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J Schaeffer

Publications and source records attributed to J Schaeffer.

At least 19 recordsLinked to original sources
PubMed2000

Nodulisporic acid opens insect glutamate-gated chloride channels: identification of a new high affinity modulator.

Nodulisporic acid (NA) is an indole diterpene fungal product with insecticidal activity. NA activates a glutamate-gated chloride channel (GluCl) in grasshopper neurons and potentiates channel opening by glutamate. The endectocide ivermectin (IVM) induces a similar, but larger current than NA. Using Drosophila melanogaster head membranes, a high affinity binding site for NA was identified. Equilibrium binding studies show that an amide analogue, N-(2-hydroxyethyl-2,2-(3)H)nodulisporamide ([(3)H]NAmide), binds to a single population of sites in head membranes with a K(D) of 12 pM and a B(max) of 1.4 pmol/mg of protein. A similar K(D) is determined from the kinetics of ligand binding and dissociation. Four lines of evidence indicate that the binding site is a GluCl. First, NA potentiates opening of a glutamate-gated chloride current in grasshopper neurons. Second, glutamate inhibits the binding of [(3)H]NAmide by increasing the rate of dissociation 3-fold. Third, IVM potently inhibits the binding of [(3)H]NAmide and IVM binds to GluCls. Finally, the binding of [(3)H]IVM is inhibited by NA. The B(max) of [(3)H]IVM is twice that of [(3)H]NAmide, and about half of the [(3)H]IVM binding sites are inhibited by NA with high affinity (K(I) = 25 pM). In contrast, [(3)H]IVM binding to Caenorhabditis elegans membranes is not inhibited by NA at 100 nM, and there are no high affinity binding sites for NA on these membranes. Thus, half of the Drosophila IVM receptors and all of the NA receptors are associated with GluCl. NA distinguishes between nematode and insect GluCls and identifies subpopulations of IVM binding sites.

Amides↗
PubMed1999

Comparison of the effects of bax-expression in yeast under fermentative and respiratory conditions: investigation of the role of adenine nucleotides carrier and cytochrome c.

A new system for bax-expression in yeast has been devised to investigate bax's effect under fermentative and respiro-fermentative conditions. This has allowed us to show unambiguously that the ability of bax to kill yeast is higher under respiratory conditions than under purely fermentative conditions. The extent of killing under respiro-fermentative conditions (non-repressive sugars) is intermediate. It has been proposed that the two proteins adenine nucleotides carrier (ANC) and cytochrome c play a crucial role in bax-induced cell death. We have investigated the effects of deletion of the genes encoding the two proteins on the toxicity induced by bax, using this new system. The absence of ANC did not modify bax-induced lethality in any way. Moreover, the absence of cytochrome c also did not prevent bax-induced death. Only the kinetics of lethality were altered. All these effects are prevented by co-expression of bcl-xL.

Apoptosis↗
PubMed1999

Characterization of the ORF YBR264c in Saccharomyces cerevisiae, which encodes a new yeast Ypt that is degraded by a proteasome-dependent mechanism.

We identified the ORF YBR264c during the systematic sequencing of the Saccharomyces cerevisiae genome. It encodes a putative protein of 218 amino acids. We demonstrate here that the gene is indeed expressed and encodes a new Ypt in yeast. This protein specifically binds guanine nucleotides and interacts via its C-terminal end with the unique Rab GDP Dissociation Inhibitor (RabGDI). In accordance with a recent proposal, the gene is now designated YPT10. No mutant phenotype could be associated with inactivation of the gene. However, overexpression of YPT10 resulted in defects in growth; microscopic examination of such cells revealed an overabundance of vesicular and tubular structures, suggesting some alteration in the function of the Golgi apparatus. In addition, degradation of the Ypt10 protein, which possesses a PEST sequence, is shown to be dependent on proteasome activity.

Amino Acid Sequence↗
PubMed1998

Alterations of synovial tissue and their potential role in the deposition of beta2-microglobulin-associated amyloid.

BACKGROUND: Beta-2-microglobulin-associated amyloidosis (AB2M) is a frequent complication of long-term dialysis treatment. Uraemic retention of beta2-microglobulin (beta2M) apparently constitutes the basis for AB2M. However, it is unclear why clinical manifestations are largely confined to osteoarticular tissues. It has been speculated that synovial inflammatory changes, induced by uraemia and/or dialysis therapy could predispose this tissue to amyloid deposition. METHODS: We investigated which local synovial alterations preceded or paralleled amyloid deposition. Using immunohistology we evaluated synovial leukocyte infiltration (B and T lymphocytes, monocytes/macrophages), cell proliferation, fibroblast activation (de novo expression of alpha-smooth-muscle actin), the expression of extracellular matrix components (heparan sulphate proteoglycan, collagen types I, III, IV), and advanced glycation end-products (AGEs). RESULTS: Synovial AB2M was detected in 20 of 36 chronic peritoneal and haemodialysis patients and none of eight non-uraemic controls. Notably, non-AB2M synovial amyloid was present in six additional dialysis and three control patients. Cellular infiltration was largely restricted to patients with advanced AB2M deposits. The infiltrates consisted mainly of macrophages and progressed with increasing degrees of AB2M deposition. In advanced cases they exhibited characteristics of a foreign-body reaction. Other infiltrating leukocyte types, altered cell proliferation, or fibroblast activation were absent or uncommon in periarticular tissue of dialysis patients with and without AB2M. Neither dialysis treatment nor the presence of AB2M deposits appreciably altered the qualitative matrix composition in periarticular tissue. AGEs were present in AB2M deposits, the extracellular synovial matrix of dialysis patients (of both, patients with and without AB2M) and, to a lesser degree, in synovia of controls. CONCLUSIONS: These data suggest that, except for AGE formation, alterations of none of the parameters assessed, and in particular no inflammatory tissue alterations, precede periarticular AB2M. Rather synovial tissue, possibly modified by AGEs, seems to have an intrinsic propensity for amyloid deposition and inflammatory changes appear to only arise secondary to amyloid deposition.

Adult↗
PubMed1998

Cell specific expression of the sst2A and sst5 somatostatin receptors in the rat anterior pituitary.

Somatostatin (SRIF), originally described as a hypothalamic hormone that inhibits the release of growth hormone was subsequently shown to inhibit the secretion of multiple pituitary hormones. Five genes encoding six different SRIF receptors (sst1, 2A, 2B, 3, 4 and 5) have been cloned and mRNAs for all five are expressed in the anterior pituitary. We used double immunostaining to determine which cells in the anterior pituitary bear sst2A and sst5 receptors. Our results show that these two receptors are widely distributed in the pituitary gland and are both present in a large percentage of GH cells. In addition, sst5 occurs in a small population of corticotrophs and a large percentage of lactotrophs whereas sst2A is found in only a few lactotrophs but a large number of corticotrophs. The sst2A receptor is also expressed in about a third of the gonadotrophs and thyrotrophs. Interestingly, sst2A and sst5 receptors colocalize in a small percentage of cells, most likely somatotrophs demonstrating that the same cells can contain multiple sst receptor subtypes. These results indicate that sst subtype specific analogs are likely to be useful for the selective regulation of individual pituitary hormones.

Animals↗
PubMed1997

A second DNA polymerase activity in yeast mitochondria.

In eukaryotic cells, there is much evidence to indicate that the replication of the mitochondrial genome is carried out by a specific DNA polymerase named DNA polymerase gamma. In the yeast S. cerevisiae, a DNA polymerase gamma has been partially purified and the gene encoding the catalytic subunit identified. The characteristics of this enzyme are the same as those found in higher eukaryotes, except for the requirement for a higher magnesium concentration. During a purification procedure of yeast mitochondrial DNA polymerase, we have isolated a second DNA polymerase activity. Using different approaches ive have ruled out the possibility of nuclear contamination or a product of proteolysis. From its properties, this new DNA polymerase activity seems to be different from any yeast DNA polymerase. This new mitochondrial DNA polymerase activity provides evidence that the animal model of mitochondrial DNA replication cannot be generalized. The presence of two DNA polymerases in yeast mitochondria could reflect a different replication or repair mechanism.

Cell Fractionation↗
PubMed1997

Beta 2-microglobulin associated amyloidosis: a vanishing complication of long-term hemodialysis?

Beta 2-microglobulin associated amyloidosis (A beta 2m amyloidosis) is considered an inevitable complication of chronic hemodialysis, particularly in hemodialysis with cellulose based membranes. We performed a single center study to assess the prevalence of A beta 2m amyloidosis in 1988 versus 1996. Randomly selected patients, studied in 1988, were matched for time on hemodialysis (mean 71 months, range 3 to 207) and age (mean 51 years, range 22 to 80) with patients of the 1996 population. Compared to 1988 patients, the 1996 patients exhibited a lower prevalence of carpal tunnel syndrome (7 of 43 in 1988 vs. 1 of 43 in 1996; P < 0.001) and radiological evidence of A beta 2m amyloidosis (13 of 34 patients vs. 3 of 34 patients positive; P < 0.001; and 33 of 272 possible sites affected in 1988 vs. 7 of 272 sites in 1996 patients; P < 0.05). Compared to the 1988 population, the 1996 population exhibited significantly lower serum aluminum levels, lower average serum creatinine (but not urea) levels, more frequent therapy with erythropoietin, less home hemodialysis, longer hemodialysis time using high-flux synthetic dialysis membranes (mean of 13% vs. 6% of the total hemodialysis time in the 1988 group), and more frequent usage of reverse osmosis water plus bicarbonate buffer for dialysate preparation. We conclude that the prevalence and severity of A beta 2m amyloidosis unexpectedly decreased by about 80% in our center between 1988 and 1996. Given the relatively short times spent on high flux hemodialysis in both groups, increased beta 2-microglobulin removal is unlikely to account for this phenomenon. Rather, other factors, for example, dialysate composition and purity, may be involved.

Adult↗
PubMed1997

Craniopharyngioma arising de novo in middle age. Case report.

The authors report the case of a 55-year-old woman who developed a symptomatic craniopharyngioma within 2 years of obtaining a normal magnetic resonance image of her brain. Craniopharyngiomas are histologically benign tumors. They are thought to arise from embryonic remnants of Rathke's pouch and sac and to manifest themselves clinically after a steady growth that commences in fetal life. To the authors' knowledge, this is the first report that documents a tumor arising de novo in the sixth decade of life. This report appears to challenge the concept of the origin and natural history of craniopharyngiomas.

Craniopharyngioma↗
PubMed1996

Electroconvulsive therapy (ECT) for intractable depression following epilepsy neurosurgery.

Psychopathology following epilepsy neurosurgery is a significant risk. Treatment modalities have not been addressed in the literature. As disproportionately elevated suicide rates have been reported, it is critical to treat aggressively any psychiatric illness wherein suicidal ideation is a key component. This case reports the safe utilization of electroconvulsive therapy (ECT) for intractable depression following epilepsy neurosurgery (24 references).

Adult↗
PubMed1996

Diagnostic aspects of beta 2-microglobulin amyloidosis.

Osteoarticular symptoms and signs, such as carpal tunnel syndrome, periarthritis humeroscapularis, synovial and joint inflammation, lead to the clinical diagnosis of beta 2-microglobulin (beta 2-M) amyloidosis. Radiologically, destructive arthropathy, spondylarthropathy and periarticular cystic bone radiolucencies can be demonstrated by plain X-ray and conventional and computed tomography. Magnetic resonance is used to visualize amyloid masses in special locations such as the cervical spine. Joint ultrasonography demonstrating thickening of synoviae and tendons has become a useful non-invasive diagnostic tool, although it is not specific for beta 2-M amyloidosis, and results depend on observer experience. Efforts to develop more specific methods for demonstration of amyloid deposits have led to two scintigraphic techniques based on the injection of radiolabelled proteins which are incorporated into the amyloid tissue. One method uses serum amyloid P component, a non-specific constituent of all types of amyloid. An alternative imaging technique based on radiolabelled beta 2-M as the specific precursor molecule of beta 2-M amyloidosis appears to be a more sensitive diagnostic method. Both tracer techniques have been used so far only in small single-centre clinical studies, and a more widespread application will require the introduction of recombinant material as the protein source for labelling. The 'gold standard' for the definitive diagnosis of beta 2-M amyloidosis, and also for reference in the evaluation of new diagnostic techniques, remains the histomorphological demonstration of beta 2-M amyloid by Congo red staining, green birefringence under polarized light, positive immunostaining with anti-beta 2-M antibodies, and electronoptic visualization of amyloid fibrils in tissue obtained invasively by biopsy, surgery or autopsy.

Amyloidosis↗
PubMed1996

Long-term performance of hemofilters in continuous hemofiltration.

We measured the filter performance of six polyamide hemofilters with a running time exceeding 72 h applied for continuous hemofiltration in intensive care patients. The sieving coefficients for urea and creatinine were close to unity and remained constant. The sieving coefficient of polyfructosan (mean molecular weight 3 kD) was around 0.75 and did not change with running time. The hydraulic permeability remained also unchanged. The relationships between blood pressure and blood flow and between blood flow and filtration rate remained linear, and the gradient did not change with time. We conclude that a daily routine change of polyamide hemofilters applied in continuous arteriovenous hemofiltration and presumably in continuous venovenous hemofiltration is not necessary within the first 72 h of treatment, unless a major decrease in the filtration rate occurs.

Acute Kidney Injury↗
PubMed1995

Pathogenetic and diagnostic aspects of dialysis-related amyloidosis.

Dialysis-related amyloidosis (DRA) is a major cause of morbidity in end-stage renal disease patients. While retention of the precursor protein beta 2-microglobulin (beta 2-m) forms the essential basis for DRA, pathogenetic concepts include: qualitative and quantitative alterations in beta 2-m metabolism; local and systemic inflammatory changes, partly related to different treatment modes; general predisposing factors such as age at the onset of dialysis treatment. Clinical and radiological signs, as well as synovial thickening on sonography, suggest the presence of DRA, but histomorphological demonstration of beta 2m-amyloid is required for definitive proof. Scintigraphic imaging of DRA represents an additional, sensitive non-invasive diagnostic tool. Successful kidney transplantation stops the progression of DRA.

Amyloidosis↗
PubMed1995

Beta 2-microglobulin amyloidosis: why and how to look for it.

Thirty years after the introduction of chronic dialysis into clinical practice, amyloidosis based on the precursor molecule beta 2-microglobulin (beta 2m-A) has emerged as an important complication of end-stage renal disease in patients on renal replacement therapies other than transplantation. For the individual patient, diagnosis of beta 2m-A is important to exclude other treatable causes of the symptoms, initiate symptomatic treatment, prevent possible life-threatening complications, and assign a high priority for transplantation. For the ESRD population as a whole, early specific diagnosis should help to assess the influence of various therapeutic modes on the development and course of beta 2m-A and to guide further the optimization of renal replacement therapy. Besides, sophisticated diagnostic techniques may yield valuable information on underlying pathogenetic mechanisms of beta 2m-A. Morphology, including immunohistochemistry, as the most definitive and specific diagnostic proof must rely on invasive procedures to obtain the appropriate material from clinically affected sites. Clinical assessment and imaging techniques such as x-ray and joint sonography suffer from non-specificity. Scintigraphic imaging of beta 2m-A after injection of radiolabelled beta 2-microglobulin is a non-invasive, specific, and highly sensitive way of diagnosis. Further refinement and more widespread use of this method can be expected to enhance the understanding of beta 2m-A pathogenesis and promote therapeutic and preventive efforts against this complication.

Amyloidosis↗
PubMed1994

Comparative analysis of mutations in the p53 and K-ras genes in pancreatic cancer.

Mutations in codon 12 of K-ras occur in a high proportion of pancreatic cancer cases. Although there is evidence that p53 mutations also occur in this tumor, few studies have been reported to date and no comparison has been made of K-ras and p53 mutations in the same tissues. Single-strand conformation polymorphism and sequencing of the PCR products were used to determine mutations in p53 gene; to detect mutations in K-ras genes, the artificial restriction fragment length polymorphism (RFLP) approach was used. Eight out of 30 tissues from primary pancreas cancer and 3 of 4 samples from metastases showed p53 mutations. Fifteen out of 17 pancreatic cancer cell lines had p53 mutations. In 2 cases, the same p53 mutation was identified in the original tumor and in a tumor-derived cell line. The majority of p53 mutations were present in exons 5-9 of the gene. Mutations at codon 12 of the K-ras gene were identified in 23/32 pancreas cancer tissues and in 14/17 cell lines. There was no relationship between the types of mutation observed in the 2 genes. In conclusion, mutations in K-ras and p53 genes are common in pancreatic cancer. p53 mutations may occur more frequently in metastatic lesions than in primary tumors, although further work is necessary to investigate this point.

Base Sequence↗
PubMed1993

Genetic heterogeneity of the c-K-ras locus in colorectal adenomas but not in adenocarcinomas.

BACKGROUND: Previous molecular genetics studies of colorectal cancer have identified multiple mutations in the c-K-ras gene (also known as KRAS2) in all phases of its development. Because of technical difficulty, prior studies rarely focused attention on the detailed distribution of c-K-ras mutations in multiple regions of the same primary tumor specimen. However, with recent development of the selective UV radiation fractionation method, characterization of c-K-ras mutations in multiple regions of the same primary tumor specimen can be performed. PURPOSE: Our purpose was to describe how c-K-ras mutations were distributed among cells obtained from multiple regions of the same primary tumor in an attempt to describe differences between early and late colorectal carcinogenesis. METHODS: Formalin-fixed, paraffin-embedded tissue blocks were obtained. Seven adenocarcinomas and seven adenomas were selected for the presence of mutant c-K-ras genes and histologic transitions between normal and neoplastic tissue. Tissue sections were prepared for analysis by the selective UV radiation fractionation method by placing thin, fixed tissue sections on a plastic slide with no coverslip. Under the microscope, small ink dots from a felt-tip pen were manually placed directly on relatively pure cell subpopulations. The slides were placed with the tissue side exposed to a UV transilluminator for 2-4 hours to inactivate the DNA present in the unprotected ("undotted") cells. Individual dots were cut out of the plastic slide into 2 x 2-mm squares and placed into microfuge tubes. The DNA was extracted and supernatant used for polymerase chain reaction (PCR) analysis. Mutations at c-K-ras codons 12 and 13 were detected. RESULTS: The selective UV radiation fractionation method and PCR analysis revealed that c-K-ras mutations never extended into normal mucosa and were present in all neoplastic cells regardless of phenotypes in all seven adenocarcinomas and three of the seven adenomas. Further examination of two carcinomas for p53 (also known as TP53) mutations or loss of heterozygosity demonstrated that these additional mutations were also present in all tumor cells, suggesting that a single transformed clone was responsible for the majority of growth. However, in four other adenomas, tumor heterogeneity was demonstrated, since c-K-ras mutations were detected only in discrete portions. CONCLUSIONS: Adenoma formation may include a stage in which multiple and genetically distinct neoplastic clones are present, while most carcinomas appear to have a homogeneous composition that may result from the successful progression of one of these clones.

Adenocarcinoma↗
PubMed1992

Colour Doppler ultrasound assessment of arteriovenous haemodialysis fistulas.

Satisfactory function of the arteriovenous fistula (AVF) is essential for adequate haemodialysis in patients with chronic renal failure. Existing methods to assess AVF function are imprecise (eg, clinical examination) or invasive (eg, angiography). We assessed the value of colour flow-doppler ultrasound (CFDU) in the investigation of clinically suspected AVF dysfunction. 51 patients with suspected impairment of AVF function were studied by CFDU, and 28 also underwent angiography. The findings were compared with the reference standard of the findings at reoperation. CFDU showed AVF stenoses in 18 patients, which were all confirmed at reoperation; the results of angiography in 13 of these 18 patients showed complete agreement with the findings of CFDU and surgery. CFDU showed partial or complete AVF thrombosis in 33 patients, confirmed in all patients at reoperation; 15 patients also underwent angiography, and thrombi were not found in 6 (in 4 because of technical failure). 7 patients had aneurysms on CFDU that were confirmed by surgery in all patients and by angiography in 2 of the 3 patients studied. CFDU enables reliable non-invasive assessment of AVF morphology and function and may become the procedure of choice for AVF assessment in patients with suspected AVF abnormalities.

Adult↗