Effect of non-surgical periodontal treatment on cytokines/adipocytokines levels among periodontitis patients with or without obesity: a systematic review and meta-analysis

Background The objective of this systematic review and meta-analysis was to evaluate the effects of non-surgical periodontal therapy (NSPT) on inflammatory-related cytokines/adipocytokines in periodontitis patients with or without obesity. Methods We followed the preferred reporting items for systematic reviews and meta-analyses statement and registered the study (CRD42022375331) in the Prospective International Register of Systematic Reviews. We screened randomized-controlled trials and controlled clinical trials from six databases up to December 2022. Quality assessment was performed with RoB-2 and ROBINS-I tools for randomized trials and non-randomized trials, respectively. Meta-analysis was carried out using a random-effect model. Results We included seventeen references in the systematic analysis, and sixteen in the meta-analysis. Baseline results of pro-inflammatory biomarkers, including serum interleukin (IL)-6, serum and gingival crevicular fluid (GCF), tumor necrosis factor (TNF)-a, serum C-reactive protein (CRP)/hs-CRP, and serum and GCF resistin, were higher in obesity subjects than in normal weight subjects. The effect of NSPT with respect to levels of cytokines/adipocytokines, including IL-6, TNF-a, CRP/hs-CRP, resistin, adiponectin, leptin and retinol binding protein 4 (RBP4), were then analyzed in the systematic and meta-analysis. After three months of NSPT, serum (MD = -0.54, CI = -0.62 – -0.46), and GCF (MD = -2.70, CI = -4.77 – -0.63) levels of IL-6, along with the serum RBP4 (MD = -0.39, CI = -0.68–0.10) decreased in periodontitis individuals with obesity. NSPT also improved GCF adiponectin levels after three months (MD = 2.37, CI = 0.29 – 4.45) in periodontitis individuals without obesity. Conclusions Obese status altered the baseline levels of cytokines/adipocytokines (serum IL-6, serum and GCF TNF-a, serum CRP/hs-CRP, and serum and GCF resistin). Then NSPT can shift the levels of specific pro-inflammatory mediators and anti-inflammatory mediators in biological fluids, both in obesity and non-obesity individuals. NSPT can reduce serum and GCF IL-6 levels together with serum RBP4 level in individuals with obesity after 3 months, besides, there is no sufficient evidence to prove that obese patients have a statistically significant decrease in the levels of other cytokines compared to patients with normal weight. NSPT can also increase GCF adiponectin level in normal weight individuals after 3 months. Our findings imply the potential ideal follow-up intervals and sensitive biomarkers for clinical bioanalysis in personalized decision-making of effect of NSPT due to patients’ BMI value. Supplementary Information The online version contains supplementary material available at 10.1186/s12903-023-03383-3.

and anti-inflammatory mediators in biological fluids, both in obesity and non-obesity individuals.NSPT can reduce serum and GCF IL-6 levels together with serum RBP4 level in individuals with obesity after 3 months, besides, there is no sufficient evidence to prove that obese patients have a statistically significant decrease in the levels of other cytokines compared to patients with normal weight.NSPT can also increase GCF adiponectin level in normal weight individuals after 3 months.Our findings imply the potential ideal follow-up intervals and sensitive biomarkers for clinical bioanalysis in personalized decision-making of effect of NSPT due to patients' BMI value.

Background
Periodontitis is a chronic, multifactorial, inflammatory disease related to dysbiotic plaque biofilms and is characterized by progressive destruction of the tooth-supporting apparatus [1][2][3].The primary clinical features of periodontitis include the loss of periodontal tissue support, and is typically identified by bleeding on probing, deepened probing depth, loss of attachment, gingival recession, halitosis, and tooth mobility [1,4].The present adopted periodontitis classification scheme, unlike the former single category, is based on characterization of the disease due to the multi-dimensional staging and grading system, which is a better assessment for the severity, risk-evaluation, anticipated outcome and management of the disease.Moreover, the current revised classification according to pathophysiology is categorized as periodontitis, necrotizing periodontitis and the one as the direct manifestation of systemic diseases [1].Periodontitis is associated with the elevation of inflammatory molecules in systemic diseases and the development of several systemic co-morbidities, such as cardiovascular disease and type 2 diabetes [5,6].Obesity, which manifested as the accumulation of excess body fat, is another common health concern that results in a significant economic and societal burden worldwide.WHO currently accepts a body mass index of 25 kg/m 2 or greater as abnormal and when BMI is 30 kg/m 2 or over the objects are categorized as obese [7,8].Furthermore, obesity is currently recognized as a state of low-grade systemic inflammation (LGSI) [9].Research has demonstrated negative associations between bone metabolism, periodontitis, and obesity.Clinical studies have found that obesity is correlated with reduced bone mass, which can lead to varying degrees of osteoporosis and alveolar bone resorption as present in periodontitis [7,10].Obese individuals also tend to have higher levels of serum inflammatory biomarkers, such as cytokines (adipokines), which are secreted from adipocytes in adipose tissues.These biomarkers include interleukins (IL-6 and IL-8), tumor necrosis factor α (TNF-α), interferon-γ (IFN-γ), C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP-1), chemerin, adiponectin, omentin, isthmin 1, nesfatin-1, leptin, retinol-binding protein 4 (RBP4), resistin, and visfatin.They modulate inflammatory, immune, and metabolic responses [11][12][13][14].
Studies have also demonstrated that the levels of the inflammatory cytokines or adipokines mentioned above exhibit varying trends of change in patients with periodontitis at different stages of the disease.The association between periodontal disease and obesity was initially discovered in obese Zucker rats by Perlstein and Bissada [15].Moreover, recent studies and reviews have further revealed the association between obesity and periodontal disease [16][17][18].Additionally, periodontal disease and obesity/overweight status may have a bidirectional relationship, to be specific, not only are obese/overweight individuals prone to periodontal disease, but also periodontal disease may exacerbate dyslipidemia [19][20][21].In fact, during the local and systemic comorbid pathological condition, both periodontal tissues and adipocytes as host immune responsive cells, when triggered by pathogens, can secret higher levels of pro-inflammatory cytokines in obese individuals (such as IL-1, IL-1β, IL-6, TNF-a, etc.) to exacerbate both disease conditions [22].Also, obesity is related to the increased susceptibility towards bacterial infection; while periodontal tissues affected by periodontal disease (a source of bacteremia) may potentially worsen the obesity condition via pathways that involve the enhanced generation of reactive oxygen species (ROS) [23,24].And the recent discovery revealed that the association between periodontal disease and obesity is the outcome of an overall imbalance between health and systemic health [16].
Non-surgical periodontal therapy (NSPT) remains the gold standard for managing chronic periodontitis.The removal of supragingival plaque and subgingival scaling and root planning is the gold standard non-surgical therapy.Nevertheless, the mere mechanical debridement may not eradicate all subgingival periopathogens, and the adjunctive non-surgical measures are sometimes utilized to eliminate bacterial biofilm and deposits and restore a balanced microbiota environment for periodontal health [25].NSPT also reduces local inflammatory stimulation, decreases pocket depth, and promotes the recovery of clinical attachment by restoring highly perfused and collagen-rich connective tissues.As there is a correlation between periodontal disease and obesity, exploring the effectiveness of NSPT for obese patients with periodontitis is reasonable [26][27][28][29].
The 2017 World Workshop had demonstrated one of the issues that should be addressed in the future research was the identification of microbial, genetic, or host response-associated biomarkers that discriminate between the periodontitis phenotypes, also the ones that can reflect whether the initiation or progression of periodontitis [1].As far as we concern, the aforementioned cytokines seem to get involved in the mechanisms of periodontitis and obesity comorbid condition, and the levels of those cytokines before and after the NSPT are expected to provide the adjunctive measurements for the effect of the therapy and the primary prediction the role of these markers involved in the recovery of the comorbid.However, limited studies or weak evidence make it unclear whether NSPT significantly impacts clinical periodontal outcomes in obese individuals compared to non-obese individuals.Additionally, the role of related cytokines or adipokines before and after NSPT, as well as their impact on treatment outcomes, remains unclear.Therefore, the purpose of this study is to systematically review the efficacy of NSPT in managing periodontitis in both obese and non-obese individuals while considering the levels of biomarkers.

Protocol and registration
This systematic review and meta-analysis were carried out in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines [30] and registered in the Prospective International Register of Systematic Reviews (PROSPERO), with approval from all authors (CRD42022375331).

Focused question and selection criteria
One specific clinical focused question was constructed according to the Participants, Interventions, Control, and Outcomes (PICO) principle [31]: "what is the efficacy of NSPT with respect to cytokine/adipocytokine levels in obese individuals?Does NSPT reduce their biofluid levels of related cytokines/ adipocytokines (IL-6, TNF-a, CRP/hs-CRP, resistin, adiponectin, leptin, and RBP4)?The secondary focused question was: "what is the efficacy of NSPT with respect to cytokine/ adipocytokine levels in obese individuals compared to non-obese chronic periodontitis patients?Are obese people more responsive to treatment in cytokines/ adipocytokines levels?"(P) Participants: individuals with obesity and periodontitis (I) Types of intervention: NSPT (C) Control intervention: NSPT in non-obese patients with chronic periodontitis (O) Outcome measures: biofluid levels of cytokines/ adipocytokines from measured from the baseline to the follow-up Studies were considered eligible once they reached the following criteria: (1) Randomized clinical trials (RCTs) were deemed the most appropriate study design, along with controlled clinical trials (CCTs), for evaluating the efficacy of NSPT on cytokine/adipocytokine levels in individuals with or without obesity.(2) the study reported the association of given cytokines/ adipocytokines level with patients affected by obesity and the control group was necessary; (3) NSPT should be applied; (4) full-text were published in English.Studies were excluded once they were (1) laboratory animal studies, case-control studies, cross-sectional studies, case series, systematic reviews, literature reviews, conference abstracts; (2) studies lacking complete data on levels of targeted cytokines/ adipocytokines (despite efforts to retrieve raw values from the original authors); (3) clinical analyses involving periodontitis patients with systemic conditions other than obesity or who received treatments beyond NSPT were excluded.Please refer to Table S1 for details on the inclusion and exclusion criteria.

Criteria for obesity and periodontal diagnosis
The WHO definition of obesity in adults considers measurements such as waist circumference, waist-hip ratio, and body fat [32]; we followed the WHO obesity BMI diagnostic criterion (Table 1).According to WHO criteria, individuals with BMI over 30 kg/m 2 are categorized as obese [7], and BMI over 27.5 kg/m 2 is the recommended BMI cut-off point for obesity in Asian populations according to the interpretation of WHO expert consultation [33].Previous studies measured metabolic [29,[34][35][36][37][38][39][40][41] and anthropometric [34][35][36][37][41][42][43][44][45] parameters following NSPT to determine whether participants remained classified as obese during follow-up, particularly for longer-term studies.Various definitions and criteria for periodontitis were used by different authors and were accepted for the purposes of this review.The NSPT ).Any disagreements between the two reviewers were resolved by a third author, J. R.

Study selection
The reviews screened titles and abstracts based on the inclusion and exclusion criteria.Full-text articles were obtained for references that did not provide sufficient information for inclusion or exclusion based on their titles and abstracts.After removing duplicates, all articles that met the eligibility criteria were included.Any disagreements between the two reviewers were resolved through discussion and consensus with a third author (J.R).The Kappa score for this stage was 0.79, indicating substantial agreement.

Data extraction and quality assessment
The same two reviewers undertook data extraction independently.Information from the accepted studies was tabulated according to the author(s), publication year, study designs, settings, participant characteristics, sample characteristics, periodontal and obesity criteria for inclusion, and follow-up outcomes with cytokines/adipocytokines investigated.Data collection was based on the focused question addressed in the systematic review.Data on baseline and post-treatment follow-up timepoints that compared the levels of cytokines/ adipocytokines among obese and nonobese patients were also extracted and calculated.The reviewers cross-checked all extracted data, and any dissent was resolved by discussion until consensus was reached.The Kappa score was 0.89.The selected studies were assessed for quality by the reviewers using the Cochrane-advocated ROB-2 tool for assessing the risk of bias in RCTs [52].For non-RCTs, the ROBINS-I tool was used for assessing risk of bias by looking into pre-intervention, intervention and postintervention domains.Studies were evaluated as low risk of bias (≤ one moderate concern in the included domains, comparable), moderate (≤ four moderate concerns, credible but cannot considered comparable); serious risk of bias (at least one serious concern or multiple moderate concerns; with important problems in the design) and critical risk of bias (critical concerns or multiple serious concerns; unreliable) [46].

Synthesis of results
Studies with methodological homogeneity were pooled together in a meta-analysis using Review Manager 5.4, which was provided by the Cochrane Collaboration.We assessed statistical inconsistency and heterogeneity by examining the forest plots, Tau 2 , and the I 2 statistics.Significance levels of overall effects were determined by Z test, and forest plots were provided to demonstrate effect sizes and the corresponding 95% CI.Between-study heterogeneity was estimated by I 2 statistic, which was based on the Cochran Q statistics [47].Additionally, unlike merely focus on I 2 > 50% or not, we evaluated clinical heterogeneity to determine the appropriate effect model.Most of the included studies reported cytokine/adipokine levels in biofluids using medians.For studies that reported median and interquartile ranges, we estimated means and standard deviations through the given series estimation formulas through simulation studies provided by Wan X, McGrath, S. et al. [48,49,51].The significance p value was set as 0.05.

Subgroup analysis
Fifty-four subgroup analyses were conducted based on the biomarker category, biofluid type (serum, saliva, and gingival crevicular fluid (GCF)), participant group, and time of follow-up after NSPT.Subgroup meta-analyses were performed using mean differences (MD) and 95% confidence intervals (CI).The synthesis of results instructions was followed for all subgroup analyses, and sensitivity analysis was performed.

Study selection
A total of 1,695 studies were identified in the electronic databases, and no additional record was found from manual searching (duplicated) or the gray literature.Initial screening of the titles and abstracts was followed to remove 925 duplicates and 737 irrelevant studies from the inclusions.Thus, 33 studies were selected for eligibility.After assessment of the full texts of the 33 articles, 16 studies were excluded, and the specific reasons were listed in Table S1 (Supplementary Information File).Seventeen studies were eventually included in the present systematic review, and sixteen were included in meta-analysis.A flowchart presenting all the abovestated phases is displayed in Fig. 1.

Study characteristics
The characteristics of the 17 incorporated studies are depicted in Table 1.The studies reflected the diversity of ethnicities as they were conducted in different countries; meanwhile, all included studies were published in English.All studies consisted of a group of obese individuals with periodontitis who were treated with NSPT.As for defining parameters of obesity in the included studies, the WHO criteria with or without assistant measures such as body fat, waist-hip ratio, and so on were taken into account.Notably, given by two BMI cut-off point [7,33] for obesity recommended by WHO as stated in the Obesity and periodontitis criterion, BMI over 27.5 kg/m2 in Asian obesity populations [33] was applied by three included studies in Asian settings [39,53,54].The number of individuals in each study ranged from 40 to 231.The follow-up time of each one ranges from six weeks to two years; the majority is about three months [34-37, 39, 40, 42-45, 54-56] and six months [41,42,45,53] after the NSPT.All studies provided related professional oral hygiene instructions and sufficient periodontal parameters at the follow-up timepoints.

NSPT and inflammatory-related cytokines/adipokines
Our systematic analysis revealed that among the various inflammatory cytokines, IL-6 and CPR/hs-CRP were the most commonly investigated by researchers.TNFa, IL-1β, IL-10, and interferon-γ were investigated to a lesser extent.In terms of adipokines, resistin, adiponectin, and leptin were the most widely studied, while RBP4 and vastatin were studied to a lesser extent.The efficacy of NSPT in respect to each of these cytokines and adipokines in different biological fluids (serum, saliva, and GCF) are presented in Tables S2 and S3.

Evaluation of the methodological quality of the incorporated studies
According to the critical evaluation instruments used (see Supplementary Tables S4 and S5), all randomized and non-randomized studies included in this systematic review and meta-analysis showed a relatively high degree (low or moderate risk of bias) of methodological quality, however, our findings should be interpreted with caution, as most of the published studies were at moderate risk of bias.The basic methodological deficiencies resulted in moderate risk of bias were the missing data due to the dropouts of more than 5% in two studies [43,45] during follow-up, and failure to prospectively calculate sample size in two studies [37,41] and the low to moderate quality could be partially attributed to the inevitable presence of confounders (confounders such as unstated smoking issues, degree of pathological condition, etc.).In the subgroup analysis that compared serum levels of IL-6 (pg/mL), five studies [34,35,40,42,43] showed that the baseline IL-6 levels of people with obesity and periodontitis (OP) were higher than those of normalweight patients with periodontitis (NP) before treatment (MD = 0.51, CI = 0.09-0.93)(Figure S1).(Figure S2).Furthermore, at the 3-month follow-up, five studies [34,35,40,42,43] showed that serum IL-6 levels in OP patients did not differ from those in NP patients (MD = 0.42, CI = -0.06-0.90)(MD = 0.42, CI = -0.06-0.90)(Figure S3).

NSPT and resistin
In the subgroup analysis comparing salivary levels of resistin (ng/mL), merely two included studies [39,53] suggested that there was no difference before and after the NSPT within the OP group (MD = -4.60,CI = -12.40-3.20)(Figure S22).
In the subgroup analysis comparing GCF levels of adiponectin (mg/L), only two included studies [35,42] suggested that the levels of the OP group were not different from those in the NP group at baseline (MD = -0.18,CI = -1.66-1.29)(Figure S38).Moreover, two studies [35,42] suggested that there was no difference before and three months after the NSPT among OP patients (MD = 1.06,CI = -1.58-3.70)(Figure S39).However, there was an increase in GCF levels of adiponectin three months after the NSPT among NP groups (MD = 2.37, CI = 0.29-4.45)[35,42] (Fig. 7).Furthermore, there was no difference in GCF levels of adiponectin between the

NSPT and RBP4
In the subgroup analysis comparing serum levels of RBP4 (mg/dL), only two studies [43,44] were incorporated, suggesting that the serum RBP4 level of the OP group was higher before the therapy compared with the level at the 3-month follow-up (MD = -0.39,CI = -0.68-0.10)(Fig. 9).Given the clinical heterogeneity of the incorporated studies in the present meta-analysis, the randomeffects model was applied in all subgroup analyses.The results of the subgroup analyses are tabulated in Table S3 (Supplementary Information File).

Discussion
Although the underlying mechanisms of the association between obesity and periodontitis, as well as the interactions between NSPT and both conditions, remain to be fully clarified, research has confirmed the essential role of pro-inflammatory and anti-inflammatory mediators in the development of each condition and their interaction.The link between periodontitis and obesity is dominated by pro-inflammatory factors that exacerbate the severity of both conditions [59,60].A meta-analysis has shown that obesity can alter serum levels of pro-inflammatory mediators (i.e., IL-6, CRP, TNF-a, resistin and leptin) in patients with periodontitis, while periodontitis can alter the levels of these mediators in patients with obesity, aggravating the inflammatory profile [61].
Previous studies have primarily focused on observational studies (basically cross-sectional studies) without the introduction of intervention like NSPT, thus unable to assess the changes in levels of relevant mediators after treatment through intervention measures.With the implementation of NSPT, there is bound to be a redistribution of pro-inflammatory and anti-inflammatory mediators, such as a decrease in typical pro-inflammatory mediators like IL-6 and an increase in anti-inflammatory mediators like adiponectin, which is the main focus of our current study.We have analyzed the levels Fig. 8 Subgroup analysis comparing 6 months follow-up serum levels of leptin after non-surgical periodontal therapy among patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups Fig. 9 Subgroup analysis comparing serum levels of RBP4 before and 3 months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups of these mediators in different biological fluids, including whole saliva, GCF, and serum.Saliva and GCF are known to carry local inflammatory mediators.GCF, in particular, is an oral fluid/ exudate that resides in close proximity to gingival tissues and contains various biomarkers and products derived from both hosts and bacteria [62].Saliva and GCF are reliable tools widely used to detect even small changes during disease processes.They can be collected non-invasively to provide a more precise reflection of the condition of periodontitis.However, unlike whole saliva, which can represent the systemic conditions in general, GCF seems to be more specific.Samples of GCF taken from deep or shallow sites of the periodontal pocket represent different pathological conditions [63].Meanwhile, serum can reflect the course of multiple diseases more comprehensively, serving as an indicator of the whole system [64].
Interleukin-6, a pro-inflammatory mediator, is known to regulate the host response to both periodontitis bacterial infection and obesity-related disorders [65,66].The results of a meta-analysis suggest that individuals with periodontitis and obesity have higher baseline serum levels of IL-6.However, after NSPT, the reduction of IL-6 levels is statistically significant in patients with obesity in a 3-month follow-up period, while no such impact is observed in normal-weight individuals with periodontitis.Thus, IL-6 levels after a 3-month follow-up interval may be an ideal clinical serum bioanalysis to detect the actual effect of NSPT in obesity patients.
Furthermore, the reduction of IL-6 levels in GCF after NSPT is also statistically significant in patients with obesity in a 3-month follow-up period.However, in followup periods longer than 3 months but less than 12 months, the impact of NSPT starts to diminish, as the IL-6 levels in GCF gradually increase in obese individuals, resulting in higher levels than those observed in non-obesity groups.These findings suggest that more frequent follow-up assessments are necessary to detect patients' conditions in a timely manner and initiate supplement treatment measures to improve prognosis, considering the time effect of the efficacy of NSPT.
TNF-α, as a pro-inflammatory mediator, has been shown to have high serum levels in individuals with periodontitis, indicating its involvement in the pathologic process of periodontitis.Moreover, TNF-α has been reported to be associated with several diseases, including diabetes, cardiovascular disease, cancer, and metabolic disorders [67].Notably, TNF-α levels are correlated with the degree of adiposity and the associated insulin resistance [9].According to the quantitative analysis, the serum level of TNF-α did not change three months after NSPT.Furthermore, both the baseline and three-month follow-up showed higher levels in obesity participants than in normal-weight participants, indicating that the positive effect of treatment on TNF-α serum levels was offset.Additionally, NSPT did not have an impact on TNF-α levels in GCF for either obese or non-obese participants, both at the three-month and distal timepoints.Interestingly, obesity participants presented with higher baseline GCF levels of TNF-α than non-obesity participants.
Elevated plasma levels of CRP, or hs-CRP, have been reported to be linked to obesity and insulin resistance [68,69], with the latter being implicated in the association between obesity and periodontitis [23,70].The meta-analysis results suggest that NSPT may be more effective in reducing overall serum levels of CRP/hs-CRP at the 3-month follow-up, as there was no significant difference between individuals with and without obesity.However, at baseline, serum levels of CRP/hs-CRP were significantly higher in obesity patients than in those without obesity.Despite this, there was no apparent reduction in systemic inflammation in either obesity or non-obese patients as measured by serum levels of CRP/hs-CRP at the 3-month follow-up.Therefore, a 3-month follow-up interval may not be sufficient to support the actual effect of NSPT, and more timepoints need to be accumulated for stronger evidence.
Intriguingly, resistin, a member of the adipokine family, is also a pro-inflammatory mediator that plays a critical role in the development of obesity, insulin resistance, and related comorbidities [71].Previous studies have shown that resistin levels increase with the severity of periodontal disease and decrease after periodontal therapy [72].However, the results of quantitative research suggest that NSPT may not have a positive effect on either the GCF or serum levels of resistin in both obese and non-obese individuals at the distal timepoints.Moreover, based on the GCF and serum levels of resistin at baseline and the distal follow-up, it was found that obese patients had a higher expression of resistin, indicating an obesity-dominant higher level of pro-inflammatory expression.
Adiponectin, an anti-inflammatory adipokine, and has been shown to be a regulator of macrophage polarization to assist in reducing inflammation [73].Besides, adiponectin and its agonists are promising candidates for the treatment of periodontitis due to emerging evidence of the link between adiponectin and periodontitis [74].Based on the results of our systematic review, two studies [35,42] demonstrated that NSPT leads to an increase in adiponectin levels in non-obese individuals.However, the meta-analysis suggests that NSPT may not have an impact on the serum levels of adiponectin at 3-or 6-months post-treatment in either obese or non-obese subjects.The same situation was observed in the GCF level of adiponectin at the 3-month follow-up in obese patients, but a significant increase in the GCF level of adiponectin was found in non-obese patients 3 months after the therapy, indicating that obesity may reduce the effectiveness of the treatment, while nonobese individuals may be more responsive to NSPT for anti-inflammation.There was no difference between obese and non-obese participants in the baseline serum level of adiponectin, as well as at the 3-month/6-month follow-up for serum adiponectin and at the 3-month follow-up for GCF adiponectin.Adiponectin may be a sensitive biomarker only in non-obese patients for a 3-month follow-up after NSPT to evaluate the treatment's effectiveness.
Leptin is one of the most well-known pro-inflammatory adipokines and is also recognized for its role in appetite regulation.Leptin resistance is considered a major risk factor for obesity [75].Recent research has shown that leptin can promote the progression of periodontitis by inducing pro-inflammatory M1 macrophage skewing through the leptin/NLRP3 signaling pathway [76].Our quantitative analysis of serum leptin levels found that NSPT did not have a significant impact on either obese or normal weight individuals at 3-month or 6-month intervals.Additionally, there were no differences in serum leptin levels between the two groups at baseline or at the 3-month follow-up.However, at the 6-month follow-up, serum leptin levels were significantly higher in the obese group compared to the non-obese group.These findings suggest that serum leptin analysis at either 3-month or 6-month intervals following NSPT may not be an accurate marker for treatment effectiveness.
RBP4, an adipokine related to obesity and insulin resistance [50], has been proposed as a potential biomarker of inflammatory activity in obesity and chronic periodontitis [77].However, due to the limited number of included studies, a subgroup analysis of RBP4 in serum levels was only conducted in obese individuals.The results suggest that NSPT contributed to a decrease in the serum levels of RBP4 at 3 months post-treatment.This decrease in RBP4 levels may be indicative of a reduction in inflammatory activity in obese individuals.
Despite the above-mentioned biomarkers, MMP-8 is another essential mediator in the systemic subclinical inflammatory response in obesity; moreover, previous research has shown that some functional polymorphisms in the MMP genes are associated with the risk of periodontal disease [78,79].Meanwhile, many oxidative stress-related metabolites, such as malondialdehyde and 8-hydroxy-deoxyguanosine in GCF, were the most consistently associated with periodontitis [80].Besides, patients with chronic periodontitis displayed higher levels of vaspin whether with obesity or not, however, the level of vaspin declined after the NSPT.These findings may provide other ideal diagnostic and prognostic indicators of CP for better therapeutic outcome [81].
The effect of obesity, specifically the adipose tissue, on the expression of pro-inflammatory cytokines may limit the effectiveness of NSPT in reducing their levels.Adipose tissue is an endocrine organ that releases various pro-inflammatory cytokines, which may increase the threshold of the NSPT's effect, making it difficult for the gingiva and periodontal bone to relieve the inflammatory state [82].The relevant indicators suitable for the comorbidity model of obesity and periodontitis have been screened out from a number of pro-inflammatory and anti-inflammatory cytokines, and the results are considerable.However, due to the limitations of current research data, a longitudinal comparison of given changing levels (Δvalues for variation for individual before and after the NSPT) of indicators between obese and non-obese subjects cannot be effectively carried out.It is widely known that periodontitis is a bacterial infectious disease, and many cytokines/adipokines related to inflammation regulate the pathophysiology of periodontitis through interactions between tissue cells and immune cells.
Additionally, the regulatory mechanisms involved in the associations between periodontitis and obesity remain to be fully elucidated.It is important to control for confounding factors by excluding individuals with other metabolic or systemic diseases to minimize selection bias, as obesity is often comorbid with other conditions.Furthermore, follow-up intervals should be standardized and the observation period prolonged to evaluate long-term efficacy.As new adipokines, such as vaspin and chemerin, continue to emerge, more research is needed to establish their relationship with periodontitis and obesity.Inevitably, with the only permission of English-published article, publish bias cannot be avoid and our findings should be interpreted with caution, as most of the published studies were at moderate risk of bias and in several meta-analyses the heterogeneity is very high, basically because of the clinical heterogeneity.These limitations present opportunities for future research in this field.

Conclusions
NSPT can impact the levels of specific pro-inflammatory and anti-inflammatory mediators in biological fluids, both in obese and non-obese individuals, as well as between the two groups.Specifically, NSPT can lead to a decrease in serum and GCF levels of IL-6 and RBP4 in obese individuals after 3 months and an increase in GCF adiponectin levels in normal-weight individuals after 3 months.Besides, for patients with periodontitis, there is no sufficient evidence to prove that obese patients have a statistically significant decrease in the levels of other cytokines compared to patients with normal weight.Our findings implied the potential ideal follow-up intervals and sensitive biomarkers for clinical bioanalysis in personalized decision-making of effect of NSPT due to patients' BMI value.These findings suggest that the 3-month follow-up interval and the aforementioned biomarkers could be valuable for clinical bioanalysis as an auxiliary chairside tool to evaluate the efficacy of NSPT.
Additional file 1: Table S1.Inclusion and exclusion criteria and studies excluded after full-text analysis and related reasons.Table S2.The detailed effect of NSPT in respect to inflammatory cytokines and adipokines.Table S3.Synthesis of results in subgroup analyses.Table S4.Risk of bias assessment of included studies according to the ROBINS-I tool.Table S5.Risk of bias assessment of the 4 included RCTs with the ROB-2 tool. Figure S1.Subgroup analysis comparing baseline serum levels of IL-6 before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S2.Subgroup analysis comparing serum levels of IL-6 before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) group.Figure S3.Comparison of 3-month follow-up of serum levels of IL-6 after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S4.Subgroup analysis comparing baseline GCF levels of IL-6 before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S5.Subgroup analysis comparing GCF levels of IL-6 before and three months after non-surgical periodontal therapy in normalweight patients with periodontitis (NP) groups.Figure S6.Comparison of 3-month follow-ups of GCF levels of IL-6 after non-surgical periodontal therapy for patients with obesity and periodontitis (OP) and normalweight patients with periodontitis (NP) groups.Figure S7.Subgroup analysis comparing GCF levels of IL-6 before and distal follow-up time after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S8.Subgroup analysis comparing GCF levels of IL-6 before and distal follow-up time after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S9.Subgroup analysis comparing baseline serum levels of TNF-a before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S10.Subgroup analysis comparing serum levels of TNF-a before and three months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S11.Subgroup analysis comparing serum levels of TNF-a before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S12.Subgroup analysis comparing baseline GCF levels of TNF-a before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S13.Subgroup analysis comparing GCF levels of TNF-a before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S14.Comparison of three-month follow-ups of GCF levels of TNF-a after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S15.Subgroup analysis comparing GCF levels of TNF-a before and distal follow-up time after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S16.Subgroup analysis comparing GCF levels of TNF-a before and distal follow-up time after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S17.
Subgroup analysis comparing distal follow-up time GCF levels of TNF-a after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S18.Subgroup analysis comparing baseline serum levels of CRP/hs-CRP before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S19.Subgroup analysis comparing serum levels of CRP/hs-CRP before and 3 months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S20.Subgroup analysis comparing serum levels of CRP/ hs-CRP before and 3 months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S21.Subgroup analysis comparing follow-up serum levels of CRP/hs-CRP 3 months after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S22.Subgroup analysis comparing salivary levels of resistin before and distal time after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S23.Subgroup analysis comparing baseline GCF levels of resistin before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S24.Subgroup analysis comparing GCF levels of resistin before and distal time after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S25.Subgroup analysis comparing GCF levels of resistin before and distal time after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S26.The comparing distal follow-up time GCF levels of resistin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S27.Subgroup analysis comparing baseline serum levels of resistin before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S28.Subgroup analysis comparing serum levels of resistin before and distal time after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S29.Subgroup analysis comparing serum levels of resistin before and distal time after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S30.Comparison of distal follow-up time serum levels of resistin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S31.Subgroup analysis comparing baseline serum levels of adiponectin before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S32.Subgroup analysis comparing serum levels of adiponectin before and three months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S33.Subgroup analysis comparing serum levels of adiponectin before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S34.Subgroup analysis comparing 3 months follow-up serum levels of adiponectin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S35.Subgroup analysis comparing serum levels of adiponectin before and six months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S36.Subgroup analysis comparing serum levels of adiponectin before and six months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S37.Subgroup analysis comparing 6 months follow-up serum levels of adiponectin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S38.Subgroup analysis comparing baseline GCF levels of adiponectin before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S39.Subgroup analysis comparing GCF levels of adiponectin before and three months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S40.Subgroup analysis comparing 3 months follow-up GCF levels of adiponectin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S41.Subgroup analysis comparing baseline serum levels of leptin before non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S42.Subgroup analysis comparing serum levels of leptin before and three months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S43.Subgroup analysis comparing serum levels of leptin before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.Figure S44.Subgroup analysis comparing 3 months follow-up serum levels of leptin after non-surgical periodontal therapy within patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups.Figure S45.Subgroup analysis comparing serum levels of leptin before and six months after non-surgical periodontal therapy in patients with obesity and periodontitis (OP) groups.Figure S46.Subgroup analysis comparing serum levels of leptin before and six months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups.

(
P) Participants: individuals with obesity and periodontitis (I) Types of intervention: NSPT (C) Comparison: without periodontal treatment (O) Outcome: biofluid levels of related cytokines/ adipocytokines

Fig. 4 Fig. 5 Fig. 6
Fig.4 Comparison of distal follow-up time GCF levels of IL-6 after non-surgical periodontal therapy among patients with obesity and periodontitis (OP) and normal-weight patients with periodontitis (NP) groups

Fig. 7
Fig. 7 Subgroup analysis comparing GCF levels of adiponectin before and three months after non-surgical periodontal therapy in normal-weight patients with periodontitis (NP) groups

Table 1
Characteristics of the included studies in the systematic review

Table 1 (
continued) oral hygiene instructions, full-mouth scaling and root planning (SRP), or SRP combined with local or systemic antimicrobial agents.No surgical procedures, such as periodontal flap surgery, were involved in the NSPT.
a Groups that not take into account; T0 initial examination, T1 examination after periodontal therapy, OP obesity with periodontitis, NP normal weight with periodontitis, O obesity, N normal weight, mon month, BMI body mass index (kg/m 2 ), MBL marginal bone loss, MT missing teeth, BF body fat, WHR waist-hip ratio, WC waist circumference (cm), OHI oral hygiene instructions, aPDT antimicrobial photodynamic therapy, PS plaque score, GBI gingival bleeding index, NR not reported, VPI full mouth visible plaque index, GBI gingival bleeding index, PI plaque index, GI gingival index, HDL high-density lipoprotein, LDL low-density lipoprotein, triglyceride, ROM plasma-reactive oxygen metabolite, TGR triglycerides (mg/dL), TC total cholesterol (mg/dL), CRP C-reactive protein (mg/dL), hs-CRP high-sensitivity C-reactive protein (mg/dL), TG triglycerides, MB marginal bleeding, F female, M male interventions included professional AND (obesity OR obese OR body mass index) AND (cytokine OR adipocytokine OR IL-6 OR TNF-a OR CRP OR hs-CRP OR resistin OR adiponectin OR leptin OR RBP4)