Oxidative stress response after prolonged exposure of domestic rabbit to a lower dosage of extracted microcystins

Oxidative stress response after prolonged exposure to a low dose of microcystins (MCs) was studied in liver, kidney and brain of domestic rabbits. Rabbits were treated with extracted MCs (mainly MC-LR and MC-RR) at a dose of 2 MC-LReq. mu g/kg body weight or saline solution every 24 h for 7 or 14 days. During the exposure of MCs, increase of lipid peroxidation (LPO) levels were detected in all the organs studied, while antioxidant enzymes responded differently among different organs. The enzyme activities Of Superoxide dismutase (SOD). catalase (CAT) and glutathione reductase (GR) in liver decreased in the MCs treated animals. In brain, there were obvious changes in glutathione peroxidase (GPx) and GR, while only CAT was obviously influenced in kidney. Therefore, daily exposure at a lower dosage of MCs, which mimicked a natural route of MCs. could also induce obvious oxidative stress in diverse organs of domestic rabbits. The oxidative stress induced by MCs in brain was as serious as in liver and kidney, suggesting that brain may also be a target of MCs in mammals. And it seems that animals may have more time to metabolize the toxins or to form an adaptive response to reduce the adverse effects when exposed to the low dose of MCs. (C) 2008 Elsevier B.V. All rights reserved.

Changes in plasma thyroid hormones and cortisol levels in crucian carp (Carassius auratus) exposed to the extracted microcystins

The endocrine response of crucian carp injected intraperitoneally with extracted microcystins (MC) was investigated in this study. Fish were injected intraperitoneally either with 0.75% NaCl (control) and Microcystis extract corresponding to 150 and 600 mu g microcystins per kg body weight. The plasma levels of triiodothyronine (T-3), thyroxine (T-4), free triiodothyronine (FT3), free thyroxine (FT4), and cortisol were determined at 0, 1, 3, 12, 24. and 48 h post-administration of MC-containing extract. Treated fish displayed abnormal behaviors, Such as a startle response and disoriented swimming, as well as changes in ventilation rates. Plasma cortisol concentrations of fish in both dose groups significantly increased after administration of extracted MC and remained high throughout the experiment, which suggested that MC elicited a stress response in treated fish. The profiles of cortisol changes in treated fish appeared to be dose dependent, indicating that fish in the high dose group experienced greater MC-incluced disturbance. Mortality occurred after 12 h in the high dose group. Plasma levels of T-4, T-3, FT4, and FT3 did not vary significantly between the control fish. In contrast to this, fish exposed to MC-containing extract showed significant declines in T-3, FT4, and FT3 levels in a dose-depenclent manner throughout the experiment. Plasma T4 levels, however, did not vary significantly in the low dose group, whereas they decreased significantly it 48 h post injection in the high dose group. This study demonstrates that administration of microcystins-containing extract causes a stress response and reduces the plasma levels of thyroid hormones in crucian carp. These results illustrate that microcystins exerted potent effects on the endocrine system of crucian carp, through activating their hypothalamus-pituitary- interrenal axis and disturbing thyroid function. (c) 2008 Elsevier Ltd. All rights reserved.

In vivo studies on the toxic effects of microcystins on mitochondrial electron transport chain and ion regulation in liver and heart of rabbit

This study examined the toxic effects of microcystins on mitochondria of liver and heart of rabbit in vivo. Rabbits were injected i.p. with extracted microcystins (mainly MC-RR and -LR) at two doses, 12.5 and 50 MCLReq. mu g/kg bw, and the changes in mitochondria of liver and heart were studied at 1, 3,12, 24 and 48 h after injection. MCs induced damage of mitochondrial morphology and lipid peroxidation in both liver and heart. MCs influenced respiratory activity through inhibiting NADH dehydrogenase and enhancing succinate dehydrogenase (SDH). MCs altered Na+-K+-ATPase and Ca2+-Mg2+-ATPase activities of mitochondria and consequently disrupted ionic homeostasis, which might be partly responsible for the loss of mitochondrial membrane potential (MMP). MCs were highly toxic to mitochondria with more serious damage in liver than in heart. Damage of mitochondria showed reduction at 48 h in the low dose group, suggesting that the low dose of MCs might have stimulated a compensatory response in the rabbits. (C) 2008 Elsevier Inc. All rights reserved.

Microcystin-induced variations in transcription of GSTs in an omnivorous freshwater fish, goldfish

The glutathione S-transferases are important enzymes in the microcystin-induced detoxication processes. In this experiment, we cloned the full-length cDNA of alpha, pi and theta-class-like glutathione S-transferase genes from goldfish (Carassius auratus Q. Their derived amino acid sequences were clustered with other vertebrate alpha, pi and theta-class GSTs in a phylogenetic tree and the goldfish GST sequences have the highest similarity with those from common carp and zebrafish. Goldfish were i.p. injected with microcystins extract at two doses (50 and 200 mu g kg(-1) BW MC-LReq) and the relative changes of the mRNA abundance in liver, kidney and intestine were analyzed by real-time PCR. The transcription of GST alpha was suppressed in both liver and intestine, but induced in the kidney. Decreased transcription of GST theta was detected in liver, kidney and intestine in the low-dose group. The transcription of GST pi was suppressed in liver and intestine post-injection in both dose groups. These results suggested that the transcription of GST isoforms varied in different ways within an organ and among organs of goldfish exposed to MCs. (C) 2008 Elsevier B.V. All rights reserved.

Hematological and plasma biochemical responses of crucian carp (Carassius auratus) to intraperitoneal injection of extracted microcystins with the possible mechanisms of anemia

Alterations in hematological indices such as decreases in blood cell counts (RBC), hematocrit (Ht) and hemoglobin (Hb) concentrations are key symptoms of anemia. However, few experiments were conducted to examine changes in hematological indices of fish exposed to microcystins that are believed to be fatal to circulatory systems of vertebrates. An acute toxicological experiment was designed to study hematological changes of crucian carp injected intraperitoneally (i.p.) with extracted microcystins at two doses, 50 and 200 mu g MC-LReqkg(-1) body weight. After being i.p. injected with microcystins, the fish exhibited behavioral abnormity. There were significant decreases in RBC in the high-dose group, and in Ht and Hb concentrations in both dose groups, while erythrocte sedimentation rate (ESR) significantly increased, indicating the appearance of normocytic anemia. There were no prominent changes in the three red cell indices, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH,), and mean corpuscular hemoglobin concentration (MCHC). Increases in blood urea nitrogen (BUN) and creatinine (CR) in both dose groups suggest the occurrence of kidney impairment. Alteration in blood indices was reversible at the low dose group. Conclusively, anemia induced by kidney impairment was a key factor to cause abnormity of swimming behaviors and high mortality of crucian carp. (c) 2007 Elsevier Ltd. All rights reserved.

Microcalorimetric investigation of the toxic action of Cr(VI) on the metabolism of Tetrahymena thermophila BF5 during growth

Tetrahymena thermophila BF5 produce heat by metabolism and movement. Using a TAM air isothermal microcalorimeter, the power-time curves of the metabolism of T thermophila BF5 during growth were obtained and the action on them by the addition of Cr(VI) were studied. The morphological change with Cr(VI) coexisted and biomass change during the process of T thermophila BF5 growth were studied by light microscope. Chromium has been regarded as an essential trace element for life. However, hexavalent chromium is a known carcinogen, mutagen, cytotoxicant and strong oxidizing agent. Cr(VI) of different concentration have different effects on T thermophila BF5 growth with the phenomenon of low dose stimulation (0-3 x 10(-5) mol L-1) and high dose inhibition (3 x 10(-5) to 2.4 x 10(-4) mol L-1). The relationship between the growth rate constant (k) and c is a typical U-shaped curve, which is a characteristic of hormesis. T thermophila BF5 cannot grow at all when the concentration of Cr(VI) is up to 2.4 x 10(-4) mol L-1. The microscopic observations agree well with the results obtained by means of microcalorimetry. And T thermophila BF5 had obviously morphological changes by the addition of Cr(VI). (c) 2006 Elsevier B.V. All rights reserved.

UV-sensitive P compounds: Release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K-m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP. Plot of K-m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.

Effect of beta-irradiation on photoluminescence of MOCVD grown GaN

The effect of beta particles interaction on the optical properties of MOCVD grown GaN is reported. A significant change in luminescence properties of GaN is observed after exposing the material with 0.6 MeV beta particles with low dose of 10(12) cm(-2). The results obtained from photoluminescence measurements of irradiated GaN samples in low dose are found contradictory to those reported in literature for samples irradiated with heavy dose (> 10(15) cm(-2)) of electron. An increase in intensity of yellow luminescence has been observed with increasing dose of beta particles which is in disagreement to the already reported results in literature for heavily irradiated samples. A model has been proposed to sort out this inconsistency. The increase in YL intensity at low dose is attributed to the increase in concentration of VGaON complex whereas production of non-radiative VGaON clusters is assumed to justify the decrease in YL intensity at high dose.

Hg胁迫对两种基因型小麦生长及其过氧化物酶活性的影响

用不同浓度Hg处理两种基因型小麦种子,较低浓度的Hg对小麦种子萌发影响比较小,对抗旱品种的小麦种子(陕合)的萌发有略微的刺激作用。小剂量、短时间的重金属处理可以提高POD的活性,发芽后受到Hg胁迫的陕合对Hg的耐受性低于发芽前就受到Hg胁迫的陕合,也低于同样胁迫处理的小麦品种(郑引)。发芽后进行Hg胁迫处理情况下,陕合对于Hg胁迫比较敏感,POD活性随着Hg浓度的升高而下降;而郑引,低浓度Hg对其POD活性有促进作用。在小麦发芽前就受到Hg胁迫的情况下,陕合和郑引的POD活性都随着Hg浓度增加表现为先上升而后下降趋势。

potential mechanisms involved in resistant phenotype of MCF-7breast carcinoma cells to ionizing radiation induced apoptosis

In the present study, we investigated the mechanisms of apoptosis resistance and the roles of the phosphorylation of BRCA1, p21, the Bax/Bcl-2 protein ratio and cell cycle arrest in IR-induced apoptosis in MCF-7 cells. X-irradiation, in particular at low dose (1 Gy), but not carbon ion irradiation, had a significant antiproliferative effect on the growth of MCF-7 cells. 1 Gy X-irradiation resulted in G1 and G2 phase arrest, but 4 Gy induced a significant G1 block. In contrast, carbon ion irradiation resulted in a significant accumulation in the G2 phase. Concomitant with the phosphorylation of H2AX induced by DNA damage,carbon ion irradiation resulted in an approximately 1.9–2.8-fold increase in the phosphorylation of BRCA1 on serine residue 1524, significantly greater than that detected for X-irradiation. Carbon ion irradiation caused a dramatic increase in p21 expression and drastic decrease in Bax expression compared with X-irradiation. The data implicated that phosphorylation of BRCA1 on serine residue 1524 might,at least partially, induce p21 expression but repress Bax expression. Together, our results suggested that the phosphorylation of BRCA1 at Ser-1524 might contribute to the G2 phase arrest and might be an upstream signal involved in preventing apoptosis signal via upregulation of p21 and downregulation of the Bax/Bcl-2 ratio.

Size modification of Au nanoparticles induced by slow highly charged ions Ar-40(q+) irradiation

Size modification of Au nanoparticles (NPs), deposited on the Au-thick film surface and irradiated by slow highly charged ions (SHCI) 40Arq+ (3 6 q 6 12) with fixed low dose of 4.3 1011 ions/cm2 and various energy ranging from 74.64 to 290.64 keV at room temperature (293.15 K), was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The effect of projectile kinetic energy on the modified size of NPs was explored by an appropriate choice of the fixed process parameters such as ion flux, irradiation temperature, incident angle, irradiation time, etc. The morphological changes of NPs were interpreted by models involving collisional mixing, Ostwald ripening (OR) and inverse Ostwald ripening (IOR) of spherical NPs on a substrate. A critical kinetic energy as well as a critical potential energy of the projectile in the Au NPs size modification process were observed.

Melatonin modulates acute testicular damage induced by carbon ions in mice

The present study was performed to obtain evidence of the radioprotective function of melatonin at different administration levels on carbon ion-induced mouse testicular damage. Outbred Kun-Ming strain mice were divided into six groups, each composed of eight animals: control group, melatonin alone group, irradiation group and three melatonin plus irradiation-treated groups. An acute study was carried out to determine alterations in DNA-single strand break, cell apoptosis, and oxidative stress parameters as well as histopathology in mouse testis 24 h after whole-body irradiation with a single dose of 4 Gy Tie results showed that pre-treatment and post-treatment with high-dose melatonin (10 mg/kg) both significantly alleviated carbon ion-induced acute testicular damage, a greater radioprotective effect being observed in the pre-treatment group. On the other hand, low-dose melatonin (1 mg/kg) had a limited radioprotective effect on irradiation-induced degeneration and DNA lesions in mouse testis. Taken together, the data suggest that prophylactic treatment with a higher dose of melatonin is probably advisable to protect against the effects of heavy-ion irradiation.

低剂量重离子辐射诱导小鼠的适应性反应和褪黑素的辐射保护作用研究

研究目的： 1.研究碳离子辐射对小鼠不同组织抗氧化酶活性及细胞周期进程的影响。 2.研究低剂量碳离子预辐射对离体培养的黑色素瘤B16细胞及正常小鼠诱导的适应性反应。 3. 研究褪黑素（MLT）对碳离子的辐射损伤防护效应。 4. 研究碳离子层叠法辐照对H22荷瘤小鼠的治疗效果。研究方法： 1.采用不同剂量的碳离子辐照小鼠，用黄嘌呤氧化酶法检测外周血、肝脏及脑组织中抗氧化酶活性变化，流式细胞仪检测细胞周期阻滞情况。 2.采用低剂量碳离子预辐射离体培养的黑色素瘤B16细胞及正常小鼠，间隔4h后再以攻击剂量辐照，常规组织切片染色观察各组织器官病理变化，流式细胞仪检测细胞周期阻滞情况，黄嘌呤氧化酶法检测小鼠胸腺、脾脏及B16细胞中抗氧化酶活性，Western-blot法检测胸腺细胞及B16细胞中P53及P21蛋白表达情况，RT-PCR法检测CHK2及CDC25mRNA的表达水平。 3.在碳离子辐照小鼠1h前腹腔注射褪黑素，单细胞电泳方法检测胸腺、脾脏细胞的DNA损伤情况，微核法表征外周血的染色体损伤，黄嘌呤氧化酶法测定胸腺、脾脏细胞的抗氧化酶活性。 4.以碳离子层叠法辐照H22荷瘤小鼠，统计不同剂量照射后的肿瘤体积变化、肿瘤抑制率、肿瘤生长延迟天数及治愈率。结果： 1、小鼠血清和肝脏组织在辐射剂量较低（≤0.75Gy）时SOD活性高于对照组，随着辐射剂量的增高，SOD活性趋于降低；MDA含量在辐射剂量较低（≤0.3Gy）时低于对照，随着辐射剂量的增高其含量趋于升高；脑组织GSH浓度在照射剂量较低（≤0.5Gy）时大于对照组，随着照射剂量的升高其浓度趋于降低；低剂量辐射小鼠引起胸腺G2期细胞比例增加，脾脏G1期细胞比例增加。 2、小鼠肝脏、脾脏、肺脏及脑组织在攻击剂量辐射后，出现明显的病理变化，低剂量预辐射处理后病理变化减轻；低剂量预辐射增加胸腺G2期细胞及脾脏G1期细胞比例；相对于单纯攻击剂量辐射组，低剂量预辐射组胸腺组织P53及P21蛋白表达升高；CHK2 mRNA水平升高，CDC25 mRNA水平降低；脾脏及胸腺组织中SOD活性降低程度减弱，MDA含量升高趋势减弱。B16细胞经低剂量预辐射处理后上述指标均未发生明显变化。 3、与辐照处理组相比，褪黑素处理后小鼠的脾脏胸腺细胞DNA损伤拖尾率及彗尾长度明显降低；SOD活性升高，MDA含量降低，外周血微核率降低。 4、在不同剂量的碳离子辐照处理后观察的12天内，各组肿瘤生长速度减慢，生长延迟，肿瘤抑制率随时间而增加。15Gy照射组肿瘤生长速度最慢，肿瘤抑制率最大，肿瘤生长延迟最为明显，而且肿瘤治愈率达到30%。结论： 1． 低剂量12C6+离子全身辐照小鼠应激激活机体抗氧化系统，随辐射剂量的增加，机体抗氧化能力明显降低，导致脂质过氧化发生；低剂量的碳离子辐射导致小鼠胸腺细胞G2期阻滞，脾脏细胞发生G1期阻滞。 2． 低剂量12C6+离子预辐射引发小鼠正常机体产生适应性反应，减轻随后的大剂量辐射造成的损伤；低剂量12C6+离子预辐射对小鼠黑色素瘤B16细胞未引发适应性反应。 3． 15mg/kg的MLT可以对小鼠的重离子辐射损伤产生明显的防护效果。 4． 12C6+离子适形治疗小鼠移植性肿瘤H22，荷瘤鼠的存活时间、肿瘤体积变化、肿瘤的控制率、治愈率等结果显示，15Gy为最佳治疗剂量

低剂量辐照下细胞辐射超敏感性研究

目的：1．比较肝癌细胞SMMC-7721和正常肝细胞L02，其辐射超敏感性和增强的辐射抗性的差异，为临床治疗提供基础研究数据。 2．对于重离子束辐照哺乳动物细胞引起的超敏感性以及增强的辐射抗性很少有报导。本研究利用兰州重离子研究装置（HIRFL）提供的12C开展高LET射线引起肝癌细胞SMMC-7721的辐射超敏感性的研究。材料和方法：1．低剂量60co γ射线辐照SMMc-7721细胞和L02细胞，低剂量高LE12c （50 MeV／u，LET＝44．56keV/μm）辐照SMMC-7721细胞，剂量范围为0-ZGy.2．利用流式细胞仪的前向光和侧向光对辐照后的细胞进行分选，精确计数。3．将细胞转入培养皿中，培养l0天，固定，染色。统计大于50个细胞的克隆。结果与讨论：1．用流式细胞仪进行细胞分选与传统的稀释法相比，存活分数没有明显的差异，标准偏差明显减少，该方法完全适用于低剂量存活的测量；2，SMMc-7721和L02细胞对低剂量60Coγ射线辐照均表现出HRS／IRR响应。但是只有当肿瘤细胞和正常组织的存活差异在3％以上时才能将HRS响应应用于临床治疗。3．用高LET12c离子束对SMMC-7721细胞进行照射，细胞也表现出明显的HRS／ IRR响应。与Y射线照射相比，C离子照射的闭值剂量为0．28Gy，比γ射线照射的要低。这可能是由于两种射线能量沉积的方式不同造成的。4．将重离子应用于临床治疗时，由于位于离子通道上的细胞受到微小剂量的照射（0．2-0.5SGy/次），细胞正好位于超敏感区域，因此，在治疗时要充分考虑离子束入射通道上细胞的HRS响应。