Molluscicidal saponins of Phytolacca dodecanra: Oleanoglycotoxin-A

The structure of one of the major molluscicidal saponins of the fruit of Phytolacca dodecandra has been elucidated as 3-[2,4-di-O-(β-d-glucopyranosyl)-β-d-glucopyranosyll-olean-12-ene-28-oic acid. The combined use of 300 Mc. PMR, MS and GC-MS led to this structural assignment.     

Dihomogammalinolenic acid, but not eicosapentaenoic acid, activates washed human platelets

Dihomogammalinolenic acid (2.5-20 microM) added to suspensions of washed human platelets induces platelet shape change and the formation of 1,2-diacylglycerol and phosphatidic acid, indicating the activation of phospholipase C. It also stimulates the phosphorylation of a 40 kDa protein, indicating the activation of protein kinase C. Dihomogammalinolenic acid is converted mainly to 12-hydroxyheptadecadienoic acid and to a smaller extent to prostaglandin E1 and thromboxane B1. Small quantities of the lipoxygenase product 12-hydroxyeicosatrienoic acid are also observed. Indomethacin, by blocking platelet cyclooxygenase, prevents the activation of phospholipase C, protein kinase C, and platelet shape change induced by dihomogammalinolenic acid. Compound UK 38485, a specific thromboxane synthetase inhibitor, does not block platelet activation induced by dihomogammalinolenic acid. The results indicate that endoperoxides derived from dihomogammalinolenic acid, such as prostaglandin G1 or prostaglandin H1, may be responsible for the stimulation of phospholipase C and protein kinase C, and for the induction of platelet shape change. Eicosapentaenoic acid does not activate platelets and is poorly metabolized by platelet cyclooxygenase and lipoxygenase. Eicosapentaenoic acid is a better inhibitor of platelet activation induced by various agonists in washed platelets than dihomogammalinolenic acid. Eicosapentaenoic acid and dihomogammalinolenic acid are, however, equally effective in inhibiting aggregation induced by collagen in platelet-rich plasma. We suggest that eicosapentaenoic acid might be a better antithrombotic agent than dihomogammalinolenic acid.     

The appearance of phospholipase and cyclo-oxygenase activities in the human promyelocytic leukemia cell line HL60 during dimethyl sulfoxide-induced differentiation

The human promyelocytic leukemia cell line HL60 can be induced to differentiate into mature granulocytes by exposure to dimethyl sulfoxide. During differentiation a phospholipase activity, which releases arachidonic acid from membrane phospholipids, is expressed. Similarly, fatty acid cyclo-oxygenase activity increases 10-fold. In addition, there is a 40-fold increase in chemotactic formyl peptide receptor binding and a dramatic increase in glucose oxidation via the hexosemonophosphate shunt. The addition of indomethacin, a potent cyclo-oxygenase inhibitor, to the culture medium reduced the cyclo-oxygenase activity of HL60 cells exposed to dimethyl sulfoxide by 97%. However, the presence of indomethacin did not block the dimethyl sulfoxide induced increases in chemotactic formyl peptide receptor binding and hexosemonophosphate shunt activity.     

The significance of electron dense deposits in mild lupus nephritis.

In patients with lupus nephritis, progression from a mild lesion to a diffuse proliferative glomerulonephritis has been reported in one to 35 percent of patients. Because of the wide variation in the rate of progression, this study was undertaken to determine those factors which would identify the patients most likely to progress. Of 21 patients with a mild lupus nephritis by light microscopy, progression to a diffuse proliferative lesion was seen in only those patients who had subendothelial deposits. While not all patients with subendothelial deposits had a deteriorating course, the persistence of such deposits on subsequent biopsies indicated a poor prognosis.     

Sphingosine inhibits phosphatidate phosphohydrolase in human neutrophils by a protein kinase C-independent mechanism

Human neutrophils have been labeled in 1-O-alkyl-phosphatidylcholine with 3H in both the alkyl chain and the choline moiety. Upon stimulation of these labeled cells with formyl-Met-Leu-Phe, C5a, or phorbol 12-myristate 13-acetate, phospholipase D is activated to produce 1-O-[3H]alkylphosphatidic acid ([3H]alkyl-PA) and [3H]choline. The [3H]alkyl-PA is then dephosphorylated by phosphatidate phosphohydrolase (PPH) to produce 1-O-[3H]alkyldiglyceride ([3H]alkyl-DG). Sphingosine, a sphingoid base known to inhibit protein kinase C (PKC), causes a dose-dependent inhibition of [3H]alkyl-DG formation. This inhibition is accompanied by increased accumulation of [3H]alkyl-PA without alterations in [3H]choline formation. Studies using various other sphingoid bases demonstrate that a long hydrocarbon chain and an amino group are required for the inhibition of DG formation. These results suggest that sphingoid bases inhibit PPH activity without altering phospholipase D activation and that they exhibit a similar structure-activity relationship for both PPH and PKC. K252a, a PKC inhibitor which acts by competing for ATP binding sites, does not inhibit the formation of [3H]alkyl-DG, [3H]alkyl-PA, or [3H]choline at a concentration (3 microM) that completely blocks phorbol 12-myristate 13-acetate-induced protein phosphorylation. Moreover, in neutrophil homogenates, sphingosine but not octylamine, inhibits PPH activity in a dose-dependent manner. Thus sphingosine inhibits PPH activity by a PKC-independent mechanism, raising the possibility that sphingoid bases may play a role in regulating PPH-mediated lipid metabolism in stimulated cells.