Inositol phosphates absorption

Sandstrom B, sandberg AS. 1992. Inhibitory effects of isolated inositol phosphates on zinc absorption in humans. Journal of Trace Elements and Electrolytes in Health and Disease 6(2) 99-103. 

The growth of ectomycorrhizal trees is frequently improved by their increased phosphorus (P) accumulation (3), and this, in turn, is related to the intensity of the mycorrhizal infection. Ectomycorrhizal fungi solubilize insoluble forms of A1 and Ca phosphates as well as inositol hexaphosphates, though a wide interstrain variability has been recorded (112). These complex P forms are digested by the secretion of extracellular acid and alkaline phosphomono- and phosphodi-ester-ases. Pi in soil solutions is easily taken up by ectomycorrhizal hyphae and then translocated to the host roots. Its absorption and efflux are probably regulated... 

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

Changes in the u.v. absorption of 2,4,6/3,5-pentahydroxycyclohexanone in alkaline phosphate buffer under anaerobic conditions have been ascribed to phosphate-catalysed enolization on exposure to oxygen, further changes occurred which were interpreted by formation of polyone compounds via enediolate intermediates, as outlined in Scheme 6. There have been further reports on the synthesis of mono- and di-phosphate esters of asymmetrically substituted m o-inositol, e.g., (30), and the mannopyranosyl ortho-ester... 

Certain ions, e.g., oxalate and phosphate, can bind Ca within the intestinal canal and high intake of phosphate can restrict calcium absorption. A similar effect is encountered by phytic acid (inositol hexaphosphate) that is present in high amounts in certain cereals. Disturbances in the fat absorption (dietary) decreases the calcium absorption because Ca is bound to nonabsorbable fatty acids. 

Certain foods such as unrefined cereals and sugar cane juice contain organic phosphates, e.g. phytate (inositol hexaphosphate), which reduce enamel solubility, apparently by reacting with calcium phosphate salts on the enamel surface. The view that this type of compound has a caries-inhibiting effect is supported by observations that dietary supplements of calcium glycerophosphate reduce caries in rats and monkeys. At the same time, the calcium-binding properties of phytate may adversely affect the absorption of calcium from the intestine (page 143). 

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