Intracellular generation of MDA-LYS epitope in foam cells

Proinflammatory effects of malondialdehyde in lymphocytes

Diabetes is an inflammatory disease promoted by alterations in immune cell function. Animal study indicates that T cells are important mediators of inflammation in diabetes. Lipid peroxidation by reactive oxygen species leads to the formation of highly reactive malondialdehyde (MDA), and extensive MDA is found in diabetes. However, the biological functions of MDA have not been studied yet. We hypothesized that increased MDA, as in diabetes, can regulate inflammatory cytokines via specific signaling pathways. This could then result in increased lymphocyte activation and skewing a particular inflammatory subset thereby exacerbates diabetes complications. Commercial cytokine antibody and RT(2)-PCR array profiling were performed with Jurkat T cells grown with or without MDA. Ingenuity pathways analysis (IPA) and pharmacological inhibitors were used for networks and signaling pathway identification, respectively. For validation, real-time PCR, RT-PCR, and Western blots were performed. MDA induced significant increases in 47 key proinflammatory molecules such as IL-25, IL-6, IL-8, ICAM-1, and light mRNA in Jurkat T cells and primary peripheral blood lymphocytes (PBLCs). A significant 2-fold increase in serum MDA also correlated the increased IL-25 and IL-8 mRNA in PBLCs of diabetic patients. Pharmacological inhibitor studies showed that MDA induced its effect via p38MAPK and protein kinase C pathways. Furthermore, IPA uncovered 5 groups of inflammatory networks and placed our candidate genes in canonical IL-6 and NF-κB signaling pathways and also suggested 5 toxic lists and 3 major toxic functions, namely cardiotoxicity, hepatotoxicity, and nephrotoxicity. These new results suggest that MDA can promote lymphocyte activation via induction of inflammatory pathways and networks.

Proinflammatory effects of advanced lipoxidation end products in monocytes

OBJECTIVE

The reactions of carbohydrate- or lipid-derived intermediates with proteins lead to the formation of Maillard reaction products, which subsequently leads to the formation of advanced glycation/lipoxidation end products (AGE/ALEs). Levels of AGE/ALEs are increased in diseases like diabetes. Unlike AGEs, very little is known about ALE effects in vitro. We hypothesized that ALEs can have proinflammatory effects in monocytes.

RESEARCH DESIGN AND METHODS

In a profiling approach, conditioned media from THP-1 cells either cultured in normal glucose (5.5 mmol/l) or treated with MDA-Lys or MDA alone were hybridized to arrays containing antibodies to 120 known human cytokines/chemokines. Pathway analyses with bioinformatics software were used to identify signalling networks.

RESULTS

Synthetic ALE (malondialdehyde-lysine [MDA-Lys]) (50 micromol/l) could induce oxidant stress and also activate the transcriptional factor nuclear factor-kappaB (NF-kappaB) in THP-1 monocytes. MDA-Lys also significantly increased the expression of key candidate proinflammatory genes, interferon-gamma-inducible protein-10, beta1- and beta2-integrins, cyclooxygenase-2 (COX-2), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 and -8, and inducible nitric-oxide synthase, which are also associated with monocyte dysfunction. Several key target proinflammatory proteins were significantly induced by MDA-Lys relative to normal glucose or MDA alone, including MCP-1; tumor necrosis factor ligand superfamily member-14; chemokine CC motif ligand-11 (CCL11); growth-related oncogene-alpha, -beta, and -gamma; and chemokine CXC motif ligand-13. Bioinformatics analyses identified a network of chemokine signaling among MDA-Lys-regulated genes. MDA-Lys also increased monocyte binding to vascular smooth muscle and endothelial cells. Furthermore, plasma from diabetic rats showed significantly higher levels of MDA-Lys and CCL11.

CONCLUSIONS

These new results suggest that ALEs can promote monocyte activation and vascular complications via induction of inflammatory pathways and networks.

Cholesterol loading augments oxidative stress in macrophages

To investigate the molecular consequence of loading free cholesterol into macrophages, we conducted a large-scale gene expression study to analyze acetylated-LDL-laden foam cells (AFC) and oxidized-LDL-laden foam cells (OFC) induced from human THP-1 cell lines. Cluster analysis was performed using 9600-gene microarray datasets from time course experiment. AFC and OFC shared common expression profiles; however, there were sufficient differences between these two treatments that AFC and OFC appealed as two separate entities. We identified 80 commonly upregulated genes and 48 commonly downregulated genes in AFC and OFC. Functional annotation of the differentially expressed genes indicated that apoptosis, extracellular matrix, oxidative stress, and cell proliferation was deregulated. We also identified 87 differentially expressed genes unique for AFC and 31 genes for OFC. The uniquely expressed genes of AFC are associated with kinase activity, ATP binding activity, and transporter activity, while unique genes for OFC are associated with cell signaling and adhesion. To validate the hypothesis that oxidative stress is a common feature for AFC and OFC, we performed a cluster analysis employing the genes related to oxidative stress, but we were unable to distinguish AFC from OFC in this manner. We performed real-time RT-PCR and ELISA on foam cells to examine the transcripts and secreted protein of interleukin 1 beta (IL1beta). IL1beta was rapidly induced in foam cells, but for AFC both RNA level and protein level dropped immediately and was attenuated. To detect levels of reactive oxygen species in foam cells we conducted hydroethidine staining and observed high levels of superoxide anion. We conclude that loading free cholesterol induces high levels of superoxide anion, increases oxidative stress, and triggers a transient inflammatory response in macrophages.

Beta-lactoglobulin is a thermal marker in processed milk as studied by electrophoresis and circular dichroic spectra

As much of the sterilization process involves heat treatment during the preparation of milk on an industrial scale, the unpredictable measures of the process are an essential issue in determining the quality of the milk. The purpose of the present study was to investigate the major protein change(s) of whey proteins in processed milk and extend the knowledge for future reference in the dairy industry. Using a native polyacrylamide gel electrophoresis, we showed almost a 90% loss and denaturation of beta-lactoglobulin (LG), but not alpha-lactalbumin (LA), in some brands of the processed and dry milks. Immunochemical analysis using Western blotting revealed that part of the loss was attributed to the formation of large multiple forms of LG in the processed product. Such denaturation was presumably associated with the heating procedure used in the process. Essentially, LG was the only major fraction converted to aggregates in milk heated at 95 degrees C for 30 min on 2-dimensional PAGE. The detailed thermal denaturation of purified LG and LA at various temperatures (50 to 95 degrees C) and time (5 to 960 s) were investigated using a circular dichroic analysis. The maximal changes of ellipticity at 205 nm (converting beta-structure to disordered structure) were correlated to heating temperature and time. There were no significant conformational changes of LG at temperatures below 70 degrees C for as long as 480 s. Pronounced and rapid changes occurred between 80 to 95 degrees C in a time-dependent manner. Fifty percent of the maximal changes could be reached within 15 s. In conclusion, the unique chemical and immunochemical loss and conformational changes made LG a superior marker for evaluating the thermal processing of milk. The detailed thermal denaturation curves of LG constructed with its time and temperature in this study provide a valuable reference for the dairy industry. We postulate that heat treatment over 80 degrees C in 15 s may induce a significant denaturation of milk LG.

Antisense directed at the Abeta region of APP decreases brain oxidative markers in aged senescence accelerated mice

Amyloid beta-peptide (Abeta) is known to induce free radical-mediated oxidative stress in the brain. Free radical-mediated damage to the neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD). Abeta is produced by proteolytic processing of the amyloid precursor protein (APP). The senescence accelerated mouse prone 8 (SAMP8) strain was developed by phenotypic selection from a common genetic pool. The SAMP8 strain exhibits age-related deterioration in memory and learning as well as Abeta accumulation, and it is considered an effective model for studying brain aging in accelerated senescence. Previous research has shown that a phosphorothiolated antisense oligonucleotide directed against the Abeta region of APP decreases the expression of APP and reverses deficits in learning and memory in aged SAMP8 mice. Consistent with other reports, our previous study showed that 12-month-old SAMP8 mice have increased levels of oxidative stress markers in the brain compared with that in brains from 4-month-old SAMP8 mice. In the current study, 12-month-old SAMP8 mice were treated with antisense oligonucleotide directed against the Abeta region of APP, and the oxidative markers in brain were decreased significantly. Therefore, we conclude that Abeta may contribute to the oxidative stress found in aged SAMP8 mice that have learning and memory impairments. These results are discussed in reference to AD.

Distinction Between Dry and Raw Milk Using Monoclonal Antibodies Prepared Against Dry Milk Proteins

It is well established that the heating process during the preparation of dry milk (DMLK) causes structural changes in some milk proteins. However, because such changes are subtle, whether they can be detected by an immunochemical approach remains questionable. The present study attempted to develop a sensitive mAb that might distinguish the DMLK from freshly prepared raw milk. To test this possibility, we immunized mice with commercially prepared DMLK and produced a panel of mAb. From 900 hybridomas screened using an ELISA, 4 clones were found to be specific to DMLK; the other 68 clones recognized both DMLK and raw milk. In contrast to polyclonal antibodies, only the specific mAb could detect the DMLK spiked into the raw milk at as low as 5% in concentration (vol/vol). Western blot analysis shows that these specific mAb were all directed against beta-lactoglobulin (LG) and LG-milk protein conjugates. These mAb reacted with raw milk heated at 95 degrees for 15 min; the reaction with LG-conjugates, however, was abolished when treated with reducing reagent. Thus, results suggests that a new antigenic epitope was exposed in a heating process, and the thio group of LG cross linked with other protein moiety played a provocative role in mAb recognition. A hypothetical model with respect to the interaction between the mAb and DMLK is proposed and discussed.

Antiphospholipid antibodies and atherosclerosis

Antiphospholipid antibodies (APA) are present in a variety of autoimmune disorders, including systemic lupus erythematosus (SLE) and the antiphospholipid syndrome (APS). Increasing evidence suggests that a subset of APA can also be detected in patients with atherosclerosis. In this review, we discuss the specificities of the autoantibodies that are present during both APS and atherosclerosis. A critical and unresolved question is whether these APA are specific for epitopes that result from lipid oxidation. Despite the fact that APA are present in patients with systemic autoimmunity and that they may participate in the pathogenesis of APS, recent studies have paradoxically proposed a beneficial role for some APA in atherosclerosis. We review the evidence that some APA specificities may be protective against plaque formation, and we discuss the putative mechanisms by which some APA could be useful in the prevention of atherosclerosis.

Bound malondialdehyde in foods: bioavailability of the N-2-propenals of lysine

The lipid peroxidation product malondialdehyde is mostly bound to proteins in foods as an N-2-propenal derivative that is released as N-epsilon-(2-propenal)lysine by digestive enzymes. N-2-Propenals have been identified as the major forms of malondialdehyde in urine. To determine whether available lysine can be released from the N-2-propenals of lysine in vivo, two preparations containing N-epsilon-(2-propenal)lysine and N-alpha-(2-propenal)lysine or N,N'-di-(2-propenal)lysine were synthesized using radioactively labeled lysine and were administered to rats by gastric intubation and intraperitoneal injection. Both preparations were absorbed from the digestive tract, although not as efficiently as free lysine, but most of the radioactivity was excreted in urine. The radioactive label was also readily excreted after intraperitoneal injection. It is concluded that the N-2-propenals of lysine are fairly stable in vivo, so that, although they are absorbed from the gut, most of the absorbed material is not metabolized and is readily excreted as nonavailable lysine.