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.     

Oral administration of the biomimetic [Cr3O(O2CCH2CH3)6(H2O)3]+ increases insulin sensitivity and improves blood plasma variables in healthy and type 2 diabetic rats

The in vivo effects of gavage administration of the synthetic, functional biomimetic cation [Cr₃O(O₂CCH₂CH₃)₆(H₂O)₃]⁺ to healthy and type 2 diabetic model rats are described. After 24 weeks of treatment (0–1,000 g Cr/kg body mass) of healthy Sprague Dawley rats, the cation results in a lowering (P<0.05) of fasting blood plasma low-density lipoprotein (LDL) cholesterol, total cholesterol, triglycerides, and insulin levels and of 2-h plasma insulin and glucose concentrations after a glucose challenge. Zucker obese rats (a model of the early stages of type 2 diabetes) and Zucker diabetic fatty rats (a model for type 2 diabetes) after supplementation (1,000 g Cr/kg) have lower fasting plasma total, high-density lipoprotein, and LDL cholesterol, triglycerides, glycated hemoglobin, and insulin levels and lower 2-h plasma insulin levels in glucose tolerance tests. The lowering of plasma insulin concentrations with little effect on glucose concentrations suggests that the supplement increases insulin sensitivity. The cation after 12 and 22 or 24 weeks of administration lowers (P<0.05) fasting plasma glycated hemoglobin levels in the Zucker diabetic and Zucker obese rats, respectively, and thus can improve the glucose status of the diabetic models. The effects cannot be attributed to the propionate ligand.Supplementary material is available for this article at .An erratum to this article can be found at     

Long-Term Exposure to [Cr3O(O2CCH2CH3)6(H2O)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. [Cr₃O(O₂CCH₂CH₃)₆(H₂O)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.     

Comparison of the potential for developmental toxicity of prenatal exposure to two dietary chromium supplements, chromium picolinate and [Cr3O(O2CCH2CH3)(6(H2O)3]+, in mice

BACKGROUND: Chromium(III) is generally thought to be an essential trace element that allows for proper glucose metabolism. However, chromium(III) picolinate, Cr(pic)₃, a popular dietary supplement form of chromium, has been shown to be capable of generating hydroxyl radicals and oxidative DNA damage in rats. The cation [Cr₃O(O₂CCH₂CH₃)₆(H₂O)₃]⁺, Cr3, has been studied as an alternative supplemental source of chromium. It has been shown to increase insulin sensitivity and lower glycated hemoglobin levels in rats, making it attractive as a potential therapeutic treatment for gestational diabetes. To date, no studies have been published regarding the safety of Cr3 supplementation to a developing fetus. METHODS: From gestation days (GD) 6–17, mated CD‐1 female mice were fed diets delivering either 25 mg Cr/kg/day as Cr(pic)₃, 3.3 or 26 mg Cr/kg/day as Cr3, or the diet only to determine if Cr3 could cause developmental toxicity. Dams were sacrificed on GD 17, and their litters were examined for adverse effects. RESULTS: No signs of maternal toxicity were observed. No decrease in fetal weight or significantly increased incidence of skeletal defects was observed in the Cr3 or Cr(pic)₃ exposed fetuses compared to the controls. CONCLUSION: Maternal exposure to either Cr(pic)₃ or Cr3 at the dosages employed did not appear to cause deleterious effects to the developing offspring in mice. Birth Defects Res (Part B), 80:1–5, 2007. © 2007 Wiley‐Liss, Inc.     

The binding of trivalent chromium to low-molecular-weight chromium-binding substance (LMWCr) and the transfer of chromium from transferrin and chromium picolinate to LMWCr

A recent model for the role of chromium in insulin signaling requires that the oligopeptide low-molecular-weight chromium-binding substance (LMWCr) tightly bind four chromic ions before the oligopeptide obtains a conformation required for binding to the tyrosine kinase active site of the insulin receptor. To test this model, the chromium-binding constant of LMWCr was determined, and the ability of LMWCr to remove chromium from Cr2-transferrin and the nutritional supplement chromium picolinate, Cr(pic)3, was examined. These results are consistent with the model of the mode of action of LMWCr; a Hill study indicates the four chromic ions bind to apoLMWCr in a highly cooperative fashion (n =3.47) with a binding constant of 1.54x 10(21). Chromium is readily transferred from transferrin to apoLMWCr at near neutral pH. The results also suggest that reduction of the chromic center of Cr(pic)3 may be required for the supplement to release chromium; thus, release of chromium is related to a mechanism by which Cr(pic)3 may generate hydroxyl radicals in cells.     

High-dose chromium(III) supplementation has no effects on body mass and composition while altering plasma hormone and triglycerides concentrations

Chromium is generally believed to be an essential element and is often claimed to have value as a weight loss or muscle building agent. Recent studies in humans and rats have failed to demonstrate effects on body composition, although recent studies with pharmacological doses of the cation [Cr(III)₃O(O₂CCH₂CH₃)6(H₂O)₃]⁺ (or Cr3) (≤1 mg Cr/kg body mass) in rats have noted a trend toward body mass loss and fat mass loss. Thus, the effects of large gavage doses of Cr3 (1–10 mg Cr/kg) on body mass, organ mass, food intake, and blood plasma variables (insulin, glucose, leptin, cholesterol, and triglycerides) were examined over a 10-wk period using male Sprague-Dawley rats. No effects on body composition were noted, although Cr3 administration lowered (p<0.05) plasma insulin, leptin, and triglycerides concentrations. As Cr3 is absorbed greater than 10-fold better than commercially available nutritional supplements, the lack of an effect of the Cr(III) compound at these levels of administration clearly indicates that Cr(III) supplements do not have an effect on body composition at any reasonable dosage.     

Absorption of the biomimetic chromium cation triaqua-μ3-oxo-μ-hexapropionatotrichromium(III) in rats

The cation [Cr₃O(O₂CCH₂CH₃)₆(H₂O)₃]⁺ has been shown in vitro to mimic to the oligopeptide chromodulin’s ability to stimulate the tyrosine kinase activity of insulin receptor and shown in healthy and type 2 diabetic model rats to increase insulin sensitivity and decrease plasma total and low-density lipoprotein cholesterol and triglycerides concentrations. However, the degree to which the complex is absorbed after gavage administration to rats had not been previously determined. The biomimetic cation at nutritional supplement levels is absorbed with greater than 60% efficiency, and at pharmacological levels, it is absorbed with greater than 40% efficiency, an order of magnitude greater absorption than that of CrCl₃, Cr nicotinate, or Cr picolinate, currently marketed nutritional supplements. The difference in degree of absorption is readily explained by the stability and solubility of the cation.     

Isolation and Characterization of Low-Molecular-Weight Chromium-binding Substance (LMWCr) from Chicken Liver

Chromodulin (also known as low-molecular-weight chromium-binding substance, LMWCr) is a chromium-binding oligopeptide proposed to play a role in insulin signaling and chromium transport in mammals. This laboratory has isolated and purified this material from a non-mammalian source, an avian. Spectroscopic and physical characterization of the isolated material suggests the material is an oligopeptide with a multinuclear chromium assembly bridged via asparatate and glutamate residues very similar to its mammalian counterparts. The isolated material also possesses a biological activity similar to other LMWCr isolates.     

Microsolvation effect and hydrogen-bonding pattern of taurine-water TA-(H2O)n (n = 1-3) complexes

The microsolvation of taurine (TA) with one, two or three water molecules was investigated by a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen bond (H-bond) interaction characteristics in TA-(H₂O)_n (n = 1–3) complexes. The results showed that the intramolecular H-bond formed between the hydroxyl and the N atom of TA are retained in most TA-(H₂O)_n (n = 1–3) complexes, and are strengthened via cooperative effects among multiple H-bonds from n = 1–3. A trend of proton transformation exists from the hydroxyl to the N atom, which finally results in the cleavage of the origin intramolecular H-bond and the formation of a new intramolecular H-bond between the amino and the O atom of TA. Therefore, the most stable TA-(H₂O)₃ complex becomes a zwitterionic complex rather than a neutral type. A many-body interaction analysis showed that the major contributors to the binding energies for complexes are the two-body energies, while three-body energies and relaxation energies make significant contributions to the binding energies for some complexes, whereas the four-body energies are too small to be significant.     

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.     

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.     

The relationship of chromium to the glucose tolerance factor. II

After incubation with CrCl₃·6H₂O (or⁵¹CrCl₃·6H₂O) for 25 days, a sterile growth medium, whole yeast cells harvested after growth on a similar chromium-containing medium for the same period, and the spent growth medium remaining after removal of the yeast were each subjected to the separation procedure reported previously [S.J. Haylock, P.D. Buckley and L.F. Blackwell, J. Inorg. Biochem., in press]. The results obtained showed that most of the eleven chromium-containing fractions isolated previously were artifacts formed as a result of direct reaction between the chromium and components of the medium. An anionic complex (which was the major chromium-containing fraction isolated) was identified as a chromium-glucose complex, but one possessing no biological activity. The biologically active chromium-containing fractions (P-3 and P-4) that were only present after yeast had been grown in the medium were further purified, however, during the purification steps, the biological activity was cleanly separated from the chromium material for both P-3 and P-4. Fraction P-4 was subsequently shown to consist of approximately 90% tyramine, but pure tyramine was not active in the yeast bioassay. Although the structure of the glucose tolerance factor-active component in fraction P-3 could not be determined due to the presence of high concentrations of salt that could not be separated on gel filtration columns, the results show that the glucose tolerance factor from brewer's yeast can no longer be regarded as a chromium complex.     

trans-(NH3)2PtII-modified deoxyoligonucleotides as potential antisense agents: cross-linking reactions between two 12-mers

 An approach is presented which probes the possible use of trans-[(NH₃)₂PtCl]⁺-modified deoxyoligonucleotides in the antisense strategy. It consists of (1) the selective platination of an oligonucleotide containing 11 pyrimidine (T, C) bases as well as a single guanine (G) as a Pt-anchoring group at the 5′-end to give trans-[(NH₃)₂Pt{5′-d(G^N7T₂C₂T₂C₂T₂C}Cl]^10– 1 ("antisense strand") and (2) subsequent hybridization with the purine 12-mer 5′-d(GA₂G₂A₂G₂A₂G)^11– ("sense strand"). According to HPLC, three major species 2–4 are formed during reaction (2), all of which are cross-linking adducts between 1 and the sense strand, as confirmed by ESI MS and melting temperature measurements. Only for the major product 3 can a structure be proposed on the basis of 1D and 2D NMR spectra. According to these, G₁ of the antisense strand is cross-linked with G₂₀ via trans-(NH₃)₂Pt^II. The complementary overhangs of the duplex represent "sticky ends" and are, in principle, capable of associating into multimers of the duplex. Received: 29 March 1999 / Accepted: 26 July 1999     

Reactivity of an extremenly sterically crowded monofunctional Pt complex, [Pt(1-MeC-N3)3(H2O)]2+ (1-MeC=1-methylcytosine), toward model nucleobases and selectivity toward guanine in single- and double-stranded deoxyoligonucleotides

 Reactions of [Pt(1-MeC-N3)₃Cl]NO₃ (1-MeC-N3=1-methylcytosine, bound to Pt via N3) and the respective aqua species [Pt(1-MeC-N3)₃(H₂O)]²⁺ with the model nucleobases 9-ethylguanine (9-EtGH), 9-methyladenine (9-MeA), single-stranded 5′d(T₃GT₃), and double-stranded [5′d(GAGA₂GCT₂CTC)]₂ have been studied in solution by means of ¹H NMR spectroscopy, HPLC, and electrospray ionization mass spectrometry. Reactions are generally slow, in particular with the chloro species, and guanine is the only reactive base in the oligonucleotides. However, unlike (dien)Pt^II, which binds randomly to the guanines in the ds dodecamer, (1-MeC-N3)₃Pt^II binds selectively to the terminal guanine only, probably because base fraying takes place at the duplex ends. The X-ray crystal structures of [Pt(1-MeC-N3)₃(9-EtG-N7)]ClO₄·8H₂O (1b) and of [Pt(1-MeC-N3)₃(9-MeA-N7)](ClO₄)₂·0.5H₂O as well as NMR spectroscopic studies of [Pt(1-MeC-N3)₃(9-EtGH-N7)] (NO₃)₂·H₂O (1a) are reported. The tetrakis(nucleobase) complexes adopt a head-tail-head orientation of the three 1-MeC bases and an orientation of the fourth base (purine) that permits a maximum of intracomplex H bonds between exocyclic groups. As far as the guanine adduct (1a, 1b) is concerned, relative orientations of the four bases are identical in the model and in the oligonucleotide adduct. Received: 19 June 1998 / Accepted: 1 October 1998     

Chromium(III)-insulin derivatives and their implication in glucose metabolism

Insulin has been reacted with five chromium(III) complexes that are capable of relatively facile substitution of aquo ligands. The new Cr(III) insulin derivatives have been characterized by means of electronic and infrared spectra, and evidence for major changes in the protein structure, including the state of aggregation, has been presented. Supporting evidence for the arguments favoring the beneficiary role of chromium(III) in glucose metabolism has been obtained using in vivo studies, and it has been shown that insulin derived with Cr(salen) (H2O)2+ is capable of reversing the blood sugar, serum cholesterol, and phospholipids levels to those of normal rats. The results emphasize the dependence of biopotency on the structure of Cr(III) complexes used for derivation of insulin and discount the postulates that Cr(III) serves to assemble insulin and receptor units through metal-sulphur bonding. The influence of Cr(III) on the structural stability and state of aggregation of insulin and their possible role in glucose metabolism is discussed.     

Lipopolysaccharide (LPS) induction of nitric oxide synthase-2 and cyclooxygenase-2 is impaired in fructose overloaded rats

AimsFructose (F) overload in rats induces metabolic dysfunctions that resemble the human metabolic syndrome. In this paper, we aimed to investigate the response of F overload rats to lipopolysaccharide (LPS) challenge in terms of nitric oxide (NO) production and prostanoids (PR) release.Main methodsNO blood steady-state concentration was monitored through the detection of nitrosyl–hemoglobin complexes (NO–Hb) by electronic spin resonance. Production of 6-keto PGF₁α, PGE₂, PGF₂α and TXB₂ was measured in aorta and mesenteric beds by HPLC. Western blot analysis was used to examine the changes in the expression levels of NOS-2 and COX-2 in aorta.Key findingsOur results showed that increases in NO circulating steady-state concentration and PR production by aorta and mesenteric beds 6 h after LPS administration were significantly attenuated in F overload rats with respect to control animals. Oxidative stress parameters were equally affected in the presence or absence of the F treatment. Aorta protein levels of NOS-2 and COX-2, two enzymes inducible by LPS, were significantly lower in F overload rats with respect to control rats at the end of the treatment (?39% and ?61% for NOS-2 and COX-2 respectively).SignificanceThese results suggest that the metabolic alterations established by 15 weeks of F overload should affect the response to LPS challenge due to an attenuation in the induction of NOS-2 and COX-2. This effect would be one of the components contributing to abnormalities in the course of the inflammatory response in other conditions associated to insulin resistance, such as diabetes.     

The vanadyl (VO2+) chelate bis(acetylacetonato)oxovanadium(IV) potentiates tyrosine phosphorylation of the insulin receptor

We have compared the insulin-like activity of bis(acetylacetonato)oxovanadium(IV) [VO(acac)₂], bis(maltolato)oxovanadium(IV) [VO(malto)₂], and bis(1-N-oxide-pyridine-2-thiolato)oxovanadium(IV) [VO(OPT)₂] in differentiated 3T3-L1 adipocytes. The insulin-like influence of VO(malto)₂ and VO(OPT)₂ was decreased compared with that of VO(acac)₂. Also, serum albumin enhanced the insulin-like activity of all three chelates more than serum transferrin. Each of the three VO²⁺ chelates increased the tyrosine phosphorylation of proteins in response to insulin, including the β-subunit of the insulin receptor (IRβ) and the insulin receptor substrate-1 (IRS1). However, VO(acac)₂ exhibited the greatest synergism with insulin and was therefore further investigated. Treatment of 3T3-L1 adipocytes with 0.25 mM VO(acac)₂ in the presence of 0.25 mM serum albumin synergistically increased glycogen accumulation stimulated by 0.1 and 1 nM insulin, and increased the phosphorylation of IRβ, IRS1, protein kinase B, and glycogen synthase kinase-3β. Wortmannin suppressed all of these classical insulin-signaling activities exerted by VO(acac)₂ or insulin, except for tyrosine phosphorylation of IRβ and IRS1. Additionally, VO(acac)₂ enhanced insulin signaling and metabolic action in insulin-resistant 3T3-L1 adipocytes. Cumulatively, these results provide evidence that VO(acac)₂ exerts its insulin-enhancing properties by directly potentiating the tyrosine phosphorylation of the insulin receptor, resulting in the initiation of insulin metabolic signaling cascades in 3T3-L1 adipocytes.     

Kinetics and DFT studies on the reaction of copper(II) complexes and H2O2

Copper(II) complexes supported by bulky tridentate ligands L1^H (N,N-bis(2-quinolylmethyl)-2-phenylethylamine) and L1^Ph (N,N-bis(2-quinolylmethyl)-2,2-diphenylethylamine) have been prepared and their crystal structures as well as some physicochemical properties have been explored. Each complex exhibits a square pyramidal structure containing a coordinated solvent molecule at an equatorial position and a weakly coordinated counter anion (or water) at an axial position. The copper(II) complexes reacted readily with H₂O₂ at a low temperature to give mononuclear hydroperoxo copper(II) complexes. Kinetics and DFT studies have suggested that, in the initial stage of the reaction, deprotonated hydrogen peroxide attacks the cupric ion, presumably at the axial position, to give a hydroperoxo copper(II) complex retaining the coordinated solvent molecule (H ^R ·S). H ^R ·S then loses the solvent to give a tetragonal copper(II)-hydroperoxo complex (H ^R ), in which the –OOH group may occupy an equatorial position. The copper(II)–hydroperoxo complex H ^R exhibits a relatively high O–O bond stretching vibration at 900 cm⁻¹ compared to other previously reported examples.Electronic Supplementary Material Supplementary material is available for this article at     

Differential Stability of the Triple Helix of (Pro-Pro-Gly)10 in H2O and D2O: Thermodynamic and Structural Explanations

Abstract

(Pro-Pro-Gly)₁₀ [(PPG₁₀)], a collagen-like polypeptide, forms a triple-helical, polyproline-II structure in aqueous solution at temperatures somewhat lower than physiological, with a melting temperature of 24.5°C. In this article, we present circular dichroism spectra that demonstrate an increase of the melting temperature with the addition of increasing amounts of D₂O to an H₂O solution of (PPG)₁₀, with the melting temperature reaching 40°C in pure D₂O. A thermodynamic analysis of the data demonstrates that this result is due to an increasing enthalphy of unfolding in D₂O vs. H₂O. To provide a theoretical explanation for this result, we have used a model for hydration of (PPG)₁₀ that we developed previously, in which inter-chain water bridges are formed between sterically crowded waters and peptide bond carbonyls. Energy minimizations were performed upon this model using hydrogen bond parameters for water, and altered hydrogen bond parameters that reproduced the differences in carbonyl oxygen-water oxygen distances found in small-molecule crystal structures containing oxygen-oxygen hydrogen bonds between organic molecules and H₂O or D₂O. It was found that using hydrogen bond parameters that reproduced the distance typical of hydrogen bonds to D₂O resulted in a significant lowering of the potential energy of hydrated (PPG)₁₀. This lowering of the energy involved energetic terms that were only indirectly related to the altered hydrogen bond parameters, and were therefore not artifactual; the intra-(PPG₁₀) energy, plus the water-(PPG₁₀) van der Waals energy (not including hydrogen bond interactions), were lowered enough to qualitatively account for the lower enthalpy of the triple-helical conformation, relative to the unfolded state, in D₂O vs. H₂O. This result indicates that the geometry of the carbonyl-D₂O hydrogen bonds allows formation of good hydrogen bonds without making as much of an energetic sacrifice from other factors as in the case of hydration by H₂O.     

Chromium activates glucose transporter 4 trafficking and enhances insulin-stimulated glucose transport in 3T3-L1 adipocytes via a cholesterol-dependent mechanism

Evidence suggests that chromium supplementation may alleviate symptoms associated with diabetes, such as high blood glucose and lipid abnormalities, yet a molecular mechanism remains unclear. Here, we report that trivalent chromium in the chloride (CrCl3) or picolinate (CrPic) salt forms mobilize the glucose transporter, GLUT4, to the plasma membrane in 3T3-L1 adipocytes. Concomitant with an increase in GLUT4 at the plasma membrane, insulin-stimulated glucose transport was enhanced by chromium treatment. In contrast, the chromium-mobilized pool of transporters was not active in the absence of insulin. Microscopic analysis of an exofacially Myc-tagged enhanced green fluorescent protein-GLUT4 construct revealed that the chromium-induced accumulation of GLUT4-containing vesicles occurred adjacent to the inner cell surface membrane. With insulin these transporters physically incorporated into the plasma membrane. Regulation of GLUT4 translocation by chromium did not involve known insulin signaling proteins such as the insulin receptor, insulin receptor substrate-1, phosphatidylinositol 3-kinase, and Akt. Consistent with a reported effect of chromium on increasing membrane fluidity, we found that chromium treatment decreased plasma membrane cholesterol. Interestingly, cholesterol add-back to the plasma membrane prevented the beneficial effect of chromium on both GLUT4 mobilization and insulin-stimulated glucose transport. Furthermore, chromium action was absent in methyl-beta-cyclodextrin-pretreated cells already displaying reduced plasma membrane cholesterol and increased GLUT4 translocation. Together, these data reveal a novel mechanism by which chromium may enhance GLUT4 trafficking and insulin-stimulated glucose transport. Moreover, these findings at the level of the cell are consistent with in vivo observations of improved glucose tolerance and decreased circulating cholesterol levels after chromium supplementation.