Localization in human diabetic peripheral nerve of N(epsilon)-carboxymethyllysine-protein adducts, an advanced glycation endproduct

The present study was designed to elucidate in situ distribution of advanced glycation endproducts (AGE) in human peripheral nerve and whether the reaction products were excessive in the diabetic condition. For the detection of AGE, immunoperoxidase staining was undertaken on peripheral nerve samples obtained from 5 non-insulin-dependent diabetic patients and 5 non-diabetic control subjects. The anti-AGE antibody used in this study contained an epitope against N(epsilon)-carboxymethyllysine. Light microscopically, AGE localized in the perineurium, endothelial cells and pericytes of endoneurial microvessels as well as myelinated and unmyelinated fibers. At the submicroscopic level, AGE deposition appeared focally as irregular aggregates in the cytoplasm of endothelial cells, pericytes, axoplasm and Schwann cells of both myelinated and unmyelinated fibers. Interstitial collagens, basement membranes of the perineurium also reacted with this antibody. The AGE depositions were detected in both control and diabetic nerves, but were more intense in the latter. The excessive AGE deposition correlated with a reduction in myelinated fiber density. However, the localization of AGE was not directly associated with degeneration of nerve fibers and the link between AGE deposition and nerve fiber degeneration is yet to be determined. The present study thus demonstrated the excessive deposition of intra- and extracellular AGE in human diabetic peripheral nerve and strengthened the contention that the enhanced glycation may play a role in the development of diabetic neuropathy.

Two intracellular signaling pathways for activation of protein kinase C are involved in oxidized low-density lipoprotein-induced macrophage growth

Recent studies demonstrated that oxidized LDL (Ox-LDL) induces macrophage growth in vitro. The present study was undertaken to elucidate the intracellular signaling pathways for macrophage growth. Ox-LDL initiated a rapid and transient rise in intracellular free calcium ion and induced activation of membrane protein kinase C (PKC). Pertussis toxin completely inhibited the Ox-LDL-induced rise in free calcium ion and significantly inhibited macrophage growth by 50%. Moreover, PKC inhibitors calphostin C and H-7 significantly inhibited Ox-LDL-induced macrophage growth by 80%. On the other hand, phospholipase A2-treated acetylated LDL did not induce a rise in calcium but significantly activated PKC and led to significant macrophage growth that was significantly inhibited by calphostin C by 90%. These results suggest the presence of two intracellular signaling pathways for activation of PKC, a rise in calcium that was mediated by pertussis toxin-sensitive G protein and the internalization of lysophosphatidylcholine through the scavenger receptors. These two pathways may play an important role in Ox-LDL-induced macrophage growth.

Inhibitory effects of HepG2 cell-derived apolipoprotein A-I-containing lipoproteins on cholesteryl ester accumulation in macrophages

We investigated the mechanisms of inhibitory effects on foam cell formation of apolipoprotein A-I-containing lipoproteins secreted by HepG2 cells (HepG2-HDL) using mouse peritoneal macrophages. When macrophages were incubated with acetylated low-density lipoprotein (acetyl-LDL) in the presence of HepG2-HDL, cholesterol ester (CE) accumulation in cells was reduced by 63%. This inhibitory capacity was almost similar to that of plasma high-density lipoprotein (HDL). When macrophages were converted to foam cells with acetyl-LDL and then reacted with HepG2-HDL or plasma HDL, the HDL-induced CE reduction was 2.2-fold greater than HepG2-HDL. Similar results were obtained using apo E-free HepG2-HDL. Since the inhibitory effect of HDL on acetyl-LDL-induced CE accumulation in macrophages is due largely to its cholesterol efflux capacity, these results suggest the presence of an additional mechanism for the inhibition of CE accumulation by HepG2-HDL. To investigate the mechanism, acetyl-LDL was reisolated from HepG2-HDL by Sephacryl S-300 gel filtration after incubation in a cell-free system. Reisolated acetyl-LDL showed a significant reduction in electrophoretic mobility. The extent of CE accumulation by reisolated acetyl-LDL was reduced by 20% compared with control acetyl-LDL. Moreover, its endocytic degradation by macrophages was reduced by 28%. HepG2-HDL also inhibited macrophage degradation of acetyl-LDL as well as oxidized LDL, a likely atherogenic lipoprotein. This inhibitory effect was ascribed to the HepG2-HDL subfraction containing pre-beta HDL. Our results indicated that apo A-I-containing lipoproteins as a physiological model of nascent HDL may inhibit foam cell formation by reducing ligand activity of atherogenic lipoproteins. These data possibly suggest inhibitory function of nascent HDL for the formation of foam cells in vivo.

HMG-CoA reductase inhibitors suppress macrophage growth induced by oxidized low density lipoprotein

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors ameliorate atherosclerotic diseases in several models of vascular disease. This is largely due to their ability to reduce plasma cholesterol levels in vivo. Proliferation of cellular components is one of the major events in the development and progression of atherosclerotic lesions. We recently demonstrated that oxidized low density lipoprotein (Ox-LDL), a likely atherogenic lipoprotein present in vivo, is capable of inducing macrophage growth in vitro. In the present study, we investigated the effect of HMG-CoA reductase inhibitors, simvastatin and pravastatin, on Ox-LDL-induced macrophage growth. Our results demonstrated that these inhibitors effectively suppressed Ox-LDL-induced macrophage growth with concentrations required for 50% inhibition by simvastatin and pravastatin being 0.1 and 80 microM, respectively, and that this inhibitory effect was reversed by mevalonate but not by squalene. Under these conditions, simvastatin did not affect the endocytic degradation of Ox-LDL, nor subsequent accumulation of intracellular cholesteryl esters. Our results suggest that a non-cholesterol metabolites(s) of mevalonate pathway may play an important role in Ox-LDL-induced macrophage growth. Since it is well known that macrophage-derived foam cells are the key cellular element in the early stage of atherosclerosis, a significant inhibition of Ox-LDL-induced macrophage growth by HMG-CoA reductase inhibitors in vitro, particularly simvastatin, may also explain, at least in part, their anti-atherogenic action in vivo.

The relationship between accumulation of advanced glycation end products and expression of vascular endothelial growth factor in human diabetic retinas

Both advanced glycation end products and vascular endothelial growth factor are believed to play a role in the pathogenesis of diabetic retinopathy. It is known that vascular endothelial growth factor causes retinal neovascularization and a breakdown of the blood-retinal barrier; how advanced glycation end products affect the retina, however, remains largely unclear. The substance-Ne-(carboxymethyl)lysine is a major immunologic epitope, i.e. a dominant advanced glycation end products antigen. We generated an anti-Ne-(carboxymethyl)lysine antibody to investigate the relationship between the localization of advanced glycation end products and that of vascular endothelial growth factor in 27 human diabetic retinas by immunohistochemistry. Nine control retinas were also examined. In all 27 diabetic retinas, Ne-(carboxymethyl)lysine was located in the thickened vascular wall. In 19 of the 27 retinas, strand-shaped Ne-(carboxymethyl)lysine immunoreactivity was also observed around the vessels. In all 27 diabetic retinas, vascular endothelial growth factor revealed a distribution pattern similar to that of Ne-(carboxymethyl)lysine. Vascular endothelial growth factor was also located in the vascular wall and in the perivascular area. Neither Ne-(carboxymethyl)lysine nor vascular endothelial growth factor immunoreactivity was detected in the 9 control retinas. Vessels with positive immunoreactivity for Ne-(carboxymethyl)lysine and/or vascular endothelial growth factor were counted. A general association was noted between accumulation of Ne-(carboxymethyl)lysine and expression of vascular endothelial growth factor in the eyes with non-proliferative diabetic retinopathy (p < 0.01) and proliferative diabetic retinopathy (p < 0.05).

Hydroxyl radical mediates N epsilon-(carboxymethyl)lysine formation from Amadori product

Recent studies demonstrated N epsilon-(carboxymethyl)lysine (CML) in several tissue proteins. Incubation of proteins with glucose leads through a Schiff base to Amadori products. Oxidative cleavage of Amadori products is considered as a major route to CML formation in vivo, whereas it is not known which reactive oxygen species (ROS) is involved. The present study is undertaken to identify such a ROS. We prepared heavily glycated human serum albumin (HSA) which contained a high level of Amadori products, but an undetectable level of CML. Incubation of glycated HSA with FeCl2, but not with H2O2, led to CML formation which was enhanced by H2O2, but inhibited by catalase or mannitol, whereas superoxide dismutase had no effect. Similar data were obtained by experiments using Boc-fructose-lysine as a model Amadori compound. These data indicate that hydroxyl radical generated by the reaction of Fe2+ with H2O2 mediates CML formation from Amadori compounds.

Photo-enhanced modification of human skin elastin in actinic elastosis by N(epsilon)-(carboxymethyl)lysine, one of the glycoxidation products of the Maillard reaction

Long-term incubation of proteins with glucose leads to the formation of advanced glycation end products (AGEs), which are characterized by fluorescence, brown color, and cross-linking. Formation of AGEs in vitro requires oxygen and is dependent on transition metal-catalyzed oxidation of glucose or Amadori products. AGEs are thought to be involved in aging and age-enhanced diseases such as diabetic complications, atherosclerosis, dialysis-related amyloidosis, and Alzheimer's disease. Chronic exposure of the skin to sunlight induces hyperplasia of the elastic tissue in the upper dermis known as actinic elastosis. Herein we used a monoclonal anti-AGE antibody (6D12) whose epitope is N(epsilon)-(carboxymethyl)lysine (CML), one of the glycoxidation products of AGEs, and demonstrated that the lesions of actinic elastosis were modified by CML. Further immunohistochemical and immunoelectron microscopic examination with 6D12 demonstrated CML accumulates predominantly in elastic fibers especially in the amorphous electron-dense materials corresponding to photo-induced degenerated area rather than the electron-lucent region. Immunochemical analyses with enzyme-linked immunosorbent assay (ELISA) of elastase-soluble fractions demonstrated that the CML levels of the sun-exposed area were significantly higher than those of the sun-unexposed area. We conclude that ultraviolet-induced oxidation may accelerate CML formation in actinic elastosis of photoaged skin.

Altered interleukin-2 receptor alpha-chain is expressed in human T-cell leukaemia virus type-I-infected T-cell lines and human peripheral blood mononuclear cells of adult T-cell leukaemia patients through an alternative splicing mechanism

A polymerase chain reaction (PCR) method was used to detect the interleukin-2 receptor alpha-chain (IL-2R alpha) chain which lacks the conventional transmembrane (TM) domain in mRNA from human T-cell leukaemia virus type-I (HTLV-I)-infected cell lines or peripheral blood mononuclear cells (PBMC) isolated from adult T-cell leukaemia (ATL) patients. Primer pairs encompassing the TM domain were selected to generate a 357-base pair (bp) fragment. A 146-bp PCR product was observed consistently in addition to the target 357-bp PCR product in mRNA from HTLV-I-infected cell lines, such as MT-1, MT-2, MT-4 and in PBMC isolated from ATL patients. However, this 146-bp PCR product was undetectable in HTLV-I-negative cell lines. The product was also detected in PBMC from normal individuals if activated in vitro with phytohaemagglutinin but not without stimulation. DNA sequence analyses revealed that exons from 5 to 7, which define a 211-bp region containing the conventional TM domain, were deleted in the 146-bp PCR product. The C-terminal amino acid sequence starting from Gly174 of the 211-bp-deleted molecule was distinct from that of conventional IL-2R alpha as a result of an altered reading frame. We identified a 45000 MW peptide generated from IL-2R alpha mRNA through this exon skip in cell lysate of MT-1 and MT-2 by Western blot analyses using an antibody raised against the peptides specific to an altered IL-2R alpha. Our results indicate that an altered IL-2R alpha chain is expressed in HTLV-I-infected T lymphocytic cell lines and in ATL patients.

Antisense oligonucleotides to p53 tumor suppressor suppress the induction of apoptosis by epidermal growth factor in NCI-H 596 human lung cancer cells

Apoptosis has become a basic tool in developing cancer research and establishing new cancer strategies. However, the molecular mechanism of apoptosis is not well understood. Recently, the authors found that epidermal growth factor (EGF) induces apoptosis in various cancer cells and that there is a novel signal pathway mediated through p53 in signal transduction of EGF. The effect of antisense gene therapy to p53 tumor suppressor on EGF-dependent apoptosis was investigated in cultured NCI-H 596 human non-small cell lung cancer cells with a wild-type p53 gene. Results showed that EGF plus p53 sense oligonucleotides induced EGF-dependent and p53-dependent apoptosis in NCI-H 596 cells within 8 hours. On the other hand, antisense gene therapy using antisense oligonucleotides to p53 tumor suppressor suppressed the induction of EGF-dependent and p53-dependent apoptosis. Mutated p53 antisense-containing mutated CG dinucleotides had the same effect as that of p53 antisense on suppression of apoptosis in NCI-H 596 cells. We found that a new nucleic acid drug, another mutated p53 antisense-containing mutation at three bases immediately 5' and 3' from the CG dinucleotides, potentiated the induction of apoptosis and failed to suppress the induction of EGF-dependent apoptosis. These results suggest that gene therapy using antisense oligonucleotides to the p53 tumor suppressor is effective on EGF-dependent apoptosis of NCI-H 596 human non-small cell lung cancer.

The receptor for advanced glycation end products mediates the chemotaxis of rabbit smooth muscle cells

Long-term incubation of proteins with glucose leads to advanced glycation end products (AGEs) with fluorescence and a brown color. We recently demonstrated immunologically the intracellular AGE accumulation in smooth muscle cell (SMC)-derived foam cells in advanced atherosclerotic lesions. To understand the mechanism of AGE accumulation in these foam cells, we have now characterized the interaction of AGE proteins with rabbit-cultured arterial SMCs. In experiments at 4 degrees C, 125I-labeled AGE-bovine serum albumin (AGE-BSA) showed a dose-dependent saturable binding to SMCs with an apparent dissociation constant (Kd) of 4.0 microg/ml. In experiments at 37 degrees C, AGE-BSA underwent receptor-mediated endocytosis and subsequent lysosomal degradation. The endocytic uptake of 125I-AGE-BSA was effectively inhibited by unlabeled AGE proteins such as AGE-BSA and AGE-hemoglobin, but not by acetylated LDL and oxidized LDL, well-known ligands for the macrophage scavenger receptor (MSR). Moreover, the binding of 125I-AGE-BSA to SMCs was affected neither by amphoterin, a ligand for one type of the AGE receptor, named RAGE, nor by 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole-hexanoic acid-BSA, a ligand for the other AGE receptors, p60 and p90. This indicates that the endocytic uptake of AGE proteins by SMCs is mediated by an AGE receptor distinct from MSR, RAGE, p60, and p90. To examine the functional role of this AGE receptor, the migratory effects of AGE-BSA on these SMCs were tested. Incubation with 1-50 microg/ml of AGE-BSA for 14 h resulted in significant dose-dependent cell migration. The AGE-BSA-induced SMC migration was chemotactic in nature and was significantly inhibited (approximately 80%) by an antibody against transforming growth factor-beta (TGF-beta), and the amount of TGF-beta secreted into the culture medium from SMC by AGE-BSA was sevenfold higher than that of control, indicating that TGF-beta is involved in the AGE-induced SMC chemotaxis. These data suggest that AGE may play a role in SMC migration in advanced atherosclerotic lesions.

Advanced glycation end products are eliminated by scavenger-receptor-mediated endocytosis in hepatic sinusoidal Kupffer and endothelial cells

Long-term incubation of proteins with glucose leads to the formation of advanced glycation end products (AGE). Physiological aspects of the catabolism of non-enzymically glycated proteins were studied in vivo and in vitro. AGE-modified BSA (AGE-BSA) was a mixture of high-Mr (cross-linked), monomeric and low-Mr (fragmented) AGE-BSA. After intravenous administration in rat, all three fractions of AGE-BSA accumulated extremely rapidly and almost exclusively in liver. Uptake in liver endothelial, Kupffer and parenchymal cells accounted for approx. 60%, 25% and 10-15% respectively of hepatic elimination. Both cross-linked and monomeric AGE-BSA were efficiently taken up and degraded in cultures of purified liver endothelial and Kupffer cells. Endocytosis of AGE-BSA by these cells was inhibited by several ligands for the scavenger receptor. Although 125I-Hb was not endocytosed in vitro, 125I-AGE-Hb was effectively endocytosed by a mechanism that was subject to inhibition by AGE-BSA. Endocytosis of N-terminal propeptide of type I procollagen, a physiological ligand for the scavenger receptor, was effectively inhibited by AGE-Hb and AGE-BSA. We conclude that AGE-modification renders macromolecules susceptible for elimination via the scavenger receptor of both liver endothelial and Kupffer cells.

Age patterns of the life table aging rate for major causes of death in Japan, 1951-1990

It has been widely supposed that human mortality from all causes increases with age nearly exponentially (at a constant rate) through adult ages except for very old ages, and that this exponential increase also holds fairly well for most major causes of death (CODs). However, the present analysis of death registration data for Japan, 1951-1990, reveals that the rate of age-related relative increase in mortality (the life table aging rate) changes with age significantly and systematically for many CODs. Above age 75, the mortality increase decelerates for most CODs; under age 75, it remains at a relatively stable pace for ischemic heart disease, decelerates for most major cancers, and accelerates for diseases related to a declining ability to maintain homeostasis (pneumonia, bronchitis, influenza, gastroenteritis, and heart failure). These results seem to suggest that significantly different types of senescent processes may underlie atherogenesis, oncogenesis, and immunosenescence.

Immunohistochemical detection of advanced glycosylation end-products in the peritoneum and its possible pathophysiological role in CAPD

It has recently been suggested that advanced glycosylation end-products (AGEs) are formed in the peritoneum in patients on CAPD. However, the exact location of AGE accumulation, the relation with the duration of CAPD and its pathophysiological role in CAPD remain unclear. If the peritoneum is glycosylated, it could bring about altered peritoneal function. Therefore, the aim of this study is to clarify the localization of AGEs in the peritoneum in accordance with the duration of CAPD and to examine its relation to the peritoneal permeability. Fifteen non-diabetic patients were divided into three groups (each 5 patients) on the basis of the mean duration (D) of CAPD (Group 1, D = 0 month; Group II, D = 34 months; Group III, D = 84 months). The AGE staining by monoclonal anti-AGE antibody in the peritoneum and the four-hour peritoneal equilibration test (PET) were compared among these groups. AGE was absent or found only weakly in Group I. However, in groups II and III, AGE was moderately or strongly positive especially in the vascular walls and it was dominant in group III. PET revealed that peritoneal permeability for glucose, creatinine, beta2-microglobulin and albumin was increased in Group II as compared to Group I, and it was further increased in Group III. The results of this study indicate that AGEs become dominantly accumulated in the vascular wall in accordance with the prolongation of CAPD treatment, and this might play some roles for the increased permeability of the peritoneal membrane in CAPD.

[A study of nursing systems in transition in developed countries]

The present study was designed to investigate nursing systems in other countries in comparison with the current system in Japan, and thereby assess how nursing personnel should be in order to improve the quality of nursing. The study focused on the actual situation of the nursing system and licensed practical nurses (LPNs) or second-level nurses similar to LPNs in other countries. The survey was conducted in regard to six countries considered to be advanced in the development of nursing activities and likely to provide useful suggestions for the future direction of nursing in Japan: Australia, Canada, France, Sweden, the United Kingdom and the United States. Questionnaires were sent to the heads or staff of a total of 29 organizations, including WHO Collaborating Centers and professional organizations for nursing, in these countries. Nineteen organizations responded (response rate: 65.5%), and an effective response with completed questionnaire forms was obtained from 15 organizations. In addition, an interview survey was conducted on three nursing administration and education experts in the United States in order to acquire clear understanding of the actual state of nursing in health care practice. The results were as follows: 1. Six countries (Japan included) excluding France had LPNs. Educational preparation for LPNs has been discontinued in the United Kingdom. 2. The number of nurses per 1,000 population was lowest in Japan: the total number of registered nurses (RNs) and LPNs in Japan was less than the number of RNs in the United Kingdom. Only in Japan the proportions of LPNs and RNs were similar, while in other countries of number of LPNs was one-third to one-fourth of the number of RNs. 3. In the five other countries having LPNs, the nurse's competency or scope of practice was clearly defined for both LPNs and RNs. In contrast, no clear line was drawn between the two in Japan. 4. The length of education required for LPNs ranged from 11 to 14 years (including the period of compulsory education) and was shortest in Japan (11 years). The educational requirement for admission to LPN school in Japan was 9 years of compulsory education (graduation from junior high school), whereas in other countries it was at the level of senior high school graduation. 5. Four countries had conversion programs for LPNs to become RNs, and the conversion courses were positioned within the framework of higher education comparable to the university level. 6. In the United Kingdom, where the educational preparation for LPNs has been discontinued, nurses are included in a single higher level profession. At the same time there was found to be a need to train and educate auxiliary personnel in order to maintain multi-level care services. Because of the increasing tendency toward advanced medical technology and highly specialized medical care associated with the rapidly increasing care needs in the community, the current educational preparation for LPNs in Japan in unsatisfactory as a training and educational system for nursing manpower to cope with the current situation. The above findings suggest that the education system for LPNs be reviewed with a view to discontinuing it and consolidating nursing education in Japan.

Histological localization of advanced glycosylation end products in the progression of diabetic nephropathy

We studied the immunohistochemical localization of advanced glycosylation end products (AGEs) in the progression of diabetic nephropathy. Fourteen NIDDM patients with diabetic nephropathy were evaluated: 2 patients with normoalbuminuria, 4 with microalbuminuria (MA) and 8 with overt proteinuria (OP). Three patients with minor glomerular abnormalities were used as nondiabetic controls. Immunoreactivity to a monoclonal anti-AGE antibody (6D12) was recognized on the internal elastic membranes of arterial walls in every diabetic group. Hyaline lesions of arterioles of the MA and OP groups demonstrated strong reactions with 6D12. A portion of the nodular and exudative lesions in glomeruli of OP group patients also revealed immunoreactivity to 6D12. No immunoreactivity to 6D12 was observed in nondiabetic control specimens. We confirm that the accumulation of AGEs began in arterial walls of the early stage and presented in glomerular lesions of the late stage of the progression of diabetic nephropathy.

Postmenopausal acceleration of age-related mortality increase

The force of natural selection to eliminate deleterious genes is attenuated with advancing age, allowing senescence to evolve. This suggests that a distinctly marked end of the reproduction period is likely to be followed by an acceleration of senescence. It is thus expected that menopause should trigger an acceleration of age-related mortality increase in human females. Such an abrupt initiation of mortality acceleration is not predicted for human males at the same ages, whose fecundity declines more gradually. Life table aging rate patterns for selected industrialized countries generally support this hypothesis. A cause-of-death decomposition analysis indicates that the sex differential in mortality acceleration is mainly due to cardiovascular diseases, which is consistent with the prevalent view that postmenopausal changes in the sex hormone status may affect lipoprotein metabolism, and in turn, raise the risk of arteriosclerosis.

Identification of advanced glycation end products of the Maillard reaction in Pick's disease

The recent identification of advanced glycation end products (AGEs) of the Maillard reaction in the central nervous system suggests their potential involvement in the aging process. Other studies have also suggested a possible link between AGEs and Alzheimer's disease. To investigate the role of AGEs in Pick's disease, another neurodegenerative disease associated with dementia, we examined the AGE-immunoreaction in Pick's bodies and ballooned neurons, two characteristic neuropathological features of Pick's disease, using antibodies against identified AGE-structures, N epsilon-(carboxymethyl)lysine and pentosidine. These two structures were observed immunohistochemically in Pick's bodies and ballooned neurons of brain tissues obtained at autopsy from three elderly patients diagnosed with Pick's disease. These immunoreactions were further confirmed by absorption experiments and double-immunostaining. The present findings suggest that AGEs are involved in the pathology of Pick's disease.

Rapid formation of advanced glycation end products by intermediate metabolites of glycolytic pathway and polyol pathway

To clarify roles of intermediate metabolites of the glycolytic pathway and the polyol pathway in nonenzymatic glycation under physiological conditions, we incubated bovine serum albumin with intermediates of both pathways in the micromolar range as well as with 20 mmol/l glucose, and observed the formation of advanced glycation end products (AGEs). We found that triose phosphates, glyceraldehyde, and a novel polyol pathway-related metabolite, fructose 3-phosphate along with its breakdown product, 3-deoxyglucosone were extremely potent glycating agents that at nearly physiological concentrations on incubation with albumin produced substantial amounts of AGEs as early as 24 hours, while 20 mmol/l glucose afforded trace amounts of AGEs after two week incubation. The results along with the previous evidence of the increased level of intermediates in diabetic states may suggest that the intermediate metabolites rather than glucose contribute to enhanced glycation in diabetic tissues, inspite of the much lower concentrations compared with glucose.

The scavenger receptor serves as a route for internalization of lysophosphatidylcholine in oxidized low density lipoprotein-induced macrophage proliferation

We have recently demonstrated that the growth of murine macrophages is induced by oxidized low density lipoprotein (Ox-LDL) and that lysophosphatidylcholine (lyso-PC), a major phospholipid component of Ox-LDL, plays an essential role in its mitogenic effect. The present study was undertaken to further characterize the role of the macrophage scavenger receptor (MSR) in Ox-LDL-induced macrophage growth. The growth-stimulating effect of Ox-LDL on murine resident peritoneal macrophages was inhibited by maleylated bovine serum albumin (maleyl-BSA), a non-lipoprotein ligand for MSR but a poor carrier of lyso-PC, while maleyl-BSA itself failed to induce macrophage growth even in the presence of lyso-PC. Moreover, it competitively inhibited the endocytic uptake of 125I-Ox-LDL and the specific uptake of lyso-PC by MSR, whereas nonspecific lyso-PC transfer to cells was not affected. Furthermore, the Ox-LDL-induced cell growth of peritoneal macrophages obtained from MSR knockout mice was significantly weaker than that of macrophages obtained from their wild-type littermates. Our results suggest that the MSR is an important and efficient internalization pathway for lyso-PC in Ox-LDL-induced macrophage growth.