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Published online before print January 15, 2009
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From the Departments of Medicine, Pathology, and Pharmacology,* New York Medical College, Valhalla, New York; the Department of Cardiology,
Harbin Medical University, Harbin, China; the Department of Internal Medicine,
College of Medicine, Yonsei University, Seoul, Korea; the Department of Internal Medicine,
Kaohsiung Medical University Hospital, Kaohsiung, Taiwan; and the Department of Pathology,** University of Queensland, Australia
| Abstract |
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| Materials and Methods |
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The animal study protocol was in accordance with National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals (U.S. Department of Health and Human Services Public Health Services, NIH, NIH Publication No. 86–23, 1985) and approved by the Institutional Animal Care and Use Committee. The type II diabetic murine model db/db mice and db/m mice were obtained from Jackson Laboratory (Bar Harbor, Maine; C57BL/6 background). The body weight and blood glucose level of mice between ages of 8 to 16 weeks were monitored throughout the study. Briefly, bone marrow from male donor db/db and db/m mice was flushed under sterile conditions with Hanks balanced salt solution (HBSS) from the medullary cavities of tibiae and femurs using a 21-gauge needle. Whole bone marrow single cell suspension was fractionated using Histopaque-1077 solution (Sigma) gradient separation. Mononuclear cells were collected, washed, and checked for viability using trypan blue exclusion technique.8 BMDCs were labeled with Cell Tracker (CM-DiI) (Invitrogen, Eugene, OR). In three independent experiments, male recipient db/db mice (age 16 weeks) received approximately 106 BMDC by tail vein injection. The db/db mice that received the BMDC from db/m mice are designated as dbTxm. The db/db mice that received the BMDC from db/db mice are designated as dbTxdb. The same transfusion procedure was repeated three times every 10 days. In additional series of experiments, db/db mice were treated with Ebselen by gavage, twice a day at 5 mg/kg/day, dissolved in 5% carboxymethyl (CM) cellulose suspension. This group of donor mice was labeled as dbEbs-in vivo and its corresponding recipient db/db mice were designated as TxdbEbs-in vivo. Control db/db mice received only CM cellulose (Sigma, St. Louis, MO) suspension (vehicle treatment; designated as dbCM and its corresponding BMDC recipient db/db mice designated as TxdbCM.) Another group of recipient db/db mice was transfused with BMDC of db/db origin, but treated with Ebs (1 µg/ml) overnight in full Dulbeccos Modified Eagle Medium (DMEM) medium at 37°C in CO2 incubator before transfusion. This group of recipient mice was designated as TxdbEbs-ex vivo. Because all animals had the same C57BL/6 background, no alloimmune or graft-versus-host response was expected (nor observed). Mice were euthanized 20 days after the final transfusion (at age 23 weeks) by intraperitoneal injection of ketamine/xylazine (60/7.7 mg/kg, respectively). A mid-laparotomy was performed and blood, thoracic aorta, kidney, and pancreas were harvested for further analyses.
Acetylcholine-Induced Vasorelaxation
Thoracic aortas were cleared of periadventitial tissue and cut transversely into rings 1.5 to 2.0 mm in diameter. Vascular rings, handled carefully to avoid damage to the inner surface, were mounted on wires in the chambers of a multivessel myograph (J.P. Trading, Aarhus, Denmark) and bathed in Krebs buffer. The medium was gassed with 95% O2 and 5% CO2 and maintained at 37°C (pH 7.4). After equilibration (30 minutes), the rings were set to an internal circumference equivalent to 90% of full relaxation under a transmural pressure of 100 mm Hg and allowed to stabilize for 20 to 30 minutes. The rings were then depolarized with potassium chloride (60 mmol/L) to evaluate maximal contraction. After washing with a Krebs buffer, the vascular preparations were contracted with phenylephrine (10–6 mol/L), and when the contractile response was stabilized (steady-state phase, 12 to 15 minutes), vasorelaxing responses to cumulative increments in the concentration of acetylcholine or NONOate were examined.14
Blood Glucose, Insulin Tolerance, and Homeostasis Model Assessment Index
Plasma glucose was measured using glucometer (OneTouch Ultra, Lifescan) by collecting 2 µl blood through nicking the end of the tail. To estimate insulin resistance, we conducted insulin tolerance test and homeostasis model assessment (HOMA) index analysis, as previously described.15,16 Briefly, for the insulin tolerance test, animals were fasted for 3 hours. The mice were weighed and 1.5 units/kg body weight of diluted regular human insulin 1:1000 (0.1 inits/ml) was injected intraperitoneally. At 90 and 180 minutes, blood glucose was sampled. HOMA index was calculated by the formula: fasting plasma insulin x fasting plasma glucose/405.
Measurement of Cytokines/Chemokines and Insulin
The Luminex multiplex assay (cat#: MCYTO-70K-PMX) was used for simultaneous quantification of the following mouse cytokines/chemokines in the plasma: interleukin (IL)-1
and β, IL-6, IL-9, IL-10, interferon (IFN)
, interferone-gamma-inducible protein (IP-10), granulocyte-colony stimulating factor (G-CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor (TNFβ), keratinocyte chemoattractant (KC), monocyte chemoattractant protein (MCP-1), macrophage inflammatory protein (MIP-1β) and mRANTES. A mixture of beads was incubated with standards or plasma samples, followed by the appropriate biotinylated antibody and streptavidin-phycoerythrin reporter. Beads were analyzed using Luminex-100. Plasma insulin, amylin, glucagon, and leptin concentration were simultaneously measured using the same technique (cat#: MENDO-75K-05).
Immunohistochemical and Immunofluorescence Staining and Analysis
Tissue samples of kidney and pancreas were fixed in a 4% paraformaldehyde solution (Electron Microscopy Sciences, Hatfield, PA) overnight at 4°C, followed by sequential incubation in 15% and 30% sucrose overnight at 4°C each. Embedding was performed in an optimal cutting temperature compound (Tissue-Tek, Torrance, CA), and embedded samples were stored at –80°C. Frozen samples were cut into 10-µm-thick sections (Cryomicrotom CM 1850, Leica Microsystems, Bannockburn, IL). Nonspecific protein binding was blocked by 1-hour incubation with PBS-bovine serum albumin (1%). The following primary antibodies were used: anti-mouse insulin (Santa Cruz Biotechnology, Santa Cruz, CA), CD31 (BD Pharmingen, San Jose, CA), and CD68 (Serotec, Oxford, UK). For CD-68 staining, horseradish peroxidase conjugated goat anti-rat IgG was used as the secondary antibody. Peroxidase activity was blocked by 15 minutes of incubation with peroxidase block solution (1:10; DakoCytomation, Glostrup, Denmark). To visualize the positive immunoreaction, the peroxidase substrate 3,3'-diaminobenzidine chromogen was used. Hematoxylin solution was used for counterstaining. Negative controls for all immunolabeling procedures were accomplished by incubation with 1% PBS-bovine serum albumin instead of the primary antibody. For immunofluorescence staining, fluorescein isothiocyanate (FITC)-conjugated secondary antibodies (Jackson ImmunoResearch Laboratories, West Grove, PA) were used. Incubations with primary antibodies were performed overnight at 4°C and incubations with secondary antibodies were performed for 1 hour at room temperature. Control samples were stained with secondary antibodies only. To visualize the nuclei, tissue sections were counterstained with 4,6-diamidino-2-phenylindole (Molecular Probes). Sections were examined using a Nikon inverted fluorescence microscope (Eclipse TE2000-U) equipped with a digital camera (Spot model 4.2; Diagnostic Instruments, Sterling Heights, MI).
For histological examination of kidneys, paraffin-embedded tissue samples were cut into 3-µm-thick sections and stained with H&E, periodic acid-Schiff, or Massons trichrome (American MasterTeck, Lodi, CA). Slides were examined and scored for abnormalities by two nephropathologists. For detection of tubular necrosis, the scoring range from 0 to 3 was used to define noticeable cell damage in the form of hydropic change, cast formation, necrosis or apoptosis in the tissue area. The scoring criteria were defined as follows: score 0 = no noticeable cell damage; 1 = noticeable cell damage in tissue area <10%; 2 = noticeable cell damage in tissue area between 10 to 50%; 3 = noticeable cell damage in tissue area >50%. Additional 3 µm-thick periodic acid-Schiff-stained paraffin sections of kidneys were evaluated for diabetic nephropathy from 4 different groups (n = 3 in each group): controls (m), diabetic (db), stem cell transplantation from control mice (Tx M) and from db mice (Tx db). Slides were examined by Olympus BX41 microscope under x40 magnification. All glomeruli were counted in a single cross section as well as the numbers of lesioned microvessels, which were expressed as per 100 glomeruli. The normal mesangial area in the control animals was assigned 0 score, with scores 1+ if these were twice the size of the control, 2+ and 3+ when expanded to 3 and 4 times, respectively.
Fluorescence-Activated Cell Sorting
Bone marrow (BM)-derived mononuclear cells were analyzed for an array of markers, including FITC or phycoerythrin (PE) conjugated anti-mouse CD117 (c-kit), CD150, sca-1, c-kit, CD34, CD31, CD44, CD45, flk,–1, and unconjucated anti-mouse vimentin, and nestin that paired with corresponding fluorescent secondary antibody (Jackson ImmunoResearch Laboratories). All primary antibodies were produced by BD Biosciences (Rockville, MD). Data were acquired using a FACScan cytometer equipped with a 488-nm argon laser and a 620-nm red diode laser and analyzed using CellQuest software (Becton Dickinson, San Jose, CA). The setup of FACScan was performed using unstained and single antibody-stained cells.
BM-Derived MSC and Endothelial Progenitor Cell Isolation
To isolate MSCs from the bone marrow of db/db and db/m mice, the fresh BMDC preparations were re-suspended in complete MSC culture medium (StemCell Technologies Inc, Canada) and seeded into 6-well plates. The cells were than kept 3 days at 37°C in a CO2 incubator, fresh medium was changed, and the adherent layer was re-fed at 7 days. For analysis of apoptosis cells from 1 to 2 passages were used. To isolate endothelial progenitor cells (EPCs), BMDC were re-suspended in mouse EPC medium (Celprogen, San Pedro, CA) supplemented with 10% fetal bovine serum. Seven days after initiation of cultures on 4-well chamber slides (Nalge Nunc International) coated with Vitronectin (10 µg/ml), EPCs were assayed by costaining with acetylated LDL (acLDL)-Dil (Biomedical Technologies) for 3 hours at 37°C and FITC-conjugated Ulex europeaus Lectin (Sigma) for 30 minutes at 37°C, both characteristically staining cells of endothelial lineage.17 Double-positive cells were counted as EPC in eight randomly selected fields of each slide. The proportion of apoptotic cells under basal and oxidative stress conditions, as detailed in Results, was examined using annexin V (BD pharmingen) and activated caspases detection using FITC-VAD-FMK (Calbiochem, La Jolla, CA).
Statistical Analysis
Results were summarized from three independent BM transfusion experiment and the numbers of mice for each study group were totaled: db/m n = 24, db/db control mice n = 20, dbCM n = 4, dbEbs-in vivo n = 5, dbTxm mice n = 10, dbTxdb mice n = 9, TxdbCM n = 4, TxdbEbs-in vivo n = 5, and TxdbEbs-ex vivo n = 5. The results were expressed as means ± SD The means of two populations were compared by Students t-test. For multiple comparisons analysis of variance was used. Differences were considered significant at P < 0.05.
| Results |
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We have previously demonstrated that conspicuous defects in endothelium-dependent vasorelaxation of aortic rings in db/db mice could be detected as early as 9 to 10 weeks of age, ie, just 2 weeks after establishment of a persistent hyperglycemia,14
in association with the increased numbers of prematurely senescent endothelial cells. Therefore, we pursued these studies of the macrovascular dysfunction in db/db mice recipients of BMDC transplants using acetylcholine-induced vasorelaxation assay. Aortic rings obtained from db/db mice showed a profound impairment of relaxation in response to the application of acetylcholine (Figure 1A)
. Maximal concentration of acetylcholine (100 µmol/L) elicited only a 29% relaxation of aortic rings compared with db/m mice. In contrast, db/db mouse-recipients of BMDC from db/db donors (dbTxdb group) showed a mild-to-moderate improvement of aortic relaxation (maximal relaxation of 56%), whereas the db/db mice receiving BMDC from their db/m littermates (dbTxm group) exhibited a dramatic improvement of aortic vasorelaxation with the maximal values achieving 81% of control db/m mice. Notably, all vessels responded to nitric oxide (NO) donor NONOate with equal relaxation (Figure 1B)
, thus indicating that the impaired responses to acetylcholine were due to defective endothelium-dependent relaxation.
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Monitoring blood glucose levels in db/db recipients of BMDC infusions (10 days after each infusion and 20 days after the last infusion) indicated a significant improvement of fasting blood glucose level in recipients of BMDC from db/m donors (dbTxm group) (Figure 2A)
. In mice that received BMDC from db/db donors (dbTxdb group), the improvement in fasting blood glucose level was transient and occurred only after the first transfusion, when the BMDC donor db/db mice were 8 weeks old (this is the age when hyperglycemia commences in db/db mice). Hyperglycemia resumed after the subsequent transfusions and was indistinguishable from non-treated db/db mice of equivalent age.
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To further address the possibility that BM adoptive transfer can improve insulin sensitivity in the recipient diabetic mice, we measured their fasting plasma insulin, amylin, and glucagon level. Compared with db/db mice that exhibited elevated plasma insulin and amylin level, mice in the dbTxm group showed normalization of hyperinsulinemia and hyperamylinemia, whereas dbTxdb mice showed no improvement in insulin and only a partial improvement in amylin level (Figure 3, A and B)
. In accord with these results, the calculated glucose/insulin ratio and HOMA index showed significant improvement in the dbTxm group compared with db/db control and dbTxdb mice (Figure 3, C and D)
. Plasma glucagon measurements showed no significant differences between all of the experimental groups (Figure 3E)
. In aggregate, having excluded the contribution of other factors to the improved insulin sensitivity, the most plausible explanation is found in the BMDC-induced alleviation of endothelial dysfunction and improvement of microcirculation.
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Another possible explanation for the observed improved insulin sensitivity was related to the modulation of pro-inflammatory mediators.18
To explore this possibility we measured the plasma concentration of 14 pro- and anti-inflammatory cyto- and chemokines (IL-1
and β, IL-6, IL-9, IL-10, IFN
, IP-10, G-CSF, GM-CSF, TNF
, KC, MCP-1, MIP-1
, and mRANTES) following BM transfusion. The results showed elevated levels of IL-1
and G-CSF after BM transfusion regardless of the donors, elevated levels of IP-10 in dbTxm and elevated IL-10 levels in recipients of db/db BMDC (supplemental Figure 1
, see http://ajp.amjpathol.org).
In addition, we analyzed the extent of macrophage/mononuclear infiltration of the pancreatic and kidney parenchyma (supplemental Figure 2A
, see http://ajp. amjpathol.org). Immunohistochemical staining showed that the CD68-positive cells were rare and scattered evenly in the pancreas and kidney sections with no differences detectable among the studied groups (supplemental Figure 2B–C, see http://ajp.amjpathol.org).
The above analyses indicated the existence of low-grade pro-inflammatory conditions following the infusion of BMDC. These data ruled out the possibility that the improved insulin sensitivity following BM transfusion was due to the improved profile of pro-inflammatory cytokines.
No Evidence of Trans-Differentiation of the Engrafted Donor BMDC to Insulin-Producing Cells in the Pancreas
To examine the possibility of trans-differentiation of engrafted donor BMDC to insulin-producing cells and evaluate its contribution to the observed benefits following BM transfusion, we studied frozen sections of the pancreas. Fluorescent microscopy confirmed the presence of CM-Dil positive donor BMDC in the recipients pancreas (supplemental Figure 2D, see http://ajp.amjpathol.org). These scattered cell tracker-labeled cells were rare and showed no difference in frequency between dbTxm and dbTxdb group. Examination of the pancreas co-stained with anti-mouse insulin antibody failed to show insulin-positive staining of engrafted donor BMDC (data not show). Immunohistochemical staining of insulin showed comparable density and normal morphology of the islets among db/m, db/db, and BMDC-treated diabetic mice (data not show). Quantification of the islets showed equal levels among different experimental groups (supplemental Figure 2E, see http://ajp.amjpathol.org). Our results suggested that a direct trans-differentiation to insulin-producing cell was not evident in the pancreas, and BMDC transfusion did not influence pancreatic islands structure and density.
Renal Function Improves in a Subgroup of db/db Mice after Treatment with BMDC from db/m Donors; Risk of Tubular Necrosis in Bone Marrow Transplantation
Effects of BMDC adoptive transfer on renal function in db/db mice were examined. The recipients of BMDC from db/m donors exhibited improved renal function (Figure 4, A and B)
judging from urinary protein/creatinine ratio and plasma creatinine level. Glomeruli showed mild to moderate hypertrophy in all db/db animals compared with controls and in addition displayed mesangial expansion (range, 2 to 2.5; average 2.3+) and arteriolar hyalinosis (range, 8% to 18%; average 9%; supplemental Figure 3
, see http://ajp.amjpathol.org). An occasional lesion of focal and segmental glomerulosclerosis, containing extracellular lipid droplets, was also evident (1/3 animals) in db/db mice. Kidneys from dbTxm group showed mild decrease in mesangial expansion (range 1.5 to 2.0; average 1.66+) and in areteriolar hyalinosis (range, 2% to 4%; average 3.3%). No lesions of focal and segmental glomerulosclerosis were present in any of these sections obtained from dbTxm mice. The decline in mesangial expansion (range, 2 to 2.5; average 2.17+) and in areteriolar hyalinosis (range, 2% to 7%; average 4.66%) were less impressive in the dbTxdb animals. An occasional lesion of focal and segmental glomerulosclerosis was evident in one of the three animals as well.
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Profiling of Cell Markers for BMDC of the Donor db/db and db/m Mice
Some of the detected beneficial effects of the adoptive transfer of BMDC in db/db mice could be secondary to the infusion of the progenitor/stem cell population present in the isolated donor BMDC. Differences in composition could hence affect their beneficial outcomes, which may also reflect the existed changes in the BM progenitor/stem cell population under normal versus disease condition. We used an array of cell surface markers to profile the freshly isolated BMDC (pooled from at least four animals for each group) using FACS analysis (Figure 5)
, including sca-1, c-kit, CD34, flk-1, CD44, vimentin, and nestin. The results from two independent experiments showed no substantial differences in the expression of detected markers between db/db and db/m mice, except for some noticeable discrepancy in sca-1 and nestin. BMDC used for transfusion were represented mostly by mesenchymal and hematopoietic stem cells nearly equally represented numerically in db/m and db/db bone marrow, but proportional differences in some markers do exist.
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Although the surface markers of cells in the transfused BMDC of either type of the donor, db/db or db/m, appeared to be little unchanged, the end-effects of their transfusion were much different, as shown in Figures 1 and 2
. To evaluate the possibility that the infused BMDC differed qualitatively, we analyzed the viability of BMDC and their progenitor/stem cell population by study the markers of apoptosis under basal and stressed conditions. FACS analysis of Annexin V staining showed comparable percentages of positive cell in freshly isolated db/db and db/m mice BMDC (Figure 6A)
. This result was confirmed with Hoechst staining. We then tested the resistance of the isolated BMDC to challenge with H2O2 (50 µmol/L) or glycated collagen I (GC, 50 µg/ml, a mimic of diabetic microenvironment; Figure 6B
). Though the frequency of apoptosis was comparable between db/db and db/m groups under the basal conditions and after exposure to native collagen (NC, 50 µg/ml), the rate of apoptosis was significantly elevated in the db/db mice on exposure to H2O2 or GC stress.
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Ex Vivo and in Vivo Ebselen Treatment Corrects Stem Cell Competence
We have previously demonstrated beneficial vascular effects of a selenoorganic peroxynitrite scavenger and antioxidant, Ebselen, in Zucker diabetic rats14
and, therefore, tested its potential to improve the resistance to stress of BMDC and their functional competence. The addition of Ebselen (Ebs) to BMDC culture medium prevented apoptosis under basal and H2O2 stress conditions, as detected by the activated caspases using FITC-VAD-FMK probe (Figure 6E)
. Compared with vehicle-treated control, in vivo chronic administration of Ebs by gavage decreased the rate of apoptosis in BMDC from db/db mice.
In view of the differences encountered during ScaI and Flk1 profiling (Figure 5)
, we further tested the possibility that the EPCs in BMDC population may vary between db/db and db/m mice. FACS analysis showed that db/db BMDC contained less ScaI+/Flk1+ cells (Figure 7C)
. EPCs cultured from db/db mice also showed decreased number and elevated apoptosis rate (Figure 7, A and B)
. In vivo treatment of db/db mice with Ebs restored viability and increased the EPC population. The recipients of the BMDC obtained from in vivo Ebs-treated db/db mice showed an increased BM EPC population and decreased apoptotic rate in EPCs (Figure 7, D–F)
. BMDC from db/db mice treated with Ebs ex vivo (overnight) also elicited improved endothelium-dependent relaxation after transplantation to db/db recipient mice, which was accompanied by increased EPC number within their BMDC population. In parallel, improvement of the endothelium-dependent relaxation in response to acetylcholine (Figure 8A
; compare with Figure 1A
) ensued. Specifically, in vivo and ex vivo therapy with Ebs resulted in maximal relaxation to acetylcholine reaching 55% and 61% of control db/m mice, respectively, compared with 38% of maximal relaxation in vehicle-treated group.
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The urine albumin/creatinine ratio of recipients of BMDC obtained from Ebs-treated donor db/db mice also showed improvement compared with recipients of BMDC obtained from vehicle-treated mice (Figure 8C)
. In conclusion, Ebselen treatment both in vivo and ex vivo restored competence to BMDC, improved EPC resistance to oxidative stress and was associated with improved vascular and renal function. These findings suggest that targeting the competence of endogenous BMDC may represent an alternative strategy in managing complications of type II diabetes and metabolic syndrome.
| Discussion |
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In the present study using db/db mice, a well recognized animal model of metabolic syndrome and type II diabetes, we made two important observations using BMDC adoptive transfer. Firstly, infusion of BMDC obtained from the db/m littermates dramatically improved the macrovascular function (acetylcholine-induced relaxation of aortic rings) and insulin sensitivity in the recipient db/db mice. Secondly, these observed beneficial effects of treatment were nearly absent when the BMDC obtained from diabetic donor mice were used. The mechanism(s) for these observed beneficial metabolic outcomes of BMDC infusion were not apparent. After an extensive search, we were able to exclude several potential candidates, such as changes in the degree of obesity (body weight remained stable), improvement of pro-inflammatory cytokines profile (in fact there was elevation of G-CSF and IL-1
, although anti-inflammatory IL-10 levels also increased, especially in the dbTxdb group), and disparate engrafting ratio of the transfused BMDCs (comparable number of engrafted CM-DiI positive cell were found). These data, in conjunction with dramatic improvement of vascular function in dbTxm mice argue in favor of a conclusion that circulatory mechanisms underlie the observed correction of insulin sensitivity. The possibility of changes in adiponectin levels being responsible for metabolic benefits in dbTxm group remains to be evaluated. It is also not clear whether the improved glycemic control in dbTxm group is responsible for amelioration of vascular and renal complications in db/db mice or BMDC transplantation has separate effects on metabolic, vascular and renal manifestations.
The differences in the study outcome using BMDCs that originated from normal or diabetic animal are striking. The possibility that it may reflect the alterations in cell composition and competence, both in general and progenitor/stem cell population, as well as alternations in cell functionality appear to deserve credence. The existence of dysfunctional EPCs originating from BM has been documented in atherosclerosis,6,22 essential hypertension,23,24 preeclampsia,25 hyperglycemia,26 smoking24,27 and type I and type II diabetes patients.28-30 It has recently been shown that diabetic state promotes aging of cardiac stem cells, a tissue resident stem cell population, and contribute to the heart failure.31
We explored this hypothesis further in our BMDC transplant setting. Referring to the initial finding that the ScaI- or Flk1-positive cell were decreased in BMDC of db/db mice, we further analyzed the cell population double-positive for ScaI and Flk1, the proposed EPC population. A decreased percentage of BM ScaI+/Flk1+ cells was documented in db/db mice by FACS analysis. This finding was supported by experiments on cultured EPC and is consistent with the results from others.28-30,32,33 Next, we qualitatively tested their viability and resistance to oxidative stress in cell culture. An increase in apoptosis under basal culture conditions was detectable in BMDC of db/db origin, as well as in the MSC and EPC. Challenging BMDC and MSC with oxidative stress (H2O2) or a glycated long-lived protein (GC) disclosed alterations in db/db mice. Proportion of apoptotic cells after H2O2 or GC treatment was significantly higher in the BMDC and MSC prepared from diabetic mice.
Having demonstrated functional incompetence of BMDC obtained from db/db mice, we attempted to correct it using the selenoorganic antioxidant and peroxynitrite scavenger Ebs. Ex vivo treatment of cultured BMDC with Ebselen resulted in a significant improvement of their resistance to oxidant stress and reduced rate of apoptosis. In vivo therapy of db/db mice with Ebs also reduced the rate of apoptosis in BMDC and EPC in culture and normalized the number of EPC. Furthermore, adoptive transfer of the BMDC from db/db mice treated with Ebs in vivo or ex vivo produced striking reduction of vasculopathy and improvement of renal function in recipient db/db mice. These functional improvements in recipient db/db mice were associated with much improved resistance to apoptosis and elevated EPC numbers in their BM. This finding may explain at least in part the compromised state of BMDC isolated from db/db mice. However, these data also added another interesting layer of complicity to the mechanisms for the benefits following adaptive transfer. In contrast to the improved vasculopathy and renal dysfunction, the beneficial effect on fasting glucose level and insulin sensitivity were absent in the recipients of BMDC transfer from db/db mice treated with Ebs (data not shown). This disparity suggests that the variety of beneficial effects in db/db recipients of db/m BMDC transfer may be well mediated through multiple mechanisms, which are all compromised in db/db mice. Some of these compromised mechanisms in db/db mice are improved with the use of antioxidant therapy, but some are not.
In contrast to renal functional improvement in the majority of recipient animals in the present study, the deterioration of renal dysfunction in a subgroup stands apart. Our own data obtained in mice with acute kidney injury,34
as well as previous findings by Prockops group35
in streptozotocin-diabetic mice all showed beneficial effect of infused MSC on renal function. In another study reported by Cooks group, transplantation of wild-type BMDC improved renal function in Col4
3–/– mice through, in part, a mechanism involving regeneration of padocytes without the gene defect.36
These distinct outcomes may be due to severity of hyperlipidemia in db/db mice or to circulating cells as referred to in the previous work by Strikers group.37
Secondly, these findings may be linked to the BMDC transplantation per se. The decades of experience with bone marrow transplantation buttress these findings. The incidence of renal dysfunction of various degrees ranges from 53% to 92% with 24% of patients requiring dialysis.19-21
Development of proteinuria was found to be near-universal after bone marrow transplantation.38
In our experimental setting, despite the fact that a syngeneic transplantation was performed, the possibility of microembolism due to cell clamping, both in BMDC from db/db and db/m donors, cannot be ruled out and was presumably the cause of the observed tubular necrosis.
In conclusion, infusion of BMDC obtained from db/m donors to db/db recipient mice benefited macrovascular function, insulin sensitivity, and, in majority of cases, renal function. The BMDC obtained from db/db mice were functionally incompetent partly secondary to their decreased viability under increased oxidative stress challenge. Our work emphasizes benefits and risks of cell therapy, and reduced competence of BMDC in db/db mice, and suggests that antioxidant targeting of BMDC, both in situ or ex vivo, may represent an alternative strategy in managing complications of type II diabetes and metabolic syndrome.
| Acknowledgements |
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| Footnotes |
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Supported by the American Heart Association Scientist Development award 0430255N (J.C.) and NIH grants DK052783, DK45462, and DK054602 (M.S.G.).
Supplemental material for this article can be found on http://ajp.amjpathol.org.
Accepted for publication November 7, 2008.
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