Toxicokinetics of hydroxocobalamin were studied in rats and in dogs after single administration. In dogs, the AUCs of free cobalamins-(III) and total cobalamins-(III) increased proportionally to the dose. Mean Cmax measured for free- and total cobalamins-(III) were 1 to 5 fold higher than those measured in humans treated with 5.0 and 10.0 g hydroxocobalamin. Terminal half-lives reached approximately 6 and 8 hours for free and total cobalamins-(III), respectively in dogs. Corresponding figures in rats amounted to 3 and 5 hours. In dogs, the clearance of total cobalamins-(III) (0.064 to 0.083 L/h/kg) was 6-7 fold lower than clearance of free cobalamins-(III).
The binding of hydroxocobalamin to proteins may be regarded as reversible metabolism. Hydroxocobalamin also reacts with cyanide thereby forming cyanocobalamin. This complex is highly stable and is therefore regarded as a physiological end product of hydroxocobalamin especially during cyanide intoxication.
Toxicokinetics of hydroxocobalamin were studied in rats and in dogs after single administration. In dogs, the AUCs of free cobalamins-(III) and total cobalamins-(III) increased proportionally to the dose. Mean Cmax measured for free- and total cobalamins-(III) were 1 to 5 fold higher than those measured in humans treated with 5.0 and 10.0 g hydroxocobalamin. Terminal half-lives reached approximately 6 and 8 hours for free and total cobalamins-(III), respectively in dogs. Corresponding figures in rats amounted to 3 and 5 hours. In dogs, the clearance of total cobalamins-(III) (0.064 to 0.083 L/h/kg) was 6-7 fold lower than clearance of free cobalamins-(III).
The binding of hydroxocobalamin to proteins may be regarded as reversible metabolism. Hydroxocobalamin also reacts with cyanide thereby forming cyanocobalamin. This complex is highly stable and is therefore regarded as a physiological end product of hydroxocobalamin especially during cyanide intoxication.
Toxicokinetics of hydroxocobalamin were studied in rats and in dogs after single administration. In dogs, the AUCs of free cobalamins-(III) and total cobalamins-(III) increased proportionally to the dose. Mean Cmax measured for free- and total cobalamins-(III) were 1 to 5 fold higher than those measured in humans treated with 5.0 and 10.0 g hydroxocobalamin. Terminal half-lives reached approximately 6 and 8 hours for free and total cobalamins-(III), respectively in dogs. Corresponding figures in rats amounted to 3 and 5 hours. In dogs, the clearance of total cobalamins-(III) (0.064 to 0.083 L/h/kg) was 6-7 fold lower than clearance of free cobalamins-(III).
Concurrent administration of chloramphenicol and vitamin B12 reportedly may antagonize the hematopoietic response to vitamin B12 in vitamin B12-deficient patients. The hematologic response to vitamin B12 in patients receiving both drugs should be carefully monitored and alternate anti-infectives should be considered. /Vitamin B12/
Prednisone has been reported to increase the absorption of vitamin B12 and secretion of intrinsic factor (IF) in a few patients with pernicious anemia, but not in patients with partial or total gastrectomy. The clinical importance of these findings is unknown. /Vitamin B12/
Ascorbic acid may destroy substantial amounts of dietary vitamin B12 in vitro; this possibility should be considered when large doses of ascorbic acid are ingested within 1 hour of oral vitamin B12 administration. /Vitamin B12/
Absorption of vitamin B12 from the GI tract may be decreased by aminoglycoside antibiotics, colchicine, extended-release potassium preparations, aminosalicylic acid and its salts, anticonvulsants (e.g., phenytoin, phenobarbital, primidone), cobalt irradiation of the small bowel, and by excessive alcohol intake lasting longer than 2 weeks. Neomycin-induced malabsorption of vitamin B12 may be increased by concurrent administration of colchicine. /Vitamin B12
Caution should be exercised when administering other cyanide antidotes simultaneously with Cyanokit, as the safety of coadministration has not been established. If a decision is made to administer another cyanide antidote with Cyanokit, these drugs should not be administered concurrently in the same IV line.
The possibility of direct transport of hydroxocobalamin from the nasal cavity into the cerebrospinal fluid after nasal administration in rats was investigated and the results were compared with a human study. Hydroxocobalamin was given to rats (n=8) both intranasally (214 ug/rat) and intravenously (49.5 ug/rat) into the jugular vein using a Vascular Access Port (VAP). Prior to and after drug administration, blood and cerebrospinal fluid samples were taken and analysed by radioimmunoassay. The AUCcerebrospinal fluid/AUCplasma ratio after nasal delivery does not differ from the ratio after intravenous infusion, indicating that hydroxocobalamin enters the cerebrospinal fluid via the blood circulation across the blood-brain barrier (BBB). This same transport route is confirmed by the cumulative AUC-time profiles in cerebrospinal fluid and plasma, demonstrating a 30 min delay between plasma absorption and cerebrospinal fluid uptake of hydroxocobalamin in rats and in a comparative human study. The present results in rats show that there is no additional uptake of hydroxocobalamin in the cerebrospinal fluid after nasal delivery compared to intravenous administration, which is in accordance with the results found in humans.
Fifty percent of the administered dose of hydroxocobalamin disappears from the injection site in 2.5 hours. Hydroxocobalamin is bound to plasma proteins and stored in the liver. It is excreted in the bile and undergoes some enterohepatic recycling. Within 72 hours after injection of 500 to 1000 mcg of hydroxocobalamin, 16 to 66 percent of the injected dose may appear in the urine. The major portion is excreted within the first 24 hours.
Hydroxocobalamin is absorbed more slowly from the site of injection than is cyanocobalamin and there is some evidence that liver uptake of hydroxocobalamin may be greater than that of cyanocobalamin. It is believed that the increased retention of hydroxocobalamin compared with that of cyanocobalamin results from the greater affinity of hydroxocobalamin for both specific and nonspecific binding proteins in blood and tissues, as well as to its slower absorption from the injection site.
In the presence of gastric acid and pancreatic proteases, dietary vitamin B12 is released from food and salivary binding protein and bound to gastric intrinsic factor. When the vitamin B12-intrinsic factor complex reaches the ileum, it interacts with a receptor on the mucosal cell surface and is actively transported into circulation. Adequate intrinsic factor, bile, and sodium bicarbonate (to provide a suitable pH) all are required for ileal transport of vitamin B12. Vitamin B12 deficiency in adults is rarely the result of a deficient diet per se; rather, it usually reflects a defect in one or another aspect of this complex sequence of absorption. Achlorhydria and decreased secretion of intrinsic factor by parietal cells secondary to gastric atrophy or gastric surgery is a common cause of vitamin B12 deficiency in adults. Antibodies to parietal cells or intrinsic factor complex also can play a prominent role in producing a deficiency. A number of intestinal diseases can interfere with absorption, including pancreatic disorders (loss of pancreatic protease secretion), bacterial overgrowth, intestinal parasites, sprue, and localized damage to ileal mucosal cells by disease or as a result of surgery. /Vitamin B-12/
The possibility of direct transport of hydroxocobalamin from the nasal cavity into the cerebrospinal fluid after nasal administration in rats was investigated and the results were compared with a human study. Hydroxocobalamin was given to rats (n=8) both intranasally (214 ug/rat) and intravenously (49.5 ug/rat) into the jugular vein using a Vascular Access Port (VAP). Prior to and after drug administration, blood and cerebrospinal fluid samples were taken and analysed by radioimmunoassay. The AUCcerebrospinal fluid/AUCplasma ratio after nasal delivery does not differ from the ratio after intravenous infusion, indicating that hydroxocobalamin enters the cerebrospinal fluid via the blood circulation across the blood-brain barrier (BBB). This same transport route is confirmed by the cumulative AUC-time profiles in cerebrospinal fluid and plasma, demonstrating a 30 min delay between plasma absorption and cerebrospinal fluid uptake of hydroxocobalamin in rats and in a comparative human study. The present results in rats show that there is no additional uptake of hydroxocobalamin in the cerebrospinal fluid after nasal delivery compared to intravenous administration, which is in accordance with the results found in humans.
重氮乙酸乙酯 、 1-氯-4-(1-氟乙烯基)苯 在
aquacobalamin氮气 作用下，
以
2,2,2-三氟乙醇 为溶剂，
反应 18.0h，
以6.9 g of 2-(4-chlorophenyl)-2-fluoro-cyclopropane carboxylic acid ethyl ester was obtained in the form of an oil (81% of theory) as a 7:3 mixture of cis/trans isomers的产率得到ethyl 2-(4-chlorophenyl)-2-fluorocyclopropanecarboxylate
The nucleotide loop in the vitamin B12 structure affects its biological and physicochemical properties, but its role in cobalamin‐catalysed reactions still remains disputable. Herein, we show the synthesis of a series of model compounds including N‐methylcobalamin (NMICbl) in a base‐off form with the nucleotide attached. The structure‐activityrelationshipstudies reveal that in the studied cobalamin‐catalysed
Characterization of Chlorovinylcobalamin, A Putative Intermediate in Reductive Degradation of Chlorinated Ethylenes
作者：Kevin M. McCauley、Scott R. Wilson、Wilfred A. van der Donk
DOI：10.1021/ja029692c
日期：2003.4.1
The first X-ray structure of a vinylcobalamin is reported. Chlorovinylcobalamin is formed in the reaction of cob(I)alamin with chloroacetylene. Subsequently, cob(I)alamin catalyzes the reduction of chlorovinylcobalamin to vinylcobalamin in the presence of excess titanium(III)citrate. Introduction of a chlorine onto the vinyl group of vinylcobalamin greatly changes its reduction potential. These results are discussed with respect to vitamin B12-catalyzed dechlorination of perchloroethylene, a pollutant on the priority list of the EPA.
Unusual Aerobic Stabilization of Cob(I)alamin by a B<sub>12</sub>-Trafficking Protein Allows Chemoenzymatic Synthesis of Organocobalamins
作者：Zhu Li、Nicholas A. Lesniak、Ruma Banerjee
DOI：10.1021/ja5077316
日期：2014.11.19
CblC, a B-12 trafficking protein, exhibits glutathione transferase and reductive decyanase activities for processing alkylcobalamins and cyanocobalamin, respectively, to a common intermediate that is subsequently converted to the biologically active forms of the cofactor. We recently discovered that the Caenorhabditis elegans CblC catalyzes thiol-dependent decyanation of CNCbl and reduction of OH(2)Cbl and stabilizes the paramagnetic cob(II)alamin product under aerobic conditions. In this study, we report the striking ability of the worm CblC to stabilize the highly reactive cob(I)alamin product of the glutathione transferase reaction. The unprecedented stabilization of the supernucleophilic cob(I)alamin species under aerobic conditions by the intrinsic thiol oxidase activity of CblC, was exploited for the chemoenzymatic synthesis of organocobalamin derivatives under mild conditions.
Comparative Study of Redox Reactions of Aqua- and Thiocyanatocobalamin
作者：D. S. Salnikov、S. V. Makarov、P. A. Ivlev
DOI：10.1134/s1070363218050201
日期：2018.5
The interaction of aqua- and thiocyanatocobalamin with sodium hydroxymethanesulfinate in neutral aqueous solution has been studied, and the kinetic as well as activation parameters of the reactions have been determined. The reduction of the aqua complex is faster in comparison with the thiocyanato one. In contrast to the earlier studied reaction of hydroxymethanesulfinate with cyanocobalamin, reduction of aquaand thiocycnatocobalamins occurs via the associative mechanism.
Kinetics and Mechanism of the Reversible Binding of Nitric Oxide to Reduced Cobalamin B<sub>12r</sub> (Cob(II)alamin)
作者：Maria Wolak、Achim Zahl、Thorsten Schneppensieper、Grazyna Stochel、Rudi van Eldik
DOI：10.1021/ja010530a
日期：2001.10.1
reduced form of aquacobalamin binds nitric oxide very effectively to yield a nitrosyl adduct, Cbl(II)-NO. UV-vis, (1)H-, (31)P-, and (15)N NMR data suggest that the reaction product under physiological conditions is a six-coordinate, "base-on" form of the vitamin with a weakly bound alpha-dimethylbenzimidazole base and a bent nitrosyl coordinated to cobalt at the beta-site of the corrin ring. The nitrosyl
