Biomedical subjects

P Keller

Publications and source records attributed to P Keller.

At least 19 recordsLinked to original sources

PubMed2006

Polyelectrolyte multilayer film coating and stability at the surfaces of oral prosthesis base polymers: an in vitro and in vivo study.

A new type of coating involving a layer-by-layer technique has been recently reported. This coating is composed of a polyelectrolyte multilayer film that confers specific properties on surfaces to which it is applied. Here, we studied the applicability of such a technique to the coating of oral prostheses, by first testing the construction of polyelectrolyte multilayer films on several polymers used in oral prosthesis bases, and, subsequently, by studying the stability of these coatings in vitro, in human saliva, and in vivo in a rat model. We demonstrated that the multilayered films are able to coat the surfaces of all tested polymers completely, thus increasing their wettability. We also showed that saliva does not degrade the film after 7 days in vitro and after 4 days in vivo. Taken together, our results establish that the layer-by-layer technique is suitable for the coating of oral devices.

Acrylates↗

PubMed2004

Colloidal structures from bulk demixing in liquid crystals.

This experimental paper deals with phase separations of binary mixtures composed of a continuous liquid crystal phase and an isotropic dispersed phase. In contrast to isotropic binary mixtures, the investigated mixtures do not lead to a full phase separation but to a self-ordering of colloidal particles, as reported earlier (Loudet, J. C. et al. Nature 2000, 407, 611). We present here further aspects of such phase separations which include the kinetics of the phase separation, the origin of the formation of dislocation-like patterns, the influence of surfactants, chiral additives, and temperature on the formed colloidal structures. The present results show that (i) the dislocations in chain arrays can be seen as kinetically frozen defects, (ii) temperature can be used to control the size of the domains formed upon demixing, (iii) a slight change in surface chemistry, via the addition of surfactants, profoundly alters the formed colloidal structures, and (iv) chiral additives allow the formation of unique helical pearl chains which reflect the symmetry of the liquid crystal phase they are embedded in.

Journal Article↗

PubMed2004

The metabolic role of IL-6 produced during exercise: is IL-6 an exercise factor?

For most of the last century, researchers have searched for a muscle contraction-induced factor that mediates some of the exercise effects in other tissues such as the liver and the adipose tissue. It has been called the 'work stimulus', the 'work factor' or the 'exercise factor'. In the search for such a factor, a cytokine, IL-6, was found to be produced by contracting muscles and released into the blood. It has been demonstrated that IL-6 has many biological roles such as: (1) induction of lipolysis; (2) suppression of TNF production; (3) stimulation of cortisol production. The IL-6 gene is rapidly activated during exercise, and the activation of this gene is further enhanced when muscle glycogen content is low. In addition, carbohydrate supplementation during exercise has been shown to inhibit the release of IL-6 from contracting muscle. Thus, it is suggested that muscle-derived IL-6 fulfils the criteria of an exercise factor and that such classes of cytokines could be termed 'myokines'.

Energy Metabolism↗

PubMed2004

Low plasma level of adiponectin is associated with stavudine treatment and lipodystrophy in HIV-infected patients.

This study tested the hypothesis that in patients with HIV-associated lipodystrophy, adiponectin levels were related to insulin resistance, TNF-alpha and IL-6 and treatment with nucleoside analogues. HIV seropositive men undergoing highly active antiretroviral treatment were enrolled into three predetermined clinical groups: lipodystrophy with central fat accumulation (n = 12); lipodystrophy without central fat accumulation (n = 15); no lipodystrophy (n = 15). HIV-negative healthy men served as controls (n = 12). Both lipodystrophic groups had a low percentage of limb fat compared to the two control groups. Patients with lipodystrophy with fat accumulation had increased truncal fat compared with controls. Levels of adiponectin did not correlate with either TNF-alpha or IL-6. Low levels of adiponectin were found in both lipodystrophic groups and were associated with current or previous treatment with stavudine. Furthermore, the adiponectin level correlated with the percentage of limb fat. Patients with lipodystrophy with fat accumulation were more insulin resistant, measured by HOMA-IR, compared with controls. However, HOMA-IR did no correlate to adiponectin or other cytokines. In conclusion, the finding of no difference between the two lipodystrophic groups with regard to adiponectin, indicates that low levels of adiponectin reflects fat atrophy, whereas the insulin resistance was best explained by increased truncal fat mass.

Adiponectin↗

PubMed2003

The role of mismatch repair in small-cell lung cancer cells.

The role of mismatch repair (MMR) in small-cell lung cancer (SCLC) is controversial, as the phenotype of a MMR-deficiency, microsatellite instability (MSI), has been reported to range from 0 to 76%. We studied the MMR pathway in a panel of 21 SCLC cell lines and observed a highly heterogeneous pattern of MMR gene expression. A significant correlation between the mRNA and protein levels was found. We demonstrate that low hMLH1 gene expression was not linked to promoter CpG methylation. One cell line (86MI) was found to be deficient in MMR and exhibited resistance to the alkylating agent MNNG. Surprisingly, MSI was not detected in 86MI and it appears to express all the major MMR components hMSH2, hMSH6, hMLH1, hPMS2, hMSH3, hMLH3, MBD4 (MED1) and hExo1. These data are consistent with at least two possibilities: (1) A missense mutation in one of the MMR genes, which dissociates MSI from drug resistance, or (2) inactivation of a second pathway that leads to MMR-deficiency and MNNG resistance, but induces negligible levels of MSI. We conclude that MMR deficiency is largely not associated with the pathogenesis of SCLC.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Searching for the exercise factor: is IL-6 a candidate?

For years the search for the stimulus that initiates and maintains the change of excitability or sensibility of the regulating centers in exercise has been progressing. For lack of more precise knowledge, it has been called the 'work stimulus', 'the work factor' or 'the exercise factor'. In other terms, one big challenge for muscle and exercise physiologists has been to determine how muscles signal to central and peripheral organs. Here we discuss the possibility that interleukin-6 (IL-6) could mediate some of the health beneficial effects of exercise. In resting muscle, the IL-6 gene is silent, but it is rapidly activated by contractions. The transcription rate is very fast and the fold changes of IL-6 mRNA is marked. IL-6 is released from working muscles into the circulation in high amounts. The IL-6 production is modulated by the glycogen content in muscles, and IL-6 thus works as an energy sensor. IL-6 exerts its effect on adipose tissue, inducing lipolysis and gene transcription in abdominal subcutaneous fat and increases whole body lipid oxidation. Furthermore, IL-6 inhibits low-grade TNF-alpha-production and may thereby inhibit TNF-alpha-induced insulin resistance and atherosclerosis development. We propose that IL-6 and other cytokines, which are produced and released by skeletal muscles, exerting their effects in other organs of the body, should be named 'myokines'.

Adipose Tissue↗

PubMed2003

Circulating adiponectin levels during human endotoxaemia.

Adiponectin, an adipocytokine secreted by fat tissue, may prevent development of diabetes type II, as high adiponectin levels are linked with insulin sensitivity. In contrast, tumour necrosis factor (TNF)-alpha, which is also produced by fat tissue, leads to insulin resistance and furthermore inhibits adiponectin mRNA production and secretion of the protein. However, adiponectin also negatively regulates TNF-alpha levels. Therefore, we set out to test whether an infusion of endotoxin would influence circulating adiponectin levels in healthy human subjects. Twenty-three healthy human subjects were injected with endotoxin (2 ng/kg body weight); eight of these subjects were also injected with saline and served as controls. Plasma levels of adiponectin, TNF-alpha and interleukin-6 were measured at 0, 1.5, 2, 4, 8 and 24 h. TNF-alpha and interleukin-6 levels peaked at 1.5 h and 2 h, respectively. Control subjects injected with saline showed a decrease in adiponectin plasma levels with time (P < 0.05) presumably owing to the effect of fasting or physical inactivity. However, there was no change in adiponectin plasma levels in endotoxin injected subjects, thus the effect of fasting was opposed. In conclusion, circulating adiponectin levels are reduced during a resting and fasting state, an effect reversed by endotoxin injection.

Adiponectin↗

PubMed2003

Transglutaminase from Streptomyces mobaraensis is activated by an endogenous metalloprotease.

Streptomyces mobaraensis secretes a Ca2+-independent transglutaminase (TGase) that is activated by removing an N-terminal peptide from a precursor protein during submerged culture in a complex medium [Pasternack, R., Dorsch, S., Otterbach, J. T., Robenek, I. R., Wolf, S. & Fuchsbauer, H.-L. (1998) Eur. J. Biochem. 257, 570-576]. However, an activating protease could not be identified, probably because of the presence of a 14-kDa protein (P14) belonging to the Streptomyces subtilisin inhibitor family. In contrast, if the microorganism was allowed to grow on a minimal medium, several soluble proteases were extracted, among them the TGase-activating protease (TAMEP). TAMEP was purified by sequential chromatography on DEAE- and Arg-Sepharose and used to determine the cleavage site of TGase. It was clearly shown that the peptide bond between Phe(-4) and Ser(-5) was hydrolyzed, indicating that at least one additional peptidase is necessary to complete TGase processing, even if TAMEP cleavage was sufficient to obtain total activity. Sequence analysis from the N-terminus of TAMEP revealed the close relationship to a zinc endo-protease from S. griseus. The S. griseus protease differs from other members of the M4 protease family, such as thermolysin, in that it may be inhibited by the Streptomyces subtilisin inhibitor. P14 likewise inhibits TAMEP in approximately equimolar concentrations, suggesting its important role in regulating TGase activity.

Amino Acid Sequence↗

PubMed2003

[Dacryolithiasis: diagnosis using nasal endoscopy].

PURPOSE: The purpose of this study was to assess the value of two new clinical findings for the diagnosis of dacryolithiasis discovered with nasal endoscopy: anatomical abnormalities of the Hasner valve (HV) and mucopurulent discharge visible at this valve. The value of these findings is compared with other clinical and radiological signs of dacryolithiasis. A hypothesis is developed as to the responsibility of the HV in the formation of dacryolithiasis. METHOD: This study was prospective and based on 797 operations performed for epiphora: 647 endonasal dacryocystorhinostomies and 150 meatotomies of the HV, with systematic preoperative nasal videoendoscopy. Ninety dacryocystographies (DCGs) and 129 lacrimal computed tomographies (LCT) were preoperatively performed. RESULTS: Dacryoliths were found in 55 of 797 patients (6.9%). The HV could be examined in 48 patients in the lithiasis group and in 687 patients in the control group. Mucopurulent discharge was observed in 22 patients with lithiasis (45.8%) and in 40 patients (5.8%) (p<10(-6)) of the control group. Anatomical abnormalities of the HV were found in 40 patients with dacryolithiasis (83.3%) as compared to 82 patients ing the control group (11.4%) (p<10(-6)). In 13 patients, the VH was very small (<2 mm), in 12 patients it was very long (>15 mm), and in 15 patients both abnormalities were observed. Other clinical signs were young age (mean, 48.2 years vs 59.1% in the control group) (p<0.05), a history of acute noninfectious dacryocystic retention (38.2% vs 9.5%) (p<10(-5)), partial obstruction of the lacrimal pathway (LP) (61.8% vs 30.5%) (p<10(-5)). The 28 LCTs that were performed in subjects who had lithiasis made it possible to diagnose 19 cases of dacryolithiasis and confirmed abnormalities of the HV causing narrowing of the LP in 20. CONCLUSION: Dacryolithiasis is frequent and often misdiagnosed. When dacryolithiasis is suspected, a nasal videoendoscopic exam must be done to seek HV abnormalities and mucopurulent discharge at this valve. This latter finding, i.e., the association of mucopurulent discharge with a patent lacrimal system, has high specificity. The finding of numerous anatomical abnormalities of the HV may be an indication that congenital malformation of the HV is the cause of many cases of lithiasis.

Adult↗

PubMed2002

[First line endonasal dacryocystorhinostomy Technique and results. Comparison between diode laser and electrocautery instrument. Study based on 422 procedures].

PURPOSE OF THE STUDY: To assess the results of the first procedures of endoscopic endonasal dacryocystorhinostomy (ENL DCR). To study the efficiency of diode laser in this operation versus electrocautery instruments (ECI). DESIGN: Prospective study; comparative study. METHODS: Intraoperative comparison between ECI and diode laser is based on 422 ENL DCR achieved between June 1997 until June 2000. Three hundreds and sixty three procedures were diode laser assisted and 59 procedures were done with the use of an ECI. The diode laser was only used to vaporize nasal mucosa laying on the osteotomy site, to realize partial turbinectomy and to vaporize polyps and synechiae. Intraoperative comparison was based on the followings: frequency and extent of bleeding, quality of visibility, perception of pain during the use of the instrument and duration of the operation. Postoperative comparison is based on 318 procedures. Comparison was based on: frequency of granuloma formation in the nasal mucosa at the site of the osteotomy, frequency of acquired nasal synechiae, frequency of important crusting reaction of the nasal mucosa; success rates after a minimum follow up of 6 months. RESULTS: Intraoperative haemorrhages were fewer and smaller in the diode laser assisted procedures than in ECI assisted procedures; visibility was better with the diode laser; the use of the diode laser was painless versus 24% of patients complaining of pain during the use of electro-cautery. The duration of the procedure was shorter with the diode laser (29'30 vs 37'). In the postoperative follow-up frequency of granuloma formation was equal with the two instruments, synechiae were fewer with the diode laser (11% vs 22%) just like crusting reaction of the nasal mucosa (7% vs 36%). Success rates were similar (diode laser: 91.94% vs EC: 86.66%). CONCLUSION: Because of the effeciency of the vaporization and coagulation, the diode laser, in comparison with the ECI, allows to shorten mean operative time, to improve the visibility and to decrase bleeding. Contrary to EC it's use is painless. Fewer important crusting reactions and fewer synechiae after diode laser assisted procedures tend to prove than postoperative inflammation and surgical trauma are smaller than with ECI. There is no statiscally signifant difference between the success rates of ENL laser diode assisted procedures and ENL ECI assisted procedures.

Age Factors↗

PubMed2001

Spatial partitioning of secretory cargo from Golgi resident proteins in live cells.

BACKGROUND: To maintain organelle integrity, resident proteins must segregate from itinerant cargo during secretory transport. However, Golgi resident enzymes must have intimate access to secretory cargo in order to carry out glycosylation reactions. The amount of cargo and associated membrane may be significant compared to the amount of Golgi membrane and resident protein, but upon Golgi exit, cargo and resident are efficiently sorted. How this occurs in live cells is not known. RESULTS: We observed partitioning of the fluorescent Golgi resident T2-CFP and fluorescent cargo proteins VSVG3-YFP or VSVG3-SP-YFP upon Golgi exit after a synchronous pulse of cargo was released from the ER. Golgi elements remained stable in overall size, shape and relative position as cargo emptied. Cargo segregated from resident rapidly by blebbing into micron-sized domains that contained little or no detectable resident protein and that appeared to be continuous with the parent Golgi element. Post-Golgi transport carriers (TCs) exited repeatedly from these domains. Alternatively, entire cargo domains exited Golgi elements, forming large TCs that fused directly with the plasma membrane. However, domain formation did not appear to be an absolute prerequisite for TC exit, since TCs also exited directly from Golgi elements in the absence of large domains. Quantitative cargo-specific photobleaching experiments revealed transfer of cargo between Golgi regions, but no discrete intra-Golgi TCs were observed. CONCLUSIONS: Our results establish domain formation via rapid lateral partitioning as a general cellular strategy for segregating different transmembrane proteins along the secretory pathway and provide a framework for consideration of molecular mechanisms of secretory transport.

Animals↗

PubMed2001

GATA1-Cre mediates Piga gene inactivation in the erythroid/megakaryocytic lineage and leads to circulating red cells with a partial deficiency in glycosyl phosphatidylinositol-linked proteins (paroxysmal nocturnal hemoglobinuria type II cells).

Patients with paroxysmal nocturnal hemoglobinuria (PNH) have blood cells deficient in glycosyl phosphatidylinositol (GPI)-linked proteins owing to a somatic mutation in the X-linked PIGA gene. To target Piga recombination to the erythroid/megakaryocytic lineage in mice, the Cre/loxP system was used, and Cre was expressed under the transcriptional regulatory sequences of GATA-1. Breeding of GATA1-cre (G) transgenic mice with mice carrying a floxed Piga (L) allele was associated with high embryonic lethality. However, double-transgenic (GL) mice that escaped early recombination looked healthy and were observed for 16 months. Flow cytometric analysis of peripheral blood cells showed that GL mice had up to 100% of red cells deficient in GPI-linked proteins. The loss of GPI-linked proteins on the cell surface occurred late in erythroid differentiation, causing a proportion of red cells to express low residual levels of GPI-linked proteins. Red cells with residual expression of GPI-linked proteins showed an intermediate sensitivity toward complement and thus resemble PNH type II cells in patients with PNH. Recombination of the floxed Piga allele was also detected in cultured megakaryocytes, mast cells, and eosinophils, but not in neutrophils, lymphocytes, or nonhematopoietic tissues. In summary, GATA1-Cre causes high-efficiency Piga gene inactivation in a GATA-1-specific pattern. For the first time, mice were generated that have almost 100% of red cells deficient in GPI-linked proteins. These animals will be valuable to further investigate the consequences of GPI-anchor deficiency on erythroid/megakaryocytic cells.

Animals↗

PubMed2001

Cholesterol and Alzheimer's disease: is there a link?

The Abeta-amyloid peptide (Abeta), the main component of amyloid plaques, is derived by proteolytic cleavage from the amyloid precursor protein (APP). Epidemiologic and biochemical data suggest a link between cholesterol, APP processing, Abeta, and Alzheimer's disease. Two recent epidemiologic studies indicate that there is a decreased prevalence of AD associated with the use of cholesterol-lowering drugs that inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase inhibitors or statins). Experiments in cell culture and in vivo demonstrate that treatment with statins reduces production of Abeta. The authors discuss how cholesterol might modulate Abeta deposit formation. As neurons receive only small amounts of exogenous cholesterol, statins that efficiently cross the blood-brain barrier may reduce the amount of neuronal cholesterol below a critical level. Decreased neuronal cholesterol levels inhibit the Abeta-forming amyloidogenic pathway possibly by removing APP from cholesterol- and sphingolipid-enriched membrane microdomains. In addition, depletion of cellular cholesterol levels reduces the ability of Abeta to act as a seed for further fibril formation. These intriguing relationships raise the hopes that cholesterol-lowering strategies may influence the progression of AD.

Aged↗

PubMed2001

FES-Cre targets phosphatidylinositol glycan class A (PIGA) inactivation to hematopoietic stem cells in the bone marrow.

A somatic mutation in the X-linked phosphatidylinositol glycan class A (PIGA) gene causes the loss of glycosyl phosphatidylinositol (GPI)-linked proteins on blood cells from patients with paroxysmal nocturnal hemoglobinuria. Because all blood cell lineages may be affected it is thought that the mutation occurs in a hematopoietic stem cell. In transgenic mice, germline transmission of an inactive Piga gene is embryonic lethal. To inactivate the murine Piga gene in early hematopoiesis we therefore chose conditional gene inactivation using the Cre/loxP system. We expressed Cre recombinase under the transcription regulatory sequences of the human c-fes gene. FES-Cre inactivated PIGA in hematopoietic cells of mice carrying a floxed Piga allele (LF mice). PIGA(-) cells were found in all hematopoietic lineages of definitive but not primitive hematopoiesis. Their proportions were low in newborn mice but subsequently increased continuously to produce for the first time mice that have almost exclusively PIGA(-) blood cells. The loss of GPI-linked proteins occurred mainly in c-kit(+)CD34(+)Lin(-) progenitor cells before the CFU-GEMM stage. Using bone marrow reconstitution experiments with purified PIGA(-) cells we demonstrate that LF mice have long-term bone marrow repopulating cells that lack GPI-linked proteins, indicating that recombination of the floxed Piga allele occurs in the hematopoietic stem cell.

Animals↗

PubMed2001

Simvastatin strongly reduces levels of Alzheimer's disease beta -amyloid peptides Abeta 42 and Abeta 40 in vitro and in vivo.

Recent epidemiological studies show a strong reduction in the incidence of Alzheimer's disease in patients treated with cholesterol-lowering statins. Moreover, elevated Abeta42 levels and the varepsilon4 allele of the lipid-carrier apolipoprotein E are regarded as risk factors for sporadic and familial Alzheimer's disease. Here we demonstrate that the widely used cholesterol-lowering drugs simvastatin and lovastatin reduce intracellular and extracellular levels of Abeta42 and Abeta40 peptides in primary cultures of hippocampal neurons and mixed cortical neurons. Likewise, guinea pigs treated with high doses of simvastatin showed a strong and reversible reduction of cerebral Abeta42 and Abeta40 levels in the cerebrospinal fluid and brain homogenate. These results suggest that lipids are playing an important role in the development of Alzheimer's disease. Lowered levels of Abeta42 may provide the mechanism for the observed reduced incidence of dementia in statin-treated patients and may open up avenues for therapeutic interventions.

Alzheimer Disease↗

PubMed2001

Interleukin-1beta induces expression of neuropeptide Y in primary astrocyte cultures in a cytokine-specific manner: induction in human but not rat astrocytes.

Previous studies have demonstrated that astrocyte cultures express neuropeptide Y (NPY) in a regulated manner, namely, phorbol ester leads to an increase in proNPY-mRNA and NPY production. In this respect, the behavior of astrocytes derived from the human fetal or rat neonatal brain is similar (Regul. Pept. 75 (1998) 293). Since astrocytes can be exposed to high levels of IL-1beta, we addressed the question: Does IL-1beta regulate NPY expression by the astrocytes? Primary astrocytes derived from the human fetal or rat neonatal cortex were cultured in serum-free medium. IL-1beta, but not IL-6 or TNF-alpha, led to an increase in NPY production dose-dependently. IL-1beta action manifested in the human but not in the rat astrocytes and it was completely abolished by IL-1 receptor antagonist. The responsiveness to IL-1beta did not diminish upon sub-culture of the astrocytes (five passages). In addition, IL-1beta led to an increase in the abundance of proNPY-mRNA, which was preceded by a rapid and transient increase in cFos-mRNA and a rapid and sustained increase in JunB-mRNA. In contrast to cFos/JunB, IL-1beta did not alter the abundance of cJun-mRNA. In summary, we demonstrate that IL-1beta induction of NPY expression in astrocytes is species- and cytokine-specific and that IL-1 receptor is involved. Moreover, induction of NPY expression is preceded by a rapid increase in the expression of two transcription factors (cFos, JunB) that have been previously (Oncogene 9 (1994) 2369; J. Neurochem. 70 (1998) 1887) implicated in transcriptional regulation of the human NPY gene.

Animals↗

PubMed2001

Determination of phenolic acids and flavonoids of apple and pear by high-performance liquid chromatography.

A new HPLC stationary phase has been applied to the analysis of phenolic acids and flavonoids with diode array and mass spectrometric detection. The separation of 26 standard compounds was achieved within 1 h. The stationary phase displayed excellent resolution especially of flavonol glycosides. The analytical system has been used for the determination of phenolic compounds in apple pomace and apple juice, and in extracts of pear fruits of different cultivars. Apple pomace was found to be a promising source of phenolics. However, yields are affected by the drying conditions applied. Furthermore, the applicability of the analytical system for the authenticity control of apple and pear juice was demonstrated by determination of characteristic quercetin and isorhamnetin glycosides, and dihydrochalcones, respectively. Since isorhamnetin-3-glucoside was present in all pear cultivars investigated, the usefulness of arbutin as a specific marker of pear products appears to be doubtful.

Chromatography, High Pressure Liquid↗

PubMed2001

Multicolour imaging of post-Golgi sorting and trafficking in live cells.

The biogenesis and maintenance of asymmetry is crucial to many cellular functions including absorption and secretion, signalling, development and morphogenesis. Here we have directly visualized the segregation and trafficking of apical (glycosyl phosphatidyl inositol-anchored) and basolateral (vesicular stomatitis virus glycoprotein) cargo in living cells using multicolour imaging of green fluorescent protein variants. Apical and basolateral cargo segregate progressively into large domains in Golgi/trans-Golgi network structures, exclude resident proteins, and exit in separate transport containers. These remain distinct and do not merge with endocytic structures suggesting that lateral segregation in the trans-Golgi network is the primary sorting event. Fusion with the plasma membrane was detected by total internal reflection microscopy and reveals differences between apical and basolateral carriers as well as new 'hot spots' for exocytosis.

Adenoviridae↗