Effect of bradykinin metabolism inhibitors on evoked hypotension in rats: rank efficacy of enzymes associated with bradykinin-mediated angioedema.

BACKGROUND AND PURPOSE: Inhibition of bradykinin metabolizing enzymes (BMEs) can cause acute angioedema, as demonstrated in a recent clinical trial in patients administered the antihypertensive, omapatrilat. However, the relative contribution of specific BMEs to this effect is unclear and confounded by the lack of a predictive pre-clinical model of angioedema. EXPERIMENTAL APPROACH: Rats were instrumented to record blood pressure and heart rate; inhibitors were infused for 35 min and bradykinin was infused during the last 5 min to elicit hypotension, as a functional marker of circulating bradykinin and relative angioedema risk. KEY RESULTS: In the presence of omapatrilat bradykinin produced dose-dependent hypotension, an effect abolished by B(2) blockade. In the presence of lisinopril (ACE inhibitor), but not candoxatril (NEP inhibitor) or apstatin (APP inhibitor), bradykinin also elicited hypotension. Lisinopril-mediated hypotension was unchanged with concomitant blockade of NEP or NEP/DPPIV (candoxatril+A-899301). However, hypotension was enhanced upon concomitant blockade of APP and further intensified in the presence of NEP inhibition to values not different from omapatrilat alone. CONCLUSIONS AND IMPLICATIONS: We demonstrated that bradykinin is degraded in vivo with an enzyme rank-efficacy of ACE>APP>>NEP or DPPIV. These results suggest the effects of omapatrilat are mediated by inhibition of three BMEs, ACE/APP/NEP. However, dual inhibition of ACE/NEP or ACE/NEP/DPPIV elicits no increased risk of angioedema compared to ACE inhibition alone. Thus, novel BME inhibitors must display no activity against APP to avoid angioedema risk due to high prevalence of ACE inhibitor therapy in patients with diabetes and cardiovascular disease.

The prostaglandin analogs, misoprostol and SC-46275, potently inhibit cytokine release from activated human monocytes.

Inflammatory mediator release is one of the body's responses to tissue injury and inflammation. These mediators, such as interleukin-1 beta (I1-1 beta), tumor necrosis factor (TNF-alpha), and products of arachidonic acid metabolism, are themselves proinflammatory. Purified human monocytes stimulated in vitro with E. coli-derived lipopolysaccharide (LPS) will release these key cytokines along with various other eicosanoid mediators. Monocytes incubated with LPS and the prostaglandin E-1 analog, misoprostol, released significantly lower levels of cytokines compared to monocytes incubated with LPS alone. Eicosanoid release was also affected by misoprostol. SC-46275, a more potent mucosal protective PGE1 analog, also altered the release of cytokines and eicosanoids from human monocytes. However SC-46275 inhibited I1-1 beta release with an IC50 value of 9 microM compared to 75 microM for misoprostol. SC-46275 and misoprostol both inhibited TNF-alpha release. These data suggest there is a potential immunomodulatory role for prostaglandin analogs in the therapeutic treatment of inflammatory diseases such as ulcerative colitis, Crohn's disease, and autoimmune inflammatory diseases of the central nervous system.

Pharmacological activity of the second generation leukotriene B4 receptor antagonist, SC-53228: effects on acute colonic inflammation and hepatic function in rodents.

Inflammatory bowel disease is a chronic inflammatory disorder of the gastrointestinal tract that includes ulcerative colitis and Crohn's disease. Leukotriene B4 is thought to be a prominent proinflammatory mediator in these diseases, in that leukotriene B4 levels are increased in the colonic mucosa of inflammatory bowel disease patients and there is increased polymorphonuclear leukocyte infiltration of these tissues. SC-53228 [(+)-(S)-7-[3-[2(-cyclopropylmethyl)-3-methoxy-4- [(methylamino)carbonyl]phenoxy]propoxy]-3,4-dihydro-8-propyl-2H-1- benzopyran-2-propanoic acid], a second generation LTB4 receptor antagonist, was evaluated for therapeutic efficacy in a rodent model of acute colonic inflammation induced by short chain organic acids, as well as for effects on rodent liver. When given intracolonically to mice, SC-53228 inhibited neutrophil infiltration, assessed by myeloperoxidase (MPO) levels, with an ED50 value of 9 +/- 1.2 mg/kg. When given by gavage, SC-53228 inhibited neutrophil influx in colitic mice with an ED50 value of 30 mg/kg. These results were also confirmed histologically. Furthermore, high dose oral SC-53228 treatment had no effect on liver cytochrome P-450 content, fatty acyl CoA oxidase or liver weight in rats and mice. Together, these data suggest that SC-53228 may be efficacious orally and locally, as well as safe for use in trials for the medical management of IBD.

Identification and characterization of rhesus macaque interleukin-8.

To establish a direct link between IL-8 and inflammation in vivo, we first isolated the gene encoding rhesus macaque IL-8. The open reading frame directs the translation of a 101 amino acid (aa) precursor, which is 94% identical to human IL-8. Rhesus IL-8 was expressed in bacteria and purified to homogeneity with ion-exchange chromatography. Pure rhesus IL-8 was biologically active as measured by its ability to bind specifically to either rhesus (Kd = 0.5 nM) or human (Kd = 2 nM) IL-8 receptors and to promote in vitro chemotaxis of rhesus (EC50 = 2 nM) or human neutrophils (EC50 = 4 nM). Moreover, a mouse monoclonal antibody, DM/C7, which neutralizes human IL-8 activity, also recognized and neutralized (IC50 = 0.5-3.0 microgram/ml) rhesus IL-8 in vitro. Systemic administration of DM/C7 completely inhibited the dermal inflammation of rhesus ears induced by the external application of phorbol myristoyl acetate. These observations reveal that rhesus IL-8 is structurally and functionally similar to human IL-8 and suggests that IL-8 plays a prominent role in a primate model of inflammation.

Antiinflammatory effects of second-generation leukotriene B4 receptor antagonist, SC-53228: impact upon leukotriene B4- and 12(R)-HETE-mediated events.

Leukotriene B4 (LTB4) and 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE] are proinflammatory products of arachidonic acid metabolism that have been implicated as mediators in a number of inflammatory diseases. When injected intradermally into the guinea pig. LTB4 and 12(R)-HETE elicit a dose-dependent migration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxyl]-3,4-dihy dro-8-propyl-2H - 1-benzopyran-2-carboxylic acid), a first-generation LTB4 receptor antagonist, inhibited the chemotactic actions of LTB4 when given orally with an ED50 value of 1.7 mg/kg. The second-generation LTB4 receptor antagonist, SC-53228 [(+)-(S)-7-(3-(2-(cyclopropylmethyl)-3-methoxy-4- [(methylamino)carbonyl]phenoxy)propoxy)-3,4-dihydro-8-propyl-2H-1- benzopyran-2-propanoic acid], inhibited LTB4-induced chemotaxis when given intragastrically with an ED50 value of 0.07 mg/kg. Furthermore, SC-53228 inhibited 12(R)-HETE-induced granulocyte chemotaxis with an oral ED50 value of 5.8 mg/kg. When dosed orally over a range of 0.03-100 mg/kg, SC-53228 gave Cmax plasma concentrations of 0.015-41.1 micrograms/ml. SC-53228 inhibited LTB4-primed membrane depolarization of human neutrophils with an IC50 value of 34 nM. As a potent LTB4 receptor antagonist, SC-53228 may well have application in the medical management of disease states such as asthma, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis, and psoriasis, in which LTB4 and/or 12(R)-HETE are implicated as inflammatory mediators.

Interleukin 8 and mast cell-generated tumor necrosis factor-alpha in neutrophil recruitment.

In the reverse passive Arthus reaction in mouse skin and immune injury of mouse dermal basement membrane, neutrophil (PMN) infiltration in mast cell deficient WBB6F1-W/Wv (W/Wv) mice was only 40% of that in WBB6F1-(+)/+ (+/+) mice that had a normal mast cell repertoire. An anti-tumor necrosis factor-alpha (TNF-alpha) monoclonal antibody (mAb) decreased PMN infiltration by 35-80% in +/+ but not W/Wv mice. In addition, an anti-human interleukin-8 (IL-8) MAb, DM/C7, inhibited PMN infiltration of the skin induced by either intradermal administration of recombinant human IL-1 beta or immune complex deposition. In both models of immune complex injury, DM/C7 reduced PMN infiltration by 40-60% in +/+ mice but not W/Wv mice. PMN infiltration and the sensitivity of this infiltration to anti-TNF-alpha or DM/C7 MAb in W/Wv mice whose mast cell population had been restored was indistinguishable from the influx observed in +/+ mice. These data suggest that TNF-alpha, IL-8, and mast cells play a fundamental role in PMN recruitment following immune complex injury.

Leukotriene B4-induced granulocyte trafficking in guinea pig dermis. Effect of second-generation leukotriene B4 receptor antagonists, SC-50605 and SC-51146.

Leukotriene B4 (LTB4) is a proinflammatory product of arachidonic acid metabolism that has been implicated as a mediator in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB4 elicits a dose-dependent migration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-p ropyl-2H-1-benzopyran-2-carboxylic acid), a first-generation LTB4 receptor antagonist inhibited the chemotactic actions of LTB4 when coadministered into the dermal site and when given orally with ED50 values of 340 ng and 1.7 mg/kg, respectively. The second-generation LTB4 receptor antagonists SC-50605 (7-[3-[2(cyclopropylmethyl)-3-methoxy-4-(4-thiazolyl)phenoxy]propoxy]- 3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid) and SC-51146 (7-[3-[2(cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl] phenoxy]propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-propanoic acid) inhibited LTB4-induced chemotaxis when coadministered with ED50 values of 70 ng and 32 ng, respectively, and when given intragastrically with ED50 values of 0.10 and 0.09 mg/kg, respectively. SC-41930, SC-50605, and SC-51146 had oral durations of action of 5.5, 15, and 21 h, respectively. These potent, LTB4 receptor antagonists may well have application in the medical management of disease states such as asthma, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis, and psoriasis, where LTB4 is implicated as an inflammatory mediator.

Inflammatory mediator changes in cotton-top tamarins (CTT) after SC-41930 anti-colitic therapy.

Use of the CTT model provides insight into the inflammatory mediator contribution in the pathogenesis of idiopathic colitis. To evaluate anti-colitic efficacy, the leukotriene B4 receptor antagonist and anti-inflammatory agent, SC-41930, was administered (10 mg/kg BW by gavage BID) for 8 weeks to CTTs with histologically confirmed persistent and defined active colitis. The inflammatory mediators LTB4, PGE2, TXB2, and PAF were assayed in colonic dialysate that was collected after 1 1/2 h from four CTTs pre-, mid-, and post-treatment, frozen at -70 degrees C, and analyzed by RIA after HPLC purification. LTB4 levels were lower at mid- and post-treatment and had little inter-animal variation post-treatment. PGE2 and PAF levels were elevated during SC-41930 treatment, but there was a trend towards lower thromboxane B2 levels. Reduced LTB4 (PMN degranulation and chemotaxis) and increased PGE2 (mucosal-protective effect) may, in part, explain the observed efficacy of SC-41930 in active tamarin colitis.

Mucosal protective activity of prostaglandin analogs in rodent colonic inflammation.

The mucosal protective prostaglandin analogs misoprostol, enisoprost, and SC-46275 (the 17E-18-cyclopentenyl analog of enisoprost) were tested in mouse and rat colitis induced by the intrarectal instillation of dilute acetic acid. Colitis was assessed by histology and colonic levels of myeloperoxidase (a neutrophil marker enzyme). When given as enemas 30 min ahead of colitis induction, 15(R)-15-methyl-PGE2 (arbaprostil) and 15(S)-15-methyl-PGE1 were inactive; however, misoprostol, enisoprost, and SC-46275 protected against colonic inflammation with ED50 values of 24, 12 and 1.3 micrograms/kg, respectively, in rats and 11, 5, and 1 micrograms/kg, respectively, in mice. These compounds may have utility in the medical management of human inflammatory bowel disease.

Optical isomers of a leukotriene B4 antagonist have differential effects on granulocyte diapedesis in the guinea pig dermis.

Leukotriene B4 (LTB4) is a proinflammatory product of arachidonic acid metabolism that has been implicated in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB4 has been shown to elicit a dose-dependent infiltration of granulocytes as assessed by the level of the neutrophil marker enzyme myeloperoxidase. SC-41930 [7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid] is a potent LTB4 receptor antagonist. When compounds were coadministered along with LTB4 (35 ng) into the dermal site, racemic SC-41930, (+)-SC-41930, and (-)-SC-41930 each inhibited granulocyte accumulation with ED50 values of 340 +/- 30, 98 +/- 5.7, and 1000 +/- 142 ng, respectively; when given intravenously inhibited with ED50 values of 0.5 +/- 0.06, 0.3 +/- 0.04, and 1.4 +/- 0.19 mg/kg, respectively; and when given intragastrically inhibited with ED50 values of 1.7 +/- 0.20, 1.4 +/- 0.23, and 3.0 +/- 0.41 mg/kg, respectively.

Effects of the prostaglandin analogue misoprostol on inflammatory mediator release by human monocytes.

The effect of misoprostol (M) on IL-1 beta, TNF-alpha, and lipid mediator release (assessed by RIA) by adherent (assessed by electron microscopy) human monocytes were studied in vitro. Human monocytes stimulated with E. Coli-derived lipopolysaccharide showed an increase in both IL-1 beta and TNF-alpha release. Incubation of the monocytes with LPS and M (18 hrs.), resulted in a reduction of both IL-1 beta and TNF-alpha levels. Leukotriene B4 levels did not increase in response to LPS or M. LPS also caused an increase in thromboxane (TXB2). M decreased TXB2 levels. 6-keto PGF1 alpha (6KP). Incubation with LPS and M stimulated release. LPS caused an increase in PGE2 levels. M (100 microM) caused an increase in PGE2 levels, M (1 microM) had no effect on PGE2. These data suggest a possible immunomodulatory role for misoprostol in inflammatory diseases.

The antiinflammatory agent SC-41930 inhibits granulocyte infiltration of the rodent dermis induced by 6-trans-leukotriene B4.

Granulocyte diapedesis in response to the generation of defined chemotaxins such as leukotriene B4 (LTB4), 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE], C5a, platelet activating factor and others is a hallmark of the inflammatory process that is thought to contribute to the tissue pathology seen in a number of diseases. 6-trans-LTB4 arises through the myeloperoxidase (MPO)-dependent metabolism of sulfidopeptide leukotrienes and through the action of 5-lipoxygenase on 12(R)-HETE. The intradermal (i.d.) injection of 6-trans-LTB4 induces a dose and time dependent influx of granulocytes into the guinea-pig (Hartley) dermis. When various doses of the LTB4 receptor antagonist and antiinflammatory agent, SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro- 8-propyl-2H-1-benzopyran-2-carboxylic acid) given 30 min ahead of i.d. injection of 6-trans-LTB4 (10 micrograms/i.d. site), granulocyte infiltration, as assessed by dermal levels of the neutrophil marker enzyme MPO was inhibited with an ED50 value of 9.8 mg/kg in the guinea-pig. When various doses (10-25 micrograms) 6-trans-LTB4 were injected in the mouse (CD-1) dermis, there was a dose-related increase in granulocyte accumulation at 4 h. Furthermore when mice were pretreated (-30 min) with SC-41930 (1 mg/kg) orally, the trafficking of granulocytes was inhibited (p less than .01) as assessed by dermal MPO levels. SC-41930 orally inhibits 6-trans-LTB4-induced granulocyte accumulation in the guinea-pig more potently than against the response to 12(R)-HETE(ED50:13.4 mg/kg) but less potently than against LTB4 (ED50:0.6 mg/kg). These multiple activities may contribute to this compound's potential as an inflammatory agent.

Effect of the leukotriene B4 receptor antagonist, SC-41930, on experimental allergic encephalomyelitis (EAE) in the guinea pig.

The accepted model for the human demyelinating disease, multiple sclerosis (MS), is experimental allergic encephalomyelitis (EAE). We assessed the ability of SC-41930(7-[3(4-acetyl-3-methoxy-2-propyl-phenoxy)-propoxy]- 3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxyl acid), to modulate the symptoms of acute EAE generated in guinea pigs. Animals were pretreated with SC-41930 (20 mg/kg, i.p.) for two days followed by thrice-weekly maintenance. At day 52, a significant number of the SC-41930-treated animals were alive as compared to EAE alone. Control animals had an increase in body weight while EAE animals lost over 20% (p less than 0.5) of their body weight by day 18. SC-41930-treatment significantly reduced, but did not completely inhibit the cachectic response. The results indirectly implicate LTB4 in the pathogenesis of EAE. Agents that modify this model be useful in the treatment of human MS.

Inflammatory mediators in cotton-top tamarins (CTT) with acute and chronic colitis.

Spontaneous colitis in CTT's presents cytological characteristics similar to chronic ulcerative colitis in humans, e.g. inflammatory cell infiltrate and crypt abscesses. To better characterize CTT colitis as a potential model for human inflammatory bowel disease (IBD), inflammatory mediators identified in colonic tissue of human IBD patients and/or experimental colitis models were assayed. Inflammatory mediator changes in plasma and colon from tamarins with acute (n = 10) and chronic (n = 10) colitis (by mucosal biopsy) were assayed by RIAs. Similar inflammatory mediators were found in the CTT's with acute colitis. In the plasma, PAF and PGE2 levels were lower in acute colitis CTT's, no LTB4 was detected, and histamine levels were not different from chronic colitic animals. In the colon, myeloperoxidase and interleukin-1 beta were significantly higher in acute colitis, PGE2 and LTB4 were higher but not significantly, and PAF was not different from chronic CTT's. These data suggest that a combination of events are occurring in the pathogenesis of tamarin colitis that involves some of the same mediators that are found in the human disease and in other experimental models. The importance of these findings to human IBD remains for further investigation; however, the spontaneous primate model offers an exciting approximation of the disease development and merits further investigation for understanding the pathogenesis of human IBD as well as to aid in development of targeted therapeutics.

Modulation of the chemotactic properties of complement fragments C5a and C3 by the anti-inflammatory agent, SC-41930.

Cleavage of the fifth component of complement yields C5a, a potent neutrophil (PMN) and eosinophil chemoattractant, and modulator of microvascular permeability. Similarly, but to a lesser degree, C3 increases vascular permeability and histamine release. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl- 2H-1-benzopyran-2-carboxylic acid), an orally-active antiinflammatory agent was tested in an in vivo model of dermal PMN chemotaxis induced by r-hu-C5a and hu-C3. Intradermal injection of C5a in the guinea pig resulted in a significant dose-dependent influx of PMNs at 4 hours as assessed by the dermal levels of myeloperoxidase (MPO). SC-41930 (20 mg/kg) given orally to guinea pigs with intradermal injections of 1 microgram C5a significantly (p less than 0.001) reduced dermal MPO content. SC-41930 was less potent against C3, requiring 40 mg/kg to significantly reduce dermal MPO levels. Agents such as SC-41930, which nullify complement's proinflammatory properties, may well have therapeutic potential.

6-trans-leukotriene B4 is a neutrophil chemotaxin in the guinea pig dermis.

The products of the 5- and 12-lipoxygenase (5-LO, 12-LO) pathways of arachidonic acid metabolism are implicated as proinflammatory mediators in a number of disease states. 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE] is present in large quantities in human psoriatic lesional skin and can be further metabolized by 5-LO to 5(S), 12(R)-dihydroxy-(6E,8Z,10E,14Z)-eicosatetraenoic acid (6-trans-LTB4). Furthermore, leukotriene B4 (LTB4) and the sulfidopeptide leukotrienes (LTC4, LTD4) can be transformed to 6-trans-LTB4. When injected into the guinea pig dermis, 6-trans-LTB4 (1.0, 10.0, 20.0 micrograms/intradermal site) caused a significant (P less than 0.02) infiltration of polymorphonuclear leukocytes (PMN) at 4 hr as assessed by histology and the levels of the PMN marker enzyme myeloperoxidase. 6-trans-LTB4 is a more potent PMN chemoattractant than 12(R)-HETE in the guinea pig dermis but is far less potent than LTB4. Pharmacological interdiction of leukotriene production or receptor binding should take into account the proinflammatory activity of 6-trans-LTB4.

Inflammation of guinea pig dermis. Effects of leukotriene B4 receptor antagonist, SC-41930.

Neutrophil (PMNL) infiltration is a prominent feature of human psoriasis. Psoriatic skin lesions contain abnormally high amounts of leukotriene B4 (LTB4), itself a potent PMNL chemoattractant both in vivo and in vitro. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid), an orally active LTB4 receptor antagonist, was tested topically in models of skin inflammation induced by 200 nmol of the calcium ionophore A23187 or 200 micrograms phorbol-12-myristate-13-acetate (PMA) applied topically to the guinea pig ear as assessed by ear weight, levels of the PMNL marker enzyme myeloperoxidase (MPO), and histological examination (PMA model) at 4 and 18 h respectively. When coapplied topically with A23187 or PMA, SC-41930 significantly inhibited epidermal inflammation with ED50 values of 0.6 and 4 mg, respectively. SC-41930 treatment also was associated with lowered dermal LTB4 levels in both models. The PMA-induced skin inflammation model also was assessed histologically and revealed acanthosis, edema, PMNL infiltration, and rete ridge prominence as long as 96 h after a single application that was completely inhibited by SC-41930 topical coapplication. Furthermore, oral treatment (40 mg/kg) significantly reduced edema and inflammatory cell infiltration in both models. These models possess many of the characteristics of human psoriasis, and agents such as SC-41930 that demonstrate activity in these models may well have therapeutic utility in the treatment of human psoriasis.