Activation of p44/42 mitogen activated protein kinases in thrombin-induced brain tolerance

BACKGROUND: Our recent studies have shown that prior intracerebral injection of a low dose of thrombin attenuates the brain edema formation that results from either an intracerebral hematoma, an intracerebral injection of a large dose of thrombin or cerebral ischemia. The aim of the current study is to investigate whether thrombin-induced tolerance (thrombin preconditioning; TPC) is associated with activation of p44/42 mitogen activated protein (MAP) kinases. METHODS: This study contained three parts. In the first, rats received an intracerebral infusion of either saline or one unit thrombin (the TPC dose) into the right caudate nucleus. After 1, 3 and 7 days, the rats will be killed and brains used to detect p44/42 MAP kinases activation using Western blot analysis and immunohistochemistry. In the second and third parts, rats received intracerebral infusions of either vehicle, one unit thrombin (TPC) or one unit thrombin and 5 nmol PD 098059. These rats were either killed to detect kinases activation after 24 h or received a second intracerebral infusion of five-unit thrombin 7 days later with brain edema being assessed after a further 24 h. RESULTS: Western blot analysis demonstrated that p44/42 MAP kinases were activated in the ipsilateral basal ganglia after the intracerebral infusion of thrombin one unit. Cells immunoreactive for activated p44/42 MAP kinases were found in the ipsilateral basal ganglia and ipsilateral cortex. PD 098059, a MAP kinase kinase inhibitor, abolished thrombin-induced activation of p44/42 MAP kinases. TPC suppressed thrombin-induced brain edema while PD 098059 blocked this protective effect. The water contents in the ipsilateral basal ganglia 24 h after infusion of thrombin five units were 82.6+/-0.8%, 79.2+/-0.4% and 81.8+/-1.9% in the control, TPC alone and TPC plus PD 098059 groups, respectively. CONCLUSION: Thrombin can activate p44/42 MAP kinases within the brain and the protective effects of thrombin preconditioning on brain edema formation are related to this activation.     

Effects of fungal toxins on renal slice calcium balance

Citrinin and ochratoxin A disrupt renal function in many animal species. The mechanism(s) underlying these actions is (are) unclear. Although citrinin has been shown to bind covalently to renal tissue, there also is evidence that it is active in the unmetabolized form. Altered calcium homeostasis has been suggested as an event which might mediate cell injury and/or death; a possible role for calcium in citrinin- or ochratoxin A-induced nephrotoxicity is reported here. Renal cortical slice calcium balance was monitored by the uptake of 45Ca. Either ochratoxin A or citrinin added to fresh renal cortex slices enhanced 45Ca accumulation. These effects were evident as early as 5 min after addition of the toxins. Greater 45Ca uptake occurred with bathing solution calcium concentration of 1.1 mM than in the absence of added carrier calcium. Finally, the effect of citrinin to reduce p-aminohippurate accumulation by renal cortical slices was greater in the presence of calcium than in its absence.     

Follow-up investigations in cerebrospinal fluid of patients with dementia with Lewy bodies and Alzheimer’s disease

Summary. Measuring proteins in cerebrospinal fluid (CSF) has gained wide acceptance for the differential diagnosis of dementia. Some groups have already extended these investigations in Alzheimers disease (AD) by asking how stable these markers are in follow-up analysis, if they depend on the stage of disease and whether they can be used to monitor the progression and biological effects of treatment. We evaluated 21 patients with dementia with Lewy bodies (DLB) and 19 patients with AD, on two occasions, with regard to levels of tau protein, tau protein phosphorylated at threonine 181 (p-tau), A42, A40 and S-100B protein, using a set of commercially available assays.Tau protein levels were lower in DLB in first and second LP compared to AD and decreased during course of both groups. P-tau levels were increased in AD and DLB and decreased during follow-up. A42 and A40 remained relatively stable during follow-up but we found a slight increase of the median A42 level in DLB, whereas in AD, A42 tends to decrease during follow-up. S-100B protein increased during follow-up in both diseases.The protein dynamics in DLB and AD are relatively similar. S-100B protein may be a useful marker for follow-up in neurodegenerative diseases but has to be analysed in longer follow-up periods. Tau protein may be used to differentiate between DLB and AD.Follow-up CSF analyses are of limited value for the differentiation of AD and DLB. We conclude that more specific markers have to be established for the differentiation and follow-up of these diseases.     

Regional Ependymal Upregulation of Vimentin in Chiari II Malformation,Aqueductal Stenosis,and Hydromyelia

Vimentin, glial fibrillary acidic protein (GFAP) and S-100 protein were studied by immunocytochemistry in the ependyma of patients with Chiari II malformations, congenital aqueductal stenosis, and hydromyelia. Paraffin sections of brains and spinal cords of 16 patients were examined, 14 with Chiari II malformations, most with aqueductal stenosis and/or hydromyelia as associated features, and 2 patients with congenital aqueductal stenosis without Chiari malformation. Patients ranged in age from 20-wk gestation to 48 years. The results demonstrated: 1) in the fetus and young infant with Chiari II malformations, congenital aqueductal stenosis, and hydromyelia, vimentin is focally upregulated in the ependyma only in areas of dysgenesis and not in the ependyma throughout the ventricular system; 2) GFAP and S-100 protein are not coexpressed, indicating that the selective upregulation of vimentin is not simple maturational delay; 3) vimentin upregulation also is seen in the ependymal remnants of the congenital atretic cerebral aqueduct, not associated with Chiari malformation; 4) in the older child and adult with Chiari II malformation, vimentin overexpression in the ependyma becomes more generalized in the lateral ventricles as well, hence evolves into a nonspecific upregulation. The interpretation from these findings leads to speculation that it is unlikely that ependymal vimentin is directly involved in the pathogenesis of Chiari II malformation, but may reflect a secondary upregulation due to defective expression of another gene. This gene may be one of rhombomeric segmentation that also plays a role in defective programming of the paraxial mesoderm for the basioccipital and supraoccipital bones resulting in a small posterior fossa. This interpretation supports the hypothesis of a molecular genetic defect, rather than a mechanical cause, as the etiology of the Chiari II malformation.     

A new structural class of proteasome inhibitors identified by microbial screening using yeast-based assay

A yeast-based growth interference assay was developed utilizing a yeast strain in which expression of Xenopus cyclin A1 was induced to elevate cell division cycle 28 (Cdc28) kinase activity. Since the hyperactivation of Cdc28 kinase in yeast results in a growth-arrest phenotype, compounds which could rescue the cyclin A1-induced growth arrest might be potential new, antitumor drug candidates acting on the cyclin-dependent, kinase-mediated, cell cycle regulation pathway. In the course of our microbial screening program, the new Streptomyces metabolites, belactosins, were identified. As reported previously, belactosin A induced cell cycle arrest at G2/M phase in human cancer cells. However, the molecular mechanism of action was unknown. We herein demonstrate the proteasome inhibition by belactosin A. Belactosin A did not inhibit yeast Cdc28 kinase and human cyclin-dependent kinase in vitro. On the other hand, it inhibited the chymotrypsin-like activity of the rabbit 20S proteasome. From the initial SAR studies, we identified a hydrophobic belactosin A derivative, KF33955, which exhibited a 100-fold greater growth-inhibitory activity against HeLa S3 cells than belactosin A, presumably due to its higher cell permeability. The biochemical analysis using KF33955 suggested that the proteasome inhibitory activity of KF33955 were irreversible and required the beta-lactone moiety to inhibit the proteasome. KF33955 increased the intracellular levels of protein ubiquitination in NIH3T3 cells. In addition, KF33955 treatment resulted in the accumulation of known proteasome substrates in HeLa S3 cells. These results identify belactosin A as a useful lead compound to target proteasome for the treatment of disease whose etiology is dependent on the unregulated ubiquitin-proteasome pathway.     

In vivo amyloid imaging in Alzheimer’s disease

Targeted approaches to therapy for Alzheimers disease have evolved based on detailed understanding of the genetic, molecular biologic, and neuropathologic basis of the disease. Given the potential for greater treatment efficacy in the earlier stages of the disease, the notion of early diagnosis has become more relevant. Current clinical and imaging diagnostic approaches lack reliability in the preclinical and prodromal phases of the disease. We review emerging studies on imaging of the molecular substrate of the disease, most notably the amyloid peptide, which hope to increase early diagnostic efficacy. We offer a brief overview of the demographics, diagnostic criteria, and current imaging tests, followed by a review of amyloid biology and developments in cerebral amyloid imaging yielded by recent in vitro, in vivo and human studies.     

Structural determinants for the activation mechanism of the angiotensin II type 1 receptor differ for phosphoinositide hydrolysis and mitogen-activated protein kinase pathways

While the mechanism whereby the angiotensin II type 1 receptor (AT(1) receptor) activates its classical effector phospholipase C-beta (PLC-beta) has largely been elucidated, there is little consensus on how this receptor activates a more recently identified effector, the p42/44 mitogen-activated protein kinases (p42/44(MAPK)). Using transfected COS-1 cells, we investigated the activation of this signaling pathway at the receptor level itself. Previous mutational studies that relied on phosphoinositide turnover as an index of receptor activation have indicated that key residues in the second and seventh transmembrane domains participate in AT(1) receptor activation mechanisms. Thus, we introduced a variety of mutations-AT(1)[D74N], AT(1)[Y292F], AT(1)[N295S], and AT(1)[AT(2) TM7], which is composed of a chimeric substitution of the AT(1) seventh transmembrane domain with its AT(2) counterpart. These mutations that strongly diminished the receptor's ability to activate PLC-beta had little to no effect on its ability to activate p42/44(MAPK), which not only suggests that p42/44(MAPK) does not exclusively lie downstream of the G-protein G(q)/PLC-beta pathway but also indicates that more than one activation state may exist for the AT(1) receptor. The failure of a protein kinase C inhibitor to block AT(1) receptor activation of p42/44(MAPK) further corroborated evidence that the receptor's activation of p42/44(MAPK) is largely independent of the G(q)/PLC-beta/PKC pathway. Taken together, the experimental evidence strongly suggests that the mechanism whereby the AT(1) receptor activates p42/44(MAPK) is fundamentally different from that for PLC-beta, even at the level of the receptor itself.     

Comparison of hippocampal G protein activation by 5-HT<Subscript>1A</Subscript> receptor agonists and the atypical antipsychotics clozapine and S16924

This study employed [³⁵S]guanosine 5-O-(3-thiotriphosphate) ([³⁵S]GTPS) binding to compare the actions of antipsychotic agents known to stimulate cloned, human 5-HT_1A receptors with those of reference agonists at postsynaptic 5-HT_1A receptors. In rat hippocampal membranes, the following order of efficacy was observed (maximum efficacy, E_max, values relative to 5-HT=100): (+)8-OH-DPAT (85), flesinoxan (62), eltoprazine (60), S14506 (59), S16924 (48), buspirone (41), S15535 (22), clozapine (22), ziprasidone (21), pindolol (7), p-MPPI (0), WAY100,635 (0), spiperone (0). Despite differences in species and tissue source, the efficacy and potency (pEC₅₀) of agonists (with the exception of clozapine) correlated well with those determined previously at human 5-HT_1A receptors expressed in Chinese hamster ovary (CHO) cells. In contrast, clozapine was more potent at hippocampal membranes. The selective antagonists p-MPPI and WAY100,635 abolished stimulation of binding by (+)8-OH-DPAT, clozapine and S16924 (p-MPPI), indicating that these actions were mediated specifically by 5-HT_1A receptors. Clozapine and S16924 also attenuated 5-HT- and (+)8-OH-DPAT-stimulated [³⁵S]GTPS binding, consistent with partial agonist properties. In [³⁵S]GTPS autoradiographic studies, 5-HT-induced stimulation, mediated through 5-HT_1A receptors, was more potent in the septum (pEC₅₀~6.5) than in the dentate gyrus of the hippocampus (pEC₅₀~5) suggesting potential differences in coupling efficiency or G protein expression. Though clozapine (30 and 100 µM) did not enhance [³⁵S]GTPS labelling in any structure, S16924 (10 µM) modestly increased [³⁵S]GTPS labelling in the dentate gyrus. On the other hand, both these antipsychotic agents attenuated 5-HT (10 µM)-stimulated [³⁵S]GTPS binding in the dentate gyrus and septum. In conclusion, clozapine, S16924 and ziprasidone act as partial agonists for G protein activation at postsynaptic 5-HT_1A receptors in the hippocampus. These data support a role of postsynaptic 5-HT_1A receptors in the functional profiles of certain antipsychotic agents.     

Activation of c—Jun and suppression of phospho—p44／42 were involved in diphenylhydantoin—induced apoptosis of cultured rat cerebellar granule neurons

AIM:To investigate possible intracellular signal molecules involved in diphenylhydantoin (DPH)-mediated apoptosis of cerebellar granule neurons (CGN) and explore possible nolecular mechanisms of neurotoxicity of DPH.METHODS: Fluorescein diacetate (FDA) stain, hochest 33258 stain, and agar gel electrophoresis were used to test morphological and biological characters of primary CGN and cortical neurons (CN) in the presence or absence of 100μmol/L DPH; Western blot and RT-PCR were employed to further investigate apoptotic/survival signal moleculars involved in the neuronal apoptotic signal transdution. RESULTS:DPH 100μmol/L induced a typical apoptosis of CGN but had no toxicity on CN. Cerebellar granule neural apoptosis induced by 100μmol/L DPH was significantly inhibited by pre-treatment with SB203580(10μmol/L) or CEP-11004(1μmol/L) for 1h. DPH markedly upregulated the levels of phospho-c-Jun (active c-Jun), total c-Jun protein and c-jun mRNA in CGN. The levels of phospho-c-Jun dramatically elevated by DPH at 8 h were significantly inhibited by SB203580(10μmol/L) or CEP-11004 (1μmol/L). Moreover, the activities of p44/42 (ERK1/ERK2), other members of MAP kinases and generally believed to be important survival effetors in CGN, were markedly suppressed. However, the activities of both JNK and p38 were little affected in the process of apoptosis of CGN induced by 100μmol/L DPH. CONCLUSION: The selective toxicity of DPH on CGN is likely due to its ability to induce apoptosis of CGN, it is a process involved activation of c-Jun and suppression of the activity of p44/42.     

CSF-tau,CSF-Aß1-42, ApoE-genotype and clinical parameters in the diagnosis of Alzheimer’s disease: combination of CSF-tau and MMSE yields highest sensitivity and specificity

Summary. This study evaluated the sensitivity and specificity of the cerebrospinal fluid (CSF) levels of tau-protein, amyloid-ß-peptide 1-42 (Aß1-42), ApoE-genotype and the degree of cognitive decline as diagnostic markers for Alzheimers disease (AD). Data was obtained from 105 AD patients and 68 controls.Median CSF-tau levels were increased (512pg/ml vs. 145pg/ml, p<0.001) and Aß1-42-levels were decreased (238.5pg/ml vs. 310pg/ml, p<0.001) in AD patients compared to controls. A weak correlation was found between CSF-Aß1-42 and MMSE score (r=.245). Within all subjects, a correlation of CSF-Aß1-42 (r=–.337) and CSF-tau (r=.384) with age was found. The combination of CSF-tau levels and MMSE revealed the highest sensitivity (92%) and specificity (87%).In summary, CSF-tau was a useful biological marker to discriminate AD from normal aging, neurological and psychiatric disorders. CSF-Aß1-42 showed no additional benefit in discriminating patients from controls but might be useful for tracking the severity of the disease.Received January 20, 2003; accepted April 29, 2003 Published online July 30, 2003