Efeito pró-oxidante do hidroperóxido de urato sobre proteínas sensíveis às alterações redox: implicações na resposta inflamatória / Pro-oxidant effect of urate hydroperoxide on redoxsensitive proteins: implications on inflammatory reponse

O hidroperóxido de urato (HOOU) é o produto da oxidação do ácido úrico por peroxidases. Sua produção é favorecida durante a inflamação e hiperuricemia, uma vez que há grande quantidade de ácido úrico, peroxidases inflamatórias e superóxido. Neste sentido, o objetivo deste estudo foi avaliar o efeito do hidroperóxido de urato sobre proteínas sensíveis à modulação redox em um ambiente inflamatório asséptico e outro que imita infecção. Assim, nesta tese comparou-se a estrutura química do HOOU obtido fotoquimicamente daquele obtido através da catálise enzimática pela mieloperoxidase. A obtenção do HOOU por foto-oxidação permitiu o melhor isolamento do composto. Este oxidante foi capaz de reagir especificamente com os aminoácidos contendo enxofre (metionina e cisteína). Neste sentido, foi investigada sua reatividade com tiol-peroxidases detoxificadoras de peróxido, a peroxiredoxina 1 e 2 (Prx1 e Prx2). O HOOU apresentou cinética rápida de reação com a Prx1, k = 4,9 × 105 M-1s-1 e Prx2, k = 2,3 × 106 M-1s-1, o que as torna um provável alvo celular, além disso, foi capaz de oxidar a Prx2 de eritrócitos humanos, mostrando ser capaz de atravessar a membrana plasmática. Além das Prxs, a albumina do soro também desempenha papel importante na homeostase redox. O HOOU foi capaz de oxidar a albumina com constante de velocidade de 0,2 × 102 M-1s- 1. Outra tiol-proteína com importante função na homeostase e sinalização redox é a tioredoxina (Trx). A Trx foi oxidada pelo HOOU com constante de reação de 2,8 × 102 M-1s-1 e foi liberada juntamente com a Prx1 e Prx2 das células de macrófagos humanos (linhagem THP-1) quando estas células foram incubadas com HOOU. A liberação dessas proteínas é reconhecidamente um sinal de estresse celular. Assim o HOOU pode estar envolvido na exacerbação do estresse oxidativo em ambiente inflamatório. Quando neutrófilos (linhagem HL- 60) e macrófagos humanos (linhagem THP-1) foram incubados na presença de ácido úrico e Pseudomonas aeruginosa houve uma diminuição na produção de ácido hipocloroso (HOCl). Isto se deveu à competição entre ácido úrico e cloreto pela mieloperoxidase e resultou em menor atividade microbicida pelas células, demonstrando que a formação do HOOU não contribui e, ao contrário, prejudica a atividade microbicida das células inflamatórias. Dessa forma, a oxidação do ácido úrico e formação do hidroperóxido de urato tanto altera a atividade microbicida das células inflamtárias, quanto leva à oxidação de tiósproteínas importantes para manutenção da homeostase redox. Assim, o HOOU pode ser o responsável pelos efeitos pró-oxidantes e pró-inflamatórios do ácido úrico solúvel, e isso indica que o papel antioxidante do ácido úrico deve ser revisto em situações de inflamação.

Urate hydroperoxide (HOOU) is the product of the oxidation of uric acid by peroxidases. The formation of HOOU is favored during inflammation and in hyperuricemia, where there is plenty amount of uric acid, inflammatory peroxidases and superoxide. Therefore, the aim of the present study was to evaluate the effect of urate hydroperoxide on redox sensitive proteins in an inflammatory environment and another that mimics infection. In this thesis the chemical structure of the HOOU produced by photo-oxidation was compared to that obtained by myeloperoxidase catalysis. The chemical production of HOOU allowed a better purification of the compound. This oxidant was able to specifically react with sulfur containing amino acids (methionine and cysteine). In this sense, its reactivity with peroxiredoxins (Prx1 and Prx2) was investigated. HOOU reacted fast with Prx1 k = 4.9 × 105 M-1s-1 and Prx2 k = 2.3 × 106 M-1s-1. In addition, HOOU was able to oxidize Prx2 from intact erythrocytes at the same extend as does hydrogen peroxide. Albumin is an important thiol-containing protein to redox homeostasis in plasma. HOOU was able to oxidize albumin with a rate constant of 0.2 × 102 M-1s-1. Another protein with important function in redox homeostasis is thioredoxin (Trx). Trx was oxidized by HOOU with a rate constant of 2.8 × 102 M-1s-1 and was released together with Prx1 and Prx2 from human macrophages cells (THP-1 cell line) that were incubated with HOOU. The release of these proteins is a signal of cellular stress. Thus, HOOU may be involved in the exacerbation of oxidative stress in inflammatory environments. When neutrophil (HL-60 cell line) and macrophages (THP-1 cell line) were incubated with uric acid and Pseudomonas aeruginosa there was a decrease in hypochlorous acid (HOCl) production because of the competition between chloride and uric acid by myeloperoxidase. It decreased HOCl and impaired the microbicidal activity of the cells, showing that HOOU does not contribute in bacteria clearance. Therefore, the oxidation of uric acid to urate hydroperoxide impairs microbicidal activity and oxidizes thiol-proteins in inflammatory cells contributing to a pro-oxidant status. In this context, the antioxidant role of uric acid in inflammatory response should be reviwed.

Utilidad de la tomografía computarizada de doble energía con un programa específico para la identificación de litiasis renales de ácido úrico / Usefulness of dual-energy computed tomography with and without dedicated software in identifying uric acid kidney stones

Objetivo. Valorar de manera prospectiva e in vivo la identificación de litiasis renales de ácido úrico con tomografía computarizada (TC) de doble energía (TCDE) con y sin software específico. Material y métodos. Se estudiaron 65 litiasis de 63 pacientes analizadas ex vivo con espectrofotometría y que habían sido estudiadas con una TCDE. Se valoró el rendimiento diagnóstico en identificar litiasis de ácido úrico con TCDE mediante el análisis de las densidades radiológicas de las litiasis utilizando el software específico, o sin utilizarlo (midiéndolo manualmente), y mediante el análisis de las ratios de densidad de las litiasis en ambas energías con o sin el software específico. Resultados. Las seis litiasis de ácido úrico incluidas fueron correctamente identificadas mediante la valoración de la ratio de densidades con un punto de corte de 1,21, tanto con el software específico como sin él, con un rendimiento diagnóstico perfecto, sin presencia de falsos positivos ni negativos. El estudio de densidades de las litiasis obtuvo valores de las curvas COR en clasificación de litiasis de ácido úrico de 0,92 para medición con la aplicación informática y de 0,89 para las mediciones manuales y una precisión diagnóstica del 84% (42/50) con el software y del 83,1% (54/65) para las mediciones manuales para un punto de corte de 538 UH. Conclusiones. El estudio de litiasis con TCDE permite identificar correctamente las litiasis de ácido úrico mediante el cálculo de la ratio de densidades en ambas energías. Los resultados obtenidos con y sin software específico son similares (AU)

Objective. To prospectively evaluate the usefulness of dual-energy computed tomography (DECT) with and without dedicated software in identifying uric acid kidney stones in vivo. Material and methods. We studied 65 kidney stones in 63 patients. All stones were analyzed in vivo by DECT and ex vivo by spectrophotometry. We evaluated the diagnostic performance in identifying uric acid stones with DECT by analyzing the radiologic densities with dedicated software and without using it (through manual measurements) as well as by analyzing the attenuation ratios of the stones in both energies with and without the dedicated software. Results. The six uric acid stones included were correctly identified by evaluating the attenuation ratios with a cutoff of 1.21, both with the dedicated software and without it, yielding perfect diagnostic performance without false positives or false negatives. The study of the attenuations of the stones obtained the following values on the receiver operating characteristic curves in the classification of the uric acid stones: 0.92 for the measurements done with the software and 0.89 for the manual measurements; a cutoff of 538 HU yielded 84% (42/50) diagnostic accuracy for the software and 83.1% (54/65) for the manual measurements. Conclusions. DECT enabled the uric acid stones to be identified correctly through the calculation of the ratio of the attenuations in the two energies. The results obtained with the dedicated software were similar to those obtained manually (AU)

Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation.

In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO2, ZnO and ZrO2) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents.

Valores séricos de proteínas totales, albúmina y ácido úrico en personal expuesto a las radiaciones electromagnéticas / Serum values of total proteins, albumin and uric acid in staff exposed to electromagnetic radiations

INTRODUCCION: La electricidad y las comunicaciones son aspectos sin los cuales es imposible la vida moderna; sin embargo, las radiaciones electromagnéticas (radiaciones no ionizantes) afectan la salud. De ahí que reviste gran importancia conocer la posible influencia que sobre el estatus oxidativo, la capacidad antioxidante y los niveles hemoquímicos pudiera ejercer la exposición a las ondas electromagnéticas no ionizantes. OBJETIVO: Valorar el comportamiento del ácido úrico, la albúmina y las proteínas totales en sujetos expuestos a las radiaciones electromagnéticas. MÉTODOS: Se realizó un estudio prospectivo, longitudinal y analítico de casos y controles en 125 sujetos del sexo masculino, con edades comprendidas entre 20 y 29 años. Se conformaron dos grupos de estudios: el primero formado por n = 63 sujetos expuestos (operan equipos de radiolocalización a través de radares) y el segundo grupo control formado por sujetos no expuestos a radiaciones ionizantes, n = 62. Para detectar diferencias significativas entre grupos fue utilizado el test T para muestras independientes. El nivel de significación fue de p ú 0,05. RESULTADOS: Al comparar ambos grupos, se observaron diferencias significativas en cuanto a los valores de proteínas totales y albúmina; sin embargo, los niveles de ácido úrico no sufrieron afectación. CONCLUSIONES: Los sujetos expuestos a radiaciones electromagnéticas no ionizantes en el orden de las supra altas frecuencias (SAF - 3 a 30 GHz) presentan un aumento significativo en los niveles de proteínas totales y de albúmina, lo cual pudiera afectar su capacidad de defensa antioxidante

INTRODUCTION: The electricity and communications are features essential in the modern life; however, the electromagnetic radiations (non-ionizing radiations affect the health. Hence, it is very important to know the potential influence that on the oxidative status, the antioxidant ability and the hemochemical levels could exert the exposition to non-ionizing electromagnetic radiations. OBJECTIVE: To assess the behavior of uric acid, the albumin and the total proteins in subjects exposed to electromagnetic radiations. METHODS: A analytical, longitudinal and prospective cases-controls study was conducted in 125 male subjects aged between 20 and 29. Two study groups were created: the first one included n= 63 exposed subjects (using radio location equipments by radar) and the second one included subjects non-exposed to ionizing radiations, n = 62. To detect significant differences among groups T test was used for independent samples. The significance level was of p ? 0,05. RESULTS: Comparing both groups it was possible to observe significant differences as regards total proteins and albumin values; however, the uric acid levels remained without affection. CONCLUSIONS: The subjects exposed to non0ionizing electromagnetic radiations in the order of very high frequencies (SAF - 3 to 30 GHz) had a significant increase in the total proteins and albumin levels, which could to affect its ability of antioxidant defense

Valores séricos de proteínas totales, albúmina y ácido úrico en personal expuesto a las radiaciones electromagnéticas / Serum values of total proteins, albumin and uric acid in staff exposed to electromagnetic radiations

INTRODUCCION: La electricidad y las comunicaciones son aspectos sin los cuales es imposible la vida moderna; sin embargo, las radiaciones electromagnéticas (radiaciones no ionizantes) afectan la salud. De ahí que reviste gran importancia conocer la posible influencia que sobre el estatus oxidativo, la capacidad antioxidante y los niveles hemoquímicos pudiera ejercer la exposición a las ondas electromagnéticas no ionizantes. OBJETIVO: Valorar el comportamiento del ácido úrico, la albúmina y las proteínas totales en sujetos expuestos a las radiaciones electromagnéticas. MÉTODOS: Se realizó un estudio prospectivo, longitudinal y analítico de casos y controles en 125 sujetos del sexo masculino, con edades comprendidas entre 20 y 29 años. Se conformaron dos grupos de estudios: el primero formado por n = 63 sujetos expuestos (operan equipos de radiolocalización a través de radares) y el segundo grupo control formado por sujetos no expuestos a radiaciones ionizantes, n = 62. Para detectar diferencias significativas entre grupos fue utilizado el test T para muestras independientes. El nivel de significación fue de p ú 0,05. RESULTADOS: Al comparar ambos grupos, se observaron diferencias significativas en cuanto a los valores de proteínas totales y albúmina; sin embargo, los niveles de ácido úrico no sufrieron afectación. CONCLUSIONES: Los sujetos expuestos a radiaciones electromagnéticas no ionizantes en el orden de las supra altas frecuencias (SAF - 3 a 30 GHz) presentan un aumento significativo en los niveles de proteínas totales y de albúmina, lo cual pudiera afectar su capacidad de defensa antioxidante(AU)

INTRODUCTION: The electricity and communications are features essential in the modern life; however, the electromagnetic radiations (non-ionizing radiations affect the health. Hence, it is very important to know the potential influence that on the oxidative status, the antioxidant ability and the hemochemical levels could exert the exposition to non-ionizing electromagnetic radiations. OBJECTIVE: To assess the behavior of uric acid, the albumin and the total proteins in subjects exposed to electromagnetic radiations. METHODS: A analytical, longitudinal and prospective cases-controls study was conducted in 125 male subjects aged between 20 and 29. Two study groups were created: the first one included n= 63 exposed subjects (using radio location equipments by radar) and the second one included subjects non-exposed to ionizing radiations, n = 62. To detect significant differences among groups T test was used for independent samples. The significance level was of p ? 0,05. RESULTS: Comparing both groups it was possible to observe significant differences as regards total proteins and albumin values; however, the uric acid levels remained without affection. CONCLUSIONS: The subjects exposed to non0ionizing electromagnetic radiations in the order of very high frequencies (SAF - 3 to 30 GHz) had a significant increase in the total proteins and albumin levels, which could to affect its ability of antioxidant defense(AU)

Thulium fiber laser lithotripsy using tapered fibers.

INTRODUCTION: The Thulium fiber laser has recently been tested as a potential alternative to the Holmium:YAG laser for lithotripsy. This study explores use of a short taper for expanding the Thulium fiber laser beam at the distal tip of a small-core fiber. METHODS: Thulium fiber laser radiation with a wavelength of 1,908 nm, 10 Hz pulse rate, 70 mJ pulse energy, and 1-millisecond pulse duration was delivered through a 2-m-length fiber with 150-microm-core-input-end, 300-microm-core-output-end, and 5-mm-length taper, in contact with human uric acid (UA) and calcium oxalate monohydrate (COM) stones, ex vivo (n = 10 each). Stone mass loss, stone crater depths, fiber transmission losses, fiber burn-back, irrigation rates, and deflection through a flexible ureteroscope were measured for the tapered fiber and compared with conventional fibers. RESULTS: After delivery of 1,800 pulses through the tapered fiber, mass loss measured 12.7+/-2.6 mg for UA and 7.2+/-0.8 mg COM stones, comparable to conventional 100-microm-core fibers (12.6+/-2.5 mg for UA and 6.8+/-1.7 mg for COM stones). No transmission losses or burn-back occurred for the tapered fiber after 36,000 pulses, while a conventional 150-microm fiber experienced significant tip degradation after only 1,800 pulses. High irrigation rates were measured with the tapered fiber inserted through the working port of a flexible ureteroscope without hindering its deflection, mimicking that of a conventional 150 microm fiber. CONCLUSIONS: The short tapered distal fiber tip allows expansion of the laser beam, resulting in decreased fiber tip damage compared to conventional small-core fibers, without compromising fiber bending, stone vaporization efficiency, or irrigation rates.

Thulium fiber laser lithotripsy: an in vitro analysis of stone fragmentation using a modulated 110-watt Thulium fiber laser at 1.94 microm.

BACKGROUND AND OBJECTIVES: The high-power Thulium fiber laser has previously been shown to rapidly vaporize and coagulate soft urinary tissues (e.g., prostate). This is the first preliminary study of a high-power Thulium fiber laser for fragmentation of urinary stones. STUDY DESIGN/MATERIALS AND METHODS: A continuous-wave, high-power Thulium fiber laser operating at a wavelength of 1.94 microm, was modulated to operate in pulsed mode with an output pulse energy of 1 J through a 300-microm-core silica fiber at a 20 milliseconds pulse length and repetition rate of 10 Hz. The fragmentation time to reduce uric acid (UA) (n = 13) and calcium oxalate monohydrate (COM) (n = 6) stones into particles < 2 mm was measured. RESULTS: Mean initial mass of the UA and COM stones measured 860+/-211 and 763 +/- 204 mg. Fragmentation rates measured 388 +/- 49 and 25 +/- 2 mg/minute. Average time needed to fragment the UA and COM stones into particles < 2 mm was 2.25 +/- 0.63 and 30.7 +/- 8.4 minutes, respectively. CONCLUSIONS: The high-power Thulium fiber laser, when operated in pulsed mode, is capable of fragmenting both soft (UA) and hard (COM) urinary stones. The Thulium fiber laser may be useful as a single laser system for use in multiple soft and hard tissue laser ablation applications in urology.

UV-Absorbing compounds in the aqueous humor from aquatic mammals and various non-mammalian vertebrates.

OBJECTIVE: To evaluate the absorbance of ultraviolet radiation (UVR) in the aqueous humor of various animal species in relation to the ambient radiation of their respective habitats, and to identify substances responsible for this absorbance. Representatives of all five classes (fish, amphibian, reptile, bird, and mammal) have been tested. METHODS: Absorbance was recorded using a spectrophotometer. The ascorbic and uric acid concentrations were determined by HPLC, and the amino acid profiles with an automatic analyzer. Screening for potential UV-absorbing substances was performed by HPLC and a total of 12 species were examined, 7 of them birds. RESULTS: UV-absorbing substances in the aqueous humor were proteins, tryptophan, tyrosine and ascorbic and uric acid. In addition, an unknown UV-absorbing component present in bird aqueous humor caused a high, red-shifted UV-absorbance spectrum, particularly in tentatively heavily exposed species such as goose when migrating at 10,000 m altitude. By comparison, the UV absorbance above the 288-nm wavelength was low in the aqueous humor of fish, frogs, aquatic mammals and two ground-living birds. The crocodile, whose aqueous humor contained significant amounts of both ascorbic and uric acid, revealed a concentration mechanism for ascorbic acid. CONCLUSIONS: The UV absorbance of aqueous humor varies considerably from one species to the next, and independent of class. It is noteworthy that the species being at highest risk for high-dose UV exposure, the migrating goose, showed the most red-shifted spectrum.

Inhibitory effect of local ischaemic preconditioning in total body irradiated rats.

The aim of this study was to explore the relationship between local ischaemic preconditioning and the effectiveness of fractionated radiotherapy. The rat serum, bone marrow, and small intestine were examined for oxidative changes induced by total body irradiation with gamma rays with applied local ischaemic preconditioning immediately before irradiation. Serum concentrations of TBA-RS examined 12 hours after the last irradiation did not reveal any differences among the groups of animals analyzed. Twenty-four hours after the last dose of irradiation, the serum concentrations of TBA-RS varied in particular groups (P<0.0001). The concentration of triglycerides in the serum of local preconditioned ischaemia and irradiated animals showed a reversed shape similar to the TBA-RS fluctuation (P<0.003). The level of uric acid in the serum of animals treated only with radiation is slightly higher than the level of this acid in the serum of the local preconditioned ischaemia radiation group (P<0.58). The number of bone marrow polychromatic erythrocytes did not appear to differ substantially in both irradiated groups. At the first 12 hours after irradiation, the frequency of micronucleated polychromatic erythrocytes is significantly different in the bone marrow of both groups either in combination with ischaemic preconditioned radiation or with radiation alone (P<0.0002). In irradiated animals without ischaemic preconditioning, on the 3rd day after irradiation the number of crypts increased and in the next days decreased achieving the level of the control group on the 7th day. Irradiated rats with local ischaemic preconditioning did not reveal an increase in the number of crypts. The difference was statistically significant (P<0.05). These data indicate that the local ischaemic preconditioning modifies the radiation peroxidising effects through inhibition of free radical-dependent lipid peroxidation and, probably, other unrecognized mechanisms.

Fragmentation of uric acid calculi with the holmium: YAG laser produces cyanide.

BACKGROUND AND OBJECTIVES: To independently test previously reported findings of cyanide evolution under holmium:yttrium aluminum garnet (Ho:YAG) (holmium) lithotripsy of uric acid calculi, determine if this occurs with other forms of intracorporeal lithotripsy, and establish if this occurs due to a photothermal, photochemical, or photoacoustic reaction. STUDY DESIGN/MATERIALS AND METHODS: Human uric acid calculi were fragmented in vitro through exposure to holmium, ultrasound, and electrohydraulic (EHL) energy sources. The following parameters were varied: total laser energy, individual laser pulse energy, ultrasonic energies, and EHL energies. Uric acid powder was suspended in solution and exposed to holmium laser energy in vitro. Serum and irrigant samples from a human patient were collected following intrarenal holmium lithotripsy of a uric acid calculus. All samples were analyzed for hydrogen cyanide (HCN) content. RESULTS: Holmium lithotripsy of solid uric acid calculi produces cyanide. The yield is linearly dependent upon total laser energy delivered. Pulse energy does not affect cyanide yield. Photothermal mechanisms coupling laser energy to the solid crystal lattice are responsible for the production of cyanide. Ultrasound and EHL lithotripsy do not produce cyanide. A clinically insignificant level of cyanide was detected in the blood of a single patient following laser lithotripsy of a uric acid calculus. CONCLUSIONS: Our study confirms that cyanide is produced by a photothermal mechanism during holmium laser lithotripsy of uric acid calculi, and that the amount produced is clinically insignificant.

UV absorption by uric acid in diurnal bird aqueous humor.

PURPOSE: To analyze the components responsible for the UV absorbance in diurnal bird aqueous humor. METHODS: The absorbance studies were carried out using a Hitachi spectrophotometer (U 2000). Uric acid was determined by high-performance liquid chromatography (LC-10 system; Shimadzu, Kyoto, Japan). Chicken and turkey eyes were examined. RESULTS: The UV absorbance in chicken aqueous was largely accounted for by the presence of protein, tryptophan, tyrosine, ascorbic acid, and uric acid. Ascorbic acid was low (23 micromol/l). Uric acid was, on the other hand, remarkably high (151 micromol/l) compared with that in mammals (cattle, 16 micromol/l). Principally the same results were obtained in chicken and turkey. CONCLUSIONS: Uric acid is a significant UV-absorbing substance in the aqueous humor of diurnal birds with its peak absorbance at 292 nm. The hypothesis that the aqueous humor acts as a UV filter seems to be valid also for the avian eye. However, in these eyes uric acid fulfills the role that ascorbic acid does in mammals.

Holmium: YAG lithotripsy: optimal power settings.

PURPOSE: We tested the hypothesis that holmium:YAG laser lithotripsy speed is best maximized by using low pulse energy at high pulse frequency. MATERIALS AND METHODS: To demonstrate that optical fiber damage increases with pulse energy and irradiation, the 365-microm optical fiber irradiated calcium hydrogen phosphate dihydrate (CHPD), calcium oxalate monohydrate (COM), cystine, magnesium ammonium phosphate hexahydrate (MAPH), and uric acid calculi at pulse energies of 0.5 to 2.0 J. Optical energy output was measured with an energy detector after 10 J to 200 J of total energy. To demonstrate that lithotripsy efficiency varies with power, fragmentation was measured at constant power settings at total energies of 200 J and 1 kJ with the 365-microm optical fiber. Fragmentation was measured for the 272-microm optical fiber at pulse energies of 0.5 J to 1.5 J at 10 Hz. To demonstrate that low pulse energy produces smaller fragments than high pulse energy, fragment size was characterized for COM and uric acid calculi after 0.25 kJ of irradiation using the 272-microm to 940-microm optical fibers at 0.5 J to 1.5 J. RESULTS: Damage to the 365-microm optical fiber was greatest for irradiation of CHPD, followed by MAPH, and COM (P<0.001). There was no significant optical fiber damage after cystine and uric acid lithotripsy. For the 365-microm optical fiber and CHPD, fragmentation after 200 J was greatest for pulse energies < or =1.0 J (P< 0.001). For other compositions, fragmentation was not statistically different among the power settings for constant irradiation. No significant difference was noted in fragmentation for any composition at different pulse energies (1.0 v. 2.0 J) for 1-kJ irradiation. However, for all compositions, the calculated lithotripsy speed was greatest at high power settings (P<0.001). For the 272-microm optical fiber, CHPD fragmentation was greatest for the 1.0-J pulse energy. The mean fragment size and relative quantity of fragments > or =2 mm both increased as pulse energy increased. CONCLUSIONS: Optical fiber degradation varies with stone composition, irradiation, and pulse energy. Holmium:YAG lithotripsy speed is maximized with higher power (either increased pulse energy or higher pulse frequency). Because low pulse energy may be safer and yields smaller fragments than high pulse energy, holmium:YAG lithotripsy speed is best increased by using pulse energies < or =1.0 J at a high repetition rate.

Identification of products from oxidation of uric acid induced by hydroxyl radicals.

The aim of the present study was to separate and characterise products formed by oxidation of uric acid by hydroxyl radicals with a view to probing for these products in vivo in clinical contexts. Aerated solutions of 200 microM uric acid, or its oxidation products, allantoin or parabanic acid, were exposed to gamma radiolysis, (52.0 Gy/min), as a source of HO. radicals, at pH 3.4 and 7.4. Aliquots were taken every 5 minutes for 20 minutes and oxidation products were separated by HPLC and analysed with a diode array detector. Identities of oxidation products were confirmed on the basis of similarity of retention times and absorbance spectra and peak purity parameters of known standards. Hydroperoxides were measured by tri-iodide formation in the 20 minute sample. Exposure of uric acid to such HO.fluxes produced a net loss of the parent compound with formation of a complex mixture of products with allantoin and parabanic acid being the predominant products at pH 3.4. The rate of uric acid degradation at physiological pH was slower and the distribution of oxidation products was different. A small but significant amount of uric acid hydroperoxide was detected at both pHs. A mechanism for uric acid oxidation under these conditions is presented.

In vitro photodecomposition of uric acid in presence of riboflavin II.

In vitro studies on the photodecomposition of uric acid in the presence of the monosodium salt of riboflavin 5'-phosphate in buffers at various pH values, in methanol, and in human plasma are reported. The decomposition rate increased with increasing pH and was independent of solvent or buffer species. The mechanism appears to be an energy transfer process involving triplet riboflavin and single oxygen. Riboflavin-enhanced photodecomposition of uric acid occurred in vitro in hyperuricemic human plasma.

[Occurrence of hyperuricemia in atrioventricular block. (Results of a study of 158 patients with isotopic pacemaker implantations)]. / Fréquence de l'hyperuricémie dans le bloc auriculo-ventriculaire. (Résultats de l'étude de 158 indications de pose d'un stimulateur cadiaque isotopique)

The frequency of hyperuricemia is high in these patients with heart block, whose mean age is 39. 91% have serum uric acid levels above the normal range and 61% present "hyperuricemia," according to "gouty risk" criteria. The mean uric acid level, before surgery, of the patients whose total heart block follows "open-heart" is the highest in our statistics.

Nucleation of monosodium urate crystals.

(1) Calcium greatly increased crystallization of monosodium urate in otherwise pure water, by enhancing both nucleation and growth. (2) Acid accelerated urate nucleation, both by its direct action and indirectly by increasing the free calcium in physiological fluids. (3) Synovial fluid from one gouty patient accelerated urate nucleation, while that from one rheumatoid patient inhibited nucleation. (4) X-rays, collagen, ethyl alcohol, cupric ion, and potassium ion all had negligible influence on urate nucleation. (5) Mechanical shock greatly increased urate nucleation.