The initial infective process of the malaria parasite in humans is between the invading parasite and hepatocytes of the host. In several studies, the portal for this invasion has implicated the heparin/heparan sulfate (H/HS) receptor systems (which we classified early on to be in a sepatate class of glycocaminoglycan biopolymers on the basis of the specificity of their optically active structures (AL Stone 1963/4 Biopolymers 2/3). Heparin also inhibits the rosetting and cytoadhesion of parasitized Plasmodium falciparum erythrocytes (PfRBC) to normal RBC and the endothelium, and to clear blockage of the microcirculation which ameliorates life-threatening symptoms of cerebral malaria when administered in children. H/HS are modulatory receptors. They are found in most tissues of the body where they not only govern the level of activity/function of numerous normal physiological systems, but they also seem to serve as receptors for various human pathogens in a mechanism(s) that needs further elucidation. Malaria ranks in the top three deadliest diseases globally (more than 300 million clinical cases per year). 1-3% of the Pf parasites are highly virulent, causing severe and cerebral malaria and the death of about 2 million people per year (90 % young children). There is no preventive vaccine, and malarial parasites are increasingly resistant to anti-malarial drugs. We have applied our library of heparin-mimetic S-oligoS produced for development of heparin-based anti-HIV drugs (see HD 001315 -14) to characterize the inhibition of the malaria parasites by heparin in vitro and explore its potential usefulness as an anti-malarial. This enabled us to find that the heparin-based inhibition of P. yoelii sporozoites (freshly isolated from infected mosquitos) to invade an hepatocyte was governed by a degree of structural specificity and concentration dependent; highest potency resided in two S-OligoS in mass class about 7200 (Cp6) and 3700 (C11) displaying 43 and 56 percent inhibition at 3.5 and 5 micromolar, resp. S-oligoS of 3700 mass have shown negligible anti-thrombin capacity. Additional Cp11 for continuing studies is in preparation. In contrast to sporozoite invasion of hepatocytes, the structure-function relation of S-oligoS library components in the erythrocyte invasion stage of malarial parasites revealed that components of mass class less than 4500 exhibited very low inhibitory capacity, while high potency was associated only with relatively high mass class equal to or greater than 10,000. Such data suggests that the molecular reactions underlying the inhibition of the two parasite stages differ. Preparation of additional Cp11 and expansion of our library of components in the mass range about 4-3000 is continuing as will the resumption of studies on inhibition of sporozoites, parasitized RBC, and rosetting as a path towards stable, inexpensive heparin-based anti-malarials against initial infection, pathologies, and/or acute cerebral malaria. LJAburadad, et al (Science319:1603 2006) recently developed a statistical analysis wich they used to calculate relaible estimate of the previously """"""""anecdotal"""""""" findings that HIV infection in malaria endemic regions is spread at a rate 8 percent higher than in other regions where HIVAIDS is on the rise, and vise-versa, due to an unexplained vulnerability of either patient to the second pathogen. Previously, our results had led us to suggest that co-treatment of malaria and HIV-AIDS would be feasible because of the close similarity in the physicochemical proerties of the respective S-oligoS inhibitors. Now, a preliminary study of the effect of co-dosing SOLIS with increasing proportions of Cp11 on the capacity of SOLIS to inhibit the cytopathic action of HIV-1 on CD4 cells in vitro is completed. Results suggest that the presence of the anti-malarial S-oligoS diminished the inhibutory effect of SOLIS in vitro. This effect is not readily predictive for an in vivo system because the mechanism of thr process is not fully understood. We think the inhibition of inhibitory capacity of our anti-HIV drug in vitro may be a reflection of a common mechanism for the biological production of the endogenous H/HS receptors for malaria and HIV-1, such as the mechanisms of specific expression of specific enzyme isoforms? in the biosynthesis of anticoagulant H/HS (revealed and elucidated by Robert D. Rosenthal and coworkers in the previous decade).? Continuation of the basic as well as practical studies on this inter-pathogen effect on disease and anti-pathogen will use, if feasible, an animal model such as that offered in an NIH intrmural program. CURRENT STUCTURAL CONSIDERATIONS indicate the S-OligoS structure contains a tetrasaccharide motif of three xyloses and a glucuronic acid as a branch on the xylan chain i.e., -D-glucuronyl-alpha 1,2 beta 1,4 D-(xylyl)3 with up to one third of the GlcA O-methylated. The sugars are within 90 percent sulfated yielding a high negative charge density. Such motif could accommodate the subtle variations in geometries involving sulfates which would be components to provide for mutifunctional mimicry of the heparins.
