Characterizing Diffusion from Microdialysis Catheters in the Human Brain: A Magnetic Resonance Imaging Study With Gadobutrol.

Cerebral microdialysis (CMD) catheters allow continuous monitoring of patients' cerebral metabolism in severe traumatic brain injury (TBI). The catheters consist of a terminal semi-permeable membrane that is inserted into the brain's interstitium to allow perfusion fluid to equalize with the surrounding cerebral extracellular environment before being recovered through a central non-porous channel. However, it is unclear how far recovered fluid and suspended metabolites have diffused from within the brain, and therefore what volume or region of brain tissue the analyses of metabolism represent. We assessed diffusion of the small magnetic resonance (MR)-detectible molecule gadobutrol from microdialysis catheters in six subjects (complete data five subjects, incomplete data one subject) who had sustained a severe TBI. Diffusion pattern and distance in cerebral white matter were assessed using T1 (time for MR spin-lattice relaxation) maps at 1 mm isotropic resolution in a 3 Tesla MR scanner. Gadobutrol at 10 mmol/L diffused from cerebral microdialysis catheters in a uniform spheroidal (ellipsoid of revolution) pattern around the catheters' semipermeable membranes, and across gray matter-white matter boundaries. Evidence of gadobutrol diffusion was found up to a mean of 13.4 ± 0.5 mm (mean ± standard deviation [SD]) from catheters, but with a steep concentration drop off so that ≤50% of maximum concentration was achieved at ∼4 mm, and ≤10% of maximum was found beyond ∼7 mm from the catheters. There was little variation between subjects. The relaxivity of gadobutrol in human cerebral white matter was estimated to be 1.61 ± 0.38 L.mmol-1sec-1 (mean ± SD); assuming gadobutrol remained extracellular thereby occupying 20% of total tissue volume (interstitium), and concentration equilibrium with perfusion fluid was achieved immediately adjacent to catheters after 24 h of perfusion. No statistically significant change was found in the concentration of the extracellular metabolites glucose, lactate, pyruvate, nor the lactate/pyruvate ratio during gadobutrol perfusion when compared with period of baseline microdialysis perfusion. Cerebral microdialysis allows continuous monitoring of regional cerebral metabolism-the volume of which is now clearer from this study. It also has the potential to deliver small molecule therapies to focal pathologies of the human brain. This study provides a platform for future development of new catheters optimally designed to treat such conditions.

Free interstitial levels of metformin in the liver of healthy and diabetic Wistar rats

Abstract In the present study, free interstitial levels reached by metformin in the liver were investigated in control and diabetic rats by microdialysis. Firstly, a bioanalytical method using an HPLC-UV system to determine the drug concentration in microdialysis samples was validated. The blood glucose levels and biochemical parameters were investigated in control and diabetic animals. Following that, both groups received a dose of 50 mg/kg of metformin iv bolus and the free interstitial levels reached in the liver were assessed by microdialysis. The method was validated according to FDA guidelines being suitable to quantify free concentrations of metformin in the liver of control and diabetics rats. Free exposure to metformin was similar in control and diabetic animals: AUC0-∞ 118.50 ± 40.18 vs 112.93 ± 50.25 µg.h/mL, respectively. The half-life in tissue was similar to that described in the literature for plasma. Hence diabetes induced by streptozotocin after administration of nicotinamide in our study did not damage the renal and hepatic function of the animals. The levels reached in the liver were 1.6 times higher than the free plasma concentrations, demonstrating higher liver penetration of metformin. This is the first investigation in liver interstitial concentration of metformin in control and diabetic rats

Microdiálisis de alta resolución. Aspectos metodológicos y aplicación al estudio de larespuesta inflamatoria cerebral / High Resolution Microdialysis. Methodological issues and application to the study of inflammatory brain response

La técnica de microdiálisis (MD) cerebral es un instrumentoque proporciona información relevante en lamonitorización del metabolismo cerebral en pacientesneurocríticos. La MD es una técnica especialmente efectivapara la detección y análisis de pequeñas moléculas,puesto que el tamaño de los poros de la membranadializante actúa como barrera restringiendo el paso deespecies mayores, tales como proteínas u otras macromoléculas.La reciente disponibilidad de catéteres demicrodiálisis con poros de mayor calibre, denominadosde “alta resolución”, permite ampliar el rango de moléculasdetectables en el dializado. Sin embargo, existencomplicaciones técnicas relacionadas con la utilizaciónde estos catéteres para estos propósitos, por lo que estacapacidad potencial para la recuperación de proteínasnecesita ser validada antes de su aplicación como herramientapara estudios de proteómica asociados a la lesióncerebral. En esta revisión se contemplan los principiosbásicos de la microdiálisis y los diferentes factores queintervienen en los procesos de recuperación de moléculasen el dializado, tales como las características físicasde la membrana dializante, así como de las moléculasque se desea investigar (AU)

Cerebral microdialysis is a tool that provides veryrelevant information in the metabolic monitoring ofbrain injured patients. It is a particularly effective technique for the detection and analysis of small molecules,given that the pores of the dialysis membrane actas a barrier to restrict the transport of larger species,such as proteins and other macromolecules. The recentavailability of microdialysis catheters with membranepores of larger size, termed “high resolution” catheters,would widen the spectrum of molecules detectablein the dialisate. However, there are technical complicationsrelated to the use of these catheters for suchpurposes, and therefore, this potential capacity for therecovery of proteins needs to be validated, in order tobegin its application as a tool in studies of proteomicsassociated with brain injuries. The following reviewdepicts the basic principles of microdialysis, and describessome of the issues involved in the recovery ofmolecules in the dialisate, including the physical propertiesof the dialysis membrane and of the moleculesof interest (AU)

Arginine and glutamate levels in the gingival crevicular fluid from patients with chronic periodontitis

The objectives of this study were to determine arginine and glutamate levels in the gingival crevicular fluid (GCF) of adult chronic periodontitis patients versus periodontally healthy controls, and to compare two kinds of microdialysis probes: normal and U-shaped probes. The analysis of GCF components was developed to improve the diagnosis of periodontal disease (PD). Proteolysis in the periodontal tissues increases the concentration of amino acids (aa) in the GCF and the levels of these aa may reveal PD features and stages. GCF samples were collected by microdialysis in situ from 5 periodontally affected sites (probing depth >5 mm, clinical attachment loss >3 mm) in 14 adult chronic periodontitis patients and from 14 adult periodontally healthy controls. Capillary zone electrophoresis coupled to laser induced fluorescence detection was used to measure concentration of arginine and glutamate in the GCF. Data were analyzed statistically by ANOVA and Tukey's post-hoc tests (?=0.05). Arginine concentration was increased (p<0.001) and glutamate concentration was decreased (p<0.001) in chronic periodontitis patients as compared to controls. There were no significant differences (p=0.069) between the normal and U-shaped probes. In conclusion, the increase of arginine and decrease of glutamate concentration in GCF were associated to the presence of periodontitis, and might be used as markers to recognize periodontally susceptible subjects as well as to evaluate the treatment course.

Os objetivos deste estudo foram determinar os níveis de arginina e glutamato no fluido gengival crevicular (FGC) em pacientes com periodontite crônica contra controles saudáveis e comparar dois tipos de cânulas de microdiálise: normais e em forma de U. A análise dos componentes do FGC desenvolveu-se para melhorar o diagnóstico da doença periodontal (DP). A proteólise dos tecidos periodontais aumenta a concentração de aminoácidos (aa) no FGC e os níveis destes aa podem revelar as características e estágios da DP. Amostras de FGC foram obtidas pela técnica de microdiálise in situ de cinco zonas com o periodonto afetado (profundidade de sondagem >5 mm, perda da inserção clínica >3 mm) em 14 pacientes adultos com periodontite crônica e 14 controles saudáveis. Para medir a concentração de arginina e glutamato no GFC, usou-se a técnica de eletroforese capilar com detecção de fluorescência induzida por laser. Nos pacientes com periodontite crônica, a concentração de arginina aumentou significantemente (p<0.001), enquanto a de glutamato diminuiu significantemente (p<0.001) em comparação aos controles. Não houve diferenças significantes (p=0.069) entre as cânulas normais e as cânulas em forma de U. Conclui-se que o aumento da concentração de arginina e diminuição de glutamato no FGC estavam associados à presença de periodontite, e podem ser usados como marcadores para identificar pacientes suscetíveis à periodontite bem como avaliar a evolução do tratamento.

Actualizaciones en los métodos de monitorización cerebral regional en los pacientes neurocríticos: presión tisular de oxígeno, microdiálisis cerebral y técnicas de espectroscopía por infrarrojos / Recent advances in regional cerebral monitoring in the neurocritical patient: brain tissue oxygen pressure monitoring, cerebral microdialysis and near-infrared spectroscopy

El resultado final de los pacientes que han presentado un traumatismo craneoencefálico (TCE) depende de las lesiones primarias, pero también, y en gran medida, de las lesiones secundarias. El diagnóstico de un gran número de lesiones secundarias, y en especial de la isquemia cerebral, se centra en la monitorización simultánea de diversas variables encefálicas y sistémicas. En el momento actual, la monitorización continua de la presión intracraneal (PIC) se considera una medida indispensable en el manejo de los pacientes con un TCE grave que presentan cualquier tipo de lesión intracraneal. Sin embargo, la información que ofrece esta variable es insuficiente para diagnosticar los complejos procesos fisiopatológicos que caracterizan a las lesiones neurotraumáticas. Por ello, cada vez es más frecuente complementar la neuromonitorización de los pacientes con un TCE con métodos de estimación del flujo sanguíneo cerebral (FSC) como el Doppler transcraneal o las técnicas de oximetría yugular. Sin embargo, en el momento actual y en la cabecera del paciente, el conocimiento de la repercusión de las lesiones tisulares y de las medidas terapéuticas sobre el metabolismo cerebral requiere un acceso directo al parénquima encefálico. En esta revisión nos centraremos en tres métodos de monitorización cerebral “regional”: la presión tisular de oxígeno, la microdiálisis cerebral y las técnicas transcutáneas de espectroscopía por infrarrojos. En cada caso se expondrán los fundamentos del método en cuestión, los valores de referencia de los parámetros monitorizados y una serie de recomendaciones sobre cómo pueden interpretarse sus resultados a la luz de los conocimientos actuales

The long term outcome of head-injured patients depends not only on the primary brain lesions but also to a large extent on the secondary lesions. The diagnosis of many secondary lesions, and specially that of brain ischemia, is based on simultaneous monitoring of several intracranial and systemic variables. Continuous intracranial pressure (ICP) monitoring is currently considered indispensable in the management of all patients with a severe head injury and intracranial lesions. However, the information provided by this technique is insufficient to diagnose some of the complex physiopathological processes that characterize traumatic brain lesions. Consequently, the use of methods to estimate cerebral blood flow such as transcranial Doppler and jugular oximetry to complement ICP monitoring is becoming increasingly widespread. Nevertheless, determining the effect of tissue lesions and therapeutic measures on cerebral metabolism currently requires direct access to the brain parenchyma at the bedside. In this review we focus on three methods of regional cerebral monitoring: oxygen tissue pressure (PtiO2) monitoring, microdialysis and near-infrared spectroscopy. The bases of each method and reference values for the bless analyzed will be discussed. We also make a series of recommendations on how results should be interpreted in light of current knowledge

Activación del sistema de los opiodes endógenos por dosis subconvulsivamantes de metrazol / Activation of the endogenous opioid system with metrazol subconvulsivant dosis

Se investigaron las alteraciones en el sistema de los opioides endógenos en el cerebro de la rata, inducidas por la administración de una dósis subconvulsivante de metrazol (PTZ) (30 mg/kg i.p.). Por medio de experimentos de microdiálisis, encontramos durante los primeros 60 min después del tratamiento, una liberación importante de opiodes endógenos en el hipocampo y la amígdala cerebral. Posteriormente, los valores regresaron a los niveles basales. Por autorradiografía se observó un decremento en los niveles de los receptores mu en varias estructuras cerebrales. Mediante el análisis de la unión a receptores las membranas cerebrales, se confirmó un decremento en el número de estos receptores, sin cambios en su afinidad. En la aplicación de la prueba de Randall-Sellito, se encontró un aumento en el umbral de respuesta a estímulos dolorosos, durante los primeros 30 min. después del PTZ. Finalmente, experimentos de hibridación in situ revelaron un incremento en los niveles de la proencefalina a las 24 hrs después del tratamiento. Nuestros resultados indican que la administración de dosis subconvulsivante de PTZ activan de manera importante al sistema de los opiodes endógenos. Estos cambios resultan relevantes para entender el proceso del epileptogénesis y los mecanismos involucrados en el mismo