唾液酸对精子的作用

唾液酸(又名神经氨酸)是一类带负电的酸性九碳单糖家族的总称。唾液酸具有多样化的分子结构,广泛分布于生物体内,通常与蛋白质和脂结合形成糖蛋白和糖脂,构成细胞膜及糖萼。唾液酸介导了生物体内许多生理功能,与人类健康和疾病息息相关,唾液酸的糖生物学已成为近年来的研究热点。在雄性生殖系统中,唾液酸在精子保护、附睾精子成熟和精卵识别等过程中都有重要作用,该文将对有关研究进展作一综述。     

干扰素基因刺激因子和自噬的相互关系

干扰素基因刺激因子（stimulator of interferon genes,STING）是病毒DNA或自身DNA激活免疫系统的关键蛋白质和重要感受器。自噬（autophagy）是降解细胞质成分、蛋白质聚集体和/或细胞器的一种生理过程。STING和自噬在细胞、组织和机体稳态中发挥着至关重要的作用。已证实,STING或自噬功能紊乱与人类多种疾病密切相关。近年来诸多研究提示,STING与自噬存在相互影响、相互作用,共同参与疾病的发生与发展过程。本文总结了最新关于STING与自噬相互调节的机制及其与人类重大疾病的关系,并深入讨论其对疾病治疗的潜在影响和科学意义。     

多聚唾液酸与多聚唾液酸转移酶

多聚唾液酸（PSA）是一种在神经细胞黏附分子（neural cell adhesion molecule,NCAM）上表达的唾液酸聚合物,在神经发育过程中起重要作用.PSA的聚合程度会影响PSA-NCAM的功能.多聚唾液酸酶主要用于合成PSA-NCAM,两种高度同源的多聚唾液酸转移酶ST8SiaⅡ和ST8SiaⅣ都属于唾液酸转移酶家族.多聚唾液酸转移酶中NCAM的识别域和多聚唾液酸化域是截然不同的,且一些异构酶在NCAM多聚唾液酸化中起明显的负作用.多聚唾液酸酶与很多疾病都有关系,以多聚唾液酸转移酶为标靶设计的药物也将成为神经系统及肿瘤治疗的新型药物.     

传染性疾病的遗传易感性

传染性疾病是威胁人类健康的主要疾病类型之一。传染病的发生、发展是致病微生物、宿主的遗传因素与环境相互作用的结果。大量以单核苷酸多态性（SNP）为遗传标记,基于家系或无关群体的连锁和关联分析,已绘制出传染性疾病易感性的基因图谱。目前易感性的研究主要集中在疟疾、获得性免疫缺陷综合征、乙肝和严重急性呼吸系统综合征等传染性疾病。     

暗色丝孢霉病的临床及研究现况

暗色真菌（dematiaceous fungi）是指菌丝和（或）孢子的细胞壁具有黑色素样颜色的一组真菌,可引起人类皮肤甚至多种组织的感染。迄今尽管有的学者仍在使用“着色霉菌病（chromomycosis）”来命名所有的暗色真菌感染,然而自20世纪90年代已形成的共识是将暗色真菌感染主要分为着色芽生菌病（chromoblastomycosis）和暗色丝孢霉病（phaeohyphomycosis）两类独立的疾病。本文主要就暗色丝孢霉病的命名、病原学、流行病学、临床类型及分子生物学研究现况进行综述。     

利用X-Neu5Ac为底物测定唾液酸酶活性在诊断细菌性阴道病的价值

目的利用5溴-4氯-3吲哚乙酰基神经氨酸盐（X-Neu5Ac）为底物测定阴道唾液酸酶活性诊断细菌性阴道病（bacterial vaginosis,BV）的价值.方法健康妇女30例,临床Amsel法诊断为BV的患者45例,共计75例进行了阴道分泌物分析和检测,并与唾液酸酶活性法诊断作了对比研究.取阴道分泌物作为标本分别进行唾液酸酶活性和阴道菌群定量分析,检测细菌包括乳酸杆菌、类杆菌、肠杆菌、葡萄球菌、肠球菌和阴道加德纳菌.唾液酸酶活性测定利用的底物为X-Neu5Ac,特异活性用其产物 ——甲氧基苯酚的纳摩尔数来表示.结果阴道液唾液酸酶活性测定诊断细菌性阴道病的敏感性、特异性、阳性预期值和阴性预期值分别为88.9%、90%、93%和84.3%.唾液酸酶法在检测细菌性阴道病上和传统的Amsel法比较,差异无显著性（P＞0.05）.唾液酸酶阳性组Gv活菌数（6.96 log CFU/g）明显高于唾液酸酶阴性组（2.05 log CFU/g）（P＜0.01）.唾液酸酶阳性组产H2O2阴道乳杆菌（LB＋）活菌数（4.26 Log CFU/g）明显低于唾液酸酶阴性组（8.66 Log CFU/g）（P＜0.01）.唾液酸酶阳性组与唾液酸酶阴性组两组的阴道液中需氧菌活菌数差异无显著性（P＞0.05）,主要包括金黄色葡萄球菌、肠球菌和肠杆菌.结论利用X-Neu5Ac作为唾液酸酶的底物测定唾液酸酶活性的方法是诊断细菌性阴道病的有效检测方法.阴道内唾液酸酶活性增强,厌氧菌数量增加,LB＋数量减少,提示BV发生恶化.     

低血压病人血液透析的护理体会

1980年,美国护理协会将护理定义为：“对人类存在的或潜在的健康问题的诊断和处理。”整体护理与新医学模式（生物一心理一社会医学模式）的确立直接相关联。新医学模式下的医学是自然科学、社会科学、人文科学的混合体,是生命科学的组成部分,是促进人类健康,解除病痛的一门综合学科。而护理学是医学的重要组成部分,医学护理模式也从过去“以疾病为中心”转变为“以病人为中心”,将生理护理与心理护理并重,注重健康宣教,重视社会因素的参与,做到预防、治疗疾病以及提高患者生活质量三者的统一。[编者按]     

唾液酸酶Neu1及其相关信号通路研究进展

唾液酸广泛存在于生物体内,常存在于糖复合物的糖链末端,对组织器官特别是脑神经的发育至关重要,并且与多种疾病的发生和发展过程密切相关.唾液酸被唾液酸酶水解后,可改变糖复合物的构象从而调控相关因子的生物学功能.在目前发现的4种唾液酸酶中,对Neu1的研究较为深入.研究表明,Neu1的剪切底物具有多样性,其与细胞表面受体的结构和功能调节密切相关.随着研究的深入,Neu1逐渐被认为是唾液酸介导的调控疾病发生过程中的重要因子,Neu1在人类疾病中的作用比预想的还要深远.本篇综述了在已有总结的唾液酸酶性质和生理病理学功能的基础上,概述了近年来Neu1的研究进展,并对其作用及与不同细胞表面受体的相互作用机制做了总结.     

龋齿及预防

龋齿及预防夏茂林（四川省平昌中学６３５４００）义务教材《生物》（第二册）的“消化和吸收”一章，在讲消化时提到了龋齿产生的原因、预防等基础知识。下面对龋齿的有关问题作些补充。龋齿俗叫“虫牙”或“虫蚀牙”，是危害人类健康三大疾病（心血管症、癌症、龋齿）之...     

神经节苷脂对细胞信号传递的影响

神经节苷脂对细胞信号传递的影响唐向东,佟振清,杨文俊（第一军医大学生理教研室,广州５１０５１５）关键词神经节苷脂,信号传递神经节苷脂是由唾液酸和己糖苷组成的一组鞘糖脂类,主要包括含单唾液酸的ＧＭ（ＧＭ１ａ,ＧＭ１ｂ,ＧＭ２,ＧＭ３）、含二唾液酸的ＧＤ...     

Diversity of microbial sialic acid metabolism.

Sialic acids are structurally unique nine-carbon keto sugars occupying the interface between the host and commensal or pathogenic microorganisms. An important function of host sialic acid is to regulate innate immunity, and microbes have evolved various strategies for subverting this process by decorating their surfaces with sialylated oligosaccharides that mimic those of the host. These subversive strategies include a de novo synthetic pathway and at least two truncated pathways that depend on scavenging host-derived intermediates. A fourth strategy involves modification of sialidases so that instead of transferring sialic acid to water (hydrolysis), a second active site is created for binding alternative acceptors. Sialic acids also are excellent sources of carbon, nitrogen, energy, and precursors of cell wall biosynthesis. The catabolic strategies for exploiting host sialic acids as nutritional sources are as diverse as the biosynthetic mechanisms, including examples of horizontal gene transfer and multiple transport systems. Finally, as compounds coating the surfaces of virtually every vertebrate cell, sialic acids provide information about the host environment that, at least in Escherichia coli, is interpreted by the global regulator encoded by nanR. In addition to regulating the catabolism of sialic acids through the nan operon, NanR controls at least two other operons of unknown function and appears to participate in the regulation of type 1 fimbrial phase variation. Sialic acid is, therefore, a host molecule to be copied (molecular mimicry), eaten (nutrition), and interpreted (cell signaling) by diverse metabolic machinery in all major groups of mammalian pathogens and commensals.     

Diversity of Microbial Sialic Acid Metabolism

Sialic acids are structurally unique nine-carbon keto sugars occupying the interface between the host and commensal or pathogenic microorganisms. An important function of host sialic acid is to regulate innate immunity, and microbes have evolved various strategies for subverting this process by decorating their surfaces with sialylated oligosaccharides that mimic those of the host. These subversive strategies include a de novo synthetic pathway and at least two truncated pathways that depend on scavenging host-derived intermediates. A fourth strategy involves modification of sialidases so that instead of transferring sialic acid to water (hydrolysis), a second active site is created for binding alternative acceptors. Sialic acids also are excellent sources of carbon, nitrogen, energy, and precursors of cell wall biosynthesis. The catabolic strategies for exploiting host sialic acids as nutritional sources are as diverse as the biosynthetic mechanisms, including examples of horizontal gene transfer and multiple transport systems. Finally, as compounds coating the surfaces of virtually every vertebrate cell, sialic acids provide information about the host environment that, at least in Escherichia coli, is interpreted by the global regulator encoded by nanR. In addition to regulating the catabolism of sialic acids through the nan operon, NanR controls at least two other operons of unknown function and appears to participate in the regulation of type 1 fimbrial phase variation. Sialic acid is, therefore, a host molecule to be copied (molecular mimicry), eaten (nutrition), and interpreted (cell signaling) by diverse metabolic machinery in all major groups of mammalian pathogens and commensals.     

Insights into the evolution of sialic acid catabolism among bacteria

Background  

Sialic acids comprise a family of nine-carbon amino sugars that are prevalent in mucus rich environments. Sialic acids from the human host are used by a number of pathogens as an energy source. Here we explore the evolution of the genes involved in the catabolism of sialic acid.     

Separation methods for sialic acids and critical evaluation of their biologic relevance

Sialic acids are biosynthesized by almost all organisms as a 9-carbon carboxylated monosaccharide and are integral components of glycoconjugates. More than 40 naturally occurring sialic acid derivatives of the three main forms of sialic acids, the N-acetyl- and N-glycolylneuraminic acid and 2-keto-3-deoxy-nonulosonic acid have been identified. Due to the great importance of sialic acids as key mediators in a plethora of cellular events, including cell-cell recognition and cell-matrix interactions, their analysis in biologic samples is useful for a deeper understanding of the various (patho)physiological processes and of value in disease diagnosis and monitoring. In this review we summarize the methodology developed to isolate and liberate sialic acids from biologic samples as well as the chromatographic, electromigration and hyphenated techniques available for their separation and analysis. A critical evaluation of the biological relevance of the results obtained by analyzing sialic acids in biologic samples is also presented.     

Achievements and challenges of sialic acid research

Sialic acids are one of the most important molecules of life, since they occupy the terminal position on macromolecules and cell membranes and are involved in many biological and pathological phenomena. The structures of sialic acids, comprising a family of over 40 neuraminic acid derivatives, have been elucidated. However, many aspects of the regulation of their metabolism at the enzyme and gene levels, as well as of their functions remain mysterious. Sialic acids play a dual role, not only are they indispensable for the protection to and adaptation of life, but are also utilised by life-threatening infectious microorganisms. In this article the present state of knowledge in sialobiology, with an emphasis on my personal experience in this research area, is outlined including a discussion of necessary future work in this fascinating field of cell biology.     

Surface alterations in calf lymphocytes oxidized by sodium periodate.

In order to investigate alterations in surface structure in transformed lymphocytes, calf submandibular lymph node cell suspensions were oxidized with NaIO4. Oxidezed lymphocytes were morphologically transformed and had higher rates of DNA synthesis by 2 days after treatment. These results were prevented by reduction of the cell suspension with NaBH4, or by neuraminidase treatment of cells prior to oxidation. The amount of 125I-labeled Agaricus bisporus lectin bound to cells immediately after oxidation and the affinity constant for binding were increased over 2-fold, while cells immediately following oxidation and reduction showed decreased receptors with still higher affinity for the lectin compared to untreated cells. The amount of Phaseolus vulgaris lectin bound to oxidezed cells was also increased, but affinity was unchanged. Immediately following oxidation and reduction, these receptor sites were unchanged in number and affinity from untreated cells. In contrast, the number and affinity of receptors for concanavalin A were not changed immediately after oxidation or oxidation and reduction. In order to define the extent of compositional changes in surface glycoprotein receptors, plasma membranes were isolated from frozen calf submandibular lymph nodes. Compared to untreated plasma membranes, oxidezed membranes had similar contents of galactose, mannose, N-acetylglucosamine, N-acetylgalactosamine, fucose, and amino acids. Sialic acid content of oxidized membranes was reduced when measured by thiobarbituric acid assay. Sialic acids of untreated plasma membranes co-chromatographed with N-glycolylneurominic acid and N-acetylneuraminic acid, while those of oxidized membranes co-chromatographed with N-glycolylneuraminic acid and 5-acetamido-3,5-dideoxy-L-arabino-7-aldehydo-2-heptulosonic acid. Therefore, specific surface conformational changes in certain classes of membrane glycoproteins are associated with mild Malapradian oxidation of membrane sialic acids. These temporally precede NaIO4-induced transformation of calf lymphocytes. This is consistent with an hypothesis of membrane-mediated stimulation of lymphocyte transformation.     

Engineering the sialic acid in organs of mice using N-propanoylmannosamine

Sialic acids play an important role during development, regeneration and pathogenesis. The precursor of most physiological sialic acids, such as N-acetylneuraminic acid is N-acetyl-D-mannosamine. Application of the novel N-propanoylmannosamine leads to the incorporation of the new sialic acid N-propanoylneuraminic acid into cell surface glycoconjugates. Here we analyzed the modified sialylation of several organs with N-propanoylneuraminic acid in mice. By using peracetylated N-propanoylmannosamine, we were able to replace in vivo between 1% (brain) and 68% (heart) of physiological sialic acids by N-propanoylneuraminic acid. The possibility to modify cell surfaces with engineered sialic acids in vivo offers the opportunity to target therapeutic agents to sites of high sialic acid concentration in a variety of tumors. Furthermore, we demonstrated that application of N-propanoylmannosamine leads to a decrease in the polysialylation of the neural cell adhesion molecule in vivo, which is a marker of poor prognosis for some tumors with high metastatic potential.     

N-acetylneuraminic acid and N-glycolylneuraminic acid in glycopeptides of colonic tumor and mucosa in rats treated with carrageenan and 1,2-dimethylhydrazine

N-linked glycopeptides were prepared from colonic tumor (adenocarcinoma) and mucosa in rats treated with carrageenan, an indigestible polysaccharide, and 1,2-dimethylhydrazine. Sialic acids, N-acetylneuraminic acid and N-glycolylneuraminic acid, obtained by acid hydrolysis of the glycopeptides were determined by HPLC. The N-acetylneuraminic acid/N-glycolylneuraminic acid ratio in colonic tumor was 25.2, while each treated mucosa had the values between 0.29 and 0.55. Thus, necessity which observes the qualitative change of sialic acid in malignant transformation was suggested.     

Efficient biochemical engineering of cellular sialic acids using an unphysiological sialic acid precursor in cells lacking UDP-N-acetylglucosamine 2-epimerase

Sialic acids comprise a family of terminal sugars essential for a variety of biological recognition systems. N-Propanoylmannosamine, an unphysiological sialic acid precursor, is taken up and metabolized by mammalian cells resulting in oligosaccharide-bound N-propanoylneuraminic acid. N-Propanoylmannosamine, applied to endogenously hyposialylated subclones of the myeloid leukemia HL60 and of the B-cell lymphoma BJA-B, both deficient in UDP-N-acetylglucosamine 2-epimerase, is efficiently metabolized to CMP-N-propanoylneuraminic acid resulting in up to 85% of glycoconjugate-associated sialic acids being unphysiological N-propanoylneuraminic acid. Thus, UDP-N-acetylglucosamine 2-epimerase-deficient cell lines provide an important experimental progress in engineering cells to display an almost homogeneous population of defined, structurally altered sialic acids.