Mast cell derived heparin activates the contact system: a link to kinin generation in allergic reactions

Contact activation occurs when plasma comes in contact with negatively charged manmade surfaces but no substance that initiates contact activation in vivo has been identified. We have isolated a mast cell heparin proteoglycan (MC-HepPG) from a Furth mouse mastocytoma-derived cell line that is analogous to human tissue-type mast cell HepPG. This material and other glycosaminoglycans (GAGs) were tested for their ability to accelerate the reciprocal activation of factor XII and prekallikrein and the autoactivation of factor XII. Quantitative analysis showed the MC-HepPG to be as active as dextran sulfate on a weight basis; hog intestine heparin, dermatan sulfate, keratan polysulfate and chondroitin sulfate C were less active, other sulfated polysaccharides were essentially inactive. Incubation of MC-HepPG in 1:4 diluted plasma resulted in complete cleavage of high molecular weight kininogen in a factor XII-dependent reaction. All of the MC-HepPG dependent reactions described above were inhibited by preincubation of MC-HepPG with heparinase I and II but not by pretreatment with heparitinase, chondroitinase ABC or the serine protease inhibitor aPMSF thus indicating that heparin proteoglycan is indeed acting as an initiating 'surface'. We analysed the proteoglycan preparation by HPLC gel filtration. Fractions spanning a molecular weight range of > 400000-8000 were active initiators. Comparison of the chromatograms obtained before and after cleavage of GAG side chains from the protein core suggested that dissociated GAGs in the MW range 69000-17000 are the most active species rather than the complete proteoglycan. MC-HepPG GAGs therefore represent a physiologic macromolecule with activity comparable to non-physiological surfaces in a purified system and with the capability to induce activation of the contact system in diluted plasma. Its ability to promote kinin generation links cellular and humoral inflammatory responses in the perivasculature and provides a possible explanation for the elevated kinin levels observed after allergen exposure.

ATP modification of serotonin-induced contraction of the rat pulmonary artery

Serotonin (5HT) and ATP are simultaneously released from activated platelets at the site of vascular injury and are hypothesized to play a significant role in hemostasis. Our laboratory investigated the modulation of vascular contraction of arterial ring segments by 5HT plus ATP as a model of the potential regulation of localized vascular tone by platelet releasates in regions of arterial damage. This study expands our focus on how these two vasoactive components, released from platelet dense granules, regulate vascular tone. 5HT- and 5HT analog-induced vasoconstrictions were measured in the presence or absence of ATP and ATP analogs with intact or deendothelialized rat pulmonary arterial ring segments suspended in organ baths. The possible presence of 5HT2 and 5HT1A receptor types in the rat pulmonary artery was demonstrated by vasoconstrictions induced by 5HT and (+)-8-hydroxy-2-(di-N-propylamino) tetralin hydrobromide (DPAT). The DPAT response was only 30%-50% of that induced by comparable concentrations of 5HT. The 5HT-induced contraction was inhibited by the 5HT2 antagonist, ketanserin. ATP equally relaxed 5HT and DPAT contracted tissue while the P2X agonist, alphabeta-methylene ATP, increased the contracted state of DPAT-treated arteries to a significantly greater extent than observed with 5HT. The P2y agonist, 3'-O-(4-benzoyl)benzoyl ATP (BzATP), the P2X agonist betagamma-methylene ATP, and ATP all relaxed 5HT-induced contractions to similar levels under a number of physiological conditions. The final level of 5HT-induced tissue contraction was the same whether ATP was added prior to, after, or simultaneously with 5HT. ATP and the phosphodiesterase inhibitor, theophylline, inhibited 5HT-induced vasoconstriction in an additive fashion. The ATP effects were endothelium dependent, while the inhibition by theophylline was not. The distribution of 5HT and ATP receptor types, as indicated by these and numerous other studies, appears to vary within different regions of the cardiovascular system. Extracellular ATP can synergistically enhance or inhibit 5HT-contracted blood vessels differentially at localized regions, which would significantly impact on localized vascular tone, and this in turn may modulate hemostasis and thrombosis.

Glomerular mesangial cell altered contractility in high glucose is Ca2+ independent

In diabetes, loss of renal arteriolar smooth-muscle cell contractility leads to intraglomerular hypertension. In glomeruli isolated from streptozotocin (STZ)-induced diabetic rats, the mesangial cells (smooth muscle-like) display loss of contractile responsiveness to angiotensin II. This study examines the mechanistic relationship between altered mesangial cell contractility and vasopressor hormone-stimulated Ca2+ signaling in high glucose. Glomeruli were isolated from normal or STZ-induced diabetic rats to observe ex vivo mesangial cell contractile function. Also, rat mesangial cells were cultured (10-20 passages) in normal (5.6 mmol/l) or high (10-25.6 mmol/l) glucose for 1-5 days. Reduction of glomerular volume and decreased planar surface area of cultured mesangial cells in response to vasoconstrictor stimulation over 60 min were measured by videomicroscopy and personal computer-based morphometry. Contraction of glomeruli isolated from STZ-administered rat in response to endothelin (ET)-1 (0.1 mumol/l) or the Ca2+ ionophore A23187 (5 mumol/l) was impaired significantly compared with that in normal glucose. In the presence of arginine vasopressin (AVP) (1.0 mumol/l) or ET-1 (0.1 mumol/l), mesangial cells demonstrated a dose-dependent loss of contractile response to increasing glucose concentrations (5.6-25.6 mmol/l) within 24 h of high-glucose exposure, which was sustained for 5 days. Mesangial cells in high glucose were consistently smaller in size compared with those in normal glucose. Mesangial cells were preloaded with myo-[2-3H]inositol and intracellular [3H] inositol phosphate release in response to AVP (1.0 mumol/l) was analyzed by Dowex chromatography. Comparing cells in normal (5.6 mmol/l) verus high (25.6 mmol/l) glucose, we observed no significant difference in stimulated inositol phosphate levels from 10 to 60 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Assembly of the human plasma kinin-forming cascade along the surface of vascular endothelial cells

The generation of bradykinin by contact activation requires autoactivation of factor XII (Hageman factor) upon initiating surfaces, conversion of prekallikrein to kallikrein, and digestion of high-molecular-weight (HMW) kininogen. Endothelial cells have a high-affinity receptor that binds either HMW kininogen or factor XII in a zinc-dependent interaction, and activation of factor XII can occur along this surface to initiate kinin formation. Tissue injury, exposure of proteoglycans, or release of mast cell heparin will markedly accelerate these reactions. The bradykinin released binds to endothelial cell B-2 receptors along the inner surface of blood vessels which results in dilatation and increased vascular permeability.

Clinical utility and validation of emerging biochemical markers for mammary adenocarcinoma

The clinical utilities of the emerging biochemical markers for mammary adenocarcinoma CA 15-3, CA 549, CA M26, CA M29, and MCA (mucin-like carcinoma-associated antigen) were assessed by a formal rating according to six desirable marker characteristics. All five indicators similarly have good specificities but limited sensitivities. As a consequence, these markers mainly meet just two desirable criteria: their frequency and degree of expression reflect tumor burden and prognosis, and they may correlate with therapeutic results. The validation of these assay properties by clinical trials was evaluated by another rating system, designed to assess proband sample selection, restrictions on allowable observations, and choice of statistical descriptors. By these benchmarks, the estimates of the prior probabilities of test outcome (sensitivity and specificity) are reasonably definitive, but conclusive judgments about the posterior probabilities of test outcome ("predictive values") and about values and costs associated with testing are not possible. Three approaches to enhance the limited clinical utility of biochemical breast cancer markers are considered: shifts of the diagnostic decision threshold, marker panels, and sequential testing. However, none of these strategies improves the described performance characteristics.

Clinical utility and validation of emerging biochemical markers for mammary adenocarcinoma

The clinical utilities of the emerging biochemical markers for mammary adenocarcinoma CA 15-3, CA 549, CA M26, CA M29, and MCA (mucin-like carcinoma-associated antigen) were assessed by a formal rating according to six desirable marker characteristics. All five indicators similarly have good specificities but limited sensitivities. As a consequence, these markers mainly meet just two desirable criteria: their frequency and degree of expression reflect tumor burden and prognosis, and they may correlate with therapeutic results. The validation of these assay properties by clinical trials was evaluated by another rating system, designed to assess proband sample selection, restrictions on allowable observations, and choice of statistical descriptors. By these benchmarks, the estimates of the prior probabilities of test outcome (sensitivity and specificity) are reasonably definitive, but conclusive judgments about the posterior probabilities of test outcome ("predictive values") and about values and costs associated with testing are not possible. Three approaches to enhance the limited clinical utility of biochemical breast cancer markers are considered: shifts of the diagnostic decision threshold, marker panels, and sequential testing. However, none of these strategies improves the described performance characteristics.

Bradykinin generation by dialysis membranes: possible role in anaphylactic reaction

Several recent reports have described a high incidence of anaphylactic reactions in patients being dialyzed with high-flux membranes while simultaneously using angiotensin-converting enzyme inhibitors. Many of these reports implicate polyacrylonitrile (PAN) as the membrane commonly involved in these reactions. To elucidate potential mechanisms of these anaphylactic reactions, whether dialysis membranes can activate the Hageman factor-dependent (contact) pathways as assessed by the in vitro generation of activated Hageman factor (Hfa), as well as the formation of kallikrein and subsequent bradykinin generation was examined. Both cuprophane (CUP) and PAN membranes were able to activate Hageman factor and convert prekallikrein to kallikrein as measured by an ELISA against kallikrein-C1-inactivator complexes. Subsequently, the active kallikrein was able to cleave bradykinin from its endogenous substrate, high-molecular-weight kininogen. However, it was found that the PAN membrane consistently led to an earlier and significantly higher formation of Hfa and kallikrein when compared with CUP. Importantly, there was also a pronounced but transient generation of bradykinin by the PAN membrane, in contrast to slower bradykinin formation by CUP, with both normal and uremic blood. It was proposed that the early and vigorous bradykinin generation induced by the contact of blood with PAN could explain, in part, the pathogenesis of the reported anaphylactoid reactions.

Activation of factor XI in plasma is dependent on factor XII

The activation of factor XI initiates the intrinsic coagulation pathway. Until recently it was believed that the main activator of factor XI is factor XIIa in conjunction with the cofactor high molecular weight kininogen on a negatively charged surface. Two recent reports have presented evidence that in a purified system factor XI is activatable by thrombin together with the soluble polyanion dextran sulfate. To assess the physiological relevance of these findings we studied the activation of factor XI in normal and factor XII-deficient plasma. We used either kaolin/cephalin or dextran sulfate as a surface for the intrinsic coagulation pathway, tissue factor to generate thrombin via the extrinsic pathway, or the addition of alpha-thrombin directly. 125I-factor XI, added to factor XI-deficient plasma at physiologic concentrations (35 nmol/L), is rapidly cleaved on incubation with kaolin. The kinetics appear to be exponential with half the maximum cleavage at 5 minutes. Similar kinetics of factor XI cleavage are seen when 40 nmol/L factor XIIa (equal to 10% of factor XII activation) is added to factor XII-deficient plasma if an activating surface is provided. Tissue factor (1:500) added to plasma did not induce cleavage of factor XI during a 90-minute incubation, although fibrin formation within 30 seconds indicated that thrombin was generated via the extrinsic pathway. Adding 1 mumol/L alpha-thrombin (equivalent to 50% prothrombin activation) directly to factor XII deficient or normal plasma (with or without kaolin/cephalin/Ca2+ or dextran sulfate) led to instantaneous fibrinogen cleavage, but again no cleavage of factor XI was observable. We conclude that in plasma surroundings factor XI is not activated by thrombin, and that proposals of thrombin initiation of the intrinsic coagulation cascade are not supportable.

Effect of Neurotropin on the activation of the plasma kallikrein-kinin system

Bradykinin (BK), an important mediator of allergic reactions and pain induction, is released by the activation of the plasma kallikrein-kinin (K-K) cascade. Neurotropin is a biological material obtained from inflamed rabbit skin inoculated with vaccinia virus and is widely used clinically in Japan as an effective agent for these disorders. Since its mechanism of action is not clearly known, we have investigated the effects of Neurotropin on the human plasma K-K system. In dextran sulfate-activated plasma, Neurotropin inhibited the formation of BK, the cleavage of high molecular weight kininogen (HK) and the formation of kallikrein-C1 inhibitor and activated coagulation factor XII (FXIIa)-C1 inhibitor complexes. Experiments using purified enzyme of the K-K cascade indicated that Neurotropin inhibited surface-mediated activation of coagulation factor XII (FXII) and the activation of prekallikrein by FXIIa. Neurotropin also inhibited the binding of FXII and HK to the activating surface. These data suggest that the ameliorating effects of Neurotropin in allergic disorders and pain syndromes may be related to this ability to inhibit activation of the K-K cascade and consequently the formation of BK.

Continuous infusion gallium nitrate for patients with advanced refractory urothelial tract tumors

A Phase I-II trial of gallium nitrate was conducted in 40 patients with bidimensionally measurable urothelial tract tumors who had failed to respond to combination chemotherapy with methotrexate, vinblastine, doxorubicin, and cisplatin. Partial responses were observed in 4 of 23 patients (17.4%) who received 350 mg/m2/d or more for 5 days by continuous intravenous infusion. In two additional patients who received 350 mg/m2/d or more, a minor response and a mixed response were observed. The median duration of response was 4 months (range, 2 to 8 months). A dose-response relationship was suggested because no responses were observed in 17 patients who received less than 350 mg/m2/d. Myelosuppression was minimal. The dose-limiting toxic reaction was a reversible optic neuropathy that occurred in 3 of 11 patients who received 400 mg/m2/d. Further evaluation of infusional gallium nitrate is warranted in patients with urothelial tract malignant tumors.

Chronic abdominal pain in adolescents

Although there are very few prospective studies of CAP, organic causes of the problem are misdiagnosed probably in less than 5% of adolescents. Response to treatment seems to be better in males who have had signs and symptoms for less than 6 months, and is rather poor for patients with complaints exceeding 2 years. An organized nomenclature is necessary for classifying dysfunctional disorders, and physicians must recognize that these patients represent a heterogeneous population. In general, adequate data for the number of the adolescent population affected by these diseases is not available, so that physicians are still required to depend to a large extent on speculation and anecdotal information in assessing and managing these patients.

Clinical pharmacology of the neuromuscular blocking agents

Neuromuscular blocking agents are among the most commonly used drugs during general anesthesia. They compete with acetylcholine and interfere with the transmission of nerve impulses resulting in skeletal muscle relaxation. Based on their mechanism of action, neuromuscular blocking agents are classified as either depolarizing or nondepolarizing. Succinylcholine is a short-acting depolarizing agent. Commonly used nondepolarizing agents are curare (long-acting), pancuronium (long-acting), atracurium (intermediate-acting), and vecuronium (intermediate-acting). Neuromuscular blocking agents are used clinically to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery. This article provides an overview of the physiology of the neuromuscular transmission and summarizes our current knowledge on the use of these agents during general anesthesia.

Cutaneous photosensitivity and coproporphyrin abnormalities in the Alagille syndrome

Porphyria cutanea tarda-like blistering, fragility, and scarring of light-exposed skin was observed in four children with the Alagille syndrome. Abnormally elevated levels of serum porphyrins, of which coproporphyrin isomers I and III together accounted for 50%-89% of the total, were found in these four children but also in three other children with the Alagille syndrome without such skin lesions. The ratio for isomer I to III for total serum coproporphyrin concentration was determined in six cases; the concentration of isomer I was greater than or equal to that of isomer III in each case. Urinary total porphyrin excretion was found to be elevated in six of the seven cases, with 72% +/- 8% occurring as coproporphyrins I and III. The ratio for urinary coproporphyrin I to III was greater than or equal to 1 in six of these patients, the reverse of the typical normal isomer distribution. Inasmuch as the presence or absence of photocutaneous lesions did not correlate with levels of porphyrins in serum or urine, other factors may be involved in the pathogenesis of the skin lesions.

Pathways of kinin formation and role in allergic diseases

We have developed new assays for the assessment of the plasma kinin forming system which have increased sensitivity and specificity. We utilize double-antibody ELISA assays for quantitation of complexes of activated Hageman factor-C1 inhibitor, kallikrein-C1 inhibitor, and kallikrein-alpha 2-macroglobulin which reflect activation of each enzyme. The fraction of cleaved high-molecular-weight kininogen is determined by immunoblotting using a monoclonal antibody to the light chain, and bradykinin is determined by radioimmunoassay. Activation of the Hageman factor-dependent pathway of kinin formation can occur when plasma is in contact with initiating surfaces or when C1 inhibitor function is diminished. The latter mechanism can occur in hereditary angioedema, in which the protein is absent or dysfunctional, or when plasma is diluted so that the effect of inhibitors is diminished and Hageman factor autoactivation is facilitated. Thus apparent "spontaneous" generation of bradykinin is seen upon incubation of plasma of hereditary angioedema patients under conditions in which normal plasma is unaffected. Studies of late-phase reactions have used a cutaneous model in which induced blisters are unroofed and challenged with antigen or buffer control using chambers which can be changed hourly. A time course of mediator release is obtained by assay of the blister fluids. Whereas most histamine is released during the first half hour, significantly elevated levels of activated Hageman factor and kallikrein complexes with C1 inactivator are seen in antigen-challenged sites between 4 and 6 hr. The presence of such complexes correlated with the presence of late-phase reactions rather than the histamine values or the magnitude of the immediate reaction. Although late-phase reactions are characterized by cellular infiltration, release of a variety of inflammatory low-molecular-weight mediators, and deposition of fibrin, activation of the Hageman factor-dependent pathway of kinin formation is also likely to be contributory.

The autoactivation of factor XII (Hageman factor) induced by low-Mr heparin and dextran sulphate. The effect of the Mr of the activating polyanion

Human Factor XII is known to undergo autoactivation in the presence of dextran sulphate of Mr 500,000. We have now studied the dependence of this reaction on the Mr of the dextran sulphate by using fractions resolved by gel filtration. We have found that autoactivation can be induced by dextran sulphate fractions with Mr as low as 3000, and there is a marked dependence of the rate constant of autoactivation on the Mr value. Fractions with Mr below 8000 gave very low rates of autoactivation; there was a sharp increase in the rate obtained when the Mr of the dextran sulphate was greater than 10,000. Various preparations of heparin were also able to support the autoactivation of Factor XII and gave a very similar relationship between molecular size and reaction rate. The data provide support for the hypothesis that the mechanism by which the 'surface' acts in contact activation involves the presence, on the same particle, of multiple binding sites for the proteins.