Pharmacological inhibition of dynamin-related protein 1 attenuates skeletal muscle insulin resistance in obesity.

Dynamin-related protein-1 (Drp1) is a key regulator in mitochondrial fission. Excessive Drp1-mediated mitochondrial fission in skeletal muscle under the obese condition is associated with impaired insulin action. However, it remains unknown whether pharmacological inhibition of Drp1, using the Drp1-specific inhibitor Mitochondrial Division Inhibitor 1 (Mdivi-1), is effective in alleviating skeletal muscle insulin resistance and improving whole-body metabolic health under the obese and insulin-resistant condition. We subjected C57BL/6J mice to a high-fat diet (HFD) or low-fat diet (LFD) for 5-weeks. HFD-fed mice received Mdivi-1 or saline injections for the last week of the diet intervention. Additionally, myotubes derived from obese insulin-resistant humans were treated with Mdivi-1 or saline for 12 h. We measured glucose area under the curve (AUC) from a glucose tolerance test (GTT), skeletal muscle insulin action, mitochondrial dynamics, respiration, and H2 O2 content. We found that Mdivi-1 attenuated impairments in skeletal muscle insulin signaling and blood glucose AUC from a GTT induced by HFD feeding (p < 0.05). H2 O2 content was elevated in skeletal muscle from the HFD group (vs. LFD, p < 0.05), but was reduced with Mdivi-1 treatment, which may partially explain the improvement in skeletal muscle insulin action. Similarly, Mdivi-1 enhanced the mitochondrial network structure, reduced reactive oxygen species, and improved insulin action in myotubes from obese humans (vs. saline, p < 0.05). In conclusion, inhibiting Drp1 with short-term Mdivi-1 administration attenuates the impairment in skeletal muscle insulin signaling and improves whole-body glucose tolerance in the setting of obesity-induced insulin resistance. Targeting Drp1 may be a viable approach to treat obesity-induced insulin resistance.

Distinct Adaptations of Mitochondrial Dynamics to Electrical Pulse Stimulation in Lean and Severely Obese Primary Myotubes.

BACKGROUND: Skeletal muscle from lean and obese subjects elicits differential adaptations in response to exercise/muscle contractions. In order to determine whether obesity alters the adaptations in mitochondrial dynamics in response to exercise/muscle contractions and whether any of these distinct adaptations are linked to alterations in insulin sensitivity, we compared the effects of electrical pulse stimulation (EPS) on mitochondrial network structure and regulatory proteins in mitochondrial dynamics in myotubes from lean humans and humans with severe obesity and evaluated the correlations between these regulatory proteins and insulin signaling. METHODS: Myotubes from human skeletal muscle cells obtained from lean humans (body mass index, 23.8 ± 1.67 kg·m-2) and humans with severer obesity (45.5 ± 2.26 kg·m-2; n = 8 per group) were electrically stimulated for 24 h. Four hours after EPS, mitochondrial network structure, protein markers of insulin signaling, and mitochondrial dynamics were assessed. RESULTS: EPS enhanced insulin-stimulated AktSer473 phosphorylation, reduced the number of nonnetworked individual mitochondria, and increased the mitochondrial network size in both groups (P < 0.05). Mitochondrial fusion marker mitofusin 2 was significantly increased in myotubes from the lean subjects (P < 0.05) but reduced in subjects with severe obesity (P < 0.05). In contrast, fission marker dynamin-related protein 1 (Drp1Ser616) was reduced in myotubes from subjects with severe obesity (P < 0.05) but remained unchanged in lean subjects. Reductions in DrpSer616 phosphorylation were correlated with improvements in insulin-stimulated AktSer473 phosphorylation after EPS (r = -0.679, P = 0.004). CONCLUSIONS: Our data demonstrated that EPS induces more fused mitochondrial networks, which are associated with differential adaptations in mitochondrial dynamic processes in myotubes from lean humans and human with severe obesity. It also suggests that improved insulin signaling after muscle contractions may be linked to the reduction in Drp1 activity.

Management of newly diagnosed type 2 Diabetes Mellitus (T2DM) in children and adolescents.

Over the past 3 decades, the prevalence of childhood obesity has increased dramatically in North America, ushering in a variety of health problems, including type 2 diabetes mellitus (T2DM), which previously was not typically seen until much later in life. The rapid emergence of childhood T2DM poses challenges to many physicians who find themselves generally ill-equipped to treat adult diseases encountered in children. This clinical practice guideline was developed to provide evidence-based recommendations on managing 10- to 18-year-old patients in whom T2DM has been diagnosed. The American Academy of Pediatrics (AAP) convened a Subcommittee on Management of T2DM in Children and Adolescents with the support of the American Diabetes Association, the Pediatric Endocrine Society, the American Academy of Family Physicians, and the Academy of Nutrition and Dietetics (formerly the American Dietetic Association). These groups collaborated to develop an evidence report that served as a major source of information for these practice guideline recommendations. The guideline emphasizes the use of management modalities that have been shown to affect clinical outcomes in this pediatric population. Recommendations are made for situations in which either insulin or metformin is the preferred first-line treatment of children and adolescents with T2DM. The recommendations suggest integrating lifestyle modifications (ie, diet and exercise) in concert with medication rather than as an isolated initial treatment approach. Guidelines for frequency of monitoring hemoglobin A1c (HbA1c) and finger-stick blood glucose (BG) concentrations are presented. Decisions were made on the basis of a systematic grading of the quality of evidence and strength of recommendation. The clinical practice guideline underwent peer review before it was approved by the AAP. This clinical practice guideline is not intended to replace clinical judgment or establish a protocol for the care of all children with T2DM, and its recommendations may not provide the only appropriate approach to the management of children with T2DM. Providers should consult experts trained in the care of children and adolescents with T2DM when treatment goals are not met or when therapy with insulin is initiated. The AAP acknowledges that some primary care clinicians may not be confident of their ability to successfully treat T2DM in a child because of the child's age, coexisting conditions, and/or other concerns. At any point at which a clinician feels he or she is not adequately trained or is uncertain about treatment, a referral to a pediatric medical subspecialist should be made. If a diagnosis of T2DM is made by a pediatric medical subspecialist, the primary care clinician should develop a comanagement strategy with the subspecialist to ensure that the child continues to receive appropriate care consistent with a medical home model in which the pediatrician partners with parents to ensure that all health needs are met.

Management of type 2 diabetes mellitus in children and adolescents.

OBJECTIVE: Over the last 3 decades, the prevalence of childhood obesity has increased dramatically in North America, ushering in a variety of health problems, including type 2 diabetes mellitus (T2DM), which previously was not typically seen until much later in life. This technical report describes, in detail, the procedures undertaken to develop the recommendations given in the accompanying clinical practice guideline, "Management of Type 2 Diabetes Mellitus in Children and Adolescents," and provides in-depth information about the rationale for the recommendations and the studies used to make the clinical practice guideline's recommendations. METHODS: A primary literature search was conducted relating to the treatment of T2DM in children and adolescents, and a secondary literature search was conducted relating to the screening and treatment of T2DM's comorbidities in children and adolescents. Inclusion criteria were prospectively and unanimously agreed on by members of the committee. An article was eligible for inclusion if it addressed treatment (primary search) or 1 of 4 comorbidities (secondary search) of T2DM, was published in 1990 or later, was written in English, and included an abstract. Only primary research inquiries were considered; review articles were considered if they included primary data or opinion. The research population had to constitute children and/or adolescents with an existing diagnosis of T2DM; studies of adult patients were considered if at least 10% of the study population was younger than 35 years. All retrieved titles, abstracts, and articles were reviewed by the consulting epidemiologist. RESULTS: Thousands of articles were retrieved and considered in both searches on the basis of the aforementioned criteria. From those, in the primary search, 199 abstracts were identified for possible inclusion, 58 of which were retained for systematic review. Five of these studies were classified as grade A studies, 1 as grade B, 20 as grade C, and 32 as grade D. Articles regarding treatment of T2DM selected for inclusion were divided into 4 major subcategories on the basis of type of treatment being discussed: (1) medical treatments (32 studies); (2) nonmedical treatments (9 studies); (3) provider behaviors (8 studies); and (4) social issues (9 studies). From the secondary search, an additional 336 abstracts relating to comorbidities were identified for possible inclusion, of which 26 were retained for systematic review. These articles included the following: 1 systematic review of literature regarding comorbidities of T2DM in adolescents; 5 expert opinions presenting global recommendations not based on evidence; 5 cohort studies reporting natural history of disease and comorbidities; 3 with specific attention to comorbidity patterns in specific ethnic groups (case-control, cohort, and clinical report using adult literature); 3 reporting an association between microalbuminuria and retinopathy (2 case-control, 1 cohort); 3 reporting the prevalence of nephropathy (cohort); 1 reporting peripheral vascular disease (case series); 2 discussing retinopathy (1 case-control, 1 position statement); and 3 addressing hyperlipidemia (American Heart Association position statement on cardiovascular risks; American Diabetes Association consensus statement; case series). A breakdown of grade of recommendation shows no grade A studies, 10 grade B studies, 6 grade C studies, and 10 grade D studies. With regard to screening and treatment recommendations for comorbidities, data in children are scarce, and the available literature is conflicting. Therapeutic recommendations for hypertension, dyslipidemia, retinopathy, microalbuminuria, and depression were summarized from expert guideline documents and are presented in detail in the guideline. The references are provided, but the committee did not independently assess the supporting evidence. Screening tools are provided in the Supplemental Information.

Evaluating women with ovarian cancer for BRCA1 and BRCA2 mutations: missed opportunities.

OBJECTIVE: To estimate the incidence of genetic counseling referral for ovarian cancer patients who are at substantial risk for a BRCA1 or BRCA2 mutation. METHODS: An analysis was performed of new ovarian cancer patients who were seen at a comprehensive cancer center from January 1, 1999, through December 31, 2007. Patients at substantial (more than 20-25%) risk for a BRCA1 or BRCA2 mutation were identified and records reviewed for referral to genetic counseling. Time to referral was estimated using the Kaplan-Meier method. RESULTS: A total of 3,765 epithelial ovarian cancer patients were seen during the 9-year period. On average, 23.8% of patients met substantial-risk criteria for BRCA mutations. In 1999, only 12% of patients at substantial-risk were referred. Referral improved over time with 48% referred in 2007 (P<.001). Newly diagnosed patients were more often referred for genetic counseling than new patients with recurrent disease or those seen as second opinions. African-American women meeting substantial-risk criteria were less likely to be referred than were white or Hispanic women (P=.009). CONCLUSION: Although dictated family history was accurate, interpretation of risk for BRCA1 or BRCA2 mutations and subsequent referral to genetic counseling was poor. Although there was significant improvement over time, 50% of substantial-risk patients still were missed. Systematic efforts to identify those ovarian cancer patients at substantial risk for a BRCA1 or BRCA2 are necessary.