Depsipeptides from a Guamanian Marine Cyanobacterium, Lyngbya bouillonii, with Selective Inhibition of Serine Proteases.

Bouillomides A (1) and B (2) are two depsipeptide analogues of dolastatin 13. Isolated from a Guamanian sample of Lyngbya bouillonii, the planar structures were elucidated on the basis of HR-ESI-MS and NMR data, while the absolute configurations were determined by employing functional group conversions, modified Marfey's analysis, and detailed analyses of ROESY correlations. Compounds 1 and 2 selectively inhibited serine proteases elastase (IC(50) = 1.9 µM for both) and chymotrypsin (IC(50) = 0.17 and 9.3 µM, respectively) while showing no inhibition of trypsin (IC(50) > 100 µM).

Polyketide assembly lines of uncultivated sponge symbionts from structure-based gene targeting.

There is increasing evidence that uncultivated bacterial symbionts are the true producers of numerous bioactive compounds isolated from marine sponges. The localization and heterologous expression of biosynthetic genes could clarify this issue and provide sustainable supplies for a wide range of pharmaceuticals. However, identification of genes in the usually highly complex symbiont communities remains a challenging task. For polyketides, one of the most important groups of sponge-derived drug candidates, we have developed a general strategy that allows one to rapidly access biosynthetic gene clusters based on chemical moieties. Using this method, we targeted polyketide synthase genes from two different sponge metagenomes. We have obtained from a sponge-bacterial association a complete pathway for the rare and potent antitumor agent psymberin from Psammocinia aff. bulbosa. The data support the symbiont hypothesis and provide insights into natural product evolution in previously inaccessible bacteria.

The marine sponge Diacarnus bismarckensis as a source of peroxiterpene inhibitors of Trypanosoma brucei, the causative agent of sleeping sickness.

Human African trypanosomiasis, also known as African sleeping sickness, is a neglected tropical disease with inadequate therapeutic options. We have launched a collaborative new lead discovery venture using our repository of extracts and natural product compounds as input into our growth inhibition primary screen against Trypanosoma brucei. Careful evaluation of the spectral data of the natural products and derivatives allowed for the elucidation of the absolute configuration (using the modified Mosher's method) of two new peroxiterpenes: (+)-muqubilone B (1a) and (-)-ent-muqubilone (3a). Five known compounds were also isolated: (+)-sigmosceptrellin A (4a), (+)-sigmosceptrellin A methyl ester (4b), (-)-sigmosceptrellin B (5), (+)-epi-muqubillin A (6), and (-)-epi-nuapapuin B methyl ester (7). The isolated peroxiterpenes demonstrated activities in the range IC(50) = 0.2-2 mug/mL.

Revisiting the sponge sources, stereostructure, and biological activity of cyclocinamide a.

The dramatic biogeographical variations in the secondary metabolites from Psammocinia aff. bulbosa have complicated our efforts to reisolate the two most cytotoxic of its metabolites, (+)-psymberin and (+)-cyclocinamide A. Reported now are the results of a new study that demonstrates our ability to repeatedly isolate these two compounds through targeted collection efforts. Additional study of the new sample of (+)-cyclocinamide A has enabled finalizing its biological activity and absolute stereochemistry as 4S, 7S, 11S, 14S.

Extending the record of meroditerpenes from Cacospongia marine sponges.

A new meroditerpene, (+)-isojaspic acid (1), along with two known meroditerpenes, cacospongin D (2) and jaspaquinol (3), have been isolated from a marine sponge Cacospongia. Comprehensive taxonomic identification distinguished this Cacospongia apart from morphologically similar Psammocinia. The absolute stereochemistry of 1 was elucidated on the basis of extensive 1D and 2D NMR techniques and analysis of the optical rotation versus (+)-zonarol (8), (+)-isozonarol (9), (-)-dactylosponol (10), and (+)-hyatellaquinone (11). Furthermore, bioactivity evaluation showed that the meroditerpenes isolated significantly inhibited Staphylococcus epidermidis.

Inhibitory activity of diacylglycerol acyltransferase (DGAT) and microsomal triglyceride transfer protein (MTP) by the flavonoid, taxifolin, in HepG2 cells: potential role in the regulation of apolipoprotein B secretion.

The purpose of the present study was to examine the role of taxifolin, a plant flavonoid, on several aspects involving apolipoprotein B (apoB) secretion and triglyceride (TG) availability in HepG2 cells. Taxifolin was shown by ELISA to markedly reduce apoB secretion under basal and lipid-rich conditions up to 63% at 200 micromol/L. As to the mechanism underlying this effect, we examined whether taxifolin exerted its effect by limiting TG availability in the microsomal lumen essential for lipoprotein assembly. Taxifolin was shown to inhibit microsomal TG synthesis by 37% and its subsequent transfer into the lumen (-26%). The reduction in synthesis was due to a decrease in diacylglycerol acyltransferase (DGAT) activity (-35%). The effect on DGAT activity was found to be non-competitive and non-transcriptional in nature. Both DGAT-1 and DGAT-2 mRNA expression remained essentially unchanged suggesting the point of regulation may be at the post-transcriptional level. Evidence is accumulating that microsomal triglyceride transfer protein (MTP) is also involved in determining the amount of lumenal TG available for lipoprotein assembly and secretion. Taxifolin was shown to inhibit this enzyme by 41%. Whether the reduction in TG accumulation in the microsomal lumen is predominantly due to DGAT and/or MTP activity remains to be addressed. In summary, taxifolin reduced apoB secretion by limiting TG availability via DGAT and MTP activity.

The chalcone xanthohumol inhibits triglyceride and apolipoprotein B secretion in HepG2 cells.

The present study examined the role of xanthohumol (XN), a plant chalcone, on apolipoprotein B (apoB) and triglyceride (TG) synthesis and secretion, using HepG2 cells as the model system. The data indicated that XN decreased apoB secretion in a dose-dependent manner under both basal and lipid-rich conditions (as much as 43% at 15 micromol/L). This decrease was associated with increased cellular apoB degradation. To determine the mechanism underlying this effect, we examined triglyceride availability, a major factor in the regulation of apoB secretion. XN inhibited the synthesis of TG in the microsomal membrane and the transfer of this newly synthesized TG to the microsomal lumen (decreases of 26 and 64%, respectively, under lipid-rich conditions), indicating that TG availability is a determining factor in the regulation of apoB secretion under the experimental conditions. The inhibition of TG synthesis was caused by a reduction in diacylglycerol acyltransferase (DGAT) activity, which corresponded to a decrease in DGAT-1 mRNA expression, but not DGAT-2 expression. Microsomal triglyceride transfer protein (MTP) may also control the rate of TG transfer from the microsomal membrane to the active lumenal pool. XN decreased MTP activity in a dose-dependent manner (as much as 30%). Whether the reduction in TG accumulation in the microsomal lumen is predominantly due to DGAT and/or MTP activity remains unknown. In summary, the data suggest that xanthohumol is a potent inhibitor of apoB secretion.