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Biomedical subjects

G R Jones

Publications and source records attributed to G R Jones.

At least 37 records · Page 2Linked to original sources
PubMed2000

Real-time studies of the interactions between epidermal growth factor and its receptor during endocytic trafficking.

The interactions of growth factors with cell surface receptors regulate fundamental cell processes, such as growth, differentiation and transformation. Understanding the nature of these interactions at the molecular level is of fundamental importance in cell biology. This is not only from the point of view of basic science, but also because of the repercussions such knowledge might have in understanding the mode of action of drugs in cells. Receptor mediated endocytosis has been implicated in the downregulation of the mitogenic signal. However, no data are thus far available on how growth factor/receptor interactions might control endocytic trafficking. Here we show that information on modes of binding and receptor conformational changes can be obtained using time-resolved fluorescence methods. We have found that fluorescent probes bound to epidermal growth factor (EGF) show dynamic fluorescence quenching when EGF is bound to internalising EGF receptors (EGFR). We propose that this dynamic quenching takes place because EGF-bound probes interact with tryptophan residues in the extracellular domain of the EGF-EGFR complex. Real-time accumulation of fluorescent decays has also allowed us to follow the time course of a conformational change in EGFR occurring during endocytosis, and correlate this information with endosomal trafficking and EGFR recycling.

Cell Line↗
PubMed1999

Extended circular dichroism measurements using synchrotron radiation show that the assembly of clathrin coats requires no change in secondary structure.

A number of models have been proposed for the assembly of clathrin triskelia into coats. However, little is known of the effects of assembly on triskelion structure. A more detailed knowledge of the way in which assembly affects triskelion structure would be valuable for assessing the relative merits of the proposed models. The development of a vacuum-ultraviolet circular dichroism (CD) instrument that uses synchrotron radiation as a light source has allowed us to extend the range of CD measurements to shorter wavelengths. This has greatly increased signal quality even for highly scattering samples. Also, we have improved CD data analysis to provide standard deviations for calculated secondary structure content. These developments have increased the precision of CD analysis beyond what has been thus far possible. Using these developments, we have determined the secondary structure content of all components of coat protein, under both assembly and dissociating conditions. The assembly of coats does not incur any change in secondary structure content, but a 10% loss of triskelion helical content accompanies assembly in the absence of AP-2. We conclude that coat assembly requires no detectable reorganization of triskelion structure. Our result indicates that AP-2 stabilizes helical structure in the triskelion, and we propose that this increases triskelion rigidity, restricting the range of coat sizes.

Adaptor Proteins, Vesicular Transport↗
PubMed1999

The alpha-helix folds on the millisecond time scale.

It has long been believed that nucleation of the alpha-helix is a very fast reaction, occurring in around 10(-7) s. We show here that helix nucleation, in fact, takes place on the millisecond time scale. The rate of alpha-helix nucleation in two polyalanine-based peptides and in lysine and glutamic acid homopolymers was measured directly by stopped-flow deep UV CD with synchrotron radiation as the light source. Synchrotron radiation CD gives far superior signal to noise than a conventional instrument. The 16-aa AK peptide folds with first-order kinetics and a rate constant of 15 s-1 at 0 degrees C. The rate-determining step is presumably the initiation of a new helix, which occurs at least 10(5) times slower than expected. Helix folding occurs in at least two steps on the millisecond time scale for the longer peptides, with a transient overshoot of helix content significantly greater than at equilibrium, similar to that seen in the folding of several proteins. We suggest that the overshoot is caused by the formation of a single long helix followed by its breakage into the two or more helices present at equilibrium.

Animals↗
PubMed1999

Selective pressure as an essential force in molecular evolution of myeloid leukemic clones: a view from the window of Fanconi anemia.

Specific chromosomal deletions are commonly found in bone marrow cells of children with Fanconi anemia (FA) whose disease has evolved to myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Identical deletions are found in adults with MDS/AML with a history of exposure to alkylating agents (secondary MDS/AML). While deleted chromosomal regions likely harbor genes encoding proteins with tumor suppressor (TS) function, such genes have not been identified and the environmental forces by which these mutant clones are selected remain unclear. A consistent signaling abnormality in cells bearing mutations of the Fanconi anemia complementation group C (FA-C) gene (FANCC) has revealed a potential selective force. Hematopoietic progenitor cells from patients and mice with FANCC mutations are hypersensitive to the inhibitory effects of IFNgamma and TNFalpha. Consequently, clonal outgrowths in FA likely result from strong selective pressure for stem and/or progenitor cells resistant to these inhibitory cytokines. Additional mutations that inactivate signaling pathways for these inhibitors would create a cell with a profound proliferative advantage over its apoptosis-prone counterparts. Here, we present preliminary evidence supporting a selection-based model of leukemic evolution and argue that MDS in FA patients is a de facto model of secondary MDS in non-FA adults.

Acute Disease↗
PubMed1999

Iron in the basal ganglia in Parkinson's disease. An in vitro study using extended X-ray absorption fine structure and cryo-electron microscopy.

Iron is found in high concentration in some areas of the brain, and increased iron in the substantia nigra is a feature of Parkinson's disease. The purpose of this study was to investigate the physical environment of brain iron in post-mortem tissue to provide information on the possible role of iron in neurodegeneration in Parkinson's disease. Iron has also been implicated as the cause of signal loss in areas of high brain iron on T2-weighted MRI sequences. Knowledge of the physical environment of the brain iron is essential in interpreting the cause of signal change. Post-mortem tissue was obtained from six cases of Parkinson's disease and from six age-matched controls. Iron levels were measured using absorption spectrophotometry. Extended X-ray absorption fine structure was used to evaluate the atomic environment of iron within the substantia nigra and both segments of the globus pallidus. Cryo-electron transmission microscopy was used to probe the iron storage proteins in these areas. Iron levels were increased in the parkinsonian nigra and lateral portion of the globus pallidus. Spectra from the extended X-ray absorption fine structure experiments showed that ferritin was the only storage protein detectable in both control and parkinsonian tissue in all areas studied. Cryo-electron transmission microscopy studies showed that ferritin was more heavily loaded with iron in Parkinson's disease when compared with age-matched controls. In summary we have shown that iron levels are increased in two areas of the brain in Parkinson's disease including the substantia nigra, the site of maximal neurodegeneration. This produces increased loading of ferritin, which is the normal brain iron storage protein. It is possible that increased loading of ferritin may increase the risk of free radical-induced damage. Differences in ferritin loading may explain regional differences in iron's effect on the T2 signal.

Aged↗
PubMed1998

Assessment criteria in identifying the sick sepsis patient.

Standard definitions of sepsis have been proposed and have been widely adopted. Recognition of the systemic inflammatory response syndrome (SIRS) and assessment of its severity can easily be achieved at the bedside using basic observations and simple laboratory tests. Fulfillment of standardized criteria defining increasing severity of sepsis or manifestation of two, three and four SIRS criteria directly correlates with risk of mortality and progression to organ failure. However, manifestation of only two SIRS criteria identifies patients who may have relatively mild disease. Furthermore, sepsis definitions take no account of pre-existing illness, source of infection or causative agent, all of which have a significant influence on outcome. Despite these limitations, manifestation of four SIRS criteria or the persistence of markers of severe sepsis identifies individuals on general wards who are at particularly high risk of death, who should be closely monitored for deterioration and discussed with an intensive-care physician at an early stage. If the source of sepsis is not clear, empirical antibiotic therapy for such individuals should be discussed with a medical microbiologist or infectious diseases physician.

Adult↗
PubMed1998

The Ontario Prehospital Advanced Life Support (OPALS) Study: rationale and methodology for cardiac arrest patients.

The Ontario Prehospital Advanced Life Support Study represents the largest prehospital study yet conducted, worldwide. This study will involve more than 25,000 cardiac arrest, trauma, and critically ill patients over an 8-year period. The study will evaluate the incremental benefit of rapid defibrillation and prehospital Advanced Cardiac Life Support measures for cardiac arrest survival and the benefit of Advanced Life Support for patients with traumatic injuries and other critically ill prehospital patients. This article describes the OPALS study with regard to the rationale and methodology for cardiac arrest patients.

Cost-Benefit Analysis↗
PubMed1998

Dynamics of carriage of Neisseria meningitidis in a group of military recruits: subtype stability and specificity of the immune response following colonization.

Meningococcal carriage and the immune response to colonization were studied in a group of military recruits undergoing basic training. Subtyping by determination of the class 1 protein sequence clearly differentiated between strains and demonstrated the dynamics of carriage and transmission. Expression of class 1 protein by each strain remained stable during prolonged carriage by different subjects. Following colonization, a marked increase in serum bactericidal response occurred, which was specific for the subtype of the acquired strain and was associated with an increase in reactivity by Western blot to the homologous class 1 protein. Subjects colonized by multiple strains showed evidence of a specific immune response to the class 1 protein of each strain acquired. The subtype specificity of the bactericidal response to meningococci and the stability of expression of the class 1 protein have important implications for the design of vaccines for prevention of serogroup B meningococcal disease.

Antibodies, Bacterial↗
PubMed1997

Effect of temperature on the secondary structure of beta-lactoglobulin at pH 6.7, as determined by CD and IR spectroscopy: a test of the molten globule hypothesis.

Previous CD measurements of changes in the conformation of beta-lactoglobulin at neutral pH as a function of temperature indicated the formation of a molten globule state above approx. 70 degrees C. New CD measurements are reported at temperatures up to 80 degrees C with an instrument on the Daresbury synchrotron radiation source which gives spectra of good signal-to-noise ratio down to 170 nm. IR spectra were recorded up to 94.8 degrees C with a ZnSe circle cell and a single simplified model of the substructure of the amide I' band was used to give the fractional contents of beta-sheet structure unambiguously and independently of the CD spectroscopy. The results of both techniques, however, were in agreement in showing a progressive loss of beta-sheet structure with increasing temperature, beginning below the denaturation temperature. Nevertheless, the CD spectroscopy showed a fairly abrupt loss of virtually all the helical conformation at approx. 65 degrees C. Comparison of the present results with other studies on the molten globule formed at acid pH in the lipocalin family suggests that above 65 degrees C a partly unfolded state is formed, possibly by destabilization of the intermolecular beta-strand I and the loss of the main helix, but it is not a classical molten globule transition.

Animals↗
PubMed1997

Very unusual ethanol distribution in a fatality.

A 48-year-old man with an extensive history of alcoholism was found dead at home. He was lying face down on a carpet. There was evidence of gastric aspiration at autopsy and histologic examination. The distribution of ethanol was very unusual (concentrations in mg/100 mL or mg/100 g): femoral blood, 257 and 273 (two samples); heart blood, 643; vitreous humor, 763; urine, 84; bile, 616; liver, 250; and gastric, 4660 (2470 mg/53 g). In addition, this man ingested isopropanol, and, according to the history, may also have ingested acetone in the form of nail polish remover. The distribution of both isopropanol and acetone was as expected, which was approximately in proportion to the aqueous content of the respective tissues. It is proposed that agonal or postmortem aspiration of the ethanol-rich vomitus and postmortem fermentation could account for the apparently elevated concentrations of ethanol in heart blood and bile. The elevated vitreous ethanol could be explained if ethanol diffused across the eye in the agonal phase or postmortem from gastric aspirate in the carpet. The relatively low urinary ethanol concentration would be consistent with a recent binge-drinking episode, which allowed only a limited time period for excretion into an already partially full, but relatively ethanol-free, bladder.

2-Propanol↗
PubMed1997

An uncommon fatality due to moclobemide and paroxetine.

A young man was found shivering and incoherent at home. He was placed in bed and was observed having seizures some time later. About four hours after he was initially found, he suffered a full cardiac arrest. Paramedics found his jaw unusually stiff and were unable to open his mouth in order to intubate him. Resuscitation attempts were unsuccessful. The autopsy findings were unremarkable, but toxicology testing revealed the following: moclobemide (subclavian blood, 18.5 mg/L; liver, 28.5 mg/kg; gastric contents, 77 mg/69 g) and paroxetine (subclavian blood, 1.58 mg/L; liver, 15.3 mg/kg; gastric contents, 0.7 mg/69 g). The cause of death was attributed to the combined toxicity of moclobemide and paroxetine. Deaths attributed primarily to these drugs are extremely rare because both are considerably less toxic than older monoamine oxidase and tricyclic antidepressant drugs. Based on the history of the case and pharmacology of the drugs involved, the most likely mechanism of death was severe "serotonin syndrome" resulting from the overdose.

Adult↗
PubMed1997

Sport-related hematuria: a review.

OBJECTIVE: To present an overview and models of the potential causes and implications of sport-related hematuria in an athletic population as provided by a literature review. DATA SOURCES: A total of 64 published scientific articles have been utilized to provide a review of sport-related hematuria. STUDY SELECTION: Reviewed studies were selected on the basis that they provided informative findings about the possible mechanisms of sport-related hematuria attributed to exercise duration and intensity. These studies used both normal adult and athletic populations. DATA EXTRACTION: A review of the literature on the potential mechanisms of sport-related hematuria led to the classification of these mechanisms as either exercise duration related or exercise intensity related. DATA SYNTHESIS: Research has revealed an increased prevalence of hematuria in athletes. The mechanisms responsible may be traced to different sources or a combination thereof. Many explanations have been directed toward a potential cause; foot-strike hemolysis, renal ischemia, hypoxic damage to the kidney, the release of a hemolyzing factor, bladder and/or kidney trauma, nonsteroidal anti-inflammatory drugs, dehydration, increased circulation rate, myoglobinuria release, and the peroxidation of red blood cells. These mechanisms are presented in two models depicting the influence of either exercise intensity or exercise duration on sport-related hematuria. CONCLUSIONS: Athletes, coaches, and sports medicine professionals should be aware of this condition because frequent high-intensity and/or long-duration workouts and competitions may promote the symptoms. Repeated red blood cell loss through the urine may be a contributing factor toward promoting anemic conditions in competitive athletes. Recognition of the potential mechanisms can spare the time and expense of invasive testing.

Dehydration↗
PubMed1997

Death of two subjects due to imipramine and desipramine metabolite accumulation during chronic therapy: a review of the literature and possible mechanisms.

In two unrelated cases, a 7-year-old boy and a 21-year-old woman died suddenly while receiving chronic imipramine therapy. In the boy, concentrations of imipramine were: Left femoral blood 0.5 mg/L, right femoral blood 1.2 mg/L, aorta blood 1.0 mg/L, liver 68 mg/Kg, and for the active metabolite, desipramine, left femoral blood 6.7 mg/L, right femoral blood 9.9 mg/L, aorta blood 8.7 mg/L, liver 400 mg/Kg. In the woman, the imipramine concentrations were: Femoral blood 0.6 mg/L, liver 37 mg/Kg, and of the active metabolite, desipramine, femoral blood 3.74 mg/L, liver 261 mg/Kg. In both cases, the scene investigation strongly indicated that neither individual had ingested an acute overdose. The very high ratios of desmethyl metabolite to parent drug are consistent with this observation. Impaired metabolism due to a genetically determined "slow metabolizer" phenotype of cytochrome CYP2D6, and/or concurrent therapy with phenothiazines, is suggested as a possible mechanism for the apparent fatal accumulation of these tricyclic antidepressants.

Adult↗