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Biomedical subjects

R Ross

Publications and source records attributed to R Ross.

At least 217 records · Page 12Linked to original sources
PubMed1990

Purification of PDGF-AB and PDGF-BB from human platelet extracts and identification of all three PDGF dimers in human platelets.

We have developed a panel of monoclonal antibodies to platelet-derived growth factor (PDGF) which have variable specificities for the three dimeric forms of the molecule (AA, AB, and BB). We have used these antibodies to detect and immunoaffinity purify the individual dimers from human platelet rich plasma. Extracts of outdated platelet preparations were initially chromatographed over CM-Sepharose and then passed over the Sepharose-coupled monoclonal antibodies in series in selectively isolate the three dimeric forms of PDGF. The PDGF eluted from the affinity columns was subsequently further purified by reversed-phase HPLC. From 300 units of outdated platelet preparations, we purified 58 micrograms of PDGF-BB and 140 micrograms of PDGF-AB. Using the monoclonal antibodies to develop PDGF dimer-specific ELISAs, it was observed that all three PDGF dimer forms are present in fresh human platelet extracts and that the ratios of the three dimer forms vary depending upon the extraction conditions used. The identification of all three PDGF dimer forms in human platelets point to the need to view PDGF isolated from human platelets by conventional techniques as a mixture of all three forms and not solely as PDGF-AB.

Amino Acid Sequence↗
PubMed1990

Mechanisms that regulate the cell cycle status of very primitive hematopoietic cells in long-term human marrow cultures. I. Stimulatory role of a variety of mesenchymal cell activators and inhibitory role of TGF-beta.

Long-term marrow cultures (LTMC) allow the proliferation and differentiation of primitive human hematopoietic progenitor cells to be maintained for many weeks in the absence of exogenously provided hematopoietic growth factors. Previous investigations focused on defining various types of cells that are present in this culture system and on measuring the cycling behavior of the different subpopulations of colony-forming cells maintained within it. These studies suggested that mesenchymal stromal elements derived from the input marrow play a key role in regulating the turnover of the most primitive, high-proliferative potential erythroid and granulopoietic colony-forming cells that are found almost exclusively in the adherent layer of LTMC. In this study we show that the re-entry into S-phase of these primitive hematopoietic progenitors that occurs after each weekly medium change is due to an as yet undefined constituent of horse serum, which is absent from fetal calf serum. However, this effect is not unique to the factor present in horse serum. It is also elicited by the addition to LTMC of several well-defined growth regulatory molecules, ie, platelet-derived growth factor (PDGF), interleukin-1 (IL-1), transforming growth factor alpha (TGF-alpha), and IL-2. None of these was able to stimulate hematopoietic colony-forming cells in methylcellulose assays, although all have known actions on mesenchymal cells including, in some cases, the ability to increase production of growth factors that can stimulate primitive high-proliferative potential hematopoietic progenitors in clonogenic assays. Interestingly, a stimulating effect was not obtained after addition of endotoxin to LTMC. TGF-beta, a direct-acting negative regulator that acts selectively on primitive hematopoietic progenitor cells if added to LTMC simultaneously with new medium or IL-1, blocked their stimulating activity. These results suggest a model in which indirect, local modulation of both positive and negative regulatory factors via effects on mesenchymal elements determines the rate of turnover of adjacent populations of very primitive hematopoietic cells that are normally maintained in a quiescent state in vivo.

Bone Marrow Cells↗
PubMed1990

Multiple receptors on human monocytes are involved in adhesion to cultured human endothelial cells.

Monocytes exhibit significant basal (unstimulated) adherence to human umbilical vein endothelium (HUVE), which is only partially inhibited by an anti-CD18 monoclonal antibody (mAb) (60.3). We examined factors modulating the residual, CD18-independent monocyte binding to HUVE by pretreating monocytes with mAb 60.3 to eliminate CD18-dependent binding. Basal adherence was reduced from 32% +/- 2% to 14% +/- 2% with mAb 60.3 (means +/- SE of eight experiments; P less than 0.01). mAb 60.3-treated monocytes were incubated with tumor necrosis factor-gamma (TNF-alpha), interleukin-1 (IL-1), lipopolysaccharide (LPS), N-formylmethionyl-leucyl-phenylalamine (FMLP), or phorbol myristate acetate (PMA). Only PMA affected CD18-independent binding. Pretreatment with PMA alone reduced adherence to 21% +/- 2% (mean +/- SE of eight experiments; P less than 0.01). In conjunction with mAb 60.3, PMA virtually eliminated monocyte adherence to HUVE (7% +/- 1%, mean +/- SE of eight experiments; P less than 0.01). We also examined CD18-independent monocyte binding to endothelial-leukocyte adhesion molecules (E-LAMs) induced by pretreatment of HUVE with LPS. Monoclonal antibody 60.3-treated monocytes increased adherence from 14% +/- 2% with unstimulated HUVE to 37% +/- 2% with LPS-stimulated HUVE (mean +/- SE of four experiments; P less than 0.01). Monocytes pretreated with both mAb 60.3 and PMA increased adherence from 5% +/- 1% with the unstimulated HUVE to 18% +/- 1% with the LPS-stimulated HUVE (mean +/- SE of four experiments; P less than 0.01). This result implies the presence of a CD18-independent and PMA-insensitive receptor on human monocytes for an E-LAM induced by LPS. In summary, we have identified two CD18-independent mechanisms of monocyte adherence to HUVE; a PMA-sensitive mechanism mediating basal adherence and a PMA-insensitive mechanism involved in binding to E-LAMs.

Antibodies, Monoclonal↗
PubMed1990

Thyroid dysfunction in a prospectively followed series of patients with progressive systemic sclerosis.

Thirty-nine patients with progressive systemic sclerosis (PSS) in stable clinical conditions were extensively evaluated for the presence of thyroid disease. Two patients had previously undetected hypothyroidism while 7 additional patients had normal serum thyroid hormone levels but an exaggerated TSH response to thyrotropin-releasing hormone (TRH) administration, consistent with subclinical hypothyroidism. Four of the 9 subjects with abnormal TRH responses had positive antithyroid antibodies and of the remaining 5, 4 had been on chlorambucil or prednisone. Basal TSH and TSH response to TRH were significantly higher in PSS patients as a group when compared to a control group and increased with increasing duration of PSS. Serum antithyroid antibodies (antithyroglobulin and/or antimicrosomal antibodies) were positive in 18% and thyroid scans were abnormal in 18% of the patients. The euthyroid sick syndrome was not seen. Our findings indicate an increased frequency of, sometimes previously unsuspected, clinical and subclinical hypothyroidism in stable PSS patients which appears to be autoimmune in nature and becomes more prevalent with increased PSS duration. Careful and regular monitoring of the thyroid function in PSS patients is advisable.

Adult↗
PubMed1990

Thrombolysis in Myocardial Infarction (TIMI) phase II trial: outcome comparison of a "conservative strategy" in community versus tertiary hospitals. The TIMI Research Group.

In the conservative strategy arm of phase II of the Thrombolysis in Myocardial Infarction (TIMI) trial, 1,461 patients were treated with intravenous recombinant tissue-type plasminogen activator (rt-PA). Coronary angiography, with angioplasty if feasible, was to be performed only for recurrent spontaneous or exercise-induced ischemia. In this study results in patients treated by this strategy in community and tertiary hospitals are compared. Despite similar baseline findings in the two groups, coronary angiography was performed within 42 days in more patients (542 [48%] of 1,155) initially admitted to a tertiary hospital (on-site coronary angiography/angioplasty available) than in those (94 [32%] of 306) admitted to a community hospital (transfer to tertiary hospital for coronary angiography/angioplasty) (p less than 0.001). This different approach resulted in a greater use of coronary angioplasty (203 [18%] of 1,155 versus 32 [11%] of 306, p less than 0.01), coronary artery bypass surgery (133 [12%] of 1,155 versus 23 [8%] of 306, p less than 0.05) and blood transfusions (139 [12%] of 1,155 versus 17 [5.5%] of 306, p less than 0.001) in patients admitted to a tertiary than to a community hospital. However, there were no significant differences between the two groups in mortality, recurrent myocardial infarction or left ventricular function. These results demonstrate that a conservative strategy after treatment of acute myocardial infarction with rt-PA is applicable in the community hospital setting.

Angioplasty, Balloon, Coronary↗
PubMed1990

Postnatal changes in serum osteocalcin and parathyroid hormone concentrations.

Cord clamping at birth leads to interruption of calcium (Ca) supply to the fetus. After birth, neonatal parathyroid hormone (PTH) secretion appears stimulated by hypocalcemia, with serum PTH increasing after birth and peaking at 24 hours of age. This rise in PTH presumably leads to bone resorption and Ca release. We theorize that bone formation may also be affected and that a serum marker of bone formation, serum osteocalcin (OC) concentrations, will decrease postnatally. OC is synthesized by osteoblasts and its serum concentrations are believed to reflect bone formation. We measured serum ionized Ca (iCa), PTH, and OC in cord blood and at 2 and 24 hours in 26 neonates born after uncomplicated pregnancies, labors, and deliveries. Serum iCa (mg/dl) decreased from 5.79 +/- 0.06 (cord, means +/- SEM) to 5.31 +/- 0.05 (2 hr), then to 4.89 +/- 0.05 (24 hr) (p less than 0.05). Serum PTH (microliter Eq/ml) increased from 35.9 +/- 4.3 (cord) to 41.7 +/- 4.0 (2 hr) (p = 0.1), and to 50.3 +/- 4.6 (24 hr) (p less than 0.01). Serum OC (ng/ml) decreased from 55.1 +/- 10.6 (cord), to 12.4 +/- 4.3 (2 hr) (p less than 0.01), then remained stable at 12.7 +/- 1.9 (24 hr). The change (cord minus 24 hr) in OC correlated inversely with the change in PTH over the first 24 hours of age (r = -0.42. p = 0.03). Therefore, there is a sudden decrease in an index of bone formation (i.e., serum OC) in the first 24 hours of life in which rising serum PTH may have had an impact.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Development↗
PubMed1990

Biology of the interleukin-1 receptor.

The biological effects of the two interleukin-1s on cells of connective tissue origin are mediated by specific cell-surface receptors. Molecular cloning studies have revealed that these receptors are identical in protein sequence to the IL-1 receptors on cells of the T-lymphocyte lineage. The functional interleukin-1 receptor on T-cells and fibroblasts is composed of a single polypeptide chain that binds both IL-1 alpha and IL-1 beta. The single chain appears to be all that is required to transduce a signal to cells. While the nature of the signal is unknown, the structure of the receptor is inconsistent with its possessing any protein tyrosine kinase activity. It is therefore not surprising that the mitogenic activity of IL-1 for fibroblasts is mediated by IL-1 induction of PDGF-A gene transcription. Finally, IL-1 is known to modulate fibroblast-matrix interactions in several ways. It is interesting therefore, that the majority of the IL-1 receptors on cultured fibroblasts are clustered into focal adhesions.

Animals↗
PubMed1990

Relative platelet-derived growth factor receptor subunit expression determines cell migration to different dimeric forms of PDGF.

Platelet-derived growth factor (PDGF) receptor transfectants of a fibroblastoid cell line (BHK) have been used to investigate the ability of the three dimeric forms of PDGF to elicit a chemotactic response. Cells transfected with the beta receptor subunit were only responsive to PDGF-BB, whereas cells expressing the alpha-receptor subunit were equally responsive to all three dimeric forms, PDGF-AA, PDGF-AB, and PDGF-BB. A positive chemotactic response correlated with rearrangement of actin organization. In a study of human arterial smooth muscle cells that express both PDGF receptor subunits endogenously, we again found that recombinant PDGF-AA could elicit a chemotactic response. However, the two smooth muscle cell isolates we examined differed in their chemotactic response to PDGF-AA. This difference correlated closely with their ability to respond mitogenically to this PDGF dimeric form, and the magnitude of both chemotactic and mitogenic responses was related to the proportion of the two receptor subunit species at the cell surface.

Animals↗
PubMed1990

Mechanisms of atherosclerosis--a review.

The response-to-injury hypothesis of atherosclerosis takes into account interactions among all of the cells found in the lesions of human atherosclerosis, the cytokines and growth factors that can be formed by each of these cells (which are in fact formed in vitro and which have been demonstrated in vivo). It should therefore be possible to develop new diagnostic tools that will help us to make early diagnoses for patients who are at risk and determine the state of lesion formation in these patients. An intriguing question that remains is the role of the T lymphocytes in these lesions. The presence of these cells, and some early preliminary data, indicating that antigens unique to the lesions of atherosclerosis are present in the lesions, suggest that many of the lesions of atherosclerosis represent immune or autoimmune responses. The nature of the antigens, the response to these antigens, and the role of antigen-antibody complexes in the process of atherogenesis are important questions to be answered before we reach an understanding of this complex disease process that causes 50% of all deaths in the United States and Western Europe.

Animals↗
PubMed1990

Derivation and properties of platelet-derived growth factor-independent rat smooth muscle cells.

The present study reports that smooth muscle cells can be derived from the adult rat aorta without being exposed to serum containing platelet releasate, these cells can also be grown and passaged in medium lacking detectable quantities of platelet-derived growth factor (PDGF). As reported earlier, smooth muscle cells grown from the newborn or injured vessels have a distinctive epithelioid appearance. The platelet factor independent smooth muscle cells have a similar appearance. Unlike the cells from newborn animals or from injured vessels, smooth muscle cells derived in this way from the adult animal do not produce PDGF, although they do display PDGF receptors. Studies in serum-free medium show that the PDGF-independent cells can respond to PDGF when all other components of serum are absent; however, growth of these smooth muscle cells proceeds equally well in low concentrations of serum, independent of the presence of PDGF or other growth factors detectable by growth-promoting assays using either 3T3 cells or smooth muscle cells whose growth is dependent on factors present in whole blood serum. Taken together with recent observations in vivo, these data suggest that growth of at least some smooth muscle cells may depend on mechanisms independent of release of growth factors by platelets.

Animals↗
PubMed1990

PDGF and FGF stimulate wound healing in the genetically diabetic mouse.

To examine the effects of recombinant growth factors in vivo, impaired wound healing was studied in genetically diabetic C57BL/KsJ-db/db mice. Large full-thickness skin wounds made on the backs of these mice exhibited significant delays in the entry of inflammatory cells into the wound, the formation of granulation tissue, and in wound closure when compared to their nondiabetic littermates. Recombinant human platelet-derived growth factor (rPDGF-BB, 1 or 10 micrograms), recombinant human basic fibroblast growth factor (rbFGF, 1 micrograms), or combinations of both were applied topically to the wounds for 5 to 14 days after wounding. Diabetic mouse wounds treated with rPDGF-BB or rbFGF had many more fibroblasts and capillaries in the wound bed at 10 and 21 days than did wounds treated with the vehicle alone. The animals treated with growth factors also had significantly greater wound closure at 21 days than those treated with the vehicle. Combinations of rPDGF-BB and rbFGF improved all parameters of healing but not to a greater extent than either growth factor alone. The effectiveness of rPDGF-BB and rbFGF suggest that recombinant growth factors may be useful in the treatment of patients with deficient wound repair.

Administration, Topical↗
PubMed1990

Vascular effects of cyclosporine A in vivo and in vitro.

The authors have evaluated the in vivo effects of cyclosporine A on the de-endothelialized rabbit carotid artery. Vascular endothelium was gently removed from the common carotid artery of 10 New Zealand White rabbits that then were treated with therapeutic doses of cyclosporine A (15 mg/kg/day), or its vehicle (Cremophor-EL). Significant intimal proliferation was observed in all cases 2 weeks after de-endothelialization. Concomitant cyclosporine A therapy had no significant effect on intimal smooth muscle proliferation, but was associated with 1) intimal smooth muscle vacuolation, 2) an increase in total intimal thickening, because of the presence of numerous macrophage-derived foam cells, and 3) incorporation of 3H-thymidine by neo-intimal monocyte/macrophages. Mean plasma cholesterol levels were moderately increased in both groups. Although this may have contributed to foam cell formation in the cyclosporine-A-treated animals, it was not the sole determinant, as foam-cell-rich lesions were not observed in control animals. In vitro, cyclosporine A reduced the rate of proliferation of rabbit aortic smooth muscle and endothelial cells in a dose-dependent fashion, and induced smooth muscle cell vacuolation. These data suggest that cyclosporine A may contribute to the formation of graft-related atherosclerosis.

Animals↗
PubMed1989

Cloning of chromosomal genes of Lactococcus by heterologous complementation: partial characterisation of a putative lactose transport gene.

A cosmid gene library of the genome of Lactococcus lactis subsp. lactis 712 has been constructed in the broad host range plasmid pLAFR1 in Escherichia coli LE392. Three lactococcal genes from the bank were identified by heterologous complementation of specific mutations in strains of E. coli. A cosmid clone encoding a putative lactose transport gene was identified by complementing an E. coli lacY mutant. The complemented clone supported the uptake of 14C lactose in transport assays. The DNA fragment responsible was subcloned and localised to a 1.28 kb fragment of the lactococcal chromosome.

Biological Transport↗
PubMed1989

Two different subunits associate to create isoform-specific platelet-derived growth factor receptors.

Recent evidence has demonstrated that there is more than one form of platelet-derived growth factor (PDGF) receptor and that these receptors differ in their specificity for the multiple isoforms of PDGF. We present evidence that high affinity binding of PDGF requires association of two different receptor subunits: an alpha-subunit that can bind either a B- or an A-chain of PDGF, and a beta-subunit that can bind only a B-chain. The alpha- and beta-subunits appear to be similar in size but can be distinguished by binding specificity and by an antireceptor monoclonal antibody, PR7212, which recognizes only the beta-subunit. In the absence of PDGF, these subunits either exist separately or form rapidly reversible complexes. In the presence of PDGF, receptor subunits of appropriate specificity interact with a PDGF molecule to form a high affinity complex. Both the absolute and relative numbers of these two PDGF receptor subunits vary on different cell types and correspond to differences in the mitogenic sensitivity of cells to the different PDGF isoforms.

Adult↗