2-OMe-lysophosphatidylcholine analogues are GPR119 ligands and activate insulin secretion from βTC-3 pancreatic cells: Evaluation of structure-dependent biological activity

GPR119 receptor has been proposed as a metabolic regulator playing a pivotal role in the modulation of glucose homeostasis in type 2 diabetes. GPR119 was identified on pancreatic β cells and its ligands have the ability to enhance glucose-stimulated insulin secretion (GSIS). Lysophosphatidylcholine (LPC) was shown to potentiate GSIS and our present studies indicate that 2-methoxy-lysophosphatidylcholine (2-OMe-LPC) analogues, unable to undergo 1 → 2 acyl migration, stimulate GSIS from murine βTC-3 pancreatic cells even more efficiently. Moreover, biological assays in engineered Tango? GPR119-bla U2OS cells were carried out to ascertain the agonist activity of 2-OMe-LPC at GPR119. 2-OMe-LPC possessing in sn-1 position the residues of myristic, palmitic, stearic and oleic acid were also evaluated as factors regulating [Ca^2 +]_i mobilization and cAMP levels. Extension of these studies to R- and S-enantiomers of 14:0 2-OMe-LPC revealed that the overall impact on GSIS does not depend on chirality, however, the intracellular calcium mobilization data show that the R enantiomer is significantly more active than S one. Taking into account differences in chemical structure between various native LPCs and their 2-methoxy counterparts the possible binding mode of 2-OMe-LPC to the GPR119 receptor was determined using molecular modeling approach.     

Aluminium interferes with hippocampal calcium signaling in a species-specific manner

Aluminium (Al) has been implicated in a number of neurodegenerative disorders and the disruption of calcium homeostasis has been proposed as a possible mechanism. To investigate ligand- and structure-specific effects of Al species, calcium imaging was used to probe the influence of five Al complexes - in comparison to inorganic Al (Al-S) - on N-methyl d-aspartate receptor (NMDAR) and voltage-dependent calcium channel (VDCC) function in hippocampal neurontos. The Al complexes utilized comprised three Al-citrate species (AlCit1-3), Al-quinate (AlQ) and Al-N-phosphonomethyliminodiacetate (AlNTAP). Our results suggest variable toxicity among the Al compounds tested: Al-S most potently affected neurons, with a full and irreversible inhibition of NMDAR and VDCC signaling at 500 μM. At all concentrations tested (10, 100, and 500 µM), all Al compounds investigated inhibited NMDA responses, however, no dose-dependency was evident. Furthermore, striking differences were noted with respect to calcium responses via VDCC activation. AlCit2 reduced calcium responses at all concentrations tested, AlQ at 10 and 100 µM, and AlNTAP at 500 µM only. In contrast, AlCit1 and AlCit3 had no significant effect. Collectively, diversely structured Al-ligand species selectively affect neuronal membrane channel function. The distinct chemical reactivity of the various Al forms reflects their unique interactions with neuronal structures and is poised to explain the diverse facets of Al toxicity.     

Differential Expression and Association of Calcium Channel Subunits in Development and Disease

Voltage-gated calcium channels (VDCC) are essential to neuronal maturation and differentiation. It is believed that important signaling information is encoded by VDCC-mediated calcium influx that has both spatial and temporal components. VDCC are multimeric complexes comprised of a pore-forming ₁ subunit and auxiliary and ₂/ subunits. Changes in the fractional contribution of distinct calcium conductances to the total calcium current have been noted in developing and differentiating neurons. These changes are anticipated to reflect the differential expression and localization of the pore-forming ₁ subunits. However, as in vitro studies have established that regulates the channel properties and targeting of ₁, attention has been directed toward the developmental expression and assembly of isoforms. Recently, changes in the component of the omega-conotoxin GVIA (CTX)-sensitive N-type VDCC have indicated differential assembly of _1B with in postnatal rat brain. In addition, unique properties of 4 have been noted with respect to its temporal pattern of expression and incorporation into N-type VDCC complexes. Therefore, the expression and assembly of specific ₁/ complexes may reflect an elaborate cellular strategy for regulating VDCC diversity. The importance of these developmental findings is bolstered by a recent study which identified mutations in the 4 as the molecular defect in the mutant epileptic mouse (lethargic; lh/lh). As 4 is normally expressed in both forebrain and cerebellum, one may consider the impact of the loss of 4 upon VDCC assembly and activity. The importance of the lb and 4 isoforms to calcium channel maturation and assembly is discussed.     

A novel neurotrophic role of secretory phospholipases A2 for cerebellar granule neurons

Cultured cerebellar granule neurons (CGNs) require membrane depolarization or neurotrophic factors for their survival in vitro and undergo apoptosis when deprived of these survival-promoting stimuli. Here, we show that secretory phospholipases A(2)s (sPLA(2)s) rescue CGNs from apoptosis after potassium deprivation. The neurotrophic effect required the enzymatic activity of sPLA(2)s, since catalytically inactive mutants of sPLA(2)s failed to protect CGNs from apoptosis. Consistently, the ability of sPLA(2)s to protect CGNs from apoptosis correlated with the extent of sPLA(2)-induced arachidonic acid release from live CGNs. The survival-promoting effect of sPLA(2) was inhibited by depletion of extracellular Ca(2+) or by the presence of L-type Ca(2+) channel blocker nicardipine, suggesting that Ca(2+) influx occurs upon sPLA(2) treatment. Among the mammalian sPLA(2)s tested, only group X sPLA(2), but not group IB nor IIA sPLA(2)s, displayed neurotrophic activity. These results suggest a novel, unexpected neurotrophin-like role of sPLA(2) in the nervous system.     

Glucosensing and glucose homeostasis: from fish to mammals

This review is focused on two topics related to glucose in vertebrates. In a first section devoted to glucose homeostasis we describe how glucose levels fluctuate and are regulated in different classes of vertebrates. The detection of these fluctuations is essential for homeostasis and for other physiological processes such as regulation of food intake. The capacity of that detection is known as glucosensing, and the different mechanisms through which it occurs are known as glucosensors. Different glucosensor mechanisms have been demonstrated in different tissues and organs of rodents and humans whereas the information obtained for other vertebrates is scarce. In the second section of the review we describe the present knowledge regarding glucosensor mechanisms in different groups of vertebrates, with special emphasis in fish.     

Multi-target novel neuroprotective compound ITH33/IQM9.21 inhibits calcium entry, calcium signals and exocytosis

Compound ITH33/IQM9.21 (ITH/IQM) belongs to a new family of l-glutamic acid derivatives with antioxidant and neuroprotective properties on in vitro and in vivo models of stroke. Because neuronal damage after brain ischemia is tightly linked to excess Ca²⁺ entry and neuronal Ca²⁺ overload, we have investigated whether compound ITH/IQM antagonises the elevations of the cytosolic Ca²⁺ concentrations ([Ca²⁺]_c) and the ensuing exocytotic responses triggered by depolarisation of bovine chromaffin cells. In fluo-4-loaded cell populations, ITH/IQM reduced the K⁺-evoked [Ca²⁺]_c transients with an IC₅₀ of 5.31 μM. At 10 μM, the compound decreased the amplitude and area of the Ca²⁺ transient elicited by challenging single fura-2-loaded cells with high K⁺, by 40% and 80%, respectively. This concentration also caused a blockade of K⁺-induced catecholamine release at the single-cell level (78%) and cell populations (55%). These effects are likely due to blockade of the whole-cell inward Ca²⁺ currents (IC₅₀ = 6.52 μM). At 10 μM, ITH/IQM also inhibited the Ca²⁺-dependent outward K⁺ current, leaving untouched the voltage-dependent component of I_K. The inward Na⁺ current was unaffected. Inhibition of depolarisation-elicited Ca²⁺ entry, [Ca²⁺]_c elevation and exocytosis could contribute to the neuroprotective effects of ITH/IQM in vulnerable neurons undergoing depolarisation during brain ischemia.     

ABCC8 genetic variants and risk of diabetes mellitus

Diabetes mellitus (DM) is a major health problem worldwide and it will rapidly increase. This disease is characterized by hyperglycemia caused by defects in insulin secretion, insulin action or both. DM has three types: T1DM, T2M and gestational DM (GDM), of them T2DM is more frequent. Multiple genes and their interactions are involved in insulin secretion pathway. Sulfonylurea receptor encoded by ABCC8 gene, together with inward-rectifier potassium ion channel (Kir6.2) regulates insulin secretion by ATP-sensitive K⁺ (KATP) channel located in the plasma membranes. Disruption of these molecules by different mutations is responsible for risk of DM. Several single nucleotide polymorphisms (SNPs) of ABCC8 gene and their interaction are involved in pathogenicity of DM. This review summarizes the current evidence of contribution of ABC8 genetic variants to the development of DM.     

New multipotent tetracyclic tacrines with neuroprotective activity

The synthesis and the biological evaluation (neuroprotection, voltage dependent calcium channel blockade, AChE/BuChE inhibitory activity and propidium binding) of new multipotent tetracyclic tacrine analogues (5–13) are described. Compounds 7, 8 and 11 showed a significant neuroprotective effect on neuroblastoma cells subjected to Ca²⁺ overload or free radical induced toxicity. These compounds are modest AChE inhibitors [the best inhibitor (11) is 50-fold less potent than tacrine], but proved to be very selective, as for most of them no BuChE inhibition was observed. In addition, the propidium displacement experiments showed that these compounds bind AChE to the peripheral anionic site (PAS) of AChE and, consequently, are potential agents that can prevent the aggregation of β-amyloid. Overall, compound 8 is a modest and selective AChE inhibitor, but an efficient neuroprotective agent against 70 mM K⁺ and 60 μM H₂O₂. Based on these results, some of these molecules can be considered as lead candidates for the further development of anti-Alzheimer drugs.     

Scaffold protein Homer 1: Implications for neurological diseases

Homer proteins are commonly known as scaffold proteins at postsynaptic density. Homer 1 is a widely studied member of the Homer protein family, comprising both synaptic structure and mediating postsynaptic signaling transduction. Both an immediate-early gene encoding a Homer 1 variant and a constitutively expressed Homer 1 variant regulate receptor clustering and trafficking, intracellular calcium homeostasis, and intracellular molecule complex formation. Substantial preclinical investigations have implicated that each of these Homer 1 variants are associated with the etiology of many neurological diseases, such as pain, mental retardation syndromes, Alzheimer's disease, schizophrenia, drug-induced addiction, and traumatic brain injury.