In-phantom neutron fluence measurements in the orthogonal Birmingham boron neutron capture therapy beam

This paper presents the results of an experimental investigation into the performance of the Birmingham accelerator-based epithermal BNCT beam. In-phantom gold foil activation and boron trifluoride tube measurements have been used. The results have been compared with calculated response rates using Monte Carlo modeling of the entire neutron system from source to phantom and detector. The excellent agreement obtained gives us confidence in the validity of the simulations and our ability to predict accurately the neutronic performance of our BNCT facility.

Human histamine N-methyltransferase pharmacogenetics: common genetic polymorphisms that alter activity

Histamine N-methyltransferase (HNMT) catalyzes a major pathway in histamine metabolism. Levels of HNMT activity in humans are regulated by inheritance. We set out to study the molecular basis for this genetic regulation. Northern blot analysis showed that HNMT is highly expressed in the kidney, so we determined levels of enzyme activity and thermal stability in 127 human renal biopsy samples. DNA was isolated from 12 kidney samples with widely different HNMT phenotypes, and exons of the HNMT gene were amplified with the polymerase chain reaction. In these 12 samples, we observed a C314T transition that resulted in a Thr105Ile change in encoded amino acid, as well as an A939G transition within the 3'-untranslated region. All remaining renal biopsy samples then were genotyped for these two variant sequences. Frequencies of the alleles encoding Thr105 and Ile105 in the 114 samples studied were 0.90 and 0.10, respectively, whereas frequencies for the nucleotide A939 and G alleles were 0.79 and 0.21, respectively. Kidney samples with the allele encoding Ile105 had significantly lower levels of HNMT activity and thermal stability than did those with the allele that encoded Thr105. These observations were confirmed by transient expression in COS-1 cells of constructs that contained all four alleles for these two polymorphisms. COS-1 cells transfected with the Ile105 allele had significantly lower HNMT activity and immunoreactive HNMT protein than did those transfected with the Thr105 allele. These observations will make it possible to test the hypothesis that genetic polymorphisms for HNMT may play a role in the pathophysiology of human disease.

Uroguanylin and guanylin: distinct but overlapping patterns of messenger RNA expression in mouse intestine

BACKGROUND & AIMS

Uroguanylin and guanylin, endogenous ligands of the guanylate cyclase C receptor, are presumed to mediate fluid and electrolyte secretion in the intestine. The aim of this study was to characterize the expression patterns of uroguanylin and guanylin messenger RNA (mRNA) in the mouse intestine.

METHODS

A mouse uroguanylin complementary DNA was amplified from a partial genomic clone, and Northern analyses and in situ hybridization were performed to localize guanylin and uroguanylin mRNA along the duodenal-colonic and crypt-villus axes.

RESULTS

Uroguanylin mRNA was expressed throughout the mouse intestine and also in the kidney. Signal intensity was greatest in the small intestine for uroguanylin and in the distal small intestine and colon for guanylin. In situ hybridization showed uroguanylin mRNA localized predominantly in intestinal villi and the corticomedullary junction of the kidney, whereas guanylin mRNA was localized in both crypts and villi in the small intestine and to superficial epithelial cells in the colon.

CONCLUSIONS

Mouse uroguanylin mRNA expression is discrete from guanylin expression in the intestine. The patterns of distribution in the intestine and the known pH optima of these ligands suggest a complementary role for these secretagogues.

The use of multiple parameters to characterize cadmium-induced renal dysfunction resulting from occupational exposure

Renal function has been examined in a group of 77 subjects occupationally exposed to cadmium fume and dust, together with a referent group of 103 age- and socioeconomically matched subjects. Fourteen biochemical parameters were measured on each subject. Three different ways of combining the information from all 14 tests were used to identify those subjects with renal dysfunction. These were first to count the number of parameters in which a subject recorded an abnormal test result. Second, the z value was computed for each parameter for each person by comparison with the mean and standard deviation of a derived normal population; these z scores were then summed. Lastly a multivariate distance measure, Mahalanobis D2, was determined for each subject from the distribution of normal subjects. The three approaches showed a considerable degree of agreement in identifying subjects with renal dysfunction, but they also displayed complementary strengths and weaknesses. The consensus of the three techniques was then taken to define truly dysfunctional subjects and each of the 14 parameters, and some combinations of pairs of parameters were tested as to their sensitivity and specificity. For this group of subjects, it was not possible to improve greatly on the use of retinol binding protein on its own. Were a second parameter to be chosen, it would be desirable to choose one reflecting the glomerular filtration rate, but the absence of a suitable sensitive biological monitoring parameter precludes a firm recommendation.

Histamine N-methyltransferase: inhibition by monoamine oxidase inhibitors

Histamine N-methyltransferase (HNMT) catalyzes the N tau-methylation of histamine. N tau-Methylhistamine can then undergo oxidation catalyzed by the mitochondrial enzyme monoamine oxidase (MAO). Addition of an MAO inhibitor such as pargyline to tissue preparations can increase the HNMT activity assayed --presumably as a result of inhibition of N tau-methylhistamine metabolism by MAO. However, pargyline-dependent "activation" of HNMT may also occur in tissue preparations that lack mitochondria. Our experiments were performed to determine whether MAO inhibitors, like many other amine compounds, could directly increase the activity of partially purified HNMT, and, if so, to study the mechanism of activation. Human kidney HNMT was partially purified by sequential ion exchange and gel filtration chromatography. The activity of the purified HNMT was increased approximately 50% in the presence of pargyline. However, enzyme kinetic experiments showed that pargyline, like many other amines, was a competitive inhibitor of HNMT. Apparent activation of the enzyme resulted from sequential shifts of histamine substrate curves to higher Vmax values in the presence of increasing concentrations of pargyline. Other acetylenic MAO inhibitors, clorgyline and the two stereoisomers of deprenyl, were also competitive inhibitors of purified human kidney HNMT. Inhibition kinetic experiments performed in the presence of varying concentrations of histamine demonstrated that Kis values for pargyline, clorgyline, (R)-deprenyl and (S)-deprenyl were 0.126, 0.144, 0.217, and 0.627 mM, respectively. When the concentration of the cosubstrate for the reaction, S-adenosyl-L-methionine, was varied in the presence of variable concentrations of pargyline, inhibition of HNMT by pargyline was noncompetitive with regard to the methyl donor, with Kii and Kis values of 1.23 and 0.95 mM, respectively. Finally, several amine compounds related structurally to pargyline were also found to be inhibitors of HNMT.

A pilot study using 99mTc to measure lead and platinum in the human kidney

A pilot study has been conducted to investigate the hypothesis that the chemotherapeutic drug, cisplatinum, can mobilize skeletal lead. In vivo measurements of lead and platinum in the kidney of chemotherapy patients were performed with the technique of x-ray fluorescence, using 99mTc in a backscatter geometry. The results of the pilot study were inconclusive; the majority of patients exhibited no evidence of kidney lead at the level of system sensitivity, and negligible blood and urine lead levels.

In vivo measurements of lead in bone in long-term exposed lead smelter workers

In-vivo measurements of lead concentrations in calcaneus (mainly trabecular bone) and tibia (mainly cortical bone) were performed by x-ray fluorescence (XRF) in 70 active and 30 retired lead smelter workers who had long-term exposure to lead. Comparison was made with 31 active and 10 retired truck assembly workers who had no known occupational exposure to lead. After physical examination, all participants provided blood and urine samples and answered a computerized questionnaire. Since 1950, blood lead has been determined repeatedly in lead workers at the smelter, which made it possible to calculate a time-integrated blood lead index for each worker. Lead concentrations in blood, urine, calcaneus, and tibia in active and retired lead workers were significantly higher than in the corresponding control groups (p < .001). The highest bone lead concentrations were found among retired lead workers (p < .001), which was the result of considerably higher lead exposure during 1940 to 1960. Lead concentrations in calcaneus in active lead workers were significantly higher than in tibia when expressed in ug of lead per gram of bone mineral, which suggests a quicker absorption over time in this mainly trabecular bone. The estimated biological half-times were 16 y in calcaneus (95% confidence interval [95% CI] = 11-29 y) and 27 y in tibia (95% CI = 16-98 y). A strong positive correlation was found between lead concentrations in calcaneus and tibia for all lead workers (r = 0.54; p < .001). A strong positive correlation was also found between the bone lead concentrations and the cumulative blood lead index. Blood lead, at the time of study, correlated well with bone lead concentrations in retired--but not in active--workers, reflecting the importance of the endogenous (skeletal) lead exposure. The findings in this study indicate that bone lead measurements by XRF can give a good index of long-term lead exposure. Tibia measurements offer a higher precision than calcaneus measurements. The method is of particular interest in epidemiologic studies of adverse health effects caused by long-term lead exposure.

Genetic segregation analysis of red blood cell (RBC) histamine N-methyltransferase (HNMT) activity

Methylation is an important pathway in the biotransformation of many drugs, neurotransmitters, and xenobiotic compounds. Histamine N-methyltransferase (HNMT) catalyzes the N tau-methylation of histamine and structurally related compounds. Measurement of HNMT activity in the RBC makes it possible to access variation in the enzyme activity that may reflect differences in less accessible tissues such as brain. Previously reported high family correlations for RBC HNMT activity suggested that genetic inheritance plays a major role in the regulation of variation in this enzyme. In the present study we completed complex segregation analyses of RBC HNMT activity of 241 individuals in 51 nuclear families that were randomly ascertained through children in the Rochester, Minnesota public school system in order to characterize the mode of inheritance of this important enzyme. We found evidence for major gene influence on the regulation of RBC HNMT activity. Both transformed and untransformed data support the presence of Mendelian major gene segregation, but the gene frequency differences do not indicate a direct correspondence between genotypes inferred from the two sets of analyses. Analyses of the skewed untransformed data indicated the presence of a relatively rare (Q = 0.121) additive major gene for high activity, with the three overlapping genotype distributions representing 77, 21, and 2% of individuals. Analyses of the normalized transformed data indicated the presence of a common (Q = 0.71) additive major gene for high activity, with the three overlapping genotype distributions accounting for 9, 41, and 50% of individuals. The analyses of transformed data give the best fit as well as the most parsimonious Mendelian major gene model.(ABSTRACT TRUNCATED AT 250 WORDS)

Design studies related to an in vivo neutron activation analysis facility for measuring total body nitrogen

Design studies relating to an in vivo prompt capture neutron activation analysis facility measuring total body nitrogen are presented. The basis of the design is a beryllium-graphite neutron collimator and reflector configuration for (alpha, n) type radionuclide neutron sources (238PuBe or 241AmBe), so as to reflect leaking, or out-scattered, neutrons towards the subject. This improves the ratio of thermal neutron flux to dose and the spatial distribution of thermal flux achieved with these sources, whilst retaining their advantage of long half-lives as compared to 252Cf based systems. The common problem of high count-rate at the detector, and therefore high nitrogen region of interest background due to pile-up, is decreased by using a set of smaller (5.1 cm diameter x 10.2 cm long) NaI(Tl) detectors instead of large ones. The facility described presents a relative error of nitrogen measurement of 3.6% and a nitrogen to background ratio of 2.3 for 0.45 mSv skin dose (assuming ten 5.1 cm x 10.2 cm NaI(Tl) detectors).

Human liver thiopurine methyltransferase pharmacogenetics: biochemical properties, liver-erythrocyte correlation and presence of isozymes

Thiopurine methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine (6-MP). TPMT activity in the human red blood cell (RBC) is controlled by a common genetic polymorphism. Gene frequencies for this polymorphism are such that approximately one in 300 subjects is homozygous for the allele for low activity and lacks RBC TPMT activity, 11% of subjects are heterozygous and have intermediate levels of enzyme activity and 89% are homozygous for the allele for high activity. Our experiments were performed to determine whether the properties of TPMT in an important human drug metabolizing organ, the liver, were similar to those of RBC TPMT and to test the hypothesis that the genetic polymorphism which controls TPMT activity in the human RBC might also regulate the level of this enzyme activity in hepatic tissue. Human liver TPMT is a cytoplasmic enzyme and the Km values for 6-MP and S-adenosyl-L-methionine, cosubstrates for the reaction, were 580 microM and 2.7 microM, respectively. These properties, as well as the sensitivity of human liver TPMT to a panel of methyltransferase inhibitors, were similar to those of RBC TPMT. The enzyme activity was then measured in 119 surgical biopsy samples of hepatic tissue. Average hepatic TPMT activity was 13.6% higher in samples from male than in those from female patients. Frequency distribution histograms demonstrated the presence of a subgroup with intermediate enzyme activity that included 8.4% of samples. In addition, when TPMT activity was measured in both RBCs and hepatic tissue for 35 patients, those with inherited intermediate levels of RBC TPMT activity also had intermediate hepatic enzyme activity. Finally, ion exchange chromatography demonstrated the presence of two isozymes of TPMT in human hepatic tissue, but the isozymes did not appear to explain the molecular mechanism responsible for the genetic polymorphism. These results were compatible with the conclusion that the genetic polymorphism which controls TPMT activity in the RBC also controls levels of this important enzyme activity in a major human drug metabolizing organ, the liver.

Chelated lead and bone lead

In this study a close correlation [correlation coefficient (r) = 0.86, P less than 0.001] was found between the blood lead level of 20 lead workers and their urinary excretion of lead for 24 h after intravenous infusion with 1 g of the chelating agent calcium disodium edetate. In addition, there were significant associations between lead levels in different bones (tibia/calcaneus: r = 0.93, P less than 0.001; tibia/phalanx: r = 0.67, P less than 0.002; calcaneus/phalanx: r = 0.80, P less than 0.001), as measured by in vivo X-ray fluorescence. Chelation produced no significant change in the lead level in either tibia or calcaneus. There was a significant correlation between chelated lead and bone lead (eg, for calcaneus, r = 0.62) in currently exposed workers. However, there was no significant relationship when a retired worker and an inactive worker were included (r = 0.14). It was concluded that chelatable lead mainly reflects the blood and soft-tissue lead pool, which is only partly dependent upon the skeletal lead content that comprises the biggest share of the total body burden.

Kidney effects in long term exposed lead smelter workers

Occupational exposure to lead may cause kidney damage. This study was carried out on a cohort of 70 active and 30 retired long term exposed lead smelter workers. Their kidney function was compared with 31 active and 10 retired truck assembly workers who had no occupational exposure to lead. The lead workers had been regularly followed up with measurements of lead concentration in blood since 1950. Previous exposure to lead was calculated as a time integrated blood lead index for each worker. Blood and urine samples were obtained from all subjects. The concentration of lead in blood (B-Pb) and urine (U-Pb) was analysed. The urinary concentrations of several sensitive indicators of early tubular (U-beta 2-microglobulin (U-beta 2-m); U-N-acetyl-beta-glucosaminidase (U-NAG)) and glomerular kidney damage (U-albumin) were determined. The B-Pb and U-Pb values were significantly higher among active and retired lead workers compared with their corresponding control groups. The highest concentrations were found among the active lead workers. The concentrations of the parameters of kidney function investigated were of the same magnitude for exposed workers and controls. No clinical signs of renal impairment were found among the workers. No correlations of clinical importance existed between concentrations of U-albumin, U-beta 2-m, and U-NAG activity on the one hand and the concentrations of B-Pb, cumulative blood lead index, U-Pb, and lead concentrations in the calcaneus and tibia on the other, among lead workers and controls. Despite many years of moderate to heavy exposure to lead, particularly for the retired lead workers, no signs of adverse effects on the kidney such as early tubular or glomerular malfunction were found. Reversible changes in kidney function during the 1950s and 1960s could not be excluded, however, due to a greater exposure to lead during that time.

Repeated measurements of tibia lead concentrations by in vivo x ray fluorescence in occupational exposure

A group of workers occupationally exposed to lead have had measurements of their tibia lead concentrations made on two occasions separated by five years; on the second occasion calcaneus lead concentrations were also measured. The results serve to confirm the reliability of the measurement technique and to illustrate the improved precision achieved through technical improvements. More importantly, the relation between tibia lead concentration and cumulative blood lead found in this longitudinal study was entirely consistent with that previously reported, which had been based on cross sectional studies. Furthermore, the relation between lead concentrations in the tibia and in calcaneus found here was similar to that previously found in a larger cross sectional survey. It is concluded that this technique of measuring bone lead concentrations non-invasively is likely to be used increasingly as a biological monitor of cumulative exposure to lead.

Multiple therapies for vaginal bleeding secondary to large uterine myomas

Acute vaginal bleeding secondary to uterine myomas can be a devastating event. We report the use of a combined therapeutic approach in a patient who presented with protracted bleeding of a myomatous uterus that was equivalent in size to a 38 week gestation. This patient's course was further complicated by her refusal of blood or blood products.

Monte Carlo modelling of in vivo x-ray fluorescence of lead in the kidney

A Monte Carlo program has been written to model the in vivo x-ray fluorescence of lead in the kidney, to aid the choice of one of four candidate fluorescing source/measurement geometry combinations: 109Cd/180 degrees, 57Co/90 degrees and 99Tcm at both 180 degrees and 90 degrees. Computational studies and practical considerations led to the choice of 99Tcm in a backscatter geometry for the measurement system.

In situ neutron spectrometry to 60 MeV in a water phantom exposed to a cancer therapy beam

In-air and in-phantom neutron spectra have been measured between 10 and 60 MeV for two field sizes on the Clatterbridge cyclotron by unfolding the response of a specially built NE213 scintillator. The in-phantom measurements show distinct spectral hardening with depth, which is reflected in changes in the spectrum-averaged mean neutron energy. These findings are confirmed using Monte Carlo calculations.

Mouse kidney histamine N-methyltransferase: assay conditions, biochemical properties and strain variation

Histamine N-methyltransferase (HNMT) catalyzes the N tau-methylation of histamine and structurally-related compounds. Levels of HNMT activity in the human red blood cell are regulated by inheritance. The inbred mouse is an ideal laboratory animal in which to study the genetics of inherited traits. Therefore, HNMT activity was measured in renal homogenates of A/J mice to establish optimal assay conditions and to determine the properties of mouse kidney HNMT as a first step toward testing the hypothesis that large strain-related variations in HNMT activity might exist among inbred strains of mice. Apparent Km values for histamine and S-adenosyl-L-methionine, the two cosubstrates for the reaction, were 26 and 1.7 microM, respectively. IC50 values for the inhibition of mouse kidney HNMT by amodiaquine and S-adenosyl-L-homocysteine were 1.67 and 11.8 microM, respectively. HNMT activity levels were then measured under optimal assay conditions in renal preparations from male animals of eleven inbred mouse strains chosen because of the availability of recombinant inbred (RI) animals derived from the parental strains. Average values for renal HNMT activity varied among strains by less than two-fold and ranged only from 26.2 +/- 0.51 (mean +/- SEM) units/mg protein in AKR/J mice to 39.1 +/- 2.58 units/mg protein in C57BL/6J animals. Renal HNMT activities in females of the three strains in which both sexes were studied were 11-13% higher than were those in renal tissue from males of the same strain. In summary, the properties of HNMT in the mouse kidney are similar to those of HNMT in other species, but strain variation in levels of enzyme activity among the 11 inbred mouse strains studied was insufficient for these animals to be used in biochemical genetic experiments.

Lead in bone: sampling and quantitation using K X-rays excited by 109Cd

Lead in bone can be measured in vivo using gamma-rays from a 109Cd source to excite lead K X-rays. Normalization of lead X-ray amplitudes to that of the elastically backscattered 88 keV gamma-rays produces a determination of the concentration of lead in bone mineral that is accurate and insensitive to variations in measurement or bone geometry. For in vivo tibia measurements, a typical precision (1 SD) of +/- 5 micrograms lead (g bone mineral)-1 is achieved for an effective dose equivalent of 2.1 microSv. Measurement can be made of any superficial bone site, but precision will vary approximately as the inverse of the square root of the mass of bone mineral sampled. The apparatus required for this technique is readily transportable, and mobile laboratory facilities are easily established.

An improved in vivo neutron activation system for measuring kidney cadmium

An in vivo neutron activation system for measuring kidney cadmium has been redesigned, firstly to reduce ambient dose levels and, secondly, to improve the cadmium signal to neutron dose ratio by modifying the neutron spectrum from 238Pu/Be, by interposing a beryllium premoderator. The ambient dose was reduced by a factor of seven. The overall system performance (lower limit of detection for a given dose) was improved by 40-50%. This 238Pu/Be based system now performs as well as or better than analogous 252Cf systems, without the drawback of the relatively short half life of 252Cf.

In vivo neutron activation analysis of organ cadmium burdens. Referent levels in liver and kidney and the impact of smoking

In vivo neutron activation measurements of liver and kidney cadmium have been made in 77 exposed workers and 101 referents. Cadmium levels were higher in exposed workers than in referents; both in liver, 25.7 cf. 0.6 micrograms/g, and kidney, 17.9 cf. 2.7 mg. The 19 referents who never smoked had lower mean organ cadmium burdens than the other referents, the difference achieving statistical significance in the kidney, p less than .01. Cigarette smoking was estimated to increase cadmium body burden by 370 +/- 140 micrograms/pack year. These referent cadmium levels are similar to, although slightly below, previous in vivo and autopsy data.

Effect of occupational lead exposure on serum 1,25-dihydroxyvitamin D levels

The effects of lead exposure on serum 1,25-dihydroxyvitamin D levels and calcium homeostasis have been studied in 63 males occupationally exposed to the metal in the UK. The exposure indices used were blood lead, reflecting short-term exposure, and an in vivo X-ray fluorescence measurement of tibia lead which reflects cumulative lead exposure. Serum 1,25-dihydroxyvitamin D levels were higher than those in a referent population, who were non-occupationally exposed to lead, and were correlated with both blood lead and tibia lead. Multiple regression analysis suggested that blood lead was the variable responsible for the increase in serum 1,25-dihydroxyvitamin D. There were no other abnormalities in calcium metabolism associated with the degree of lead exposure.

In vivo measurements of bone lead--a comparison of two x-ray fluorescence techniques used at three different bone sites

In vivo bone lead measurements have been made on a group of about 120 people, most of whom were lead exposed workers. Two different x-ray fluorescence (XRF) techniques were used to make measurements at three bone sites. Finger lead was measured using 57Co sources, and lead measurements were made in both tibia and calcaneus with a technique based on 109Cd sources. The results of the bone lead measurements correlated strongly with each other and with the index of cumulative exposure, thus confirming the value and reliability of these in vivo measurements as a tool in the study of chronic lead exposure. Measurement precision, +/- 1 standard deviation, was highest for tibia +/- 7.4 micrograms (g bone mineral)-1, +/- 16.6 micrograms (g bone mineral)-1 for the calcaneus and lowest for phalangeal lead +/- 25.0 micrograms (g bone mineral)-1. Maximum absorbed doses to the skin were comparable for all three measurements (1-3 mGy). The mean whole body dose equivalents were all low, but that for the finger measurement, 0.1 microSv, was significantly less than for the calcaneus and tibia measurements 3-5 microSv.