RESUMEN
Myokines, such as irisin, have been purported to exert physiological effects on skeletal muscle in an autocrine/paracrine fashion. In this study, we aimed to investigate the mechanistic role of in vivo fibronectin type III domain-containing 5 (Fndc5)/irisin upregulation in muscle. Overexpression (OE) of Fndc5 in rat hindlimb muscle was achieved by in vivo electrotransfer, i.e., bilateral injections of Fndc5 harboring vectors for OE rats (n = 8) and empty vector for control rats (n = 8). Seven days later, a bolus of D2O (7.2 mL/kg) was administered via oral gavage to quantify muscle protein synthesis. After an overnight fast, on day 9, 2-deoxy-d-glucose-6-phosphate (2-DG6P; 6 mg/kg) was provided during an intraperitoneal glucose tolerance test (2 g/kg) to assess glucose handling. Animals were euthanized, musculus tibialis cranialis muscles and subcutaneous fat (inguinal) were harvested, and metabolic and molecular effects were evaluated. Muscle Fndc5 mRNA increased with OE (~2-fold; P = 0.014), leading to increased circulating irisin (1.5 ± 0.9 to 3.5 ± 1.2 ng/mL; P = 0.049). OE had no effect on protein anabolism or mitochondrial biogenesis; however, muscle glycogen was increased, along with glycogen synthase 1 gene expression (P = 0.04 and 0.02, respectively). In addition to an increase in glycogen synthase activation in OE (P = 0.03), there was a tendency toward increased glucose transporter 4 protein (P = 0.09). However, glucose uptake (accumulation of 2-DG6P) was identical. Irisin elicited no endocrine effect on mitochondrial biogenesis or uncoupling proteins in white adipose tissue. Hindlimb overexpression led to physiological increases in Fndc5/irisin. However, our data indicate limited short-term impacts of irisin in relation to muscle anabolism, mitochondrial biogenesis, glucose uptake, or adipose remodeling.
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Fibronectinas/genética , Músculo Esquelético/metabolismo , Grasa Subcutánea/metabolismo , Animales , Desoxiglucosa/metabolismo , Óxido de Deuterio , Electroporación , Fibronectinas/metabolismo , Expresión Génica , Glucosa/metabolismo , Prueba de Tolerancia a la Glucosa , Transportador de Glucosa de Tipo 4/genética , Glucosa-6-Fosfato/análogos & derivados , Glucosa-6-Fosfato/metabolismo , Glucógeno/metabolismo , Glucógeno Sintasa/genética , Glucógeno Sintasa/metabolismo , Miembro Posterior , Masculino , Proteínas Desacopladoras Mitocondriales/genética , Biogénesis de Organelos , Biosíntesis de Proteínas , ARN Mensajero/metabolismo , RatasRESUMEN
In contrast to previously reported elevations in serum sclerostin levels in diabetic patients, the present study shows that the impaired bone microarchitecture and cellular turnover associated with type 2 diabetes mellitus (T2DM)-like conditions in ZDF rats are not correlated with changes in serum and bone sclerostin expression. INTRODUCTION: T2DM is associated with impaired skeletal structure and a higher prevalence of bone fractures. Sclerostin, a negative regulator of bone formation, is elevated in serum of diabetic patients. We aimed to relate changes in bone architecture and cellular activities to sclerostin production in the Zucker diabetic fatty (ZDF) rat. METHODS: Bone density and architecture were measured by micro-CT and bone remodelling by histomorphometry in tibiae and femurs of 14-week-old male ZDF rats and lean Zucker controls (n = 6/group). RESULTS: ZDF rats showed lower trabecular bone mineral density and bone mass compared to controls, due to decreases in bone volume and thickness, along with impaired bone connectivity and cortical bone geometry. Bone remodelling was impaired in diabetic rats, demonstrated by decreased bone formation rate and increased percentage of tartrate-resistant acid phosphatase-positive osteoclastic surfaces. Serum sclerostin levels (ELISA) were higher in ZDF compared to lean rats at 9 weeks (+40 %, p < 0.01), but this difference disappeared as their glucose control deteriorated and by week 14, ZDF rats had lower sclerostin levels than control rats (-44 %, p < 0.0001). Bone sclerostin mRNA (qPCR) and protein (immunohistochemistry) were similar in ZDF, and lean rats at 14 weeks and genotype did not affect the number of empty osteocytic lacunae in cortical and trabecular bone. CONCLUSION: T2DM results in impaired skeletal architecture through altered remodelling pathways, but despite altered serum levels, it does not appear that sclerostin contributes to the deleterious effect of T2DM in rat bone.
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Proteínas Morfogenéticas Óseas/fisiología , Remodelación Ósea/fisiología , Diabetes Mellitus Experimental/fisiopatología , Diabetes Mellitus Tipo 2/fisiopatología , Marcadores Genéticos/fisiología , Adipocitos/patología , Animales , Glucemia/metabolismo , Glucemia/fisiología , Peso Corporal/fisiología , Densidad Ósea/fisiología , Proteínas Morfogenéticas Óseas/sangre , Proteínas Morfogenéticas Óseas/genética , Hueso Esponjoso/diagnóstico por imagen , Hueso Esponjoso/fisiopatología , Células Cultivadas , Hueso Cortical/diagnóstico por imagen , Hueso Cortical/fisiopatología , Diabetes Mellitus Experimental/sangre , Diabetes Mellitus Tipo 2/sangre , Marcadores Genéticos/genética , Dureza , Masculino , Osteocitos/metabolismo , ARN Mensajero/genética , Ratas Zucker , Microtomografía por Rayos X/métodosRESUMEN
BACKGROUND: Equine type 1 polysaccharide storage myopathy (PSSM1) is associated with a missense mutation (R309H) in the glycogen synthase (GYS1) gene, enhanced glycogen synthase (GS) activity and excessive glycogen and amylopectate inclusions in muscle. METHODS: Equine muscle biochemical and recombinant enzyme kinetic assays in vitro and homology modelling in silico, were used to investigate the hypothesis that higher GS activity in affected horse muscle is caused by higher GS expression, dysregulation, or constitutive activation via a conformational change. RESULTS: PSSM1-affected horse muscle had significantly higher glycogen content than control horse muscle despite no difference in GS expression. GS activity was significantly higher in muscle from homozygous mutants than from heterozygote and control horses, in the absence and presence of the allosteric regulator, glucose 6 phosphate (G6P). Muscle from homozygous mutant horses also had significantly increased GS phosphorylation at sites 2+2a and significantly higher AMPKα1 (an upstream kinase) expression than controls, likely reflecting a physiological attempt to reduce GS enzyme activity. Recombinant mutant GS was highly active with a considerably lower Km for UDP-glucose, in the presence and absence of G6P, when compared to wild type GS, and despite its phosphorylation. CONCLUSIONS: Elevated activity of the mutant enzyme is associated with ineffective regulation via phosphorylation rendering it constitutively active. Modelling suggested that the mutation disrupts a salt bridge that normally stabilises the basal state, shifting the equilibrium to the enzyme's active state. GENERAL SIGNIFICANCE: This study explains the gain of function pathogenesis in this highly prevalent polyglucosan myopathy.
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Enfermedad del Almacenamiento de Glucógeno/enzimología , Enfermedad del Almacenamiento de Glucógeno/epidemiología , Glucógeno Sintasa/genética , Caballos/metabolismo , Mutación/genética , Adenilato Quinasa/metabolismo , Secuencia de Aminoácidos , Animales , Western Blotting , Cruzamiento , Activación Enzimática , Transportador de Glucosa de Tipo 4/metabolismo , Glucosa-6-Fosfato/metabolismo , Glucógeno/metabolismo , Glucógeno Sintasa/química , Glucógeno Sintasa/metabolismo , Glucógeno Sintasa Quinasa 3 beta/metabolismo , Cinética , Modelos Moleculares , Músculo Esquelético/enzimología , Proteínas Mutantes/metabolismo , Fosforilación , Prevalencia , Subunidades de Proteína/metabolismo , Homología Estructural de Proteína , Uridina Difosfato Glucosa/metabolismoRESUMEN
Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 µm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell-cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health.
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Micropartículas Derivadas de Células/metabolismo , Dieta Alta en Grasa/efectos adversos , Grasas de la Dieta/efectos adversos , Células Endoteliales/efectos de los fármacos , Animales , Grasas de la Dieta/administración & dosificación , Células Endoteliales/metabolismo , Inflamación/patología , Resistencia a la Insulina , Masculino , Miocardio/citología , Miocardio/metabolismo , Obesidad/patología , Estrés Oxidativo/efectos de los fármacos , Ratas , Ratas Wistar , Especies Reactivas de Oxígeno/metabolismo , Molécula 1 de Adhesión Celular Vascular/genética , Molécula 1 de Adhesión Celular Vascular/metabolismoRESUMEN
Insulin resistance (IR) in skeletal muscle is a prerequisite for type 2 diabetes and is often associated with obesity. IR also develops alongside muscle atrophy in older individuals in sarcopenic obesity. The molecular defects that underpin this syndrome are not well characterized, and there is no licensed treatment. Deletion of the transforming growth factor-ß family member myostatin, or sequestration of the active peptide by overexpression of the myostatin propeptide/latency-associated peptide (ProMyo) results in both muscle hypertrophy and reduced obesity and IR. We aimed to establish whether local myostatin inhibition would have a paracrine/autocrine effect to enhance glucose disposal beyond that simply generated by increased muscle mass, and the mechanisms involved. We directly injected adeno-associated virus expressing ProMyo in right tibialis cranialis/extensor digitorum longus muscles of rats and saline in left muscles and compared the effects after 17 days. Both test muscles were increased in size (by 7 and 11%) and showed increased radiolabeled 2-deoxyglucose uptake (26 and 47%) and glycogen storage (28 and 41%) per unit mass during an intraperitoneal glucose tolerance test. This was likely mediated through increased membrane protein levels of GLUT1 (19% higher) and GLUT4 (63% higher). Interestingly, phosphorylation of phosphoinositol 3-kinase signaling intermediates and AMP-activated kinase was slightly decreased, possibly because of reduced expression of insulin-like growth factor-I in these muscles. Thus, myostatin inhibition has direct effects to enhance glucose disposal in muscle beyond that expected of hypertrophy alone, and this approach may offer potential for the therapy of IR syndromes.
Asunto(s)
Transportador de Glucosa de Tipo 4/genética , Glucosa/metabolismo , Resistencia a la Insulina , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Miostatina/metabolismo , Animales , Transportador de Glucosa de Tipo 4/metabolismo , Células HEK293 , Humanos , Hipertrofia , Masculino , Miostatina/genética , Precursores de Proteínas/genética , Ratas , Ratas Transgénicas , Ratas Wistar , Distribución Tisular , Regulación hacia Arriba/genéticaRESUMEN
AIMS/HYPOTHESIS: Urocortins are the endogenous ligands for the corticotropin-releasing factor receptor type 2 (CRFR2), which is implicated in regulating energy balance and/or glucose metabolism. We determined the effects of chronic CRFR2 activation on metabolism in vivo, by generating and phenotyping transgenic mice overproducing the specific CRFR2 ligand urocortin 3. METHODS: Body composition, glucose metabolism, insulin sensitivity, energy efficiency and expression of key metabolic genes were assessed in adult male urocortin 3 transgenic mice (Ucn3(+)) under control conditions and following an obesogenic high-fat diet (HFD) challenge. RESULTS: Ucn3(+) mice had increased skeletal muscle mass with myocyte hypertrophy. Accelerated peripheral glucose disposal, increased respiratory exchange ratio and hypoglycaemia on fasting demonstrated increased carbohydrate metabolism. Insulin tolerance and indices of insulin-stimulated signalling were unchanged, indicating these effects were not mediated by increased insulin sensitivity. Expression of the transgene in Crfr2 (also known as Crhr2)-null mice negated key aspects of the Ucn3(+) phenotype. Ucn3(+) mice were protected from the HFD-induced hyperglycaemia and increased adiposity seen in control mice despite consuming more energy. Expression of uncoupling proteins 2 and 3 was higher in Ucn3(+) muscle, suggesting increased catabolic processes. IGF-1 abundance was upregulated in Ucn3(+) muscle, providing a potential paracrine mechanism in which urocortin 3 acts upon CRFR2 to link the altered metabolism and muscular hypertrophy observed. CONCLUSIONS/INTERPRETATION: Urocortin 3 acting on CRFR2 in skeletal muscle of Ucn3(+) mice results in a novel metabolically favourable phenotype, with lean body composition and protection against diet-induced obesity and hyperglycaemia. Urocortins and CRFR2 may be of interest as potential therapeutic targets for obesity.
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Grasas de la Dieta/efectos adversos , Hiperglucemia/metabolismo , Hiperglucemia/prevención & control , Obesidad/metabolismo , Obesidad/prevención & control , Urocortinas/genética , Urocortinas/metabolismo , Animales , Composición Corporal/efectos de los fármacos , Composición Corporal/fisiología , Grasas de la Dieta/farmacología , Modelos Animales de Enfermedad , Metabolismo Energético/efectos de los fármacos , Metabolismo Energético/fisiología , Glucosa/metabolismo , Insulina/sangre , Factor I del Crecimiento Similar a la Insulina/metabolismo , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Fenotipo , Receptores de Hormona Liberadora de Corticotropina/deficiencia , Receptores de Hormona Liberadora de Corticotropina/genética , Receptores de Hormona Liberadora de Corticotropina/metabolismoRESUMEN
Peripherally inserted central catheters (PICC) are widely used to provide central venous access, often in chronically ill patients with long-term intravenous access requirements. There are a number of significant complications related to both insertion and maintenance of PICC lines, including catheter malposition, migration, venous thrombosis, and line fracture. The incidence of these complications is likely to rise as the number of patients undergoing intravenous outpatient therapy increases, with a corresponding rise in radiologist input. This paper provides an overview of the relevant peripheral and central venous anatomy, including anatomical variations, and outlines the complications of PICC lines. Imaging examples demonstrate the range of radiological findings seen in these complications.
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Cateterismo Venoso Central/efectos adversos , Cateterismo Periférico/efectos adversos , Catéteres de Permanencia/efectos adversos , Complicaciones Posoperatorias/diagnóstico por imagen , Brazo/irrigación sanguínea , Cateterismo Venoso Central/instrumentación , Cateterismo Venoso Central/métodos , Cateterismo Periférico/instrumentación , Migración de Cuerpo Extraño/diagnóstico por imagen , Humanos , Radiografía , Venas/anatomía & histología , Trombosis de la Vena/diagnóstico por imagen , Trombosis de la Vena/etiologíaRESUMEN
Some anti-diabetic therapies can have adverse effects on bone health and increase fracture risk. In this study, we tested the skeletal effects of chronic administration of two Glucagon-like peptide-1 receptor agonists (GLP-1RA), increasingly used for type 2 diabetes treatment, in a model of osteoporosis associated bone loss and examined the expression and activation of GLP-1R in bone cells. Mice were ovariectomised (OVX) to induce bone loss and four weeks later they were treated with Liraglutide (LIR) 0.3mg/kg/day, Exenatide (Ex-4) 10 µg/kg/day or saline for four weeks. Mice were injected with calcein and alizarin red prior to euthanasia, to label bone-mineralising surfaces. Tibial micro-architecture was determined by micro-CT and bone formation and resorption parameters measured by histomorphometric analysis. Serum was collected to measure calcitonin and sclerostin levels, inhibitors of bone resorption and formation, respectively. GLP-1R mRNA and protein expression were evaluated in the bone, bone marrow and bone cells using RT-PCR and immunohistochemistry. Primary osteoclasts and osteoblasts were cultured to evaluate the effect of GLP-1RA on bone resorption and formation in vitro. GLP-1RA significantly increased trabecular bone mass, connectivity and structure parameters but had no effect on cortical bone. There was no effect of GLP-1RA on bone formation in vivo but an increase in osteoclast number and osteoclast surfaces was observed with Ex-4. GLP-1R was expressed in bone marrow cells, primary osteoclasts and osteoblasts and in late osteocytic cell line. Both Ex-4 and LIR stimulated osteoclastic differentiation in vitro but slightly reduced the area resorbed per osteoclast. They had no effect on bone nodule formation in vitro. Serum calcitonin levels were increased and sclerostin levels decreased by Ex-4 but not by LIR. Thus, GLP-1RA can have beneficial effects on bone and the expression of GLP-1R in bone cells may imply that these effects are exerted directly on the tissue.
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Huesos/efectos de los fármacos , Receptor del Péptido 1 Similar al Glucagón/agonistas , Liraglutida/administración & dosificación , Osteogénesis/efectos de los fármacos , Osteoporosis/tratamiento farmacológico , Péptidos/administración & dosificación , Ponzoñas/administración & dosificación , Proteínas Adaptadoras Transductoras de Señales , Animales , Resorción Ósea , Huesos/diagnóstico por imagen , Huesos/metabolismo , Calcitonina/sangre , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Modelos Animales de Enfermedad , Exenatida , Femenino , Glicoproteínas/sangre , Glicoproteínas/metabolismo , Inmunohistoquímica , Péptidos y Proteínas de Señalización Intercelular , Ratones , Ratones Endogámicos C57BL , Osteoblastos/citología , Osteoblastos/metabolismo , Osteoclastos/metabolismo , Osteocitos/citología , Ovariectomía , ARN Mensajero/metabolismo , Tibia/diagnóstico por imagen , Microtomografía por Rayos XRESUMEN
Adiponectin is an adipokine whose plasma levels are inversely related to degrees of insulin resistance (IR) or obesity. It enhances glucose disposal and mitochondrial substrate oxidation in skeletal muscle and its actions are mediated through binding to receptors, especially adiponectin receptor 1 (AdipoR1). However, the in vivo significance of adiponectin sensitivity and the molecular mechanisms of muscle insulin sensitization by adiponectin have not been fully established. We used in vivo electrotransfer to overexpress AdipoR1 in single muscles of rats, some of which were fed for 6 wk with chow or high-fat diet (HFD) and then subjected to hyperinsulinemic-euglycemic clamp. After 1 wk, the effects on glucose disposal, signaling, and sphingolipid metabolism were investigated in test vs. contralateral control muscles. AdipoR1 overexpression (OE) increased glucose uptake and glycogen accumulation in the basal and insulin-treated rat muscle and also in the HFD-fed rats, locally ameliorating muscle IR. These effects were associated with increased phosphorylation of insulin receptor substrate-1, Akt, and glycogen synthase kinase-3ß. AdipoR1 OE also caused increased phosphorylation of p70S6 kinase, AMP-activated protein kinase, and acetyl-coA carboxylase as well as increased protein levels of adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain, and leucine zipper motif-1 and adiponectin, peroxisome proliferator activated receptor-γ coactivator-1α, and uncoupling protein-3, indicative of increased mitochondrial biogenesis. Although neither HFD feeding nor AdipoR1 OE caused generalized changes in sphingolipids, AdipoR1 OE did reduce levels of sphingosine 1-phosphate, ceramide 18:1, ceramide 20:2, and dihydroceramide 20:0, plus mRNA levels of the ceramide synthetic enzymes serine palmitoyl transferase and sphingolipid Δ-4 desaturase, changes that are associated with increased insulin sensitivity. These data demonstrate that enhancement of local adiponectin sensitivity is sufficient to improve skeletal muscle IR.
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Glucosa/metabolismo , Resistencia a la Insulina/fisiología , Insulina/farmacología , Músculo Esquelético/metabolismo , Receptores de Adiponectina/metabolismo , Transducción de Señal/fisiología , Proteínas Quinasas Activadas por AMP/metabolismo , Adiponectina/metabolismo , Animales , Técnica de Clampeo de la Glucosa , Glucógeno Sintasa Quinasa 3/metabolismo , Glucógeno Sintasa Quinasa 3 beta , Proteínas Sustrato del Receptor de Insulina/metabolismo , Lisofosfolípidos/metabolismo , Masculino , Músculo Esquelético/efectos de los fármacos , Fosforilación/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/metabolismo , Ratas , Ratas Wistar , Receptores de Adiponectina/genética , Transducción de Señal/efectos de los fármacos , Esfingosina/análogos & derivados , Esfingosina/metabolismoRESUMEN
APPL1 is an adaptor protein that binds to both AKT and adiponectin receptors and is hypothesised to mediate the effects of adiponectin in activating downstream effectors such as AMP-activated protein kinase (AMPK). We aimed to establish whether APPL1 plays a physiological role in mediating glycogen accumulation and insulin sensitivity in muscle and the signalling pathways involved. In vivo electrotransfer of cDNA- and shRNA-expressing constructs was used to over-express or silence APPL1 for 1 week in single tibialis cranialis muscles of rats. Resulting changes in glucose and lipid metabolism and signalling pathway activation were investigated under basal conditions and in high-fat diet (HFD)- or chow-fed rats under hyperinsulinaemic-euglycaemic clamp conditions. APPL1 over-expression (OE) caused an increase in glycogen storage and insulin-stimulated glycogen synthesis in muscle, accompanied by a modest increase in glucose uptake. Glycogen synthesis during the clamp was reduced by HFD but normalised by APPL1 OE. These effects are likely explained by APPL1 OE-induced increase in basal and insulin-stimulated phosphorylation of IRS1, AKT, GSK3ß and TBC1D4. On the contrary, APPL1 OE, such as HFD, reduced AMPK and acetyl-CoA carboxylase phosphorylation and PPARγ coactivator-1α and uncoupling protein 3 expression. Furthermore, APPL1 silencing caused complementary changes in glycogen storage and phosphorylation of AMPK and PI3-kinase pathway intermediates. Thus, APPL1 may provide a means for crosstalk between adiponectin and insulin signalling pathways, mediating the insulin-sensitising effects of adiponectin on muscle glucose disposal. These effects do not appear to require AMPK. Activation of signalling mediated via APPL1 may be beneficial in overcoming muscle insulin resistance.
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Proteínas Portadoras/metabolismo , Glucógeno/metabolismo , Músculo Esquelético/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Fosfatidilinositol 3-Quinasa/metabolismo , Transducción de Señal , Proteínas Adaptadoras Transductoras de Señales , Animales , Proteínas Portadoras/genética , Grasas de la Dieta/efectos adversos , Proteínas Activadoras de GTPasa/metabolismo , Silenciador del Gen , Técnica de Clampeo de la Glucosa , Glucógeno Sintasa Quinasa 3/metabolismo , Glucógeno Sintasa Quinasa 3 beta , Insulina/metabolismo , Proteínas Sustrato del Receptor de Insulina/metabolismo , Resistencia a la Insulina , Masculino , Proteínas del Tejido Nervioso/genética , Fosforilación , Proteínas Proto-Oncogénicas c-akt/metabolismo , ARN Interferente Pequeño , Ratas , Ratas WistarRESUMEN
Epidemiological studies in many distinct human populations have associated low weight or thinness at birth with a substantially increased risk of cardiovascular and metabolic disorders, including hypertension and insulin resistance/type 2 diabetes, in adult life. The concept of fetal "programming" has been advanced to explain this phenomenon. Prenatal glucocorticoid therapy reduces birthweight, and steroids are known to exert long-term organizational effects during specific "windows" of development. Therefore, we hypothesized that fetal overexposure to endogenous glucocorticoids might underpin the link between early life events and later disease. In rats, birthweight is reduced following prenatal exposure to the synthetic glucocorticoid dexamethasone, which readily crosses the placenta, or to carbenoxolone, which inhibits 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the physiological feto-placental "barrier" to endogenous glucocorticoids. Although the offspring regain the weight deficit by weaning, as adults they exhibit permanent hypertension, hyperglycemia, and increased hypothalamic-pituitary-adrenal axis activity. Moreover, physiological variations in placental 11beta-HSD2 activity near term correlate directly with fetal weight. In humans, 11beta-HSD2 gene mutations produce a low birthweight, and some studies show reduced placental 11beta-HSD2 activity in association with intrauterine growth retardation. Moreover, low birthweight babies have higher plasma cortisol levels throughout adult life, indicating that hypothalamic-pituitary-adrenal axis programming also occurs in humans. The molecular mechanisms of glucocorticoid programming are beginning to be unraveled and involve permanent and tissue-specific changes in the expression of key genes, notably of the glucocorticoid receptor itself. Thus, glucocorticoid programming may explain, in part, the association between fetal events and subsequent disorders in adult life.
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Feto/fisiología , Glucocorticoides/fisiología , Hidroxiesteroide Deshidrogenasas/fisiología , 11-beta-Hidroxiesteroide Deshidrogenasas , Animales , Femenino , Humanos , Placenta/enzimología , EmbarazoRESUMEN
AIMS/HYPOTHESIS: Thiazolidinediones can enhance clearance of whole-body non-esterified fatty acids and protect against the insulin resistance that develops during an acute lipid load. The present study used [(3)H]-R-bromopalmitate to compare the effects of the thiazolidinedione, rosiglitazone, and the biguanide, metformin, on insulin action and the tissue-specific fate of non-esterified fatty acids in rats during lipid infusion. METHODS: Normal rats were treated with rosiglitazone or metformin for 7 days. Triglyceride/heparin (to elevate non-esterified fatty acids) or glycerol (control) were then infused for 5 h, with a hyperinsulinaemic clamp being performed between the 3rd and 5th hours. RESULTS: Rosiglitazone and metformin prevented fatty-acid-induced insulin resistance (reduced clamp glucose infusion rate). Both drugs improved insulin-mediated suppression of hepatic glucose output but only rosiglitazone enhanced systemic non-esterified fatty acid clearance (plateau plasma non-esterified fatty acids reduced by 40%). Despite this decrease in plateau plasma non-esterified fatty acids, rosiglitazone increased fatty acid uptake (two-fold) into adipose tissue and reduced fatty acid uptake into liver (by 40%) and muscle (by 30%), as well as reducing liver long-chain fatty acyl CoA accumulation (by 30%). Both rosiglitazone and metformin increased liver AMP-activated protein kinase activity, a possible mediator of the protective effects on insulin action, but in contrast to rosiglitazone, metformin had no significant effect on non-esterified fatty acid kinetics or relative tissue fatty acid uptake. CONCLUSIONS/INTERPRETATION: These results directly demonstrate the "lipid steal" mechanism, by which thiazolidinediones help prevent fatty-acid-induced insulin resistance. The contrasting mechanisms of action of rosiglitazone and metformin could be beneficial when both drugs are used in combination to treat insulin resistance.