during the last decades , evidence has emerged to support the relationship between periodontal infection and systemic conditions including cardiovascular diseases , diabetes , obesity and metabolic syndrome . unlike the most common form of chronic periodontitis ( cp ) , aggressive periodontitis ( agp ) develops early in life , progresses faster , and presents more destructive clinical features . it has been indicated that systemic factors play a greater role in the etiology of agp , which in turn exert greater effects on systemic conditions . as expected , higher serum levels of inflammatory mediators , such as interleukin ( il)-17 , tumor necrosis factor- ( tnf- ) and c - reactive protein ( crp ) , have been detected in patients with cp compared to controls , which became even higher in agp patients , even if whose clinical parameters were less severe . the increased systemic inflammation burden has been suggested to be a possible link between periodontal disease and systemic health . for example , pro - inflammatory cytokines were shown to play important roles in the development of dyslipidemia and impaired glucose tolerance , which have been considered as risk factors for many systemic diseases . leptin , since discovered in 1994 , has provided important insights into the intricate network linking nutrition , metabolism , and immune homeostasis . this 16-kda adipose tissue - derived molecule plays important roles in regulating lipid and glucose metabolism , and elevated plasma leptin concentrations have been suggested as an independent risk factor for cardiovascular diseases . in recent years , clinical studies indicated an association between leptin and periodontal infection . serum leptin concentration was reported to be significantly elevated in cp patients compared with periodontal healthy subjects , and was positively correlated with periodontal parameters including probing depth and clinical attachment loss , and could be effectively reduced by periodontal treatment . these results suggested that the systemic leptin level could be greatly influenced by the periodontal conditions , and is a potential mediator between periodontitis and systemic health . we and others have shown elevated systemic inflammatory markers including peripheral leukocytes counts , crp and il-6 in patients with agp . however , evidence is still lacking about whether there is an association between the circulating leptin concentration and the systemic inflammation in patients with agp . the aim of the present study was to evaluate the change of leptin concentration in peripheral blood in patients with agp , and to explore the relationship between leptin and systemic inflammation markers . the present study was conducted with the written informed consent of all subjects and was approved by the ethics committee of the peking university health science center . ninety patients with generalized agp ( 33 males and 57 females ) , aged 1442 years , were recruited from the clinic of the periodontology department , peking university school and hospital of stomatology between july 2001 and may 2006 . the diagnosis criteria were defined according to the classification developed at the international workshop for a classification of periodontal diseases and conditions in 1999 : the onset of periodontal disease generally occurred at < 35 years of age , and there were at least eight teeth with probing depth ( pd ) > 6 mm and with radiographic evidence of alveolar bone loss . other factors were also considered : familial aggregation , rapid progression , and the relationship between local factors and periodontal destruction . forty - four healthy volunteers ( 16 males and 28 females ) , aged 2048 years , were recruited from the staff and students of the peking university school and hospital of stomatology . the inclusion criteria were no site with clinical attachment loss , no site with pd > 3 mm , no bone loss on radiographs , and less than 10% of sites with bleeding on probing . the exclusion criterions included systemic diseases , smoking , periodontal therapy within the previous year , antibiotics intake within the previous 3 months , and pregnancy . by their own acknowledgment , all study subjects were free of systemic diseases and were not taking any medication known to affect periodontal status . all recruited subjects accepted a comprehensive blood examination and were referred to physicians when necessary . all subjects belonged to the han race , which makes up the majority of the chinese population . each study subject filled out a questionnaire that noted general background ( including weight and height ) , medical and dental care history , oral hygiene habits , and social status . the body mass index ( bmi ) was calculated as weight in kilograms divided by height in meters squared . according to our previous results , systemic inflammatory markers including white blood cell ( wbc ) count , il-1 , il-6 , crp and tnf- may be correlated with periodontal infection . serum protein variables such as albumin ( alb)/globulin ratio ( a / g ) were also associated with the severity of periodontal destruction . a peripheral blood sample was obtained from each fasting examinee by venipuncture between 8:00 a.m. and 10:00 a.m. , and was divided into two tubes . one tube contained ethylenediaminetetraacetic acid ( edta ) and was used for blood cell analysis by hematology analyzers ( sysmex kx-21 , sysmex , kobe , japan ) ; the other did not contain edta and was used for serum protein analyses by a biochemical analyzer ( hitachi 7060 , hitachi , tokyo , japan ) . serum protein parameters included total protein , alb , globulin , and a / g . plasma samples were obtained from edta - containing tubes and were separated and immediately stored frozen at 70c until required for analysis . plasma levels of leptin , il-1 and il-6 were determined using commercially available enzyme - linked immunosorbent assay ( elisa ) kits ( r and d systems , inc . , minneapolis , mn , usa ) ; and the lower limits of detection were 7.8 pg / ml , 1 pg / ml and 0.16 pg / ml respectively . plasma level of crp was measured using a commercially available elisa kit ( diagnostic system laboratories , inc . , plasma levels of tnf- were measured using a commercially available elisa kit ( bender medsystems , inc . , vienna , austria ) and the lower limit of detection was 0.13 pg / ml . these assays were performed according to the manufacturer 's protocol . plasma leptin levels were analyzed with the analysis of covariance model , controlling for age , gender , and bmi as confounders . partial correlation coefficients between leptin and other parameters including clinical values , hematologic parameters , and pro - inflammatory cytokines were determined , controlling for the potential confounders mentioned above . the values of age , bmi , plasma leptin level , blood cell and serum protein variables were described by mean  standard deviation ( sd ) . plasma levels of crp , il-6 , il-1 and tnf- were described by median and interquartile range , and were log10 transformed for the correlation and regression analyses as a result of their nonnormal distributions . chicago , il , usa ) was used for analyses , and p < 0.05 was considered as statistically significant . the present study was conducted with the written informed consent of all subjects and was approved by the ethics committee of the peking university health science center . ninety patients with generalized agp ( 33 males and 57 females ) , aged 1442 years , were recruited from the clinic of the periodontology department , peking university school and hospital of stomatology between july 2001 and may 2006 . the diagnosis criteria were defined according to the classification developed at the international workshop for a classification of periodontal diseases and conditions in 1999 : the onset of periodontal disease generally occurred at < 35 years of age , and there were at least eight teeth with probing depth ( pd ) > 6 mm and with radiographic evidence of alveolar bone loss . other factors were also considered : familial aggregation , rapid progression , and the relationship between local factors and periodontal destruction . forty - four healthy volunteers ( 16 males and 28 females ) , aged 2048 years , were recruited from the staff and students of the peking university school and hospital of stomatology . the inclusion criteria were no site with clinical attachment loss , no site with pd > 3 mm , no bone loss on radiographs , and less than 10% of sites with bleeding on probing . the exclusion criterions included systemic diseases , smoking , periodontal therapy within the previous year , antibiotics intake within the previous 3 months , and pregnancy . by their own acknowledgment , all study subjects were free of systemic diseases and were not taking any medication known to affect periodontal status . all recruited subjects accepted a comprehensive blood examination and were referred to physicians when necessary . all subjects belonged to the han race , which makes up the majority of the chinese population . each study subject filled out a questionnaire that noted general background ( including weight and height ) , medical and dental care history , oral hygiene habits , and social status . the body mass index ( bmi ) according to our previous results , systemic inflammatory markers including white blood cell ( wbc ) count , il-1 , il-6 , crp and tnf- may be correlated with periodontal infection . serum protein variables such as albumin ( alb)/globulin ratio ( a / g ) were also associated with the severity of periodontal destruction . a peripheral blood sample was obtained from each fasting examinee by venipuncture between 8:00 a.m. and 10:00 a.m. , and was divided into two tubes . one tube contained ethylenediaminetetraacetic acid ( edta ) and was used for blood cell analysis by hematology analyzers ( sysmex kx-21 , sysmex , kobe , japan ) ; the other did not contain edta and was used for serum protein analyses by a biochemical analyzer ( hitachi 7060 , hitachi , tokyo , japan ) . serum protein parameters included total protein , alb , globulin , and a / g . plasma samples were obtained from edta - containing tubes and were separated and immediately stored frozen at 70c until required for analysis . plasma levels of leptin , il-1 and il-6 were determined using commercially available enzyme - linked immunosorbent assay ( elisa ) kits ( r and d systems , inc . , minneapolis , mn , usa ) ; and the lower limits of detection were 7.8 pg / ml , 1 pg / ml and 0.16 pg / ml respectively . plasma level of crp was measured using a commercially available elisa kit ( diagnostic system laboratories , inc . plasma levels of tnf- were measured using a commercially available elisa kit ( bender medsystems , inc . , vienna , austria ) and the lower limit of detection was 0.13 pg / ml . these assays were performed according to the manufacturer 's protocol . plasma leptin levels were analyzed with the analysis of covariance model , controlling for age , gender , and bmi as confounders . partial correlation coefficients between leptin and other parameters including clinical values , hematologic parameters , and pro - inflammatory cytokines were determined , controlling for the potential confounders mentioned above . the values of age , bmi , plasma leptin level , blood cell and serum protein variables were described by mean  standard deviation ( sd ) . plasma levels of crp , il-6 , il-1 and tnf- were described by median and interquartile range , and were log10 transformed for the correlation and regression analyses as a result of their nonnormal distributions . chicago , il , usa ) was used for analyses , and p < 0.05 was considered as statistically significant . mean ages of control and agp groups were 25.6  3.8 years and 26.2  4.9 years , respectively . there was no difference in the mean values for age and bmi between the two groups and no significant difference for gender distribution . mean plasma leptin level of agp group was 19.7  4.4 ng / ml , significantly higher than that of the control group ( 7.5  1.3 ng / ml , p < 0.01 ) . table 1 also presented the results of blood cell analysis and serum protein assessment . compared with the control group , significantly higher wbc and neutrophil counts were observed in the agp group ; the alb and a / g were significantly lower in the agp group than in the control group ( p < 0.01 ) . population variables and blood parameters of control and agp groups * compared to the control group , p < 0.01 . bmi : body mass index ; wbc : white blood cell ; neut : neutrophil ; lym : lymphocyte ; alb : albumin ; a / g : albumin / globulin ratio ; agp : aggressive periodontitis ; sd : standard deviation . plasma levels of crp , il-1 , il-6 and tnf- were significantly higher in agp patients compared with controls ( p < 0.01 ) . plasma levels of inflammatory cytokines of control and agp groups * compared with the control group , p < 0.01 . il : interleukin ; crp : c - reactive protein ; tnf- : tumor necrosis factor- ; iqr : interquartile range ; agp : aggressive periodontitis . results of partial correlation analyses were shown in tables 35 . when all the subjects in both groups were pooled for analyses , after controlling for age , gender and bmi , plasma leptin level was significantly positively correlated with wbc and neutrophil counts as well as log - transformed levels of pro - inflammatory cytokines , and the partial correlation coefficients ranged from 0.199 to 0.376 ( p < 0.05 ) . a negative correlation was observed between plasma leptin level and a / g as well as alb , and the r values were 0.246 and  0.198 respectively ( p < 0.01 ) . multiple linear regression analysis was performed to explore the relationship between leptin and other parameters . gender , age , bmi and significant variables in the partial correlation analysis were evaluated . using stepwise method , log - transformed il-1 and il-6 entered the final model , and the standardized  values were 0.422 and 0.461 , respectively ( p < 0.001 ) . the relationship between the levels of plasma leptin and blood parameters ( controlling for age , gender and bmi ) * p < 0.05 ; p < 0.01 . wbc : white blood cell ; neut : neutrophil ; lym : lymphocyte ; alb : albumin ; a / g : albumin / globulin ratio ; bmi : body mass index . the relationship between the levels of plasma leptin and inflammatory cytokines ( controlling for age , gender and bmi ) * p < 0.05 ; p < 0.01 . il : interleukin ; crp : c - reactive protein ; tnf- : tumor necrosis factor- ; bmi : body mass index . results of multiple linear regression analysis , stepwise method used ( adjusted r = 0.376 ) although numerous research have investigated the serum leptin levels in patients with gingivitis and cp , few evidence is present about that in patients with agp , which is a distinct form of periodontitis and characterized by early onset and rapid and severe periodontal destruction , as well as its relationship with systemic inflammatory markers . as far as we knew , this study provided the first evidence about the positive association between plasma leptin levels and systemic inflammatory markers including wbc and neutrophil counts , il-1 and il-6 in patients with agp . however , previous evidence showed that resident cells in the inflammatory periodontal tissue could be an important source of inflammatory mediators , among which il-1 and il-6 were both involved . leptin , with a striking structural similarity with il-6 , shares regulatory and functional similarity with il-6 as well . another research from our group has shown that healthy resident cells in periodontal tissues , such as gingival epithelial cells , gingival connective cells and periodontal ligament cells , all expressed leptin to some extent both in vivo and in vitro . thus , the mechanism contributing to the up - regulation of plasma il-6 levels in periodontitis may propose the same effect on the change of plasma leptin levels . on the other hand , the released lipopolysaccharide , tnf and il-1 from periodontal infection may increase the adipose tissue leptin mrna expression , hereby circulating leptin levels more significantly as suggested by animal studies . in consistent , plasma leptin level positively correlated with the values of systemic inflammation markers even after controlling for age , gender , and bmi . results from multiple linear regression analysis suggested that the higher plasma leptin level in agp group may attribute to elevated plasma il-1 and il-6 levels , which have been observed in agp patients according to our present and previous studies . previous studies have observed that serum leptin levels increased as the severity of periodontal inflammation progressed , which were lowest in the controls , moderate in patients with chronic gingivitis and highest in those with cp . our previous study found that the plasma leptin level in agp reached 20 ng / ml on average , even higher than the reported 12 ng / ml in cp with comparable pd . the rise of serum leptin level above 10 ng / ml is considered as a risk factor for cardiovascular disease . preliminary evidence has shown the elevated serum leptin level in cp was associated with type 2 diabetes and acute myocardial infarction . thus , it is reasonable to suspect that the even higher serum leptin levels in patients with agp may provide a stronger interrelationship between local infection and systemic conditions . in summary , plasma leptin levels may be associated with the inflammatory cytokines from periodontal infection , especially in an aggressive form . these results suggested that leptin could be a potential connection between local infection and systemic health . one of the explanations is that other factors that may affect the circulating leptin level such as body fat percentage and lifestyles were not considered in our study . within the limitation of the present study , elevated plasma leptin concentration was associated with increased systemic levels of inflammatory markers , especially il-1 and il-6 , in agp patients after controlling for age , gender , and bmi .
background : increasing evidence supports an association between periodontitis and systemic diseases . 
 leptin is involved both in the energy metabolism and inflammatory processes and is suggested to be a link between periodontal infection and systemic health . 
 the present study aimed to evaluate the peripheral leptin concentration in patients with aggressive periodontitis ( agp ) and to explore the relationship between leptin and systemic inflammation.methods:ninety patients with agp visiting the clinic of the periodontology department , peking university school and hospital of stomatology between july 2001 and may 2006 , and 44 healthy controls ( staff and student volunteers in the same institute ) were recruited . 
 plasma levels of leptin and inflammatory cytokines including interleukin ( il)-1 , il-6 , tumor necrosis factor- ( tnf- ) and c - reactive protein ( crp ) were measured by enzyme - linked immunosorbent assay . 
 correlation and multiple linear regression analysis were performed to analyze the association between plasma leptin level and other variables.results:plasma leptin level of agp group was significantly higher than that of the control group ( 19.7  4.4 ng / ml vs. 7.5  1.3 ng / ml , p < 0.01 ) . after controlling for age , gender , and body mass index , 
 positive correlation was observed between plasma leptin concentration and log - transformed levels of pro - inflammatory cytokines ( il-1 , il-6 , tnf- and crp ) , and the partial correlation coefficients ranged from 0.199 to 0.376 ( p < 0.05 ) . 
 log - transformed il-1 and il-6 levels entered the final regression model ( standardized  were 0.422 and 0.461 respectively , p < 0.01).conclusions : elevated plasma leptin concentration may be associated with increased systemic levels of inflammatory markers in agp patients .