Nitric oxide-induced inhibition of transport by thick ascending limbs from Dahl salt-sensitive rats.

The factor responsible for salt sensitivity of blood pressure in Dahl rats is unclear but presumably resides in the kidney. We tested the hypotheses that (1) thick ascending limbs of Dahl salt-sensitive rats (DS) absorb more NaCl than those of Dahl salt-resistant rats (DR) and (2) NO inhibits transport to a lesser extent in thick ascending limbs from DS. We found that basal chloride absorption (J(Cl)) by thick ascending limbs from DR was 105.8+/-10.0 pmol. mm(-1). min(-1) (n=6). Ten and 100 micromol/L spermine NONOate, an NO donor, decreased J(Cl) in DR to 65.8+/-8.5 and 46.8+/-7.0 pmol. mm(-1). min(-1), respectively. Basal J(Cl) in DS was 131.6+/-13.4 pmol. mm(-1). min(-1) (n=7). In DS, 10 and 100 micromol/L spermine NONOate decreased J(Cl) to 111.5+/-12.8 and 46.8+/-6.2 pmol. mm(-1). min(-1), respectively. No difference was observed in basal or NO-inhibited Na absorption by cortical collecting ducts or in basal or NO-inhibited oxygen consumption by inner medullary collecting ducts. Because NO acts via generation of cGMP, we measured cGMP production by thick ascending limbs from DS and DR to see whether a difference in cGMP production could account for the difference in basal or NO-inhibited transport. Basal rates of cGMP production were similar between the 2 strains. Although NO increased cGMP production by thick ascending limbs from both strains, no difference existed between DS and DR. We concluded that the reduced ability of NO to block transport in thick ascending limbs in DS may account for at least part of the salt sensitivity of blood pressure in this strain.     

Induction of aldose reductase and sorbitol in renal inner medullary cells by elevated extracellular NaCl.

Aldose reductase [aldehyde reductase 2; alditol:NAD(P)+ 1-oxidoreductase, EC 1.1.1.21] catalyzes conversion of glucose to sorbitol. Although its activity is implicated in the progression of ocular and neurological complications of diabetes, the normal function of the enzyme in most cells is unknown. Both aldose reductase activity and substantial levels of sorbitol were previously reported in renal inner medullary cells. In this tissue, the extracellular NaCl concentration normally is high and varies considerably depending on the urine concentration. We report here on a line of renal medullary cells in which medium that is high in NaCl greatly increases both aldose reductase activity and intracellular sorbitol. In these tissue culture cells (and presumably also in the renal inner medulla), the intracellular sorbitol helps balance the osmotic pressure of elevated extracellular NaCl and thus prevents cellular dehydration.     

Sensitivities of rat kidney thick ascending limbs and collecting ducts to vasopressin in vivo.

Clearance experiments were performed to characterize the sensitivity to vasopressin of the thick ascending limbs and collecting duct system of the rat kidney. The response of the thick ascending limbs was evaluated by measuring the Mg2+ excretion rate in the urine, since the [arginine-8] vasopressin-mediated effects on Mg2+ excretion are the direct result of a stimulation of Mg2+ reabsorption in this nephron segment, and the response of the collecting ducts was evaluated by changes in urine flow. To avoid the effects of parathyroid hormone, glucagon, and calcitonin, which stimulate Mg2+ reabsorption in the thick ascending limb and distal tubule, and of calcitonin, which increases the permeability of the cortical collecting ducts to water, experiments were performed on Brattleboro D. I. rats (with hereditary diabetes insipidus, due to a lack of [Arg8]vasopressin) acutely deprived of endogenous parathyroid hormone, calcitonin, and glucagon. Vasopressin infused at rates up to 5 pg/min did not reduce the Mg2+ fractional excretion rate, whereas at 5 pg/min water excretion was decreased by 50%. The half-maximal reduction of Mg2+ excretion occurred at vasopressin infusion rates 4-6 times higher than those necessary to diminish the water excretion rate to the same extent. We conclude that in vivo, two segments involved in the production of concentrated urine have different sensitivities to vasopressin and that this difference in sensitivity is very similar for the biological response in vivo and the adenylate cyclase activation in vitro. We suggest that both the magnitude and the nature of the effects of [Arg8]vasopressin on the kidney may vary according to the required antidiuretic response.     

Stimulation of ornithine decarboxylase activity by arginine vasopressin in the rat medullary thick ascending limb of Henle's loop

The effect of arginine vasopressin (AVP) on rat renal ornithine decarboxylase (ODC) activity was investigated by a cytochemical technique optimized for use in the medullary thick ascending limb of Henle's loop (mTAL). Stimulation of ODC activity by AVP was confined to the mTAL. Peaks in enzyme activity in cultured rat renal segments occurred after tissue had been exposed to AVP for 3 or 8 min and these times of maximal stimulation did not change with the concentration of AVP. There was a dose-dependent response in ODC activity over the AVP concentration range 0.01 10 fmol/l. The ODC response to AVP was totally blocked by specific antiserum to AVP and reduced by 70% with the specific inhibitor to ODC, difluoromethyl ornithine.     

Differential effects of hyperosmolality on Na-K-ATPase and vasopressin-dependent cAMP generation in the medullary thick ascending limb and outer medullary collecting duct.

Hyperosmolality in the renal medullary interstitium is generated by the renal countercurrent multiplication system, in which the medullary thick ascending limb (MAL) and the outer medullary collecting duct (OMCD) primarily participate. Since arginine vasopressin (AVP) regulates Na-K-ATPase activity directly via protein kinase A and indirectly via hyperosmolality, we investigated the acute and chronic effects of hyperosmolality on Na-K-ATPase and AVP-dependent cAMP generation in the MAL and OMCD. Microdissected MAL and OMCD from control and dehydrated rats were used for the measurement of Na-K-ATPase activity, mRNA expression of alpha-1, beta-1, and beta-2 subunits of Na-K-ATPase, and AVP-dependent cAMP generation. Na-K-ATPase activity in the MAL from dehydrated rats, as measured in isotonic medium, was higher than that of control rats. Moreover, incubation of samples in hypertonic medium (490 mOsm/kg H2O) further increased Na-K-ATPase activity. Dehydration increased alpha-1, beta-1, and beta-2 mRNA expression in the MAL without changing that in the OMCD. Western blot analysis revealed that in the outer medulla, the expression of beta-1, but not that of alpha-1 or beta-2, was stimulated by dehydration. Incubation of MAL or OMCD in hypertonic medium increased AVP-dependent cAMP generation. Higher levels of AVP-dependent cAMP were generated in the MAL from dehydrated rats than that of controls, although incubation in hypertonic medium did not lead to additional increases in AVP-dependent cAMP accumulation. In contrast, AVP-dependent cAMP generation in the OMCD was stimulated by dehydration, and was further stimulated by incubation in hypertonic medium. These findings demonstrate that Na-K-ATPase is upregulated short- and long-term hyperosmolality in the MAL, but not in OMCD.     

Superoxide stimulates NaCl absorption in the thick ascending limb via activation of protein kinase C

Abnormal production of superoxide (O(2)(-)) contributes to hypertension, in part because of its effects on the kidney. The thick ascending limb absorbs 20% to 30% of the filtered load of NaCl. O(2)(-) stimulates NaCl absorption by the thick ascending limb by enhancing Na(+)/K(+)/2Cl(-) cotransporter activity; however, the signaling mechanism is unknown. We hypothesized that O(2)(-) stimulates NaCl absorption by activating protein kinase C (PKC). To test this, we measured the effect of O(2)(-) on: (1) Cl(-) absorption in the presence and absence of PKC inhibitors, (2) total PKC activity, and (3) activation of specific PKC isoforms. Isolated perfused medullary thick ascending limbs were exposed to O(2)(-) generated by xanthine oxidase (1 mU/mL) and hypoxanthine (0.5 mmol/L). O(2)(-) increased Cl(-) absorption by 42% (from 76.2+/-3.6 to 108.2+/-11.9 pmol/min per millimeter; n=5; P<0.05). After treatment with the general PKC inhibitor staurosporine (10 nmol/L), O(2)(-) did not stimulate Cl(-) absorption (Delta-5.7+/-8.6%; n=6). In thick ascending limb suspensions, O(2)(-) increased total PKC activity by 33% (from 66+/-11 to 88+/-12 mU/mg protein; n=5; P<0.05) and increased PKC-alpha and PKC-delta activity by 1.75- and 0.37-fold, respectively. The PKC-alpha/beta-selective inhibitor G?976 (100 nmol/L) blocked the ability of O(2)(-) to stimulate Cl(-) absorption by isolated perfused medullary thick ascending limbs (Delta4.5+/-15.0%; n=5). The role of PKC-delta could not be studied because of cell necrosis caused by the selective inhibitor rottlerin. We conclude that PKC-alpha is required for O(2)(-)-stimulated NaCl absorption in the thick ascending limb.     

Carvedilol decreases elevated oxidative stress in human failing myocardium

BACKGROUND: Oxidative stress has been implicated in the pathogenesis of heart failure. However, direct evidence of oxidative stress generation in the human failing myocardium has not been obtained. Furthermore, the effect of carvedilol, a vasodilating beta-blocker with antioxidant activity, on oxidative stress in human failing hearts has not been assessed. This study was therefore designed to determine whether levels of lipid peroxides are elevated in myocardia of patients with dilated cardiomyopathy (DCM) and whether carvedilol reduces the lipid peroxidation level. Methods and Results- Endomyocardial biopsy samples obtained from 23 patients with DCM and 13 control subjects with normal cardiac function were studied immunohistochemically for the expression of 4-hydroxy-2-nonenal (HNE)-modified protein, which is a major lipid peroxidation product. Expression of HNE-modified protein was found in all myocardial biopsy samples from patients with DCM. Expression was distinct in the cytosol of cardiac myocytes. Myocardial HNE-modified protein levels in patients with DCM were significantly increased compared with the levels in control subjects (P<0.0001). Endomyocardial biopsy samples from 11 patients with DCM were examined before and after treatment (mean, 9+/-4 months) with carvedilol (5 to 30 mg/d; mean dosage, 22+/-8 mg/d). After treatment with carvedilol, myocardial HNE-modified protein levels decreased by 40% (P<0.005) along with amelioration of heart failure. CONCLUSIONS: Oxidative stress is elevated in myocardia of patients with heart failure. Administration of carvedilol resulted in a decrease in the oxidative stress level together with amelioration of cardiac function.     

糖尿病血糖波动与氧化应激

糖尿病血糖波动与氧化应激对靶器官的损伤和并发症的影响正成为糖尿病防治研究的新热点.血糖波动产生的氧化应激与糖尿病及其并发症的发生、发展有着密切的联系,减少血糖波动对氧化应激的影响,逆转氧化应激对组织细胞的损伤,从而可能阻止或延缓糖尿病及其并发症的产生.本文就近年来发表的相关文献和相关进展综述如下.     

Analysis of the carbonyl compounds produced in beta thalassaemic erythrocytes by oxidative stress

Several carbonyls more toxic than malonaldehyde (MDA) are also generated during the propagation of lipid peroxidation stimulated "in vitro" in human erythrocytes. As regards thalassaemia, after "in vitro" treatment with tert-butyl hydroperoxide (TBHP), the total amount of aldehydes formed (MDA plus the other carbonyls) is significantly increased in the red cells from homozygous as compared to heterozygous and normal subjects. These findings lead to the conclusion that the extent of lipid peroxidation in erythrocytes is actually wider than that measurable in terms of malonaldehyde only, and that aldehydes of the hydroxyalkenal class in particular may play a role in the pathogenesis of reduced red cell survival in haemolytic anaemias.     

不同糖调节受损人群血糖波动与氧化应激的相关性分析

目的 采用动态血糖监测系统研究不同糖调节受损人群的血糖波动与氧化应激的相关性.方法 2008年1月至7月选取北京地区稳定人群66名,根据美国糖尿病学会(ADA)2003年标准分为正常糖耐量组(13例),糖尿病前期组(17例),2型糖尿病组(36例);所有受试对象均行72 h动态血糖临测,选取平均血糖波动幅度评价血糖波动情况;其间第48～72小时留取24 h尿,采用酶联免疫吸附法检测8-异前列腺素F2α(8-isoPGF2α)评价氧化应激水平.2型糖尿病组给予"重组赖脯胰岛素25"强化治疗12周,其间定期随访、指导生活方式干预并调整胰岛素用量.对干预前、后血糖波动、氧化应激和各项代谢指标的变化行方差分析,并对其影响因素行相关分析及多元逐步回归分析.结果 (1)基线时2型糖尿病组24 h尿游离8-isoPGF2α分泌率(8-isoPGF2α/Cr)为(1706±477)pg/mg,与糖尿病前期组[(216±65)pg/mg]和正常糖耐量组[(269±60)pg/mg]比较升高690%和534%,差异有统计学意义(F=27.304,P<0.05);2型糖尿病组平均血糖波动幅度(MAGE)为6.04 mmol/L,与糖尿病前期组[(2.7±1.2)mmol/L]和正常糖耐量组[(1.7±0.5)mmol/L]比较升高124%和249%,差异有统计学意义(F=67.729,P均<0.05).(2)2型糖尿病组经"重组赖脯胰岛素25"干预后,24 h尿8-isoPGF2α/Cr、MAGE、糖化血红蛋白、甘油三酯与干预前比较分别降低34.53%,31.81%,18.50%,28.79%,差异有统计学意义(F值分别为6.108、18.378、39.322、5.942,P均<0.05);此外,收缩压、舒张压、空腹血糖、餐后2 h血糖与干预前比较显著下降(F值分别为7.879、11.684、38.952、61.207,P均<0.01).(3)Pearson相关分析显示24 h尿8-isoPGF2α/Cr与MAGE呈显著相关(r=0.593,P<0.01);与空腹血糖(r=0.415,P<0.01)、餐后2 h 血糖(r=0.472,P<0.01)、高密度脂蛋白胆固醇(r=-0.307,P<0.01)、甘油三酯(r=0.296,P<0.01)、收缩压(r=0.268,P<0.05)显著相关;而与糖化血红蛋白无相关(r=0.186,P>0.05).(4)以24 h尿8-isoPGF2α/Cr为因变量,以上述与其有相关性的变量为自变量进行多元逐步同门分析,只有MAGE和高密度脂蛋白胆固醇进入最终方程(决定系数r2分别为0.354、0.346,P均<0.01);偏相关分析与卜述结果 一致.结论 (1)2型糖尿病组与正常糖耐昔组、糖尿病前期组比较血糖波动幅度大,氧化应激水平高;(2)2型糖尿病氧化应激活化程度与血糖波动和部分血脂代谢相关;(3)经胰岛素强化干预后,血糖波动幅度下降,氧化应激反应减轻.     

Involvement of oxidative stress and the JNK pathway in glucose toxicity

The hallmark of type 2 diabetes is pancreatic beta-cell dysfunction and insulin resistance. Normal beta-cells can compensate for insulin resistance by increasing insulin secretion, but insufficient compensation leads to the onset of glucose intolerance. Once hyperglycemia becomes apparent, beta-cell function gradually deteriorates and insulin resistance becomes aggravated. Such phenomena are collectively called "glucose toxicity". Under diabetic conditions, oxidative stress is induced and the JNK pathway is activated, which is involved in "glucose toxicity". Activation of the JNK pathway suppresses insulin biosynthesis and interferes with insulin action. Indeed, suppression of the JNK pathway in diabetic mice improves insulin resistance and ameliorates glucose tolerance. Consequently, the JNK pathway plays a crucial role in the progression of pancreatic beta-cell dysfunction and insulin resistance and thus could be a potential therapeutic target for the "glucose toxicity" found in diabetes.     

高游离脂肪酸血症所致胰岛素抵抗与氧化应激的关系

研究高游离脂肪酸(FFA)血症所致大鼠机体氧化应激及胰岛素抵抗之间的相互关系,以及其对机体抗氧化能力的影响,探讨胰岛素抵抗的病理生理机制.经研究证实大鼠高FFA血症不仅使组织活性氧簇生成增加[(886±105 vs 427±42)mmol/L,P<0.05],同时损伤机体抗氧化能力,细胞内还原捌谷胱甘肽生成减少[(272±47 vs 561±36)μmol/L,P<0.05],导致氧化应激,从而促进胰岛素抵抗的形成.     

Dynamic regulation of metabolism and respiration by endogenously produced nitric oxide protects against oxidative stress

One of the many biological functions of nitric oxide is the ability to protect cells from oxidative stress. To investigate the potential contribution of low steady state levels of nitric oxide generated by endothelial nitric oxide synthase (eNOS) and the mechanisms of protection against H(2)O(2), spontaneously transformed human ECV304 cells, which normally do not express eNOS, were stably transfected with a green fluorescent-tagged eNOS cDNA. The eNOS-transfected cells were found to be resistant to injury and delayed death following a 2-h exposure to H(2)O(2) (50-150 microM). Inhibition of nitric oxide synthesis abolished the protective effect against H(2)O(2) exposure. The ability of nitric oxide to protect cells depended on the presence of respiring mitochondria as ECV304+eNOS cells with diminished mitochondria respiration (rho(-)) are injured to the same extent as nontransfected ECV304 cells and recovery of mitochondrial respiration restores the ability of nitric oxide to protect against H(2)O(2)-induced death. Nitric oxide also found to have a profound effect in cell metabolism, because ECV304+eNOS cells had lower steady state levels of ATP and higher utilization of glucose via the glycolytic pathway than ECV304 cells. However, the protective effect of nitric oxide against H(2)O(2) exposure is not reproduced in ECV304 cells after treatment with azide and oligomycin suggesting that the dynamic regulation of respiration by nitric oxide represent a critical and unrecognized primary line of defense against oxidative stress.     

糖化血红蛋白水平和血糖波动与氧化应激关系的研究

目的探讨HbA₁c水平、血糖波动与氧化应激(OS)的关系。方法选取2017年8月至2019年8月于山西白求恩医院内分泌科住院的新诊断T2DM患者115例,分为低HbA₁c(5.5%~6.5%)组、中HbA₁c(6.5%~7.5%)组、高HbA₁c(7.5%~8.5%)组,行持续葡萄糖监测,记录包括平均血糖波动幅度(MAGE)、血糖标准差(SDBG)、最大血糖波动幅度(LAGE)及日间血糖平均绝对差(MODD);ELISA法测定OS血清指标8-羟基脱氧鸟苷(8-OHdG),分析HbA₁c水平和血糖波动与8-OHdG的关系。结果与低HbA₁c组比较,中HbA₁c组SDBG、MAGE升高(P<0.05);高HbA₁c组LAGE、SDBG、MAGE及MODD均高于低HbA₁c、中HbA₁c组(P<0.05)。随着HbA₁c水平升高,各组8-OHdG水平依次升高(P<0.01)。Pearson相关性分析显示,HbA₁c水平与LAGE、SDBG、MAGE及MODD呈正相关(P<0.01),高HbA₁c组8-OHdG与MAGE呈正相关(r=0.202,P=0.036)。结论 SDBG、MAGE是反映血糖波动更敏感的指标,HbA₁c<7.5%时显示血糖异常波动。T2DM患者血糖波动随HbA₁c水平升高而增加,OS随血糖波动增加而加重。     

NADPH oxidase inhibition attenuates oxidative stress but not hypertension produced by chronic ET-1

Experiments were conducted to test the hypothesis that hypertension produced by chronic ET-1 infusion is mediated by NADPH oxidase-dependent superoxide production. Mean arterial pressure (MAP) was continuously monitored in male Sprague Dawley rats by telemetry. After baseline measurements, rats were placed on a high-salt diet (8% NaCl) and osmotic minipumps were implanted to infuse ET-1 (5 pmol/kg per minute intravenous) for 12 days. Control rats were maintained on the high-salt diet only. Separate groups of rats were also infused with ET-1 and given the superoxide dismutase mimetic, tempol (1 mmol/L), or the NADPH oxidase inhibitor, apocynin (1.5 mmol/L), in the drinking water. Infusion of ET-1 significantly increased MAP when compared with baseline values (132+/-3 versus 114+/-2 mm Hg, P<0.05). Neither tempol nor apocynin treatment had any effect on the increase in MAP produced by ET-1 when compared with baseline values (127+/-5 versus 113+/-2 and 130+/-3 versus 115+/-2 mm Hg, respectively). Plasma 8-isoprostane, an indicator of oxidative stress, was significantly increased in ET-1-infused rats compared with rats on a high-salt diet alone (128+/-33 versus 51+/-5 pg/mL; P<0.05). Both tempol and apocynin treatment significantly attenuated the ET-1-induced increase in plasma 8-isoprostane (72+/-10 and 61+/-6 pg/mL, respectively). Similarly, ET-1 infusion also significantly increased aortic superoxide production (chemiluminescence and dihydroethidium staining techniques), which was prevented by both tempol and apocynin. These data provide evidence that chronic ET-1 infusion increases vascular NADPH oxidase-dependent superoxide production but does not account for chronic ET-1-induced hypertension.     

Biochemical relevance between oxidative/carbonyl stress and elevated viscosity of erythrocyte suspensions

The effects of various aldehydes such as secondary products of peroxidized lipids and other aldehydes on rheological parameters and their relation with aging process were studied. Malondialdehyde (MDA) in different concentrations can increase significantly viscosity and plastic viscosity of erythrocytes suspended in plasma and HEPES buffer solution. Simultaneously, oxidation induced by Fe2+ can also enhance the viscosity of erythrocyte suspensions. All of these data suggest that MDA as one of the most studied unsaturated carbonyl products of lipid peroxidation leading to protein crosslinking may carry important information in understanding carbonyl stress-related rheological change in acute as well as chronic diseases and aging.     

表没食子儿茶素没食子酸酯对高糖环境下内皮细胞氧化应激的影响

目的研究不同剂型表没食子儿茶素没食子酸酯（EGCG）对高糖诱导人脐静脉内皮细胞（HUVEC）氧化应激损伤所引起凋亡的抑制作用及人核因子-κB P65（NF-κB P65）表达的影响。方法从新鲜脐带中分离培养HUVEC。用高糖诱导HUVEC表达NF-κB P65,实验组加入不同浓度的EGCG（12．5、25、50、100、200μmol／L）进行干预,PCR检测NF-κB P65mRNA的表达,AV-PI法检测凋亡细胞。结果高糖可诱导HUVEC凋亡,NF-κB P65表达增高;EGCG可抑制NF-κB P65的表达,降低凋亡指数,具有一定的时效关系、剂量关系。结论EGCG可在一定程度上抑制高糖诱导的氧化应激损伤所致的细胞凋亡。EGCG可能是通过抑制高糖所致的NF-κB增高,从而调控HUVEC细胞凋亡过程,发挥对HUVEC的保护作用。