Intestinal Absorption of Hemoglobin Iron-Heme Cleavage by Mucosal Heme Oxygenase

Metabolism of heme and bilirubin in rat and human small intestinal mucosa.

“…Thus, a reciprocal relationship appears to exist between the heme protein content and heme oxygenase activity of mucosal subfractions. With experimental manipulations, also, such as dietary iron deficiency, reciprocal changes in cytochrome P-450 and heme oxygenase have been observed (9,27). These findings closely resemble those reported earlier for liver (28), suggesting that endogenous heme, derived from cytochrome P-450, induces heme oxygenase, albeit results at variance with this interpretation have been reported (29).…”

“…The necessity for a heme-splitting activity in the release of free iron has been postulated, and, recently, heme oxygenase activity in mucosal extracts was demonstrated (9). The activity in vitro is similar to that present in liver and is increased in young rats maintained on an iron-deficient diet (9). It remains to be determined whether it is directed primarily towards breakdown of luminal (dietary) heme, endogenous mucosal heme, or both.…”

Influence of the extent of haemoglobin hydrolysis on the digestive absorption of haem iron in the rat. An in vitro study

“…This model was previously used in absorption studies of minerals and peptides (Tom e et al 1987;Atisook & Madara, 1991;Vaghefi et al 1998). The absorption and metabolism of haem iron, and their regulation depending on the dose and iron status, are known to be similar in rat and human mucosa, even if the absorption of haem iron is lower in the rodent (Wheby et al 1970;Raffin et al 1974;Hartmann & Bissel, 1982;Huebers et al 1990;Pallar es et al 1993;Roberts et al 1993). …”

“…The uptake is assumed to be the main determining factor (Roberts et al 1993), particularly at low doses (Hallberg et al 1979); at higher doses the regulation of iron transfer, involving haem splitting in the enterocyte and the rate of transport of iron out of mucosa could be limiting to haem iron absorption in normal animals (Wheby et al 1970;Wheby & Spyker, 1981;Carpenter & Mahoney, 1992). Haem splitting is enhanced in iron-deficient animals (Wheby et al 1970;Raffin et al 1974). Therefore increasing haem uptake by the intestinal epithelium could be of interest in promoting haem iron bioavailability.…”

Influence of the Extent of Haemoglobin Hydrolysis on the Digestive Absorption of Haem Iron in the Rat. an in Vitro Study

“…That explains why concentrating haem issued from haemoglobin hydrolysis and purification yielded poorly absorbed iron (Conrad et al 1966;Calvo et al 1989;Martinez, 1998). The absorption of haem iron uses a pathway distinct from that for non-haem iron: it is absorbed as an intact metalloporphyrin across the intestinal brush border and is cleaved inside the enterocyte by a haem oxygenase (Raffin et al 1974). It then enters the common enterocyte pool of inorganic iron and the bloodstream.…”