Nearly 60 y ago, chromium, as the trivalent ion, was proposed to be an essential element, but the results of new studies indicate that chromium currently can only be considered pharmacologically ...active and not an essential element. Regardless, articles still continue to appear in the literature claiming chromium is an essential element. Chromium has been marketed as an agent to reduce body mass and develop muscle; however, such marketing claims are no longer allowed in the United States because these claims, similar to claims of essential status, are not supported by experiments. Trivalent chromium has also been proposed as a therapeutic agent to increase insulin sensitivity and affect lipid metabolism. Although effective in certain rodent models, beneficial effects in humans have not been unequivocally established. Molecular mechanisms have been proposed for the beneficial effects but have not been definitively shown to occur in animals.
PURPOSE OF REVIEWChromium(III) has been proposed to have a nutritional or pharmacological role in changing body composition and improving symptoms of insulin resistance, type 2 diabetes, and related ...conditions although the mode of action of Cr(III) at a molecular level has failed to be elucidated. This review details the current status of studies into Cr(III) supplementation.
RECENT FINDINGSClinical trials, meta-analyses and systematic reviews have failed to demonstrate clinically significant effects from Cr(III) supplementation on body composition or symptoms of insulin resistance and related conditions in humans and farm animals. Although new Cr(III) supplements continue to appear in the scientific literature, studies have failed to elucidate the mechanism of chromium action at a molecular level. Conflicting results on a role of transferrin in Cr(III) transport and detoxification have appeared.
SUMMARYCr(III) supplementation cannot currently be recommended in humans or farm animals. Further studies are required to probe the mechanism of Cr(III) action in increasing insulin sensitivity and glucose uptake in rodent models of insulin resistance and diabetes, with particular attention being turned to a potential role of transferrin in Cr(III) transport and detoxification.
Unmanned aerial vehicles (UAVs) have the potential to revolutionize the way research is conducted in many scientific fields 1, 2. UAVs can access remote or difficult terrain 3, collect large amounts ...of data for lower cost than traditional aerial methods, and facilitate observations of species that are wary of human presence 4. Currently, despite large regulatory hurdles 5, UAVs are being deployed by researchers and conservationists to monitor threats to biodiversity 6, collect frequent aerial imagery 7–9, estimate population abundance 4, 10, and deter poaching 11. Studies have examined the behavioral responses of wildlife to aircraft 12–20 (including UAVs 21), but with the widespread increase in UAV flights, it is critical to understand whether UAVs act as stressors to wildlife and to quantify that impact. Biologger technology allows for the remote monitoring of stress responses in free-roaming individuals 22, and when linked to locational information, it can be used to determine events 19, 23, 24 or components of an animal’s environment 25 that elicit a physiological response not apparent based on behavior alone. We assessed effects of UAV flights on movements and heart rate responses of free-roaming American black bears. We observed consistently strong physiological responses but infrequent behavioral changes. All bears, including an individual denned for hibernation, responded to UAV flights with elevated heart rates, rising as much as 123 beats per minute above the pre-flight baseline. It is important to consider the additional stress on wildlife from UAV flights when developing regulations and best scientific practices.
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•Cardiac biologgers reveal that bears exhibit a stress response to UAV flights•Bears rarely display a behavioral response, measured by GPS collars, to UAV flights•Magnitudes of heart rate spikes were correlated with wind speed and proximity of UAV
Unmanned aerial vehicles (UAVs; i.e., “drones”) are increasingly popular tools for ecological research. Ditmer et al. used GPS collars and cardiac biologgers to assess effects of UAV flights on free-roaming bears. All bears exhibited a stress response to UAV flights as evidenced by elevated heart rates while rarely exhibiting a behavioral response.
Fifty years ago the element chromium was proposed to be an essential element for mammals with a role in maintaining proper carbohydrate and lipid metabolism. Over the next several decades, chromium ...nutritional supplements became so popular for weight loss and muscle development that sales were second only to calcium among mineral supplements. However, the failure to identify the responsible biomolecules that bind Cr and their mode of action has resulted in the status of Cr being readdressed in recent years. This review considers research on the biochemistry of Cr(III) over the last two decades and how the results have affected the current status of Cr as an essential element.
A recent report has shown the active site of the beta subunit of mitochondrial ATP synthase is probably the site of action of Cr(III) action, independent of the insulin signaling pathway. This works ...appears to answer an important question about the mode of action of Cr(III) at a molecular level when supplied in supra-nutritional levels to rodents. However, as with any good research, the research also raises several questions. The relationship between this study and the results of rodent studies of chromium supplementation and between this study and the current understanding the chromium(III) transport and detoxification system are put into perspective.
Causes of autosomal-recessive intellectual disability (ID) have, until very recently, been under researched because of the high degree of genetic heterogeneity. However, now that genome-wide ...approaches can be applied to single multiplex consanguineous families, the identification of genes harboring disease-causing mutations by autozygosity mapping is expanding rapidly. Here, we have mapped a disease locus in a consanguineous Pakistani family affected by ID and distal myopathy. We genotyped family members on genome-wide SNP microarrays and used the data to determine a single 2.5 Mb homozygosity-by-descent (HBD) locus in region 5p15.32–p15.31; we identified the missense change c.2035G>A (p.Gly679Arg) at a conserved residue within NSUN2. This gene encodes a methyltransferase that catalyzes formation of 5-methylcytosine at C34 of tRNA-leu(CAA) and plays a role in spindle assembly during mitosis as well as chromosome segregation. In mouse brains, we show that NSUN2 localizes to the nucleolus of Purkinje cells in the cerebellum. The effects of the mutation were confirmed by the transfection of wild-type and mutant constructs into cells and subsequent immunohistochemistry. We show that mutation to arginine at this residue causes NSUN2 to fail to localize within the nucleolus. The ID combined with a unique profile of comorbid features presented here makes this an important genetic discovery, and the involvement of NSUN2 highlights the role of RNA methyltransferase in human neurocognitive development.
A decade ago, the author assessed the status of chromium as the trivalent ion as an essential element and as a therapeutic agent based on rodent studies for this journal. The current review was ...undertaken to update considerations regarding the status of chromium, focusing on studies of Cr supplementation of diabetic rodent models over the last decade. Cr can no longer be considered an essential trace element for humans. Observed effects of Cr on rodent models of insulin resistance and diabetes are best interpreted in terms of a pharmacological role for Cr. The review of studies on the effects of Cr on rat models of diabetes is updated, and the results continue to suggest Cr increases insulin sensitivity in peripheral tissues of the rodent models. The lack of effects in human studies may stem from humans receiving a comparably smaller dose than the rodent models. However, given the different responses to Cr in the rodent models, humans could potentially have different responses to Cr. Recent studies primary utilizing rodents suggest two potential complementary but also contradictory modes of action for Cr(III) at a molecular level.
Chromium as the trivalent ion is believed to pharmaceutically active, increasing insulin sensitivity in high doses in genetic rodent models of diabetes. However, contradictory results have been ...obtained chemical rodent models of diabetes. The current review analyses the effects of dietary Cr supplementation of rodent models of prediabetes, where the condition is administered using a high-fat or high-sugar diet. Rat model studies display a range of quality, with studies utilizing basal diets of known Cr content suggesting Cr beneficially affects insulin sensitivity. Mouse model studies display too much heterogeneity in results for any firm conclusions to be drawn. Comparison of these results with those of clinical trials suggest that the effective dose of Cr may be proportionally lower for rodents than humans, if one exists for humans.
Although recent studies have shown that chromium (as the trivalent ion) is not an essential trace element, it has been demonstrated to generate beneficial effects at pharmacologically relevant doses ...on insulin sensitivity and cholesterol levels of rodent models of insulin insensitivity, including models of type 2 diabetes. The mode of action of Cr(III) at a molecular level is still an area of active debate; however, the movement of Cr(III) in the body, particularly in response to changes in insulin concentration, suggests that Cr(III) could act as a second messenger, amplifying insulin signaling. The evidence for the pharmacological mechanism of Cr(III)’s ability to increase insulin sensitivity by acting as a second messenger is reviewed, and proposals for testing this hypothesis are described.
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