Detection of endotoxins in radiopharmaceutical preparations--III. Limulus test assessment using radiopharmaceutical preparations; correlation with the rabbit pyrogen test

Experiments using 17 radiopharmaceuticals containing known amounts of added endotoxin show that none of them inhibits the pyrogenic reaction of the rabbit. Gelation of the Limulus amoebocyte lysate (LAL) is inhibited by 4 of them: colloidal erbium 169Er citrate, colloidal rhenium 186Re sulfide, colloidal technetium 99mTc (Re) sulfide for liver scintigraphy and the colloidal technetium 99mTc (Re) sulfide for lymphography. This inhibition is cancelled, either by dilution or after neutral pH adjustment. Both controls were performed on 313 batches of various radiopharmaceuticals, 95% of results were identical (93% negative, 2% positive). The remaining 5% correspond to positive LAL tests vs negative rabbit tests on the same batches. No negative LAL test vs positive rabbit test was observed.     

Use of Technegas as a radiopharmaceutical for the measurement of gastric emptying

Many radiopharmaceuticals and test meals that are used to measure gastric emptying are less than optimal. A vegetable-based solid meal, such as rice, labelled with a radiopharmaceutical that also has the capacity to measure gastric emptying of liquids, is likely to be ideal. The role of Technegas as a radioisotopic marker to measure gastric emptying of rice and liquids was evaluated. Technegas-labelled rice was incubated in 0.9% saline, 1 M HCl and simulated gastric fluid (3.2 g/l pepsinogen, pH 2–3) to assess stability of the label. In eight healthy volunteers gastric emptying of two meals – 200 g rice (370 kcal) and 75 g dextrose dissolved in 300 ml water (300 kcal), both labelled with 20 MBq of Technegas – was measured scintigraphically. Over 4 h, the average label stability was 93.7%±0.5% in 0.9% saline, 91.0%±0.4% in 1 M HCl and 93.6%±0.7% in simulated gastric juice. The lag phase was longer for rice than dextrose (25±7 min vs 4±2 min; P<0.05), but there was no difference in the post-lag emptying rate (2.1±0.3 kcal/min vs 1.7±0.2 kcal/min; P=0.2) between the two meals. We conclude that Technegas is a suitable radiopharmaceutical for measurement of gastric emptying of rice and nutrient-containing liquids. Received 8 March and in revised form 19 April 1999     

Interaction of some sterilizing filter materials with some technetium-99m radiopharmaceuticals

The retention of a variety of ^99mTc radiopharmaceuticals on four different sterilizing filter membranes has been evaluated. It was demonstrated that some ^99mTc radiopharmaceuticals show significant retention on certain types of sterilizing filters, presumably due to interactions between the radiopharmaceutical and the filter material.     

Use of Technegas as a radiopharmaceutical for the measurement of gastric emptying.

Many radiopharmaceuticals and test meals that are used to measure gastric emptying are less than optimal. A vegetable-based solid meal, such as rice, labelled with a radiopharmaceutical that also has the capacity to measure gastric emptying of liquids, is likely to be ideal. The role of Technegas as a radioisotopic marker to measure gastric emptying of rice and liquids was evaluated. Technegas-labelled rice was incubated in 0.9% saline, 1 M HCl and simulated gastric fluid (3.2 g/l pepsinogen, pH 2-3) to assess stability of the label. In eight healthy volunteers gastric emptying of two meals - 200 g rice (370 kcal) and 75 g dextrose dissolved in 300 ml water (300 kcal), both labelled with 20 MBq of Technegas - was measured scintigraphically. Over 4 h, the average label stability was 93.7%+/-0.5% in 0.9% saline, 91.0%+/-0.4% in 1 M HCl and 93.6%+/-0.7% in simulated gastric juice. The lag phase was longer for rice than dextrose (25+/-7 min vs 4+/-2 min; P<0.05), but there was no difference in the post-lag emptying rate (2.1+/-0.3 kcal/min vs 1.7+/-0.2 kcal/min; P=0.2) between the two meals. We conclude that Technegas is a suitable radiopharmaceutical for measurement of gastric emptying of rice and nutrient-containing liquids.     

The paper spot test: a rapid method for quantitating stannous concentrations in radiopharmaceutical kits

We have developed a simplified, semiquantitative test for the determination of stannous tin in pyrophosphate and other tin-containing radiopharmaceuticals, excluding those stabilized with ascorbic acid and MAA preparations. The test involves the formation and disappearance of a positive red color complex in the presence of Sn(II) and in acidified porphyrin solution. With this technique, the time of spot disappearance is directly proportional to the Sn(II) concentration spotted. The procedure is easy to use, requiring only a high-intensity light source (30-watt light bulb) and a timing device. The test is accurate, reproducible, and sensitive to Sn(II) levels as low as 40 micrograms/ml. Because the procedure is rapid (requiring less than 5 min), it can easily be incorporated into the routine radiopharmaceutical quality-control program of any nuclear medicine facility.     

Use of a nonstationary temporal Wiener filter in nuclear medicine

The use of the Wiener filter is proposed for temporal filtering of nuclear medicine dynamic studies. This filter adapts to the signal and noise levels of each pixel activity curve in a dynamic study to produce an "optimal" suppression of noise, while maintaining the signal content of the curve. The filter is derived to be a simple function of the power spectrum of the time-activity curve. Examples of its use for temporally filtering gated blood-pool studies for cine viewing and functional image formation are shown.     

Initial investigations of 99mTc-labeled morpholinos for radiopharmaceutical applications

This laboratory is evaluating phosphorothioate deoxyribonucleic acids (DNAs) and peptide nucleic acids (PNAs) for a variety of nuclear medicine applications. Morpholinos (MORFs) are a new class of oligomers with a nuclease-resistant, nonionic and water-soluble phosphorodiamidate backbone. We now report on the in vitro and in vivo properties of MORFs labeled with technetium-99m. Both 15-mer and 18-mer MORFs were obtained, each with a primary amine attached to the 3' equivalent end via a three-carbon beta-alanine linker. The amine was used to conjugate with NHS-MAG3 for ^99mTc radiolabeling. By surface plasmon resonance at room temperature, the association rate constant for hybridization of the 18-mer MORF to its complementary oligomer (cMORF) was equivalent to that of DNAs and PNAs of comparable length. Hybridization of ^99mTc-MORF in vitro to free cMORF, to a cMORF polymer and to cMORF beads was nearly quantitative under a variety of conditions. Kinetic studies in vitro at room temperature showed rapid (2-5 min) and nearly quantitative (90%) binding to cMORF beads. Using size-exclusion high-performance liquid chromatography, the stability of the ^99mTc-MORF was found to be greater than 85% over 24 h in 37°C serum with minimal protein binding. In normal mice, the ^99mTc-MORF showed rapid pharmacokinetics, with only 21% and 8% remaining in the whole body at 3 and 24 h post administration, respectively. In vivo targeting with ^99mTc-MORF of cMORF beads in one thigh of normal mice compared to control beads in the other thigh showed target/control thigh ratios of 2-10 between 3 and 24 h. These results demonstrate that MORF oligomers are capable of in vivo hybridization. Their properties of hybridization affinity and kinetics and their in vivo stability and pharmacokinetics make them suitable subjects for in vivo studies.     

Evaluation of 3H-paroxetine as a radiopharmaceutical for lung function

The potential of 3H-paroxetine as a radiotracer for in vivo study of the function in mouse lung was examined. A high accumulation of radioactivity in the mouse lung was observed after intravenous administration of 3H-paroxetine. However, the distributions of radioactivity in the mouse lung were not significantly decreased by treatment with paroxetine or other monoamine uptake inhibitors (6-nitroquipazine, desipramine and GBR 12909). It was found that the radioactivity in the mouse lung at 1 hr after intravenous administration of 3H-paroxetine was due to unmetabolized 3H-paroxetine from TLC and HPLC analyses. Furthermore, 3H-paroxetine exhibits both saturable and high affinity binding sites in mouse lung with a maximal number of binding sites (Bmax) of 303 fmoles/mg protein and a dissociation constant (Kd) of 92.2 pM. These results suggest that 3H-paroxetine would be a suitable radiopharmaceutical for in vivo study of the function of lung as a metabolic organ of serotonin.     

Initial investigations of 99mTc-labeled morpholinos for radiopharmaceutical applications.

This laboratory is evaluating phosphorothioate deoxyribonucleic acids (DNAs) and peptide nucleic acids (PNAs) for a variety of nuclear medicine applications. Morpholinos (MORFs) are a new class of oligomers with a nuclease-resistant, nonionic and water-soluble phosphorodiamidate backbone. We now report on the in vitro and in vivo properties of MORFs labeled with technetium-99m. Both 15-mer and 18-mer MORFs were obtained, each with a primary amine attached to the 3' equivalent end via a three-carbon beta-alanine linker. The amine was used to conjugate with NHS-MAG3 for 99mTc radiolabeling. By surface plasmon resonance at room temperature, the association rate constant for hybridization of the 18-mer MORF to its complementary oligomer (cMORF) was equivalent to that of DNAs and PNAs of comparable length. Hybridization of 99mTc-MORF in vitro to free cMORF, to a cMORF polymer and to cMORF beads was nearly quantitative under a variety of conditions. Kinetic studies in vitro at room temperature showed rapid (2-5 min) and nearly quantitative (90%) binding to cMORF beads. Using size-exclusion high-performance liquid chromatography, the stability of the 99mTc-MORF was found to be greater than 85% over 24 h in 37 degrees C serum with minimal protein binding. In normal mice, the 99mTc-MORF showed rapid pharmacokinetics, with only 21% and 8% remaining in the whole body at 3 and 24 h post administration, respectively. In vivo targeting with 99mTc-MORF of cMORF beads in one thigh of normal mice compared to control beads in the other thigh showed target/control thigh ratios of 2-10 between 3 and 24 h. These results demonstrate that MORF oligomers are capable of in vivo hybridization. Their properties of hybridization affinity and kinetics and their in vivo stability and pharmacokinetics make them suitable subjects for in vivo studies.     

Omega-halofatty acids: a probe for mitochondrial membrane integrity. In vitro investigations in normal and ischaemic myocardium

Long-chain omega-halofatty acids, especially omega-123I-iodoheptadecanoic acid (IHA), are widely used clinically as radiopharmaceuticals for functional heart imaging. The metabolic interpretation of the various elimination rates, however, remains in dispute. It has been previously shown (Kloster and St?cklin 1982) that in isolated perfused guinea-pig hearts halide diffusion from the mitochondrion to the blood is the rate-determining step of IHA pharmacokinetics in normal myocardium. We have now extended these in vitro experiments to normal and globally ischaemic isolated perfused rabbit hearts. Again, in normal hearts a single phase iodide elimination half-time (14.3 +/- 2.1 min) was observed. In hearts made globally ischaemic for 90 min, the iodide elimination was biphasic with a first fast phase (T 1/2 = 3.8 +/- 0.49 min) and a late slow phase (T 1/2 = 60.5 +/- 14.0 min). The first fast phase is attributed to iodide ion released by residual beta-oxidation (more rapid than in normal hearts due to damaged membranes in ischaemia), while the late slow phase is explained by beta-oxidation of IHA slowly released by hydrolysis of intracellular lipid stores. These data were compared with published data from investigations in patients which seem to support our interpretation.     

A study of 11C-benzoate as a radiopharmaceutical for renal imaging

11C-benzoic acid prepared in a radiochemical purity over 90% was studied radiopharmacologically in mice and rabbits. The uptake of 11C-benzoate in ICR mice increased quickly. The ratio of kidney uptake rate to that in other organs reached values between 9 and 55 with a maximum at 10 min after i.v. injection. Gamma camera imaging of rabbits showed that uptake in the kidneys began at 2 min after injection and that activity began to appear in the bladder 4 min later. Rabbits with left renal artery ligature showed no uptake in the left kidney but the right kidney was imaged to the same extent as that of a rabbit without artery ligature. The kidney imaging of 11C-benzoic acid may be a useful method for renal diagnosis.     

Development of a 99Tcm-labelled radiopharmaceutical for cerebral blood flow imaging

A new radiopharmaceutical, 99Tcm-hexamethylpropyleneamine oxime (99Tcm-HM-PAO) has shown considerable promise for single photon emission tomographic (SPECT) imaging of the brain. In animal biodistribution studies this complex demonstrates good brain uptake with prolonged retention of activity in brain. Further improvement of these properties, resulting in higher brain uptake with very slow washout and fixed regional distribution has been achieved following the isolation of the d,1-diastereoisomer of HM-PAO.     

Use of the Bird's Nest filter in oversized inferior venae cavae.

An inferior vena cava (IVC) diameter of greater than 28 mm has been considered a contraindication to the intracaval placement of Greenfield, LG-Medical (LGM), and Simon nitinol filters, necessitating biiliac placement of these devices. With the Bird's Nest filter (BNF), the maximum span of the struts, which immobilize the device, is 60 mm; this allows the placement of the BNF in an oversized IVC having a diameter of greater than 28 mm. Over a 44-month period, 799 IVC filters (547 BNF, 136 Greenfield filters, and 116 LGM filters) were inserted. BNFs were placed in 18 patients (2.3%) with an oversized IVC (diameter range, 29-42 mm); all filters were placed via the femoral route. Patient records were reviewed to determine if problems were associated with filter insertion (including insertion site femoral vein thrombosis) and to determine the prevalence of filter migration, caval thrombosis, and new or recurrent pulmonary emboli (PE) after insertion. No difficulties were encountered during insertion. There was no documented case of device migration, caval thrombosis, or clinically apparent new or recurrent PE. The data suggest that the BNF is the filtering device of choice in patients with an oversized IVC.     

Biodistribution of tantalum-178 A short-lived radiopharmaceutical for blood pool imaging

¹⁷⁸Ta is a short lived radionuclide (half life=9.3 min), which results in favorable radiation exposure compared to ^99mTc (half life 6 h). The energy spectrum of ¹⁷⁸Ta consists of imageable photons in the 55–65 keV (61.2%) and 93 keV (33.7%) range but also 6% of disintegrations result in photons with energies greater than 500 keV. These high energy photons cause septal penetration in low energy collimators so that resolution is degraded. However, a medium energy collimator prevents the septal penetration of these higher energy photons. Serial blood samples obtained from dog and rabbit models indicate that ¹⁷⁸Ta is retained in the blood pool for at least 20–30 min after intravenous injection. The ¹⁷⁸Ta appears to be associated with the protein fraction of the plasma and not primarily with the red blood cell fraction as determined by centrifugation and column chromatography. Gated equilibrium blood pool images using ¹⁷⁸Ta were comparable in quality to images using the ^99mTc labelled red blood cell technique. Therefore, ¹⁷⁸Ta may allow comparable equilibrium gated blood pool imaging with much more favorable radiation dosimetry. Thus, serial studies over prolonged periods of observation may be obtained.Supported in part by Ischemic SCOR HL26215 and Cardiovascular Training Grant HL07416 from the National Institutes of Health Betheseda, Maryland     

Use of a TrapEase device as a temporary caval filter

Inferior vena cava (IVC) thrombosis in younger patients presents a difficult management problem and is associated with a significant incidence of pulmonary embolism (PE). Treatment options include anticoagulation, mechanical thrombectomy, or thrombolytic therapy, often in combination with placement of a filter above the thrombus. The authors report the use of a permanent filter in a temporary fashion while performing thrombectomy and thrombolysis of an IVC thrombus.