Murine matrix metalloproteinase 13 and its human homologue are involved in remodelling processes after myocardial infarction

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): German Centre for Cardiovascular Research (DZHK)

Background

Cardiovascular diseases such as myocardial infarction (MI) are a leading cause of death worldwide. Since matrix metalloproteinases (MMPs) are essential for the cleavage of collagen as well as for the modification of inflammatory proteins and cytokines, they play a substantial role in remodelling processes after MI.

Purpose

Previous results of our group revealed, that Mmp13 expression is upregulated post-MI in mice, while it is downregulated after Ischemia/Reperfusion (I/R), indicating an involvement in remodelling processes. In humans, the functional homologue of Mmp13 is MMP1. Single nucleotide polymorphisms (SNPs) in the promotor of MMP1 can lead to alterations in its gene expression level. We analysed the genotype for 3 MMP1 SNPs in a human cohort containing ~2000 patients who presented to the emergency department with suspected MI to identify their associations with development of MI and outcome after MI.

Methods

The Mmp13 expression in different cardiac cell types was investigated at quiescent stage and under ischaemic conditions, to determine the cellular origin of Mmp13 expression. A MMP13-knockout (KO) mouse model was examined after induction of MI or I/R. Thus, gene expression analysis, histological staining and hemodynamic measurements were conducted to analyse differences between KO and WT as well as between MI and I/R. Out of the human cohort, 2 patient groups (non-MI and MI) were restricted, and Hazard ratios were calculated to evaluate risk for MI and risk for death after MI in dependency of the SNPs.

Results

The Mmp13 expression in macrophages (6.6-fold to control; p=0.0286) and fibroblasts (4.9-fold; p=0.0079) increased significantly after activation with ischaemic secretome of cardiomyocytes, while Mmp13 expression of leucocytes was unaltered. After stimulation with ischaemic secretome of fibroblasts, Mmp13 expression in macrophages (4.3-fold; p=0.0286) and leukocytes (2.3-fold; p=0.0260) was significantly elevated as well. Comparing MI and I/R, the immune cell infiltration revealed significant differences 1-day post-intervention. About 50% of WT mice but only few KO mice died (p=0.0107) after MI due to cardiac rupture. Moreover, KO mice showed an improved cardiac function compared to WT mice after MI. Risk for death was significantly altered between the investigated genotypes in 2 of 3 investigated SNPs in the BACC cohort.

Conclusion

Activated macrophages and leucocytes express high levels of Mmp13 in cell culture experiments. The infiltrating immune cell types are different between MI and I/R, which might lead to differences in Mmp13 expression in these models. MMP13 KO mice are protected from cardiac rupture after MI and unveiled improved cardiac function 28 days post-MI. SNPs of the human homologue of Mmp13 – MMP1 – showed an association of MMP1 with remodelling processes after MI.

LIPSS-based functional surfaces produced by multi-beam nanostructuring with 2601 beams and real-time thermal processes measurement

A unique combination of the ultrashort high-energy pulsed laser system with exceptional beam quality and a novel Diffractive Optical Element (DOE) enables simultaneous production of 2601 spots organized in the square-shaped 1 × 1 mm matrix in less than 0.01 ms. By adjusting the laser and processing parameters each spot can contain Laser Induced Periodic Surface Structures (LIPSS, ripples), including high-spatial frequency LIPSS (HFSL) and low-spatial frequency LIPSS (LSFL). DOE placed before galvanometric scanner allows easy integration and stitching of the pattern over larger areas. In addition, the LIPSS formation was monitored for the first time using fast infrared radiometry for verification of real-time quality control possibilities. During the LIPSS fabrication, solidification plateaus were observed after each laser pulse, which enables process control by monitoring heat accumulation or plateau length using a new signal derivation approach. Analysis of solidification plateaus after each laser pulse enabled dynamic calibration of the measurement. Heat accumulation temperatures from 200 to 1000 °C were observed from measurement and compared to the theoretical model. The temperature measurements revealed interesting changes in the physics of the laser ablation process. Moreover, the highest throughput on the area of 40 × 40 mm reached 1910 cm²/min, which is the highest demonstrated throughput of LIPSS nanostructuring, to the best of our knowledge. Thus, showing great potential for the efficient production of LIPSS-based functional surfaces which can be used to improve surface mechanical, biological or optical properties.

Apparent Lack of BRAF V600E Derived HLA Class I Presented Neoantigens Hampers Neoplastic Cell Targeting by CD8+ T Cells in Langerhans Cell Histiocytosis

Langerhans Cell Histiocytosis (LCH) is a neoplastic disorder of hematopoietic origin characterized by inflammatory lesions containing clonal histiocytes (LCH-cells) intermixed with various immune cells, including T cells. In 50-60% of LCH-patients, the somatic BRAF ^V600E driver mutation, which is common in many cancers, is detected in these LCH-cells in an otherwise quiet genomic landscape. Non-synonymous mutations like BRAF ^V600E can be a source of neoantigens capable of eliciting effective antitumor CD8⁺ T cell responses. This requires neopeptides to be stably presented by Human Leukocyte Antigen (HLA) class I molecules and sufficient numbers of CD8⁺ T cells at tumor sites. Here, we demonstrate substantial heterogeneity in CD8⁺ T cell density in n = 101 LCH-lesions, with BRAF ^V600E mutated lesions displaying significantly lower CD8⁺ T cell:CD1a⁺ LCH-cell ratios (p = 0.01) than BRAF wildtype lesions. Because LCH-lesional CD8⁺ T cell density had no significant impact on event-free survival, we investigated whether the intracellularly expressed BRAF ^V600E protein is degraded into neopeptides that are naturally processed and presented by cell surface HLA class I molecules. Epitope prediction tools revealed a single HLA class I binding BRAF ^V600E derived neopeptide (KIGDFGLATEK), which indeed displayed strong to intermediate binding capacity to HLA-A^*03:01 and HLA-A^*11:01 in an in vitro peptide-HLA binding assay. Mass spectrometry-based targeted peptidomics was used to investigate the presence of this neopeptide in HLA class I presented peptides isolated from several BRAF ^V600E expressing cell lines with various HLA genotypes. While the HLA-A^*02:01 binding BRAF wildtype peptide KIGDFGLATV was traced in peptides isolated from all five cell lines expressing this HLA subtype, KIGDFGLATEK was not detected in the HLA class I peptidomes of two distinct BRAF ^V600E transduced cell lines with confirmed expression of HLA-A^*03:01 or HLA-A^*11:01. These data indicate that the in silico predicted HLA class I binding and proteasome-generated neopeptides derived from the BRAF ^V600E protein are not presented by HLA class I molecules. Given that the BRAF ^V600E mutation is highly prevalent in chemotherapy refractory LCH-patients who may qualify for immunotherapy, this study therefore questions the efficacy of immune checkpoint inhibitor therapy in LCH.

The RING ubiquitin E3 RNF114 interacts with A20 and modulates NF-κB activity and T-cell activation

Accurate regulation of nuclear factor-κB (NF-κB) activity is crucial to prevent a variety of disorders including immune and inflammatory diseases. Active NF-κB promotes IκBα and A20 expression, important negative regulatory molecules that control the NF-κB response. In this study, using two-hybrid screening we identify the RING-type zinc-finger protein 114 (RNF114) as an A20-interacting factor. RNF114 interacts with A20 in T cells and modulates A20 ubiquitylation. RNF114 acts as negative regulator of NF-κB-dependent transcription, not only by stabilizing the A20 protein but also IκBα. Importantly, we demonstrate that in T cells, the effect of RNF114 is linked to the modulation of T-cell activation and apoptosis but is independent of cell cycle regulation. Altogether, our data indicate that RNF114 is a new partner of A2O involved in the regulation of NF-κB activity that contributes to the control of signaling pathways modulating T cell-mediated immune response.

SUMOylation regulates AKT1 activity

Serine threonine kinase AKT has a central role in the cell, controlling survival, proliferation, metabolism and angiogenesis. Deregulation of its activity underlies a wide range of pathological situations, including cancer. Here we show that AKT is post-translationally modified by the small ubiquitin-like modifier (SUMO) protein. Interestingly, neither SUMO conjugation nor activation of SUMOylated AKT is regulated by the classical AKT targeting to the cell membrane or by the phosphoinositide 3-kinase pathway. We demonstrate that SUMO induces the activation of AKT, whereas, conversely, down-modulation of the SUMO machinery diminishes AKT activation and cell proliferation. Furthermore, an AKT SUMOylation mutant shows reduced activation, and decreased anti-apoptotic and pro-tumoral activities in comparison with the wild-type protein. These results identify SUMO as a novel key regulator of AKT phosphorylation and activity.

Glycaemic index methodology

The glycaemic index (GI) concept was originally introduced to classify different sources of carbohydrate (CHO)-rich foods, usually having an energy content of >80 % from CHO, to their effect on post-meal glycaemia. It was assumed to apply to foods that primarily deliver available CHO, causing hyperglycaemia. Low-GI foods were classified as being digested and absorbed slowly and high-GI foods as being rapidly digested and absorbed, resulting in different glycaemic responses. Low-GI foods were found to induce benefits on certain risk factors for CVD and diabetes. Accordingly it has been proposed that GI classification of foods and drinks could be useful to help consumers make 'healthy food choices' within specific food groups. Classification of foods according to their impact on blood glucose responses requires a standardised way of measuring such responses. The present review discusses the most relevant methodological considerations and highlights specific recommendations regarding number of subjects, sex, subject status, inclusion and exclusion criteria, pre-test conditions, CHO test dose, blood sampling procedures, sampling times, test randomisation and calculation of glycaemic response area under the curve. All together, these technical recommendations will help to implement or reinforce measurement of GI in laboratories and help to ensure quality of results. Since there is current international interest in alternative ways of expressing glycaemic responses to foods, some of these methods are discussed.

The molecular genetics of sulfonylurea receptors in the pathogenesis and treatment of insulin secretory disorders and type 2 diabetes

Sulfonylurea receptors (SURs) form an integral part of the ATP-sensitive potassium (K(ATP)) channel complex that is present in most excitable cell types. K(ATP) channels couple cellular metabolism to electrical activity and provide a wide range of cellular functions including stimulus secretion coupling in pancreatic β cells. K(ATP) channels are composed of SURs and inward rectifier potassium channel (Kir6.x) subunits encoded by the ABCC8/9 and KCNJ8/11 genes, respectively. Recent advances in the genetics, molecular biology, and pharmacology of SURs have led to an increased understanding of these channels in the etiology and treatment of rare genetic insulin secretory disorders. Furthermore, common genetic variants in these genes are associated with an increased risk for type 2 diabetes. In this review we summarize the molecular biology, pharmacology, and physiology of SURs and K(ATP) channels, highlighting recent advances in their genetics and understanding of rare insulin secretory disorders and susceptibility to type 2 diabetes.

Electrically detected magnetic resonance of neutral donors interacting with a two-dimensional electron gas

We have measured the electrically detected magnetic resonance of donor-doped silicon field-effect transistors in resonant X- (9.7 GHz) and W-band (94 GHz) microwave cavities. The two-dimensional electron gas resonance signal increases by 2 orders of magnitude from X to W band, while the donor resonance signals are enhanced by over 1 order of magnitude. Bolometric effects and spin-dependent scattering are inconsistent with the observations. We propose that polarization transfer from the donor to the two-dimensional electron gas is the main mechanism giving rise to the spin resonance signals.

Electrically detected magnetic resonance in a W-band microwave cavity

We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94  GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7  GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.

The molecular mechanisms and pharmacotherapy of ATP-sensitive potassium channel gene mutations underlying neonatal diabetes

Neonatal diabetes mellitus (NDM) is a monogenic disorder caused by mutations in genes involved in regulation of insulin secretion from pancreatic β-cells. Mutations in the KCNJ11 and ABCC8 genes, encoding the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel Kir6.2 and SUR1 subunits, respectively, are found in ∼50% of NDM patients. In the pancreatic β-cell, K(ATP) channel activity couples glucose metabolism to insulin secretion via cellular excitability and mutations in either KCNJ11 or ABCC8 genes alter K(ATP) channel activity, leading to faulty insulin secretion. Inactivation mutations decrease K(ATP) channel activity and stimulate excessive insulin secretion, leading to hyperinsulinism of infancy. In direct contrast, activation mutations increase K(ATP) channel activity, resulting in impaired insulin secretion, NDM, and in severe cases, developmental delay and epilepsy. Many NDM patients with KCNJ11 and ABCC8 mutations can be successfully treated with sulfonylureas (SUs) that inhibit the K(ATP) channel, thus replacing the need for daily insulin injections. There is also strong evidence indicating that SU therapy ameliorates some of the neurological defects observed in patients with more severe forms of NDM. This review focuses on the molecular and cellular mechanisms of mutations in the K(ATP) channel that underlie NDM. SU pharmacogenomics is also discussed with respect to evaluating whether patients with certain K(ATP) channel activation mutations can be successfully switched to SU therapy.

Avian influenza A virus monitoring in wild birds in Bavaria: occurrence and heterogeneity of H5 and N1 encoding genes

To define avian influenza virus prevalence in wild birds in Bavaria, 12,930 tracheal, cloacal swabs or tissue samples from various waterfowl species were screened between January 2006 and December 2007. In 291 (2.3%) birds, genomes of influenza A viruses were detected by reverse transcription real-time PCR (rRT-PCR) targeting the matrix protein genes. Furthermore, solitary H5 hemagglutinin or N1 neuraminidase encoding genes were identified in 35 (0.3%) apparently healthy birds; whereas highly pathogenic (HPAI) H5N1 virus genomes were only diagnosed in dead wild birds (n = 93; 0.7%) found across this federal state region. In this study, multiple import events for H5N1 viruses were confirmed during 2006 and 2007. In addition, our findings argue against an existing HPAI H5N1 reservoir in aquatic birds in Bavaria. By contrast, phylogenetic analyses of the H5 or N1 sequences of low pathogenic avian influenza (LPAI) viruses revealed a marked diversity and multiple genetic lineages. This diversity of LPAI H5 and N1 subtype components indicates the existence of LPAI HA and NA gene pools which differ from the Bavarian HPAI H5N1. Moreover, the hemagglutinin amino acid differences between LPAI H5 viruses of a western European genotypic lineage observed in wild birds suggest a continuous evolution of LPAI viruses in Bavaria.

Ge(1-x) Mn(x) clusters: central structural and magnetic building blocks of nanoscale wire-like self-assembly in a magnetic semiconductor

Controlled nanoscale self-assembly of magnetic entities in semiconductors opens novel perspectives for the tailoring of magnetic semiconductor films and nanostructures with room temperature functionality. We report that a strongly directional self-assembly in growth direction in Mn-alloyed Ge is due to a stacking of individual Ge(1-x)Mn(x) clusters. The clusters represent the relevant entities for the magnetization of the material. They are formed of a core-shell structure displaying a Mn concentration gradient. While the magnetic moments seem to be carried by the shells of the clusters, their core is magnetically inactive.

Glycemic and insulinemic responses to six cereal products in healthy adults

Glycemic index (GI) and insulin index (II) scores of six cereal-based foods (biscuits and shortbreads) were determined and the relationship between the glycemic and insulin responses of the foods was examined. The study was conducted using recommended by FAO/WHO methodology using glucose as a standard food. We obtained a range of GI scores from 49 to 68% and II scores from 51 to 75%. The test foods' blood insulin responses were in parallel to their glycemic responses although in every case the level of II was higher than the level of GI. The foods' II scores were closely related to their GI scores (r=0.80).

ABIN-2 forms a ternary complex with TPL-2 and NF-kappa B1 p105 and is essential for TPL-2 protein stability

NF-kappa B1 p105 forms a high-affinity, stoichiometric interaction with TPL-2, a MEK kinase essential for TLR4 activation of the ERK mitogen-activated protein kinase cascade in lipopolysaccharide (LPS)-stimulated macrophages. Interaction with p105 is required to maintain TPL-2 metabolic stability and also negatively regulates TPL-2 MEK kinase activity. Here, affinity purification identified A20-binding inhibitor of NF-kappa B 2 (ABIN-2) as a novel p105-associated protein. Cotransfection experiments demonstrated that ABIN-2 could interact with TPL-2 in addition to p105 but preferentially formed a ternary complex with both proteins. Consistently, in unstimulated bone marrow-derived macrophages (BMDMs), a substantial fraction of endogenous ABIN-2 was associated with both p105 and TPL-2. Although the majority of TPL-2 in these cells was complexed with ABIN-2, the pool of TPL-2 which could activate MEK after LPS stimulation was not, and LPS activation of TPL-2 was found to correlate with its release from ABIN-2. Depletion of ABIN-2 by RNA interference dramatically reduced steady-state levels of TPL-2 protein without affecting levels of TPL-2 mRNA or p105 protein. In addition, ABIN-2 increased the half-life of cotransfected TPL-2. Thus, optimal TPL-2 stability in vivo requires interaction with ABIN-2 as well as p105. Together, these data raise the possibility that ABIN-2 functions in the TLR4 signaling pathway which regulates TPL-2 activation.

NF-kappaB1 p105 negatively regulates TPL-2 MEK kinase activity

Activation of the oncogenic potential of the MEK kinase TPL-2 (Cot) requires deletion of its C terminus. This mutation also weakens the interaction of TPL-2 with NF-kappaB1 p105 in vitro, although it is unclear whether this is important for the activation of TPL-2 oncogenicity. It is demonstrated here that TPL-2 stability in vivo relies on its high-affinity, stoichiometric association with NF-kappaB1 p105. Formation of this complex occurs as a result of two distinct interactions. The TPL-2 C terminus binds to a region encompassing residues 497 to 534 of p105, whereas the TPL-2 kinase domain interacts with the p105 death domain. Binding to the p105 death domain inhibits TPL-2 MEK kinase activity in vitro, and this inhibition is significantly augmented by concomitant interaction of the TPL-2 C terminus with p105. In cotransfected cells, both interactions are required for inhibition of TPL-2 MEK kinase activity and, consequently, the catalytic activity of a C-terminally truncated oncogenic mutant of TPL-2 is not affected by p105. Thus, in addition to its role as a precursor for p50 and cytoplasmic inhibitor of NF-kappaB, p105 is a negative regulator of TPL-2. Insensitivity of C-terminally truncated TPL-2 to this regulatory mechanism is likely to contribute to its ability to transform cells.

Peptide fragments released from Phe-caseinomacropeptide in vivo in the rat

The aim of this study was to investigate the pharmacokinetics of bovine Phe-caseinomacropeptide (Phe-CMP) in the rat after oral administration. This polypeptide was monophosphorylated and mainly nonglycosylated: Phe-CMP-1P. During gastrointestinal digestion and absorption, Phe-CMP-1P was degraded. Intact Phe-CMP-1P and CMP-1P were rapidly released from the stomach. In contrast, partial hydrolysis by pancreatic enzymes was observed. In vitro hydrolysis by brush-border membrane vesicles also indicated that the peptide was degraded. In the blood, "CMP-immunoreactive material" appeared rapidly, reaching a maximum level of 5.5 microg/ml at 60 min.

A new detection algorithm for implantable cardioverter defibrillator

One of the most important subsystems of implantable cardioverter defibrillator (ICD) is the sensing stage, since it determines the sensitivity and specificity of the device to detect the heart rate and the underlying arrhythmia. This paper aims to investigate a new detection algorithm for ICD, which operates fully automatically. The algorithm ARGUS was implemented as a computer model and tested with intracardiac electrograms recorded (band-pass: 0.05 to 500 Hz; sampling rate: 1-4 kHz) under different rhythm condition like sinus rhythm (n = 18), atrial tachycardia (n = 16), and ventricular tachycardia as well as fibrillation (n = 139) during electrophysiological tests or ICD implantation. The results of the tests were visually inspected on a beat-to-beat basis. In total 31,934 events were classified by the algorithm (18,758 as long intervals (LI) with cycle length > 300 ms; 13,176 as short intervals (SI)). 195 out of the 13,176 SI and 572 out of 18,758 LI were incorrectly classified (SI: 1.48%; LI: 3.05%). In conclusion the new algorithm yield high sensitivity (99.9%) and specificity (97.0%) as known from conventional ICD algorithms but need no manual adjustments.

Differential roles of Lck and Itk in T cell response to antigen recognition revealed by calcium imaging and electron microscopy

Ag recognition triggered at the interface between a T cell and an APC is conditioned by cell-cell adhesion and cytoskeletal remodeling. The role played in these phenomena by Lck and Itk, two protein tyrosine kinases essential for T cell signaling, was examined. Early T cell responses (membrane ruffling, Ca(2+) response, APC-T cell adhesion) were monitored in T cells overexpressing kinase-defective (KD) Lck and Itk mutants by combining fluorescence imaging and electron microscopy. Neither Lck nor Itk appears to be involved in the Ag-independent formation of a small and labile contact interface between T cells and APCS: By contrast, the Ag-induced Ca(2+) response in a cell population is similarly blunted in both KD transfectants. However, the underlying mechanisms are strikingly different for the two kinases. The major effect of Lck-KD is to reduce the probability of giving rise to quasi-normal Ca(2+) responses, whereas overexpression of Itk-KD results in a tuning down of all single-cell Ca(2+) responses. In addition, Lck, but not Itk, is required for the formation of a stable T/APC conjugate and for T cell polarization after Ag stimulation. Overall, our results lead to a clear distinction between Lck and ITK: Lck plays an ignition role, controlling all the downstream events tested here, whereas Itk amplifies the Ca(2+) response, but is dispensable for APC-induced adhesive and morphological responses.

Varying the protein source in mixed meal modifies glucose, insulin and glucagon kinetics in healthy men, has weak effects on subjective satiety and fails to affect food intake

OBJECTIVE

To evaluate the influence of three dietary protein types (casein, gelatin, soy protein) on satiety and food intake, at two levels of loading (total energy of test meals: 3.6 or 1.8 MJ).

DESIGN

The study employed a repeated measures design. Test meals were controlled for energy, macronutrients, fiber and palatability, and contained about 23% energy as protein (of which about 65% was experimentally manipulated). Postprandial subjective satiety and hunger, plasma glucose, insulin and glucagon were assessed for 8 h, and energy and macronutrient intakes were monitored for 24 h.

SUBJECTS

Nine healthy normal-weight men.

RESULTS

No effect of the type of protein on 24 h energy and macronutrient intakes was observed despite a significant effect of protein source on the kinetics of peripheral metabolic responses (but only after 3.6 MJ lunches), and inconsistent effects on subjective hunger and satiety responses A casein-enriched lunch delayed glucose and insulin responses for 1.5 h, compared with soy protein, probably due to a lag in gastric emptying.

CONCLUSION

Varying the protein source in a mixed meal modifies glucose, insulin and glucagon kinetics in healthy men, but these variations in satiety-implicated factors have inconsistent effects on subjective satiety and fail to affect food intake.

SPONSORSHIP

Eridania Béghin-Say, Vilvoorde, Belgium and Association Nationale de la Recherche Technique, France (Convention CIFRE no 537/94).

Fyn membrane localization is necessary to induce the constitutive tyrosine phosphorylation of Sam68 in the nucleus of T lymphocytes

A close relationship between Sam68, a tyrosine and proline-rich RNA-binding protein, and Src protein tyrosine kinases (PTK) has already been established, also in T lymphocytes. A constitutive phosphorylation of the molecule has also been documented in various transformed T cells, which probably reflects an increased expression of PTK of the Src family. Using the hybridoma T cell line, T8.1, or Jurkat T cells, we investigated the respective contribution of the two Src kinases Fyn and Lck, expressed in T cells, in this phenomenon. By overexpressing the two proteins, we show that the constitutive phosphorylation of Sam68 in vivo directly correlates with cellular Fyn levels, but not with Lck expression, despite the capacity of the PTK to strongly phosphorylate the molecule in vitro. Overexpressed Fyn is mainly localized at the cell membrane. We find that Sam68 phosphorylation, including in the nuclear fraction in which the molecule is predominantly expressed, is lost with a delocalized Fyn mutant deleted of its N-terminal membrane-anchoring domain. Finally, we demonstrate, using a construct encoding a Sam68 molecule without its nuclear localization signal, that nuclear expression of Sam68 is not required for phosphorylation. We conclude that the constitutive phosphorylation of Sam68 in T cells is a Fyn-dependent process occurring in a cell-membrane compartment from which phospho-Sam68 molecules can thereafter accumulate into the nucleus.

Euglycemic hyperinsulinemic clamp to assess posthepatic glucose appearance after carbohydrate loading. 1. Validation in pigs

BACKGROUND

Precise knowledge of the rate of glucose absorption after meal feeding requires invasive methods in humans.

OBJECTIVE

This study aimed to validate in an animal model a technique combining the euglycemic hyperinsulinemic clamp and oral carbohydrate loading (OC-Clamp) as a noninvasive procedure to quantify the posthepatic appearance of glucose after oral carbohydrate loading.

DESIGN

Twenty-one pigs were fitted with arterial, jugular, portal, and duodenal catheters and a portal blood flow probe. At glucose clamp steady state, duodenal glucose (0.9 g/kg; DG-Clamp) and oral carbohydrate (140 g corn or mung bean starch as part of a mixed meal; OC-Clamp) were administered while the glucose infusion was progressively reduced to compensate for the incremental posthepatic appearance of glucose. [3-3H]glucose was used to assess the glucose turnover rate.

RESULTS

Hepatic glucose production was totally suppressed by insulin infusion, and the whole-body glucose turnover rate remained stable during glucose absorption. The incremental portal appearance of glucose after the DG load was not altered by hyperinsulinemia, and the cumulative posthepatic appearance of glucose was 63 +/- 3% (x +/- SEM) of the DG load. The net hepatic portal appearance of glucose remained constant during absorption (34 +/- 3% of the load). After the OC load, the respective portal appearance rates of glucose were significantly different between carbohydrate sources; however, the rates paralleled those of the posthepatic appearance of glucose. Again, net hepatic glucose uptake expressed as portal appearance was similar for both carbohydrates.

CONCLUSIONS

The results validate the OC-Clamp method to monitor the posthepatic appearance of glucose after carbohydrate ingestion and to discriminate between different carbohydrate sources. The results suggest that the technique be used in humans.

Euglycemic hyperinsulinemic clamp to assess posthepatic glucose appearance after carbohydrate loading. 2. Evaluation of corn and mung bean starches in healthy men

BACKGROUND

The rate of absorption of glucose from carbohydrates is important in several aspects of health. We recently validated a noninvasive technique in pigs, euglycemic hyperinsulinemic clamp plus oral carbohydrate loading (OC-Clamp), to quantify the rate of net posthepatic appearance of glucose after ingestion of carbohydrates.

OBJECTIVE

The OC-Clamp procedure was performed in 8 healthy men to compare the net posthepatic appearance of glucose after ingestion of 1 of 3 carbohydrates.

DESIGN

Human volunteers underwent the OC-Clamp procedure at an insulin infusion rate of 1.5 mU x kg(-1) x min(-1) (n = 5). The oral carbohydrate load (1 g/kg) consisted of glucose, cornstarch, or mung bean starch. During the OC-Clamp procedure, the glucose infusion rate decreased during absorption to maintain plasma glucose steady state and the decrease reflected the net posthepatic appearance of glucose. In addition, carbohydrates were loaded without insulin infusion (n = 6) and glycemic indexes were calculated (with glucose as the reference).

RESULTS

The mean (+/-SEM) glycemic index of cornstarch was higher (95 +/- 18) than that of mung bean starch (51 +/- 13). In the OC-Clamp experiments, the posthepatic appearance of glucose and cornstarch did not differ significantly and represented 79.4 +/- 5.0% and 72.6 +/- 4.0%, respectively, of the load after complete absorption (within 3 h). In contrast, the net posthepatic appearance of glucose from mung bean starch was significantly lower (35.6 +/- 4.6% of the load, P < 0.001) than that from glucose and cornstarch, even 4.5 h postprandially.

CONCLUSIONS

The OC-Clamp technique allows a continuous assessment of net posthepatic appearance of glucose after ingestion of carbohydrates and significant discrimination between corn and mung bean starches.

Prediction of the onset of atrial fibrillation after cardiac surgery using the monophasic action potential

OBJECTIVE

To show that the monophasic action potential (MAP) recorded continuously from human epicardium may be used to predict the imminent onset of atrial fibrillation or flutter (AF) following surgery, thus allowing prophylactic treatment to be started.

PATIENTS

22 patients (14 male, 8 female; mean (SD) age 64 (12) years) undergoing aortic valve replacement.

SETTING

Tertiary referral centre.

METHODS

Over a mean observation period of 8 (2.7) days (range 4 to 14), nine episodes of AF were seen in six patients. Before AF, specific and significant alterations of the MAP morphology were observed. In seven of nine episodes the MAP shortened (25 (4)% 60 minutes before AF), developed a triangular shape, and the plateau amplitude decreased from 5.3 (1.2) to 2 (0.2) mV. In the two remaining episodes the beat to beat variability of cycle length and MAP duration at 90% repolarisation (MAPd90) increased significantly from 24 (7) ms and 12 (8) ms (24 hours before AF) to 137 (27) ms and 56 (11) ms (30 minutes before AF) respectively. AF was successfully treated by the administration of sotalol in three cases and by a combination of verapamil and digoxin in a further four. Previously observed changes of MAPd90 and MAP morphology regressed after conversion to sinus rhythm.

CONCLUSIONS

The continuous and intermediate term recording of the MAP from atrial epicardium appears to be a valid tool for detecting imminent AF after cardiac surgery with a high sensitivity (99%) and specificity (88%). Optimised antiarrhythmic treatment may thus be given selectively for prophylaxis.

F(ab')2 molecules made from Escherichia coli produced Fab' with hinge sequences conferring increased serum survival in an animal model

Fab's with hinges based on the human gamma1 sequence containing 1, 2, or 4 cysteines have been produced by high level Escherichia coli periplasmic secretion, and coupled in vitro by reduction/oxidation to form F(ab')2. We find that the F(ab')2 made with hinges containing 2 or 4 cysteines have a high level (approximately 70%) of multiple disulphide bonds. These F(ab')2 molecules have an increased pharmacokinetic stability as measured by area under the curve compared to those made by direct coupling through a single disulphide bond. One particular molecule containing 4 hinge cysteines has a greater pharmacokinetic stability than a F(ab')2 formed by chemical cross-linking. F(ab')2 made from the Fab' with 4 hinge cysteines is also relatively resistant to chemical reduction in vitro allowing partial reduction to expose reactive hinge thiols. These hinge sequences provide a simple method for producing robust F(ab')2 in vitro, obviating the need to use chemical cross-linkers, and provide a route to hinge specific chemical modification with thiol-reactive conjugates.

Satiating effect of proteins in healthy subjects: a comparison of egg albumin, casein, gelatin, soy protein, pea protein, and wheat gluten

The influence of six dietary protein types (egg albumin, casein, gelatin, soy protein, pea protein, and wheat gluten) on satiety and food intake was investigated. Twelve healthy subjects ingested six protein-manipulated lunches (approximately 5.2 MJ, 22% of energy as protein) according to a within-subjects design. Test meals were controlled for energy, macronutrients, fiber, and palatability. Nearly 65% of total protein varied between sessions. After lunch, satiety was assessed for 8 h and energy and macronutrients intakes were measured for 24 h. Blood was collected for determination of postprandial plasma glucose and insulin responses. Results showed no effect of the type of protein on satiety, on 24-h energy or macronutrient intakes, or on postprandial plasma glucose and insulin concentrations. These findings differ in part from those obtained previously in humans, which suggested that proteins may be differentiated in terms of their satiating capacities. We conclude that varying the protein source in a mixed meal does not affect food behavior in healthy humans, probably because coingestion of carbohydrate and fat with protein buffers the kinetics of the physiologic mechanisms implicated in postprandial satiety after a protein load.

Increased monophasic action potential dispersion in endothelin-1-induced ventricular arrhythmias

The aim of this study was to investigate the changes in monophasic action potentials (MAP) from different sites in the heart and to determine MAP dispersion during endothelin-1 (ET-1) infusion. Standard ECG, left ventricular anterior, right ventricular lateral, right ventricular septal, and right ventricular apical MAPs and intra-arterial blood pressure were monitored in seven anesthetized open-chest mongrel dogs. After radiofrequency atrioventricular node ablation, ventricular pacing (70/min) was performed and intracoronary ET-1 (60 pmol/min) was administered into the left anterior descending coronary artery. Both MAPd90 and MAPd90 dispersion increased significant during ET-1 infusion. The onset of spontaneous monomorphic and polymorphic sustained ventricular tachycardias (sVT) was observed in five dogs (around 40 min), and nonsustained VTs (nsVT) developed in another two dogs. The increases in MAP and MAP dispersion lasted until the appearance of polymorphic nsVTs and sVTs, but at the time of these VTs this difference decreased. At the termination of the experiments, ventricular fibrillation occurred in six cases. In four cases third-phase early afterdepolarizations were recorded. Our results suggest that increased MAP dispersion and development of EAD contribute to the arrhythmogenic action of ET-1, and these phenomena might explain the pathogenesis of a wide variety of ventricular arrhythmias with different morphology observed in this study.