Researchers here demonstrate the creation of artificial pseudo-organelles capable of generating adenosine triphosphate (ATP). ATP is a chemical energy store molecule that is produced by mitochondria. It is vital to cell function. Mitochondrial production of ATP falters with age, as well as in tissues that become poorly supplied with nutrients. Finding a way to provide additional ATP could be quite helpful as a compensatory therapy, though whether or not a constant oversupply of ATP has meaningful negative consequences will have to be explored in greater detail than has been the case to date.
Cells have small compartments known as organelles to perform complex biochemical reactions. These compartments have multiple enzymes that work together to execute important cellular functions. Research have now successfully mimicked these nano spatial compartments to create 'artificial mitochondria'. This was achieved through reprogramming of 'exosomes', which are small vesicles (diameter ~120 nm) that cells use for intercellular signaling. The researchers carried out the experiments using microfluidic droplet reactors, which generated small droplets that were of similar size as typical cells. The researchers first aimed to facilitate controlled fusion of these exosomes within the droplets while preventing unwanted fusions.
These customized exosomes were then preloaded with different reactants and enzymes, which turned them into biomimetic nano factories. The team demonstrated this multienzyme biocatalytic cascade function by encapsulating glucose oxidase (GOx) and horseradish peroxidase (HRP) inside the exosomes. The GOx first converts glucose into gluconic acid and hydrogen peroxide. The HRP in turn uses the hydrogen peroxide generated in the first reaction to oxidize Amplex Red to a fluorescent product, resorufin. Next, the researchers wanted to know exactly how well these mini reactors can be uptaken and internalized by the cells. The cells derived from human breast tissues were fed with fused exosome nanoreactors, and their internalization over the next 48 hours was observed. It was found that cells were able to uptake these customized exosomes primarily through endocytosis, along with multiple other mechanisms.
Armed with this knowledge, the team sought to create functional artificial mitochondria that are capable of producing energy inside the cells. To achieve this, ATP synthase and bo3 oxidase were reconstituted into the earlier exosomes containing GOx and HRP, respectively. These exosomes were in turn fused to create nanoreactors that can produce ATP using glucose and dithiothreitol (DTT). It was found that the fused exosomes were capable of penetrating deep into the core part of a solid spheroid tissue and produce ATP in its hypoxic environment.