Chromium (D-phenylalanine)3 alleviates high fat-induced insulin resistance and lipid abnormalities

High-fat diet has been implicated as a major cause of insulin resistance and dyslipidemia. The objective of this study was to evaluate the impact of dietary-supplementation of chromium (d-phenylalanine)₃ [Cr(d-Phe)₃] on glucose and insulin tolerance in high-fat diet fed mice. C57BL/6-mice were randomly assigned to orally receive vehicle or Cr(d-Phe)₃ (45 μg of elemental chromium/kg/day) for 8-weeks. High-fat-fed mice exhibited impaired whole-body-glucose and -insulin tolerance and elevated serum triglyceride levels compared to normal chow-fed mice. Insulin-stimulated glucose up-take in the gastrocnemius muscles, assessed as 2-[³H-deoxyglucose] incorporation was markedly diminished in high-fat fed mice compared to control mice. Treatment with chromium reconciled the high-fat diet-induced alterations in carbohydrate and lipid metabolism. Treatment of cultured, differentiated myotubes with palmitic acid evoked insulin resistance as evidenced by lower levels of insulin-stimulated Akt-phosphorylation, elevated JNK-phosphorylation, (assessed by Western blotting), attenuation of phosphoinositol-3-kinase activity (determined in the insulin-receptor substrate-1-immunoprecipitates by measuring the extent of phosphorylation of phosphatidylinositol by γ-³²P-ATP), and impairment in cellular glucose up-take, all of which were inhibited by Cr(d-Phe)₃. These results suggest a beneficial effect of chromium-supplementation in insulin resistant conditions. It is likely that these effects of chromium may be mediated by augmenting downstream insulin signaling.     

Exposure of pregnant mice to chromium picolinate results in skeletal defects in their offspring

BACKGROUND: Chromium(III) picolinate, [Cr(pic)(3)], is a widely marketed dietary supplement. However, Cr(pic)(3) has been associated with oxidative damage to DNA in rats and mutations and DNA fragmentation in cell cultures. In isolated case reports, Cr(pic)(3) supplementation has been said to cause adverse effects, such as anemia, renal failure, liver dysfunction, and neuronal impairment. To date, no studies have been published regarding the safety of chromium picolinate supplementation to a developing fetus, although Cr(pic)(3) has been recommended for pregnant women who are diagnosed with gestational diabetes. METHODS: From gestation days (GD) 6-17, pregnant CD-1 mice were fed diets containing either 200 mg/kg Cr(pic)(3), 200 mg/kg CrCl(3), 174 mg/kg picolinic acid, or the diet only to determine if Cr(pic)(3), CrCl(3), or picolinic acid could cause developmental toxicity. Dams were sacrificed on GD 17, and their litters were examined for adverse effects. RESULTS: The incidence of bifurcated cervical arches was significantly increased in fetuses from the Cr(pic)(3) group as compared to the diet-only group. Fetuses in the picolinic acid-treated group had an incidence double that of the control group; however, this increase was not statistically significant. Fetuses in the CrCl(3) group did not differ from the controls in any variable examined. No maternal toxicity was observed in any of the treatment groups. CONCLUSIONS: High maternal oral exposures to chromium picolinate can cause morphological defects in developing offspring of mice.     

Anti-diabetic effect of ginsenoside Re in ob/ob mice

We evaluated the anti-diabetic effects of ginsenoside Re in adult male C57BL/6J ob/ob mice. Diabetic ob/ob mice with fasting blood glucose levels of approximately 230 mg/dl received daily intraperitoneal injections of 7, 20 and 60 mg/kg ginsenoside Re for 12 consecutive days. Dose-related effects of ginsenoside Re on fasting blood glucose levels were observed. After the 20 mg/kg treatment, fasting blood glucose levels were reduced to 188+/-9.2 and 180+/-10.8 mg/dl on Day 5 and Day 12, respectively (both P<0.01 compared to vehicle group, 229+/-9.5 and 235+/-13.4 mg/dl, respectively). The EC(70) of ginsenoside Re was calculated to be 10.3 mg/kg and was used for subsequent studies. Consistent with the reduction in blood glucose, there were significant decreases in both fed and fasting serum insulin levels in mice treated with ginsenoside Re. With 12 days of ginsenoside treatment, glucose tolerance of ob/ob mice increased significantly, and the area under the curve for glucose decreased by 17.8% (P<0.05 compared to vehicle treatment). The hypoglycemic effect of the ginsenoside persisted even at 3 days of treatment cessation (blood glucose levels: 198+/-13.1 with ginsenoside treatment vs. 253+/-20.3 mg/dl with vehicle, P<0.01). There were no significant changes in body weight or body temperature. Preliminary microarray analysis revealed differential expression of skeletal muscle genes associated with lipid metabolism and muscle function. The results suggest that ginsenoside Re may prove to be useful in treating type 2 diabetes.     

A newly synthetic chromium complex--chromium(phenylalanine)3 improves insulin responsiveness and reduces whole body glucose tolerance

Low-molecular-weight organic chromium complexes such as chromium picolinate are often used as dietary supplements to improve insulin sensitivity and to correct dyslipidemia. However, toxicity associated with such chromium compounds has compromised their therapeutic value. The aim of this study was to evaluate the impact of a newly synthesized complex of chromium with phenylalanine, Cr(pa)3 on insulin-signaling and glucose tolerance. Cr(pa)3 was synthesized by chelating chromium(III) with D-phenylalanine ligand in aqueous solution. In mouse 3T3-adipocytes, Cr(pa)3 augmented insulin-stimulated glucose-uptake as assessed by a radioactive-glucose uptake assay. At the molecular level, Cr(pa)3 enhanced insulin-stimulated phosphorylation of Akt in a time- and concentration-dependent manner without altering the phosphorylation of insulin receptor. Oral treatment with Cr(pa)3 (150 microg/kg/d, for six weeks) in ob/ob+/+ obese mice significantly alleviated glucose tolerance compared with untreated obese mice. Unlike chromium picolinate, Cr(pa)3 does not cleave DNA under physiological reducing conditions. Collectively, these data suggest that Cr(pa)3 may represent a novel, less-toxic chromium supplement with potential therapeutic value to improve insulin sensitivity and glycemic control in type II diabetes.     

Effects of taurine on oxidative stress parameters and chromium levels altered by acute hexavalent chromium exposure in Mice Kidney tissue

The kidney has been regarded as a critical organ of toxicity induced by acute exposure to hexavalent chromium [Cr(VI)] compounds. Reactive intermediates and free radicals generated during reduction process might be responsible for Cr(VI) toxicity. In this study, the effects of pretreatment or posttreatment of taurine on Cr(VI)-induced oxidative stress and chromium accumulation in kidney tissue of Swiss albino mice were investigated. Single intraperitoneal (ip) potassium dichromate treatment (20 mgCr/kg), as Cr(VI) compound, significantly elevated the level of lipid peroxidation as compared with the control group (p<0.05). This was accompanied by significant decreases in nonprotein sulfhydryls (NPSH) level, superoxide dismutase (SOD), and catalase (CAT) enzyme activities as well as a significant chromium accumulation (p<0.05). Taurine administration (1 g/kg, ip) before or after Cr(VI) exposure resulted in reduction of lipid peroxidation levels and improvement in SOD enzyme activity (p<0.05). On the other hand, administration of the antioxidant before Cr(VI) exposure restored the NPSH level and CAT enzyme activity and also reduced tissue chromium levels (p<0.05), whereas postreatment had only slight effects on these parameters. In view of the results, taurine seems to exert some beneficial effects against Cr(VI)-induced oxidative stress and chromium accumulation in mice kidney tissue.     

Changes in urinary dinor dihydro F(2)-isoprostane metabolite concentrations, a marker of oxidative stress, during and following asthma exacerbations

To investigate changes in oxidant stress during and following acute asthma exacerbations, this study measured 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP (F(2)-IsoP-M), the major urinary metabolite of 15-F(2t)-IsoP, in eight asthmatic adults, during and following an asthma hospitalization. F(2)-IsoP-M concentrations at admission and follow-up were significantly higher than discharge (admission median: 4.12 ng/Cr mg, range 1.89-7.8; follow-up: 2.47 ng/Cr mg (1.56-6.86); discharge: 1.42 ng/Cr mg (0.7-4.44); both p<0.01), but not significantly different between admission and follow-up. F(2)-IsoP-M concentrations at follow-up were higher than a control group with stable asthma (0.68 ng/Cr mg (0.31-1.5), p=0.0008). In conclusion, asthma exacerbations requiring hospitalization are associated with 6-fold higher urinary F(2)-IsoP-M concentrations compared to stable asthmatics. F(2)-IsoP-M concentrations decreased significantly during hospitalization, but significant elevations 3 months following hospitalization suggest ongoing oxidative stress despite clinical improvement. Urinary F(2)-IsoP-M may be a clinically useful, simple non-invasive systemic measure of oxidative stress in asthmatics, providing information not captured by spirometry or symptoms.     

Chromium supplementation improves glucose tolerance in diabetic Goto-Kakizaki rats

Chromium supplementation (Cr) may be useful in the management of diabetes and appears to improve some aspects of glucose handling. However, several studies have used either high doses of Cr supplementation or have placed control animals on a Cr-deficient diet. We therefore wanted to test whether Cr dosages in the ranges that more closely approximate recommended levels of supplementation in humans are efficacious in glycemic control under normal dietary conditions. Euglycemic Wistar or diabetic Goto-Kakizaki (GK) rats (a model of nonobese NIDDM) were assigned to water (control) or chromium picolinate (Cr-P) supplementation (1 or 10 mg/kg/day) groups for up to 32 weeks. Glucose tolerance was tested following an overnight fast by injecting sterile glucose (1.0 g/kg, i.p.) and then measuring blood glucose at select times to determine the sensitivity to glucose by calculation of the area under the curve. Cr-P did not significantly alter the growth of the animals. In the euglycemic Wistar rats, Cr-P supplementation did not alter the response to a glucose tolerance test. In the GK rats, Cr-P supplementation significantly improved glucose tolerance at both levels of Cr-P supplementation (1 mg/kg/day: H20; 100 +/- 11%; Cr-P 70 +/- 8%; 10 mg/kg/day: H(2)0; 100 +/- 10%; Cr-P 66 +/- 9 %). Cr-P supplementation produced a small improvement in some indices of glycemic control. There were no differences observed for the two levels of Cr-P supplementation suggested that we did not identify a threshold for Cr-P effects, and future studies may use lower doses to find a threshold effect for improving glucose tolerance in diabetics.     

Chromium alleviates glucose intolerance, insulin resistance, and hepatic ER stress in obese mice

Objective: Chromium has gained popularity as a nutritional supplement for diabetic patients. This study evaluated the effect of chronic administration of a chromium complex of d ‐phenylalanine (Cr(d ‐phe)₃) on glucose and insulin tolerance in obese mice. The study tested the hypothesis that Cr(d ‐phe)₃ suppresses endoplasmic reticulum (ER) stress and insulin resistance in these animals. Methods and Procedures: C57BL lean and ob/ob obese mice were randomly divided to orally receive vehicle or Cr(d ‐phe)₃ (3.8 μg of elemental chromium/kg/day) for 6 months. Insulin sensitivity was evaluated by glucose and insulin tolerance tests. Protein levels of phosphorylated pancreatic ER kinase (PERK), α subunit of translation initiation factor 2 (eIF2α) and inositol‐requiring enzyme‐1 (IRE‐1), p‐c‐Jun, and insulin receptor substrate‐1 (IRS‐1) phosphoserine‐307 were assessed by western blotting. In vitro ER stress was induced by treating cultured muscle cells with thapsigargin in the presence or absence of Cr(d ‐phe)₃. Results: ob/ob mice showed poor glucose and insulin tolerance compared to the lean controls, which was attenuated by Cr(d ‐phe)₃. Markers of insulin resistance (phospho‐c‐Jun and IRS‐1 phosphoserine) and ER stress (p‐PERK, p‐IRE‐1, p‐eIF2α), which were elevated in ob/ob mice, were attenuated following Cr(d ‐phe)₃ treatment. Chromium treatment was also associated with a reduction in liver triglyceride levels and lipid accumulation. In cultured myotubes, Cr(d ‐phe)₃ attenuated ER stress induced by thapsigargin. Discussion: Oral Cr(d ‐phe)₃ treatment reduces glucose intolerance, insulin resistance, and hepatic ER stress in obese, insulin‐resistant mice.     

Chromium (D-phenylalanine)3 improves obesity-induced cardiac contractile defect in ob/ob mice

Objective: Low‐molecular weight chromium compounds, such as chromium picolinate [Cr(pic)₃], improve insulin sensitivity, although toxicity is a concern. We synthesized a novel chromium complex, chromium (d ‐phenylalanine)₃ [Cr(d ‐phe)₃], in an attempt to improve insulin sensitivity with reduced toxicity. The aim of this study was to compare the two chromium compounds on cardiac contractile function in ob/ob obese mice. Research Methods and Procedures: C57BL lean and ob/ob obese mice were randomly divided into three groups: H₂O, Cr(d ‐phe)₃, or Cr(pic)₃ (45 µg/kg per day orally for 6 months). Results: The glucose tolerance test displayed improved glucose clearance by Cr(d ‐phe)₃ but not Cr(pic)₃. Myocytes from ob/ob mice exhibited depressed peak shortening (PS) and maximal velocity of shortening/relengthening (±dL/dt), prolonged time‐to‐PS and time‐to‐90% relengthening (TR90), reduced electrically stimulated rise in intracellular Ca²⁺ (Δfura‐2 fluorescence intensity), and slowed intracellular Ca²⁺ decay. Although a 3‐month Cr(d ‐phe)₃ treatment for a separate group of ob/ob and lean 2‐month‐old mice only rectified reduced ±dL/dt in ob/ob mice, all mechanical and intracellular Ca²⁺ abnormalities were significantly attenuated or ablated by 6 months of Cr(d ‐phe)₃ but not Cr(pic)₃ treatment (except TR90). Sarco(endo)plasmic reticulum Ca²⁺ ATPase activity and Na⁺‐Ca²⁺ exchanger expression were depressed in ob/ob mice, which were reversed by both Cr(d ‐phe)₃ and Cr(pic)₃, with a more pronounced effect from Cr(d ‐phe)₃. Cr(d ‐phe)₃ corrected reduced insulin‐stimulated glucose uptake and improved basal phosphorylation of Akt and insulin receptor, as well as insulin‐stimulated phosphorylation of Akt and insulin receptor in ob/ob myocytes. Heart homogenates from ob/ob mice had enhanced oxidative stress and protein carbonyl formation compared with the lean group, which were attenuated by both Cr(d ‐phe)₃ and Cr(pic)₃. Discussion: Our data suggest that the new Cr(d ‐phe)₃ compound possesses better cardio‐protective and insulin‐sensitizing properties against obesity.     

Chromium-induced excretion of urinary lipid metabolites,DNA damage,nitric oxide production,and generation of reactive oxygen species in Sprague-Dawley rats

Chromium and its salts induce cytotoxicity and mutagenesis, and vitamin E has been reported to attenuate chromate-induced cytotoxicity. These observations suggest that chromium produces reactive oxygen species which may mediate many of the untoward effects of chromium. We have therefore examined and compared the effects of Cr(III) (chromium chloride hexahydrate) and Cr(VI) (sodium dichromate) following single oral doses (0.50 ld₅₀) on the production of reactive oxygen species by peritoneal macrophages, and hepatic mitochondria and microsomes in rats. The effects of Cr(III) and Cr(VI) on hepatic mitochondrial and microsomal lipid peroxidation and enhanced excretion of urinary lipid metabolites as well as the incidence of hepatic nuclear DNA damage and nitric oxide (NO) production were also examined. Increases in lipid peroxidation of 1.8- and 2.2-fold occurred in hepatic mitochondria and microsomes, respectively, 48 hr after the oral administration of 25 mg Cr(VI)/kg, while increases of 1.2- and 1.4-fold, respectively, were observed after 895 mg Cr(III)/kg. The urinary excretion of malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT) and acetone (ACON) were determined at 0–96 hr after Cr administration. Between 48 and 72 hr post-treatment, maximal excretion of the four urinary lipid metabolites was observed with increases of 1.5- to 5.4-fold in Cr(VI) treated rats. Peritoneal macrophages from Cr(VI) treated animals 48 hr after treatment resulted in 1.4- and 3.6-fold increases in chemiluminescence and iodonitrotetrazolium reduction, indicating enhanced production of Superoxide anion, while macrophages from Cr(III) treated animals showed negligible increases. Increases in DNA single strand breaks of 1.7-fold and 1.5-fold were observed following administration of Cr(VI) and Cr(III), respectively, at 48 hr post-treatment. Enhanced production of NO by peritoneal exudate cells (primarily macrophages) was monitored following Cr(VI) administration at both 24 and 48 hr post-treatment with enhanced production of NO being observed at both timepoints. The results indicate that both Cr(VI) and Cr(III) induce an oxidative stress at equitoxic doses, while Cr(VI) induces greater oxidative stress in rats as compared with Cr(III) treated animals.     

Protein degradation by peroxide catalyzed by chromium (III): role of coordinated ligand

In order to understand the role of coordinated ligands in controlling the biotoxicity of chromium (III), interactions of three types of chromium (III) complexes viz. trans-diaquo [1,2 bis (salicyledeneamino) ethane chromium (III) perchlorate, [(Cr(salen)(H(2)O)(2)](ClO(4)); tris (ethylenediamine) chromium (III) chloride, [Cr(en)(3)]Cl(3), and monosodium ethylene diamine tetraacetato monoaquo chromiate (III), [Cr(EDTA)(H(2)O)]Na with BSA has been investigated. Spectroscopic and equilibrium dialysis studies show that the two cationic complexes Cr(salen)(H(2)O)(+)(2) and Cr(en)(3+)(3) bind to the protein with a protein-metal ratio of 1:8 and 1:4. The anionic complex Cr(EDTA)(H(2)O)(-) binds to the protein with a protein-metal ratio of 1:2. The binding constant K(b) as estimated from the fluorescence quenching studies has been found to be 7.6 +/- 0.4 x 10(3) M(-1), 3.1 +/- 0.2 x 10(2) M(-1), and 1.8 +/- 0.2 x 10(2) M(-1) for Cr(salen)(H(2)O)(+)(2), Cr(en)(3+)(3), and Cr(EDTA)(H(2)O)(-) respectively indicating that the thermodynamic stability of protein-chromium complex is Cr(salen)(H(2)O)(+)(2) > Cr(en)(3+)(3) approximately Cr(EDTA)(H(2)O)(-). The complexes Cr(salen)(H(2)O)(+)(2) and Cr(EDTA)(H(2)O)(-) in the presence of hydrogen peroxide have been found to bring about protein degradation, whereas Cr(en)(3+)(3) does not bring about any protein damage. This clearly shows that the nature of the chromium (III) complex plays a major role in the biotoxicity of chromium (III).     

Atrial natriuretic peptide prevents diabetes-induced endothelial dysfunction

Atrial natriuretic peptide (ANP) exerts beneficial effects on the cardiovascular system in part by exerting antioxidant activity. Given that oxidant stress is a key cause of endothelial dysfunction in diabetes, we investigated whether ANP improves endothelial function in rats with diabetes. Rats were injected with streptozotocin (55 mg/kg iv) to induce type 1 diabetes or the citrate vehicle as controls (n=12). After 4 weeks the diabetic rats were treated with ANP (10 pmol/kg/min sc, n=12) or the antioxidant tempol (1.5 mmol/kg/day sc, n=11), both by osmotic minipump, ramipril (1 mg/kg per day in the drinking water) or remained untreated (n=11). After a further 4 weeks, anaesthetised rats were killed by exsanguination and the thoracic aortae collected for examination of vascular activity and measurement of superoxide generation. Diabetic rats showed elevated plasma glucose concentration (45+/-3 mM) compared to controls (10+/-1 mM) and this was not affected by ANP (43+/-3 mM), ramipril (41+/-2 mM) or tempol (43+/-2 mM). Endothelium-dependent relaxation ex vivo in response to acetylcholine was impaired in diabetic rats (Rmax=66+/-4%) compared to control rats (Rmax=94+/-1%) but treatment with ANP (Rmax=80+/-4%), ramipril (Rmax=88+/-2%) or tempol (Rmax=81+/-5%) significantly improved those responses. Relaxant responses to the endothelium-independent vasodilator sodium nitroprusside were enhanced by treatment of diabetic rats with ANP or ramipril and their combination; but not by tempol. Superoxide generation was significantly elevated in aorta from untreated diabetic rats (649+/-146% of control). In diabetic rats, superoxide generation was significantly attenuated by ANP (to 229+/-78%) or tempol (to 186+/-64%). This study demonstrates that ANP improves vascular oxidant stress in concert with endothelial function, independent of any effect on plasma glucose levels. These studies may lead to new therapies, based on natriuretic peptide and/or antioxidant approaches, for ameliorating the vascular complications of diabetes.     

Chromium and yogurt effects on hepatic lipid and plasma glucose and insulin of obese mice

Dietary chromium (Cr) supplements in casein or yogurt-based diets were fed to genetically obese C57BL/6J-OB (ob/ob) mice to investigate the effects of Cr and yogurt on total hepatic lipid, plasma glucose, insulin, and cholesterol levels. Diet groups were casein control (C), yogurt control (Y), yogurt plus CrCl₃ (Y + Cr) (1.83 ppm Cr), and casein plus CrCl₃ (C + Cr) (1.85 ppm Cr). Food and water were availablead libitum. No significant differences were observed in final body weight. In obese mice, total hepatic lipid was significantly greater in the C than in the C + Cr group and in the Y than in the Y + Cr group. Plasma immunoreactive insulin levels tended to be lower in animals fed C + Cr and Y + Cr diets. Plasma insulin was significantly correlated with hepatic lipid and with plasma cholesterol. By analysis of variance, bone Cr was elevated by Cr supplementation. In the obese mouse, a model for insulin resistance, Cr supplementation apparently affects both hepatic lipid concentration and bone chromium.     

Oxidative stress induced by chronic administration of sodium dichromate [Cr(VI)] to rats

Chromium occurs in the workplace primarily in the valence forms Cr(III) and Cr(VI). Recent studies have demonstrated that sodium dichromate [Cr(VI)] induces greater oxidative stress as compared with Cr(III), as indicated by the production of reactive oxygen species by peritoneal macrophages and hepatic mitochondria and microsomes, and enhanced excretion of urinary lipid metabolites and hepatic DNA-single strand breaks (SSB) following acute oral administration of Cr(III) and Cr(VI). We have therefore examined the chronic effects of sodium dichromate dihydrate [Cr(VI); 10 mg (33.56 μmol)/kg/day] on hepatic mitochondrial and microsomal lipid peroxidation, enhanced excretion of urinary lipid metabolites including malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT), acetone (ACON) and propionaldehyde (PROP), and hepatic DNA damage over a period of 90 days. The maximal increases in hepatic lipid peroxidation and DNA damage were observed at approximately 45 days of treatment. Maximum increases in the urinary excretion of MDA, FA, ACT, ACON and PROP were 3.2-, 2.6-, 4.1-, 3.3- and 2.1-fold, respectively, while a 5.2-fold increase in DNA-SSB was observed. The results clearly indicate that chronic sodium dichromate administration induces oxidative stress resulting in tissue damaging effects which may contribute to the toxicity and carcinogenicity of hexavalent chromium.     

The Protective and Antidotal Effects of Taurine on Hexavalent Chromium-Induced Oxidative Stress in Mice Liver Tissue

Acute exposure to hexavalent chromium [Cr(VI)] compounds can cause hepatotoxicity. Reactive intermediates and free radicals generated during reduction process may be responsible for Cr(VI) toxicity. In this study, the effects of pretreatment or posttreatment of taurine on Cr(VI)-induced oxidative stress and chromium accumulation in liver tissue of Swiss Albino mice were investigated. Single intraperitoneal (ip) potassium dichromate treatment (20 mgCr/kg), as Cr(VI) compound, significantly elevated the level of lipid peroxidation as compared with control group (p < 0.05). This was accompanied by significant decreases in nonprotein sulfhydryls (NPSHs) level, superoxide dismutase (SOD), and catalase (CAT) enzyme activities as well as a significant chromium accumulation in the tissue (p < 0.05). Taurine administration (1 g/kg, ip) before or after Cr(VI) exposure resulted in reduction of lipid peroxidation (p < 0.05) showed rebalancing effect on tissue NPSH levels either in pretreatment or in posttreatment (p < 0.05). Enzyme activities of SOD and CAT were restored by taurine pretreatment (p < 0.05), whereas posttreatment had less pronounced effects on these parameters. On the other hand, taurine treatment, before or after exposure, could exert only slight decreases in tissue Cr levels (p > 0.05). In view of the results, taurine seems to exert some beneficial effects against Cr(VI)-induced oxidative stress in liver tissue.     

Enhanced Anti-Diabetic Activity of a Combination of Chromium(III) Malate Complex and Propolis and its Acute Oral Toxicity Evaluation

In order to obtain the additional benefit of anti-diabetic activity and protective effects of liver injury for diabetes, the anti-diabetic effect and acute oral toxicity of a combination of chromium(III) malate complex (Cr(2)(LMA)(3)) and propolis were assessed. The anti-diabetic activity of the combination of the Cr(2)LMA(3) and propolis was compared with Cr(2)(LMA)(3) and propolis alone in alloxan-induced diabetic mice by daily oral gavage for a period of 2 weeks. Acute oral toxicity of the combination of the Cr(2)LMA(3) and propolis was tested using ICR mice at the dose of 1.0-5.0 g/kg body mass by a single oral gavage and observed for a period of 2 weeks. The results of the anti-diabetic activity of the combination from the aspects of blood glucose level, liver glycogen level, and the activities of aspartate transaminase, alanine transaminase, and alkaline phosphatase indicated that the increased anti-diabetic activity and the protective efficacy of liver injury for diabetes were observed. In acute toxicity study, LD(50) (median lethal dose) value for the combination was greater than 5.0 g/kg body mass. The combination of Cr(2)LMA(3) and propolis might represent the nutritional supplement with potential therapeutic value to control blood glucose and exhibit protective efficacy of liver injury for diabetes and non-toxicity in acute toxicity.     

Chromium picolinate attenuates hyperglycemia-induced oxidative stress in streptozotocin-induced diabetic rats

Chromium picolinate is advocated as an anti-diabetic agent for impaired glycemic control. It is a transition metal that exists in various oxidation states and may thereby act as a pro-oxidant. The present study has been designed to examine the effect of chromium picolinate supplementation on hyperglycemia-induced oxidative stress. Diabetes was induced in male Wistar rats by a single intraperitoneal injection of streptozotocin (50 mg/kg body weight) and chromium was administered orally as chromium picolinate (1 mg/kg body weight) daily for a period of four weeks after the induction of diabetes. As is characteristic of diabetic condition, hyperglycemia was associated with an increase in oxidative stress in liver in terms of increased lipid peroxidation and decreased glutathione levels. The activity of antioxidant enzymes like superoxide dismutase, catalase and glutathione reductase were significantly reduced in liver of diabetic animals. Levels of α-tocopherol and ascorbic acid were found to be considerably lower in plasma of diabetic rats. Chromium picolinate administration on the other hand was found to have beneficial effect in normalizing glucose levels, lipid peroxidation and antioxidant status. The results from the present study demonstrate potential of chromium picolinate to attenuate hyperglycemia-induced oxidative stress in experimental diabetes.     

Epidermal growth factor in serum, urine, submandibular glands and kidneys of diabetic mice

Levels of epidermal growth factor (EGF) in serum were significantly decreased in streptozotocin (STZ)-diabetic mice (446 +/- 168 pg/ml after 1 week and 423 +/- 52 after 4 weeks vs 766 +/- 162 pg/ml in controls, P.002 and less than .001. respectively) and in genetically diabetic ob/ob mice (455 +/- 285 vs 962 +/- 453 pg/ml in nondiabetic ob/+ controls, P.043). The urinary excretion of EGF was significantly increased in STZ mice (104 +/- 53 vs 51 +/- 23 ng/h, P.013) but unchanged in ob/ob mice (33 +/- 9 vs 45 +/- 16 ng/h, P.134). However, when expressed per mg creatinine it was decreased in both cases: in STZ mice to 680 +/- 250 ng/mg at 1 week and 684 +/- 211 at 4 weeks vs 1250 +/- 303 ng/mg in controls (P less than .01); and in the ob/ob mice to 552 +/- 117 vs 1237 +/- 300 ng/mg in ob/+ controls (P less than .01). EGF content of the submandibular glands of STZ mice remained unchanged at 1 week (13.1 +/- 2.9 vs 11.0 +/- 1.8 micrograms/mg protein, P.170) but dropped by 4 weeks (4.7 +/- 1.2 micrograms/mg, P less than .001); in the ob/ob mice it was less than 20% that of controls (2.1 +/- 0.8 vs 12.2 +/- 3.6 micrograms/mg protein). In kidneys, the EGF content was not altered in either ob/ob (524 +/- 50 vs 571 +/- 33 pg/mg protein) or STZ mice (652 +/- 183 vs 665 +/- 80 pg/mg). The preproEGF mRNA level in STZ-treated mice was reduced after 4 weeks in submandibular glands but not in kidneys. The results show that diabetes affects EGF production, utilization and/or excretion in mice and that kidneys are spared from suppression of EGF synthesis that is pronounced in the submandibular glands.     

The biomimetic [Cr3O(O2CCH2CH3)6(H2O)3]+ decreases plasma insulin, cholesterol, and triglycerides in healthy and type II diabetic rats but not type I diabetic rats

The in vivo effects of administration of the synthetic, functional biomimetic cation [Cr(3)O(O(2)CCH(2)CH(3))(6)(H(2)O)(3)](+) to healthy and type I and type II diabetic model rats are described. In contrast to current chromium-containing nutrition supplements, which only serve as sources of absorbable chromium, the trinuclear cation has been shown in in vitro assays to interact with the insulin receptor, activating its kinase activity, presumably by trapping the receptor in its active conformation. Thus, treatment of rats with the trinuclear cation would be expected to result in changes in lipid and carbohydrate metabolism related to insulin action. After 24 weeks of intravenous administration (0-20 micro g Cr/kg body mass), the cation results in a concentration-dependent lowering of levels of fasting blood plasma LDL cholesterol, total cholesterol, triglycerides, and insulin and of 2-h plasma insulin and glucose levels after a glucose challenge; these results confirm a previous 12-week study examining the effect of the synthetic cation on healthy rats and are in stark contrast to those of administration of other forms of Cr(III) to rats, which have no effect on these parameters. The cation has little, if any, effect on rats with STZ-induced diabetes (a type I diabetes model). However, Zucker obese rats (a model of the early stages of type II diabetes) after 24 weeks of supplementation (20 micro g/kg) have lower fasting plasma total, HDL, and LDL cholesterol, triglycerides, and insulin levels and lower 2-h plasma insulin levels. The lowering of plasma insulin concentrations with little effect on glucose concentrations suggests that the supplement increases insulin sensitivity.     

Superoxide formation and interaction with nitric oxide modulate systemic arterial pressure and renal function in salt-depleted dogs

To determine the role of superoxide (O(2)(-)) formation in the kidney during alterations in the renin-angiotensin system, we evaluated responses to the intra-arterial infusion of an O(2)(-) - scavenging agent, tempol, in the denervated kidney of anesthetized salt-depleted (SD, n=6) dogs and salt-replete (SR, n=6) dogs. As expected, basal plasma renin activity was higher in SD than in SR dogs (8.4 +/- 1.0 vs. 2.3 +/- 0.6 ng angiotensin 1/ml/hr). Interestingly, the basal level of urinary F(2)-isoprostanes excretion (marker for endogenous O(2)(-) activity) relative to creatinine (Cr) excretion was also significantly higher in SD compared to SR dogs (9.1 +/- 2.8 vs. 1.6 +/- 0.4 ng F(2)-isoprostanes/mg of Cr). There was a significant increase in renal blood flow (4.3 +/- 0.5 to 4.9 +/- 0.6 ml/min/g) and decreases in renal vascular resistance (38.2 +/- 5.8 to 33.2 +/- 4.7 mm Hg/ml/min/g) and mean systemic arterial pressure (148 +/- 6 to 112 +/- 10 mm Hg) in SD dogs but not in SR dogs during infusion of tempol at 1 mg/kg/min for 30 mins. Glomerular filtration rate and urinary sodium excretion (U(Na)V) did not change significantly during tempol infusion in both groups of dogs. Administration of the nitric oxide synthase inhibitor nitro-L-arginine (50 mug/kg/min) during tempol infusion caused a reduction in U(Na)V in SR dogs (47% +/- 12%) but did not cause a decrease in SD dogs. These data show that low salt intake enhances O(2)(-) activity that influences renal and systemic hemodynamics and thus may contribute to the regulation of arterial pressure in the salt-restricted state.