Evolutionary food web model based on body masses gives realistic networks with permanent species turnover.

The networks of predator-prey interactions in ecological systems are remarkably complex, but nevertheless surprisingly stable in terms of long term persistence of the system as a whole. In order to understand the mechanism driving the complexity and stability of such food webs, we developed an eco-evolutionary model in which new species emerge as modifications of existing ones and dynamic ecological interactions determine which species are viable. The food-web structure thereby emerges from the dynamical interplay between speciation and trophic interactions. The proposed model is less abstract than earlier evolutionary food web models in the sense that all three evolving traits have a clear biological meaning, namely the average body mass of the individuals, the preferred prey body mass, and the width of their potential prey body mass spectrum. We observed networks with a wide range of sizes and structures and high similarity to natural food webs. The model networks exhibit a continuous species turnover, but massive extinction waves that affect more than 50% of the network are not observed.

Foraging theory predicts predator-prey energy fluxes.

1. In natural communities, populations are linked by feeding interactions that make up complex food webs. The stability of these complex networks is critically dependent on the distribution of energy fluxes across these feeding links. 2. In laboratory experiments with predatory beetles and spiders, we studied the allometric scaling (body-mass dependence) of metabolism and per capita consumption at the level of predator individuals and per link energy fluxes at the level of feeding links. 3. Despite clear power-law scaling of the metabolic and per capita consumption rates with predator body mass, the per link predation rates on individual prey followed hump-shaped relationships with the predator-prey body mass ratios. These results contrast with the current metabolic paradigm, and find better support in foraging theory. 4. This suggests that per link energy fluxes from prey populations to predator individuals peak at intermediate body mass ratios, and total energy fluxes from prey to predator populations decrease monotonically with predator and prey mass. Surprisingly, contrary to predictions of metabolic models, this suggests that for any prey species, the per link and total energy fluxes to its largest predators are smaller than those to predators of intermediate body size. 5. An integration of metabolic and foraging theory may enable a quantitative and predictive understanding of energy flux distributions in natural food webs.

Inhibition by boswellic acids of human leukocyte elastase.

Frankincense extracts and boswellic acids, biologically active pentacyclic triterpenes of frankincense, block leukotriene biosynthesis and exert potent anti-inflammatory effects. Screening for additional effects of boswellic acids on further proinflammatory pathways, we observed that acetyl-11-keto-beta-boswellic acid, an established direct, nonredox and noncompetitive 5-lipoxygenase inhibitor, decreased the activity of human leukocyte elastase (HLE) in vitro with an IC50 value of about 15 microM. Among the pentacyclic triterpenes tested in concentrations up to 20 microM, we also observed substantial inhibtion by beta-boswellic acid, amyrin and ursolic acid, but not by 18beta-glycyrrhetinic acid. The data show that the dual inhibition of 5-lipoxygenase and HLE is unique to boswellic acids: other pentacyclic triterpenes with HLE inhibitory activities (e.g., ursolic acid and amyrin) do not inhibit 5-lipoxygenase, and leukotriene biosynthesis inhibitors from different chemical classes (e.g., NDGA, MK-886 and ZM-230,487) do not impair HLE activity. Because leukotriene formation and HLE release are increased simultaneously by neutrophil stimulation in a variety of inflammation- and hypersensitivity-based human diseases, the reported blockade of two proinflammatory enzymes by boswellic acids might be the rationale for the putative antiphlogistic activity of acetyl-11-keto-beta-boswellic acid and derivatives.

Acetyl-11-keto-beta-boswellic acid (AKBA): structure requirements for binding and 5-lipoxygenase inhibitory activity.

1. 5-Lipoxygenase (5-LOX) products from endogenous arachidonic acid in ionophore-stimulated peritoneal polymorphonuclear leukocytes (PMNL) and from exogenous substrate (20 microM) in 105,000 g supernatants were measured. 2. The effects of natural pentacyclic triterpenes and their derivatives on 5-LOX activity were compared with the inhibitory action of acetyl-11-keto-beta-boswellic acid (AKBA), which has been previously shown to inhibit the 5-LOX by a selective, enzyme-directed, non-redox and non-competitive mechanism. 3. The 5-LOX inhibitory potency of AKBA was only slightly diminished by deacetylation of the acetoxy group or reduction of the carboxyl function to alcohol in intact cells (IC50 = 1.5 vs. 3 and 4.5 microM, respectively) and in the cell-free system (8 vs. 20 and 45 microM). 4. beta-Boswellic acid (beta-BA), lacking the 11-keto function, inhibited 5-LOX only partially and incompletely, whereas the corresponding alcohol from beta-BA, as well as amyrin, acetyl-11-keto-amyrin, 11-keto-beta-boswellic acid methyl ester had no 5-LOX inhibitory activity up to 50 microM in either system. 5. beta-BA only partially prevented the AKBA-induced 5-LOX inhibition, whereas the non-inhibitory compounds, amyrin and acetyl-11-keto-amyrin, almost totally antagonized the AKBA effect and shifted the concentration-inhibition curve for the incomplete inhibitor beta-BA to the right. In contrast, the non-inhibitory 11-keto-beta-BA methyl ester exerted no antagonizing effect. 6. The results demonstrate that the pentacyclic triterpene ring system is crucial for binding to the highly selective effector site, whereas functional groups (especially the 11-keto function in addition to a hydrophilic group on C4 of ring A) are essential for 5-LOX inhibitory activity.

Boswellic acids and protease activities.

The involvement of human leukocyte elastase (HLE) in several inflammatory processes and the reported inhibitory effect of ursolic acid on HLE has prompted the authors to start investigation on the effects of acetyl-11-keto-ß-boswellic acid (AKBA) on serine proteinases including HLE.

The orthopan tomoscintigram--a new application of emission computed tomography for facial bone scanning.

The exact regional correlation of findings of facial bone scans, planar or SPECT, to dental orthopan X-ray films (OPT) is difficult because of the very different projection techniques. To improve correlative imaging in this regard a projection algorithm was developed that uses SPECT data of the skull for reconstructing an orthopan tomoscintigraphic projection. Fourteen conventional SPECT slices of the upper and lower jaws were obtained during bone scanning. All mandibular slices were superimposed resulting in a horseshoe shaped structure, while was marked by an ROI which was divided into segments. All 14 SPECT slices were then masked by this segmental ROI, thereby marking the teeth-carrying bone in all slices. The information from this horseshoe like ROI is then transformed into lines. Line by line arrangement results in an orthopan projection, the orthopan tomoscintigram. This new display allows 1:1 true scale superimposition with the X-ray OPT and markedly facilitates correlative imaging.