Effects of dexmedetomidine or methylprednisolone on inflammatory responses in spinal cord injury

BACKGROUND

The aim of this study was to compare the anti-inflammatory response of methylprednisolone and the alpha2-agonist dexmedetomidine in spinal cord injury (SCI).

METHODS

Twenty-four male adult Wistar albino rats, weight 200-250 g, were included in the study. The rats were divided into four groups as follows: the control group (n: 6) received only laminectomy; the SCI group (n: 6) with trauma alone; the SCI+methylprednisolone group (n: 6) with trauma and 30 mg/kg methylprednisolone, followed by a maintenance dose of 5.4 mg/kg/h; and the SCI+dexmedetomidine group (n: 6) with trauma and 10 microg/kg dexmedetomidine treatment intraperitoneally. Twenty-four hours after the trauma, spinal cord samples were taken for histopathological examination and serum samples were collected for interleukin-6 (IL-6) and tumor necrosis factor (TNF)-alpha measurement.

RESULTS

TNF-alpha (P=0.009) and IL-6 (P=0.009) levels were significantly increased in the SCI group. TNF-alpha and IL-6 levels were significantly decreased with methylprednisolone (P=0.002, 0.002) and dexmedetomidine (P=0.002, 0.009) treatment, respectively. Methylprednisolone and dexmedetomidine treatment reduced neutrophils' infiltration in SCI.

CONCLUSIONS

The current study does not clarify the definitive mechanism by which dexmedetomidine decreases inflammatory cytokines but it is the first study to report the anti-inflammatory effect of dexmedetomidine in SCI. Further studies are required to elucidate the effects of dexmedetomidine on the inflammatory response.

Phenotype-dependent susceptibility of cholinergic neuroblastoma cells to neurotoxic inputs

A preferential loss of brain cholinergic neurons in the course of Alzheimer's disease and other encephalopathies is accompanied by a proportional impairment of acetyl-CoA synthesizing capacity in affected brains. Particular susceptibility of cholinergic neurons to neurodegeneration might results from insufficient supply of acetyl-CoA for energy production and acetylcholine synthesis in these conditions. Exposure of SN56 cholinergic neuroblastoma cells to dibutyryl cAMP and retinoic acid for 3 days caused their morphologic differentiation along with the increase in choline acetyltransferase activity, acetylcholine content and release, calcium content, and the expression of p75 neurotrophin receptors. Acetyl-CoA content correlated inversely with choline acetyltransferase activity in different lines of SN56 cells. In differentiated cells, aluminum (1 mM), amyloid beta(25-35) (0.001 mM), and sodium nitroprusside (1 mM), caused much greater decrease of pyruvate dehydrogenase and choline acetyltransferase activities and cell viability than in nondifferentiated ones. Aluminum (1 mM) aggravated suppressory effects of amyloid beta on choline acetyltransferase and pyruvate dehydrogenase activities and viability of differentiated cells. Similar additive inhibitory effects were observed upon combined exposure of differentiated cells to sodium nitroprusside and amyloid beta(25-35). None or much smaller suppressory effects of these neurotoxins were observed in nondifferentiated cells. Increase in the fraction of nonviable differentiated cells positively correlated with losses of choline acetyltransferase, pyruvate dehydrogenase activities, and cytoplasmic cytochrome c content in different neurotoxic conditions. These data indicate that highly differentiated cholinergic neurons may be more susceptible to aluminum and other neurotoxins than the nondifferentiated ones due to relative shortage of acetyl-CoA, increased content of Ca(2+), and expression of p75 receptors, yielding increase in cytoplasmic cytochrome c and subsequently grater rate of death of the former ones.

The effects of VEGF and VEGFR-2 on survival in patients with gastric cancer

Prognostic criteria of the patients with gastric cancer are of critical importance in their management and follow-up. Angiogenesis is essential for the growth and metastasis of solid tumors. Tumor angiogenesis is a multi-step interactive process, and vascular endothelial growth factor (VEGF) and its receptors have a major role in tumor angiogenesis. Thus, we investigated the effects of VEGF and VEGF receptor-2 (VEGFR-2, KDR) on survival in patients with gastric cancer. We analyzed 51 patients who had undergone total or subtotal gastric resection. The patients were divided into two subgroups according to their VEGF and VEGFR-2 (KDR) expression in resected specimens. There was no significant difference between sex, surgical method, lymph node metastasis, serosal invasion, hematogenous metastasis, chemotherapy status of the two subgroups. Mean follow-up time was 24.22 +/- 15.38 months. We found the survival rates of the patients with VEGF positive tumors to be significantly shorter than those of the patients with VEGF negative tumors. There was no significant difference between the survival rates of VEGFR-2 (KDR) positive and negative patients. It was established that the presence of VEGF expression was significantly associated with the short survival rates in patients with gastric cancer. Analysis of VEGF expression in resected specimens may provide additional guidance in determining the prognosis of such patients. If more extensive studies confirm the significance of VEGF and its receptors in gastric cancer, new therapeutic approaches targeting VEGF and its receptors may be considered in gastric cancer management.

Ionization characteristics and chemical influences of aspartic acid residue 158 of papain and caricain determined by structure-related kinetic and computational techniques: multiple electrostatic modulators of active-centre chemistry

The pK(a) of (Asp(158))-CO(2)H of papain (EC 3.4.22.2) was determined as 2.8 by using 4-chloro-7-nitrobenzofurazan (Nbf-Cl) as a reactivity probe targeted on the thiolate anion component of the Cys(25)/His(159) nucleophilic-acid/base motif of the catalytic site. The possibility of using Nbf-Cl for this purpose was established by modelling the papain-Nbf-Cl Meisenheimer intermediate by using QUANTA/CHARMM and performing molecular orbital calculations with MOPAC interfaced with Cerius 2. A pH-dependent stopped-flow kinetic study of the reaction of papain with Nbf-Cl established that the striking rate maximum at pH 3 results from reaction in a minor ionization state comprising (Cys(25))-S(-)/(His(159))-Im(+)H (in which Im represents imidazole) produced by protonic dissociation of (Cys(25))-SH/(His(159))-Im(+)H with pK(a) 3.3 and (Asp(158))-CO(2)H. Although the analogous intermediate in the reaction of caricain (EC 3.4.22.30) with Nbf-Cl has similar geometry, the pH-k profile (k being the second-order rate constant) lacks a rate maximum under acidic conditions. This precludes the experimental determination of the pK(a) value of (Asp(158))-CO(2)H of caricain, which was calculated to be 2.0 by solving the linearized Poisson-Boltzmann equation with the program UHBD ('University of Houston Brownian dynamics'). A value lower than 2.8 had been predicted by consideration of the hydrogen-bonded networks involving Asp(158) and its microenvironments in both enzymes. The difference between these pK(a) values (values not previously detected in reactions of either enzyme) accounts for the lack of the rate maximum in the caricain reaction and for the differences in the electronic absorption spectra of the two S-Nbf-enzymes under acidic conditions. The concept of control of cysteine proteinase activity by multiple electrostatic modulators, including (Asp(158))-CO(2)(-), which modifies traditional mechanistic views, is discussed.

The kinetic basis of a general method for the investigation of active site content of enzymes and catalytic antibodies: first-order behaviour under single-turnover and cycling conditions

The theoretical foundation has been laid for the investigation of catalytic systems using first-order kinetics and for a general kinetic method of investigation of the active site content, E(a), of enzymes, catalytic antibodies, and other enzyme-like catalysts. The method involves a combination of steady-state and single-turnover kinetics to provide Vmax and Km and k(lim)(obs) and K(app)(m), respectively. The validity of the method is shown to remain valid for two extensions of the simple two-step enzyme catalysis model (a) when the catalyst preparation contains molecules (Eb) that bind substrate but fail to catalyse product formation and (b) when the catalyst itself binds substrate non-productively as well as productively. The former is a particularly serious complication for polyclonal catalytic antibodies and the latter a potential complication for all catalysts. For the simple model and for (b) Vmax/k(lim)(obs) provides the value of [Ea]T and for (a) its upper limit. This can be refined by consideration of the relative values of Km and the equilibrium dissociation constant of EbS. For the polyclonal catalytic antibody preparation investigated, the fact that K(app/m) > Km demonstrates for the first time the presence of a substrate-binding but non-catalytic component in a polyclonal preparation. First-order behaviour in catalytic systems occurs not only with a large excess of catalyst over substrate but also with lower catalyst/substrate ratios, including the equimolar condition, when K(app)(m) >> [S]0, a phenomenon that is not widely appreciated.

Therapeutic potential of platelet-activating factor antagonism in the management of myocardial infarction

BACKGROUND

Antagonists of platelet-activating factor (PAF) reduce myocardial postischemia reperfusion injury when given before the onset of ischemia. However, the effects of PAF antagonists when administered at a clinically modelled time (during ischemia but before reperfusion) are controversial. Moreover, the extended survival (eight day) and the characteristics of scar formation after treatment with PAF antagonists have not been investigated.

OBJECTIVES

To determine the therapeutic potential of PAF antagonist TCV-309 for the treatment of regional myocardial ischemia-reperfusion injury; and to determine the effects of TCV-309 on cardiovascular recovery, evolution of scar formation and survival eight days after a myocardial infarction treated with reperfusion.

ANIMALS AND METHODS

Swine underwent regional myocardial ischemia for 60 mins by ligation of the left anterior descending coronary artery, followed by reperfusion for eight days. The treated group (n=7) received PAF antagonist TCV-309 (0.1 mg/kg) 45 mins after ligation; the untreated group (n=7) received vehicle only.

RESULTS

Untreated animals experienced significantly (P<0.001) lower systemic arterial blood pressure during the reperfusion period than animals treated with TCV-309. Furthermore, untreated animals required significantly more (P<0.01) antiarrhythmic and inotropic support. Only two of seven animals in the untreated group survived, which was significantly different (P<0.05) from the six of seven treated animals that survived for eight days. Morphometric analyses did not show differences between groups in the characteristics of scar formation following reperfusion for eight days.

CONCLUSIONS

PAF antagonist TCV-309 improves survival and reduces cardiovascular dysfunctions associated with regional myocardial ischemia reperfusion injury when administered at a clinically modelled time.

A general kinetic approach to investigation of active-site availability in macromolecular catalysts

A potentially general kinetic method for the investigation of active-site availability in preparations of macromolecular catalysts was developed. Three kinetic models were considered: (a) the conventional two-step model of enzyme catalysis, where the preparation contains only active catalyst (E(a)) and inert (i.e. non-binding, non-catalytic) material (E(i)); (b) an extension of the conventional model (a) involving only E(a) and E(i), but with non-productive binding to E(a) (in addition to productive binding); (c) a model in which the preparation contains also binding but non-catalytic material (E(b)), predicted to be present in polyclonal catalytic antibody preparations. The method involves comparing the parameters V(max) and K(m) obtained under catalytic conditions where substrate concentrations greatly exceed catalyst concentration with those (klim/obs, the limiting value of the first-order rate constant, k(obs), at saturating concentrations of catalyst; and Kapp/m) for single-turnover kinetics, in which the reverse situation obtains. The active-site contents of systems that adhere to model (a) or extensions that also lack E(b), such as the non-productive binding model (b), may be calculated using [E(a)](T)=V(max)/klim/obs. This was validated by showing that, for alpha-chymotrypsin, identical values of [E(a)](T) were obtained by the kinetic method using Suc-Ala-Ala-Pro-Phe-4-nitroanilide as substrate and the well-known 'all-or-none' spectroscopic assay using N-trans-cinnamoylimidazole as titrant. For systems that contain E(b), such as polyclonal catalytic antibody preparations, V(max)/klim/obs is more complex, but provides an upper limit to [E(a)](T). Use of the kinetic method to investigate PCA 271-22, a polyclonal catalytic antibody preparation obtained from the antiserum of sheep 271 in week 22 of the immunization protocol, established that [E(a)](T) is less than approx. 8% of [IgG], and probably less than approx. 1% of [IgG].

A classical enzyme active center motif lacks catalytic competence until modulated electrostatically

The cysteine proteinase superfamily is a source of natural structural variants of value in the investigation of mechanism. It has long been considered axiomatic that catalytic competence of these enzymes mirrors the generation of the ubiquitous catalytic site imidazolium-thiolate ion pair. We here report definitive evidence from kinetic studies supported by electrostatic potential calculations, however, that at least for some of these enzymes the ion pair state which provides the nucleophilic and acid-base chemistry is essentially fully developed at low pH where the enzymes are inactive. Catalytic competence requires an additional protonic dissociation with a common pKa value close to 4 possibly from the Glu50 cluster to control ion pair geometry. The pH dependence of the second-order rate constant (k) for the reactions of the catalytic site thiol groups with 4,4'-dipyrimidyl disulfide is shown to provide the pKa values for the formation and deprotonation of the (Cys)-S-/(His)-Im+H ion pair state. Analogous study of the reactions with 2,2'-dipyridyl disulfide reveals other kinetically influential ionizations, and all of these pKa values are compared with those observed in the pH dependence of kcat/Km for the catalyzed hydrolysis of N-acetylphenylalanylglycine 4-nitroanilide. The discrepancy between the pKa value for ion pair formation and the common pKa value close to 4 related to generation of catalytic activity is particularly marked for ficin (pKa 2.49 +/- 0.02) and caricain (pKa 2.88 +/- 0.02) but exists also for papain (pKa 3.32 +/- 0.01).

Evidence for conformational changes in Escherichia coli porphobilinogen deaminase during stepwise pyrrole chain elongation monitored by increased reactivity of cysteine-134 to alkylation by N-ethylmaleimide

Porphobilinogen deaminase from Escherichia coli becomes progressively more susceptible to inactivation by the thiophilic reagent N-ethylmaleimide (NEM) as the catalytic cycle proceeds through the enzyme-intermediate complexes ES, ES2, ES3, and ES4. Site-directed mutagenesis of potentially reactive cysteines has been used to identify cysteine-134 as the key residue that becomes modified by the reagent and leads to inactivation. Since cysteine-134 is buried at the interface between domains 2 and 3 of the E. coli deaminase molecule, the observations suggest that a stepwise conformational change occurs between these domains during each stage of tetrapyrrole assembly. Interestingly, mutation of the invariant active-site cysteine-242 to serine leads to an enzyme with up to a third of the catalytic activity found in the wild-type enzyme. Electrospray mass spectrometry indicates that serine can substitute for cysteine as the dipyrromethane cofactor attachment site.

Fatty acid composition of phospholipids from platelets and erythrocytes in multiple sclerosis

The fatty acid composition of the phospholipids of red blood cells and blood platelets has been investigated in multiple sclerosis patients and in normal individuals. The variation in the platelet phospholipid fatty acid pattern in normals has been measured for the first time and has been shown to be small. The relative level of linoleate, expressed as a percentage of the five main fatty acids, was found to be significantly lower in the multiple sclerosis patients than in healthy individuals, both in the red cells and platelets. A highly significant correlation was found between serum linoleate and both platelet and red cell linoleate.