Although side effects as paresthesia
Although side effects as paresthesia due to the application of β-alanine are known, a study in 2006 pointed out that there are no clinical (biochemical or hematological) changes after a long-term supplementation with β-alanine. In 2015, the International Society of Sports Nutrition rejected any arguments for an inappropriate effect on health. Thus, as a nontoxic endogenous amino acid, it might open new possibilities in the treatment or prevention of mesenteric ischemia injury even in the clinic because β-alanine has a plasma half-life of about 25 min in regard to glycine that has a half-life of only 5 min in blood.18, 34
Introduction Trifluoroacetic IGF-1, human recombinant synthesis is widely used in organic chemistry, particularly in peptide synthesis, where it functions as an ion-pairing agent during the HPLC purification step of peptide synthesis. The addition of trifluoroacetic acid increases the hydrophobicities of peptides by forming ionic pairs with their charged groups, favoring interactions between peptides and a hydrophobic stationary phase, thus enabling separation (García, 2005). It binds to the free amino termini of peptides as well as the side chains of positively charged lysine, histidine and arginine residues (Cornish et al., 1999), forming trifluoroacetate (TFA) salts. This ion pairing is extremely strong and requires an additional ion replacement step during purification to remove TFA from the purified peptides. Thus, HPLC-purified peptides are often prepared and used as TFA salts, resulting in purified peptides with varying levels of TFA contamination. Trifluoroacetic acid is also a major metabolite of the volatile anesthetics halothane, isoflurane and desflurane (Cohen, 1971, Hitt et al., 1974). It is thought to be responsible for the development of halothane-induced hepatitis and neurotoxicity (Gut et al., 1995, Ma et al., 1990) and may play a role in the cardioprotective effects of isofluorane (Han et al., 2001). A large number of protein targets of inhaled anesthetics have been identified, among them members of the cys-loop receptor family such as the glycine (GlyR) and γ-aminobutyric acid (GABAA-R) receptors (Franks, 2006). Both the GlyR (Harrison et al., 1993, Mascia et al., 1996) and GABAA-R (Wakamori et al., 1991, Nishikawa et al., 2002) are sensitive to clinically-relevant concentrations of a wide variety of volatile anesthetics that are hypothesized to interact with these receptors at defined molecular sites (Mascia et al., 2000). However, whether a metabolite of some of these anesthetics could also affect the functioning of these cys-loop receptors, and possibly contribute to anesthetic actions, has thus far not been investigated. Based on multiple published reports of inhaled anesthetic modulation of ion channels and our previous work that identified novel peptides that act as allosteric modulators at the GlyR (Tipps et al., 2010), we tested TFA for its effects on the functioning of several cys-loop receptors. We found that TFA reversibly modulates GlyR responses and that these modulatory effects do not extend to other members of the cys-loop receptor family. These results are relevant to the development and testing of future peptide-based drugs, as well as highlighting possible secondary central nervous system effects following the administration and metabolism of some inhaled anesthetics.
Materials and methods
Discussion Our findings demonstrate that TFA, a common contaminant in synthesized peptides and a major metabolite of halothane, isofluorane and desflurane, acts to enhance GlyR function. TFA enhancement of the effects of low concentrations of glycine was reversible, and no TFA effect was seen when it was co-applied with a maximally-effective glycine concentration, suggesting that it acts as a transient allosteric modulator. These effects are similar to those seen when ethanol or inhaled anesthetics enhance GlyR function. The lack of a TFA effect at a saturating glycine concentration indicates that TFA is not exerting its effects by increasing channel conductance. This leaves the possibility that TFA increases channel mean open times, decreases closed channel lifetimes or increases burst durations, similar to ethanol (Welsh et al., 2009), but differentiating among these possibilities will require obtaining single channel recordings.