glucagonlike peptide1 ( glp1 ) , the most potent incretin hormone , stimulates glucoseinduced insulin secretion and inhibits glucagon secretion , which consequently leads to a decrease in hepatic glucose production and blood glucose levels .
in addition to its ability to modulate insulin and glucagon secretion , glp1 inhibits gastric emptying and gastric acid secretion , which suppress appetite and energy intake in obese individuals , and in patients with type  2 diabetes .
glp1 is secreted from intestinal l  cells in response to ingestion of nutrients , including carbohydrate and lipids .
a previous study showed that alphalinolelic acid ( la ) promoted glp1 secretion through the stimulation of gproteincoupled receptor ( gpr ) 120 , which is abundantly expressed in the intestine , in mice .
furthermore , a recent study has shown that eicosapentaenoic acid ( epa ) and docosahexaenoic acid ( dha ) , metabolites of la , stimulate endogenous glp1 secretion in mice .
these reports show that 3 polyunsaturated fatty acids ( pufa ) , including la , epa and dha , increase glp1 secretion in mice .
however , no evidence that 3 pufa ingestion increases glp1 secretion is available in humans .
as compared with americans and europeans , japanese eat more fish , which is a major source of epa and dha . hence , serum epa or dha concentrations are higher in japanese than those in americans or europeans . evidence that fish intake prevents atherosclerosisrelated cardiovascular disease have been accumulating .
a recent study has shown a significant inverse correlation between serum epa or dha concentrations and cardiovascular risk .
furthermore , some studies showed that fish intake reduced the rates of incidence for diabetes in patients with metabolic syndrome , and reduced the rates of death in patients with type  2 diabetes .
however , the direct effects of epa or dha consumption on glycemic control in patients with type  2 diabetes have remained uncertain .
dpp4 inhibitor increases endogenous active glp1 levels through inhibition of dpp4 enzyme activity , leading to increased circulating insulin levels and decreased blood glucose levels .
the circulating glp1 levels were reported to be lower in patients with type  2 diabetes than in nondiabetic patients .
therefore , dpp4 inhibitor might be more effective in increasing circulating glp1 levels in patients with type  2 diabetes if they have low glp1 levels . based on these lines of evidence , we hypothesized that dpp4 inhibitor would be effective in patients with type  2 diabetes with high serum 3 pufa concentrations . in the present study , therefore , we investigated the relationship between serum epa or dha concentrations and a decrease in hemoglobin a1c in patients with type  2 diabetes prescribed dpp4 inhibitors .
serum epa and dha concentrations were measured in 62 consecutive patients with type  2 diabetes recruited from the outpatient clinic at kyoto prefectural university of medicine , kyoto , japan , who were newly given dpp4 inhibitor as a monotherapy or as an addon therapy to oral hypoglycemic agents ( oha ) .
patients with advanced renal dysfunction ( serum creatinine concentration was equal to or more than 2.0  mg / dl ) were excluded from the present study .
sitagliptin at a daily dose of 50  mg , which was the standard dose in japanese patients , was continuously given once daily during the observation period .
the prior diet , exercise program and dosage of oha in the study patients were maintained during the observation period .
after 24  weeks of treatment with dpp4 inhibitor , we evaluated the relationships between a decrease in hemoglobin a1c from baseline and serum epa or dha concentrations , as well as age , sex , body mass index ( bmi ) , hemoglobin a1c at baseline and usage of antidiabetic concomitant drugs .
type  2 diabetes was diagnosed according to the report of the expert committee on the diagnosis and classification of diabetes mellitus .
approval for the study was obtained from the local research ethics committee , and informed consent was obtained from all patients .
serum total cholesterol , highdensity lipoprotein cholesterol and triglyceride concentrations were assessed using standard enzymatic methods .
hemoglobin a1c was assayed using highperformance liquid chromatography and was expressed as a national glycohemoglobin standardization program unit as recommended by the japan diabetes society
skewed variables , such as epa and dha , are presented as the median ( interquartile range ) , and continuous variables are presented as the mean    standard deviation ( sd ) .
paired ttest was carried out to assess the statistical significance of difference in hemoglobin a1c between baseline and after dpp4 inhibitor treatment , and unpaired ttest was carried out to assess the statistical significance of difference in a decrease in hemoglobin a1c between groups using stat view software ( version 5.0 ; sas institute , cary , nc , usa ) . because epa and dha showed skewed distributions , logarithm ( log ) transformation was carried out before performing correlation and regression analysis . the relationship between log epa , log dha or log ( epa  +  dha ) and a decrease in hemoglobin a1c
was examined by linear regression analysis . in multiple regression analysis to assess the effects of various factors on decrease in hemoglobin a1c , we included independent variables that were significantly correlated with a decrease in hemoglobin a1c in the univariate analyses .
serum epa and dha concentrations were measured in 62 consecutive patients with type  2 diabetes recruited from the outpatient clinic at kyoto prefectural university of medicine , kyoto , japan , who were newly given dpp4 inhibitor as a monotherapy or as an addon therapy to oral hypoglycemic agents ( oha ) .
patients with advanced renal dysfunction ( serum creatinine concentration was equal to or more than 2.0  mg / dl ) were excluded from the present study .
sitagliptin at a daily dose of 50  mg , which was the standard dose in japanese patients , was continuously given once daily during the observation period .
the prior diet , exercise program and dosage of oha in the study patients were maintained during the observation period .
after 24  weeks of treatment with dpp4 inhibitor , we evaluated the relationships between a decrease in hemoglobin a1c from baseline and serum epa or dha concentrations , as well as age , sex , body mass index ( bmi ) , hemoglobin a1c at baseline and usage of antidiabetic concomitant drugs .
type  2 diabetes was diagnosed according to the report of the expert committee on the diagnosis and classification of diabetes mellitus .
approval for the study was obtained from the local research ethics committee , and informed consent was obtained from all patients .
serum total cholesterol , highdensity lipoprotein cholesterol and triglyceride concentrations were assessed using standard enzymatic methods .
hemoglobin a1c was assayed using highperformance liquid chromatography and was expressed as a national glycohemoglobin standardization program unit as recommended by the japan diabetes society .
means , medians or frequencies of potential confounding variables were calculated . skewed variables , such as epa and dha ,
are presented as the median ( interquartile range ) , and continuous variables are presented as the mean    standard deviation ( sd ) .
paired ttest was carried out to assess the statistical significance of difference in hemoglobin a1c between baseline and after dpp4 inhibitor treatment , and unpaired ttest was carried out to assess the statistical significance of difference in a decrease in hemoglobin a1c between groups using stat view software ( version 5.0 ; sas institute , cary , nc , usa ) . because epa and dha showed skewed distributions , logarithm ( log ) transformation was carried out before performing correlation and regression analysis . the relationship between log epa , log dha or log ( epa  +  dha ) and a decrease in hemoglobin a1c
was examined by linear regression analysis . in multiple regression analysis to assess the effects of various factors on decrease in hemoglobin a1c
, we included independent variables that were significantly correlated with a decrease in hemoglobin a1c in the univariate analyses .
characteristics of the 62 patients with type  2 diabetes enrolled in the present study are shown in table  1 .
the median ( interquartile range ) serum epa concentration was 62.6  g / ml ( 39.588.0 ) and the median ( interquartile range ) serum dha concentration was 139.1  g / ml ( 109.4165.7 ) . among 62 patients
, 16 patients were given dpp4 inhibitor as a monotherapy and 46 patients were given it as an addon therapy ( 34 sulfonylurea , 25 metformin , 8 pioglitazones , 5 alphaglucosidase inhibitor ) .
data are n , mean    sd or median ( interquartile range ) .
mean hemoglobin a1c was significantly decreased from 8.1    1.1% at baseline to 7.2    1.0% at 24  weeks after administration of dpp4 inhibitor .
correlation between log epa , log dha or log ( epa  + dha ) and other variables are shown in table  2 .
log epa and log ( epa  +  dha ) correlated with a decrease in hemoglobin a1c .
log dha tended to correlate with a decrease in hemoglobin a1c , but it did not reach statistical significance .
dha , docosahexaenoic acid ; epa , eicosapentaenoic acid . a decrease in hemoglobin a1c correlated with bmi ( r  =  0.396 , p  =  0.0013 ) , age ( r  =  0.275 p  =  0.0032 ) , hemoglobin a1c at baseline ( r  =  0.490 , p  <  0.0001 ) , log epa ( r  =  0.285 , p  =  0.0246 ) and log ( epa  +  dha ) ( r  =  0.260 , p  =  0.0411 ) . there were no significant differences in decrease in hemoglobin a1c between male and female patients ( 1.0    0.8% vs 1.0    0.9% , p  =  0.9758 ) . decrease in hemoglobin a1c was greater in patients treated with antidiabetic concomitant drugs compared with that in patients without those ( 1.1    0.9% vs 0.6    0.4% , p  =  0.0342 ) . in the multiple regression analysis to examine the effects of variables on the decrease in hemoglobin a1c , we included the following independent variables , which were significantly correlated with a decrease in hemoglobin a1c in the univariate analyses : age , bmi , hemoglobin a1c at baseline , usage of antidiabetic concomitant drugs and log epa .
multiple regression analysis showed that bmi , hemoglobin a1c at baseline and log epa were independent determinants of a decrease in hemoglobin a1c ( table  3 ) .
presence of antidiabetic concomitant drugs ( no  =  0 , yes  =  1 ) .
in the present study , serum epa concentrations correlated with a decrease in hemoglobin a1c .
this correlation remained significant after adjustment for age , bmi , hemoglobin a1c at baseline and usage of antidiabetic concomitant drugs .
the median ( interquartile range ) serum epa concentration was 62.6  g / ml ( 39.588.0 ; the mean serum epa concentration was 68.6    34.1  g / ml ) , which was almost consistent with previous reports of the epa concentration in general japanese .
serum epa concentrations increase with age in apparently healthy japanese . in the present study , however , there was no significant correlation between log epa and age in patients with type  2 diabetes .
dpp4 inhibitor increases endogenous active glp1 levels through prevention of glp1 degradation , leading to an increase in circulating insulin levels and a decrease in blood glucose levels . because of the pharmacological action of dpp4 inhibitor on insulin secretion , dpp4 inhibitor is effective in type  2 diabetic patients with impaired insulin secretion , which is a characteristic of japanese patients with type  2 diabetes . indeed , as compared with american and european patients with type  2 diabetes , japanese patients with type  2 diabetes might be higher responders to dpp4 inhibitor .
interestingly , the present study has shown a strong correlation between bmi and decrease in hemoglobin a1c , suggesting that dpp4 inhibitor is more effective in lean patients who generally have impaired insulin secretion , rather than in obese patients with insulin resistance .
this is consistent with a recent study reporting the association of bmi with efficacy of the dpp4 inhibitor , sitagliptin .
previous studies showed that dpp4 inhibitor was effective as an addon therapy to some antidiabetic drugs , including metformin , pioglitazone and sulfonylurea .
the profile of diabetic therapy before dpp4 inhibitor administration was as follows : 16 used diet , 15 received sulfonylurea monotherapy , 12 received metformin monotherapy , eight received sulfonylurea and metformin , five received sulfonylurea and pioglitazone , two received sulfonylurea and alphaglucosidase inhibitor , and four took three drugs .
we analyzed the correlations between serum epa concentrations and a decrease in hemoglobin a1c in patients with dpp4 inhibitor monotherapy , dpp4 inhibitor addon therapy to sulfonylurea , to metformin , and to sulfonylurea and metformin .
log epa tended to correlate with a decrease in hemoglobin a1c only in patients with dpp4 inhibitor addon therapy to metformin , although it did not reach statistical significance ( r  =  0.526 , p  =  0.0796 ) .
there were no significant correlations between log epa and decrease in hemoglobin a1c in other treatment groups .
it seems to be difficult to show these results because of the small sample size in each treatment group . in basic studies
have shown that gpr120 functioned as a receptor for unstructured longchain fatty acids , and that the stimulation of gpr120 with la promoted glp1 secretion in  vitro and in  vivo .
furthermore , gpr120 has been shown to be abundantly expressed in the intestine both in humans and mice .
. however , the mechanism of glp1 secretion by 3 pufa has been less clear . in the present study , furthermore , serum dha concentrations did not show a significant association with the efficacy of dpp4 inhibitor , although they tended to positively correlate with a decrease in hemoglobin a1c .
further studies are required to clarify the mechanism of 3 pufastimulated glp1 secretion . taken together with these previous studies , and the ability of dpp4 inhibitor to increase endogenous active glp1 levels , the present result that serum epa concentrations correlated with the efficacy of dpp4 inhibitor might provide indirect evidence that epa has a potential to promote glp1 secretion in humans .
limitations of the present study included a small sample size and a short observation period .
therefore , the direct link between serum epa concentration and glp1 or insulin concentrations could not be assessed .
furthermore , because ingested fatty acids are generally absorbed within the small intestine , epa might be expected to act on gpr120 inadequately after oral administration .
there are no reports of a linear relationship between epa intake and serum epa concentrations . however , serum epa concentrations positively correlated with epa intake assessed by a selfadministered diet history questionnaire in a subgroup of patients with type  2 diabetes ( n  =  40 , r  =  0.419 , p  =  0.0066 ) .
therefore , we hope that serum epa concentrations could be a marker of epa intake . to our knowledge , this is the first report of the relationship between serum epa concentrations and the efficacy of dpp4 inhibitor in patients with type  2 diabetes , and suggests new avenues for research into incretin therapies .
large interventional studies are required to better assess the contributions of epa to the efficacy of dpp4 inhibitor in patients with type  2 diabetes . in conclusion ,
dpp4 inhibitor is effective in patients with type  2 diabetes with high serum epa concentrations .
 abstractaims / introduction :   eicosapentaenoic acid ( epa ) stimulates glucagonlike peptide1 ( glp1 ) secretion in mice . 
 we investigated the relationship between serum epa concentrations and the efficacy of dipeptidylpeptidase  iv ( dpp4 ) inhibitor in patients with type  2 diabetes.materials and methods :   serum epa concentrations were measured in 62 consecutive patients with type  2 diabetes who were newly given dpp4 inhibitor as a monotherapy or as an addon therapy to oral hypoglycemic agents . 
 the dosage of oral hypoglycemic agents was maintained during the observation period . 
 after 24  weeks of treatment with dpp4 inhibitor , we evaluated the relationships between a decrease in hemoglobin a1c from baseline and serum epa concentrations , as well as age , sex , body mass index ( bmi ) , hemoglobin a1c at baseline and usage of antidiabetic concomitant drugs.results :   hemoglobin a1c was significantly decreased from 8.1    1.1% to 7.2    1.0% by dpp4 inhibitor . a decrease in hemoglobin a1c correlated with bmi ( r  =  0.396 , p  =  0.0013 ) , age ( r  =  0.275 , p  =  0.0032 ) , hemoglobin a1c at baseline ( r  =  0.490 , p  <  0.0001 ) and log epa ( r  =  0.285 , p  =  0.0246 ) . 
 multiple regression analysis showed that bmi (   =  0.419 , p  =  0.0002 ) , hemoglobin a1c at baseline (   =  0.579 , p  <  0.0001 ) and log epa (   =  0.220 , p  
 =  0.0228 ) were independent determinants of decrease in hemoglobin a1c.conclusions :   dpp4 inhibitor is effective in patients with type  2 diabetes with high serum epa concentrations . 
 ( j diabetes invest , doi : 10.1111/j.20401124.2012.00220.x , 2012 ) 
Introduction
Materials and Methods
Patients
Biochemical Analyses
Statistical Analysis
Results
Discussion