The pathogenetic basis for diabetic neuropathy has been enigmatic. Using two different animal models of diabetes, we have investigated the hypothesis that experimental diabetic neuropathy results from destruction of the vasa nervorum and can be reversed by administration of an angiogenic growth factor. Nerve blood flow, as measured by laser Doppler imaging or direct detection of a locally administered fluorescent lectin analogue, was markedly attenuated in rats with streptozotocin-induced diabetes, consistent with a profound reduction in the number of vessels observed. A severe peripheral neuropathy developed in parallel, characterized by significant slowing of motor and sensory nerve conduction velocities, compared with nondiabetic control animals. In contrast, 4 weeks after intramuscular gene transfer of plasmid DNA encoding VEGF-1 or VEGF-2, vascularity and blood flow in the nerves of treated animals were similar to those of nondiabetic control rats; constitutive overexpression of both transgenes resulted in restoration of large and small fiber peripheral nerve function. Similar experiments performed in a rabbit model of alloxan-induced diabetes produced comparable results. These findings support the notion that diabetic neuropathy results from microvascular ischemia involving the vasa nervorum and suggest the feasibility of a novel treatment strategy for patients in whom peripheral neuropathy constitutes a secondary complication of diabetes.
Endothelial cells used in transendothelial migration assays have been derived from different sources including human umbilical vein and bovine pulmonary artery. As plasma-induced activation of endothelial cells for enhanced transmigration of leukocytes may be pathophysiologically relevant, the role of species differences between plasma and endothelial cells was studied. The effects of human plasma on human umbilical vein and bovine pulmonary artery endothelial cells with regard to transmigration of neutrophils were compared. Transendothelial migration of neutrophils was tested employing endothelial cell-covered Transwell cell culture chamber inserts with micropore filters of 5 microns pore size. Results showed that human plasma induces neutrophil transmigration of both human umbilical vein and bovine pulmonary artery endothelial cell monolayers. Plasma samples from 50 to 69 year old men with and without carotid arteriosclerosis (N = 152) stimulated endothelial cells of human origin significantly stronger for transmigration of neutrophils than endothelial cells of bovine origin. Analyses of limits of agreement and of correlation of the two methods indicated that bovine pulmonary artery and human umbilical vein endothelial cells cannot replace each other in assays of plasma-induced activation of transmigration. Plasma levels of soluble adhesion molecule P-selectin, which are elevated in patients with arteriosclerotic diseases, are inversely related to plasma-induced activation of neutrophil transmigration of endothelial monolayers of human origin but not of bovine origin (N = 65). As rates of transmigration that were induced by plasma from subjects without carotid arteriosclerosis (N = 73) were significantly related between human and bovine endothelium, elevated plasma levels of soluble P-selectin may thus affect results of assays for plasma-induced activation of neutrophil transmigration of endothelial monolayers in a species-specific manner.
Some infectious agents may contribute to atherosclerosis by maintaining a heightened state of inflammatory response. Although the risk for atherosclerosis was associated with elevated plasma levels of endotoxin, it is difficult to firmly establish what place endotoxin assumes in the etiology of this disease. As the ability for endotoxin to promote disease may depend on its ability to initiate an inflammatory response, it may be controlled by additional regulatory factors. We measured plasma levels of endotoxin and serum levels of neopterin and soluble interleukin-2 receptor in a random population of 402 men and women, 50—79 years old at the 1990 baseline evaluation (Bruneck Study). End point of the prospective survey was incident (early) atherosclerosis in the carotid arteries as assessed with duplex ultrasound. Subjects with high endotoxin levels (90th percentile) in combination with low neopterin or soluble interleukin-2 receptor levels (below median) did not differ from those with low endotoxin in their risk of incident atherosclerosis. The risk associated with high endotoxin, however, was markedly elevated in subjects with high (above median) neopterin or soluble interleukin-2 receptor levels. The study provides epidemiological evidence that the atherogenic potential of endotoxemia is affected by concomitant immune activation.
Introduction - Secretoneurin (SN) represents a sensory, inflammatory neuropeptide which was recently demonstrated to act as an angiogenic and vasculogenic cytokine in vitro and in vivo. The present study was conducted to test the hypothesis that SN may be implicated in reparative angiogenesis. Furthermore, we challenged the healing potential of SN applied as a newly generated SN gene therapy vector in the setting of limb ischemia. Methods and Results - We cloned the human SN coding sequence into the pAAV plasmid containing a cytomegalovirus enhancer/promoter sequence. Bioactivity of recombinant SN was shown by proliferative and chemotactic activity on endothelial cells in vitro. Unilateral limb ischemia was induced in C57/bl mice by femoral artery resection. By Real Time PCR, Western Blotting, SN-specific RIA and Immunhistochemistry, we documented that SN is up-regulated in ischemic muscles. Next, we tested whether SN gene therapy may exert curative effects in this ischemia model. Injection of the SN plasmid into ischemic adductor muscles increased capillary (0.67 vs. 0.35, n = 24, p = 0.02) and arteriole (0.16 vs. 0.8, n = 24, p = 0.04) density, reduced endothelial cell apoptosis, and accelerated perfusion recovery as shown by Laser Doppler Perfusion Index (LDPI ratio ischemic/control leg after 28 days of ischemia 1.1 vs. 0.7, n = 24, p < 0.01) in comparson to pAAV-GFP (green-fluorescence protein) treated mice. Furthermore, SN gene therapy significantly reduced toe necrosis of ischemic limbs compared to control animals (26% vs. 50%, n = 24, p < 0.05). In bone marrow transplantation models, increased vascularity of ischemic hind-limbs after SN gene therapy was shown to be mediated, at least in part, by enhanced recruitment of bone marrow-derived endothelial progenitor cells. Conclusions -These results suggest that the novel angiogenic cytokine Secretoneurin is up-regulated by ischemia in skeletal muscle cells. Furthermore, results from gene therapy in this ischemia model suggest that Secretoneurin represent a promising new substance for therapeutic angiogenesis.
Background— Secretoneurin is an abundant neuropeptide of the central, peripheral, and autonomic nervous systems, located in nerve fibers characterized by a close interaction with blood vessels and known to stimulate endothelial cell migration. Methods and Results— We hypothesized that secretoneurin might act as an angiogenic cytokine and tested for these effects in vivo using a mouse cornea neovascularization model and in vitro by assessing capillary tube formation in a matrigel assay. In vivo, secretoneurin-induced neovasculature is characterized by a distinct pattern of arterial and venous vessels of large diameter and length. Immunohistochemical staining for CD-31 revealed endothelial lining of the inner surface of these vessels, and recruitment of α-smooth muscle actin–positive perivascular cells suggests vessel maturation. In vitro, secretoneurin-induced capillary tube formation was dose dependent and specific, confirming that effects of secretoneurin occur directly on endothelial cells. Secretoneurin also stimulated proliferation and exerted antiapoptotic effects on endothelial cells and activated intracellular phosphatidylinositol 3′ kinase/Akt and mitogen-activated protein kinase pathways, as demonstrated by increased phosphorylation of Akt and extracellular signal–regulated kinase. Conclusions— These data show that secretoneurin represents a novel direct angiogenic cytokine and reiterate the coordinated relationship between nervous and vascular systems.
