Identification of N alpha-acetyl-epsilon-(2-propenal)lysine as a urinary metabolite of malondialdehyde

Although orally administered malondialdehyde (MDA), a reactive hepatotoxic and mutagenic product of lipid peroxidation, is extensively metabolized to CO2, a portion is excreted in the urine in acid labile "bound" forms. Since much of the MDA in the diet is apparently bound to protein, the metabolism of protein-bound MDA was investigated. MDA was reacted with serum albumin and fed to rats. A urinary metabolite was detected which was shown to be identical to a metabolite of the lysine-MDA enaminal N epsilon-(2-propenal)lysine. After isolation by ion exchange and high performance liquid chromatography the metabolite was identified using high field nuclear magnetic resonance spectroscopy and fast atom bombardment-mass spectroscopy as N alpha-acetyl-epsilon-(2-propenal)lysine. This compound also was a major urinary metabolite of the Na enol salt of MDA administered by stomach intubation, and was excreted in increased amounts by rats fed a diet containing a highly peroxidizable oil (cod liver oil). It was also detected in the urine of fasted animals after injection with NaMDA, indicating that it is formed as a product of lipid peroxidation in vivo as well as of peroxidation of dietary lipids.     

Simultaneous analysis of lysine, Nepsilon-carboxymethyllysine and lysinoalanine from proteins

Protein quality was assayed by simultaneous measurement of lysine (Lys), carboxymethyllysine (CML) and lysinoalanine (LAL). GC-FID analysis of N-tert-butyl dimethylsilyl (tBDMSi) derivatives of these amino acids was undertaken. tBDMSi derivates were separated on a CP-SIL 5CB commercially fused silica capillary column (25 m x 0.25 mm i.d., 0.25 microm film thickness) employing a thermal gradient programmed from 200 to 300 degrees C. The identity of tBDMSi derivatives of Lys, CML and LAL was established by GC-MS while FID detection was employed for quantification. Analytical parameters such as linearity (lysine 350-4200 microM, LAL 3-81 microM, CML 16-172 microM), precision (1-13% variation coefficients), accuracy (85-108% average recovery) and limits of detection (lysine 0.4 mg/100 g protein, LAL 5.0 mg/100 g protein, CML 3.4 mg/100 g protein) and quantification (lysine 1.4 mg/100g protein, LAL 15.2 mg/100 g protein, CML 11.2 mg/100 g protein) were determined for validation of the analytical approach. Model systems and real foods have been studied. Kinetic of CML formation from different food proteins (BSA, soy protein, casein and gluten) was performed employing model systems. Carboxymethylation rate depended on the source of protein. Maillard reaction progressed to advanced stages damaging the protein quality of stored infant foods, soy drinks, boiled eggs and dry powdered crepes. CML values ranged from 62 to 440 mg/100 g protein were measured. LAL was also formed during boiling eggs (21-68 mg/100g protein) indicating additional damage by crosslinking reaction. In agreement, lysine content was affected by both food processing and storage.     

Simultaneous quantitative analysis of sphingoid base 1-phosphates in biological samples by o-phthalaldehyde precolumn derivatization after dephosphorylation with alkaline phosphatase

This paper describes a simultaneous analytical method for the measurement of sphingoid base 1-phosphates and sphingoid bases from a variety of biological samples. This method consists of two steps of sample pretreatment: the enzymatic dephosphorylation of sphingoid base 1-phosphates by alkaline phosphatase (APase) and the subsequent analysis of o-phthalaldehyde (OPA) derivatives of the liberated sphingoid bases by HPLC. By introducing C17-sphingosine 1-phosphate and C17-sphingosine as internal standards, not only phytosphingosine 1-phosphate, sphingosine 1-phosphate, and sphinganine 1-phosphate but also phytosphingosine, sphingosine, and sphinganine present in a sample could be quantified in 12 min on a C18 reversed-phase column with a simple mobile phase of acetonitrile:deionized distilled water (90:10, v/v). With this HPLC method, we could reproducibly analyze the levels of sphingoid base 1-phosphates over a broad range of concentrations from 0.5 to 100.0 pmol from various biological samples including serum, cultured cells, and rat tissue homogenates. The conversion of sphingoid base 1-phosphates into sphingoid bases increased the stability of the OPA adducts. Thus, this indirect measurement of sphingoid base 1-phosphates increased the sensitivity and reproducibility of the method. This HPLC method was also used to measure the changes in the levels of sphingoid base 1-phosphates in cultured cells after treatment with 1,25-(OH)2D3, a sphingosine kinase activator, or with fumonisin B1, a sphinganine N-acyltransferase inhibitor.     

Protein-bound advanced glycation endproducts (AGEs) as bioactive amino acid derivatives in foods

Summary. The Maillard reaction or nonenzymatic browning is of outstanding importance for the formation of flavour and colour of heated foods. Corresponding reactions, also referred to as “glycation”, are known from biological systems, where the formation of advanced glycation endproducts (AGEs) shall play an important pathophysiological role in diabetes and uremia. In this review, pathways leading to the formation of individual protein-bound lysine and arginine derivatives in foods are described and nutritional consequences resulting from this posttranslational modifications of food proteins are discussed.     

Antioxidant properties of Krebs cycle intermediates against malonate pro-oxidant activity in vitro: a comparative study using the colorimetric method and HPLC analysis to determine malondialdehyde in rat brain homogenates

A variety of Krebs cycle intermediaries has been shown to possess antioxidant properties in different in vivo and in vitro systems. Here we examined whether citrate, succinate, malate, oxaloacetate, fumarate and alpha-ketoglutarate could modulate malonate-induced thiobarbituric acid-reactive species (TBARS) production in rat brain homogenate. The mechanisms involved in their antioxidant activity were also determined using two analytical methods: 1) a popular spectrophotometric method (Ohkawa, H., Ohishi, N., Yagi, K., 1979. Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction. Analytical Biochemistry 95, 351-358.) and a high performance liquid chromatographic (HPLC) procedure (Grotto, D., Santa Maria, L. D., Boeira, S., Valentini, J., Char?o, M. F., Moro, A. M., Nascimento, P. C., Pomblum, V. J., Garcia, S. C., 2006. Rapid quantification of malondialdehyde in plasma by high performance liquid chromatography-visible detection. Journal of Pharmaceutical and Biomedical Analysis 43, 619-624.). Citrate, malate, and oxaloacetate reduced both basal and malonate-induced TBARS production. Their effects were not changed by pre-treatment of rat brain homogenates at 100 degrees C for 10 min. alpha-Ketoglutarate increased basal TBARS without changing malonate-induced TBARS production in fresh and heat-treated homogenates. Succinate reduced basal--without altering malonate-induced TBARS production. Its antioxidant activity was abolished by KCN or heat treatment. Fumarate reduced malonate-induced TBARS production in fresh homogenates; however, its effect was completely abolished by heat treatment. There were minimal differences among the studied methods. Citrate, oxaloacetate, malate, alpha-ketoglutarate and malonate showed iron-chelating activity. We suggest that antioxidant properties of citrate, malate and oxaloacetate were due to their ability to cancel iron redox activity by forming inactive complexes, whereas alpha-ketoglutarate and malonate pro-oxidant activity can be due to formation of active complexes with iron. In contrast, succinate and fumarate antioxidant activity was probably due to some enzymatic system.     

An ion-exchange chromatography procedure for the isolation and concentration of basic amino acids and polyamines from complex biological samples prior to high-performance liquid chromatography.

The original objective of this study was to develop a selective and sensitive method for the analysis and quantification of basic amino acids from biological samples via reversed-phase high-performance liquid chromatography. Using various previously described techniques for the separation of amino acids, we were unsuccessful in measuring levels of histidine, arginine, ornithine, and lysine in biological samples due to the presence of interfering compounds. A "cleanup" procedure for the isolation of the basic amino acids using a weakly acidic cation exchange resin, Biorex-70 (Bio-Rad), is described in detail. Upon separation from the bulk of the neutral and acidic amino acids, the basic amino acids were subjected to precolumn fluorescence derivatization using 9-fluorenylmethyl chloroformate (FMOC) and the fluorescent derivatives were separated by RP-HPLC. The advantages of this method over previously described amino acid analysis techniques are (i) isolation and stable recovery (greater than 95%) of the desired basic amino acids, (ii) sensitivity of detection (low pmol range), (iii) complete resolution of derivatized amino acids via HPLC, (iv) limited amount of sample required for analysis, and (v) samples readily concentrated by lyophilization or rotoevaporating. This ion-exchange cleanup procedure was also adapted for the analysis of polyamines in concentrated culture media samples and proved additionally advantageous by eliminating the use of costly C-18 extraction columns required by previously described techniques.     

Determination of dimethylamine in biological samples by high-performance liquid chromatography

A reversed-phase HPLC method for the quantification of dimethylamine in serum and urine is presented. Dimethylamine (DMA) is converted into a stable fluorescent product by precolumn derivatization with fluorenylmethylchloroformate. The DMA derivative is resolved from derivatives of other amines and amino acids by gradient elution with a total run-time of 15 min. The lower limit of determination in biological samples is 0.1 μmol/1. Recoveries from spiked serum samples were 99–107%. Within- and between-run precision were better than 6%. Concentrations of DMA in serum from normal human subjects (n=8) and from continuous ambulatory peritoneal dialysis patients (n=15) were 3.3±1.5 and 29.2±12.1 μmol/1, respectively.     

Involvement of lysine residues in the binding of ovine chorionic somatomammotropin to lactogenic and somatotropic receptors

The biological activities of several ovine chorionic somatomammotropin (oCS) derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit mammary homogenates (lactogenic activity, L.A.) and liver homogenates (somatotropic activity, S.A.). Even if the control treatment with BH-4 markedly decreased the L.A., it was clear that methylation mainly affected the S.A. and that ethylation reduced both activities. Guanidination inactivated almost completely both activities and acetimidination at a very low degree (3 of 14 lysines) led to less than 50% of both activities. These results show the involvement of lysine residues in the interaction of oCS with lactogenic and somatotropic receptors.     

Determination of antisense phosphorothioate oligonucleotides and catabolites in biological fluids and tissue extracts using anion-exchange high-performance liquid chromatography and capillary gel electrophoresis

Chemically modified phosphorothioate oligodeoxynucleotides (ODNs) have become critical tools for research in the fields of gene expression and experimental therapeutics. Bioanalytical assays were developed that utilized fast anion-exchange high-performance liquid chromatography (HPLC) and capillary gel electrophoresis (CGE) for the determination of 20-mer ODNs in biological fluids (plasma and urine) and tissues. A 20 mer ODN in the antisense orientation directed against DNA methyltransferase (denoted as MT-AS) was studied as the model ODN. The anion-exchange HPLC method employed a short column packed with non-porous polymer support and a ternary gradient elution with 2 M lithium bromide containing 30% formamide. Analysis of the MT-AS is accomplished within 5 min with a detection limit of approximately 3 ng on-column at 267 nm. For plasma and urine, samples were diluted with Nonidet P-40 in 0.9% NaCl and directly injected onto the column, resulting in 100% recovery. For tissue homogenates, a protein kinase K digestion and phenol–chloroform extraction were used, with an average recovery of about 50%. Since the HPLC assay cannot provide one-base separation, biological samples were also processed by an anion-exchange solid-phase extraction and a CGE method to characterize MT-AS and its catabolites of 15–20-mer, species most relevant to biological activity. One base separation, under an electric field of 400 V/cm at room temperature, was achieved for a mixture of 15–20-mer with about 50 pg injected. Assay validation studies revealed that the combined HPLC–CGE methods are accurate, reproducible and specific for the determination of MT-AS and its catabolites in biological fluids and tissue homogenates, and can be used for the pharmacokinetic characterization of MT-AS.     

Identification of N-(2-propenal)ethanolamine as a urinary metabolite of malondialdehyde

N-(2-propenal)ethanolamine was isolated from rat and human urine using anion exchange, cation exchange, size exclusion and high performance liquid chromatography. Acid hydrolysis of the isolate yielded malondialdehyde (MDA) and ethanolamine (E) in a 1:1 molar ratio. A 1:1 E-MDA adduct was synthesized and found to be chromatographically inseparable from the urinary metabolite. Its NMR and UV spectra and lack of fluorescence were consistent with those of an enaminal formed by a Schiff's base reaction. The identification in urine of an adduct of MDA with ethanolamine, and the previous identification of an adduct with serine, constitutes direct evidence for the oxidative decomposition in vivo of polyunsaturated fatty acids present in the relevant phospholipids. The absence in urine of MDA adducts with other alpha-amino compounds (at least in comparable amounts) indicates that the ethanolamine and serine derivatives are formed in situ and not as a result of reactions with MDA generated in enzymatic processes.     

In vitro degradation of neurotensin in human plasma

To study the degradation of neurotensin in plasma in vitro, fresh human plasma was incubated with neurotensin in the presence and absence of the peptidase inhibitors pepstatin A, EDTA, PMSF and aprotinin. The half-time of disappearance of neurotensin at 37 degrees C was calculated to be 226 min in vitro as opposed to 1.4 min in vivo when measured by radioimmunoassay with a C-terminally directed neurotensin antiserum. Both gel filtration and reversed phase high-pressure liquid chromatography (HPLC) showed that the main degradation product of neurotensin in human plasma in vitro was chromatographically and immunologically identical to neurotensin 1-8 and HPLC also demonstrated the formation of neurotensin 1-11. The loss of neurotensin incubated in human plasma in vitro was greatly reduced by EDTA but not by the other peptidase inhibitors tested. In this respect peptidase(s) responsible for the degradation of neurotensin in plasma differ from those present in brain homogenates. EDTA may be of importance in the preservation of neurotensin in plasma samples.     

Involvement of lysine residues in the binding of hGH and bGH to somatotropic receptors

The biological activities of human (hGH) and bovine (bGH) growth hormone derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit liver homogenates for somatotropic activity (SA). Control treatment with BH₄⁻ had a very slight effect on the SA, whereas the methylation and ethylation drastically reduced the acitivty of both hormones. Guanidination of these hormones and even acetimidination at a lower rate are accompanied by a considerable loss of biological activity. These results show the involvement of lysine residues in the interaction of hGH and bGH with somatotropic receptors. The structure-function relationship of these molecules is discussed, suggesting that the lysine or arginine residues in positions 41, 64, 70 and 115 might be particularly implicated.     

Isoprostanes, a novel markers of oxidative stress in schizophrenic disorders

It is a well known fact that 3H-panthenol (PL) has a high bioavailability, so we studied its biotransformation and its protective action against lipoperoxide activation in homogenates and mitochondrial-synaptosomal fraction (11 000 g) of rat brain. The lipoperoxidation was initialized by Fe²⁺-ascorbate complex (Fe²⁺-Asc). In experiments in vivo , after 30 min, we demonstrated accumulation of intermediate products of CoA biosynthesis – pantothenic acid (PA), phospho-PA, and phosphopantetheine – in postmitochondrial fraction of brain, by using a HPLC technique. Addition of the PL (10 m m ) to brain hemispheres homogenates or mitochondrial-synaptosomal fraction caused a remarkable reduction of malondialdehyde production. However, 30 min preincubation with the PL, but not with PA, was ineffective. The data obtained may be a reason for a high neuroprotective activity of PL in curing brain diseases with vessel or alcohol-induced damages.     

Determination of S-nitrosoglutathione in human and rat plasma by high-performance liquid chromatography with fluorescence and ultraviolet absorbance detection after precolumn derivatization with o-phthalaldehyde.

An analytical method is described for the quantification of S-nitrosoglutathione (GSNO), a potent physiological vasodilator and inhibitor of platelet aggregation, in the presence of a high excess of reduced glutathione (GSH). The method is based on the quantitative elimination of GSH by N-ethylmaleimide, the conversion of GSNO by 2-mercaptoethanol to GSH, its reaction with o-phthalaldehyde (OPA) to form a highly fluorescent and UV-absorbing tricyclic isoindole derivative, and subsequent high-performance liquid chromatographic (HPLC) separation with fluorescence and/or UV absorbance detection. The OPA derivatives of GSH and GSNO obtained by this method were found to be identical by mass spectrometry. GSH (up to 50 microM) did not interfere with the analysis of GSNO (up to 1000 nM). The limits of detection of the method for buffered aqueous solutions of GSNO were determined as 3 nM using fluorescence and 70 nM using UV absorbance detection. Isolation of GSNO by HPLC analysis (pH 7.0) of plasma ultrafiltrate samples (200 microl) prior to derivatization allows specific and artifact-free quantification of GSNO in human and rat plasma. Reduced and oxidized glutathione, nitrite, and cysteine did not interfere with the measurement of GSNO in human and rat plasma. The limit of quantitation (LOQ) of the combined method was determined as 100 nM of GSNO in human plasma ultrafiltrate using fluorescence detection. No endogenous GSNO could be detected in ultrafiltrate samples of plasma of 10 healthy humans at concentrations exceeding the LOQ of the method. After iv infusion of GSNO (125 micromol/kg body wt) in a rat for 20 min GSNO and GSH were detected in rat plasma at 60 and 130 microM, respectively. The method should be useful to investigate formation, metabolism, and reactions of GSNO in vitro and in vivo at physiologically relevant concentrations.     

Biotransformation of D‐panthenol and its action in protection of activation of oxidizing processes in brain

It is a well known fact that 3H‐panthenol (PL) has a high bioavailability, so we studied its biotransformation and its protective action against lipoperoxide activation in homogenates and mitochondrial‐synaptosomal fraction (11 000 g) of rat brain. The lipoperoxidation was initialized by Fe²⁺‐ascorbate complex (Fe²⁺‐Asc). In experiments in vivo, after 30 min, we demonstrated accumulation of intermediate products of CoA biosynthesis – pantothenic acid (PA), phospho‐PA, and phosphopantetheine – in postmitochondrial fraction of brain, by using a HPLC technique. Addition of the PL (10 mm ) to brain hemispheres homogenates or mitochondrial‐synaptosomal fraction caused a remarkable reduction of malondialdehyde production. However, 30 min preincubation with the PL, but not with PA, was ineffective. The data obtained may be a reason for a high neuroprotective activity of PL in curing brain diseases with vessel or alcohol‐induced damages.     

Fully automated method for simultaneous determination of total cysteine,cysteinylglycine, glutathione and homocysteine in plasma by HPLC with UV absorbance detection

A fully automated HPLC method for the simultaneous determination of total thiols in plasma samples has been developed. The method involves reductive conversion of disulfides to their reduced counterparts with the use of tris(2-carboxyethyl)phosphine. After reduction the newly formed sulfhydryl groups are reacted with 2-chloro-1-methylquinolinium tetrafluoroborate to form 2-S-quinolinium derivatives followed by deproteinization by dialysis. The reaction products are separated by reversed-phase HPLC, detected and quantified by UV absorbance detection at 355 nm. The recommended HPLC procedure enables measurement of four main plasma aminothiols cysteine, cysteinylglycine, glutathione, and homocysteine with low imprecision (mean relative standard deviations within calibration range, 3.47%, 5.34%, 4.25% and 3.26%, respectively) and good sensitivity. Accuracy, expressed as the mean measured amount as percentage of added amount, was within 97.5–103.0%, 98.3–102.5%, 96.3–99.5% and 97.1–99.1%, respectively. The lower limit of quantification for all thiols was 0.5 μM. The whole unattended instrument acquisition time amounts 13 min.     

Determination of urea, allantoin and lysine pyroglutamate in cosmetic samples by hydrophilic interaction chromatography

A new HPLC method using a Polyhydroxyethyl A column involving hydrophilic interaction chromatography (HILIC) is described for the simultaneous determination of urea, allantoin and lysine pyroglutamate in a cosmetic cream. Validation of the method was accomplished with respect to linearity, repeatability and limits of detection/quantification. Compound recoveries approach 100% with acceptable RSD values. The method is very simple since no derivatisation is necessary. Furthermore, it allows the rapid and direct chromatographic analysis of urea and hence could provide an alternative to other methods used to determine this compound in biological or cosmetic samples.     

Measurement of Aldehydes in Low Density Lipoprotein by High Performance Liquid Chromatography

A modified procedure is presented for the HPLC determination of nanomolar concentrations of n-alkanals, hydroxyalkenals, malondialdehyde and furfural in biological fluid. The modifications allow aldehyde profile analysis of small samples of fresh, human, low density lipoprotein (LDL), enabling more detailed studies of LDL fatty acid peroxidation. Aldehydes are reacted with 1,3-cyclohexanedione to produce fluorescent derivatives which are separated by gradient, reversed phase, high performance liquid chromatography (HPLC). Analysis time has been reduced by shortening the sample preparation. Sensitivity has been increased by miniaturization of the derivatisation procedure, reducing required sample size. Recoveries of added aldehydes have been improved. In addition, the method presented allows determination of three further aldehydes, not measured previously by CHD methods: malondialdehyde, formaldehyde and furfural. Recovery and variability data and concentrations of aldehydes found in human LDL are given. The capacity of the method for further development, to enable determination of other aldehydes such as the trans, 2-alkenals, is also demonstrated.     

Determination of epsilon (gamma-glutamyl)lysine crosslink in proteins using phenylisothiocyanate derivatization and high-pressure liquid chromatographic separation

A sensitive, reproducible high-performance liquid chromatographic method is reported for the determination of the epsilon (gamma-glutamyl)lysine isopeptide bond, which is usually formed by protein-crosslinking transglutaminases between polypeptide chains. The procedure is based on the separation and quantitation of epsilon (gamma-glutamyl)lysine isodipeptide following exhaustive proteolytic digestion of the crosslinked peptide. It involves preliminary separation steps on a cation exchanger resin and a silica HPLC column, precolumn derivatization with phenylisothiocyanate, and reversed-phase high-pressure liquid chromatographic separation on a C18 column. The derivatized isodipeptide gave a linear concentration-response relationship, with a detection limit of 10 pmol/mg of protein. The combination of the preliminary separation steps and the sensitive detection system permits the determination of the epsilon (gamma-glutamyl)lysine crosslink in complex biological systems including total tissue homogenates.     

Superoxide radical detection in cells, tissues, organisms (animals, plants, insects, microorganisms) and soils

A simple protocol is presented for the assessment of superoxide radical in organisms (animal/plant tissues, microorganisms, cell cultures, biological/culture fluids) and soils, through the quantification of 2-hydroxyethidium (2-OH-E+), its specific reaction product with hydroethidine (HE). It is an alternative to the quantification of 2-OH-E+ by HPLC (restricted to cell cultures), offering the advantage of the in vivo assessment of superoxide radical in a wide range of experimental systems. The protocol includes alkaline-acetone extraction of the sample, purification by microcolumn cation exchange and hydrophobic chromatographies, and fluorescence detection of the isolated 2-OH-E+/HE-oxidation products mixture before and after consumption of 2-OH-E+ by a horseradish peroxidase/hydrogen peroxide system. The protocol is sensitive at <1 pmol 2-OH-E+ per mg protein (extended to the femto level when using large samples) in biological systems, and in soils at 9 pmol superoxide radical per gram of soil. The protocol includes a cytochrome c-based subprotocol for superoxide radical detection in soils at 770 pmol g(-1) soil. For processing ten samples and depending on the experimental material used (soil or biological), the approximate procedure time would be 2-7 h.