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Peng LN, Yu PC, Hsu CC, Tseng SH, Lee WJ, Lin MH, Hsiao FY, Chen LK. Sarcojoint®, the branched-chain amino acid-based supplement, plus resistance exercise improved muscle mass in adults aged 50 years and older: A double-blinded randomized controlled trial. Exp Gerontol 2021; 157:111644. [PMID: 34838980 DOI: 10.1016/j.exger.2021.111644] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 10/30/2021] [Accepted: 11/22/2021] [Indexed: 01/06/2023]
Abstract
Functional ability and intrinsic capacity are key elements of healthy aging, in which exercise and good nutrition play important roles. This 12-week double-blinded randomized controlled trial enrolled community-dwelling adults aged 50 years and older to examine the effects of Sarcojoint®, a comprehensive formula for the musculoskeletal system, plus resistance exercise on muscle mass. This study intended to enroll 80 participants with a randomly selected subsample of 32 participants (16 from the intervention group and 16 from controls) for magnetic resonance imaging (MRI) to assess the cross-sectional area of the bilateral mid-thighs. The participants were then randomly assigned to the intervention group (Sarcojoint® 1 package twice a day) and control group (vitamin B as placebo) at a 1: 1 ratio. All the participants were required to undergo a regular exercise program (45 min at the gym per week and two sessions of 30-min exercise at home). The data from 66 participants (68.1 ± 7.1 years and 16.7% males; intervention group: 32, control group: 34) were available for analysis. The whole study was pre-registered and data reporting followed Consolidated Standards of Reporting Trials with the primary endpoints of muscle mass, 30-s chair-rise test, and gait speed. Results of MRI were the subgroup analysis to examine muscle mass and intramuscular adiposity. The baseline characteristics of all the participants between groups were similar, as well as those of the MRI subgroups. Within-group comparisons showed that the intervention group, but not the control group, significantly reduced the total body fat percentage (34.3 ± 5.5 vs. 35.0 ± 5.4%, P = 0.021). Serum vitamin D was increased in the intervention group (24.1 ± 6.1 vs. 21.1 ± 7.0 ng/mL; P = 0.025) and was reduced in the control group (18.0 ± 5.2 vs. 20.2 ± 5.8 ng/mL; P = 0.006). The physical performance tests of both groups were significantly improved. The between-group analysis showed no significant differences in 30-s chair stand test, handgrip strength and appendicular muscle mass. The sub-group analysis showed significant improvement in the serum levels of vitamin D (6.70 ± 8.20 vs. -0.50 ± 3.90 ng/mL; P = 0.001) and the mid-thigh cross-sectional area of the nondominant legs (165.4 ± 291.4 vs. -61.1 ± 195.0 mm2; P = 0.034) in the intervention group. In conclusion, Sarcojoint® plus resistance exercise significantly increased muscle mass and serum levels of vitamin D, but not significantly better in muscle strength and physical performance than controls. More investigations are needed to evaluate the long-term effects of Sarcojoint® on middle-aged and older adults.
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Affiliation(s)
- Li-Ning Peng
- Aging and Health Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan; Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Pei-Chin Yu
- Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan; Institute of Neuroscience, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Chia-Chia Hsu
- Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan; Institute of Hospital and Health Care Administration, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Sung-Hua Tseng
- Aging and Health Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan; Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Wei-Ju Lee
- Aging and Health Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan; Department of Family Medicine, Taipei Veterans General Hospital Yuanshan Branch, Yi-Land, Taiwan
| | - Ming-Hsien Lin
- Aging and Health Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan; Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Fei-Yuan Hsiao
- Graduate Institute of Clinical Pharmacy, National Taiwan University, Taipei, Taiwan; School of Pharmacy, National Taiwan University, Taipei, Taiwan; Department of Pharmacy, National Taiwan University Hospital, Taipei, Taiwan
| | - Liang-Kung Chen
- Aging and Health Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan; Center for Geriatrics and Gerontology, Taipei Veterans General Hospital, Taipei, Taiwan; Taipei Municipal Gan-Dau Hospital (Managed by Taipei Veterans General Hospital), Taipei, Taiwan.
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Chen CH, Cheng TL, Chang CF, Huang HT, Lin SY, Wu MH, Kang L. Raloxifene Ameliorates Glucosamine-Induced Insulin Resistance in Ovariectomized Rats. Biomedicines 2021; 9:biomedicines9091114. [PMID: 34572301 PMCID: PMC8466068 DOI: 10.3390/biomedicines9091114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 08/22/2021] [Accepted: 08/24/2021] [Indexed: 12/15/2022] Open
Abstract
Osteoarthritis (OA) and osteoporosis (OP) are common among older women, especially postmenopausal women. Glucosamine (GlcN) is a common medication for OA, but it may induce insulin resistance and β-cell dysfunction, especially if ovarian hormones are lacking. Raloxifene (RLX) is a selective estrogen receptor modulator and also an OP drug. Previously, we found that estrogen could improve GlcN-induced insulin resistance in ovariectomized (OVX) rats. Here, we further hypothesized that RLX, similarly to estrogen, can ameliorate GlcN-induced insulin resistance in OVX rats. We used GlcN to induce insulin resistance in OVX rats as a model for evaluating the protective effects of RLX in vivo. We used a pancreatic β-cell line, MIN-6, to study the mechanisms underlying the effect of RLX in GlcN-induced β-cell dysfunction in vitro. Increases in fasting plasma glucose, insulin, and homeostasis model assessments of insulin resistance in OVX Sprague Dawley rats treated with GlcN were reversed by RLX treatment (n = 8 in each group). Skeletal muscle GLUT-4 increased, liver PEPCK decreased, pancreatic islet hypertrophy, and β-cell apoptosis in OVX rats treated with GlcN was ameliorated by RLX. The negative effects of GlcN on insulin secretion and cell viability in MIN-6 cells were related to the upregulation of reticulum (ER) stress-associated proteins (C/EBP homologous protein, phospho-extracellular signal-regulated kinase, phospho-c-JunN-terminal kinase), the expression of which was reduced by RLX. Pretreatment with estrogen receptor antagonists reversed the protective effects of RLX. GlcN can induce insulin resistance, β-cell dysfunction, and apoptosis in OVX rats and increase ER stress-related proteins in β-cells, whereas RLX can reverse these adverse effects. The effects of RLX act mainly through estrogen receptor α; therefore, RLX may be a candidate drug for postmenopausal women with OA and OP.
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Affiliation(s)
- Chung-Hwan Chen
- Orthopaedic Research Center, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Regeneration Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Departments of Orthopedics, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University, Kaohsiung 80145, Taiwan
- Department of Healthcare Administration and Medical Informatics, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Institute of Medical Science and Technology, National Sun Yat-Sen University, Kaohsiung 80420, Taiwan
- Graduate Institute of Animal Vaccine Technology, College of Veterinary Medicine, National Pingtung University of Science and Technology, Pingtung 912301, Taiwan
- Graduate Institute of Materials Engineering, College of Engineering, National Pingtung University of Science and Technology, Pingtung 912301, Taiwan
| | - Tsung-Lin Cheng
- Orthopaedic Research Center, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Regeneration Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Physiology, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
| | - Chi-Fen Chang
- Department of Anatomy, School of Medicine, China Medical University, Taichung 40402, Taiwan
| | - Hsuan-Ti Huang
- Orthopaedic Research Center, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Regeneration Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Departments of Orthopedics, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University, Kaohsiung 80145, Taiwan
| | - Sung-Yen Lin
- Orthopaedic Research Center, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Regeneration Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Departments of Orthopedics, College of Medicine, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
- Department of Orthopedics, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University, Kaohsiung 80145, Taiwan
- Department of Healthcare Administration and Medical Informatics, Kaohsiung Medical University, Kaohsiung 80701, Taiwan
| | - Meng-Hsing Wu
- Department of Obstetrics & Gynecology, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan
- Department of Obstetrics and Gynecology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan
| | - Lin Kang
- Department of Obstetrics & Gynecology, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan
- Department of Obstetrics and Gynecology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan
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Gaster M. The diabetic phenotype is preserved in myotubes established from type 2 diabetic subjects: a critical appraisal. APMIS 2018; 127:3-26. [DOI: 10.1111/apm.12908] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2018] [Accepted: 11/05/2018] [Indexed: 01/08/2023]
Affiliation(s)
- Michael Gaster
- Laboratory for Molecular Physiology Department of Pathology and Department of Endocrinology Odense University Hospital Odense Denmark
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Ibáñez L, Oberfield SE, Witchel S, Auchus RJ, Chang RJ, Codner E, Dabadghao P, Darendeliler F, Elbarbary NS, Gambineri A, Garcia Rudaz C, Hoeger KM, López-Bermejo A, Ong K, Peña AS, Reinehr T, Santoro N, Tena-Sempere M, Tao R, Yildiz BO, Alkhayyat H, Deeb A, Joel D, Horikawa R, de Zegher F, Lee PA. An International Consortium Update: Pathophysiology, Diagnosis, and Treatment of Polycystic Ovarian Syndrome in Adolescence. Horm Res Paediatr 2018; 88:371-395. [PMID: 29156452 DOI: 10.1159/000479371] [Citation(s) in RCA: 191] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 07/10/2017] [Indexed: 12/11/2022] Open
Abstract
This paper represents an international collaboration of paediatric endocrine and other societies (listed in the Appendix) under the International Consortium of Paediatric Endocrinology (ICPE) aiming to improve worldwide care of adolescent girls with polycystic ovary syndrome (PCOS)1. The manuscript examines pathophysiology and guidelines for the diagnosis and management of PCOS during adolescence. The complex pathophysiology of PCOS involves the interaction of genetic and epigenetic changes, primary ovarian abnormalities, neuroendocrine alterations, and endocrine and metabolic modifiers such as anti-Müllerian hormone, hyperinsulinemia, insulin resistance, adiposity, and adiponectin levels. Appropriate diagnosis of adolescent PCOS should include adequate and careful evaluation of symptoms, such as hirsutism, severe acne, and menstrual irregularities 2 years beyond menarche, and elevated androgen levels. Polycystic ovarian morphology on ultrasound without hyperandrogenism or menstrual irregularities should not be used to diagnose adolescent PCOS. Hyperinsulinemia, insulin resistance, and obesity may be present in adolescents with PCOS, but are not considered to be diagnostic criteria. Treatment of adolescent PCOS should include lifestyle intervention, local therapies, and medications. Insulin sensitizers like metformin and oral contraceptive pills provide short-term benefits on PCOS symptoms. There are limited data on anti-androgens and combined therapies showing additive/synergistic actions for adolescents. Reproductive aspects and transition should be taken into account when managing adolescents.
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Affiliation(s)
- Lourdes Ibáñez
- Endocrinology, Hospital Sant Joan de Deu, Esplugues, Barcelona, Spain.,CIBERDEM, ISCIII, Madrid, Spain
| | - Sharon E Oberfield
- Division of Pediatric Endocrinology, CUMC, New York-Presbyterian Morgan Stanley Children's Hospital, New York, New York, USA
| | - Selma Witchel
- Division of Pediatric Endocrinology, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, USA
| | | | - R Jeffrey Chang
- Department of Reproductive Medicine, UCSD School of Medicine, La Jolla, California, USA
| | - Ethel Codner
- Institute of Maternal and Child Research, University of Chile, School of Medicine, Santiago, Chile
| | - Preeti Dabadghao
- Department of Endocrinology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
| | | | | | - Alessandra Gambineri
- Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy
| | - Cecilia Garcia Rudaz
- Division of Women, Youth and Children, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Kathleen M Hoeger
- Department of OBGYN, University of Rochester Medical Center, Rochester, New York, USA
| | - Abel López-Bermejo
- Pediatric Endocrinology, Hospital de Girona Dr. Josep Trueta, Girona, Spain
| | - Ken Ong
- MRC Epidemiology Unit, University of Cambridge, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom
| | - Alexia S Peña
- The University of Adelaide and Robinson Research Institute, Adelaide, South Australia, Australia
| | - Thomas Reinehr
- University of Witten/Herdecke, Vestische Kinder- und Jugendklinik, Pediatric Endocrinology, Diabetes, and Nutrition Medicine, Datteln, Germany
| | - Nicola Santoro
- Pediatrics, Yale School of Medicine, New Haven, Connecticut, USA
| | | | - Rachel Tao
- Division of Pediatric Endocrinology, CUMC, New York-Presbyterian Morgan Stanley Children's Hospital, New York, New York, USA
| | - Bulent O Yildiz
- Department of Internal Medicine, Division of Endocrinology and Metabolism, Hacettepe University School of Medicine, Ankara, Turkey
| | - Haya Alkhayyat
- Medical University of Bahrain, BDF Hospital, Riffa, Bahrein
| | - Asma Deeb
- Mafraq Hospital, Abu Dhabi, United Arab Emirates
| | - Dipesalema Joel
- Department of Paediatrics and Adolescent Health, University of Botswana Teaching Hospital, Gaborone, Botswana
| | - Reiko Horikawa
- Endocrinology and Metabolism, National Center for Child Health and Development, Tokyo, Japan
| | - Francis de Zegher
- Department Pediatrics, University Hospital Gasthuisberg, Leuven, Belgium
| | - Peter A Lee
- Department of Pediatrics, Penn State College of Medicine, Hershey, Pennsylvania, USA
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Abstract
OBJECTIVE Glucosamine (GlcN), which has been reported to induce insulin resistance (IR), is a popular nutritional supplement used to treat osteoarthritis in menopausal women. We previously demonstrated that GlcN treatment caused IR in ovariectomized rats by reducing the expression of glucose transport protein subtype 4 (GLUT-4) in skeletal muscle. In the present study, we hypothesized that endurance exercise training can reverse GlcN-induced IR. METHODS Fifty female rats were randomly divided into five groups with 10 rats in each group: (1) sham-operated group; (2) sham-operated group with GlcN treatment for 14 days; (3) ovariectomy (OVX) group; (4) OVX with GlcN treatment; and (5) OVX with GlcN treatment followed by exercise training (running program) for 8 weeks. RESULTS Fasting plasma glucose increased in the OVX + GlcN group, and fasting plasma insulin and the homeostasis model assessment-insulin resistance (HOMA-IR) were significantly higher only in this group. After the rats received exercise training for 8 weeks, no increase in the fasting plasma glucose, insulin, or HOMA-IR was observed. In an intraperitoneal glucose tolerance test, the plasma glucose, plasma insulin, HOMA-IR, and glucose-insulin index were significantly elevated only in the OVX with GlcN treatment group. However, the plasma glucose, plasma insulin, HOMA-IR, and glucose-insulin index decreased after exercise training for 8 weeks, implying that GlcN-induced IR in OVX rats could be reversed through exercise. A histological analysis revealed that exercise training can reduce islet hypertrophy and maintain GLUT-4 in skeletal muscle. CONCLUSIONS Exercise training can alleviate IR in OVX rats treated with GlcN. Islet hyperplasia was subsequently prevented. Preserving GLUT-4 expression may be one of the mechanisms by which exercise prevents IR.
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Chang NJ, Lin YT, Lin CC, Wang HC, Hsu HC, Yeh ML. The repair of full-thickness articular cartilage defect using intra-articular administration of N-acetyl-D-glucosamine in the rabbit knee: randomized controlled trial. Biomed Eng Online 2015; 14:105. [PMID: 26582033 PMCID: PMC4652361 DOI: 10.1186/s12938-015-0100-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 11/06/2015] [Indexed: 01/13/2023] Open
Abstract
Background Although various alterative models of therapy are used for cartilage repair, no definite conclusion has been reached. Glucosamine (GlcN) is widely used as a nutritional supplement. However, the clinical- evidence-based outcome of GlcN administration remains controversial. N-acetyl-d-glucosamine (GlcNAc), a derivative of GlcN, shows chondroprotective activity and mediates the activation of articular chondrocytes. Therefore, we investigated the effect of intra-articular administration of GlcNAc in rabbits’ knee joints with experimental full-thickness articular cartilage (FTAC) defects. Methods Twelve male adult New Zealand white rabbits, providing 24 knees, were used in this study. FTAC defects were created in the high-weight-bearing area of the medial femoral condyles of bilateral knees. All rabbits were randomly allocated to analysis at postsurgical week 4 or postsurgical week 12. In the week 4 group, rabbits’ knees (six per group) were intra-articularly injected with normal saline or with GlcNAc twice per week for 3 weeks, beginning 1 week postoperatively. In the week 12 group, the rabbits’ knees (six in each group) were intra-articularly injected with normal saline or with GlcNAc twice per week for 4 weeks, beginning 1 week postoperatively. Rabbits were sacrificed at 4 or 12 weeks after surgery for macroscopic, histological and radiological examinations of the knee joints. Results All rabbits had no systemic or local adverse effects. The saline and GlcNAc groups showed visible differences in healing of the FTAC defect at the end of testing. At week 4, the GlcNAc group had a higher level of collagen type II (COL II) and showed up-regulated production of transforming growth factor (TGF)-β2 and TGF-β3, suggesting the involvement of endogenous growth factors. At week 12, the GlcNAc group displayed formation of hyaline-like cartilage regeneration with mature chondrocytes (SOX9+), robust glycosaminoglycan (GAG) content, and positive COL II content in both the adjacent cartilage and reparative sites. However, the saline group demonstrated mainly fibrocartilage scar tissue, indicating COL I expression. Furthermore, the GlcNAc group had significantly higher bone volume per tissue volume and higher trabecular thickness than the saline group. Conclusions Intra-articular GlcNAc may promote the repair of experimental FTAC defects in the rabbit knee joint model.
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Affiliation(s)
- Nai-Jen Chang
- Department of Sports Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
| | - Yi-Ting Lin
- Department of Biomedical Engineering, National Cheng Kung University, 1 University Rd., Tainan, 701, Taiwan.
| | - Chih-Chan Lin
- Laboratory Animal Center, Department of Medical Research, Chi-Mei Medical Center, Tainan, Taiwan.
| | - Hsueh-Chun Wang
- Department of Biomedical Engineering, National Cheng Kung University, 1 University Rd., Tainan, 701, Taiwan.
| | - Horng-Chaung Hsu
- Department of Orthopedics, China Medical University Hospital, Taichung, Taiwan.
| | - Ming-Long Yeh
- Department of Biomedical Engineering, National Cheng Kung University, 1 University Rd., Tainan, 701, Taiwan. .,Medical Device Innovation Center, National Cheng Kung University, Tainan, 701, Taiwan.
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Glucosamine-induced insulin resistance in ovariectomized rats is relevant to decreasing the expression of glucose transport protein subtype 4 in the skeletal muscle and in increasing the size of pancreatic islets. Menopause 2012; 19:496-502. [DOI: 10.1097/gme.0b013e31823a40d9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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The combined effects of menopause and dietary glucosamine on the development of insulin resistance. Menopause 2012; 19:487-8. [DOI: 10.1097/gme.0b013e3182504111] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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The role of glucosamine-induced ER stress in diabetic atherogenesis. EXPERIMENTAL DIABETES RESEARCH 2012; 2012:187018. [PMID: 22474416 PMCID: PMC3296270 DOI: 10.1155/2012/187018] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Accepted: 11/27/2011] [Indexed: 12/14/2022]
Abstract
Cardiovascular disease (CVD) is the major cause of mortality in individuals with diabetes mellitus. However the molecular and cellular mechanisms that predispose individuals with diabetes to the development and progression of atherosclerosis, the underlying cause of most CVD, are not understood. This paper summarizes the current state of our knowledge of pathways and mechanisms that may link diabetes and hyperglycemia to atherogenesis. We highlight recent work from our lab, and others', that supports a role for ER stress in these processes. The continued investigation of existing pathways, linking hyperglycemia and diabetes mellitus to atherosclerosis, and the identification of novel mechanisms and targets will be important to the development of new and effective antiatherosclerotic therapies tailored to individuals with diabetes.
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Bremer AA. Polycystic ovary syndrome in the pediatric population. Metab Syndr Relat Disord 2011; 8:375-94. [PMID: 20939704 DOI: 10.1089/met.2010.0039] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Polycystic ovary syndrome (PCOS) is a common disorder characterized by hyperandrogenism and disordered gonadotropin secretion, often associated with insulin resistance. The syndrome, which modulates both hormonal and metabolic processes, is the most common endocrinopathy in reproductive-age women and increases a woman's risk of infertility, endometrial pathology, and cardiometabolic disease. As it is currently defined, PCOS most likely encompasses several distinct diseases with similar clinical phenotypes but different underlying pathophysiological processes. However, hyperandrogenism remains the syndrome's clinical hallmark. The clinical manifestations of PCOS often emerge during childhood or in the peripubertal years, suggesting that the syndrome is influenced by fetal programming and/or early postnatal events. However, given that the full clinical spectrum of PCOS does not typically appear until puberty, a "two-hit" hypothesis has been proposed: (1) a girl develops hyperandrogenism via one or more of many different potential mechanisms; (2) the preexisting hyperandrogenism subsequently disturbs the hypothalamic–pituitary–ovarian axis, resulting in ovulatory dysfunction and sustained hyperandrogenism. No consensus guidelines exist regarding the diagnosis and management of PCOS in the pediatric population; however, because the syndrome is a diagnosis of exclusion, the clinical evaluation of girls suspected of having PCOS is aimed at excluding other causes of androgen excess and menstrual dysfunction. For the syndrome's management, emphasis is placed on lifestyle and symptom-directed treatment.
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Affiliation(s)
- Andrew A Bremer
- Department of Pediatrics, Division of Endocrinology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-9170, USA.
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Raciti GA, Iadicicco C, Ulianich L, Vind BF, Gaster M, Andreozzi F, Longo M, Teperino R, Ungaro P, Di Jeso B, Formisano P, Beguinot F, Miele C. Glucosamine-induced endoplasmic reticulum stress affects GLUT4 expression via activating transcription factor 6 in rat and human skeletal muscle cells. Diabetologia 2010; 53:955-65. [PMID: 20165829 DOI: 10.1007/s00125-010-1676-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 12/18/2009] [Indexed: 01/18/2023]
Abstract
AIMS/HYPOTHESIS Glucosamine, generated during hyperglycaemia, causes insulin resistance in different cells. Here we sought to evaluate the possible role of endoplasmic reticulum (ER) stress in the induction of insulin resistance by glucosamine in skeletal muscle cells. METHODS Real-time RT-PCR analysis, 2-deoxy-D: -glucose (2-DG) uptake and western blot analysis were carried out in rat and human muscle cell lines. RESULTS In both rat and human myotubes, glucosamine treatment caused a significant increase in the expression of the ER stress markers immunoglobulin heavy chain-binding protein/glucose-regulated protein 78 kDa (BIP/GRP78 [also known as HSPA5]), X-box binding protein-1 (XBP1) and activating transcription factor 6 (ATF6). In addition, glucosamine impaired insulin-stimulated 2-DG uptake in both rat and human myotubes. Interestingly, pretreatment of both rat and human myotubes with the chemical chaperones 4-phenylbutyric acid (PBA) or tauroursodeoxycholic acid (TUDCA), completely prevented the effect of glucosamine on both ER stress induction and insulin-induced glucose uptake. In both rat and human myotubes, glucosamine treatment reduced mRNA and protein levels of the gene encoding GLUT4 and mRNA levels of the main regulators of the gene encoding GLUT4 (myocyte enhancer factor 2 a [MEF2A] and peroxisome proliferator-activated receptor-gamma coactivator 1alpha [PGC1alpha]). Again, PBA or TUDCA pretreatment prevented glucosamine-induced inhibition of GLUT4 (also known as SLC2A4), MEF2A and PGC1alpha (also known as PPARGC1A). Finally, we showed that overproduction of ATF6 is sufficient to inhibit the expression of genes GLUT4, MEF2A and PGC1alpha and that ATF6 silencing with a specific small interfering RNA is sufficient to completely prevent glucosamine-induced inhibition of GLUT4, MEF2A and PGC1alpha in skeletal muscle cells. CONCLUSIONS/INTERPRETATION In this work we show that glucosamine-induced ER stress causes insulin resistance in both human and rat myotubes and impairs GLUT4 production and insulin-induced glucose uptake via an ATF6-dependent decrease of the GLUT4 regulators MEF2A and PGC1alpha.
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MESH Headings
- Activating Transcription Factor 6/genetics
- Activating Transcription Factor 6/metabolism
- Analysis of Variance
- Animals
- Blotting, Western
- Cell Line
- Cells, Cultured
- Chromatin Immunoprecipitation
- Dose-Response Relationship, Drug
- Endoplasmic Reticulum/drug effects
- Endoplasmic Reticulum/metabolism
- Endoplasmic Reticulum Chaperone BiP
- Glucosamine/metabolism
- Glucosamine/pharmacology
- Glucose/metabolism
- Glucose/pharmacology
- Glucose Transporter Type 4/genetics
- Glucose Transporter Type 4/metabolism
- Heat-Shock Proteins/genetics
- Heat-Shock Proteins/metabolism
- Humans
- Insulin/metabolism
- Insulin/pharmacology
- Insulin Resistance/physiology
- MADS Domain Proteins/genetics
- MADS Domain Proteins/metabolism
- MEF2 Transcription Factors
- Middle Aged
- Molecular Chaperones/genetics
- Molecular Chaperones/metabolism
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/drug effects
- Muscle Fibers, Skeletal/metabolism
- Myogenic Regulatory Factors/genetics
- Myogenic Regulatory Factors/metabolism
- Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Small Interfering/genetics
- RNA, Small Interfering/metabolism
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Rats
- Reverse Transcriptase Polymerase Chain Reaction
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- G A Raciti
- Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli Federico II, Via Sergio Pansini, 5, Naples 80131, Italy
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14
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Gaster M. Fibre Type Dependent Expression of Glucose Transporters in Human Skeletal Muscles. APMIS 2008. [DOI: 10.1111/j.1600-0463.2007.apmv115s121.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Bremer AA, Miller WL. The serine phosphorylation hypothesis of polycystic ovary syndrome: a unifying mechanism for hyperandrogenemia and insulin resistance. Fertil Steril 2008; 89:1039-1048. [PMID: 18433749 DOI: 10.1016/j.fertnstert.2008.02.091] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 12/20/2007] [Accepted: 02/07/2008] [Indexed: 11/19/2022]
Abstract
Polycystic ovary syndrome (PCOS) is a common endocrinopathy affecting 4%-8% of reproductive-aged women. The syndrome is characterized by hyperandrogenemia and disordered gonadotropin secretion and is often associated with insulin resistance. However, rather than being one disease entity caused by a single molecular defect, PCOS under its current diagnostic criteria most likely includes a number of distinct disease processes with similar clinical phenotypes but different pathophysiologic mechanisms. The serine phosphorylation hypothesis can potentially explain two major features of PCOS--hyperandrogenemia and insulin resistance. Further defining the molecular mechanisms regulating androgen biosynthesis and insulin action in PCOS patients will permit a better understanding of the syndrome and may lead to the generation of novel specific pharmacologic therapies.
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Affiliation(s)
- Andrew A Bremer
- Department of Pediatrics, Division of Endocrinology, University of California-Davis, Sacramento, California.
| | - Walter L Miller
- Department of Pediatrics, Division of Endocrinology, University of California-San Francisco, San Francisco, California
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16
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Lin YC, Liang YC, Sheu MT, Lin YC, Hsieh MS, Chen TF, Chen CH. Chondroprotective effects of glucosamine involving the p38 MAPK and Akt signaling pathways. Rheumatol Int 2008; 28:1009-16. [PMID: 18340449 DOI: 10.1007/s00296-008-0561-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2007] [Accepted: 03/01/2008] [Indexed: 01/18/2023]
Abstract
The purpose of the present study was to elucidate the possible signal transduction pathway involved in the underlying mechanism of glucosamine (GLN)'s influence on the gene expression of matrix metalloproteinases (MMPs) in chondrocytes stimulated with IL-1beta. Using chondrosarcoma cells stimulated with IL-1beta, the effects of GLN on the mRNA and protein levels of MMP-3, the activation of JNK, ERK, p38, NF-kappaB, and AP-1, the nuclear translocation of NF-kappaB/Rel family members, and PI3-kinase/Akt activation were studied. GLN inhibited the expression and the synthesis of MMP-3 induced by IL-1beta, and that inhibition was mediated at the level of transcription involving both the NF-kappaB and AP-1 transcription factors. Translocation of NF-kappaB was reduced by GLN as a result of the inhibition of IkappaB degradation. A slightly synergistic effect on the activation of AP-1 induced by IL-1beta was shown in the presence of GLN. Among MAPK pathways involved in the transcriptional regulation of AP-1, phosphorylation of JNK and ERK was found to increase with the presence of GLN under IL-1beta treatment, while that for p38 decreased. It was also found that GLN alone, but also synergistically with IL-1beta, was able to activate the Akt pathway. The requirements of NF-kappaB translocation and p38 activity are indispensably involved in the induction of MMP-3 expression in chondrosarcoma cells stimulated by IL-1beta. Inhibition of the p38 pathway in the presence of GLN substantially explains the chondroprotective effect of GLN on chondrocytes that regulate COX-2 expression, PGE(2) synthesis, and NO expression and synthesis. The chondroprotective effect of GLN through the decrease in MMP-3 production and stimulation of proteoglycan synthesis may follow another potential signaling pathway of Akt.
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Affiliation(s)
- Yi-Cheng Lin
- Department of Orthopedics, Mackay Memorial Hospital, Taipei, Taiwan, ROC
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17
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Muniyappa R, Karne RJ, Hall G, Crandon SK, Bronstein JA, Ver MR, Hortin GL, Quon MJ. Oral glucosamine for 6 weeks at standard doses does not cause or worsen insulin resistance or endothelial dysfunction in lean or obese subjects. Diabetes 2006; 55:3142-50. [PMID: 17065354 DOI: 10.2337/db06-0714] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucosamine is a popular nutritional supplement used to treat osteoarthritis. Intravenous administration of glucosamine causes insulin resistance and endothelial dysfunction. However, rigorous clinical studies evaluating the safety of oral glucosamine with respect to metabolic and cardiovascular pathophysiology are lacking. Therefore, we conducted a randomized, placebo-controlled, double-blind, crossover trial of oral glucosamine at standard doses (500 mg p.o. t.i.d.) in lean (n = 20) and obese (n = 20) subjects. Glucosamine or placebo treatment for 6 weeks was followed by a 1-week washout and crossover to the other arm. At baseline, and after each treatment period, insulin sensitivity was assessed by hyperinsulinemic-isoglycemic glucose clamp (SI(Clamp)) and endothelial function evaluated by brachial artery blood flow (BAF; Doppler ultrasound) and forearm skeletal muscle microvascular recruitment (ultrasound with microbubble contrast) before and during steady-state hyperinsulinemia. Plasma glucosamine pharmacokinetics after oral dosing were determined in each subject using a high-performance liquid chromatography method. As expected, at baseline, obese subjects had insulin resistance and endothelial dysfunction when compared with lean subjects (SI(Clamp) [median {25th-75th percentile}] = 4.3 [2.9-5.3] vs. 7.3 [5.7-11.3], P < 0.0001; insulin-stimulated changes in BAF [% over basal] = 12 [-6 to 84] vs. 39 [2-108], P < 0.04). When compared with placebo, glucosamine did not cause insulin resistance or endothelial dysfunction in lean subjects or significantly worsen these findings in obese subjects. The half-life of plasma glucosamine after oral dosing was approximately 150 min, with no significant changes in steady-state glucosamine levels detectable after 6 weeks of therapy. We conclude that oral glucosamine at standard doses for 6 weeks does not cause or significantly worsen insulin resistance or endothelial dysfunction in lean or obese subjects.
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Affiliation(s)
- Ranganath Muniyappa
- Chief, Diabetes Unit, National Center for Complementary and Alternative Medicine, National Institutes of Health, 10 Center Dr., Bldg. 10, Rm. 6C-205, Bethesda, MD 20892, USA
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18
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Zachara NE, Hart GW. Cell signaling, the essential role of O-GlcNAc! Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1761:599-617. [PMID: 16781888 DOI: 10.1016/j.bbalip.2006.04.007] [Citation(s) in RCA: 290] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2005] [Revised: 04/20/2006] [Accepted: 04/24/2006] [Indexed: 11/28/2022]
Abstract
An increasing body of evidence points to a central regulatory role for glucose in mediating cellular processes and expands the role of glucose well beyond its traditional role(s) in energy metabolism. Recently, it has been recognized that one downstream effector produced from glucose is UDP-GlcNAc. Levels of UDP-GlcNAc, and the subsequent addition of O-linked beta-N-acetylglucosamine (O-GlcNAc) to Ser/Thr residues, is involved in regulating nuclear and cytoplasmic proteins in a manner analogous to protein phosphorylation. O-GlcNAc protein modification is essential for life in mammalian cells, highlighting the importance of this simple post-translational modification in basic cellular regulation. Recent research has highlighted key roles for O-GlcNAc serving as a nutrient sensor in regulating insulin signaling, the cell cycle, and calcium handling, as well as the cellular stress response.
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Affiliation(s)
- Natasha E Zachara
- Department of Biological Chemistry, Johns Hopkins Singapore, 31 Biopolis Way, #02-01 The Nanos, 138669 Singapore
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19
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Marshall S, Nadeau O, Yamasaki K. Glucosamine-induced activation of glycogen biosynthesis in isolated adipocytes. Evidence for a rapid allosteric control mechanism within the hexosamine biosynthesis pathway. J Biol Chem 2005; 280:11018-24. [PMID: 15647256 DOI: 10.1074/jbc.m413499200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Enhanced flux through the hexosamine biosynthesis pathway (HBP) induces insulin resistance and facilitates lipid storage through the up-regulation of enzyme mRNA levels. Both actions occur over several hours and require gene expression. We now identify a regulatory arm of the HBP that involves rapid allosteric activation of glycogen synthase (GS) and stimulation of glycogen biosynthesis (GBS). When insulin-pretreated adipocytes were exposed to 2 mM GlcN, incorporation of [14C]glucose into glycogen doubled by 10 min (t(1/2) of <5 min), whereas UDP-glucose levels were concomitantly decreased during this time (t(1/2) of 1.4 min; >90% depletion). Stimulation of GBS and depletion of UDP-glucose both correlated with an early and rapid rise in the levels of glucosamine-6-phosphate (GlcN-6-P), a known activator of GS. The lowering of GlcN-6-P levels by removing extracellular GlcN (>80% reduction by 45 min) was accompanied by the restoration of UDP-glucose levels. Prolonged GlcN treatment (20 min to 2 h) inhibited GBS, which corresponded to a massive intracellular accumulation of GlcN-6-P (t(1/2) of approximately 32 min; >1,400 nmol/g). From these data, we conclude the following. 1) GlcN treatment elevated intracellular GlcN-6-P levels within minutes, resulting in allosteric activation of GS, stimulation of GBS, and a reduction in steady-state levels of UDP-glucose due to increased precursor utilization. 2) Prolonged treatment with high concentrations of GlcN caused massive accumulation of GlcN-6-P that adversely affected cellular metabolism and reduced GBS. 3) The biphasic actions of GlcN on GBS may explain many of the discrepant reports on the role of the HBP in glycogen metabolism.
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20
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Gosmanov AR, Umpierrez GE, Karabell AH, Cuervo R, Thomason DB. Impaired expression and insulin-stimulated phosphorylation of Akt-2 in muscle of obese patients with atypical diabetes. Am J Physiol Endocrinol Metab 2004; 287:E8-E15. [PMID: 15010337 DOI: 10.1152/ajpendo.00485.2003] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although a pharmacological dose of insulin produces a dramatic increase in phosphorylation and activity of Akt isoforms 1 and 2 in mammalian skeletal muscle, few studies have examined the effect of physiological concentrations of insulin on the phosphorylation of Akt-1 and -2 in normal and diabetic tissue. This study examined the patterns of insulin-stimulated Akt isoform phosphorylation and protein expression in muscle biopsies obtained from obese patients with atypical diabetes immediately after a hyperglycemic crisis and again after near-normoglycemic remission. In obese patients with new-onset diabetes mellitus presenting with hyperglycemic crisis (plasma glucose 30.5 +/- 4.8 mM), in vitro stimulation of vastus lateralis muscle biopsies with 100 microU/ml (0.6 nM) insulin increased insulin receptor phosphorylation threefold and Akt-1 phosphorylation on Ser(473) twofold, whereas Akt-2 phosphorylation was not stimulated. After 10-wk intensive insulin therapy that led to near-normoglycemic remission and discontinuation of insulin therapy, both Akt-2 expression and insulin-stimulated Akt-2 Ser(474) phosphorylation doubled. Hyperglycemic crisis did not affect insulin-stimulated threonine phosphorylation of either Akt-1 or Akt-2. The decreased Akt-2 expression at presentation was accompanied by reduced GLUT4 protein expression and increased expression of enzymes counterregulatory to insulin action. Thus a physiological concentration of insulin stimulated Akt-1 and Akt-2 phosphorylation in human skeletal muscle in the absence of hyperglycemia, but Akt-2 expression and stimulation appeared to be impaired in muscle of obese patients with atypical diabetes presenting with severe hyperglycemia.
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Affiliation(s)
- Aidar R Gosmanov
- Dept. of Physiology, College of Medicine, Univ. of Tennessee Health Science Center, 894 Union Ave., Memphis, TN 38163, USA
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21
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Marshall S, Nadeau O, Yamasaki K. Dynamic actions of glucose and glucosamine on hexosamine biosynthesis in isolated adipocytes: differential effects on glucosamine 6-phosphate, UDP-N-acetylglucosamine, and ATP levels. J Biol Chem 2004; 279:35313-9. [PMID: 15199059 DOI: 10.1074/jbc.m404133200] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose and glucosamine (GlcN) cause insulin resistance over several hours by increasing metabolite flux through the hexosamine biosynthesis pathway (HBP). To elucidate the early events underlying glucose-induced desensitization, we treated isolated adipocytes with either glucose or GlcN and then measured intracellular levels of glucose-6-P (G-6-P), GlcN-6-P, UDP-Glc-NAc, and ATP. Glucose treatment rapidly increased G-6-P levels (t((1/2)) < 1 min), which plateaued by 15 min and remained elevated for up to 4 h (glucose ED(50) = 4mm). In glucose-treated cells, GlcN-6-P was undetectable; however, GlcN treatment (2 mm) caused a rapid and massive accumulation of GlcN-6-P. Levels increased by 5 min ( approximately 400 nmol/g) and continued to rise over 2 h (t((1/2)) approximately 20 min) before reaching a plateau at >1,400 nmol/g (ED(50) = 900 microm). Thus, at high GlcN concentrations, unrestricted flux into the HBP greatly exceeds the biosynthetic capacity of the pathway leading to a rapid buildup of GlcN-6-P. The GlcN-induced rise in GlcN-6-P levels was correlated with ATP depletion, suggesting that ATP loss is caused by phosphate sequestration (with the formation of GlcN-6-P) or the energy demands of phosphorylation. As expected, GlcN and glucose increased UDP-GlcNAc levels (t((1/2)) approximately 14-18 min), but greater levels were obtained with GlcN (4-5-fold for GlcN, 2-fold for glucose). Importantly, we found that low doses of GlcN (<250 microm, ED(50) = 80 microm) could markedly elevate UDP-GlcNAc levels without increasing GlcN-6-P levels or depleting ATP levels. These studies on the dynamic actions of glucose and GlcN on hexosamine levels should be useful in exploring the functional role of the HBP and in avoiding the potential pitfalls in the pharmacological use of GlcN.
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22
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Tannis AJ, Barban J, Conquer JA. Effect of glucosamine supplementation on fasting and non-fasting plasma glucose and serum insulin concentrations in healthy individuals. Osteoarthritis Cartilage 2004; 12:506-11. [PMID: 15135147 DOI: 10.1016/j.joca.2004.03.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2003] [Accepted: 03/20/2004] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To test the hypothesis that glucose intolerance does not occur when healthy adults consume normal, recommended dosages of glucosamine sulfate. METHODS Healthy adults (N=19) ingested 1500 mg of glucosamine sulfate or placebo (double blind) each day for 12 weeks. Three-hour oral glucose tolerance tests (OGTT) were performed using 75 g of dextrose. These occurred before the start of supplementation, at 6 weeks, and at the completion of supplementation (12 weeks). RESULTS There were no significant differences between fasted levels of serum insulin or blood glucose. Glucosamine sulfate supplementation did not alter serum insulin or plasma glucose during the OGTT. There were no significant differences within or between treatments, ages or gender. Glycated hemoglobin measurements at the three time points showed no significant change over time, within or between treatments, ages or gender. The lack of significant changes may have been due to large standard deviations in the data. CONCLUSION The data suggests that glucosamine supplementation, with normal recommended dosages, does not cause glucose intolerance in healthy adults. This cannot be determined conclusively, however, until further studies are conducted using alternative types of testing.
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Affiliation(s)
- Allison J Tannis
- University of Guelph, Department of Human Biology and Nutritional Sciences, Ontario, Canada
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23
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Hazel M, Cooksey RC, Jones D, Parker G, Neidigh JL, Witherbee B, Gulve EA, McClain DA. Activation of the hexosamine signaling pathway in adipose tissue results in decreased serum adiponectin and skeletal muscle insulin resistance. Endocrinology 2004; 145:2118-28. [PMID: 14684615 DOI: 10.1210/en.2003-0812] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Overexpression of the rate-limiting enzyme for hexosamine synthesis (glutamine:fructose-6-phosphate amidotransferase) in muscle and adipose tissue of transgenic mice was previously shown to result in insulin resistance and hyperleptinemia. Explanted muscle from transgenic mice was not insulin resistant in vitro, suggesting that muscle insulin resistance could be mediated by soluble factors from fat tissue. To dissect the relative contributions of muscle and fat to hexosamine-induced insulin resistance, we overexpressed glutamine:fructose-6-phosphate amidotransferase 2.5-fold, specifically in fat under control of the aP2 promoter. Fasting glucose, insulin, and triglycerides were unchanged in the transgenic mice; leptin and beta-hydroxybutyrate levels were 91% and 29% higher, respectively. Fasted transgenic mice have mild glucose intolerance and skeletal muscle insulin resistance in vivo. In fasting transgenic mice, glucose disposal rates with hyperinsulinemia were decreased 27% in females and 10% in males. Uptake of 2-deoxy-D-glucose into muscle was diminished by 45% in female and 21% in male transgenics. Serum adiponectin was also lower in the fasted transgenics, by 37% in females and 22% in males. TNF alpha and resistin mRNA levels in adipose tissue were not altered in the fasted transgenics; levels of mRNA for leptin were increased and peroxisome proliferator-activated receptor gamma decreased. To further explore the relationship between adiponectin and insulin sensitivity, we examined mice that have been refed for 6 h after a 24-h fast. Refeeding wild-type mice resulted in decreased serum adiponectin and increased leptin. In transgenic mice, however, the regulation of these hormones by refeeding was lost for adiponectin and diminished for leptin. Refed transgenic female and male mice no longer exhibited decreased serum adiponectin in the refed state, and they were no longer insulin resistant as by lower or unchanged insulin and glucose levels. We conclude that increased hexosamine levels in fat, mimicking excess nutrient delivery, are sufficient to cause insulin resistance in skeletal muscle. Changes in serum adiponectin correlate with the insulin resistance of the transgenic animals.
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Affiliation(s)
- Mark Hazel
- Department of Medicine, University of Utah, Salt Lake City, Utah 84132, USA
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24
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Bosch RR, Pouwels MJJM, Span PN, Olthaar AJ, Tack CJ, Hermus ARMM, Sweep CGJ. Hexosamines are unlikely to function as a nutrient-sensor in 3T3-L1 adipocytes: a comparison of UDP-hexosamine levels after increased glucose flux and glucosamine treatment. Endocrine 2004; 23:17-24. [PMID: 15034192 DOI: 10.1385/endo:23:1:17] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2003] [Revised: 12/12/2003] [Accepted: 12/22/2003] [Indexed: 11/11/2022]
Abstract
Whether the hexosamine biosynthesis pathway acts as a nutrient-sensing pathway is still unclear. Glucose is directed into this pathway by GFAT. Because the activity of GFAT is tightly regulated, we examined whether UDP-hexosamine levels can increase significantly and dose-dependently in response to elevated glucose concentrations. In glucosamine-treated 3T3-L1 adipocytes, inhibition of insulin-stimulated glucose uptake was highly correlated with UDP-hexosamine levels (r = -0.992; p < 0.0001 for UDP-GlcNAc and r = -0.996; p < 0.0001 for UDP-GalNAc). Incubation of 3T3-L1 adipocytes with 0.1 microM insulin for 24 h in medium containing 1 and 5 mM glucose increased the rate of glucose uptake by 365% and 175% compared to untreated cells, respectively. This increase was not observed when the cells were incubated for 24 h with insulin in medium containing 10 or 25 mM glucose. However, treatment of cells with insulin and 1, 5, 10, or 25 mM glucose resulted in similar increases in levels of UDP-GlcNAc and UDP-GalNAc that always amounted to approx 30-40% above baseline values. This led us to conclude that despite exposure of adipocytes to conditions of extreme and prolonged glucose disposal, the increases in cellular UDP-hexosamines were minimal and not dependent on the extracellular glucose concentration. Taken together, our results are in line with the hypothesis that in glucosamine-treated adipocytes UDP-hexosamines influence insulin-stimulated glucose uptake. However, our observations in glucose-treated adipocytes argue against the possibility that UDP-hexosamines function as a nutrient-sensor, and question the role of the hexosamine biosynthesis pathway in the pathogenesis of insulin resistance.
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Affiliation(s)
- Remko R Bosch
- Department of Chemical Endocrinology, University Medical Centre Nijmegen, The Netherlands.
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25
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Abstract
Insulin is a key hormone regulating the control of metabolism and the maintenance of normoglycaemia and normolipidaemia. Insulin acts by binding to its cell surface receptor, thus activating the receptor's intrinsic tyrosine kinase activity, resulting in receptor autophosphorylation and phosphorylation of several substrates. Tyrosine phosphorylated residues on the receptor itself and on subsequently bound receptor substrates provide docking sites for downstream signalling molecules, including adapters, protein serine/threonine kinases, phosphoinositide kinases and exchange factors. Collectively, those molecules orchestrate the numerous insulin-mediated physiological responses. A clear picture is emerging of the way in which insulin elicits several intracellular signalling pathways to mediate its physiologic functions. A further challenge, being pursued by several laboratories, is to understand the molecular mechanisms that underlie insulin action at the peripheral level, deregulation of which ultimately leads to hyperglycaemia and Type 2 diabetes. We review how circulating factors such as insulin itself, TNF-alpha, interleukins, fatty acids and glycation products influence insulin action through insulin signalling molecules themselves or through other pathways ultimately impinging on the insulin-signalling pathway. Understanding how the mechanism by which molecular insulin action is modulated by these factors will potentially provide new targets for pharmacological agents, to enable the control of altered glucose and lipid metabolism and diabetes.
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Affiliation(s)
- L Pirola
- INSERM Unit 145, Faculty of Medicine, Nice, France
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26
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Green A, Rumberger JM, Stuart CA, Ruhoff MS. Stimulation of lipolysis by tumor necrosis factor-alpha in 3T3-L1 adipocytes is glucose dependent: implications for long-term regulation of lipolysis. Diabetes 2004; 53:74-81. [PMID: 14693700 DOI: 10.2337/diabetes.53.1.74] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Tumor necrosis factor-alpha (TNF-alpha) and hyperglycemia both impair insulin sensitivity in vivo. This may be secondary to stimulation of adipose tissue lipolysis and consequent increased circulating free fatty acids (FFAs). Here we report that neither TNF-alpha nor glucose alone has a pronounced effect on lipolysis in 3T3-L1 adipocytes. However, the combination of TNF-alpha plus glucose markedly stimulates lipolysis. Glucose does not affect the ability of isoproterenol to stimulate lipolysis. Alternative substrates such as acetate, pyruvate, and lactate do not allow the TNF-alpha effect. Mannose was almost as effective as glucose; fructose was marginally effective, but galactose was ineffective. The effectiveness of the sugars corresponded with production of lactate, i.e., the cells readily produced lactate from glucose or mannose, slightly from fructose, and not at all from galactose. The ability of TNF-alpha to phosphorylate extracellular signal-regulated kinase 1 (ERK1) and ERK2 and to downregulate perilipin (which has been implicated in the lipolytic effect of TNF-alpha) was not affected by glucose. We conclude that the lipolytic action of TNF-alpha is influenced by glucose in 3T3-L1 adipocytes. The findings suggest that glucose metabolism is required for the lipolytic response to TNF-alpha but not for early signaling events. These findings suggest novel mechanisms by which TNF-alpha and hyperglycemia raise FFA levels and induce insulin resistance.
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Affiliation(s)
- Allan Green
- Bassett Research Institute, Bassett Healthcare, Cooperstown, New York 13326, USA.
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27
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Abstract
It is established that plasma leptin is associated with satiety and that leptin stimulates lipid metabolism, and increases energy expenditure. These effects implicate leptin as a major regulator of energy homeostasis, which may serve to limit excess energy storage. As plasma leptin concentrations are tightly coupled with fat mass in humans, decreases in adipose mass with weight loss coincide with decreased concentrations of circulating leptin. However, due to many confounding factors, the effects of exercise on circulating leptin are less clear. The data from investigations examining single exercise bouts suggest that serum leptin concentrations are unaltered by short duration (41 minutes or less), non-exhaustive exercise, but may be affected by short duration, exhaustive exercise. More convincingly, studies investigating long duration exercise bouts indicate that serum leptin concentrations are reduced with exercise durations ranging from one to multiple hours. These findings raise speculation that exercise-associated reductions in leptin may be due to alterations in nutrient availability or nutrient flux at the level of the adipocytes, the primary site of leptin production and secretion. Thus, one purpose of this review is to discuss the effects of exercise on circulating leptin concentrations with special emphasis on studies that have examined single exercise bouts that are associated with high levels of energy expenditure and energy deficit. In addition, a 'nutrient sensing pathway' (the hexosamine biosynthetic pathway), which regulates leptin gene expression, will be discussed as a possible mechanism by which exercise-induced energy deficit may modulate serum leptin concentrations.
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Affiliation(s)
- Matthew W Hulver
- Department of Physiology, East Carolina University, Greenville, North Carolina, USA.
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28
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Bosch RR, Janssen SWJ, Span PN, Olthaar A, van Emst-de Vries SE, Willems PHGM, Martens J M G, Hermus ARMM, Sweep CCJ. Exploring levels of hexosamine biosynthesis pathway intermediates and protein kinase C isoforms in muscle and fat tissue of Zucker Diabetic Fatty rats. Endocrine 2003; 20:247-52. [PMID: 12721503 DOI: 10.1385/endo:20:3:247] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2002] [Revised: 12/02/2002] [Accepted: 01/09/2003] [Indexed: 11/11/2022]
Abstract
Many studies suggest that insulin resistance develops and/or is maintained by an increased flux of glucose through the hexosamine biosynthesis pathway. This pathway may attenuate insulin-stimulated glucose uptake by activating protein kinase C (PKC). Therefore, we investigated whether the concentrations of the major hexosamine metabolites, uridine diphosphate- N-acetyl-glucosamine (UDP-GlcNAc) and uridine diphosphate- N-acetyl-galactosamine (UDP-GalNAc), and the expression levels of PKC isoforms were affected in Zucker Diabetic Fatty (ZDF) rats, an animal model widely used to study type 2 diabetes mellitus. At the age of 6 wk, control and ZDF rats were normoglycemic. Whereas control rats remained normoglycemic, the ZDF rats became hyperglycemic. The amount of UDP-GlcNAc and UDP-GalNAc in muscle tissue of ZDF rats was similar at 6, 12, 18, and 24 wk of age. Moreover, the concentration of both hexosamines did not differ among ZDF, phlorizin-treated ZDF, and control rats. Western blot analysis revealed that PKCalpha, delta, epsilon, andzeta, but not PKCbeta and gamma, were expressed in muscle and fat tissues from 6- and 24-wk-old control and ZDF rats. In addition, we did not observe changes in the expression levels of the PKC isoforms following prolonged hyperglycemia. Taken together, these findings indicate that the amounts of several metabolites from the hexosamine biosynthesis pathway and PKC isoforms, both hypothesized to be important in the development and/or maintenance of the insulin-resistant state of muscle and fat tissue, are not different in ZDF compared with nondiabetic rats.
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Affiliation(s)
- Remko R Bosch
- Department of Chemical Endocrinology, University Medical Centre Nijmegen, Nijmegen, The Netherlands.
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29
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Burt DJ, Gruden G, Thomas SM, Tutt P, Dell'Anna C, Viberti GC, Gnudi L. P38 mitogen-activated protein kinase mediates hexosamine-induced TGFbeta1 mRNA expression in human mesangial cells. Diabetologia 2003; 46:531-7. [PMID: 12679868 DOI: 10.1007/s00125-003-1075-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2002] [Revised: 09/12/2002] [Indexed: 10/20/2022]
Abstract
AIMS/HYPOTHESIS The hexosamine pathway has been implicated in the induction of TGFbeta1 expression and in the pathophysiology of diabetic glomerulopathy. Glucose-induced TGFbeta1 expression is mediated by p38 mitogen-activated-protein-kinase (p38-MAPK) and this kinase is activated in the diabetic glomeruli. We examined whether the p38-MAPK is implicated in hexosamine-induced TGFbeta1 mRNA expression in human mesangial cells. GFAT overexpression induced an increase in p38-MAPK activation after 6 and 12 h incubation in normal glucose, and this was prevented by the GFAT inhibitor azaserine. Furthermore, high glucose enhanced p38-MAPK activation in GFAT tranfected cells ( p</=0.04). P38-MAPK inhibition using SB202190 (1 micro mol/l) reduced hexosamine-induced TGFbeta1 expression in normal and high glucose. The activation of the p38-MAPK was dependent on protein kinase-C. METHODS The products of the hexosamine biosynthetic pathway were increased by the addition of glucosamine or by the overexpression of the rate-limiting enzyme of the hexosamine pathway, glutamine: fructose-6-phosphate amidotransferase (GFAT). RESULTS Glucosamine addition resulted in cell death. UDP-N-Acetylglucosamine, one of the major hexosamine end-products, was increased in normal (7 mmol/l) and high (25 mmol/l) glucose conditions in GFAT-transfected cells compared to control transfected cells by twofold and 1.7-fold respectively ( p</=0.04) and this was accompanied by a 1.6- and 2.3-fold increase ( p</=0.02) in TGFbeta1 mRNA expression. Addition of the GFAT inhibitor azaserine (10 micro mol/l) prevented the induction of TGFbeta1 in GFAT transfected cells. CONCLUSION/INTERPRETATION Overexpression of GFAT increases hexosamine accumulation which mediates TGFbeta1 expression via a protein kinase-C and p38-MAPK dependent mechanism. Increased glucose concentrations magnify these effects.
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Affiliation(s)
- D J Burt
- Department of Diabetes, Endocrinology and Internal Medicine, Guys Hospital, King's College, 5th Floor Thomas Guy House, SE1 9RT, London, UK
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30
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Margetic S, Gazzola C, Pegg GG, Hill RA. Leptin: a review of its peripheral actions and interactions. Int J Obes (Lond) 2002; 26:1407-33. [PMID: 12439643 DOI: 10.1038/sj.ijo.0802142] [Citation(s) in RCA: 667] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2001] [Revised: 04/02/2002] [Accepted: 05/27/2002] [Indexed: 12/11/2022]
Abstract
Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain.
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Affiliation(s)
- S Margetic
- Central Queensland University, School of Chemical and Biomedical Sciences, Queensland, Australia
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31
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Ma L, Rudert WA, Harnaha J, Wright M, Machen J, Lakomy R, Qian S, Lu L, Robbins PD, Trucco M, Giannoukakis N. Immunosuppressive effects of glucosamine. J Biol Chem 2002; 277:39343-9. [PMID: 12176986 DOI: 10.1074/jbc.m204924200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucosamine is a naturally occurring derivative of glucose and is an essential component of glycoproteins and proteoglycans, important constituents of many eukaryotic proteins. In cells, glucosamine is produced enzymatically by the amidation of glucose 6-phosphate and can then be further modified by acetylation to result in N-acetylglucosamine. Commercially, glucosamine is sold over-the-counter to relieve arthritis. Although there is evidence in favor of the beneficial effects of glucosamine, the mechanism is unknown. Our data demonstrate that glucosamine suppresses the activation of T-lymphoblasts and dendritic cells in vitro as well as allogeneic mixed leukocyte reactivity in a dose-dependent manner. There was no inherent cellular toxicity involved in the inhibition, and the activity was not reproducible with other amine sugars. More importantly, glucosamine administration prolonged allogeneic cardiac allograft survival in vivo. We conclude that, despite its documented effects on insulin sensitivity, glucosamine possesses immunosuppressive activity and could be beneficial as an immunosuppressive agent.
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Affiliation(s)
- Linlin Ma
- Department of Surgery, T. E. Starzl Transplantation Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA
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32
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McClain DA, Lubas WA, Cooksey RC, Hazel M, Parker GJ, Love DC, Hanover JA. Altered glycan-dependent signaling induces insulin resistance and hyperleptinemia. Proc Natl Acad Sci U S A 2002; 99:10695-9. [PMID: 12136128 PMCID: PMC125016 DOI: 10.1073/pnas.152346899] [Citation(s) in RCA: 269] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Insulin resistance and beta cell toxicity are key features of type 2 diabetes. One leading hypothesis suggests that these abnormalities result from excessive flux of nutrients through the UDP-hexosamine biosynthetic pathway leading to "glucose toxicity." How the products of the hexosamine pathway mediate these effects is not known. Here, we show that transgenic overexpression of an enzyme using UDP-GlcNAc to modify proteins with O-GlcNAc produces the type 2 diabetic phenotype. Even modest overexpression of an isoform of O-GlcNAc transferase, in muscle and fat, leads to insulin resistance and hyperleptinemia. These data support the proposal that O-linked GlcNAc transferase participates in a hexosamine-dependent signaling pathway that is linked to insulin resistance and leptin production.
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Affiliation(s)
- Donald A McClain
- Department of Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City, UT 84112, USA
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33
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Federici M, Menghini R, Mauriello A, Hribal ML, Ferrelli F, Lauro D, Sbraccia P, Spagnoli LG, Sesti G, Lauro R. Insulin-dependent activation of endothelial nitric oxide synthase is impaired by O-linked glycosylation modification of signaling proteins in human coronary endothelial cells. Circulation 2002; 106:466-72. [PMID: 12135947 DOI: 10.1161/01.cir.0000023043.02648.51] [Citation(s) in RCA: 258] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Hyperglycemia impairs functional properties of cytosolic and nuclear proteins via O-linked glycosylation modification (O-GlcNAcylation). We studied the effects of O-GlcNAcylation on insulin signaling in human coronary artery endothelial cells. METHODS AND RESULTS O-GlcNAcylation impaired the metabolic branch of insulin signaling, ie, insulin receptor (IR) activation of the IR substrate (IRS)/phosphatidylinositol 3-kinase (PI3-K)/Akt, whereas it enhanced the mitogenic branch, ie, ERK-1/2 and p38 (mitogen-activated protein kinase). Both in vivo and in vitro phosphorylation of endothelial nitric oxide synthase (eNOS) by Akt were reduced by hyperglycemia and hexosamine activation. Insulin-induced eNOS activity in vivo was reduced by hyperglycemia and hexosamine activation, which was coupled to increased activation and expression of matrix metalloproteinase-2 and -9; these phenomena were reversed by inhibition of the hexosamine pathway. Finally, carotid plaques from type 2 diabetic patients showed increased endothelial O-GlcNAcylation with respect to nondiabetics. CONCLUSIONS Our data show that hyperglycemia, through the hexosamine pathway, impairs activation of the IR/IRS/PI3-K/Akt pathway, resulting in deregulation of eNOS activity.
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Affiliation(s)
- Massimo Federici
- Department of Internal Medicine, University of Tor Vergata, Rome, Italy.
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Gaster M, Petersen I, Højlund K, Poulsen P, Beck-Nielsen H. The diabetic phenotype is conserved in myotubes established from diabetic subjects: evidence for primary defects in glucose transport and glycogen synthase activity. Diabetes 2002; 51:921-7. [PMID: 11916908 DOI: 10.2337/diabetes.51.4.921] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The most well-described defect in the pathophysiology of type 2 diabetes is reduced insulin-mediated glycogen synthesis in skeletal muscles. It is unclear whether this defect is primary or acquired secondary to dyslipidemia, hyperinsulinemia, or hyperglycemia. We determined the glycogen synthase (GS) activity; the content of glucose-6-phosphate, glucose, and glycogen; and the glucose transport in satellite cell cultures established from diabetic and control subjects. Myotubes were precultured in increasing insulin concentrations for 4 days and subsequently stimulated acutely by insulin. The present study shows that the basal glucose uptake as well as insulin-stimulated GS activity is reduced in satellite cell cultures established from patients with type 2 diabetes. Moreover, increasing insulin concentrations could compensate for the reduced GS activity to a certain extent, whereas chronic supraphysiological insulin concentrations induced insulin resistance in GS and glucose transport activity. Our data suggest that insulin resistance in patients with type 2 diabetes comprises at least two important defects under physiological insulin concentrations: a reduced glucose transport under basal conditions and a reduced GS activity under acute insulin stimulation, implicating a reduced glucose uptake in the fasting state and a diminished insulin-mediated storage of glucose as glycogen after a meal.
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Affiliation(s)
- Michael Gaster
- Department of Endocrinology, Odense University Hospital, Odense, Denmark.
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35
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Perriott LM, Kono T, Whitesell RR, Knobel SM, Piston DW, Granner DK, Powers AC, May JM. Glucose uptake and metabolism by cultured human skeletal muscle cells: rate-limiting steps. Am J Physiol Endocrinol Metab 2001; 281:E72-80. [PMID: 11404224 DOI: 10.1152/ajpendo.2001.281.1.e72] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To use primary cultures of human skeletal muscle cells to establish defects in glucose metabolism that underlie clinical insulin resistance, it is necessary to define the rate-determining steps in glucose metabolism and to improve the insulin response attained in previous studies. We modified experimental conditions to achieve an insulin effect on 3-O-methylglucose transport that was more than twofold over basal. Glucose phosphorylation by hexokinase limits glucose metabolism in these cells, because the apparent Michaelis-Menten constant of coupled glucose transport and phosphorylation is intermediate between that of transport and that of the hexokinase and because rates of 2-deoxyglucose uptake and phosphorylation are less than those of glucose. The latter reflects a preference of hexokinase for glucose over 2-deoxyglucose. Cellular NAD(P)H autofluorescence, measured using two-photon excitation microscopy, is both sensitive to insulin and indicative of additional distal control steps in glucose metabolism. Whereas the predominant effect of insulin in human skeletal muscle cells is to enhance glucose transport, phosphorylation, and steps beyond, it also determines the overall rate of glucose metabolism.
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Affiliation(s)
- L M Perriott
- Department of Veterans Affairs Medical Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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36
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Abstract
The glucose-fatty acid cycle as proposed four decades ago by Randle suggests that insulin resistance develops in consequence of alterations of the metabolic pressure of lipids. The more recently published 'hexosamine pathway theory' and the 'malonyl-CoA hypothesis' depict insulin resistance as a consequence of an imbalance between utilization of lipids and carbohydrates. The latter is finely tuned by entry of fatty acids into the mitochondria and/or by entry of glucose to the hexosamine pathway. A significant body of evidence has also been accumulated which points to the complex effects of leptin, an adipocyte-derived signal of lipid stores, on the storage and metabolism of fats and carbohydrates. These are mediated either directly, through actions on specific tissues, or indirectly, via CNS, endocrine and neural mechanisms. The available literature also provides good evidence that leptin orchestrates the metabolic changes in a number of organs and tissues, and alters nutrient fluxes to favor energy expenditure over energy storage. In this article, the proposed lipopenic effects of leptin as studied in various animal models of diet-induced insulin resistance, and possible regulations of leptin production and action by marine fish oil feeding are reviewed.
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Affiliation(s)
- J Ukropec
- Diabetes and Nutrition Research Laboratory, Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
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37
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Gaster M, Handberg A, Beck-Nielsen H, Schroder HD. Glucose transporter expression in human skeletal muscle fibers. Am J Physiol Endocrinol Metab 2000; 279:E529-38. [PMID: 10950819 DOI: 10.1152/ajpendo.2000.279.3.e529] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study was initiated to investigate GLUT-1 through -5 expression in developing and mature human skeletal muscle. To bypass the problems inherent in techniques using tissue homogenates, we applied an immunocytochemical approach, employing the sensitive enhanced tyramide signal amplification (TSA) technique to detect the localization of glucose transporter expression in human skeletal muscle. We found expression of GLUT-1, GLUT-3, and GLUT-4 in developing human muscle fibers showing a distinct expression pattern. 1) GLUT-1 is expressed in human skeletal muscle cells during gestation, but its expression is markedly reduced around birth and is further reduced to undetectable levels within the first year of life; 2) GLUT-3 protein expression appears at 18 wk of gestation and disappears after birth; and 3) GLUT-4 protein is diffusely expressed in muscle cells throughout gestation, whereas after birth, the characteristic subcellular localization is as seen in adult muscle fibers. Our results show that GLUT-1, GLUT-3, and GLUT-4 seem to be of importance during muscle fiber growth and development. GLUT-5 protein was undetectable in fetal and adult skeletal muscle fibers. In adult muscle fibers, only GLUT-4 was expressed at significant levels. GLUT-1 immunoreactivity was below the detection limit in muscle fibers, indicating that this glucose transporter is of minor importance for muscle glucose supply. Thus we hypothesize that GLUT-4 also mediates basal glucose transport in muscle fibers, possibly through constant exposure to tonal contraction and basal insulin levels.
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Affiliation(s)
- M Gaster
- Department of Endocrinology, Odense University Hospital, Denmark
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