Cooperative effect of TNFalpha, bFGF, and VEGF on the formation of tubular structures of human microvascular endothelial cells in a fibrin matrix. Role of urokinase activity.

In angiogenesis associated with tissue repair and disease, fibrin and inflammatory mediators are often involved. We have used three-dimensional fibrin matrices to investigate the humoral requirements of human microvascular endothelial cells (hMVEC) to form capillary-like tubular structures. bFGF and VEGF165 were unable to induce tubular structures by themselves. Simultaneous addition of one or both of these factors with TNFalpha induced outgrowth of tubules, the effect being the strongest when bFGF, VEGF165, and TNFalpha were added simultaneously. Exogenously added u-PA, but not its nonproteolytic amino-terminal fragment, could replace TNFalpha, suggesting that TNFalpha-induced u-PA synthesis was involved. Soluble u-PA receptor (u-PAR) or antibodies that inhibited u-PA activity prevented the formation of tubular structures by 59-99%. epsilon-ACA and trasylol which inhibit the formation and activity of plasmin reduced the extent of tube formation by 71-95%. TNFalpha or u-PA did not induce tubular structures without additional growth factors. bFGF and VEGF165 enhanced of the u-PAR by 72 and 46%, but TNFalpha itself also increased u-PAR in hMVEC by 30%. Induction of mitogenesis was not the major contribution of bFGF and VEGF165 because the cell number did not change significantly in the presence of TNFalpha, and tyrphostin A47, which inhibited mitosis completely, reduced the formation of tubular structures only by 28-36%. These data show that induction of cell-bound u-PA activity by the cytokine TNFalpha is required in addition to the angiogenic factors VEGF165 and/or bFGF to induce in vitro formation of capillary-like structures by hMVEC in fibrin matrices. These data may provide insight in the mechanism of angiogenesis as occurs in pathological conditions.

Role of interleukin 1 and granulocyte colony-stimulating factor in photofrin-based photodynamic therapy of rat rhabdomyosarcoma tumors.

Neutrophils play an important role in the efficacy of photodynamic therapy (PDT). These leukocytes rapidly accumulate into the tumor lesion after PDT and most likely eradicate the remaining attenuated tumor cells. The underlying mechanism of the accumulation of neutrophils at the time of PDT is not known. Therefore, we determined the effect of PDT on the course of mature and immature neutrophils in the circulation of rhabdomyosarcoma-bearing rats and studied the changes in the level of interleukin (IL)-1beta as an important stimulator of the proliferation of precursor cells of the granulocyte lineage in the bone marrow. We found that the effect of PDT on tumor growth was preceded by a rapid and specific increase of the number of mature neutrophils in the peripheral blood as early as 4 h after the start of PDT treatment and reaching maximum values after 8 h. At 24 h, the neutrophil numbers in the PDT-treated rats were still elevated as compared to sham-treated rats. In sham-treated rats, the numbers of blood monocytes and lymphocytes decreased by about 50% after 2 h and returned to their normal levels as soon as 2 h later. In PDT-treated rats, the course of monocyte numbers showed a similar pattern; however, lymphocyte numbers did not reach the normal range until 24 h. The specific increment of neutrophils was preceded by an increase of band neutrophil numbers and elevated serum levels of IL-1beta which were maximal at 2 h after the start of PDT. Pearson correlation analysis showed a significant association between the serum levels of IL-1beta at this time point and the number of band neutrophils at 4 h (R2 = 0.58; P = 0.03) and the number of mature neutrophils at 8 h (R2 = 0.54; P = 0.04). This suggests that PDT evoked an IL-1-dependent increased production rate of neutrophils in the bone marrow. Further investigation showed that the injection of anti-granulocyte colony-stimulating factor (G-CSF) antibodies not only attenuated the increase in neutrophil numbers but also greatly decreased the efficacy of PDT. On this basis, we suppose that an IL-1-induced release of G-CSF by PDT underlies this nonspecific immune reaction to the tumor. Apparently, G-CSF not only stimulates the production rate of neutrophils in the bone marrow but also increases the functional activity of these leukocytes to become indispensable tumor cell killers.

Evidence for an important role of neutrophils in the efficacy of photodynamic therapy in vivo.

To investigate the role of neutrophils in the efficacy of photodynamic therapy (PDT) in rhabdomyosarcoma-bearing rats, the number of these circulating phagocytes was decreased or increased before interstitial PDT by use of rabbit anti-rat neutrophil serum or granulocyte colony-stimulating factor, respectively. After administration of the antiserum, the number of circulating neutrophils decreased by 99.9%. However, the number of monocytes, lymphocytes, and platelets decreased as well (by 100%, 80%, and 25%, respectively). Under these conditions, PDT did not retard tumor growth at all. However, after cessation of the antiserum treatment 5 days after PDT, a striking decrease in the growth rate occurred subsequent to an increase above the normal range of the number of circulating neutrophils. Administration of the granulocyte colony-stimulating factor led to a specific 4-fold increase in the number of circulating neutrophils. In these rats, the tumor growth at day 2 after PDT was retarded as compared with PDT-treated rats that received saline only. Statistical evaluation of both experimental conditions showed that the efficacy of PDT, expressed as the percentage of change in tumor volume at day 2 after treatment, was dependent on the number of circulating neutrophils present at the day of PDT (P = 0.001; r2 = 0.482). Apparently, neutrophils are indispensable for successful PDT in vivo.

Expression of Tcf/Lef and sFrp and localization of beta-catenin in the developing mouse lung.

Recent evidence that Wnts and other genes in the Wnt signaling pathway are expressed in embryonic and adult mouse lung suggests that this pathway is important for cell fate decisions and differentiation of lung cell types. We therefore examined the expression and protein distribution of several Wnt pathway components during prenatal mouse lung development using whole-mount in situ hybridization and immunohistochemistry. Between embryonic days 10.5 and 17.5 (E10.5-E17.5), beta-catenin was localized in the cytoplasm, and often also the nucleus, of the undifferentiated primordial epithelium (PE), differentiating alveolar epithelium (AE; present from E14.5 onward), and adjacent mesenchyme. Tcf1, Lef1, Tcf3, Tcf4, sFrp1, sFrp2 and sFrp4 were also expressed in the PE, AE, and adjacent mesenchyme in specific spatio-temporal patterns.

Prevention of late lumen loss after coronary angioplasty by photodynamic therapy: role of activated neutrophils.

Restenosis after coronary angioplasty arises from fibrocellular intimal hyperplasia and possibly failure of the artery to enlarge adequately. Which mechanisms underlie this process is only partly understood. No drugs have been clinically effective in reducing the incidence of restenosis. Since recently, photodynamic therapy (PDT) is being investigated as a possible treatment for intimal hyperplasia. PDT involves the systemic administration of a light-excitable photosensitizer that is taken up rather preferentially by rapidly proliferating cells. During laser irradiation light energy is transferred from the photosensitizer to oxygen generating the highly reactive singlet oxygen. This potent oxidizer can cause severe cellular damage. After PDT of a balloon-injured artery from the rat and rabbit the media remained acellular for several weeks to months, and intimal hyperplasia did not occur. The endothelial lining regenerated by two weeks, but why smooth muscle cells did not repopulated the media is not known. Neutrophils seem to play an important role in the prevention of restenosis after coronary angioplasty, since the activation status of this type of phagocyte is directly related to vessel diameter at late follow-up. Furthermore, it has been observed that neutrophils adhere to the microvascular wall upon PDT in vivo. In vitro findings suggest that the increased neutrophil adherence was not dependent on a decreased release of the anti-adhesive factors NO and prostacyclin by the PDT-treated endothelial cells. Furthermore, PDT did not stimulate the expression of P-selectin by the endothelial cells, one of the adhesion receptors for neutrophils. The endothelial cells only retract upon PDT allowing the adherence of neutrophils by their beta 2-integrin adhesion receptors to the subendothelial matrix. On the basis of these findings, we presume that the successful prevention of intimal hyperplasia by PDT partly depends on the presence of the neutrophil at the site of the lesion.

Photodynamic treatment of human endothelial cells promotes the adherence of neutrophils in vitro.

The effects of photodynamic treatment (PDT) on venules include vascular leakage accompanied by oedema formation, vasoconstriction and blood flow stasis. The goal of this study was to gain insight into the mechanism underlying these vascular events by studying one of the earliest observations after PDT, granulocyte adhesion, in an in vitro model. For this purpose human umbilical vein endothelial cells (HUVECs) preincubated with Photofrin II (PII) were illuminated with red light and incubated with neutrophils. PDT led to a dramatic change in the morphology of the endothelial cells. Clearly, neutrophils adhered to the subendothelial matrix and their adherence coincided with an increase in the percentage of exposed subendothelial matrix by the gradual contraction of endothelial cells. Furthermore, the increase in adherence was dependent on drug dose, illumination time and the time delay after PDT. The neutrophil adherence could be inhibited by anti-beta2-integrin antibodies, which suggests that the alphaL-, alphaM- or alphaX-beta2 receptors of the neutrophil mediated this phenomenon. At 4 degrees C or by preincubation of the neutrophils with staurosporin, their adherence to the subendothelial matrix exposed by PDT of endothelial cells could be prevented. Apparently, activation of the beta2-integrin receptor by interaction with the subendothelial matrix is necessary for the increased binding of neutrophils. Taken together, these in vitro findings suggest that the PDT-induced contraction of the endothelial cells permits neutrophil adherence to the subendothelial matrix. It is conceivable that a similar mechanism contributes to the initial adherence of granulocytes to the vessel wall as observed after PDT in vivo.

Regulation of matrix metalloproteinase expression in human vein and microvascular endothelial cells. Effects of tumour necrosis factor alpha, interleukin 1 and phorbol ester.

Matrix metalloproteinases (MMPs) play a role in tissue remodelling and angiogenesis. We have investigated the expression and regulation of MMP-1 (interstitial collagenase), MMP-2 (gelatinase A), MMP-3 (stromelysin 1), MMP-7 (matrilysin), MMP-9 (gelatinase B) and their inhibitors TIMP-1 and TIMP-2 in human umbilical vein, femoral vein and microvascular endothelial cells, and compared these data with those obtained with human synovial fibroblasts. Non-stimulated vein endothelial cells expressed the mRNAs for MMP-1, MMP-2, TIMP-1 and TIMP-2. MMP-3 mRNA and protein were undetectable or only weakly expressed, but could be stimulated by the inflammatory mediator tumour necrosis factor alpha (TNF alpha). The expression of MMP-3 and MMP-1 was further enhanced by phorbol 12-myristate 13-acetate (PMA). Phorbol ester also induced TIMP-1 and MMP-9, the expression of the latter being further enhanced by TNF alpha or interleukin 1 alpha (IL-1 alpha). Similar stimulatory effects were observed in microvascular endothelial cells. Hence the inflammatory mediator TNF alpha induces/enhances the production of several matrix metalloproteinases in human endothelial cells. On the other hand, MMP-2 and TIMP-2 were not affected or were affected in a variable way by TNF alpha and/or phorbol ester, suggesting a dissimilar regulation of these proteins. The cyclic AMP-enhancing agent forskolin affected the production of MMPs in a cell-type-specific way. In human vein endothelial cells it enhanced the PMA-mediated induction of MMP-9, whereas it suppressed this induction in human microvascular endothelial cells and in synovial fibroblasts. On the other hand, forskolin suppressed the PMA-mediated induction of MMP-1 and MMP-3 in synovial fibroblasts, while it enhanced or did not affect this induction in various types of human endothelial cells. These observations may have implications for future pharmacological intervention in angiogenesis.