Biomedical subjects

J Machann

Publications and source records attributed to J Machann.

26 records · Page 2Linked to original sources

PubMed1999

Association of increased intramyocellular lipid content with insulin resistance in lean nondiabetic offspring of type 2 diabetic subjects.

Insulin resistance plays an important role in the pathogenesis of type 2 diabetes; however, the multiple mechanisms causing insulin resistance are not yet fully understood. The aim of this study was to explore the possible contribution of intramyocellular lipid content in the pathogenesis of skeletal muscle insulin resistance. We compared insulin-resistant and insulin-sensitive subjects. To meet stringent matching criteria for other known confounders of insulin resistance, these individuals were selected from an extensively metabolically characterized group of 280 first-degree relatives of type 2 diabetic subjects. Some 13 lean insulin-resistant and 13 lean insulin-sensitive subjects were matched for sex, age, BMI, percent body fat, physical fitness, and waist-to-hip ratio. Insulin sensitivity was determined by the hyperinsulinemic-euglycemic clamp method (for insulin-resistant subjects, glucose metabolic clearance rate [MCR] was 5.77+/-0.28 ml x kg(-1) x min(-1) [mean +/- SE]; for insulin-sensitive subjects, MCR was 10.15+/-0.7 ml x kg(-1) x min(-1); P<0.002). Proton magnetic resonance spectroscopy (MRS) was used to measure intramyocellular lipid content (IMCL) in both groups. MRS studies demonstrated that in soleus muscle, IMCL was increased by 84% (11.8+/-1.6 vs. 6.4+/-0.59 arbitrary units; P = 0.008 ), and in tibialis anterior muscle, IMCL was increased by 57% (3.26+/-0.36 vs. 2.08+/-0.3 arbitrary units; P = 0.017) in the insulin-resistant offspring, whereas the extramyocellular lipid content and total muscle lipid content were not statistically different between the two groups. These data demonstrate that in these well-matched groups of lean subjects, IMCL is increased in insulin-resistant offspring of type 2 diabetic subjects when compared with an insulin-sensitive group matched for age, BMI, body fat distribution, percent body fat, and degree of physical fitness. These results indicate that increased IMCL represents an early abnormality in the pathogenesis of insulin resistance and suggest that increased IMCL may contribute to the defective glucose uptake in skeletal muscle in insulin-resistant subjects.

Adult↗

PubMed1999

[In-vivo 1H-MR spectroscopy: the determination of the intra- and extramyocellular lipid content depending on the insulin effect in the direct offspring of type-2 diabetics].

PURPOSE: Differentiation and assessment of intra- (IMCL) and extramyocellular lipids (EMCL) in offspring of type II diabetic subjects by means of 1H-MR spectroscopy. METHODS: Out of a group of more than 250 metabolically characterized offspring of type II diabetics, twenty subjects were selected and matched for anthropometric parameters. Glucose clamp was performed prior to MRS in all subjects for metabolic characterization. Ten individuals were classified as insulin resistant (MCR < 7 ml/kg/min) and ten were found to be insulin sensitive (MCR > 7 ml/kg/min). MRS was performed in the tibialis anterior muscle and in the soleus muscle. RESULTS: For insulin resistant individuals the MRS results revealed a higher IMCL content in both muscles. In the tibialis anterior muscle IMCL was increased by 1.6 fold (arbitrary units +/- SEM: 3.2 +/- 0.4 vs 2.0 +/- 0.3; p < 0.01) and in the soleus muscle by 2.0 fold (arbitrary units +/- SEM: 13.0 +/- 1.9 vs 6.6 +/- 0.9; p < or = 0.01). There was no correlation between EMCL and MCR in the soleus muscle. In addition, no relationship between the amount of IMCL and the subcutaneous fat layer was found. CONCLUSIONS: A significantly increased intramyocellular lipid content in insulin resistant offspring of type II diabetic subjects was assessed non-invasively by 1H-MR spectroscopy.

Adult↗

PubMed1997

Highly selective water and fat imaging applying multislice sequences without sensitivity to B1 field inhomogeneities.

Improved selectivity to one chemical shift component was obtained using simultaneous slice-selective and chemical shift-selective excitation in sequences with usual spin-echo refocusing. The new type of sequences can be applied on modern whole-body units and permits multislice operation. Spatial-spectral excitation is based on prior research in this field, but the proposed improved version provides off-center slice excitation by the usual processing of the RF pulse envelopes. In addition, no irregular gradient shapes are necessary. The required B0 homogeneity of the new method is similar to conventional "fat-sat" techniques. In contrast to fat-sat methods, selectivity to water is not reduced by unavoidable misadjustments of the transmitter or B1 field inhomogeneities in the newly developed approach. Thus, the reported method has the potential to replace standard frequency selective fat-sat sequences for most applications.

Humans↗

PubMed1996

Sequence parameters of double spin-echo sequences affect quantification of citrate.

Quantification of citrate by localized 1H spectroscopy is usually performed using the water signal as reference, but the signal behavior of the J-coupled AB spin system of citrate after multipulse excitation is not as trivial as for uncoupled substances. The influence of the timing scheme of double spin-echo sequences and of the spatial flip angle distribution of (nonideal) refocusing pulses was analyzed systematically for the citrate resonances. Both single echo times of the double spin-echo sequence were varied between 20 ms and 250 ms in theoretical and experimental approaches. Relatively long total echo times (TE > 120 ms) provide high selectivity to citrate signals, since signals from triglycerides at 2.6 ppm are markedly reduced. Asymmetrical timing schemes of the double spin-echo sequence with one short single echo time of 20 ms and one longer single echo time of about 120 ms result in high integral signal from the central lines of citrate, whereas symmetrical timing leads to high sensitivity for total echo times TE near 100 ms. The integral citrate signals in spectra with relatively long echo times (TE > 120 ms) were found to depend markedly on the type of the refocusing pulses, affecting quantitative citrate measurements in vitro and in vivo.

Citric Acid↗

PubMed1995

Magnetic resonance bone densitometry. Comparison of different methods based on susceptibility.

RATIONALE AND OBJECTIVES: Three different magnetic resonance techniques for the assessment of the density of trabecular bone are presented and compared. METHODS: All methods are based on the susceptibility difference between marrow and bony components. Localized spectroscopic (PRESS single voxel spectroscopy) and two different imaging approaches (FLASH gradient echo imaging and MAGSUS imaging) are demonstrated to be sensitive to the trabecular structures on application to the distal femur of a healthy volunteer. This region was chosen because a continuous rarefication of the trabecular density from the epiphysis to the metaphysis occurs physiologically. In addition, results from the heel-bones of five young healthy volunteers were compared with data from three patients with severe osteoporosis. RESULTS: All methods allowed differentiation between the two groups. Advantages and disadvantages of the methods concerning spatial resolution, preparation and measuring time, necessity of postprocessing, problems with shim adjustment, and occurrence of several chemical shift components are reported. The MAGSUS technique combines simple application and avoidance of postprocessing for at least qualitative assessment of bone density with sufficient spatial resolution. CONCLUSIONS: A reliable assessment of osteoporosis by magnetic resonance is possible in peripheral marrow regions of adults. Further studies are needed to establish standard measuring protocols.

Adult↗

PubMedDate not supplied

Improved clinical echo-planar MRI using spatial-spectral excitation.

Echo-planar imaging (EPI) is markedly susceptible to B0 field distortions and to frequency differences caused by chemical shift, because the phase of the signals is accumulating during the acquisition train. Thus, only water proton signals are usually recorded after frequency-selective suppression of the fat portions of magnetization. Otherwise, a shifted signal frequency from fat results in ghosting artifacts. In this article, a technique is presented working with spatial-spectral excitation for highly selective water or fat EPI. The proposed method allows recording in multislice operation on EPI scanners without irregular gradient or RF pulse shapes. Examples of gradient-echo and spin-echo EPI using spatial-spectral excitation by series of two to eight single slice-selective RF pulses are demonstrated. The method is not sensitive to misadjustments or inhomogeneities of the B1 field, but sufficient homogeneity of the static magnetic field B0 is required. Especially the quality of diffusion-weighted echo-planar images can be markedly improved by the new technique compared to conventional EPI, because artifacts from undesired chemical shift components are completely avoided.

Adult↗

PubMedDate not supplied

Relationship between serum adiponectin concentration and intramyocellular lipid stores in humans.

The recently identified adipocytokine adiponectin has been shown to improve insulin action and decrease triglyceride content in skeletal muscle (by stimulating lipid oxidation) in mice. In the present study, we tested the hypothesis that high serum concentrations of adiponectin are associated with lower intramyocellular (IMCL) fat content by promoting lipid oxidation in humans. IMCL-content in predominantly non-oxidative tibialis anterior muscle and oxidative soleus was determined by proton magnetic resonance spectroscopy in a cross- sectional study involving 63 healthy volunteers. In a second set of experiments, changes in IMCL in both muscles were measured after a three days dietary lipid challenge (n = 18) and after intravenous lipid challenge (n = 12) with suppressed lipid oxidation under hyperinsulinemia. Adiponectin serum concentrations were found to be negatively correlated with IMCL in the oxidative soleus muscle (IMCL [sol]) (r = - 0.46, p < 0.001) independent of measures of obesity, but not with IMCL in the non-oxidative tibialis anterior muscle (IMCL [tib]) (p = 0.40). Adiponectin serum concentrations were negatively correlated with the observed increase in IMCL load after dietary lipid challenge in the tibialis (r = 0.53, p = 0.03) but not in the soleus muscle. During suppression of lipid oxidation by hyperinsulinemia, no effect of adiponectin on IMCL was observed in either soleus or tibialis muscle. Overall, the presented findings are consistent with the hypothesis that adiponectin promotes lipid oxidation in humans resulting in lower intracellular lipid content in human muscle. These results are consistent with animal data, where adiponectin could be shown to enhance lipid oxidation and reduce muscle triglycerides.

Adiponectin↗

PubMedDate not supplied

[Examination of trabecular bone structures of the foot skeleton with MRI imaging].

AIMS: To assess trabecular density and structures at various cancellous bone sites in the foot using MR imaging. To compare the MRI findings with the bone mineral density (BMD) values obtained by quantitative computed tomography (QCT) in the lumbar vertebrae. MATERIALS AND METHODS: Bone mineral densities were measured by QCT in lumbar vertebrae 1 to 3 in ten patients with suspected osteoporosis. Sagittal images of the feet were obtained from these patients and also from seven healthy volunteers applying spin-echo and gradient-echo MR techniques. RESULTS: MR imaging revealed differences between patients with osteoporosis and individuals with healthy bones. Comparison of MR and BMD data revealed a significant dependence of MR data on the bone density measured by QCT (alpha < 0.05). In addition, a good correlation (r = 0.73) was found between the results of the different MRI techniques. CONCLUSIONS: The MR imaging techniques investigated offer an interesting tool for the non-invasive assessment of bony structures, at least at peripheral locations with yellow bone marrow. To enable reliable application in the clinical routine setting, additional studies are required to identify suitable standardized methods and establish normal ranges.

Adult↗