Iron metabolism in mynah birds (Gracula religiosa)resembles human hereditary haemochromatosis

Abstract

Iron overload is a very frequent finding in several animal species and a genetic predisposition is suggested. In one of the most commonly reported species with susceptibility for iron overload (mynah bird), it was recently shown that the cause of this pathophysiology is high uptake and retention of dietary iron. Here we compare susceptible (mynahs) with non-susceptible avian species (chickens) by evaluating iron uptake at the intestinal absorptive cell level. Enterocytes from mynahs and chickens were isolated and uptake of Fe(II) and Fe(III) was studied in vitro. It was found that Fe(III) uptake is much lower than Fe(II) uptake for both species. Although liver iron, present only in hepatocytes, was at least 10-fold higher in mynahs than chickens, enterocyte Fe(II) uptake was considerably higher in mynahs. Fe(II) uptake showed saturation at the studied concentrations in both species. Kinetic studies revealed a three-fold increase in Vmax for mynahs. Calculated values for the uptake kinetics of the probable membrane transporter suggest that mynah bird enterocytes have a significantly higher limiting uptake rate, due to the possible increase in the number of transporters when compared with chicken enterocytes. The susceptibility of this species is due to intestinal iron uptake despite hepatic iron accumulation, implicating a 'mis-sensing' of body iron similarly to human hereditary haemochromatosis.

The Pathology of Comparative Animal Models of Human Haemochromatosis

“…This supports the hypothesis that some species may have maximized their efficiency for iron uptake from low iron-content food in their natural habitat and cannot adapt to higher food iron content in captivity (Otten et al, 2001). Experimental studies of mynah birds and starlings suggest that the intestinal absorption of iron in birds is not as tightly regulated as it is in mammals and that susceptible species are unable adequately to down-modulate the uptake of iron to prevent iron storage disease (Ward et al, 1991;Mete et al, 2001Mete et al, , 2003. Mynah birds have greater intestinal uptake of iron compared with chickens and doves.…”

“…Mynah birds have greater intestinal uptake of iron compared with chickens and doves. Isolated mynah bird enterocytes showed considerably higher iron uptake compared with chicken enterocytes (Mete et al, 2003). The transporter affinity (Km) was similar for both species, but a three-fold higher uptake rate (V max ) was found, suggesting an increase in the number of iron transporters.…”

“…Some bird families, especially Sturnidae, Ramphastidae and Paradisaeidae, may be predisposed due to a specific sensitivity to dietary iron uptake (Lowenstine and Munson, 1999). The pathophysiology of avian iron storage syndromes remains obscure; however, Mete et al (2001Mete et al ( , 2003Mete et al ( , 2005 have shown for mynah birds that the intestinal iron uptake and transfer into circulation is increased compared with species that are not susceptible. Therefore, at least in some avian species, the rate of iron load appears to be influenced by species-specific physiological mechanisms.…”

Diabetes mellitus concurrent with hepatic haemosiderosis in two macaws (Ara severa, Ara militaris)

“…It has been suggested that these species develop EIS under captive conditions due to a highly efficient intestinal iron absorption (Oglesbee et al, 1997;Lumeij, 1999). More recently, it has been shown that iron metabolism in hill mynahs (Gracula religiosa ) resembles that of human patients suffering from hereditary haemochromatosis (Mete et al, 2003), and that high levels of iron transporter proteins are expressed by the small intestine of these birds (Mete et al, 2005). In humans, EIS is strongly associated with DM (Wilson et al, 2003;Platis et al, 2004).…”

Praise ye the god of iron1

“…Mynahs are uncommonly susceptible to hepatic iron overload and have a defect in iron metabolism that resembles human hemochromatosis. 9 Although other animal species, such as New World Monkeys 10 and the black rhinoceros, 11 and some other bird families such as toucans and birds of paradise, 12 show a high prevalence of iron overload and progressive hepatic iron deposition, this is the most common metabolic disorder in the mynah, which is also the most frequently reported bird species to suffer from hemochromatosis. 13 What better crest for a common human liver disease could there be?…”