N-acyl dehydroalanines scavenge oxygen radicals and inhibit in vitro free radical mediated processes

A comparison of reversible versus irreversible protein glutathionylation

Glutathionylation is generally a reversible posttranslational modification that occurs to cysteine residues that have been exposed to reactive oxygen species (P-SSG). This cyclical process can regulate various clusters of proteins, including those involved in critical cellular signaling functions. However, certain conditions can favor the formation of dehydroamino acids, such as 2,3-didehydroalanine (2,3-dehydroalanine, DHA) and 2,3-didehydrobutyrine (2,3-dehydrobutyrine), which can act as Michael acceptors. In turn, these can form Michael adducts with glutathione (GSH), resulting in the formation of a stable thioether conjugate, an irreversible process referred to as nonreducible glutathionylation. This is predicted to be prevalent in nature, particularly in more slowly turning over proteins. Such nonreducible glutathionylation can be distinguished from the more facile cycling signaling processes and is predicted to be of gerontological, toxicological, pharmacological, and oncological relevance. Here, we compare reversible and irreversible glutathionylation.

NovelN-acyl dehydroalanine derivatives as antioxidants: Studies on rat liver lipid peroxidation levels and DPPH free radical scavenging activity

Oxidative stress has been implicated in the development of many neurodegenerative diseases such as Parkinson and Alzhemier's disease and is also responsible for aging, artherosclerosis, rheumatoid arthritis and carcinogenesis. Olefins such as dehydroalanines have been shown to inactivate free radicals by forming stabilized free radical adducts. Among these molecules N-acyl dehydroalanines react with and scavenge oxygen and hydroxyl radicals. This study describes the synthesis, characterization and in vitro effects on rat liver lipid peroxidation levels, and DPPH free radical scavenging activities of some N-acyl dehydroalanine derivatives. Compounds c, f and j slightly scavenged the level of DPPH radical at 10(-3) M concentration by about 27, 46, and 56%, respectively while compounds a, d, e, f, g, h showed a strong inhibitory effect on lipid peroxidation at 10(-3)M and 10(-4)M concentrations and inhibition was in the range of 76-90%. The possible antioxidant mechanism of the compounds was discussed.

Dehydroalanine derived from cysteine is a common post-translational modification in human serum albumin

The conversion of a cysteine residue into dehydroalanine (DHA) in proteins was previously described. This post-translational modification (PTM) can be generated artificially as a result of heat and an alkaline environment. The presence of this PTM on human serum albumin (HSA) in plasma collected from healthy volunteers and critically ill patients as well as in commercially available HSA was studied. Using liquid chromatography/mass spectrometry (LC/MS) and matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) methods, a fragment containing DHA was identified in the trypsin digest of commercial HSA and isolated HSA from plasma. The sequence (RPC*FSALEVDETYVPK) corresponded to the expected molecular mass and fragmentation pattern of a tryptic peptide of HSA where the cysteine residue (cys487) was modified to DHA. The presence of this common PTM of HSA has potential effects on ligand binding to HSA, plasma clearance of this oxidized form of HSA, protein-protein interactions, and oxidation-reduction potential.

Identification of the free radical formed by addition of hydroxyl radical to dehydroalanine compounds

N-substituted dehydroalanines, a class of compounds with both acceptor and donor substituents (ADs), react with and scavenge oxygen radicals. Interest in these compounds is based on their potential to lessen the cardiotoxicity of drugs with antineoplastic activity such as Adriamycin. The reactivity of these compounds with hydroxyl radical is evident from their inhibition of hydroxyl radical adduct formation. ESR spin trapping studies of the species formed by reaction of the AD series of compounds with the hydroxyl radical are reported here for the first time. ESR results show that hydroxyl radical attack on the capto-dative site of the AD compounds produces the predicted carbon-centered free radical.

Effects of N-acyl dehydroalanines on phorbol ester-elicited tumor development and other events in mouse skin

The free radical scavengers N-acyl dehydroalanines (AD compounds) were examined for their effect on several 12-O-tetradecanoylphorbol-13-acetate (TPA) elicited events in mouse skin. The induction of oxidant production by TPA in isolated mouse epidermal cells was reduced by approximately 70% by 1 mM paramethoxyphenyl-acetyl dehydroalanine (AD5) and 80% by 1 mM parasulfoxyphenyl-acetyl dehydroalanine (AD19). These AD compounds also completely suppressed the TPA-dependent stimulation of prostaglandin E2 synthesis in primary cultures of epidermal cells. Single and multiple topical applications on the dorsal skin of SENCAR mice of either AD5 or AD 19 inhibited TPA-induced epidermal hyperplasia but failed to inhibit epidermal ornithine decarboxylase induction. When used with TPA on initiated mice, AD19 did not inhibit papilloma formation; however, after 40 weeks of promotion, the carcinoma incidence was reduced by 50% in the AD19 group. These results suggest that reactive oxygens may be more important to the conversion of benign to malignant tumors than in the initial development of the benign tumors.

Increase in the survival time of mice exposed to ionizing radiation by a new class of free radical scavengers

N-acyl dehydroalanines react with and scavenge mainly superoxide radical (O-2.) and hydroxyl radical (HO.). The ortho-methoxyphenylacetyl dehydroalanine derivative, indexed as AD-20, protects mice against damage resulting from total body X-irradiation, as measured by the increase in their survival time. AD-20 increases the LD50 at 30 days from 6.1 to 7.3 Gy in animals exposed to a wide range of X-rays (6 to 10 Gy). The dose reduction factor (D R F) of AD-20 is 1.20. We postulate that such radioprotective effect may result from its free radical scavenging activity.