Stem cell therapy and diabetic erectile dysfunction: A critical review

Table 1 List of articles on stem cell therapy in animal models of diabetic erectile dysfunction

Ref.	Animal model (species, age, n number)	ED model	Evidence of previous DE	Type of stem cell	Source of stem cell	Characterization of stem cell	Number of cells injected and site of injection	Modification	Duration of follow-up	Parameter of therapy	Conclusion
Garcia et al[68]	10-wk-old Zucker (fa/fa) rats; n = 10 in each group (ADSCs and control)	Obese and type 2 diabetic rats with ED	Yes, CN electrostimulation	ADSCs; Autologous	Perigonadal adipose tissue	Not clear	1 × 106/IC	None	3 wk	ICP-MAP, nNOS, corporal body collagen, and corporal body endothelial cell	ADSCs improve ED
Liu et al[57]	10-wk-old male Sprague-Dawley rats; n = 12 in each group (lentivirus-VEGF, GFP ADSCs, VEGF/GFP ADSCs, control)	Type 1 diabetes induced by streptozotocin with ED	Yes, APO procedure	ADSCs; Allogenic	Bilateral groin	Yes, by flow cytometry	1 × 106/IC	VEGF, GFP	3 wk	ICP-MAP, VEGF, and e-NOS in vivo Endothelial, smooth muscle, and pericyte marker	Injection of ADSCs expressing VEGF displayed more efficiently and significantly raised ICP-MAP and increased endothelial markers
Ouyang et al[55]	Male Sprague-Dawley rats unspecific age; n = 10 in control group, n = 15 in each treatment group (USCs, lentivirus FGF2, USCs-FGF2)	High-fat diet following streptozotocin-induced diabetes	Yes, APO procedure	HUDSCs	Human urine	Yes, flow cytometry (CD24, CD29, CD31, CD34, CD44, CD45, CD73, CD90, CD105, CD146)	1 × 106/IC	FGF-2	4 wk	ICP-MAP, expression of endothelial markers (CD31, VEGF, and eNOS), smooth muscle markers (desmin and smoothelin), histological changes	USCs or USCs-FGF2 improved erectile function in type 2 diabetic rats
Li et al[69]	8-wk-old BALB/c mice; n = 8 in each group (control and treatment)	Streptozotocin-induced diabetes with ED	Not clear	BMSCs; Allogenic	Unspecified bone marrow	Yes, by flow cytometry. Identification with Sca-1 micromagnetic, identification of CD29, CD44, CD13, and CD34	Not mentioned	None	3 wk	ICP-MAP, penile histology	Flk-1 Sca-1 MSCs differentiate into skeletal and endothelial cells in vivo and in vitro
Liu et al[45]	Male Sprague-Dawley rats with no mentioned age; n = 10 in each group (negative control, ADSCs, ADSCs + hepatocyte growth factor)	Streptozotocin-induced diabetes with ED	Not clear	ADSCs	Not mentioned	Yes	2 × 106/IC	Hepatocyte growth factor	4 wk	ICP-MAP, smooth muscle, and endothelium (PECAM-1, SMA), apoptotic index	Significantly enhance the erectile function
Wang et al[70]	10-wk-old Male Sprague-Dawley rats; n = 15-16 in each group (control, normoxia AMCS, and hypoxia AMCS)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs; Allogenic	Inguinal adipose	Yes, fluorescent-activated cell sorting (CD90, CD29, CD34, CD45)	1 × 106/IC	Normoxia-hypoxia	4 wk	ICP-MAP, n-NOS, endothelial and smooth muscle histology	Hypoxia AMSCs improved ICP-MAP, nNOS. Hypoxia AMSCs condition effective to enhance theuraphetic effect of ED
Kovanecz et al[71]	7-mo-old Zucker (fa/fa) rats; n = 8 in each group (untreated, early diabetic treated with SC, early diabetic with high glucose treated with SC, late diabetic treated with SC, non-diabetic untreated)	Not mentioned specifically	Not clear	MSDCs; Allogenic	Hindlimb muscles	Not clear	1 × 106/IC	Early and late diabetes	8 wk	ICP-MAP, nNOS-eNOS, collagen ratio, calponin, inflammation marker	Stem cell decreased collagen and fat infiltration, upregulated nNOS-eNOS, and improved erectile function
Ryu et al[46]	12-wk-old C57BL/6J mice; n = 6 in each group (control, diabetic, diabetic with PBS, and diabetic with BMSCs)	Streptozotocin-induced diabetic mouse	Not clear	BMSCs; Allogenic	Tibiae and Femur	Yes, flow cytometry (CD3, CD44, CD45, CD103, CD105, CD117, MHC-1, and Sca-1)	3 × 105/IC	None	2 wk	e-NOS-nNOS, endothelial and smooth muscle content histology	BMSCs improved significant recovery of erectile tissue
Zhou et al[48]	8-wk-old male Sprague-Dawley; n = 5 in each group (negative control, ASCs + ad-luc-myocardin, ASCs + ad-luc, ED without treatment)	Streptozotocin-induced diabetic mouse	Not clear	ADSCs; Autologous	Paratesticular fat tissue	Not clear	1 × 106 ADSC/IC	Insulin and neutral protamine hagedorn	4 wk	ICP-MAP, AGEs, and RAGE; growth factors and cytokine in penis	ADSCs combined with insulin improved erectile function and pathological changes
Wang et al[52]	10-wk-old male Sprague-Dawley rats; n = 14-15 in each group (negative control, icariin, ADMSCs, ADMSCs + icariin)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs; Allogenic	Inguinal adipose	Yes, fluorescent-activated cell sorting (CD90, CD29, CD34, CD45)	1 × 106/IC	Icariin	4 wk	ICP-MAP, histology and immunohistology of penis tissue, intracellular ROS levels	Icariin-enhanced ADSCs in erectile function Icariin could protect ADSCs against oxidative stress
Zhou et al[50]	8-wk-old male Sprague-Dawley rats; (n = 8 in control, n = 20 in treated groups)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs; Allogenic	Paratesticular fat tissue	Not clear	1 × 106 ADSC and 1 × 104 ADSCs per MT/IC	Microtissues (MTs)	4 wk	ICP-MAP, nNOS, smooth and endothelial content histology	MTs improved histopathology and erectile function rather than traditional ADSC
Zhu et al[49]	10-wk-old male Sprague-Dawley rats; n = 8-10 in each group (non-diabetic controls, diabetic with PBS, ADSCs, ADSCs + Magnetic application	Streptozotocin-induced diabetic mouse	Not clear	ADSCs; Autologous	Paratesticular fat tissue	Yes, by flow cytometry (CD34, CD45, CD44)	1 × 106 ADSC	Magnetic iron oxide nanoparticle	4 wk	ICP-MAP, contents, smooth muscle (α-SMA), endothelium (von Willebrand factor), VEGF	ADSCs improved erectile function External magnetic field improved efficiency of labeled ADSC in the corpus cavernosum
Jeon et al[56]	8-wk-old male Sprague-Dawley rats; n = 12 in each group (control, DM ED, BM-MSC, SDF-1 (stromal cell-derived factor-1)	Streptozotocin-induced diabetic with ED	Not clear	BMSCs	Not mentioned	Not mentioned	1 × 106/IC	SDF-1	4 wk	ICP-MAP, nNOS-eNOS, FGF-VEGF in vivo	SDF-1 improved ED recovery and smooth muscle content, increased nNOS-eNOS, FGF-VEGF
Chen et al[42]	Male Sprague-Dawley rats with unspecific age; n = 10 in each group (ADSC, BMSC, and control)	ED in type 2 rats with diabetes induced by high-fat and high-sugar diet and streptozotocin	Yes, by APO procedure	ADSCs and BMSCs; Allogenic	Medullary cavity of femur, tibia, and fibula	Yes, by flow cytometry Identification with CD34,CD45,CD73,CD90, and CD105	1 × 106/IC	None	2 wk	ICP-MAP, number of blood vessels, collagen	Stem cell improved ICP-MAP, increased the number of blood vessels, and reduced collagen content
Ouyang et al[72]	Male Sprague-Dawley rats with unspecific age; n = 8 in each group (control and treatment)	Streptozotocin-induced diabetes	Yes, APO procedure	HUDSCs	Human urine	Yes, flow cytometry and Western blot (CD63 and protein calnexin)	Not mentioned	None	4 wk	ICP-MAP, eNOA, phospho-eNOS, nNOS, and endothelial markers (CD31)	Human-derived stem cells improved ICP, eNOS, nNOS, and endothelial markers
Zhang et al[51]	Male Sprague-Dawley rats; n = 10 in each group (negative control, ASCs + ad-luc-myocardin, ASCs + ad-luc, ED without treatment)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs; Allogenic	Inguinal fat tissue	Yes, flow cytometry (CD29, CD90, CD34, and CD45)	1 × 106/IC	Ad-luc-myocardin modified	3 wk	ICP-MAP, collagen and smooth muscle histology: myocardin, collagen 1, cleaved caspase 3, α-SMA, and calponin	Myocardin enhanced therapeutic for ASCs for ED in diabetic mouse
Zhang et al[58]	CCECs culture, not specific rats; n = 15 each group (case and control)	CCECs treated with advanced glycation end products and streptozotocin-induced diabetic mouse	In vivo CCECs mimicking diabetic and APO procedure	HUDSCs	Human urine	Yes, by flow cytometry (CD24, CD31, CD34, CD44, CD45, CD73, CD90, CD105)	Not mentioned	None	4 wk	ICP-MAP, eNOS, p-NOS, VEGFRA, VEGFR2, authophagic flux	Urine stem cell improved cavernosal endothelium through upregulated authophagic activity
Zhang et al[47]	8-wk-old male Sprague-Dawley rats; n = 9 in each group (control group, DM with ED, ADSCs, ADSCs-EFGP, ADSCs + iNOS)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs; Allogenic	Inguinal fat tissues	Yes, by flow cytometry (CD2, CD31, CD49, CD90, CD106, CD34, CD45, CD73)	5 × 105/IC	EFGP and iNOS	2 wk	ICP-MAP, endothelial and smooth muscle content marker (NO, collagen-I, collagen IV, TGF-β, β- actin)	ADSCS-iNOS significantly reduced penile fibrosis
Song et al[54]	Male Sprague-Dawley rats; n = 7-8 in each group (BMSC-EXO, ADSC-EXO, CCSMC-EXO, control)	Streptozotocin-induced diabetic mouse	Yes, APO procedure	ADSCs and BMSCs; Allogenic	Inguinal adipose and rat femoral	Yes, flow cytometry (CD29, CD34, CD45, and CD90	100 μg of exosome/IC	Exosome CCSMC	4 wk	ICP-MAP, α-SMA collagen, TGF-β1, β-actin, e-NOS, and n-NOS, NO, and cGMP	CCSMC-EXOs improve erectile function, reducing collagen deposition and expression of eNOS-nNOS, NO, and cGMP
Wang et al[53]	Male Sprague-Dawley rats with unspecified age; no data on n number, four experimental groups in total (negative control, DM, DM + ADSC-EXO, DM + siCorin-ADSC-EXO)	Streptozotocin-induced diabetic mouse	Yes, but not mention what method	ADSCs; Allogenic	Not Mention	Yes, CD29, CD90, CD44, CD105, and von Willebrand factor	100 μL of exosome from ADSCs/IV	siCorin ADSC-EXO	2 wk	ICP-MAP, neurovascular function (ANP, BNP, nNOS, cGMP, β-actin) , inflammatory factor (IL6, IL1β), expression, delivery of corin	ADSC-EXO enhanced endothelial recovery and decreased inflammatory process

APO: Apomorphine; ADSCs: Adipose-derived stem cells; BMSCs: Bone marrow stem cells; CCECs: Cavernosal vascular endothelial cells; CCSMC: Corpus cavernosal smooth muscle cell; DM: Diabetes mellitus; ED: Erectile dysfunction; HUDSCs: Human urine-derived stem cells; IC: Intracavernosal; ICP-MAP: Intracavernosal pressure-mean arterial pressure; MSCs: Muscle-derived stem cells; PMSCs: Placental matrix stem cells.

Table 2 List of articles on stem cell therapy in humans with diabetic erectile dysfunction

Ref.	Study subject and n number	Type of ED	Evidence of previous DE	Type of stem cell	Source of stem cell	Stem cell characterization	Number of cells injected and site of injection	Modification	Duration of follow-up	Parameter of therapy	Conclusion
Bahk et al[61]	Impotent diabetic type 2 patients range from 57 yr to 87 yr; n = 7 in treated groups, n = 3 in controls.	Diabetic ED	Yes, by clinical diagnosis and other parameters	UCBSCs; Allogenic	Umbilical cord	Yes, by flow cytometry (CD13, CD14, CD34, CD31, CD45, CD44, CD49e, CD54, CD90, CD106, and HLA-DR)	1.5 × 107/IC	None	9 mo	IIEF-5, SEP, GAQ, erection diary, blood glucose diary	Umbilical cord blood stem cell had positive effects on ED
Levy et al[59]	Men aged 40-70 yr who had organic ED at least 6 mo; n = 8	Diabetic ED	Yes, by clinical diagnosis and other parameters	PM-MSCs; Allogenic	Placenta	Not clear	1 mL PM-MSCs /IC	None	6 wk, 3 mo, 6 mo	Peak systolic velocity, end-diastolic velocity, stretched penile length, penile width, IIEF-5	The treatment may be beneficial
Al demour et al[60]	Men aged 25-65 yr who had ED at least 6 mo; n = 4	Diabetic ED	Yes, by clinical diagnosis and other parameters	BMSCs; Autologous	Iliac crest	Yes, positive for CD90, CD105, CD73, and CD44	15 × 106/IC	None	2 yr	IIEF-5, EHS	Stem cell effective and improved erectile function
Protogerou et al[62]	Male with ED due to DM, hypertension, hypercholesterolemia, and Peyronie’s disease; n = 5 in each group (control and ADSC treated)	Diabetic ED	Yes, by clinical diagnosis	ADSCs; Autologous	Not mentioned	Yes, alizarin red S and alcian blue staining, flow cytometry	2 × 105/IC	None	3 mo	IIEF-5, penile triplex	No difference in IIEF-5 between the case and control group, but significant between before and after treatment in both groups

ADSCs: Adipose-derived stem cells; BMSCs: Bone marrow stem cells; ED: Erectile dysfunction; GAQ: Global assessment questions; IIEF-5: International index of erectile function; PMSCs: Placental matrix stem cells; SEP: Sexual encounter profile; UCBSCs: Umbilical cord blood stem cells.