RESUMEN

Despite of improved survival of premature infants, the incidence of long term pulmonary complications, mostly associated with ventilation-induced lung injury, remains high. Non invasive ventilation (NIV) is able to reduce the adverse effects of mechanical ventilation. Although nasal continuous positive airway pressure (NCPAP) is an effective mode of NIV, traumatic nasal complications and intolerance of the nasal interface are common. Recently high flow nasal cannula (HFNC) is emerging as a better tolerated form of NIV, allowing better access to the baby's face, which may improve nursing, feeding and bonding. HFNC may be effective in the treatment of some neonatal respiratory conditions while being more user-friendly for care-givers than conventional NCPAP. Limited evidence is available to support the specific role, efficacy and safety of HFNC in newborns and to demonstrate efficacy compared with NCPAP; some studies suggest a potential role for HFNC in respiratory care of the neonate as a distinct non invasive ventilatory support. We present the preliminary data of a randomized clinical trial; the aim of this study was to assess efficacy and safety of HFNC compared to NCPAP in preterm newborns with mild to moderate respiratory distress syndrome (RDS).

Asunto(s)

RESUMEN

Transparent, ultrathin Pt electrodes permit the simultaneous electrochemical and spectroscopic investigation of self-assembled monolayers of electrochromic compounds. Voltage stimulations applied to the Pt substrate reversibly alter the redox state of the chemisorbed molecules and, hence, modulate the intensity of the light transmitted through the Pt/monolayer assembly.

RESUMEN

Nanosecond and picosecond absorption and emission spectroscopic techniques were applied to the investigation of the reactivity from the lowest excited states of some 6-fluoro-7-piperazino-4-quinolone-3-carboxylic acids (FQs) in aqueous media at neutral pH, in the absence and presence of different sodium salts. Following the detection of various transients, we proposed a mechanism for the cleavage of the carbon-fluorine bond that proceeded through different reaction pathways, dependent on the molecular structure and the characteristics of the medium. The drug lomefloxacin (LOM), a 6,8-difluoroquinolone derivative, underwent heterolytic cleavage of the C8-F bond from the excited singlet state. With the 6-monofluoroquinolone norfloxacin (NOR) and the corresponding 1,8-naphthyridinone enoxacin (ENX), the lowest singlet state was not significantly reactive and an important deactivation channel was intersystem crossing (ISC) to the triplet manifold. The lowest triplet state underwent cleavage of the C6-F bond through a solvent mediated process possibly via a cyclohexadienyl anionic adduct. In the presence of sulfite or phosphate buffer a novel defluorination mechanism, induced by electron transfer from the inorganic anions to the FQ triplet state, was observed. The correlation between the transients observed and the final photoproducts in the different media was elucidated.

Asunto(s)

RESUMEN

The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide, in homogeneous media and in the beta-cyclodextrin (beta-CD) cavity has been investigated. The photoreactivity of the free molecule has been rationalized on the basis of an intramolecular nitro to nitrite rearrangement followed by cleavage of the nitrite intermediate. The twisted geometry of the nitro group with respect to the aromatic plane plays a key role in triggering such a photoprocess. Incorporation of FM in the beta-CD cavity leads to dramatic effects on both the efficiency and the nature of the photochemical deactivation pathways of the guest molecule. A 20-fold increase in the FM photodecomposition quantum yield and the formation of photoproducts originated by both reduction of the nitro group and cleavage of the amide bond were observed in the presence of the macrocycle. Such a behavior cannot be attributed exclusively to the micropolarity of beta-CD and/or to its role as a reactant. The induced circular dichroism spectra and the nature of the photoproducts formed in these experimental conditions provide indications that the photoreactivity in the beta-CD microenvironment could likely be mediated by structural changes of FM upon complexation.

Asunto(s)

RESUMEN

The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP-) was studied in water and in 0.1 M phosphate buffer solutions in the pH range 5.7-11.0 by laser-induced optoacoustic spectroscopy (LIOAS, T range 9.5-31.6 degrees C). Upon exciting KP- with 355 nm laser pulses under anaerobic conditions, two components in the LIOAS signals with well-separated lifetimes were found (tau 1 < 20 ns; 250 < tau 2 < 500 ns) in the whole pH range, whereas a long-lived third component (4 < tau 3 < 10 microseconds) was only detected at pH < or = 6.1. The heat and structural volume changes accompanying the first step did not depend on pH or on the presence of buffer. The carbanion resulting from prompt decarboxylation within the nanosecond pulse (< 10 ns) drastically reduces its molar volume ([-18.9 +/- 2.0] cm3/mol) with respect to KP- and its enthalpy content is (256 +/- 10) kJ/mol. At acid pH (ca 6), a species is formed with a lifetime in the hundreds of ns. The enthalpy and structural volume change for this species with respect to KP- are (181 +/- 15) kJ/mol and (+0.6 +/- 2.0) cm3/mol, respectively. This species is most likely a neutral biradical formed by protonation of the decarboxylated carbanion, and decays to the final product 3-ethylbenzophenone in several microsecond. At basic pH (ca 11), direct formation of 3-ethylbenzophenone occurs in hundreds of ns involving a reaction with the solvent. The global decarboxylation reaction is endothermic ([45 +/- 15] kJ/mol) and shows an expansion of (+14.5 +/- 0.5) cm3/mol with respect to KP-. At low pH, the presence of buffer strongly affects the magnitude of the structural volume changes associated with intermolecular proton-transfer processes of the long-lived species due to reactions of the buffer anion with the decarboxylated ketoprofen anion.

Asunto(s)

RESUMEN

The effects of beta-cyclodextrin complexation on the photochemical and photosensitizing properties of tolmetin have been investigated. Absorption, emission, circular dichroism and NMR measurements were used to characterize the host-guest complex. Nanosecond laser flash photolysis and steady-state photolysis experiments were performed to clarify the photoreactivity of the drug in the macrocycle. The decarboxylation of the drug is markedly reduced upon inclusion and the rate constants of the decay of the transient intermediates involved in tolmetin photodecomposition were slowed down due to their incorporation in the hydrophobic cavity. This also influenced the distribution of the stable photoproducts. A remarkable cyclodextrin-mediated protection against the tolmetin-photoinduced damage on biological substrates was observed. A rationale for these biological effects is provided.

Asunto(s)

RESUMEN

The potential phototoxic activity of naphazoline (NP), 2-(1-naphthylmethyl)imidazoline, was investigated by studying its photoreactivity toward DNA. Photocleavage studies combined with laser flash photolysis experiments provide clear evidence that the transient species produced under NP photolysis react with DNA, thereby promoting its breakage under both aerobic and anaerobic conditions. Hydrated electrons and nitrogen-centered radicals are involved in the photodamage under anaerobic conditions. Hydroxyl radicals generated by Haber-Weiss reaction seem to initiate the photocleavage observed under aerobic conditions. A photodynamic mechanism involving the participation of singlet oxygen does not seem to play a crucial role in the photoinduced DNA breakage. The interaction between the NP and the biopolymer is also investigated by using both steady state and time-resolved spectroscopy.

Asunto(s)

RESUMEN

The UVA irradiation of 9-fluoro-2,3-dihydro-10-4'-methyl-1' -piperazinyl-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzo-thiazine-6-carboxylic acid, rufloxacin, a fluoroquinolone antibacterial that shows photosensitizing properties toward biological substrates, leads to formation of two main steady photoproducts characterized by a decarboxylation process and an opening of the piperazinyl ring, respectively. The deprotonation of the 10-piperazinyl group and the dissociation of the 6-carboxyl group of rufloxacin are strictly pH dependent. The photosensitizing activity was tested toward membranes as biological targets. Red blood cell hemolysis and lipid peroxidation were considered as markers of photosensitization. Ultraviolet A-induced damage is strongly influenced by the presence of oxygen, it is triggered by transient species, such as singlet oxygen and free radicals, photogenerated via rufloxacin irradiation, whereas no drug photoproduct is involved in the photosensitization process.

Asunto(s)

RESUMEN

A combined differential scanning calorimetry (DSC) and photosensitization study has been carried out on the interaction of several NSAID on DNA, both from calf thymus and pBR 322 plasmid. The investigated compounds were both non-steroidal anti-inflammatory drugs as well as compounds related to NSAIDs for structural similar properties, to find evidence for their ability to interact with DNA as a function of steric hindrance and polarity of the chemical structures. The considered NSAIDs were diflunisal (DFN, a salicylic derivative), naproxen (NAP), ketoprofen (KPF), suprofen (SPF) and tiaprofenic acid (TIA, arylpropionic acids). The structural criterion used was related to three different aromatic groups, biphenyl, naphthalene and benzophenone (BZP). In fact drug-DNA interaction can be revealed by variations of the enthalpies and temperatures of unfolding of DNA obtained by comparison of calorimetric peaks, where a decrease of the enthalpy is associated with the drug-DNA interaction, by engaging electrostatic bonds. Testing their ability in inducing DNA cleavage when UVA irradiated can evidence the photosensitizing properties of the drug. A good correlation was found between calorimetric and photosensitization studies. From the results obtained it can be reasonably supposed that the photocleavage depends only on the drug molecules bound to DNA.

Asunto(s)

RESUMEN

Abstract- The transient photochemistry of tolmetin (TM), 5-(p-toluoyl)-1-methyl-2-pyrrolyacetic acid, a drug belonging to the nonsteroidal anti-inflammatory class, has been studied in aqueous solution by using nanosecond laser flash photolysis techniques. The photoreactivity of TM is characterized by an adiabatic pathway involving a triplet carbanion as the key intermediate in the photodecarboxylation. A short-lived triplet is proposed as the precursor of this transient species. A minor channel for laser photodecomposition involving photoionization has also been identified. This latter photoprocess occurs predominantly through a biphotonic mechanism.

RESUMEN

The photosensitizing activity of enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- 1,8-naphthyridine-3-carboxilic acid (ENX), toward membranes and DNA has been studied, taking into account human erythrocyte photohemolysis, unilamellar liposome alterations and plasmid pBR322 DNA photocleavage. Hydroxyl radicals and an aromatic carbene generated from ENX photodefluorination seem to be the active intermediates involved in the photosensitization process. The steady-state photolysis products do not participate in the process. The mechanism of photosensitization responsible for the membrane damage depends on the oxygen concentration and follows a different path with respect to that operative for DNA cleavage. Between oxygenated radicals, the hydroxyl seems the species mainly responsible for membrane damage, whereas DNA cleavage is mainly produced by the carbene intermediate. A molecular mechanism of the photosensitization induced by ENX is proposed.

Asunto(s)

RESUMEN

The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a function of the temperature, the concentration and the presence of oxygen by steady-state and time-resolved photochemical techniques. The process is characterized by an activation energy of 9-10 kcal/mol, the precursor state being the lowest triplet which is of pi-pi* nature. The reactivity of the drug was also studied in the beta-cyclodextrin inclusion complex and an additional photoreaction involving the macrocycle as reactive species was observed. Representative NMR and circular dichroism measurements were performed. Singlet molecular oxygen formation was also investigated.

Asunto(s)

RESUMEN

The spectroscopic and photochemical behavior of Enoxacin (ENX), 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- 1,8-naphthyridine-3-carboxylic acid, has been investigated in aqueous solutions between pH 3.5 and pH 12. The absorption and emission properties of ENX are strongly affected by pH. The fluorescence quantum yield, 4 x 10(-3) at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH. The photodegradation quantum yield also depends on pH, being maximum in neutral conditions (ca 0.04). Nanosecond flash photolysis experiments confirm that the yield of absorbing transients is maximum at neutral pH while it decreases to zero at acid and alkaline pH. These results indicate that both the dissociation of the carboxylic group and the protonation of the piperazinyl residues are key steps for the formation of the photochemically active form of ENX. Loss of F by heterolytic cleavage of the C-F bond is proposed to occur from the triplet state of the zwitterion with formation of a carbocation. A path for the evolution of this intermediate to the final product is also proposed.

Asunto(s)

RESUMEN

The inhibitory effect of Cu2+, Mn2+, Co2+, and I- on naproxen-induced photohemolysis was investigated. In order to better understand this effect, these ions were also tested for lipid peroxidation and protein crosslinking, which are among the main processes involved in erythrocyte membrane damage. The overall results support the hypothesis that metal cations act via a redox scavenging of the radicals which are produced on the lipid component of the membrane. This process occurs through hydrogen abstraction operated by photogenerated naproxen radicals. Moreover, copper can also act as a superoxide anion scavenger: its decay is noxious in photohemolysis, whereas it is not in lipid peroxidation. Metal cations, besides, are not able to scavenge protein crosslinking. On the other hand, iodide is able to reduce both processes because it acts as a heavy atom, favoring intersystem crossing to the unreactive triplet state of the drug, thus reducing naproxen photolysis and, as a consequence, the amount of the damaging species produced. This mechanism was supported by luminescence experiments performed in the absence and in the presence of iodide.

Asunto(s)

RESUMEN

Photocleavage of DNA induced by naproxen and the correlated protective effect by some inorganic ions have been considered. The presence of a DNA complex is suggested and only associated naproxen seems to be responsible for the cleavage, for which the quantum yield of single strand breaks was calculated. The inorganic ions I-, Mn2+, Co2+ and Cu2+ decrease naproxen-photoinduced DNA cleavage. Iodide acts by a heavy atom mechanism, thus inhibiting naproxen photolysis and decreasing the amount of free radicals responsible for the photocleavage both in aerobic and anaerobic conditions. Metallic ions protect only within a range of concentrations, as for higher amounts damaging processes are observed. The protective efficiency of cations decreases with the increase of free drug concentration in the bulk of the solution, due to their involvement in the scavenging of naproxen radicals generated by photolysis of the free drug. In the presence of EDTA the cations show a better protective action. The most likely hypothesis is an inhibiting effect on the damaging processes via a redox cycle. The different behaviors of copper and of the two other cations can be justified by the influence of redox potentials of free and complexed metals and by the superoxide dismutase-like activity of copper.

Asunto(s)

RESUMEN

The photosensitizing properties of tolmetin, 5-(p-toluoyl)-1-methyl-2-pyrrolyacetic acid (TLM), have been studied in vitro following the lysis of erythrocytes in phosphate buffer suspensions irradiated with UVA light in the presence of the drug. It was found that the phototoxic properties of the drug are negligible in nitrogen and significant in aerated medium, but that they decrease in oxygen-saturated solution. The investigation of the drug photolysis showed that TLM undergoes photodecarboxylation to p-tolyl 1,2-dimethyl-5-pyrrolyl ketone in nitrogen and to p-tolyl 1-methyl-2-hydroxymethyl-5-pyrrolyl ketone and 5-(p-toluoyl)-1-methyl-2-pyrrole carbaldehyde in air. These photoproducts also undergo photodegradation. The comparison between the photohaemolysis and photolysis results and the effect of suitable additives such as sodium azide, mannitol, butylated hydroxy-anisole, reduced glutathione, superoxide dismutase and copper (II) suggest that the phototoxicity of TLM can be attributed essentially to singlet oxygen in the first step and to its photoproducts when they accumulate and compete with the starting drug in light absorption. Their phototoxic effect is much higher with respect to that of TLM, as shown by comparison of the doses needed to attain 50% photohaemolysis.

Asunto(s)

RESUMEN

Ultraviolet-A irradiation of a suprofen (2-[4-2(2-thenoyl) phenyl]propionic acid) (SPF) buffered solution (pH 7.4) in the presence of supercoiled pBR322 DNA leads to single strand breaks with the formation of an open circular form and subsequent linearization of the plasmid. On the basis of agarose gel electrophoresis data of samples irradiated in an air-saturated solution or in an oxygen-modified atmosphere, and the effects of sodium azide, D20, mannitol, copper(II), superoxide dismutase, 2-H-propanol, deferoxamine and surfactants, we suggest a photosensitization mechanism involving singlet oxygen and free radicals. The higher rate of photocleavage in nitrogen compared to that in an air-saturated solution and the results obtained from oxygen consumption measurements support the hypothesis that both the type I and type II photosensitization mechanisms are operative and that oxygen quenches the excited state of the irradiated drug. The photosensitization model applied was in agreement with that previously applied to cell membrane SPF photoinduced damage. Interaction of the drug with DNA, studied through circular dichroism and fluorescence anisotropy, probably occurs through a surface binding mode. The experimental techniques used for assessing the photodamaging activity of this drug may be useful for screening of phototoxic compounds in the environment and for determining the active species involved.

Asunto(s)

RESUMEN

Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with UVC (254 nm) and UVB (300 nm) light. The irradiation provoked lipid peroxidation and liposome lysis with release of entrapped glucose-6-phosphate. At the same intensity of absorbed light, the photochemical effect at 254 nm is higher than at 300 nm. The addition of copper(II) and manganese(II) reduced both the peroxidation and the lysis. The copper showed an inhibitory effect only on the process provoked by the 254 nm irradiation, whereas the manganese was efficient both at 254 and 300 nm. The results are interpreted with a mechanism of peroxidation and quenching, involving photoformation of peroxyl radicals that are scavenged by manganese(II) and copper(I), with consequent breaking of the radical chain and reduction of the peroxidation rate. The copper(I), which is the active species, can be formed only at 254 nm by electron capture. The experimental data fit the kinetic equations obtained by the proposed mechanism by means of computer software.

Asunto(s)

RESUMEN

Unilamellar liposomes (LH) of phosphatidylcholine (PC), dispersed in phosphate buffer at pH 7 (PB), underwent lipid peroxidation and lysis with release of entrapped glucose-6-phosphate when irradiated with UVA light in the presence of 2-(3-benzoylphenyl)propionic acid (ketoprofen, KPF) or 2-(6-methoxy-2-naphthyl)propionic acid (naproxen, NAP), which were used as photosensitizers. Lipid photoperoxidation and consequent lysis were reduced when copper(II), up to 5 microM, was present in the irradiated samples. Suitable experiments were performed to evidence the species responsible for the lipid peroxidation, the copper effect on the drug photodegradation, and the mechanism of the copper antioxidant activity. The overall results suggest that the photoperoxidation was probably initiated by organic radicals obtained from the irradiation of KPF and NAP and the inhibition by copper could be attributed to its interaction with the peroxyl radicals of the drug and/or the liposomes, breaking the propagation of the radical chain.

Asunto(s)

RESUMEN

Red blood cell lysis photosensitized by Suprofen (SPF) and the photolysis of the drug were investigated. The photohemolysis process occurs at a higher rate in anaerobic than aerobic conditions. The effect of additives demonstrates the involvement of free radicals and, to a lesser extent, singlet oxygen and hydroxyl radicals in the process. Photolysis of the drug at 310-390 nm in deaerated buffered solutions (pH 7.4) leads to a decarboxylation process with the formation of p-ethylphenyl 2-thienyl ketone (I), whereas in aerated solutions formation of photoproduct I and of the photoproducts p-acetylphenyl 2-thienyl ketone (II) and p-(1-hydroxyethyl)phenyl-2-thienyl ketone (III) occurs. The photodegradation products, which were separated and characterized, show a moderate lytic and photolytic activity. The rate of SPF photodegradation decreases in the presence of oxygen and increases in the presence of hydrogen donors. The overall results lead us to propose a mechanism of SPF photodegradation and a hemolysis scheme in which cell damage is provoked principally by the direct attack of drug radicals and secondarily by singlet oxygen and hydroxyl radicals.

Asunto(s)