HPLC and LC-MS studies of hydroxylation of phenylalanine as an assay for hydroxyl radicals generated from Udenfriend's reagent

Biomimetic synthesis of hydroxytyrosol from conversion of tyrosol by mimicking tyrosine hydroxylase

Hydroxytyrosol, one of the most powerful natural antioxidants, exhibits certificated benefits for human health. In this study, a biomimetic approach to synthesize hydroxytyrosol from the hydroxylation of tyrosol was established. EDTA-Fe²⁺ coordination complex served as an active center to simulate tyrosine hydroxylase. H₂O₂ and ascorbic acid were used as oxygen donor and hydrogen donor, respectively. Hydroxy radical and singlet oxygen contributed to active species. The biomimetic system displayed analogous component, structure, and activity with TyrH. Hydroxytyrosol titer of 21.59 mM, and productivity of 9985.92 mg·L^-1·h^-1 was achieved with 100 mM tyrosol as substrate. The proposed approach provided efficient and convenient route to quickly produce high amount of hydroxytyrosol.

Bioactive and health-promoting properties of enzymatic hydrolysates of legume proteins: a review

This study comprehensively reviewed the effect of controlled enzymatic hydrolysis on the bioactivity of pulse protein hydrolysates (PPHs). Proteolysis results in the partial structural unfolding of pulse proteins with an increase in buried hydrophobic groups of peptide sequences. The use of PPHs in a dose-dependent manner can enhance free radical scavenging and improve antioxidant activities regarding inhibition of lipid oxidation, ferric reducing power, metal ion chelation, and β-carotene bleaching inhibition. Ultrafiltered peptide fractions with low molecular weights imparted angiotensin-I converting enzyme (ACE) inhibitory effects during in vitro simulated gastrointestinal digestion and in vivo conditions. Ultrasonication, high-pressure pretreatments, and glycosylation as post-treatments can improve the antiradical, antioxidant, and ACE inhibitory activities of PPHs. The electrostatic attachment of pulse peptides to microbial cells can inhibit the growth and activity of bacteria and fungi. Bioactive pulse peptides can reduce serum cholesterol and triglycerides, and inhibit the formation of adipocyte lipid storage, allergenic factors, inflammatory markers, and arterial thrombus without cytotoxicity. The combination of germination and enzymatic hydrolysis can significantly increase the protein digestibility and bioavailability of essential amino acids. Moreover, the utilization and enrichment of bakery and meat products with functional PPHs ensure quality, safety, and health aspects of food products.

The Intestinal and Biliary Metabolites of Ibuprofen in the Rat with Experimental Hyperglycemia

Hyperglycemia is reported to be associated with oxidative stress. It can result in changes in the activities of drug-metabolizing enzymes and membrane-integrated transporters, which can modify the fate of drugs and other xenobiotics; furthermore, it can result in the formation of non-enzyme catalyzed oxidative metabolites. The present work aimed to investigate how experimental hyperglycemia affects the intestinal and biliary appearance of the oxidative and Phase II metabolites of ibuprofen in rats. In vivo studies were performed by luminal perfusion of 250 μM racemic ibuprofen solution in control and streptozotocin-treated (hyperglycemic) rats. Analysis of the collected intestinal perfusate and bile samples was performed by HPLC-UV and HPLC-MS. No oxidative metabolites could be detected in the perfusate samples. The biliary appearance of ibuprofen, 2-hydroxyibuprofen, ibuprofen glucuronide, hydroxylated ibuprofen glucuronide, and ibuprofen taurate was depressed in the hyperglycemic animals. However, no specific non-enzymatic (hydroxyl radical initiated) hydroxylation product could be detected. Instead, the depression of biliary excretion of ibuprofen and ibuprofen metabolites turned out to be the indicative marker of hyperglycemia. The observed changes impact the pharmacokinetics of drugs administered in hyperglycemic individuals.

Effect of Packaging Materials and the Leached Iron on the Stability of Butorphanol Tartrate Injection

The aim of this study was to investigate the effect of various parameters on the stability of butorphanol tartrate injection and to screen the optimal packaging material. The effect of the headspace oxygen levels, ampoule color, manufacturer, and size on the stability of butorphanol tartrate formulation were evaluated. The headspace oxygen levels controlled by nitrogen purging were found to be particularly effective in improving stability of the butorphanol formulation, especially below 2%. Although it is a photolabile drug, butorphanol tartrate was getting degraded at much higher extent in amber color ampoules in comparison to clear ampoules. The degradation by oxidation was found to be a free radical-mediated process catalyzed by the presence of iron ions leached from the amber ampoules. The ampoule manufacturers also had a significant effect on the stability of butorphanol. Two-milliliter ampoules provided a better stability of the butorphanol tartrate injection than 1mL ampoules as 2-mL ampoules had the lower headspace oxygen level at the same level of oxygen content. The oxidation mechanism of the butorphanol tartrate injection was investigated under various conditions, which include iron powder spiking, removal of excipients, exposure to oxygen/nitrogen, exposure to stainless steel and at different pH. Iron powder spiking, presence of citric acid, exposure to oxygen, exposure to stainless steel, and high pH accelerated the oxidative degradation. The effect of oxygen, iron ion and citric acid is in agreement with a metal-catalyzed oxidation mechanism called Udenfriend reaction. Based on the formulation test results, limiting headspace oxygen level, ampoule color, manufacturer, size, controlling iron ion contamination, and pH are recommended for formulation development. In conclusion, it can be suggested that this study can lead to a better understanding of the degradation mechanism of butorphanol tartrate; hence, it would contribute to the development of butorphanol tartrate injection with improved stability. Virous packaging materials have different effects on the stability of butorphanol tartrate injection, and the leached iron of packaging ampoules and stainless steel can trigger Udenfriend reaction with butorphanol tartrate and citric acid (CA), which lead to the oxydative degradation of butorphanol tartrate injection.

Silk Hydrogels with Controllable Formation of Dityrosine, 3,4-Dihydroxyphenylalanine, and 3,4-Dihydroxyphenylalanine-Fe3+ Complexes through Chitosan Particle-Assisted Fenton Reactions

The oxidation of tyrosine residues of silk fibroin involves the generation of dityrosine and 3,4-dihydroxyphenylalanine (DOPA). However, it remains a challenge to selectively control the reaction pathway to produce dityrosine or DOPA in a selective fashion. Here, silk hydrogels with controllable formation of not only dityrosine and DOPA but also DOPA-Fe3+ complexes within the cross-linked networks were developed. The use of chitosan particles in the Fenton reaction allowed the interaction of Fe3+ ions with silk fibroin to be limited through the adsorption of Fe3+ ions onto chitosan particles by manipulating contact time between the reaction medium and chitosan particles. This led to significant suppression of the premature formation of β-sheet structures that cause steric hindrance to the collisions between tyrosyl radicals and thus enabled higher selectivity toward the formation of dityrosine than DOPA. Remarkably, the addition of ethylenediaminetetraacetic acid (EDTA) to the chitosan particle-assisted Fenton reactions resulted in hydrogels that significantly favored the formation of DOPA over dityrosine due to the increase in the hydroxylation of phenol in the presence of EDTA. Despite the existence of Fe3+-EDTA complexes, Raman spectra indicated the DOPA-Fe3+ complexation in the hydrogels. Mechanistically, the hydrogel networks with small-sized and uniformly distributed β-sheet structures as well as the abundance of DOPA appear to make non-EDTA-chelated Fe3+ ions more accessible to complexation with DOPA. These findings have important implications for understanding the oxidation of tyrosine residues of silk fibroin by metal-catalyzed oxidation systems with potential benefits for future studies on silk protein-based hydrogels capable of generating intrinsic adhesive features as well as for exploring dual-cross-linked silk hydrogels constructed by chemical cross-linking and metal-coordinate complexation.

Thermoase-hydrolysed pigeon pea protein and its membrane fractions possess in vitro bioactive properties (antioxidative, antihypertensive, and antidiabetic)

Enzymatic hydrolysis can liberate bioactive peptides from protein materials, thus, pigeon pea was hydrolysed using thermoase. Crude hydrolysate (PPHT) was subjected to ultrafiltration using different molecular weight cutoffs to collect <1, 1-3, 3-5, 5-10, and >10 kDa peptide fractions. Fractions were analysed for in vitro antioxidative, antihypertensive, and antidiabetic properties. The peptide fractions had stronger DPPH^• scavenging and renin inhibition when compared to PPHT. In contrast, ACE inhibition was stronger for the PPHT and <1 kDa peptide fraction while activity decreased as peptide size increased. The <1 kDa peptide also showed significantly stronger ferric reducing antioxidant power, OH^• scavenging and inhibition of linoleic acid oxidation when compared to PPHT. α-amylase and α-glucosidase were inhibited by all the peptide fractions, though the 3-5 and >10 kDa had higher values. We conclude that the PPHT and peptide fractions could serve as potential ingredients to formulate antihypertensive and antidiabetic functional foods and nutraceuticals. PRACTICAL APPLICATIONS: Oxidative stress promotes the generation of free radicals, which have a significant impact in the pathogenesis of human chronic diseases such as cardiovascular impairment, cancer, and diabetes. Peptides generated from enzymatic hydrolysis of proteins have been identified to impart beneficial health effects. In this work, we showed that a thermoase digest of pigeon pea protein as well as the fractionated peptides had strong antioxidant properties in addition to exhibiting inhibitory activities against renin and angiotensin converting enzyme, the main therapeutic targets for antihypertensive agents. The peptide products also inhibited α-amylase and α-glucosidase activities, providing potential ingredients that can be used to formulate antidiabetic functional foods.

Anti-Helicobacter pylori and Anti-Inflammatory Effects and Constituent Analysis of Modified Xiaochaihutang for the Treatment of Chronic Gastritis and Gastric Ulcer

Chronic gastritis and gastric ulcers are prevalent throughout the world and are considered to be a global health problem. Modified Xiaochaihutang (MXCHT) prescription is broadly used in traditional medicine hospital for the treatment of gastritis. In order to assess the anti-Helicobacter pylori (H. pylori) effect of MXCHT, agar diffusion method in vitro and fluid dilution method for the minimal inhibitory concentration (MIC) were established. The anti-inflammatory effects were then evaluated using mouse ear edema model and rat paw edema model. The ethanol-induced gastric ulcer method was employed to verify the gastroprotective effect of active extracts in MXCHT. HPLC-TOF-MS/MS was used for analyzing the possible active constituents after oral administration of effective extracts in ethanol-induced gastric ulcer models. MXCHT and 4 different extracts of the bacterial inhibition diameter and MIC were dramatically decreased compared with control group, showing anti-Helicobacter pylori effects. High dose groups of MXCHT, water extract, EtOAc extract, and n-BuOH extract displayed significant anti-inflammatory effects in xylene-induced mouse ear edema model and carrageenan-induced rat paw edema model test. MXCHT and all active extracts exhibited gastroprotective activity and prevented gastric lesions induced by ethanol in rats. 4 prototype components and 4 metabolites were identified after oral administration of EtOAc extract. In addition, 6 prototype components and 6 metabolites were identified in n-BuOH extract. MXCHT, EtOAc extract, and n-BuOH extract demonstrate gastroprotective effects through anti-Helicobacter pylori and anti-inflammatory activities. Thus, this prescription may be a suitable natural source for the prevention and treatment of chronic gastritis and gastric ulcers.

Oxidation of Hydroxy- and Dihydroxybenzoic Acids Under the Udenfriend's Conditions. An HPLC Study

Background:

Non-enzymatic hydroxylation of aromatic compounds to the respective phenolic derivatives is a possible metabolic pathway of xenobiotics. The formed metabolites can undergo consecutive oxidative reactions with free radicals to form potential toxic molecules.

Objective:

Development of HPLC methods to separate, identify and quantitate the main products formed from salicylic acid, 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid under in vitro hydroxylation conditions (Udenfriend's system).

Method:

An RP-HPLC-UV-Vis method was developed to separate salicylic acid and isomeric dihydroxybenzoic acids formed in the Udenfriend's system. Confirmation of structures of the oxidized products of salicylic acid, 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid was performed by HPLC-ESI-MS/MS method.

Results:

The HPLC-UV-Vis method was evaluated for a number of validation characteristics (selectivity, repeatability and intermediate precision, LOD, LOQ and calibration range). It was found that oxidation of salicylic acid resulted in the formation of 2,3- and 2,5-dihydroxybenzoic acids. Furthermore, the hydroxylated metabolites can be further metabolized under the Udenfriend’s conditions.

Conclusion:

The results give evidence for possible involvement of the oxidized metabolites of salicylic acid in the development of biological action of salicylates at the site of inflammation, where high hydroxyl radical level can be detected.

Amino acid composition, antioxidant and functional properties of protein hydrolysates from Cucurbitaceae seeds

In this study, the effect of enzymatic hydrolysis of globulin fraction of C. moschata (CMH), C. lanatus (CLH) and L. siceraria (LSH) on antioxidant capacity, functional properties, structural and micro-structural properties, as well as amino acid compositions were evaluated. All the hydrolysates exhibited significant antioxidant properties. The essential amino acids content in LSH (92.7 mg/g) was higher than CMH (79.9 mg/g) and CLH (70.5 mg/g). Water absorption capacity (5 g/g), heat stability (89%), emulsifying activity index (98.3 m2/g) and emulsifying stability index (45.1 min) were statistically more significant for LSH as compared to CMH and CLH. In addition, LSH had significantly higher FS and FC at pH 3-9. Among all hydrolysates, LSH showed highest solubility (87.3%) as compared to other hydrolysates. The results suggested that enzymatic hydrolysis improve the antioxidant and functional properties. Thus, the globulin hydrolysates might be served as an innovative source with promising nutritive values, good antioxidant and functional properties. Moreover, these could be used in food and pharmaceutical industries for the development of novel functional foods.

Roles of the tyrosine isomers meta-tyrosine and ortho-tyrosine in oxidative stress

The damage to cellular components by reactive oxygen species, termed oxidative stress, both increases with age and likely contributes to age-related diseases including Alzheimer's disease, atherosclerosis, diabetes, and cataract formation. In the setting of oxidative stress, hydroxyl radicals can oxidize the benzyl ring of the amino acid phenylalanine, which then produces the abnormal tyrosine isomers meta-tyrosine or ortho-tyrosine. While elevations in m-tyrosine and o-tyrosine concentrations have been used as a biological marker of oxidative stress, there is emerging evidence from bacterial, plant, and mammalian studies demonstrating that these isomers, particularly m-tyrosine, directly produce adverse effects to cells and tissues. These new findings suggest that the abnormal tyrosine isomers could in fact represent mediators of the effects of oxidative stress. Consequently the accumulation of m- and o-tyrosine may disrupt cellular homeostasis and contribute to disease pathogenesis, and as result, effective defenses against oxidative stress can encompass not only the elimination of reactive oxygen species but also the metabolism and ultimately the removal of the abnormal tyrosine isomers from the cellular amino acid pool. Future research in this area is needed to clarify the biologic mechanisms by which the tyrosine isomers damage cells and disrupt the function of tissues and organs and to identify the metabolic pathways involved in removing the accumulated isomers after exposure to oxidative stress.

Xiaochaihutang prevents depressive-like behaviour in rodents by enhancing the serotonergic system

Objectives

Xiaochaihutang (XCHT) has been used in China for thousands of years to treat ‘Shaoyang syndrome’, which involves depressive-like symptoms. However, no studies were conducted to demonstrate its antidepressant effect and mechanism. This study was designed to confirm the antidepressant effect of XCHT and explore its mechanism using the pharmacological methods.

Methods

Ultra-HPLC and mass spectrometry was used to identify the chemical constituents of XCHT. Forced swimming test (FST) and tail suspension test (TST) were used to determine the antidepressant-like activity of XCHT in mice and rats. The possible mechanism of XCHT was elucidated by the reserpine-induced hypothermia and 5-hydroxytryptophan (5-HTP)-induced head-twitch in mice. The levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured in prefrontal cortex and hippocampus tissue of both mice and rats. Moreover, the extracellular 5-HT in rat hippocampus was assessed by using microdialysis coupled to HPLC with electrochemical detection.

Key findings

Forty-four components were detected in XCHT. XCHT significantly reduced immobility time in the TST and the FST, antagonized reserpine-induced depressive-like behaviours, increased 5-HTP-induced head-twitches, elevated 5-HT and 5-HIAA levels, and increased 5-HT turnover at doses that did not affect general activity.

Conclusions

These data demonstrate that XCHT has therapeutic effects in animal models of depression by enhancing the serotoninergic system in the prefrontal cortex and hippocampus.

Amino acid composition and antioxidant properties of pea seed ( Pisum sativum L.) enzymatic protein hydrolysate fractions

The amino acid composition and antioxidant activities of peptide fractions obtained from HPLC separation of a pea protein hydrolysate (PPH) were studied. Thermolysin hydrolysis of pea protein isolate and ultrafiltration (3 kDa molecular weight cutoff membrane) yielded a PPH that was separated into five fractions (F1-F5) on a C(18) reverse phase HPLC column. The fractions that eluted later from the column (F3-F5) contained higher contents hydrophobic and aromatic amino acids when compared to fractions that eluted early or the original PPH. Fractions F3-F5 also exhibited the strongest radical scavenging and metal chelating activities; however, hydrophobic character did not seem to contribute to reducing power of the peptides. In comparison to glutathione, the peptide fractions had significantly higher (p < 0.05) ability to inhibit linoleic acid oxidation and chelate metals. In contrast, glutathione had significantly higher (p < 0.05) free radical scavenging properties than the peptide fractions.

Analysis of hydroxylation and nitration products of D-phenylalanine for in vitro and in vivo radical determination using high-performance liquid chromatography and photodiode array detection

D-phenylalanine is capable of trapping reactive oxygen species (ROS) and reactive nitrogen species (RNS) by forming three major hydroxylation (o-, m-, p-tyrosine) and two major nitration products (nitrophenylalanine, nitrotyrosine). Here, we show how a method for the analysis of these phenylalanine derivatives was established using isocratic HPLC (Nucleosil120, C18 column) coupled with photodiode array detection and validated for cell-free in vitro and in vivo determination of radical formation. An ideal separation was achieved using a mobile phase consisting of 5% acetonitrile, 50mM KH(2)PO(4), pH 3.0, a column temperature of 35 degrees C and a flow rate of 1.0 mL/min. Limits of detection were in the range of 5-100 nM. Linearity was given within 5 nM-100 microM (correlation coefficient >0.999). Retention times as well as peak heights exhibited a high precision (RSD: <or=0.1% and <1.5%, respectively). The feasibility of d-phenylalanine for ROS/RNS measurement was demonstrated in a cell-free in vitro assay using peroxynitrite and by analysis of brain samples of mice treated with the dopaminergic neurotoxin 6-hydroxydopamine.

Nonenzymatic formation of a novel hydroxylated sulfamethoxazole derivative in human liver microsomes: implications for bioanalysis of sulfamethoxazole metabolites

Sulfamethoxazole is metabolized by microsomal CYP2C9 to a hydroxylamine that is thought to be responsible for the relatively high incidence of hypersensitivity reactions associated with the drug. Accurate quantification of the hydroxylamine requires the loss of metabolite through autoxidation to be blocked with ascorbate. In this study, a partly nonenzymatically generated arylhydroxylated derivative of sulfamethoxazole was identified by liquid chromatography/mass spectrometry in incubations of human liver microsomes, and it was found to coelute with the isomeric hydroxylamine under the conditions of three published high-performance liquid chromatography (HPLC) assays. Partial inhibition of the aryl hydroxylation by 1-aminobenzotriazole suggested some involvement of cytochrome P450. However, the formation of this compound was ascorbate-dependent, and it was enhanced by the addition of Fe2+/EDTA and inhibited by desferrioxamine but not by mannitol. These findings are consistent with the phenol being generated via an Fe2+/ascorbate/O2-oxygenating system that does not involve hydroxyl radicals. It was also produced by H2O2/ascorbate. Because the compound shares close chromatographic similarities with the hydroxylamine metabolite, it is possible that previous studies may have inaccurately characterized or quantified sulfamethoxazole metabolism.

Measuring reactive species and oxidative damage in vivo and in cell culture: how should you do it and what do the results mean?

Free radicals and other reactive species (RS) are thought to play an important role in many human diseases. Establishing their precise role requires the ability to measure them and the oxidative damage that they cause. This article first reviews what is meant by the terms free radical, RS, antioxidant, oxidative damage and oxidative stress. It then critically examines methods used to trap RS, including spin trapping and aromatic hydroxylation, with a particular emphasis on those methods applicable to human studies. Methods used to measure oxidative damage to DNA, lipids and proteins and methods used to detect RS in cell culture, especially the various fluorescent "probes" of RS, are also critically reviewed. The emphasis throughout is on the caution that is needed in applying these methods in view of possible errors and artifacts in interpreting the results.