SIRT3 Acts as a Neuroprotective Agent in Rotenone-Induced Parkinson Cell Model

Neurochemical Research - SIRT3 is a member of Sirtuins family, which belongs to NAD+ dependent class III histone deacetylases. Emerging evidence suggests that SIRT3 plays a pivotal role in...     

Amyloid formation by pro-islet amyloid polypeptide processing intermediates: examination of the role of protein heparan sulfate interactions and implications for islet amyloid formation in type 2 diabetes

Amyloid formation has been implicated in a wide range of human diseases including Alzheimer's disease, Parkinson's disease, and type 2 diabetes. In type 2 diabetes, islet amyloid polypeptide (IAPP, also known as amylin) forms cytotoxic amyloid deposits in the pancreas, and these are believed to contribute to the pathology of the disease. The mechanism of islet amyloid formation is not understood; however, recent proposals have invoked a role for incompletely processed proIAPP. In this model, incompletely processed proIAPP containing the N-terminal pro region is excreted and binds to heparan sulfate proteoglycans (HSPGs) of the basement membrane thereby establishing a high local concentration which can act as a seed for amyloid formation. Here we report biophysical proof-of-principle experiments designed to test the viability of this model. The model predicts that interactions with HSPGs should accelerate amyloid formation by the proIAPP processing intermediate, and this is indeed what is observed. Interaction with heparan sulfate leads to the rapid formation of an intermediate state with partial helical content which then converts, on a slower time scale, to amyloid fibrils. TEM shows that fibrils formed by the proIAPP processing intermediate in the presence and in the absence of heparan sulfate have the classic features of amyloid. Fibrils formed by the proIAPP processing intermediate are competent to seed amyloid formation by mature IAPP. The seeding experiments support a second major premise of the model, namely, that fibrils formed by the processing intermediate are capable of seeding amyloid formation by the mature peptide.     

Sulfur dioxide derivatives modulate Na/Ca exchange currents and cytosolic [Ca2+]i in rat myocytes

We have recently shown that sulfur dioxide (SO(2)) derivatives (bisulfite and sulfite, 1:3 M/M) modulated L-type calcium, sodium, and potassium channels in rat myocytes. The aim of this study was to investigate whether SO(2) derivatives could alter Na/Ca exchanger current and the intracellular free [Ca(2+)]. The nickel-sensitive Na/Ca exchanger current was measured in rat myocytes exposed to ramp pulses in Tyrode's solution containing ouabain, nifedipine, and +/-Ni (5 mmol/l). Myocytes were loaded with the fluorescent Ca(2+) indicator Fura-2/AM to estimate intracellular Ca(2+) concentration. SO(2) derivatives significantly inhibited both outward and inward Ni-sensitive Na/Ca exchanger currents without a shift in the reversal potential. The intracellular free [Ca(2+)] was raised by SO(2) derivatives in several concentrations. SO(2) derivatives increased [Ca(2+)](i) in rat myocytes and its mechanism might involve SO(2) derivatives significantly inhibiting Na/Ca exchanger current and enhancing L-type calcium channel.     

Oxidation of glycosphingolipids under basic conditions: synthesis of glycosyl "serine acids" as opposed to "ceramide acids". Precursors for neoglycoconjugates with increased ligand binding affinity.

Two types of oxidative cleavage of the double bond of glycosphingolipids (GSLs) are described. Oxidation of peracetylated GSL precursors with stoichiometric proportions of KMnO4 and an excess of NaIO4, in a neutral aqueous tert-butanol solvent system, gave nearly quantitative yields of the glycosyl ceramide acid, 2-hydroxy-3-(N-acyl)-4-(O-glycosyl)oxybutyric acid [Mylvaganam, M., and Lingwood, C. A. (1999) J. Biol. Chem. 274, 20725-20732]. However, if the reaction medium was made alkaline, the hydroxyallylic function of the sphingolipid, as a whole, was oxidized and the glycosyl serine acid, 2-(N-acyl)-3-(O-glycosyl)oxypropionic acid, was obtained in good yield. This represents a new type of oxidation reaction. Optimized conditions gave glycosyl ceramide or serine acids with greater than 90% selectivity and in good yields (90%). Oxidation of dGSLs gave serine and ceramide oligosaccharides, devoid of hydrocarbon chains. An intriguing glycosyl species containing 5-hydroxy-4-oxo-3-hydroxy-2-(N-acyl)sphingosine (hydroxy-acyl intermediate) was identified via ESMS analyses. We propose that further oxidation of this intermediate is pH-dependent and will be oxidized to either serine or ceramide acids. On the basis of MS-MS analysis of specific homologues of serine and ceramide acids, two types of collision-induced dissociation (CID) patterns have been established. These CID patterns were then used in the identification of serine and ceramide acids synthesized from natural GSL samples. Also, on a qualitative basis, this oxidation protocol, in conjunction with ESMS, provides a novel method for characterizing the aglycone composition (acyl chain length, unsaturation position, dihydrosphingosine content, etc.) of natural GSLs. A novel class of neohydrocarbon conjugates were synthesized by coupling the acids to rigid hydrocarbon frames such as 2-aminoadamantane. Preliminary studies with conjugates derived from globotriaosyl ceramide (Gb3C), lactosyl ceramide (LC), and galactosyl ceramide (GalC) bound verotoxin with the expected specificity but with affinities much greater than that of the natural glycolipid. Also, the ceramide acid-based conjugates were better ligands than serine acid conjugates.     

Incorporation of esterified soybean isoflavones with antioxidant activity into low density lipoprotein.

We have recently reported that dietary intake of soybean isoflavone phytoestrogens resulted in increased oxidation resistance of isolated low density lipoprotein (LDL). In order to explore the underlying mechanisms we designed two types of in vitro experiments. First, we prepared several different isoflavone fatty acid esters to increase their lipid solubility and studied their incorporation into LDL. Second, the oxidation resistance of the isoflavone-containing LDLs was investigated with Esterbauer's 'conjugated diene' method using Cu2+ as prooxidant. Unesterified daidzein and genistein as well as genistein stearic acid esters were incorporated into LDL to a relatively small extent (0.33 molecules per LDL particle, or less) and they did not significantly influence oxidation resistance. The oleic acid esters of isoflavones were incorporated more effectively, reaching a level of 2.19 molecules per LDL particle or more, and the 4',7-O-dioleates of daidzein and genistein exhibited prolongations of lag times by 46% (P<0.05) and 202% (P<0.01), respectively. A smaller but significant increase in lag time (20.5%, P<0.01) was caused by daidzein 7-mono-oleate. In summary, esterification of soybean isoflavones daidzein and genistein with fatty acids at different hydroxyl groups provided lipophilicity needed for incorporation into LDL. Some isoflavone oleic acid esters increased oxidation resistance of LDL following their incorporation.     

模糊聚类分析在中国伞形科当归亚族分类中的应用

针对伞形科前胡族当归亚族上属间界线划分的分歧,采用模糊聚类分析方法,在形态方面以属为分类单位,定量阐明了属间亲缘关系。化学方面,以裂解－气相色谱信息为分类依据肉获得的２７个种的数据揭示了当归亚族中属间的分类关系,结果表明,当归属和在中国分布的山芹属与广义当归属类群相近,并显示了东北长鞘当归和骨缘当归是一个较特殊的类群。