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Biomedical subjects

J G Lewis

Publications and source records attributed to J G Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1983

Venous thrombosis in a family with defective release of vascular plasminogen activator and elevated plasma factor VIII/von Willebrand's factor.

A family is described in which venous thrombosis developed in five members as early as 14 years of age. Routine coagulation studies, plasma antithrombin III, factor V, plasminogen, beta-thromboglobulin, fibrinopeptide A, prothrombin fragment F1+2, and thrombin-antithrombin III complex were all within normal limits. However, defective release of vascular plasminogen activator was observed on several occasions in all five subjects as compared with a control population of 125 persons (0.04 Committee on Thrombolytic Agents [CTA] units/ml plasma as compared with 0.21 CTS units/ml). In addition, levels of factor VII/von Willebrand's factor were significantly elevated above the normal range in this pedigree.

Adolescent↗
PubMed1983

The kinetics of DNA alkylation, repair and replication in hepatocytes, Kupffer cells, and sinusoidal endothelial cells in rat liver during continuous exposure to 1,2-dimethylhydrazine.

We have previously shown that when rats are continually exposed to 1,2-dimethylhydrazine (SDMH) in a manner that induces malignant hemangioendotheliomas of the liver there was both accumulation of promutagenic DNA damage, as measured by O6-methylguanine (O6MG) and a selective increase in cell replication in the target cell population, the nonparenchymal cells (NPC). Hepatocytes rapidly repaired O6MG and had only modest increases in cell replication. In this study, we have further separated the NPC into Kupffer cells (KC) and sinusoidal endothelial cells (SEC) and have determined the kinetics of O6MG and 7-methylguanine (7MG) formation and repair, and cell replication in each individual cell type. O6MG concentrations were highest over the entire exposure period in the SEC, lowest in the hepatocytes, with intermediate concentrations occurring in KC. 7MG concentrations were lower in SEC than in KC or hepatocytes resulting in greatly increased O6/7MG ratios in SEC suggesting a lower capacity for SDMH metabolism and O6MG repair. Moreover, the concentrations of 7MG and the pattern of accumulation were sufficiently similar in KC and hepatocytes to suggest similar capacities of these two cell types to activate SDMH. Rates of cell replication were greatly elevated in both KC and SEC by SDMH, while hepatocyte replication was barely affected. These data suggest that SEC and to a lesser extent KC have greater potential for initiation due to mispairing of O6MG than do hepatocytes. The data further suggest that alkylation in SEC may arise from metabolites generated by neighboring hepatocytes or KC.

Alkylation↗
PubMed1982

The alpha 2 HS glycoprotein receptor on lymphocytes transformed by Epstein--Barr virus.

The alpha 2HS glycoprotein receptor from lymphocytes transformed by Epstein--Barr Virus was isolated by affinity chromatography. The protein receptor has a monomer Mr of 48 000, which is similar to the Epstein--Barr virus-determined nuclear antigen (EBNA), and pI = 7.2. Like EBNA the 48 000 Mr component in unfractionated labelled detergent solubilised cell supernatants also binds DNA. These results may suggest some similarity between the alpha 2HS receptor and EBNA.

Blood Proteins↗
PubMed1982

Detection of herpes simplex virus type 2 glycoproteins expressed in virus-transformed rat cells.

Rat embryo fibroblasts transformed by herpes simplex virus type 2 (HSV-2) were assayed for the expression of certain virus-specific glycoproteins on the surface membranes. Monospecific antisera to HSV-2-specific glycoproteins, designated gAgB, gC, and gX, were used in membrane immunofluorescence studies with HSV-2-transformed cell lines tREF-G-1, tREF-G-2, and a tumor-derived rat fibrosarcoma cells line produced in syngeneic rats inoculated with tREF-G-1 cells. Analysis of the three HSV-2-transformed cell lines showed that antisera to the gAgB and gX glycoproteins were reactive with these cells. In contrast, no significant reactivity was observed when anti-gC serum was reacted with the HSV-2-transformed cell lines. All three antiglycoprotein sera reacted positively with rat cells productively infected with HSV-2. Additionally, the HSV-2-transformed and tumor-derived cell lines showed positive internal immunofluorescence after reaction with antiserum to an early, nonstructural viral protein designated VP143 (molecular weight, 143,000). Infectivity of HSV-2 in standard plaque assays was neutralized by hyperimmune rat antisera to tREF-G-2 or rat fibrosarcoma cells and to HSV-2 virions and by sera from rats bearing the fibrosarcoma. Adsorption of rat-anti-HSV-2 serum with tREF-G-2 or rat fibrosarcoma cells reduced neutralizing activity to 10 and 12%, respectively, compared with 90% neutralization by antiserum adsorbed with nontransformed rat embryo fibroblast cells and 100% neutralization with unadsorbed antiserum. In summary, HSV-2-transformed rat cells retained and expressed genetic information necessary for the production of HSV-2 glycoproteins and a nonstructural protein after high passage in tissue culture or in the syngeneic host.

Animals↗
PubMed1982

A colorimetric assay for releasable plasminogen activator.

We describe an equilibrium assay for measuring release of plasminogen activator form blood-vessel walls and report data from 125 individuals free of overt thromboembolic disease. Excess human plasminogen is added to the euglobulin fraction of plasma obtained before and after venous occlusion at mean systolic pressure. To measure plasmin generation in these samples, we used the chromogenic plasmin substrate D-Val-Leu-Lys-p-nitroanilide, which liberates p-nitroaniline upon cleavage. Releasable plasminogen activator in 24 subjects was determined by this colorimetric assay and by the radiocasein assay previously reported by this laboratory (Am. J. Clin. Pathol. 76,403-409, 1981), and the results were compared. The correlation coefficient was 0.97. The colorimetric assay offers several advantages over the radiocasein assay: shorter incubation (6 vs 16 h) and no preparation or quantification of a radioactive substrate and its cleavage products.

Adult↗
PubMed1982

Cell specificity in hepatocarcinogenesis: preferential accumulation of O6-methylguanine in target cell DNA during continuous exposure to rats to 1,2-dimethylhydrazine.

Concentrations of the major methylated DNA purines were determined in two liver cell cell populations of Fischer 344 rats during administration of 30 ppm 1,2-dimethylhydrazine (SDMH) in the drinking water for periods of up to 4 weeks. Quantitation of 7-methylguanine and O6-methylguanine (O6MG) was achieved by highly sensitive optical methods following separation of DNA bases by high-performance liquid chromatography. Overall alkylation as indicated by the concentration of 7-methylguanine was near maximum in both hepatocytes and liver nonparenchymal cells by the third day of SDMH administration. Similar amounts of 7-methylguanine were present in the two liver cell populations at seven of nine time points during 4 weeks of exposure. In contrast, dramatic differences in the cumulative concentrations of O6MG were seen in the two cell populations. Nonparenchymal cells accumulated O6MG during the first 8 days of exposure and had up to a 30-fold greater concentration of this product than did the corresponding hepatocytes. In the hepatocytes, a rapid decline in O6MG concentration was observed between 1 and 3 days of exposure to SDMH. Thereafter, only low levels of this promutagenic lesion were present in hepatocytes. Exposure of rats to the same regimen of SDMH for up to 10 months caused angiosarcomas in the livers of over 90% of the animals, while hepatocellular carcinomas occurred in only 40%. Thus, a strong correlation exists between the inability to repair O6MG and cell specificity for carcinogenesis.

1,2-Dimethylhydrazine↗
PubMed1981

Fibrinolytic response and oral contraceptive associated thromboembolism.

A case-control study of fibrinolytic activity was conducted comparing 12 women with a recent history of thromboembolism while taking oral contraceptives and 28 matched female controls without a history of thromboembolism. All subjects had stopped using oral contraceptives at least 12 months prior to study. A new assay, recently developed in this laboratory, was used to evaluate the mean fibrinolytic response to venous occlusion in both cases and controls. The fibrinolytic response of all subjects was stratified into quartiles as previously described. While the controls segregated as expected, all 12 cases occurred in subjects whose fibrinolytic response fell in the first two quartiles with 8 of the 12 subjects having first quartile responses. The mean fibrinolytic response for all controls was 12.3 units while cases showed a mean response of only 3.9 units. The above data supports and extends our recent suggestion that low fibrinolytic response may signal a natural predisposition to venous thromboembolism which could be triggered by use of synthetic estrogens. However, these data do not support the use of this assay as a screening test for oral contraceptive related risk to thromboembolism since at least 50% of the control population also segregate in the first two quarters.

Caseins↗
PubMed1981

Simple and sensitive assay employing stable reagents for quantification of plasminogen activator.

A simple and sensitive indirect assay for quantifying plasminogen activator using [3H]-casein as substrate is described. The assay has been used to measure plasminogen activators from various sources including bacteria, cultured cells, and human plasma. The assay is linear with respect to concentration of plasminogen activator and time of incubation and is independent of concentration of plasminogen. The assay can routinely be used to quantify as few as 8 X 10(-3) international units ml-1 of streptokinase. Results obtained with the [3H]-casein assay correlate well with those obtained by the fibrin plate method (R = 0.83 by Spearman's ranked co-efficient of correlation). The reagents are extremely stable and easily stored. The ease with which the assay can be performed gives the clinical laboratory the potential to test large numbers of patients upon short notice and within a short period of time.

Animals↗
PubMed1981

Binding of alpha 2HS glycoprotein in peripheral blood monocytes.

The binding of 125I-alpha 2HS glycoprotein to peripheral blood monocytes was investigated at 4 degrees C. Equilibrium was attained after 60 min incubation with little internalization of radiolabeled protein. Binding was partially dependent on Ca++. Scatchard plot analysis revealed a dissociation constant of 10(-4) M with 10(6) sites/cell. The low binding affinity between alpha 2HS glycoprotein and peripheral blood monocytes may be offset by the relatively high serum concentration of this protein in the expression of its phagocytic enhancing properties.

Binding Sites↗
PubMed1981

Enhancement of human monocyte phagocytic function by alpha 2HS glycoprotein.

Human alpha 2HS glycoprotein was isolated from normal adult serum and its effect on monocyte phagocytic function (in vitro) was investigated. The results demonstrate that alpha 2HS glycoprotein enhances the ability of peripheral blood monocytes to take up radiolabelled latex particles compared to control cells. Enhanced uptake required the simultaneous presence of cells, substrate and alpha 2HS glycoprotein. This uptake was dependent on the concentration of alpha 2HS glycoprotein offering the possibility that reduced levels of this protein, as in malignant and inflammatory disease, may result in decreased phagocytic function.

Adult↗
PubMed1980

Differential repair of O(6)-methylguanine in DNA of rat hepatocytes and nonparenchymal cells.

Chronic administration of several chemical carcinogens to laboratory animals induces a variety of tumours which arise from specific cell populations within the liver. In the rat, diethylnitrosamine induces hepatocellular carcinomas, dimethylnitrosamine induces both angiosarcomas and hepatocellular carcinomas, vinyl chloride primarily induces angiosarcomas, and 1,2-dimethylhydrazine induces malignant haemangioendotheliomas. One of the principal mechanisms thought to be involved in initiating carcinogenesis is the alkylation of specific sites on DNA, such as the O(6) position of guanine. Previous investigations of alkylation and repair have, however, analysed DNA prepared from whole liver. This approach does not localize alkylation or repair capacity in the different cell types which give rise to neoplasia. Furthermore, although hepatocytes account for more than 90% of the liver's mass, they only comprise 60-70% of its cells. The nonparenchymal cell (NPC) population, which consists almost entirely of endothelial and Kupffer cells, accounts for the remaining 30-40% and contains 10-20% of the DNA. Therefore, we decided to investigate the alkylation and repair of O(6)-and 7-methylguanine in the target and non-target cells following oral administration of 1,2-dimethylhydrazine. We report here that although initial alkylation was slightly less in NPCs, removal of O(6)-methylguanine was significantly slower. This led to a preferential accumulation of O(6)-methylguanine in NPC 24 h after administering a second daily dose. In contrast, 7-methylguanine decreased at similar rates, resulting in a 28-fold greater O(6)-methylguanine/7-methylguanine ratio in the target cell population.

Animals↗
PubMed1980

Physical conditioning augments the fibrinolytic response to venous occlusion in healthy adults.

The effects of a 10-week physical-conditioning program on fibrinolytic activity at rest and after stimulation by venous occlusion were studied in 69 healthy adults 25 to 69 years old. Physical conditioning was documented by treadmill performance, and fibrinolysis was measured with a newly developed radioenzymatic assay. Whereas fibrinolysis declined at rest from 16.2 +/- 1.3 to 11.4 +/- 0.8 units (mean +/- S.E.M.) (P = 0.0017), the increment in fibrinolysis produced by venous occlusion was increased from 21.7 +/- 2.9 to 33.8 +/- 4.7 units (P = 0.0037). This augmentation was most marked in women, persons with low initial levels of stimulated fibrinolysis, and persons with low initial physical fitness. We conclude that physical conditioning can enhance the augmentation of fibrinolytic activity that occurs in response to venous occlusion. Enhanced fibrinolysis in response to thrombotic stimuli could be an important mechanism in the beneficial effect of habitual physical activity on the risk of cardiovascular disease.

Adult↗
PubMed1980

Effect of human alpha 2HS glycoprotein on mouse macrophage function.

alpha 2HS glycoprotein was isolated from normal adult serum. The ability of alpha 2HS glycoprotein to promote the endocytosis of radiolabelled DNA and radiolabelled latex particles by mouse macrophages was investigated. The results using both radiolabelled latex particles and radiolabelled DNA show that alpha 2HS glycoprotein enhances the ability of mouse macrophages to take up these radiolabelled substrates as compared to control cells.

Adult↗
PubMed1979

The effect on plasma potassium of a combined preparation of frusemide and slow-release potassium chloride (Diumide-K Continus tablets).

An open trial was carried out on ten middle-aged and elderly patients in cardiac failure to assess the effect on plasma potassium levels of one or more tablets containing 40 mg frusemide and a controlled-release formulation containing 600 mg potassium chloride. Patients had previously been maintained on frusemide and potassium supplements given as separate tablets. No significant rise or fall was observed when treatment was changed to the combined tablet.

Administration, Oral↗