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Biomedical subjects

W A Thomas

Publications and source records attributed to W A Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1990

Galactosyl transferase-dependence of neurite outgrowth on substratum-bound laminin.

The cell surface enzyme beta 1-4 galactosyl transferase (galtase) has been implicated in a number of cellular events involving adhesion and recognition, among them migration of neural crest and mesenchymal cells as well as initiation and elongation of neurites from PC12 cells. Results presented here demonstrate that reagents that specifically alter galtase activity modulate the rate of neurite outgrowth from chick dorsal root ganglia on substrata coated with the large extracellular matrix glycoprotein, laminin (LN), a known substrate for galtase activity. Not all neurites responded equally to reagent addition, and in every experiment a subset of neurites was ostensibly unaffected by reagent, even at the highest concentration tested. Those neurites that were affected demonstrated an ability to adapt to the continued presence of reagent and resume normal elongation. These results support the hypothesis that cell surface galtase activity plays an important role in mediating neurite elongation and suggest further that differential expression of galtase at the nerve growth cone might contribute to axonal guidance through glycoconjugate-rich environments in vivo.

Animals↗
PubMed1989

Modification of lipoprotein patterns and retardation of atherogenesis by a fish oil supplement to a hyperlipidemic diet for swine.

We have studied the effect of addition of 30 ml cod liver oil (FO) daily to a highly atherogenic butter (BT) diet for swine on lesion development in the coronary arteries and aorta, plasma lipoprotein (LP) patterns, plasma levels of thiobarbituric acid-reactive substances (TBARS) and on tritiated thymidine-labeling indices ([3H]TdR LI) of smooth muscle cells (SMC) and monocyte/macrophages (M/M phi) in the atherosclerotic lesions. Seventeen male Yorkshire swine (11.1 +/- 0.4 kg) were divided into 3 groups: BT (n = 6), BT + FO (n = 6) and mash (n = 5). They were fed the respective diets for 4 months. Terminally, fasting plasma was obtained and cholesterol contents were determined in various fractions of lipoproteins separated by density gradient ultracentrifugation, Pevikon block electrophoresis and immunoelectrophoresis. Apoprotein (B, A-I, E and C) contents of the plasma and lipoprotein fractions were determined by polyacrylamide gel electrophoresis and densitometry of gels stained with Coomassie blue. Swine were injected intramuscularly with 0.5 mCi/kg of [3H]TdR 2 h before death. The aorta and coronary arteries were perfusion fixed in situ under anesthesia. Samples were obtained for microscopic morphometry, autoradiography and immunohistochemistry from distal abdominal aorta, thoracic aorta, and proximal coronary arteries; left main (LM), left anterior descending (LAD), left circumflex (LCX), right main (RM), and right coronary artery (RCA). On the BT diet without FO there was extensive atherosclerotic (AS) lesion development, which was drastically reduced by the addition of FO to the BT diet in all sites by from 71 to 94%. The overall plasma cholesterol (CH) levels were reduced only modestly by the FO (816 +/- 64 to 629 +/- 14 mg/dl) but the distribution of CH in the various lipoprotein classes was remarkably altered. The CH in the large lipoprotein molecules containing both B and E apoproteins was reduced from 488 +/- 84 to 204 +/- 17 mg/dl by the FO with an almost corresponding increase in the conventional LDL molecules containing apo B only (158 +/- 29 to 344 +/- 15 mg/dl). We offer the hypothesis that the large apo B,E containing molecules are much more atherogenic than the smaller apo B containing molecules. This hypothesis is supported by a highly significant correlation between extent of lesion development in all arterial sites and plasma levels of CH in apo B,E containing lipoproteins. Plasma TBARS were elevated by the BT + FO diet but seemed to have no significant effect on the lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Endothelial cell denudation, labelling indices and monocyte attachment in advanced swine coronary artery lesions.

This study shows that frank endothelial denudation, as measured by scanning electron microscopy, is associated with coronary artery atherosclerotic lesions in swine fed hyperlipidemic diets for 9 or 18 months. The largest areas of endothelial cell denudation were found to be associated with the most advanced atherosclerotic lesions, and lesser areas of denudation were present in less severely atherosclerotic arteries. Overall, the study suggests that frank endothelial denudation in swine coronaries occurs secondarily to advanced lesion development, and is proportionate to the amount of lesion present. In contrast attachment of monocytes to the endothelial surface was not proportionate to the amount of lesion present. While the number of attached monocytes after 9 or 18 months of a hyperlipidemic diet was much greater than in the mash-fed swine, there was no difference between the two hyperlipidemic groups. In both hyperlipidemic groups, the attached monocytes were concentrated over lesion areas. By scanning electron microscopy, most attached monocytes in these perfused coronary arteries showed a slender foot process extending into a gap between endothelial cells. Endothelial cell turnover, as measured by tritiated thymidine labelling indices, increased with the amount of coronary artery atherosclerosis. However, it did not become significantly greater than in mash-fed swine until advanced lesions developed.

Animals↗
PubMed1988

The "turning off" of excessive cell replicative activity in advanced atherosclerotic lesions of swine by a regression diet.

We studied progression of atherosclerotic lesions in the coronaries and abdominal aortas of swine fed hyperlipidemic (HL) diets producing serum cholesterol levels of about 700 mg/dl for up to 18 months with killings at 9, 13.5 and 18 months on diet. We studied changes in lesions in subsets given after 9 months on the HL diet a low fat, low cholesterol mash diet with killings at 4.5 and 9 months on the regression diet. Lesion cell numbers were evaluated using mean nuclear profiles per cross-section (Np/Cx) in an anatomically defined portion of artery as an index. Lesion sizes were evaluated using mean cross-sectional area (area/Cx) as an index. Tritiated thymidine labeling indices (LI) were used as an index of cell proliferative activity in the coronaries. We also determined the percentage of lesions occupied by lipid rich calcific necrotic debris. For further comparisons all of the same values were determined for normal intimal cell masses (ICM) in control groups fed a low fat, low cholesterol mash diet throughout. The atherosclerotic lesions in the HL swine appeared to arise mainly in the ICM. These became lesions and increased tremendously in size and cell numbers. The greatest increase was in the abdominal aorta even when lesion values were normalized by being expressed as percentages of the wall (intima + media). Lipid-rich calcific necrotic debris occupied about 25% of the lesion by 9 months and the percentage was similar at 18 months although size of lesions and their necrotic regions had increased 3-fold over the 9-month interval. Lesion [3H]thymidine LIs were 3-4-fold greater than in the control ICM. In the period 9-18 months on an HL diet lesions increased about 3-fold in size and cell numbers. In the swine put on a regression diet for the 9-18 month period growth of the lesions stopped completely. In fact, there was a numerical decrease in lesion sizes and cell numbers and this was statistically significant for the left anterior descending coronary. The lesion growth stoppage was partly accounted for by the "turning off" of excessive DNA synthesis activity of the lesion cells as indicated by the return of [3H] thymidine LIs to the normal values in the mash controls. Another factor was the lack of increase and in fact marked reduction in the size of the regions of lipid rich necrotic debris.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Can retinal adhesion mechanisms determine cell-sorting patterns: a test of the differential adhesion hypothesis.

Embryonic chick neural retina cells possess two classes of adhesion mechanism, one Ca2+-independent, one Ca2+-dependent, responsible for short-term cell aggregation. This study investigates the role of these mechanisms in the long-term cell sorting potentially relevant to in vivo histogenesis. Retina cells are prepared either with both (E cells) or with only one mechanism (TC cells, CD; LTE cells, CI), respectively. The two types of cell preparations are differentially labelled using fluorescein or rhodamine isothiocyanate, mixed and allowed to aggregate in the presence or absence of cycloheximide at 0.5 microgram ml-1 to retard metabolic recovery of the removed adhesive mechanism. When observed by fluorescence and phase-contrast microscopy, the aggregates formed in cycloheximide show cell sorting, the cells with both mechanisms assuming a more interior position relative to those with a single adhesion mechanism. In parallel hanging-drop experiments, preformed aggregates of cells with a single adhesion mechanism are seen to spread upon aggregates of cells with both mechanisms. No sorting occurs amongst cells from a given stage prepared using any single dissociation protocol. The observed cell sorting would thus seem to derive exclusively from differential cell adhesiveness dependent upon the different dissociation conditions and maintained in the presence of cycloheximide. The experiments support the hypothesis that the dual CI and CD adhesion mechanisms in question can play a central role in governing cell-sorting behaviour during normal histogenesis.

Animals↗
PubMed1987

Production of monoclonal antibodies selective for aggregation-competent chick neural retina cells. An immunosuppressive approach.

We present here a rapid means of preparing mouse monoclonal antibodies which bind selectively to aggregation-competent, embryonic chick neural retina cells. The approach couples two existing technologies: well-defined procedures for manipulating the adhesive properties of embryonic retinal cells through control of the dissociation conditions, and an immunosuppressive technique designed to reduce the immune response against unwanted 'background' antigens. This approach greatly increases the likelihood of generating monoclonal antibodies directed against cell surface molecules mediating intracellular adhesion in this tissue. Fab prepared from the combined supernates of all IgG-producing clones obtained in this manner inhibited retinal Ca2+-dependent adhesion, suggesting that at least one clone in the group was reactive with elements of the Ca2+-dependent adhesion mechanism.

Animals↗
PubMed1987

Atherosclerotic lesions in the coronary arteries of hyperlipidemic swine. Part 1. Cell increases, divisions, losses and cells of origin in first 90 days on diet.

The intima of the proximal portion of the coronary arteries of young swine is normally thickened by accumulations of cells about 90% of which are smooth muscle cells (SMC) and about 10% are of probable monocyte origin. Extracellular components such as collagen and elastic tissue are also present but we have chosen to emphasize their cellular nature by calling the regions of thickened intima, intimal cell masses (ICM). We have previously shown that atherosclerotic lesions produced in the coronary arteries of swine by 90 days of feeding a hyperlipidemic (HL) diet arise almost exclusively in the normally occurring ICM. We are reporting here a study of the pathogenesis of these lesions following killing at 0, 14, 49 and 90 HL diet days with comparisons between ICM in control mash-fed swine and ICM-lesions in the HL swine. We found that in the ICM: lipid accumulation was present by 14 days and increased thereafter; the lipid was mostly in SMC but percentage wise the monocyte-macrophages were involved as much or more, cell division activity was increased 3-4-fold by 49 days, cell numbers in ICM were similar in HL and control swine at 49 days but were about 6-fold greater in the HL swine at 90 days, (now in ICM-lesions), at 90 days, circa 90% of the cells appeared to be of SMC and circa 10% of monocyte origin both in the ICM-lesions of the HL swine and in the normal ICM of the controls. The data suggest but do not prove that early lipid accumulation precedes increased cell divisions especially among the SMC component and this in turn precedes increased numbers of cells in the ICM. Although SMC constitute the major cell component of the ICM-lesion at 90 days, the monocyte-macrophage-like cells also increase in number as a result of the HL diet and constitute a small but definite minor component. One possible explanation for the increased cell division activity is that one of the lipid constituents is acting as mitogen; another possibility is that the effect of a well known mitogen such as platelet-derived growth factor is enhanced by the lipid; another is that the monocytes are being stimulated to produce monocyte-derived growth factor. In any event in the very early stage of atherogenesis in the coronary arteries in these experiments excessive proliferation of resident SMC in the ICM appears to be the predominant feature.

Animals↗
PubMed1986

Atherosclerotic lesions in coronary arteries of hyperlipidemic swine. Part 2. Endothelial cell kinetics and leukocyte adherence associated with early lesions.

The role of endothelial cells (EC) in the development and progression of early swine intimal cell mass (ICM)-derived coronary artery lesions in 55 swine fed either a mash or hyperlipidemic diet for 14, 49 or 90 days was investigated. Characteristics studied were endothelial cell turnover (using tritiated thymidine autoradiography), adhesion of leukocytes (presumably chiefly monocytes) to endothelium, and the presence or absence of endothelial cell denudation. The major findings were: An increased adherence of leucocytes to endothelial cells over ICM-lesions in the HL-90 day group compared to the corresponding mash value at 90 days as well as to that of each of the other HL and mash groups. Significant positive correlation between the labeling indices (LI) of endothelial cells lying over coronary artery lesion cells and the labeling indices of the underlying ICM-lesion cells; also, a significant positive correlation between the labeling indices of endothelial cells over lesions of the abdominal aorta and those of the coronary arteries. At 90 days the endothelial cell LI over lesions in the HL group was significantly higher than the corresponding values in the mash group. Since the EC increase rates by growth in the two groups are also significantly different, the differences in LIs reflect at least in part EC growth differences and no strong conclusion can be made regarding possible cell turnover differences. No frank endothelial denudation was found. The findings suggest that in swine coronary arteries participation by monocytes from circulating blood is a factor in the early progression of the lesion as well as smooth muscle cell proliferation.

Animals↗
PubMed1986

Intimal cell mass-derived atherosclerotic lesions in the abdominal aorta of hyperlipidemic swine. Part 2. Investigation of endothelial cell changes and leukocyte adherence associated with early smooth muscle cell proliferative activity.

We have investigated several aspects of endothelial cell (EC) behavior during the initiation and early development of intimal cell mass (ICM)-derived atherosclerotic lesions in the distal abdominal aortas of young swine fed hyperlipidemic (HL) diets for 0, 14, 49, or 90 days. By scanning electron microscopy no breaks in endothelial integrity or other abnormalities were observed even at 90 days on diet after lesions were well established. Also, counts of leukocytes adherent to the endothelium by both scanning and light microscopy revealed no greater numbers in HL than in mash control swine. Estimates of individual EC losses over ICM-lesions in the HL swine (based on calculations from tritiated thymidine labeling indices and EC growth rates determined by counts) suggested a loss of approximately one per 100 EC/day. This loss over ICM lesion was not significantly greater than that over ICM in mash controls, but was significantly greater than that of EC not over ICM lesions in the same HL animal. In any event, the estimated loss seems to be too trivial for the endothelial barrier to be compromised even transiently in a biologically significant fashion. A significant correlation was observed between tritiated thymidine labeling indices of cells within the ICM lesions and of those of the overlying EC that was not observed with the ICM in the controls. Possibly the positive correlation may be a result of the abluminal surface of the overlying EC being exposed to the abnormal milieu of the ICM lesion. It is emphasized that results reported here apply only to ICM-derived lesions at an early stage of development and that they do not contradict results obtained by others with other lesion types such as those derived from monocytes. Furthermore, in later stages of development of ICM-derived lesions in the same model we know that extensive endothelial cell damage can be demonstrated. Also, functional changes in endothelial permeability may have been present in early stages that would not have been detected with the methods used in this study.

Animals↗
PubMed1986

Peptide derivatives as prodrugs.

The results quoted here suggest strongly that peptides as prodrugs are a real possibility for future forms of therapy. Pharmacokinetics and bioavailability are certainly altered by such modifications, usually in a positive sense. The possibilities in utilizing active transport permeases to direct drugs to the desired receptor are an obvious reality, and will undoubtedly lead to new methods for treating bacterial, fungal or even viral infections, and for improved ways of presenting anti-tumour agents. The number of patents appearing in this field is indicative of the interest shown in the pharmaceutical industry.

Amino Acids↗
PubMed1985

Mosaicism in female hybrid hares heterozygous for glucose-6-phosphate dehydrogenase. VII. Evidence for selective advantage of one phenotype over the other in ditypic samples from aortas of hares fed cholesterol oxidation products.

In a previous study the authors demonstrated monotypic foci, all of timidus type, in the atherosclerotic lesions and normal aortic tissue of glucose-6-phosphate dehydrogenase (G-6-PD) mosaic hares fed 25-hydroxycholesterol or triol in addition to a high-cholesterol diet. Other hares fed the high-cholesterol diet without the cholesterol oxidation product additives did not develop monotypic foci. In the current study the question asked was whether ditypic samples from lesions or aortic mediae of the same hares fed the additives would show a higher percentage of timidus type G-6-PD than the hares fed the cholesterol alone. The results showed a significantly higher percentage of timidus type in both lesions and mediae in the groups fed either 25-hydroxycholesterol or triol than in the group fed cholesterol alone. The observations suggest that the change from ditypism to monotypism reported earlier with these cholesterol oxidation products was the result of progressive elimination of the europaeus type to leave only the timidus G-6-PD. This is consistent with the "selective advantage of one phenotype over the other" hypothesis for explaining the observed monotypism as opposed to the "genetic transformation" hypothesis.

Animals↗
PubMed1985

Differential counts by electron microscopy of cell types in normal intimal cell masses in swine abdominal aortas.

Hyperlipidemic diet-induced atherosclerotic lesions show a predilection for locating at the site of normal collections of intimal cells in the swine abdominal aorta. This implies that preexisting intimal cell masses (ICM) evolve into early diet-induced lesions. This study characterizes in detail the distal abdominal aortic ICM of young normal swine as a basis for a better understanding of lesion development. Seventeen male Yorkshire swine were used, from neonates to 20 weeks of age. Only three of six neonates showed multilayered ICM, the remaining three showed scattered individual cells or a single layer of cells. All older swine had multilayered ICM at a predictable ventral site corresponding to Evans blue in vivo staining. The majority of cells counted by electron microscopy were smooth muscle (89 to 94%), the remaining were macrophages (1 to 8%) and poorly differentiated cells (3 to 5%). Weanling and older swine showed high proportions of contractile smooth muscle cells. Ergastoplasm-rich smooth muscle cells comprised nearly half of the neonatal population. Stainable lipids were demonstrable in 20-week-olds, but not in younger swine. No foam cells were seen, but cells containing a few droplets totaled 2%; macrophages comprised a high proportion of these. Pyknotic dead cells were rare, being found in the neonate and 20-week-old swine. Mitoses were observed in two ergastoplasm-rich smooth muscle cells in the neonate and one each in contractile smooth muscle cells of a 14- and a 20-week-old swine. Saddlebag-shaped, atypical-appearing cells were present in all age groups, involving all three cell types, and ranging from 1 to 3%. These represented either bridged nuclei and cytoplasm or more likely artefactual distortion of relatively normal cells.

Animals↗
PubMed1985

Endothelial cell labeling indices in swine aortas in relation to intimal cell mass-derived atherosclerotic lesions.

In the swine abdominal aorta, most atherosclerotic lesions arise from naturally occurring collections of intimal cells called intimal cell masses. The main objective of this study was to determine if the tritiated thymidine labeling index of endothelial cells lying over intimal cell masses was greater than that of endothelial cells not over intimal cell masses. A higher endothelial cell labeling index over intimal cell masses would indicate possibly a greater turnover in the area. Such a finding would suggest possible transient but repeated breaks in the endothelial cell barrier that might contribute to the initiation of the atherosclerotic lesion in intimal cell masses. In 2 groups of mash-fed swine, 2 and 11 months old, no differences were found in labeling indices of endothelial cells lying over or not over intimal cell masses. It appears that the initiation of atherosclerosis in swine abdominal aorta is not dependent upon pre-existing altered endothelial cell kinetics as measured by tritiated thymidine labeling indices. The labeling index of cells within the intimal cell mass was significantly higher than in the media; this also is obviously not dependent upon an increased labeling index of the covering endothelial cells. Another group of swine were killed at 11 months of age after receiving a hyperlipidemic diet for 270 days. The labeling index of endothelial cells over atherosclerotic lesions was significantly higher than the labeling index of endothelial cells not over lesions in these swine, and also significantly higher than that of endothelial cells over intimal cell masses in the 11-month old mash-fed group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1985

Intimal cell mass-derived atherosclerotic lesions in the abdominal aorta of hyperlipidemic swine. Part 1. Cell of origin, cell divisions and cell losses in first 90 days on diet.

Atherosclerotic lesions may originate and develop in a variety of ways. In this study we are focusing our attention on atherosclerotic lesions arising in normally occurring intimal cell masses (ICM) in the abdominal aortas of hyperlipidemic (HL) swine. Times chosen for study were 0, 14, 49 and 90 days on HL diet; mash-fed swine were used as controls. Total numbers of cells in the ICM of HL and mash swine were similar at 14 and 49 days; by 90 days the number of cells had increased dramatically in the HL swine to 8-fold greater than control values. Changes present at 49 days and thus preceding increase in cell numbers included extensive intracellular lipid accumulation with by count nearly half of the ICM cells involved and elevated tritiated thymidine labeling indices (LI) 4-fold greater than control. Differential cell counts by transmission electron microscopy were made on the ICM lesions in the HL swine at 49 and 90 days. More than 95% of all cells were smooth muscle cells (SMC), with relatively few monocytes being present. Calculations from the LI and total cell counts showed that the entire increase in cell numbers could be accounted for by divisions among the resident SMC in the ICM. Further calculations suggested that cell losses (deaths) from the ICM were minimal. Scanning electron microscopy studies reported elsewhere revealed no loss of endothelial integrity. The results suggest: (1) that the lesions arise by stimulation of the resident SMC in the ICM to hyperplastic activity, (2) that the role of monocytes in the early development of these lesions is minimal if any, (3) that in view of the intact endothelium platelets are not likely to play an important role, (4) that ICM cell death is not a major factor, (5) that the most likely candidate for the cell growth stimulatory role (? mitogen) is some component(s) of the excess lipid that accumulates in the ICM.

Animals↗
PubMed1985

Association of plasma intermediate density lipoproteins with atherogenic intimal proliferative activity in abdominal aortas of hyperlipidemic swine.

In an earlier study of swine fed hyperlipidemic (HL) diets containing either butter or corn oil we found wide differences in atherogenic intimal proliferative responses among the swine, especially in the corn oil group, that could not be entirely accounted for by differences in serum cholesterol levels. We hypothesized that there might be differences in some lipoprotein constituents other than total cholesterol that might better account for the differences in intimal proliferative responses. In the current experiment, 11 swine were fed HL diets containing butter (n = 5) or corn oil (n = 6). At 90 days on HL diet, plasma was obtained for lipoprotein fractionation. At 120 days the swine were killed and the lesion areas and number of nuclear profiles in the intima or lesions in multiple cross-sections of the distal abdominal aorta were determined under light microscopy. Tritiated thymidine labeling indices of the intima or lesion cells were also determined. On comparing the butter and corn oil groups, only IDL-cholesterol and tritiated thymidine labeling indices of the cells in the lesions were significantly different. Based on the number of nuclear profiles per cross-section (Np/Cx) 7 were classified as high intimal proliferative responders (5 butter, 2 corn oil) and 4 as low responders (4 corn oil). The high-proliferative responders had plasma IDL levels 6-fold greater than those of the low responders with no overlaps. LDL, VLDL and HDL were not significantly different between the high- and low-proliferative responders. Among correlation coefficients between Np/Cx and plasma lipoprotein variables for all swine (n = 11), IDL cholesterol level was best correlated with Np/Cx. However, in the high responder group LDL values showed a highly significant correlation with the amount of intimal proliferation.

Animals↗