Total Serum Radioactivity Research Articles

Tissue distribution of sprifermin (recombinant human fibroblast growth factor 18) in the rat following intravenous and intra-articular injection

Fibroblast growth factor 18 (FGF18) is involved in chondrogenesis and articular cartilage repair. We investigated tissue distribution and pharmacokinetics of radioactive [3H]sprifermin, a recombinant human FGF18, in rats after a single intravenous (i.v.) or intra-articular (i.a.) injection. In two studies (48-96-h [n=23] and 28-day [n=12]), 35 male albino (Sprague Dawley) rats received single i.v. or i.a. dose [3H]sprifermin (0.24mg/kg). Radioactivity was measured in blood, serum, and (in animals receiving i.a. administration) in the knee joint by liquid scintillation counting. Radioactivity in organs, tissues, and distribution in the whole body were measured with whole-body autoradiography. After i.v. injection, radioactivity peaked in serum and whole blood after 4 and 24h, respectively, with greater total radioactivity in serum. After i.a. injection, radioactivity peaked in serum and whole blood after 24 and 48h, respectively; intact [3H]sprifermin was not detected in vena caval serum and systemic exposure was low, approximately 20% of that with i.v. injection. Following i.v. injection, radioactivity was mainly found in the liver, adrenal glands, kidney, and spleen; following i.a. injection, radioactivity was preferentially concentrated in articular cartilage after initial distribution in the joint capsule, and still evident in the joint after 28 days. After i.a. injection of [3H]sprifermin in rats, radioactivity was concentrated in the knee joint, particularly articular cartilage, with low levels in other investigated tissues. Systemic exposure to sprifermin was greater with i.v. than i.a. injection. Subsequent clinical investigation in patients with osteoarthritis has reported consistent results.

Abstract C123: A phase 1 study to evaluate the absorption, metabolism, and excretion of the vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor (TKI) tivozanib.

Abstract Background: Tivozanib is a potent, selective, long half-life tyrosine kinase inhibitor (TKI) of vascular endothelial growth factor receptors (VEGFR)-1, -2, and -3. Tivozanib has demonstrated antitumor activity in a Phase II study in subjects with renal cell carcinoma. This study was conducted to determine the absorption, metabolism, and excretion of a single 1.5 mg dose of [14C]-tivozanib administered to healthy male subjects. Methods: This study was approved by an independent institutional review board and enrolled 8 healthy male subjects; each received a single 1.5 mg (∼160 μCi) dose of oral [14C]-tivozanib. Whole blood, serum, urine, and feces were collected for up to 28 days post dose for assessment of total radioactivity and/or for determination of [14C]-tivozanib concentrations. All subjects were kept confined as inpatients for the duration of the study. Safety assessments included laboratory tests, electrocardiograms, physical examinations, vital signs, and recording of adverse events. Pharmacokinetic data were analyzed by noncompartmental methods. Results: Subjects had a mean age of 32 years (range 19 to 46 years) and mean body mass index of 25 kg/m2 (range: 23 to 29 kg/m2). Of the 8 subjects enrolled, 7 completed the study. [14C]-tivozanib and total radioactivity were slowly absorbed and eliminated from serum; median Tmax was 10.0 hours, and mean (±SD) t1/2 for [14C]-tivozanib and total radioactivity in serum was 89.3 hours (± 23.5 hours) and 99.1 hours (± 32.5 hours), respectively. Mean (±SD) Cmax and AUC0−∞ values for [14C]-tivozanib were 12.1 ng/mL (±46.9 ng/mL) and 1084 ng*hr/mL (±417 ng*hr/mL), respectively; these values were approximately 93% and 80% of the values for total radioactivity in serum, respectively. Mean blood to serum concentration ratios ranged from 0.495 to 0.615 through 312 hours post dose, indicating minimal association of radioactivity with red blood cells. Overall, mean (±SD) recovery of total radioactivity was 91.1% (±11.0%), with 11.8% (±4.6%) recovered in urine and 79.3% (±8.8%) recovered in feces. No unchanged tivozanib was found in the urine. A single therapeutic dose of tivozanib was well tolerated in healthy subjects. Conclusion: These results indicate that after an oral dose of 1.5 mg (∼160 μCi) of [14C]-tivozanib, the majority of circulating drug in the systemic circulation was unchanged tivozanib. The main route of elimination of [14C]-tivozanib was via feces, with at least 11.8% of the administered total radioactive dose being absorbed into systemic circulation. No unchanged tivozanib was found in the urine, indicating that tivozanib does not undergo renal excretion. In this study, the mean half-life of [14C]- tivozanib was 89.3 hours, one of the longest half-lives among VEGF TKIs. Tivozanib is currently being tested in a Phase III study in subjects with RCC and Phase I/II studies in other solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C123.

Transcription, expression and tissue binding in vivo of INGAP and INGAP-related peptide in normal hamsters

We studied islet neogenesis-associated protein (INGAP) transcription and its immunocytochemical presence in and binding in vivo of 125I-tyrosylated INGAP pentadecapeptide ( 125I-T-INGAP-PP) to different normal male hamster tissues. 125I-T-INGAP-PP was injected intraperitoneally with or without unlabeled T-INGAP-PP (0–1 mg/100 g bw), drawing blood samples at different times after injection; radioactivity was measured in serum, brain, skeletal muscle, dorsal root ganglia, liver, kidney, small intestine and pancreas samples, expressing results as organ:serum ratio. INGAP transcription (RT-PCR) and immunopositive cells were investigated in liver, kidney, brain, small intestine and pancreas. Total serum radioactivity increased progressively as a function of time; whereas 71% of this activity was displaced by unlabeled T-INGAP-PP at 5, 10 and 20 min, only 9% was at 60 min. Only liver, pancreas and small intestine specifically bound 125I-T-INGAP-PP. The pancreas tissue dose–response curve showed a 50% displacement at 3.9 × 10 4 ng/100 g bw, suggesting a low binding affinity of its receptor. INGAP-mRNA was only identified in pancreatic islets and exocrine tissue. Our results suggest that INGAP transcription/expression is probably restricted to pancreas cells exerting its effect in a paracrine fashion. INGAP would be released and circulate bound to a serum protein from where it is bound and inactivated by the liver. Tissue binding could also explain INGAP's immunocytochemical presence in small intestine, where it could affect epithelial cell turnover.

Safety, Pharmacokinetics (PK), Metabolism, and Mass Balance of [14C]-AMN107, a Novel Aminopyrimidine Inhibitor of Bcr-Abl Tyrosine Kinase, in Healthy Subjects.

Background: AMN107, a selective and potent inhibitor of Bcr-Abl tyrosine kinase signaling, has demonstrated activity against imatinib resistant forms of Bcr-Abl in patients with chronic myelogenous leukemia at daily oral doses of ≥200 mg in a phase I clinical trial. These studies also showed dose proportional systemic exposure to drug in the 50 - 200 mg range, but progressively less than proportional increases and higher variability in drug exposure with daily doses >200 mg. The present study in healthy volunteer subjects was conducted to determine the safety, PK, metabolism, and mass balance of AMN107 to aid in the understanding of the processes that may contribute to the drug's PK behavior and potentially impact safety and efficacy.Methods: 4 male volunteer subjects (age 23 to 46 years) received, after an overnight fast, a single oral 400 mg dose of AMN107 radiolabeled with carbon-14 to a specific activity of 0.25 μCi/mg. Quantitative urine and fecal collections, and sequential blood and serum collections for determination of levels of total radioactivity, unchanged AMN107, and AMN107 metabolites, were obtained for up to 7 days post dose. Subjects were in good health based on medical history, clinical laboratory and vital signs assessment at baseline, and were monitored for safety during the 7 days study duration and an end-of-study evaluation on day 14 post dose.Results: There were no clinically significant changes from baseline in laboratories, vital signs, and medical examination. Mild headache was noted in 3/4 subjects which resolved without intervention. Complete recovery (97.9% of dose) was achieved within 7 days, 4.4% in urine and 93.5% in feces (69% unchanged AMN107), indicating incomplete oral absorption amounting to at least 31% of dose, and rapid elimination and no significant retention of drug and metabolites in the body. Peak serum concentrations of total radioactivity and AMN107 were observed at about 4 h post dose. AMN107 represented >75% of the total serum radioactivity at all time points monitored post dose. The terminal elimination half-life of AMN107 was about 16 hours. The major circulating metabolite, a carboxylic acid derivative of AMN107, accounting for approximately 7% of serum exposure and 4% of dose elimination in feces, was formed via an AMN107 carbinol derivative, which accounted for approximately 5% of serum exposure and 4% of dose elimination in feces. Several minor metabolites resulting from oxidation of AMN107 were also detected. Metabolite profiles were similar in whole blood and serum.Conclusions: AMN107 administered as a single 400 mg oral dose to healthy volunteer subjects was safe and well tolerated. Complete recovery of single dose suggests absence of drug retention with chronic treatment. The elimination rate of AMN107 supports once or twice daily dosing, the latter representing a potential approach to increasing the absorption of the daily dose.

Dose-linear pharmacokinetics, tissue distribution, and excretion of a recombinant fusion protein 125I-GST-TatdMt possessing potent anti-obesity activity

This study first examined the pharmacokinetic disposition of GST-TatdMt, a recombinant Tat protein possessing potent anti-obesity activity, in rats after i.v. injection. GST-TatdMt was over-expressed in E. coli, purified, and radioiodinated using the IODO-GEN method. The radioiodinated 125I-GST-TatdMt was administered to rats at doses of 9 μg (1640 nCi), 18 μg (3388 nCi), and 35 μg (6420 nCi). Upon administration, the total radioactivity in serum declined bi-exponentially, with the average terminal elimination half-life ranging from 13.7 to 15.7 h. There was a linear relationship between dose and AUC INF ( r 2=1.000) and between dose and Co ( r 2=0.999). The fraction of administered radioactivity excreted in feces was low (mean range 1.5–2.8%), while the majority of the radioactivity was excreted in urine (mean range 54.9–61.4%). The radioactivity found in the liver, lungs, spleen, and kidneys were higher than in serum, but the tissue-to-serum ratios were relatively low (<1.64). The radioactivity in testes, adipose tissue, heart, and brain was lower than in serum (tissue-to-serum ratios 0.046–0.27). The findings of this study indicate dose-linear pharmacokinetics of 125I-GST-TatdMt in rats over the i.v. dose range studied.

Comparison of the clearances of serum chylomicron triglycerides enriched with eicosapentaenoic acid or oleic acid

Rat mesenteric lymph chylomicrons containing triglycerides enriched with either [14C]oleic acid (OA) or [14C]-eicosapentaenoic acid (EPA) were prepared by ultracentrifugation of lymph samples collected for 6 hr after a single duodenal infusion of an emulsion containing either fatty acid. These chylomicrons were injected into the jugular vein of recipient rats and, at various time intervals, blood was drawn and serum was assayed for radioactivity. In separate animals, serum lipoprotein fractions were separated by ultracentrifugation, and the redistribution of labeled fatty acid among circulating lipoproteins was determined by liquid scintillation spectrometry. When the early disappearance rates (10 min) of either total serum radioactivity or specifically the chylomicron fraction were compared, there were no differences between the groups receiving OA- or EPA-enriched chylomicrons. However, disappearance rates of EPA-enriched chylomicrons were slower than those of OA-enriched chylomicrons from 25 to 90 min. The small but significant differences in the disappearance rates for the longer time periods cannot be ascertained without further studies. At 5 min after injection of either type of chylomicron, the d less than 1.006 g/ml lipoprotein fraction of serum chylomicrons and very low density lipoproteins contained almost 90% of the original radioactivity. By 240 min, when less than 2% of the radioactivity remained, this radioactivity in the d less than 1.006 g/ml fraction was 43-46%, with concomitant increases in the low and high density lipoprotein fractions and in the lipoprotein-free serum.

Transport of macromolecules in malnourished animals: II. Intravenous clearance after antigen absorption

It has been demonstrated that increased quantities of bovine serum albumin (BSA) and/or its large molecular weight breakdown products are present in the serum of malnourished rats after its instillation into the duodenum. However, it has not been established whether this increased circulating BSA is related to enhanced intestinal permeability due to changes in the mucosal barrier or to other factors associated with malnutrition such as impaired intravenous clearance of the protein after it has crossed the mucosal barrier. To determine if altered clearance of intravascular antigens occurred. 125I-BSA was injected intravenously into 4 malnourished and 4 control rats and total serum radioactivity measured both before and after precipitation with TCA at intervals for 4 hours. Uptake and degradation of 125I-BSA by the liver were also measured. Both total and TCA precipitable serum radioactivity did not differ significantly between study groups at any of the times tested. Furthermore, the rate of BSA uptake by the liver was nearly identical for both groups although the malnourished degraded it to a slightly lesser extent than the controls. These findings appear to eliminate the possibility that delayed intravascular clearance accounts for increased serum levels of antigen in malnourished animals and supports the hypothesis of increased intestinal permeability to macromolecules in malnutrition.

Disposition pharmacokinetics of bezafibrate in man.

The disposition kinetics of bezafibrate, a newly developed drug of great lipid-lowering potency, were investigated in normal male subjects. Five male volunteers received14C-labelled bezafibrate orally in solution, and a further 10 were given the same dose (300 mg) of un-labelled drug as tablets. The concentration of bezafibrate in serum and urine from the latter was determined by GC, and in the former total radioactivity in serum, urine and feces was followed for 48 h, and urinary excretion products were analysed by TLC and GC-MS. Rapid absorption from the gastrointestinal tract led to peak serum levels 30 min and 2 h after administration of solution and tablets, respectively. Since approximately 95% of the administered14C-bezafibrate was excreted in urine within 48 h, and almost all the remainder was detected in feces, absorption can be regarded as complete after administration in solution. The relative optimal bioavailability from the tablets was also complete, since in both cases approximately 50% of the administered dose was detected as unchanged bezafibrate in urine within 24 h by GC in the tablet study, and by TLC in the solution study. Of the decomposition products, more than 20% of the dose was present as glucuronides and the remainder consisted of several more polar compounds, one of which was identified as a hydroxyderivative of bezafibrate. Since the apparent halflife of bezafibrate in serum was 2.1 h, this new drug possesses favourable pharmacokinetic features: rapid and complete absorption, even from tablets, combined with a conveniently short half-life, and clearance which is half renal (56 ml/min) and half metabolic (43 ml/min), giving a total clearance of 99 ml/min.

Effects of partial hepatectomy on the utilization of 3h-thymidine in mice

1. 1. Thymidine availability and specificity for DNA synthesis in various organs of hepatectomized and intact mice and the magnitude of catabolism of administered 3H-thymidine were investigated. 2. 2. The serum thymidine radioactivity 5 min after administration was 1.5 % of the total administered dose. The radioactivity decreased rapidly and was reduced to 1 % of the 5 min value after 2hr. 3. 3. β-AIB accumulated m serum until 20 min after injection and then its level decreased. The levels of thymidine and β-AIB radioactivity were increased 2–3 times after partial hepatectomy. 4. 4. Volatile radioactivity constituted 90% of the total serum radioactivity 60 min after injection. 5. 5. The level of acid soluble radioactivity in liver and kidney was higher, whilst that in spleen, thymus and cerebrum was lower than the serum acid soluble radioactivity until 60 min after injection. Liver and kidney acid soluble radioactivity was increased, but that of spleen, thymus and cerebrum was unaffected by partial hepatectomy. 6. 6. Sixty minutes after injection, the radioactivity in RNA was 1–10% of that in DNA per gram of spleen, thymus and regenerating liver, but 25 and 50 % of that in kidney and intact liver respectively. Incorporation of 3H-activity into liver RNA was increased 48 hr after partial hepatectomy; no difference was obtained in other organs. 7. 7. The main incorporation of 3H-thymidine into DNA was confined to the first 20 min after injection. The DNA radioactivity of the spleen was 2.3 %, thymus 0.4%, kidney 0.2% and that of intact liver 0.6 % of the total injected dose 60 min after injection. Forty-eight hours after partial hepatectomy the DNA radioactivity in the liver was 5 times that of control liver. At 24–72 hr after resection, incorporation of 3H-thymidine into DNA/g of liver was in the same range as that of thymus and spleen. The radioactivity of thymus and kidney DNA was reduced while that of liver DNA was at a maximum.

Interruption of the enterohepatic circulation of digitoxin by cholestyramine. II. Effect on metabolic disposition of tritium-labeled digitoxin and cardiac systolic intervals in man.

Previous studies of digitalis glycoside metabolism and excretion have indicated that these compounds undergo a significant enterohepatic cycle in some species. It has been suggested that the existence of such a cycle in man contributes to the prolonged action of certain cardiac glycosides. Previous studies have demonstrated that cholestyramine binds digitoxin and digoxin in vitro and accelerates the metabolic disposition of digitoxin in rats and guinea pigs, presumably by interrupting the enterohepatic circulation. In order to assess the role of the enterohepatic circulation in the metabolism of digitalis glycosides in humans, maintenance doses of cholestyramine were administered to 7 of 15 normal human subjects beginning 8 hr after digitalization with 1.2 mg of digitoxin-(3)H. All subjects had frequent measurements of serum radioactivity, left ventricular ejection time (LVET), and electromechanical systole (QS(2)), the latter recorded as the interval from onset of Q wave to first major component of second heart sound. Measurement of the LVET and QS(2) intervals affords a sensitive index of the cardiac response to digitalis. In addition, chloroform extraction of serum was performed to separate unchanged digitoxin and active metabolites from cardioinactive metabolites of digitoxin. Cholestyramine treatment resulted in reduction in half-life to total serum radioactivity from 11.5 to 6.6 days, and in chloroform-extractable radioactivity from 6.0 to 4.5 days, as compared to controls. In addition, cholestyramine treatment was accompanied by more rapid return to base line values of digitoxin-induced changes in the LVET and QS(2) intervals. A significant positive correlation was found between QS(2) values and chloroform-extractable radioactivity, the latter reflecting unchanged digitoxin-H(3) (r=0.64; P=<0.01). The results indicate that administration of cholestyramine to digitalized human subjects accelerates the metabolic disposition of digitoxin and abbreviates the physiologic response to the glycoside. This effect is presumably mediated by interruption of the enterohepatic circulation of digitoxin by cholestyramine.

The distribution of 3H-labelled cardenolides between isolated guinea-pig atrial tissue and circulating, oxygenated whole blood.

1. An experimental method was developed that allowed the incubation of isolated organs in circulating whole blood. The circulating blood was oxygenated with a specially designed disc-oxygenator and drawn through the system by means of a roller pump.2. The method proved suitable for guinea-pig isolated atria, rabbit duodenum and to a lesser extent for chronically denervated rat diaphragm. Isolated atria could be kept for several hours. Various parameters of the circulating blood (haemolysis, pH, O(2) saturation, concentration of electrolytes) remained satisfactory for at least 5 hr. The method proved convenient for pharmacological and kinetic studies on isolated organs, suspended in whole blood of the corresponding species. The organs showed normal spontaneous mechanical activity and also responded to electrical stimuli and various drugs.3. The uptake of (3)H-labelled ouabain, digoxin, digitoxin and digitoxigenin was studied in guinea-pig isolated atria, suspended in circulating blood. The uptake reached equilibrium after 60-90 min. With respect to the total serum radio-activity the "apparent" tissue/medium (T/M) ratios obtained for the four drugs were within the range 0.4-1.1. If, however, the amount of free, non protein bound drug was taken as a base for the calculations, the following "true" T/M ratios were obtained: (3)H-ouabain 0.45; (3)H-digoxin 1.6; digitoxin 8.8; digitoxigenin 8.4. These values are virtually the same as those obtained with atria, suspended in an aqueous medium. Obviously, the uptake of (3)H-cardenolides from whole blood is determined by the amount of free non-protein-bound drug.4. (3)H-digitoxin and (3)H-digitoxigenin were taken up by guinea-pig erythrocytes to a small extent. No measurable amounts of (3)H-ouabain and (3)H-digoxin were taken up by erythrocytes.

The three-hour conversation ratio: a test for hyperthyroidism.

ABSTRACT Serum organic radioiodine was determined at 3 and 24 h after an oral tracer dose of 131I. With the method used radioactive iodoamino acids (radio-IAA) rather than total protein-bound radioiodine was measured. The radio-IAA was expressed both as such (%/l serum) and as the conversion ratio (CR, % of total serum radioactivity). The results of these measurements and of 3 and 24 h % uptake determinations were compared in 181 euthyroid and 59 hyperthyroid patients sent for routine diagnostic assessment of thyroid function with 131I. The 3-h radio-IAA did not have any diagnostic value. The diagnostic accuracy of the 3-h CR equalled or surpassed that of the other tests. It was found to discriminate eu- from hyperthyroidism even in the presence of iodine deficiency (where % uptake tests fail) and small thyroidal iodine pools (where other serum tests fail). Only in renal insufficiency and in cardiac failure may the 24-h radio-IAA effect a better differentiation between hyperthyroid and euthyroid patients. A fair degree of correlation between the 3-h CR and the 24-h radio-IAA was found both in hyperthyroid and in euthyroid patients with small thyroidal iodine pools, but the variation of the 3-h CR with the 24-h radio-IAA was much smaller in the latter group. Values for several parameters tended to decrease with increasing age. Factors influencing the radio-IAA and CR are discussed. The new test should increase the diagnostic accuracy obtainable with the short-lived isotope 132I.

In vivo Labelling of Extractable Iodotyrosines in Serum of Rat and Dog

SummaryExtraction was made of the protein fraction, Fraction 1, (after passage through a Sephadex G-25 column) of serum of rats fed 125-1 for 50-57 days. The presence of labelled iodotyrosines, 11-13% of the organic labelled iodine, was established. In dogs injected once with 125-1, 12-18% of total serum radioactivity was extractable as iodotyrosines by 12 hours after labelling. In man, iodotyrosines in serum were not found to be labelled, with one possible exception.

Thyroiditis following administration of thyroid-stimulating hormone.

ABSTRACT The administration of 10 units of one lot of commercial thyroid-stimulating hormone (TSH) on two successive mornings to 21 healthy male adults produced acute thyroiditis in 10 of them. The thyroiditis was not accompanied or followed by the appearance of antibody reacting with the TSH used or with an extract of normal human thyroid, as measured by precipitin or hemagglutinin titers in serum. Hence these cases of acute thyroiditis did not appear to belong in the group of auto-immune reactions as seen in chronic thyroiditis. The occurrence of thyroiditis enhanced the net thyroidal uptake of I131 at forty-eight hours and raised the 24-hour and 48-hour conversion ratios (serum PBI131 as a percentage of the total serum radioactivity). Both groups of patients, i.e., those with and without thyroiditis, manifested comparable increases in the serum PBT level. These increases, on the average, were of the order of magnitude observed in subjects given another lot of TSH which did not produce thyroiditis.