Cobinamide as a disease-modifying treatment for Marfan Syndrome: optimizaation of absorption

Project Summary Marfan Syndrome (MFS) is a genetic disorder with a prevalence of ~1 in 5,000 people. Aneurysms in the ascending aorta are the most serious manifestation of the condition and can lead to sudden death due to spontaneous rupture. The aneurysms are due in part to increased oxidative stress in the smooth muscle cells of the aortic wall. Existing medical treatments are not disease-modifying and are only partially effective. Surgical aneurysm repair is the only proven method to prevent death. Cobinamide is the penultimate precursor in the biosynthesis of vitamin B12 (cobalamin). We have shown recently that cobinamide is a powerful and versatile antioxidant, more potent than other well-known antioxidants and able to neutralize both reactive oxygen and reactive nitrogen species. When administered as bis(histidyl)cobinamide in drinking water, cobinamide prevented aortic dilation and abolished oxidative stress and pathological changes in the aorta of mice with a mutation in fibrillin-1, analogous to mutations that occur in Marfan patients. Cobinamide thus has the potential to be a disease-modifying treatment for MFS. Under a Phase I SBIR grant, we found that bis(histidyl)cobinamide has low bioavailability, only 0.8% was absorbed after oral administration. The goal of the current project is to increase intestinal absorption of cobinamide to make it a more practical therapy for conditions like MFS where long-term treatment is needed. This will be accomplished by varying the ligands coordinated to the central cobalt atom of cobinamide and by using permeation enhancers. Bis(histidyl)cobinamide is hydrophilic with a low log P value, retarding its movement across cells. Hydrophobic ligands can increase the hydrophobicity/lipophilicity of the resulting cobinamide complex, and we found that a phenyl-containing ligand increased cellular uptake of cobinamide and cobinamide bioavailability ~2-fold compared to bis(histidyl)cobinamide. We now plan to test a variety of hydrophobic ligands, with the intent of finding ligands that increase cobinamide permeation through a human intestinal tissue model (EpiIntestinalTM) 4-5-fold compared to bis(histidyl)cobinamide. We will then combine these liganded cobinamide complexes with a permeation enhancer. Chitosan, a well-known permeation enhancer, increased cobinamide absorption across mouse gingiva, and salcaprozate sodium, another permeation enhancer, increases intestinal vitamin B12 (cobalamin) absorption. We will test these and other enhancers, with the overall goal to increase cobinamide permeation through EpiIntestinalTM by 8-10-fold compared to bis(histidyl)cobinamide. We will then evaluate bioavailability of the top performing cobinamide formulations (complex-enhancer combinations) in rats, with the goal of finding one or more formulations that yields a bioavailability of ≥6% in male and female animals. A number of drugs have bioavailabilities ranging from 1-10%.