Chromium, question of essentiality for mammals: its subcellular mechanism, toxicity, uses as a probe for DNA binding
Chromium was proposed to be an essential trace element over 50 years ago and was accepted as an essential element for over thirty years. Several studies were performed to address the question of essentiality. Male Zucker lean rats were housed in specially designed metal-free cages for six months and fed the purified AIN-93G diet with no added chromium in the mineral mix component of the diet, the standard purified AIN-93G diet, the standard purified AIN-93G diet supplemented with 200 Μg Cr/kg, or the standard purified AIN-93G diet supplemented with 1000 Μg Cr/kg. This study revealed that a diet with as little chromium as reasonably possible had no effect on body composition or glucose metabolism or insulin sensitivity compared to a chromium "sufficient" diet. The diets supplemented with Cr had beneficial effects on the rats; the effects at these doses are pharmacological effects, the mechanism of which requires further research. Zucker obese and Zucker diabetic fatty (ZDF) rats were used to establish whether rats under stress (diabetes and obesity associated insulin resistance) have altered levels of chromium absorption compared to Zucker lean rats. If these conditions lead to increases in chromium absorption, then increased urinary Cr losses resulting from the conditions are unlikely to lead to chromium deficiency. The study revealed that increases in urinary Cr loss associated with insulin resistance or diabetes are offset by increased absorption. Together with the results of other recent studies, these results clearly indicate that chromium can no longer be considered an essential element. Chromium(III) picolinate, [Cr(pic)_3 ], is a commonly used nutritional supplement in humans, that has also been approved for use in animals. Health concerns have arisen over the use of [Cr(pic)_3 ] in high doses. Male CD-1 mice were used to further assess the potential for reproductive or developmental toxicity at a dose of 200 mg/kg/day [Cr(pic)_3 ]. The results suggest that paternal dietary exposure to [Cr(pic)_3 ] has little potential for adverse reproductive effects. Studies with chromium nicotinate and chromium basic carboxylate complexes containing trifluoroacetate, 3-fluoropyridine, 3-trifluoromethylpyridine, and 4-trifluoromethylpyridine are described.