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Biomedical subjects

S Freeman

Publications and source records attributed to S Freeman.

At least 19 recordsLinked to original sources
PubMed1992

Cloning, overexpression and mechanistic studies of carboxyphosphonoenolpyruvate mutase from Streptomyces hygroscopicus.

The enzyme carboxyphosphonoenolpyruvate mutase catalyses the formation of one of the two C-P bonds in bialaphos, a potent herbicide isolated from Streptomyces hygroscopicus. The gene encoding the enzyme has been cloned from a subgenomic library from S. hygroscopicus by colony hybridisation using an exact nucleotide probe. An open reading frame has been identified that encodes a protein of molecular mass 32700 Da, in good agreement with the subunit molecular mass of the carboxyphosphonoenolpyruvate mutase recently isolated from this source [Hidaka, T., Imai, S., Hara, O., Anzai, H., Murakami, T., Nagaoka, K. & Seto, H. (1990) J. Bacteriol. 172, 3066-3072]. The gene shares significant sequence similarity with that of phosphoenolpyruvate mutase, an enzyme that catalyses the related interconversion of phosphoenolpyruvate and phosphonopyruvate. When the carboxyphosphonoenolpyruvate-mutase gene was subcloned into the vector pET11a, the mutase was expressed as about 20% of the total soluble cellular protein in Escherichia coli. The mutase has been purified to homogeneity in three steps in 40% yield. With malate dehydrogenase/NADH, (hydroxyphosphinyl)pyruvate gives (hydroxyphosphinyl)lactate (kcat 164 s-1 and Km 680 microM) and this spectrophotometric assay for the product of the mutase reaction has been employed in the mechanistic studies. The kinetics for the mutase reaction have been evaluated for the substrate, carboxyphosphonoenolpyruvate, and for the putative reaction intermediate carboxyphosphinopyruvate, both of which have been prepared by chemical synthesis. Carboxyphosphonoenolpyruvate is converted to (hydroxyphosphinyl)pyruvate with a kcat of 0.020 s-1 and a Km of 270 microM, and carboxyphosphinopyruvate is converted to (hydroxyphosphinyl)pyruvate with a kcat of 7.6 x 10(-4) s-1 and a Km of 2.2 microM. Although the exogenously added intermediate is not kinetically competent, these results suggest that the mechanism for the mutase reaction involves an initial rearrangement to the intermediate carboxyphosphinopyruvate, followed by decarboxylation to yield the product (hydroxyphosphinyl)pyruvate.

Amino Acid Sequence↗
PubMed1992

Is metabolism an important arbiter of anticancer activity of ether lipids? Metabolism of SRI 62-834 and hexadecylphosphocholine by [31P]-NMR spectroscopy and comparison of their cytotoxicities with those of their metabolites.

Antineoplastic ether lipids have entered phase I clinical trial and, although their mechanism of action remains unclear, it is widely believed that the plasma membrane is the primary cellular drug target. In the present study the hypothesis was tested that metabolism of ether lipids acts as a detoxification process. [31P]-nuclear magnetic resonance (NMR) spectroscopy was used to study the metabolism of the ether lipid SRI 62-834 (SRI) and the phosphate ester hexadecylphosphocholine (HPC) in the presence of both isolated phospholipases C and D and post-mitochondrial rat liver homogenate. Both SRI and HPC were slowly metabolised by phospholipase D to their alkyl phosphates and choline, and the alkyl phosphates were subsequently metabolised by phosphatase to yield the alcohols and inorganic phosphate. These studies failed to detect any metabolism of either SRI or HPC by phospholipase C, and the metabolism of platelet-activating factor (PAF) by this enzyme was not inhibited by the addition of either compound. The cytotoxicity of SRI, the related compound HPC and their metabolites was determined in vitro using three cell lines. Cytotoxicity was measured by analysis of cell growth kinetics, MTT assay and lactate dehydrogenase release. Closely similar results were obtained in the JB1 rat hepatoma cell line, in the non-transformed BL8 rat hepatocyte cell line, and in A549 human lung adenocarcinoma cells. SRI was the most toxic of the compounds analysed, the concentration required to produce 50% toxicity or growth inhibition (IC50) being 6-9 microM. The putative metabolite of SRI, 2,2'-bis(hydroxymethyl)tetrahydrofuran, and the known metabolites [2'-(octadecyloxymethyl)tetrahydrofuran-2'-yl]methyl phosphate and 2-hydroxymethyl-2-octadecyloxymethyltetrahydrofuran exhibited IC50 values of > 200, > 100 and 40-70 microM, respectively, consistent with metabolic detoxification. HPC was more cytotoxic (IC50, 37 microM) than its phosphate metabolite (IC50, 140 microM), but its toxicity was similar to that of its metabolite hexadecanol (IC50, 28 microM), suggesting that only the former metabolic route leads to detoxification.

Adenocarcinoma↗
PubMed1992

Photodynamic inactivation of retrovirus by benzoporphyrin derivative: a feline leukemia virus model.

The ability of a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA), and either broad-spectrum (400-1200 nm) or narrow-band (600-700 nm) red light to kill feline leukemia virus (FeLV) and FeLV-infected cat T cells (cell line 3201) was investigated in culture medium containing fetal calf serum and in blood from infected cats. A molecular clone of FeLV, 61E, is minimally pathogenic and productively infects 3201 cells while causing no change in rate of cell division, viability, or size. Active virus (either free or within infected cells) was quantified by using a limiting dilution assay that involved cocultivation of test samples with naive 3201 cells, after which either the polymerase chain reaction or a reverse transcriptase assay was used to detect the presence of virus. It was shown that 61E-infected T cells in culture were slightly more sensitive to photodynamic killing than were uninfected cells. Infected cells and free virus were eliminated from whole blood taken from infected cats by using 4 micrograms per mL of BPD-MA and 40 J per cm2 of red light. These results correlate well with previous results with BPD-MA and vesicular stomatitis virus in whole human blood and suggest that this photosensitizer is a promising agent for the elimination of retroviruses that are either free or located within infected cells in blood.

Animals↗
PubMed1992

Effects of a nursing education intervention on parents' knowledge of hydrocephalus and shunts.

The purpose of this nursing intervention study, which used a pre- and posttest design, was to determine the effect of an education program on parents' knowledge of hydrocephalus and shunt dynamics in a sample of parents of children with hydrocephalus. Study participants were parents of hydrocephalic children treated with an initial shunt or a shunt revision. The convenience sample of 41 subjects was divided into two groups (A or B). Group A participants were parents whose child received an initial shunt. Group B participants were parents whose child was admitted for a shunt revision. The shunt education intervention had three components: a shunt handbook, a preoperative teaching session with the clinical nurse specialist and a subsequent reinforcement teaching session. The pre- and posttest were the same seven multiple choice questions on hydrocephalus and shunts. In both groups, the pretest was given before the shunt education intervention. The posttest was given 2-3 weeks after the patient's surgery. There was a statistically significant change in the scores from the pre- and posttests for Group A (p = 0.0092). The nursing education appeared to have a positive effect upon this group's knowledge of hydrocephalus and shunts.

Adolescent↗
PubMed1992

Occupational contact dermatitis in New South Wales.

Five hundred and seventy patients with occupational contact dermatitis (OCD) were seen between 1984 and 1990 at the Skin and Cancer Foundation in Sydney. Data derived from these patients demonstrated that hairdressing, food, construction and the medical industries were the most at risk of OCD. The hairdressing and food industries had a high percentage of apprentices suffering OCD whilst the 35 to 44 year age bracket was most at risk in the construction industry. Allergic contact dermatitis was responsible for 38.2% of cases. The main allergens were chromate, thiuram, epoxy resin, nickel and cobalt. A third (33.9%) of patients were atopic. The average time lost from work was 16 days each year and the calculated yearly cost of OCD in New South Wales was approximately $12 million.

Adolescent↗
PubMed1992

Cerebral metabolic responses and vasopressin and oxytocin secretions during progressive water deprivation in rats.

Progressive water deprivation increased plasma osmolality, plasma Na+ concentration, and hematocrit in proportion to the severity of dehydration. With increases of 2% in plasma osmolality (24 h dehydration), glucose utilization increased in the supraoptic nuclei and tended to increase in the neural lobe. With further dehydration, glucose utilization also increased in the paraventricular nuclei. These increases were paralleled by depletion of vasopressin and oxytocin contents in the neural lobe and by the enhanced secretion of both hormones into plasma, with a predominant increase of vasopressin. These changes were proportional to the degree of dehydration. With progression of dehydration, decreases in intracellular and extracellular volumes accentuate. Reductions in extracellular volume result in increased angiotensin II (ANG II) formation. Accordingly, glucose utilization in the subfornical organ (SFO), a primary site of ANG II action, increased after 48 and 72 h of dehydration. The median preoptic nucleus, which receives direct inputs from the SFO, also increased glucose utilization at these times. Glucose utilization also increased in the organum vasculosum laminae terminalis, probably in response to the converging inputs from osmoreceptors, volume receptors, and ANG II receptors. Decreases in glucose utilization were observed in the caudal and rostral ventrolateral medulla, perhaps as compensatory responses to decreased extracellular volume to prevent fall in arterial blood pressure.

Animals↗
PubMed1991

Effects of chemical stimulation of the subfornical organ on metabolic activity of the hypothalamo-neurohypophysial system in rats.

Topical stimulation of the subfornical organ (SFO) with angiotensin II (ANG II) or acetylcholine (ACh) increased blood pressure, water intake, and the activity of the hypothalamo-neurohypophysial system (HNS). The pressor and drinking responses were higher and the metabolic activity of the HNS, measured with the [14C]deoxyglucose (DG) method, was lower with ANG-II than with ACh. Glucose utilization in the neural lobe increased by 165% with ACh as opposed to 65% with ANG II. These results demonstrate the ANG II and ACh mobilize differentially the mechanisms increasing blood pressure, drinking responses, and the activity of the HNS.

Acetylcholine↗
PubMed1991

Urticarial contact dermatitis in food handlers.

OBJECTIVE: To show that prick testing (using fresh samples of the food suspected from the patient's history) and not only patch testing is the appropriate investigation in selected cases of hand dermatitis in patients who spend considerable time handling foods (for example, catering workers, cooks). SETTING: The Contact and Occupational Dermatitis Clinic at the Skin and Cancer Foundation, a tertiary referral centre in Sydney. PATIENTS: Fourteen patients with hand dermatitis present for an average of 6.17 years referred by dermatologists and occupational health physicians. INTERVENTIONS: Patch and prick tests were performed for each patient. RESULT: In all patients prick tests identified the food allergens. Seafood was the most common allergen giving positive results in 10 patients. Patch tests did not identify any of the food allergens. Of the 14 patients nine were followed up and seven of these had been forced to change their career direction. CONCLUSION: Prick testing is the appropriate investigation in selected cases for the diagnosis of urticarial contact dermatitis in food handlers.

Adolescent↗
PubMed1991

The effect of stimulus repetition rate on the diagnostic efficacy of the auditory nerve-brain-stem evoked response.

This study investigates the hypothesis that an increase in the click presentation rate during diagnostic testing with the auditory nerve-brain-stem response (ABR) will increase the efficiency with which lesions may be detected in the nervous system. Cats were exposed to conditions of hypoxia, hypercapnia and acidemia, and hypoglycemia was induced in rats. ABR was recorded using the standard 10/sec click rate and also a higher (55/sec) rate during both the control state and experimental state. Various parameters of the ABR were compared at the two click rates in the control and experimental states to see if the higher click rate was more effective in detecting pathology in the nervous system. It was found that in only a very few cases was the higher stimulus presentation rate more effective, and that in general ABR recordings at one stimulus rate only is quite sufficient for work in a clinical setting.

Acidosis↗
PubMed1991

Contrast sensitivity of optokinetic nystagmus.

To determine the threshold characteristics of optokinetic nystagmus (OKN), contrast thresholds for involuntary OKN were measured for gratings of different spatial frequency to yield an OKN-contrast sensitivity function (OKN-CSF). The OKN-CSF resembled an inverted U-shaped function with temporal-to-nasal and nasal-to-temporal movement yielding similar functions. In addition, when psychophysical CSFs were determined for separate form and movement thresholds, it was discovered that the OKN-CSF approximated the psychophysical-movement CSF rather than the psychophysical-form CSF.

Adult↗
PubMed1991

Hypoxia induced hearing loss in animal models of the fetus in-utero.

The human fetus in-utero has low arterial oxygen tension. It has, therefore, been suggested that at greater than 28 weeks gestational age, the fetus may have a sensori-neural hearing loss comparable to that seen in adult cats exposed to similar degrees of hypoxia. This is due to hypoxia induced depression of the endocochlear potential. However, fetal blood is provided with compensatory mechanisms (elevated hematocrit and hemoglobin and special fetal hemoglobin) which enable pick up and transport of more oxygen from the placenta than adult blood under the same physiological conditions. Therefore, the hypothesis of a fetal sensori-neural hearing loss due to oxygen lack was tested in the following animal models: a) Adult cats to which feline red blood cells were infused thus causing a polycythemia similar to fetal conditions; b) Adult rats acclimated to altitude in a hypobaric chamber, inducing erythropoiesis with elevated hematocrit and hemoglobin; c) Neonatal guinea pigs and goats studied when they were less than 12 hours old so that the fetal compensatory mechanisms were still present. In each model, hypoxia (PaO2 20-30 mmHg) induced an ABR threshold elevation resembling that obtained in the uncompensated adult animal. Thus these experiments seem to have confirmed the hypothesis of a fetal, hypoxic induced sensori-neural hearing loss even though such experiments have not been conducted directly on fetal animals.

Animals↗
PubMed1991

Allergic contact dermatitis to ultra violet cured inks.

Two employees of a factory using an automated screen printing process and ultraviolet cured inks to print onto plastic bottles developed an allergic contact dermatitis, principally on the face and periorbital areas. On patch testing a contact allergy was found to the ultraviolet cured ink UV 50-85, and its multifunctional acrylic monomer component, tripropylene glycol diacrylate.

Acrylates↗
PubMed1991

The black and deaf movements in America since 1960. Parallelism and an agenda for the future.

This paper traces the political and educational movements of both black and hearing-impaired Americans since 1960 and compares their common as well as disparate but equally significant experiences. The purpose of the comparisons is to identify problems and proven solutions that collectively suggest a strategy for the continuing movement of hearing-impaired people. The authors, through their ethnicity--three are black and two are white--and personal and professional experiences bring divergent but relevant points of view to the question of multicultural coalitions and their abilities to effect social change. Four principles or suggestions for advancing the agenda of hearing-impaired Americans are presented: (1) the need to define the issues that will continue to confront hearing-impaired Americans through the year 2000, (2) the need to enlarge the membership and participation of existing coalitions, (3) the need to address local, vocational, technical, and educational issues, and (4) the need to facilitate hearing-impaired networking groups within religious, social, business, and cultural organizations.

Black or African American↗
PubMed1991

Auditory brainstem response (ABR) latency shifts in animal models of various types of conductive and sensori-neural hearing losses.

Clinical ABR studies in patients with peripheral hearing loss have led to conflicting results, some reporting increases in brainstem transmission time (BTT), some decreases, and others no change. In order to study this in a carefully controlled fashion, various types of peripheral hearing losses were induced in experimental animals: conductive hearing loss by occluding auditory meatus (rats) (CHL), noise induced temporary sensori-neural hearing loss (rats) (NI-SNHL), stimulus intensity attenuation (rats), (Atten.), and controlled hypoxemia induced temporary sensori-neural hearing loss (cats) (HI-SNHL). ABR latencies and thresholds were determined in each animal before (control) and during the induced hearing loss (experimental) states. The data in each group in each state were analyzed by calculating group average values for latency of waves 1 and 4, their interpeak latency (BTT), paired t-tests for changes between the control and experimental states and linear regression analysis of latency changes on threshold shift. In each group, there were small decreases in BTT in the experimental state (not significant in the CHL group only). This was caused by the prolongation of latency of wave 1 to a greater extent than that of wave 4. These changes were smaller than the standard deviation of the BTT in the control state. Therefore, in attempting to apply these results to the human clinical situation, these small decreases in BTT would not be considered abnormal. Possible mechanisms of these BTT changes are considered.

Animals↗
PubMed1990

The evolution of the scrotum: a new hypothesis.

The adaptive significance of the scrotum is unresolved after more than 60 years of debate and experimentation. The "training hypothesis" introduced here suggests that testicular descent is a mechanism for improving sperm quality. The hypothesis proposes that: (1) testicular descent decreases blood supply to maturing sperm cells, (2) sperm mitochondria respond to the resulting oxygen stress by enhancing their enzymatic machinery for oxidative metabolism, as do oxygen-stressed muscle cell mitochondria, and (3) the resulting increase in aerobic fitness of sperm cells is advantageous in inter-ejaculate competition. The hypothesis suggests that there is a quantity-quality trade-off in sperm production, where taxa with internal testes produce large volumes of low-quality sperm while taxa with scrotal testes produce smaller volumes of higher-quality sperm.

Animals↗
PubMed1990

Characterisation of a siderophore from Acinetobacter calcoaceticus.

The Gram-negative bacterium Acinetobacter calcoaceticus was examined for production of siderophores and iron-repressible outer membrane proteins following growth in iron-restricted media. The iron chelator, 2,3-dihydroxybenzoic acid was identified in the culture supernatant by 1H nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). A group of outer membrane proteins between 80 and 85 kDa were induced under iron restriction.

Acinetobacter↗
PubMed1990

Desmopressin, but not vasopressin, decreases activity of the hypothalamo-neurohypophysial system in Brattleboro rats.

The pituitary neural lobe of homozygous Brattleboro rats has high rates of glucose utilization not affected by chronic treatment with exogenous vasopressin, despite attenuation of polydipsia and polyuria. We evaluated whether this effect may result from the inability of vasopressin to affect the hypothalamo-neurohypophysial metabolism or from the development of resistance to chronic vasopressin treatment. We used the [14C]deoxyglucose method to compare 28-h effects of vasopressin treatment (5 U/kg, i.m., twice a day) with that of desmopressin (100 micrograms/kg, i.p., once a day), a long-lasting antidiuretic hormone, on glucose utilization of the hypothalamo-neurohypophysial system and related structures in conscious homozygous Brattleboro rats. Vasopressin and desmopressin reduced water intake, plasma osmolality and plasma Na+ concentration similarly. Vasopressin decreased glucose utilization in the supraoptic nucleus, subfornical organ and median preoptic nucleus, but did not alter activity in the paraventricular nucleus and neural lobe. Desmopressin decreased glucose utilization in all these structures. The results indicate that desmopressin has a more potent inhibitory action on the hypothalamo-neurohypophysial system than vasopressin over this short duration of treatment. The lack of response in the neural lobe from chronic treatment with vasopressin seems to be due to its inability to affect the paraventricular nucleus metabolism. The maintenance of metabolic activity in the paraventricular nucleus of vasopressin-treated Brattleboro rats suggests that this structure contributes importantly to the metabolism of neural lobe.

Animals↗