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Biomedical subjects

S A Roberts

Publications and source records attributed to S A Roberts.

At least 19 recordsLinked to original sources
PubMed2002

Development of a novel rapid assay to assess the fidelity of DNA double-strand-break repair in human tumour cells.

Cellular survival following ionising radiation-mediated damage is primarily a function of the ability to successfully detect and repair DNA double-strand breaks (DSBs). Previous studies have demonstrated that radiosensitivity, determined as a reduction in colony forming ability in vitro, may be related to the incorrect repair (misrepair) of DSBs. The novel rapid dual fluorescence (RDF) assay is a plasmid-based reporter system that rapidly assesses the correct rejoining of a restriction-enzyme produced DSBs within transfected cells. We have utilised this novel assay to determine the fidelity of DSB repair in the prostate tumour cell line LNCaP, the bladder tumour cell line MGH-U1 and a radiosensitive subclone S40b. The two bladder cell lines have been shown in previous studies to differ in their ability to correctly repair plasmids containing a single DSB. Using the RDF assay we found that a substantial portion of LNCaP cells [80.4 +/- 5.3(standard error)%] failed to reconstitute reporter gene expression; however, there was little difference in this measure of DSB repair fidelity between the two bladder cell lines (48.3 +/- 3.5% for MGH-U1; 39.9 +/- 8.2% for S40b). The RDF assay has potential to be developed to study the relationship between DSB repair fidelity and radiosensitivity as well as the mechanisms associated with this type of repair defect.

Cell Survival↗
PubMed2002

Chromosomal radiosensitivity in young cancer patients: possible evidence of genetic predisposition.

PURPOSE: To investigate the G2 chromosomal radiosensitivity of patients with cancers diagnosed when the patients are less than 20 years of age. Earlier studies demonstrated an enhanced sensitivity in substantial proportions of patients with breast or colorectal cancer, and in early onset head and neck cancer cases. Heritability of chromosomal radiosensitivity in families of breast cancer patients was also demonstrated. It is suggested that elevated sensitivity in this assay could be a marker of genetic predisposition to cancer, mediated through inherited genetic determinants of low penetrance. MATERIALS AND METHODS: Stimulated lymphocytes were exposed to 0.5 Gy X-rays in the G2-phase of the cell cycle and chromatid aberrations were scored in metaphase cells. RESULTS: The assay was performed on 32 patients with early onset cancers (aged 0.5-19 years) of various types and their sensitivity was compared with that of 41 young normal controls (0.25-19 years) and 32 adult normals (20-60 years). The proportion of cases showing enhanced sensitivity in the three groups was 44, 15 and 10%, respectively. The difference between the young patients and normals was highly significant (p = 0.004). CONCLUSIONS: The results suggest the possibility that a substantial proportion of early onset cancers are associated with the inheritance of predisposing genes of low penetrance. However, support for this hypothesis requires that the heritability of chromosomal radiosensitivity be demonstrated in family members. In addition, a larger study is now required to investigate the chromosomal radiosensitivity of specific early onset cancers.

Adolescent↗
PubMed2001

Tumor apoptosis in cervical cancer: its role as a prognostic factor in 42 radiotherapy patients.

To investigate tumor apoptosis as a prognostic factor for outcome following radiation therapy, comparisons were made of apoptotic index (AI) as a predictor of short- vs. long-term response and pretreatment vs. radiation-induced apoptosis. Forty-two patients with proven squamous cell carcinoma of the uterine cervix were treated by radiation alone. Apoptosis was measured by light microscopic observation of hematoxylin and eosin-stained sections from biopsies taken before treatment and 4 and 24 hr after 2 Gy. Patients were evaluated at the end of the external radiation for determination of short-term response and for long-term outcome as well (median follow-up of 27 months). Patients with high spontaneous AI showed poor short-term response, local control, and survival. The significance of AI as a predictor of short-term response was lost after allowing for differences in tumor size. The positive predictive value of AI for local control and survival was independent of tumor size and stage. High AI was associated with poor local control and long-term prognosis in advanced squamous cell carcinoma of the cervix. The in vivo radiation-induced AI after 4 or 24 hr did not predict radiation therapy outcome.

Adult↗
PubMed2001

Ligand-induced heme ruffling and bent no geometry in ultra-high-resolution structures of nitrophorin 4.

The nitrophorins are a family of proteins that use ferric heme to transport nitric oxide (NO) from the salivary glands of blood-sucking insects to their victims, resulting in vasodilation and reduced blood coagulation. We have refined atomic resolution structures of nitrophorin 4 (NP4) from Rhodnius prolixus complexed with NO (1.08 A) and NH(3) (1.15 A), yielding a highly detailed picture of the iron coordination sphere. In NP4-NO, the NO nitrogen is coordinated to iron (Fe-N distance = 1.66 A) and is somewhat bent (Fe-N-O angle = 156 degrees ), with bending occurring in the same plane as the proximal histidine ring. The Fe(NO)(heme)(His) coordination geometry is unusual but consistent with an Fe(III) oxidation state that is stabilized by a highly ruffled heme. Heme ruffling occurs in both structures, apparently due to close contacts between the heme and leucines 123 and 133, but increases on binding NO even though the steric contacts have not changed. We also report the structure of NP4 in complexes with histamine (1.50 A) and imidazole (1.27 A). Unexpectedly, two mobile loops that rearrange to pack against the bound NO in NP4-NO, also rearrange in the NP4-imidazole complex. This conformational change is apparently driven by the nonpolar nature of the NO and imidazole (as bound) ligands. Taken together, the desolvation of the NO binding pocket through a change in protein conformation, and the bending of the NO moiety, possibly through protein-assisted heme ruffling, may lead to a nitrosyl-heme complex that is unusually resistant to autoreduction.

Animals↗
PubMed2001

Lymphocyte radiosensitivity is a significant prognostic factor for morbidity in carcinoma of the cervix.

PURPOSE: To study the relationship between pretreatment peripheral blood lymphocyte radiosensitivity and morbidity following radiation therapy. METHODS AND MATERIALS: A prospective study was carried out in which patients with carcinoma of the cervix underwent radiation therapy. Intrinsic radiosensitivity was measured on pretreatment peripheral blood lymphocytes, using a limiting dilution clonogenic assay. Late morbidity was assessed using the Franco-Italian glossary. Results were correlated in an actuarial analysis. RESULTS: There were no correlations between the measured lymphocyte radiosensitivity (SF2) and colony-forming efficiency, patient age, tumor grade, or disease stage. For 83 patients, lymphocyte SF2 was a significant prognostic factor for the probability of developing both any (p = 0.002) and Grade 3 (p = 0.026) morbidity. In 174 patients, stage showed borderline significance as a prognostic factor for morbidity (p = 0.056). However, the type of treatment (intracavitary alone, intracavitary plus parametrial irradiation, single insertion plus whole-pelvis irradiation) was significantly associated with the probability of developing late complications (p = 0.013). There was a weak significant inverse correlation between lymphocyte SF2 and grade of morbidity (r = -0.34, p = 0.002). CONCLUSION: These data highlight the importance of normal cell radiosensitivity as a factor determining radiation therapy response. They also show that peripheral blood lymphocyte SF2 is a highly significant prognostic factor for the probability of developing late radiation morbidity, and that carcinoma of the cervix is a good model for testing radiobiologic principles in the clinic.

Age Factors↗
PubMed2001

Pneumococcal bacteraemia and opportunities for prevention.

AIMS: Despite availability of active antimicrobial agents for its treatment, the mortality from pneumococcal bacteraemia (PB) may reach 30% to 40% in high-risk groups. Greater vaccine use may reduce the incidence of PB. The aim of this study was to determine the proportion of patients with PB who had indications for, but had not received, pneumococcal vaccination. METHODS: From December 1998 to March 2000, all episodes of PB in adults in four Auckland hospitals were followed prospectively. Underlying disease, outcome, and pneumococcal vaccination history were recorded. RESULTS: 96 patients had PB: the median age was 63 years, range 16 to 93 years. 42 (44%) were > or = 65 years. The relative risk (RR) of acquiring PB for Maori and Pacific Island people was more than two times that of both European and other ethnic groups: RR 2.3 (95% CI 1.5 - 3.6) and 2.4 (1.6 - 3.8), respectively. The most common presentation was pneumonia; 84 (88%), of which 74 (88%) were community acquired. Five (5%) patients had meningitis. The overall mortality was 18%. Eleven (11%) pneumococcal isolates had intermediate susceptibility to penicillin and six (6%) were resistant. 69 (72%) patients had one or more condition for which pneumococcal vaccination is recommended but only two (2%) patients had received it. 82 (85%) patients were infected with serotypes included in the current pneumococcal vaccine. CONCLUSIONS: Most adult patients with PB have underlying medical conditions for which vaccination is recommended but only rare patients get vaccinated. Emerging antimicrobial resistance is a further incentive to increase the use of pneumococcal vaccination. Greater use of pneumococcal vaccine will probably require a change in its funding status, similar to the current policy for influenza vaccine. It may also be appropriate to consider targeted use of the vaccine in Maori and Pacific Island people given their higher rates of disease.

Adolescent↗
PubMed2001

Chromosomal radiosensitivity as a marker of predisposition to common cancers?

We previously found that 40% of breast cancer patients showed enhanced sensitivity to X-ray induced chromosome damage in G(2)lymphocytes and suggested that this might indicate a low penetrance predisposition to breast cancer, for which there is good epidemiological evidence. We have now tested the hypothesis that elevated G(2)radiosensitivity is a marker of such predisposition to other common cancers. We tested patients with colorectal cancer, for which there is also good epidemiological evidence of inherited risk in a substantial proportion of cases, and patients with cancers having a strong environmental aetiology (lung and cervix). We also repeated our study of breast cancer cases and tested patients with chronic diseases other than cancer. The results support our hypothesis, in that 30% (12/37) of colorectal cases showed enhanced sensitivity compared with 9% (6/66) of normal healthy controls (P = 0.01), whereas the proportions of sensitive cervix (11%, 3/27, P = 0.72) and lung cancer cases (23%, 8/35, P = 0.07) were not significantly above normals. We confirmed the enhanced sensitivity of 40% (12/31, P = 0.001) of breast cancer patients and found that patients with non-malignant disease had a normal response in the assay (12%, 4/34, P = 0.73). We suggest that enhanced G(2)chromosomal radiosensitivity is a consequence of inherited defects in the ability of cells to process DNA damage from endogenous or exogenous sources, of a type that is mimicked by ionizing radiation, and that such defects predispose to breast and colorectal cancer.

Adult↗
PubMed2001

Ribozyme minigene-mediated RAD51 down-regulation increases radiosensitivity of human prostate cancer cells.

The strand transferase RAD51 is a component of the homologous recombination repair pathway. To examine the contribution of RAD51 to the genotoxic effects of ionising radiation, we have used a novel ribozyme strategy. A reporter gene vector was constructed so that expression of an inserted synthetic double-stranded ribozyme-encoding oligonucleotide would be under the control of the cytomegalovirus immediate-early gene enhancer/promoter system. The prostate tumour cell line LNCaP was transfected with this vector or a control vector, and a neomycin resistance gene on the vector was used to create geneticin-resistant stable cell lines. Three stable cell lines were shown by western blot analysis to have significant down-regulation of RAD51 to 20-50% of the levels expressed in control cell lines. All three cell lines had a similar increased sensitivity to gamma-irradiation by 70 and 40%, respectively, compared to normal and empty vector-transfected cells, corresponding to dose-modifying factors of approximately 2.0 and 1.5 in the mid-range of the dose-response curves. The amount of RAD51 protein in transfected cell lines was shown to strongly correlate with the alpha parameter obtained from fitted survival curves. These results highlight the importance of RAD51 in cellular responses to radiation and are the first to indicate the potential use of RAD51-targeted ribozyme minigenes in tumour radiosensitisation.

Base Sequence↗
PubMed2001

Sensitivity to radiation-induced chromosome damage may be a marker of genetic predisposition in young head and neck cancer patients.

We previously showed that levels of chromosome damage induced by ionizing radiation were, on average, higher in G(2)and G(0)lymphocytes of breast cancer patients than of normal healthy controls, but that there was no correlation between the results in the two assays. We proposed that enhanced sensitivity to G(2)or G(0)irradiation was a marker of low-penetrance predisposition to breast cancer, and have recently demonstrated heritability of sensitivity in families of breast cancer cases. We have now applied these assays to patients with head and neck cancers, for whom there is epidemiological evidence of inherited predisposition in addition to environmental causes. The mean frequency of radiation-induced G(2)aberrations was higher in the 42 patients than in 27 normal controls, but not significantly so. However, cases less than 45 years old were significantly more sensitive than normals of the same age range (P = 0.046), whereas there was no difference between patients and normals of less than 45 years. Also, there was an inverse correlation between G(2)sensitivity and age for patients but not for normals. Radiation-induced micronuclei in G(0)cells were more frequent in 49 patients than in 31 normals (P = 0.056) but, as with the G(2)assay, the greatest difference was seen between early-onset patients and young normals. Again there was an inverse correlation with age for patients but not for normals. Six patients with enhanced toxicity to radiotherapy were G(2)tested and four other such patients were G(0)tested; levels of chromosome damage were not significantly greater than in patients with normal reactions. Both assays were used on 64 individuals (39 patients, 25 normals) and there was no significant correlation between the results. We suggest that a proportion of early-onset head and neck cancer patients are genetically predisposed and that each of the two assays detects a different subset of these cases.

Adult↗
PubMed2001

Infection of orthopedic prostheses after Staphylococcus aureus bacteremia.

We prospectively evaluated 53 patients with prosthetic joints and 27 patients with other orthopedic prosthetic devices who developed Staphylococcus aureus bacteremia (SAB). After exclusion of patients with primary postoperative infections, the risk of a prosthesis becoming infected by means of hematogenous seeding after SAB was 34% (15 of 44 patients) for prosthetic joints and 7% (1 of 15 patients) for other orthopedic prostheses.

Adult↗
PubMed2001

Normal tissue radiobiology: from the laboratory to the clinic.

This manuscript is in four parts, presenting the four talks given in a symposium on normal tissue radiobiology. The first part addresses the general concept of the role of parenchymal cell radiosensitivity vs. other factors, highlighting research over the last decade that has altered our understanding of factors underlying normal tissue response. The other three parts expand on specific themes raised in the first part dealing in particular with (1) modifications of fibroblast response to irradiation in relation to the induction of tissue fibrosis, (2) the use of the linear-quadratic equation to model the potential benefits of using different means (both physical and biologic) of modifying normal tissue response, and (3) the specific role of the growth factor TFG-beta1 in normal tissue response to irradiation. The symposium highlights the complexities of the radiobiology of late normal tissue responses, yet provides evidence and ideas about how the clinical problem of such responses may be modified or alleviated.

Animals↗
PubMed2001

The required number of treatment imaging days for an effective off-line correction of systematic errors in conformal radiotherapy of prostate cancer--a radiobiological analysis.

BACKGROUND AND PURPOSE: To use radiobiological modelling to estimate the number of initial days of treatment imaging required to gain most of the benefit from off-line correction of systematic errors in the conformal radiation therapy of prostate cancer. MATERIALS AND METHODS: Treatment plans based on the anatomical information of a representative patient were generated assuming that the patient is treated with a multi leaf collimator (MLC) four-field technique and a total isocentre dose of 72 Gy delivered in 36 daily fractions. Target position variations between fractions were simulated from standard deviations of measured data found in the literature. Off-line correction of systematic errors was assumed to be performed only once based on the measured errors during the initial days of treatment. The tumour control probability (TCP) was calculated using the Webb and Nahum model. RESULTS: Simulation of daily variations in the target position predicted a marked reduction in TCP if the planning target volume (PTV) margin was smaller than 4 mm (TCP decreased by 3.4% for 2 mm margin). The systematic components of target position variations had greater effect on the TCP than the random components. Off-line correction of estimated systematic errors reduced the decrease in TCP due to target daily displacements, nevertheless, the resulting TCP levels for small margins were still less than the TCP level obtained with the use of an adequate PTV margin of approximately 10 mm. The magnitude of gain in TCP expected from the correction depended on the number of treatment imaging days used for the correction and the PTV margin applied. Gains of 2.5% in TCP were estimated from correction of systematic errors performed after 6 initial days of treatment imaging for a 2 mm PTV margin. The effect of various possible magnitudes of systematic and random components on the gain in TCP expected from correction and on the number of imaging days required was also investigated. CONCLUSIONS: Daily variations of target position markedly reduced the TCP if small margins were used. Off-line correction of systematic errors can only partly compensate for these TCP reductions. The adequate number of treatment imaging days required for systematic error correction depends on the magnitude of the random component compared with the systematic component, and on the size of PTV margin used. For random components equal to or smaller than the systematic component, 3 consecutive treatment imaging days are estimated to be sufficient to gain most of the benefit from correction for current clinically used margins (6-10 mm); otherwise more days are required.

Humans↗
PubMed2001

Experience with laparoscopic ultrasonography for defining tumour resectability in carcinoma of the pancreatic head and periampullary region.

BACKGROUND: Computed tomography (CT) is currently the most widely available staging investigation for pancreatic tumours. However, the accuracy of CT for determining tumour resectability is variable and can be poor. Laparoscopic ultrasonography (LUS) is potentially a more accurate method for disease staging. The authors' experience of LUS for staging carcinoma of the pancreatic head and periampullary region is described. METHODS: Fifty-one patients with potentially resectable pancreatic tumours defined at CT underwent further investigation with LUS. Twenty-seven patients subsequently had an open laparotomy. The evaluations of tumour resectability at CT and LUS were compared with the operative findings. RESULTS: At LUS, 24 patients were considered to have resectable tumours, 21 non-resectable tumours and six patients were shown to have no pancreatic tumour mass. Twenty-two patients deemed to have a resectable tumour at LUS underwent surgery. Twenty patients were confirmed to have resectable disease and two patients had non-resectable disease. A further five patients underwent surgery. In all five the ultrasonographic diagnosis was confirmed at surgery (four patients with non-resectable disease and no pancreatic tumour in one patient). LUS prevented unnecessary extensive surgery in 53 per cent of patients. For the 22 patients who underwent surgery for potentially resectable disease, the positive predictive value of LUS for defining tumour resectability was 91 per cent. CONCLUSION: LUS is an accurate additional investigation for defining tumour resectability and directing management in patients with potentially resectable carcinoma of the pancreatic head or periampullary region.

Adult↗
PubMed2001

Investigation of an outbreak of multi-drug resistant Acinetobacter baumannii in an intensive care burns unit.

Over a three month period there was an outbreak of infection, due to a multi-drug resistant Acinetobacter baumannii in the intensive care burns unit with spread of infection to other patients, both within the unit and elsewhere in the hospital. Microbiological sampling of the environment and of the healthcare workers' (HCWs) hands were carried out. Strain relatedness of the isolates was confirmed by pulsed field gel electrophoresis. Fifteen patients were involved in the outbreak, whose infections were all hospital-acquired. The burns room environment was contaminated with the A. baumannii, as was the door handle of the door leading from the ante-chamber between both rooms. This allowed the hands of HCWs to be contaminated by A. baumannii despite appropriate handwashing procedures prior to leaving the rooms. Two staff members were colonized with A. baumannii. One HCW who was directly involved in patient care was found to be "heavily" colonized, the other, with less patient contact, was only "lightly" colonized. Review of handwashing practices revealed that chlorhexidine/alcohol hand wash solution was not used by the HCW whose hands were heavily colonized.A combination of a review of handwashing practice, education about the spread of bacteria via hands and contaminated environment, and the revision of infection control procedures in the unit contributed to a prompt termination of the outbreak.

Acinetobacter↗
PubMed2001

Tyrosine requirement of healthy men receiving a fixed phenylalanine intake determined by using indicator amino acid oxidation.

BACKGROUND: The currently accepted total aromatic amino acid requirement for adults is based on nitrogen balance measurements in individuals who received their intake of aromatic amino acids solely as phenylalanine. OBJECTIVE: The objective of this study was to determine the requirement for the amino acid tyrosine in healthy men receiving an adequate, but not excessive, intake of phenylalanine (9 mg x kg(-1) x d(-1)). DESIGN: The effect of a graded intake of tyrosine was determined in 6 healthy men consuming energy-sufficient diets containing 1 g protein x kg(-1) x d(-1). The tyrosine requirement was determined by using indicator amino acid oxidation methodology with L-[1-13C]lysine as the indicator. Subjects were studied at each of 7 tyrosine intakes. RESULTS: A graded intake of tyrosine had no effect on lysine flux. The mean tyrosine requirement was determined from the response of the oxidation of L-[1-13C]lysine to breath 13CO2. A 2-phase linear regression crossover analysis of breath 13CO2 identified the breakpoint and upper 95% confidence limit, which represents the mean and safe intakes, to be 6.0 and 7.0 mg x kg(-1) x d(-1), respectively. CONCLUSIONS: The safe intake of total aromatic amino acids calculated from the present results for tyrosine and our previous estimate for phenylalanine is estimated to be 21 mg x kg(-1) x d(-1). This intake is 1.5 times the currently recommended total aromatic amino acid intake of the FAO/WHO/UNU (1985), 14 mg x kg(-1) x d(-1). Furthermore, the absolute aromatic amino acid requirement may be dependent on the proportional balance of these amino acids in the diet.

Adult↗
PubMed2001

A new MMPI-derived indicator of liability to develop schizophrenia: evidence from the New York High-Risk Project.

A large body of research indicates that the liability to develop schizophrenia is largely genetically mediated, although phenotypic expression requires environmental triggers/insults and/or epigenetic and/or stochastic factors. In an effort to identify the precise environmental factors that precipitate a predisposition to schizophrenia, researchers have implemented a high-risk model-the prospective study of offspring born to schizophrenic parents. As it is difficult to ascertain exactly which of the "high-risk" participants will actually develop the disorder, we examined the validity of an experimental MMPI scale, Schizophrenia Proneness (SzP), and the Moldin-Gottesman psychometric index to identify such individuals. Results suggest that the SzP scale can be an effective predictor of schizophrenia-related psychoses. A revised psychometric index is offered for further study.

Adolescent↗
PubMed2001

The effect of graded intake of glycyl-L-tyrosine on phenylalanine and tyrosine metabolism in parenterally fed neonates with an estimation of tyrosine requirement.

Although tyrosine is considered indispensable during the neonatal period, its poor solubility has limited its inclusion in parenteral amino acid solutions to less than 1% of total amino acids. Dipeptides of tyrosine are highly soluble, have been shown to be well used and safe in animal models and humans, and, therefore, may be used as an effective means of providing tyrosine in the parenterally fed neonate. The goal of the present study was to determine the tyrosine requirement of the parenterally fed neonate receiving graded intakes of glycyl-L-tyrosine as a source of tyrosine. Thirteen infants receiving adequate energy (340 +/- 38 kJ. kg(-1).d(-1)) and protein (2.4 +/- 0.4 g.kg(-1).d(-1)) were randomized to receive parenteral nutrition with one of five graded levels of glycyl-L-tyrosine. The mean requirement and safe level of intake were estimated using a 1-(13)C-phenylalanine tracer and linear regression cross-over analysis that identified a break point in the response of label appearance in breath CO(2) (F(13)CO(2)) and phenylalanine oxidation to graded tyrosine intake. Based on the mean estimates of whole-body phenylalanine oxidation, the tyrosine mean requirement and safe level of intake were found to be 74 mg.kg(-1). d(-1) and 94 mg.kg(-1).d(-1), respectively. This represents 3.1 and 3.9% of total amino acids, respectively, considerably higher than levels found in present commercially available pediatric amino acid solutions. These data raise concern regarding the adequacy of aromatic amino acid intake in the parenterally fed neonate.

Amino Acids↗