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M T Smith

Publications and source records attributed to M T Smith.

At least 109 records · Page 6Linked to original sources
PubMed1996

The Bacillus subtilis DNA replication terminator.

The recent discovery of the Bacillus subtilis plasmid terminator TerLS20 with bidirectional fork arrest activity has provided the opportunity to probe further the structural and functional features of B. subtilis replication terminators in general. The minimal TerI and TerLS20 terminators each comprise two 13 nt segments flanking a central trinucleotide, which is almost completely conserved in all terminators. It corresponds to the region of overlap of the two RTP binding sites (A and B) on the DNA. It has been shown that, despite this conservation, considerable variation in this trinucleotide region still allows fork arrest activity. Thus, the productive interaction of the RTP dimers, which presumably occurs in the vicinity of this trinucleotide region, is not dependent upon stringently defined contacts with the bases in this region. A completely synthetic and highly symmetrical terminator was constructed by replacing the 13 nt segment of the A site of TerI with an opposed segment identical to that in the B site. The efficient bidirectional activity of this new terminator, TerSymB, established more firmly the need for two opposed RTP binding sites in a functional terminator. TerSymB was used to investigate the effect of sequence deviation in one of the 13 nt segments, from that in the B site, on bidirectionality of the terminator. It was found that the deviations introduced converted the terminator significantly towards polarity of action. The partial symmetry within each of the 13 nt segments of TerSymB, and the presumed recognition of this symmetry in the binding of a symmetrical dimer of RTP to each overlapping site, suggest that the bound dimers are centred over positions in the DNA sequence separated by 15 nt. This separation distance has been used in conjunction with the mode of binding of RTP to DNA proposed by Bussiere et al., based on their crystal structure for RTP, to model the interaction of the two dimers of RTP with unbent B-form DNA. Increased separation of the two binding sites of TerSymB was performed by inserting an extra three, seven or ten nucleotides centrally within the TerSymB sequence. The effects of these insertions on RTP binding and fork arrest activity were consistent with the proposed positioning of the RTP dimers within the terminator sequence, and interaction between the dimers bound to TerSymB. A model to account for the generation of RTP-terminator complexes with bidirectional or polar fork arrest activity utilising TerSymB or TerI-VI is presented.

Bacillus subtilis↗
PubMed1996

Hematotoxicity among Chinese workers heavily exposed to benzene.

Benzene is a well-established hematotoxin. However, reports of its effects on specific blood cells have been somewhat inconsistent and the relative toxicity of benzene metabolites on peripheral blood cells in humans has not been evaluated. We compared hematologic outcomes in a cross-sectional study of 44 workers heavily exposed to benzene (median: 31 parts permillion [ppm] as an 8-hr time-weighted average [TWA] and 44 age and gender-matched unexposed controls from Shanghai, China. All hematologic parameters (total white blood cells [WBC], absolute lymphocyte count, platelets, red blood cells, and hematocrit) were decreased among exposed workers compared to controls, with the exception of the red blood cell mean corpuscular volume (MCV), which was higher among exposed subjects. In a subgroup of workers who were not exposed to more than 31 ppm benzene on any of 5 sampling days (n = 11, median 8 hr TWA = 7.6 ppm, range = 1-20 ppm), only the absolute lymphocyte count was significantly different between exposed workers (mean [sd]1.6 [0.4] x 10(3) mu L) and controls (1.9 [0.4] x l0(3) uL, p = 0.03). Among exposed subjects, a dose response relationship with various measures of current benzene exposure (i.e., personal air monitoring, benzene metabolites in urine) was present only for the total WBC count, the absolute lymphocyte count, and the MCV. Correlations between benzene metabolites and hematologic parameters were generally similar, although hydroquinone was somewhat more strongly associated with a decrease in the absolute lymphocyte count, and catechol was more strongly associated with an increase in MCV. Morphologic review of peripheral blood slides demonstrated an excess of red blood cell abnormalities (i.e., stomatocytes and target cells) only in the most heavily exposed workers, with no differences in granulocyte, lymphocyte, or platelet morphology noted. Although benzene can affect all the major peripheral blood elements, our results support the use of the absolute lymphocyte count as the most sensitive indicator of benzene-induced hematotoxicity.

Adult↗
PubMed1996

Use of the fluorescent micronucleus assay to detect the genotoxic effects of radiation and arsenic exposure in exfoliated human epithelial cells.

The exfoliated cell micronucleus (MN) assay using fluorescent in situ hybridization (FISH) with a centromeric probe is a rapid method for determining the mechanism of MN formation in epithelial tissues exposed to carcinogenic agents. Here, we describe the use of this assay to detect the presence or absence of centromeric DNA in MN induced in vivo by radiation therapy and chronic arsenic (As) ingestion. We examined the buccal cells of an individual receiving 6,500 rads of photon radiation to the head and neck. Exfoliated cells were collected before, during, and after treatment. After radiation exposure a 16.6-fold increase in buccal cell MN frequency was seen. All induced MN were centromere negative (MN-) resulting from chromosome breakage. This finding is consistent with the clastogenic action of radiation and confirmed the reliability of the method. Three weeks post-therapy, MN frequencies returned to baseline. We also applied the assay to exfoliated bladder cells of 18 people chronically exposed to high levels of inorganic arsenic (In-As) in drinking water (average level, 1,312 micrograms As/L) and 18 matched controls (average level, 16 micrograms As/L). The combined increase in MN frequency was 1.8-fold (P = 0.001, Fisher's exact test). Frequencies of micronuclei containing acentric fragments (MN-) and those containing whole chromosomes (MN+) both increased (1.65-fold, P = 0.07, and 1.37-fold, P = 0.15, respectively), suggesting that arsenic may have both clastogenic and weak aneuploidogenic properties in vivo. After stratification on sex, the effect was stronger in male than in female bladder cells. In males the MN- frequency increased 2.06-fold (P = 0.07) while the frequency of MN+ increased 1.86-fold (P = 0.08). In addition, the frequencies of MN- and MN+ were positively associated with urinary arsenic and its metabolites. However, the association was stronger for micronuclei containing acentric fragments. By using FISH with centromeric probes, the mechanism of chemically induced genotoxicity can now be determined in epithelial tissues.

Adult↗
PubMed1996

Effects of morphine-3-glucuronide and morphine on the K+-evoked release of [3H]-glutamic acid and [14C]-gamma-aminobutyric acid from rat brain synaptosomes.

The effects of morphine-3-glucuronide (M3G) and morphine on the K+-evoked release of [14C]-gamma-aminobutyric acid (GABA) and [3 H]-glutamic acid were investigated in rat brain synaptosomes using superfusion techniques. K+-evoked release of both [14C]-GABA and [3H]-glutamic acid from rat brain synaptosomes was eliminated in the absence of calcium, indicating that K+-evoked neurotransmitter release was from vesicular stores in a manner analagous to that which occurs in vivo following an action potential (1). Addition of M3G or morphine in a range of concentrations (0.1-10 microM) to the superfusion medium did not alter the K+-evoked release of [14C]-GABA or [3H]-glutamic acid from rat brain synaptosomes, suggesting that the CNS excitation observed following central administration of M3G (2-5) and supra-analgesic doses of morphine (2,3,6,7) does not occur by a generalized inhibition of GABA release or facilitation of glutamic acid release from pre-synaptic nerve terminals.

Action Potentials↗
PubMed1996

Psychoactive constituents of the genus Sceletium N.E.Br. and other Mesembryanthemaceae: a review.

The use by the Khoisan of South Africa of Sceletium plants in psychoactive preparations has often been alluded to in the literature. However, much of it is fragmentary and contradictory. The current review reassembles the historical data recorded over a 300-year period, describes techniques for the preparation and use of "kougoed' from plants of Sceletium and documents the subjective experiences of a number of contemporary users. Apart from chewing the dried product, after "fermentation', there are reports of uses as tinctures for sedation and analgesia, chewing the material directly and smoking the residue after chewing. The symbolic connections of Sceletium with eland antelopes, the "trance animals' par excellence of the San hunter-gatherers is noted. Observations by Paterson (1789) and reports of contemporary users indicate a synergism and potentiation with smoked Cannabis. There is no evidence to support the view that "kougoed' or Sceletium alkaloids are hallucinogenic. The alkaloid distribution in Sceletium and other members of the family Mesembryanthemaceae are considered. Chemical studies have indicated as many as nine alkaloids in Sceletium which fall into three distinct structural categories. Mesembrine, the alkaloid first isolated and named is not the dominant constituent of plants and is weakly narcotic. Evidence is assembled to suggest that traditional and contemporary methods of preparation serve to reduce levels of potentially harmful oxalates, which are found in Sceletium and other Mesembryanthemaceae. It is concluded that there is a need for further pharmacological studies on these alkaloids, based on their narcotic-anxiolytic properties, strong synergism with other psychomimetics, moderate toxicity and anti-cancer activity.

Alkaloids↗
PubMed1996

Effects of meperidine on the pancreatic and biliary sphincter.

BACKGROUND: Opioids are traditionally avoided during sphincter of Oddi manometry because of indirect evidence suggesting that these agents cause sphincter of Oddi spasm. This study was undertaken to determine the direct effects of meperidine on the biliary and pancreatic sphincter. METHODS: Forty-seven patients were prospectively evaluated by sphincter of Oddi manometry in the conventional retrograde fashion. Manometry was initially performed with intravenous diazepam sedation alone. The manometry was repeated 3 to 5 minutes after meperidine was administered. RESULTS: The basal sphincter pressure of the biliary sphincter, pancreatic sphincter, and the combined sphincter group were not significantly altered by meperidine. Concordance (normal versus abnormal) between the basal sphincter pressure before and after meperidine was seen in 44 of 47 patients (94%). Meperidine produced a significant increase in the pancreatic, biliary, and combined sphincter phasic frequency and a significant decrease in the phasic duration. The pancreatic and combined sphincter phasic pressures were significantly reduced following meperidine administration. Seventeen manometry tracings (36%) were believed to be qualitatively better after meperidine, while only four (8.5%; p < .001) were qualitatively better with diazepam alone. CONCLUSION: Meperidine can be used for additional analgesia during sphincter of Oddi manometry if the basal sphincter pressure is the parameter used to determine therapy.

Humans↗
PubMed1996

Alterations in pancreatic ductal morphology following polyethylene pancreatic stent therapy.

BACKGROUND: Polyethylene stents placed in the main pancreatic duct induce morphologic alterations that may resemble chronic pancreatitis. METHODS: We reviewed the sequential pancreatograms of stented patients who had long-term follow-up after stent removal. RESULTS: Forty patients (66%) had a normal baseline pancreatogram, whereas 21 (34%) showed changes of chronic pancreatitis. In 49 of 61 patients (80.3%), one or more had new morphologic changes immediately after stent withdrawal graded as mild (69%), moderate (29%), or severe (2%). Changes included ductal irregularity (49%), narrowing (35.5%), and side branch change (15.5%). Sixteen of the 21 patients (76.1%) with an abnormal baseline pancreatogram had worsening of the baseline abnormality or additional changes while stented, whereas 33 of 40 (82.5%) with a normal baseline developed new morphologic changes. Correlation of stent-induced changes with stent size, length, patency at removal, and duration of stenting failed to show an association. Twenty-five patients with stent-induced changes had a follow-up pancreatogram at a mean of 192 days (10 to 740) after stent removal. There was complete resolution of the changes in 64%, partial resolution in 32%, and no improvement in 5%. CONCLUSION: Morphologic changes induced by polyethylene pancreatic duct stents occurred in 80% of patients. More than one third of these changes did not resolve during the follow-up period. Because of concern over stent-induced fibrosis, the use of pancreatic stents should remain largely experimental.

Follow-Up Studies↗
PubMed1996

Stent-induced pancreatic ductal and parenchymal changes: correlation of endoscopic ultrasound with ERCP.

BACKGROUND: Polyethylene pancreatic duct stents induce morphologic changes of the pancreatic duct in the majority of patients. This study was undertaken to determine if parenchymal abnormalities are present in patients undergoing short-term pancreatic duct stenting and to correlate these findings with the pancreatogram obtained at stent removal. METHODS: Twenty-five patients underwent pancreatic duct stenting and had an endoscopic ultrasound evaluation of the pancreas at stent removal. The pancreatograms were evaluated at stent removal for ductal irregularity, narrowing, and side branch changes. Endoscopic ultrasound was used to assess for differences in the echo characteristics of the pancreatic parenchyma around the stent compared with the rest of the gland. RESULTS: Of the 16 patients evaluated by ERCP at stent removal, 9 (56%) had 1 or more new ductographic changes. Endoscopic ultrasound identified parenchymal changes in the stented region in 17 of 25 patients (68%). Four patients who had parenchymal changes in the stented region on endoscopic ultrasound at stent removal had a follow-up study at a mean time of 16 months. Two patients had (new) changes suggestive of focal chronic pancreatitis in the stented region. CONCLUSION: Short-term pancreatic duct stenting induced both ductal and parenchymal changes in more than 50% of patients. Chronic pancreatitis may be a consequence of pancreatic duct stenting.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1996

Tetrasomy 8 detected by interphase cytogenetics in a child with acute lymphocytic leukemia.

Tetrasomy 8 is a rare clonal anomaly in human acute leukemia. Here we present a case of a 7-year-old boy with acute lymphoblastic leukemia (ALL) displaying a tetrasomy 8 clone that could not be detected by conventional cytogenetics. In this study, bone marrow and peripheral blood cells were collected at five different diagnostic stages and analyzed by double targeted fluorescence in situ hybridization (FISH) with centromeric DNA probes for chromosomes 7, 8, 9, and 12. FISH analysis revealed a significant increase in tetrasomy 8 frequency, but not in other chromosomes examined. A smaller increase in trisomy 8 was also detected. At one stage over 60% of the cells were hyperdiploid with 40% being tetrasomic. The size of the tetrasomic clone changed during the course of the disease. The hyperdiploid frequencies of chromosome 8 detected by interphase FISH analysis in bone marrow and peripheral blood were similar. Our findings indicate the utility of FISH analysis in cytogenetic monitoring of leukemia patients and further show that tetrasomy 8 may play a specific role in a subtype of ALL.

Aneuploidy↗
PubMed1996

Dyadic deaths involving Huntington's disease: a case report.

Huntington's disease is a hereditary neurodegenerative disorder characterized by involuntary choreiform movements and progressive dementia. Although controversy exists regarding the exact risk of suicide in patients with Huntington's chorea, the literature supports an increased risk of suicide, especially in the early stages of this disease. We describe a case of homicide-suicide involving a father and son. The 60-year-old father, the homicide victim, suffered from advanced Huntington's disease; his 30-year-old son, the assailant, had a history of depression but had not been diagnosed with Huntington's disease at the time of his suicide. The psychiatric implications of this dementing disease, including the risk of suicide, are discussed. The gross, histologic, and molecular genetic features of this neurodegenerative disease are also described. The recognition of this autosomal dominantly inherited disorder at autopsy can make a profound impact on the lives of surviving family members.

Adult↗
PubMed1996

Overview of benzene-induced aplastic anaemia.

The scientific literature is replete with reports of cases of benzene-induced toxicity to the haematopoietic system. These mainly involve aplastic anaemia, the first cases of which were reported in 1897. At high level of benzene exposure (air concentration > 100 p.p.m.), the incidence of aplastic anaemia is approximately 1/100 individuals exposed, but this drops precipitously at lower levels of exposure (10-20 p.p.m.) to around 1/10,000. Factors that affect susceptibility may include high liver cytochrome P450 2E1 activity and low folic acid intake. The mechanism of benzene-induced aplastic anaemia remains unclear, but is likely to involve: (a) metabolism of benzene in the liver; (b) transport of metabolites to the marrow and their secondary activation to toxic quinones and free radicals by peroxidase enzymes; (c) induction of apoptosis, DNA damage and altered differentiation in early progenitor cells; and (d) depletion of the stem cell pool.

Anemia, Aplastic↗
PubMed1996

The mechanism of benzene-induced leukemia: a hypothesis and speculations on the causes of leukemia.

An overall hypothesis for benzene-induced leukemia is proposed. Key components of the hypothesis include a) activation of benzene in the liver to phenolic metabolites; b) transport of these metabolites to the bone marrow and conversion to semiquinone radicals and quinones via peroxidase enzymes; c) generation of active oxygen species via redox cycling; d) damage to tubulin, histone proteins, topoisomerase II, other DNA associated proteins, and DNA itself; and e) consequent damage including DNA strand breakage, mitotic recombination, chromosome translocations, and aneuploidy. If these effects take place in stem or early progenitor cells a leukemic clone with selective advantage to grow may arise, as a result of protooncogene activation, gene fusion, and suppressor gene inactivation. Epigenetic effects of benzene metabolites on the bone marrow stroma, and perhaps the stem cell itself, may then foster development and survival of the leukemic clone. Evidence for this hypothesis is mounting with the recent demonstration that benzene induces gene-duplicating mutations in human bone marrow and chromosome-specific aneuploidy and translocations in peripheral blood cells. If this hypothesis is correct, it also potentially implicates phenolic and quinonoid compounds in the induction of "spontaneous" leukemia in man.

Aneuploidy↗
PubMed1996

Interphase cytogenetics of workers exposed to benzene.

Fluorescence in situ hybridization (FISH) is a powerful new technique that allows numerical chromosome aberrations (aneuploidy) to be detected in interphase cells. In previous studies, FISH has been used to demonstrate that the benzene metabolites hydroquinone and 1,2,4-benzenetriol induce aneuploidy of chromosomes 7 and 9 in cultures of human cells. In the present study, we used an interphase FISH procedure to perform cytogenetic analyses on the blood cells of 43 workers exposed to benzene (median = 31 ppm, 8-hr time-weighted average) and 44 matched controls from Shanghai, China. High benzene exposure (> 31 ppm, n = 22) increased the hyperdiploid frequency of chromosome 9 (p < 0.01), but lower exposure (< or = 31 ppm, n = 21) did not. Trisomy 9 was the major form of benzene-induced hyperdiploidy. The level of hyperploidy in exposed workers correlated with their urinary phenol level (r = 0.58, p < 0.0001), a measure of internal benzene dose. A significant correlation was also found between hyperdiploidy and decreased absolute lymphocyte count, an indicator of benzene hematotoxicity, in the exposed group (r = -0.44, p = 0.003) but not in controls (r = -0.09, p = 0.58). These results show that high benzene exposure induces aneuploidy of chromosome 9 in nondiseased individuals, with trisomy being the most prevalent form. They further highlight the usefulness of interphase cytogenetics and FISH for the rapid and sensitive detection of aneuploidy in exposed human populations.

Adult↗
PubMed1996

An epidemiologic study of early biologic effects of benzene in Chinese workers.

Benzene is a recognized hematotoxin and leukemogen, but its mechanisms of action in humans are still uncertain. To provide insight into these processes, we carried out a cross-sectional study of 44 healthy workers currently exposed to benzene (median 8-hr time-weighted average; 31 ppm), and unexposed controls in Shanghai, China. Here we provide an overview of the study results on peripheral blood cells levels and somatic cell mutation frequency measured by the glycophorin A (GPA) gene loss assay and report on peripheral cytokine levels. All peripheral blood cells levels (i.e., total white blood cells, absolute lymphocyte count, platelets, red blood cells, and hemoglobin) were decreased among exposed workers compared to controls, with the exception of the red blood cell mean corpuscular volume, which was higher among exposed subjects. In contrast, peripheral cytokine levels (interleukin-3, interleukin-6, erythropoietin, granulocyte colony-stimulating factor, tissue necrosis factor-alpha) in a subset of the most highly exposed workers (n = 11) were similar to values in controls (n = 11), suggesting that benzene does not affect these growth factor levels in peripheral blood. The GPA assay measures stem cell or precursor erythroid cell mutations expressed in peripheral red blood cells of MN heterozygous subjects, identifying NN variants, which result from loss of the GPA M allele and duplication of the N allele, and N phi variants, which arise from gene inactivation. The NN (but not N phi) GPA variant cell frequency was elevated in the exposed workers compared with controls (mean +/- SD, 13.9 +/- 8.4 mutants per million cells versus 7.4 +/- 5.2 per million cells, (respectively; p = 0.0002), suggesting that benzene produces gene-duplicating but not gene-inactivating mutations at the GPA locus in bone marrow cells of exposed humans. These findings, combined with ongoing analyses of benzene macromolecular adducts and chromosomal aberrations, will provide an opportunity to comprehensively evaluate a wide range of early biologic effects associated with benzene exposure in humans.

Adult↗
PubMed1996

Population toxicokinetics of benzene.

In assessing the distribution and metabolism of toxic compounds in the body, measurements are not always feasible for ethical or technical reasons. Computer modeling offers a reasonable alternative, but the variability and complexity of biological systems pose unique challenges in model building and adjustment. Recent tools from population pharmacokinetics, Bayesian statistical inference, and physiological modeling can be brought together to solve these problems. As an example, we modeled the distribution and metabolism of benzene in humans. We derive statistical distributions for the parameters of a physiological model of benzene, on the basis of existing data. The model adequately fits both prior physiological information and experimental data. An estimate of the relationship between benzene exposure (up to 10 ppm) and fraction metabolized in the bone marrow is obtained and is shown to be linear for the subjects studied. Our median population estimate for the fraction of benzene metabolized, independent of exposure levels, is 52% (90% confidence interval, 47-67%). At levels approaching occupational inhalation exposure (continuous 1 ppm exposure), the estimated quantity metabolized in the bone marrow ranges from 2 to 40 mg/day.

Bayes Theorem↗
PubMed1996

mhatomic pathology turnaround times. Use and abuse.

Anatomic pathology service is judged by accuracy of diagnosis and rapidity of reporting of that diagnosis to clinicians. Turnaround times have been used in anatomic pathology to show how long it take to produce a tissue report. Rapid tissue diagnosis is important to patients, clinicians, administrators, and anatomic pathologists. Documentation of turnaround times (TAT) to substantiate efficient service can be similarly important. The authors describe how turnaround times can be used and discuss their impact from different perspectives.

Humans↗
PubMed1995

Babjevia gen. nov.--a new genus of the Lipomycetaceae.

The species described as Lipomyces anomalus Babjeva & Gorin shows significant genetic and phenotypic divergence from the type species Lipomyces starkeyi Lodder & Kreger-van Rij in terms of rRNA base sequence substitution and ascosporal and septal ultrastructure. The species is consequently reclassified in the new, unispecific genus Babjevia, as Babjevia anomala.

Microscopy, Electron↗