Amplification of pvmdr1 associated with multidrug-resistant Plasmodium vivax

BACKGROUND

Multidrug-resistant strains of Plasmodium vivax are emerging in Southeast Asia.

METHODS

In vitro drug susceptibility and pvmdr1 genotype were determined in P. vivax field isolates from Indonesia and Thailand.

RESULTS

Increased pvmdr1 copy number was present in 21% of isolates from Thailand (15/71) and none from Indonesia (0/114; P < .001). Compared with Indonesian isolates, the median IC(50) of Thai isolates was lower for chloroquine (36 vs. 114 nmol/L; P < .001) but higher for amodiaquine (34 vs. 13.7 nmol/L; P = .032), artesunate (8.33 vs. 1.58 nmol/L; P < .001), and mefloquine (111 vs. 9.87 nmol/L; P < .001). In 11 cryopreserved Thai isolates, those with increased pvmdr1 copy number had a higher IC(50) for mefloquine (78.6 vs. 38 nmol/L for single-copy isolates; P = .006). Compared with isolates with the wild-type allele, the Y976F mutation of pvmdr1 was associated with reduced susceptibility to chloroquine (154 nmol/L [range, 4.6-3505] vs. 34 nmol/L [range, 6.7-149]; P < .001) but greater susceptibility to artesunate (1.8 vs. 9.5 nmol/L; P = .009) and mefloquine (14 vs. 121 nmol/L; P < .001).

CONCLUSIONS

Amplification of pvmdr1 and single-nucleotide polymorphisms are correlated with susceptibility of P. vivax to multiple antimalarial drugs. Chloroquine and mefloquine appear to exert competitive evolutionary pressure on pvmdr1, similar to that observed with pfmdr1 in Plasmodium falciparum.

Abolishment of serotonergic neurotransmission to cardiac vagal neurons during and after hypoxia and hypercapnia with prenatal nicotine exposure

Cardioinhibitory cardiac vagal neurons (CVNs) do not receive inspiratory-related excitatory inputs under normal conditions. However, excitatory purinergic and serotonergic pathways are recruited during inspiratory activity after episodes of hypoxia and hypercapnia (H/H). Prenatal nicotine (PNN) exposure is known to dramatically change cardiorespiratory responses and decrease the ability to resuscitate from H/H. This study tested whether PNN exposure alters excitatory neurotransmission to CVNs in the nucleus ambiguus during and after H/H. Spontaneous and inspiratory evoked excitatory postsynaptic currents were recorded in CVNs from rats that were exposed to nicotine (6 mg x kg(-1) x d(-1)) throughout the prenatal period. In contrast to unexposed animals, in PNN animals H/H recruited excitatory neurotransmission to CVNs during inspiratory-related activity that was blocked by the alpha3beta4 nicotinic acetylcholine receptor (nAChR) blocker alpha-conotoxin AuIB (alpha-CTX AuIB, 100 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50 microM) and d(-)-2-amino-5-phosphonopentanoic acid (AP5, 50 microM), selective AMPA/kainate and N-methyl-d-aspartate receptor blockers, respectively. Following H/H, there was a significant increase in inspiratory-related excitatory postsynaptic currents that were unaltered by alpha-CTX AuIB or ondansetron, a 5-HT3 receptor blocker, but were subsequently inhibited by pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid (100 microM), a purinergic receptor blocker and CNQX and AP5. The results from this study demonstrate that with PNN exposure, an excitatory neurotransmission to CVNs is recruited during H/H that is glutamatergic and dependent on activation of alpha3beta4-containing nAChRs. Furthermore, exposure to PNN abolishes a serotonergic long-lasting inspiratory-related excitation of CVNs that is replaced by recruitment of a glutamatergic pathway to CVNs post H/H.

Our experience on management of Boerhaave's syndrome with late presentation

A retrospective review of 18 patients treated for Boerhaave's syndrome in our center from 1954 to 2006 was undertaken. The patients were divided into two groups: group 1, the time delayed before treatment was less than 24 hours; group 2, the time delayed was more than 24 hours. The time interval between perforation and the onset of treatment in group 2 was from 50 hours to 30 days. Roentgenograms of the chest and esophagogram with a water-soluble contrast medium are able to reveal the perforation in most cases, and thoracentesis or thoracic drainage after swallow methylene blue may provide help as well. Surgical intervention was adopted in all three patients in group 1 and 12 in group 2, and conservative intervention in three in group 2. In group 1, two patients recovered uneventfully, the other one developed a postoperative respiratory infection, and he recovered after the infection was controlled. The mortality in group 2 was 33.3% (5/15), and the mortality in patients with conservative intervention was 100% (3/3). Five complications occurred after surgical intervention in group 2, including four fistulae and one incision infection. In conclusion, it may be appropriate to manage patients aggressively with primary repair and adequate mediastinal and pleural drainage when patients present late. Because of the syndrome's initial severity and a tendency to postoperative complications, patients should be closely monitored, and correct antibiotic therapy and adequate nutrition are very important in treatment.

Combination of the dipeptidyl peptidase IV inhibitor LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] with the angiotensin II type 1 receptor antagonist valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl]methyl]-L-valine] enhances pancreatic islet morphology and function in a mouse model of type 2 diabetes

LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] is an inhibitor of dipeptidyl peptidase IV that delays the degradation of glucagon-like peptide-1 (GLP-1). Valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-l-valine] is an antagonist of the angiotensin II type 1 receptor (AT1R) that reduces the incidence of type 2 diabetes mellitus. LAF237 and valsartan act on a common target through separate pathways to improve pancreatic islet cell function. We hypothesize that the combination of these two drugs acts in a synergistic or additive manner on islet function and structure. To test this hypothesis, we performed in vitro and in vivo studies. To measure the acute effect of the treatment, pancreatic islets of db/db mice were isolated and stimulated in vitro with glucose in the presence of valsartan (1 microM) and exendin-4 (100 nM), a GLP-1 receptor agonist. Combination treatment with valsartan and exendin-4 significantly enhanced glucose-stimulated insulin secretion from isolated islets. For studies of chronic effect, db/db mice received LAF237 (1 mg/kg/day) and/or valsartan (10 mg/kg/day). Islet cell reactive oxygen species (ROS), proliferation, apoptosis, fibrosis, beta-cell area, and glucose homeostasis were evaluated after 8 weeks of treatment, which showed that combination treatment resulted in a significant increase in pancreatic islet beta-cell area compared with monotherapy. This beneficial effect correlated with an increase in beta-cell proliferation and a decrease in ROS-induced islet apoptosis and fibrosis. These in vitro and in vivo data indicate that combination treatment with LAF237 and valsartan has significant beneficial additive effects on pancreatic beta-cell structure and function compared with their respective monotherapeutic effects.

Clinical features of patients with multiple sclerosis from a survey in Shanghai, China

Objective

To describe clinical features of patients with multiple sclerosis (MS) in Shanghai, China.

Methods

Prevalent patients with MS were identified and investigated by a network of physicians in 11 districts of Shanghai during the period from 1 September 2004 to 31 August 2005. Admission registries of each hospital in the study area were checked systematically for patients with a diagnosis of MS, neuromyelitis optica or other demyelinating disorders. All patients with collected information were evaluated by four senior neurologists according to the McDonald criteria.

Results

There were 249 (146 female and 103 male) patients with a confirmed MS diagnosis, at a female-to-male ratio of 1.4. The mean age at onset of MS was 37.4 years for the 249 patients with MS and, on the prevalence day, 42.7 years. The most frequent location of clinical MS lesions in the central nervous system was the spinal cord (61%), followed by the cerebrum (55%) and optic nerves (41%). Nearly all (96%) of the patients with MS had been examined by magnetic resonance imaging, and 226 (94%) patients of those examined were suggestive of MS. No family history of MS was found in any of the patients. Most (86%) of the patients had no or mild disability on the prevalence day (31 December 2004). Almost all (96%) patients with MS had been treated with corticosteroids.

Conclusion

Clinical features of patients with MS are described based on the information from the largest case series reported among Chinese. Comparisons and discussions are made with findings from the other populations.

No association of the POLI Thr706Ala polymorphism with the risk of cervical carcinoma

OBJECTIVE

To investigate the association of repair gene POLI genetic polymorphisms with cervical carcinoma.

MATERIALS AND METHODS

Four hundred sixty one cervical carcinoma patients and 628 normal women were randomly selected for this study. Single nucleotide polymorphisms (SNPs) (POLI Thr706Ala) were genotyped, and the epidemiological risk factor was assessed.

RESULTS

Compared with the POLI Thr706Thr genotype, neither POLI Thr706Ala nor POLI Ala706Ala elevated or decreased the risk of cervical carcinoma or cervical squamous cell carcinoma [ORs and 95% CIs 1.25(0.97-1.61), 1.11(0.67-1.83), 1.22(0.94-1.58), 1.06(0.63-1.78), respectively]. When analyzing the risk of the POLI Thr706Ala variant genotype for cervical carcinoma in different histological types or HPV infection status, very similar risk factors were observed for the squamous cell carcinoma group or the HPV positive group to the overall carcinoma. Regardless of sexual or reproductive histories, patients with the POLI Thr706Ala or POLI Ala706Ala genotype showed a significantly increased risk of cervical carcinoma.

CONCLUSION

The POLI Thr706Ala genotype was not associated with cervical carcinoma in a Chinese population, but we cannot exclude the possibility that the POLI polymorphism might be associated with sexual and reproductive history.

Recruitment of excitatory serotonergic neurotransmission to cardiac vagal neurons in the nucleus ambiguus post hypoxia and hypercapnia

Inhibitory GABAergic and glycinergic neurotransmission to cardioinhibitory cardiac vagal neurons (CVNs) increase during inspiratory activity and likely mediate respiratory sinus arrhythmia, while the frequency of excitatory postsynaptic currents (EPSCs) in CVNs are unaltered during the different phases of respiration. However, following hypoxia and hypercapnia (H/H), the parasympathetic activity to the heart increases and thus far, identification of the pathways and neurotransmitters that are responsible for exciting CVNs post H/H are unclear. This study identifies different excitatory pathways to CVNs recruited post H/H. Spontaneous and inspiratory-related EPSCs were recorded in CVNs before, during, and after 10 min of H/H in an in vitro slice preparation that retains rhythmic respiratory activity. Before and during H/H, EPSCs in CVNs were completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and d(-)-2-amino-5-phosphonopentanoic acid (AP5), selective AMPA/kainate and N-methyl-d-apartate (NMDA) receptor blockers, respectively. However, after H/H, there was a significant increase in EPSCs during each inspiratory burst. While some of the inspiratory-related EPSCs were blocked by the broad purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid (PPADS) and the specific P2X receptor antagonist 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate monolithium trisodium salt (TNP-ATP) a P2X receptor blocker, most of the recruited excitatory neurotransmission to CVNs is serotonergic because odansetron, a selective 5-HT3 antagonist, abolished the majority of the spontaneous and inspiratory-related EPSCs evoked during recovery from H/H. The results from this study suggest that following episodes of H/H, two nonglutamatergic excitatory pathways, purinergic and serotonergic, activating P2X and 5-HT3 receptors, respectively, are recruited to excite CVNs in the post H/H recovery period.

Microdialysis for pharmacokinetic-pharmacodynamic studies

Microdialysis (MD) has become one of the major tools to sample endogenous and exogenous substances in extracellular spaces. It is more suitable for pharmacokinetic-pharmacodynamic (PK-PD) studies than other techniques. This review aims to give an overview of MD for PK-PD (MD/PK-PD) studies, including PK-PD studies, three aspects (principles, recovery, advantages) of MD/PK-PD, and application examples of MD/PK-PD organized by types of drugs and information collected. It can be concluded that MD offers an unique opportunity, to study simultaneously pharmacokinetic (PK) behavior of a drug and its effect on the extracellular levels of endogenous compounds, which may facilitate proof-of-concept demonstrations for target modulation, enhance the rational selection of an optimal drug dose and schedule. In addition, MD/PK-PD can also minimize uncertainties associated with predicting drug safety and efficacy, reduce the high levels of drug attrition during development, accelerate drug approval, and decrease the overall costs of drug development.

A population-based survey of multiple sclerosis in Shanghai, China

OBJECTIVE

To conduct a large population-based survey on multiple sclerosis (MS) prevalence in Shanghai, China.

METHODS

We established a network of physicians, mainly neurologists, for identifying prevalent patients with MS and systematically checked inpatient registers at each hospital in the study area for patients with a diagnosis of MS, neuromyelitis optica, or other demyelinating disorders. MS diagnosis in patients was validated by senior neurologists according to the McDonald criteria.

RESULTS

In total, 123 patients with a validated MS diagnosis from the study population, 8.86 million inhabitants with permanent residence in Shanghai, were alive on the prevalence day. The crude MS prevalence rate was 1.39 cases per 100,000 inhabitants (95% CI: 1.16 to 1.66 cases) in the study population in Shanghai. There were 79 female and 44 male patients with MS, a female-to-male ratio of 1.8. Nearly all (96%) of the patients with validated MS had been examined by MRI.

CONCLUSION

Multiple sclerosis prevalence in Shanghai is in line with that reported for other Asian populations.

Distribution of human papillomavirus genotypes in the patients with cervical carcinoma and its precursors in Zhejiang Province, China

Various evidences reveal that the human papillomavirus (HPV) is the single most important etiologic agent in cervical carcinoma (CC). To investigate the distribution of HPV genotypes in the patients with CC and its precursors in Zhejiang Province, China, a total of 631 eligible samples from patients in Zhejiang Province with CC (N = 181), cervical intraepithelial neoplasia (CIN) II-III (N = 345), and CIN I (N = 105) were detected. Age-matched samples of 217 women without cervical neoplasia were detected as control. An improved polymerase chain reaction (PCR)-restriction fragment length polymorphism assay validated by Hybrid Capture II and PCR sequencing was designed for HPV genotype. The prevalence of HPV was 95.0% in CC, 88.4% in CIN II-III, and 73.3% in CIN I, while only 41.9% in control. High-risk/low-risk HPV ratio showed a significant trend of increase with increased grade of CIN and transformation to carcinoma. A total of 24 HPV genotypes were detected in CC and its precursors. Of those, HPV 16 (65.2%), 18 (9.4%), and 58 (9.4%) were the major HPV genotypes in CC, while HPV 16 (37.6%), 58 (19.1%), 33 (10.6%), and 18 (5.4%) in CIN. In conclusion, the distribution of predominant HPV genotypes in the patients with CC and its precursors in Zhejiang Province is HPV 16, 58, and 18, probably as well as 33, which may be high-risk factors for CC.

Predictive factors for prognosis of hilar cholangiocarcinoma: Postresection radiotherapy improves survival

AIMS

Several studies have analyzed the determinants of long-term survival in hilar cholangiocarcinoma (HCCA) patients, but the majority of these have not speculated adjuvant therapy on prognosis. We conduct this study to identify potential predictive factors for prognosis of HCCA focusing on aspects dealing with adjuvant therapy.

PATIENTS AND METHODS

Data from 75 consecutive HCCA patients undergoing surgical resection with curative intent were recorded prospectively. The survivals of patients were comparable with respect to different factors followed by a univariate and multivariate analysis.

RESULTS

Actual 1-year, 3-year, and 5-year survival rates were 84.0, 44.4 and 12.0%, respectively. By Cox proportional hazards survival analysis, the most powerful predictors of outcome was resection type (Hazard Ratio [HR] 17.4, 95% confidence interval [CI] 16.8-17.8), followed by adjuvant radiotherapy (RT) (HR 4.3, 95% CI 3.6-4.9), regional lymph nodes involvement (HR 2.1, 95% CI 1.7-2.6), and preoperative maximum serum total bilirubin level (HR 2.0, 95% CI 1.5-2.5).

CONCLUSIONS

Our study showed overall a highly significant benefit in survival in favor of RT, and the difference was especially significant after R1/R2 resection and in patients with Bismuth III/IV type tumors. Postresection chemotherapy (CTx) did not show any clinical benefits. R0 resection still significantly improves survival. Lower total serum bilirubin level, no regional lymph nodes involvement conferred survival advantage.

Loss of OPCML expression and the correlation with CpG island methylation and LOH in ovarian serous carcinoma

PURPOSE

To detect the expression of OPCML in ovarian serous carcinoma and investigate the correlation with CpG island methylation and LOH of OPCML.

METHODS

20 normal tissues, 75 ovarian serous tumors, three cell lines, SKOV-3, CAOV3 and 3AO, were detected in OPCML expression by RT-PCR, CpG island methylation by methylation-sensitive restriction enzyme-PCR, and LOH analysis at four microsatellite marks (D11S4085, D11S1320, D11S874 and D11S969).

RESULTS

Loss of OPCML expression in ovarian serous carcinomas was significantly higher than in ovarian adenomas and normal tissues. OPCML expression was detectable in 3AO, but not in SKOV-3 and CAOV3. CpG island methylation was found in 53.4% of the carcinomas, while in none of the adenomas or normal tissues. Meanwhile, CpG island methylation was detectable in SKOV-3 and CAOV3, but not in 3AO. The correlation between CpG island methylation and loss of OPCML expression was found in carcinomas. The LOH rate at D11S4085 in carcinomas was significantly higher than that for adenomas and normal tissues. LOH at D11S4085 was also correlated with loss of OPCML expression.

CONCLUSIONS

These results indicate that loss of OPCML expression occurs frequently in ovarian serous carcinoma. CpG island methylation and LOH are probably two mechanisms of OPCML inactivation.

A case–control study of Guillain–Barre syndrome in Harbin, China

We evaluated the putative factors for the onset of Guillain-Barré syndrome (GBS) in Harbin, China by a case-control study based on the information from GBS patients identified from a population-based incidence survey, which is the first study of this kind in China. Sixty-nine GBS patients were identified during a 1-year period from 1 October 1997 to 30 September 1998, and they were matched with 69 controls for gender and age (+/-5 years). GBS diagnosis was validated by senior neurologists and GBS patients were followed up for 6 months after onset. Odds ratio (OR) and 95% confidence intervals (CI) for each putative factor for the onset of GBS were calculated and compared between GBS cases and controls. Precedent respiratory infections within 2 months before onset were found to be significantly more frequent in GBS patients than in controls (OR = 1.68, 95% CI: 1.21-2.33). Although the number of cases with gastroenteritis among GBS patients was more than double of that in the controls, the difference was not statistically significant (OR = 2.25, 95% CI: 0.73-6.96). Other putative factors as well as characteristics regarding family situation, education level, occupation, etc., were not found to be statistically different between GBS patients and controls.

Establishment of a cervical cancer model via inoculating SiHa Cells into humanized severe combined immunodeficient mice

PURPOSE OF INVESTIGATION

To establish a human papillomavirus (HPV) 16 positive cervical cancer model in the humanized severe combined immunodeficient (SCID) mouse.

METHODS

A HPV16 positive cervical carcinoma cell line (SiHa) was transplanted subcutaneously into SCID mice (SiHa-SCID); human peripheral blood lymphocyte (Hu-PBL) was transplanted intraperitoneally (Hu-PBL-SCID), Hu-PBL was transplated intraperitoneally and SiHa subcutaneously (Hu-PBL-SiHa-SCID), and, PBS was transplanted subcutaneously (PBS-SCID) as a control. The biological and immunological features were investigated.

RESULTS

The transplanted tumor grew slowly and no metastasis was found. The survival time of Hu-PBL-SiHa-SCID was significantly longer than that of SiHa-SCID. HPV16 DNA could be detected in all of the tumor tissues, but not in peripheral blood and organ tissues. Human serum IgG levels in Hu-PBL-SCID and Hu-PBL-SiHa-SCID were significantly elevated following immuno-reconstructed time elongating, and significantly higher in Hu-PBL-SiHa-SCID than those in Hu-PBL-SCID. The numbers of human CD3+, CD4+ and CD8+ T cells were significantly increased in the peripheral blood and spleen of Hu-PBL-SiHa-SCID and Hu-PBL-SCID mice, and significantly higher in Hu-PBL-SiHa-SCID than those of Hu-PBL-SCID mice. The weight of the spleen was significantly increased in Hu-PBL-SiHa-SCID. Tumor infiltrating lymphocytes (TILs) and human CD4+ T cells were detected in Hu-PBL-SiHa-SCID but not in SiHa-SCID mice. The spleen cells of Hu-PBL-SiHa-SCID mice displayed significantly stronger cytotoxicity to target cells than those of SiHa-SCID mice. No graft-versus-host disease (GVHD) was found in either Hu-PBL or Hu-PBL-SiHa-SCID mice.

CONCLUSION

A HPV16 positive cervical carcinoma model has been successfully established in SCID mice. This model can perfectly simulate the biological features of spontaneous human cervical cancer, and present anti-tumor immune response after the human immune system is reconstructed.

Approximation of flammability region for natural gas-air-diluent mixture

The growing implementation of exhaust gas recirculation (EGR) in reducing NO(x) emissions of engine is of paramount motivation to perform a fundamental research on the flammability characteristics of fuel-air-diluent mixtures. In this work, the influences of EGR on the flammability region of natural gas-air-diluent flames were experimentally studied in a constant volume bomb. An assumption of critical burning velocity at flammability limit is proposed to approximately determine the flammability region of these mixtures. Based on this assumption, an estimation of the flammability map for natural gas-air-diluent mixtures was obtained by using the empirical formula of burning velocity data. The flammability regions of natural gas-air mixtures with EGR are plotted versus the EGR rate. From the comparison of estimated results and experimental measurements, it is suggested that the accuracy of prediction is largely dependent upon the formula of burning velocity used. Meanwhile, the influence of pressure on the critical burning velocity at flammability limit is also investigated. On the basis of the pressure dependence criterion, the estimation was performed for the circumstance of high temperature and pressure, and the prediction results still agree well with those of experiments.

Regression of NMU-induced mammary tumors with the combination of melatonin and 9-cis-retinoic acid

A significant increase in tumor regression was induced in N-nitroso-N-methylurea-induced mammary tumors in rats treated with the combination of melatonin and 9-cis-retinoic acid (9cRA). Treatment groups included: control (ethanolic saline), 9cRA (30 mg/kg chow/day), melatonin 500 microg/day, melatonin 1000 microg/day, melatonin 500 microg/day+9cRA and melatonin 1000 microg/day+9cRA. Rats treated with the lower dose of melatonin 500 microg+9cRA show the greatest degree of tumor regression (78%), with 54% undergoing complete regression and a significant increase in apoptotic cells observed by TUNEL Assay. Furthermore, tumor multiplicity and burden were significantly decreased by the combination of melatonin and 9cRA.

Effects of factor IX or factor XI deficiency on ferric chloride-induced carotid artery occlusion in mice

Factor XI (FXI) and factor IX (FIX) are zymogens of plasma serine proteases required for normal hemostasis. The purpose of this work was to evaluate FXI and FIX as potential therapeutic targets by means of a refined ferric chloride (FeCl(3))-induced arterial injury model in factor-deficient mice. Various concentrations of FeCl(3) were used to establish the arterial thrombosis model in C57BL/6 mice. Carotid artery blood flow was completely blocked within 10 min in C57BL/6 mice by application of 3.5% FeCl(3). In contrast, FXI- and FIX-deficient mice were fully protected from occlusion induced by 5% FeCl(3), and were partially protected against the effect of 7.5% FeCl(3). The protective effect was comparable to very high doses of heparin (1000 units kg(-1)) and substantially more effective than aspirin. While FXI and FIX deficiencies were indistinguishable in the carotid artery injury model, there was a marked difference in a tail-bleeding-time assay. FXI-deficient and wild-type mice have similar bleeding times, while FIX deficiency was associated with severely prolonged bleeding times (>5.8-fold increase, P < 0.01). Given the relatively mild bleeding diathesis associated with FXI deficiency, therapeutic inhibition of FXI may be a reasonable strategy for treating or preventing thrombus formation.

Experimental study of flammability limits of natural gas-air mixture

Flammability limits data are essential for a quantitative risk assessment of explosion hazard associated with the use of combustible gas. The present work is to obtain the fundamental flammability data for prevention of the hazards in the practical applications. Experiments have been conducted in a constant volume combustion bomb, and the fuel considered here is natural gas (NG). The pressure histories in the combustion bomb are recorded and a criterion of 7% pressure rise has been used to judge a flammable mixture. The effects of ethane on NG-air flammability limits have been investigated. By adding diluent (carbon dioxide, nitrogen or their mixture) into NG-air mixture, the dilution effects on the flammability limits have been explored as well, and the results are plotted as functions of diluent ratio.

Novel beta-carotene ketolases from non-photosynthetic bacteria for canthaxanthin synthesis

We reported previously that the Rhodococcus erythropolis strain AN12 synthesizes the monocyclic carotenoids 4-keto gamma-carotene and gamma-carotene. We also identified a novel lycopene beta-monocyclase in this strain. Here we report the identification of the rest of the carotenoid synthesis genes in AN12. Two of these showed apparent homology to putative phytoene dehydrogenases. Analysis of Rhodococcus knockout mutants suggested that one of them ( crtI) encodes a phytoene dehydrogenase, whereas the other ( crtO) encodes a beta-carotene ketolase. Expression of the beta-carotene ketolase gene in an Escherichia coli strain which accumulates beta-carotene resulted in the production of canthaxanthin. In vitro assays using a crude extract of the E. coli strain expressing the crtO gene confirmed its ketolase activity. A crtO homologue (DR0093) from Deinococcus radiodurans R1 was also shown to encode a beta-carotene ketolase, despite its sequence homology to phytoene dehydrogenases. The Rhodococcus and Deinococcus CrtO ketolases both catalyze the symmetric addition of two keto groups to beta-carotene to produce canthaxanthin. Even though this activity is similar to the CrtW-type of ketolase activity, the CrtO ketolases show no significant sequence homology to CrtW-type ketolases. The presence of six conserved regions may be a signature for the CrtO-type of beta-carotene ketolases.

Origin and evolution of the light-dependent protochlorophyllide oxidoreductase (LPOR) genes

Light-dependent NADPH-protochlorophyllide oxidoreductase (LPOR) is a nuclear-encoded chloroplast protein in green algae and higher plants which catalyzes the light-dependent reduction of protochlorophyllide to chlorophyllide. Light-dependent chlorophyll biosynthesis occurs in all oxygenic photosynthetic organisms. With the exception of angiosperms, this pathway coexists with a separate light-independent chlorophyll biosynthetic pathway, which is catalyzed by light-independent protochlorophyllide reductase (DPOR) in the dark. In contrast, the light-dependent function of chlorophyll biosynthesis is absent from anoxygenic photosynthetic bacteria. Consequently, the question is whether cyanobacteria are the ancestors of all organisms that conduct light-dependent chlorophyll biosynthesis. If so, how did photosynthetic eukaryotes acquire the homologous genes of LPOR in their nuclear genomes? The large number of complete genome sequences now available allow us to detect the evolutionary history of LPOR genes by conducting a genome-wide sequence comparison and phylogenetic analysis. Here, we show the results of a detailed phylogenetic analysis of LPOR and other functionally related enzymes in the short chain dehydrogenase/reductase (SDR) family. We propose that the LPOR gene originated in the cyanobacterial genome before the divergence of eukaryotic photosynthetic organisms. We postulated that the photosynthetic eukaryotes obtained their LPOR homologues through endosymbiotic gene transfer.

Investigating antigenic variation and other parasitehost interactions in Plasmodium falciparum infections in nave hosts

Mathematical models of the in-host dynamics of malaria infections provide a valuable tool to explore aspects of the host-parasite interaction that are not possible to investigate experimentally. This paper presents predictions of several important parameter values for 2 parasite strains/groups: parasite PfEMP1 switching rates, dynamics of host anti-PfEMP1 antibodies and parameters related to specific and non-specific host immune responses. A stochastic simulation model of the in-host dynamics of Plasmodium falciparum infections in naïve hosts was used to make these predictions. This model incorporates a novel process to simulate antigenic variation by the parasite, and specific and non-specific immune responses by the host. Comparison of model output to a range of published statistics indicated that the model is capable of reproducing the features of clinical P. falciparum infections, including the characteristic recrudescent behaviour. Using the model, we explored the hypothesized switching mechanism of a fast overall rate of antigenic variation early in an infection and found that it is compatible with chronic infections when the var genes are split into 2 groups; fast and slow switching.

Asymmetrically acting lycopene beta-cyclases (CrtLm) from non-photosynthetic bacteria

Carotenoids have important functions in photosynthesis, nutrition, and protection against oxidative damage. Some natural carotenoids are asymmetrical molecules that are difficult to produce chemically. Biological production of carotenoids using specific enzymes is a potential alternative to extraction from natural sources. Here we report the isolation of lycopene beta-cyclases that selectively cyclize only one end of lycopene or neurosporene. The crtLm genes encoding the asymmetrically acting lycopene beta-cyclases were isolated from non-photosynthetic bacteria that produced monocyclic carotenoids. Co-expression of these crtLm genes with the crtEIB genes from Pantoea stewartii (responsible for lycopene synthesis) resulted in the production of monocyclic gamma-carotene in Escherichia coli. The asymmetric cyclization activity of CrtLm could be inhibited by the lycopene beta-cyclase inhibitor 2-(4-chlorophenylthio)-triethylamine (CPTA). Phylogenetic analysis suggested that bacterial CrtL-type lycopene beta-cyclases might represent an evolutionary link between the common bacterial CrtY-type of lycopene beta-cyclases and plant lycopene beta- and epsilon-cyclases. These lycopene beta-cyclases may be used for efficient production of high-value asymmetrically cyclized carotenoids.