Phospholipase A2 (PLA2) is the name for the class of lipolytic enzymes that hydrolyze the acyl group from the sn-2 position of glycerophospholipids, generating free fatty acids and lysophospholipids. The products of the PLA2-catalyzed reaction can potentially act as second messengers themselves, or be further metabolized to eicosanoids, platelet-activating factor, and lysophosphatidic acid. All of these are recognized as bioactive lipids that can potentially alter many ongoing cellular processes. The presence of PLA2 in the central nervous system, accompanied by the relatively large quantity of potential substrate, poses an interesting dilemma as to the role PLAS has during both physiologic and pathologic states. Several different PLA2 enzymes exist in brain, some of which have been partially characterized. They are classified into two subtypes, Ca 2~-dependentand Ca2-independent, based on their catalytic dependence on Ca~.Under physiologic conditions, PLA 2 may be involved in phospholipid turnover, membrane remodeling, exocytosis, detoxification of phospholipid peroxides, and rieurotransmitter release. However, under pathological situations, increased PLA2 activity may result in the loss of essential membrane glycerophospholipids, resulting in altered membrane permeability, ion homeostasis, increased free fatty acid release, and the accumulation of lipid peroxides. These processes, along with loss of ATP, may be responsible for the loss of membrane phospholipid and subsequent neuronal injury found in ischemia, spinal cord injury, and other neurodegenerative diseases. This review outlines the current knowledge of the PLA2 found in the central nervous system and attempts to define the role of PLA2 during both physiologic and pathologic conditions.

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Abstract:We purified an 80-kDa Ca 2ϩ -independent phospholipase A 2 (iPLA 2 ) from rat brain using octylSepharose, ATP-agarose, and calmodulin-agarose column chromatography steps. This procedure gave a 30,000-fold purification and yielded 4 g of a near-homogeneous iPLA 2 with a specific activity of 4.3 mol/ min/mg. Peptide sequences of the rat brain iPLA 2 display considerable homology to sequences of the iPLA 2 from P388D 1 macrophages, Chinese hamster ovary cells, and human B lymphocytes. Under optimal conditions, the iPLA 2 revealed the following substrate preference toward the fatty acid chain in the sn-2 position of phosphatidylcholine: linoleoyl Ͼ palmitoyl Ͼ oleoyl Ͼ arachidonoyl. The rat brain iPLA 2 also showed a head group preference for choline Ն ethanolamine ӷ inositol. The iPLA 2 is inactivated when exposed to pure phospholipid vesicles. The only exception is vesicles composed of phosphatidylcholine and phosphatidylinositol 4,5-bisphosphate. Studies on the regional distribution and ontogeny of various phospholipase A 2 (PLA 2 ) types in rat brain indicate that the iPLA 2 is the dominant PLA 2 activity in the cytosolic fraction, whereas the group IIA secreted PLA 2 is the dominant activity in the particulate fraction. The activities of these two enzymes change during postnatal development. Key Words: Ca 2ϩ -independent phospholipase A 2 -Ontogeny-Regional distribution-Purification-Peptide sequence-Substrate specificity.

Objective: The objective of this study was to assess the effects of a continuous overnight infusion of des-acyl ghrelin (DAG) on acylated ghrelin (AG) levels and glucose and insulin responses to a standard breakfast meal (SBM) in eight overweight patients with type 2 diabetes. Furthermore, in the same patients and two additional subjects, the effects of DAG infusion on AG concentrations and insulin sensitivity during a hyperinsulinemic-euglycemic clamp (HEC) were assessed. Research design and methods: A double-blind, placebo-controlled cross-over study design was implemented, using overnight continuous infusions of 3 and 10 mg DAG/kg per h and placebo to study the effects on a SBM. During a HEC, we studied the insulin sensitivity. Results: We observed that, compared with placebo, overnight DAG administration significantly decreased postprandial glucose levels, both during continuous glucose monitoring and at peak serum glucose levels. The degree of improvement in glycemia was correlated with baseline plasma AG concentrations. Concurrently, DAG infusion significantly decreased fasting and postprandial AG levels. During the HEC, 2.5 h of DAG infusion markedly decreased AG levels, and the M-index, a measure of insulin sensitivity, was significantly improved in the six subjects in whom we were able to attain steady-state euglycemia. DAG administration was not accompanied by many side effects when compared with placebo. Conclusions: DAG administration improves glycemic control in obese subjects with type 2 diabetes through the suppression of AG levels. DAG is a good candidate for the development of compounds in the treatment of metabolic disorders or other conditions with a disturbed AG:DAG ratio, such as type 2 diabetes mellitus or Prader-Willi syndrome.

Activation of free fatty acid receptor 1 (GPR40) by synthetic partial and full agonists occur via distinct allosteric sites. A crystal structure of GPR40-TAK-875 complex revealed the allosteric site for the partial agonist. Here we report the 2.76-Å crystal structure of human GPR40 in complex with a synthetic full agonist, compound 1, bound to the second allosteric site. Unlike TAK-875, which acts as a Gαq-coupled partial agonist, compound 1 is a dual Gαq and Gαs-coupled full agonist. compound 1 binds in the lipid-rich region of the receptor near intracellular loop 2 (ICL2), in which the stabilization of ICL2 by the ligand is likely the primary mechanism for the enhanced G protein activities. The endogenous free fatty acid (FFA), γ-linolenic acid, can be computationally modeled in this site. Both γ-linolenic acid and compound 1 exhibit positive cooperativity with TAK-875, suggesting that this site could also serve as a FFA binding site.