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Biomedical subjects

J Santoro

Publications and source records attributed to J Santoro.

At least 73 records · Page 4Linked to original sources

Assignment and conformation of neurotensin in aqueous solution by 1H NMR.

A complete assignment of exchangeable and unexchangeable proton resonances of neurotensin 1-13 in aqueous solution has been carried out with the help of its 1-8 and 8-13 fragments. To detect formation of a secondary structure, the effects of peptide fragmentation, temperature decrease, pH changes and addition of denaturing agents on the neurotensin 1H NMR spectrum were investigated. The small changes observed in all cases support the conclusion that neurotensin exists mainly as a flexible random coiled polypeptidic chain in aqueous solution in agreement with previous CD studies.

Hydrogen-Ion Concentration↗

1H NMR detection of cerebral myo-inositol.

A previously unassigned group of prominent multiplets of the 360 MHz 1H NMR spectrum of acid stable metabolite extracts from rat brain is shown to arise from free myo-inositol. This conclusion is derived from a systematic analysis of the high-resolution 1H NMR spectra of brain acid extracts, in which appropriate conditions and optimal proton signals have been selected for the quantitative analysis of up to 15 metabolites. Developmental variations in the cerebral content of myo-inositol could be readily detected using this approach, which provides a novel alternative to study myo-inositol metabolism under physiological or pathological conditions.

Animals↗

NH resonances of Ribonuclease S-peptide in aqueous solution. Low temperature n.m.r. study.

A detailed study of the NH resonances of Ribonuclease-S-peptide (1-19 N-terminal fragment of Ribonuclease A) has been carried out in H2O, pH 3.0, in the temperature range 1-31 degrees, and ionic strength 0-1 M. Individual assignments of all NH amide signals have been achieved by means of extensive double resonance experiments. The folding of S-peptide at low temperature has been monitored by examination of the several NH resonance parameters: first, the nonlinearity of chemical shift vs. temperature plots; second, the selective broadening observed for signals assigned to residues 3-13; and third, the decrease of 3JHNCH coupling constants belonging to this region of the polypeptide chain. All these results are in agreement with the formation of a folded structure at low temperature, which is similar to the one found for the S-peptide in the RNase S crystal.

Amides↗

On the fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated ribonuclease A S-peptide.

The fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated S-peptide (1-19 N-terminal fragment of Ribonuclease A) is demonstrated from the comparison of the helix contents, at 0 degrees C, of S-peptide and related peptides. Helix contents have been determined from the analysis of proton chemical shift vs. temperature curves. The observed data can be accounted for by assuming that two side-chain interactions contribute to stabilize the 3-13 helix of S-peptide, the salt bridges Glu 2- ... Arg 10+ and Glu 9-... His 12+, the former being more effective. The salt bridge Glu 9- ... Arg 10+ turns to a weaker interaction, a hydrogen bond Glu 2 (C delta = 0) ... Arg 10+, on protonation or esterification of the Glu 2 carboxylate.

Amino Acid Sequence↗

The effect of upper gastrointestinal endoscopy on arterial O2 tension in smokers and nonsmokers with and without premedication.

Fiberoptic upper gastrointestinal endoscopy has become an accepted procedure with recognized and acceptable complication rates. Recently, significant hypoxemia during upper gastrointestinal endoscopy has been identified. This report evaluates changes in arterial blood gases and investigates the effects of drugs, smoking, and length of procedure. Upper gastrointestinal endoscopy was performed on 60 patients--15 patients in four different groups. Group I and II were smokers and nonsmokers who received sedation; groups III and IV were smokers and nonsmokers who received no sedation. A significant drop in PaO2 was noted in each group. Sedation, length of procedure, or smoking did not affect the PaO2 levels significantly. No significant change in PaCO2 was noted in any of the four groups. A V/Q mismatch related to vasospasm and/or bronchospasm is proposed as the main reason for the hypoxemia.

Adolescent↗

Low-temperature 1H-NMR evidence of the folding of isolated ribonuclease S-peptide.

The temperature (-7 degrees C to 45 degrees C, pH 5.4) and pH (0 degrees C) dependence of 1H chemical shifts of ribonuclease S-peptide (5 mM, 1 M NaCl) has been measured at 360 MHz. The observed variations evidence the formation of a partial helical structure, involving the fragment Thr-3-Met-13. Two salt-bridges stabilize the helix: those formed by Glu-9- ...His-12+ and Glu-2- ...Arg-10+. The structural features deduced from the 1H-NMR at low temperature for the isolated S-peptide are compatible with the structure shown by the same molecule in the ribonuclease S crystal.

Amino Acid Sequence↗

1H n.m.r. parameters of the N-terminal 19-residue S-peptide of ribonuclease in aqueous solution.

The 1H n.m.r. chemical shifts and the spin-spin coupling constants of the N-terminal 19-residue S-peptide of ribonuclease A have been measured in a 10 mM solution in D2O, pD 3.0, 27 degrees, at 300 MHz. The titration parameters for end groups Lys-1 and Ala-19 and side chains Lys-1, Glu-2, Lys-7, Glu-9, Arg-10, His-12 and Asp-14 have been determined at 90 MHz. An assignment of observed signals to individual residue protons based upon characteristic shifts, spectral analysis, double resonance, titration shifts and comparison with the spectrum of C-peptide (N-terminal 13-residue) is proposed. Differences in the observed chemical shifts, pKa's and titration shifts with reference to those proposed as "random coil" parameters are not large enough to assume the existence of a significant population of secondary structure in the conditions studied. The H alpha chemical shifts differences can be accounted for by the Phe-8 phenyl ring current for an extended peptide backbone conformation and appropriate values for the torsion angles chi 1 Phe-8 and chi 2 Phe-8.

Amino Acid Sequence↗

Carbon-13 NMR investigations on ribonuclease A.

The proposed interaction between the amino acid residues Asp 14 and His 48 of ribonuclease A has been confirmed by 13C-NMR spectroscopy. The titration behaviour of the resonance of the side-chain carboxyl group of Asp 14 suggests a pKa of 6.5--7.0 for His 48. An equilibrium between different conformation process of His 48. Upon this deprotonation a hydrogen bond between the side-chains of Asp 14 or His 48 and Tyr 25 seems to be formed as is suggested by the behaviour of a tyrosine C zeta resonance assigned to Tyr 25. One phenylalanine resonance broadens and moves upfield on the addition of the inhibitor Cyd-2'-P, being therefore assigned to Phe 120. The behaviour of this resonance suggests that the upfield shift results from the anisotropy of the cytidine ring. Three signals are assigned to the three Phe residues.

Animals↗

In vitro activity and pharmacokinetics of cefaclor in normal volunteers and patients with renal failure.

In both Mueller-Hinton agar (MHA) and antibiotic medium no. 1 (AB1) cefaclor was more active than cephalothin or cephalexin against Enterobacteriaceae. Its activity was equivalent to cephalexin against S. aureus in MHA. Cefaclor was particularly active against P. mirabilis. The activity of this antibiotic was greated in AB1 than in MHA. The inoculum effect was pronounced for cefaclor when compared with cephalothin, but cefaclor retained greater activity even against the higher inoculum. In volunteers with normal renal function, cefaclor produced slightly lower blood levels than those reported for cephalexin. Absorption after eating was decreased and delayed. Despite severe renal failure, substantial urine levels of antibiotic were still achieved. In contrast to cephalexin, plasma half-life for cefaclor was only moderately prolonged by renal failure (two-to-threefold) and only minimally shortened by haemodialysis. Adequate concentrations of cefaclor in sputum, active against common respiratory pathogens, could not be consistently demonstrated after the oral administration of a 1 gram dose of cefaclor.

Adult↗

13C NMR investigations on Npi-[13C1]carboxymethyl-histidine-119 ribonuclease.

The ribonuclease A derivative Npi-[13C1]carboxymethyl-histine-119 ribonuclease prepared by using [13C1]bromoacetate as alkylating reagent has been investigated with high resolution 13C NMR spectroscopy. In the 13C NMR spectra two carbon resonances of relatively high intensity appear which can be assigned to carboxyl groups attached to His-119 and Met-30, their intensity ratio being 10 : 1. The pH dependence of the carbon resonance of the carboxy-methyl group bound to the Npi of His-119 differs in the absence and presence of Cyd-2'-P, thus indicating that the catalytically inactive derivative does bind nucleotides. A mechanism of the alkylation reaction at pH 5.6 is proposed in which the epsilon-amino group of Lys-41 acts as the binding site for the carboxyl group of bromoacetate pushing the bromomethylene group towards the Npi of His-119 or the Ntau of His-12.

Histidine↗

Treatment of experimental Staphylococcus aureus endocarditis: comparison of cephalothin, cefazolin, and methicillin.

The effectiveness of cefazolin in Staphylococcus aureus endocarditis has been questioned because of in vitro inactivation by staphylococcal beta-lactamase. Cefazolin, although inactivated in vitro by S. aureus beta-lactamase, was as effective as cephalothin in the treatment of left-sided S. aureus endocarditis in rabbits. Cefazolin (20 mg/kg every 6 or 8 h), cephalothin (40 mg/kg every 6 h), and methicillin (40 mg/kg every 6 h), administered intramuscularly, were compared in the treatment of left-sided endocarditis caused in rabbits by a highly penicillin-resistant strain of S. aureus. The three antibiotics were all effective in reducing titers in vegetations. However, at the dose used, methicillin reduced the titers more rapidly than cephalothin or cefazolin. Cefazolin concentrations in serum were about double those achieved with cephalothin or methicillin. However, cefazolin was only half as active as methicillin and one-eighth as active as cephalothin in vitro in a serum assay. The half life in serum of cefazolin, cephalothin, and methicillin were each about 30 min. Serum bactericidal activities of the three antibiotics were very similar.

Animals↗

Pharmacology and efficacy of netilmicin.

Twenty-six patients, 20 to 77 years of age, were treated with netilmicin, mean dose 2 mg/kg every 8 h intramuscularly or in a 20-min intravenous infusion. The mean serum half-lives in patients with creatinine clearances of >/=90 ml/min and 60 to 90 ml/min were 3.2 and 3.4 h, respectively. In patients with serum creatinines of </=1.4 mg/100 ml and creatinine clearances of >/=60 ml/min, mean serum levels were 9.0 and 1.2 mug/ml, respectively, 5 to 15 min and 7.5 h post-intravenous infusion, and 7.1 and 1.7 mug/ml, respectively, 1 and 8 h post-intramuscular injection. Twenty-five patients had acute pyelonephritis; 7 of the 25 had bacteremia. The infecting bacteria were Escherichia coli (15), Proteus mirabilis (5), Pseudomonas aeruginosa (2), Klebsiella pneumoniae (1), Enterobacter hafniae (1), and both Proteus rettgeri and Proteus morganii (1). All were inhibited by 6.3 mug of netilmicin per ml, except for the P. rettgeri, which required 25 mug/ml for inhibition. Of 23 patients who could be evaluated, 19 were bacteriologically and clinically cured at follow-up. Of the remaining four, one relapsed, two became reinfected, and one was lost to follow-up. Five patients developed nephrotoxicity; two of the five had previous renal insufficiency. Three patients, one with abnormal renal function, developed ototoxicity detected only with audiograms. These studies suggest that netilmicin is effective in serious gram-negative bacillary infections, but is nephrotoxic and ototoxic in humans.

Adult↗

Pharmacology of cefaclor in normal volunteers and patients with renal failure.

After a 500-mg dose of cefaclor, the mean peak plasma level was 12.4 mug/ml and after a 250-mg dose it was 5 mug/ml in normal volunteers. Food intake significantly reduced absorption. Probenecid prolonged plasma levels. Mean plasma half-life in normal volunteers was 0.8 h. Only about 50% of the dose was excreted in the urine within 4 h in normal volunteers. Plasma half-life in patients with renal insufficiency was only about 3 h, which suggests that cefaclor may be eliminated by nonrenal mechanisms in humans. Urinary levels of cefaclor were adequate to inhibit susceptible pathogens even in patients with moderately severe renal failure. Plasma half-life during hemodialysis was 2.1 h and rose to 2.8 h after dialysis.

Adult↗

Rat model of experimental endocarditis.

A simple model of infective endocarditis was produced in rats. With the aid of a guide wire, polyethylene catheters were passed into the left ventricle through the right carotid artery of Sprague-Dawley rats weighing 300 to 350 g. A volume of 1 ml of an overnight culture of Streptococcus mitis, Staphylococcus aureus, or Streptococcus faecalis was intravenously injected 1 to 2 days after catheterization. Bacterial titers of Streptococcus mitis in vegetations were about 10(4)-fold greater than in other tissues. Blood cultures were always positive after 6 h. Mortality was 19% at 1 week and 82% at 2 weeks. Catheters were pulled 24 h after infection, and vegetation titers of greater than 7.0 log10 colony-forming units per g were sustained at 5 days. In intravenously infected rats without catheters, blood and tissues were sterile after 3 to 5 days. With Staphylococcus aureus, vegetations had greater than 9.0 log10 colony-forming units and with Streptococcus faecalis 8.8 +/- 0.3 log10 colony-forming units per g at 2 days. The rat model of infective endocarditis should prove to be suitable for further pathological and therapeutic studies.

Animals↗

In vitro activity and clinical efficacy of clindamycin in the treatment of infections due to anaerobic bacteria.

Clindamycin, rosamicin, josamycin, and metronidazole had similar inhibitory activity against 29 clinical isolates of Bacteroides fragilis, i.e., 100% of strains were inhibited by 0.8 microng of metronidazole or josamycin/ml and 100% by 1.6 microng of clindamycin or rosamicin/ml. Metronidazole was bactericidal against 97% of the isolates, and clindamycin or rosamicin (in concentrations of 1.6 microng/ml) was bactericidal against 80%. Erythromycin and josamicin were the least bactericidal agents in vitro. Thirty-two patients with pleuropulmonary and intraabdominal or pelvic infections caused by anaerobic bacteria were treated with clindamycin. Cure was achieved in 27 patients. In another group of 37 patients treated with parenteral clindamycin, diarrhea developed in 30% and was significantly more common in those patients with abdominal or pelvic infection. Only one patient developed pseudomembranous colitis. These observations suggest that clindamycin is an excellent and relatively safe antibiotic for treatment of infections caused by anaerobes when combined with surgery or with other antibiotics selected for activity against aerobic gram-negative bacilli.

Aminoglycosides↗

In vitro activity of cefaclor, a new orally administered cephalosporin antibiotic.

The in vitro antibacterial activity of cefaclor, cephalothin, and cephalexin against 261 clinical isolates of Staphylococcus aureus and Enterobacteriaceae was compared. Cefaclor and cephalexin were about equally active against S. aureus. Cefaclor was the most active cephalosporin against Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae. The effect on the antimicrobial activity using a relatively high and low inoculum was pronounced for cefaclor when compared with that of cephalothin.

Bacteria↗

In vitro activity of josamycin and rosamicin against Bacteroides fragilis compared with clindamycin, erythromycin, and metronidazole.

The inhibitory and bactericidal activities of josamycin and rosamicin against 29 clinical isolates of Bacteroides fragilis were compared with those of clindamycin, erythromycin, and metronidazole by a broth dilution technique. Josamycin and rosamicin had similar inhibitory activity to metronidazole and clindamycin. Rosamicin had similar bactericidal activity to clindamycin but was less bactericidal than metronidazole (the most bactericidal agent tested). Josamycin was slightly more bactericidal than erythromycin (the least bactericidal agent tested), but less so than rosamicin and clindamycin.

Aminoglycosides↗