Volume 4, Number 1, March 2007

EDITORIALCardio-diabetes alliances
Clifford J Bailey, K George MM Alberti

Diabetes Vasc Dis Res 2007;4:6-7.

POPULAR
TOPICREVIEWHuman islet isolation: semi-automated and manual methods
Michelle Paget, Hilary Murray, Clifford J Bailey, Richard Downing

Large yields of high-viability human islets are necessary to service the expanding programmes of islet transplantation worldwide; similarly, there is an increasing demand from diabetes researchers for a reliable and cost-effective supply of human islets. The two main isolation methods are ‘semi-automated’ and ‘manual’. Both methods rely on prompt and careful removal and transfer of the donor pancreas to allow isolation to commence, preferably within eight hours. Each method involves exocrine digestion with high-activity collagenase (Liberase).
The semi-automated method is standardised, generally provides higher islet yields and is used for clinical transplant purposes, although it is not suitable for all donor pancreata. The manual method is less expensive and more adaptable and enables islets to be isolated for research from most donor pancreata.

Diabetes Vasc Dis Res 2007;4:7-12.

POPULAR
TOPICREVIEWThe insulin resistance syndrome: physiological considerations
Sangeeta R Kashyap, Ralph A DeFronzo

The insulin resistance syndrome, also referred to as the ‘metabolic syndrome’ or ‘syndrome X’, is associated with a primary cellular defect in insulin action (insulin resistance) and a compensatory increase in insulin secretion. The combination of insulin resistance and subsequent hyperinsulinaemia causes a number of metabolic and cardiovascular changes that result in a syndrome typically characterised by type 2 diabetes, obesity, dyslipidaemia, coronary artery disease and hypertension. Moreover, disturbances in sleep (sleep apnoea) and ovarian dysfunction are also characterised by insulin resistance. The pathophysiological basis for these disturbances reflects the impact of variable genetic and environmental influences. At a molecular level, insulin resistance involves defects of insulin signalling such as reduced insulin receptor tyrosine kinase activity and reduced post-receptor phosphorylation steps that impinge on metabolic and vascular effects of insulin.

Diabetes Vasc Dis Res 2007;4:13-19.

POPULAR
TOPICREVIEWTreating insulin resistance: future prospects
Clifford J Bailey

Insulin resistance typically reflects multiple defects of insulin receptor and post-receptor signalling that impair a diverse range of metabolic and vascular actions. Many potential intervention targets and compounds with therapeutic activity have been described. Proof of principle for a non-peptide insulin mimetic has been demonstrated by specific activation of the intracellular B-subunit of the insulin receptor. Potentiation of insulin action has been achieved with agents that enhance phosphorylation and prolong the tyrosine kinase activity of the insulin receptor and its protein substrates after activation by insulin. These include inhibitors of phosphatases and serine kinases that normally prevent or terminate tyrosine kinase signalling. Additional approaches involve increasing the activity of phosphatidylinositol 3-kinase and other downstream components of the insulin signalling pathways.
Experimental interventions to remove signalling defects caused by cytokines, certain adipocyte hormones, excess fatty acids, glucotoxicity and negative feedback by distal signalling steps have also indicated therapeutic possibilities. Several hormones, metabolic enzymes, minerals, co-factors and transcription co-activators have shown insulin-sensitising potential.
Since insulin resistance affects many metabolic and cardiovascular diseases, it provides an opportunity for simultaneous therapeutic attack on a broad front.

Diabetes Vasc Dis Res 2007;4:20-31.

POPULAR
TOPICREVIEWMetabolic syndrome, or What you will: definitions and epidemiology
Caroline Day

The ‘metabolic syndrome’ is a clustering of risk factors which predispose an individual to cardiovascular morbidity and mortality. There is general consensus regarding the main components of the syndrome (glucose intolerance, obesity, raised blood pressure and dyslipidaemia [elevated triglycerides, low levels of high-density lipoprotein cholesterol]) but different definitions require different cut points and have different mandatory inclusion criteria. Although insulin resistance is considered a major pathological influence, only the World Health Organization (WHO) and European Group for the study of Insulin Resistance (EGIR) definitions include it amongst the diagnostic criteria and only the International Diabetes Federation (IDF) definition has waist circumference as a mandatory component.
The prevalence of metabolic syndrome within individual cohorts varies with the definition used. Within each definition, the prevalence of metabolic syndrome increases with age and varies with gender and ethnicity. There is a lack of diagnostic concordance between different definitions. Only about 30% of people could be given the diagnosis of metabolic syndrome using most definitions, and about 35–40% of people diagnosed with metabolic syndrome are only classified as such using one definition. There is currently debate regarding the validity of the term metabolic syndrome, but the presence of one cardiovascular risk factor should raise suspicion that additional risk factors may also be present and encourage investigation. Individual risk factors should be treated.

Diabetes Vasc Dis Res 2007;4:32-38.

ORIGINAL PAPERInter-subject differences in constitutive expression levels of the clock gene in man
Anthony J Balmforth, Peter J Grant, Eleanor M Scott, Stephen B Wheatcroft, Mark T Kearney, Bart Staels, Nikolaus Marx

Circadian rhythms are generated, both at the level of the whole organism and at the cellular level, by biological clocks involving a set of clock genes. We previously performed a randomised, placebo-controlled, double-blind trial examining the effect of six months of pioglitazone (30 mg per day) therapy on neointima volume after coronary stenting in patients with coronary artery disease but without diabetes. In a subgroup of 15 patients from each group, a whole blood sample was taken at the beginning of the trial and at an eight-week clinical follow-up for isolation of total RNA using a PAXgene system. Using real time RT-PCR with relative quantitation, we investigated whether pioglitazone treatment altered clock gene expression in RNA extracted from peripheral white blood cells (PBCs). No significant changes in clock gene expression were noted in either placebo (99+45%) or pioglitazone-treated subjects (101+35%) after eight weeks. These data potentially extend previous findings that the clock gene is constitutively expressed over 24 hours to eight weeks.
We observed a large range of inter-subject differences in expression levels of the clock gene. The difference between the mean value for the lowest expression individual (ΔCT 8.8) and the highest expression individual (ΔCT 3.7) revealed an approximately 34-fold difference in relative clock gene expression levels. These differences may arise through differences in light exposure, polymorphic variants of the clock gene affecting gene expression and/or post-transcriptional regulation. They could influence susceptibility to disruption of normal circadian rhythms, which occur in pathophysiological conditions pertaining to diabetes and cardiovascular disease.

Diabetes Vasc Dis Res 2007;4:39-43.

POPULAR
TOPICORIGINAL PAPERMulti-modal magnetic resonance imaging quantifies atherosclerosis and vascular dysfunction in patients with type 2 diabetes mellitus
Justin MS Lee, Cheerag Shirodaria, Clare E Jackson, Matthew D Robson, Charalambos Antoniades, Jane M Francis, Frank Wiesmann, Keith M Channon, Stefan Neubauer, Robin P Choudhury

Vascular magnetic resonance imaging (MRI) is emerging as a powerful research tool. We studied 18 patients with type 2 diabetes mellitus and 20 controls (all with coronary artery disease). MRI measured distensibility, pulse wave velocity (PWV) and atherosclerosis in the aorta, and brachial artery flow-mediated dilatation (FMD). Patients with diabetes showed lower aortic distensibility (2.1 x 10^-3 vs. 3.5 x 10^-3 mmHg^-1, p<0.01), faster PWV (8.8 vs., 6.2 m/s, p<0.01) and impaired FMD (8.5% vs. 13.8%, p<0.05). Diabetes was an independent negative predictor of distensibility. Aortic atherosclerosis was similar in the two groups. There was a negative correlation between aortic distensibility and atherosclerosis in control subjects only, suggesting that other factors such as protein cross-linking may explain lower aortic distensibility in diabetes. MRI provides comprehensive vascular phenotyping in patients with type 2 diabetes and is likely to be useful in studies of disease progression and drug therapy.

Diabetes Vasc Dis Res 2007;4:44-48.

ORIGINAL PAPERInfluence of metabolic risk factors on the presence of carotid artery disease in patients with type 2 diabetes and coronary artery disease
Marijan Bosevski, Vladimir Borozanov, Ljubica Georgievska-Ismail

The aim of the study was to evaluate the prevalence of carotid artery disease in type 2 diabetes patients with coronary artery disease, and to establish the influence of metabolic factors on its occurrence.
In all, 145 patients (aged 59.85+8.43 years, diabetes duration 8.89+6.29 years) were randomly selected in a cross-sectional study. Carotid ultrasound was used for evaluation of the presence of carotid plaque (CP) and stenosis (CS). A logistic regression model was constructed to define the influence of risk factors – arterial hypertension, systolic blood pressure, weight, waist to hip ratio, high blood glucose and plasma lipid levels.
Carotid artery disease was present in these patients with a prevalence of 81.9% for CP, 25.2% for unilateral CS and 13.5% for bilateral CS. The low-density lipoprotein (LDL) cholesterol level was an independent predictor for CS (OR 1.936; 95% CI 1.241–3.026). Non-high density lipoprotein (HDL) cholesterol (OR 1.374; 95% CI 1.035–1.825) and glycaemia (OR 1.214; 95% CI 1.022–1.442) were predictors for carotid plaque.

Diabetes Vasc Dis Res 2007;4:49-52.

ORIGINAL PAPERTwo-week treatment with pravastatin improves ventriculo-vascular haemodynamic interactions in young men with type 1 diabetes
Rowan G Casey, Myles Joyce, Kevin Moore, Chris Thompson, Patricia Fitzgerald, David J Bouchier-Hayes

Young patients with diabetes but without established vascular disease have altered conduit and resistance artery reactivity. Early endothelial dysfunction is an initial step in atherogenesis: reductions in nitric oxide (NO) production in these vascular beds are implicated.
The study aim was two-fold: first, to detect baseline abnormalities in cardiac function, conduit vessels and the microcirculation using applanation tonometry, brachial artery ultrasound and laser Doppler fluximetry, respectively; and second, to investigate any modification in these parameters with the use of pravastatin.
Nine young men with diabetes and normoalbuminuria were randomised in a double-blind cross-over fashion to placebo or pravastatin (40 mg) treatment for two weeks. They underwent scans on three separate occasions. Control patients (n=12) underwent a baseline scan but were not given any drug treatment.
It was found that patients with diabetes had significantly higher systolic and diastolic blood pressures, heart rate and Buckberg index (propensity to myocardial ischaemia). Brachial artery reactivity and microcirculatory dilation were both reduced. Levels of von Willebrand Factor, a marker of endothelial damage, were also elevated. Pravastatin treatment restored these sub-clinical abnormalities towards normal levels.
In conclusion, pravastatin improves vascular abnormalities in young male patients with diabetes through alterations in microcirculation and conduit vessel function, with secondary myocardial effects. This may be of benefit in preventing end-organ injury.

Diabetes Vasc Dis Res 2007;4:53-61.

ORIGINAL PAPERIntracoronary ultrasound examinations reveal significantly more advanced coronary atherosclerosis in people with type 1 diabetes than in age- and sex-matched non-diabetic controls
Jakob R Larsen, Taro Tsunoda, E Murat Tuzcu, Paul Schoenhagen, Magne Brekke, Harald Arnesen, Kristian F Hanssen, Steven E Nissen, Knut Dahl-Jorgensen

Aims/hypothesis: The extent of coronary atherosclerosis is significantly more advanced in symptomatic type 1 diabetes patients than in symptomatic non-diabetic patients. Whether this difference exists between asymptomatic individuals with diabetes and controls is not documented. In vivo imaging techniques allow quantification of the difference at a preclinical stage.
Methods: The degree of coronary atherosclerosis in early onset type 1 diabetes patients without symptoms of cardiovascular disease was compared with that of age- and sex-matched controls. Intracoronary ultrasound (IVUS) examinations were performed to determine the degree of atherosclerosis. The mean age of the patients was 43 years (35–58), they had a mean duration of disease of 30 (23–39) years and the diagnosis of type 1 diabetes was made at a mean age of 12.5 years. The controls were people with transplanted hearts; donors were sex- and age-matched and had a mean age of 43 (35–58) years.
Results: The degree of subclinical coronary atherosclerosis was significantly more severe in type 1 diabetes patients than in controls. This was the case for all parameters measured. The mean plaque area was > 40% in 71% (54/76) of diabetic arteries as opposed to 33% (25/76) of arteries from controls (p<0.0001). The mean plaque thickness was 0.59+0.38 mm vs. 0.44+0.30mm in controls (p<0.0001). The mean lumen area was 8.6+3.8mm² in type 1 diabetes and 12.1+4.3 mm² in controls (p<0.0001).
Conclusions/interpretation: Asymptomatic individuals with type 1 diabetes have significantly more advanced subclinical coronary atherosclerosis than controls. Coronary atherosclerosis in type 1 diabetes develops at an early age.

Diabetes Vasc Dis Res 2007;4:62-65.

LETTERCorrelation between radial artery tonometry- and fingertip tonometry-derived augmentation index in children with type 1 diabetes
Michael J Haller, Janet H Silverstein, Jonathan J Shuster

Diabetes Vasc Dis Res 2007;4:66.