Anti-oxidized low-density lipoprotein antibodies in myeloperoxidase-positive vasculitis patients preferentially recognize hypochlorite-modified low density lipoproteins

Many patients surviving vasculitis are prone to accelerated atherosclerosis and often have enhanced levels of antibodies to oxidized low-density lipoprotein (oxLDL). To measure anti-oxLDL antibodies, oxidation of LDL is achieved with copper (Cu) or malondialdehyde (MDA). Because, in vivo, LDL may be oxidized with myeloperoxidase (MPO) or its product hypochlorite, we measured anti-hypochlorite LDL antibodies in patients with vasculitis, haemodialysis patients and healthy controls. A newly developed enzyme-linked immunosorbent assay (ELISA) was used to detect antibodies to oxLDL as modified by hypochlorite. Results are compared with data obtained by standard LDL oxidation using MDA-LDL or Cu-LDL as substrate. Results were compared between anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) patients (n = 93), haemodialysis (HD) patients (n = 59) and healthy controls (HC; n = 43). Furthermore, patients with MPO-ANCA-associated vasculitis (n = 47) were compared with patients with proteinase 3 (PR3)-ANCA associated vasculitis (n = 46). Optimal cut-off points were determined by receiver operator characteristic (ROC) curve analysis. Anti-oxLDL antibodies are enhanced in AAV patients (MDA-LDL and hypochlorite-LDL) and in HD patients (hypochlorite-LDL), when compared to HC. Furthermore, patients with MPO-ANCA-associated vasculitis had higher levels of antibodies to hypochlorite-LDL than patients with PR3-ANCA-associated vasculitis. Our newly developed assay, in which hypochlorite-LDL is used as substrate, seems a more sensitive assay than traditional assays to measure oxLDL antibodies. Furthermore, our results suggest that enhanced MPO-mediated LDL oxidation occurs in patients with MPO-ANCA.     

Increased expression of high-affinity low-density lipoprotein receptors on human T-blasts

Like all cells, lymphocytes need cholesterol for proper function, a requirement met by a finely tuned homeostasis between intracellular synthesis and uptake from the environment via low-density lipoproteins (LDL). We used flow cytometry to analyze the receptor activity of resting cells and T blasts incubated/activated in serum-free culture medium, or in medium supplemented with 25-5,000 micrograms/ml LDL. Dioctadecyl-indocarbocyanine has proved to be a useful fluorescent probe for investigating the LDL receptor activity of lymphocytes. The results show the receptor activity of day-3 resting T cells to be reduced more than 50% by 50 microgram LDL/ml, whereas 100-fold higher concentrations are necessary to achieve the same level of reduction in day-3 PHA blasts. The LDL receptor activities of individual blood donors' resting T cells, in vitro cholesterol-deprived resting T cells, and activated T blasts, were compared using two analytical techniques: spectrofluorometric analysis of detergent-solubilized cell suspensions and flow cytometric analysis of single living cells. Receptor affinity was determined by Scatchard analysis of spectrofluorometric binding curves, and by Line-weaver-Burke plots of flow cytometric data. Both methods yielded essentially identical dissociation constants (Kd) for cholesterol-deprived resting T cells and mitogen-activated T blasts, which fell in the expected range for the high-affinity LDL receptor (4.1-8.9 nM). In addition, spectrofluorometric analysis, but not flow cytometry, permitted quantification of LDL uptake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Netrin-1 overexpression in kidney proximal tubular epithelium ameliorates cisplatin nephrotoxicity

Netrin-1, a multifunctional laminin-related protein is widely expressed in various tissues, including kidney. The pathophysiological roles of netrin-1 in toxic acute kidney injury are unknown. To determine the role of netrin-1 in cisplatin-induced nephrotoxicity, we used netrin-1 transgenic mice that overexpress netrin-1 in the proximal tubular epithelium using the fatty acid binding protein promoter. Administration of cisplatin caused severe renal injury in WT mice but not in netrin-1 transgenic mice. Functional improvement was associated with better preservation of morphology, reduced cytokine expression and oxidative stress in the kidney, and reduced serum and urine cytokine and chemokine levels of transgenic mice as compared with WT mice. Cisplatin induced an increase in neutrophil infiltration into the kidney of WT mice, which was not significantly reduced in netrin-1 transgenic mice. Interestingly, ischemia reperfusion induced a large increase in apoptosis in WT mice but not in netrin-1 transgenic mice (215 ± 40 vs 94 ± 20 cells/5 HPF ( × 400), P < 0.0001), which was associated with reduced caspase-3 and p53 activation in the transgenic kidney. These results suggest that netrin-1 protects renal tubular epithelial cells against cisplatin-induced kidney injury by suppressing apoptosis and inflammation.     

Minimally oxidized low-density lipoprotein induces tissue factor expression in cultured human endothelial cells.

Oxidatively modified low-density lipoprotein is present in atherosclerotic lesions and has been proposed to play an important role in atherogenesis through its biologic effects on vascular cells. This study examined the effects of minimally oxidized preparations of LDL (MM-LDL) on tissue factor (TF) expression by cultured human endothelial cells. Low-density lipoprotein purified from normal donors was modified by exposure to iron or by prolonged storage, resulting in levels of thiobarbituric acid-reacting substances of approximately 2.5 to 4 nmoles/mg cholesterol. Preparations had less than 2.5 pg of endotoxin per microgram LDL and had no intrinsic procoagulant activity. This form of modified but not native LDL induced TF expression in endothelial cells in a time- and dose-dependent manner. Peak TF coagulant activity in cells exposed to 40 micrograms/ml MM-LDL were observed at 4 to 6 hours, and ranged from 50 to 500 pg/10(5) cells, compared with less than 10 pg/10(5) cells exposed to native LDL. Northern blot analysis showed TF mRNA levels to increase approximately 30-fold with exposure to MM-LDL for 2 hours. Induction of TF activity was dependent on the concentration of MM-LDL from 1 microgram/ml to 80 micrograms/ml, a range in which cell viability and morphology were unaffected. The findings suggest that minimally oxidized LDL may be a local mediator promoting thrombosis in atherosclerotic lesions.     

人血白蛋白对近端肾小管上皮细胞ACE2表达的影响

目的： 研究人血白蛋白对人近端肾小管上皮细胞（HK-2）血管紧张素转换酶2（ACE2）及血管紧张素转换酶（ACE）表达的影响，探讨白蛋白对肾脏损害的机制。方法: 不同浓度人血白蛋白（0、1、5、10、15 g/L）分别加入到培养的人近端肾小管上皮细胞培养48 h，用RT-PCR法和Western blotting法分别检测HK-2细胞ACE2和ACE mRNA和蛋白表达。结果: 正常培养状态下HK-2细胞（空白对照组）存在ACE2 mRNA和蛋白表达，加入不同浓度（5-15 g/L）的人血白蛋白剂量依赖抑制HK-2细胞ACE2 mRNA和蛋白表达（P<0.01）。正常培养状态下HK-2细胞ACE mRNA和蛋白表达水平较低，随着加入白蛋白浓度的增加其表达水平逐渐升高，10 g/L白蛋白显著促进了HK-2细胞ACE mRNA和蛋白表达（P<0.05）。结论: 在体外培养的HK-2细胞存在ACE及ACE2 mRNA和蛋白表达，人血白蛋白可抑制其ACE2表达而促进ACE表达,这可能是白蛋白促肾小管间质损伤及肾小球硬化、间质纤维化的机制之一。     

Oxidized low-density lipoprotein activates migration and degranulation of human granulocytes

Oxidized low-density lipoprotein (oxLDL) has been reported as a major participant in the pathogenesis of atherosclerosis. We hypothesized that oxLDL can also interact with granulocytes during inflammatory airway diseases, such as asthma. To test the chemotactic effect of oxLDL, isolated human peripheral granulocytes were added to the upper chambers of Transwell filters and migration in response to oxLDL was determined. Cu+2-oxidized LDL stimulated neutrophil (23.4 +/- 3.2% for 100 microg/ml oxLDL versus 2.9 +/- 1.1% for buffer, P < 0.05) and eosinophil (19.3 +/- 3.5% versus 0.6 +/- 0.02% for buffer, P < 0.05) chemotaxis in a concentration-dependent manner. The magnitude of chemotaxis was dependent on the degree of LDL oxidation. Granulocyte transmigration across IL-1beta-activated human pulmonary microvascular endothelial cell monolayers was similarly stimulated by oxLDL. OxLDL activated significant degranulation of both neutrophils (100.9 +/- 9.8 versus 49.6 +/- 8.4 ng lactoferrin released/5 x 105 neutrophils for buffer, P < 0.05) and eosinophils (342 +/- 115.4 versus 85.8 +/- 30.4 ng eosinophil-derived neurotoxin/1 x 106 eosinophils for buffer, P < 0.05). Therefore, in vivo influx and oxidation of LDL may be an important mediator for the initiation of bronchial inflammation where granulocytes are recruited to the lung.     

Immunochemical characterization of purified human oxidized low-density lipoprotein antibodies

The goal of this study was to characterize the isotypes and reactivity of human autoantibodies to copper oxidized LDL (oxLDL). Forty-six purified oxLDL antibodies contained immunoglobulins of the three major isotypes, with a predominance of IgG, subclasses 1 and 3. These IgG isotypes are known to interact with FcRgammaI and to activate the complement system and thus are potentially able to activate macrophages and cause foam cell formation. The same purified antibodies were tested for cross-reactivity with malondialdehyde (MDA)-, glycated (Glyc)-, and native (n)LDL and cardiolipin. Absorption with oxLDL resulted in a decrease of reactivity of 77.2 +/- 4.7%. Absorption with MDA-LDL resulted in a wider range of reduction of reactivity values, ranging from 50 to 87%, possibly reflecting differences in the degree of MDA modification. Absorption with Glyc- and nLDL caused a minor decrease in the reactivity of antibodies to oxLDL (5.9 +/- 7.1 and 6.8 +/- 6. 4%, respectively), comparable to the reduction of reactivity (2.1 +/- 4.0%) measured after absorption with transferrin, an irrelevant protein used as a negative control. These results suggest that oxLDL antibodies recognize primarily MDA epitopes. To determine whether purified oxLDL antibodies also recognize other epitopes known to be generated during copper oxidation of LDL, such as 4-hydroxynonenal (HNE)- and N(epsilon)(carboxymethyl)-lysine (CML), two additional sets of experiments were carried out. First, we monitored the formation of CML-, MDA-lysine, and HNE-lysine at different times during copper oxidation of two LDL pools. Both pools showed simultaneous increases in protein modification, as indicated by increasing fluorescence emission at 430 nm, and in immunoreactivity with oxLDL antibodies, coinciding closely with MDA modification of lysine groups. Second, we assessed whether the reactivity of oxLDL antibodies could be blocked by absorption with CML- or HNE-LDL. HNE-LDL did not react with isolated oxLDL antibodies. Highly modified CML-LDL (>90% of lysine residues modified) reduced the reactivity of oxLDL antibodies, but only by 25.5%. Finally, we investigated the possible cross-reactivity of oxLDL antibodies with cardiolipin. Seventeen purified oxLDL antibodies were used in this study, which showed that absorption with oxLDL or nLDL did not affect their reactivity with immobilized cardiolipin.     

人血清白蛋白对近端肾小管上皮细胞骨调素和CD44表达的影响

目的：研究人血清白蛋白能否刺激人近端肾小管上皮细胞产生骨调素（OPN）和CD44。方法： 用人血清白蛋白刺激人近端肾小管上皮细胞系（HK-2细胞），分不同时间（0-48 h）、不同浓度（0.1-10 g/L）两组，以RT-PCR方法分别检测两组细胞表达的OPN mRNA，以Western blotting分别检测两组细胞表达的OPN。用免疫荧光法、激光共聚焦显微镜观察1 g/L的人血清白蛋白刺激HK-2细胞24 h、48 h后OPN、CD44的表达。结果： 人血清白蛋白刺激HK-2细胞上调表达OPN mRNA和蛋白，呈时间和剂量相关性。CD44的表达与OPN同步。 结论： 人血清白蛋白可刺激HK-2细胞表达OPN与CD44。     

The effect of gentamicin on human renal proximal tubular cells

Human renal proximal tubular cells were exposed to gentamicin (0, 0.1, 0.5, 1.0, 5.0, 10.0 mg/ml medium) for 3, 7, 10, and 14 days. Cells were counted and cell viability was estimated by lactate dehydrogenase release. In addition, brush border-associated (gamma-glutamyltransferase) and lysosomal (acid phosphatase, N-acetyl-beta-glucosaminidase, and sphingomyelinase) enzyme activities were measured (0.01, 1.0, 3.3 mg/ml gentamicin for 3, 7, 10 and 14 days). The number of cells did not change significantly after gentamicin treatment. Cell viability, however, significantly decreased after 3 and 7 days exposure to 5 and 10 mg/ml gentamicin. Total lactate dehydrogenase activity was significantly decreased at 7, 10, and 14 days exposure to gentamicin greater than or equal to 5.0 mg/ml. gamma-Glutamyltransferase, acid phosphatase, and sphingomyelinase were decreased at 3, 7, and 10 days exposure to gentamicin greater than or equal to 1.0 mg/ml. Continued exposure to gentamicin less than or equal to 1.0 mg/ml appeared to have little or no effect on the activity of these enzymes at 14 days. N-Acetyl-beta-glucosaminidase activity, in contrast, was elevated (120-140% control) in the gentamicin-treated (greater than or equal to 1.0 mg/ml) groups at all time periods studied. Thus, gentamicin exposure resulted in changes in some of the enzyme activities in human renal proximal tubular cell cultures, but longer exposure (14 days) to gentamicin (less than or equal to 1.0 mg/ml) resulted in a return to control levels of some activities.     

Seasonal change of membrane potential across the proximal tubular epithelium in bullfrog kidneys.

In order to examine the seasonal changes in the relationship between the membrane potential and potassium activity of proximal tubular epithelium, a micropuncture study was performed with potassium selective microelectrodes on the kidney of the bullfrog (Rana catesbeiana) in two different seasons: winter (7 degrees C) and summer (20 degrees C). The potasssium activity in winter animals (7 degrees C) was 2.92 +/- 0.33 (mean +/- S.D., n = 20), 63.2 +/- 12.7 (n = 26), and 2.68 +/- 0.19 (n = 26) mM for the tubular fluid, cell, and plasma, whereas that in summer animals (20 degrees C) was 2.84 +/- 0.05 (n = 22), 61.8 +/- 11.2 (n = 24), 2.63 +/- 0.24 (n = 24) mM, respectively, indicating no seasonal difference. On the other hand, the mean values of the membrane PD in winter animals were 59.4 +/- 1.8 (n = 26) and 71.7 "/- 7.2 (n = 26) mV for the luminal and peritubular borders, whereas those in summer animals were 55.1 +/- 1.7 (n = 24) and 63.9 +/- 6.9 (n = 24) mV, respectivley, indicating that there was a significant seasonal difference (p less than 0.05 and p less than 0.001). Hence, compared to winter animals, the changes in the electrochemical profile for potassium in summer animals were: 1) the peritubular membrane PD is lower and 2) the transtubular electrochemical gradient is less steep. The sodium permeability calculated as the best fitting for a modified Goldman equation was 0.01 and 0.03 for winter and summer animals, respectively. In view of the fact the potassium in the cell and luminal fluid of the proximal tubule is kept at similar levels, potassium homeostasis is maintained in both groups of animals. The seasonal changes in electrical potentials are probably be due to an increase of cellular membrane permeability to ions other than potassium and to increased paracellular shunt conductance through the epithelium.     

Ontogeny of CLCN3 chloride channel gene expression in human pulmonary epithelium

Human fetal bronchopulmonary epithelia secrete liquid, and this chloride (Cl)-dependent process is important for normal lung growth. At the time of birth there is a maturational transition from a secretory to an absorptive phenotype. The pathways for Cl exit from the apical membrane which are required for fetal lung liquid secretion are unknown but are thought to be independent of the cystic fibrosis transmembrane conductance regulator. We determined the ontogeny of expression of the CLCN family of voltage-dependent Cl channel genes (CLCN2 through 6, K(a) and K(b)) in the human lung to identify potential pathways for pulmonary liquid secretion. Only CLCN3 and CLCN6 messenger RNA were detected by Northern analysis of fetal whole lung tissue. Ribonuclease protection assays confirmed the expression of CLCN3 and also revealed expression of CLCN2. The ontogeny of expression of these two channels was similar, peaking in midgestation and declining postnatally. In situ hybridization localized the CLCN2 and CLCN3 messages to airway and distal pulmonary epithelia and to pulmonary blood vessels. We conclude that CLCN3 is expressed in human airway epithelia and expression is developmentally regulated. The contribution of these channels to pulmonary epithelial liquid transport and lung development remains to be determined.     

Resistance of native and circulating modified low-density lipoproteins in human blood to association

The resistance of native and circulating modified low-density lipoproteins from human blood to spontaneous and polyethylene glycol-induced association was studied by recording light transmission fluctuations. Circulating modified low-density lipoproteins were less resistant to association than native low-density lipoproteins. Polyethylene glycol-induced association of low-density lipoproteins was irreversible. Our results suggest that atherogenic activity of circulating modified low-density lipoproteins is associated with their increased predisposition to irreversible association.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 10, pp. 428–431, October, 2004