Stability of radioiodinated monoclonal antibodies: in vitro storage and plasma analysis

The in vitro stability and immunointegrity of four radioiodinated monoclonal antibodies was evaluated in various storage conditions and also in plasma samples. The monoclonal antibodies studied included T101, B72.3, Lym1, and 16.88. Stabilities of typical monoclonal antibody therapy solutions, with radioactivities ranging from 2220 to 3700 MBq (60-100 mCi) were assessed using conventional instant thin layer chromatography and size exclusion high performance liquid chromatography. Radioimmunoreactivity was assessed using a live cell attenuated cell, or mucin-linked bead assay. Results of the study demonstrated that therapy solutions were stable to degradation, if properly stored in 5 or 10% human serum albumin at 4 degrees C for the duration of the study (5 days). Minor losses in immunoreactivity were also measured in stabilized therapy solutions. When incubated in plasma samples, radioiodinated monoclonal antibodies generally remained stable for the duration of the study (3 days). However, significant decreases in immunoreactivity were measured for specific radioiodinated monoclonal antibody preparations.

Insulin-like growth factor-binding proteins in hypophysectomized rat liver: characterization and subcellular localization

We have characterized binding proteins for insulin-like growth factors (IGFs) in hepatic subcellular fractions and in the washed supernatants of these fractions in normal and hypophysectomized (hypox) rats. In the course of assessing IGF-II-binding sites on rat liver microsomes, we observed that [125I] IGF-II binding to the microsomal membranes of hypox rats was much lower than that in normal rats. Paradoxically, binding increased in hypox animals at low concentrations (0.5-5 ng/ml) of unlabeled IGF-II. After resuspension and centrifugation (washing) of the microsomes, no difference was found in [125I]IGF-II binding to hypox vs. normal microsomes. However, the binding of [125I]IGF-II to the washing supernatant (SN) from hypox rat microsomes was greater than binding to that from normal animals. Binding to SN was inhibited by unlabeled IGF-II in a dose-dependent manner. Scatchard analyses indicated that the affinity constant for binding by hypox SN was higher than that of normal SN and the microsomal fractions of both hypox and normal rats. After further subfractionation of the liver, no binding activity was found in SN from plasmalemma, whereas it was about 20% of input counts per min of [125I]IGF-II in SN from combined Golgi-endosome fractions of hypox rat liver. We next compared IGF-binding moieties in microsomal SN with those in plasma using cross-linking of [125I]IGF-II followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In normal rat plasma, we observed the presence of 42K, 39K, 31K, and 27K binding complexes. In hypox rat plasma only a 42-39K doublet was found. In the SN of normal rat microsomes, the predominant complex migrated at 39K and was distinguishable only after acidification. In the SN of hypox rat microsomes, the 42K complex was predominant, with a minor 34K complex. These studies have identified IGF-binding moieties in hepatic tissues, particularly in hepatic vesicular elements, which interfere in the binding of IGF-II to membrane receptors. Their presence in these receptor-rich elements may influence IGF binding to intracellular receptors and, hence, the biological activity of the peptide.

Insulin-like growth factor (IGF) binding in hypophysectomized rat liver microsomes: alteration by a soluble binding moiety

In this study, we compared the binding of IGF-I and IGF-II to liver microsomes of normal and hypophysectomized (Hypox) rats. The binding of [125I]-IGF-II, measured by centrifugation of membrane-bound ligand, was lower in hypox than in normal rats (15 +/- 2 vs 26 +/- 1%, p less than 0.001) but binding was increased (46 +/- 1.5 vs 31 +/- 1%, p less than 0.001) when bound and free hormones were separated using polyethyleneglycol (PEG) precipitation. This was due to the presence of soluble binding activity which dissociated from membranes to compete for IGF binding. When soluble binding activity was first removed from microsomal membranes by a washing procedure no difference was found in [125I]-IGF-II binding to microsomes of Hypox and normal animals (33 +/- 1 s 32 +/- 1%). However, in the microsomal washing supernatant from Hypox (containing soluble binding activity) IGF-II binding was much higher than in that from normals (17 +/- 2 vs 6 +/- 0.5%, p less than 0.001). The binding of [125I]-IGF-I was lower than that of [125I]-IGF-II but was comparably changed. By contrast, [125I]-insulin binding was similar in Hypox and normal rats and was not influenced by PEG precipitation or prewashing of the membranes. Inhibition dose-response curves showed a paradoxical increase in [125I]-IGF-II binding to unwashed microsomes of Hypox rats in the range of 0.5-5 ng/ml cold IGF-II. In normal animals [125I]-IGF-II binding to microscomes was progressively inhibited by IGF-II in a range of 0.5-500 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentration of native prolactin and prolactin binding sites in hepatic subcellular fractions from hyperprolactinemic rats

Lactogen binding and prolactin content were measured in hepatic subcellular fractions from tumor-bearing rats (TBR; MtT/F4, MtT/W5, MtT/W10) with elevated prolactin and growth hormone levels and from control animals. Specific binding of 125I-oPRL to Golgi fractions from tumor-bearing animals was 2.5 to 7 fold greater than that from controls. Binding to plasmalemma was 6-fold greater in tumor-bearing rats. The specific binding of 125I-labelled bGH and insulin showed less marked differences between TBR and controls. Subcellular fractions were extracted with HCl to determine hormonal content. The content of prolactin and growth hormone in Golgi fractions from TBR was at least 20-fold that in fractions from controls. Rat prolactin extracted from Golgi heavy elements was 50% as effective as native material in binding to lactogen receptors as judged by radioreceptor assay. These studies demonstrate that the chronic elevation of prolactin was associated with an increase of receptors not only in the intracellular compartment but on the cell surface as well. Furthermore, they demonstrate that native prolactin is internalized and accumulated in rat liver Golgi fractions.

Immunologic similarity of insulin receptors in Golgi and plasma membranes from rat liver

Insulin receptor antibodies (IRA) have been shown to inhibit 125I-labeled insulin binding to plasmalemma and whole cells. An earlier study claimed that IRA was less able to inhibit 125I-labeled insulin binding to intracellular receptors than plasmalemma of rat liver. We have examined the effect of IRA serum from a patient with insulin-resistant diabetes mellitus on 125I-labeled insulin binding to plasmalemma and Golgi fractions prepared from female rat liver. Maximum inhibitions of 125I-labeled insulin binding were 44, 48, 55, and 51% for plasmalemma, Golgi light, Golgi intermediate, and Golgi heavy, respectively, and these were maintained at a serum dilution of up to 1:100. Half-maximal inhibition occurred at a serum dilution of 1:900. The IRA serum had no inhibitory effect on 125I-labeled ILAs and ovine prolactin (oPRL) binding to either plasma membrane or Golgi fractions. Analysis of the effect of the IRA serum showed that its inhibition of 125I-labeled insulin binding linearized the Scatchard plot, with abolition of the high affinity portion of the curve, and reduced the number of low affinity sites. The affinity of binding to Golgi but not plasmalemma insulin receptors was decreased. We conclude that there is immunologic similarity between intracellular and cell surface insulin receptors of rat liver. This is compatible with a fairly rapid equilibration between these two receptor populations, as expected with an active membrane recycling process.

Effect of colchicine on internalization of prolactin in female rat liver: an in vivo radioautographic study

Binding and internalization of 125I-ovine prolactin into hepatocytes of female rats was visualized by the in vivo radioautographic method (Bergeron, J. J. M., G. Levine, R. Sikstrom, D. O'Shaughnessey, B. Kopriwa, N. J. Nadler, and B. I. Posner, 1977, Proc. Natl. Acad. Sci. USA, 745:051-5055). Receptor-mediated internalization of label was observed into lipoprotein-filled vesicles in the Golgi/bile canalicular region of the hepatocyte. Colchicine treatment had no effect on the internalization of label into the lipoprotein-filled vesicles. However, the location of the radio-labeled lipoprotein-filled vesicles was altered from the Golgi/bile canalicular region to subsinusoidal. Radioactive content of hepatocytes decreased as a function of time after injection of 125I-prolactin; however, colchicine treatment markedly retarded this loss of label. Subcellular fractionation experiments indicated that colchicine treatment led to decreased levels of 125I-prolactin accumulation in microsomes but augmented the accumulation of label in the L fraction. It is concluded that in normal female rats prolactin is internalized into lipoprotein-filled vesicles in the Golgi region before degradation of the hormone. Colchicine treatment accumulates labeled lipoprotein-containing vesicles in a subsinusoidal region and retards hormone catabolism. The labeled vesicles observed after colchicine treatment may correspond to the unique vesicles previously observed in the L fraction and found to be enriched in prolactin receptors (Khan, M. N., B. I. Posner, A. K. Verma, R. J. Khan, and J. J. M. Bergeron, 1981, Proc. Natl. Acad. Sci. USA, 78:4980-4981).

Effect of colchicine on the uptake of prolactin and insulin into Golgi fractions of rat liver

In previous studies we have shown that 125I-labeled prolactin is taken up by a receptor-dependent process and concentrated in an intact form in Golgi elements from female rat liver (J. Biol. Chem., 1979, 254:209-214). In this study we have examined the effect of colchicine on this uptake process into Golgi elements. Colchicine [25 mumol (10 mg)/100 gm body wt] was injected intraperitoneally in adult female rats, and hepatic Golgi fractions were prepared at 1, 2, and 3 h postinjection. The enzyme recoveries and morphological appearance of fractions from colchicine-treated and control (alcohol alone) animals were similar. At times greater than 1 h after colchicine there was a marked (greater than 60%) inhibition of uptake of 125I-ovine prolactin (125I-oPRL) into Golgi light and intermediate fractions but no inhibition of uptake into Golgi heavy and plasmalemma elements. At times from 2 to 45 min postinjection, 125I-oPRL was extracted from Golgi elements and found to be largely intact as judged by rebinding to receptors. The inhibitory effect of colchicine was seen at doses ranging from 0.25 mumol to 25 mumol/100 g body wt. Vincristine also inhibited 125I-oPRL uptake into the Golgi light and intermediate fractions but lumicolchicine had no inhibitory effect. There was a smaller effect of colchicine both at early (1 h) and later (3 h) times on the extent and pattern of 125I-insulin uptake. Colchicine treatment did not produce a significant change in lactogen receptor levels in the Golgi fractions. These results demonstrate that colchicine treatment inhibited the transfer of prolactin into Golgi vesicular elements. The much smaller effect on insulin uptake suggests that there may be differences in the manner in which the two hormones are handled in the course of internalization.