Expression of the alpha4 isoform of the nicotinic acetylcholine receptor in the fetal human cerebral cortex

Nicotinic acetylcholine receptors are likely to play an important role in neuronal migration during development. Furthermore, the alpha4 receptor subunit gene is related to a hereditary juvenile form of epilepsy. Only little information is available, however, on the expression of cerebrocortical nicotinic acetylcholine receptors during human fetal development. Using non-isotopic in situ hybridization and immunohistochemistry, we have studied the distribution of the alpha4 subunit of the nicotinic acetylcholine receptor mRNA and protein in the human frontal cortex at middle (17-24 weeks of gestation) and late (34-42 weeks of gestation) fetal stages. Both, alpha4 receptor mRNA and alpha4 receptor protein were observed beginning during week 17-18 of gestation. At this time of development, a few weakly labeled mRNA-containing cells were present mainly in the ventricular zone, the subplate and the cortical plate. A similar distribution pattern was found for the receptor protein. Around week 38 of gestation, the distribution in the cerebral cortex of alpha4 subunit-containing cells was similar to that of adult human cortices with the highest densities of labeled neurons found in layers II/III, followed by layers V and VI. Nicotinic acetylcholine receptor-containing neurons appear rather early in human fetal development. Given functional maturity, they may interact during cortical development with acetylcholine released from corticopetal fibers or other yet unknown sources subserving the process of neuronal migration and pathfinding.

Use of a three-day estimated food record, a 72-hour recall and a food-frequency questionnaire for dietary assessment in a Mediterranean Spanish population

AIM

To assess the validity and the short-term reproducibility of a semi-quantitative, self-administrated food frequency questionnaire and a structured 72-hour recall in a Mediterranean Spanish population.

METHODS

44 free-living volunteers participated in the study. Macronutrient, vitamin and mineral intake, recorded on the food frequency questionnaire and the structured 72-h recall were compared with intakes derived from a three-day food record (reference method). Validity of the dietary assessment methods was further assessed by comparing urinary nitrogen, plasma vitamin C, plasma beta-carotene and whole blood glutathione peroxidase activity levels with the corresponding nutrient intakes from the questionnaires. The food frequency questionnaire and the 72-h recall were administered twice to assess the short term reproducibility.

RESULTS

Pearson's correlation coefficients between urinary nitrogen, plasma vitamin C, plasma beta-carotene and whole blood glutathione peroxidase activity levels and the reported nitrogen, vitamin C, beta-carotene and selenium intakes were 0.26, 0.53, 0.17, 0.26 for the food frequency questionnaire; 0.41, 0.09, 0.34, 0.42 for the structured 72-h recall and 0.50, 0.54, 0.44, 0.38 for the three-day food record, respectively. The short term reproducibility of analysed nutrient intake showed average intra-class correlation coefficients of 0.91 and 0.69 for the food frequency questionnaire and the structured 72-h recall irrespectively.

CONCLUSION

The food frequency questionnaire and the structured 72-h recall provide valid estimates of nutrient intake and could be used for dietary assessments.

C-terminal Splice Variants of the Mouse µ-Opioid Receptor Differ in Morphine-induced Internalization and Receptor Resensitization

The main analgesic effects of the opioid alkaloid morphine are mediated by the mu-opioid receptor. In contrast to endogenous opioid peptides, morphine activates the mu-opioid receptor without causing its rapid endocytosis. Recently, three novel C-terminal splice variants (MOR1C, MOR1D, and MOR1E) of the mouse mu-opioid receptor (MOR1) have been identified. In the present study, we show that these receptors differ substantially in their agonist-selective membrane trafficking. MOR1 and MOR1C stably expressed in human embryonic kidney 293 cells exhibited phosphorylation, internalization, and down-regulation in the presence of the opioid peptide [d-Ala(2),Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO) but not in response to morphine. In contrast, MOR1D and MOR1E exhibited robust phosphorylation, internalization, and down-regulation in response to both DAMGO and morphine. DAMGO elicited a similar desensitization (during an 8-h exposure) and resensitization (during a 50-min drug-free interval) of all four mu-receptor splice variants. After morphine treatment, however, MOR1 and MOR1C showed a faster desensitization and no resensitization as compared with MOR1D and MOR1E. These results strongly reinforce the hypothesis that receptor phosphorylation and internalization are required for opioid receptor reactivation thus counteracting agonist-induced desensitization. Our findings also suggest a mechanism by which cell- and tissue-specific C-terminal splicing of the mu-opioid receptor may significantly modulate the development of tolerance to the various effects of morphine.

Effects of alpha-tocopherol, beta-carotene and ascorbic acid on oxidative, hormonal and enzymatic exercise stress markers in habitual training activity of professional basketball players

BACKGROUND

Intense physical exercise has been associated with an increase of free radical production. When the body's natural defense systems against free radicals are overwhelmed, oxidative stress increases.

AIM OF THE STUDY

This study examined the effects of a vitamin antioxidant supplement, (composed of 600 mg alpha-tocopherol, 1000 mg ascorbic acid and 32 mg beta-carotene) on oxidative, hormonal, and enzymatic exercise stress markers during habitual training activity over 35 days.

METHODS

The plasma concentrations of ascorbic acid, alpha-tocopherol, beta-carotene, testosterone, cortisol and lipid peroxides and the serum activities of lactate dehydrogenase and creatine kinase were measured at four time points: pre-supplementation (PS), pre-training (PT), after training (AT) and 24 h after training (24h-AT) in 13 professional basketball players of the first Spanish Basketball League (ACB).

RESULTS

Antioxidant supplementation led to a significant increase of alpha-tocopherol and beta-carotene from PS to PT. Plasma lipid peroxides decreased about 27.7% after 35 days of antioxidant treatment. A significant decrease of lactate dehydrogenase serum activity was observed during the 24 h recuperation time. During this time the anabolic/catabolic balance increased about 29.8% in the antioxidant supplemented group, although this increase did not reach statistical significance.

CONCLUSIONS

The results of the present study suggest that supplementation with alpha-tocopherol, beta-carotene and ascorbic acid might partially account for the hormonal and enzymatic stress marker profile observed during habitual training activity of professional basketball players.

Classical Alzheimer features and cholinergic dysfunction: towards a unifying hypothesis?

OBJECTIVE

Our autopsy studies show possible links between classical Alzheimer pathology and decreased expression of nicotinic acetylcholine receptors. For further elucidation we are now using in vitro models. We report preliminary evidence for the impact of beta-amyloid on nicotinic receptor expression in hippocampal dissociation culture.

METHODS

Cultures (E18 rats) were grown in a serum-free medium and incubated at 8 days in vitro for 3 days with 1 microM Abeta1-42. Expression of alpha4, alpha7, and beta2 nicotinic receptor subunit protein was assessed immunohistochemically and rated semiquantitatively.

RESULTS

Abeta1-42 incubation resulted in a massive reduction of alpha4 protein-expressing neurons, this effect was less pronounced for the alpha7 and beta2 subunit protein.

CONCLUSION

These findings provide first evidence for a direct impact of classical Alzheimer pathology features on nicotinic receptor expression in vitro. Our model will be useful for testing the potential of drugs to stop or reverse these effects.

Parvalbumin-containing interneurons of the human cerebral cortex express nicotinic acetylcholine receptor proteins

Cholinergic fibers from the basal forebrain are known to contact cholinoceptive cortical pyramidal neurons. Recent electrophysiological studies have revealed that nicotinic acetylcholine receptors are also present in human cerebrocortical interneurons. A direct visualization of nicotinic receptor subunits in cortical interneurons has, however, not yet been performed. We have applied double-immunofluorescence using antibodies against parvalbumin --a marker for the Chandelier and basket cell subpopulation of interneurons--and to the alpha4 and alpha7 subunit proteins of the nicotinic acetylcholine receptor. The vast majority of the parvalbuminergic interneurons was immunoreactive for the alpha4 and the alpha7 nicotinic acetylcholine receptor. Provided these receptors would be functional--as suggested by recent electrophysiological findings--the connectivity pattern of cholinergic afferents appears much more complex than thought before. Not only direct cholinergic impact on cortical projection neurons but also the indirect modulation of these by cholinergic corticopetal fibers contacting intrinsic cortical cells would be possible.

Comorbid anxiety and affective disorder in alcohol-dependent patients seeking treatment: the first Multicentre Study in Germany

The goals of this study were to describe demographic variables, drinking history, and the 6-month prevalence of Axis I comorbidity among alcohol-dependent subjects in GERMANY: The variables: amount of alcohol consumption, age at onset of the first alcohol consumed, age at onset of daily alcohol consumption, age at onset of withdrawal symptoms and number of detoxifications were related to the different comorbid disorders and gender. In this study, 556 patients from 25 alcohol treatment centres were enrolled between 1 January 1999 and 30 April 1999. After a minimum of 10 days of sobriety patients who fulfilled ICD-10 and DSM-IV criteria of alcohol dependence were interviewed for data collection using the Mini-DIPS (German version of the Anxiety Disorders Interview Schedule) and a standardized psychosocial interview. The 6-month prevalence of comorbid Axis I disorders was 53.1%. Among the patients with comorbidity, affective and anxiety disorders were most frequent. Comorbid stress disorder was associated with an early start of drinking, an early beginning of withdrawal symptoms, highest number of detoxifications, and the highest amount of alcohol consumed. Female patients with anxiety disorder consumed more alcohol and started earlier than females without this comorbid disorder. The data do not answer the question of the pathogenesis of comorbid disorders and alcoholism, but indicate that stress disorders in alcoholic patients and anxiety disorders in female alcoholics influence the course and severity of alcoholism.

Homo- and heterodimerization of somatostatin receptor subtypes. Inactivation of sst(3) receptor function by heterodimerization with sst(2A)

Several recent studies suggest that G protein-coupled receptors can assemble as heterodimers or hetero-oligomers with enhanced functional activity. However, inactivation of a fully functional receptor by heterodimerization has not been documented. Here we show that the somatostatin receptor (sst) subtypes sst(2A) and sst(3) exist as homodimers at the plasma membrane when expressed in human embryonic kidney 293 cells. Moreover, in coimmunoprecipitation studies using differentially epitope-tagged receptors, we provide direct evidence for heterodimerization of sst(2A) and sst(3). The sst(2A)-sst(3) heterodimer exhibited high affinity binding to somatostatin-14 and the sst(2)-selective ligand L-779,976 but not to the sst(3)-selective ligand L-796,778. Like the sst(2A) homodimer, the sst(2A)-sst(3) heterodimer stimulated guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding, inhibition of adenylyl cyclase, and activation of extracellular signal-regulated kinases after exposure to the sst(2)-selective ligand L-779,976. However, unlike the sst(3) homodimer, the sst(2A)-sst(3) heterodimer did not promote GTPgammaS binding, adenylyl cyclase inhibition, or extracellular signal-regulated kinase activation in the presence of the sst(3)-selective ligand L-796,778. Interestingly, during prolonged somatostatin-14 exposure, the sst(2A)-sst(3) heterodimer desensitized at a slower rate than the sst(2A) and sst(3) homodimers. Both sst(2A) and sst(3) homodimers underwent agonist-induced endocytosis in the presence of somatostatin-14. In contrast, the sst(2A)-sst(3) heterodimer separated at the plasma membrane, and only sst(2A) but not sst(3) underwent agonist-induced endocytosis after exposure to somatostatin-14. Together, heterodimerization of sst(2A) and sst(3) results in a new receptor with a pharmacological and functional profile resembling that of the sst(2A) receptor, however with a greater resistance to agonist-induced desensitization. Thus, inactivation of sst(3) receptor function by heterodimerization with sst(2A) or possibly other G protein-coupled receptors may explain some of the difficulties in detecting sst(3)-specific binding and signaling in mammalian tissues.

Nucleus basalis Meynert lesions and the expression of nicotinic acetylcholine receptor proteins in the rat frontal cerebral cortex

An important feature of cholinergic dysfunction in Alzheimer's disease (AD) is the degenerative loss of magnocellular cholinergic neurons in the basal nucleus of Meynert. In search for suitable animal models of Alzheimer dementia, rats with lesioned basal nuclei rats have been shown to display learning and memory disturbances. We here report on the quantitative assessment of the expression of the nicotinic acetylcholine receptor alpha4 protein in the rat frontal cerebral cortex following a unilateral lesion of the basal nucleus. Cortical alpha4 isoform expression shows a significant increase on the lesioned vs. the non-lesioned control side 1 week after lesioning. By contrast, no differences were observed 4 weeks after lesioning. In consideration of these results basal nucleus lesions appear as a questionable model of AD which in contrast to the present findings shows a decrease of cortical alpha4 nicotinic acetylcholine receptor protein expression.

NO-independent regulatory site on soluble guanylate cyclase

Nitric oxide (NO) is a widespread, potent, biological mediator that has many physiological and pathophysiological roles. Research in the field of NO appears to have followed a straightforward path, and the findings have been progressive: NO and cyclic GMP are involved in vasodilatation; glycerol trinitrate relaxes vascular smooth muscles by bioconversion to NO; mammalian cells synthesize NO; and last, NO mediates vasodilatation by stimulating the soluble guanylate cyclase (sGC), a heterodimeric (alpha/beta) haem protein that converts GTP to cGMP2-4. Here we report the discovery of a regulatory site on sGC. Using photoaffinity labelling, we have identified the cysteine 238 and cysteine 243 region in the alpha1-subunit of sGC as the target for a new type of sGC stimulator. Moreover, we present a pyrazolopyridine, BAY 41-2272, that potently stimulates sGC through this site by a mechanism that is independent of NO. This results in antiplatelet activity, a strong decrease in blood pressure and an increase in survival in a low-NO rat model of hypertension, and as such may offer an approach for treating cardiovascular diseases.

A cluster of childhood leukaemias near two neighbouring nuclear installations in Northern Germany: prevalence of chromosomal aberrations in peripheral blood lymphocytes

PURPOSE

Between 1990 and 1991 a leukaemia cluster was observed in children living close to the combined site of a nuclear power plant and a nuclear research facility in Elbmarsch, a region in Lower Saxony (Germany). We aim to investigate the prevalence of presumably radiation-induced chromosomal aberrations in peripheral blood lymphocytes of children in Elbmarsch and children of a control region in order to find out whether there was an uncontrolled release of radioactive material which resulted in a substantial exposure.

MATERIALS AND METHODS

The frequency of dicentric and ring chromosomes in lymphocytes of the peripheral blood in 42 children in Elbmarsch and 30 children in Plön was investigated. Children in both groups had been permanent residents of the study area.

RESULTS

The mean frequency of dicentric and ring chromosomes in Elbmarsch was 14/32580 cells (=0.430 x 10(-3); 95% CI 0.24-0.70 x 10(-3) cells), and in Plön it was 17/24065 cells (=0.706 x 10(-3); 95% CI 0.42-1.10 x 10(-3) cells).

CONCLUSIONS

No difference in the frequency of dicentric and ring chromosomes was observed between children in Elbmarsch living close to a combined site of a nuclear power plant and a nuclear research facility and children living in the control area Plön. The power of the study to detect a threefold or higher increase in the aberration frequency was at least 0.86.

Synergistic inhibition of cyclooxygenase-2 expression by vitamin E and aspirin

The use of aspirin in rheumatoid arthritis is limited since inhibition of the pro-inflammatory enzyme cyclooxygenase-2 occurs only at higher aspirin doses that are often associated with side effects such as gastric toxicity. Using a macrophage cell line (J774. 1A), the present study explores possible synergistic effects of aspirin and vitamin E on the expression and activity of cyclooxygenase-2. Lipopolysaccharide-induced prostaglandin E(2) formation was significantly reduced by aspirin (1-100 microM) or vitamin E (100-300 microM). When combined with vitamin E, aspirin-dependent inhibition of prostaglandin E(2) formation was increased from 59% to 95% of control. Likewise, lipopolysaccharide-induced cyclooxygenase-2 protein and mRNA expression were virtually abolished by the combined treatment of aspirin and vitamin E, whereas the two agents alone were only modestly effective. Vitamin C did not mimic the actions of vitamin E under these conditions, suggesting that redox-independent mechanisms underlie the action of vitamin E. In agreement with this, vitamin E and aspirin were without effect on lipopolysaccharide-induced translocation of the redox-sensitive transcription factor NF-kappa B. Our results show that co-administration of vitamin E renders cyclooxygenase-2 more sensitive to inhibition by aspirin by as yet unknown mechanisms. Thus, anti-inflammatory therapy might be successful with lower aspirin doses when combined with vitamin E, thereby possibly avoiding the side effects of the usually required high dose aspirin treatment.

Cellular expression of alpha7 nicotinic acetylcholine receptor protein in the temporal cortex in Alzheimer's and Parkinson's disease--a stereological approach

Cognitive deficits in Alzheimer's and Parkinson's disease are closely related to disturbed cholinergic transmission. The decrease of nicotinic acetylcholine receptor protein has been assessed by Western blotting and immunohistochemistry. Stereology, however, has not been used to assess numbers of receptor-expressing human cerebrocortical neurons. Our approach applies a combination of alpha7 subunit-immunohistochemistry with a stereological technique using defined stretches of pial surface as reference standard. The number of alpha7 subunit protein-expressing neurons in the Alzheimer temporal cortices amounted to approximately half of that of controls while numbers in Parkinson patients lay in between. No differences in the total number of neurons were seen. These results corroborate nonstereological studies on Alzheimer cortices and for the first time show a similar decrease in receptor expression in Parkinson's disease. They provide evidence that not only Alzheimer dementia but also cognitive deficits in Parkinson's disease may be related to decreased nicotinic receptor expression.

Increased cytosolic Ca2+ amplifies oxygen radical-induced alterations of the ultrastructure and the energy metabolism of isolated rat pancreatic acinar cells

BACKGROUND

Oxygen radicals have been implicated as important mediators in the early pathogenesis of acute pancreatitis, but the mechanism by which they produce pancreatic tissue injury remains unclear. We have, therefore, investigated the effects of oxygen radicals on isolated rat pancreatic acinar cells as to the ultrastructure, cytosolic Ca2+ concentration and energy metabolism.

METHODS

Acinar cells were exposed to an oxygen radical-generating system consisting of xanthine oxidase, hypoxanthine and chelated iron ions. Cell injury was assessed by LDH release and electron microscopy. Cytosolic Ca2+ levels and mitochondrial membrane potential were determined by flow cytometry; adenine nucleotide concentrations by HPLC. Mitochondrial dehydrogenase activity was measured by spectrophotometric assay.

RESULTS

Oxygen radicals damaged the plasma membrane as shown by a 6-fold LDH increase in the incubation medium within 180 min. At the ultrastructural level, mitochondria were the most susceptible to oxidative stress. In correlation to the pronounced mitochondrial damage, the mitochondrial dehydrogenase activity declined by 70%, whereas the mitochondrial membrane potential was enhanced by 27% after 120 min. Together this may cause the 85% decrease in the ATP concentration and the corresponding increase in ADP/AMP observed in parallel. In addition, an immediate 26% increase in cytosolic Ca2+ was found, a change which could be inhibited by BAPTA, reducing cellular damage.

CONCLUSION

Cytosolic Ca2+ synergizes with oxygen radicals causing alterations of the ultrastructure and energy metabolism of acinar cells which might contribute to the cellular changes found in early stages of acute pancreatitis.

Benzodiazepine receptor inverse agonist-induced kindling of rats alters learning and glutamate binding

Kindling, recognized as a model of epilepsy, can be obtained by applications of repeated nonconvulsive stimulations that finally lead to generalized seizures. Epileptics often show cognitive impairments. The present work analyzed the learning performance of male Wistar rats kindled with a convulsant inverse agonist of the GABA(A)-benzodiazepine receptor complex, methyl beta-carboline-3-carboxylate (beta-CCM). This compound is also known to have an action on learning processes. It was thus interesting to verify if beta-CCM kindling had the same impairing action on learning as other kindling agents, such as pentylenetetrazol (PTZ). A two-way active-avoidance shuttle-box learning task was chosen, because a deficit was found after PTZ kindling in this learning model. On the other hand, hippocampal glutamate binding, has previously been shown to be modified by both seizures and learning. Thus, the level of glutamate binding was also measured in the present study. Results showed that fully kindled rats had poorer learning performance after the third day of test than controls or not fully kindled animals. L-[3H] glutamate binding to hippocampal membrane fractions of the fully kindled animals was significantly higher when compared with controls, whereas L-[3H] glutamate binding of not fully kindled subjects did not differ from that of controls. Neuronal plasticity changes are a possible explanation for the correlation between kindling, learning deficits, and increased glutamate binding.

Reference typing report for complement factor B

Factor B (BF) reference typing was carried out on the occasion of the VIIth Complement Genetics Workshop in Mainz, May 1998. Two different sets of samples were analysed by agarose electrophoresis and/or isoelectric focusing at the protein level, and by PCR-RFLP analysis at the DNA level. These results confirmed the reliability of the standard agarose electrophoresis technique for the identification of the major BF alleles as well as for the identification of cathodic and anodic variants. However, the exact alphanumeric designation of individual variants relative to the reference distance between alleles S and F1 turned out to be more difficult. Using PCR-RFLP analysis, the common alleles F and S as well as the FA and FB subtypes in 6 samples containing an F allele were all assigned correctly. However, the variants F1 and S07 were not detected by this method, as they could not be distinguished from the accompanying S allele. Therefore, a combined application of all three typing methods is recommended for a reliable identification of factor B alleles, variants and FA/FB subtypes.

Reference typing report for complement component C6: protein typing

Within the C6/C7/C9 Session of the VIIth Complement Genetics Workshop and Conference, various C6 protein allotypes collected from four laboratories were examined using polyacrylamide gel isoelectric focusing (PAGIF) followed by direct immunofixation. Nineteen different variants including 17 recognized allotypes and introducing two new allotypes were distinguished besides the two common allotypes C6 A and C6 B. They were designated basically according to the previous statement on C6 nomenclature. Details on C6 DNA markers and associations of C6 markers with deficiencies of terminal complement components are published in the preceding paper of this issue.

Expression of nicotinic acetylcholine receptors in Alzheimer's disease: postmortem investigations and experimental approaches

Nicotinic ligand binding studies have shown rather early that the cholinoceptive system is affected in Alzheimer's disease (AD). Today, molecular histochemistry enables one to study the nicotinic acetylcholine receptor (nAChR) subunit expression on the cellular level in human autopsy brains, in animal models and in in vitro approaches, thus deciphering the distribution of nAChRs and their role as potential therapeutic targets. The studies on the nAChR expression in the frontal and temporal cortex of AD patients and age-matched controls could demonstrate that both, the numbers of alpha4- and alpha7-immunoreactive neurons and the quantitative amount, in particular of the alpha4 protein, were markedly decreased in AD. Because the number of the corresponding mRNA expressing neurons was unchanged these findings point to a translational/posttranslational rather than a transcriptional event as an underlying cause. This assumption is supported by direct mutation screening of the CHRNA4 gene which showed no functionally important mutations. To get more insight into the underlying mechanisms, two model systems organotypic culture and primary hippocampal culture - have been established, both allowing to mimic nAChR expression in vitro. In ongoing studies the possible impact of beta-amyloid (Abeta) on nAChR expression is tested. Preliminary results obtained from primary cultures point to an impaired nAChR expression following Abeta exposure.

Allelic variation S268P of the human mu-opioid receptor affects both desensitization and G protein coupling

The decrease in mu-opioid receptor activity after chronic agonist exposure (1 microM [D-Ala(2),N-MePhe(4),Gly-ol(5)]-enkephalin) is largely due to kinase-mediated phosphorylation of intracellular receptor domains. We have recently shown that the substitution of two putative Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) phosphorylation sites, S261 and S266, by alanines in the third intracellular loop of the rat mu-opioid receptor (rMOR1) confers resistance to CaMK II-induced receptor desensitization. In the present study, we show that the injection of active CaMK II in Xenopus laevis oocytes led to the desensitization of S261A but not S266A receptor mutant, indicating that S266 is the primary CaMK II phosphorylation site of the rMOR1. For the corresponding phosphorylation site in the human mu-opioid receptor (hMOR), an allelic variation S268P has been recently identified. After expression in X. laevis oocytes and human embryonic kidney 293 cells, this human S268P receptor and a corresponding rat S266P receptor mutant revealed a loss of CaMK II-induced receptor desensitization and a decreased G protein coupling compared with the wild-type receptors. Our results suggest that serines 266 (rMOR1) and 268 (hMOR) play crucial role in receptor desensitization and signaling and that the allelic variation S268P results in a human receptor type with a weaker but persistent G protein coupling after agonist treatment.

A common pathway for nitric oxide release from NO-aspirin and glyceryl trinitrate

NO-Aspirin (NCX-4016) releases nitric oxide (NO) in biological systems through as yet unidentified mechanisms. In LLC-PK1 kidney epithelial cells, a 5-h pretreatment with glyceryl trinitrate (GTN, 0.1-1 microM) significantly attenuated the cyclic GMP response to a subsequent challenge with both NO-aspirin or GTN. Similarly, NO-aspirin (10-100 microM) was found to induce tolerance to its own cyclic GMP stimulatory action and to that of GTN. In contrast, cyclic GMP stimulation by the spontaneous NO donor SIN-1, which releases NO independently of enzymatic catalysis, remained unimpaired in cells pretreated with GTN or NO-aspirin. The observed cross-tolerance between NO-aspirin and GTN cells indicates that bioactivation pathways of organic nitrates, which have been shown to involve cytochrome P450, may also be responsible for NO release from NO-aspirin. Prolonged treatment with NO-aspirin causes down-regulation of the cellular cyclic GMP response, suggesting that tolerance may occur during therapy with NO-aspirin.

Multistep mechanism of substrate binding determines chaperone activity of Hsp70

The 70 kDa heat shock proteins (the Hsp70 family) assist refolding of their substrates through ATP-controlled binding. We have analyzed mutants of DnaK, an Hsp70 homolog, altered in key residues of its substrate binding domain. Substrate binding occurs by a dynamic mechanism involving: a hydrophobic pocket for a single residue that is crucial for affinity, a two-layered closing device involving independent action of an alpha-helical lid and an arch, and a superimposed allosteric mechanism of ATP-controlled opening of the substrate binding cavity that operates largely through a beta-structured subdomain. Correlative evidence from mutational analysis suggests that the ADP and ATP states of DnaK differ in the frequency of the conformational changes in the alpha-helical lid and beta-domain that cause opening of the substrate binding cavity. The affinity for substrates, as defined by this mechanism, determines the efficiency of DnaJ-mediated and ATP hydrolysis mediated locking-in of substrates and chaperone activity of DnaK.

Heme oxygenase-1 is a cGMP-inducible endothelial protein and mediates the cytoprotective action of nitric oxide

Inducible heme oxygenase (HO-1) has recently been recognized as an antioxidant and cytoprotective gene. By use of Western blotting, cell viability analysis, and antisense technique, the present study investigates the involvement of HO-1 in endothelial protection induced by the clinically used nitric oxide (NO) donor molsidomine (specifically, its active metabolite 3-morpholinosydnonimine [SIN-1]) and the second messenger cGMP. In bovine pulmonary artery endothelial cells, SIN-1 and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) at 1 to 100 micromol/L induced the synthesis of HO-1 protein in a concentration-dependent fashion up to 3-fold over basal levels. HO-1 induction by SIN-1 was inhibited in the presence of the NO scavenger phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide and the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole[4, 3-a]quinoxalin-1-one. 8-Bromo-cGMP (1 to 100 micromol/L) and dibutyryl cGMP (1 to 100 micromol/L) as well as the activator of particulate guanylyl cyclase atrial natriuretic peptide (1 to 100 nmol/L) produced increases in HO-1 protein similar to those produced by SIN-1. SIN-1 and 8-bromo-cGMP increased heme oxygenase activity (bilirubin formation). Cytoprotection by NO donors was abrogated in the presence of the heme oxygenase inhibitor tin protoporphyrin IX. Pretreatment of cells with a phosphorothioate-linked HO-1 antisense oligonucleotide prevented protection by SIN-1 or 8-bromo-cGMP against tumor necrosis factor-alpha cytotoxicity, whereas sense and scrambled HO-1 were without effect under these conditions. Our results show for the first time that HO-1 is a cGMP-sensitive endothelial gene and establish conclusively a causal relationship between HO-1 induction and endothelial protection by the NO/cGMP system. By targeting cytoprotective HO-1, NO donors may therefore be expected to induce antioxidant, antiatherogenic, and anti-inflammatory effects.

Complement component C6 polymorphism: novel protein-typing technique and distribution of allotypes in Germany

The genetic polymorphism of human C6 was investigated in Germany using an improved technique: polyacrylamide gel isoelectric focusing and subsequent direct immunofixation with monospecific C6 antisera. Typing of C6 was performed on native serum samples from 1,775 unrelated persons. The gene frequencies in the population study were as follows: C6*A 0.6313, C6*B 0.3566 and the rare alleles C6*R 0. 0121. In total, 8 rare allotypes were analysed. The gene frequencies obtained are in good agreement with those previously published.

Quantitative assessment of nicotinic acetylcholine receptor proteins in the cerebral cortex of Alzheimer patients

Cholinergic transmission has for long been known to be one of the most severely affected systems in Alzheimer's disease (AD), resulting clinically in massive cognitive deficits. The molecular basis of this dysfunction--on both the pre- and the postsynaptic sites--is still a matter of ongoing investigations. Here, we report on the quantitative assessment of nicotinic acetylcholine receptor isoform expression in AD vs. control cortices. For both subunit proteins assessed, the alpha4 and the alpha7 isoform, highly significant decreases in diseased vs. normal cortices were observed. Both alpha4 and alpha7 subunits are known to be important constituents in hetero- (alpha4beta2) and homooligomeric (alpha7) receptor subtypes. Their decreased expression may contribute to the decreased nicotinic binding known to be accompanied by AD and severe cognitive deficits. The quantitative assessment of nicotinic acetylcholine receptor expression will help to determine those subunits suited as targets for pharmacological stimulation.