2. Current Insights on Resveratrol Treatment and Periodontal Disease
In this work, we investigated the effects of resveratrol administration on PD progression in preclinical studies. Out of the eleven selected studies, ten evaluated ABL and nine observed improvement of this parameter after resveratrol administration
[19][20][21][22][23][24][25][26][27]. Such results may be related to an improvement of oxidative stress and anti-inflammatory properties
[3][8].
Resveratrol increases the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), which are key components against reactive oxygen species (ROS)
[28]. Moreover, the host response to periodontal pathogens promotes local and systemic elevations of proinflammatory cytokines that alter the expression of the receptor activator of nuclear factor-kappa B ligand (RANKL) on the osteoblast surface
[29]. RANKL is responsible for activating osteoclasts through its interaction with the receptor activator of nuclear factor-kappa B (RANK), initiating bone resorption
[29]. High levels of ROS acting as intracellular signal transducers result in autophagy, which plays a dual role in periodontitis by promoting cell death or blocking apoptosis in infected cells
[30]. In addition, ROS may influence the activation of signaling nuclear factor-κB (NF-κB), resulting in an increase of proinflammatory cytokines and, consequently, stimulating the differentiation of osteoclasts
[30]. Considering that PD can be worsened due to the increase of pro-inflammatory cytokines and ROS, resveratrol acts on both fronts attenuating the progression of this disease
[8].
One of the retrieved studies, Chin et al.
[31] found no significant improvement in ABL in animals treated with resveratrol (even with the largest dose of 25 mg/kg/day). However, the treatment period was maintained for only seven days.
[31]. It is possible that there is some mechanism related to the time of action or even to the administration period of this (prior to or following induction of PD). More studies should be conducted to determine the effective optimal dose and duration needed to attenuate ABL. Regarding toxicity, no side effects were reported for resveratrol consumption in any of the selected studies.
Regarding administration route, only two studies evaluated the injectable administration of resveratrol
[21][27]. Even a single 0.001% (
w/
w) dose delivered one day prior to PD induction promoted ABL reduction, inflammatory profile, and oxidative stress improvements in C57BL/6J wild-type mice
[27]. The highest percentages of ABL reduction were observed in studies where resveratrol was injected
[21][27]. This fact may be related to the reduction of resveratrol bioavailability after gastrointestinal absorption
[32].
The mechanisms involved in resveratrol regulation in periodontal inflammation have not yet been fully elucidated
[21]. It is known that resveratrol can decrease the expression of toll-like receptor type 4 (TRL4) which is activated by lipopolysaccharides (LPS)
[21]. An activation of TLR4 observed in chronic periodontitis increases the production of proinflammatory cytokines
[33]. Another possible mechanism is by increasing anti-inflammatory mediators such as IL-4
[26], as well as a suppression of both matrix metalloproteinase (MMP-2 and MMP-9) and cyclooxygenase-2 (COX-2)
[21]. IL-4 suppress the production of IL-17 and IL-1β
[26], which play an important role in the periodontitis pathogenesis and inhibit both Th1 pro-inflammatory response and bone resorption
[34].
All analyzed studies used rat or mice. Rodent periodontium has a good similarity with humans
[35]. The induction of periodontitis involved the ligature in all experiments. This model has several advantages such as low cost and the possibility of investigation in a wide genetic variety of rodents, besides allowing the exploration of the interaction between the oral microorganisms and host response during the development of periodontitis
[7]. Even though rats are not natural hosts for some bacteria found in human oral cavity, both
A. actinomycetemcomitans and
P. gingivalis have been reported in rodents’ microbiota after ligature
[36][37][38].
Regarding the quality assessment of studies, most of the categories were classified as excellent or average. A previous systematic review
[39] using the ARRIVE guidelines reported that most animal studies lack a clear indication of the reasons for choosing a particular animal model, contributing to a lower score for this item. This item also received the lowest score. This aspect is considered an important criterion for preclinical animal trials
[39]. Thus, even if it is already well-known that some results of studies in rodents can be extrapolated to humans, it is important to highlight the relevance of the model used.
Another ARRIVE item that scored as low in several studies was the “interpretation/scientific implications” since only a few articles commented about the limitations and bias as well as mentioned the 3Rs (replacement, refinement, and reduction) principles adopted in experiments with animal studies. Similar results were also reported by Dereka et al.
[40], in which only 10% of the studies attended this question.
Among the risk of bias assessed, the domains “allocation concealment”, “random housing”, “blinding of participants and personnel”, “random outcome assessment”, and “blinding of outcome assessment domains” presented a high risk of bias or were not clearly described. These same domains were classified as unclear or with a high risk of bias according to the Syrcle tool in previous study
[41]. In a systematic review of animal studies
[39], 40% and 60% of studies presented a high risk of bias and an unclear risk in the “allocation concealment” domain, respectively. Randomized housing during the experiment reduces the bias risk once these conditions (such as lighting, humidity, temperature, etc.) are known to influence study outcomes
[42]. An implementation of a blind evaluation in animal studies is also crucial, especially for subjective measurements
[43].
This systematic review was conducted according to the PRISMA criteria
[44] and the protocol for the preparation, registration, and publication of systematic reviews of animal intervention studies
[45]. In order to minimize bias, each step of searching or ranking was performed by two independent researchers. Additionally, to prevent the exclusion of any article, a careful search was conducted. It is important to emphasize that, in the searches performed, we have not found previous systematic review or meta-analysis studies involving the main question addressed in this study.
The results of meta-analysis demonstrated that, in rats, bone loss was significantly lower due to resveratrol administration. However, only a few studies were eligible for the meta-analysis (seven), and it was not possible to assess the publication bias. Considering the potential benefits of resveratrol on periodontal health, further studies should be conducted investigating the effects of this compound in PD models. In addition, future studies should focus on reducing the risk of bias, especially in the areas related to “allocation concealment” and "blinding of participants and personnel" which contributed to the greatest risk of bias.