Impact of cadmium exposure on swine enterocytes.

We tested cadmium (Cd2+) effects on porcine IPEC-J2 cells, which represent an in vitro model of the interaction between intestinal cells and both infectious and non-infectious stressors. Accordingly, we investigated the effects of low (2 µM) to moderate (20 µM) concentrations of Cd2+, in terms of pro-inflammatory gene expression and protein release, as well as of infectivity in a Salmonella typhimurium penetration model. Our data showed a significant (P < .001) increase of intracellular Cd2+ after 3, 6 and 24 h of exposure with respect to levels at 1 h. These data showed the ability of IPEC-J2 to absorb Cd2+ as a function of both time and concentration. Also, the absorption of this heavy metal was related to a significant modulation of important pro-inflammatory messengers. In particular, down-regulation of IL-8 was associated with a significant decrease of Salmonella typhimurium ability to penetrate into IPEC-J2 cells, in agreement with a previous study in which an anti-IL 8 antibody could significantly inhibit Salmonella penetration into the same cells (Razzuoli et al., 2017). This finding demonstrates the ability of Cd2+ to affect the outcome of an important host-pathogen relationship. In conclusion, our study highlighted the ability of an environmental pollutant like Cd2+ to modulate innate immune responses in terms of chemokine release and gene expression, and susceptibility to microbial infections.

Distinct chemotactic and angiogenic activities of peptides derived from Kaposi's sarcoma virus encoded chemokines.

The vMIPs are chemokine-like proteins expressed by the Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8) during the lytic phase of viral infection. vMIP-I activates CCR8, a chemokine receptor expressed by Th2 lymphocytes and cultured monocytes. vMIP-II is an agonist for CCR3, a receptor expressed by eosinophils, and an antagonist for several other chemokine receptors. Both are highly angiogenic in the chick chorio-allantoic membrane. We designed and tested three 26-mer peptides, derived from vMIP-I (pK-I), from vMIP-II (pK-II) and from the control MIP-1alpha (pM), spanning key residues of chemokines. pK-I, pK-II and pM all were able to activate a strong chemotactic response in monocytes, higher than parental vMIP-I and II. This corresponded to induction of calcium fluxes in these cells, typical of chemokines. Interestingly, pK-II and pM were also active on PMN neutrophils. In vivo studies (matrigel sponge and rabbit cornea models) showed that pK-I retains the strong angiogenic potential exerted by vMIP-I, while pK-II and pM induced an inflammatory response, probably mediated by PMN recruitment. Our observations indicate that chemokine-derived peptides can show biological activity at pharmacological concentrations. pK-I, in particular, displays the angiogenic activity of full-length vMIP-I, while all peptides appear to have acquired additional properties, stimulating new cellular targets.

Phenotypic alterations in Kaposi's sarcoma cells by antisense reduction of perlecan.

Metastasis is a sequence of events including proliferation, migration, adhesion, invasion and subsequent metastatic growth of tumour cells in distant organs. We previously showed that highly metastatic variants of murine melanoma cells express higher levels of the basement membrane proteoglycan perlecan than low or non metastatic variants and expression of an antisense perlecan can reduce metastatic potential. In contrast, antisense expression of perlecan in fibrosarcoma cells was reported to enhance tumorigenesis. To better understand the role of perlecan in angiogenesis we have transfected KS-IMM, an immortalized cell line derived from a human Kaposi s sarcoma, with an antisense perlecan construct and investigated the positive/negative role of perlecan in KS. KS-IMM cells were transfected with either empty vector (neo) or the antisense perlecan construct and clones were isolated. Immuno-blot analysis showed a reduction of perlecan levels in two (AP3 and AP4) isolated clones, in Northern blot analysis endogenous perlecan was undetectable in the AP3 and AP4 clones, while it was present in the neo control clones. AP clones had a reduced migration to HGF in Boyden chambers as compared to neo clones. Proliferation in low serum or serum-free conditions was strongly reduced in the AP clones as compared to the neo control cells. The neotransfected cells showed rapid proliferation in low serum supplemented with HGF and VEGF, while antisense transfected clones showed little response. Finally, AP-trasfected KS-IMM cells had significantly reduced migration to VEGF and HGF with respect to controls. In contrast, when the AP transfected cells were injected in nude mice they paradoxically showed enhanced tumor growth as compared to controls. Our preliminary data indicate that perlecan reduction plays a crucial role on Kaposi s sarcoma cell migration and proliferation in vitro. However, in vivo KS-IMM depleted of perlecan had a growth advantage. A possible hypothesis is that perlecan is necessary for growth of KS-IMM cells in vitro, however its down-regulation might promote angiogenesis through increased angiogenic growth factor diffusion, resulting in enhanced tumor growth in vivo.

Inhibition of angiogenesis and vascular tumor growth by interferon-producing cells: A gene therapy approach.

We developed an in vivo gene therapy approach to characterize and optimize the anti-angiogenic activity of class I interferons (IFNs), using packaging cell lines producing an amphotropic LXSN-based retrovirus expressing either IFN-alpha1 (alpha1Am12), IFN-beta (betaAm12) murine cDNAs, or the vector alone (neoAm12). Pretreatment of endothelial-like Eahy926 cells in vitro with conditioned media (CM) from alpha1Am12 or betaAm12 cells for 48 hours significantly inhibited their migration and invasion as compared to neoAm12-CM-treated cells. betaAm12-CM also inhibited the formation of capillary-like structures on Matrigel by EAhy926 cells. In vivo, inclusion of the betaAm12 cells strongly inhibited, and alpha1Am12 partially inhibited, the angiogenic response in the Matrigel sponge model in both immune-competent and athymic nude mice. Electron microscopy showed a reduction of host cell infiltration in alpha1Am12- and betaAm12-containing sponges and reduction of invading tubular clefts of host cells as compared to controls. Finally, inoculation of either alpha1Am12 or betaAm12 cells (10%) along with a highly angiogenic Kaposi's sarcoma cell line (90%) resulted in a powerful reduction of tumor growth in nude mice in vivo, as did infection with the interferon-alpha-producing retroviruses. These data suggest that a gene therapy approach using class I interferons can effectively inhibit tumor angiogenesis and growth of vascular tumors.

N-acetylcysteine inhibits endothelial cell invasion and angiogenesis.

The thiol N-acetylcysteine (NAC) is a chemopreventive agent that acts through a variety of mechanisms and can prevent in vivo carcinogenesis. We have previously shown that NAC inhibits invasion and metastasis of malignant cells as well as tumor take. Neovascularization is critical for tumor mass expansion and metastasis formation. We investigated whether a target of the anti-cancer activity of NAC could be the inhibition of the tumor angiogenesis-associated phenotype in vitro and in vivo using the potent angiogenic mixture of Kaposi's sarcoma cell products as a stimulus. Two endothelial (EAhy926 and human umbilical vein endothelial [HUVE]) cell lines were utilized in a panel of assays to test NAC ability in inhibiting chemotaxis, invasion, and gelatinolytic activity in vitro. NAC treatment of EAhy926 and HUVE cells in vitro dose-dependently reduced their ability to invade a reconstituted basement membrane, an indicator of endothelial cell activation. Invasion of HUVE cells was inhibited with an ID50 of 0.24 mM NAC, whereas inhibition of chemotaxis required a 10 fold higher doses, indicating that invasion is a preferential target. NAC inhibited the enzymatic activity and conversion to active forms of the gelatinase produced by endothelial cells. The matrigel in vivo assay was used for the evaluation of angiogenesis; NAC strongly inhibited neovascularization of the matrigel sponges in response to Kaposi's sarcoma cell products. NAC prevented angiogenesis while preserving endothelial cells, implying that it could be safely used as an anti-angiogenic treatment.

Somatostatin controls Kaposi's sarcoma tumor growth through inhibition of angiogenesis.

Somatostatin and its analogs are active in the inhibition of SST receptor-positive endocrine neoplasms, but their activity and mechanism in nonendocrine tumors is not clear. Somatostatin potently inhibited growth of a Kaposi's sarcoma xenograft in nude mice, yet in vitro the tumor cells did not express any known somatostatin receptors and were not growth inhibited by somatostatin. Histological examination revealed limited vascularization in the somatostatin-treated tumors as compared with the controls. Somatostatin was a potent inhibitor of angiogenesis in an in vivo assay. In vitro, somatostatin inhibited endothelial cell growth and invasion. Migration of monocytes, important mediators of the angiogenic cascade, was also inhibited by somatostatin. Both cells types expressed somatostatin receptor mRNAs. These data demonstrate that somatostatin is a potent antitumor angiogenesis compound directly affecting both endothelial and monocytic cells. The debated function of somatostatin in tumor treatment and the design of therapeutic protocols should be reexamined considering these data.

The role of the thiol N-acetylcysteine in the prevention of tumor invasion and angiogenesis.

We have extensively studied the effects of N-acetylcysteine (NAC), a cytoprotective drug that can prevent in vivo carcinogenesis. Here we review our findings NAC completely inhibits gelatinolytic activity of metalloproteases and chemotactic and invasive activities of tumor cells. In addition, NAC reduces the number of lung metastases when malignant murine melanoma cells are injected into nude mice. NAC treatment decreases the weight of primary tumors and produces a dose-related increase in tumor latency. Moreover, oral administration of NAC reduces the formation of spontaneous metastases. In experimental metastasis assays, we have found a synergistic reduction in the number of lung metastases after treatment with doxorubicin (DOX) and NAC in nude mice. In tumorigenicity and spontaneous metastasis assays, the combined administration of DOX and oral NAC again has shown synergistic effects on the frequency and weight of primary tumors and local recurrences and completely prevented the formation of lung metastases. The addition of NAC to endothelial cells strongly reduces their invasive activity in response to angiogenic stimuli. NAC inhibited the degradation and release of radiolabeled type IV collagen by activated endothelial cells, indicating that NAC blocks gelatinase activity. Oral administration of NAC reduces the angiogenic response induced by KS tumor cell products, confirming the ability of NAC to inhibit the invasive activity of endothelial cells in vivo and thereby blocking angiogenesis.

beta Interferon inhibits HIV-1 Tat-induced angiogenesis: synergism with 13-cis retinoic acid.

Kaposi's sarcoma (KS) is a highly angiogenic lesion which frequently presents as an aggressive form in HIV-infected male patients. We have previously shown that the HIV-1 Tat protein induces endothelial cell migration and invasion in vitro and a rapid angiogenic response in vivo, suggesting that it acts as a cofactor in epidemic KS. In this study we tested beta interferon (IFN beta) and retinoic acid (RA) for the inhibition of Tat-induced angiogenesis using in vivo and in vitro models. IFN beta, at a concentration above 2500 U/ml, was an effective inhibitor of Tat-stimulated growth, migration and morphogenesis of an endothelial cell line in vitro and of angiogenesis in vivo. A strong reduction of properties associated with neovascularisation was induced by 10,000 U/ml. In vivo, RA alone was on ineffective inhibitor of angiogenesis, and in vitro gave only a limited inhibition of endothelial cell growth. However, 13-cis RA used in combination with IFN beta impressively potentiated its effects. A combination of lower doses of IFN beta (2500 U/ml) and 13-cis RA induced a virtually complete inhibition of the Tat-related angiogenic phenotype both in vivo and in vitro. The potentiation of the anti-angiogenic activity of IFN beta by 13-cis RA suggests that this combination could be a useful approach for the therapy of epidemic KS.

TIMP-2 over-expression reduces invasion and angiogenesis and protects B16F10 melanoma cells from apoptosis.

The matrix metalloproteinase (MMP) inhibitor TIMP-2 has a high specificity for gelatinase A/MMP-2. An imbalance between gelatinase A and TIMP-2 in favor of enzymatic activity is linked to the degradation of the extracellular matrix (ECM) associated with several physiologic and pathologic events, including angiogenesis, invasion and metastasis. Since TIMPs are secreted molecules, they have the potential to be used for gene therapy of certain tumors. We transfected B16F10 murine melanoma cells, a highly invasive and metastatic cell line, with an expression vector harboring a cDNA encoding for human TIMP-2. The clones obtained were isolated and examined for TIMP-2 over-expression and changes in tumor cell phenotype. The amount of recombinant TIMP-2 produced correlated with a reduction in invasion. In an in vivo angiogenesis assay, TIMP-2-transfected clones showed reduced levels of blood vessel formation, and in vitro conditioned media from TIMP-2 transfectants showed diminished induction of endothelial cell migration and invasion. TIMP-2 over-expression limited tumor growth in vivo and neoangiogenesis when cells were injected subcutaneously in mice in the presence of Matrigel. However, TIMP-2 overexpressing clones were found to be more resistant to apoptosis than parental and control melanoma cells, while necrosis was increased. Our data confirm the role of TIMP-2 in the down-regulation of metastasis and angiogenesis but indicate a possible involvement in tumor cell survival.

Vascular endothelial growth factor regulates angiogenesis and vascular permeability in Kaposi's sarcoma.

Abundant vasculature with increased permeability is a prominent histological feature of Kaposi's sarcoma (KS), a multifocal, cytokine-regulated tumor. Here we report on the role of vascular endothelial growth factor (VEGF) in AIDS-KS angiogenesis and vascular permeability. We demonstrate that different cytokines, which were previously shown to be active in KS development, modulate VEGF expression in KS spindle cells and cooperate with VEGF on the functional level. Northern blot analysis as well as studies on single cells using in situ hybridization revealed that VEGF expression in cultivated AIDS-KS spindle cells is up-regulated by platelet-derived growth factor-B and interleukin-1 beta. Western blot and enzyme-linked immunosorbent assay analysis of cell culture supernatants demonstrated that the VEGF protein is secreted by stimulated AIDS-KS spindle cells in sufficiently high amounts to activate proliferation of human dermal microvascular endothelial cells. Basic fibroblast growth factor did not increase VEGF expression but acted synergistically with VEGF in the induction of angiogenic KS-like lesions in a mouse model in vivo. Angiogenesis and cellularity of KS-like lesions were clearly increased when both factors were injected simultaneously into the flanks of mice, compared with separate injection of each factor. A comparable angiogenic reaction as obtained by simultaneous injection of basic fibroblast growth factor and VEGF was observed when cell culture supernatants of AIDS-KS spindle cells were used for these experiments. Finally, analysis of primary human AIDS-KS lesions revealed that high amounts of VEGF mRNA and protein were present in KS spindle cells in vivo. These data provide evidence that VEGF, in concert with platelet-derived growth factor-B, interleukin-1 beta, and basic fibroblast growth factor, is a key mediator of angiogenesis and vascular permeability in KS lesions in vivo.

Synergism between N-acetylcysteine and doxorubicin in the prevention of tumorigenicity and metastasis in murine models.

The thiol N-acetylcysteine (NAC) is a promising cancer chemopreventive agent which acts through a variety of mechanisms, including its nucleophilic and antioxidant properties. We have recently shown that NAC inhibits type-IV collagenase activity as well as invasion, tumor take and metastasis of malignant cells in mice. NAC is also known to attenuate the cardiotoxicity of the cytostatic drug doxorubicin (DOX, Adriamycin). The present study was designed to evaluate whether the combination of NAC and DOX treatments in mice injected with cancer cells could affect their tumorigenic and metastatic properties. Six separate experiments were carried out, using a total of 291 adult female mice. In experimental metastasis assays, in which B16-F10 melanoma cells were injected i.v. into (CD-1)BR nude mice, DOX significantly reduced the number of lung metastases when administered i.v. at a dose of 10 mg/kg body weight, 3 days after the i.v. injection of cancer cells. NAC inhibited lung metastases when added to the medium of cancer cells before their i.v. injection. The combined treatment with DOX and NAC, under various experimental conditions, was highly effective, showing a synergistic reduction in the number of mestastases. In tumorigenicity and spontaneous metastasis assays, in which B16-BL6 melanoma cells were injected s.c. into the footpad of C57BL/6 mice, DOX decreased the number of lung metastases when given i.p. at 2 mg/kg body weight. Oral NAC exerted significant protective effects, and considerably prolonged survival of mice. The combined treatment with DOX and NAC again showed synergistic effects on the frequency and weight of primary tumors and local recurrences, and completely prevented the formation of lung metastases in the experiment in which these end-points were evaluated at fixed times. While injection of DOX 7 days after implantation of cancer cells failed to improve the cancer-protective effects of NAC, its injection after I day resulted in a striking inhibition of lung metastases. These findings demonstrate an evident synergism between DOX (given parenterally) and NAC (given with drinking water) in preventing tumorigenicity and metastases. The indications of these animal studies warrant further evaluation in clinical trials.

RB1 oncosuppressor gene over-expression inhibits tumor progression and induces melanogenesis in metastatic melanoma cells.

The retinoblastoma gene (RB1) is frequently deleted or mutated in many tumor types and in all cases of retinoblastoma. Apart from its role in regulation of the cell cycle, the RB1 gene product (p110RB1) appears to be involved in control of differentiation. Malignant metastatic cells show many properties of poorly differentiated cells, and are highly invasive in vitro and in vivo. We have transfected the human RB1 cDNA in an expression vector under the control of the beta-actin promoter into B16F10 murine melanoma cells. These cells highly overexpress RB1 mRNA and the p110RB1 product, show reduced growth rate and increased melanogenesis in vitro. Vector control transfectants showed no alteration of invasiveness. The p110RB1 over-expressing cells also had a reduced capacity to migrate and invade through an artificial basement membrane, key characteristics of metastatic cells. When injected into nude mice, the p110RB1 over-expressing cells showed reduced tumor growth and reduced metastatic potential. The few metastasis observed were predominantly melanotic. These data indicate that RB1 gene expression is involved in melanoma cell differentiation and plays a role in downregulation of migration, invasion and metastatic potential of these cells.

Promotion of tumour metastases and induction of angiogenesis by native HIV-1 Tat protein from BK virus/tat transgenic mice.

OBJECTIVE: To characterize the T53 cell line and its clones derived from an adenocarcinoma of BK virus (BKV)/tat transgenic mice and to establish the role of native Tat in tumorigenicity, induction of metastases and angiogenesis. DESIGN AND METHODS: Tat was quantified by flow cytometry and chloramphenicol acetyltransferase (CAT) assays. Tumorigenicity and metastatic ability of cell lines were assayed in nude mice. Production of proteases was evaluated by a plasmin chromogenic assay and gelatinase zymography. The angiogenic effect was studied in vivo with conditioned medium from tumour cell lines. RESULTS: Tat protein was detected in tumour cell lines in amounts from 600-7000 molecules/cell. Conditioned medium from tumour cell lines was able to transactivate an LTR-CAT in HL3T1 cells, indicating release of extracellular Tat. Tumour cell lines, inoculated into nude mice induced angiogenic tumours with remarkable recruitment of host endothelial cells. Metastases were detected in lymph nodes, lungs, kidneys, and heart. Cell lines produced relevant amounts of proteases. Conditioned medium implanted in mice with matrigel induced an angiogenic response, enhanced by addition of heparin. Preincubation with an anti-Tat antibody abolished the angiogenic effect. CONCLUSIONS: Tat from cells from BKV/tat transgenic mice promotes tumorigenesis and formation of metastases and induces angiogenic activity. Angiogenesis occurs at physiological concentrations of Tat lower than 20 ng/ml. The effects of Tat on induction of metastases and angiogenesis appear to be mediated by activation of proteases.

Invasive phenotype of MCF10A cells overexpressing c-Ha-ras and c-erbB-2 oncogenes.

Infection with erbB-2 (E) of Ha-ras (H) oncogene-transfected cells has been previously shown to cooperatively induce anchorage-independent growth of the MCF10A human mammary epithelial cell line in vitro, but not to induce nude mouse tumorigenicity. Here we show that oncogene-transformed MCF10A are able to halt in the lungs of nude mice, a sign of organ colonization potential. We have therefore studied the transformants for in vitro migratory and invasive properties known to correlate with the metastatic potential of human mammary carcinoma cells in nude mice. MCF10A transfected with Ha-ras, infected with a recombinant retroviral vector containing the human c-erB-2 proto-oncogene (MCF10A-HE cells), show a higher invasive index than either the single transfectant (MCF10A-H) or MCF10A-erB-2(MCF10A-E) cells in the Boyden chamber chemotaxis and chemoinvasion assays. The MCF10A-HE cells also adopted an invasive stellate growth pattern when plated or embedded in Matrigel, in contrast to the spherical colonies formed by the single transformants MCF10A-H, MCF10A-E, and the parental cells. Dot-blot analysis of gelatinase A and TIMP-2 mRNA levels revealed increasing gelatinase A mRNA levels (HE > E > H > MCF10A) and reduced TIMP-2 expression in both single and double transformants. Furthermore, MCF10A-HE cells show more MMP-2 activity than parental MCF10A cells or the single transformants. CD44 analysis revealed differential isoform banding for the MCF10A-HE cells compared to parental cells, MCF10A-H and MCF10A-E, accompanied by increased binding of hyaluronan by the double transformants. Our results indicate that erB-2 and Ha-ras co-expression can induce a more aggressive phenotype in vitro, representative of the malignancy of mammary carcinomas.

Production of angiogenesis inhibitors and stimulators is modulated by cultured growth plate chondrocytes during in vitro differentiation: dependence on extracellular matrix assembly.

Secretion of angiogenesis inhibitors and stimulators is modulated during in vitro differentiation of embryonic chick growth plate chondrocytes. Supernatants from dedifferentiated cells undergoing maturation to hypertrophic chondrocytes in suspension progressively inhibited vascular cell random migration and invasion of basement membrane matrix by endothelial cells. Maximal inhibition was exhibited by conditioned medium from hypertrophic chondrocytes. The same medium also repressed vascular cell migration induced by highly angiogenic Kaposi's sarcoma cell supernatants and prevented formation of an anastomosed network of tube-like structures by endothelial cells plated on matrigel. On the contrary, when the suspension culture of hypertrophic chondrocytes was supplemented with ascorbic acid, a condition leading to the formation of a mineralized tissue similar to calcified cartilage, a dramatic switch to production of angiogenic activity was observed. Medium conditioned by osteoblast-like cells derived from hypertrophic chondrocytes also induced vascular cell migration and invasion of basement membrane matrix. The presence of angiogenic activity in the conditioned medium was assessed also by an in vivo assay in mice using reconstituted basement membrane associated with heparin. Therefore, interactions of chondrocytes with their extracellular matrix are an absolute requirement for the expression of angiogenic activities by hypertrophic chondrocytes at late developmental stages.

Mechanisms of kaposis-sarcoma cell supernatant-induced vascular cell invasion.

Kaposi's sarcoma (KS) is a highly angiogenic lesion frequently associated with acquired immune deficiency syndrome. Histologically the lesions appear to contain proliferative 'spindle shaped' cells with a mixed smooth muscle-endothelial-fibroblastic histotype and a conspicuous neovascularization, derived from host cell recruitment. Media conditioned by cultured KS cells (KS-CM) have angiogenic properties. KS-CM is able to promote endothelial and smooth muscle cell migration and invasion. The mechanisms of this KS-CM activity are still unknown. We hypothesize that KS-CM contains numerous factors with different roles in inducing the neo angiogenic process. We show that AIDS-IST-KS cell supernatants induce gelatinase A production and plasminogen activator (PA) up-regulation in vascular cells. KS-CM activity in vivo is heparin dependent. Also bFGF alone, a heparin dependent factor, alone can induce endothelial and smooth muscle cell invasion, MMP-2 production and PA activity. However, antibodies to bFGF do not block KS-CM activity and do not reduce the effect on PA up-regulation. This evidence suggests that heparin-binding factors other than bFGF may be present. Chromatography of KS-CM on heparin-sepharose demonstrates the presence of two heparin-binding fractions with chemotactic and gelatinase A inducing activity. The flow through was also active. KS-CM absorption on heparin-sepharose beads did not modify its induction of PA activity, further evidence for the presence of non heparin-binding factors as well.

Angiogenic potential in vivo by Kaposi's sarcoma cell-free supernatants and HIV-1 tat product: inhibition of KS-like lesions by tissue inhibitor of metalloproteinase-2.

OBJECTIVE: To determine the neoplastic nature of Kaposi's sarcoma (KS). A highly vascularized lesion, KS is frequently associated with AIDS, indicating HIV products may be involved. DESIGN AND METHODS: We determined the angiogenic properties of KS cell-secreted products and the HIV-1-tat gene product in vivo. Cell-free secreted products (KS-CM) from cultured epidemic and sporadic KS spindle cells or recombinant (r) HIV-1 tat protein were injected into mice with a matrix support (Matrigel). RESULTS: KS-CM produced lesions carrying all the phenotypic hallmarks of KS, as observed by light and electron microscopy: spindle-shaped cells, haemorrhages and an inflammatory infiltrate, as well as Factor VIII-positive endothelial cells lining new blood vessels. Electron microscopy indicated an initial granulocyte invasion, with spindle-cell migration and neocapillary formation in the centre of the matrix. These lesions required the cofactor heparin; KS-CM or heparin alone were poorly angiogenic. A less intense angiogenesis, with lower cellularity and few granulocytes, was observed in basic fibroblast growth factor (bFGF)/heparin lesions, indicating that factors other than bFGF are present in the KS spindle-cell products. When the collagenase inhibitor tissue inhibitor of metalloproteinases (TIMP)-2 was added to the sponges, KS-CM-induced angiogenesis was reduced by approximately 65% and bFGF-induced angiogenesis inhibited completely. Recombinant HIV-1 tat protein, a growth factor for KS cells, induced vascularization that was also enhanced by heparin, implying that HIV-1 tat could contribute to the aetiology of HIV-associated KS. CONCLUSIONS: KS-like lesions were obtained by injecting cell-free secreted products, suggesting that KS is a 'self-propagating' proliferative lesion caused by a cytokine imbalance and not a true neoplasm. Heparin-binding factors appear to be involved, and HIV-1 tat angiogenic properties implicate this molecule in AIDS-associated KS. Inhibition of KS-CM-induced KS-like lesions by TIMP-2 suggests that metalloproteinase inhibitors could be potential therapeutic agents for KS.