The prevalence of diabetes mellitus (DM) is rapidly rising worldwide. Globally, an estimated 382 million people are suffering from DM, and the number is projected to reach 592 million by 2035 [
Another research area to improve graft survival focuses on coculture of islets with mesenchymal stem cells (MSCs). MSCs are the most well-characterized adult stem cells. MSCs have evoked considerable research interest owing to their capacity for multipotent self-renewal and multilineage differentiation. MSCs have potent immunoregulatory properties [
A similar meta-analysis by de Souza et al. was published in 2017 [
This review was conducted in accordance with the PRISMA statement [
The electronic databases (PubMed, Embase, and Web of Science) were searched for relevant literature published between January 2000 and May 2019 in English language. The following key words/medical subject headings (MeSH) were used for the search: (“mesenchymal stem/stromal cell” OR “mesenchymal cell” OR “mesenchymal stem cell transplantation” OR “mesenchymal cell research”) AND (“pancreas/pancreatic islet” OR “islets of Langerhans” OR “pancreas/pancreatic islet transplantation” OR “islet transplantation”). The “related articles” function was used to widen the search, and the references of the retrieved articles were manually screened to identify potential eligible literature.
Two investigators independently evaluated all the articles by reviewing the titles and abstracts; if necessary, the full text of the articles was reviewed. Discrepancies, if any, were resolved by discussion or in consultation with a senior reviewer. Eligible studies were selected according to the following inclusion criteria: (1) original research articles that compared the outcomes of pancreatic islets cultured alone with those of islets and MSCs coculture and (2) studies that reported at least one of the outcomes of interest (see below) and the mean (±standard deviation) values for continuous variables of interest. The exclusion criteria were literature reviews and case reports, studies published in languages other than English, and duplicate publications.
The outcomes of interest included islet viability and function in vitro, the concentrations of cytokines, and the in vivo experimental results. If the article did not contain complete data, the authors were contacted to obtain complete data using a detailed data extraction form. For the direct coculture model, islets were seeded directly onto the MSC monolayer in a plate. For the indirect coculture model, cell culture transwells with a semipermeable membrane to which islets were added were inserted into each well with the MSC monolayer. The meta-analysis is based on the studies published previously; therefore, ethical approval was not required.
Two investigators independently extracted the following data from each included study: first author, country, year of publication, islet origin (human/murine/pig), MSC origin (human/murine), type of MSCs (bone marrow/umbilical cord blood/adipose tissue/kidney-derived MSCs), method of coculture (indirect/direct/coencapsulated), culture duration, results of islet viability and function (as
For the viability outcomes, we classified the staining dyes based on whether they stained viable or dead cells, e.g., fluorescein diacetate (FDA)/propidium iodide (PI), acridine orange (AO)/PI, Syto-Green/ethidium bromide (EB), ethidium homodimer-1 (EH-1)/calcein AM, or trypan blue. For the islet function outcomes, the analyzed data included insulin secretion index (ISI; rate of high- to low-glucose-stimulated insulin secretion) and the level of insulin secreted after glucose stimulation when the basic level of insulin was not provided. For the posttransplantation outcomes, we compared the levels of FBG at different days posttransplantation. The outcomes of IPGTT were also compared.
Grading of Recommendation Assessment, Development and Evaluation (GRADE) guidelines [
The meta-analysis was performed using the Cochrane Collaboration Review Manager 5.3. For continuous variables, statistical analysis was carried out using the weighted mean differences (WMD) with 95% confidence intervals (CI) as the summary statistic. Results were considered statistically significant at
Due to considerable variability among the included studies with respect to experimental conditions and parameters, significant heterogeneity was expected. To further control for heterogeneity, subgroup meta-analyses were performed to assess the possible association between different variables (such as coculture methods) and outcomes.
A total of 17704 articles were retrieved on database search. After a meticulous review of titles and abstracts, 17588 studies were excluded. After further detailed review, another 91 studies were excluded due to ineligible study design, lack of outcomes of interest, or experimental trials. Twenty-five studies qualified the inclusion criteria [
Schematic illustration of the literature search and study selection criteria.
Characteristics of the eligible studies included in the meta-analysis.
Author [reference] | Year | Outcome evaluated | Technique used | Viability test | Islet origin/MSC tissue origin | Type of coculture | Time of coculture |
---|---|---|---|---|---|---|---|
Arzouni et al. [ |
2017 | ISI | Radioimmunoassay | — | Human/hAD-MSC | Direct | 4 d |
Arzouni et al. [ |
2019 | ISI | Radioimmunoassay | — | Human, mouse/hAD-MSC, hBM-MSC, mAD-MSC, mKidney-MSC | Direct | 1 d/2 d/3 d |
Chen et al. [ |
2013 | Viability, ISI | Radioimmunoassay | AO/PI | Rat/rBM-MSC | Direct | 2 w |
Davis et al. [ |
2012 | ISI | ELISA | — | Mouse/mBM-MSC | Encapsulation | 7 d |
Duprez et al. [ |
2011 | ISI | ELISA | — | Human/hBM-MSC | Direct | 2 d |
Jun et al. [ |
2014 | ISI, viability | ELISA | Calcein AM/ethidium homodimer-1 | Rat/rAD-MSC | Encapsulation | 7 d/14 d |
Jung et al. [ |
2011 | Viability, VEGF, TNF- |
ELISA | FDA/PI | Rat/rBM-MSC | Indirect/direct | 1 w/4 w |
Karaoz et al. [ |
2010 | Viability, IL-6, ISI | ELISA | FDA/PI | Rat/rBM-MSC | Indirect | 2 w |
Karaoz et al. [ |
2011 | Insulin | ELISA | Rat/rBM-MSC | Direct | 16 d | |
Kerby et al. [ |
2013 | ISI | Radioimmunoassay | Mouse/mKidney-MSC | Encapsulation | 3 d | |
Kono et al. [ |
2014 | Viability, VEGF | — | EH 1/calcein AM | Mouse/hAD-MSC | Indirect | 6 d |
Lu et al. [ |
2010 | ISI | ELISA | — | Rat/rBM-MSC | Direct | 3 d/4 d |
Ayenehdeh et al. [ |
2017 | Insulin | ELISA | — | Mouse/mAD-MSC | Encapsulation | — |
Montanari et al. [ |
2017 | ISI | ELISA | — | Human/hBM-MSC | Indirect/direct | 3 d |
Park et al. [ |
2009 | ISI, VEGF, IL-6, TNF- |
ELISA | — | Human/hBM-MSC, hUCB-MSC | Indirect | 2 d |
Park et al. [ |
2010 | ISI, viability | ELISA | AO/PI | Mouse/hUCB-MSC | Indirect | 2 d |
Rackham et al. [ |
2013 | ISI | Radioimmunoassay | — | Mouse/mKidney-MSC | Indirect/direct | 3 d |
Rackham et al. [ |
2014 | ISI | Radioimmunoassay | — | Mouse/mAD-MSC | Direct | 3 d |
Rackham et al. [ |
2016 | ISI | Radioimmunoassay | Mouse/mAD-MSC | Direct | 3 d | |
Scuteri et al. [ |
2014 | Viability, insulin | ELISA | Calcein AM | Rat/rBM-MSC | Indirect/direct | 1 w |
Yamada et al. [ |
2014 | Viability, IL-6, VEGF, TNF- |
ELISA | Trypan blue staining | Pig/hAD-MSC | Indirect | 2 d |
Yoshimatsu et al. [ |
2013 | Viability, ISI | ELISA | Syto-Green/EB | Rat/rBM-MSC | Direct/encapsulation | 3 d |
Yoshimatsu et al. [ |
2015 | Viability, ISI, insulin | ELISA | Syto-Green/EB | Mouse/mBM-MSC | Direct | 1 d/4 d |
Ren et al. [ |
2019 | — | — | — | Mouse/mAD-MSC | Cotransplantation | — |
Note. MSC = mesenchymal stromal cells; ISI = insulin stimulation index; FDA/PI = fluorescein diacetate/propidium iodide; EB = ethidium bromide; EH 1 = ethidium homodimer-1; VEGF = vascular endothelial growth factor; IL-6 = interleukin-6; TNF-
The quality of the studies included in the meta-analysis was assessed using the GRADE [
Three parameters were used to assess the function of islets in vitro: viability, ISI, and the level of insulin secreted after glucose stimulation. A total of 10 studies reported data pertaining to islet viability; however, concrete data pertaining to islet viability was not available for one study. Therefore, nine studies were included in the quantitative pooled analysis for viability of islets. Seventeen studies reported ISI; four studies reported the level of insulin secretion. In comparison to islet cultured alone, islet cocultured with MSCs showed significantly increased islet viability (WMD, -15.59; -22.34 to -8.83;
Forest plot of meta-analysis of islet viability, comparing islets cultured alone with islets cocultured with MSCs.
Forest plot of meta-analysis of islet insulin secretion index, comparing islets cultured alone with islets cocultured with MSCs.
Forest plot of meta-analysis of islet-secreted insulin level, comparing islets cultured alone with islets cocultured with MSCs.
Meta-analysis of islet viability and ISI in subgroups.
Outcome | Subgroup | Studies | Meta-analysis | |||
---|---|---|---|---|---|---|
Mean difference | 95% CI | |||||
Viability | Direct coculture | 12 | -19.82 | -26.56~-13.07 | <0.00001 | 89 |
Indirect coculture | 4 | -1.14 | -7.82~5.54 | 0.74 | 74 | |
ISI | Direct coculture | 21 | -2.42 | -3.94~-0.89 | 0.002 | 99 |
Indirect coculture | 9 | -2.54 | -4.79~-0.28 | 0.03 | 99 |
Note. ISI = insulin stimulation index; CI = confidence interval.
Five studies had compared the concentration of cytokines in the supernatant of the culture medium [four studies for vascular endothelial growth factor (VEGF), three studies for interleukin-6 (IL-6), and three studies for tumor necrosis factor-
Meta-analysis of cytokines outcomes in studies that compared islets cultured alone with islets cocultured with MSCs.
Outcome | Studies reported outcome | Meta-analysis | ||||
---|---|---|---|---|---|---|
Number | Unit | Mean difference | 95% CI | |||
VEGF | 4 | pg/ |
-1.19 | -2.25~-0.14 | 0.03 | 100 |
Excluding indirect | 4 | pg/ |
-1.82 | -3.34~-0.30 | 0.02 | 100 |
TNF- |
3 | pg/mL | 2.70 | -0.50~5.91 | 0.10 | 91 |
Excluding indirect | 3 | pg/mL | 1.86 | -3.53~7.24 | 0.50 | 93 |
IL-6 | 3 | pg/mL | -1225.66 | -2044.47~-406.86 | 0.003 | 100 |
Note. CI = confidence interval; VEGF = vascular endothelial growth factor; IL-6 = interleukin-6; TNF-
Eight studies that reported the level of FBG and IPGTT after transplantation were included in the meta-analysis (Table
Characteristics of studies included in the meta-analysis that performed islet transplantation
Author [reference] | Year | Outcome evaluated | Number of transplantation cell | Encapsulation | Transplantation site | Islet origin | Recipient origin | |
---|---|---|---|---|---|---|---|---|
Islet | MSCs | |||||||
Davis et al. [ |
2012 | IPGTT | 600 IEQ | 600 | Yes | Peritoneal cavity | SD rat | Balb/C mouse |
Karaoz et al. [ |
2011 | FBG | 350 IEQ | 450-500 | Yes | Peritoneal cavity | C57BL/6J | C57BL/6J |
Ayenehdeh et al. [ |
2017 | FBG | 100 IEQ | No | Peritoneal cavity | Balb/C | C57BL/6 | |
Montanari et al. [ |
2017 | IPGTT | 4500–5000 IEQ | 450-500 | Yes | Peritoneal cavity | Human | C57BL/6 mouse |
Rackham et al. [ |
2013 | FBG, IPGTT | 100 IEQ | No | Underneath the kidney capsule | C567BL/6 | C567BL/6 | |
Ren et al. [ |
2019 | FBG | 150–225IEQ | No | Underneath the kidney capsule | C57BL/6 | C57BL/6 | |
Yamada et al. [ |
2014 | FBG, IPGTT | 1500 IEQ | Yes | Peritoneal cavity | Wistar rat | Balb/C mouse | |
Yoshimatsu et al. [ |
2015 | FBG, IPGTT | 500 IEQ | No | Femur muscle | Balb/C | Balb/C |
Note. FBG = fasting blood glucose; IPGTT = intraperitoneal glucose tolerance test; IEQ = islet equivalent.
Meta-analysis of fasting blood glucose level in studies that performed islet transplantation
Outcome | Meta-analysis | |||
---|---|---|---|---|
Mean difference | 95% CI | |||
FBG-POD7 | 75.97 | -10.79~162.74 | 0.09 | 99 |
Encapsulation | 5.05 | -153.86~63.96 | 0.95 | 98 |
Unencapsulation | 127.47 | 47.17~207.77 | 0.002 | 99 |
FBG-POD14 | 97.65 | -1.82~197.12 | 0.05 | 99 |
Encapsulation | 20.15 | -145.74~186.05 | 0.81 | 98 |
Unencapsulation | 154.69 | 46.13~263.25 | 0.005 | 99 |
FBG-POD21 | 102.60 | 27.14~178.05 | 0.008 | 99 |
Encapsulation | 117.19 | -44.39~278.76 | 0.16 | 98 |
Unencapsulation | 93.20 | -25.59~212.00 | 0.12 | 99 |
FBG-POD28 | 121.19 | 49.56~192.82 | 0.0009 | 99 |
Encapsulation | 105.73 | -66.80~278.25 | 0.23 | 99 |
Unencapsulation | 133.85 | 29.47~238.23 | 0.01 | 99 |
Note. FBG = fasting blood glucose; POD = postoperative day; CI = confidence interval.
Meta-analysis of IPGTT in studies performing islet transplantation in vivo.
Outcome | Meta-analysis | |||
---|---|---|---|---|
Mean difference | 95% CI | |||
BG-30 min | 85.92 | 5.33~166.51 | 0.04 | 99 |
Encapsulation | 132.60 | -1.06~266.27 | 0.05 | 99 |
Unencapsulation | 10.07 | -16.26~36.40 | 0.45 | 45 |
BG-60 min | 100.47 | 37.39-163.55 | 0.002 | 98 |
Encapsulation | 123.21 | -14.56~260.99 | 0.08 | 99 |
Unencapsulation | 71.26 | 27.83~114.70 | 0.001 | 81 |
BG-90 min | 57.59 | -44.23~159.40 | 0.27 | 99 |
Encapsulation | 123.41 | -8.75~255.56 | 0.07 | 99 |
Unencapsulation | -41 | -114.45~32.45 | 0.27 | 73 |
BG-120 min | 66.77 | -48.25~181.79 | 0.26 | 99 |
Encapsulation | 139.47 | 11.81~267.13 | 0.03 | 99 |
Unencapsulation | -42.35 | -108.67~23.98 | 0.21 | 99 |
Note. CI = confidence interval; BG = blood glucose.
In addition to the quantity, the function and vitality of islets are also key determinants of the success of islet transplantation. The remarkable advances in islet isolation and purification techniques have augmented islet yield, improved islet function, and produced better outcomes after single donor islet allotransplantation by ensuring an increased functional
MSCs have previously been shown to help preserve
Our study showed that the concentrations of VEGF and IL-6 in the supernatant of islets cocultured with the MSC group were significantly higher than those in the islet cultured alone group; however, the concentration of TNF-
We compared the levels of FBG and results of IPGTT after islet/MSC transplantation in order to evaluate the function of islet in vivo. We found that the level of FBG on postoperative days 21 and 28 was higher in the islet alone transplantation group. Interestingly, subgroup analysis showed that the level of FBG on postoperative days 7, 14, and 28 was significantly lower when unencapsulated islets and MSCs were cotransplanted. Due to inflammation, hypoxic ischemic environment, and immunological factors, early loss of functional
Some limitations of our study should be considered while interpreting our findings. First, since studies included in our meta-analysis were not blinded, the quality of evidence was low. The strength of proof is relatively low, and due caution should be exercised while drawing conclusions. Second, there was considerable variability between the included studies with respect to the origin and types of MSCs, the origins of islets, and the duration of coculture. Also, the included studies involved different kinds of transplantations (syngeneic, allogeneic, or xenotransplantation) and transplantation sites. All these factors contributed to significant heterogeneity. In addition, different coculture methods were used in the included studies; however, we performed subgroup analysis to minimize the influence of heterogeneity. Third, the methods used for the assessment of islet viability and function were not completely consistent across studies; in addition, the assessments were performed at different time points. Despite the limitations mentioned above, we believe that our study obviously decreases the heterogeneity by subgroup analysis and provides important information regarding change in viability and function of pancreatic islets after coculture with MSCs.
Our study demonstrated that MSCs can significantly improve the viability and function of islets when they are directly or indirectly cocultured. MSCs may exert their protective effect by modulating the secretion of cytokines, such as VEGF, TNF-
The authors declared that they have no conflicts of interest.
Xiaohang Li designed the study, analyzed the data, and drafted the manuscript; Hongxin Lang and Baifeng Li conducted the database searches and acquired the data; Chengshuo Zhang undertook the statistical analysis and interpretation of the data; Ning Sun and Jianzhen Lin acquired the data and revised the manuscript; and Jialin Zhang contributed in the concept of the study and revision. All authors read and approved the final manuscript.
This work was supported by the Scientific Research Foundation of the 1st Hospital of CMU (No. FSFH201711), the Clinical Medicine Discipline Promotion Program of China Medical University (Surgery) (No. 111-3110118051), and the Key Research & Development and Guidance Plan Project of Liaoning Province (No. 2017225031).