Friday, April 15, 2011

are exosomes the Priuses of RNAi transport?

Knocking out insidious genes using RNA-interference (RNAi) has been massively pursued as a therapeutic technique since its discovery.  Specifically, methods of delivering RNAi through the blood stream to target tissues have been of great interest.  Scientists have successfully packaged and delivered RNAi in  lentiviruses, micelles and other nanoparticles.  However, the search for cost-effectiveness, efficiency and target accuracy never sleeps (insert wise crack about the tendency of their funding to hibernate).

In a study recently published in Nature Biotechnology, exosomes are suggested to be a significant improvement over other vehicles.  The scientists used dendritic cells -- derived from bone marrow progenitor cells, and not to be confused with neural somas -- and proceeded to test the efficiency and accuracy of their RNAi packaging and delivery.  They purified the exosomes, tagged them with muscle or brain targeting peptides, loaded them with exogenous cargo (siRNA for GADPH, a housekeeping gene), and tested their delivery both in vitro and in vivo.

Alvarez-Erviti and colleagues achieved a marked knockdown of GADPH in vitro, and an even more impressive knockdown in several peripheral organ and brain region tissues in vivo, suggesting an improved blood brain barrier-transcending capacity compared to other methods.  The exosome delivery method was accurate, and achieved a 60% knockdown of mRNA and a 62% knockdown of protein expression using, allegedly, 10% of the siRNA cargo that other methods have used.

62% efficiency is generally accepted as a pretty high yield in the biomedical sciences.  Whether this exosomal packing and delivery system can be optimized to better penetrate the blood brain barrier remains to be seen.  However, with its cost-effective, accurate and non-invasive methods, the exosome may be the Prius of siRNA delivery.
Alvarez-Erviti L, Seow Y, Yin H, Betts C, Lakhal S, & Wood MJ (2011). Delivery of siRNA to the mouse brain by systemic injection of targeted exosomes. Nature biotechnology, 29 (4), 341-5 PMID: 21423189

Thursday, April 14, 2011

Saccharomyces boulardii improves migration of new epithelial cells

The lifespan of healthy intestinal epithelia is generally accepted to be about 5 days.  These cells, once departed and sloughed off into the fecal stream, are replaced by newer, younger, healthier cells which proceed through the same life-cycle.  In the case of inflammatory bowel diseases (IBDs), in addition to inflammation/ulceration/tissue injury, the migration process of these new epithelial cells is stunted.  Since the replacement cells have trouble reaching their destination, damage to the intestinal lining is exacerbated.

A recent study -- published in PLoS ONE and open access if anyone wants to take a peek -- investigated the capacity of a nonpathogenic yeast to alleviate this stunted migration of new epithelial cells to the tips of intestinal villi (the fingers of tissue that protrude from the intestinal wall to create surface area for absorption).  Saccharomyces boulardii (Sb) is typically used to treat issues such as diarrhea, the idea being that it stimulates growth factors that help restore homeostasis to the gut.

This nigh-rockstar study strikes me because it is targeting a curative mechanism as opposed to a squelching of symptoms.  To achieve actual remission in IBDs, one has to pwn both inflammatory and repair dysfunctions.  The inflammatory component is predominantly targeted by the entourage of immuno-suppressants with which Crohns are so familiar.  Repair is seldom highlighted as it should be -- excepting methods of balancing gut flora.

The team of scientists in France, lead by one Frederic Andre, looked at the beneficial effects of Sb in both mice and an in vitro wound model (this is a strain of cultured epithelial cells which are attacked gently with a toothpick... rather cute).

The first major finding was that mice who were fed Sb for one week doubled new epithelial cell migration.  Only one downer for me in this study was that the mice were all healthy, with no in vivo IBD model for comparison.  Nonetheless quite encouraging, no?

The second conclusion was that the wounded cell line closed its wound (or, repaired its injury) by roughly 70%.  Their video supplement to this end is quite something.

The scientists conclude that Sb improves new epithelial migration both in vivo and in vitro.  Interestingly, the study suggests that increased migration is due to increased motility of cells and not to increased proliferation (the generation of new cells).  Sb may be stimulating this activity by secreting factors that stimulate  a target signaling pathway FAX/paxillin, which leads to several physiological changes in the intestinal epithelial lining that enable motility of new epithelial cells.

The thing about supplement studies such as this one is that they make me want to stop by the grocery and pick some up on my way home...
Canonici A, Siret C, Pellegrino E, Pontier-Bres R, Pouyet L, Montero MP, Colin C, Czerucka D, Rigot V, & André F (2011). Saccharomyces boulardii Improves Intestinal Cell Restitution through Activation of the α2β1 Integrin Collagen Receptor. PloS one, 6 (3) PMID: 21483797