Search PubMed⌕ Search

Biomedical subjects

A Clark

Publications and source records attributed to A Clark.

At least 19 recordsLinked to original sources
PubMed2006

An association analysis of the HLA gene region in latent autoimmune diabetes in adults.

AIMS/HYPOTHESIS: Pathophysiological similarities between latent autoimmune diabetes in adults (LADA) and type 1 diabetes indicate an overlap in genetic susceptibility. HLA-DRB1 and HLA-DQB1 are major susceptibility genes for type 1 diabetes but studies of these genes in LADA have been limited. Our aim was to define patterns of HLA-encoded susceptibility/protection in a large, well characterised LADA cohort, and to establish association with disease and age at diagnosis. MATERIALS AND METHODS: Patients with LADA (n = 387, including 211 patients from the UK Prospective Diabetes Study) and non-diabetic control subjects (n = 327) were of British/Irish European origin. The HLA-DRB1 and -DQB1 genes were genotyped by sequence-specific PCR. RESULTS: As in type 1 diabetes mellitus, DRB1 0301_DQB1 0201 (odds ratio [OR] = 3.08, 95% CI 2.32-4.12, p = 1.2 x 10(-16)) and DRB1 0401_DQB1 0302 (OR = 2.57, 95% CI 1.80-3.73, p = 4.5 x 10(-8)) were the main susceptibility haplotypes in LADA, and DRB1 1501_DQB1 0602 was protective (OR = 0.21, 95% CI 0.13-0.34, p = 4.2 x 10(-13)). Differential susceptibility was conferred by DR4 subtypes: DRB1 0401 was predisposing (OR = 1.79, 95% CI 1.35-2.38, p = 2.7 x 10(-5)) whereas DRB1 0403 was protective (OR = 0.37, 95% CI 0.13-0.97, p = 0.033). The highest-risk genotypes were DRB1 0301/DRB1 0401 and DQB1 0201/DQB1 0302 (OR = 5.14, 95% CI 2.68-10.69, p = 1.3 x 10(-8); and OR = 6.88, 95% CI 3.54-14.68, p = 1.2 x 10(-11), respectively). These genotypes and those containing DRB1 0401 and DQB1 0302 associated with a younger age at diagnosis in LADA, whereas genotypes containing DRB1 1501 and DQB1 0602 associated with an older age at diagnosis. CONCLUSIONS/INTERPRETATION: Patterns of susceptibility at the HLA-DRB1 and HLA-DQB1 loci in LADA are similar to those reported for type 1 diabetes, supporting the hypothesis that autoimmune diabetes occurring in adults is an age-related extension of the pathophysiological process presenting as childhood-onset type 1 diabetes.

Adult↗
PubMed2006

Transcriptional noise and cellular heterogeneity in mammalian macrophages.

Transcriptional noise is known to play a crucial role in heterogeneity in bacteria and yeast. Mammalian macrophages are known to exhibit cell-to-cell variation in their responses to pathogens, but the source of this heterogeneity is not known. We have developed a detailed stochastic model of gene expression that takes into account scaling effects due to cell size and genome complexity. We report the results of applying this model to simulating gene expression variability in mammalian macrophages, demonstrating a possible molecular basis for heterogeneity in macrophage signalling responses. We note that the nature of predicted transcriptional noise in macrophages is different from that in yeast and bacteria. Some molecular interactions in yeast and bacteria are thought to have evolved to minimize the effects of the high-frequency noise observed in these species. Transcriptional noise in macrophages results in slow changes to gene expression levels and would not require the type of spike-filtering circuits observed in yeast and bacteria.

Animals↗
PubMed2006

Guided self diagnosis: an innovative approach to triage for emergency dental care.

BACKGROUND: The basic model of triage, developed more than 200 years ago by the French, is based on categorization of patient needs and thus the urgency and time required for care. This model in various forms is used in most hospitals throughout the world. METHODS: In this study, a fully computerized guided self-diagnosis system (based on a neural network design) was designed, prototyped, developed and trialled by front line non-clinically trained personnel in emergency dentistry. RESULTS: A total of 699 patients were seen as a result of the triage assessment within 14 days of their initial phone call and/or first contact. Patients categorized as requiring care on the day (Category 1) were provided more items of care (50 per cent of all items) and the greatest number of extractions (76 per cent) and endodontic treatments (78 per cent). Other categories were found to require less urgent care. CONCLUSIONS: The triage system developed in this study clearly holds significant promise in reducing the impact of emergency dental patients on dental health care systems. However, it is recognized that the system still requires some adjustment to ensure all Category 1 patients are examined before less urgent categories.

Dental Care↗
PubMed2006

Variability in pupil size estimation.

BACKGROUND: The clinical estimation of pupil size and reactivity is central to the neurological assessment of patients, particularly those with or at risk of neurological damage. Health care professionals who examine pupils have differing levels of skill and training, yet their recordings are passed along the patient care pathway and can influence care decisions. The aim of this study was to determine if any statistical differences existed in the estimation of pupil size by different groups of health care professionals. METHODS: A total of 102 health care professionals working in the critical care environment were asked to estimate and record the pupil size of a series of 12 artificial eyes with varying pupil diameter and iris colour. All estimations were performed indoors under ambient lighting conditions. RESULTS: Our results established a statistically significant difference between staff groups in the estimation of pupil size. CONCLUSION: The demonstrated variability in pupil size estimation may not be clinically significant. However, it remains desirable to have consistency of measurement throughout the patient care pathway.

Analysis of Variance↗
PubMed2005

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro.

AIMS/HYPOTHESIS: Long-term exposure of beta cells to lipids, particularly saturated fatty acids in vitro, results in cellular dysfunction and apoptosis (lipotoxicity); this could contribute to obesity-related diabetes. Our aims were to relate cell death to intracellular triglyceride concentration, composition and localisation following incubation of INS1 cells in saturated and unsaturated NEFA in high and low glucose concentrations. MATERIALS AND METHODS: Insulin-producing INS1 cells were cultured (24 h; 3 and 20 mmol/l glucose) with palmitic, oleic or linoleic acids and the resulting intracellular lipids were analysed by gas chromatography and microscopy. Cell death was determined by quantitative microscopy and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and glucose-stimulated insulin secretion by ELISA. RESULTS: All NEFA (0.5 mmol/l, 0.5% albumin) inhibited glucose-stimulated (20 mmol/l) insulin secretion. Cytotoxicity was evident only with palmitic acid (p<0.05), in which case intracellular triglyceride consisted largely of tripalmitin in angular-shaped dilated endoplasmic reticulum. Cytotoxicity and morphological disruption were reduced by addition of unsaturated NEFA. Triglyceride content (control cells; 14.5 ng/mug protein) increased up to 10-fold following incubation in NEFA (oleic acid 153.2 ng/mug protein; p<0.05) and triglyceride and phospholipid fractions were both enriched with the specific fatty acid added to the medium (p<0.05). CONCLUSIONS/INTERPRETATION: In INS1 cells, palmitic acid is converted in the endoplasmic reticulum to solid tripalmitin (melting point >65 degrees C), which could induce endoplasmic reticulum stress proteins and signal apoptosis; lipid-induced apoptosis would therefore be a consequence of the physicochemical properties of these triglycerides. Since cellular triglycerides composed of single species of fatty acid are not likely to occur in vivo, destruction of beta cells by saturated fatty acids could be predominantly an in vitro scenario.

Animals↗
PubMed2005

Fetal and neonatal exposure to AZT and low-protein diet affects glucose homeostasis: a model with implications for AIDS prevention.

Zidovudine (AZT) lowers the perinatal transmission of HIV but can impair mitochondrial function by depleting mitochondrial DNA (mtDNA). AZT therapy and perinatal nutritional deprivation affect the body fat distribution, which influences glucose tolerance. We sought to model intrauterine exposure to AZT in humans to determine whether it interacts with low-protein diet (LPD) to impact on birth weight and glucose homeostasis in the offspring. Pregnant dams and their offspring were given AZT, an LPD, or AZT and an LPD (LPD + AZT). AZT reduced mtDNA copy number in liver and birth weight in the offspring and increased their fasting glucose and insulin (P = 0.021, 0.03, 0.001, and 0.011 respectively) at 6-8 wk of age. LPD decreased litter size and birth weight (P = 0.01 and 0.012). In the LPD + AZT group, birth weight and litter size were reduced compared with untreated controls, and fasting blood glucose and insulin were raised. There was a significant interaction between LPD and AZT on fasting insulin levels (P = 0.025). Islet size was not significantly affected, but the mean beta-cell area/islet was reduced in the LPD + AZT group compared with controls (P < 0.05). Early exposure to AZT interacts with LPD to impair fetal development in this model. This combination appeared to impair the supply of insulin and, hence, glucose homeostasis, perhaps as a result of impaired mitochondrial function. Although it is not certain that this can be extrapolated to humans, maternal nutritional deprivation combined with AIDS therapy could influence both birth weight and onset of diabetes.

Acquired Immunodeficiency Syndrome↗
PubMed2005

Patients strategies for managing medication for chronic heart failure.

OBJECTIVES: To explore patients views of the management of medication of chronic heart failure (CHF); to explore in what circumstances they have difficulties in managing medication. DESIGN: Qualitative analysis of in-depth interviews using a constant comparative approach. PARTICIPANTS: Patients attending an outpatients clinic with a primary diagnosis of CHF due to left ventricular systolic dysfunction, NYHA Class II or III symptoms, and a history of hospital admission for heart failure. RESULTS: 50 patients were recruited, average age 67.1 years with ranges between 41 and 80 years. 26 were classified as NYHA Class II and 24 Class III. Patients reported developing routines and back up strategies to help with the complex task of medication-taking. They also described circumstances in which they were more likely not to take medication. CONCLUSIONS: This study demonstrates, with a large sample of respondents, the complexities of medication-taking and the difficulties of maintaining constant medication over a long period of time. The study provides examples of patients' strategies for so doing. Health care professionals should recognise that concordance may vary but explore ways in which they can help patients establish routines.

Adult↗
PubMed2005

Quantification of secondary CPP insult severity in paediatric head injured patients using a pressure-time index.

This paper describes and validates a new Cumulative Pressure-Time Index (CPT) which takes into account both duration and degree of cerebral perfusion pressure (CPP) derangement and determines critical thresholds for CPP, in a paediatric head injury dataset. Sixty-six head-injured children, with invasive minute-to-minute intracranial pressure (ICP) and blood pressure monitoring, had their pre-set CPP derangement episodes (outside the normal range) identified in three childhood age-bands (2-6, 7-10, and 11-16 years) and global outcome assessed at six months post injury. The new cumulative pressure-time index more accurately predicted outcome than previously used summary measures and by varying the threshold CPP values, it was found that these physiological threshold values (< or = 48, < or = 52 and < or = 56 mmHg for 2-6, 7-10, and 11-16 years respectively) best predicted brain insult in terms of subsequent mortality and morbidity.

Adolescent↗
PubMed2005

Comparison of the collagen VI content within the islet-exocrine interface of the head, body, and tail regions of the human pancreas.

Efficient islet isolation depends on the use of collagenase to digest the extracellular matrix within the islet-exocrine interface, the molecular structure of which is poorly understood. Recently it has been reported that transplantable yields of islets can be isolated from the tail segment of the pancreas alone. This study aimed to quantify and compare the amount of collagenase-resistant collagen VI within the islet-exocrine interface of the head, body, and tail of the human pancreas. Human adult pancreata (n = 5) were retrieved from heart-beating donors (age range, 40-62 years; cold ischemia times <10 hours). Tissue blocks from the head, body, and tail region of each pancreas were fixed in formalin and processed for immuno-labelling of collagen VI, which was quantified in the islet-exocrine interface using a Zeiss KS-400 image analysis system. Data were expressed as area of collagen at the interface relative to the islet area. Statistical analysis was done using paired t test. The mean islet areas in the head, body, and tail regions were not significantly different. Collagen VI was uniformly present within the islet-exocrine interface of all regions of the pancreas and was 0.326 +/- 0.064, 0.324 +/- 0.060, and 0.334 +/- 0.052 microm(2)/islet area (P = .441) in the head, body, and tail, respectively. The content of collagen VI within the islet-exocrine interface was uniform throughout all parts of the adult pancreas. Targeting this collagen subtype with novel collagenase blends may result in consistently improved islet yields and enable a wider number of available donor pancreata to be used.

Adult↗
PubMed2005

Specific and common changes in Nicotiana benthamiana gene expression in response to infection by enveloped viruses.

Microarrays derived from Solanum tuberosum expressed sequence tags were used to test the hypothesis that genetically distinct enveloped viruses elicit unique changes in Nicotiana benthamiana gene expression. The results of our study, which included Sonchus yellow net virus (SYNV), a plant rhabdovirus that replicates in the nucleus of infected cells, and Impatiens necrotic spot virus (INSV), a plant bunyavirus that replicates in the cytoplasm, were consistent with this hypothesis. Statistically significant changes (P< or =0.01) in the expression of 275, 2646 and 4165 genes were detected in response to INSV at 2, 4 and 5 days post-inoculation (d.p.i.), respectively. In contrast, 35, 665 and 1458 genes were expressed differentially in response to SYNV at 5, 11 and 14 d.p.i., respectively. The microarray results were verified by Northern hybridization using a subset of these genes as probes. Notably, INSV, but not SYNV, induced expression of small heat-shock protein genes to high levels. In contrast to SYNV, infection by INSV resulted in downregulation of all histone genes, of which the downregulation of histone 2b expression to very low levels was confirmed by Northern hybridization. The expression of a putative WRKY transcription factor at 11 d.p.i., but not at 5 or 14 d.p.i., in SYNV-infected tissue suggested that the temporal response to virus infection was identified readily using our experimental design. Overall, infection by INSV resulted in larger fold changes in host gene expression relative to infection by SYNV. Taken together, the present data demonstrate differential responses of a common host to two genetically distinct viruses.

Gene Expression Profiling↗
PubMed2005

Involvement of 5-HT receptors in the regulation of food intake in Siberian hamsters.

The Siberian hamster provides a physiological model for understanding the hypothalamic control of energy metabolism as it undergoes annual photoperiod-regulated cycles of body weight (i.e. fattening in summer, and catabolism of fat stores in winter). As a first step to investigate whether enhanced serotonergic (5-HT) tone might underlie the catabolic processes in short days, we investigated whether serotonergic stimulation can produce catabolic actions in fat hamsters housed in long days. Acute treatment with the serotonin reuptake inhibitor (+/-) fenfluramine (8 mg/kg, i.p.) produced a prolonged, dose-dependent reduction in food intake in both photoperiods. Behavioural observations and radiotelemetry analyses revealed that this anorectic effect of fenfluramine was associated with short-term increases in locomotor activity and in core body temperature. In a subsequent series of studies, hamsters were pretreated with the 5-HT2C receptor antagonist SB242084 (4 mg/kg, i.p.). This 5-HT2C receptor antagonist completely blocked the anorectic actions of fenfluramine, but did not decrease the hyperthermia or hyperlocomotion induced by fenfluramine; thus, the anorectic actions of fenfluramine probably reflect actions via the 5-HT2C receptor. Consistent with these observations, treatment of hamsters with the 5-HT2C receptor agonist VER 3323 (10 mg/kg, i.p.) or the 5-HT1B/2C receptor agonist mCPP (3 mg/kg, i.p.) reduced food intake. The response to manipulation of serotonergic pathways was not affected by the ambient photoperiod in any of these studies. We conclude that the anorectic actions of fenfluramine are not an indirect consequence of serotonergic actions on arousal pathways, and that its actions on feeding in the Siberian hamster are most likely to be mediated by the 5-HT2C receptor.

Aminopyridines↗
PubMed2004

Interactions between low concentrations of ethanol and nicotine on firing rate of ventral tegmental dopamine neurones.

This study investigated interactions between ethanol and nicotine on dopamine-sensitive neurone firing in the ventral tegmental area (VTA), recorded in midbrain slices. No changes in spontaneous activity of the neurones were seen with nicotine at 10, 25, or 100 nM; at 250 nM there was a small significant increase in firing rate. Ethanol, applied alone, caused a significant increase in firing rate at 40 mM and at 60 nM but not at 20 mM. Combinations of 10 or 25 nM nicotine with 20 or 40 mM ethanol did not result in increased firing rates compared with either drug alone. However, nicotine 100 nM plus ethanol 60 mM significantly increased the rate of spontaneous firing compared with that after either drug alone at these concentrations. In contrast, nicotine at 250 nM plus ethanol at 60 mM did not increase firing rate, compared with each drug alone. Ketanserin, 2 microM, prevented the potentiating effect of nicotine 100 nM plus ethanol 60 mM. The results show synergism between ethanol and nicotine at specific concentrations that are likely to be present in the brain during the behavioural effects of these drugs, but the interaction is complex and may involve multiple drug actions.

Animals↗
PubMed2004

Identification of iduronate-2-sulfatase in mouse pancreatic islets.

The lysosomal enzyme iduronate-2-sulfatase (IDS) is expressed in pancreatic islets and is responsible for degradation of proteoglycans, such as perlecan and dermatan sulfate. To determine the role of IDS in islets, expression and regulation of the gene and localization of the enzyme were investigated in mouse pancreatic islets and clonal cells. The Ids gene was expressed in mouse islets and beta- and alpha-clonal cells, in which it was localized intracellularly in lysosomes. The transcriptional expression of Ids in mouse islets increased with glucose in a dose-dependent manner (11.5, 40.2, 88, and 179% at 5.5, 11.1, 16.7, and 24.4 mM, respectively, P < 0.01 for 16.7 and 24.4 mM glucose vs. 3 mM glucose). This increase was not produced by glyceraldehyde (1 mM) or 6-deoxyglucose (21.4 mM) and was blocked by the addition of mannoheptulose (21.4 mM). Neither insulin content nor secretory response to glucose (16.7 mM) was altered in mouse islets infected with lentiviral constructs carrying the IDS gene in sense orientation. Furthermore, no decrease in islet cell viability was observed in mouse islets carrying lentiviral contracts compared with controls. However, insulin content was reduced (35% vs. controls, P < 0.001) in islets infected with IDS antisense construct, while the secretory response of those islets to glucose was maintained. Inhibition of IDS by antisense infection led to an increase in lysosomal size and a high rate of insulin granule degradation via the crinophagic route in pancreatic beta-cells. We conclude that IDS is localized in lysosomes in pancreatic islet cells and expression is regulated by glucose. IDS has a potential role in the normal pathway of lysosomal degradation of secretory peptides and is likely to be essential to maintain pancreatic beta-cell function.

Animals↗
PubMed2004

Islet amyloid: a complication of islet dysfunction or an aetiological factor in Type 2 diabetes?

The role of islet amyloidosis in the onset and progression of Type 2 diabetes remains obscure. Islet amyloid polypeptide is a 37 amino-acid, beta-cell peptide which is co-stored and co-released with insulin. Human islet amyloid polypeptide refolds to a beta-conformation and oligomerises to form insoluble fibrils; proline substitutions in rodent islet amyloid polypeptide prevent this molecular transition. Pro-islet amyloid polypeptide (67 amino acids in man) is processed in secretory granules. Refolding of islet amyloid polypeptide may be prevented by intragranular heterodimer formation with insulin (but not proinsulin). Diabetes-associated abnormal proinsulin processing could contribute to de-stabilisation of granular islet amyloid polypeptide. Increased pro-islet amyloid polypeptide secretion as a consequence of islet dysfunction could promote fibrillogenesis; the propeptide forms fibrils and binds to basement membrane glycosamino-glycans. Islet amyloid polypeptide gene polymorphisms are not universally associated with Type 2 diabetes. Transgenic mice expressing human islet amyloid polypeptide gene have increased islet amyloid polypeptide concentrations but develop islet amyloid only against a background of obesity and/or high fat diet. In transgenic mice, obese monkeys and cats, initially small perivascular deposits progressively increase to occupy 80% islet mass; the severity of amyloidosis in animal models is related to the onset of hyperglycaemia, suggesting that islet amyloid and the associated destruction of islet cells cause diabetes. In human diabetes, islet amyloid can affect less than 1% or up to 80% of islets indicating that islet amyloidosis largely results from diabetes-related pathologies and is not an aetiological factor for hyperglycaemia. However, the associated progressive beta-cell destruction leads to severe islet dysfunction and insulin requirement.

Amino Acid Sequence↗