Preserving Heart Tissue After a Heart Attack: Umbilical Cord-Coated Stem Cell Spheres

Eliana Martinez and her colleagues from the laboratories of Chuen Lee and Theo Kofidis at the National University of Singapore have published an extremely interesting paper in the journal Stem Cells and Development. In this paper, Martinez and her colleagues use a novel approach to deliver stem cells to the hearts of rats after a heart attack.

Usually, stem cells are given to heart attack patients in one of several ways. In laboratory animals, it is common to simply inject the stem cells directly into the heart muscle. This is done after the animals’ chest has been cut open. This procedure, known as a thoracotomy, is feasible in human patients, but unless the patient is undergoing coronary artery graft bypass surgery, cracking the chest leaves the patients in severe pain, greatly weakened, and with a very long recovery period. Therefore, unless necessary, this procedure is not preferred. Secondly, stem cells are delivered through the coronary arteries by means of the same technology used to deliver stents (percutaneous coronary intervention or PCI). In this case the cells are delivered through the coronary arteries while the arteries are propped open. This procedure is relatively easy to perform and no special equipment or training is required to deliver the cells, but several studies have shown that only a fraction of the cells make it to the heart muscle. The third technique uses direct injection into the heart muscle without cracking the patient’s chest. This technique uses special injection devices under the direction of sophisticated heart imaging technologies. Special equipment and specialized training is required to deliver the cells. Only a few centers offer this mode of delivery. The cells are well retained in the heart muscle, but a percentage of them leak out and find their way into the lung and other organs.

All of these techniques have their ups and downs. To that end, Martinez and her colleagues decided to deliver small spheres of stem cells surrounded by umbilical cord cells. These subamnion-cord-lining mesenchymal stem cell angiogenic spheroids (say that fast five times) consist of a special cell type from human umbilical cord called human umbilical cord vein endothelial cells or HUVECs that were used to encase another type of umbilical cord stem cell called cord-lining mesenchymal stem cells or CL-MSCs.

CL-MSCs have been evaluated in the laboratory and they seem to possess a robust ability to evade detection by the immune system and suppress inflammation, and do a better job of inducing healing than bone marrow-based stem cells (see Deuse T, et al., Cell Transplant. 2011;20(5):655-67). These cells also showed a marked ability to repair the heart after a heart attack (see Lilyana and others, Tissue Eng Part A 19:1303-1315).

To this end, Kofidis and his co-workers decided to use the spheroid technique because stem cells grown in liquid suspension and not flat culture dishes seem to do a better job of holding onto their healing properties than stem cell grown under standard conditions. Next, Martinez and others added HUVEC cells, which make blood vessels, the encase the CL-MSCs. Once they spheroids were made, they used fibrin (the protein found in blood clots) to paste the spheroids to the heart tissue after inducing a heart attack in laboratory rats.

These spheroids were mercifully called SASGs, since the proper name of these clusters was subamnion-cord mesenchymal stem cells angiogenic spheroids embedded within fibrin grafts (exhale). The laboratory animals were either given fibrin grafts without SASGs, neither fibrin grafts nor SASGs, and SASGs while the animal had its chest cracked, SASGs delivered without a thoracotomy (under video-assisted thoracoscopic surgery, and fibrin grafts under with no SASGs without have the chest cracked open.

In both cases in which SASGs were delivered, the structure and function of the heart improved in every physiological category examined. The heart beat more efficiently, the heart scar was smaller, there were more blood vessels, less, cell death, less sign of heart failure,

Even though this was a relatively small study in laboratory animals, it shows that a minimally invasive procedure can deliver stem cells to the heart that will stay in the heart and deliver healing to it,

This strategy should be expanded to larger numbers of animals and then, if it still statistically pans out, larger animal model systems should be examined (e.g., minipigs).   This is an ingenious technique, and hopefully, other laboratories will confirm the efficacy of this technique and the robust healing capabilities of this particular stem cell type from umbilical cord.

Remote Ischemic Conditioning Enhances Stem Cell Retention in the Heart

Stem cell administration to the heart after a heart attack is a difficult venture. Direct injection into the heart muscle is definitely the most sure-fire way to get stem cells into the heart tissue. However, direct injection requires that the physician crack the patient’s chest (thoracotomy), which is exquisitely unpleasant for the patient. Alternatively, there are devices that an deliver stem cell injections into the heart through the large veins in the legs, but these procedures require special equipment and lots of skills that your average cardiologist does not have. Another way is to administer stem cells through angioplasty. Using the same procedure as stent implantation, a delivery device is replaced at the site of heart damage through over-the-wire angioplasty technology, and the stem cells are delivered slowly and gradually through the coronary blood vessels. This does not require fancy equipment, and your average cardiologist could perform this technique pretty easily.

Problems exist with both procedures. Direct injection places cells and fluid into the heart wall and there is a risk of rupture. Likewise, with over-the-wire delivery of stem cells, there is the risk of clogging the coronary artery.

With both techniques, many stem cells end up in places other than the heart. In fact, the majority of the stem cells end up somewhere else – the lungs and liver mostly. Is there a better way?

Intravenous administration would be sweet, but that has been tried and the bottom line is that it bombed (Barbash et al., Circulation. 2003 19;108(7):863-8; Freyman et al., Eur Heart J. 2006 May;27(9):1114-22).

Well, some very enterprising scientists from China had an idea to get the intravenously administered stem cells to go to the heart and stay there. Bone marrow stem cells respond to a molecule called SDF1alpha (stromal cell derived factor-1alpha). On their cell surfaces, bone marrow cells have a receptor called CXCR4 which binds the SDF1alpha and bone marrow cells move towards higher and higher concentrations of SDF1alpha. Therefore, can you get the heart to make more SDF1alpha?

Sure. You can genetically engineer it to make more SDF1alpha. If you do that, the stem cells will pour out of the bone marrow and go to the heart and help fix it (Sundararaman S et al., Gene Ther. 2011 18(9):867-73). However, is there another way to get more SDF1alpha in the heart?

Yes there is. Let me introduce Remote Ischemic Conditioning or RIC. RIC increases the protection against injury that results from loss of blood flow to an organ. The way RIC works is that the blood supply to another organ is clamped so that this other organ is deprived of oxygen long enough to sound the alarm, but not long enough to do it serious damage. This deprivation of oxygen induces a flash of SDF1alpha production, which brings stem cells from bone marrow to the bloodstream and to the damaged organ.

Qin Jiang and colleagues from the Peking Union Medical College in Beijing, China used RIC in animals that had undergone a heart attack to determine if RIC could recruit more stem cells to the heart. Also, they administered bone marrow stem cells intravenously to see if RIC increased stem cell retention in the heart.

Jiang and others broke their laboratory rats into three groups (it gets a little complicated).

The first group was given heart attacks and then split into two subgroups. One subgroup received RIC and the second subgroup received surgery but no RIC.

The second group was given a heart attack and then split into six subgroups. Once subgroup was given RIC and intravenous bone marrow mesenchymal stem cells. the second received bone marrow mesenchymal stem cells by no RIC, only the incision, the third subgroup only received intravenous mesenchymal stem cells, the fourth group received RIC and intravenous saline, the fifth subgroup received no RIC, only an incision and intravenous saline, and the sixth subgroup received only intravenous saline.

The third group was given heart attacks and then split into two groups, one of which received RIC, intravenous mesenchymal stem cells and intravenous antibodies against CXCR4, and the other of which received RIC, mesenchymal stem cells and an antibody against nothing in particular.

The results showed that RIC GREATLY increased the amount of SDF1alpha in the heart. There was simply no getting around this. At 1 hour after RIC, SDF1alpha and VEGF (vascular endothelial growth factor) levels were up, but these levels decreased by 3 hours and back to normal by 6 hours after RIC.

Did these increased SDF1alpha levels increase stem cell retention? Oh yes!! The RIC-treated rats had almost twice the number of stem cells in their hearts than the animals that did not have RIC. Did this make a functional difference? Again, yes! The RIC-treated animals had hearts that functioned more normally (relatively speaking) than hearts from the non-RIC-treated animals.

The third experiment was even more informative, since the co-administration of the CXCR4 antibody abrogated the response induced by RIC. This demonstrates that effects of RIC are mediated by the SDF1alpha/CXCR4 axis and blocking this signaling axis prevented any benefits from RIC.

This paper is short, but very informative. It suggests that a relatively simple procedure like RIC could potentially improve the clinical efficacy of stem cell treatments. If this can be shown to work in larger animals, then clinical trials might be warranted. In fact clinical trials are presently underway in which SDF1alpha is being engineered into the heart to treat heart attack patients (see Hajjar RJ, Hulot JS. Circ Res. 2013 Mar 1;112(5):746-7).