Efficacy of stem cells in bone rehabilitation in patients with alveolar bone atrophy: a systematic review.

BACKGROUND: Biomedical engineering proposes the use of stem cells as a bone rehabilitation treatment in patients with alveolar bone defects. Many authors suggest that this innovative technique could represent the future of bone regeneration in dentistry. The present study systematically reviewed the efficacy of stem cells in bone regeneration in patients with alveolar bone atrophy. MATERIAL AND METHODS: The study was developed following the criteria of the PRISMA guideline (2020). The literature review was conducted in Pubmed, Medline Complete, and Scopus. The search algorithms used the following key words: stem cells, bone regeneration, and alveolar ridge augmentation. To assess the risk of bias, the CASPe methodology was used. RESULTS: Seven clinical trials in humans were included in this systematic review. In all the studies, the proposed objective of bone regeneration by using stem cells was achieved, although in a different way with different results. Although the authors of the analysed clinical trials achieved favourable results, they highlighted the presence of multiple limitations throughout bone regeneration treatments, such as scarce scientific literature on stem cells, a reduced number of follow-up studies, and a lack of a standardized international protocol. CONCLUSIONS: Based on the analysed studies, it is concluded that the therapy proposed by tissue engineering through the use of stem cells to rehabilitate patients with bone atrophies can be considered effective. In addition, the need for further studies and standardization of protocols is highlighted.

Different ß-adrenoceptor subtypes coupling to cAMP or NO/cGMP pathways: implications in the relaxant response of rat conductance and resistance vessels.

BACKGROUND AND PURPOSE: To analyse the relative contribution of ß1 -, ß2 - and ß3 -adrenoceptors (Adrb) to vasodilatation in conductance and resistance vessels, assessing the role of cAMP and/or NO/cGMP signalling pathways. EXPERIMENTAL APPROACH: Rat mesenteric resistance artery (MRA) and aorta were used to analyse the Adrb expression by real-time-PCR and immunohistochemistry, and for the pharmacological characterization of Adrb-mediated activity by wire myography and tissue nucleotide accumulation. KEY RESULTS: The mRNAs and protein for all Adrb were identified in endothelium and/or smooth muscle cells (SMCs) in both vessels. In MRA, Adrb1 signalled through cAMP, Adrb3 through both cAMP and cGMP, but Adrb2, did not activate nucleotide formation; isoprenaline relaxation was inhibited by propranolol (ß1 , ß2 ), CGP20712A (ß1 ), and SQ22536 (adenylyl cyclase inhibitor), but not by ICI118,551 (ß2 ), SR59230A (ß3 ), ODQ (soluble guanylyl cyclase inhibitor), L-NAME or endothelium removal. In aorta, Adrb1 signalled through cAMP, while ß2 - and ß3 -subtypes through cGMP; isoprenaline relaxation was inhibited by propranolol, ICI118,551, ODQ, L-NAME, and to a lesser extent, by endothelium removal. CL316243 (ß3 -agonist) relaxed aorta, but not MRA. CONCLUSION AND IMPLICATION: Despite all three Adrb subtypes being found in both vessels, Adrb1, located in SMCs and acting through the adenylyl cyclase/cAMP pathway, are primarily responsible for vasodilatation in MRA. However, Adrb-mediated vasodilatation in aorta is driven by endothelial Adrb2 and Adrb3, but also by the Adrb2 present in SMCs, and is coupled to the NO/cGMP pathway. These results could help to understand the different physiological roles played by Adrb signalling in regulating conductance and resistance vessels.