Potent anti-metastatic activity of combretastatin-A4

The requirement for tumour vascularisation to permit the expansion of solid tumours beyond a threshold size of approximately 1 mm diameter has focussed attention on anti-vascular and anti-angiogenic agents for cancer therapy. Combretastatin-A4 (cis CA-4P) is a tubulin-binding agent that is cytotoxic for proliferating endothelial cells in vitro and causes anti-vascular effects in the established tumour vessels of some primary tumours. Preliminary data from Phase I clinical trials indicate that cis CA-4 may also be effective in targeting the vasculature of human tumours. As metastatic disease is the principal cause of mortality in cancer, we have investigated the effects of cis CA-4 on metastatic development using an in vivo model. We show that bolus or continuous administration of cis CA-4P results in potent inhibition of metastases derived from ectopic primary Lewis lung carcinomas in mice whereas the trans CA-4 isomer is without effect. These data further characterise the activity of CA-4 in vivo and suggest that the drug should be evaluated clinically as an anti-metastatic agent.

A common phenotype associated with atherogenesis in diverse mouse models of vascular lipid lesions

The introduction of a range of different genetic modifications in mice results in altered lipoprotein metabolism and the development of vascular lipid lesions. At present, however, it is unclear to what extent the molecular events underlying lipid lesion formation are similar in these different mouse models of atherosclerosis. The aim of this study was to compare the protein expression pattern of lipid lesions from seven different mouse lines with varying susceptibility to vascular lipid lesion development, to determine to what extent lesions induced by different genetic interventions have a similar composition. The proteins we have measured, using quantitative immunofluorescence, are proteins whose expression is known to be modulated during atherogenesis in humans, including plasminogen activator inhibitor (PAI)-1, transforming growth factor (TGF)-beta 1, osteopontin and the macrophage marker CD11b. In all the mice lines we have investigated, PAI-1 was elevated wherever lesions developed. Active TGF-beta was depressed in the vessel wall of mice which developed lipid lesions, particularly in the intima. In contrast, TGF-beta 1 antigen (active plus latent TGF-beta 1) was increased at lesion sites. Accumulation of osteopontin and, with the marked exception of apolipoprotein(a) transgenic mice, tissue macrophages occurred at sites of lipid deposition in the vessel wall. Each lesion, irrespective of its size and the mouse strain in which it developed, had similar amounts of PAI-1, active TGF-beta and osteopontin per unit area of lesion. These data are consistent with a common phenotype accompanying atherogenesis, irrespective of the genetic basis of susceptibility.

Expression of Klf9 and Klf13 in mouse development

Klf9 and Klf13 are members of the C(2)H(2) zinc finger family of transcription factors that are thought to be involved in regulating basal transcription. The mRNA localization of Klf9 and Klf13 during development was determined by in situ hybridization of mouse E8, E11, E13 and E16 embryo sections. The data showed that Klf9 and Klf13 are widely expressed at all the mouse embryo stages examined. Whilst the expression patterns of the two genes largely overlap there are differences in the localization or level of expression in some tissues. At E11, both genes are expressed in high levels in the cephalic mesenchyme whilst Klf13 and not Klf9 is expressed at high levels in the developing heart at E8 and E11. In the gut and bladder at E16, Klf13 is expressed in the epithelial cell layer whereas Klf9 is expressed in both the muscle and epithelial layers. Both Klf9 and Klf13 are expressed at high levels in the epidermis at E11, E13 and E16.

Microsatellite mutation of type II transforming growth factor-beta receptor is rare in atherosclerotic plaques

A somatic mutation within a microsatellite polyA tract in the coding region of the type II transforming growth factor (TGF)-beta receptor gene was reported to occur in human atherosclerotic and restenotic lesions. This mutation occurs frequently in colorectal cancer with the replication error repair phenotype and results in loss of sensitivity to the growth inhibitory effects of TGF-beta in cells from the tumors. The mutation was proposed to account for the clonal expansion of vascular smooth muscle cells observed in atherosclerotic plaques, through loss of the growth inhibitory effect of TGF-beta. The frequency of the mutation and the extent of clonal expansion of the mutated cells have major implications for the mechanism of atherogenesis and therapeutic strategies. We analyzed a set of 22 coronary arterial and 9 aortic samples containing early to advanced atherosclerotic lesions for the mutation in the type II TGF-beta receptor polyA tract. Only 1 coronary arterial sample from an advanced lesion showed detectable amounts of the mutation, present at a low level (8% of the DNA sample). The data imply that the mutation occurs only at low frequency and is not a major mechanistic contributor to the development of atherosclerosis.

Tamoxifen effects on endothelial function and cardiovascular risk factors in men with advanced atherosclerosis

BACKGROUND

Tamoxifen and its analogues act as selective estrogen receptor modulators (SERMs) in women, with estrogen-like activities on some plasma cardiovascular risk factors (eg, lipoproteins). Effects of SERMs on men with coronary artery disease (CAD) have not been reported.

METHODS AND RESULTS

Thirty-one men with angiographically proven CAD were recruited; 16 were treated with tamoxifen (40 mg/d) for 56 days, and 15 were untreated. All the CAD patients were medicated with aspirin and an HMG-CoA reductase inhibitor for >/=6 weeks before entering the study. Ten men with angina-like symptoms but normal coronary arteries by angiography (NCA group) were also treated with tamoxifen. Blood samples were collected at days -7, 0, 7, 14, 21, 28, and 56 of treatment. Endothelium-dependent flow-mediated dilatation (ED-FMD) of the brachial artery was measured by high-resolution ultrasound at 5 visits. Tamoxifen caused an increase in %ED-FMD maximal at 28 days in the CAD group (2.1+/-0.3% to 7.5+/-0.7%; P<0.0001) and the NCA group (3.8+/-0.4% to 7.9+/-1.0%; P<0.0001), with no significant change in the untreated group. Tamoxifen also caused decreases in several plasma cardiovascular risk factors, including total cholesterol, triglycerides, lipoprotein(a), and fibrinogen. Except for the triglyceride response, these effects were similar to those reported for postmenopausal women treated with tamoxifen.

CONCLUSIONS

Tamoxifen substantially increased ED-FMD in men with CAD who were taking conventional medication. Together with the effects on risk factors, the data strongly support clinical evaluation of SERMs for the treatment of men with CAD.

Combretastatin-A4 disrupts neovascular development in non-neoplastic tissue

Combretastatin-A4 phosphate (cis-CA-4) is a tubulin-binding agent currently undergoing clinical trials as an anti-tumour drug. We have investigated whether CA-4 functions as a tumour-specific anti-vascular agent using the hyperplastic thyroid as a novel in vivo model of neovascularization. CA-4 elicited pathological changes in normal tissue, manifested as the induction of multiple, discrete intravascular thrombi. These vascular-damaging effects indicate that CA-4P does not function as a tumour-specific agent but targets neovasculature irrespective of the primary angiogenic stimulus.

Targeting tumour vasculature: the development of combretastatin A4

The requirement for neovascularisation to permit the development of solid tumours beyond a threshold size, has focused attention on the therapeutic potential of agents that prevent angiogenesis. The multistep nature of angiogenesis presents several targets for intervention, including the inhibition of the endothelial-cell migration or proliferation normally associated with developing vessels. Compounds that damage established tumour vasculature are also of potential clinical use. We review the development of one such antivascular drug, combretastatin A4. This tubulin-binding agent was originally isolated from an African shrub, Combretum caffrum. The disodium combretastatin A4 phosphate prodrug is currently undergoing phase I clinical trials in the UK and USA. This review assesses the in vitro and in vivo data for combretastatin and the prodrug, and the preliminary data that have emerged from the phase I clinical trials.

Inhibiting mutations in the transforming growth factor beta type 2 receptor in recurrent human breast cancer

Members of the transforming growth factor beta (TGF-beta) family are potent inhibitors of the growth of many epithelial cell types. Transmembrane signaling by TGF-beta occurs via a complex of the serine/threonine kinases TGF-beta type 1 receptor and TGF-beta type 2 receptor (TGFBR2), and inactivating mutations in the latter have recently been detected in some primary tumors and in several types of tumor-derived cell lines. The most common mutations that have been identified in TGFBR2 are frameshifts in a repetitive polyadenine region in replication error-positive colorectal carcinomas that result in a truncated protein and absence of receptor expression at the cell surface. A number of point mutations in the highly conserved serine/threonine kinase domain of TGFBR2 have also been reported, some of which have been correlated with either loss of trans-phosphorylation of TGF-beta type 1 receptor or constitutive activation of trans-phosphorylation. No TGFBR2 mutations have been reported in human breast tumors, but anomalous expression of TGF-beta in breast carcinomas suggests that TGF-beta signaling may be defective. We have therefore systematically examined unmatched sets of 17 primary and 17 recurrent breast tumor samples for mutations in TGFBR2, restricted to those regions of the gene in which mutations have previously been reported. None of the previously reported mutations was detected, but four novel mutations (V387M, N435S, V447A, and L452M) were found in the kinase domain in recurrent tumors. No mutations were detected in primary tumors. TGF-beta signaling was significantly inhibited by each of the N435S, V447A, and L452M mutations.

Nov gene encodes adhesion factor for vascular smooth muscle cells and is dynamically regulated in response to vascular injury

Nephroblastoma overexpressed (NOV) is a member of the CCN family (connective tissue growth factor, CYR61, and NOV) of proteins that are involved in regulating the proliferation, differentiation, and adhesion of a variety of cell types. We have examined the expression of the NOV: gene and NOV protein by vascular smooth muscle cells (VSMCs), in vitro and in vivo, and the effects of recombinant NOV on VSMCs. Rat aortic VSMCs were found to express NOV: mRNA and NOV protein in vitro and in vivo. NOV: expression in adult rat tissues was very high in the aorta and was detected only weakly in the brain and lung by Northern analysis (relative levels 33:3:1). During postnatal development (3 days to 12 weeks), the expression of NOV: was correlated with markers of the differentiated smooth muscle cell phenotype (smooth muscle myosin heavy chain and SM22 alpha). In the rat carotid artery balloon injury model, NOV: was detectable by in situ hybridization and was downregulated in the media of the injured artery compared with the uninjured artery at 7 and 14 days after injury. Expression in the developing intima was barely detectable at 7 days after injury except for strong expression at the luminal surface. At 14 days after injury, NOV: expression was substantially increased throughout the intima. In vitro studies of the function of NOV protein showed that it promoted VSMC adhesion via a mechanism that was divalent cation and Arg-Gly-Asp independent but that it did not modulate VSMC proliferation or phenotype. The strong expression and dynamic regulation of NOV: in the arterial wall, together with its ability to promote VSMC adhesion, suggest that it may be involved in homeostasis and repair.

Dietary fat and reduced levels of TGFbeta1 act synergistically to promote activation of the vascular endothelium and formation of lipid lesions

Transforming growth factor-(beta) (TGF(beta)) has a wide range of activities on vascular cells and inflammatory cells, suggesting it may have different functions during various stages of atherogenesis. We report that mice heterozygous for the deletion of the tgfb1 gene (tgfb1(+/-) mice) have reduced levels of TGF(beta)1 in the artery wall until at least 8 weeks of age. On a normal mouse chow diet, the vascular endothelium of tgfb1(+/-) mice is indistinguishable from wild-type littermates, assessed by morphology and intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression. In contrast, levels of the smooth muscle isoforms of actin and myosin in medial smooth muscle cells of tgfb1(+/-) mice are significantly reduced. Following feeding a cholesterol-enriched diet for 12 weeks, high levels of ICAM-1 and VCAM-1 were detected in the vascular endothelial cells of tgfb1(+/-) mice, but not wild-type mice. Furthermore, marked deposition of lipid into the artery wall was only observed in the tgfb1(+/-) mice on the cholesterol-enriched diet. These vascular lipid lesions were accompanied by local invasion of macrophages. We conclude that deletion of a single allele of the tgfb1 gene results in a reduced level of TGFbeta1 antigen in the aorta together with reduced smooth muscle cell differentiation, whereas the addition of a high fat dietary challenge is required to activate the vascular endothelium and to promote the formation of fatty streaks resembling early atherosclerosis in humans.

Estimation of systolic and diastolic free intracellular Ca2+ by titration of Ca2+ buffering in the ferret heart

Spectroscopic Ca(2+)-indicators are thought to report values of free intracellular Ca(2+) concentration ([Ca(2+)](i)) that may differ from unperturbed values because they add to the buffering capacity of the tissue. To check this for the heart we have synthesized a new (19)F-labelled NMR Ca(2+) indicator, 1, 2-bis-[2-bis(carboxymethyl)amino-4,5-difluorophenoxy]ethane ('4, 5FBAPTA'), with a low affinity (K(d) 2950 nM). The new indicator and four previously described (19)F-NMR Ca(2+) indicators 1,2-bis-[2-(1 - carboxyethyl)(carboxymethyl)amino - 5 - fluorophenoxy]ethane ('DiMe-5FBAPTA'), 1, 2-bis-[2-(1-carboxyethyl)(carboxymethyl)amino-4-fluorophenoxy]ethane ('DiMe-4FBAPTA'), 1, 2-bis-[2-bis(carboxymethyl)amino-5-fluorophenoxy]ethane ('5FBAPTA') and 1, 2-bis-[2-bis(carboxymethyl)amino-5-fluoro-4-methylphenoxy]ethane ('MFBAPTA'), with dissociation constants for Ca(2+) ranging from 46 to 537 nM, have been used to measure [Ca(2+)](i), over the range from less than 100 nM to more than 3 microM, in Langendorff-perfused ferret hearts (30 degrees C, pH 7.4, paced at 1.0 Hz) by (19)F-NMR spectroscopy. Loading hearts with indicators resulted in buffering of the Ca(2+) transient. The measured end-diastolic and peak-systolic [Ca(2+)](i) were both positively correlated with indicator K(d). The positive correlations between indicator K(d) and the measured end-diastolic and peak-systolic [Ca(2+)](i) were used to estimate the unperturbed end-diastolic and peak-systolic [Ca(2+)](i) by extrapolation to K(d)=0 (diastolic) and to K(d)=infinity (systolic) respectively. The extrapolated values in the intact beating heart were 161 nM for end-diastolic [Ca(2+)](i) and 2650 nM for peak-systolic [Ca(2+)](i), which agree well with values determined from single cells and muscle strips.

Ca2+ buffering in the heart: Ca2+ binding to and activation of cardiac myofibrils

The measurement of cardiac Ca(2+) transients using spectroscopic Ca(2+) indicators is significantly affected by the buffering properties of the indicators. The aim of the present study was to construct a model of cardiac Ca(2+) buffering that satisfied the kinetic constraints imposed by the maximum attainable rates of cardiac contraction and relaxation on the Ca(2+) dissociation rate constants and which would account for the observed effects of (19)F-NMR indicators on the cardiac Ca(2+) transient in the Langendorff-perfused ferret heart. It is generally assumed that the Ca(2+) dependency of myofibril activation in cardiac myocytes is mediated by a single Ca(2+)-binding site on troponin C. A model based on 1:1 Ca(2+) binding to the myofilaments, however, was unable to reproduce our experimental data, but a model in which we assumed ATP-dependent co-operative Ca(2+) binding to the myofilaments was able to reproduce these data. This model was used to calculate the concentration and dissociation constant of the ATP-independent myofilament Ca(2+) binding, giving 58 and 2.0 microM respectively. In addition to reproducing our experimental data on the concentration of free Ca(2+) ions in the cytoplasm ([Ca(2+)](i)), the resulting Ca(2+) and ATP affinities given by fitting of the model also provided good predictions of the Ca(2+) dependence of the myofibrillar ATPase activity measured under in vitro conditions. Solutions to the model also indicate that the Ca(2+) mobilized during each beat remains unchanged in the presence of the additional buffering load from Ca(2+) indicators. The new model was used to estimate the extent of perturbation of the Ca(2+) transient caused by different concentrations of indicators. As little as 10 microM of a Ca(2+) indicator with a dissociation constant of 200 nM will cause a 20% reduction in peak-systolic [Ca(2+)](i) and 30 microM will cause approx. 50% reduction in the peak-systolic [Ca(2+)](i) in a heart paced at 1.0 Hz.

TGF-beta in blood: a complex problem

The cytokine transforming growth factor-beta (TGF-beta) was initially purified from human platelets, a rich source of this protein. In addition to platelets, TGF-beta1 is also found in other blood fractions, including plasma and the circulating leukocytes. However, more than 15 years after the initial isolation of TGF-beta1, there remains no consensus on how much TGF-beta1 is present in normal human plasma. Here we review the difficulties associated with measuring TGF-beta concentrations in complex biological fluids, and discuss the current state of knowledge on the distribution of TGF-beta isoforms in various blood fractions as well as the nature of the TGF-beta-containing protein complexes.

Four isoforms of serum response factor that increase or inhibit smooth-muscle-specific promoter activity

Serum response factor (SRF) is a key transcriptional activator of the c-fos gene and of muscle-specific gene expression. We have identified four forms of the SRF coding sequence, SRF-L (the previously identified form), SRF-M, SRF-S and SRF-I, that are produced by alternative splicing. The new forms of SRF lack regions of the C-terminal transactivation domain by splicing out of exon 5 (SRF-M), exons 4 and 5 (SRF-S) and exons 3, 4 and 5 (SRF-I). SRF-M is expressed at similar levels to SRF-L in differentiated vascular smooth-muscle cells and skeletal-muscle cells, whereas SRF-L is the predominant form in many other tissues. SRF-S expression is restricted to vascular smooth muscle and SRF-I expression is restricted to the embryo. Transfection of SRF-L and SRF-M into C(2)C(12) cells showed that both forms are transactivators of the promoter of the smooth-muscle-specific gene SM22alpha, whereas SRF-I acted as a dominant negative form of SRF.

Mouse BTEB3, a new member of the basic transcription element binding protein (BTEB) family, activates expression from GC-rich minimal promoter regions

Members of the three-zinc-finger family of transcription factors play an important role in determining basal transcription. We have cloned mouse BTEB3 (mBTEB3), a new member of the basic transcription element binding protein (BTEB) family, which is expressed in a wide variety of tissues. mBTEB3 activates transcription of the simian virus 40 early promoter (4-fold) and of the tissue-specific SM22alpha promoter (100-fold), suggesting that, like BTEB1 and Sp1, mBTEB3 is a basal transcription factor.

Monocyte chemoattractant protein-1 but not tumor necrosis factor-alpha is correlated with monocyte infiltration in mouse lipid lesions

BACKGROUND

Apolipoprotein (apo)(a) transgenic mice and C57BL/6 mice fed a high fat diet develop similar-sized lipid lesions, but lesions in apo(a) mice are devoid of macrophages. We used this observation to identify which proinflammatory proteins might be involved in mediating monocyte recruitment during atherogenesis.

METHODS AND RESULTS

Macrophage-deficient apo(a) transgenic mouse lesions contained similar levels of several different proinflammatory proteins, both adhesion molecules (intercellular adhesion molecule-1 [ICAM-1] and vascular cell adhesion molecule-1 [VCAM-1]) and cytokines (tumor necrosis factor-alpha [TNF-alpha] and macrophage inflammatory protein-1alpha [MIP-1alpha]), similar to the macrophage-rich lesions of C57BL/6 mice.

CONCLUSIONS

From this we conclude that ICAM-1, VCAM-1, TNF-alpha, and MIP-1alpha may all be necessary for vascular monocyte recruitment in vivo, but they cannot be sufficient. Monocyte chemoattractant protein-1 (MCP-1) protein was undetectable in the vessel wall taken from apo(a) transgenic mice fed a high fat diet compared with high expression in mice with lipid lesions (C57BL/6 and apoE knockout mice). Therefore elevated expression of MCP-1 but not TNF-alpha, MIP-1alpha, ICAM-1, or VCAM-1 is correlated with vascular macrophage accumulation. To test the hypothesis that monocyte infiltration during atherogenesis is MCP-1 dependent, it will be necessary to develop specific pharmacological inhibitors of MCP-1 activity.

Genetic control of the circulating concentration of transforming growth factor type beta1

The concentration of transforming growth factor beta (TGF-beta) in plasma has been correlated with the development of several diseases, including atherosclerosis and certain forms of cancer. However, the mechanisms that control the concentration of TGF-beta in plasma are poorly understood. In a study of 170 pairs of female twins (average age 57.7 years) we show that the concentration of active plus acid-activatable latent TGF-beta1 [(a+l) TGF-beta therefore is predominantly under genetic control (heritability estimate 0.54). Single strand conformation polymorphism (SSCP) mapping of the TGF-beta1 gene promoter has identified two single base substitution polymorphisms. The two polymorphisms (G-->A at position -800 bp and C-->T at position -509 bp) are in linkage disequilibrium (correlation coefficient Delta = 0.215, P < 0.01). The C-509T polymorphism is significantly associated with the plasma concentration of (a+l) TGF-beta1, explaining 8.2% of the additive genetic variance of (a+l) TGF-beta1 concentration. It is therefore possible that predisposition to atherosclerosis, bone diseases or various forms of cancer may be correlated with the presence of particular alleles at the TGFB1 locus.

Transforming growth factor-beta1 gene polymorphisms and coronary artery disease

1. Transforming growth factor-beta1 is a cytokine with a very wide spectrum of biological activities. Previous studies have shown that it is involved in a number of physiological and pathological processes including heart disease. In our study we aimed to scan the transforming growth factor-beta1 locus for polymorphisms and to identify haplotypes significantly associated with a predisposition to coronary atherosclerosis.2. Two patient groups comprising 244 angiographically normal individuals and 655 patients with coronary artery disease were recruited from London and Sheffield. DNA samples from these subjects were screened for mutations in the transforming growth factor-beta1 locus and all subjects were genotyped by a coupled polymerase chain reaction-restriction enzyme digestion method.3. Five polymorphisms have been identified in the transforming growth factor-beta1 gene at positions G-800A, C-509T in the promoter region, Leu10-->Pro, Arg25-->Pro in exon 1 and Thr263-->Ile in exon 5. No significant difference in frequencies for any of the five polymorphisms was found between controls and patients with coronary artery disease. Similarly, there was no correlation between these polymorphisms and hypertension.4. The genotypes of all the individuals participating in the study were assigned to seven main haplotypes of the transforming growth factor-beta1 locus. Based on species comparison data we propose that GCCGC is the ancestral haplotype in humans.5. Our data suggest that these transforming growth factor-beta1 polymorphisms are not associated with coronary artery disease and therefore their presence alone would not be a genetic risk factor for predisposition to coronary artery disease.

Transforming growth factor-beta dynamically regulates vascular smooth muscle differentiation in vivo

Variations in the levels of smooth muscle-specific isoforms of contractile proteins have been reported to occur in many different vascular diseases. However, although much work has been done in vitro to investigate the regulation of smooth muscle cell differentiation, the molecular mechanisms which regulate the differentiation of vascular smooth muscle tissue in vivo are unknown. Using quantitative immunofluorescence, we show that in rat arteries levels of smooth muscle differentiation markers correlate with the levels of the cytokine TGF-beta. In young mice with one allele of the TGF-beta1 gene deleted, the levels of both TGF-beta1 and smooth muscle differentiation markers are reduced compared to wild-type controls. This regulation of smooth muscle differentiation by TGF-beta during post-natal development also occurs dynamically in the adult animal. Following various pharmacological or surgical interventions, including treatment of mice with tamoxifen and balloon injury of rat carotid arteries, there is a strong correlation between the changes in the levels of TGF-beta and changes in the levels of smooth muscle differentiation markers (r=0. 9, P&lt;0.0001 for n=26 experiments). We conclude that TGF-beta dynamically regulates smooth muscle differentiation in rodent arteries in vivo.

Expression of alternatively spliced human latent transforming growth factor beta binding protein-1

Latent transforming growth factor beta binding protein-1 (LTBP1) is important in regulating the localisation and activation of transforming growth factor beta(TGFbeta). Three forms of LTBP1 mRNA have previously been described, LTBP1L, LTBP1S and LTBPdelta53. Here, we have analysed the LTBP1 coding sequence and identified two other spliced forms, LTBP1delta55 and LTBP1delta41. LTBP1delta55 is a short form of LTBPIL which lacks 55 amino acids including two consensus N-glycosylation sites and LTBP1delta41 is a form of LTBP1 which lacks the 12th EGF-like repeat. Furthermore, sequencing of genomic clones showed that splicing to generate LTBP1L occurs using an intra-exonic 3' splice acceptor site in the first coding exon of LTBP1S and that LTBP1delta55 arises from the alternative use of an exonic 3' splice acceptor site at the end of the following intron. LTBP1delta41 arises from skipping the exon which encodes the 12th EGF-like repeat. LTBP1delta55 and LTBP1delta41 mRNA are expressed in a wide variety of human tissues but the proportions of each splice form vary in the tissues.

Increased PAI activity and PAI-1 antigen occurring with an oral fat load: associations with PAI-1 genotype and plasma active TGF-beta levels

Whether the post-prandial lipemic response is linked to potentially pro-atherogenic and/or prothrombotic changes in plasminogen activator inhibitor (PAI) and transforming growth factor-beta (TGF-beta) is uncertain. The aim of our study was to determine whether PAI-1 antigen and PAI activity were elevated during post-prandial lipemia following a standard fat tolerance test. We also investigated changes in TGF-beta1 antigen and TGF-beta activity, to determine whether changes in TGF-beta activity were associated with changes in PAI measurements. Lastly, the influence of genotype at a common insertion/deletion polymorphism in the PAI-1 promoter on changes in PAI activity and PAI-1 antigen was examined. Fat tolerance tests were undertaken in 57 healthy middle-aged men to investigate associations between plasma concentrations of lipoproteins, PAI (antigen and activity) and TGF-beta. PAI-1 concentration increased by 76% after 8 h (P < 0.0001). PAI activity also increased by 64% (P = 0.0054) and TGF-beta activity decreased by 10% (P < 0.0001). Increases in PAI-I antigen and PAI activity varied markedly between individuals. To investigate these heterogeneous responses we examined whether genotype at the common insertion/deletion polymorphism of the PAI-1 promoter accounted for these differences. Individuals with at least one 4G (deletion) allele showed potentially pro-atherogenic changes in both PAI-1 and TGF-beta, compared to individuals who were homozygous for the 5G (insertion) allele. In conclusion, increased PAI and decreased TGF-beta activity occur during a fat tolerance test and this effect may be modulated by a common insertion/deletion polymorphism in the PAI-1 promoter.

Biological responses to electromagnetic fields

Electrification in developed countries has progressively increased the mean level of extremely low-frequency electromagnetic fields (ELF-EMFs) to which populations are exposed; these humanmade fields are substantially above the naturally occurring ambient electric and magnetic fields of approximately 10(-4) Vm(-1) and approximately 10(-13) T, respectively. Several epidemiological studies have concluded that ELF-EMFs may be linked to an increased risk of cancer, particularly childhood leukemia. These observations have been reinforced by cellular studies reporting EMF-induced effects on biological systems, most notably on the activity of components of the pathways that regulate cell proliferation. However, the limited number of attempts to directly replicate these experimental findings have been almost uniformly unsuccessful, and no EMF-induced biological response has yet been replicated in independent laboratories. Many of the most well-defined effects have come from gene expression studies; several attempts have been made recently to repeat these key findings. This review analyses these studies and summarizes other reports of major cellular responses to EMFs and the published attempts at replication. The opening sections discuss quantitative aspects of exposure to EMFs and the incidence of cancers that have been correlated with such fields. The concluding section considers the problems that confront research in this area and suggests feasible strategies.

Loss of a consensus heparin binding site by alternative splicing of latent transforming growth factor-beta binding protein-1

Latent transforming growth factor-beta binding protein-1 (LTBP-1), plays an important role in controlling localisation and activation of transforming growth factor-beta (TGF-beta). We show that alternative splicing generates a form of mRNA which lacks bases 1277-1435 (termed LTBP-1delta53). The 53 amino acids encoded by these bases include the eighth cysteine of the first cysteine repeat and a consensus heparin binding sequence. Sequencing of genomic clones showed that alternative splicing resulted from the use of an intra-exonic 3' splice acceptor site. The loss of the heparin binding site implies that LTBP-1delta53 will bind to the extracellular matrix less efficiently than LTBP-1.

Transforming growth factor beta is sequestered into an inactive pool by lipoproteins

Elevated plasma concentrations of low density lipoprotein (LDL) and very-low density lipoprotein (VLDL) have been correlated with the development of atherosclerosis. These lipoproteins may promote atherogenesis by direct deposition of lipid in the vessel wall. In addition, previous data suggested that there was an inverse correlation between serum LDL-cholesterol concentration and the proportion of transforming growth factor beta (TGF-beta) in an active form (Grainger et al. 1995. Nature Med. 1:74). Here we have investigated whether lipoproteins can affect the activity of TGF-beta1 in plasma and show that TGF-beta can associate with the lipoprotein fraction. In the plasma of healthy males, 16 +/- 5% (mean +/- standard deviation; n = 57) of the total plasma TGF-beta1 was associated with the lipoprotein fraction, with the major proportion (64 +/- 15%) in the HDL-3 subfraction. However, in ten diabetic subjects with moderately poor glucose control (Hb alc > 8.0), the proportion of total plasma TGF-beta in the lipoprotein fraction was 68 +/- 21%. This large increase in TGF-beta1 associated with the lipoprotein fraction was mainly due to association with VLDL, chylomicrons, and LDL. The lipoprotein fraction inhibits TGF-beta1 binding to the type II TGF-beta receptor extracellular domain in an ELISA and inhibits TGF-beta1 activity in the mink lung cell bioassay. We propose that sequestration of TGF-beta into lipoproteins represents a novel mechanism by which TGF-beta activity in circulation may be regulated. Lipoprotein sequestration of TGF-beta may therefore contribute to the severe depression of TGF-beta activity in advanced atherosclerosis.

Tamoxifen decreases cholesterol sevenfold and abolishes lipid lesion development in apolipoprotein E knockout mice

BACKGROUND

Apolipoprotein E (apo E) knockout mice develop severe vascular lipid lesions resembling human atherosclerotic plaques, irrespective of the fat content of their diet.

METHODS AND RESULTS

Oral tamoxifen (TMX) at a dose of 1.9 mg.kg body wt-1.d-1 abolished lipid lesion development, assayed by oil red O staining, whether the mice were fed a normal diet or a diet with high fat content. The TMX-treated mice showed a sevenfold decrease in total cholesterol. However, the proportion of plasma cholesterol present in VLDL remained unchanged, whereas the proportion in LDL decreased by 37%, and that in HDL increased by 64%. Consistent with the shift from LDL to HDL cholesterol, there was a 62% decrease in total triglycerides. The concentrations of active and acid-activatable latent plus active TGF-beta in the aorta were substantially elevated by TMX (87% and 24% increase, respectively).

CONCLUSIONS

Although the mechanism of cardiovascular protection by TMX in apo E knockout mice is unknown, the inhibition of lipid lesion formation may be attributable to the changes in lipoprotein profile and the elevated levels of TGF-beta, both of which are thought to be protective against atherosclerosis in humans and animal models.

Feedback mechanism of focal vascular lesion formation in transgenic apolipoprotein(a) mice

Apolipoprotein(a) (apo(a)), the distinguishing protein of atherogenic lipoprotein(a), directs accumulation of the lipoprotein(a) particle to sites in the arterial wall where atherosclerotic lipid lesions develop in man and in transgenic mice expressing human apo(a). It has been proposed that focal apo(a) accumulation in the transgenic mouse vessel wall causes the observed severe local inhibition of transforming growth factor-beta (TGF-beta) activity and the consequent activation of the smooth muscle cells, which subsequently accumulate lipid to form lesions if the mice are fed a high fat diet. We show that blocking formation of these vascular lesions by two independent mechanisms, tamoxifen treatment and increasing high density lipoprotein, also abolishes apo(a) accumulation, inhibition of TGF-beta activity, and activation of smooth muscle cells. The data are consistent with a feedback mechanism in which an initial accumulation of apo(a) inhibits local TGF-beta activity, leading to further accumulation of apo(a). Breaking the feedback loop prevents smooth muscle cell activation and therefore lipid lesion development.

Carbonic anhydrase and cardiac pH regulation

Membrane-bound carbonic anhydrase (CA) has recently been identified in mammalian cardiac tissue. In this study, we have investigated the histochemical location and functional role of CA in the ferret heart. Heart sections stained by a modified Hansson's technique showed CA to be located on capillary endothelial membranes as well as on sarcolemmal membranes. In the Langendorff-perfused heart, washout of CO2 brought about by switching perfusion between 25 mM HCO3(-)-5% CO2-buffered solution and nominally HCO3(-)-CO2-free solution caused a transient rise in intracellular pH (pHi) measured by the chemical shift of 2-deoxy-D-glucose 6-phosphate with 31P nuclear magnetic resonance spectroscopy. The initial rate of change of pHi, measured over the first 60-75 s of CO2 efflux, was significantly reduced from 0.41 +/- 0.03 pH units/min (n = 9) in control hearts to 0.28 +/- 0.02 pH units/min (n = 5) in the presence of the membrane-permeable CA inhibitor 6-ethoxzolamide (P < 0.05 compared with control) and to 0.22 +/- 0.04 pH units/min (n = 5) in the presence of the membrane-impermeable CA inhibitor CL-11,366 (P < 0.01 compared with control). After reperfusion of the ischemic myocardium, both CA inhibitors caused a significant slowing of initial rate of change in pH (and initial rate of recovery of contractile function) compared with control hearts. These results suggest that CA, by facilitating the hydration-dehydration of CO2-H2CO3, alters the relative concentrations of CO2 inside and outside the cells, thus enhancing the rate of CO2 transfer from the intracellular to extracellular compartments, which contributes significantly to pHi recovery after reperfusion of the ischemic myocardium.

Optimization of immunofluorescence methods by quantitative image analysis

There is a growing trend towards the objective quantification of immunohistochemical staining. However, quantification has not been used previously to optimize the original published immunohistochemical methods. We present a quantitative method for analyzing immunofluorescence staining employing the Applied Imaging MAGISCAN image analysis system, which has then been used to optimize major aspects of the standard immunofluorescent staining protocols. The optimization process resulted in a method that increased specific staining up to fivefold over typical published protocols, with no increase in nonspecific staining. The method is extremely reproducible. For slides stained by a single experimenter in one batch on one day, the coefficient of variation between replicate means is 1.2%. The image analysis protocol gave a linear response with increasing antigen concentration, as determined by using purified antigen dried onto slides. The revisions to the standard protocol presented here can also be applied to nonquantitative staining. It will help users of immunofluorescence to maximize their staining and may enable the detection of previously undetected antigens.

Angiotensin II stimulates sodium-dependent proton extrusion in perfused ferret heart

The Na+/H+ antiport and Na(+)-HCO3- coinflux carrier contribute to recovery from intracellular acidosis in cardiac tissue. The effects of angiotensin II (10(-12)-10(-6) M) on H+ fluxes after intracellular acid loading and during reperfusion after myocardial ischemia have been investigated in the isovolumic, Langendorff-perfused ferret heart. Intracellular pH (pHi) was estimated using 31P nuclear magnetic resonance (NMR) spectroscopy from the chemical shift of intracellular deoxyglucose-6-phosphate or inorganic phosphate. Angiotensin II produced concentration-dependent stimulation (maximum at 10(-6) M: 67%) of 5-(N-ethyl-N-isopropyl)amiloride (EIPA)-sensitive Na(+)-dependent of H+ efflux consistent with stimulation of the Na+/H+ antiport. Half-maximal stimulation of H+ efflux occurred at approximately 10(-9) M, which is close to the dissociation constant of the cardiac angiotensin AT1 receptor. Stimulation via this receptor was confirmed with the nonpeptide AT1 receptor blocker, GR-117289. Angiotensin II had less pronounced effects on HCO3(-)-dependent pHi recovery after acid loading with no effect on pHi recovery after intracellular alkalosis. During reperfusion, angiotensin II significantly increased H+ extrusion but impaired contractile recovery. The results support the hypothesis that angiotensin II facilitates H+ extrusion in the heart. This may help maintain physiological homeostasis, but the hypothesized obligated Na+ influx could exacerbate cellular dysfunction during reperfusion.

Cultures of proliferating vascular smooth muscle cells from adult human aorta

Abnormal proliferation of human vascular smooth muscle cells (hVSMCs) is a central event in the development of atherosclerosis (1-3) As a result, there is considerable interest in the establishment of hVSMC cultures as a mode1 of this disease process However, it has been noted in the past (4,5) that hVSMCs, especially when cultured by the enzyme-dispersal technique (hVSMC,(ED)), grow poorly in culture compared to VSMCs from other species (e.g., rat) This has limited their use for cell-culture studies. We have recently reported that the reduced proliferative capacity of hVSMC(ED) from adult aorta can be attributed to the endogenous production of active TGF-β(6,7). We (6-8) and others (9-11) have shown that TGF-β; is a potent inhibtior of smooth muscle cell proliferation. Moreover, recent studies in animal models of atherosclerosis (12) have suggested that TGF-P plays a pivotal role in regulation of vessel wall architecture (13). We have also shown that hVSMCs derived by the alternative method of explanting (hVSMC(EX)) have a greater proliferative capacity than the hVSMC(ED) (14) In accordance with our hypotheses, the cells grown from explanted tissue did not produce TGF-β; (14).

No effect of 60 Hz electromagnetic fields on MYC or beta-actin expression in human leukemic cells

Epidemiological studies have shown weak correlations between exposure to extremely low-frequency electromagnetic fields (ELF EMFs) and the incidence of several cancers, particularly childhood leukemias, although negative studies have also been reported. These observations have prompted a broad range of in vitro cellular studies in which effects of ELF EMFs have been observed. However, no reported response has been replicated widely in independent laboratories. One potentially important response is the rapid activation of proto-oncogenes and other genes in human leukemic (HL60) cells and a wide variety of other eukaryotic cells, because of the role of these genes in cell proliferation. We describe quantitative Northern analysis of MYC and beta-actin mRNAs from HL60 cells exposed to fields under conditions very similar to those reported previously to activate these genes, namely 60 Hz sinusoidal magnetic fields of 0.57, 5.7 or 57 microT for 20 min. In addition we have used a new design of field-exposure system and introduced a number of other modifications to the protocol to optimize any response. We have also developed a novel method providing enhanced accuracy for the quantitative measurement of mRNA. No significant effect of ELF EMFs on gene expression was observed using any of these systems and analytical methods.

Tamoxifen elevates transforming growth factor-beta and suppresses diet-induced formation of lipid lesions in mouse aorta

When C57B16 male mice are fed a high-fat diet, they develop significant fatty streak lesions in the aorta. Addition of tamoxifen (TMX) to a high-fat diet, equivalent to a dose of approximately 1 mg TMX per kg body weight per day, suppressed the diet-induced increase in the area of lipid staining in the aortic sinus of the mice by 88% and in the average number of lesions by 86%. The TMX-treated mice had 11% +/- 5% less total plasma cholesterol, with most of the reduction in the high density lipoprotein fraction, whereas plasma triglycerides were significantly elevated, and circulating concentrations of 17 beta-estradiol and testosterone were unaffected. Both circulating and aortic concentrations of active and latent transforming growth factor-beta (TGF-beta) were substantially elevated by TMX. The inhibition of lesion formation may be due, at least in part, to cardiovascular protection by TGF-beta.

Cloning and analysis of the promoter region of the rat SM22 alpha gene

We have cloned and sequenced a 1.9 kb fragment of the 5'-upstream sequence of the smooth-muscle-specific gene SM22 alpha. The region cloned consisted of the SM22 alpha promoter, a 65 bp exon containing most of the 5'-untranslated region and 307 bp of the first intron. A 1.5 kb fragment at the 5' end of this sequence was able to drive the expression of a reporter chloramphenicol acetyltransferase (CAT) gene in both vascular smooth-muscle cells and Rat-1 fibroblasts. This promoter region did not contain a consensus TATAA box but contained the sequence TTTAAA 25 bp from the major start site identified by primer extension. Deletion analysis showed that a fragment of the promoter from +65 to -303 was more active in both cell types than the 1.5 kb fragment suggesting that there are silencer sequences in the region 5' to the core promoter. CAT activity was also observed with fragments containing bases +65 to -193 and +65 to -117 in smooth-muscle cells. In contrast with the smooth-muscle cells, no CAT activity was detected in Rat-1 fibroblasts with the smallest two fragments. The residual promoter activity in the smallest fragment of the SM22 alpha promoter tested suggested that, unlike the smooth-muscle alpha-actin promoter, transcription from the SM22 alpha promoter can occur in smooth-muscle cells in the absence of factors binding to CC(A/Trich)6GG (CArG box) or CANNTG (E box) motifs.

Release and activation of platelet latent TGF-beta in blood clots during dissolution with plasmin

Transforming growth factor beta 1 (TGF-beta 1) is a platelet-derived cytokine involved in both normal wound healing and scarring. We show that human platelets contain two pools of latent TGF-beta 1, which constitute more than 95% of the total TGF-beta assayed in whole platelets. During clotting, one pool, the large latent TGF-beta complex consisting of latent TGF-beta binding protein (LTBP), the latency-associated peptide (LAP) and the 25-kD mature TGF-beta 1 dimer is released into the serum. A second pool, which contains LAP but not LTBP, is retained in the clot, but can be released by RGD peptide. When the clot is dissolved by plasmin this bound TGF-beta 1 is gradually activated and released. If similar mechanisms operate in vivo, the clot will act as a slow-release capsule of TGF-beta 1 activity during wound healing.

ID--a dominant negative regulator of skeletal muscle differentiation--is not involved in maturation or differentiation of vascular smooth muscle cells

Rat aortic vascular smooth muscle cells (VSMCs) expressing the MyoD gene formed myotubes at a low frequency in the presence of serum but at a high frequency in the absence of serum. Expression of an antisense Id gene increased myotube formation in the presence of serum indicating that a reduction in Id levels is a major mechanism by which serum withdrawal promotes myotube formation. The role of Id in the development of VSMCs was investigated by expressing an antisense Id gene in neonatal VSMCs. No evidence was found for the conversion of neonatal VSMCs to adult VSMCs in the presence of the antisense Id gene. Similarly reduction in Id by serum withdrawal also failed to cause conversion of the neonatal VSMCs to the adult phenotype. These data suggest that the maturation of neonatal smooth muscle cells is not controlled by a VSMC homologue of the skeletal muscle basic-helix-loop-helix proteins.

Proliferation of human aortic vascular smooth muscle cells in culture is modulated by active TGF beta

OBJECTIVE

Human vascular smooth muscle cells (VSMC) prepared by enzyme dispersal have been reported to proliferate more slowly and remain more differentiated than VSMC derived by explant culture. The aim of this study was to investigate whether these differences are attributable to the production of transforming growth factor beta (TGF beta), a major modulator of VSMC properties in culture, by enzyme dispersal, but not explant, cultures.

METHODS

Human aortic VSMC cultures were prepared by enzymatic dissociation of aortic media or by outgrowth of cells from explants derived from the vessel media. Properties, including rate of proliferation and differentiation, of the two different types of culture obtained from 10 donors (age 3-54 years, of either sex) were compared. The role of TGF beta as mediator of these differences was investigated.

RESULTS

VSMC from enzyme dispersal cultures proliferated with a long doubling time in 20% fetal calf serum of 68(SEM 2) h, reaching a low saturation density with no "hills and valleys", and the cells were predominantly of stellate morphology. VSMC from explant cultures proliferated with a shorter doubling time of 35(2) h, reached a higher saturation density with "hills and valleys", and showed a spindle shaped morphology. The enzyme dispersed cells, but not the explant cells, released TGF beta into the medium. Addition of exogenous TGF beta to the explant cells extended the doubling time, while addition of a neutralising antibody to the enzyme dispersed cells decreased the doubling time. Tamoxifen, an anti-oestrogenic drug, decreased the rate of proliferation of the explant cells (ED50 = 50 nM; n = 3) but not enzyme dispersed cells by stimulating production of TGF beta. The explant and enzyme dispersal cultures also differed in response to growth factors. The explant cultures stimulated DNA synthesis in response to platelet derived growth factor (PDGF) AA and BB. Enzyme dispersal cultures stimulated DNA synthesis in response to PDGF-BB but response to AA was weaker and also variable.

CONCLUSIONS

Human explant derived VSMC systematically differ from enzyme dispersed VSMC obtained from the same donor tissue. Wherever the potential role of TGF beta was investigated, the differences between enzyme dispersal and explant cultures were due to autocrine production of TGF beta by the enzyme dispersal, but not explant cultures.

Transforming growth factor-beta: the key to understanding lipoprotein(a)?

Most large studies of the blood parameters that act as risk factors for myocardial infarction, stroke and atherosclerosis have identified elevated circulating levels of lipoprotein(a) as an important risk factor. Lipoprotein(a) consists of an LDL particle that is covalently bound to the distinguishing protein component apolipoprotein(a). Ever since apolipoprotein(a) was cloned in 1987 and the marked sequence homology to plasminogen was noted, mechanisms for the atherogenic activity of lipoprotein(a), based on the competitive inhibition of plasminogen activity, have been proposed. However, with the availability of transgenic mice expressing both human apolipoprotein(a) and lipoprotein(a), recent studies have demonstrated that lipoprotein(a) acts to inhibit plasminogen activation in vivo. One consequence of this is reduced activation of the cytokine transforming growth factor-beta, an important regulator of vessel wall structure.

Active and acid-activatable TGF-beta in human sera, platelets and plasma

Assays which measure active and latent forms of transforming growth factor beta (TGF-beta) separately in human serum and plasma are required to investigate the biological role of TGF-beta in a variety of human diseases. We have developed an enzyme-linked immunosorbent assay (ELISA) using two polyclonal antibodies against TGF-beta which rapidly determines the amount of active plus acid-activatable, latent TGF-beta forms ((a+l)TGF-beta) present in human serum and plasma in the range 4 pmol/l to 2000 pmol/l. To measure active TGF-beta alone, we have developed a second ELISA using the extracellular domain of the TGF-beta type II receptor as the capture reagent which detects active TGF-beta in serum and plasma samples in the range 20 pmol/l to 4000 pmol/l. Both assays detect TGF-beta 1 and TGF-beta 3 with similar sensitivity, are > 10-fold less sensitive to TGF-beta 2 and are not affected by a range of other peptide growth factors. The mean (a+l)TGF-beta present in human serum was 330 pmol/l but the range was very large (< 4 pmol/l to 1400 pmol/l). The mean active TGF-beta present was 230 pmol/l (range < 20 pmol/l to 1400 pmol/l) and the proportion of the (a+l)TGF-beta present which was active [a/(a+l)] varied from < 10% to 100%. The concentration of (a+l)TGF-beta and the proportion of TGF-beta which was active were very similar in the serum and platelet-poor plasma prepared from the same whole blood sample. The clot formed during serum preparation retained all of the TGF-beta which was detected by the (a+l)TGF-beta ELISA in the corresponding platelet releasate, although the PDGF in platelets was released into the serum. In contrast, platelet-poor plasma contained no detectable PDGF demonstrating that the (a+l)TGF-beta assayed in the plasma was not due to platelet degranulation after bleeding. Serum active TGF-beta and (a+l)TGF-beta concentrations therefore provide a reliable estimate of these forms of TGF-beta present in plasma.

The serum concentration of active transforming growth factor-beta is severely depressed in advanced atherosclerosis

Recent evidence has led us to propose that transforming growth factor-beta (TGF-beta) is a key inhibitor of atherosclerosis. We show here that a population of patients with advanced atherosclerosis all have less active TGF-beta in their sera than patients with normal coronary arteries, with a fivefold difference in average concentration between the two groups. This correlation with atherosclerosis is much stronger than for other known major risk factors and it may therefore have important diagnostic and prognostic significance. Aspirin medication correlates with an increase in active TGF-beta concentration, indicating that therapeutic interventions for TGF-beta are possible.

Activation of transforming growth factor-beta is inhibited in transgenic apolipoprotein(a) mice

A HIGH concentration of serum lipoprotein(a) is a risk factor for atherosclerosis. Lipoprotein(a) consists of low-density lipoprotein with the additional protein component, apolipoprotein(a), a homologue of plasminogen. Lipoprotein(a) and apolipoprotein(a) enhance proliferation of human vascular smooth muscle cells (hVSMCs) in culture by inhibiting activation of plasminogen to plasmin, thus blocking the proteolytic activation of transforming growth factor-beta (TGF-beta), an autocrine inhibitor of hVSMC proliferation. The hypothesis that this pathway is a key step in atherogenesis is tested on transgenic mice expressing the human apolipoprotein(a) gene. We show here that the activation of TGF-beta is inhibited in the aortic wall and serum of mice expressing apolipoprotein(a), as a consequence of apolipoprotein(a) inhibition of plasminogen activation. These effects are closely correlated with VSMC activation.