Like the airport's security barriers that either clarify authorized travelers or block unauthorized travelers and their luggage from accessing key operating areas, the blood-brain barrier (BBB) closely controls the transport of essential nutrients and energy metabolites in the brain and saves unwanted substances circulating in the bloodstream. It is important that it be highly organized structure of thin blood vessels, and supporting cells are also the major obstacle to life-saving drugs coming from the brain to effectively treat cancer, neurodegeneration and other central nervous system disorders. In a number of brain diseases, the BBB can also locally break down, causing neurotoxic substances, blood cells and pathogens to leak into the brain and constitute irreparable devastation.
To study BBB and drug transport across the board, researchers have mostly invoked animal models such as mice. However, the exact makeup and transport functions of BBBs in these models can differ significantly from those in human patients, making them unreliable for predicting drug delivery and therapeutic efficiencies. Also, in vitro models attempting to recreate the human BBB using primary brain tissue-derived cells have so far failed to mimic the BBB's physical barrier, transport functions, and drug and antibody shuttling activities close enough to be useful as therapeutic development tools.
Now, a team led by Donald Ingber, M.D., Ph.D. at Harvard's Wyss Institute for Biologically Inspired Engineering has overcome these limitations by utilizing its microfluidic organ-chip (Organ Chips) technique in combination with a development-inspired hypoximimitation method to differentiate human pluripotent stem cells (iPS) into brain microvascular endothelial cells (BMVEC). The resulting "hypoxia-enhanced BBB Chip" recapitulates cellular organization, tight barrier functions and transport ability of the human BBB; and it allows the transport of drugs and therapeutic antibodies in a manner that mimics the transports over BBB in in vivo than existing in vitro systems. Their study is reported in nature Communications.
"Our way of modeling drug and antibody shuttling across the human BBB in vitro with such high and unprecedented fidelity provides significant progress over existing opportunities in this hugely challenging area of research," said Wyss Institute, Founder Director Ingber. needs of drug development programs throughout the pharma and biotech world that we are now striving to help overcome with a dedicated "Blood-Brain Barrier Transport Program" at the Wyss Institute with our unique talent and resources. "Ingber is also Judah Folkman Professor of Vascular Biology at the HSE and vascular biology program at Boston Children's Hospital, and professor of bioengineering at SEAS.
BBB consists of thin capillary blood vessels formed by BMVECs, multifunctional cells called pericytes that wrap around the outside of the vessels and star-shaped astrocytes, which are non-neuronal brain cells that also contact blood vessels with foot-like processes. In the presence of pericytes and astrocytes, endothelial cells can generate the tightly sealed vessel wall typical of the human BBB.
Ingber's team first differentiated human iPS cells into brain endothelial cells in the cultivation right using a method previously developed by co-author Eric Shusta, Ph.D. . "For the embryo to form BBB under low oxygen conditions (hypoxia), we separated iPS cells for a long time into an atmosphere of only 5% instead of the normal 20% oxygen concentration," said first author Tae-Eun Park, Ph.D. "As a result, the iPS cells initiated a development program that is essentially similar to that of the embryo, which produces BMVECs that exhibited higher functionality than BMVEC generated under normal oxygen conditions." Park was a postdoctoral fellow at Ingber's Law and is now an assistant professor at Ulsan National Institute of Science and Technology in the Republic of Korea.
Based on a previous human BBB model, the researchers transferred the hypoxia-induced human BMVEC values to one of two parallel channels of a microfluidic organ-on-chip unit shared by a porous membrane and continuously perfused with medium. The other channel is populated with a mixture of primary human brain appetites and astrocytes. After a further day of hypoxia treatment, the human BBB chip could be kept stable for at least 14 days at normal oxygen concentrations, which is far beyond previous human BBB models previously tried.
During the shear stress of the fluids that perfect BBB Chip, BMVEC continues to form a blood vessel and develops a dense interface with peric surfaces adapted to them on the other side of the porous membrane, as well as with astrocytes extending processes against them through small openings in the membrane. "The clear morphology of the constructed BBB is paralleled with the formation of a denser barrier containing increased numbers of selective transport and drug pendulum systems compared to control BBBs that we generated without hypoxia or fluid shear stress or with endothelium derived from adult brain rather than iPS cells. ", says Nur Mustafaoglu, Ph.D., a first author of the study and postdoctoral fellow who works at Ingber's law. "In addition, we were able to mimic the effects of treatment strategies in patients in the clinic. For example, we opened the BBB for a short while by increasing the concentration of a mannitol solution. [osmolarity] to allow the passage of large drugs such as the anti-cancer antibody Cetuximab. "
To provide further evidence that the hypoxia-enhanced human BBB Chip can be used as an effective tool for studying drug delivery to the brain, the team examined a number of transport mechanisms that either prevent drugs from reaching their targets in the brain by pumping them back into the brain. blood flow (outflow) or which allows selective transport of nutrients and drugs over BBB (transcytosis).
"When we specifically blocked the function of P-gp, a key endothelial outflow pump, we could significantly increase the transport of anti-cancer drugs doxorubicin from the vascular canal to the brain canal, similar to what has been observed in human patients," says Park. in vitro systems are used to identify new methods to reduce outflow and thereby facilitate the transport of drugs in the brain in the future. "
In another site, drug developers are trying to utilize "receptor-mediated transcytosis" as a means of shuttling drug-loaded nanoparticles, larger chemical and protein drugs, and therapeutic antibodies over the BBB. "The hypoxia-enhanced human BBB Chip recapitulates the function of critical transcytosis pathways, such as those used by LRP-1 and the transferrin receptors responsible for addressing vital lipoproteins and iron from circulating blood and releasing them into the brain on the other side of BBB. Utilizing the receptors using different preclinical strategies, we can mimic the previously shown shuttling of therapeutic antibodies targeting transferrin receptors in vivo while maintaining the BBB integrity in vitro, Mustafaoglu says.
Based on these findings, the Wyss Institute has initiated a "Blood-Brain Barrier Transport Program". "Initially, the BBB transport program strives to discover new shuttle targets enriched in the BMVEC core surface, using new transcriptomics, proteomics, and iPS cellular approaches. At the same time, we are developing complete human antibody shuttles targeting known shuttle targets with improved brain targeting. capacity, "said James Gorman, MD, Ph.D., Staff Lead for the BBB Transport Program working with Ingber. "We strive to work with several biopharmaceutical partners in a pre-competitive relationship to develop shuttles that offer outstanding efficiency and agility in antibody and protein drug incorporation, as this is so much needed by patients and the entire field".
The authors believe that besides drug development studies, the hypoxia-enhanced human BBB Chip can also be used to model aspects of brain diseases that affect BBB such as Alzheimer's and Parkinson's disease and advanced personal personal approaches using patient-derived iPS cells.
Microbiological physiology in humans can now be studied in vitro using the Organ Chip technique
Elevated human blood brain barrier chip performs in vivo-like drugs and antibody transports (2019, June 13)
June 13, 2019
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