Guidelines for radioiodine therapy of differentiated thyroid cancer

INTRODUCTION

The purpose of the present guidelines on the radioiodine therapy (RAIT) of differentiated thyroid cancer (DTC) formulated by the European Association of Nuclear Medicine (EANM) Therapy Committee is to provide advice to nuclear medicine clinicians and other members of the DTC-treating community on how to ablate thyroid remnant or treat inoperable advanced DTC or both employing large 131-iodine ((131)I) activities.

DISCUSSION

For this purpose, recommendations have been formulated based on recent literature and expert opinion regarding the rationale, indications and contraindications for these procedures, as well as the radioiodine activities and the administration and patient preparation techniques to be used. Recommendations also are provided on pre-RAIT history and examinations, patient counselling and precautions that should be associated with (131)I iodine ablation and treatment. Furthermore, potential side effects of radioiodine therapy and alternate or additional treatments to this modality are reviewed. Appendices furnish information on dosimetry and post-therapy scintigraphy.

Randomized comparison of a nutrient-dense formula with an energy-supplemented formula for infants with faltering growth

INTRODUCTION

The practice of supplementing standard infant formula with energy for infants with faltering growth has been widespread. This increases energy density but disturbs the protein : energy ratio, and increases risks of microbial contamination and errors in feed preparation. This study aimed to compare the effectiveness of a nutrient-dense formula (NDF) with an energy-supplemented formula (ESF) in infants with faltering growth.

METHODS

In an open, parallel, randomized study, 49 infants with faltering growth were randomized to receive a NDF (4.2 kJ mL(-1)) or an ESF (4.2 kJ mL(-1)), for 6 weeks. Anthropometry, biochemistry, feed intake, stool and vomit frequency were collected.

RESULTS

No significant differences in tolerance, feed volumes or energy intakes were recorded but the NDF group received 42% more protein and 15-40% more vitamins and minerals. Blood urea concentration in the ESF group fell by 50% over the trial period, suggesting a suboptimal protein : energy ratio in the ESF feed. The NDF group retained a normal mean blood urea concentration, a higher urinary potassium concentration and did not have the significant fall in length z-score seen in the ESF group.

CONCLUSION

Increasing the energy content of normal infant formula without also increasing protein and micronutrients should not be practiced in infants with faltering growth.

A Critical Evaluation of the Experimental Design of Studies of Mechanism Based Enzyme Inhibition, with Implications for In Vitro-In Vivo Extrapolation

The published literature on mechanism based inhibition (MBI) of CYPs was evaluated with respect to experimental design, methodology and data analysis. Significant variation was apparent in the dilution factor, ratio of preincubation to incubation times and probe substrate concentrations used, and there were some anomalies in the estimation of associated kinetic parameters (k(inact), K(I), r). The impact of the application of inaccurate values of k(inact) and K(I) when extrapolating to the extent of inhibition in vivo is likely to be greatest for those compounds of intermediate inhibitory potency, but this also depends on the fraction of the net clearance of substrate subject to MBI and the pre-systemic and systemic exposure to the inhibitor. For potent inhibitors, the experimental procedure is unlikely to have a material influence on the maximum inhibition. Nevertheless, the bias in the values of the kinetic parameters may influence the time for recovery of enzyme activity following re-synthesis of the enzyme. Careful attention to the design of in vitro experiments to obtain accurate kinetic parameters is necessary for a reliable prediction of different aspects of the in vivo consequences of MBI. The review calls for experimental studies to quantify the impact of study design in studies of MBI, with a view to better harmonisation of protocols.

Endaural or postaural incision for myringoplasty: does it make a difference to the patient?

The aim of this study was to find out from patients who had undergone a myringoplasty via either an endaural or postaural approach whether or not they had experienced problems or symptoms relating to their scar, and if these differed depending on which incision had been used. A questionnaire was sent to 91 patients who had undergone myringoplasty between 18 and 62 months earlier. Thirty-four patients who had undergone previous or subsequent ear surgery were excluded. The only statistically significant difference found between groups having either a postauricular or endaural incision was in how likely others were to comment on their scar. There seem to be few long-term sequealae relating to the scar from myringoplasty. From a patient perspective, between 18 and 62 months postoperatively, there was very little difference in symptoms or problems whether or not an endaural or a postaural incision had been used for the surgery.

Localized breeding of the Anopheles gambiae complex (Diptera: Culicidae) along the River Gambia, West Africa

A study was undertaken to identify the major larval habitats of the Anopheles gambiae (Giles) complex in rural Gambia. Mosquito larvae and pupae were sampled along transects and in specific habitats in the central region of the country during the rainy seasons of 1996 and 1997. The sampling showed that the major breeding sites were located on the flooded alluvial soils bordering the river. The largest numbers of larvae were found during September, one month after the peak rains. Polymerase chain reaction analysis of specimens showed that Anopheles melas (Theobald) was the dominant species in the flooded areas (81.5%), followed by A. gambiae sensu stricto (Giles) (18.0%) and A. arabiensis (Patton) (0.5%). By sampling in specific habitats it was evident that A. arabiensis was mainly breeding in rain-fed rice fields along the edge of the alluvial soils. Anopheles melas and A. gambiae s.s. often coexisted but whereas A. melas were found in water with a salinity of up to 72% sea water (25.2 g NaCl l(-1)), A. gambiae s.s. only occurred in water with up to 30% sea water (10.5 g NaCl l(-1)). Anopheles melas larvae were found in association with plant communities dominated by sedges and grasses (Eleocharis sp., Paspalum sp., Sporobolus sp.) and sea-purslane Sesuvium portulacastrum (L.) and the presence of cattle hoof prints, whereas A. gambiae s.s. larvae mainly occurred in association with Paspalum sp. and Eleocharis sp. The study showed that even during the peak rainy season, breeding of the A. gambiae complex is almost entirely restricted to the extensive alluvial areas along the river.

Irrigated crop production is associated with less malaria than traditional agricultural practices in Tanzania

There is concern that crop irrigation that results in increased numbers of vector mosquitoes will lead to a rise in malaria in local communities. We evaluated the level of malaria experienced in 3 communities in northern Tanzania with different agricultural practices: rice irrigation, sugar-cane irrigation and traditional maize cultivation. Five cross-sectional surveys were used to measure the prevalence of infection with falciparum malaria in 1-4 years old children in each community over a period of 12 months. Active case detection was also carried out to record clinical episodes of malaria during the study period. Information on antimalarial measures was also recorded. Results from the cross-sectional surveys showed that the overall prevalence of malaria parasites was less near the rice irrigation (12.5%) and sugar-cane (16.9%) schemes than the savannah village (29.4%). There were also significantly fewer clinical episodes of malaria in the rice village (15 cases/1000 child-weeks at risk [cwar]) than either the sugar-cane (36 cases/1000 cwar) or savannah (40 cases/1000 cwar) villages. Overall, rice irrigation was associated with less malaria than alternative agricultural practices, despite the considerable numbers of vectors produced in the paddies. This finding supports other studies that indicate that irrigation in much of sub-Saharan Africa will not lead to increased malaria. Nonetheless, African governments planning irrigation projects need effective policies to encourage local communities to use personal protection measures, such as insecticide-treated bednets, and to ensure that these communities have access to effective antimalarial drugs and efficient health services.

Expression, purification, and biochemical characterization of a human cytochrome P450 CYP2D6-NADPH cytochrome P450 reductase fusion protein

Cytochrome P450 CYP2D6 metabolizes a wide range of pharmaceutical compounds. A CYP2D6 fusion enzyme (CYP2D6F), containing an amino-terminal human CYP2D6 sequence and a carboxyterminal human NADPH-cytochrome P450 oxidoreductase (CPR) moiety, was constructed. High levels of expression were achieved in Escherichia coli (60-100 nmol/liter) and the enzyme was catalytically active with optimal activities achieved in the presence of the antioxidant, GSH. Turnover values for bufuralol 1'-hydroxylation, metoprolol alpha-hydroxylation, O-desmethylation, and dextromethorphan O-demethylation, using membranes expressing the fusion enzyme, were 5.6, 0.4, 0.72, and 6.19 min(-1), respectively. These values were similar to E. coli membranes which coexpressed human CYP2D6 and CPR (CYP2D6/R). The K(m) and k(cat) values for bufuralol metabolism were estimated to be 10.2 microM and 4.1 min(-1), respectively. The enzyme was purified using ion-exchange chromatography, affinity chromatography (2'-5' ADP-Sepharose), and gel filtration. Estimated turnover rates for bufuralol 1'-hydroxylation, metoprolol alpha-hydroxylation, O-desmethylation, and dextromethorphan O-demethylation were 1.2, 0.52, 0.79, and 0.76 min(-1), respectively. Bufuralol 1'-hydroxylase activity by purified CYP2D6F was enhanced by phospholipids and added CPR. The CYP2D6F enzyme was able to stimulate CYP3A4 testosterone 6beta-hydroxylase activity in a reconstitution system indicating that electron transfer may be largely intermolecular. The catalytically self-sufficient CYP2D6F enzyme will facilitate investigations of P450-CPR interactions and the development of new biocatalysts.

Multisite kinetic models for CYP3A4: simultaneous activation and inhibition of diazepam and testosterone metabolism

Some substrates of cytochrome P450 (CYP) 3A4, the most abundant CYP in the human liver responsible for the metabolism of many structurally diverse therapeutic agents, do not obey classical Michaelis-Menten kinetics and demonstrate homotropic and/or heterotropic cooperativity. The unusual kinetics and differential effects observed between substrates of this enzyme confound the prediction of drug clearance and drug-drug interactions from in vitro data. We have investigated the hypothesis that CYP3A4 may bind multiple molecules simultaneously using diazepam (DZ) and testosterone (TS). Both substrates showed sigmoidal kinetics in B-lymphoblastoid microsomes containing a recombinant human CYP3A4 and reductase. When analyzed in combination, TS activated the formation of 3-hydroxydiazepam (3HDZ) and N-desmethyldiazepam (NDZ) (maximal activation 374 and 205%, respectively). For 3HDZ, V(max) values remained constant with increasing TS, whereas the S(50) and Hill values decreased, tending to make the data less sigmoidal. Similar trends were observed for the NDZ pathway. DZ inhibited the formation 6beta-hydroxytestosterone (maximal inhibition, 45% of control), causing a decrease in V(max) but no significant change to the S(50) and Hill values, suggesting that DZ may inhibit via a separate effector site. Multisite rate equation models have been derived to explore the analysis of such complex kinetic data and to allow accurate determination of the kinetic parameters for activation and inhibition. The data and models presented are consistent with proposals that CYP3A4 can bind and metabolize multiple substrate molecules simultaneously; they also provide a generic solution for the interpretation of the complex kinetic data derived from CYP3A4 substrates.

Effect of passive zooprophylaxis on malaria transmission in The Gambia

The effect of zooprophylaxis on malaria transmission has not been studied on the African continent despite that the World Health Organization has recommended this intervention method since 1982. The effect of passive zooprophylaxis on malaria vector abundance, mosquito feeding preferences, and infectivity was studied in an area of moderate seasonal transmission in The Gambia. A paired cohort of 204 children <7 yr of age was selected and matched in groups for presence or absence of cattle (Bos taurus) within 20 m of their bedroom. Comparisons were made between mosquitoes collected from the bedrooms of the two groups of children. Other ruminants and equines were present in both groups of compounds. Most of the anopheline mosquitoes (98.5%) collected were Anopheles gambiae sensu lato. There was no difference in the geometric mean number of An. gambiae s.l. mosquitoes caught in houses near or far from cattle. The species composition of the An. gambiae complex was similar in both groups. Blood meal analysis of specimens collected in houses without cattle showed a human blood index (HBI) of 82% for An. Arabiensis (Patton), 56% for An. gambiae sensu stricto (Giles), and 36% for Anopheles Melas (Theobald), indicating that each of these sibling species fed readily on animals. The presence of cattle reduced the HBI of An. arabiensis but did not significantly alter the HBI of An. gambiae s.s. or An. melas. There was no significant difference between the groups in the sporozoite rates of An. gambiae s.l. nor in the estimated malaria transmission risk. These findings suggest that passive zooprophylaxis using cattle does not alter the individual exposure to malaria parasites in The Gambia.

Do untreated bednets protect against malaria?

Bednets are thought to offer little, if any, protection against malaria, unless treated with insecticide. There is also concern that the use of untreated nets will cause people sleeping without nets to receive more mosquito bites, and thus increase the malaria risk for other community members. Regular retreatment of nets is therefore viewed as critical for malaria control. However, despite good uptake of nets, many control programmes in Africa have reported low re-treatment rates. We investigated whether untreated bednets had any protective benefit (in October and November 1996) in The Gambia where nets, although widely used, are mostly untreated. Cross-sectional prevalence surveys were carried out in 48 villages and the risk of malaria parasitaemia was compared in young children sleeping with or without nets. Use of an untreated bednet in good condition was associated with a significantly lower prevalence of Plasmodium falciparum infection (51% protection [95% CI 34-64%], P < 0.001). This finding was only partly explained by differences in wealth between households, and children in the poorest households benefited most from sleeping under an untreated net (62% protection [14-83%], P = 0.018). There was no evidence that mosquitoes were diverted to feed on children sleeping without nets. These findings suggest that an untreated net, provided it is in relatively good condition, can protect against malaria. Control programmes should target the poorest households as they may have the most to gain from using nets.

Utility of metabolic stability screening: comparison of in vitro and in vivo clearance

1. The ability of hepatic microsomal metabolic stability assessments to predict in vivo clearance in rat has been retrospectively evaluated for 1,163 compounds from 48 programmes of chemistry. Using a simple binary classification system, the in vivo clearances of approximately 64% of the compounds were correctly classified. 2. About 24% of compounds were metalbolically stable yet had clearance greater than half of liver blood flow in vivo. This might be expected as microsomes only contain a limited number of fully functioning drug-metabolizing enzymes and cannot be expected to account for extrahepatic or non-metabolic clearance processes. 3. About 13% of compounds had in vivo clearances of less than half liver blood flow despite being classified as metabolically unstable. Despite overcoming metabolic instability, these compounds had other undesirable properties and were generally more highly bound to plasma proteins, had smaller volumes of distribution (and shorter half-lives despite their clearance) and were more inhibitory against the major human cytochrome P450s. 4. Taking plasma protein binding into consideration reduced the proportion of misclassified low-clearance compounds but did not improve the overall success appreciably. Somewhat surprisingly, human microsomes were nearly as effective as rat microsomes at classifying rat in vivo clearance.

Role of radionuclide imaging in hyperthyroid patients with no clinical suspicion of nodules

The purpose of the study was to assess the role of radionuclide imaging of hyperthyroid patients with no suspicion of nodules. (99)Tc(m) radionuclide scans performed on all 190 patients referred over a 2-year period with symptoms and thyroid function tests compatible with thyrotoxicosis were retrospectively reviewed. 73% of patients were referred by a hospital clinician and 27% were referred direct from the general practitioner. Referral letters and, where applicable, the clinical notes were reviewed and patients with suspected thyroid nodules were excluded. The results of (99)Tc(m) thyroid scans of the 190 patients (age range 23-93 years, mean 48 years) were reviewed. 152 (80%) patients had Graves' disease, 10 (5.3%) had Graves' disease with nodules, 6 (3.2%) had Graves' disease with non-functioning nodules, 5 (2.6%) had viral thyroiditis, 5 (2.6%) had autonomously functioning nodules and 12 (6.3%) were normal studies. Therefore, 20% of patients had a diagnosis other than solely Graves' disease. These diagnoses are important with respect to clinical management. In conclusion, routine radionuclide imaging is worthwhile, as a significant proportion of patients with clinical "Graves' disease" in this study would have received incorrect treatment without the result of this scan.

Isotopic evaluation and therapy in patients with malignant endocrine disease

The contribution of nuclear medicine to the diagnosis and treatment of endocrine malignancy is increasing. Advances in molecular biology offer new opportunities for tumour targeting via surface receptor recognition and tumour-specific metabolic markers. Imaging the biodistribution of these markers allows quantitative, in vivo characterization of tumour function. There is growing interest in the therapeutic potential of nuclear medicine targeting, substituting therapeutic beta-emitting radionuclides for the gamma-emitters used in diagnostic imaging. Limited clinical experience supports the rationale of this approach in patients with inoperable or disseminated disease and controlled trials are in progress. This chapter outlines the place of nuclear medicine techniques in the routine management of endocrine malignancy and explores areas for further development.

Carotid plaque characterization by magnetic resonance imaging: review of the literature

Magnetic resonance imaging (MRI) of carotid plaque has undergone significant improvements in the last decade. Early studies utilizing ex vivo specimens and spin-echo or fast spin-echo imaging led to the conclusion that T2 weighting is the best single contrast to characterize carotid plaque morphology. On these images, the fibrous plaque appears bright and the lipid core is dark; thrombus can have variable intensity. There can be an overlap in T2-weighted signal intensities among the various plaque components, which can be partially offset by the use of multispectral analysis of multiple contrast images. With improvements in coil design, sequence design, and main field and gradient capabilities, accurate in vivo differentiation and measurement of these various carotid plaque components should be possible in 3 to 5 years. Ex vivo and in vivo studies have yielded high-resolution measurements of the complex three-dimensional lumen geometry, which are being used to predict hemodynamic forces acting on the lumenal surface. Carotid plaque burden can be accurately measured in vivo today; ongoing longitudinal studies should lead to a better understanding of the relationship between plaque burden and the risk of thromboembolic complications, as well as the effect of diet and drug therapy in hyperlipidemic patients. With these developments in place or soon to be available, MRI of the diseased carotid artery wall may prove to be even more important than magnetic resonance angiography.

Cribriform variant papillary thyroid cancer: a characteristic of familial adenomatous polyposis

Inherited cancer syndromes may predispose to more than one type of cancer, and these characteristically develop at an earlier age than their sporadic counterparts. The occurrence in a single individual of multiple, early onset primary cancers may indicate an inherited cancer susceptibility. Familial adenomatous polyposis (FAP), an autosomal, dominantly inherited susceptibility to colorectal adenomas and cancer also predisposes to childhood medulloblastomas and to a specific rare histologic type (cribriform variant) of papillary thyroid cancer. We describe a patient who developed a childhood medulloblastoma of the cerebellum, and subsequently a cribriform papillary thyroid cancer. These cancers predated the diagnosis of FAP in this patient, who was later found to have several relatives with FAP. The adenomatous polyposis coli (APC) mutation delineated in this family was in the region associated with those causing an increased risk of thyroid cancer. We submit that the diagnosis of the cribriform variant of papillary thyroid cancer in a young individual, especially after a previous cancer diagnosis, should alert the physician to the possibility of a diagnosis of FAP.

Phenyl benzenesulfonamides are novel and selective 5-HT6 antagonists: identification of N-(2,5-dibromo-3-fluorophenyl)-4-methoxy-3-piperazin-1-ylbenzenesulfonamide (SB-357134)

Substituted N-phenyl-4-methoxy-3-piperazin-1-ylbenzenesulfonamides and conformationally restricted analogues have been identified as high affinity and selective 5-HT6 antagonists. Compounds from this series had a range of pharmacokinetic profiles in rat and in general there was a correlation between clearance and CNS penetration. Based on its overall biological profile 2 (SB-357134) was selected for further pre-clinical evaluation.

Characterization of SB-271046: a potent, selective and orally active 5-HT(6) receptor antagonist

SB-271046, potently displaced [(3)H]-LSD and [(125)I]-SB-258585 from human 5-HT(6) receptors recombinantly expressed in HeLa cells in vitro (pK(i) 8.92 and 9.09 respectively). SB-271046 also displaced [(125)I]-SB-258585 from human caudate putamen and rat and pig striatum membranes (pK(i) 8.81, 9.02 and 8.55 respectively). SB-271046 was over 200 fold selective for the 5-HT(6) receptor vs. 55 other receptors, binding sites and ion channels. In functional studies on human 5-HT(6) receptors SB-271046 competitively antagonized 5-HT-induced stimulation of adenylyl cyclase activity with a pA(2) of 8.71. SB-271046 produced an increase in seizure threshold over a wide-dose range in the rat maximal electroshock seizure threshold (MEST) test, with a minimum effective dose of < or =0.1 mg kg(-1) p.o. and maximum effect at 4 h post-dose. The level of anticonvulsant activity achieved correlated well with the blood concentrations of SB-271046 (EC(50) of 0.16 microM) and brain concentrations of 0.01-0.04 microM at C(max). These data, together with the observed anticonvulsant activity of other selective 5-HT(6) receptor antagonists, SB-258510 (10 mg kg(-1), 2-6 h pre-test) and Ro 04-6790 (1-30 mg kg(-1), 1 h pre-test), in the rat MEST test, suggest that the anticonvulsant properties of SB-271046 are likely to be mediated by 5-HT(6) receptors. Overall, these studies demonstrate that SB-271046 is a potent and selective 5-HT(6) receptor antagonist and is orally active in the rat MEST test. SB-271046 represents a valuable tool for evaluating the in vivo central function of 5-HT(6) receptors.

The effectiveness of topical treatment in discharging ears with in-dwelling ventilation tubes

The efficacy and tolerability of topical treatment (both drops and spray) in the treatment of otorrhoea in those ears with ventilation tubes in-situ was studied. Sixty patients were randomised into two treatment groups. One group used an antibacterial/anti-inflammatory ear drop preparation (Otosporin) and the other group a similar preparation administered as an ear spray (Otomize). A 'blind' clinical assessment was made one and three weeks after commencing treatment. Both treatments (drops and spray) significantly improved patients' symptoms and signs after one week (p < 0.001). The spray was significantly easier to administer (p < 0.01) and caused less discomfort on application (p < 0.02).

Biarylcarbamoylindolines are novel and selective 5-HT(2C) receptor inverse agonists: identification of 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]- 5-pyridyl]carbamoyl]-6-trifluoromethylindoline (SB-243213) as a potential antidepressant/anxiolytic agent

The evolution, synthesis, and biological activity of a novel series of 5-HT(2C) receptor inverse agonists are reported. Biarylcarbamoylindolines have been identified with excellent 5-HT(2C) affinity and selectivity over 5-HT(2A) receptors. In addition, (pyridyloxypyridyl)carbamoylindolines have been discovered with additional selectivity over the closely related 5-HT(2B) receptor. Compounds from this series are inverse agonists at the human cloned 5-HT(2C) receptor, completely abolishing basal activity in a functional assay. The new series have reduced P450 inhibitory liability compared to a previously described series of 1-(3-pyridylcarbamoyl)indolines (Bromidge et al. J. Med. Chem. 1998, 41, 1598) from which they evolved. Compounds from this series showed excellent oral activity in a rat mCPP hypolocomotion model and in animal models of anxiety. On the basis of their favorable biological profile, 32 (SB-228357) and 40 (SB-243213) have been selected for further evaluation to determine their therapeutic potential for the treatment of CNS disorders such as depression and anxiety.

Comparison of two blood pool contrast agents for 0.5-T MR angiography: experimental study in rabbits

PURPOSE

To evaluate two experimental blood pool agents for potential use in equilibrium phase abdominal magnetic resonance (MR) angiography.

MATERIALS AND METHODS

MR imaging at 0.5 T was performed in 37 rabbits before and after intravenous injection of a gadolinium-based blood pool contrast agent (SH L 643 A), superparamagnetic iron oxide blood pool agent (SH U 555 C), or gadopentetate dimeglumine. T1-weighted fast spoiled gradient-echo images from the renal arteries to below the iliac bifurcation were obtained. The aorta-to-tissue signal difference-to-noise ratio (SDNR) was measured over time.

RESULTS

Both blood pool agents yielded excellent demonstration of the rabbit abdominal aorta. At a dose of 0.1 mmol/kg, both provided a statistically significant increase in aorta-to-tissue SDNR in comparison with that achieved with gadopentetate dimeglumine (200% increase for SH L 643 A, 95% increase for SH U 555 C; P < .05). A 0.1 mmol/kg dose of SH L 643 A provided a 24% increase in SDNR relative to the increase with a 0.37 mmol/kg dose of gadopentetate dimeglumine. Time-dependent enhancement properties of the blood pool agents differed due to differences in elimination method.

CONCLUSION

Both blood pool agents were found to be promising contrast agents for 0.5-T MR angiography; however, their clinical applicability warrants further investigation. The gadolinium-based agent had several advantages over the iron oxide compound, including less T2* dephasing, lack of susceptibility artifacts, and fast renal elimination.

CYP3A4 drug interactions: correlation of 10 in vitro probe substrates

AIMS

Many substrates of cytochrome P450 (CYP) 3A4 are used for in vitro investigations of drug metabolism and potential drug-drug interactions. The aim of the present study was to determine the relationship between 10 commonly used CYP3A4 probes using modifiers with a range of inhibitory potency.

METHODS

The effects of 34 compounds on CYP3A4-mediated metabolism were investigated in a recombinant CYP3A4 expression system. Inhibition of erythromycin, dextromethorphan and diazepam N-demethylation, testosterone 6beta-hydroxylation, midazolam 1-hydroxylation, triazolam 4-hydroxylation, nifedipine oxidation, cyclosporin oxidation, terfenadine C-hydroxylation and N-dealkylation and benzyloxyresorufin O-dealkylation was evaluated at the apparent Km or S50 (for substrates showing sigmoidicity) value for each substrate and at an inhibitor concentration of 30 microM.

RESULTS

While all CYP3A4 probe substrates demonstrate some degree of similarity, examination of the coefficients of determination, together with difference and cluster analysis highlighted that seven substrates can be categorized into two distinct substrate groups. Erythromycin, cyclosporin and testosterone form the most closely related group and dextromethorphan, diazepam, midazolam and triazolam form a second group. Terfenadine can be equally well placed in either group, while nifedipine shows a distinctly different relationship. Benzyloxyresorufin shows the weakest correlation with all the other CYP3A4 probes. Modifiers that caused negligible inhibition or potent inhibition are generally comparable in all assays, however, the greatest variability is apparent with compounds causing, on average, intermediate inhibition. Modifiers of this type may cause substantial inhibition, no effect or even activation depending on the substrate employed.

CONCLUSIONS

It is recommended that multiple CYP3A4 probes, representing each substrate group, are used for the in vitro assessment of CYP3A4-mediated drug interactions.

Amlodipine lowers blood pressure without affecting cerebral blood flow as measured by single photon emission computed tomography in elderly hypertensive subjects

AIM

To evaluate the effect of amlodipine on blood pressure and cerebral blood flow in elderly subjects with mild to moderate hypertension.

METHODS

A double-blind, parallel group study of 26 patients. After a 4-week placebo run-in period, amlodipine (5-10 mg) or matching placebo was given once daily for 8 weeks.

RESULTS

Amlodipine significantly reduced blood pressure compared with baseline. Diastolic blood pressure was significantly reduced by amlodipine compared with placebo (P< 0.02 to P< 0.01). Ambulatory blood pressure monitoring showed that blood pressure control was sustained over the 24-h dosing interval. Relative regional cerebral blood flow, assessed using single photon emission computed tomography, was not significantly affected by amlodipine. Three placebo patients, but no amlodipine patients, withdrew because of adverse events.

CONCLUSION

Amlodipine was a well-tolerated and effective antihypertensive agent, and did not reduce regional cerebral blood flow in elderly hypertensive patients.

Characterization of the cytochrome P450 enzymes involved in the in vitro metabolism of rosiglitazone

AIMS

To identify the human cytochrome P450 enzyme(s) involved in the in vitro metabolism of rosiglitazone, a potential oral antidiabetic agent for the treatment of type 2 diabetes-mellitus. Method The specific P450 enzymes involved in the metabolism of rosiglitazone were determined by a combination of three approaches; multiple regression analysis of the rates of metabolism of rosiglitazone in human liver microsomes against selective P450 substrates, the effect of selective chemical inhibitors on rosiglitazone metabolism and the capability of expressed P450 enzymes to mediate the major metabolic routes of rosiglitazone metabolism. Result The major products of metabolism following incubation of rosiglitazone with human liver microsomes were para-hydroxy and N-desmethyl rosiglitazone. The rate of formation varied over 38-fold in the 47 human livers investigated and correlated with paclitaxel 6alpha-hydroxylation (P<0.001). Formation of these metabolites was inhibited significantly (>50%) by 13-cis retinoic acid, a CYP2C8 inhibitor, but not by furafylline, quinidine or ketoconazole. In addition, both metabolites were produced by microsomes derived from a cell line transfected with human CYP2C8 cDNA. There was some evidence for CYP2C9 playing a minor role in the metabolism of rosiglitazone. Sulphaphenazole caused limited inhibition (<30%) of both pathways in human liver microsomes and microsomes from cells transfected with CYP2C9 cDNA were able to mediate the metabolism of rosiglitazone, in particular the N-demethylation pathway, albeit at a much slower rate than CYP2C8. Rosiglitazone caused moderate inhibition of paclitaxel 6alpha-hydroxylase activity (CYP2C8; IC50=18 microm ), weak inhibition of tolbutamide hydroxylase activity (CYP2C9; IC50=50 microm ), but caused no marked inhibition of the other cytochrome P450 activities investigated (CYP1A2, 2A6, 2C9, 2C19, 2D6, 2E1, 3A and 4A). Conclusion CYP2C8 is primarily responsible for the hydroxylation and N-demethylation of rosiglitazone in human liver; with minor contributions from CYP2C9.

Radionuclide therapy in the United Kingdom in 1995

A postal survey was conducted in the UK in 1996 to determine the facilities available and the level of activity at centres where radionuclide therapy was practised in 1995. A response rate of 79% indicated that 102 centres were providing radionuclide therapy, with 339 clinicians holding ARSAC certificates, 57% of whom were clinical oncologists. There were 84 beds available for therapy and the total number of patients treated was 11,435. Patient numbers treated by disease or procedure were: haematological, 569 (5%); benign thyroid disease, 9059 (79.2%); malignant thyroid disease, 911 (8%); bone pain palliation, 425 (3.5%); radiosynovectomy, 321 (2.8%); neuroendocrine tumour therapy, 76 (0.7%); and intra-cavitary, 56 (0.5%). The total amounts of activity of individual radiopharmaceuticals administered in GBq were: 131I, 16,695; 90Y-colloid, 88; 32P, 94.6; 131I-MIBG, 646; 89Sr, 57.6; and 186Rh-HEDP, 16. Average waiting times varied from 1 to 5 weeks, with a range of 0 to 52 weeks for some therapies. Most centres had the services of a physicist available. Compared with teaching hospitals, the 61 district hospitals had fewer allocated beds, but treated almost half of all patients. The numbers of therapies undertaken were increasing at many centres and this has implications for long-term planning.

Aldehyde oxidase-catalysed oxidation of methotrexate in the liver of guinea-pig, rabbit and man

Although 7-hydroxymethotrexate is a major metabolite of methotrexate during high-dose therapy, negligible methotrexate-oxidizing activity has been found in-vitro in the liver in man. The goals of this study were to determine the role of aldehyde oxidase in the metabolism of methotrexate to 7-hydroxymethotrexate in the liver and to study the effects of inhibitors and other substrates on the metabolism of methotrexate. Methotrexate, (+/-)-methotrexate and (-)-methotrexate were incubated with partially purified aldehyde oxidase from the liver of rabbit, guinea-pig and man and the products analysed by HPLC. Rabbit liver aldehyde oxidase was used for purposes of comparison. In-vitro aldehyde oxidase from the liver of man catalyses the oxidation of methotrexate to 7-hydroxymethotrexate, but the turnover is low. However, formation of 7-hydroxy-methotrexate from all forms of methotrexate by the liver in guinea-pig and man was significantly inhibited in the presence of 100 microM menadione and chlorpromazine, potent inhibitors of aldehyde oxidase. Allopurinol (100 microM) had a negligible inhibitory effect on liver aldehyde oxidase from guinea-pig and man. Allopurinol is a xanthine oxidase inhibitor. The production of 7-hydroxymethotrexate was enhanced in the presence of allopurinol. Although aldehyde oxidase is also responsible for some of this conversion, it is also possible that the closely related xanthine oxidase is responsible for the formation of 7-hydroxymethotrexate. By employing potent selective inhibitors of aldehyde oxidase, menadione and chlorpromazine, we have demonstrated for the first time that liver aldehyde oxidase from man is minimally involved in methotrexate oxidation.

Quality assurance in myocardial perfusion tomography: a collaborative BNCS/BNMS audit programme. British Nuclear Cardiology Society/British nuclear Medicine Society

The aim of this study was to assess the status of acquisition and reporting of myocardial perfusion tomography in the UK. Centres were asked to provide an expert panel with clinical and technical information, digital and hard copy of raw data and reconstructed tomograms, as well as their report (optional) for five randomly selected studies. Ninety studies were received from 18 centres; report text was provided for 66 studies. Six parameters (stress technique, radiopharmaceutical usage, image acquisition and processing, report images and text) were scored as good (2), adequate (1) or poor (0) by consensus. Centres received the quality scores for each study and a consensus clinical report from the panel. Stress technique was scored as inadequate in 10 (11%) studies, radiopharmaceutical usage and image acquisition as inadequate in 5 (6%) studies, image processing as inadequate in 8 (10%) studies and report images as inadequate in 2 (3%) studies. Report text was felt to be inadequate in 21 of 66 (32%) studies; in 11 of these (52%), the report text was judged to be incorrect and in 10 (48%) it was essentially correct but misleading because of poor phraseology. The mean quality score per study was 1.3 (range 0.5-2.0). Seventeen of 88 (19%) studies scored less than 1.0 and were considered to be of poor quality. In conclusion, a large variation in standards of myocardial perfusion tomography was seen. Data acquisition was generally satisfactory, but 32% of reports were inadequate.

Nuclear medicine and endocrinology: diagnosis and management

Most endocrine disorders result in a disturbance of function, so radionuclide imaging provides a unique view of disordered function which complements the structural information provided by other imaging techniques. Nuclear medicine is used in the management of benign and malignant thyroid, parathyroid and adrenal disorders both diagnostically and by identifying suitable patients for radionuclide therapy.

Sexually transmitted diseases among teenagers in England and Wales

A profile of sexually transmitted diseases (STDs) and HIV infections among teenagers in England and Wales was obtained from reports of newly diagnosed STDs among teenagers attending genitourinary medicine (GUM) clinics in 1995, laboratory reports of newly diagnosed HIV infections between 1985 when reporting began and the end of 1995, and the prevalence of HIV (unlinked anonymous programme) among teenagers attending genitourinary medicine clinics and antenatal clinics in 1994 and 1995. STD reports were analysed by sex, age group, and place of residence of patients--whether in the NHS Thames regions or elsewhere in England and Wales. High rates of STDs were reported in teenagers, particularly in girls. The incidences of gonorrhoea, chlamydia infection, and first attack genital wart infections were higher in teenage girls than in any other age group. Boys under 16 years of age had substantially higher rates of infection with all STDs in the Thames regions than elsewhere. Rates of gonorrhoea in teenagers of both sexes in the Thames regions were more than twice those in the rest of the country. Infection rates for genital herpes, and chlamydia in girls, were also higher in the Thames regions, although the geographical differences were less marked. The seroprevalence of HIV among heterosexual teenagers was very low. In contrast, 226 HIV infections among teenage boys had probably been acquired through sexual intercourse with other males. Unlinked anonymous testing revealed HIV antibody in 7.5% of routinely collected serology specimens taken from teenage homosexual or bisexual males attending GUM clinics in London. The high rates of STDs among teenage girls and all teenagers in the Thames regions make these groups a high priority for sexual health promotion, with special consideration given to homo/bisexual male teenagers. Detailed surveillance of risk factors for STDs, and further studies of teenage sexual behaviour will help to effectively target resources to improve the sexual health of teenagers in England and Wales.

CYP4A1 gene transfection studies and the peroxisome proliferator-activated receptor: development of a high-throughput assay to detect peroxisome proliferators

An in vitro reporter gene assay has been established to examine cytochrome P4504A1 (CYP4A1) induction. A response element from the upstream region of the rat CYP4A1 gene containing a peroxisome proliferator response element (PPRE) has been linked to the chloramphenicol acetyl-transferase (CAT) gene in a reporter vector (1). This CYP4A1 reporter construct has been co-transfected into human HepG2 cells in the presence and absence of expression vectors encoding the transcription factors PPAR alpha and RXR alpha. The assay employs calcium phosphate-DNA co-precipitate mediated transfection. Reporter gene products have been quantitated using chemiluminescent based assays. We have shown that, in the presence of PPAR alpha, the above CYP4A1 construct is transcriptionally activated by a range of structurally different peroxisome proliferators including Wy-14,643, ciprofibrate, clofibric acid and nafenopin. Our future efforts will focus on the establishment of a high-throughput assay for the detection of peroxisome proliferators. Such an assay would provide an invaluable in vitro test for the screening of developmental drug candidates prior to in vivo studies.

In vitro identification of the human cytochrome P450 enzymes involved in the metabolism of R(+)- and S(-)-carvedilol

Both the R(+) and the S(-) enantiomers of carvedilol were metabolized in human liver microsomes primarily to 4'- (4OHC) and 5'-(5OHC) hydroxyphenyl, 8-hydroxy carbazolyl (8OHC) and O-desmethyl (ODMC) derivatives. The S(-) enantiomer was metabolized faster than the R(+) enantiomer although the same P450 enzymes seemed to be involved in each case. A combination of multivariate correlation analysis, the use of selective inhibitors of P450, and microsomes from human lymphoblastoid cells expressing various human P450s enabled phenotyping of the enzymes involved in the oxidative metabolism of carvedilol. CYP2D6 was primarily responsible for 4OHC and 5OHC production, although considerable activity was observed in a CYP2D6 poor metabolizer liver and the variability of these activities across a human liver bank was not high. There was some evidence that CYP2E1, CYP2C9, and CYP3A4 were also involved in the production of these metabolites. CYP1A2 was primarily responsible for the 8OHC pathway with additional contributions from CYP3A4. The ODMC was clearly associated with CYP2C9 with some evidence for the partial involvement of CYP2D6, CYP1A2, and CYP2E1. With its complex P450 phenotype pattern and the known contribution of non-oxidative pathways of elimination, the activity (or lack of activity) of any particular P450 would have a limited influence on the disposition of carvedilol in an individual.

The development of regional nuclear medicine audit in south Thames

A programme of audit, including clinical audit, organizational audit and patient/clinician satisfaction surveys, has been implemented in nuclear medicine departments throughout the South Thames Regional Health Authority (RHA). The clinical topics which have been audited include. ventilation-perfusion lung imaging, bone imaging, liver imaging, thyroid imaging and renal static DMSA imaging. Guidelines have been set for nuclear medicine practice in each of these areas against which further audit can be performed. Organizational audits have been performed in 10 nuclear medicine departments in the South Thames RHA and a confidential report supplied to the head of each department, consisting of findings and recommendations. A programme of re-audit has also commenced. The main findings have been a lack of facilities and space. Patient satisfaction surveys have been implemented in nine departments and a high level of patient satisfaction has been demonstrated. A clinical satisfaction survey has been implemented in 13 departments. It is hoped to continue this successful programme of audit to improve nuclear medicine practice by closing audit loops.

In vitro oxidation of famciclovir and 6-deoxypenciclovir by aldehyde oxidase from human, guinea pig, rabbit, and rat liver

Famciclovir, a 9-substituted guanine derivative, is a new antiviral agent which undergoes rapid hydrolysis and oxidation in man to yield the active antiherpes agent, penciclovir. Studies with human liver cytosol have indicated that the oxidation of the penultimate metabolite, 6-deoxypenciclovir, to penciclovir is catalyzed by the molybdenum hydroxylase, aldehyde oxidase. In the present study the oxidation of famciclovir and 6-deoxypenciclovir with partially purified molybdenum hydroxylases from human, guinea pig, rabbit, and rat livers and bovine milk xanthine oxidase has been investigated. Famciclovir and 6-deoxypenciclovir were oxidized predominantly to 6-oxo-famciclovir and penciclovir, respectively, by human, guinea pig, and rat liver aldehyde oxidase. Small amounts of 8-oxo and 6,8-dioxo-metabolites were also formed from each substrate. Famciclovir and 6-deoxypenciclovir were good substrates for rabbit liver aldehyde oxidase but, in each case, two major metabolites were formed. 6-Deoxypenciclovir was converted to penciclovir and 8-oxo-6-deoxypenciclovir in approximately equal quantities; famciclovir was oxidized to 6-oxo-famciclovir and a second metabolite which, on the basis of chromatographic and UV spectral data, was thought to be 8-oxo-famciclovir. Two groups of Sprague Dawley rats were identified; those containing hepatic aldehyde oxidase and xanthine oxidase and those with only xanthine oxidase. These have been designated AO-active and AO-inactive rats, respectively. Famciclovir was not oxidized by enzyme from AO-inactive rats or bovine milk xanthine oxidase although 6-deoxypenciclovir was slowly converted to penciclovir by rat liver or milk xanthine oxidase. Inhibitor studies showed in human, guinea pig, and rabbit liver that xanthine oxidase did not contribute to the oxidation of famciclovir and 6-deoxypenciclovir; thus it is proposed that drug activation in vivo would be catalyzed solely by aldehyde oxidase.

In vitro identification of the P450 enzymes responsible for the metabolism of ropinirole

The in vitro metabolism of ropinirole was investigated with the aim of identifying the cytochrome P450 enzymes responsible for its biotransformation. The pathways of metabolism after incubation of ropinirole with human liver microsomes were N-despropylation and hydroxylation. Enzyme kinetics demonstrated the involvement of at least two enzymes contributing to each pathway. A high affinity component with a K(M) of 5-87 microM and a low affinity component with a K(M) of approximately two orders of magnitude greater were evident. The high affinity component could be abolished by pre-incubation of the microsomes with furafylline. Additionally, incubation of ropinirole with microsomes derived from CYP1A2 transfected cells readily produced the N-despropyl and hydroxy metabolites. Some inhibition of ropinirole metabolism was also observed with ketoconazole, indicating a minor contribution by CYP3A. Multivariate correlation data were consistent with the involvement of the cytochrome P450 enzymes 1A2 and 3A in the metabolism of ropinirole. Thus, it could be concluded that the major P450 enzyme responsible for ropinirole metabolism at lower (clinically relevant) concentrations is CYP1A2 with a contribution from CYP3A, particularly at higher concentrations.

Registration bone scan in the evaluation of wrist pain

We assessed the value of bone scintigraphy combined with X-ray registration for the diagnosis and management of wrist pain in 65 patients. Studies were reported independently by two observers before and after registration. Registration improved localization of scan abnormalities in 53% (observer 1) and 61% (observer 2). In these patients, the bone scan contributed to the diagnosis independently of the X-ray in 37% and the management was altered in 31%. The value of the bone scan in the early diagnosis and management of wrist pain is increased when it is registered with X-rays.

SPECT bone scintigraphy of anterior cruciate ligament injury

This retrospective analysis of SPECT bone scans of the knee was undertaken to define typical bone scan appearances and to assess the sensitivity of this method. We looked at 14 patients, mostly with chronic knee pain, who had anterior cruciate ligament (ACL) tears detected by MRI.

METHOD

Of the 14 patients, 10 were referred for bone scanning following injury and 4 complained of chronic knee pain without injury. Planar scans were performed 4 hr after the injection of 750 MBq of 99mTc-MDP. Tomographic images were obtained by a 64 x 20-sec acquisition over 360 degrees using a high-resolution collimator. MRI imaging included axial and sagittal, T1 weighted and coronal fast field echo (FFE) sequences. Ten patients also had arthroscopy performed.

RESULTS

MRI scans showed 6 lone ACL tears and 8 combined with other ligamentous injuries. SPECT scans showed abnormalities in 10 patients in the region of ACL insertions but only 4 planar studies were abnormal. SPECT identified focal activity at the upper (n = 8) or lower (n = 2) insertion of the ACL. Six of 10 arthroscopies confirmed ACL tears, 2 complete and 4 partial. Overall, agreement was found with MRI in 10 of 14 cases and in 8 of 10 with arthroscopy. Abnormalities were identified in 10 of 11 regions of other ligament or bone injury identified by MRI.

CONCLUSION

SPECT bone scanning of the knee is superior to planar imaging in detecting ACL injury and is a sensitive technique. Focal activity may be seen at either end of ACL attachment but more commonly at the upper femoral insertion. Knee SPECT may be a valuable examination in suspected ACL injury, particularly if MRI is not available, is equivocal or where clinical signs are absent.

Landscape-Level Ecological Regions: Linking State-Level Ecoregion Frameworks with Stream Habitat Classifications

Regionalization is a form of spatial classification, where boundaries are drawn around areas that are relatively homogeneous in landscape characteristics. The process of delineating ecological regions, or ecoregions, includes the analysis of ecosystem structure. To date, ecoregions have been developed at national and state scales for research and resource management. Stream classification is another method to order the variability of aquatic habitats that spans spatial scales from microhabitat to valley segment. In this study, landscape-level ecoregions are developed for the upper Grande Ronde River basin in northeastern Oregon, 3000 sq km in area. The ecoregion framework presented here is proposed to bridge the gap between stream habitat and state-level ecoregion classifications. Classification at this scale is meant to address issues of management at local scales: to aid in sampling design, in extrapolation of the results of site-specific studies, and in the development of best management practices that are more predictive of ecosystem response than current methods.

Technetium-99m-DMSA studies in pediatric urinary infection

Urinary tract infection (UTI) is a common condition in children and may lead to renal scarring with a risk of later hypertension and renal insufficiency. We made a cross-sectional study of the 99mTc-DMSA findings in 496 children referred for following symptomatic UTI to a Department of Nuclear Medicine and we categorized the results, to provide a framework for further study.

METHOD

A standard 99mTc-DMSA protocol was used to study 496 children (157 males, 339 females) aged from birth to 14 yr. Findings were classified according to the image appearance and relative function of each kidney. These were related to age, sex, history and timing of UTI and the results on micturating cysto-urethrography (MCU).

RESULTS

Images were normal, with function within limits (45%-50% in one kidney), in approximately half the boys and girls studied. The other images were classified as equivocal in 68 children, abnormal unilaterally in 105 and bilaterally in 76, and they were subdivided according to the image appearance. No image changes could be identified that were specifically associated with acute UTI. Diffuse change alone was uncommon. A high proportion of abnormal images was found in infant boys, older girls with recurrent UTI and those children with vesico-ureteric reflux (VUR). Of the bilateral abnormal images, 98% were seen in children with VUR.

CONCLUSION

Our findings suggest that infective renal change may be superimposed on underlying congenital lesions (perhaps detectable antenatally) or may be acquired following UTI in the presence of reflux and are thus potentially preventable. This study also suggests that VUR is almost certain to have occurred in a child who has bilateral abnormal 99mTc-DMSA images following UTI and is also commonly present in those with definite unilateral defects.

Radiation doses to patient's relatives following radioiodine therapy

A total of 10 volunteers were monitored for radiation doses, whose spouses were given radio-iodine (131I) orally. Nine of the spouses were given radio-iodine for Graves' disease and one for thyroid carcinoma. It was found that the highest radiation dose received by the volunteer was only 13.5% of the annual dose limit for individual members of the public. Hence, patients treated with radio-iodine do not pose a significant radiation hazard to the public.

Technetium-99m tetrofosmin myocardial perfusion scan: comparison of 1-day and 2-day protocols

Nineteen patients with angina were recruited in this study for comparison of two 1-day protocols (stress-4h rest and rest-4-h stress) and a 2-day protocol of technetium-99m tetrofosmin single-photon emission tomography (SPET). All of them underwent coronary angiography before or after the study. Exercise stress-rest study and rest-stress study were performed on two consecutive days. Delayed imaging was performed before the rest injection on the 2nd day. The stress study on the 1st day and rest study on the 2nd day were considered as a 2-day protocol. The 1-day stress-rest protocol had a sensitivity of 100% (18/18) and an accuracy of 100% (19/19) in diagnosing ischaemic heart disease. The 1-day rest-stress protocol had a sensitivity of 94.4% (17/18) and an accuracy of 94.7% (18/19). These differences were not statistically significant (P=0.5 for sensitivity and accuracy). There was also no statistically significant difference between the two protocols in the diagnosis of ischaemic heart disease in individual artery territories. For the left descending artery, sensitivity was 88.2% (15/17) vs 76.5% (13/17) (P=0.48) for the stress-rest and rest-stress studies respectively. For the left circumflex artery, sensitivity was 90% (9/10) vs 80% (8/10) (P=1) and specificity was 66.7% (6/9) vs 77.8% (7/9) (P=1) respectively. For the right coronary artery, the sensitivity was 100% (16/16) vs 94% (15/16) (P=1) respectively, while the specificity was 33.3% (1/3) in both studies. Three hundred and forty-two myocardial segments were analysed. The stress-rest and 2-day protocols showed no statistically significant difference in the overall identification of segments with reversible ischaemia (48/141 segments vs 48/141 segments) or in respect of individual artery territories. There was also no significant difference in the identification of reversible ischaemic segments between the rest-stress and 2-day protocols (48/141 segments vs 34/135 segments, P=0.14). Abdominal activity was seen in 36 studies and interpretation was affected in five of them. Five patients with 24-h delayed images were evaluated and 24 segments with washout were identified. It is concluded that 99mTc-tetrofosmin is a valuable new tracer in the investigation of ischaemic heart disease. The 1-day stress-rest protocol is as good as the 1-day rest-stress protocol in diagnosing coronary heart disease. The 1-day protocols and the 2-day protocol display no difference in identifying segments with reversible ischaemia.

Rapid screening of taxol metabolites in human microsomes by liquid chromatography/electrospray ionization-mass spectrometry

Liquid chromatography with an electrospray ionization (ESI) interface has been applied to study the anticancer drug taxol and its metabolites after incubation with human hepatic microsomes. The parent drug and its metabolites were monitored in the positive-ionization mode. Since ESI gave only quasi-molecular ions for taxol and its analogues, collision-induced dissociation experiments were carried out in order to generate fragment ions, by increasing the cone voltage at the ESI source. The product-ion mass spectra of taxol and its metabolites contained diagnostic fragment ions, which enabled the presence of hydroxylated and deacetylated metabolites of taxol to be established.

An evaluation of 99Tcm-DMSA SPET with three-dimensional reconstruction in 68 patients with varied renal pathology

Sixty-eight patients (135 kidneys) with varied renal pathology were evaluated with 99Tcm-dimercaptosuccinic acid (DMSA) single photon emission tomography (SPET) to determine whether it is possible to detect more renal abnormalities and to reduce the number of false-positives due to anatomical variants when compared with planar imaging. The patients ranged in age from 1 to 78 years and their pathologies included urinary tract infection (n = 50), space occupying lesions (n = 5), calculi (n = 4), hypertension (n = 4) and others (n = 5). Planar scans were performed 3 h after the injection of 80 MBq of 99Tcm-DMSA and a 64 x 20 s acquisition over 360 degrees was used for SPET. High-resolution collimation was used for both. Slices were displayed as transaxial, coronal and sagittal and/or oblique sagittal in the plane of the kidney. Three-dimensional (3D) images were formed by volume rendering. Each kidney was divided into three regions and each region scored separately for the presence of an abnormality. Planar scans were reviewed alone and then in conjunction with SPET and 3D images. Planar imaging detected 95 abnormal regions compared with 103 using SPET. SPET reduced the number of equivocal regions in 8 (12%) patients. The diagnosis was altered by SPET in 17 (4%) regions in 14 (21%) patients. SPET and 3D 99Tcm-DMSA allow more abnormalities to be detected but also allow more specific definition of apparent abnormalities on planar imaging.

Determination of P4501A2 activity in human liver microsomes using [3-14C-methyl]caffeine

1. Caffeine N3-demethylation, the major pathway of caffeine metabolism in man, is mediated by P4501A2. The carbon of the methyl group lost during N3-demethylation is eliminated as carbon dioxide in vivo, or as formaldehyde and formic acid in vitro. 2. A simple and sensitive assay was developed to quantify the [14C]formaldehyde/[14C]formic acid produced following incubation of human microsomes with [3-14C-methyl]caffeine. This assay, using solid-phase extraction, enables quantitation of [14C]formaldehyde/[14C]formic acid with acceptable precision (within 5%) and accuracy (within 10%). 3. Typical Km and Vmax for the N3-demethylation of caffeine were determined by this assay to be 500 (range 220-1200) microM, and 250 (range 115-450) pmol.mg protein-1.min-1 respectively. 4. The N3-demethylation activity determined in microsomes from a range of human livers correlated significantly with other P4501A2 activities (p < 0.001) and was inhibited (> 95%) by furafylline. In addition, caffeine N3-demethylation was catalysed by microsomes from cell lines transfected with human P4501A2 cDNA. 5. This assay, for quantitation of [14C]formaldehyde/[14C]formic acid in human liver microsomes, is suitable for use in in vitro drug interaction studies as a probe for P4501A2 activity.