Critical care usage after major gastrointestinal and liver surgery: a prospective, multicentre observational study

BACKGROUND

Patient selection for critical care admission must balance patient safety with optimal resource allocation. This study aimed to determine the relationship between critical care admission, and postoperative mortality after abdominal surgery.

METHODS

This prespecified secondary analysis of a multicentre, prospective, observational study included consecutive patients enrolled in the DISCOVER study from UK and Republic of Ireland undergoing major gastrointestinal and liver surgery between October and December 2014. The primary outcome was 30-day mortality. Multivariate logistic regression was used to explore associations between critical care admission (planned and unplanned) and mortality, and inter-centre variation in critical care admission after emergency laparotomy.

RESULTS

Of 4529 patients included, 37.8% (n=1713) underwent planned critical care admissions from theatre. Some 3.1% (n=86/2816) admitted to ward-level care subsequently underwent unplanned critical care admission. Overall 30-day mortality was 2.9% (n=133/4519), and the risk-adjusted association between 30-day mortality and critical care admission was higher in unplanned [odds ratio (OR): 8.65, 95% confidence interval (CI): 3.51-19.97) than planned admissions (OR: 2.32, 95% CI: 1.43-3.85). Some 26.7% of patients (n=1210/4529) underwent emergency laparotomies. After adjustment, 49.3% (95% CI: 46.8-51.9%, P<0.001) were predicted to have planned critical care admissions, with 7% (n=10/145) of centres outside the 95% CI.

CONCLUSIONS

After risk adjustment, no 30-day survival benefit was identified for either planned or unplanned postoperative admissions to critical care within this cohort. This likely represents appropriate admission of the highest-risk patients. Planned admissions in selected, intermediate-risk patients may present a strategy to mitigate the risk of unplanned admission. Substantial inter-centre variation exists in planned critical care admissions after emergency laparotomies.

Nonsyndromic tooth agenesis patterns and associated developmental dental anomalies: a literature review with radiographic illustrations

Tooth agenesis is one of the most intriguing phenomena, because it is frequently associated with other oral anomalies, structural variations and malformations of other teeth, late eruption, transposition and crowding. The diagnosis can be quite challenging as radiographic examination is critical for the diagnosis but not always possible and the late developing teeth may be sometimes scored developmentally missing. Accurate diagnosis therefore requires radiographic, clinical, and dental cast examinations. It is an important clinical and public health problem. Patients with missing permanent teeth may suffer from a reduced chewing ability, inarticulate pronunciation, and an unfavorable aesthetic appearance. Clinically, early diagnosis of a dental anomaly can alert the clinician to the possible development of other associated dental anomalies in the same patient or family, and avoid the possible sequelae. Understanding of tooth agenesis patterns and their impact on diagnosis, prevention, and eventually therapeutics are becoming integral parts of comprehensive dental care. Dental examination with radiographic screening of hypodontia in early childhood should be emphasized as part of public oral health policy to allow early diagnosis and timely intervention.

Effect of hyperthermia on the pharmacokinetic profile of oxaliplatin administered by intraperitoneal route in rats

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Background: Whereas in vitro studies have demonstrated that hyperthermia enhances the cytotoxicity and tissue penetration of oxaliplatin, in vivo studies conducted so far have failed to document clearly such effect in the context of heated intraperitoneal chemotherapy. The purpose of this study is to assess the effect of heat on the pharmacokinetic profile of oxaliplatin administered intraperitonealy in rats. Methods: Under general anesthesia, 25 Sprague-Dawly rats of 258 g (235–440 g) were submitted to 3 different doses of intraperitoneal oxaliplatin (460, 920 and 1840 mg/m2) at 3 different temperatures of perfusion (37, 40 and 43°C) during 25 minutes. At the end of perfusion, samples in different compartments were harvested for dosage of oxaliplatin concentration: 2 ml of perfusate, 1 ml of portal blood, 1 ml of systemic blood, 100 mm3 of parietal peritoneum and 100 mm3 of mesentery. Dosage of oxaliplatin was performed by high performance liquid chromatography. Results: We observed a linear and proportional correlation between the concentration of oxaliplatin in the perfusate and the concentration of oxaliplatin for all compartments (R2 : 0.9833 for systemic blood, 0.9874 for portal blood, 0.9053 for parietal peritoneum and 0.9999 for mesentery). Regarding the effect of temperature, we observed a linear and proportional correlation of heat on the concentration of oxaliplatin in parietal peritoneum (R2 : 0.8543), no effect on mesentery (R2: 0.1371) and a tendency of heat to limit concentration of oxaliplatin in portal and systemic blood (R2 = 0.0994 and 0.5854 respectively). Conclusion: Heat improves the absorption of oxaliplatin into the peritoneal cells and seems to limit the systemic absorption of oxaliplatin, the latter observation suggesting a decrease in systemic toxicity. These are two strong arguments supporting the use of oxaliplatin by intraperitoneal route, as it is currently done in the human treatment of peritoneal carcinomatosis from colorectal origin.

No significant financial relationships to disclose.

Structural organisation of the head-to-tail interface of a bacterial virus

In tailed icosahedral bacteriophages the connection between the 5-fold symmetric environment of the portal vertex in the capsid and the 6-fold symmetric phage tail is formed by a complex interface structure. The current study provides the detailed analysis of the assembly and structural organisation of such an interface within a phage having a long tail. The region of the interface assembled as part of the viral capsid (connector) was purified from DNA-filled capsids of the Bacillus subtilis bacteriophage SPP1. It is composed of oligomers of gp6, the SPP1 portal protein, of gp15, and of gp16. The SPP1 connector structure is formed by a mushroom-like portal protein whose cap faces the interior of the viral capsid in intact virions, an annular structure below the stem of the mushroom, and a second narrower annulus that is in direct contact with the helical tail extremity. The layered arrangement correlates to the stacking of gp6, gp15, and gp16 on top of the tail. The gp16 ring is exposed to the virion outside. During SPP1 morphogenesis, gp6 participates in the procapsid assembly reaction, an early step in the assembly pathway, while gp15 and gp16 bind to the capsid portal vertex after viral chromosome encapsidation. gp16 is processed during or after tail attachment to the connector region. The portal protein gp6 has 12-fold cyclical symmetry in the connector structure, whereas assembly-naïve gp6 exhibits 13-fold symmetry. We propose that it is the interaction of gp6 with other viral morphogenetic proteins that drives its assembly into the 12-mer state.

Three-dimensional structure of the anaphase-promoting complex

The anaphase-promoting complex (APC) is a cell cycle-regulated ubiquitin-protein ligase, composed of at least 11 subunits, that controls progression through mitosis and G1. Using cryo-electron microscopy and angular reconstitution, we have obtained a three-dimensional model of the human APC at a resolution of 24 A. The APC has a complex asymmetric structure 140 A x 140 A x 135 A in size, in which an outer protein wall surrounds a large inner cavity. We discuss the possibility that this cavity represents a reaction chamber in which ubiquitination reactions take place, analogous to the inner cavities formed by other protein machines such as the 26S proteasome and chaperone complexes. This cage hypothesis could help to explain the great subunit complexity of the APC.

Arrangement of RNA and proteins in the spliceosomal U1 small nuclear ribonucleoprotein particle

In eukaryotic cells, freshly synthesized messenger RNA (pre-mRNA) contains stretches of non-coding RNA that must be excised before the RNA can be translated into protein. Their removal is catalysed by the spliceosome, a large complex formed when a number of small nuclear ribonucleoprotein particles (snRNPs) bind sequentially to the pre-mRNA. The first snRNP to bind is called U1; other snRNPs (U2, U4/U6 and U5) follow. Here we describe the three-dimensional structure of human U1 snRNP, determined by single-particle electron cryomicroscopy at 10 A resolution. The reconstruction reveals a doughnut-shaped central element that accommodates the seven Sm proteins common to all snRNPs, supporting a proposed model of circular Sm protein arrangement. By taking earlier biochemical results into account, we were able to assign the remaining density of the map to the other known components of U1 snRNP, deriving a structural model that describes the three-dimensional arrangement of proteins and RNA in U1 snRNP.

Interaction between transmembrane domains five and six of the alpha -factor receptor

The alpha-factor pheromone receptor (STE2) activates a G protein signal pathway that induces conjugation of the yeast Saccharomyces cerevisiae. Previous studies implicated the third intracellular loop of this receptor in G protein activation. Therefore, the roles of transmembrane domains five and six (TMD5 and -6) that bracket the third intracellular loop were analyzed by scanning mutagenesis in which each residue was substituted with cysteine. Out of 42 mutants examined, four constitutive mutants and two strong loss-of-function mutants were identified. Double mutants combining Cys substitutions in TMD5 and TMD6 gave a broader range of phenotypes. Interestingly, a V223C mutation in TMD5 caused constitutive activity when combined with the L247C, L248C, or S251C mutations in TMD6. Also, the L226C mutation in TMD5 caused constitutive activity when combined with either the M250C or S251C mutations in TMD6. The residues affected by these mutations are predicted to fall on one side of their respective helices, suggesting that they may interact. In support of this, cysteines substituted at position 223 in TMD5 and position 247 in TMD6 formed a disulfide bond, providing the first direct evidence of an interaction between these transmembrane domains in the alpha-factor receptor. Altogether, these results identify an important region of interaction between conserved hydrophobic regions at the base of TMD5 and TMD6 that is required for the proper regulation of receptor signaling.

Connective tissue growth factor expression in the rat remnant kidney model and association with tubular epithelial cells undergoing transdifferentiation

Connective tissue growth factor (CTGF) has been shown to mediate many actions of transforming growth factor-beta (TGF-beta) in the fibrotic response in several diseases. We compared expression of CTGF, TGF-beta, platelet-derived growth factor (PDGF), TNF-alpha, and interleukin-1 (IL-1) by in situ hybridization in Sprague-Dawley rats euthanized at 0, 2, 4, and 8 weeks after 5/6 nephrectomy using the rat remnant kidney model of renal failure. Collagen was evaluated by trichrome stains, immunohistochemistry, and electron microscopy. We compared expression patterns to cells undergoing metaplasia. Tubular epithelial regeneration and transdifferentiation to myofibroblasts were assessed morphologically and by proliferating cell nuclear antigen, smooth muscle actin, desmin, and vimentin immunohistochemistry. CTGF expression was minimal in controls, mild at 2 weeks and marked by 4 to 8 weeks in interstitial fibroblasts, coinciding with damage, regeneration, and fibrosis. TGF-beta expression was increased in many cell types at 2 weeks, increased further by 4 weeks, then remained constant. PDGF-B messenger RNA was found in many stromal cells at 2-4 weeks, but expression decreased at 8 weeks. No significant IL-1 or TNF-alpha staining was detected. We conclude that CTGF and interacting factors are associated with development or progression of chronic interstitial fibrosis. Proximity of CTGF, TGF-beta, and PDGF mRNA expression to regenerative epithelial cells and those transdifferentiating to myofibroblasts suggests that growth factors may modulate renal tubular epithelial differentiation.

Structure of a molluscan hemocyanin didecamer (HtH1 from Haliotis tuberculata) at 12 A resolution by cryoelectron microscopy

A 12 A resolution three-dimensional density map of the Haliotis tuberculata hemocyanin type 1 (HtH1) didecamer has been obtained by cryoelectron microscopy of unstained molecules and angular reconstitution. The dyad symmetry of the 8 MDa D5 HtH1 didecamer, formed by the pairing of two asymmetric 4 MDa ring-like C5 decamers, is emphasised. The major and minor surface helical grooves of the didecamer are well defined, in agreement with earlier data on molluscan hemocyanins. The location of the obliquely orientated repeating unit, a subunit dimer, within the decamer has been defined. Following interactive extraction of this dimer, several new structural features of the dimer and of the subunit have now emerged with improved detail. The subunit dimer possesses pseudo 2-fold symmetry, resulting from the steric arrangement of the wall domains/functional units (FUs-abcdef) of the two subunits. The arc and collar FUs (g and h) depart from this inherent 2-fold symmetry and are thereby responsible for the asymmetry of the C5 decamer, with the internalised collar/arc complex at one edge of the decamer. The FU heterodimers forming the wall morphological units have a hollow centre, and thus create a series of repeating channels that extend within the wall through all three tiers of the decamer. The connections between the wall and the arc are defined with improved clarity, and evidence is provided to indicate that the arc and collar FU pairs have a homodimeric composition (gg and hh, respectively). Two possibilities for the subunit path within the subunit dimer are presented, which correlate with the available structural, immunolabelling and protease cleavage data from HtH1 and other molluscan hemocyanins.

Transient exotropia after posterior spinal fusion in a child: a new case

Ocular complications after spinal surgery are rare, although ischemic optic neuropathy, occipital lobe infarcts, and central retinal vein thrombosis have been reported. Our purpose is to report a case of an acute, comitant, postoperative exotropia that rapidly and spontaneously resolved. This case is particularly interesting in that it may indirectly shed some light on mechanisms of vergence control.

Structure of the 13-fold symmetric portal protein of bacteriophage SPP1

We have determined the three-dimensional structure of bacteriophage SPP1 portal protein (gp6) using electron microscopy at liquid-helium temperatures and angular reconstitution. The 13-fold symmetric gp6 oligomer is a turbine-shaped structure with three distinct regions: a conical stem with a central channel; the turbine wings region; and a fringe of small 'tentacles' at the end of the channel exposed to the viral head interior. The tentacle region appears flexible and may be associated with a particular function - sensing when the correct amount of DNA has been packaged. The three-dimensional structure of the gp6 SizA mutant, which packages a smaller chromosome, reveals significant differences in that region.

Treatment of liver metastases with moderate peritoneal carcinomatosis by hepatectomy and cytoreductive surgery followed by immediate post-operative intraperitoneal chemotherapy: feasibility and preliminary results

BACKGROUND/AIMS

Peritoneal carcinomatosis (PC) discovered during hepatectomy is usually a contraindication to resection. A potentially efficient treatment of PC is the resection of the macroscopic disease and the treatment of the residual microscopic disease with immediate post-operative intraperitoneal chemotherapy (IPIC) (before the entrapment of cancer cells inside the fibrin deposit which rapidly cover the injured tissues). Feasibility and survival results of this treatment, combined with major hepatectomy, have never been evaluated. The purpose of this study is to report tolerance and preliminary results in patients with liver metastases synchronous to moderate PC, treated with hepatectomy, complete cytoreductive surgery, and IPIC.

METHODOLOGY

Twelve patients with liver metastases and moderate PC from miscellaneous origins, underwent: 1) hepatectomy (9 of them were major hepatectomies); 2) complete cytoreductive surgery of the PC resecting between 20 and 150 nodules; and, 3) IPIC, for 5 days, according to histology.

RESULTS

There was no mortality. Morbidity was mainly due to four transient biliary leakages (33%) and there was no systemic complication due to the chemotherapy. After a median follow-up of 14.4 months, there was no detectable recurrence of the PC. Preliminary results concerning survival are promising with 7 patients without recurrent disease.

CONCLUSIONS

When a minimal or moderate PC is discovered during laparotomy for liver resection of metastases, the combination of hepatectomy with complete cytoreductive surgery of the peritoneal disease, followed with IPIC is logical and feasible. This aggressive treatment is well tolerated although the frequency of biliary leakage seems to be higher than that after standard hepatectomy. No recurrence of the peritoneal disease was detected and survival results are very promising.

Identification of a polar region in transmembrane domain 6 that regulates the function of the G protein-coupled alpha-factor receptor

The alpha-factor pheromone receptor (Ste2p) of the yeast Saccharomyces cerevisiae belongs to the family of G protein-coupled receptors that contain seven transmembrane domains (TMDs). Because polar residues can influence receptor structure by forming intramolecular contacts between TMDs, we tested the role of the five polar amino acids in TMD6 of the alpha-factor receptor by mutating these residues to nonpolar leucine. Interestingly, a subset of these mutants showed increased affinity for ligand and constitutive receptor activity. The mutation of the most polar residue, Q253L, resulted in 25-fold increased affinity and a 5-fold-higher basal level of signaling that was equal to about 19% of the alpha-factor induced maximum signal. Mutation of the adjacent residue, S254L, caused weaker constitutive activity and a 5-fold increase in affinity. Comparison of nine different mutations affecting Ser254 showed that an S254F mutation caused higher constitutive activity, suggesting that a large hydrophobic amino acid residue at position 254 alters transmembrane helix packing. Thus, these studies indicate that Gln253 and Ser254 are likely to be involved in intramolecular interactions with other TMDs. Furthermore, Gln253 and Ser254 fall on one side of the transmembrane helix that is on the opposite side from residues that do not cause constitutive activity when mutated. These results suggest that Gln253 and Ser254 face inward toward the other TMDs and thus provide the first experimental evidence to suggest the orientation of a TMD in this receptor. Consistent with this, we identified two residues in TMD7 (Ser288 and Ser292) that are potential contact residues for Gln253 because mutations affecting these residues also cause constitutive activity. Altogether, these results identify a new domain of the alpha-factor receptor that regulates its ability to enter the activated conformation.

Correlation of the expansion segments in mammalian rRNA with the fine structure of the 80 S ribosome; a cryoelectron microscopic reconstruction of the rabbit reticulocyte ribosome at 21 A resolution

Samples of 80 S ribosomes from rabbit reticulocytes were subjected to electron cryomicroscopy combined with angular reconstitution. A three-dimensional reconstruction at 21 A resolution was obtained, which was compared with the corresponding (previously published) reconstruction of Escherichia coli 70 S ribosomes carrying tRNAs at the A and P sites. In the region of the intersubunit cavity, the principal features observed in the 70 S ribosome (such as the L1 protuberance, the central protuberance and A site finger in the large subunit) could all be clearly identified in the 80 S particle. On the other hand, significant additional features were observed in the 80 S ribosomes on the solvent sides and lower regions of both subunits. In the case of the small (40 S) subunit, the most prominent additions are two extensions at the base of the particle. By comparing the secondary structure of the rabbit 18 S rRNA with our model for the three-dimensional arrangement of E. coli 16 S rRNA, these two extensions could be correlated with the rabbit expansion segments (each totalling ca 170 bases) in the regions of helix 21, and of helices 8, 9 and 44, respectively. A similar comparison of the secondary structures of mammalian 28 S rRNA and E. coli 23 S rRNA, combined with preliminary modelling studies on the 23 S rRNA within the 50 S subunit, enabled the additional features in the 60 S subunit to be sub-divided into five groups. The first (corresponding to a total of ca 335 extra bases in helices 45, 98 and 101) is located on the solvent side of the 60 S subunit, close to the L7/L12 area. The second (820 bases in helices 25 and 38) is centrally placed on the solvent side of the subunit, whereas the third group (totaling 225 bases in helices 18/19, 27/29, 52 and 54) lies towards the L1 side of the subunit. The fourth feature (80 bases in helices 78 and 79) lies within or close to the L1 protuberance itself, and the fifth (560 bases in helix 63) is located underneath the L1 protuberance on the interface side of the 60 S subunit.

The 80S rat liver ribosome at 25 A resolution by electron cryomicroscopy and angular reconstitution

BACKGROUND

The ribosome is central to protein synthesis in all living organisms. Single-particle electron cryomicroscopy has recently led to the determination of three-dimensional structures of bacterial ribosomes to approximately 20 A, which have since revolutionised our understanding of ribosomal function. The structure we present here of the 80S rat liver ribosome leads the way to similar progress for mammalian ribosomes.

RESULTS

Among the new details revealed by our 25 A structure of the 80S rat liver ribosome are channels within the subunits, a large 'flat ribosomal surface' (FRS) on the outer surface of the large subunit and structural extensions of the mammalian compared to the bacterial ribosome. The main large subunit channel in both the bacterial and the mammalian species starts at the peptidyl transferase centre, below the central protuberance, and ends in the FRS, at the lower back of the large subunit. Structurally, the channels of both species can be directly superimposed.

CONCLUSIONS

The mammalian structural extensions--none of which trespass the FRS--can be interpreted in terms of rRNA inserts and additional protein content over that of bacterial ribosomes. The main large subunit channel, which ends at the FRS, is the best candidate for the exit channel for proteins targeted for the endoplasmic reticulum.

Afr1p regulates the Saccharomyces cerevisiae alpha-factor receptor by a mechanism that is distinct from receptor phosphorylation and endocytosis

The alpha-factor pheromone receptor activates a G protein signaling pathway that induces the conjugation of the yeast Saccharomyces cerevisiae. Our previous studies identified AFR1 as a gene that regulates this signaling pathway because overexpression of AFR1 promoted resistance to alpha-factor. AFR1 also showed an interesting genetic relationship with the alpha-factor receptor gene, STE2, suggesting that the receptor is regulated by Afr1p. To investigate the mechanism of this regulation, we tested AFR1 for a role in the two processes that are known to regulate receptor signaling: phosphorylation and down-regulation of ligand-bound receptors by endocytosis. AFR1 overexpression diminished signaling in a strain that lacks the C-terminal phosphorylation sites of the receptor, indicating that AFR1 acts independently of phosphorylation. The effects of AFR1 overexpression were weaker in strains that were defective in receptor endocytosis. However, AFR1 overexpression did not detectably influence receptor endocytosis or the stability of the receptor protein. Instead, gene dosage studies showed that the effects of AFR1 overexpression on signaling were inversely proportional to the number of receptors. These results indicate that AFR1 acts independently of endocytosis, and that the weaker effects of AFR1 in strains that are defective in receptor endocytosis were probably an indirect consequence of their increased receptor number caused by the failure of receptors to undergo ligand-stimulated endocytosis. Analysis of the ligand binding properties of the receptor showed that AFR1 overexpression did not alter the number of cell-surface receptors or the affinity for alpha-factor. Thus, Afr1p prevents alpha-factor receptors from activating G protein signaling by a mechanism that is distinct from other known pathways.

Structure of keyhole limpet hemocyanin type 1 (KLH1) at 15 A resolution by electron cryomicroscopy and angular reconstitution

A three-dimensional reconstruction of keyhole limpet hemocyanin type 1 (KLH1) has been obtained using electron cryomicroscopy at liquid helium temperatures and single particle image processing. The use of a high-contrast embedding medium, 1% (w/v) glucose and 2% (w/v) ammonium molybdate (pH 7.0), enables high-resolution electron micrographs to be recorded close to focus, i.e. with excellent transfer of high-resolution information, while maintaining enough image contrast to localise the individual macromolecules in the images. When low-pass filtered to approximately 45 A resolution, the new 15 A resolution reconstruction is very similar to the earlier reconstructions of gastropodan hemocyanins of specimens embedded in vitreous ice. The map shows much detail and reveals many new symmetry elements in this very large cylindrical molluscan hemocyanin. The full KLH1 didecamer has D5 pointgroup symmetry, yet within the KLH1 decameric half-molecules local 2-fold axes have emerged that make the wall of the KLH1 decamer, in spite of its having an exact C5 symmetry only, resemble the D5-symmetric wall of the decameric cephalopod hemocyanins. In fact, the outside of each tier of this six-tiered gastropodan hemocyanin was found to have an approximate D5 symmetry. Local 2-fold axes also relate the "functional units" within the dimeric "morphological units" of the wall and the collar areas of the 8 MDa KLH1 molecule. Certain local-symmetry-related surface motifs may be present up to 60 times on the outside wall of this highly symmetric cylindrical hemocyanin. Keyhole limpet hemocyanin is used clinically as an immunostimulant. The very strong immune reaction elicited by this hemocyanin may be associated with its intricate hierarchy of local-symmetry components.

Intrinsic versus imposed curvature in cyclical oligomers: the portal protein of bacteriophage SPP1

Large cyclical oligomers may be formed by (curvi-) linear polymerization of monomers until the n(th) monomer locks in with the first member of the chain. The subunits in incomplete structures exhibit a natural curvature with respect to each other which can be perturbed when the oligomer closes cyclically. Using cryo-electron microscopy and multivariate statistical image processing we report herein a direct structural observation of this effect. A sub-population (approximately 15%) of incomplete oligomers was found within a sample of SPP1 bacteriophage portal proteins embedded in vitreous ice. Whereas the curvature between adjacent subunits of the closed circular 13-fold symmetric oligomer is 27.7 degrees, in these incomplete oligomers the angle is only 25.8 degrees, a value which almost allows for a 14-subunit cyclical arrangement. A simple model for the association of large cyclical oligomers is suggested by our data.

Mutation of Pro-258 in transmembrane domain 6 constitutively activates the G protein-coupled alpha-factor receptor

The alpha-factor pheromone receptor stimulates MATa yeast cells to undergo conjugation. The receptor contains seven transmembrane domains that function in ligand binding and in transducing a signal to the cytoplasmic receptor sequences to mediate G protein activation. A genetic screen was used to isolate receptor mutations that constitutively signal in the absence of alpha-factor. The Pro-258-->Leu (P258L) mutation caused constitutive receptor signaling that was equivalent to about 45% of the maximum level observed in wild-type cells stimulated with alpha-factor. Mutations of both Pro-258 and the adjacent Ser-259 to Leu increased constitutive signaling to > or = 90% of the maximum level. Since Pro-258 occurs in the central portion of transmembrane domain 6, and since proline residues are expected to cause a kink in alpha-helical domains, the P258L mutation is predicted to alter the structure of transmembrane domain 6. The P258L mutation did not result in a global distortion of receptor structure because alpha-factor bound to the mutant receptors with high affinity and induced even higher levels of signaling. These results suggest that sequences surrounding Pro-258 may be involved in ligand activation of the receptor. Conformational changes in transmembrane domain 6 may effect a change in the adjacent sequences in the third intracellular loop that are thought to function in G protein activation. Greater than 90% of all G protein-coupled receptors contain a proline residue at a similar position in transmembrane domain 6, suggesting that this aspect of receptor activation may be conserved in other receptors.

The 70S Escherichia coli ribosome at 23 A resolution: fitting the ribosomal RNA

BACKGROUND

The ribosome--essential for protein synthesis in all organisms--has been an evasive target for structural studies. The best available structures for the 70S Escherichia coli ribosome or its 30S and 50S subunits are based on electron microscopical tilt experiments and are limited in resolution to 28-55 A. The angular reconstitution approach, which exploits the random orientations of particles within a vitreous ice matrix, can be used in conjunction with cryo-electron microscopy to yield a higher-resolution structure.

RESULTS

Our 23 A resolution map of the 70S ribosome elucidates many structural details, such as an extensive system of channels within the 50S subunit and an intersubunit gap ideally shaped to accommodate two transfer RNA molecules. The resolution achieved is sufficient to allow the preliminary fitting of double-helical regions of an earlier three-dimensional ribosomal RNA model.

CONCLUSIONS

Although we are still a long way from attaining an atomic-resolution structure of the ribosome, cryo-electron microscopy, in combination with angular reconstitution, is likely to yield three-dimensional maps with gradually increasing resolution. As exemplified by our current 23 A reconstruction, these maps will lead to progressive refinement of models of the ribosomal RNA.

Structure of Lumbricus terrestris hemoglobin at 30 A resolution determined using angular reconstitution

The three-dimensional (3D) structure of the giant hemoglobin of the common earthworm Lumbricus terrestris was determined from cryomicroscopical images of a vitrified molecular solution. From about 5000 molecular images, the best-fit 3D structure was calculated using recently developed analysis techniques. Multivariate statistical analysis data compression and automatic classification were used to find the characteristic projection images of the oligomer. The angular reconstitution approach was then applied to find the Euler angle orientations of these characteristic views. The Lumbricus hemoglobin molecule has an overall D6 (622) point-group symmetry and is found to have a local threefold symmetry axis within the 1/12th subunit. This additional symmetry appears to predict the presence of 36 abcd globin tetramers in the Lumbricus hemoglobin or a total of 144 heme chains for the whole oligomer. A distinct doughnut-shaped structure is elucidated in the center of the molecule. This central subunit, representing around 10% of the protein volume, may consist of non-heme-containing linker chains found generally in giant annelid hemoglobins.

Regulation of contact hypersensitivity by interleukin 10

Contact hypersensitivity (CHS) responses require the participation of T cells, along with a variety of cytokines and adhesion molecules. In the classical CHS, antigen-specific T cells are recruited to a site of antigenic challenge, where they react with antigen, release cytokines, and attract other inflammatory cells. In the mouse model of CHS, this reaction is elicited in sensitized mice by application of the immunogen 4-7 d after immunization. The reaction peaks at 24 h, is slightly reduced by 48 h, and can return to normal by 72 h. This is in spite of the fact that some antigen is still present at the site of challenge. Here we examined the hypothesis that locally produced interleukin 10 (IL-10) regulates the duration of the response. Our data show that IL-10 protein peaked 10-14 h after antigenic challenge and returned to background by 24 h. The production of IL-10 protein corresponded with, and followed IL-10 mRNA transcription as detected by reverse transcriptase-polymerase chain reaction. During peak IL-10 production after antigenic challenge, it was not possible to transfer CHS with immune lymphoid cells, unless neutralizing antibody to IL-10 was given first. Additionally, when sensitized mice were given neutralizing anti-IL-10 antibody at the time of antigenic challenge, the duration of CHS was prolonged well beyond the natural course of the response. Finally, we demonstrate that rIL-10, when injected into the skin before antigenic challenge, prevented the elicitation of CHS in previously sensitized mice. Taken together, our data show an important role for IL-10 in the natural regulation of CHS responses in vivo.

The immune response and the eye: a role for TNF alpha in anterior chamber-associated immune deviation

PURPOSE

Interleukin-1 and tumor necrosis factor (TNF) alpha are proinflammatory cytokines and crucial mediators in many aspects of immunity. In this study, their role in anterior chamber-associated immune deviation (ACAID) was investigated.

METHODS

The role of these cytokines was examined by the use of neutralizing antibodies to TNF and interleukin (IL)-1 alpha, IL-1 beta, and IL-1 receptor. These reagents were co-injected with antigen into the anterior chamber and the effect on ACAID assessed. In addition, reverse transcriptase polymerase chain reaction (RT-PCR) was performed on eyes injected with TNP-spleen or bovine serum albumin to determine the levels of TNF alpha mRNA induced.

RESULTS

Neutralizing antibody to TNF, when injected with TNP-spleen cells into the anterior chamber, blocked ACAID to the TNP hapten. Antibodies to IL-1 alpha, IL-1 beta, and IL-1 receptors either alone or in combination did not block the establishment of ACAID: Studies with reverse transcriptase polymerase chain reaction (Rt-PCR) confirmed that early (within 2 hours) after anterior chamber injection of TNP-cells, messenger RNA levels for TNF alpha were dramatically increased. The induction of ACAID to bovine serum albumin also required the production of TNF alpha. Further studies showed that the production of blood borne "ACAID-inducing" signals after anterior chamber injection of bovine serum albumin or TNP-spleen were dependent on TNF.

CONCLUSIONS

TNF alpha plays a crucial role in ACAID: Induction of TNF alpha within the eye may be an important event in the complex series of events that induce ACAID and possibly maintain immunologic privilege.

The portal protein of bacteriophage SPP1: a DNA pump with 13-fold symmetry

Electron microscopy in combination with image processing is a powerful method for obtaining structural information on non-crystallized biological macromolecules at the 10-50 A resolution level. The processing of noisy microscopical images requires advanced data processing methodologies in which one must carefully avoid the introduction of any form of bias into the data set. Using a novel multivariate statistical approach to the analysis of symmetry, we studied the structure of the bacteriophage SPP1 portal protein oligomer. This portal structure, ubiquitous in icosahedral bacteriophages which package dsDNA, is located at the site of symmetry mismatch between a 5-fold vertex of the icosahedral shell and the 6-fold symmetric (helical) tail. From previous studies such 'head-to-tail connector' structures were generally accepted to be homododecamers assembled in a 12-fold symmetric ring around a central channel. Using a new analysis methodology we have found that the phage SPP1 portal structure exhibits 13-fold cyclical symmetry: a new point group organization for oligomeric proteins. A model for the DNA packaging mechanism by 13-fold symmetric portal protein assemblies is presented which attributes a coherent functional meaning to their unusual symmetry.

Direct determination of cadmium in urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

A procedure is described for the direct determination of cadmium in human urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction. Except for a straightforward 1 + 1 V/V dilution of samples with 1.5% nitric acid, no matrix modifier or sample pre-treatment was necessary, thus reducing the risk of contamination. The concentration of cadmium in urine was evaluated directly from a calibration graph prepared using a metal-spiked human urine pool. In this way the time-consuming method of standard additions was avoided, permitting an increased sample throughput (120-150 samples per day; 90 s per analysis) with minimal attention of the analyst. In routine use, the precision (both within day and day to day) and limit of detection were of the order of less than 10% and 0.05 micrograms l-1 of Cd, respectively. The method is suitable for the biological monitoring of cadmium in the general population or in occupationally exposed persons.

Radiation therapy in the treatment of early glottic carcinoma: the experience of Villejuif

A retrospective analysis of 197 early glottic carcinoma treated with small field irradiation to a dose of 65 Gy is presented. The 5-year survival rate was 77.3%. Thirty-eight local failures have been observed, and the 5-year local control rate was 85.7%. Suspicion of extra glottic extension was the main prognostic factor. Final local control rate, taking into account the salvage treatment, was 90% at 5 years. Excellent functional results were observed.

Expression of a maize storage protein gene in petunia plants is not restricted to seeds

Genes encoding maize seed storage proteins, zeins, are expressed in developing endosperm tissue. To determine whether the DNA sequences controlling the developmental expression of these genes are recognized in dicots, we introduced a gene encoding a M(r) 19,000 zein protein into petunia by Agrobacterium tumefaciens mediated transformation. Southern blot analysis of DNA from regenerated transgenic plants showed that between 1 and 12 copies of the zein gene were integrated at various locations in the petunia genome. S1 nuclease mapping with 5' and 3' probes for zein mRNA showed that transcription of the gene was correctly initiated and terminated in seeds of the transgenic plants. The mRNA was first detected in petunia seeds 10 days after pollination and disappeared 17 days after pollination. However, only small amounts of zein transcripts were synthesized and protein could not be detected at any stage of development. We also found low levels of zein mRNA in leaves, stems, and flowers of the transgenic plants, suggesting that DNA sequences responsible for developmental regulation are not readily recognized in petunia plants.

Esophageal reconstruction: an experimental approach to the control of reflux after esophageal resection

A study of the properties of replacement gastric tubes and colonic segments, and their use in the prevention of reflux after esophageal resection indicates that, in order to prevent reflux, these tubes must be maintained in a subdiaphragmatic position. Gastric tubes have a higher intrinsic pressure barrier than colonic tubes--a 2.5- to 6-cm segment prevents reflux and the tube maintains a pressure barrier 10 cm H2O higher than stomach presure, whereas colonic segments require 12 cm of subdiaphragmatic length to control reflux and maintain a pressure barrier only 2 cm H2O above gastric pressure. Removal of the intrinsic pressure barrier by myotomy allows free reflux in tubes that previously had prevented reflux.

Control of massive cardiac haemorrhage by balloon catheter

The use of a balloon catheter to achieve the control of haemorrhage from the chambers of the heart has not been described previously. A case is reported in which this method was used in an emergency situation. It has been tested successfully, as a planned procedure, during four closed mitral valvotomy operations.

Balloon catheters have been used in vascular surgery for some time. Taylor and Williams (1962) used a Foley's catheter to prevent haemorrhage from an arteriovenous fistula at the time of its repair. Fogarty et al. (1963) described the use of Fogarty's catheter during extraction of arterial emboli and thrombi. Control of hepatic venous bleeding by placing a balloon catheter in the inferior vena cava in seven dogs was described by Doty and Berman (1970), and Foster, Morgan, and Threlkel (1971) used balloon catheters to achieve proximal control of the abdominal aorta. Thomas (1971) described the use of Fogarty catheters and Bakes common bile duct dilators to control bleeding during operation in complicated peripheral vascular lesions. Arbulu and Thomas (1972) reported a case of a gunshot wound in which haemorrhage from the inferior vena cava close to the heart was controlled by using a Foley's catheter.