Multiscale calculations reveal new insights into the reaction mechanism between KRASG12C and α, β-unsaturated carbonyl of covalent inhibitors

Utilizing α,β-unsaturated carbonyl group as Michael acceptors to react with thiols represents a successful strategy for developing KRASG12C inhibitors. Despite this, the precise reaction mechanism between KRASG12C and covalent inhibitors remains a subject of debate, primarily due to the absence of an appropriate residue capable of deprotonating the cysteine thiol as a base. To uncover this reaction mechanism, we first discussed the chemical reaction mechanism in solvent conditions via density functional theory (DFT) calculation. Based on this, we then proposed and validated the enzymatic reaction mechanism by employing quantum mechanics/molecular mechanics (QM/MM) calculation. Our QM/MM analysis suggests that, in biological conditions, proton transfer and nucleophilic addition may proceed through a concerted process to form an enolate intermediate, bypassing the need for a base catalyst. This proposed mechanism differs from previous findings. Following the formation of the enolate intermediate, solvent-assisted tautomerization results in the final product. Our calculations indicate that solvent-assisted tautomerization is the rate-limiting step in the catalytic cycle under biological conditions. On the basis of this reaction mechanism, the calculated kinact/ki for two inhibitors is consistent well with the experimental results. Our findings provide new insights into the reaction mechanism between the cysteine of KRASG12C and the covalent inhibitors and may provide valuable information for designing effective covalent inhibitors targeting KRASG12C and other similar targets.

Immunization with recombinant Streptococcus pneumoniae neuraminidase NanA protects chinchillas against nasopharyngeal colonization

Immunization with recombinant S. pneumoniae neuraminidase NanA (rNanA) resulted in a significant reduction in pneumococcal colonization in the chinchilla model. The bacteria were eliminated from the nasopharynx 1 week earlier than that from the control cohort. Our data suggest that rNanA affords protection against pneumococcal nasopharyngeal colonization.

An improved thermoanalytical approach to quantifying trace levels of polymorphic impurity in drug powders

Accurate quantification of impurities existing as separate crystalline phases at trace levels in drug materials is an important issue in the pharmaceutical industry. In the present study, a thermoanalytical approach previously developed for quantifying trace levels of polymorphic impurity (form II metastable nuclei) in commercial salmeterol xinafoate powders has been successfully applied with slight modifications to ribavirin, an antiviral drug exhibiting roughly similar polymorph-dependent crystallization kinetics in melts to that of salmeterol xinafoate. Essentially, the approach involved modeling of the crystallization kinetics of both tested and reference drug materials in melts using the Avrami-Erofe'ev (AE) rate expression, derivation of a mathematical equation for relating the AE kinetic constant to the composition of reference polymorph mixtures, and the use of this derived equation (in the form of a calibration curve) to calculate the impurity contents of the tested samples from their computed AE constants. For ribavirin, modification of the latter equation by incorporation of an empirical exponent was found necessary to account for the composition-dependent changes in crystallization kinetics of the reference mixtures. Such modification has made possible the determination of polymorphic impurity content of as low as 0.004% (w/w) in ribavirin samples induced by different forms of grinding treatment.

Immunization with native or recombinant Streptococcus pneumoniae neuraminidase affords protection in the chinchilla otitis media model

Streptococcus pneumoniae neuraminidase has been implicated as a virulence factor in the pathogenesis of pneumococcal otitis media. In this study, native neuraminidase was partially purified from cultures of S. pneumoniae by serial chromatography with DEAE-Sepharose and Sephacryl S-200. Recombinant neuraminidase, a 3,038-bp fragment of the neuraminidase A (nanA) gene, was cloned into the pET-28b vector and then expressed at high levels in Escherichia coli. Chinchillas were immunized subcutaneously with either the gel-purified native or recombinant neuraminidase, and all responded with elevated titers of antineuraminidase antibody in serum. Immunization with neuraminidase resulted in a significant reduction in nasopharyngeal colonization as well as in the incidence of otitis media with effusion. These data demonstrate for the first time that neuraminidase affords protection against S. pneumoniae nasopharyngeal colonization and experimental otitis media.

Differential expression of cytokine genes and inducible nitric oxide synthase induced by opacity phenotype variants of Streptococcus pneumoniae during acute otitis media in the rat

Phase variation in the colonial opacity phenotype of Streptococcus pneumoniae has been implicated as a factor in bacterial adherence, colonization, and invasion in the pathogenesis of pneumococcal otitis media (OM). The purpose of this study was to determine whether S. pneumoniae opacity variants influence the induction of gene expression for proinflammatory mediators in vivo using the rat model of OM. Both the opaque and transparent phenotype variants induced a significant up-regulation in gene expression for interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, IL-10, tumor necrosis factor alpha, and inducible nitric oxide synthase (iNOS) compared to saline sham-inoculated controls at both 4 and 24 h postinoculation (P < 0.05 in all cases). Furthermore, whereas a significant difference in gene expression was evident for only IL-6 (greater following challenge with the opaque variant) and IL-1beta (greater following challenge with the transparent variant) at 4 h, by 24 h the opaque variant cohort demonstrated a significant increase in gene expression for IL-1alpha, IL-1beta, IL-6, IL-10, and iNOS relative to animals inoculated with the transparent phenotype variant (P < 0.05 in all cases). Enzyme-linked immunosorbent assay results confirmed the gene expression data as determined by real-time PCR. Moreover, the concentrations of the opaque variant in the middle ear lavage fluid were a full log higher than those of the transparent variant. The aforementioned results indicate that the opaque phenotype variant is more efficient at survival and multiplication within the middle ear space, resulting in the accumulation of more inflammatory cells and the enhanced expression and production of inflammatory mediators. However, when the data were normalized to account for differences in middle ear bacterial titers, it became apparent that the transparent variant of S. pneumoniae is a more potent inducer of inflammation, triggering the accumulation of more inflammatory cells and substantially greater fold increases in the expression and production of inflammatory mediators. Data from this study indicate that S. pneumoniae opacity variants influence the temporal mRNA expression of inflammatory mediators within the middle ear.

Expression of cytokine and chemokine genes by human middle ear epithelial cells induced by influenza A virus and Streptococcus pneumoniae opacity variants

Real-time PCR and enzyme-linked immunosorbent assay were used to evaluate the ability of influenza A virus and Streptococcus pneumoniae opacity variants, either alone or in combination, to induce cytokine and chemokine genes in primary cultures of human middle ear epithelial (HMEE) cells. Following treatment with influenza A virus, the induction of gene expression, which occurred in a dose- and time-dependent manner, was strong for macrophage inflammatory protein 1 alpha (MIP-1 alpha) and MIP-1 beta; moderate for tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and IL-8; and weak for IL-1 beta and monocyte chemotactic peptide 1 (MCP-1). Except for TNF-alpha, all the gene products were detected in the cell culture supernatants. In contrast, infection of HMEE cells with S. pneumoniae alone induced low levels of mRNA expression of MIP-1 alpha and MIP-1 beta and did not significantly induce the transcription of the other cytokines and chemokines examined. However, both S. pneumoniae opacity variants increased mRNA expression of MIP-1 alpha, MIP-1 beta, IL-6, and MCP-1 in HMEE cells activated by a prior influenza A virus infection compared to levels in cells treated with either agent alone. Up-regulation of IL-6, IL-8, and MCP-1 mRNA expression and production by the virus in combination with opaque S. pneumoniae was two- to threefold higher than that induced by the virus combined with the transparent S. pneumoniae variant. These data indicate that the activation of HMEE cells by influenza A virus enhances the induction of cytokine and chemokine gene transcripts by S. pneumoniae and that this effect appears to be most pronounced when S. pneumoniae is in the opaque phase.

Comparison of alteration of cell surface carbohydrates of the chinchilla tubotympanum and colonial opacity phenotype of Streptococcus pneumoniae during experimental pneumococcal otitis media with or without an antecedent influenza A virus infection

Experimental and clinical studies suggest that influenza A virus promotes Streptococcus pneumoniae-induced otitis media; however, the mechanism underlying this synergistic interaction has not been completely defined. In this study, glycoconjugate expression patterns were evaluated on the cell surface in the chinchilla eustachian tube (ET) lumen of a cohort challenged intranasally (i.n.) with S. pneumoniae type 6A, which is predominantly transparent and a cohort with an antecedent influenza A virus infection, followed by i.n. inoculation with S. pneumoniae. The labeling patterns obtained with six lectin probes revealed that the binding of Bandeiraea simplicifolia lectin II, succinylated wheat germ agglutinin, and peanut agglutinin were significantly increased in the lumenal surface of the ET in the cohort infected with both pathogens compared to the cohort inoculated with only S. pneumoniae, which indicated that N-acetylglucosamine (GlcNAc) and D-galactose residues were exposed. A significant decreased labeling with Sambucus nigra agglutinin in the combined influenza A virus and pneumococcus infection cohort suggested that there were few sialic acid residues remaining in the ET epithelium. In addition, the colonial opacity of S. pneumoniae during the disease course was examined. The opaque phenotype was predominant among the pneumococcus isolates from the middle-ear fluid in the cohort infected with the both pathogens. Together, these data suggest that the synergic effect of influenza A virus and S. pneumoniae on the changes of the carbohydrate moieties in the ET epithelium and that the selection of the opaque variant may facilitate the pneumococcal invasion of the middle ear.

Comparison of structural changes of cell surface carbohydrates in the eustachian tube epithelium of chinchillas infected with a Streptococcus pneumoniae neuraminidase-deficient mutant or its isogenic parent strain

Six different lectin probes were used to examine alterations of the cell surface carbohydrates in the chinchilla eustachian tube (ET) lumen subsequent to the intranasal (i.n.) challenge with the Streptococcus pneumoniae parent strain, D39, or its isogenic derivative, DeltaNA1, which is deficient in neuraminidase NanA. The labelling pattern revealed that the binding of wheat germ agglutinin (WGA), Erythrina cristagalli lectin (ECL), peanut agglutinin (PNA), Bandeiraea simplicifolia lectin II (BSL II) and succinylated wheat germ agglutinin (SWGA) were increased in the lumenal surface of the ET in the D39 inoculated cohort compared to the uninfected control, which indicated that N-acetylglucosamine (GlcNAc) and D-galactose residues were exposed. Concurrently, decreased labelling with Sambucus nigra agglutinin (SNA) indicated that there were few sialic acid residues remaining in the ET epithelium subsequent to i.n. inoculation with D39. The DeltaNA1 neuraminidase deficient mutant, however, did not induce any significant changes in the lectin labelling patterns, and was comparable to that of the control cohort. We propose that products of the nanA gene have a significant impact on the changes of the carbohydrate moieties in the ET epithelium and may be responsible for the previously reported increased ability of the D39 parent to colonize the nasopharynx and invade the middle ear.

Expression of cytokine and chemokine genes by human middle ear epithelial cells induced by formalin-killed Haemophilus influenzae or its lipooligosaccharide htrB and rfaD mutants

To define the role of nontypeable Haemophilus influenzae (NTHI) lipooligosaccharide (LOS) in the induction of proinflammatory cytokine gene expression during otitis media, we compared the abilities of formalin-killed NTHI strain 2019 and its LOS htrB and rfaD mutants to stimulate human middle ear epithelial (HMEE) cell cytokine and chemokine gene expression and production in vitro. Strain DK-1, an rfaD gene mutant, expresses a truncated LOS consisting of only three deoxy-D-manno-octulosonic acid residues, a single heptose, and lipid A. Strain B29, an isogenic htrB mutant, possesses an altered oligosaccharide core and an altered lipid A. HMEE cells were incubated with formalin-killed NTHI 2019, B29, or DK-1. The supernatants and the cells were collected at 2, 4, 8, and 24 h after stimulation. Expression of genes for the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin lbeta (IL-1beta), and IL-6 and for the chemokines macrophage inflammatory protein 1beta (MIP-1beta), monocyte chemotactic peptide 1 (MCP-1), and IL-8 was quantitated by real-time PCR. NTHI B29 did not significantly stimulate any cytokine or chemokine mRNA expression in HMEE cells. In striking contrast, NTHI 2019 induced up to 105-, 139-, and 187-fold increases in HMEE cell expression of IL-1beta, TNF-alpha, and MIP-1beta, respectively (P < 0.01 [2019 versus B29]). NTHI 2019 also induced upregulation of IL-8, IL-6, and MCP-1 mRNA expression (by 26-, 44-, and 14-fold, respectively [P < 0.05 (2019 versus B29)]). The significant induction of cytokine genes was confirmed by quantitating the secretion of cytokines in culture supernatants with an enzyme-linked immunosorbent assay. There were no significant differences in mRNA expression of IL-8, IL-6, and MCP-1 between the 2019- and DK-1-treated groups. The low levels of gene transcripts observed after incubation of HMEE cells with B29 indicate that products of the disrupted NTHI htrB LOS gene may play a major role in induction of these particular inflammatory mediators.

Characterization of two polymorphs of salmeterol xinafoate crystallized from supercritical fluids

PURPOSE

To characterize two polymorphs of salmeterol xinafoate (SX-I and SX-II) produced by supercritical fluid crystallization.

METHODS

SX-I and SX-II were crystallized as fine powders using Solution Enhanced Dispersion by Supercritical Fluids (SEDS). The two polymorphs and a reference micronized SX sample (MSX) were characterized using powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), aqueous solubility (and dissolution) determination at 5-40 degrees C, BET adsorption analysis, and inverse gas chromatography (IGC).

RESULTS

Compared with SX-I, SX-II exhibited a lower enthalpy of fusion, a higher equilibrium solubility, a higher intrinsic dissolution rate, a lower enthalpy of solution (based on van't Hoff solubility plots), and a different FTIR spectrum (reflecting differences in intermolecular hydrogen bonding). Solubility ratio plot yielded a transition temperature (-99 degrees C) below the melting points of both polymorphs. MSX showed essentially the same crystal form as SX-I (confirmed by PXRD and FTIR), but a distinctly different thermal behaviour. Mild trituration of SX-I afforded a similar DSC profile to MSX while prolonged grinding of SX-I gave rise to an endotherm at -109 degrees C, corresponding to solid-solid transition of SX-I to SX-II. Surface analysis of MSX, SX-I, and SX-II by IGC revealed significant differences in surface free energy in terms of both dispersive (nonpolar) interactions and specific (polar) acid-base properties.

CONCLUSIONS

The SEDS-processed SX-I and SX-II display high polymorphic purity and distinctly different physical and surface properties. The polymorphs are related enantiotropically with SX-I being the thermodynamically stable form at room temperature.

Detection of mucin gene expression in normal rat middle ear mucosa by reverse transcriptase-polymerase chain reaction

Hypersecretion of mucin is a common feature of chronic and mucoid otitis media which may play an important role in hearing loss. The mechanisms controlling mucin secretion in the middle ear are not completely understood. Our reverse transcriptase-polymerase chain reaction results demonstrate that mRNAs of MUC1, MUC2, MUC3, MUC4 and MUC5AC are expressed in normal rat middle ear mucosa. Moreover, the expression of mRNA of the secretory mucins MUC2, MUC3 and MUC5AC was threefold lower in normal middle ear mucosa than that in the intestine or trachea. In contrast, expression of the membrane-bound mucins MUC1 and MUC4 was approximately the same in both middle ear mucosa and the intestine or trachea. MUC5AC proteins were also identified immunohistochemically in normal rat middle car epithelium. The methodology used in this study provides useful baseline information for investigation of the mechanisms of regulation of mucin gene expression during otitis media.

Effect of influenza A virus infection on nasopharyngeal colonization and otitis media induced by transparent or opaque phenotype variants of Streptococcus pneumoniae in the chinchilla model

Phase variation in the colonial opacity of Streptococcus pneumoniae has been implicated as a factor in bacterial adherence, colonization, and invasion in the pathogenesis of pneumococcal disease. Additionally, the synergistic effects of influenza A virus and S. pneumoniae in the development of otitis media (OM) have been reported. This study examined the ability of opaque or transparent S. pneumoniae from the same strain in combination with an antecedent influenza A virus infection to colonize the nasopharynx and invade the middle ear in the chinchilla model. Our data indicated that there was no significant difference in the level of nasopharyngeal colonization and induction of OM between the opaque and transparent variants unless there was a prior challenge with influenza A virus. Subsequent to influenza A virus infection, there was a significant difference between the variants in the ability to colonize and persist in the nasopharynx and middle ear. The concentrations of the opaque variant in nasopharyngeal-lavage samples and middle-ear fluid remained consistently higher than those of the transparent variant for 10 days postinoculation. Data from this study indicate that the effects of influenza A virus on the pathogenesis of experimental S. pneumoniae-induced OM differ depending on the opacity phenotype involved.

Effect of adenovirus type 1 and influenza A virus on Streptococcus pneumoniae nasopharyngeal colonization and otitis media in the chinchilla

Considerable evidence has implicated respiratory tract virus potentiation of bacterial adherence, colonization, and superinfection as a significant factor contributing to the pathogenesis of otitis media (OM). Influenza A and B viruses, adenovirus, and respiratory syncytial virus are the primary respiratory tract viruses associated with this disease. Investigations have established a dramatic increase in the development of experimental OM in chinchillas co-inoculated with influenza A virus and Streptococcus pneumoniae (Spn). The mechanism underlying this phenomenon was suggested to involve, in part, viral compromise of eustachian tube mucosal integrity and function. This study was designed to assess and compare the effect of adenovirus and influenza A virus infection on adherence, the kinetics of colonization, and invasion of the middle ear by Spn in the chinchilla model of OM. Cohorts were inoculated intranasally with adenovirus type 1 or influenza A virus, and then inoculated intranasally 7 days later with Spn 6A. All cohorts were observed over a 14-day period after challenge with Spn, and the incidence and severity of OM were assessed by several methods, including culture of the nasopharynx and middle ear effusions. The data indicated that influenza A virus promotes a significant increase in nasopharyngeal colonization by Spn, an increased incidence and severity of OM, and a sustained presence of Spn in the effusions. Adenovirus infection, however, did not enhance colonization by Spn or result in an increased incidence or severity of OM.

Evaluation of phase variation of nontypeable Haemophilus influenzae lipooligosaccharide during nasopharyngeal colonization and development of otitis media in the chinchilla model

Nontypeable Haemophilus influenzae (NTHI) has four loci, lic-1 to lic-3 and lgtC, that generate phase-variable lipooligosaccharide (LOS) structures. lic-1, which is required for the expression of phosphorylcholine (ChoP), is the best characterized and is associated with an enhanced ability of H. influenzae to persist within the nasopharynges of infant rats. Recent data indicate that LOS impacts various aspects of NTHI virulence in the chinchilla model of nasopharyngeal colonization and otitis media (OM). In this study the effects of ChoP expression and the sequences of lic-1 to lic-3 and lgtC of NTHI strain 2019 were evaluated in the chinchilla OM model. Nasopharyngeal colonization data showed that a switch from the ChoP(-) to the ChoP(+) phenotype was observed as early as day 3 after intranasal inoculation. Chinchillas colonized by strains with the ChoP(+) phenotype demonstrated a significantly higher level of NTHI 2019 per milliliter of nasal lavage fluid than chinchillas colonized with predominantly the ChoP(-) variant (P < 0.05). The concentration of cells with the ChoP(+) phenotype in the middle ear was 3 log units higher than that of cells with the ChoP(-) variant (P < 0.01). There was a statistically significant association between ChoP(+) expression in the nasal lavage and the development of OM with culture-positive middle ear fluids in this model. These data suggest that expression of the ChoP(+) phenotype promotes enhanced nasopharyngeal colonization and development of OM.

Evaluation of the virulence of a Streptococcus pneumoniae neuraminidase-deficient mutant in nasopharyngeal colonization and development of otitis media in the chinchilla model

Considerable evidence has implicated Streptococcus pneumoniae neuraminidase in the pathogenesis of otitis media (OM); however, its exact role has not been conclusively established. Recently, an S. pneumoniae neuraminidase-deficient mutant, DeltaNA1, has been constructed by insertion-duplication mutagenesis of the nanA gene of S. pneumoniae strain D39. The relative ability of DeltaNA1 and the D39 parent strain to colonize the nasopharynx and to induce OM subsequent to intranasal inoculation and to survive in the middle ear cleft after direct challenge of the middle ear were evaluated in the chinchilla model. Nasopharyngeal colonization data indicate a significant difference in the ability of the DeltaNA1 mutant to colonize as well as to persist in the nasopharynx. The neuraminidase-deficient mutant was eliminated from the nasopharynx 2 weeks earlier than the D39 parent strain. Both the parent and the mutant exhibited similar virulence levels and kinetics during the first week after direct inoculation of the middle ear. The DeltaNA1 neuraminidase-deficient mutant, however, was then completely eliminated from the middle ear by day 10 postchallenge, 11 days before the D39 parent strain. Data from this study indicate that products of the nanA gene have an impact on the ability of S. pneumoniae to colonize and persist in the nasopharynx as well as the middle ear.

Effect of lacto-N-neotetraose, asialoganglioside-GM1 and neuraminidase on adherence of otitis media-associated serotypes of Streptococcus pneumoniae to chinchilla tracheal epithelium

The adherence of Streptococcus pneumoniae (Spn) otitis media-associated serotypes 3, 6A and 14 to ciliated chinchilla respiratory epithelium was investigated using a whole organ perfusion technique. We demonstrated that Spn adhere to chinchilla tracheal epithelium within 30 min and exhibit saturation kinetics indicating that the effect being observed is receptor mediated. Inhibition of adherence was achieved by prior incubation of Spn with lacto-N-neotetraose (LNnT) or asialoIganglioside GM1 (aGM1), recognized by glycoconjugate analogs of known Spn receptors. NeurIaminidase treatment of the tracheae increased Spn adherence in vitro and reversed the inhibition effect of LNnT suggesting that neuraminidase treatment resulted in an increase in the number of available receptors for Spn. The chinchilla trachea organ perfusion culture system used in this study imitates eustachian tube conditions more closely than isolated cell culture systems and is a useful model for investigating the role of Spn adherence in vitro in the pathogenesis of OM.

Effect of tumor necrosis factor alpha and interleukin 1-alpha on the adherence of Streptococcus pneumoniae to chinchilla tracheal epithelium

The trachea whole organ perfusion technique was used to study the effect of tumor necrosis factor alpha (TNF alpha) and interleukin-1 alpha (IL-1 alpha) on the adherence of otitis media pathogen Streptococcus pneumoniae (Spn) type 6A. Tracheas were removed from chinchillas and divided equally. One-half trachea was activated by incubation with 1-10 ng/ml of either TNF alpha or IL-1 alpha prior to the addition of Spn 6A to the organ culture perfusion chamber. Colony forming units (cfu) of Spn/millimeter trachea were determined for activated tracheas and controls. Dose response and kinetics data were generated for each cytokine. The specificity of each reaction was determined by neutralization studies with specific anti-cytokine antibodies. The data indicate that both TNF alpha and IL-1 alpha increase the adherence of Spn to the respiratory epithelium of this tubal organ and suggest a mechanism which may facilitate enhanced adherence in vivo and thereby contribute to the pathogenesis of otitis media and other upper respiratory tract diseases.

Molecular characterization of mutations in the hprt gene of normal human skin keratinocytes treated with N-ethyl-N-nitrosourea: influence of O6-alkylguanine alkyltransferase

O6-Alkylguanine-DNA alkyltransferase (AGT) is responsible for repairing the O6-alkylguanine lesion in DNA. There is wide variation in the levels of AGT between organ and cell types, which appears to correlate with cell and tissue type sensitivity to the mutagenic and carcinogenic effects of alkylating agents. In order to investigate the role of AGT in modulating the frequency and types of mutations induced in one type of normal human parenchymal cells, we examined the types and frequency of mutations in the hypoxanthine (guanine) phosphoribosyltransferase (hprt gene in 116 mutants derived from two N-ethyl-N-nitrosourea (ENU)-treated normal human skin keratinocyte cell lines. O6-Benzylguanine (O6-BZ; 5 microM x 2 hours) was used to specifically inhibit AGT activity before ENU treatment (0 to 5 mM x 1 hour). O6-BZ increased both the cytotoxic and mutagenic effects of ENU by 1.8- and 3- to 5-fold, respectively. In both treatment groups, most of the mutations were base substitutions (72%). The proportion of GC to AT transitions in the O6-BZ group (14/31) was twice that in the group treated with ENU alone, consistent with the loss of AGT activity in these cells. There was no strand specificity of GC to AT and AT to GC transitions in both groups. Base transversions accounted for 28% of total base substitutions. A lower than expected proportion of AT to TA transversions were observed in both cell lines, which decreased in the O6-BZ pretreated group. A strand bias was observed for GC to TA and AT to TA transversions. Most of the G to A and G to T base substitutions had one or more purines flanking 3' to the mutated deoxyguanosines. There were more deletion mutants with the deletion of exon 1, 4, 6, and 8 in the BZ group than in the control group. These data, characterizing the mutational spectra of ENU in normal human keratinocytes treated in vitro, indicate that GC to AT and AT to GC transition mutations predominate in these cells depleted or not depleted of AGT.

Effect of novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), on the osmoprotectant activity of glycine betaine, choline and L-proline in Escherichia coli

A novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), was found to block the osmoprotectant activity of choline and L-proline, but not glycine betaine in Escherichia coli. MPMS was more active against salt-sensitive than salt-resistant strains, but had no effect on the salt tolerance of a mutant which was unable to transport choline, glycine betaine and proline. Growth of E. coli in NaCl was inhibited by MPMS and restored by glycine betaine, but not by choline or L-proline. Uptake of radiolabeled glycine betaine, choline or L-proline by cells grown at high osmolarity was not inhibited when MPMS and the radioactive substrates were added simultaneously. Preincubation for 5 min with MPMS reduced the uptake of choline and L-proline, but not glycine betaine. Similar incubation with MPMS had no effect on the uptake of radiolabeled glucose or succinate. The toxicity of MPMS was much lower than that of the L-proline analogues L-azetidine-2-carboxylic acid and 3,4-dehydro-DL-proline. The exact mechanism by which MPMS exerts its effect is not entirely clear. MPMS or a metabolite may interfere with the activity of several independent permeases involved in the uptake of osmoprotective compounds, or the conversion of choline to glycine betaine, or effect the expression of some of the osmoregulatory genes.

Structure-activity relationship of glycine betaine analogs on osmotolerance of enteric bacteria

Bacterial cells have the ability to accumulate compatible solutes within the cytoplasm to maintain their osmolarity above that of the extracellular milieu. Glycine betaine (GB) and its biosynthetic precursor choline (Chol) are the major compatible solutes that bacteria accumulate when osmotically challenged. Different osmotically triggered active transport mechanisms have been identified for GB and Chol. In the present study we examined the bioisosteric replacement of the carboxylic group of GB with sulfonic, phosphonic or benzenesulfonamido groups. The sulfonic acid analog (sulfobetaine, compound 3) showed osmoprotectant activity equivalent to that of GB. In addition, we tested the possibility of utilizing GB/Chol transport systems to deliver cytotoxic analogs of GB into three strains of E. coli that differed in their salt resistance. We found that N1-betainyl-N4-(haloacetyl)sulfanilamides (compounds 17c-e) that are GB analogs containing alkylating side chain within their structures inhibited the bacterial growth of the tested standard and salt sensitive strains of E. coli. We also showed that the (N-methyl-cyclic ammonio)methanesulfonates (compounds 21a-c) are able to block Chol transport system in both the standard and the salt-sensitive E. coli strains used. At the concentration used (0.1 mM), none of the tested compounds showed any significant effect on the salt-resistant strain used.

Naturally-occurring, osmo-remedial variants of Escherichia coli

Two clones of Escherichia coli O27:K1:H31 and O2:H7, isolated from patients with urinary tract infection or bacteraemia, failed to grow in a synthetic minimal medium (MM) of low osmolality. They were considered to be osmo-remedial because they grew well when sufficient amounts of NaCl, mannitol or sucrose were added to raise the osmolality of the medium to > 300 mOsm/kg. The defect could also be corrected by nicotinamide or its precursors quinolinic and aspartic acids. Each clone had a unique DNA restriction enzyme profile, fimbriae and antibiotic susceptibility patterns. The osmo-remedial variants were unstable and underwent phenotypic modulation to form mixtures with osmo-tolerant forms when grown in MM. They tended to form satellites of small colonies around large colonies of osmo-tolerant cells on MM agar plates. The penicillin method of Davis was used to separate the two forms. Nicotinamide induced the expression of ompF when the osmo-remedial strains were grown under conditions of low osmolality. It is possible that the variants are defective in the synthesis of membrane-derived oligosaccharides or outer-membrane proteins, but this has yet to be determined.