Intravenous immune globulin in symptomatic paediatric human immunodeficiency virus infection

Seven paediatric patients with symptomatic human immunodeficiency virus (HIV) infection were prospectively studied for 6-24 months after the start of intravenous immune globulin (IVIG) therapy. There was substantial clinical benefit during IVIG treatment with marked reduction of febrile and infectious episodes, normalization of physical and psychomotor development, and absence of mortality. The immunologic monitoring revealed some discrete objective improvements. The results of this study favourably compare to previous reports. It is concluded that IVIG should be standard therapy for symptomatic childhood HIV infection.

Uptake of HDL unesterified and esterified cholesterol by human endothelial cells. Modulation by HDL phospholipolysis and cell cholesterol content

Human HDL (1.070-1.210), doubly labelled with 3H/14C-labelled unesterified cholesterol and 3H-labelled esterified cholesterol were incubated for 1-5 h with monolayer cultures of human endothelial cells. HDL were preincubated for 60-120 min the presence of albumin and with/without purified phospholipase A2 (control HDL, phospholipase A2 HDL) before dilution in the cell culture medium. Average phosphatidylcholine (PC) degradation was 62.10% +/- 2.57% (range 45-80%). A purified lipase/phospholipase A1 from guinea pig pancreas was used in some experiments (range of PC hydrolysis: 16-70%). (1) 3H/14C-labelled unesterified cholesterol and 3H-labelled esterified cholesterol appeared in cells during 0-5 h incubations. Trypsin treatment allowed a simple adsorption of HDL onto the cell surface to be avoided, and most of the 3H-labelled esterified cholesterol transferred to cells was hydrolysed. Cell uptake of radioactive cholesterol increased as a function of HDL concentration but no saturation was achieved at the highest lipoprotein concentration used (200 micrograms cholesterol/ml). Flux of 3H/14C-labelled unesterified cholesterol was related to the cell cholesterol content, suggesting that it might partly represent an exchange process. The cell cholesterol content was slightly increased after 5 h incubation with HDL (+16%). (2) Pretreatment of HDL with purified phospholipase A2 doubled on average the amount of cell recovered 3H-labelled esterified cholesterol, while the flux of 3H/14C-labelled unesterified cholesterol was enhanced by 15-25%. Both transfer and cell hydrolysis of 3H-labelled esterified cholesterol were increased. A stimulation was also observed using purified lipase/phospholipase A1, provided that a threshold phospholipid degradation was achieved (between 27 and 45%). (3) Endothelial cells were conditioned in different media so as to modulate their charge in cholesterol. The uptake of 3H-labelled esterified cholesterol was found to be significantly higher in cholesterol-enriched cells compared to the sterol-depleted state. Finally, movements of 3H-labelled esterified cholesterol from HDL to endothelial cells were essentially unaffected by cell density or by the presence of partially purified cholesterol ester transfer protein. The possible roles of the transfer of HDL esterified cholesterol to endothelial cells and its modulation by phospholipases are discussed.

High density lipoprotein and low density lipoprotein utilization by human granulosa cells for progesterone synthesis in serum-free culture: respective contributions of free and esterified cholesterol

Human preovulatory granulosa cells cultured in serum- and gonadotropin-free medium secreted progressively less progesterone as time elapsed. Addition of purified high density lipoproteins (HDL) as well as low density lipoproteins [very low density (VLDL) plus low density lipoproteins (LDL)] restored optimal synthesis of progesterone, and HDL was as effective as VLDL + LDL. The use of cholesterol doubly labeled lipoproteins allowed calculation of the proportions of free and esterified cholesterol converted into progesterone. Granulosa cells used either free or esterified cholesterol from VLDL + LDL. In contrast, HDL-esterified cholesterol was a poor substrate for progesterone synthesis, while HDL-free cholesterol was used preferentially. LH increased the use of both kinds of lipoproteins without changing the way in which they were used. Pretreatment of HDL by purified phospholipase A2 increased the conversion of free cholesterol into progesterone. Similar treatment of VLDL + LDL had little effect on progesterone secretion. We conclude that HDL as well as VLDL + LDL can provide cholesterol to human preovulatory granulosa cells and that utilization of HDL-cholesterol may depend on gonadotropin (LH) and enzymatic (phospholipase) regulation.

Triacylglycerol increase in plasma very low density lipoproteins in cyclophosphamide-treated rabbit: relationship with cholesteryl ester transfer activity

We have studied the cholesteryl ester transfer between HDL and VLDL in cyclophosphamide-treated rabbits, in order to explain the abnormal cholesteryl ester partition between these two lipoprotein classes. The hypertriglyceridemia caused by treatment with the drug was associated with cholesteryl ester- and triacylglycerol-rich VLDL and with HDL poor in esterified cholesterol but relatively enriched in triacylglycerol. These two lipoprotein classes were characterized by their chemical composition and by gel filtration chromatography. VLDL particles were slightly larger in size, compared with controls. Different transfer combinations were envisaged between these abnormal lipoproteins and control ones. The transfer study involved the plasma fraction of d greater than 1.21 g/ml containing the cholesteryl ester transfer protein (CETP). It appeared that the chemical composition of lipoproteins was responsible for the level of cholesteryl ester transfer between lipoproteins. Actually, when the cholesteryl ester acceptor lipoproteins (VLDL) were enriched in triacylglycerol, the transfer was enhanced. Therefore, the effect of lipolysis on the transfer has also been explored. Lipoprotein lipase seemed to enhance the transfer of cholesteryl ester from HDL to VLDL when these lipoproteins were normal, but an important decline was obtained when triacylglycerol-rich VLDL were lipolyzed. This study defines the relationship between lipoprotein chemical composition and transfer activity of cholesteryl ester from HDL to VLDL.

Platelet arachidonic acid metabolism in severe cerebrovascular disease

The ability of platelets to synthetise thromboxane B2 and hydroxylated fatty acids from arachidonic acid was studied simultaneously with arachidonic acid-induced aggregation in 42 patients suffering from severe cerebral atherosclerosis and also in 34 healthy controls. Additionally, phospholipase-A2-induced aggregation was performed as a probe for arachidonic acid located at the platelet surface. All the assays were performed with washed platelets, eliminating a possible influence of plasma. Platelets from patients were found responsive to significantly lower concentrations of arachidonic acid whereas thromboxane and hydroxylated fatty acid biosynthesis did not differ from controls. In the experimental conditions used, 75% of the control platelets underwent aggregation with phospholipase A2 plus sphingomyelinase C, in comparison to only 50% for the patients, indicating the necessity for further analysis of the platelet membrane lipids in atherosclerosis.

Organization and role of platelet membrane phospholipids as studied with phospholipases A2 from various venoms and phospholipases C from bacterial origin

Phospholipases A2 from various snake or bee venoms and phospholipases C secreted as exotoxins by several bacteria have been used to study the transverse distribution of phospholipids in the platelet plasma membrane and their role in platelet activation. An asymmetric distribution was described for phospholipids, characterized by a preferential localization of sphingomyelin and phosphatidylcholine in plasma membrane outer leaflet, whereas the inner half contains almost all of the anionic procoagulant phosphatidylserine and phosphatidylinositol. Such a distribution might explain the latency of procoagulant activity in resting platelets and implies an intracellular localization of arachidonic acid, the precursor of prostaglandins and thromboxanes. The external arachidonic acid is involved in phospholipase A2-induced aggregation, whereas phospholipase C from Clostridium welchii stimulates platelets through a thromboxane-independent pathway. The latter one is directly linked to the formation of phosphatidic and lysophosphatidic acids, which are able to activate cells through calcium mobilization. So, phospholipase C represents an interesting tool for studying the biochemical processes accompanying stimulation, since it is shown that it mimics the effects of an intracellular phospholipase C, the role of which in platelet activation is discussed.

Studies on topological distribution of arachidonic acid replacement in platelet phospholipids and on enzymes involved in the phospholipid effect accompanying platelet activation

In this short review recent results obtained on platelet phospholipid metabolism are summarized. The first part reports a topological study of arachidonic acid (AA) replacement in platelet phospholipids. It is shown that incubation of platelets with radioactive free arachidonic acid leads to a labelling of the phospholipids present inside the platelet, whereas the exchange of intact phosphatidylcholine (PC) molecules with the plasma lipoproteins occurs on the platelet outer surface. This should allow a selective labelling of the small external pool of AA in order to follow its behaviour during platelet activation. In the second part, some enzymes involved in the metabolism of phosphatidylinositol (PI) have been further characterized. The first one is a diglyceride-lipase, which is located in the plasma membrane and releases the two fatty acids esterifying the diglycerides formed from PI by the action of the platelet phospholipase C. Such an enzyme is probably responsible for the release of AA from PI occurring upon platelet activation. On the other hand, cytosolic phospholipid exchange proteins able to catalyse the transfer of PI between membranes have been identified. The possible role of the enzymes involved in the acceleration of PI turnover occurring during platelet activation is discussed.

Asymmetric distribution of arachidonic acid in the plasma membrane of human platelets. A determination using purified phospholipases and a rapid method for membrane isolation

1. Non-lytic degradation of human platelet phospholipids have been performed using a combination of bee venom phospholipase A2 (phosphatide 2-acyl-hydrolase, EC 3.1.1.4) and Staphylococcus aureus sphingomyelinase C (sphingomyelin choline phosphohydrolase). Under these conditions, 25.4% of total phospholipds are degraded and 6.4% of total platelet arachidonic acid is released. 2. A new method for rapid isolation of platelet plasma membrane is described, based on the use of [3H]concanavalin A as a membrane marker and of self-generating gradients of Percoll. Plasma membranes are enriched 5.2 fold in lectin marker and 0.43 in N-acetyl-beta-D-glucosaminidase, the main contaminant. This method allows to estimate that 57% of the total cell phospholipids and 61% of the total arachidonic acid content are located in the plasma membrane. 3. The distribution of phospholipids and arachidonic acid between the two leaflets of the plasma membrane has been deduced by using these values and those obtained from non-lytic treatment of intact platelets by phospholipases. It is concluded that 45% of plasma membrane phospholipids, comprising 93% of sphingomyelin, 45% of phosphatidylcholine, 9% of phosphatidylserine, 16% of phosphatidylinositol and 20% of phosphatidylethanolamine form the outer half of the human platelet plasma membrane. The phospholipids appear to bear only 10% of the total membrane arachidonic acid.

Platelet Activation : Role of Exogenous and Endogenous Phospholipases

Phosoholipase A2 from bee venom induces aggregation of human platelets, provided that phospholipid hydrolysis is enabled by simultaneous incubation with sphingomyelinase C. Inhibition of the platelet response by indomethacin indicates that aggregation is due to arachidonic acid release. On another hand, this model allows to describe an asymmetrie distribution of arachidonic acid, whose only 6% is located in the outer leaflet of the plasma membrane.

During platelet aggregation by phospholipase C, the diacylglycerol and its hydrolysis product 2-acyl-glycerol are phosphorylated into phosphatide and lysophosphatidic acids, respectively. As the same kinds of changes occur in the presence of thrombin, a unifying hypothesis for platelet activation is proposed, involving the stimulation of an endogenous phospholipase C, whose some properties will be reported (neutral optimal pH, Ca-requlrement, phosphatidylinositol specificity and cytosol-localization). This model can be related to the recent finding that phosphatide acid behaves as a calcium-ionophore (Gerrard, J.M. et al., Prostaglandins Med., 1978, 1, 387) and provides an alternative pathway for arachidonic acid mobilization.