Generation and initial characterization of a novel polyclonal antibody directed against homocysteine thiolactone-modified low density lipoprotein

Elevated plasma homocysteine (homocysteinemia) are presumed to be responsible for the development of coronary artery disease, however, the precise etiology is unclear. We examined the possibility that the adduct formed from the reaction between homocysteine thiolactone, a metabolic product of homocysteine, and apolipoprotein B-100 lysyl residues of low density lipoprotein (LDL) was immunogenic. New Zealand White rabbits were immunized with this adduct at 6-week intervals. Antisera collected following the 3rd immunization was assayed for antibody titers using solid phase ELISA techniques. Titers (defined as the inverse of the greatest serum dilution in which there was a significant difference (P < 0.05) between the percentage antibody bound from the antiserum and the pre-immune serum) were approximately 10(5). In competition-based ELISAs, homocysteine thiolactone-treated LDL competed for binding with the antiserum, as the 50% inhibitory concentration was approximately 10 microg/ml. Neither homocysteine, homocystine (homocysteine disulfide), nor Cu2-oxidized LDL competed for binding. LDL in which lysyl residues were derivatized by acetylation or methylation were not recognized by the antiserum. Homocysteine thiolactone-treated plasma competed for binding to the antiserum, whereas native plasma did not. All lipoprotein fractions from the homocysteine thiolactone-treated plasma competed for binding to the antiserum. We conclude that homocysteine thiolactone-modified LDL is highly immunogenic and specific for homocysteine thiolactone-modified lysines. The potential for using this antibody as a diagnostic tool for measuring plasma homocysteine concentrations and the implications for understanding diseases induced by homocysteinemia are discussed.

Conversion of Amadori product of Maillard reaction to Nepsilon-(carboxymethyl)lysine in alkaline condition

Nepsilon-(carboxymethyl)lysine (CML) is known to be formed by oxidative cleavage of Amadori products between C-2 and C-3 of the carbohydrate chain. We report here that CML formation from Amadori compounds is highly accelerated under alkaline conditions. Incubation of glycated human serum albumin (HSA) in 0.1 N NaOH led to the formation of CML whereas glycated HSA reduced by NaCNBH3 or non-glycated HSA did not generate CML. Nalpha-t-butyloxycarbonyl-Nepsilon-fructoselysine (Boc-FL), a model compound of Amadori product, was converted to CML under alkaline conditions. CML level of human sera (n=224) preincubated with 0.1 N NaOH correlated well with glycated albumin value (r=0.912) and hemoglobin A1c (r=0.797).

Protein modification by lipid peroxidation products: formation of malondialdehyde-derived N(epsilon)-(2-propenol)lysine in proteins

Malondialdehyde (MDA), a naturally occurring dialdehyde produced in the membrane lipid peroxidation, is known to react with lysine residues of proteins, but the MDA-lysine adducts generated in the proteins have not been characterized adequately. In the present study, we provide evidence that the enaminal-type MDA-lysine adduct, N(epsilon)-(2-propenal)lysine, is formed in human low-density lipoprotein (LDL) upon reaction with MDA or Cu2+. We found that the incubation of N(alpha)-acetyllysine with MDA generated N(alpha)-acetyl-N(epsilon)-(2-propenal)lysine as the predominant product. In addition, a polyclonal antiserum raised against the MDA-modified protein was found to contain antibody populations that could be purified by affinity gel prepared by covalent attachment of N(alpha)-acetyl-N(epsilon)-(2-propenal)lysine. It was concluded that the affinity-purified anti-N(epsilon)-(2-propenal) lysine antibody was highly specific to the enaminal derivative of both lysine residues and phosphatidylethanolamine, based on the observations that (i) MDA was the only aldehyde which generated immunoreactive materials in proteins; (ii) among structurally defined MDA-lysine adducts tested, the antibody recognized the enaminal adduct only; and (iii) immunoreactivity to N-(2-propenal)serine was still significant but much weaker than its reactivity to N-(2-propenal)ethanolamine. Furthermore, analysis of antibody recognition sites with a variety of N-(2-propenal)alkylamines revealed that the mono-specific antibody recognized the N-2-propenal-N-ethyl moiety [-(CH2)2-NH-CH=CH-CHO] of enaminal adducts. Determination by a competitive enzyme-linked immunosorbent assay demonstrated that N(epsilon)-(2-propenal)lysine accounted for 33.7 and 3.1% of the lysine residues that disappeared during in vitro incubation of LDL with MDA and Cu2+, respectively. These results suggest that N(epsilon)-(2-propenal)lysine represents a major form of MDA covalently attached to proteins.

Technical note. The serum concentration of the advanced glycation end-product N epsilon-(carboxymethyl)lysine is increased in uremia

Advanced glycation end products (AGEs) such as pentosidine and N epsilon-(carboxymethyl)lysine (CML) have been traditionally quantified by HPLC or gas chromatography--mass spectrometry (GC/MS). Enzyme-linked immunosorbent assays (ELISA) have been introduced as a convenient alternative to simplify the detection and measurement of AGEs in proteins and tissues, but some of these studies are limited by the lack of information on the structure of the epitopes recognized by antibodies to AGE-proteins. In this work we demonstrate that an antibody used in a previous study, reporting increased levels of AGEs in patients with diabetes or on continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis (HD), recognizes CML as its major epitope. We also show that there is a significant correlation between the concentration of AGEs in serum measured by ELISA and a GC/MS assay for CML in serum proteins. Both analyses yielded comparable results, with patients on CAPD and HD having about threefold higher AGE- or CML-concentrations in their serum. Our data suggest that ELISA assays for CML should be useful for the clinical measurement of AGEs in serum proteins.

Chromosomal mapping of core histone acetylation by immunoselection

Acetylation of specific lysine residues in the N-terminal domains of core histones is a biochemical marker of active genes. To determine the spatial and temporal distribution of this reversible posttranslational modification, affinity-purified polyclonal antibodies recognizing the epitope epsilon-acetyllysine have been used in immunoselection procedures with mononucleosomes and salt-soluble chromatin fragments generated by micrococcal nuclease. The DNA of the antibody-selected chromatin was slot-blotted and probed with a variety of gene sequences: an enhanced hybridization signal, with respect to that from the DNA of the input chromatin, demonstrated elevated acetylation levels on the histones associated with the probing sequences. Using chicken embryonic erythrocytes as chromatin source and probes from the beta globin locus, it was shown that both the embryonic epsilon and adult beta genes are acetylated at 5 and 15 days, and the acetylation uniformly covers the whole of the locus, precisely comapping with the 33 kb of open chromatin structure. Studies with proliferating human K562 cells show that the inactive but poised PDGF-beta gene is already hyperacetylated and that its acetylation status is not enhanced on induction. These results indicate that acetylation is not a consequence of transcription but a prerequisite and that it may be responsible for either generating or maintaining the open structure of poised and active genes.

Monoclonal antibodies against Nalpha-(5'-phosphopyridoxyl)-L-lysine. Screening and spectrum of pyridoxal 5'-phosphate-dependent activities toward amino acids

Cofactors may be expected to expand the range of reactions amenable to antibody-assisted catalysis. The biological importance of pyridoxal 5'-phosphate (PLP) as enzymic cofactor in amino acid metabolism and its catalytic versatility make it an attractive candidate for the generation of cofactor-dependent abzymes. Here we report an efficient procedure to screen antibodies for PLP-dependent catalytic activity and detail the spectrum of catalytic activities found in monoclonal antibodies elicited against Nalpha-(5'-phosphopyridoxyl)-L-lysine. This hapten is a nonplanar analog of the planar, resonance-stabilized coenzyme-substrate adducts formed in the PLP-dependent reactions of amino acids. The hapten-binding antibodies were screened for binding of the planar Schiff base formed from PLP and D- or L-norleucine by competition enzyme-linked immunosorbent assay. The Schiff base (external aldimine) is an obligatory intermediate in all PLP-dependent reactions of amino acids. This simple, yet highly discriminating screening step eliminated most of the total 24 hapten-binding antibodies. Three positive clones bound the Schiff base with L-norleucine, two preferred that with the D-enantiomer. The positive clones were assayed for catalysis of Schiff base formation and of the alpha,beta-elimination reaction with the D- and L-enantiomers of beta-chloroalanine. Three antibodies were found to accelerate aldimine formation, and two of these catalyzed the PLP-dependent alpha,beta-elimination reaction. One of the alpha, beta-elimination-positive antibodies catalyzed the transamination reaction with hydrophobic D-amino acids and oxoacids (Gramatikova, S. I., and Christen, P. (1996) J. Biol. Chem. 271, 30583-30586). All catalytically active antibodies displayed continuous turnover. No PLP-dependent reactions other than aldimine formation, alpha, beta-elimination of beta-chloroalanine and transamination were detected. The successive screening steps plausibly simulate the functional selection pressures having been operative in the molecular evolution of primordial PLP-dependent protein catalysts to reaction- and substrate-specific enzymes.

Increased accumulation of the glycoxidation product N(epsilon)-(carboxymethyl)lysine in human tissues in diabetes and aging

N(epsilon)-(Carboxymethyl)lysine (CML), a major product of oxidative modification of glycated proteins, has been suggested to represent a general marker of oxidative stress and long-term damage to proteins in aging, atherosclerosis, and diabetes. To investigate the occurrence and distribution of CML in humans an antiserum specifically recognizing protein-bound CML was generated. The oxidative formation of CML from glycated proteins was reduced by lipoic acid, aminoguanidine, superoxide dismutase, catalase, and particularly vitamin E and desferrioxamine. Immunolocalization of CML in skin, lung, heart, kidney, intestine, intervertebral discs, and particularly in arteries provided evidence for an age-dependent increase in CML accumulation in distinct locations, and acceleration of this process in diabetes. Intense staining of the arterial wall and particularly the elastic membrane was found. High levels of CML modification were observed within atherosclerotic plaques and in foam cells. The preferential location of CML immunoreactivity in lesions may indicate the contribution of glycoxidation to the processes occurring in diabetes and aging. Additionally, we found increased CML content in serum proteins in diabetic patients. The strong dependence of CML formation on oxidative conditions together with the increased occurrence of CML in diabetic serum and tissue proteins suggest a role for CML as endogenous biomarker for oxidative damage.

DNA-alginate complex recognized by autoantibodies against DNA

Double-stranded DNA was effectively complexed with alginic acid and immobilized on a surface of polystyrene microtiter plate. Dose-dependent binding of anti-DNA autoantibodies was finely observed to the solid phase DNA-alginate complex in enzyme-linked immunosorbent assay (ELISA). In contrast, non-specific binding of antibodies to alginate was scarcely detected rather than to poly-L-lysine. These results shown an availability of the solid phase DNA-alginate complex as an antigen in ELISA for detection of anti-DNA antibodies.

Effects of site-directed mutagenesis of basic residues (Arg 94, Lys 95, Lys 99) of lipopolysaccharide (LPS)-binding protein on binding and transfer of LPS and subsequent immune cell activation

LPS-binding protein (LBP) is a 60-kDa acute phase glycoprotein capable of binding the LPS of Gram-negative bacteria and facilitating its diffusion. This process is thought to be of potential importance in inflammatory reactions and pathogenic states such as septic shock syndrome. Here, we report on the identification of a LPS binding domain within the LBP molecule and on the identification of single amino acids important for binding of LPS by LBP. Several synthetic LBP peptides inhibited LPS-LBP interaction, and amino acids Arg 94 and Lys 95 were centrally located in these inhibitory peptides. LBP mutants with amino acid exchanges within this region were expressed and tested in five different functional assays: binding to immobilized LPS; facilitation of binding of LPS aggregates to monocytes; transfer of LPS monomers from aggregates to soluble CD14; transfer of soluble CD14-bound LPS monomers to high density lipoprotein (HDL); and enhancement of LPS-induced cell activation. The double mutant Glu 94/Glu 95 was completely lacking LPS binding, transfer, and cell stimulatory activity, indicating that the integrity of amino acids 94 and 95 is required for LBP function. While mutations of amino acids Arg 94 or Lys 95 into alanine reduced the LPS binding activity of LBP dramatically, the ability to facilitate binding of LPS aggregates to membrane CD14 at the cell surface was retained. These findings emphasize the distinction between binding of LPS aggregates to cells, which is not associated with cell stimulation, and binding of LPS monomers to CD14, which leads to cell stimulation.

Amyloid beta 2-microglobulin is modified with N epsilon-(carboxymethyl)lysine in dialysis-related amyloidosis

Recent work from this laboratory revealed that advanced glycation end product was localized to amyloid deposits in patients with dialysis-related amyloidosis by immunohistochemistry using a monoclonal antibody to advanced glycation end product. To elucidate the epitope of the antibody, N alpha-p-tosyl-L-lysine-methyl ester was incubated with glucose in vitro, and then a compound reactive to the antibody was purified from the incubate by buthanol extraction, XAD-2 column chromatography, and high-performance liquid chromatography while the reactivity was examined by enzyme linked immunosorbent assay. The purified compound was identified as N epsilon-(carboxymethyl)-N alpha-p-tosyl-L-lysine-methyl ester by using secondary ion mass spectrometry, and 1H- and 13C-nuclear magnetic resonance spectroscopy. The epitope of the antibody was identified as -CH2-NH-CH2-COOH by enzyme-linked immunosorbent assay of compounds with structures similar to N epsilon-(carboxymethyl)lysine. Immunochemical study using the antibody demonstrated the presence of N epsilon-(carboxymethyl)lysine in the beta 2-microglobulin dimer (molecular weight 23929) isolated from the synovium amyloid of a hemodialysis patient with dialysis-related amyloidosis. In conclusion, amyloid beta 2-microglobulin is modified with N epsilon-(carboxymethyl)lysine in dialysis-related amyloidosis.

Immunochemical detection of carboxymethylated Apo B-100 in copper-oxidized LDL

The objective of this study was to detect carboxymethyllysine (CML) moieties in biological materials using immunological methods. We prepared a polyclonal antibody specific to the carboxymethylated protein. The antibody recognizes the CML moiety in protein. Protein-bound carboxymethylcysteine (CMS) is scarcely recognized by the antibody. By use of the antibody, the formation of carboxymethylated apo B in copper-oxidized low density lipoprotein (ox-LDL) was immunochemically confirmed. To clarify the source compounds of carboxymethylation, various aldehyde-modified BSAs were prepared, and their reactivities with the antibody were investigated. Among the aldehyde-modified BSAs used, the glyoxal-BSA adduct showed a strong antigenicity. As far as we know, this is the first report of the detection of the CML moiety in ox-LDL using immunological methods.

Determination of gizzerosine activity in fish meal with a homologous radioimmunoassay

A homologous RIA for the determination of toxic gizzerosine activity in commercial fish meals has been developed. Three polyclonal antibodies (GR316, GR415, and GR418) were produced in female rabbits and extensively characterized for their potential use in individual RIA. The RIA had lower detection limits of 0.048, 0.78, and 0.39 ng/mg using the three respective antibodies. Because gizzerosine is derived from lysine and histidine, crossreactivity with these amino acids, and with histamine was examined. The antibodies crossreacted with histamine from 21 to 100%. No crossreactivity with histidine or lysine was observed for any of the three antibodies. Antibody GR415 was chosen for determination of gizzerosine in extracted fish meal samples because crossreactivity of histamine using this antibody was only present at high concentrations, and the Ka value for gizzerosine was 10-fold greater than for histamine. A mild buffer extraction procedure was used, resulting in 98% gizzerosine recovery. Displacement curves from extracted and serially diluted fish meal samples were parallel with gizzerosine standard. Inter-and intra-assay coefficients of variation were 11 and 15%, respectively. We used the RIA for determination of gizzerosine activity in a pool of 23 fish meal samples of known gizzerosine scores (determined with a chick bioassay), and histamine content. The partial correlation coefficient between gizzerosine content determined by the RIA and gizzerosine scores from the bioassay was high (0.83), and significant (P < 0.01). There were also significant correlations between gizzerosine scores and histamine content of the fish meals (0.63, P < 0.01), and between histamine content and gizzerosine levels determined by the RIA (0.59, P < 0.01). The application of the homologous RIA for the determination of gizzerosine activity in commercial fish meals could be of importance for the prevention of gizzard erosions in the poultry industry, and for studying gizzerosine-induced pathology and metabolism.

N (epsilon)-(carboxymethyl)lysine protein adduct is a major immunological epitope in proteins modified with advanced glycation end products of the Maillard reaction

Long-term incubation of proteins with glucose leads to the formation of advanced glycation end products (AGE). Recent immunological studies have suggested the potential role of AGE in atherosclerosis, aging, and diabetic complications. We previously prepared a monoclonal (6D12) as well as a polyclonal anti-AGE antibody and proposed the presence of a common AGE structure(s) that may act as a major immunochemical epitope [Horiuchi, S., Araki, N., & Morino, Y. (1991) J. Biol. Chem. 266, 7329-7332]. The purpose of the present study was to determine the major epitope. Amino acid analysis of AGE-proteins indicated that N(epsilon)-(carboxymethyl)lysine (CML) was a major modified lysine residue. Immunologic studies demonstrated the positive reaction of 6D12 not only to all CML-modified proteins tested, but also to BSA modified with several aldehydes known to generate a CML-protein adduct, and a linear correlation between the CML contents of CML-BSA and their immunoreactivity to 6D12 up to approximately 8 mol/mol of protein. Further experiments with CML analogs revealed that the epitope of 6D12 is a CML-protein adduct with an important carbonyl group. In contrast to 6D12, our polyclonal anti-AGE antibody showed a significant but much weaker immunoreactivity to CML-BSA, suggesting that the polyclonal antibody contains two populations, one reactive to CML (CML-PA) and the other unreactive to CML (Non-CML-PA). Non-CML-PA separated from CML-PA by CML-BSA affinity chromatography did not react with all CML-modified preparations, but retained its property to react commonly with AGE preparations obtained from proteins, lysine derivatives, and monoaminocarboxylic acids. Therefore, it is clear that a CML-protein adduct is a major immunological epitope in AGE structures, but there still exist other major epitope(s) expressed commonly in AGE-proteins.

High-density presentation of an immunodominant minimal peptide on B cells is MHC-linked to Th1-like immunity

Ligand-directed differences in the amount of peptide presented on a specific APC subset could influence the functional outcome of any given immune response. We have investigated this issue with a biochemically determined immunodominant peptide that is presented at a higher density on the APC of Th1 responders (I-As genotypes) than on the APC of Th2 responders (I-Ab genotypes). MHC-linked high peptide density is expressed on B lymphocytes, predominantly those that bear the B7-2 activation marker/costimulatory ligand. We further investigated the role of I-As-specific polymorphism with transfected cells bearing an R-->Q change at position-70 of A beta (found only in the I-As allele). Strikingly, I-Ab-restricted Th1 and Th2 clones proliferate at a peptide dose 10- to 100-fold lower than wild-type on transfected fibroblasts bearing this single s-like substitution in A beta b. Moreover, the shift in the clone dose response is sensitive to the peptide's C-terminus, as is MHC-linked Th1-like immunity to this peptide in vivo. Together, these data suggest that ligand-density can dictate Th1/Th2 selection via a single MHC polymorphism that determines the level of peptide presented to a given TCR on activated B cells.

Immunological detection of glycated proteins in normal and streptozotocin-induced diabetic rats using anti hexitol-lysine IgG

A polyclonal antibody specific for the Amadori compound, a product of an early stage of the Maillard reaction, was raised in rabbits by immunization with hexitol-lysine (1-glucitol-lysine or 1-mannitol-lysine) coupled with various carrier proteins. The affinity purified antibody has a high titre and preferentially recognizes the glucose adduct, in the presence of sodium borohydride, as judged on enzyme-linked immunosorbent assay as well as immunoblot analysis. The glycated proteins (Amadori products) in various tissues of normal and streptozotocin-induced diabetic rats were examined by immunoblot analysis. In diabetic conditions, kidney, liver, lens, brain and lung proteins are more susceptible to glycation than other tissue proteins. Heart, spleen, adrenal gland and muscle proteins exhibit similar extents of glycation in both normal and diabetic conditions. This is the first demonstration of a specific antibody against the Amadori compound being raised with a synthetic compound, and of the tissue distribution of glycated proteins in normal and diabetic conditions. The antibody was very useful for in vitro and in vivo experiments on the Maillard reaction.

N epsilon-(carboxymethyl)lysine is a dominant advanced glycation end product (AGE) antigen in tissue proteins

Advanced glycation end products (AGEs) and glycoxidation products are formed during Maillard or browning reactions between sugars and proteins and are implicated in the pathophysiology of aging and the complications of diabetes. To determine the structure of AGEs, antibodies were prepared to protein browned by incubation with glucose and used in ELISA assays to measure AGEs formed in model reactions between bovine serum albumin (BSA) or N alpha-acetyllysine and glucose, fructose, or glyoxal. AGEs were formed from glucose and fructose only under oxidative conditions, but from glyoxal under both oxidative and antioxidative conditions. Gel permeation chromatographic analysis indicated that a similar AGE was formed in reactions of N alpha-acetyllysine with glucose, fructose, and glyoxal and that this AGE co-eluted with authentic N alpha-acetyl-N epsilon-(carboxymethyl)lysine. Amino acid analysis of AGE proteins revealed a significant content of N epsilon-(carboxymethyl)lysine (CML). In ELISA assays using polyclonal antibodies against AGE proteins, CML-BSA (approximately 25 mol of CML/mol of BSA), prepared by chemical modification of BSA, was a potent inhibitor of the recognition of AGE proteins and of AGEs in human lens proteins. We conclude that AGEs are largely glycoxidation products and that CML is a major AGE recognized in tissue proteins by polyclonal antibodies to AGE proteins.

Antibodies made against a formaldehyde-protein adduct cross react with an acetaldehyde-protein adduct. Implications for the origin of antibodies in human serum which recognize acetaldehyde-protein adducts

Acetaldehyde, the major metabolite of ethanol, reacts with lysine and other free amino groups on proteins to form acetaldehyde-protein adducts. The presence of antibodies which recognize such acetaldehyde-protein adducts in sera from alcoholics has been attributed to an immune response to such adducts. Complicating this conclusion is the finding that sera from non-alcoholic control subjects also contain antibodies which recognize acetaldehyde-protein adducts. In the current research we sought to determine whether antibodies which recognize epitopes formed by the reaction of a protein with acetaldehyde can be formed in response to a protein modified with a structurally related protein adduct. We modified lysine residues on apolipoprotein (apo) B-100 with acetaldehyde and formaldehyde under reducing conditions, to form epsilon-N-methyl- and epsilon-N-ethyl-lysine residues, and with acetic anhydride to form epsilon-N-acetyl-lysine residues, and made antibodies against these modified proteins in guinea-pigs. In ELISA assays antibodies made against methylated apoB-100 (Me-apoB) cross-reacted effectively with ethylated apoB-100 (Et-apoB), while antibodies made against acetic anhydride-modified apoB-100 did not cross-react. We conclude that methyl-lysine shares one or more immunoreactive epitopes with ethyl-lysine, and that antibodies which recognize acetaldehyde-modified proteins can be formed in response to formaldehyde-modified proteins. We demonstrate that sera from both alcoholics and non-drinkers contain antibodies which recognize Me-apoB and Et-apoB and that the titres of these antibodies are comparable. These data raise the possibility that some human serum antibodies which recognize acetaldehyde-modified protein epitopes may have been made against formaldehyde-modified protein epitopes.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning of a 30-kilodalton lysine-rich surface antigen from a nonpathogenic Entamoeba histolytica strain and its expression in a pathogenic strain

A monoclonal antibody (MAb), 318-28, that specifically reacts with a 30-kDa antigen present on membrane surfaces of all nonpathogenic (NP) Entamoeba histolytica strains tested and which did not react with pathogenic (P) strains was used for the isolation of the cDNA coding for this antigen from an expression library of an NP E. histolytica strain. The deduced amino acid composition was rich in lysine residues (14.5%), with some sequence similarity to a polyadenylate-binding protein. Southern and Northern (RNA) blot analyses, as well as amplifications of DNA segments by PCR, indicate that a very similar gene (identity of 96.5%) exists in P strains of E. histolytica. Unexpectedly, the NP-specific antigen was also identified by MAb 318-28 on the surfaces of a cloned, xenically cultivated and well-characterized P strain (BNI:0591) that was recently isolated from a human liver abscess. Binding of the MAb, both to the cell surfaces and to Western blots (immunoblots), was abolished, however, upon axenization of the BNI:0591 cultures. Oligonucleotide primers, designed to anneal only to specific DNA sequences of the NP 30-kDa protein gene copy, amplified a DNA segment from P strain BNI:0591 which was identical in sequence to that of the NP 30-kDa protein gene. Our findings indicate that a P strain of E. histolytica can possess and express, under certain growth conditions, an antigen that is usually detected only in NP strains.

ELISA of pentosidine, an advanced glycation end product, in biological specimens

Pentosidine is a fluorescent protein cross-link and glycoxidation marker for the advanced glycation reaction in diabetes, aging, and uremia. We raised polyclonal antibodies in New Zealand White rabbits against this hapten coupled to keyhole limpet hemocyanin. The antibodies detected by ELISA reacted strongly with free pentosidine but not with pentosidine-like compounds. The working range of the competitive ELISA for standard pentosidine was 0.1-100 pmol. Pentosidine was detectable in bovine serum albumin incubated with ribose as a function of incubation time. Immunoblotting studies showed that pentosidine specifically stained in oligomers of lysozyme incubated with ribose. Digestion with protease (Pronase E, 20 g/kg) as well as acid hydrolysis enhanced the immunoreactivity of samples, the pentosidine values in digested human plasma correlating with those measured by HPLC (r = 0.98). Pentosidine in diabetic and uremic plasma digested with Pronase E was significantly higher than normal (P < 0.01; mean +/- SD): 1620 +/- 1940 and 2630 +/- 1320 [corrected] nmol/L, respectively, vs 151 +/- 55 nmol/L (normal). Amounts of pentosidine in hydrolyzed skin collagen increased with age and were increased in diabetes and uremia. This ELISA provides a new tool for assessing the role of the advanced Maillard reaction in aging and age-related diseases.

Identification of the dihydrolipoamide acetyltransferase subunit of the human pyruvate dehydrogenase complex as an autoantigen in halothane hepatitis. Molecular mimicry of trifluoroacetyl-lysine by lipoic acid

Trifluoroacetylated (CF3CO-) proteins, elicited upon exposure of animals or humans to halothane, were recognized by anti-CF3CO antibody, monospecific for the hapten derivative N6-trifluoroacetyl-L-lysine. Anti-CF3CO antibodies cross-reacted with the dihydrolipoamide acetyltransferase (E2 subunit) of pyruvate dehydrogenase, indicating that epitopes on the E2 subunit of pyruvate dehydrogenase molecularly mimic those on CF3CO-proteins. Lipoic acid, the prosthetic group of the E2 subunit of pyruvate dehydrogenase was essential in this process, in that only the lipoylated form of the recombinantly expressed inner lipoyl domain of the human E2 subunit of pyruvate dehydrogenase, but not the unlipolyated form, was recognized by anti-CF3CO antibody. Furthermore, based on a high degree of structural relatedness, both CF3CO-Lys and (6RS)-lipoic acid, as well as the lipoylated peptide ETDK(lipoyl)ATIG specifically inhibited the recognition by anti-CF3CO antibody of the E2 subunit of pyruvate dehydrogenase, of trifluoroacetylated rabbit serum albumin and of human liver CF3CO-proteins. In sera of patients with halothane hepatitis, autoantibodies with properties identical to those of anti-CF3CO antibody were identified which could not discriminate between CF3CO-proteins and the E2 subunit of pyruvate dehydrogenase. These data suggest that the E2 subunit pyruvate of dehydrogenase is an autoantigen in halothane hepatitis and that molecular mimicry of CF3CO-proteins by the E2 subunit of pyruvate dehydrogenase is due to the similar structures of CF3CO-Lys and lipoic acid.

Specificity of N-ethyl lysine of a monoclonal antibody to acetaldehyde-modified proteins prepared under reducing conditions

A monoclonal antibody has been developed that recognizes only protein-acetaldehyde (AA) adducts prepared under reducing conditions: 5 mM AA with 30 mM sodium cyanoborohydride overnight at 37 degrees. This monoclonal antibody is a mouse IgG2b that has been designated RT1.1. The primary adduct formed when proteins are exposed to acetaldehyde under reducing conditions is N-ethyl lysine (NEL). To examine the epitope specificity of RT1.1, inhibition ELISAs were developed using NEL and other possible inhibitors, such as arginine, ethylamine, lysine and proteins modified with AA under non-reducing conditions. RT1.1 (at half-maximum optical density, 50 ng/mL) was inhibited only by NEL and was independent of the carrier or the pH of the buffer used in the ELISA. Further evidence indicating that NEL is the epitope recognized by RT1.1 was obtained using mouse and human epidermal growth factor (EGF). Both proteins contain one alpha amino group but only the human-EGF contains lysine residues with epsilon amino groups. In experiments where these two proteins were modified with AA under reducing conditions, RT1.1 reacted only with human-EGF. These studies demonstrate that RT1.1 is specific for NEL that is formed by the ethylation of proteins with acetaldehyde under reducing conditions. Additionally, these studies demonstrate that the procedures and methods used herein may be useful for characterizing other antibodies prepared to AA-modified proteins under a variety of defined in vitro chemical conditions.

Application of 13C NMR spectroscopy to paratope mapping for larger antigen-Fab complexes

For the purpose of engineering the antibody combining site, mapping residues that are involved in antigen binding provide us with valuable information. By use of 13C NMR spectroscopy with selectively 13C-labeled Fv fragments, we have established a general strategy to identify the residues that are perturbed upon binding of small antigen (hapten) molecules [(1990) Biochemistry 30, 6604-6610]. In the present paper, we demonstrate that this strategy can be extended to molecular structural analyses of the complexes of an Fab fragment and a larger antigen molecule such as Pseudomonas aeruginosa exotoxin A with a molecular mass of 67 kDa.

ApoE-deficient mice are a model of lipoprotein oxidation in atherogenesis. Demonstration of oxidation-specific epitopes in lesions and high titers of autoantibodies to malondialdehyde-lysine in serum

Apolipoprotein (apo) E-deficient transgenic mice develop marked hyperlipidemia and progressive atherosclerotic lesions. To explore whether oxidative modification of lipoproteins is involved in atherogenesis in this murine model, we performed extensive immunocytochemical studies. Atherosclerotic lesions ranging from early fatty streaks to very advanced plaques were examined from the aortic valve region and the thoracic and abdominal aorta. Using guinea pig antisera against malondialdehyde (MDA)-lysine and 4-hydroxynonenal-lysine, two epitopes generated during the oxidative modification of low-density lipoprotein (LDL), we demonstrated the presence of these "oxidation-specific epitopes" in atherosclerotic lesions. In early lesions, oxidation-specific epitopes were found predominantly in macrophage-rich areas, whereas diffuse extracellular staining predominated in necrotic areas of advanced lesions. We have previously shown that autoantibodies against MDA-lysine are present in the circulation of humans and rabbits and that the immunoglobulin fraction extracted from their lesions contains autoantibodies against several "oxidation-specific" epitopes. Sera from apoE-deficient mice also contained circulating autoantibodies to MDA-lysine, and both early and advanced lesions were rich in murine immunoglobulins. Titers of serum autoantibodies were significantly higher in apoE-deficient mice than in C57BL/6 mice. Autoantibodies in murine plasma recognized MDA-lysine epitopes in atherosclerotic lesions of rabbits, and the immunostaining was competitively inhibited by excess human MDA-LDL. Similar findings were obtained by competitive radioimmunoassay. Finally, a morphometric technique was developed and tested in these mice that allows a quantitative assessment of aortic atherosclerosis. These findings suggest that in apoE-deficient mice, lipoprotein oxidation is involved in atherogenesis and that these transgenic mice constitute an appropriate model with which to study the antiatherogenic effect of antioxidant intervention.