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PubMed2004

In vitro Ca-P precipitation on biodegradable thermoplastic composite of poly(epsilon-caprolactone-co-DL-lactide) and bioactive glass (S53P4).

Bioactive properties of composites containing poly(epsilon-caprolactone-co-DL-lactide) with molar ratio 96/4 and bioactive glass (BAG), S53P4, were tested in vitro. The glass content in the tested materials was 40, 60 or 70 wt%, and two granule size ranges (<45 and 90-315 microm) were used. The composites were analysed for their apatite-forming ability. This was determined as a function of time by the dissolution pattern of Si and Ca ions and structural changes on the specimen surfaces. Composite specimens were immersed in simulated body fluid at 37 degrees C for up to 6 months. The changes in Si and Ca concentrations of the immersion medium were determined with UV-Vis and atomic absorption spectrophotometry. The calcium phosphate precipitation and apatite formation were evaluated by scanning electron microscopy (SEM) and infra-red spectroscopy (IR) using the attenuated total reflectance (ATR) system. The SEM and SEM-EDX analysis of the depositions formed on the composite surfaces was in line with the changes in ion concentrations. The clearest results with IR were seen in the material containing 60 wt% small glass particles. The results indicate that composites containing over 40 wt% BAG granules are bioactive, and that a higher BAG surface area/volume ratio favors the apatite formation in vitro.

Absorbable Implants↗

PubMed2000

In vitro bioactivity of glass and glass-ceramics of the 3CaO x P2O5-CaO x SiO2-CaO x MgO x 2SiO2 system.

A glass of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5 CaF2 has been obtained (G13). The glass showed in vitro bioactivity evidenced by the formation on its surface of a calcium phosphate-rich layer when soaked in a solution with ionic composition analogous to human plasma. By thermal treatments of G13, a glass-ceramic (GC13) containing apatite, diopside, althausite and akermanite as crystalline phases was developed. GC13 as-made did not show in vitro bioactivity. However, after chemical treatment of GC13 with 1 M HCl (GC13-HCl), the in vitro studies showed the formation of an apatite-like layer covering certain areas of the material surface. The influence of both chemical and morphological factors on the in vitro bioactivity has been studied.

Calcium Compounds↗

PubMed2002

High level expression and purification of bioactive bovine interleukin-18 using a baculovirus system.

Bioactive recombinant bovine interleukin-18 (rboIL-18) was expressed using a baculovirus system. Normally, IL-18 is translated as a precursor form of a 24kDa polypeptide and processed by IL-1beta converting enzyme (ICE) to a mature bioactive form of 18kDa protein. Hence, to express active form IL-18, we constructed two recombinant baculoviruses containing boIL-18 and human ICE (hICE) genes, respectively, and superinfected these viruses into insect cells. Superinfection of both recombinant viruses into the cells resulted in the expression of a 24kDa precursor form and an 18kDa mature form detectable in the supernatant by immunoblotting using anti-porcine IL-18 antibody. Culture supernatant from the superinfected cells showed a synergistic effect with recombinant boIL-12 for production of interferon-gamma (IFN-gamma) in bovine peripheral mononuclear cells. By addition of histidine hexamer at the C-terminal of boIL-18, the mature IL-18 was purified. Bioactivity remained after purification.

Animals↗

PubMed2000

Polyurethane coatings release bioactive antibodies to reduce bacterial adhesion.

This study describes the formulation of a biomedical grade polyurethane hydrogel coating containing solid dispersed bioactive antibodies cast from an organic solvent onto a model polymer biomaterial substrate. A prepolymer dispersion in anhydrous isopropanol containing a uniformly distributed slurry of 22 microm sieved commercial lyophilized polyclonal pooled human immunoglobulin G (IgG) solids was coated onto polymer substrates by simple immersion. Maximum antibody release was approximately 50 microg/cm(2) from a 15% w/w IgG polymer coating. In vitro antimicrobial studies utilized Escherichia coli to compare performance of bare uncoated tubing, hydrogel-coated tubing with added aqueous phase antibodies, and antibody-dispersed hydrogel-coated tubing. Bacterial adhesion was reduced significantly (p<0.05) in the presence of antibodies with the greatest reduction seen with the antibody releasing coating. The presence of antibody also significantly enhanced the killing of the bacteria in an in vitro opsonophagocytic assay using freshly isolated blood neutrophils over 2 h indicating that antibody bioactivity is maintained. This controlled release polyurethane hydrogel coating imparts infection resistance by exploiting the low adhesive properties of the biomedical grade hydrogel and the intrinsic bioactive role of the antibodies to reduce bacterial adhesion and promote clearance via natural immune mechanisms.

Antibodies, Bacterial↗

PubMed1998

Elevated serum tumor necrosis factor-alpha concentrations and bioactivity in Type 2 diabetics and patients with android type obesity.

The role of tumor necrosis factor-alpha in insulin resistance has been studied in 59 patients with Type 2 diabetes, 28 with android type obesity and 35 healthy lean controls. Immunoreactive concentrations and bioactivity of serum tumor necrosis factor-alpha have repeatedly been determined in 8 weeks intervals for 12 months, five times per patients, by using ELISA and L929 cell cytotoxicity bioassay. Significantly higher immunoreactive tumor necrosis factor-alpha concentrations and bioactivity have been found in both, the Type 2 diabetic and obese groups as compared to the healthy persons. Tumor necrosis factor-alpha concentrations and bioactivity have showed a significant positive linear correlation with the elevated basal serum C-peptide levels and body mass indexes in both groups of patients. According to these data the cytokine might play a role in insulin resistance in obesity as well in Type 2 diabetes.

Adipose Tissue↗

PubMed1997

Bioactive substance accumulation and septic complications in a burn trauma patient: effect of perioperative blood transfusion?

Evidence has emerged that suggests adverse effects to perioperative homologous blood transfusion are related to the age of the blood products. Recently, time-dependent accumulation of bioactive substances in red cell suspensions, standard platelet concentrates and fresh frozen plasma during storage have been shown. The potential adverse effects of these bioactive substances were analysed in a burn trauma patient. A patient with 40 per cent second and third degree burn trauma without other injuries underwent a two-step transplantation operation. Samples for analyses of histamine, eosinophil cationic protein (ECP), eosinophil protein X (EPX), neutrophil myeloperoxidase (MPO) and interleukin 6 (IL-6) were drawn frequently from the patient before, during and after the operations, and from all transfused red cell, platelet and fresh frozen plasma units. Urine was sampled every hour during the first operation for analyses of ECP and EPX excretion. All analyses were performed by ELISA and RIA methods, and results compared to patient outcome. The patient received a total of 48 and 8 SAGM blood, 6 and 0 platelet and 12 and 4 fresh frozen plasma units at the two operations, respectively. Transfused products contained a total of 64.54 nmol and 17.50 nmol histamine, 115518 ng and 25764 ng ECP, 174457 ng and 38770 ng EPX, 6950915 ng and 1505125 ng MPO, and 14740 pg and 5600 pg IL-6 at the two operations, respectively. The accumulation of the substances in patient plasma correlated to postoperative septic reactions, without any disclosure of bacteraemia after the first operation, while the accumulation at the second operation correlated to the septic reaction and Pseudomonas aeruginosa infection. Time-dependent accumulation of bioactive substances in blood products during storage may be related to the development of post-transfusion adverse effects.

Adult↗

PubMed1999

Prestorage leukocyte filtration may reduce leukocyte-derived bioactive substance accumulation in patients operated for burn trauma.

Adverse effects of perioperative blood transfusion appear to be storage-time-dependent and may be related to extracellular accumulation of bioactive substances in blood products. In this study the clinical effects of leukofiltered and non-filtered blood products in patients undergoing surgery for burn trauma are investigated. 24 consecutive patients were randomly selected to receive transfusion with non-filtered blood components (group A, n = 12) or similar products, which were prestorage leukofiltered (group B, n = 12). The burn injury was scored using the Bull and Fischer index of age and burn surface area. Histamine, interleukin-6 (IL-6), plasminogen activator inhibitor-1 (PAI-1), eosinophil cationic protein (ECP) and myeloperoxidase (MPO) were analysed in plasma or serum collected from all patients 30 min before skin incision, at skin incision and 5, 10 and 30 min and thereafter every 30 min after skin incision until the grafts were secured by wrapping. Samples were also taken 8 h after skin incision and in the morning of postoperative days 1-5. The amount of blood products transfused from admission until day 5 postoperatively was recorded. All patients were followed until discharge or death. The Bull and Fischer index was comparable in the two groups. Prestorage leukofiltration reduced the amount of blood products required for transfusion significantly (p < 0.05) compared with non-filtered products. The levels of the various bioactive substances changed during and after the operation. In particular, ECP and MPO levels increased significantly (p < 0.05) in group A patients compared with unchanged (ECP) or decreased (MPO) levels in group B patients. IL-6 analyses showed, that the trauma had more severe impact on group B patients than on group A patients. Nevertheless, 4 patients died in group A and 2 in group B; all with a Bull and Fischer index between 1.0 and 2.0. Prestorage leukocyte filtration may reduce transfusion related accumulation of various bioactive substances and the requirement for blood in burn trauma patients.

Adult↗

PubMed2003

Ewing's sarcoma and peripheral primitive neuroectodermal tumor cells produce large quantities of bioactive tumor necrosis factor-alpha (TNF-alpha) after radiation exposure.

PURPOSE: In the present study, we examined human Ewing's sarcoma (ES) and peripheral primitive neuroectodermal tumor (pPNET) cell lines that are able to produce TNF-alpha as part of the response to irradiation. Radiation-induced tumor cell production of TNF-alpha may enhance irradiation efficacy and improve the effect of local tumor irradiation. On the other hand, radiation-induced tumor cell production of TNF-alpha may adversely affect the normal tissue. METHODS AND MATERIALS: Twelve different ES/pPNET cell lines were investigated in vitro and (after establishment as tumor xenografts in athymic nude mice) in vivo for their TNF-alpha mRNA expression (real-time quantitative reverse transcriptase polymerase chain reaction) and TNF-alpha protein production (in vitro: enhanced amplified sensitivity immunoassay; in vivo: immunohistochemistry) after exposure to different irradiation doses (2, 5, 10, 20, 30, or 40 Gy) and after different time intervals (1, 3, 6, 12, 24, 48, or 72 h after irradiation). The bioactivity of the TNF-alpha protein was evaluated in chromogenic cytotoxicity and neutralization assays. RESULTS: Nine out of 12 ES/pPNET cell lines express constitutively significant quantities of bioactive TNF-alpha in vitro. ES/pPNET cells originating from primary tumors secreted higher TNF-alpha levels than cells derived from metastatic lesions. In 5 of the 9 TNF-alpha-producing cell lines, TNF-alpha mRNA and protein levels were upregulated after irradiation exposure in a time- and dose-dependent manner. After establishment of the ES/pPNET cell lines in athymic nude mice, the radiation-induced TNF-alpha release could be demonstrated also in the xenograft tumors in vivo (analogous to the in vitro experiments). Using the same methods for quantitative analysis, it was determined that the TNF-alpha expression of the radiation-responsive tumor cells was up to 2000-fold higher compared to the maximal radiation-induced TNF-alpha release in normal lung tissue measured during the pneumonic phase. CONCLUSION: Certain ES/pPNET cell lines produce extremely large quantities of bioactive TNF-alpha after radiation exposure in a time- and dose-dependent manner. Radiation-induced TNF-alpha production of tumor cells may be of paramount importance in respect to not only tumor behavior, but also to potential damage to normal tissue and the clinical status of the host.

Animals↗

PubMed2001

Superimposition-based protocol as a tool for determining bioactive conformations. II. Application to the GABA(A) receptor.

The natural templates (NT) superimposition method is used to determine the pharmacophoric requirements of the A subtype of the gamma-aminobutyric acid (GABA) receptor. Bioactive conformations for antagonists and agonists are found by superimposing them on a relatively rigid alkaloid bicuculline, which itself is a competitive antagonist at this ligand-gated ion channel receptor. As has been usual in the application of this modeling method, consideration of available experimental data is the cornerstone for obtaining realistic models. The identification of two substructural fragments of bicuculline permitted classification of the ligands. Analysis of the antagonists and agonists with respect to the two substructural fragments revealed two bioactive conformations of the highly flexible GABA molecule, one of which is extended with the nonhydrogenic atoms roughly coplanar torsional angles of -37 and -179 degrees at N-C-C-C and C-C-C-C (carboxyl), respectively. The second bioactive compound is clearly non planar (torsional angles of -81 and -109 degrees at N-C-C-C and C-C-C-C (carboxyl), respectively).

Bicuculline↗

PubMed2003

Effects of nonsteroidal anti-inflammatory drugs on transforming growth factor-beta expression and bioactivity in rat osteoblast-enriched culture.

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to suppress bone remodeling in normal and repaired bones. Our previous results indicated that ketorolac and indomethacin suppressed proliferation, stimulated early differentiation, and induced apoptosis in cultured osteoblasts. Transforming growth factor-beta (TGF-beta) has been reported to enhance proliferation, suppress differentiation, and prevent apoptosis in osteoblasts. We proposed that one pathway of NSAID effects on osteoblast function might be through inhibition of the expression and/or bioactivity of TGF-beta in osteoblasts. We tested the effects of ketorolac and indomethacin on the expression of TGF-beta1 mRNA and protein and the bioactivity of TGF-beta in osteoblast-enriched cultures derived from fetal calvaria. The effects of prostaglandin E1 (PGE1) and PGE2 on TGF-beta expression and bioactivity were also examined in order to understand more about the role of prostaglandins in osteoblast function. Simultaneously, we estimated whether these NSAID effects on osteoblasts were prostaglandin-related. The results showed that 24-hour treatments with both PGEs and theoretic therapeutic concentrations of ketorolac and indomethacin had no significant effects on the levels of either transcription or translation of TGF-beta or the post-translational function of TGF-beta in osteoblasts. These results suggest that NSAIDs do not affect osteoblast function through changes in TGF-beta action in osteoblasts.

Animals↗

PubMed2000

Occurrence and biochemical characteristics of natural bioactive substances in bovine milk lipids.

Bovine milk lipids (BML) contain a number of bioactive substances with positive as well as negative properties, mainly in the class of fatty acids. Besides trans fatty acids (TFA), conjugated linoleic acids (CLA) are of particular interest. Apart from ruminant meat products the main source of CLA in food are BML. Although TFA as well as saturated fatty acids (12:0-16:0) are thought to be positively correlated with atherosclerosis and coronary heart disease, CLA are considered antiatherogenic. Further, CLA are reported to reduce adipose fat and to have anticarcinogenic properties. The varying CLA and TFA contents of lipids from milk and dairy products are positively correlated with one another. However, TFA are also negatively correlated with 12:0-16:0 in BML. Anticarcinogenic effects are also ascribed to butyric acid as well as to some phospholipids and ether lipids present in BML. Moreover, the essential fatty acids 18:2n-6 and 18:3n-3 are found in BML which are involved in a variety of biochemical processes and thus have numerous functions in human metabolism. Contents of the individual bioactive components of BML are summarised taking into account also seasonal variations. The total content of bioactive substances in BML is approximately 75 % but their overall impact on human health considering benefits and drawbacks is difficult to assess.

Adipose Tissue↗

PubMed2000

Effects of bioactive substances in milk on mineral and trace element metabolism with special reference to casein phosphopeptides.

Bioactivity of phosphopeptides yielded after tryptic hydrolysis of casein (CPP) was reported more than 50 years ago when CPP were found to improve calcium balance in rachitic newborns. Several investigations have been carried out to study the effects of CPP mainly on calcium metabolism but also on other minerals like iron and zinc. Most of the experiments were in vitro studies or short-term experiments like the effects of CPP after single meals or their effect on mineral disappearance from intestinal everted sac or ligated loop. Investigations on calcium balance were also mainly short term, i.e. 3-4 weeks, and mainly done in rats. A few experiments have been carried out in minipigs, an animal model that is closer to the human than the rat. Studies in human were rare and short term. To date a variety of other peptides have been isolated after enzymatic hydrolysis, and some have been investigated for bioactivity, with equivocal findings. Bioactivity of phosphopeptides seemed to be more obvious when investigations were done in vitro or short term. Results were less clear in metabolic balance studies, especially under physiological conditions. The composition of the basal diet, i.e. content of calcium and phytate, or the protein source had a significant impact on the effect of phosphopeptides. It was concluded that phosphopeptides revealed positive effects on mineral solubility and absorbability, and bone mineralisation under certain experimental conditions. Accordingly they could have a beneficial effect on bone health for some groups of the population.

Animals↗

PubMed2006

Evaluation of allelopathic potential and quantification of momilactone A,B from rice hull extracts and assessment of inhibitory bioactivity on paddy field weeds.

Rice (Oryza sativa L.) hull extracts were used in a bioassay to evaluate the allelopathic potential of rice on the germination and growth of barnyard grass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi), to quantify momilactone A and B levels in rice hull germplasm and to assess the inhibitory bioactivity of momilactone A and B as a potential natural source of herbicide for weed control in paddy fields. Four varieties of weeds including E. crus-galli P. Beauv. var. oryzicola Ohwi, Monochoria vaginalis var. plantaginea, Scirpus juncoides, and Eleocharis kuroguwai were tested in the paddy field. Of 99 rice varieties, the top five including Noindari exhibited inhibition effects greater than 50% in average inhibition of dry weight (AIDW). Noindari among them exerted the strongest effect (55.6%). The next five in the ranking exhibited inhibition effects of greater than 40%. Also, 46 varieties had inhibition effects between 20 and 40%, and 29 varieties had inhibition effects greater than 10%. Fourteen varieties had very low inhibitory effects (less than 10%), the lowest of which was Heunbe (4.7%). These varieties showed a mean inhibition of 19.8% for germination rate (GR), 9.9% for germination percentage (GP), 16.6% for leaf dry weight (LDW), 38.9% for straw dry weight (SDW), and 26.8% for root dry weight (RDW). Rice varieties were classified into six categories based on their total momilactones (TMs) (momilactone A + momilactone B). The highest level of momilactone A was found in the Baekna rice variety (34.7 microg g(-1)), and Baekgwangok contained the highest level of momilactone B (37.8 microg g(-1)). In allelopathic potential with genetic properties and morphological characteristics, the total inhibition rate (TIR) was 18.3% for Korean rice varieties, 19.0% for middle maturing varieties, 17.8% for colorless hull varieties, 18.3% for awn varieties, and 19.0% for colorless awn varieties. In addition, Korean varieties showed higher TMs (4.5 microg g(-1)) as compared with varieties that were late maturing (4.4 microg g(-1)), had colorless hulls (4.1 microg g(-1)), awns (4.7 microg g(-1)), and colorless awns (4.8 microg g(-1)). Momilactone A levels were generally higher than momilactone B levels. Total inhibition rates on barnyard grass correlated with average inhibitions of germination (AIG) (r2 = 0.62***), AIDW (r2 = 0.92***), and were affected by the inhibition rate of GP (r2 = 0.57***). Regions of origin for rice varieties correlated with the AIG (r2 = -0.23***), and maturing time showed a positive correlation with SDW (r2 = 0.15**) and RDW (r2 = 0.19**). Levels of momilactones were also correlated with the region of origin (r2 = -0.32***), maturing time (r2 = 0.13***), and awns (momilactone A, r2 = 0.23***; momilactone B, r2 = 0.14**), suggesting that rice varieties with awns, Korean varieties, and varieties with later maturing times contain higher levels of momilactone. Also, the investigation of the momilactone A and B bioactivity (0, 250, 500, 1000, 2000, and 4000 g a.i./ha) for weed control in paddy fields indicated that momilactones A and B exhibited no toxicity (0 in all concentrations) against rice plants, and the inhibitory bioactivity on weeds with momilactone A was higher than that of momilactone B. When compared with no momilactone control, the highest inhibitory effect (50%) on E. crus-galli P. Beauv. var. oryzicola Ohwi was shown on the 14th day after the application of momiactone A. The inhibitory effect increased with the concentration of the compound from 250 to 4000 g a.i./ha. Furthermore, momilactone A showed greater suppression than momliactone B toward toward E. crus-galli P. Beauv. var. oryzicola Ohwi, M. vaginalis var. plantaginea, S. juncoides, and E. kuroguwai. In broad weed species, momilactone A showed the highest inhibitory effect (90% in 4000 g a.i./ha) on S. juncoides, 14 days after the application as compared with no momilactone control. Further studies on allelopathic effects and momilactones from the germplasm of rice varieties using genetic properties and morphological characteristics may facilitate the development of rice varieties with higher allelopathic potential. Momilactones A and B present in rice hulls may serve as a potential natural herbicide source for weed control in paddy fields reducing the dependence on synthetic herbicides.

Diterpenes↗

PubMed2001

A new approach to search for the bioactive conformation of glucagon: positional cyclization scanning.

In search for the bioactive conformation of glucagon, "positional cyclization scanning" was used to determine secondary structures of glucagon required for maximal interaction with the glucagon receptor. Because glucagon is flexible in nature, its bioactive conformation is not known except for an amphiphilic helical conformation at the C-terminal region. To understand the conformational requirement for the N-terminal region that appears to be essential for signal transduction, a series of glucagon analogues conformationally constrained by disulfide or lactam bridges have been designed and synthesized. The conformational restrictions via disulfide bridges between cysteine i and cysteine i + 5, or lactam bridges between lysine i and glutamic acid i + 4, were applied to induce and stabilize certain corresponding secondary structures. The results from the binding assays showed that all the cyclic analogues with disulfide bridges bound to the receptor with significantly reduced binding affinities compared to their linear counterparts. On the contrary, glucagon analogues containing lactam bridges, in particular, c[Lys(5), Glu(9)]glucagon amide (10) and c[Lys(17), Glu(21)]glucagon amide (14), demonstrated more than 7-fold increased receptor binding affinities than native glucagon. These results suggest that the bioactive conformation of glucagon may adopt a helical conformation at the N-terminal region as well as the C-terminal region, which was not evident from earlier biophysical studies of glucagon.

Adenylyl Cyclases↗

PubMed2000

Bioactive compounds from Combretum erythrophyllum.

A methanol extract of Combretum erythrophyllum showed inhibitory bioactivities in a yeast-based microtiter assay for DNA-damaging agents. Bioassay-guided fractionation of this extract yielded two known bioactive compounds, combretastatin A-1 and (-)-combretastatin, and two new bioactive glucosides, combretastatin A-1 2'-beta-D-glucoside (1) and combretastatin B-1 2'-beta-D-glucoside (2). The structures of the new compounds were assigned by (1)H and (13)C NMR, DEPT, HMQC, and HMBC spectra.

Antineoplastic Agents, Phytogenic↗

PubMedDate not supplied

Fatty acid beta-oxidation-dependent bioactivation of halogenated thiaalkanoic acids in isolated rat hepatocytes.

5,6-Dichloro-4-thia-5-hexenoic acid (DCTH), the desamino analog of the nephrotoxic cysteine S-conjugate S-(1,2-dichlorovinyl)-L-cysteine, is toxic to liver and kidney mitochondria. The mechanism by which DCTH produces mitochondrial dysfunction has not been defined. The objective of the present experiments was to test the hypothesis that DCTH is bioactivated by the mitochondrial fatty acid beta-oxidation system to cytotoxic intermediates. Incubation of isolated rat hepatocytes with DCTH produced a time- and concentration-dependent decrease in cell viability. The even-chain, elongated analog 7,8-dichloro-6-thia-7-octenoic acid was also cytotoxic, whereas the odd-chain-length analogs 6,7-dichloro-5-thia-6-heptenoic acid and 8,9-dichloro-7-thia-8-nonenoic acid were not. Sodium benzoate reduced the cytotoxicity of DCTH, indicating a role for coenzyme A in the bioactivation of DCTH. DCTH decreased cellular ATP concentrations, the cellular energy charge, and cellular glutathione concentrations; these changes preceded the decrease in cell viability, indicating that mitochondrial dysfunction may be an early event in DCTH-induced cytotoxicity. 6-Chloro-5,5,6-trifluoro-4-thiahexanoic acid and 5,6,7,8,8-pentachloro-4-thia-5,7-octadienoic acid were also cytotoxic in isolated hepatocytes, whereas 4-(2-benzothiazolyl)-4-thiabutanoic acid was not. These data are consistent with the hypothesis that the mitochondrial fatty acid beta-oxidation system is involved in the bioactivation of DCTH and that mitochondria may be important cellular targets in DCTH-induced cytotoxicity.

Animals↗

PubMed2002

Comparative study on the bioactivation mechanisms and cytotoxicity of Te-phenyl-L-tellurocysteine, Se-phenyl-L-selenocysteine, and S-phenyl-L-cysteine.

Tellurium compounds are effective antioxidants and chemoprotectors, even more active than their selenium and sulfur analogues. In addition to these properties, some selenium compounds, such as selenocysteine Se-conjugates, possess significant chemopreventive and antitumor activities, and selenol metabolites are considered as active species. In the present study, we have synthesized Te-phenyl-L-tellurocysteine and evaluated its bioactivation and cytotoxicity. The activities of this compound were compared with those of the corresponding selenium and sulfur analogues. Te-Phenyl-L-tellurocysteine is bioactivated into its corresponding tellurol, as detected by GC-MS, by cysteine conjugate beta-lyase and amino acid oxidase, analogously to what has been shown previously for Se-phenyl-L-selenocysteine. The rate of beta-elimination may reflect the bond strength of the corresponding C-S, C-Se, and C-Te bond. Bioactivation of Te-phenyl-L-tellurocysteine and its selenium and sulfur analogues by oxidative enzymes was evaluated by measuring NADPH-dependent activation of hepatic mGST and inhibition of EROD. Te-Phenyl-L-tellurocysteine and Se-phenyl-L-selenocysteine displayed strong and time-dependent mGST activation, while S-phenyl-L-cysteine resulted in no significant activation. Te-Phenyl-L-tellurocysteine was also a strong inhibitor of EROD activity. In addition to EROD inhibition, Te-phenyl-L-tellurocysteine was the strongest inhibitor of several human cytochrome P450 isoenzymes followed by Se-phenyl-L-selenocysteine, while S-phenyl-L-cysteine was the weakest inhibitor. Interestingly, Te-phenyl-L-tellurocysteine selectively inhibited cytochrome P450 1A1 directly, which is, for example, responsible for the activation of several procarcinogens. Preliminary cytotoxicity studies with Te-phenyl-L-tellurocysteine in freshly isolated rat hepatocytes showed a time-dependent depletion of GSH and LDH leakage comparable with the relatively nontoxic drug paracetamol, while the selenium and sulfur analogues were nontoxic toward rat hepatocytes. In conclusion, because the chemopreventive and antitumor activities of selenium compounds are thought to be mediated via their selenol metabolites and tellurium compounds might be even more active than selenium compounds, tellurocysteine Te-conjugates might be an interesting novel class of prodrugs for the formation of biologically active tellurols.

Animals↗

PubMed2004

Glutathione transferase zeta-catalyzed bioactivation of dichloroacetic acid: reaction of glyoxylate with amino acid nucleophiles.

Dichloroacetic acid (DCA) is a drinking water contaminant, a therapeutic agent, and a rodent carcinogen. Glutathione transferase zeta (GSTZ1-1) catalyzes the biotransformation of a range of alpha-haloalkanoates and the cis-trans isomerization of maleylacetoacetate. GSTZ1-1 catalyzes the bioactivation of fluorine-lacking dihaloacetates to S-(alpha-halocarboxymethyl)glutathione, a reactive intermediate that covalently modifies and inactivates the enzyme or is hydrolyzed to glyoxylate. The purpose of this study was to examine the GSTZ1-1-catalyzed bioactivation of DCA, including the reaction of DCA-derived glyoxylate with amino acid nucleophiles and the characterization of the structures and kinetics of adduct formation by LC/MS. The binding of [1-(14)C]DCA-derived label to bovine serum albumin required both GSTZ1-1 and GSH, whereas the binding to dialyzed rat liver cytosolic protein was increased in the presence of GSH. Studies with model peptides (antiflammin-2 and IL-8 inhibitor) indicated that glyoxylate, rather than S-(alpha-chlorocarboxymethyl)glutathione, was the reactive species that modified amino acid nucleophiles. Both addition (+74 Da) and addition-elimination (+56 Da) adducts of glyoxylic acid were observed. Addition adducts (+74 Da) could not be characterized completely by mass spectrometry, whereas addition-elimination adducts (+56 Da) were characterized as 2-carboxy-4-imidazolidinones. 2-Carboxy-4-imidazolidinones were formed by the rapid equilibrium reaction of glyoxylate with the N-terminal amino group of antiflammin-2 to give an intermediate carbinolamine (K(eq) = 0.63 mM(-1)), which slowly eliminated water to give an intermediate imine (k(2) = 0.067 hour(-1)), which rapidly cyclized to give the 2-carboxy-4-imidazolidinone. Glucose 6-phosphate dehydrogenase was inactivated partially by glyoxylate when reactants were reduced with sodium borodeuteride, which may indicate that glyoxylate reacts with selective lysine epsilon-amino groups. The results of the present study demonstrate that GSTZ1-1 catalyzes the bioactivation of DCA to the reactive metabolite glyoxylate. The reaction of glyoxylate with cellular macromolecules may be associated with the multiorgan toxicity of DCA.

Acetoacetates↗