Hydrogen Sulfide Induces Dental Pulp Stem Cells to Become Liver Cells

The gas hydrogen sulfide smells like rotten eggs, and it is also poisonous in high quantities. It is produced throughout the body, and the exact role of it is unknown. However, scientists from the Nippon Dental University in the laboratory of Ken Yaegaki have shown that small quantities of this gas can induce particular adult stem cells to differentiate into liver cells.

Human teeth contain several stem cell populations, and one of these, the dental pulp stem cells, can make liver cells with remarkable efficiency. Dental pulp is composed of connective tissue and cells and dental pulp stem cells can be obtained from teeth after extraction.

Human tooth pulp stem cells contain a subpopulation that possesses a particular cell surface molecule called “CD117,” which is also known as the mast/stem cell growth factor receptor.  Those cells with this surface protein were isolated from the rest of the stem cells.  They then grew these stem cells in culture, and transferred them to a culture medium that contained a basic nutrient medium (Dulbecco’s modified Eagle’s medium for those who might be interested) and added to that medium, insulin, an iron-binding protein called transferrin, and two growth factors (embryotrophic factor and hepatocyte growth factor) for five days. Then they transferred the cells to another medium that was similar to the previous medium, but also had a cytokine called “oncostatin” and a steroid drug called dexamethasone for 15 days.  The atmosphere for these cells included either 5% carbon dioxide, and no or a small amount of hydrogen sulfide (0.05 ng ml−1).

After growing cells under these conditions, those cells that had been grown in the presence of hydrogen sulfide were more liver-like when it came to their biochemistry.  Liver cells store large amounts of sugar in the form of glycogen, produce a waste product called urea as a result of a pathway called the urea cycle, and make a large cadre of enzymes and proteins that are specific to the liver.  In almost every case, the cells grown in the presence of hydrogen sulfide made more liver-specific proteins than those grown without hydrogen sulfide.  The production of urea and glycogen were also increased, and glycogen storage was about five times greater in the hydrogen sulfide-treated group than in the control.  especially glycogen which was approximately five times greater compared to the control (p < 0.01). As a result of these experiments, the research group concluded that physiological concentrations of hydrogen sulfide increase the ability of human tooth pulp stem cells to undergo differentiation into liver cells.

Yaegaki commented, “Until now, nobody has produced the protocol to regenerate such a large number of hepatic (liver) cells for human transplantations.  Compared to the traditional method of using fetal bovine serum to produce the cells, our method is productive and, most importantly, safe.”  Yaegaki continued: “Moreover, these facts suggest that patients undergoing transplantation with the hepatic cells may have no possibility of developing teratomas or cancers, as can be the case when using bone marrow stem cells.”

Clearly, dental stem cells are from a tissue that is normally thrown out.  This new life for exfoliated teeth might provide a new role for these tooth-bound stem cells, and might also provide a new way to treat those with devastating liver diseases.  For example, systemic lupus erythematosis can decimate the patient’s liver, and without a transplant, the patient might die.  Adaptation of this protocol might drive other adult stem cell populations to produce liver cells for therapeutic purposes.  The potential is certainly great.

High Blood Pressure Medicine Improves Mesenchymal Stem Cell Treatments of Heart Attacks

Mesenchymal stem cells (MSCs) exist in a variety of places throughout the body. They are found in bone marrow, the lower levels of the skin, umbilical cord and umbilical cord blood, placenta, amniotic membrane, muscle, blood vessels, liver, synovial membranes that surround joints, endometrial glands, fat, tendons, and other locations as well. MSCs have the ability to differentiate into cartilage-making cells, fat-making cells, muscle-making cells or bone-making cells  Other protocols exist to differentiate MSCs into heart muscle (Williams AR, Hare JM. Mesenchymal stem cells: biology, pathophysiology, translational findings, and therapeutic implications for cardiac disease.Circ Res. 2011 Sep 30;109(8):923-40; Song YH, Pinkernell K, Alt E.Stem cell induced cardiac regeneration: fusion/mitochondrial exchange and/or transdifferentiation? Cell Cycle. 2011 Jul 15;10(14):2281-6.), neurons (Scuteri A, Miloso M, Foudah D, Orciani M, Cavaletti G, Tredici G.Mesenchymal stem cells neuronal differentiation ability: a real perspective for nervous system repair? Curr Stem Cell Res Ther. 2011 Jun;6(2):82-92), and liver cells (Al Battah F, De Kock J, Vanhaecke T, Rogiers V. Current status of human adipose-derived stem cells: differentiation into hepatocyte-like cells. ScientificWorldJournal. 2011;11:1568-81).  The therapeutic possibilities of MSCs has been widely recognized by stem cell scientists and MSCs have been the subject of many past and ongoing clinical trials.

The use of MSCs to treat heart attack patients has been the subject of several clinical trials (Mazo M, Araña M, Pelacho B, Prosper F. Mesenchymal stem cells and cardiovascular disease: a bench to bedside roadmap. Stem Cells Int. 2012;2012:175979).  While MSCs do provide a modicum of healing to damaged hearts, the ability of MSCs to differentiate into heart muscle is low.  Many experiments have focused upon increasing the percentage of implanted MSCs  that differentiate into heart muscle cells.  However, a recent paper from a research group at the Keio University School of Medicine and the National Institute for Child Health and Development in Tokyo, Japan has taken a different approach to this problem.

Drugs that treat blood pressure include the “angiotensin II receptor blockers” or ARBs.  ARBs prevent a small polypeptide called angiotensin II from binding its receptor.  WHen it binds to its receptor, angiotensin II causes rather substantial constriction of blood vessels throughout the body, and this raises blood pressure.  By preventing blood vessel constriction, ARBs can lower blood pressure.  Also, many heart attack patients are on blood pressure medicines, and ARBs are one of the those normally given to heart attack patients.

One particular ARB is called candesartan, and the commercial names are Atacand, Amias, Blopress, and Ratacand.  In this paper by Yohei Namasawa and colleagues in the laboratories of Kaoru Segawa, Satoshi Ogawa, and Akihiro Umezawa, determined if treating human MSCs from bone marrow could increase the ability of these cells to form heart muscle cells.  To induce heart muscle cells, they used a popular technique from the literature that grows MSCs in culture with mouse heart muscle cells.  The interaction between the MSCs and the heart muscle cells in culture drives the MSCs to form heart muscle-like cells at a somewhat low-frequency.  This group determined if MSCs became heart muscle cells by testing for the presence of heart muscle-specific proteins (cardiac-specific troponin-I).  To prevent them from confusing MSCs with the mouse heart muscle cells, the MSCs were pre-labeled with a fluorescent protein.

Candesartan treatment of MSCs more than doubled the ability of MSCs to form heart muscle cells in culture.  When these same cells were transplanted into the hearts of rats that had suffered heart attacks, the results were even more interesting.  MSC transplantation into the hearts of rats that had recently suffered a heart attack.  Those animals that had undergone surgery but were not given any heart attacks, showed an average reduction of about 3% in their ejection fraction (percentage of blood that pumped from the heart during each heart beat).  Given that the standard deviation was close to this number, this change is not significant.  The control animals that were not given MSC treatments showed an average decrease of just over 10% in their ejection fraction.  Animals treated with MSCs that had suffered heart attacks showed a decrease of about 6-7%.  This is significantly less of a decrease than in the control, but it is still a decrease.  When the rat hearts were treated with MSCs that had been pretreated with candesartan, they showed an average 3-4% increase in ejection fraction.  If the rats were given candesartan after the heart attack, it raised the ejection fraction 1-2%.  If the rats were given candesartan, and treated with bone marrow cells after the heart attack, their ejection fractions decreased by the same as the sham group.  However, if the rats were given candesartan and MSCs that had been pretreated with candesartan after the heart attack, their ejection fractions increased by 10-12%.  Other heart function indicators improved too, since transplantation of the candesartan-treated bone marrow cells improved the “end systolic dimension,” which is an indication of how well the heart contracts.

When hearts were examined after the animals died, those animals that had received transplantations of the candesartan-pretreated bone marrow cells had 2-3 times more heart muscle cells derived from the implanted MSCs than did the controls transplanted with non-treated bone marrow.  Also, post-mortem examination of hearts from the treated rats showed that the rats treated with candesartan-pretreated bone marrow cells had much small heart scars than the other groups (5%-7% smaller).

These experiments, though pre-clinical, suggest that pre-treatment of MSCs with compounds like candesartan can increase their ability to differentiate into heart muscle cells.  This would certainly augment their ability of heal the hearts of patients after a heart attack.  While further work is certainly warranted, a clinical study should be proposed to test if this efficacy applies to human hearts as well.

Induced Pluripotent Stem Cells Form Red Blood Cells

Concerns over the mutations that occur when adult cells are reprogrammed into induced pluripotent stem cells has caused scientists to step back and take a second look at this technology. Can such a technology be used to treat human patients safely?

Some cells in our bodies lack nuclei. For example, platelets and red blood cells do not have nuclei, and therefore, they lack a human genome. If red blood cells can be made from pluripotent stem cells, they could potentially treat patients who suffer from anemia. The red blood cells will not harbor any mutations because they do not have DNA. Thus, induced pluripotent stem cells could potentially be used to treat patients.

A paper in Stem Cells and Development by Jessica Dias and colleagues in the laboratory of Igor Slukvin at the University of Wisconsin, Madison has reported the generation of red blood cells from human induced pluripotent stem cells (J. Dias, et al., Stem Cells and Dev 20, no 9 (2011): 1639-47).

To make red blood cells from induced pluripotent stem cells (iPSCs), they made human iPSCs from skin cells called “fibroblasts” that were taken from new-born babies.  They made they iPSCs with methods that did not use viruses.  Instead they placed in the fibroblasts, small circles of DNA that contained all the genes necessary to create iPSCs.  These small circles of DNA are called “episomes.” and they can create iPSCs without maintaining themselves in the cells.  That is to say, once the episomes convert the adult cells into iPSCs, they are lost and do contaminate the genome of the iPSCs.

After making iPSCs, they grew them for seven days with two other cells; human embryonic stem cells and a mouse bone marrow cell line called OP9.  This combination converted the iPSCs into bone marrow stem cells.  The bone marrow stem cells were isolated and cultured for five days with chemicals that are known to push bone marrow stem cells to become red blood cells.  These chemicals (erythropoietin, stem cell factor, thrombopoietin, interleukin-3, dexamethasone, insulin, interleukin-6, and iron), drove the stem cells to become red blood cell-like cells.  Because these cells were also grown under conditions that prevented them from attaching they grew and differentiated.  After five days, the cells were maintained on another mouse bone marrow cells line called MS5 cells.

Dias and her colleagues also used an alternative technique that worked just as well that did not include isolating the bone marrow stem cells, but subjected the cells to a Percoll centrifugation that also isolated the differentiating cells from the other cells.  This technique seemed faster and less troublesome.

Neither of these techniques could be employed if these cells were to be used for human treatments.  The use of animal cells lines could contaminate the iPSCs with animal viruses or animal proteins.  Both of these would cause the human immune system to react adversely to the cells (Martin MJ, Muotri A, Gage F, Varki A. Human embryonic stem cells express an immunogenic nonhuman sialic acid.Nat Med. 2005 Feb;11(2):228-32).  Therefore, some other protocol will need to be devised if this type of treatment is employed for anemic humans.

Nevertheless, this culture did generate red blood cells that expressed mainly embryonic and fetal types of hemoglobin.  While there was some adult hemoglobin made, it was the minority molecule.  All of the cells produced by this cell culture system were of the same type as those that produce red blood cells (erythroid), and not of those that make white blood cells (myeloid).  This shows that it is feasible to make red blood cells from iPSCs, and it might even be feasible to produce them in a culture system that makes large quantities of them.  Other uses for culture systems like this could include making red blood cells to grow malarial parasites for drug research.  Clearly this is a remarkable discovery that may lead to a source of red blood cells for patients and laboratories alike.