Endothelial cell activation by pore-forming structures: pivotal role for interleukin-1alpha

BACKGROUND

Interaction of complement with endothelial cells (ECs) underlies the development of inflammation and coagulation in disease. Assembly of the membrane attack complex (MAC) of complement on EC membrane, like stimulation with cytokines, upregulates tissue factor and cyclooxygenase-2 but does so via the intermediary action of IL-1alpha. We asked whether the MAC activates porcine aortic and microvascular ECs in a global manner by this mechanism and whether this mechanism is used by membrane pore-forming structures.

METHODS AND RESULTS

Exposure of ECs to complement caused upregulation of mRNAs for E-selectin, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, Ikappa-Balpha, interleukin (IL)-1alpha, IL-1beta, IL-8, and plasminogen activator inhibitor-1 over a period of 6 hours. The expression of these genes was not a primary response to stimulation, however, because IL-1 receptor antagonist inhibited expression of these genes. Activation of ECs by complement depended on the autocrine action of IL-1alpha, because complement-mediated EC activation was inhibited by anti-IL-1alpha antibodies. Melittin and mastoparan, amphiphilic pore-forming peptides like the MAC, induced E-selectin through intermediary action of IL-1.

CONCLUSIONS

These findings suggest that transmembrane pore-forming proteins, as a class of molecules, activate ECs through the autocrine effects of IL-1alpha.

Expression of tissue factor mRNA in cardiac xenografts: clues to the pathogenesis of acute vascular rejection

BACKGROUND

Acute vascular rejection destroys vascularized xenografts over a period of hours to days and is now considered the major hurdle to the clinical application of xenotransplantation. The hallmark of acute vascular rejection is diffuse intravascular coagulation; however, the pathogenesis of coagulation is a matter of controversy. One line of evidence points to activated endothelial cells and another to activated inflammatory cells as a source of tissue factor and thus as a primary cause of this lesion. The distinction between the two mechanisms inducing coagulation in the xenograft provides an opportunity for specific intervention.

METHODS

To explore these mechanisms, we studied the expression of tissue factor mRNA by in situ reverse transcriptase-polymerase chain reaction in relation to the histopathologic manifestations of acute vascular rejection in guinea pig hearts transplanted into rats treated by cobra venom factor to avoid the hyperacute rejection.

RESULTS

Three hours after transplantation and before the deposition of fibrin, tissue factor mRNA was expressed in the endothelial cells lining small and medium blood vessels and in smooth muscle cells of guinea pig cardiac xenografts. Sixteen hours after transplantation, while rat tissue factor mRNA was expressed only in occasional infiltrating cells, cardiac xenografts showed prominent deposits of fibrin in small vessels. Maximum expression of tissue factor on rat infiltrating cells was observed 48 hr after transplantation.

CONCLUSIONS

These results suggest that in acute vascular rejection, coagulation is initiated on the donor vascular system, while the procoagulant characteristics of infiltrating cells may reflect a response to tissue injury rather than a cause.

Induction of procoagulant function in porcine endothelial cells by human natural killer cells

NK cells may mediate effector functions other than target cell cytotoxicity. To explore such noncytotoxic effector mechanisms, we tested whether human PBL and purified NK (CD56+) cells might induce expression of tissue factor by cultured porcine aortic endothelial cells. Tissue factor is the major coagulation factor that binds to factor VIIa and initiates coagulation. The addition of freshly isolated NK cells but not T cells to endothelial cells resulted in the induction of tissue factor activity. NK-depleted (CD56-) effector cells did not induce tissue factor activity; however, the combination of CD56+ cells and NK-depleted cells induced tissue factor activity to the same extent as unseparated cells. PBL induced tissue factor mRNA in porcine endothelial cells and NK depletion resulted in a significant decrease of the induction. Induction of tissue factor activity in porcine endothelial cells by human NK cells required direct cell-to-cell contact, as transfer of supernatants from NK-endothelial cell cultures to secondary cultures did not induce tissue factor activity, and anti-LFA-1alpha Abs inhibited the induction of tissue factor activity. Induction of tissue factor activity in endothelial cells by NK cells may represent one of a variety of ways in which NK cells mediate noncytotoxic effects.

Induction of procoagulant function in porcine endothelial cells by human natural killer cells

NK cells may mediate effector functions other than target cell cytotoxicity. To explore such noncytotoxic effector mechanisms, we tested whether human PBL and purified NK (CD56+) cells might induce expression of tissue factor by cultured porcine aortic endothelial cells. Tissue factor is the major coagulation factor that binds to factor VIIa and initiates coagulation. The addition of freshly isolated NK cells but not T cells to endothelial cells resulted in the induction of tissue factor activity. NK-depleted (CD56-) effector cells did not induce tissue factor activity; however, the combination of CD56+ cells and NK-depleted cells induced tissue factor activity to the same extent as unseparated cells. PBL induced tissue factor mRNA in porcine endothelial cells and NK depletion resulted in a significant decrease of the induction. Induction of tissue factor activity in porcine endothelial cells by human NK cells required direct cell-to-cell contact, as transfer of supernatants from NK-endothelial cell cultures to secondary cultures did not induce tissue factor activity, and anti-LFA-1alpha Abs inhibited the induction of tissue factor activity. Induction of tissue factor activity in endothelial cells by NK cells may represent one of a variety of ways in which NK cells mediate noncytotoxic effects.

Complement-mediated regulation of tissue factor activity in endothelium

Inflammation and immunity may be associated with endothelial cell (EC) injury and thrombus formation. We explored the mechanisms through which a humoral immune response directed against the endothelium might promote coagulation. Using the interaction of anti-EC antibodies and complement (C) with cultured EC as a model, we studied the expression and function of tissue factor, a cofactor for factor VIIa-mediated conversion of factor X to Xa. Exposure of EC to anti-EC antibodies and C in sublytic amounts stimulated the synthesis of tissue factor over a period of 16-42 h. Cell surface expression of tissue factor activity required activation of C and assembly of the membrane attack complex, because expression was inhibited by soluble CR1 and was not detected in the absence of C8. Elaboration of tissue factor messenger RNA was observed over a period of 8-30 h and required protein synthesis. Expression of tissue factor was not a direct consequence of the action of C on the EC but was a secondary response that required as an intermediate step the release of interleukin 1 alpha, an early product of the EC response to C activation. These findings suggest that, after the assembly of membrane attack complex on EC, the production of tissue factor and initiation of coagulation in a blood vessel depend on the production of interleukin 1 alpha and on its availability to stimulate affected EC.

Single-strand conformational polymorphism and direct sequencing applied to carrier testing in families with ornithine transcarbamylase deficiency

Single-strand conformational polymorphism (SSCP) and direct sequencing were used to confirm or deny carrier status in three families with ornithine transcarbamylase (OTC) enzyme deficiency. Two male probands with "late onset" OTC deficiency, whose "private" mutations were previously characterized, inherited the mutations form their heterozygous mothers. One of the heterozygous mothers had a false negative allopurinol test. Three female siblings of the two male probands were tested, one proved to be a carrier of the respective mutation while the other two were found to have normal alleles. In the third family, the proband was a female with "late onset" presentation of OTC deficiency. We found a new point mutation in this girl consisting of a guanine-to-cytosine transversion at nucleotide 520 resulting in a substitution of proline for alanine at amino acid 142 of the mature OTC protein. We confirmed that this mutation occurred spontaneously and that neither of the two parents carries this mutation. We conclude that SSCP, in conjunction with direct sequencing, is a useful technique that can be practically applied for carrier testing in families with OTC deficiency.

Six new mutations in the ornithine transcarbamylase gene detected by single-strand conformational polymorphism

We describe six new mutations in the ornithine transcarbamylase (OTC) gene found in patients with OTC deficiency. These mutations were detected by single-strand conformational polymorphism analysis of amplified genomic DNA and characterized by direct sequencing of double-stranded DNA. Three of the mutations were found in males who had neonatal onset of hyperammonemia. The mutations are a single base deletion (guanine) in exon 5 at nucleotide 403 causing a frame-shift error, a guanine to adenine substitution at the 3' end of intron 2 nucleotide 217 (-1) causing an acceptor splicing site error, and a guanine to adenine substitution at base 236 changing the code from glycine to glutamic acid at position 47 of the mature enzyme. Two different mutations were found in two males whose onset of clinical problems occurred after the neonatal period. One patient had a guanine to cytosine transversion in the sense strand of exon 3 at nucleotide 281 resulting in a substitution of threonine for arginine in position 62 of the mature OTC protein. This substitution changes the composition of the putative active site for carbamyl phosphate from Ser-Thr-Arg-Thr-Arg to Ser-Thr-Arg-Thr-Thr. The second patient has a guanine to thymine substitution at nucleotide 912 of the sense strand of exon 9, changing the code for leucine to phenylalanine in position 272 of the mature OTC protein. This changes a conserved domain of the gene likely to be the ornithine binding site from Phe-Leu-His-Cys-Leu-Pro to Phe-Leu-His-Cys-Phe-Pro.(ABSTRACT TRUNCATED AT 250 WORDS)

Screening for gene deletions and known mutations in 13 patients with ornithine transcarbamylase deficiency

We analyzed DNA from 13 males with ornithine transcarbamylase (OTC) deficiency for gene deletions and known point mutations using the polymerase chain reaction (PCR), allelle-specific oligonucleotide (ASO) hybridization, and Southern blotting with full-length OTC cDNA and exon-specific probes. Three patients were found to have deletions: one was missing the whole OTC gene; a second patient had a deletion of both exon 7 and 8; and the third had a deletion of exon 9. Only one of the remaining 10 patients had a known point mutation consisting of a G-to-A change in nucleotide 422 of the sense strand resulting in a glutamine substitution for arginine at amino acid 109 of the mature OTC protein. This study describes the integration of various molecular methods to screen OTC-deficient patients for deletions and points mutations. Two new deletions within the OTC gene are described.

Prospective versus clinical diagnosis and therapy of acute neonatal hyperammonaemia in two sisters with carbamyl phosphate synthetase deficiency

Two female siblings were treated for acute neonatal hyperammonaemia due to complete carbamyl phosphate synthetase I deficiency. The first child was detected clinically at 65 hours of age and therapy started at 79 hours. The second child was followed from birth and therapy started at 5 hours of age. The extrapolated rate of increase of blood ammonia, in the first hours of life before therapy started, was 19 mumol L-1 h-1 in both babies. Peak blood ammonia level was 2235 mumol/L in the first (clinically detected) child and 271 mumol/L in the second (prospectively followed) child. The second child became symptomatic at 3 hours of age when blood ammonia level was as low as 90 mumol/L, whereas blood ammonia levels above 100 mumol/L caused no symptoms during recovery. The child detected clinically required haemodialysis and peritoneal dialysis to treat the hyperammonaemia. In the prospectively treated child, early therapy with intravenous sodium benzoate and sodium phenylacetate slowed the rate of increase in blood ammonia level, but this therapy did not prevent the need for peritoneal dialysis.

Heterogeneity of patients with late onset ornithine transcarbamylase deficiency

Fourteen patients, 10 males and 4 females, with "late onset" ornithine transcarbamylase (OTC) deficiency were diagnosed by enzyme assays performed on their liver tissues. Age of first clinical presentation ranged widely from 10 weeks to 23 y (mean = 6.1 y). Peak plasma ammonia levels varied widely from a low of 105 mumol/L to as high as 800 mumol/L. All patients had elevated plasma levels of glutamine whereas plasma levels of citrulline were normal in 6 patients. Plasma ornithine levels were not elevated in any patient. Orotic aciduria of variable degree was detected in 13 patients. Residual hepatic OTC activity was detectable in 13 out of the 14 patients ranging from 0.7 to 28.3 mumol/g/min (normal = 80.6 +/- 19.1, mean +/- SD, n = 52). Ten patients were alive at the time of this report and 5 of them had psychomotor delay.

X-chromosome inactivation in the liver of female heterozygous OTC-deficient sparse-furash mice

X-chromosome inactivation patterns were investigated in livers of nine spfash female heterozygous ornithine transcarbamylase (OTC)-deficient mice. Quantitative morphometric analysis of cellular mosaicism was performed on sections of frozen liver reacted with purified anti-OTC antibody and prepared for immunofluorescent microscopy. Analysis of enzymatic OTC activity was performed on sections of these livers using a radiochromatographic technique. Several areas of cellular mosaicism were seen in each of the histological sections that were studied. The distribution of the volume fraction of the liver tissue cells having cells with normal OTC content among the nine mice ranged from 20 to 70% and it correlated (r = 0.8, P = 0.005) with the enzymatic activities of the respective livers. The extreme variegation of mosaic patches in the liver suggests the high probability that a single needle biopsy will be diagnostic in females heterozygous for an OTC mutation. This study also suggests that at the time of X inactivation, the number of primordial liver embryonic cells is small and the observed variegation of liver mosaicism probably results from complex migration patterns of liver cells during fetal development. This study shows that the spfash mouse is a suitable animal model for quantitative studies of X-chromosome inactivation in liver using immunohistochemical staining of OTC protein.

Human hepatic N-acetylglutamate content and N-acetylglutamate synthase activity. Determination by stable isotope dilution

N-Acetyl-L-glutamate (N-acetylglutamate) content and N-acetylglutamate synthase activity ranges were established in human liver tissue homogenates by stable isotope dilution. The methods employ N-[methyl-2H3]acetyl[15N]glutamate as internal standard, extraction of N-acetylglutamate by anion-exchange technique and its determination by g.l.c.-mass spectrometry by using selected ion monitoring. Hepatic N-acetylglutamate content in 16 different human livers, normal in structure and function, ranged from 6.8 to 59.7 nmol/g wet wt. (25.0 +/- 13.4 mean +/- S.D.) or from 64.6 to 497.6 nmol/g of protein (223.2 +/- 104.2 mean +/- S.D.). In vitro, N-acetylglutamate synthase activity in liver tissue homogenate ranged from 44.5 to 374.5 (132.0 +/- 90.6 mean +/- S.D.) nmol/min per g wet wt. or from 491.7 to 3416.9 (1159.6 +/- 751.1 mean +/- S.D.) nmol/min per g of protein. No correlation was found between hepatic N-acetylglutamate concentrations and the respective maximal enzymic activities in vitro of N-acetylglutamate synthase. The marked variability in this system among individual livers may reflect its regulatory role in ureagenesis.

Immunochemical analysis of carbamyl phosphate synthetase I and ornithine transcarbamylase deficient livers: elevated N-acetylglutamate level in a liver lacking carbamyl phosphate synthetase protein

Liver tissue from 3 patients with carbamyl phosphate synthetase I deficiency and 11 patients with ornithine transcarbamylase deficiency was analyzed by Western blots for the presence of carbamyl phosphate synthetase I and ornithine transcarbamylase cross-reactive material with anti-rat enzyme antibodies. One patient with carbamyl phosphate synthetase I deficiency had no cross-reactive material with the antibody to this enzyme, one had reduced amounts, and one had similar to normal amounts. Only one of the patients with ornithine transcarbamylase deficiency had apparently normal amounts of enzyme protein in his liver, another patient had markedly reduced amounts, and the other nine patients had traces or absence of reactive ornithine transcarbamylase protein. N-acetylglutamate content in the carbamyl phosphate synthetase I deficient liver with absent enzyme protein, was higher (98.4 nmol/g) than that measured in 5 normal controls (41.6 +/- 19.3 mean +/- SD, n = 5) and much higher than the N-acetylglutamate level (2.2 nmol/g) in another carbamyl phosphate synthetase I deficient liver with normal amounts of enzyme protein. Hepatic N-acetylglutamate content in 3 patients with complete ornithine transcarbamylase deficiency was below the normal mean but within 2 standard deviations from the mean (8.5-12.8 nmol/g) whereas it was higher (30.7 nmol/g) in another partial ornithine transcarbamylase deficient patient. Most patients with ornithine transcarbamylase deficiency have markedly reduced or undetectable enzyme protein in their liver, therefore. Western blot analysis could help to establish this diagnosis in most patients. Absent carbamyl phosphate synthetase I enzyme protein may have caused elevation of the hepatic content of its cofactor, N-acetylglutamate, by an as yet unknown mechanism.

N-acetylglutamate content in liver and gut of normal and fasted mice, normal human livers, and livers of individuals with carbamyl phosphate synthetase or ornithine transcarbamylase deficiency

N-acetylglutamate (NAG) content was measured in homogenates of liver and small intestine obtained from normal and 24-h starved syngeneic mice. Subsequently, NAG was determined in normal, and in carbamyl phosphate synthetase I and ornithine transcarbamylase enzyme-deficient human liver tissue homogenates. The method used in this study, which is direct and highly specific, used anion exchange extraction, gas chromatographic separation, and mass spectrometric detection and quantitation. Hepatic NAG content in the fed animals was 94.8 +/- 19.8 nmol/g tissue or 602.5 +/- 168.4 nmol/g protein (mean +/- SD, n = 5), whereas it was much lower in the fasted mice (49.4 +/- 13.0 nmol/g tissue or 330.1 +/- 113.9 nmol/g protein, mean +/- SD, n = 5). The magnitude of the difference was much smaller for intestinal NAG content, 19.8 +/- 5.4 nmol/g tissue or 205.3 +/- 70.3 nmol/g protein (mean +/- SD, n = 5) in the fed mice and 14.2 +/- 4.3 nmol/g tissue or 168.1 +/- 80.8 nmol/g protein (mean +/- SD, n = 5) in the fasted mice. The concentrations of hepatic NAG in normal human livers (controls) ranged from 19.3 to 67.1 nmol/g tissue (41.6 +/- 19.3, mean +/- SD, n = 5) or from 193 to 764.3 nmol/g of protein (437.5 +/- 233.4, mean +/- SD, n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbamyl phosphate synthetase and ornithine transcarbamylase activities in enzyme-deficient human liver measured by radiochromatography and correlated with outcome

Sensitive and specific radiochromatographic methods to measure enzymatic activities of carbamyl phosphate synthetase I (CPS I) and ornithine transcarbamylase (OTC) were developed. The activities of these enzymes were assayed in frozen liver tissue obtained from 23 individuals with hyperammonemia caused by CPS I (five patients) and OTC deficiency (18 patients). In addition, livers of one aborted fetus with OTC deficiency and four normal individuals were studied. The assays use radioactive ornithine as a substrate followed by separation of citrulline formed in the reactions by HPLC and quantitation of the radioactivity in both amino acids by a radioactivity flow monitor or by a scintillation counter. Both CPS I and OTC assays were linear with respect to length of incubation time and concentration of tissue homogenate. The sensitivity of the methods allowed measurements of CPS I and OTC activities as low as 0.1 mumol/g/min on 5 mg of liver tissue and the diagnosis of CPS I or OTC deficiency could be established on as low as 0.5 and 0.05 mg of tissue, respectively. CPS I activity in different sections of four normal livers was 3.01 +/- 0.16 mumol/g/min (mean +/- SEM, n = 19) and OTC activity was 93.4 +/- 6.3 (mean +/- SEM, n = 19). Residual enzymatic activity could be detected and measured in the liver tissues of one of the five subjects with CPS I deficiency and in 14 of 19 subjects with OTC deficiency. OTC/CPS I activity ratio in normal liver tissue was 31.2 +/- 1.3 (mean +/- SEM, n = 19), whereas this ratio ranged from 343 to greater than 5000 in CPS I deficient livers and from less than 0.02 to 1.55 in OTC deficient livers.(ABSTRACT TRUNCATED AT 250 WORDS)