John Y.C. Chan

6 Post-partum hyperthyroidism

: The importance of recognizing the frequent occurrence of the destructive (i.e. PPT) and stimulatory (i.e. PGD) causes of PH have been discussed. The estimated prevalence of PH in several geographical regions of Japan, North America and Europe ranges from 2.0-5%. Although the autoimmune basis for GD has been well-established, the clinical and laboratory features of PPT as well as the alterations of humoral and cellular thyroidal immune parameters, the typical needle biopsy evidence of lymphocytic infiltration, and the association with HLA and Gm allotypes associated with the PPT syndrome, favour the view that it is also likely a variant form of subclinical ATD which becomes transiently more active post-partum. Post-partum transient hyperthyroidism with or without transient or permanent hypothyroidism and relapse of GD thyrotoxicosis have been observed in patients with or without a previous history of GD. Hence, an RAIU test is the preferred diagnostic test in differentiating between these two entities, especially in the absence of associated stigmata of GD. When the RAIU test is suppressed, other causes such as thyrotoxicosis factitia and iodine exposure should be excluded. Without an RAIU test, only a rapid and spontaneous resolution of post-partum hyperthyroidism, accompanied by laboratory confirmation of a subsequent hypothyroid phase, can indirectly facilitate the differentiation between PGD and PPT. In the first trimester of pregnancy, an increased FT4I has been proposed as a risk factor for PGD and an increased AMA titre for PPT. Depending upon clinical manifestations, severity, patient and physician preferences, PGD can be treated by one of several choices of conventional therapy. The transient thyrotoxic phase of PPT when relatively asymptomatic may require no therapy, but when symptomatic, only conservative therapy with beta-adrenergic blockers, sedatives and/or tranquilizers is indicated. Close follow-up and long-term surveillance of mothers with PH due to PPT is essential for early detection and management of a possible subsequent hypothyroid phase, which may be symptomatic, but is seldom permanent. Treatment of recurrent episodes of PPT is controversial. Thyrotoxic symptoms are usually mild and transient and can best be managed by symptomatic therapy as indicated. In a few exceptional patients with recurrent episodes, prophylactic treatment with corticosteroid may be warranted but thyroidectomy and ablative radioactive iodine therapy is seldom justified.(ABSTRACT TRUNCATED AT 400 WORDS)

The inhibition of activated factor XII (hageman factor) by antithrombin III: The effect of other plasma proteinase inhibitors

Abstract Human factor XII was activated by adsorption onto kaolin in the presence of high molecular weight kininogen. The washed kaolin-containing precipitates activate prekallikrein to kallikrein. When antithrombin III was added to the reaction mixture, the conversion of prekallikrein to kallikrein was inhibited, the degree of inhibition depending on the concentration of antithrombin and the time of incubation. Heparin had a slight enhancing effect with low concentrations of antithrombin and short incubation times. However, the inhibition of the generated kallikrein by antithrombin III was markedly enhanced by heparin. Antithrombin III inhibited also the effect of activated factor XII on the partial thromboplastin time, using factor XII-deficient plasma. Of other plasma proteinase inhibitors used (α1-antitrypsin, α2-macroglobulin, C l -inactivator) only C l -inactivator inhibited activated factor XII.

Interaction between factor XII (Hageman factor), high molecular weight kininogen and prekallikrein.

Abstract Adsorption of factor XII and plasma kallikrein onto kaolin induces activation of factor XII. Trace amounts of high molecular weight (HMW)-kininogen markedly enhances the rate and the amount of activation of factor XII. Activation of factor XII was measured by its capacity to convert prekallikrein to kallikrein. This potentiating effect is dependent on the amount of HMW-kininogen. Low molecular weight kininogen has no enhancing effect. When the reactants are adsorbed to kaolin and the latter separated by centrifugation the prekallikrein-converting activity is detectable only in the kaolin-containing precipitates. Less activation of factor XII occurs when the HMW-kininogen is added not initially to the kaolin-factor XII mixture, but to the prekallikrein, indicating that the HMW-kininogen probably acts when factor XII is being activated, rather than at a later stage. Treatment of HMW-kininogen with excess trypsin, plasmin or kallikrein abolishes its potentiating effect. When HMW-kininogen is treated with increasing concentrations of kallikrein there is an inverse relationship between the generated kinin and the ability of the kininogen to enhance the activation of factor XII.

Encoding of human basic and glycosylated proline-rich proteins by the PRB gene complex and proteolytic processing of their precursor proteins

Proline-rich proteins (PRPs) constitute a family of about 20 members in human saliva that are encoded by six genes. Assignment of genomic DNA coding regions is complicated because of the occurrence of many alleles and the great similarity of amino acid sequences of PRPs. To overcome these problems, the nucleotide sequences of the genes encoding basic and glycosylated PRPs from one person were determined and then aligned with her previously determined protein sequences. This, together with additional protein data, has also resolved various discrepancies between corresponding protein and DNA sequences. For the first time in one person it is now possible to account for all the regions in the PRB genes encoding basic and glycosylated PRPs, and the primary structures of all secreted basic and glycosylated PRPs have been determined. Each gene encodes a precursor protein that subsequently undergoes proteolytic cleavage, thereby giving rise to the secreted proteins. The results have allowed identification of all the proteolytic cleavage sites in the precursor proteins, which all conform to a consensus cleavage site for furin. To evaluate if furin is responsible for the precursor protein cleavages, a recombinant precursor protein was synthesized by in vitro transcription translation of a PRB1 allele. The protein was shown to be correctly cleaved by furin, giving rise to the expected secreted proteins.

Purification of factor XII (Hageman factor) from human plasma.

Abstract Factor XII was purified from human plasma in four steps, in the presence of a contact activation inhibitor, hexadimethrine bromide, and soy bean trypsin inhibitor (SBTI), an inhibitor of plasma proteases, which act on factor XII. After adsorption with aluminum hydroxide (1 : 10), the plasma was precipitated with polyethylene glycol. The protein precipitating between 4.0 and 16% saturation was redissolved in about 30% of the starting plasma volume and chromatographed. The first chromatographic step was anion exchange chromatography on QAESephadex, in the presence of hexadimethrine bromide and SBTI. The SBTI was used also during the first half of chromatography on CM-Sephadex, from which factor XII eluted in the second half. As a fourth preparative step factor XII was subjected to either gel filtration on Sephadex G-100 or affinity chromatography. The latter consisted of an immunoadsorbent column, the antibody being against contaminating proteins isolated from factor XII-deficient plasma. The final product exhibited a sharp intense band by SDS-disc gel electrophoresis, with an estimated molecular weight of 78,000. The method is suitable for the purification of factor XII, which is a trace protein, from large volumes of plasma.

Surface activation of factor XII (Hageman factor) — Critical role of high molecular weight kininogen and another potentiator

When factor XII was adsorbed to kaolin it slowly became activated and converted prekallikrein to kallikrein. In the presence of HMW-kininogen the rate of activation of factor XII and consequently that of prekallikrein was markedly enhanced. The enhancing effect of HMW-kininogen was a dose-dependent phenomenon. In order to enhance the activation of factor XII on a surface the HMW-kininogen molecule had to be intact. Cleavage of HMW-kininogen by kallikrein decreased the enhancing effect of HMW-kininogen, there being an inverse relation between the bradykinin-generated and the capacity to enhance factor XII activation. Another ‘potentiator’ of factor XII activation was isolated from proteins adsorbed to aluminum hydroxide. This potentiator further increased the activation of factor XII, also in a dose-dependent fashion. It was postulated that factor XII is slowly converted into its active form by exposure to negatively charged surfaces; that this process is enhanced by kallikrein and further accelerated by HMW-kininogen and the ‘potentiator’; and that these enhancing substances probably act by opening active sites on the factor XII molecule.

High molecular weight kininogen: its inability to correct the clotting of kininogen-deficient plasma after cleavage of bradykinin by plasma kallikrein, plasmin or trypsin.

Abstract Human high molecular weight (HMW)-kininogen was cleaved with trypsin, plasmin or plasma kallikrein to release bradykinin. ‡ When an excess of enzyme was used and all releasable peptide was released, the residual HMW-kininogen could not correct the clotting deficiency of kininogen-deficient plasma. There was an inverse relationship between the amount of bradykinin released and the capacity of the kininogen to correct the abnormal partial thromboplastin time of kininogen-deficient plasma. These findings and earlier ones indicate that the intact HMW-kininogen molecule is required for contact mediated clotting and activation of factor XII.

Coagulation of human plasma by asbestos fibers.

Abstract Negatively and positively charged asbestos fibers shorten the partial thromboplastin time of human plasma, indicating coagulation of the plasma. A sample containing short (