Search PubMed⌕ Search

Biomedical subjects

L F Brown

Publications and source records attributed to L F Brown.

At least 91 records · Page 5Linked to original sources
PubMed1994

Vascular endothelial growth factor/vascular permeability factor is temporally and spatially correlated with ocular angiogenesis in a primate model.

Ischemia often precedes neovascularization. In ocular neovascularization, such as occurs in diabetic retinopathy, a diffusible angiogenic factor has been postulated to be produced by ischemic retina and to lead to neovascularization of the retina, optic nerve, or iris. However, no angiogenic factor has been conclusively identified that satisfies this hypothesis. Vascular endothelial growth factor/vascular permeability factor, hereafter referred to as VEGF, is a likely candidate for an ocular angiogenic factor because it is a secreted mitogen, specific for endothelial cells, and is upregulated by hypoxia. We investigated the association of VEGF with the development of experimental iris neovascularization in the cynomolgus monkey. Following the production of retinal ischemia by laser occlusion of all branch retinal veins, VEGF was increased in the aqueous fluid, and the aqueous VEGF levels changed synchronously and proportionally with the severity of iris neovascularization. Northern analysis and in situ hybridization revealed that VEGF messenger RNA is upregulated in the ischemic retina. These observations support the hypothesis that ocular neovascularization is regulated by a diffusible factor and identify VEGF as a likely candidate for a retina-derived vascular permeability and angiogenesis factor in vivo.

Animals↗
PubMed1994

Osteopontin expression and distribution in human carcinomas.

Osteopontin (OPN), a secreted adhesive glycoprotein, is significantly overexpressed in a variety of experimental models of malignancy. Moreover, increased levels of OPN have been detected in the blood of patients with metastatic carcinoma. To investigate OPN expression and distribution in human carcinomas directly, we studied a wide variety of common tumors by Northern analysis, in situ hybridization, and immunohistochemistry. All 14 tumors studied by Northern analysis showed very substantial increases in OPN messenger (m)RNA when compared to corresponding normal tissues. Moreover, intense labeling for OPN mRNA was detected in 71 of 76 carcinomas studied by in situ hybridization. In most of the carcinomas studied (colon, stomach, duodenum, pancreas, breast, lung, bladder, prostate, ovary, thyroid, and melanoma), tumor cells did not label detectably for OPN mRNA; however, macrophages intimately associated with tumor cells labeled strongly for the OPN transcript. In carcinomas of the kidney and endometrium, both tumor cells and host macrophages labeled strongly for OPN mRNA. The presence of OPN mRNA in macrophages was particularly pronounced at the edge of tumors (ie, the tumor/stroma interface) and in areas of tumor necrosis. Although in most cases tumor cells did not label detectably for OPN mRNA, both tumor cells and macrophages stained for OPN protein, suggesting that OPN secreted by macrophages may bind to tumor cells, possibly through the glycine-arginine-glycine-aspartate-serine cell binding domain in OPN. Collectively, these data suggest that OPN functions in adhesive interactions at the tumor/host interface and thereby may influence processes such as invasion and metastasis.

Blotting, Northern↗
PubMed1993

Expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in adenocarcinomas of the gastrointestinal tract.

Vascular permeability factor (VPF) is one of the most potent known inducers of microvascular hyperpermeability; in addition, it is a selective endothelial cell growth factor, hence its alternate name, vascular endothelial growth factor. VPF exerts its actions on the microvasculature by interacting with specific endothelial cell receptors. VPF is expressed by many transplantable animal tumors, by tumor cell lines in culture, and by certain normal cells in situ. The purpose of the present investigation was to determine whether and with what consistency VPF and its endothelial cell receptors are expressed in primary autochthonous human tumor of gastrointestinal tract origin, as determined by in situ hybridization and immunohistochemistry. Twenty-one primary adenocarcinomas (17 colon, 2 stomach, 1 small bowel, and 1 pancreas) were studied. The malignant epithelial cells expressed VPF mRNA strongly, in contrast to normal epithelium, hyperplastic polyps, and adenomas, which expressed little or no VPF mRNA. VPF expression was further increased in tumor cells immediately adjacent to zones of tumor necrosis; in such areas, occasional stromal cells also expressed VPF mRNA. In the ten colon carcinomas studied, tumor cells stained for VPF protein by immunohistochemistry. The endothelial cells of nearby stromal blood vessels also stained for VPF by immunohistochemistry and in addition expressed mRNAs encoding the VPF receptors flt-1 and kdr as determined by in situ hybridization. Endothelial cells away from the tumor did not stain for VPF and no definite mRNA expression for flt-1 or kdr was detected by in situ hybridization. The ganglion cells of the myenteric plexus of normal bowel expressed VPF mRNA and protein. These data indicate that primary autochthonous human tumors of gastrointestinal origin regularly express both VPF mRNA and VPF protein and that adjacent stromal vessels express mRNAs for both known VPF receptors. VPF is likely to contribute to tumor growth by promoting angiogenesis and stroma formation, both directly, through its action as an endothelial cell growth factor, and indirectly, by increasing vascular permeability, thereby leading to plasma protein extravasation, fibrin deposition, and the eventual replacement of the resulting matrix with vascularized stroma.

Adenocarcinoma↗
PubMed1993

Synthesis and secretion of vascular permeability factor/vascular endothelial growth factor by human retinal pigment epithelial cells.

The presence of the secreted angiogenic molecule, vascular permeability factor/vascular endothelial growth factor, was investigated in human retinal pigment epithelial cells. Northern and in situ hybridization analysis of cultured cells identified vascular permeability factor/vascular endothelial growth factor mRNA. Western analysis of cell lysates identified a 42 kD protein that comigrated with human recombinant vascular permeability factor/vascular endothelial growth factor. Immunoassay measurements detected vascular permeability factor/vascular endothelial growth factor protein in cell lysates and conditioned media in vitro and in cell lysates isolated directly from post-mortem eyes. These data demonstrate that human retinal pigment epithelial cells can synthesize the secreted angiogenic peptide vascular permeability factor/vascular endothelial growth factor in vitro and in situ. The production and secretion of this factor by human retinal pigment epithelial cells may be important in the pathogenesis of ocular neovascularization.

Antisense Elements (Genetics)↗
PubMed1993

Vascular permeability factor (VPF, VEGF) in tumor biology.

Vascular permeability factor (VPF), also known as vascular endothelial growth factor (VEGF), is a multifunctional cytokine expressed and secreted at high levels by many tumor cells of animal and human origin. As secreted by tumor cells, VPF/VEGF is a 34-42 kDa heparin-binding, dimeric, disulfide-bonded glycoprotein that acts directly on endothelial cells (EC) by way of specific receptors to activate phospholipase C and induce [Ca2+]i transients. Two high affinity VPF/VEGF receptors, both tyrosine kinases, have thus far been described. VPF/VEGF is likely to have a number of important roles in tumor biology related, but not limited to, the process of tumor angiogenesis. As a potent permeability factor, VPF/VEGF promotes extravasation of plasma fibrinogen, leading to fibrin deposition which alters the tumor extracellular matrix. This matrix promotes the ingrowth of macrophages, fibroblasts, and endothelial cells. Moreover, VPF/VEGF is a selective endothelial cell (EC) growth factor in vitro, and it presumably stimulates EC proliferation in vivo. Furthermore, VPF/VEGF has been found in animal and human tumor effusions by immunoassay and by functional assays and very likely accounts for the induction of malignant ascites. In addition to its role in tumors, VPF/VEGF has recently been found to have a role in wound healing and its expression by activated macrophages suggests that it probably also participates in certain types of chronic inflammation. VPF/VEGF is expressed in normal development and in certain normal adult organs, notably kidney, heart, adrenal gland and lung. Its functions in normal adult tissues are under investigation.

Animals↗
PubMed1993

Increased expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in kidney and bladder carcinomas.

Vascular permeability factor (VPF), also known as vascular endothelial growth factor, is a secreted protein implicated in tumor-associated microvascular hyperpermeability and angiogenesis. Tumor cells in 11 of 12 renal cell carcinomas expressed high levels of VPF messenger RNA (mRNA) by in situ hybridization, the only exception being a case of the relatively avascular papillary variant. Expression was further accentuated adjacent to areas of necrosis. Both tumor cells and endothelial cells in small vessels adjacent to tumor stained strongly for VPF protein by immunohistochemistry. Endothelial cells did not express detectable VPF mRNA, but did express high levels of mRNA for the VPF receptors flt-1 and KDR indicating that the endothelial cell staining likely reflects binding of VPF secreted by adjacent tumor cells. Three transitional cell carcinomas also labeled strongly for VPF mRNA. These data suggest an important role for VPF in the vascular biology of these two common human malignancies.

Base Sequence↗
PubMed1993

A technique for the high-speed characterization of ultrasonic transducer insertion loss performance.

A characterization technique has been developed to address the problems associated with calibrating very-high frequency (i.e., > 50 MHz) ultrasound transducers. The technique is based on using a pc-controlled network analyzer to acquire the through-transmission voltage transfer function spectrum from a pair of ultrasound transducers which are closely spaced in water. This spectrum, which includes electrical feed-through noise and multiple reflection artifacts, is then corrected for the water's attenuation and the transfer response of the electronics system. An inverse Fourier transform is then performed, to produce the time domain response of the transducers. The portion of the response which corresponds to the first acoustic arrival is then gated out of this response, and a Fourier transform is performed to compute the transducers' true transfer function (insertion loss) spectrum. A pc-controlled automated calibration system based on this technique has been developed and numerous transducer pairs have been tested. Excellent agreement has been shown between this method and the conventional tone-burst technique for accurately characterizing insertion loss spectra. In this paper, a detailed description of the technique, actual transducer test results, and comparisons with the conventional tone-burst method are presented in detail.

Calibration↗
PubMed1993

Fibroblast migration in fibrin gel matrices.

In healing wounds and many solid tumors, locally increased microvascular permeability results in extravasation of fibrinogen and its extravascular coagulation to form a fibrin gel, with concomitant covalent cross-linking of fibrin by factor XIIIa. Subsequently, inflammatory cells, fibroblasts, and endothelial cells migrate into the gel and organize it into granulation tissue and later into mature collagenous connective tissue. To gain insight into some of the cell migration events associated with these processes, we developed a quantitative in vitro assay that permits the study of fibroblast migration in fibrin gels. Early passage human or rat fibroblasts were allowed to attach to tissue culture dishes and then were overlaid with a thin layer of fibrinogen that was clotted with thrombin. Fibroblasts began to migrate upwards into the fibrin within 24 hours and their numbers and the distance migrated were quantified over several days. The extent of fibroblast migration was affected importantly by the nature of the fibrin clot. Fibroblasts migrated optimally into gels prepared from fibrinogen at concentrations of -3 mg/ml; ie, near normal plasma fibrinogen levels. Migration was greatly enhanced by extensive cross-linking of the fibrin alpha-chains by factor XIIIa, as occurs when clotting takes place in vivo. When fibrinogen was clotted in Dulbecco's modified Eagle's medium, gamma-chains were cross-linked, but alpha-chain cross-linking was strikingly inhibited, and fibroblasts migrated poorly. Gels prepared from factor XIII-depleted fibrinogen exhibited neither alpha-nor gamma-chain cross-linking and did not support fibroblast migration. Further purification of fibrinogen by anion exchange high pressure liquid chromatography depleted fibrinogen of fibronectin, plasminogen, and other impurities; this purified fibrinogen clotted to form fibrin gels that supported reproducible fibroblast migration.

Animals↗
PubMed1993

Macrophages and fibroblasts express embryonic fibronectins during cutaneous wound healing.

Fibronectins (FN) comprise a family of adhesive glycoproteins that are prominent components of wound healing. These proteins arise by alternative splicing of a single gene transcript at three sites, termed EIIIA, EIIIB, and V. Extravasated plasma FN, which lacks the EIIIA and EIIIB domains, along with fibrin, comprise the "provisional" matrix that forms within minutes of tissue injury. By 2 days after cutaneous excisional wounding in rats, total FN messenger RNA (mRNA) expression is increased locally and dramatically within the surrounding dermis, in the subjacent muscle (panniculus carnosus) and, notably, at the wound margins. Moreover, in contrast to normal skin, 2-day wounds express EIIIA- and EIIIB-containing "embryonic" FN mRNAs. To identify the cells responsible for synthesizing the various FN isoforms, we performed in situ hybridization with probes for the various FN mRNAs. Collagen and lysozyme probes were employed to distinguish fibroblasts from macrophages. At early intervals (2 days) after wounding, macrophages were the principal cells that expressed FN mRNA. Moreover, many of these cells expressed embryonic FN mRNAs. At 7 to 10 days, when the wound defect was maturing, fibroblasts were the major cells synthesizing these embryonic FNs. It is widely accepted that wound macrophages phagocytose debris and provide degradative enzymes and cytokines essential for early stages of tissue repair. Our findings suggest an additional function for wound macrophages--synthesis of embryonic FNs providing an extracellular matrix that facilitates wound repair, perhaps by promoting cell migration.

Animals↗
PubMed1992

Expression of vascular permeability factor (vascular endothelial growth factor) by epidermal keratinocytes during wound healing.

Persistent microvascular hyperpermeability to plasma proteins even after the cessation of injury is a characteristic but poorly understood feature of normal wound healing. It results in extravasation of fibrinogen that clots to form fibrin, which serves as a provisional matrix and promotes angiogenesis and scar formation. We present evidence indicating that vascular permeability factor (VPF; also known as vascular endothelial growth factor) may be responsible for the hyperpermeable state, as well as the angiogenesis, that are characteristic of healing wounds. Hyperpermeable blood vessels were identified in healing split-thickness guinea pig and rat punch biopsy skin wounds by their capacity to extravasate circulating macromolecular tracers (colloidal carbon, fluoresceinated dextran). Vascular permeability was maximal at 2-3 d, but persisted as late as 7 d after wounding. Leaky vessels were found initially at the wound edges and later in the subepidermal granulation tissue as keratinocytes migrated to cover the denuded wound surface. Angiogenesis was also prominent within this 7-d interval. In situ hybridization revealed that greatly increased amounts of VPF mRNA were expressed by keratinocytes, initially those at the wound edge, and, at later intervals, keratinocytes that migrated to cover the wound surface; occasional mononuclear cells also expressed VPF mRNA. Secreted VPF was detected by immunofluoroassay of medium from cultured human keratinocytes. These data identify keratinocytes as an important source of VPF gene transcript and protein, correlate VPF expression with persistent vascular hyperpermeability and angiogenesis, and suggest that VPF is an important cytokine in wound healing.

Animals↗
PubMed1992

Vascular permeability factor mRNA and protein expression in human kidney.

Vascular permeability factor (VPF), also known as vascular endothelial growth factor (VEGF), is a potent microvascular permeability-enhancing mediator as well as a selective mitogen for vascular endothelium. In this study, in situ hybridization and immunohistochemistry co-localized VPF mRNA and protein to glomerular visceral epithelial cells in human kidneys. Northern analysis confirmed the presence of VPF mRNA of expected size. The finding of VPF in renal glomerular epithelium identifies a potent mediator of permeability and endothelial proliferation whose role in renal physiology and pathology requires investigation.

Amino Acid Sequence↗
PubMed1992

Expression and distribution of osteopontin in human tissues: widespread association with luminal epithelial surfaces.

Osteopontin, a glycoprotein with a glycine-arginine-glycine-aspartate-serine (GRGDS) cell-binding domain, has been described in bone and is also known to be expressed in other organs, particularly kidney. The goal of the present work was to define the distribution of osteopontin synthesis and deposition in a wide variety of normal adult human tissues using a multifaceted approach that included immunohistochemistry, in situ hybridization, and Northern analysis. Immunohistochemical studies have revealed the unexpected finding that osteopontin is deposited as a prominent layer at the luminal surfaces of specific populations of epithelial cells of the gastrointestinal tract, gall bladder, pancreas, urinary and reproductive tracts, lung, breast, salivary glands, and sweat glands. Northern analyses identified gallbladder as a major site of osteopontin gene transcription comparable in magnitude with that of kidney, and immunoblotting identified osteopontin in bile. In situ hybridization localized osteopontin gene transcripts predominantly to the epithelium of a variety of organs as well as to ganglion cells of bowel wall. Osteopontin of epithelial cell origin, like bone-derived osteopontin, promoted GRGDS-dependent cell spreading in attachment assays. We postulate that osteopontin secreted by epithelium binds integrins on luminal surfaces. Collectively, these findings suggest an important role for osteopontin on many luminal epithelial surfaces communicating with the external environment.

Amino Acid Sequence↗
PubMed1992

Vascular permeability factor (vascular endothelial growth factor) gene is expressed differentially in normal tissues, macrophages, and tumors.

Vascular permeability factor (VPF), also known as vascular endothelial growth factor (VEGF), increases microvascular permeability and is a specific mitogen for endothelial cells. Expression of VPF/VEGF previously was demonstrated in a variety of tumor cells, in cultures of pituitary-derived cells, and in corpus luteum. Here we present evidence, by Northern analysis and in situ hybridization, that the VPF/VEGF gene is expressed in many adult organs, including lung, kidney, adrenal gland, heart, liver, and stomach mucosa, as well as in elicited peritoneal macrophages. The highest levels of VPF/VEGF transcripts were found in epithelial cells of lung alveoli, renal glomeruli and adrenal cortex, and in cardiac myocytes. The prominence of VPF/VEGF mRNA in these tissues suggests a possible role for VPF/VEGF in regulating baseline microvascular permeability, which is essential for tissue nutrition and waste removal. We also demonstrate particularly high VPF/VEGF mRNA levels in several human tumors, where it may be involved in promoting tumor angiogenesis and stroma generation, both as an endothelial cell mitogen and indirectly by its permeability enhancing effect that leads to the deposition of a provisional fibrin gel matrix.

Animals↗
PubMed1992

In vivo imaging using a copolymer phased array.

Phased-array images have been obtained in vivo with a steered copolymer array operating at 2.5 MHz. The array was fabricated using 28 microns copolymer film, lambda/4 resonant at 21 MHz, which was bonded to a glass ceramic backing with a thin film bond. The 32 array elements were created by laser ablation of the continuous gold electrode on one side of the film. The transducer was driven by 200 V shock excitation, and the received signal was processed by 32 custom IC preamplifiers that were mounted to the array connector. The amplifiers had a high input impedance compared to that of the array elements and their output impedance matched that of the coaxial cable that connected to the scanner. Because the copolymer transducer had a broad bandwidth, the spectrum of the pulse echo image was modified by the frequency dependent attenuation of tissue and the bandpass of the ultrasound scanner, resulting in a center frequency of 2.5 MHz. The performance of the copolymer array was compared to that of a 3 MHz, PZT array with similar dimensions. On the Duke phased-array scanner, the copolymer sensitivity was 28 dB less than that of PZT. The copolymer elements had a 6 dB pulse-echo angular response of 30 degrees, and the interelement cross-coupling was -35 dB. Phased-array images were made of the heart of a 25 year-old normal male.

Equipment Design↗
PubMed1992

AIDS knowledge in three sites in Bas-Zaire.

This study surveyed 5,494 women in one urban and two rural sites of Bas-Zaire on their knowledge, attitudes, and practices regarding AIDS. The AIDS Risk Reduction Model (ARRM) was used to analyze the results to better understand factors that may be related to motivation for behavior change. The results show that there are considerable barriers to achieving the first stage of the 3-stage model. Most notably, only a third of the women believed they were at risk of getting AIDS. Those aged 25-29, educated, and married felt themselves to be most at risk. Results are compared to other knowledge, attitudes, and practices studies conducted in Zaire. Policy implications of these results are discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Distribution of vascular permeability factor (vascular endothelial growth factor) in tumors: concentration in tumor blood vessels.

Vascular permeability factor (VPF) is a highly conserved 34-42-kD protein secreted by many tumor cells. Among the most potent vascular permeability-enhancing factors known, VPF is also a selective vascular endothelial cell mitogen, and therefore has been called vascular endothelial cell growth factor (VEGF). Our goal was to define the cellular sites of VPF (VEGF) synthesis and accumulation in tumors in vivo. Immunohistochemical studies were performed on solid and ascites guinea pig line 1 and line 10 bile duct carcinomas using antibodies directed against peptides synthesized to represent the NH2-terminal and internal sequences of VPF. These antibodies stained tumor cells and, uniformly and most intensely, the endothelium of immediately adjacent blood vessels, both preexisting and those newly induced by tumor angiogenesis. A similar pattern of VPF staining was observed in autochthonous human lymphoma. In situ hybridization demonstrated VPF mRNA in nearly all line 10 tumor cells but not in tumor blood vessels, indicating that immunohistochemical labeling of tumor vessels with antibodies to VPF peptides reflects uptake of VPF, not endogenous synthesis. VPF protein staining was evident in adjacent preexisting venules and small veins as early as 5 h after tumor transplant and plateaued at maximally intense levels in newly induced tumor vessels by approximately 5 d. VPF-stained vessels were also hyperpermeable to macromolecules as judged by their capacity to accumulate circulating colloidal carbon. In contrast, vessels more than approximately 0.5 mm distant from tumors were not hyperpermeable and did not exhibit immunohistochemical staining for VPF. Vessel staining disappeared within 24-48 h of tumor rejection. These studies indicate that VPF is synthesized by tumor cells in vivo and accumulates in nearby blood vessels, its target of action. Because leaky tumor vessels initiate a cascade of events, which include plasma extravasation and which lead ultimately to angiogenesis and tumor stroma formation, VPF may have a pivotal role in promoting tumor growth. Also, VPF immunostaining provides a new marker for tumor blood vessels that may be exploitable for tumor imaging or therapy.

Amino Acid Sequence↗
PubMed1989

Pathogenesis of tumor stroma generation: a critical role for leaky blood vessels and fibrin deposition.

Tumor stroma formation results from the interaction of tumor cells and their products with the host and certain of its normal defense mechanisms, particularly the clotting and fibrinolytic systems. It is a process in which tumor cells render local venules and veins hyperpermeable with the result that fibrinogen and other proteins extravasate and clot, forming an extravascular crosslinked fibrin gel. Coagulation is mediated by an interaction between extravasated plasma clotting factors and tumor-associated and perhaps other tissue procoagulants. Parallel activation of the fibrinolytic system leads to substantial fibrin turnover, but fibrin nonetheless accumulates in amounts, variable from tumor to tumor, that are sufficient to provide a provisional stroma. This provisional stroma imposes on tumor cells a structure that persists even as tumor cells multiply and as the fibrin provisional stroma is replaced by mature connective tissue. The provisional fibrin stroma also serves to regulate the influx of macrophages, and perhaps other inflammatory cells, but at the same time, and in ways that are not fully understood, facilitates the inward migration of new blood vessels and fibroblasts, integral components of mature tumor stroma. Ascites tumors differ from solid tumors in that fibrin gel is not ordinarily deposited in body cavities and, as a result, there is no provisional stroma to impose an initial structure. Tumor stroma generation resembles the process of wound healing in many respects. However, it differs in the mechanism of its initiation, and in the apparent lack of a role for platelets. It also differs fundamentally in that invading tumor cells continually render new vessels hyperpermeable to plasma, thus perpetuating the cycle of extravascular fibrin deposition. In this sense, tumors behave as wounds that do not heal. Largely neglected in this review has been discussion of the numerous cytokines, mitogens, and growth factors that are widely believed to play important roles in tumor angiogenesis and wound healing; i.e., PDGF, FGF, EGF, TGF alpha, TGF beta, TNF, interferons, etc. This omission has been intentional, and for two reasons. First, these cytokines have already received considerable attention [100,123-128]. Second, it is not yet clear how closely the actions of these molecules, as described in vitro, relate to their functions in vivo. At present we are deluged with a surfeit of factors that have the capacity to induce new blood vessel formation in angiogenesis assays; these factors include not only peptides but lipids and even ions [126,129-131].(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Coagulation↗