Frederic Mármol

Lithium: bipolar disorder and neurodegenerative diseases Possible cellular mechanisms of the therapeutic effects of lithium.

Bipolar illness is a major psychiatric disorder that affects 1-3% of the worldwide population. Epidemiological studies have demonstrated that this illness is substantially heritable. However, the genetic characteristics remain unknown and a clear personality has not been identified for these patients. The clinical history of lithium began in mid-19th century when it was used to treat gout. In 1940, it was used as a substitute for sodium chloride in hypertensive patients. However, it was then banned, as it had major side effects. In 1949, Cade reported that lithium could be used as an effective treatment for bipolar disorder and subsequent studies confirmed this effect. Over the years, different authors have proposed many biochemical and biological effects of lithium in the brain. In this review, the main mechanisms of lithium action are summarised, including ion dysregulation; effects on neurotransmitter signalling; the interaction of lithium with the adenylyl cyclase system; inositol phosphate and protein kinase C signalling; and possible effects on arachidonic acid metabolism. However, none of the above mechanisms are definitive, and sometimes results have been contradictory. Recent advances in cellular and molecular biology have reported that lithium may represent an effective therapeutic strategy for treating neurodegenerative disorders like Alzheimers disease, due to its effects on neuroprotective proteins like Bcl-2 and its actions on regulators of apoptosis and cellular resilience, such as GSK-3. However, results are contradictory and more specific studies into the use of lithium in therapeutic approaches for neurodegenerative diseases are required.

Demonstration of inhibition of cyclic AMP accumulation in brain by very low concentrations of lithium in the presence of α-adrenoceptor blockade

In the present paper, we have studied the effect of lithium on cAMP levels induced by isoprenaline and norepinephrine in the presence of alpha- or beta-adrenoceptor antagonists. Our results show that low lithium concentrations, starting at 0.3 x 10(-3) M, have a significant inhibitory effect on cAMP content induced by isoprenaline in brain tissue pretreated with the alpha-adrenoceptor blocker phenoxybenzamine. On the other hand, the inhibitory effect of lithium on cAMP levels induced by norepinephrine when beta-adrenoceptors are blocked with propranolol, is observed at concentrations starting at 2.5 x 10(-3) M. These results show that in the presence of alpha blockade, low lithium concentrations which are within the therapeutic plasma range for treatment of manic patients, are able to act on an adenylate cyclase-cAMP system coupled to beta-adrenoceptors.

Loss of adaptation to oxidative stress as a mechanism for aortic damage in aging rats

Cells are armed with a vast repertoire of antioxidant defence mechanisms to prevent the accumulation of oxidative damage. The cellular adaptive response is an important antioxidant mechanism against physiological and pathophysiological oxidative alterations in a cell’s microenvironment. The aim of this paper was to study, in the rat aorta, whether this adaptive response and the inflammation associated with oxidative stress were expressed throughout the aging process. We examined the rat aorta, as it is a very sensitive tissue to oxidative stress. Male Wistar rats of 1.5, 3, 12, 18 and 24 months of age were used. Superoxide anion (O2−) generation; levels of two antioxidant enzymes, superoxide dismutase (SOD) and catalase; and the levels of prostaglandin E2 (PGE2), an inflammatory marker, were measured. The results for rats at different ages were compared with those for 3 months of age. A balance between production of O2− and SOD activity was found in the aorta of rats from 1.5 to 12 months old. Oxidative stress was present in the aorta of old animals (18–24) months), due to a failure in the mechanisms of adaptation to oxidative stress. The observed increase in PGE2 levels in these rats reflected an inflammatory response. All together suggest that vascular oxidative stress and the inflammatory process observed in the old groups of rats could be closely related to vascular aging. Our results also remark the importance of the adaptative response to oxidative stressResumenLas células están equipadas con una amplia gama de mecanismos de defensa antioxidante para prevenir la acumulación de lesiones oxidativas. La respuesta celular de adaptación constituye un importante mecanismo antioxidante para prevenir las alteraciones en el microentorno celular tanto a nivel fisiológico como patofisiológico. El propósito de este trabajo fue estudiar en aorta de rata si la respuesta de adaptación así como la inflamación, asociadas ambas con el estrés oxidativo, se expresan a lo largo del proceso de envejecimiento. Se ha empleado aorta de rata ya que constituye un tejido muy sensible al estrés oxidativo. Se utilizaron ratas macho Wistar de 1,5,3,12,18 y 24 meses de edad y se estudiaron la producción de anion superoxido (O2−), los niveles de dos enzimas antioxidantes, superoxido dismutasa (SOD) y catalasa, así como los niveles de prostaglandina E2 (PGE2), un indicador de la inflamación. Los resultados obtenidos a las diferentes edades se compararon con los obtenidos con las ratas de 3 meses de edad. Nuestros resultados demostraron un equilibrio entre producción de O2− y actividad de SOD en las ratas de entre 1,5 y 12 meses de edad. En la aorta de los animales viejos (18–24 meses) se detectó mayor estrés oxidativo debido a un fallo en los mecanismos de adaptación al mismo, mientras que el aumento observado en los niveles de PGE2 en estos animales refleja una respuesta inflamatoria. En conjunto, nuestros resultados sugieren que tanto el estrés oxidativo vascular, como el proceso inflamatorio observados en los grupos de ratas viejas podrían estar fuertemente relacionados con el envejecimiento vascular. Nuestros resultados remarcan también la importancia de la respuesta de adaptación al estrés oxidativo.

Oxidative stress markers in the neocortex of drug-resistant epilepsy patients submitted to epilepsy surgery

PURPOSE While there is solid experimental evidence of brain oxidative stress in animal models of epilepsy, it has not been thoroughly verified in epileptic human brain. Our purpose was to determine and to compare oxidative stress markers in the neocortex of epileptic and non-epileptic humans, with the final objective of confirming oxidative stress phenomena in human epileptic brain. METHODS Neocortical samples from drug-resistant epilepsy patients submitted to epilepsy surgery (n=20) and from control, non-epileptic cortex samples (n=11) obtained from brain bank donors without neurological disease, were studied for oxidative stress markers: levels of reactive oxygen species (ROS), such as superoxide anion (O2(-)); activity of antioxidant enzymes: superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione reductase (GR); and markers of damage to biomolecules (lipid peroxidation and DNA oxidation). RESULTS Compared with non-epileptic controls, the neocortex of epileptic patients displayed increased levels of superoxide anion (P≤0.001), catalase (P≤0.01), and DNA oxidation (P≤0.001); a decrease in GPx (P≤0.05), and no differences in SOD, GR and lipid peroxidation. CONCLUSIONS Our findings in humans are in agreement with those found in animal models, supporting oxidative stress as a relevant mechanism also in human epilepsy. The concurrent increase in catalase and decrease in GPx, together with unchanged SOD levels, suggests catalase as the main antioxidant enzyme in human epileptic neocortex. The substantial increase in the levels of O2(-) and 8-oxo-dG in epileptic patients supports a connection between chronic seizures and ROS-mediated neural damage.

Anti-oxidative effects produced by environmental enrichment in the hippocampus and cerebral cortex of male and female rats.

Both physical and intellectual activity may reduce the incidence of neurodegenerative disorders. There is evidence that environmental enrichment (EE) can induce profound behavioral, neurochemical and neuroanatomical changes, thus producing lasting improvements in memory and learning tasks. In this study we evaluated the anti-oxidative effects produced by EE in the hippocampus and the cerebral cortex of male and female rats. The animals had been reared in either EE or control conditions. The parameters studied were: thiobarbituric acid reactive substances (TBARS), protein oxidation, total radical antioxidant parameter, catalase, superoxide dismutase and superoxide anion activity. The results showed that our EE protocol reduced markers of oxidative stress in the hippocampus and in the cerebral cortex. Overall, the measures taken in the two cerebral regions revealed that EE rats showed higher values for antioxidant measures and lower values for oxidative stress parameters than control animals. More importantly, a consistent sex difference was found, indicating that in female rats the hippocampus and cerebral cortex are plastic brain regions receptive to external stimulation such as EE. Although EE males have higher levels for antioxidant capacity, catalase and SOD, it is likely that females do not need to activate all the antioxidant defenses since they have a greater capacity to assimilate external stimuli. This is suggested by the similarity of protein oxidation and TBARS levels in hippocampus in both sexes, and the even lower levels of protein oxidation and superoxide anion activity in the cerebral cortex in EE females.

Post-train administration of 9-amino-1,2,3,4,-tetrahydroacridine enhances passive avoidance retention and decreases β-adrenoceptor-linked cyclic AMP formation in middle-aged rats

The possible involvement of beta-adrenoceptor system in the effectiveness of 9-amino-1,2,3,4-tetrahydroacridine (THA) to attenuate retention deficits exhibited by middle-aged rats in a one-trial passive avoidance task has been investigated. THA (2.5 mg.kg-1), injected i.p. after training, induced a significant increase in test step-through latency (STL) in middle-aged rats. Post-training injection of THA reduced basal and isoprenaline stimulated cyclic AMP accumulation in cortex and hippocampus of every group of rats. It is suggested that the effect of THA on memory processes may involve an action on beta-adrenoceptor-linked cyclic AMP accumulation.

Oxidative stress, nitric oxide and prostaglandin E2 levels in the gastrointestinal tract of aging rats

Objectives To evaluate the presence of oxidative stress and alterations in the levels of two cytoprotective agents, prostaglandin E2 and nitric oxide, in the gastrointestinal tract of aging rats.

Effect of α2-adrenoceptor blockade on lithium action in the rat brain

The inhibitory effect of different concentrations of lithium (0.15-10 x 10(-3) M) on cAMP production induced by isoprenaline (1 x 10(-4) M) after the blockade of alpha(2)-adrenoceptors in the rat cerebral cortex was investigated. Low lithium concentrations (0.3-0.6 x 10(-3) M) exerted a significant inhibitory effect after yohimbine (1 x 10(-5) M) addition, but had no effect when isoprenaline alone or prazosin (1 x 10(-7) M) was added. The recovery of [3H]yohimbine binding after irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was evaluated in cortical membranes to study how alpha(2)-adrenoceptor repopulation affects the action of lithium on the adenylyl cyclase-cAMP system. When the density of alpha(2)-adrenoceptors was lower than 21%, lithium showed a significant inhibitory effect at all concentrations tested. However, at higher densities, increased concentrations of lithium were required to inhibit cAMP production. Our results suggest that the inhibitory effect of lithium on cAMP levels in the rat brain is conditioned by alpha(2D)-adrenoceptors.

Effects of age on α1‐adrenoceptor subtypes in the heart ventricular muscle of the rat

Abstract— The effects of ageing on α1‐adrenoceptor subtypes have been examined in heart ventricular muscle of young (2–3 months) and middle‐aged (18 months) Sprague‐Dawley rats. Radioligand binding studies with [3H]prazosin revealed an age‐related loss of binding sites (Bmax 56·7 ± 1·93 fmol (mg protein)−1 age 2 months vs 31·7 ± 2·45 fmol (mg protein)−l age 18 months) not followed by changes in the dissociation constant value (Kd 0·16 ± 0·03 nm age 2 months and 0·10 ± 0·03 nm age 18 months). Competition curves with WB 4101 showed two distinct sites with different affinities, the proportion of sites with high affinity being similar for both age groups (22·2 ± 1·89% vs 17·8 ± 1·96% for animals aged 2 and 18 months, respectively). Agonist displacement curves of [3H]prazosin indicate the existence of two different affinity sites for the agonist, that are maintained regardless of the ageing process (Rhigh= 16·2 ± 1·54% and Rlow = 83·8 ± 1·89% in rats aged 2 months and Rhigh= 16·3 ± 3·23% and Rlow = 83·7 ± 3·95% in rats aged 18 months). The fractional inactivation of α1‐adrenoceptors by chloroethylclonidine resulted in a loss of [3H]prazosin specific binding, and a percentage of 22·5 ± 0·95 and 22·6 ± 4·2 of remaining binding sites for the groups of 2 and 18 months of age, respectively. The percentage of chloroethylclonidine‐insensitive [3H]prazosin binding sites was similar to those with high affinity for WB 4101. The present study confirms a decline of α1‐adrenoceptors with increasing age and reveals that the equilibrium of the expression of the two existing subpopulations of the receptor is maintained during ageing.

Chronic treatment of guinea pigs with lithium chloride: effects on myenteric plexus preparations and on cyclic AMP levels

We studied the effects of lithium chloride, given i.p. in doses of 0.05, 1, 2, 4 and 8 mEq/kg twice daily for 14 days, on preparations of guinea pig myenteric plexus. The effects of lithium added to isolated myenteric plexus preparations derived from chronically treated animals showed that relatively low lithium concentrations produced a statistically significant decrease in the force of contraction, this effect being concentration-dependent. 3-Isobutyl-1-methylxanthine (IBMX) induced a statistically significant inhibition, between 30 and 50%, of the lithium effects. cAMP levels in animals treated chronically with lithium were studied, using an isotopic displacement technique. Our results show that only the highest dose of lithium (8 mEq/kg per day) significantly decreased basal levels of cAMP. In the presence of IBMX, low doses of lithium (1 mEq/kg per day) induced a very significant decrease in cAMP levels, but the inhibition remained constant, approximately 30-35%, at doses from 2 mEq/kg per day. In guinea pig myenteric plexus preparations from acutely treated animals, our results show a direct relationship between lithium concentration and inhibition of the cAMP accumulation induced by IBMX.