Gibberellin Biosynthetic Inhibitors Make Human Malaria Parasite Plasmodium falciparum Cells Swell and Rupture to Death

Malaria remains as one of the most devastating infectious disease, and continues to exact an enormous toll in medical cost and days of labor lost especially in the tropics. Effective malaria control and eventual eradication remain a huge challenge, with efficacious antimalarials as important intervention/management tool. Clearly new alternative drugs that are more affordable and with fewer side effects are desirable. After preliminary in vitro assays with plant growth regulators and inhibitors, here, we focus on biosynthetic inhibitors of gibberellin, a plant hormone with many important roles in plant growth, and show their inhibitory effect on the growth of both apicomplexa, Plasmodium falciparum and Toxoplasma gondii. Treatment of P. falciparum cultures with the gibberellin biosynthetic inhibitors resulted in marked morphological changes that can be reversed to a certain degree under hyperosmotic environment. These unique observations suggest that changes in the parasite membrane permeability may explain the pleiotropic effects observed within the intracellular parasites

Review Article : Feudalism or Absolute Monarchism?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68809/2/10.1177_009770049001600304.pd

Synthesis and evaluation of (-)- and (+)-[(11)C]galanthamine as PET tracers for cerebral acetylcholinesterase imaging.

Improved radiopharmaceuticals for imaging cerebral acetylcholinesterase (AChE) are needed for the diagnosis of Alzheimer's disease (AD). Thus, (11)C-labeled (-)-galanthamine and its enantiomers were synthesized as novel agents for imaging the localization and activity of AChE by positron emission tomography (PET). C-11 was incorporated into (-)- and (+)-[(11)C]galanthamine by N-methylation of norgalanthamines with [(11)C]methyl triflate. Simple accumulation of (11)C in the brain was measured in an in vivo biodistribution study using mice, whilst donepezil was used as a blocking agent in analogous in vivo blocking studies. In vitro autoradiography of rat brain tissue was performed to investigate the distribution of (-)-[(11)C]galanthamine, and confirmed the results of PET studies in mice. The radiochemical yields of N-methylation of (-)- and (+)-norgalanthamines were 13.7% and 14.4%, respectively. The highest level of accumulation of (11)C in the brains of mice was observed at 10min after administration (2.1% ID/g). Intravenous pretreatment with donepezil resulted in a 30% decrease in accumulation of (-)-[(11)C]galanthamine in the striatum; however, levels in the cerebellum were unchanged. In contrast, use of (+)-[(11)C]galanthamine led to accumulation of radioactivity in the striatum equal to that in the cerebellum, and these levels were unaffected by pretreatment with donepezil. In in vitro autoradiography of regional radioactive signals of brain sections showed that pretreatment with either (-)-galanthamine or donepezil blocked the binding of (-)-[(11)C]galanthamine to the striatum, while sagittal PET imaging revealed accumulation of (-)-[(11)C]galanthamine in the brain. These results indicate that (-)-[(11)C]galanthamine showed specific binding to AChE, whereas (+)-[(11)C]-galanthamine accumulated in brain tissue by non-specific binding. Thus, optically pure (-)-[(11)C]galanthamine could be a useful PET tracer for imaging cerebral AChE

Transmission electron microscopy of parasitized erythrocytes treated with inhibitors.

<p>(A) Sections through an erythrocyte containing a trophozoite-stage parasite exposed to 0.1% DMSO for 6 h, 50 µM INA for 6 h or 250 µM AMO-1618 for 8 h, respectively. (B) Asynchronized parasites were treated with 0.1% DMSO (a–d) or 50 µM INA for 6 h (e–h). Sections from representative stages during intraerythrocytic development: ring- (a and e), early trophozoite- (b and f), mature trophozoite- (c and g) and schizont-stage parasites (d and h) are shown. Nuclei (n), food vacuoles (fv), merozoites (m), nuclei of merozoites (mn) and abnormal gaps between the nuclei and the nuclear envelopes (arrowheads) are indicated. Scale bar is indicated at the bottom of the images.</p

Isoprenoid biosynthetic pathways and known inhibitors in various organisms.

<p>Broken arrows indicate blocks in the biosynthesis due to specific inhibitors. “R” indicates various functional groups specific to individual compounds. CPPS, copalyl-diphosphate synthase (EC 5.5.1.13); KO, <i>ent</i>-kaurene oxidase (EC 1.14.13.78); CAS, cycloartenol synthase (EC 5.4.99.8); LS, lanosterol synthase (EC 5.4.99.7); KS, <i>ent</i>-kaurene synthase (EC 4.2.3.19); PP, pyrophosphate.</p

Fluorescence microscopy of INA-treated parasites.

<p>Infected erythrocytes were stained with (A) acridine orange, (B) Nile Red, (C) rhodamine 123 and (D) LysoTracker™ Red DND-99. INA was introduced at: (A) 100 µM for 9 h, (B) 50 µM for 6 h, and (C and D) 50 µM for 4 h. 100 µg/ml acridine orange was applied to thin blood smears made from intraerythrocytic parasites treated with INA. For other fluorescence dyes, <i>P. falciparum</i> cultures were incubated with probes for 1 h at the following concentrations: Nile Red, 1 µg/ml; rhodamine 123, 10 ng/ml; and LysoTracker® Red DND-99, 75 nM. Cells were not washed prior to fluorescence microscopy to minimize damage due to osmotic changes. Scale bar, 3 µm. An arrow indicates a lipid body in (B).</p