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PubMed1990

[Study of the blink reflex in spinocerebellar degeneration].

Blink reflex (BR) was composed of R1 and R2. R1 is considered to indicate the brainstem function. The purpose of this study was to evaluate the brainstem function of spinocerebellar degeneration (SCD) by the R1 latency (R1). BR was evoked by the percutaneous stimulation of supraorbital nerve. And R1 was measured by the action potential of orbucularis oculi muscle. Direct response was recorded by the percutaneous stimulation of facial nerve to determine the terminal latency of facial nerve (D). By these methods R1, D, R1/D and difference between at right and left side of these data (delta R1, delta D, delta R1/D) were measured in 21 normal subjects (57.7 +/- 10.1 ys.) and 28 cases of SCD (56.6 +/- 8.2 ys.), including 12 cases of sporadic type olivopontocerebellar atrophy (SOPCA), 4 of Menzel type olivopontocerebellar atrophy (MOPCA), 6 of late cortical cerebellar atrophy (LCCA) and 6 of Holmes type cortical cerebellar atrophy (HCCA). There was no difference between all types of SCD and normal subject at D, but significant difference of R1 and R1/d was observed between at MOPCA and normal subject. Concerning the difference between right and left side delta R1 and delta R1/D showed the significant difference with MOCA and SOPCA, but delta D showed no difference. Elongation of R1 and R1/D without the delay of facial nerve and the significant difference of R1 and R1/d between at right and left side suggested the synaptic transmission disorder form trigeminal nerve to facial nerve at brainstem of MOCA.

Adult↗
PubMed1978

Chemo-immunotherapy for unresectable bronchogenic carcinoma.

Seventy-nine patients with metastatic or unresectable bronchogenic carcinoma were treated with a regimen of combination chemotherapy which included methotrexate, Oncovin (vincristine), cyclophosphamide, and adriamycin (MOCA), and were randomized to receive no additional therapy, immunotherapy with bacillus Calmette-Guérin, or immunotherapy with Corynebacterium parvum (C. parvum). The response rate and estimated median survival time were 68% and 42 weeks in small cell carcinoma and 18% and 29 weeks in other histologic types. Improved survival correlated with high performance status and response to therapy. Immunotherapy did not improve response, time to progression, or hematopoietic tolerance of chemotherapy. C. parvum was associated with significant morbidity and was poorly tolerated. MOCA appears to be of modest value in the treatment of bronchogenic carcinoma, particularly of the small cell type. A role for immunotherapy remains unproven.

BCG Vaccine↗
PubMed1986

A 10-year experience with combined modality therapy for stage III small cell lung carcinoma.

During the past 10 years, 240 patients with Stage III small cell lung carcinoma (SCLC) were treated with one of five chemotherapy programs plus thoracic irradiation. In addition, prophylactic cranial irradiation was administered concurrently with thoracic irradiation to 194 patients receiving CAML-HC, VCAM, or MOCA. Seventy-two patients had disease confined to the chest (Stage IIIM0), 30 patients had disease in the chest plus ipsilateral supraclavicular nodal involvement (Stage IIIM0SCN+), and 138 patients had distant metastatic disease (Stage IIIM1); the median survivals were 15.2 months, 12.6 months, and 8.4 months, respectively. The overall complete response rate was 30% and the overall response rate (complete and partial) was 76%. The overall response rates by stage were 86% for Stage IIIM0, 90% for Stage IIIM0SCN+, and 67% for Stage IIIM1. Eight patients (3%) were alive and free of disease at 24 months. Due to continued disease relapse in this group (four of eight patients), long-term survivors should not be identified for a minimum of 3.5 years from the time of initial therapy. Prophylactic cranial irradiation (PCI) effectively reduced the incidence of central nervous system (CNS) relapse in patients with a complete response to therapy (44% relapse without PCI versus 13% relapse with PCI, P less than 0.01). More effective chemotherapy is required for the successful treatment and improved long-term survival of patients with SCLC.

Altretamine↗
PubMed2025

The Effect of APOE ε4 Allele on Dynamic Local Spontaneous Brain Activity and Functional Integration in Alzheimer's Disease.

The apolipoprotein E (APOE) ε4 allele is the most important genetic risk factor for sporadic Alzheimer's disease (AD), yet its mechanisms in AD pathology and cognitive decline remain unclear. Using a sliding-time window approach to directly quantify the instantaneous fluctuations of various local metrics based on continuous time series and calculate voxel-wise concordance of these metrics, we explored the impact of APOE ε4 on dynamic local brain activity and functional integration in AD, and its interrelations with plasma biomarkers and cognition. Results showed that APOE ε4 widely affected dALFF, dReHo, dGSCorr, and voxel-wise concordance. For AD patients, APOE ε4 carriers uniquely exhibited correlations between dALFF in the right angular gyrus/supramarginal gyrus and MoCA scores and orientation function, and between voxel-wise concordance in the right caudate nucleus (CAU) and general cognition, attention, language function, orientation function, plasma Aβ42. Critically, APOE ε4-related altered voxel-wise concordance in the right CAU mediated the relationship between plasma Aβ and language cognition in AD. Moreover, the combined model incorporating dynamic metrics, plasma AD biomarkers, and demographic data effectively distinguished AD from NC (AUC = 0.94, sensitivity = 87.69%, specificity = 86.84%). In conclusion, the APOE ε4 allele might play a pivotal role in modulating brain dynamic functional activities in AD, which may contribute to the association between Aβ pathology and cognitive decline. Our findings may provide imaging markers and targets for the diagnosis and treatment of AD.

Humans↗
PubMed1992

New opportunities for screening and early detection of bladder cancer.

In the United States, over 51,000 new cases of urinary bladder tumors are diagnosed annually. Approximately 75-85% of all newly diagnosed cases are superficial transitional cell carcinomas (TCCs). Incidence is highest (80% of the cases) in the 50-79 year age group. Recent studies have reported that 21-25% of risk for bladder cancer among United States white males is due to occupational exposure. The DuPont Chambers Works in Deepwater, New Jersey, was a major producer of two chemicals now known to be human bladder carcinogens (beta-naphthylamine and benzidine) as well as two suspected human bladder carcinogens [ortho-toluidine and 4,4'-methylene- bis,2-chloroaniline (MOCA)]. Between 1954 and 1982, DuPont screened 1723 exposed employees annually at the Chambers Works using the Papanicolaou test for urinary cytology and microscopic urinalysis. A review of the prior screening program found that employees who developed bladder cancer during this time period were approximately twice as likely to have had hematuria than those comparably exposed who did not develop bladder cancer. Building on this finding, a three-year screening study evaluated a home self-test for microscopic hematuria to aid early detection of treatable urologic conditions among exposed workers at this chemical plant. Every six months, subjects tested their urine at home for 14 consecutive days, for the presence of blood. A high degree of adherence to our protocol (over 92% completed and returned the self-testing record) as well as high compliance with repeat screening (85% returned for screening in subsequent quarters) demonstrated good acceptance and performance of the recommended schedule of self-testing. Through the first 7 periods of screening, two new cases and one recurrence of TCC of the bladder were detected.

Humans↗
PubMed1994

Molecular and genetic characterization of the rhizopine catabolism (mocABRC) genes of Rhizobium meliloti L5-30.

Rhizopine (L-3-O-methyl-scyllo-inosamine, 3-O-MSI) is a symbiosis-specific compound, which is synthesized in nitrogen-fixing nodules of Medicago sativa induced by Rhizobium meliloti strain L5-30. 3-O-MSI is thought to function as an unusual growth substrate for R. meliloti L5-30, which carries a locus (mos) responsible for its synthesis closely linked to a locus (moc) responsible for its degradation. Here, the essential moc genes were delimited by Tn5 mutagenesis and shown to be organized into two regions, separated by 3 kb of DNA. The DNA sequence of a 9-kb fragment spanning the two moc regions was determined, and four genes were identified that play an essential role in rhizopine catabolism (mocABC and mocR). The analysis of the DNA sequence and the amino acid sequence of the deduced protein products revealed that MocA resembles NADH-dependent dehydrogenases. MocB exhibits characteristic features of periplasmic-binding proteins that are components of high-affinity transport systems. MocC does not share significant homology with any protein in the database. MocR shows homology with the GntR class of bacterial regulator proteins. These results suggest that the mocABC genes are involved in the uptake and subsequent degradation of rhizopine, whereas mocR is likely to play a regulatory role.

Amino Acid Sequence↗
PubMed1995

The quality of DNA double-strand breaks: a Monte Carlo simulation of the end-structure of strand breaks produced by protons and alpha particles.

The quality of DNA damage induced by protons and alpha-particles of various linear energy transfer (LET) was studied. The aim was to single out specific lesions in the DNA molecule that might lead to biological endpoints such as inactivation. A DNA model coupled with a track structure code (MOCA-15) were used to simulate the lesions induced on the two helixes. Four categories of DNA breaks were considered: single-strand breaks (ssb), blunt-ended double-strand breaks (dsb, with no or few overlapping bases), sticky-ended double-strand breaks (with cohesive free ends of many bases), and deletions (complex lesions which involve at least two dsb within a small number of base pairs). Calculations were carried out assuming various sets of parameters characterizing the production of these different DNA breaks. No large variations in the yields of ssb and blunt- or sticky-ended dsb were found in the LET range between 10 and 200 keV/mu m. On the other hand, the yield of deletions increases up to about 100 keV/mu m and seems to reach a plateau at higher LET values. In the LET interval from 30 to 60 keV/mu m, protons proved to be more efficient than alpha-particles in inducing deletions. The induction of these complex lesions is thus dependent not simply on LET but also on the characteristics of the track structure. Comparison with RBE values for cell killing shows that this special class of dsb might play an important role in radiation-induced cell inactivation.

Alpha Particles↗
PubMed2004

Embryonic turkey liver: activities of biotransformation enzymes and activation of DNA-reactive carcinogens.

Avian embryos are a potential alternative model for chemical toxicity and carcinogenicity research. Because the toxic and carcinogenic effects of some chemicals depend on bioactivation, activities of biotransformation enzymes and formation of DNA adducts in embryonic turkey liver were examined. Biochemical analyses of 22-day in ovo turkey liver post-mitochondrial fractions revealed activities of the biotransformation enzymes 7-ethoxycoumarin de-ethylase (ECOD), 7-ethoxyresorufin de-ethylase (EROD), aldrin epoxidase (ALD), epoxide hydrolase (EH), glutathione S-transferase (GST), and UDP-glucuronyltransferase (GLUT). Following the administration of phenobarbital (24 mg/egg) on day 21, enzyme activities of ECOD, EROD, ALD, EH and GLUT, but not of GST, were increased by two-fold or higher levels by day 22. In contrast, acute administration of 3-methylcholanthrene (5 mg/egg) induced only ECOD and EROD activities. Bioactivation of structurally diverse pro-carcinogens was also examined using (32)P-postlabeling for DNA adducts. In ovo exposure of turkey embryos on day 20 of gestation to 2-acetylaminofluorene (AAF), 4,4'-methylenebis(2-chloroaniline) (MOCA), benzo[a]pyrene (BaP), and 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx) resulted in the formation of DNA adducts in livers collected by day 21. Some of the DNA adducts had (32)P-postlabeling chromatographic migration patterns similar to DNA adducts found in livers from Fischer F344 rats exposed to the same pro-carcinogens. We conclude that 21-day embryonic turkey liver is capable of chemical biotransformation and activation of genotoxic carcinogens to form DNA adducts. Thus, turkey embryos could be utilized to investigate potential chemical toxicity and carcinogenicity.

2-Acetylaminofluorene↗
PubMed2004

Over-expression of SR-cyclophilin, an interaction partner of nuclear pinin, releases SR family splicing factors from nuclear speckles.

Pre-mRNA splicing takes place within a dynamic ribonucleoprotein particle called the spliceosome and occurs in an ordered pathway. Although it is known that spliceosome consists of five small nuclear RNAs and at least 50 proteins, little is known about how the interaction among the proteins changes during splicing. Here we identify that SR-cyp, a Moca family of nuclear cyclophilin, interacts and colocalizes with nuclear pinin (pnn), a SR-related protein involving in pre-mRNA splicing. Nuclear pnn interacts with SR-cyp via its C-terminal RS domain. Upon SR-cyp over-expression, however, the subnuclear distribution of nuclear pnn is altered, resulting in its redistribution from nuclear speckles to a diffuse nucleoplasmic form. The diffuse subnuclear distribution of nuclear pnn is not due to epitope masking, accelerated protein turnover or post-translational modification. Furthermore, we find that SR-cyp regulates the subnuclear distribution of other SR family proteins, including SC35 and SRm300, in a similar manner as it does on nuclear pnn. This result is significant because it suggests that SR-cyp plays a general role in modulating the distribution pattern of SR-like and SR proteins, similar to that of Clk (cdc2-like kinase)/STY on SR family splicing factors. SR-cyp might direct its effect via either alteration of protein folding/conformation or of protein-protein interaction and thus may add another control level of regulation of SR family proteins and modification of their functions.

Animals↗
PubMed2003

Morphometric analysis of cytolysis in cultured cell monolayers: a simple and versatile method for the evaluation of the lytic activity and the fate of LAK cells.

The assessment of cytolytic activity of killer cells may not only be useful to improve routine analysis, e.g., in clinical settings, but may also offer new opportunities for the fundamental analysis of the mutual interaction between cytotoxic cells and their targets. We have developed a morphometric method to estimate cytolytic activity of activated natural killer (NK) cells by measuring the clearance of a precultured confluent monolayer of adherent target cells, e.g., immortalized fibroblasts. Cytotoxic cells are inoculated on top of confluent monolayers of target cells and after 2 h, nonadherent cells are washed off and intact adherent cells are fixed and stained with a Coomassie blue solution. Elementary computer-assisted analysis of the resulting microscopic images and measurement of the cleared area provide us with a sensitive and reproducible parameter of target cell lysis. We found that the assay can be used with targets of very different origin, as long as they form confluent monolayers, and with different populations of killer cells. The morphometric cytotoxicity assay (MoCA) offers several advantages: storage of samples for postponed analysis, increased sensitivity as compared to radioactive assays, continuous visualization during assay, availability of targets and effectors for subsequent analysis after interaction.

Animals↗
PubMed1999

Detoxification of carcinogenic aromatic and heterocyclic amines by enzymatic reduction of the N-hydroxy derivative.

The metabolic activation pathways associated with carcinogenic aromatic and heterocyclic amines have long been known to involve N-oxidation, catalyzed primarily by cytochrome P4501A2, and subsequent O-esterification, often catalyzed by acetyltransferases (NATs) and sulfotransferases (SULTs). We have found a new enzymatic mechanism of carcinogen detoxification: a microsomal NADH-dependent reductase that rapidly converts the N-hydroxy arylamine back to the parent amine. The following N-OH-arylamines and N-OH-heterocyclic amines were rapidly reduced by both human and rat liver microsomes: NOH-4-aminoazobenzene, N-OH-4-aminobiphenyl (N-OH-ABP), N-OH-aniline, N-OH-2-naphthylamine, N-OH-2-aminofluorene, N-OH-4,4'-methylenebis(2-chloroaniline) (N-OH-MOCA), N-OH-1-naphthyamine, N-OH-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP), N-OH-2-amino-alpha-carboline (N-OH-AalphaC), N-OH-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (N-OH-MeIQx), and N-OH-2-amino-3-methylimidazo[4,5-f]quinoline (N-OH-IQ). In addition, primary rat hepatocytes and human HepG2 cells efficiently reduced N-OH-PhIP to PhIP. This previously unrecognized detoxification pathway may limit the bioavailability of carcinogenic N-OH heterocyclic and aromatic amines for further activation, DNA adduct formation, and carcinogenesis.

Animals↗
PubMed2002

Presenilin-interacting proteins.

Familial Alzheimer's disease (FAD) accounts for 5-10% of deaths from Alzheimer's disease (AD), and approximately 50% of these cases have been definitely linked to missense mutations in three genes, encoding the amyloid precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2). Of these, the vast majority of FAD-linked mutations are within PS1. There has been an extensive effort to identify proteins that functionally interact with PS1 and PS2 because of their clear roles in FAD. The goal of this review is to describe these proteins and to discuss in more detail the probable biological functions of a subset of the better-studied interacting proteins. In particular, the review examines APP, Notch, nicastrin, modifier of cellular adhesion (MOCA), beta-catenin, and the group of proteins involved in cell death, calcium metabolism and cell adhesion. We argue that, although a few of the interacting proteins are unambiguously involved in well-studied cellular pathways, their exact roles within these pathways have not been clearly defined, and indeed might vary between cell types. We also question the physiological relevance of some of the work linking PS to cell death pathways. Finally, we point out the value of using flies and worms to sort out the often contradictory work in the PS field, and we mention how knowledge of PS-interacting pathways will contribute to the development of new therapeutic strategies in AD.

Alzheimer Disease↗
PubMed1997

Aromatic amines and cancer.

Epidemiological evidence on the relation between aromatic amines and cancer risk is reviewed. In particular, cancer risk in humans resulting from exposure to aromatic amines from occupational sources and tobacco smoking is assessed with reference to ecologic, cohort, and case-control studies. Seven arylamines have been classified by the International Agency for Research on Cancer: benzidine-based dyes and MOCA (4,4'-methylene bis 2-choloroaniline) were considered 'probably' carcinogenic, Group 2A, because of a high level of evidence in experimental animals; two occupational chemicals (2-naphthylamine and benzidine), one drug (Chlornaphazine), and two manufacturing processes (manufacture of auramine and magenta) were included in Group 1 on the basis of 'sufficient' evidence of carcinogenicity in humans. Occupational exposures to aromatic amines explain up to 25 percent of bladder cancers in some areas of Western countries; these estimates might be higher in limited areas of developing countries. Aromatic amines contaminate the ambient air as a component of environmental tobacco smoke. There is increasing evidence that the excess of bladder cancer in smokers is attributable to aromatic amines rather than to other contaminants of tobacco smoke such as polycyclic aromatic hydrocarbons (PAH). A modulating role in the risk of bladder cancer associated with exposure to aromatic amines is played by metabolic polymorphisms, such as the N-acetyltransferase genotype, raising important social and ethical issues. The consistent observation of a difference between men and women in bladder cancer risk, after allowing for known risk factors, suggests consideration of gender-related biological determinants for future investigation.

2-Naphthylamine↗
PubMed2004

Determination of amines as pentafluoropropionic acid anhydride derivatives in biological samples using liquid chromatography and tandem mass spectrometry.

Determination of amines in biological samples as markers of exposure to the amines or the corresponding isocyanates is an important tool for industrial exposure assessment. In this study, a liquid chromatography and tandem mass spectrometry (LC-MS/MS) method for determination of amines in biological samples as perfluorofatty amides derivatives is presented. The method enables determination of diamines such as methylene diamine (MDA), toluene diamine (TDA), naphthalene diamine (NDA), hexamethylene diamine (HDA), isophorone diamine (IPDA), methylenedi(cyclohexylamine)(HMDA) and 4,4'-methylene-(2-chloroaniline)(MOCA) in human urine and plasma. The work-up procedure included hydrolysis of the biological samples with 3 M H(2)SO(4) at 100 degrees C for 16 h and extraction of the amines into toluene, where derivatisation of the amines with perfluorofatty acid anhydride was performed. Following removal of excess reagent and the acid formed and an exchange of solvent, the derivatives were analysed using gradient elution with an acetonitrile/water mobile phase composition and electrospray ionisation (ESI) with multiple reaction monitoring (MRM) of [M - H](-)-->[M - H - 120](-) or [119](-). Several perfluorofatty acid anhydrides were evaluated as derivatisation reagents, but the LC chromatographic properties of the pentafluoropropionic acid anhydride (PFPA) derivatives were favourable. Quantification of amine-PFPA derivatives was performed using deuterium labelled amine-PFPA derivatives as internals standards with good precision and linearity in the investigated range of 0-20 ng ml(-1) urine. The instrumental detection limits for the amine-PFPA derivatives were 0.2-3 fmol for MRM of [M - H](-)-->[119](-) and 0.3-8 fmol for [M - H](-)-->[M - H - 120](-). In 10 urine and 6 plasma samples from workers exposed to isocyanates, determination of TDA and MDA as PFPA derivatives was performed using LC-MS/MS and a reference GC-MS method. No significant difference between the two methods was observed.

Amines↗
PubMed1978

The generation of aerosols of carcinogenic aromatic amines.

A system for producing test atmospheres of carcinogenic aromatic amines is discussed. The aerosol generator, a specially disigned compressed-gas nebulizer, operated at a temperature above each compound's melting point utlizing nitrogen as the driving force. The nebulizer output and size distributions of aerosols of 4,4'-methylenebis(2-chloroaniline) (MOCA), benzidine, and 3,3'-dichlorobenzidine are given.

3,3'-Dichlorobenzidine↗
PubMed1981

Effect of 2,2'-diaminodiphenyldisulfide, a resin hardener, on rats.

Guided by structure-activity relationships among carcinogenic aromatic amines, a sulfur-containing aromatic diamine was designed as a possible noncarcinogenic replacement for the resin hardener 4,4'-methylenebis(2-chloroaniline) (MOCA). However, in small-scale tests in rats the analog diaminodiphenyldisulfide (DDDS) caused necrotic changes in the liver, acanthosis and hyperkeratosis of the forestomach, and atrophy and hyperplasia of the ductal epithelium of the kidney. One case of hepatocellular carcinoma was also noted. Furthermore, DDDS caused alterations in the hepatocellular carcinoma was also noted. Furthermore, DDDS caused alterations in the phospholipid pattern of liver, kidney, and spleen, increasing total phospholipid and cholesterol but decreasing triglyceride levels. However, it was not mutagenic in a Salmonella test system, even in the presence of S9 and microsomal fractions from Aroclor 1254-treated rats.

Aniline Compounds↗
PubMed2002

Lack of DNA binding in the rat nasal mucosa and other tissues of the nasal toxicants roflumilast, a phosphodiesterase 4 inhibitor, and a metabolite, 4-amino-3,5-dichloropyridine, in contrast to the nasal carcinogen 2,6-dimethylaniline.

The phosphodiesterase 4 inhibitor Roflumilast (B9302-107) (RF) and its metabolite 4-amino-3,5-dichloropyridine (ADCP) produced nasal toxicity in preclinical safety studies with rats. The purpose of this study was to assess the possible formation of DNA adducts, by RF and ADCP, in the nasal mucosa, liver and testes of male rats using the 32P-postlabeling assay. For comparison, rats were exposed to the DNA-reactive carcinogens 2,6-dimethylaniline (DMA), also known as 2,6-xylidine, a nasal carcinogen, and the aromatic amine carcinogens 4,4'-methylene-bis(2-chloroaniline) (MOCA), which yields monocyclic DNA adducts, and 2-acetylaminofluorene (2-AAF). In the case of RF, possible sources of DNA adducts include the parent molecule and its ADCP moiety by enzymatic N-hydroxylation and sulfation, reactions typical of carcinogenic aromatic amines. 4-Acetoxylamino-3,5-dichloropyridine (N-acetoxy-ADCP), a chemically activated derivative of ADCP, was prepared and used to modify DNA which was then used to establish the chromatographic conditions with which to reliably detect whether or not such adducts were formed metabolically from RF and ADCP. Similarly, a standard N-hydroxy-DMA was prepared, but the corresponding N-acetoxy derivative was unstable and decomposed during synthesis. Both N-hydroxy-DMA and N-acetoxy-ADCP were mutagenic in the Salmonella typhimurium Ames assay using strain TA100 without an exogenous bioactivation system, with the former being more potent. N-hydroxy-ADCP was essentially inactive in this assay. For the 32P-postlabeling assay, male Wistar rats were exposed to the test substances and carrier control compounds by intragastric instillation at the selected dose levels for 7 days. Subsequently, the nasal mucosa, liver, and testes of the rats exposed to the test or control compounds were extirpated, the DNA extracted and the samples postlabeled. The patterns of adducts formed with the test compounds were compared to those formed in N-acetoxy-ADCP- and N-hydroxy-DMA-adducted DNA, which were assayed by both nuclease P1 and butanol enhancement methods. Based upon the similarity of results from the two enhancement methods, only the former was used for the in vivo studies. No evidence was obtained for the formation of DNA adducts from RF or its metabolites, specifically ADCP, under the conditions of these assays despite the ability to detect adducts from DNA modified chemically with N-acetoxy-ADCP and DNA adducts from the other compounds in their target organs. In the absence of a pattern of compound-related spots, we conclude that RF does not form DNA adducts having the potential to initiate neoplasia in these three tissues.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2002

Microdosimetric properties of ionizing electrons in water: a test of the PENELOPE code system.

The ability to simulate the tortuous path of very low-energy electrons in condensed matter is important for a variety of applications in radiobiology. Event-by-event Monte Carlo codes such as OREC, MOCA and PITS represent the preferred method of computing distributions of microdosimetric quantities. However, event-by-event Monte Carlo is computationally expensive, and the cross sections needed to transport simulations to this level of detail are usually only available for water. In the recently developed PENELOPE code system, 'hard' electron and positron interactions are simulated in a detailed way while soft' interactions are treated using multiple scattering theory. Using this mixed simulation algorithm, electrons and positrons can be transported down to energies as low as 100 eV. To our knowledge, PENELOPE is the first widely available, general purpose Monte Carlo code system capable of transporting electrons and positrons in arbitrary media down to such low energies. The ability to transport electrons and positrons to such low energies opens up the possibility of using a general purpose Monte Carlo code system for microdosimetry. This paper presents the results of a code intercomparison study designed to test the applicability of the PENELOPE code system for microdosimetry applications. For sites comparable in size to a mammalian cell or cell nucleus, single-event distributions, site-hit probabilities and the frequency-mean specific energy per event are in reasonable agreement with those predicted using event-by-event Monte Carlo. Site-hit probabilities and the mean specific energy per event can be estimated to within about 1-10% of those predicted using event-by-event Monte Carlo. However, for some combinations of site size and source-target geometry, site-hit probabilities and the mean specific energy per event may only agree to within 25-60%. The most problematic source-target geometry is one in which the emitted electrons are very close to the tally site (e.g., a point source on the surface of a cell). Although event-by-event Monte Carlo will continue to be the method of choice for microdosimetry, PENELOPE is a useful, computationally efficient tool for some classes of microdosimetry problem. PENELOPE may prove particularly useful for applications that involve radiation transport through materials other than water or for applications that are too computationally intensive for event-by-event Monte Carlo, such as in vivo microdosimetry of spatially complex distributions of radioisotopes inside the human body.

Dose-Response Relationship, Radiation↗