Protective Effects of Liraglutide and Linagliptin in C. elegans as a New Model for Glucose-Induced Neurodegeneration.

Liraglutide and linagliptin are novel drugs for the treatment of diabetes. Antioxidative and neuroprotective effects have been described for both compounds. However, it is not yet known, whether these mechanisms are also protective against diabetic retinal neurodegeneration. We assessed the antioxidative and neuroprotective capabilities of liraglutide and linagliptin as well as the signaling pathways involved, by using C. elegans as a model for glucose-induced neurodegeneration. C. elegans were cultivated under conditions, which mimic clinical hyperglycemia, and treated with 160 µmol/l liraglutide or 13 µmol/l linagliptin. Oxidative stress was reduced by 29 or 78% and methylglyoxal-derived advanced glycation endproducts (AGEs) by 33 or 22%, respectively. This resulted in an improved neuronal function by 42 or 60% and an extended mean lifespan by 9 or 11%, respectively. Antioxidative and AGE reducing effects of liraglutide and linagliptin were not dependent on v-akt murine thymoma viral oncogene homologue 1/forkhead box O1 (AKT1/FOXO). Neuroprotection by liraglutide was AKT1/FOXO dependent, yet AKT1/FOXO independent upon linagliptin treatment. Both liraglutide and linagliptin exert neuroprotective effects in an experimental model for glucose-induced neurodegeneration, however, the signaling pathways differ in the present study. Further pharmacological intervention with these pathways may help to delay the clinical onset of diabetic retinopathy by preserving neuronal integrity.

Is diabetes an acquired disorder of reactive glucose metabolites and their intermediates?

AIMS/HYPOTHESIS: We hypothesised that diabetic patients would differ from those without diabetes in regard to the handling of glucose-derived reactive metabolites, evidenced by triosephosphate intermediates (TP(INT)) and methylglyoxal (MG), irrespective of the type of diabetes, plasma glucose level or HbA(1c) value. METHODS: To test this hypothesis, erythrocytes were isolated from patients with type 1 (n = 12) and type 2 (n = 12) diabetes with varying blood glucose and HbA(1c) levels. These were then compared with erythrocytes isolated from individuals without diabetes (n = 10), with respect to MG, as determined by HPLC, and TP(INT), as determined by endpoint enzymatic assays. RESULTS: The concentrations of intracellular TP(INT) and MG were significantly elevated in erythrocytes from diabetic patients. Normalisation of either TP(INT) or MG to intracellular glucose concentration (nmol glucose/mgHb) confirmed that erythrocytes from diabetic patients accumulated more reactive metabolites than did those from healthy controls. CONCLUSIONS/INTERPRETATION: Diabetic patients can be characterised by an increased formation of TP(INT) and MG. The 25-fold increase of MG in type 1 and the 15-fold increase in type 2 diabetes, together with a several-fold increase in TP(INT) and decreased glyceraldehyde-3-phosphate dehydrogenase activity even under normal glucose conditions, imply that normalising glucose level cannot completely prevent late diabetic complications until this acquired error of metabolism has been restored.

Urinary L-FABP and anaemia: distinct roles of urinary markers in type 2 diabetes.

BACKGROUND: Urinary liver-type fatty acid binding protein (L-FABP) and kidney injury molecule (KIM)-1, novel urinary biomarkers of renal tubulointerstitial function, have previously been associated with acute ischaemic kidney injury. We studied the clinical significance of urinary L-FABP, KIM-1 and N-acetyl-beta-glucosaminidase (NAG) as potential markers of renal function and chronic ischaemic injury in patients with diabetic nephropathy. MATERIAL AND METHODS: A total of 130 type 2 diabetes patients with early diabetic nephropathy and 40 healthy controls were studied. Urinary L-FABP, KIM-1, NAG, albumin excretion rate (AER) and creatinine clearance were obtained from 24-h urine samples, and correlated with measures of red blood cell count, renal function and metabolic control. RESULTS: Urinary L-FABP was significantly increased in diabetes patients compared with healthy controls [8.1 (interquartile 0.6-11.6) vs. 2.4 (0.5-3.6) microg/g creatinine, P < 0.001] and correlated with AER (r = 0.276, P = 0.002), creatinine clearance (r = -0.189, P = 0.033) and haemoglobin levels (r = -0.190, P = 0.030). In multivariable linear regression analysis, haemoglobin (beta = -0.247, P = 0.015) and AER (beta = 0.198, P = 0.046) were significant predictors of urinary L-FABP. Prevalent anaemia was independently associated with a 6-fold risk for increased tubulointerstitial kidney damage (upper vs. lower two L-FABP tertiles: OR, 6.06; 95% CI: 1.65-22.23; P = 0.007). Urinary KIM-1 was not significantly associated with kidney function, AER, or measures of red blood cell count while urinary NAG was associated with parameters of glucose control and renal function. CONCLUSIONS: Different urinary biomarkers may reflect distinct pathophysiological mechanisms of tubulointerstitial damage in early diabetic nephropathy: Urinary L-FABP could be a novel biomarker for chronic intrarenal ischaemia.

Changes in adiponectin multimer distribution in response to atorvastatin treatment in patients with type 2 diabetes.

OBJECTIVE: Multimeric high molecular weight (HMW) forms of adiponectin were previously shown to be inversely associated with the extent of atherosclerosis in males and are down-regulated in patients with the metabolic syndrome and type 2 diabetes. In this study, potential influences of atorvastatin therapy on adiponectin multimer distribution were studied in patients with type 2 diabetes. DESIGN, PATIENTS AND MEASUREMENTS: The effect of 40 mg atorvastatin on HMW, medium molecular weight (MMW), and low molecular weight (LMW) isoforms of adiponectin were investigated in 75 patients (23 females; 52 males) with type 2 diabetes in an 8-week-long, placebo-controlled and randomized study. Adiponectin multimeric isoforms were detected by Western blot analysis. RESULTS: After atorvastatin therapy the median serum concentration of HMW adiponectin increased significantly by 42.3% (1.68 vs. 2.39 microg/ml; P < 0.001), while concentrations of MMW adiponectin and LMW adiponectin significantly decreased by 20.8% and 23.2%, respectively (MMW: 3.31 vs. 2.62 microg/ml, P = 0.047; LMW: 0.56 vs. 0.43 microg/ml, P = 0.033). Median total adiponectin levels were not significantly altered by atorvastatin treatment (6.0 vs. 6.2 microg/ml, P = 0.898). Consequently, the HMW: total-adiponectin ratio significantly increased by 25.0% (0.40 vs. 0.50; P = 0.013). CONCLUSIONS: Atorvastatin therapy is associated with significant changes in adiponectin multimer distribution in patients with type 2 diabetes. Since total adiponectin levels were not affected by intervention, atorvastatin may shift adiponectin size towards the HMW form.

The -174G>C IL-6 gene promoter polymorphism and diabetic microvascular complications.

This study examined a possible association of the G>C polymorphism at nucleotide -174 in the promoter region of the interleukin-6 (IL-6) gene (rs1800795) with the prevalence of diabetic complications in 235 patients with type 1 and 498 patients with type 2 diabetes. Genotyping was performed using polymerase chain reaction (PCR) and subsequent cleavage by Nla III restriction endonuclease. Analyzing all diabetic patients together demonstrated that 301 patients (41.1%) carried the GG genotype, 114 (15.6%) the CC genotype, and 318 (43.3%) were heterozygous for the GC genotype. However, there was no correlation of any of the genotypes with the prevalence of diabetic nephropathy or diabetic neuropathy, but subjects with the CC genotype had a significantly higher prevalence of diabetic retinopathy compared to patients with the GC and GG genotype (p=0.016). This association was mainly lost when a logistic regression model was adjusted for diabetes duration (p=0.07). Consistently, a weak but not significant association of the polymorphism with diabetic retinopathy was observed when type 1 and type 2 diabetic patients were analyzed separately (patients with type 1 diabetes: p=0.12; patients with type 2 diabetes: p=0.09). Analogically, no association of the polymorphism was found for diabetic nephropathy or diabetic neuropathy in these groups. In conclusion these data suggest no major influence of the -174G>C variant in the promoter region of the IL-6 gene on the development of microvascular complications in patients with diabetes.

Clinical benefit of a short term dietary oatmeal intervention in patients with type 2 diabetes and severe insulin resistance: a pilot study.

AIMS/HYPOTHESIS: To evaluate the potential effectiveness of 'carbohydrate days' as a dietary intervention to overcome insulin resistance in type 2 diabetes. MATERIALS AND METHODS: Patients (n=14) with uncontrolled type 2 diabetes and insulin resistance as defined by a dosage of more than 1 IU/day (*)kg BW were consecutively enrolled in this prospective study. Primary outcomes were daily insulin requirement and mean blood glucose levels which were evaluated before, after, and 4 weeks after the intervention. RESULTS: All patients had a metabolic syndrome, 75% had microvascular and 57.1% macrovascular complications. Hospital setting and diabetes adapted diet alone led to improved glycemic control with a mean blood glucose 158+/-47 mg/dl. Intervention with two days of oatmeal diet further decreased mean blood glucose to 118+/-37 mg/dl (p<0.05). This was associated with a significant reduction of insulin dosage by 42.5% (before: 145+/-68.9 U/d, after 83+/-34.2 U/d, p<0.001) as well as a significant reduction (-26.4%, p<0.01) of serum leptin levels. After the four weeks outpatient period, insulin dosage remained significantly decreased (83+/-20.2 U/kg (*)d, p<0.01). Glycemic control was comparable (mean blood glucose141+/-20.78 mg/dl) to glucose levels within the hospital setting. Adiponectin levels increased significantly by 53.8% (p<0.05). CONCLUSIONS: In this uncontrolled pilot study, hospital admission and diabetes adapted diet followed by oatmeal intervention achieved a approximately 40% reduction of insulin dosage required to achieve controlled glucose levels. This effect was conserved after a 4 week outpatient phase with normal diet.

A M55V polymorphism in the SUMO4 gene is associated with a reduced prevalence of diabetic retinopathy in patients with Type 1 diabetes.

AIMS: We studied the association between a functionally relevant M55V polymorphism in the SUMO4 gene with microvascular diabetic complications in patients with type 1 diabetes. METHODS: 223 patients with type 1 diabetes were studied using polymerase chain reaction and subsequent cleavage by restriction endonucleases for the M55V SUMO4 gene variant. RESULTS: No effect of the polymorphism on diabetic neuropathy or diabetic nephropathy was found, but heterozygous or homozygous patients for the M55V polymorphism in the SUMO4 gene had a markedly reduced prevalence of diabetic retinopathy (odds ratio 0.37, 95%-confidence interval (CI) [0.32;0.43]; p=0.004). Furthermore, a multiple logistic regression model showed an age and diabetes duration independent effect of the M55V polymorphisms on the prevalence of diabetic retinopathy (p=0.03), but not of diabetic neuropathy or nephropathy. CONCLUSIONS: Our data indicate that the M55V polymorphism in the SUMO4 gene is associated with a reduced risk of diabetic retinopathy in type 1 diabetes. Thus, the results of our study suggest that posttranslational modification of proteins via SUMO4 could contribute to the development of certain diabetic complications.

The DG10S478 variant in the TCF7L2 gene is not associated with microvascular complications in type 2 diabetes.

OBJECTIVE: The DG10S478 variant in the transcription factor 7-like 2 (TCF7L2) gene is a tetranucleotide repeat with six alleles. Alleles 0, 8 and 12 were found to account for 98% of chromosomes in population based controls. The composite allele X (non zero) has been associated with type 2 diabetes while allele 0 (no insertion) was described as protective. However, no data exist about the influence of DG10S478 variants on manifestation of diabetes and development of diabetic complications. METHODS: 250 patients with type 2 diabetes were tested for the DG10S478 allele X and its association with diabetic complications, age at diagnosis of diabetes and BMI. RESULTS: Allele 0 was found in 42.4% of the examined patients, 45.2% of the participants were found to be heterozygous and 12.4% homozygous for the composite allele X. The correlation of allele X with the age at diagnosis of diabetes was not significant. There was also no association of allele X with retinopathy, nephropathy or neuropathy. Only the correlation with BMI was statistically significant. CONCLUSIONS: The DG10S478 variant seems to have no influence on manifestation of diabetes and the development of microvascular complications.

Non-invasive diagnostic imaging techniques as a window into the diabetic heart: a review of experimental and clinical data.

Epidemiological and clinical studies show a clear association of diabetes mellitus with congestive heart failure and cardiovascular events independent of blood pressure and ischemic heart disease. The definition of 'diabetic cardiomyopathy' as a clinical entity, however, relies on distinct myocellular and interstitial alterations found in the myocardium of patients with diabetes. The histological findings comprise myocellular hypertrophy, thickening of capillary basement membranes, interstitial fibrosis and rarification of mitochondria on the ultrastructural level. For clinical routine, early detection of diabetic cardiomyopathy seems crucial for identification of patients at cardiovascular risk since the prevalence of heart failure in individuals with diabetes is markedly increased. Recent technical developments in cardiac magnetic resonance imaging (MRI), echocardiography as well as nuclear scintigraphy have advanced the diagnostic applications for the detection of diabetic heart disease. This review aims to present distinct aspects of diabetic cardiomyopathy that were identified using non- invasive imaging techniques. Due to the wide availability and the low costs of echocardiography, it is the most frequently used imaging technique to detect left ventricular dysfunction in patients with diabetes. MRI on the other hand can provide assessment of myocardial structure with higher spatial resolution and allows objective assessment of left ventricular function. This makes MRI an attractive alternative for the detection of discrete alterations, particularly in patients with poor echogenic windows. Finally, nuclear scintigraphy can provide information on cardiac autonomic integrity and accurately detect defects in autonomic control, which are considered a major cardiovascular risk factor in patients with diabetes.

Diabetes-associated sustained activation of the transcription factor nuclear factor-kappaB.

Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) has been suggested to participate in chronic disorders, such as diabetes and its complications. In contrast to the short and transient activation of NF-kappaB in vitro, we observed a long-lasting sustained activation of NF-kappaB in the absence of decreased IkappaBalpha in mononuclear cells from patients with type 1 diabetes. This was associated with increased transcription of NF-kappaBp65. A comparable increase in NF-kappaBp65 antigen and mRNA was also observed in vascular endothelial cells of diabetic rats. As a mechanism, we propose that binding of ligands such as advanced glycosylation end products (AGEs), members of the S100 family, or amyloid-beta peptide (Abeta) to the transmembrane receptor for AGE (RAGE) results in protein synthesis-dependent sustained activation of NF-kappaB both in vitro and in vivo. Infusion of AGE-albumin into mice bearing a beta-globin reporter transgene under control of NF-kappaB also resulted in prolonged expression of the reporter transgene. In vitro studies showed that RAGE-expressing cells induced sustained translocation of NF-kappaB (p50/p65) from the cytoplasm into the nucleus for >1 week. Sustained NF-kappaB activation by ligands of RAGE was mediated by initial degradation of IkappaB proteins followed by new synthesis of NF-kappaBp65 mRNA and protein in the presence of newly synthesized IkappaBalpha and IkappaBbeta. These data demonstrate that ligands of RAGE can induce sustained activation of NF-kappaB as a result of increased levels of de novo synthesized NF-kappaBp65 overriding endogenous negative feedback mechanisms and thus might contribute to the persistent NF-kappaB activation observed in hyperglycemia and possibly other chronic diseases.

Locally applied mononuclear bone marrow cells restore angiogenesis and promote wound healing in a type 2 diabetic patient.

We treated a patient with type 2 diabetes suffering from chronic venous and neuro-ischemic wounds not healing under standard care with local application of autologous bone marrow cells (mBMC) isolated from bone marrow aspirate. This procedure led to a reduction of wound size, a markedly increased vascularization and infiltration of mononuclear cells, 7 days after treatment, without any signs of a systemic reaction to treatment. Locally applied mBMC could, therefore, provide a treatment option in end stage diabetic wound healing disorders.

Adult vascular progenitor cells and tissue regeneration in metabolic syndrome.

Adult vascular progenitor cells (for example endothelial progenitor cells, EPC) have been studied for their contribution to vascular repair and angiogenesis. These cells can differentiate from bone marrow cells as well as circulating cells carrying hematopoetic stem cell markers. In vivo, they take part in vasculogenesis in different animal models of limb ischemia, myocardial infarction and wound healing. In metabolic disease, the outgrowth and function of EPC in vitro is defective and numbers of EPC correlate with classical risk factors of cardiovascular disease suggesting a role of EPC in the development of vascular complications. Pilot studies for the treatment of myocardial infarction and limb ischemia with autologous bone marrow showed a distinct therapeutic benefit that is presumably mediated by vasculogenesis in damaged tissues. However, little is known about the nature of EPC and their capability to differentiate into functional cells for tissue regeneration. In this article, we review and discuss the hitherto identified physiological function of EPC, the mechanisms leading to dysfunction of these cells and potential therapeutic applications in patients with metabolic syndrome or diabetes mellitus and vascular complications.

A 63bp deletion in the promoter of rage correlates with a decreased risk for nephropathy in patients with type 2 diabetes.

Several polymorphisms have been identified in the RAGE-promoter region that might modulate the outcome of disease. Here we analyse the association of a 63bp deletion (delta63) spanning from bp - 407 to bp - 345 with diabetic nephropathy. The deletion was determined using the polymerase chain reaction (PCR) in a cross-sectional study with 1087 patients with type 1 diabetes (n = 559) and type 2 diabetes (n = 528). 475 patients with osteoporosis served as disease independent control. The prevalence of the heterozygous genotype did not significantly differ between the three groups (type 1: 2.15 %, type 2: 2.27 %, controls: 1.47 %), indicating that heterozygous delta63 is not related to the manifestation of diabetes. Homozygous carriers were not identified in this study. The heterozygous delta63 genotype, was associated with a reduced prevalence of diabetic nephropathy in patients with type 2 diabetes (OR = 0.06; 95 % CI: [0.05, 0.07]), but not in patients with type 1 (OR = 1.49; 95 % CI: [1.14, 1.94]). We conclude, that patients with type 2 diabetes and the 63bp deletion in the promoter of RAGE seem to be protected from diabetic nephropathy. The observed difference between type 1 and type 2 diabetes might point to diverse pathomechanisms of nephropathy in both types of diabetes.

Effects of stress reduction on cardiovascular risk factors in type 2 diabetes patients with early kidney disease - results of a randomized controlled trial (HEIDIS).

Current guidelines for the treatment of type 2 diabetes focus on pharmacological treatment of glucose and cardio-vascular risk factors. The aim of this prospective randomized controlled intervention study was to examine the effects of a psychosocial intervention on clinical endpoints and risk factors in patients with type 2 diabetes and early diabetic kidney disease.110 patients were randomized to receive an 8-week mindfulness-based stress reduction (MBSR) training (n = 53) compared to standard care (n = 57). The study was carried out open-labelled and randomization was performed computer-generated in a 1:1 ratio. Primary outcome of the study was the change in urinary albumin excretion (albumin-creatinine-ratio, ACR); secondary outcomes were metabolic parameters, intima media thickness (IMT), psychosocial parameters and cardiovascular events.89 patients (42 in control group and 47 in intervention group) were analysed after 3 years of follow-up. After 1 year, the intervention group showed a reduction of ACR from 44 [16/80] to 39 [20/71] mg/g, while controls increased from 47 [16/120] to 59 [19/128] mg/g (p = 0.05). Parallel to the reduction of stress levels after 1 year, the intervention-group additionally showed reduced catecholamine levels (p < 0.05), improved 24 h-mean arterial (p < 0.05) and maximum systolic blood pressure (p < 0.01), as well as a reduction in IMT (p < 0.01). However, these effects were lost after 2 and 3 years of follow-up.This is the first study to show that a psychosocial intervention improves cardiovascular risk factors in high risk type 2 diabetes patients. Trial-Registration: NCT00263419 http://clinicaltrials.gov/ct2/show/NCT00263419 TRIAL REGISTRATION: clinicaltrials.gov-Identifier: NCT00263419.

Urinary n-acetyl-beta-d-glucosaminidase excretion: an indicator of neuropathy in type 2 diabetes.

The established marker for tubular damage, urinary n-acetyl-beta-d-glucosaminidase is significantly increased in type 1 and 2 diabetes patients and is related to albuminuria and other diabetic complications. In this cross sectional study of type 2 diabetes patients with a history of albuminuria, we studied the relationship between excretion of n-acetyl-beta-d-glucosaminidase in urine and diabetic neuropathy.160 type 2 diabetes patients were screened for diabetic peripheral neuropathy and cardiovascular autonomic neuropathy. N-acetyl-beta-d-glucosaminidase excretion was detected in 24 h urine samples.Urinary excretion of n-acetyl-beta-d-glucosaminidase correlated significantly with -glucose control (fasting glucose r=0.18; p=0.04; HbA1c r=0.20; p=0.02) and urine albumin excretion (r=0.22; p=0.01). Binary regression analyses showed that increased urinary n-acetyl-beta-d-glucosaminidase concentration is an independent predictor for presence of clinical symptoms of peripheral neuropathy (OR 1.8 [95%CI 1.2-2.74] and vibration deficiency [OR 1.7; 95% CI 1.2-2.66]. There was also a significant negative association between urinary n-acetyl-beta-d-glucosaminidase and E/I-Ratio (r=-0.21, p<0.02) as well as the 30:15-Ratio (r=-0.24; p<0.01) of heart rate variability. Furthermore, increased n-acetyl-beta-d-glucosaminidase excretion independently predicted cardiovascular autonomic diabetic neuropathy with an OR for decreased E/I-Ratio of 1.7 [95%CI 1.1-2.75]; (p<0.02) and 30:15-Ratio:OR 2.4 [95% CI 1.26-4.45]; (p<0.01).Urinary n-acetyl-beta-d-glucosami-nidase excretion is an independent marker for diabetic peripheral and cardiovascular autonomic neuropathy in type 2 diabetic patients.

Rosiglitazone reduces angiotensin II and advanced glycation end product-dependent sustained nuclear factor-kappaB activation in cultured human proximal tubular epithelial cells.

Tubular damage is a major feature in the development of diabetic nephropathy. This study investigates the effects of the thiazolidindione rosiglitazone on angiotensin II and advanced glycation end product-induced tubular activation in human proximal tubular epithelial cells IN VITRO. Angiotensin II and advanced glycation end products, both induced a dose-dependent sustained activation of the redox-sensitive transcription factor, Nuclear Factor KAPPA B (NF-kappaB). Nuclear translocation of NF-kappaB was evident already after one hour and persistent for more than four days. Co-incubation of proximal tubular epithelial cells with rosiglitazone significantly reduced angiotensin II and advanced glycation end product-mediated generation of reactive oxygen species, angiotensin II-dependent advanced glycation end product formation, NF-kappaB activation, and NF-kappaB-dependent pro inflammatory gene expression. Most importantly, rosiglitazone effects on NFkappaB activation were maximal at later time points, indicating that rosiglitazone treatment confers long lasting renoprotective effects.

sRAGE and esRAGE are not associated with peripheral or autonomic neuropathy in type 2 diabetes.

The receptor for glycation end-products RAGE was previously shown to play a central role in the development of diabetic neuropathy. The present study was aimed to investigate, whether plasma levels of the soluble forms of RAGE are associated with neuropathy in type 2 diabetes. One-hundred and eight patients were screened for peripheral and autonomic diabetic neuropathy using standardized screening tests. No differences in the levels of soluble RAGE or the more defined endogenous secretory RAGE were observed in patients categorized into having no, mild, moderate, or severe deficits in the neuropathy disability or symptom score. In bivariate analysis, neither soluble RAGE nor endogenous secretory RAGE correlated with the expiration to inspiration ratio of heart rate variability. In multivariate models, the neuropathy disability score was independently associated with age (beta=0.38, p<0.01), glomerular filtration rate (beta=0.28, p<0.01) and the presence of retinopathy (beta=0.27, p<0.01), while the neuropathy symptom score was associated with age (beta=0.31, p<0.01) and fasting glucose (beta=0.24, p<0.05). The expiration to inspiration ratio of heart rate variability was associated with age (beta=-0.42, p<0.01), the body-mass-index (beta=-0.28, p<0.01) and presence of retinopathy (beta=-0.19, p<0.05). In contrast to classical risk factors, plasma soluble RAGE and endogenous secretory RAGE are not associated with measures of diabetic neuropathy in type 2 diabetes patients.

Retinol-binding protein 4 is associated with components of the metabolic syndrome, but not with insulin resistance, in men with type 2 diabetes or coronary artery disease.

AIMS/HYPOTHESIS: Retinol-binding protein 4 (RBP4) has recently been reported to be associated with insulin resistance and the metabolic syndrome. This study tested the hypothesis that RBP4 is a marker of insulin resistance and the metabolic syndrome in patients with type 2 diabetes or coronary artery disease (CAD) or in non-diabetic control subjects without CAD. METHODS: Serum RBP4 was measured in 365 men (126 with type 2 diabetes, 143 with CAD and 96 control subjects) and correlated with the homeostasis model assessment of insulin resistance index (HOMA-IR), components of the metabolic syndrome and lipoprotein metabolism. RBP4 was detected by ELISA and validated by quantitative Western blotting. RESULTS: RBP4 concentrations detected by ELISA were shown to be strongly associated with the results gained in quantitative Western blots. There were no associations of RBP4 with HOMA-IR or HbA(1c) in any of the groups studied. In patients with type 2 diabetes there were significant positive correlations of RBP4 with total cholesterol, LDL-cholesterol, VLDL-cholesterol, plasma triacylglycerol and hepatic lipase activity. In patients with CAD, there were significant associations of RBP4 with VLDL-cholesterol, plasma triacylglycerol and hepatic lipase activity, while non-diabetic control subjects without CAD showed positive correlations of RBP4 with VLDL-cholesterol and plasma triacylglycerol. CONCLUSIONS/INTERPRETATION: RBP4 does not seem to be a valuable marker for identification of the metabolic syndrome or insulin resistance in male patients with type 2 diabetes or CAD. Independent associations of RBP4 with pro-atherogenic lipoproteins and enzymes of lipoprotein metabolism indicate a possible role of RBP4 in lipid metabolism.