Low serum ferritin and iron overload? The curious case of the black rhino...
Black rhinos in captivity develop iron overload, which is a significant cause of morbidity and mortality in this critically endangered species. The reasons for the iron overload are unknown and have been the topic of much debate/discussion.
Here I would like to draw your attention to (and hopefully get your comments on!) an interesting paper on the utility of using serum ferritin to diagnose iron overload in black rhinos. The authors report that one rhino (#19) died of iron overload disorder (IOD), but did not display elevated serum ferritin levels until shortly before death.
Is anyone in the iron community aware of any situations in which serum ferritin levels are not elevated during iron overload?
I read the paper on the Rhinoceros that dealt with the question if serum ferritin is a valuable index for iron overload, that is a major problem for these big animals. The answer of the work is not, serum ferritin is not related to iron stores in Rhinos!. A major example was an animal that died of disease related to iron overload, but had low ferritin. Very few data are given about these animals, not even the serum iron levels, so that it is difficult to give an interpretation. A possibility of the abnormal low ferritin levels is vitamin C deficiency, which is known to be one of the few, if not the only cause of ferritin reduction. But unfortunately I know nothing about ascorbate metabolism in Rhinos.
I was surprise to find that they detected serum ferritin levels as high as 180,000 ug/ml (c.a. 0.2 g/l) with an Elisa assay based and calibrated on Rhinoceros liver ferritin. If correct, that could be an interesting sample to purify serum ferritin!!!.
Irrespective of the controversial issue of serum ferritin and iron overload, what is not less amazing is the fact that despite the high degree of iron accumulation (referred as overload) in several organs of African rhinoceros held in captivity, there was no overt pathology in those organs. Moreover, the Indian species showed also some abnormal iron accumulation, but in different organs. The idea that the accumulation might not be of a systemic nature (i.e. via iron overloaded plasma) is plausible, but also that "excessive" accumulation (overload) might not always generate toxic effects. One can learn several things from the above story, even that that "no generalization is worth a damn, including this one" (O. Holmes)