The anti-inflammatory and osteoinductive effect of Simvastatin, possibilities of its use for treatment of periodontal diseases

Introduction

Nowadays the number of patients with diagnoses: "gingivitis and periodontal disease (K05)", " partial teeth loss (K08.1)", "the alveolar crest atrophy (K08. 2)" still increase. So various methods aimed to improve the therapy effectiveness for patients with these diagnoses analyzing and searching are very important. The surgical and drug-induced methods of jaw bone tissue restoration treatment is successful using is convincingly confirmed in clinical practice. Also, technologies for potentiating the osteoinductive properties of osteoplastic materials to restore bone volume to have been in progress now [1,2]. Thus, data based on experimental work aimed on anti-inflammatory therapy and osteogenic differentiation of mesenchymal stem cells (MSCs) were collected and analyzed in this literature review. There are many experimental and clinical researches studying as the bone regeneration stimulation as anti-inflammatory response in the periodontal diseases’ treatment. The one of the new and promising areas of regenerative action is the inclusion in the osteoplastic materials composition statins as in individual form as in combination with MSCs. Statin drugs usually are used for reduction the cholesterol systemic level during the atherosclerosis treatment and prevention. Statin drugs action is based on the inhibition of hydroxymethylglutaryl-coenzyme A-reductase in the liver, one is involved in the cholesterol synthesis through the mevalonic acid cycle. Statins are structural analogues of hydroxymethylglutaryl-coenzyme A-reductase. So, statin drugs function is used to reduce the risk of atherosclerotic plaque formation and is actively used in various cardiovascular system diseases.

Some scientists have identified other statins functions and usage domain. The decreasing in the number of limb fractures and a strong bone mineral density against the statin therapy background were shown in retrospective cohort studies and meta-analysis studies. Data from 45,342 people aged 50 to 90 years who were treated with statins from January 1, 2001 to December 31, 2013 were selected from the Taiwan Health Insurance Research database. The control group data consisted from 115,594 patients who did not receive statin therapy. Over the course of 13 years, 16,146 (10.03%) of all subjects included in the study developed osteoporosis: 3,097 (6.83%) statin users and 13,049 (11.29%) non-statin users. Overall, statin therapy reduced the risk of osteoporosis by 48% [3]. Correlation between osteoporosis and hypercholesterolemia by W. Wei et al. (2015) is associated with the induction of the pituitary endogenous estrogen α-receptor. Cholesterol is an agonist of this nuclear receptor. Thus hypercholesterolemia can lead to osteoporosis through the induction of the endogenous estrogen α-receptor [4]. So, hypercholesterolemia is a risk factor in patients with bone pathology [5]. But despite of the positive Simvastatin effects on bone tissue, it is necessary to take into account the treatment duration and individual dose [6], the Simvastatin bioavailability for bone tissue [7].

Also there are some studies about the genetic relationship between simvastatin and malformations of the maxillofacial region. Thus it was shown, that metabolic cholesterol disorders are caused by a the DHCR7 gene violation (which is involved in cholesterol synthesis) and the proteins INSIG1 and INSIG2 (which provide cholesterol biosynthesis down-regulation) in the Suzuki., et al., (2020) experimental work. Such enzymes lead to osteoblast differentiation disorders. But it was shown that the normalization of these processes was achieved while the cholesterol metabolism normalization using the Simvastatin [8]. Also there is also data on KLF4 protein inhibition by Simvastatin with followed decrease in metastasis [9], apoptosis of neoplastic cells [10] and increasing of the polycythemia combined treatment effectiveness [11]. In the work by A. Horecka et al. (2016) was made an assumption that Simvastatin using in the osteoarthritis treatment in menopausal women has a positive effect. The authors have found a positive correlation between the concentration of calcium and silicon in the blood of patients who took Simvastatin for more than 1 year [12].

The Simvastatin anti-inflammatory effect proved in the work by Lin C. P. (2016). Simvastatin reduces the increase in serum TNF-α, soluble TNFR1, 3-nitrothyrosine. Proinflammatory cytokines, oxidative stress, and TNFR1 play a role in inducing aortic calcification. In the work by C. P. Lin et al. (2015) human aortic smooth muscle cells were used for investigating the TNF-α, oxidative stress, and TNFR1 role in inducing aortic calcification and to clarify the mechanism by what Simvastatin protects aorta from calcification. Also it was shown that human aortic smooth muscle cells processing with TNF-α leads to the accumulation of Ca2+ in the cells, anв increasing in the activity of alkaline phosphatase, NADP oxidase, NF-kB subunit p65, BMP2, MSX2, and the expression of RUNX2. So, Simvastatin suppressed TNF-α-induced activation of the NADP oxidase subunit p47, the previous mentioned bone markers, and TNFR1 expression. Also p65, p47, and TNFR1 mRNAs inhibited TNF-α-mediated stimulation of BMP2, MSH2, and RUNX2 expression. Simvastatin, apocynin, and acetylcysteine partially inhibit or completely block TNF-α-induced formation of H2O2 or superoxide. Such results suggest that Simvastatin, regardless of its cholesterol-lowering effect, suppresses the progression of vascular diseases by inhibiting the inflammatory mediators TNF-α and TNFR1 [13]. But there were noted some negative effects in the systemic Simvastatin using. One can disrupt bone marrow thrombopoiesis and leukopoiesis [14, 15]. The main side effect of statin-type drugs is rhabdomyolysis [16], but there is also evidence that Simvastatin has a negative side effect on muscle tissue [17]. Because of the low half-life period, and risk of side effects, statin-type drugs are ineffective and not rational for systemic using in relation to bone tissue. Therefore, the idea of their local application to optimize the reparative regeneration of the jaw bones was put forward. In the work by G. Mundy et al.(1999) was shown the effect of statins on the new bone formation was demonstrated by subcutaneous Simvastatin administration in the area of a bone defect in mice [18]. Nowadays there are many directions for Simvastatin effects studying on dental problems. For example, in the review by Gupta S., et al. (2019) was shown that the Simvastatin administration demonstrates positive results in the treatment of periodontal infection, alveolar bone regeneration, soft tissue transplantation, relief of inflammatory processes in the temporomandibular joint and cartilage regeneration [19]. Treatment of reversible pulpitis with a conservative method of direct Simvastatin application to the pulp horn also showed a positive result [20].

Simvastatin, cell differentiation

Any cell in the human body goes through certain stages for full formation, in other words, differentiates. Both certain conditions and growth factors are necessary for cell differentiation. Currently, there are many studies on inducing the MSCs differentiation of on various vectors and in combination with growth factors [21, 22].

In the work by Nantavisai S. et al. (2019) the ability of Simvastatin in small dosages (0.1 and 1 µmol / L) to induce MSCs differentiation was demonstrated. On the other hand, at high dosages (10 and 100 µmol/l) one is the inhibitor of MSC differentiation, with a parallel inflammatory response. The research authors emphasized the work of simvastatin-induced differentiation using markers: the cell cycle regulators Cyclin D1 and Cyclin D2, the proliferation marker Ki-67, and the anti-apoptotic gene Bcl-2.The pluripotent markers ZFP42 and Oct-4 also tended to increase when using low doses [23]. So there is a certain criteria in the Simvastatin dose-dependent effect on the MSCs differentiation. However, there are other data on Simvastatin-induced cell differentiation. For example, Babakhani A. et al. (2019) showed in an "in vitro" experiment a positive Simvastatin effect on the differentiation of hair follicle stem cells into epithelial cells. The Simvastatin-inducing doses for differentiation and comparison were 1, 2, and 5 µmol/l. To assess the cells activity, a colorometric MTT test was used (it reflects the cells metabolic activity). It was shown that the most productive results were obtained at a Simvastatin dose of 5 µmol/L [24].

In the study by Shao P. L. et al. the MSCs osteogenic differentiation under the Simvastatin is associated with the integrin-a5 gene expression. Alizarin red staining and PCR studies were used to assess osteogenic differentiation. An increase in the concentration of alkaline phosphatase, calcium precipitation and quantitative levels of the integrin-a5 expression mRNA and osteogenic gene markers (BMP2, RUNX2, type I collagen, alkaline phosphatase, and osteocalcin) was detected [25]. By Zanette D. L. et al. (2015) MSCs from amniotic fluid and bone marrow were isolated and characterized based on the criteria of the International Society for Cell Therapy (ISCT). Simvastatin-treated cells and control cells were stained to assess proliferation, and their RNA was used for PCR analysis. As a result, MSCs treated with simvastatin showed a larger number of cells in one population, which indicates slow aging and induced differentiation of MSCs under the Simvastatin [26].

In experimental work by R. Wu et al. (2015) took into account the indirect revascularization of bone defects and the differentiation of MSCs under the Simvastatin. In the control group of 39 patients, the operation was performed only with the MSCs mobilization, and 39 patients in the experimental group were given Simvastatin injections a week after operation. The Simvastatin positive effect on the MSCs differentiation by the number of hematopoietic progenitor cells in the peripheral blood mononuclear cells of patients was demonstrated [27].

The researh by Tai I. C. et al. (2015) showed that statins cause osteogenic differentiation both "in vitro" and "in vivo". Activation of RhoA signaling increases cytoskeletal tension, which plays a crucial role in osteogenic MSCs differentiation. The authors suggested that RhoA signaling is involved in Simvastatin-induced osteogenesis in bone marrow MSCs. It was found that Simvastatin treatment move the RhoA protein localization from the membrane to the cytosol, the dose-dependent Simvastatin using activates RhoA. Simvastatin also increased the expression of osteogenic proteins, actin filament density, the number of focal adhesions and cellular tension. The actin filament density increases with Simvastatin-induced ectopic bone formation as it was shown in "in vivo" study. The authors demonstrated for the first time that maintaining intact actin cytoskeletons and increasing cell stiffness are critical in Simvastatin-induced osteogenesis. The obtained results show that Simvastatin, which is an osteoinductive factor, acts by increasing the organization of actin filaments and cell stiffness in combination with osteoconductive biomaterials, can promote bone regeneration based on stem cells [28].

But one more Simvastatin positive effect of in relation to the MSCs differentiation was shown by G. P. Jahromi et al. (2018). It is known that GABA-Coa reductase inhibitors increase the neurons survival and promote the MSCs migration to inflammation areas. But the exact mechanisms of improved neurological functional recovery in Stokes models after combined Simvastatin and MSCs treatment are still poorly understood. An embolic stroke model was used to induce focal ischemic brain injury by inserting a pre-formed clot into the middle cerebral artery in the experiment. After a stroke, the animals were treated with either intraperitoneal Simvastatin injection, intravenous MSCs injection, or a combination of both. Through 7 days off the combination of Simvastatin and MSCs resulted in a significant increase in MSCs movement, endogenous neurogenesis, arteriogenesis, and astrocyte activation, while reducing neuron damage compared to MSCs alone. These results further demonstrate the synergistic benefits of MSCs and Simvastatin [29].

In the study by Zhang M. et al. (2018) was considered the Simvastatin ability to promote osteogenic MSCs differentiation by modulating the Wnt/β-catenin pathway so to promote fracture healing. Third-generation MSCs were cultured in osteoinduction universe containing Simvastatin with a gradient concentration or with the highest Simvastatin dose that did not cause cell proliferation. The Simvastatin effect on osteogenic differentiation of MSCs was assessed by the activity of alkaline phosphatase, alizarin red staining, and expression of osteoblast-specific genes. A Wnt DKK1 pathway antagonist and a β-catenin-disrupting agent were added to the MSCs to determine the activity of alkaline phosphatase by alizarin red staining of osteoblast-specific MSCs. It was found that the concentration of 0.3 nmol / l is the highest dose that does not cause the MSCs proliferation. After Simvastatin treatment with 0.3 nmol/l of for 7 days, the activity of alkaline phosphatase and the number of calcified cells increased significantly. However the expression of genes associated with osteoblasts: alkaline phosphatase, RUNX2, osteocalcin, and OPN, was elevated. But in cases of MSCs processing with DKK1 for 7 days, the activity of alkaline phosphatase and the expression of genes associated with osteoblasts, including alkaline phosphatase, RUNX2, osteocalcin, and OPN, were reduced. Simvastatin significantly increased the beta-catenin protein expression. So Simvastatin can stimulate the differentiation of rat MSCs into osteoblast-like cells and it could be realised through the Wnt/β-catenin pathway [30].

In the work by Both T. et al. (2018) the direct hydroxychlorine effect on the osteoblasts activity derived from human MSCs was studied. The cultures were processing with different doses of hydroxychlorine (0, 1, and 5 mcg / ml). The activity of alkaline phosphatase and calcium, the osteoblasts differentiation and activity were evaluated. Detailed analysis was performed using micromatrix analysis and PCR. Besides the Simvastatin effect on the MSCs differentiation was compared. It was found out that hydroxychlorine inhibits the differentiation and mineralization of osteoblasts obtained from MSCs "in vitro". Micromatrix analysis and additional PCR revealed a significant activation of the: cholesterol biosynthesis, lysosomal and extracellular matrix, in cells processing with 5 mcg/ml of hydroxychlorine, compared with the control (without processing). In addition, it was demonstrated that Simvastatin at 1 µmol/l also reduces the differentiation and mineralization of osteoblasts obtained from MSCs, compared with the control. So, the hydroxychlorine positive effect on bone mineral density (BMD) cannot be explained by the stimulation of osteoblast differentiation. The mismatch between high BMD and MSCs-derived osteoblasts decreased function due to hydroxychlorine treatment may be caused by systemic factors that stimulate bone formation and /or local factors that reduce bone resorption, which is absent in cell cultures. The work result highlighted the dose-dependent inhibition of MSC differentiation by Simvastatin [31].

Bone marrow-derived MSCs have great therapeutic potential for many diseases. But the MSCs local application is still a complex problem. Simvastatin stimulates phosphorylation of protein kinases B (AKT), and p-AKT affects the expression of the chemokine receptor—4 as it is shown in recently obtained data. The expression of CXCR4 in MSCs and microRNAs could be improved with the Simvastatin using. In a study by W. Bing et al. (2016) was demonstrated that Simvastatin increases both total and surface expression of CXCR4 in MSCs. One also stimulated SDF-1a-induced stromal cell migration, and this action was inhibited by AMD 3100 (a chemokine receptor antagonist for CXCR4). Simvastatin activated the PI3K/AKT pathway. Also the overexpression of LY294002 is caused by Simvastatin. MiR-9 specifically inhibited CXCR4 in MSCs in rats, and Simvastatin reduced MiR—9 expression. p-AKT affected MiR-9 expression; as AKT phosphorylation increased, MiR—9 expression decreased. In addition, LY294002 increased miR-9 expression. Finally Simvastatin improved the migration of MSCs via the PI3K/AKT pathway. MiR-9 was also involved in this process and AKT phosphorylation affected the expression of MiR-9. The authors concluded that Simvastatin could have a beneficial effect in stem cell therapy [32].

Simvastatin and periodontitis

The inflammatory response in the human body is due to cellular-molecular and genetic factors. The periodontal complex alterations to varying degrees lead to immuno-inflammatory reactions. The exudative stage of inflammation is presented by the non-specific immune defense cells migration , proinflammatory cytokines. Bone resorption is the result of vicarious and prolonged inflammatory process in the periodontal tissues. Nowadays more and more facts that periodontitis is associated with a number of chronic diseases, including osteoporosis are developed. Periodontitis and osteoporosis are diseases that are accompanied by a decrease in bone mineral density and one's resorption. Certain inflammatory factors that are also involved in the progression of periodontitis, contributing to the alveolar bone resorption alveolar bone could increase in case of osteoporosis. Simvastatin has pleiotropic effects, including anti-catabolic and anabolic effects on bone metabolism. By X. Xu., et al., (2014) the Simvastatin local and systemic effects on maxillary bone tissue in rats with both osteoporosis and periodontitis was studied. 36 4th — month — old Sprague Dawley rats were selected and randomly divided into six groups: I — control, II — ligature, III — ovariectomized+ligature, IV — ovariectomized+ligature with local Simvastatin administration, V-ovariectomized+ligature with Simvastatin orally, VI-local and oral Simvastatin administration to rats with ligature ovariectomized. 1 month after ovariectomy, ligatures were placed on the maxillary first (M1) and second molars (M2) for 4 weeks in all rats except those in the control group, under the Simvastatin processing for 2 months. For further researches, biopsies of the maxilla, blood serum, and femur were selected. The main research' methods were: microcomputer tomography (micro-CT), histological examination with hematoxylin and eosin staining, tartrate-resistant acid phosphatase staining, enzyme-linked immunosorbent assay, and a three-point bend test. Finally it was found that local Simvastatin administration increased the alveolar crest height and prevented local loss of the alveolar process without changing the systemic bone mass loss. Orally Simvastatin administration prevented local and systemic bone mass loss without affecting the alveolar crest height. By the research results is shown that Simvastatin has the potential to promote bone formation and reduce the loss of the maxillar alveolar process after ovariectomy (ovariectomized) and ligature placement in rats [33].

Diabetes mellitus is known as a risk factor for the development of periodontal pathology varying severity, due to metabolic disorders in the tissues of the periodontal complex. Simvastatin has an anabolic effect on bones. By A. R. Kim et al. (2018) is shown the Simvastatin effect on the bone mass loss mineral density of the tibia and alveolar bone in rats with type I diabetes and periodontitis. Periodontitis was caused by ligature of the first mandibular molars. The rats were orally administered a vector or Simvastatin (30 mg / kg) on the first 3 days, on the 10th and on the 20th day. The alveolar and tibial bones mass loss was recorded using histological analysis and micro-CT analysis. The number of osteoclasts and sclerostin-positive osteocytes in the tibia was investigated using tartrate-resistant acid phosphatase and immunohistochemical staining. The bone mass loss analysis showed that the animals of the control group I, compared with the rats treated with Simvastatin (group II), at all times had a lower bone volume fraction, bone mineral density, surface bone density and the number of trabeculae in the tibia. In the group II an increase in these indicators in the early stages compared to group I were administrated. On day 3, the number of osteoclasts and sclerostin-positive osteocytes in group II on day 3 and 20 was significantly lower than in group I. These results gives an opportunity to suggest Simvastatin to reduce the losing of tibial bone but not alveolar bone mineral density in rats with type I diabetes with periodontitis. The decreasing of the tibial bone mineral density losing due to Simvastatin administration may be associated with the inhibition of osteoclast formation and a decrease in sclerostin expression [34].

In the experimental research by Bahammam M. A., et al., (2018) the relationship between IL—6, TNF-α concentration in the gingival sulcus fluid and also the Visfatin and Simvastatin using in patients with diabetes mellitus and chronic periodontitis were studied. 80 outpatient patients were divided into 4 equal groups: I — healthy periodontitis, II — chronic periodontitis and type II diabetes, III — chronic periodontitis, IV — chronic periodontitis and type II diabetes with Simvastatin therapy. Distribution were based on the bone volume loss X-ray picture, levels of clinical symptoms, studies of the periodontal pockets depth examination and gum criteria indicators. In group II, there was a significant increase in the IL—6, TNF-α level and Visphatin compared to group I and III. Reduced ones levels were in group IV. A positive relationship was observed between periodontal parameters and the concentration of IL-6, TNF-α and Visphatin. Periodontal tissue alterations and diabetes have a synergistic effect on increasing the inflammatory cytokines level. Simvastatin may be useful for improving periodontal health in patients with diabetes [35].

A laser therapy as an adjunct one for calcified debris removing and leveling the surface of the tooth roots (SRP, Scaling and Root Planing) in combination with Simvastatin was evaluated by Swerts A. A. (2017). 180 rats with periodontitis in the mandible first molar area were divided into two groups: I — oral Polyethyleneglycol administration; II — Simvastatin orally administration. After 7 days, the ligature was removed, and the animals were divided into subgroups according to the further experiment methods: NT — without treatment; SRP and saline irrigation; SRP; laser therapy. 10 animals in each subgroup were killed on the 7th, 15th, and 30th day. The levels of oxidative stress were analyzed by the severity of tripeptidglutathione, malonaldehyde, and carbonylated proteins. In group II animals, the level of tripeptidglutathione was higher, and malonaldehyde and carbonylated proteins were lower in comparasing with group I. In the intragroup analysis, laser therapy showed less bone mass loss, compared to NT and SRP. In addition, lower bone mass levels were observed in group I animals treated with laser therapy compared to SRP in group II. In conclusion of this study, the laser therapy could be concluded as effective adjuvant treatment in the SRP group, protecting against the occurrence of oxidative tissue alteration and in combination with Simvastatin for reducing the alveolar process mass loss in experimentally induced periodontitis in rats [36].

In the research by S. S. Martande et al., (2017) was made the comparasing of the efficacy of 1.2% Atorvastatin and 1.2% Simvastatin, in addition to SRP, in the treatment of intraosseous defects in patients with chronic periodontitis. 96 patients were divided into 3 groups depending on the treatment method: SRP+Atorvostatin, SRP+Simvastatin and SRP+placebo. The comparasing parametrs were: periodontal index, the dentoalveolar sulcus bleeding index, the depth of periodontal pockets, and the related level of attachment before SRP and after 3, 6, and 9 months of the experiment duration. Bone defects were evaluated radiographically. As Atorvostatin as Simvastatin treatment showed a significant reduction in periodontal pocket depth and relative attachment level than the in placebo group. The Atorvostatin group showed a greater average decrease in the periodontal pockets depth and an average increase in the relative level of attachment compared to the Simvastatin group at 3, 6, and 9 months. After 6 and 9 months of the experiment duration in the Atorvostatin group the more significant decrease in the depth of the radiographic defect was observed in comparasing with the Simvastatin group (by 33.23 and 34.84% and by 30.39 and 32.15%, respectively). Atorvostatin provide the more noticeable improvement in clinical parameters with a higher proportion of reduction in the the radiographic defect depth compared to Simvastatin in the intraosseous defects treatment in patients with chronic periodontitis [37].

In the research by Santos B. F. et al. (2017) the statins as adjuvants for the treatment by SRP of periodontal diseases induced in rats was evaluated. Periodontitis was induced in 90 rats using a cotton thread placed in the left first mandibular molar. After 7 days of induction, the irritant was removed and the animals were divided into three groups: I — without treatment; II — SRP and irrigation with a control gel; III — SRP and irrigation with Simvastatin. From each group, 10 animals were killed 7, 15, and 30 days after treatment. Gum biopsy samples were processed to analyze the expression of matrix metalloproteinase 8 (MMP—8). The rats mandibles were removed and subjected to X-ray and laboratory tests. Group III showed significantly lower MMP-8 expression and significantly lower bone mass loss compared to groups I and II in all experimental periods. In this study, it can be concluded that a topically administered statin was effective as an adjunct in combination with SRP in rats with induced periodontal disease [38].

In a study by Agarwal S. et al. (2016) the efficacy of 1.2 mg simvastatin on a biodegradable controlled-release carrier gel as a supplement to SRP was evaluated. A total of 60 sites with a pocket depth of ≥5 mm, two from each of the 30 patients after SRP, were divided into two treatment groups: I — placebo subgingival, II — simvastatin. Clinical parameters (including periodontal indices) were recorded at the research beginning and after 1, 3 and 6 months experimental duration. The volume of intraosseous defects was evaluated radiologically by measuring the vertical size (INFRA 1) and the angle of the defect (INFRA 2) from the initial level to 6 months. All patients were treated with the drug without any complications. Treatment improved periodontal health in both groups, but there was a significant decrease in PPD and INFRA 1, along with an increase in the level of clinical attachment and INFRA 2 in group II. An unexpected 5 mm reduction in INFRA 1 was detected at one site. Local delivery of simvastatin enhances the beneficial effect of SRP, in terms of reducing the periodontal pocket, increasing the level of clinical attachment and restoring the intraosseous defect in periodontal diseases [39].

Grover H. S. et al. (2016) also highlighted the effect of Simvastatin, a cholesterol-lowering drug, on bone metabolism and suggested a complex interaction of Simvastatin with cholesterol metabolites, hormones, inflammatory mediators, and growth factors, which has a direct impact on the degree and severity of periodontitis. The study “in vivo” evaluated the effect of a subgingival-delivered Simvastatin gel (1.2 mg) as a topical agent on clinical parameters and on the content of IL-6, IL-8, and IL—10 in the gingival sulcus fluid in patients with chronic periodontitis. For this purpose, 50 patients were divided into two treatment groups: control (scaling and polishing of roots) and experimental (scaling and polishing of roots with the application of Simvastatin gel). Biochemical and clinical parameters were evaluated after 1 and 3 months. Simvastatin had an inhibitory effect on the pro-inflammatory cytokines IL-6, IL-8, and a stimulating effect on anti-inflammatory cytokines (IL-10) in the gingival sulcus fluid of patients with periodontitis. The use of Simvastatin significantly improved all clinical parameters, except for the relative level of attachment. Thus, the addition of Simvastatin changes the concentration of cytokines further [40].

According to the presented studies analysis results, the Simvastatin positive proliferative effect on MSCs could be considered proven. In most "in vitro" and "in vivo" studies of the Simvastatin effect on the MSCs differentiation, different signaling MSCs differentiation induction pathways were observed (Table 1). The dose-dependent Simvastatin effects are also shown (Table 2). In most described researches, different Simvastatin doses were used. Some authors consider a dosage greater than 1 µmol/l to be toxic and leading to inhibition of MSC differentiation; on the other hand, some consider 5 µmol / L to be the most acceptable dosage. The authors used the criterion of genetic expression of the main bone morphogenetic genes and proteins: RUNX2, BMP2, osteocalcin, alkaline phosphatase, osteoprotegerin while considering the possible MSCs differentiation ways and the Simvastatin effect on them.

Table 1. MSCs differentiation pathway under the Simvastatin.

Table 2. Simvastatin prospect dosages for MSCs differentiation

Conclusion

The experimental studies on the Simvastatin effect on periodontal diseases were considered in this literature review. So, the bacterial plaque removal and subgingival Simvastatin delivery significantly modulate the chemokines present in the gingival sulcus fluid. Also, Simvastatin suppresses the progression of local inflammatory by inhibiting the inflammatory mediators such as TNF-α and TNFR1, IL-6, apartof its cholesterol-lowering effect. Bone mass loss in periodontitis is a complex and unsolved problem of modern surgical dentistry. In this literature review of the literature several studies on the bone mass loss stabilization in periodontitis using combined methods of treatment (SRP, laser therapy) together with Simvastatin are described. The article authors attribute this effect to the osteoclastic resorption stabilization. Clinically, the evaluation criteria for most studies were the concentrations of tripeptide glutathione, malonaldehyde, and carbonylated proteins, bone mass level, periodontal index, dentoalveolar sulcus bleeding index, and computed tomography results. Simvastatin is the promising drug as in the periodontitis treatment, as in bone regeneration in cause of co-using with MSCs and other therapies.