ABSTRACT
OBJECTIVE: To determine if concentrations of free thyroxine (FT4) measured by semi-automated chemiluminescent immunoassay (CLIA) correspond to FT4 determined by equilibrium dialysis (ED) in hypothyroid dogs positive for thyroglobulin antibody (TGA). ANIMALS: Thirteen TGA-positive dogs classified as hypothyroid based on subnormal FT4 concentrations by ED. METHODS: Qualitative assessment of canine TGA was performed using an enzyme-linked immunosorbent assay. Serum total thyroxine and total triiodothyronine concentrations were measured by radioimmunoassay. Serum FT4 concentration was determined by ED, and also by semi-automated CLIA for human FT4 (FT4h) and veterinary FT4 (FT4v). Canine thyroid stimulating hormone concentration was measured by semi-automated CLIA. RESULTS: Each dog's comprehensive thyroid profile supported a diagnosis of hypothyroidism. For detection of hypothyroidism, sensitivities of CLIA for FT4h and FT4v were 62% (95% CI, 32-85%) and 75% (95% CI, 36-96%), respectively, compared to FT4 by ED. Five of 13 (38%) dogs had FT4h and 2 of 8 (25%) dogs had FT4v concentrations by CLIA that were increased or within the reference range. Percentage of false-negative test results for FT4 by CLIA compared to ED was significantly (P < .0001 for FT4h and P < .001for FT4v) higher than the hypothesized false-negative rate of 0%. CONCLUSIONS AND CLINICAL IMPORTANCE: Caution should be exercised in screening dogs for hypothyroidism using FT4 measured by CLIA alone. Some (25-38%) TGA-positive hypothyroid dogs had FT4 concentrations determined by CLIA that did not support a diagnosis of hypothyroidism.
Subject(s)
Autoantibodies/immunology , Dog Diseases/blood , Hypothyroidism/veterinary , Luminescent Measurements/veterinary , Thyroglobulin/immunology , Thyroxine/blood , Animals , Dog Diseases/diagnosis , Dog Diseases/immunology , Dogs , Enzyme-Linked Immunosorbent Assay/veterinary , False Positive Reactions , Female , Hashimoto Disease/blood , Hashimoto Disease/diagnosis , Hashimoto Disease/immunology , Hashimoto Disease/veterinary , Hypothyroidism/blood , Hypothyroidism/diagnosis , Hypothyroidism/immunology , Luminescent Measurements/methods , Male , Thyroiditis, Autoimmune/blood , Thyroiditis, Autoimmune/diagnosis , Thyroiditis, Autoimmune/immunology , Thyroiditis, Autoimmune/veterinary , Thyrotropin/blood , Triiodothyronine/bloodABSTRACT
PURPOSE: Cisplatin (DDP) is an effective antitumor agent limited in its efficacy by the development of tumor cell resistance. The defective accumulation of DDP has been shown to be a prominent feature in many DDP-resistant cell lines. In an effort to circumvent this problem, we examined the cellular accumulation of DDP in the presence of terbium (Tb3+). We also examined the effects of verapamil on the cellular accumulation of DDP in order to delineate the specific interaction of Tb3+ and DDP. All experiments were performed on DDP-sensitive or DDP-resistant MDA-MB-231 human breast tumor cells. METHODS: The cellular accumulation of DDP and verapamil were determined by electrothermal atomic absorption spectrophotometry. Time-resolved luminescence spectroscopy was used to obtain equilibrium binding constants for the Tb3+/MDA cell complexes. RESULTS: We found that 100 microM Tb3+ increased DDP accumulation in the parent MDA cell line, 5.7-fold resistant MDA/A13 and 10-fold resistant MDA/CH cells by 56.2 +/- 7.4, 71.9 +/- 9.4 and 50.8 +/- 9.4%, respectively (P < 0.0001 for all MDA cell types). In contrast, 20 microM verapamil had no significant effect on DDP accumulation in the MDA cell lines. In addition, a positive correlation between the membrane binding of Tb3+ and the cellular accumulation of DDP was found to exist in the parent cell line and sublines (r = 0.9). CONCLUSIONS: In agreement with earlier studies, the plasma membrane of MDA cell lines contain a specific Tb(3+)-binding protein. Our findings suggest that the Tb(3+)-binding protein may be intimately associated with the accumulation of DDP in breast tumor cells.
Subject(s)
Antineoplastic Agents/metabolism , Breast Neoplasms/metabolism , Cisplatin/metabolism , Terbium/pharmacology , Analysis of Variance , Calcium Channel Blockers/pharmacology , Drug Resistance, Neoplasm , Female , Humans , Middle Aged , Terbium/metabolism , Tumor Cells, Cultured/metabolism , Verapamil/pharmacologyABSTRACT
In this investigation, we report a relationship between the terbium (Tb3+) binding protein and the accumulation of cisplatin in human ovarian cancer cells. The number of Tb3+ binding sites in cisplatin-resistant C13+ cells is significantly greater by 79% than those in cisplatin-sensitive 2008 cells. Exposure to Tb3+ also increased the cellular accumulation of cisplatin. The accumulation of cisplatin as a function of the Tb3+ concentration in the C13+ cells (0.85%/microM Tb3+) was significantly greater than the accumulation of cisplatin in 2008 cells with respect to Tb3+ (0.46%/microM Tb3+). The number of Tb3+ binding sites in revertant RH4 cells was similar to that in 2008 cells. The RH4 cells were less sensitive to the stimulatory effects of Tb3+ than the C13+ cells. Our results show that the Tb3+ binding protein correlates with cisplatin resistance, and the receptor binding of Tb3+ increases the accumulation of cisplatin in cisplatin-resistant cells.
