Chromium is not an essential trace element for mammals: effects of a "low-chromium" diet

The effects of dietary supplementation with chromium picolinate throughout gestation on productive performance, Cr concentration, serum parameters, and colostrum composition in sows

The objective of this study was to determine the effects of supplemental chromium as chromium picolinate (CrPic) on productive performance, chromium (Cr) concentration, serum parameters, and colostrum composition in sows. Thirty Yorkshire sows were bred with semen from a pool of Landrace boars. The sows were equally grouped and treated with either a diet containing 0 (control) or 400 ppb dietary Cr supplementation throughout gestation. The sows received the same basal diet based on corn-DDGS meal. Supplemental CrPic increased (P < 0.05) the sow body mass gain from the insemination to the day 110 of gestation in sows. No differences (P > 0.50) were observed in the gestation interval, sow mass, and backfat at insemination, after farrowing, at weaning and lactation loss. The number of piglets born alive, piglets per litter at weaning, and litter weaned mass were increased (P < 0.05) for those supplemented with CrPic compared with the control. However, the total number of piglets born, total born litter mass, average piglet birth body mass, born alive litter mass, and average born alive piglet mass did not differ among the treatments (P > 0.05). The placental masses of sows were similar among treatments (P > 0.05). Dietary supplementation with CrPic throughout gestation in sows showed increased (P < 0.01) concentration of Cr in the colostrum or serum at days 70 and 110. Compared with the control group, dietary supplementation with CrPic throughout gestation in sows decreased (P < 0.05) the serum insulin concentration, the glucose or serum urea nitrogen concentration at days 70 and 110. However, no differences (P > 0.05) were observed in total protein concentration among treatments. No differences (P > 0.05) were observed in total solids, protein, fat or lactose among sows fed the diets supplemented with CrPic compared with the control. This exciting finding provides evidence for an increase in mass gain and live-born piglets in sows supplemented with CrPic throughout gestation.

Lack of effect of dietary chromium supplementation on growth performance and serum insulin, glucose, and lipoprotein levels in broilers reared under heat stress condition

This study evaluated the effects of supplemental dietary chromium (Cr) on the performance, carcass traits, and some serum parameters of broilers under a heat stress (23.9 to 37 °C cycling) condition. A total of 150 1-day-old broiler chicks (Cobb 500) according to a completely randomized design were assigned into five treatment groups. Each treatment consisted of three replicates and each replicate contained ten chicks. Treatments were supplemented with 0 (control), 600, and 1,200 μg kg(-1) Cr in the form of Cr chloride (CrCl3) and Cr L-methionine from 1 to 49 days of age. Blood samples were collected from two birds in each replicate to determine serum parameters at 35 and 49 days of age. The body mass, feed intake, and conversion ratio were not influenced by dietary Cr (P > 0.05). Dietary supplementation of Cr from either CrCl3 or Cr L-methionine caused increased serum concentrations of Cr (P < 0.05), but had no effect on serum insulin and glucose concentrations at both sampling times (P > 0.05). Serum triglycerides, very low-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were also not significantly affected (P > 0.05) by dietary treatments, whereas total cholesterol concentration decreased in chicks fed Cr L-methionine compared to the control (P < 0.05).

Urinary chromium excretion in response to an insulin challenge is not a biomarker for chromium status

Over 50 years ago, chromium (Cr) was proposed to be an essential trace element; however, recent studies indicate that this status should be removed as the effects of Cr supplementation appear to be pharmacological rather than nutritional. The pharmacological basis for Cr's effects can explain the inability of investigators to discover a biomarker for Cr status. One potential biomarker has not been examined to date. Cr is known to be mobilized in the body in response to insulin (or insulin release in response to a glucose challenge), resulting in an increase in urinary Cr excretion. The magnitude of increase in urinary Cr loss as a function of dietary Cr intake was tested as a potential biomarker for Cr. Zucker lean rats housed in carefully controlled metal-free conditions were provided a series of purified diets containing variable Cr contents (from 16 μg/kg diet to 2,000 μg/kg) for 23 weeks. The 16 μg/kg diet contained less Cr than any diet examined to date. Urine samples were collected before and after insulin and glucose challenges (0, 2, 6, and 12 h postinjection). Urinary Cr levels were analyzed by the standard method of addition using graphite furnace atomic absorption. The rate of urinary Cr loss after a glucose or insulin challenge was found to not be dependent on the Cr content of the rats' diets. Blood iron levels of the rats were also measured to determine if the addition of Cr to the diet altered iron status. The Cr content of the diet was found to have no affect on blood iron levels. Overall, the study demonstrated that insulin-stimulated urinary Cr excretion cannot be used as a biomarker for Cr status.

Chromium levels in insulin-sensitive tissues and the thigh bone are modulated by prednisolone and high-fat diets in mice

Glucocorticoids (GCs) are often prescribed in clinics but many adverse effects are also attributed to GCs. It is important to determine the role of GCs in the development of those adverse effects. Here, we investigated the impact of GCs on trivalent chromium (Cr) distribution in animals. Cr has been proposed to be important for proper insulin sensitivity, and deficits may lead to disruption of metabolism. For comparison, the effect of a high-fat diet on Cr modulation was also evaluated. C57BL/6JNarl mice were fed regular or high-fat diets for 12 weeks and further grouped for treatment with prednisolone or saline. Cr levels in tissues were determined 12 h after the treatments. Interestingly, prednisolone treatment led to significantly reduced Cr levels in fat tissue in mice fed regular diets; compared to the high-fat diet alone, prednisolone plus the high-fat diet led to a further reduction in Cr levels in the liver, muscle, and fat. Notably, a single dose of prednisolone was linked with elevated Cr levels in the thigh bones of mice fed by either regular or high-fat diets. In conclusion, this report has provided evidence that prednisolone in combination with a high-fat diet effects modulation of Cr levels in selected tissues.

Comparison of tissue metal concentrations in Zucker lean, Zucker obese, and Zucker diabetic fatty rats and the effects of chromium supplementation on tissue metal concentrations

Diabetes results in several metabolic changes, including alterations in the transport, distribution, excretion, and accumulation of metals. While changes have been examined in several rat models of insulin resistance and diabetes, the metal ion concentrations in the tissues of Zucker lean, Zucker obese (an insulin resistance and early stage diabetes model), and Zucker diabetic fatty (ZDF, a type 2 diabetes model) have not previously been examined in detail. The concentration of Cu, Zn, Fe, Mg, and Ca were examined in the liver, kidney, heart and spleen, and Cr concentration in the liver and kidney of these rats were examined. Zucker obese rats have a reduction in the concentration of Cu, Zn, Fe, Mg in the liver compared to ZDF and/or lean Zucker rats, presumably as a result of the increased fat content of the liver of the obese rats. ZDF rats have increased concentrations of kidney Cu compared to the lean rats, while kidney Ca concentrations are increased in the Zucker obese rats. Spleen Fe concentrations are decreased in Zucker obese rats compared to the lean rats. No effects on metal concentrations in the heart were observed between the lean, obese, and ZDF rats, and no effects on Cr concentrations were identified. Cr(III) complexes have previously been shown to have beneficial effects on the signs of insulin resistance in Zucker obese and ZDF rats. The effects of daily gavage administration of chromium picolinate ([Cr(pic)(3)]) (1 mg Cr/kg body mass), CrCl(3) (1 mg Cr/kg body mass), and Cr3 ([Cr(3)O(propionate)(6)(H(2)O)(3)](+)) (33 μg and 1 mg Cr/kg body mass) on metal concentrations in these tissues were examined. Treatment with CrCl(3) and Cr3, but not [Cr(pic)(3)], at 1 mg Cr/kg resulted in a statistically significant accumulation of Cr in the kidney of lean and obese but not ZDF rats but resulted in lowering the elevated levels of kidney Cu in ZDF rats, suggesting a beneficial effect on this symptom of type 2 diabetes.

Long-term exposure to [Cr(3)O(O (2)CCH (2)CH (3)) (6)(H (2)O) (3)] (+) in Wistar rats fed normal or high-fat diets does not alter glucose metabolism

The essentiality of chromium(III) has been the subject of much debate, particularly in healthy subjects. Chromium(III)-containing supplements are widely used for body mass loss, building of lean muscle mass, and improving glucose and lipid metabolism. [Cr(3)O(O(2)CCH(2)CH(3))(6)(H(2)O)(3)](+), Cr3, is one of the most-studied chromium nutritional supplements. The current study evaluates the effects of long-term (15 months) supplementation with Cr3 on body mass and glucose metabolism in Wistar rats on traditional and cafeteria-style (high fat, high carbohydrate) diets. Male Wistar rats were randomly assigned to one of four treatment groups: (1) control diet (milled Harlan Teklad LM-485 rodent diet), (2) control diet+1 mg Cr3/kg body mass/day, (3) a cafeteria-style (CAF) diet (high fat, high carbohydrate), or (4) CAF diet+1 mg Cr3/kg/day. Cr3 supplementation had no effect on fasting blood glucose levels or blood glucose levels in response to glucose and insulin challenges. Rats consuming the CAF+Cr3 diet tended to have a significantly higher body mass than rats consuming the CAF diet, but necropsy results showed no difference in visceral fat or body wall thickness between groups. These data suggest that long-term Cr3 supplementation does not significantly affect body mass in rats consuming a normal diet or glucose levels or metabolism in rats consuming either diet.

Assessment of the mode of action underlying development of rodent small intestinal tumors following oral exposure to hexavalent chromium and relevance to humans

Abstract Chronic exposure to high concentrations of hexavalent chromium (Cr(VI)) in drinking water causes intestinal adenomas and carcinomas in mice, but not in rats. Cr(VI) causes damage to intestinal villi and crypt hyperplasia in mice after only one week of exposure. After two years of exposure, intestinal damage and crypt hyperplasia are evident in mice (but not rats), as are intestinal tumors. Although Cr(VI) has genotoxic properties, these findings suggest that intestinal tumors in mice arise as a result of chronic mucosal injury. To better understand the mode of action (MOA) of Cr(VI) in the intestine, a 90-day drinking water study was conducted to collect histological, biochemical, toxicogenomic and pharmacokinetic data in intestinal tissues. Using MOA analyses and human relevance frameworks proposed by national and international regulatory agencies, the weight of evidence supports a cytotoxic MOA with the following key events: (a) absorption of Cr(VI) from the intestinal lumen, (b) toxicity to intestinal villi, (c) crypt regenerative hyperplasia and (d) clonal expansion of mutations within the crypt stem cells, resulting in late onset tumorigenesis. This article summarizes the data supporting each key event in the MOA, as well as data that argue against a mutagenic MOA for Cr(VI)-induced intestinal tumors.

The need for combined inorganic, biochemical, and nutritional studies of chromium(III)

The history of biochemical and nutritional studies of the element is unfortunately full of twists and turns, most leading to dead ends. Chromium (Cr), as the trivalent ion, has been proposed to be an essential element, a body mass and muscle development agent, and, in the form of the most popular Cr-containing nutritional supplement, to be toxic when given orally to mammals. None of these proposals, despite significant attention in the popular media, has proven to be correct. Trivalent chromium has also been proposed as a therapeutic agent to increase insulin sensitivity and affect lipid metabolism, although a molecular mechanism for such actions has not been elucidated. Greater cooperative research interactions between nutritionists, biochemists, and chemists might have avoided the earlier issues in nutritional and biochemical Cr research and is necessary to establish the potential role of Cr as a therapeutic agent at a molecular level.

Chromium: is it essential, pharmacologically relevant, or toxic?

Over fifty years ago, the element chromium (as the trivalent ion) was proposed to be an essential element for mammals with a role in maintaining proper carbohydrate and lipid metabolism. Evidence for an essential role came from dietary studies with rodents, studies on the effects of chromium on subjects on total parenteral nutrition, and studies of the absorption and transport of chromium. Over the next several decades, chromium-containing 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(s) that bind chromium(III) and their mode of action, particularly a postulated species named glucose tolerance factor or GTF, resulted in the status of chromium being questioned in recent years, such that the question of its being essential needs to be formally readdressed. At the same time as chromium(III)'s popularity as a nutritional supplement was growing, concerns over its safety appeared. While chromium has been conclusively shown not to have beneficial effects on body mass or composition and should be removed from the list of essential trace elements, chromium(III) compounds are generally nontoxic and have beneficial pharmacological effects in rodents models of insulin insensitivity, although human studies have not conclusively shown any beneficial effects. Mechanisms have been proposed for these pharmacological effects, but all suffer from a lack of consistent supporting evidence.

The effects of chromium picolinate and chromium histidinate administration on NF-κB and Nrf2/HO-1 pathway in the brain of diabetic rats

The objective of this experiment was to investigate the effects of supplemental chromium picolinate (CrPic) and chromium histidinate (CrHis) on nuclear factor-kappa B (NF-κB p65) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in diabetic rat brain. Nondiabetic (n = 45) and diabetic (n = 45) male Wistar rats were either not supplemented or supplemented with CrPic or CrHis via drinking water to consume 8 μg elemental chromium (Cr) per day for 12 weeks. Diabetes was induced by streptozotocin injection (40 mg/kg i.p., for 2 weeks) and maintained by high-fat feeding (40 %). Diabetes was associated with increases in cerebral NF-κB and 4-hydroxynonenal (4-HNE) protein adducts and decreased in cerebral nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha (IκBα) and Nrf2 levels. Both Cr chelates were effective to decrease levels of NF-κB and 4-HNE protein adducts and to increase levels of IκBα and Nrf2 in the brain of diabetic rats. However, responses of these increases and decreases were more notable when Cr was supplemented as CrHis than as CrPic. In conclusion, Cr may play a protective role in cerebral antioxidant defense system in diabetic subjects via the Nrf2 pathway by reducing inflammation through NF-κB p65 inhibition. Histidinate form of Cr was superior to picolinate form of Cr in reducing NF-κB expression and increasing Nrf2 expression in the brain of diabetic rats.

Effects of combined dietary chromium(III) propionate complex and thiamine supplementation on insulin sensitivity, blood biochemical indices, and mineral levels in high-fructose-fed rats

Insulin resistance is the first step in glucose intolerance and the development of type 2 diabetes mellitus, thus effective prevention strategies should also include dietary interventions to enhance insulin sensitivity. Nutrients, such as microelement chromium(III) and thiamine, play regulatory roles in carbohydrate metabolism. The objective of this study was to evaluate the insulin-sensitizing potential of the combined supplementary chromium(III) propionate complex (CrProp) and thiamine in insulin resistance animal model (rats fed a high-fructose diet). The experiment was carried out on 40 nine-week-old male Wistar rats divided into five groups (eight animals each). Animals were fed ad libitum: the control diet (AIN-93 M) and high-fructose diets with and without a combination of two levels of CrProp (0.1 and 1 mg Cr/kg body mass/day) and two levels of thiamine (0.5 and 10 mg/kg body mass/day) for 8 weeks. At the end of the experiment rats were sacrificed to collect blood and internal organs for analyses of blood biochemical and hematologic indices as well as tissular microelement levels that were measured using appropriate methods. It was found that both supplementary CrProp and thiamine (given alone) have significant insulin-sensitizing and moderate blood-lipid-lowering properties, while the combined supplementation with these agents does not give synergistic effects in insulin-resistant rats. CrProp given separately increased kidney Cu and Cr levels, while thiamine alone increased hepatic Cu contents and decreased renal Zn and Cu contents.

Hepatoprotective activity of CrPic against alloxan-induced hepatotoxicity in mice

This study focused on oxidation hepatic injury induced by alloxan treatment in mice and the hepatoprotective effect of chromium picolinate (CrPic) against such injury. The mice were randomly divided into three groups (control, alloxan, and CrPic). The CrPic mice were given Cr(3+) (40 μg/kg bm/day), and other mice were given equivalent intragastric doses of water every day. After 4 weeks, the groups alloxan and CrPic were treated with alloxan (40 mg/kg/day) through intraperitoneal injection daily for 6 days. Biochemical and enzymatic characteristics were assayed in these animals. The MDA levels of the control and CrPic groups were 33.93 % and 28.45 % lower, respectively, than that of the alloxan group. The levels of superoxide dismutase (SOD) and GSH-Px in the alloxan group were 15.30 % and 15.69 % higher, respectively,than those of the control group. Both the SOD and GSH-Px levels of the control and CrPic groups were about the same. Levels of CuZnSOD mRNA of the control and CrPic groups were 0.27 fold and 1.03 fold lower than in the alloxan group. The transcription levels of GSH-Px in the control and CrPic groups were 1.57 fold and 0.99 fold below those of the alloxan group. These results show that significant hepatic injury can be induced by alloxan treatment in mice; in addition, CrPic may be useful in health products meant to treat human liver disease.

Effect of bauxite mineralized soil on residual metal levels in some post harvest food crops in Jamaica

The concentrations of nine residual metals in some Jamaican foods were determined using inductively coupled plasma mass spectrometry technique. Cadmium concentration was highest in yellow yam (0.21 mg/kg). Sweet potato had the highest concentrations of lead (0.31 mg/kg), arsenic (0.70 mg/kg) and mercury (0.35 mg/kg). Samples from Grove Place exceeded the regulatory limits of 0.1 mg/kg for cadmium, lead and arsenic and 0.05 mg/kg for mercury. Significant correlations were found between soil and agricultural produce concentrations for cadmium and lead (r(2) ≥ 0.5). These results suggest that the elements were available in soluble forms in the soil for absorption by food crops.

Chromium picolinate modulates serotonergic properties and carbohydrate metabolism in a rat model of diabetes

Chromium picolinate (CrPic) has shown both antidepressant and antidiabetic properties. In this study, the effects of CrPic on serotonergic properties and carbohydrate metabolism in diabetic rats were evaluated. Sixty male Sprague-Dawley rats were divided into four groups. (1) The control group received only standard diet (8 % fat). (2) The CrPic group was fed standard diet and CrPic (80 μg CrPic per kilogram body mass (b.m.)/day), for 10 weeks (microgram/kilogram b.m./day). (3) The HFD/STZ group fed a high-fat diet (HFD, 40 % fat) for 2 weeks and then received streptozotocin (STZ, 40 mg/kg, i.p.) (i.v.) HFD-STZ-CrPic group treated as the previous group and then were administered CrPic. CrPic administration to HFD/STZ-treated rats increased brain chromium levels and improved all measurements of carbohydrate metabolism and serotonergic properties (P<0.001). CrPic also significantly increased levels of insulin, tryptophan, and serotonin (P<0.001) in the serum and brain, and decreased cortisol levels in the serum (P<0.01). Except chromium levels, no significant effect of CrPic supplementation was detected on the overall measured parameters in the control group. CrPic administration was well tolerated without any adverse events. The results support the use of CrPic supplementation which improves serotonergic properties of brain in diabetes.

Monocarboxylate transporters are not responsible for Cr(3+) transport from endosomes

Cr(3+), similar to Fe(3+), is transported into cells primarily via endocytosis as the metal-transferrin complex. As Cr(3+) ions are not readily reduced under biological conditions, the ion cannot be transported from endosomes by the same mechanism as iron that utilized divalent metal ion transporters. Cr(3+) has been hypothesized to potentially be transported as small ligand complexes with a free carboxylate functionality by monocarboxylate transporters (MCT), in a similar fashion to that proposed for Al(3+). Consequently, mouse C2C12 muscle cells were utilized to determine if Cr(3+) is potentially transported by MCT by examining the effects of MCT inhibitors on Cr and Fe transport and subcellular distribution when the metals are added as their transferrin complexes. The results suggest that Cr is not primarily transported by MCT from the endosomes to the cytosol, and that another mechanism for this transport needs to be identified.

Efficacy of dietary chromium (III) supplementation on tissue chromium deposition in finishing pigs

The study was conducted to evaluate the efficacy of different forms of trivalent chromium (Cr) supplementation on tissue chromium deposition in finishing pigs. A total of 96 pigs with an initial average body mass 65.57±1.05 kg were blocked by body mass and randomly assigned to four treatments with three replicates. Pigs were offered one of four diets including a control diet or the control diet supplemented with 200 μg/kg chromium from either chromium chloride (CrCl(3)), chromium picolinate (CrPic) or chromium nanocomposite (CrNano) for 40 days. During the trial, all pigs were given free access to feed and water. After feeding trial, eight pigs from each treatment were slaughtered for samples collection. The results showed that supplemental CrNano increased Cr content in blood, longissimus muscle, heart, liver, kidney, jejunum, and ileum (P<0.05). Supplemental Cr from three sources increased Cr excretion from all feces (P<0.05). Urinary Cr excretion was increased by CrNano or CrPic supplementation significantly. These results suggested that chromium nanocomposite exhibited more effective on tissue Cr deposition in pigs, which indicated higher absorption compared with CrCl(3) and CrPic.

Caffeic acid inhibits chromium(VI)-induced oxidative stress and changes in brush border membrane enzymes in rat intestine

We have previously shown that a single oral dose of potassium dichromate results in a decrease in the activities of several brush border membrane enzymes, produces oxidative stress, and alters the activities of several antioxidant enzymes in the small intestine of rats. In the present study, we have investigated the effect of treatment with the dietary antioxidant caffeic acid on potassium dichromate-induced biochemical changes in the rat intestine. Adult male Wistar rats were randomly divided into four groups: control, potassium dichromate alone, caffeic acid alone, and potassium dichromate + caffeic acid. Administration of a single oral dose of potassium dichromate alone (100 mg/kg body mass) led to a decrease in the activities of brush border membrane enzymes, increase in lipid peroxidation, decrease in sulfhydryl groups, and changes in the activities of several antioxidant enzymes. Two oral doses of caffeic acid (each of 250 mg/kg body mass) greatly attenuated the potassium dichromate-induced changes in all these parameters, but the administration of caffeic acid alone had no effect. Thus, caffeic acid is an effective agent in reducing the effects of potassium dichromate on the intestine and could prove to be useful in alleviating the toxicity of chromium(VI) compounds.

[Hungarian Diet and Nutritional Status Survey -- the OTAP2009 study. V. Intake of microelements in the Hungarian population]

For a healthy status the adequate intake of microelements is vital.

AIM AND METHOD

The Hungarian Diet and Nutritional Status Survey - joining to the European Health Interview Survey - studied the dietary habits of the Hungarian population. The present paper demonstrates the microelement intake.

RESULTS

While the intake of iron, copper and zinc was sufficient in males, it was deficient in females according to the Hungarian recommendations. Especially women in their reproductive age ingested iron below the recommendation, thus representing a health risk. In comparison to earlier Hungarian data, zinc and chromium intake decreased unfavorable.

CONCLUSIONS

Since in Hungary the consumption of the whole grain products with high trace element content is traditionally low, as also reflected in the present study, it would be desirable to increase the contribution of these foods in the diet in order to enhance the intake of microelements.

Molecular mechanisms of chromium in alleviating insulin resistance

Type 2 diabetes is often associated with obesity, dyslipidemia and cardiovascular anomalies and is a major health problem approaching global epidemic proportions. Insulin resistance, a prediabetic condition, precedes the onset of frank type 2 diabetes and offers potential avenues for early intervention to treat the disease. Although lifestyle modifications and exercise can reduce the incidence of diabetes, compliance has proved to be difficult, warranting pharmacological interventions. However, most of the currently available drugs that improve insulin sensitivity have adverse effects. Therefore, attractive strategies to alleviate insulin resistance include dietary supplements. One such supplement is chromium, which has been shown to reduce insulin resistance in some, but not all, studies. Furthermore, the molecular mechanisms of chromium in alleviating insulin resistance remain elusive. This review examines emerging reports on the effect of chromium, as well as molecular and cellular mechanisms by which chromium may provide beneficial effects in alleviating insulin resistance.

Chromium supplementation can alleviate the negative effects of heat stress on growth performance, carcass traits, and meat lipid oxidation of broiler chicks without any adverse impacts on blood constituents

This study was conducted to determine the effects of dietary supplementation with Cr nicotinate and Cr chloride and their optimum inclusion rate on performance, carcass traits, meat oxidative stability, serum metabolites, hematological parameters, and liver chromium concentration in heat-stressed broilers. A total number of 420, 1-day-old male broiler chicks were randomly assigned to seven treatments with four replicates of 15 chicks. The dietary treatments consisted of the basal diet supplemented with 0 (control), 500, 1,000, and 1,500 μg/kg Cr in the form of Cr nicotinate and Cr chloride. Chicks were raised for 6 weeks in heat stress condition (33 ± 2°C). Supplements of organic and inorganic Cr particularly at 1,500 μg/kg incorporation increased feed consumption (P < 0.05) and body mass gain of broilers (P < 0.01). Cr supplementation increased carcass yield and decreased abdominal fat (P < 0.01). Supplementation of 1,500 μg/kg Cr nicotinate (P < 0.05) enhanced liver Cr concentration. Storage time increased lipid oxidation of meat (P < 0.01). Cr decreased lipid oxidation of breast and thigh muscles over 2 (P < 0.01) or 6 (P < 0.05) days of storage time. Birds fed 1,500 μg/kg Cr nicotinate, had lower concentration of serum glucose and triglyceride at 21 days (P < 0.05). Hematological parameters tested at 21 and 42 days, were not influenced. The results suggested that dietary Cr supplementation regardless of its source have a positive effect on productive, and carcass traits, also enhances oxidative stability of refrigerated meat in broilers reared under heat stress conditions.

[Is chromium an essential trace element in human nutrition?]

It has been recognized that chromium is an essential trace element associated with carbohydrate metabolism, and chromium deficiency causes an impaired glucose tolerance. Recently, however, Vincent et al. have reported that chromium is not an essential trace element. In the present report, the author evaluated the nutritional essentiality of chromium by reviewing several previous reports. In almost all previous reports, the chromium concentration in the animal feed used was higher than 0.1 μg/g, and it is difficult to consider that the experimental animals were in a low-chromium state. In addition, the amount of chromium administered to the animals for the improvement of glucose tolerance was at a pharmacological level, and corresponded to a level that far exceeded the human daily chromium intake (20 to 80 μg/day). On the other hand, recent research has clearly shown that feeding with a severely low-chromium diet (0.016 μg/g) does not impair glucose tolerance. The amount of chromium absorbed in humans estimated from chromium intake (20 to 80 μg/day), chromium absorption rate (1%), and urinary chromium excretion (<1 μg/day) is less than 1 μg/day, which is much lower than those of other essential trace elements. In addition, because there is an inconsistency between the chromium concentration in food and chromium intake, chromium intake seems to be dependent on chromium contamination during food processing and cooking. It is concluded that there is a high possibility that chromium is not an essential trace element.

The effect of different levels of organic and inorganic chromium supplementation on production performance, carcass traits and some blood parameters of broiler chicken under heat stress condition

A total of 250 broilers in a completely randomized design selected to evaluate the effect of different levels of chromium (Cr) supplementation on performance, carcass traits and some blood parameters of heat-stressed broiler chicks. All birds were kept under heat stress temperature (33 ± 3°C) and divided into five treatments groups. Each treatment consisted of five pens with 10 birds in each pen. The basal diets were supplemented with 0 ppb (control), 800 ppb Cr-L-Met (T(1)), 1,200 ppb Cr-L-Met (T(2)) or 800 ppb CrCl(3) (T(3)), and 1,200 ppb CrCl(3) (T(4)). The feed intake and body mass were measured at 10, 21, and 42 days of age. Blood samples were collected from two birds in each replicates to determine biological and hematological values at 28 and 42 days of age. There were no significant difference in mass gain and feed conversion of broilers that received Cr supplementations compared with controls. The serum glucose concentration decreased in broilers received organic chromium methionine supplements compared with other treatments groups. Slight but not significant increases were observed in serum high-density lipoprotein (HDL) concentration of treated groups than controls while the mean serum HDL concentration was significantly higher in T(2) group compared with control group. Serum low-density lipoprotein level decreased in broiler received organic Cr supplements (p < 0.05).

Potential of chromium(III) picolinate for reproductive or developmental toxicity following exposure of male CD-1 mice prior to mating

Chromium(III) picolinate, [Cr(pic)(3)], is a commonly used nutritional supplement in humans, which has also been approved for use in animals. Health concerns have arisen over the use of [Cr(pic)(3)]. At high [Cr(pic)(3)] doses, developmental toxicity tests in female mice have shown a higher litter incidence of split cervical arch in exposed fetuses, but this was not consistently reproducible. In the current study, male CD-1 mice were used to further assess the potential for reproductive or developmental toxicity. Four weeks prior to mating, the males were fed a diet providing 200 mg/kg/day [Cr(pic)(3)] for comparison with untreated controls. Females were not treated. Each male was mated with two females, which were sacrificed on gestation day 17, and their litters were examined for adverse effects. Mating and fertility indices were not significantly altered by treatment. Male exposure to [Cr(pic)(3)] also had no effect on prenatal mortality, fetal weight, or gross or skeletal morphology. These results suggest that paternal dietary exposure to chromium(III) picolinate has little potential for adverse reproductive effects, even at exposure levels considerably higher than expected human exposures from nutritional supplements (1 mg of Cr per day or less).

Evaluation of anti-diabetic potential of chromium(III) propionate complex in high-fat diet fed and STZ injected rats

The aim of this study was to examine the anti-diabetic potential of the chromium(III) propionate complex (CrProp) in a diabetic rat model. Male Wistar rats (n=28, 8-week old) were divided into 4 groups (with 7 rats each) and fed at libitum: the control diet (AIN-93M), and high-fat diets with or without supplementary CrProp (10 and 50mg Crkg(-1) diet; 1 and 5 mg kg(-1) body mass per day) for 5 weeks, and subsequently injected with STZ to induce diabetes. Rats were further fed the same diets for another week until the end of the experiment. Blood indices and the contents of minerals (Fe, Zn, Cu and Cr) in rat tissues were determined by atomic absorption spectrometry. Supplementary CrProp did not affect blood glucose level, but significantly improved insulin sensitivity (HOMA-IR index) and reduced serum levels of triacylglycerols, total and LDL cholesterols. Both supplementary dosages of CrProp (10 and 50mg Cr kg(-1) diet) normalized the increased liver Fe content, reduced hepatic and renal Cu levels and elevated renal Cr contents in diabetic rats. In conclusion, CrProp has a significant anti-diabetic (insulin-sensitizing and hypolipidemic) potential; thus it might be a candidate for a therapeutic agent in diabetes.

Metal-based anti-diabetic drugs: advances and challenges

The current status and likely future directions of complexes of V(V/IV), Cr(III), Mo(VI), W(VI), Zn(II), Cu(II), and Mn(III) as potential oral drugs against type 2 diabetes are reviewed. We propose a unified model of extra- and intracellular mechanisms of anti-diabetic efficacies of V(V/IV), Mo(VI), W(VI), and Cr(III), centred on high-oxidation-state oxido/peroxido species that inhibit protein tyrosine phosphatases (PTPs) involved in insulin signalling. The postulated oxidative mechanism of anti-diabetic activity of Cr(III) via carcinogenic Cr(VI/V) (which adds to safety concerns) is consistent with recent clinical trials on Cr(III) picolinate, where activity was apparent only in patients with poorly controlled diabetes (high oxidative stress), and the correlation between the anti-diabetic activities and ease of oxidation of Cr(III) supplements and their metabolites in vivo. Zn(II) and Cu(II) anti-diabetics act via different mechanisms and are unlikely to be used as specific anti-diabetics due to their diverse and unpredictable biological activities. Hence, future research directions are likely to centre on enhancing the bioavailability and selectivity of V(V/IV), Mo(VI), or W(VI) drugs. The strategy of potentiating circulating insulin with metal ions has distinct therapeutic advantages over interventions that stimulate the release of more insulin, or use insulin mimetics, because of many adverse side-effects of increased levels of insulin, including increased risks of cancer and cardiovascular diseases.

Characterization of the organic component of low-molecular-weight chromium-binding substance and its binding of chromium

Chromium was proposed to be an essential element over 50 y ago and was shown to have therapeutic potential in treating the symptoms of type 2 diabetes; however, its mechanism of action at a molecular level is unknown. One chromium-binding biomolecule, low-molecular weight chromium-binding substance (LMWCr or chromodulin), has been found to be biologically active in in vitro assays and proposed as a potential candidate for the in vivo biologically active form of chromium. Characterization of the organic component of LMWCr has proven difficult. Treating bovine LMWCr with trifluoroacetic acid followed by purification on a graphite powder micro-column generates a heptapeptide fragment of LMWCr. The peptide sequence of the fragment was analyzed by MS and tandem MS (MS/MS and MS/MS/MS) using collision-induced dissociation and post-source decay. Two candidate sequences, pEEEEGDD and pEEEGEDD (where pE is pyroglutamate), were identified from the MS/MS experiments; additional tandem MS suggests the sequence is pEEEEGDD. The N-terminal glutamate residues explain the inability to sequence LMWCr by the Edman method. Langmuir isotherms and Hill plots were used to analyze the binding constants of chromic ions to synthetic peptides similar in composition to apoLMWCr. The sequence pEEEEGDD was found to bind 4 chromic ions per peptide with nearly identical cooperativity and binding constants to those of apoLMWCr. This work should lead to further studies elucidating or eliminating a potential role for LMWCr in treating the symptoms of type 2 diabetes and other conditions resulting from improper carbohydrate and lipid metabolism.

Competitive binding of Fe3+, Cr3+, and Ni2+ to transferrin

Competitive binding of Fe(3+), Cr(3+), and Ni(2+) to transferrin (Tf) was investigated at various physiological iron to Tf concentration ratios. Loading percentages for these metal ions are based on a two M(n+) to one Tf (i.e., 100% loading) stoichiometry and were determined using a particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) method. Serum iron concentrations typically found in normal, iron-deficient, iron-deficient from chronic disease, iron-deficient from inflammation, and iron-overload conditions were used to determine the effects of iron concentration on iron loading into Tf. The PB/HC-OES method allows the monitoring of metal ions in competition with Fe(3+) for Tf binding. Iron-overload concentrations impeded the ability of chromium (15.0 μM) or nickel (10.3 μM) to load completely into Tf. Low Fe(3+) uptake by Tf under iron-deficient or chronic disease iron concentrations limited Ni(2+) loading into Tf. Competitive binding kinetic studies were performed with Fe(3+), Cr(3+), and Ni(2+) to determine percentages of metal ion uptake into Tf as a function of time. The initial rates of Fe(3+) loading increased in the presence of nickel or chromium, with maximal Fe(3+) loading into Tf in all cases reaching approximately 24%. Addition of Cr(3+) to 50% preloaded Fe(3+)-Tf showed that excess chromium (15.0 μM) displaced roughly 13% of Fe(3+) from Tf, resulting in 7.6 ± 1.3% Cr(3+) loading of Tf. The PB/HC-OES method provides the ability to monitor multiple metal ions competing for Tf binding and will help to understand metal competition for Tf binding.