Extracellular vesicles derived from a type of immune cell called a macrophage may have potential as a less invasive delivery system for TPP1 – the enzyme missing in patients with CLN2 or late infantile Batten disease – to the brains of affected people.
The preclinical study with this result, “Delivery of TPP1 to lysosomes with extracellular vesicles and their improved cerebral distribution in the animal model of Batten disease,»Was published in the journal Advanced health materials.
Like other lysosomal storage disorders, CLN2 or infantile end Batten disease is caused by genetic mutations that prevent cells from effectively breaking down waste products inside lysosomes, which are cell structures that digest and recycle different types of molecules.
Patients with CLN2 disease carry mutations in the TPP1 gene, resulting in severe deficiency or complete absence of the enzyme TPP1. This results in incomplete degradation of protein fragments, called peptides, inside lysosomes. As a result, toxic waste builds up inside cells, mainly in the nervous system, causing the signs and symptoms of CLN2 disease.
The administration of a functional TPP1 to the central nervous system (CNS, brain and spinal cord) has been considered a basic approach to treat the disease. In fact, it forms the basis of the only approved treatment for this condition: Brieneura (cerliponase alfa, Sold by BioMarin), a enzyme replacement therapy which delivers a functional TPP1 enzyme to the brain.
However, the administration of this therapy requires invasive infusions known as intraventricular injections into brain fluid.
One of the main reasons why therapeutics are not successfully delivered to the CNS using less invasive systemic methods – into the bloodstream, for example – is the existence of multiple biological barriers that limit delivery. drug efficacy to the CNS, eg.particularly the blood brain barrier (BBB), a highly selective semipermeable membrane that separates circulating blood from the brain.
To work around this problem, researchers at University of North Carolina at Chapel HilI propose to use extracellular vesicles (EVs) as nanosupports to effectively deliver TPP1 to the brain, even when administered systemically (into the blood).
Electric vehicles are naturally occurring microscopic membrane vesicles used by cells to communicate with each other “and therefore may provide unprecedented opportunities for drug delivery,” the researchers wrote.
Electric vehicles have been suggested as drug delivery vehicles for a variety of purposes, including the delivery of anti-inflammatory or anti-cancer agents.
To optimize the delivery of TPP1 to the brain, scientists tested certain electric vehicles that are found specifically in immune cells called macrophages that participate in inflammatory responses. The death of nerve cells is often accompanied by neuroinflammation in lysosomal storage disorders, such as Batten’s disease. This is why macrophage electric vehicles have the potential to deliver site-specific TPP1 to regions of the brain affected by inflammation.
In this study, researchers generated electric vehicles derived from TPP1-loaded macrophages and tested whether these transporters could efficiently deliver the therapeutic protein to cell and mouse models of CLN2 disease.
To this end, TPP1 has been loaded onto electric vehicles derived from macrophages using two different methods: macrophages have been genetically engineered to produce TPP1 and charge it on electric vehicles; or TPP1 has been incorporated into empty electric vehicles derived from macrophages.
Both methods have made it possible to effectively integrate the functional TPP1 in electric vehicles.
As expected, electric vehicles protected TPP1 from degradation and enabled efficient transport of the functional enzyme to in vitro cell models of CLN2 (skin cells from patients grown in petri dishes).
Most EV-TPP1 (about 70%) was confirmed to be delivered to lysosomes, the cell compartment where the TPP1 enzyme is missing.
It is important to note that when the researchers routinely administered electric vehicles loaded with TPP1 to mouse models of Batten disease (late infantile NCL mice), there was a strong build-up of these vesicles in the brain, accompanied by a significantly extended lifespan.
“Overall, nanocarriers from electric vehicles efficiently accumulate in lysosomes, which are the target organelles for the delivery of depleted lysosomal enzymes. This suggests that electric vehicles derived from macrophages may be a promising drug delivery platform for enzyme replacement therapy to treat different LSDs. [lysosomal storage disorders]”, concluded the researchers.