Structures, functions and adaptations of the human LINE-1 ORF2 protein

The LINE-1 (L1) retrotransposon is an ancient genetic parasite that has written around one-third of the human genome through a 'copy and paste' mechanism catalysed by its multifunctional enzyme, open reading frame 2 protein (ORF2p)1. ORF2p reverse transcriptase (RT) and endonuclease activities have been implicated in the pathophysiology of cancer2,3, autoimmunity4,5 and ageing6,7, making ORF2p a potential therapeutic target. However, a lack of structural and mechanistic knowledge has hampered efforts to rationally exploit it. We report structures of the human ORF2p 'core' (residues 238-1061, including the RT domain) by X-ray crystallography and cryo-electron microscopy in several conformational states. Our analyses identified two previously undescribed folded domains, extensive contacts to RNA templates and associated adaptations that contribute to unique aspects of the L1 replication cycle. Computed integrative structural models of full-length ORF2p show a dynamic closed-ring conformation that appears to open during retrotransposition. We characterize ORF2p RT inhibition and reveal its underlying structural basis. Imaging and biochemistry show that non-canonical cytosolic ORF2p RT activity can produce RNA:DNA hybrids, activating innate immune signalling through cGAS/STING and resulting in interferon production6-8. In contrast to retroviral RTs, L1 RT is efficiently primed by short RNAs and hairpins, which probably explains cytosolic priming. Other biochemical activities including processivity, DNA-directed polymerization, non-templated base addition and template switching together allow us to propose a revised L1 insertion model. Finally, our evolutionary analysis demonstrates structural conservation between ORF2p and other RNA- and DNA-dependent polymerases. We therefore provide key mechanistic insights into L1 polymerization and insertion, shed light on the evolutionary history of L1 and enable rational drug development targeting L1.

Role of Hydrogen Sulfide in Inflammatory Bowel Disease

Hydrogen sulfide (H2S), originally known as toxic gas, has now attracted attention as one of the gasotransmitters involved in many reactions in the human body. H2S has been assumed to play a role in the pathogenesis of many chronic diseases, of which the exact pathogenesis remains unknown. One of them is inflammatory bowel disease (IBD), a chronic intestinal disease subclassified as Crohn's disease (CD) and ulcerative colitis (UC). Any change in the amount of H2S seems to be linked to inflammation in this illness. These changes can be brought about by alterations in the microbiota, in the endogenous metabolism of H2S and in the diet. As both too little and too much H2S drive inflammation, a balanced level is needed for intestinal health. The aim of this review is to summarize the available literature published until June 2023 in order to provide an overview of the current knowledge of the connection between H2S and IBD.

The influence of liver transplantation on the interplay between gut microbiome and bile acid homeostasis in children with biliary atresia

BACKGROUND

Biliary atresia (BA) causes neonatal cholestasis and rapidly progresses into cirrhosis if left untreated. Kasai portoenterostomy may delay cirrhosis. BA remains among the most common indications for liver transplantation (LT) during childhood. Liver function and gut microbiome are interconnected. Disturbed liver function and enterohepatic signaling influence microbial diversity. We, herein, investigate the impact of LT and reestablishment of bile flow on gut microbiome-bile acid homeostasis in children with BA before (pre, n = 10), 3 months (post3m, n = 12), 12 months (post12m, n = 9), and more than 24 months (post24 + m, n = 12) after LT.

METHODS

We analyzed the intestinal microbiome of BA patients before and after LT by 16S-rRNA-sequencing and bioinformatics analyses, and serum primary and secondary bile acid levels.

RESULTS

The gut microbiome in BA patients exhibits a markedly reduced alpha diversity in pre (p = 0.015) and post3m group (p = 0.044), and approximated healthy control groups at later timepoints post12m (p = 1.0) and post24 + m (p = 0.74). Beta diversity analysis showed overall community structure similarities of pre and post3m (p = 0.675), but both differed from the post24 + m (p < 0.001). Longitudinal analysis of the composition of the gut microbiome revealed the Klebsiella genus to show increased abundance in the post24 + m group compared with an age-matched control (p = 0.029). Secondary bile acid production increased 2+ years after LT (p = 0.03). Multivariable associations of microbial communities and clinical metadata reveal several significant associations of microbial genera with tacrolimus and mycophenolate mofetil-based immunosuppressive regimens.

CONCLUSIONS

In children with BA, the gut microbiome shows strongly reduced diversity before and shortly after LT, and approximates healthy controls at later timepoints. Changes in diversity correlate with altered secondary bile acid synthesis at 2+ years and with the selection of different immunosuppressants.

Posterior circulation ischaemic stroke diagnosis and management

This narrative review provides an overview of the posterior circulation and the clinical features of common posterior circulation stroke (PCS) syndromes in the posterior arterial territories and how to distinguish them from mimics. We outline the hyperacute management of patients with suspected PCS with emphasis on how to identify those who are likely to benefit from intervention based on imaging findings. Finally, we review advances in treatment options, including developments in endovascular thrombectomy (EVT) and intravenous thrombolysis (IVT), and the principles of medical management and indications for neurosurgery. Observational and randomised clinical trial data have been equivocal regarding EVT in PCS, but more recent studies strongly support its efficacy. There have been concomitant advances in imaging of posterior stroke to guide optimal patient selection for thrombectomy. Recent evidence suggests that clinicians should have a heightened suspicion of posterior circulation events with the resultant implementation of timely, evidence-based management.

Cerebroprotection in the endovascular era: an update

Despite advances in clinical diagnosis and increasing numbers of patients eligible for revascularisation, ischaemic stroke remains a significant public health concern accounting for 3.3 million deaths annually. In addition to recanalisation therapy, patient outcomes could be improved through cerebroprotection, but all translational attempts have remained unsuccessful. In this narrative review, we discuss potential reasons for those failures. We then outline the diverse, multicellular effects of ischaemic stroke and the complex temporal sequences of the pathophysiological cascade during and following ischaemia, reperfusion, and recovery. This evidence is linked with findings from prior cerebroprotective trials and interpreted for the modern endovascular era. Future cerebroprotective agents that are multimodal and multicellular, promoting cellular and metabolic health to different targets at time points that are most responsive to treatment, might prove more successful.

Developing a metabolic clearance rate framework as a translational analysis approach for hyperpolarized 13C magnetic resonance imaging

Hyperpolarized carbon-13 magnetic resonance imaging is a promising technique for in vivo metabolic interrogation of alterations between health and disease. This study introduces a formalism for quantifying the metabolic information in hyperpolarized imaging. This study investigated a novel perfusion formalism and metabolic clearance rate (MCR) model in pre-clinical stroke and in the healthy human brain. Simulations showed that the proposed model was robust to perturbations in T₁, transmit B₁, and k_PL. A significant difference in ipsilateral vs contralateral pyruvate derived cerebral blood flow (CBF) was detected in rats (140 ± 2 vs 89 ± 6 mL/100 g/min, p < 0.01, respectively) and pigs (139 ± 12 vs 95 ± 5 mL/100 g/min, p = 0.04, respectively), along with an increase in fractional metabolism (26 ± 5 vs 4 ± 2%, p < 0.01, respectively) in the rodent brain. In addition, a significant increase in ipsilateral vs contralateral MCR (0.034 ± 0.007 vs 0.017 ± 0.02/s, p = 0.03, respectively) and a decrease in mean transit time (31 ± 8 vs 60 ± 2 s, p = 0.04, respectively) was observed in the porcine brain. In conclusion, MCR mapping is a simple and robust approach to the post-processing of hyperpolarized magnetic resonance imaging.

Hydrogen Sulfide Metabolizing Enzymes in the Intestinal Mucosa in Pediatric and Adult Inflammatory Bowel Disease

Hydrogen sulfide (H2S) is a toxic gas that has important regulatory functions. In the colon, H2S can be produced and detoxified endogenously. Both too little and too much H2S exposure are associated with inflammatory bowel disease (IBD), a chronic intestinal disease mainly classified as Crohn's disease (CD) and ulcerative colitis (UC). As the pathogenesis of IBD remains elusive, this study's aim was to investigate potential differences in the expression of H2S-metabolizing enzymes in normal aging and IBD. Intestinal mucosal biopsies of 25 adults and 22 children with IBD along with those of 26 healthy controls were stained immunohistochemically for cystathionine-γ-lyase (CSE), 3-mercapto-sulfurtransferase (3-MST), ethylmalonic encephalopathy 1 protein (ETHE1), sulfide:quinone oxidoreductase (SQOR) and thiosulfate sulfurtransferase (TST). Expression levels were calculated by multiplication of the staining intensity and percentage of positively stained cells. Healthy adults showed an overall trend towards lower expression of H2S-metabolizing enzymes than healthy children. Adults with IBD also tended to have lower expression compared to controls. A similar trend was seen in the enzyme expression of children with IBD compared to controls. These results indicate an age-related decrease in the expression of H2S-metabolizing enzymes and a dysfunctional H2S metabolism in IBD, which was less pronounced in children.

Role of Energy Metabolism and Mitochondrial Function in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic recurring inflammation of the intestine which can be debilitating for those with intractable disease. However, the etiopathogenesis of inflammatory bowel disorders remains to be solved. The hypothesis that mitochondrial dysfunction is a crucial factor in the disease process is being validated by an increasing number of recent studies. Thus mitochondrial alteration in conjunction with previously identified genetic predisposition, changes in the immune response, altered gut microbiota, and environmental factors (eg, diet, smoking, and lifestyle) are all posited to contribute to IBD. The implicated factors seem to affect mitochondrial function or are influenced by mitochondrial dysfunction, which explains many of the hallmarks of the disease. This review summarizes the results of studies reporting links between mitochondria and IBD that were available on PubMed through March 2021. The aim of this review is to give an overview of the current understanding of the role of mitochondria in the pathogenesis of IBD.

Expression of Oxidative Phosphorylation Complexes and Mitochondrial Mass in Pediatric and Adult Inflammatory Bowel Disease

INTRODUCTION

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC), is a multifactorial intestinal disorder but its precise etiology remains elusive. As the cells of the intestinal mucosa have high energy demands, mitochondria may play a role in IBD pathogenesis. The present study is aimed at evaluating the expression levels of mitochondrial oxidative phosphorylation (OXPHOS) complexes in IBD. Material and Methods. 286 intestinal biopsy samples from the terminal ileum, ascending colon, and rectum from 124 probands (34 CD, 33 UC, and 57 controls) were stained immunohistochemically for all five OXPHOS complexes and the voltage-dependent anion-selective channel 1 protein (VDAC1 or porin). Expression levels were compared in multivariate models including disease stage (CD and UC compared to controls) and age (pediatric/adult).

RESULTS

Analysis of the terminal ileum of CD patients revealed a significant reduction of complex II compared to controls, and a trend to lower levels was evident for VDAC1 and the other OXPHOS complexes except complex III. A similar pattern was found in the rectum of UC patients: VDAC1, complex I, complex II, and complex IV were all significantly reduced, and complex III and V showed a trend to lower levels. Reductions were more prominent in older patients compared to pediatric patients and more marked in UC than CD.

CONCLUSION

A reduced mitochondrial mass is present in UC and CD compared to controls. This is potentially a result of alterations of mitochondrial biogenesis or mitophagy. Reductions were more pronounced in older patients compared to pediatric patients, and more prominent in UC than CD. Complex I and II are more severely compromised than the other OXPHOS complexes. This has potential therapeutic implications, since treatments boosting biogenesis or influencing mitophagy could be beneficial for IBD treatment. Additionally, substances specifically stimulating complex I activity should be tested in IBD treatment.

Rapamycin Induces an eNOS (Endothelial Nitric Oxide Synthase) Dependent Increase in Brain Collateral Perfusion in Wistar and Spontaneously Hypertensive Rats

BACKGROUND AND PURPOSE

Rapamycin is a clinically approved mammalian target of rapamycin inhibitor that has been shown to be neuroprotective in animal models of stroke. However, the mechanism of rapamycin-induced neuroprotection is still being explored. Our aims were to determine if rapamycin improved leptomeningeal collateral perfusion, to determine if this is through eNOS (endothelial nitric oxide synthase)-mediated vessel dilation and to determine if rapamycin increases immediate postreperfusion blood flow.

METHODS

Wistar and spontaneously hypertensive rats (≈14 weeks old, n=22 and n=15, respectively) were subjected to ischemia by middle cerebral artery occlusion (90 and 120 minutes, respectively) with or without treatment with rapamycin at 30-minute poststroke. Changes in middle cerebral artery and collateral perfusion territories were measured by dual-site laser Doppler. Reactivity to rapamycin was studied using isolated and pressurized leptomeningeal anastomoses. Brain injury was measured histologically or with triphenyltetrazolium chloride staining.

RESULTS

In Wistar rats, rapamycin increased collateral perfusion (43±17%), increased reperfusion cerebral blood flow (16±8%) and significantly reduced infarct volume (35±6 versus 63±8 mm³, P<0.05). Rapamycin dilated leptomeningeal anastomoses by 80±9%, which was abolished by nitric oxide synthase inhibition. In spontaneously hypertensive rats, rapamycin increased collateral perfusion by 32±25%, reperfusion cerebral blood flow by 44±16%, without reducing acute infarct volume 2 hours postreperfusion. Reperfusion cerebral blood flow was a stronger predictor of brain damage than collateral perfusion in both Wistar and spontaneously hypertensive rats.

CONCLUSIONS

Rapamycin increased collateral perfusion and reperfusion cerebral blood flow in both Wistar and comorbid spontaneously hypertensive rats that appeared to be mediated by enhancing eNOS activation. These findings suggest that rapamycin may be an effective acute therapy for increasing collateral flow and as an adjunct therapy to thrombolysis or thrombectomy to improve reperfusion blood flow.

Somatic retrotransposition is infrequent in glioblastomas

Background

Gliomas are the most common primary brain tumors in adults. We sought to understand the roles of endogenous transposable elements in these malignancies by identifying evidence of somatic retrotransposition in glioblastomas (GBM). We performed transposon insertion profiling of the active subfamily of Long INterspersed Element-1 (LINE-1) elements by deep sequencing (TIPseq) on genomic DNA of low passage oncosphere cell lines derived from 7 primary GBM biopsies, 3 secondary GBM tissue samples, and matched normal intravenous blood samples from the same individuals.

Results

We found and PCR validated one somatically acquired tumor-specific insertion in a case of secondary GBM. No LINE-1 insertions present in primary GBM oncosphere cultures were missing from corresponding blood samples. However, several copies of the element (11) were found in genomic DNA from blood and not in the oncosphere cultures. SNP 6.0 microarray analysis revealed deletions or loss of heterozygosity in the tumor genomes over the intervals corresponding to these LINE-1 insertions.

Conclusions

These findings indicate that LINE-1 retrotransposon can act as an infrequent insertional mutagen in secondary GBM, but that retrotransposition is uncommon in these central nervous system tumors as compared to other neoplasias.

Electronic supplementary material

The online version of this article (doi:10.1186/s13100-016-0077-5) contains supplementary material, which is available to authorized users.

Structure and properties of the esterase from non-LTR retrotransposons suggest a role for lipids in retrotransposition

Non-LTR retrotransposons are mobile genetic elements and play a major role in eukaryotic genome evolution and disease. Similar to retroviruses they encode a reverse transcriptase, but their genomic integration mechanism is fundamentally different, and they lack homologs of the retroviral nucleocapsid-forming protein Gag. Instead, their first open reading frames encode distinct multi-domain proteins (ORF1ps) presumed to package the retrotransposon-encoded RNA into ribonucleoprotein particles (RNPs). The mechanistic roles of ORF1ps are poorly understood, particularly of ORF1ps that appear to harbor an enzymatic function in the form of an SGNH-type lipolytic acetylesterase. We determined the crystal structures of the coiled coil and esterase domains of the ORF1p from the Danio rerio ZfL2-1 element. We demonstrate a dimerization of the coiled coil and a hydrolytic activity of the esterase. Furthermore, the esterase binds negatively charged phospholipids and liposomes, but not oligo-(A) RNA. Unexpectedly, the esterase can split into two dynamic half-domains, suited to engulf long fatty acid substrates extending from the active site. These properties indicate a role for lipids and membranes in non-LTR retrotransposition. We speculate that Gag-like membrane targeting properties of ORF1ps could play a role in RNP assembly and in membrane-dependent transport or localization processes.

Dimerization and direct membrane interaction of Nup53 contribute to nuclear pore complex assembly

Nuclear pore formation depends on membrane curvature. The membrane deforming activity of Nup53 is required for nuclear pore complex (NPC) assembly during interphase.

Nuclear pore complexes (NPCs) fuse the two membranes of the nuclear envelope (NE) to a pore, connecting cytoplasm and nucleoplasm and allowing exchange of macromolecules between these compartments. Most NPC proteins do not contain integral membrane domains and thus it is largely unclear how NPCs are embedded and anchored in the NE. Here, we show that the evolutionary conserved nuclear pore protein Nup53 binds independently of other proteins to membranes, a property that is crucial for NPC assembly and conserved between yeast and vertebrates. The vertebrate protein comprises two membrane binding sites, of which the C-terminal domain has membrane deforming capabilities, and is specifically required for de novo NPC assembly and insertion into the intact NE during interphase. Dimerization of Nup53 contributes to its membrane interaction and is crucial for its function in NPC assembly.

Roles of retrotransposons in benign and malignant hematologic disease

Nearly half of our genomes are repetitive sequences derived from retrotransposons. These repeats have accumulated by a 'copy-and-paste' mechanism whereby: (i.) a genomic template sequence is transcribed to RNA, (ii.) the RNA is reverse-transcribed, and (iii.) the DNA copy is inserted at a new location in the host genome. As we remain susceptible to new retrotransposition events, many of these insertions are highly polymorphic. Transposons are of interest since insertions into both coding and non-coding gene regions have been associated with a wide variety of functional sequelae and because transposable elements can be involved in genomic rearrangements in transformed cells. In this review, we highlight how expression of retrotransposons, de novo and polymorphic transposon insertions, and genomic rearrangements that these repeats potentiate contribute to both benign and neoplastic hematopoietic diseases.

Ethanol inhibits spontaneous activity of central nucleus of the amygdala neurons but does not impair retention in the passive-avoidance task

BACKGROUND

Behavioral studies using pharmacological manipulations that increase neuronal activity of the central nucleus of the amygdala (CeA) have implicated the CeA in enhancement of memory modulation. To date, however, there has been a dearth of studies investigating the effect of a drug that decreases CeA activity on memory modulation-a drug that inhibits the neuronal activity of the CeA might be expected to impair memory modulation. To determine whether ethanol inhibits CeA activity and, if so, whether decreased CeA activity is associated with impairment of memory modulation, this study investigated the effect of ethanol on spontaneous single-unit activity of CeA neurons and retention in the passive-avoidance task.

METHODS

The effect of ethanol (0.35, 0.75, 1.5, 2.5 g/kg) was determined on spontaneously firing neurons in the CeA in urethane-anesthetized rats by use of standard in vivo single-unit electrophysiological recording techniques. Additionally, the effect of ethanol when administered immediately after training in a standard passive-avoidance task was determined on retention the following day.

RESULTS

Ethanol profoundly inhibited spontaneous CeA firing rates in urethane-anesthetized rats at all doses tested. Maximal inhibition was related to dose. Each dose of ethanol significantly inhibited CeA activity within 15 min of administration; within 35 min of administration, 0.75 g/kg of ethanol inhibited CeA activity by 65.2%, and the highest dose (2.5 g/kg) produced nearly complete suppression of CeA activity (81.3%). Although ethanol markedly inhibited CeA activity, these same doses of ethanol failed to impair retention in the passive-avoidance task: 0.35, 0.75, 1.5, and 2.5 g/kg of ethanol, administered immediately after training, failed to alter latency to step-through the following day.

CONCLUSIONS

These results show that ethanol profoundly inhibits spontaneous CeA activity and suggest that inhibition of the CeA is not sufficient to impair retention in the passive-avoidance task.

Induction of pulmonary allergen-specific IgA responses or airway hyperresponsiveness in the absence of allergic lung disease following sensitization with limiting doses of ovalbumin-alum

Respiratory allergies represent a failure to generate nonpathogenic responses to innocuous foreign materials. Herein we assessed the role of the sensitizing dose of allergen in this response/nonresponse paradigm, sensitizing BALB/c mice with 5 ng-2 microg of OVA-alum and assessing their responses to repeated OVA aerosol challenge. Mice sensitized with < or = 25 ng of OVA-alum did not develop atopic antibodies, airway hyperresponsiveness (AHR), eosinophilia, or pulmonary Th2 responses, but the 25-ng group animals did develop significant IgA responses. The mice sensitized with 100 ng of OVA-alum developed AHR in the absence of detectable allergic disease, while the mice sensitized with 250 ng-2 microg of OVA/alum developed full-spectrum allergic disease (i.e., eosinophilia, IgE, IgG1, pulmonary Th2 cytokine responses, and AHR). These data indicate that limiting doses of allergen can differentially induce IgA or AHR in the absence of atopic disease in mice.

Dose-sensitive excitation and inhibition of spontaneous amygdala activity by propranolol

The effect of systemically administered propranolol was determined on spontaneous activity of neurons in the central nucleus (CeA) of the amygdala, a brain site implicated in fear-related learning and memory. Extracellular recordings of single units in the CeA were obtained in vivo from rats administered saline or the centrally and peripherally acting beta-adrenergic receptor blocker propranolol (4, 7, 10 mg/kg i.p.). The high dose (10 mg/kg) of propranolol markedly increased spontaneous activity of CeA neurons. In contrast, the low (4 mg/kg) and intermediate (7 mg/kg) doses of propranolol significantly decreased spontaneous CeA activity, with the suppressant effect of propranolol on CeA firing rates weakening as the dosage increased from 4 to 7 mg/kg. These results suggest that (1) spontaneous activity of CeA neurons is tonically influenced by competing excitatory and inhibitory modulatory circuits, and (2) propranolol's effect on the two modulatory circuits is dose dependent: the high dose increasing spontaneous CeA activity by preferentially blocking an inhibitory circuit, the low dose decreasing spontaneous CeA activity by preferentially blocking an excitatory circuit, and the intermediate dose weakly suppressing CeA activity by blocking both the excitatory and inhibitory modulatory circuits. Disinhibition of CeA activity by the high dose of propranolol may explain the enhancement of retention observed in the passive-avoidance task when this dose of the drug is administered systemically, and may have implications for the use of propranolol clinically in treating aversive-memory-related anxiety disorders such as posttraumatic stress syndrome.

Beta-adrenergic receptor blockade by propranolol enhances retention in a multitrial passive-avoidance procedure

The effect of beta-adrenergic receptor blockade on retention in a mildly aversive passive-avoidance procedure was investigated. Rats were given passive-avoidance training--1 trial per day for 4 days-and were administered saline, the centrally and peripherally acting beta-adrenergic blocker propranolol (4 or 10 mg/kg ip), or the peripherally acting beta-adrenergic blocker sotalol (4 or 10 mg/kg ip) immediately or 2 hr after the 1st trial. Enhanced retention occurred only with the higher dose (10 mg/kg) of propranolol and only when it was administered immediately after training. The enhanced retention produced by propranolol is discussed in terms of opposing, regionally specific actions of beta-adrenergic receptor-mediated neural circuits on modulation of memory.

Provocative angiography in patients with gastrointestinal hemorrhage of obscure origin

OBJECTIVE

A standard diagnostic evaluation including upper and/or lower endoscopy, tagged red blood cell scintigraphy, and visceral angiography identifies the source of GI bleeding in the majority of patients who present with acute GI hemorrhage. However, in a small group of patients the source of bleeding remains obscure; this form of GI hemorrhage is uncommon but represents a considerable diagnostic challenge. Some investigators have advocated provocation of bleeding with vasodilators, anticoagulants, and/or thrombolytics in association with tagged red blood cell scans or angiography. Unfortunately, the available literature on this topic is limited. Therefore, the purpose of this study is to report our experience with provocative GI bleeding studies.

METHODS

The radiology databases at Duke University Medical Center and the Durham Veterans Administration Medical Center were reviewed from 1994 to 1999. Any patient who received a vasodilator, anticoagulant, or thrombolytic to induce bleeding during a tagged red blood cell scan or visceral angiogram was included.

RESULTS

Seven provocative bleeding studies were performed on seven patients. All patients underwent a visceral angiogram with intra-arterial administration of tolazoline (a vasodilator), heparin (an anticoagulant), and/or urokinase (a thrombolytic). Of the seven provocative studies, only two induced angiographically identifiable bleeding. Both of these patients underwent surgical therapy. There were no complications attributed to the provocative bleeding studies.

CONCLUSIONS

These results suggest that provocative GI bleeding studies can be performed safely. However, because an active bleeding source was identified in only a small proportion of patients, we believe that further study is required to optimize patient selection and to clarify the cost-effectiveness of this approach in patients with GI hemorrhage of obscure origin.

Use of specialized bone screws for intermaxillary fixation

Fixation of the injured mandible to the maxilla is a proven method of stabilizing mandibular fractures and ensuring proper occlusion. The authors report their results with new specialized intraoral bone screws (IMF Screw System; Howmedica Leibinger, Inc., Carrollton, TX) that are designed for the purpose of achieving intermaxillary fixation (IMF). Nineteen patients were placed into rigid IMF using IMF screws alone. Indications were nondisplaced mandibular fractures; symphyseal, body, and angle fractures; midfacial fractures requiring temporary IMF; and edentulous patients with any of these fracture types and an adequate prosthesis. All procedures were performed with the patient under general anesthesia. The authors found that the operative time was markedly shorter than with standard IMF techniques, patient satisfaction was high, and there were no infections related to the screws. All 19 patients remained in stable, accurate occlusion and had adequate healing. One patient continues to have paraesthesias in the mental nerve distribution after screw removal. Although there is the potential for tooth and nerve injury when screws are placed improperly, the IMF Screw System seems to be a safe and reliable method of achieving secure mandibular fixation.

Lead hydro sodalite [Pb2(OH)(H2O)3]2[Al3Si3O12]2: synthesis and structure determination by combining X-ray rietveld refinement, 1H MAS NMR FTIR and XANES spectroscopy

Ion exchange of the sodium hydro sodalites [Na3(H2O)4]2-[Al3Si3O12]2 [Na4(H3O2)]2[Al3Si3O12]2 and [Na4(OH)]2[Al3Si3O12]2 with aqueous Pb(NO3)2 solutions yielded, whichever reactant sodalite phase was used, the same lead hydro sodalite, [Pb2(OH)-(H2O)3]2[Al3Si3O12]2. Thus, in the case of the non-basic reactant [Na3(H2O)4]2-[Al3Si3O12]2 an overexchange occurs with respect to the number of nonframework cationic charges. Rietveld structure refinement of the lead hydro sodalite based on powder X-ray diffraction data (cubic, a = 9.070 A, room temperature, space group P43n) revealed that the two lead cations within each polyhedral sodalite cage form an orientationally disordered dinuclear [Pb2(micro-OH)(micro-H2O)(H2O)2]3+ complex. Due to additional lead framework oxygen bonds the coordination environment of each metal cation (CN 3+3) is approximately spherical, and clearly the lead 6s electron lone pair is stereochemically inactive. This is also suggested by the absence of a small peak at 13.025 keV, attributed in other Pb2+-O compounds to an electronic 2p-6s transition, in the PbL3 edge XANES spectrum. 1H MAS NMR and FTIR spectra show that the hydrogen atoms of the aqua hydroxo complex (which could not be determined in the Rietveld analysis) are involved in hydrogen bonds of various strengths.

N-methyl-D-aspartate receptor agonists modulate homocysteine-induced developmental abnormalities

We showed previously that the induction of neural crest (NC) and neural tube (NT) defects is a general property of N-methyl-D-aspartate receptor (NMDAR) antagonists. Since homocysteine induces NC and NT defects and can also act as an NMDAR antagonist, we hypothesized that the mechanism of homocysteine-induced developmental defects is mediated by competitive inhibition of the NMDAR by homocysteine. If this hypothesis is correct, homocysteine-induced defects will be reduced by NMDAR agonists. To test the hypothesis, we treated chicken embryos during the process of neural tube closure with sufficient homocysteine thiolactone to induce NC and NT defects in approximately 40% of survivors or with homocysteine thiolactone in combination with each of a selected set of NMDAR agonists in 0. 05-5000 nmol doses. Glutamate site agonists selected were L-glutamate and N-methyl-D-aspartate. Glycine site agonists were glycine, D-cycloserine, and aminocyclopropane-carboxylic acid. Glycine was the most effective overall, reducing defects significantly at two different doses (each P>0.001). These results support the hypothesis that homocysteine may affect NC and NT development by its ability to inhibit the NMDAR. One potentially important consequence of this putative mechanism is that homocysteine may interact synergistically with other NMDAR antagonists to enhance its effect on development.

Use of subatmospheric pressure to prevent progression of partial-thickness burns in a swine model

The poorly understood, complex series of events that follows thermal injury frequently results in progressive loss of tissue. The concept of reversing this distinctive series of events has focused on the zone of stasis. Tissues in the zone of stasis that surround burn injuries usually die over a period of 48 to 72 hours postinjury, resulting in a more severe injury. Application of a controlled subatmospheric pressure (125 mm Hg) in an artificially closed space to partial-thickness burns in pigs significantly decreased the maximum depth of cellular death under the burn when the pressure was applied within 12 hours after burn creation (depth of control burns = 0.885 +/- 0.115 mm; subatmospheric pressure treated burns (0-hour delay) = 0.095 +/- 0.025 mm). A decrease in the depth of cell death was noted when subatmospheric pressure was applied for as little as 6 hours. In summary, the application of the negative pressure to partial-thickness burn injuries prevented progression of the wound to a deeper injury in this experimental pig model. A 12-hour working window exists between injury and treatment with reduced pressure, with an application time of as little as 6 hours for successful prevention of injury progression. This technique may represent a new, inexpensive, 'low tech' method for the treatment of partial-thickness burn injuries.

Elecsys CEA, PSA and AFP. Clinical results of a multicentre evaluation

Three tumormarker assays, Elecsys CEA, PSA and AFP, have been evaluated in an international multicentre study to characterize their clinical performance and to verify the comparability with the corresponding tests of the Enzymun-Test product line and other methods. For each of the markers results were obtained from four laboratories. On the basis of 314 and 199 specimens respectively, (preliminary) reference ranges could be established for CEA and PSA. For the prostate marker, the age dependence of the antigen level could be clearly confirmed. Mean concentrations range between 0.51 ng/ml (< 40 years) and 3.57 ng/ml (> 70 years). Referring to CEA, 95th percentiles of 4.31 ng/ml and 2.69 ng/ml were elaborated for smokers and nonsmokers. In general, good to excellent correlations (r > 0.98) were found between the Elecsys and Enzymun-Tests. Regarding the systematic comparability of both systems, most of the slopes derived from the individual method comparison studies are within the +/- 10% range of the respective standardization results. The specific distribution pattern of the individual tumormarker values elaborated with sample material of known clinical background, reflects the well established categorization of different benign and malignant diseases according to their characteristic marker levels. Of utmost importance, however, is the excellent comparability of the Elecsys assays with the corresponding Enzymun-Tests and the FDA approved AIA 1200 tests from TOSOH in follow-up studies. Almost superimposable concentration curves guarantee that identical diagnostic information is derived from all three methods. Especially for PSA, a series of measurements on sera of prostatectomized patients proved the usability and clinical value of the test also for this particular indication. For either one of the Elecsys tests, the feasibility of using plasma as sample material was verified.

Iodine-131-metaiodobenzylguanidine uptake in metastatic carcinoid tumor to the orbit

Metastatic tumor is one of several etiologies of space-occupying masses in the orbit that accounts for 1%-13% of all orbital masses (1). In the adult patient population, breast cancer is the most common tumor to metastasize to the orbit followed by metastases from the lung, prostate and gastrointestinal tract (2). It is rare for carcinoid tumors to metastasize to the eye or to the orbit. Carcinoid tumors arise from Kulchitsky cells that originate in the neural crest. Histologically, these tumors resemble, but are not as aggressive as, adenocarcinomas. Most carcinoids arise in the gastrointestinal tract or the lung. The most common site for carcinoid metastases is the liver. On anatomical imaging studies, such as CT and magnetic resonance imaging, metastatic orbital carcinoid tumors appear as nonspecific tumor masses. Carcinoid tumors have an affinity for uptake of the radiopharmaceutical 131I-metaiodobenzylguanidine (MIBG) (3). We report a case of a patient with a known carcinoid tumor who developed a left orbital mass that demonstrated abnormal uptake of 131I-MIBG indicative of metastatic carcinoid tumor to the orbit.

A controlled subatmospheric pressure dressing increases the rate of skin graft donor site reepithelialization

The ability to increase the rate of skin graft donor site reepithelialization significantly in a cost-effective manner has important implications for the patient undergoing major reconstructive procedures. In this study the effect of externally applied reduced pressure (the V.A.C.) on the rate of healing of donor site wounds was initially investigated using a porcine model (N = 4), then repeated on humans (N = 10). Split-thickness skin grafts were harvested from the backs of pigs using standard technique. Half of the donor sites were treated with subatmospheric pressure (125 mmHg) and half were treated with an OpSite dressing. Biopsies taken every 48 hours demonstrated that sites exposed to reduced pressure healed at a much faster rate than sites treated with a standard occlusive dressing. Similarly, donor sites in humans reepithelialized faster in 7 of 10 patients, the rate was the same in 2 of 10 patients, and OpSite was faster in 1 of 10 patients. We believe this technology has the potential to be a relatively simple and cost-efficient method for increasing the rate of donor site healing.

Metastatic head and neck cancer to the percutaneous endoscopic gastrostomy exit site: a case report and review of the literature

Percutaneous endoscopic gastrostomy (PEG) is a relatively safe procedure and is an important supportive treatment adjunct for patients with head and neck cancer. We report a case in which squamous cell carcinoma of the larynx implanted at a PEG exit site. This was resected for cure. In this case, and in five others reviewed in the literature, the PEG placement method was the "pull" technique. It is unknown whether other methods of PEG placement may reduce metastatic implants at the PEG exit site, but the possibility of this complication must be considered.

Dominant-negative action of the jimpy mutation in mice complemented with an autosomal transgene for myelin proteolipid protein

Mutations in genes encoding membrane proteins have been associated with cell death of unknown cause from invertebrate development to human degenerative diseases. A point mutation in the gene for myelin proteolipid protein (PLP) underlies oligodendrocyte death and dysmyelination in jimpy mice, an accurate model for Pelizaeus-Merzbacher disease. To distinguish the loss of PLP function from other effects of the misfolded protein, we took advantage of the X chromosomal linkage of the gene and have complemented jimpy with a wild-type PLP transgene. In this artificial heterozygous situation, the jimpy mutation emerged as genetically dominant. At the cellular level oligodendrocytes showed little increase in survival although endogenous PLP gene and autosomal transgene were truly coexpressed. In surviving oligodendrocytes, wild-type PLP was functional and immunodetectable in myelin. Moreover, compacted myelin sheaths regained their normal periodicity. This strongly suggests that, despite the presence of functional wild-type PLP, misfolded jimpy PLP is by itself the primary cause of abnormal oligodendrocyte death.

Predictors of behavior problems in three-year-old sons of alcoholics: early evidence for the onset of risk

We investigated risk factors in a population-based sample of alcoholic (father) and comparison families with 3-year-old sons. Alcoholic and comparison parents did not differ in socioeconomic status (SES), education, years married, family size, or cognitive functioning. Antisocial behavior and depression were significantly greater in alcoholic parents. High risk children were more impulsive than comparison children, but there were no differences in developmental age, IQ, or behavior problems. A higher percentage of high-risk children were rated in the extreme clinical range for behavior problems than were comparison children. For alcoholic families, mothers' ratings of their children's total behavior problems, externalizing behavior problems, and internalizing behavior problems were predicted by mothers' lifetime alcohol problems, current depression, and family SES. Father variables failed to predict children's behavior problems. Maternal variables were stronger predictors of their 3-year-old sons' problem behaviors than were paternal variables.

Improved safety and efficacy in adaptive control of arterial blood pressure through the use of a supervisor

This paper presents a dual approach to adaptive control of arterial blood pressure using sodium nitroprusside. In the clinical environment, a controller must be aggressive to achieve specific step response characteristics (less than 10 min settling time, less than 10 mm Hg overshoot), yet conservative enough to prevent overreactions to large disturbances, which are common in both the operating room and the intensive care unit. These mutually exclusive requirements make it difficult to design a closed-loop controller for this environment. To prevent possible overreactions, while maintaining proper step response, an aggressive adaptive controller has been designed to achieve the desired step response, and a SUPERVISOR has been designed around the adaptive controller to limit potential overreactions in the presence of disturbances. Simulations and dog experiments demonstrate the potential for increased safety and efficacy using this dual approach to the control of a complex physiological system.

Supervisory adaptive control of arterial pressure during cardiac surgery

A supervisory adaptive controller has been designed for the closed-loop control of mean arterial pressure during cardiac surgery, using sodium nitroprusside. This controller consists of a pole-placement and proportional-plus-integral feedback regulator, multiple-model adaptation, and a supervisor. The pole-placement and proportional-plus-integral regulator was designed to meet aggressive step response characteristics. Multiple-model adaptation was chosen to ensure rapid and stable adjustments for changes in key patients parameters. The supervisor was designed to provide safety and efficacy of control during disturbances that are common during cardiac surgery. We studied the ability of this supervisory adaptive controller to regulate arterial pressure during cardiac surgery on nineteen patients. The controller, through the action of the supervisor, detected and responded appropriately to the great majority of disturbances. This study demonstrated that supervisory adaptive control has the potential to provide clinically acceptable regulation of arterial pressure.

Neutrophil short-lived oxidant production: enhancement following onset of sepsis-induced lung injury

Generation of superoxide anion (O2-) by activated neutrophils (PMN) is implicated in the pathogenesis of endothelial cell injury in sepsis. To quantitate this phenomenon we studied the kinetics of O2- production by PMN following in vivo and in vitro exposure to Pseudomonas aeruginosa. PMN were isolated from young swine before and after a 1-hr infusion with 5 x 10(8) organisms/ml at 0.3 ml/20 kg/min. Baseline PMN were studied in an in vitro system where 1 x 10(6) porcine PMN were incubated with live Pseudomonas for 1 hr at 37 degrees C. Neutrophils from septic pigs exhibited a significantly increased (P less than 0.05) initial rate of O2 production, which was 125% greater at 2 min following initial stimulation than saline controls (P less than 0.001). Neutrophils exposed in vitro displayed a similar enhancement of the rate of O2- production; however, the rate was 3.6 times greater than that noted in vivo. The in vivo change in PMN oxidant generation was associated with a rise in both extravascular lung water (EVLW) and increased bronchoalveolar lavage protein (BAL-P) content. These data suggest that sepsis-induced acute lung injury is accompanied by "priming" of circulating PMN; however, important factors are present in the circulation in sepsis that serve to attenuate the damaging potential of PMN oxidant species.

Treatment results with an aggressive chemotherapeutic regimen (MACOP-B) for intermediate- and some high-grade non-Hodgkin's lymphomas

Seventy previously untreated patients with stage II, III, and IV intermediate- or high-grade lymphoma were treated with methotrexate, doxorubicin, cyclophosphamide, vincristine, prednisone, and bleomycin (MACOP-B) between September 1985 and November 1987. Forty-nine of these patients had diffuse large-cell lymphoma (DLCL), and eight of these patients were human immunodeficiency virus (HIV)-positive. Complete responses were achieved in 54% of all patients and 52% of those with DLCL. With follow-up extending to 36 months, 45% of all DLCL patients are alive, and 50% are still living, if the HIV-positive patients are excluded from the analysis. Chemotherapy was quite toxic. Seventy-five percent of patients had severe mucositis, 42% had peripheral neuropathy, 50% required hospitalization, and 54% experienced leukopenia with a WBC count below 1,000/microL. Seven percent (five patients) died of toxicity related to the chemotherapy. Our analysis of prognostic parameters indicated that B symptoms, a performance status below 80, and, to a lesser extent, elevation of serum lactic acid dehydrogenase (LDH) (in HIV-negative DLCL patients) were associated with an inferior survival. Advanced age, sex, and bulky disease were not found to have a statistically significant effect on survival. Our preliminary results indicate that MACOP-B chemotherapy is an effective regimen for high- and intermediate-grade lymphomas. However, the survival for patients with DLCL treated with MACOP-B is no different than that achieved with previous regimens at our institution.

Bacillus subtilis strains carrying two non-tandem duplications of the trpE-ilvA and the purB-tre regions of the chromosome

Bacillus subtilis strains possessing the trpE30 marker (splitting of the trpE locus and a non-tandem duplication of chromosome segment Ib: purB-tre) when transformed or transduced to tryptophan independence mainly give rise to haploid cells with the genetic structure of strain 168. However, among the Trp+ transformants or transductants about 10% are merodiploid carrying a non-tandem duplication of segment C (trpE-ilvA) while maintaining that of segment Ib. Linkage and segregation studies made it possible to determine their genetic structure, which can be represented by three different maps. In map a the copies of Ib are inverted repeats and one of them is flanked by two direct repeats of segment C; in map b two Ib-C segments are inverted repeats and in map c the copies of C are inverted repeats with one of them flanked by direct repeats of Ib. It is proposed that transition from map a to map b and then to map c, and vice versa, may occur by recombination between inverted repeats of either Ib or C. The merodiploids are unstable, recombination between direct repeats leading to haploid cells of 168-type structure. The models proposed for merodiploid formation call for fusion of two recipient chromosomes mediated by the donor segment and recombination between copies of a DNA sequence of the two chromosomes located in different regions. In the case of PBS-1 mediated transduction the greater length of the donor DNA segment makes it possible to obtain the merodiploids with a single recipient chromosome and this needs only a slight modification of the models. No trpE30+ merodiploids are found in transformation when the recipient carries a deletion of the SP beta prophage, or in transduction when both donor and recipient possess this deletion. These results indicate that the homologous sequences involved may be part of the SP beta prophage or that a sequence of bacterial DNA has a good homology with it.

Dynamic response of local pulmonary blood flow to alveolar gas tensions: analysis

It has been reported that left lower lobe pulmonary blood flow (Q) and alveolar CO2 decrease then oscillate in a progressively damped manner when the lobar inspirate is changed from pure O2 to N2. This damped oscillatory response of lobar Q is abolished by maintaining lobar CO2 constant. We set out to develop the simplest mathematical model that can simulate these experimental results by using techniques derived from control theory. Different models were tested. The simplest model that predicts the experimental data incorporates an exponential decrease of lobar Q to local alveolar hypoxia (time constant 3 min) and a damped oscillatory response of lobar Q to local alveolar hypocapnia. The response to hypocapnia has two components: a vasodilator effect possibly related to intracellular [H+] and a vasoconstrictor effect possibly related to changes of molar CO2. Both these components (time constants of 4.8 min) interact with each other by cross-coupled elements (time constants of 4.8 min). This model can be used to forecast results so that its validity can be tested by experiment.

Genetic structure and internal rearrangements of stable merodiploids from Bacillus subtilis strains carrying the trpE26 mutation

Transformation and transduction to tryptophan independence of strains of Bacillus subtilis carrying the "trpE26" chromosomal aberrations (a translocation and an inversion) with a "normal" 168 type strain as donor induce a tandem duplication of the thrA-ilvA region of the chromosome. The clones possessing this unstable duplication segregate besides the Trp- some stable Trp+ cells which retain only part of the duplication (the trpE-ilvA region) in nontandem configuration. Such clones may also be produced directly during the crosses. The genetic map of these clones (designated as class I stable merodiploids) was constructed: they possess the translocation and the inversion of the trpE26 parental strain. Another type of stable Trp+ clones (class II) also appears, although more rarely, in similar crosses. Studies on their genetic structure revealed that they are haploid for the trpE-ilvA region and carry a nontandem duplication of the thrA-trpE region. In these clones the cysB-tre region has the orientation of the 168 type strain. The duplications in both classes are stable, that of class I being more stable than that of class II where loss of one copy of the thrA-trpE region leads to about 1% haploid cells. Detailed genetic studies on heterozygous clones from both classes have shown exchange of alleles between copies of the nontandem duplications. Models are proposed for the formation of each class of merodiploids and for recombination events taking place in them. These models imply recombination at sequences of intrachromosomal homology and (or) introduction of heterologous junctions ("novel joints") by transformation or transduction.

A New Tax on Gasoline: Estimating Its Effect on Consumption

Based on extrapolation of a recent estimate of the elasticity of demand for gasoline, it is concluded that a tax of 5 cents per gallon per year over the period 1979 to 1988 can be expected to produce significant reductions in gasoline consumption, contrary to widely expressed opinions.

Recruitment in networks of pulmonary capillaries

To improve our understanding of the pressure-flow characteristics of pulmonary capillaries, we analyzed by means of computer stimulation a theoretical model composed of 50 interconnected nonlinear elements. Each element required a critical pressure across it before flow occurred and there was a subsequent linear pressure-flow region whose slope, or resistance, could be related to the transmural pressure of the element ("distensibility"). The critical pressures and resistances of each element of the network were randomly chosen from distributions. We found that recruitment (i.e., onset of flow) occurred over a large range of network upstream or "arterial" pressures, and that relatively high arterial pressures were required before all elements had no distensibility. Intermittent and reverse flow were commonly seen in some elements as the arterial pressure was raised in steps. These flow reversals were particularly common when the critical pressures and resistances of the elements were inversely related. The critical pressures required for such behavior in the capillary segments of the pulmonary microcirculation were calculated to be extremely small, of the order of 0.02 cmH2O. Pressures of this magnitude might result from sticking of red cells to capillary walls or to each other. The properties of such a network may explain the patchiness of flow in the pulmonary microcirculation and the large range of arterial pressures over which recruitment is observed to occur.