Introduction Work-related asthma accounts for ≥25% of asthma in working-age populations, though the relationship between work exposures and symptoms is frequently missed, leading to poor health and employment outcomes. We hypothesised that inhalable exposures at work are associated with poor asthma control in severe asthma (SA).Methods We searched the Birmingham (UK) Regional NHS SA Service clinical database (n=1453 records; 1 March 2004 to 1 March 2021) and undertook a cross-sectional study using baseline data collected at diagnosis. We included all employed patients aged 16–64 with documented current occupation (n=504), and collected socio-demographic, general health and asthma-specific data, including Asthma Control Questionnaire 7 (ACQ7) score. The Occupational Asthma Specific Job-Exposure Matrix (OAsJEM) was employed to determine the likelihood of exposure to respiratory sensitisers, irritants, cleaning agents and detergents; associations between exposures and ACQ7 were investigated using binary and multinomial regression.Results Frequently reported occupations were care assistants (7%) and nurses (6%); 197/504 (39%) patients were exposed to an asthmagen, including respiratory sensitisers (30%), airway irritants (38%) and cleaning products/disinfectants (29%). ACQ7 score was available for 372/504 (74%) patients, of whom 14% had adequate control (ACQ7=0–1.5). After adjustment for major confounders there were no significant associations between inhaled asthmagens and ACQ7 score (either as binary or multinomial outcomes).Conclusion JEM-determined workplace exposures to inhaled asthmagens are not associated with asthma control in SA; 29–39% of patients may have current exposure to workplace asthmagens. Routine collection of lifetime occupational data including current job role and level of exposure, in the national asthma registry, would give further insights into this relationship.

BACKGROUND:Clinical trials and real world studies demonstrated benefit of mepolizumab treatment in severe asthma but data on its effectiveness beyond 2 years remain limited. Herein, we provide mepolizumab treatment evaluation up to 4 years. METHODS:we studied all patients initiated on mepolizumab in our center from June 2017 to August 2018. Clinical outcomes data were retrieved from the local dendrite systems registry. Comparison analyses and logistic regression were conducted to explore longevity and predictors of response to mepolizumab treatment. RESULTS:a total of 66 patients initiated on mepolizumab with a median follow-up of 45.8 (42.4,48.1) months were included in the study [mean age 50.3 years (range 18-79), females 50 (73%) ]. At 20.7 months of treatment, 42 patients (63.6%) had positive response, 13 (19.7%) negative response, and 11 (16.7%) discontinued due to other factors. At 45.8 months, 35 (53%) patients were still on mepolizumab, 21 (31.8%) switched to a different biologic, and 10 (15.2%) discontinued biologics. Two deaths were recorded during the study period.The median blood eosinophil was reduced from 0.43x109/L (0.27, 0.75) to 0.04 (0.0, 0.1) (p < 0.00001)]. The median annual exacerbations were reduced from 6.0 (4,8) to 1.0 (0.0,3.0) (p < 0.00001), and mOCS use was reduced from59% to 29%, p = 0.001. The mean asthma control questionnaire-6 (ACQ6) improved from 3.1 ± 1.7 to 2.1 ± 1.3 (p < 0.00001). CONCLUSIONS:mepolizumab clinical benefit was sustained over 4 years. However, approximately half of the cohort discontinued the treatment prompting the need for further research into the treatment response longevity.

Background: some female patients experience perimenstrual worsening of asthma. The prevalence and impact of perimenstrual worsening on severe asthma patients is not known. Aim: to investigate perimenstrual worsening of asthma in severe asthma population. Methods: Patients with severe asthma completed a structured questionnaire to determine the relationship between asthma symptoms and menstrual period. Demographics and clinical outcomes of females with and without perimenstrual worsening of asthma were compared using data from our local severe asthma registry. Results: a total of 755 female patients (mean age 42.9±15) with confirmed diagnosis severe asthma were included, of whom 102 (13.6%) had perimenstrual worsening. Compared to non-menstrual asthma those with perimenstrual worsening were younger (mean age 36.5±12 yrs vs 44.1±15.4, <0.001), had younger age of onset of symptoms (14.7±13.7yrs vs 20.8±18.3, p 0.002), more likely to be on maintenance oral corticosteroids [50/99 (50.5%) vs 223/648 (34.4%), p 0.002], more atopic [74/95 (77.9%) vs 421/614 (68.6%), p 0.06], and more eczema [38/99 (38%) vs 165/625 (26.4%), p 0.016]. The two groups were similar in terms of lung function, blood eosinophils, exhaled nitric oxide, exacerbations frequency, hospital admissions and intensive care or ventilation episodes. Conclusion: a minority of severe asthma patients experience perimenstrual worsening of symptoms. They are younger with an earlier age of onset of asthma and more likely to be on maintenance OCS than those without menstrual link. Further research is needed to delineate underlying mechanisms.

Background: clinical trials demonstrated effectiveness of mepolizumab in treatment of severe eosinophilc asthma, but real world evidence on its longterm outcomes remains limited. Aims: to describe the long-term efficacy and safety of mepolizumab in severe asthma. Methods: patients who had at least one treatment of mepolizumab and follow up data of 2+ years were considered for this study. Clinical and safety outcome were retrieved from the local registry. Results: a total of 66 patients were included [mean age 50 years (range 18-79), 73% females, BMI 32.6±7.3kg/m2, %FEV1 predicted 72.2±22, 59% on maintenance oral corticosteroids (OCS)]. Satisfactory clinical response was observed in 35 (53%) at 12 months, 42 (63.6%) at 18 months, and 41 (62%) at 45months. There was sustained reduction in annual severe exacerbations from 6.7±3.0 to 2.0±2.5 (p <0.001) (figure), and complete wean off maintenance OCS at 45months in 46% patients. Compared to baseline, we observed continued improvement at 45 months in asthma control questionnaire [n=57, 3.35±1.3 vs 2.3±1.4, difference -1.01, p<0.0001), blood eosinophil suppression [n=34, 0.5x109/L (0.35, 0.79) vs 0.04 (0.00, 0.10) p<0.0001], but no change in FeNO [n=17, 52(25.5,98) ppb vs 62 (14.7,105, p=0.5], or FEV1 (data not shown). Of the total stopped treatment (n=25/66), 13/25 (52%) were due to lack of response, and 12/25 (48%) were due to side effects or other causes (e.g. pregnancy). Two patients died from non-mepolizumab/asthma related causes. Conclusion: significant proportion of severe asthma patients had positive sustained response to mepolizumab over follow-up period of 45months. Minority stopped treatment due to lack of response or side effects.

Additional structure-activity relationship studies on potent cyclic peptide inhibitors of very late antigen-4 (VLA-4) are reported. The new N- to C-terminal cyclic hexa-, hepta- and octapeptide inhibitors like cyclo(MeIle/MePhe-Leu-Asp-Val-X) (X = 2-4 amino acids containing hydrophobic and/or basic side chains) were synthesized using solid phase peptide synthesis methods. The peptides were evaluated in in vitro cell adhesion assays and in in vivo inflammation models. Many of the peptides like cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-D-Phe) (20), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-MePhe) (21) and cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg-D-Ala-D-Ala) (23) were potent inhibitors of VLA-4-mediated cell adhesion and inhibited ovalbumin-induced delayed type hypersensitivity (DTH) response in mice. The more potent compounds were highly selective and did not affect U937 cell adhesion to fibronectin (VLA-5), phorbolmyristate acetate or PMA-differentiated U937 cell adhesion to intercellular cell adhesion molecule-1 (ICAM-1)-expressing Chinese hamster ovary cells (LFA-1) and adenosine diphosphate (ADP)-induced platelet aggregation (GPIIb/IIIa). In contrast to the inhibitors like Ac-cyclo(D-Lys-D-Ile-Leu-Asp-Val) and cyclo(CH2CO-Ile-Leu-Asp-Val-Pip-CH2CO-Ile-Leu-Asp-Val-Pip) described earlier, the new compounds were much more compatible with the depot formulations based on poly(DL-lactide-co-glycolide) polymers. The hexapeptide cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17) inhibited MOLT-4 cell adhesion to fibronectin and vascular cell adhesion molecule-1 (VCAM-1) with IC50 values of 260 and 330 nM, respectively, and did not show any significant effect against other integrins (IC50 > 300 microM). ZD7349 inhibited ovalbumin-induced DTH response in mice when administered continuously using a mini-pump (ED50 0.01 mg/kg/day) or when given as an s.c. or i.v. bolus injection at a dose of 1-10 mg/kg. ZD7349 was also active in type II collagen-induced arthritis (CIA) and experimental autoimmune encephalomyelitis (EAE) tests at a dose of 3-10 mg/kg. The peptide was released from some formulations over a period of 10-20 days. ZD7349 is currently undergoing pre-clinical investigation.

Potent monomeric and dimeric cyclic peptide very late antigen-4 (VLA-4) inhibitors have been designed based on a tetrapeptide (Ile-Leu-Asp-Val) sequence present in a 25-amino acid peptide (CS-1) reported in the literature. The peptides, synthesized by the SPPS techniques, were evaluated in the in vitro cell adhesion assays and in the in vivo inflammation models. The N- to C-terminal cyclic peptides such as cyclo(Ile-Leu-Asp-Val-NH-(CH2)2-S-(CH2)2-CO) (28) and cyclo(MeIle-Leu-Asp-Val-D-Ala-D-Ala) (31), monomeric and dimeric peptides containing piperazine (Pip) or homopiperazine (hPip) residues as linking groups, e.g. cyclo(MeIle-Leu-Asp-Val-Pip-CH2CO-NH-(CH2)2-S-CH2-CO) (49) and cyclo(MeIle-Leu-Asp-Val hPip-CH2CO-MeIle-Leu-Asp-Val-hPip-CH2CO) (58) and cyclic peptides containing an amide bond between the side chain amino group of an amino acid such as Lys and the C-terminal Val carboxyl group, e.g. Ac-cyclo(D-Lys-D-Ile-Leu-Asp-Val) (62) and beta-Ala-cyclo(D-Lys-D-Leu-Leu-Asp-Val) (68) were more potent than CS-1 in inhibiting the adhesion of the VLA-4-expressing MOLT-4 cells to fibronectin. The more potent compounds were highly selective and did not affect U937 cell adhesion to fibronectin (VLA-5), PMA-differentiated U937 cell adhesion to intercellular cell adhesion molecule- 1-expressing Chinese hamster ovary cells (LFA-1) and ADP-induced platelet aggregation (GPIIb/IIIa). A number of the more potent compounds inhibited ovalbumin-induced delayed type hypersensitivity in mice and some were 100-300 times more potent (ED50 = 0.003-0.009 mg/kg/day, s.c.) than CS-1. Two peptides, Ac-cyclo(D-Lys D-Ile-Leu-Asp-Val) (62) and cyclo(CH2CO-Ile-Leu-Asp-Val-Pip-CH2CO-Ile-Leu-Asp-Val-Pip) (55), were formulated in poly(DL-lactide-co-glycolide) depots and the release profile was investigated in vitro over a 30-day period.

We have investigated the ability to quantitate atherosclerosis in the aortic arch of the Watanabe rabbit using noninvasive 3-D ultrasound, Our methodology utilizes postprocessing of videotaped freehand 2-D interrogations to form a compound 3-D data block. Structures may then be segmented on the attributed grey-scale level and volumes measured. Analysis of 3-D reconstructions revealed a low echo structure in the aortic arch of atherosclerotic rabbits, absent in nonatherosclerotic rabbits, at recognized sites of plaque predilection. This structure volume correlated closely with fatty streak volume determined from histology (r = 0.890). During a 30-week study, this structure volume increased in untreated animals, but was blocked by treatment with the antiatherosclerotic agent probucol. Thus, a new 3-D ultrasound methodology has been used noninvasively to detect and quantitate a low echo structure corresponding to fatty streaks in the Watanabe rabbit aortic arch, This new methodology could potentially aid plaque burden quantification in human peripheral arteries. (C) 1999 World Federation for Ultrasound in Medicine & Biology.

1. Small, N- to C-terminal cyclized peptides containing the leucyl-aspartyl-valine (LDV) motif from fibronectin connecting segment-1 (CS-1) have been investigated for their effects on the adhesion of human T-lymphoblastic leukaemia cells (MOLT-4) to human plasma fibronectin in vitro mediated by the integrin Very Late Antigen (VLA)-4 (alpha4beta1, CD49d/CD29). 2. Cyclo(-isoleucyl-leucyl-aspartyl-valyl-aminohexanoyl-) (c(ILDV-NH(CH2)5CO)) was approximately 5 fold more potent (IC50 3.6+/-0.44 microM) than the 25-amino acid linear CS-1 peptide. Cyclic peptides containing two more or one less methylene groups had similar potency to c(ILDV-NH(CH2)5CO) while a compound containing three less methylene groups, c(ILDV-NH(CH2)2CO), was inactive at 100 microM. 3. c(ILDV-NH(CH2)5CO) had little effect on cell adhesion mediated by two other integrins, VLA-5 (alpha5,beta1, CD49e/CD29) (K562 cell adhesion to fibronectin) or Leukocyte Function Associated molecule-1 (LFA-1, alphabeta2, CD11a/CD18) (U937 cell adhesion to Chinese hamster ovary cells transfected with intercellular adhesion molecule-1) at concentrations up to 300 microM. 4. c(ILDV-NH(CH2)5CO) inhibited ovalbumin delayed-type hypersensitivity or oxazolone contact hypersensitivity in Balb/c mice when dosed continuously from subcutaneous osmotic mini-pumps (0.1-10 mg kg(-1) day(-1)). Maximum inhibition (approximately 40%) was similar to that caused by the monoclonal antibody PS/2 (7.5 mg kg(-1) i.v.) directed against the alpha4 integrin subunit. 5. c(ILDV-NH(CH2)5CO) also inhibited oxazolone contact hypersensitivity when dosed intravenously 20 h after oxazolone challenge (1-10 mg kg(-1)). Ear swelling was reduced at 3 h and 4 h but not at 1 h and 2 h post-dose (10 mg kg(-1)). 6. Small molecule VLA-4 inhibitors derived from c(ILDV-NH(CH2)5CO) may be useful as anti-inflammatory agents.

Oestrogens regulate the expression of genes both positively and negatively in a range of cell types. These effects are mediated via the oestrogen receptor (ER) and involve direct interactions between the ER and DNA response elements, as well as interactions between the ER and other nuclear proteins. We have examined the potential of the ERα to regulate the expression of reporter genes under the control of oestrogen response elements (EREs), NFκB response elements (NREs) or AP-1/TPA response elements (TREs) in HeLa cells and in human embryonic kidney (HEK-293) cells. Transiently transfected ERα was able to activate expression of β-galactosidase under the control of EREs in an oestradiol (E2)-dependent manner in both HeLa and HEK-293 cells. The ERα was able to repress by 80% the TNF-mediated expression of β-galactosidase under the control of NREs in an E2-dependent manner in HeLa cells but not in HEK-293 cells. ERα/E2 also induced a two-fold potentiation of TPA-mediated expression of β-galactosidase under the control of TREs in HeLa cells but not in HEK-293 cells. These results suggest that the ERα is capable of regulating gene expression in a cell-specific manner. We further investigated the mechanisms by which the ERα regulates gene expression in these systems by co-expressing the ERα and the reporter gene constructs with known co-factors of the ERα. We have shown that expression of steroid receptor coactivator-1 alpha (SRC-1α) and receptor interacting protein-140 (RIP-140) have no effect on the capacity of the ERα to modulate NFκB reporter gene activity in HeLa cells. Furthermore, the expression of SRC-1α or RIP-140 does not enable the ERα to repress NFκB or to potentiate an AP-1 response in HEK-293 cells. This suggests that factors other than SRC-1α or RIP-140 are responsible for the cell-specific effects seen with ERα.

Hypertriglyceridemia may contribute to the development of atherosclerosis by increasing expression of cell adhesion molecules (CAMs). Although the cellular expression of CAMs is difficult to assess clinically, soluble forms of CAMs (sCAMs) are present in the circulation and may serve as markers for CAMs. In this study, we examined the association between sCAMs and other risk factors occurring with hypertriglyceridemia, the effect of triglyceride reduction on sCAM levels, and the role of soluble vascular cell adhesion molecule-1 (sVCAM-1) in monocyte adhesion in vitro. Compared with normal control subjects (n=20), patients with hypertriglyceridemia and low HDL (n=39) had significantly increased levels of soluble intercellular adhesion molecule-1 (sICAM-1) (316+/-28.8 versus 225+/-16.6 ng/mL), sVCAM-1 (743+/-52.2 versus 522+/-43.6 ng/mL), and soluble E-selectin (83+/-5.9 versus 49+/-3.6 ng/mL). ANCOVA showed that the higher sCAM levels in patients occurred independently of diabetes mellitus and other risk factors. In 27 patients who received purified n-3 fatty acid (Omacor) 4 g/d for > or =7 months, triglyceride level was reduced by 47+/-4.6%, sICAM-1 level was reduced by 9+/-3.4% (P=.02), and soluble E-selectin level was reduced by 16+/-3.2% (P<.0001), with the greatest reduction in diabetic patients. These results support previous in vitro data showing that disorders in triglyceride and HDL metabolism influence CAM expression and treatment with fish oils may alter vascular cell activation. In a parallel-plate flow chamber, recombinant sVCAM-1 at the concentration seen in patients significantly inhibited adhesion of monocytes to interleukin-1-stimulated cultured endothelial cells under conditions of flow by 27.5+/-7.2%. Thus, elevated sCAMs may negatively regulate monocyte adhesion.

BACKGROUND:Numerous studies have demonstrated the ability of angiotensin II (Ang II) receptor antagonists and angiotensin-converting enzyme (ACE) inhibitors to inhibit intimal hyperplasia after balloon dilation of noncoronary arteries in small-animal models, suggesting an important role for Ang II in the response to injury. Although ACE inhibitors have not been similarly effective in nonhuman coronary models or in human restenosis trials, questions remain regarding the efficacy ACE inhibitors against tissue ACE and the contributions of ACE-independent pathways of Ang II generation. Unlike ACE inhibitors, Ang II receptor antagonists have the potential to inhibit responses to Ang II independent of its biosynthetic origin.METHODS AND RESULTS:In separate studies, three Ang II receptor antagonists, including AT1 selective (L-158,809), balanced AT1/AT2 (L-163,082), and AT2 selective (L-164,282) agents, were evaluated for their ability to inhibit vascular intimal thickening in a porcine coronary artery model of vascular injury. Preliminary studies in a rat carotid artery model revealed that constant infusion of L-158,809 (0.3 or 1.0 mg X kg-1 X d-1) reduced the neointimal cross-sectional area by up to 37% measured 14 days after balloon dilatation. In the porcine studies, animals were treated with vehicle or test compound beginning 2 days before and extending 28 days after experimental angioplasty. Left anterior descending, left circumflex, and/or right coronary arteries were injured by inflation of commercially available angioplasty balloons with placement of coiled metallic stents. Infusion of L-158,809 (1 mg X kg-1 X d-1), L-163,082 (1 mg X kg-1 X d-1), or L-164,282 (1.5 mg X kg-1 X d-1) in the study animals yielded plasma drug levels sufficient either to chronically block or, for L-164,282, to spare pressor responses to exogenous Ang II. Neither L-158,809, L-163,082, nor L-164,282 had statistically significant effects (P=.12, P=.75, and P=.48, respectively, compared with vehicle-treated controls) on neointimal thickness (normalized for degree of injury) measured by morphometric analysis at day 28 after angioplasty.CONCLUSIONS:These findings indicate that chronic blockade of Ang II receptors by either site-selective or balanced AT1/AT2 antagonists is insufficient to inhibit intimal hyperplasia after experimental coronary vascular injury in the pig. The results further suggest that, unlike in the rat carotid artery, Ang II is not a major mediator of intimal thickening in the pig coronary artery.

We have expressed human monocyte chemoattractant protein-1 (hMCP-1) in preerythroid mouse erythroleukemia (MEL) C88 cells using the locus control region/MEL expression system and studied the biological activity of the purified protein in a range ofin vitroexperimental systems. The recombinant hMCP-1 is expressed at high levels (∼10 mg/liter) in this system and is modified in a manner which is very similar to native hMCP-1. We have developed a simple high-yielding two-step purification route employing dye ligand and ion exchange chromatographies which enables us to separate glycosylated and unglycosylated hMCP-1. The purified glycosylated and unglycosylated forms of hMCP-1 have equivalent biological activities in all of the assay systems tested.

A variety of evidence suggests that vascular smooth muscle cells (SMC) exhibit a more immature phenotype when stimulated by injury to replicate in the adult. One growth characteristic common to immature (embryonic, fetal, and neonatal) SMC is a markedly reduced responsiveness to platelet-derived growth factor (PDGF) and other mitogenic stimuli. Here we demonstrate that SMC isolated from the 14-day neointima of experimentally injured carotid arteries exhibit a similar growth phenotype. The proliferative responses of neointimal cells to the BB homodimer of PDGF, which interacts with both forms of the PDGF receptor, were up to twenty-fold less (as assessed by BrdU immunocytochemistry) than that of adult control tunica media eel Is over a wide range of PDGF concentrations. Paradoxically, these cells expressed abundant mRNA for the alpha- and beta-subunits of the PDGF receptor (by RT-PCR) and expressed abundant PDGF receptor protein (by Western blotting). Addition of PDGF-BB to neointimal SMC induced significant autophosphorylation of the PDGF receptor, suggesting that the PDGF receptors were fully functional. The chemotactic responses of neointimal SMC to PDGF, in in vitro migration assays, were identical to that of control medial cells. The data further establish the existence of vascular SMC phenotypes characterized by a refractoriness to growth stimulation by specific mitogens, and provide further evidence for the reiteration of developmentally regulated programs following vascular injury in vivo. (C) 1996 Wiley-Liss, Inc.

Monocyte chemoattractant protein-1 (MCP-1) is a member of the Cys-Cys chemokine family. Two related MCP-1 receptors have been identified (CC-CKR2A and CC-CKR2B), although the precise kinetics of ligand binding and calcium signaling of these receptors has yet to be investigated, To examine this more closely, the human MCP-1 receptors were cloned and expressed in Chinese hamster ovary (CHO) cells. Membranes prepared from cells expressing CC-CKR2B bind MCP-1 selectively and with high affinity (Kd = 120 pM). MCP-1 stimulation of recombinant CHO cells expressing CC-CKR2B induces a rapid increase in intracellular Ca2+ through both receptor-operated Ca2+ channels and mobilization of Ca2+ from intracellular stores, and leads to a rapid temperature-dependent internalization of the ligand/receptor complexes. In contrast, recombinant CHO cells expressing CC-CKR2A, and membranes prepared from these cells, fail to bind detectable levels of MCP-1. However, MCP-1 stimulation of cells expressing CC-CKR2A induces a small but significant increase in intracellular Ca2+. Repeated stimulation of these cells with MCP-1 leads to a potentiation of the response to a level comparable to that seen in cells expressing CC-CKR2B. These observations suggest that the levels of cell surface CC-CKR2A are controlled by novel mechanisms.

The aggregation of platelets from a variety of animal species in response to thrombin receptor-derived activating peptides was evaluated. A series of 14-(SFLLRNPNDKYEPF), 7-(SFLLRNP-NH2), 6-(SFLLRN-HN2) or 5-(SFLLR-NH2) residue peptides, the structures of which were based on the deduced amino acid sequence of the human thrombin receptor, promoted full aggregation of platelets in plasma from humans, African Green and Rhesus monkeys, baboons and guinea pigs at 4-50 microM depending on the peptide used. Platelets in plasma from rabbit, dog, pig, and hamster underwent a shape change but failed to aggregate in response to these peptides over 3 log units of peptide up to 800 microM, despite being fully responsive to human thrombin. However, because the receptor peptides induced shape change in the platelets from these non-aggregating species, they apparently can activate some of the intracellular signaling system(s) usually initiated by thrombin in these platelets. In contrast, platelets from rats did not undergo shape change or aggregate in response to the peptides. A 7-residue receptor-derived peptide based on the deduced amino acid sequence of the clone of the hamster thrombin receptor (SFFLRNP-N2) was nearly as efficacious as the corresponding human receptor-derived 7-residue peptide to promote aggregation of human platelets. However, the hamster peptide could not promote aggregation of hamster platelets in plasma at up to 800 microM peptide, while a shape change response was elicited. Platelets from rats, rabbits and pigs also did not aggregate in response to this peptide derived from the hamster thrombin receptor, but all species except the rat underwent a shape change.(ABSTRACT TRUNCATED AT 250 WORDS)

BACKGROUND The brisk fibrinolytic response of canines has impaired efforts to develop a canine model of chronic thromboembolic pulmonary hypertension. Difficulties in retaining chronic embolic residuals were partially overcome by administration of tranexamic acid (TXA) (Circulation. 1991;83:1272-1279.). In this study, we used type 1 plasminogen activator inhibitor (PAI-1), a major inhibitor of the endogenous fibrinolytic system, to determine its efficacy in the suppression of thrombolysis in canines. METHODS AND RESULTS Thrombus was induced in the inferior vena cava of anesthetized mongrel dogs with thrombin and a special double-balloon catheter; 2 hours later, the thrombus was embolized. In one group of dogs, activated type 1 plasminogen activator inhibitor (PAI-1) (130 micrograms) was delivered directly into the forming thrombus; in another, TXA (110 mg/kg) was given intravenously before thrombus formation; in controls, thrombus was induced without inhibitors. Cross-linked fibrin degradation product (D-dimer) appeared in the blood of control animals within 1 hour of thrombus induction (176 +/- 62.5 versus 1.02 +/- 0.39 ng/mL baseline; mean +/- SEM), was maximal by 4 hours (413 +/- 110 ng/mL) and remained elevated at 24 hours (90.8 +/- 19.5 ng/mL). Compared with controls, PAI-1 and TXA suppressed D-dimer release by 80% and 85%, respectively, over the first 24 hours. One week later, animals were killed, and residual emboli were harvested. Perfusion scan defects persisted in all animals at this time, but there were no scan defect differences among groups. However, emboli recovered from animals receiving PAI-1 still harbored immunoreactive PAI-1 and were, on average, more than twofold greater in mass (393 +/- 56 mg) than emboli recovered from either controls (183 +/- 76 mg) or animals receiving TXA (180 +/- 80 mg). CONCLUSIONS Intravenous TXA and intrathrombus PAI-1 effectively suppress thrombolysis for 24 hours in canines. Thromboemboli enriched with PAI-1 appear to resist lysis for longer periods of time (up to 1 week). These findings are consistent with the hypothesis that PAI-1 remains associated with the embolus, where it continues to inhibit lysis, whereas TXA eventually diffuses out of the embolus, allowing lysis to ensue.

The role of the thrombin receptor tethered ligand hypothesis in mediating the mitogenic responses of cells to thrombin was explored. We have found that small (5-14 amino acid) peptides corresponding to the proposed amino terminus of thrombin activated human and hamster thrombin receptors are mitogenic for the Chinese hamster fibroblast cell line, CCL39. Hirudin and hirugen block the mitogenic effects of thrombin but not the activity of the agonist peptides. Pertussis toxin treated cells do not respond to either alpha-thrombin or the agonist peptides. The data support the idea that the thrombin receptor on CCL39 cells, which is homologous to the thrombin receptor on human platelets, is capable of transmitting mitogenic signals by a mechanism consistent with the tethered ligand hypothesis.