Biosynthesis of Vitamin B1 (Thiamin): An Instance of Biochemical Diversity

The elucidation of the biosynthetic pathway to thiamin (Vitamin B₁) and its pyrophosphate ester, the important coenzyme “cocarboxylase”, has challenged researchers for many years and continues to do so. The problem of the origin of thiamin can be separated into three parts: the independent pathways to the pyrimidine moiety 4-amino-5-hy-droxymethyl-2-methylpyrimidine and to the thiazole moiety 5-(2-hydroxyethyl)-4-methylthiazole, and the route from these subunits to the vitamin. The steps in the latter process were fully established some twenty years ago, and it was shown that the route in aerobic bacteria and yeast differs to some extent from that in enteric bacteria. The pathways to the subunits, on the other hand, are still not clarified. Significant differences exist in the routes whereby each of the two subunits, the pyrimidine moiety and the thiazole moiety, originate in bacteria and yeast. One difficulty that delayed progress was that the incorporation patterns of labeled precursors, which were observed by different research groups in different microorganisms, could not be reconciled on the basis of a single pathway to each of the two subunits. It is now accepted that in each case different pathways exist in enteric bacteria and yeast, and that the biosynthesis of Vitamin B₁ represents an instance of biochemical diversity. A second factor that added to the difficulties is the minute amount of thiamin synthesized in microbiological cultures (about 15 μg per L culture). This limited the investigations until very recently either to the use of radioactive tracers or to the use of stable isotopes in conjunction with mass spectrometric analysis. It is widely recognized that both methods are associated with pitfalls in the interpretation of results. High-field ¹³C NMR, the most powerful modern method available for the determination of incorporation patterns, has only very recently been successfully employed in investigations of thiamin biosynthesis. As a result of the conceptual and experimental problems, even the primary precursors of each of the two relatively simple heterocyclic subunits of thiamin are still not completely established. A search for committed intermediates, the study of the enzymes, and identification of the genes that are involved are the matter of current research.     

Comprehensive characterization of amino acids and water-soluble vitamins in a pentylenetetrazole-induced seizures rat model

Epilepsy is a complex neurological disease characterized by spontaneous recurrent seizures that affect around 1% of the global population. Despite the significant progress in the mechanisms of epileptogenesis, there is still about 60% of cases in which the cause is unknown. Thus, revealing the molecular mechanisms of epileptogenesis will greatly improve the development of epilepsy treatment. Since the comprehensive characterization of amino acids and water-soluble vitamins is important in understanding the underlying mechanisms of epilepsy or seizures, we developed two liquid chromatography-tandem mass spectrometry methods to quantify 17 water-soluble vitamins and 46 amino acids and applied them to our pentylenetetrazole-induced kindling rat model. All water-soluble vitamins were detected with a linearity of r > 0.992 and limits of quantitation between 0.1 and 5 ng/ml except for nicotinic acid. For amino acids, the linearities obtained were good with correlation coefficients higher than 0.99, and matrix effects were between 85.3% and 110%. To handle the multidimensional data more effectively, multivariate statistical analysis approaches used in non-targeted metabolomics were creatively exploited in the visualization, interpretation, and exploration of the results.     

松花粉干预卵巢早衰大鼠肝脏的广泛靶向代谢组学分析

卵巢早衰是妇科领域的常见病,中医认为卵巢早衰与肝肾的正常与否息息相关,通过药食两用物质对肝脏代谢的调理是治疗卵巢早衰的一种重要手段。该研究基于超高效液相色谱-三重四极杆质谱(UHPLC-MS/MS)建立的广泛靶向代谢组学技术,探讨破壁松花粉对环磷酰胺诱导的卵巢早衰模型大鼠肝脏代谢的影响,旨在通过测定对照组、模型组、雌激素阳性对照组及施以不同剂量的松花粉干预组的SD大鼠肝脏组织中代谢物的含量变化,结合主成分分析(PCA)、正交偏最小二乘判别分析(OPLS-DA)等多元统计方法揭示松花粉干预卵巢早衰大鼠肝脏代谢的作用机制。通过正、负离子模式共检测出687种肝脏代谢物,PCA与OPLS-DA显示环磷酰胺诱导的模型组能够与对照组、阳性对照组、松花粉干预组等组别之间的代谢物较好的分离。通过单变量分析中的t检验(p<0.05)、变异倍数(FC>2或<0.5)与多变量分析中变量投影重要性(VIP值)>1相结合对差异代谢物进行筛选。与对照组相比,模型组SD大鼠肝脏中的32个生物标志物含量显著升高,28个生物标志物含量显著降低,主要涉及α-亚麻酸代谢、维生素B6代谢、嘌呤代谢、赖...     

RP-HPLC法分离测定动物肝脏中多种维生素

建立了一种同时测定4种水溶性维生素的高效液相色谱方法。采用Shimadzu VP-ODS(150 mm×4.6 mm i.d.,5.0μm)色谱柱,以甲醇-0.05 mol/L磷酸氢二钾缓冲溶液梯度洗脱,在波长为267 nm处进行检测。维生素C、B1、B6和B2分别在22.3~116.0,2.4~152.5,2.2~340.0,1.7~272.0μg/mL呈良好的线性关系,相对标准偏差为(n=6)1.1%~1.6%,平均回收率在98.6%~102.3%范围以内。可用于同时测定动物肝脏中维生素C、B1、B6和B2。     

Supercritical fluid extraction as an on-line clean-up technique for determination of riboflavin vitamins in food samples by capillary electrophoresis with fluorimetric detection

An automatic method for the separation and determination of riboflavin (RF) vitamins (RF, flavin mononucleotide and flavin adenine dinucleotide) in food samples (chicken liver, tablet and powder milk) is proposed. The method is based on the on-line coupling of a supercritical fluid extractor (SFE) with a continuous flow-CE system with guided optical fiber fluorimetric detection (CF-CE-FD). The whole SFE-CF-CE-FD arrangement allowed the automatic treatment of food samples (clean-up of the sample followed by the extraction of the analytes), and the direct introduction of a small volume of the extracted plug to the CE-FD system for the determination of RF vitamins. Fluorescence detection introduced an appropriated sensitivity and contributed to avoid interferences of nonfluorescent polar compounds coming from the matrix samples in the extracted plug. Electrophoretic responses were linear within the 0.05-1 microg/g range, whereas the detection limits of RF vitamins were in the 0.036-0.042 microg/g range. The proposed arrangement opens up interesting prospects for the direct determination of polar analytes in complex samples with a good throughput and high level of automation.     

Simultaneous determination of eight B‐vitamins in rat intestinal perfusate to identify effects of osmotic pressures on absorptions

A rapid and accurate HPLC‐DAD method was developed and validated to simultaneously determine eight B‐vitamins (VBs, namely thiamine, riboflavin, niacinamide, calcium pantothenic, pyridoxine, biotin, folic acid and cyanocobalamin) and phenolsulfonphthalein in rat intestinal perfusate. Chromatographic separation was achieved using an Inertsil ODS‐3 column (250 × 4.6 mm i.d., 5 μm) at a temperature of 40°C. Gradient elution mode was applied at the flow rate of 1.0 mL/min with the mobile phase of acetonitrile–30 mm K₂HPO₄ (pH 5.80). The method was successfully applied to identify the effects of osmotic pressures on the absorption of the VBs. The absorption profiles of single and mixed VBs were also compared. Histological section technology was applied to observe the microstructure of small bowel mucosa after perfusion. The results indicated that each compound possessed a better absorption profile under isotonic conditions than under hypotonic or hypertonic conditions for single or mixed solutions. Compared with single VBs, better absorptions in mixed VBs were observed. Pathological tissue slice test suggested that hypotonic and hypertonic solutions changed or damaged the microstructure of mucosa to varying degrees. Taken together, the investigations indicated that multi‐VBs administered orally under isotonic condition could generate fast and complete absorption profiles for VBs.     

Quantum‐Assisted Metrology of Neutral Vitamins in the Gas Phase

It has recently been shown that matter‐wave interferometry can be used to imprint a periodic nanostructure onto a molecular beam, which provides a highly sensitive tool for beam displacement measurements. Herein, we used this feature to measure electronic properties of provitamin A, vitamin E, and vitamin K1 in the gas phase for the first time. The shift of the matter‐wave fringes in a static electric field encodes the molecular susceptibility and the time‐averaged dynamic electric dipole moment. The dependence of the fringe pattern on the intensity of the central light‐wave diffraction grating was used to determine the molecular optical polarizability. Comparison of our experimental findings with molecular dynamics simulations and density functional theory provides a rich picture of the electronic structures and dynamics of these biomolecules in the gas phase with β‐carotene as a particularly interesting example.     

Components of Certain Species of the Elaeagnaceae Family

Data from the last 50 years for various classes of compounds from certain plant species of the oleaster (Elaeagnaceae) family are reviewed