Referencing strategies and techniques in stable isotope ratio analysis

Stable isotope ratios are reported in the literature in terms of a deviation from an international standard (delta-values). The referencing procedures, however, differ from instrument to instrument and are not consistent between measurement facilities. This paper reviews an attempt to unify the strategy for referencing isotopic measurements. In particular, emphasis is given to the importance of identical treatment of sample and reference material ('IT principle'), which should guide all isotope ratio determinations and evaluations. The implementation of the principle in our laboratory, the monitoring of our measurement quality, the status of the international scales and reference materials and necessary correction procedures are discussed.

Processing of generator-produced 68Ga for medical application

The (68)Ge/(68)Ga generator provides an excellent source of positron-emitting (68)Ga. However, newly available "ionic" (68)Ge/(68)Ga radionuclide generators are not necessarily optimized for the synthesis of (68)Ga-labeled radiopharmaceuticals. The eluates have rather large volumes, a high concentration of H(+) (pH of 1), a breakthrough of (68)Ge, increasing with time or frequency of use, and impurities such as stable Zn(II) generated by the decay of (68)Ga, Ti(IV) as a constituent of the column material, and Fe(III) as a general impurity.

METHODS

We have developed an efficient route for the processing of generator-derived (68)Ga eluates, including the labeling and purification of biomolecules. Preconcentration and purification of the initial generator eluate are performed using a miniaturized column with organic cation-exchanger resin and hydrochloric acid/acetone eluent. The purified fraction was used for the labeling of nanomolar amounts of octreotide derivatives either in pure aqueous solution or in buffers.

RESULTS

Using the generator post-eluate processing system, >97% of the initially eluated (68)Ga activity was obtained within 4 min as a 0.4-mL volume of a hydrochloric acid/acetone fraction. The initial amount of (68)Ge(IV) was decreased by a factor of 10(4), whereas initial amounts of Zn(II), Ti(IV), and Fe(III) were reduced by factors of 10(5), 10(2), and 10, respectively. The processed (68)Ga fraction was directly transferred to solutions containing labeling precursors-for example, DOTA-dPhe(1)-Tyr(3)-octreotide (DOTATOC) (DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid). Labeling yields of >95% were achieved within 10 min. Overall yields reached 70% at 20 min after generator elution relative to the eluted (68)Ga activity, not corrected for decay. Specific activities of (68)Ga-DOTATOC were 50 MBq/nmol using a standard protocol, reaching 450 MBq/nmol under optimized conditions.

CONCLUSION

Processing on a cation-exchanger in hydrochloric acid/acetone media represents an efficient strategy for the concentration and purification of generator-derived (68)Ga(III) eluates. The developed scheme guarantees high yields and safe preparation of injectable (68)Ga-labeled radiopharmaceuticals for routine application and is easy to automate. Thus, it is being successfully used in clinical environments and might contribute to a new direction for clinical PET, which could benefit significantly from the easy and safe availability of the radionuclide generator-derived metallic positron-emitter (68)Ga.

Ionization enhancement in atmospheric pressure chemical ionization and suppression in electrospray ionization between target drugs and stable-isotope-labeled internal standards in quantitative liquid chromatography/tandem mass spectrometry

The phenomena of ionization suppression in electrospray ionization (ESI) and enhancement in atmospheric pressure chemical ionization (APCI) were investigated in selected-ion monitoring and selected-reaction monitoring modes for nine drugs and their corresponding stable-isotope-labeled internal standards (IS). The results showed that all investigated target drugs and their co-eluting isotope-labeled IS suppress each other's ionization responses in ESI. The factors affecting the extent of suppression in ESI were investigated, including structures and concentrations of drugs, matrix effects, and flow rate. In contrast to the ESI results, APCI caused seven of the nine investigated target drugs and their co-eluting isotope-labeled IS to enhance each other's ionization responses. The mutual ionization suppression or enhancement between drugs and their isotope-labeled IS could possibly influence assay sensitivity, reproducibility, accuracy and linearity in quantitative liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). However, calibration curves were linear if an appropriate IS concentration was selected for a desired calibration range to keep the response factors constant.

Quantitative mouse brain proteomics using culture-derived isotope tags as internal standards

An important challenge for proteomics is to be able to compare absolute protein levels across biological samples. Here we introduce an approach based on the use of culture-derived isotope tags (CDITs) for quantitative tissue proteome analysis. We cultured Neuro2A cells in a stable isotope-enriched medium and mixed them with mouse brain samples to serve as internal standards. Using CDITs, we identified and quantified a total of 1,000 proteins, 97-98% of which were expressed in both mouse whole brain and Neuro2A cells. CDITs also allow comprehensive and absolute protein quantification. Synthetic unlabeled peptides were used to quantify the corresponding proteins labeled with stable isotopes in Neuro2A cells, and the results were used to obtain the absolute amounts of 103 proteins in mouse whole brain. The expression levels correlated well with those in Neuro2A cells. Thus, the use of CDITs allows both relative and absolute quantitative proteome studies.

The preparation of DTPA-coupled antibodies radiolabeled with metallic radionuclides: an improved method

Isotopes of iodine are often employed as radiolabels for antibodies used in radioimmunodetection studies in which tumor localization is determined by external imaging. Because of drawbacks associated with the use of these isotopes, alternative labeling methods have been considered; such as covalently attaching strong chelators so that the coupled protein may be radiolabeled with metallic radionuclides by chelation. We have developed a method of coupling the strong chelator diethylenetriaminepentaacetic acid (DTPA) which is simple, efficient, and superior to reported methods. Using the cyclic anhydride, coupling to IgG antibody is about 75% efficient and is completed in less than 1 min at neutral pH. Because the concentration of hydrolytic products is small, the coupled protein is rapidly purified for use or storage. Labeling of the protein is also accomplished rapidly and the labeled product has been shown to be stable both in vitro and in vivo.

Biological monitoring and biochemical effect monitoring of exposure to polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous carcinogenic substances to which man is exposed in the environment and at certain workplaces. Estimation of the resulting health risk is therefore of great occupational-medical and environmental-medical importance. Determination of the DNA and protein adducts of PAHs is the most suitable way of estimating this risk. The analytical methods used thus far, above all, 32P postlabeling, immunoassays, and synchronous fluorescence spectroscopy, are, however, too nonspecific; therefore, the results lack accuracy and are not comparable with one another. Only the use of very specific methods of instrumental analysis [above all, high-performance liquid chromatography (HPLC) and gas chromatography/ mass spectrometry (GC/MS)] can counteract this deficit. However, these methods can successfully be used mainly to determine the protein adducts of PAHs. Hemoglobin adducts, for example, do not have repair mechanisms like DNA adducts. They therefore occur in higher concentrations and can thus be analytically detected more easily. At present, mainly the monohydroxylated metabolites of PAHs are being determined in urine with great success. Using specific enrichment methods and HPLC with fluorescence detection it is even possible today to determine the internal PAH exposure of the general population. The detection limits lie in the lower nanogram-per-liter range. In view of the importance of this group of substances, determination of PAH adducts and the detection of their metabolites in urine will remain at the center of future occupational-medical and environmental-medical/toxicological research. In general, the lack of reference substances must be lamented.

Standardization approaches in absolute quantitative proteomics with mass spectrometry

Mass spectrometry-based approaches have enabled important breakthroughs in quantitative proteomics in the last decades. This development is reflected in the better quantitative assessment of protein levels as well as to understand post-translational modifications and protein complexes and networks. Nowadays, the focus of quantitative proteomics shifted from the relative determination of proteins (ie, differential expression between two or more cellular states) to absolute quantity determination, required for a more-thorough characterization of biological models and comprehension of the proteome dynamism, as well as for the search and validation of novel protein biomarkers. However, the physico-chemical environment of the analyte species affects strongly the ionization efficiency in most mass spectrometry (MS) types, which thereby require the use of specially designed standardization approaches to provide absolute quantifications. Most common of such approaches nowadays include (i) the use of stable isotope-labeled peptide standards, isotopologues to the target proteotypic peptides expected after tryptic digestion of the target protein; (ii) use of stable isotope-labeled protein standards to compensate for sample preparation, sample loss, and proteolysis steps; (iii) isobaric reagents, which after fragmentation in the MS/MS analysis provide a final detectable mass shift, can be used to tag both analyte and standard samples; (iv) label-free approaches in which the absolute quantitative data are not obtained through the use of any kind of labeling, but from computational normalization of the raw data and adequate standards; (v) elemental mass spectrometry-based workflows able to provide directly absolute quantification of peptides/proteins that contain an ICP-detectable element. A critical insight from the Analytical Chemistry perspective of the different standardization approaches and their combinations used so far for absolute quantitative MS-based (molecular and elemental) proteomics is provided in this review.

Standardisation and decay data of 177Lu and 188Re

The activity values of 177Lu and 188Re standard sources were measured using the 4pibeta-gamma-coincidence method and by liquid scintillation counting. The X- and gamma-ray emission probabilities per disintegration were determined by means of photon spectrometry with calibrated Ge and Si(Li) detectors and using the pertinent activity values. The half-lives were measured with ionization chambers, yielding T(1/2)(177Lu) = 6.646(5) d and T(1/2)(188Re) = 0.70848(9) d.

On the origins and development of the (32)P-postlabelling assay for carcinogen-DNA adducts

The (32)P-postlabelling method for the analysis of carcinogen-DNA adducts originated 30years ago from Baylor College of Medicine in Houston and was the work of a team comprised of Kurt and Erica Randerath, Ramesh Gupta and Vijay Reddy. With subsequent modifications and developments, it has become a highly sensitive and versatile method for the detection of DNA adducts that has been applied in a wide range of human, animal and in vitro studies. These include monitoring human exposure to environmental and occupational carcinogens, investigating genotoxicity of chemicals, elucidating pathways of metabolic activation of carcinogens, mechanistic studies of DNA repair, analysing the genotoxicity of complex mixtures and in ecotoxicology studies. Its use has been instrumental in providing new clues to the aetiology of some cancers and in identifying a new human carcinogen.

Impact of Sample Matrix on Accuracy of Peptide Quantification: Assessment of Calibrator and Internal Standard Selection and Method Validation

Protein quantification based on peptides using LC-MS/MS has emerged as a promising method to measure biomarkers, protein drugs, and endogenous proteins. However, the best practices for selection, optimization, and validation of the quantification peptides are not well established, and the influence of different matrices on protein digestion, peptide stability, and MS detection has not been systematically addressed. The aim of this study was to determine how biological matrices affect digestion, detection, and stability of peptides. The microsomal retinol dehydrogenase (RDH11) and cytosolic soluble aldehyde dehydrogenases (ALDH1As) involved in the synthesis of retinoic acid (RA) were chosen as model proteins. Considerable differences in the digestion efficiency, sensitivity, and matrix effects between peptides were observed regardless of the target protein's subcellular localization. The precision and accuracy of the quantification of RDH11 and ALDH1A were affected by the choice of calibration and internal standards. The final method using recombinant protein calibrators and stable isotope labeled (SIL) peptide internal standards was validated for human liver. The results demonstrate that different sample matrices have peptide, time, and matrix specific effects on protein digestion and absolute quantification.

A test of comparative equilibration for determining non-exchangeable stable hydrogen isotope values in complex organic materials

Comparative equilibration has been proposed as a methodological approach for determining the hydrogen isotopic composition (deltaD) of non-exchangeable hydrogen in complex organic materials, from feathers to blood and soils. This method depends on using homogenized standards that have been previously calibrated for their deltaD values of non-exchangeable H, that are compositionally similar to unknown samples, and that span an appropriate isotopic range. Currently no certified organic reference materials with exchangeable H exist, and so isotope laboratories have been required to develop provisional internal calibration standards, such as the keratin standards currently used in animal migration studies. Unfortunately, the isotope ratios of some samples fall outside the range of keratin standards currently used for comparative equilibration. Here we tested a set of five homogenized keratin powders as well as feathers from Painted Buntings and Dark-eyed Juncos to determine the effects of extrapolating comparative equilibration normalization equations outside the isotopic range of keratin standards. We found that (1) comparative equilibration gave precise results within the range of the calibration standards; (2) linear extrapolation of normalization equations produced accurate deltaD results to approximately 40 per thousand outside the range of the keratins standards used (-187 to -108); and (3) for both homogenized keratin powders and heterogeneous unknown samples there was no difference in variance between samples within and outside the range of keratin standards. This suggested that comparative equilibration is a robust and practical method for determining the deltaD of complex organic matrices, although caution is required for samples that fall far outside the calibration range.

Natural abundance deuterium and 18-oxygen effects on the precision of the doubly labeled water method

The doubly labeled water method for measuring total energy expenditure is subject to error from natural variations in the background 2H and 18O in body water. There is disagreement as to whether the variations in background abundances of the two stable isotopes covary and what relative doses of 2H and 18O minimize the impact of variation on the precision of the method. We have performed two studies to investigate the amount and covariance of the background variations. These were a study of urine collected weekly from eight subjects who remained in the Madison, WI locale for 6 wk and frequent urine samples from 14 subjects during round-trip travel to a locale > or = 500 miles from Madison, WI. Background variation in excess of analytical error was detected in six of the eight nontravelers, and covariance was demonstrated in four subjects. Background variation was detected in all 14 travelers, and covariance was demonstrated in 11 subjects. The median slopes of the regression lines of delta2H vs. delta18O were 6 and 7, respectively. Modeling indicated that 2H and 18O doses yielding a 6:1 ratio of final enrichments should minimize this error introduced to the doubly labeled water method.

Inter-laboratory calibration of new silver orthophosphate comparison materials for the stable oxygen isotope analysis of phosphates

Stable oxygen isotope compositions (δ(18)O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off-line oxygen extraction in the form of CO(2) which was analyzed on a dual inlet and triple collector isotope ratio mass spectrometer, while labs (2) and (3) employed an isotope ratio mass spectrometer coupled to a high-temperature conversion/elemental analyzer (TC/EA) where Ag(3)PO(4) samples were analyzed as CO in continuous flow mode. The δ(18)O values for the proposed new comparison materials were linked to the generally accepted δ(18)O values for Vennemann's TU-1 and TU-2 standards as well as for Ag(3)PO(4) extracted from NBS120c. The weighted average δ(18)O(VSMOW) values for the new comparison materials UMCS-1, UMCS-2 and AGPO-SCRI were determined to be + 32.60 (± 0.12), + 19.40 (± 0.12) and + 14.58 (± 0.13)‰, respectively.

Automated chemoenzymatic synthesis of no-carrier-added [carbonyl-11C]propionyl L-carnitine for pharmacokinetic studies

Propionyl-L-carnitine (PLC) is under development as a therapeutic for the treatment of peripheral artery disease, coronary heart disease and chronic heart failure. Three methods were examined for labelling PLC in its propionyl group with positron-emitting carbon-11 (t12 = 20.3 min), one chemical and two chemoenzymatic. The former was based on the preparation of [11C]propionyl chloride as labelling agent via 11C-carboxylation of ethylmagnesium bromide with cyclotron-produced [11C]carbon dioxide and subsequent chlorination. Reaction of carrier-added [11C]propionyl chloride with L-carnitine in trifluoroacetic acid gave [11C]PLC in 12% radiochemical yield (decay-corrected) from cyclotron-produced [11C]carbon dioxide. However, the radiosynthesis was unsuccessful at the no-carrier-added (NCA) level of specific radioactivity. [11C]Propionate, as a radioactive precursor for chemoenzymatic routes, was prepared via carboxylation of ethylmagnesium bromide with [11C]carbon dioxide and hydrolysis. NCA [11C]PLC was prepared in 68 min in 14% radiochemical yield (decay-corrected) from [11C]propionate via sequential conversions catalysed by acetate kinase, phosphotransacetylase and carnitine acetyltransferase. A superior chemoenzymatic synthesis of NCA [11C]PLC was developed, based on the use of a novel supported Grignard reagent for the synthesis of [11C]propionate and conversions by S-acetyl-CoA synthetase and carnitine acetyltransferase. This gave an overall radiochemical yield of 30-48% (decay-corrected). This synthesis was automated for radiation safety and provides pure NCA [11C]PLC in high radioactivities ready for intravenous administration within 25 min from radionuclide production. The [11C]PLC is suitable for pharmacokinetic studies in human subjects with PET and the elucidation of the fate of the propionyl group of PLC in vivo.

Stable Isotope Labeling for Improved Comparative Analysis of RNA Digests by Mass Spectrometry

Even with the advent of high throughput methods to detect modified ribonucleic acids (RNAs), mass spectrometry remains a reliable method to detect, characterize, and place post-transcriptional modifications within an RNA sequence. Here we have developed a stable isotope labeling comparative analysis of RNA digests (SIL-CARD) approach, which improves upon the original ¹⁸O/¹⁶O labeling CARD method. Like the original, SIL-CARD allows sequence or modification information from a previously uncharacterized in vivo RNA sample to be obtained by direct comparison with a reference RNA, the sequence of which is known. This reference is in vitro transcribed using a ¹³C/¹⁵N isotopically enriched nucleoside triphosphate (NTP). The two RNAs are digested with an endonuclease, the specificity of which matches the labeled NTP used for transcription. As proof of concept, several transfer RNAs (tRNAs) were characterized by SIL-CARD, where labeled guanosine triphosphate was used for the reference in vitro transcription. RNase T1 digestion products from the in vitro transcript will be 15 Da higher in mass than the same digestion products from the in vivo tRNA that are unmodified, leading to a doublet in the mass spectrum. Singlets, rather than doublets, arise if a sequence variation or a post-transcriptional modification is present that results in a relative mass shift different from 15 Da. Moreover, the use of the in vitro synthesized tRNA transcript allows for quantitative measurement of RNA abundance. Overall, SIL-CARD simplifies data analysis and enhances quantitative RNA modification mapping by mass spectrometry. Graphical Abstract ᅟ.

Accurate dosimetry: an essential step towards good clinical practice in nuclear medicine

In nuclear medicine, an increasing number of radiolabelled agents are under investigation for future use in diagnostic imaging and for applications in radionuclide therapy. All these studies require large amounts of human data to allow for statistical comparisons with existing and well established diagnostic or therapeutic methodologies. In the framework of a good clinical practice environment, clinical trials should be carried out according to international guidelines and regulations as described in the Declaration of Helsinki. Studies involving ionizing radiation, as is the case in nuclear medicine, require special consideration to comply with the ALARA (as low as reasonably achievable) principle. Special publications of the International Commission of Radiological Protection and the World Health Organization deal with this topic in medical research. From the legislation point of view, the 97/43/EURATOM Directive represents the reference to clinical research using ionizing radiation within the European Union. In order to keep the radiation dose of (healthy) volunteers as low as possible, predictive dosimetry studies based on in-vivo animal biokinetics are essential. On the other hand, patients included in dose-escalation radionuclide therapy trials should be monitored individually with respect to dosimetry of the tumour and the critical organs. In this paper the importance and methodology of contemporary patient dosimetry in diagnostic and therapeutic nuclear medicine research are reviewed. It is concluded that reliable dosimetry is essential in performing scientific clinical studies according to the principle of good clinical practice.

Failure to label red blood cells adequately in daily practice using an in vivo method: methodological and clinical considerations

This study was conducted to evaluate the frequency and possible causes of poor red blood cell (RBC) labelling when performing equilibrium gated blood pool (GBP) radionuclide angiography at rest with an in vivo method. The influence of the mode of administration on tagging efficiency was studied by investigating the image quality in 160 patients referred for evaluation of left ventricular (LV) function prior to or after coronary angiography, while using a roughly standardized administration protocol. The patients were subclassified into four groups according to the way both molecules involved in the tagging procedure were administered. When poor image quality was found (in 9.4% of the patients), the labelling efficiency was quantified and the frequency of failed tagging in each group was calculated. A significant association was found between poor labelling and the use of a Teflon catheter or butterfly needle for the injection of the stannous agent. In another 737 patients, in order to avoid the problems observed in the first group, a strict administration protocol was applied to analyse the frequency of poor tagging and its possible causes. Suboptimal image quality was present in 88 patients (11.9%). Quantitatively confirmed poor tagging was present in 36 of the 88 (40.9%, or 4.9% of the whole group); the remaining 52 patients showed borderline normal labelling (> 80% bound fraction). Drug interference was studied by comparing the medications used by the 36 patients showing poor binding with those used by 44 control patients. A significant relationship was found between the use of heparin or chemotherapy and the tagging. The influence of several clinical factors on the labelling was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

The calibration of the intramolecular nitrogen isotope distribution in nitrous oxide measured by isotope ratio mass spectrometry

Two alternative approaches for the calibration of the intramolecular nitrogen isotope distribution in nitrous oxide using isotope ratio mass spectrometry have yielded a difference in the 15N site preference (defined as the difference between the delta15N of the central and end position nitrogen in NNO) of tropospheric N2O of almost 30 per thousand. One approach is based on adding small amounts of labeled 15N2O to the N2O reference gas and tracking the subsequent changes in m/z 30, 31, 44, 45 and 46, and this yields a 15N site preference of 46.3 +/- 1.4 per thousand for tropospheric N2O. The other involves the synthesis of N2O by thermal decomposition of isotopically characterized ammonium nitrate and yields a 15N site preference of 18.7 +/- 2.2 per thousand for tropospheric N2O. Both approaches neglect to fully account for isotope effects associated with the formation of NO+ fragment ions from the different isotopic species of N2O in the ion source of a mass spectrometer. These effects vary with conditions in the ion source and make it impossible to reproduce a calibration based on the addition of isotopically enriched N2O on mass spectrometers with different ion source configurations. These effects have a much smaller impact on the comparison of a laboratory reference gas with N2O synthesized from isotopically characterized ammonium nitrate. This second approach was successfully replicated and leads us to advocate the acceptance of the site preference value 18.7 +/- 2.2 per thousand for tropospheric N2O as the provisional community standard until further independent calibrations are developed and validated. We present a technique for evaluating the isotope effects associated with fragment ion formation and revised equations for converting ion signal ratios into isotopomer ratios.

Absolute Quantification of Apolipoproteins Following Treatment with Omega-3 Carboxylic Acids and Fenofibrate Using a High Precision Stable Isotope-labeled Recombinant Protein Fragments Based SRM Assay

Stable isotope-labeled standard (SIS) peptides are used as internal standards in targeted proteomics to provide robust protein quantification, which is required in clinical settings. However, SIS peptides are typically added post trypsin digestion and, as the digestion efficiency can vary significantly between peptides within a protein, the accuracy and precision of the assay may be compromised. These drawbacks can be remedied by a new class of internal standards introduced by the Human Protein Atlas project, which are based on SIS recombinant protein fragments called SIS PrESTs. SIS PrESTs are added initially to the sample and SIS peptides are released on trypsin digestion. The SIS PrEST technology is promising for absolute quantification of protein biomarkers but has not previously been evaluated in a clinical setting. An automated and scalable solid phase extraction workflow for desalting and enrichment of plasma digests was established enabling simultaneous preparation of up to 96 samples. Robust high-precision quantification of 13 apolipoproteins was achieved using a novel multiplex SIS PrEST-based LC-SRM/MS Tier 2 assay in non-depleted human plasma. The assay exhibited inter-day coefficients of variation between 1.5% and 14.5% (median = 3.5%) and was subsequently used to investigate the effects of omega-3 carboxylic acids (OM3-CA) and fenofibrate on these 13 apolipoproteins in human plasma samples from a randomized placebo-controlled trial, EFFECT I (NCT02354976). No significant changes were observed in the OM3-CA arm, whereas treatment with fenofibrate significantly increased apoAII and reduced apoB, apoCI, apoE and apoCIV levels. The reduction in apoCIV following fenofibrate treatment is a novel finding. The study demonstrates that SIS PrESTs can facilitate the generation of robust multiplexed biomarker Tier 2 assays for absolute quantification of proteins in clinical studies.

Methodological approaches to the study of metabolism across individual tissues in man

PURPOSE OF REVIEW

This article is intended to briefly overview available methodological approaches for the study of regional metabolism in man in vivo, and to summarize recent advances in this field of research.

RECENT FINDINGS

Several methods have been developed and currently allow for the qualitative and quantitative assessment of energy interconversions and substrate fluxes across individual tissues of man, including the measurement of arteriovenous concentration differences, microdialysis, and nuclear magnetic resonance spectroscopy of carbon, hydrogen, and phosphorus isotopes. Each method alone has been used rather extensively to examine certain aspects of organ and tissue metabolism under a variety of experimental conditions, and has contributed novel information in this regard. The most exciting development appears to be the combined use of more than one investigational technique, across one or more tissues simultaneously. A handful of recent studies have employed complex experimental designs or hybrid methodologies, ultimately demonstrating the potential for a more detailed assessment of metabolism at the local level.

SUMMARY

Clearly, advances in the use, performance, and applications of available methods are expected to provide improved and more powerful tools for the metabolic investigation of organs and tissues in humans in vivo.

Procedure for radiolabeling gizzerosine and basis for a radioimmunoassay

A method for the labeling of gizzerosine (GZ), a biogenic amine found in fish meal, is described. The labeling procedure with (125)I using a water-soluble Bolton-Hunter reagent and a mild water-insoluble oxidant (Iodogen) reagent is rapid and reproducible. The (125)I-GZ hapten was demonstrated to be immunologically active in a radioimmunoassay developed with polyclonal antibodies to GZ absorbed with a histamine-Sepharose column. The curves were linear in the range of 0.0001 and 0.1 microgram/mL. Samples of fish meal previously extracted of histamine with methanol and submitted to acid hydrolysis were contaminated with known amounts of GZ and submitted to the assay. The fish meal samples contaminated with GZ show a dose-response effect similar to the standard curve, and apparently the other component present in the sample did not interfere with the binding of the antibodies to (125)I-GZ. These data indicate the suitability of the radioimmunoassay to determine specifically GZ in fish meal.

Quality control of colloid and particulate 99mTc-labeled radiopharmaceuticals

A procedure for the radiochemical purity control of colloid and particulate 99mTc-labeled radiopharmaceuticals is described. The proposed technique is based on the use of two chromatograms, using in both, 15% H3PO4 as solvent and impregnated glass fiber media (Gelman ITLC type SG) as stationary phase. A pretreatment of the radiopharmaceutical with 6 N NaOH is involved prior to one chromatographic run. The procedure is fast and the different species (free pertechnetate, 99mTc-Sn-colloid and labeled 99mTc) in a 99mTc-labeled radiopharmaceutical can be determined accurately and with reliability.

Facile access to 154Eu, a new reference source for calibration in gamma ray spectrometry

Europium-154 can be obtained as a by-product from the large-scale production of Samarium-153 and possesses attractive features (t1/2 8.592 yr; Egamma 0.12-1.6 MeV) for use as a reference source similar to 152Eu (t1/2 13.516 yr; Egamma 0.12-1.4 MeV), which is the gold standard for calibration in gamma ray spectrometry. Thermal neutron irradiation of 5mg of 98% enriched 153Sm2O3 target in the reactor led to approximately 200 GBq 153Sm and 1.26 MBq 154Eu. A typical batch control sample of 153SmCl3 solution and final radiopharmaceutical product formulation of 153Sm-phosphonate (153Sm-EDTMP) pooled together contained about 20% of total yield, requiring post decay disposal of 153Sm as radioactive waste. Such spent solutions pooled on quarterly basis led to availing 756 kBq of 154Eu. The radioactivity content and radionuclide purity (approximately 82%) of the recovered 154Eu sample were envisaged as adequate to prepare reference sources for calibration of gamma ray spectrometers. At present, one batch of 153Sm is handled per month at our institution, with the possibility for weekly processing in future. Access to approximately 3.5 MBq of 154Eu on quarterly basis is envisaged, apart from obviating the need for instituting steps to tackle disposal of the long-lived 154Eu in the spent solution. Up to 60-120 units of 20-100 kBq of 154Eu reference sources per year could thus be available by the proposed strategy.

The good laboratory practice and good clinical practice requirements for the production of radiopharmaceuticals in clinical research

Radiopharmaceuticals account for more than 95% of the group of sterile pharmaceutical products and should therefore be handled and produced with care. Since the introduction of the European directive, all pharmaceuticals used in clinical studies must be prepared under good manufacturing practice (GMP) conditions. This review aims to give an overview of the basic principles and guidelines for the preparation of radiopharmaceuticals. Special attention is given to the production area environment and personnel, the two basic requirements for GMP productions. Especially for the production area, two philosophies have to be combined: the cascade system of over-pressure for the production of pharmaceuticals and the under pressure system for the manufacturing of radioisotopes. Personnel should be selected based on education and regularly given special training for the handling of radioactive material. Compared to pharmaceuticals, radiopharmaceuticals have their own labels, taking into account their specific nature. Besides the standard quality control, other items for quality control of radiopharmaceuticals are also discussed in this article.

Secondary standardisation of 95mTc

The radionuclide 95mTc, which has a half-life of 61(2)days and emits a number of gamma-rays, may be used in radiochemical analysis as a yield tracer for the long-lived fission product 99Tc. In this work, we present (i) the production of 95mTc via an (alpha, 2n) reaction with stable 93Nb (a method which does not result in the production of any 97mTc, 98Tc or 99Tc), (ii) the chemical separation of 95mTc from niobium via coprecipitation, liquid-liquid extraction and liquid chromatography, and (iii) the secondary standardisation of 95mTc with high-resolution gamma-ray spectrometry and an ionisation chamber system.