Low-dose metformin improves hyperglycaemia related to myotonic dystrophy

Diabetes with GLP-1R polymorphism (rs3765467) accompanied by myotonic dystrophy: A case of myotonic dystrophy with p.R131Q polymorphism at the glucagon-like peptide-1 receptor (rs3765467) resulting in marked effects of its agonist, dulaglutide

A 47-year-old woman was diagnosed with myotonic dystrophy when admitted for traumatic subarachnoid hemorrhage. Her glycemic control was poor despite administration of pioglitazone, a PPARɤ agonist, and subcutaneous insulin infusion. However, adding a GLP-1 receptor (GLP-1R) agonist markedly improved blood glucose levels, resulting in eventual insulin withdrawal. Genetic testing revealed a heterozygous variant, p.R131Q, in the GLP1R (rs3765467), a common variant in Asia. This variant is known to be associated with increased endogenous insulin from beta cells in response to exogenous GLP-1 infusion. This is the first report and short review of a Japanese case of myotonic dystrophy accompanied by GLP-1R gene polymorphism.

Pharmacological and exercise-induced activation of AMPK as emerging therapies for myotonic dystrophy type 1 patients

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder with variable clinical features. Currently, there is no cure or effective treatment for DM1. The disease is caused by an expansion of CUG repeats in the 3' UTR of DMPK mRNAs. Mutant DMPK mRNAs accumulate in nuclei as RNA foci and trigger an imbalance in the level and localization of RNA-binding proteins causing the characteristic missplicing events that account for the varied DM1 symptoms, a disease mechanism referred to as RNA toxicity. In recent years, multiple signalling pathways have been identified as being aberrantly regulated in skeletal muscle in response to the CUG expansion, including AMPK, a sensor of energy status, as well as a master regulator of cellular energy homeostasis. Converging lines of evidence highlight the benefits of activating AMPK signalling pharmacologically on RNA toxicity, as well as on muscle histology and function, in preclinical DM1 models. Importantly, a clinical trial with metformin, an activator of AMPK, resulted in functional benefits in DM1 patients. In addition, exercise, a known AMPK activator, has shown promising effects on RNA toxicity and muscle function in DM1 mice. Finally, clinical trials involving moderate-intensity exercise also induced functional benefits for DM1 patients. Taken together, these studies clearly demonstrate the molecular, histological and functional benefits of AMPK activation and exercise-based interventions on the DM1 phenotype. Despite these advances, several key questions remain; in particular, the extent of the true implication of AMPK in the observed beneficial improvements, as well as how, mechanistically, activation of AMPK signalling improves the DM1 pathophysiology.

Targeting Myotonic Dystrophy Type 1 with Metformin

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder of genetic origin. Progressive muscular weakness, atrophy and myotonia are its most prominent neuromuscular features, while additional clinical manifestations in multiple organs are also common. Overall, DM1 features resemble accelerated aging. There is currently no cure or specific treatment for myotonic dystrophy patients. However, in recent years a great effort has been made to identify potential new therapeutic strategies for DM1 patients. Metformin is a biguanide antidiabetic drug, with potential to delay aging at cellular and organismal levels. In DM1, different studies revealed that metformin rescues multiple phenotypes of the disease. This review provides an overview of recent findings describing metformin as a novel therapy to combat DM1 and their link with aging.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3'-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

Myotonic dystrophy type 1 drug development: A pipeline toward the market

Myotonic dystrophy type 1 (DM1) is a multisystemic neuromuscular genetic disease with an estimated prevalence of approximately at least half a million individuals based on its vast ethnic variation. Building upon a well-known physiopathology and several proof-of-concept therapeutic approaches, herein we compile a comprehensive overview of the most recent drug development programs under preclinical and clinical evaluation. Specifically, close to two dozen drug developments, eight of which are already in clinical trials, explore a diversity of new chemical entities, drug repurposing, oligonucleotide, and gene therapy-based approaches. Of these, repurposing of tideglusib, mexiletine, or metformin appear to be therapies with the most potential to receive marketing authorization for DM1.

Diabetes, metformin and cancer risk in myotonic dystrophy type I

Myotonic dystrophy type I (DM1) is an autosomal dominant multisystem disorder characterized by myotonia and muscle weakness. Type 2 diabetes (T2D) and cancer have been shown to be part of the DM1 phenotype. Metformin, a well-established agent for the management of T2D, is thought to have cancer-preventive effects in the general population. In our study, we aimed to assess the association between T2D, metformin use and the risk of cancer in DM1 patients. We identified a cohort of 913 DM1 patients and an age-, sex- and clinic-matched cohort of 12,318 DM1-free controls from the UK Clinical Practice Research Datalink, a large primary care records database. We used Cox regression models to assess cancer risk in T2D patients who were metformin users or nonusers compared to patients without T2D. Separate analyses were conducted for DM1 patients and controls. T2D was more prevalent in DM1 than in controls (8% vs. 3%, p < 0.0001). DM1 patients with T2D, compared to those without T2D, were more likely to develop cancer (hazard ratio [HR] = 3.60, 95% confidence interval [CI] = 1.18-10.97; p = 0.02), but not if they were treated with metformin (HR = 0.43, 95% CI = 0.06-3.35; p = 0.42). Among controls, we observed no significant associations between T2D and cancer risk in either users or nonusers of Metformin (HR = 1.28, 95% CI = 0.91-1.79; p = 0.16 and HR = 1.13, 95% CI = 0.72-1.79; p = 0.59, respectively). These results show an association between T2D and cancer risk in DM1 patients and may provide new insights into the possible benefits of Metformin use in DM1.

Insulin Signaling as a Key Moderator in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic disease characterized by multi-system involvement. Affected organ system includes skeletal muscle, heart, gastro-intestinal system and the brain. In this review, we evaluate the evidence for alterations in insulin signaling and their relation to clinical DM1 features. We start by summarizing the molecular pathophysiology of DM1. Next, an overview of normal insulin signaling physiology is given, and evidence for alterations herein in DM1 is presented. Clinically, evidence for involvement of insulin signaling pathways in DM1 is based on the increased incidence of insulin resistance seen in clinical practice and recent trial evidence of beneficial effects of metformin on muscle function. Indirectly, further support may be derived from certain CNS derived symptoms characteristic of DM1, such as obsessive-compulsive behavior features, for which links with altered insulin signaling has been demonstrated in other diseases. At the basic scientific level, several pathophysiological mechanisms that operate in DM1 may compromise normal insulin signaling physiology. The evidence presented here reflects the importance of insulin signaling in relation to clinical features of DM1 and justifies further basic scientific and clinical, therapeutically oriented research.

Small Molecules Which Improve Pathogenesis of Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults for which there is currently no treatment. The pathogenesis of this autosomal dominant disorder is associated with the expansion of CTG repeats in the 3'-UTR of the DMPK gene. DMPK transcripts with expanded CUG repeats (CUGexpDMPK) are retained in the nucleus forming multiple discrete foci, and their presence triggers a cascade of toxic events. Thus far, most research emphasis has been on interactions of CUGexpDMPK with the muscleblind-like (MBNL) family of splicing factors. These proteins are sequestered by the expanded CUG repeats of DMPK RNA leading to their functional depletion. As a consequence, abnormalities in many pathways of RNA metabolism, including alternative splicing, are detected in DM1. To date, in vitro and in vivo efforts to develop therapeutic strategies for DM1 have mostly been focused on targeting CUGexpDMPK via reducing their expression and/or preventing interactions with MBNL1. Antisense oligonucleotides targeted to the CUG repeats in the DMPK transcripts are of particular interest due to their potential capacity to discriminate between mutant and normal transcripts. However, a growing number of reports describe alternative strategies using small molecule chemicals acting independently of a direct interaction with CUGexpDMPK. In this review, we summarize current knowledge about these chemicals and we describe the beneficial effects they caused in different DM1 experimental models. We also present potential mechanisms of action of these compounds and pathways they affect which could be considered for future therapeutic interventions in DM1.

The Role of AMPK in Neuromuscular Biology and Disease

AMP-activated protein kinase (AMPK) is a primary regulator of cellular metabolism. Recent studies have revealed that AMPK also mediates the maintenance and plasticity of α-motoneurons, the neuromuscular junction, and skeletal muscle. Furthermore, AMPK stimulation by either genetic, pharmacological, or physiological approaches elicits beneficial phenotypic remodeling in neuromuscular disorders (NMDs). Here, we review the role of AMPK as a governor of neuromuscular biology, and present evidence for AMPK as an effective molecular target for therapeutic pursuit in the context of the most prevalent NMDs, including Duchenne muscular dystrophy, spinal muscular atrophy, and myotonic dystrophy type 1. This information may be useful for engineering AMPK-targeted pharmacological- or lifestyle-based strategies to treat disorders of the neuromuscular system.

In Vitro and In Vivo Modulation of Alternative Splicing by the Biguanide Metformin

Major physiological changes are governed by alternative splicing of RNA, and its misregulation may lead to specific diseases. With the use of a genome-wide approach, we show here that this splicing step can be modified by medication and demonstrate the effects of the biguanide metformin, on alternative splicing. The mechanism of action involves AMPK activation and downregulation of the RBM3 RNA-binding protein. The effects of metformin treatment were tested on myotonic dystrophy type I (DM1), a multisystemic disease considered to be a spliceopathy. We show that this drug promotes a corrective effect on several splicing defects associated with DM1 in derivatives of human embryonic stem cells carrying the causal mutation of DM1 as well as in primary myoblasts derived from patients. The biological effects of metformin were shown to be compatible with typical therapeutic dosages in a clinical investigation involving diabetic patients. The drug appears to act as a modifier of alternative splicing of a subset of genes and may therefore have novel therapeutic potential for many more diseases besides those directly linked to defective alternative splicing.

Dramatic improvement of blood glucose control after pioglitazone treatment in poorly controlled over-weight diabetic patients with myotonic dystrophy

Insulin resistance is mainly present in skeletal muscle in non-obese patients with myotonic dystrophy. Thiazolidinediones are reported to reduce insulin resistance in these patients. However, the effects of pioglitazone in overweight patients with myotonic dystrophy and type 2 diabetes mellitus have not been established. Here, we evaluated the effect of pioglitazone in two poorly-controlled over-weight diabetic patients with myotonic dystrophy. Case 1 was a 41- year-old women (BMI 27.8 kg/m(2)) with myotonic dystrophy and type 2 diabetes had been treated with 3 mg/day glimepiride and 500 mg/day metformin, but the treatment failed to achieve good glycemic control (HbA(1C) 11.8 %). Following admission to the hospital, she was treated with low-dose insulin and 30 mg/day pioglitazone. At 10 days after initiation of therapy, glycemic control was improved, serum IL-6 and hs-CRP decreased, and adiponectin level increased rapidly. Case 2 was a 47-year-old women (BMI 29.2 kg/m(2)) with myotonic dystrophy and type 2 diabetes mellitus had been treated with insulin without successful glycemic control (HbA(1C) 10.3 %). After admission, she was treated with 15 mg/day pioglitazone. This improved glycemic control, reduced daily insulin requirement, decreased IL-6 and hs-CRP levels rapidly and increased adiponectin level at 10 days after initiation of therapy. In both cases, pioglitazone rapidly improved glycemic control, enhanced adiponectin production, and reduced inflammatory cytokines. These results suggest that pioglitazone may be suitable for these patients.

A cross-sectional study for glucose intolerance of myotonic dystrophy

We made a cross-sectional study to analyze glucose intolerance of myotonic dystrophy type 1 (DM1) with several examination including oral glucose tolerance test (OGTT), insulin tolerance test (ITT) and adiponectin. Ninety-five DM1 patients participated in this study. Health examination data from general people were used as controls. In DM1, homeostasis model assessment-insulin resistance (HOMA-IR) was higher than control even in the lowest fasting blood sugar (FBS) stage (<80 mg/dl) and insulin sensitivity assessed by ITT was low regardless of their FBS. Insulinogenic index of DM1 was positively correlated to HOMA-IR. Insulinogenic index and sum of IRI in OGTT were markedly elevated in the lowest FBS stage and declined along with elevation of FBS. Consequently, as many as 13.3% of DM1 patients with 90-110 mg/dl of FBS exhibited DM pattern, while only 1.9% in control. Adiponectin was higher in DM1 than control. Although age correlated with adiponectin in both control and DM1, its impact was stronger in DM1. DM1 predisposes insulin resistance and compensatory hyperinsulinemia exist even in patients with low FBS. We should pay attention to glucose intolerance of DM1 patients earlier than that of the general population. It seemed that 90 mg/dl of FBS is an important index as an indication of careful managements.

New classification and treatment for myotonic disorders

Myotonia is repetitive firing of muscle action potentials causing prolonged muscle contractions even after mechanical stimulations to the muscles have ceased. Most common myotonic disorder is myotonic dystrophy which is now termed DM1, myotonic dystrophy type 1. In Japan, proximal myotonic myopathy, which is now called DM2 has not been reported. Both DM1 and DM2 have Cl channel abnormality which causes myotonia. Less commonly we encounter Thomsen's disease, and autosomal recessive generalized myotonia (Becker type) which also have a Cl channel abnormality. There are other myotonic disorders related to Na channelopathy which include three disorders: paramyotonia congenita, adynamia episodica hereditaria, and myotonia fluctuans. Myotonia has been treated by various Na channel blockers, mexiletine, phenytoin, and carbamazepine, but they were originally developed for cardiac arrhythmia, or seizure disorders and they have undesirable side effects, weakness. Comprehensive treatment includes myotonia control without reducing the strength, and care for systemic manifestations of DM1.