Pharmacologic inhibition of nitric oxide synthases and cyclooxygenases enhances intimal hyperplasia in balloon-injured rat carotid arteries.

OBJECTIVE: Extensive proliferation and migration of smooth muscle cells (SMCs) contribute to development of fibromuscular intimal hyperplasia in response to balloon catheter-induced injury of the left carotid artery in Fischer 344 rats. The purpose of the present study was to test the hypothesis that endogenously generated nitric oxide (NO) and prostaglandins act synergistically to limit the extent of neointimal hyperplasia. METHODS: The left carotid artery of Fischer 344 rats was injured with a 2F balloon catheter. The following treatment was initiated 24 hours before arterial injury, and was continued for 2 weeks: N-nitro-l-arginine (L-NA; 10 mg/kg/d, in drinking water), indomethacin (1.5 mg/kg/d per gavage), and L-NA (10 mg/kg/d) plus indomethacin (1.5 mg/kg/d). After application of an overdose of pentobarbital animals were formalin-fixed. Subsequently, paraffin-embedded cross sections of the uninjured and injured carotid arteries were analyzed morphometrically. SMC proliferation was determined by incorporation of 5-bromo-2'-deoxyuridine. RESULTS: Two weeks after injury, L-NA caused a 1.29-fold +/- 0.29-fold (mean +/- SD; n = 14; P <.05) increase in the intima-media ratio, compared with control animals, whereas indomethacin had no effect. Combined treatment with L-NA plus indomethacin further increased intima-media ratio (1.65-fold +/- 0.5-fold over control; n = 14; P <.05). SMC proliferation in the neointima of rats treated with L-NA and L-NA plus indomethacin was elevated. Furthermore, neointimal cell density (nuclei per square millimeter) was reduced after combined inhibition of cyclooxygenases and NO synthases. CONCLUSION: The present results of pharmacologic NO synthase and cyclooxygenase inhibition suggest that NO and prostaglandins are part of an endogenous growth inhibitory mechanism that synergistically suppresses intimal thickening. CLINICAL RELEVANCE: The role of cyclooxygenase-1 (COX1) and cyclooxygenase-2 (COX2) during vascular recurrent stenosis and atherosclerosis is not clear yet. In particular, the effects of selective COX2 inhibitors on the frequency of cardiovascular events is still controversial. It is shown here in rats that the application of a non-selective COX inhibitor does not affect arterial stenosis. However, the concurrent inhibition of endogenous nitric oxide generation and COX1 or COX2 causes overshooting neointimal hyperplasia. These results suggest that increased vascular stenosis can result from administration of drugs that pharmacologically block 2 or more inhibitory pathways that normally counterbalance the effect of promotors of neointimal hyperplasia.

Arterial injury repair in nonhuman primates-the role of PDGF receptor-beta.

BACKGROUND: This study documents the time course of the response to injury of the saphenous artery in baboons and the role of the platelet-derived growth factor-beta. Fundamental differences with the well-characterized rat arterial injury model have been found. MATERIALS AND METHODS: Thirty-eight baboons received a unilateral balloon injury to the saphenous artery and were treated with a chimeric blocking antibody to PDGFR-beta or vehicle control for 7, 14, or 28 days. The arteries were evaluated morphologically and for cell proliferation. RESULTS: Both medial and intimal smooth muscle cell proliferation were elevated 7 days after injury and were back close to baseline at 14 days. Unlike the rat, blockade of PDGFR-beta inhibited medial proliferation over 80% at 7 and 14 days, while intimal proliferation was only inhibited at 14 days (>95%). Also, unlike the rat, the baboon arterial media, as well as the intima, increased in size by 14 days after injury. Blockade of PDGFR-beta completely inhibited both intimal and medial growth at 14 days, but there was less of an effect on intimal growth at 28 days. CONCLUSION: Blockade of PDGFR-beta may be a clinical approach to inhibit intimal hyperplasia in humans, but this study raises concerns about the long-term efficacy of this treatment.

Concomitant blockade of platelet-derived growth factor receptors alpha and beta induces intimal atrophy in baboon PTFE grafts.

OBJECTIVE: Although current treatments for restenosis attempt to prevent the development of intimal hyperplasia, an alternative strategy is to induce intimal atrophy after restenosis has developed. Because platelet-derived growth factor (PDGF) is a smooth muscle cell growth and survival factor, we tested the hypothesis that complete blockade of PDGF by using antibodies against PDGF receptors alpha and beta would cause intimal atrophy in a baboon vascular graft model. METHODS: We administered chimeric antibodies against PDGF receptor alpha or PDGF receptor beta, either separately or together, to baboons with bilateral prosthetic aortoiliac grafts, the intimas of which had reached maximal size before treatment was begun. High blood flow, which we have previously shown to cause intimal atrophy, was induced through one graft to serve as a positive control. After 2 weeks, the intima lining the grafts was assessed for cross-sectional area, cell proliferation, and apoptosis by standard morphologic and immunohistochemical techniques. RESULTS: Blocking both PDGF receptors simultaneously reduced the cross-sectional area of the normal-flow graft intima by 44% (P <.05 vs control), whereas treatment with the individual antibodies did not significantly alter intimal area. Blockade of both receptors also inhibited smooth muscle cell proliferation by 66% (P <.05 vs control), whereas neither antibody alone altered proliferation. In contrast, all treatments increased smooth muscle cell apoptosis threefold to fivefold. CONCLUSIONS: These data suggest that simultaneous inhibition of cell proliferation and stimulation of cell death by the administration of antibodies to both PDGF receptor alpha and receptor beta is required for intimal atrophy in this baboon graft model. In addition, these data provide an in vivo model for the pharmacologic induction of intimal atrophy and introduce a novel clinical approach to treat intimal hyperplasia. Clinical relevance This study introduces the concept of pharmacologic induction of intimal atrophy. Intimal hyperplasia plagues all forms of arterial reconstruction. Currently, the only effective treatment of these restenotic lesions is balloon angioplasty or operative revision. An alternative approach to patients with clinically significant intimal hyperplasia might be to stimulate intimal regression by modulating growth and survival factors required for intimal maintenance. Although PDGF is known to be critical in intimal formation, the results of this study suggest that PDGF is also critical for intimal maintenance. Inhibition of the PDGF system may prove to be a clinically applicable approach for inducing intimal atrophy.

Blockade of the epidermal growth factor receptor decreases intimal hyperplasia in balloon-injured rat carotid artery.

HYPOTHESIS: Arterial intimal hyperplasia is induced by injury and is frequently the cause of luminal narrowing after vascular reconstruction. Smooth muscle cells (SMC) respond to injury by proliferating and migrating into the intima. This process is regulated by thrombin, endothelin, and angiotensin II, all ligands of G protein-coupled receptors. Signal transduction from these receptors in cultured cells depends in part on transactivation of epidermal growth factor receptor (EGFR). We hypothesize that EGFR has a substantial role in activation of SMC in vivo and development of intimal hyperplasia. METHODS: Intimal hyperplasia was induced in rat carotid arteries by passage of a balloon catheter. Animals were given a monoclonal blocking antibody to rat EGFR, matched mouse immunoglobulin G (IgG) control antibody, or saline solution. RESULTS: Blocking EGFR antibody inhibited medial SMC proliferation, as determined by 5-bromo-2'-deoxyuridine labeling at 2 days (IgG control, 8.0% +/- 2.0%; anti-EGFR, 3.2% +/- 0.8%) and intimal hyperplasia at 14 days (intimal area: IgG control, 0.07 +/- 0.01 mm(2); anti-EGFR, 0.04 +/- 0.01 mm(2)). CONCLUSION: Activation of EGFR is important for early induction of SMC proliferation and subsequent intimal thickening.

Increased plasmin and serine proteinase activity during flow-induced intimal atrophy in baboon PTFE grafts.

High blood flow causes intimal atrophy and loss of extracellular matrix in PTFE aortoiliac grafts. We have investigated whether matrix-degrading proteinases are altered in this baboon model of atrophy using zymography, western analysis, and a versican degradation assay. After four days of high flow, urokinase was increased and plasminogen activator inhibitor-1 was decreased in the intima. Plasminogen was increased after seven days. Pro-matrix metalloproteinase (MMP)-2, activated MMP-2, and proMMP-9 levels were modestly increased by high flow at 7 days, whereas MMP-3 and tissue inhibitor of metalloproteinases-1 were not altered. Extracts of 4-day high-flow intimas degraded more 35S-methionine-labeled versican than low-flow intimal extracts, and this activity was inhibited by AEBSF, a serine proteinase inhibitor, and a plasmin antibody. In contrast, this activity was not inhibited by the MMP inhibitor, BB-94 (Batimastat). These data suggest that serine proteinases, including plasmin, may be largely responsible for extracellular matrix degradation in this primate model of flow-induced intimal atrophy.

SOCIAL SUPPORT, PSYCHOLOGICAL DISTRESS, AND PARENTING STRAINS IN MOTHERS OF VERY LOW BIRTHWEIGHT INFANTS.

This study investigated maternal psychological distress, perceptions of social supports, and parenting strains after the birth of a very low birthweight (VLBW) infant. Compared to mothers of term infants, mothers of VLBW infants had significantly higher incidence of psychological distress during the neonatal period, but did not differ from mothers of term infants in their feelings of role restriction, parenting competence, or social supports. Lower general social support predicted high distress levels, but only for mothers of VLBW infants. Mothers with a low sense of parenting competence, but support from spouse/partners reported lower maternal distress.