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Biomedical subjects

G Stevens

Publications and source records attributed to G Stevens.

At least 19 recordsLinked to original sources
PubMed1995

Radiosensitization of mouse skin by oxygen and depletion of glutathione.

PURPOSE: To determine the oxygen enhancement ratio (OER) and shape of the oxygen sensitization curve of mouse foot skin, the extent to which glutathione (GSH) depletion radiosensitized skin, and the dependence of such sensitization on the ambient oxygen tension. METHODS AND MATERIALS: The feet of WHT mice were irradiated with single doses of 240 kVp x-rays while mice were exposed to carbogen or gases with oxygen/nitrogen mixtures containing 8-100% O2. The anoxic response was obtained by occluding the blood supply to the leg of anesthetized mice with a tourniquet, surrounding the foot with nitrogen, and allowing the mice to breathe 10% O2. Further experiments were performed to assess the efficacy of this method to obtain an anoxic response. Radiosensitivity of skin was assessed using the acute skin-reaction assay. Glutathione levels were modified using two schedules of DL-buthionine sulphoximine (BSO) and diethylmaleate (DEM), which were considered to produce extensive and intermediate levels of GSH depletion in the skin of the foot during irradiation. RESULTS: Carbogen caused the greatest radiosensitization of skin, with a reproducible enhancement of 2.2 relative to the anoxic response. The OER of 2.2 is lower than other reports for mouse skin. This may indicate that the extremes of oxygenation were not produced, although there was no direct evidence for this. When skin radiosensitivity was plotted against the logarithm of the oxygen tension in the ambient gas, a sigmoid curve with a K value of 17-21% O2 in the ambient gas was obtained. Depletion of GSH caused minimal radiosensitization when skin was irradiated under anoxic or well-oxygenated conditions. Radiosensitization by GSH depletion was maximal at intermediate oxygen tensions of 10-21% O2 in the ambient gas. Increasing the extent of GSH depletion led to increasing radiosensitization, with sensitization enhancement ratios of 1.2 and 1.1, respectively, for extensive and intermediate levels of GSH depletion. In mice exposed to 100% O2, a significant component of skin radiosensitivity was due to diffusion of oxygen directly through the skin. Pentobarbitone anesthesia radiosensitized skin in mice exposed to 100% O2 by a factor of 1.2, but did not further sensitize skin in mice exposed to carbogen. CONCLUSIONS: Glutathione levels and the local oxygen tension at the time of irradiation were important determinants of mouse foot skin radiosensitivity. The extent to which GSH levels altered the radiosensitivity of skin was critically dependent on the local oxygen tension. These results have significant implications for potential clinical application of GSH depletion.

Animals↗
PubMed1995

Patterns of fractionation for palliation of bone metastases.

The patterns of fractionation used to treat bone metastases in a single centre in two time periods were determined. Clinical audit was carried out, for two periods of 6 months each, in 1988 and 1993. Data recorded included patient, tumour and treatment variables. Palliation of bone metastases represented 40% and 44% of palliative treatment courses, and 20% and 21% of total treatment courses, respectively, in both time periods. Shorter treatment schedules were used in 1993 compared to 1988, with mean fraction numbers of 6.4 versus 8.5, respectively (P < 0.001). This reduction in fraction numbers occurred for the common primary tumour sites. In 1993, the mean numbers of fractions used were related to the primary tumour site (7.8 fractions for breast, 5.0 for lung, 6.7 for melanoma, 6.4 for other primary sites, P = 0.05), the treatment site (7.3 fractions for weight-bearing bones, 4.0 for non-weight-bearing bones, P < 0.001) and patient address (6.0 fractions for city postcode vs 7.8 for country postcode, P = 0.02). Treating radiation oncologist (5.7-7.8 mean fractions, P = 0.06) and patient age (P = 0.56) were not significant factors for the number of fractions used. It is likely that there were multiple causes for a reduction in the number of fractions used to treat bone metastases, including the results of clinical trials and increasing pressure to optimize the use of scarce resources. However, patients who may have a better prognosis (breast primary) and those with metastases in weight-bearing bones continued to receive longer treatment schedules.

Analysis of Variance↗
PubMed1995

An intragenic deletion of the P gene is the common mutation causing tyrosinase-positive oculocutaneous albinism in southern African Negroids.

Tyrosinase-positive oculocutaneous albinism (OCA2), an autosomal recessive disorder of the melanin biosynthetic pathway, is the most common recessive disorder occurring in southern African Bantu-speaking Negroids, with an overall prevalence of 1/3,900. The OCA2 gene, P, has been mapped to chromosome 15q11-q13, and recently alterations in the P gene have been identified in OCA2 individuals. An intragenic deletion has been described and proposed to be of African origin because of its occurrence in four unrelated African American OCA2 individuals and in two individuals, one from Zaire and the other from Cameroon. This study shows that the intragenic deletion is a common cause of OCA2 in southern African Negroids (114/146 [.78]; OCA2 chromosomes) and is associated with one common haplotype (43/55 [.78]; OCA2 chromosomes), confirming the African origin of this allele. On the basis of haplotype data, it would appear that at least seven additional, less frequent OCA2 mutations occur in this population.

Albinism, Oculocutaneous↗
PubMed1994

Beta/A4-evoked degeneration of differentiated SH-SY5Y human neuroblastoma cells.

beta/A4 peptides are known to induce neurodegeneration in cultures of rat brain cells and rat neural cell lines (Yankner et al: Science 250:279-282, 1990; Behl et al: Biochem Biophys Res Commun 186:944-950, 1992). The current data show that these peptides induce similar neurodegeneration in SH-SY5Y neuroblastoma cells, extending characterization of beta/A4 toxicity to a human nerve cell line. Human SH-SY5Y cells respond to aggregated beta/A4 with changes in cell shape, membrane blebbing, antigenic modification, loss of attachment to the substrate, and cell death. beta/A4 peptides require aggregation for maximum toxic effects, as cellular degeneration is evoked by aggregated beta/A4 1-42 and 4-41 cysteine but not by monomeric beta/A4 1-40. Aged (pre-aggregated) beta/A4 1-40 also evoked neurodegeneration. Antigenic changes comprise upregulation of Alzheimer's-type tau epitopes, recognized by the PHF-1 and Alz-50 monoclonals. These particular changes in tau support the connectivity between this in vitro model and mechanisms leading to neurodegeneration in Alzheimer's disease. A significant feature of the SH-SY5Y response is that cells must be differentiated before they become sensitive to the degeneration evoked by beta/A4. Signaling pathways leading to beta/A4-evoked neurodegeneration thus are under experimental control, becoming complete only when proliferating cells withdraw from the cell cycle and develop a postmitotic phenotype.

Alzheimer Disease↗
PubMed1994

Treatment of early carcinoma of the vocal cords by radiotherapy.

A total of 145 patients with early carcinoma of the vocal cords (T1,2N0) were treated by radiotherapy from 1979 to 1989. Survival and local control data were available for 135 and 127 patients, respectively. The respective 5 and 10 year results for overall survival were 75 and 68%. The 5 and 10 year probabilities of local control by radiotherapy were 89 and 86%, respectively, for T1 tumours and 70% at both time intervals for T2 tumours. Tumour recurrence following radiotherapy was documented in 18 of 127 patients. Tumour stage predicted significantly for local control, with recurrence rates for T1 and T2 tumours of 11 and 27%, respectively (P = 0.02). There was a higher proportion of recurrences for total radiation doses < or = 6200 cGy (17%) compared with > 6200 cGy (8%), but the difference was not statistically significant. Increasing duration of treatment was related significantly to increased recurrence for T2 (P = 0.01), but not T1, tumours. Most recurrences (60%) were salvaged successfully by laryngectomy. Three patients required laryngectomy for laryngeal oedema without recurrent tumour; all had been treated using a large field size (7 x 6 cm). There were 20 metachronous tumours, including five lung and two head and neck tumours. These results are similar to previous reports and confirm that radiotherapy is very effective for early glottic cancer, with high local control rates and effective salvage if local recurrences are recognized early.

Adult↗
PubMed1994

The effect of BW12C on the radiosensitivity and necrosis of murine tissues and tumours.

BW12C is a drug that has the potential to induce normal tissue and tumour hypoxia by binding to haemoglobin, increasing its affinity for oxygen and thereby reducing oxygen availability to tissues. Initial results suggested that BW12C administration caused significant radioprotection of normal tissues and induced tumour necrosis, but variable results have been reported subsequently. This work was carried to extend the range of observations concerning the ability of BW12C to radioprotect normal tissues and tumours and to induce necrosis of tumours of the mouse. BW12C was administered as 70 mg/kg i.v. 15 min before irradiation of jejunum in CBA mice and of foot skin in WHT mice with single doses of 240 kVp X-rays while mice breathed gases of varying oxygen tensions. The radiosensitivities of these tissues were assessed by the crypt survival assay and the acute skin reaction, respectively. The radiosensitivity of CaNT tumours to single fraction irradiation was assessed by the regrowth delay assay following administration of single or multiple doses of BW12C at varying times to air-breathing CBA mice. The radiation response was compared to the radiosensitivity of clamped tumours. The effect of BW12C alone on tumours was assessed by regrowth delay and histological examination for necrosis. BW12C did not change the radiosensitivity of jejunal crypts irradiated while mice breathed air or 10% O2, or of foot skin when mice breathed 12% O2. BW12C protected foot skin by a factory of 1.1 when mice breathed air. Single or multiple doses of BW12C did not influence the radiosensitivity of CaNT tumours, although marked radioprotection could be induced by clamping the tumours during irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Cerebral metastases from malignant melanoma.

A retrospective study was undertaken of factors affecting survival in 129 patients with cerebral metastases from malignant melanoma referred to the Department of Radiation Oncology from June 1982 to January 1990. Their ages ranged from 19 to 83 years and the time interval from diagnosis of the primary tumour to development of cerebral metastases ranged from one month to 17 years. Cerebral metastases were apparently solitary in 59 (46%) and multiple in 70 (54%) patients respectively. Craniotomy with resection of tumour was performed in 49 patients, of whom 24 had a solitary cerebral metastasis as the only evidence of disease. Most patients (94%) received a course of radiotherapy. Median survival of the whole group after detection of cerebral metastases was 5 months (range less than 1-87+). Univariate analysis indicated that a solitary cerebral metastasis, absence of extracranial disease and tumour resection predicted improved survival, but only surgical intervention was of independent prognostic significance in a multivariate analysis. The effect of cranial irradiation on survival could not be assessed, but the dose of radiation did not influence survival. Of the 10 patients who survived for more than 2 years, eight had total resection of a solitary cerebral metastasis.

Adult↗
PubMed1992

Non small cell carcinoma of the lung. A retrospective study. Presented at the 41st annual meeting of the Royal Australasian College of Radiologists, September 1990, Perth.

A retrospective study was undertaken in 1990 of 188 patients with the diagnosis of non small cell carcinoma of the lung referred to the Department of Radiation Oncology in 1984. Most patients (178/188) received a course of radiotherapy. This was definitive in 23, palliative in 148 (primary site in 113, metastases in 16, primary plus metastases in 19) and postoperative in 7. This report is a 5 year followup of the 171 patients treated by radiation alone, to assess factors that influence survival. Tumour histology was 50% squamous, 23% adenocarcinoma, 16% large cell and 4% unspecified, non small cell carcinoma. In 8% no histological diagnosis was obtained. The most common symptoms were cough (44%), dyspnoea (43%), chest pain (37%), haemoptysis (33%) and systemic symptoms (36%). Tumour stage (TNM) was assessed retrospectively as I(5%), II(8%), IIIA(18%), IIIB(22%) and IV(28%). A subgroup of 31 cases (18%) of uncertain staging (I-III) was analysed separately and in 2 cases (1%) no staging information was available. Palliative intent of treatment and poorer performance status were related significantly to increasing stage of disease. The effects of palliative treatment were recorded in 79 cases; in 71 there was a reduction in symptoms. The median survival from diagnosis was 8 months (range < 1-72). Using univariate and multivariate analyses, significant and independent prognostic factors for improved survival were good performance status, absence of systemic symptoms, lower tumour stage and curative intent of treatment (higher radiation dose). However the 5-year survival was only 2%. Long-term survival was associated predominantly with early stage disease but not with the type or intent of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma↗
PubMed1992

The tyrosinase-positive oculocutaneous albinism locus maps to chromosome 15q11.2-q12.

Tyrosinase-positive oculocutaneous albinism (ty-pos OCA), an autosomal recessive disorder of the melanin biosynthetic pathway, is the most common type of albinism occurring worldwide. In southern African Bantu-speaking negroids it has an overall prevalence of about 1/3,900. Since the basic biochemical defect is unknown, a linkage study with candidate loci, candidate chromosomal regions, and random loci was undertaken. The ty-pos OCA locus was found to be linked to two arbitrary loci, D15S10 and D15S13, in the Prader-Willi/Angelman chromosomal region on chromosome 15q11.2-q12. The pink-eyed dilute locus, p, on mouse chromosome 7, maps close to a region of homology on human chromosome 15q, and we postulate that the ty-pos OCA and p loci are homologous.

Albinism, Oculocutaneous↗
PubMed1991

Randomized, double-masked study of cyclosporine compared to prednisolone in the treatment of endogenous uveitis.

Fifty-six patients with bilateral sight-threatening noninfectious intermediate or posterior uveitis participated in a randomized double-masked study of the use of cyclosporine vs prednisolone in their treatment. Applying the end-point definitions, visual acuity or vitreal haze improved in only 13 of 28 (46%) patients in each group. The macular edema resolved in seven of 15 patients of the cyclosporine-treated group, and in ten of 16 patients of the prednisolone-treated group (P = .376). Patients whose therapies failed both cyclosporine and prednisolone trials were treated with both drugs, which resulted in additional patient improvements. Secondary effects were observed in both therapeutic alternatives, the most notable being alterations in serum creatinine concentration and hypertension with the dosage of cyclosporine used.

Adolescent↗
PubMed1991

Early detection of damage following bilateral renal irradiation in the mouse.

The rate and early pattern of development of radiation-induced renal damage has been determined in the mouse by measuring reductions in both haematocrit and excretion of 51Cr-EDTA, and increases in both urination frequency and urine volume. Kidneys of CBA mice were irradiated bilaterally with 2 fractions of X-rays, one week apart. Renal function was determined immediately prior to irradiation and at 3-4 weekly intervals to 22 weeks post-irradiation. Onset of damage was detected as early as 3-6 weeks using the urination frequency assay. This was confirmed by estimating the volume of urine excreted. A significant fall in haematocrit was not detected until 6-9 weeks post-treatment and a fall in isotope clearance was not detected significantly until 12 weeks. This early detection of damage was consistent with reports using both mouse and other species. The time at which damage was detected first was independent of radiation dose for the frequency and haematocrit assays. For 51Cr-EDTA clearance, there was the suggestion of earlier functional loss for the higher doses. Following the onset of damage, a steady, dose-dependent decline in renal function was measured by all assays. The latency period is defined as the time required to reach a given level of functional damage. This time decreased with increasing radiation dose, to a minimum value set by the time of onset of damage, which varied from 3 to 12 weeks, depending on the assay used. The differences in response measured prior to 12 weeks post-irradiation represent the first occasion on which a dissociation between these 3 assays has been detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Synchronous cisplatin infusion during radiotherapy for the treatment of metastatic melanoma.

In two pilot studies, 55 patients with symptomatic metastases from malignant melanoma were treated with irradiation and concurrent cisplatin. In the first group, cisplatin was given as a continuous intravenous infusion of 20 mg/m2 per day on days 1-5 and 22-26, with irradiation on days 2, 5, 9, 16, 23 and 26. The second group received 20 mg cisplatin over 24 h commencing 1 h before each fraction of irradiation on days 1, 4, 8, 11, 15 and 18. The first series of 28 patients had 30 lesions treated. Nine (30%) of these lesions responded completely and 10 (33%) achieved partial response for an overall response rate of 63% (95% confidence interval 44-80%). Survival was not evaluated in this group. The second group was comprised of 27 patients, with one irradiated lesion each. 1 patient achieved a complete response and 13 (48%) a partial response for an overall response rate of 52% (32-71%). Median survival was 21 weeks (16-31 weeks). Treatment was well tolerated with nausea and vomiting being the most common toxicity. Synchronous cisplatin infusion with radiotherapy achieves high response rates in metastatic melanoma. Whether it is superior to radiotherapy alone will require evaluation in a randomised trial.

Adult↗
PubMed1991

Ifosfamide-induced Fanconi's syndrome with growth failure in a 2-year-old child.

Fanconi's syndrome with phosphopenic rickets is described in a 2-year-old girl who had been treated for an embryonal sarcoma with multiagent chemotherapy including high-dose ifosfamide. The radiological and biochemical signs of rickets disappeared after treatment with 25-OH vitamin D3 and phosphorus supplements. Monitoring of tubular function in children during and after treatment with ifosfamide is mandatory.

Child, Preschool↗