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Biomedical subjects

L Chiche

Publications and source records attributed to L Chiche.

At least 73 records · Page 4Linked to original sources
PubMed1995

Orthotopic liver transplantation in fulminant and subfulminant hepatitis. The Paul Brousse experience.

OBJECTIVE: The authors report on the experience of orthotopic liver transplantation in fulminant hepatitis at Paul Brousse Hospital. SUMMARY BACKGROUND DATA: Liver transplantation is a breakthrough in the treatment of patients with fulminant hepatitis. However, the indications, the timing for transplantation, the type of transplantation, and the use of ABO incompatible grafts in this setting still are debated. METHODS: Transplantation was indicated in patients with confusion or coma and factor V less than 20%, younger than 30 years of age, and confusion or coma and factor V less than 30% older than 30 years of age. RESULTS: Among 139 patients who met the aforementioned criteria for transplantation, 1 recovered, 22 died before transplantation, and 116 underwent transplants with a 1-year survival of 68%. Survival was 83% in patients with grade 1 and 2 comas at transplantation versus 56% (p < 0.001) in those with grade 3 comas; it was 51% versus 81% (p < 0.001) in those transplanted with high risk (ABO-incompatible, split, or steatotic) and low-risk grafts, respectively. In a multivariate analysis, steatotic and partial grafts were predictive of poorer patient survival, and ABO incompatibility was predictive of poorer graft survival. CONCLUSIONS: Orthotopic liver transplantation is an effective treatment in fulminant hepatitis. Use of high-risk grafts permitted transplantation of 83% of patients, but was responsible for higher mortality.

ABO Blood-Group System↗
PubMed1994

Heparin-related thrombocytopenia and adrenal hemorrhagic necrosis following aortic surgery.

Adrenal hemorrhagic necrosis is one of several possible complications of heparin-related thrombocytopenia. We report a case in which adrenal hemorrhagic necrosis developed after aortofemoral bypass. This serious complication remains difficult to diagnose in the absence of a high index of suspicion. A routine search for this condition in the setting of heparin-related thrombocytopenia is essential since a favorable outcome is dependent on early diagnosis.

Adrenal Glands↗
PubMed1994

Homology modelling of annexin I: implicit solvation improves side-chain prediction and combination of evaluation criteria allows recognition of different types of conformational error.

Annexin I homology models were built from the annexin V crystal structure. Three methods for side-chain prediction were tested based on molecular mechanics conformational search, the use of a rotamer database, or a combination of these two methods. We showed that rotamer-based methods were more efficient and that molecular mechanics energy minimizations, prior to rotamer selection, did not afford clearly improved predictions. Models built in vacuo and with an implicit solvation term were compared with the annexin I crystal structure which became available during the course of this study. The analysis of solvation energies, root mean square deviations, chi 1 angles and hydrogen bonds showed that models built with implicit solvation were of better quality. In annexin V, repeat III displays A-B and D-E loop conformations quite different from other repeats. Since the sequence differences suggest that repeat III in annexin I might present a conformation similar to other repeats, two annexin I models with different repeat III conformations were built and compared to determine whether the correct conformation could have been predicted. We show that using a combination of evaluation criteria, it is possible to discriminate unequivocally between the native and the incorrect fold, stressing that only one criterion should not be used to evaluate protein structures.

Amino Acid Sequence↗
PubMed1994

Site-directed mutagenesis of a calcium binding site modifies specifically the different biochemical properties of annexin I.

All the functions of annexins in vitro as well as in vivo are mediated and probably regulated by calcium. We have used recombinant annexin I, synthesized by Escherichia coli, and we have performed site-directed mutagenesis. We have mutated the endonexin fold of domain 2 that binds calcium. Mutations were performed in this domain of the molecule because it perfectly matches the calcium binding consensus sequence. The two glycines of this fold were mutated into glutamic acid. The helix content and the stability of the mutants are identical to those of the wild-type, suggesting that the mutations did not drastically affect the structure of the protein. The two mutants showed modified calcium binding affinities. However, the calcium binding affinity of the G131E mutant was far more altered than that of the G129E mutant. Furthermore, other biochemical properties of these mutants were modified to different extents. The binding to phospholipid was not seriously affected, whereas the self-association was lost by the G131E mutant. In the same way, liposome aggregation is conserved, but modified, while the calcium affinity measured by equilibrium dialysis is dramatically altered.

Annexin A1↗
PubMed1994

[Two cases of cystic adventitial disease of the popliteal artery. Current diagnostic approach].

The authors report two cases of cystic adventitial disease of the popliteal artery. Both patients complained of calf claudication and presented a thrombosis of the popliteal artery. In one case, magnetic resonance imaging exhibited a specific preoperative diagnosis. In both cases, at least one communication between the cysts and the capsule of the knee joint was demonstrated, supporting the congenital hypothesis of the disease. The two cases have been treated by vein graft replacement of the occluded popliteal arteries. Both patients have remained asymptomatic and the two grafts have remained patent during the ninth and twelfth month follow-up periods.

Adult↗
PubMed1993

Characterization and 2D NMR study of the stable [9-21, 15-27] 2 disulfide intermediate in the folding of the 3 disulfide trypsin inhibitor EETI II.

The three disulfide Ecballium elaterium trypsin inhibitor II (EETI II) reduction with dithiothreitol (DTT) and reoxidation of the fully reduced derivative have been examined. A common stable intermediate has been observed for both processes. Isolation and sequencing of carboxymethylated material showed that the intermediate lacks the [2-19] bridge. The NMR study showed a very strong structural conservation as compared to the native EETI II, suggesting that the bridges are the [9-21] and [15-27] native ones. The differences occurred in sections 2-7 (containing the free cysteine 2 and the Arg 4-Ile 5 active site) and 19-21 (containing the second free cysteine). Distance geometry calculations and restrained molecular dynamics refinements were also in favor of a [9-21, 15-27] arrangement and resulted in a well-conserved (7-28) segment.

Amino Acid Sequence↗
PubMed1993

Learning and alignment methods applied to protein structure prediction.

Learning techniques are able to extract structural knowledge specific to a selected set of proteins. We describe two algorithms that optimize scores expressing the propensity of a polypeptide sequence to adopt a local fold. The first algorithm generates secondary structure prediction rules based on a dictionary of geometrical patterns frequently found in the learning database. The second algorithm leads to scores that indicate the fit between an amino acid and a given local structural environment. Dynamic programming is then used to align structural information profiles by modifying the local mutation cost with the above learned functions. The main features of the system are exemplified on the structural prediction of the N-terminal domain of the CD4 antigen. Then the usefulness of additional 3-D information in the alignment is benchmarked on eight pairs of weakly homologous proteins.

Algorithms↗
PubMed1993

Molecular modeling of coiled-coil alpha-tropomyosin: analysis of staggered and in register helix-helix interactions.

In register and staggered models of tropomyosin coiled-coil were built from X-ray C alpha coordinates and refined via molecular dynamics. The two models show similar structural features with the X-ray structure of GCN4 leucine zipper. Empirical energetic methods used to compare the in register and staggered models indicate that both are equally probable. The two models have similar profiles of solvation free energy of folding for residues at positions a and d of the repeating heptad, indicating that residues at these positions are as well buried in an in register structure as in a staggered one. Neither the in register nor the 14 residues staggered structure can be ruled out based on hydrophobic or e-g' (g-e') electrostatic interactions which are not able to distinguish between the two models and are therefore not selective. However, the eg-b'c' electrostatic interactions, although smaller in magnitude, are in favor of the in register model. Furthermore, analysis of hydrophobic and electrostatic interactions along the tropomyosin sequence shows that bulky residues in positions a and d prevent the formation of inter-chain salt bridges.

Computer Simulation↗
PubMed1993

Solution conformation of a synthetic bis-headed inhibitor of trypsin and carboxypeptidase A: new structural alignment between the squash inhibitors and the potato carboxypeptidase inhibitor.

The trypsin carboxypeptidase peptide inhibitor (TCPI) which inhibits both trypsin and carboxypeptidase A has been chemically engineered by modification of the Ecballium elaterium trypsin inhibitor II (EETI-II). The solution conformation of TCPI, studied by two-dimensional nuclear magnetic resonance, was shown to be very close to those of squash inhibitors. Only limited deviations of the trypsin binding loop compared to its location in the EETI-II/trypsin complex were detected. It was also shown that the position of the C-terminal tail did not significantly change from the position observed in the complex between carboxypeptidase A and the potato carboxypeptidase inhibitor (PCI). The conformation of TCPI was carefully compared with the PCI one and a new structural alignment between the two microproteins is proposed. This alignment points out the very good conservation in the two inhibitors of a subdomain comprising segments 7-15, 19-22 and 25-28. Most importantly, the 2-19 disulfide bridge of TCPI was not structurally conserved in PCI and appeared to be rather unimportant for the early folding process of these molecules. This result agrees with the recent observation that the 2-19 bridge is the last to be formed in the folding of the squash inhibitor EETI-II and suggests that this is also the case during the folding of the potato carboxypeptidase inhibitor.

Amino Acid Sequence↗
PubMed1993

Improved alignment of weakly homologous protein sequences using structural information.

Protein sequence alignments can be improved when at least one of the proteins to be aligned has a known 3-D structure. In this work, geometrical constraints extracted from the target fold are evaluated in independent units that deal with complementary structural features. This information is used to set up mutation tables specific to the locally observed structural environments. The resulting partial evaluations are then combined linearly into a global function which is optimized by dynamic programming. Eventually, a score based on tertiary interactions can be used as a selection criterion to discriminate among a set of suboptimal alignments. The relevance of the scores given by each unit is tested on a representative set of protein families. Finally, a method for combining the different scores is described and its efficiency is evaluated on a few pairs of weakly homologous proteins.

Algorithms↗
PubMed1993

Relationship between gastric acid secretion and the rate of recurrent ulcer after parietal cell vagotomy.

OBJECTIVE: This study assessed the effect of gastric secretion on the rate of recurrent ulcer after parietal cell vagotomy for duodenal ulcer. SUMMARY BACKGROUND DATA: Three hundred patients who underwent parietal cell vagotomy for duodenal ulcer between 1975 and 1986 were evaluated. The mean follow-up period for 280 patients was 5 years. METHODS: The gastric secretion tests concerned basal acid output (BAO) and peak acid output stimulated by pentagastrin or insulin. Tests were preoperative for 172 patients and postoperative for 118. RESULTS: At the end of that time, the overall incidence of symptomatic recurrent ulcer was 15%. Two criteria were shown to be important predictors of recurrent ulcer: preoperative BAO > 7 mmol/hr, for which the recurrence rate 5 years after vagotomy was 30% versus 11% for values below this threshold (p = 0.01), and postoperative BAO > 1.4 mmol/hr, for which the recurrence rate at 5 years was 72% versus 8% for lower values (p = 0.0001). All patients with recurrent ulcer had either a postoperative BAO > 7 mmol/hr and/or a postoperative reduction in BAO < 80%. CONCLUSION: Preoperative BAO > 7 mmol/hr and postoperative BAO > 1.4 mmol/hr were shown to be factors predictive of RU. All patients with RU presented either with preoperative BAO > 7 mmol/hr and/or a reduction in BAO < 80%. Consequently, in our opinion, these criteria could be used either to select patients for vagotomy or to assess the effectiveness of vagotomy of different types, especially those performed by celioscopy.

Adult↗
PubMed1993

Liver resection versus transplantation for hepatocellular carcinoma in cirrhotic patients.

OBJECTIVE: Currently, there is considerable controversy about the place of transplantation in the treatment of hepatocellular carcinoma (HCC). This study compared resection to transplantation in cirrhotic patients with HCC in order to determine reasonable indications of each treatment. SUMMARY BACKGROUND DATA: The usual procedure is to resect when feasible and to transplant in other cases. METHODS: Three-year survival with and without recurrence was analyzed in 60 patients who underwent resection and 60 who underwent transplantation. Several prognostic factors, such as size, number of nodules, portal thrombus, and histologic form, were studied. RESULTS: In terms of overall survival rates, resection and transplantation yield the same results (50% vs. 47%, respectively, at 3 years). For transplantation, however, the rate for survival without recurrence is better than that for resection (46% vs. 27%, respectively; p < 0.05). In the case of small uninodular or binodular tumors (< 3 cm), transplantation has much better results than resection (survival without recurrence, 83% vs. 18%, respectively; p < 0.001). However, it seems that a group of patients with high risk of recurrence after transplantation can be determined (diffuse form, more than two nodules > 3 cm, or presence of portal thrombus). CONCLUSIONS: The best indication for transplantation seems to be patients with small and uninodular or binodular tumors; until now, these patients were considered to be the best candidates for resection. Patients undergoing transplantation for unresectable, large, multinodular or diffuse tumors seem to represent bad indications for transplantation. These results could help define reasonable indications for transplantation in an era with a shortage of liver grafts.

Carcinoma, Hepatocellular↗
PubMed1993

A modular learning environment for protein modeling.

We propose in this paper a modular learning environment for protein modeling. In this system, the protein modeling problem is tackled in two successive phases. First, partial structural informations are determined via numerical learning techniques. Then, in the second phase, the multiple available informations are combined in pattern matching searches via dynamic programming. It is shown on real problems that various protein structure predictions can be improved in this way, such as secondary structure prediction, alignment of weakly homologous protein sequences or protein model evaluations.

Amino Acid Sequence↗