Inhibitory Effect of Ascorbic Acid on the Hydrolytic Polymerization of Iron and a Consideration of the Effect in the Intestinal Absorption of Iron

アスコルビン酸による鉄の加水分解重合阻止とその鉄吸収に与える効果の考察

Imamura Tsuneaki

Hatanaka Chitoshi

Takahashi Kokichi

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

著者らはこれまで,鉄－糖錯体の調製について報告してきた。その目的は新しい鉄強化剤の開発にあるが,得られた標品の腸管壁透過性は,諸外国の報文に反して,予想外に悪かった。この原因は,鉄の加水分解重合による高分子量多核錯体の形成にあると考え,若干の糖および糖誘導体によるポリマー化阻止を調べた。その結果,アスコルビン酸(AsA)が著しい阻止効果をもつことを確かめ,このことが鉄の腸管吸収に与える影響について考察した。

鉄は希薄(10^-2～10^-4M)なFeCl3溶液として用い,吸収スペクトルの変化によってポリマー生成の定性的な確認をし,全鉄量とイオン性鉄量の測定値の差からポリマー化程度を調べた。このとき必要な鉄の定量は,o-フェナンスロリン法で行なった。

本研究に用いたFeCl3を含めて,第一鉄塩がアルカリ性溶液中で加水分解重合し易いことはよく知られているが,われわれの実験結果は,酸性条件でもかなり速かにポリマー化することを示した(Fig.2)。このポリマー化は,等モル比のAsAを加えることによりほぼ完全に,ソルビットによって1/3程度に阻止されたが,グルコースとフルクトースにこの効果はなかった(Fig.3)。AsAは鉄と錯体を形成するが(Fig.4),沪紙紙電気泳動の結果から,このものは,溶液のpHによって正もしくは負に荷電していることが分った(Fig.5)。この表面荷電に関する考察に付随して,多核鉄ポリマーの鉄にAsAが配位して表面錯体を形成している構造を推察した。

以上の結果,すなわち鉄ポリマーの低分子量化と荷電が,鉄の腸管腸収に良い影響を与えると考えた。

The Fe-sugar complexes prepared so far in this laboratory were found to be difficult in their intestinal absorptions. For the reason we considered the formation of high molecular weight Fe-polymers under the experimental conditions. Therefore, the inhibitory effects of glucose, fructose, sorbitol, and ascorbic acid (AsA) on the hydrolytic polymerization of Fe were examined in this work.

As the Fe-salt, FeCl3 was used in the concentrations of 1×10^-2－1×10^-4M. The amounts of Fe were determined by the o-phenanthroline method and the polymerization degree of Fe was obtained from the difference between the amounts of the total Fe and the ionic Fe in the sample solutions.

On the basis of the change in the absorption spectra of the FeCl3 solutions at various pH values, we concluded that the hydrolytic polymerization of Fe occurs rapidly even in acidic media, especially in aqueous media of above pH 4.5. The polymerization of Fe was markedly inhibited by AsA. Sorbitol also showed a considerable inhibition and its addition to the FeCl3 solution lowered the polymerization to about one-third. However, almost no effect was observed by the addition of glucose or fructose. When AsA was added to the FeCl3 solution, an Fe-AsA complex was formed. The paper electrophoretograms of the Fe-AsA complex, of which the molecular weight was rather small and presumed to be about 5,000, revealed that the charge of the complex was negative in alkaline or neutral media and was positive in acidic media. The electric charge of the complex is considered to be produced by formation of the surface complex of AsA on the surface of Fe atoms, which constitute generally a polynuclear Fe-hydroxo complex in aqueous media; AsA probably coordinates to the Fe atoms just like a cover that coats the polynuclear polymer. The changes of the dissociation of the coated AsA with pH values of the media produce the negative or the positive charges.

Some nutritional considerations of the intestinal absorption of Fe were given in connection with the inhibitory effect of AsA on the hydrolytic polymerization of Fe.

Medical sciences [ 490 ]

eng

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563

[NAID] 40003288837