Monoglyceride lipase (MGL) influences energy metabolism by at least two mechanisms. First, it hydrolyzes monoacylglycerols (MG) into fatty acids and glycerol. These products can be used for energy production or synthetic reactions. Second, MGL degrades 2-arachidonoyl glycerol (2-AG), the most abundant endogenous ligand of cannabinoid receptors (CBR). Activation of CBR affects energy homeostasis by central orexigenic stimuli, by promoting lipid storage, and by reducing energy expenditure. To characterize the metabolic role of MGL in vivo, we generated an MGL-deficient mouse model (MGL-ko). These mice exhibit a reduction in MG hydrolase activity and a concomitant increase in MG levels in adipose tissue, brain, and liver. In adipose tissue, the lack of MGL activity is partially compensated by hormonesensitive lipase. Nonetheless, fasted MGL-ko mice exhibit reduced plasma glycerol and triacylglycerol, as well as liver triacylglycerol levels indicative for impaired lipolysis. Despite a strong elevation of 2-AG levels, MGL-ko mice exhibit normal food intake, fat mass, and energy expenditure. Yet mice lacking MGL show a pharmacological tolerance to the CBR agonist CP 55,940 suggesting that the elevated 2-AG levels are functionally antagonized by desensitization of CBR. Interestingly, however, MGL-ko mice receiving a high fat diet exhibit significantly improved glucose tolerance and insulin sensitivity in comparison with wild-type controls despite equal weight gain. In conclusion, our observations implicate that MGL deficiency impairs lipolysis and attenuates diet-induced insulin resistance. Defective degradation of 2-AG does not provoke cannabinoid-like effects on feeding behavior, lipid storage, and energy expenditure, which may be explained by desensitization of CBR. Monoacylglycerols (MG)3 are short lived intermediates of lipid catabolism derived from extracellular or intracellular sources. Pancreatic lipase and lipoprotein lipase generate MG by the hydrolysis of dietary triacylglycerols (TG) and circulating lipoproteins, respectively (1, 2). The lipolytic products, MG and free fatty acids (FFA), are subsequently taken up by cells, and MG are hydrolyzed into FFA and glycerol or re-esterified by the monoacylglycerol acyltransferase reaction (3). Within cells, MG are derived from the hydrolysis of glycerophospholipids or TG. Glycerophospholipids may be degraded by phospholipase C generating sn-1,2-diacylglycerols (DG), which are further hydrolyzed by sn-1-specific DG lipase resulting in the formation of 2-MG (4). The breakdown of TG is initiated by adipose triglyceride lipase (ATGL), and the produced DG is hydrolyzed by hormone-sensitive lipase (HSL) (5). The stereospecificity of ATGL has not been studied so far. Yet, similar to DG lipase, HSL hydrolyzes DG preferentially in sn-1(3) position generating 2-MG (6). Monoglyceride lipase (MGL) degrades sn-1(3) and 2-MG at identical specific rates (7). The enzyme is expressed in most cell types and is considered the rate-limiting enzyme in the degradation of MG (8, 9).In ad...

The aim of our study was to explore the antiproliferative and pro-apoptotic action of roscovitine (ROSC) on human breast cancer MCF-7 cells. We examined the effect of ROSC on cell proliferation, cell cycle progression, nucleolar morphology, posttranslational modifications of histones as well as on induction of apoptosis. The effects of ROSC on the argyrophilic nucleolar organizer regions (AgNORs) and nucleolar RNA of MCF-7 cells were marked: ROSC treatment changed the pattern of AgNORs in a time-dependent manner. The disintegration of nucleoli manifested by increasing number of nucleolar fragments already began at 6 hr posttreatment. This was accompanied by a redistribution of the nucleolin from the nucleolus beginning after 6 hr and preceded a decrease of histone acetylation and phosphorylation. Congenital and acquired resistance to chemotherapy and radiotherapy has been a major obstacle for successful cure of human malignancies. Therefore, alternative drugs intended to overcome this clinical hindrance are searched. 1 The inhibitors of cyclindependent kinases (CDKs) represent a well-defined group of biologically active compounds suitable for nonconventional treatments. 2,3 One potential adjunct of the CDK inhibitors to classical cytostatics is direct induction of programmed cell death (PCD). The CDK inhibitors stimulate cell death from any stage of the cell cycle, 4 whereas the DNA-damaging drugs kill more efficaciously S-phase cells. 1 Roscovitine (ROSC) belongs to chemical inhibitors of CDK; the mechanism turns out to be a competitive inhibition of ATP binding. 3,5,6 ROSC occupies the purine-binding pocket, located in the cleft between the small and large lobes of the kinase. The kinase specificity of ROSC was investigated with 25 highly purified kinases. 3 Most kinases were not significantly inhibited by ROSC. However, cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E and cdk5/p35 were substantially inhibited by ROSC. 3 Considering this unique selectivity for some CDK, ROSC clearly provides a useful reagent not only for cell cycle studies 3 but also offers a potent drug for efficient anticancer therapy. 1 The effect of ROSC on the cell cycle progression is independent of the tumour-suppressor protein p53, a primary controller of the endogenous cell-cycle inhibitor p21 waf1/Cip1 , because an inhibition was observed irrespective of p53 status: normal vs. mutated/deleted. Recently, ROSC has been shown to drive the estrogen-negative MDA-MB-231 human breast cancer cells in apoptotic cell death. 7 Therefore, it appeared interesting to address the question whether ROSC's capability to initiate the apoptosis in breast cancer cells is dependent on the estrogen-receptor status. Furthermore, it also seemed attractive to examine whether wt p53 in human breast carcinoma cells can be activated by ROSC. The p53 protein, a product of a tumour suppressor gene, is known to exert in response to various types of stress not only antiproliferative effects including a transient cell cycle arrest or terminal cellular senescence, but also...

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Abstract-N1 -methylnicotinamide (MNA ϩ ) has until recently been thought to be a biologically inactive product of nicotinamide metabolism in the pyridine nucleotides pathway. However, the latest observations imply that MNA ϩ may exert antithrombotic and anti-inflammatory effects through direct action on the endothelium. We examined both in vivo and in vitro whether the compound might induce vasorelaxation in human blood vessels through the improvement of nitric oxide (NO) bioavailability and a reduction of oxidative stress mediated by endothelial NO synthase (eNOS) function. MNA ϩ treatment (100 mg/m 2 orally) in healthy normocholesterolemic and hypercholesterolemic subjects increased the L-arginine (L-NMMA)-inhibitable flow-mediated dilation (FMD) of brachial artery responses that also positively correlated with MNA ϩ plasma concentrations (rϭ0.73 for normocholesterolemics and rϭ0.78 for hypercholesterolemics; PϽ0.0001). MNA ϩ increased FMD at the same concentration range at which it enhanced NO release from cultured human endothelial cells after stimulation with either the receptor-dependent (acetylcholine) or the receptor-independent endothelial NO synthase agonists (calcium ionophore A23187). MNA ϩ restored the endothelial NO synthase agonist-stimulated NO release after the exposure of the cells to oxidized low-density lipoprotein. This effect was also associated with the normalization of the 1 In contrast to NA, MNA ϩ has until recently been construed to be biologically inactive.2 However, the most recent studies suggest an antithrombotic activity of MNA ϩ related to both the inhibition of platelet aggregation and the activation of fibrinolysis, offering certain advantages over the use of NA.3-6 These observations have been provisionally attributed to the release of endothelial mediators such as prostacyclin, which boasts antiaggregatory and profibrinolytic properties. However, the actual mechanism of MNA ϩ effects still begs comprehensive clarification.An improvement in the dysfunctional endothelial NO synthase (eNOS)/NO pathway is an attractive strategy in preventing and treating cardiovascular diseases.7-10 Although NO bioavailability is decreased in dysfunctional endothelium, the levels of eNOS mRNA and protein are maintained or even enhanced but associated with the increased NO synthasedependent superoxide (O 2 ·Ϫ ) formation because of the enzymatic "uncoupling" of NO synthase; electron flow through the eNOS enzyme is then diverted to molecular oxygen rather than to l-arginine, which facilitates the production of O 2 ·Ϫ rather than NO. 7,[9][10][11] This consequently leads to an O 2 ·Ϫ reaction with NO, resulting in the formation of highly reactive and cytotoxic peroxynitrite and the loss of NO bioavailability.