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Biomedical subjects

J E Silbert

Publications and source records attributed to J E Silbert.

At least 55 records · Page 3Linked to original sources
PubMed1986

Glycosaminoglycan production by bovine aortic endothelial cells cultured in sulfate-depleted medium.

Bovine aortic endothelial cells were cultured in medium containing [3H]glucosamine and concentrations of [35S]sulfate ranging from 0.01 to 0.31 mM. While the amount of [3H]hexosamine incorporated into chondroitin sulfate and heparan sulfate was constant, decreasing concentrations of sulfate resulted in lower [35S]sulfate incorporation. Sulfate concentrations greater than 0.11 mM were required for maximal [35S]sulfate incorporation. Chondroitin sulfate was particularly affected so that the sulfate to hexosamine ratio in [3H]chondroitin [35S]sulfate dropped considerably more than the sulfate to hexosamine ratio in [3H] heparan [35S]sulfate. Sulfate concentration had no effect on the ratio of chondroitin 4-sulfate to chondroitin 6-sulfate. The ratios of sulfate to hexosamine in cell-associated glycosaminoglycans were essentially identical with the ratios in media glycosaminoglycans at all sulfate concentrations. DEAE-cellulose chromatography confirmed that sulfation of chondroitin sulfate was particularly sensitive to low sulfate concentrations. While cells incubated in medium containing 0.31 mM sulfate produced chondroitin sulfate which eluted later than heparan sulfate, cells incubated in medium containing less than 0.04 mM sulfate produced chondroitin sulfate which eluted before heparan sulfate and near hyaluronic acid, indicating that many chains were essentially unsulfated. At intermediate concentrations of sulfate, chondroitin sulfate was found in very broad elution patterns suggesting that most did not fit an "all or nothing" mechanism. Heparan sulfate produced at low concentrations of sulfate eluted with narrower elution patterns than chondroitin sulfate, and there was no indication of any "all or nothing" sulfation.

Animals↗
PubMed1986

Effects of heparan sulfate removal on attachment and reattachment of fibroblasts and endothelial cells.

Human skin fibroblasts and calf aorta endothelial cells were grown as tissue culture monolayers in the presence of [35S]sulfate in order to label the glycosaminoglycan portions of proteoglycans for investigation of their role in cell attachment. The [35S]glycosaminoglycans were then selectively removed from the cell monolayers by the addition of various glycosaminoglycan-degrading enzymes. As previously described, in contrast to trypsin treatment none of these enzymes removed any cells from the culture plates. Incubation with a preparation from Flavobacterium heparinum left only small stubs of [35S]glycosaminoglycans on the cell monolayers, indicating that all the cell-surface proteoheparan [35S]sulfate and proteochondroitin [35S]sulfate was accessible to this enzyme preparation. The treatment did not change the amount or time of incubation with trypsin necessary for release of the cells from the monolayers. Thus, cell attachment was not weakened by removal of heparan sulfate or chondroitin sulfate. In contrast, neither fibroblasts nor endothelial cells in suspension would reattach in the presence of the F. heparinum preparation while reattachment occurred readily in the presence of chondroitin ABC lyase. This provides evidence that heparan sulfate, but not chondroitin sulfate, is involved in the process of cell attachment even though neither is necessary for maintaining attachment.

Animals↗
PubMed1986

Effects of hypoxia and hyperoxia on proteoglycan production by bovine pulmonary artery endothelial cells.

Bovine pulmonary artery endothelial cells in culture were used to assess the influence of oxygen tension on proteoglycan synthesis. Cells exposed to 3% O2 (hypoxia) for 72 h and then labeled with [35S]sulfate for 5 h accumulated significantly less [35S]proteoglycan in medium than cells exposed to 20% O2 (control). This decrease was due primarily to a reduction in heparan sulfate. Cells exposed to 80% O2 (hyperoxia) for 72 h secreted slightly more [35S]proteoglycan into medium than controls. Greater accumulation of chondroitin sulfate was responsible for the increase. The amount of cell-associated proteoglycan did not change significantly in cells cultured in 3% or 80% O2 as compared with control cells cultured in 20% O2. Proteoglycans produced by hypoxia- or hyperoxia-treated cells were found to be similar in size to proteoglycans produced by cells cultured at 20% O2. Glycosaminoglycan sulfation, as measured by ion-exchange chromatography, did not appear to change with varying oxygen tensions. Our results demonstrate that production of proteoglycans secreted by endothelial cells in culture is sensitive to oxygen tension.

Animals↗
PubMed1985

The development of benign prostatic hyperplasia among volunteers in the Normative Aging Study.

This study describes the development of benign prostatic hyperplasia among 2,036 volunteers in the Veterans Administration Normative Aging Study, a longitudinal study of human aging situated in Boston. Men were followed from enrollment in the study (between 1961 and 1970) until their last examination prior to May 15, 1982. Two indications of benign prostatic hyperplasia were considered: 1) a clinical diagnosis made at a uniform physical examination, and 2) surgical treatment. Incidence rates for both a clinical diagnosis and surgery for benign prostatic hyperplasia increased through the eighth decade. Life table analysis estimated the lifetime probability of surgical treatment to be 0.29. Known risk factors for cardiovascular disease and diabetes as well as marital and socioeconomic status, religion, cigarette smoking and alcohol and coffee consumption were evaluated as risk factors. Controlling for age in proportional hazards models, statistically significant predictors of surgery were prior clinical diagnosis, lower socioeconomic status, Jewish religion, and not currently smoking cigarettes; whereas only body mass index was a significant predictor of a clinical diagnosis. Although a prior clinical diagnosis was an important predictor of surgery (adjusted odds ratio 3.52, 95% confidence interval = 1.93-6.42), this diagnosis is neither sensitive nor specific in its association with surgery.

Adult↗
PubMed1984

Trace metals in drinking water: lack of influence on blood pressure.

It has been suggested that certain trace metals may affect human blood pressure. We recently measured trace metals in the tapwater from the homes of 246 male participants of the Normative Aging Study. Participants were free of any disease or medication known to influence blood pressure. No statistically significant relationship was found between lead concentration and systolic blood pressure in an analysis of covariance, controlling for age and body mass index. Diastolic pressure was examined as well and the results were almost identical. Since educational level and town of residence were potential confounders, we stratified on these variables but no association between lead concentration and blood pressure emerged. Similarly, no statistically significant relationships were found between blood pressure and copper or iron. Blood pressure did differ significantly among zinc concentration groups but no uniform trend appeared. In light of evidence from other studies suggesting that blood pressure is influenced by lead or other elements in drinking water, further investigations with more highly exposed subjects or a prospective design appear warranted.

Adult↗
PubMed1983

Trends in serum uric acid levels 1961--1980.

Uric acid levels of adult male volunteers in a longitudinal study of human aging rose steadily between 1961 and 1978. In the 1,141 men with 3 serial physical examinations, who developed no diseases and who took no drugs known to affect uric acid levels, levels rose from means below 5.5 mg/dl in 1961--1963 to means above 6.5 mg/dl in 1975--1978. The best predictor of a longitudinal increase in uric acid level was a gain in weight, but this, and other significant predictors, explained only a small portion of the increase in this population. Preliminary data available from a fourth examination indicate that the rising trend has leveled off.

Adult↗
PubMed1983

Cell surface heparan sulfate mediates some adhesive responses to glycosaminoglycan-binding matrices, including fibronectin.

Proteins with affinities for specific glycosaminoglycans (GAC's) were used as probes for testing the potential of cell surface GAG's to mediate cell adhesive responses to extracellular matrices (ECM). Plasma fibronectin (FN) and proteins that bind hyaluronate (cartilage proteo-glycan core and link proteins) or heparan sulfate (platelet factor 4 [PF4]) were adsorbed to inert substrata to evaluate attachment and spreading of several 3T3 cell lines. Cells failed to attach to hyaluronate-binding substrata. The rates of attachment on PF4 were identical to those on FN; however, PF4 stimulated formation of broad convex lamellae but not tapered cell processes fibers during the spreading response. PF4-mediated responses were blocked by treating the PF4-adsorbed substratum with heparin (but not chondroitin sulfate), or alternatively the cells with Flavobacter heparinum heparinase (but not chondroitinase ABC). Heparinase treatment did not inhibit cell attachment to FN but did inhibit spreading. Cells spread on PF4 or FN contained similar Ca2+-independent cell-substratum adhesions, as revealed by EGTA-mediated retraction of their substratum-bound processes. Microtubular networks reorganized in cells on PF4 but failed to extend into the broadly spread lamellae, where fine microfilament bundles had developed. Stress fibers, common on FN, failed to develop on PF4. These experiments indicate that (a) heparan sulfate proteoglycans are critical mediators of cell adhesion and heparan sulfate-dependent adhesion via PF4 is comparable in some, but not all, ways to FN-mediated adhesion, (b) the uncharacterized and heparan sulfate-independent "cell surface" receptor for FN permits some but not all aspects of adhesion, and (c) physiologically compatible and complete adhesion of fibroblasts requires binding of extracellular matrix FN to both the unidentified "cell surface" receptor and heparan sulfate proteoglycans.

Animals↗
PubMed1982

Alteration in plasma proteins and platelet functions with aging and cigarette smoking in healthy men.

Blood samples were obtained on four different occasions from 18 cigarette smoking and 34 non-smoking healthy men (age 40-69) and analyzed to assess age- and smoking-associated changes in plasma proteins, blood coagulation and platelet functions. Collagen-induced platelet aggregation was significantly increased with aging in non-smokers. Significant changes in chronic smokers were increases in platelet count and fibrinogen in plasma; elevation of platelet factor-3 (PF-3) activity in platelet-poor plasma (PPP); increase in serum levels of alpha 1-antitrypsin, orosomucoid, haptoglobin and properdin factor B; and shortening of the lag period of collagen-induced platelet aggregation. Filtration of PPP through Millipore filters removed PF-3 membranes. The differences in PF-3 activities in filtered plasma were no longer significant between smokers and non-smokers. Results suggest that chronic smokers have higher levels of acute phase proteins reflecting underlying inflammatory processes, and higher levels of PF-3 activity in plasma due to liberation of PF-3 membranes from platelets.

Adult↗
PubMed1982

Xylosylphosphoryldolichol synthesized by chick embryo epiphyses. Not an intermediate in proteoglycan biosynthesis.

Incubation of chick embryo epiphyseal microsomes with UDP-[14C]xylose in the presence of pyrophosphatase inhibitors resulted in the incorporation of [14C]xylose into proteoglycan and the formation of small amounts of 14C-labeled material soluble in chloroform:methanol. Synthesis of the [14C]xylose-lipid was stimulated by exogenous dolichol phosphate whereas the addition of retinol plus ATP had no effect. The [14C]xylosyl-lipid was identified as [14C]xylosylphosphoryldolichol by chromatography on SG-81 paper and DEAE-cellulose and by acid hydrolysis. Addition of UDP-galactose and UDP-glucuronic acid to incubations of epiphyseal microsomes with UDP-[14C]xylose did not stimulate [14C]xylose incorporation into lipid nor into proteoglycan. Under several different conditions, [14C]xylose was not transferred from [14C]xylosylphosphoryldolichol to proteoglycan, indicating that [14C]xylosylphosphoryldolichol was not an intermediate in proteoglycan biosynthesis. Chick embryo epiphyseal microsomes also synthesized [14C]glucosylphosphoryldolichol. In addition, [14C]glucose was transferred from [14C]glucosylphosphoryldolichol into oligosaccharide lipids in the chloroform:methanol:water extract and into glycoproteins in the pellet fraction. Competition experiments with UDP-glucose and UDP-xylose suggested that xylosylphosphoryldolichol was synthesized by the glucosyltransferase involved with glucosylphosphoryldolichol biosynthesis.

Animals↗
PubMed1982

Alterations in alveolar basement membranes during postnatal lung growth.

We studied the ultrastructural characteristics of alveolar basement membranes (ABM) and capillary basement membranes (CBM) in rat lungs at birth, at 8-10 d of age, during alveolar formation, and at 6-10 wk of age, after most alveoli have formed. We also measured in vitro lung proteoglycan and heparan sulfate synthesis at each age. We noted three major age-related changes in pulmonary basement membranes. (a) Discontinuities in the ABM through which basilar cytoplasmic foot processes extend are present beneath alveolar type-2 cells but not alveolar type-1 cells. These discontinuities are most prevalent at birth but also exist in the adult. (b) Discontinuities are also present in CBM at the two earliest time points but are maximal at 8 d of age rather than at birth. Fusions between ABM and CBM are often absent at 8 d of age, but CBM and CBM/ABM fusions were complete in the adult. (c) Heparan sulfate proteoglycans identified with ruthenium red and selective enzyme degradation are distributed equally on epithelial and interstitial sides of the ABM lamina densa at birth, but decrease on the interstitial side with age. In vitro proteoglycan and heparan sulfate accumulation at birth was two times that at 8 d and five times that in the adult. Discontinuities in ABM allow epithelial-mesenchymal interactions that may influence type-2 cells cytodifferentiation. Discontinuities in CBM suggest that capillary proliferation and neovascularization are associated with alveolar formation at 8 d. When CBM becomes complete and forms junctions with ABM, lung neovascularization likely ends as does the ability to form new alveoli.

Animals↗
PubMed1982

Assessment of abdominal fat content by computed tomography.

Computed tomography (CT) produces thin cross-sectional radiographs that may prove very useful in body composition research. CT images of the abdomen allow computerized measurement of total fat area, and also enable the differentiation of subcutaneous fat from intraabdominal fat. The preset investigation examines whether a single CT scan of the abdomen provides an accurate indication of overall abdominal adiposity. Graphs of measurements from seven sequential scans of the abdomen in eight patients showed that rankings of total abdominal area, total fat area, subcutaneous and intraabdominal fat area are relatively consistent no matter which abdominal level is chosen. Correlations of 0.89 to 0.99 between single scans and the average values for all scans show that a single CT image contains the same information on adiposity as a series of scans. These results suggest that future CT studies of body composition can limit radiation exposure by using single scans at different anatomical sites. If only a single scan at one site can be obtained, the level of the umbilicus may be the most useful, because it contains the largest percentage of fat in the body, and best allows differentiation of intraabdominal from subcutaneous fat.

Abdomen↗
PubMed1982

Structure and metabolism of proteoglycans and glycosaminoglycans.

Proteoglycans and glycosaminoglycans have the common structural characteristics of linear polysaccharide chains consisting of a hexosamine alternating with another sugar. They play an important role in skin as part of the support matrix of connective tissue, and may be related to cell-cell, and cell-matrix interactions. In general the polysaccharide chains are covalently linked to protein and may contain varying amounts of sulfate resulting in a strong negative charge. Biosynthesis consists of the formation of the protein core followed by the sequential addition of sugars and sulfate to the nonreducing ends of growing chains. The synthetic process is highly organized with the final polysaccharide polymerization and sulfation taking place in the Golgi. Degradation of the proteoglycans is less well understood but probably involves endoglycosidases, exoglycosidases, and proteases which work in concert to degrade these substances.

Chemical Phenomena↗
PubMed1982

Changes in cholesterol and triglyceride as predictors of ischemic heart disease in men.

We examined the relation of longitudinal changes in cholesterol and triglyceride to the subsequent development of heart disease. The data were from 1437 participants of the Normative Aging Study, a prospective study of men from the Boston area who were free of ischemic heart disease on two examinations approximately 5 years apart. Forty-four had symptoms or ECG findings of ischemic heart disease after their second but before their third examination, a period of 3-5 years. The risk of heart disease was studied using a multiple logistic risk model that took into account smoking and other risk factors. Changes in cholesterol and triglyceride levels between Exams 1 and 2, when corrected for regression to the mean, were better predictors of heart disease incurred between Exams 2 and 3 than initial levels of cholesterol, triglyceride or systolic blood pressure. When two age groups (28-52 years and 53-85 years) were considered, changes were important predictors in each age group. These findings suggest the importance of monitoring lipid changes over time.

Adult↗
PubMed1982

The relationship of pulmonary function to copper concentrations in drinking water.

Copper has been shown to be an important cofactor for certain enzymatic reactions. Specifically, cross-linking of elastin is inhibited by copper deficiency. In animal models, this inhibition leads to weakened connective tissue and pathologic changes in the lungs consistent with emphysema. To explore the potential relationship of copper exposure to level of pulmonary function in humans, we examined copper concentrations in tap water in the homes of 297 adult male subjects involved in the Normative Aging Study. Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were obtained by standard techniques. The relationship of tap water copper concentration to pulmonary function was explored using multiple regression analysis, controlling for other potential confounding variables (age, height, smoking status, and educational attainment). Separate regressions were performed for each of 3 smoking status groups: never, former, and current. Among never smokers, tap water copper was significantly and positively related to levels of both FVC (p = 0.014) and FEV1 (p = 0.027). No significant trend was found among former or current smokers. These data suggest that copper intake may be an important determinant of level of pulmonary function and deserves further investigation.

Adult↗
PubMed1981

Inhibition of the action of pyrophosphatase and phosphatase on sugar nucleotides.

Sugar nucleotide degradation by Zn2+-requiring nucleotide pyrophosphatase and phosphatase was effectively inhibited by the addition of the chelator 2,3-dimercaptopropan-1-ol, along with low concentrations of nucleotides or their analogues. The addition of dimercaptopropanol alone completely inhibited alkaline phosphatase. This chelator has a much higher association constant for Zn2+ than for the Mn2+ needed for glycosyltransferase reactions, enabling selective chelation of Zn2+. Neither the chelator alone nor in combination with low concentrations of nucleotides was inhibitory to glycosyltransferase activities, as shown by xylosyltransferase in chick embryo epiphyseal microsomes and galactosyltransferase in rat serum.

Alkaline Phosphatase↗