Serum amyloid A protein (SAA) has been considered to play an important role for the modification of pathophysiolgical situation in inflammatory diseases and the developments of the complications. Its participation on the pathogeneses has been elucidated by the basic and clinical studies on the tissue amyloid deposit and SAA. Since the causes of individual inflammatory reactions and the pathogeneses are very variable and complicated, the causes and chemical compositions of amyloid deposits are not always identical. It is considered that the amyloid formation is a defence mechanism against the inflammatory stimuli, but it causes often diverse effects on various organs. Thereafter, it is necessary to know the sources of the inflammatory reactions and the secondary effects on various metabolism to understand the regulation of the amyloid formation.

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Nitric oxide (NO) is a bioactive molecule for leukocyte, endothelial cells of blood vessels and neurons. NO is generated from L-arginine by the action of NO synthase (NOS). Endothelial NOS (eNOS) was phosphorylated by protein kinase C (PKC) and protein kinase A. Phosphorylation of eNOS by PKC reduced the NOS activity. eNOS mRNA is constitutively expressed in endothelial cells and regulated by intracellular Ca²⁺ concentration. To examine the regulation of eNOS mRNA by cytokines, atherogenic lipids and mechanical stretch, we employed RNase protection assay and Western blotting in cultured bovine aortic endothelial cells. Interferon α/β upregulates eNOS mRNA expression in a transcriptional level. Moreover, mechanical stretch upregulated eNOS mRNA expression and NO production. TNF-α downregulated eNOS mRNA through destabilization of mRNA. In atherosclerotic arteries endothelium-dependent relaxation (EDR) is impaired. To clarify the mechanisms of impaired EDR, we investigated the effect oxidized LDL on EDR. Fractionation of individual lipids revealed that lysophosphatidylcholine (LPC) inhibited EDR. OX-LDL or LPC inhibited accumulation of IP₃ followed by the increase of intracellular Ca²⁺ concentration induced by agonists including bradykinin. On the other hand, atherogenic lipidsuch as oxidized LDL and lysiphosphatidylcholine increased eNOS mRNA and protein. From these results, LPC in ox-LDL may cause the impairment of EDR in atherosclerotic arteries.

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Thrombin is a multifunctional serine protease generated at sites of vascular injury. While it is best known for its ability to cleave fibrinogen and trigger fibrin formation, thrombin is also a powerful agonist for a variety of cellularesponses. Thrombin acts on the vascular endothelium to stimulate production of prostacyclin, plasminogen activator inhibitor, and the potent smooth muscle cell mitogen platelet-derived growth factor. Recent studiesuggest that many of these disparate functions of thrombin are mediated by a common receptor. Robust thrombin receptor expression was noted in human atherosclerotic plaques by in situ hybridization. In the normal arterial wall, however, thrombin receptor was expressed only in endothelial cells. The high and selective expression of thrombin receptor in atherosclerotic lesionsuggests a possible role for thrombin receptor activation in restenosis and in atherogenesis itself. Thrombin receptor is activated by an unique mechanism. Its amino terminal exodomain includes a putative thrombin cleavage site resembling the known thrombin cleavage site in protein C. Carboxyl to this site was a sequence resembling the carboxyl tail of hirudin, a leech protein known to interact with thrombin's anion-binding exosite. Cleavage of extracellular amino-terminus at this site is necessary and sufficient for receptor activation. Thrombin recognizes high affinity binding site and bind with docking mechanism, and cleaves amino terminal activation peptide to unmask new amino terminus. The new amino terminus then functin as a tethered ligand and stimulates receptor, which is essentially a peptide receptor predominantly by intramolecular liganding. After activation, thrombin receptor is phosphorylated and desensitized at least in part by BARK2-like kinase. Thrombin receptor sensitivity to inhibition by BARK2 required the presence of specific serine and threonine residues in the receptor's cytoplasmic domain. After being internalized into the endosomal compartment, unlike beta2 adrenergic receptor which recycle to the plasma membrane, thrombin receptor is targeted to lysosome. This mechanism is unique in the thrombin receptor among the G-protein coupled receptors and is reasonable, because the receptor is not re-usable once activated. Thrombin inhibitors have been tried to prevent thrombin-mediated arteriosclerosis. However, difficulty in controling bleeding time was a limiting for clinical imprecation. Direct inhibitors of thrombin receptor which dissociates receptor activity from thrombin's proteolytic activity is necessary to solve this problem

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Murine models of atherosclerosis is increasingly used for the studies of atherosclerosis. 1) We compared atherosclerosis of LDLR-/-, apo E-/-or LDLR-/-;apo E-/- mice in light of their lipoprotein profiles. The mice were fed a nomlal chow, and sacrified at age 12 months. Aortic lesions were visualized by staining with Sudan IV. Wild type mice had no lesins. The lesions of the LDLR-/- mice were restricted to the aortic arch, couprising only 5% of the total surface area of the aorta. On the other hand, the lesions of the apo E-/- mice were more extensive and involved 30% of the total surface area. The aortic arches were totally diseased with skipping lesions in other parts of the aorta. Lesions in the LDLR-/-;apo E-/- mice deVeloped advanced further. Most of he luminal surface of he aorta (80%) was covered with lesion coalescence. Mean plasma cholesterol levels of the wild type, LDLR-/-, apo E-/-, and LDLR-/-;apo E-/- mice were 101, 388, 543, and 578mg/dl, respectively. Thus, the differences in atherosclerotic progression between apo E-/- and LDLR-/-;apo E-/- mice were not attributable to the differences in plasua cholesterol levels but to a coubined elevation of LDL and reunants. In conclusion, LDL accelerates atherosclerosis synergis. tically with reunant lipoproteins. LDLR-/-;apo E-/- mice may serve as a model of rampant atherosclerosis. 2) Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of triglyceride-rich lipoproteins. Conflicting results have been reported concerning its role in atherogenesis. To determine the effects of the overexpressed LPL on diet-induced atherosclerosis, we have generated low density lipoprotein receptor (LDLR) knockout mice which overexpressed huuan LPL transgene (LPL/LDLRKO) and compared their plasma lipoproteins and atherosclerosis with those in non-expressing LDLR-knockout mice (LDLRKO). On a normal chow diet, LPL/LDLRKO mice showed marked suppression of mean plasma triglyceride levels (32 vs 236mg/dl) andmodest decrease in mean cholesterol levels (300 vs 386mg/dl) as compared with LDLRKO mice. Larger lipoprotein particles of LDL/LDL were selectively reduced in LPL/LDLRKO mice. On an atherogenic diet, both mice exhibited severe hypercholesterolemia. But, mean plasua cholesterol levels in LPL/LDLRKO mice were still suppressed as coupared with that in LDLRKO mice (1, 357 vs 2, 187mg/dl). Marked reduction in a larger subfraction of IDL/LDL, which conceivably corresponds to remnant lipoproteins, was observed in the LPL/LDLRKO mice. LDLKO mice developed severe fatty streak lesions in the aortic sinus after feeding with the atherogenic diet for 8 weeks. In contrast, mean lesion area in the LPL/LDLRKO uice was 18-fold smaller than than that in LDLRKO mice. We suggest that the altered lipoprotein profile, in particular, reduced level of remnant lipoproteins is mainly responsible for the protection by LPL against atherosclerosis.

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Effects of 12 weeks treatment with S, a bile acid sequestrant (C), B, or P were compared in 32, 16, 30, and 22 patients with hyperlipoproteinemia. Plasma levels of lipoprotein subfraction-cholesterol (C), and activities of LCAT and CETP were measured at 0 and 12 weeks. LDL receptor activities in lymphocytes cultured in lipoprotein-deficient medium were also assayed. S, B, and P reduced plasma levels of VLDL-C and IDL-C but C did not. S, C, and P reduced plasma levels of LDL1 (1.019<d<1.045)-C but B did not. S and B reduced plasma levels of LDL₂ (1.045<d<1.063)-C but C and P did not change. P markedly reduced plasma levels of HDL₂-C but S, C, and B did not change them. B increased plasma levels of HDL₃-C and P decreased them. S and B decreased the cholesterol esterification rate but C and P did not change. P markedly increased CETP activities and S and B decreased them. LDL receptor activities positively correlated with the druginduced reduction of LDL-C and LDL₁-C.
We conclude that the reduction of plasma lev ls of large, light LDL by drug treatment is mainly regulated by LDL receptor activities and the reduction of LDLi by drug treatment is more prominent in patients with lower LDL receptor activities.

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