With the evolution of the stem cell era, BMSCs, hADSCs, and hAFSCs have been available sources of cell-based therapy. Different research groups had identified and compared cellular morphology, surface markers, and differentiation abilities of stem cells from several sources [11, 22]. In this study, we directly compared the therapeutic potentials of MSCs of different sources including rBMSCs, hADSCs, and hAFSCs in the setting of cisplatin-induced early and late kidney injury. Prior to that, we reported a full characterization of different MSCs used. FACS analysis showed all MSCs were positive for expression of a cluster of differentiation (CD) of a mesenchymal nature (CD29, CD44, and CD90) and negative for the hematopoietic lineage markers (CD34 and CD45). Moreover, the differentiation abilities of MSCs of different sources were also established. Cells showed multipotent differentiation potential into the three lineages of osteogenesis, chondrogenesis, and adipogenesis that is a standard for defining MSCs. This was evaluated by using special stain for each lineage; Alizarin Red stain for osteogenesis, safranin O stain for chondrogenesis, and Oil-red-O stain for adipogenesis that stains cytoplasmic lipid droplets.

In addition, hAFSCs showed similar MSC properties with either rBMSCs or hADSCs in their morphology and surface markers. In the third passage, hAFSCs exhibited a spindle-shaped morphology analogous to that of rBMSCs and hADSCs. Human AFSCs were comparable to rBMSCs and hADSCs in their mesenchymal differentiating potentials. Human ADSCs and AFSCs showed MSC features as defined by the ISCT minimum criteria: a spindle shape, multilineage differentiation, and surface marker expression. Kern et al. [22] showed that ADSCs were preferable as they hold the highest frequency of MSCs; however, hAFSCs seemed to be more expandable. Such studies aimed for more detailed description of stem cell biology of various sources.

The direction to use hAFSCs in cell-based therapy is its better senescence patterns which vary between MSC sources [23]. Zaim et al. [24] observed that senescence was age-dependent. In addition, it was demonstrated that neonatal MSCs showed no sign of cellular senescence over long-term culture [25]. The biological properties of neonatal MSCs were determined to be different from adult MSCs. One study showed a significant decrease in stem cell characteristics with advancing donor age in humans MSCs [26]. In addition, hAFSCs showed great expansion potential and senescence retardation than ADSCs and BMSCs in spite of their longer culture time [27]. Further studies of MSC senescence are required to address these issues.

A major concern that remains to be uncovered is determining which cell source is most appropriate and effective in a specific disease model. Here, we directly compared the therapeutic potentials of rBMSCs, hADSCs, and hAFSCs in the context of cisplatin-induced early and late kidney injury and the role of a probable antioxidant mechanism. MSCs of the three sources were able to ameliorate cisplatin-induced renal function deterioration and tissue damage. The rat BMSCs-treated group had the lowest serum creatinine by day 30 compared to hADSCs and hAFSCs. Moreover, all MSCs-treated groups had nearly equal antioxidant activities at different time intervals. To quantitatively test the paracrine properties of various MSCs, oxidative stress markers were assessed in renal tissue homogenate of different groups. Increased MDA free radical and decreased GSH level and SOD activity occurred with cisplatin toxicity. On the other hand, the level of these markers was significantly changed in all MSC treatment groups.

It is necessary to recognize the mechanism of MSC-induced tissue recovery since this may explain the several aspects of tissue repair. Earlier studies showed that MSCs had the capacity to home to the site of injury and differentiate into specific cell lineages through a mechanical effect [28]. In our data, MSCs from the three different sources injected intravenously had a specific mechanism underlying their therapeutic benefit and this could be related to the paracrine role of secreted growth factors and cytokines [29] that modify the cellular microenvironment, decreasing oxidative stress, limiting damage, and enhancing tissue repair. The early administration of a single dose of stem cells permits the speculation of an antioxidant paracrine-protective mechanism for stem cells of the three sources against the acute nephrotoxicity of cisplatin.

Assessment of renal tissue proliferative activity by the evolution of Ki67-positive cells means that the migrating stem cells (whether extrarenal or intrarenal from the niche of the inner medulla) aggregated but remained quiescent in the earlier periods (day 4) till they reached the interstitium as aggregates of peritubular solid sheets in the later period (day 11) where they began to colonize the necrotic tubules and started to divide actively and regenerate the damaged tissues. After complete regeneration (day 30), all compartments of the kidney returned quiescent Ki67-negative except the cortex. We speculated that the Ki67-positive cells were migrating extrarenal stem cells by their time-course appearance in kidney tissue. Inconsistent with our results, one detailed study demonstrated a time-linked evidence of incorporation of extrarenal BMSCs during regeneration in a renal ischemia rat model [30]. Contrarily to this speculation, exogenous stem cells may modulate the renal microenvironment through paracrine action that enhances or mobilizes interstitial renal residents [31].

To the best of our knowledge, this is the first study to directly compare the therapeutic potentials of MSCs of different sources including rBMSCs, hADSCs, and hAFSCs in the setting of early and late kidney injury and the role of a probable antioxidant mechanism. The limitation of the present study is that the rat BMSCs used were not completely pure as noticed from the results of the FACS (CD29, 48.9 % and CD90, 54.9 %). These cells did not exactly meet one of the minimal criteria of MSCs. Still, other criteria such as plastic adherence and differentiation are fulfilled [10].