Theodor Koschinsky

Dietary Advanced Glycation Endproducts and Oxidative Stress

Advanced glycation endproducts (AGEs) and oxidative stress (OS) contribute to the development and progression of diabetic complications. We have reported that dietary AGEs and OS induce acute endothelial dysfunction in vivo, but little is known about their effects on adipokines. Twenty inpatients with type 2 diabetes mellitus (mean age: 55.9; range: 32–71 years), received a standard diabetes diet for 6 days. On days 4 and 6, the acute effects of a high‐AGE (HAGE) or a low‐AGE (LAGE) meal (15.100 vs. 2.750 kU AGE) were studied in a randomized, cross‐over, investigator‐blinded design. Measurements were performed after an overnight fast, at baseline (B) and at 2, 4, and 6 h after the HAGE or LAGE meals. Both meals had the same ingredients and differed only by the cooking method. Two h following HAGE, a significant decrease from baseline occurred in adiponectin (−10%*‡ vs. +0%) and leptin (−22%*‡ vs. −13%*), and a significant increase occurred in vascular cell adhesion molecule 1 (+19%*‡ vs. −5%) and thiobarbituric acid reactive substances (+23%*‡ vs. +6%). These changes did not occur, or occurred to a lesser extent, following LAGE. At 4 h following HAGE, an increase in methylglyoxal (+20%‡ vs. −5%) and E‐selectin (+54%*‡ vs. −3%) occurred. Urinary AGEs increased only after HAGE (+51%*‡ vs. −2%; values presented as HAGE vs. LAGE; *P < 0.05 vs. baseline, ‡P < 0.05 vs. LAGE). The postprandial excursions in glucose, insulin, and triglycerides were similar between both meals. A meal rich in AGEs induces acute endothelial and adipocyte dysfunction. These effects were prevented by changing the cooking method.

Glucose sensors and the alternate site testing-like phenomenon: relationship between rapid blood glucose changes and glucose sensor signals.

In the last few years blood glucose meters have been developed allowing glucose measurements in capillary blood samples collected at sites other than the fingertips. The main reason for establishing this so-called alternate site testing (AST) was to sample blood from locations with reduced pain perception. It is well known that capillary blood glucose is closely correlated to systemic (i.e., arterial) glucose levels and that under steady-state conditions, glucose values measured in blood samples collected from alternate sites are virtually identical to those collected from the fingertip. However, during rapid changes in blood glucose levels, glucose concentrations in capillary blood samples from the fingertips can differ considerably in both domains (time and concentration) from those determined in capillary blood from alternate sites (i.e., the so-called AST phenomenon). Such differences can have serious clinical consequences (e.g., risky delays in hypoglycemia detection). There is evidence that all skin sites exhibiting a reduced blood flow (in comparison with the fingertip) within the superficial skin layers are prone to this AST phenomenon. Nearly all glucose sensors having been developed so far or being currently under development measure glucose levels at alternate sites and also in another compartment [e.g., interstitial fluid (ISF)] than blood. So, in principle they might be prone to an AST-like phenomenon (i.e., rapid changes in systemic blood glucose levels may also result in delayed ISF glucose readings). Our knowledge about the impact of an AST-like phenomenon on the performance of glucose monitoring systems is presently very limited. Glucose kinetics in the different compartments during dynamic systemic blood glucose changes have not been fully elucidated yet. If an AST-like phenomenon plays a role with glucose sensors should therefore be studied. Depending on the measurement technology used for the individual type of glucose monitoring system probably this phenomenon has a variable impact on the results obtained.

Advanced glycation end products strongly activate platelets.

BackgroundDiabetes mellitus is characterized by hyperglycemia that plays an important role in the pathogenesis of diabetic complications including cardiovascular diseases. Moreover, hyperglycemia induces increased generation of advanced glycation end products (AGEs). The activation of platelets is associated with the development of cardiovascular diseases.Aim of the studyThe question whether AGEs acutely induce platelet activation as a response to exogenous stimulus is addressed.Materials and methodsThe effect of AGEs derived from food and human serum being purified by lysozyme affinity chromatography was examined by incubating in vitro freshly isolated blood platelets from fasted subjects at various concentrations and different time points. Platelet activation, determined as expression of surface markers CD62 and CD63, and the presence of the receptor for AGEs (RAGE) in platelet membranes was measured by flow cytometric analysis using specific antibodies.ResultsIncubation with food-derived as well as serum-derived AGEs stimulated significantly the expression of CD62 up to 7.1-fold and CD63 up to 2.2-fold at the platelet surface membrane as a function of concentration and time. Incubation with thrombin or AGEs significantly increased RAGE expression twofold at the platelet surface membrane.ConclusionsThe increase in surface activation marker and RAGE expression in platelets, resulting from concentrations of AGEs that occur in vivo after a meal or a drink as a source of exogenous AGEs, points to signaling mechanisms for food AGEs that could favor the precipitation of acute postprandial ischemic events.

Skin Autofluorescence Increases Postprandially in Human Subjects

BACKGROUND Skin autofluorescence (SAF) is a property used for the noninvasive assessment of skin advanced glycation end products (AGEs) and concentration of redox-regulated fluorophores. SAF was shown to closely mirror cardiovascular risk and to constitute a more sensitive parameter for diabetes screening than fasting glucose and hemoglobin A1c. It has also been suggested that SAF measurement is independent of fasting status. Our study was designed in order to test whether SAF changes postprandially. METHODS We have investigated 21 Caucasian subjects (10 healthy subjects, 11 subjects with type 2 diabetes mellitus). SAF was measured in the fasting state, as well as 2 and 4 h following a meal with a medium AGE content. RESULTS Two hours postprandially, SAF significantly increased by 10.2% in the whole group, by 11.6% in the group of individuals with diabetes, and by 8.7% in healthy subjects (for all measurements P < 0.05 vs. baseline). CONCLUSIONS SAF increases postprandially in individuals with diabetes mellitus and in healthy subjects. Therefore, we suggest that measurements of SAF should be performed in the fasting state in order to increase sensitivity and specificity of the method for assessing cardiovascular risk and diabetes screening.

Increased growth of human fibroblasts and arterial smooth muscle cells from diabetic patients related to diabetic serum factors and cell origin

Fibroblasts from 3 diabetic patients (DF) grew faster, resulting in higher cell counts in the stationary phase than fibroblasts from 3 age-matched healthy volunteers (NF). This difference was apparent when DF or NF were cultured in either diabetic (DS) or normal serum (NS). Diabetic serum increased growth of both DF and NF compared with normal serum. Total protein content per plate paralleled the increase of cell number per plate in relation to cell origin and serum type. DS increased growth and total protein per plate in the arterial smooth muscle cell line from a non-diabetic patient in a way similar to in DF and NF. It is concluded that increased growth of DF in vivo could result in an increased turnover of vascular cells with a shortened replicative lifespan, leading to an accumulation of basal lamina. This effect would be even further accentuated by exposure of DF to DS. Taken together with the increased protein synthesis the accelerated development of diabetic angiopathy could be the final consequence.

Increased growth stimulation of human vascular cells by serum from patients with primary hyper-LDL-cholesterolemia☆

Premature atherosclerosis in hypercholesterolemic patients may be due, in part, to increased growth of vascular cells. Therefore, the growth stimulating effect of serum and serum fractions from patients with primary hyper-LDL-cholesterolemia (LDL-cholesterol: 7.5 +/- 1.7 mmol/l) and from healthy subjects on human arterial smooth muscle cells and fibroblasts has been investigated over 5-7 days in culture. Human hypercholesterolemic sera increased the growth of both cell types up to a mean of 133% compared with normal sera (100%) (P less than 0.001). Removal of the dialyzable serum fraction (m.w. less than 3,500 daltons) reduced the growth effect of the hypercholesterolemic sera by 32% (P less than 0.001) and of the normal sera by 11% (P less than 0.01). Readdition of the hypercholesterolemic serum dialysate to its dialyzed serum restored completely the original growth effect. There was no significant difference in growth stimulation between the dialyzed hypercholesterolemic and normal sera excluding a major additional growth effect by LDL-cholesterol. The low molecular weight growth factor(s) of hypercholesterolemic serum (m.w. less than 3,500 daltons) showed a linear dependence of growth stimulation over a 20-fold concentration range. Increased amounts of this factor(s) might easily penetrate the arterial wall, thus contributing to atherogenesis.

Increased growth stimulation of fibroblasts from diabetics by diabetic serum factors of low molecular weight

Serum factors from non-ketotic poorly controlled diabetic patients when compared to serum factors from normal subjects, stimulate growth and protein synthesis of cultured fibroblasts from diabetic patients by 25-50%. This increased growth stimulating effect of diabetic serum is mainly related to low molecular weight components (mol. wt. < 12,000 daltons), but not to insulin or glucose. These low molecular weight components of diabetic serum are effective only in combination with serum factors of a molecular weight > 12,000 daltons which are essential for initiation and continuous stimulation of cellular growth. As the growth stimulation by diabetic serum factors with a molecular weight < 12,000 daltons does not differ from comparable normal serum factors, the relevance of these serum factors (e.g. growth hormone, lipoproteins) for the increased growth stimulation of mesenchymal cells in diabetes mellitus seems to be only of limited importance. In as much as these in vitro results represent the in vivo situation, chronic exposure of vascular cells from diabetics to these serum factors could be related to the increased angiopathic risk in diabetes mellitus.

Regulation of diabetic serum growth factors for human vascular cells by the metabolic control of diabetes mellitus

Serum factors from non-ketotic poorly controlled non-insulin-dependent diabetic patients stimulated growth and protein synthesis of human arterial smooth muscle cells and fibroblasts by 15-42%, compared to serum factors from well controlled diabetics. In contrast, the growth stimulating effect of pooled sera from well controlled diabetics did not differ from the effect of normal sera. Single sera from the same diabetics before and after improvement of the metabolic control stimulated cell growth to a similar degree as the respective pooled sera from different diabetic populations. As far as increased growth stimulation of vascular cells is related to increased angiopathic risk in diabetics, this metabolic regulation of growth factors supports the demand for a continuous optimal control of diabetic metabolism.

Considerations for an institution for evaluation of diabetes technology devices to improve their quality in the European Union.

All medical devices used for self-monitoring of blood glucose (BG), insulin injection, continuous subcutaneous insulin infusion, and continuous glucose monitoring in the European Union (EU) must have a Communauté Européenne (CE) mark. However, the approval process for obtaining this mark is different from that used by the European Medicines Agency in the EU for drugs or by the Food and Drug Administration in the United States for such medical and in vitro diagnostic devices. The notified bodies involved in the CE mark process perform this evaluation in cooperation with the manufacturers. They have only limited diabetes know-how; they have to handle all kinds of medical devices. There are devices for therapy on the market in the EU (i.e., they have market approval) that do not fulfill quality requirements, as indicated, for example, in the international norm ISO 15197 for BG test systems. Evaluation of the performance of such systems is usually provided by the manufacturers. What is missing in the EU is an independent institution that performs regular and critical evaluation of the quality of devices used for diabetes therapy before and also after their market approval. The work of such an institution would focus on BG test systems (these represent two-thirds of the market of medical devices for diabetes treatment) but would also evaluate the performance of other devices. It has to be clarified what legal framework is required for such an institution and how it can be financed; probably this can be done in a shared manner by the manufacturers of such devices and the health insurance companies. Positive evaluation results should be a prerequisite prior to any reimbursement for such devices.

Parameters Affecting Postprandial Blood Glucose: Effects of Blood Glucose Measurement Errors

Background: The Diabetes Error Test Model (DETM) has been developed to characterize the clinical relevance of the large and varying margins of error of parameters affecting postprandial blood glucose (BG) levels, which increase the risk for hypo- or hyperglycemia. Methods: The DETM is based on a treatment concept aimed at normoglycemia after meals. The model includes as parameters (a) preprandial BG measurement by patient self-monitoring (SMBG), (b) patient estimate of carbohydrate amounts (CARB-P) in food, (c) effect of CARB-P on maximum BG increase, (d) effect of insulin on maximum BG decrease, and (e) insulin dosage. Covering the relevant range of preprandial BG (30–330 mg/dl), the DETM simulates the maximum effect of these parameters and their margins of error on postprandial BG values. Results: According to the DETM, a SMBG error of +20% results in normoglycemia (BG range: 60–160 mg/dl) as the postprandial outcome if preprandial BG values are in the range of 30–130 or 260–330 mg/dl, but can unexpectedly result in hypoglycemia if preprandial BG values are between 131 and 259 mg/dl. If the SMBG error of +20% is combined, e.g., with an error of CARB-P estimate in the food of +20%, hypoglycemia as the postprandial outcome is worsened. If one combines the effects of errors of more than two parameters, even with errors that are so small that they have no clinically relevant dysglycemic effect on postprandial BG per se (e.g., ±6%), this can result in postprandial hypo- or hyperglycemic values. Conclusion: The DETM simulates the effects of errors of parameters affecting postprandial BG within the clinically relevant BG range. The DETM offers the opportunity to evaluate the clinical relevance of these errors and their contribution to the increased risk of meal-related excessive glucose excursions during intensified insulin therapy.