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Biomedical subjects

L M Green

Publications and source records attributed to L M Green.

At least 37 records · Page 2Linked to original sources
PubMed1996

Leukemia following occupational exposure to 60-Hz electric and magnetic fields among Ontario electric utility workers.

In a nested case-control study of 1,484 cancer cases and 2,179 matched controls from a cohort of 31,543 Ontario Hydro male employees, the authors evaluated associations of cancer risk with electric field exposure and reevaluated the previously reported findings for magnetic fields. Pensioners were followed from January 1, 1970, and active workers (including those who left the corporation) from January 1, 1973, with both groups followed through December 31, 1988. Exposures to electric and magnetic fields and to potential occupational confounders were estimated through job exposure matrices. Odds ratios were elevated for hematopoietic malignancies with cumulative electric field exposure. After adjustment, the odds ratio for leukemia in the upper tertile was 4.45 (95% confidence interval (CI) 1.01-19.7). Odds ratios were also elevated for acute nonlymphoid leukemia, acute myeloid leukemia, and chronic lymphoid leukemia. For cumulative magnetic field exposure, there were similar elevations that fell with adjustment. Evaluation of the combined effect of electric and magnetic fields for leukemia showed significant elevations of risk for high exposure to both, with a dose-response relation for increasing exposure to electric fields and an inconsistent effect for magnetic fields. There was some evidence of a nonsignificant association for brain cancer and benign brain tumors with magnetic fields. For lung cancer, the odds ratio for high exposure to electric and magnetic fields was 1.84 (95% CI 0.69-4.94).

Adult↗
PubMed1996

Reduced cell-cell communication in experimentally induced autoimmune thyroid disease.

We have recently described a spontaneous murine model of autoimmune thyroid disease. The disorder was in part characterized by reduced thyroid epithelial cell-cell communication that was associated with abnormalities in three major connexins. To compare whether this finding was a common secondary occurrence in autoimmune thyroid disease, or unique to the spontaneous development in the MRL mice, we induced thyroiditis in Lewis rats. Immunization with thyroid extract and thyroglobulin resulted in extensive lymphocytic infiltration and increased expression of major histocompatibility gene complex (MHC) class II surface antigen in the diseased thyroid. Both experimental and control rat thyroid tissues produced gap junction proteins connexin 43, connexin 32, and connexin 26. The connexins in nondiseased tissue was located in the plasma membrane at points of cell-cell contact and labeled as discrete arrays of punctate fluorescence. The quantity of all three connexins were reduced in the diseased thyroid tissue. More importantly, the connexin proteins were not distributed as gap junctions at contacting cell interfaces. Both nondiseased and diseased thyroid tissue expressed messenger RNA (mRNA) for the three connexins, but the diseased tissue had reduced levels of mRNA for connexin 43 (45%), and to a lesser extent, connexin 26 (25%) and connexin 32 (20%). The reduced connexin mRNA, protein, and lack of assembled gap junctions measured in the diseased tissue were obtained under conditions where the infiltrating cells and their potent cytokine products were continuously present. To determine if this difference persisted when these inflammatory components were absent, primary cultures of thyroid cells from control and experimental rats were established and connexin localization experiments repeated. The diseased thyroid cells, like the diseased tissue, lacked plasma membrane associated connexin protein. The lack of gap junction assembly in the thyrocytes cultured from the diseased tissue was accompanied by a loss of functional coupling. Collectively, the data document that autoimmune diseased thyroid tissue from both the spontaneous mouse and induced rat models have reduced plasma membrane assembled gap junctions and deficient intercellular communication as determined by the inability to transfer lucifer yellow dye to contiguous cells. Nondiseased cultured thyrocyte monolayers and follicles transferred dye to second and third order neighboring cells in 80 and 95% of trials, respectively. In contrast, only 5-10% of the diseased thyrocytes transferred microinjected dye, and in these cases the transit was limited to primary contacting cells. Culturing removed inequities introduced by the infiltrating cells and their products. However, the established cultures of diseased thyroid cells retained their communication deficiency. This suggests that the loss of communication may be a common abnormality in autoimmune disease, and furthermore, this uncoupling could contribute to the loss of coordinated hormonal regulation (hypothyroidism) in the diseased thyroid gland in the absence of thyroid cell destruction.

Animals↗
PubMed1995

Characterization of autoimmune thyroiditis in MRL-lpr/lpr mice.

MRL-lpr/lpr mice are genetically predisposed to develop a systemic lupus erythematosus-like syndrome that is clinically very similar to the human disease. The results presented here demonstrate, for the first time to our knowledge, that MRL-lpr/lpr mice also develop thyroiditis as part of their systemic autoimmune disorder. The thyroid gland was infiltrated by immunocomponent cells with defined lymphoid follicular centers and extensive interstitial lymphocytes dispersed throughout the thyroid epithelium. All the diseased mice were hypothyroid with reduced, relative levels of thyroid hormone (free T4) and elevated levels of thyroid-stimulating hormone (TSH). They also had high concentrations of circulating IgG class autoantibodies directed against thyroglobulin, thyroperoxidase and double-stranded DNA. The MRL-+/+ age-matched allelic counterpart mice had relatively few lymphocytes in their thyroid tissue, and normal levels of thyroxine and TSH. The non-diseased mice also had undetectable levels of thyroid reactive autoantibodies tested for by enzyme-linked immunosorbent assays. Collectively these findings document that the MRL-lpr/lpr mice spontaneously develop autoimmune thyroiditis and can be used as a model for the study of thyroid-specific autoimmunity.

Animals↗
PubMed1995

Reduced cell-cell communication in a spontaneous murine model of autoimmune thyroid disease.

MRL-lpr/lpr mice manifest a systemic lupus-like autoimmune disease. As part of this syndrome, the mice spontaneously develop autoimmune thyroiditis, which is morphologically and biochemically similar to human autoimmune thyroiditis. In this study we investigated whether thyroid tissue obtained from sites of chronic inflammation had altered gap junctional communication. Fresh tissue sections revealed that thyroid from the nondiseased mice (MRL-(+)/+) had connexins (Cx) localized to the plasma membrane at points of thyroid cell-cell contact. In contrast, the Cx in diseased mouse (MRL-lpr/lpr) thyroid tissue were not localized to the plasma membrane, and the fluorescent intensity was reduced for Cx43 and Cx26. Northern analysis confirmed that murine thyroid tissue expressed messenger RNA for these Cx. However, the diseased tissue expressed lower levels of Cx32 and Cx26 messenger RNA. The infiltrating cells and their biologically active products present in the diseased thyroid tissue may mediate the reduced Cx expression and aberrant gap junctional assembly. We established primary thyrocyte cultures to determine whether these differences persisted when the inflammatory factors were removed. The nondiseased thyroid cells were communication competent, with fluorescent dye transfer proceeding from the injected cell to primary contacts (95%) and to second and third order neighboring cells in 75% of the trials. Thyroid cells from the diseased mice were communication incompetent, in that 80% of microinjections failed to result in dye transfer to cells in direct contact. Immunocytochemistry indicated that the functional coupling in the normal mouse thyroid cells was associated with Cx43 located in the plasma membrane as assembled gap junctional plaques. The communication-deficient diseased thyroid cells had internalized Cx43 predominantly localized to perinuclear regions of the cells. Collectively, these data document altered Cx-protein distribution in the autoimmune diseased thyroid. The diseased thyroid tissue was devoid of plasma membrane identifiable gap junctions and deficient in intercellular communication. Culturing removed the inflammatory mediators; however, the disease cells retained their communication incompetence. These results suggest that if this deficiency was initiated by components of the inflammation process, then protracted changes must have occurred so that the continued presence of these factors was no longer required to sustain this difference.

Animals↗
PubMed1994

Serum soluble CD23 in patients with hypogammaglobulinaemia.

Serum levels of the soluble form of the low-affinity receptor for IgE (FcERII, CD23) (sCD23) are elevated in autoimmune conditions associated with hypergammaglobulinaemia and B cell hyperactivity. Very high levels of sCD23 are found in patients with B-chronic lymphatic leukaemia (B-CLL) who are, however, frequently hypogammaglobulinaemic. We therefore compared the serum levels of sCD23 in healthy controls (n = 33) with three conditions associated with hypogammaglobulinaemia (HGG) and varying B cell numbers: X-linked agammaglobulinaemia (XLA, n = 12), common variable immunodeficiency (CVI, n = 20) and B-chronic lymphatic leukaemia (n = 33). Serum levels of sCD23 showed a significant correlation with the CD19+ B cell count in both normals and patients with CVI (r = 0.65, P < 0.0001). Amongst the different clinical groups, serum levels of sCD23 were increased in the order XLA < CVI < normals < CLL (medians 2.5, 7.7, 11.1 and 540, respectively; P < 0.001 for all comparisons except CVI versus normals P < 0.03 in a one-tailed test). In the CVI group, serum sCD23 was lowest amongst four patients with low B cell numbers. There was no overlap in sCD23 between patients with XLA and this subgroup of CVI patients. Serum sCD23 is, therefore, derived predominantly from B cells, and is significantly related to the peripheral blood B cell count.

Agammaglobulinemia↗
PubMed1993

NMR and computational evidence that high-affinity bradykinin receptor antagonists adopt C-terminal beta-turns.

Three tetrapeptides were prepared, each corresponding to the four C-terminal amino acid residues of highly potent, second-generation bradykinin receptor antagonists. The tetrapeptides are (IA) Ser-D-Phe-Oic-Arg, (IIA) Ser-D-Tic-Oic-Arg, and (IIIA) Ser-D-Hype(trans-propyl)-Oic-Arg. Solution conformations for each were determined by incorporating interproton distance restraints, determined by 2D NMR experiments performed in water at neutral pH, into a series of distance geometry/simulated annealing model building calculations. Similarly, systematic conformational analyses were performed for each using molecular mechanics calculations. Both the NMR-derived structures, as well as the calculated structures, are shown to adopt a beta-turn as the primary conformation. Excellent agreement between the predicted structures and the NMR-derived structures is demonstrated. Aside from being the first examples of linear tetrapeptides reported to be ordered in aqueous solvent, the results presented support the hypothesis that high-affinity bradykinin receptor antagonists must adopt C-terminal beta-turn conformations.

Amino Acid Sequence↗
PubMed1993

In situ regulation of cell-cell communication by the cAMP-dependent protein kinase and protein kinase C.

The effects of cAMP-dependent protein kinase A and protein kinase C on cell-cell communication have been examined in primary ovarian granulosa cells microinjected with purified components of these two regulatory cascades. These cells possess connexin43 (alpha 1)-type gap junctions, and are well-coupled electrotonically and as judged by the cell-to-cell transfer of fluorescent dye. Within 2-3 min after injection of the protein kinase A inhibitor (PKI) communication was sharply reduced or ceased, but resumed in about 3 min with the injection of the protein kinase A catalytic subunit. A similar resumption also occurred in PKI-injected cells after exposure to follicle stimulating hormone. Microinjection of the protein kinase C inhibitor protein caused a transient cessation of communication that spontaneously returned within 15-20 min. Treatment of cells with activators of protein kinase C, TPA or OAG for 60 min caused a significant reduction in communication that could be restored within 2-5 min by the subsequent injection of either the protein kinase C inhibitor or the protein kinase A catalytic subunit. With a longer exposure to either protein kinase C activator communication could not be restored and this appeared to be related to the absence of aggregates of connexin43 in membrane as detected immunologically. In cells injected with alkaline phosphatase communication stopped but returned either spontaneously within 20 min or within 2-3 min of injecting the cell with either the protein kinase A catalytic subunit or with protein kinase C. When untreated cells were injected with protein kinase C communication diminished or ceased within 5 min. Collectively these results demonstrate that cell-cell communication is regulated by both protein kinase A and C, but in a complex interrelated manner, quite likely by multiple phosphorylation of proteins within or regulating connexin-43 containing gap junctions.

Animals↗
PubMed1993

HIV induces deletion of T cell receptor variable gene product-specific T cells.

Using a flow cytometric method, CD4+, CD8+, alpha beta TCR+ and TCR variable region gene product (TVRGP)-specific T cells were analysed in healthy heterosexual males (HHeM), HIV-seronegative homosexual males (SNHM), asymptomatic seropositive homosexual males (ASPH) and homosexual males with AIDS who were either well (AIDS-A), or unwell in hospital (AIDS-B). Total CD4+ and CD8+ T cell numbers were similar in HHeM and SNHM. CD4+ T cells were significantly reduced in ASPH relative to both HHeM and SNHM and in AIDS-A and AIDS-B relative to SNHM. TVRGP-specific T cells expressed as a percentage of TCR alpha beta + cells showed no significant difference in HHeM, SNHM and AIDS-B. The proportion of alpha beta + cells expressing the V beta 5.1, V beta 12 and V alpha 2 gene product (GP) was, however, significantly reduced in ASPH and AIDS-B relative to HHeM, SNHM and AIDS-A. Possible causes of TVRGP-specific T cell deletion are discussed.

CD4 Antigens↗
PubMed1991

Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols.

Epidemiological studies have revealed an increased risk of cancer, notably soft-tissue sarcomas and non-Hodgkin's lymphomas, in people occupationally exposed to chlorophenoxy herbicides, including those contaminated by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). We report here a historical cohort study of mortality in an international register of 18,910 production workers or sprayers from ten countries. Exposure was reconstructed through questionnaires, factory or spraying records, and job histories. Cause-specific national death rates were used as reference. No excess was observed in all-cause mortality, for all neoplasms, for the most common epithelial cancers, or for lymphomas. A statistically non-significant two-fold excess risk, based on 4 observed deaths, was noted for soft-tissue sarcoma with a standardised mortality ratio (SMR) of 196 and 95% confidence interval (Cl) 53-502; this was concentrated as a six-fold statistically significant excess, occurring 10-19 years from first exposure in the cohort as a whole (SMR = 606 [165-1552]) and, for the same time period, as a nine-fold excess among sprayers (SMR = 882 [182-2579]). Risks appeared to be increased for cancers of the testicle, thyroid, other endocrine glands, and nose and nasal cavity, based on small numbers of deaths. The excess of soft-tissue sarcomas among sprayers is compatible with a causal role of chlorophenoxy herbicides but the excess does not seem to be specifically associated with those herbicides probably contaminated by TCDD.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1991

Dysplasia and the natural history of cervical cancer: early results of the Toronto Cohort Study.

A sample of 176,808 Pap smears, taken from 70,236 women, was constructed from the records of a large cytopathology laboratory between 1962 and 1981. The prevalence of cervical dysplasia, based on the distribution of initial smear results, rose from 42.7 to 94.9 per 1000 during the study period. The relative risks (RR) for the manifestation of a malignancy (carcinoma in situ or worse) in a subsequent cervical smear were 1.48, 3.42, 20.9 and 71.5 for women with minimal, mild, moderate and severe dysplasia, respectively, compared with the entire cohort. The initial degree of dysplasia for women developing a malignancy was much more likely to be interpreted as moderate (RR = 5.0) or severe (RR = 42.3) than were those for controls. These results are strongly supportive of the hypothesis that the degree of dysplasia is related to the risk of development of cancer of the cervix.

Adult↗
PubMed1991

An abnormal T cell repertoire in hypergammaglobulinaemic primary Sjögren's syndrome.

T cell antigen specificity is determined by the products of the genes which encode the variable regions of their receptors. Of the T cell receptor (TCR) variable region gene products examined, only V beta 6.7a TCR-positive lymphocytes were reduced in primary Sjögren's syndrome patients with IgG1 hypergammaglobulinaemia compared with an age-, sex- and HLA-matched control population. The levels of V beta 6.7a T cells were also significantly reduced when these patients were compared with an age- and sex-matched but HLA-unmatched control group and non-tissue typed normal people of both sexes. Since published studies show no such abnormality in rheumatoid arthritis, systemic lupus erythematosus or other autoimmune diseases, this abnormality may reflect a pathogenic process specific to primary Sjögren's syndrome.

Adult↗
PubMed1991

A cohort mortality study of forestry workers exposed to phenoxy acid herbicides.

A cohort mortality study was undertaken of forestry workers at a public electrical utility who had worked for six months or more during 1950-82 and who were routinely exposed to herbicides including phenoxy acids. A total of 1222 men with 25 274 years at risk experienced 80 deaths. Ascertainment of vital state at the end of follow up was 95.5%. The male population of the province (Ontario) was used as the reference group. Overall, no excess mortality was found in this cohort relative to the reference population. A statistically significant increase in deaths occurred, however, due to suicide (SMR = 210, 95% confidence interval, 95% CI 105-376) for the cohort as a whole. No deaths were seen due to cancers such as soft tissue sarcoma and non-Hodgkin's lymphoma that have been cited by other authors as being associated with exposure to phenoxy acid herbicides. Although the cohort is not large, the absence of deaths due to these cancers is consistent with findings from other studies with sufficient numbers to allow examination of specific risks. The cohort is still young, however, and at the end of follow up most had not reached an age when increased incidence of cancer would normally be expected.

Adult↗
PubMed1990

Retroviral nucleocapsid protein-metal ion interactions: folding and sequence variants.

Retroviral nucleocapsid proteins contain one or two proposed metal-binding sequences of the form Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys. Previously, we reported that an 18-amino acid peptide derived from the nucleocapsid protein of Rauscher murine leukemia virus (RMLV) binds metals such as Co2+ and Zn2+. We have now synthesized the entire nucleocapsid protein from RMLV. We report here that the protein also binds Co2+ and Zn2+ and does so with a higher affinity than does the peptide. Limited proteolysis and circular dichroism studies reveal that metal binding induces folding of the metal-binding domain and, perhaps, the regions adjacent to it but the remainder of the protein remains in a relatively unstructured state. In addition, we have synthesized sequence variants of the metal-binding domain that correspond to viral mutations reported in the literature. In many cases, the metal-binding properties of these peptides correlate with the observed biological activity, providing further evidence for the importance of metal binding to nucleocapsid function.

Amino Acid Sequence↗
PubMed1989

Cytotoxicity mediated by tumor necrosis factor in variant subclones of the ME-180 cervical carcinoma line: modulation by specific inhibitors of DNA topoisomerase II.

The mechanism of tumor necrosis factor (TNF)-induced cytotoxicity has been investigated using two clonal variants of the ME-180 human cervical carcinoma cell line. The clonal lines were characterized with respect to their expression of TNF receptors, kinetics of cell death, and their ability to communicate intercellularly through gap junctions. The ME-180.4 and ME-180.8 clones were identified by their relative sensitivity to TNF induced lysis in a 24-h assay. The dose of TNF required to kill 50% of the target cells was 60 pM for the sensitive ME-180.4 and 2.5 nM for the ME-180.8. However, when assay times were extended, the dose response for both clones was the same, indicating that a difference in the kinetics of cell death and not absolute TNF sensitivity existed between the ME-180.4 and ME-180.8 clones. Both clones were gap junction deficient as judged by their inability to transfer Lucifer yellow or 6-carboxyfluorescein, a characteristic phenotype of cells sensitive to cytotoxicity by TNF. The level of surface receptor expressed on these clones was nearly identical with a Kd = 0.3 nM and 5,000 binding sites per cell. Measurement of the kinetics of cell death revealed that the time between the addition of TNF and the onset of observed cell death (induction phase) was much shorter for the ME-180.4 (32-55 h) than for the resistant ME-180.8 (55-80 h). Mitomycin C, a DNA alkylating agent, significantly reduced the length of the induction phase for both clones, although the kinetic difference between the clones remained unchanged. Two epipodophyllotoxins, VP-16 and VM-26, which specifically inhibit the rejoining activity of DNA topoisomerase II, showed a 10-100-fold synergistic effect when combined with TNF as shown by isobologram analysis. VM-26 when added to the resistant ME-180.8 clones decreased the length of induction phase and abolished the kinetic difference observed with the ME-180.4 clone. These results indicate that the variance in the TNF response of these two clones was closely associated with DNA topoisomerase II, and suggest that this enzyme may play an important role in TNF mediated cytotoxicity.

Cell Communication↗
PubMed1989

A retroviral Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys peptide binds metal ions: spectroscopic studies and a proposed three-dimensional structure.

Retroviral gag gene-encoded core nucleic acid binding proteins contain either one or two sequences of the form Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys. Previously, one of us has proposed that these sequences form metal-binding domains in analogy with the "zinc finger" domains first observed in transcription factor IIIA. We report that an 18-amino acid peptide derived from the core nucleic acid binding protein from Rauscher murine leukemia virus binds metal ions such as Co2+ and Zn2+. The absorption spectrum of the peptide-Co2+ complex is highly suggestive of tetrahedral coordination involving three cysteinates and one histidine. Titration experiments indicate that the dissociation constant for the peptide-Co2+ complex is 1.0 microM and that Zn2+ binds more tightly than Co2+. A detailed three-dimensional structure for this domain based on conserved substructures in other crystallographically characterized metalloproteins and on a detailed analysis of the Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys sequences from retroviruses and other related sources is proposed.

Amino Acid Sequence↗