Heparin stimulates the proliferation of bovine aortic endothelial cells probably through activation of endogenous basic fibroblast growth factor

The role of valvular endothelial cell paracrine signaling and matrix elasticity on valvular interstitial cell activation

The effects of valvular endothelial cell (VlvEC) paracrine signaling on VIC phenotype and nodule formation were tested using a co-culture platform with physiologically relevant matrix elasticities and diffusion distance. 100 μm thin poly(ethylene glycol) (PEG) hydrogels of 3-27 kPa Young's moduli were fabricated in transwell inserts. VICs were cultured on the gels, as VIC phenotype is known to change significantly within this range, while VlvECs lined the underside of the membrane. Co-culture with VlvECs significantly reduced VIC activation to the myofibroblast phenotype on all gels with the largest percent decrease on the 3 kPa gels (~70%), while stiffer gels resulted in approximately 20-30% decrease. Additionally, VlvECs significantly reduced αSMA protein expression (~2 fold lower) on both 3 and 27 kPa gels, as well as the number (~2 fold lower) of nodules formed on the 27 kPa gels. Effects of VlvECs were prevented when nitric oxide (NO) release was inhibited with l-NAME, suggesting that VlvEC produced NO inhibits VIC activation. Withdrawal of l-NAME after 3, 5, and 7 days with restoration of VlvEC NO production for 2 additional days led to a partial reversal of VIC activation (~25% decrease). A potential mechanism by which VlvEC produced NO reduced VIC activation was studied by inhibiting initial and mid-stage cGMP pathway molecules. Inhibition of soluble guanylyl cyclase (sGC) with ODQ or protein kinase G (PKG) with RBrcGMP or stimulation of Rho kinase (ROCK) with LPA, abolished VlvEC effects on VIC activation. This work contributes substantially to the understanding of the valve endothelium's role in preventing VIC functions associated with aortic valve stenosis initiation and progression.

Synthesis of a glucuronic acid and glucose conjugate library and evaluation of effects on endothelial cell growth

Compounds that alter endothelial cell growth are of interest in the development of angiogenesis modulators. A structurally diverse series of saccharide derivatives (glycosylamide conjugates) have been synthesized and evaluated for their effects on bovine aortic endothelial cell (BAEC) growth. Heparin-albumin (HA) reduced BAEC growth by 32% at 10 microg/mL and a number of the novel saccharide conjugates from the library were found to mimic the effect of HA as they also inhibit endothelial cell survival under identical conditions. Two thiophene conjugates, thioglucamide (24% inhibition at 35 microM) and a related glucuronide (26% inhibition at 33 microM) were the most potent inhibitors of BAEC growth, as determined using a methylthiazol tetrazolium (MTT) assay. The effects of thioglucamide and HA on absolute cell number were also studied using cell counting experiments; thioglucamide (47% after 24 h) was more potent than indicated by the MTT assay and initially reduced the BAEC number to a greater extent than HA (30% after 24 h); however, its actions were over more rapidly than were HA's as cell growth had returned to levels of the control after 72 h where HA still caused 25% inhibition. The binding of the monosaccharide conjugates to fibroblast growth factor (FGF-2) in competition with heparin-albumin by ELISA was investigated to establish the possible mechanism by which glycoconjugates could alter growth but there was no general correlation between reduction in viable cell population and binding to FGF-2. No glycoconjugate reduced the proliferation of mouse mammary epithelial cells, nor did any alter gross cell morphology, supporting a proposal that the reduction in BAEC survival by monosaccharide conjugates such as thioglucamide is a result of the inhibition of cell proliferation rather than being an induction of cytotoxicity. These studies indicate that cell biological studies to determine the mechanism of action of the simple monosaccharide conjugates may be worthwhile.

Heparin increases prolactin and modifies the effects of fgf-2 upon prolactin accumulation in pituitary primary cultures

We have studied the effects of heparin on prolactin accumulation in the medium from primary pituitary cultures, and whether heparin interferes with the effects of fibroblast growth factor-2 (FGF-2) on PRL regulation in vitro. In the absence of exogenous FGF-2, hepa-rin increased prolactin accumulation in the culture medium in a dose-dependent manner. FGF-2 also increased the prolactin levels of primary cells in a time- and dose-dependent manner. However, low doses of heparin reduced the effects of FGF-2, but higher doses of heparin increased the maximal FGF-2-induced prolactin secretion and ED50. In vivo estrogenization of rats resulted in the abolition of FGF-2 capability to promote prolactin release in vitro. However, heparin restored cell responsiveness to FGF-2. Our results suggest that heparin, when present in the medium, binds FGF-2, therefore reducing its ability to interact with FGF receptors in a dose-dependent manner up to a critical molar concentration, at which heparin itself starts to activate the FGF receptor, and strengthens the activation induced by its proper ligand, FGF-2. Prolactin responses to FGF-2 are blocked by estrogen pretreatment, and it is probable that this introduces lactotroph cells in the proliferative stage. In conclusion, heparin modulates PRL secretion and PRL responses to FGF-2 in vitro.

Evaluation of an in vitro endothelialized vascular graft under pulsatile shear stress with a novel radiolabeling procedure

OBJECTIVE

To improve the hemocompatibility of vascular grafts, endothelial cell (EC) seeding of biomaterials prior to implantation is critical. The current in vitro study was designed to investigate such a feasibility on a collagen-coated heparin-bonded graft and to evaluate cell detachment upon pulsatile shear stress.

MATERIALS AND METHODS

Endothelial cells (EA-hy-926) were seeded onto grafts. The endothelialization of the grafts was evaluated by the [3H]-thymidine incorporation, scanning electron microscopy (SEM) and histological examinations. After in situ EC radiolabeling with a novel 99mTc technique, the prostheses were exposed to pulsatile shear stress (0.27 N/m2), mimicking the shear rate occurring in a superficial femoral artery, for 3 h in a flow circuit and EC loss quantified by gamma camera detection.

RESULTS

Complete EC coverage was achieved after 5 days. Three hours of artificial perfusion resulted in a low EC loss (12.9+/-0.8%, n = 7). SEM shows EC withstanding shear stress in valleys of prosthesis circumvolutions.

CONCLUSIONS

These satisfactory results could be explained by the high affinity of EC for heparinized surfaces in addition to cell surface receptors involved in adhesion to collagen.

Heparin inhibits phorbol ester-induced ornithine decarboxylase gene expression in endothelial cells

Glycosaminoglycans regulate angiogenesis by affecting the availability of different growth factors for the endothelial cell (EC). However, little is known about the molecular and functional consequences resulting from direct interaction of these polyelectrolytes with the EC. Here we show that heparin markedly inhibited serum-stimulated DNA synthesis and ornithine decarboxylase (ODC) mRNA expression in human endothelial cells (HEC). About 50% of the serum effect on DNA synthesis and ODC gene expression was prevented by the selective protein kinase C (PKC) inhibitor chelerythrine or by PKC down-regulation. Heparin was ineffective in counteracting that part of the effect of serum that was resistant to PKC inhibition or down-regulation. In serum-free cultured HEC, heparin completely abolished the increase in DNA synthesis and ODC mRNA expression elicited by a number of PKC activators. Cell exposure to difluoromethylornithine, an irreversible inhibitor of ODC enzyme, dramatically antagonised both serum- and phorbol 12-myristate 13-acetate (PMA)-stimulated DNA synthesis. These results suggest that inhibition of PKC-mediated ODC gene expression by glycosaminoglycans may represent an important mechanism in the regulation of HEC proliferation.