The impact of cardiovascular co-morbidities and duration of diabetes on the association between microvascular function and glycaemic control.

BACKGROUND: Good glycaemic control in type 2 diabetes (T2DM) protects the microcirculation. Current guidelines suggest glycaemic targets be relaxed in advanced diabetes. We explored whether disease duration or pre-existing macrovascular complications attenuated the association between hyperglycaemia and microvascular function. METHODS: 743 participants with T2DM (n = 222), cardiovascular disease (CVD = 183), both (n = 177) or neither (controls = 161) from two centres in the UK, underwent standard clinical measures and endothelial dependent (ACh) and independent (SNP) microvascular function assessment using laser Doppler imaging. RESULTS: People with T2DM and CVD had attenuated ACh and SNP responses compared to controls. This was additive in those with both (ANOVA p < 0.001). In regression models, cardiovascular risk factors accounted for attenuated ACh and SNP responses in CVD, whereas HbA1c accounted for the effects of T2DM. HbA1c was associated with ACh and SNP response after adjustment for cardiovascular risk factors (adjusted standardised beta (ß) -0.096, p = <0.008 and -0.135, p < 0.001, respectively). Pre-existing CVD did not modify this association (ß -0.099; p = 0.006 and -0.138; p < 0.001, respectively). Duration of diabetes accounted for the association between HbA1c and ACh (ß -0.043; p = 0.3), but not between HbA1c and SNP (ß -0.105; p = 0.02). CONCLUSIONS: In those with T2DM and CVD, good glycaemic control is still associated with better microvascular function, whereas in those with prolonged disease this association is lost. This suggests duration of diabetes may be a better surrogate for "advanced disease" than concomitant CVD, although this requires prospective validation.

Ethnic differences in microvascular function in apparently healthy South African men and women.

Microvascular dysfunction precedes the clinical manifestations of cardiovascular disease. Given the ethnic disparities in cardiovascular disease, we aimed to investigate ethnic differences in microvascular endothelial function in a group of young (18-33 years old), apparently healthy individuals (n = 33, nine Black African, 12 mixed ancestry and 12 Caucasian). Microvascular endothelium-dependent and -independent function was assessed by laser Doppler imagery and iontophoresis of ACh and sodium nitroprusside (SNP), respectively, adjusting for skin resistance. Microvascular reactivity was expressed as maximum absolute perfusion, percentage change from baseline and area under the curve (AUC). Skin resistance was significantly lower in the Caucasian group in response to ACh (Caucasian, mean 0.16 ± 0.03 Ω versus Black, 0.21 ± 0.04 Ω and mixed ancestry, 0.20 ± 0.02 Ω, P < 0.01) and SNP (Caucasian, 0.08 ± 0.01 Ω versus Black, 0.11 ± 0.02 Ω and mixed ancestry, 0.12 ± 0.01 Ω, P < 0.01). Microvascular function in response to ACh was significantly higher in the Caucasian group compared with the other two groups; however, after adjusting for skin resistance these differences were no longer significant. Conversely, the microvascular SNP response remained significantly higher in the Caucasian group, even after adjusting for skin resistance (P < 0.01). Diastolic blood pressure was inversely associated with the AUC of ACh (r = -0.4) and all SNP responses (r = -0.3 to -0.6). Skin resistance was inversely associated with AUC and maximum absolute ACh response (r = -0.59 and -0.64, respectively) and all SNP responses (r = -0.37 to -0.79). Ethnic differences in endothelium-independent microvascular function may contribute to ethnic disparities in cardiovascular disease. Moreover, skin resistance plays a significant role in the interpretation of the microvascular response to outcomes of iontophoresis in a multiethnic group.

Adiposity is a major determinant of plasma levels of the novel vasodilator hydrogen sulphide.

AIMS/HYPOTHESIS: Hydrogen sulphide is a recently identified endogenous endothelium-dependent vasodilator. Animal models of diabetes have shown that low plasma H(2)S levels are associated with marked endothelial dysfunction and insulin resistance. However, human studies on H(2)S and vascular function in health and disease are lacking. METHODS: Plasma was obtained from male patients with type 2 diabetes (n = 11), overweight (n = 16) and lean (n = 11) volunteers. H(2)S levels were determined by zinc trap spectrophotometry. Anthropometric measurements (BMI/waist:hip ratio), lipid profile, systemic blood pressure, biochemical indices of diabetes (fasting glucose, insulin sensitivity, Hb(1Ac)) and microvascular function (minimum vascular resistance) were determined. RESULTS: Median plasma H(2)S levels (25th, 75th percentiles) in age-matched lean, overweight and type 2 diabetes individuals were 38.9 (29.7, 45.1) micromol/l, 22.0 (18.6, 26.7) micromol/l and 10.5 (4.8, 22.0) micromol/l, respectively. Median plasma H(2)S levels were significantly lower in patients with type 2 diabetes compared with lean (p = 0.001, Mann-Whitney) and overweight participants (p = 0.008). Median plasma H(2)S levels in overweight participants were significantly lower than in lean controls (p = 0.003). Waist circumference was an independent predictor of plasma H(2)S (R (2) = 0.423, standardised beta: -0.650, p < 0.001). This relationship was independent of diabetes, which only contributed a further 5% to the model (R (2) = 0.477). Waist circumference or other measures of adiposity (waist:hip ratio/BMI) remained independent predictors of plasma H(2)S after adjustment for systolic blood pressure, microvascular function, insulin sensitivity, glycaemic control and lipid profile. CONCLUSIONS/INTERPRETATION: Plasma H(2)S levels are reduced in overweight participants and patients with type 2 diabetes. Increasing adiposity is a major determinant of plasma H(2)S levels.

Capillary pressure may predict preclinical changes in the eye.

AIMS/HYPOTHESIS: Microvascular dysfunction is associated with end-organ damage. Macular oedema is an important component of diabetic retinopathy. Macular thickness can be accurately quantified by optical coherence tomography (OCT), enabling accurate assessment of the macular prior to clinically apparent abnormalities. We investigated whether macular (fovea) thickness in non-diabetic individuals is related to the microvascular variables controlling fluid filtration across a blood vessel wall, in particular capillary pressure and the microvascular filtration capacity (Kf). METHODS: We recruited 50 non-diabetic individuals (25 men, 25 women; age range: 26-78 years; BMI range: 20-46 kg/m(2)). Fovea thickness was assessed by OCT. Microvascular assessments included: finger nailfold capillary pressure; Kf; microvascular structural assessments, i.e. skin vasodilatory capacity, minimum vascular resistance (MVR) and microvascular distensibility; and endothelial function. RESULTS: At 214.6 (19.9) microm (mean [SD]), fovea thickness was within normal range. Capillary pressure, adjusted for BMI, was associated with fovea thickness (standardised beta 0.573, p = 0.006, linear regression). Fovea thickness was not associated with Kf, microvascular structural assessments or endothelial function. Capillary pressure was still associated with fovea thickness when adjusted for microvascular variables (Kf, vasodilatory capacity, MVR, microvascular distensibility or endothelial function), or for risk factors for diabetes (systemic blood pressure, insulin sensitivity, inflammation, glycaemic status and lipids) and age. CONCLUSIONS/INTERPRETATION: Capillary pressure, a key determinant of movement of fluid across a blood vessel wall, is associated with fovea thickness in non-diabetic individuals. This suggests that with regard to potential preventative or therapeutic targets, attention should be directed at the mechanisms determining retinal microvascular pressure.

Sex pheromone in the dog.

Methyl p-hydroxybenzoate has been identified in the vaginal secretions of female dogs in estrus. When small amounts of this compound were applied to the vulvas of anestrous or spayed females, males placed with these females became sexually aroused and attempted to mount them.

Building ruggedness into HPLC quality control procedures.

HPLC methods for protein and peptide analysis are excellent in terms of resolution, selectivity and recovery. They are, however, complex procedures involving multiple parameters including instrumentation, columns and mobile phases that may lead to inter- or intra-laboratory deviations. The factors that contribute to differences in retention, selectivity and sensitivity are discussed, followed by suggestions for eliminating or compensating for the differences.

The insulin sensitiser pioglitazone does not influence skin microcirculatory function in patients with type 2 diabetes treated with insulin.

AIMS/HYPOTHESIS: Insulin resistance is associated with abnormal microvascular function. Treatment with insulin sensitisers may provoke oedema, suggesting microvascular effects. The mechanisms underlying the peripheral oedema observed during glucose-lowering treatment with thiazolidinediones are unclear. Therefore we examined the effect of pioglitazone on microvascular variables involved in oedema formation. METHODS: Subjects (40-80 years) with type 2 diabetes and on insulin were randomised to 9 weeks of pioglitazone therapy (30 mg/day; n=14) or placebo (n=15). The following assessments were performed at baseline and 9 weeks: microvascular filtration capacity; isovolumetric venous pressure; capillary pressure; capillary recruitment following venous or arterial occlusion; postural vasoconstriction; and maximum blood flow. A number of haematological variables were also measured including vascular endothelium growth factor (VEGF), IL-6 and C-reactive protein (CRP). RESULTS: Pioglitazone did not significantly influence any microcirculatory variable as compared with placebo (analysis of covariance [ANCOVA] for microvascular filtration capacity for the two groups, p=0.26). Mean VEGF increased with pioglitazone (61.1 pg/ml), but not significantly more than placebo (9.76 pg/ml, p=0.94). HbA(1c) levels and the inflammatory markers IL-6 and CRP decreased with pioglitazone compared with placebo (ANCOVA: p=0.009, p=0.001 and p=0.004, respectively). CONCLUSIONS/INTERPRETATION: Pioglitazone improved glycaemic control and inflammatory markers over 9 weeks but had no effect on microcirculatory variables associated with oedema or insulin resistance in type 2 diabetic patients treated with insulin.

Impact of hormone replacement therapy on microvascular function in healthy and Type 2 diabetic postmenopausal women.

AIMS: Hormone replacement therapy (HRT) has been previously reported to modulate vascular function and cardiovascular risk. Its impact on the macrocirculation has previously been explored, however, little data is available on its impact on the microcirculation. This study aimed to determine the impact of HRT on microvascular function in healthy and Type 2 diabetic postmenopausal women (n=20 and 17, respectively). METHODS: Microvascular function was assessed by skin maximum hyperaemia, skin hyperaemic response to iontophoretically applied acetylcholine (endothelial-dependent vasodilator) and sodium nitroprusside (endothelial-independent vasodilator), capillary pressure and the microvascular filtration capacity. Microvascular assessments were carried out at baseline and repeated following 6 months' oral hormone replacement therapy (1 mg oestradiol/0.5 mg norethisterone or 1 mg unopposed oestradiol for hysterectomized women). RESULTS: Following 6 months' therapy there were no significant changes in microvascular assessments in the healthy women. In the diabetic women there was a reduction in the skin hyperaemic response to acetylcholine [median pretreatment peak response: 1.95 (25th, 75th centiles: 1.54, 2.30) V vs. post-treatment peak response: 1.53 (1.30, 1.91) V (P=0.011, Wilcoxon's signed rank test)] and sodium nitroprusside [median peak response 1.59 (1.37, 1.99) vs. 1.35 (0.92, 1.63) V (P=0.011)] with HRT, but no other changes. CONCLUSION: These data suggests that HRT does not affect microvascular function in healthy women, but adversely affects it in diabetic women. These findings may help to explain why HRT fails to provide the predicted cardiovascular protection, and raises the possibility that HRT influences microangiopathy progression in diabetic women.

Comparison of porous silica packing materials for preparative ion-exchange chromatography.

Although analytical high-performance liquid chromatographic columns have been successfully used for purification of milligram amounts of proteins, they do not appear to be ideal for preparing gram or kilogram quantities because of cost and load capacities. In this paper the development of preparative weak anion-exchange materials is described. These materials possess similar chromatographic characteristics to analytical 5-10 micron materials, yet also have high load capacities. A number of inorganic packings were examined to determine which had the best combination of high load capacity, good resolution, stability, and low cost. When appropriate flow-rates and gradient shapes were used, 30-50 micron materials produced resolution of components of a commercial ovalbumin sample that was comparable to that achieved on a 6-micron material. An amount of 3 g of a protein could be loaded onto a 250 X 21 mm-I.D. column with adequate resolution to separate it from some of its impurities.

Rapid analysis of bilirubin in neonatal serum. I. The binding of bilirubin to albumin.

Evaulation of the severity of jaundice in the neonate may be determined by measuring the reserve binding capacity of serum proteins for free bilirubin. Determination of protein-bound bilirubin has been labor intensive, necessitating multiple runs on gel-permeation chromatography columns or, more recently, enzyme assays or fluorescence quenching analysis. We present a method for quantitation of free bilirubin and of bilirubin-binding capacity of serum by liquid chromatography. A gel-permeation column binds free bilirubin while allowing passage and quantitation of protein-bound bilirubin. Subsequent injection of a desorbing agent releases the adsorbed bilirubin from the column, permitting quantitation of free bilirubin. Bound and free serum bilirubin may be determined directly in less than 15 min using 10 microL of serum. The binding of bilirubin to neonatal serum is seen to be quite different from the binding to adult serum. Ion-exchange chromatography of adult and neonatal serum samples shows that their protein profiles are radically different. This difference probably accounts for the binding characteristics.

Optimization of preparative hydrophobic interaction chromatographic purification methods.

The chromatographic behavior of five proteins on hydrophobic interaction matrices having six different ligand arms was investigated using gradient elution with ammonium sulfate and ammonium acetate buffers at two pH values. The nature of the mobile phase and/or the ligand chain arm of the matrix was found to have substantial effect on the resolution, retention, and selectivity. Ovalbumin was moderately or highly retained with ammonium sulfate on all columns; however, with ammonium acetate, ovalbumin was not retained on SynChropak Hydroxypropyl and Propyl columns. Chromatographic conditions developed for analytical hydrophobic interaction chromatography columns containing 6.5-micron packings were adapted to preparative columns packed with 30-micron SynChroprep packings for the separation of serum components. Dynamic load capacities were 4-13 mg of ovalbumin per ml of column volume.

A continuous-flow enzyme detector for liquid chromatography.

A detection system has been developed for the selective and sensitive detection of enzymes eluting from a liquid chromatographic column. This system monitors a reaction that the enzyme catalyzes and provides a chemical amplification ranging from 10(4) to 10(5). The detection system consists of a reagent or substrate pump, a post-column reactor packed with non-porous spherical glass beads, and a photometric detector. A linear and selective response to a series of enzymes of clinical importance is demonstrated.