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University of Helsinki, Department of Medicine, and Abdominal Center, Endocrinology, Helsinki University Central Hospital, Helsinki, Finland
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University of Helsinki, Department of Medicine, and Abdominal Center, Endocrinology, Helsinki University Central Hospital, Helsinki, Finland
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University of Helsinki, Department of Medicine, and Abdominal Center, Endocrinology, Helsinki University Central Hospital, Helsinki, Finland
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University of Helsinki, Department of Medicine, and Abdominal Center, Endocrinology, Helsinki University Central Hospital, Helsinki, Finland
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Saturated fatty acids are implicated in the development of insulin resistance, whereas unsaturated fatty acids may have a protective effect on metabolism. We tested in primary human myotubes if insulin resistance induced by saturated fatty acid palmitate can be ameliorated by concomitant exposure to unsaturated fatty acid oleate. Primary human myotubes were pretreated with palmitate, oleate or their combination for 12 h. Glucose uptake was determined by intracellular accumulation of [3H]-2-deoxy-d-glucose, insulin signalling and activation of endoplasmic reticulum (ER) stress by Western blotting, and mitochondrial reactive oxygen species (ROS) production by fluorescent dye MitoSOX. Exposure of primary human myotubes to palmitate impaired insulin-stimulated Akt-Ser473, AS160 and GSK-3β phosphorylation, induced ER stress signalling target PERK and stress kinase JNK 54 kDa isoform. These effects were virtually abolished by concomitant exposure of palmitate-treated myotubes to oleate. However, an exposure to palmitate, oleate or their combination reduced insulin-stimulated glucose uptake. This was associated with increased mitochondrial ROS production in palmitate-treated myotubes co-incubated with oleate, and was alleviated by antioxidants MitoTempo and Tempol. Thus, metabolic and intracellular signalling events diverge in myotubes treated with palmitate and oleate. Exposure of human myotubes to excess fatty acids increases ROS production and induces insulin resistance.
Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Objectives
Simvastatin use is associated with muscular side effects, and increased risk for type 2 diabetes (T2D). In clinical use, simvastatin is administered in inactive lipophilic lactone-form, which is then converted to active acid-form in the body. Here, we have investigated if lactone- and acid-form simvastatin differentially affect glucose metabolism and mitochondrial respiration in primary human skeletal muscle cells.
Methods
Muscle cells were exposed separately to lactone- and acid-form simvastatin for 48 h. After pre-exposure, glucose uptake and glycogen synthesis were measured using radioactive tracers; insulin signalling was detected with Western blotting; and glycolysis, mitochondrial oxygen consumption and ATP production were measured with Seahorse XFe96 analyzer.
Results
Lactone-form simvastatin increased glucose uptake and glycogen synthesis, whereas acid-form simvastatin did not affect glucose uptake and decreased glycogen synthesis. Phosphorylation of insulin signalling targets Akt substrate 160 kDa (AS160) and glycogen synthase kinase 3β (GSK3β) was upregulated with lactone-, but not with acid-form simvastatin. Exposure to both forms of simvastatin led to a decrease in glycolysis and glycolytic capacity, as well as to a decrease in mitochondrial respiration and ATP production.
Conclusions
These data suggest that lactone- and acid-forms of simvastatin exhibit differential effects on non-oxidative glucose metabolism as lactone-form increases and acid-form impairs glucose storage into glycogen, suggesting impaired insulin sensitivity in response to acid-form simvastatin. Both forms profoundly impair oxidative glucose metabolism and energy production in human skeletal muscle cells. These effects may contribute to muscular side effects and risk for T2D observed with simvastatin use.
Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Medicine, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
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Department of Cell Biology and Anatomy, Department of Medicine, Turku PET Centre, Department of Radiology, Medical Imaging Centre of Southwest Finland, Department of Endocrinology, Abdominal Center: Endocrinology, Minerva Foundation Institute for Medical Research, Institute of Biomedicine, University of Turku, FI-20520 Turku, Finland
Department of Cell Biology and Anatomy, Department of Medicine, Turku PET Centre, Department of Radiology, Medical Imaging Centre of Southwest Finland, Department of Endocrinology, Abdominal Center: Endocrinology, Minerva Foundation Institute for Medical Research, Institute of Biomedicine, University of Turku, FI-20520 Turku, Finland
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Department of Cell Biology and Anatomy, Department of Medicine, Turku PET Centre, Department of Radiology, Medical Imaging Centre of Southwest Finland, Department of Endocrinology, Abdominal Center: Endocrinology, Minerva Foundation Institute for Medical Research, Institute of Biomedicine, University of Turku, FI-20520 Turku, Finland
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Department of Cell Biology and Anatomy, Department of Medicine, Turku PET Centre, Department of Radiology, Medical Imaging Centre of Southwest Finland, Department of Endocrinology, Abdominal Center: Endocrinology, Minerva Foundation Institute for Medical Research, Institute of Biomedicine, University of Turku, FI-20520 Turku, Finland
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Insulin signaling in bone-forming osteoblasts stimulates bone formation and promotes the release of osteocalcin (OC) in mice. Only a few studies have assessed the direct effect of insulin on bone metabolism in humans. Here, we studied markers of bone metabolism in response to acute hyperinsulinemia in men and women. Thirty-three subjects from three separate cohorts (n=8, n=12 and n=13) participated in a euglycaemic hyperinsulinemic clamp study. Blood samples were collected before and at the end of infusions to determine the markers of bone formation (PINP, total OC, uncarboxylated form of OC (ucOC)) and resorption (CTX, TRAcP5b). During 4 h insulin infusion (40 mU/m2 per min, low insulin), CTX level decreased by 11% (P<0.05). High insulin infusion rate (72 mU/m2 per min) for 4 h resulted in more pronounced decrease (−32%, P<0.01) whereas shorter insulin exposure (40 mU/m2 per min for 2 h) had no effect (P=0.61). Markers of osteoblast activity remained unchanged during 4 h insulin, but the ratio of uncarboxylated-to-total OC decreased in response to insulin (P<0.05 and P<0.01 for low and high insulin for 4 h respectively). During 2 h low insulin infusion, both total OC and ucOC decreased significantly (P<0.01 for both). In conclusion, insulin decreases bone resorption and circulating levels of total OC and ucOC. Insulin has direct effects on bone metabolism in humans and changes in the circulating levels of bone markers can be seen within a few hours after administration of insulin.
