Biomedical subjects

Xi-Ming Yuan

Publications and source records attributed to Xi-Ming Yuan.

12 recordsLinked to original sources

PubMed2006

Oxysterol mixtures, in atheroma-relevant proportions, display synergistic and proapoptotic effects.

Apoptotic cells in atheroma lesions may contribute to plaque development and instability. Oxysterols constitute the major toxic component in oxLDL and are present in mixed forms in human atheroma lesions. However, the cellular effects of oxysterols have been mostly studied individually. In the present study, we investigated the cytotoxic effects of 7beta-hydroxycholesterol (7betaOH), 7-ketocholesterol (7keto), 25-hydroxycholesterol (25OH), and 27-hydroxycholesterol (27OH) on U937 monocytic cells, both individually and in atheroma-relevant mixtures mimicking the oxysterol composition reported in human atheroma lesions. Apoptosis and necrosis were studied by examining cell morphology, phosphatidylserine exposure, caspase activation, and the terminal dUTP nick end-labeling technique. Cellular reactive oxygen species and total amount of reduced thiols were measured by using fluorescence probes and 5,5'-dithiobis-(2-nitrobenzoic acid), respectively. We found that 7betaOH and 7keto induced caspase activation, ROS production, cellular thiol depletion, permeabilization of lysosomal and mitochondrial membranes, and cell death. 25OH and 27OH did not cause any of the above alterations, whereas 7betaOH and 7keto exerted synergistic toxic effects. Although single 25OH or 27OH exhibited quenching effects on both 7betaOH- and 7keto-induced cell death, the combination of all four oxysterols in atheroma-relevant proportions was proapoptotic. Our findings indicate that the major oxysterols accumulated in human atheroma are proapoptotic and may contribute to atherosclerotic lesion development.

Apoptosis↗

PubMed2006

Cytocidal effects of atheromatous plaque components: the death zone revisited.

OBJECTIVE: Earlier we suggested that atheroma lesions constitute a "death zone" containing toxic materials that may cause dysfunction and demise of invading macrophages to prevent the removal of plaque materials. Here we have assessed the cytotoxic effects of nonfractionated gruel and insoluble (ceroid-like) material derived from advanced human atheroma. METHODS AND RESULTS: The insoluble material within advanced atherosclerotic plaque was isolated following protease K digestion and extensive extraction with aqueous and organic solvents. FTIR, Raman, and atomic absorption spectroscopy suggested that, despite its fluorescent nature, this material closely resembled hydroxyapatite and dentin, but also contained a significant amount of iron and calcium. When added to J774 cells and human macrophages in culture, this insoluble substance was phagocytosed, and progressive cell death followed. However, an even more cytotoxic activity was found in the atheromatous "gruel" that contains abundant carbonyls/aldehydes. Cell death caused by both crude gruel and ceroid could be blocked by preincubating cells with the lipophilic iron chelator salicylaldehyde isonicotinoyl hydrazone, apoferritin, BAPTA/AM, or sodium borohydride, indicating that cellular iron, calcium, and reactive aldehyde(s) are responsible for the observed cytotoxicity. CONCLUSIONS: Toxic materials within atheromatous lesions include both ceroid and even more cytotoxic lipidaceous materials. The cytotoxic effects of these plaque components may help explain the persistence of atherosclerotic lesions.

Animals↗

PubMed2006

Abnormal beta-catenin and reduced axin expression are associated with poor differentiation and progression in non-small cell lung cancer.

We studied the expression of axin and beta-catenin and their relation to clinicopathologic factors in 100 non-small cell lung cancers (NSCLCs) by immunohistochemical analysis. The mutation in exon 3 of the beta-catenin gene was examined by polymerase chain reaction and direct sequencing. Preserved axin expression was significantly higher in well- and moderately differentiated NSCLC samples than in poorly differentiated ones. Reduced membranous expression of beta-catenin was shown in 80 cases, whereas 26 cases had aberrant nuclear expression. Poor differentiation and lymph node metastasis were associated significantly with reduced beta-catenin expression. Lower axin expression was related significantly to higher nuclear beta-catenin expression. However, this study failed to detect any exon 3 mutation in the beta-catenin gene in the 100 NSCLC samples. We conclude that reduced beta-catenin and axin expression might predict poor differentiation in NSCLC. Reduced axin expression, but not mutation in exon 3, might be an important explanation for the abnormal beta-catenin expression in NSCLC.

Adult↗

PubMed2005

Foam cell death induced by 7beta-hydroxycholesterol is mediated by labile iron-driven oxidative injury: mechanisms underlying induction of ferritin in human atheroma.

Human atherosclerotic lesions typically contain large amounts of ferritin associated with apoptotic macrophages and foam cells, although the reasons are unknown. In the present investigation, we studied the relationship between ferritin induction and occurrence of apoptosis in 7beta-hydroxycholesterol (7beta-OH)-treated monocytic cells and macrophages. We found that 7beta-OH enlarges the intracellular labile iron pool, increases formation of reactive oxygen species (ROS), and induces ferritin and cytosolic accumulation of lipid droplets, lysosomal destabilization, and apoptototic macrophage death. Since ferritin is a phase II-type protective protein, our findings suggest that ferritin upregulation here worked as an inefficient defense mechanism. Addition to the culture medium of both a membrane-permeable iron chelator 10-phenanthroline and the non-membrane-permeable iron chelators apoferritin and desferrioxamine afforded significant protection against the 7beta-OH-induced effects. Consequently, endocytosed iron compounds dramatically augmented 7beta-OH-induced cytotoxicity. We conclude that oxidized lipid 7beta-OH causes not only foam cell formation but also oxidative damage with abnormal metabolism of cellular iron. The findings suggest that modulation of iron metabolism in human atheroma may be a potential therapeutic strategy against atherosclerosis.

Animals↗

PubMed2004

Alpha-tocopherol and astaxanthin decrease macrophage infiltration, apoptosis and vulnerability in atheroma of hyperlipidaemic rabbits.

The composition of atherosclerotic plaques, not just macroscopical lesion size, has been implicated in their susceptibility to rupture and the risk of thrombus formation. By focusing on the quality of lipids, macrophages, apoptosis, collagen, metalloproteinase expression and plaque integrity, we evaluated the possible anti-atherosclerotic effect of the antioxidants alpha-tocopherol and astaxanthin in Watanabe heritable hyperlipidemic (WHHL) rabbits. Thirty-one WHHL rabbits were divided into three groups and were fed a standard diet, as controls (N =10), or a standard diet with the addition of 500 mg alpha-tocopherol per kg feed (N =11) or 100 mg astaxanthin per kg feed (N =10) for 24 weeks. We found that both antioxidants, particularly astaxanthin, significantly decreased macrophage infiltration in the plaques although they did not affect lipid accumulation. All lesions in the astaxanthin-treated rabbits were classified as early plaques according to the distribution of collagen and smooth muscle cells. Both antioxidants also improved plaque stability and significantly diminished apoptosis, which mainly occurred in macrophages, matrix metalloproteinase three expressions and plaque ruptures. Although neither antioxidant altered the positive correlations between the lesion size and lipid accumulation, the lesion size and apoptosis were only positively correlated in the control group. Astaxanthin and alpha-tocopherol may improve plaque stability by decreasing macrophage infiltration and apoptosis in this atherosclerotic setting. Apoptosis reduction by alpha-tocopherol and astaxanthin may be a new anti-atherogenic property of these antioxidants.

Animals↗

PubMed2004

Secretion of ferritin by iron-laden macrophages and influence of lipoproteins.

Increasing evidence supports a role of cellular iron in the initiation and development of atherosclerosis. We and others reported earlier that iron-laden macrophages are associated with LDL oxidation, angiogenesis, nitric oxide production and apoptosis in atherosclerotic processes. Here we have further studied perturbed iron metabolism in macrophages, their interaction with lipoproteins and the origin of iron accumulation in human atheroma. In both early and advanced human atheroma lesions, hemoglobin and ferritin accumulation correlated with the macrophage-rich areas. Iron uptake into macrophages, via transferrin receptors or scavenger receptor-mediated erythrophagocytosis, increased cellular iron and accelerated ferritin synthesis at both mRNA and protein levels. The binding activity of iron regulatory proteins was enhanced by desferrioxamine (DFO) and decreased by hemin and iron compounds. Iron-laden macrophages exocytosed both iron and ferritin into the culture medium. Exposure to oxidized low-density lipoprotein (oxLDL, >or=50 microg/mL) resulted in <20% apoptosis of iron-laden human macrophages, but cells remained impermeable after a 24 h period and an increased excretion of ferritin could be observed by immunostaining techniques. Exposure to high-density lipoprotein (HDL) significantly decreased ferritin excretion from these cells. We conclude: (i) erythrophagocytosis and hemoglobin catabolism by macrophages contribute to ferritin accumulation in human atherosclerotic lesions and; (ii) iron uptake into macrophages leads to increased synthesis and secretion of ferritin; (iii) oxidized LDL and HDL have different effects on these processes.

Arteriosclerosis↗

PubMed2004

Macrophage hemoglobin scavenger receptor and ferritin accumulation in human atherosclerotic lesions.

We previously proposed that erythrophagocytosis and iron metabolism by macrophages may contribute to iron-driven oxidative stress in atherogenesis. Recent studies have indicated that the macrophage hemoglobin scavenger receptor (HbSR/CD163) is a key molecule in the process of removing hemoglobin released from senescent erythrocytes. In this study we investigated erythrophagocytosis and its relation to ferritin accumulation and the involvement of CD163 in ferritin induction in human atheroma lesions. Normal and atherosclerotic human arterial segments obtained at autopsy and surgery were collected for iron histochemistry, hemoglobin and ferritin immunohistochemistry, and computerized image analysis. The lesion-dependent accumulation of ferritin and hemoglobin was seen in atherosclerotic carotid and coronary arteries. The immunoreactivity of hemoglobin was significantly correlated to the same regions of ferritin immunoreactivity on serial sections. The staining intensity of hemoglobin and ferritin was also significantly correlated. Hemoglobin deposition is often associated with microvessels adjacent to the lipid core areas in advanced lesions, where most CD68-positive macrophages were. CD163 expression appeared in both early and advanced lesions. The accumulation of tissue iron and ferritin also frequently occurs in CD163-positive and vessel-rich regions in the advanced atheroma. Although they were not always correspondingly positive on the serial sections, tissue iron and ferritin were significantly correlated. We conclude that erythrophagocytosis and hemoglobin catabolism by macrophages contribute to iron deposition and ferritin induction in human atheroma. The involvement of CD163 during ferritin induction may play an important role in modulating inflammatory processes in atherogenesis.

Arteriosclerosis↗

PubMed2004

Enhanced expression of natural resistance-associated macrophage protein 1 in atherosclerotic lesions may be associated with oxidized lipid-induced apoptosis.

The natural resistance-associated macrophage proteins (Nramps) can modulate inflammatory reactions. Nramps are not only responsible for intracellular divalent metal transport but also determine the macrophage functions in inflammatory processes. In the present study we tested whether Nramp1 is involved in macrophage apoptosis induced by oxidized lipids in atherogenesis. Arterial segments of Watanabe heritable hyperlipidemic rabbits were used for an examination of Nramp1 mRNA by in situ RT-PCR and macrophage immunohistochemistry. Annexin V/PI staining and terminal dUTP nick-end labeling (TUNEL) techniques were used for apoptosis detection. We found that, in macrophage-rich areas (positive to RMA-11) of the rabbit atherosclerotic aorta, there were lesion-dependent increases in Nramp1 mRNA, which are mainly apoptotic foamy macrophages that are positive to TUNEL staining. U937 cells were treated with 7beta-hydroxycholesterol (7beta-OH) in the presence or absence of the redox-active iron chelator desferrioxamine (DFO) or 1,10-phenanthroline. The cellular iron chelators considerably reduced, whereas iron compounds enhanced, 7beta-OH-induced apoptosis and necrosis. DFO also decreased mRNA levels of Nramp1, whereas both iron compounds and 7beta-OH dramatically enhanced the expression of Nramp1 mRNA, particularly among 7beta-OH-induced apoptotic cells. We conclude that the enhanced expression of Nramp1 in macrophage regions of atherosclerotic lesions may be associated with ferrous iron-enhanced, oxidized lipid-induced apoptosis. This finding reveals a novel function of Nramp1 in atherogenesis.

Animals↗

PubMed2004

Increased expression and translocation of lysosomal cathepsins contribute to macrophage apoptosis in atherogenesis.

It has been recently reported that atherosclerotic lesions in both humans and mice express several lysosomal proteases, including cathepsins B, D, L, and S, which may affect plaque development and stability. The mechanisms responsible for the extralysosomal expression of lysosomal cathepsins and the related atherogenic implications remain unknown. We find that the lesion-dependent expression of cathepsins B and L is mainly in macrophage-infiltrated areas of human carotid atheroma. These enzymes appear in the cytoplasm and nuclei of apoptotic macrophages (normally confined to the lysosomal compartment) and in the extracellular areas. After exposure to oxidized low-density lipoprotein (oxLDL) or 7beta-hydroxycholesterol (7beta-OH), macrophages initially transform into foam cells and then undergo apoptotic cell death. The oxidized lipids induce lysosomal destabilization, with leakage to the cytosol of lysosomal enzymes (cathepsins B, D, and L), as detected by cytochemistry and immunocytochemistry. A remarkable increase in cathepsin D mRNA levels was observed after 7beta-OH exposure. Like macrophages within atheroma, intralysosomal cathepsins B and L are translocated to the cytoplasm and nuclei of 7beta-OH-exposed cells. Our results suggest that endocytosed oxLDL and oxysterols not only destabilize the acidic vacuolar compartment but also cause the upregulation and translocation of lysosomal cathepsins, which may act as cleaving enzymes during the apoptotic process. The increased macrophage apoptosis and nuclear and matrix degradation by lysosomal enzymes in atheroma may play important roles in plaque development and rupture.

Apoptosis↗

PubMed2003

3-Aminopropanal, formed during cerebral ischaemia, is a potent lysosomotropic neurotoxin.

Cytotoxic polyamine-derived amino aldehydes, formed during cerebral ischaemia, damage adjacent tissue (the so-called 'penumbra') not subject to the initial ischaemic insult. One such product is 3-aminopropanal (3-AP), a potent cytotoxin that accumulates in ischaemic brain, although the precise mechanisms responsible for its formation are still unclear. More relevant to the present investigations, the mechanisms by which such a small aldehydic compound might be cytotoxic are also not known, but we hypothesized that 3-AP, having the structure of a weak lysosomotropic base, might concentrate within lysosomes, making these organelles a probable focus of initial toxicity. Indeed, 3-AP leads to lysosomal rupture of D384 glioma cells, a process which clearly precedes caspase activation and apoptotic cell death. Immunohistochemistry reveals that 3-AP concentrates in the lysosomal compartment and prevention of this accumulation by the lysosomotropic base ammonia, NH(3), protects against 3-AP cytotoxicity by increasing lysosomal pH. A thiol compound, N-(2-mercaptopropionyl)glycine, reacts with and neutralizes 3-AP and significantly inhibits cytoxocity. Both amino and aldehyde functions of 3-AP are necessary for toxicity: the amino group confers lysosomotropism and the aldehyde is important for additional, presently unknown, reactions. We conclude that 3-AP exerts its toxic effects by accumulating intralysosomally, causing rupture of these organelles and releasing lysosomal enzymes which initiate caspase activation and apoptosis (or necrosis if the lysosomal rupture is extensive). These results may have implications for the development of new therapeutics designed to lessen secondary damage arising from focal cerebral ischaemia.

Acridine Orange↗

PubMed2003

The iron hypothesis of atherosclerosis and its clinical impact.

The iron hypothesis as an alternative explanation for the gender difference in the incidence and mortality of atherosclerosis has provoked increased debates and public health concerns. In this review we summarize the historical and recent literature on the iron hypothesis and discuss several related clinical issues and their implications. Apart from misconstruction of study populations, lack of a good method to reflect the iron contents of tissues may be the major factor for causing inconsistent results from epidemiological studies. Published data from 11 countries clearly indicate that the mortality from cardiovascular diseases is correlated with liver iron. We propose that redox-active iron in tissue is the atherogenic portion of total iron stores. Recently developed magnetic resonance imaging techniques in combination with Fe chelators may allow future studies to examine this component of body iron in lesions and the whole body. Several clinical situations characterized by increased iron stores have been proposed as 'human models' suitable for further tests of the iron hypothesis. Patients with end-stage renal disease may be the most unique cohort, having significant increases in their iron stores, low-density lipoprotein (LDL) oxidation, and cardiovascular events. Other patient groups may be well suited for specific studies of different atherogenic events. With a better understanding of iron-driven oxidative damage, well controlled and effectively designed studies on these models will finally bring us to the truth of the iron hypothesis.

Arteriosclerosis↗

PubMed2002

Lysosomal destabilization in p53-induced apoptosis.

The tumor suppressor wild-type p53 can induce apoptosis. M1-t-p53 myeloid leukemic cells have a temperature-sensitive p53 protein that changes its conformation to wild-type p53 after transfer from 37 degrees C to 32 degrees C. We have now found that these cells showed an early lysosomal rupture after transfer to 32 degrees C. Mitochondrial damage, including decreased membrane potential and release of cytochrome c, and the appearance of apoptotic cells occurred later. Lysosomal rupture, mitochondrial damage, and apoptosis were all inhibited by the cytokine IL-6. Some other compounds can also inhibit apoptosis induced by p53. The protease inhibitor N-tosyl-l-phenylalanine chloromethyl ketone inhibited the decrease in mitochondrial membrane potential and cytochrome c release, the Ca(2+)-ATPase inhibitor thapsigargin inhibited only cytochrome c release, and the antioxidant butylated hydroxyanisole inhibited only the decrease in mitochondrial membrane potential. In contrast to IL-6, these other compounds that inhibited some of the later occurring mitochondrial damage did not inhibit the earlier p53-induced lysosomal damage. The results indicate that apoptosis is induced by p53 through a lysosomal-mitochondrial pathway that is initiated by lysosomal destabilization, and that this pathway can be dissected by using different apoptosis inhibitors. These findings on the induction of p53-induced lysosomal destabilization can also help to formulate new therapies for diseases with apoptotic disorders.

Animals↗