Mesna (2-mercaptoethane sodium sulfonate) functions as a regulator of myeloperoxidase

Myeloperoxidase (MPO), an abundant protein in neutrophils, monocytes, and macrophages, is thought to play a critical role in the pathogenesis of various disorders ranging from cardiovascular diseases to cancer. We show that mesna (2-mercaptoethanesulfonic acid sodium salt), a detoxifying agent, which inhibits side effects of oxazaphosphorine chemotherapy, functions as a potent inhibitor of MPO; modulating its catalytic activity and function. Using rapid kinetic methods, we examined the interactions of mesna with MPO compounds I and II and ferric forms in the presence and absence of chloride (Cl^-), the preferred substrate of MPO. Our results suggest that low mesna concentrations dramatically influenced the build-up, duration, and decay of steady-state levels of Compound I and Compound II, which is the rate-limiting intermediate in the classic peroxidase cycle. Whereas, higher mesna concentrations facilitate the porphyrin-to-adjacent amino acid electron transfer allowing the formation of an unstable transient intermediate, Compound I*, that displays a characteristic spectrum similar to Compound I. In the absence of plasma level of chloride, mesna not only accelerated the formation and decay of Compound II but also reduced its stability in a dose depend manner. Mesna competes with Cl^-, inhibiting MPO's chlorinating activity with an IC₅₀ of 5µM, and switches the reaction from a 2e^- to a 1e^- pathway allowing the enzyme to function only with catalase-like activity. A kinetic model which shows the dual regulation through which mesna interacts with MPO and regulates its downstream inflammatory pathways is presented further validating the repurposing of mesna as an anti-inflammatory drug.

Persistent adult zebrafish behavioral deficits results from acute embryonic exposure to gold nanoparticles

As the number of products containing nanomaterials increase, human exposure to nanoparticles (NPs) is unavoidable. Presently, few studies focus on the potential long-term consequences of developmental NP exposure. In this study, zebrafish embryos were acutely exposed to three gold NPs that possess functional groups with differing surface charge. Embryos were exposed to 50 μg/mL of 1.5 nm gold nanoparticles (AuNPs) possessing negatively charged 2-mercaptoethanesulfonic acid (MES) or neutral 2-(2-(2-mercaptoethoxy)ethoxy)ethanol (MEEE) ligands or 10 μg/mL of the AuNPs possessing positively charged trimethylammoniumethanethiol (TMAT). Both MES- and TMAT-AuNP exposed embryos exhibited hypo-locomotor activity, while those exposed to MEEE-AuNPs did not. A subset of embryos that were exposed to 1.5 nm MES- and TMAT-AuNPs during development from 6 to 120 h post fertilization was raised to adulthood. Behavioral abnormalities and the number of survivors into adulthood were evaluated at 122 days post fertilization. We found that both treatments induced abnormal startle behavior following a tap stimulus. However, the MES-AuNPs exposed group also exhibited abnormal adult behavior in the light and had a lower survivorship into adulthood. This study demonstrates that acute, developmental exposure to 1.5 nm MES- and TMAT-AuNPs, two NPs differing only in the functional group, affects larval behavior, with behavioral effects persisting into adulthood.

Determination of the sodium 2-mercaptoethanesulfonate based on surface-enhanced Raman scattering

Based on the surface-enhanced Raman scattering (SERS) sodium 2-mercaptoethanesulfonate (mesna) was determined using unmodified gold colloid as the probe. The Raman scattering intensity was obviously enhanced in the presence of sodium chloride. The influence of experimental parameters, such as incubation time, sodium chloride concentration and pH value on SERS performance was examined. Under the optimum conditions, the SERS intensity is proportional to the concentration of mesna in the range of 9.0×10(-8) to 9.0×10(-7) mol/L and detection limit (S/N=3) is 1.16×10(-8) mol/L. The corresponding correlation coefficient of the linear equation is 0.996, which indicates that there is a good linear relationship between SERS intensity and mesna concentration. The experimental results indicate that the proposed method is a viable method for determination of mesna. The real samples were analyzed and the results obtained were satisfactory.

Chemoselective protein and peptide immobilization on biosensor surfaces

Site-specific immobilization of proteins and peptides on a sensor surface represents a significant challenge for bioanalytical applications such as surface plasmon resonance (SPR). The most common protocols for covalent protein immobilization usually result in heterogeneous presentation of the ligand at the surface, which can in some instances yield conflicting results with analogous data obtained in solution. Here, we discuss two complementary and generic bioconjugation methods that allow chemoselective immobilization of peptides and proteins via either their C-terminus (native chemical ligation) or their N-terminus (oxime ligation). While the protocols described in this chapter were designed for use in a Biacore instrument, the methods should also be applicable to other SPR instruments and, with slight adjustments, to many other types of bioanalytical applications that rely on protein-functionalized surfaces.

Inhibition of HSV-1 attachment, entry, and cell-to-cell spread by functionalized multivalent gold nanoparticles

The use of modified nanoparticles in interactions with biological targets is attracting rapidly increasing attention. In this Full Paper, the application of gold nanoparticles capped with mercaptoethanesulfonate (Au-MES NPs) as effective inhibitors of Herpes simplex virus type 1 infection based on their ability to mimic cell-surface-receptor heparan sulfate is described. Mechanistic studies reveal that Au-MES NPs interfere with viral attachment, entry, and cell-to-cell spread, thereby preventing subsequent viral infection in a multimodal manner. The ligand multiplicity achieved with carrier nanoparticles is crucial in generating polyvalent interactions with the virus at high specificity, strength, and efficiency. Such multivalent-nanoparticle-mediated inhibition is a promising approach for alternative antiviral therapy.

Determination and applications of the molar absorptivity of phenolic adducts with captopril and mesna

Captopril and mesna are molecules with a free thiol group, used as active ingredients due to their hypotensor and mucolytic properties, respectively. These compounds cross the hematoencephalic barrier and, due to the reactivity of their thiol group, can form adducts with the o-quinones formed during the oxidation of mono- and o-diphenols. Polyphenol oxidase from plants and fungi can be used as a tool for generating o-quinones in their action on o-diphenols and facilitate the formation of adducts in the presence of captopril or mesna. The spectrophotometric characterization of these adducts is useful from several points of view. Here, using the end-point method, which involves the exhaustion of oxygen in the medium, we determined the molar absorptivity of the adducts of different o-diphenols with captopril and mesna. Besides the analytical interest of this approach, we also use it to make a kinetic characterization of polyphenol oxidase as it acts on o-diphenolic substrates that produce unstable o-quinones.

[Study on interaction of acetaldehyde with thioalcohols by infrared spectroscopy]

The reaction of acetaldehyde with thioalcohols, Mesna (monothiol) and Unithiol (vicinal dithiol) was investigated by infrared spectroscopy. Unithiol was more active in the reaction of acetaldehyde fixation than Mesna. This property may explain high efficiency of peroral administration of Unithiol for treatment of postalcoholic intoxication (hangover).

Direct interaction of coenzyme M with the active-site Fe-S cluster of heterodisulfide reductase

Heterodisulfide reductase (HDR) catalyzes the formation of coenzyme M (CoM-SH) and coenzyme B (CoB-SH) by the reversible reduction of the heterodisulfide, CoM-S-S-CoB. This reaction recycles the two thiol coenzymes involved in the final step of microbial methanogenesis. Electron paramagnetic resonance (EPR) and variable-temperature magnetic circular dichroism spectroscopic experiments on oxidized HDR incubated with CoM-SH revealed a S=1/2 [4Fe-4S]3) cluster, the EPR spectrum of which is broadened in the presence of CoM-33SH [Duin, E.C., Madadi-Kahkesh, S., Hedderich, R., Clay, M.D. and Johnson, M.K. (2002) Heterodisulfide reductase from Methanothermobacter marburgensis contains an active-site [4Fe-4S] cluster that is directly involved in mediating heterodisulfide reduction. FEBS Lett. 512, 263-268; Duin, E.C., Bauer, C., Jaun, B. and Hedderich, R. (2003) Coenzyme M binds to a [4Fe-4S] cluster in the active site of heterodisulfide reductase as deduced from EPR studies with the [33S]coenzyme M-treated enzyme. FEBS Lett. 538, 81-84]. These results provide indirect evidence that the disulfide binds to the iron-sulfur cluster during reduction. We report here direct structural evidence for this interaction from Se X-ray absorption spectroscopic investigation of HDR treated with the selenium analog of coenzyme M (CoM-SeH). Se K edge extended X-ray absorption fine structure confirms a direct interaction of the Se in CoM-SeH-treated HDR with an Fe atom of the Fe-S cluster at an Fe-Se distance of 2.4A.

Effect of the electrostatic interaction on the redox reaction of positively charged cytochrome C adsorbed on the negatively charged surfaces of acid-terminated alkanethiol monolayers on a Au(111) electrode

The electrochemical properties of cytochrome c (cyt c) adsorbed on mixed self-assembled monolayers (SAMs) of 2-mercaptoethanesulfonate (MES)/2-mercaptoethanol (MEL) are compared with those on single-component SAMs of MES, MEL, and mercaptopropionic acid (MPA), using cyclic voltammetry and potential-modulated UV-vis reflectance spectroscopy. The rate constant of electron transfer (ET), k(et), of cyt c adsorbed on the SAM of MPA decreases from 1450 +/- 210 s(-1) at pH 7 to 890 +/- 100 s(-1) at pH 9. In contrast, the value of k(et) of cyt c on the SAM of MES is pH-independent at 100 +/- 15 s(-1). Those facts suggest that a large negative charge density on the SAM surface slows down the ET between cyt c and the electrode. The surface charge density of the SAM affects also the amount of electroactive cyt c, Gamma(e), which decreases from 10.0 +/- 1.0 to 5.3 +/- 1.1 pmol cm(-2) with increasing pH from 7 to 9 on the SAM of MPA. Similarly, the k(et) of cyt c adsorbed on the mixed SAMs of MES/MEL sharply decreases from 900 +/- 300 s(-1) to 110 s(-1) as the surface mole fraction of MES increases beyond 0.5, suggesting the presence of a negative surface charge threshold beyond which the rate of ET of cyt c is dramatically lowered. The decrease in the k(et) on the SAMs at high negative charge densities probably results from the confinement of adsorbed cyt c by the strong electrostatic force to an orientation that is not optimal for the ET reaction.

Photoactivated luminescent CdSe quantum dots as sensitive cyanide probes in aqueous solutions

Water-soluble luminescent CdSe quantum dots surface-modified with 2-mercaptoethane sulfonate were synthesized for the selective determination of free cyanide in aqueous solution with high sensitivity (detection limit of 1.1 x 10(-6) M), via analyte-induced changes in their photoluminescence after photoactivation.

The stereoselectivity and catalytic properties of Xanthobacter autotrophicus 2-[(R)-2-Hydroxypropylthio]ethanesulfonate dehydrogenase are controlled by interactions between C-terminal arginine residues and the sulfonate of coenzyme M

2-[(R)-2-Hydroxypropylthio]ethanesulfonate (R-HPC) dehydrogenase (DH) catalyzes the reversible oxidation of R-HPC to 2-(2-ketopropylthio)ethanesulfonate (2-KPC) in a key reaction in the bacterial conversion of chiral epoxides to beta-keto acids. R-HPCDH is highly specific for the R-enantiomer of HPC, while a separate enzyme, S-HPCDH, catalyzes the oxidation of the corresponding S-enantiomer. In the present study, the features of substrate and enzyme imparting stereospecificity have been investigated for R-HPCDH. S-HPC was a substrate for R-HPCDH with a K(m) identical to that for R-HPC but with a k(cat) 600 times lower. Achiral 2-propanol and short-chain (R)- and (S)-2-alkanols were substrates for R-HPCDH. For (R)-alkanols, as the carbon chain length increased, K(m) decreased, with the K(m) for (R)-2-octanol being 1700 times lower than for 2-propanol. At the same time, k(cat) changed very little and was at least 90% lower than k(cat) for R-HPC and at least 22 times higher than k(cat) for S-HPC. (S)-2-Butanol and (S)-2-pentanol were substrates for R-HPCDH. The K(m) for (S)-2-butanol was identical to that for (R)-2-butanol, while the K(m) for (S)-2-pentanol was 7.5 times higher than for (R)-2-pentanol. Longer chain (S)-2-alkanols were sufficiently poor substrates for R-HPCDH that kinetic parameters could not be determined. Mutagenesis of C-terminal arginine residues of R-HPCDH revealed that R152 and R196 are essential for effective catalysis with the natural substrates R-HPC and 2-KPC but not for catalysis with 2-alkanols or ketones as substrates. Short-chain alkylsulfonates and coenzyme M (2-mercaptoethanesulfonate) were found to modify the kinetic parameters for 2-butanone reduction by R-HPCDH in a saturable fashion, with the general effect of increasing k(cat), decreasing K(m), and increasing the enantioselectivity of 2-butanone reduction to a theoretical value of 100% (S)-2-butanol. The modulating effects of ethanesulfonate and propanesulfonate provided thermodynamic binding constants close to K(m) for the natural substrates R-HPC and 2-KPC. The effects of alkylsulfonates on modulating the enantioselectivity and kinetic properties of R-HPCDH were abolished in R152A and R196A mutants but not in mutants of other C-terminal arginine residues. Collectively, the results suggest that interactions between the sulfonate of CoM and specific arginine residues are key to the enantioselectivity and catalytic efficiency of R-HPCDH. A model is proposed wherein sulfonate-arginine interactions within an alkylsulfonate binding pocket control the catalytic properties of R-HPCDH.

Probing the reactivity of Ni in the active site of methyl-coenzyme M reductase with substrate analogues

Methyl-coenzyme M reductase (MCR) catalyses the reduction of methyl-coenzyme M (CH(3)-S-CoM) with coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. It contains the nickel porphyrinoid F(430) as prosthetic group which has to be in the Ni(I) oxidation state for the enzyme to be active. The active enzyme exhibits an axial Ni(I)-derived EPR signal MCR-red1. We report here on experiments with methyl-coenzyme M analogues showing how they affect the activity and the MCR-red1 signal of MCR from Methanothermobacter marburgensis. Ethyl-coenzyme M was the only methyl-coenzyme M analogue tested that was used by MCR as a substrate. Ethyl-coenzyme M was reduced to ethane (apparent K(M)=20 mM; apparent V(max)=0.1 U/mg) with a catalytic efficiency of less than 1% of that of methyl-coenzyme M reduction to methane (apparent K(M)=5 mM; apparent V(max)=30 U/mg). Propyl-coenzyme M (apparent K(i)=2 mM) and allyl-coenzyme M (apparent K(i)=0.1 mM) were reversible inhibitors. 2-Bromoethanesulfonate ([I](0.5 V)=2 micro M), cyano-coenzyme M ([I](0.5 V)=0.2 mM), 3-bromopropionate ([I](0.5 V)=3 mM), seleno-coenzyme M ([I](0.5 V)=6 mM) and trifluoromethyl-coenzyme M ([I](0.5 V)=6 mM) irreversibly inhibited the enzyme. In their presence the MRC-red1 signal was quenched, indicating the oxidation of Ni(I) to Ni(II). The rate of oxidation increased over 10-fold in the presence of coenzyme B, indicating that the Ni(I) reactivity was increased in the presence of coenzyme B. Enzyme inactivated in the presence of coenzyme B showed an isotropic signal characteristic of a radical that is spin coupled with one hydrogen nucleus. The coupling was also observed in D(2)O. The signal was abolished upon exposure of the enzyme to O(2). 3-Bromopropanesulfonate ([I](0.5 V)=0.1 micro M), 3-iodopropanesulfonate ([I](0.5 V)=1 micro M), and 4-bromobutyrate also inactivated MCR. In their presence the EPR signal of MCR-red1 was converted into a Ni-based EPR signal MCR-BPS that resembles in line shape the MCR-ox1 signal. The signal was quenched by O(2). 2-Bromoethanesulfonate and 3-bromopropanesulfonate, which both rapidly reacted with Ni(I) of MRC-red1, did not react with the Ni of MCR-ox1 and MCR-BPS. The Ni-based EPR spectra of both inactive forms were not affected in the presence of high concentrations of these two potent inhibitors.

Stability of Cyclophosphamide and Mesna Admixtures in Polyethylene Infusion Bags

BACKGROUND

Cyclophosphamide (CYP) is used to treat cancers in combination with mesna to prevent cystitis. The use of extemporaneously prepared admixtures of these drugs must be supported by documentation of their chemical stability.

OBJECTIVE

To evaluate the chemical stability of CYP and mesna admixtures in dextrose 5% polyethylene infusion bags.

METHODS

The drugs were diluted in 100-mL dextrose 5% infusion bags to final concentrations of CYP 10.8 mg/mL with mesna 3.2 mg/mL (solution A) and CYP 1.8 mg/mL with mesna 0.54 mg/mL (solution B). Six infusion bags from each solution were stored at 4 degrees C and 6 were stored at room temperature. Triplicate HPLC determinations were performed on each bag to measure drug concentrations at 0, 1, 2, 4, 6, 12, 24, 48, and 96 hours.

RESULTS

At 96 hours, drug concentrations in all solutions stored at room temperature were found to be <80% compared with the initial concentrations. The solutions stored at 4 degrees C retained at least 90% of the initial drug concentrations at 48 hours. The pH of solutions A and B stored at room temperature decreased significantly by 4.44 and 4.31 units, respectively. The pH of the refrigerated infusion bags decreased significantly by 1.46 units for solution B.

CONCLUSIONS

Admixtures stored at 4 degrees C (pH 7.90 +/- 0.004; mean +/- SD) are stable for 48 hours. The CYP and mesna combination can be infused at room temperature over 6 hours without significant degradation of the drugs. Stabilities are dependent on pH, temperature, and/or concentration.

Biocatalytic conversion of epoxides

Epoxides are attractive intermediates for producing chiral compounds. Important biocatalytic reactions involving epoxides include epoxide hydrolase mediated kinetic resolution, leading to the formation of diols and enantiopure remaining substrates, and enantioconvergent enzymatic hydrolysis, which gives high yields of a single enantiomer from racemic mixtures. Epoxides can also be converted by non-hydrolytic enantioselective ring opening, using alternative anionic nucleophiles; these reactions can be catalysed by haloalcohol dehalogenases. The differences in scope of these enzymatic conversions is related to their different catalytic mechanisms, which involve, respectively, covalent catalysis with an aspartate carboxylate as the nucleophile and non-covalent catalysis with a tyrosine that acts as a general acid-base. The emerging new possibilities for enantioselective biocatalytic conversion of epoxides suggests that their importance in green chemistry will grow.

Inactivation of acrolein by sodium 2-mercaptoethanesulfonate using headspace-solid-phase microextraction gas chromatography and mass spectrometry

Acrolein, the metabolite of cyclophosphamide and ifosphamide, is an irritant of mucous membranes and seems to play an important role in hemorrhagic cystitis. Several methods are available to reduce the risk of hemorrhagic cystitis. Mesna is a regional detoxificant which inactivates acrolein. However, the interaction of mesna and acrolein has never been reported because no available method can detect acrolein. In this study, we measured acrolein to evaluate the effect of mesna in urine or phosphate-buffered saline using a headspace-solid-phase microextraction gas chromatography and mass spectrometry method which we had previously established. We also investigated the effect of mesna at different conditions of pH. Mesna was effective in a dose-dependent (10 microM to 20 mM) fashion in both urine and phosphate-buffered saline and completely inactivated acrolein at concentrations over 10 mM. Furthermore, mesna was more effective in alkaline conditions than in acid.

Catalysis by methyl-coenzyme M reductase: a theoretical study for heterodisulfide product formation

Hybrid density functional theory has been used to investigate the catalytic mechanism of methyl-coenzyme M reductase (MCR), an essential enzyme in methanogenesis. In a previous study of methane formation, a scheme was suggested involving oxidation of Ni(I) in the starting square-planar coordination to the high-spin Ni(II) form in the CoM-S-Ni(II)F(430) octahedral intermediate. The methyl radical, concomitantly released by methyl-coenzyme M (CoM), is rapidly quenched by hydrogen atom transfer from the coenzyme B (CoB) thiol group, yielding methane as the first product of the reaction. The present investigation primarily concerns the second and final step of the reaction: oxidation of CoB and CoM to the CoB-S-S-CoM heterodisulfide product and reduction of nickel back to the Ni(I) square-planar form. The activation energy for the second step is found to be around 10 kcal/mol, implying that the first step of methane formation with an activation energy of 20 kcal/mol should be rate-limiting. An oxygen of the Gln147 residue, occupying the rear axial position in the oxidized Ni(II) state, is shown to stabilize the intermediate by 6 kcal/mol, thereby slightly decreasing the barrier for the preceding rate-limiting transition state. The mechanism suggested is discussed in the context of available experimental data. An analysis of the flexibility of the F(430) cofactor during the reaction cycle is also given.

New approaches to drug discovery and development: a mechanism-based approach to pharmaceutical research and its application to BNP7787, a novel chemoprotective agent

Any approach applied to drug discovery and development by the medical community and pharmaceutical industry has a direct impact on the future availability of improved, novel, and curative therapies for patients with cancer. By definition, drug discovery is a complex learning process whereby research efforts are directed toward uncovering and assimilating new knowledge to create and develop a drug for the purpose of providing benefit to a defined patient population. Accordingly, a highly desirable technology or approach to drug discovery should facilitate both effective learning and the application of newly discovered observations that can be exploited for therapeutic benefit. However, some believe that drug discovery is largely accomplished by serendipity and therefore appropriately addressed by screening a large number of compounds. Clearly, this approach has not generated an abundance of new drugs for cancer patients and suggests that a tangibly different approach in drug discovery is warranted. We employ an alternative approach to drug discovery, which is based on the elucidation and exploitation of biological, pharmacological, and biochemical mechanisms that have not been previously recognized or fully understood. Mechanism-based drug discovery involves the combined application of physics-based computer simulations and laboratory experimentation. There is increasing evidence that agreement between simulations based on the laws of physics and experimental observations results in a higher probability that such observations are more accurate and better understood as compared with either approach used alone. Physics-based computer simulation applied to drug discovery is now considered by experts in the field to be one of the ultimate methodologies for drug discovery. However, the ability to perform truly comprehensive physics-based molecular simulations remains limited by several factors, including the enormous computer-processing power that is required to perform the formidable mathematical operations and data processing (e.g. memory bandwidth, data storage and retrieval). Another major consideration is the development of software that can generate an appropriate and increasingly complex physical representation of the atomic arrangements of biological systems. During the past 17 years, we have made tremendous progress in addressing some of these obstacles by developing and optimizing physics-based computer programs for the purpose of obtaining increasingly accurate and precise information and by improving the speed of computation. To perform physics-based simulations that involve complex systems of biological and pharmaceutical interest, we have developed methods that enable us to exceed Moore's law. This has been accomplished by parallel processing as well as other methods that have enabled us to study more complex and relevant molecular systems of interest. This paper provides an overview of our approach to drug discovery and describes a novel drug, currently in clinical development, which has directly resulted from the application of this approach.

The chemical reactivity of BNP7787 and its metabolite mesna with the cytostatic agent cisplatin: comparison with the nucleophiles thiosulfate, DDTC, glutathione and its disulfide GSSG

PURPOSE

BNP7787 is a new chemoprotective agent presently under clinical investigation to protect against cisplatin-induced toxicities, especially nephrotoxicity and neurotoxicity. In the kidneys BNP7787 is postulated to undergo selective conversion into mesna, which can locally detoxify cisplatin. The reactivity of cisplatin with this new chemoprotective agent and with its metabolite mesna was investigated at clinically observed plasma concentrations and compared with the nucleophiles thiosulfate (TS) and DDTC, and with the endogenous compounds glutathione (GSH) and oxidized glutathione (GSSG).

METHODS

Reaction kinetics experiments were performed at 37 degrees C and pH 7.4 in the presence of a high chloride concentration (0.15 M). The degradation of cisplatin was measured over time using HPLC with off-line flameless atomic absorption spectrophotometry.

RESULTS

The degradation half-lives of cisplatin (13.5 microM) with 17.2 m M BNP7787, 340 microM mesna and 17.2 m M mesna were 124 min, about 790 min and 73 min, respectively. Cisplatin reacted at least 9.5 times more slowly with 17.2 mM BNP7787 and 5.5 times more slowly with 17.2 mM mesna than with 17.2 mM of the modulating agents DDTC or TS (i.e. half-lives 11 and 13 min, respectively). The half-lives of cisplatin with 17.2 m M GSH and GSSG (i.e. 122 and 115 min, respectively) were comparable with the half-life obtained with BNP7787. The thiol mesna was shown to be a stronger nucleophile than its corresponding disulfide BNP7787.

CONCLUSIONS

The much slower relative reactivity of BNP7787, the short residence of BNP7787 (approximately 2 h) and the much lower concentration of mesna in the circulation following BNP7787 administration precludes chemical inactivation of cisplatin in the circulation, and thus the antitumor activity of cisplatin is maintained.

Nickel uptake and utilization by microorganisms

Nickel is an essential nutrient for selected microorganisms where it participates in a variety of cellular processes. Many microbes are capable of sensing cellular nickel ion concentrations and taking up this nutrient via nickel-specific permeases or ATP-binding cassette-type transport systems. The metal ion is specifically incorporated into nickel-dependent enzymes, often via complex assembly processes requiring accessory proteins and additional non-protein components, in some cases accompanied by nucleotide triphosphate hydrolysis. To date, nine nickel-containing enzymes are known: urease, NiFe-hydrogenase, carbon monoxide dehydrogenase, acetyl-CoA decarbonylase/synthase, methyl coenzyme M reductase, certain superoxide dismutases, some glyoxylases, aci-reductone dioxygenase, and methylenediurease. Seven of these enzymes have been structurally characterized, revealing distinct metallocenter environments in each case.

Vibrational spectroscopic studies of mesna and dimesna

Raman, and infrared spectra of mesna and dimesna have been collected in the present spectroscopic studies. Based on the group frequencies, relative intensities and Raman depolarization measurements, some vibrational assignments have been suggested. For both mesna and dimesna, at least two rotational conformers have been identified. Adsorption behavior was investigated from the recorded surface-enhanced Raman scattering (SERS) spectra. It was found that both mesna and dimesna adsorbed as thiolate on silver sol particles with the cleavage of the S-H bond in mesna and the S-S bond in dimesna. For the adsorbed thiolate, two conformers existed in the adsorption state.

Coenzyme B induced coordination of coenzyme M via its thiol group to Ni(I) of F430 in active methyl-coenzyme M reductase

Methyl-coenzyme M reductase (MCR) catalyzes the reaction of methyl-coenzyme M (CH3-S-CoM) with coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. At the active site, it contains the nickel porphinoid F430, which has to be in the Ni(I) oxidation state for the enzyme to be active. How the substrates interact with the active site Ni(I) has remained elusive. We report here that coenzyme M (HS-CoM), which is a reversible competitive inhibitor to methyl-coenzyme M, interacts with its thiol group with the Ni(I) and that for interaction the simultaneous presence of coenzyme B is required. The evidence is based on X-band continuous wave EPR and Q-band hyperfine sublevel correlation spectroscopy of MCR in the red2 state induced with 33S-labeled coenzyme M and unlabeled coenzyme B.

Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicus

The synthesis of formyl-methanofuran and the reduction of the heterodisulfide (CoM-S-S-CoB) of coenzyme M (HS-CoM) and coenzyme B (HS-CoB) are two crucial, H2-dependent reactions in the energy metabolism of methanogenic archaea. The bioenergetics of the reactions in vivo were studied in chemostat cultures and in cell suspensions of Methanothermobacter thermautotrophicus metabolizing at defined dissolved hydrogen partial pressures ( pH2). Formyl-methanofuran synthesis is an endergonic reaction (DeltaG degrees ' = +16 kJ.mol-1). By analyzing the concentration ratios between formyl-methanofuran and methanofuran in the cells, free energy changes under experimental conditions (DeltaG') were found to range between +10 and +35 kJ.mol-1 depending on the pH2 applied. The comparison with the sodium motive force indicated that the reaction should be driven by the import of a variable number of two to four sodium ions. Heterodisulfide reduction (DeltaG degrees ' = -40 kJ.mol-1) was associated with free energy changes as high as -55 to -80 kJ.mol-1. The values were determined by analyzing the concentrations of CoM-S-S-CoB, HS-CoM and HS-CoB in methane-forming cells operating under a variety of hydrogen partial pressures. Free energy changes were in equilibrium with the proton motive force to the extent that three to four protons could be translocated out of the cells per reaction. Remarkably, an apparent proton translocation stoichiometry of three held for cells that had been grown at pH2<0.12 bar, whilst the number was four for cells grown above that concentration. The shift occurred within a narrow pH2 span around 0.12 bar. The findings suggest that the methanogens regulate the bioenergetic machinery involved in CoM-S-S-CoB reduction and proton pumping in response to the environmental hydrogen concentrations.

Structural basis for CO2 fixation by a novel member of the disulfide oxidoreductase family of enzymes, 2-ketopropyl-coenzyme M oxidoreductase/carboxylase

The NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC) is the terminal enzyme in a metabolic pathway that results in the conversion of propylene to the central metabolite acetoacetate in Xanthobacter autotrophicus Py2. This enzyme is an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase (DSOR) family of enzymes that include glutathione reductase, dihydrolipoamide dehydrogenase, trypanothione reductase, thioredoxin reductase, and mercuric reductase. In contrast to the prototypical reactions catalyzed by members of the DSOR family, the NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase catalyzes the reductive cleavage of the thioether linkage of 2-ketopropyl-coenzyme M, and the subsequent carboxylation of the ketopropyl cleavage product, yielding the products acetoacetate and free coenzyme M. The structure of 2-KPCC reveals a unique active site in comparison to those of other members of the DSOR family of enzymes and demonstrates how the enzyme architecture has been adapted for the more sophisticated biochemical reaction. In addition, comparison of the structures in the native state and in the presence of bound substrate indicates the binding of the substrate 2-ketopropyl-coenzyme M induces a conformational change resulting in the collapse of the substrate access channel. The encapsulation of the substrate in this manner is reminiscent of the conformational changes observed in the well-characterized CO2-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxidase (Rubisco).

Structural basis for CO2 fixation by a novel member of the disulfide oxidoreductase family of enzymes, 2-ketopropyl-coenzyme M oxidoreductase/carboxylase

The NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC) is the terminal enzyme in a metabolic pathway that results in the conversion of propylene to the central metabolite acetoacetate in Xanthobacter autotrophicus Py2. This enzyme is an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase (DSOR) family of enzymes that include glutathione reductase, dihydrolipoamide dehydrogenase, trypanothione reductase, thioredoxin reductase, and mercuric reductase. In contrast to the prototypical reactions catalyzed by members of the DSOR family, the NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase catalyzes the reductive cleavage of the thioether linkage of 2-ketopropyl-coenzyme M, and the subsequent carboxylation of the ketopropyl cleavage product, yielding the products acetoacetate and free coenzyme M. The structure of 2-KPCC reveals a unique active site in comparison to those of other members of the DSOR family of enzymes and demonstrates how the enzyme architecture has been adapted for the more sophisticated biochemical reaction. In addition, comparison of the structures in the native state and in the presence of bound substrate indicates the binding of the substrate 2-ketopropyl-coenzyme M induces a conformational change resulting in the collapse of the substrate access channel. The encapsulation of the substrate in this manner is reminiscent of the conformational changes observed in the well-characterized CO2-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxidase (Rubisco).

Negative regulation of CD45 by differential homodimerization of the alternatively spliced isoforms

The regulation of receptor-like protein tyrosine phosphatases (RPTPs) is not well understood. Although CD45 can be negatively regulated by dimerization, how dimerization is modulated is unclear. Here we show that various isoforms of CD45 differentially homodimerize in T cells. The dimerization is modulated by the sialylation and O-glycosylation of alternatively spliced CD45 exons in the extracellular domain. Thus, the smallest isoform, CD45RO--which undergoes the least extracellular sialylation and O-glycosylation--homodimerizes with the highest efficiency, resulting in decreased signaling via the T cell receptor. Because CD45 is required for T cell activation, our findings may reveal a mechanism that contributes to the termination of the primary T cell response. Our results not only demonstrate the biological significance of alternative splicing in the immune system, but also suggest a model for regulating RPTP dimerization and function.

Kinetic analysis of the reactions of 4-hydroperoxycyclophosphamide and acrolein with glutathione, mesna, and WR-1065

The kinetics of the reactions of glutathione (GSH) with 4-hydroperoxycyclophosphamide (4OOH-CP) and acrolein, a metabolite of 4OOH-CP, were investigated in a cell-free medium (pH approximately 7.5) and peripheral blood mononuclear cells. The ability of the thiol drugs, sodium 2-mercaptoethane sulfonate (mesna) and S-2-(3-aminopropylamino)ethanethiol (WR-1065), to affect the reactions of cellular GSH with the alkyalting agents was also studied. The amount of unreacted thiols in the various reactions was determined by derivatization with monobromobimane, followed by separation of fluorescent-labeled thioether adducts using high-pressure liquid chromatography. The second-order rate constants (k(2)) for reactions of GSH, mesna, and WR-1065 with 4OOH-CP in solution were 38 +/- 5, 25 +/- 5, and 880 +/- 50 M(-1) s(-1), respectively. The corresponding k(2) for reactions of GSH, mesna, and WR-1065 with acrolein were 490 +/- 100, 700 +/- 150, and >2000 M(-1) s(-1), respectively. The apparent rate constants for reactions of cellular GSH with acrolein and 4OOH-CP were smaller than those obtained in solution. Assuming that the k(2) is the same inside and outside cells, we estimate the first-order rate constant (k(1)) for transfer of 4OOH-CP and acrolein across the cell membrane as approximately 0.01 and approximately 0.04 s(-1), respectively. WR-1065 was more effective than mesna in blocking depletion of cellular GSH (because it passes into the cell more quickly and has higher reaction rates with the alkylators than the latter compound). When WR-1065 and mesna were used together, the protection against cellular depletion of GSH was additive. Our results are relevant to the administration of thiol drugs with high-dose alkylating agents.

Polysulfonates derived from metal thiolate complexes as inhibitors of HIV-1 and various other enveloped viruses in vitro

Sodium 2-mercaptoethanesulfonate reacts with the metal ions Pd(II), Pt(II), Ag(I), Cd(II) and Zn(II) to yield complexes containing multiple anionic sulfonate sites. On the basis of spectroscopic and other analytical data the complexes were assigned the tentative molecular formulas: Pd6(SCH2CH2SO3Na)12, Ptn(SCH2CH2SO3Na)2n+2, Agn(SCH2CH2SO3Na)n, Na2Zn4(SCH2CH2SO3Na)10, and Na2Cd4(SCH2CH2SO3Na)10. The complexes displayed a variety of differences in activity towards DNA and RNA viruses. The platinum complex showed no measurable cytotoxicity and exhibited a spectrum of antiviral activity resembling that of dextran sulfate. It was active against HIV-1 and HIV-2, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), thymidine kinase-deficient HSV-1, human cytomegalovirus, vesicular stomatitis virus (VSV), influenza A virus, respiratory syncytial virus (RSV), Sindbis virus, Junin virus and Tacaribe virus. The palladium complex also showed no measurable cytotoxicity, but was completely inactive against most viruses, with one notable exception: both HIV-1 and HIV-2 were substantially inhibited by the palladium complex. The silver complex showed significantly less antiviral activity and greater cytotoxicity than the platinum complex but did show some selectivity against RSV. The zinc complex showed only modest activity against VSV, RSV, Junin virus, and Tacaribe virus, and like the silver compound was more cytotoxic than either the platinum or palladium complex. The cadmium complex was toxic to all of the cell lines used for in vitro evaluation of antiviral activity. Based on these results, the platinum and palladium compounds appear to be promising candidates for further studies, that is, as vaginal microbicides in the prevention of genital HIV and/or HSV transmission.

Elucidation of methanogenic coenzyme biosyntheses: from spectroscopy to genomics

Methanogenesis, the anaerobic production of methane from CO2 or simple carbon compounds, requires seven organic coenzymes. This review describes pathways for the biosynthesis of methanofuran, 5,6,7,8-tetrahydromethanopterin, coenzyme F420, coenzyme M (2-mercaptoethanesulfonic acid) and coenzyme B (7-mercaptoheptanoyl-L-threonine phosphate). Spectroscopic evidence for the pathways is reviewed and recent efforts are described to identify and characterize the biosynthetic enzymes from methanogenic archaea. The literature from 1971 to September 2001 is reviewed, and 169 references are cited.

Novel thiols of prokaryotes

Glutathione metabolism is associated with oxygenic cyanobacteria and the oxygen-utilizing purple bacteria, but is absent in many other prokaryotes. This review focuses on novel thiols found in those bacteria lacking glutathione. Included are glutathione amide and its perthiol, produced by phototrophic purple sulfur bacteria and apparently involved in their sulfide metabolism. Among archaebacteria, coenzyme M (2-mercaptoethanesulfonic acid) and coenzyme B (7-mercaptoheptanoylthreonine phosphate) play central roles in the anaerobic production of CH4 and associated energy conversion by methanogens, whereas the major thiol in the aerobic phototrophic halobacteria is gamma-glutamylcysteine. The highly aerobic actinomycetes produce mycothiol, a conjugate of N-acetylcysteine with a pseudodisaccharide of glucosamine and myo-inositol, AcCys-GlcNalpha(1 --> 1)Ins, which appears to play an antioxidant role similar to glutathione. Ergothioneine, also produced by actinomycetes, remains a mystery despite many years of study. Available data on the biosynthesis and metabolism of these and other novel thiols is summarized and key areas for additional study are identified.

Zinc-thiolate intermediate in catalysis of methyl group transfer in Methanosarcina barkeri

Methyl group transfer reactions are essential in methane-forming pathways in all methanogens. The involvement of zinc in catalysis of methyl group transfer was studied for the methyltransferase enzyme MT2-A important for methanogenesis in Methanosarcina barkeri growing on methylamines. Zinc was shown to be required for MT2-A activity and was tightly bound by the enzyme with an apparent stability constant of 10(13.7) at pH 7.2. Oxidation was a factor influencing activity and metal stoichiometry of purified MT2-A preparations. Methods were developed to produce inactive apo MT2-A and to restore full activity with stoichiometric reincorporation of Zn(2+). Reconstitution with Co(2+) yielded an enzyme with 16-fold higher specific activity. Cysteine thiolate coordination in Co(2+)-MT2-A was indicated by high absorptivity in the 300-400 nm charge transfer region, consistent with more than one thiolate ligand at the metal center. Approximate tetrahedral geometry was indicated by strong d-d transition absorbance centered at 622 nm. EXAFS analyses of Zn(2+)-MT2-A revealed 2S + 2N/O coordination with evidence for involvement of histidine. Interaction with the substrate CoM (2-mercaptoethanesulfonic acid) resulted in replacement of the second N/O group with S, indicating direct coordination of the CoM thiolate. UV-visible spectroscopy of Co(2+)-MT2-A in the presence of CoM also showed formation of an additional metal-thiolate bond. Binding of CoM over the range of pH 6.2-7.7 obeyed a model in which metal-thiolate formation occurs separately from H(+) release from the enzyme-substrate complex. Proton release to the solvent takes place from a group with apparent pK(a) of 6.4, and no evidence for metal-thiolate protonation was found. It was determined that substrate metal-thiolate bond formation occurs with a Delta G degrees ' of -6.7 kcal/mol and is a major thermodynamic driving force in the overall process of methyl group transfer.

Intein-mediated ligation and cyclization of expressed proteins

Protein splicing is a posttranslational processing event that releases an internal protein sequence from a protein precursor. During the splicing process the internal protein sequence, termed an intein, embedded in the protein precursor self-catalyzes its excision and the ligation of the flanking protein regions, termed exteins. The dissection of the splicing pathway, which involves the precise cleavage and formation of peptide bonds, and the identification of key catalytic residues at the splice junctions have led to the modulation of the protein splicing process as a protein engineering tool. Novel strategies have been developed to use intein-catalyzed reactions for the production and manipulation of proteins and peptides. These new approaches have broken down the size limitation barrier of chemical synthetic methods and are less technically demanding. The purpose of this article is to describe how to use self-splicing inteins in protein semisynthesis and backbone cyclization. The first two sections of the article provide a brief review of the distinct chemical steps that underlie protein splicing and intein enabled technology.

Crystallization and preliminary X-ray analysis of a NADPH 2-ketopropyl-coenzyme M oxidoreductase/carboxylase

NADPH 2-ketopropyl-coenzyme M (2-mercaptoethanesulfonate) oxidoreductase/carboxylase is the terminal enzyme in a metabolic pathway that results in the conversion of propylene to the central metabolite acetoacetate. This enzyme is an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase family of enzymes and catalyzes the cleavage and carboxylation of 2-ketopropyl-coenzyme M to form acetoacetate and coenzyme M. Crystallization trials have revealed that the highest diffraction quality crystals (better that 2.0 A resolution) could be achieved when the substrate or product of the reaction was added to the enzyme in a stoichiometric excess.

The kinetics and mechanisms of the reaction of Mesna with cisplatin, oxiplatin and carboplatin

BACKGROUND

Mesna is a sulfohydrate administered as a supportive drug in conjunction with oxazaphosphorines to prevent bladder toxicity from metabolites. When oxazaphosphorines are given simultaneously with platinum drugs, Mesna binds with platinum drugs as well. Previously we showed in cell culture, that Mesna reduces the efficacy of some platinum drugs. Here we elucidate the chemical reaction mechanism.

MATERIAL AND METHODS

Cisplatin, Carboplatin and a novel platinum agent Oxiplatin were incubated with Mesna and the rate of disappearance of Mesna was measured, using an oxidation/reduction reaction between MTT and Mesna.

RESULTS

All three platinum agents reacted with Mesna, but the chemical details differed largely. The molar ratios were 3:1, 2:1, and 1:1 for the reactions of Mesna with Oxiplatin, Cisplatin, and Carboplatin, respectively. The speed of the reaction followed a similar pattern, being fastest for Oxiplatin and slowest for Carboplatin.

CONCLUSION

When considering the pharmacokinetics of Mesna and these platinum compounds and their reactivity, it appears unlikely that the reaction of Mesna with Carboplatin will become clinically relevant, while Cisplatin, might react with Mesna in patient serum.

Characterization of a naturally occurring trans-splicing intein from Synechocystis sp. PCC6803

A naturally occurring trans-splicing intein from the dnaE gene of Synechocystis sp. PCC6803 (Ssp DnaE intein) was used to characterize the intein-catalyzed splicing reaction. Trans-splicing/cleavage reactions were initiated by combining the N-terminal splicing domain of the Ssp DnaE intein containing five native N-extein residues and maltose binding protein as the N-extein with the C-terminal Ssp DnaE intein splicing domain (E(C)) with or without thioredoxin fused in-frame to its carboxy terminus. Observed rate constants (k(obs)) for dithiothreitol-induced N-terminal cleavage, C-terminal cleavage, and trans-splicing were (1.0 +/- 0.5) x 10(-3), (1.9 +/- 0.9) x 10(-4), and (6.6 +/- 1.3) x 10(-5) s(-1), respectively. Preincubation of the intein fragments showed no change in k(obs), indicating association of the two splicing domains is rapid relative to the subsequent steps. Interestingly, when E(C) concentrations were substoichiometric with respect to the N-terminal splicing domain, the levels of N-terminal cleavage were equivalent to the amount of E(C), even over a 24 h period. Activation energies for N-terminal cleavage and trans-splicing were determined by Arrhenius plots to be 12.5 and 8.9 kcal/mol, respectively. Trans-splicing occurred maximally at pH 7.0, while a slight increase in the extent of N-terminal cleavage was observed at higher pH values. This work describes an in-depth kinetic analysis of the splicing and cleavage activity of an intein, and provides insight for the use of the split intein as an affinity domain.

Characterization of five catalytic activities associated with the NADPH:2-ketopropyl-coenzyme M [2-(2-ketopropylthio)ethanesulfonate] oxidoreductase/carboxylase of the Xanthobacter strain Py2 epoxide carboxylase system

The bacterial metabolism of propylene proceeds by epoxidation to epoxypropane followed by carboxylation to acetoacetate. Epoxypropane carboxylation is a minimetabolic pathway that requires four enzymes, NADPH, NAD(+), and coenzyme M (CoM; 2-mercaptoethanesulfonate) and occurs with the overall reaction stoichiometry: epoxypropane + CO(2) + NADPH + NAD(+) + CoM --> acetoacetate + H(+) + NADP(+) + NADH + CoM. The terminal enzyme of the pathway is NADPH:2-ketopropyl-CoM [2-(2-ketopropylthio)ethanesulfonate] oxidoreductase/carboxylase (2-KPCC), an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase family of enzymes and that catalyzes the reductive cleavage and carboxylation of 2-ketopropyl-CoM to form acetoacetate and CoM according to the reaction: 2-ketopropyl-CoM + NADPH + CO(2) --> acetoacetate + NADP(+) + CoM. In the present work, 2-KPCC has been characterized with respect to the above reaction and four newly discovered partial reactions of relevance to the catalytic mechanism, and each of which requires the formation of a stabilized enolacetone intermediate. These four reactions are (1) NADPH-dependent cleavage and protonation of 2-ketopropyl-CoM to form NADP(+), CoM, and acetone, a reaction analogous to the physiological reaction but in which H(+) is the electrophile; (2) NADP(+)-dependent synthesis of 2-ketopropyl-CoM from CoM and acetoacetate, the reverse of the physiologically important forward reaction; (3) acetoacetate decarboxylation to form acetone and CO(2); and (4) acetoacetate/(14)CO(2) exchange to form (14)C(1)-acetoacetate and CO(2). Acetoacetate decarboxylation and (14)CO(2) exchange occurred independent of NADP(H) and CoM, demonstrating that these substrates are not central to the mechanism of enolate generation and stabilization. 2-KPCC did not uncouple NADPH oxidation or NADP(+) reduction from the reactions involving cleavage or formation of 2-ketopropyl-CoM. N-Ethylmaleimide inactivated the reactions forming/using 2-ketopropyl-CoM but did not inactivate acetoacetate decarboxylation or (14)CO(2) exchange reactions. The biochemical characterization of 2-KPCC and the associated five catalytic activities has allowed the formulation of an unprecedented mechanism of substrate activation and carboxylation that involves NADPH oxidation, a redox active disulfide, thiol-mediated reductive cleavage of a C-S thioether bond, the formation of a CoM:cysteine mixed disulfide, and enolacetone stabilization.

In vitro carboplatin-mesna interaction in aqueous solution, human plasma and urine

The chemotherapeutic benefit of synergistic drug combinations and higher drug dosages has generated interest in the application of these regimens to cancer patients. A major obstacle in the application of these strategies to the treatment of cancer is the dose-limiting toxicities of drug combinations. Sodium 2-mercaptoethane-sulfonate (mesna), a chemoprotective drug, may reduce the nephrotoxicity of carboplatin [CBDCA, paraplatin, JM-8, cis-diammine (1,1-cyclobutane dicarboxylato) platinum II] when administered in combination chemotherapy. The purpose of this study was to evaluate, compare and contrast in vitro the interaction of mesna with carboplatin in aqueous solution, human plasma and urine. Carboplatin and mesna were incubated separately and together at clinically relevant concentrations in plasma and urine. The concentration of carboplatin was assayed by HPLC, and the decay of carboplatin alone and in combination with mesna was compared. The incubation of carboplatin with mesna in human plasma up to 8 days did not result in a statistically significant interaction: the half-life of carboplatin in plasma when it was combined with mesna was 1.62 +/- 0.08 (SE) days compared to 1.85+/- 0.04 (SE) days for carboplatin by itself. The incubation of drugs in fresh human urine up to 15 days gave a half-life of 3.43+/- 0.8 (SE) days for carboplatin alone and 2.78 +/- 0.7 (SE) days for carboplatin when it was combined with mesna. Our results show that carboplatin and mesna do not significantly interact in plasma. Although a statistically significant difference between the half-life of carboplatin and the half-life of the carboplatin/mesna combination is detected in urine, it is not likely to be clinically significant, as there is no significant interaction detected in the first 48 h). It is thus unlikely that mesna would substantially affect the pharmacokinetics of carboplatin when both are given together to patients as part of combination chemotherapy regimens.

Mesna inactivates platinum agents in vitro

BACKGROUND

Platinum agents are frequently combined with ifosfamide. Mesna, originally coadministered to protect from ifosfamide side effects, might also react with the platinum agents in these combinations.

METHODS

Malignant glioma cells were incubated with cisplatin, carboplatin and mesna. Cell numbers were measured by counting and by MTT-tests.

RESULTS

In cell free solution mesna turned MTT to its blue farmazan product. Mesna's effect on cells were cell-line specific: It penetrated U87 cells without effect on growth, reduced cell numbers in C6 and T98G cells and did not alter U251 cells. The concentration of cisplatin killing 50% of the cells were 7 x 10(-7) in C6, 9.7 x 10(-6) in T98G, 1.2 x 10(-5) in U251 and 2.4 x 10(-4) in U87 cells. For the same effect, carboplatin required 3-10 times higher concentrations. Mesna protected all cell lines from the cytotoxicity of the platinum agents.

CONCLUSION

Clinical studies should specify in detail, infusion schedules of mesna and platinum agents.

Synthesis and characterization of 2-mercaptoethanesulfonic acid albumin

Autoimmune patients treated with ifosfamide (CAS 3778-73-2) and mesna (2-mercaptoethanesulfonic acid, CAS 3375-50-6) in some cases suffered from severe allergic reactions that were proposed to be due to mesna linked to serum albumin by a disulfide bond. To prove the existence of the hypothetic mesna albumin adduct in vivo it was synthesized: The free thiol group of albumin (molecular mass determined by MALDI spectroscopy: 67009 Da) was converted to S-phenylsulfonyl albumin and reacted with mesna to albumin mesna (molecular mass: 67159 Da). In an alternative synthesis albumin was incubated with mesna at pH 8, 40 degrees C (molecular mass of the adduct: 67166 Da).

[Osmolarity of solutions used in nebulization]

Inhaled medications are widely used in patients suffering from bronchial diseases. Beside their pharmacological properties, nebulised solutions have physico-chemical characteristics that can alter bronchial reactivity. Non-isotonic solutions can induce a bronchial hyperresponsiveness and/or a severe bronchonconstriction. Nevertheless, multiple drugs are used for nebulisation despite their unknown osmolarity. The aim of this study was to measure the tonicity of drug solutions commonly used for nebulisation in patients suffering from bronchial disease. Drug solutions were prepared either according to manufacturer recommendations or by diluting the stock in 5 ml of NaCl (0.9%) or H2CO3 (0.14%). Although bronchodilatator solutions (i.e. salbutamol, terbulatine, ipratropium bromide) were nearly isotonic, some drugs prepared for nebulisation had either a very high (e.g. mesna, netilmicine) or a very low (e.g. gomenol, sodium cromoglycate) tonicity. These values may be responsible for bronchoconstriction. Some hypertonic solutions, prepared with drugs such as acetylcytein or netilmycin, are not commercialised for nebulisation but are commonly used for aerosol therapy. In addition, solutions initially isotonic could become significantly hypertonic towards the end of nebulisation. Taken together, these results suggest that non-isotonic solutions should be used with caution specially in patients with bronchial hyperresponsiveness, even when aerosol therapy is prescribed for upper airways.

Crystal structure of methyl-coenzyme M reductase: the key enzyme of biological methane formation

Methyl-coenzyme M reductase (MCR), the enzyme responsible for the microbial formation of methane, is a 300-kilodalton protein organized as a hexamer in an alpha2beta2gamma2 arrangement. The crystal structure of the enzyme from Methanobacterium thermoautotrophicum, determined at 1.45 angstrom resolution for the inactive enzyme state MCRox1-silent, reveals that two molecules of the nickel porphinoid coenzyme F430 are embedded between the subunits alpha, alpha', beta, and gamma and alpha', alpha, beta', and gamma', forming two identical active sites. Each site is accessible for the substrate methyl-coenzyme M through a narrow channel locked after binding of the second substrate coenzyme B. Together with a second structurally characterized enzyme state (MCRsilent) containing the heterodisulfide of coenzymes M and B, a reaction mechanism is proposed that uses a radical intermediate and a nickel organic compound.

Stability of ifosfamide in solutions for multiday infusion by external pump

The stability of ifosfamide in Ringer lactate buffer solution either alone or mixed with mesna at 37 degrees C for a 7-day period was analyzed by HPLC. This study was performed to investigate the feasibility of continuous infusion of ifosfamide by a multiday pump in order to reduce the toxicity and to increase the production of active alkylating metabolites of the parent drug. The total decay of ifosfamide activity did not exceed 3.2% at day 7. We conclude that ifosfamide can be safely delivered in a 7-day infusion with no significant loss of activity.

Synthesis and cytotoxic evaluation of mesna adducts of some 1-aryl-4,4-dimethyl-5-(1-piperidino)-1-penten-3-one hydrochlorides

Reaction of 1-(4-bromophenyl)-4,4-dimethyl-5-(1-piperidino)-1-penten-3-one hydrochloride (1f) with sodium 2-mercaptoethanesulphonate (mesna) gave rise to the thiol adduct. 3. Recrystallization of this compound led to the formation of the corresponding zwitterion 4f. A series of analogues of 4f were prepared and the structure of a representative compound was confirmed by X-ray crystallography. In general, the thiol adducts had similar activity towards P388 cells and human tumour cell lines as the precursor enones 1 although greater selectivity to malignant diseases was found with the thiol adducts. A stability study of representative compounds conducted by 1H NMR spectroscopy revealed that the thiol adducts decomposed in solution. In one case regeneration of the ketone was noted while for the other compounds, the decomposition products were not identified.

Prebiotic syntheses of vitamin coenzymes: I. Cysteamine and 2-mercaptoethanesulfonic acid (coenzyme M)

The reaction of NH3 and SO3(2-) with ethylene sulfide is shown to be a prebiotic synthesis of cysteamine and 2-mercaptoethanesulfonic acid (coenzyme M). A similar reaction with ethylene imine would give cysteamine and taurine. Ethylene oxide would react with NH3 and N(CH3)3 to give the phospholipid components ethanolamine and choline. The prebiotic sources of ethylene sulfide, ethylene imine and ethylene oxide are discussed. Cysteamine itself is not a suitable thioester for metabolic processes because of acyl transfer to the amino group, but this can be prevented by using an amide of cysteamine. The use of cysteamine in coenzyme A may have been due to its prebiotic abundance. The facile prebiotic synthesis of both cysteamine and coenzyme M suggests that they were involved in very early metabolic pathways.

The direct hydrolysis of proteins containing tryptophan on polyvinylidene difluoride membranes by mercaptoethanesulfonic acid in the vapor phase

A procedure for the amino acid analysis of polypeptides that contain tryptophan on polyvinylidene difluoride membranes is described. Lysozyme, carbonic anhydrase, phytochrome, and ovalbumin were tested. The protein, which was separated from others by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, was blotted from the gel onto a polyvinylidene difluoride membrane and directly hydrolyzed by 3 N mercaptoethanesulfonic acid vapor in a vacuum at 176 degrees C for 25 min. The hydrolysate was extracted with 0.1 N HCl and 30% methanol and used for amino acid analysis. The tested proteins were adequately hydrolyzed, and the recovery of tryptophan was very efficient.

Differential effects of thiols on DNA modifications via alkylation and Michael addition by alpha-acetoxy-N-nitrosopyrrolidine

The hepatocarcinogen NPYR is metabolically activated by alpha-hydroxylation mediated by cytochrome P-450 enzymes to yield a 4-oxobutylating agent and 2-butenal (crotonaldehyde). Both are reactive intermediates capable of modifying DNA with guanine either by simple alkylation or by Michael type addition, respectively. In order to assess the roles of these pathways in NPYR tumorigenesis, we are interested in identifying agents which can selectively modify one of these two pathways. In this study, we examined the effects of three thiols--(mesna), glutathione (Glu), and N-acetylcysteine (Nac)--on DNA adduct formation by alpha-acetoxyNPYR, a stable precursor of alpha-hydroxyNPYR. Calf thymus DNA isolated from incubation of alpha-acetoxyNPYR with or without thiol was hydrolyzed and analyzed for the adducts formed by alkylation (adducts 1 and 2) and Michael addition (adducts 3-5). The results showed that the addition of mesna completely blocked the formation of the crotonaldehyde-derived adducts 3-5, whereas it exerted little effect on the formation of the alkylated adducts 1 and 2. These results indicate the preferential conjugation of mesna with crotonaldehyde. In contrast, Nac had little selectivity on adduct formation; levels of adducts 1 to 5 were were reduced by 36-75%. These results suggest that Nac conjugated with both alkylating agent and crotonaldehyde. Similar to mesna, Glu blocked the formation of the crotonaldehyde-derived adducts (adducts 3-5) efficiently. However, unlike mesna, Glu inhibited the formation of adduct 1, while it did not inhibit the formation of adduct 2, although both adducts are presumably derived from the 4-oxobutylating agent.(ABSTRACT TRUNCATED AT 250 WORDS)

The stability of ifosfamide in aqueous solution and its suitability for continuous 7-day infusion by ambulatory pump

Dose fractionation is known to reduce the toxicity of ifosfamide and also results in an increased production of alkylating metabolites. Administration by slow infusion using the convenience of ambulatory pumps is therefore of interest. We used HPLC to investigate the stability of ifosfamide in aqueous solution (either alone, solution A, or mixed with mesna, solution B) under various conditions over a 9-day period. At both ambient temperature in daylight and 27 degrees C in a dark environment, there was no evidence of ifosfamide decay in either solution. However, at 37 degrees C in a dark environment, a fall was detected in both solutions, which at 9 days amounted to a loss of 7% of the amount of ifosfamide present at time zero. At 70 degrees C, levels of ifosfamide in both solutions fell within 72 h to markedly lower levels than controls, thus confirming that the methods used were indicative of stability. We conclude that ifosfamide, either alone or mixed with mesna, is stable for 9 days at temperatures up to 27 degrees C; even at 37 degrees C, the measured loss is small. The continuous infusion of ifosfamide over 7 days by ambulatory pump is now a practical proposition.

Sodium 2-mercaptoethanesulfonate in reversible adduct formation and water solubilization

Sodium 2-mercaptoethanesulfonate (MESNA, coenzyme M) forms 1:1 covalent adducts with highly pi-electron deficient heterocycles. The addition is caused by the thiol function, and the adducts become water soluble as sulfonates. 1H NMR spectroscopy has been used to obtain information about electronic and steric effects on the equilibria between 2-pyrimidinones and their 1:1 MESNA adducts. The adducts are potential prodrugs for biologically interesting 2-pyrimidinones.