Differential recognition of snake venom proteins expressing specific Arg-Gly-Asp (RGD) sequence motifs by wild-type and variant integrin alphaIIbbeta3: further evidence for distinct sites of RGD ligand recognition exhibiting negative allostery

Several studies have demonstrated that the amino acid residues flanking the Arg-Gly-Asp (RGD) sequence of high-affinity ligands modulate their specificity of interaction with integrin complexes. Because of the absence of structural data for integrin complexes with bound ligand, the molecular basis for this specificity modulation remains obscure. In a previous paper [Rahman, Lu, Kakkar and Authi (1995) Biochem. J. 312, 223-232] we demonstrated that two genetically distinct venom-derived RGD proteins, kistrin and dendroaspin (both containing the sequence PRGDMP), were simple competitors, indicating the recognition of an identical binding site on the alpha(IIb)beta(3) complex. Furthermore, both kistrin and dendroaspin inhibited the binding of the disintegrin elegantin (containing the sequence ARGDNP) via a non-competitive mechanism, suggesting that the binding of elegantin to the alpha(IIb)beta(3) complex was at a remote site and down-regulated via an allosteric mechanism. Here we present further evidence for distinct RGD ligand recognition sites on the alpha(IIb)beta(3) complex that exhibit a negative allosteric relationship. A panel of well-characterized recombinant dendroaspin and elegantin derivatives were employed for this study. These recombinant molecules were constructed as glutathione S-transferase fusion proteins with either an Ala or Pro residue N-terminal to the RGD sequence in combination with either a Met or an Asn residue immediately C-terminal. Equilibrium competition experiments showed that elegantin binding to ADP-treated platelets was inhibited by derivatives Eleg. AM (ARGDMP) and Eleg. PM (PRGDMP) via an allosteric competitive mechanism, providing direct evidence that modulation of the RGD motif can alter competitive behaviour. In addition, recombinant kistrin and dendroaspin both inhibited elegantin binding via a non-competitive mechanism, confirming our previous observations. Further evidence for distinct binding sites employing an independent approach was obtained by analysing the binding of the panel of venom proteins to the functionally defective heterodimer alpha(IIb)beta(3) Ser(123)-->Ala expressed on Chinese hamster ovary cells. These studies demonstrated that simple competitors kistrin and dendroaspin bound with high affinity to the variant integrin complex. In contrast, the binding of elegantin and most significantly, recombinant Dendro. PN (PRGDNP) and Dendro. AN (ARGDNP) were abolished. These observations, taken together, are consistent with a model depicting the presence of distinct sites of RGD ligand recognition on the alpha(IIb)beta(3) complex that show the preferential recognition of specific RGD motifs. Competition experiments demonstrate a negative allosteric relationship between these RGD recognition sites.

A pilot study of posttraumatic stress and nonadherence in pediatric liver transplant recipients

BACKGROUND

Symptoms of posttraumatic stress disorder (PTSD) were described in survivors of life-threatening diseases, the trauma being the experiences associated with the disease or its treatment. Their prevalence in liver transplant recipients is unknown. Based on clinical observations, we hypothesize that a significant proportion of pediatric liver transplant recipients suffers from PTSD symptoms. We further hypothesize that nonadherence (noncompliance) to medical management may, in some cases, be associated with these symptoms. Traumatized patients, according to this hypothesis, will avoid taking their medications, because these serve as painful reminders of the disease.

OBJECTIVES

To determine the prevalence of PTSD symptoms in a sample of pediatric liver transplant recipients. To determine whether symptoms of PTSD are associated with nonadherence in these patients. To describe the clinical presentation of PTSD and the management of severe nonadherence in patients who suffer from this disorder.

METHODS

Nineteen pediatric liver transplant recipients and their caretakers were interviewed, using the UCLA Post Traumatic Stress Disorder Reaction Index (PTSRI). Data were obtained on a few demographic parameters and perception of disease threat. Adherence was evaluated by 2 methods: 1) a clinician panel (taking into account the clinical sequelae of severe nonadherence); and 2) computation of the standard deviations (SDs) of consecutive determinations of blood levels of Tacrolimus (a higher SD means higher variability between individual measures and is therefore an indicator of nonadherence). As an illustration of the general phenomenon, we describe 3 cases of liver transplant recipients who were nonadherent and who suffered from PTSD.

RESULTS

Six of 19 patients had positive scores on all 3 components of the PTSRI (PTSD patients). Three of these, and none of the others, were considered significantly nonadherent by the panel. Therefore, nonadherence was significantly associated with the existence of symptoms from all 3 domains of PTSD (Fisher's exact test) in our sample. In particular, a high avoidance score on the PTSRI was highly correlated with panel-determined nonadherence. Further, SD of medication levels were significantly higher in PTSD patients, compared with the rest of our sample. No significant differences were found in perception of disease threat or demographic variables between PTSD patients and the rest of our sample. The 3 cases that we describe became adherent to their medications when symptoms of PTSD subsided during the course of therapy.

CONCLUSIONS

Clinically significant nonadherence, determined by 2 different methods, was associated with the full spectrum of PTSD symptoms in this sample. It was especially associated with a high avoidance score, which suggests that avoidance of reminders of the disease (eg, medications) may be a mechanism of nonadherence. Screening for and management of these symptoms, therefore, may improve adherence. This novel concept may be applicable to other patient populations. However, more data are needed before any definite conclusions can be drawn.

Clinical and serological associations with anti-RNA polymerase antibodies in systemic sclerosis

There are three classes of RNA polymerase enzyme (RNAPs I, II and III). In systemic sclerosis (SSc), three main groups of anti-RNAP sera have been characterized by radioimmunoprecipitation techniques: anti-RNAP I/III sera, anti-RNAP I/II/III sera, and a group precipitating both RNAP II and topoisomerase I (topo I). Some sera in this third group precipitate the phosphorylated (IIO) form of RNAP II in the absence of the unphosphorylated (IIA) form. Certain other antinuclear antibodies (ANA) have also been detected in anti-RNAP IIO/IIA/topo I and anti-RNAP IIO/topo I sera. In the present study of 155 SSc patients, clinical features of individuals from each of these antibody groups were assessed and compared with those of patients from other autoantibody-defined groups. The anti-RNAP I/II/III antibody specificity was closely associated with the presence of diffuse cutaneous SSc (dc-SSc) (77.8%; cf. remaining group, 12.4%; P < 0.001; relative risk (RR) 6.3). Patients with anti-RNAP I/III antibodies also had an increased incidence of dc-SSc, but this was not significant (42.9%; cf. remainder, 15.7%). Anti-RNAP+ patients had a significantly increased incidence of renal involvement (29.0%, cf. remainder, 11.3%; P < 0.05; RR 2.6), with 40% of anti-RNAP I/II/III patients having renal disease. Meanwhile, the presence of anti-centromere antibodies (ACA) was associated with limited cutaneous SSc (lc-SSc) (100.0%; cf. remainder, 75.3%; P < 0. 005), together with reduced incidences of both renal disease (2.4%, cf. remainder, 22.1%: P < 0.01) and pulmonary fibrosis (21.4%, cf. remainder, 52.3%; P < 0.005; RR 1.9). Anti-topo I antibodies were associated with the presence of pulmonary fibrosis (69.7%; cf. remainder, 32.6%; P < 0.001; RR 2.1). A majority of anti-topo I sera were from lc-SSc patients, regardless of whether anti-topo I antibodies occurred alone (75.0%) or together with anti-RNAP IIO + IIA antibodies (75.0%), and this was similar to the remainder (86. 5%; NS). However, when anti-topo I+ patients were compared with the ACA group, and then with all anti-RNAP I+ patients (37.5% lc-SSc), significant differences were found in the occurrence of dc- versus lc-SSc (P < 0.005 and P < 0.05, respectively). In conclusion, these results confirm that there are three main groups of SSc sera, each characterized by the presence of a mutually exclusive SSc-specific autoantibody (ACA, anti-topo I or anti-RNAP I), and distinguished by patterns of cutaneous involvement and specific clinical features. It appears that, in each of the three groups of SSc patients, distinct pathological processes are occurring, which are responsible for the characteristic symptoms, for the modification of particular autoantigens and, consequently, for the production of particular autoantibodies. Based on these data, together with our previous results, it is further hypothesized that anti-RNAP II antibodies may be produced in the context of two different immune response pathways.

Role of hypoxia-induced Bax translocation and cytochrome c release in reoxygenation injury

We investigated mechanisms of cell death during hypoxia/reoxygenation of cultured kidney cells. During glucose-free hypoxia, cell ATP levels declined steeply resulting in the translocation of Bax from cytosol to mitochondria. Concurrently, there was cytochrome c release and caspase activation. Cells that leaked cytochrome c underwent apoptosis after reoxygenation. ATP depletion induced by a mitochondrial uncoupler resulted in similar alterations even in the presence of oxygen. Moreover, inclusion of glucose during hypoxia prevented protein translocations and reoxygenation injury by maintaining intracellular ATP. Thus, ATP depletion, rather than hypoxia per se, was the cause of protein translocations. Overexpression of Bcl-2 prevented cytochrome c release and reoxygenation injury without ameliorating ATP depletion or Bax translocation. On the other hand, caspase inhibitors did not prevent protein translocations, but inhibited apoptosis during reoxygenation. Nevertheless, they could not confer long-term viability, since mitochondria had been damaged. Omission of glucose during reoxygenation resulted in continued failure of ATP production, and cell death with necrotic morphology. In contrast, cells expressing Bcl-2 had functional mitochondria and remained viable during reoxygenation even without glucose. Therefore, Bax translocation during hypoxia is a molecular trigger for cell death during reoxygenation. If ATP is available during reoxygenation, apoptosis develops; otherwise, death occurs by necrosis. By preserving mitochondrial integrity, BCL-2 prevents both forms of cell death and ensures cell viability.

Middle cerebral artery occlusion in the rat: consistent protocol for a model of stroke

Variability in the effects of the intraluminal suture method of middle cerebral artery occlusion (MCAO) in the rat has been a common and disadvantageous finding. Therefore, we systematically investigated the effects of suture type and rat strain on outcome. First, the clinical and neuropathological effects of permanent MCAO with either an uncoated or a silicone-coated nylon suture were studied over 7 days in Sprague-Dawley rats (n = 36 for each type of suture). Outcome was less severe with the uncoated compared with the silicone-coated suture (e.g. total cerebral infarct volume at 24 h before any fatalities was 119.9 +/- 79.8 mm3, cf. 183.0 +/- 36.5 mm3, n = 12 for each, P < 0.05; and overall mortality rate was 12.5% cf. 33%, respectively), but much more variable (coefficient of variation was 66.6% cf. 19.9%, respectively). Second, being more consistent in its effects, the silicone-coated suture was further studied in Wistar and Fischer-344 rats (n = 12 for each). Seventy-five per cent of the Wistar's died prematurely from gross hemispheric oedema. Motor deficit and extent of infarction in the Fischer-344 rats were both significantly greater compared with Sprague-Dawley rats (e.g. total cerebral infarct volume at 24 h in the former was 253.6 +/- 25.4 mm3, n = 11, P < 0.05), and more consistent (coefficient of variation was only 10.0%). It was concluded that the silicone-coated suture and the Fischer-344 rats strain produced the most consistent results and their novel combination provides a reliable acute stroke model.

Expression of fibroblast growth factor receptors in peri-implantation mouse embryos

FGF receptor (FGFR) function is essential during peri-implantation mouse development. To understand which receptors are functioning, we tested for the expression of all four FGF receptors in peri-implantation blastocysts. By RT-PCR, FGFR-3 and FGFR-4 were detected at high levels, FGFR-2 at lower levels, and FGFR-1 was detected at background levels compared to control tissues. Because FGFR-3 and FGFR-4 were detected at the highest levels, we studied these in detail. Between 3.5 days after fertilization (E3.5) and E6.0, FGFR-4 mRNA was detected ubiquitously in the peri-implantation embryo, restricted to the inner cell mass (ICM) and its derivatives and primitive endoderm by E6.0, and was not detected at E6.5. FGFR-3 mRNA was detected ubiquitously in the peri-implantation embryo with a tendency towards extraembryonic cells. We tested blastocyst outgrowths, a model for implantation, for FGFR-3 and FGFR-4 protein. FGFR-3 protein was detected in all cells early during the outgrowth. Later, FGFR-3 was detected in the extraembryonic endoderm and trophoblast giant cells (TGC), but not in the ICM. FGFR-4 protein was detected in all cells of the implanting embryo, but was restricted to the ICM/primitive endoderm in later stage outgrowths. The distribution of the receptor proteins in the blastocyst outgrowths is similar to the distribution of the mRNA detected by in situ hybridization of sections of embryos. The data suggest roles for FGFR-3 and FGFR-4 in peri-implantation development.

FGF is an essential regulator of the fifth cell division in preimplantation mouse embryos

Fibroblast growth factor (FGF) signaling is required prior to gastrulation in the mouse embryo. To test for the spatial and temporal requirements of FGF signaling, a dominant negative FGF receptor (dnFGFR) was used to make transgenic mouse embryos. In mosaic embryos, cell division ceased at the fifth cell division in all cells that expressed the mutant receptor, but cell death did not increase. After the fifth cell division, the progeny of unaltered cells and cells expressing lacZ continued to accumulate at the same rate, suggesting that the FGF requirement is cell autonomous. In mosaic embryos, lacZ, but not dnFGFR expression was detected in mitotic trophoblasts adjacent to the ICM. Conversely, dnFGFR-expressing extraembryonic ectoderm cells were detected at the abembryonic pole in postmitotic cells. In blastocysts expressing the dnFGFR in all cells, the morphology appeared normal and inner cell masses (ICMs) formed, but resultant embryos had only one-third the number of cells as control embryos. In these blastocysts, cell division had also ceased at the fifth cell division, but cavitation, a concurrent morphogenetic event, initiated and progressed normally. To test for the continuing requirement of FGF, FGFR-3 was overexpressed in all cells and resulted in an increase in cell numbers after the fifth cell cycle. In a model for postimplantation development, addition of FGF-4 to blastocyst outgrowths increased the number of extraembryonic ectoderm cells, suggesting a continuing role for FGF. Thus, FGF signaling induces the cell division of embryonic and extraembryonic cells in the preimplantation mouse embryo starting at the fifth cell division. The signal requirement for FGF is cell autonomous, but is not required to prevent cell death. This provides the first evidence for the necessity of a growth factor before implantation.

Development of porous defects in plasma membranes of adenosine triphosphate-depleted Madin-Darby canine kidney cells and its inhibition by glycine

Studies during the past decade have led to the recognition of a fundamental, widely expressed mechanism of structural damage in energy-deprived cells, which is suppressed by physiologic levels of glycine and is independent of Ca2+ availability or alterations of cytosolic free Ca2+. To gain insight into this process, Madin-Darby canine kidney (MDCK) cells were depleted of adenosine triphosphate (ATP) by a mitochondrial uncoupler in glucose-free medium, and intracellular free Ca2+ was clamped at 100 nM to avoid calcium cytotoxicity. Although the ATP-depleted cells swelled and blebbed and their plasma membranes appeared to be under tension, they nevertheless became permeable to macromolecules. The plasma membranes of these cells retained structural continuity, as determined by morphologic observations, and confocal microscopy of a plasma membrane protein label (Biotin: Ultra Avidin-Texas Red) and a lipid label (NBD-sphingomyelin). Using fluoresceinated dextrans of graded molecular size, membrane permselectivity was examined noninvasively by confocal microscopy. Measured as inside/outside ratios of fluorescence intensity, the permeability indices showed progressively greater restriction to diffusion of increasingly larger dextran molecules across plasma membranes, with sharp break-points between 70,000 and 145,000 daltons (d). The results indicated that the membranes behaved as if they were perforated by water-filled channels or "pores," with size-exclusion limits of molecular dimensions. The membrane defects evolved from small pores permeable only to propidium iodide (668 d) and the smallest dextran (4,000 d), before enlarging with time to become permeable to larger dextrans. Inclusion of glycine during ATP depletion did not affect cell swelling or blebbing but completely prevented the development of permeability defects. Treatment of cells before ATP depletion with a membrane-impermeant homobifunctional "nearest neighbor" cross-linking agent, 3,3' dithiobis(sulfosuccinimidylpropionate), suppressed the development of permeability defects, even in the absence of glycine. These observations suggest that the cellular abnormality that is suppressed by glycine involves rearrangement of plasma membrane proteins to form water-filled pores large enough to leak macromolecules.

Coarctation of the aorta presenting in a 79-year-old male

We present a case of coarctation of the aorta with a post-stenotic aneurysm in a 79-year-old male patient. Diagnostic studies included computed tomographic angiogram, magnetic resonance angiogram and digital subtraction angiogram. Our patient underwent operative therapy that resulted in improvement of his hypertension and cardiac function.

Cell type specific repression of the varicella zoster virus immediate early gene 62 promoter by the cellular Oct-2 transcription factor

The cellular transcription factor Oct-2.1 has previously been shown to repress the transactivation of the varicella zoster virus (VZV) immediate early gene promoter by viral transactivators but not to inhibit its basal activity. In the case of the related virus herpes simplex virus (HSV), the effect of Oct-2 on the IE promoters has been shown to be cell type specific and to differ between the different alternatively spliced forms of Oct-2. Here we show that as well as Oct-2.1, the Oct-2.4 and 2.5 isoforms which are expressed in neuronal cells can inhibit transactivation of the VZV immediate early promoter regardless of the cell type used. In contrast, all the isoforms of Oct-2 can inhibit basal activity of the VZV promoter in neuronal cells but not in other cell types indicating that this effect is cell type specific. These effects are discussed in terms of the differential regulation of latent infections with HSV or VZV in dorsal root ganglia.

Insulin receptor substrate-1 is expressed at high levels in all cells of the peri-implantation mouse embryo

Insulin and insulinlike growth factors are important for embryonic growth and metabolism. Intracellular transduction for these factors has not been studied in the preimplantation mouse embryo. Peri-implantation mouse embryos synthesize insulinlike growth factor (IGF)-II ligand, insulin receptor, IGF-I receptor, and IGF-II receptor and respond to IGF-II, IGF-I, and insulin metabolically and mitogenically. Maternal tissues in the oviduct and uterus are also sources of IGF-I and insulin. Signaling of IGFs occurs through insulin receptor substrate (IRS)-1 and IRS-2. This paper shows that IRS-1 mRNA and protein are highly expressed in preimplantation mouse embryos, in embryonic cell lines, and in cultured blastocyst outgrowths. IRS-1 mRNA and protein are detected in embryo-derived cell lines cultured to produce the three cell lineages (stem cells, endoderm, and trophoblast cells). IRS-1 mRNA is detected by reverse transcription-polymerase chain reaction (RT-PCR) in the E3.5 blastocyst before implantation and in F9 teratocarcinoma stem cells and parietal endoderm cells. IRS-1 mRNA is detected by Northern blot hybridization at high levels in stem cells and in differentiated progeny of F9 cells and C3H/NE trophectoderm cells. IRS-1 protein was detected in these cell lines and in an overexpressing CHO-IRS-1 fibroblast cell line by immunocytochemistry. Cultured blastocyst outgrowths are a model for implantation events of the trophoblast/placenta lineage and endoderm/yolk sac lineage. In the blastocyst outgrowth, IRS-1 protein is detected in inner cell mass cells (ICM cells), primitive endoderm, parietal endoderm, and trophectoderm cells. These data suggest that IRS-1 is expressed in all cell lineages of the peri-implantation mouse embryo and mediates some effects of insulin and IGFs at this stage.

Functional characterization of PM6/13, a beta3-specific (GPIIIa/CD61) monoclonal antibody that shows preferential inhibition of fibrinogen binding over fibronectin binding to activated human platelets

We report the characterization of a monoclonal antibody (MAb) PM6/13 which recognises glycoprotein IIIa (GPIIIa) on platelet membranes and in functional studies inhibits platelet aggregation induced by all agonists examined. In platelet-rich plasma, inhibition of aggregation induced by ADP or low concentrations of collagen was accompanied by inhibition of 5-hydroxytryptamine secretion. EC50 values were 10 and 9 microg/ml antibody against ADP and collagen induced responses respectively. In washed platelets treated with the cyclooxygenase inhibitor, indomethacin, PM6/13 inhibited platelet aggregation induced by thrombin (0.2 U/ml), collagen (10 microg/ml) and U46619 (3 microM) with EC50 = 4, 8 and 4 microg/ml respectively, without affecting [14C]5-hydroxytryptamine secretion or [3H]arachidonate release in appropriately labelled cells. Studies in Fura 2-labelled platelets revealed that elevation of intracellular calcium by ADP, thrombin or U46619 was unaffected by PM6/13 suggesting that the epitope recognised by the antibody did not influence Ca2+ regulation. In agreement with the results from the platelet aggregation studies, PM6/13 was found to potently inhibit binding of 125I-fibrinogen to ADP activated platelets. Binding of this ligand was also inhibited by two other MAbs tested, namely SZ-21 (also to GPIIIa) and PM6/248 (to the GPIIb-IIIa complex). However when tested against binding of 125I-fibronectin to thrombin stimulated platelets, PM6/13 was ineffective in contrast with SZ-21 and PM6/248, that were both potent inhibitors. This suggested that the epitopes recognised by PM6/13 and SZ-21 on GPIIIa were distinct. Studies employing proteolytic dissection of 125I-labelled GPIIIa by trypsin followed by immunoprecipitation with PM6/13 and analysis by SDS-PAGE, revealed the presence of four fragments at 70, 55, 30 and 28 kDa. PM6/13 did not recognize any protein bands on Western blots performed under reducing conditions. However Western blotting analysis with PM6/13 under non-reducing conditions revealed strong detection of the parent GPIIIa molecule, of trypsin treated samples revealed recognition of an 80 kDa fragment at 1 min, faint recognition of a 60 kDa fragment at 60 min and no recognition of any product at 18 h treatment. Under similar conditions, SZ-21 recognized fragments at 80, 75 and 55 kDa with the 55 kDa species persisting even after 18 h trypsin treatment. These studies confirm the epitopes recognised by PM6/13 and SZ-21 to be distinct and that PM6/13 represents a useful tool to differentiate the characteristics of fibrinogen and fibronectin binding to the GPIIb-IIIa complex on activated platelets.

The diagnostic yield of lower endoscopy plus biopsy in nonbloody diarrhea

BACKGROUND

Patients presenting with diarrhea frequently undergo lower endoscopy plus biopsy as part of their diagnostic evaluation. The diagnostic yield of this approach has not been systematically evaluated.

METHODS

To evaluate the diagnostic yield of endoscopy and biopsy in the investigation of nonbloody diarrhea, we performed a retrospective analysis using the endoscopy unit database of a tertiary care university hospital over a 3-year period. The database was searched for cases in which colonoscopy was performed for the single indication of diarrhea. The endoscopic findings and initial biopsy reports were extracted from a chart review, and each clinician was interviewed for the patient's current clinical diagnosis. The clinical diagnoses were compared with the endoscopy and biopsy results to determine whether the tests had contributed to making the clinical diagnoses.

RESULTS

Three hundred six patients were identified. One hundred one were excluded for standardized predefined exclusion criteria, leaving 205 evaluable patients, of whom 77 had flexible sigmoidoscopy and 128 had colonoscopy. Eighteen percent had specific clinical diagnoses facilitated by endoscopy and/or biopsy. Endoscopy and biopsy results were normal in 74% of cases. In 8% of the cases either the endoscopy or biopsy findings were inconsistent with the final clinical diagnoses.

CONCLUSIONS

Endoscopy and biopsy are important diagnostic tools in the evaluation of patients with nonbloody diarrhea, leading to a specific diagnosis in nearly one fifth of cases.

Fibroblast growth factor receptor (FGFR)-4, but not FGFR-3 is expressed in the pregnant ovary

The intraovarian mechanisms for follicle recruitment, growth, maturation, and ovulation are not well understood. The data suggest that fibroblast growth factor (FGF)-2 is expressed in granulosa and theca cells of growing and mature follicles and in luteal cells during pregnancy. Exogenous FGF-2 modulates steroidogenesis, stimulates tissue plasminogen activator (tPA), and induces germinal vesicle breakdown (GVBD) in cultured follicles. Previously, we have reported that another FGF ligand, FGF-4, is expressed in ovulated mouse oocytes. Two studies have examined the expression of receptors (FGFR) for FGF ligands in the ovary. These prior reports have been limited to FGFR-1, one of the four isoforms that are variably expressed in adult mammalian tissues. This study evaluates FGFR-4 and FGFR-3 mRNA expression in the ovary. Granulosa cells from several follicular stages express the receptor for FGFR-4 mRNA as assayed by in situ hybridization. FGFR-4 mRNA is not expressed in theca cells or the oocyte. FGFR-3 mRNA is not detected in the ovary by in situ hybridization. These results suggest that FGFR-4 may play a role in mediating the effects of FGF ligands in follicular development in the ovary.

Effects of combined glutamate and platelet-activating factor inhibition on the outcome of focal cerebral ischaemia - an initial screening study

Since both glutamate excitotoxicity and inflammatory responses have been implicated in ischaemic neuronal death, we questioned whether joint inhibition of both processes would be more neuroprotective than either on its own. Therefore we assessed the effects of combined inhibition of both glutamate release (with a use-dependant sodium channel blocker, 619C89) and inflammatory processes (with a platelet-activating factor (PAF) receptor antagonist, BB-823) on the degree of motor deficit and the extent of cerebral (cortical and sub-cortical grey matter) infarction produced by middle cerebral artery occlusion (MCAO) in the rat, and compared results to appropriate single agent, vehicle and positive controls. The combination of both agents produced the greatest reduction in motor deficit, but the effect was only significant (p<0.05) acutely (4 to 6 hours post-MCAO). The extent of cortical infarction at 24 hours post-MCAO was significantly reduced in all experimental groups compared to vehicle-controls (p<0.05) and the greatest reduction occurred in the combination group (55%), though it was not significantly better than either of the single agent groups. Similarly the greatest reduction in sub-cortical infarction was in the combination group, but this was also not significantly better than the single agents. The results of this novel combination of pharmacological interventions suggest that inhibition of both glutamate excitotoxicity and inflammatory responses afforded an overall enhanced, if modest, neuroprotective effect, compared to inhibition of either process alone. The possible mechanisms involved are discussed, but warrant further clarification before therapeutic strategies are developed.

The diagnosis and management of acromegaly: a Canadian consensus report

OBJECTIVE

To reach a Canadian consensus on the diagnosis and management of acromegaly.

OPTIONS

DIAGNOSIS

documenting autonomous growth-hormone hypersecretion and imaging of the pituitary.

TREATMENT

surgical resection, adjunctive therapy with bromocriptine or octreotide and radiation therapy.

OUTCOMES

Reduction of the morbidity and mortality associated with acromegaly.

EVIDENCE

Review of international literature.

VALUES

Achievement of consensus among a panel of Canadian endocrinologists.

BENEFITS, HARMS AND COSTS

Acromegaly is a chronic debilitating condition that is associated with morbidity and mortality. This consensus statement is designed to improve the diagnosis and management of this rare condition in order to minimize the negative outcomes. Costs were not considered.

RECOMMENDATIONS

The diagnosis of acromegaly is established by documenting autonomous growth-hormone hypersecretion and by imaging the pituitary. Surgical resection is the cornerstone of treatment; however, adjunctive therapy is often needed. Although growth-hormone reduction is often associated with alleviation of symptoms, an attempt should also be made to normalize levels of growth hormone and its target growth factor, insulin-like growth factor-I (IGF-I). Persistent secretion of excess growth hormone and IGF-I may pose significant long-term health risks. A suggested therapeutic algorithm is provided. The ease of administration of bromocriptine should prompt a trial of therapy with this agent. The subcutaneous use of octreotide is of particular benefit to those patients with persistently high levels of growth hormone and IGF-I that cannot be suppressed by other means. Because acromegaly is relatively rare and complex, its diagnosis and treatment require the concerted efforts of an endocrinologist, an neurosurgeon and a radiation oncologist.

Hepatocyte growth factor and its receptor are expressed in cardiac myocytes during early cardiogenesis

In the mouse, the heart primordium arises when mesoderm is set aside during gastrulation, is induced by pharyngeal endoderm, migrates ventrally to the midline of the embryo, forms a tube, and begins beating. Little is known of the molecular mechanisms that mediate the determination, mitosis, differentiation, and migration that lead to the beating heart. Transcripts for hepatocyte growth factor/scatter factor (HGF) and its receptor are coexpressed transiently and dynamically in the premyocardium but not in other heart progenitor cells. Transcripts the HGF ligand and receptor are first detected before cardiac function and looping and persist through the first looping stage, when heart morphology begins to elaborate. HGF ligand and receptor mRNA are detectable after the putative heart transcription factor, Csx/Nkx2-5, and concomitantly with the heart structural gene, cardiac actin. HGF receptor mRNA is detected in the mesoderm of the headfold stage and persists in myocardial precursors of the ventricles and atria (but not in the outflow-tract smooth muscle cells) through the 14-somite stage at approximately 8.75 days after fertilization (day E8.75). At the headfold stage, between E7.5 and E8.0, HGF receptor mRNA was detected in myocardial cells before fusion at the ventral midline. HGF ligand and receptor mRNA transcripts are coexpressed in the embryo, except in the headfold state (when only the HGF receptor can be detected) and in the heart at the 14- to 18-somite stage (when only HGF ligand can be detected). The dynamic pattern of coexpression suggests an autoregulatory role for HGF and its receptor in early heart development.

Effects of antigen presentation on superantigen-induced apoptosis mediated by Fas/Fas ligand interactions in human T cells

Stimulation of T cells with bacterial superantigens has several distinct functional outcomes including proliferation, anergy and apoptosis. At present however, the mechanisms that dictate whether activation, anergy, or apoptosis predominate are unclear. In this study we have investigated the effects of superantigen presentation to mature superantigen-reactive human T-cell lines. Despite expressing major histocompatibility complex (MHC) class II molecules, these lines failed to proliferate in response to superantigen in the absence of antigen-presenting cells (APC) but proliferated when minimal APC were added. In the absence of APC a significant proportion of the T cells underwent apoptosis. This response was rapid, antigen dependent and largely abolished by the addition of cyclosporin A. Interestingly the response was not blocked by the addition of a number of antibodies to cell surface molecules including MHC class II and intracellular adhesion molecule-1. Using both a bioassay and messenger RNA analysis we were able to demonstrate that stimulation of these T cells with superantigen resulted in the induction of Fas-ligand expression on the T cells and furthermore, the ability of these cells to induce apoptosis was inhibited by the addition of blocking Fas antibodies as well as a Fas-Fc fusion protein. These data demonstrate that stimulation of T cells with staphylococcal enterotoxin B induces expression of Fas-ligand resulting in T-cell apoptosis; however, the final outcome of proliferation or apoptosis is determined by the presence of APC.

Cytoprotection of kidney epithelial cells by compounds that target amino acid gated chloride channels

Glycine, strychnine and certain chloride channel blockers were reported to protect cells against lethal cell injury. These effects have been attributed to interactions with membrane proteins related to CNS glycine gated chloride channel receptors. We have investigated the pharmacology of these actions. Madin-Darby canine kidney (MDCK) epithelial cells were depleted of adenosine triphosphate (ATP) by incubation in glucose free medium containing a mitochondrial uncoupler. Medium Ca2+ was adjusted to 100 nM in the presence of an ionophore such that intracellular Ca2+ did not increase, and Ca(2+)-related injury mechanisms were inhibited. This permitted more sensitive quantitation of protection against cell injury attributable to glycine or other agents whose actions might be related to those of the amino acid. Two classes of compounds showed cytoprotective activity in this system: (1) ligands at chloride channel receptors, such as glycine, strychnine and avermectin B1a; (2) chloride channel blockers, including cyanotriphenylboron and niflumic acid, both of which are known to bind to channel domains of CNS glycine receptors. Morphological and functional studies showed that the compounds preserved plasma membrane integrity, but permitted cell swelling. Substitution of medium chloride by gluconate, or chloride salts by sucrose, did not substantially modify lethal damage or its prevention by glycine or other drugs. The compounds did not modify ATP declines. At least for some compounds, cytoprotection appeared to be specific to structural features on the molecules. These observations are consistent with the hypothesis that a plasma membrane protein related to glycine-gated chloride channel receptors plays a significant role in cell injury, but indicate that the mechanisms of injury and protection by compounds active in this system are not related to chloride fluxes.

Post-translationally modified 14-3-3 isoforms and inhibition of protein kinase C

This report compares the ability of individual members of the 14-3-3 protein family to inhibit particular protein kinase C (PKC) isoforms. We also show that two of these 14-3-3 isoforms (alpha and delta) specific to mammalian and avian brain are in vivo post-translationally modified forms of beta and zeta respectively. The presence of this modification enhances the activity of 14-3-3 as an inhibitor of protein kinase C nearly two fold. A method for analysing isoforms of 14-3-3 on acid-urea gels is also described. This permits the complete separation of all major isoforms and their unequivocal identification by a range of isoform specific antisera. The activity of recombinant 14-3-3 and isoforms renatured by a novel method after separation by reverse phase HPLC are compared. The effects of diacylglycerol and the phorbol ester, PMA (phorbol 1 2-myristate 13 acetate) on the inhibition suggest that one of the sites of interaction of 14-3-3 may be the cysteine-rich (C1) domain in PKC.

Effects of Ca++ and glycine on lipid breakdown and death of ATP-depleted MDCK cells

The relationships between cytosolic free calcium (Caf), cell associated glycine, phospholipid hydrolysis and cell death were investigated in Madin-Darby canine kidney (MDCK) cells injured by depletion of adenosine triphosphate (ATP). Glucose free incubation for three hours with a mitochondrial uncoupler resulted in progressive loss of glycine from cells. However, they were not lethally injured unless a perturbation of Ca++ homeostasis was also induced. Exposure to a Ca++ ionophore and uncoupler in 1.25 mM Ca++ medium (+Ca) resulted in accelerated cell death. ATP depleted cells with ionophore in 100 nM Ca++ medium (-Ca) were also lethally injured, but after a significant delay. Depletion of glycine preceded death in both groups of cells. Exogenous glycine (5 mM) protected +Ca cells against lethal membrane damage, but the beneficial effects were lost over a period of time. In contrast, -Ca cells were completely protected throughout. Phospholipid mass and radioactive label in lipid fractions of cells prelabeled with 3H-oleic acid were measured. Accelerated death of +Ca cells was accompanied by large decreases of phospholipid mass, loss of phospholipid label, and accumulation of unesterified labeled fatty acid. These changes were greatly decreased by incubation in -Ca medium. On the other hand, protection by glycine could not be attributed to modifications of either the massive breakdown of phospholipids that occurred in +Ca cells, or the modest changes seen in -Ca cells. In +Ca cells, the deleterious effects of increased Caf and phospholipid breakdown ultimately prevailed over protection by the amino acid. Thus, separate pathways of cell death associated with increased Caf and decreased glycine were defined in ATP depleted, Ca(+)- permeabilized MDCK cells. Calcium excess and massive phospholipid loss are features of a damage process that occurs independently of whether cells are protected by glycine or not. Conversely, the glycine sensitive component of injury is expressed regardless of whether intracellular Ca++ is increased, or large phospholipid losses occur. ATP depletion in -Ca medium provides a system to study mechanisms of glycine cytoprotection uncomplicated by Ca++ toxicity.

14-3-3 alpha and delta are the phosphorylated forms of raf-activating 14-3-3 beta and zeta. In vivo stoichiometric phosphorylation in brain at a Ser-Pro-Glu-Lys MOTIF

The 14-3-3 protein family has received considerable attention recently in the literature, because of the finding that beta and zeta isoforms interact with and activate Raf. We had previously shown that these 14-3-3 isoforms also exist as phosphorylated forms in mammalian and avian brain. The presence of this modification enhances the activity of 14-3-3 as an inhibitor of protein kinase C nearly 2-fold. In this report we show by a combination of electrospray mass spectrometry and protein microsequencing that alpha and delta are in vivo post-translationally modified forms of beta and zeta, respectively, and the site of phosphorylation, serine 185, is in a consensus sequence motif for proline-directed kinases.

Expression and structural analysis of 14-3-3 proteins

The 14-3-3 family of proteins plays a role in a wide variety of cellular functions including regulation of protein kinase C and exocytosis. Using antisera specific for the N termini of 14-3-3 isoforms described previously and an additional antiserum specific for the C terminus of epsilon isoform, protease digestion of intact 14-3-3 showed that the N-terminal half of 14-3-3 (a 16 kDa fragment) was an intact, dimeric domain of the protein. Two isoforms of 14-3-3, tau and epsilon, were expressed in E. coli and their secondary structure was shown by circular dichroism to be identical to wild-type protein, and expression of N-terminally-deleted epsilon 14-3-3 protein showed that the N-terminal 26 amino acids are important for dimerization. Intact 14-3-3 is a potent inhibitor of protein kinase C, but the N-terminal domain does not inhibit PKC activity. Site-specific mutagenesis of several regions in the tau isoform of 14-3-3, including the mutation of a putative pseudosubstrate site to a potential substrate sequence, did not alter its inhibitory activity. Intact 14-3-3 proteins are phosphorylated by protein kinase C with a low stoichiometry, but truncated isoforms are phosphorylated much more efficiently by this kinase. This may imply that the proteins may adopt a different structural conformation, possibly upon binding to the membrane, which could modulate their activity. 14-3-3 proteins are found at high concentration on synaptic plasma membranes and this binding is mediated through the N-terminal 12 kDa of 14-3-3.