Monte Carlo simulation of the photon beam characteristics from medical linear accelerators

The MCNPX code has been employed on a personal computer to calculate the dosimetric characteristics of the photon beams from the 6 MV Siemens MX2 and the 10 MV Varian Clinac 2100C linear accelerators. A model of the treatment head includes the major geometric structure within the beam path. The model was used to calculate the energy spectra of the photon beam, percentage depth dose and the dose profiles. The accuracy of the calculated results is examined by comparing them with the measured dose distributions for the two machines. The computed and measured depth dose curves agree to within 2% for all the depths beyond the build-up region for both treatment machines. The calculations agree to within 2% of the measured profiles within the 100-50% dose level. It has been found that the MCNPX code is an effective tool for simulating the clinical photon beam.

On the relationship between dose-, energy- and LET-response of thermoluminescent detectors

Measurements of the response of thermoluminescent (TL) detectors after gamma ray doses high enough to observe signal saturation provide input to microdosimetric models which relate this gamma-ray response with the energy response after low doses of photons (gamma rays and low-energy X rays) and after high-LET irradiation. To measure their gamma ray response up to saturation, LiF:Mg,Ti (MTS-7 and MTT), LiF:Mg,Cu,P (MCP-7), CaSO4:Dy (KCD) and Al2O3:C detectors were irradiated with 60Co gamma rays over the range 1-5000 Gy. The X-ray photon energy response and TL efficiency (relative to gamma rays) after doses of beta rays and alpha particles, were also measured, for CaSO4:Dy and for Al2O3:C. Microdosimetric and track structure modelling was then applied to the experimental data. In a manner similar to LiF:Mg,Cu,P, the experimentally observed under response of alpha-Al2O3:C to X rays <100 keV, compared with cross-section calculations, is explained as a microdosimetric effect caused by the saturation of response of this detector without prior supralinearity (saturation of traps along the tracks). The enhanced X-ray photon energy response of CaSO4:Dy is related to the supralinearity observed in this material after high gamma ray doses, similarly to that in LiF:Mg,Ti. The discussed model approaches support the general rule relating dose-, energy- and ionisation density-responses in TL detectors: if their gamma ray response is sublinear prior to saturation, the measured photon energy response is lower, and if it is supralinear, it may be higher than that expected from the calculation of the interaction cross sections alone. Since similar rules have been found to apply to other solid-state detector systems, microdosimetry may offer a valuable contribution to solid-state dosimetry even prior to mechanistic explanations of physical phenomena in different TL detectors.

Thermoluminescence emission spectra for the LiF:Mg,Cu,Na,Si thermoluminescent materials with various concentrations of the dopants (3-D measurement)

The thermoluminescence (TL) emission spectra from LiF TL materials, called KLT-300 (LiF:Mg,Cu,Na,Si) with various dopant concentrations are measured and analysed. These KLT-300 materials were developed by the Korea Atomic Energy Research Institute (KAERI) to achieve an enhancement of the thermal stability in TL readings. Six types of samples are prepared with different dopant concentrations in the following ranges; Mg (0-0.20 mol%), Cu (0-0.05 mol%), Na and Si (0-0.9 mol%). The spectra measurements are carried out for the six types of samples using a TL emission spectra measurement device. The spectra measurement device consists of a monochromator, photomultiplier tube and temperature control unit to thermally stimulate the samples. The measured data shows the light emission during heating of the sample as a function of temperature and wavelength (three-dimensional TL spectra). The spectra were analysed using a method of deconvolution based on gaussian curve. The wavelength of a main peak of the emission spectra changes depending on the existence of the Cu dopant, while intensity of the spectra rapidly changes with the Cu dopant concentrations. The 385 nm emission is mainly observed in all the spectra from the samples with the Cu dopant, but in those from the samples without the Cu dopant a very weak 401 nm emission is mainly observed. However, any change in the wavelength at a main peak of the TL emission spectra from the sample materials with Na and Si dopants is not observed but that in the intensity at a peak of the spectra is observed.

Species status and phylogeography of two closely related Coptolabrus species (Coleoptera: Carabidae) in South Korea inferred from mitochondrial and nuclear gene sequences

We investigated the species status and intraspecific phylogeography in South Korea of two ground beetle species, Coptolabrus jankowskii and Coptolabrus smaragdinus (Coleoptera: Carabidae), using statistical parsimony networks and nested clade analyses based on sequences from the mitochondrial cytochrome oxidase subunit I (COI) and nuclear phosphoenolpyruvate carboxykinase (PepCK) and wingless (Wg) genes. Although traditional parsimony tree construction generally failed to resolve interspecific relationships and construct biologically meaningful genealogies, analysis using statistical parsimony networks yielded statistically significant inter- and intraspecific genealogical structures. We found that although these two species represent a notable case of trans-species polymorphisms in both mitochondrial and nuclear gene sequences, their status as separate species was evidenced by the nonrandom association between species and nested clades at various nesting levels. The exceptional occurrence of shared identical or very similar COI sequences was considered to be the result of introgressive hybridization. In addition, range expansion and fragmentation events across the Korean Peninsula and adjacent islands were inferred from nested clade phylogeographical analyses. The COI gene revealed the geographical divergence of major eastern and western clades and historical biogeographical events within each major clade, whereas the nuclear PepCK gene, which did not reveal corresponding east-west clades, indicated past fragmentation and range expansion across wide areas that may have been the result of older biogeographical events. Thus, phylogeographical inferences drawn from analyses of mitochondrial and nuclear genes can reveal different and potentially complementary information about phylogeographical processes.

In vitro Characterization of TGF-??1 Release from Genetically Modified Fibroblasts in Ca2+-Alginate Microcapsules

This study was undertaken to develop an in situ source of transforming growth factor-beta1 (TGF-beta1), one of several molecules potentially useful for a tissue-engineered bioartificial cartilage. Primary human fibroblasts and murine NIH 3T3 cells were genetically modified via viral transfection to express human TGF-beta1. Two viral constructs were used, one expressing a gene encoding for the latent and the other for the constitutively active form of the growth factor. Unmodified cells served as controls. Four genetically modified cohorts and two controls were separately encapsulated in a 1.8% alginate solution using a vibrating nozzle and 0.15M calcium chloride crosslinking bath. Diameter of the spherical capsules was 410 +/- 87 microm. In vitro release rate measured over 168 hours varied with cell types and ranged from 2-17 pg/(milligram of capsules x 24 h) or 2-17 ng/(10(6) cells x 24 h). None of the formulations exhibited a large initial bolus release. Even when serum-supplemented medium was not replenished, cell viabilities remained over 55% after 1 week for all cell types. Microencapsulated genetically modified cells were capable of a constitutive synthesis and delivery of biologically significant quantity of TGF-beta1 for at least 168 hours and thus are of potential utility for artificial cartilage and other orthopedic tissue engineering applications.

Current asthma and respiratory symptoms among pupils in relation to dietary factors and allergens in the school environment

The aim was to study asthma and allergy in relation to diet and the school environment. Pupils (5-14 years) in eight schools received a questionnaire, 1014 participated (68%). Settled dust was collected on ALK-filters and analyzed for allergens from cat (Fel d 1), dog (Can f 1), horse (Equ cx), house dust mites (Der p 1, Der f 1), and cockroach (Bla g 1) by ELISA. In total, 6.8% reported cat allergy, 4.8% dog allergy, 7.7% doctor's diagnosed asthma and 5.9% current asthma, and 7.8% reported wheeze. Current asthma was less common among those consuming more fresh milk (P < 0.05) and fish (P < 0.01). Poly-unsaturated fatty acids was associated with more wheeze (P < 0.05), olive oil was associated with less doctors' diagnosed asthma (P < 0.05). Totally, 74% of the classrooms had mean CO(2) <1000 ppm. The median concentration per gram dust was 860 ng/g Fel d 1, 750 ng/g Can f 1 and 954 U/g Equ cx. Horse allergen was associated with more wheeze (P < 0.05), daytime breathlessness (P < 0.05), current asthma (P < 0.05) and atopic sensitization (P < 0.05). Dog allergen was associated with wheeze (P < 0.05) and daytime breathlessness (P < 0.05). The associations between allergens and respiratory symptoms were more pronounced among those consuming margarine, not consuming butter, and with a low intake of milk. In conclusion, cat, dog and horse allergens in schools could be a risk factor for asthma and atopic sensitization, and dietary factors may interact with the allergen exposure.

PRACTICAL IMPLICATIONS

Previous school studies performed by us in mid-Sweden, showed that most classrooms did not fulfill the ventilation standards. In this study, most of the classrooms fulfilled the ventilation standard, but despite that had widespread allergen contamination. Most previous studies have focused on cat allergen, but our study has shown that also dog and horse allergens can be risk factors for asthma and allergy in schools. As allergens are transported from other environments, mainly the home environment, the main prevention should be to minimize transfer of allergens. This could be achieved by reducing contacts with furry pets and horses, or using different clothes at home and at school (e.g. school uniforms). Increased cleaning in the schools may reduce allergen levels, but the efficiency of this measure must be evaluated in further intervention studies. Finally, our study supports the view that dietary habits among pupils should not be neglected and interaction between dietary factors and indoor allergen exposure needs to be further investigated.

Dosimetric properties of the newly developed KLT-300 (LiF:Mg,Cu,Na,Si) TL detector

The dosimetric properties of the newly developed KLT-300 (KAERI LiF:Mg,Cu,Na,Si TL detector) in KAERI (Korea Atomic Energy Research Institute) were investigated. The sensitivity of the TL detector was about 30 times higher than that of the TLD-100 by light integration. In the study of the dose linearity of the detector, the dose response was very linear up to 10 Gy and a sublinear response was observed at higher doses. The energy response of the detector was studied for photon energies from 20 to 662 keV. The results show that a maximum response of 1.004 at 53 keV and a minimum response of 0.825 at 20 keV were observed. The reproducibility study for the TL detector was also carried out. The coefficients of variation for each detector separately did not exceed 0.016, and for all the 10 detectors collectively it was 0.0054. IEC Standard requires that the coefficient of variation shall not exceed 0.075. So, the reproducibility of this new TL detector sufficiently satisfied the IEC requirements. A detection threshold of the detector was investigated and found to be 70 nGy by Harshaw 4500 TLD Reader.

On the roles of the dopants in LiF: Mg,Cu,Na,Si thermoluminescent material

In this paper, some results of the study on the roles of the dopants in the LiF:Mg,Cu,Na,Si thermoluminescent (TL) material that was developed at the Korea Atomic Energy Research Institute for radiation protection are presented. Although there have been many studies to investigate the roles of the dopants in LiF:Mg,Cu,P TL material in the TL process, there are some discrepancies in the understanding of the roles of Cu and P between various researchers. In case of LiF:Mg,Cu,Na,Si TL material, there are a few studies on the roles of the dopants. Three kinds of samples in each of which one dopant is excluded, and the optimised sample, were prepared for this study. The measurements and analysis of the three-dimensional TL spectra, based on the temperature, wavelength and intensity, and the glow curves for those samples are used in this study. The results show that Mg plays a role in the trapping of the charge carriers and Cu plays a role in the luminescence recombination process; however, the effect of Na and Si on the glow curve structure and the TL emission spectra is much less than that of Mg and Cu. It is considered that Na and Si each plays a role in the improvement of the luminescence efficiency.

A computer program for the deconvolution of thermoluminescence glow curves

A quick and efficient computer program was developed in order to resolve the peaks from the thermoluminescence (TL) glow curve. The program was designed to be easily used on any MS Windows-based computer with a graphical user interface. In this program, a new method based on the general one-trap TL equation was adopted to analyse the TL glow curve with the traditional first-order, second-order and general-order kinetics model. The method described here, general approximation, generates TL glow peaks and interpolates the relevant TL parameters from the glow data. The program was tested with simulated and experimental TL glow data and the results were found to be adequate and reliable.

Developments in the synthesis of LiF:Mg,Cu,Na,Si TL material

A procedure for synthesis of the highly sensitive pellet-type LiF:Mg,Cu,Na,Si thermoluminescent (TL) detector has been newly developed. It was found that the optimum concentrations of dopants for a pellet-type LiF:Mg,Cu,Na,Si TL detector were found to be Mg: 0.2 mol %, Cu: 0.05 mol %, Na: 0.9 mol%, and Si: 0.9 mol%. The TL sensitivity of this new detector was about 30 times higher than that of the TLD-100 by light integration measurements. Reusability study of the detector was carried out for 10 cycles. The results show that the coefficients of variation for each detector separately did not exceed 0.016, and that for all 10 detectors collectively was 0.0054.

Recovery, growth, and development of Acanthoparyphium tyosenense (Digenea: Echinostomatidae) in experimental chicks

Chicks were experimentally infected with Acanthoparyphium tyosenense (Digenea: Echinostomatidae) metacercariae per os, and the growth and development of worms in this host were observed from days I to 38 postinfection (PI). The worms grew rapidly and matured sexually in the small intestine (chiefly in the jejunum) of chicks by day 5 PI. and survived at least up to day 38 Pi, although worm recovery decreased after day 5 PI. Both parenchymal and reproductive organs increased greatly in size from day 2 to day 10 PI and then continued to increase gradually in size up to day 38 PI. The number of uterine eggs reached a peak on days 10 and 15 PI and then decreased gradually. The results suggest that chicks are a fairly suitable definitive host for experimental infection with A. tyosenense.

Emission of a hot electron jet from intense femtosecond-laser-cluster interactions

A directional hot electron jet with energy higher than 100 keV was generated along the laser propagation direction from Ar clusters irradiated with a laser pulse of duration 28 fs and intensity 1 x 10(17) W/cm(2). The hot electron jet was detected only with linearly polarized laser pulses, not with circularly polarized pulses. Channel betatron resonance is believed to be the main accelerating mechanism for this directional hot electron jet.

Microdosimetric interpretation of the photon energy response of LiF:Mg,Ti detectors

Photon energy response of MTS-N (LiF:Mg,Ti) detectors (TLD Poland) and of MTS-N detectors sensitised with 200 Gy of 60Co gamma rays, followed by UV irradiation (sMTS-N), has been determined using X rays with narrow energy spectra, in the energy range from 20 to 300 keV. The over-response of LiF:Mg,Ti detectors for X rays (relative TL efficiency eta = 1.1) can be explained as an ionisation density effect. Low energy X rays produce short electron tracks, which locally deposit a high radiation dose and, consequently, lead to an enhanced (supralinear) response. This over-response has not been observed in sensitised MTS-N where supralinearity in the response after gamma ray doses above 1 Gy is not seen. Using the dose-response curves measured for MTS-N detectors after 137Cs gamma ray irradiation and local doses calculated using Monte Carlo generated electron tracks, it was possible to predict the relative TL effectiveness for different X ray energies. The calculation procedure can be applied to predict the photon energy response of LiF:Mg,Ti detectors in an arbitrary photon field.

Thermoluminescence characteristics of teflon embedded CaSO4:Dy TLD

The Korea Atomic Energy Research Institute (KAERI) is manufacturing CaSO4:Dy Teflon TL pellets which have more sensitivity and stability than commercial TLD. A method is presented of preparing the CaSO4:Dy phosphor-embedded Teflon powder, which is then compressed to a thin pellet form used as the TLD element. Investigations are made to determine optimum preparation conditions and dosimetric characteristics of the CaSO4:Dy Teflon pellet such as the sensitivity, energy response, dose response, fading, re-usability, and lowest level of detection. The results show that the sensitivity of the CaSO4:Dy pellet is 2 times higher than that of the commercial Teledyne CaSO4:Dy pellet. A dose-response was observed to be linear in the range from 10(-5) to 10 Gy. The relative energy response in the low energy region was 9.6 (normalised to the 137Cs gamma source), and the fading rate was about 10% for five months. The re-usability was estimated to be more than 60 cycles, and the low level of detection dose was 22 microGy. From the results, the CaSO4:Dy pellet developed in KAERI can be successfully used in personal dosemeters through appropriate filter design for compensating the energy response.

Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets have been developed for application in radiation dosimetry. LiF:M,Cu,Na,Si TL pellets were made from TL powders using a sintering process, that is, pressing and heat treatment. These pellets have a diameter of 4.5 mm, and a thickness of 0.8 mm are blue in colour and have a mass of 28 mg each. After 400 pellets had been produced they were irradiated with 137Cs gamma radiation and samples having a sensitivity within a +/-5% standard deviation were selected for experimental use. In the present study, the physical and dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets were investigated for their emission spectrum, dose response, energy response and fading characteristics. Photon irradiation for the experiments was carried out using X ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and 10(-6) - 10(2) Gy respectively. The glow curves were measured with a manual type thermoluminescence dosimetry reader (system 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5 degrees C.s(-1). the main dosimetric peak of the glow curve appeared at 234 degrees C, its activation energy was 2.34 eV and the frequency factor was 1.00 x 10(23). The TL emission spectrum appeared at the blue region centred at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to the 137Cs response were within +/-20% in the overall photon energy region. No fading of the TL sensitivity of the pellets stored at room temperature was found over the course of a year. Therefore LiF:Mg,Cu,Na,Si TL pellets can be used for personal dosimetry, but more research is needed to improve the characteristics for repeated use.

Comparison of TLD algorithms for monochromatic fluorescent radiation and continuous spectrum X rays

A personal dosimetry system is required to measure the personal dose equivalent accurately in a wide range of radiation fields. However, the dose evaluation algorithm at the Korea Atomic Energy Research Institute (KAERI) has been developed with the spectral X ray fields described in the American National Standards Institute (ANSI) Standard N13.11 and the actual fields to be monitored may be significantly different from these. To evaluate the dose more accurately when workers are exposed to non-ANSI N13.11 radiation fields, a dose evaluation algorithm using monochromatic radiation (monochromatic algorithm) was developed using the experimental data of the energy responses of CaSO4:Dy thermoluminescent materials irradiated by monochromatic fluorescent X ray fields recently established at KAERI; this was compared with another algorithm developed on the basis of the ANSI N13.11 continuous spectrum X ray fields (spectrum algorithm). The paper concludes with discussions about some results of the algorithm test, including mixed field irradiation and angular response, conducted in an International Atomic Energy Authority/Regional Cooperation of Asia (IAEA/RCA) intercomparison study.

Analysis of the glow curves obtained from LiF:Mg,Cu,Na,Si TL material using the general order kinetics model

Three-dimensional thermoluminescence (TL) spectra based on temperature, wavelength and intensity for newly developed LiF:Mg,Cu,Na,Si TL material at the Korea Atomic Energy Research Institute (KAERI) were measured and analysed. The glow curves were obtained by integration of luminescence intensity over all wavelengths at each temperature, and various trapping parameters related to the traps were determined by analysing these curves. A computerised glow curve deconvolution (CGCD) method which was based on the general order kinetics (GOK) model was used for the glow curve analysis. The glow curves of LiF:Mg,Cu,Na,Si TL material were deconvoluted to six isolated glow curves which have peak temperatures at 333, 374, 426, 466, 483 and 516 K. The main glow peak of peak temperature at 466 K had activation energy of 2.06 eV and a kinetic order of 1.05. This TL material was also found to have three recombination centres, 1.80 eV, 2.88 eV and 3.27 eV by analysis of the TL spectra.

5-HT2A receptor gene promoter polymorphism -1438A/G and bipolar disorder

Genetic factors, such as the genes involved in the serotonin pathway, probably play an important role in the pathogenesis of bipolar disorder, and serotonin type 2A (5-HT2A) receptor gene promoter polymorphism -1438A/G has been reported. This study investigated the association between -1438A/G polymorphism of 5-HT2A receptor gene promoter and bipolar disorder in a Korean population. Using the polymerase chain reaction, -1438A/G polymorphism typed in 142 patients with bipolar disorder and in 148 normal control subjects. Differences in genotype distributions and allele frequencies of -1438A/G between patients with bipolar disorder and normal control subjects were tested for significance using the chi-squared test. There were significant differences in genotype distributions [chi2 = 9.697, degrees of freedom (df) = 2, P = 0.008] and allele frequencies (chi2 = 7.284, df = 1, P = 0.007) of -1438A/G between patients with bipolar disorder and normal control subjects. Although further studies are necessary, these results in a Korean population suggest that -1438A/G polymorphism of 5-HT2A receptor gene promoter may be causally related to the development of bipolar disorder.

A nationwide survey of the prevalence of human Gymnophalloides seoi infection on western and southern coastal islands in the Republic of Korea

A nationwide survey was performed to know the distribution and prevalence of human Gymnophalloides seoi infection on western and southern coastal islands in the Republic of Korea. A total of 4,178 fecal specimens were collected from residents on 45 (24 western and 21 southern) islands, and examined by Kato-Katz and formalin-ether sedimentation techniques. Eggs of G. seoi were detected from 160 (3.8%) people living on 22 (13 western and 9 southern) islands. The prevalence varied by the location of islands; higher on western islands than on southern islands. The highest prevalence was found on Amtaedo (25.3%), followed by Cheungdo (25.0%), and Anchwado (20.9%) (Shinan-gun). A little lower prevalence was observed on Munyodo (13.3%), Shinshido (12.9%), and Sonyudo (10.3%) (Kunsan-shi). Of the remaining islands, the regions showing the prevalence greater than 5% included Kohado, Dallido (Mokpo-shi), Pyeongildo, Kogumdo (Wando-gun), and Keogumdo (Kohung-gun). A strong age predilection was noted (p < 0.05); 95% of the infected people were over 40 years old. Females showed a little higher prevalence than males. The results indicate that human G. seoi infection is more widely distributed than previously considered. Nine of 11 islands (excluding the 2 known areas Munyodo and Sunyudo) that showed greater prevalence than 5% are regarded as new endemic foci of G. seoi.

High endemicity of Metagonimus yokogawai infection among residents of Samchok-shi, Kangwon-do

A small-scale epidemiological survey was undertaken during 1997-1998 on the residents along the Osib-chon (Stream), Samchok-shi (City), Kangwon-do (Province), to evaluate the status of Metagonimus yokogawai infection. A total of 165 fecal samples was collected and examined by cellophane thick smear and formalin-ether sedimentation techniques. The egg positive rate of M. yokogawai was 29.7%, showing a remarkable difference between males (46.6%) and females (16.3%). To obtain the adult flukes of M. yokogawai, 11 egg positive persons were treated with praziquantel and purged with magnesium sulfate. A total of 242,119 adult flukes (average 22,010 per person, 367-119,650 in range) was collected from diarrheic stools, all of which were identified as M. yokogawai. The results show that M. yokogawai is still highly endemic in this area.

Structure and Function of Hepatitis C Virus NS3 Helicase

Hepatitis C Virus helicase activity has been mapped to the COOH-terminal 450 residues of the NS3 protein. Due to its complexity and presumed essentiality for viral replication, the helicase is an attractive target for drug discovery. The elucidation of the atomic structure of the HCV NS3 helicase in complex with oligonucleotide and with ADP has helped clarify our understanding of potential sites for inhibitor binding. Molecular details of the mechanism of this enzyme, and in particular, a better understanding of the mechanism by which ATP hydrolysis is coupled to unwinding of double-stranded substrate may facilitate more efficient structure-based drug design.

TATA element recognition by the TATA box-binding protein has been conserved throughout evolution

Cocrystal structures of wild-type TATA box-binding protein (TBP) recognizing 10 naturally occurring TATA elements have been determined at 2.3-1.8 A resolution, and compared with our 1.9 A resolution structure of TBP bound to the Adenovirus major late promoter (AdMLP) TATA box (5'-TATAAAAG-3'). Minor-groove recognition by the saddle-shaped protein induces the same conformational change in each of these oligonucleotides, despite variations in promoter sequence that reduce the efficiency of transcription initiation. Three molecular mechanisms explain assembly of diverse TBP-TATA element complexes. (1) T --> A and A --> T transversions leave the minor-groove face unchanged, permitting formation of TBP-DNA complexes on many A/T-rich core promoter sequences. (2) Cavities in the interface between TBP and the minor-groove face of the AdMLP TATA box accommodate the exocyclic NH(2) groups of G in a TACA box and in a TATAAG box. (3) Formation of a C:G Hoogsteen basepair in a TATAAAC box eliminates steric clashes that would be produced by the Watson-Crick base pair. We conclude that the structure of the TBP-TATA box complex found at the heart of the polymerase II (pol II) transcription machinery has remained constant over the course of evolution, despite variations in TBP and its DNA targets.

New hydrolysis method for extremely small amount of lipids and capillary gas chromatographic analysis as n(O)-tert.-butyldimethylsilyl fatty acid derivatives compared with methyl ester derivatives

The organic basic solution, 1 M tetramethylammonium hydroxide (TMAH) in methanol, was employed for the hydrolysis of extremely small amounts of lipids compared to the classical inorganic basic solution, 1 M KOH in ethanol. The hydrolysed fatty acids were derivatized as N(O)-tert.-butyldimethylsilyl (tBDMSi) esters with N-methyl-N-(tert.-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) and compared with the classical derivatives, the methyl esters, made by the BF3-methanol method. Recoveries of fatty acids determined on the standard fatty acids and soybean oil hydrolysed with TMAH were high: about 1.1-2.1- and 2.0-5.4-times, respectively, in all fatty acids compared with the hydrolysis by KOH regardless of derivatization method. The relative standard deviations (RSDs) on the recoveries of standard fatty acids were less than 5% when hydrolysed with TMAH, regardless of derivatives, but when hydrolysed with KOH, RSDs were more than 5% for most fatty acids, especially for long-chain fatty acids. The RSDs on the recoveries of fatty acids on the soybean oil were also very high in the KOH hydrolysis. Fatty acid compositions of soybean oil were similar in the main fatty acids regardless of hydrolysis methods, but showed slightly different values, depending on the methods of derivatization. RSDs were also very high in the KOH hydrolysis. In view of these results, precision of analysis by KOH hydrolysis was very poor, so we could not rely on the data. On the other hand, the reliability of data by TMAH hydrolysis method was very high, so it is a useful new hydrolysis method for extremely small amounts of lipid samples. Both derivatives of 35 standard fatty acids were successfully separated on a HP-1 nonpolar capillary column. tBDMSi derivatives were completely resolved in 70 min by 295 degrees C. In the methyl ester derivatives it took about 80 min to get satisfying resolution, but these derivatives were completely resolved by 250 degrees C. The sensitivity of tBDMSi derivatives was about 1.5-6.3-times higher than that with methyl ester derivatives. The stability of tBDMSi derivatives was constant for about 144 h except arachidic, docosahexanoic, behenic and heneicosanoic acids, which were stable for only 86 h.

Structure-based mutagenesis study of hepatitis C virus NS3 helicase

The NS3 protein of hepatitis C virus (HCV) is a bifunctional protein containing a serine protease in the N-terminal one-third, which is stimulated upon binding of the NS4A cofactor, and an RNA helicase in the C-terminal two-thirds. In this study, a C-terminal hexahistidine-tagged helicase domain of the HCV NS3 protein was expressed in Escherichia coli and purified to homogeneity by conventional chromatography. The purified HCV helicase domain has a basal ATPase activity, a polynucleotide-stimulated ATPase activity, and a nucleic acid unwinding activity and binds efficiently to single-stranded polynucleotide. Detailed characterization of the purified HCV helicase domain with regard to all four activities is presented. Recently, we published an X-ray crystallographic structure of a binary complex of the HCV helicase with a (dU)(8) oligonucleotide, in which several conserved residues of the HCV helicase were shown to be involved in interactions between the HCV helicase and oligonucleotide. Here, site-directed mutagenesis was used to elucidate the roles of these residues in helicase function. Four individual mutations, Thr to Ala at position 269, Thr to Ala at position 411, Trp to Leu at position 501, and Trp to Ala at position 501, produced a severe reduction of RNA binding and completely abolished unwinding activity and stimulation of ATPase activity by poly(U), although the basal ATPase activity (activity in the absence of polynucleotide) of these mutants remained intact. Alanine substitution at Ser-231 or Ser-370 resulted in enzymes that were indistinguishable from wild-type HCV helicase with regard to all four activities. A mutant bearing Phe at Trp-501 showed wild-type levels of basal ATPase, unwinding activity, and single-stranded RNA binding activity. Interestingly, ATPase activity of this mutant became less responsive to stimulation by poly(U) but not to stimulation by other polynucleotides, such as poly(C). Given the conservation of some of these residues in other DNA and RNA helicases, their role in the mechanism of unwinding of double-stranded nucleic acid is discussed.

Macrophage depletion alters vein graft intimal hyperplasia

BACKGROUND

The principal cause of vein graft failure is intimal hyperplasia (IH); however, its etiology remains unclear. In a rat model of vein graft IH we have observed prolonged transmural macrophage infiltration, leading us to hypothesize that these cells regulate IH. To test this, we used liposome-encapsulated dichloromethylene bisphosphonate (L-Cl2MBP) to deplete rat macrophages and observed the effects on IH.

METHODS

Epigastric vein-to-femoral artery grafts were microsurgically placed in male Lewis rats that had been intravenously injected with L-Cl2MBP, phosphate-buffered saline solution liposomes, or phosphate-buffered saline solution alone 2 days before surgery. Several animals in each group received a second equivalent dose at 2 weeks. Grafts, contralateral epigastric veins, spleens, and livers were harvested at 1, 2, and 4 weeks for histologic examination, immunohistochemistry, and transmission electron microscopy.

RESULTS

In the L-Cl2MBP-treated animals splenic and hepatic macrophages were greatly reduced, confirming the efficacy of the agent. At 1 to 2 weeks graft macrophages were significantly decreased, and there was a trend toward decreased IH. At 4 weeks macrophage numbers were normal and IH development had resumed. In contrast, the 4-week grafts treated with 2 doses of L-Cl2MBP had fewer macrophages and displayed severely attenuated IH.

CONCLUSIONS

The results indicate a suppression of IH as macrophages are depleted, with a resumption of the process as macrophages repopulate the graft.