Structural effects of the binding of GTP to the wild-type and oncogenic forms of the ras-gene-encoded p21 proteins

Molecular dynamics calculations have been performed to determine the average structures of ras-gene-encoded p21 proteins bound to GTP, i.e., the normal (wild-type) protein and two oncogenic forms of this protein, the Val 12- and Leu 61-p21 proteins. We find that the average structures for all of these proteins exhibit low coordinate fluctuations (which are highest for the normal protein), indicating convergence to specific structures. From previous dynamics calculations of the average structures of these proteins bound to GDP, major regional differences were found among these proteins [Monaco et al. (1995), J. Protein Chem., in press]. We now find that the average structures of the oncogenic proteins are more similar to one another when the proteins are bound to GTP than when they are bound to GDP [Monaco et al. (1995), J. Protein Chem., in press]. However, they still differ in structure at specific amino acid residues rather than in whole regions, in contradistinction to the results found for the p21-GDP complexes. Two exceptions are the regions 25-32, in an alpha-helical region, and 97-110. The two oncogenic (Val 12- and Leu 61-) proteins have similar structures which differ significantly in the region of residues 97-110. This region has recently been identified as being critical in the interaction of p21 with kinase target proteins. The differences in structure between the oncogenic proteins suggest the existence of more than one oncogenic form of the p21 protein that can activate different signaling pathways.

Determination of disulfide bridge pattern in omega-conopeptides

Synthetic versions of seven naturally occurring omega-conopeptides were subjected to structural analyses in order to determine their disulfide bridge pattern. The method applied in this study uses a combination of amino-acid composition and peptide sequence analysis of various peptide fragments generated by different enzymatic digestions. A temperature modification in the Edman degradation cycles of a protein sequencer allowed the unambiguous detection of the cleavage of cystine residues. The appearance of the cystine residues in particular cycles of the sequence analysis was characteristic of one or several of the theoretically possible 15 isomers. In the case of multiple choices, possible isomers were further eliminated by the amino-acid and sequence analysis of peptide fragments generated by the enzymatic digestion. All synthetic peptides, SNX-111, -157, -159, -183, -185, -230 and -231, were found to have the same disulfide bridge pattern as determined for the naturally occurring omega-conopeptide G-VI-A, i.e. disulfide bridges between the half-cystines 1-16, 8-20 and 15-25 (using the amino-acid numbering of SNX-111).

Comparison of the computed three-dimensional structures of oncogenic forms (bound to GDP) of the ras-gene-encoded p21 protein with the structure of the normal (non-transforming) wild-type protein

The ras-oncogene-encoded p21 protein becomes oncogenic if amino acid substitutions occur at critical positions in the polypeptide chain. The most commonly found oncogenic forms contain Val in place of Gly 12 or Leu in place of Gln 61. To determine the effects of these substitutions on the three-dimensional structure of the whole p21 protein, we have performed molecular dynamics calculations on each of these three proteins bound to GDP and magnesium ion to compute the average structures of each of the three forms. Comparisons of the computed average structures shows that both oncogenic forms with Val 12 and Leu 61 differ substantially in structure from that of the wild type (containing Gly 12 and Gln 61) in discrete regions: residues 10-16, 32-47, 55-74, 85-89, 100-110, and 119-134. All of these regions occur in exposed loops, and several of them have already been found to be involved in the cellular functioning of the p21 protein. These regions have also previously been identified as the most flexible domains of the wild-type protein and have been bound to be the same ones that differ in conformation between transforming and nontransforming p21 mutant proteins neither of which binds nucleotide. The two oncogenic forms have similar conformations in their carboxyl-terminal domains, but differ in conformation at residues 32-47 and 55-74. The former region is known to be involved in the interaction with at least three downstream effector target proteins. Thus, differences in structure between the two oncogenic proteins may reflect different relative affinities of each oncogenic protein for each of these effector targets. The latter region, 55-74, is known to be a highly mobile segment of the protein. The results strongly suggest that critical oncogenic amino acid substitutions in the p21 protein cause changes in the structures of vital domains of this protein.

SNX-325, a novel calcium antagonist from the spider Segestria florentina

A novel selective calcium channel antagonist peptide, SNX-325, has been isolated from the venom of the spider Segestria florentina. The peptide was isolated using as bioassays the displacement of radioiodinated omega-conopeptide SNX-230 (MVIIC) from rat brain synaptosomal membranes, as well as the inhibition of the barium current through cloned expressed calcium channels in oocytes. The primary sequence of SNX-325 is GSCIESGKSCTHSRSMKNGLCCPKSRCNCRQIQHRHDYLGKRKYSCRCS, which is a novel amino acid sequence. Solid-phase synthesis resulted in a peptide that is chromatographically identical with the native peptide and which has the same configuration of cysteine residues as the spider venom peptide omega-Aga-IVa [Mintz, I. M., et al., (1992) Nature 355, 827-829]. At micromolar concentrations, SNX-325 is an inhibitor of most calcium, but not sodium or potassium, currents. At nanomolar concentrations, SNX-325 is a selective blocker of the cloned expressed class B (N-type), but not class C (cardiac L), A, or E, calcium channels. SNX-325 is approximately equipotent with the N-channel selective omega-conopeptides (GVIA and MVIIA as well as closely related synthetic derivatives) in blocking the potassium induced release of tritiated norepinephrine from hippocampal slices (IC50s, 0.1-0.5 nM) and in blocking the barium current through cloned expressed N-channels in oocytes (IC50s 3-30 nM). By contrast, SNX-325 is 4-5 orders of magnitude less potent than is SNX-111 (synthetic MVIIA) at displacing radioiodinated SNX-111 from rat brain synaptosomal membranes. SNX-325 will be a useful comparative tool in further defining the function and pharmacology of the N- and possibly other types of high-voltage activated calcium channels.

Structure-activity analysis of a Conus peptide blocker of N-type neuronal calcium channels

The synthetic peptide SNX-111 corresponding to the sequence of the omega-conopeptide MVIIA from the venom of the marine snail Conus magus is a highly potent and selective antagonist of N-type calcium channels. We have synthesized and characterized a large number of analogs of SNX-111 in order to elucidate the structural features of the peptide involved in blocking N-type calcium channels. Comparison of the binding of SNX-111 and its analogs to rat brain synaptosomal membranes rich in N-type channels revealed that, among the four lysines and two arginines in the molecule, lysine in position 2 and arginines at position 10 and 21 are important for the interaction of SNX-111 with N-type channels. The importance of the middle segment from residues 9 through 14 for this binding interaction was revealed by substitution of the individual residues as well as by the construction of hybrid peptides in which the residues 9-12 in SNX-111 and another conopeptide, SNX-183, corresponding to a peptide SVIB from Conus striatus, were interchanged. Introduction of the sequence SRLM from SNX-111 in place of RKTS in position 9-12 in SNX-183 resulted in a 38-fold increase in affinity.

5-Oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of human eosinophil migration

Human neutrophils and monocytes contain a highly specific dehydrogenase which converts 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). We have previously shown that 5-oxo-ETE is a potent stimulus of neutrophil calcium levels and migration and have now investigated its effects on human eosinophils. 5-Oxo-ETE is a potent stimulus of eosinophil migration, with significant effects being detected at concentrations as low as 1 nM and a maximal response at 1 microM. The responses elicited by 5-oxo-ETE were about two to three times greater than those to platelet-activating factor (PAF) and 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid (5-oxo-15-hydroxy-ETE) at all concentrations tested between 10 nM and 1 microM. Leukotrienes B4 and D4 also significantly stimulated eosinophil migration, but the maximal responses to these agonists were only about 4% of the maximal response to 5-oxo-ETE. A low concentration of 5-oxo-ETE (1 nM) potentiated eosinophil migration in response to PAF. Eosinophils were capable of converting 5-HETE to 5-oxo-ETE, and this reaction was enhanced by phorbol myristate acetate. Stimulation of eosinophils with A23187 in the presence of low concentrations of arachidonic acid and phorbol 12-myristate 13-acetate led to the formation of 5-oxo-ETE and 5-oxo-15-hydroxy-ETE, but the amounts were considerably less than those of other eicosanoids such as leukotriene C4, cysteine-containing lipoxins, and 5,15-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid. In summary, of all the lipid mediators tested, 5-oxo-ETE was the most effective in stimulating migration of human eosinophils. Although eosinophils are capable of synthesizing 5-oxo-eicosanoids, the amounts detected were relatively small, and other leukocytes such as neutrophils, monocytes, or macrophages may be more important sites for the synthesis of this compound.

5-Oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of human eosinophil migration

Human neutrophils and monocytes contain a highly specific dehydrogenase which converts 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). We have previously shown that 5-oxo-ETE is a potent stimulus of neutrophil calcium levels and migration and have now investigated its effects on human eosinophils. 5-Oxo-ETE is a potent stimulus of eosinophil migration, with significant effects being detected at concentrations as low as 1 nM and a maximal response at 1 microM. The responses elicited by 5-oxo-ETE were about two to three times greater than those to platelet-activating factor (PAF) and 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid (5-oxo-15-hydroxy-ETE) at all concentrations tested between 10 nM and 1 microM. Leukotrienes B4 and D4 also significantly stimulated eosinophil migration, but the maximal responses to these agonists were only about 4% of the maximal response to 5-oxo-ETE. A low concentration of 5-oxo-ETE (1 nM) potentiated eosinophil migration in response to PAF. Eosinophils were capable of converting 5-HETE to 5-oxo-ETE, and this reaction was enhanced by phorbol myristate acetate. Stimulation of eosinophils with A23187 in the presence of low concentrations of arachidonic acid and phorbol 12-myristate 13-acetate led to the formation of 5-oxo-ETE and 5-oxo-15-hydroxy-ETE, but the amounts were considerably less than those of other eicosanoids such as leukotriene C4, cysteine-containing lipoxins, and 5,15-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid. In summary, of all the lipid mediators tested, 5-oxo-ETE was the most effective in stimulating migration of human eosinophils. Although eosinophils are capable of synthesizing 5-oxo-eicosanoids, the amounts detected were relatively small, and other leukocytes such as neutrophils, monocytes, or macrophages may be more important sites for the synthesis of this compound.

Auer rod-like inclusions in adult common acute lymphoblastic leukemia

We report a case of adult common acute lymphoblastic leukemia, defined by enzyme histochemistry and immunophenotypic analysis, which had rod-shaped cytoplasmic inclusions that on Wright's-stained peripheral blood smear resembled Auer rods. Electron microscopic analysis of a buffy coat preparation revealed that the inclusions were not characteristic of Auer rods, but rather that they were composed of concentric lamellar structures with no limiting membrane and were closely associated with the nuclear membrane. Therefore, the presence of Auer rod-like inclusions in blasts on a Wright's-stained peripheral blood smear does not preclude a diagnosis of acute lymphoblastic leukemia.

Arterial pressure-flow relationships in hypertensive dogs: effect of carotid sinus baroreflex

The effect of the carotid sinus baroreflex reflex on arterial pressure-flow relationships was studied in Goldblatt hypertensive and normotensive dogs on cardiopulmonary bypass. Dogs were anesthetized with pentobarbital sodium, vagotomized, and the carotid sinuses were isolated at controlled carotid sinus pressures (CSP). The mean arterial pressure-flow relationships were measured at different levels of CSP. The arterial pressure-flow relationship was found to be linear except at extreme levels of flow. The slopes derived from the linear regression of the pressure-flow relationships [total peripheral resistance (TPR)] were 1.466 +/- 0.111 and 0.786 +/- 0.13 mmHg.ml-1 x min.kg at CSP of 50 and 200 mmHg in the normotensive group and 1.758 +/- 0.183 and 0.937 +/- 0.114 mmHg.ml-1 x min.kg at CSP of 50 and 250 mmHg in the hypertensive group. The increases in slope measured when CSP was decreased from saturation to threshold were 0.68 mmHg.ml-1 x min.kg (187% increase) in the normotensive group and 0.82 mmHg.ml-1 x min.kg (188% increase) in the hypertensive group. Zero-flow arterial pressures at CSP of 50, 125, and 200 mmHg were found to be 23.1 +/- 2.9, 21.7 +/- 2.2, and 17.1 +/- 1.8 mmHg in the normotensive group and 28.4 +/- 2.2, 23.8 +/- 1.5, and 20.0 +/- 1.2 mmHg in the hypertensive group. A nonlinear model fit was found to give a significantly better fit [coefficient of determination (r2) = 0.932 linear, 0.956 nonlinear] of the arterial pressure-flow relationships. We conclude that, in experimental hypertension, carotid baroreflex control of TPR is shifted to a higher operating point without any reduction in overall reflex gain.

Molecular cloning of the murine JAK1 protein tyrosine kinase and its expression in the mouse central nervous system

Degenerate oligonucleotide primers were employed in PCRs to clone protein tyrosine kinases that may play potential roles in the development of the mammalian CNS. Using one PCR clone to screen a mouse eye cDNA library, a full-length cDNA of a cytoplasmic tyrosine kinase, the homolog of human JAK1, was obtained. The murine JAK1 kinase belongs to a new family of cytoplasmic kinases that contain two tandem catalytic domains. Northern analyses indicated that murine JAK1 mRNA is expressed in a variety of tissues and cell lines. In the adult mouse eye, in situ hybridization and immunohistochemistry showed that JAK1 mRNA and protein were expressed in the retinal ganglion cell layer and the inner part of the inner nuclear layer, presumably in amacrine cells. JAK1 protein was also detected in horizontal cells and in the two synaptic layers of the adult retina. During retinal development, JAK1 protein was first detected in retinal ganglion cells and in their axons as early as embryonic day 14. Expression of JAK1 protein in amacrine cells and horizontal cells occurred only postnatally. This pattern of expression was also observed in the chick retina, suggesting an evolutionarily conserved function of JAK1 kinase in vertebrate retinal development and/or function. Immunohistochemical staining against JAK1 was detected in two areas of the adult mouse brain, the olfactory bulb and a group of cells in the hypothalamus. Together, these expression studies suggest a role for JAK1 kinase in the differentiation or function of a subset of CNS neurons.

Small bowel obstruction secondary to incarcerated Richter's hernia from laparoscopic hernia repair

Presented herein is a case of a patient who, during a laparoscopic herniorrhaphy, developed profound bradycardia upon introduction of the pneumoperitoneum. Following discharge, the patient presented 24 h later with herniation through the trocar port incision. With laparoscopic surgery being used more frequently, there will be an increase in the incidence of these types of complications; however, with better awareness, they may be avoided.

Pathways for activation of the ras-oncogene-encoded p21 protein

The ras-oncogene-encoded p21 protein is known to cause a large number of human tumors. This protein differs from its normal counterpart protein, which is present in all eukaryotic cells, in that it contains a single amino acid substitution at critical positions in the polypeptide chain, such as at Gly 12, Gly 13, Ala 59, and Gln 61. Using computer-based molecular modeling, it has been found that one region of this protein that is a candidate for interacting with other intracellular proteins is the region from residues 35 to 47. In oocyte microinjection experiments, it was found that this peptide strongly inhibits the mitogenic effects of oncogenic (Val 12-containing)p21 but does not inhibit the cellular effects of activation of normal p21 protein. Furthermore, it has been shown that the cellular effects of oncogenic p21 protein can be completely inhibited by selectively blocking protein kinase C (PKC) with a highly specific inhibitor of this protein, CGP 41 251, a staurosporine derivative. This inhibitor, however, only weakly inhibits the effects of normal cellular ras-p21 protein. In addition, a photoaffinity-labeled p21 protein has been microinjected into NIH 3T3 fibroblasts and have isolated intracellular proteins of MW 35, 43 and 61 kda covalently bound to it. The 43 kda protein is the major one and appears to be critical to the functioning of the p21 protein. Our results suggest that oncogenic and normal p21 proteins utilize overlapping but distinct pathways; the oncogenic pathway can be blocked selectively and requires the activation of PKC and the presence of the 43 kda protein.

Activated conformations of the ras-gene-encoded p21 protein. 1. An energy-refined structure for the normal p21 protein complexed with GDP

A complete three-dimensional structure for the ras-gene-encoded p21 protein with Gly 12 and Gln 61, bound to GDP, has been constructed in four stages using the available alpha-carbon coordinates as deposited in the Brookhaven National Laboratories Protein Data Bank. No all-atom structure has been made available despite the fact that the first crystallographic structure for the p21 protein was reported almost four years ago. In the p21 protein, if amino acid substitutions are made at any one of a number of different positions in the amino acid sequence, the protein becomes permanently activated and causes malignant transformation of normal cells or, in some cell lines, differentiation and maturation. For example, all amino acids except Gly and Pro at position 12 result in an oncogenic protein; all amino acids except Gln, Glu and Pro at position 61 likewise cause malignant transformation of cells. We have constructed our all-atom structure of the non-oncogenic protein from the x-ray structure in order to determine how oncogenic amino acid substitutions affect the three-dimensional structure of this protein. In Stage 1 we generated a poly-alanine backbone (except at Gly and Pro residues) through the alpha-carbon structure, requiring the individual Ala, Pro or Gly residues to conform to standard amino acid geometry and to form trans-planar peptide bonds. Since no alpha-carbon coordinates for residues 60-65 have been determined, these residues were modeled by generating them in the extended conformation and then subjecting them to molecular dynamics using the computer application DISCOVER and energy minimization using DISCOVER and the ECEPP (Empirical Conformational Energies for Peptides Program). In Stage 2, the positions of residues that are homologous to corresponding residues of bacterial elongation factor Tu (EF-Tu) to which p21 bears an overall 40% sequence homology, were determined from their corresponding positions in a high-resolution structure of EF-Tu. Non-homologous loops were taken from the structure generated in Stage 1 and were placed between the appropriate homologous segments so as to connect them. In Stage 3, all bad contacts that occurred in this resulting structure were removed, and the coordinates of the alpha-carbon atoms were forced to superimpose as closely as possible on the corresponding atoms of the reference (x-ray) structure. Then the side chain positions of residues of the non-homologous loop regions were modeled using a combination of molecular dynamics and energy minimization using DISCOVER and ECEPP respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of cardiac transplantation and cyclosporine therapy on digoxin pharmacokinetics

Most patients needing cardiac transplantation are treated with digoxin for heart failure. Because of its narrow therapeutic range, even recommended doses of digoxin may cause severe toxicity. Several drugs, including quinidine, amiodarone, verapamil, and propafenone can interact with digoxin, leading to toxic accumulation of the glycoside. The authors have recently reported two cases of severe digitalis toxicity after the initiation of cyclosporine treatment in patients awaiting cardiac transplantation. A preliminary study on two additional patients suggested that cyclosporine reduced the plasma clearance and volume of distribution of digoxin. To assess the mechanism of this interaction, the authors studied digoxin pharmacokinetics in patients awaiting cardiac transplantation and again after the surgery, during chronic cyclosporine therapy. To separate the effects of transplantation and cyclosporine on digoxin pharmacokinetics, pharmacokinetic studies were subsequently performed in dogs to allow controlled experimental conditions for evaluation of the digoxin-cyclosporine interaction.

Relationship between the pharmacokinetics and iron excretion pharmacodynamics of the new oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one in patients with thalassemia

Single-dose and steady-state pharmacokinetics of the new oral iron chelator, 1,2-dimethyl-3-hydroxypyrid-4-one (L1) were studied in 14 patients with thalassemia and correlated with iron excretion. Food prolongs the rate of absorption of L1, but it does not affect significantly the extent of absorption measured by the area under the plasma concentration-time curve. Similarly, it does not affect the chelation potential of the drug. The mean elimination half-life of the drug is 3 hours, suggesting that a divided dose every 8 hours may assure better chelation. Our steady-state studies reveal that urinary iron excretion is independently influenced by body iron load (measured by ferritin levels) and by steady-state trough concentrations of the drug. While patients were receiving an unchanged regimen of 75 mg/kg/day, we have detected a gradual and significant decrease in trough concentrations in the presence of unchanged patients' compliance monitored by the Medication Event Monitoring System, diaries, and pill count. These findings suggest self-induction of L1 metabolism or decreased absorption during long-term therapy. Because of the concentration-dependent iron excretion, patients may need increasing doses to achieve negative iron balance.

Aging and the trophic effects of cholecystokinin, bombesin and pentagastrin on the rat pancreas

We examined the effect of age on the trophic response of the pancreas to chronic treatment with cholecystokinin (CCK), bombesin, or pentagastrin. Three age groups (3-, 12-, and 24-months) male F344 rats received saline; CCK-8 (5 ng/kg), bombesin (10 micrograms/kg), or pentagastrin (100 micrograms/kg) by intraperitoneal injection t.i.d. for 2 weeks. Rats were then killed and the pancreases excised, weighed, and assayed for DNA, RNA, protein, and polyamine (putrescine, spermidine, and spermine) concentrations and contents. We found that none of the treatments altered body weight at any age. All three hormones increased pancreas size and cell number in 3-month old rats, but by 12 months, all three had increased only pancreatic RNA content. Pancreatic spermidine concentration was decreased by all three hormone regimens in 3- but not in 12-month old rats, and pancreatic putrescine concentration and content were increased in 12-month old rats receiving all three hormones. There was no change in any parameter following any of the three hormones, tested at 24 months of age. We conclude that, at the dosages tested, the trophic response of pancreas to chronic administration of CCK, bombesin, and pentagastrin, which is normally present in young adult rats, is lost with aging.

A high-performance liquid chromatographic method for the measurement of the iron chelator 1,2-dimethyl-3-hydroxypyridin-4-one in human plasma

1,2-Dimethyl-3-hydroxypyridin-4-one (CP020 or L1) is a novel oral iron chelator that has proved to be effective in animals and humans. A rapid, accurate, and sensitive high-performance liquid chromatography method is described for measuring L1 in human plasma using a Hypercarb 7 microns column and monitoring the column eluent by ultraviolet absorption at 280 nm. CP020 and the internal standard (CP094) were extracted into dichloromethane (2 x 5 ml) from plasma at neutral pH [0.25 ml of plasma + 0.75 ml of 60 mM 3-(N-morpholino)propanesulfonic acid buffer, pH 7.4]. The method proved to be linear (r2 = 0.998) in the clinical range of 0.5-50 micrograms/ml when 0.25 ml of plasma was used, with the coefficient of variation less than 10% even at the lower concentration range.

In vivo incorporation of N-acetyl-D-[U-14C]mannosamine into brain gangliosides of rats with quinolinic acid-induced lesions of the forebrain nucleus basalis magnocellularis

Quinolinic acid, an excitotoxic agent, was applied unilaterally to the nucleus basalis magnocellularis of the rat forebrain, which resulted in neuronal destructions and consequently, loss of cholinergic projections to the cortex. The effects on ganglioside metabolism in brain cortical matter were studied. Total ganglioside contents in lesioned brains (n = 8) were found to be significantly decreased (range, 20-60%) but changes in brain ganglioside patterns on thin layer chromatograms were not apparent. On the other hand, in vivo incorporation of N-acetyl-D-[U-14C]mannosamine into brain gangliosides ranged from 19 to 36% (mean, 26%) of radiolabel in controls, and 5 to 21% (mean, 13%), a significant reduction in lesioned brains. Labeling of brain glycoproteins or of nonganglioside lipids was not affected. Since central cholinergic hypofunctions are also important neurochemical characteristics of Alzheimer's disease, abnormal ganglioside metabolism found in the lesioned rats may be of significance in the human disorder, where reduced brain ganglioside contents have also been reported.

Comparison of oral iron chelator L1 and desferrioxamine in iron-loaded patients

The efficacy of the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) was compared with that of subcutaneous desferrioxamine in 26 patients with transfusional iron overload. Immediately after red-cell transfusion, 20 patients were randomised to receive either desferrioxamine (50 mg/kg daily as a 12 h subcutaneous infusion), or L1 (50 mg/kg daily by mouth). Patients were evaluated during treatment with the other drug after transfusion the next month. Mean (SD) daily urinary iron excretion was lower during L1 than during desferrioxamine (12.3 [6.7] vs 18.2 [15.3] mg/day). In 5 patients the dose of L1 was raised from 50 to 75 mg/kg daily; mean urinary iron excretion rose from 13.8 (7.0) mg/day to 26.7 (17.8) mg/day, comparable with that during desferrioxamine (24.9 [24.3] mg/day). Faecal iron excretion rose slightly over baseline in 6 patients studied during L1 administration (from 8.5 [0.9] mg/day to 12.2 [0.9] mg/day). Pharmacokinetic studies showed an elimination half-life for L1 of 117-237 min. Studies in dogs and in volunteers showed no absorption of the L1-iron complex, excluding a contribution of absorption of intraluminal complexes of L1 and food iron to urinary iron excretion. Further animal toxicity testing is needed before L1 can be studied in a broader group of patients.

Interaction between trimethoprim-sulfamethoxazole and methotrexate in children with leukemia

Because trimethoprim-sulfamethoxazole (TMP-SMX) causes neutropenia in children with leukemia, we investigated the possibility that pharmacokinetic interaction between methotrexate (MTX) and TMP-SMX causes accumulation of the antileukemia agent. We studied the pharmacokinetics of MTX given intravenously or orally to nine children with acute lymphoblastic leukemia, once with and once without TMP-SMX. There was an increase in free MTX fraction during TMP-SMX therapy in all patients, from (mean +/- SD) 37.4 +/- 11% without TMP-SMX to 52.2 +/- 6.4% with TMP-SMX (p less than 0.01). Plasma clearance of total MTX did not change significantly, whereas clearance of free MTX decreased significantly (from 12.5 +/- 4 to 7.6 +/- 1.5 ml/kg/min; p less than 0.05). There was a consistent decrease in the renal clearance of free MTX (from 12.1 +/- 6.8 to 5.6 +/- 2.4 ml/kg/min; p less than 0.05). Elimination half-life of MTX was not affected significantly by TMP-SMX. There was a significant correlation between serum concentrations of TMP-SMX and the percentage of decrease in the renal clearance of free MTX (r = 0.91; p less than 0.05). These changes in protein binding and tubular clearance of MTX, caused by competition with TMP-SMX, result in a mean 66% increase in systemic exposure to MTX and may explain the myelotoxicity often observed with the coadministration of the two drugs.

Preliminary study on the antinociceptive effect of elephant beta-endorphin

1. Intraventricular administration of human beta-endorphin and elephant beta-endorphin significantly prolonged the tail flick response tested 30 min later. However, elephant beta-endorphin was about 7-8 times more potent than human beta-endorphin in the tail flick test. 2. beta-Endorphin antagonized the antinociceptive effect of both human beta-endorphin and elephant beta-endorphin by the same extent. Naloxone also antagonized the antinociceptive effects of the beta-endorphins but it was less effective than beta-endorphin. 3. Human beta-endorphin and elephant beta-endorphin were of equal potency in inhibiting the abdominal constriction response induced by intraperitoneal (i.p.) acetic acid. Both beta-endorphin and naloxone antagonized these effects of the beta-endorphins with naloxone being more effective. 4. The present study showed that different opioid receptor subtypes may be involved in the tail flick test and the abdominal constriction test. Furthermore, elephant beta-endorphin was a better antinociceptive agent than human beta-endorphin in the tail flick test.

Multiple Genotypen bei Ashkenazim mit Faktor-XI-Mangel

Die Struktur des Faktor-XI-Gens wurde bei sechs nicht verwandten Ashkenazim mit Faktor-XI-Mangel analysiert. Es wurden keine groben Veränderungen dieser Gene durch Southern-Blot-Analyse der genomischen DNA gefunden. Die Klonierung der Faktor-XI-Gene, die Polymerase-Chain-Reaction(PCR)-Analyse und die Sequenzierung der Exone und der Exon/Intron-Verbindungen machte es möglich, eine Mutation der Spleiß Verbindung, eine Nonsens-Mutation und eine SauSAI-Mutation zu identifizieren. Diese drei Arten von Allelen zusammen erklären alle genetischen Defekte bei diesen sechs Personen. Das Vorkommen multipler Allelmutationen läßt die Hypothese des selektiven Vorteils gegenüber der genetischen Verschiebungshypothese als Erklärung des Überlebens des abnormen Faktor-XI-Gens wahrscheinlicher erscheinen.