Concentration-Dependent Binding of Small Ligands to Multiple Saturable Sites in Membrane Proteins.

Membrane proteins are primary targets for most therapeutic indications in cancer and neurological diseases, binding over 50% of all known small molecule drugs. Understanding how such ligands impact membrane proteins requires knowledge on the molecular structure of ligand binding, a reasoning that has driven relentless efforts in drug discovery and translational research. Binding of small ligands appears however highly complex involving interaction to multiple transmembrane protein sites featuring single or multiple occupancy states. Within this scenario, looking for new developments in the field, we investigate the concentration-dependent binding of ligands to multiple saturable sites in membrane proteins. The study relying on docking and free-energy perturbation provides us with an extensive description of the probability density of protein-ligand states that allows for computation of thermodynamic properties of interest. It also provides one- and three-dimensional spatial descriptions for the ligand density across the protein-membrane system which can be of interest for structural purposes. Illustration and discussion of the results are shown for binding of the general anesthetic sevoflurane against Kv1.2, a mammalian ion channel for which experimental data are available.

SAHA attenuates sevoflurane-induced learning and memory impairments in fetal mice.

Previous studies have found that children with multiple exposures to anesthesia at an early age are at increased risk of learning and memory impairment. Sevoflurane is the most commonly used inhalational anesthetic for general anesthesia in children. Multiple exposures to sevoflurane have been shown to induce neuroinflammation, inhibit neurogenesis, and cause subsequent learning and memory impairments in fetal mice. Histone-tail acetylation has been implicated in memory formation. In this study, we employed suberanilohydroxamic acid (SAHA), an inhibitor of histone deacetylases, to treat sevoflurane-induced learning and memory impairments. Six-day-old C57BL/6 mice were exposed to sevoflurane for 2 h daily for 3 days. Morris water maze test performed to evaluate learning and memory impairments and the expression of genes related in to synaptic remodeling/plasticity, or regulated by neuronal activity or the cell cycle were detected by real-time PCR. We found that SAHA attenuated sevoflurane-induced learning and memory impairments in fetal mice. Our findings suggest that SAHA may have potential as a therapeutic agent for preventing or treating the neurotoxicity associated with anesthesia.

Comparison of the effects of epidural or intravenous methadone on the minimum alveolar concentration of isoflurane in dogs.

The effects of epidural and intravenous (IV) methadone (0.5mg/kg) on the minimum alveolar concentration of isoflurane (ISO(MAC)) were compared in dogs. Six dogs (16.5 ± 2.5 kg bodyweight) received three treatments in random order during isoflurane anaesthesia, with a 7 day washout interval between each study. Methadone was injected via a lumbosacral epidural catheter introduced 10 cm cranially into the epidural canal and the electrical stimulation for ISO(MAC) determination was applied either to the thoracic (EP(T) treatment) or to the pelvic limb (EP(P) treatment) during separate study days. In the IV treatment, ISO(MAC) was determined via electrical stimulation of the pelvic limb. Variables were recorded before (baseline), 2.5 and 5h after drug injection. The ISO(MAC) decreased significantly (P<0.05) from baseline at 2.5 and 5h after methadone in all treatments. At 2.5h, the magnitude of ISO(MAC) reduction did not differ between treatments (mean decreases from baseline: 30-33%). The ISO(MAC) reduction lasted longer following epidural methadone in the thoracic limb (decreases from baseline: 30% at 5h in the EP(T) treatment vs. 19% and 16% in the EP(P) and IV treatments, respectively). Although the isoflurane sparing effect provided by epidural methadone was not significantly greater than IV methadone during the initial stage (2.5h), it was more prolonged than the IV route in specific dermatomes (5h in the thoracic limb) with the epidural technique employed. Methadone may therefore provide a greater isoflurane sparing effect when administered epidurally, compared to IV, when noxious stimulation occurs in specific dermatomes.

Minimum alveolar concentrations and hemodynamic effects of two different preparations of sevoflurane in pigs.

BACKGROUND: Original sevoflurane (Sevo A) is made with water, while a generic sevoflurane (Sevocris) is produced with propylene glycol as a stabilizing additive. We investigated whether the original and generic sevoflurane preparations differed in terms of their minimum alveolar concentration (MAC) values and hemodynamic effects. METHODS: Sixteen pigs weighing 31.6+/-1.8 kg were randomly assigned to the Sevo A or Sevocris groups. After anesthesia induction via mask with the appropriate sevoflurane preparation (6% in 100% oxygen), the MAC was determined for each animal. Hemodynamic and oxygenation parameters were measured at 0.5 MAC, 1 MAC and 1.5 MAC. Histopathological analyses of lung parenchyma were performed. RESULTS: The MAC in the Sevo A group was 4.4+/-0.5%, and the MAC in the Sevocris group was 4.1+/-0.7%. Hemodynamic and metabolic parameters presented significant differences in a dose-dependent pattern as expected, but they did not differ between groups. Cardiac indices and arterial pressures decreased in both groups when the sevoflurane concentration increased from 0.5 to 1 and 1.5 MAC. The oxygen delivery index (DO(2)I) decreased significantly at 1.5 MAC. CONCLUSION: Propylene glycol as an additive for sevoflurane seems to be as safe as a water additive, at least in terms of hemodynamic and pulmonary effects.

Minimum alveolar concentrations and hemodynamic effects of two different preparations of sevoflurane in pigs

BACKGROUND: Original sevoflurane (Sevo A) is made with water, while a generic sevoflurane (Sevocris) is produced with propylene glycol as a stabilizing additive. We investigated whether the original and generic sevoflurane preparations differed in terms of their minimum alveolar concentration (MAC) values and hemodynamic effects. METHODS: Sixteen pigs weighing 31.6±1.8 kg were randomly assigned to the Sevo A or Sevocris groups. After anesthesia induction via mask with the appropriate sevoflurane preparation (6 percent in 100 percent oxygen), the MAC was determined for each animal. Hemodynamic and oxygenation parameters were measured at 0.5 MAC, 1 MAC and 1.5 MAC. Histopathological analyses of lung parenchyma were performed. RESULTS: The MAC in the Sevo A group was 4.4±0.5 percent, and the MAC in the Sevocris group was 4.1±0.7 percent. Hemodynamic and metabolic parameters presented significant differences in a dose-dependent pattern as expected, but they did not differ between groups. Cardiac indices and arterial pressures decreased in both groups when the sevoflurane concentration increased from 0.5 to 1 and 1.5 MAC. The oxygen delivery index (DO2I) decreased significantly at 1.5 MAC. CONCLUSION: Propylene glycol as an additive for sevoflurane seems to be as safe as a water additive, at least in terms of hemodynamic and pulmonary effects.

Can determining the minimum alveolar anesthetic concentration of volatile anesthetic be used as an objective tool to assess antinociception in animals?

UNLABELLED: We intended to evaluate the reliability of the minimum anesthetic alveolar concentration (MAC)-sparing effect as an objective measure of the antinociceptive properties of a drug. For this purpose, we tested different variables and analyzed the significance of the results obtained. In a first set of experiments, we studied rats under mechanical ventilation and sevoflurane anesthesia. Outcome variables such as gross purposeful movements consecutive to tail clamping, paw withdrawal consecutive to increasing pressure, and cardio-circulatory reactivity (MACBAR) after these stimuli were recorded. In a second set of experiment, sevoflurane-anesthetized rats under spontaneous breathing conditions were used. Thermal stimuli were compared with pressure. The MAC-sparing effect of several doses of sufentanil and clonidine was evaluated in both anesthetized and awake rodents. When considering the stimulus applied, larger concentrations of sevoflurane were required to suppress reactivity after tail clamp than after paw pressure or radiant heat (1.81 +/- 0.28 versus 1.45 +/- 0.22 and 1.53 +/- 0.26; P < 0.05). For the two first stimuli, no significant differences were noted between the concentrations that suppress motor or cardio-circulatory reactions. All doses of sufentanil tested significantly reduced (P < 0.05) the different MAC values except the smallest one (0.005 micro g x kg(-1) x min(-1)) that significantly increased MACBAR in ventilated animals and both MAC and MACBAR in spontaneously breathing rodents (P < 0.05). Clonidine, at its optimal dose (10 micro g/kg), significantly reduced both MAC and MACBAR to the same degree. In awake animals submitted to radiant heat or pressure challenge, none of the clonidine doses nor sufentanil doses (0.005 and 0.07) were active. In conclusion, the MAC-sparing effect provides several reliable and quantifiable variables that allow comparison between different analgesic substances. However, the observations made are not simply the result of antinociceptive effects of the tested drugs but rather that of complex interactions between these drugs and a halogenated vapor. IMPLICATIONS: The MAC-sparing effect provides several variables that allow comparison between different analgesic substances. However, the observations made are not simply the result of the antinociceptive effects of the tested drugs but rather the result of complex interactions between these drugs and a halogenated vapor.

Mechanism of action of volatile anesthetics: involvement of intracellular calcium signaling.

There have been extensive efforts to characterize the mechanism of action of volatile anesthetics, but their molecular and cellular actions are still a matter of debate. Volatile anesthetics act primarily on synaptic transmission in the central nervous system but proof of this as the predominant mechanism of action remains elusive. Changes in neurotransmitter release may relate to direct interaction of the anesthetic molecule with an ion channel protein or synaptic protein, but can also be a consequence of alterations in intracellular signaling. Calcium is one of the most important messengers in cells and its intracellular concentration may be modified by several agents including volatile anesthetics. Neuronal excitability is in part determined by calcium availability that is controlled by several mechanisms. Because voltage-gated calcium channels (VGCC) play a key role in controlling Ca2+ entry and in initiating cellular responses to stimulation through an elevation of intracellular calcium concentration ([Ca2+](i)), they are thought to be one of the targets for volatile anesthetics. However, [Ca2+](i) can also be altered without the participation of VGCC through receptor-mediated pathways. Indeed, calcium homeostasis is also controlled by plasma membrane Ca2+ -adenosine triphosphatase, sarcoplasmic-endoplasmic reticular Ca2+ -ATPase, the Na+ -Ca2+ exchanger, and mitochondrial Ca2+ sequestration. Alteration of any of those mechanisms that control [Ca2+](i) may lead to a change in presynaptic transmission or postsynaptic excitability. Here we will review some of the recent progress in identifying putative actions of volatile anesthetics, specifically the effect on intracellular calcium homeostasis in neurons.

Mechanism of action of volatile anesthetics: role of protein kinase C.

1. It is not completely clear how volatile anesthetics cause anesthesia, but one possible consequence of their action is to alter presynaptic activity and the release of neurotransmitters due to alterations in intracellular signaling. 2. Protein kinase C (PKC) is a signal transducing enzyme that is an important regulator of multiple physiological processes like neurotransmitter release, ion channel activity, and neurotransmitter receptor desensitization. Thus, PKC is an attractive molecular target for the synaptic action of general anesthetics. 3. However, the effects of these agents on PKC activity are not yet fully understood and there are several contradictory data on the literature regarding the in vitro and in vivo preparations. 4. Here, we will review some evidence for volatile anesthetics effects on neuronal PKC activation.

Anestesia inhalatoria con circuito cerrado y flujos mínimos / Inhalatory anesthesia with closed circuit and minimum flows

La anestesia inhalatoria con circuito cerrado y flujos mínimos es la técnica más apropiada para suministrar al paciente la cantidad "exacta" de los agentes inhalatorios necesarios para lograr la concentración y la presión deseadas en el sistema nervioso central y en el aire alveolar espirado. Además, con esta técnica, es posible llevar al paciente al plano de anestesia quirúrgica que necesita y mantenerlo allí, así como reducir la pérdida de calor y humedad, al no tener que calentar y humidificar grandes volúmenes de gases frescos, factores que permitirán que el paciente se encuentre en una condición más confortable y permanezca hemodinámicamente estable. Por otra parte, la anestesia inhalatoria con circuito cerrado y flujos mínimos disminuye la contaminación del quirófano y del medio ambiente con vapores anestésicos, al restringir al mínimo la polución generada por estos vapores, y reduce enormemente el costo de la anestesia al consumir cantidades ínfimas de agentes inahalatorios. Para lograr los objetivos mencionados se requiere la capacitación y el entrenamiento del anestesiólogo en la técnica de los circuitos cerrados con flujos mínimos, la disponibilidad de máquinas de anestesia y ventiladores adecuados y la existencia de monitores multiparamétricos que permitan controlar la fracción inspirada y la fracción espirada de los agentes inhalatorios.

Anestesia inhalatoria con circuito cerrado y flujos mínimos / Inhalatory anesthesia with closed circuit and minimum flows

La anestesia inhalatoria con circuito cerrado y flujos mínimos es la técnica más apropiada para suministrar al paciente la cantidad "exacta" de los agentes inhalatorios necesarios para lograr la concentración y la presión deseadas en el sistema nervioso central y en el aire alveolar espirado. Además, con esta técnica, es posible llevar al paciente al plano de anestesia quirúrgica que necesita y mantenerlo allí, así como reducir la pérdida de calor y humedad, al no tener que calentar y humidificar grandes volúmenes de gases frescos, factores que permitirán que el paciente se encuentre en una condición más confortable y permanezca hemodinámicamente estable. Por otra parte, la anestesia inhalatoria con circuito cerrado y flujos mínimos disminuye la contaminación del quirófano y del medio ambiente con vapores anestésicos, al restringir al mínimo la polución generada por estos vapores, y reduce enormemente el costo de la anestesia al consumir cantidades ínfimas de agentes inahalatorios. Para lograr los objetivos mencionados se requiere la capacitación y el entrenamiento del anestesiólogo en la técnica de los circuitos cerrados con flujos mínimos, la disponibilidad de máquinas de anestesia y ventiladores adecuados y la existencia de monitores multiparamétricos que permitan controlar la fracción inspirada y la fracción espirada de los agentes inhalatorios. (AU)

Efectos de la hipotermia sobre las drogas anestésicas utilizadas en el intraoperatorio / Hypothermia effects on anesthetic drugs used intraoperatively

Objetivos: En el presente artículo se analiza toda la información publicada en los últimos años sobre la relación entre la hipotermia y su interacción con las diferentes drogas anestésicas, durante el intraoperatorio. Lugar: Hospital de Gastroenterología de Buenos Aires "Dr. Carlos B. Udaondo". Base de datos: Base electrónica Medline e información publicada en los últimos 10 años. Estrategia de búsqueda: Hipotermia, intraoperatorio, drogas anestésicas. Conclusiones: La hipotermia es una situación clínica que se presenta en el 70 por ciento de los pacientes sometidos a procedimientos anestésicos. Los neonatos, niños pequeños y los gerontes son los más propensos a sufrir sus efectos deletéreos. Como consecuencia de la misma el metabolismo y excreción de las drogas anestésicas se encuentra alterado. Por lo tanto la dosificación de los diferentes fármacos debe ser cuidadosamente adecuada para cada paciente de acuerdo al grado de hipotermia registrada durante un continuo y exhaustivo monitoreo intraoperatorio de la temperatura.

Efectos de la hipotermia sobre las drogas anestésicas utilizadas en el intraoperatorio / Hypothermia effects on anesthetic drugs used intraoperatively

Objetivos: En el presente artículo se analiza toda la información publicada en los últimos años sobre la relación entre la hipotermia y su interacción con las diferentes drogas anestésicas, durante el intraoperatorio. Lugar: Hospital de Gastroenterología de Buenos Aires "Dr. Carlos B. Udaondo". Base de datos: Base electrónica Medline e información publicada en los últimos 10 años. Estrategia de búsqueda: Hipotermia, intraoperatorio, drogas anestésicas. Conclusiones: La hipotermia es una situación clínica que se presenta en el 70 por ciento de los pacientes sometidos a procedimientos anestésicos. Los neonatos, niños pequeños y los gerontes son los más propensos a sufrir sus efectos deletéreos. Como consecuencia de la misma el metabolismo y excreción de las drogas anestésicas se encuentra alterado. Por lo tanto la dosificación de los diferentes fármacos debe ser cuidadosamente adecuada para cada paciente de acuerdo al grado de hipotermia registrada durante un continuo y exhaustivo monitoreo intraoperatorio de la temperatura. (AU)