Adult Stem Cells and the Treatment of Diabetes
Taken from: The Therapeutic Potential of Stimulating Endogenous Stem Cell Mobilization
The ability of bone marrow stem cells to leave the bone marrow, migrate to the pancreas and become insulin producing cells was beautifully shown by Ianus et al. (2003).
In brief, female mice were lethally irradiated and then transplanted with male bone marrow stem cells that express, using a CRE-LoxP system, green fluorescent protein if the insulin gene is actively transcribed.
When analyzed 4-6 weeks after the transplantation, green fluorescent protein-positive cells were found in the pancreas (Figure 2).
Fig. 2. FISH and immunofluorescence marking of bone marrow-derived insulin-producing cells. Immunofluorescence and FISH of isolated, dispersed pancreatic islet cells after transplantation of lethally irradiated female mice with male bone marrow stem cells that express, using a CRE-LoxP system, green fluorescent protein if the insulin gene is actively transcribed.
a) Bright-field phase, b) green fluorescent protein imaging note slight autofluorescence of control isolated islet cells; c) Immunostaining with rhodamine X-labeled secondary antibody for insulin; d) FISH for Y chromosome (in yellow) and nucleus stain with DAPI (blue). Y chromosome is present only in green fluorescent protein-positive cells. Scale bar, 5 µm; X630. (Taken from Ianus et al., 2003)
The green fluorescent protein-positive cells were also positive for insulin, for insulin RNA, and for Y-chromosome, demonstrating that they originated from the transplanted bone marrow stem cells. These cells showed functional characteristics typical of normal pancreatic ß-cells, such as fluctuations of intracellular calcium upon exposure to various concentrations of glucose.
Within the time frame of that study (4-6 weeks), 1.7-3% of bone marrow-derived green fluorescent protein-positive cells were detected in the pancreatic islets. In a similar study, bone marrow stem cells were also shown to participate into the development of new blood vessels, further supporting the regeneration of the pancreatic tissue (Mathews et al., 2004; Gao et al., 2008).
Then, using a protocol similar to that used by Ianus et al., Hasegawa et al. (2007) further demonstrated that mobilization of bone marrow stem cells was not only effective but essential for pancreatic regeneration.
Hasegawa et al. induced diabetes by injection of streptozotocin (STZ) in lethally irradiated female mice followed by infusion of bone marrow stem cells from green fluorescent protein transgenic mice.
Infusion of bone marrow stem cells led to the incorporation of green fluorescent protein-positive bone marrow stem cells into islets of Langerhans in the pancreatic tissue, partially restoring pancreatic islet number and size, and improving STZ-induced hyperglycemia.
However, when the same experiment was done while simply infusing the pancreas with bone marrow stem cells, without preirradiation, no improvement was obtained. Furthermore, when the experiment was repeated with full bone marrow stem cell transplant in a model of mice with impaired ability to mobilize stem cells, no benefits were obtained.
Therefore, natural mobilization of bone marrow stem cells from the bone marrow appears essential for the regeneration of pancreatic function after inducing diabetes with STZ.
Fig. 3. Pancreatic islets of STZ-treated mice receiving subsequent bone marrow transplant. Double immunostaining of pancreases with anti-insulin and anti-glucagon antibodies. Green indicates insulin-positive and red glucagon-positive cells.
Pancreases from normoglycemic control mouse (a), hyperglycemic control mouse (b), and STZ-treated mouse receiving bone marrow transplant (c). Bone marrow transplant improved STZ-induced hyperglycemia. (Taken from Hasegawa et al., 2007)
In one recent study in humans, endogenous stem cell mobilization showed great promise in the treatment of diabetes. The study selected individuals recently diagnosed for diabetes and the treatment consisted of both stem cell mobilization and autologous stem cell transplant.
The patients first received injections of G-CSF in order to harvest peripheral blood stem cells, followed later by autologous stem cell transplant and, 5 days post-transplant, a second round of G-CSF treatment. The endpoints monitored in the study were overall morbidity along with temporal changes in exogenous insulin requirements.
Before the treatment, all patient required daily insulin injection. By the end of the study, 14 of the 15 patients had experienced insulin-free episodes ranging between 1 and 35 months (mean 16.2 months) (Voltarelli et al., 2007).
In this study the patients benefited from two instances of endogenous stem cell mobilization and one instance of autologous stem cell transplant.
It is not possible to determine what were the respective contributions of the endogenous stem cell mobilization and stem cell injection, however it is likely that the mobilizations by themselves significantly contributed to the benefits experienced.
While the first mobilization lasted several days and the second mobilization lasted about one week, there was only one instance of stem cell injection.
Diabetes is an interesting disease to study the link between disease progression and the number of circulating peripheral blood stem cells, as it follows a series of relatively well defined stages with regard to carbohydrate metabolism status, namely normal glucose tolerance, impaired fasting glucose, impaired glucose tolerance, and newly diagnosed diabetes mellitus.
Fadini et al. (2010) quantified the number of circulating CD34+ cells by flow cytometry in 425 individuals divided among these four stages of disease progression. The data showed a clear trend of decreased number of peripheral blood stem cells with disease progression through impaired fasting glucose, impaired glucose tolerance and diabetes mellitus (Figure 4).
The number of circulating peripheral blood stem cells was significantly lower in the impaired glucose tolerance and diabetes mellitus groups when compared to the normal glucose tolerance group.
The reduction in the number of peripheral blood stem cells can either be a consequence of higher blood glucose levels that might affect the ability of stem cells to mobilize from the bone marrow or a causal factor in the development of diabetes mellitus whereby a reduced number of circulating peripheral blood stem cells reduces the ability of the pancreas to renew itself over the years, or both.
This supports the view previously suggested that diabetes could be a stem cell disease (Fadini et al., 2009).
Fig. 4. Variation of circulating CD34+ cells and diabetes. Variation of circulating CD34+ cells in patients grouped according to carbohydrate metabolism, namely normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) or diabetes mellitus (DM) duration, as appropriate.
The mean value of patients with NGT was taken to represent the zero point. Bars indicate 95% CIs of means. * Values significantly different when compared to NGT. (Taken from Fadini et al., 2009)
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