Lactate induces insulin resistance in skeletal muscle by suppressing glycolysis and impairing insulin signaling

Elevation of plasma lactate levels induces peripheral insulin resistance, but the underlying mechanisms are unclear. We examined whether lactate infusion in rats suppresses glycolysis preceding insulin resistance and whether lactate-induced insulin resistance is accompanied by altered insulin signaling and/or insulin-stimulated glucose transport in skeletal muscle. Hyperinsulinemic euglycemic clamps were conducted for 6 h in conscious, overnight-fasted rats with or without lactate infusion (120 micromol x kg(-1) x min(-1)) during the final 3.5 h. Lactate infusion increased plasma lactate levels about fourfold. The elevation of plasma lactate had rapid effects to suppress insulin-stimulated glycolysis, which clearly preceded its effect to decrease insulin-stimulated glucose uptake. Both submaximal and maximal insulin-stimulated glucose transport decreased 25-30% (P < 0.05) in soleus but not in epitrochlearis muscles of lactate-infused rats. Lactate infusion did not alter insulin's ability to phosphorylate the insulin receptor, the insulin receptor substrate (IRS)-1, or IRS-2 but decreased insulin's ability to stimulate IRS-1- and IRS-2-associated phosphatidylinositol 3-kinase activities and Akt/protein kinase B activity by 47, 75, and 55%, respectively (P < 0.05 for all). In conclusion, elevation of plasma lactate suppressed glycolysis before its effect on insulin-stimulated glucose uptake, consistent with the hypothesis that suppression of glucose metabolism could precede and cause insulin resistance. In addition, lactate-induced insulin resistance was associated with impaired insulin signaling and decreased insulin-stimulated glucose transport in skeletal muscle.     

Understanding muscle coordination of the human leg with dynamical simulations

Muscles coordinate multijoint motion by generating forces that cause reaction forces throughout the body. Thus, a muscle can redistribute existing segmental energy by accelerating some segments and decelerating others. In the process, a muscle may also produce or absorb energy, in which case its summed energetic effect on the segments is positive or negative, respectively. This Borelli Lecture shows how dynamical simulations derived from musculoskeletal models reveal muscle-induced segmental energy redistribution and muscle co-functions and synergies. Synergy occurs when co-excited muscles distribute segmental energy differently to execute the motor task. In maximum height jumping, high vertical velocity at lift-off occurs desirably at full body extension because biarticular leg muscles redistribute the energy produced by the uniarticular leg muscles. In pedaling, synergistic ankle plantarflexor force generation during leg extension allows the high energy produced by the uniarticular hip and knee extensors to be delivered to the crank. An analogous less-powerful flexor synergy exists during leg flexion. Hamstrings reduce crank deceleration during the leg extension-to-flexion transition by not only producing energy but delivering it to the crank through its contribution to the tangential (accelerating) crank force, though this hamstrings function occurs at the opposite (flexion-extension) transition when pedaling backwards. In walking, the eccentric quadriceps activity in early stance not only decelerates the leg but also accelerates the trunk. In mid-stance, the uni- and biarticular plantarflexors, by having opposite segmental energetic effects, act in synergy to support the whole body, so segmental potential and kinetic energy exchange can occur. To conclude, the extraction of unmeasurable variables from dynamical simulations emulating task kinematics, kinetics, and EMGs shows how the production of force and energy by individual muscles contribute to the energy flow among the individual segments during task execution.     

Cytokine regulation of periportal fibrosis in humans infected with Schistosoma mansoni: IFN-gamma is associated with protection against fibrosis and TNF-alpha with aggravation of disease

Hepatic periportal fibrosis, which affects 5-10% of subjects infected by Schistosoma mansoni, is caused by the T cell-dependent granuloma that develop around schistosome eggs. Experimental models of infection have shown that granuloma and fibrosis are tightly regulated by cytokines. However, it is unknown why advanced periportal fibrosis occurs only in certain subjects. The goal of the present study was to evaluate the cytokine response of S. mansoni-infected subjects with advanced liver disease in an attempt to relate susceptibility to periportal fibrosis with an abnormal production of cytokines that regulate granuloma and fibrosis. Fibrosis was evaluated by ultrasound on 795 inhabitants of a Sudanese village in which S. mansoni is endemic: advanced periportal fibrosis was observed in 12% of the population; 35% of the affected subjects exhibited signs of portal hypertension. Age (odds ratio (OR), 11.5), gender (OR, 4.2), and infection levels (OR, 2.2) were significantly (p < or = 0.01) associated with hepatic fibrosis. Cytokines produced by egg-stimulated blood mononuclear cells from 99 subjects were measured (75 with no or mild fibrosis; 24 subjects with advanced fibrosis). Multivariate analysis of cytokine levels showed that high IFN-gamma levels were associated with a marked reduction of the risk of fibrosis (p = 0.01; OR, 0.1); in contrast, high TNF-alpha levels were associated with an increased risk (p = 0.05; OR, 4.6) of periportal fibrosis. Moreover, infection levels were negatively associated with IFN-gamma production. These results with observations in experimental models strongly suggest that IFN-gamma plays a key role in the protection of S. mansoni-infected patients against periportal fibrosis, whereas TNF-alpha may aggravate the disease.     

A tomato enzyme catalyzing the phosphorylation of 3,4-dihydroxy-2-butanone

A riboflavin biosynthesis ribB mutant of Escherichia coli deficient of 3,4-dihydroxy-2-butanone 4-phosphate synthase was complemented with a cDNA library from Lycopersicon esculentum. The complementing gene was isolated and expressed in E. coli. The resulting protein was shown to specify a 62 kDa protein which phosphorylates dihydroxyacetone, both enantiomers of 3,4-dihydroxy-2-butanone, and several other aldoses and ketoses. Sequence analysis revealed homology to dihydroacetone kinases (dak) genes from plants, animals, fungi and some eubacteria. Genes with similarity to the 5' part of the dak gene from tomato were found in many other eubacteria. The physiological role of the dak gene is still incompletely known.     

Quantitative high-performance liquid chromatography/electrospray ionization tandem mass spectrometric analysis of 2- and 3-series prostaglandins in cultured tumor cells

This paper describes a rapid and simple technique for the simultaneous quantitative analysis of PGE(2), PGE(3), and other closely related prostaglandins from cultured cells using liquid chromatography/electrospray ionization tandem mass spectrometry. This method permits quantification of selected individual prostaglandins derived either from arachidonic acid (AA) or eicosapentaenoic acid (EPA) from cell extracts without tedious derivatization, lengthy sample preparation, and separation required by GC-MS- or HPLC-UV-based methods. The validation assessment showed that the quantitative determination is linear (r(2)>0.999) for both PGE(2) and PGE(3) in the range tested (1-500 ng/ml, 0.0028-1.4 microM) and a coefficient of variation lower than 10% was obtained for samples analyzed on 3 separate days. The detection limit was 2.5 pg for both PGE(2) and PGE(3). Extraction efficiency of PGE(2) and PGE(3) from cell suspensions ranged from 89.4 to 98.2%. As an application of the method, prostaglandins formed by EPA in human lung cancer A549 cells were determined. A 62% reduction of PGE(2) formation was noted when A549 cells were treated with 10 microM of EPA. Concomitantly, EPA increased formation of PGE(3) by 10-fold in A549 cells. This is the first report that unequivocally demonstrates that EPA can be converted to PGE(3) by cyclooxygenase in human cancer cells.     

Alpha-helix structure in Alzheimer's disease aggregates of tau-protein

The discovery of beta-sheet structure in Alzheimer's amyloid fibrils, and then in many other disease-related protein fibrils, has led to the widely believed view that beta-sheet formation is the general mechanism of aberrant protein aggregation leading to disease. This notion is further reinforced by recent findings, which indicate that normal proteins can be induced to form beta-sheet fibrils in vitro. Alzheimer's disease, a paradigm proteopathy, is accompanied by the formation of two distinct aggregates, amyloid fibrils and paired helical filaments (PHFs). Electron microscope images of PHFs show pairs of twisted ribbons with 80 nm periodicity. However, there is little information of the molecular structure of PHFs, as previous studies have failed to identify signs of regular structure. Using far-UV circular dichroism and Fourier-transformed infrared spectroscopy, we find that PHFs are comprised of alpha-helices. This is remarkable as tau-protein, PHF's primary constituent, has a high abundance of helix-breaking amino acids and is unstructured in solution. We also find that PHFs are very stable, as judged by their high melting temperature and resistance to protease digestion. PHFs are the first example of pathological aggregation associated to the formation of alpha-helix.     

Characterization of Surfactin-like Cyclic Depsipeptides Synthesized by Bacillus pumilus from Ascidian Halocynthia aurantium

A marine bacterium (KMM 1364), identified as Bacillus pumilus, was isolated from the surface of ascidian Halocynthia aurantium. Structural analysis revealed that the strain KMM 1364 produced a mixture of lipopeptide surfactin analogs with major components with molecular masses of 1035, 1049, 1063, and 1077. The variation in molecular weight represents changes in the number of methylene groups in the lipid and/or peptide portions of the compounds. Structurally, these lipopeptides differ from surfactin in the substitution of the valine residue in position 4 by leucine, and have been isolated as two carboxy-terminal variants, with valine or isoleucine in position 7. As constituents of the lipophilic part of the peptides, only β-hydroxy-C₁₅-, β-hydroxy-C₁₆-, and a high amount of β-hydroxy-C₁₇ fatty acid were determined.     

Breakdown of Ficus and Eucalyptus leaves in an organically polluted river in India: fungal diversity and ecological functions

1. At two organically polluted sites in the River Nethravathi, banyan and eucalypt leaves were colonized by one or two species of aquatic hyphomycetes. A total of three or four species were identified at the two sites in samples of water and naturally occurring leaves.
2. Spore production from stream‐exposed leaves by aquatic hyphomycetes was lower by a factor of up to 1 million compared with an earlier study in geographically close but unpolluted streams.
3. Exponential decay rates and loss rates of phosphorus and calcium, were not statistically different from an earlier study in unpolluted streams. Nitrogen increased during decomposition more slowly in the current study.
4. The microbial community on both leaves released enzymes active against starch, pectin, cellulose and xylan.
5. Banyan leaves conditioned for 12 weeks were more palatable to the gastropod Notopala sp. than unconditioned leaves.
6. Together with earlier data from unpolluted streams, the study provides evidence that organic pollution severely restricts diversity of aquatic hyphomycetes and their reproductive output, but does not have an equally strong effect on ecological functions generally associated with this group.