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Biomedical subjects

J C Pickup

Publications and source records attributed to J C Pickup.

At least 19 recordsLinked to original sources
PubMed2005

Glucose-dependent changes in NAD(P)H-related fluorescence lifetime of adipocytes and fibroblasts in vitro: potential for non-invasive glucose sensing in diabetes mellitus.

The aim of this study was to test the hypothesis that glucose can be monitored non-invasively by measuring NAD(P)H-related fluorescence lifetime of cells in an in vitro cell culture model. Autofluorescence decay functions were measured in 3T3-L1 adipocytes by time-correlated single-photon counting (excitation 370nm, emission 420-480nm). Free NADH had a two-exponential decay but cell autofluorescence fitted best to a three-exponential decay. Addition of 30mM glucose caused a 29% increase in autofluorescence intensity, a significantly shortened mean lifetime (from 7.23 to 6.73ns), and an increase in the relative amplitude and fractional intensity of the short-lifetime component at the expense of the two longer-lifetime components. Similar effects were seen with rotenone, an agent that maximizes mitochondrial NADH. 3T3-L1 fibroblasts stained with the fluorescent mitochondrial marker, rhodamine 123 showed a 16% quenching of fluorescence intensity when exposed to 30mM glucose, and an increase in the relative amplitude and fractional intensity of the short lifetime at the expense of the longer lifetime component. We conclude that, though the effect size is relatively small, glucose can be measured non-invasively in cells by monitoring changes in the lifetimes of cell autofluorescence or of a dye marker of mitochondrial metabolism. Further investigation and development of fluorescence intensity and lifetime sensing is therefore indicated for possible non-invasive metabolic monitoring in human diabetes.

3T3-L1 Cells↗
PubMed2003

Activation of the innate immune system as a predictor of cardiovascular mortality in Type 2 diabetes mellitus.

AIMS: Activation of innate immunity may play a major role in the development and pathophysiology of Type 2 diabetes; we therefore investigated whether a marker of innate immunity (serum sialic acid) predicts cardiovascular disease (CVD) and all-cause mortality in Type 2 diabetes. METHODS: Type 2 diabetic subjects (n=128, age 31-64 years at outset) participating in the Lewisham Diabetes Survey were followed up for a mean of 12.8 years. Baseline measurements were made of serum sialic acid and known or putative risk factors for CVD. Cause of death was coded from death certificates, post mortem examination and hospital records. RESULTS: Fifty-six (43%) subjects had died after 12.8 years. The major cause of death was CVD (71.4%), predominantly coronary heart disease (62.5%). Baseline variables significantly associated with CVD mortality were sialic acid and CVD (borderline significance smoking and cholesterol). In multivariate analysis, significant independent predictors of CVD mortality were sialic acid [standardized relative risk (95% confidence interval) 1.53 (1.12, 2.10)], age, male sex and existing CVD. CONCLUSIONS: Activated innate immunity (low-grade inflammation) is a risk factor for CVD mortality in Type 2 diabetes, independently of other known risk factors, including existing CVD. Since activation of the innate immune system predicts Type 2 diabetes, it may be a common antecedent of both Type 2 diabetes and CVD.

Adult↗
PubMed2003

Performance assessment of the Medtronic-MiniMed Continuous Glucose Monitoring System and its use for measurement of glycaemic control in Type 1 diabetic subjects.

AIMS: To assess the accuracy, reliability and measurement of glycaemic control associated with the Medtronic-MiniMed Continuous Glucose Monitoring System (CGMS) in comparison with blood glucose self-monitoring (BGSM) in Type 1 diabetic patients. METHODS: Type 1 diabetic patients (n = 18) underwent glucose monitoring by the CGMS for up to 3 days, when control was also assessed by BGSM performed eight times daily. RESULTS: Ninety-five per cent of paired non calibration samples were in the clinically acceptable zones of the Clarke error grid, and 97% in a consensus grid. The median bias was 0.1 mmol/l and relative bias 15%. The failure rate of sensors was 28% of those initially inserted. The CGMS detected significantly more hypoglycaemia and post-prandial hyperglycaemia, but total duration of hyperglycaemia, blood glucose oscillations and day-to-day variability were similarly assessed by CGMS and BGSM. CONCLUSIONS: The CGMS has acceptable clinical accuracy. Detection by the CGMS of more hypoglycaemia and post-prandial hyperglycaemia than BGSM promises a valuable tool for control assessment and optimization of treatment.

Adult↗
PubMed2001

Molecular distribution sensing in a fluorescence resonance energy transfer based affinity assay for glucose.

A newly developed method for determining molecular distribution functions is applied to a widely researched glucose affinity sensor. The reduction in fluorescence resonance energy transfer (FRET) to a malachite green (MG)-dextran complex from allophycocyanin (APC) bound to concanavalin A (ConA) due to displacement of the complex by glucose from ConA provides the basis of the assay. The higher sensitivity and specificity of a new approach to fluorescence decay analysis, over the methods based on conventional Forster-type models, is demonstrated and critical parameters in competitive binding FRET sensing derived.

Concanavalin A↗
PubMed2001

Near-infrared fluorescence lifetime assay for serum glucose based on allophycocyanin-labeled concanavalin A.

We describe an assay scheme for glucose based on fluorescence resonance energy transfer (FRET) between concanavalin A (con A), labeled with the near-infrared fluorescent protein allophycocyanin (APC) as donor, and dextran labeled with malachite green (MG) as acceptor. Glucose competitively displaces dextran-MG and leads to reduction in FRET, assessed by time-domain fluorescence lifetime measurements using time-correlated single-photon counting. The assay is operative in the glucose concentration range 2.5-30 mM, and therefore suitable for use in monitoring diabetes control. Albumin and serum inhibit FRET but the interference can be prevented by removal of high molecular weight substances by membrane filters. APC shows promise for incorporation in an implanted glucose sensor which can be interrogated from outside the body.

Blood Glucose↗
PubMed2001

Fluorescence nanotomography using resonance energy transfer: demonstration with a protein-sugar complex.

A new approach to structural sensing, fluorescence resonance energy transfer nanotomography, which interprets fluorescence decay measurement in terms of site density analysis of molecular distributions, has been applied to a glucose sensor based on competitive binding with malachite green labelled dextran to the sugar binding protein concanavalin A labelled with allophycocyanin. Opportunities for structural sensing in clinical medicine are highlighted.

Coloring Agents↗
PubMed2001

Relationship between plasma sialic acid concentration and microvascular and macrovascular complications in type 1 diabetes: the EURODIAB Complications Study.

OBJECTIVE: To test the hypothesis that an increased plasma concentration of sialic acid, a marker of the acute-phase response, is related to the presence of diabetic micro- and macrovascular complications in type 1 diabetes. RESEARCH DESIGN AND METHODS: We investigated the relationship between plasma sialic acid concentration and nephropathy, retinopathy, neuropathy, and coronary heart disease (CHD) in a cross-sectional survey of 1,369 people with type 1 diabetes. Subjects were participants in the EURODIAB IDDM Complications Study, which involved 31 centers in 16 European countries. RESULTS: There was a significantly increasing trend of plasma sialic acid with severity of retinopathy (P < 0.001 in men) and with degree of urinary albumin excretion (P < 0.001 men, P < 0.01 women). Plasma sialic acid correlated with increasing plasma creatinine concentration (P < 0.009 men, P < 0.0002 women), and men with neuropathy had a higher plasma sialic acid concentration than those without (P < 0.006). There was no significant correlation between plasma sialic acid and CHD in either sex. Elevated plasma sialic acid concentrations were also associated with several risk factors for diabetic vascular disease: diabetes duration, HbA1c, plasma triglyceride and cholesterol concentrations, waist-to-hip ratio, hypertension and smoking (in men), and low physical exercise (in women). In multiple logistic regression analysis, plasma sialic acid was independently related to proliferative retinopathy and urinary albumin excretion rate in men. CONCLUSIONS: We conclude that an elevated plasma sialic concentration is strongly related to the presence of microvascular complications in type 1 diabetes, especially retinopathy and nephropathy. Further study of acute-phase response markers and mediators as indicators or predictors of diabetic microvascular complications is therefore justified.

Adult↗
PubMed2000

Plasma interleukin-6, tumour necrosis factor alpha and blood cytokine production in type 2 diabetes.

Type 2 diabetes is associated with increased circulating concentrations of markers of the acute-phase response and interleukin-6 (IL-6). An augmented acute-phase response may be a mechanism which explains many of the clinical and biochemical features of type 2 diabetes and its complications. We sought to confirm that circulating concentrations of the cytokine acute-phase mediators IL-6 and tumour necrosis factor alpha [TNFalpha] are elevated in type 2 diabetes, and investigated blood as a source of cytokines in type 2 diabetes. Blood samples from 20 type 2 diabetic and 17 age-matched healthy subjects were incubated in vitro for 24 hr with and without lipopolysaccharide (LPS) stimulation and secreted cytokines measured. Plasma IL-6 and TNFalpha were significantly increased in type 2 diabetes compared to normal subjects. However, basal production of IL-6 and TNFalpha in cultured diabetic blood was markedly depressed in comparison with non-diabetic samples. IL-6 and TNFalpha production was increased in blood in response to LPS, reaching similar levels in diabetic and non-diabetic subjects, though IL-6 was slightly but significantly higher in controls. We conclude that circulating levels of IL-6 and TNFalpha are increased in type 2 diabetes but there is downregulation of basal cytokine production in blood cells in type 2 diabetes. Blood has the capacity to produce cytokines in diabetes which contribute to the augmented acute-phase response, but the main source of the increased plasma IL-6 and TNFalpha concentrations may be from non-circulating cells.

Acute-Phase Reaction↗
PubMed2000

A time-resolved near-infrared fluorescence assay for glucose: opportunities for trans-dermal sensing.

We report a time-resolved near-infrared fluorescence assay for glucose detection that incorporates pulsed diode laser excitation. Reduction in fluorescence resonance energy transfer to a malachite green-Dextran complex from allophycocyanin bound to concanavalin A (ConA) due to displacement of the complex by glucose from ConA provides the basis of the assay. The fluorescence quenching kinetics are analysed and discussed in detail. The change in fluorescence decay kinetics in the presence of glucose is found from dimensionality studies to be brought about by a change in the distribution of malachite green-Dextran acceptors. Glucose concentrations are measured in solution to within +/- 10% over the range 0-30 mM.

Blood Glucose↗
PubMed2000

The innate immune response and type 2 diabetes: evidence that leptin is associated with a stress-related (acute-phase) reaction.

OBJECTIVE: Leptin is produced by adipose tissue and controls food intake and body weight. Although blood levels of leptin reflect energy stores, cytokines also stimulate leptin production from fat. Because we have proposed that type 2 diabetes mellitus is associated with a cytokine-mediated acute-phase or stress response, part of the innate immune system, we sought evidence that leptin is increased in type 2 diabetes partly as a stress response, independently of obesity and sex. DESIGN: We selected two groups of type 2 diabetic patients with either a low acute-phase response (< 2.30 mmol/l serum concentration of the acute-phase marker sialic acid) or high response (> 2.30 mmol/l sialic acid), but pair-matched for body mass index (BMI) and sex. PATIENTS: Twenty type 2 diabetic subjects (11 male, 9 female) in each group, whose body mass index (BMI) and age were comparable (mean +/- SD: 28.8 +/- 3.8 vs. 28.9 +/- 3.8 kg/m2, and 60.7 +/- 8.9 vs. 61.9 +/- 12.3 years, low vs. high acute-phase responders, respectively). The glycaemic control was also similar in each group (glycated haemoglobin: 9.1 +/- 2.2 vs. 8.9 +/- 1.9%). MEASUREMENTS: Serum concentrations of sialic acid, leptin, interleukin-6 (IL-6) (the major cytokine mediator of the acute-phase response) and cortisol were assayed in fasting venous blood samples from patients and the results compared. RESULTS: Serum leptin concentration was increased in the high compared to the low acute-phase group (median 13.2 (range 3.6-55) vs. 8.1 (2.0-22.5) microg/l, P = 0.004). IL-6 and cortisol concentrations were also higher in the high-stress group (1.9 (1.0-6.4) vs. 1.4 (0.4-7.5) ng/l, P = 0.02; and 409 (180-875) vs. 290 (157-705) nmol/l, P = 0.02, respectively). Leptin was strongly correlated with BMI (r = 0.61, P < 0.001), but also with sialic acid (r = 0.40, P = 0.01) and IL-6 (r = 0.38, P = 0.04). CONCLUSIONS: Serum leptin concentrations in type 2 diabetes are partly related to an acute-phase or stress response, independent of BMI and sex. The association of hyperleptinaemia with elevated serum cortisol provides a mechanism for leptin resistance in type 2 diabetes (glucocorticoids inhibit the central action of leptin). This study provides further support for the theory that type 2 diabetes is asociated with chronic innate immune activation.

Acute-Phase Reaction↗
PubMed1998

Is type II diabetes mellitus a disease of the innate immune system?

Type II (non-insulin-dependent) diabetes mellitus is associated with increased blood concentrations of markers of the acute-phase response, including sialic acid, alpha-1 acid glycoprotein, serum amyloid A, C-reactive protein and cortisol, and the main cytokine mediator of the response, interleukin-6. The dyslipidaemia common in Type II diabetes (hypertriglyceridaemia and low serum levels of HDL cholesterol) is also a feature of natural and experimental acute-phase reactions. We review evidence that a long-term cytokine-mediated acute-phase reaction occurs in Type II diabetes and is part of a wide-ranging innate immune response. Through the action of cytokines on the brain, liver, endothelium, adipose tissue and elsewhere, this process could be a major contributor to the biochemical and clinical features of metabolic syndrome X (glucose intolerance, dyslipidaemia, insulin resistance, hypertension, central obesity, accelerated atherosclerosis) but also provides a mechanism for many other abnormalities seen in Type II diabetes, including those in blood clotting, the reproductive system, metal ion metabolism, psychological behaviour and capillary permeability. In the short-term, the innate immune system restores homeostasis after environmental threats; we suggest that in Type II diabetes and impaired glucose tolerance long-term lifestyle and environmental stimulants, probably in those with an innately hypersensitive acute-phase response, produce disease instead of repair.

Acute-Phase Reaction↗
PubMed1998

Ethnic differences in correlates of microalbuminuria in NIDDM. The role of the acute-phase response.

OBJECTIVE: To investigate whether microalbuminuria is associated with markers of the acute-phase response in NIDDM and whether there are ethnic differences in this association among the three main racial groups in Malaysia. RESEARCH DESIGN AND METHODS: NIDDM patients of Chinese, Indian, and Malay origin attending a diabetic clinic in Kuala Lumpur, Malaysia, were matched for age, sex, diabetes duration, and glycemic control (n = 34 in each group). Urinary albumin-to-creatinine ratio was measured in an early morning urine sample. Biochemical measurements included markers of the acute-phase response: serum sialic acid, triglyceride, and (lowered) HDL cholesterol. RESULTS: The frequency of microalbuminuria did not differ among the Chinese, Indian, and Malay patients (44, 41, and 47%, respectively). In Chinese patients, those with microalbuminuria had evidence of an augmented acute-phase response, with higher serum sialic acid and triglyceride and lower HDL cholesterol levels; and urinary albumin-to-creatinine ratio was correlated with serum sialic acid and triglyceride. The acute-phase response markers were not different in Indians, with microalbuminuria being high in even the normoalbuminuric Indians; only the mean arterial blood pressure was correlated with urinary albumin-to-creatinine ratio in the Indians. Malay NIDDM subjects had an association of microalbuminuria with acute-phase markers, but this was weaker than in the Chinese subjects. CONCLUSIONS: Microalbuminuria is associated with an acute-phase response in Chinese NIDDM patients in Malaysia, as previously found in Caucasian NIDDM subjects. Elevated urinary albumin excretion has different correlates in other racial groups, such as those originating from the Indian subcontinent. The acute-phase response may have an etiological role in microalbuminuria.

Acute-Phase Reaction↗
PubMed1997

NIDDM as a disease of the innate immune system: association of acute-phase reactants and interleukin-6 with metabolic syndrome X.

Non-insulin-dependent diabetes mellitus (NIDDM) is commonly associated with hypertriglyceridaemia, low serum HDL-cholesterol concentrations, hypertension, obesity and accelerated atherosclerosis (metabolic syndrome X). Since a similar dyslipidaemia occurs with the acute-phase response, we investigated whether elevated acute-phase/stress reactants (the innate immune system's response to environmental stress) and their major cytokine mediator (interleukin-6, IL-6) are associated with NIDDM and syndrome X, and may thus provide a unifying pathophysiological mechanism for these conditions. Two groups of Caucasian subjects with NIDDM were studied. Those with any 4 or 5 features of syndrome X (n = 19) were compared with a group with 0 or 1 feature of syndrome X (n = 25) but similar age, sex distribution, diabetes duration, glycaemic control and diabetes treatment. Healthy non-diabetic subjects of comparable age and sex acted as controls. Overnight urinary albumin excretion rate, a risk factor for cardiovascular disease, was also assayed in subjects to assess its relationship to the acute-phase response. Serum sialic acid was confirmed as a marker of the acute-phase response since serum concentrations were significantly related to established acute-phase proteins such as alpha-1 acid glycoprotein (r = 0.82, p < 0.0001). There was a significant graded increase of serum sialic acid, alpha-1 acid glycoprotein, IL-6 and urinary albumin excretion rate amongst the three groups, with the lowest levels in non-diabetic subjects, intermediate levels in NIDDM patients without syndrome X and highest levels in NIDDM patients with syndrome X. C-reactive protein and cortisol levels were also higher in syndrome X-positive compared to X-negative patients and serum amyloid A was higher in both diabetic groups than in the control group. We conclude that NIDDM is associated with an elevated acute-phase response, particularly in those with features of syndrome X. Abnormalities of the innate immune system may be a contributor to the hypertriglyceridaemia, low HDL cholesterol, hypertension, glucose intolerance, insulin resistance and accelerated atherosclerosis of NIDDM. Microalbuminuria may be a component of the acute-phase response.

Acute-Phase Proteins↗
PubMed1996

Novel hexacyanoferrate (III)-modified carbon electrodes: application in miniaturized biosensors with potential for in vivo glucose sensing.

We adapted a new technology for the modification of carbon base electrodes for use as probe-type, potentially implantable glucose sensors. Carbon rods (diameter 0.3 mm) were modified by repeated potential cycling in 0.1 M potassium hexacyanoferrate (III). The modified-carbon electrodes were sealed in plastic pipette tips with an exposed reaction area where glucose oxidase was immobilized using glutaraldehyde. An outer membrane of Nafion, followed by 15% (w/v) polyurethane, was applied over the enzyme layer. The miniature modified-carbon glucose sensors displayed a sensitivity to glucose in phosphate-buffered saline of 91.4 +/- 19 nA/mM (mean +/- SEM) and a linear range up to 5.3 +/- 1 mM glucose when operated at 750 mV versus a silver/silver chloride reference. Corresponding, unmodified-carbon based glucose sensors displayed a lower sensitivity of 20.7 +/- 3 nA/mM with a linear range up to 3.8 +/- 0.5 mM. The modified-carbon glucose sensors responded to glucose when operated in plasma but with a reduced sensitivity compared with that in buffered saline. Glucose sensors displayed good stability for up to 6.5 days during continuous operation in 5 mM buffered glucose solution. Interference from ascorbate and 4-acetamidophenol at both physiological and pharmacological ranges was significantly lower at the modified-carbon base electrodes than that at the unmodified-carbon base electrodes. Also, the relatively large effect of ascorbate and 4-acetamidophenol at the unmodified-carbon base electrode was reduced considerably when the base electrode was coated with glucose oxidase, Nafion and polyurethane membranes.

Acetaminophen↗
PubMed1995

Comparison of micro-enzymatic and high-performance liquid chromatographic methods for the assay of serum 1,5-anhydroglucitol.

Serum 1,5-anhydro-D-glucitol (AG) has been proposed as a marker of glycaemic control in diabetic patients. Two methods have been developed which could be applied to routine clinical monitoring of serum AG. We have compared the assay characteristics of an adapted enzyme assay, based on the enzyme pyranose oxidase, with a high-performance anion-exchange chromatographic method using pulsed amperometric detection (HPAEC-PAD). Linearity and minimum detectable concentrations were practically identical (to at least 400 mumol/l and 4 mumol/l AG, respectively), though intra- and inter-assay precision was better with the HPAEC PAD system at a clinically relevant concentration of 40 mumol/l AG (9.8% vs. 11.8% and 9.2% vs. 13.0%, respectively). The recovery of added AG to serum samples was lower with the micro-enzyme assay than the HPAEC-PAD assay (74 +/- 15% vs. 102 +/- 8%). Despite good agreement by linear regression (r = 0.974, P < 0.005), the assay methods did not demonstrate satisfactory agreement when using a difference plot (limits of agreement -16.1 to 18.7 mumol/l). We conclude that although both assay methods are applicable to routine analyses, the HPAEC-PAD is more precise and is more specific for AG than the enzyme based assay.

Blood Chemical Analysis↗
PubMed1995

Plasma sialic acid in animal models of diabetes mellitus: evidence for modulation of sialic acid concentrations by insulin deficiency.

An elevated circulating sialic acid concentration is a risk factor for cardiovascular disease. Serum sialic acid levels are elevated in NIDDM but not in uncomplicated IDDM. To study why sialic acid is increased in some types of diabetes, we assayed plasma sialic acid in various animal models of diabetes: obese (ob/ob) mice, before and after streptozotocin treatment, neonatal streptozotocin-treated (nSTZ) rats, and diabetic BB rats during and after insulin treatment. In obese mice, which exhibit moderate hyperglycemia and marked hyperinsulinemia, plasma sialic acid was decreased by 45% (fed) and 42% (fasted), compared to lean controls. Fasting reduced plasma glucose and insulin but increased sialic acid in the obese and lean mice. There was a negative correlation (r = -0.84, P < 0.001) between log plasma insulin and sialic acid in the lean and obese mice. The plasma sialic acid:globulin ratio was reduced by 35% in obese mice vs. lean controls, indicating that there may be altered sialylation of glycoproteins in obese mice. Streptozotocin treatment of obese and lean mice reduced plasma insulin but increased sialic acid. In nSTZ rats, hyperglycemia was associated with mild hypoinsulinemia, but not significantly different from control animals, and sialic acid was not altered. In diabetic BB rats, plasma glucose rose from a mean of 4.9 to 23.5 mM 48 hr after insulin withdrawal but sialic acid did not change. We conclude that an elevated plasma sialic acid level is associated with marked insulin deficiency, rather than hyperglycemia per se. The magnitude and speed of this change in sialic acid varies between species.

Animals↗