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Biomedical subjects

R E Mitchell

Publications and source records attributed to R E Mitchell.

At least 19 recordsLinked to original sources
PubMed1999

The toxicity of cyanobacterial toxins in the mouse: I microcystin-LR.

Blooms of cyanobacteria or blue-green algae are known to have caused poisoning in fish, waterfowl, animals and man. One of the toxins responsible for this is the hepatotoxin microcystin-LR which has been found to occur in blooms present intermittently in sources used for domestic water supplies. Three sets of experiments were undertaken to investigate the acute toxicity of microcystin-LR in mice and rats by the oral and intraperitoneal routes, the potential for effects on foetal development in the mouse, and the effects of repeated oral dosing over 13 weeks in the mouse. The results of this work were as follows: (1) Microcystin-LR is 30-100 times less toxic via oral ingestion than via intraperitoneal injection; (2) Microcystin-LR is not a selective developmental toxicant in the mouse. There was a No Observed Adverse Effect Level (NOAEL) of 600 microg kg(-1) bodyweight per day given on days 6-15 of pregnancy for any form of developmental toxicity; (3) There was a clear NOAEL for tissue damage in the liver of 40 microg kg(-1) bodyweight per day of microcystin-LR. Using this data, a value of 1 microg l(-1) microcystin-LR would be an appropriate guideline value for drinking water.

Abnormalities, Drug-Induced↗
PubMed1999

The toxicity of cyanobacterial toxins in the mouse: II anatoxin-a.

Blooms of cyanobacteria are known to have caused poisoning in fish, waterfowl, animals and man. One of the low molecular weight toxins responsible for this is the neurotoxin anatoxin-a which has been detected in reservoirs used for domestic water supplies. While the acute behaviour of this alkaloid is clear, there is uncertainty regarding the effects on man of ingestion of anatoxin-a at low levels over longer periods. In order to assess this risk, a series of in vitro and in vivo experiments were undertaken to investigate the pharmacology, subacute toxicity, and the teratogenicity of anatoxin-a in the mouse. The results of this work were as follows: (1) Pharmacological screening studies confirmed that anatoxin-a is a potent nicotinic agonist which can produce neuromuscular blockade and death by respiratory arrest. Recovery from a single sub-lethal dose is rapid and complete; (2) Repeated sub-lethal oral administration over 28 days in the mouse did not produce any reliable evidence of treatment-related toxicity; (3) From a preliminary screening study anatoxin-a does not appear to be a developmental toxicant in the mouse. These results indicate that a guideline value for anatoxin-a in drinking water of 1 microg l(-1) would provide an adequate margin of safety.

Abnormalities, Drug-Induced↗
PubMed1996

Long-term health outcomes and medical effects of torture among US Navy prisoners of war in Vietnam.

OBJECTIVE: To characterize incidence of illnesses and injuries from 1979 to 1993 in former naval aviator prisoners of war (POWs) from the Vietnam War and a comparison group of naval aviators from the same war. DESIGN: Cohort analytic study. SETTING: A US Navy primary care clinic. PARTICIPANTS: Volunteer sample consisting of 70 former naval aviator POWs (white men, aged 47 to 69 years in 1993) and a comparison group of 55 naval aviators who served in Vietnam but were not POWs, matched on race, age, marital status, education, rank, year of entry into the navy, and pilot status. Subjects participated in an annual health screening program. This study reports data sampled on a biennial basis from subjects screening both in 1979 and 1993. MAIN OUTCOME MEASURE: Medically diagnosed incidence of illness and injury based on a standard protocol. RESULTS: POWs had higher incidence rates than the comparison group did of disorders of the peripheral nervous system (relative risk [RR], 8.4; 95% confidence interval [CI], 2.7-25.9; P<.001), joints (RR, 1.5; 95% CI, 1.2-2.0; P<.006), and back RR, 1.8; 5% CI, 1.0-3.0; P<.037). These findings also were statistically significant according to Kaplan-Meier survival analyses that included 131 (95%) of 138 POWs and 115 (83%) of the 138 members of the comparison group. Survival analyses revealed that, in addition to these disorders, POWs had higher hazard rates of peptic ulcer (P<.01). CONCLUSIONS: During captivity, ropes, ratchet handcuffs, leg irons, or stocks were used to put tightly constrictive pressure around the extremities of POWs as a means of torture, resulting in painful ischemia and subsequent neuropathies. Being a former POW was associated with increased cumulative incidence rates of chronic disorders of the peripheral nervous system, joints, and back and an increased hazard rate of peptic ulcer.

Aged↗
PubMed1995

Stabilisation of purified human collagenase by site-directed mutagenesis.

During purification, human fibroblast collagenase breaks down into two major forms, an N-terminal 22000/25000-Mr fragment and a C-terminal 27000-Mr fragment; the most likely mechanism being autolysis. The cleavage site has been identified (Pro269- Ile270) and in an attempt to obtain full-length human collagenase (i.e., Mr 42570), this cleavage site and another potential cleavage site (Ala258- Ile259) have been mutated by PCR- directed mutagenesis: Ile270Ser and Ile259Leu. The mutated cDNA was then cloned into the expression vector, pGEX2T, and expressed in Escherichia coli as a fusion protein with glutathione-S-transferase (GST). After cleavage with factor Xa, the mutated collagenase was purified on a peptide hydroxamic acid affinity column. The mutated recombinant collagenase is stable, remains full length and retains the ability to cleave collagen.

Alanine↗
PubMed1995

Recombinant porcine collagenase: purification and autolysis.

Collagenase is a member of the matrix metalloproteinase family whose members are all capable of degrading extracellular matrix components. The mature form of porcine collagenase has been expressed in Escherichia coli using the pAX5 expression vector. The fusion protein consists of beta-galactosidase at the N-terminus joined to a collagen hinge region and a blood-coagulation factor Xa cleavage site linked to an active form of collagenase. Recombinant collagenase was biologically active in the form of a fusion protein; this was cleaved with factor Xa to yield collagenase with the authentic N terminus (phenylalanine) found in vivo and purified in a single step on a peptide hydroxamic acid affinity column. On purification the recombinant porcine collagenase undergoes autolysis at a number of different bonds in the region connecting the active site domain with the C-terminal hemopexin-like domain. This may represent a loop region of poor secondary structure, making it susceptible to relatively nonspecific cleavage. The N-terminal fragment retains a reduced level of collagenolytic activity, along with that against casein and gelatin.

Amino Acid Sequence↗
PubMed1995

Empowerment praxis in community coalitions.

Community coalitions address a wide variety of community problems, espousing a community development processes that promotes individual and collective self-determination. They offer a promising venue for the study of empowerment of individuals and organizations. This study utilizes data from members of 35 community coalitions organized for the prevention of alcohol and other drug problems to address the following questions: What individual characteristics are related to the psychological empowerment of coalition members? What organizational characteristics are related to the collective empowering of members? What organization characteristics are related to a coalition being organizationally empowered to succeed in achieving its objectives? At the individual level, psychological empowerment was most strongly related to individuals' participation levels, sense of community, and perceptions of a positive organizational climate. At the group level, the strongest predictors of collective empowering (our operationalization of the empowering organization) were net benefits of participation, commitment, and positive organization climate. Psychological empowerment and positive organizational climate were the two predictors of organizational effectivenes (the empowered organization). Implications and limitations of these findings are discussed.

Adolescent↗
PubMed1995

Achalasia. A new modality for treatment.

This lesion of the esophagus, first described in 1682 by Thomas Willis, been subject to many forms of therapy. We feel botulinum toxin injection to be an acceptable alternative treatment modality for select patients with primary esophageal achalasia. Traditional methods of treating achalasia consist of medical therapy for short-term relief, balloon dilation and myotomy. Botulinum toxin injection is an alternative method of treatment, suggested by Pasricha et al and used successfully in our patient, which does not seem to cause the significant complications of perforation or gastroesophageal reflux and which may be more attractive to patients less able to undergo dilation or myotomy. This method of injecting botulinum toxin directly into the LES appears to be a relatively safe modality of treatment. Reports suggest symptoms of achalasia may recur (in up to a year's time) and repeated injections may be needed. Even so, this would seem to be acceptable in the overall management of achalasia. We agree that long-term follow-up of these patients is indicated. Data to date, plus our personal experiences, have been encouraging. We feel this represents an option for non-surgical patients and may even be considered prior to the endoscopic balloon surgery approach. It is certainly more cost effective. We are currently evaluating a second patient for botulinum toxin therapy.

Aged↗
PubMed1995

Orthopedic injuries experienced by U.S. prisoners of war during Operation Desert Storm: a descriptive analysis.

U.S. prisoners of war from Operation Desert Storm suffered significant orthopedic injuries. The repatriated prisoners of war (RPOWs) have been medically evaluated over a 3-year period with orthopedic follow-up. A significant proportion of the musculoskeletal injuries were located around the neck and spine, shoulder, and upper extremity. Aircraft ejection was the cause of the majority of these injuries. Lower extremity injuries after ejection, aside from the knee, were not reported. Flail injuries of the lower extremities were absent as well. These results were examined with reference to Vietnam RPOW data.

Adult↗
PubMed1992

Physical and functional characterization of the gene cluster encoding the polyketide phytotoxin coronatine in Pseudomonas syringae pv. glycinea.

Pseudomonas syringae pv. glycinea PG4180 produces the polyketide phytotoxin coronatine. The coronatine synthesis genes in PG4180 were previously shown to reside on a 90-kb plasmid designated p4180A. In the present study, clones containing a 34-kb region of p4180A were saturated with Tn5, and 71 unique mutations were recombined into p4180A by marker exchange. The effect of each mutation on coronatine synthesis was determined by analyzing the organic acids produced by the mutants by reverse-phase high-performance liquid chromatography. The organic acids of selected mutants were derivatized to their methyl esters and analyzed by gas chromatography and gas chromatography-mass spectrometry. Mutations in a 20.5-kb region of p4180A completely blocked the synthesis of coronafacic acid and coronatine. Mutations within a 4.4-kb region of p4180A prevented the formation of coronatine but allowed for production of coronafacic acid, coronafacoylvaline, coronafacoylisoleucine, and coronafacoylalloisoleucine. The phenotypes of selected mutants were further confirmed in feeding experiments in which coronafacic acid or coronamic acid was added to the culture media. The results of this study allow us to speculate on the likely sequence of steps in the later stages of coronatine biosynthesis.

Amino Acids↗
PubMed1991

Implications of toxins in the ecology and evolution of plant pathogenic microorganisms: bacteria.

This review attempts to rationalise what is known about bacterial phytotoxins and associate it with the ecology and possible evolution of the producing organisms. Study of non-toxin producing variants gives insight into the ecological role of the toxin. Elucidation of chemical structures of phytotoxins has shown that many exist as families of analogous compounds. Studies on the variation of chemical structures and how they are distributed across species and genera can lead to development of hypotheses on evolutionary relationships. Knowledge on biosynthetic pathways to toxins allows recognition of specific enzymatic steps involved in developing the characteristic features of the structures. Phytotoxins often have a potent biochemical activity, and in some cases the producing organism has associated mechanisms to prevent action of the toxin upon itself; in such cases toxigenesis is clearly not a chance event. The various aspects of bacterial toxigenesis indicate that bacterial phytotoxins are special secondary metabolic products that play beneficial roles to the producing organisms in their various ecological niches.

Amino Acid Sequence↗
PubMed1991

Comparative evaluation of treated bovine pericardium as a xenograft for hernia repair.

Two forms of bovine pericardium (BPC) were assessed as hernia repair materials: non-cross-linked (lyophilized) and cross-linked through treatment with glutaraldehyde (GA). These were compared with polypropylene mesh (Marlex) in a rabbit model. Over 52 wk implantation, the GA BPC grafts developed a strong, stable, fibrous tissue replacement with good incorporation into the abdominal muscle wall. The lyophilized BPC grafts were substantially resorbed within 12 wk of implantation, however the thin, fibrous replacement tissue was inadequate for abdominal wall support. Marlex grafts provided sufficient abdominal support, however these grafts were associated with extensive adhesion formation and, in this model, fat deposition around the perimeter of the graft. Control (ungrafted) rabbit abdominal muscle in the transverse orientation had an ultimate tensile load (UTL) of 11.4 +/- 5.1 N (x +/- s.d.) and a strain at UTL of 35 +/- 12% (n = 169). At 52 weeks the UTL of the repair sites was 7.3 +/- 4.5 N (n = 6), 5.1 +/- 3.5 N (n = 6) and 5.6 +/- 2.7 N (n = 6) for GA BPC, lypophilized BPC and Marlex grafts, respectively.

Animals↗
PubMed1989

Plasmid-mediated production of the phytotoxin coronatine in Pseudomonas syringae pv. tomato.

Pseudomonas syringae pv. tomato PT23.2 produces the chlorosis-inducing phytotoxin coronatine. Thirty-eight chlorosis-defective mutants of PT23.2 were previously generated by using the transposon Tn5. Five mutants contained Tn5 insertions in the indigenous plasmid pPT23A; the remaining 33 mutants either were missing pPT23A (29 mutants) or contained deletions in this plasmid (4 mutants). These results suggested that pPT23A was involved in coronatine production in strain PT23.2. This plasmid was introduced into P. syringae pv. syringae PS61, which does not produce coronatine. A bioassay for coronatine suggested that PS61(pPT23A) transconjugants were able to make this phytotoxin. In a chemical analysis, organic acids were isolated from PT23.2, PS61, and the transconjugant PS61(pPT23A); these were derivatized to their methyl esters and analyzed by gas chromatography. The derivatized organic acids extracted from PT23.2 and PS61(pPT23A) contained peaks that corresponded to coronafacic acid, coronafacoylvaline, and coronatine, but these were absent in the extracts from the wild-type strain PS61. The identification of these components was confirmed by combined gas chromatography-mass spectrophotometry. Therefore, the acquisition of pPT23A by PS61 resulted in biosynthesis of coronafacic acid, coronafacoylvaline, and coronatine, clearly demonstrating the involvement of pPT23A in coronatine production in P. syringae pv. tomato.

Amino Acids↗