Statin therapy and the expression of genes that regulate calcium homeostasis and membrane repair in skeletal muscle

In skeletal muscle of patients with clinically diagnosed statin-associated myopathy, discrete signs of structural damage predominantly localize to the T-tubular region and are suggestive of a calcium leak. The impact of statins on skeletal muscle of non-myopathic patients is not known. We analyzed the expression of selected genes implicated in the molecular regulation of calcium and membrane repair, in lipid homeostasis, myocyte remodeling and mitochondrial function. Microscopic and gene expression analyses were performed using validated TaqMan custom arrays on skeletal muscle biopsies of 72 age-matched subjects who were receiving statin therapy (n = 38), who had discontinued therapy due to statin-associated myopathy (n = 14), and who had never undergone statin treatment (n = 20). In skeletal muscle, obtained from statin-treated, non-myopathic patients, statins caused extensive changes in the expression of genes of the calcium regulatory and the membrane repair machinery, whereas the expression of genes responsible for mitochondrial function or myocyte remodeling was unaffected. Discontinuation of treatment due to myopathic symptoms led to a normalization of gene expression levels, the genes encoding the ryanodine receptor 3, calpain 3, and dystrophin being the most notable exceptions. Hence, even in clinically asymptomatic (non-myopathic) patients, statin therapy leads to an upregulation in the expression of genes that are concerned with skeletal muscle regulation and membrane repair.

Effect of two beta-alanine dosing protocols on muscle carnosine synthesis and washout

Carnosine (β-alanyl-L-histidine) is found in high concentrations in skeletal muscle and chronic β-alanine (BA) supplementation can increase carnosine content. This placebo-controlled, double-blind study compared two different 8-week BA dosing regimens on the time course of muscle carnosine loading and 8-week washout, leading to a BA dose-response study with serial muscle carnosine assessments throughout. Thirty-one young males were randomized into three BA dosing groups: (1) high-low: 3.2 g BA/day for 4 weeks, followed by 1.6 g BA/day for 4 weeks; (2) low-low: 1.6 g BA/day for 8 weeks; and (3) placebo. Muscle carnosine in tibialis-anterior (TA) and gastrocnemius (GA) muscles was measured by 1H-MRS at weeks 0, 2, 4, 8, 12 and 16. Flushing symptoms and blood clinical chemistry were trivial in all three groups and there were no muscle carnosine changes in the placebo group. During the first 4 weeks, the increase for high-low (TA 2.04 mmol/kgww, GA 1.75 mmol/kgww) was ~twofold greater than low-low (TA 1.12 mmol/kgww, GA 0.80 mmol/kgww). 1.6 g BA/day significantly increased muscle carnosine within 2 weeks and induced continual rises in already augmented muscle carnosine stores (week 4-8, high-low regime). The dose-response showed a carnosine increase of 2.01 mmol/kgww per 100 g of consumed BA, which was only dependent upon the total accumulated BA consumed (within a daily intake range of 1.6-3.2 g BA/day). Washout rates were gradual (0.18 mmol/kgww and 0.43 mmol/kgww/week; ~2%/week). In summary, the absolute increase in muscle carnosine is only dependent upon the total BA consumed and is not dependent upon baseline muscle carnosine, the muscle type, or the daily amount of supplemented BA.

Optimizing human in vivo dosing and delivery of β-alanine supplements for muscle carnosine synthesis

Interest into the effects of carnosine on cellular metabolism is rapidly expanding. The first study to demonstrate in humans that chronic β-alanine (BA) supplementation (~3-6 g BA/day for ~4 weeks) can result in significantly augmented muscle carnosine concentrations (>50%) was only recently published. BA supplementation is potentially poised for application beyond the niche exercise and performance-enhancement field and into other more clinical populations. When examining all BA supplementation studies that directly measure muscle carnosine (n=8), there is a significant linear correlation between total grams of BA consumed (of daily intake ranges of 1.6-6.4 g BA/day) versus both the relative and absolute increases in muscle carnosine. Supporting this, a recent dose-response study demonstrated a large linear dependency (R2=0.921) based on the total grams of BA consumed over 8 weeks. The pre-supplementation baseline carnosine or individual subjects' body weight (from 65 to 90 kg) does not appear to impact on subsequent carnosine synthesis from BA consumption. Once muscle carnosine is augmented, the washout is very slow (~2%/week). Recently, a slow-release BA tablet supplement has been developed showing a smaller peak plasma BA concentration and delayed time to peak, with no difference in the area under the curve compared to pure BA in solution. Further, this slow-release profile resulted in a reduced urinary BA loss and improved retention, while at the same time, eliciting minimal paraesthesia symptoms. However, our complete understanding of optimizing in vivo delivery and dosing of BA is still in its infancy. Thus, this review will clarify our current knowledge of BA supplementation to augment muscle carnosine as well as highlight future research questions on the regulatory points of control for muscle carnosine synthesis.

Ischemic muscle necrosis leading to life-threatening hyperkalemia. Case report and review of the literature

Objective: Description of a cat with ischemic muscle necrosis that suffered from cardiopulmonary arrest due to hyperkalemia. Pathogenesis, clinical signs and therapy of ischemic muscle necrosis are discussed and possible causes, symptoms and treatment of hyperkalemia are shown. Material and methods: case report of a four-year-old male castrated domestic shorthair cat. Results: The cat was successfully resuscitated and hyperkalemia was treated with different treatment modalities. Conclusion: Ischemic muscle necrosis can lead to severe live-threatening hyperkalemia which has to be anticipated, monitored and treated adequately. Aggressive fluid therapy might be responsible for a higher risk of hyperkalemia in predisposed cases. Clinical relevance: Potassium concentrations and acid-base disturbances must be closely monitored in patients with ischemic muscle necrosis