Rafael Rodríguez-Puertas

Nutritional omega-3 deficiency abolishes endocannabinoid-mediated neuronal functions

The corollaries of the obesity epidemic that plagues developed societies are malnutrition and resulting biochemical imbalances. Low levels of essential n-3 polyunsaturated fatty acids (n-3 PUFAs) have been linked to neuropsychiatric diseases, but the underlying synaptic alterations are mostly unknown. We found that lifelong n-3 PUFAs dietary insufficiency specifically ablates long-term synaptic depression mediated by endocannabinoids in the prelimbic prefrontal cortex and accumbens. In n-3–deficient mice, presynaptic cannabinoid CB1 receptors (CB1Rs) normally responding to endocannabinoids were uncoupled from their effector Gi/o proteins. Finally, the dietary-induced reduction of CB1R functions in mood-controlling structures was associated with impaired emotional behavior. These findings identify a plausible synaptic substrate for the behavioral alterations caused by the n-3 PUFAs deficiency that is often observed in western diets.

Profiling and Imaging of Lipids on Brain and Liver Tissue by Matrix-Assisted Laser Desorption/ Ionization Mass Spectrometry Using 2-Mercaptobenzothiazole as a Matrix

2-Mercaptobenzothiazole (MBT) is employed for the first time as a matrix for the analysis of lipids from tissue extracts using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We demonstrate that the performance of MBT is superior to that of the matrixes commonly employed for lipids, due to its low vapor pressure, its low acidity, and the formation of small crystals, although because of the strong background at low m/z, it precludes detection of species below approximately 500 Da. This inconvenience can be partly overcome with the formation of Cs adducts. Using a polymer-based dual calibration, a mass accuracy of approximately 10 ppm in lipid extracts and of approximately 80 ppm in tissues is achieved. We present spectra from liver and brain lipid extracts where a large amount of lipid species is identified, in both positive and negative ion modes, with high reproducibility. In addition, the above-mentioned special properties of MBT allow its employment for imaging mass spectrometry. In the present work, images of brain and liver tissues showing different lipid species are presented, demonstrating the advantages of the employment of MBT.

Matrix-assisted laser desorption ionization imaging mass spectrometry in lipidomics

The relevant structural, energetics, and regulatory roles of lipids are universally acknowledged. However, the high variability of lipid species and the large differences in concentrations make unraveling the role played by the different species in metabolism a titanic task. A recently developed technique, known as imaging mass spectrometry, may shed some light on the field, as it enables precise information to be obtained on the location of lipids in tissues. A review of the state of the art of the technique is presented in this manuscript, including detailed analysis of sample-preparation steps, data handling, and the identification of the species mapped so far.

Characterization of receptor-mediated [35S]GTPγS binding to cortical membranes from postmortem human brain

The [35S]GTPgammaS binding assay represents a functional approach to assess the coupling between receptors and G-proteins. The optimal conditions for [35S]GTPgammaS binding to human brain homogenates were established in postmortem samples of prefrontal cortex. The influence of protein content, incubation time, GDP, Mg(2+), and NaCl concentrations on the [35S]GTPgammaS binding were assessed in the absence and presence of the alpha(2)-adrenoceptor agonist UK14304 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine). In conditions of 50 microM GDP and 100 mM NaCl, UK14304 increased the apparent affinity of the specific [35S]GTPgammaS binding without changing the apparent density. Concentration-response curves to agonists of alpha(2)-adrenoceptors, mu-opioid, 5-HT(1A), cholinergic muscarinic, and GABA(B) receptors displayed, in the presence of NaCl, maximal stimulations between 24% and 61% with EC(50) values in the micromolar range. Selective antagonists shifted to the right the agonist-induced stimulation curves. The G(i)/G(o)-protein alkylating agent N-ethylmaleimide decreased basal [35S]GTPgammaS binding in a concentration-dependent manner and inhibited the stimulation induced by the different agonists. In cortical sections, [35S]GTPgammaS binding to gray matter was stimulated by the agonist UK14304. The present study demonstrates that functional studies of the receptor coupling to G(i)/G(o)-proteins can be performed in postmortem human brain samples.

Distribution of lipids in human brain

The enormous abundance of lipid molecules in the central nervous system (CNS) suggests that their role is not limited to be structural and energetic components of cells. Over the last decades, some lipids in the CNS have been identified as intracellular signalers, while others are known to act as neuromodulators of neurotransmission through binding to specific receptors. Neurotransmitters of lipidic nature, currently known as neurolipids, are synthesized during the metabolism of phospholipid precursors present in cell membranes. Therefore, the anatomical identification of each of the different lipid species in human CNS by imaging mass spectrometry (IMS), in association with other biochemical techniques with spatial resolution, can increase our knowledge on the precise metabolic routes that synthesize these neurolipids and their localization. The present study shows the lipid distribution obtained by MALDI-TOF IMS in human frontal cortex, hippocampus, and striatal area, together with functional autoradiography of cannabinoid and LPA receptors. The combined application of these methods to postmortem human brain samples may be envisioned as critical to further understand neurological diseases, in general, and particularly, the neurodegeneration that accompanies Alzheimer’s disease.

Effects of age, postmortem delay and storage time on receptor-mediated activation of G-proteins in human brain.

The influence of age, postmortem delay and freezing storage period on receptor-mediated G-protein activity was quantified in cortical membranes from 34 healthy subjects. Concentration-response curves of the [35S]GTPγS binding stimulation by agonists for α2-adrenoceptors (UK14304), μ-opioid (DAMGO), 5-HT1A (8-OH-DPAT), GABAB (baclofen) and muscarinic (carbachol) receptors were analyzed. Immunoreactivities of Gα-protein subunits were also determined. Basal binding and UK14304, 8-OH-DPAT, and baclofen potency to stimulate [35S]GTPγS binding decreased with aging (1–88 years) without changes of efficacy. DAMGO-mediated stimulation increased both in potency and efficacy with aging. A negative correlation between age and immunoreactivity was observed for Gαi1/2-, but not for Gαi3-, Gαo-,and Gαs-proteins. Neither [35S]GTPγS binding nor Gα-proteins changed with the postmortem delay (8–92 h). Basal [35S]GTPγS binding decreased with the sample storage period (1–85 months). A careful match between cases and controls should be taken into account when designing signal transduction studies in human disorders, specially for variables such as age and storage period.

Blockade of monoacylglycerol lipase inhibits oligodendrocyte excitotoxicity and prevents demyelination in vivo.

The endocannabinoids 2‐araquidonoylglycerol (2‐AG) and anandamide (AEA) are bioactive lipids crucially involved in the regulation of brain function in basal and pathological conditions. Blockade of endocannabinoid metabolism has emerged as a promising therapeutic strategy for inflammatory diseases of the central nervous system, including myelin disorders such as multiple sclerosis. Nevertheless, the biological actions of endocannabinoid degradation inhibitors in oligodendrocytes and white matter tracts are still ill defined. Here we show that the selective monoacylglycerol lipase (MAGL) inhibitor JZL184 suppressed cell death by mild activation of AMPA receptors in oligodendrocytes in vitro, an effect that was mimicked by MAGL substrate 2‐AG and by the second major endocannabinoid AEA, in a concentration‐dependent manner, whereas inhibition of the AEA metabolizing enzyme fatty acid amide hydrolase with URB597 was devoid of effect. Pharmacological experiments suggested that oligodendrocyte protection from excitotoxicity resulting from MAGL blockade involved the activation of cannabinoid CB1 receptors and the reduction of AMPA‐induced cytosolic calcium overload, mitochondrial membrane depolarization, and production of reactive oxygen species. Administration of JZL184 under a therapeutic regimen decreased clinical severity, prevented demyelination, and reduced inflammation in chronic experimental autoimmune encephalomyelitis. Furthermore, MAGL inactivation robustly preserved myelin integrity and suppressed microglial activation in the cuprizone‐induced model of T‐cell‐independent demyelination. These findings suggest that MAGL blockade may be a useful strategy for the treatment of immune‐dependent and ‐independent damage to the white matter. GLIA 2015;63:163–176

Type-1 Cannabinoid Receptor Activity During Alzheimer's Disease Progression

The activity of CB1 cannabinoid receptors was studied in postmortem brain samples of Alzheimers disease (AD) patients during clinical deterioration. CB1 activity was higher at earlier AD stages in limited hippocampal areas and internal layers of frontal cortex, but a decrease was observed at the advanced stages. The pattern of modification appears to indicate initial hyperactivity of the endocannabinoid system in brain areas that lack classical histopathological markers at earlier stages of AD, indicating an attempt to compensate for the initial synaptic impairment, which is then surpassed by disease progression. These results suggest that initial CB1 stimulation might have therapeutic relevance.

Imaging mass spectrometry (IMS) of cortical lipids from preclinical to severe stages of Alzheimer's disease

Alzheimers disease (AD) is a progressive neurodegenerative disease affecting millions of patients worldwide. Previous studies have demonstrated alterations in the lipid composition of lipid extracts from plasma and brain samples of AD patients. However, there is no consensus regarding the qualitative and quantitative changes of lipids in brains from AD patients. In addition, the recent developments in imaging mass spectrometry methods are leading to a new stage in the in situ analysis of lipid species in brain tissue slices from human postmortem samples. The present study uses the matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), permitting the direct anatomical analysis of lipids in postmortem brain sections from AD patients, which are compared with the intensity of the lipid signal in samples from matched subjects with no neurological diseases. The frontal cortex samples from AD patients were classified in three groups based on Braaks histochemical criteria, ranging from non-cognitively impaired patients to those severely affected. The main results indicate a depletion of different sulfatide lipid species from the earliest stages of the disease in both white and gray matter areas of the frontal cortex. Therefore, the decrease in sulfatides in cortical areas could be considered as a marker of the disease, but may also indicate neurochemical modifications related to the pathogenesis of the disease. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Development of New Drugs that Act Through Membrane Receptors and Involve an Action of Inverse Agonism

Synaptic transmission and, consequently, neurological processes are regulated by neurotransmitters and other neuro-modulators that recognize specific receptors. There are two main families of receptors that are targets for most of the compounds which act in the central nervous system (CNS); ion channel coupled receptors and G-protein coupled receptors (GPCR). The drugs that act through these receptors and are used for the treatment of different diseases related with the CNS, have traditionally been classified as agonists or antagonists. However, since the discovery of the constitutive activity of some neurotransmitter receptors during the eighties, the inverse agonist drugs have emerged as a new group of bioactive compounds with the ability to decrease receptor basal activity. New experimental evidence indicates that pathologies associated with different diseases that affect the CNS physiology could involve constitutively active receptors. Therefore, different methods and systems have been patented to explore the receptors that show high basal activity and to test the decrease of the receptor activity produced by inverse agonist compounds. In recent years some inverse agonist drugs and their targets have been patented which are capable of treating CNS related disorders. These include inverse agonists that are selective for serotonin or histamine receptors aimed at treating neuropsychiatric disorders, cannabinoids with an anorexigenic effect and inverse agonists selective for gabaergic receptors for the treatment of neurodegenerative or cognitive disorders.