Identification of thiopurine methyltransferase (TPMT) polymorphisms cannot predict myelosuppression in systemic lupus erythematosus patients taking azathioprine.

OBJECTIVE: To determine whether the presence of polymorphisms associated with reduced or absent activity of thiopurine methyltransferase (TPMT), an enzyme involved in azathioprine metabolism, can predict side-effects, particularly myelosuppression, in patients taking this drug. METHODS: The TPMT genotype was determined in 120 patients with systemic lupus erythematosus (SLE) together with 15 patients with inflammatory bowel disease (IBD) and correlated with the effects of clinical exposure to azathioprine. RESULTS: TPMT polymorphisms were detected in eight patients. Severe marrow toxicity occurred in the single homozygote identified. Azathioprine was generally well tolerated, but 11 drug-associated neutropenias were detected. In only one of the 11 cases was a TPMT polymorphism identified. CONCLUSION: Homozygous TPMT deficiency was associated with severe marrow suppression. In the majority of cases, however, TPMT genotyping prior to azathioprine therapy would not have predicted myelosuppressive events and may augment, but not replace, regular blood monitoring.

Fibrinogen receptor (GPIIb-IIIa) antagonists derived from 5,6-bicyclic templates. Amidinoindoles, amidinoindazoles, and amidinobenzofurans containing the N-alpha-sulfonamide carboxylic acid function as potent platelet aggregation inhibitors.

A series of highly potent and specific fibrinogen receptor antagonists have been discovered and optimized through structural modification of the novel amidinoindole and benzofuran compounds, I and II. Systematic linker optimization afforded the amidinobenzofuran-containing inhibitor 29, which displayed an IC50 value of 250 nM in platelet aggregation assays. Attempts to enhance activity by modification of the beta-position of the beta-alanyl carboxylate group of 29 had only a modest effect on inhibitory activity in aggregation assays. Analogues prepared to enhance the activity by conformational restriction were also found to be equally or less potent. In contrast, modification at the alpha-position of the beta-alanyl carboxylate group resulted in the identification of extremely potent and novel amidinobenzofuran-containing derivatives 46-49. Reexamination of 5,6-bicyclic aromatic nucleus led to the further identification of amidinoindole- and amidinoindazole-containing derivatives 53-55. These analogues, 46-49 and 53-55, exhibited potent in vitro activity with IC50 values of 25-65 nM in platelet aggregation assays and an IC50 value of 2 nM in fibrinogen binding assays and demonstrated a selectivity of > 50,000-fold for GPIIb-IIIa versus the most closely related integrin, the vitronectin receptor, alpha v beta 3.

Organ-specific contribution to circulating C7 levels by the bone marrow and liver in humans.

Many cells types can produce complement component C7, although the major site of C7 synthesis is unknown. Conversion from recipient to donor allotype following organ transplantation has demonstrated the synthetic sites of several complement proteins, but in the case of C7 this was not possible until recently. A novel C7 polymorphism (C7 M/N) has been described based on the reactivity with the monoclonal antibody WU 4-15 which identifies in allotype of C7 (C7 M). Bone marrow and hepatic C7 production was quantified in bone marrow transplant and liver transplant recipients, respectively, where a mismatch for the C7 allotypes distinguished by the monoclonal antibody had occurred. In the bone marrow transplant group, one informative transplant was identified and donor-derived C7 was detected by enzyme-linked immunosorbent assay. It contributed to 18-27% of the total circulating C7 during the post-transplant phase and was increased during episodes of inflammation. In the liver transplant group, the hepatic contribution to the C7 levels were 30% and 52%, respectively, in two patients identified prospectively. A further three informative liver transplant patients were identified retrospectively and in these individuals, 56-62% of the circulating C7 was liver-derived. This study demonstrates that the majority of the circulating C7 is derived from the liver and bone marrow with a lesser contribution from other sources. These findings provide further support for the concept that locally secreted complement proteins have an important role in inflammation.

Extrahepatic secreted complement C3 contributes to circulating C3 levels in humans.

The majority of complement protein C3 is synthesized by the liver, but many other cell types produce small amounts of functionally active C3. The overall contribution of such extrahepatic C3 production to the total circulating C3 level is unknown. Bone marrow and extrahepatic C3 productions were quantified in bone marrow transplant (BMT) and liver transplant (LT) recipients, respectively, where a mismatch for the C3 allotypes distinguished by the mAb HAV 4-1 had occurred. In the BMT group, donor-derived C3 was detected by ELISA and immunoblotting techniques. It contributed to 0.1 to 2.6% of the total circulating C3 during the immediate post-BMT period in response to inflammatory stimuli. Cell culture and immunostaining techniques demonstrated that monocytes were the source of the C3. By 6 wk following BMT, donor-derived C3 levels had decreased to below the detection limit of the assays. By contrast in the LT group, total extrahepatic C3 levels were higher (3.1-5.7% of the total circulating C3) and remained stable for up to 1 yr post-LT. This study demonstrates that extrahepatic derived C3 forms a larger proportion of the circulating C3 levels than was considered previously and that in the resting state, most of this extrahepatically derived C3 comes from nonmyeloid sources. In addition, monocytes, which in the resting state contribute negligible amounts of C3, have the potential when stimulated to contribute significantly to the total systemic C3 pool. These findings highlight the importance of locally secreted complement proteins.

C3 nephritic factor and SLE: report of four cases and review of the literature.

We present four patients with C3 nephritic factor associated with partial lipodystrophy and/or mesangiocapillary glomerulonephritis type II. Each of these patients subsequently developed features of SLE, with an onset between 2 and 24 years after the development of the lipodystrophy or glomerulonephritis. All four patients had antinuclear antibodies and three of the four had anti-Ro antibodies. These patients bring to six the number of reported cases of this association. Possible explanations for the link between these two conditions are discussed.

Characterization of the integrin specificities of disintegrins isolated from American pit viper venoms.

A new series of homologous disintegrins was isolated from the venoms of new world pit viper genus Bothrops, Crotalus, and Lachesis. The relative activities of each disintegrin in blocking adhesive protein binding activities of GPIIb-IIIa, alpha v beta 3, and alpha 5 beta 1 were determined and correlated with their primary amino acid sequences. Four disintegrins contained the RGDW sequence and were found to be approximately twice as effective in blocking the binding of fibrinogen to GPIIb-IIIa than inhibiting the binding of vitronectin to alpha v beta 3 in solid-phase ligand binding assays (IC50 = 7.3 and 17.2 nM, respectively). A second group of seven disintegrins contained the RGDNP sequence and were found to be more potent inhibitors of vitronectin binding to alpha v beta 3 than fibrinogen binding to GPIIb-IIIa (IC50 = 4.3 and 19 nM, respectively). The RGDNP containing disintegrins were also greater than 10-fold more potent than RGDW containing disintegrins in blocking the adhesion of cells mediated by alpha 5 beta 1. These data illustrate that amino acid sequences immediately adjacent to the RGD site of disintegrins can create an extended RGD locus which coupled with conformational display of the RGD sequence may be involved in determining integrin selectivity and affinity. This information has been used in separate studies to design conformationally constrained integrin antagonists with high affinity for platelet GPIIb-IIIa.

Design of potent and specific integrin antagonists. Peptide antagonists with high specificity for glycoprotein IIb-IIIa.

Members of the snake venon-derived, "disintegrin" peptide family containing the Arg-Gly-Asp (RGD) amino acid sequence are among the most potent inhibitors of the binding of adhesive proteins to platelet glycoprotein (GP) IIb-IIIa. However, GPIIb-IIIa antagonists containing the RGD sequence are not integrin specific and inhibit the adhesive functions of many other RGD-dependent integrins. The single disintegrin peptide, barbourin, containing a conservative amino acid substitution of Lys (K) for Arg (R) in the RGD sequence, is however, highly specific for GPIIb-IIIa. Using this information we have tested the hypothesis that both structural and conformational elements of barbourin are important for its high affinity and selectivity for platelet GPIIb-IIIa by synthesizing a series of conformationally constrained, disulfide-bridged peptides containing the KGD amino acid sequence. Incorporation of the KGD sequence into a cyclic peptide template, followed by systematic optimization of the cyclic ring size, optimization of secondary hydrophobic binding site interactions, and the derivatization of the lysyl side chain functionality of the KGD sequence has resulted in peptide analogs which display inhibitory potency and GPIIb-IIIa selectivity comparable to that of barbourin. This study demonstrates that the specificity and potency of the disintegrin family of antagonists, in particular barbourin, can be mimicked by small, conformationally restrained peptides.

Tethered ligand agonist peptides. Structural requirements for thrombin receptor activation reveal mechanism of proteolytic unmasking of agonist function.

The human platelet thrombin receptor is activated when thrombin cleaves its receptor's amino-terminal extension to reveal a new amino terminus that functions as a tethered peptide ligand. Exactly how this "agonist peptide domain" remains cryptic within the uncleaved receptor and becomes functional after receptor cleavage is unknown. In this report we define the structural features of the thrombin receptor's agonist peptide domain important for receptor activation. Studies with mutant thrombin receptors have suggested that agonist peptide domain residues 2-6 contained determinants critical for receptor activation, and the synthetic peptide SFLLR-NH2 representing the 1st 5 amino-terminal residues of the agonist peptide domain was sufficient to specify agonist activity. Acetylating or removing the agonist peptide's amino-terminal ammonium group greatly attenuated agonist activity. Agonist peptide residue Phe2 was vital for agonist function; residues Leu4 and Arg5 individually played less important roles. These structure-function relationships held for both platelet activation and activation of the cloned receptor expressed in transfected mammalian cells. Our studies suggest that structures at the extreme amino terminus of the thrombin receptor's agonist peptide domain, in particular the free ammonium group of Ser1 and the phenyl ring of Phe2, are critical for receptor activation and that the agonist function of this domain is expressed when receptor proteolysis unmasks such determinants. In addition to revealing details of the thrombin receptor's proteolytic triggering mechanism, these studies open avenues to the development of drugs targeting the thrombin receptor and to further definition for the role of the thrombin receptor in cellular regulation.

Treatment of acute post-infective polyneuropathy by means of plasma exchange.

15 patients with acute post-infective polyneuropathy of the Guillain-Barré type have been treated by means of plasma exchange. The clinical course and outcome of these patients is compared to that in a retrospectively matched control series who were treated with supportive therapy only. All patients had severe rapidly evolving muscle weakness and approximately half the patients in each group required ventilatory assistance. Both the duration of muscle weakness and the hospitalisation time was significantly shorter in the patients treated by means of plasma exchange. These results suggest that plasma exchange is of significant benefit in the treatment of patients with the Guillain-Barré syndrome.

Glycosylated plasma protein: a simple method for the elimination of interference by glucose in its estimation.

Interference by glucose in the colorimetric estimation of glycosylated plasma protein was effectively eliminated by the precipitation of the proteins with trichloroacetic acid. The procedure was rapid and the recovery of protein quantitative. Results were highly reproducible. Preliminary clinical data obtained using the modified procedure showed rapid reflection by glycosylated plasma protein of the short-term control of glucose levels in diabetics when glycosylated haemoglobin values failed to indicate changes.

Interaction of choriocarcinoma cells and human peripheral blood lymphocytes. Resistance of cultured choriocarcinoma cells to cell-mediated cytotoxicity by mitogen-activated lymphocytes.

Cultured choriocarcinoma (Be Wo) cells exist that share many of the morphologic and bio-synthetic properties of normal human trophoblasts. In an attempt to develop a model for the immunologic relationship between a sensitized mother and fetus, we mixed Be Wo cells with mitogen-activated cytotoxic lymphocytes in vitro. Be Wo cells were resistant to the cytolytic effects of the activated lymphocytes despite 24-h exposure and intimate cell-to-cell contact as determined by microscopy. Control target cells, a line of human hepatoma cells, were readily destroyed. Cytotoxicity was measured by determining residual radioactivity of [(3)H]thymidine-labeled target cells after exposure to activated lymphocytes. Employing the quantitative assay, we confirmed the morphologic results and showed that Be Wo and a number of other choriocarcinoma cell lines were resistant to the cytotoxic effects of lymphocytes activated by phytohemagglutinin, pokeweed mitogen, and allogeneic cells in mixed lymphocyte cultures. Moreover, Be Wo cells were resistant to injury over a wide range of killer to target cell ratios. Significant killing of the Be Wo cells occurred only after prolonged exposure (48 and 72 h) to the activated lymphocytes. We suggest that one mechanism that may assist the fetus (or a choriocarcinoma) in its immunologic survival is the intrinsic resistance of trophoblast cells to lymphocyte-mediated cytotoxicity.

Umbilical uptake of amino acids in the unstressed fetal lamb.

The whole blood concentrations of 22 amino acids were measured in a chronic, unstressed fetal lamb preparations. Samples were taken daily from the umbilical artery, umbilical vein, and maternal artery over the latter quarter of gestation. 73 sets of samples (from the umbilical artery and vein and the maternal artery) from 13 animals were analyzed for amino acid levels. Oxygen contents were determined simultaneously in 48 sets (umbilical artery and vein) to relate fetal oxygen consumption to amino acid uptake via the umbilical circulation. The results indicate that there is no umbilical uptake of the acidic amino acids, glutamate and aspartate; there is, in fact, a net flux of glutamate out of the fetus into the placenta. As both of these amino acids are major constituents of body proteins, the data indicate that they are formed within the fetus. The umbilical uptake of some neutral and basic amino acids (e.g., valine, leucine, isoleucine, arginine, phenylalanine, and tyrosine) is in considerable excess of estimated growth requirements, suggesting that some amino acids undergo extensive transamination and oxidative degradation in the fetus. Finally, the net uptake of nitrogen, carbon, and calories by the growing ovine fetus in the form of amino acids, glucose, and lactate is compared to estimated requirements as determined in previous studies.

Human chorionic gonadotropin in human neoplastic cells.

Peroxidase-labeled antibody against the beta chain of human chorionic gonadotropin was used to demonstrate that 25 human malignant tumors contained this antigen. The antigen was localized both in the cytoplasm and on the surface of the malignant cells. Human chorionic gonadotropin may be responsible for both selective maternal immuno-suppression by fetal tissue and host immunosuppression by tumors.

Localization of the beta chain of human chorionic gonadotropin on human tumor cells and placental cells.

With the use of peroxidase-labeled antibody to the beta chain of human chorionic gonadotropin, sections of ten human malignant tumors were found to react with this antibody. It is postulated that both selective host immunosuppression by tumors and selective maternal immunosuppression by fetal tissues may be mediated by human chorionic gonadotropin.

Human chorionic gonadotropin: its possible role in maternal lymphocyte suppression.

Human chorionic gonadotropin completely inhibits the response of lymphocytes to phytohemagglutinin. The effect is both reversible and noncytotoxic. These observations support the theory that the fetus is accepted because human chorionic gonadotropin represents trophoblastic surface antigen and blocks the action of maternal lymphocytes.