Effects of iodotyrosine deiodinase inhibition on serum concentrations and turnover of diiodotyrosine (DIT) and thyroxine (T4) in the rat

Serum concentrations and metabolic clearance rates (MCR) of diiodotyrosine (DIT) and thyroxine (T4) have been measured by radioimmunoassay and tracer kinetic technique in both normal rats and rats treated with 3-nitro-L-tyrosine (MNT), a potent inhibitor of iodotyrosine deiodinase. In normal rats, DIT serum levels were 0.27 +/- 0.12 nmol/l (mean +/- SD); MCR was 15.9 ml/h . 100 g body weight (bw), and the turnover rate was 4.3 pmol/h . 100 g bw. Inhibition of iodotyrosine deiodination by treatment with 50 mumol MNT per day for 1 week caused a highly significant elevation of DIT serum levels to 4.80 +/- 3.30 nmol/l, a decrease of MCR to 9.0 ml/h . 100 g bw and a ten-fold increase of the DIT turnover rate to 43.2 pmol/h . 100 g bw. Serum concentrations of T4 and T3 decreased slightly, whereas the T4 turnover rate (37.5 vs 37.8 pmol/h . 100 g bw) and rT3 serum levels remained unchanged under MNT treatment. The study demonstrates the presence of measurable DIT serum concentrations in the normal rat. Inhibition of intra- and extrathyroidal iodotyrosine deiodinase leads to a situation in which circulating iodotyrosines play an equally important role in peripheral iodine turnover as the iodothyronines. Since DIT serum levels in normal and enzyme-blocked rats were comparable to those in normal human subjects and patients with iodotyrosine deiodinase defect respectively, MNT-treated rats afford a suitable experimental model for this disease.     

Measurement of platelet-associated IgG in animal models of immune and nonimmune thrombocytopenia

Platelet-associated IgG (PAIgG) is elevated in idiopathic thrombocytopenic purpura (ITP), but it also is elevated in other thrombocytopenic disorders traditionally considered to be nonimmune. Consequently it is possible that elevated PAIgG is a nonspecific finding secondary to thrombocytopenia. To study this issue we developed a rabbit model of immune and nonimmune mediated thrombocytopenia. The mechanism of the thrombocytopenia was validated by platelet survival studies. Immune thrombocytopenia was produced by injection of antirabbit platelet serum that was raised in guinea pigs. Nonimmune aregenerative thrombocytopenia was produced by irradiation of the animals; nonimmune consumptive thrombocytopenia was produced by injection of adenosine diphosphate (ADP). PAIgG was measured in a direct binding assay using 125I-labeled staphylococcal protein A (SpA). Washed platelets from normal, nonthrombocytopenic rabbits bound an average of 81 molecules of SpA per platelet (81 +/- 168, mean +/- 2 SD, n = 39). Infusion of the antiplatelet antiserum produced thrombocytopenia with a rise in PAIgG that was closely correlated with the level of PAIgG (r = 0.86, n = 12). The thrombocytopenia was consumptive, as shown by a very short platelet life span using 111In- labeled platelets. In contrast, both nonimmune thrombocytopenic states resulted in an equal or greater drop in the platelet count but no change in the level of PAIgG. The animals with aregenerative thrombocytopenia had normal or only moderately reduced platelet life spans; however, in every animal the level of PAIgG was not different from the nonthrombocytopenic controls, irrespective of the platelet count. Similarly, the level of PAIgG was unchanged in those rabbits with nonimmune consumptive thrombocytopenia following infusion of ADP (82 +/- 55 molecules of SpA per platelet, mean +/- SD, n = 6). These studies indicate that elevated PAIgG is a specific finding of immune thrombocytopenia and is not secondary to thrombocytopenia itself. Indirectly these results support our hypothesis that immune mechanisms contribute to more thrombocytopenic disorders than was once thought likely.     

Allogeneic stem cell transplantation from related and unrelated donors for aplastic anaemia in adults—a single-centre experience

Aplastic anaemia (AA) is a rare bone marrow failure syndrome treated either by immunosuppressive therapy or allogeneic stem cell transplantation (SCT). At present, no randomised clinical trials evaluating both treatment options, and in particular SCT from unrelated donors, are available. We here report the clinical course and outcome of allogeneic SCT for 20 consecutive adult patients with AA. Newly diagnosed and untreated patients (n = 8) or patients pre-treated by immunosuppressive therapy (n = 12) were transplanted either from human-leukocyte-antigen (HLA) identical family donors (n = 13) or matched (n = 6) and mismatched (n = 1) unrelated donors, respectively. Conditioning varied depending on donor type and included cyclophosphamide with or without anti-thymocyte globulin (ATG) and fludarabine–cyclophosphamide–ATG with or without low-dose total body irradiation. With a median follow-up of more than 40 months, all patients have had favourable outcomes with stable haematopoietic engraftment and high performance scores. Six patients developed acute (five I°–II°; one >II°) and four limited chronic graft-versus-host disease. In this group of AA patients, allogeneic SCT has proven very successful, independent of donor type and pre-treatment. Studies with greater cohorts of patients are warranted to better determine indication and timing of SCT especially from unrelated donors in AA.