Sulfur oxidation of free methionine by oxygen free radicals

Sexually dimorphic effects of methionine sulfoxide reductase A (MsrA) on murine longevity and health span during methionine restriction

Methionine restriction (MR) extends lifespan in various model organisms, and understanding the molecular effectors of MR could expand the repertoire of tools targeting the aging process. Here, we address to what extent the biochemical pathway responsible for redox metabolism of methionine plays in regulating the effects of MR on lifespan and health span. Aerobic organisms have evolved methionine sulfoxide reductases to counter the oxidation of the thioether group contained in the essential amino acid methionine. Of these enzymes, methionine sulfoxide reductase A (MsrA) is ubiquitously expressed in mammalian tissues and has subcellular localization in both the cytosol and mitochondria. Loss of MsrA increases sensitivity to oxidative stress and has been associated with increased susceptibility to age-associated pathologies including metabolic dysfunction. We rationalized that limiting the available methionine with MR may place increased importance on methionine redox pathways, and that MsrA may be required to maintain available methionine for its critical uses in cellular homeostasis including protein synthesis, metabolism, and methylation. Using a genetic mutant mouse lacking MsrA, we tested the requirement for this enzyme in the effects of MR on longevity and markers of healthy aging late in life. When initiated in adulthood, we found that MR had minimal effects in males and females regardless of MsrA status. MR had minimal effect on lifespan with the exception of wild-type males where loss of MsrA slightly increased lifespan on MR. We also observed that MR drove an increase in body weight in wild-type mice only, but mice lacking MsrA tended to maintain more stable body weight throughout their lives. We also found that MR had greater benefit to males than females in terms of glucose metabolism and some functional health span assessments, but MsrA generally had minimal impact on these metrics. Frailty was also found to be unaffected by MR or MsrA in aged animals. We found that in general, MsrA was not required for the beneficial effects of MR on longevity and health span.

Protect from Light: Photodegradation and Protein Biologics

The exposure of proteins to light and the ensuing chemical and physical degradation has been studied extensively for many years. The residues in proteins that undergo primary photooxidation include tryptophan, tyrosine, phenylalanine, and cysteine/cystine. While photooxidation has been recognized as a major contributor to protein degradation, the effects of photoinduced damage have not been widely studied for biopharmaceuticals. This is particularly important since photodegradation can lead to changes in primary, secondary, and tertiary structures of protein and these changes, while not definitively established, could lead to differences in long-term stability, bioactivity, or immunogenicity. In this review we briefly describe the major pathways of photodegradation for proteins followed by a description of the limited data on photodegradation of biopharmaceuticals and methods that have been used to reduce or prevent damage. It is our intent to spur additional research in this area for increasing the safety and effectiveness of biopharmaceutical products.

Inactivation of ?1-Antiproteinase Induced by Phenylbutazone: Participation of Peroxyl Radicals and Hydroperoxide

To clarify the action of a side-effect of phenylbutazone, we investigated the inactivation of alpha(1)-antiproteinase induced by phenylbutazone in the presence of horseradish peroxidase (HRP) and H(2)O(2) (HRP-H(2)O(2)). The activity of alpha(1)-antiproteinase was rapidly lost during the interaction of phenylbutazone with HRP-H(2)O(2) under aerobic conditions. Phenylbutazone showed a marked spectral change under aerobic conditions but not under anaerobic conditions. Spin trap agents were very effective in inhibiting alpha(1)-antiproteinase inactivation induced by phenylbutazone. Oxidation of phenylbutazone was stopped by catalase, but the inactivation reaction of alpha(1)-antiproteinase proceeded even after removal of H(2)O(2) in the reaction mixture. Formation of the peroxidative product from phenylbutazone was detected by iodometric assay. These results indicate that both peroxyl radicals and the peroxidative product of phenylbutazone participated in the inactivation of alpha(1)-antiproteinase. Other anti-inflammatory drugs did not inactivate alpha(1)-antiproteinase during interaction with HRP-H(2)O(2). Inactivation of alpha(1)-antiproteinase may contribute to serious side effects of phenylbutazone.

Effect of cystathionine as a scavenger of superoxide generated from human leukocytes or derived from xanthine oxidase in vitro

We studied the direct effects of cystathionine on human leukocyte-generated or xanthine-xanthine oxidase-derived superoxide radicals in vitro. Washed leukocyte suspensions (10(6) cells/ml) prepared from healthy male volunteers were stimulated with phorbol myristate acetate (1 mu M) or opsonized zymosan (1 mg/ml) to generate superoxide radicals, which were measured with a 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-alpha] pyrazin-3-one hydrochloride (MCLA)-chemiluminescence method. Cystathionine (30 mu M to 10 mM) significantly reduced superoxide radical-dependent chemiluminescence in the leukocyte system in a concentration-dependent manner. In addition, in the two different methods of determination of superoxide radicals (MCLA chemiluminescence and nitroblue tetrazolium reduction), cystathionine significantly scavenged the superoxide radicals derived from the xanthine-xanthine oxidase system. However, cystathionine did not inhibit the activity of xanthine oxidase during superoxide generation. On the other hand, cystathionine did not show a scavenging effect against hydroxyl radicals derived from Fe2+ -H2O2 on the erythrocyte membrane. These results indicate that cystathionine itself may possess a scavenging function against superoxide radicals rather than against hydroxyl radicals in vitro.

Purification of rat liver glucokinase

A new purification method for rat liver glucokinase was developed. Glucokinase was purified to homogeneity in a yield of 70% in 5 days. The procedure consists of DEAE-cellulose ion-exchange chromatography, QAE-Toyopearl ion-exchange chromatography, glucosamine-Sepharose affinity chromatography, and HiLoad Superdex 200 gel filtration. Purified glucokinase had a specific activity of 200 units/mg protein and was highly stable in the presence of 100 mM glucose, 300 mM KCl, and 20% glycerol. We found that some of the methionine residues of glucokinase were oxidized to methionine sulfoxide residues during dialysis in the presence of glucose. It would appear that this oxidation is caused by formation of hydroxyl radicals in the presence of glucose and contaminating transition metal(s).

Determination of L-methionine-dl-sulphoxide in tissue extracts

The amino acid fraction from rat liver, heart and skeletal muscle was prepared by the separation of sulphosalicylic acid extract on Dowex 50 H+ form. The presence of L-methionine-dl-sulphoxide in these extracts was identified and compared by three independent chromatographic methods: ion-exchange, Pico-Tag and reversed-phase high-performance liquid chromatography after precolumn derivatisation with diethylethoxymethylenemalonate. Quantitative data indicate that L-methionine-dl-sulphoxide is present in the intracellular pool at the levels of free methionine.

Methionine oxidation and inactivation of alpha 1-proteinase inhibitor by Cu2+ and glucose

The effect of glucose/Cu2+ incubation on (a) pure methionine oxidation, (b) the oxidation of active-site methionine in alpha 1-proteinase inhibitor (alpha 1PI) and (c) the resulting activity and structural changes of this inhibitor was investigated. While no methionine was oxidized during a 24 day, 37 degrees C incubation with 0.01 M EDTA and 100 mM glucose, 64.2% oxidation occurred in 6 days when 0.01 mM Cu2+ was added to the 100 mM glucose. The first-order rate constant for oxidation in 10 mM glucose, 0.01 mM Cu2+ was 0.0218 day-1. Oxidation was inhibited by catalase, but accelerated by ascorbate ion. The active-site methionyl residue of alpha 1PI was oxidized 71.3% after a 4 day incubation in 100 mM glucose, 0.01 mM Cu2+ (pH 7.45), 0.1 M phosphate buffer. The elastase and trypsin inhibiting activities were lowered to 3.1 and 1.5% of control samples during this incubation. The inclusion of 1 mM DETAPAC, a transition metal chelator, resulted in a 98 + % retention of activity. Intrinsic fluorescence (350 nm excitation, 415 nm emission) of alpha 1PI increased 576% over control for the sample incubated in 100 mM glucose, 0.01 mM Cu2+ and SDS-PAGE revealed protein fragment molecular weights of 44.4 and 39.8 kDa. These studies suggest that both methionine oxidation and free radical induced fragmentation contribute to loss of alpha 1PI activity during glucose/Cu2+ incubations.