Issues in Medicine

Rasmussen aneurysms are abnormalities of the pulmonary arterial system caused by tuberculosis (TB). They are associated with a highmortality rate when they cause life-threatening haemoptysis. High TB-prevalence regions have a large burden of TB-related haemoptysisbut often limited resources. This series of 25 patients who presented with life-threatening haemoptysis from current and/or previous TBwere found to have abnormal pulmonary arteries on computed tomography pulmonary angiogram (CTPA), which were judged to belikely contributors to their bleeding, either in isolation or with concomitant abnormal bronchial or systemic vasculature. These patientsunderwent transcatheter placement of Amplatzer vascular plugs in the feeder pulmonary artery. Bronchial and systemic lesions wereaddressed separately as needed. Immediate technical success was achieved in all patients, but four of them experienced intraoperativehaemoptysis related to dislodgement of the occluding platelet plug by the high-pressure automatic injector and wire. At 48 hours after theprocedure, 18 (72%) remained haemoptysis-free. Six of these experienced recurrence within 1 year of their procedure. Pulmonary arteryplacement of an Amplatzer vascular plug is a feasible option for treating bleeding Rasmussen aneurysms, but should be part of a combinedapproach to addressing suspected culprit vascular lesions in all intrathoracic vascular systems.

First 5-year TAVR/TAVI Outcomes from the South African SHARE-TAVI national registry and the influence of malignancy on late outcomes

Introduction

The South African (SA) national prospective multicentre observational SHARE-TAVI registry aims to provide local outcomes data on all TAVIs in State & Private sectors, to support local evidence-based policy evaluations, comparing outcomes to international data & identifying local variations.

Method

All 20 implant centres voluntarily capture all-comers data into the web-based registry. 2266 patients from 1 Sept 2014 to 28 Feb 2022 had pre-TAVI clinical evaluations and 1502 proceeded to TAVI & had procedural data & complications (VARC2 criteria), 30d & annual follow up recorded. The 5-yr cohort of 289 patients have clinical history and profile similar to international data (Table 1).

Results

Procedural success of 93.43% and 1-year mortality of 15.92% in the 5-yr cohort (STS score 8.85%) are similar to reported international data in early TAVI programmes. All-cause mortality at 5-years is 44.3% (in PARTNER 1 – 67.8%, PARTNER 2.0 – 46.0%), and the greatest proportion of non-cardiac mortality (38.5%) occurs in period >1–2yr post-TAVI (lowest proportion 29.4% in >3–4yr period). Outcomes measures in a more recent 2020 patient cohort (n=219, success 98.63% and 1-yr mortality 8.85%, STS risk score 5.51%) have improved compared to the 5-yr cohort.

Patients with “Prior or current malignancy” (POCM) at TAVI evaluation have increased mortality in both the 1-yr outcome (n=637) cohort, 18.7% 1-yr mortality vs 9.3% in those without POCM, and same trend in the 2-year outcome cohort n=443 (28.0% 2-year mortality vs 12.8% without malignancy). Frail patients with POCM in the 2-yr cohort have substantially higher mortality at 2 years, 34.8% than frail patients without POCM 15.9%

At evaluation 66% of patients are NYHA class III+IV, post-TAVI only 5.9% at 30d & 8.8% at 1-year, at 1-year 30% of patients have maintained improvement by 2 or 3 NYHA classes.

Conclusion

5-yr outcomes in SA are comparable to international data, and procedural outcomes have improved further as to be expected with maturation of the programme and technology. The NYHA class distribution at 1-yr shows improvements which should translate into improved quality of life, future studies should include patient self-reported quality of life assessments to verify this benefit. Malignancy, even if prior, may predict poorer outcomes in the longer term, possibly due to reported higher frailty in these patients. Amongst other factors, prior or current malignancy may be considered relevant when assessing patients for futility for TAVI in SA's severely constrained healthcare resource environment.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Educational and Research Grants from SA Heart Association and Medtronic, Edwards Life Sciences

2022 SASCI/SCTSSA joint consensus statement and guideline on transcatheter aortic valve implantation (TAVI) in South Africa

Patients with severe symptomatic aortic stenosis (AS) have traditionally been treated with surgical aortic valve replacement (sAVR). Transcatheter aortic valve implantation is a percutaneous option that has been shown to be at least as effective as sAVR in numerous subgroups of patients with severe AS. This is an update on the previous joint consensus statement and guideline on transcatheter aortic valve implantation (TAVI) in South Africa, published in 2016. It provides guidance on which patients should preferably be offered TAVI over sAVR, with special consideration of the resource-constrained environment in South Africa.

TAVI In South Africa's resource-constrained economy: the role of local data in overcoming funding resistance

 

The South African (SA) prospective multi-centre observational SHARE-TAVI registry aims to provide local outcomes data on all TAVIs in State & Private sectors, to support local evidence-based policy evaluations, comparing outcomes to international data & identifying local variations.

Methods and results

All 14 implants centres voluntarily capture data into the web-based SHARE-TAVI registry. 1375 patients from Sept 2014-Jan 2020 had pre-TAVI clinical evaluations, 998 proceeded to TAVI & procedural data & complications recorded (VARC-2 criteria), 30d & annual follow up. State sector hospitals provide limited tertiary cardiac care due to severe resource constraints. 13% of TAVIs in SA are in State teaching hospitals, 6.2% of State implants are 2nd generation (2G) devices. In the Private sector the roll-out of TAVI is inhibited by funding resistance, particularly to higher-cost 2G valves. 1st generation (1G) implants comprise 30% of 2019 implants, funding policies leave patients with unaffordable co-payments for 2G valves. Local data (Table 1) shows peri- & 1-year mortality, & procedural success (average 95.4%, & in 2019 98.91%), which are comparable with international data. TAVI in SA is successful despite low volumes & resource limitations. Local data supports superiority of 2G over 1G i.t.o this data and hospital stay length, & unplanned valve-in-valves. No significant differences between 1G & 2G in re-admissions in year 1, but improved quality of life patients experience with TAVI implantation is notable in the NYHA class.

Funding Acknowledgement

Type of funding source: Other. Main funding source(s): SA Heart Association registry project funding. Unrestricted educational grants by Medtronic and Edwards Life Sciences

P6518Radial artery dilatation to improve access and lower complication rates during coronary angiography (RADIAL): a randomized controlled trial

Background

Transradial catheterization has become the preferred access site for coronary angiography. The transradial approach is however not without challenges and complications. Cannulation is technically challenging and may require multiple cannulation attempts or access may fail. Local access site complications may occur postprocedurally.

Purpose

To explore the use of prolonged occlusion flow mediated dilatation (PO-FMD) to dilate the radial artery prior to cannulation to reduce puncture attempts, increase cannulation success and reduce access site complications in transradial coronary angiography.

Methods

1156 patients undergoing transradial coronary angiography were randomized into PO-FMD and sham PO-FMD groups. PO-FMD was achieved by a 10 minute inflation of a blood pressure cuff on the arm to above systolic pressure, followed by deflation with resultant radial artery dilation. In the sham PO-FMD group the cuff was not inflated. The operators were blinded to the intervention.

Results

580 patients were randomized to the sham PO-FMD group and 576 to the PO-FMD group. The number of puncture attempts were reduced with the use of PO-FMD, with a median number of attempts of 1 in the PO-FMD group and 2 in the sham PO-FMD group (p<0.001). Cannulation failure was reduced with PO-FMD FMD with cannulation failure rates of 2.7% in the PO-FMD group and 5.8% in the sham PO-FMD group (p=0.01). Radial artery pulsation loss (RAPL) was reduced with PO-FMD with 1.4% in the PO-FMD group and 3.8% in the sham PO-FMD group (p=0.02).

Conclusion

PO-FMD decreases puncture attempts, reduces cannulation failure rates and decreases RAPL during transradial coronary angiography.

P3692Funding resistance and 1-year outcomes in SHARE-TAVI, a local South African TAVR/TAVI registry

Methods and results

Participation in this voluntary registry, with 93% capture compliance, was incentivized by linking the capture of TAVI evaluation data with the funding application process, leading to a reduction in funding decision waiting time from average +180 days (2014) to current average of 92 days. Restrictive funding policies limit the expansion of TAVI in SA, with approximately 200 TAVIs recorded annually each in 2017 and 2018 from combined participation of 8 Private and 3 State TAVI centres, 9 of which do <20 implants/year.

From Sept 2014 to Dec 2018 inclusive, 894 patients were entered into the registry as part of TAVI evaluations, currently 102 patients await funding decisions (outstanding decisions ranging from 2–1185d). Deteriorating patient health during delayed Funder responses resulted in mortality prior to TAVI date for 8 patients whose funding was approved, & ineligibility for TAVI due to deterioration for 9 awaiting decisions (mean wait 115d). Mortality occurred in 21 others awaiting funding approval. 36% of patients declined funding (n=21/59) died within 1 year.

For the 663 patients who received implants, procedural & complications data were entered according to VARC-2 criteria, & postoperative follow-up at 30d & annually to 5 years. The implanted cohort is comparable to similar registry & trial populations (GARY, SOURCE 3, & US Corevalve Pivotal), in mean age [80.1±7.2yrs], gender [54.9% male], & mean risk predictions 7.0±7.4% [STSPROM], 23.0±15.7 [logEuroSCORE] & 6.4±5.0% [EuroSCORE 2], and Clinical History/Risk.

All-cause mortality of 10.48% (n=48/458) at 1-year compares favourably to published TAVI populations [14,2% US Corevalve, 12.6% SOURCE 3, 20% GARY], with non-cardiac mortality at 33% (n=16/48) mostly attributable to cancer, pneumonia and renal failure. State and Private care offer similar procedural success (State 93.1%, Private 93.7%), and hospital stays - mean ICU [State 1.43±1.58d, Private 2.48±1.99d] & total length of stay [State LOS 4.51±2.87d, Private LOS 5.19±4.24d]. At 30d new permanent pacemaker implantation is needed in 7.5% patients (n=50/663), & in 9.85% at 1-year (n=45/458), these comparatively low rates are being investigated in a sub-study of SHARE-TAVI.

Conclusions

Cumbersome TAVI funding processes & funding resistance contribute to unacceptable mortality figures in appropriately selected patients awaiting funding approval decisions, despite the SHARE-TAVI registry offering independent local data that confirms that TAVI in local resource-constrained settings compares favourably to international best practice standards, even with relatively low volumes at both State and Private centres.

Acknowledgement/Funding

Edwards and Medtronic Unrestricted Educational grants, SA Heart Association Registry Projects

Application of finite element analysis to the design of tissue leaflets for a percutaneous aortic valve

Percutaneous Aortic Valve (PAV) replacement is an attractive alternative to open heart surgery, especially for patients considered to be poor surgical candidates. Despite this, PAV replacement still has its limitations and associated risks. Bioprosthetic heart valves still have poor long-term durability due to calcification and mechanical failure. In addition, the implantation procedure often presents novel challenges, including damage to the expandable stents and bioprosthetic leaflets. In this study, a simplified version of Fung's elastic constitutive model for skin, developed by Sun and Sacks, was implemented using finite element analysis (FEA) and applied to the modelling of bovine and kangaroo pericardium. The FEA implementation was validated by simulating biaxial tests and by comparing the results with experimental data. Concepts for different PAV geometries were developed by incorporating valve design and performance parameters, along with stent constraints. The influence of effects such as different leaflet material, material orientation and abnormal valve dilation on the valve function was investigated. The stress distribution across the valve leaflet was also examined to determine the appropriate fibre direction for the leaflet. The simulated attachment forces were compared with suture tearing tests performed on the pericardium to evaluate suture density. It is concluded that kangaroo pericardium is suitable for PAV applications, and superior to bovine pericardium, due to its lower thickness and greater extensibility.

Anti-VEGFR-2 scFvs for cell isolation. Single-chain antibodies recognizing the human vascular endothelial growth factor receptor-2 (VEGFR-2/flk-1) on the surface of primary endothelial cells and preselected CD34+ cells from cord blood

Five specific single-chain antibodies recognizing the human vascular endothelial growth factor receptor-2 (VEGFR-2/KDR) were selected from a V-gene phage display library constructed from mice immunized with the extracellular domain of VEGFR-2 (Ig-like domain 1-7). All five scFv antibodies (A2, A7, B11, G3, and H1) bound to the purified native antigen in enzyme-linked immunosorbent assay and Dot Blot, and showed no crossreactivity to the human VEGF-receptor 1 (VEGFR-1). The selected antibodies recognize a conformation-dependent epitope of the native receptor and do not recognize denatured antigen in Western blots, as well as linear overlapping peptides comprising the sequence of the human VEGFR-2. The five scFv antibodies bind to the surface of endothelial cells overexpressing human VEGFR-2 c-DNA (PAE/VEGFR-2 cells) as detected by surface immunofluorescence using confocal microscopy. In addition scFv A7 specifically detected VEGFR-2 expressing endothelial cells in the glomerulus of frozen human kidney tissue sections. Therefore, A7 has potential clinical application as a marker for angiogenesis in cryosections of different human tissues. Additionally, two recombinant scFvs (A2 and A7) very efficiently recognize VEGFR-2 on PAE/VEGFR-2 cells and freshly prepared human umbilical vein endothelial cells by fluorescence-activated cell sorter (FACS) analysis. The scFv fragment A7, which was the most sensitive antibody in FACS analysis, recognizes human CD34+VEGFR-2+ hematopoietic immature cells within the population of enriched CD34+ cells isolated from human cord blood. The dissociation constant of A7 was determined to be K(d) = 3.8 x 10(-9) M by BIAcore analysis. In conclusion, scFv fragment A7 seems to be an important tool for FACS analysis and cell sorting of vascular endothelial cells, progenitor cells and hematopoitic stem cells, which are positive for VEGFR-2 gene expression.

Poor responder-high responder: the importance of soluble vascular endothelial growth factor receptor 1 in ovarian stimulation protocols

This study was designed to detect vascular endothelial growth factor (VEGF) and its soluble receptor (sVEGFR-1) in follicular fluid specimens and to evaluate the importance of sVEGFR-1 with respect to ovarian response to gonadotrophin stimulation. A total of 69 patients was treated for IVF with recombinant human follicle stimulating hormone (FSH). Concentrations of VEGF and sVEGFR-1 were quantified in follicular fluids from oocyte retrievals. Patients were designated to three groups with respect to the number of harvested oocytes: group A, 1-5 oocytes; group B, 6-10 oocytes; group C, >10 oocytes. In group A, 1133 +/- 870 pg VEGF/ml follicular fluid per oocyte were quantified, in group B 426 +/- 262 pg VEGF/ml per oocyte, and in group C 274 +/- 179 pg VEGF/ml per oocyte. Soluble VEGFR-1 concentrations resulted in 1200 +/- 523 pg/ml follicular fluid per oocyte in group A, 255 +/- 193 pg/ml per oocyte in group B, and 79 +/- 69 pg/ml per oocyte in group C. No free sVEGFR-1 could be detected in any follicular fluid. An index to estimate the biological activity of VEGF by dividing VEGF/sVEGFR-1 revealed an increasing availability of VEGF with higher ovarian response to gonadotrophin therapy. In group A this index was 1.03, in group B 1.71, and in group C 3.21. A delicate balance between VEGF and sVEGFR-1 is necessary to allow an adequate ovarian reaction to gonadotrophin therapy. Excess of bio-active VEGF increases the risk for ovarian hyperstimulation syndrome. Excess of sVEGFR-1 results in poor response and goes in parallel with reduced chances for conception.

Expression of vascular endothelial growth factor receptors 1, 2 and 3 in placentas from normal and complicated pregnancies

Extensive angiogenesis and invasion of the maternal decidua by trophoblasts are essential for the development and function of the placenta. Vascular endothelial growth factors (VEGF), placenta growth factor (PlGF) and their receptors VEGFR-1/Flt-1, VEGFR-2/KDR and VEGFR-3/Flt4 have important roles in vasculogenesis and angiogenesis. We have studied the localization of these proteins by immunohistochemistry and Western blotting in the placenta and of PlGF in maternal serum, and their association with diabetes, pre-eclampsia, fetal growth restriction (FGR) and fetal alcohol syndrome (FAS). VEGFR-1 and VEGFR-3 were detected mainly in the syncytiotrophoblastic layer whereas VEGFR-2 was detected in the vascular endothelial cells of the placenta. VEGFR-1, but not the other receptors, showed increased expression in placental syncytiotrophoblasts from 50% of patients with severe pre-eclampsia and FGR when compared with normal placentas. PlGF was undetectable in 38 of 44 samples of amniotic fluid of mothers with normal and complicated pregnancies. However, maternal serum PlGF concentrations were significantly lower in pre-eclamptic patients and in those with FGR when compared to diabetic women or healthy controls. These results suggest that low maternal serum PlGF and increased placental expression of its receptor VEGFR-1 are associated with pre-eclampsia and FGR.

Amniotic fluid--soluble vascular endothelial growth factor receptor-1 in preeclampsia

OBJECTIVE

To measure the levels of the soluble receptor for the potent angiogenic agent vascular endothelial growth factor (VEGF) in amniotic fluid (AF) in healthy and complicated pregnancies, and compare them with levels of erythropoietin, another factor upregulated by hypoxia.

METHODS

We assessed amniotic fluid from the second (n = 35, gestational weeks 14-19) and third (n = 29) trimesters of healthy women, and from the third trimesters of preeclamptic (n = 22) and diabetic women with (n = 11) or without preeclampsia (n = 34) and from women with fetal growth restriction (FGR) (n = 14) for soluble VEGF receptor-1 (VEGFR-1) by enzyme-linked immunosorbent assay.

RESULTS

In early normal pregnancy, AF-soluble VEGFR-1 levels were higher (median 22 ng/mL, range 2.3-29.5 ng/mL) than in the third trimester (median 13 ng/mL, range 0.5-32 ng/mL; P < .05). In preeclamptic women during the third trimester, levels were higher (median 20 ng/mL, range 10.5-37 ng/mL; P < .05) than healthy controls. The lowest third-trimester levels were in diabetic women (median 11 ng/mL, range 0.5-27 ng/mL). In women with preeclampsia and diabetes, AF-soluble VEGFR-1 levels remained lower (median 13, range 6-32 ng/mL; P < .05) than in women with preeclampsia alone. Amniotic fluid levels of soluble VEGFR-1 in women with FGR (median 19.5 ng/mL, range 5-40 ng/mL) did not statistically differ from those of controls. The AF levels of soluble VEGFR-1 did not correlate with those of erythropoietin. Soluble VEGFR-1 was clearly detectable (median 14 ng/mL, range 9-22 ng/mL) in culture media from placental biopsies (n = 20).

CONCLUSION

Preeclampsia is associated with increased levels of soluble VEGFR-1, which are independent of erythropoietin, another hypoxia-inducible factor.

VEGFR-3 and its ligand VEGF-C are associated with angiogenesis in breast cancer

Recently, monoclonal antibodies against the human vascular endothelial growth factor receptor VEGFR-3 were shown to provide a specific antigenic marker for lymphatic endothelium in various normal tissues. In this study we have investigated the expression of VEGFR-3 and its ligand VEGF-C in normal breast tissue and in breast tumors by immunohistochemistry. VEGFR-3 was weakly expressed in capillaries of normal breast tissue and in fibroadenomas. In intraductal breast carcinomas, VEGFR-3 was prominent in the "necklace" vessels adjacent to the basal lamina of the tumor-filled ducts. VEGF receptor 1 and 2 as well as blood vessel endothelial and basal lamina markers were colocalized with VEGFR-3 in many of these vessels. Antibodies against smooth muscle alpha-actin gave a weak staining of the necklace vessels, suggesting that they were incompletely covered by pericytes/smooth muscle cells. A highly elevated number of VEGFR-3 positive vessels was found in invasive breast cancer in comparison with histologically normal breast tissue (P < 0.0001, the Mann-Whitney test). VEGF-C was located in the cytoplasm of intraductal and invasive cancer cells. The results demonstrate that the expression of VEGFR-3 becomes up-regulated in the endothelium of angiogenic blood vessels in breast cancer. The results also suggest that VEGF-C secreted by the intraductal carcinoma cells acts predominantly as an angiogenic growth factor for blood vessels, although this paracrine signaling network between the cancer cells and the endothelium may also be involved in modifying the permeabilities of both blood and lymphatic vessels and metastasis formation.

Hypoxia down-regulates placenta growth factor, whereas fetal growth restriction up-regulates placenta growth factor expression: molecular evidence for "placental hyperoxia" in intrauterine growth restriction

Early placental development occurs in an environment of relative hypoxia. Hypoxia promotes angiogenesis and up-regulates vascular endothelial growth factor (VEGF) expression while it down-regulates placenta growth factor (PIGF) that possess 53% homology with VEGF. Morphological studies show poor placental vascular development and an increase in the mitotic index of cytotrophoblasts in intrauterine growth restriction (IUGR). We hypothesized that the reported relatively high oxygen level in the intervillous space in contact with IUGR placental villi will limit angiogenesis by changes in VEGF and PIGF expression and function. Western immunoblot analysis demonstrates a diametric expression of PIGF and VEGF proteins throughout pregnancy with PIGF levels increasing and VEGF levels decreasing, consistent with placental oxygenation. In IUGR placentae, the ratio of PIGF/GAPDH mRNA was increased by 2.3-fold (p < 0.03) and PIGF protein levels were also increased, (p < 0.05) as compared with gestationally-matched normal placentae. PIGF mRNA and protein were localized to the trophoblast bilayer and villous mesenchyme of the human placenta throughout gestation. In vitro studies demonstrated that increasing oxygen tension (hyperoxia) up-regulated PIGF protein in term placental villous explants, whereas hypoxic culture of a term trophoblast choriocarcinoma cell line (BeWo) down-regulated PIGF mRNA and protein and VEGFR-1 (Flt-1) autophosphorylation. The addition of PIGF-1 to a spontaneously transformed first trimester cytotrophoblast cell line stimulated DNA synthesis while PIGF-2 had little effect. VEGF and PIGF exert their biological actions by means of a common receptor VEGFR-1. In the first trimester trophoblast cells, PIGF-1 increased the association of phosphorylated extracellular signal-related kinase (ERK) with VEGFR-1 immunoprecipitates while both PIGF-1 and PIGF-2 also potentiated endogenous VEGF mediated association of phosphorylated extracellular related kinase (ERK) with VEGFR-2 (KDR). More importantly, the addition of PIGF-1 had little effect while PIGF-2 inhibited cell growth in cultured endothelial cells derived from human umbilical vein. Nitric oxide (NO) is reported to promote angiogenesis and PIGF-2 inhibited the basal release of NO from the first trimester trophoblast. The tissue expression and functional studies support the hypothesis of "placental hyperoxia" in early-onset IUGR because hypoxia down-regulates trophoblast PIGF levels, PIGF expression is increased in IUGR, and PIGF-2 inhibits endothelial cell growth. Taken together, these changes provide a cellular explanation for the observed poor angiogenesis in the pathogenesis of IUGR and show that the two PIGF isoforms may modulate trophoblast and endothelial cell function differently, possibly through potentiation of VEGF mediated activation of VEGF-2.

A recombinant mutant vascular endothelial growth factor-C that has lost vascular endothelial growth factor receptor-2 binding, activation, and vascular permeability activities

The vascular endothelial growth factor (VEGF) and the VEGF-C promote growth of blood vessels and lymphatic vessels, respectively. VEGF activates the endothelial VEGF receptors (VEGFR) 1 and 2, and VEGF-C activates VEGFR-3 and VEGFR-2. Both VEGF and VEGF-C are also potent vascular permeability factors. Here we have analyzed the receptor binding and activating properties of several cysteine mutants of VEGF-C including those (Cys156 and Cys165), which in other platelet-derived growth factor/VEGF family members mediate interchain disulfide bonding. Surprisingly, we found that the recombinant mature VEGF-C in which Cys156 was replaced by a Ser residue is a selective agonist of VEGFR-3. This mutant, designated DeltaNDeltaC156S, binds and activates VEGFR-3 but neither binds VEGFR-2 nor activates its autophosphorylation or downstream signaling to the ERK/MAPK pathway. Unlike VEGF-C, DeltaNDeltaC156S neither induces vascular permeability in vivo nor stimulates migration of bovine capillary endothelial cells in culture. These data point out the critical role of VEGFR-2-mediated signal transduction for the vascular permeability activity of VEGF-C and strongly suggest that the redundant biological effects of VEGF and VEGF-C depend on binding and activation of VEGFR-2. The DeltaNDeltaC156S mutant may provide a valuable tool for the analysis of VEGF-C effects mediated selectively via VEGFR-3. The ability of DeltaNDeltaC156S to form homodimers also emphasizes differences in the structural requirements for VEGF and VEGF-C dimerization.

Increased expression of placenta growth factor in proliferative diabetic retinopathy

Proliferative diabetic retinopathy is thought to be mediated by the hypoxic regulation of angiogenic growth factors, in particular the vascular endothelial growth factor (VEGF) family. The aim of this study was to determine if placental growth factor (PIGF), a recently identified member of the VEGF family, was expressed in diabetic eyes undergoing preretinal neovascularization. Rabbit anti-PIGF antiserum was raised using a 20-amino acid N-terminal sequence to PIGF and did not cross react with VEGF165. Immunohistochemistry was performed on specimens of normal retina (n = 8), diabetic retina in the absence (n = 7) and presence (n = 4) of proliferative retinopathy, scatter laser-treated diabetic retina (n = 7), excised fibrovascular preretinal membranes (n = 12), and nondiabetic fibrocellular epiretinal (n = 7) membranes. PIGF levels were also determined in vitrectomy specimens from patients with either proliferative diabetic retinopathy or macular hole. PIGF immunoreactivity was intensely localized to the endothelial and perivascular regions of newly formed blood vessels of excised fibrovascular preretinal membranes. Intense localization of PIGF protein was also observed in superficial retinal vessels in diabetic retinae adjacent to neovascular preretinal membranes. Localization of PIGF was weak or absent in diabetic retinae that showed no evidence of neovascular proliferation. PIGF protein was also absent in normal retinae, in diabetic retinae that had received extensive treatment with scatter laser photocoagulation, and in nonvascularized epiretinal membranes. PIGF was present in all diabetic vitreous samples (mean 103 pg/ml) but nondetectable in control samples. These results strongly implicate a role for PIGF in the pathogenesis of proliferative diabetic retinopathy.

Tat-human immunodeficiency virus-1 induces human monocyte chemotaxis by activation of vascular endothelial growth factor receptor-1

Human immunodeficiency virus-1 (HIV-1) Tat protein can be released by infected cells and activates mesenchymal cells. Among these, monocytes respond to Tat by migrating into tissues and releasing inflammatory mediators. In the present study, we have examined the molecular mechanism of monocyte activation by Tat, showing that this viral protein signals inside the cells through the tyrosine kinase receptor for vascular endothelial growth factor encoded by fms-like tyrosine kinase gene (VEGFR-1/Flt-1). Subnanomolar concentrations of Tat induced monocyte chemotaxis, which was inhibited by cell preincubation with vascular-endothelial growth factor-A (VEGF-A). This desensitisation was specific for VEGF-A, because it not was observed with FMLP. In addition, the soluble form of VEGFR-1 specifically inhibited polarization and migration induced by Tat and VEGF-A, thus confirming the common use of this receptor. Binding studies performed at equilibrium by using radiolabeled Tat showed that monocytes expressed a unique class of binding site, with a kd of approximately 0.2 nmol/L. The binding of radiolabeled Tat to monocyte surface and the cross-linking to a protein of 150 kD was inhibited specifically by an excess of cold Tat or VEGF-A. Western blot analysis with an antibody anti-VEGFR-1/Flt-1 performed on monocyte phosphoproteins immunoprecipitated by an monoclonal antibody anti-phosphotyrosine showed that Tat induced a rapid phosphorylation in tyrosine residue of the 150-kD VEGFR-1/Flt-1. Taken together, these results suggest that biologic activities of HIV-1 Tat in human monocytes may, at least in part, be elicited by activation of VEGFR-1/Flt-1.

The vascular endothelial growth factor receptor Flt-1 mediates biological activities. Implications for a functional role of placenta growth factor in monocyte activation and chemotaxis

Two distinct receptors for vascular endothelial growth factor (VEGF), the tyrosine kinase receptors Flt-1 and Flk-1/KDR, have been described. In this study we show that monocytes, in contrast to endothelium, express only the VEGF receptor Flt-1, and that this receptor specifically binds also the VEGF homolog placenta growth factor (PlGF). Both VEGF and PlGF stimulate tissue factor production and chemotaxis in monocytes at equivalent doses. In contrast, endothelial cells expressing both the Flt-1 and the Flk-1/KDR receptors produce more tissue factor upon stimulation with VEGF than after stimulation with PlGF. Neutralizing antibodies to the KDR receptor reduce the VEGF-stimulated tissue factor induction in endothelial cells to levels obtained by stimulation with PlGF alone, but do not affect PlGF-induced tissue factor induction in endothelial cells nor the VEGF-dependent tissue factor production in monocytes. These findings strongly suggest Flt-1 as a functional receptor for VEGF and PlGF in monocytes and endothelial cells and identify this receptor as a mediator of monocyte recruitment and procoagulant activity.

Localisation of placenta growth factor (PIGF) in human term placenta

Placenta growth factor (PlGF) is a growth factor which belongs to the vascular endothelial growth factor (VEGF) family and is known to bind to the fms-like tyrosine kinase receptor (flt-1). Using Western blot analysis a 50 kDa band was identified in placental protein extract which corresponded to PlGF homodimer. Immunoreactive PlGF was localised to the vasculosyncytial membrane and in the media of large blood vessels of the placental villi, while staining within the mesenchyme was weak and diffuse. There was moderate staining for PlGF in discrete cells in the chorion and no staining in the epithelial layer of the amnion. The maternal decidual cells showed strong staining for PlGF immunoreactive protein. PlGF mRNA was predominantly expressed by the vasculosyncytial membrane of villous trophoblast, whilst there was no apparent expression of PlGF mRNA within the villous mesenchyme. These results suggest that PlGF may be an important paracrine factor for vascular endothelial cells in placental angiogenesis and an autocrine mediator of trophoblast function.

Human keratinocytes express the three major splice forms of vascular endothelial growth factor

Vascular endothelial growth factor is a powerful mitogen for endothelial cells, recently reported to be produced by keratinocytes. In the present work, we examined human keratinocytes in primary culture for the splice variants of vascular endothelial growth factor. In situ hybridization revealed that 100% of cultured human keratinocytes expressed mRNA for this cytokine, and analysis by reverse transcriptase-polymerase chain reaction indicated that three species of mRNA were produced. Southern hybridization and size calculations of PCR products revealed mRNA species corresponding to 121, 165, and 189 amino-acid forms of this cytokine. Using a rabbit anti-vascular endothelial growth factor antiserum, we radioimmunoprecipitated two molecular weight forms (approximately 45 and 58 kDa, non-reducing conditions) from keratinocyte culture supernatants. Under reducing conditions, three bands of approximately 15, 20, and 24 kDa appeared, corresponding with the predominant forms of vascular endothelial growth factor described. We propose that secretion of vascular endothelial growth factor by human keratinocytes in vivo sustains angiogenesis during physiologic tissue repair and in pathologic states accompanied by neovascularization.

Signalling properties of FLT4, a proteolytically processed receptor tyrosine kinase related to two VEGF receptors

The FLT4, FLT1 and KDR/FLK1 genes encode structurally similar endothelial cell receptor tyrosine kinases. Recently it has been shown that the FLT1 and KDR/FLK-1 proteins function as high-affinity receptors for vascular endothelial growth factor (VEGF). Here we show that FLT4 does not act as a receptor for VEGF, as VEGF did not show specific binding to the FLT4 tyrosine kinase or induce its autophosphorylation. Also, FLT4 did not interact with KDR in response to VEGF. However, when fused with the ligand binding domain of the colony stimulating factor-1 receptor (CSF-1R), the FLT4 tyrosine kinase was specifically activated by CSF-1. The activated FLT4 tyrosine kinase domain was found to interact with the Src homology 2 domains of the SHC and GRB2 adaptor proteins in vitro and with SHC in cells. CSF-1 stimulation of the CSF-1R/FLT4 receptor chimera induced thymidine incorporation in serum-starved NIH3T3 fibroblasts, but not in porcine aortic or murine lung capillary endothelial cells, although tyrosyl phosphorylation of the receptor and SHC occurred in these cells as well. These results suggest that the endothelial cell FLT4 receptor tyrosine kinase transmits signals for an as yet unidentified growth factor.

Coronary artery plaque rapidly induced by local electromagnetic stimulation in the baboon

A reliable method has been developed to produce stenosis of the right coronary artery of baboons as a consequence of electrostimulation of the vessel at a chosen position. At that site a pair of electrodes were implanted and activated with a train of 9-volt pulses (length: 10 ms, separation: 100 ms) for 30 min, 5 days/week, up to 6 weeks. 13 animals were included in the experiment, 2 of those served as controls. Pathohistologically the structure of the artificially produced constrictions is similar to atherosclerotic lesions. On average the stenoses occupied 55% of the available lumen; total occlusion and no stenosis were observed in 1 case each.

Determination of extraction fraction by a double-tracer method

A relatively simple dual-tracer method for measuring renal extraction fraction was compared with the direct method. In the dual-tracer method an extracted and nonextracted tracer are mixed together and administered into the arterial circuit and samples of venous blood are obtained. The ratio of recovered to injected tracer then determines the extraction fraction. In the direct method tracer is administered directly into the renal artery and the total venous effluent is collected. Extraction fraction is then calculated as arteriovenous difference divided by the quantity injected. In our experiments the extraction for 201Tl and 203Hg-chlormerodrin were determined. The extraction fraction for 201Tl averaged 81 +/- 5% by the direct method and 81 +/- 6% by the dual-tracer technique (r = 0.94). The extraction fraction for 203Hg-chlormerodrin was found to change as a function of the renal blood flow. At normal flow the extraction fraction averaged 48% by the direct method and 45% by the dual-tracer technique. At reduced flow, in contrast, it averaged 78% by the direct method and 71% by the dual-tracer technique.