Association of mitochondrial DNA copy number with metabolic syndrome and type 2 diabetes in 14 176 individuals

BACKGROUND

Mitochondria play an important role in cellular metabolism, and their dysfunction is postulated to be involved in metabolic disturbances. Mitochondrial DNA is present in multiple copies per cell. The quantification of mitochondrial DNA copy number (mtDNA-CN) might be used to assess mitochondrial dysfunction.

OBJECTIVES

We aimed to investigate the cross-sectional association of mtDNA-CN with type 2 diabetes and the potential mediating role of metabolic syndrome.

METHODS

We examined 4812 patients from the German Chronic Kidney Disease (GCKD) study and 9364 individuals from the Cooperative Health Research in South Tyrol (CHRIS) study. MtDNA-CN was measured in whole blood using a plasmid-normalized qPCR-based assay.

RESULTS

In both studies, mtDNA-CN showed a significant correlation with most metabolic syndrome parameters: mtDNA-CN decreased with increasing number of metabolic syndrome components. Furthermore, individuals with low mtDNA-CN had significantly higher odds of metabolic syndrome (OR = 1.025; 95% CI = 1.011-1.039, P = 3.19 × 10-4 , for each decrease of 10 mtDNA copies) and type 2 diabetes (OR = 1.027; 95% CI = 1.012-1.041; P = 2.84 × 10-4 ) in a model adjusted for age, sex, smoking and kidney function in the meta-analysis of both studies. Mediation analysis revealed that the association of mtDNA-CN with type 2 diabetes was mainly mediated by waist circumference in the GCKD study (66%) and by several metabolic syndrome parameters, especially body mass index and triglycerides, in the CHRIS study (41%).

CONCLUSIONS

Our data show an inverse association of mtDNA-CN with higher risk of metabolic syndrome and type 2 diabetes. A major part of the total effect of mtDNA-CN on type 2 diabetes is mediated by obesity parameters.

Electrical pulse stimulation of cultured skeletal muscle cells as a model for in vitro exercise - possibilities and limitations

The beneficial health-related effects of exercise are well recognized, and numerous studies have investigated underlying mechanism using various in vivo and in vitro models. Although electrical pulse stimulation (EPS) for the induction of muscle contraction has been used for quite some time, its application on cultured skeletal muscle cells of animal or human origin as a model of in vitro exercise is a more recent development. In this review, we compare in vivo exercise and in vitro EPS with regard to effects on signalling, expression level and metabolism. We provide a comprehensive overview of different EPS protocols and their applications, discuss technical aspects of this model including critical controls and the importance of a proper maintenance procedure and finally discuss the limitations of the EPS model.

Global mRNA sequencing of human skeletal muscle: Search for novel exercise-regulated myokines

Objective

Skeletal muscle is an important secretory organ, producing and releasing numerous myokines, which may be involved in mediating beneficial health effects of physical activity. More than 100 myokines have been identified by different proteomics approaches, but these techniques may not detect all myokines. We used mRNA sequencing as an untargeted approach to study gene expression of secreted proteins in skeletal muscle upon acute as well as long-term exercise.

Methods

Twenty-six middle-aged, sedentary men underwent combined endurance and strength training for 12 weeks. Skeletal muscle biopsies from m. vastus lateralis and blood samples were taken before and after an acute bicycle test, performed at baseline as well as after 12 weeks of training intervention. We identified transcripts encoding secretory proteins that were changed more than 1.5-fold in muscle after exercise. Secretory proteins were defined based on either curated UniProt annotations or predictions made by multiple bioinformatics methods.

Results

This approach led to the identification of 161 candidate secretory transcripts that were up-regulated after acute exercise and 99 that where increased after 12 weeks exercise training. Furthermore, 92 secretory transcripts were decreased after acute and/or long-term physical activity. From these responsive transcripts, we selected 17 candidate myokines sensitive to short- and/or long-term exercise that have not been described as myokines before. The expression of these transcripts was confirmed in primary human skeletal muscle cells during in vitro differentiation and electrical pulse stimulation (EPS). One of the candidates we identified was macrophage colony-stimulating factor-1 (CSF1), which influences macrophage homeostasis. CSF1 mRNA increased in skeletal muscle after acute and long-term exercise, which was accompanied by a rise in circulating CSF1 protein. In cultured muscle cells, EPS promoted a significant increase in the expression and secretion of CSF1.

Conclusion

We identified 17 new, exercise-responsive transcripts encoding secretory proteins. We further identified CSF1 as a novel myokine, which is secreted from cultured muscle cells and up-regulated in muscle and plasma after acute exercise.

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Numerous transcripts were identified that were regulated in human skeletal muscle after acute and/or long-term exercise.

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These transcripts encode potential myokines, which may play key roles in local and systemic adaptations to exercise.

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CSF1 was identified as a novel myokine. CSF1 was increased after acute exercise, and secreted from cultured human myotubes in response to EPS.

The exercise-regulated myokine chitinase-3-like protein 1 stimulates human myocyte proliferation

AIM

Chitinase-3-like protein 1 (CHI3L1) is involved in tissue remodelling and inflammatory processes. Plasma levels are elevated in patients with insulin resistance and T2DM. We recently showed that CHI3L1 and its receptor protease-activated receptor 2 (PAR-2) are expressed in skeletal muscle. Activation of PAR-2 by CHI3L1 protects against TNF-α-induced inflammation and insulin resistance. However, the effect of exercise on CHI3L1 and PAR-2 signalling remains unknown. The aim of this work was to study the impact of exercise on CHI3L1 production and the effect of CHI3L1/PAR-2 signalling on skeletal muscle growth and repair.

METHODS

Three human exercise studies were used to measure CHI3L1 plasma levels (n = 32). In addition, muscle and adipose tissue CHI3L1 mRNA expression was measured in response to acute and long-term exercise (n = 24). Primary human skeletal muscle cells were differentiated in vitro, and electrical pulse stimulation was applied. In addition, myoblasts were incubated with CHI3L1 protein and activation of MAP kinase signalling as well as proliferation was measured.

RESULTS

Circulating CHI3L1 levels and muscle CHI3L1 mRNA were increased after acute exercise. In addition, CHI3L1 mRNA expression as well as CHI3L1 secretion was enhanced in electrically stimulated cultured myotubes. Incubation of cultured human myoblasts with CHI3L1 protein leads to a strong activation of p44/42, p38 MAPK and Akt as well as enhanced myoblast proliferation.

CONCLUSION

Our findings suggest that CHI3L1 is induced by acute exercise and that CHI3L1/PAR-2 signalling activates myocyte proliferation, which is important for restructuring of skeletal muscle in the response to exercise training.

Contractile activity of human skeletal muscle cells prevents insulin resistance by inhibiting pro-inflammatory signalling pathways

AIMS/HYPOTHESIS

Obesity is closely associated with muscle insulin resistance and is a major risk factor for the pathogenesis of type 2 diabetes. Regular physical activity not only prevents obesity, but also considerably improves insulin sensitivity and skeletal muscle metabolism. We sought to establish and characterise an in vitro model of human skeletal muscle contraction, with a view to directly studying the signalling pathways and mechanisms that are involved in the beneficial effects of muscle activity.

METHODS

Contracting human skeletal muscle cell cultures were established by applying electrical pulse stimulation. To induce insulin resistance, skeletal muscle cells were incubated with human adipocyte-derived conditioned medium, monocyte chemotactic protein (MCP)-1 and chemerin.

RESULTS

Similarly to in exercising skeletal muscle in vivo, electrical pulse stimulation induced contractile activity in human skeletal muscle cells, combined with the formation of sarcomeres, activation of AMP-activated protein kinase (AMPK) and increased IL-6 secretion. Insulin-stimulated glucose uptake was substantially elevated in contracting cells compared with control. The incubation of skeletal muscle cells with adipocyte-conditioned media, chemerin and MCP-1 significantly reduced the insulin-stimulated phosphorylation of Akt. This effect was abrogated by concomitant pulse stimulation of the cells. Additionally, pro-inflammatory signalling by adipocyte-derived factors was completely prevented by electrical pulse stimulation of the myotubes.

CONCLUSIONS/INTERPRETATION

We showed that the effects of electrical pulse stimulation on skeletal muscle cells were similar to the effect of exercise on skeletal muscle in vivo in terms of enhanced AMPK activation and IL-6 secretion. In our model, muscle contractile activity eliminates insulin resistance by blocking pro-inflammatory signalling pathways. This novel model therefore provides a unique tool for investigating the molecular mechanisms that mediate the beneficial effects of muscle contraction.

Cannabinoid type 1 receptors in human skeletal muscle cells participate in the negative crosstalk between fat and muscle

AIMS/HYPOTHESIS

Cannabinoid type 1 receptor (CB1R) antagonists such as rimonabant (Rim) represent a novel approach to treat obesity and related metabolic disorders. Recent data suggest that endocannabinoids are also produced by human adipocytes. Here we studied the potential involvement of endocannabinoids in the negative crosstalk between fat and muscle.

METHODS

The protein level of CB1R in human skeletal muscle cells (SkM) during differentiation was analysed using western blotting. SkM were treated with adipocyte-conditioned medium (CM) or anandamide (AEA) in combination with the CB1R antagonists Rim or AM251, and insulin-stimulated Akt phosphorylation and glucose uptake were determined. Furthermore, signalling pathways of CB1R were investigated.

RESULTS

We revealed an increase of CB1R protein in SkM during differentiation. Twenty-four hour incubation of SkM with CM or AEA impaired insulin-stimulated Akt(Ser473) phosphorylation by 60% and up to 40%, respectively. Pretreatment of cells with Rim or AM251 reduced the effect of CM by about one-half, while the effect of AEA could be prevented completely. The reduction of insulin-stimulated glucose uptake by CM was completely prevented by Rim. Short-time incubation with AEA activated extracellular regulated kinase 1/2 and p38 mitogen-activated protein kinase, and impaired insulin-stimulated Akt(Ser473) phosphorylation, but had no effect on Akt(Thr308) and glycogen synthase kinase 3alpha/beta phosphorylation. In addition, enhanced IRS-1 (Ser307) phosphorylation was observed.

CONCLUSIONS/INTERPRETATION

Our results show that the CB1R system may play a role in the development of insulin resistance in human SkM. The results obtained with CM support the notion that adipocytes may secrete factors which are able to activate the CB1R. Furthermore, we identified two stress kinases in the signalling pathway of AEA and enhanced IRS-1(Ser307) phosphorylation, potentially underlying the development of insulin resistance.

IGF-1 receptor signalling determines the mitogenic potency of insulin analogues in human smooth muscle cells and fibroblasts

AIMS/HYPOTHESIS

Mitogenic activity of insulin and insulin analogues and the involvement of the IGF-1 receptor (IGF-1R) is still a controversial issue. We compared levels of the proteins IGF-1R and insulin receptor (InsR) in fibroblasts and smooth muscle cells from healthy donors and assessed the downstream signalling and growth-promoting activity of insulin and insulin analogues.

METHODS

DNA synthesis was monitored in human fibroblasts and coronary artery smooth muscle cells. Using small interfering RNAs, the levels of IGF-1 and InsR were reduced by 95 and 75%, respectively.

RESULTS

Enhanced mitogenic potency of insulin and insulin analogues was observed which correlated with increased levels of IGF-1R and/or IRS-1. A reduction in the IGF-1R level significantly blunted stimulation of Akt phosphorylation by IGF-1, AspB10 and glargine by 72, 58 and 40%, respectively. Akt phosphorylation in response to insulin remained unaffected. Silencing of InsR did not significantly alter Akt phosphorylation in response to IGF-1, AspB10 and glargine. IGF-1R knockdown reduced the stimulation of DNA synthesis in response to IGF-1 and glargine to a level identical to that produced by insulin.

CONCLUSIONS/INTERPRETATION

These data show a prominent role of IGF-1R/Akt signalling in mediating the mitogenic effects of insulin analogues. Regular insulin stimulates DNA synthesis by exclusively activating InsR, whereas insulin analogues mainly signal through IGF-1R. It is suggested that inter-individual differences in the levels of proteins of the IGF-1R system may function as a critical determinant of the mitogenic potency of insulin analogues.

Insulin-like growth factors decrease oxygen-regulated erythropoietin production by human hepatoma cells (Hep G2)

We examined the effects of insulin-like growth factors (IGFs) and insulin on erythropoietin (EPO) production by human hepatoma cells (Hep G2). Compared with normoxia (20% O2), EPO production by Hep G2 cells during a 72-h incubation was stimulated fivefold by exposure to low oxygen tension (1% O2) and nearly threefold by exposure to cobalt chloride (100 microM). IGF-I caused a concentration-dependent attenuation of EPO formation under normoxic conditions and inhibited (maximally 50%) EPO production stimulated by either low oxygen tension or cobalt [half-maximal effect (ED50) approximately 5 nM]. The increase of EPO mRNA levels in response to hypoxia was significantly reduced by IGF-I. Similarly to IGF-I, IGF-II (ED50 approximately 8 nM) and insulin (ED50 approximately 80 nM) also inhibited EPO formation in Hep G2 cells. IGF-I (100 pM-100 nM) stimulated the incorporation of radiolabeled alanine as a measure for total protein synthesis, 3H-labeled thymidine incorporation into DNA, and glycogen synthesis at 20 and 1% O2 in a concentration-dependent fashion. IGF-I exhibited a high affinity for the IGF-I receptor (apparent Kd approximately 3 nM). Unlabeled insulin was greater than 100-fold less potent than IGF-I in competing for 125I-IGF-I binding (apparent Kd approximately 360 nM). Conversely, insulin bound to the insulin receptor with high affinity (apparent Kd approximately 0.3 nM), whereas IGF-I was less than 1% as potent in competing for 125I-insulin binding. In summary, IGFs and insulin exert a negative control function on oxygen-regulated EPO production in Hep G2 cells. The inhibitory effect of IGFs and insulin on EPO formation appears to be mediated via the IGF-I receptor.

[Relationship between chemical structure and toxicologic-pharmacokinetic properties of new ampicillin derivatives]

The toxicity and the bioavailability of new ampicillin derivatives with glyoxylic acid benzhydrazones as site chain depend on the hydrophobic properties of the site chain. Substituents with lower hydrophobicity (expressed by the hydrophobic substituent constant pi according to Hansch) show a lower toxicity (maximal tolerated doses) and also a lower bioavailability.

[New ampicillin derivatives with glyoxyloylbenzhydrazone side chains]

New ampicillin derivatives were synthesized from glyoxylic acid benzhydrazones by reaction with chloroformates via mixed anhydrides and ampicillin. These compounds were tested in an agar diffusion test against six different bacterial strains and also for their stability against beta-lactamases. Studies about structure-activity relationships have shown, that the activity against different bacterial strains is influenced in different manner by hydrophilic or hydrophobic and electronic properties of substituents.

[Synthesis and antibacterial activity of benzoylaminoacyl-penicillins and related compounds with and without acylated catechol substituents]

Synthesis and Antibacterial Activity of Benzoylaminoacyl Penicillins and Related Compounds with and without Acylated Catechol Substituents. Syntheses of benzoyl, cinnamoyl, and benzoylhydrazido glyoxyloyl aminoacyl penicillins with and without acylated catechol substituents by condensation of corresponding acids or acylchlorides with ampicillin or amoxycillin and also of a 6-a-methoxy-derivative and corresponding esters are reported. Acylated catechol substituents improve the antibacterial activity against Gram-negative bacteria, especially against Pseudomonas strains and Salmonella. MIC tests of bacterial mutants with higher outer membrane penetrability and of the corresponding wild typs show that the increase of antibacterial activity by catechol substituents is caused by improvement of the penetration through the bacterial outer membran. The affinity to penicillin binding proteins is not influenced by catechol substituents. Stability against beta-lactamases is partly higher than that of azlocillin.

[Biosynthesis of anthracycline: a new interpretation of the results for daunomycin biosynthesis]

On the basis of literature data and our own experiments the "late" biosynthetic pathway to daunomycin has been interpreted from a new point of view considering both the in vivo biosynthesis and formation of shunt products. In contrast to existing hypotheses proposed by other authors we discuss a modified sequence leading to C-11 oxidation and, as a consequence, understand epsilon-rhodomycinone as a shunt product instead of a biosynthetic intermediate. In addition, a new hypothesis about the "early" steps of the ring formation from polyketides by a sequence of enzyme reactions has been proposed.

Advances in bioconversion of anthracycline antibiotics

During the last decade new anthracycline-type structures with potential usefulness in cancer treatment have been supplied both by new microbial strains and by bioconversions of precursor molecules employing cells or enzymes. We highlight recent advances in bioconversion of anthracycline structures with the main focus on late transformations such as are carried out by oxidoreductases.

Biosynthesis of anthracyclinones: isolation of a new early cyclization product aklaviketone

Five metabolites were isolated from fermentations of a mutant strain S 383 of Streptomyces galilaeus. Components S 383-O and S 383-A were identified as known derivatives of anthraquinone and naphthacenequinone, respectively, previously isolated from cultures of other blocked mutants of S. galilaeus strains. Component S 383-X was identical with 7-deoxyaklavinone. Compound S 383-Y (aklaviketone) was found to be a new metabolite. Its chemical structure has been determined by physico-chemical methods including mass spectrometry and NMR spectral studies. The compound (7-dehydro-7-deoxy-7-oxoaklavinone) is most likely the first cyclization product along the metabolic chain possessing the tetracyclic carbon skeleton of anthracyclinones. A proposed pathway is discussed.

Biosynthesis of anthracyclinones

Recent biosynthetic studies confirmed that anthraquinones are involved as intermediates in the pathway to anthracyclines. The present knowledge in this field has been reviewed. Furthermore, a new generalized order of biosynthetic intermediates from the hypothetical polyketide to aklavinone and related anthracyclinones has been proposed involving tricyclic precursors and 7-hydroxy-naphthacenequinones, which also have been found in mutants of anthracycline-producing strains.

Aklanonic acid-producing mutants of Streptomyces galilaeus and Streptomyces peucetius var. caesius

A number of blocked mutants was investigated which were obtained from taxonomically identified Streptomyces strains producing anthracyclines. Two of these mutants, NTG 061 derived from S. galilaeus F 198 and mutant 135 derived from S. peucetius var. caesius 601 F.I.1), accumulated an anthraquinone derivative which was identified as aklanonic acid. The results supplied further evidence that this compound was an intermediate of the biosynthetic pathway leading to different types of anthracyclines. It occurred before ring closure to the final tetracyclic anthracyclinone skeleton.

Biotransformation of aklanonic acid by blocked mutants of anthracycline-producing strains of Streptomyces galilaeus and Streptomyces peucetius

Aklanonic acid is an anthracyclinone-related pigment that was found to be an intermediate at an early stage of the biosynthesis of daunomycinone glycosides by Streptomyces griseus. We now isolated anthracycline-negative mutants of other Streptomyces species and used them in feeding experiments with both natural and radioactive aklanonic acid. In cultures of the mutant Streptomyces galilaeus S 727 exogenous aklanonic acid was biotransformed to cinerubin A as the major product. The spectrum of the conversion products was qualitatively comparable to that of the parent strain. In cultures of mutant 21/8 derived from Streptomyces peucetius var. caesius the predominant conversion product was epsilon-rhodomycinone. Daunomycinone glycosides were isolated in small amounts. According to results obtained with the radioactively labelled precursor aklanonic acid was completely incorporated into the molecules of the conversion products. Our findings suggest that aklanonic acid is also a natural intermediate in the biosynthesis of anthracyclines by Streptomyces galilaeus and Streptomyces peucetius. Proposed biosynthetic pathways have been constructed.

Isolation and chemical structure of aklanonic acid, an early intermediate in the biosynthesis of anthracyclines

The fermentation, isolation and structure elucidation of aklanonic acid are described. The compound was isolated from fermentations of Streptomyces strain ZIMET 43,717. Aklanonic acid is a yellow-orange crystalline substance, melting at 203-204 degrees C (dec), having the molecular formula C21H16O8, and possessing UV maxima at 258, 282 (sh) and 438 nm (CHCl3). In dimethyl sulfoxide or pyridine aklanonic acid is unstable and a new compound (aklanone) is formed as a conversion product. The elucidation of the structures has shown that aklanonic acid and aklanone are derivatives of 1,8-dihydroxyanthraquinone.

[Leukaemomycin-blocked mutants of Streptomyces griseus and their pigments. III. 11-Desoxydaunomycinone derivatives from the mutant ZIMET 43699/G44]

The isolation and identification of several anthracyclinones (designated as G44-K4/5, G44-G1, G44-G2) and anthracyclines (G44-A, B, C, D, E, F, G) produced by the mutant strain IMET JA 3933/G44 of the daunomycin-producing Streptomyces griseus strain IMET JA 3933 are described. G44-K4/5 was found to be identical with 7,11-dideoxy-13-dihydrodaunomycinone previously isolated from a mutant strain of Streptomyces coeruleorubidus. Compound G44-G1 was identified as 11-deoxydaunomycinone, the aglycone of the antibiotic 11-deoxydaunomycin. G44-G2 was found to be a stereoisomer of G44-G1. The NMR and CD spectral data suggest strongly that the compound is 7-epi-11-deoxydaunomycinone. Of the 7 isolated G44-glycosides only the major component G44-B could be identified. Comparison with an authentic sample revealed that this compound is 11-deoxydaunomycin which had previously been isolated from cultures of Streptomyces peucetius var. aureus and Micromonospora peucetica. As reported for S. coeruleorubidus, S. peucetius var. aureus, and Micromonospora peucetica the 11-deoxydaunomycinone derivatives described in this paper were isolated from the fermentation broth of a mutant of a daunomycin-producing wild type strain. This suggest that in general the accumulation of 11-deoxydaunomycinone derivatives may be the result of a block of C11-hydroxylation in the normal biosynthetic pathway of daunomycin and its analogues.

[Late results following pisiform transplantation in lunate malacia]

The two cases shown, which have been followed up for four years, demonstrate that pisiform grafting after Beck in Stage I aseptic necrosis of the lunate provides a means by which the configuration of the carpus and the function of the wrist are preserved better than by any other previously published method, and by which further collapse of the lunate can be prevented.

Constitution and absolute stereochemistry of the antibiotic sarubicin A

By spectral (UV-VIS, IR, NMR, MS and CD) methods the quinone antibiotics sarubicin A and U-58,431 were shown to have identical constitution and stereochemistry. Chiroptical data and their theoretical analysis have settled the common absolute configuration as 5S, 6R, 8R, 10R.

Tunicamycins, streptovirudins, and corynetoxins, a special subclass of nucleoside antibiotics

Tunicamycins, streptovirudins, and very recently, corynetoxins have been determined to be structurally related nucleoside antibiotics. Because of their special biological activity as inhibitors of protein glycosylation and their relatively complicated chemical structures, which differ from the common nucleoside antibiotics, they can be grouped together as a special subclass. A general specification system based on structural characteristics is included. The complete separation of the natural complex is still problematical, but seems to be necessary because differences in the biological activities of the individual components were observed.

Sarubicin b, a new quinone antibiotic, isolated from the fermentation broth of a streptomyces strain

Sarubicin B, isolated from the culture filtrate of a Streptomyces strain JA 2861, is a new quinone antibiotic. The compound was isolated as an orange crystalline powder, mp 282 approximately 284 degrees C. In vitro sarubicin B was found to inhibit Gram-positive bacteria. It was not active against Gram-negative microorganisms.

Isolation and characterization of sarubicin A, a new antibiotic

The new antibiotic sarubicin A [red crystals, mp. 194 approximately 195 degrees C, C18H14N2O6 (I)] was isolated from fermentations of a Streptomyces strain. The compound is moderately active in vitro against Micrococcus luteus.