Current Pharmaceutical Design - Volume 19, Issue 38, 2013

Background: Bioavailability (F) and clearance (CL) are two pharmacokinetic parameters difficult to differentiate from simple plasma measurement when a drug is administered orally. Venous (V) / artery (A) concentration ratio of a drug could be a reliable index of its CL if measurements of plasma concentration were performed during a period of time where the absorption process was not longer operative, then during a pure elimination phase. Objective: A novel subrogate using two protocolized saliva samples sequentially collected (first, S1, and second, S2) was designed in order to replace V and A free plasma drug concentrations, respectively. Two drugs, phenytoin (PHT) and carbamazepine (CBZ), which are well-known for their inducer properties and their dose-dependent clearance variations, were studied taking into account the sex of individuals. Setting and patients: A multicentre two-phase collaborative study was done. The first phase was performed with healthy volunteers in order to determine salivary pharmacokinetic parameters after single dose administration. Twelve volunteers (6 male and 6 female) received 400 mg of CBZ (2 tablets x 200 mg, immediate release product). Twenty four volunteers (10 male and 14 female) received 100 mg of PHT. The second phase was carried out with epileptic patients under CBZ (11 male 15 female) or PHT (11 male and 11 female) monotherapy, in order to study dose-related and sex-related pharmacokinetic differences. Main outcome measures: In the single dose trials, peaks (Tmax, Cmax) were computed directly from the data. Areas under concentrationtime curves (AUC∞), AUC∞xW (area corrected by weight) and half-lives (t1/2) were calculated. In the case of CBZ, AUCCBZ-10,11- epoxide/AUCCBZ metabolic ratios were also calculated. After multiple dose administration, S1 and S2 trough morning drug concentrations were measured. Results: Cmax and AUC differed significantly between sexes for the two drugs after single dose administration. Nevertheless, the apparent clearance (CL/F) per unit of body weight did not differ (CBZ) or slightly differed (PHT) between sexes. Higher metabolic ratio for CBZ in women would lead to lower F and therefore lower CL in this gender. In the case of PHT, women would have either lower F or higher CL than men. After multiple dose administration, S1/S2 saliva drug concentration ratio correlated positively with S2 for CBZ, showing that CBZ clearance increases with daily dose. Gender differences were also observed for CBZ-10,11-epoxide concentration, being bioavailability the main parameter responsible for this difference. S1/S2 saliva PHT concentration ratio correlated negatively with S2, showing that PHT clearance diminishes with dose as it has been previously reported. Since a significant difference was found for S1/S2 ratio between male and females, CL is the pharmacokinetic parameter influenced by gender in PHT disposition. Conclusion: S1/S2 saliva drug concentration ratio was sensitive enough for detecting systemic clearance changes. Both CBZ and PHT would modify their bioavailability and clearance by inducing efflux transporter throughout chronic treatments, from the first dose to multiple dose administration.

Glutamic acid (Glu) is the major excitatory neurotransmitter in the central nervous system, and interacts with two classes of receptor: metabotropic and ionotropic receptors. Ionotropic receptors are divided according to the affinity of their specific agonists: Nmethyl- D-aspartate (NMDA), amino acid-3-hydroxy-5-methyl-4-isoxazole acid (AMPA) and kainic acid (KA). NMDA receptors (NMDA-R) are macromolecular structures that are formed by different combinations of subunits: NMDAR1 (NR1), NMDAR2 (NR2) and NMDAR3 (NR3). The study of this receptor has aroused great interest, partly due to its role in synaptic plasticity but mainly because of its permeability to the Ca2+ ion. This review examines the molecular composition of NMDA-R and the variants of NR1 subunit editing in association with NR2 subunit dimers, which form the main components of this receptor. Their composition, structure, function and distinct temporal and spatial expression patterns demonstrate the versatility and diversity of functionally different isoforms of NR1 subunits and the various pharmacological properties of the NR2 subunit. Finally, the involvement of NMDA-R in the excitotoxicity phenomenon, as well as, its expression changes under these conditions as neuronal response are also discussed.

This review summarizes the effects of resveratrol in neurodegenerative diseases and speculates on the direction the field will take in the immediate future. In particular, we emphasize studies on the effects of resveratrol on new pathways related to neurodegenerative diseases such as inflammatory processes, mitochondrial biogenesis and its control through gamma coactivator 1-α (PGC1α), and the role of the tandem sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK) in neurodegeneration and in neurohormesis. While not all reported results are free from controversy, the demographic shift toward an older population makes compounds with this broad spectrum of potential clinical applications particularly interesting.

P-glycoprotein (P-gp) has been associated with pharmacoresistance and mechanisms regulating the membrane potential. However, at present it is unknown if P-gp overexpression in brain is associated with changes in membrane depolarization in refractory epilepsy. Experiments were designed to evaluate the membrane depolarization and P-gp overexpression induced by repetitive pentilenetetrazole (PTZ)-induced-seizures. Wistar rats were daily treated with PTZ during 4 to 7 days (PTZ4 and PTZ7 groups), and the brain was used to evaluate membrane potential by in vitro electrophysiological procedures and using bis-oxonol dye, [bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4(3)], a fluorescence dye voltage-sensitive to membrane potentials. Rats with repetitive PTZ-induced seizures demonstrated lower phenytoin-induced anticonvulsant effects, increased number of DiBAC4(3) fluorescence cells and P-gp overexpression in hippocampus and neocortex, as well as augmentation of the induced fEPSP in CA1 field. These changes were more evident in PTZ7 group. Phenytoin or phenytoin plus nimodipine (a P-gp antagonist) avoided the enhanced fEPSP and decreased DiBAC4(3) fluorescence in animals from PTZ4 group. However, in PTZ7 group these effects were evident only when phenytoin was combined with nimodipine. An additional flow cytometry study demonstrated increased intracellular accumulation of DiBAC4(3) in K562 leukemic cells that overexpress MDR-1 and COX-2 genes, and are refractory to specific cytotoxic agents. These results represent the first evidence supporting the notion that brain P-gp overexpression contributes to a progressive seizure-related membranes depolarization in hippocampus and neocortex. Further experiments should be carried out to confirm the role of P-gp on membrane depolarization and epileptogenesis process.

The more common sporadic form of Alzheimer disease (SAD) and the metabolic syndrome are two highly prevalent pathological conditions of Western society due to incorrect diet, lifestyle, and vascular risk factors. Due to the increasing aging of populations, prevalence of AD in western industrialized countries will rise in the near future and, thus, new knowledge in the area of molecular biology and epigenetics will probably help to reverse the neurodegenerative process. Recent data have suggested metabolic syndrome as an independent risk factor for SAD. Furthermore, biological plausibility for this relationship has been framed within the metabolic cognitive syndrome concept, and some authors designed SAD as a brain diabetes or diabetes 3. Then, impaired signaling of insulin and from some adipokines involved in the so called adipoinsular axis, like leptin, ghrelin or amylin could give a metabolic basis to explain the origin and progression of SAD. Thus, dipokines like leptin, ghrelin and amylin, or their mimetic compounds, could contribuite to inhibit apoptosis and inflammation processes and, thus, generate protective responses in the nervous system. Moreover, these adipokines might promote the activation of a cognitive process which may retard or even partially reverse selected aspects of Alzheimer’s disease or ageing memory loss.

The majority of patients suffering from Alzheimer’s disease (AD) demonstrate cerebral vascular changes and impaired regulation of cerebral blood flow, which has been assumed to play an important role in AD pathogenesis (vascular hypothesis of AD). There is strong evidence that both β-amyloid (Aβ) oligomers and plaques contribute to vascular injuries and functional impairments of the neurovascular unit. Vice versa, Aβ lesions can be triggered by hypertension and ischemic brain injury, while Aβ aggregates appear to have anti-angiogenic properties. Cholinergic dysfunction may result in impaired cerebral blood flow with consequences on normal function of the neurovascular unit including processing of the amyloid precursor protein (APP). To characterize in vivo the developmental relationship between Aβ formation and deposition, cortical cholinergic innervation and cerebrovascular abnormalities, transgenic Tg2576 mice that overexpress the Swedish double mutation of human APP, and demonstrate significant cerebral cortical deposition of Aβ plaques at ages from 9 months onwards, were considered as an appropriate animal model. Using the somatosensory cortex as a representative region, serial cryocut sections, were obtained from mice at ages ranging from 4 up to 18 months. These were subjected to immunohistochemistry to label vascular endothelial cells (anti-glucose transporter 1 (GluT1) immunostaining), cholinergic nerve terminals (anti-vesicular acetylcholine transporter (VAChT) immunostaining) and β-amyloid plaques (thioflavin S, and/or Solanum tuberosum lectin staining). This was followed by a thorough quantitative evaluation of the age-related spatial relationship between cerebral cortical capillaries, Aβ plaques and cholinergic terminals, using computer-assisted image analysis. The density of cholinergic terminals estimated by evaluation of VAChT immunohistochemistry in somatosensory cortical sections of wild type mice did not change with aging regardless of the cortical layer examined, while in cortical layers II/III and IV of somatosensory cortex of transgenic Tg2576 mice age-related decreases in cholinergic fiber densities were assessed. However, quantitative morphometric analysis demonstrated an age-related reduction in the number of varicosities on cholinergic fibers, particularly in layer IV, in both transgenic Tg2576 mice and non-transgenic littermates. Cholinergic innervation of microvessels in the somatosensory cortex decreased with aging in both Tg2576 mice and non-transgenic littermates, as revealed by estimating the ratio of the number of cholinergic vascular contacts and total length of blood vessel. There was no significant difference in the perivascular cholinergic innervation in areas that demonstrated significant plaque load and those with no plaque deposits regardless of the cortical layer examined. The density of blood vessels estimated in the somatosensory cortex of transgenic mice by anti-GluT-1 immunohistochemistry did not differ to that obtained in wild type mice before the onset of plaque deposition (younger than 10 months). However, in aged, 18-month-old Tg2576 mice, demonstrating high plaque loads, decreased blood vessel densities, particularly in layer IV of the somatosensory cortex, were observed. The data obtained in this study strongly support the idea of an age-related interplay between Aβ accumulation, cholinergic dysfunction, and vascular impairments. However, it remains to be elucidated as to which processes play a causative role and which events are secondary. A potential mechanism is provided by the vascular hypothesis of AD. Aging-, and life-style-associated damage of the brain microvasculature may affect Aβ clearance and perivascular drainage, promoting cerebrovascular Aβ deposition, inducing partial loss of cholinergic vascular innervation and changes in vascular function, angiogenesis and upregulation of the vesicular endothelial growth factor (VEGF) with consequences on APP processing and Aβ accumulation.

All common contributing factors to epilepsy such as trauma, malignancies and infections are accompanied by different levels of central nervous system inflammation that in turn have been associated with the occurrence of seizure. Emerging data from human brain tissue and experimental models of epilepsy support the proposed involvement of inflammation in epilepsy. Key mediators of this process include, among others: interleukin (IL) -1β, IL-6, tumor necrosis factor-α, adhesion molecules and component of complement. Recent advances suggest the involvement of specific inflammatory pathways in the pathogenesis of seizures in patients with pharmacoresistant temporal lobe epilepsy, highlighting the potential for new therapeutic strategies. This review provides an overview of the current knowledge on the relationship between inflammatory mediators and epilepsy. We also describe experimental and clinical evidence of inflammation in epilepsy with special emphasis on clinical aspects once the epileptogenic focus has been resected. Further insight into the complex role of inflammation in epileptogenesis may provide new treatment options.

Ghrelin is a gastric hormone that stimulates growth hormone (GH) secretion and food intake to regulate energy homeostasis and body weight by binding to its receptor, GH secretagogue receptor (GHSR1a), which is most highly expressed in the pituitary and hypothalamus. Nowadays there is considerable evidence showing that the GHSR1a is also expressed in numerous extra-hypothalamic neuronal populations and the physiological role of ghrelin is by far wider than considered before including learning and memory, anxiety, depression and neuroprotection. The present review attempts to provide a comprehensive picture of the role of ghrelin in the central nervous system and to highlight recent findings showing its potential as an innovative therapeutic agent in neurodegenerative diseases including Alzheimer’s disease and Parkinson’s disease.

Neuronal damage secondary to brain injuries such as cerebral hypoxia, seizures as well as neurodegenerative process, may include pro-inflammatory changes. The activation of a common mechanism related to survival or cell death, mediated by the stabilization and trans-activation of Hypoxia-Inducible Factor 1 (HIF-1), has been observed in these conditions. HIF-1 may induce over expression of P-glycoprotein, the product multidrug-resistance gene (MDR-1), both on blood-brain barrier as well as on the cerebral damaged cells, producing the refractoriness to therapeutic strategies for neuroprotection. However, in these same cells, HIF-1 can also induce the expression of erythropoietin receptor (Epo-R). Irrespective of its known properties on hematopoiesis, it was proposed that erythropoietin can trigger neuroprotective mechanisms mediated by Epo-R activation. Brain hypoxia, epilepsy, neurodegeneration and inflammation, can share the induction of Epo-R and several other growth factor receptors as well as signal transductions pathways after HIF-1 transactivation. Perhaps, the use of the intranasal route for the exogenous administration of Epo, (or other biological compounds) could help neuroprotection as well as to repair the brain areas damaged.

Antiepileptic drugs can cause some adverse effects ranging from mild to acute and serious ones. The inducing properties of some of them may result in vitamin D, vitamin K and estrogens catabolism and thus risk of fractures or efflux transport overexpression at the blood brain barrier and consequently lack of effect at the action site. Some are responsible for the formation of reactive metabolites, such as arene oxides or atropaldehyde intermediates, in skin, liver and other organs, causing hypersensitivity reactions or can enhance a commonly minor metabolic pathway increasing the formation of toxic metabolites. Drug-induced myopia and other visual problems have also been described with the use of antiepileptic agents. A pharmacological insight of the possible concentration-dependent mechanism involved in these reactions is given in this review and in some cases some preventive measures to revert them.

Brain structural and functional integrity exquisitely relies on a regular supply of oxygen. In order to circumvent the potential deleterious consequences of deficient oxygen availability, brain triggers endogenous adaptive and pro-survival mechanisms - a phenomenon known as brain hypoxic tolerance. The highly conserved hypoxia-inducible family (HIF) of transcription factors is the “headquarter” of the homeostatic response of the brain to hypoxia. HIF acts as a cellular oxygen sensor and regulates the expression of proteins involved in a broad range of biological processes, including neurogenesis, angiogenesis, erythropoiesis, and glucose metabolism, and thus, enables brain cells to survive in low-oxygen conditions. Hypoxia, as well as hypoxia-reoxygenation, is intimately implicated in the clinical and pathological course of several neurodegenerative diseases. Thus, two major questions can arise: Is HIF signaling and brain response to hypoxia compromised in neurodegenerative diseases? If so, are HIF stabilizers a possible therapeutic strategy to halt or prevent the progression of neurodegenerative diseases? This review highlights the current knowledge pertaining the role of HIF on brain response to hypoxia and its close association with the development of Alzheimer’s, and Parkinson’s disease and amyotrophic lateral sclerosis. Finally, the potential therapeutic effects of HIF stabilizers (deferoxamine, clioquinol, M30, HLA20, DHB, FG0041, and VK-28) against the symptomatic and neuropathological features of the abovementioned neurodegenerative diseases will be discussed.

Our understanding of the magnitude and physiological significance of proteome lysine acetylation remained incipient for five decades since it was first described. State-of-the-art methodologies, ranging from functional genomics to large-scale proteomics, have recently uncovered that this modification is more broadly represented in proteins than previously recognized, thus constituting the “acetylome.” At present, it is estimated that acetylome covers only one tenth of the proteome, however, due its potential significance in physiology is capturing great attention. The first components of the cellular machinery, which finely orchestrate acetylome homeostasis, were identified by the end of last century. Since then, the majority of our growing knowledge concerning the physiological relevance of proteome reversible acetylation comes from the study of sirtuins, a unique type of lysine deacetylase that uses NAD+. Sirtuins participate in a variety of cellular processes, ranging from transcription, DNA repair, energy balance, mitochondrial biogenesis and cell division, to apoptosis, autophagy and aging. Within the brain, besides their widespread epigenetic effects of dynamically modifying histones, sirtuins also target a variety of non-histone proteins either commonly deregulated in pathologies, or that participate in normal cerebral functions. For example, they modulate critical elements of the circadian rhythms, neurogenesis, synapses, cognition, serotonin synthesis, myelination, and proteins involved in neuropathology. Acetylome dynamics, and its regulation by sirtuins, may also help to better understand the molecular mechanisms underlying brain aging. This work reviews the pathways as orchestrated by the interplay between acetylome and sirtuins in the brain, from physiology involvement, to aging processes, and pathological settings.