Mutation of the cohesin related gene PDS5 causes cell death with predominant apoptotic features in Saccharomyces cerevisiae during early meiosis

Pds5p is a cohesin related protein. It is required for maintenance of sister chromatid cohesion in mitosis and meiosis. Here we report that pds5-1 causes cell death in yeast Saccharomyces cerevisiae during early meiosis. The pds5-1 caused cell death possesses characteristics of apoptosis and necrosis, including externalization of phosphatidylserine at cytoplasmic membrane, accumulation of DNA breaks, chromatin condensation and fragmentation, nuclei fragmentation, membrane degeneration and cell size enlargement. Our results also suggest that (1) The defect of DNA repair; (2) The production of reactive oxygen species, in pds5-1 mutant are involved in pds5-1 induced cell death.

Expression of PHA polymerase genes of Pseudomonas putida in Escherichia coli and its effect on PHA formation

Poly-3-hydroxyalkanoates (PHAs) are synthesized by many bacteria as intracellular storage material. The final step in PHA biosynthesis is catalyzed by two PHA polymerases (phaC) in Pseudomonas putida. The expression of these two phaC genes (phaC1 and phaC2)was studied in Escherichia coli, either under control of the native promoter or under control of an external promoter. It was found that the two phaC genes are not expressed in E. coli without an external promoter. During heterologous expression of phaC from Plac on a high copy number plasmid, a rapid reduction of the number of colony forming units was observed, especially for phaC2. It appears that the plasmid instability was partially caused by high-level production of PHA polymerase. Subsequently, tightly regulated phaC2 expression systems on a low copy number vector were applied in E. coli. This resulted in PHA yields of over 20 of total cell dry weight, which was 2 fold higher than that obtained from the system where phaC2 is present on a high copy number vector. In addition, the PHA monomer composition differed when different gene expression systems or different phaC genes were applied.

Possible Involvement of NADPH Oxidase and JNK in Homocysteine-Induced Oxidative Stress and Apoptosis in Human Umbilical Vein Endothelial Cells

Hyperhomocysteinemia is an independent risk factor for cardiovascular diseases, although the mechanism leading to vascular dysfunction is not clear. The aim of this study was to examine the effect of homocysteine (Hcy) on oxi-dative stress and apoptosis in human umbilical vein endothelial cells (HUVECs). HUVECs were challenged for 24 h with Hcy (10 microM-3 mM) in the presence of various stress signaling inhibitors, including the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin (100 microM), the p38 mito-gen-activated protein kinase inhibitor SB203580 (2.5 microM), the extracellular signal-regulated kinase inhibitor U0126 (2.5 microM), the stress-activated protein kinase (SAPK)/c-Jun NH2-terminal kinase (JNK) inhibitor JNK inhibitor II (10 microM), and antioxidants alpha-tocopherol (5 microg/mL) and N-acetyl cysteine (NAC, 2 mM). Reactive oxygen species (ROS) were detected using 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate. Apoptosis was evaluated by 4',6'-diamidino-2'-phenylindoladihydrochloride staining, annexin-V phosphatidyl- serine/propidium iodide, and caspase-3 assay. NADPH oxidase and SAPK/JNK signal were evaluated with immunoblotting. Hcy significantly enhanced ROS generation and apoptosis after 24-h incubation. Apocynin prevented Hcy-induced ROS generation but only partially restored Hcy-induced apoptosis. JNK inhibitor II, alpha-tocopherol, and NAC partially reduced Hcy-induced apoptosis, although SB203580 and U0126 had no effect. Immunoblotting analysis confirmed upregulation of NADPH oxidase and SAPK/JNK signaling. Collectively, our results suggested that Hcy may induce oxidative stress and apopto-sis through an NADPH oxidase and/or JNK-dependent mechanism(s).

Somatic mutation analysis of p53 and ST7 tumor suppressor genes in gastric carcinoma by DHPLC

AIM: To verify the effectiveness of denaturing high-performance liquid chromatography (DHPLC) in detecting somatic mutation of p53 gene in gastric carcinoma tissues. The superiority of this method has been proved in the detection of germline mutations, but it was not very affirmative with respect to somatic mutations in tumor specimens. ST7 gene, a candidate tumor suppressor gene identified recently at human chromosome 7q31.1, was also detected because LOH at this site has also been widely reported in stomach cancer.

METHODS: DNA was extracted from 39 cases of surgical gastric carcinoma specimen and their correspondent normal mucosa. Seven fragments spanning the 11 exons were used to detect the mutation of p53 gene and the four exons reported to have mutations in ST7 gene were amplified by PCR and directly analyzed by DHPLC without mixing with wild-type allele.

RESULTS: In the analysis of p53 gene mutation, 9 aberrant DHPLC chromatographies were found in tumor tissues, while their normal-adjacent counterparts running in parallel showed a normal shape. Subsequent sequencing revealed nine sequence variations, 1 polymorphism and 8 mutations including 3 mutations not reported before. The mutation rate of p53 gene (21%) was consistent with that previously reported. Furthermore, no additional aberrant chromatography was found when wild-type DNA was added into the DNA of other 30 tumor samples that showed normal shapes previously. The positivity of p53 mutations was significantly higher in intestinal-type carcinomas (40%) than that in diffuse-type (8.33%) carcinomas of the stomach. No mutation of ST7 gene was found.

CONCLUSION: DHPLC is a very convenient method for the detection of somatic mutations in gastric carcinoma. The amount of wild type alleles supplied by the non-tumorous cells in gastric tumor specimens is enough to form heteroduplex with mutant alleles for DHPLC detection. ST7 gene may not be the target gene of inactivation at 7q31 site in gastric carcinoma.

[Genomic variations in the locus for aminopeptidase N:a putative cellular receptor for SARS-CoV spike glycoprotein]

Aminopeptidase N has been identified as the cellular receptor for human coronavirus HCoV-229E and was a putative receptor for the spike glycoprotein encoded by the SARS-associated coronavirus (SARS-CoV). We report here identification of 9 single nucleotide polymorphisms (SNPs) in ANPEP, encoding human aminopeptidase N, in Chinese. All ANPEP exons and their flanking intronic sequences were amplified from unrelated normal individuals by polymerase chain reaction (PCR) and screened using denaturing high-performance liquid chromatography (DHPLC). Nine SNPs were revealed after direct sequencing of PCR amplified fragments which showed changes of DHPLC chromatogram. Four of these polymorphisms, T321M(962C > T), S651L(1952C > T), S752N(2255G > A) and G764R(2290G > A), were non-synonymous; the remaining exonic synonymous and intronic ones were T795T(2385C > T), IVS7 + 17G > A, IVS14-16A > G, IVS17 + 12C > G and IVS17 + 44C > T. Our data may be useful for studies to investigate the role of host genetic factors in SARS pathogenesis, especially for identifying SARS-susceptible and/or anti-SARS alleles.

Comparative DNA microarray analysis of host cell transcriptional responses to infection by Coxiella burnetii or Chlamydia trachomatis

DNA microarray analysis was conducted to investigate the transcriptional responses of the human monocytic leukemia cell line THP-1 to infection by Chlamydia trachomatis or Coxiella burnetii. RNA was isolated from mock infected cells and cells infected for 36 hours using TRIzol reagent. Biotinylated probes synthesized from RNA samples were hybridized to an Affymetrix U133A human genome chip consisting of 18,462 human gene probe sets. A total of 335 and 548 THP-1 genes were up- or downregulated at least twofold in cells infected with C. burnetii or C. trachomatis, respectively, when compared to uninfected cells. There was a high degree of overlap in transcriptional responses to infection with shared responses observed for 39 downregulated and 189 upregulated genes. Numerous pathogen-specific transcriptional responses were also observed. Quantitative RT-PCR and immunoblotting confirmed up- or down-regulation of a subset of THP-1 genes in response to infection by C. burnetii. This study provides insight into the host transcriptional responses to infection by Chlamydia and Coxiella that may affect the infectious cycle of each organism.

Loss of heterozygosity on chromosome 18 in microdissected gastric cancer cells

AIM: To detect loss of heterozygosity (LOH) on chromosome 18 in primary gastric carcinomas.

METHODS: Short insertion deletion polymorphism (SIDP) markers on chromosome 18 were analyzed using high fidelity-whole genome amplification (HF-WGA) and denatured high pressure liquid chromotography (DHPLC) to detect LOH in gastric cancer cells purified by laser capture microdissection (LCM).

RESULTS: LOH in 3 (MID148, MID150 and MID352) of 9 SIDP loci was found. Three of 10 samples of gastric cancer showed LOH at the same SIDP locus (MID150) (30%) and one of them also demonstrated LOH at the other 2 SIDP loci (MID148, MID352). No LOH was detected in 6 of 9 SIDP loci.

CONCLUSION: Detection of LOH in cancer cells can be achieved by the combination of LCM, HF-WGA and the analysis of SIDP marker by DHPLC. This study provides an alternative new way to map tumor suppressor genes on chromosome 18.

Effects of ectopically expressed neuronal Wiskott-Aldrich syndrome protein domains on Rickettsia rickettsii actin-based motility

Neuronal Wiskott-Aldrich syndrome protein (N-WASP) and the actin-related protein 2/3 (Arp2/3) complex have emerged as critical host proteins that regulate pathogen actin-based motility. Actin tail formation and motility in Listeria monocytogenes require the Arp2/3 complex but bypasses N-WASP signaling. Motility of Shigella flexneri and vaccinia virus requires both N-WASP and the Arp2/3 complex. Functional roles for these cytoskeletal regulatory proteins in actin-based motility of Rickettsia rickettsii have not been established. In this study, functional domains of N-WASP tagged with green fluorescent protein that have characterized effects on Shigella and vaccinia virus actin-based motility were ectopically expressed in HeLa cells infected with R. rickettsii to assess their effects on rickettsial motility. S. flexneri-infected cells were used as a control. Expressed N-WASP domains did not localize to R. rickettsii or their actin tails. Expression of N-WASP missing the VCA domain (for "verprolin homology, cofilin homology, and acidic domains"), which acts as a dominant-negative form of N-WASP, completely inhibited actin-based motility of S. flexneri while only moderately inhibiting motility of R. rickettsii. Similarly, expression of the VCA domain, which acts as a dominant-negative with respect to Arp2/3 complex function, severely inhibited actin-based motility of S. flexneri (no motility observed in the majority of expressing cells) but only moderately inhibited R. rickettsii motility. These results, taken together with the differential effects on motility observed upon expression of other N-WASP domains, suggest that actin-based motility of R. rickettsii is independent of N-WASP and the Arp2/3 complex.

A Controllable and Observable Protein Cystallization Facility

A Controllable and Observable Protein Crystallization Facility (ACOP) was developed in 1999 for space experiment in the Get Away Special canister of Space Shuttle. To regulate the vapor diffusion rate, in a crystallization chamber, five cells each containing precipitant solution of different concentrations, exposed to one protein cell in turn. Five layers of chambers were overlapped coaxially. The crystallization process was observed and recorded by digital cameras. Structure of facility and result of image sequence were given.

Evaluation of apolipoprotein A-II as a positional candidate gene for familial Type II diabetes, altered lipid concentrations, and insulin resistance

AIMS/HYPOTHESIS

We hypothesized that apolipoprotein A-II sequence variation was responsible for the observed linkage of Type II (non-insulin-dependent) diabetes mellitus to the apolipoprotein A-II region in Northern European families ascertained for multiple diabetic siblings, and might also influence insulin sensitivity and secretion, non-esterified fatty acids, and lipids.

METHODS

We recruited 698 members of 63 families for pedigree studies and additional unrelated people providing 117 diabetic and 130 control subjects. We screened the apolipoprotein A-II gene by single strand conformation polymorphism analysis and fluorescent sequence analysis. Variants were typed by oligonucleotide ligation assay, restriction digest of amplification products, or radioactive fragment analysis for the microsatellite polymorphism. Association of each variant with Type II diabetes was tested in the case-control population by chi-square analysis, or using transmission disequilibrium test in families. Haplotypes were established in families using SIMWALK and tested for association with diabetes and quantitative traits.

RESULTS

No detected variant altered the coding sequence of the gene. Three single nucleotide polymorphisms showed modest evidence for an association, but no variant or haplotype was associated with diabetes in families. Similarly, we found no association with non-esterified fatty acid concentrations, HDL concentrations, or fasting insulin. In contrast, we found evidence for an association of some haplotypes and individual variants with 2-h post-challenge glucose and measures of insulin secretion.

CONCLUSION/INTERPRETATION

Apolipoprotein A-II is not likely to explain the observed linkage of Type II diabetes, but variation in this gene could alter insulin secretion and post-challenge glucose.

GM1 ganglioside induces phosphorylation and activation of Trk and Erk in brain

We investigated the ability of GM1 to induce phosphorylation of the tyrosine kinase receptor for neurotrophins, Trk, in rat brain, and activation of possible down-stream signaling cascades. GM1 increased phosphorylated Trk (pTrk) in slices of striatum, hippocampus and frontal cortex in a concentration- and time-dependent manner, and enhanced the activity of Trk kinase resulting in receptor autophosphorylation. The ability of GM1 to induce pTrk was shared by other gangliosides, and was blocked by the selective Trk kinase inhibitors K252a and AG879. GM1 induced phosphorylation of TrkA > TrkC > TrkB in a region-specific distribution. Adding GM1 to brain slices activated extracellular-regulated protein kinases (Erks) in all three brain regions studied. In striatum, GM1 elicited activation of Erk2 > Erk1 in a time-and concentration-dependent manner. The GM1 effect on Erk2 was mimicked by other gangliosides, and was blocked by the Trk kinase inhibitors K252a and AG879. Pertussis toxin, as well as Src protein tyrosine kinase and protein kinase C inhibitors, did not prevent the GM1-induced activation of Erk2, apparently excluding the participation of Gi and Gq/11 protein-coupled receptors. Intracerebroventricular administration of GM1 induced a transient phosphorylation of TrkA and Erk1/2 in the striatum and hippocampus complementing the in situ studies. These observations support a role for GM1 in modulating Trk and Erk phosphorylation and activity in brain.

Production of chiral R-3-hydroxyalkanoic acids and R-3-hydroxyalkanoic acid methylesters via hydrolytic degradation of polyhydroxyalkanoate synthesized by pseudomonads

A novel and efficient method for the production of enantiomericaly pure R-3-hydroxyalkanoic acids and R-3-hydroxyalkanoic acid methylesters was developed. The described method is based on hydrolysis of poly(hydroxyalkanoate) copolymers synthesized by Pseudomonas putida. The polymer was isolated via solvent recovery and hydrolyzed by acid methanolysis. The obtained 3-hydroxyalkanoic acid methylester mixture was distilled into several fractions with an overall yield of 96.6% (w/w). Gas chromatography-mass spectrometry analysis of the fractions showed that 3-hydroxyhexanoic-, 3-hydroxyoctanoic-, 3 hydroxydecanoic-, and 3-hydroxydodecanoic acid methylesters were enriched to purities exceeding 96 mol%, with distillation yields of 99.9, 99.8, 88.4, and 56.8% (w/w), respectively. Subsequent saponification of the purified methylester fractions yielded the corresponding 3-hydroxyalkanoic acids, which were recovered up to 92.8% (w/w). Chiral gas chromatography analysis confirmed that both 3-hydroxyoctanoic acid and 3-hydroxyoctanoic acid methylester are present in the R-form at a very high enantiomeric excess (>99.9%).

A bacterial cytochrome c heme lyase. CcmF forms a complex with the heme chaperone CcmE and CcmH but not with apocytochrome c

Biogenesis of c-type cytochromes in Escherichia coli involves a number of membrane proteins (CcmA-H), which are required for the transfer of heme to the periplasmically located apocytochrome c. The pathway includes (i) covalent, transient binding of heme to the periplasmic domain of the heme chaperone CcmE; (ii) the subsequent release of heme; and (iii) transfer and covalent attachment of heme to apocytochrome c. Here, we report that CcmF is a key player in the late steps of cytochrome c maturation. We demonstrate that the conserved histidines His-173, His-261, His-303, and His-491 and the tryptophan-rich signature motif of the CcmF protein family are functionally required. Co-immunoprecipitation experiments revealed that CcmF interacts directly with the heme donor CcmE and with CcmH but not with apocytochrome c. We propose that CcmFH forms a bacterial heme lyase complex for the transfer of heme from CcmE to apocytochrome c.

Physical interaction of CcmC with heme and the heme chaperone CcmE during cytochrome c maturation

Biogenesis of c-type cytochromes requires the covalent attachment of heme to the apoprotein. In Escherichia coli, this process involves eight membrane proteins encoded by the ccmABCDEFGH operon. CcmE binds heme covalently and transfers it to apocytochromes c in the presence of other Ccm proteins. CcmC is necessary and sufficient to incorporate heme into CcmE. Here, we report that the CcmC protein directly interacts with heme. We further show that CcmC co-immunoprecipitates with CcmE. CcmC contains two conserved histidines and a signature sequence, the so-called tryptophan-rich motif, which is the only element common to cytochrome c maturation proteins of bacteria, archae, plant mitochondria, and chloroplasts. We report that mutational changes of these motifs affecting the function of CcmC in cytochrome c maturation do not influence heme binding of CcmC. However, the mutants are defective in the CcmC-CcmE interaction, suggesting that these motifs are involved in the formation of a CcmC-CcmE complex. We propose that CcmC, CcmE, and heme interact directly with each other, establishing a periplasmic heme delivery pathway for cytochrome c maturation.

Histone H2A.Z acetylation modulates an essential charge patch

Histone H2A.Z is structurally and functionally distinct from the major H2As. To understand the function of H2A.Z acetylation, we performed a mutagenic analysis of the six acetylated lysines in the N-terminal tail of Tetrahymena H2A.Z. Tetrahymena cannot survive with arginines at all six sites. Retention of one acetylatable lysine is sufficient to provide the essential function of H2A.Z acetylation. This essential function can be mimicked by deleting the region encompassing all six sites, or by mutations that reduce the positive charge of the N terminus at the acetylation sites themselves, or at other sites in the tail. These properties argue that the essential function of H2A.Z acetylation is to modify a "charge patch" by reducing the charge of the tail.

Complete genome sequence of an M1 strain of Streptococcus pyogenes

The 1,852,442-bp sequence of an M1 strain of Streptococcus pyogenes, a Gram-positive pathogen, has been determined and contains 1,752 predicted protein-encoding genes. Approximately one-third of these genes have no identifiable function, with the remainder falling into previously characterized categories of known microbial function. Consistent with the observation that S. pyogenes is responsible for a wider variety of human disease than any other bacterial species, more than 40 putative virulence-associated genes have been identified. Additional genes have been identified that encode proteins likely associated with microbial "molecular mimicry" of host characteristics and involved in rheumatic fever or acute glomerulonephritis. The complete or partial sequence of four different bacteriophage genomes is also present, with each containing genes for one or more previously undiscovered superantigen-like proteins. These prophage-associated genes encode at least six potential virulence factors, emphasizing the importance of bacteriophages in horizontal gene transfer and a possible mechanism for generating new strains with increased pathogenic potential.

Engineering of Biological Systems for the Synthesis of Tailor-made Polyhydroxyalkanoates, a Class of Versatile Polymers

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are bacterial polyesters which are produced in nature by certain Pseudomonas strains. These biopolymers are of interest because of their chirality, biodegradability and elastomeric property, while the 3-hydroxy acid monomers are a potential source of chiral synthons. Since wild-type bacteria can only be used to a limited extent for the production of tailor-made functionalized PHAs, various recombinant bacteria have been generated in order to elucidate the PHA synthesis pathway and to control and modify the metabolic carbon flux towards PHA synthesis. Production of PHAs with altered monomer composition and physical properties has already been achieved by pathway engineering. An alternative to the in vivo synthesis strategies using whole microorganisms is PHA synthesis in vitro with isolated enzymes, which is of interest for incorporation of specific monomers that are not taken up or metabolized by bacterial cells. The various synthesis strategies are discussed in the context of the possible future production of tailor-made functionalized PHAs.

O-Glucuronidation of the lung carcinogen 4-(methylnitrosamino)-1- (3-pyridyl)-1-butanol (NNAL) by human UDP-glucuronosyltransferases 2B7 and 1A9

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are potent lung carcinogens in animals. UGT-mediated O-glucuronidation of NNAL is an important detoxification pathway for these carcinogens. To better characterize this pathway in humans, we screened a series of UGT-overexpressing cell lines and baculosome preparations for their ability to O-glucuronidate NNAL and examined multiple human liver and lung specimens for NNAL-glucuronidating activity and their levels of expression of NNAL-glucuronidating UGTs. Human liver microsomal fractions exhibited significant levels of NNAL-glucuronidating activity, with the NNAL-Gluc II diastereomer formed at a rate 3.4 times that observed for NNAL-Gluc I. As with liver microsomal fractions, NNAL-Gluc II was the major diastereomer formed by homogenates from UGT2B7-overexpressing HK293 cells or UGT2B7-overexpressing baculosomes; the major diastereomer formed by homogenates from UGT1A9-overexpressing V79 cells was NNAL-Gluc I. No significant O-glucuronidating activity of NNAL was detected in UGT1A1-, UGT1A4-, UGT1A6-, UGT2B4-, or UGT2B15-overexpressing HK293 or V79 cell homogenates, or in UGT1A1-, UGT1A3-, UGT1A7-, or UGT1A10-overexpressing baculosomes. Significant levels of UGT2B7 mRNA were detected by reverse transcriptase-polymerase chain reaction in human liver and at low levels in human lung specimens. UGT1A9 mRNA was detected in liver but not in lung. These results suggest that although both UGT2B7 and UGT1A9 play an important role in the overall glucuronidation of NNAL in humans, UGT2B7 potentially plays an important role in the detoxification of NNAL in the lung.

Recovery of active medium-chain-length-poly-3-hydroxyalkanoate polymerase from inactive inclusion bodies using ion-exchange resin

A novel process for the purification of active medium-chain-length-polyhydroxyalkanoate (mcl-PHA) polymerase was developed. This process is based on solubilization and activation of inactive polymerase inclusion bodies by incubation with ion-exchange resin. The mcl-PHA polymerase 1 from Pseudomonas oleovorans was overproduced from the Palk promoter. Most of the polymerase produced was sequestered in the cytoplasm as an inactive form in insoluble aggregates. By incubating the protein aggregates with S-Sepharose ion-exchange resin in the presence of dithiothreitol and glycerol, the mcl-PHA polymerase could be extracted in an active and soluble form with a final yield of about 5.2 mg/g of cell dry weight. The solubilized polymerase was able to catalyse the in vitro synthesis of mcl-PHA without any additional cell components, suggesting its potential application for production of biopolymer. The procedure used here may be of general value in solubilizing and activating purified inactive labile enzymes.

Ablation rate of PMMA and human cornea with a frequency-quintupled Nd:YAG laser (213 nm)

BACKGROUND AND OBJECTIVE

As an alternative to the standard excimer laser used for PRK, we investigated the ablation rate at 213 nm of PMMA, and human corneas under controlled hydration.

STUDY DESIGN/MATERIALS AND METHODS

The output of a frequency-quintupled Nd:YAG laser (213 nm) was transformed into a quasi-Gaussian beam. PMMA and corneal lenticules maintained under controlled hydration were ablated until perforation was detected.

RESULTS

The ablation rate of PMMA and cornea at 213 nm were similar to that at 193 nm when radiant exposure was below 200 mJ/cm2 and increased gradually between one and two times faster than that at 193 nm when radiant exposure was > 200 mJ/ cm2.

CONCLUSIONS

PMMA and cornea ablation at 213 nm are similar to that at 193 nm and are different from that at 248 nm. The difference between PMMA and cornea ablation rates should be considered when using PMMA to test ablated diopter and smoothness for photorefractive surgery.

Development of an improved in vitro activity assay for medium chain length PHA polymerases based on CoenzymeA release measurements

An improved activity assay for polyhydroxyalkanoate (PHA) polymerases from Pseudomonas oleovorans GPo1 was developed. The activity assay is based on the detection of released Coenzyme A (CoA) using 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB), a compound which specifically reacts with thiol groups. The formed adduct was measured spectrophotometrically with high sensitivity and accuracy. The assay was used to study the effect of several additives on the activity of granule-associated PHA polymerase. Mild non-ionic detergents such as Tween-20, Triton X-100, CHAPS and Hecameg all appeared to be strongly inhibitory. In contrast, bovine serum albumin (BSA) had a strong stimulatory effect on the activity and stability of the PHA polymerases. Using optimized conditions, activities up to 5.8 U/mg granule-bound polymerase have been measured.

[Effect of acute hypobaric hypoxia on renal function and structure in rats]

OBJECTIVE

To observe renal damage due to acute hypobaric hypoxia.

METHOD

Thirty-six male wistar rats were randomly divided into three groups A, B and C (n = 12 for each). Group A served as control, while groups B and C were exposed to 5000 m altitude for 30 min. Sample of serum and renal tissues were taken from group B rats 20 min and from group C rats 24 h after the exposure respectively.

RESULT

Serum ureanitrogen (BUN) and creatinine (Crea) increased significantly in group B and C rats after exposure to hypoxia (P< 0.01). Cl- and alkaline phosphatase (AKP) in serum also increased (P < 0.05), but renal endothelin (ET) decreased significantly (P < 0.01). All changes in group C rats tended to recover to normal level, except Cl- which continued to increase. Dilation of renal vessels was found under optic-microscope, and pathological changes were found in mitochondra and epithelial cells.

CONCLUSION

Acute hypobaric hypoxia might be harmful to renal function and structure.

FabG, an NADPH-dependent 3-ketoacyl reductase of Pseudomonas aeruginosa, provides precursors for medium-chain-length poly-3-hydroxyalkanoate biosynthesis in Escherichia coli

Escherichia coli hosts expressing fabG of Pseudomonas aeruginosa showed 3-ketoacyl coenzyme A (CoA) reductase activity toward R-3-hydroxyoctanoyl-CoA. Furthermore, E. coli recombinants carrying the poly-3-hydroxyalkanoate (PHA) polymerase-encoding gene phaC in addition to fabG accumulated medium-chain-length PHAs (mcl-PHAs) from alkanoates. When E. coli fadB or fadA mutants, which are deficient in steps downstream or upstream of the 3-ketoacyl-CoA formation step during beta-oxidation, respectively, were transformed with fabG, higher levels of PHA were synthesized in E. coli fadA, whereas similar levels of PHA were found in E. coli fadB, compared with those of the corresponding mutants carrying phaC alone. These results strongly suggest that FabG of P. aeruginosa is able to reduce mcl-3-ketoacyl-CoAs generated by the beta-oxidation to 3-hydroxyacyl-CoAs to provide precursors for the PHA polymerase.

Properties of engineered poly-3-hydroxyalkanoates produced in recombinant Escherichia coli strains

To prepare medium-chain-length poly-3-hydroxyalkanoates (PHAs) with altered physical properties, we generated recombinant Escherichia coli strains that synthesized PHAs with altered monomer compositions. Experiments with different substrates (fatty acids with different chain lengths) or different E. coli hosts failed to produce PHAs with altered physical properties. Therefore, we engineered a new potential PHA synthetic pathway, in which ketoacyl-coenzyme A (CoA) intermediates derived from the beta-oxidation cycle are accumulated and led to the PHA polymerase precursor R-3-hydroxyalkanoates in E. coli hosts. By introducing the poly-3-hydroxybutyrate acetoacetyl-CoA reductase (PhbB) from Ralstonia eutropha and blocking the ketoacyl-CoA degradation step of the beta-oxidation, the ketoacyl-CoA intermediate was accumulated and reduced to the PHA precursor. Introduction of the phbB gene not only caused significant changes in the monomer composition but also caused changes of the physical properties of the PHA, such as increase of polymer size and loss of the melting point. The present study demonstrates that pathway engineering can be a useful approach for producing PHAs with engineered physical properties.

[Relation of GFR and endothelin in the plasma in pilots and ground crew]

OBJECTIVE

To observe the specitic property of Glomeoular Filtration Rate (GFR) and its relation to endothelin of plasma in pilots.

METHOD

GFR was assessed with single photon emisson computed tomography (SPECT), tracer for 99mTc-DTPA, enthlion of plasma were measured by radio immunossay in forty-six pilots, thirty ground crew and renal disease patients.

RESULT

Endothelin were not correlation with GFR in pilots. GFR of pilots and ground crew had not a significant difference. Compared with ground crew and pilots, endothelin of renal disease patients had a significant increased, and GFR had a significant decreased. Age were a linear negative correlation with total GFR r = (0.84, P < 0.01), flying time, age had not correlation with endothelin. After thirty-one ground endothelin had a significant difference with ground crew.

CONCLUSION

It suggested that the endothelin has no influence on GFR in pilots when it was increased with in the limits of a level, pilots and ground crew may use the same stand on GFR.

Contemporary Sample Preparation Methods for the Detection of Ignitable Liquids in Suspect Arson Cases

The isolation of ignitable liquid components, usually petroleum-based distillates from fire debris, is an important step in deciding whether a fire is of natural or incendiary origin. Steady progress has been made to develop sample preparation methods capable of enriching target analytes in high yield and within a short period of time. Heated headspace enrichment methods are currently most widely used. There are several variations of this basic technique. Carbon-based adsorbents are most popular. They come in different forms and shapes, including a flat sheet of polymer, impregnated with carbon particles. The analyst cuts a small strip from this sheet and suspends it in the heated headspace above the debris sample. The volatiles adsorb onto the carbon surface, eventually reaching an equilibrium condition. The process is usually carried out in an oven. This convenient method, called the static method, has largely replaced the dynamic method, which uses a granular charcoal adsorbent. In the latter, the heated headspace is drawn over a short trap packed with charcoal, using a source of vacuum such as a pump or pushed along using pressurized nitrogen. The headspace volatiles in both the static and dynamic method are recovered by elution with a solvent, usually carbon disulfide. Recently, a promising variation of the static headspace method has been introduced. It is based on the use of a tiny amount of a polysiloxane polymer which has been coated onto the tip of a thin silica fiber. The fiber can be retracted into a syringe-type needle and the adsorbed headspace vapor can be conveniently introduced into the heated injector port of a gas chromatograph. No solvent is required. This technique, abbreviated SPME (for solid-phase microextraction) has many attractive advantages but it is not without some problems. Low boiling range accelerants, including water-soluble polar substances such as ethanol, are poorly retained on methylsiloxane type polymers. The recent introduction of hybrid fibers containing a combination of carbon and a methylpolysiloxane polymer has extended the usefulness of SPME toward the high volatility end. With judicious optimization of experimental conditions, it is now possible to obtain an adequately representative sample of the headspace above the fire debris sample. It is thus possible to characterize the full spectrum of potential liquid accelerants, ranging from alcohols and similar water-soluble substances to high boiling range fuel oils.

Glucuronidation of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by rat UDP-glucuronosyltransferase 2B1

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are potent lung carcinogens in animals. UDP-glucuronosyltransferase (UGT)-mediated glucuronidation of NNAL is a potentially important detoxification pathway for these carcinogens. To identify the UGT isozyme(s) involved in this pathway, we examined the glucuronidation of NNAL in rat liver microsomes and homogenates from cell lines overexpressing specific UGT isozymes. NNAL glucuronidation was induced in liver microsomes from rats treated with family 2 UGT inducers including phenobarbitol and 3, 5-di-tert-butyl-4-hydroxytoluene, which exhibited 1.7- and 2.6-fold higher rates of glucuronidation than microsomes from control rats. The rates of NNAL glucuronidation in liver microsomes from GUNN (deficient in family 1 UGTs) and RHA parental control rats were similar. All rat liver microsomes used in the present study catalyzed the glucuronidation of (S)-NNAL at a rate between 3.5 and 5.5 times that of the glucuronidation of (R)-NNAL. Liver microsomes from Wistar rats exhibiting the low-androsterone glucuronidation phenotype characteristic of the UGT2B2-deficient genotype glucuronidated NNAL at a rate similar to microsomes from Wistar rats exhibiting the high-androsterone glucuronidation phenotype/UGT2B2 [+] genotype. Homogenates from UGT2B1-overexpressing cells catalyzed the glucuronidation of NNAL at a K(m) of 745 microM. As with rat liver microsomes, NNAL-Gluc I was the major diastereomer formed by UGT2B1. Glucuronidation of NNAL was not detected with homogenates from UGT2B12-overexpressing cells. These results suggest that UGT2B1 plays an important role in the glucuronidation of NNAL in the rat.

[The development of a hemorrhologity observating and measuring instrument]

A new instrument for observing blood cell state and the process of variation on hemorrheology has been developed. There are three ways of shear rate: setting by hand, automatically setting and simulating pulsative state. It can provide different variable flow fields. The shear rate can be set in the range from 0.1 to 1000 s-1. It needs only a little blood. It can be easyly and rapidely operated. it has clear images. The hemorrheology state of blood cells can be directly perceived through thd instrument by eyes. The display and measurement and record of blood cell's hemorrheology state can be finished in real time dynamically and simultaneously.

[Low level of residual renal function in the initial month and high transport characteristic as important causes of peritoneal dialysis failure]

OBJECTIVE

To evaluate what kind of patients was at high risk on peritoneal dialysis (PD) treatment.

METHODS

96 patients on PD for (23.1 +/- 10.0) months were studied. The patients were divided into two groups. Group A: patients (25) who died or switched to hemodialysis because of cardiovascular disease, malnutrition, ultrafiltration inefficiency, hydrothora, relapsing peritonitis, etc. Group B: stable PD patients (71) up to now. Age, body surface area (BSA) and dialysate fill volume (DV) were not different between the two groups. The nutritional status, dialysis adequacy, peritoneal membrane transport characteristics, and residual renal function (RRF) in the initial month of dialysis were compared. Patient survival rate was studied by Kaplan-Meier method.

RESULTS

It was demonstrated that Kt/V and Ccr in group A were lower than those in group B (P < 0.05). Meanwhile, RRF was significantly different between the two groups; patients with better RRF (> or = 2 ml/min) had higher survival. The percentage of high transporters in group A was greater than in group B.

CONCLUSION

Higher clearance in the initial month of dialysis seems to keep PD successful. PD failure maybe related to high transport characteristic and its treatment modality is DAPD. Hemodialysis will be a better choice when RRF is very low as water balance is poorly controlled by DAPD.

Production of medium-chain-length poly(3-hydroxyalkanoates) from gluconate by recombinant Escherichia coli

It was shown recently that recombinant Escherichia coli, defective in the beta-oxidation cycle and harboring a medium-chain-length (MCL) poly(3-hydroxyalkanoate) (PHA) polymerase-encoding gene of Pseudomonas, is able to produce MCL PHA from fatty acids but not from sugars or gluconate (S. Langenbach, B. H. A. Rehm, and A. Steinbüchel, FEMS Microbiol. Lett. 150:303-309, 1997; Q. Ren, Ph.D. thesis, ETH Zürich, Zürich, Switzerland, 1997). In this study, we report the formation of MCL PHA from gluconate by recombinant E. coli. By introduction of genes coding for an MCL PHA polymerase and the cytosolic thioesterase I ('thioesterase I) into E. coli JMU193, we were able to engineer a pathway for the synthesis of MCL PHA from gluconate. We used two expression systems, i.e., the bad promoter and alk promoter, for the 'thioesterase I- and PHA polymerase-encoding genes, respectively, which enabled us to modulate their expression independently over a range of inducer concentrations, which resulted in a maximum MCL PHA accumulation of 2.3% of cell dry weight from gluconate. We found that the amount of PHA and the 'thioesterase I activity are directly correlated. Moreover, the polymer accumulated in the recombinant E. coli consisted mainly of 3-hydroxyoctanoate monomers. On the basis of our data, we propose an MCL PHA biosynthesis pathway scheme for recombinant E. coli JMU193, harboring PHA polymerase and 'thioesterase I, when grown on gluconate, which involves both de novo fatty acid synthesis and beta-oxidation.

[The visible spectra study of the conformation equilibrium of iron-metal-free porphyrin dimers]

A series of iron(III)-metal-porphyrin dimers linked with flexible alkoxyl chain at para position of two phenyl rings have been synthesized and characterized. An equilibrium of two conformations of porphyrin dimers (open and closed) has been studied by visible spectra. The intensity of absorption band 680 nm relates to equilibrium of two conformations. With the increase of the length of the alkoxyl chain,the closed conformation forms more easily. With the addition of axial ligand, the ferric ion of the dimers tends to bind with imidazole, and the intensity of the band 680 nm gradually decreases and disappears.

Cytotoxicity and DNA fragmentation associated with sequential gemcitabine and 5-fluoro-2'-deoxyuridine in HT-29 colon cancer cells

The combined cytotoxic effects of the antimetabolites gemcitabine (dFdCyd) and 5-fluoro-2'-deoxyuridine (FdUrd) were studied. Cytotoxicity, biochemical perturbations, and DNA damage seen with dFdCyd and FdUrd alone and in combination were evaluated in HT-29 human colon cancer cells. A 4-h exposure to dFdCyd followed by FdUrd for 24 h produced more than additive cytotoxicity and marked S-phase accumulation. Cells progressed through the cell cycle, however, after a 22-h drug-free interval. [3H]dFdCyd was rapidly metabolized to the 5'-triphosphate and incorporated into DNA. [3H]FdUrd was anabolized exclusively to FdUrd monophosphate, and preexposure to dFdCyd did not affect FdUrd monophosphate formation. Thymidylate synthase catalytic activity was inhibited by 48% after a 4-h exposure to 10 nM FdUrd and by 80% after exposure to the combination. Sequential 4-h exposures to 15 nM dFdCyd and 10 nM FdUrd led to greater depletion of dTTP pools (29% of control) than with either drug alone. Greater effects on nascent DNA integrity were seen with sequential dFdCyd followed by FdUrd. Although parental DNA damage was not evident immediately after exposure to 15 nM dFdCyd for 4 h followed by 10 nM FdUrd for 24 h, high molecular mass DNA fragmentation was evident 72-96 h after drug removal. Sequential dFdCyd/FdUrd was associated with prominent disturbance of the cell cycle, dTTP pool depletion, dATP/dTTP imbalance, and nascent DNA damage. Induction of double-strand parental DNA damage and cell death was delayed, consistent with postmitotic apoptosis.

Palmitoylation of neurofascin at a site in the membrane-spanning domain highly conserved among the L1 family of cell adhesion molecules

This report presents the first evidence that a member of the L1 family of nervous system cell-adhesion molecules is covalently modified by thioesterification with palmitate, and identifies a highly conserved cysteine in the predicted membrane-spanning domain as the site of modification. Neurofascin is constitutively palmitoylated at cysteine-1213 at close to a 1:1 molar stoichiometry. Kinetics of palmitate incorporation into neurofascin expressed in resting neuroblastoma cells indicate that the palmitate modification has the same turnover rate as the polypeptide chain and does not affect the protein stability of neurofascin. Palmitoylation of neurofascin expressed in dorsal root ganglion neurons is not required for delivery of neurofascin to the plasma membrane or targeting to axons. Palmitoylation also has no effect on ankyrin-binding activity of neurofascin, on the oligomeric state of neurofascin in solution, or on cell-adhesion activity of neurofascin expressed in neuroblastoma cells. A significant difference between native and C1213L neurofascin is that these proteins were localized in distinct fractions within a low-density membrane population enriched in signaling molecules. These results indicate a palmitate-dependent targeting of neurofascin to a specialized membrane microdomain.

p53, but not p16 mutations in oral squamous cell carcinomas are associated with specific CYP1A1 and GSTM1 polymorphic genotypes and patient tobacco use

Inactivation of tumor suppressor genes like p53 and p16 play a key role in tumor progression, with a high incidence of mutations existing for both genes in oral squamous cell carcinomas. Previous studies have demonstrated, (i) a correlation between the prevalence of p53 mutations and tobacco use [Brennan et al. (1995) New Engl. J. Med., 332, 712-717; Lazarus et al. (1996) Carcinogenesis, 17, 733-739], and (ii) a link between genotypes in specific xenobiotic metabolizing enzymes and oral cancer susceptibility [Park et al. (1997) Cancer Epid. Biomarkers Prev., 6, 791-797). In this paper, we present results of our examination of a series of 80 oral squamous cell carcinomas for p53 exons 5-9 and p16 exons 1-2 mutations, and the potential association of these mutations with specific genotyping patterns. p53 mutation prevalence in oral tumors was linked with increased patient tobacco use using several stratification criteria. There was a significantly higher prevalence of p53 mutations in OCSCCs from patients who smoked > 30 pack-years as compared to tumors from patients who smoked < or = 30 pack-years (OR = 2.8; CI = 1.1-7.2). No significant association was observed with patient alcohol consumption. There was a significant association between the prevalence of p53 mutations in oral tumors and CYP1A1 genotyping patterns in these oral cancer patients, with the highest p53 mutation prevalence observed in subjects with the CYP1A1 [val]/GSTM1 [+] genotype (OR = 6.0; CI = 1.2-29.7). A significant association was not observed between the prevalence of p16 mutations in oral tumors and tobacco use, or CYP1A1 [val] or GSTM1 (0/0) genotypes. These data suggest that the induction of mutations in specific tumor suppressor genes or oncogenes in oral tumors may be associated with specific carcinogen exposures, and that this association may be linked to specific polymorphic genotypes in xenobiotic-metabolizing enzyme genes.

Modulation of fluorouracil cytotoxicity by interferon-alpha and -gamma

Because interferons (IFN)-alpha and -gamma individually have increased fluorouracil (FUra) cytotoxicity in several in vitro models, we studied the effects of FUra combined with IFN-alpha + gamma in HT29 colon cancer cells. A 96-hr exposure to IFN-alpha (500 units/ml) plus IFN-gamma (10 units/ml) and a 72-hr exposure to 0. 25-1 microM FUra (hr 24-96) inhibited cell growth and colony formation in an additive or more-than-additive fashion. When cells were exposed to IFN-alpha + gamma and FUra, free FdUMP levels became detectable, whereas [3H]FUra-RNA incorporation decreased. Exposure to IFN-alpha + gamma, FUra, or the combination decreased dTTP pools to 58%, 43%, and 17% of control, respectively. A marked increase in the dATP to dTTP ratio was seen with FUra with or without IFN-alpha + gamma. Thymidylate synthase catalytic activity was reduced to 28% and 24% of control with FUra with or without IFN-alpha + gamma, suggesting that the enhanced dTTP depletion must be due to another mechanism. FUra-mediated thymidylate synthase inhibition was accompanied by a 124-fold increase in total deoxyuridylate immunoreactivity and a 31-fold increase in dUTP pools, but the addition of IFN-alpha + gamma attenuated the accumulation. Treatment with IFN-alpha + gamma and FUra individually interfered with nascent DNA chain elongation, whereas the three-drug combination produced the most striking effects. IFN-alpha + gamma plus FUra produced the greatest amount of single-strand breaks in nascent DNA and dramatically decreased net DNA synthesis. IFN-alpha + gamma with or without FUra produced double-strand breaks in parental DNA. These results suggest that dTTP depletion, dATP/dTTP imbalance, pronounced inhibition of DNA synthesis, and damage to nascent and parental DNA contribute to the enhanced cytotoxicity with the triple combination.

CYP1A1 and GSTM1 polymorphisms and oral cancer risk

The importance of both the CYP1A1 exon 7 (ile:val) and GSTM1 (0/0) polymorphisms in oral cancer susceptibility was assessed by examining polymorphic prevalences in 135 patients with oral cancer and 135 noncancer controls frequency-matched by age at diagnosis (+/- 5 years), race, sex, and institute of patient recruitment. The prevalence of the GSTM1 (0/0) genotype was approximately 51% in both cases and controls. The prevalence of the CYP1A1 (ile:val) polymorphism [including both the (ile/val) and (val/val) genotypes] was significantly higher in cases as compared to controls (17.6% versus 7.6%, respectively; crude odds ratio, 2.6; confidence interval, 1.2-5.7). No association was observed between polymorphic prevalence and levels of smoking or alcohol consumption in cases. These results suggest that the GSTM1 null genotype is not associated with oral cancer risk. These results also suggest that individuals with the CYP1A1 exon 7 ile:val polymorphism are at increased risk for oral cancer, and that this risk may not be influenced by differences in exposure to tobacco smoke.

[Rapid determination of low molecular weight aldehydes in air by gas chromatography]

This paper reports a method for determination of low molecular weight aldehydes in polluted air by GC-FID using a GDX-401 packed column (3 mm x 3 m). The advantages of this method are simple, rapid, accurate and sensitive. The method requires only 8 minutes for the whole analysis. In the concentration range of 1.7-442.4 mg/m3 for formaldehyde and 0.5-680 mg/m3 for acetaldehyde and propionaldehyde the calibration curves are linear. The minimun detectable amounts are 3.5 ng, 1 ng and 1 ng, and the average recoveries (n=5) are 89.4%, 89.6%, 88.1% for formaldehyde, acetaldehyde and propionaldehyde respectively. The quantitative determination is performed by external standard calibration method. The results of sample analysis are satisfactory.

Tyrosine phosphorylation at a site highly conserved in the L1 family of cell adhesion molecules abolishes ankyrin binding and increases lateral mobility of neurofascin

This paper presents evidence that a member of the L1 family of ankyrin-binding cell adhesion molecules is a substrate for protein tyrosine kinase(s) and phosphatase(s), identifies the highly conserved FIGQY tyrosine in the cytoplasmic domain as the principal site of phosphorylation, and demonstrates that phosphorylation of the FIGQY tyrosine abolishes ankyrin-binding activity. Neurofascin expressed in neuroblastoma cells is subject to tyrosine phosphorylation after activation of tyrosine kinases by NGF or bFGF or inactivation of tyrosine phosphatases with vanadate or dephostatin. Furthermore, both neurofascin and the related molecule Nr-CAM are tyrosine phosphorylated in a developmentally regulated pattern in rat brain. The FIGQY sequence is present in the cytoplasmic domains of all members of the L1 family of neural cell adhesion molecules. Phosphorylation of the FIGQY tyrosine abolishes ankyrin binding, as determined by coimmunoprecipitation of endogenous ankyrin and in vitro ankyrin-binding assays. Measurements of fluorescence recovery after photobleaching demonstrate that phosphorylation of the FIGQY tyrosine also increases lateral mobility of neurofascin expressed in neuroblastoma cells to the same extent as removal of the cytoplasmic domain. Ankyrin binding, therefore, appears to regulate the dynamic behavior of neurofascin and is the target for regulation by tyrosine phosphorylation in response to external signals. These findings suggest that tyrosine phosphorylation at the FIGQY site represents a highly conserved mechanism, used by the entire class of L1-related cell adhesion molecules, for regulation of ankyrin-dependent connections to the spectrin skeleton.

Cytoplasmic protein mRNA interaction mediates cGMP-modulated translational control of the asialoglycoprotein receptor

Expression of the asialoglycoprotein receptor by the human hepatocellular carcinoma cell line HuH-7 in response to intracellular cGMP concentrations was previously shown to be regulated at the translational level. In a cell-free system, initiation of asialoglycoprotein receptor mRNA translation was dependent on the presence of the 7-methylguanylate cap site and was independent of 8-bromo-cGMP levels in which the cells were grown prior to RNA isolation. Stable transfection of COS-7 cells with deletion constructs of the asialoglycoprotein receptor H2b subunit localized the cGMP-responsive cis-acting element to the mRNA 5'-untranslated region (UTR). Addition of biotin (an activator of guanylate cyclase) induced the expression of beta-galactosidase present as a chimeric plasmid containing the H2b 187-nucleotide 5'-UTR. An RNA gel retardation assay identified a 37-nucleotide cognate sequence within this 187-nucleotide region. Titration of the 5'-UTR with a cytosolic fraction isolated from HuH-7 grown in the presence or absence of 8-bromo-cGMP or biotin provided direct evidence for an RNA-binding protein responsive to intracellular levels of cGMP. Based on these findings, it seems reasonable to propose that reduction of intracellular levels of cGMP by biotin deprivation results in a negative trans-acting factor associating with the 5'-UTR of asialoglycoprotein receptor mRNAs, thereby inhibiting translation.

[Simultaneous analysis of theophylline, phenobarbital, amobarbital and carbamazepine in serum by high performance liquid chromatography]

Theophylline, phenobarbital, amobarbital and carbamazepine are the chief therapeutic drugs in clinical practice. Because of the differences among inter-individuals in the metabolic clearance of these drugs and their toxicity at certain levels of concentration in serum, the dosage should be regulated to maintain a therapeutic blood drugs level. To achieve this a rapid and accurate assay method for drugs in blood is necessary. This paper reports that a reversed phase high performance liquid chromatographic (HPLC) method had been established for the simultaneous separation and quantitative determination of the four drugs in serum. The separation was performed on RP-C18 column using methanol:water (1:1) as mobile phase and 4-aminoantipyrime as internal standard. The eluted substances were detected at 210nm.

Determinants of cytotoxicity with prolonged exposure to fluorouracil in human colon cancer cells

To explore the determinants of cytotoxicity during prolonged exposure to pharmacologically relevant concentrations of 5-fluorouracil (FUra), we studied the effects of FUra at concentrations ranging from 0.1 to 1 microM in HCT 116 and HT 29 colon cancer cells grown in the presence of physiologic levels of leucovorin. A 5- and 7-day exposure to 1 microM FUra reduced cell growth to 46% and 20% of control in HT 29 cells and to 74% and 38% of control in HCT 116 cells. Concurrent exposure to thymidine (10 or 20 microM) or uridine (1 mM) provided partial protection against FUra toxicity in HT 29 cells, but did not protect HCT 116 cells. After a 24-h exposure to 1 microM [3H]FUra, free 5-fluoro-2'-deoxyuridine-5' -monophosphate (FdUMP) and FUDP. + FUTP levels were 0.7 and 144 pmol/10(6) cells in HT 29 cells, respectively, and 3.9 and 178 pmol/10(6) cells in HCT 116 cells. FdUMP and FUDP + FUTP pools increased by 5.7- and 2.0-fold in HT 29 cells and by 1.7- and 3.3-fold in HCT 116 cells over the next 48 h, but did not accumulate thereafter. After a 24-h exposure to 1 microM [3H]FUra, FUra-RNA levels were 158 and 280 fmol/microgram in HT 29 and HCT 116 cells, respectively; FUra-RNA levels increased over time, and reached 700 and 1156 fmol/microgram at day 5. Concurrent exposure to 1 mM uridine for 72 h did not diminish [3H]FUra-RNA incorporation. Upon removal of [3H]FUra following a 24-h exposure, FUra-RNA levels remained relatively stable with 57-78% retained at 120 h. A low level of [3H]FUra-DNA incorporation was detected in HT 29 cells. Thymidylate synthase (TS) catalytic activity in control cells was 2-fold higher in HCT 116 cells compared to HT 29 cells (47 vs. 23 pmol/min/mg). Total TS content increased 1.5- to 3-fold over control in both cell lines during FUra exposure, and ternary complex formation was evident for up to 96 h-dTTP pools were not depleted in FUra-treated cells, suggesting that residual TS catalytic activity was sufficient to maintain dTTP pools relative to demand. Surprisingly, the partial inhibition of TS was accompanied by a striking accumulation of immunoreactive "dUMP" pools in both lines; dUTP pools also increased 2-to 3-fold. In summary, the gradual and stable accumulation of FUra in RNA noted in both lines may account for the thymidine-insensitive component of FUra toxicity. Because dTTP pools were not appreciably diminished, the interference with nascent DNA chain elongation and induction of single-strand breaks in newly synthesized DNA in both cell lines may be due to misincorporation of deoxyuridine nucleotides.

Effect of 2,3-dimercaptosuccinic acid on nephrosclerosis in the Dahl rat. I. Role of reactive oxygen species

2,3-Dimercaptosuccinic acid (DMSA), a sulfhydryl-containing chelator, has previously been shown to reduce mean blood pressure in lead-treated rats. In the present study we have demonstrated that DMSA (0.5% for 5 days every 2 weeks) also reduces mean blood pressure in the Dahl salt-sensitive (SS) rat. Six-week-old Dahl SS and salt resistant (SR) rats were placed on a 0.3% NaCl diet for two weeks, followed by an 8% NaCl diet for four weeks. Eight SS and 8 SR rats remained untreated while 8 SS and 8 SR rats were treated with DMSA. DMSA treatment ameliorated the mean blood pressure rise in the Dahl SS rats (141 +/- 5 vs. 120 +/- 4 mm Hg at 6 weeks, P < 0.001). Nephrosclerosis was severe in untreated SS rats but absent in treated SS rats as well as in both treated and untreated SR rats. Reactive oxygen species formation, as assessed by kidney cortex content of malondialdehyde (MDA) and immunohistochemical demonstration of nitrotyrosine (a byproduct of peroxynitrite) in interlobular arteries, was increased in Dahl SS rats, but abolished by DMSA (MDA 9.65 +/- 0.33 nmol/g wet wt, untreated SS, vs. 6.46 +/- 0.51, treated SS, P < 0.001). The anti-nephrosclerotic action of DMSA was clearly disproportionate to the reduction in blood pressure. We conclude that the effect of DMSA was related instead to the reactive oxygen species scavenging properties of the thiol groups.