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Biomedical subjects

G Frank

Publications and source records attributed to G Frank.

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

Cell cycle-dependent and DNA damage-inducible nuclear localization of FEN-1 nuclease is consistent with its dual functions in DNA replication and repair.

Flap endonuclease-1 (FEN-1), a 43-kDa protein, is a structure-specific and multifunctional nuclease. It plays important roles in RNA primer removal of Okazaki fragments during DNA replication, DNA base excision repair, and maintenance of genome stability. Three functional motifs of the enzyme were proposed to be responsible for its nuclease activities, interaction with proliferating cell nuclear antigen, and nuclear localization. In this study, we demonstrate in HeLa cells that a signal located at the C terminus (the nuclear localization signal (NLS) motif) facilitates nuclear localization of the enzyme during S phase of the cell cycle and in response to DNA damage. Truncation of the NLS motif prevents migration of the protein from the cytoplasm to the nucleus, while having no effect on the nuclease activities and its proliferating cell nuclear antigen interaction capability. Site-directed mutagenesis further revealed that a mutation of the KRK cluster to three alanine residues completely blocked the localization of FEN-1 into the nucleus, whereas mutagenesis of the KKK cluster led to a partial defect of nuclear localization in HeLa cells without observable phenotype in yeast. Therefore, the KRKXXXXXXXXKKK motif may be a bipartite NLS driving the protein into nuclei. Yeast RAD27Delta cells transformed with human mutant M(krk) survived poorly upon methyl methanesulfonate treatment or when they were incubated at an elevated temperature.

Cell Cycle↗
PubMed2000

Interrelationships between the size of the pancreas and the weight of patients with eating disorders.

OBJECTIVE: Starvation severely affects normal pancreatic function in children suffering from Kwashiorkor and in animals undergoing food deprivation. This study examines whether pancreatic size, as determined by ultrasound, is dependent on starvation or on eating patterns in patients with eating disorders. METHOD: In 109 inpatients with eating disorders, 86 with anorexia nervosa and 23 with bulimia nervosa, we determined the pancreatic size by means of abdominal ultrasonography before increase in weight. Twenty-four inpatients with other psychiatric disorders served as controls. Pancreatic size was defined by the maximal diameter and the length of the head, the diameter of the head at the confluence of the splenic and mesenteric veins, and the diameters of the body and tail. In 41 eating disorder patients, pancreatic size was also measured during the course of therapy and increase in weight. RESULTS: Pancreatic size correlates highly with body mass index (BMI). Counteracting actions such as purging do not seem to influence this pathophysiologic finding. Dystrophy of the pancreas is reversible in a short period of time. The increase in pancreatic size after maintenance of a normal eating pattern, however, exceeded the size expected by regression equation with an increase in the BMI. Pancreatic size seems to correlate with the actual amount of digested food. The increase in BMI is only an indicator of food intake. DISCUSSION: Pancreatic size might therefore be useful for the assessment of normalization of the eating pattern. Future research is necessary to investigate the impairment of pancreatic function resulting from dystrophy, the impact of possible pancreatic malfunction on the course of eating disorders, and the regulatory mechanisms responsible for the change of pancreatic size.

Adolescent↗
PubMed2000

Confidential enquiry into avoidable vehicle accident deaths in the province of Modena, Italy.

The authors describe the methods and results of a kind of study confidential enquiries into avoidable deaths very rarely performed in the Mediterranean area. After assessing some quali/ quantitative evaluation criteria, an independent expert panel investigated the quality of each step in emergency health care. Information was collected by clinical and forensic reports (clinical method). Of 102 cases, 4 were avoidable deaths and 18 probably avoidable. These results, which are comparable with other similar ones found in Italy (autoptic method) and abroad, have been useful in highlighting some health care errors: in particular, in on-site care and in emergency department diagnosis and treatment. Other avoidable factors emerging were the inappropriateness of transporting severe trauma cases to a small hospital lacking proper equipment and trained staff, and the importance of staff training in first emergency care of severe trauma on ambulance. This situation had been highlighted previously and led to implementation of trauma centres. The methods implemented turned out to be quite statistically reproducible and have been used in local health care planning, especially in the rearrangement of ambulance deployment and emergency staff training.

Accidents, Traffic↗
PubMed2000

Does cerebral blood flow decline in healthy aging? A PET study with partial-volume correction.

UNLABELLED: It remains a matter of controversy as to whether cerebral perfusion declines with healthy aging. In vivo imaging with PET permits quantitative evaluation of brain physiology; however, previous PET studies have inconsistently reported aging reductions in cerebral blood flow (CBF), oxygen metabolism, and glucose metabolism. In part, this may be because of a lack of correction for the dilution effect of age-related cerebral volume loss on PET measurements. METHODS: CBF PET scans were obtained using [15O]H2O in 27 healthy individuals (age range, 19-76 y) and corrected for partial-volume effects from cerebral atrophy using an MR-based algorithm. RESULTS: There was a significant difference (P = 0.01) in mean cortical CBF between young/midlife (age range, 19-46 y; mean +/- SD, 56+/-10 mL/100 mL/min) and elderly (age range, 60-76 y; mean +/- SD, 49+/-2.6 mL/100 mL/min) subgroups before correcting for partial-volume effects. However, this group difference resolved after partial-volume correction (young/midlife: mean +/- SD, 62+/-10 mL/100 mL/min; elderly: mean +/- SD, 61+/-4.8 mL/100 mL/min; P = 0.66). When all subjects were considered, a mild but significant inverse correlation between age and cortical CBF measurements was present in the uncorrected but not the corrected data. CONCLUSION: This study suggests that CBF may not decline with age in healthy individuals and that failure to correct for the dilution effect of age-related cerebral atrophy may confound interpretation of previous PET studies that have shown aging reductions in physiologic measurements.

Adult↗
PubMed1999

Limiting dynamics of high-frequency electromechanical transduction of outer hair cells.

High-frequency resolution is one of the salient features of peripheral sound processing in the mammalian cochlea. The sensitivity originates in the active amplification of the travelling wave on the basilar membrane by the outer hair cells (OHCs), where electrically induced mechanical action of the OHC on a cycle-by-cycle basis is believed to be the crucial component. However, it is still unclear if this electromechanical action is sufficiently fast and can produce enough force to enhance mechanical tuning up to the highest frequencies perceived by mammals. Here we show that isolated OHCs in the microchamber configuration are able to overcome fluid forces with almost constant displacement amplitude and phase up to frequencies well above their place-frequency on the basilar membrane. The high-frequency limit of the electromotility, defined as the frequency at which the amplitude drops by 3 dB from its asymptotic low-frequency value, is inversely dependent on cell length. The frequency limit is at least 79 kHz. For frequencies up to 100 kHz, the electromotile response was specified by an overdamped (Q = 0.42) second-order resonant system. This finding suggests that the limiting factor for frequencies up to 100 kHz is not the speed of the motor but damping and inertia. The isometric force produced by the OHC was constant at least up to 50 kHz, with amplitudes as high as 53 pN/mV being observed. We conclude that the electromechanical transduction process of OHCs possesses the necessary high-frequency properties to enable amplification of the travelling wave over the entire hearing range.

Animals↗
PubMed1999

Evolutionary adaptations of cochlear function in Jamaican mormoopid bats.

Mormoopid bat species have their echolocation system adapted to different hunting strategies. To study the corresponding mechanical properties of their inner ear, we measured distortion-product otoacoustic emissions to assess cochlear sensitivity and tuning. Mormoops blainvillii, Pteronotus macleayii and P. quadridens use frequency-modulated echolocation signals, sometimes preceded by a short narrowband signal component. Their distortion-product otoacoustic emission-threshold curves are most sensitive between 30 and 50 kHz and show no adaptation to the narrowband echolocation components. In contrast, the constant-frequency bat P. parnellii always uses long constant-frequency call components. Its inner ear is maximally sensitive at 62 kHz, the echo-frequency of the dominant constant-frequency component, and pronounced insensitivities at 61 and 93 kHz (CF2 and CF3 call frequency) are the major evolutionary change in comparison to its relatives. Furthermore, in P. parnellii, the optimum cochlear frequency separation is minimal at 62 and 93 kHz, associated with enhanced cochlear tuning, while for the other mormoopids there is no indication of enhanced tuning. The phylogeny of mormoopids, assessed by mitochondrial DNA analysis, shows a close relationship between the Pteronotus species. This suggests that major cochlear redesign, associated with the acquisition of echolocation-call specific cochlear processing in P. parnellii, has occurred within a relatively short evolutionary time scale.

Acoustic Stimulation↗
PubMed1999

Enhanced airborne radioactivity during a pine pollen release episode.

A single episode of pine pollen release in the highly contaminated area of Novozybkov, Russian Federation, which led to enhanced atmospheric concentrations of 137Cs is discussed. The pollen grains were sampled by a rotating arm impactor and analysed by gamma-spectrometry for 137Cs activity and by image analysis for their size. In the vicinity of a forest, a maximum concentration of 4.5+/-0.4 mBq m(-3) was measured, and a mean activity per pollen grain of 260+/-80 nBq was determined. The emission rate of the Novozybkov mixed pine forest was estimated to be approximately 400 Bq m(-2) per year. Because of the large size of pine pollen grains (about 50 microm) and the short emission period of 5-8 days per year, the estimated potential annual inhalation doses are very low. Biological emissions including pollen release may be a source of increased airborne radionuclide concentrations at larger distances from the source areas as well.

Accidents↗
PubMed1999

Ethnicity and attitudes towards life sustaining technology.

The ethical and legal implications of decisions to withhold and withdraw life support have been widely debated. Making end-of-life decisions is never easy, and when the cultural background of doctor and patient differ, communication about these issues may become even more difficult. In this study, we examined the attitudes of people aged 65 and older from different ethnic groups toward foregoing life support. To this end, we conducted a survey of 200 respondents from each of four ethnic groups: European-American, African-American, Korean-American and Mexican-American (800 total), followed by in-depth ethnographic interviews with 80 respondents. European-Americans were the least likely to both accept and want life-support (p < 0.001). Mexican-Americans were generally more positive about the use of life-support and were more likely to personally want such treatments (p < 0.001). Ethnographic interviews revealed that this was due to their belief that life-support would not be suggested if a case was truly hopeless. Compared to European-Americans, Korean-Americans were very positive regarding life-support (RR = 6.7, p < 0.0001); however, they did not want such technology personally (RR = 1.2, p = 0.45). Ethnographic interviews revealed that the decision of life support would be made by their family. Compared to European-Americans, African-Americans felt that it was generally acceptable to withhold or withdraw life-support (RR = 1.6, p = 0.06), but were the most likely to want to be kept alive on life-support (RR = 2.1, p = 0.002). Ethnographic interviews documented a deep distrust towards the health care system and a fear that health care was based on one's ability to pay. We concluded that (a) ethnicity is strongly related to attitudes toward and personal wishes for the use of life support in the event of coma or terminal illness, and (b) this relationship was complex and in some cases, contradictory.

Black or African American↗
PubMed1999

Development of a unique phantom to assess the geometric accuracy of magnetic resonance imaging for stereotactic localization.

OBJECTIVE: To test the spatial accuracy of coordinates generated from magnetic resonance imaging (MRI) scans, using the Brown-Roberts-Wells head frame and localizer system (Radionics, Inc., Burlington, MA). METHODS: An anthropomorphic head phantom, consisting of a two-dimensional lattice of acrylic spheres (4-mm diameter) spaced 10 mm apart and embedded in a brain tissue-mimicking gelatin-agar gel, was constructed. The intersphere distances for the target lattice positions in MRI and computed tomographic scan sets were compared. The data sets were fused, and differences in fiducial marker and intraphantom target positions were measured. RESULTS: Intersphere distances were identical for the MRI and computed tomographic scan sets (10 +/- 0.1 mm). Differences in fiducial marker positions [maximal lateral difference, 0.97 mm; mean absolute lateral difference, 0.69 +/- 0.22 mm; maximal anteroposterior (AP) difference, 1.99 mm; mean absolute AP difference, 1.29 +/- 0.67 mm] were correlated with differences in intraphantom target positions (maximal lateral difference, 0.83 mm; mean absolute lateral difference, 0.28 +/- 0.24 mm; maximal AP difference, -1.97 mm; mean absolute AP difference, 1.63 +/- 25 mm; maximal vertical difference, -0.73 mm; mean absolute vertical difference, 0.34 +/- 0.21 mm). This suggested that improper fiducial rod identification and the subsequent transformation to stereotactic coordinate space were the greatest sources of spatial uncertainty. CONCLUSION: With computed tomographic data as the standard, these differences resulted in maximal and minimal composite uncertainties of 2.06 and 1.17 mm, respectively. The measured uncertainties exceed recommended standards for radiosurgery but allow the possible use of MRI-based stereotactic treatment planning for certain intracranial lesions, if the errors are corrected using appropriate software. Clinicians must recognize that error magnitudes vary for different systems, and they should perform systematic, scheduled, institutional error analyses as part of their ongoing quality assurance processes. This phantom provides one tool for measuring such variances.

Brain Mapping↗
PubMed1999

Perfect DiViSy technology for video network in medicine (Moscow Information Network for Teleoncology).

A large telemedicine project is now under development in Moscow. The general task of the project is to link oncology research centres and hospitals meeting the project profile, and to provide on-line (using real-time video conferences) and off-line (via distributed database of medical information) information exchange. There was no existing technology available for use at the project's base which was ready to meet all requirements, so we are using specially created technology for video networks (DiViSy V.97). We suppose this technology to be more applicable for use in telemedicine networks than are business video conference technologies and classical Internet/Intranet technologies. We affirm in our conclusion that now is the time for developing special telemedicine standards, recommendations of compatibility, etc., and that we are ready to take part in this process.

Computer Communication Networks↗
PubMed1998

Partial functional deficiency of E160D flap endonuclease-1 mutant in vitro and in vivo is due to defective cleavage of DNA substrates.

To assess the roles of the active site residues Glu160 and Asp181 of human FEN-1 nuclease in binding and catalysis of the flap DNA substrate and in vivo biological processes of DNA damage and repair, five different amino acids were replaced at each site through site-directed mutagenesis of the FEN-1 gene. The mutants were then expressed in Escherichia coli and purified using a His-tag. Even though the mutants bind to the flap DNA to different degrees, most of the mutants lost flap nuclease activity with the exception of an E160D mutant. This mutant retained wild type-like binding ability, specificity, and partial catalytic activity. Detailed steady state and pre-steady state kinetic analysis revealed that the functional deficiency of this mutant was due to retardation of the endonucleolytic cleavage. When the mutant enzyme E160D was expressed in yeast, it partially complements the biological functions of the homologous yeast gene, RAD27, and reverses the hyper-temperature lethality and hypersensitivity to methyl methanesulfonate, in a manner corresponding to the in vitro activity.

Base Sequence↗
PubMed1998

Newly discovered archaebacterial flap endonucleases show a structure-specific mechanism for DNA substrate binding and catalysis resembling human flap endonuclease-1.

Mammalian flap endonuclease-1 (FEN-1) is a structure-specific metalloenzyme that acts in processing of both the Okazaki fragments during lagging strand DNA synthesis and flap intermediates during DNA damage repair. We identified and cloned three open reading frames encoding a flap endonuclease from Archaeglobus fulgidus, Methanococcus jannaschii, and Pyrococcus furiosus, respectively. The deduced FEN-1 protein sequences share approximately 75% similarity with the human FEN-1 nuclease in the conserved nuclease domains, and extensive biochemical experiments indicate that the substrate specificities and catalytic activities of these enzymes have overall similarities with those of the human enzyme. Thus, FEN-1 enzymes and likely reaction mechanisms are conserved across the eukaryotic and archaeal kingdoms. Detailed comparative analysis, however, reveals subtle differences among these four enzymes including distinctive substrate specificity, tolerance of the archaebacterial enzymes for acidic pHs and elevated temperatures, and variations in the metal-ion dependence of substrate cleavage. Although the archaebacterial enzymes were inactive at temperatures below 30 degreesC, DNA binding occurred at temperatures as low as 4 degreesC and with or without metal ions. Thus, these archaeal enzymes may provide a means to dissect the specific binding and catalytic mechanisms of the entire FEN-1 family of structure-specific nucleases.

Acids↗