Leveraging a Clinical Phase Ib Proof-of-Concept Study for the GPR40 Agonist MK-8666 in Patients With Type 2 Diabetes for Model-Informed Phase II Dose Selection.

GPR40 mediates free fatty acid-induced insulin secretion in beta cells. We investigated the safety, pharmacokinetics, and glucose response of MK-8666, a partial GPR40 agonist, after once-daily multiple dosing in type 2 diabetes patients. This double-blind, multisite, parallel-group study randomized 63 patients (placebo, n = 18; 50 mg, n = 9; 150 mg, n = 18; 500 mg, n = 18) for 14-day treatment. The results showed no serious adverse effects or treatment-related hypoglycemia. One patient (150-mg group) showed mild-to-moderate transaminitis at the end of dosing. Median MK-8666 Tmax was 2.0-2.5 h and mean apparent terminal half-life was 22-32 h. On Day 15, MK-8666 reduced fasting plasma glucose by 54.1 mg/dL (500 mg), 36.0 mg/dL (150 mg), and 30.8 mg/dL (50 mg) more than placebo, consistent with translational pharmacokinetic/pharmacodynamic model predictions. Maximal efficacy for longer-term assessment is projected at 500 mg based on exposure-response analysis. In conclusion, MK-8666 was generally well tolerated with robust glucose-lowering efficacy.

Could the mechanisms of bariatric surgery hold the key for novel therapies? report from a Pennington Scientific Symposium.

Bariatric surgery is the most effective method for promoting dramatic and durable weight loss in morbidly obese subjects. Furthermore, type 2 diabetes is resolved in over 80% of patients. The mechanisms behind the amelioration in metabolic abnormalities are largely unknown but may be due to changes in energy metabolism, gut peptides and food preference. The goal of this meeting was to review the latest research to better understand the mechanisms behind the 'magic' of bariatric surgery. Replication of these effects in a non-surgical manner remains one of the ultimate challenges for the treatment of obesity and diabetes. Promising data on energy metabolism, gastrointestinal physiology, hedonic response and food intake were reviewed and discussed.

Culture in low levels of oxygen enhances in vitro proliferation potential of satellite cells from old skeletal muscles.

The proliferation ability of satellite cells (considered the 'stem cells' of mature myofibers) declines with increasing age when cultured under standard cell culture conditions of 21% oxygen. However, actual oxygen levels in the intact myofiber in vivo are an order of magnitude lower. No studies to date have addressed the issue of whether culturing satellite cells from old muscles under more 'physiologic' conditions would enhance their proliferation and/or differentiation ability. Therefore, we analyzed satellite cells derived from 31-month-old rats in standard cultures with 21% O2 and in lowered (approximately 3%) O2. Under the lowered O2 conditions, we noted a remarkable increase in the percentage of large-sized colonies, activation of cell cycle progression factors, phosphorylation of Akt, and downregulation of the cell cycle inhibitor p27Kip1. These data suggest that lower O2 levels provide a milieu that stimulates proliferation by allowing continued cell cycle progression, to result ultimately in the enhanced in vitro replicative life span of the old satellite cells. Such a method therefore provides an improved means for the ex vivo generation of progenitor satellite cell populations for potential therapeutic stem cell transplantation.

Long-term insulin-like growth factor-I expression in skeletal muscles attenuates the enhanced in vitro proliferation ability of the resident satellite cells in transgenic mice.

Insulin-like growth factor-I (IGF-I) overexpression for 1-month in mouse skeletal muscle increases satellite cell proliferation potential. However, it is unknown whether this beneficial enhancement by IGF-I expression would persist over a longer-term duration in aged mice. This is an important issue to address if a prolonged course of IGF-I is to be used clinically in muscle-wasting conditions where satellite cells may become limiting. Using the IGF-I transgenic (IGF-I Tg) mouse that selectively expresses the IGF-I transgene in striated muscles, we found that 18-months of continuous IGF-I overexpression led to a loss in the enhanced in vitro proliferative capacity of satellite cells from Tg skeletal muscles. Also 18-month-old IGF-I Tg satellite cells lost the enhanced BrdU incorporation, greater pRb and Akt phosphorylations, and decreased p27(Kip1) levels initially observed in cells from 1-month-old IGF-I Tg mice. The levels of those biochemical markers reverted to similar values seen in the 18-months WT littermates. These findings, therefore, suggest that there is no further beneficial effect on enhancing satellite cell proliferation ability with persistent long-term expression of IGF-I in skeletal muscles of these transgenic mice.

The molecular responses of skeletal muscle satellite cells to continuous expression of IGF-1: implications for the rescue of induced muscular atrophy in aged rats.

Approximately 50% of humans older than 85 years have physical frailty due to weak skeletal muscles. This indicates a need for determining mechanisms to combat this problem. A critical cellular factor for postnatal muscle growth is a population of myogenic precursor cells called satellite cells. Given the complex process of sarcopenia, it has been postulated that, at some point in this process, a limited satellite cell proliferation potential could become rate-limiting to the regrowth of old muscles. It is conceivable that if satellite cell proliferative capacity can be maintained or enhanced with advanced age, sarcopenia could potentially be delayed or prevented. Therefore, the purposes of this paper are to describe whether IGF-I can prevent muscular atrophy induced by repeated cycles of hindlimb immobilization, increase the in vitro proliferation in satellite cells from these muscles and, if so, the molecular mechanisms by which IGF-I mediates this increased proliferation. Our results provide evidence that IGF-I can enhance aged muscle regrowth possibly through increased satellite cell proliferation. The results also suggest that IGF-I enhances satellite cell proliferation by decreasing the cell cycle inhibitor, p27Kip1, through the PI3'-K/Akt pathway. These data provide molecular evidence for IGF-I's rescue effect upon aging-associated skeletal muscle atrophy.

IGF-I restores satellite cell proliferative potential in immobilized old skeletal muscle.

One of the key factors responsible for the age-associated reduction in muscle mass may be that satellite cell proliferation potential (number of doublings contained within each cell) could become rate limiting to old muscle regrowth. No studies have tested whether repeated cycles of atrophy-regrowth in aged animals deplete the remaining capacity of satellite cells to replicate or what measures can be taken to prevent this from happening. We hypothesized that there would be a pronounced loss of satellite cell proliferative potential in gastrocnemius muscles of aged rats (25- to 30-mo-old FBN rats) subjected to three cycles of atrophy by hindlimb immobilization (plaster casts) with intervening recovery periods. Our results indicated that there was a significant loss in gastrocnemius muscle mass and in the proliferative potential of the resident satellite cells after just one bout of immobilization. Neither the muscle mass nor the satellite cell proliferation potential recovered from their atrophied values after either the first 3-wk or later 9-wk recovery period. Remarkably, application of insulin-like growth factor I onto the atrophied gastrocnemius muscle for an additional 2 wk after this 9-wk recovery period rescued approximately 46% of the lost muscle mass and dramatically increased proliferation potential of the satellite cells from this muscle.

Insulin-like growth factor-I extends in vitro replicative life span of skeletal muscle satellite cells by enhancing G1/S cell cycle progression via the activation of phosphatidylinositol 3'-kinase/Akt signaling pathway.

Interest is growing in methods to extend replicative life span of non-immortalized stem cells. Using the insulin-like growth factor I (IGF-I) transgenic mouse in which the IGF-I transgene is expressed during skeletal muscle development and maturation prior to isolation and during culture of satellite cells (the myogenic stem cells of mature skeletal muscle fibers) as a model system, we elucidated the underlying molecular mechanisms of IGF-I-mediated enhancement of proliferative potential of these cells. Satellite cells from IGF-I transgenic muscles achieved at least five additional population doublings above the maximum that was attained by wild type satellite cells. This IGF-I-induced increase in proliferative potential was mediated via activation of the phosphatidylinositol 3'-kinase/Akt pathway, independent of mitogen-activated protein kinase activity, facilitating G(1)/S cell cycle progression via a down-regulation of p27(Kip1). Adenovirally mediated ectopic overexpression of p27(Kip1) in exponentially growing IGF-I transgenic satellite cells reversed the increase in cyclin E-cdk2 kinase activity, pRb phosphorylation, and cyclin A protein abundance, thereby implicating an important role for p27(Kip1) in promoting satellite cell senescence. These observations provide a more complete dissection of molecular events by which increased local expression of a growth factor in mature skeletal muscle fibers extends replicative life span of primary stem cells than previously known.