General Pharmacology-the Vascular System最新文献

Angiogenesis is a biological process by which new capillaries are formed and it occurs in many physiological and pathological conditions. It is controlled by the net balance between molecules that have positive and negative regulatory activity and this concept had led to the notion of the “angiogenic switch,” depending on an increased production of one or more of the positive regulators of angiogenesis. Numerous inducers of angiogenesis have been identified and this review offers a historical account of the relevant literature concerning the discovery of the best-characterized angiogenic factors.

Microvascular corrosion casting was used to assess the effects of thrombin and D609, a phospholipase C inhibitor, on the vascularity of the chick embryo chorioallantoic membrane (CAM). Discs containing vehicle, thrombin or D609 were placed on the CAM of fertilized white Leghorn eggs on Day 9 of gestation and vascularity was assessed on Day 11. Thrombin caused significant increases in the numbers (43%), diameters (5%) and lengths (17%), of both pre- and postcapillaries (first-order vessels by centripetal ordering). Conversely, D609 caused a decrease in the numbers (27%), lengths (12%) and diameters (8%) of first-order vessels. D609 decreased the total vascular volume of first- to third-order vessels by 32%, whereas thrombin increased vascular volume by 27%. Additionally, thrombin increased capillary plexus density by 6%, whereas D609 decreased capillary plexus density by 3%. These findings provide a quantitative assessment of changing vascularity in the chick CAM—a model assay system in the development of pro- and antiangiogenic agents.

Following chronic ischemia, vascular endothelial growth factor (VEGF) is induced primarily in the ganglion cell layer of the retina. This often results in neovascularization (NV) that originates from the vascular bed closest to the ganglion cell layer. To study the effects of VEGF, independent lines of transgenic mice that express VEGF in the lens and in the retina have been generated. Expression in the lens results in excessive proliferation and accumulation of angioblasts and endothelial cells in proximity to the lens. However, VEGF expression is not sufficient to direct blood vessel organization or maturation in the prenatal mouse. Abnormal vessels do form on the retinal surface, but not until the second postnatal week. In transgenic mice expressing VEGF in the photoreceptors, NV originates from the deep capillary bed—the vascular bed closest to the photoreceptors. NV is accompanied by localized blood–retinal barrier breakdown. NV is also induced in PDGF-B transgenic mice. PDGF-B expression in the lens occurs prenatally and, during this time, mainly affects the perilenticular vessels. Postnatally, transgenic mice expressing PDGF-B in the lens or photoreceptors show a similar phenotype. In both models, a highly vascularized cell mass containing endothelial cells, pericytes, and glia forms in the superficial retina, and the formation of the deep capillary bed is inhibited. The phenotype suggests that an additional factor is necessary for the maturation and penetration of vascular endothelial cells into the retina to form the deep capillary bed.

Peroxisome proliferator-activated receptor γ (PPARγ) immunohistochemical expression was analyzed in 75 human bladder tumor specimens, where the expression of some angiogenic factors, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived endothelial cell growth factor (PDECGF), and tumor progression markers, such as epidermal growth factor receptor (EGFr), p16, mutated p53, and normal pRB, were also analyzed. The results were then compared to the clinical and pathological characteristics of the disease. PPARγ was expressed more significantly in papillary tumors than in solid cancers, and its presence was associated with statistical significance to low incidence of tumor recurrence or progression. This significant association was observed also when PPARγ was expressed in the presence of PDECGF, which resulted, when considered alone, to an angiogenic factor typical of solid cancers and appeared related to poor prognosis. In the presence of bFGF, on the contrary, PPARγ expression no longer resulted to a significant association with low incidence of tumor recurrence or progression, suggesting a possible worsening role of this angiogenic factor, typical of papillary cancers, in its interaction with PPARγ.

The α-thrombin peptide, TP508, accelerates the healing of full-thickness wounds in both normal and ischemic skin. In wounds treated with TP508, a pattern of increased vascularization is consistently observed both grossly and microscopically when compared to wounds treated with saline. One possible mechanism by which the peptide accelerates wound healing is by promoting revascularization of granulation tissue at the injured site. To evaluate the angiogenic potential of TP508, the peptide was tested in the chick embryo chorioallantoic membrane (CAM), where it increased the density and size of CAM blood vessels relative to controls. Additionally, TP508 stimulated chemokinesis and chemotaxis in a dose-dependent fashion in cultured human aortic and human microvascular endothelial cells. Taken together, these in vivo and in vitro data support an angiogenic role for TP508 in wound healing. A working model is presented to explain how this 23-amino-acid peptide, which lacks proteolytic activity, is generated during wound healing and contributes to the nonproteolytic functions associated with α-thrombin during tissue repair.

Antiangiogenic agents target migratory and proliferative endothelial cells (EC) in the process of forming new vessels, resulting in growth inhibition or cell death. Here we have shown that the antiangiogenic activity of angiostatin on EC is enhanced in culture when the microenvironmental extracellular pH (pH_e) is reduced to levels similar to that of many tumors. In a migration/scratch assay and during tube formation, angiostatin in combination with reduced pH_e synergistically resulted in an increased EC death—an effect not seen with either stimulus individually. Lowering of pH_e decreased intracellular pH (pH_i), and a further lowering of pH_i occurred when low pH_e was combined with angiostatin. These data suggest that low pH_e plays a role in the relative specificity and efficacy of angiostatin for tumor neovasculature and indicate roles for both pH_e and pH_i in the mechanism of angiostatin action. A receptor for angiostatin, the α-subunit of ATP synthase, was found on the surface of EC. We show that cell surface receptor distribution is increased on Matrigel, a basement-like matrix, as opposed to fibronectin or RGD peptide substrates, and redistributed to a more punctuate appearance at low pH_e. Furthermore, positive cell surface histochemical staining for α-ATP synthase was blocked by preincubation with angiostatin. These data indicate that substrate and pH_e are critical parameters in the evaluation of this antiangiogenic substance, and probably for others as well.

In addition to its central role in blood coagulation and hemostasis, human α-thrombin is a growth factor for a variety of cell types, including monocytes and endothelial cells, involved in the control of angiogenesis. Different cytokines produced by mononuclear cells have been implicated in angiogenic processes associated with tissue repair and certain human malignancies. We have previously shown that thrombin enhances proliferative responses in T lymphocytes. More recently, we reported that interferon-γ-differentiated monocytes have increased expression of protease-activated receptor-1 (PAR-1) and increased thrombin binding. Since cytokines may be involved directly and indirectly in angiogenesis, we initiated studies to determine thrombin effects on the induction of cytokines, such as interleukin (IL)-1 and IL-6, in human mononuclear cells. IL-1 and IL-6 protein expression was significantly enhanced by thrombin (P<.05), as determined by enzyme-linked immunosorbent assay (ELISA). Treating mononuclear cells with the PAR-1 peptide, SFLLRN, has effects similar to those of thrombin. Thus, it appears that these thrombin effects are mediated through activation of PAR-1. These results confirm that thrombin is a strong activator of monocytes and could be involved in angiogenesis by inducing cytokines that could enhance the angiogenic process in tissue repair.

The effect of allopurinol (an inhibitor of xanthine oxidase) on oxidative stress, renal dysfunction, and histologic alterations was evaluated during the renal ischemia–reperfusion in uninephrectomized rats. Renal malondialdehyde and serum creatinine levels significantly increased after renal ischemia–reperfusion. However, the pretreatment with allopurinol demonstrated a protector effect in these parameters. Renal ischemia–reperfusion provoked a significant renal damage in the operated group. Tubular atrophy and interstitial fibrosis were attenuated by allopurinol when given prior to the surgery. In our study, allopurinol had a strong tendency to exert a beneficial effect during renal ischemia–reperfusion in uninephrectomized rats.

β-Adrenoceptor blockers with disparate properties may have differential influences on arterial pulse wave velocity (PWV). Therefore, influences of single medium doses of bisoprolol, propranolol and celiprolol on PWV were compared in healthy subjects. Arterial PWV was obtained from the time delay between flow pulses measured from the root of the aorta and the popliteal artery. Bisoprolol and propranolol decreased arterial PWV more than placebo (P≤.002) and celiprolol (P<.0001). In conclusion, the acute effects of bisoprolol and propranolol on arterial PWV in normotensive subjects seem to differ from that of celiprolol.

In the present study, we observed that pentoxifylline (PTX) significantly augmented the nitric oxide (NO) production and the iNOS gene expression by interleukin-1β (IL-1β)-stimulated vascular smooth muscle cells (VSMCs). The enhancing effects of PTX on the IL-1β-induced NO production was associated with an increased intracellular cyclic AMP (cAMP) levels, and the synergistic effects of PTX on the IL-1β-induced NO production was blocked by cAMP-dependent protein kinase A (PKA) inhibitors. PKA inhibitors, KT5720 and H89, markedly decreased the augmented expression of iNOS gene whereas ODQ, a soluble guanylate cyclase inhibitor, did not affect the enhancing effect. In addition, the pretreatment with KT5720 or H89 abolished the increased translocation of the p65 subunit of NF-κB into the nucleus by PTX in the IL-1β-stimulated VSMCs. These results suggest that enhancing effects of PTX on the iNOS gene expression in the IL-1β-stimulated VSMCs is mediated predominantly through the activation of NF-κB via cAMP-dependent PKA pathway.