Intrinsic Factor Preparations

Latner et al. Intrinsic factor preparation from hog pyloric and duodenal mucosa 1—4 mg... 

Glass, Stephanson, Rich and Laughton Intrinsic factor preparation from human gastric juice 2.2 mg... 

Jl. Jacob, T. A., Williams, D. E., Howe, E. E., and Glass, G. B. J., Ultracentrifugation and paper electrophoresis of highly active intrinsic factor preparations. Arch. Biochem. Biophys. 81, 522-525 (1959). 

Cell fractionation studies of homogenates of the gastric mucosa have demonstrated that the intrinsic factor is found both in mitochondria and the supernatant fluid. The factor remains difficult to assay a variety of methods have been used, but none is entirely satisfactory. These methods include (1) administration of intrinsic factor preparation to gastrectomized animals (rats or hogs) (2) measurement of vitamin 6 2 binding capacity of the preparation (3) measurement of vitamin Bi2 uptake in tissue and (4) evaluation of the inhibition of cobamide coenzyme activity in the glutamate isomerase reaction. 

In testing intrinsic factor preparations unreliable subjects can be excluded and fecal excretion methods are satisfactory. The technique of Baker and Mollin (1955) is particularly suitable. With the use of a fixed dose of Co -labeled B12, two intrinsic factor preparations can be tested in parallel in successive weeks in the same patient over a range of doses wide enough to permit comparison of the absorption gradients obtained for each of the preparations (page 163). 

Pharmacokinetics The parietal cells of the stomach secrete intrinsic factor, which regulates the amount of vitamin B-12 absorbed in the terminal ileum. Bioavailability of oral preparations is approximately 25%. Vitamin B12 is primarily stored in the liver. Enterohepatic circulation plays a key role in recycling vitamin B-12 from mainly bile. If plasma-binding proteins are saturated, excess free vitamin B- 2 will be excreted in the kidney. 

Cyanocobalamin and the derivative hydroxo-cobalamin, given IM or deep subcutaneously, are indicated for treating vitamin B12 deficiency. Only in strict vegetarians oral preparations may be effective. Oral preparations with added intrinsic factor mostly are not reliably in patients with pernicious anemia. More than half the dose of cyanocobalamin injected is excreted in the urine within 48 hours and the therapeutic advantages of doses higher than 100 pg are questionable because of this rapid eiimination. As... 

Unusual features of vitamin Bn observed by some investigators include (1) the cyanide group is an artifact of preparation (2) the only vitamin synthesized in appreciable amounts only by microorganisms (possible in tumors) (3) only vitamin with a metal ion (4) works with glutathione (5) glutathione content decreased on B12 deficiency (6) mitosis retarded in B12 deficiency (7) requires intrinsic factor (enzyme) for oral activity (8) increases tumor size (Rous sarcoma) (9) diamagnetic properties (10) no acidic or basic groups revealed on titration (no pKa). 

Vitamin B12 is available in pure form for oral administration or in combination with other vitamins and minerals for oral or parenteral administration. The choice of a preparation always must be made with recognition of the cause of the deficiency. Although oral preparations may be used to supplement deficient diets, they are of relatively little value in the treatment of patients with deficiency of intrinsic factor or ileal disease. Even though small amounts of vitamin B12 may be absorbed by simple diffusion, the oral route of administration cannot be relied upon for effective therapy in the patient with a marked deficiency of vitamin B12 and abnormal hematopoiesis or neurological deficits. Therefore, the preparation of choice for treatment of a vitamin B12-deficiency state is cyanocobal-amin, and it should be administered by intramuscular or deep subcutaneous injection. 

V2. Visuri, K., and Gras beck, R., Human intrinsic factor, isolation by improved conventional methods and properties of the preparation. Biochim. Biophys. Acta 310, 508-517 (1973). 

About 70% of patients also have antiintrinsic factor antibodies in plasma, saliva, and gastric juice. These canbe either blocking antibodies, which prevent the binding of vitamin B12 to intrinsic factor, or precipitating antibodies, which precipitate both free intrinsic factor and intrinsic factor-vitamin B12 complex. Some patients have both types of antiintrinsic factor antibody. Although the oral administration of partially purified preparations of intrinsic factor will restore the absorption of vitamin B12 in many patients withpernicious anemia, this can eventually result in the production of antiintrinsic factor antibodies, so parenteral administration of vitamin B12 is the preferred means of treatment. 

Bi2-Sepharose has also been used in the preparation of human intrinsic factor from gastric juice. Affinity chromatography was the sole purification technique and yielded a protein 853-fold purified [91]. A series of derivatives of B12, lacking the nucleotide portion of the molecule, coupled to Sepharose were used in the resolution of two hog B12 binding proteins, termed intrinsic and non-intrinsic factor. The total B12 binding protein population, from which the two forms were resolved, was isolated by affinity chromatography on B -Sepharose [92]. 

B34. Bromer, W. W., and Davisson, E. O., Preparation and characterization of a clinically effective porcine intrinsic factor-vitanain B,2 complex. Vitamin B 2 and Intrinsic Factor, 2. Europ. Symp., Hamburg, 1961, pp. 457-461. Enke, Stuttgart, 1962. 

C2. Capraro, V., Cresseri, A., and Cantone, A., Some biological properties of gastric mucin preparations. Vitamin Bjg und Intrinsic Factor, I. Europ. Symp., Hamburg, 19S6, pp. 283-291. Enke, Stuttgart, 1957. 

E4a. Ellenbogen, L., and Williams, W. L., Preparation and properties of purified intrinsic factor. Biochem. Biophys. Res. Commun. 2, 340-343 (1960). 

J5. Jasmin, G., Selye, H., and Steelman, S. L., Anaphylactoid inflammatory responses to preparations of duodenal intrinsic factor and of gastric mucin. Am. ]. Dig. Diseases 21, 245-247 (1954). 

D. Cobalamin is transported in the blood by transcobalamins. Cyanocobalamin, the pharmacologic preparation of cobalamin available in vitamin pills, is an active as is. Cobalamin is not active with an iron cofactor. The intrinsic factor is produced by parietal cells in the stomach. Cobalamin must be reduced to the Co+ state for activity. 

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