Gene and cell therapy will save from amputation
Blockade of blood vessels, often developing in old age or as a complication of diabetes mellitus, leads to a decrease in blood flow and, accordingly, a deterioration in the supply of oxygen to cells and tissues (ischemia), and subsequently to the development of gangrene. In such situations, doctors are often forced to resort to amputation of limbs.
In experiments on a mouse model of this condition, Johns Hopkins University researchers, working under the guidance of Professor Gregg Semenza, have developed a set of therapeutic approaches that can enhance blood flow, improve mobility of affected limbs and reduce the degree of tissue damage, thus reducing the likelihood of amputation. The results of the work published on December 1 in the preliminary on-line version of the Proceedings of the National Academy of Sciences in the article "Synergistic effect of HIF-1α gene therapy and HIF-1-activated bone marrow-derived angiogenic cells in a mouse model of limb ischemia" indicate the possibility of developing clinical treatment methods.
In a young healthy body, hypoxia (lack of oxygen) triggers the synthesis of factors that ensure the formation of new blood vessels. However, with age, the work of this mechanism is disrupted. The authors managed to use gene therapy and stem cells to help the body restore its natural response to hypoxia and save limbs.
Earlier, the same group of scientists created a virus containing the gene of the active form of the HIF-1 protein (hypoxia-inducible factor 1, hypoxia-induced factor 1), activating the genes necessary to trigger the formation of new vessels. The introduction of this virus into the hind legs of healthy mice and rabbits partially restored artificially reduced blood flow in the vessels of the extremities.
Diabetes increases the risk of gangrene and subsequent limb amputation by 40 times, so the researchers tested the effectiveness of gene therapy on a mouse model of diabetes and, in parallel, on healthy animals. All mice had artificially disrupted blood flow in one of the hind limbs. 21 days after the introduction of the therapeutic virus, the level of blood flow restoration in experimental animals averaged 85%, whereas for the control group of mice injected with pure saline solution, this indicator was only 24%. Moreover, in mice with diabetes, the introduction of the virus significantly reduced the degree of tissue damage. These results are published in the November issue of Proceedings of the National Academy of Sciences in the article "Adenoviral transfer of HIF-1α enhances vascular responses to critical limb ischemia in diabetic mice".
In their latest work, the authors studied the effectiveness of therapy depending on age. They showed that in three–month-old mice, femoral artery blockade leads to limb loss in about 30% of cases, whereas in thirteen-month-old animals - in 100% of cases. At the same time, the introduction of a therapeutic virus improved the blood flow and tissue condition of young mice, but did not have a significant effect on the condition of elderly animals.
It is known that HIF-1 attracts cells of various types, including angiogenic bone marrow stem cells, to the area in need of the formation of new vessels. The researchers isolated these cells from mice and cultured them under special conditions that trigger the activation of the HIF-1 protein.
Simultaneous administration of such cells and a therapeutic virus to elderly mice reduced the likelihood of limb loss compared to control group animals.
Further study of the state of the organism of experimental animals showed that the activation of HIF-1 triggers the work of a number of genes that not only promote the movement of cells into the affected limb, but also their fixation in the affected area. To study the mechanisms underlying this phenomenon, scientists used a microfluidic chamber in which cells were placed and analyzed their ability to attach to the surface in a fluid flow, the speed of which corresponded to the speed of blood flow through the vessels. It turned out that the ability of cells to adhere is much stronger in hypoxia, but only under the condition of active functioning of the HIF-1 protein.
The obtained results demonstrate the possibility of improving the prognosis of the course of critical limb ischemia associated with age or diabetes using a combination of gene and cell therapy methods. The authors believe that over time, the approach they have developed will find its place in clinical practice.