Magíster en Bioquímica, área de especialización en Bioquímica Toxicológica y Diagnóstico Molecular / Memoria para optar al Título de Bioquímico / Recientemente, se demostró que la metabolización de etanol a acetaldehído es indispensable para que su consumo sea reforzante; sin embargo, no se conoce el mecanismo cerebral por el cual se produce este efecto. Se ha postulado que el salsolinol, un producto racémico de la condensación no enzimática de acetaldehído con dopamina, es responsable del efecto reforzante del etanol. La concentración cerebral de salsolinol aumenta luego del consumo de etanol y el salsolinol es una molécula reforzante más potente que el acetaldehído y el etanol, probablemente activando al receptor μ de opioides. Sin embargo, el salsolinol de Sigma-Aldrich, caracterizado como reforzante en los estudios en la literatura, está compuesto por 4 isómeros: R- y S-salsolinol, y R- y S-isosalsolinol (este último es un producto secundario de la condensación no enzimática de acetaldehído y dopamina). Queda por esclarecer: cuál o cuáles de estas moléculas son reforzantes y si estas moléculas alcanzan su concentración reforzante cuando se consume etanol. Además, se ha reportado la existencia de una enzima R-salsolinol sintasa cuyos sustratos son dopamina y acetaldehído. Si la formación de R-salsolinol es responsable del efecto reforzante del etanol, esta enzima podría ser necesaria para que el etanol sea reforzante; sin embargo, no se ha publicado su secuencia aminoacídica. A partir de estos antecedentes se postula que un producto de la condensación de dopamina y acetaldehído es responsable del efecto reforzante del etanol, y este producto alcanza su concentración reforzante a través de su síntesis enzimática (por una R-salsolinol sintasa) o su síntesis no enzimática. Así, el primer objetivo de esta tesis fue detectar, caracterizar y purificar una enzima cerebral con actividad R-salsolinol sintasa en rata, que tenga como sustratos dopamina y acetaldehído. Se abordó la búsqueda de actividad R-salsolinol sintasa en las siguientes preparaciones de cerebro de ratas: homogeneizado completo, sobrenadante citosólico y proteínas purificadas en una resina modificada con dopamina. Se incubaron estas preparaciones con los sustratos dopamina y acetaldehído más cofactores que podrían ser requeridos por esta enzima. No se encontró actividad salsolinol sintasa en muestra alguna. Además, la revisión crítica de los artículos que reportan la presencia de la enzima como de peso molecular bajo 2 kDa y actividad de menor magnitud que la síntesis no enzimática, tornó su búsqueda infundada. Por lo tanto, se descartó esta línea de investigación. La búsqueda de una síntesis enzimática mostró que la velocidad de síntesis no enzimática de salsolinol podría ser suficiente para formar la cantidad reforzante de salsolinol. Luego de esta nueva evidencia, se siguió el objetivo alternativo en esta tesis: determinar cuál es el isómero de salsolinol reforzante, y si su concentración activa en el cerebro es alcanzable a partir de dopamina y acetaldehído. Primeramente, se determinó si las velocidades de síntesis no enzimática de los regioisómeros de salsolinol, salsolinol e isosalsolinol, son suficientemente rápidas para generar sus concentraciones reforzantes. Se midió la formación de salsolinol e isosalsolinol mediante cromatografía líquida de alta eficacia. Se calculó que la concentración reforzante de salsolinol, y no la de isosalsolinol, se alcanza en el cerebro partir de la concentración de acetaldehído reforzante; a través del uso de un modelo de estado estacionario que determina la concentración de salsolinol que se alcanza cuando sus velocidades de síntesis y de degradación se igualan. Debido a que las preparaciones de salsolinol (Sigma-Aldrich) usadas en estudios previos para determinar su efecto reforzante estaban contaminadas con isosalsolinol, era importante confirmar si el salsolinol sin isosalsolinol mantiene su efecto reforzante. Existe evidencia de que al menos un isómero de salsolinol activa al receptor μ de opioides y que, posiblemente, este sea el mecanismo que ejerce su efecto reforzante. Por esto, se realizó un estudio de acoplamiento molecular in silico de los 4 isómeros de salsolinol en el receptor μ de opioides (recientemente cristalizado) que pudiera identificar a cada isómero como activo o inactivo, antes de estudiarlos in vivo. Se observó que todos los isómeros de salsolinol calzan correctamente en el bolsillo de morfina del receptor μ de opioides. Esto no esclarece si cada isómero es agonista (o antagonista) del receptor. Para determinar in vivo si el salsolinol sin isosalsolinol es reforzante, se realizaron dos ensayos: (i) se estudió si, presionando una palanca, ratas se autoadministran intracerebralmente salsolinol; y (ii) se estudió si el salsolinol infundido intracerebralmente provoca una preferencia de lugar condicionada por esta infusión de salsolinol en ratas. La autoadministración intracerebral de salsolinol resultó negativa, posiblemente por la dificultad de la metodología. En el ensayo de preferencia de lugar, las ratas mostraron una tendencia a preferir el lado en el cuál se infundió salsolinol racémico, sin isosalsolinol, y no cuando se infundió la mezcla de ambos regioisómeros. Los resultados en este trabajo (i) indican que el salsolinol racémico no necesita de isosalsolinol para ser reforzante, sugieren que (ii) el isosalsolinol disminuye la capacidad reforzante del salsolinol, y que (iii) el salsolinol racémico alcanza su concentración reforzante no enzimáticamente y podría ser responsable del efecto reforzante del etanol. / Recently, it was shown that the metabolism of ethanol to acetaldehyde is essential for its consumption to be reinforcing; however the cerebral mechanism by which this effect occurs is not known. It has been postulated that salsolinol, a racemic non-enzymatic condensation product of acetaldehyde with dopamine, is responsible for the reinforcing effect of ethanol. The concentration of salsolinol in the brain increases after consumption of ethanol and salsolinol is a more powerfully reinforcing molecule than acetaldehyde and ethanol, possibly activating the μ-opioid receptor. However, the Sigma-Aldrich salsolinol that has been characterized in the literature studies comprises 4 isomers: R- and S-salsolinol, and R- and S-isosalsolinol (the latter is a secondary non-enzymatic condensation product of acetaldehyde and dopamine). Which of these molecules is reinforcing and if this molecule reaches its reinforcing concentration in the brain when ethanol is consumed remains to be elucidated. Furthermore, the existence of an enzyme R-salsolinol synthase whose substrates are acetaldehyde and dopamine has been reported. If the R-salsolinol formation is responsible for the reinforcing effect of ethanol, this enzyme may be necessary for ethanol to be reinforcing; however, its amino acid sequence has not been reported. From this background it is postulated that a condensation product of acetaldehyde and dopamine is responsible for the reinforcing effect of ethanol, and this product reaches its reinforcing concentration through either an enzymatic synthesis (by an R-salsolinol synthase) or a non-enzymatic synthesis. Thus, the first objective of this thesis was to detect, characterize and purify a brain enzyme with R-salsolinol synthase activity in rat, having dopamine and acetaldehyde as its substrates. The search for R-salsolinol synthase activity was addressed by using the following rat brain preparations: whole brain homogenates, cytosolic supernatant and proteins purified in a resin modified with dopamine. These preparations were incubated with the substrates dopamine and acetaldehyde, and cofactors that may be required by this enzyme. No salsolinol synthase activity was found in any sample. In addition, a critical review of articles reporting the presence of the enzyme with a molecular weight lower than 2 kDa and an activity of lesser magnitude than the non-enzymatic rate of synthesis, turned his search unfounded. Therefore, this line of research was discarded. The search for an enzymatic synthesis revealed that the rate of non-enzymatic synthesis of salsolinol may be sufficient for the formation of the reinforcing amount of salsolinol. After this new evidence, we followed the alternative objective in this thesis: to determine which salsolinol isomer is reinforcing and whether its active concentration in the brain can be reached from dopamine and acetaldehyde. Firstly, we investigated whether non-enzymatic synthesis rates of salsolinol and isosalsolinol were fast enough to generate its reinforcing concentrations. The formation of salsolinol and isosalsolinol was measured by high performance liquid chromatography. It was calculated that the reinforcing concentration of salsolinol, and not of isosalsolinol, can be reached in the brain if synthesized from the reinforcing concentrations of acetaldehyde; by means of a steady state model which determines the concentration of salsolinol achieved when its rate of synthesis and degradation are equal. Given that the salsolinol (Sigma-Aldrich) preparations used to determine its reinforcing effect in previous studies were contaminated with isosalsolinol, it was important to confirm that salsolinol without isosalsolinol retains its reinforcing effect. There is evidence that at least one salsolinol isomer activates the μ-opioid receptor and that, possibly, this is the mechanism that exerts its reinforcing effect. Therefore, we performed molecular docking studies of the 4 salsolinol isomers to the μ-opioid receptor (recently crystallized) aimed at identifying each isomer as active or inactive, before studying these in vivo. It was observed that all salsolinol isomers properly fit in the morphine pocket of the μ-opioid receptor. This result does not clarify if an isomer is an agonist (or antagonist) for this receptor. Subsequently, to determine in vivo if salsolinol without isosalsolinol is reinforcing, two assays were performed: (i) we studied if rats self-administered salsolinol directly in the brain by pressing a lever, and (ii) we examined whether salsolinol infused in the brain is capable of inducing a conditioned place preference in rats. The intracraneal salsolinol self-administration was negative, possibly because of the difficulty of the methodology. In the place preference test, rats showed a tendency to prefer the side on which racemic salsolinol without isosalsolinol was infused, and not when a mixture of both regioisomers was infused. The results in this study (i) indicate that racemic salsolinol does not need isosalsolinol to be reinforcing, suggest that (ii) the isosalsolinol decreases the salsolinol reinforcing capability, and (iii) racemic salsolinol reaches its reinforcing concentration non-enzymatically and could be responsible for the reinforcing effect of ethanol. / Fondecyt

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The purpose of this investigation was to evaluate the effects of smoking and gender on 1) tetrahydroisoquinolines (TIQs) and beta-carbolines (BCs) in a population of healthy subjects and 2) TIQs in an alcohol-dependent population undergoing in-patient detoxification. Comparison in plasma TIQs between the populations was additionally conducted. To support the clinical investigations, a HPLC-FD method was developed and validated to assess plasma concentrations of BCs, harman and norharman, while a HPLC-ESI-MS/MS method was validated to quantify the TIQs, R/S-salsolinol along with dopamine. Forty-one young volunteers were recruited including 19 nonsmokers (NS), 11 light smokers (LS) and 11 heavy smokers (HS), stratified by their smoking history. Each group had, at least, 5 males and females. Plasma samples were obtained for analyte measurement within 30 minutes of smoking for LS and HS groups. Two–way ANCOVA was performed on the log-transformed concentrations. Significant differences were found between HS-NS and LS-NS in analyte concentrations. A comparison to eighteen subjects (6 NS, LS and HS) abstaining from smoking for 15 hours resulted in a difference only between NS and HS, suggesting that acute tobacco smoking has a major influence on circulating TIQs and BCs between smoking status groups. In a study involving thirty-five alcohol dependent subjects (12 NS, 11 LS, and 12 HS, balanced with gender), TIQ measurements were taken on day 1, 2, 3, 8 and 15 of inpatient detoxification. A significant effect of time was observed, with TIQ concentrations slightly increasing from admission to day 15. Both factors of smoking status and gender did not have a significant effect on plasma TIQ's at any of the time points evaluated. Although, measures of acute and chronic alcohol intake had no effect on TIQ levels, liver function showed moderate correlation with plasma TIQs. Comparison of both populations showed that alcoholics had a lower average TIQ concentration than healthy subjects. The results indicate that smoking status 1) has an effect on plasma TIQs and BCs in healthy individuals and 2) does not have an effect in alcoholics during detoxification. The alcoholics possessed lower TIQ concentrations than the healthy subjects. No gender effect was observed in either study.

Neurotoxlns represent unique chemical tools, providing a means to 1) gain insight into cellular mechanisms of apopotosis and necrosis, 2) achieve a morphological template for studies otherwise unattainable, 3) specifically produce a singular phenotype of denervation, and 4) provide the starting point to delve into processes and mechanisms of nerve regeneration and sprouting. There are many other notable uses of neurotoxins in neuroscience research, and ever more being discovered each year. The objective of this review paper is to highlight the broad areas of neuroscience in which neurotoxins and neurotoxicity mechanism come into play. This shifts the focus away from neurotoxins per se, and onto the major problems under study today. Neurotoxins broadly defined are used to explore neurodegenerative disorders, psychiatric disorders and substance use disorders. Neurotoxic mechanisms relating to protein aggregates are indigenous to Alzheimer disease, Parkinson's disease. NeuroAIDS is a disorder in which microglia and macrophages have enormous import. The gap between the immune system and nervous system has been bridged, as neuroinflammation is now considered to be part of the neurodegenerative process. Related mechanisms now arise in the process of neurogenesis. Accordingly, the entire spectrum of neuroscience is within the purview of neurotoxins and neurotoxicity mechanisms. Highlights on discoveries in the areas noted, and on selective neurotoxins, are included, mainly from the past 2 to 3 years.

Neurotoxins, in the general sense, represent novel chemical structures which when administered in vivo or in vitro, are capable of producing neuronal damage or neurodegeneration - with some degree of specificity relating to neuronal phenotype or populations of neurons with specific characteristics (.e., receptor type, ion channel type, astrocyte-dependence, etc.). The broader term 'neurotoxin' includes this categorization but extends the term to include intra- or extracellular mediators involved in the neurodegenerative event, including necrotic and apoptotic factors. Moreover, as it is recognized that astrocytes are essential supportive satellite cells for neurons, and because damage to these cells ultimately affects neuronal function, the term 'neurotoxin' might reasonably be extended to include those chemical species which also adversely affect astrocytes. This review is intended to highlight developments that have occurred in the field of 'neurotoxins' during the past 5 years, including MPTP/MPP+, 6-hydroxydopamine (6-OHDA), meth-amphetamine; salsolinol; leukoaminochrome-o-semi-quinone; rotenone; iron; paraquat; HPP+; veratridine; soman; glutamate; kainate; 3-nitropropionic acid; peroxynitrite anion; and metals (copper, manganese, lead, mercury). Neurotoxins represent tools to help elucidate intra- and extra-cellular processes involved in neuronal necrosis and apoptosis, so that drugs can be developed towards targets that interrupt the processes leading towards neuronal death.