THE EFFECTS OF LOW LEVEL LASER THERAPY ON PROLIFERATION AND DIFFERENTIATION OF MESENCHIMAL STEM CELLS: A LITERATURE REVIEW

Utilization of a low-energy light intensity within the visible red and near infrared portion of the electromagnetic spectrum has been shown to stimulate irradiated cellular activity. This phenomenon has been referred to as photobiomodulation (PBM) or low level laser therapy (LLLT). Many cellular responses have been observed after photobiomodulation, including increase of mitochondrial respiration and ATP production, the synthesis of proteins and cell migration, proliferation and differentiation. Few studies have investigated the use of LLLT on Mesenchimal stem cells (MSCs) in order to promote proliferation and/or differentiation. The aim of this literature review is to highlight the current findings about the effects of PBM on proliferation and differentiation of mesenchimal stem cells. The parameters used to perform LLLT will also be evaluated. The electronic search was conducted with PubMed database for English-language articles published until May 2019. Following 14 MeSH terms and keywords were used in combination and/or separately: Low Level Laser Therapy; Low Level Light Therapy; Low Level Laser Irradiation; Low Level Light Irradiation; LLLT; LLLI; Stem Cells; Bone Marrow; Adipose; Periodontal Ligament; Dental Pulp; Mesenchymal; Cell Proliferaton; Cell Differentiation. The selection of studies was initiated by the review of articles’ titles and the eligible papers were classified as in vivo or in vitro experimental studies which assessed the use of PBM on dental (DMSC), adipose (ADSC) or bone marrow (BMSC) stem cells in order to promote their proliferation and/or differentiation. Articles without a case-control design were excluded. Articles found after first research were 430 and 338 papers were excluded after screening of titles and abstracts. Fifty-nine papers were excluded after full text analysis. From the preliminary list of papers, 33 articles met the search criteria and were included in the present review. All reviewed papers showed positive outcomes both for proliferation’s and differentiation’s rates exept for two. In vivo studies were 7 (21%), while in vitro studies were 26 (79%); 31 papers evaluated proliferation rate and 16 papers (48,5%) evaluated differentiation rate. The most widely used stem cells were BMSC (13 papers, 39,4%). Results shows that most frequently PBM was performed with diode laser (InGaAlP) (13 papers, 39,4%), with visible wavelengths of 660nm (17 papers, 52%) and Fluence values between 0.5 e 5 J/ (24 papers, 73%). Low-level laser therapy has positive and stimulatory effects on the proliferation and differentiation of stem cells. With the appropriate use of LLLT the proliferation and/or differentiation rate of cultured stem cells (MSCs), can be increased, which would be very useful in tissue engineering and regenerative medicine.