Maria Speth

Arabinoxylan consumption decreases postprandial serum glucose, serum insulin and plasma total ghrelin response in subjects with impaired glucose tolerance

Objective:Arabinoxylan (AX) consumption is associated with metabolic improvement during diabetes and with modulation of ghrelin, an orexigenic gut hormone. The effect of AX consumption on ghrelin secretion in disturbed metabolic states is unknown. Therefore, we investigated the postprandial responses to AX consumption of serum glucose, insulin and triglycerides and plasma total and acylated ghrelin in subjects with impaired glucose tolerance (IGT).Design:Randomized, single-blind, controlled, crossover intervention trial.Subjects:Seven female and four male adults with IGT, aged 55.5 years, and body mass index (BMI) 30.1 kg/m2.Intervention:Subjects received either placebo or 15 g AX supplement for 6 weeks with a 6-week washout period in-between.Main outcome measurements:Postprandial responses of serum glucose, insulin and triglycerides, and plasma total and acylated ghrelin after a liquid meal challenge test (LMCT) measured at the beginning and at the end of the dietary intervention at −20, −5, 0, 15, 30, 45, 60, 90, 120, 150, 180, 210 and 240 min.Results:After LMCT, AX consumption resulted in lower postprandial responses in serum glucose, insulin and triglycerides (P<0.05). Compared to placebo, total plasma ghrelin was also reduced by 42±8 pg/ml (P<0.001) after AX consumption with no difference in plasma acylated ghrelin.Conclusion:AX consumption improved postprandial metabolic responses after an LMCT in subjects with IGT and reduced total ghrelin response. However, acylated ghrelin responses were unchanged, suggesting that the acylated ghrelin-mediated orexigenic regulation is not improved as only total plasma ghrelin decreased.Sponsorship:Federal Ministry of Education and Research Germany (PTJ-BIO/0313042C).

Interaction between heparin and cardiac troponin T and troponin I from patients after coronary bypass surgery.

OBJECTIVES Heparin is thought to play a crucial role in the clinical monitoring of patients with acute coronary syndrome as well as after coronary bypass surgery in that it interferes with different commercial immunoassay test systems for cardiac troponin T (cTnT) and troponin I (cTnI). The mechanism, however, by which heparin apparently affects the cTnT and cTnI levels in plasma is not yet resolved. DESIGN AND METHODS We analyzed the effect of heparin by simultaneously collecting serum and heparin plasma samples from 32 patients after coronary bypass surgery. The cTnT and cTnI levels were determined using the Roche/Elecsys, the Dade-Behring/Opus and the Bayer/ACS:Centaur immunoassay systems in the absence or in the presence of either heparinase or protamine. Association between the cardiac troponins and the anticoagulant has been demonstrated by affinity chromatography using heparin as the ligand. RESULTS The data obtained indicate that heparin produces an apparent decrease in cTnT as well as of cTnI levels, analyzed either by the Elecsys, the Opus or the ACS:Centaur immunoassay systems. Individual patients show a wide variation in the discrepancies between serum and heparin plasma troponin especially in the cTnT immunoassay. Pretreatment of the heparin plasma samples either with heparinase or protamine cannot completely reverse the heparin-induced decrease in cTnT and cTnI levels and therefore addition of these reagents to the commercial test systems could not significantly improve the performance of the assay. When serum is supplemented with increasing concentrations of heparin, and cardiac troponin levels were reanalysed, significantly lower recoveries for the cTnT than for the cTnI immunoassays were detectable. Affinity chromatography with heparin Sepharose demonstrates that cTnT and cTnI interact differentially with the negatively charged ligand. Whereas cTnI shows minor affinity to the immobilized heparin and is eluted at near physiological conditions, cTnT is bound and can be quantitatively recovered only by solutions of high ionic strength. CONCLUSIONS We conclude, therefore, that the apparent decrease in cTnT values by addition of heparin is a result of direct molecular interaction between the negatively charged glycosaminoglycan and clusters of basic residues within the sequence of the cardiac protein. In contrast, the effect of heparin on the cTnI immunoassay systems, is primarily indirect, most possibly induced by changes within the sample matrix itself.

Increased acylated plasma ghrelin, but improved lipid profiles 24-h after consumption of carob pulp preparation rich in dietary fibre and polyphenols

We have recently shown that a polyphenol-rich insoluble dietary fibre preparation from carob pulp (Ceratonia siliqua L; carob fibre) decreased postprandial acylated ghrelin, TAG and NEFA during an acute liquid meal challenge test. However, delayed effects of carob fibre consumption are unknown. Therefore, a randomized controlled crossover study in nineteen healthy volunteers consuming foods with or without 50 g carob fibre was conducted. On the subsequent day (day 2), glucose, TAG, total and acylated ghrelin as well as insulin, NEFA and leptin were assessed at baseline and at timed intervals for 300 min after ingestion of standardized bread. Consumption of carob fibre-enriched foods did not affect fasting concentrations of glucose, TAG, total ghrelin, NEFA, insulin and leptin. Fasting acylated ghrelin was increased on the day subsequent to carob fibre consumption compared with control (P = 0.046). After consumption of the standard bread on day 2, glucose response (P = 0.029) was increased, and TAG (P = 0.033) and NEFA (P < 0.001) responses were decreased compared with control. Postprandial responses of total and acylated ghrelin, insulin and leptin on day 2 were unaffected by carob fibre consumption the previous day. In conclusion, an increase in total and acylated plasma ghrelin accompanied by enhanced lipid metabolism after carob fibre consumption suggests higher lipid utilization and suppressed lipolysis on the day subsequent to carob fibre consumption. However, elevated glucose levels after carob fibre consumption need to be addressed in future studies.

Hormone-induced effects on the rat liver microsomal glucose-6-phosphatase system in vitro.

Abstract We studied the effects of various glucocorticoids, glucagon and insulin on the activity of rat liver microsomal glucose-6-phosphatase. Preincubation of microsomes with corticosterone, cortisone, cortisol and dexamethasone as well as glucagon increased the rate of glucose-6-phosphate hydrolysis by about 1.5 fold relative to the controls. The maximum activation occurred at about 10 nM steroids and 0.3 nM glucagon, respectively. On the other hand, increasing concentrations (8.3 – 50 nM) of insulin progressively inhibited glucose-6-phosphatase up to 26%; the activity of which, however, remains completely in a latent state within the microsomal membrane and can be released from it by Triton treatment. In terms of the substrate transport hypothesis, the results are interpreted as evidence that regulation of glucose-6-phosphate hydrolysis is achieved by direct interactions either of the hormones themselves or of a possible second messenger with the carrier moiety of the rat liver microsomal glucose-6-phosphatase system.

Increase in serum resistin during weight loss in overweight subjects is related to lipid metabolism

Objective:Human resistin has been stated to influence preadipocyte cell numbers and to stimulate adipocyte triglyceride lipolysis in vivo and in vitro. However, its role in human obesity remains unclear.Design:Cross-sectional study for comparisons of lean and obese subjects, and subsequent longitudinal 4-month weight loss intervention study in obese subjects.Subjects:Healthy subjects, lean (n=20, BMI<25) and overweight (n=43, BMI⩾25).Measurements:Serum resistin, body weight, body fat, waist-to-hip ratio, as well as markers of insulin resistance and lipid metabolism at baseline and after 4 months of intervention.Results:Serum resistin was positively correlated to HOMA-IR (partial r=0.288; P=0.055), serum fructosamines (partial r=0.280; P=0.062), serum NEFA (partial r=0.276; P=0.066) and negatively to age (partial r=−0.349; P=0.019) and serum apolipoprotein A-1 (partial r=−0.363; P=0.014). During the intervention, serum resistin increased significantly (P<0.001). The increase was inversely related to changes in waist-to-hip ratio (P=0.025) and positively to serum apolipoprotein B (P=0.011). In males only, the increase in resistin during weight loss was predicted by total serum cholesterol at baseline (r=0.703, P=0.007). No relation was observed between changes in resistin and changes in HOMA-IR.Conclusion:The present study indicates an association between serum resistin and markers of abdominal fat distribution as well as the regulation of lipid metabolism. However, human resistin is unlikely to play an independent role in the regulation of glucose metabolism.

Is thermostability of glucose‐6‐phosphatase indeed dependent on a stabilizing protein?

Partial purification of glucose‐6‐phosphatase from rat liver microsomes by solubilization of the membranes with the non‐ionic detergent Triton X‐144 at pH 6.5 and the removal of inactivating detergent by hydrophobic chromatography results in a thermostable enzyme protein which is not dependent on stabilizing phospholipids or proteins. The readdition of low amounts of detergent immediately causes a conversion into a thermo‐unstable phosphodydrolase protein. Thus these findings present evidence that heatinstability of partially purified glucose‐6‐phosphatase derives from traces of inactivating detergent changing the structural properties of the phosphohydrolase rather than from the absence of the postulated specific stabilizing protein.

Accessibility of glucose 6-phosphate: phosphohydrolase to antibody attack in modified microsomal vesicles.

Recent investigations supported the existence of 2 components of the endoplasmic reticulum participating in the process of glucose 6-phosphate hydrolysis: the glucose 6-phosphate-specific transporter that mediates the movement of the substrate from the cytoplasmic membrane surface into the lumen and the unspecific phosphohydrolase on the luminal side of the membrane [ 1,2]. However, this model has not been generally accepted; especially the proposed molecular arrangement of the glucose 6-phosphatase components within the membrane is contradictory [3-71. Furthermore, immunological studies [6] have suggested that the glucose 6-phosphate: phosphohydrolase is presumably not freely accessible on the luminal surface which, however, is one of the prerequisites of the substrate-transport hypothesis as described in [ 1,2]. Therefore, we have reinvestigated the transverse topology of the glucose 6-phosphatase by detailed immunological studies on detergent-modified and mechanically disrupted microsomes. These findings support our preliminary concept and demonstrate that, indeed, the glucose 6-phosphate:phosphohydrolase is not attached to the luminal membrane surface, but buried within the microsomal membrane.

Protease inhibitors but not proteases inhibit the glucose-6-phosphatase of native rat liver microsomes

Controlled proteolytic digestion by trypsin or bacterial proteases limited to the cytosolic side of the native microsomal membrane is not efficient to inhibit glucose-6-phosphate hydrolysis. Modification of the microsomes with deoxycholate prior to protease treatment is prerequisite to allow accessibility of the integral protein and inhibition of enzyme activity. Glucose-6-phosphatase of native microsomes, however, is rapidly inactivated by micromolar concentrations of TPCK as well as TLCK. In deoxycholate-modified microsomes both reagents do not affect glucose-6-phosphate hydrolysis. These results indicate that in the native, intact microsomal membrane glucose-6-phosphatase is not accessible to proteolytic attack from the cytoplasmic surface. The putative inhibitory effect of some trypsin or bacterial protease preparations on glucose-6-phosphatase of native microsomes observed most possibly is a result of contaminating agents as TPCK or TLCK.

Cardiac Troponin I: A valuable biomarker indicating the cardiac involvement in Fabry disease

Objectives Assessment of the clinical severity of Fabry disease (FD), an X-linked, rare, progressive disorder based on a genetic defect in alpha-galactosidase is challenging, especially regarding cardiac involvement. The aim of the study was to evaluate the diagnostic value of cardiac troponin I (cTnI) in discriminating FD patients with cardiac involvement in a large FD patient cohort. Methods cTnI levels were measured with a contemporary sensitive assay in plasma samples taken routinely from FD patients. The assay was calibrated to measure cTnI levels ≥0.01 ng/ml. Elevated cTnI values (cut-off ≥0.04 ng/ml) were correlated with clinical data. Results cTnI was assessed in 62 FD patients (median age: 47 years, males: 36%). Elevated cTnI levels were detected in 23 (37%) patients. Patients with a cTnI elevation were older (median 55 years versus 36 years, p<0.001). Elevated cTnI levels were associated with the presence of a LVH (16/23 versus 1/39; OR 65.81, CI: 6.747–641.859; p<0.001). In almost all patients with a left ventricular hypertrophy (LVH) elevated cTnI levels were detected (16/17, 94%). Absolute cTnI levels in patients with LVH were higher than in those without (median 0.23 ng/ml versus 0.02 ng/ml; p<0.001). A cTnI level <0.04ng/ml had a high negative predictive value regarding the presence of a LVH (38/39, 97%). In a control group of non-FD patients (n = 17) with LVH (due to hypertension) none showed cTnI levels ≥0.01 ng/ml. Conclusions Elevated cTnI levels are common in FD patients, reflecting cardiac involvement. FD patients might benefit from a continuous cTnI monitoring.