Jeffrey W. Stephens

Association of telomere length with type 2 diabetes, oxidative stress and UCP2 gene variation

Objective High oxidative stress potentially leads to accelerated telomere shortening and consequent premature cell senescence, implicated in type 2 diabetes (T2D) development. Therefore, we studied the association of leukocyte telomere length (LTL) with the presence of T2D, as well as the effect on the patients’ LTL of plasma oxidative stress and of variation in UCP2, a gene involved in the mitochondrial production of reactive oxygen species. Methods Mean LTL was determined in 569 Caucasian, 103 South Asian and 70 Afro-Caribbean T2D patients aged from 24 to 92 years, 81 healthy Caucasian male students aged from 18 to 28 years and 367 healthy Caucasian men aged from 40 to 61 years by real-time PCR. Plasma total antioxidant status (TAOS) was measured in the T2D patients by a photometric microassay. The patients were also genotyped for the UCP2 functional variants −866G>A and A55V. Results Afro-Carribeans had 510 bp longer mean length compared to Caucasians (p < 0.0001) and 500 bp longer than South Asians (p = 0.004). T2D subjects displayed shorter age-adjusted LTL compared to controls [6.94(6.8–7.03) vs. 7.72(7.53–7.9), p < 0.001] with subjects in the middle and the lowest tertile of LTL having significantly higher odds ratios for T2D compared to those in the highest tertile [1.50(1.08–2.07) and 5.04(3.63–6.99), respectively, p < 0.0001]. In the patients, LTL was correlated negatively with age (r = −0.18, p < 0.0001) and positively with TAOS measures (r = 0.12, p = 0.01) after adjusting for age, while carriers of the UCP2 −866A allele had shorter age-adjusted LTL than common homozygotes [6.86(6.76–6.96) kb vs. 7.03(6.91–7.15) kb, p = 0.04]. Conclusion The present data suggest that shorter LTL is associated with the presence of T2D and this could be partially attributed to the high oxidative stress in these patients. The association of the UCP2 functional promoter variant with the LTL implies a link between mitochondrial production of reactive oxygen species and shorter telomere length in T2D.

Obesity, metabolic syndrome and sleep apnoea: all pro-inflammatory states.

Obesity is associated with significant morbidity and mortality and is increasing in prevalence worldwide. Associated conditions include insulin resistance (IR), diabetes, hypertension and dyslipidaemia; a clustering of these has recently been termed as metabolic syndrome. Weight gain is a major predictor of the metabolic syndrome with waist circumference being a more sensitive indicator than body mass index as it reflects both abdominal subcutaneous adipose tissue and visceral adipose tissue (VAT). VAT has more metabolic activity and secretes a number of hormones and pro‐inflammatory cytokines which are linked with the metabolic abnormalities listed above. Central obesity also increases the risk of obstructive sleep apnoea syndrome (OSAS), where the sleep disordered breathing may also independently lead to/or exacerbate IR, diabetes and cardiovascular risk. The contribution of OSAS to the metabolic syndrome has been under‐recognized. The putative mechanisms by which OSAS causes or exacerbates these other abnormalities are discussed. We propose that activation of nuclear factor kappa B by stress hypoxia and/or by increased adipokines and free fatty acids released by excess adipose tissue is the final common inflammatory pathway linking obesity, OSAS and the metabolic syndrome both individually and, in many cases, synergistically.

IL6 gene promoter polymorphisms and type 2 diabetes: joint analysis of individual participants' data from 21 studies

Several lines of evidence indicate a causal role of the cytokine interleukin (IL)-6 in the development of type 2 diabetes in humans. Two common polymorphisms in the promoter of the IL-6 encoding gene IL6, −174G>C (rs1800795) and −573G>C (rs1800796), have been investigated for association with type 2 diabetes in numerous studies but with results that have been largely equivocal. To clarify the relationship between the two IL6 variants and type 2 diabetes, we analyzed individual data on >20,000 participants from 21 published and unpublished studies. Collected data represent eight different countries, making this the largest association analysis for type 2 diabetes reported to date. The GC and CC genotypes of IL6 −174G>C were associated with a decreased risk of type 2 diabetes (odds ratio 0.91, P = 0.037), corresponding to a risk modification of nearly 9%. No evidence for association was found between IL6 −573G>C and type 2 diabetes. The observed association of the IL6 −174 C-allele with a reduced risk of type 2 diabetes provides further evidence for the hypothesis that immune mediators are causally related to type 2 diabetes; however, because the association is borderline significant, additional data are still needed to confirm this finding.

The diabetic foot

Diabetes is reaching epidemic proportions and with it carries the risk of complications. Disease of the foot is among one of the most feared complications of diabetes. The ultimate endpoint of diabetic foot disease is amputation, which is associated with significant morbidity and mortality, besides having immense social, psychological and financial consequences. As the majority of amputations are preceded by foot ulceration, it is crucial to identify those at an increased risk. Diabetic foot ulcers may develop as a result of neuropathy, ischaemia or both and when infection complicates a foot ulcer, the combination can become limb and life threatening. Structural abnormalities such as calluses, bunions, hammer toes, claw toes, flat foot and rocker bottom foot need to be identified and managed.

The Significant Increase in Cardiovascular Disease Risk in APOEɛ4 Carriers is Evident Only in Men Who Smoke: Potential Relationship Between Reduced Antioxidant Status and ApoE4

Data from 1668 men (316 cardiovascular disease events) from the Framingham Offspring Study was reanalysed, specifically examining APOE:smoking interactions. Overall hazard ratio (HR) for smoking was 1.95 (1.52, 2.50) compared to non‐smokers. Using ɛ3/3 as a referent group, in non‐smokers HRs for ɛ2 carriers (ɛ2+; 1.04 (0.61, 1.76) and ɛ4 carriers (ɛ4+; 1.04 (0.70, 1.54) showed no major risk increase. In smokers, HRs were 1.96 (1.26, 2.78) in ɛ3ɛ3 men, 3.46 (2.14, 5.60; p = 0.09 for interaction) in ɛ2+ and 3.81 (2.49, 5.84; p = 0.01 for interaction), with a significant interaction between daily cigarette consumption and APOE genotype on risk (p = 0.03). The potential mechanism for this APOEɛ4:smoking interaction was examined in a second study of 728 Caucasian patients with diabetes, where markers of reactive oxygen species were available. APOE genotype was not associated with plasma OX‐LDL or total antioxidant status (TAOS) in non‐smokers. However, in smokers ɛ4+ had 26.7% higher plasma OX‐LDL than other genotypes (APOE:smoking interaction p = 0.04), while ɛ2+ had 28.4% higher plasma TAOS than ɛ3ɛ3 and ɛ4+ combined (APOE:smoking interaction p = 0.026). Although direct extrapolation needs to be considered with caution, these results identify that the cardiovascular disease risk‐raising effect of ɛ4+ is confined to smokers, and a feasible mechanism is presented by the reduced antioxidant capacity/increased OX‐LDL of apoE4.

Cardiovascular risk and diabetes. Are the methods of risk prediction satisfactory

Background Methods available to predict cardiovascular disease (CVD) and coronary heart disease (CHD) risk include the Joint British Societies Risk Chart (JBSRC), the CardioRisk Manager (CRM) calculator, the PROCAM calculation and specific to diabetes, the UKPDS risk engine. Our aim was to examine their efficacy in a clinic-based population of diabetic patients. Design Patients were identified who attended clinic at baseline (1990–1991) and categorised by the presence/absence of CHD/CVD at follow-up (2000–2001). Ten-year risk was calculated using JBSRC, CRM, PROCAM and the UKPDS risk engine. Methods A total of 798 patients were identified under follow-up (2000–2001), with sufficient data for risk prediction. Risk prediction methods were assessed by: (1) the Hosmer-Lemeshow test (calibration test); (2) the C-index, derived from the ROC curve [a discriminatory measure ranging from 0.5 (no discrimination) to 1.0 (perfect discrimination)]; and (3) Spearman correlation of the observed and predicted risk. Results All tests (except PROCAM) demonstrated acceptable discrimination with respect to CHD/CVD, however, all underestimated the risk of future events. With respect to CVD, the JBSRC had a C-index of 0.80, CRM: 0.76, UKPDS: 0.74 and PROCAM: 0.67. With respect to CHD the C-indexes were 0.77, 0.73, 0.65 and 0.76 respectively. Risk prediction by CRM had a stronger relationship with observed events than UKPDS and PROCAM (r = 0.97, 0.86, 0.81 respectively). Conclusions All scores have reasonable discrimination, but underestimate future events. The CRM showed the strongest correlation between observed and predicted risk with the least amount of scatter from the line of best fit. The CRM, when adjusted by the calibration factor, provides the most accurate method of risk prediction.

Gene-environment interaction and oxidative stress in cardiovascular disease.

Coronary heart disease (CHD) is a leading cause of death worldwide. CHD is complex and despite increased knowledge within vascular biology, traditional risk factors appear not to contribute to risk in a proportion of the population. Within this review, we look at the concept of gene-environment interaction in relation to plasma markers of oxidative stress and cardiovascular disease (CVD) risk. Growing evidence suggests that increased oxidative burden plays an important role in CVD. Genetic variation in antioxidant genes may determine the homeostatic response in an environment (e.g. smoking) of increased oxidative burden. To date, the influence of genetic variation on such plasma markers has been limited due to the lack of a robust measurement in a large number of samples often required in gene-association studies. This also explains the inability to look at gene-environment interaction within the limited number of published studies. We examine in detail the association between plasma markers of oxidative stress and LDL-oxidation with variants from three specific candidate genes: apolipoprotein E (a plasma lipoprotein), mitochondrial uncoupling protein 2 (a mitochondrial antioxidant) and glutathione-S-transferase (a cellular antioxidant protein).

Joint analysis of individual participants' data from 17 studies on the association of the IL6 variant -174GC with circulating glucose levels, interleukin-6 levels, and body mass index

Background. Several studies have investigated associations between the -174G>C single nucleotide polymorphism (rs1800795) of the IL6 gene and phenotypes related to type 2 diabetes mellitus (T2DM) but presented inconsistent results. Aims. This joint analysis aimed to clarify whether IL6 -174G>C was associated with glucose and circulating interleukin-6 concentrations as well as body mass index (BMI). Methods. Individual-level data from all studies of the IL6-T2DM consortium on Caucasian subjects with available BMI were collected. As study-specific estimates did not show heterogeneity (P>0.1), they were combined by using the inverse-variance fixed-effect model. Results. The main analysis included 9440, 7398, 24,117, or 5659 non-diabetic and manifest T2DM subjects for fasting glucose, 2-hour glucose, BMI, or circulating interleukin-6 levels, respectively. IL6 -174 C-allele carriers had significantly lower fasting glucose (−0.091 mmol/L, P=0.014). There was no evidence for association between IL6 -174G>C and BMI or interleukin-6 levels, except in some subgroups. Conclusions. Our data suggest that C-allele carriers of the IL6 -174G>C polymorphism have lower fasting glucose levels on average, which substantiates previous findings of decreased T2DM risk of these subjects.

Plasma heat shock protein 60 and cardiovascular disease risk: the role of psychosocial, genetic, and biological factors

Abstract The Whitehall Study is a prospective epidemiological study of cardiovascular risk factors in healthy members of the British Civil Service, which has identified psychological distress as a major risk factor for coronary heart disease. The levels of circulating Hsp60 in 860 participants from the Whitehall cohort and 761 individuals diagnosed with diabetes have been measured and related to psychological, biological, and genetic factors. In the Whitehall participants, concentrations of Hsp60 ranged from undetectable to mg/mL levels. Circulating Hsp60 correlated with total and low-density lipoprotein (LDL) cholesterol and was positively associated with a flattened slope of cortisol decline over the day. Levels of this stress protein also correlated with measures of psychological stress including psychological distress, job demand, and low emotional support. Mass spectrometric analysis of circulating immunoreactive Hsp60 reveal that it is predominantly the intact protein with no mitochondrial import peptide, suggesting that this circulating protein emanates from mitochondria. The Hsp60 is stable when added to plasma and the levels in the circulation of individuals are remarkably constant over a 4-year period, suggesting plasma levels are partly genetically controlled. Sequence analysis of the HSP60-HSP10 intergenic promoter region identified a common variant 3175 C>G where the G allele had a frequency of 0.30 and was associated with higher Hsp60 levels in 761 type 2 diabetic patients. The extended range of plasma Hsp60 concentrations in the general population is genuine and is likely to be related to genetic, biological, and psychosocial risk factors for coronary artery disease.

A combined insulin reduction and carbohydrate feeding strategy 30 min before running best preserves blood glucose concentration after exercise through improved fuel oxidation in type 1 diabetes mellitus

Abstract In this study, we examined the glycaemic and fuel oxidation responses to alterations in the timing of a low glycaemic index carbohydrate and 75% reduced insulin dose, prior to running, in type 1 diabetes individuals. After carbohydrate (75 g isomaltulose) and insulin administration, the seven participants rested for 30 min, 60 min, 90 min or 120 min (conditions 30MIN, 60MIN, 90MIN, and 120MIN, respectively) before completing 45 min of running at 70% peak oxygen uptake. Carbohydrate and lipid oxidation rates were monitored during exercise and blood glucose and insulin were measured before and for 3 h after exercise. Data were analysed using repeated-measures analysis of variance. Pre-exercise blood glucose concentrations were lower for 30MIN compared with 120MIN (P < 0.05), but insulin concentrations were similar. Exercising carbohydrate and lipid oxidation rates were lower and greater, respectively, for 30MIN compared with 120MIN (P < 0.05). The drop in blood glucose during exercise was less for 30MIN (3.7 mmol · l−1, s[xbar] = 0.4) compared with 120MIN (6.4 mmol · l−1, s[xbar] = 0.3) (P = 0.02). For 60 min post-exercise, blood glucose concentrations were higher for 30MIN compared with 120MIN (P < 0.05). There were no cases of hypoglycaemia in the 30MIN condition, one case in the 60MIN condition, two in the 90MIN condition, and five in the 120MIN condition. In conclusion, a low glycaemic index carbohydrate and reduced insulin dose administered 30 min before running improves pre- and post-exercise blood glucose responses in type 1 diabetes.