Hypertension and cognitive performance in African Americans with Alzheimer disease.

The authors examined the relationship between hypertension and cognitive performance in 34 African-American patients with probable Alzheimer disease. Multiple regression analyses indicated that hypertension was associated with poorer overall performance on the Mattis Dementia Rating Scale, particularly the Initiation/Perseveration and Conceptualization subscales, after controlling for gender, age, and education. The findings suggest that African-American patients with hypertension exhibit greater cognitive impairment, possibly reflecting executive dysfunction.

Apolipoprotein E and age at onset of Alzheimer's disease in African American patients.

The authors examined whether the APOE-epsilon4 allele is associated with an earlier age at onset of AD in 71 African American patients with probable AD. The authors found a linear dose effect in which each copy of the epsilon4 allele was associated with a 3.6-year earlier onset of AD, indicating a dose-dependent relationship between APOE-epsilon4 and age at onset of AD in African Americans.

Water diffusion changes in Wallerian degeneration and their dependence on white matter architecture.

This study investigates water diffusion changes in Wallerian degeneration. We measured indices derived from the diffusion tensor (DT) and T2-weighted signal intensities in the descending motor pathways of patients with small chronic lacunar infarcts of the posterior limb of the internal capsule on one side. We compared these measurements in the healthy and lesioned sides at different levels in the brainstem caudal to the primary lesion. We found that secondary white matter degeneration is revealed by a large reduction in diffusion anisotropy only in regions where fibers are arranged in isolated bundles of parallel fibers, such as in the cerebral peduncle. In regions where the degenerated pathway crosses other tracts, such as in the rostral pons, paradoxically there is almost no change in diffusion anisotropy, but a significant change in the measured orientation of fibers. The trace of the diffusion tensor is moderately increased in all affected regions. This allows one to differentiate secondary and primary fiber loss where the increase in trace is considerably higher. We show that DT-MRI is more sensitive than T2-weighted MRI in detecting Wallerian degeneration. Significant diffusion abnormalities are observed over the entire trajectory of the affected pathway in each patient. This finding suggests that mapping degenerated pathways noninvasively with DT-MRI is feasible. However, the interpretation of water diffusion data is complex and requires a priori information about anatomy and architecture of the pathway under investigation. In particular, our study shows that in regions where fibers cross, existing DT-MRI-based fiber tractography algorithms may lead to erroneous conclusion about brain connectivity.

Homocysteine elicits a DNA damage response in neurons that promotes apoptosis and hypersensitivity to excitotoxicity.

Elevated plasma levels of the sulfur-containing amino acid homocysteine increase the risk for atherosclerosis, stroke, and possibly Alzheimer's disease, but the underlying mechanisms are unknown. We now report that homocysteine induces apoptosis in rat hippocampal neurons. DNA strand breaks and associated activation of poly-ADP-ribose polymerase (PARP) and NAD depletion occur rapidly after exposure to homocysteine and precede mitochondrial dysfunction, oxidative stress, and caspase activation. The PARP inhibitor 3-aminobenzamide (3AB) protects neurons against homocysteine-induced NAD depletion, loss of mitochondrial transmembrane potential, and cell death, demonstrating a requirement for PARP activation and/or NAD depletion in homocysteine-induced apoptosis. Caspase inhibition accelerates the loss of mitochondrial potential and shifts the mode of cell death to necrosis; inhibition of PARP with 3AB attenuates this effect of caspase inhibition. Homocysteine markedly increases the vulnerability of hippocampal neurons to excitotoxic and oxidative injury in cell culture and in vivo, suggesting a mechanism by which homocysteine may contribute to the pathogenesis of neurodegenerative disorders.

Preventing stroke in patients with transient ischemic attacks.

Stroke is the third most common overall cause of death and the leading cause of adult disability in the United States. New therapeutic interventions instituted in the period immediately after a stroke have revolutionized the approach to ischemic cerebrovascular disease. Recognition of a transient ischemic attack provides an opportunity to prevent a subsequent stroke. Specific stroke prevention treatment depends on the cause of the transient ischemic attack, its cerebrovascular localization and the presence of associated coexisting medical problems. Modification of stroke risk factors is the principal therapeutic approach. Antiplatelet agents and anticoagulants have been shown to be effective in reducing the occurrence of stroke in certain populations. Several well-designed studies have recently demonstrated the effectiveness of carotid endarterectomy in preventing strokes related to extracranial carotid artery disease.

Intractable diarrhea from cytomegalovirus enterocolitis in an immunocompetent infant.

Infection with cytomegalovirus (CMV) in infants can be congenital or perinatal. Infected infants may be asymptomatic or present with pneumonia, rash, hepatosplenomegaly, or encephalitis.1 In the presence of an immunodeficiency, severe and sometimes fatal disease may occur. To our knowledge, CMV has not been identified previously as a cause of intractable diarrhea of infancy. We report the case of a 5-week-old immunocompetent infant with intractable diarrhea attributable to CMV-induced enterocolitis. Recognition of this infection and initiation of ganciclovir therapy was associated with a rapid improvement and resolution of the diarrhea.

Regulation of the activity of IFN-gamma promoter elements during Th cell differentiation.

Before they can deliver their effector functions, CD4+ Th cells must differentiate into Th1 or Th2 subsets. We have prepared reporter transgenic mice that express the luciferase gene under the control of proximal (prox.IFN-gamma) and distal (dist.IFN-gamma) regulatory elements from the IFN-gamma promoter to permit investigation of mechanisms that regulate IFN-gamma gene transcription during Th cell differentiation. Precursor Th cells (pTh) contain high levels of cAMP response element binding protein-activation transcription factor-1 (CREB-ATF1) proteins that bind these promoter elements from the IFN-gamma gene, and these cells fail to express promoter activity. Restimulated effector Th (eTh) cells have reduced levels of CREB-ATF1 proteins, their nuclear extracts exhibit reduced CREB-ATF1 binding and greater Jun and Jun-ATF2 binding to dist.IFN-gamma), and eTh cells express promoter activity. CREB directly competes with effector T cell nuclear proteins for dist.IFN-gamma binding, and overexpression of CREB inhibits both prox.IFN-gamma- and dist.IFN-gamma-directed transcription in Jurkat T cells. IL-12-stimulated Thl differentiation increases dist.IFN-gamma activity in restimulated eTh1 cells; eTh1 nuclear extracts form increased levels of Jun-ATF2-dist.IFN-gamma complexes. Taken together, these data suggest that both de-repression and trans-activation contribute to the induction of IFN-gamma gene transcription during Th1 differentiation.

Ischemic strokes secondary to vitamin B12 deficiency-induced hyperhomocystinemia.

A 45-year-old woman sustained two ischemic cerebral infarctions 16 years after ileal resection for Crohn's disease. Her evaluation showed an elevated random serum homocystine level, a low serum vitamin B12 level, and an increased mean corpuscular volume (MCV) without anemia. A methionine-loading test resulted in a marked increase in the homocystine levels 2, 4, and 6 hours after the load. A Schilling test demonstrated a malabsorption of vitamin B12. Vitamin B12 injections normalized her fasting homocystine level and her MCV. She has had no recurrent strokes during a year follow-up.

Increased endothelial expression of intercellular adhesion molecule-1 in symptomatic versus asymptomatic human carotid atherosclerotic plaque.

BACKGROUND AND PURPOSE: The mechanisms that cause carotid atherosclerotic plaque to become symptomatic remain unclear. Evidence suggests that mediators of inflammation are not only instrumental in the formation of plaque but may also be involved in the rapid progression of atheromatous lesions leading to plaque fissuring, endothelial injury, and intraluminal thrombosis. Our goal is to determine whether intercellular adhesion molecule-1 (ICAM-1), a known component of the inflammatory pathway, is preferentially expressed on symptomatic versus asymptomatic carotid plaques. METHODS: Carotid plaques from symptomatic (n = 25) and asymptomatic (n = 17) patients undergoing carotid endarterectomy with lesions involving >60% stenosis were snap-frozen at the time of surgery. Immunofluorescence studies were performed to measure the percentage of luminal endothelial surface that expressed ICAM-1. The relationships of stroke risk factors, white blood cell count, percent stenosis, and soluble ICAM-1 (sICAM-1) plasma levels to endothelial ICAM-1 expression were investigated. RESULTS: An increased expression of ICAM-1 was found in the high-grade regions of symptomatic (29.5%+/-2.4%, mean+/-SEM) versus asymptomatic (15.7%+/-2.7%, mean+/-SEM) plaques (P=0.002) and in the high-grade versus the low-grade region of symptomatic plaques (29.5+/-2.4, mean+/-SEM, versus 8.9+/-1.6; P<0.001). Plasma sICAM-1 levels were not predictive of symptomatic disease, and no significant correlation between risk factor exposure and endothelial ICAM-1 expression was found. CONCLUSIONS: An elevation in ICAM-1 expression in symptomatic versus asymptomatic plaque suggests that mediators of inflammation are involved in the conversion of carotid plaque to a symptomatic state. The data also suggest a differential expression of ICAM-1, with a greater expression found in the high-grade region than in the low-grade region of the plaque specimen.

Interferon-gamma expression by Th1 effector T cells mediated by the p38 MAP kinase signaling pathway.

Signal transduction via MAP kinase pathways plays a key role in a variety of cellular responses, including growth factor-induced proliferation, differentiation and cell death. In mammalian cells, p38 MAP kinase can be activated by multiple stimuli, such as pro-inflammatory cytokines and environmental stress. Although p38 MAP kinase is implicated in the control of inflammatory responses, the molecular mechanisms remain unclear. Upon activation, CD4+ T cells differentiate into Th2 cells, which potentiate the humoral immune response or pro-inflammatory Th1 cells. Here, we show that pyridinyl imidazole compounds (specific inhibitors of p38 MAP kinase) block the production of interferon-gamma (IFNgamma) by Th1 cells without affecting IL-4 production by Th2 cells. These drugs also inhibit transcription driven by the IFNgamma promoter. In transgenic mice, inhibition of the p38 MAP kinase pathway by the expression of dominant-negative p38 MAP kinase results in selective impairment of Th1 responses. In contrast, activation of the p38 MAP kinase pathway by the expression of constitutivelyactivated MAP kinase kinase 6 in transgenic mice caused increased production of IFNgamma during the differentiation and activation of Th1 cells. Together, these data demonstrate that the p38 MAP kinase is relevant for Th1 cells, not Th2 cells, and that inhibition of p38 MAP kinase represents a possible site of therapeutic intervention in diseases where a predominant Th1 immune response leads to a pathological outcome. Moreover, our study provides an additional mechanism by which the p38 MAP kinase pathway controls inflammatory responses.

Differential transcription directed by discrete gamma interferon promoter elements in naive and memory (effector) CD4 T cells and CD8 T cells.

Acquisition of the ability to produce gamma interferon (IFN-gamma) is a fundamental property of memory T cells and enables one subset (T helper 1 [TH1]) to deliver its effector functions. To examine regulation of IFN-gamma gene expression in a model system which recapitulates TH1 differentiation, we prepared reporter transgenic mice which express the luciferase gene under the control of proximal and distal regulatory elements (prox.IFN gamma and dist.IFN gamma) from the IFN-gamma promoter. Memory T cells, but not naive T cells, secreted IFN-gamma and expressed both prox.IFN gamma and dist.IFN gamma transcriptional activities. Naive T cells required priming to become producers of IFN-gamma and to direct transcription by these elements. While both CD4+ and CD8+ T cells produced IFN-gamma, only CD4+ T cells expressed prox.IFN gamma transcriptional activity. Induction of transcriptional activity was inhibited by known antagonists of effector T-cell populations. Cyclosporin A inhibited transcriptional activity directed by both elements in effector T cells. Elevated cyclic AMP inhibited transcriptional activity directed by prox.IFN gamma in primed CD4+ T cells but enhanced transcriptional activity directed by dist.IFN gamma in primed CD8+ T cells. Taken together, these data show that prox.IFN gamma and dist.IFN gamma transcriptional activities mirror IFN-gamma gene expression in naive and memory CD4+ T cells but suggest that differences exist in regulation of IFN-gamma gene expression in CD4+ and CD8+ T-cell subsets.

The proximal regulatory element of the interferon-gamma promoter mediates selective expression in T cells.

Interferon-gamma (IFN-gamma) is produced by natural killer cells and certain subsets of T cells, but the basis for its selective expression is unknown. Within the region between -108 and -40 base pairs of the IFN-gamma promoter are two conserved and essential regulatory elements, which confer activation-specific expression in T cells. This report describes studies indicating that the most proximal of these two regulatory elements is an important determinant of its restricted expression. The proximal element is a composite site that binds members of the CREB/ATF, AP-1, and octamer families of transcription factors. Jun is essential for activation-induced transcription and binds preferably as a heterodimer with ATF-2. In contrast, CREB appears to dampen transcription from this element. The CpG dinucleotide in this element is selectively methylated in Th2 T cells and other cells that do not express IFN-gamma, and methylation markedly reduces transcription factor binding. As a target for DNA methylation and for binding of transcription factors that mediate or impede transcription, this element appears to play a central role in controlling IFN-gamma expression.

Felbamate block of the N-methyl-D-aspartate receptor.

The anticonvulsant felbamate may act as an N-methyl-D-aspartate (NMDA) receptor antagonist, but the mechanism of block has not been fully characterized. We sought to identify the sites at which felbamate exerts its NMDA receptor blocking action using radioligand binding to rat forebrain membranes and whole-cell voltage clamp and single-channel recordings from cultured rat hippocampal neurons. Equilibrium binding isotherms for [3H]dizocilpine, a channel blocking ligand, were obtained in the presence of saturating glutamate and glycine. At a concentration of 1 mM, felbamate competitively inhibited specific [3H]dizocilpine binding, indicating that felbamate interacts with the channel blocking site. At a higher concentration (3 mM), felbamate also reduced the maximal saturation binding, demonstrating an additional allosteric action. The dissociation constant (Kb), estimated from fits to the binding isotherms, was 0.7-1.1 mM. It has been proposed that felbamate block of NMDA receptors occurs via competitive glycine site antagonism. However, the slowing of [3H]dizocilpine dissociation by felbamate, unlike the slowing produced by 7-chlorokynurenic acid, was not reversed by increasing the glycine concentration. In addition, felbamate did not reduce specific binding of [3H]5,7-dichlorokynurenic acid, a glycine site ligand. In whole-cell voltage clamp recordings of NMDA receptor currents, its blocking time constant (69 +/- 0.4 msec) was substantially faster than the dissociation time constant of glycine (390 +/- 23 msec), whereas the time constant for 5,7-dichlorokynurenic acid (390 +/- 20 msec) was similar. These observations indicate that felbamate block of NMDA receptors does not occur by an action at the glycine site.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of susceptibility to audiogenic seizures following cardiac arrest cerebral ischemia in rats.

Susceptibility to audiogenic seizures (AGS) was investigated in Sprague-Dawley rats subjected to cardiac arrest cerebral ischemia (CACI), produced by compression of the major cardiac vessels. The onset of AGS was regularly observed 1 day after CACI of > 5 min duration. The duration of postischemic susceptibility to AGS was directly related to the density of cerebral ischemia, with 50% of more severely ischemic animals still showing AGS susceptibility 8 weeks after CACI. Lesioning of the inferior colliculi (IC) abolished the onset of AGS; no such effect was observed after lesioning the medial geniculate (MG). Glutamic acid decarboxylase (GAD) immunochemistry revealed approximately 50% loss of GAD-positive neurons in the IC, which was similar in animals with various durations of AGS susceptibility. Otherwise, there was a conspicuous sprouting of gamma-aminobutyric acid (GABA)-ergic terminals in the ventral thalamic nuclei, which peaked approximately 1 month after the CACI. Evaluation of GABA-A inhibitory function in the hippocampus by the paired pulse stimulation revealed changes indicating loss of GABA-A inhibition coinciding with the onset of AGS, and its return in animals tested 2 months after CACI. Our observations suggest a potential role of GABA-ergic dysfunction in the postischemic development of AGS.

Genetics of ischemic stroke.

Advances in the study of cerebrovascular disease suggest that many risk factors for stroke are under genetic influence. Epidemiologic studies show that parental and sibling histories of cerebral ischemic events are associated with an increased risk of stroke. Explanations for familial stroke aggregation include differential phenotypic expression of apolipoprotein (a) and apolipoprotein E, racial variations in the distribution of vascular disease, identification of the autosomal-dominant disorder cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy, specific point mutations in the mitochondrial-related disorders, and identification of the clinical significance of hereditable coagulopathies. Greater understanding of these factors may lead to early recognition of and intervention in stroke.

Diminished expression of CD40 ligand by activated neonatal T cells.

CD40 and CD40 ligand (gp39) mediate contact-dependent T-B cell interaction. We determined the expression of CD40 ligand by activated neonatal T cells and the response of neonatal B cells when activated through CD40. Although expression of CD40 ligand peaked simultaneously in both activated adult and neonatal cells, neonatal T cells expressed significantly less CD40 ligand surface protein and mRNA than adult T cells. Activated thymocytes also expressed far less CD40 ligand than adult T cells. Consistent with these results, activated neonatal T cells exhibited less helper function than activated adult T cells. Neonatal T cells primed and restimulated in vitro expressed CD40 ligand in amounts comparable with adult T cells and provided B cell help more effectively. This suggests that the poor expression of CD40 ligand reflects antigenic naiveté rather than an intrinsic defect of neonatal T cells. Neonatal B cells cultured with soluble CD40 ligand (sgp39) and IL-10 produced IgM in amounts comparable with adult cells, but much less IgG and IgA. Nevertheless, neonatal B cells were capable of proliferation and class switching, since sgp39 and IL-4 induced proliferation and IgE production comparable to adult B cells and production of modest amounts of IgG. Together, these results indicate that diminished CD40 ligand expression, along with decreased production of lymphokines, may be responsible, at least in part, for the transient immunodeficiency observed in human neonates.

Differentiation of the T helper phenotypes by analysis of the methylation state of the IFN-gamma gene.

Th1 and Th2 CD4+ T cell clones have been defined by their ability to produce different lymphokines. However, the processes by which CD4+ T cells differentially regulate lymphokine gene expression have not been well defined. In this report, we demonstrate that the methylation status of a CpG dinucleotide contained within a TATA proximal regulatory element of the IFN-gamma promoter correlates with the transcription of the gene. In murine Th1 clones and two human CD4+ Th0 clones, this site is either completely or partially hypomethylated, whereas in murine Th2 clones this site is > 98% methylated. Treatment of murine Th2 clones with 5-azacytidine, an agent that inhibits methylation of the DNA, converts these cells to IFN-gamma producers. Additional targets for methylation outside the transcriptional control regions of the IFN-gamma genetic locus were found to be hypomethylated in Th2 cells but not in Th1 cells. Electrophoretic mobility shift assays (EMSA) revealed at least five distinct protein-DNA complexes that are formed with an oligonucleotide containing the IFN-gamma promoter TATA proximal regulatory element, and in vitro methylation of this site results in a loss of these three complexes. Furthermore, a comparison of nuclear extracts prepared from Th1 and Th2 clones revealed that the EMSA patterns were qualitatively similar but differed quantitatively. In addition, transient transfection of a murine IFN-gamma promoter-chloramphenicol acetyl transferase (CAT) gene construct into both Th1 and Th2 clones produced CAT activity that was not inducible by anti-CD3, indicating that hypomethylation per se of the promoter alone is not sufficient for inducible gene expression.