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Oxidative stress is linked to iron levels in black rhinos
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High iron levels may increase inflammation and oxidative stress in captive black rhinos, as Alex Brugman reports

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Black rhinos could be predisposed to iron accumulations, potentially leading to iron overload disorder

Inflammation and oxidative stress may be part of the pathogenesis of iron overload disorder (IOD) in black rhinos in captivity, new research suggests.

IOD is a syndrome in which free iron accumulates in cells. It is frequently described in black rhinos in captivity, but has not been reported in wild black rhinos, nor in white rhinos, either in captivity or the wild.

It is thought that IOD may arise due to the discrepancy between the natural diet of black rhinos (a browsing species) and the diets fed in captivity, with diets in captivity potentially leading to increased iron absorption.

Haemochromatosis is a similar disorder occurring in people, in which the body absorbs too much iron from the food consumed. It is considered to be an inflammatory disease with increased oxidative stress. The new research, published in PLoS ONE, aimed to assess the theory that inflammation and oxidative stress may also play a part in IOD in black rhinos.

To understand more, the researchers compared the inflammation status, oxidative stress levels and iron status in 15 black rhinos and 29 white rhinos across 22 European zoos. Liver and muscle function parameters were also analysed, as these tissues are usually the first to be affected by IOD.

The study found that, when compared with white rhinos, black rhinos had higher iron concentrations and higher levels of inflammatory and oxidative stress markers.

The researchers suggest that black rhinos could be predisposed to iron accumulations, potentially leading to IOD and enhanced inflammatory and oxidative states. Both oxidative stress and inflammation may also cause secondary diseases, rapid ageing and organ damage in black rhinos.

IOD is known to result in oxidative stress due to free radical formation. The body cannot eliminate these free radicals, resulting in inflammation and tissue damage (such as organ fibrosis). Moreover, because this inflammation also induces iron storage in tissues, this pathogenic process is self-sustaining. This may also be a factor that contributes to the elevation of oxidative stress and inflammatory markers.

The researchers recommend that serum iron and total iron-binding capacity should be included in regular blood tests for captive black rhinos. Iron levels, and thus the progression of IOD, could then be controlled through diet or regular therapeutic phlebotomies.

However, further investigations are needed to assess the value of inflammatory and oxidative markers for determining the prognosis of captive black rhinos with IOD, particularly for evaluating the impact of reduced-iron and antioxidant-supplemented diets.

Black rhinos are considered to be critically endangered by the International Union for Conservation of Nature. The International Rhino Foundation reports there are around 5500 left in the wild. As of 2018, 184 black rhinos were held in captivity worldwide.

Hanae Pouillevet, vet intern at ZooParc de Beauval, France, and lead author of this research, said: ‘[zoo animals] deserve our attention and our research efforts to help improve captive animals’ health and welfare, all the more when talking about endangered species that partly rely on ex situ conservation.’ ●

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