The Entering of Indium-111 and Iron-59 into the Hepatocytes from Partially Hepatectomized Rats Differ from That of Gallium-67

Evaluating abdominal oedema during experimental sepsis using an isotope technique

PURPOSE

Abdominal oedema is common in sepsis. A technique for the study of such oedema may guide in the fluid regime of these patients.

PROCEDURES

We modified a double-isotope technique to evaluate abdominal organ oedema and fluid extravasation in 24 healthy or endotoxin-exposed ('septic') piglets. Two different markers were used: red blood cells (RBC) labelled with Technetium-99m ((99m)Tc) and Transferrin labelled with Indium111 ((111)In). Images were acquired on a dual-head gamma camera. Microscopic evaluation of tissue biopsies was performed to compare data with the isotope technique.

RESULTS

No (99m)Tc activity was measured in the plasma fraction in blood sampled after labelling. Similarly, after molecular size gel chromatography, (111)In activity was exclusively found in the high molecular fraction of the plasma. Extravasation of transferrin, indicating the degree of abdominal oedema, was 4·06 times higher in the LPS group compared to the healthy controls (P<0·0001). Abdominal free fluid, studied in 3 animals, had as high (111)In activity as in plasma, but no (99m)Tc activity. Intestinal lymphatic vessel size was higher in LPS (3·7 ± 1·1 μm) compared to control animals (0·6 + 0·2 μm; P<0·001) and oedema correlated to villus diameter (R(2) = 0·918) and lymphatic diameter (R(2) = 0·758). A correlation between a normalized index of oedema formation (NI) and intra-abdominal pressure (IAP) was also found: NI = 0·46*IAP-3·3 (R(2) = 0·56).

CONCLUSIONS

The technique enables almost continuous recording of abdominal oedema formation and may be a valuable tool in experimental research, with the potential to be applied in the clinic.

The Effect of Blood Decrease on 67Ga Uptake by the Liver in Partially Hepatectomized Rats

As (67)Ga is injected into the blood, (67)Ga is immediately bound to transferrin (Tf) and transported to various tissues and the Tf-(67)Ga complex binds to Tf receptor on various tissues. In partial hepatectomy (PH) a part of blood in circulation is lost together with removed liver tissues, consequently the amounts of blood cells and Tf in circulation decrease. In order to investigate the effect of those decreases on (67)Ga uptake by the liver, we compared the uptake in partially hepatectomized rats with that in venesectioned rats in which only a part of blood in circulation decreased. A two-thirds PH was performed. Two milliliters of blood was venesectioned. Each treated rat was intraveneously injected with (67)Ga. The changes of erythrocyte and reticulocyte contents after PH did not differ from those after venesection (VS) at all. But (67)Ga uptake by reticulocytes significantly increased after VS but did not after PH. On the other hand, (67)Ga uptake by the liver significantly increased after PH but did not after VS. These differences must be related to the different expression of Tf receptors on the liver after PH and VS.

The Involvement of Transferrin in the Uptake of Iron-59 by Hepatocytes of Carbon Tetrachloride-Damaged Rats

We have reported that transferrin (Tf)-unbound Gallium-67 ((67)Ga) was taken up into hepatocytes 1 d after carbon tetrachloride (CCl(4))-treatment in rats. It had been reported that the binding affinity of Iron-59 ((59)Fe) to Tf was greater than that of (67)Ga. In the present study, we investigated whether or not Tf was involved in (59)Fe uptake by hepatocytes of CCl(4)-damaged rats. The results showed that the uptake of (59)Fe by hepatocytes and the number of Tf-receptor decreased 1 d after CCl(4)-treatment and increased 2 d after the treatment. Our data demonstrated that the uptake of (59)Fe by hepatocytes differed from that of (67)Ga and Tf was involved in that of (59)Fe. We expect that these finding could serve to analyze the inflammatory stages, disorder stage at 1 d and regeneration stage at 2 d after CCl(4)-treatment.

An indium:calcium phosphate colloid that specifically targets fibrin

The ability of indium to target fibrin in vitro was evaluated. The radionuclide (114m)Indium (114mIn) was prepared as a soluble and colloidal (In:In) form, as well as, a mixed indium:calcium phosphate (In:CaP) colloid. Soluble 114mIn was prepared by maintaining acid pH (50 mM HCl). Colloidal 114mIn (In:In) was prepared under slightly basic conditions (50 mM Tris-Cl, pH 7.6). The mixed In:CaP colloid was prepared by incubation of 114mIn with calcium (10 mM) and phosphate (250 microM) under slightly basic conditions (50 mM Tris-Cl, pH 7.6). To assess fibrin binding, the three 114mIn preparations were mixed with diluted human plasma (source of fibrinogen). Fibrin polymerization was initiated by addition of calcium (5 mM) and thrombin (0.5 U/ml). Following incubation (15 min, 37 degrees C), the fibrin matrix was condensed, removed from the reaction mixture, and washed briefly. Fibrin uptake of 114mIn (soluble, colloidal, or In:CaP) was determined by gamma counting. Results demonstrated that soluble 114mIn exclusively bound a plasma protein electrophoretically and immunologically identified as transferrin. Although both colloidal 114mIn and 114mIn:CaP bound fibrin, the mixed 114mIn:CaP colloid demonstrated substantially higher fibrin binding activity (about 2-fold). The target of indium binding was confirmed as fibrin due to the presence of characteristic cross-linked gamma-gamma dimers (100 kDa) and beta-monomers (58 kDa) by SDS-PAGE. 114mIn colloid and the mixed 114mIn:CaP colloid demonstrated no ability to bind fibrin's precursor, fibrinogen. 114mIn:CaP fibrin binding was associated with formation of CaP, as evidenced by its dependence on phosphate concentration. The biocompatibility of CaP including its ability to bind 114mIn and specifically target fibrin may be of potential value for diagnostic imaging studies to identify regions of occult vascular stenosis (i.e., atherosclerotic plaques, deep vein thrombosis, pulmonary embolus).