Species of 67Ga-binding acid mucopolysaccharide in liver

It was determined from measuring neutral saccharide in the structure that the principal 67Ga-binding acid mucopolysaccharide in liver was keratan sulfate and/or keratan polysulfate. On the other hand, it was clarified from the results of mucopolysaccharase treatment that the main 67Ga-binding acid mucopolysaccharide in liver was not either one of keratan sulfate, heparan sulfate, heparin, chondroitin sulfate A, B and C. Based on the present results, it was deduced that the main 67Ga-binding acid mucopolysaccharide in liver was keratan polysulfate.

Relation between 67Ga uptake and the stage of inflammation induced by turpentine oil in rats

For the establishment of the experimental system to judge easily the effect of anti-inflammatory drug, 67Ga-citrate was used. The weight of granuloma tissues induced by inflammable agent, turpentine oil, gradually increased and reached a maximum at 6 days after the administration of turpentine oil. Gallium-67 accumulation in the inflammatory lesions showed also a maximum at 6 days after that. Both patterns were closely similar each other. These results showed that the processes and/or stages of inflammation could be indicated by the pattern of 67Ga uptake.

In vitro binding of 67Ga to isolated rat liver cells

In order to understand the mechanism of the accumulation of gallium citrate (Ga-67) in normal liver, an in vitro investigation system was developed using isolated rat liver cells, and various basal factors relating to 67Ga binding to normal rat liver cells were studied. In this study, the values of 67Ga binding to the liver cells increased in parallel with the number of cells; however, binding was hardly affected by higher doses of 67Ga. The binding of 67Ga to the cells was inhibited by the presence of ethylenediaminetetraacetate (EDTA) and citrate. Phosphate and bicarbonate (10(-2) M) slightly inhibited 67Ga binding to the cells. The binding of 67Ga to the cells increased as the pH was decreased. These results suggest that 67Ga binding to normal rat liver cells may occur in 'free' gallium. Moreover, the utilization of isolated rat liver cells is useful for understanding the 67Ga accumulation mechanism in normal liver.

Evaluation of PLED as a chelating ligand in the preparation of gallium and indium radiopharmaceuticals

The 68Ga and 111In complexes of PLED (N,N'-dipyridoxylethylenediamine-N,N'-diacetic acid) were prepared and their biodistribution determined as a function of time following i.v. injection into rats. The 68Ga and 111In complexes behaved identically and were rapidly cleared from the blood via the kidneys into the urine. Similar rapid urinary excretion was observed in the gamma images obtained from a stump-tailed macaque injected with 111In-PLED. Paper electrophoresis at pH 7.35 showed a single radioactive peak for 111In-PLED which migrated towards the anode. PLED administered by i.p. injection was found to speed the blood pool clearance of previously administered 67Ga-citrate.

Mechanism of gallium-67 accumulation in inflammatory lesions

Multiple factors contribute to the accumulation and retention of gallium-67 in inflammatory lesions. Adequate blood supply is essential. Gallium-67, mainly in the form of transferrin-Ga-67 complex, is delivered to the inflammatory lesions through capillaries with increased permeability. At the site of inflammation, some Ga-67 is taken up by leukocytes and bacteria when they are present. In addition, Ga-67 may also bind to lactoferrin and bacterial siderophores. Multiple contributing factors often coexist at any given inflammatory lesion. The nature and intensity of the inflammation affects the relative contribution of these factors. Thus, there may be situations in which all the contributing factors are present, but in such a low intensity that they escape clinical detection by Ga-67 scans. On the other hand, there may be situations in which one or more contributing factors are missing, such as in patients with agranulocytosis, while they are readily detected by Ga-67 scans.

The effect of amphotericin B on 67Ga biodistribution

The effect of Amphotericin B (AMB) on radiogallium biodistribution in mice was studied at various time intervals. Two doses of AMB (1 mg/kg and 10 mg/kg) were administered intraperitoneally into mice bearing EMT-6 mammary sarcomas. The tumor and tissue uptakes of 67Ga were calculated when the radioactivity was administered either as 67Ga-citrate or 67Ga-transferrin (Ga-Tf). The role of transferrin was also investigated by using doubly-labeled 67Ga-125I-Tf. Our results indicate that both the doses of AMB and the chemical form of the radiogallium administered affect the pattern of distribution in some distinct fashion. It was also found that although the administration of AMB results in an increase in tumor-associated transferrin, this does not necessarily result in a concomitant increase in radiogallium uptake. In general, the effects of AMB on various tissues uptake of 67Ga appear to be related to both acute and subacute toxicity.

Study of competitive binding of gallium and iron by tumor cells

The influence of iron and gallium carriers on the in vitro and in vivo uptake of 67Ga and 59Fe by tumor cells has been studied. The results appear to indicate that ferritin might be involved in most of the systemic accumulation of 67Ga but that the mechanism of tumor uptake might be different.

Gallium-67 uptake by the liver: studies using isolated rat hepatocytes and perfused livers

We studied the hepatic uptake of carrier-free Ga-67 using isolated rat hepatocytes and perfused livers. The results indicate that: (a) the liver can take up Ga-67 and secrete it into the bile, even in the absence of transferrin; (b) transferrin inhibits hepatic uptake of Ga-67 and its biliary excretion; and (c) iron deficiency markedly enhances hepatic uptake of Ga-67.

[Uptake of 67Ga into the rat liver after treatment with thioacetamide]

67Ga uptake of the liver began to elevate from the 1st day and reached a maximum at the 2nd day of treatment with thioacetamide (TIAA). Incorporation of 3H-thymidine into the liver DNA fraction was reached a maximum at the 1.5th day, and the value was 5.7 times of the control. The uronic acid content and 35S incorporation in the 1.2 M NaCl-soluble fraction which contained predominantly heparan sulfate (HS), were both peaked at the 2nd day. These patterns were in good agreement with that of 67Ga uptakes in the liver treated with TIAA. Pretreatment of aminoacetonitrile, an inhibitor of fibrosis, was effective in lowering the elevated uptake of 67Ga in TIAA-treated rat liver. Uptake of the 67Ga in the TIAA-treated liver was also inhibited when they were treated with cycloheximide, an inhibitor of protein synthesis. On the other hand no significant inhibition was observed in the cytosine arabinoside-treated-TIAA rats. These results suggest that HS may be involved in the 67Ga uptake in damaged liver, and that relation between 67Ga uptake and cell proliferation is secondary.

[67gallium. Diagnostic possibilities and usefulness as a tracer]

As a consequence of its affinity to leukocytes and tumour cells, 67Gallium-Citrate is a good isotope for detecting infections and tumoral pathology. Its sensitivity is greater for lymphatic system malignancies, primary lung cancer, primary liver carcinoma and melanoma. It is a useful method with more sensitivity than diagnostic specificity.

In vitro binding of 67Ga to Ehrlich ascites tumor cells

The binding of 67Ga to Ehrlich ascites tumor cells (ETC) was studied in vitro. Acid mucopolysaccharide (AMPS) present at the cell surface of ETC was identified as heparan sulfate (HS). The extent of 67Ga binding to ETC reached a plateau (ca. 10% of the added dose) at 1-2 h after the start of incubation. The binding was higher under neutral or alkaline conditions than under acidic conditions. Heparin and heparitinase treatment both significantly decreased the extent of 67Ga binding to ETC. Mild treatment with protease, including trypsin or papain, also decreased the binding. On the contrary, the treatment with trypsin under severe conditions markedly increased the extent of 67Ga binding to ETC. These results support the hypothesis that HS plays an important role as a 67Ga receptor in the mechanism of gallium binding to ETC.

67Ga-binding substances in abscess and normal tissues

Abscess-induced animals and normal animals were treated with 67Ga-citrate. Abscess, kidney, heart, lung, and spleen were excised and homogenized. After removal of the nuclear fraction, each of these homogenates was digested with protease. After digestion, the supernatants of the reaction mixtures were applied to a Sephadex G-100 column. Resultant eluates were analyzed for radioactivity, protein, uronic acids, and sialic acids. Sodium sulfate-35S was administered to animals that were then treated by the same procedure as that followed for animals treated with 67Ga-citrate. In abscess, kidney, lung, heart, and spleen, sizeable amounts of 67Ga had been bound to the sulfated acid mucopolysaccharides with molecular weights of about 10,000, and to the sulfated acid mucopolysaccharides, a species whose molecular weights exceeded 40,000. Based on the results presented here, it is clear that 67Ga-binding substances in abscess and also in the above four organs are sulfated acid mucopolysaccharides.

Phenolic aminocarboxylic acids as gallium-binding radiopharmaceuticals

The phenolic aminocarboxylic acids ethylenediamine di [o-hydroxyphenylacetic acid] (EDDHA) and N,N'-bis [2-hydroxybenzyl] ethylenediamine N,N'-diacetic acid (HBED) form gallium complexes having high stability constants which enable them to resist exchange of gallium with plasma transferrin. 67Ga complexes were synthesized with these ligands, placing substituent groups in the phenolic ring to direct excretion via the renal or hepatobiliary route. The amount of 67Ga-Br-EDDHA excreted via the hepatobiliary route was comparable with that of some of the 99mTc agents. Excretion of 67Ga-Br-HBED was similar but with delayed transit from the liver. 67Ga COOH-EDDHA was excreted exclusively via the renal route. These findings provide a basis for developing new 67Ga or 68Ga radiopharmaceuticals, the latter for use in positron emission tomography, using these phenolic aminocarboxylates.

Deposition and retention of inhaled aggregate 67Ga2O3 particles in beagle dogs, Fischer-344 rats, and CD-1 mice

Deposition and retention of inhaled 67Ga2O3 aerosols were measured in ten beagle dogs to provide reasonable estimates for human deposition and in Fischer-344 rats and CD-1 mice to estimate lung burdens in small animals frequently used in toxicological evaluations. Aggregated particles of 67Ga2O3, 0.1 micron mass median diameter (MMD), were produced using heat treatment of 67Ga tetramethylheptanedione. Whole-body counting and gamma camera imaging were used to measure deposition. Pulmonary deposition in dogs was measured as 25% of the inhaled particles for the 0.1 micron particles. Tracheobronchial and nasopharyngeal deposition were much lower, 7% and 7% respectively. Pulmonary deposition of 0.1 micron (MMD) particles was calculated as 10% and 11% of inhaled particles in Fischer-344 rats and 15 and 20% in mice for two separate nose-only exposures of each species.

Different actions of deferoxamine and iron on Ga-67 abscess detection in rats

The contrast-enhancing properties of iron (Fe) and deferoxamine (DFO) in abscess imaging with Ga-67 citrate were compared in rats bearing turpentine-induced abscesses. Iron administration shifted Ga-67 from plasma into tissues such as muscle and fat. As a result, the abscess-to-plasma ratio increased whereas the abscess-to-muscle ratio decreased. DFO enhanced the abscess-to-muscle and abscess-to-plasma ratios by increasing urinary Ga-67 excretion. In contrast to Fe, DFO removed abscess-bound Ga-67, thus representing a disadvantage of DFO compared with Fe. As a result, the abscess-to-plasma ratio was more effectively enhanced by Fe than by DFO. We conclude that abscess imaging with Ga-67 citrate may be improved by administration of Fe for detection of abscesses masked by blood activity, or DFO for detection of abscesses surrounded by muscle tissue.

Lacrimal gland accumulation of 67Ga-citrate in patients with Sjögren's syndrome

The extent of 67Ga accumulation in the two lacrimal glands in patients with keratoconjunctivitis sicca (KCS) of Sjögren's syndrome was studied. Of the two main groups one consisted of 69 subjects without ophthalmic complaints (control group), the other consisted of 26 patients with KCS of Sjögren's syndrome. Of the 26 patients with KCS, 7 had been diagnosed as probable KCS (probable sub-group) and the other 19 had been diagnosed definite KCS (definite sub-group). About 3 mCi (111 MBq) 67Ga-citrate was injected IV into each subject and this was followed by scintigraphy at 24, 48, and 72 h after the injection of 67Ga. A positive finding in the lacrimal gland was noted in 64 of 69 subjects (92.7%) in the control group and in 7 of 7 patients (100%) with probable KCS. Three of 19 patients with definite KCS (15.7%) showed positive findings under scintigraphy. When the scintigraphic finding in the lacrimal gland is not positive in patients with suspected KCS of Sjögren's syndrome, they can then be diagnosed with little risk as definite KCS cases. Shirmer's test was performed on subjects in the probable and definite groups. There was statistical significance between the positive and equivocal or negative scintigraphic finding and Schirmer's values. These results suggest a correlation between gallium accumulation in the lacrimal gland and the tear production.

The role of ferritin in the intracellular distribution of gallium 67

The binding of gallium 67 or iron 59 to ferritin in vitro was investigated using equilibrium dialysis. Gallium 67 did not bind to apo-ferritin until the protein was transformed into ferritin in the presence of iron citrate. Apotransferrin inhibited the binding of 67Ga to ferritin, especially in the presence of sodium bicarbonate and citrate, thus indicating that 67Ga has not gained access to ferritin from its complex with transferrin. Similar inhibition was observed for ferritin-59Fe. The release of 59Fe from its transferrin complex was enhanced by ATP, citrate, or ascorbic acid, while these reagents did not stimulate the dissociation of 67Ga from its transferrin complex. On the other hand, 67Ga injected intravenously in vivo was not found in the ferritin fractions of rat liver, kidney, and tumor. The difference between experimental results in vivo and in vitro supports the hypothesis that 67Ga in the cytoplasm is not labile enough to be bound to ferritin. We have indicated a significant role of ferritin in distinguishing between 67Ga and 59Fe in the cell, and provided some clues to interpret the chemical forms of 67Ga in the cytoplasm.

The effects of inadvertent administration of antineoplastic agents prior to Ga-67 injection: concise communication

Alteration of the gallium-67 (Ga-67) distribution after administration of chemotherapeutic agents has been demonstrated in experiments on both normal and tumor-bearing animals. We have encountered eight patients who had Ga-67 scintigrams in which the findings were similar to those in the animals experiments: markedly increased uptake in bone, with suppressed uptake in liver, muscle, and tumor. Five of the patients had hematologic neoplasms, and three had solid tumors, and each had received one or more chemotherapeutic agents during the 24 hr preceding Ga-67 administration. In three patients while not on antineoplastic medication subsequent Ga-67 images showed a return to the usual Ga-67 distribution pattern. The altered Ga-67 distribution may result from inhibition of protein synthesis or of a serum-binding agent for Ga-67, or from competitive blockage of specific Ga-67 organ receptors by the antineoplastic agents.

Tumor uptake of high and low molecular weight fractions from 67Ga-citrate labelled blood plasma

Blood plasma from tumor-bearing rats was incubated with 67Ga-citrate, and two fractions of high molecular weight (proteins) and low molecular weight were isolated by dialysis and by gel-filtration chromatography. Both fractions showed a different in vivo uptake by DS-sarcoma-bearing animals, the high molecular weight fraction being accumulated to a lesser extent. Compared to 67Ga-citrate the low molecular weight fraction showed a different uptake which for most tissues was significatively higher. This behavior suggests the presence of 67Ga in chemical forms other than citrate in the low molecular weight fraction. The lower uptake of the blood protein fraction is discussed.

Biokinetics and metabolism of radiogallium

The large number of publications dealing with biokinetics, metabolism and factors influencing tissue uptake of 67Ga-citrate could not clarify the mechanism responsible for the uptake of this compound into tumor tissue. The present paper reviews biokinetic data obtained from clinical investigations and animal experiments and briefly points out some possible pathways of the mechanism for gallium localisation in tumors as well as in abscesses and inflammatory lesions.

67Ga-citrate distribution in solid hepatoma 22

The intracellular distribution of 67Ga was studied in solid hepatoma 22 implanted in C3Ha/6 mice and in normal liver tissue from the same animals at different time intervals. The tissues were fractionated according to differential centrifugation principles, and subcellular fractions were isolated consecutively. The enzyme activities and the accumulation of 67Ga were determined in each fraction. The subcellular distribution of 67Ga in the tumor tissue was different compared with normal liver; in tumor it was found mainly in the nuclear fraction and this distribution was independent of time, but in normal liver the accumulation was mainly in the mitochondrial fraction, this was time-dependent and the maximal uptake was found 48 h after 67Ga administration.