Use of pH-Active Catechol-Bearing Polymeric Nanogels with Glutathione-Responsive Dissociation to Codeliver Bortezomib and Doxorubicin for the Synergistic Therapy of Cancer

Synergistic therapy holds promising potential in cancer treatment. Here, the inclusion of catechol moieties, a disulfide cross-linked structure, and pendent carboxyl into the network of polymeric nanogels with glutathione (GSH)-responsive dissociation and pH-sensitive release is first disclosed for the codelivery of doxorubicin (DOX) and bortezomib (BTZ) in synergistic cancer therapy. The pendent carboxyl groups and catechol moieties are exploited to absorb DOX through electrostatic interaction and conjugate BTZ through boronate ester, respectively. Both electrostatic interactions and boronate ester are stable at neutral or alkaline pH, while they are instable in an acidic environment to further recover the activities of BTZ and DOX. The polymeric nanogels possess a superior stability to prevent the premature leakage of drugs in a physiological environment, while their structure is destroyed in response to a typical endogenous stimulus (GSH) to unload drugs. The dissociation of the drug-loaded nanogels accelerates the intracellular release of DOX and BTZ and further enhances the therapeutic efficacy. In vitro and in vivo investigations revealed that the dual-drug loaded polymeric nanogels exhibited a strong ability to suppress tumor growth. This study thus proposes a new perspective on the production of multifunctional polymeric nanogels through the introduction of different functional monomers.

Overcoming multidrug resistance by intracellular drug release and inhibiting p-glycoprotein efflux in breast cancer

Doxorubicin (DOX) is limited to use in clinical practice because of poor targeting, serious side effects and multidrug resistance (MDR). Vitamin E and its derivatives are currently considered as hydrophobic material that can reverse tumor MDR by suppressing the action of p-glycoprotein (p-gp). Therefore, reduction-sensitive amphiphilic heparosan polysaccharide-cystamine-vitamin E succinate (KSV) copolymers were designed to reverse breast cancer MDR cells. The spherical micelles (DOX/KSV) micelles which had suitable particle size presented redox-sensitive release character. Simultaneously, DOX-loaded reduction insensitive heparosan-adipic dihydrazide-vitamin E succinate (KV) micellar system was designed as a control. DOX/KSV and DOX/KV micelles had the higher capability to overcome tumor MDR than that free DOX. However, DOX/KSV had the highest amount of cellular uptake which might be caused by the synergistic intracellular drug release and inhibition of p-gp expression. The mechanism experiments revealed that DOX/KSV could be fast disassembled to release DOX after internalization into tumor cells. Moreover, DOX/KSV produced more ROS than free DOX and DOX/KV resulting in enhanced anticancer effect. In vivo tumor-bearing mice study suggested that DOX/KSV micelles could efficiently enhance antitumor effect by overcoming tumor MDR and reduce toxicity of DOX. The DOX/KSV micelles could synergistically increase the therapeutic effect of chemotherapeutic drug on tumor MDR cells.

Relationship between three polymorphisms of methylenetetrahydrofolate reductase (MTHFR C677T, A1298C, and G1793A) gene and risk of prostate cancer: a case-control study

BACKGROUND

We hypothesized that genetic polymorphisms in methylenetetrahydrofolate reductase (MTHFR) gene are associated with prostate cancer risk.

METHODS

We genotyped three MTHFR polymorphisms (C677T, A1298C, and G1793A) and measured serum total homocysteine (tHcy), folate, and vitamin B12 levels in a case-control study of 174 cases and 348 normal healthy controls. The cancer-free controls were frequency matched to the cases by age (±2 years), educational level, occupational status, ethnicity, and smoking status.

RESULTS

We found that the MTHFR 677TT and 1298CC genotypes were associated with an about 40% reduction in risk of prostate cancer (adjusted OR = 0.59, 95% CI = 0.41-0.94, and adjusted OR = 0.58, 95% CI = 0.32-0.91, respectively) compared to the 677CC, and 1298AA genotypes. The combined variant genotypes of 1298AC + 677CC were associated with a 30% reduction in risk of prostate cancer (OR = 0.70; 95% CI = 0.53-0.79). In contrast, the variant genotypes of 1793GA + 677CT were associated with slightly increased risk for prostate cancer (OR = 1.64; 95% CI = 0.86-2.15). Regarding prostate cancer aggressiveness, the 677TT genotype was associated with more than 50% decreased risk of high-grade prostate cancer (Gleason score >7) compared with the 677CC and 677CT genotypes (OR = 0.35, 95% CI = 0.24-0.64; P = 0.001). There was no significant difference in plasma levels of tHcy, folate, and vitamin B12 between the two groups with any genotypes.

CONCLUSION

These data suggest that all three MTHFR polymorphisms may play a pivotal role in the developing prostate cancer. Larger studies in different ethnic populations and incorporating dietary folate intake are needed to replicate our findings.

The physiological role of the Gomori-positive glia: a new hypothesis

On the basis of histological observations of the brains of intact animals and of those injected with a sulfur-containing material (cystamine) we propose that the main, if not unique, role of the Gomori-positive glia is to scavenge the brain for sulfur-containing material because such material when physiologically present (e.g. neurophysin) may give rise to free cysteine that is toxic to neurons, being a long-recognized neurotoxin.

Studies on the reducing systems for plant and animal thioredoxin-independent methionine sulfoxide reductases B

Two distinct stereospecific methionine sulfoxide reductases (Msr), MsrA and MsrB reduce the oxidized methionine (Met), methionine sulfoxide [Met(O)], back to Met. In this report, we examined the reducing systems required for the activities of two chloroplastic MsrB enzymes (NtMsrB1 and NtMsrB2) from tobacco (Nicotiana tabacum). We found that NtMrsB1, but not NtMsrB2, could use dithiothreitol as an efficient hydrogen donor. In contrast Escherichia coli thioredoxin (Trx) could serve as a reducing agent for NtMsrB2, but not for NtMsrB1. Similar to previously reported human Trx-independent hMsrB2 and hMsrB3, NtMsrB1 could also use bovine liver thionein and selenocysteamine as reducing agents. Furthermore, the unique plant Trx-like protein CDSP32 was shown to reduce NtMsrB1, hMsrB2 and hMsrB3. All these tested Trx-independent MsrB enzymes lack an additional cysteine (resolving cysteine) that is capable of forming a disulfide bond on the enzyme during the catalytic reaction. Our results indicate that plant and animal MsrB enzymes lacking a resolving cysteine likely share a similar reaction mechanism.

Differential gene expression in mouse liver associated with the hepatoprotective effect of clofibrate

Pretreatment of mice with the peroxisome proliferator clofibrate (CFB) protects against acetaminophen (APAP)-induced hepatotoxicity. Previous studies have shown that activation of the nuclear peroxisome proliferator activated receptor-alpha (PPARalpha) is required for this effect. The present study utilizes gene expression profile analysis to identify potential pathways contributing to PPARalpha-mediated hepatoprotection. Gene expression profiles were compared between wild type and PPARalpha-null mice pretreated with vehicle or CFB (500 mg/kg, i.p., daily for 10 days) and then challenged with APAP (400 mg/kg, p.o.). Total hepatic RNA was isolated 4 h after APAP treatment and hybridized to Affymetrix Mouse Genome MGU74 v2.0 GeneChips. Gene expression analysis was performed utilizing GeneSpring software. Our analysis identified 53 genes of interest including vanin-1, cell cycle regulators, lipid-metabolizing enzymes, and aldehyde dehydrogenase 2, an acetaminophen binding protein. Vanin-1 could be important for CFB-mediated hepatoprotection because this protein is involved in the synthesis of cysteamine and cystamine. These are potent antioxidants capable of ameliorating APAP toxicity in rodents and humans. HPLC-ESI/MS/MS analysis of liver extracts indicates that enhanced vanin-1 gene expression results in elevated cystamine levels, which could be mechanistically associated with CFB-mediated hepatoprotection.

Cystamine and cysteamine increase brain levels of BDNF in Huntington disease via HSJ1b and transglutaminase

There is no treatment for the neurodegenerative disorder Huntington disease (HD). Cystamine is a candidate drug; however, the mechanisms by which it operates remain unclear. We show here that cystamine increases levels of the heat shock DnaJ-containing protein 1b (HSJ1b) that are low in HD patients. HSJ1b inhibits polyQ-huntingtin-induced death of striatal neurons and neuronal dysfunction in Caenorhabditis elegans. This neuroprotective effect involves stimulation of the secretory pathway through formation of clathrin-coated vesicles containing brain-derived neurotrophic factor (BDNF). Cystamine increases BDNF secretion from the Golgi region that is blocked by reducing HSJ1b levels or by overexpressing transglutaminase. We demonstrate that cysteamine, the FDA-approved reduced form of cystamine, is neuroprotective in HD mice by increasing BDNF levels in brain. Finally, cysteamine increases serum levels of BDNF in mouse and primate models of HD. Therefore, cysteamine is a potential treatment for HD, and serum BDNF levels can be used as a biomarker for drug efficacy.

Post-translational disulfide modifications in cell signaling--role of inter-protein, intra-protein, S-glutathionyl, and S-cysteaminyl disulfide modifications in signal transmission

Cell signaling entails a host of post-translational modifications of effector-proteins. These modifications control signal transmission by regulating the activity, localization or half-life of the effector-protein. Prominent oxidative modifications induced by cell-signaling reactive oxygen species (ROS) are cysteinyl modifications such as S-nitrosylation, sulfenic acid and disulfide formation. Disulfides protect protein sulfhydryls against oxidative destruction and simultaneously influence cell signaling by engaging redox-regulatory sulfhydryls in effector-proteins. The types of disulfides implicated in signaling span (1) protein S-glutathionylation, e.g. as a novel mode of Ras activation through S-glutathionylation at Cys-118 in response to a hydrogen-peroxide burst, (2) intra-protein disulfides, e.g. in the regulation of the stability of the protein phosphatase Cdc25C by hydrogen-peroxide, (3) inter-protein disulfides, e.g. in the hydrogen peroxide-mediated inactivation of receptor protein-tyrosine phosphatase alpha (RPTPalpha) by dimerization and (4) protein S-cysteaminylation by cystamine. Cystamine is a byproduct of pantetheinase-catalyzed pantothenic acid recycling from pantetheine for biosynthesis of Coenzyme A (CoA), a ubiquitous and metabolically indispensable cofactor. Cystamine inactivates protein kinase C-epsilon (PKCepsilon), gamma-glutamylcysteine synthetase and tissue transglutaminase by S-cysteaminylation-triggered mechanisms. The importance of protein S-cysteaminylation in signal transmission in vivo is evident from the ability of cystamine administration to rescue the intestinal inflammatory-response deficit of pantetheinase knockout mice. These mice lack the predominant epithelial pantetheinase isoform and have sharply reduced levels of cystamine/cysteamine in epithelial tissues. In addition, intraperitoneal administration of cystamine significantly delays neurodegenerative pathogenesis in a Huntington's disease mouse model. Thus, cystamine may serve as a prototype for the development of novel therapeutics that target effector-proteins regulated by S-cysteaminylation.

Vanin-1-/- mice exhibit a glutathione-mediated tissue resistance to oxidative stress

Vanin-1 is an epithelial ectoenzyme with pantetheinase activity and generating the amino-thiol cysteamine through the metabolism of pantothenic acid (vitamin B(5)). Here we show that Vanin-1(-/-) mice, which lack cysteamine in tissues, exhibit resistance to oxidative injury induced by whole-body gamma-irradiation or paraquat. This protection is correlated with reduced apoptosis and inflammation and is reversed by treating mutant animals with cystamine. The better tolerance of the Vanin-1(-/-) mice is associated with an enhanced gamma-glutamylcysteine synthetase activity in liver, probably due to the absence of cysteamine and leading to elevated stores of glutathione (GSH), the most potent cellular antioxidant. Consequently, Vanin-1(-/-) mice maintain a more reducing environment in tissue after exposure to irradiation. In normal mice, we found a stress-induced biphasic expression of Vanin-1 regulated via antioxidant response elements in its promoter region. This process should finely tune the redox environment and thus change an early inflammatory process into a late tissue repair process. We propose Vanin-1 as a key molecule to regulate the GSH-dependent response to oxidative injury in tissue at the epithelial level. Therefore, Vanin/pantetheinase inhibitors could be useful for treatment of damage due to irradiation and pro-oxidant inducers.

In vitro proteoglycan sulfation derived from sulfhydryl compounds in sulfate transporter chondrodysplasias

Mutations in a sulfate-chloride antiporter gene, the diastrophic dysplasia sulfate transporter (DTDST), have been associated with a family of skeletal dysplasias including recessive multiple epiphyseal dysplasia, diastrophic dysplasia (DTD), atelosteogenesis type 2, and achondrogenesis type 1B (ACG1B). DTDST function is crucial for uptake of extracellular sulfate required for proteoglycan (PG) sulfation; the tissue-specific expression of the clinical phenotype may be the consequence of the high rate of PG synthesis in chondrocytes and the ensuing high sulfate requirement. We have studied the contribution of cysteine and its derivatives to PG sulfation in fibroblast and chondrocyte cultures from sulfate transporter dysplasia patients. Incubation of ACG1B fibroblasts in medium containing different concentrations of cystine indicated partial recovery of PG sulfation as measured by HPLC disaccharide analysis of chondroitin sulfate PGs; similar results were observed after incubation with N-acetylcysteine. When both compounds were tested in primary chondrocytes from a DTD patient, partial rescue of PG sulfation was observed, suggesting that the metabolic pathways producing cytoplasmic sulfate from thiols are also active in this cell type.

Transglutaminase potentiates ligand-dependent proteasome dysfunction induced by polyglutamine-expanded androgen receptor

Expansion of the CAG trinucleotide repeat encoding glutamine in the androgen receptor gene leads to spinobulbar muscular atrophy (SBMA), a neurodegenerative disorder in a family of polyglutamine diseases with enigmatic pathogenic mechanisms. One established property of glutamine residues is their ability to act as an amine accepter in a transglutaminase-catalyzed reaction, resulting in a proteolytically resistant glutamyl-lysine cross-link. To examine underlying disease mechanisms we investigated the relationship between polyglutamine-expanded androgen receptor and transglutaminase. We found androgen receptor N-terminal fragments are a substrate for transglutaminase. Western blots of the proteins following incubation with transglutaminase show that several different epitopes of the AR appear to be lost. We propose that this is due to the transglutaminase cross-linking of the AR, which interferes with antibody recognition. Furthermore, HEK GFP(u)-1 cells expressing polyglutamine-expanded androgen receptor and transglutaminase exhibit ligand-dependent proteasome dysfunction; this effect was not observed in the presence of cystamine, a transglutaminase inhibitor. In addition, transglutaminase-mediated isopeptide bonds were detected in brains of SBMA transgenic mice, but not in controls, suggesting involvement of transglutaminase-catalyzed reactions in polyglutamine disease pathogenesis. Our hypothesis is that cross-linked AR cannot to be degraded by the proteasome and obstructs the proteasome pore, preventing normal function. Because of the central role the ubiquitin-proteasome degradation system plays in fundamental cellular processes, any alteration in its function could cause cell death, ultimately contributing to SBMA pathogenesis.

Cystamine transport in spheroplasts of Saccharomyces cerevisiae

This work is the first demonstration that cystamine is actively accumulated in spheroplasts of Saccharomyces cerevisiae. We have identified and quantitatively determined the transported cystamine in extracts of spheroplasts that have been incubated over different time periods and in the presence of different amounts of cystamine. The method used, already reported in literature for the identification of natural aliphatic polyamines in biological fluids, consists of a derivatization of spheroplast extracts with dabsyl-chloride and subsequent chromatographic analysis in HPLC. Our results show that cystamine accumulation is a function of time, it increases up to 2.5 min then decreases. Transport is inhibited by natural aliphatic polyamines, which, at the same concentration of cystamine (1 mM), cause a decrease in cystamine transport of about 90% for spermidine, 50% for spermine and only 15% for putrescine. Furthermore, transport is energy-dependent as demonstrated by a significant decrease observed in the presence of 2,4-dinitrophenol, ouabain and vanadate. In particular 0.2 mM ouabain causes a decrease of more than 60% in cystamine transport. Our data suggest that cystamine is transported in Saccharomyces cerevisiae spheroplasts via the same polyamine transport system(s) known to be operating in higher eukaryotic cells.

Ligand association with the rabbit kidney and brain Y1, Y2 and Y5-like neuropeptide Y (NPY) receptors shows large subtype-related differences in sensitivity to chaotropic and alkylating agents

The binding to rabbit kidney or hypothalamic particulates of the subtype-selective neuropeptide Y (NPY) receptor ligands [125I](Leu31,Pro34)hPYY (as Y1 site label at 2 nM human pancreatic polypeptide (hPP)), [125I]-hPYY(3-36) (Y2 label), and [125I]-hPP (Y5 label) displayed great differences in sensitivity to alkylators and chaotropic agents. Sensitivity to a nonionic chaotrope, urea, was much higher for the Y1 binding than for the Y5-like binding or the Y2 binding. The non-selective alkylator N-ethylmaleimide (NEM) and several alkylators selective for aminergic receptors were much more efficacious against the Y1 relative to the Y2 binding. Similar differences could be confirmed with the attachment of Y1 and Y2-selective tracers to CHO cells expressing the cloned guinea-pig Y1 or Y2 receptors. The Y5-like binding was quite insensitive to NEM, but sensitive to chloroethylclonidine (CEC) and prazobind, which were less potent at the Y1, and especially at the Y2 site. The unrestricted-access alkylator 2-aminoethyl methanethiosulfonate inhibited the binding to all subtypes, while the restricted-access agent 2-(trimethylammonium)ethylmethanethiosulfonate poorly inhibited the Y5-like binding, or the guanine nucleotide-insensitive Y2 binding. These results are compatible with an active conformation of the Y5-like site dependent on maintenance of a shared hydrophobic cavity. The Y2 sites resistant to guanosine polyphosphates and restricted-access alkylators were detected mainly in particulates slowly solubilized by cholate at 0-5 degrees C; these sites could be clustered.

Heparin-selenocystamine conjugate with selenol groups

Heparin-selenocystamine conjugate, which was intended to mimic the heparin-selenoprotein P complex, was prepared. The conjugate had glutathione peroxidase-like activity and activity was observed toward hydrogen peroxide, tert-butyl hydroperoxide, and cumene hydroperoxide. The ultraviolet spectrum of an aqueous solution of the conjugate was stable and had a similar shape to that observed transiently when selenocystamine was reduced by sodium cyanoborohydride; this suggests that the diselenide bond of selenocystamine introduced into heparin was cleaved during conjugate preparation and the selenol group is preserved. The conjugate reacted to the same degree as cysteine with 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) releasing thionitro-benzoic acid, which indicated that the selenium in the conjugate is present as selenol. However, the reaction rate of the conjugate was slower than cysteine which may be due to partially restricted access of DTNB to the selenol group in the conjugate. This conjugate had 1,1-diphenyl-2-picryl-hydrazyl(DPPH) radical scavenging activity as well as superoxide anion scavenging activity. These results indicate that the conjugate serves as a useful model compound with a stable selenol group having a range of biological activities, and suggest a possible antioxidant defensive role for the complex of endogenous heparin-like substance and selenoprotein P.

Free radical production by Nd:YAG laser photodisruption

BACKGROUND AND OBJECTIVES

Plasma and cavitation bubble formation during optical breakdown in aqueous media may produce hydroxyl (*OH) radicals. The authors' objectives were to detect *OH produced by a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser photodisruptor and to determine *OH concentration in relation to laser energy.

MATERIALS AND METHODS

*OH was assayed by measuring absorbance of triiodide (I3-) in a potassium iodide (KI) solution exposed to optical breakdown by an Nd:YAG laser. The concentration-dependent reduction of radical production in relation to cystamine concentration was evaluated.

RESULTS

I3- concentration increased linearly with total irradiation energy and decreased exponentially with increasing cystamine concentration. *OH concentration was calculated using extinction coefficients of I3- and chemical equations relating I3- formation to *OH.

CONCLUSIONS

The authors calculated that approximately 4 x 10(-12) moles of *OH are produced in a typical posterior capsulotomy of 100 mJ of total energy. This *OH concentration could produce strand breaks in approximately 0.4% of vitreous hyaluronic acid molecules, but is unlikely to produce clinical effects.

Characterisation of a cloned human 5-HT1A receptor cell line using [35S]GTP gamma S binding

Compound potencies and efficacies depend upon receptor reserve and hence estimating this parameter in assay systems allows for a more meaningful interpretation of the data generated. This study describes a method whereby the degree of receptor reserve, with respect to 5-hydroxytryptamine (5-HT), was determined for a HeLa cell line expressing the human 5-HT1A receptor using the agonist-induced [35S]guanosine 5'[gamma-thio]triphosphate ([35S]GTP gamma S) binding assay, followed by a comparison of the potencies and relative efficacies of several compounds. Following irreversible antagonism with benextramine 5-HT yielded a pKA of 7.3, compared with a pKobs of 8.4 from saturation analysis, indicating the presence of high and low affinity state receptors. A 20% receptor occupancy elicited a half-maximal functional response consistent with the presence of receptor reserve. 5-HT, 5-carboxamidotryptamine (5-CT), 8-hydoxy-dipropylamino-tetralin (8-OH-DPAT), 5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)-1 H-indole (RU24969), buspirone, gepirone, mesulergine and sumatriptan were equally efficacious. 1-(2-Methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN 190) displayed reduced relative efficacy and methiothepin inverse agonism.

Cysteamine oxidation by lentil seedling amine oxidase

Cysteamine is oxidatively deaminated by lentil amine oxidase. It shows saturation kinetic K(m) = 9 x 10(-4) M like other substrates, but the aldehyde produced leads to loss of enzyme activity, which is restored by dialysis. When putrescine is the substrate of the amine oxidase cysteamine behaves like a competitive inhibitor, and shows Ki = 5 x 10(-5) M. The possible involvement of the oxidation of cysteamine and the inhibitory effects of thioacetaldehyde in the cystamine oxidation by amine oxidase is discussed.

Characterization of the active site cysteine residues of the thioredoxin-like domains of protein disulfide isomerase

The dithiol/disulfide active sites of each of the two isolated thioredoxin-like domains of protein disulfide isomerase (PDI) expressed in Escherichia coli have been characterized in order to understand their catalytic mechanisms and their functions in PDI. In each of the folded domains, as in other proteins of the thioredoxin family, only one of the cysteine residues of the active site sequence -Cys-Gly-His-Cys- is accessible, and its thiol group is highly reactive and has a low pKa value. The kinetics and equilibria have been measured of the reactions between the active site cysteine residues and glutathione, the predominant thiol/disulfide reagent of the endoplasmic reticulum. A disulfide bond can be formed very rapidly between the pair of cysteine residues of each domain, but each disulfide bond is very unstable and reacts rapidly with reduced glutathione. The very low stabilities of these disulfide bonds, which destabilize the protein structures, account for the efficiency with which PDI and each of the isolated domains can introduce disulfide bonds into proteins. These kinetics and equilibrium data go far in helping to understand the catalytic mechanism of PDI and its individual domains.

The uptake and metabolism of cystamine and taurine by isolated perfused rat and rabbit lungs

Cystamine has been reported to be taken up and metabolized to taurine by the rat lung slices. The objectives of the present study were to compare the uptake and metabolism of cystamine and taurine in isolated perfused lungs of rats and rabbits and examine the action of glutathione (GSH) on these processes. The uptake and metabolism of [14C]cystamine and [14C]taurine were studied at 20 microM concentrations each in isolated, ventilated, perfused rat and rabbit lungs. In some experiments, 1 microM GSH was included in the perfusate prior to the addition of cystamine. The perfusate and lung homogenate samples were analyzed for cystamine and its metabolites. [14C]cystamine uptake with and without GSH was 13 and 14% in rat lungs and 37 and 32% in rabbit lungs. [14C]taurine uptake was 10% in rat and 37% in rabbit lungs. The levels of radiolabeled cystamine and its metabolites were (nmol/g lung): 20.0 +/- 10.0 and 11.5 +/- 7.0 cystamine, 4.7 +/- 0.5 and 3.2 +/- 0.5 hypotaurine and 56.0 +/- 16.0 and 49.4 +/- 6.0 taurine, for rat and rabbit lungs, respectively, when perfused without GSH; and 18.0 +/- 1.0 and 2.5 +/- 0.5 cystamine, 6.6 +/- 0.5 and 18 +/- 10 hypotaurine and 60.0 +/- 12.0 and 33.6 +/- 9.0 taurine, when perfused with GSH, for rats and rabbit lungs, respectively. Taurine did not undergo any further metabolism in either of the lungs. These studies show that cystamine is taken up and metabolized to taurine via hypotaurine by both rat and rabbit lungs in a manner similar to that seen in rat lung slices. However, rat lungs have much greater capacity to metabolize cystamine to taurine than rabbit. Inclusion of GSH did not significantly alter the ability of lungs to sequester cystamine from the perfusate but the metabolism of hypotaurine to taurine was markedly decreased in rabbit lungs. Taurine was not metabolized any further. It is concluded that rat and rabbit lungs take up cystamine from the systemic circulation, metabolize it via hypotaurine to taurine, and effuse most of the latter in to the circulation.

Glutaredoxin accelerates glutathione-dependent folding of reduced ribonuclease A together with protein disulfide-isomerase

Glutaredoxin (Grx) contains a redox-active disulfide and catalyzes thiol-disulfide interchange reactions with specificity for GSH. The dithiol form of Grx reduces mixed disulfides involving GSH or protein disulfides. During oxidative refolding of 8 microM reduced and denatured ribonuclease RNase-(SH)8 in a redox buffer of 1 mM GSH and 0.2 mM GSSG to yield native RNase-(S2)4, a large number of GSH-mixed disulfide species are formed. A lag phase that precedes formation of folded active RNase at a steady-state rate was shortened or eliminated by the presence of a catalytic concentration (0.5 microM) of Escherichia coli Grx together with protein disulfide-isomerase (PDI), its procaryotic equivalent E. coli DsbA, or the PDI analogue the E. coli thioredoxin mutant protein P34H. A mutant Grx in which one of the active site cysteine residues (Cys-11 and Cys-14) had been replaced by serine, C14S Grx, had similar effect compared with its wild-type counterpart. This demonstrated that Grx acted by a monothiol mechanism involving only Cys-11 and that RNase-S-SG-mixed disulfides were the substrates. Grx displayed synergistic activity together with PDI only in GSH/GSSG redox buffers with sufficiently low redox potential (E'0 of -208 or -181 mV) to allow reduction of the active site of Grx. In refolding systems that do not depend on glutathione, like cystamine/cysteamine or in the presence of selenite (SeO3(2-)), no synergistic activity of Grx was observed with PDI. We conclude that Grx acts by reducing mixed disulfides between GSH and RNase that are rate-limiting in enzyme-catalyzed refolding.

Binding profile of benextramine at neuropeptide Y receptor subtypes in rat brain areas

Binding studies in rat whole brain, frontoparietal cortex and brainstem membrane preparations revealed that benextramine displaced [3H]neuropeptide Y specific binding from a low and a high affinity site with IC50 values in the microM (36 +/- 2, 4.4 +/- 1.4 and 300 +/- 120 microM, respectively) and the pM (29.3 +/- 12.1, 0.35 +/- 0.11 and 0.42 +/- 0.03 pM, respectively) range, whereas in rat hippocampus benextramine displaced [3H]neuropeptide Y specific binding from one site only with an IC50 value of 22.8 +/- 5.7 microM. With the exception of frontoparietal cortex binding assay, benextramine was not able to completely inhibit [3H]neuropeptide Y specific binding revealing the presence of a benextramine nonsensitive third binding site. Benextramine pretreatment followed by membrane washing demonstrated that benextramine inhibited irreversibly both high and low affinity sites.

Thioltransferase can utilize cysteamine as same as glutathione as a reductant during the restoration of cystamine-treated glucose 6-phosphate dehydrogenase activity

Glucose 6-phosphate dehydrogenase (G6PD) [EC 1.1.1.49] is inactivated by the incubation with cystamine very efficiently, but not by oxidized glutathione. This inactivation advanced following the incubation-time and concentration of cystamine. The inactivated-G6PD is restored its activity by the treatment of thioltransferase with 1 mM cysteamine or reduced glutathione (GSH) much more effectively than only by thiols. For the first time, we suggested thioltransferase can utilize cysteamine in stead of GSH during its thiol/disulfide exchange reaction activity.

Kinetics and cellular localisation of putrescine uptake in human lung tissue

BACKGROUND

The polyamines (putrescine, spermidine, and spermine) are involved in cellular growth, proliferation, and differentiation. In the lungs of various species, polyamines are accumulated by an active uptake system which also mediates the uptake of cystamine and paraquat. In the rat lung putrescine uptake has been shown to be cell-specific, occurring predominantly in the alveolar epithelium. The aim of this study was to characterise the uptake of putrescine in human lung.

METHODS

Lung tissue was obtained from 31 patients undergoing surgery for lung cancer. Slices (0.7 mm thick) from non-tumour containing lung parenchyma were incubated for 15-60 minutes in Krebs-Ringer phosphate buffer with various concentrations of putrescine (2.5 to 80 mumol/l) containing 0.1 microCi [1,4-14C]-putrescine. Uptake was assessed from tissue radioactivity. For autoradiographic imaging, slices were incubated for 30 minutes with 2.5 mumol/l putrescine containing 2.5 mCi [1,4n-3H]-putrescine.

RESULTS

The accumulation of [14C]-putrescine into slices was time-dependent and energy-dependent, and obeyed saturation kinetics, with mean calculated values for Vmax (maximal rate of uptake) of 414 nmol/g/hour and for Km (medium concentration at which the rate of uptake is half Vmax) of 7.2 mumol/l, with a large interindividual variation. Competitive inhibition was observed on incubation with cystamine, which appears to have a high affinity for the uptake system since its calculated Ki (concentration of inhibitor at which the Km is doubled) was 3.2 mumol/l. Ultrastructural autoradiography showed labelling over both type I and type II cells of the alveolar epithelium, but not over the endothelium or any cells of the interstitium. Alveolar macrophages were also devoid of label.

CONCLUSIONS

These results show that the human lung possesses an active uptake system for putrescine, and probably also cystamine, which is located in both cell types of the alveolar epithelium. These findings may be used to develop tests for the assessment of the alveolar epithelium.

Determination of cysteamine and cystamine by gas chromatography with flame photometric detection

A gas chromatographic method for the determination of cysteamine and its disulphide cystamine is described. Cysteamine and cystamine are converted into N,S-diisobutoxycarbonyl and N,N-diisobutoxycarbonyl derivatives, respectively. The derivatives are analysed by gas chromatography with flame photometric detection, using a DB-210 capillary column. The calibration curves for cysteamine and cystamine in the range of 0.2-5.0 nmol are linear and sufficiently reproducible for quantitative analysis, and the detection limit is about 0.5 pmol injected. Cysteamine in mouse tissues is found in the free reduced, free oxidized and protein-bound forms. Free oxidized and protein-bound forms are reduced to free cysteamine by the use of sodium borohydride, and then derivatized. Cysteamine and cystamine in mouse tissues can be measured without any interference from coexisting substances by this method. The recoveries of cysteamine and cystamine added to the tissue samples are 91-106%, and their reproducibilities are found to be satisfactory. Analytical results for the determination of various forms of cysteamine in mouse tissues are presented.

Benextramine-neuropeptide Y receptor interactions: contribution of the benzylic moieties to [3H]neuropeptide Y displacement activity

Analogs of N,N'-bis[6-[(2-methoxybenzyl)amino]hex-1-yl]cystamine (benextramine, BXT, 2) were synthesized using solution-phase peptide synthesis methodology and analyzed for activity in displacing specifically bound 1 nM N-[propionyl-3H]neuropeptide Y([3H]NPY) from benextramine-sensitive neuropeptide Y (NPY) binding sites in rat brain. Our new synthetic approach to these analogs began with the acylation of cystamine with the N-hydroxysuccinimide ester of tert-butyloxycarbonyl (t-Boc) protected 6-aminohexanoic acid, followed by deprotection of the t-Boc groups with 4 N HCl in dioxane. Acylation of this symmetric diamine with N-hydroxysuccinimide esters of appropriately substituted benzoic acids, followed by reduction of the resultant tetraamides with diborane in refluxing THF, afforded the target compounds. The BXT analog lacking the benzylic group (i.e., compound 11) had no [3H]NPY displacement activity at concentrations up to 1.4 x 10(-3) M. The 9-fold range in activities observed for the ortho, meta, and para regioisomers of the methoxy, chloro, and hydroxy benextramine analogs at benextramine-sensitive NPY rat brain binding sites does not differ from the range of potencies observed at alpha-adrenoceptors. However, the order of potencies at [3H]NPY sites differs from the order of potencies at alpha-adrenoceptors, with the m-methoxyphenyl (9a), m-hydroxyphenyl (10b), and 2-naphthyl (9f) analogs being the most active at [3H]NPY binding sites. The present results demonstrate the importance of the benzylic moiety for BXT's NPY antagonist activity, and suggest that the BXT binding site on the NPY receptor is significantly distinct from that on the alpha-adrenoceptor.

Introduction of sulfhydryl groups into proteins at carboxyl sites

A two-step procedure for introduction of sulfhydryl groups at protein carboxyl groups is described. The resultant proteins contain 2-aminoethanethiol residues bound by amide linkages to the protein carboxyl groups. First an amide bond is formed between a carboxyl group of the protein and one of the amino groups of cystamine. Then the disulfide bond is reduced with dithiothreitol, yielding the amide of 2-aminoethanethiol. This procedure was used to incorporate sulfhydryl groups into carbonic anhydrase and adrenocorticotropic hormone. The effect of carbodiimide concentration and pH of the coupling reaction on stoichiometry of sulfhydryl group incorporation was examined. The method was used to prepare bovine carbonic anhydrase containing up to nine sulfhydryl groups per molecule with no loss of enzymatic activity and biologically active adrenocorticotropic hormone containing one sulfhydryl group per molecule.

The accumulation of cystamine and its metabolism to taurine in rat lung slices

The objective of these studies was to determine the accumulation and fate of the disulphide, cystamine by rat lung slices. Cystamine was accumulated by two active uptake systems that obeyed saturation kinetics, with apparent Km values of 12 and 503 microM, and maximal rates of 530 and 5900 nmol/g wet weight/hr respectively. The high affinity system was competitively inhibited by the diamine, putrescine and the herbicide paraquat, which are themselves accumulated. Thus, this pulmonary uptake process appears to be identical for all three compounds. In contrast, the low affinity process was not inhibited by putrescine, and this process results from the diffusion of cystamine into the cell and its subsequent metabolism. Upon accumulation, cystamine was metabolised, predominantly to the sulphonic acid, taurine, with 10-20% of the intracellular label covalently binding to protein. Conversion to taurine was unaffected by amine oxidase inhibitors, but was decreased after GSH depletion, suggesting that pulmonary cystamine metabolism is glutathione-dependent, and is not mediated by diamine oxidase. Both cystamine and taurine have been implicated as antioxidants, and we suggest that cystamine is actively accumulated by the lung as part of the process to protect pulmonary tissue against oxidative stress.

Glucose-6-phosphate dehydrogenase and glutathione reductase activity in methemoglobin reduction by methylene blue and cystamine. Study on glucose-6-phosphate dehydrogenase-deficient individuals, on normal subjects and on riboflavin-treated subjects

The authors have standardized methods for evaluation of the activity of the glucose-6-phosphate dehydrogenase and of glutathione reductase. The general principle of the first method was based on methemoglobin formation by sodium nitrite followed by stimulation of the glucose-6-phosphate dehydrogenase with methylene blue. Forty six adults (23 males and 23 females) were studied. Subjects were not G6PD deficient and were aged 20 to 30 years. The results showed that methemoglobin reduction by methylene blue was 154.40 and 139.90 mg/min (p<0.05) for males and females, respectively, in whole blood, and 221.10 and 207.85 mg/min (n.s.), respectively, in washed red cells. These data showed that using washed red cells and 0.7g% sodium nitrite concentration produced no differences between sexes and also shortened reading time for the residual amount of methemoglobin to 90 minutes. Glutathione reductase activity was evaluated on the basis of the fact that cystamine (a thiol agent) binds to the SH groups of hemoglobin, forming complexes. These complexes are reversed by the action of glutathione reductase, with methemoglobin reduction occurring simultaneously with this reaction. Thirty two adults (16 males and 16 females) were studied. Subjects were not G6PD deficient and were aged 20 to 30 years. Methemoglobin reduction by cystamine was 81.27 and 91.13 mg/min (p<0.01) for males and females, respectively. These data showed that using washed red cells and 0.1 M cystamine concentration permits a reading of the residual amount of methemoglobin at 180 minutes of incubation. Glutathione reductase activity was evaluated by methemoglobin reduction by cystamine in 14 females before and after treatment with 10 mg riboflavin per day for 8 days. The results were 73.69 and 94.26 jug/min (p<0.01) before and after treatment, showing that riboflavin treatment increase glutathione reductase activity even in normal individuals. Three Black G6PD-deficient individuals (2 males and 1 female) were also studied. The G6PD and glutathione reductase were partially activated, the change being more intense in males. On the basis of race and of the laboratory characteristics observed, it is possible to suggest that the G6PD deficiency of these individuals is of the African type and that the female is heterozygous for this deficiency. Analysis of the results as a whole permitted us to conclude that the methods proposed here were efficient for evaluating the activity of the glucose-6-phosphate dehydrogenase and of glutathione reductase. The latter is dependent on the pentose pathway, which generates NADPH, and on riboflavin, a FAD precursor vitamin.

Cysteamine-induced decrease of somatostatin in rat brain synaptosomes in vitro

The mechanism of somatostatin depletion induced by cysteamine [2-mercaptoethylamine (CySH)] was studied in isolated nerve endings (synaptosomes) from rat brain in vitro. A dose-dependent reduction of somatostatin-like immunoreactivity (SLI) was observed which reached its maximal extent (41%) at a concentration of 300 microM CySH after 1-5 min. There was no release of somatostatin into the incubation medium. CySH at concentrations of up to 10 mM did not interfere in the RIA. Among a variety of compounds, structurally related to CySH 4-aminothiophenol, 2-aminothiophenol and N,N-dimethylaminothiol exhibited the highest efficacy in decreasing somatostatin (60%, 50%, 30%, respectively, at 10 mM and 10 min). The disulfide form of CySH cystamine and dimercaprol resulted in about 15% reduction after 10-min incubation, whereas taurine, alanine, cysteine, and mercaptoethanol were inactive. A saturable, sodium-dependent uptake process was found for the disulfide form of [35S]CySH cystamine [Michaelis-Menten constant (Km) = 18.6 microM, maximum velocity (Vmax) = 2.3 nmol/mg protein X 3 min) which was inhibited by cysteine (87% at 1 mM). [35S]CySH, at concentrations of 20 microM or less, was not stable in buffer solution. It underwent considerable nonenzymatic conversion into its dimeric form (60% at 37 C and 3 min), however it exhibited the same kinetic data for its uptake. Size exclusion HPLC of purified hypothalamic synaptosomes revealed a major SLI peak coeluting with synthetic somatostatin-14 and two minor peaks representing somatostatin-28 and a 13,000 mol wt protein. The three molecular forms of somatostatin were reduced to varied extent by CySH (somatostatin-14 by about 70%, somatostatin-28 by 15%, and the high mol wt form by 30%). Our experiments suggest that high affinity uptake of CySH may precede its action in decreasing somatostatin levels. Increased release or inhibition of synthesis of somatostatin have been excluded as possible mechanisms. It is suggested that SLI is equally affected in nerve endings and in perikarya.

The interaction of cystamine with bovine brain tubulin

Microtubule assembly in vitro is sensitive to a variety of non-physiological sulfhydryl-oxidizing agents, but the physiological significance of this phenomenon is unknown, since no physiological sulfhydryl-oxidizing agent has been shown to affect microtubule assembly in vitro. We have accordingly investigated the interaction of tubulin with cystamine. We have found that millimolar concentrations of cystamine inhibit microtubule assembly and induce an abnormal form of tubulin polymerization. Cystamine-induced polymerization does not occur at cold temperature. Formation of the polymer requires reaction of cystamine with two sulfhydryls which become available at 37 degrees C. In addition, cystamine reacts with about three sulfhydryls at 0 degrees C without inducing polymerization. This latter set of sulfhydryls appear to include one or both of the previously defined beta s sulfhydryls whose reaction with N, N'-ethylene-bis(iodoacetamide) is markedly inhibited by GTP, maytansine and vinblastine [Roach, M. C. & Luduena, R. F. (1984) J. Biol. Chem. 259, 12063-12071]. Cystamine's specific manner of interacting with tubulin suggests that it may mimic an endogenous sulfhydryl-directed regulator of microtubule assembly.

[Radioprotective effect of drug combinations on the small intestine]

The study of the radioprotective effect of complexes containing small amounts of cystamine or gammaphos mixed with mexamine, gutimine and ethyrone on mouse small intestine showed high efficiency of the drugs as determined by cellularity and DNA-synthesizing activity of intestinal epithelium. This is connected with the influence of the complex mexamine + gutimine + ethyrone on the pharmacodynamics and pharmacokinetics of cystamine and gammaphos.

Methylthio-capping of selenocysteamine: preliminary studies on selective toxicity for cancer chemotherapy

Dimethyl disulfide markedly increased the cytotoxicity of selenocystamine by 2 orders of magnitude, from 40 microM to 0.5 microM for 50% inhibition of growth in 45 hr. When mice were injected ip with 22 microMole/Kg of selenocystamine on Day 0, all were dead on Day 4. If dimethyl disulfide (500 microMole/Kg) was either mixed with the selenocystamine or injected immediately prior to it, the mice survived treatment for at least 21 days afterwards, suggesting that methylthio-capping of selenocysteamine reduced host toxicity. Such combined treatment may be of value in chemotherapy.

Cysteamine depletes cystinotic leucocyte granular fractions of cystine by the mechanism of disulphide interchange

Cystinotic lysosome-rich leucocyte granular fractions, loaded with [35S]cystine, were exposed to different cystine-depleting agents. During a 30 min incubation at 37 degrees C, untreated cystinotic granular fractions lost negligible [35S]cystine when corrected for lysosome rupture. Granular fractions exposed to 0.1 mM-cysteamine lost 64% of their initial cystine, and hexosaminidase activity was decreased by 10%. This was accompanied by the formation of high concentrations of [35S]cysteine-cysteamine mixed disulphide within the granular-fraction pellet, and, in the presence of N-ethylmaleimide, increasing amounts of [35S]cysteine-N-ethylmaleimide adduct outside the granular fraction. In separate experiments, [35S]cystine exited cystinotic leucocyte lysosomes at a negligible rate (half-times 199 and 293 min), but [35S]cysteine-cysteamine mixed disulphide exhibited substantial egress (half-times 66 and 88 min) and was recovered intact outside the granular-fraction pellet. We conclude that cysteamine depletes lysosomes of cystine by participating in a thiol-disulphide interchange reaction to produce cysteine and cysteine-cysteamine mixed disulphide, both of which traverse the cystinotic leucocyte lysosomal membrane.

Kinetic mechanism and specificity of bovine milk sulphydryl oxidase

Sulphydryl oxidase is known to catalyse the synthesis de novo of disulphide bonds in a variety of thiol-containing compounds. Reduced glutathione is the best thiol substrate; however, D- and L-cysteine, cysteamine and N-acetyl-L-cysteine, as well as cysteine-containing peptides and proteins, are also effectively oxidized. In contrast, oxidation of the thiol groups of mercaptoethanol, mercaptopyridine, dithiothreitol, dithioerythritol, mercaptoacetate, mercaptopropionate or lipoic acid is not detectably catalysed. In bovine milk, sulphydryl oxidase is closely associated with another glutathione-metabolizing enzyme, gamma-glutamyltransferase. Covalent chromatography of crude preparations on cysteinylsuccinamidopropyl-glass resolves the oxidase from the transferase, thus permitting the kinetic characterization of glutathione oxidation. Initial-rate data imply a Ter Bi substituted-enzyme mechanism, and the observed substrate inhibition by thiols suggest that O2 binds first. Independent, non-kinetic, data, namely the immobilization of sulphydryl oxidase on cysteinyl-matrices, support formation of a mixed-disulphide intermediate between the thiol and enzyme, as predicted by the proposed mechanism. The enzyme-catalysed reaction appears not to be mediated via a superoxide intermediate, since O2 consumption is not affected by the presence of Nitro Blue Tetrazolium. FAD, NAD+, NADP+ and Nitro Blue Tetrazolium are all inactive as electron acceptors for sulphydryl oxidase catalysis.

Determination of cystamine by high-performance liquid chromatography

A highly sensitive and specific assay method for cystamine using high-performance liquid chromatography has been developed. The method is based on postcolumn derivatization of cystamine with o-phthaladehyde in the presence of 2-mercaptoethanol and sodium hypochlorite. The separation of cystamine was achieved using a cation exchange column (ISC-05/S0504). The assay was linear over the concentration range of 2 to 200 pmol. For the application of this assay method to biological materials, the pretreatment with a cation exchange column (Dowex 50W X 8) was necessary to remove interfering o-phthaladehyde-reactive substances. Since cysteamine in biological materials was quantitatively converted to cystamine during these sampling procedures, this method was found to be suitable for assaying the cysteamine plus cystamine content in various organs and tissues. The cysteamine-cystamine content in various tissues of rat determined by the present assay method has been presented.

The irreversible alpha-blocker benextramine interacts with two different thiol groups

beta-Haloalkylamines bind at two sites on the adrenergic alpha-receptor, one related to the noradrenaline-recognition site and the other possibly concerned with the calcium channel. In order to verify whether this might apply to other alpha-blockers the tetramine disulfide benextramine was selected owing to its unprecedented covalent selectivity towards the adrenergic alpha-receptor. The fast acting beta-haloalkylamine DMPEA and the "classical" calcium antagonist verapamil were used for protection experiments against benextramine blockade of rat vas deferens adrenergic alpha-receptor. It was demonstrated that two target thiols are probably involved in benextramine binding and one of them might possibly be located at the periphery of, or masked within, the calcium channel which may be connected physiologically to the adrenergic alpha-receptor. However, the hypothesis that the present results could indicate the selective interaction of benextramine with two different subtypes of the adrenergic alpha-receptor is also discussed.

[Mechanisms of potentiating and prolonging the radioprotective effect of multicomponent compounds]

A study was made of the effect of mexamine, etiron and gutimine on the pattern of distribution of cystamine within the body and the rate of its conversion in tissues of albino mice. It was shown that the potentiation and prolongation of the radioprotective effect is based on the ability of the complex of these preparations to inhibit the conversion of the S-containing radioprotective agent.

Molecular properties of the adrenergic alpha-receptor. I--Structural requirements for specific covalent occupancy by N,N'-bis--(5-aminopentyl)cystamine derivatives

The synthesis and alpha-adrenoreceptor blocking activity of several substituted analogs of the prototype alpha-blocker N,N'-bis-(5-aminopentyl)cystamine (APC) are described. The three optical forms of the analog carrying methyl groups on the carbons alpha- to the sulfurs were synthesized and shown to be equipotent and somewhat less active than APC. The omega, omega'-bis-guanidino analog of APC was less active. Significant improvement in potency was observed only with APC analogs carrying benzyl and substituted benzyl groups on the terminal nitrogens. Linking the terminal nitrogens of APC with a p.xyledenyl group so as to give the 26-membered analog caused a sharp drop in activity. The significance of these results as regards the alpha-receptor topography is discussed.

[Comparative study of cystamine conversion in the tissues of white mice and rats]

At different periods following introduction to animals of radioprotector cystamine its unchanged form and oxidation products (hypotaurine and taurine) in tissues were determined. In the tissues of mice and rats the cystamine metabolism is shown to proceed at varying rates, correlating with the level of basal metabolism.

Oxidation of selenocystamine by diamineoxidase

Selenocystamine is oxidatively deaminated by pig kidney diamineoxidase. The first product of the reaction is the corresponding cyclized aminoaldehyde, selenocystaldimine, which then undergoes further degradation. The oxidative deamination is thus the first step of a series of cyclic reactions which give rise to extensive cleavage of selenocystamine.