Earlier I blogged about an experiment that encapsulated mesenchymal stem cells into alginate hydrogels and implanted them into the hearts of rodents after a heart attack. The encapsulated mesenchymal stem cells showed much better retention in the heart and survival and elicited better healing and recovery of cardiac function than their non-encapsulated counterparts.
This idea seems to be catching on because another paper reports doing the same thing with cardiac stem cells extracted from heart biopsies. Audrey Mayfield and colleagues in the laboratory of Darryl Davis at the University of Ottawa Heart Institute and in collaboration with Duncan Steward and his colleagues from the Ottawa Hospital Research Institute used cardiac stem cells extracted from human patients that were encased in agarose hydrogels to treat mice that had suffered heart attacks. These experiments were reported in the journal Biomaterials (2013).
Cardiac stem cells (CSCs) were extracted from human patients who were already undergoing open heart procedures. Small biopsies were taken from the “atrial appendages” and cultured in cardiac explants medium for seven days.
Migrating cells in the culture were harvested and encased in low melt agarose supplemented with human fibrinogen. To form a proper hydrogel, the cells/agarose mixture was added drop-wise to dimethylpolysiloxane (say that fast five times) and filtered. Filtration guaranteed that only small spheres (100 microns) were left. All the larger spheres were not used.
Those CSCs that were not encased in hydrogels were used for gene profiling studies. These studies showed that cultured CSCs expressed a series of cell adhesion molecules known as “integrins.” Integrins are 2-part proteins that are embedded in the cell membrane and consist of an “alpha” and “beta” subunit. Integrin subunits, however, come in many forms, and there are multiple alpha subunits and multiple beta subunits.
This mixing and matching of integrin subunits allows integrins to bind many different types of substrates. Consequently it is possible to know what kinds of molecules these cells will stick to based on the types of integrins they express. The gene prolifing experiments showed that CSC expressed integrin alpha-5 and the beta 1 and 3 subunits, which shows that CSC can adhere to fibronectin and fibrinogen.
When encapsulated CSCs were supplemented with fibrinogen and fibronectin, CSCs showed better survival than their unencapsulated counterparts, and grew just as fast ans unencapsulated CSCs. Other experiments showed that the encapsulated CSCs made just as many healing molecules as the unencapsulated CSCs, and were able to attract circulating angiogenic (blood vessel making) cells. Also, the culture medium of the encapsulated cells was also just as potent as culture medium from suspended CSCs.
With these laboratory successes, encapsulated CSCs were used to treat non-obese diabetic mice with dysfunctional immune systems that had suffered a heart attack. The CSCs were injected into the heart, and some mice received encapsulated CSCs, other non-encapsulated CSCs, and others only buffer.
The encapsulated CSCs showed better retention in the heart; 2.5 times as many encapsulated CSCs were retained in the heart in comparison to the non-encapsulated CSCs. Also, the ejection fraction of the hearts that received the encapsulated CSCs increased from about 35% to almost 50%. Those hearts that had received the non-encapsulated CSCs showed an ejection fraction that increased from around 33% to about 39-40%. Those mice that had received buffer only showed deterioration of heart function (ejection fraction decreased from 36% to 28%). Also, the heart scar was much smaller in the hearts that had received encapsulated CSCs. Less than 10% of the heart tissue was scarred in those mice that received encapsulated CSCs, but 16% of the heart was scarred in the mice that received free CSCs. Those mice that received buffer had 20% of their hearts scarred.
Finally, did encapsulated CSCs engraft into the heart muscle? CSCs have been shown to differentiate into heart-specific tissues such as heart muscle, blood vessels, and heart connective tissue. Encapsulation might prevent CSCs from differentiating into heart-specific cell types and connecting to other heart tissues and integrating into the existing tissues. However, at this point, w have a problem with this paper. The text states that “encapsulated CSCs provided a two-fold increase in the number of engrafted human CSCs as compared transplant of non-encapsulated CSCs.” The problem is that the bar graft shown in the paper shows that the non-encapsulated CSCs have twice the engraftment of the capsulated CSCs. I think the reviewers might have missed this one. Nevertheless, the other data seem to show that encapsulation did not affect engraftment of the CSCs.
The conclusion of this paper is that “CSC capsulation provides an easy, fast and non-toxic way to treat the cells prior to injection through a clinically acceptable process.”
Hopefully large-animal tests will come next. If these are successful, then maybe human trials should be on the menu.