Creatine is an endogenous compound synthesized from arginine, glycine and methionine. This dietary supplement can be acquired from food sources such as meat and fish, along with athlete supplement powders. Since the majority of creatine is stored in skeletal muscle, dietary creatine supplementation has traditionally been important for athletes and bodybuilders to increase the power, strength, and mass of the skeletal muscle. However, new uses for creatine have emerged suggesting that it may be important in preventing or delaying the onset of neurodegenerative diseases associated with aging. On average, 30% of muscle mass is lost by age 80, while muscular weakness remains a vital cause for loss of independence in the elderly population. In light of these new roles of creatine, the dietary supplement’s usage has been studied to determine its efficacy in treating congestive heart failure, gyrate atrophy, insulin insensitivity, cancer, and high cholesterol. In relation to the brain, creatine has been shown to have antioxidant properties, reduce mental fatigue, protect the brain from neurotoxicity, and improve facets/components of neurological disorders like depression and bipolar disorder. The combination of these benefits has made creatine a leading candidate in the fight against age-related diseases, such as Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, long-term memory impairments associated with the progression of Alzheimer’s disease, and stroke. In this review, we explore the normal mechanisms by which creatine is produced and its necessary physiology, while paying special attention to the importance of creatine supplementation in improving diseases and disorders associated with brain aging and outlining the clinical trials involving creatine to treat these diseases.

Acid-sensing ion channels (ASICs) evolved to sense changes in extracellular acidity with the divalent cation calcium (Ca2+) as an allosteric modulator and channel blocker. The channel-blocking activity is most apparent in ASIC3, as removing Ca2+ results in channel opening, with the site’s location remaining unresolved. Here we show that a ring of rat ASIC3 (rASIC3) glutamates (Glu435), located above the channel gate, modulates proton sensitivity and contributes to the formation of the elusive Ca2+ block site. Mutation of this residue to glycine, the equivalent residue in chicken ASIC1, diminished the rASIC3 Ca2+ block effect. Atomistic molecular dynamic simulations corroborate the involvement of this acidic residue in forming a high-affinity Ca2+ site atop the channel pore. Furthermore, the reported observations provide clarity for past controversies regarding ASIC channel gating. Our findings enhance understanding of ASIC gating mechanisms and provide structural and energetic insights into this unique calcium-binding site.

The human voltage-gated proton channel (Hv1) is a membrane protein consisting of four transmembrane domains and intracellular amino-and carboxy-termini. The protein is activated by membrane depolarization, similar to other voltage-sensitive proteins. However, the Hv1 proton channel lacks a traditional ion pore. The human Hv1 proton channel has been implicated in mediating sperm capacitance, stroke, and most recently as a biomarker/mediator of cancer metastasis. Recently, the three-dimensional structures for homologues of this voltage-gated proton channel were reported. However, it is not clear what artificial environment is needed to facilitate the isolation and purification of the human Hv1 proton channel for structural study. In the present study, we generated a chimeric protein that placed an enhanced green fluorescent protein (EGFP) to the amino-terminus of the human Hv1 proton channel (termed EGFP-Hv1). The chimeric protein was expressed in a baculovirus expression system using Sf9 cells and subjected to detergent screening using fluorescence-detection size-exclusion chromatography. The EGFP-Hv1 proton channel can be solubilized in the zwitterionic detergent Anzergent 3-12 and the nonionic n-dodecyl-b-D-maltoside (DDM) with little protein aggregation and a prominent monomeric protein peak at 48 h postinfection. Furthermore, we demonstrate that the chimeric protein exhibits a monomeric protein peak, Published by Wiley-Blackwell. V C 2014 The Protein Society which is distinguishable from protein aggregates, at the final size-exclusion chromatography purification step. Taken together, we can conclude that solubilization in DDM will provide a useable final product for further structural characterization of the full-length human Hv1 proton channel.

Acid-sensing ion channels (ASICs) are proton-sensitive sodium channels that open in response to lowered extracellular pH and are expressed in the central and peripheral nervous systems. The ASIC3 subtype is found primarily in the periphery where the channel mediates pain signals caused by ischemia and inflammation. Here, we provide identify 4-chlorophenylguanidine (4-CPG) as an ASIC3 positive allosteric modulator and newest member of the growing group of guanidine modulators of ASICs. Furthermore, the 4-CPG reversed the effects of ASIC3 desensitization. The molecule 4-CPG offers a novel chemical backbone for the design of new ASIC3 ligands to study ASIC3 in vivo.

Acid‐sensing ion channels are sodium selective channels that are sensitive to extracellular protons, specifically those following ischemia and injury. The peripheral ASIC3 subtype plays an important role in pain perception. Protons and inflammatory mediators can activate or modulate ASIC3 to produce the pain signal, suggesting that ASIC3 is a pharmacological target for pain therapy. The large extracellular domain of ASICs offers multiple sites for interacting with protons and guanidinium group containing compounds. Guanidinium compounds such as 2‐guanidine‐4‐methylquinazoline (GMQ), amiloride, and agmatine are known to modulate the electrophysiological properties of ASIC3. Here we identified a dietary supplement (DS) that shares molecular similarity to these ASIC ligands and modulate ASICs. We utilize whole‐cell patch‐clamp electrophysiology recording to determine the interaction of DS with rat ASIC3 (rASIC3), transiently expressed in CHO‐K1 cells. Our preliminary data suggests that ASIC3 peak current amplitude and steady‐state current is reduced in the presence of DS. In the absence of extracellular calcium, DS reduces the rASIC3 proton sensitivity by shifting pH‐activation profile to lower pH. Future studies will focus on determining the effect of DS on the ASIC3 window current and other ASIC3 properties to resolve the mechanism of action of the DS influence on channel activity.