Gestational Diabetes-Placental Expression of Human Equilibrative Nucleoside Transporter 1 (hENT1): Is Delayed Villous Maturation an Adaptive Pattern?

Gestational diabetes mellitus (GDM) is a metabolic disease that can affect placental villous maturation and villous vascularity. The main effects of GDM on placental growth are a delay of villous maturation (DVM) and decreased formation of vasculo-syncytial membranes (VSM). Human equilibrative nucleoside transporter-1 (hENT1) is an adenosine transporter expressed in the human umbilical vein endothelial cells (HUVEC) and human placental microvascular endothelium cells (hPMEC). Its role is crucial in maintaining physiological fetal adenosine levels during pregnancy, and its reduction has been described in GDM. Twenty-four placentas from pregnancies with a confirmed diagnosis of GDMd and twenty-four matched non-GDM placentas (controls) were retrospectively analyzed to investigate the immunohistochemical expression of hENT1 in HUVEC and hPMEC. The study included the quantitative evaluation of VSM/mm² in placental tissue and the immunohistochemical quantitative evaluation of Ki-67, PHH3, and p57 in villous trophoblast. hENT1 expression was higher in all the vascular districts of the control cases compared to the GDMd placentas (p < 0.0001). The VSM/mm² were lower in the GDMd cases, while the Ki-67, PHH3, and p57 were higher when compared to the control cases. To our knowledge, this is the first report of hENT1 expression in the human placentas of GDM patients. The absence/low expression of hENT1 in all the GDMd patients may indicate a potential role in microvascular adaptative mechanisms. The trophoblasts' proliferative/antiapoptotic pattern (high Ki-67, high PHH3, and high p57 count) may explain the statistically significant lower number of VSM/mm² found in the GDMd cases.

Quality of care to institutionalized patients with diabetes in Italy: a national survey

PURPOSE

To evaluate the epidemiology of diabetes and quality of care of institutionalized patients with diabetes in Italian nursing homes. More specifically, to evaluate the adherence to the national/international guidelines for the management of older people with diabetes.

METHODS

Data related to the epidemiology of diabetes and the quality of care were collected from questionnaires sent to 41 nursing homes. Data were extracted from papers, electronic medical records and validated operating protocols regulating the management of patients with diabetes in various homes. Completed questionnaires were returned in electronic format and centrally processed.

RESULTS

Out of 4692 residents, 906 (19.3%) had diabetes. Among these residents, excluding patients undergoing diet treatment, more than half were on insulin treatment (alone or in combination with oral antidiabetic agents). The critical findings can be summarized as follows: a lack of shared diagnostic-therapeutic protocols, specifically related to evaluation of frailty; the preparation of nutritional and physical activity plans; the clarification of the objectives of the treatment; the timing of insulin administration (frequent use of sliding scale); the frequency and timing of capillary blood glucose; metabolic control methods; hypoglycemia and hyperglycemia treatment; and the scant use of new drugs that do not cause hypoglycemia.

CONCLUSION

Our data revealed substantial heterogeneity in the treatment of nursing home residents with diabetes in Italy with many discrepancies between what is recommended in the guidelines and real-world practice. The implementation of local diagnostic-therapeutic protocols shared by all caregivers should be encouraged and properly funded to overcome communication problems between doctors and nurses and eventually improve the quality of care for institutionalized patients with diabetes.

Metabolic control and complications in Italian people with diabetes treated with continuous subcutaneous insulin infusion

BACKGROUND AND AIM

The objective of this cross-sectional study was to evaluate the degree of glycaemic control and the frequency of diabetic complications in Italian people with diabetes who were treated with continuous subcutaneous insulin infusion (CSII).

METHODS AND RESULTS

Questionnaires investigating the organisation of diabetes care centres, individuals' clinical and metabolic features and pump technology and its management were sent to adult and paediatric diabetes centres that use CSII for treatment in Italy. Information on standard clinical variables, demographic data and acute and chronic diabetic complications was derived from local clinical management systems. The sample consisted of 6623 people with diabetes, which was obtained from 93 centres. Of them, 98.8% had type 1 diabetes mellitus, 57.2% were female, 64% used a conventional insulin pump and 36% used a sensor-augmented insulin pump. The median glycated haemoglobin (HbA_1c) level was 60 mmol/mol (7.6%). The HbA_1c target (i.e. <58 mmol/mol for age <18 years and <53 mmol/mol for age >18 years) was achieved in 43.4% of paediatric and 23% of adult participants. Factors such as advanced pump functions, higher rate of sensor use, pregnancy in the year before the study and longer duration of diabetes were associated with lower HbA_1c levels. The most common chronic complications occurring in diabetes were retinopathy, microalbuminuria and hypertension. In the year before the study, 5% of participants reported ≥1 episode of severe hypoglycaemic (SH) episodes (SH) and 2.6% reported ≥1 episode of ketoacidosis.

CONCLUSIONS

Advanced personal skills and use of sensor-based pump are associated with better metabolic control outcomes in Italian people with diabetes who were treated with CSII. The reduction in SH episodes confirms the positive effect of CSII on hypoglycaemia.

CLINICAL TRIAL REGISTRATION NUMBER

NCT 02620917 (ClinicalTrials.gov).

Decreased Homocysteine Trans-Sulfuration in Hypertension With Hyperhomocysteinemia: Relationship With Insulin Resistance

CONTEXT

Homocysteine is an independent cardiovascular risk factor and is elevated in essential hypertension. Insulin stimulates homocysteine catabolism in healthy individuals. However, the mechanisms of hyperhomocysteinemia and its relationship with insulin resistance in essential hypertension are unknown.

OBJECTIVE

To investigate whole body methionine and homocysteine kinetics and the effects of insulin in essential hypertension.

DESIGN AND SETTING

Eight hypertensive male subjects and six male normotensive controls were infused with l-[methyl-2H3,1-13C]methionine for 6 hours. In the last 3 hours a euglycemic, hyperinsulinemic clamp was performed. Steady-state methionine and homocysteine kinetics were determined in postabsorptive and hyperinsulinemic conditions.

RESULTS

Postabsorptive hypertensive subjects had elevated homocysteine concentrations (+30%, P = 0.035) and slightly (by 15% to 20%) but insignificantly lower methionine rates of appearance (Ras) (P = 0.07 to P = 0.05) and utilization for protein synthesis (P = 0.06) than postabsorptive normotensive controls. Hyperinsulinemia suppressed methionine Ra and protein synthesis, whereas it increased homocysteine trans-sulfuration, clearance, and methionine transmethylation (the latter only in the normotensive subjects). However, in the hypertensive subjects trans-sulfuration was significantly lower (P < 0.05) and increased ~50% less [by +1.59 ± 0.34 vs +3.45 ± 0.52 µmol/kg lean body mass (LBM) per hour, P < 0.005] than in normotensive controls. Homocysteine clearance through trans-sulfuration was ~50% lower in hypertensive than in normotensive subjects (P < 0.005). In the hypertensive subjects, insulin-mediated glucose disposal was ~45% lower (460 ± 44 vs 792 ± 67 mg/kg LBM per hour, P < 0.0005) than in normotensive controls and was positively correlated with the increase of trans-sulfuration (P < 0.0015).

CONCLUSIONS

In subjects with essential hypertension, hyperhomocysteinemia is associated with decreased homocysteine trans-sulfuration and probably represents a feature of insulin resistance.

Carotid plaque calcification predicts future cardiovascular events in type 2 diabetes

OBJECTIVE

The presence of carotid plaques is associated with future cardiovascular events, with local plaque composition being an independent outcome predictor. We examined the association between ultrasonographically determined carotid plaque calcification and incident major adverse cardiovascular events (MACE) and death in type 2 diabetes (T2D).

RESEARCH DESIGN AND METHODS

We enrolled 581 patients with T2D who underwent routine carotid ultrasonography. Plaques were classified as echolucent (lipid rich), heterogenous, and echogenic (calcific). We collected demographic, anthropometric, and clinical data at baseline and followed the patients for up to 9 years.

RESULTS

Plaques were detected in 81.8% of the patients (echolucent in 16.4%, heterogenous in 43.2%, and echogenic in 22.2%). During follow-up (4.3 ± 0.1 years), 58 deaths (27 cardiovascular) and 236 fatal and nonfatal MACE occurred. In univariate analyses, presence versus absence of any carotid plaque was associated with incident MACE, and the hazard ratio (95% CI) progressively increased from echolucent (1.97 [0.93-3.44]), to heterogeneous (3.10 [2.09-4.23]), to echogenic (3.71 [2.09-5.59]) plaques. Compared with echolucent plaques, echogenic plaques were associated with incident MACE independently from confounders. This association was attenuated after adjusting for the degree of stenosis, but in patients with stenosis ≤30%, echogenic plaque type still predicted total and atherosclerotic MACE, even after further adjusting for mean intima-media thickness.

CONCLUSIONS

In T2D, carotid plaque calcification predicts MACE, especially in patients with a low degree of stenosis. The biology of atherosclerotic calcification in diabetes needs to be further elucidated to understand the basis of this association.

Microangiopathy is independently associated with presence, severity and composition of carotid atherosclerosis in type 2 diabetes

BACKGROUND AND AIMS

Common mechanisms for the development of micro- and macroangiopathic diabetic complications have been suggested. We aimed to cross-sectionally investigate strength and characteristics of the association between carotid atherosclerosis and microangiopathy in type 2 diabetic patients.

METHODS AND RESULTS

Common carotid artery intima-media thickness (cIMT), carotid plaque (CP) type and degree of stenosis were evaluated by ultrasound, along with the determination of anthropometric parameters, HbA1c, lipid profile, assessment of diabetic retinopathy and nephropathy, in 662 consecutive patients with type 2 diabetes mellitus (T2DM). Patients were divided according to high/low cIMT, presence/absence of CP and of retinopathy and nephropathy. Patients with CP were older, more prevalently males, past smokers, had longer diabetes duration, significantly lower HDL cholesterol and more prevalent ischemic heart disease (all p<0.05) as compared to those with cIMT < 1 mm. Microangiopathies were more prevalent in patients with CP than in those without. At multivariate logistic regression, factors independently associated with the presence of CP were age, past smoke, HDL cholesterol, retinopathy and retinopathy plus nephropathy. A significant independent correlation of CP stenosis with stage of retinopathy and nephropathy was found. Finally, echolucent CPs were associated with a lower prevalence of proliferative retinopathy than CP containing calcium deposits.

CONCLUSION

In T2DM, retinopathy, alone or in combination with nephropathy, is independently associated to CP, and severity of microangiopathy correlates with severity of carotid atherosclerosis. These observations, together with the different prevalence of proliferative retinopathy according to CP types, point to possible common pathogenic mechanisms in micro- and macrovascular complications.

Nitric oxide synthesis is reduced in subjects with type 2 diabetes and nephropathy

OBJECTIVE

Nitric oxide (NO) is a key metabolic and vascular regulator. Its production is stimulated by insulin. A reduced urinary excretion of NO products (NOx) is frequently found in type 2 diabetes, particularly in association with nephropathy. However, whether the decreased NOx excretion in type 2 diabetes is caused by a defective NOx production from arginine in response to hyperinsulinemia has never been studied.

RESEARCH DESIGN AND METHODS

We measured NOx fractional (FSR) and absolute (ASR) synthesis rates in type 2 diabetic patients with diabetic nephropathy and in control subjects, after l-[(15)N(2)-guanidino]-arginine infusion, and use of precursor-product relationships. The study was conducted both before and after an euglycemic hyperinsulinemic ( approximately 1,000-1,200 pmol/l) clamp.

RESULTS

In type 2 diabetes, NOx FSR was reduced both under basal (19.3 +/- 3.9% per day, vs. 22.9 +/- 4.5% per day in control subjects) and hyperinsulinemic states (24.0 +/- 5.6% per day, vs. 37.9 +/- 6.4% per day in control subjects; P < 0.03 by ANOVA). Similarly, in type 2 diabetes, NOx ASR was lower than in control subjects under both conditions (basal, 0.32 +/- 0.06 vs. 0.89 +/- 0.34 mol per day; hyperinsulinemia, 0.35 +/- 0.07 vs. 1.15 +/- 0.38 mol per day; P = 0.01 by ANOVA). In type 2 diabetes, the ability of insulin to stimulate both the FSR (4.7 +/- 3.2% per day) and the ASR (0.03 +/- 0.04 mol per day) of NOx was several-fold lower than that in control subjects (15.0 +/- 2.9% per day and 0.25 +/- 0.07 mol per day, P < 0.03 and P < 0.02, respectively). Also the fraction of arginine flux converted to NOx (basal, 0.22 +/- 0.05% vs. 0.65 +/- 0.25%; hyperinsulinemia, 0.32 +/- 0.06% vs. 1.03 +/- 0.33%) was sharply reduced in the patients (P < 0.01 by ANOVA).

CONCLUSIONS

In type 2 diabetic patients with nephropathy, intravascular NOx synthesis from arginine is decreased under both basal and hyperinsulinemic states. This defect extends the concept of insulin resistance to NO metabolism.

Fibrinogen kinetics and protein turnover in hypertension: Effects of insulin

BACKGROUND AND AIM

Hyperfibrinogenemia, a cardiovascular risk factor, is frequent in hypertension and largely unexplained. In this study, we measured fibrinogen production and whole-body protein turnover under both basal and hyperinsulinemic states, in hypertensive [H] and control [C] subjects, using a leucine stable isotope tracer and precursor-product relationships.

METHODS AND RESULTS

Since hypertension is often a feature of the "metabolic", insulin resistance syndrome, which in turn affects both fibrinogen kinetics and whole-body protein turnover, we selected hypertensive subjects without the metabolic syndrome. Following basal measurements, an euglycemic, approximately euaminoacidemic, hyperinsulinemic clamp was performed, with plasma insulin raised to 700-900 pmol/L. In H, rates of the fractional and absolute synthesis (FSR and ASR, respectively) of fibrinogen were 30%-40% greater (p<0.05 or less) than in C in both states, whereas leucine turnover was normal. Hyperinsulinemia did not modify fibrinogen synthesis in either group with respect to baseline, whereas it suppressed leucine appearance from endogenous proteolysis by approximately 40% to same extent in both groups. Amino acid clearance was similar in both the H and C subjects. In H, the insulin-mediated glucose disposal (M) was approximately 25% lower, (although insignificantly) than in controls, showing no overall insulin resistance. There was an inverse correlation between M and fibrinogen FSR during the clamp.

CONCLUSIONS

In essential hypertension fibrinogen production is increased, is not further stimulated by insulin, and is inversely related to insulin sensitivity at high-physiological insulin concentrations. Amino acid disposal and basal as well as insulin-responsive protein degradation rates are instead normal.

Hepatic lipid metabolism and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is an increasingly recognized pathology with a high prevalence and a possible evolution to its inflammatory counterpart (non-alcoholic steatohepatitis, or NASH). The pathophysiology of NAFLD and NASH has many links with the metabolic syndrome, sharing a causative factor in insulin resistance. According to a two-hit hypothesis, increased intrahepatic triglyceride accumulation (due to increased synthesis, decreased export, or both) is followed by a second step (or "hit"), which may lead to NASH. The latter likely involves oxidative stress, cytochrome P450 activation, lipid peroxidation, increased inflammatory cytokine production, activation of hepatic stellate cells and apoptosis. However, both "hits" may be caused by the same factors. The aim of this article is to overview the biochemical steps of fat regulation in the liver and the alterations occurring in the pathogenesis of NAFLD and NASH.

Gender differences in endothelial progenitor cells and cardiovascular risk profile: the role of female estrogens

OBJECTIVE

Endothelial progenitor cells (EPCs) participate in vascular homeostasis and angiogenesis. The aim of the present study was to explore EPC number and function in relation to cardiovascular risk, gender, and reproductive state.

METHODS AND RESULTS

As measured by flow-cytometry in 210 healthy subjects, CD34(+)KDR(+) EPCs were higher in fertile women than in men, but were not different between postmenopausal women and age-matched men. These gender gradients mirrored differences in cardiovascular profile, carotid intima-media thickness, and brachial artery flow-mediated dilation. Moreover, EPCs and soluble c-kit ligand varied in phase with menstrual cycle in ovulatory women, suggesting cyclic bone marrow mobilization. Experimentally, hysterectomy in rats was followed by an increase in circulating EPCs. EPCs cultured from female healthy donors were more clonogenic and adherent than male EPCs. Treatment with 17beta-estradiol stimulated EPC proliferation and adhesion, via estrogen receptors. Finally, we show that the proangiogenic potential of female EPCs was higher than that of male EPCs in vivo.

CONCLUSIONS

EPCs are mobilized cyclically in fertile women, likely to provide a pool of cells for endometrial homeostasis. The resulting higher EPC levels in women than in men reflect the cardiovascular profile and could represent one mechanism of protection in the fertile female population.

Glucose tolerance is negatively associated with circulating progenitor cell levels

AIMS/HYPOTHESIS

Circulating progenitor cells participate in cardiovascular homeostasis. Depletion of the pool of endothelial progenitor cells (EPCs) is associated with increased cardiovascular risk. Furthermore, EPCs are reduced in the presence of classical risk factors for atherosclerotic disease, including diabetes mellitus. This study was designed to evaluate progenitor cell levels in volunteers with different degrees of glucose tolerance.

METHODS

Cardiovascular parameters and the levels of circulating CD34(+) and CD34(+) kinase insert domain receptor (KDR)(+) cells were determined in 219 middle-aged individuals with no pre-diagnosed alterations in carbohydrate metabolism. Glucose tolerance was determined by fasting and 2 h post-challenge glucose levels, with IFG and IGT considered as pre-diabetic states.

RESULTS

CD34(+) and CD34(+)KDR(+) cells were significantly reduced in individuals who were found to have diabetes mellitus, and were negatively correlated with both fasting and post-challenge glucose in the whole population. While only CD34(+) cells, but not CD34(+)KDR(+) cells, were significantly reduced in pre-diabetic individuals, post-challenge glucose was an independent determinant of the levels of both CD34(+) and CD34(+)KDR(+) cells.

CONCLUSIONS/INTERPRETATION

Glucose tolerance was negatively associated with progenitor cell levels in middle-aged healthy individuals. Depletion of endothelial progenitors with increasing fasting and post-meal glucose may be one cause of the high incidence of cardiovascular damage in individuals with pre-diabetes.

Acute effect of insulin on nitric oxide synthesis in humans: a precursor-product isotopic study

Nitric oxide (NO) is a key regulatory molecule with wide vascular, cellular, and metabolic effects. Insulin affects NO synthesis in vitro. No data exist on the acute effect of insulin on NO kinetics in vivo. By employing a precursor-product tracer method in humans, we have directly estimated the acute effect of insulin on intravascular NO(x) (i.e., the NO oxidation products) fractional (FSR) and absolute (ASR) synthesis rates in vivo. Nine healthy male volunteers were infused iv with L-[(15)N(2)-guanidino]arginine ([(15)N(2)]arginine) for 6 h. Timed measurements of (15)NO(x) and [(15)N(2)]arginine enrichments in whole blood were performed in the first 3 h in the fasting state and then following a 3-h euglycemic-hyperinsulinemic clamp (with plasma insulin raised to approximately 1,000 pmol/l). In the last 60 min of each experimental period, at approximately steady-state arginine enrichment, a linear increase of (15)NO(x) enrichment (mean r = 0.9) was detected in both experimental periods. In the fasting state, NO(x) FSR was 27.4 +/- 4.3%/day, whereas ASR was 0.97 +/- 0.36 mmol/day, accounting for 0.69 +/- 0.27% of arginine flux. Following hyperinsulinemia, both FSR and ASR of NO(x) increased (FSR by approximately 50%, to 42.4 +/- 6.7%/day, P < 0.005; ASR by approximately 25%, to 1.22 +/- 0.41 mmol/day, P = 0.002), despite a approximately 20-30% decrease of arginine flux and concentration. The fraction of arginine flux used for NO(x) synthesis was doubled, to 1.13 +/- 0.35% (P < 0.003). In conclusion, whole body NO(x) synthesis can be directly measured over a short observation time with stable isotope methods in humans. Insulin acutely stimulates NO(x) synthesis from arginine.

Altered chaperone and protein turnover regulators expression in cultured skin fibroblasts from type 1 diabetes mellitus with nephropathy

In type-1 diabetes mellitus (T1DM) with diabetic nephropathy (DN), accumulation of abnormal proteins in the kidney and other tissues may derive from constitutive alterations of intracellular protein recognition, assembly, and turnover. We characterized the proteins involved in these functions in cultured skin fibroblasts from long-term T1DM patients with [DN+] or without [DN-] nephropathy but similar metabolic control, and from matched healthy subjects. 2-D gel electrophoresis and MS-MALDI analysis were employed. The [DN+] T1DM patients, compared with the two other groups, exhibited increased abundance of a high-molecular weight isoform of protein disulphide-isomerase A3 and a decrease of two low-molecular weight isoforms. They also had increased levels of heat shock protein (HSP) 60 kDa isoform #A4, of HSP71 kDa isoform #A30, and of HSP27 kDa isoform #6, whereas the HSP27 kDa isoforms #A90 and #A71 were decreased. Cathepsin beta-2 (#40), the cation-independent mannose 6-phosphate receptor binding protein 1 (CIMPR) (#A27), and annexin 2 (#A9) were also decreased in the [DN+] T1DM patients, whereas the RNA-binding protein regulatory subunity (#38) and the translationally-controlled tumor protein (TCTP) (#A45) were increased. These changes of chaperone-like proteins in fibroblasts may highlight those of the kidney and be patho-physiologically related to the development of nephropathy in T1DM.

Circulating CD34+ cells, metabolic syndrome, and cardiovascular risk

AIMS

Circulating progenitor cells are believed to participate in cardiovascular (CV) homeostasis and their exhaustion has been linked to CV damage. As general agreement on their characterization is lacking, this work was carried out to assess the relationships between different antigenic profiles of progenitor cells and CV risk, with special regard to metabolic syndrome (MetSyn).

METHODS AND RESULTS

CD34, CD133, and KDR were used to quantify circulating progenitors in 214 subjects at different levels of CV risk. In a cross-analysis of six different cell subtypes (CD34(+), CD133(+), CD34(+)CD133(+), CD34(+)KDR(+), CD133(+)KDR(+), and CD34(+)CD133(+)KDR(+)), CD34(+) progenitors showed the best correlation with CV parameters and risk estimates. Components of the MetSyn were all characterized by reduction of CD34(+) cells and acted synergistically in decreasing CD34(+) cell count. Moreover, CD34(+) cell count demonstrated a high performance in detecting high CV risk.

CONCLUSION

These data demonstrate that CD34 identifies progenitor cells linked to CV risk, showing a close negative correlation between CD34(+) cells and CV risk, as well as a synergic detrimental effect of clustered metabolic components. Progenitor cell count may be used as a surrogate marker of CV risk, whereas extensive antigenic characterization may not be useful for this purpose.

Peripheral blood CD34+KDR+ endothelial progenitor cells are determinants of subclinical atherosclerosis in a middle-aged general population

BACKGROUND AND PURPOSE

Disruption of the endothelial layer is the first step in the atherogenic process. Experimental studies have shown that endothelial progenitor cells (EPCs) are involved in endothelial homeostasis and repair. Conversely, EPC depletion has been demonstrated in the setting of established atherosclerotic diseases. With this background, we evaluated whether variations in the number of EPCs are associated with subclinical atherosclerosis in healthy subjects.

METHODS

Carotid intima-media thickness (IMT), high-sensitive C-reactive protein (hsCRP), levels of circulating EPCs, and cardiovascular risk were compared in 137 healthy subjects. Six subpopulations of progenitor cells were determined by flow cytometry on the basis of the surface expression of CD34, CD133, and KDR antigens: CD34(+), CD133(+), CD34(+)CD133(+), CD34(+)KDR(+), CD133(+)KDR(+), and CD34(+)CD133(+)KDR(+).

RESULTS

Among different antigenic profiles of EPCs, only CD34(+)KDR(+) cells were significantly reduced in subjects with increased IMT. Specifically, CD34(+)KDR(+) cells were inversely correlated with IMT, even after adjustment for hsCRP and 10-year Framingham risk and independently of other cardiovascular parameters.

CONCLUSIONS

Depletion of CD34(+)KDR(+) EPCs is an independent predictor of early subclinical atherosclerosis in healthy subjects and may provide additional information beyond classic risk factors and inflammatory markers.

Effects of insulin on methionine and homocysteine kinetics in type 2 diabetes with nephropathy

Although hyperhomocysteinemia, an independent cardiovascular risk factor, is common in type 2 diabetes with nephropathy, the mechanism(s) of this alteration is not known. In healthy humans, hyperinsulinemia increases methionine transmethylation, homocysteine transsulfuration, and clearance. No such data exist in type 2 diabetes either in the fasting state or in response to hyperinsulinemia. To this purpose, seven male type 2 diabetic patients with albuminuria (1.2 +/- 0.4 g/day, three with mild to moderate renal insufficiency) and seven matched control subjects were infused for 6 h with L-[methyl-(2)H(3), 1-(13)C]methionine. Methionine flux, transmethylation, and disposal into proteins as well as homocysteine remethylation, transsulfuration, and clearance were determined before and after euglycemic hyperinsulinemia (approximately 1,000 pmol/l). In type 2 diabetic subjects, homocysteine concentration was twofold greater (P < 0.01) and methionine transmethylation and homocysteine clearance lower (from approximately 15 to >50% and from approximately 40 to >100%, respectively; P < 0.05) than in control subjects. The insulin-induced increments of methionine transmethylation, homocysteine transsulfuration, and clearance were markedly reduced in type 2 diabetic subjects (by more than threefold, P < 0.05 or less vs. control subjects). In contrast, methionine methyl and carbon flux were not increased in the patients. In conclusion, pathways of homocysteine disposal are impaired in type 2 diabetes with nephropathy, both in postabsorptive and insulin-stimulated states, possibly accounting for the hyperhomocysteinemia of this condition.

Insulin in methionine and homocysteine kinetics in healthy humans: plasma vs. intracellular models

Methionine is a sulfur-containing amino acid that is reversibly converted into homocysteine. Homocysteine is an independent cardiovascular risk factor frequently associated with the insulin resistance syndrome. The effects of insulin on methionine and homocysteine kinetics in vivo are not known. Six middle-aged male volunteers were infused with L-[methyl-2H3,1-13C]methionine before (for 3 h) and after (for 3 additional hours) an euglycemic hyperinsulinemic (150 mU/l) clamp. Steady-state methionine and homocysteine kinetics were determined using either plasma (i.e., those of methionine) or intracellular (i.e., those of plasma homocysteine) enrichments. By use of plasma enrichments, insulin decreased methionine rate of appearance (Ra; both methyl- and carbon Ra) by 25% (P < 0.003 vs. basal) and methionine disposal into proteins by 50% (P < 0.0005), whereas it increased homocysteine clearance by approximately 70% (P < 0.025). With intracellular enrichments, insulin increased all kinetic rates, mainly because homocysteine enrichment decreased by approximately 40% (P < 0.001). In particular, transmethylation increased sixfold (P < 0.02), transsulfuration fourfold (P = 0.01), remethylation eightfold (P < 0.025), and clearance eightfold (P < 0.004). In summary, 1) physiological hyperinsulinemia stimulated homocysteine metabolic clearance irrespective of the model used; and 2) divergent changes in plasma methionine and homocysteine enrichments were observed after hyperinsulinemia, resulting in different changes in methionine and homocysteine kinetics. In conclusion, insulin increases homocysteine clearance in vivo and may thus prevent homocysteine accumulation in body fluids. Use of plasma homocysteine as a surrogate of intracellular methionine enrichment, after acute perturbations such as insulin infusion, needs to be critically reassessed.

Effect of sodium intake on blood pressure and albuminuria in Type 2 diabetic patients: the role of insulin resistance

AIMS/HYPOTHESIS

This study was done to measure the effect of Na+ intake on blood pressure and albuminuria, in relation with insulin sensitivity and kidney haemodynamics, in Type 2 diabetic patients with and without microalbuminuria.

METHODS

Type 2 diabetic patients, 20 with microalbuminuria, 21 without, spent two consecutive 7-day periods, one on a high (250 mmol), the other on a low-Na+ (20 mmol) diet. Body weight, 24-h blood pressure and albuminuria were measured at the end of each period. At the end of high-Na+ diet insulin sensitivity (euglycaemic insulin clamp; 2 mU.kg(-1).min(-1)) and kidney haemodynamics were measured in nine patients from each group.

RESULTS

Switching from low to high-Na+ diet resulted in an increase in blood pressure (7.4+/-4.7 mmHg; p<0.001), body weight (1.9+/-0.4 kg; p<0.05) and albuminuria [from 80 (31-183) microg/min to 101 (27-965) microg/min; p<0.01) in patients with microalbuminuria. No changes occurred in patients without microalbuminuria. Patients with microalbuminuria also had greater intraglomerular pressure (44+/-1 mmHg vs 36+/-1; p<0.001), calculated from glomerular filtration rate, renal plasma flow, plasma protein concentration and the relationship between pressure and natriuresis. In these patients insulin sensitivity was lower (5.16+/-49 vs 7.36+/-0.63 mg.kg(-1).min(-1); p=0.007). Urinary albumin excretion (r=0.40; p=0.009) and insulin sensitivity (r=-0.59; p=0.01) were correlated with intraglomerular pressure.

CONCLUSION/INTERPRETATION

High salt intake increases blood pressure and albuminuria in Type 2 diabetic patients with microalbuminuria. These responses are associated with insulin resistance and increased glomerular pressure. Insulin resistance could contribute to greater salt sensitivity, increased glomerular pressure and albuminuria.

Concomitance of diabetic retinopathy and proteinuria accelerates the rate of decline of kidney function in type 2 diabetic patients

OBJECTIVE

To evaluate the rate of progression of renal disease in proteinuric type 2 diabetic patients with and without retinopathy.

RESEARCH DESIGN AND METHODS

Thirty-eight proteinuric type 2 diabetic patients with diabetic retinopathy and 27 without were enrolled in an observational study for the evaluation of rate of glomerular filtration rate (GFR) decline and followed up for a median period of 6 years. GFR was determined at least once per year, and blood pressure, glycated hemoglobin, and proteinuria were determined every 4 months.

RESULTS

Although the two groups had comparable GFR, albuminuria, blood pressure, and HbA(1c) at entry of the study, the rate of decline of GFR was higher in type 2 diabetic patients with retinopathy (-6.5 +/- 4.4 ml/year) than in those without (-1.8 +/- 4.8 ml/year; P < 0.0001). Protein and albumin excretion rate increased significantly in patients with retinopathy, while they did not change in those without. Mean blood pressure between the two groups of patients were similar both at entry and during the follow-up, although the proportion of patients treated with at least two antihypertensive drugs was higher in patients with retinopathy. On a multiple regression analysis, only mean blood pressure and proteinuria were significant determinants of progression of renal disease in type 2 diabetic patients with retinopathy.

CONCLUSIONS

The rate of progression of renal disease in proteinuric type 2 diabetic patients with retinopathy is faster than that observed in those without retinopathy. The screening for retinopathy identifies patients at high risk for rapid deterioration of kidney function.