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Biomedical subjects

R Giordani

Publications and source records attributed to R Giordani.

At least 19 recordsLinked to original sources
PubMed1999

Enzymatic and physiological properties of the tungsten-substituted molybdenum TMAO reductase from Escherichia coli.

The trimethylamine N-oxide (TMAO) reductase of Escherichia coli is a molybdoenzyme that catalyses the reduction of the TMAO to trimethylamine (TMA) with a redox potential of +130 mV. We have successfully substituted the molybdenum with tungsten and obtained an active tungsto-TMAO reductase. Kinetic studies revealed that the catalytic efficiency of the tungsto-substituted TMAO reductase (W-TorA) was increased significantly (twofold), although a decrease of about 50% in its kcat was found compared with the molybdo-TMAO reductase (Mo-TorA). W-TorA is more sensitive to high pH, is less sensitive to high NaCl concentration and is more heat resistant than Mo-TorA. Most importantly, the W-TorA becomes capable of reducing sulphoxides and supports the anaerobic growth of a bacterial host on these substrates. The evolutionary implication and mechanistic significance of the tungsten substitution are discussed.

Dose-Response Relationship, Drug↗
PubMed1998

Gamma-glutamyltransferase is a reliable marker for tubular effects of contrast media.

The aim of this study was to evaluate the usefulness of the measurement of urinary excretion of the brush-border enzyme gamma glutamyl-transferase (GGT), in comparison with that of alanine aminopeptidase (AAP), as a marker for tubular toxicity due to contrast media (CM). Urinary activities of AAP and GGT were measured prior to the administration of CM and 1, 3 and 5 days after in forty-nine adult renal patients undergoing a radiological examination with intravascular administration of CM. The behavior of GGT was similar to that of AAP. In fact, urinary activities of both AAP and GGT increased greatly after CM. This effect was maximal on the 1st day and statistically significant for both enzymes. Furthermore, on the 1st day a relevant increase of enzyme activity (at least +50% over the basal value) was observed in the same number of patients (67%) for AAP and GGT. The concordance between GGT and AAP variations was high and statistically significant. Finally, different variables (osmolarity, dose of CM, and baseline renal function of the patients) had a similar effect on urinary excretion of AAP and GGT. The repeatability of duplicated determinations of GGT resulted better than that of AAP. In conclusion, the good concordance of the results of GGT with those of AAP justifies the use of GGT as a marker for tubular effects due to CM. Furthermore, the measurement of GGT has a better repeatability than that of AAP.

Adult↗
PubMed1998

Urinary excretion of proteins and tubular enzymes in renal transplant patients.

The aim of this study was to evaluate, in renal transplant recipients with different function of the graft, the urinary excretion of some low molecular weight proteins and tubular enzymes frequently employed as indicators of tubular dysfunction. Urinary excretion of proteins and enzymes was measured in 51 renal transplant patients and, for comparison, in 73 patients affected by different kidney diseases with various degrees of renal function. Values of urinary beta 2-microglobulin and retinol-binding protein higher than normal were found in most transplanted patients, even in those with good renal function. On the other hand, in renal patients the urinary excretion of low molecular weight proteins was high only when creatinine clearance was lower than 30 mL/min/1.73 m2. Furthermore, an increased urinary excretion of tubular enzymes was found in a higher number of transplanted patients than of renal patients. This behavior was particularly evident for lysosomal enzyme N-acetyl-beta-D-glucosaminidase. In conclusion, a tubular dysfunction occurs in the transplanted kidneys, even in those with well preserved glomerular function.

Adult↗
PubMed1998

[Comparative analysis of 2 thromboplastins].

BACKGROUND: This study was performed to evaluate the prothrombin time in normal healthy people (102 subjects) by means of two thromboplastins. METHODS: Dade Thromboplastin IS (rabbit brain thromboplastin) and Dade Innovin (recombinant tissue factor) were used. Derived fibrinogen, Claus fibrinogen and in vitro sensibility of these thromboplastins to known amount of heparin were also measured. RESULTS: A different behaviour of prothrombin time measurement linked to different thromboplastin sensibility connected to the age was observed. A different fibrinogen (Claus and derived) behaviour connected to the age that may help to explain thromboplastin sensibility difference with the age was also observed. Finally different sensibility of these two thromboplastins to heparin in vitro was observed. CONCLUSIONS: This result should be considered when anticoagulation is started with oral anti coagulant drug and heparin together.

Adult↗
PubMed1998

[A new test for monitoring heparin therapy].

A simple and easy assay for plasma heparin measurement (international units/ml) is described. The method is based upon the heparin neutralization and titration by polybrene. Heparin biological activity is measured first by activated partial thromboplastin time prolongment and then by means of polybrene titration: plasma heparin concentration was evaluated in international units/ml (IU/ml). The design and properties of this method are reported. Application in clinical practice of monitoring heparinization during hemodialysis is evaluated.

Anticoagulants↗
PubMed1997

Kinetics of membrane-bound nitrate reductase A from Escherichia coli with analogues of physiological electron donors--different reaction sites for menadiol and duroquinol.

We have compared the steady-state kinetics of wild-type nitrate reductase A and two mutant forms with altered beta subunits. To mimic conditions in vivo as closely as possible, we used analogues of the physiological quinols as electron donors and membranes with overexpressed nitrate reductase A in preference to a purified alpha beta gamma complex. With the wild-type enzyme both menadiol and duroquinol supply their electrons for the reduction of nitrate at rates that depend on the square of the quinol concentration, menadiol having the higher catalytic constant. The results as a whole are consistent with a substituted-enzyme mechanism for the reduction of nitrate by the quinols. Kinetic experiments suggest that duroquinol and menadiol deliver their electrons at different sites on nitrate reductase, with cross-inhibition. Menadiol inhibits the duroquinol reaction strongly, suggesting that menaquinol may be the preferred substrate in vivo. To examine whether electron transfer from menadiol and duroquinol for nitrate reduction requires the presence of all of the Fe-S centres, we have studied the steady-state kinetics of mutants with beta subunits that lack an Fe-S centre. The loss of the highest-potential Fe-S centre results in an enzyme without menadiol activity, but retaining duroquinol activity; the kinetic parameters are within a factor of two of those of the wild-type enzyme, indicating that this centre is not required for the duroquinol activity. The loss of a low-potential Fe-S centre affects the activity with both quinols: the enzyme is still active but the catalytic constants for both quinols are decreased by about 75%, indicating that this centre is important but not essential for the activity. The existence of a specific site of reaction on nitrate reductase for each quinol, together with the differences in the effects on the two quinols produced by the loss of the Fe-S centre of +80 mV, suggests that the pathways for transfer of electrons from duroquinol and menadiol are not identical.

Escherichia coli↗
PubMed1997

A synergistic effect of Carica papaya latex sap and fluconazole on Candida albicans growth.

A mixture of Carica papaya latex (0.41 mg protein ml-1) and fluconazole (2 micrograms ml-1) showed a synergistic action on the inhibition of Candida albicans growth. Thus, with this mixture an equivalent inhibition rate was observed to that obtained when C. albicans was cultured in a medium supplemented with a two-fold concentration (4 micrograms ml-1) of fluconazole alone. This synergistic effect resulted in partial cell wall degradation as indicated by transmission electron microscopy observations. An increase of fluconazole concentration from 2 micrograms ml-1 to 4 micrograms ml-1 involved a small decrease of MIC 80% from latex (150 to 130 micrograms protein ml-1). Measure of MIC 80% from fluconazole mixed with latex in a subinhibitory concentration (85 micrograms protein ml-1) allows the determination of an effective fluconazole concentration (4 micrograms ml-1) inferior to mean plasmatic dose observed in human therapy. The potential therapeutic use of latex in combination with a synthetic antifungal is discussed.

Antifungal Agents↗
PubMed1997

Coagulation activation in extracorporeal hemodialysis.

The authors evaluated the behavior of protein C activity, factor X and factor VII coagulant activity and serum lipoprotein(a) before and after dialytic treatment in patients on maintenance hemodialysis. They observed depressed protein C activity that significantly (p < 0.005) increased and became normal immediately after hemodialysis while factor X and factor VII increased (p < 0.01; p < 0.05) despite heparinization together with amount of serum lipoprotein(a). In vitro incubation (30' at 37 degrees C) of uremic and healthy blood showed a decrease in serum lipoprotein(a) concentration. After heparin addition (final concentration 0.5 U/ml) lipoprotein(a) increased in the uremic blood only. The clinical and physiopathological implications of these results are discussed.

Adult↗
PubMed1996

Tubular toxicity is the main renal effect of contrast media.

The aim of this study is to evaluate the effects of contrast media on both tubular and glomerular function. Different parameters of tubular and glomerular function were determined before and at 1, 3, and 5 days after the intravascular administration of contrast media in 100 adult renal patients (plasma creatinine 0.6-10.8 mg/dL, mean: 1.3). Urinary activities of five tubular enzymes (alanine aminopeptidase, gamma-glutamyltransferase, alkaline phosphatase, lactate dehydrogenase, N-acetyl-beta-D-glucosaminidase) increased significantly on the first day after the administration of contrast media, indicating a tubular damage. Glomerular filtration rate and the conventional tests of glomerular function (plasma creatinine, creatinine clearance, and urinary proteins) presented only slight variations after the administration of contrast media. In conclusion, contrast media principally affected the renal tubule (as demonstrated by enzymuria), while their effects on glomerular function were very mild.

Acetylglucosaminidase↗
PubMed1996

Glomerular and tubular effects of contrast media diatrizoate and iopromide.

The aim of this study is to evaluate the nephrotoxicity of two contrast media (CM), with different physicochemical characteristics: diatrizoate (ionic high-osmolar), iopromide (nonionic low-osmolar). Intravenous urography was performed in 34 patients: 17 were examined with diatrizoate and 17 with iopromide, randomly assigned. Different parameters of glomerular and tubular function were measured before and at 6, 24, and 48 h after urography. Both contrast media induced a reversible increase of urine enzymes, which was significantly higher after diatrizoate. In particular, diatrizoate determined a relevant increase of brush border enzymes gamma-glutamyltransferase (GGT) and alkaline phosphatase (ALP) and of cytosolic enzyme lactate dehydrogenase (LDH), while, after iopromide increases of urinary enzymes were less evident and were significant only for GGT and ALP. In addition, diatrizoate affected other tubular functions (clearances of phosphorus and uric acid) and slightly decreased glomerular function in a few patients. In no case did these glomerular and tubular effects have a clinical relevance. In conclusion, the nonionic low-osmolar contrast medium iopromide appeared less nephrotoxic than diatrizoate. The cost-benefit ratio needs further examination.

Alkaline Phosphatase↗
PubMed1996

Renal effects of prolonged antihypertensive treatment with diltiazem.

The effects of diltiazem (DTZ) treatment on blood pressure, renal function and renal hemodynamics over a six week period of therapy were evaluated in 14 adult patients with mild to moderate hypertension. Their creatinine clearances were 64 to 153 ml/min. After a week of treatment with placebo, DTZ was administered orally at a daily dose of 120 mg b.i.d. Blood pressure decreased from a mean value of 152/99 mm Hg (+/-13/6 SD) up to 144/91 (+/-17/8, P < 0.005) in the supine position and from 149/107 (+/-14/9) to 141/96 (+/-16/9, P < 0.005) in standing position. Heart rate decreased from 74 (+/-9) to 69 (+/-8). Plasma urea, creatinine, uric acid and their clearances as well as GFR and ERPF remained stable throughout the trial. Plasma glucose increased from 81 (+/-15) mg/dl to 98 (+/-30, P < 0.05) and plasma potassium decreased from 4.0 mEq/liter to 3.7 (+/-0.3, P < 0.005). Plasma cholesterol and triglycerides were unmodified. DTZ is an effective antihypertensive agent which does not significantly affect renal function. The effects on plasma glucose and potassium require periodical check-ups of these parameters.

Adult↗
PubMed1996

Zidovudine glucuronidation in human liver: interindividual variability.

Zidovudine 3'-azido-3'-deoxythymidine is the drug chosen for the treatment of patients suffering from AIDS; zidovudine being a potent inhibitor of HIV replication. The drug is extensively metabolized by conjugation with glucuronic acid into an inactive compound, and 30-40% of the dose is eliminated presystemically. We studied the variability and characterized the frequency distribution of the activity of zidovudine glucuronosyl transferase in 93 specimens of human liver. A rapid and reproducible radiometric assay for the glucuronidation of 14C-zidovudine is reported. The method is based on the extraction of the unreacted zidovudine into organic solvents and the radioactivity of the unextractable zidovudine glucuronide was measured in the aqueous phase residue. The rate of zidovudine glucuronidation was neither sex- nor age-dependent, ranged over 1 order of magnitude, and was positively skewed. The possibility that endogenous bilirubin should interact with glucuronidation of zidovudine was explored and the endogenous concentration of bilirubin was measured in the microsomal preparations of 59 liver samples. The final concentration of bilirubin in the assay mixture for zidovudine glucuronidation ranged between 2.2 and 13.2 microM and did not interact with the rate of zidovudine glucuronidation. The kinetics of glucuronosyl transferase towards zidovudine was studied in 20 livers, Michaelis-Menten kinetics were observed and the K(m) estimate ranged over 2-fold with an average of 2.89 mM. These in vitro results are consistent with the view that the rate of glucuronidation varies over 1 order of magnitude in the human liver and its distribution is positively skewed. This variability may modulate the patient's exposition to zidovudine and thereby the efficacy of therapy.

Adult↗
PubMed1996

[Coagulation in hemodialysis].

The authors have evaluated the behaviour of protein C activity, factor X and factor VII coagulant activity, and serum lipoprotein(a) before and after haemodialytic treatment in the plasma of patients on maintenance haemodialysis. The plasma level of protein C activity, depressed before haemodialysis, significantly increased during the course of haemodialysis; factor X and factor VII increased as well despite heparinization; serum lipoprotein(a) was abnormally elevated before haemodialysis and did not change after haemodialysis. In vitro incubation (30' at 37 degrees C) of uremic and healthy blood samples resulted in a decrease of serum lipoprotein(a) concentration. After heparin addition (final concentration 0.5 U/ml) lipoprotein(a) became higher in uremic blood only.

Adult↗
PubMed1995

Kinetic studies of a soluble alpha beta complex of nitrate reductase A from Escherichia coli. Use of various alpha beta mutants with altered beta subunits.

A soluble alpha beta complex of nitrate reductase can be obtained from a strain of Escherichia coli that lacks the narI gene and expresses only the alpha and beta subunits. The beta subunit contains four Fe-S centres and the alpha subunit contains the molybdenum cofactor, which is the site at which nitrate is reduced. Despite the lack of the gamma subunit of the complete enzyme, this complex can still catalyse the reduction of nitrate with artificial electron donors such as benzyl viologen, so that it is suitable for studying the transfer of electrons between these two types of redox centre. To examine whether the electrons from reduced benzyl viologen are initially delivered to the Fe-S centres, or directly to the molybdenum cofactor, or both, we have studied the steady-state kinetics and the binding of benzyl viologen to the alpha beta complex and mutants alpha beta* with altered beta subunits. Reduction of the enzyme by reduced benzyl viologen in the absence of nitrate showed that all four Fe-S centres and the molybdenum cofactor could be reduced. Two classes of site with different equilibrium constants could be distinguished. The kinetic results suggest that benzyl viologen supplies its electrons directly to the molybdenum cofactor, at a rate showing a hyperbolic dependence on the square of the concentration of the electron donor. A reaction mechanism is proposed for the reduction of nitrate catalysed by the alpha beta complex of nitrate reductase with artificial electron donors.

Benzyl Viologen↗
PubMed1995

[An increase in bile acids in the serum of patients with chronic kidney failure].

Measurement of serum bile acids was performed in 86 uremic patients without any liver or bile tract diseases. Thirty-six patients (23 males and 13 females, aged 21-60 years) were on conservative dietary treatment, whereas 50 uremics (31 males and 19 females, aged 23-82 years) were on maintenance hemodialysis. The assays were made by means of enzymatic procedure and confirmed by RIA method too. Elevated serum concentrations of bile acids (> 6 mumol/L) were found in 24 out of the 86 uremics (27.9%), and the prevalence was similar in patients on conservative (10/36, 27.7%) and on dialysis treatment (14/50, 28%). Then, abnormally elevated concentrations of circulating bile acids are present in a quite high percentage of uremics both on hemodialysis and on conservative dietary therapy. The existence of a subclinical liver disease or an abnormal entero-hepatic cycle of bile acids might explain these findings.

Adult↗
PubMed1992

Determination of blood constituents reference values in broilers.

Eight hundred broilers were examined to define the reference values of nine blood constituents (total proteins, albumin, total and free cholesterol, triglycerides, aspartate aminotransferase (AST), alkaline phosphatase (ALP), calcium, and phosphorus). The broilers, coming from 20 different commercial poultry operations, were equally divided into different groups according to age (21 and 45 days), strain (Arbor Acres and Hybro), sex, and sampling season (summer or winter). Age and sampling season were the variation sources that most influenced the values of the hematochemical variables examined. The interaction of age with strain influenced total proteins total and free cholesterol, triglycerides, and ALP. The interaction of age with sampling season influenced all hematochemical constituents except triglycerides. Reference limits defined by .975 and .025 fractiles were computed for each blood constituent according to the significance of different variation sources and their combinations. Reference limits defined herein could be used as indicators of metabolic and health conditions of a poultry farm.

Age Factors↗