Heparin and growth control of vascular cells

A sensitive ELISA for the detection of bovine crude heparin in porcine heparin

Heparin is an effective anticoagulant drug which has been purified for decades from bovine or porcine tissues. However, with the emergence of BSE, heparin purification is today restricted to porcine intestinal mucosa. To control the origin of crude heparins, polyclonal antibodies were raised against bovine contaminants. These antibodies were used to develop one sandwich and two competitive indirect ELISAs. Optimal results were obtained with competitive indirect ELISA, using bovine crude heparin for the coating and anti-bovine crude heparin as a detector antibody. The detection limit of the assay was 1 ppm of bovine crude heparin in a porcine heparin. Taking into account the variability of the background obtained for 10 crude and 9 pure porcine heparins from known origin, the detection level was 5 ppm. Ovine and caprine crude heparins cross-reacted slightly (6-17 ppm).

Binding of the NG2 proteoglycan to kringle domains modulates the functional properties of angiostatin and plasmin(ogen)

Interactions of the developmentally regulated chondroitin sulfate proteoglycan NG2 with human plasminogen and kringle domain-containing plasminogen fragments have been analyzed by solid-phase immunoassays and by surface plasmon resonance. In immunoassays, the core protein of NG2 binds specifically and saturably to plasminogen, which consists of five kringle domains and a serine protease domain, and to angiostatin, which contains plasminogen kringle domains 1-3. Apparent dissociation constants for these interactions range from 12 to 75 nm. Additional evidence for NG2 interaction with kringle domains comes from its binding to plasminogen kringle domain 4 and to miniplasminogen (kringle domain 5 plus the protease domain) with apparent dissociation constants in the 18-71 nm range. Inhibition of plasminogen and angiostatin binding to NG2 by 6-aminohexanoic acid suggests that lysine binding sites are involved in kringle interaction with NG2. The interaction of NG2 with plasminogen and angiostatin has very interesting functional consequences. 1) Soluble NG2 significantly enhances the activation of plasminogen by urokinase type plasminogen activator. 2) The antagonistic effect of angiostatin on endothelial cell proliferation is inhibited by soluble NG2. Both of these effects of NG2 should make the proteoglycan a positive regulator of the cell migration and proliferation required for angiogenesis.

Effects of chronic heparin administration on coronary vascular adaptation to hypertension and ventricular hypertrophy in sheep

BACKGROUND

Hypertension decreases myocardial perfusion capacity in adults for several reasons, including insufficient coronary angiogenesis with left ventricular (LV) hypertrophy, arteriolar hypertrophy, and altered vasomotion. Heparin influences growth factors that promote angiogenesis and vasodilation and inhibit arteriolar wall thickening.

METHODS AND RESULTS

Adult sheep were given heparin 200 U/kg body wt SC twice daily throughout 6 weeks of LV and coronary hypertension from a progressively constricted ascending aortic band (n=14). They were compared with untreated sheep with (n=13) and without (n=13) aortic stenosis. After 6 weeks, maximum myocardial perfusion was measured during adenosine infusion in the conscious state by the microsphere method. Sheep with aortic stenosis had less maximum coronary flow per gram, less conductance reserve, and thicker arteriolar walls in the LV and nonhypertrophied right ventricle. Capillary density decreased in the LV endomyocardium and remained unchanged in the right ventricle. Heparin-treated sheep had significant partial normalization of coronary conductance reserve and maximum perfusion in both ventricles and capillary density in the LV endomyocardium. Arteriolar wall thickness was unchanged. Compared with untreated sheep with aortic stenosis, in heparin-treated sheep LV FGF-2 protein increased 2-fold, whereas FGF-2 mRNA remained unchanged. VEGF mRNA and protein increased 3-fold and 1.4-fold, respectively, whereas TGF-beta(1) mRNA declined 3-fold.

CONCLUSIONS

Heparin administration during LV hypertension increases heparin-binding angiogenic factors FGF-2 and VEGF in the LV and ameliorates decreases in LV perfusion capacity and capillary density.

Carboxymethyl benzylamide sulfonate dextrans (CMDBS), a family of biospecific polymers endowed with numerous biological properties: a review

The functionalized dextrans termed carboxymethyl benzylamide sulfonate dextran (CMDBS) represent a family encompassing a wide range of polymers. These soluble macromolecular compounds, which are substituted with specific chemical functional groups, are designed to interact with living systems. By analogy with glycosaminoglycan heparin, a natural highly charged anionic polysaccharide that exerts a variety of biological effects, we postulated that CMDBS compounds also possess binding sites capable of specific interactions with biological constituents, depending on the overall composition of the polymer. The synthesis and heparin-like properties of these CMDBS have been extensively investigated. Thus, it appears that dextran derivatives can mimic the action of heparin in regard to its interactions with antithrombin and serine proteases involved in blood coagulation. Other derivatives interact with various components of the immune system or with adhesive proteins such as fibronectin in modulating the proliferation of Staphylococcus aureus. Because they are able to stimulate wound healing in various in vivo models, these polysaccharides may also constitute a family of tissue repair agents because of their protecting and potentiating effects with heparin binding growth factors. Moreover, dextran derivatives in contact with cells such as endothelial cells, smooth muscle cells, or tumoral cells can affect both cell proliferation and metabolism. It appears that these bioactive polymers are also efficient tools to investigate the precise mechanism of action of individual biological activities by contrasting their mode of action to that of heparin. In addition to their numerous biological properties and biospecificity, functionalized dextrans are relatively simple to manufacture and exempt of donor contaminant, which make them attractive in a variety of clinical applications.

Nitric oxide degradation of heparin and heparan sulphate

NO is a bioactive free radical produced by NO synthase in various tissues including vascular endothelium. One of the degradation products of NO is HNO2, an agent known to degrade heparin and heparan sulphate. This report documents degradation of heparin by cultured endothelial-cell-derived as well as exogenous NO. An exogenous narrow molecular-mass preparation of heparin was recovered from the medium of cultured endothelial cells using strong-anion exchange. In addition, another narrow molecular-mass preparation of heparin was gassed with exogenous NO under argon. Degradation was evaluated by gel-filtration chromatography. Since HNO2 degrades heparin under acidic conditions, the reaction with NO gas was studied under various pH conditions. The results show that the degradation of exogenous heparin by endothelial cells is inhibited by NO synthase inhibitors. Exogenous NO gas at concentrations as low as 400 p.p.m. degrades heparin and heparan sulphate. Exogenous NO degrades heparin at neutral as well as acidic pH. Endothelial-cell-derived NO, as well as exogenous NO gas, did not degrade hyaluronan, an unrelated glycosaminoglycan that resists HNO2 degradation. Peroxynitrite, a metabolic product of the reaction of NO with superoxide, is an agent that degrades hyaluronan; however, peroxynitrite did not degrade heparin. Thus endothelial-cell-derived NO is capable of degrading heparin and heparan sulphate via HNO2 rather than peroxynitrite. These observations may be relevant to various pathophysiological processes in which extracellular matrix is degraded, such as bone development, apoptosis, tissue damage from inflammatory responses and possible release of growth factors and cytokines.

Endogenous basic fibroblast growth factor displaced by heparin from the lumenal surface of human blood vessels is preferentially sequestered by injured regions of the vessel wall

BACKGROUND

Proliferation of smooth muscle cells (SMCs) of the arterial wall in response to local injury is an important factor in vascular proliferative disorders. Among the growth factors that promote SMC proliferation is basic fibroblast growth factor (bFGF), which is characterized by a high affinity for heparin and is associated with heparan sulfate on cell surfaces and extracellular matrices. We investigated whether heparin can displace endogenous active bFGF from the lumenal surface of blood vessels, whether bFGF is preferentially bound to injured blood vessels, and whether a synthetic, polyanionic, heparin-mimicking compound (RG-13577) can prevent sequestration of bFGF by the vessel wall.

METHODS AND RESULTS

Injured and noninjured saphenous vein segments were perfused with or without heparin, in the absence or presence of 125I-bFGF and/or RG-13577 (a polymer of 4-hydroxyphenoxy acetic acid). Heparin displaced bFGF from the lumenal surface of the vein, and the released bFGF stimulated proliferation of SMCs. Likewise, systemic administration of heparin during open heart surgery resulted in a marked increase in plasma bFGF levels. Injured veins sequestered 125I-bFGF to a much higher extent than noninjured vein segments, both in the absence and presence of heparin. This sequestration was inhibited by compound RG-13577.

CONCLUSIONS

Despite its beneficial effects, heparin may displace active bFGF, which subsequently may be preferentially deposited on injured vessel walls, thus contributing to the pathogenesis of restenosis. This effect may be prevented by a synthetic heparin-mimicking compound.

Inhibition of smooth muscle cell proliferation and experimental angioplasty restenosis by beta-cyclodextrin tetradecasulfate

Heparin inhibits smooth muscle cell proliferation in vitro, a property that makes it potentially useful in preventing restenosis after angioplasty. Its utility in this setting is limited by the inability to use high doses (secondary to anticoagulant effects) and the need for subcutaneous administration. We tested the ability of beta-cyclodextrin tetradecasulfate (CDT), a nonanticoagulant synthetic heparin mimic, to inhibit smooth muscle cell proliferation in vitro and tested its efficacy when orally administered for the prevention of angioplasty restenosis in a rabbit atherosclerosis model. Vascular smooth muscle cells were cultured from rabbit aortas by the explant technique. Passaged cells were plated at low density in microtiter plates in the presence or absence of varying concentrations of heparin or CDT in culture medium containing 10% fetal calf serum. Using both 3H-thymidine incorporation and total protein assays, both heparin and CDT caused a similar dose-dependent inhibition of proliferation. We next tested the effect of orally administered CDT in the prevention of restenosis in focal femoral artery arteriosclerotic lesions created in hypercholesterolemic New Zealand White rabbits by air-dessication endothelial injury and subsequent peripheral angioplasty. Animals were followed up for 1 month and were fed normal chow supplemented by tap water with or without CDT. In animals receiving the highest concentration of CDT (2 mg/mL drinking water), the percentage of arterial cross-sectional area with intimal hyperplasia decreased from 50.5 +/- 1.7% (control) to 26.9 +/- 2.2% (p < 0.001), with the intimal/medial ratio being decreased from 1.4 +/- 0.4 to 0.5 +/- 0.2 (p = 0.056).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the separation of bovine heparin by strong anion exchange and by gel filtration chromatography

Heparin has been fractionated by strong anion exchange chromatography followed by elution of the pools on a gel filtration column. This resulted in the expected inverse relationship in the elution order for the pools run by the two methods. Also chromatography of heparin was performed in the reverse order: gel filtration first, followed by anion exchange of the pools. For this order of separation four of the five gel filtration pools of different molecular weights eluted at a similar LiCl concentration. The specific activities of different pools of heparin were evaluated using a colorimetric microwell kinetics assay using antithrombin and thrombin. For the pools separated by ion exchange first, there was an exponential increase of specific activity with increasing molecular weight for all pools. For the pools isolated by gel filtration first, the specific activities became level after an initial increase in relation to molecular weight. Thus, unique pools of heparin species are being isolated by different modes of chromatography.

Heparanase activity in cultured endothelial cells

This study was undertaken to identify a heparan sulfate (HS) degradation endoglycosidase (heparanase) in cultured endothelial cells (EC) and to characterize the requirements for its release and subsequent degradation of HS side chains in the subendothelial extracellular matrix (ECM). Intact EC, EC lysates, or EC conditioned media from different sources were incubated with metabolically Na2(35)SO4-labeled ECM produced by bovine EC. The released sulfated products were analyzed by gel filtration on Sepharose 6B. Human umbilical vein endothelial cells (HUVEC) and human saphenous vein endothelial cells (HSVEC) lysates expressed heparanase activity as indicated by release of most of the radioactivity from ECM as HS fragments that are one-fifth to one-sixth the size of the intact HS side chains. These fragments were sensitive to deamination with nitrous acid and were not produced in the presence of heparin. Rabbit coronary microvascular EC and bovine brain capillary EC lysates showed less heparanase activity (30-35%), whereas bovine aortic and corneal EC showed no activity. Intact HUVEC, plated directly on the labeled ECM, expressed low enzyme activity that was not changed when cells were exposed to various agents. Exposure of HUVEC to interleukin-1, phorbol myristate acetate, tumor necrosis factor, endotoxin, thrombin, calcium ionophore A23187, fibroblast growth factor, or radiation did not induce release of the enzyme to the medium or degradation of HS in the ECM, as long as the cells remained viable. EC differ from various normal and malignant cells that degrade HS by virtue of their inability to release the enzyme. We suggest that heparanase release during vessel wall injury may regulate the growth of EC and smooth muscle by release of HS degradation products in processes such as wound healing, neovascularization, and atherosclerosis.

Extracellular matrix of the developing heart in normal and cardiac lethal mutant axolotls, Ambystoma mexicanum

As part of an ongoing study of heart development in normal and cardiac lethal mutant axolotls (Mexican salamanders) we examined the extracellular matrix (ECM) by microscopical methods. With scanning electron microscopy we are unable to detect ECM on the apical surface of cells of the early cardiogenic mesoderm. During the period of lateral plate migration, which coincides with the period of cardiogenic induction of mesoderm by anterior endoderm, there is little ECM, aside from some microfibrils, on the basal surface of the endoderm or mesoderm of the pharyngeal region. Later, a basal lamina (BL) is found on the endoderm and along portions of the developing endocardial and myocardial tubes. By the time of heartbeat initiation the BLs are complete and invested with striated collagen-like fibrils that are sparsely distributed in the "cardiac jelly" of normal and mutant hearts. Striated fibril deposition, which increases with time, is generally random in orientation, with the exception of some regions where there is a preferred directionality. During the post-hatching period striated fibrils appear in the subepicardial space. In addition, branching fibers that are probably elastin appear in the bulbus arteriosus. In these later stages the density of fibrils in the cardiac lethal mutant heart is much less than normal. Indirect immunofluorescent microscopy reveals laminin and fibronectin in the basal laminae of the endocardial and myocardial tubes of both normal and cardiac lethal mutant hearts. In addition, punctate and fibrillar staining for fibronectin, and punctate staining for laminin are found in the cardiac jelly. These matrix proteins are not abundant at the apical (exterior) surface of the myocardium until the epicardium appears.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial angiogenesis and coronary perfusion in left ventricular pressure-overload hypertrophy in the young lamb. Evidence for inhibition with chronic protamine administration

In contrast to young growing animals, pressure-overload hypertrophy in adults is frequently associated with diminished myocardial capillary density and maximal coronary flow per gram. To determine the role of angiogenesis in maintaining perfusion capacity in the hypertrophying heart, the angiogenesis inhibitor protamine sulfate was administered to young lambs during the development of left ventricular (LV) pressure-overload hypertrophy. Baseline and maximum (adenosine) myocardial perfusion was measured in four groups of chronically instrumented 10-week-old lambs subjected to 1) ascending aortic bands since the age of 4 weeks (LVH group, n = 10), 2) sham operation at the age of 4 weeks (SHAM group, n = 8), 3) aortic bands and twice daily injections of protamine since the age of 4 weeks (LVH + P group, n = 9), 4) sham operation and injection of protamine (SHAM + P group, n = 8). Capillary density was measured postmortem. Peak LV pressure and the LV/body weight ratio were similarly increased in LVH and LVH + P compared with sham-operated lambs (p less than 0.001). In LVH lambs, LV capillary number increased by 32% compared with sham-operated lambs (p less than 0.05), and capillary density, coronary flow reserve, and minimal coronary resistance remained normal. In contrast, LVH + P lambs had no significant increase over SHAM lambs in LV capillaries and total maximum coronary flow. The LVH + P lambs had lower LV subendomyocardial capillary density and higher minimal coronary resistance per gram (p less than 0.05 versus LVH lambs). Right ventricular capillary density and minimal resistance were similar in all groups. These findings support the hypotheses that myocardial angiogenesis with pressure-overload hypertrophy is important in maintaining maximal LV coronary flow in the young and that impairment of angiogenesis results in diminished coronary flow capacity.

Modes of FGF release in vivo and in vitro

The fibroblast growth factors (FGFs) are a family of polypeptide growth regulators. The prototypes of this family are acidic and basic FGF. Unusual among their characteristics are a high affinity for the glycosaminoglycan heparin and the lack of a signal sequence for secretion. Other members of the FGF family include a number of oncogene products that also display heparin affinity but do possess signal sequences. Results from early tissue culture studies were consistent with the prediction that acidic and basic FGF would not be secreted. Investigators found that virtually no FGF was secreted into conditioned media, instead it remained cell-associated and was deposited into the basement membrane. More recently, however, a number of studies have indicated that a small amount of FGF is 'released' from cells where it is postulated to act as an autocrine regulator. Acidic and basic FGF have been localized in basement membranes both in vivo and in vitro. The mode of release to this site is also unclear but may be secondary to the mechanisms cited above with soluble FGF becoming bound to heparan sulfate molecules in the extracellular matrix. A number of observations have indicated that matrix-bound FGF is biologically active in vitro. There are no data to indicate whether the same is true for FGF bound to basement membranes in vivo. In addition to its apparent sequestration in the basement membrane, FGF has also been localized to the surface of a variety of normal and tumor cell types. In particular, endothelial cells have been shown to possess two classes of FGF-binding sites: low abundance, high-affinity receptors that mediate the biological activity as well as high abundance, low affinity binding sites. The physiologic relevance of FGF binding to these low affinity sites is not clear. The possibility of locally high concentrations of heparin released by mast cells, as well as the presence of heparan sulfate-degrading enzymes, suggests that this glycosaminoglycan bound FGF might be released from these binding sites under some circumstances. Cell surface binding of FGF has also been demonstrated in vivo; in rabbits plasma levels of the growth factor were shown to be dramatically elevated following intravenous heparinization. Since the FGFs were first noted to lack a signal sequence, cell injury has been suspected to be the most likely route for FGF release in vivo. A number of studies using different models of cell injury, including endotoxins and irradiation, have revealed that damaged cells do release FGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Heparin-mediated release of fibroblast growth factor-like activity into the circulation of rabbits

Fibroblast growth factors (FGFs) are a family of structurally related proteins that influence the growth and differentiation of a variety of cell types, including the cells of the vascular system. Due to the lack of signal sequence, basic FGF is not actively secreted. However, it has been detected in the extracellular matrix bound, at least in some cases, via heparin-like molecules. Heparin has been shown to displace FGF from cells and matrices in vitro, and we have investigated the possibility that a similar phenomenon might occur in vivo. Heparin was infused intravenously into anesthesized rabbits; plasma samples taken 30 min later and monitored using [3H]thymidine incorporation into BALB/c 3T3 cells were found to contain 3-fold more stimulatory activity than control plasma samples. Addition of heparin directly to the 3T3 cells or to the plasma samples following their collection did not affect the level of stimulatory activity. A time course of stimulatory activity in rabbit plasma following heparin administration revealed that 3T3 cell stimulatory activity rapidly increased following heparin infusion, peaked at 30 min, and declined to control levels by 90-120 min. The anticoagulant action of heparin followed a different time course, providing evidence that these two effects of heparin are functionally distinct. The binding affinity of the plasma-derived stimulatory activity for heparin was used to demonstrate that the activity is FGF-like in nature. Additionally, administration of [125I]bFGF to rabbits that had been "precleared" by heparin infusion resulted in an immediate peak of circulating labeled bFGF that decreased to plateau level by 20-45 min following injection.(ABSTRACT TRUNCATED AT 250 WORDS)