Methylmercury alters the in vitro uptake of glutamate in GLAST- and GLT-1-transfected mutant CHO-K1 cells

In order to maintain normal functioning of the brain, glutamate homeostasis and extracellular levels of excitotoxic amino acids (EAA) must be tightly controlled. This is accomplished, in large measure, by the astroglial high-affinity Na⁺-dependent EAA transporters glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1). Methylmercury (MeHg) is a potent neurotoxicant. Astrocytes are known targets for MeHg toxicity, representing a site for mercury localization. Mehg is known to cause astrocytic swelling, EAA release, and uptake inhibition in astrocytes, leading to increased extracellular glutamate levels and ensuing neuronal excitotoxicity and degeneration. However, the mechanisms and contribution of specific glutamate transporters to MeHg-induced glutamate dyshomeostasis remain unknown. Accordingly, the present study was carried out to investigate the effects of MeHg on the transport of [d-2, 3-³H]-d-aspartate, a nonmetabolizable glutamate analog in Chinese hamster ovary cells (CHO) transfected with the glutamate transporter subtypes GLAST or GLT-1. Additional studies examined the effects of MeHg on mRNA and protein levels of these transporters. Our results indicate the following (1) MeHg selectively affects glutamate transporter mRNA expression. MeHg treatment (6 h) led to no discernible changes in GLAST mRNA expression; however, GLT-1 mRNA expression significantly (p<0.001) increased following treatments with 5 or 10 μM MeHg. (2) Selective changes in the expression of glutamate transporter protein levels were also noted. GLAST transporter protein levels significantly (p<0.001, both at 5 and 10 μM MeHg) increased and GLT-1 transporter protein levels significantly (p<0.001) decreased followign MeHg exposure (5 μM). (3) MeHg exposure led to significant inhibition (p<0.05) of glutamate uptake by GLAST (both 5 and 10 μM MeHg), whereas GLT-1 transporter activity was significantly (p<0.01) increased following exposure to 5 and 10 μM MeHg. These studies suggest that MeHg contributes to the dysregulation of glutamate homeostasis and that its effects are distinct for GLAST and GLT-1.     

Postnatal Methylmercury Exposure Induces Hyperlocomotor Activity and Cerebellar Oxidative Stress in Mice: Dependence on the Neurodevelopmental Period

During the early postnatal period the central nervous system (CNS) is extremely sensitive to external agents. The present study aims at the investigation of critical phases where methylmercury (MeHg) induces cerebellar toxicity during the suckling period in mice. Animals were treated with daily subcutaneous injections of MeHg (7 mg/kg of body weight) during four different periods (5 days each) at the early postnatal period: postnatal day (PND) 1–5, PND 6–10, PND 11–15, or PND 16–20. A control group was treated with daily subcutaneous injections of a 150 mM NaCl solution (10 ml/kg of body weight). Subjects exposed to MeHg at different postnatal periods were littermate. At PND 35, behavioral tests were performed to evaluate spontaneous locomotor activity in the open field and motor performance in the rotarod task. Biochemical parameters related to oxidative stress (levels of glutathione and thiobarbituric acid reactive substances, as well as glutathione peroxidase and glutathione reductase activity) were evaluated in cerebellum. Hyperlocomotor activity and high levels of cerebellar thiobarbituric acid reactive substances were observed in animals exposed to MeHg during the PND 11–15 or PND 16–20 periods. Cerebellar glutathione reductase activity decreased in MeHg-exposed animals. Cerebellar glutathione peroxidase activity was also decreased after MeHg exposure and the lowest enzymatic activity was found in animals exposed to MeHg during the later days of the suckling period. In addition, low levels of cerebellar glutathione were found in animals exposed to MeHg during the PND 16–20 period. The present results show that the postnatal exposure to MeHg during the second half of the suckling period causes hyperlocomotor activity in mice and point to this phase as a critical developmental stage where mouse cerebellum is a vulnerable target for the neurotoxic and pro-oxidative effects of MeHg.     

Intrastriatal Administration of Methylmercury Increases In Vivo Dopamine Release

Mercury is a neurotoxin that exists in a number of physical and chemical forms, producing different effects in the brain. In the present work, we have studied the effects of intrastriatal administration of different doses (40 M, 400 M, and 4 mM) of organic mercury (methylmercury, MeHg) on the dopaminergic system of rat striatum, in conscious and freely-moving animals, using microdialysis coupled to Liquid Chromatography. In previous works, we have discussed the effects of chronic and acute administration of MeHg on striatal dopaminergic system assessing changes in both release and metabolism of striatal dopamine (DA). In the present study we report that the intrastriatal administration of different doses of MeHg (40 M, 400 M, and 4 mM) produced significant increases (907 ± 31%, 2324 ± 156%, and 9032 ± 70% of basal levels, respectively for the different doses) in DA release from rat striatal tissue associated with significant decreases in extracellular levels of its main metabolites dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) using the dose of 4 mM MeHg (35 ± 3% and 48 ± 1%, respectively), whereas non-significant changes in metabolite levels were observed with the doses of 40 M and 400 M MeHg. We explain these effects as a result of stimulated DA release and/or decreased DA intraneuronal degradation.     

Importance of Molar Ratios in Selenium-Dependent Protection Against Methylmercury Toxicity

The influence of dietary selenium (Se) on mercury (Hg) toxicity was studied in weanling male Long Evans rats. Rats were fed AIN-93G-based low-Se torula yeast diets or diets augmented with sodium selenite to attain adequate- or rich-Se levels (0.1, 1.0 or 15 μmol/kg, respectively) These diets were prepared with no added methylmercury (MeHg) or with moderate- or high-MeHg (0.2, 10 or 60 μmol/kg, respectively). Health and weights were monitored weekly. By the end of the 9-week study, MeHg toxicity had impaired growth of rats fed high-MeHg, low-Se diets by approximately 24% (p < 0.05) compared to the controls. Growth of rats fed high-MeHg, adequate-Se diets was impaired by approximately 8% (p < 0.05) relative to their control group, but rats fed high-MeHg, rich-Se diets did not show any growth impairment. Low-MeHg exposure did not affect rat growth at any dietary Se level. Concentrations of Hg in hair and blood reflected dietary MeHg exposure, but Hg toxicity was more directly related to the Hg to Se ratios. Results support the hypothesis that Hg-dependent sequestration of Se is a primary mechanism of Hg toxicity. Therefore, Hg to Se molar ratios provide a more reliable and comprehensive criteria for evaluating risks associated with MeHg exposure.     

Methylmercury accumulation and fluxes across the intestine of channel catfish,Ictalurus punctatus

The excised intestines of channel catfish, Ictalurus punctatus, were perfused at 20 or 4 degrees C for 1 h 45 min, with methylmercury (CH(3)HgCl) alone, or in the presence of excess L-cysteine (L-Cys), D-cysteine (D-Cys), L-methionine (L-Met); or with ouabain or probenecid to identify the potential CH(3)Hg(II) uptake pathways in fish intestines. A temperature effect was noted, with CH(3)Hg(II) concentrations in tissues perfused at 20 degrees C being higher than at 4 degrees C, substantiating the idea that mechanisms requiring metabolic energy are involved in CH(3)Hg(II) uptake in fish intestines. The results indicate that, when CH(3)Hg(II) is complexed as the CH(3)Hg-L-Cys complex, it is taken up via an L-neutral amino acid carrier and rapidly transported to the serosal side of the intestine. Methylmercury uptake could be inhibited by probenecid and ouabain, although probenecid had less impact on CH(3)Hg(II) uptake than ouabain. Our results for CH(3)Hg(II) uptake in the presence of D-Cys, L-Met in excess of L-Cys, or with a metal mixture further established that CH(3)Hg(II) uptake across fish intestines occurs via a variety of pathways, including an energy-dependent L-neutral amino acid carrier, and that the route and amount of accumulation were a function of CH(3)Hg(II) speciation in the digestive tract of the fish.     

Human paleopathology and some diseases in living primitive societies: A review of the recent literature

The paper reviews publications in human paleopathology since about 1960, especially with regard to the implications of disease in man's evolution. Recent publications pertaining to pathology and illness in present day “primitive” societies that might be analogous to conditions prevailing in the past, are also noted.     

Inhibition of Amino Acid Transport and Protein Synthesis by HgCl2 and Methylmercury in Astrocytes: Selectivity and Reversibility

Abstract: The previously reported observation that submi-cromolar concentrations of HgCl₂ inhibit glutamate uptake reversibly in astrocytes, without effect on 2-deoxyglucose uptake, suggested that elemental mercury vapor, which is oxidized to mercuric mercury in the brain, might cause neurodegenerative change through the mediation of glutamate excitotoxicity. Here, selectivity is explored further by measuring the inhibition of other amino acid transporters and protein synthesis as a function of HgCl₂ concentration. The properties of MeHgCl were compared under identical conditions, and some morphological correlates of function were examined. Inhibition of amino acid transport by HgCl₂ was selective, whereas MeHgCl was nonselective. The 50% inhibitory concentrations of HgCl₂ for uptake of α-aminoiso-butyric acid by system A, uptake of α-aminoisobutyric acid or kynurenine by a system L variant, and uptake of γ-ami-nobutyric acid were all two- to fourfold greater than that for uptake of glutamate. The submicromolar concentrations of HgCl₂ that inhibited glutamate transport also inhibited protein synthesis, but in a rapidly reversible fashion, and elicited only discrete ultrastructural changes (heterochromatin. increased numbers of lysosomal bodies, and increased complexity of cell surface). In contrast, inhibition of protein synthesis by MeHgCl was acutely (1-h) irreversible and became marked only at concentrations higher than those that elicited gross morphologic change in the form of "bleb"-like swellings. The results lend support to the proposed excitotoxic mediation of mercury vapor neurotoxicity and reveal a sharp contrast between the effects of HgCl₂ and MeHgCl on astrocytes.     

Poliomyelitis and parenteral injections; a review of recent literature

Data presented in the literature as to the relationship of poliomyelitis and recent prior injections include several aspects. the coincidence of paralysis in the same site as a recent injection has been considered the most definitive evidence. The fact of an inordinately large number of cases of paralysis of an arm where a recent previous antigen injection was recorded offered less specific corroboration. The larger number of cases among persons who had had an injection in the month preceding onset than among persons with injections in more distant months was noted. This observation was supported when similar information was obtained in a comparison of injection histories for persons who had the disease with the histories of persons who did not have it. The interval between injection and onset among persons who had the disease within a month of injection suggested something other than chance relationship. There is limited information indicating increased severity of paralysis in the injected limb. Evidence is divided on whether or not there is more paralytic disease among patients with recent injections. Similarly, the evidence is no more than suggestive with regard to increased severity of spinal paralytic disease. The mechanism or nature of such a phenomenon is unexplained. However, as Anderson and Skaar said, "considerable attention must be attached to the fact of uniformity of results in a series of independent observations even though each may be small."     

Parental gender preferences and reproductive behaviour: a review of the recent literature

This paper reviews various theoretical approaches towards an explanation of parental gender preferences and empirical findings from developing as well as from industrialized countries, focusing on the role of gender preferences in reproductive decisions. Although various attempts have been made to shed light on the mechanisms underlying the observed patterns of sex preferences for children, a fully satisfying theoretical explanation is still not at hand. Empirically, a distinct and stable preference for at least one child of each sex can be observed as a common pattern of parental sex preferences across many different social, economic and cultural contexts. Further - and ideally multidisciplinary - research that helps to improve our understanding of this phenomenon is highly desirable.     

Factors in Fish Modifying Methylmercury Toxicity and Metabolism

We report here some results of a long-term (19 month) study with cats fed methylmercury (MeHg) in nutritionally balanced diets based on fish. By using either freshwater pike (low in Se) or canned tuna (high in Se) as the major protein source, basal diets with low levels of MeHg were prepared having different Se content, all Se being of natural origin. The basal diets produced no signs of toxicity or pathological changes over the l9-month period. In cats fed basal diets spiked with medium or high levels of MeHg, evidence for delayed onset of toxic effects from the added MeHg was observed with the tuna diets compared to pike diets. In brain, muscle, and blood, the activity of GSH peroxidase, a selenoenzyme, was decreased by Hg. In liver, substantial accumulation of Hg with Se occured (molar Hg/Se ratio approximately 1.4 to 1.8) but GSH peroxidase activity was unaffected. We suggest that the coaccumulation of Hg and Se in liver measures the extent to which MeHg has been metabolically transformed by metabolism to Hg++, and inactivated by deposition as a Hg/Se complex of low bioavailability. The accumulation of Hg and Se in liver was much greater in cats fed tuna compared to pike, out of proportion to the relatively small differences in Hg and Se content of the tuna and pike basal diets. Some mechanisms are described by which selenium, vitamin E, and other factors might facilitate MeHg breakdown to inorganic Hg during long term low level exposure to MeHg.     

Determinants of the sex ratio at birth: review of recent literature

The fact that more boys are born than girls (104-107 boys for every 100 girls) has been known since 1662. Factors determining the sex ratio at birth rate are of 2 kinds: factors determining the primary sex ratio, i.e., sex ratio at conception, and factors determining the survival of the embryo in utero. Y-bearing and X-bearing sperm may have different motility or different survival time. The age of the ovum at fertilization and the chemical balance of the female genital tract have an effect on sex ratio at conception. High levels of circulating gonadotropins may imply a lower sex ratio at birth as well as a higher rate of dizygotic twinning. Male conception also appears to be higher early and late in the menstrual cycle. The fact that women exposed to higher coital rates conceive earlier in the menstrual cycle may account for the greater number of boys born during wars. Prenatal male mortality is reportedly highest between gestational months 3-5, lower between months 6-8, and higher again st term. Also, immunological interaction between mother and embryo may account for some sex selective spontaneous abortions. 3 sociodemographic determinants of sex ratio at birth are thought to be maternal age, paternal age, and birth order. Higher prenatal male mortality may be correlated with socioeconomic conditions, since higher socioeconomic status lowers prenatal mortality in general. The effects of parental age, birth order, and parity are less clear. Race is also a factor, since the sex ratio at birth for blacks is lower (102-104) than for whites (106). 14 univariate and 19 multivariate studies of effects of maternal age, paternal age, parity, birth order, race, and socioeconomic status on sex ratio at birth, with sample sizes in the millions from various countries have been analyzed. More boys are born to younger parents, and lower order births have a higher proportion of males than do higher order births. In the multivariate analyses, when the effects of paternal and and birth order are controlled for, the effect of maternal age weakens, and the effect of paternal age appears to be stronger. The effect of birth order remains but is very small, and the effect of race persists independent of any effect of other variables. Maternal age, parity, and birth order are positively correlated with proportion of male stillbirths. The results of the multivariate analyses show all of the effects to be very small, but that maternal age has no effect on sex ratio at birth; paternal age and birth order have a negative effect, and the racial effect persists independent of any other effect. The racial effect is clearly biologically determined at conception because blacks have higher levels of circulating gonadotropin and therefore a higher probability of conceiving girls. Parents in higher socioeconomic classes are more likely to have sons, but the effect is largely due to the excess male mortality during most of the gestational period.     

Microorganisms and Maillard reaction products: a review of the literature and recent findings

Research on the impact of Maillard reaction products (MRPs) on microorganisms has been reported in the literature for the last 60 years. In the current study, the impact of an MRP-rich medium on the growth of three strains of Escherichia coli was measured by comparing two classic methods for studying the growth of bacteria (plate counting and optical density at 600 nm) and by tracing MRP utilisation. Early stage and advanced MRPs in the culture media were assessed by quantifying furosine and N ^ε -carboxymethyllysine (CML) levels, respectively, using chromatographic methods. These measures were performed prior to and during bacterial growth to estimate the potential use of these MRPs by Escherichia coli CIP 54.8. Glucose and lysine, the two MRP precursors used in the MRP-rich medium, were also quantified by chromatographic means. Compared to control media, increased lag phases and decreased growth rates were observed in the MRP-rich medium for two out of the three Escherichia coli strains tested. In contrast, one strain isolated from the faeces of a piglet fed on a MRP-rich diet was not influenced by the presence of MRPs in the medium. Overall, CML as well as the products obtained by the thermal degradation of glucose and lysine, regardless of the Maillard reaction, did not affect the growth of the three strains tested. In addition, no degradation of fructoselysine or CML was found in the presence of Escherichia coli CIP 54.8.     

Regional Cerebral Glucose Metabolism and Blood Flow During the Silent Phase of Methylmercury Neurotoxicity in Rats

Methylmercuric chloride was given to rats in a neurotoxic dose regimen (six daily doses of 8 mg kg-1 p.o.). During the silent (asymptomatic) phase of intoxication, the rates of cerebral glucose influx and cerebral glucose phosphorylation were measured simultaneously using 2-deoxyglucose. Regional cerebral blood flow was also measured using iodoantipyrine. The unidirectional flux of glucose into brain was not affected by methylmercury, and differences in the rates of glucose phosphorylation from region to region remained coupled to the regional cerebral blood flow. However, the blood flow was reduced throughout the brain, an observation suggesting that the operational level of metabolically regulated blood flow had been reset. Thus, in spite of a generalised reduction in blood flow, there was no indication of impaired cerebral glucose supply or utilization during the silent phase of methylmercury intoxication.     

FNA diagnosis of poorly differentiated thyroid carcinoma. A review of the recent literature

Poorly differentiated thyroid carcinoma (PDTC) is a follicular cell‐derived tumour that was recognised as a distinct entity by the World Health Organisation in 2004. The natural history and pathological features of PDTC are reported to be intermediate between those of well‐differentiated and undifferentiated (anaplastic) thyroid carcinomas. Preoperative identification of PDTC could facilitate better initial patient management in many cases, namely more extensive surgery, without any delay. However, according to some experts, a diagnosis of PDTC can only be rendered on histologic specimens based on criteria recommended in the Turin proposal. Although high‐grade features (namely necrosis and mitoses) can be recognised in FNA material, other cytomorphological features have limited value for the preoperative diagnosis of PDTC and specific features for a definitive diagnosis of PDTC have not yet been clearly defined. Here, we review the current status and future prospects for cytological recognition of PDTC; we emphasise the features that should raise suspicion of this rare condition in FNA cytology and provide an update on molecular features and management of PDTC. Despite proposed histological criteria for the diagnosis of PDTC, its recognition on routine thyroid cytology presents a notable challenge. Current and future advances in molecular testing could contribute to the cytological diagnosis of PDTC.     

重组苏云金杆菌ICP基因工程菌研究进展

综述了苏云金杆菌ICP基因及重组ICP工程菌的研究进展,描述了工程菌构建的主要方法,以及目前构建获得的各类ICP工程菌的特点,讨论了ICP工程菌的应用前景和发展方向。     

细菌分裂蛋白及FtsZ抑制剂的研究进展

近年来,由于抗生素的滥用,耐药性细菌广泛出现,对人体健康的威胁日益严峻.随着临床用药的选择不断减少,迫切需要开发新的抗菌药物,特别是新作用机制的抗菌分子来对抗出现的耐药菌.细胞分裂温度敏感.突变体Z (filamenting temperature-setnsitive mutant Z,FtsZ)作为细菌分裂的必需蛋白质,是目前研究最热门的作用靶点之一.FtsZ是一高度保守的蛋白质,在大多数原核细胞的细胞分裂中发挥着关键作用,本文回顾了细菌分裂蛋白的结构特点及其生物学功能,并综述了以FtsZ为靶点的抗菌药物研究的进展.     

N-acetylaspartate: a literature review of animal research on brain ischaemia

The present review examines and discusses the changes in N-acetylaspartate (NAA) concentration in the ischaemic brain from the existing literature of animal research. By summarizing the current knowledge on NAA metabolic pathways and reviewing the data obtained in animal models of global and focal ischaemia, the following conclusions emerge from this compilation: (i) both magnetic resonance spectroscopy (MRS) and the absolute HPLC method of NAA quantification give converging information; (ii) decreases in brain NAA concentration in acute stroke can be considered as an index of neuronal loss or dysfunction, although NAA redistribution by glial cells and NAA trapping in cell debris restrict its use as a quantitative neuronal marker; (iii) further studies on NAA metabolism in pathologic brain are required before using NAA measurement in the chronic stage of ischaemia for evaluating neuroprotective strategies.     

氯丙嗪在斑马鱼胚胎和早期幼鱼发育过程中的神经毒性作用

目的 采用模式动物斑马鱼作为研究对象,观察氯丙嗪（chlorpromazine,CPZ）暴露对胚胎和幼鱼早期神经发育的影响.方法 在一般毒性评价的基础上,通过整体胚胎细胞凋亡检测和脑组织病理学检查,了解CPZ对神经发育的器质性改变;采用神经行为学方法,包括幼鱼触动逃避反应、自发运动以及惊恐逃避反射等,研究氯丙嗪暴露所致的神经发育功能性障碍.结果斑马鱼胚胎受精后6 h（6 hpf）～72 hpf暴露于CPZ（≥5 mg/L）可引起胚胎和幼鱼死亡、致畸和幼鱼孵化延迟,并呈浓度和时间依赖性;采用吖啶橙染色检测36 hpf整体胚胎凋亡细胞,发现凋亡细胞主要集中在胚胎中脑、后脑、丘脑以及中后脑连接区、脊索和尾部等处;脑组织病理学检测发现,7dpf幼鱼颅腔增大、脑体积减小、脑细胞缩小且细胞间隙增宽.6～72 hpf CPZ（≥0.0625 mg/L）暴露后,幼鱼神经行为学研究发现,CPZ（≥0.125 mg/L）可引起3dpf幼鱼触觉运动能力下降;CPZ（≥0 5 mg/L）可浓度依赖性地抑制幼鱼自发运动,并出现僵直不动、震颤或快速刻板式转圈运动等行为改变;光惊恐实验中,暗环境下各暴露组幼鱼对突发强光刺激均表现为惊跳逃避,并且暗-光交替期运动加速度变化与对照组无显著差异;在撤除光源后,1mg/L和2 mg/L暴露组幼鱼暗适应时程缩短,而0.125 mg/L和0.25 mg/L暴露组暗适应时程延长,提示CPZ对外界刺激引发的幼鱼活跃游动有抑制和促进双重毒性作用.结论 CPZ暴露对斑马鱼胚胎和幼鱼具有明显的神经发育毒性作用.模式动物斑马鱼作为一种高通量筛选模型在外源性化合物神经发育毒性评价中具有较好的应用前景.