Photo-induced formation of radical anion peptides. Electron photodetachment dissociation experiments.
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Angiotensins↗
Biomedical subjects
Michel Broyer
Publications and source records attributed to Michel Broyer.
Spectroscopy of isolated, mass-selected tryptophan-Ag3 complexes: a model for photoabsorption enhancement in nanoparticle-biomolecule hybrid systems.
We wish to show that gas-phase studies of small metal cluster-biomolecule complexes provide fundamental insights into the mechanism leading to enhanced optical absorption in nanoparticle-biomolecular hybrid systems. Here we present, for the first time, a joint experimental and theoretical study of photoabsorption and photofragmentation of the silver trimer-tryptophan cation complex ([Trp.Ag3]+). We demonstrate that binding the metal cluster to a biomolecule leads to a remarkably high optical absorption as compared to the bare tryptophan or the [Trp.Ag]+ complex. As calculations show this arises due to coupling between the excitations in the metallic subunit with a charge transfer excitation to the tryptophan molecule.
Models, Biological↗
Electron photodetachment dissociation of DNA polyanions in a quadrupole ion trap mass spectrometer.
We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer single strands and 12-base pair double strands. In all cases, laser irradiation causes electron detachment from the multiply charged DNA anions. Electron photodetachment efficiency directly depends on the number of guanines in the strand, and maximum efficiency is observed between 260 and 275 nm. Subsequent collision-induced dissociation (CID) of the radical anions produced by electron photodetachment results in extensive fragmentation. In addition to neutral losses, a large number of fragments from the w, d, a*, and z* ion series are obtained, contrasting with the w and (a-base) ion series observed in regular CID. The major advantage of this technique, coined electron photodetachment dissociation (EPD) is the absence of internal fragments, combined with good sequence coverage. EPD is therefore a highly promising approach for de novo sequencing of oligonucleotides. EPD of nucleic acids is also expected to give specific radical-induced strand cleavages, with conservation of other fragile bonds, including noncovalent bonds. In effect, preliminary results on a DNA hairpin and on double strands suggest that EPD could also be used to probe intra- and intermolecular interactions in nucleic acids.
DNA↗
Optical properties of gas-phase tryptophan-silver cations: charge transfer from the indole ring to the silver atom.
We present a joint experimental and theoretical investigation of the electronic excitation spectra of the tryptophan-silver complex. The photodissociation spectrum of gas-phase [Trp-Ag]+ was measured from 215 to 330 nm using a quadrupole ion trap coupled to an optical parametric-oscillator laser. The calculated time-dependent density functional theory (TD-DFT) absorption spectra for different prototypes of structures are presented. Low-energy transitions that are experimentally observed are only calculated for the charge-solvation (CS) structures. These transitions are a signature of the metal-pi interaction in [Trp-Ag]+. The recorded spectrum is compared to a Boltzmann average of the absorption spectrum obtained from direct molecular dynamics (MD) simulations involving simultaneous transitions to excited states based on semiempirical configuration interaction (CI) calculations. The results demonstrate that charge transfer can be photoinduced from the indole ring to the silver atom.
Cations, Monovalent↗
UV photodissociation of phospho-seryl-containing peptides: laser stabilization of the phospho-seryl bond with multistage mass spectrometry.
Protonated precursor ions of phosphorylated peptides containing a tyrosyl residue have been subjected to UV laser-induced dissociation (LID) at a wavelength of 220 nm and to collision-induced dissociation (CID) in an ion trap. As expected, neutral loss of the phosphate group is one of the predominant fragmentation channels during CID together with H2O elimination. In contrast, LID leads mainly to the homolytic cleavage of the tyrosyl side chain and a restrained loss of the phosphate group. Interestingly, the intensity of the dephosphorylated fragment ion is greatly minimized when CID is carried out next on the radical precursor ion of the singly and doubly charged species.
Amino Acid Sequence↗
[Corticosensitive nephrotic syndrome (or nephrosis) in children. Therapeutic guideline proposed by the Pediatric Society of Nephrology].
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Adrenal Cortex Hormones↗
Entropic stabilization of isolated beta-sheets.
Temperature-dependent electric deflection measurements have been performed for a series of unsolvated alanine-based peptides (Ac-WA(n)-NH(2), where Ac = acetyl, W = tryptophan, A = alanine, and n = 3, 5, 10, 13, and 15). The measurements are interpreted using Monte Carlo simulations performed with a parallel tempering algorithm. Despite alanine's high helix propensity in solution, the results suggest that unsolvated Ac-WA(n)-NH(2) peptides with n > 10 adopt beta-sheet conformations at room temperature. Previous studies have shown that protonated alanine-based peptides adopt helical or globular conformations in the gas phase, depending on the location of the charge. Thus, the charge more than anything else controls the structure.
Alanine↗
Photodissociation spectroscopy of trapped protonated tryptophan.
We have coupled a quadrupole ion trap with a frequency doubled optical parametric oscillator laser. The photodissociation spectrum of the protonated tryptophan ion from 215 to 320 nm is reported. The yields of fragmentation on each mass channel as a function of the laser wavelength were obtained. We also report experiments involving multiple stages of laser induced dissociation and discuss possible structures for the fragmentation products.
Gas Chromatography-Mass Spectrometry↗
Specific photodissociation of peptides with multi-stage mass spectrometry.
We report collision-induced dissociation (CID) and laser-induced dissociation (LID) performed at different wavelengths between 220 and 280 nm of the peptides leucine-enkephalin (protonated) and gramicidin A (sodiated). Hydrogen-atom losses and side-chain cleavages were observed in LID experiments. These losses depend on the laser wavelength and lead to the formation of radical ions. The fragmentations of these radicals, which are not observed in CID experiments, were investigated in multi-stage mass spectrometry experiments.
Enkephalin, Leucine↗
Glucocorticoid pharmacokinetics and growth retardation in children with renal transplants.
Long-term glucocorticoid treatment contributes to the growth retardation in children after renal transplantation. We investigated whether determination of prednisone (PN) and prednisolone (PL) in plasma and PN, PL, and 6-beta-hydroxyprednisolone (betaOH-PL) in urine could help to predict growth. PN and PL pharmacokinetics were studied in 36 children, from 5 to 15 years of age, receiving daily (D) or alternate-day (AD) oral PN treatment. Statural growth velocity was evaluated over a 1-year period. We compared three groups of children according to the growth kinetics during the study year (catch-up, stable, or decline) for clinical and pharmacokinetic parameters. A multiple linear regression analysis was performed in order to determine pharmacokinetic parameters able to explain height 1 year after inclusion. Height at the beginning of the study, creatinine clearance, and type of D or AD treatment explained 94.2% of height variance 1 year after inclusion. Only PL clearance was associated with growth evolution, but introduction of PL clearance in the multivariate model did not improve the variance of height accounted for by the previous model. We, therefore, do not recommend using glucocorticoid pharmacokinetics to predict growth retardation in children with renal transplantation.
Adolescent↗
Long-term social outcome of children after kidney transplantation.
BACKGROUND: There are few data concerning the social outcome at adult age of children who received a kidney transplant. The aim of this study was to collect information on this outcome in a cohort of 366 children who underwent transplantation between 1973 and 1985. METHODS: Information was obtained through a simple questionnaire in 244 patients. The mean age of the patients was 31.7 years, and they had undergone grafting at a mean age of 11.9 years. RESULTS: As of December 2000 or at last visit, 77% had a functioning graft. The mean height was 156.6 cm for male patients and 147.4 cm for female patients. The distribution of educational level was lower than national averages: 27.4% were at the lowest level versus 3% of the general population, 41.4% were at the middle level, 31.2% had reached the baccalaureate level, and 11% had followed a university cursus. Activity was similar to the general population: 73% had paid employment versus 72%, 6.5% were unemployed versus 10.5%, and 18.7% received a disablement pension. Among the 149 male patients, 39 (27%) had a marital life and 12 (8.3%) had children, whereas among the 95 female patients, 48 (50%) had a marital life and 26 (27%) had at least one child. Lodging was the parent's home in 46% and independent in 54%. Multivariate analysis showed a significant correlation between educational level, paid activity, marital life, and independent housing with final height. CONCLUSIONS: The long-term social outcome of patients who underwent grafting in childhood more than 15 years previously is encouraging. The importance of reaching a normal height is stressed.
Adolescent↗
Application of molecular beam deflection time-of-flight mass spectrometry to peptide analysis.
The application of molecular beam deflection time-of-flight mass spectrometry (MBD-TOFMS) to peptide identification is described. The technique permits a simultaneous measurement of molecular mass and electric dipole susceptibility. The mass and susceptibility are not strongly correlated, and the results can be presented as a two-dimensional map. The susceptibility provides a useful way to disperse isobaric and isomeric peptides, and at least for small peptides, the susceptibility is significantly different for different amino acid sequences. Results for peptides in the mass range 1000-2300 Da show that the mass and susceptibility lead to a higher identification score than mass spectra alone.
Algorithms↗
Direct probing of zwitterion formation in unsolvated peptides.
Molecular beam electric deflection measurements have been used to determine electric susceptibilities for small unsolvated alanine-based peptides. The electric susceptibility provides information about the charge distribution within the peptide and can be used to distinguish between zwitterionic and canonical forms. Measured electric susceptibilities for WAn peptides (n = 1-5) are similar to those for capped Ac-WAn-NH2 peptides (which cannot form zwitterions). Susceptibilities calculated using a simulated tempering-based approach are substantially larger for the zwitterionic form than for the canonical form. The measured susceptibilities are in good agreement with those calculated for the canonical form. For the larger peptides, the lowest potential energy structure found in the simulations is hairpin-like, while the lowest free energy structure found at room temperature is extended. The zwitterionic form is constrained by intramolecular interactions which make it entropically unfavorable.
Alanine↗
In vivo expression of putative LMX1B targets in nail-patella syndrome kidneys.
The nail-patella syndrome (NPS) is characterized by nail and bone abnormalities, associated with glomerular involvement in approximately 40% of patients. Typical glomerular changes consist of fibrillar material in the irregularly thickened glomerular basement membrane. NPS is inherited as an autosomal dominant trait and caused by heterozygous loss of function mutations in LMX1B, a member of the LIM homeodomain protein family. Mice with homozygous inactivation of the gene exhibit nail and skeletal defects, similar to those observed in patients, associated with glomerular abnormalities. Strong reduction in the glomerular expression of the alpha3 and alpha4 chains of type IV collagen, and of podocin and CD2AP, two podocyte proteins critical for glomerular function, has been observed in Lmx1b null mice. The expression of these proteins appeared to be regulated by Lmx1b. To determine whether these changes in podocyte gene expression are involved in the development of NPS nephropathy, using immunohistological techniques, we analyzed the podocyte phenotype and the renal distribution of type IV collagen chains in the kidneys of seven NPS patients with severe glomerular disease. We also examined the nature of the fibrillar material present within the glomerular extracellular matrix. The glomerular basement membrane fibrillar material was specifically labeled with anti-type III collagen antibodies, suggesting a possible regulation of type III collagen expression by LMX1B. The expression of the alpha3 and alpha4 chains of type IV collagen, and of podocin and CD2AP, was found to be normal in the seven patients. These findings indicate that heterozygous mutations of LMX1B do not appear to dramatically affect the expression of type IV collagen chains, podocin, or CD2AP in NPS patients.
Adaptor Proteins, Signal Transducing↗
Steroid-sensitive nephrotic syndrome: from childhood to adulthood.
BACKGROUND: The clinical presentation, treatment, and outcome of steroid-sensitive nephrotic syndrome (SSNS) during childhood have been extensively studied. Conversely, few data regarding the outcome in adulthood of childhood SSNS have been published previously. We undertook to conduct a retrospective study of the outcome in adulthood of a large cohort of patients diagnosed with an SSNS during childhood. METHODS: We identified all children born between 1970 and 1975 who had been admitted to our institution for an SSNS. Data regarding the outcome in adulthood of these patients were obtained through mailed questionnaires or phone calls to patients and/or their parents or through attending physicians. RESULTS: One hundred seventeen patients were identified. Data regarding the outcome of SSNS in adulthood were available for 102 patients (87.2%). Forty-three patients (42.2%) experienced at least one relapse of nephrotic syndrome in adulthood. By univariate analysis, young age at onset (<6 years) and more severe disease in childhood, indicated by a greater number of relapses (12.9 for adulthood relapsers versus 5.4 for adulthood nonrelapsers; P < 0.0001) and more frequent use of immunosuppressors (74.4% versus 31.6%; P < 0.0001) or cyclosporine (42.9% versus 7.3%; P < 0.0001) were predictive of the occurrence of SSNS relapse in adulthood. Conversely, relapse rate in the first 6 months of disease was not predictive of further relapses in adulthood. By multivariate analysis, only number of relapses during childhood was predictive of adulthood relapses (P < 0.0058). Long-term side effects of steroids were found in 44.2% of adulthood relapsers; the most frequent were osteoporosis and excess weight. CONCLUSION: The incidence of childhood SSNS relapses in adulthood was relatively high in our study. Further studies are required to assess long-term complications in adults with relapses and a history of prolonged steroid and immunosuppressor use.
Adolescent↗
A multicenter, open-label, pharmacokinetic/pharmacodynamic safety, and tolerability study of basiliximab (Simulect) in pediatric de novo renal transplant recipients.
BACKGROUND: Basiliximab (Simulect) has been shown to be safe and effective in adult renal transplant recipients, when used in combination with cyclosporine (Neoral) and corticosteroids. We report on the safety and preliminary efficacy of basiliximab in pediatric de novo renal transplant recipients. METHODS: This was an open-label, 12-month study of basiliximab in 41 patients (2 cohorts: <9 and 9 to <16 years). In phase 1, two intravenous (IV) bolus injections of basiliximab (12 mg/m ) were administered (before and 4 days postsurgery). In phase 2, two injections (<40 kg, 10 mg and > or =40 kg, 20 mg) were administered at the same time points. Most patients (26/41 [63%]) received cadaveric kidneys. Almost half of the patients had three human leukocyte antigen mismatches with the organ donors. Concurrent immunosuppression included Neoral and corticosteroids. Azathioprine was allowed after 28 days. RESULTS: All patients completed the 1-year study. The acute tolerability of basiliximab via IV bolus injection was good, without evidence of cytokine-release syndrome or acute local reactions. All patients experienced adverse events, but most (71%) were mild or asymptomatic. No deaths or malignancies occurred. The incidence and types of serious adverse events (59%) and serious infections (44%) were as expected in this patient population, and few were drug-related (7% and 5%, respectively). Thirty-eight patients (93%) had infections, mostly urinary tract infections, as expected for renal transplant patients. Six patients (15%) had drug-related adverse events. Biopsy-confirmed acute rejection episodes occurred in 6/41 (15%) of patients during the first 6 months posttransplantation and in 9/41 (22%) patients during the first 12 months. Five patients (12%) experienced graft loss, none of which were preceded by acute rejection episodes. CONCLUSIONS: Basiliximab is safe and well tolerated when administered by IV bolus injection in de novo pediatric renal transplant recipients. These preliminary data suggest that basiliximab, given in combination with cyclosporine and corticosteroids, is an effective immunosuppressive regimen for the prevention of acute rejection in pediatric renal transplantation.
Adolescent↗
A rational dosing algorithm for basiliximab (Simulect) in pediatric renal transplantation based on pharmacokinetic-dynamic evaluations.
BACKGROUND: The pharmacokinetics and immunodynamics of basiliximab were assessed in 39 pediatric de novo kidney allograft recipients to rationally chose a dose regimen for this age group. METHODS: In study part 1, patients were given 12 mg/m(2) of basiliximab by bolus intravenous injection before surgery and on day 4. An interim pharmacokinetic evaluation supported a fixed-dose approach for study part 2 in which infants and children received two 10-mg doses and adolescents received two 20-mg doses. Blood samples were collected over a 12-week period for analysis of basiliximab and soluble interleukin-2 receptor concentrations, flow cytometry, and screening for anti-idiotype antibodies. RESULTS: Basiliximab clearance in infants and children (n=25) was reduced by approximately half compared with adults from a previous study and was independent of age (1-11 years), weight (9-37 kg), and body surface area (0.44-1.20 m(2) ). Clearance in adolescents (12-16 years, n=14) approached or reached adult values. CD25-saturating basiliximab concentrations were maintained for 31+/-12 days in study part 1 with mg/m(2) dosing and for 36+/-14 days in study part 2 based on the fixed-dose regimen ( P=0.31). A single patient experienced a rejection episode during CD25 saturation. The duration of CD25 saturation in patients who experienced a rejection episode after desaturation did not differ from those who remained rejection-free for the full 6-month period: 34+/-6 days (n=6) vs. 35+/-14 days (n=33 patients); P=0.74. Anti-idiotype antibodies were detected in two patients; however, this did not influence the clearance of basiliximab or the duration of CD25 saturation. CONCLUSIONS: To achieve similar basiliximab exposure as is efficacious in adults, pediatric patients <35 kg should receive two 10-mg doses and those > or =35 kg should receive two 20-mg doses of basiliximab by intravenous infusion or bolus injection. The first dose is given before surgery and the second on day 4 after transplantation.
Algorithms↗