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Biomedical subjects

D Kessler

Publications and source records attributed to D Kessler.

At least 19 recordsLinked to original sources
PubMed2000

Crystal structure of the cystine C-S lyase from Synechocystis: stabilization of cysteine persulfide for FeS cluster biosynthesis.

FeS clusters are versatile cofactors of a variety of proteins, but the mechanisms of their biosynthesis are still unknown. The cystine C-S lyase from Synechocystis has been identified as a participant in ferredoxin FeS cluster formation. Herein, we report on the crystal structure of the lyase and of a complex with the reaction products of cystine cleavage at 1.8- and 1.55-A resolution, respectively. The sulfur-containing product was unequivocally identified as cysteine persulfide. The reactive persulfide group is fixed by a hydrogen bond to His-114 in the center of a hydrophobic pocket and is thereby shielded from the solvent. Binding and stabilization of the cysteine persulfide represent an alternative to the generation of a protein-bound persulfide by NifS-like proteins and point to the general importance of persulfidic compounds for FeS cluster assembly.

Amino Acid Sequence↗
PubMed2000

Fibroblast-matrix interactions in wound healing and fibrosis.

The regulation of matrix deposition is a key event in many physiological and pathological situations. It involves the activity of mediators in autocrine and paracrine fashions and the contact of cells with the surrounding extracellular matrix as well. The tightly regulated balance of both mechanisms guarantees rapid and adaptive cellular responses to meet changes in the biological requirements of the environment. Disturbances lead to wound healing defects or the development of fibrosis. The molecular mechanisms for these regulatory events are only partially understood, but involve the activity of integrins and a structural continuum of extracellular matrix-receptor-cytoskeleton-nucleus for transfer of information and the regulation of activated genes.

Collagen↗
PubMed2000

Sexual motives, gender, and sexual behavior.

The roles of gender and the sexual motives of Love, Pleasure, Conformity, Recognition, Dominance, and Submission in numerous usual and unusual sexual behaviors were investigated. In a survey of 191 college undergraduates it was found that Love, Pleasure, Conformity, and Recognition motives, often in interaction with gender, were all important predictors of sexual behavior. Gender was the best predictor of initiating usual sexual behavior, whereas the Love motive was the best predictor of actually engaging in usual sexual behavior. Pleasure and Recognition in interaction with gender were the best predictors of engaging in unusual sexual behavior. None of the sexual motives predicted initiating unusual sexual behavior. Findings suggest that a variety of sexual motives may underlie sexual behavior.

Adolescent↗
PubMed2000

Formulation development and antitumor activity of a filter-sterilizable emulsion of paclitaxel.

PURPOSE: Paclitaxel is currently administered i.v. as a slow infusion of a solution of the drug in an ethanol:surfactant:saline admixture. However, poor solubilization and toxicity are associated with this drug therapy. Alternative drug delivery systems, including parenteral emulsions, are under development in recent years to reduce drug toxicity, improve efficacy and eliminate premedication. METHODS: Paclitaxel emulsions were prepared by high-shear homogenization. The particle size of the emulsions was measured by dynamic light scattering. Drug concentration was quantified by HPLC and in vitro drug release was monitored by membrane dialysis. The physical stability of emulsions was monitored by particle size changes in both the mean droplet diameter and 99% cumulative distribution. Paclitaxel potency and changes in the concentration of known degradants were used as chemical stability indicators. Single dose acute toxicity studies were conducted in healthy mice and efficacy studies in B 16 melanoma tumor-bearing mice. RESULTS: QW8184, a physically and chemically stable sub-micron oil-in-water (o/w) emulsion of paclitaxel, can be prepared at high drug loading (8-10 mg/mL) having a mean droplet diameter of <100 nm and 99% cumulative particle size distribution of <200 nm. In vitro release studies demonstrated low and sustained drug release both in the presence and absence of human serum albumin. Based on single dose acute toxicity studies, QW8184 is well tolerated both in mice and rats with about a 3-fold increase in the maximum-tolerated-dose (MTD) over the current marketed drug formulation. Using the B16 mouse melanoma model, a significant improvement in drug efficacy was observed with QW8184 over Taxol. CONCLUSIONS: QW8184, a stable sub-micron o/w emulsion of paclitaxel has been developed that can be filter-sterilized and administered i.v. as a bolus dose. When compared to Taxol, this emulsion exhibited reduced toxicity and improved efficacy most likely due to the composition and dependent physicochemical characteristics of the emulsion.

Animals↗
PubMed2000

Surveillance of HIV-1 genetic subtypesand diversity in the US blood supply.

BACKGROUND: Recent reports of variant (non-subtype B) HIV infections in US populations have raised concerns about the sensitivity of subtype B virus-based donor screening and diagnostic assays. This study was designed to determine the prevalence and genetic diversity of HIV subtypes in US blood donors over the last two decades. STUDY DESIGN AND METHODS: Three groups were studied: hemophiliacs infected by clotting factor concentrates in the early 1980s (n = 49), blood donors retrospectively identified as being seropositive in 1985 (n = 97), and blood donors identified as seropositive between 1993 and 1996 (n = 405). Subtype assignment was based primarily on heteroduplex mobility analysis (HMA) of HIV-1 env, with DNA sequence confirmation of selected specimens. HIV peptide-based EIA serotyping was used to rule out HIV-2 and group O infections and to serotype HMA-refractory specimens. RESULTS: Of 551 specimens, 535 (97%) were assigned subtypes; 532 (99%) of these were subtype B. Three postscreening donations (1%) were assigned non-B subtypes (2 A, 1 C). Two of these three donors were born in Africa; the third was born in the United States and reported no risk factors other than heterosexual activity. HMA distribution plots showed an increase in env diversity among HIV-1 group B strains over time. CONCLUSION: The results support the need for continued surveillance of HIV subtype diversity and ongoing validation of the sensitivity of HIV diagnostic assays to non-B subtype infections.

Blood Donors↗
PubMed1999

[Parallel use of medical services? Patterns of using complementary medicine and biomedicine].

In order to identify behavioural patterns within the pluralistic medical system, 38 patients have been observed over a period of two years. The most notable quality of behaviour is its flexibility. Single patients use complementary medicine and biomedicine in pragmatic and differentiated ways that change over time. Parallelism can be observed among the offered medical services, while their use is to be divided into parallel, alternate, alternative and complementary forms. Phases of exclusive use of complementary medicine occur, but during the two year period under investigation, all patients have made use of biomedicine.

Adult↗
PubMed1999

Cross sectional study of symptom attribution and recognition of depression and anxiety in primary care.

OBJECTIVES: To examine the effect of patients' causal attributions of common somatic symptoms on recognition by general practitioners of cases of depression and anxiety and to test the hypothesis that normalising attributions make recognition less likely. DESIGN: Cross sectional survey. SETTING: One general practice of eight doctors in Bristol. SUBJECTS: 305 general practice attenders. MAIN OUTCOME MEASURE: The rate of detection by general practitioners of cases of depression and anxiety as defined by the general health questionnaire. RESULTS: Consecutive attenders completed the general health questionnaire and the symptom interpretation questionnaire, which scores style of symptom attribution along the dimensions of psychologising, somatising, and normalising. General practitioners detected depression or anxiety in 56 (36%; 95% confidence interval 28% to 44%) of the 157 patients who scored highly on the general health questionnaire. Subjects with a normalising attributional style were less likely to be detected as cases; doctors did not make any psychological diagnosis in 46 (85%; 73% to 93%) of 54 patients who had high questionnaire and high normalising scores. Those with a psychologising style were more likely to be detected; doctors did not detect 21 (38%; 25% to 52%) of 55 patients who had high questionnaire and high psychologising scores. The somatisation scale was not associated with low detection rates. This pattern of results persisted after adjustment for age, sex, general health questionnaire score, and general practitioner. CONCLUSIONS: Normalising attributions minimise symptoms and are non-pathological in character. The normalising attributional style is predominant in general practice attenders and is an important cause of low rates of detection of depression and anxiety.

Adolescent↗
PubMed1999

Evidence for cysteine persulfide as reaction product of L-Cyst(e)ine C-S-lyase (C-DES) from Synechocystis. Analyses using cystine analogues and recombinant C-DES.

The pyridoxal phosphate-dependent monomeric L-cysteine/cystine C-S-lyase (C-DES), previously isolated from Synechocystis PCC 6714 by its capacity to direct [2Fe-2S] cluster assembly of ferredoxin in vitro (Leibrecht, I., and Kessler, D. (1997) J. Biol. Chem. 272, 10442-10447), has now been cloned, sequenced, and overexpressed in Escherichia coli. The amino acid sequence of C-DES was found to be nearly identical (92% identity) to the open reading frame slr2143 of Synechocystis PCC 6803 and showed a more distant relationship to the NifS family of proteins (about 27% identity). Recombinant C-DES displayed activities equal to the isolate from Synechocystis in terms of the cyst(e)ine lyase reaction and holoferredoxin formation which recommended its use for functional and mechanistic studies. Investigation of the substrate spectrum for beta-elimination found L-cysteine to be a poor substrate (kcat approximately 0.15 s-1) in contrast to L-cystine (kcat = 36 s-1) and several related compounds. Of these compounds, desaminocystine (S-(carboxyethylthio)-L-cysteine) was used for C-DES-mediated persulfide generation. Stabilization of the linear persulfide 3-(disulfanyl)-propionic acid was achieved by cyclization as a novel intramolecular trapping reaction; this yielded 1,2-dithiolan-3-one which was isolated and identified by chemical analyses.

Amino Acid Sequence↗
PubMed1999

Interactions of fibroblasts with the extracellular matrix: implications for the understanding of fibrosis.

The cellular organization and the compartmentalization in multicellular organisms is mediated by the extracellular matrix (ECM). This structure is composed by a wide variety of different macromolecules which carry distinct domains with defined structural and/or biological activities. Cells are known to interact with these molecules via specific receptors. Following activation, these receptors transduce signals either directly to the intracellular cytoskeleton or via different signalling cascades. Cell-matrix interactions, therefore, not only control the shape and orientation of cells but can also directly regulate cellular functions, including migration, differentiation, proliferation, and the expression of different genes. These cell-matrix interactions have been elucidated in detail for several biological processes, especially morphogenesis and differentiation, but also play an important role during pathological situations, e.g. wound healing and tumor progression. Although much less investigated, similar mechanisms are thought to regulate the biological behavior of fibroblastic cells, the final target cells in fibrosis. The activity of these cells depends in various ways on the presence of ECM molecules. First, some of the molecules are known to bind to and modulate the activity of those growth factors and cytokines, which lead to the activation of fibroblasts during the early phases of fibrosis. Second, deposition of large amounts of ECM molecules alters the environment and the mechanical load on the cells which are embedded in this matrix. Third, ECM molecules directly modulate fibroblast metabolism via certain integrin receptors. This review summarizes recent developments in all three domains. It mainly focuses on the direct role of ECM molecules in the biosynthetic activity of fibroblasts.

Animals↗
PubMed1999

Multivessel coronary artery bypass surgery without cardiopulmonary bypass.

BACKGROUND: There is limited experience with complete myocardial revascularization on a beating heart. Using a mechanical stabilization system, we sought to determine if complete coronary revascularization is feasible without cardiopulmonary bypass and what the short-term clinical outcome would be. METHODS: From February through September 1998, 26 patients underwent complete myocardial revascularization with Medtronics Octopus Tissue Stabilization System. Mean age for the group was 62 +/- 7 years (range 48 to 78 years); 11% had prior interventions. Mean preoperative ejection fraction was 49% +/- 14% (range 20% to 66%); 38% of operations were performed urgently. The mean number of vessels grafted was 3.0 +/- 0.9 (range 1 to 5 grafts/patient). In 96% of patients, at least one arterial graft was used. Fifteen percent of patients had 2 or more arterial grafts. In 58% of patients, a branch of circumflex coronary artery was bypassed. RESULTS: The median time to extubation was 2 hours (range 0 to 37 hours). None of the patients had perioperative myocardial infarction, cerebrovascular accident, or renal failure requiring dialysis. The 30-day survival rate was 100%. Angiographic follow-up was not available. At a mean follow-up period of 3.8 +/- 2.9 months, all patients remained free of angina and none has required cardiac reintervention. CONCLUSIONS: Complete myocardial revascularization on a beating heart can be achieved with the currently available stabilization systems and is associated with low perioperative complications and satisfactory short-term clinical outcomes. The long-term outcomes and graft patency remain to be determined.

Aged↗
PubMed1998

Conventional and hypobaric activation of an ultrasound contrast agent.

Hypobaric activation is a new injection technique for use with the contrast agent EchoGen and, in this study, the agent's ability to produce parenchymal enhancement in vivo, with and without prior hypobaric activation, was investigated. Injections, ranging in dose from 0.05 to 0.5 mL/kg, were administrated through a peripheral vein to eight woodchucks with multiple hepatomas. At the 0.10 mL/kg dose level, seven of eight injections following hypobaric activation (88%) resulted in definite parenchymal enhancement. Conversely, dosages of 0.10 mL/kg without prior hypobaric activation produced no grey-scale changes. Only at the 0.4 and 0.5 mL/kg dosage level did the conventional administration technique obtain similar results (4 of 5 injections increased the echogenicity for a 0.4 mL/kg dose). These differences were statistically significant (p = 0.031). In vitro experiments were conducted to establish the physical mechanisms behind hypobaric activation. Relative measurements of contrast microbubble sizes were performed with a phase Doppler particle analyzer after hypobaric and after conventional (bolus) activation. Hypobaric activation produced approximately 20 times more microbubbles per unit volume than the conventional method. In conclusion, this investigation has demonstrated the benefits of prior hypobaric activation when performing in vivo contrast studies with EchoGen and determined the physical mechanisms behind this new injection technique. Hypobaric activation of EchoGen increases contrast enhancement and reduces dose size.

Animals↗
PubMed1998

Effect of 50 milliliters of 50% dextrose in water administration on the blood sugar of euglycemic volunteers.

OBJECTIVE: To evaluate the effect of administration of 1 ampule of 50% dextrose in water solution (D50W) on serum glucose levels in healthy adult volunteers, the authors set out to determine whether a pre-D50W serum glucose level can be predicted from the ED sample. METHODS: This was a prospective, interventional study conducted from the ED of an urban, university-affiliated hospital. All subjects were healthy employee volunteers between 25 and 40 years of age. Baseline serum glucose levels were determined and all subjects were given an i.v. bolus of 25 grams of 50% dextrose solution. The main outcome measures were post-D50W serum glucose levels (observed) at 5 predetermined time intervals (5 min, 15 min, 30 min, 1 hr, and 2 hr). An expected change in serum glucose was calculated using the volume of distribution formula for glucose. RESULTS: Twenty-five volunteers (17 males and 8 females) participated in the study. The mean baseline serum glucose was 82.3 +/- 13.5 mg/dL. The mean post-infusion levels were: 244.4 +/- 44.6 mg/dL (5 min), 145.8 +/- 52.3 mg/dL (15 min), 88.1 +/- 28.8 mg/dL (30 min), 77.6 +/- 13.6 mg/dL (60 min), and 83.2 +/- 11.4 mg/dL (120 min). Using a mixed-effect regression model, statistically significant increases in serum glucose levels were found at 5 minutes (p < 0.001) and 15 minutes (p < 00001) following administration of D50W. There was a return to baseline serum glucose by 30 minutes. The expected change based on the volume of distribution formula (53.7 +/- 34.9) did not correlate with the observed changes at any measured time interval. CONCLUSION: Without pre-intervention blood drawing by emergency medical services, it is not possible to accurately predict pre-D50W serum glucose levels based on post-D50W glucose levels. The diagnosis of hypoglycemia as the etiology of altered mental status must therefore remain a diagnosis of exclusion. In addition, the return of serum glucose to baseline after 30 minutes suggests the duration of the effect of 1 ampule of D50W. Frequent re-evaluation of the serum glucose levels of suspected or proven hypoglycemic patients after administration of D50W should be considered.

Adult↗
PubMed1997

A novel L-cysteine/cystine C-S-lyase directing [2Fe-2S] cluster formation of Synechocystis ferredoxin.

Iron-sulfur proteins acquire their clusters by posttranslational assembly. To identify components involved in this process an in vitro assay for holoprotein formation was established using the [2Fe-2S] ferredoxin of the cyanobacterium Synechocystis as a model. Conversion of apoferredoxin to the holo- form was observed in an anaerobic reaction medium containing Fe(NH4)2(SO4)2, L-cysteine, glutathione, and catalytic amounts of Synechocystis extract, specifically depleted of endogeneous ferredoxin. An approximate 2500-fold purification of the converter activity yielded a monomeric, 43-kDa, pyridoxal phosphate-containing enzyme, which catalyzed the breakdown of L-cysteine to yield sulfide (assembled in ferredoxin), pyruvate, and ammonia; 1 mol of [2Fe-2S] ferredoxin was formed per 2 mol of cysteine utilized. The purified enzyme also catalyzed the beta-elimination reaction with cysteine in the absence of apoferredoxin. An increased reactivity was found with cystine instead of cysteine, which should yield cysteine persulfide as the primary product. These results provide a function-based identification of a cysteine/cystine C-S-lyase as a participant in ferredoxin Fe-S cluster formation. A substrate-derived cysteine persulfide could be involved in this reaction.

Anaerobiosis↗
PubMed1997

Convenience store robberies in selected metropolitan areas. Risk factors for employee injury.

Circumstances of injury were abstracted from police reports for 1835 convenience store robberies that occurred during 1992 or 1993 in selected metropolitan areas of seven eastern states. Subset analyses were performed using the data (758 robberies) from four states with relatively complete risk factor information. The purpose of this study was to estimate the risk of injury in a robbery situation for various risk factors. The overall risk of employee robbery-related injury could not be estimated because the probability of robbery is unknown. Of the 1835 robberies, 59% of the total robberies occurred at nighttime (9 p.m. to 3 a.m.), 47% occurred in stores previously robbed in the study period, 63% involved the use of a firearm, and 12% were associated with an injury to at least one employee. In the subset analysis of 758 robberies in four states, the employee probability of injury in a robbery was lower with firearm use compared with no weapon or use of a blunt instrument, and the probability of severe injury (defined as death, or an injury necessitating a trip to a hospital) was lower with a firearm compared with the use of a blunt instrument. However, all five fatalities were firearm-related. Other factors that were associated with a lower probability of employee injury included robbery occurrence in stores that had been robbed multiple times, compared with stores robbed only once; having 1 to 999 dollars stolen, compared with having no money stolen; and the presence of a customer(s) in the store at the time of the robbery. The employee risk of injury was not significantly different between one- (0.106) and multiple-employee (0.111) stores. Similarly, the employee risk of severe injury was not significantly different between one- (0.029) and multiple-employee stores (0.022). We conclude that there are several potential risk factors for employee injury in convenience store robberies, some of which are amenable to interventions. Further research on these factors and their relationship to employee injury is indicated.

Chi-Square Distribution↗