Oxysterols as promising small molecules for bone tissue engineering: Systematic review

Table 3 Descriptive summaries of the identified studies investigating the effect of oxysterols on bone formation in critical-sized calvarial defect models (n = 6)

Ref. (level of evidence)	Species (n)	Surgical model and scaffold(s) used	Experimental groups (n)	Assessment method and time point	Bone regeneration (%):1
Aghaloo et al[17], 2007 (V)	Rat (n = 15)	Regeneration of critical-sized, bilateral parietal defects (5-mm) using PLGA (porosity: 92%) scaffolds supplemented with 20(S)-OHC and 22(S)-OHC.	A. PBS only (control) (n = 12 defects)	Bone regeneration as assessed via µ-CT at 6 weeks of healing.	A. approximately 12%
			B. 70-ng 20(S)-OHC + 70-ng 22(S)-OHC (n = 9 defects)		B. approximately 21%a
			C. 700-ng 20(S)-OHC + 700-ng 22(S)-OHC (n = 9 defects)		C. approximately 22%a
Hokugo et al[30], 2014 (V)	Rat (n = not reported)	Regeneration of critical-sized, right parietal defects (5-mm) using a gelatin hydrogel soaked with 20(S)-OHC or incorporating 20(S)-OHC-containing micelles.	A. No implantation (empty defect) (n = 4 defects)	Percent bone regeneration was not reported; however, via μ-CT observation at 6 wk, “no” bone regeneration was observed in untreated defects, “some” bone formation was noted in the periphery of defects implanted with gelatin hydrogel and gelatin hydrogel + 20(S)-OHC, and “robust” bone formation was observed in defects treated with gelatin hydrogel + 20(S)-OHC-micelle.
			B. Gelatin hydrogel alone (n = 4 defects) (mass not reported)
			C. 20(S)-OHC-gelatin hydrogel (without micelle) (n = 4 defects) (mass not reported)
			D. 20(S)-OHC-micelle-gelatin hydrogel (n = 4 defects) (mass not reported)
Hokugo et al[32], 2016 (V)	Rabbit (n = 25)	Regeneration of critical-sized cranial defect (6-mm; 4 defects/cranium) using a collagen sponge supplemented with rhBMP-2 and/or Oxy49.	A. No treatment (empty defect) (n = 5)	Bone regeneration as assessed via µ-CT at 6 weeks of healing.	A. approximately 10%a
			B. Collagen sponge only (n = 5)		B. approximately 35%
			C. 75-μg rhBMP-2 (n = 5)		C. approximately 65%a
			D. 1-mg Oxy49 (n = 5)		D. approximately 55%a
			E. 10-mg Oxy49 (n = 5)		E. approximately 65%a
Li et al[36], 2017 (V)	Rabbit (n = not reported)	Regeneration of critical-sized cranial defect (8-mm; 4 defects/cranium) using a collagen sponge supplemented with Oxy1332 and/or rhBMP-2.	A. No treatment (n ≥ 6 defects)	Percent bone regeneration was not reported; however, via micro-CT analysis at 6 wk, significantly greater bone formation was observed following treatment with either 10-mg Oxy133 or 7-μg rhBMP-2 relative to treatment with collagen alone.
			B. Collagen sponge only (n ≥ 6 defects)
			C. 7-μg rhBMP-2 (n ≥ 6 defects)
			D. 1-mg Oxy133 (n ≥ 6 defects)
			E. 10-mg Oxy133 (n ≥ 6 defects)
Cui et al[34], 2017 (V)	Mouse (n = 12)	Regeneration of critical-sized, right side cranial defects (3-mm) using MeGC hydrogels supplemented with BMSCs and either SA/Cholesterol or SA/20(S)-OHC sterosomes.	A. No treatment (empty defect) (n = 4)	Bone regeneration as assessed via µ-CT at 6 wk of healing.	A. 7%
			B. SA/Cholesterol sterosome (n = 4) (mass not reported)		B. 31%
			C. SA/20(S)-OHC sterosome (n = 4) (mass not reported)		C. 61%a
Huang et al[38], 2019 (V)	Rabbit (n = 6)	Regeneration of critical-sized cranial defect (6-mm; 4 defects/cranium) using an inorganic bovine bone graft (Bio-Oss) supplemented with SVA and/or 20(S)-OHC.	A. No supplementation (Bio-Oss only; control) (n = 6 defects)	Percent bone regeneration was not reported; however, via histological analysis at 4 wk, bone regeneration was increased following treatment with SVA, 20(S)-OHC, and, especially, SVA + 20(S)-OHC, relative to no supplementation (Bio-Oss only control). A synergistic effect was observed with combinatorial treatment of SVA and 20(S)-OHC.
			B. 0.5-mg of SVA (n = 6 defects)
			C. 1.0-μg of 20(S)-OHC (n = 6 defects)
			D. 0.5-mg of SVA + 1.0-μg of 20(S)-OHC (n = 6 defects)

¹Percent bone regeneration of critical-sized defect.

²Oxy133 and Oxy21 are identical.

^aP < 0.05 compared to PBS only (Aghaloo et al[17]), collagen sponge only (Hokugo et al[32]), or no treatment (empty defect) (Cui et al[34]). rhBMP-2: Recombinant human bone morphogenetic protein-2; PLGA: Poly(lactic-co-glycolic acid); SVA: Simvastatin; OHC: Hydroxycholesterol; µ-CT: Micro-computed tomography; MeGC: Methacrylated chitosan; SA: Stearylamine; BMSCs: Bone marrow-derived mesenchymal stem/stromal cells.