Th. B. Twickler

Insulin-like growth factors and pancreas beta cells.

Insulin‐like growth factors (IGFs) have been implicated in normal growth, and especially foetal pancreas beta‐cell development. As low birth weight has been implicated in the development of obesity and type 2 diabetes, much research has evolved into the importance of IGF and their signalling pathways for pancreas beta‐cell development, and for type 2 diabetes. Insulin‐like growth factor‐I signalling has a lot in common with insulin signalling, and is involved in diverse cellular effects such as antiapoptosis, protein synthesis, cell growth and mitogenesis. Insulin‐like growth factor‐II can be bound by the insulin receptor A subtype and the IGF‐1 receptor, which may explain its antiapoptotic effect.

Diurnal triglyceride profiles in healthy normolipidemic male subjects are associated to insulin sensitivity, body composition and diet

Elevated fasting and postprandial triglycerides (TG) are established risk factors for Coronary Heart Disease (CHD). Usually, fasting plasma TG are measured, although TG are mainly produced in a postprandial state. Our objective was to investigate diurnal TG profiles using serial capillary TG measurements, in normolipidemic healthy males.

Homozygous and heterozygous expression of a novel mutation of the acid-labile subunit

CONTEXTnAcid-labile subunit (ALS) deficiency due to homozygous inactivation of the ALS gene (IGFALS) is associated with moderate short stature, and in few cases pubertal delay. The clinical expression of heterozygosity is unknown.nnnOBJECTIVEnTo investigate the clinical, laboratory, and radiological features of homozygous and heterozygous carriers of a novel mutation in the ALS gene in comparison with non-carriers.nnnSUBJECTSnThree short Kurdish brothers and their relatives.nnnRESULTSnThe index cases presented with short stature, microcephaly, and low circulating IGF-I and IGF-binding protein-3 (IGFBP-3), and undetectable ALS levels. Two were known with a low bone mineral density and one of them had suffered from two fractures. We found a novel homozygous ALS gene mutation resulting in a premature stop codon (c.1490dupT, p.Leu497PhefsX40). The IGF-I, IGFBP-3, and ALS 150 kDa ternary complex was absent, and ALS proteins in serum were not detected with western blot. IGFPB-1 and IGFPB-2 were low and there was a mild insulin resistance. Five heterozygous carriers tended to have a lower height and head circumference than five non-carriers, and had low plasma ALS and IGFBP-3 levels. Bone mineral (apparent) density was low in two out of three homozygous carriers, and also in four out of nine relatives.nnnCONCLUSIONSnThe clinical presentation of homozygous ALS mutations may, besides short stature, include microcephaly. Heterozygous carriers may have less statural and head growth, suggestive for a gene dosage effect.

High Dose of Simvastatin Normalizes Postprandial Remnant-Like Particle Response in Patients With Heterozygous Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) and disturbances in postprandial lipoprotein metabolism are both associated with premature atherosclerosis. The effect of &bgr;-hydroxy-&bgr;-methylglutaryl coenzyme A reductase inhibitors on plasma cholesterol levels in patients with FH is well established; however, it is not known whether postprandial lipoproteins are also influenced. In this case-controlled intervention study, we investigated the effects of high-dose simvastatin on postprandial lipoproteins. We used a new method to analyze remnant lipoproteins based on the immunoseparation principle (remnant-like particle cholesterol [RLP-C] assay) and the well-established measurement of retinyl ester (RE) analysis in plasma and in the Svedberg flotation unit (Sf)<1000 fraction. Seven heterozygous FH patients and 7 control subjects matched for sex, age, body mass index, triglycerides, and apolipoprotein E genotype were enrolled in the study. An oral vitamin A (RE) fat-loading test was performed at baseline in both groups and after 3 months of high-dose simvastatin (80 mg/d) treatment in the FH patients. Before treatment, FH patients had significantly higher fasting and postprandial concentrations of lipoprotein remnants (plasma RLP-C 42±19 mg/dL and area under the RLP-C curve 415±82 mg · L−1 · h−1, respectively) than did control subjects (7±3 mg/dL and 101±35 mg · L −1 · h−1, respectively;P <0.05), suggesting a delayed clearance of chylomicron remnant particles in the FH patients. Treatment with simvastatin significantly reduced fasting and postprandial remnant lipoprotein cholesterol concentrations (13±3 mg/dL and 136±53 mg · L −1 · h−1, respectively;P <0.05 for both). Postprandial RE in the Sf<1000 fraction, not total RE in plasma, was also significantly higher in FH patients than in control subjects (24±10 versus 6.3±5.9 mg · L −1 · h−1, P <0.05), but treatment with simvastatin did not result in improvement of the postprandial RE response, either in the Sf<1000 fraction or in plasma. It is concluded that heterozygous FH patients have increased fasting and postprandial remnant lipoprotein concentrations. Treatment with simvastatin significantly reduced the fasting and postprandial RLP-C concentrations but did not result in improved postprandial RE response.

Isolation of remnant particles by immunoseparation: a new approach for investigation of postprandial lipoprotein metabolism in normolipidemic subjects.

Abnormal postprandial lipoproteins are associated with an increased risk for cardiovascular disease. Postprandial remnant lipoproteins were usually analyzed indirectly using retinyl esters (RE) as a chylomicron core label during an oral fat loading test. Apo B-100 containing VLDL remnants in addition to apo B-48 containing chylomicron remnants can also be directly quantified using the RLP-Cholesterol Immunoseparation Assay. This recently available method uses monoclonal antibodies to apo A-I and apo B-100 to remove non-remnant lipoproteins and quantifies cholesterol in the remaining apo E-rich remnant fraction. In the present study we compared the analysis of retinyl ester with the immuno-based RLP-Cholesterol (RLP-C) analysis in measuring postprandial remnant lipoproteins in healthy normolipidemic subjects. Sixteen healthy normolipidemic subjects were selected for this study. Postprandial plasma retinyl esters peaked at 5.0+/-1.2 h, whereas plasma RLP-C showed a peak significantly earlier (P<0.001) at 3.5+/-0.6 h. In comparison, postprandial plasma TG and FFA peaked at 3.3+/-1.1 h (P<0.005 compared to retinyl esters). In conclusion, levels of RLP-C changed, during the postprandial phase, in parallel with plasma TG and FFA concentrations and peaked significantly earlier than retinyl esters. Postprandial measurements of RLP-C can be considered as a fast alternative method for the more laborious retinyl-ester analysis in clinical studies.

The atherogenic plasma remnant-like particle cholesterol concentration is increased in the fasting and postprandial state in active acromegalic patients

BACKGROUND Premature atherosclerosis is a clinical feature in untreated acromegaly. Increased postprandial lipoprotein remnant levels are associated with premature atherosclerosis. In most studies, remnants have been measured indirectly using retinyl esters (RE) as a chylomicron core label. Remnants can also be directly quantified by immunoseparation using monoclonal antibodies to apolipoprotein (apo) AI and apo B100 to remove nonremnant lipoproteins. Cholesterol is quantified in the remaining apo E‐rich remnant fraction (RLP‐C).

Effects of Growth Hormone Deficiency and Recombinant Growth Hormone Therapy on Postprandial Gallbladder Motility and Cholecystokinin Release

In addition to cholecystokinin, other hormones have been suggested to be involved in regulation of postprandial gallbladder contraction. We aimed to evaluate effects of growth hormone (GH) on gallbladder contractility and cholecystokinin release. Gallbladder and gastric emptying (by ultrasound) and cholecystokinin release were determined before and after 6 months of recombinant human GH (rhGH) therapy in 12 patients with GH deficiency, after either a mixed (n = 5) or a liquid (n = 7) meal. Basal postprandial gallbladder contraction was severely impaired (19±2 and 26±3% of fasting volume after mixed and liquid meal, respectively). Histology and cholecystokinin sulfation patterns in duodenal biopsies from two patients were normal. After 6 months of rhGH therapy, fasting gallbladder volumes increased (from 20.8±0.9 to 25.9±1.1 mL, P < 0.05) and postprandial gallbladder emptying was restored (70±6 and 70±7% of fasting volume after mixed and liquid meal, respectively), without change of gastric emptying. Cholecystokinin secretion after a mixed meal and gallbladder sensitivity to cholecystokinin were significantly enhanced during rhGH replacement compared to the basal state. Postprandial cholecystokinin release, gallbladder responsiveness to cholecystokinin, and gallbladder emptying are severely impaired in the absence of GH. Reversibility during GH suppletion suggests its involvement in regulation of gallbladder contractility.

Endothelial insulin receptor expression in human atherosclerotic plaques : linking micro- and macrovascular disease in diabetes?

OBJECTIVEnExogenous insulin use in patients with type 2 diabetes (DM2) has been associated with an increased risk of cardiovascular events. Through which mechanisms insulin may increase atherosclerotic plaque vulnerability is currently unclear. Because insulin has been suggested to promote angiogenesis in diabetic retinopathy and tumors, we hypothesized that insulin enhances intra-plaque angiogenesis.nnnMETHODSnAn in vitro model of pathological angiogenesis was used to assess the potential of insulin to enhance capillary-like tube formation of human microvascular endothelial cells (hMVEC) into a three dimensional fibrin matrix. In addition, insulin receptor expression within atherosclerotic plaques was visualized in carotid endarterectomy specimens of 20 patients with carotid artery stenosis, using immunohistochemical techniques. Furthermore, microvessel density within atherosclerotic plaques was compared between 68 DM2 patients who received insulin therapy and 97 DM2 patients who had been treated with oral glucose lowering agents only.nnnRESULTSnInsulin, at a concentration of 10(-8)M, increased capillary-like tube formation of hMVEC 1.7-fold (p<0.01). Within human atherosclerotic plaques, we observed a specific distribution pattern for the insulin receptor: insulin receptor expression was consistently higher on the endothelial lining of small nascent microvessels compared to more mature microvessels. There was a trend towards an increased microvessel density by 20% in atherosclerotic plaques derived from patients using insulin compared to plaques derived from patients using oral glucose lowering agents only (p=0.05).nnnCONCLUSIONnExogenous insulin use in DM2 patients may contribute to increased plaque vulnerability by stimulating local angiogenesis within atherosclerotic plaques.