The long-acting somatostatin analogue octreotide alleviates symptoms by reducing posttranslational conversion of prepro-glucagon to glucagon in a patient with malignant glucagonoma, but does not prevent tumor growth

A 52-year-old female with metastatic glucagonoma secreting glucagon and chromogranin A was treated with the somatostatin analogue octreotide for 2 years without any additional tumor-reducing interventions. Before therapy plasma glucagon was above 8 μg/l (normal <0.2) and within 2 days 3 × 200 μg octreotide daily suppressed plasma glucagon to 2.2-2.5 μg/l. Concomitantly, chromogranin A dropped from 0.85 mg/l (normal <0.1) to 0.2. After 3 weeks the preexisting disabling necrolytic migratory erythema had vanished completely, and weight loss was temporarily stopped. During therapy chromogranin A and plasma glucagon rose, exceeding pretreatment levels after 3 and 14 months, respectively. After 1 year the erythema recurred, responding only transiently to increasing doses of octreotide. The patient died after 2 years of therapy of tumor cachexy despite very highdosesof octreotide (4 × 600 μg/day). Throughout treatment octreotide did not prevent tumor growth, as demonstrated by computed tomography and sonography. Determination of immunoreactive glucagon before and during octreotide therapy in fractions of plasma samples subjected to gel chromatography revealed a reduction in the ratio of glucagon to preproglucagon from 1.83 (before) to 0.56 (during therapy), indicating inhibition of posttranslational processing of preproglucagon by octreotide, thereby reducing circulating bioactive glucagon. In summary, octreotide induced a remission of clinical symptoms by inhibiting posttranslational conversion of preproglucagon to glucagon but did not prevent tumor growth. Therefore, octreotide is a valuable therapy for rapid relief of clinical symptoms, thereby improving the possibilities for other tumor-reducing therapies

Klinische Bedeutung der Bestimmung der Bindung von Trijodthyronin an Serumproteine mittels Dextran-Gel-Filtration

Neben den bewährten älteren Verfahren zur Bestimmung des proteingebundenen127Jods und des Radiojodumsatzes hat sich die gleichzeitige Bestimmung des sog. freien und des proteingebundenen Anteils an in vitro mit Serum inkubiertem L-Trijodthyronin-131Jod mittels Dextran-Gel-Filtration klinisch zur Differentialdiagnose von Hyperthyreose und Euthyreose bewährt. Bei Ausnützung der Verdrängung von proteingebundenem L-Trijodthyronin-131Jod durch nichtmarkiertes Hormon und bei Variation der Dextran-Gel-Menge in der Säule bietet die Methode gute Differenzierungsmöglichkeiten auch für die Schilddrüsenfunktionszustände Euthyreose und Hypothyreose. Bei dem Verfahren wird der Patient nicht mit radioaktivem Jod belastet, ein für die Kinderklinik wichtiger Gesichtspunkt. Manche Störfaktoren, die den131Jodspeicherungstest und die Bestimmung des proteingebundenen Jods (PB127I) verfälschen, haben keinen Einfluß auf die mit der Dextran-Gel-Filtration untersuchten Proteinbindungsverhältnisse für L-Trijodthyronin-131Jod. So hat sich das Verfahren für die Untersuchung von Patienten mit operativ oder durch131Jodbehandlung verkleinerten Schilddrüsen, mit endokrinem Exophthalmus und in Fällen mit vorausgegangener Jodgabe, z. B. in Form von Kontrastmitteln, besonders bewährt. Mit der Bestimmung des sog. freien L-Trijodthyronin-131Jods wird ein physiologisch und pathogenetisch wichtiger Parameter der Schilddrüsenfunktion ermittelt. Die klinische Bedeutung der Bestimmung der Bindungs-und Transportverhältnisse für Trijodthyronin mittels Dextran-Gel-Filtration wird diskutiert.In addition to conventional methods of assay of protein bound iodine (PB127I) and of131iodine turnover in the thyroid, the simultaneous determination of socalled free and protein bound 1-triiodothyronine-131I, added in vitro to serum, using dextran gel filtration was found to be clinically helpful for diagnosis of euthyroidism and hyperthyroidism. Employing discharge effects of non-labelled triiodothyronine on protein bound 1-triiodothyronine-131I and varying the amount of dextran gel in the columns, the method provides reasonably good differentiation of euthyroid and hypothyroid states. No radioactive iodine is given to patients during this procedure, a fact of importance for pediatriciens. Some factors, that influence131iodine uptake or PB127I levels, do not disturb protein binding of 1-triiodothyronine-131I as determined by dextran gel filtration. The latter method was found to be especially useful for the examination of patients with surgically, or by therapy with131iodine dissected thyroid glands, with endocrine exophthalmos, and in cases of previous iodine administration (e.g. X-ray procedures). Determination of socalled free 1-triiodothyronine-131I provides information about a factor of physiological and pathogenetical significance, its clinical meaning is discussed

Thyroid peroxidase forms thionamide-sensitive homodimers: relevance for immunomodulation of thyroid autoimmunity

Thyroid peroxidase (TPO) is the key enzyme in thyroid hormone production and a universal autoantigen in Graves’ and other autoimmune thyroid diseases. We wished to explore the expression of TPO and whether it was affected by thionamide antithyroid drugs. We studied recombinant TPO, stably expressed by a Chinese hamster ovary cell line (CHO-TPO) and transiently expressed TPO-enhanced green fluorescent protein (eGFP) and -FLAG fusion proteins. Immunoblotting of CHO-TPO cell extracts showed high-molecular weight (HMW) TPO isoforms that were resistant to reduction, as well as 110 kDa monomeric TPO. Co-immunoprecipitation and enzyme-linked-immunosorbent assay (ELISA) binding studies of FLAG- and eGFP-tagged TPO demonstrated TPO dimerisation. CHO-TPO cells cultured in methimazole (MMI) for 10 days showed a significant reduction in HMW-TPO isoforms at MMI concentrations of 1 µM and above (p < 0.01), whereas monomeric TPO expression was unchanged. We observed a similar reduction in HMW-TPO in CHO-TPO cells cultured in propylthiouracil (10 µM and above). Binding of Graves’ disease patient sera and TPO-Fabs to enzymatically active TPO that was captured onto solid phase was not abrogated by MMI. The cellular localisation of TPO in CHO-TPO cells was unchanged by MMI treatment. Our demonstration of homodimeric TPO and the reduction in HMW-TPO isoforms during thionamide treatment of CHO-TPO cells shows, for the first time, an effect of thionamides on TPO structure. This suggests a structural correlate to the effect of thionamides on TPO enzymatic activity and opens up a novel potential mechanism for thionamide immunomodulation of autoimmune thyroid disease