Interaction of diethylstilbestrol and ioxynil with transthyretin in chicken serum

The association of suspected endocrine-disrupting chemicals (EDCs), diethylstilbestrol (DES), ioxynil and pentachlorophenol (PCP), with chicken serum proteins was investigated in relation to thyroid system disruption. All of these chemicals strongly inhibited l-[(125)I]thyroxine ([(125)I]T(4)) binding to purified transthyretin (TTR) whereas PCP was less potent inhibitor than DES and ioxynil of [(125)I]T(4) binding to diluted whole chicken serum. This result suggested that PCP interacted with serum proteins other than TTR in whole chicken serum. Following the incubation of chicken serum with each chemical (final concentrations 0.25-1.0 microM), serum proteins were fractionated by gel filtration chromatography (Cellulofine GCL-1000) and affinity chromatography (human retinol-binding protein coupled to Sepharose 4B). Although all chemicals were detected in the gel filtration chromatography 50-100 kDa fractions, DES and ioxynil, but not PCP, were co-eluted with TTR during affinity chromatography. Our results indicated that a significant proportion of DES and ioxynil, but a low proportion of PCP, interacted with TTR in whole chicken serum.

Myocardial uptake of iodine-125-labeled 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid is decreased in chronic diabetic rats with changes in subcellular distribution

Iodine-123-labeled 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid (123I-BMIPP) is widely used to detect myocardial metabolic changes, but the preferred energy substrates in the myocardium would be expected to be altered in the presence of metabolic disorders such as diabetes mellitus (DM). We investigated the metabolism of branched-chain fatty acids in the myocardium of rats with DM. Streptozotocin-induced DM rats were examined 48 h (acute; AD) and 6 weeks (chronic; CD) after injection of streptozotocin. Hearts were excised 15 min or 60 min after injection of 0.185 MBq of 125I-BMIPP, followed by homogenization in an EDTA-Tris buffer. The homogenates were subjected to differential centrifugation to obtain the mitochondrial (MF) and cytoplasmic (CF) fractions. Myocardial 125I uptake tended to increase in the AD group, but the change was not significant. Myocardial 125I uptake at 15 min was significantly lower in the CD group than in the control group, even in the insulin-treated rats [control (CC), 4.4+/-0.4; not treated (CDN), 3.3+/-0.5; insulin-treated (CDI), 3.4+/-0.4 x 10(4) cpm/g, p<0.05 in each case]. The 125I count value corrected for the blood count (counts/min (cpm) per g of protein divided by blood cpm) in the MF decreased by 40% at 60 min in the CC group, but increased by 60% in the CDN group. The results of the present study suggest that the myocardial uptake of branched-chain fatty acids is decreased in rats with chronic diabetes, probably as a result of mitochondrial dysfunction.

Do we still need to collect stool? Evaluation of visualized fatty acid absorption: experimental studies using rats

BACKGROUND

Short-gut syndrome is likely to impair enteric fat utilization. This study was undertaken to develop a clinical test of lipid absorption without fecal collection.

METHODS

The absorption of enterally fed radioactive long-chain fatty acid, beta-methyl-p-(123I)-iodophenylpentadecanoic acid was investigated with continuous chyle collection in rats. The changes in excretion and time-dependent biodistribution of radioactivity of the enterally fed agent were assessed in normal control animals. Similarly, sequential urinary excretion and biodistribution were studied along with scintigraphy using sham-operated and short-gut animals.

RESULTS

Approximately 64% of the enterally fed radioactivity was recovered in the collected chyle (24 hours). A comparison of normal control, sham-operated, and short-gut animals showed significantly less urinary and greater fecal excretions of radioactivity in short-gut animals. With the use of sequential scintigraphy, the small intestine, whole-body soft tissues, and urinary bladder were well visualized in sham-operated animals, whereas the large intestine and feces were demonstrated earlier in short-gut animals.

CONCLUSIONS

Our results suggest that enteral feeding of the agent might be feasible for determining lipid absorption from the the dynamic changes of radioactivity in visualized abdominal organs and in urine.

High-performance liquid chromatographic determination of the X-ray imaging contrast agent, iofratol, in plasma and urine

Iofratol is currently under evaluation as a potential X-ray contrast medium for angiography and myelography. An HPLC method for assaying iofratol in rat and human plasma and urine samples is described. The analysis is based on the reversed-phase chromatographic separation of iofratol and the internal standard (iopamidol) from the endogenous components of biological fluids, and detection by UV absorption at 242 nm. The selectivity of the method was satisfactory. The mean absolute recovery was greater than 90%. The precision and accuracy of the analytical methods were in the range 0.8-7.4 and -7.8 to +9.7%, respectively. The detection limits in plasma (0.1 ml) and urine (0.5 ml) were 0.1 and 0.4 microg (iofratol)/ml, respectively. The analyte was stable in the different biological matrices when stored at room temperature (20 degrees C) for at least 1 day, 4 degrees C for 1 month and -20 degrees C for 1 year.

Uptake and washout of I-123-MIBG in neuronal and non-neuronal sites in rat hearts: relationship to renal clearance

We investigated the uptake and washout of I-123-metaiodobenzylguanidine (MIBG) in neuronal (both intra- and extravesicular) and non-neuronal sites in the heart and its relationship to renal clearance. Acute renal failure was induced in rats by ligating the renal vessels, and the findings were compared with those of sham-operated rats. Each group consisted of control, reserpine-treated and 6-hydroxydopamine (6-OHDA)-treated subgroups. Rats were sacrificed at 10 minutes and 4 hours after injection of MIBG. MIBG activity was calculated in specimens of heart, spleen, lung and blood. At 10 minutes, no significant difference in MIBG uptake in the heart was observed among the subgroups or between sham-operated and renal failure rats despite a significantly higher blood MIBG activity in the latter. At 4 hours, however, the hearts of both reserpine-treated and 6-OHDA-treated rats showed significantly lower MIBG uptake than control rats. Furthermore, the hearts of renal failure rats showed higher MIBG uptake in the control and reserpine-treated rats than in the corresponding subgroups in sham-operated rats. Intra and extravesicular neuronal uptake of MIBG in the heart were estimated using control, reserpine-treated and 6-OHDA-treated rats. Vesicular uptake values were similar in both the sham-operated group (0.51% ID/g) and the renal failure group (0.44% ID/g). But extravesicular neuronal uptake values were quite different in the renal failure group (0.86% ID/g) and the sham-operated group (0.19% ID/g). In conclusion, uptake to and washout from extravesicular neuronal sites may depend on the concentration of MIBG in the blood or the state of renal clearance, but vesicular uptake may be independent of these factors.

High-performance liquid chromatographic determination of metaiodobenzylguanidine in whole blood and plasma of cancer patients

An accurate and simple high-performance liquid chromatographic (HPLC) assay is presented for the quantitative determination of metaiodobenzylguanidine (MIBG) in human whole blood and plasma. The sample pretreatment involves a solid-phase extraction on Bakerbond SPE cyano columns. The HPLC system comprises a microBondapak C18 column and ammonium phosphate (pH4.0; 25 mM)-acetonitrile (80:20, v/v) as the mobile phase. Detection is performed by UV absorbance measurements at 254 nm. Linear regression with weighting factor l/chi 2 yielded the smallest sum of per cent relative concentration residuals over the concentration range of the assay (0.1-10 micrograms ml-1). MIBG levels, at the end of a 3-h infusion, in whole blood and plasma of carcinoid patients were measured and compared with the results obtained with radiodetection after addition of iodine-131-labelled MIBG.

Tracer kinetics of 15-(ortho-123/131I-phenyl)-pentadecanoic acid (oPPA) and 15-(para-123/131I-phenyl)-pentadecanoic acid (pPPA) in animals and man

The human myocardium retains oPPA as opposed to pPPA. Therefore turnover of oPPA was compared with that of pPPA in rat hearts and in man, the latter by using substrates double-labeled with 123/131I and 14C. Moreover, substrate binding to coenzyme-A was tested in vitro. In rats, oPPA remained mainly in the pool of free fatty acids, as opposed to pPPA, which was metabolized by mitochondrial beta-oxidation. Binding to coenzyme-A at maximum was 62% for oPPA, 81% for pPPA and 90% for palmitic acid. In man, after i.v. and intracoronary injection of double-labeled oPPA, the two radionuclides reappeared together in venous blood and in coronary sinus respectively, in an unchanged ratio but at a significantly lower rate than with pPPA. It can be concluded that oPPA is bound to coenzyme-A and is retained in the cytosolic lipid pool, while pPPA is metabolized by mitochondrial beta-oxidation. A dual-tracer application of oPPA and pPPA has the potential of being a specific probe for the function of the carnitine shuttle.

Alkaline diuresis for acute poisoning with chlorophenoxy herbicides and ioxynil

The relation between blood chlorophenoxy herbicide and ioxynil concentrations and toxicity, and the effect of alkaline diuresis on outcome, have been studied in 41 patients. More than one herbicide was found in 38 cases. 6 of 30 patients who had ingested chlorophenoxy compounds alone died; 16 patients (mostly in grade 3-4 coma) had alkaline diuresis and 15 survived. 7 of 11 patients who had co-ingested ioxynil died; 3 had alkaline diuresis and all survived. Alkaline diuresis reduced plasma chlorophenoxy half-lives to values observed after doses that had no adverse effects (ie, below 30 h), but did not influence ioxynil clearance. Alkaline diuresis should be used to treat acute poisoning with chlorophenoxy herbicides or ioxynil in the presence of coma or other poor prognostic indicators, such as acidaemia, or if plasma total chlorophenoxy concentrations are 0.5 g/l or more.

HPLC measurement of chlorophenoxy herbicides, bromoxynil, and ioxynil, in biological specimens to aid diagnosis of acute poisoning

A simple high-performance liquid-chromatographic assay for eight chlorophenoxy (2,4-D and related compounds) and two benzonitrile (bromoxynil and ioxynil) herbicides has been developed to aid in the diagnosis of acute poisoning. Sample (whole blood, plasma/serum, urine, or tissue homogenate) or standard (100 microL) is vortex-mixed (ca. 5 s) with 20 microL of internal standard solution [1.00 g/L 2,4,5-TP in 0.02 mol/L Tris buffer, pH 9.6:methanol (1 + 1)]. Dilute (0.2 mL/L) hydrochloric acid in methanol, 200 microL, is added and the mixture is again vortex-mixed (30 s). After centrifugation (9950 X g, 2 min) a 10-20 microL portion of the supernate is analyzed on a 250 X 5 mm (i.d.) Spherisorb S5 Phenyl column, with aqueous potassium dihydrogen orthophosphate (50 mmol/L, pH 3.5) and acetonitrile (3 to 1 by vol) at a flow-rate of 1.8 mL/min as eluent. The method is capable of resolving the chlorophenoxy/benzonitrile mixtures (2,4-D/MCPP, 2,4-D/DCPP, 2,4-D/ioxynil, 2,4-D/MCPP/DCPP, 2,4-D/2,4,5-T, and MCPP/ioxynil) encountered in the U.K. The limit of detection (at 240 nm) is 20 mg/L (10 mg/L for bromoxynil and ioxynil). Intra-assay and interassay CVs were less than 5% and less than 8%, respectively, for all analytes. Plasma:whole blood distribution ratios ranged from ca. 1.7 for 2,4-DB to ca. 2.0 for 2,4-D, emphasizing that results of whole-blood measurements must be multiplied by a factor of ca. 2 for comparison with plasma/serum data.

Pulmonary retention of iodobenzyl-propanediamine in humans. Effect of cigarette smoking

N,N,N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3-propanediamine (HIPDM), a synthetic basic compound with high affinity for lung tissue of various animal species, was labeled with 123I and injected into normal smokers (n = 9) and into asymptomatic smokers (n = 9). Time/activity curves were recorded for 90 min by gamma camera. HIPDM lung clearance was described by two exponential components. In smokers, the mean time of the first component, 10 +/- 1.4 min (mean +/- SEM), did not significantly differ from that of nonsmokers (9.7 +/- 0.9 min), whereas the mean time of the second component (12.9 +/- 0.6 h) was longer than that of nonsmokers (6.7 +/- 0.2 h). The intercept to the ordinate of the second exponential component was significantly higher in smokers (90.3 +/- 1.5%) than in nonsmokers (80.7 +/- 1.9%). Control studies in rabbits showed that, 2 min after intravenous injection, 95% of HIPDM is taken up by the lung; time/activity curves were similar to those obtained in humans. The longer pulmonary persistence of HIPDM in smokers may reflect an increased number of cellular binding sites or may be the expression of hindered HIPDM biotransformation. The rabbit can be used as a model to further investigate HIPDM kinetics in relation to lung dysfunction.

Comparison of MIBG and monoamines uptake mechanisms: pharmacological animal and blood platelets studies

The uptake of MIBG, a scintigraphic agent widely used in the detection of APUD tumours, was studied with a pharmacological approach on an in vitro and an in vivo models. MIBG as well as norepinephrine (NE) was taken up by human blood platelets, a model for presynaptic nerve endings amine uptake, with a thermodependant mechanism. MIBG and NE uptake was inhibited by desimipramine and reserpine. However, MIBG but not NE uptake was inhibited by fluvoxamine, a serotonin (5HT) uptake inhibitor. This suggests that MIBG is a NE and also a 5HT uptake tracer which involves uptake one and vesicular storage mechanisms. In rats treated with 6-hydroxydopamine to induce a chemical sympathectomy, we observed an inhibition of uptake similar for MIBG and NE in the heart, the salivary glands and the spleen, but no effect was observed in the liver. Some clinical inferences to best investigate specific monoamine uptake are drawn from these results.

Evaluation of the brain-specific delivery of radioiodinated (iodophenyl)alkyl-substituted amines coupled to a dihydropyridine carrier

To evaluate the potential usefulness of radioiodinated phenylamines attached to dihydropyridine carriers as a means of brain-specific delivery of radiopharmaceuticals, 1-methyl-3-[N-[beta- (4-[125I]iodophenyl)ethyl]carbamoyl]-1,4-dihydropyridine ([125I]-9) and 1-methyl-3-[N-(4-[125I]iodophenyl)carbamoyl]-1,4-dihydropyridine ([125I]-13) have been prepared by dithionite reduction of the corresponding pyridinium precursors, [125I]-8 and [125I]-12, respectively. Formation of 8 involved coupling of (p-aminophenyl)ethylamine with N-succinimidyl (1-methyl-3-pyridinio)formate iodide (4) followed by transformation to the corresponding N-piperidinyl- (6) or (diethylamino)- (7) triazines that were converted to 8 by treatment with HI. Alternatively, 12 was prepared by initial conversion of (4-amino-phenyl)mercuric acetate (10) to 4-iodoaniline (11) by treatment with I2 and then coupling with 4. The radioiodinated quaternary products, 8 and 12, showed low brain uptake and low brain to blood ratios, whereas the dihydropyridine analogues, 9 and 13, showed comparatively good brain uptake and good brain to blood ratios in rats. These data demonstrate that dihydropyridine-coupled radiopharmaceuticals can cross the blood-brain barrier and the technique may be useful for the measurement of cerebral blood perfusion.

Effect of uptake-one inhibitors on the uptake of norepinephrine and metaiodobenzylguanidine

The mechanisms underlying the uptake of the radiopharmaceutical metaiodobenzylguanidine (MIBG) and the catecholamine norepinephrine (NE) were studied using cultured bovine adrenomedullary cells as an in vitro model system. Sodium-dependent and sodium-independent uptake systems have been identified and characterized for both MIBG and NE. The sodium-dependent uptake of NE and MIBG was inhibited by the selective Uptake-one inhibitors, desmethylimipramine (DMI) and cocaine, whereas the sodium-independent uptake for NE and MIBG was much less sensitive to inhibition by these agents. The sodium-dependent uptake system fulfills the criteria for the neuronal Uptake-one system, and the sodium-independent uptake system fulfills the criteria for a passive diffusion mechanism. Both NE and MIBG were transported into cultured bovine adrenomedullary cells by both uptake systems; the relative role of each uptake system was dependent upon the concentration of NE and MIBG in the media. Arterial concentrations proximal to the dog adrenal were very small suggesting that the sodium-dependent (Uptake-one) system is predominant in vivo. Consistent with the in vitro observations, the in vivo uptake of MIBG and NE into dog adrenal medullae was effectively blocked by pretreatment with DMI or cocaine. Therefore, iodine-131 MIBG scintigraphy of the adrenal appears to reflect uptake by way of the Uptake-one system.

Salivary gland accumulation of meta-[131I]iodobenzylguanidine

Intense uptake of m-[131I] iodobenzylguanidine (I-131 MIBG ) has been observed in the salivary glands of patients undergoing scintigraphy for the location of suspected pheochromocytomas. This uptake of radioactivity was not due to free I-131 derived from the I-131 MIBG but rather to uptake of I-131 MIBG by sympathetic neuronal elements in the salivary glands. In keeping with this, administration of tricyclic antidepressants reversibly blocked salivary uptake of I-131 MIBG . Furthermore, I-131 MIBG uptake was markedly diminished by the ipsilateral salivary glands in a patient with Horner's syndrome, and was bilaterally diminished in a patient with severe idiopathic sympathetic autonomic neuropathy. The salivary gland uptake of I-131 MIBG may provide a means for the study of sympathetic innervation of these organs, and thus for the study of generalized disorders of autonomic innervation.

In vivo and in vitro studies with omega-[rho-123I-phenyl]-pentadecanoic acid in rats

Biodistribution, plasma clearance and urinary excretion of omega-[p-123I-phenyl]-pentadecanoic acid were investigated in rats. The affinity of this radiopharmaceutical to red blood cells and to the plasma proteins was determined in vitro. Various radioactive metabolites were analysed by paper electrophoresis both in blood and urine at various intervals after administration of the compound. Protein-binding in plasma was determined by both electrophoresis and TCA precipitation. In vitro studies showed 30% uptake by red blood cells at equilibrium (30 min post-injection). 48% of the activity in the red cells could be removed after repeated washing with saline. The maximum uptake by myocardium occurred at 1 min and the maximal heart-to-blood ratios at 3 min. Although in vitro protein-binding was high, in vivo studies showed a very rapid plasma clearance (94% in 3 min) which indicated a weak binding. The amount of free iodine in plasma was less than 1% at any time after injection, thus not presenting a background problem or unnecessary radiation dose to thyroid and whole body. The major radioactive metabolites were 123I-p-hippuric acid and 123I-p-benzoic acid. In urine 123I-p-hippuric acid was excreted almost quantitatively. The metabolism was very fast, even 3 min post-injection the first metabolites could be found in the blood stream. Urinary excretion did not reach a plateau until 48 h. The total amount of radioactivity excreted was 56% within 48 h.