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A potential molecular pathway mediating the nexus between inflammation and wound healing in oral tissues.

overview _ LLLT I Our clinical study recruited 30 patients sched- uled to undergo multiple extractions for complete dentures. Following institutional ethical approval and obtaining informed consent, two sites in each patient were used in our study, each patient acting as their own control. Following tooth extraction, one site was irradiated with a 10 mW, 904 nm GaAs laserincontactfor5minforatotaldoseof3J/cm2 . A small soft tissue biopsy was obtained from the two sites and wound healing parameters like in- flammatory infiltrate, vascularity, matrix synthe- sis-organization and TGF- 1 expression were as- sessed using routine histopathology and im- munostaining. We observed a better organized healingresponseinlaserirradiatedoraltissuesand it is significant to note that the laser accelerated healing did not preclude any normal wound heal- ing phase, demonstrating all the usual phases but seem to occur at a more rapid pace (Fig. 1). This ac- celerated laser healing correlated with an in- creased expression of TGF- 1 immediately post laser irradiation. A major regulatory step in defin- ing the physiological role of TGF- invivo is its ac- tivation from a naturally-secreted latent complex. Various physico-chemical modalities like heat, ex- treme pH, proteases and reactive oxygen species (ROS) that all induce a change in the conformation of the latent complex causing dissociation and, hence, activation of the TGF- 1 dimer. Therefore, the ability to activate the latent TGF- (LTGF- 1) complex would provide a precise and natural man- ner of exploiting its role in various biological processes. The histological analysis from our clini- cal study suggested that a potential source of LTGF- 1 could be the abundant degranulating platelets from the serum present in the early woundenvironmentthatareamongknownpotent sourceofinvivoLTGF- 1.Wethenusedacell-free systemwithserumandassessmentbyanisoform- specific ELISA and a reporter based (p3TP) assay system to demonstrate the ability of LLLT to acti- vate the latent TGF-beta complexes in vitro at varying fluences from 10 sec (0.1 J/cm2 ) to 600 secs (6 J/cm2 ). We conclude that activation of la- tent TGF- 1 by LLLT could contribute to the pho- tobiomodulatory effects and promote oral wound healing.18 _Potential mechanisms of LLLT on inflammation and healing DespitetheincreasedclinicalpopularityofLLLT due to its non-invasive, physiological mode of ac- tion, lack of information on the precise molecular mechanisms and well-controlled clinical trials have prevented LLLT from being more widely ac- cepted as a routine treatment option. LLLT broadly utilizes wavelengths in the red and near-infrared spectrumtochangeintra-cellularphotoreceptors such as endogenous growth factor complexes, porphyrins, flavins, surface transmembrane re- ceptors and cytochrome c oxidase in the respira- tory chain. To broadly categorize these intermedi- ates, we outline a putative hierarchical level of in- teraction from the literature in the context of the LLLT and cell-tissue compartments (Figure 2). Our work with a latent growth factor complex Transforming Growth Factor- (TGF- ), a multi- faceted cytokine, and LLLT has unraveled one such molecular pathway providing an attractive mo- lecular mechanism for photobiomodulation.18 TGF- plays key roles in biological processes like development, wound healing and malignancies andhasamyriadrangeofeffectsbasedonitsspa- tio-temporal expression on a wide range of cells from epithelial keratinocytes to fibroblasts, en- dothelial,neuralandinflammatorycells.Theintri- cate role of TGF- on inflammatory cell subsets displays a fascinating dichotomy between its im- mune-suppresser versus immune surveillance functions and is an ongoing area of intense lab in- vestigation. Interestingly, although primarily identified as a pro-matrix, fibrosis promoting wound cytokine, TGF- transgenic mice have shown a startling variety of healing phenotypes further indicating its diverse roles on epithelial migration and survival, chemotaxsis of mono- cytes-macrophages and mechanical homeostasis of the matrix milieu.19 The activation of such a multifaceted growth factor by LLLT with its broad effects on various component of inflammatory- healingprocesscould‘short-circuit’or‘kick-start’ the complex cascade of biological events effect- ing the eventual healing and regenerative out- comes. Clinically, one of the most attractive fea- tures of exploiting this mechanism is the activa- tion of endogenous levels of TGF- and thus, potentially only gently nudging the natural phys- iologicalprocessalong,withoutamajorperturba- tion of the biological system as seen with addition of exogenous factors. We speculate that there might be more such latent molecular complexes amenabletolowpowerlasermodulationinthein- flammatory and early wounding scenarios. Our present research has established that the photo- physical and photochemical events can correlate with large magnitudes of laser fluences. In con- trast, the photobiological events are tightly lim- ited within a narrower range of laser fluences through an unknown biological regulatory mech- anism.Thismechanismalongwithpotentialchro- mophores, wavelength and fluence parameters affecting the latent TGF- activation process by LLLT for oral wound healing and other biological applications are our present focus of research. laser2_2010