Blood Repairs Damaged Liver, Brain and Heart 

A person's blood repairing liver, brain and heart may sound like science fiction. But, two research teams have suggested such a prospect. One team at the Argonne National Laboratory (ANL) showed that monocytes, a type of white blood cells deprived of nutrients could morph into cells like brain cells and liver cells. Another team at the Mayo Clinic found that in adults cells produced by the bone marrow could form new heart muscle cells. 

Both discoveries came as a surprise. In the body, such white blood cells migrate into tissues and mature into specialised immune cells, such as macrophages. The team at ANL was studying the cellular signals that drive such maturation. "One day we found that some of the white blood cells left without nutrients turned into cells that did not look like immune cells," says Eliezer Huberman, the leader of the ANL team. "Intrigued by this chance finding, we isolated and studied those immune cells."

The ANL team found that the isolated cells had the potential to turn into various kinds of cells. Such cells are called stem cells. "Exposing these cells to a chemical called nerve growth factor turned 90 percent of the cells into cells having shape and projections like the nerve cells," write Huberman and his teammates in a recent issue of Proceedings of the National Academy of Sciences. "These cells also contained typical nerve cell proteins and enzymes." Using different growth factors, Huberman and his colleagues switched the isolated white blood cells (monocytes) into liver cells, blood vessel cells and immune cells unrelated to the original blood cells.

The team at Mayo Clinic studied four female patients with leukaemia. These patients had survived 35 to 600 days after receiving bone marrow from male donors. Heart tissue samples examined at autopsy showed that a small portion of the heart muscle cells harboured male genetic material. This proved that the heart muscle cells definitely produced by the donor marrow.

This study for the first time shows that progenitor cells from outside the heart could form new heart muscle cells. "After their birth in the bone marrow, the progenitor cells circulate in the blood," explains Dr. Noel Caplice, a cardiologist who led the Mayo Clinic research team. "They are like stem cells having potential to develop into various kinds of cells. Given the right biological signals we have now shown they could become heart cells."

The findings of the study have been published in a recent issue of Circulation, a journal of American Heart Association. "Until recently, the heart has been seen as an organ that can not be healed," says Caplice. "This study points the way to a process that could lead to heart repair." Under normal conditions, less than one per cent heart muscle cells originate from the progenitor cells, which hardly add to the heart's pumping strength. 

"But, if we determine the mechanism that causes progenitor cells to develop into heart muscle cells, we may increase the production," says Caplice. "Possibly, a growth hormone delivered to the heart could generate new muscle around an area of scar tissue thereby healing the heart damaged by heart attack." 

Till date, it was known that most adult tissues are either devoid of stem cells or harbour ones that only reproduce the tissue in which they reside. Some sporadic experiments suggested marrow cells' potential to yield non-blood cells like nerve and muscle cells. But Huberman's team's finding is unique. Because, his team identified a white blood cell (monocyte) population that differs from those multipurpose bone marrow cells. 

"Our cells have the typical monocyte-macrophage identity," Huberman says adding, "it will be easier to harvest the blood cells from a person." It will make the painful surgical removal of bone marrow obsolete. These researches show that we need not slaughter human embryos to harvest stem cells for therapeutic purposes. Instead, they could be harvested from adults.