Stem cells and pain

Table 2 Table 2 Articles that used stem cells to treat inflammatory pain (stem cell-based treatment of inflammatory pain or in models where pain is certainly involved, but was not investigated)

Ref.	Stem cell therapy design	Key findings	Pain-related highlights	Route of administration	Number of cells or amount of extracellular vesicles and exosomes
Hsueh et al[69], 2023	iPSC-derived EVs for the treatment of rabbit articular cartilage OA in an in vivo model and an in vitro interleukin (IL)-1β-induced model	Improvement in both in vivo and in vitro models of OA by stimulation of chondrocytes proliferation and decreasing senescence were accompanied by: Decreasing of TNF-α); IL-6; protein 21 (p21); MMP 13; ADAMTS5; and increasing of collagen II	Indirect: Specific pain receptors/pathways weren’t investigated	i.a.	100 μg iPSC-EV
Gao et al[184], 2022	Small EVs from iPSC-derived mesenchymal stem-cells ameliorate tendinopathy pain by inhibiting mast cell activation	The treatment was able to decrease acute pain in tendinopathy, as well as inhibit infiltration of activated mast cells and interactions with nerve fibers in vivo. In the in vitro experiments, the treatment decreased mast cell degranulation and the expression of pro-inflammatory cytokines and genes involved in the hypoxia inducible factor-1 signaling pathway	Pain behavior was measured by the von Frey method. And the weight distribution on the knees by SWB; immunofluorescence staining of tendon sections for tryptase (mast cell marker) and PGP9.5 (nerve fiber marker) was performed to assess the number of activated mast cells and the anatomical interaction between mast cells and nerve fibers. In addition, the SWB and CatWalk test was also. carried out	Local injection (quadriceps tendon)	1 × 109 particles
Yu et al[185], 2022	Intravital imaging and single cell transcriptomic analysis for engraftment of mesenchymal stem-cells in an animal model of interstitial cystitis/bladder pain syndrome	The transplanted cells formed a perivascular-like structure. They were also shown to express cyclin-dependent FOSe kinase-1 which played a key role in modulating the migration, engraftment and anti-inflammatory functions of multipotent MSCs, which determined their therapeutic potency in vivo	In vivo two-photon intravital microscopy and single-cell transcriptome analysis were used to assess the effects of stem cell treatment on interstitial cystitis/bladder pain syndrome	Injected into the outer layer of the anterior wall and dome of the bladder	106
Zhang et al[186], 2022	EVs derived from MSCs alleviate neuroinflammation and mechanical allodynia in interstitial cystitis rats by inhibiting NLRP3 inflammasome activation	SC treatment decreased suprapubic mechanical allodynia and frequent urination in rats with interstitial cystitis. It also decreased glial cell activity as well as neuroinflammation in the spinal cord. Furthermore, the treatment was able to decrease the activation of NLRP3 inflammasomes and the TLR4/NF-κB signaling pathway	Behavioral test (von Frey) was performed to measure allodynia and western blot and immunofluorescence for protein related to inflammation and central sensitization analysis: CD9, CD63, CD81, ALIX, TNF-α, IL-1β, IL-6, IBA-1, GFAP, NLRP3, Caspase-1, IL-18, TLR4, p65 NK-κB, phospho-p65 NK-κB (western blot). NLRP3, neuron-specific nuclear protein, GFAP and OX-42 labeling (immunofluorescence)	i.t.	20 μg
González-Cubero et al[86], 2022	EV and soluble fractions of adipose tissue-derived MSCs secretome induce inflammatory cytokines modulation in an in vitro model of discogenic pain	There was a decrease in the expression of IL-6, IL-8 and IL-17	Indirect method: The authors measured the regulatory capacity of EVs on the inflammatory molecules IL-1α, IL-1β, IL-6, IL-8, IL-17, nerve growth factor, brain-derived neurotrophic factor, IFN-γ, NF-κB and TNF and MMP-1, MMP-2, MMP-3, MMP-13 and ADAMTS-5	In vitro model	1 × 106
Yang et al[91], 2020	Anti-inflammatory protein TSG-6 secreted by bone marrow MSCs attenuates neuropathic pain by inhibiting the TLR2/MyD88/NF-κB signaling pathway in spinal microglia	Stem cells are capable of secreting TSG-6. This article demonstrated that i.t. administration of this protein leads to a decrease in mechanical allodynia and heat hyperalgesia. In addition to inhibiting neuroinflammation in the spinal cord (IBA-1), the protein administration inhibited the activation of the TLR2/MyD88/NF-κB pathway in the dorsal horn of the ipsilateral spinal cord by the secretion of TSG-6 and reduced the production levels of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α	The activation of the TLR2/MyD88/NF-κB signaling pathway was evaluated by western blot and by immunofluorescence. Mechanical allodynia and heat hyperalgesia were observed by behavioral tests	i.t.	5 × 106
Zhang et al[187], 2019	MSCs exosomes alleviate temporomandibular joint OA by attenuating inflammation and restoring matrix homeostasis	It was observed that the treatment led to repair of the temporomandibular joint, along with a reduction in inflammation and pain. Treatment increased IL-1β-impaired sulfated glycosaminoglycan synthesis and suppressed IL-1β-induced nitric oxide and MMP13 production. These effects were partially abrogated by inhibitors of adenosine receptor, protein kinase B, ERK and adenosine monophosphate activated protein kinase phosphorylation	Mechanical hyper-nociception was assessed using the von Frey microfilament. The expression of inflammatory mediators and other components was measured using quantitative polymerase chain reaction	i.a.	100 μg
Ebbinghaus et al[88], 2018	A promising new approach for the treatment of inflammatory pain: Transfer of stem cell-derived tyrosine hydroxylase-positive cells (mouse model)	It has been demonstrated that the administration of endogenous tyrosine hydroxylase positive cells (iTH+) cells, prior to the induction of antigen-induced arthritis, was not sufficient to suppress the disease. However, the treatment was able to decrease pain behavior evoked by inflammation, largely due to the production of IL-4 induced by iTH+ cells. Furthermore, the treatment was able to reduce the levels of pro-inflammatory molecules, in addition to increasing the number of M2 macrophages in dorsal root ganglia	Inflammatory molecules were quantified, such as: IFN-γ, IL-2, IL-4, IL-6, IL-10, CCL3, CCL5, CXCL1, CXCL2, CXCL10, and CXCL12. Additionally, pain-related behavior tests and IBA-1 and arginase 1 labeling in the dorsal root ganglion via immunofluorescence was performed	i.v.	106
Ichiseki et al[92], 2018	I.a.-injected MSC stimulate anti-inflammatory molecules and inhibits pain related protein and chondrolytic enzymes in a monoiodoacetate-induced rat arthritis model	The treatment was able to inhibit central pain sensitization (decreased expression of CGRP in the spinal cord) and increase the secretion of TSG-6 by stem cells, an anti-inflammatory factor and cartilage protector	For the evaluation of central sensitization, CGRP staining was performed by immunofluorescence. And the histochemical technique was also used for the evidence in the joint of ADAMTS5 and TSG-6	i.a.	5.0 × 106
Fodor and Paulseth[90], 2016	Adipose derived stromal cell injections for pain management of OA in the human knee joint	After 3 mo of treatment, patients showed improvement in WOMAC and VAS scores, which were maintained for 1 yr. ROM and TUG improved until the third month. All patients achieved full activity with decreased knee pain and no infections or adverse effects reported	Patients were evaluated by following scores on the WOMAC, VAS pain scale, ROM, TUG, and magnetic resonance imaging	i.a.	14.1 × 106 nucleated stromal vascular fraction cells per knee
Pettine et al[93], 2016	Treatment of discogenic back pain with autologous bone marrow concentrate injection with minimum two-year follow-up (humans)	Stem cell treatment reduced visual analog scale and Initial Oswestry Disability Index scores. In addition to reducing pain in patients. The treatment proved to be effective for up to 2 yr after the injection	Pain was assessed using scores provided by patients	Intradiscal injection	(0.5-1) × 106
Durand et al[89], 2015	Persistent visceral allodynia in rats exposed to colorectal irradiation is reversed by MSC treatment	Induced a time-dependent reversion of the visceral allodynia and a reduction of the number of anatomical interactions between mast cells and PGP9.51 nerve fibers	Spinal sensitization (was available for labeling of phospho-ERK neurons), colonic neuroplasticity (as increased density of substance P1 nerve fibers); s, visceral sensitivity was evaluated by studying the contraction of the abdominal muscles in response to colorectal distension	i.v.	1.5 × 106
Watanabe et al[87], 2015	Early transplantation of MSC after SCI relieves pain hypersensitivity through suppression of pain-related signaling cascades and reduced inflammatory cell recruitment	The treatment was able to decrease thermal and mechanical hypersensitivity. Improvements in pain were mediated by suppression of PKC-γ and p-CREB expression in dorsal horn neurons. The authors also reported a decrease in the levels of pro-inflammatory cytokines (TNF-α, IL-6), mediators of early secondary vascular pathogenesis (MMP9) and macrophage recruitment factors (CCL2, CCL5 and CXCL10). All in addition to increased levels of a microglial stimulating factor GM-CSF)	Mechanical allodynia and thermal sensitivity were recorded. In addition, immunofluorescence was performed on spinal cord sections, labeling for: PKC-γ or p-CREB, GFAP, cD11B and phospho-protein 38. For immunoblot analysis, components of the mitogen-activated protein kinase family, inflammatory mediators (TNF-α, IL-6, MMP-9), macrophage recruiting factors (CCL2, CCL5, and CXCL10) and GM-CSF (a microglial stimulating factor) were analyzed	Injection into the middle of the contusion site, identified as the middle point of the laminectomy area	2.0 × 105
Emadedin et al[188], 2012	Intra-articular injection of autologous MSC in six patients with knee OA	The treatment was able to improve scores related to pain, the functional status of the knee and the distance covered up to six months after the injection	VAS which is a subjective assessment that represents the patient’s perception of the current pain state with a higher score reflecting more severe pain. Functional status of the knee was assessed by WOMAC OA index. This index evaluates pain, joint stiffness, physical and social function of patients with OA of the knee	i.a.	(20-24) × 106

iPSC: Induced pluripotent stem cells; OA: Osteoarthritis; IL: Interleukin; TNF-α: Tumor necrosis factor alpha; p21: Protein 21; MMP: matrix metalloproteinase; ADAMTS5: A disintegrin and metalloproteinase with thrombospondin motifs 5; i.a.: Intra-articular; EV: Extracellular vesicle; SWB: Static weight bearing; PGP9.5: Protein gene product 9.5; CDK1: Cyclin-dependent FOSe kinase 1; MSC: Mesenchymal stem cells; NLRP3: NOD-like receptor protein 3; i.t.: Intrathecal; TLR: Toll-like receptor; NF-κB: Nuclear factor kappa B; IBA-1: Ionized calcium-binding adapter molecule 1; GFAP: Glial fibrillary acidic protein; CD: Cluster of differentiation; IFN-γ: interferon-gamma; TSG-6: Tumor necrosis factor alpha-stimulated gene 6; MyD88: Myeloid differentiation primary response 88; ERK: Extracellular signal-regulated kinase 1; iTH+: Tyrosine hydroxylase positive cells; CCL: C-C motif chemokine ligand; CXCL: C-X-C motif chemokine ligand; DRG: Dorsal root ganglion; i.v.: Intravenous; CGRP: Calcitonin gene-related peptide; WOMAC: Western Ontario and McMaster Universities Arthritis Index; VAS: Visual Analogue Scale; ROM: Range of motion; TUG: Timed ascent and descent; PKC-γ: Protein kinase C gamma; GM-CSF: Granulocyte-macrophage colony stimulating factor; p-CREB: Phospho cyclic AMP response element binding protein; p-p38: Phospho-protein 38.