Effect of a high dose of simvastatin on muscle mitochondrial metabolism and calcium signaling in healthy volunteers.

Statin use may be limited by muscle side effects. Although incompletely understood to date, their pathophysiology may involve oxidative stress and impairments of mitochondrial function and of muscle Ca(2+) homeostasis. In order to simultaneously assess these mechanisms, 24 male healthy volunteers were randomized to receive either simvastatin for 80 mg daily or placebo for 8 weeks. Blood and urine samples and a stress test were performed at baseline and at follow-up, and mitochondrial respiration and Ca(2+) spark properties were evaluated on a muscle biopsy 4 days before the second stress test. Simvastatin-treated subjects were separated according to their median creatine kinase (CK) increase. Simvastatin treatment induced a significant elevation of aspartate amino transferase (3.38±5.68 vs -1.15±4.32 UI/L, P<0.001) and CK (-24.3±99.1±189.3 vs 48.3 UI/L, P=0.01) and a trend to an elevation of isoprostanes (193±408 vs 12±53 pmol/mmol creatinine, P=0.09) with no global change in mitochondrial respiration, lactate/pyruvate ratio or Ca(2+) sparks. However, among statin-treated subjects, those with the highest CK increase displayed a significantly lower Vmax rotenone succinate and an increase in Ca(2+) spark amplitude vs both subjects with the lowest CK increase and placebo-treated subjects. Moreover, Ca(2+) spark amplitude was positively correlated with treatment-induced CK increase in the whole group (r=0.71, P=0.0045). In conclusion, this study further supports that statin induced muscular toxicity may be related to alterations in mitochondrial respiration and muscle calcium homeostasis independently of underlying disease or concomitant medication.

Artificial beta-cell: clinical experience toward an implantable closed-loop insulin delivery system.

AIM: Restoration of long-term normal blood glucose control in diabetic patients supports the elaboration of an artificial beta cell. The possibility of implantation of the three crucial components of such a system (insulin delivery device, glucose sensor and controller) is analyzed. METHODS: The Long-Term Sensor System project, aiming at a fully implantable artificial beta cell, assessed the feasibility of glucose control by the combined implantation of a pump for peritoneal insulin delivery and a central intravenous glucose sensor close to the right atrium, connected via a subcutaneous lead. It was initiated in 10 Type 1 diabetic patients in our clinic from 2000. Data obtained during this experience are reviewed and confronted to reported closed-loop trials using other approaches. RESULTS: No significant complication related to prolonged implantation of intravenous sensors occurred and the combined implants were well tolerated. Glucose measurement by the intravenous sensors correlated well with meter values (r=0.83-0.93, with a mean absolute deviation of 16.5%) and accuracy has been sustained for an average duration of 9 months. Uploading of pump electronics by algorithms designed for closed-loop insulin delivery allowed in-patient 48 hour-trials aiming at automated glucose control. Glucose control was similar to that reported by investigations combining subcutaneous sensors to wearable pumps for subcutaneous insulin infusion. The benefits of more physiological insulin kinetics due to intra-peritoneal delivery have been hampered by the slow response time of intravenous sensors. CONCLUSION: Although the concept of a fully implantable artificial beta cell has been validated as feasible, the limited performance in achieving glucose control requests improvements in the sensor structure to increase its longevity and decrease sensor delay.

Ca-dependence of isometric force kinetics in single skinned ventricular cardiomyocytes from rats.

OBJECTIVES: The effects of Ca2+ on the rate of tension redevelopment following a brief release/restretch were investigated in single chemically-skinned ventricular myocytes from the rat. METHODS: The myocytes were enzymatically isolated and skinned using Triton-X100. They were then attached with an optical adhesive glue to glass micropipettes fixed to a piezoelectric translator and a force transducer. Tension redevelopment was measured at various levels of Ca activation after disrupting force-generating crossbridges by a brief (20 ms) step release/restretch equivalent to 20% of the original 2.1 microns sarcomere length. Most of tension redevelopment was well fitted by a monoexponential function. RESULTS: At maximal Ca concentrations, pCa 4.5 maximal force was obtained at 2.1 microns sarcomere length and averaged 11.8 +/- 0.7 microN. The rate of tension redevelopment (ktr) increased with increasing Ca concentrations up to 5.19 +/- 0.37.s-1 at maximal Ca activation. The relation between the rate of tension redevelopment and Ca concentration was sigmoidal and could be fitted by the Hill equation with coefficients similar to those describing the tension-pCa relation. The relation between relative rate of tension redevelopment and relative steady activated tension was curvilinear increasing with increasing Ca concentration. CONCLUSIONS: In cardiac muscle, Ca2+ modulates both the number and the kinetics of force-generating crossbridges in a manner similar to that previously reported in skeletal muscle.

P2Y receptor activation enhances insulin release from pancreatic beta-cells by triggering the cyclic AMP/protein kinase A pathway.

Adenine nucleotides stimulate insulin secretion by binding to P2 receptors of the pancreatic beta-cells; the stimulus-secretion coupling is not yet clearly established and may depend on the receptor subtype. The aim of the present study was to further investigate the mechanism whereby P2Y receptor agonists enhance glucose-induced insulin secretion. Experiments were performed in rat pancreatic islets and in the INS-1 secreting cell line in the presence of a slightly stimulating glucose concentration (8.3 mmol/l). In isolated islets, the P2Y receptor agonist ADPbetaS (50 micromol/l) induced a significant fivefold increase in the cyclic AMP (cAMP) content, from 43.4+/-3.7 fmol/10 islets in controls to 210.6+/-12.0; it still induced a 4.5-fold increase in cAMP content in the absence of calcium. In another series of experiments, ADPbetaS (50 micromol/l) significantly increased glucose-induced insulin secretion from 7.7+/-0.6 ng/3 islets in controls to 11.2+/-1.0. The adenylyl cyclase inhibitor SQ 22,536 (9-[tetrahydro-2-furanyl]-9 H-purin-6-amine; 100 micromol/l), which was ineffective alone, completely prevented the stimulating effect of ADPbetaS. In a set of experiments in which ADPbetaS increased glucose-induced insulin secretion from 10.0+/-0.7 ng/3 islets to 12.6+/-0.8, the inhibitor of cAMP-dependent protein kinase, TPCK (tos-phe-chloromethylketone; 3 micromol/l), which was ineffective alone, also prevented the stimulating effect of ADPbetaS. In incubated INS-1 cells, the P2Y receptor ligand ATPalphaS increased significantly both the content of cAMP and the release of insulin, in a concentration-dependent manner in the range of 50-150 micromol/l; the insulin release was significantly correlated with the cAMP content. In conclusion, the present results show that P2Y receptor agonists, ADPbetaS and ATPalphaS, amplify glucose-induced insulin secretion by activating beta-cell adenylyl cyclase and the subsequent cAMP/protein kinase A signaling pathway.

[Comparison of echocardiographic automatic border detection and magnetic resonance imaging. Measurements of the left ventricle in normal subjects]. / Comparaison des mesures ventriculaires gauches par échocardiographie en quantification acoustique et par imagerie magnétique nucléaire chez le sujet normal.

Echocardiographic automatic border detection (ABD) has been the object of several studies with diverging results. The aim of this study was to verify the validity of ABD measurements by comparison with magnetic resonance imaging (MRI). Twenty healthy subjects underwent measurement of end systolic surface (ESA) and end diastolic surface areas (EDA) and fraction of surface variation (FSV), end systolic volume (ESV), end diastolic volume (EDV and ejection fraction (EF). These results were compared with the same parameters measured by cine MRI and a study of the variability of interpretation was performed on the echocardiographic parameters. An ABD analysis was possible in 80% of the study population. The correlations were satisfactory between the EDA and EDV (EDA; r = 0.84; SD = 1.9 cm2; EDV; r = 0.90; SD = 12 ml) with acceptable confidence intervals (CI) (EDA; [-4.02; 1.19 cm2]/EDV; [26; +7.9 ml]) and an underestimation of ABD values (EDA; -9%/EDV: -10%). With regards to the end systolic measurements, the correlations were not as good (ESA: r = 0.68; SD = 1.5 cm2/EDV: r = 0.59; +12 ml) with a more important measurement error (ESA: -2.05; +3.45 cm2)/EDA: (-9; +27 ml) and an overestimation of the ABD values (ESA; +10%; ESV; +18%). No correlation was observed between the FSV and EF. The intra and inter-observer errors were compared with those of conventional echocardiography (intra-observer error; 10.7-16.9%/inter-observer error; 10.8-16.6%). The authors conclude that ABD has a non-negligeable measurement error which limits its application in clinical practice. New transducers, automatisation of gain adjustment and new technologies should improve ABD measurements.

Direct rosiglitazone-induced modifications in insulin secretion, action and clearance: a single-dose hyperglycaemic clamp study.

AIMS/HYPOTHESIS: In addition to the improvement in insulin sensitivity, it has been shown that thiazolidinediones modulate beta cell function and insulin clearance in type 2 diabetic subjects. However, interactions between all these actions, and confounding factors due to co-morbidities and co-treatments in diabetic individuals, complicate the identification of specific effects. The aim of this pilot study was to investigate the potential acute effects of rosiglitazone on beta cell function and insulin sensitivity by the hyperglycaemic clamp technique in healthy volunteers. SUBJECTS AND METHODS: Twelve healthy men were included in a randomised, double-blind crossover study. Rosiglitazone (8 mg) or placebo was given orally 45 min before the hyperglycaemic clamp (10 mmol/l for 2 h). RESULTS: The second phase of the insulin response was significantly decreased by rosiglitazone: 13,066 +/- 1,531 vs 16,316 +/- 2,813 pmol l(-1) 110 min in controls (p < 0.05), without change in the first phase. Serum C-peptide was not modified. Rosiglitazone treatment significantly increased insulin clearance (molar ratio of the C-peptide to insulin AUCs: 12.80 +/- 1.34 vs 11.38 +/- .33, p < 0.05) and the insulin sensitivity index (12.0 +/- 1.5 vs 8.5 +/- 1.1 micromol m(-2) min(-1) pmol(-1)l, p < 0.01). CONCLUSIONS/INTERPRETATION: The present results show that a single dose of rosiglitazone rapidly increases insulin clearance and insulin sensitivity index in healthy volunteers, with no direct effect on insulin secretion. The precise mechanisms mediating these actions remain to be determined.