An excess of intracellular free cholesterol (Chol) is cytotoxic, and its homeostasis is crucial for cell viability. Apolipoprotein A-I (apoA-I) is a highly efficient Chol acceptor because it activates complex cellular pathways that tend to mobilize and export Chol from cellular depots. We hypothesize that membrane composition and/or organization is strongly involved in Chol homeostasis. To test this hypothesis, we constructed a cell line overexpressing stearoyl coenzyme A (CoA) desaturase (SCD cells), which modifies plasma membrane (PM) composition by the enrichment of monounsaturated fatty acids, and determined this effect on membrane properties, cell viability, and Chol homeostasis. PM in SCD cells has a higher ratio of phospholipids to sphingomyelin and is slightly enriched in Chol. These cells showed an increase in the ratio of cholesteryl esters to free Chol; they were more resistant to Chol toxicity, and they exported more caveolin than control cells. The data suggest that cell functionality is preserved by regulating membrane fluidity and Chol exportation and storage.

Apolipoprotein (Apo)A-I plays a key role in reverse cholesterol transport, a process of antiatherogenic relevance that removes excess cholesterol from peripheral tissues. This protein is constituted almost exclusively of amphipathic a-helices and undergoes large conformational changes during its functional cycle. Conformational changes in relationship with the functional role of this protein are discussed, with focus on a central a-helix pair with a particular charge distribution. This domain inserts preferentially into cholesterol-containing membranes where it facilitates cholesterol desorption, and it is also responsible for triggering mobilization of intracellular cholesterol depots towards the cell membrane. It is proposed that the active domain would be an intermolecular a-helix bundle formed by two central helix pairs belonging to both ApoA-I molecules, which constitute a discoidal high-density lipoprotein particle. For the activity of this domain, a specific sequence would not be required, but the charge distribution of class gamma amphipathic a-helices and an adequate orientation of the hydrophobic and hydrophilic helix faces would be necessary.

Reverse cholesterol transport is a process of high antiatherogenic relevance in which apolipoprotein AI (apoA-I) plays an important role. The interaction of apoA-I with peripheral cells produces through mechanisms that are still poorly understood the mobilization of intracellular cholesterol depots toward plasma membrane. In macrophages, these mechanisms seem to be related to the modulation of the activity of acyl-CoA cholesterol acyltransferase (ACAT), the enzyme responsible for the intracellular cholesterol ester biosynthesis that is stored in lipid droplets. The activation of ACAT and the accumulation of lipid droplets play a key role in the transformation of macrophages into foam cells, leading to the formation of atheroma or atherosclerotic plaque. ApoA-I Helsinki (or a dagger K107) is a natural apoA-I variant with a lysine deletion in the central protein region, carriers of which have increased atherosclerosis risk. We herein show that treatment of cultured RAW macrophages or CHOK1 cells with a dagger K107, but not with wild-type apoA-I or a variant containing a similar deletion at the C-terminal region (a dagger K226), lead to a marked increase (more than 10 times) in the intracellular ACAT1 protein level as detected by western blot analysis. However, we could only detect a slight increase in cholesteryl ester produced by a dagger K107 mainly when Chol loading was supplied by low-density lipoprotein (LDL). Although a similar choline-phospholipid efflux is evoked by these apoA-I variants, the change in phosphatidylcholine/sphyngomyelin distribution produced by wild-type apoA-I is not observed with either a dagger K107 or a dagger K226.

Dexamethasone depresses DELTA6 and DELTA5 and increases DELTA9 desaturase and synthase activities. Therefore, we investigated the effect on the fatty acid composition of microsomal liver lipids and phosphatidylcholine (PtdCho) molecular species. After 15 d of treatment we found a notable decrease in arachidonic acid, a small decrease in stearic acid, and increases of linoleic, oleic, palmitoleic, and palmitic acids in liver microsomal total lipids and PtdCho. The study of the distribution of the PtdCho molecular species indicated that 18:0/20:4n-6, 16:0/20:4n-6, and 16:0/18:2n-6 predominated in the control animals. Dexamethasone, as expected because of its depressing effect on arachidonic acid synthesis and activation of oleic and palmitic acid synthesis, evoked a very significant decrease in 18:0/20:4n-6 PtdCho (P<0.001) and an important increase in 16:0/18:2n-6. The invariability of 16:0/20:4n-6 PtdCho could be related to the antagonistic effect of arachidonic and palmitic acid synthesis. PtdCho species containing oleic acid were not significant. The bulk fluidity and dynamic properties of the microsomal lipid bilayer measured by fluorometry using the probes 1,6-diphenyl-1,3,5-hexatriene and 4-trimethylammonium-phenyl-6-phenyl-1,3,5-hexatriene showed no significant modification, probably owing to a compensatory effect of the different molecular species, but changes of particular domains not detected by this technique are possible. However, the extremely sensitive Laurdan detected increased lipid packing in the less-fluid domains of the polar-nonpolar interphase of the bilayer, possibly evoked by the change of molecular species and cholesterol/phospholipid ratio. The most important effect found is the decrease of arachidonic acid pools in liver phospholipids as one of the corresponding causes of dexamethasone-dependent pharmacological effects.

This essay is on the writings of sanitary doctor Geraldo Horácio de Paula Souza in Eugenia e Imigração (1928) and, after an official trip to the Orient, in Digressões sobre a medicina chinesa clássica (1942) and A sabedoria chinesa diante da ciência ocidental e a Escola Médica de Pequim (1943). The documents, analyzed according to the conceptual approach of Carlo Ginzburg, indicate a change in his view of the Chinese. Trained according to the Rockefeller Foundation's model of experimental medicine, Geraldo de Paula Souza was guided in his work by scientific rigor and record imagery. In his youth he was of the opinion that the Chinese civilization was stagnated, but this view changed after his visit, when he perceived the Chinese republic's capacity to modernize.