Biomedical subjects
Publications and source records attributed to Mark A Brown.
The correlation between epigenetic aberrations and disease underscores the importance of epigenetic mechanisms. Here, we review recent findings regarding chromatin modifications and their relevance to cancer.
BACKGROUND: Disrupting the balance of histone lysine methylation alters the expression of genes involved in tumorigenesis including proto-oncogenes and cell cycle regulators. Methylation of lysine residues is commonly catalyzed by a family of proteins that contain the SET domain. Here, we report the identification and characterization of the SET domain-containing protein, Smyd2. RESULTS: Smyd2 mRNA is most highly expressed in heart and brain tissue, as demonstrated by northern analysis and in situ hybridization. Over-expressed Smyd2 localizes to the cytoplasm and the nucleus in 293T cells. Although accumulating evidence suggests that methylation of histone 3, lysine 36 (H3K36) is associated with actively transcribed genes, we show that the SET domain of Smyd2 mediates H3K36 dimethylation and that Smyd2 represses transcription from an SV40-luciferase reporter. Smyd2 associates specifically with the Sin3A histone deacetylase complex, which was recently linked to H3K36 methylation within the coding regions of active genes in yeast. Finally, we report that exogenous expression of Smyd2 suppresses cell proliferation. CONCLUSION: We propose that Sin3A-mediated deacetylation within the coding regions of active genes is directly linked to the histone methyltransferase activity of Smyd2. Moreover, Smyd2 appears to restrain cell proliferation, likely through direct modulation of chromatin structure.
PURPOSE: To describe and evaluate the accuracy of water-saturation MRI and a computer segmentation program for quantification of visceral adipose tissue (VAT). MATERIALS AND METHODS: MRI was performed on five patients with whole-volume coverage of the abdomen using two different sequences: 1) a T1-weighted spoiled gradient-echo breath-hold sequence (non-water-saturation) and 2) a T1-weighted spoiled gradient-echo water-saturation breath-hold sequence (water-saturation). The computer segmentation program analyzed the data and calculated VAT volumes (cm3) from both sequences. The data from one patient were additionally processed with the use of a manual technique. The intrastudy reproducibility of the proposed method using the water-saturation MRI sequence and the computer segmentation technique was tested by repeated measures of the automated system analysis (x 10) on MRI data from a single subject to calculate variability. RESULTS: VAT volumes measured by the water-saturation MRI sequences were consistently greater than those measured by the non-water-saturation sequences. Comparison of VAT volumes derived from the water-saturation images and measured by the computer segmentation technique vs. the manual technique showed good correlation (K = 0.8), with a significant time-saving benefit associated with the automated method (5 minutes vs. 1 hour). There was poor correlation between VAT volume measurement calculated by the manual technique and the computer segmentation technique using non-water-saturation images. The reproducibility of the computer segmentation technique using data derived from water-saturation images was high, with a low variability (+/- 5%). CONCLUSION: The results obtained demonstrate that the proposed method may be able to provide accurate quantification of VAT in a highly reproducible and efficient manner.
BACKGROUND: To determine the extent of discrepancies between ambulatory blood pressure measurement (ABPM) devices and mercury sphygmomanometry in pre-use testing in routine clinical practice and whether such discrepancies are associated with patient characteristics and subsequent 24-h ABPM readings. METHODS: A retrospective analysis of a database of 683 prospectively collected records was performed. The study population comprised of patients referred for ABP monitoring at a Sydney teaching hospital. Patients had same-arm sequential measurements with a mercury sphygmomanometer and Spacelabs 90207 or 90217 device before 24-h ABPM. The discrepancy between the test devices and the standard mercury sphygmomanometer were then described by two measures, calculated for both systolic and diastolic pressures for each patient: 1) difference of means (DeltaBP average), and 2) the mean of differences between device measurement and the range of mercury sphygmomanometer readings, analogous to the British Hypertension Society protocol (DeltaBP sequential). The main outcome measures were DeltaBP average and DeltaBP sequential and their relationship to patient characteristics. RESULTS: The median DeltaBP average was 1/2 mm Hg (ABPM device underestimation) and the median DeltaBP sequential was 3/2 mm Hg. Age, gender, arm circumference, body mass index, and degree of hypertension influenced the accuracy of ABPM readings on multivariate analysis. Device accuracy was slightly weaker in patients with higher mercury or ABPM-derived systolic BP. CONCLUSIONS: These ABPM devices are accurate enough for routine clinical use in a variety of patients. Factors such as age, weight, gender, and severity of hypertension are statistically associated with greater device error but the differences are small enough to be unlikely to affect clinical practice.
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OBJECTIVE: The aim of this study was to quantify adiponectin levels in women with normal and hypertensive pregnancies to determine whether there is an independent association, while controlling for body fat and insulin sensitivity. METHODS: A cross-sectional study was conducted in the following categories: 12 normotensive non-pregnant women, 10 normotensive, 12 gestational hypertensive, 13 essential hypertensive, and 12 preeclamptic women. All subjects underwent measurements of body fat by bio-impedance analysis and blood sampling. RESULTS: Percentage of body fat and insulin resistance were greater in all pregnant groups compared with non-pregnant women. Adiponectin concentrations were significantly lower in women with normal pregnancies (18.6 +/- 1.4 microg/mL, p = 0.02) compared with non-pregnant women (24.0 +/- 1.5 microg/mL). However, adiponectin levels were not significantly different among normal pregnancy, gestational hypertension (19.0 +/- 3.1 microg/mL), essential hypertension (24.0 +/- 3.7 microg/mL) and pre-eclampsia (22.4 +/- 2.5 microg/mL) groups. Adiponectin levels were inversely related to percent body fat and insulin resistance. When adiponectin levels were corrected for percent body fat and insulin resistance, no significant differences were seen among the study groups. CONCLUSIONS: Adiponectin levels are decreased in normal pregnancy, however this difference disappears when adiponectin levels are corrected for the pregnancy-related increases in body fat and insulin resistance. Adiponectin levels are not altered significantly in states of hypertension in pregnancy compared with normal pregnancy.
Vitamin K-dependent gamma-glutamyl carboxylase catalyzes the conversion of glutamyl residues to gamma-carboxyglutamate. Its substrates include vertebrate proteins involved in blood coagulation, bone mineralization, and signal transduction and invertebrate ion channel blockers known as conotoxins. Substrate recognition involves a recognition element, the gamma-carboxylation recognition site, typically located within a cleavable propeptide preceding the targeted glutamyl residues. We have purified two novel gamma-carboxyglutamate-containing conotoxins, Gla-TxX and Gla-TxXI, from the venom of Conus textile. Their cDNA-deduced precursors have a signal peptide but no apparent propeptide. Instead, they contain a C-terminal extension that directs gamma-carboxylation but is not found on the mature conotoxin. A synthetic 13-residue "postpeptide" from the Gla-TxXI precursor reduced the K(m) for the reaction of the Conus gamma-carboxylase with peptide substrates, including FLEEL and conantokin-G, by up to 440-fold, regardless of whether it was positioned at the N- or C-terminal end of the mature toxin. Comparison of the postpeptides to propeptides from other conotoxins suggested some common elements, and amino acid substitutions of these residues perturbed gamma-carboxylation of the Gla-TxXI peptide. The demonstration of a functional and transferable C-terminal postpeptide in these conotoxins indicates the presence of the gamma-carboxylation recognition site within the postpeptide and defines a novel precursor structure for vitamin K-dependent polypeptides. It also provides the first formal evidence to prove that gamma-carboxylation occurs as a post-translational rather than a cotranslational process.
A key responsibility of the healthcare system is to develop a sustainable workforce through education and training. The complexity of postgraduate medical education and training in Australia requires: recognition that there are many stakeholders (junior medical officers, registrars, teaching clinicians, health departments, governments, colleges and society) with overlapping but competing interests and responsibilities; a national dialogue to clarify the necessary resource investments and to assign explicit accountabilities; and improved coordination and governance, while maintaining appropriate flexibility. In other countries, stronger mechanisms of governance for oversight of postgraduate medical education have emerged, and Australia can learn from these.
BACKGROUND: The significance of dipstick or microscopic hematuria in pregnancy is uncertain, with some studies suggesting this is associated with a greater risk for preeclampsia. We sought to determine the prevalence and clinical significance of microscopic hematuria during pregnancy. METHODS: This was a prospective case-control study in the antenatal Clinic of St George Hospital, Kogarah, Australia, a teaching hospital without tertiary referral antenatal care, with approximately 2,600 deliveries per year. One thousand pregnant women attending for routine antenatal care were invited to have a routine urinalysis performed and be referred to a nephrology clinic for further investigation if dipstick microscopic hematuria was detected on more than 1 occasion before 32 weeks' gestation. Main outcome measures were the prevalence of dipstick hematuria, prevalence of hematuria confirmed by urine microscopy, and the development of preeclampsia or gestational hypertension or delivery of a small-for-gestational-age baby. RESULTS: One hundred seventy-eight of 902 women (20%) who entered the study had dipstick hematuria on at least 2 occasions in pregnancy; 66 of 126 women (53%) who had hematuria before 32 weeks attended the nephrology clinic, where microscopic hematuria was confirmed in 40 women (61%). Renal imaging results were normal in all except 1 woman, and all women had a serum creatinine level of 0.90 mg/dL or less (< or =80 micromol/L). The development of preeclampsia or gestational hypertension or delivery of a small-for-gestational-age baby were similar in women with and without dipstick hematuria. Microscopic hematuria persisted in half (15 women) of those who attended for follow-up after 3 months postpartum. CONCLUSION: Dipstick hematuria is very common during pregnancy, but rarely signifies a disorder likely to impact on the pregnancy outcome. Postpartum follow-up is recommended to detect women who have persistent hematuria and presumed underlying mild glomerulonephritis.
The characterization of blood pressure in treatment trials assessing the benefits of blood pressure lowering regimens is a critical factor for the appropriate interpretation of study results. With numerous operators involved in the measurement of blood pressure in many thousands of patients being screened for entry into clinical trials, it is essential that operators follow pre-defined measurement protocols involving multiple measurements and standardized techniques. Blood pressure measurement protocols have been developed by international societies and emphasize the importance of appropriate choice of cuff size, identification of Korotkoff sounds, and digit preference. Training of operators and auditing of blood pressure measurement may assist in reducing the operator-related errors in measurement. This paper describes the quality control activities adopted for the screening stage of the 2nd Australian National Blood Pressure Study (ANBP2). ANBP2 is cardiovascular outcome trial of the treatment of hypertension in the elderly that was conducted entirely in general practices in Australia. A total of 54 288 subjects were screened; 3688 previously untreated subjects were identified as having blood pressure >140/90 mmHg at the initial screening visit, 898 (24%) were not eligible for study entry after two further visits due to the elevated reading not being sustained. For both systolic and diastolic blood pressure recording, observed digit preference fell within 7 percentage points of the expected frequency. Protocol adherence, in terms of the required minimum blood pressure difference between the last two successive recordings, was 99.8%. These data suggest that adherence to blood pressure recording protocols and elimination of digit preferences can be achieved through appropriate training programs and quality control activities in large multi-centre community-based trials in general practice. Repeated blood pressure measurement prior to initial diagnosis and study entry is essential to appropriately characterize hypertension in these elderly patients.
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OBJECTIVE: White coat hypertension (WCH) is a common phenomenon with a long term prognosis intermediate between those with true hypertension and true normotension. The natural history of this phenomenon throughout pregnancy remains unknown. We assessed the likelihood of women with an initial diagnosis of WCH developing pre-eclampsia (PE) as their pregnancy progressed. DESIGN: Prospective observational study. SETTING: St George Hospital, a teaching and University hospital. POPULATION: Two hundred and forty-one pregnant women with an early pregnancy diagnosis of essential hypertension (EH). METHODS: Eighty-six women had this diagnosis (EH) confirmed pre-pregnancy by 24-hour ambulatory blood pressure monitoring (ABPM) or repeated automated home blood pressure (BP) self-measurement. The remaining 155 underwent 24-hour ABPM in early pregnancy to establish their diagnosis. Women found to have WCH did not receive antihypertensives during their pregnancy, whereas those with confirmed EH received oxprenolol or methyldopa. Women with WCH had repeated 24-hour ABPM and/or BP assessments in a pregnancy day assessment unit until delivery. MAIN OUTCOME MEASURE: The development of PE in women with WCH or EH. RESULTS: The overall prevalence of WCH was 32%. Half retained this phenomenon throughout pregnancy and had good pregnancy outcomes. Forty percent developed (benign) gestational hypertension and also had good pregnancy outcomes while 8% developed proteinuric PE, significantly fewer than in women with confirmed EH (22%), P= 0.008. No BP parameter at study entry permitted discrimination between those women with WCH who retained this phenomenon and those who developed GH or PE. CONCLUSION: WCH is a common phenomenon in pregnant women who appear to have EH according to routine BP measurement early in pregnancy. Antihypertensives may be withheld from this group initially and they can be advised they will have better pregnancy outcomes than women with true EH. However, continued monitoring throughout pregnancy remains important to detect the small group of white coat hypertensives who develop PE.
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BACKGROUND: Hospitals distant from the immediate site of an incident involving a hazardous materials (HAZMATs) release which could include chemical warfare agents, must develop emergency response plans (ERPs) to protect healthcare professionals if they receive potentially contaminated victims. The ERP must address OSHA, EPA, and JCAHO requirements. METHODS: The VHA convened groups to develop a hazard and exposure assessment, identify actions for compliance with existing regulatory standards, and review site and operational planning issues. Exposure modeling results were used to derive relationships between operational parameters (time and distance from sites/sources) and potential exposure for healthcare workers. RESULTS: According to exposure modeling, level C personal protective equipment is adequate to protect hospital staff distant from the chemical release site. Decontamination runoff and contaminated clothing should also be controlled to limit exposure. CONCLUSIONS: Development and coordination of ERPs must include the local emergency planning committee, with clear assignment of tasks, locations, and training in order to prevent exposures to healthcare workers.
BACKGROUND: Despite the recognition of chemical emergencies, terrorist events, and ongoing threats, little practical guidance exists for healthcare facilities. METHODS: An approach and materials developed by the Veterans Health Administration in a five-element program over the last 2 years to enhance the existing emergency management program is outlined. Nine steps to the development of a comprehensive all-hazards, emergency plan and program, with auditing and improvement tools are offered. RESULTS: Cognitive aids for clinical use are available on-line and in hard copy. A hazard assessment modeled patients as emission sources documenting the operations strategies under which level C personal protective equipment will protect healthcare workers. The development of this response program appears to support a broader, long-standing VHA approach to problem solving. This involves bringing together individual talented field staff, representing specific skills, geographic regions, and work styles; investing in face-to-face consensus development; and developing programs with extensive internal peer-review ("field-based," "bottom-up and top-down," and external reviews). CONCLUSIONS: Comprehensive and effective programs can be constructed at low cost with reasonable speed within large systems with a public mandate, leading to responsible use of public funds internally, and as models for private sector programs. It is the long-term operational cost implications, under budget constraints in health care, which often present the true challenge.
A new method for efficiently processing MRS data acquired with phased-array coils is presented. The method consists of performing phase compensation (i.e., redefining the signal phase relative to a common reference) of the signals in the time domain prior to combining the signals. The resulting spectra are equivalent to those obtained by previously published methods for phased-array spectral data processing (i.e., processing the signals individually and then combining them in the frequency domain). The method allows spectra acquired with phased-array coils to be processed as efficiently as those acquired with non-phased-array coils. Both single voxel spectroscopy (SVS) and chemical shift imaging (CSI) data sets may be processed by this method.
OBJECTIVE: To determine prospectively in hypertensive pregnant women 1) the accuracy of dipstick testing for proteinuria using automated urinalysis, 2) factors that might affect such accuracy, and 3) the potential impact of automated dipstick testing on the accuracy of diagnosis of preeclampsia according to acceptance of proteinuria at either 1 + or 2 + level. DESIGN: Prospective study. SETTING: Antenatal day assessment unit and antenatal ward of St George Hospital, a teaching hospital in Sydney, Australia. POPULATION: 170 hypertensive pregnant women attending as outpatients or inpatients. METHODS: 503 midstream urine samples were collected prospectively on separate occasions from 170 women. Full urinalysis was recorded using the Bayer Clinitek 50 automated urinalysis device and Multistix 10SG urinalysis strips (Bayer Diagnostics, Victoria, Australia). Each MSU was analysed for spot protein/creatinine ratio and also for culture and sensitivity if symptoms of a urinary tract infection were present or dipstick included positive nitrites. Urinalysis protein results were compared with spot urinary protein/creatinine ratio (previously shown to correlate with 24-hr urine protein excretion) to determine the accuracy of urinalysis. True proteinuria was defined as a ratio >/= 30 mg protein/mmol creatinine. RESULTS: False positive dipstick tests ranged from 7% at 3 + level to 71% at 1 + proteinuria level while false negative rates were 7% for "nil" and 14% for "trace" proteinuria, 9% overall. Accepting the dipstick proteinuria result at face value led to an incorrect diagnosis of preeclampsia or gestational hypertension in 85 (50%) women. Dipstick proteinuria was significantly more likely to be correct (true positive/true negative) if diastolic blood pressure was elevated > 90 mmHg (p = 0.032) and in the absence of ketonuria (p = 0.001). Accepting a diagnosis of preeclampsia on the basis of de novo hypertension and dipstick testing alone was accurate less often (70%) when > 1 + was used as a discriminant value than at the 82% of presentations when > 2 + was used (p = 0.001). CONCLUSION: Accepting "nil" or "trace" proteinuria as a true negative dipstick results fails to identify approximately 1 in 11 hypertensive pregnant women with true proteinuria, a false negative rate that may be acceptable provided these women are subject to ongoing vigilant clinical review. Even with automated urinalysis the false positive rate for dipstick levels >/= 1 + is very high, particularly in the presence of ketonuria and relying on this alone to diagnose preeclampsia leads to significant errors in diagnosis. Accepting >/= 2 + dipstick proteinuria improves overall diagnostic accuracy for preeclampsia at the expense of a higher false negative rate. This study emphasizes the need to confirm dipstick proteinuria with a further test such as a spot urine protein/creatinine ratio in all hypertensive pregnant women, particularly in research studies.
BACKGROUND: Pyelonephritis accounts for a significant number of hospital admissions. It is unclear from existing literature whether all patients requiring admission to hospital should undergo renal imaging or if there is a subset that indicates clinical parameters for those who are more likely to have significant renal imaging abnormalities. METHOD AND RESULTS: We undertook a retrospective study of 60 consecutive patients hospitalized with pyelonephritis, the majority of whom underwent renal ultrasound at the time of admission. Clinical data collected included age, sex, fever, serum creatinine, days for resolution of fever, premorbid conditions, and results of renal imaging. Sixteen per cent were found to have new and clinically significant abnormal findings; predominantly, urinary tract obstruction. We found no significant difference between the groups with abnormal and normal renal imaging in terms of any easily detectable clinical parameter such as change in serum creatinine, premorbid conditions, age, days for fever to resolve or white cell count on admission. We found a high proportion of Escherichia coli resistant to ampicillin (46%) but not to amoxycillin/clavulinic acid. CONCLUSION: Although our study did not test whether immediate imaging is more advantageous than delaying imaging for those who fail to respond to treatment, our findings suggest that early imaging is a cost-effective part of management. On the basis of these data, we recommend renal imaging for all patients requiring hospital admission for pyelonephritis, and suggest that initial empirical therapy should include an intravenous dose of cephalosporin but not ampicillin.