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Biomedical subjects

J Clark

Publications and source records attributed to J Clark.

At least 181 records · Page 10Linked to original sources
PubMed1997

Biliary elimination of oral 2,4-dichlorophenoxyacetic acid and its metabolites in male and female Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters.

The role of biliary elimination in the metabolic disposition of 2,4-D was evaluated in male and female Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters. Following cannulation of the bile duct, an intragastric (ig) dose of 2,4-D (200 mg/kg) was administered and bile was collected at 30- or 60-min intervals for up to 6 h. Bile flow rates were constant in rats, increased in mice, and decreased in hamsters throughout the collection periods. Total recovery of radioactivity was greatest in male mice (about 7% of administered dose over 4 h). Female mice and rats of both sexes excreted about 3% over the same interval and male and female hamsters about 1%. About 71-88% of the activity in bile was parent compound. The glycine conjugate of 2,4-D was found in bile from mice, rats, and hamsters and the taurine conjugate in bile from mice. The only sex-dependent difference in the metabolite profile was in mice. Male mice excreted twice as much glycine conjugate as female mice. An additional minor metabolite (4-7%) was present in rat and mouse bile. This was tentatively identified as 2,4-D-glucuronide based on its hydrolysis by beta-glucuronidase. One more very minor metabolite (3%) was detected in rat bile but was not characterized due to its lability. The results of this study indicate that there are species-dependent differences in the biliary elimination of 2,4-D but not sex-dependent differences.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1997

The doctor's role in discussing advance preferences for end-of-life care: perceptions of physicians practicing in the VA.

OBJECTIVES: Although previous studies have shown physicians support advance directives, little is known about how they actually participate in decision-making. This study investigate (1) how much experience physicians have had discussing and following advance preferences and (2) how physicians perceive their role in the advance decision-making process. DESIGN: Mail survey conducted in 1993. SETTING: The Department of Veterans Affairs. PARTICIPANTS: A national probability sample of 1050 VA internists, family physicians, and generalists. MEASUREMENTS AND MAIN RESULTS: Questionnaires were returned by 67% of participants. In the last year, 79% stated they had discussed advance preference with at least one patient, and 19% had talked to more than 25. Seventy-three percent had used a written directive to make decisions for at least one incompetent patient. Younger age, board certification, spending less time in the outpatient setting, and personal experience with advance decision-making, were all associated independently with having advance preference discussions. Among physicians who had discussions, 59% said they often initiated the discussion, 55% said discussions often occurred in inpatient settings, and 31% said discussions often occurred in outpatient settings. Eighty-two percent of those responding thought physicians should be responsible for initiating discussions. Most would try to persuade a patient to change a decision that was not well informed (91%), not medically reasonable (88%), or not in the patient's best interest (88%); few would attempt to change decisions that conflicted with their own moral beliefs (14%). CONCLUSIONS: Physicians report that they are actively involved with their patients in making decisions about end-of-life care. Most say they have had recent discussions with at least some of their patients and feel that as physicians they should play a large and important role in soliciting and shaping patient preferences.

Adult↗
PubMed1997

Initial experience with a co-radial bipolar pacing lead.

A new type of endocardial bipolar pacing lead has been designed to overcome the potential drawbacks of the conventional coaxial bipolar pacing lead. We prospectively evaluated the new co-radial bipolar pacing leads (Intermedics Thin-Line), which are thinner (5 Fr vs 6-8 Fr) than standard coaxial bipolar leads. X-ray visibility and lead handling were subjectively assessed (excellent, good, adequate, or poor) at implant; lead impedance, sensitivity threshold, and pacing threshold were measured at implant, then at 1, 3, 6, 12, and 18 months. The results were as follows: 103 patients (51 M; age 63.8 +/- 17.4 years) received 71 atrial (A) and 89 ventricular (V) leads. X-ray visibility was excellent in 59/103; good in 23/103; adequate in 11/103; and poor in 10/103. Overall handling was excellent in 56/71 A and 69/89 V; good in 11/71 A and 18/89 V; adequate in 3/71 A and 1/89 V; poor in 1/71 A and 1/89 V. There were two perioperative complications. At implant: impedance in A and V were 370.1 +/- 74.7 and 501.5 +/- 124.4 omega, sensing thresholds in A and V were 3.0 +/- 1.5 and 9.9 +/- 5.0 mV, pacing thresholds at 0.45 ms in A and V were 0.59 +/- 0.21 and 0.41 +/- 0.15 volt, respectively. At 1, 3, 6, 12, and 18 months of follow-up: no pacing lead related complications were reported; pacing lead characteristics remained outstanding and stable. This new lead appears to have significant clinical advantages over the conventional coaxial bipolar pacing lead. Long-term follow-up is required to confirm its reliability and chronic performance characteristics.

Adolescent↗
PubMed1997

Role of transmembrane pH gradient and membrane binding in nisin pore formation.

Nisin is a cationic antimicrobial peptide that belongs to the group of lantibiotics. It is thought to form oligomeric pores in the target membrane by a mechanism that requires the transmembrane electrical potential delta psi and that involves local pertubation of the lipid bilayer structure. Here we show that nisin does not form exclusively voltage-dependent pores: even in the absence of a delta psi, nisin is able to dissipate the transmembrane pH gradient (delta pH) in sensitive Lactococcus lactis cells and proteoliposomes. The rate of dissipation increases with the magnitude of the delta pH. Nisin forms pores only when the delta pH is inside alkaline. The efficiency of delta psi-induced pore formation is strongly affected by the external pH, whereas delta pH-induced pore formation is rather insensitive to the external pH. Nisin(1-12), an amino-terminal fragment of nisin, and (des-deltaAla5)-(nisin(1-32) amide have a strongly reduced capacity to dissipate the delta psi and delta pH in cytochrome c oxidase proteoliposomes and L. lactis cells. Both variants bind with reduced efficiency to liposomes containing negatively charged phospholipids, suggesting that both ring A and rings C to E play a role in membrane binding. Nisin(1-12) competes with nisin for membrane binding and antagonizes pore formation. These findings are consistent with the wedge model of nisin-induced pore formation.

Animals↗
PubMed1997

Heterozygous alpha 1-antitrypsin phenotypes in patients with end stage liver disease.

OBJECTIVE: The objective of the study was to determine the prevalence and associations of abnormal alpha1-antitrypsin phenotypes in Caucasian adults with end stage liver disease with particular emphasis on heterozygous phenotypes and disease from hepatitis C virus. METHODS: All patients (788) with end stage liver disease considered for liver transplantation from July 1990 to June 1996 in a referral-based university hospital transplant center (University of Nebraska Medical Center, Omaha, NE) comprised the study population. Data for the study population was determined by retrospective review of the transplantation database at the transplant center. Hepatitis C virus infection was determined by a second generation ELISA method, and alpha1-antitrypsin phenotyping was performed on agarose gel with serum quantitation using a Behring Nephelometer. RESULTS: Among 683 Caucasian patients with severe liver disease, the prevalences of Pi ZZ, Pi MZ, and Pi MS were 0.4, 7.3, and 8.2%, respectively, compared with 0, 2.8, and 4.2% in the control population. The odds of having a heterozygous Z phenotype were significantly increased in Caucasian patients with hepatitis C virus (odds ratio (OR) = 4.3, 95% confidence interval (CI) = 2.1-9.0), alcoholic liver disease (OR = 5.0, 95% CI = 2.6-9.6), primary hepatic malignancy (OR = 7.4, 95% CI = 2.9-19.0), and cryptogenic cirrhosis (OR = 2.6, 95% CI = 1.1-6.3) compared with the control population. Caucasian patients with hepatitis C or B virus were 3.6 times more likely to have a heterozygous Z phenotype than a normal phenotype compared with patients with diseases of autoimmune etiology. CONCLUSION: This study provides evidence of an association of heterozygous Z alpha1-antitrypsin phenotype with end stage liver disease of several etiologies, not hepatitis C virus alone.

Adult↗
PubMed1996

Structure-activity relationships in the peptide antibiotic nisin: antibacterial activity of fragments of nisin.

The post-translationally modified peptide antibiotic nisin has been cleaved by a number of proteases and the fragments produced purified, characterised chemically, and assayed for activity in inhibiting the growth of Lactococcus lactis MG1614 and Micrococcus luteus NCDO8166. These results provide information on the importance of different parts of the nisin molecule for its growth-inhibition activity. Removal of the C-terminal five residues leads to approximately a 10-fold decrease in potency, while removal of a further nine residues, encompassing two of the lanthionine rings, leads to a 100-fold decrease. There are some differences between analogous fragments of nisin and subtilin, suggesting possible subtle differences in mode of action. Cleavage within, or removal of, lanthionine ring C essentially abolishes the activity of nisin. The fragment nisin1-12 is inactive itself, and specifically antagonises the growth-inhibitory action of nisin. These results are discussed in terms of current models for the mechanism of action of nisin.

Amino Acid Sequence↗
PubMed1996

Fusion of the EWS gene to CHN, a member of the steroid/thyroid receptor gene superfamily, in a human myxoid chondrosarcoma.

The specific chromosomal translocation t(9;22)(q22-31;q11-12) has been observed in the myxoid variant of human chondrosarcoma. In agreement with this observation we report that the EWS gene located at chromosome band 22q12 becomes fused to CHN, a member of the steroid/thyroid receptor gene superfamily located at 9q22-31, in a skeletal myxoid chondrosarcoma. CHN appears to be the human homologue of the rat gene NOR1, which was recently identified as a sequence overexpressed in rat brain cells undergoing apoptosis. Our results also indicate that the chimaeric EWS-CHN gene encodes a EWS-CHN fusion protein in which the C-terminal RNA-binding domain of EWS is replaced by the entire CHN protein, comprising a long N-terminal domain, a central DNA binding domain and a C-terminal ligand-binding/dimerisation domain.

Amino Acid Sequence↗
PubMed1996

Expression of an efficient small molecular weight tumour necrosis factor/lymphotoxin antagonist.

TNF-alpha and lymphotoxin are proinflammatory cytokines that are non-homologous in sequence, have similar homotrimeric structure and they exert their biological activity by aggregating two types of shared cell surface receptors. The natural inhibitors of TNF and lymphotoxin are the shed extracellular domains of the p55 and p75 TNF receptors. However recombinant inhibitors composed of the extracellular domains of p75 or p55 receptors dimerized on IgG backbone have been shown to be much more effective. We have produced a dimeric form of the human p75 TNF receptor extracellular domain based on the structure of the native soluble shed receptor. The dimer was engineered by genetically linking the monomeric forms with a polyglycine-serine linker. Biochemical characterization showed that this dimeric TNF receptor elutes from a TNF affinity column at a lower pH than the monomeric form. Biological assay revealed this novel antagonist to be as efficient as a dimer based on an immunoglobulin backbone. However this new dimer is smaller, stable, and could have greater penetration into tissues.

Amino Acid Sequence↗
PubMed1996

B lymphocyte hyperactivity in families of patients with systemic lupus erythematosus.

Blood cells spontaneously secreting IgG and IgM and the level of plasma immunoglobulins and antibodies to dsDNA, ssDNA and influenza virus haemagglutinin have been determined in families of patients with SLE, in 'normal' families and groups of 'normal' individuals. IgM values were consistently higher in females than in males. About one in three of healthy blood relatives gave values in excess of the sex-matched control range in one or more of these test, particularly notable being raised values of IgG anti-dsDNA and total IgG shown by female relatives. High-scoring relatives were more likely to be offspring or parents than siblings of patients, suggesting, together with evidence from a spouse group, the involvement of environmental as well as genetic factors in these families. Correlation analysis between the various assays in the different groups showed a clear distinction between the female control group, where there were no associations, and the female relative group where there were strong associations, including a significant correlation between IgM and IgG antibodies to dsDNA. The male groups produced a more variable picture but the patients gave a remarkably consistent pattern of moderate positive associations. Pokeweed mitogen induced a higher level of IgG production in blood cells of relatives than in controls. These findings are suggestive of a breakdown in relatives of normal antibody regulation. Investigation of immunological abnormalities in family members provides a powerful tool for the analysis of a complex disease.

Adolescent↗
PubMed1996

Phase II study of 5-fluoruracil leucovorin and azidothymidine in patients with metastatic colorectal cancer.

The primary objective of this study was to determine the response rate of patients with metastatic colorectal cancer to combined therapy with 5-fluorouracil (5-FU), leucovorin, and intravenous azidothymidine (AZT), a thymidine nucleoside analog. By itself, AZT has limited antineoplastic efficacy. However, experimental studies indicate that 5-FU enhances the antitumor activity of AZT by inhibiting synthesis of normal thymidine nucleotides with which AZT competes for incorporation into nucleic acids. A phase I study defined the maximum tolerated dose of AZT as 7 g/m2 with hypotension during the infusion being the dose-limiting toxicity. A phase II study was performed with oral leucovorin (100 mg p.o. hourly for 4 h prior to 5-FU and 4 h and 8 h after 5-FU), bolus 5-FU (400 mg/m2) followed 1 h later by a 2-h infusion of AZT (7 g/m2). Treatment was given weekly for 4 weeks followed by a 1-week break, which constituted a cycle of therapy. Responses were evaluated after every two cycles. Patients continued on therapy as long as they tolerated treatment and did not have progressive disease. Of 15 evaluable patients who had received no chemotherapy there was 1 complete response and 4 partial responses (a 33% response rate), whereas only 1 of 6 patients who had received prior adjuvant chemotherapy had a partial response (17%). An additional 10 patients had stable disease lasting 2-14 months. Therapy was well tolerated with the only one instance each of grade 3 nausea and vomiting, diarrhea, anemia, and hypotension. Approximately 50% of treatments were accompanied by mild hypotension, which was easily corrected by increasing the rate of normal saline infusion. There was no difficulty administering this regimen in the outpatient setting. While the overall response rate (29%) is comparable to that seen with combinations of 5-FU and leucovorin alone, in most reported series a considerably higher dose of 5-FU was utilized than in this study. Since patients in the present study experienced relatively little 5-FU toxicity, increasing the dose of 5-FU in this regimen would appear to be feasible and might result in a higher response rate.

Adenocarcinoma↗
PubMed1996

Human kinesin light (beta) chain gene: DNA sequence and functional characterization of its promoter and first exon.

Kinesins are tubulin molecular motors whose function is to transport organelles within cells. Very little is known about the regulation of expression of these proteins. We have characterized the gene product of one differentially spliced mRNA of the human light chain kinesin and cloned its promoter region. A full-length kinesin cDNA was translated in vitro in a cell-free system, producing a 70-kDa protein. Using this cDNA as a probe, we isolated and sequenced the promoter, first exon, and part of the first intron of this gene from a genomic lambda EMBL3 human placental DNA library. The whole gene spans more than 90 kb. The beta kinesin promoter region confers only constitutive transcription to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene. In permanently transfected human HeLa and NB100 neuroblastoma cells, a reporter gene containing the promoter and part of the first exon of beta kinesin was 75-fold more active than the HSV-tk promoter. The first exon contains the 5'-untranslated sequence capable of forming a stable double-hairpin loop, which functions as a translational enhancer. Its deletion decreases the efficiency of in vitro translation of beta kinesin mRNA and confers increased translation to a CAT reporter gene.

Amino Acid Sequence↗
PubMed1996

The t(X;1)(p11.2;q21.2) translocation in papillary renal cell carcinoma fuses a novel gene PRCC to the TFE3 transcription factor gene.

The specific chromosomal translocation t(X;1)(p11.2;q21.2) has been observed in human papillary renal cell carcinomas. In this study we demonstrated that this translocation results in the fusion of a novel gene designated PRCC at 1q21.2 to the TFE3 gene at Xp11.2. TFE3 encodes a member of the basic helix-loop-helix (bHLH) family of transcription factors originally identified by its ability to bind to microE3 elements in the immunoglobin heavy chain intronic enhancer. The translocation is predicted to result in the fusion of the N-terminal region of the PRCC protein, which includes a proline-rich domain, to the entire TFE3 protein. Notably the generation of the chimaeric PRCC-TFE3 gene appears to be accompanied by complete loss of normal TFE3 transcripts. This work establishes that the disruption of transcriptional control by chromosomal translocation is important in the development of kidney carcinoma in addition to its previously established role in the aetiology of sarcomas and leukaemias.

Adult↗
PubMed1996

Specificity and affinity of 26 monoclonal antibodies against the CA 125 antigen: first report from the ISOBM TD-1 workshop. International Society for Oncodevelopmental Biology and Medicine.

The specificity of 26 monoclonal antibodies against the CA 125 antigen was investigated in two phases of the ISOBM TD-1 workshop. The binding specificity was studied using CA 125 immunoextracted by specific antibodies immobilized on various solid phases, or on the surface of human cell lines. Immunometric assays using all possible antibody combinations were used to study the topography of antibody binding sites on the antigen. We conclude that the CA 125 antigen carries only two major antigenic domains, which classifies the antibodies as OC125-like (group A) or M11-like (group B). One antibody, OV 197, showed binding specificity related to some of the OC125-like antibodies, but was classified into a separate group C. The OC125-like group of antibodies has four subgroups with different binding specificities. These are A1 = OC 125 and K 95, A2 = K 93, A3 = B43.13, and A4 = ZS 33, B27.1 and CCD 247. Binding of nonlabelled OC 125 or K 95 to CA 125 caused a marked increase in binding of labelled OV 197 to the complex. This conformational change was not observed with any other antibody combinations. Antibody B43.13 could form immunometric assay combinations particularly with antibodies of subgroup A4, indicating that the B43.13 epitope is in the periphery of the binding area of OC125-like antibodies. The M11-like group of antibodies is more homogenous with strong cross-inhibition between most antibodies. Only one antibody, ZR 38, would form an immunoassay combination with other M11-like antibodies and thus represents a distinct subgroup. The main group of M11-like antibodies are M 11, ZR 45, MA602-6, K 91, OV 185, K 101, K 90, K 96, K 97, K 102, CCD 242, 145-9, and 130-22. Antibody OV 197 binds to a domain designated C and is unique, as stated above. Antibody pairs from any two of the three groups may be used in immunometric assays. Three antibodies were not studied by complete cross-inhibition due to low affinity (OV 198 and K 100) or lack of material (MA602-1). OV 198 and K 100 are most likely OC125-like and MA602-1 is M11-like. Antibody affinity was estimated with labelled antigen in solution or with antigen absorbed on microtiter wells. Western blot analysis showed staining both in the stacking gel and corresponding to a molecule of 200 kDa. There was a marked difference between the antibodies in their ability to bind to CA 125 immobilized on a membrane. Strongest binding was observed with the M11-like antibodies, particularly M 11, K 96, K 97, MA602-6, 145-9. Antibodies belonging to the subgroup A4 were the only OC 125-like antibodies which reacted well with CA 125 in Western analysis. Digestion of CA 125 with proteolytic enzymes showed it to be particularly sensitive to trypsin cleavage. However, no low molecular weight fragments with preserved immunoreactivity were found.

Animals↗
PubMed1996

Inhaled tryptase causes bronchoconstriction in sheep via histamine release.

Allergen-induced bronchoconstriction involves mast cell activation. Tryptase is a mast cell serine protease that is released during this process, but little is known about the action of tryptase in the airway. The purpose of this study was to determine: (1) if aerosolized tryptase causes bronchoconstriction, and (2) the mechanism by which this occurs. We measured mean pulmonary flow resistance (RL) in five allergic sheep before and after consecutive inhalations of 100 and 500 ng tryptase (in 2 ml total volume). Inhaled tryptase at 100 and 500 ng increased RL (mean +/- SE) by 33 +/- 12 and 122 +/- 8% (p < 0.05) over baseline. The response was reproducible upon repeat challenges. These studies were repeated in the same animals after pretreatment with aerosolized APC 366 (9 mg/3 ml), a specific tryptase inhibitor. In APC-366-treated sheep, tryptase increased RL by 10 +/- 3 and 6 +/- 2% (p < 0.05 versus control values) at 100 and 500 ng, respectively. The response to tryptase was also blocked by pretreating the sheep intravenously with the histamine H1-antagonist chlorpheniramine (2 mg/kg), in which RL increased only 5 +/- 4 and 7 +/- 6% after 100 and 500 ng tryptase. APC 366, however, did not block histamine-induced bronchoconstriction. Consistent with these findings was the observation that segmental bronchial challenge with tryptase (1 microgram) resulted in a significant increase in histamine levels in bronchoalveolar lavage. Inhaled tryptase (500 ng) also caused airway hyperresponsiveness to aerosolized carbachol 2 h after tryptase challenge. This tryptase-induced airway hyperresponsiveness could be blocked either by pretreating the sheep with APC 366 (30 min before challenge) or by treating the sheep 30 min after challenge. These results indicate that inhaled tryptase causes bronchoconstriction and airway hyperresponsiveness in allergic sheep by an event that may involve mast cell activation.

Administration, Inhalation↗
PubMed1996

Grammaticality judgments and sentence comprehension in Parkinson's disease: a comparison with Broca's aphasia.

In order to test the hypothesis that significant linguistic deficits could be associated with predominantly subcortical dopaminergic pathways which projected to the frontal lobes (in patients with Parkinson's Disease-PD), we compared language performance in PD patients to that of Broca's aphasics with linguistic deficits. On tests of grammaticality judgements and sentence comprehension, performance by patients with Parkinson's Disease did not vary with different types of sentence structure (as was the case with the aphasics) and was instead, uniformly high (about 75% correct). Comprehension performance, however, did significantly decline in a subgroup of patients with PD who were tested when withdrawn from their dopaminergic medications. We conclude that patients with treated Parkinson's Disease evidence no selective linguistic dysfunction. When, however, they are withdrawn from dopaminergic medication language functions suffer.

Adult↗