Pharmacological and mechanistic aspects concerning the use of heparin and ?-cyclodextrin tetradecasulfate for the treatment of vascular restenosis

A chemically modified dextran inhibits smooth muscle cell growth in vitro and intimal in stent hyperplasia in vivo

PURPOSE

Intimal smooth muscle cell (SMC) hyperplasia is a main component of the arterial wall response to injury. We have investigated the capacity of a water-soluble nonanticoagulant functionalized dextran (E9) in inhibition of SMC growth in vitro and in vivo.

METHODS

E9 was obtained with chemical substitutions with anionic and hydrophobic groups on the dextran backbone. SMC proliferation (cell counting, thymidine uptake, cell cycle analysis) was followed in culture in the presence of E9. Western blot analysis against phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase 1/2, and assessment of MAPK activity on serum-stimulated SMCs also were investigated. Binding/displacement experiments, electron microscopy, and cell fractionations were used to follow the binding and internalization of radiolabeled and fluorescentlabeled E9. New Zealand white rabbit iliac arteries were injured with balloon dilatation and stent deployment. Animals were treated for 14 days with saline solution or E9 (5 mg/kg injected subcutaneously, twice daily). Morphometric analyses were carried out in each group (n = 6 arteries, 18 sections).

RESULTS

Nonanticoagulant E9 inhibited SMC proliferation in vitro. Tyrosine phosphorylation of MAPK 1/2 and MAPK activity were inhibited with E9 within 5 minutes of incubation. The binding and rapid cytoplasmic internalization of the synthetic compound was evidenced, but, in contrast to heparin, we did not detect any nuclear localization of the antiproliferative E9. In the in vivo model, qualitative modifications of neointimal structure with a thinner fibrocellular neointima were noticed after E9 treatment. Morphometric analyses of stented arteries in E9-treated animals indicated an important reduction (P <.01) of intimal growth: 33% and 45% for intimal area and intima/media ratio, respectively.

CONCLUSION

Cytoplasmic internalization of the synthetic polysaccharide correlated to the SMC growth inhibition that involved the MAPK pathway. In vivo inhibition of intimal instent hyperplasia with this nonanticoagulant derived dextran is shown providing a new candidate for a potential selective treatment of SMC proliferation.

Interactions of functionalized dextran-coated liposomes with vascular smooth muscle cells

Synthetic polymers are commonly used in the medical field as implants, polymeric drugs, or drug delivery systems. Among them, bioactive sulfated polysaccharides such as chemically modified dextrans are described to exhibit various properties including the inhibition of smooth muscle cell (SMC) growth. SMCs are key cellular components involved in the physiopathology of the vascular walls especially in atherosclerosis or after vascular surgeries. Interestingly, binding sites on vascular SMCs were already observed for an antiproliferative functionalized dextran (FDx). In this context, we hypothesized that this bioactive polymer could be used as a targeting moiety on the surface of drug delivery systems. In this work, liposomes constituted of phosphatidylcholine, phosphatidylethanolamine and cholesterol (70/10/20 mol.%) were prepared and coated with FDx hydrophobized by a cholesterol anchor (CholFDx) which penetrates the lipid bilayer during the liposome formation. The liposome interactions with SMCs were then followed using radiolabeled liposomes and fluorolabeled liposomes. Results of radioactivity on SMCs indicated higher interactions with CholFDx-coated liposomes as compared to uncoated liposomes. The fluorescence of cells incubated with fluorolabeled CholFDx-coated liposomes also evidenced the liposome binding on SMC membranes. These data demonstrated that liposomes coated with FDx interacted with vascular SMCs. Consequently, the coating with such bioactive polymers appears promising for the design of new drug delivery systems for the targeting of vascular cells.

A combined histochemical and double immunohistochemical labeling protocol for simultaneous evaluation of four cellular markers in restenotic arteries

We designed an effective quadruple staining protocol that combines histochemistry (HC) and double-labeling immunohistochemistry (IHC: IHC) to stain simultaneously several different morphological features and cell types in vascular lesions. Morphometric image analysis to quantitate vascular wall thickening, lumen area, and proliferating smooth muscle cells on consecutive serial sections is adequate, but morphometric precision and dependable cellular characterization and co-localization could be obtained if analyses are performed on one tissue section. The development of a neointima in the rat carotid artery was induced by angioplasty with a balloon catheter. Tissues were stained for elastin by a modified van Gieson method, then processed for double-labeling IHC:IHC for proliferating cell nuclear antigen and smooth muscle actin followed by hematoxylin staining. The four resulting tissue stains labeled elastin filaments black, proliferating nuclei brown, smooth muscle actin red and nonproliferating nuclei blue. Our staining protocol improved the descriptive and quantitative analysis of relation between smooth muscle cell proliferation and protein expression. Also, neointimal thickening could be measured to analyze its relation to cellular proliferation. Providing one slide with four stains maximizes the information from a single slice of tissue, reduces slide preparation and analysis time, and overcomes the restriction of tissue sample availability. This technique can be applied to a wide spectrum of morphologic and morphometric studies.

Troglitazone suppresses intimal formation following balloon injury in insulin-resistant Zucker fatty rats

Troglitazone, a thiazolidinedione derivative, overcomes insulin resistance through promoting insulin receptor function. However, the effect of the resultant enhancement of insulin action on the regulation of cellular proliferation remains unknown. We investigated the effect of troglitazone on intimal proliferation after balloon injury in insulin-resistant Zucker fatty rats. Troglitazone markedly decreased blood glucose and triglyceride levels at the therapeutic dosage. The area of neointima significantly decreased in treated animals 2 weeks after operation, as compared with the untreated control animals (0.0526 +/- 0.0292 and 0.115 +/- 0.0354 mm2, respectively). The ratio of neointimal to medial area in treated rats (0.75 +/- 0.26) decreased by as much as 53% compared with untreated rats (1.40 +/- 0.05). We next examined DNA synthesis in cultured smooth muscle cells (SMCs) derived from non-insulin-resistant rats, to assess whether troglitazone suppresses the proliferation of vascular SMCs independent of metabolic effects. The result showed that troglitazone decreased [methyl-3H]thymidine incorporation into DNA. In conclusion, treatment with troglitazone in Zucker fatty rats resulted in a reduction in neointima formation after balloon injury, and also corrected hypertriglyceridemia and hyperglycemia. In addition, in vitro studies revealed that the anti-proliferative effect of troglitazone stems from its direct action on DNA synthesis rather than any accompanying metabolic changes. Therefore, troglitazone seems to be applicable in preventing atherosclerosis in patients with insulin resistance.

Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells

Heparin and heparan are potent inhibitors of vascular smooth muscle cell (VSMC) proliferation. To investigate the mechanisms by which heparin suppresses growth factor stimulated mitogenesis, the present experiments investigated the effects of heparin on platelet-derived growth factor (PDGF) stimulated signal transduction pathways. Heparin treatment substantially inhibited PDGF-BB stimulated rat VSMC growth. Western analysis showed a 30 min PDGF-BB treatment of VSMC induced the tyrosine phosphorylation of multiple protein bands; cotreatment with heparin inhibited mitogen-activated protein (MAP) kinase tyrosine phosphorylation but had little effect on PDGF receptor tyrosine phosphorylation. In-gel kinase assays demonstrated that heparin inhibited PDGF-BB stimulated MAP kinase activity at late (25 min) but not early (10 min) time points. These data indicate that heparin does not inhibit the initial signalling events after PDGF-BB binding but instead acts through an alternate mechanism to inhibit MAP kinase. To investigate if heparin directly stimulates tyrosine phosphatase-mediated suppression of MAP kinase, we treated VSMC with orthovanadate, a tyrosine phosphatase inhibitor. Heparin inhibited MAP kinase tyrosine phosphorylation after orthovanadate treatment, indicating that heparin does not suppress MAP kinase by enlistment of a tyrosine phosphatase. Experiments were performed to investigate signalling pathways upstream of MAP kinase. To determine if protein kinase C (PKC) mediates PDGF-BB, serum, and EGF stimulation of MAP kinase, we treated VSMC overnight with phorbol ester (PMA) to downregulate PKC. Abolition of conventional and novel PKC activity significantly suppressed both serum and PDGF-BB induced MAP kinase activation, indicating protein kinase C is an important mediator for these mitogens. In contrast, downregulation of these PKC isoforms had little effect on EGF stimulation of MAP kinase. As heparin inhibits PDGF and serum but not EGF stimulation of MAP kinase, there data precisely correlate heparin inhibition of MAP kinase with activation through PKC-dependent pathways. Immunoprecipitation analysis found that heparin inhibited serum, PMA, and PDGF but not EGF induced raf-1 phosphorylation. These studies demonstrate that heparin did not block PDGF-BB receptor activation, which initiates the mitogenic signalling cascade. Heparin did inhibit specific postreceptor second messenger signals, such as the late phase activation of MAP kinase, which may be mediated by suppression of PKC-dependent pathways.

Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery

The objective of this Review is to summarize and critique recent findings and applications of both unmodified and modified cyclodextrins for in vivo drug delivery. This review focuses on the use of cyclodextrins for parenteral, oral, ophthalmic, and nasal drug delivery. Other routes including dermal, rectal, and pulmonary delivery are also briefly addressed. This Review primarily focuses on newer findings concerning cyclodextrin derivatives which are likely to receive regulatory acceptance due to improved aqueous solubility and safety profiles as compared to the unmodified cyclodextrins. Many of the applications reviewed involve the use of hydroxypropyl-beta-cyclodextrins (HP-beta-CDs) and sulfobutylether-beta-cyclodextrins (SBE-beta-CDs) which show promise of greater safety while maintaining the ability to form inclusion complexes. The advantages and limitations of HP-beta-CD, SBE-beta-CD, and other cyclodextrins are addressed.

Smooth muscle cells isolated from the neointima after vascular injury exhibit altered responses to platelet-derived growth factor and other stimuli

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 cells 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.

Effects of subtype-selective and balanced angiotensin II receptor antagonists in a porcine coronary artery model of vascular restenosis

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.