receptors may be required.

Molecular cloning and functional characterization of murine cysteinyl-leukotriene 1 (CysLT(1)) receptors

We sought to clone and characterize the murine cysteinyl-leukotriene D(4) receptor (mCysLT(1)R) to complement our studies with leukotriene-deficient mice. A cDNA, cloned from trachea mRNA by reverse transcriptase-polymerase chain reaction, has two potential initiator ATG codons that would encode for polypeptides of 352 and 339 amino acids, respectively. These two potential forms, predicted to be seven transmembrane-spanning domain proteins, have 87% amino acid identity with the human CysLT(1) receptor (hCysLT(1)R). Membrane fractions of Cos-7 cells transiently expressing the short mCysLT(1)R demonstrated high affinity and specific binding for leukotriene D(4) (LTD(4), K(d) = 0.25 +/- 0.04 nM). In competition binding experiments, LTD(4) was the most potent competitor (K(i) = 0.8 +/- 0.2 nM) followed by LTE(4) and LTC(4) (K(i) = 86.6 +/- 24.5 and 100.1 +/- 17.1 nM, respectively) and LTB(4) (K(i) > 1.5 microM). Binding of LTD(4) was competitively inhibited by the specific CysLT(1) receptor antagonists MK-571 [(+)-3-(((3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl) ((3-(dimethylamino)-3-oxopropyl)thio)methyl)thio)propanoic acid], pranlukast (Onon), and zafirlukast (Accolate), while the CysLT(1)/CysLT(2) receptor antagonist BAY-u9773 [6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z),14(Z)-eicosatetrenoic acid] was 1000 times less potent than LTD(4). In transiently transfected HEK293-T cells expressing either the long or short form of mCysLT(1)R, LTD(4) induced an increase of intracellular calcium. In Xenopus laevis melanophores transiently expressing either isoform, LTD(4) induced the dispersion of pigment granules, consistent with the activation by LTD(4) of a G(alphaq) (calcium) pathway. Functional elucidation of mCysLT(1)R properties as described here will enable further experiments to clarify the selective role of LTD(4) in murine models of inflammation and asthma.

Structure-activity relationship of cinnamic acylsulfonamide analogues on the human EP3 prostanoid receptor

Potent and selective antagonists of the human EP3 receptor have been identified. The structure-activity relationship of the chemical series was conducted and we found several analogues displaying sub-nanomolar K(i) values at the EP3 receptor and micromolar activities at the EP1, EP2 and EP4 receptors. The effect of added human serum albumin (HSA) on the binding affinity at the EP3 receptor was also investigated.

Prostaglandin receptor EP(4) mediates the bone anabolic effects of PGE(2)

Prostaglandin (PG) E(2) is a potent inducer of cortical and trabecular bone formation in humans and animals. Although the bone anabolic action of PGE(2) is well documented, the cellular and molecular mechanisms that mediate this effect remain unclear. This study was undertaken to examine the effect of pharmacological inactivation of the prostanoid receptor EP(4), one of the PGE(2) receptors, on PGE(2)-induced bone formation in vivo. We first determined the ability of EP(4)A, an EP(4)-selective ligand, to act as an antagonist. PGE(2) increases intracellular cAMP and suppresses apoptosis in the RP-1 periosteal cell line. Both effects were reversed by EP(4)A, suggesting that EP(4)A acts as an EP(4) antagonist in the cells at concentrations consistent with its in vitro binding to EP(4). We then examined the effect of EP(4) on bone formation induced by PGE(2) in young rats. Five- to 6-week-old rats were treated with PGE(2) (6 mg/kg/day) in the presence or absence of EP(4)A (10 mg/kg/day) for 12 days. We found that treatment with EP(4)A suppresses the increase in trabecular bone volume induced by PGE(2). This effect is accompanied by a suppression of bone formation indices: serum osteocalcin, extent of labeled surface, and extent of trabecular number, suggesting that the reduction in bone volume is due most likely to decreased bone formation. The pharmacological evidence presented here provides strong support for the hypothesis that the bone anabolic effect of PGE(2) in rats is mediated by the EP(4) receptor.

Key Structural Features of Prostaglandin E2 and Prostanoid Analogs Involved in Binding and Activation of the Human EP1 Prostanoid Receptor

The structure-activity relationship (SAR) of prostaglandin (PG) E(2) at the human EP(1) prostanoid receptor (designated hEP(1)) was examined via the binding and activation of this receptor by a series of 55 prostanoids and analogs. Using clonal human embryonic kidney 293 cell lines expressing recombinant hEP(1), affinity (K(i)), potency (EC(50)), and efficacy data were obtained using a radioligand competitive binding assay and an aequorin-based calcium functional assay. All compounds behaved as full agonists (90-100% of the response elicited by PGE(2)) in this assay, and the correlation between the K(i) and EC(50) values was highly significant (R(2) = 0.86). The results from the SAR analysis can be summarized as follows: 1) the existence and configuration of hydroxyl groups at the 11 and 15 positions of PGE(2) and prostanoid analog structures play a critical role in agonist activity; 2) the carboxyl group is also important for activity and modification of the carboxylic acid to various esters results in greatly reduced affinity and potency; 3) the activity of structures with moderate or weak potency can be enhanced by modification of the omega-tail; and 4) modifications to the ketone at the 9-position are better tolerated, with 9-deoxy-9-methylene-PGE(2) being the most potent agonist tested in the functional assay. The impact of other modifications on agonist potency is also discussed. The results from this study have identified, for the first time, the key structural features of PGE(2) and related prostanoids and prostanoid analogs necessary for activation of hEP(1).

Structure-activity relationship on the human EP3 prostanoid receptor by use of solid-support chemistry

Potent and selective EP3 receptor ligands were found by making a library using solid-support chemistry. These compounds can be obtained by a Suzuki coupling reaction of a solid-supported benzyl bromide using various boronic acids. The yields obtained for this reaction were in the range of 24-95% of arylmethyl cinnamic acid 1 after cleavage from the Wang resin.

Characterization of the human cysteinyl leukotriene 2 receptor

The contractile and inflammatory actions of the cysteinyl leukotrienes (CysLTs), LTC(4), LTD(4), and LTE(4), are thought to be mediated through at least two distinct but related CysLT G protein-coupled receptors. The human CysLT(1) receptor has been recently cloned and characterized. We describe here the cloning and characterization of the second cysteinyl leukotriene receptor, CysLT(2), a 346-amino acid protein with 38% amino acid identity to the CysLT(1) receptor. The recombinant human CysLT(2) receptor was expressed in Xenopus oocytes and HEK293T cells and shown to couple to elevation of intracellular calcium when activated by LTC(4), LTD(4), or LTE(4). Analyses of radiolabeled LTD(4) binding to the recombinant CysLT(2) receptor demonstrated high affinity binding and a rank order of potency for competition of LTC(4) = LTD(4) LTE(4). In contrast to the dual CysLT(1)/CysLT(2) antagonist, BAY u9773, the CysLT(1) receptor-selective antagonists MK-571, montelukast (Singulair(TM)), zafirlukast (Accolate(TM)), and pranlukast (Onon(TM)) exhibited low potency in competition for LTD(4) binding and as antagonists of CysLT(2) receptor signaling. CysLT(2) receptor mRNA was detected in lung macrophages and airway smooth muscle, cardiac Purkinje cells, adrenal medulla cells, peripheral blood leukocytes, and brain, and the receptor gene was mapped to chromosome 13q14, a region linked to atopic asthma.

Species-specific monoclonal antibodies to Escherichia coli-expressed p36 cytosolic protein of Mycoplasma hyopneumoniae

The p36 protein of Mycoplasma hyopneumoniae is a cytosolic protein carrying species-specific antigenic determinants. Based on the genomic sequence of the reference strain ATCC 25934, primers were designed for PCR amplification of the p36-encoding gene (948 bp). These primers were shown to be specific to M. hyopneumoniae since no DNA amplicons could be obtained with other mycoplasma species and pathogenic bacteria that commonly colonize the porcine respiratory tract. The amplified p36 gene was subcloned into the pGEX-4T-1 vector to be expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST). The GST-p36 recombinant fusion protein was purified by affinity chromatography and cut by thrombin, and the enriched p36 protein was used to immunize female BALB/c mice for the production of anti-p36 monoclonal antibodies (MAbs). The polypeptide specificity of the nine MAbs obtained was confirmed by Western immunoblotting with cell lysates prepared from the homologous strain. Cross-reactivity studies of the anti-p36 MAbs towards two other M. hyopneumoniae reference strains (ATCC 25095 and J strains) and Quebec field strains that had been isolated in culture suggested that these anti-p36 MAbs were directed against a highly conserved epitope, or closely located epitopes, of the p36 protein. No reactivity was demonstrated against other mycoplasma species tested. Clinical signs and lesions suggestive of enzootic pneumonia were reproduced in specific-pathogen-free pigs infected experimentally with a virulent Quebec field strain (IAF-DM9827) of M. hyopneumoniae. The bacteria could be recovered from lung homogenates of pigs that were killed after the 3-week observation period by both PCR and cultivation procedures. Furthermore, the anti-p36 MAbs permitted effective detection by indirect immunofluorescence of M. hyopneumoniae in frozen lung sections from experimentally infected pigs. However, attempts to use the recombinant p36 protein as an antigen in an indirect enzyme-linked immunosorbent assay for the detection of antibodies in sera from convalescent pigs showed no correlation with clinical and pathological findings.

Extension of cell life-span and telomere length in animals cloned from senescent somatic cells

The potential of cloning depends in part on whether the procedure can reverse cellular aging and restore somatic cells to a phenotypically youthful state. Here, we report the birth of six healthy cloned calves derived from populations of senescent donor somatic cells. Nuclear transfer extended the replicative life-span of senescent cells (zero to four population doublings remaining) to greater than 90 population doublings. Early population doubling level complementary DNA-1 (EPC-1, an age-dependent gene) expression in cells from the cloned animals was 3.5- to 5-fold higher than that in cells from age-matched (5 to 10 months old) controls. Southern blot and flow cytometric analyses indicated that the telomeres were also extended beyond those of newborn (<2 weeks old) and age-matched control animals. The ability to regenerate animals and cells may have important implications for medicine and the study of mammalian aging.

The utilization of recombinant prostanoid receptors to determine the affinities and selectivities of prostaglandins and related analogs

Stable cell lines that individually express the eight known human prostanoid receptors (EP(1), EP(2), EP(3), EP(4), DP, FP, IP and TP) have been established using human embryonic kidney (HEK) 293(EBNA) cells. These recombinant cell lines have been employed in radioligand binding assays to determine the equilibrium inhibitor constants of known prostanoid receptor ligands at these eight receptors. This has allowed, for the first time, an assessment of the affinity and selectivity of several novel compounds at the individual human prostanoid receptors. This information should facilitate interpretation of pharmacological studies that employ these ligands as tools to study human tissues and cell lines and should, therefore, result in a greater understanding of prostanoid receptor biology.

New class of biphenylene dibenzazocinones as potent ligands for the human EP1 prostanoid receptor

A new class of potent and selective ligands for the human EP1 prostanoid receptor is described. SAR studies reported herein allowed the identification of several potent dibenzazocinones bearing an acylsulfonamide side chain. The binding affinity of these compounds on all eight human prostanoid receptors is reported.

Characterization of the cloned guinea pig leukotriene B4 receptor: comparison to its human orthologue

A cDNA clone coding for the guinea pig leukotriene B4 (BLT) receptor has been isolated from a lung cDNA library. The guinea pig BLT receptor has an open reading frame corresponding to 348 amino acids and shares 73% and 70% identity with human and mouse BLT receptors, respectively. Scatchard analysis of membranes prepared from guinea pig and human BLT receptor-transfected human embryonic kidney (HEK) 293 EBNA (Epstein-Bar Virus Nuclear Antigen) cells showed that both receptors displayed high affinity for leukotriene B4 (Kd value of approximately 0.4 nM) and were expressed at high levels (Bmax values ranging from 9 to 12 pmol/mg protein). The rank order of potency for leukotrienes and related analogs in competition for [3H]leukotriene B4 specific binding at the recombinant guinea pig BLT receptor is leukotriene B4 > 20-OH-leukotriene B4 > 12(R)-HETE ((5Z,8Z,10E,12(R)14Z)-12-hydroxyeicosatetraen -1-oic acid) > 12(S)-HETE ((5Z,8Z,10E,12(S)14Z)-12-Hydroxyeicosatetraen -1-oic acid) > 20-COOH-leukotriene B4 > U75302 (6-(6-(3-hydroxy-1E,5Z-undecadienyl)-2-pyridinyl)-1,5-hexane diol) >> leukotriene C4 = leukotriene D4 = leukotriene E4. For the human receptor the rank order of 12(S)-HETE, 20-COOH-leukotriene B4 and U75302 was reversed. Xenopus melanophore and HEK aequorin-based reporter gene assays were used to demonstrate that the guinea pig and human BLT receptors can couple to both the cAMP inhibitory and intracellular Ca2+ mobilization signaling pathways. However, in the case of the aequorin-expressing HEK cells (designated AEQ17-293) transfected with either the guinea pig or human BLT receptor, expression of Galpha16 was required to achieve a robust Ca2+ driven response. Leukotriene B4 was a potent agonist in functional assays of both the guinea pig and human BLT receptors. U-75302 a leukotriene B4 analogue which possesses both agonistic and antagonistic properties behaved as a full agonist of the guinea pig and human BLT receptors in AEQ17-293 cells and not as an antagonist. The recombinant guinea pig BLT receptor will permit the comparison of the intrinsic potencies of leukotriene B4 receptor antagonists used in guinea pig in vivo models of allergic and inflammatory disorders.

Characterization of the human cysteinyl leukotriene CysLT1 receptor

The cysteinyl leukotrienes-leukotriene C4(LTC4), leukotriene D4(LTD4) and leukotriene E4(LTE4)-are important mediators of human bronchial asthma. Pharmacological studies have determined that cysteinyl leukotrienes activate at least two receptors, designated CysLT1 and CysLT2. The CysLT1-selective antagonists, such as montelukast (Singulair), zafirlukast (Accolate) and pranlukast (Onon), are important in the treatment of asthma. Previous biochemical characterization of CysLT1 antagonists and the CysLT1 receptor has been in membrane preparations from tissues enriched for this receptor. Here we report the molecular and pharmacological characterization of the cloned human CysLT1 receptor. We describe the functional activation (calcium mobilization) of this receptor by LTD4 and LTC4, and competition for radiolabelled LTD4 binding to this receptor by the cysteinyl leukotrienes and three structurally distinct classes of CysLT1-receptor antagonists. We detected CysLT1-receptor messenger RNA in spleen, peripheral blood leukocytes and lung. In normal human lung, expression of the CysLT1-receptor mRNA was confined to smooth muscle cells and tissue macrophages. Finally, we mapped the human CysLT1-receptor gene to the X chromosome.

A series of non-quinoline cysLT1 receptor antagonists: SAR study on pyridyl analogs of Singulair

The structure-activity relationship of a series of styrylpyridine analogs of MK-0476 (montelukast, Singulair) is described. This work has led to the identification of a number of potent and orally active cysLT1 receptor (LTD4 receptor) antagonists including 2ab (L-733,321) as an optimized candidate.

A novel photoaffinity probe for the LTD4 receptor

A novel photoaffinity probe for the leukotriene D4 receptor (LTD4) is described. L-745310, which is structurally related to the potent LTD4 antagonist MK-0476 (Singulair), was found to selectively label a 43-kDa protein in guinea-pig lung membrane previously identified as the LTD4 receptor.

Molecular cloning and characterization of the four rat prostaglandin E2 prostanoid receptor subtypes

We have characterized the rat prostanoid EP1, EP2, EP3alpha and EP4 receptor subtypes cloned from spleen, hepatocyte and/or kidney cDNA libraries. Comparison of the deduced amino acid sequences of the rat EP receptors with their respective homologues from mouse and human showed 91% to 98% and 82% to 89% identity, respectively. Radioreceptor binding assays and functional assays were performed on EP receptor expressing human embryonic kidney (HEK) 293 cells. The KD values obtained with prostaglandin E2 for the prostanoid receptor subtypes EP1, EP2, EP3alpha and EP4 were approximately 24, 5, 1 and 1 nM, respectively. The rank order of affinities for various prostanoids at the prostanoid receptor subtypes EP2, EP3alpha and EP4 receptor subtypes was prostaglandin E2 = prostaglandin E1 > iloprost > prostaglandin F2alpha > prostaglandin D2 > U46619. The rank order at the prostanoid EP1 receptor was essentially the same except that iloprost had the highest affinity of the prostanoids tested. Of the selective ligands, butaprost was selective for prostanoid EP2, M&B28767 and sulprostone were selective for EP3alpha and enprostil displayed dual selectivity, interacting with both prostanoid receptor subtypes EP1 and EP3alpha. All four receptors coupled to their predominant signal transduction pathways in HEK 293 cells. Notably, using a novel aequorin luminescence assay to monitor prostanoid EP1 mediated increases in intracellular calcium, both iloprost and sulprostone were identified as partial agonists. Finally, by Northern blot analysis EP3 transcripts were most abundant in liver and kidney whereas prostanoid EP2 receptor mRNA was expressed in spleen, lung and testis and prostanoid EP1 receptor mRNA transcripts were predominantly expressed in the kidney. The rat prostanoid EP1 probes also detected additional and abundant transcripts present in all the tissues examined. These were found to be related to the expression of a novel protein kinase gene and not the prostanoid EP1 gene [Batshake, B., Sundelin, J., 1996. The mouse genes for the EP1 prostanoid receptor and the novel protein kinase overlap. Biochem. Biophys. Res. Commun. 227. 1329-1333].

Molecular cloning and characterization of the human prostanoid DP receptor

A cDNA encoding a functional human prostanoid DP (hDP) receptor has been constructed from a genomic clone and a fragment cloned by 3'-rapid amplification of cDNA ends-polymerase chain reaction. The hDP receptor consists of 359 amino acid residues with a predicted molecular mass of 40,276 and has the putative heptahelical transmembrane domains characteristics of G-protein-coupled receptors. The deduced amino acid sequence of the hDP receptor, when compared with all other members of the prostanoid receptor family, shows the highest degree of identity with the hIP and hEP2 receptors, followed by the hEP4 receptor. Radioreceptor binding studies using membranes prepared from mammalian COS-M6 cells transiently transfected with an expression vector containing the DP receptor cDNA showed that the rank order of affinities for prostaglandins and prostaglandin analogs, in competition for [3H]prostaglandin D2 (PGD2) specific binding sites, was as predicted for the DP receptor, with PGD2 >> PGE2 > PGF2 alpha = iloprost > U46619. The signal transduction pathway of the cloned hDP receptor was studied by transfecting the hDP expression vector in HEK 293(EBNA) cells. Activation of the hDP receptor with PGD2 resulted in an elevation of intracellular cAMP and in mobilization of Ca2+, but did not lead to generation of inositol 1,4,5-trisphosphate. Northern blot analysis of human tissue showed that the hDP receptor was a very discrete tissue distribution and was detectable only in retina and small intestine. In summary, we have cloned and expressed a functional cDNA for the hDP receptor.

Ultrastructural characteristics and morphogenesis of porcine reproductive and respiratory syndrome virus propagated in the highly permissive MARC-145 cell clone

A Québec reference strain of PRRSV (IAF-KLOP) was successfully propagated in MARC-145 cells, a highly permissive cell clone to PRRSV derived from the MA-104 cell line. Purified extracellular virions appeared as pleomorphic but mostly spherical enveloped particles, 50-72 nm in diameter, with an isometric core about 25-30 nm. By indirect immunofluorescence, detection of viral antigens within the cytoplasm was possible as soon as 6 h.p.i. Nucleocapsids, budding at smooth endoplasmic reticulum (ER), and enveloped viral particles that tended to accumulate in the lumen of ER or Golgi vesicles, were the main features of the viral morphogenesis. The virus apparently was released by exocytosis.

Characterization of specific binding sites for cysteinyl leukotrienes in sheep lung

Specific binding sites for [3H]leukotriene (LT)D4 and [3H]LTC4 have been identified in sheep lung parenchymal membranes. [3H] LTD4 specific binding was of high affinity (KD = 0.56 nM), saturable (Bmax = 43 fmol/mg of protein), stimulated by divalent cations and inhibited by nonhydrolyzable GTP analogs. LTs and LTD4-receptor antagonists competed for [3H]LTD4 specific binding with the rank order of potency predicted for the LTD4 receptor: LTD4 > ONO-1078 > ICI 204,219 > MK-571 > LTE4 > LTC4 > BAY u9773 >> LTB4. In contrast, [3H]LTC4 specific binding was of lower affinity (KD = 27 nM), abundant (Bmax = 87 pmol/mg of protein) and although stimulated by divalent cations was unaffected by GTP analogs. LTs and LTC4 analogs competed for [3H]LTC4 specific binding with the following rank order of potency: LTC2 > LTC3 > LTC4 > LTC5 >> N-methyl-LTC4 >> LTD4 approximately LTB4 approximately LTB4. [3H]LTD4 specific binding to sheep lung membranes has, therefore, the characteristics of being to a G-protein-coupled LTD4 receptor, whereas the profile of [3H]LTC4 specific binding strongly suggests that these sites are not LT-receptor related. Photolabeling of sheep lung membranes using [125I]azido-LTC4, a photoactivable LTC4 analog, resulted in the selective photolabeling of two polypeptides migrating at 30 kDa and 19 kDa. The selective photolabeling of the 19 kDa polypeptide could be modulated in an identical manner to [3H]LTC4 specific binding. This protein is, therefore, a candidate for being the principal [3H]LTC4 specific site in sheep lung membranes and has a comparable molecular mass to microsomal glutathione S-transferase, recently shown to be the predominant LTC4 binding protein in cellular membranes.

Microsomal glutathione S-transferase is the predominant leukotriene C4 binding site in cellular membranes

Dimethyl sulfoxide-differentiated U937 (dU937) cells express high affinity G-protein-coupled receptors for leukotriene (LT)D4 and LTB4 and, as described here, specific binding sites for LTC4. The specific binding of [3H]LTC4 was of low affinity (KD = 26 nM) and high abundance (Bmax = 33 pmol/mg of protein), as compared to LTD4 and LTB4 receptors. In addition, although [3H]LTC4 specific binding was enhanced by divalent cations, it was not inhibited by nonhydrolyzable GTP analogs. [3H]LTC4 specific binding to dU937 cell membranes does not have, therefore, the characteristics of binding to a G-protein-coupled receptor. Competition for [3H]LTC4 specific binding to dU937 cell membranes by leukotrienes and related analogs, including N-methylated LTC4, as well as glutathione, suggested a dependence on the presence of an arachidonic acid backbone, although varying degrees of saturation were well tolerated, and that the glutathione moiety of LTC4 in particular was important in determining affinity. The possibility that [3H]LTC4 specific binding was to a member of the glutathione S-transferase (GST) family of enzymes, such as LTC4 synthase, cytosolic GST, or microsomal GST, was therefore investigated. [3H]LTC4 specific binding sites could be separated from LTC4 synthase and cytosolic GSTs by differential detergent solubilization, but cofractionated with microsomal GST during solubilization and subsequent anion exchange chromatography. In membranes that were depleted of LTC4 synthase and cytosolic GSTs, 125I-azido-LTC4 (a photoaffinity probe based on LTC4) specifically photolabeled in a cation-dependent manner a 17-kDa polypeptide that was comparable in mass to the microsomal GST polypeptide. Furthermore, [3H]LTC4 bound specifically to purified human microsomal GST with the same characteristics as to the endogenous dU937-cell membrane specific binding sites. The principal [3H]LTC4 specific binding site present in dU937 cells, therefore, is not a G-protein-coupled receptor, LTC4 synthase, or cytosolic GSTs, but is microsomal GST. Finally, the 1:3 stoichiometry of [3H]LTC4 specific binding to purified microsomal GST is consistent with the enzyme functioning as a homotrimer.

Cloning, functional expression, and characterization of the human prostaglandin E2 receptor EP2 subtype

A cDNA clone encoding the human prostaglandin (PG) E2 receptor EP2 subtype has been isolated from a human lung cDNA library. The 1.9-kilobase pair cDNA, hEP2, encodes for a 488-amino acid protein with a predicted molecular mass of 53,115 and has the seven putative transmembrane domains characteristic of G protein-coupled receptors. The specific binding of [3H]PGE2 to COS cell membranes transfected with the hEP2 cDNA was of high affinity with an equilibrium dissociation constant (Kd) of 1 nM and the rank order of potency for prostaglandins in competition for [3H]PGE2 specific binding was PGE1 = PGE2 >> iloprost > PGF2 alpha > PGD2. In competition studies using more selective prostanoid-receptor agonist and antagonists, the [3H]PGE2 specific binding was competed by MB28767, an EP3 agonist, but not by the EP1-preferring antagonists AH6809 and SC19220, or by the EP2 agonist butaprost. Electrophysiological studies of Xenopus oocytes co-injected with hEP2 and cystic fibrosis transmembrane conductance regulator (cAMP-activated Cl- channel) cDNAs detected PGE2-specific inward Cl- currents, demonstrating that the hEP2 cDNA encoded a functional receptor which produced an increase in cAMP levels. Thus, we have cloned the human EP2 receptor subtype which is functionally coupled to increase in cAMP. Northern blot analysis showed that hEP2 is expressed as a 3.8-kilobase mRNA in a number of human tissues with the highest expression levels present in the small intestine.

Expression and sorting of rat plasma kallikrein in POMC-producing AtT-20 cells

A vaccinia virus (VV) vector was used to express rat plasma kallikrein (rPK) in the constitutively secreting cells, BSC-40, and in the endocrine regulated cells, AtT-20. Using a specific rPK antibody and a fluorogenic substrate, Phe-Phe-Arg-AMC, we demonstrated that in both cell lines VV infections resulted in the synthesis of an immunoreactive enzyme predominantly present as a zymogen which can be activated with trypsin. Stimulation of VV:rPK-infected AtT-20 cells with either 5mM 8-bromo-cAMP or 56 mM KCl resulted in a different pattern of rPK and ACTH secretion, strongly suggesting that rPK follows the constitutive secretory pathway. Finally, the 10% rPK activity found within AtT-20 cell extracts had no effect on pro-opiomelanocortin (POMC) processing either intracellularly or extracellularly. The above data show that the biosynthetic machinery of both cell lines analyzed does not allow the efficient activation of plasma prekallikrein. Finally, despite the PK's demonstrated ability to cleave various hormone precursors in vitro at pairs of basic residues, in vivo, we did not obtain evidence that this hepatic enzyme can also act as an intracellular pro-protein processing enzyme.

Mouse plasma kallikrein: cDNA structure, enzyme characterization, and comparison of protein and mRNA levels among species

There is differential regulation of liver mRNA levels of rat (r) and mouse (m) plasma kallikrein (PK), as observed on Northern blots. Affinity purification of mPK and rPK, microsequencing, and radioimmunoassay in either rat or mouse showed that the difference in mRNA levels does not appreciably affect the circulating PK concentration. Nuclear run-off assays demonstrated that the regulation of the mRNA level of PK is post-transcriptionally controlled. Complete cDNA sequence determination of mPK was achieved using a combination of polymerase chain reaction and lambda gt11 library screening procedures. Within the coding region, the overall sequence homology between mPK and rPK is about 91-92% in amino acid and nucleotide sequence. Although the 3' noncoding segment of mPK is shorter than that of rPK, we calculate a 53% homology with a 5% higher A/T content for mPK. The largest difference is found at the 5' end of the mRNAs: whereas rPK is predicted from its gene structure to have a 167-nucleotide leader sequence, mPK is expected to have more than 605 nucleotides, of which the last 291 are very similar to those found in the rPK gene. The regulation of the mRNA stability and/or turnover rate of PK may possibly be affected by its 5' end in a species-dependent manner.

Fast (4-h) or slow (24-h) infusions of pamidronate disodium (aminohydroxypropylidene diphosphonate (APD)) as single shot treatment of hypercalcaemia

Twenty-five patients with hypercalcaemia (ionised calcium, 1.57 +/- 0.04 mM; total calcium, 3.33 +/- 0.06 mM) due to malignancy were randomised to receive pamidronate (1 mg/kg body wt.) by infusion over 4 h (12 patients) or 24 h (13 patients). Forced saline diuresis was not utilised. Two patients died within 24 h and were not included in the analysis. Both groups combined (n = 23) showed a decrease in ionised calcium to 1.44 +/- 0.04 mM by 2 days (P less than 0.05 vs. day 0). By 4 days there had been a further fall to 1.27 +/- 0.05 mM (P less than 0.05 vs. day 2) and 7 days after treatment ionised calcium was 1.19 +/- 0.05 mM (P less than 0.05 vs. day 4). Total calcium declined from 3.33 +/- 0.06 to 2.65 +/- 0.11 mM over 7 days (P less than 0.001). Separate analyses of the two groups showed that the fast (4-h) infusion led to an earlier reduction in calcium than did the 24-h infusion (P less than 0.02), although after 7 days there was little difference between the two groups (4 h, 1.18 +/- 0.09 mM; 24 h, 1.23 +/- 0.06 mM, n.s.). Hypercalcaemic symptoms (analogue rating scale) improved between each of the time intervals 0, 4 and 7 days (P less than 0.05) and did not differ between the two groups. We recommend a single 4-h infusion of pamidronate (1 mg/kg) as primary treatment for malignancy-induced hypercalcaemia.

Rat plasma kallikrein: purification, NH2-terminal sequencing and development of a specific radioimmunoassay

Rat plasma kallikrein (rPK) was purified to homogeneity form plasma using affinity and high-performance liquid chromatography techniques, and subjected to NH2-terminal sequencing. The data showed that the sequenced segments of the regulatory (heavy) and catalytic (light) chains of the proteinase, respectively, display 73 and 91% sequence similarity with their counterpart in human plasma kallikrein. This sequence homology in conjunction with the determined molecular structure and inhibitor sensitivity support the identity of the isolated enzyme as plasma kallikrein. A polyclonal antiserum against rPK was obtained after immunization of rabbits with the purified enzyme, and a specific radioimmunoassay was developed. Since Tyr-iodinated rPK was not recognized by the antiserum, two alternative approaches were found to be successful. These included the use of a tracer consisting of rPK modified with either the affinity reagent 125I-labeled DTyr-Glu-Phe-Lys-Arg chloromethyl ketone or with the Bolton Hunter reagent. The usable range of the assay is between 15-150 fmol per tube. The antibody was shown to bind both monomeric and dimeric forms of rPK. Denaturation of the enzyme in sodium dodecyl sulfate does not abolish immune recognition only as long as the regulatory subunit is attached to the catalytic chain. Oxidation or reduction of rPK results in complete loss of immunoreactivity. This observation suggests that perhaps the disulfide linkage of the catalytic and regulatory polypeptides somehow helps to protect the antigenic epitope from denaturation. Alternatively, the epitope(s) recognized by the antibody spans a domain which includes both Tyr and Cys residues necessary for immune recognition.

One-shot high-dose pamidronate disodium (APD): effective, simple treatment for hypercalcaemia in haematological malignancy

Fifteen patients with haematological malignancy and hypercalcaemia (mean +/- SEM calcium 3.44 +/- 0.14 mmol/l) received pamidronate (1 mg/kg) by infusion on 17 occasions (two patients were retreated 2 and 6 months after the first dose). After 4 days the plasma calcium had fallen to 2.84 +/- 0.14 mmol/l (P less than 0.001; n = 17), and in 10/17 episodes was less than 2.6 mmol/l. The mean fall was 0.61 mmol/l (95% confidence intervals 0.49-0.72 mmol/l). By 7 days a further decrease to 2.53 +/- 0.10 mmol/l had occurred, continuing to 2.38 +/- 0.11 mmol/l after 14 days. Plasma phosphate fell from 1.18 +/- 0.16 to 0.74 +/- 0.07 mmol/l at 7 days (P less than 0.001; n = 12). In 9 of the 17 episodes plasma creatinine initially exceeded 120 mumol/l (four of these greater than 300 mumol/l). This did not impair the response to pamidronate and there was no significant change in plasma creatinine following treatment. A single large dose of pamidronate was a simple, well-tolerated and very reliable treatment for hypercalcaemia complicating haematological malignancy, irrespective of renal function.

Progressive hypokalaemia in elderly patients taking three thiazide potassium-sparing diuretic combinations for thirty-six months

Three different thiazide potassium-sparing diuretic combinations were given to elderly patients for heart failure. Eighty patients received their allocated combinations for 3 years and had 6-monthly measurements of plasma potassium. A further 84 were recruited for study but 29 died within 6 months and 55 had to be withdrawn from the trial. The triamterene-containing preparation was discontinued most frequently (6/44) because of hypokalaemia (plasma potassium less than 3.0 mmol/l); amiloride (5/44) and spironolactone (1/47). The median fall in plasma potassium over 3 years in those patients not withdrawn because of hypokalaemia was similar in each case (P greater than 0.05) and possibly failed to reach significance because of the withdrawal rate (9%). The trend was for a greater fall in those patients taking triamterene. The spironolactone-containing preparation may be the least unsatisfactory of the three.

Prevalence, concentration, and prognostic importance of proteinuria in patients with malignancies

Protein was found significantly more frequently in single urine samples from 504 patients with malignancy (290; 58%) than in 529 controls (119; 22%) (p less than 0.01). Median protein concentration was greater (p less than 0.001) in patients with neoplasia (0.14 g/l) than in controls (0.07 g/l). Actuarial analysis showed a median survival of 4.5 months in patients with proteinuria compared with 10 months in those without (p less than 0.001). The association between proteinuria and shorter survival was statistically significant for patients with gut tumours, lung tumours, and tumours at other sites analysed as a group. Patients with myeloma or urinary tract tumours were not studied. In many patients with malignancy the presence of proteinuria may be associated with a substantially reduced survival time.

Clinical aspects of the acquired immune deficiency syndrome in the United Kingdom

Between August and November 1983, seven new patients with AIDS were seen at this hospital; two with disseminated Kaposi's sarcoma, and five with opportunist infections, of whom three have died. We present the case histories of the five patients with opportunist infections, which show the wide clinical range of AIDS and suggest that the pattern of infection in the UK may differ from that reported in the USA.