Degradation of rat C-reactive protein by macrophages

Chlamydia pneumoniae infections augment atherosclerotic lesion formation: a role for serum amyloid P

Multiple reports have demonstrated an association between Chlamydia pneumoniae (Cpn) and cardiovascular disease. In this study we evaluated the effect of Cpn infections on early lesion progression in C57BL/6J mice. Since plaque formation in these mice does not develop past the initial stage, we thought these mice might be a better model for unravelling the effect of Cpn infection on early lesion type progression. C57BL/6J mice were fed an atherogenic diet and injected 10 times with 5 x 10(7) IFU Cpn or mock. At sacrifice, lesion number, size and type were analysed. To study the role of Cpn in inflammation, serum amyloid P (SAP) in plasma was determined as well as T-cells, macrophages and SAP in the lesions. In the aortic sinus of both groups, type 2 lesions were found. Cpn infection resulted in a 2.2-fold increase in total lesion size (Cpn: 10821+/-2429 microm(2)vs mock: 5022+/-1348 microm(2); p=0.04). No difference in lesion number was observed. Also, Cpn infection increased SAP in the lesions from 1.10(-4)+/-0.1.10(-4) SAP-positive cells/lesion area to 10.10(-4)+/-1.10(-4) SAP-positive cells/lesion area (p=0.05). The influx of T-lymphocytes and macrophages in the lesions as well as SAP plasma levels were not different between groups. Multiple Cpn infections resulted in a significant increase in total lesion size of C57BL/6J mice. Increase in total SAP-positive area in infected mice suggests a role for this acute-phase protein in lesion enlargement.

The regulation of superoxide generation and nitric oxide synthesis by C-reactive protein

Activated macrophages utilize both reactive oxygen intermediates and reactive oxynitrogen intermediates for defence against microbes. However, simultaneous generation of superoxide (O- 2;) and nitric oxide (NO) could be harmful to host cells due to the production of peroxynitrite, nitrogen dioxide and hydroxyl radicals. Therefore, the regulation of the production of these molecules is critical to host survival. During periods of inflammation or infection, the level of serum C-reactive protein (CRP) increases in many species. Human and rat CRP have been shown to bind and interact with phagocytic cells. Since many of the interactions of CRP involve the binding to the phosphocholine ligand, we studied the role of CRP in O- 2; and NO generation through the modulation of phosphatidylcholine (PC) metabolism in macrophages. This study has shown that, while rat CRP inhibited phorbol myristate acetate- (PMA) induced release of O- 2; by rat macrophages, CRP-treated macrophages released NO in a time- and dose-dependent manner. CRP increased inducible nitric oxide synthase (iNOS) enzyme as well as iNOS mRNA levels in rat macrophages. Tricyclodecan-9-yl-xanthogenate (D609), an inhibitor to PC phospholipase C (PC-PLC), suppressed iNOS induction but enhanced PMA-induced release of O- 2;. These data indicate that an increased level of CRP during periods of inflammation may result in differential regulation of macrophage NADPH oxidase and iNOS activity. Increased hepatic synthesis of CRP may contribute to the mechanism by which phagocytic cells avoid simultaneous O- 2; and NO synthesis, and this could possibly be mediated through the regulation of PC-PLC.

The disodium salt of EDTA inhibits the binding of vasoactive intestinal peptide to macrophage membranes: endodontic implications

The purpose of this study was to investigate the effect of the disodium salt of ethylenediamine tetraacetate (EDTA), a calcium ion chelator used in the root canal therapy, on vasoactive intestinal peptide (VIP) binding to macrophage membranes (MM's). Binding assays were conducted at 15 degrees C in 0.5 ml of 50 mM Tris-HCl buffer (pH 7.5) containing 1.6% (w/v) bovine serum albumin, 1.2 mg/ml of bacitracin, and different EDTA concentrations, using 45 pM of [125I]VIP as tracer. Results showed that EDTA inhibits VIP binding to MM's in a dose-dependent manner, with an IC50 value of 5.4 mM (p < 0.01). EDTA concentrations equal or higher than 100 mM of abolished VIP-MM interaction. Taking into account that the macrophage plays an essential role in inflammatory reactions and the immune response, we conclude that the apical extrusion of EDTA during root canal therapy could modify VIP-macrophage interaction modulating the inflammatory mechanisms involved in periapical lesions.

Structure and function of the pentraxins

Over the past two years, the three-dimensional structure of the serum amyloid P component was defined by X-ray diffraction, the first such visualization of a pentraxin. Binding sites for calcium, ligands and complement were identified. New fusion proteins with amino acid sequence homology to the pentraxins were described, and new insights were gained into pentraxin phylogeny, biosynthesis, ligands, complement activation, leukocyte reactivity and biological functions in vivo.

Changes in serum concentration and mRNA level of rat C-reactive protein

C-reactive protein (CRP) is a typical acute-phase protein found in many animals. Several stimuli, including IL-6 produced by macrophages localized around the site of tissue injury and/or bacterial infection, induce CRP synthesis in liver. One of the authors (W.N.) reported previously that sex hormones also affect the serum CRP concentration in rats. However, little is known about the process of CRP production, including time-dependent changes in the CRP mRNA level in liver. In the present study, we observed time-dependent changes in the serum concentration of CRP and the CRP mRNA level in liver after the injection of turpentine-oil or estradiol-17 beta in rats (Wistar strain). After turpentine-oil injection, CRP mRNA increased, followed by an increase in the serum CRP concentration, indicating that inflammation enhances transcription of the CRP gene. In contrast, upon estradiol-17 beta administration, the serum CRP concentration decreased without any decline in the CRP mRNA level in liver. The latter finding suggests that rats may have an alternative mechanism for regulating the serum concentration of CRP.

Rat C-reactive protein causes a charge modification of LDL and stimulates its degradation by macrophages

We have previously shown the binding of low-density lipoprotein (LDL) to immobilized rat C-reactive protein (CRP) and the formation of a fluid-phase complex between these two proteins. In this report we used immunoelectrophoresis and agarose gel electrophoresis to show increased anodic migration of the LDL particle as a result of the modification of LDL by rat CRP. The degradation of the modified 125I-LDL by rat peritoneal macrophages was increased more than twofold in the presence of rat CRP. The increase in rat CRP-mediated 125I-LDL degradation by macrophages was dependent on the concentrations of 125I-LDL and rat CRP. This increased 125I-LDL degradation was inhibited by phosphorylcholine. In contrast, the degradation of 125I-acetyl-LDL by macrophages was not affected by rat CRP, although acetylated LDL inhibited the rat CRP-stimulated degradation of 125I-LDL. Increasing concentrations of LDL did not affect the degradation of rat 125I-CRP by the macrophages, which suggested that the rat CRP and the modified LDL did not enter the cell as a complex. Our results suggested that the increased degradation of 125I-LDL was caused by the charge modification of 125I-LDL by rat CRP, due to a fluid-phase complex formation between 125I-LDL and rat CRP, and that the degradation involved the scavenger receptor present on the macrophages.