Cellular technologies: treatment, recovery, rejuvenation
General regenerating effect of stem cell transplantationSTEMCELLS.RU
Many studies have been carried out in which the possibilities of treating various diseases with stem cell transplantation were studied, and in many cases systemic administration was used; but usually the task was not to trace the overall effect of transplantation.
It is proved that both systemic and local administration of stem cells gives a proven multiple positive effect, the mechanisms of which are currently partially understood and still need further study. It is possible that the development of a number of diseases is facilitated by the lost ability of the SC CM to enter the peripheral bloodstream with age and restore and/ or regulate the function of damaged organs. In this case, the systemic administration of stem cells will significantly restore the impaired functions. Bone marrow SC secrete a number of cytokines with anti-apoptotic and angiogenetic effects, they realize their potential not only due to substitutive, but also due to inductive and informational properties that are maintained in these cells by an adequate microenvironment.
The results of transplants of autologous adult bone marrow stem cells indicate the safety of using these cells in the clinic: none of the published clinical studies indicated the development of any complications associated with the use of SC CM.
Various stem cells (most often hematopoietic or mesenchymal bone marrow) were injected intravenously and carried with the blood flow throughout the body. In animal experiments, genetically labeled cells were usually introduced, which made it possible to trace their further fate. Cells of donor origin were found in all organs, and they differentiated into cells of the corresponding tissues. For example, in experiments on mice, it was shown that with intravenous administration of whole bone marrow or its individual fractions, donor cells took root in bone marrow, skin, muscles, liver, brain, heart and other organs and tissues (Eglitis, Mezey 1997, Bittner et al. 1999, Orlic et al. 2001, Badiavas et al. 2003, Fathke et al. 2004, Newsome 2003). The same thing happens when stem cells are transplanted to humans – this was shown during biopsy or post-mortem examination of various organs of patients who had bone marrow transplanted from a donor of another sex. For example, when examining the brain of deceased female recipients of male bone marrow, donor cells with a Y chromosome were found in various brain regions, differentiated into neurons, astrocytes and microglia (Mezey et al. 2003, Cogle et al. 2004); myocytes and vascular cells with a Y chromosome were found in the heart (Quaini et al. 2002); biopsy showed the presence of donor cells in the liver, skin and gastrointestinal tract (Korbling et al. 2002).
ResearchesOf greater importance is the fact that in case of damage to an organ and subsequent stem cell transplantation, the regeneration of this organ takes place with the active participation of donor cells, and the proportion of cells of donor origin embedded in it is several times higher than in cases when this organ was not damaged.
This has been proven in numerous animal experiments – for example, during intravenous transplantation of hematopoietic cells to rats with an ischemic stroke model, they migrated to the brain, mainly to the affected area and differentiated into neurons and glial cells, providing restoration of impaired functions (Chen et al. 2001, Willing et al. 2003).
It has been shown that transplanted allogeneic bone marrow cells in rats with glomerulonephritis integrate into glomerular structures, turning into the endothelium and mesangium of the glomeruli. Moreover, their number turns out to be several times more than when transplanted to animals with intact kidneys (Rookmaaker et al. 2003). With systemic administration of MSCs to mice with developing toxic pulmonary fibrosis, donor cells differentiated into the pulmonary epithelium and reduced the intensity of chronic inflammation (Ortiz et al. 2003). During intravenous transplantation of the umbilical cord blood mononuclear fraction, angiogenesis of the infected myocardium was observed in NOD/SCID mice, and the cells were embedded only in the defective myocardium (Ma et al. 2005). Skin damage stimulated the engraftment of intravenously transplanted bone marrow cells and induced their differentiation into skin cells (Badiavas et al. 2003, Fathke et al. 2004). When mouse neural stem cells were injected into the brain of a rat with an ischemic stroke model, neurons of donor origin were found only in the damaged, but not in the healthy hemisphere (Park 2000).
The mechanisms of this phenomenon have been revealed – substances that are released during tissue damage and attract stem cells to the site of damage, as well as directing their differentiation in the right direction. For example, chemotaxis of injected MSCs to the area of ischemic brain injury is provided by the interaction between chemokine stromal-derived factor-1 (SDF-1, or CXCL12) released in the penumbra region (the zone of reversible changes in brain tissue – VM) and its receptor CXCR4 on the stem cell membrane (Hill et al. 2004). It has been shown that biochemical signals from a damaged (regardless of the type of damage) liver are able to induce transdifferentiation of mouse hematopoietic SC into hepatocytes and other liver cells; these cells restored normal liver function (Jang et al. 2004). During cocultivation of MSCs with overheating-damaged respiratory epithelium, they differentiated into epithelial cells (Spees et al. 2003).
It has been proved that when stem cells are injected into the site of the lesion, cell death of this organ decreases and regeneration processes are significantly enhanced, even when only a very small proportion of donor cells differentiate into cells of the corresponding tissue. This happens due to the release of various biologically active substances by donor cells – growth factors, trophic factors, etc. For example, it has been shown that with intravenous stem cell transplantation (MSC CM) in the treatment of experimental stroke, a positive effect is achieved mainly by stimulating the processes of neurogenesis and angiogenesis and reducing apoptosis of nerve cells, and not by transdifferentiation. In the ischemic area, an increase in the level of endogenous vascular endothelial growth factor (VEGF) was observed by 0.7 times. On the culture of cells of the vascular endothelium of the mouse brain, it was shown that with the addition of a supernatant of a medium conditioned with SC CM, there is a significant stimulation of capillary formation. This effect was blocked when neutralizing antibodies to VEGFR2 were added to the culture. Thus, the angiogenesis-stimulating effect of SC CM in ischemic stroke is mediated by an increase in the concentration of VEGF and its receptor (Chen et al. 2003). Umbilical cord blood stem cells injected into rats with a stroke model stimulate endogenous neuro- and angiogenesis; after the introduction of cells in the brain of stroke animals, an increase in the concentration of GDNF (glial cell line-derived neurotrophic factor) was detected by 68%; the concentration of 3 neurotrophic factors (GDNF, NGF, BDNF) increased in peripheral blood by ~15% (Borlongan et al. 2004). Similar results were obtained with intravenous transplantation of umbilical cord blood cells in a model of spinal cord injury in rats (Lu et al. 2002).
Transplanted hematopoietic stem cells of bone marrow and umbilical cord blood stimulate liver recovery in the acute toxic hepatitis model, although the proportion of newly formed hepatocytes of donor origin is insignificant (Wang et al. 2003). Heinrich-Heine-University successfully used autologous bone marrow cell transplantation to accelerate liver regeneration during extensive resections (am Esch et al. 2005). The use of allogeneic tissue grafts for wound and burn healing is also based on the effect of regeneration stimulation – donor cells do not take root, but induce healing processes due to the substances they release (Ehrlich 2004). The transplanted culture of bone marrow stromal cells has a distinct inducing effect on the course of osteoreparative processes – even where post-traumatic osteogenesis does not occur under normal conditions, for example, with skull defects (Krebsbach et al. 1998).
It has been shown that the synthesis of growth factors and trophic factors by stem cells that stimulate regeneration and reduce apoptosis increases dramatically in response to specific substances released during damage. For example, substances released during stroke give an increase in the synthesis of neurotrophic and angiogenic factors by transplanted SC CM. If extracts from the brain of rats with stroke were added to the culture of SC CM, there was a significant increase in the synthesis of neurotrophic (brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF)) and angiogenic (vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF)) growth factors (Chen et al. 2002). Wound microenvironment induces proliferation of bone marrow cells and their synthesis of collagen, and also stimulates differentiation of bone marrow cells into fibroblasts and their synthesis of extracellular matrix proteins (Ai et al. 2002).
The role of stem cells in the formation of a network of new vessels, especially in ischemic areas, has been well studied, and they both differentiate themselves into vascular wall cells and stimulate the process of neoangiogenesis in the recipient's body. For example, during intravenous transplantation of the umbilical cord blood mononuclear fraction, angiogenesis of the infused myocardium was observed in NOD/SCID mice. The cells migrated and were embedded only in the defective myocardium. The density of capillaries in the periinfarction zone in the cell transplantation group was 20% higher than in the control group (Botta et al. 2004, Ma et al. 2005). Similar results were obtained in clinical trials – with intracoronary transplantation of autologous cells – mononuclear bone marrow or endothelial progenitor cells from peripheral blood, after acute myocardial infarction, there was a significant improvement in left ventricular function due to stimulation of angiogenesis (Strauer et al. 2002, Schachinger et al. 2004). Intramuscular injections of hematopoietic stem cells to rats with a model of limb ischemia led to a significant improvement in blood flow and an increase in capillary density (Murohara et al. 2000); not only increased the number of arterioles in the ischemic focus, but also stimulated skeletal muscle regeneration (Pesce et al. 2003).
Transplantation of the mononuclear fraction of autologous bone marrow leads to stimulation of angiogenesis in rabbits with lower limb ischemia (Shintani et al. 2001). In another study, the transplantation of unfractionated bone marrow in lower limb ischemia did not lead to the integration of injected cells into the vessel walls, but stimulated local angiogenesis due to the formation of a cellular environment around new microvessels (Ziegelhoeffer et al. 2004). The method of autotransplantation of bone marrow cells was successfully applied in Japan at Yamaguchi University School of Medicine to patients with chronic diseases of the peripheral arteries of the lower extremities (Esato et al. 2002). In clinical trials, the possibility of stem cell re-endothelization of damaged vessels with obliterating atherosclerosis of the lower extremities of the III and IV degrees (chronic ischemia) has been shown. There was a decrease or disappearance of pain, an increase in skin temperature, stimulation of ulcer healing. Instrumentally, an improvement in limb perfusion was shown (Huang et al. 2004). Human MSCs of CM were administered intravenously to rats a day after occlusion of the middle cerebral artery (stroke model). Morphologically, an increase in the number of vessels and capillary neoplasm at the border of the ischemic focus was shown (Chen et al. 2003).
After the use of autologous bone marrow cells, complete closure of wounds was obtained in patients with skin lesions that had not healed for more than a year (Badiavas, Falanga 2003). Autologous bone marrow cells were injected subchondrally into the site of the defect in patients with aseptic osteonecrosis of the femoral head. Progressive reduction of necrosis foci was registered, patients noted a significant reduction in pain syndrome and improvement in joint function. The mechanism of action of cells is associated with the stimulation of osteogenesis (due to the "fresh" stromal fraction) and angiogenesis (due to CD34(+) cells) of the "dead zones" of bone (Gangji et al. 2004).
Some of the intravenously injected stem cells also turn into skin cells, providing a beneficial cosmetic effect due to the mechanisms already described above – enhancing regeneration processes and improving nutrition. The significant role of bone marrow stem cells (SC CM) in skin homeostasis and regeneration has been shown (Badiavas 2004, Satoh et al. 2004, Deng et al. 2005), and damage stimulates the engraftment of SC CM in the skin and induces their differentiation into skin cells (Badiavas et al. 2003). It was found that during wound healing, adjacent epidermal cells participate in the restoration of the epithelium, whereas both local mesenchymal dermal cells and SC CM are involved in the restoration of the dermal fibroblast population (Fathke et al. 2004). The involvement of MSCs in the repair of the skin epithelium is also confirmed by the fact that after a transgender (male to female) transplant, Y+ cells expressing cytokeratins are detected in the basal layer of the skin epithelium with a frequency of 2-7% (Korbling et al. 2002). One of the possible mechanisms of healing of skin lesions is the differentiation of CM MSCs into fibroblasts in the defect zone and their synthesis of extracellular matrix proteins; in addition, MSCs stimulate the migration of "inflammation cells" and "healing cells" secreting IL-6, IL-8 and G-CSF into the wound, thus initiating the regeneration process (Ai et al. 2002). All these mechanisms of stimulation of regeneration also act in cases of various microdefects and skin damage, therefore, the systemic introduction of stem cells leads to improvement and improvement of the appearance of the skin.
In clinical practice, the local use of various living cells for the treatment of non-healing wounds and burns is already quite widespread. Cultured allogeneic fibroblasts and keratinocytes are most often used, but good results have also been obtained for bone marrow stem cells (Shumakov et al., 2002, Smirnov et al. 2003, Badiavas, Falanga 2003, Sivan-Loukianova et al. 2003). In rats, it was shown that intradermal injections of bone marrow MSCs accelerated wound healing, while very thin scars remained; the histological structure of collagen at the site of the healed wound was close to that in intact skin and was very different in control group rats (who did not receive injections). Thus, MSCs provide wound healing with regeneration of the normal structure of the dermis (Satoh et al. 2004). Cellular technologies are also used in medical cosmetology – for example, to eliminate rough scars and other skin defects. With the local introduction of cells by mesotherapy (fibroblasts are usually used), it is possible to achieve a significant and long-lasting cosmetic effect by stimulating the vital activity of the skin with biologically active substances secreted by living cells. The effectiveness was proved by a significant decrease in skin relief (measured by laser profilometry), thickening of the dermal layer, an increase in the number of fibroblasts and collagen density in it, as well as a subjective assessment of patients (Watson et al. 1999, Boss et al. 2000). In addition, local administration of fibroblasts is successfully used to treat baldness, providing increased hair growth.
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