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.     

Molecular basis of chromium insulin interactions

The physiological role of chromium (III) in diabetes mellitus has been an area of inconclusive research for many years. It is of great interest to explore the interactions made by chromium (III) to get a better insight into their role in glucose metabolism. To understand the molecular basis of chromium action we have carried out spectroscopic and crystallographic investigations on the binding of Cr(III)-Salen with insulin, as Cr(III)-Salen is reported to result in the enhancement of insulin activity. The Cr(III)-insulin complex formation has been characterised at two pHs, viz., 3.5 and 9.0 using UV-Vis and fluorescence studies. The crystallographic analysis of Cr(III)-Salen soaked cubic insulin crystals, using anomalous difference Fourier method, revealed B21 Glu to be the binding site for chromium (III).     

Combined effect of vanadium(V) and chromium(III) on lipid peroxidation in liver and kidney of rats

Since chromium(III) was demonstrated to have antioxidative action, we have decided to study the effect of this element on V-induced LPO in liver and kidney of rats. Outbred 2-month-old, albino male Wistar rats received daily, for a period of 12 weeks: group I (control), deionized water to drink; group II, sodium metavanadate (SMV) solution at a concentration of 0.100mgV/mL; group III, chromium chloride (CC) solution at a concentration of 0.004mgCr/mL and group IV, SMV-CC solution at a concentration of 0.100mgV and 0.004mgCr/mL. The particular experimental groups took up with drinking water about 8.6mgV/kg b.w./24h (group II), 0.4mgCr/kg b.w./24h (group III), 9mgV and 0.36mgCr/kg b.w./24h (group IV). The V- or Cr-treated groups had higher concentrations of these two elements in liver and kidney compared to the controls. The administration of vanadium alone caused a significant decrease in fluid intake and in body weight gain compared to the controls. In liver supernatants obtained from all tested rats a statistically significant increase in MDA concentration was demonstrated in spontaneous LPO in comparison with the control rats. Moreover, in rats intoxicated with vanadium alone a statistically significant increase in liver MDA level was observed in the presence of 100microM NaVO(3). Instead, in supernatants of liver received from rats treated with chromium alone, a statistically significant increase in MDA concentration in comparison with the controls was found in the presence of 400microM NaVO(3). In kidney supernatants obtained from rats treated with chromium alone, a statistically significant increase in lipid peroxidation was shown in the presence of 30microM FeSO(4) and 400microM NaVO(3). These results show that the tested doses of vanadium(V) and chromium(III) ingested by rats with their drinking water caused significant alterations in internal organs, especially in liver. Under the conditions of our experiment, Cr(III) did not demonstrate antioxidant action, it rather had an oxidant effect.     

Chromate metabolism in liver microsomes

The carcinogenicity and mutagenicity of various chromium compounds have been found to be markedly dependent on the oxidation state of the metal. The carcinogen chromate was reduced to chromium(III) by rat liver microsomes in vitro. Metabolism of chromate by microsomal enzymes occurred only in the presence of either NADPH or NADH as cofactor. The chromium(III) generated upon metabolism formed a complex with the NADP⁺ cofactor. Significant binding of chromium to DNA occurred only when chromate was incubated in the presence of microsomes and NADPH. Specific inhibitors of the mixed function oxidase enzymes, 2′-AMP, metyrapone, and carbon monoxide, inhibited the rate of reduction of chromate by microsomes and NADPH. The possible relationship of metabolism of chromate and its interaction with nucleic acids to its carcinogenicity and mutagenicity is discussed.     

Heavy metals biosorption from aqueous solution by simple eucaryotic organisms

Biosorption of cadmium and chromium (III) ions by means of selected yeast species has been estimated. Kinetics and equilibrium measurements have shown the reliable efficiency of both metals removal for Candida tropicalis. The influence of pH and ionic strength on biosorption process has been examined as well. For both metals the adsorption isotherms have been presented. The equilibrium of chromium (III) sorption has appeared compatible to Langmiur model and the maximum sorption capacity has been determined.     

Chromium(III) hydrolytic oligomers: their relevance to protein binding

The nature of chromium(III) complexes has been found to show a profound influence in its interaction with collagen. The hydrothermal stability of rat tail tendon (RTT) fibres treated with dimeric, trimeric and tetrameric species of chromium(III) has been found to be 102, 87 and 68 degrees C, while that of native RTT is 62 degrees C. This shows that the efficiency of crosslinking of collagen by chromium(III) species is dimeric > trimeric > tetrameric. This order of stabilisation is again confirmed by cyanogen bromide (CNBr) cleavage of RTT collagen treated with dimeric, trimeric and tetrameric chromium(III) species. CNBr has been found to cleave the collagen treated with tetrameric chromium(III) species extensively. On the other hand, dimer-treated collagen does not undergo any cleavage on CNBr treatment. The equilibrium constants for the reaction of a nucleophile like NCS(-) to the dimeric, trimeric and tetrameric species of chromium(III) have been found to be 15.7+/-0.1, 14.6+/-0.1 and 1.2+/-0.1 M(-1), respectively. These equilibrium constant values reflect the relative thermodynamic stability of the chromium(III) species-nucleophile complex. The low stabilising effect of the tetrameric species can be traced to its low thermodynamic affinity for nucleophiles.     

The action of chromium(III) in fixation of animal tissues

Summary Chromic salts have been studied as fixatives of mammalian tissues for light microscopy, and the binding of the metal has been examined histochemically. Tissues bind chromium(III) from aqueous solutions less acid than pH 2.5; the metal attaches mainly to collagen and basement membranes. Solutions containing chromium(III) as the only active ingredient cannot be used as fixatives because they destroy cytoplasm and cause great structural distortion. When mixed with other fixative agents, however, chromic salts can bring about considerable improvement in structural preservation. In aqueous mixtures more acid than pH 2, and in aqueous-methanolic solutions in the pH range 4.0–5.3, a chromic salt provides only a nonspecific osmotic effect: little or no metal is bound to the tissue, and an aluminium or a sodium salt can be effectively substituted. In less acid (pH 2.3–3.2) aqueous mixtures, the beneficial action of chromium(III) cannot be imitated by aluminium or sodium ions.Chromium(III) forms coordinate bonds that cross-link ionized carboxyl groups of macromolecules. The reaction occurs so slowly that such cross-links can internally strengthen a tissue only after the structure has been stabilized by rapidly acting fixative agents. Thus, a valuable future use of chromic salts may be in a post-fixation treatment to protect specimens against the adverse effects of embedding in paraffin wax. Chromium(III) might also be useful for enhancing the opacity of collagen fibrils in electron microscopy.Address until 30 June 1986: Department of Anatomy and Cell Biology, University of Sheffield, Sheffield, S10 2TN, UK     

Stabilization of chromium(V) species in bovine serum albumin adduct

A detailed investigation of molecular interactions of the protein bovine serum albumin (BSA) with potassium dichromate has been made. Compelling evidence for the formation of a relatively stable Cr(V) species which decays only slowly to afford Cr(III) products has been obtained. The resulting final chromium(III) product mediates in cross-linking of BSA. The implications of the formation of a relatively stable chromium(V) as well as chromium(III)-mediated cross-links in the marker protein are discussed in the context of the metal ion-induced biotoxicity.     

Spectroscopic markers of the T<-->R quaternary transition in human hemoglobin

In this work, we use a sol-gel protocol to trap and compare the R and T quaternary states of both the deoxygenated (deoxyHb) and carbonmonoxide (HbCO) derivatives of human hemoglobin. The near infrared optical absorption band III and the infrared CO stretching band are used to detect the effect of quaternary structure on the spectral properties of deoxyHb and HbCO; comparison with myoglobin allows for an assessment of tertiary and quaternary contributions to the measured band shifts. The R<-->T transition is shown to cause a blue shift of the band III by approximately 35 cm(-1) for deoxyHb and a red shift of the CO stretching band by only approximately 0.3 cm(-1) for HbCO. This clearly shows that quaternary structure changes are transmitted to the heme pocket and that effects on deoxyHb are much larger than on HbCO, at least as far as the band energies are concerned. Experiments performed in the ample temperature interval of 300-10K show that the above quaternary structure effects are "static" and do not influence the dynamic properties of the heme pocket, at least as probed by the temperature dependence of band III and of the CO stretching band. The availability of quaternary structure sensitive spectroscopic markers and the quantitative measurement of the quaternary structure contribution to band shifts will be of considerable help in the analysis of flash-photolysis experiments on hemoglobin. Moreover, it will enable one to characterize the dynamic properties of functionally relevant hemoglobin intermediates and to study the kinetics of both the T-->R and R-->T quaternary transitions through time-resolved spectroscopy.     

Mass Spectrometric and Spectroscopic Studies of the Nutritional Supplement Chromium(III) Nicotinate

Despite chromium nicotinate’s popular use as a chromium nutritional supplement, the structure and composition of chromium nicotinate have only been poorly described. As solid chromium nicotinate is intractable, being insoluble or unstable in common solvents, studies on the solid have been limited, and studies of the solution from which the “compound” precipitates have additionally provided little additional data. The results of mass spectrometric and spectroscopic investigations designed to further elucidate the structure and composition of chromium nicotinate are described. The results demonstrated that the three common methods for producing “chromium nicotinate” all yield different compounds, all of which are polymers of Cr(III), oxygen-bound nicotinate, hydroxide, and water. Implications for interpreting results of nutritional studies of “chromium nicotinate” are discussed.     

Fluorescence resonance energy transfer from tryptophan to a chromium(III) complex accompanied by non-specific cleavage of albumin: a step forward towards the development of a novel photoprotease

A chromium(III) complex, transdiaqua [N, N'-propylenebis(salicylideneimino)chromium(III)]perchlorate ([Cr(salprn)(H2O)(2)]ClO(4)) in the presence of sodium azide and upon photoexcitation was found to bring about non-selective cleavage of bovine serum albumin (BSA). Electron paramagnetic resonance (EPR) evidence has been obtained for the formation of a Cr(V) species upon photolysis of a solution containing the chromium(III) complex and sodium azide. This Cr(V) species non-selectively cleaves BSA. The fluorescence excitation spectrum of BSA-[Cr(salprn)(H2O)(2)]+ adduct showed a band at lambda(max)(ex) nm due to charge transfer transition of the chromium(III) complex as well as a prominent band at 290 nm attributable to tryptophan absorption. This indicated an efficient Forster type fluorescence energy transfer (FRET) from the tryptophan residues to the chromium(III) complex indicating that the Cr(III) complex binds in the vicinity of the tryptophan residue.     

Interaction of chromium(III) complex of chiral binaphthyl tetradentate ligand with DNA

Since conformation of the molecule plays a vital role in the activity of drug, we have investigated the DNA interaction of a chromium(III) complex with ligands in two conformations. Chromium(III) complexes derived from chiral binaphthyl Schiff base ligands, viz. R- and S-2,2'-bis(salicylideneamino) 1,1'-binaphthyl, have been synthesized and characterized by mass, IR, and electronic spectra. The interaction of these R- and S-binaphthyl Schiff base chromium(III) complexes with CT-DNA was investigated with the goal of examining whether the chirality has an influence on the chromium(III)-DNA binding properties. The difference in chirality of the ligand did not show any striking difference in binding properties. The binding constants for R and S conformers were estimated to be 18 (+/-0.4) x 10(3) and 9.4 (+/-0.3) x 10(3) M(-1), respectively, through spectroscopic titrations. All the experimental results are suggestive that both the isomers are DNA groove binders. The results of steady-state as well as time-resolved fluorescence experiments, however, suggest that the R conformer has restricted mobility when bound to DNA because it is more deeply buried in the groove of DNA compared to the S isomer.     

Effect of Rhamnolipids on Chromium-Contaminated Kaolinite

Hexavalent chromium Cr(VI) is a common environmental pollutant that is treated by its reduction to the trivalent form Cr(III). The latter can be re-oxidized to the toxic form, Cr(VI), under specific conditions. A study was conducted on the removal of Cr(III) to eliminate the hazard imposed by its presence in soil as there has been some evidence that organic compounds can decrease its sorption. The effect of addition of negatively-charged biosurfactants (rhamnolipids) on chromium contaminated kaolinite was studied. Results showed that the rhamnolipids have the capability of extracting 25% portion of the stable form of chromium, Cr(III), from the kaolinite, under optimal conditions. The removal of hexavalent chromium was also enhanced compared to water by a factor of 2 using a solution of rhamnolipids. Results from the sequential extraction procedure showed that rhamnolipids remove Cr(III) mainly from the carbonate and oxide/hydroxide portions of the kaolinite. The rhamnolipids had also the capability of reducing close to 100% of the extracted Cr(VI) to Cr(III) over a period of 24 days. This study indicated that rhamnolipids could be beneficial for the removal or long–term conversion of chromium Cr(VI) to Cr(III).     

A study of the interaction of Cr(III) complexes and their selective binding with B-DNA: a molecular modeling approach

Molecular modeling and energy minimisation calculations have been used to investigate the interaction of chromium(III) complexes in different ligand environments with various sequences of B-DNA. The complexes are [Cr(salen)(H(2)O)(2)](+); salen denotes 1, 2 bis-salicylideneaminoethane, [Cr(salprn)(H(2)O)(2)](+); salprn denotes 1, 3 bis- salicylideneaminopropane, [Cr(phen)(3)](3+); phen denotes 1, 10 phenanthroline and [Cr(en)(3)](3+); en denotes ethylenediamine. All the chromium(III) complexes are interacted with the minor groove and major groove of d(AT)(12), d(CGCGAATTCGCG)(2) and d(GC)(12) sequences of DNA. The binding energy and hydrogen bond parameters of DNA-Cr complex adduct in both the groove have been determined using molecular mechanics approach. The binding energy and formation of hydrogen bonds between chromium(III) complex and DNA has shown that all complexes of chromium(III) prefer minor groove interaction as the favourable binding mode.     

Complexes of iron and cobalt tetrasulfonated phthalocyanines with apocytochrome c

Artificial cytochromes c have been prepared with Fe(III) and Co(III) tetrasulfonated phthalocyanines in place of heme. Their structure and properties have been investigated by difference spectroscopy, CD, epr, electrophoresis, molecular weight estimation, and potentiometric measurements. The visible absorption spectra show the main peak at 650 nm for the iron compound 685 nm for the cobalt one. It is shown by CD experiments that incorporation of Fe(III)L or Co(III)L into apocytochrome c markedly increases helical content of the protein. Its conformation is, however, significantly altered as compared with the native cytochrome c. The epr and spectroscopic data show that the iron and cobalt phthalocyanine models represent the low spin species with the metal ions in trivalent state. Electrophoresis and molecular weight estimation indicate these complexes to be monomers. Both phthalocyanine complexes have not affinity for additional ligands characteristic for hemoglobin. They react, however, with CO, NO, and CN- when they are reduced with dithionite. Moreover, Co(II)L-apocyt c is able to combine with oxygen suggesting a structural feature in common with the oxygen-carrying heme proteins. Iron(II) complex in the same conditions is oxidized directly to the ferric state. The half-reduction potentials of Fe(III)L-apocyt c and Co(III)L-apocyt c are +374 mV and +320 mV, respectively. These complexes are reduced by cytochrome c and cytochrome c reductase (cytochrome bc1).     

Chromium removal from a real tanning effluent by autochthonous and allochthonous fungi

Heavy metals represent an important ecological and health hazard due to their toxic effects and their accumulation throughout the food chain. Conventional techniques commonly applied to recover chromium from tanning wastewaters have several disadvantages whereas biosorption has good metal removal performance from large volume of effluents. To date most studies about chromium biosorption have been performed on simulated effluents bypassing the problems due to organic or inorganic ligands present in real industrial wastewaters that may sequestrate the Cr(III) ions. In the present study a tanning effluent was characterized from a mycological point of view and different fungal biomasses were tested for the removal of Cr(III) from the same tanning effluent in which, after the conventional treatments, Cr(III) amount was very low but not enough to guarantee the good quality of the receptor water river. The experiments gave rise to promising results with a percentage of removed Cr(III) up to 40%. Moreover, to elucidate the mechanisms involved in biosorption process, the same biomasses were tested for Cr(III) removal from synthetic aqueous solutions at different Cr(III) concentrations.     

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.     

Proton nuclear magnetic resonance studies of hemoglobin Malm?: implications of mutations at homologous positions of the alpha and beta chains.

The abnormal human hemoglobin Malm? (beta97FG4 His leads to Gln) has been studied and its properties are compared with those of normal adult hemoglobin A. The data presented here show that the ring-current shifted proton resonances of both HbCO and HbO2 Malm? are very different from the corresponding forms of Hb A. The hyperfine shifted proton resonances of deoxy-Hb Malm? do not differ drastically from those of deoxy-Hb A. This result, together with the finding that the exchangeable proton resonances of the deoxy form of the two hemoglobins are similar, suggests that unliganded Hb Malm? can assume a deoxy-like quaternary structure both in the absence and presence of organic phosphates We have also compared the properties of Hb Malm? with those of Hb Chesapeake (alpha92FG4 Arg leads to Leu). This allows us to study the properties of two abnormal human hemoglobins with mutations at homologous positions of the alpha and beta chains in the three-dimenstional structure of the hemoglobin molecule. Our present results suggest that the mutaion at betaFG4 has its greatest effect on the teritiary structure of the heme pocket of the liganded forms of the hemoglobin while the mutation at alphaFG4 alters the deoxy structure of the hemoglogin molecule but does not alter the teriary structure of the heme pockets of the liganded form of the hemoglobin molecule. Both hemoglobins undergo a transition from the deoxy (T) to the oxy (R) quaternary structure upon ligation. The abnormally high oxygen affinities and low cooperativities of these two hemoglobins must therefore be due to either the structural differences which we have observed and/or to an altered transition between the T and R structures.     

Altered expression of HES-1, BETA2/NeuroD, and PDX-1 is involved in impaired insulin synthesis induced by glucocorticoids in HIT-T15 cells

Rat tail tendon (RTT) collagen has been reacted with a homologous series of chromium(III) complexes viz., (H2O)(4)Cr(OH)(2)Cr(H2O)(4+)(4) 1 (dimer), Cr(3)(OH)(4)(H2O)(5+)(9) 2 (trimer), and Cr(4)(OH)(4)(O2)(H2O)(4+)(12) 3 (tetramer), and the structural alterations brought about by these complexes have been investigated through atomic force microscopy (AFM) and circular dichroism (CD) studies. Examination of Cr(III)-treated tendons using AFM revealed changes in the D-periodicity of collagen, which may arise due to differences in the topological distribution of various Cr(III) complexes. Evidence for organisation of monomeric collagen into quarter staggered fibrils in the presence of Cr(III) dimer, 1, has been obtained. The quaternary structural changes induced by chromium in the protein have been correlated to the conformational changes of collagen in the absence of denaturation.     

微生物铬转化和抗性机制与生物修复研究进展

铬(Chromium,Cr)是过渡金属元素,在自然界中以六价[CrO_4~(2-),Cr_2O_7~(2-),Cr(Ⅵ)]和三价[Cr(OH)_3,Cr(Ⅲ)]为主。很多微生物在长期铬胁迫的条件下,进化出了一系列铬转化和抗性机制。微生物对铬的转化包括Cr(Ⅵ)的还原和Cr(Ⅲ)的氧化。微生物的Cr(Ⅵ)还原可以将毒性强的六价铬转化为毒性弱或无毒的三价铬,这类微生物有较强的土壤和水体铬污染治理潜力。Cr(Ⅲ)的氧化也在铬的生物地球化学循环过程中起着至关重要的作用。除了Cr(Ⅵ)的还原,微生物对铬的抗性机制还有:(1)减少摄入;(2)外排;(3)清除胞内氧化压力;(4)DNA修复。本文主要介绍微生物的铬转化和抗性机制,以及其在铬污染生物修复中应用的最新研究进展。