Gastrointestinal uptake

Weiner, N., and Chia-Ming Chiang (1988). Gastrointestinal uptake of liposomes, in Liposomes as Drug Carriers Recent Trends and Progress (G. Gregoriadis, ed.), John Wiley and Sons, Chichester, pp. 599-607. 

Vitamin B12 consists of a porphyrin-like ring with a central cobalt atom attached to a nucleotide. Various organic groups may be covalently bound to the cobalt atom, forming different cobalamins. Deoxyadenosylcobalamin and methylcobalamin are the active forms of the vitamin in humans. Cyanocobalamin and hydroxocobalamin (both available for therapeutic use) and other cobalamins found in food sources are converted to the active forms. The ultimate source of vitamin Bi2 is from microbial synthesis the vitamin is not synthesized by animals or plants. The chief dietary source of vitamin Bi2 is microbially derived vitamin B12 in meat (especially liver), eggs, and dairy products. Vitamin Bi2 is sometimes called extrinsic factor to differentiate it from intrinsic factor, a protein normally secreted by the stomach that is required for gastrointestinal uptake of dietary vitamin B12. 

Bslum, J., Molhave, L., Honore Hansen, S. Dossing, M. (1993) Hepatic metabolism of toluene after gastrointestinal uptake in humans. Scand. J. Work Environ. Health, 19, 55-62... 

The interest in oxines has now moved from antimicrobial therapy to nuclear medicine and the chemotherapy of malaria. A few other applications have also been found 5,7-diiodo-oxinate enhances gastrointestinal uptake of zinc, an element whose deficiency may cause acrodermatis enteropathica1905 several halogenated oxines - 5-chloro-7-iodooxine (Entero-Vioform), 5,7-diiodooxine (Diodoquin) - have been used in the treatment of amoebic dysentry but this is now a discontinued therapy. 5-Methyloxine has proved an effective therapy in the treatment of cholera in humans191,1925. 

Strategies to eliminate the problem of degradation by nucleases are based on chemical modification such as phosphorothioates (Kurreck et al. 2002) or meth-oxyethyl phosphorothioates (Agrawal et al. 1995). Furthermore, the co-administration of permeation enhancers such as medium chain fatty acid turned out to be a promising strategy to increase the gastrointestinal uptake (Raoofet al. 2002). 

The ability to synthesise ascorbic acid from glucose is absent in a small group of animal species that include man, primates, the guinea pig and the fruit-bat this is due to the absence of the gene that codes for one of the enzymes required for ascorbate synthesis. These species are therefore dependent on an external source of the vitamin in their diet and it is needed as a cofactor for several hydroxylase enzymes, notably the iron-dependent proline and lysine hydroxylases and the copper-dependent dopamine-(3-hydroxylase the function of ascorbate in these enzymes is likely to be its ability to keep the metal in the reduced form which is necessary for hydroxylation. The ability of ascorbate to reduce Fe3+ to Fe2+ is important in promoting the gastrointestinal uptake of iron and for its release from the iron store ferritin. 

Lavelle EC, Charif S, Thomas NW, Holland J, Davis SS (1995) The importance of gastrointestinal uptake of particles in the design of oral delivery systems. Adv Drug Del Revs 18 5-22... 

Absorption of CR after aerosol inhalation is rapid with a plasma half-life of 5 min this is consistent with half-life estimates following intravenous administration (Upshall, 1977) and gastrointestinal uptake (French et al, 1983). Corneal tissue has been demonstrated to take up CR and metabolize it to the lactam derivative (Balfour, 1978 King and Holmes, 1997). 

The vitamin B12 receptor which facilitates uptake of the vitamin-intrinsic factor vitamin-binding protein complex has been used to enhance oral delivery and gastrointestinal uptake of peptides and proteins as their vitamin B12 conjugates (37). Commercial efforts are under way to exploit this receptor as well as the fetal Pc receptor which facilitates intestinal uptake of antibodies from colostrum/milk (38) and the polymeric immunoglobulin receptor which facilitates the serosal to mucosal transport of IgA and IgM (39). 

Desai, M.P. Labhasetwar, V. Amidon, G.L. Levy, R.J. Gastrointestinal uptake of biodegradable microparticles effect of particle size. Pharm. Res. 1996, 13, 1838-1845. 

Microparticles between 1 and 5 pm in diameter cross the intestinal mucosa, whereas microparticles of 5 to 1 0 pm remain in the lumen or in the Peyer s patches (mucosal immunization) (78). Interestingly, the gastrointestinal uptake of particles < 1 pm is higher than the uptake particles >1 pm (79). 

McMinn, L. H., G.M. Hodges, K.E. Carr, Gastrointestinal uptake and translocation of microparticles in the streptozotocin-diabetic rat. 

The transdermal route of agent administration could be advantageous in the delivery of many therapeutic proteins, because proteins are susceptible to gastrointestinal degradation and exhibit poor gastrointestinal uptake, and transdermal devices are more acceptable to patients than injections. 

Reffit DM, Jugdaohsingh R, Thompson RP, Powell JJ (1999) Silicic acid its gastrointestinal uptake and urinary excretion in man and effects on aluminium excretion. J Inorg Biochem 76 141-147... 

Gastrointestinal uptake from contaminated foodstuffs or by dust particles taken in through the nose or mouth enteral exposure). 

Fractional absorption values proposed, in ICRP publication no. 48 (1986), for the gastrointestinal uptake of... 

Comments ICRP Publication no. 48 is probably the most authoritative document with respect to gastrointestinal uptake of actinide elements. However, further information can be found in several other compilations and a number of more recent research papers, see text for details of references. 

Finally, it should be noted that gastrointestinal uptake cannot be considered to be purely a function of actinide speciation or initial physicochemical form. The physiological state of the individual should always be considered, e.g., with respect to fasting state or iron-deficiency status, as this may increase the f value by an order of magnitude (Taylor 1989b, Sullivan and Ruemmler 1988). 

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