Activation of acyl-coenzyme A:cholesterol acyltransferase activity by cholesterol is not due to altered mRNA levels in HepG2 cells

Many studies have shown that sterols can stimulate acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in cells. To elucidate this mechanism, effects of sterol-mediated induction on both the enzyme activity of ACAT and its mRNA levels were studied in human hepatoblastoma cell line, HepG2 cells. When HepG2 cells were loaded with cholesterol and 25-hydroxycholesterol, both the whole-cell ACAT activity and the microsomal ACAT activity were increased by 85.1% and 41.3%. In contrast, cholesterol depletion of HepG2 cells with compactin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, resulted in a decrease in both the whole-cell and the microsomal ACAT activity by 46.4% and 58.3%. Under identical conditions, RT-PCR and Northern blotting analyses revealed that neither cholesterol loading nor cholesterol depletion of HepG2 cells altered the amounts of ACAT mRNA. Moreover, these treatments had no effect on the enzymatic ACAT activity determined by the reconstituted assay in which HepG2 cell homogenate had been supplemented in vitro with a saturating level of exogenous cholesterol. These results indicate that cholesterol-induced up-regulation of ACAT activity in HepG2 cells does not occur at the level of transcription, but rather at a posttranscriptional level.

Accumulation of advanced glycation end products of the Maillard reaction with age in human hippocampal neurons

The recent immunological demonstration of advanced glycation end products (AGE) of the Maillard reaction in several human tissues suggests a possible involvement of AGE in the aging process. We previously prepared a monoclonal anti-AGE antibody (6D12) which recognized N epsilon-(carboxymethyl)lysine. We examined, immunohistochemically, the effect of aging on AGE-immunoreactivity in hippocampal pyramidal neurons in ten brain tissue samples obtained at autopsy from subjects aged 20-85 years old. Using 6D12 antibody, our results demonstrated a positive correlation between AGE-immunoreactivity in hippocampal pyramidal neurons and age. A more intense immunoreaction was observed in the CA3-4 pyramidal neurons compared with that of the CA1 neurons, known to be vulnerable to the formation of neurofibrillary tangles. Our results suggest that AGE are probably involved in the aging process affecting the human central nervous system, and that AGE do not mainly contribute to the formation of neurofibrillary tangles, at least in the CA1 neurons.

Lysophosphatidylcholine potentiates the mitogenic activity of modified LDL for human monocyte-derived macrophages

The growth of murine peritoneal macrophages is induced by oxidized LDL (Ox-LDL), and lysophosphatidylcholine (lysoPC) plays an important role in its mitogenic activity. In the present++ study, Ox-LDL-induced macrophage growth was examined with human monocyte-derived macrophages. The cell growth of human macrophages was significantly induced by Ox-LDL but not by acetylated LDL (acetyl-LDL). The treatment of acetyl-LDL with phospholipase A2, however, led to a marked increase in its mitogenic activity, with a concomitant conversion of 75% of its phospholipids to lysoPC. The growth-stimulating activity became positive only when both acetyl-LDL and lysoPC were coincubated, although neither of them exhibited cell growth-promoting activity. These results suggest that Ox-LDL could stimulate the growth of human monocyte-derived macrophages, and lysoPC may play an essential role in the mitogenic activity of Ox-LDL.

Identification of pentosidine as a native structure for advanced glycation end products in beta-2-microglobulin-containing amyloid fibrils in patients with dialysis-related amyloidosis

beta-2-Microglobulin (beta-2m) is a major constituent of amyloid fibrils in patients with dialysis-related amyloidosis (DRA). Recently, we found that the pigmented and fluorescent adducts formed nonenzymatically between sugar and protein, known as advanced glycation end products (AGEs), were present in beta-2m-containing amyloid fibrils, suggesting the possible involvement of AGE-modified beta-2m in bone and joint destruction in DRA. As an extension of our search for the native structure of AGEs in beta-2m of patients with DRA, the present study focused on pentosidine, a fluorescent cross-linked glycoxidation product. Determination by both HPLC assay and competitive ELISA demonstrated a significant amount of pentosidine in amyloid-fibril beta-2m from long-term hemodialysis patients with DRA, and the acidic isoform of beta-2m in the serum and urine of hemodialysis patients. A further immunohistochemical study revealed the positive immunostaining for pentosidine and immunoreactive AGEs and beta-2m in macrophage-infiltrated amyloid deposits of long-term hemodialysis patients with DRA. These findings implicate a potential link of glycoxidation products in long-lived beta-2m-containing amyloid fibrils to the pathogenesis of DRA.

Purification of a marine bacterial glucose dehydrogenase from Cytophaga marinoflava and its application for measurement of 1,5-anhydro-D-glucitol

A novel glucose dehydrogenase (GDH) from a marine bacterium Cytophaga marinoflava IFO 14170 was isolated from its membrane fraction. This GDH catalyzes the oxidation of a hydroxy group of glucose, but does not react in its C-1 position. This enzyme is composed of a single peptide with a mol wt of 67,000. The GDH can react under high salinity. The optimum pH is around 8.0, showing typical property of marine bacterial enzymes. Using this novel enzyme, and enzymatic determination of 1,5-anhydro-D-glucitol (1,5AG) utilizing 2,6-dichrolophenolindophenol (DCIP) and phenazine methosulfate (PMS) as electron mediators was carried out. A good linear correlation was observed from 0.5 mM to 4 mM of 1,5AG.

Stimulation of macrophage DNA synthesis by polyanionic substances through binding to the macrophage scavenger receptor

We previously demonstrated that ligands of macrophage scavenger receptors such as acetylated low density lipoprotein (LDL), oxidized LDL and advanced glycation-end products (AGE) of the Maillard reaction induce the growth of peritoneal exudate macrophages, and that the activity of AGE is inhibited by the presence of an antibody for granulocyte/macrophage colony-stimulating factor (GM-CSF). To evaluate the suggested role of the scavenger receptor in the induction of macrophage growth, we compared the effect of various polyanionic compounds which were reported to either have or not to have competent activity for the binding of acetylated LDL to scavenger receptors on macrophage DNA synthesis. Among the polyanions exhibiting such activity, polyguanilic acid (poly G) and dextran sulfate strongly augmented macrophage DNA synthesis, although they did not increase macrophage cell number. On the other hand, polyanions which are not ligands for the scavenger receptors did not show a significant augmenting effect, suggesting that the binding of polyanions to the scavenger receptor is important but not, by itself, sufficient. The augmentation of DNA synthesis in macrophages cultured with dextran sulfate or poly G was inhibited by the co-presence of anti-GM-CSF antibody, suggesting that the reaction is mediated by GM-CSF. However, dextran sulfate did not augment the production of GM-CSF in macrophages. Therefore, GM-CSF spontaneously present in macrophages might be a prerequisite for the induction of DNA synthesis.

The heparin-bound fraction of human lipoprotein-deficient serum inhibits endocytic uptake of oxidized low density lipoprotein by macrophages

We recently demonstrated that bovine lactoferrin, a cationic whey protein from bovine milk, interacts with the negative charges of modified low density lipoproteins (modified LDL) such as acetylated LDL (acLDL) and oxidized LDL (oxLDL), which markedly interferes with their endocytic uptake by rat peritoneal macrophages (Kajikawa M, Ohta T, Takase M, Kawase K, Shimamura S, Matsuda I. Biochim Biophys Acta 1994;1213:82-90). In the present study, we examined whether human lipoprotein-deficient serum (LPDS) might contain protein(s) that could inhibit the endocytic uptake of oxLDL by mouse macrophages. We fractionated LPDS by heparin affinity chromatography and found that the cellular binding of oxLDL to mouse macrophages and subsequent endocytic uptake were inhibited by 50%-60% with the heparin-bound fraction, whereas the heparin-unbound fraction had no effect. Similar results were obtained in the experiments with acetylated LDL. Sephacryl S-300 gel-filtration chromatography of a mixture of oxLDL and the heparin-bound fraction revealed that a 150-kDa protein was associated with oxLDL. These results indicate that the electrostatic interaction of oxLDL with some component(s) of the heparin-bound fraction might interfere with the endocytic uptake of oxLDL by the macrophage scavenger receptor.

Reconstituted high density lipoprotein reduces the capacity of oxidatively modified low density lipoprotein to accumulate cholesteryl esters in mouse peritoneal macrophages

Oxidized low density lipoprotein (ox-LDL) was incubated with discoidal complexes of apolipoprotein A-I (apo A-I) and dimyristoylphosphatidylcholine (DMPC) (DMPC/apo A-I) in a cell-free system and re-isolated on Sephacryl S-400 gel filtration chromatography. Analyses of re-isolated ox-LDL showed that apo A-I was transferred from DMPC/apo A-I to ox-LDL, which accounted for 10% of the total protein of ox-LDL. Re-isolated ox-LDL also showed a 2.2-fold increase in phospholipid and a 14% decrease in cholesterol content on an apo B basis. The electrophoretic mobility of re-isolated ox-LDL was markedly reduced almost to that of native LDL. Moreover, the amounts of re-isolated ox-LDL to be degraded by mouse peritoneal macrophages as well as the capacity of re-isolated ox-LDL to accumulate cholesteryl esters (CE) in these cells were markedly reduced (60% and 80% reduction, respectively), suggesting that the ligand activity of ox-LDL for the scavenger receptor was significantly reduced upon treatment with DMPC/apo A-I. Parallel incubation of ox-LDL with free apo A-I led to a similar incorporation of apo A-I into ox-LDL. However, it had no effects on the ligand activity of ox-LDL. Thus, it is likely that the reduction in the ligand activity of ox-LDL by DMPC/apo A-I is explained by the change in the lipid moiety (mainly phospholipid) of ox-LDL. Since discoidal high density lipoprotein (HDL) is known to occur in vivo, this phenomenon might explain one of the anti-atherogenic functions of HDL.

Fluoridation of hydroxyapatite powder by ammonium hexafluorosilicate

Diamine silver fluoride [AgF: (NH3)2AgF] is a unique fluoride solution used clinically in Japan for primary teeth. AgF has been shown to reduce dental caries and dentine hypersensitivity. However, AgF also stains teeth black due to sulfide precipitation and thus is unacceptable for permanent teeth. In the present study, the potential value of ammonium hexafluorosilicate [SiF: (NH4)2SiF6], which has a formula similar to that of AgF but contains no Ag, was studied with respect to its ability to fluoridate apatite. Hydroxyapatite [HAP: Ca10(PO4)6(OH)2] powder was treated with several topical fluoride solutions, i.e. neutral sodium fluoride, acidulated phosphate fluoride (APF) along with AgF and SiF. Following treatment, the HAP powders were analyzed for their fluorine content, crystallinity changes, and solubility in acidic solution. The highest level of fluoridated HAP [FAP: Ca10(PO4)6(OH)xF2-x] was observed in HAP powder treated with SiF, even though more total fluorine in the form of FAP and CaF2 was observed in HAP powder samples treated with APF. Presumably as a consequence of this higher level of FAP formation after SiF treatment, the highest level of crystallinity along with the lowest solubility in acidic solution were observed in HAP powder treated with SiF solution. We concluded, therefore, that SiF may have potential value for use as a topical fluoride solution.

Roles of advanced glycation end-products in the progression of diabetic nephropathy

Available data indicate that the development of diabetic nephropathy is linked to hyperglycaemia. Glucose reacts nonenzymatically with proteins to form Schiff base and Amadori products. Further incubation of these early products leads to the formation of advanced glycation end-products (AGEs). AGEs seem to play a central role in the progression of diabetic nephropathy. Immunohistochemically, AGEs were also detected in an expanded mesangial matrix, especially in nodular lesions from patients with diabetic nephropathy. AGEs staining was noted in the Bowman's capsule, periglomerular fibrosis in sclerosing glomeruli. In our ultrastructural study of mesangial matrix from patients with diabetic nephropathy by high-resolution scanning electron microscopy after cellular removal, the meshwork structure was evident at higher magnification. In nodular lesions, the loose meshwork structure appeared to be composed of various sized strands, ranging from 6 to 24 nm (mean +/- SD: 11.4 +/- 3.8 nm). The pore sizes were variable, ranging from 4 to 70 nm (mean +/- SD: 23.6 +/- 12.3 nm), and were statistically larger than those of normal controls. As the AGEs are localized most notably in nodular lesions, advanced glycations play a role in the progression of diabetic nephropathy through impairment of the assembly of matrix proteins in vivo. Because type V and type VI collagens are the major components of nodular lesions, increases in these interstitial and fibril or microfibril collagens may contribute to the formation of wider strands in the mesangial matrix of a nodular lesion. As no metalloprotease that is specific for type VI collagen has been identified thus far, AGEs formation might occur preferentially in type VI collagen-rich nodular lesions, which are sites of slow turnover.

Role of polyol pathway in nonenzymatic glycation

In order to confirm the link between nonenzymatic glycation and the polyol pathway, we observed the effect of treatment with epalrestat (Ep), an aldose reductase inhibitor, on the concentration of advanced glycation end-products (AGEs) in erythrocytes from diabetic patients. We also examined the effect of the drug on erythrocyte fructose 3-phosphate (F3P), a novel metabolite that has been reported to relate to the polyol pathway, and ascertained the glycation capability of F3P and its possible breakdown product, 3-deoxyglucosone (3DG), by incubating the metabolites with bovine serum albumin (BSA). Incubation of BSA with F3P or 3DG resulted in a greater production of AGEs in comparison with the incubation with glucose or fructose. F3P was significantly increased in erythrocytes from diabetic patients compared with those from nondiabetic individuals and was lower in patients who had been treated with Ep than in those who were free from the compound. A treatment of patients with Ep for 1 month resulted in a significant decrease in F3P. Erythrocyte AGEs were significantly elevated in diabetic patients compared with nondiabetic individuals and tended to be lower in patients taking Ep than in those without Ep. Administration of Ep for 2 months decreased AGEs. These results show that the polyol pathway is likely to play a substantial role in the nonenzymatic glycation of proteins and the suppression of E3P as well as AGEs by an aldose reductase inhibitor may explain in part the preventive effect of the drug on diabetic complications.

Advanced glycation end products stimulate plasminogen activator activity via GM-CSF in RAW 264.7 cells

The effects of advanced glycation end products (AGE) on the plasminogen activator (PA) activity were investigated with murine macrophage cell line RAW 264.7 cells. AGE-bovine serum albumin (BSA) showed a dose-dependent induction for the urokinase-type PA (uPA) activity. The uPA induction by AGE-BSA was effectively suppressed by the antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF). The uPA activity of these cells was also induced by ligands for the macrophage scavenger receptor (MSR). These data provide evidence that AGE-BSA stimulates the uPA activity via GM-CSF through MSR in RAW cells. These findings, taken together with a recent demonstration of endocytic uptake of AGE-proteins by MSR in vitro and the presence of AGE-proteins in atherosclerotic lesions, strongly suggest that the uPA induction by AGE-proteins via MSR plays an important role in human atherogenesis.

A new type of advanced third-stage larvae of the genus Gnathostoma in freshwater eels, Fluta alba, from Nakhon Nayok, central Thailand

Five advanced third-stage larvae of a newly identified type of genus Gnathostoma were collected from freshwater eels, Fluta alba, which were purchased at a market in Nakhon Nayok, central Thailand. The most remarkable characteristic of the newly identified larvae was the larger body size compared with any other larva of Gnathostoma spp. They were also distinguishable from other species by the shape of their hooklets, which branched in a complex manner at the base: this had not been previously observed in any other larval Gnathostoma. The newly described larvae had an average number of 44.5, 45.0, 49.0 and 55.1 hooklets on the head-bulb from the first to the fourth rows, respectively, which were comparable to those of larval G. spinigerum. However, the average number of nuclei in each intestinal cell was 2.21 and fewer than those of the larvae of G. spinigerum. These results suggest that the new type of larvae belong to either G. vietnamicum, G. malaysiae, or constitute a new species of the genus Gnathostoma.

Localization of advanced glycation end products of Maillard reaction in bovine tissues and their endocytosis by macrophage scavenger receptors

In aged bovines, the accumulation of advanced glycation end-products (AGEs) in macrophages, endothelial cells, adventitial cells, or pericytes; epithelial or parenchymal cells of some organs such as the liver, adrenals, and kidneys; neuronal cells in the brain; and extracellular matrix was demonstrated by immunohistochemistry using anti-AGE monoclonal antibody 6D12. Immunoelectron microscopy demonstrated the localization of AGEs in the endosomal and lysosomal compartments of various types of cell and in the extracellular matrix. By biochemical characterization of the interaction of AGEs with bovine alveolar macrophages using [125I]AGE-bovine serum albumin (BSA), the cell association and subsequent endocytic degradation of [125I]AGE-BSA were confirmed. To investigate the possible participation of scavenger receptors in the endocytosis of AGEs, these cells were incubated with AGE-BSA conjugated with colloidal gold particles (AGE-BSA-Au particles) and examined by immunoelectron microscopy with a monoclonal antibody for bovine macrophage scavenger receptors, D2. In these macrophages, AGE-BSA-Au particles were bound to the D2-positive scavenger receptors on the surface membrane, endocytosed, and directed to secondary lysosomes. The scavenger receptors were dissociated from the ligands in late endosomes and recycled via a trans-Golgi system to the cell surface membrane. These data suggest that scavenger receptors participate in the endocytic process of AGEs by macrophages.

Localization of advanced glycation endproducts in the kidney of experimental diabetic rats

Advanced glycation endproducts (AGE) have been proposed as a major mediator in the development of various diabetic complications. In order to evaluate the involvement of AGE in the development of diabetic nephropathy, we examined the localization of AGE in the kidney of the streptozotocin-induced diabetic rats immunohistochemically using a monoclonal antibody directed to AGE. In the diabetic rats, glomerular hypertrophy, thickening of the glomerular basement membrane, and expansion of mesangial matrix were observed. AGE was detected in expanded mesangial area and glomerular basement membrane in the kidneys of diabetic rats. The present results suggest that AGE may participate in the development of diabetic nephropathy.

Immunohistochemical and ultrastructural detection of advanced glycation end products in atherosclerotic lesions of human aorta with a novel specific monoclonal antibody

To elucidate the deposition of advanced glycation end products (AGEs) in aortic atherosclerosis, aortic walls were obtained from 25 autopsy cases and examined immunohistochemically and immunoelectron microscopically with a monoclonal antibody specific for AGEs, 6D12. Among the autopsy cases, atherosclerotic lesions were found in the aortas of 22 cases and were composed of diffuse intimal thickening, fatty streaks, atherosclerotic plaques, and/or complicated lesions. In these cases, intracellular AGE accumulation was demonstrated in the intimal lesions of aortic atherosclerosis in 12 cases. Compared with the diffuse intimal thickening, intracellular AGE accumulation was marked in the fatty streaks and atherosclerotic plaques. Immunohistochemical double staining with 6D12 and monoclonal antibodies for macrophages or muscle actin or a polyclonal antibody for scavenger receptors demonstrated that the AGE accumulation in macrophages or their related foam cells was marked in the diffuse intimal thickening and fatty streak lesions and that almost all macrophages and macrophage-derived foam cells possessed scavenger receptors. Immunoelectron microscopic observation revealed the localization of 6D12-positive reaction in lysosomal lipid vacuoles or electron-dense granules of the foam cells. These results indicate that AGE accumulation occurs in macrophages, smooth muscle cells, and their related foam cells.

Interaction of rat liver lysosomes with basic polypeptides

In order to gain knowledge on the interaction of lysosomes with proteins, we have assessed the equilibrium densities of the lysosomal membrane and matrix markers after in vitro incubation of rat liver lysosomes with various polypeptides. The addition of basic polypeptides, polylysine or protamine, to the suspension of lysosomes brought about a profound alteration of lysosomal membrane, causing extensive leakage of lysosomal matrix enzymes. Electron microscopic observation revealed a remarkable aggregation of lysosomes by the basic polypeptides. Polyglutamic acid, an acidic polypeptide, did not produce such effect. ATP was found to stabilize lysosomes during incubation, particularly with basic polypeptides.

Ultrastructure of nonenzymatically glycated mesangial matrix in diabetic nephropathy

Advanced protein glycation has been proposed as a major factor in the development of diabetic nephropathy. Advanced glycation end products (AGEs) have altered the structure of extracellular matrix component and impaired self association in vitro. To elucidate the role of AGEs in the progression of diabetic nephropathy, the present study was undertaken to localize glomerular AGEs immunohistochemically. Ultrastructural changes of the mesangial matrix were analyzed with high resolution scanning electron microscopy. No glomerular AGEs staining was noted in normal control kidney specimens, or in tissue from glomerulonephritis patients without diabetes mellitus. The mesangium showed a positive AGEs staining in advanced stages of diabetic nephropathy, and the most characteristic finding was the strong AGEs staining in nodular lesions. By high resolution scanning electron microscopy, control and diabetic mesangial matrices revealed a meshwork structure composed of fine fibrils (10 nm in width) and numerous pores (12 to 13 nm in diameter). In the nodular lesions, however, loosening of the meshwork was significant, and the diameter of the pores was enlarged (approximately 24 nm). This study provides the first immunohistochemical evidence that AGEs are localized in diabetic glomeruli, most notably to nodular lesions. Advanced glycation might play a role in the progression of diabetic nephropathy through impairment of the assembly of matrix proteins in vivo.

Production of functional chick liver HMG 2a protein in Escherichia coli

An efficient Escherichia coli system for the production of a variant form of high-mobility group-2a protein (HMG 2a), having the additional 5 amino acid residues (Ala-Pro-Thr-Leu-Glu) at the NH2-terminal, has been constructed. cDNA encoding HMG 2a was ligated with the Omp A signal peptide sequence and was inserted into an inducible bacterial expression vector pSH-L. After the plasmid introduced into E. coli was expressed by temperature shift, the recombinant product was purified by trichloacetic acid precipitation followed by Bio-Rex 70 column chromatography. The purified product showed the expected NH2-terminal sequence and the superhelical activity of circular DNA similar to the authentic HMG 2a isolated from chick liver.

Macrophage scavenger receptor mediates the endocytic uptake and degradation of advanced glycation end products of the Maillard reaction

Modification of proteins by long-term incubation with glucose leads to the formation of advanced glycation end products (AGE). Recent immunological demonstration of the presence of AGE proteins in several human tissues suggests that they may be involved in aging, diabetic complications and atherosclerosis. AGE proteins are taken up by macrophages via the AGE receptor, which is similar to the macrophage scavenger receptor (MSR). In the present study, we examined whether MSR could mediate the endocytic uptake of AGE proteins by using Chinese hamster ovary (CHO) cells overexpressing bovine type II MSR (CHO-SRII). 125I-labelled AGE bovine serum albumin (125I-AGE-BSA) as well as 125I-acetylated low-density lipoprotein (125I-acetyl-LDL) underwent endocytic degradation by CHO-SRII cells, but not by control CHO cells. Endocytic degradation of 125I-acetyl-LDL and 125I-AGE-BSA by CHO-SRII cells was significantly inhibited by unlabeled AGE-BSA, as well as by acetyl-LDL. Immunoelectron microscopic studies using both AGE-BSA conjugated with gold particles and anti-(bovine MSR) antibody (D2) revealed co-localization of gold particles and the reactive sites for the antibody at coated pits of plasma membranes as well as in endosomes. These results clearly show that MSR mediates the endocytic uptake and degradation of AGE proteins, suggesting a new role of MSR in biological recognition of AGE in vivo.

Laparoscopic microwave coagulo-necrotic therapy for hepatocellular carcinoma: a feasible study of an alternative option for poor-risk patients

In spite of the development of techniques for liver resection, preoperative evaluation of hepatic functional reserve and some other therapeutic options such as transcatheter arterial embolization (TAE) and percutaneous ethanol injection therapy (PEIT), liver failure after surgery is sometimes observed. Some patients, who have small liver cancers (under 2 cm in diameter) are diagnosed by various tests, but hepatic resection is not an option for the subset who have lowered hepatic functional reserve. Conventionally, such cases have been treated by TAE and/or PEIT. For the tumors in segments 7 or 8, as termed by Couinaud, which are located just beneath the diaphragm and are difficult to investigate by ultrasonography (US), or to perform PEIT, we have recently applied laparoscopic microwave coagulo-necrotic therapy (LMCNT) with the guidance of US and in some cases, thoracoscopic MCNT (TMCNT), which is performed across the diaphragm to necrotize the tumor, again with the help of US. Here, we report some cases treated by this technique, and the intraoperative color doppler US, which helps evaluate the effectiveness of MCNT.