Evaluation of Iron Bioavailability From Iron Chlorophyllin in Young Women Using the Iron Stable Isotopic Method

New approaches to treat iron deficiency include developing novel iron compounds with possible iron absorption routes that increase iron bioavailability and reduce gastrointestinal side effects. Heme iron is considered to be highly bioavailable (10-20%) and less affected by meal composition than non-heme iron. Heme iron is iron (Fe2+) that is bound to the iron protoporphyrin IX prosthetic groups of proteins, mainly hemoglobin and myoglobin, which are present in animal tissue. Heme is released from hemoglobin during digestion so that it can be taken up by the duodenal enterocytes. The intact iron porphyrin is transported across the brush border membrane by the Heme Carrier Protein 1 (HCP1). Once inside the cell, the iron is released, and it is then likely to enter the low molecular weight pool of iron. The use of heme analogues from vegetable origin could provide an alternative iron source of potentially high bioavailability.

Sodium iron chlorophyllin (SIC) is a water-soluble semisynthetic chlorophyll derivative where the magnesium in the porphyrin ring has been substituted by iron. It is a greenish brown pigment that dissolves in water, alcohols, and chloroform, but not ethers. SIC is known to have a superior processing stability to chlorophyll and is commonly used as food colorings in Asian countries including in Korea and Japan, for foods that do not contain meat or fish. Magnesium Chlorophyllin has an E number of E140 and is approved as a food additive in Europe. Currently sodium iron chlorophyllin is present in the Designated Additives List in Japan with a number 261. Designated additives are those designated by the Minister of Health, Labour and Welfare as substances that are unlikely to harm human health based on Article 10 of the Food Sanitation Act.

Given the porphyrin ring heme-like structure of SIC, it may be an alternative delivery route for iron, suitable also for vegetarians and vegans, yet there are few studies investigating the use of SIC for this purpose.

A recent study by Ding et al. 2019 suggests a positive effect of SIC on hemoglobin (Hb) values in iron-deficiency anemia (IDA) in children and adults after 1 month of treatment. They assume that SIC is taken up by the heme carrier protein. The researchers used shengxuening tablets, also known as SXN, which are based on chlorophyll/porphyrin structures extracted from silkworms in which the Mg is replaced by the Fe and then coadjutants are added. This study provided no data on the absorption pathway of the SXN compound. Thus, it remains unclear if it was taken up by the heme transporter or whether it was digested and the Fe released in the gut lumen to join the non heme Fe pool, and thereby improved Hb in the IDA subjects. The authors also describe Xray diffraction assays to assess if the chlorophyllin porphyrin ring contained Fe and not Mg, however these data are not reported.

Miret et al. (2010) studied the stability of heme-analogous SIC absorption using the Caco-2 cell model. The SIC remained stable and only 5% of the Fe from the compound was released at pH 2 to 4. In-house dissolution studies conducted at the Human Nutrition Laboratory (HNL) show only a 2% release of Fe from the compound at similar pH levels. Using solid phase extraction at a higher pH of 7, similar to that in the duodenum, we observed a 5% Fe loss, which may correspond to free iron or iron liberated from any other binding sites on the chlorophyll structure.