Efficient double-clad thulium-doped fiber laser with a ring cavity

We have constructed a novel ring cavity for a double-clad thulium-doped fiber laser, by placing the fiber's 45 degrees angle-polished output end before the input end and relaunching the pump and the laser power into the fiber. This design can reduce reabsorption by using short fibers without loss of pump efficiency. The dependence of the laser's performance on the fiber's length and the output coupler's reflectivity is investigated experimentally and theoretically. With an 80-cm-long fiber, 2.7-W single-mode continuous-wave output is generated for 11.5 W of launched pump power.

Methylenetetrahydrofolate reductase polymorphisms increase risk of esophageal squamous cell carcinoma in a Chinese population

Methylenetetrahydrofolate reductase (MTHFR) plays a central role in folate metabolism that affects DNA methylation and synthesis. Because germ-line mutations at nucleotides 677 (C-->T) and 1298 (A-->C) in the MTHFR gene cause diminished enzyme activity, and aberrant DNA methylation is oncogenic, we examined the relationship between these two MTHFR polymorphisms and susceptibility to esophageal squamous cell carcinoma (ESCC) in 240 ESCC cases and 360 age- and sex-matched controls in northern CHINA: We found that the allele frequency of MTHFR 677T was significantly higher among cases than among controls (63% versus 41%, P < 0.001). Subjects with the 677TT genotype had a more than 6-fold increased risk of developing ESCC [adjusted odds ratio (OR), 6.18; 95% confidence interval (CI), 3.32-11.51] compared with those who had the 677CC genotype. Furthermore, the elevated ESCC risk associated with the 677 polymorphism was in an allele-dose relationship (trend test, P = 0.0001) with ORs of 1.00, 3.14 (95% CI, 1.94-5.08), and 6.18 (95% CI, 3.32-11.51) for the CC, CT, and TT genotype, respectively, after adjustment for age, sex, smoking status, and the MTHFR 1298 polymorphism. The allele frequency for the MTHFR 1298C was 14% among cases and 17% among controls. The 1298CC genotype was extremely rare in both controls (1.4%) and cases (2.9%) and was also associated with an elevated risk of ESCC (adjusted OR, 4.43; 95% CI, 1.23-16.02) compared with the 1298AA genotype, whereas the 1298AC genotype had no effect on the risk of ESCC. Thus, our findings support the hypothesis that genetic polymorphisms in the MTHFR gene may contribute to susceptibility to carcinogenesis of the esophagus in the at-risk Chinese population.

Prevention of ischemic ventricular tachycardia of Purkinje origin: role for alpha(2)-adrenoceptors in Purkinje?

Recent studies have shown the presence of postjunctional alpha(2)-adrenergic receptors on canine Purkinje fibers but not muscle cells. Stimulation of these receptors results in prolongation of the action potential duration and the Purkinje relative refractory period. We studied the effect of alpha(2)-adrenergic agonists on inducible ischemic ventricular tachycardia (VT) of both Purkinje fiber and myocardial origin. Open-chest dogs in whom VT was induced with extrastimuli after occlusion of the anterior descending coronary artery were studied. A mapping system, incorporating Purkinje signals, characterized the mechanisms of VT. The alpha(2)-adrenergic agonists clonidine (0.5-4.0 microg/kg) or UK 14,304 (4-5 microg/kg) versus saline were given intravenously after reproducibility of inducible sustained monomorphic VT had been demonstrated. Eighteen dogs were given clonidine, eleven of which had focal Purkinje VT. Of these 11 dogs, clonidine blocked VT induction in 9 (81.9%) and rendered VT nonsustained in 1 (9.1%), and VT remained inducible in 1 dog (9.1%), although this was focal midmyocardial VT only. In the seven dogs with VT of myocardial origin, six (85.6%) remained inducible with clonidine, whereas one dog (14.4%) had only nonsustained VT after clonidine. Of the six dogs, UK 14,304 blocked VT induction in four (66.6%) and rendered VT nonsustained in one (16.7%), and VT remained inducible in one dog (16.7%). In four dogs with VT of myocardial origin, VT remained inducible. In the eight control dogs that were given saline, focal Purkinje VT was repeatedly inducible. Pharmacological stimulation of postjunctional alpha(2)-adrenoceptors on Purkinje fibers may selectively prevent induction of VT of Purkinje fiber origin in the ischemic canine ventricle.

[The effect of culture conditions on the fatty acid composition in the mycelium of the Cephalosporium sp]

The optimal condition of Cephalosporium sp. to culture mycelia and accumulate polyunsaturated fatty acid (PUFA) was researched. The optimal culture condition to get mycelium productivity was: maltose 60 g/L, KNO3 3 g/L, initial pH 6.0, 100 mL medium in 500 mL flask, seeding 25% (v/v), 25 degrees C culture it for 10 days. The optimal condition to accumulation PUFA proportion to total fatty acid was: glucose 10-20 g/L, NH4Cl or (NH4)2SO4 3 g/L, initial pH 4.0, 100 mL medium in 500 mL falsk, seeding 10-20% (v/v) and lighted it when it was cultured. It was suggested that two step could be used in the producing progress. A proposal was put forward that the oileic acid transformed to linoleic acid was the key step to produce PUFA. This proposal gave a base to research the optimal culture condition and enzyme regulation.

Myocardial ischemia-reperfusion damage impacts occurrence of ventricular fibrillation in dogs

To define the relationship between ischemia-reperfusion-induced myocardial damage (IRD) and the occurrence of ventricular tachycardia (VT) and fibrillation (VF), we studied 23 dogs with a three-dimensional activation mapping system. Left anterior descending (LAD) coronary artery occlusion and reperfusion were performed while recording electrograms during VF and atrial pacing. Prior nonischemic sites showing IRD, defined as at least 10% loss of electrogram voltage after reperfusion, had the longest ventricular effective refractory periods (ERPs). IRD sites also occurred more frequently in dogs with reperfusion VF (44 +/- 2 sites, P < 0.01) compared with dogs with VT (18 +/- 5 sites) and no VT (16 +/- 3 sites). In dogs (n = 3) with 3 h of reperfusion, 95% of IRD sites still had lower voltage than those recorded during occlusion. Activation mapping of the first eight complexes of VF had Purkinje or endocardial focal origin in 57%, and complexes originated from IRD sites in 28%. In contrast, dogs with only reperfusion VT also had Purkinje or endocardial focal origin in 79%, but only 5% (P < 0.01 vs. VF dogs) of the sites of origin had IRD. Therefore, dogs with reperfusion VF had more IRD sites where the ERP was longest, and more focal ventricular complexes originated from IRD sites, indicating that IRD may be one important factor in the occurrence of VF during reperfusion.

CYP 1A1 polymorphism and risk of lung cancer in relation to tobacco smoking: a case-control study in China

The impact of genetic polymorphisms in CYP1A1 on susceptibility to lung cancer has received particular interest in recent years since this enzyme plays a central role in activation of major classes of tobacco carcinogens. Several polymorphisms in the CYP1A1 locus have been identified and their genotypes appear to exhibit population frequencies that depend on ethnicity. We have assessed the role of CYP1A1 genotype in lung cancer risk in the Chinese population via a case-control study. Three polymorphisms, m1 (MSP:I), m2 (exon 7 Ile-->Val) and m4 (exon 7 Thr-->Asn), were determined by PCR-RFLP in 404 controls and 217 lung cancer cases. While no polymorphic alleles were detectable in the m4 site among our study subjects, the allele frequencies for CYP1A1 m1 and CYP1A1 m2 were found to be 35.6 and 25.6% among controls, compared with 42.6 and 34.2% among cases. Multivariate analysis showed an elevated risk for lung cancer in subjects having at least one m1 allele [odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1.4-2.8] or having at least one m2 allele (OR = 1.9, 95% CI = 1.3-2.7). However, this increased risk was limited to squamous cell carcinoma (SCC), but not adenocarcinoma or other histological types of lung cancer. Stratified analysis indicated a multiplicative interaction between tobacco smoking and variant CYP1A1 m1 genotypes on the risk of SCC. The ORs of SCC for the variant CYP1A1 m1 genotype, tobacco smoking and both factors combined were 2.8, 9.1 and 29.9, respectively. When the data was stratified by the pack-year values, this joint effect was consistent and stronger among the heaviest smokers. The interaction between tobacco smoking and the variant CYP1A1 m2 genotypes followed the same pattern. Our findings support the conclusion that CYP1A1 m1 and CYP1A1 m2 polymorphisms are associated with smoking-related lung cancer risk in Chinese.

[Genetic polymorphism in hOGG1 and susceptibility to esophageal cancer in Chinese]

OBJECTIVE

To examine the association between Ser326Cys polymorphism in hOGG1 gene, which is involved in the repair of 8-hydroxyguanine in damaged DNA, and investigate the risk of squamous cell carcinoma of the esophagus in Chinese.

METHODS

Ser326Cys polymorphism in hOGG1 gene was determined by PCR-SSCP approach among 201 normal controls and 196 patients with squamous cell carcinoma of the esophagus. The association between this genetic polymorphism and the risk of the cancer was examined by a multivariate analysis.

RESULTS

The Cys/Cys genotype of hOGG1 was found in 21.4% of patients with the cancer and in 13.4% of controls (P<0.05). Homozygosity for the Cys/Cys genotype significantly increased the risk of developing esophageal cancer, with the odds ratio adjusted for age, sex and smoking being 1.9(95% CI 1.3-2.6). Smoking also significantly increased esophageal cancer risk in this case-control study (adjusted OR 2.6; 95% CI 1.7- 3.9). No interaction between smoking and Cys/Cys genotype was observed for the risk of esophageal cancer.

CONCLUSION

Polymorphism of hOGG1 Ser326Cys may play a role in esophageal carcinogenesis.

Investigation of an aerosol challenge model as alternative to the intracerebral mouse protection test for potency assay of whole cell pertussis vaccines

The current potency test for whole cell pertussis vaccines, the intracerebral mouse protection test, is still the only assay which has shown a correlation with protection in children. However, it has considerable disadvantages as it uses a severe challenge procedure and the results tend to show significant intra- and inter-laboratory variation. An alternative assay based on non-lethal aerosol challenge of mice has been investigated as a replacement for the current intracerebral mouse protection test. Evaluation of this indicated that the aerosol system allowed consistent inoculation of bacteria into mice and gave good reproducibility. The protective capacity of different vaccine preparations was distinguished by this assay. Furthermore, the viable counts of Bordetella pertussis in the lungs of challenged mice were immunisation dose-dependent, which allowed the relative potency of vaccines to be calculated. Comparison of potency of five batches of vaccine from different manufacturers assayed by both the intracerebral and the aerosol challenge methods ranked the vaccines in identical order. The results suggest that this method has potential for use as a potency test for whole cell pertussis vaccine which would result in a great reduction in the number of animals used. It would also replace the lethal challenge by a non-lethal procedure and thereby avoid the use of the severe intracerebral challenge procedure.

Transcriptional effects on double-strand break-induced gene conversion tracts

Transcription stimulates spontaneous homologous recombination, but prior studies have not investigated the effects of transcription on double-strand break (DSB)-induced recombination in yeast. We examined products of five ura3 direct repeat substrates in yeast using alleles that were transcribed at low or high levels. In each strain, recombination was stimulated by DSBs created in vivo at an HO site in one copy of ura3. Increasing transcription levels in donor or recipient alleles did not further stimulate DSB-induced recombination, nor did it alter the relative frequencies of conversion and deletion (pop-out) events. This result is consistent with the idea that transcription enhances spontaneous recombination by increasing initiation. Gene conversion tracts were measured using silent restriction fragment length polymorphisms (RFLPs) at approximately 100bp intervals. Transcription did not alter average tract lengths, but increased transcription in donor alleles increased both the frequency of promoter-proximal (5') unidirectional tracts and conversion of 5' markers. Increased transcription in recipient alleles increased the frequency of bidirectional tracts. We demonstrate that these effects are due to transcription per se, and not just transcription factor binding. These results suggest that transcription influences aspects of gene conversion after initiation, such as strand invasion and/or mismatch repair (MMR).

[Expression of T cell factor 4 in renal cell carcinoma]

OBJECTIVE

To investigate of the transduction of Wnt/Frizzled pathway in nuclei and the function of TCF4 (T Cell Factor) in renal cell carcinoma.

METHODS

TCF4 mRNA are tested through RT-PCR and Northern Blot in renal cancer tissue and renal cancer cell strain (GRC-I).

RESULTS

It has been certificated that TCF4 are expressed in renal cell carcinoma, at the same time, there are some different splice of TCF4 in renal cancer. A new 300bp mutant gene are found.

CONCLUSION

TCF4, an important molecular of Wnt/Frizzled pathway, takes part in the formation and progression of renal cell carcinoma, different splice of TCF4 is one of the mechanism.

Somatic embryogenesis of Echinodorus orisis L. and the kinetic changes of the endogenous hormones contents during the embryogenetic process

Somatic embryogenesis was achieved in young Leaf cuttings of Echinodorus orisis L., an aquatic ornamental plant, in a short period (25 days). Among the cytokinins and their combinations tested, 6-BA (1 mg/L) and Zt (1 mg/L) in MS medium induced the highest efficiency (100%) of somatic embryogenesis, with a maximum of 4.87 embryoids per explant. Roots instead of somatic embryos were formed when NAA (0.5 mg/L) was added to MS medium containing Zt (1 mg/L). Matured embryoids were germinated and rooted in MS medium with IAA (1 mg/L) after 5 days cultivation. Seventy-two percent of the rooted plantlets transplanted survived in the aquarium. The endogenous hormone contents in various stages of somatic embryogenetic process were measured by HPLC. The concentrations of all the hormones tested were about 2 times that of the cuttings from the untreated fresh leaves after 10 days incubation. Meanwhile, the concentration of IAA presents two peaks after 10 and 25 days of cultivation, respectively. The cytokinin (Zt and ZR) peak, about 8 times more than CK, appeared in 15 days cultivation when the heart-shaped embryos formed. The fluctuation of the GA3 concentration was very similar to that of cytokinin. The ABA, however, remains stable at quite high concentration after 10 days of cultivation.

Synthesis, biodistribution, and primate imaging of fluorine-18 labeled 2beta-carbo-1'-fluoro-2-propoxy-3beta-(4-chlorophenyl)tr opanes. Ligands for the imaging of dopamine transporters by positron emission tomography

2beta-(R)-Carbo-1-fluoro-2-propoxy-3beta-(4-chlorophenyl) tro pane ((R)-FIPCT, R-6) and 2beta-(S)-carbo-1-fluoro-2-propoxy-3beta-(4-chlorophenyl) tro pane ((S)-FIPCT, S-6) were prepared and evaluated in vitro and in vivo for dopamine transporter (DAT) selectivity and specificity. High specific activity [(18)F](R)-FIPCT and [(18)F](S)-FIPCT were synthesized in 5% radiochemical yield (decay-corrected to end of bombardment (EOB)) by preparation of the precursors 2beta-carbo-R-1-mesyloxy-2-propoxy-3beta-(4-chlorop hen yl)tropane (R-12) and 2beta-carbo-S-1-mesyloxy-2-propoxy-3beta-(4-chlorop hen yl)tropane (S-12) followed by treatment with no carrier-added potassium[(18)F]fluoride and kyrptofix K222 in acetonitrile. Competition binding in cells stably expressing the transfected human DAT and serotonin transporter (SERT) labeled by [(3)H]WIN 35428 and [(3)H]citalopram, respectively, demonstrated the following order of DAT affinity (K(i) in nM): GBR 12909 (0.36) > CIT (0.48) > (S)-FIPCT (0.67) >> (R)-FIPCT (3.2). The affinity of (S)-FIPCT and (R)-FIPCT for SERT was 127- and 20-fold lower, respectively, than for DAT. In vivo biodistribution studies were performed in male rats and demonstrated that the brain uptake of [(18)F](R)-FIPCT and [(18)F](S)-FIPCT were selective and specific for DAT rich regions (caudate and putamen). PET brain imaging studies in monkeys demonstrated high [(18)F](R)-FIPCT and [(18)F](S)-FIPCT uptake in the caudate and putamen which resulted in caudate-to-cerebellum and putamen-to-cerebellum ratios of 2.5-3.5 at 115 min. [(18)F](R)-FIPCT uptake in the caudate/putamen achieved transient equilibrium at 75 min. In an imaging experiment with [(18)F](S)-FIPCT in a rhesus monkey with its left hemisphere lesioned with MPTP, radioactivity was reduced to background in the caudate and putamen of the lesioned hemisphere. The high specific activity one-step radiolabeling preparation and high specificity and selectivity of [(18)F](R)-FIPCT and [(18)F](S)-FIPCT for DAT indicate [(18)F](R)-FIPCT and [(18)F](S)-FIPCT are potential radioligands for mapping brain DAT in humans using PET.

18F-labeled FECNT: a selective radioligand for PET imaging of brain dopamine transporters

Fluorine-18 labeled 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(2-fluoroethyl)nort ropane (FECNT) was synthesized in the development of a dopamine transporter (DAT) imaging ligand for positron emission tomography (PET). The methods of radiolabeling and ligand synthesis of FECNT, and the results of the in vitro characterization and in vivo tissue distribution in rats and in vivo PET imaging in rhesus monkeys of [18F]FECNT are described. Fluorine-18 was introduced into 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(2-fluoroethyl)nort ropane (4) by preparation of 1-[18F]fluoro-2-tosyloxyethane (2) followed by alkylation of 2beta-carbomethoxy-3beta-(4-chlorophenyl)nortropane (3) in 21% radiochemical yield (decay corrected to end of bombardment [EOB]). Competition binding in cells stably expressing the transfected human DAT serotonin transporter (SERT) and norepinephrine transporter (NET) labeled by [3H]WIN 35428, [3H]citalopram, and [3H]nisoxetine, respectively, indicated the following order of DAT affinity: GBR 12909 > CIT >> 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(3-fluoropropyl) nortropane (FPCT) > FECNT. The affinity of FECNT for SERT and NET was 25- and 156-fold lower, respectively, than for DAT. Blocking studies were performed in rats with a series of transporter-specific agents and demonstrated that the brain uptake of [18F]FECNT was selective and specific for DAT-rich regions. PET brain imaging studies in monkeys demonstrated high [18F]FECNT uptake in the caudate and putamen that resulted in caudate-to-cerebellum and putamen-to-cerebellum ratios of 10.5 at 60 min. [18F]FECNT uptake in the caudate/putamen peaked in less than 75 min and exhibited higher caudate- and putamen-to-cerebellum ratios at transient equilibrium than reported for 11C-WIN 35,428, [11C]CIT/RTI-55, or [18F]beta-CIT-FP. Analysis of monkey arterial plasma samples using high performance liquid chromatography determined that there was no detectable formation of lipophilic radiolabeled metabolites capable of entering the brain. In equilibrium displacement experiments with CIT in rhesus monkeys, radioactivity in the putamen was displaced with an average half-time of 10.2 min. These results indicate that [18F]FECNT is a radioligand that is superior to 11C-WIN 35,428, [11C]CIT/RTI-55, [18F]beta-CIT-FP, and [18F]FPCT for mapping brain DAT in humans using PET.

Development of a nitric oxide induction assay as a potential replacement for the intracerebral mouse protection test for potency assay of pertussis whole cell vaccines

The intracerebral mouse protection test (Kendrick test) for the potency assay of pertussis vaccines is a complex and time consuming in vivo test which has a significant intra- and interlaboratory variation. Thus, there is a pressing need to develop a replacement for the Kendrick test. There is now convincing evidence to suggest that Bordetella pertussis can be taken up and survive within macrophages in the lungs and that cell-mediated immunity plays a role in protection. It was hypothesised that murine macrophages could be activated by immunisation with whole cell pertussis vaccines and therefore induce NO production. An alternative in vitro assay based on the determination of reactive nitrogen intermediates produced as a result of macrophage activation has been examined as a possible replacement for the current intracerebral (i.c.) mouse protection test. NO induction was studied in the peritoneal macrophages of female NIH mice immunised with normal and denatured whole cell B. pertussis vaccines respectively. Compared with controls receiving diluent only, macrophages and spleen cells from mice immunised with whole cell pertussis vaccine responded in vitro to selected pertussis antigens by NO synthesis. The production of NO in response to in vitro culture with bacterial antigen was immunisation dose dependent and was correlated with protective immunity in vivo as determined by i.c. challenge. The results suggest that NO production may serve as a marker of macrophage activation in mice immunised with whole cell vaccine, and could form the basis of a potential replacement potency assay.

Cortical spreading depression in the gyrencephalic feline brain studied by magnetic resonance imaging

1.Time-lapse diffusion-weighted magnetic resonance imaging (DWI) was used to detect and characterize complex waves of cortical spreading depression (CSD) evoked with KCL placed upon the suprasylvian gyrus of anaesthetized cats. 2. The time-lapse representations successfully demonstrated primary CSD waves that propagated with elliptical wavefronts selectively over the ipsilateral cerebral hemispheres with a velocity of 3.8 +/- 0.70 mm min(-1) (mean +/- S.E.M. of 5 experiments). 3. In contrast, the succeeding secondary waves often remained within the originating gyrus, were slower (velocity 2.0 +/- 0.18 mm min(-1), more fragmented and varied in number. 4. Computed traces of the apparent diffusion coefficients (ADCs) showed negative deflections followed by monotonic decays (amplitudes: primary wave, -19.9 +/- 2.8%; subsequent waves, -13.6 +/- 1.9% duration at half-maximal decay, 150-200 s) when determined from regions of interest (ROIs) through which both primary and succeeding CSD waves propagated. 5. The passage of both the primary and the succeeding waves often correlated with transient DC potential deflections recorded from the suprasylvian gyrus. 6. The detailed waveforms of the ADC and the T2*-weighted (blood oxygenation level-dependent: BOLD) traces showed a clear reciprocal correlation. These imaging features that reflect disturbances in cellular water balance agree closely with BOLD measurements that followed the propagation velocities of the first and subsequent CSD events. They also provide a close physiological correlate for clinical observations of cortical blood flow disturbances associated with human migraine.

A study of rotationally invariant and symmetric indices of diffusion anisotropy

This study investigated the properties of a class of rotationally invariant and symmetric (relative to the principal diffusivities) indices of the anisotropy of water self-diffusion, namely fractional anisotropy (FA), relative anisotropy (RA), and volume ratio (VR), with particular emphasis to their measurement in brain tissues. A simplified theoretical analysis predicted significant differences in the sensitivities of the anisotropy indices (AI) over the distribution of the principal diffusivities. Computer simulations were used to investigate the effects on AI image quality of three magnetic resonance (MR) diffusion tensor imaging (DTI) acquisition schemes, one being novel: the schemes were simulated on cerebral model fibres varying in shape and spatial orientation. The theoretical predictions and the results of the simulations were corroborated by experimentally determined spatial maps of the AI in a normal feline brain in vivo. We found that FA mapped diffusion anisotropy with the greatest detail and SNR whereas VR provided the strongest contrast between low- and high-anisotropy areas at the expense of increased noise contamination and decreased resolution in anisotropic regions. RA proved intermediate in quality. By sampling the space of the effective diffusion ellipsoid more densely and uniformly and requiring the same total imaging time as the published schemes, the novel DTI scheme achieved greater rotational invariance than the published schemes, with improved noise characteristics, resulting in improved image quality of the AI examined. Our findings suggest that significant improvements in diffusion anisotropy mapping are possible and provide criteria for the selection of the most appropriate AI for a particular application.

Physico-chemical analysis of Bordetella pertussis antigens

Physico-chemical methods are being developed for use in the control and standardization of acellular pertussis vaccines and their individual components. We have compared native and detoxified preparations of the B. pertussis antigens, pertussis toxin (PT), filamentous haemagglutinin (FHA), and the 69-kDa outer membrane protein (P69) using circular dichroism (CD), fluorescence spectroscopy, SDS-PAGE and FPLC gel filtration chromatography. Upon aldehyde detoxification, PT underwent a large change in its intrinsic fluorescence maximum (8-10 nm red-shift) and a large increase in its apparent size, detected by chromatography. Polyacrylamide gels showed individual subunits of the same apparent molecular weight (M(r)) as well as some polypeptides of higher M(r). FHA also changed conformation (5-nm red-shift in intrinsic fluorescence) upon aldehyde detoxification, with a resultant increase in the M(r)of its major constituent. The P69 protein appeared quite robust to formaldehyde treatment as measured by the same methods. Its near-UV CD spectrum contains a prominent tryptophan band; so this method may be more suitable for observing differences in conformation. We also examined an aluminium-desorbed DTaP preparation by these methods. When used in conjunction with immunochemical and toxicological assays, these methods are informative and useful in the characterization of candidate standards and should be valuable methods for ensuring the consistency of manufactured vaccines.

Evaluation of transmission electron microscopy for examination of components of acellular pertussis and combination vaccines

New acellular pertussis and combination vaccines vary in the concentration and presence or absence of specific components and in extent of adsorption to adjuvants. There is a pressing need to develop new control methods for acellular pertussis vaccines. Negative staining electron microscopy has been evaluated as a method for assessing the purity of individual vaccine components and the amount of adsorption to aluminium gels. Negative staining showed the characteristic morphology of vaccine components and permitted detection of contaminants and morphological changes. Reproducible results were obtained by use of a standardized negative staining technique and confidence in the technique was increased by comparison of previously unexamined specimens with a specimen that had been characterized by repeated observations. The degree of adsorption to aluminium adjuvants could only be assessed by observation of the amount of non-adsorbed material in the specimen. Negative staining electron microscopy can be used as one of a number of techniques for control of acellular pertussis combination vaccines.

A comparative study of acquisition schemes for diffusion tensor imaging using MRI

This study has investigated the effects of the selection of the diffusion-weighted (DW) gradient directions on the precision of a diffusion tensor imaging (DTI) experiment. The theoretical analysis provided a quantitative framework in which the noise performance of DTI schemes could be assessed objectively and for the development of novel DTI schemes, which employ multiple DW gradient directions. This generic framework was first applied to the examination of two commonly used DTI schemes, which employed 6 DW gradient directions and hitherto were used indiscriminately under the sole condition of noncollinearity. It was then used to design and assess a novel 12-DW-gradient-direction DTI protocol, which employed the same total number of DW acquisitions as the two conventional schemes (12). This theoretical investigation was then corroborated using rigorous simulation and DTI experiments on both an isotropic phantom and a healthy human brain. Both the theoretical and the experimental analysis demonstrated that the two conventional schemes showed a significantly different noise performance and that use of the new multiple-DW-gradient-direction scheme clearly improved the precision of the DTI measurements.

Optimised diffusion-weighting for measurement of apparent diffusion coefficient (ADC) in human brain

This work studies the effect of diffusion-weighting on the precision of measurements of the apparent diffusion coefficient (ADC, or D) by diffusion-weighted magnetic resonance imaging. The precision in the value of the ADC was described in terms of a diffusion-to-noise ratio (DNR) which was calculated as the signal-to-noise ratio in the resultant ADC. A theoretical analysis decomposed the DNR into the signal-to-noise ratio in the diffusion-weighted image and the sensitivity of diffusion-weighting, "KD". The latter reflects the effect of the sampling strategy in the diffusion-weighting domain on the DNR. The theoretical analysis demonstrated that optimal two-point diffusion-weighting could be achieved in the vicinity of zeta = D(b2-b1) = 1.1, where zeta is a non-dimensional parameter of diffusion-weighting, and b1 and b2 are the diffusion-weighting factors for the two-point diffusion-weighting. This approach also derived an optimised signal averaging scheme. The limitations and restrictions of the two-point scheme for in vivo ADC measurement were also considered; these included a detailed discussion on partial volume effects. The theory was verified by experiments on phantoms and on the brain of a healthy volunteer using a diffusion-weighted echo-planar imaging protocol. This led to an optimal two-point diffusion-weighting for ADC measurement in human brain using b1 = 300, and b2 = 1550 +/- 100 s/mm2. Such a two-point scheme successfully measured values of the ADC in gray matter, white matter and cerebrospinal fluid in human brain. It thus offers an alternative to the commonly used multiple-point schemes and has the advantage of requiring significantly shorter imaging times.

[Molecular bypass, the application of VEGF to gene therapy of limb ischemia]

OBJECTIVE

To investigate the feasibility of using VEGF gene directly for treating limb ischemia.

METHODS

The human VEGF165 cDNA was cloned into the eukaryotic expression vector pcDNA3 under the control of cytomegalovirus immediate-early promoter/enhancer. When gene suture was used, the recombinant plasmid was transferred into the hindlimb's adductor of rat, of which the distal extreme of external iliac artery was ligated and the femoral artery was completely excised. With RT-PCR, Western blot, immunohistochemistry analysis, and angiography, the expression and biological effects of VEGF gene in experimental animals were investigated.

RESULTS

Seven days after initiation of therapy, the transcription and expression of VEGF gene in experimental group were significantly higher than those of control groups. The results from angiography, feet temperature measuring and observation of clinical symptom showed that the transfer of VEGF gene can stimulate the formation of focal neovessles, establish colleteral circulation, augment blood perfusion, and ameliorate distal limb necrosis.

CONCLUSION

These findings reveal that the "molecular bypass" using VEGF gene may represent a potential therapeutic modality for treating tissue ischemia.

Purification of a mammalian homologue of Escherichia coli endonuclease III: identification of a bovine pyrimidine hydrate-thymine glycol DNAse/AP lyase by irreversible cross linking to a thymine glycol-containing oligoxynucleotide

We purified a homologue of the Escherichia coli DNA repair enzyme endo nuclease III 5000-fold from calf thymus which, like endonuclease III, demonstrates DNA-glycosylase activity against pyrimidine hydrates and thymine glycol and AP lyase activity (DNA strand cleavage at AP sites via beta-elimination). The functional similarity between the enzymes suggested a strategy for definitive identification of the bovine protein based on the nature of its enzyme-substrate (ES) intermediate. Prokaryotic DNA glycosylase/AP lyases function through N-acylimine (Schiff's base) ES intermediates which, upon chemical reduction to stable secondary amines, irreversibly cross link the enzyme to oligodeoxynucleotides containing substrate modified bases. We incubated endonuclease III with a 32P- labeled thymine glycol-containing oligodeoxynucleotide in the presence of NaCNBH3. This resulted in an increase in the apparent molecular weight of the enzyme by SDS-PAGE. Phosphorimaging confirmed irreversible cross linking between enzyme and DNA. Identical treatment of the most purified bovine enzyme fraction resulted in irreversible cross linking of the oligodeoxynucleotide to a predominant 31 kDa species. Amino acid analysis of the 31 kDa species revealed homology to the predicted amino acid sequence of a Caenorhabditis elegans 27.8 kDa protein which, in turn, has homology to endonuclease III. The translated amino acid sequences of two partial 3' cDNAs, from Homo sapiens and Rattus sp., also demonstrate homology to the C. elegans and bovine sequences suggesting a homologous family of endonuclease III-like DNA repair enzymes is present throughout phylogeny.

Measurement of pulsatile flow using MRI and a Bayesian technique of probability analysis

This work shows that complete spatial information of periodic pulsatile fluid flows can be rapidly obtained by Bayesian probability analysis of flow encoded magnetic resonance imaging data. These data were acquired as a set of two-dimensional images (complete two-dimensional sampling of k-space or reciprocal position space) but with a sparse (six point) and nonuniform sampling of q-space or reciprocal displacement space. This approach enables more precise calculation of fluid velocity to be achieved than by conventional two q-sample phase encoding of velocities, without the significant time disadvantage associated with the complete flow measurement required for Fourier velocity imaging. For experimental comparison with the Bayesian analysis applied to nonuniformly sampled q-space data, a Fourier velocity imaging technique was used with one-dimensional spatial encoding within a selected slice and a uniform sampling of q-space using 64 values of the pulsed gradients to encode fluid flow. Because the pulsatile flows were axially symmetric within the resolution of the experiment, the radial variation of fluid velocity, in the direction of the pulsed gradients, was reconstructed from one-dimensional spatial projections of the velocity by exploiting the central slice theorem. Data were analysed for internal consistency using linearised flow theories. The results show that nonuniform q-space sampling followed by Bayesian probability analysis is at least as accurate as the combined uniform q-space sampling with Fourier velocity imaging and projection reconstruction method. Both techniques give smaller errors than a two-point sampling of q-space (the conventional flow encoding experiment).

Novel DNA binding motifs in the DNA repair enzyme endonuclease III crystal structure

The 1.85 A crystal structure of endonuclease III, combined with mutational analysis, suggests the structural basis for the DNA binding and catalytic activity of the enzyme. Helix-hairpin-helix (HhH) and [4Fe-4S] cluster loop (FCL) motifs, which we have named for their secondary structure, bracket the cleft separating the two alpha-helical domains of the enzyme. These two novel DNA binding motifs and the solvent-filled pocket in the cleft between them all lie within a positively charged and sequence-conserved surface region. Lys120 and Asp138, both shown by mutagenesis to be catalytically important, lie at the mouth of this pocket, suggesting that this pocket is part of the active site. The positions of the HhH motif and protruding FCL motif, which contains the DNA binding residue Lys191, can accommodate B-form DNA, with a flipped-out base bound within the active site pocket. The identification of HhH and FCL sequence patterns in other DNA binding proteins suggests that these motifs may be a recurrent structural theme for DNA binding proteins.