-
The Possible Protective Role
ofGlucagon-LikePeptide1onEndotheliumDuring theMeal and Evidencefor
an “Endothelial Resistance” toGlucagon-Like Peptide 1 in
DiabetesANTONIO CERIELLO, MD1
KATHERINE ESPOSITO, MD2
ROBERTO TESTA, MD3
ANNA RITA BONFIGLI, PHD3
MAURIZIO MARRA, PHD3
DARIO GIUGLIANO, MD2
OBJECTIVE—Glucagon-like peptide 1 (GLP-1) stimulates insulin
secretion. However, GLP-1also improves endothelial function in
diabetes.
RESEARCHDESIGNANDMETHODS—Sixteen type 2 diabetic patients and 12
controlsubjects received a meal, an oral glucose tolerance test
(OGTT), and two hyperglycemic clamps,with or without GLP-1. The
clamps were repeated in diabetic patients after 2 months of
strictglycemic control.
RESULTS—During the meal, glycemia, nitrotyrosine, and plasma
8-iso prostaglandin F2a(8-iso-PGF2a) remained unchanged in the
control subjects, whereas they increased in diabeticpatients.
Flow-mediated vasodilation (FMD) decreased in diabetes, whereas
GLP-1 increased inboth groups. During the OGTT, an increase in
glycemia, nitrotyrosine, and 8-iso-PGF2a and adecrease in FMD were
observed at 1 h in the control subjects and at 1 and 2 h in the
diabeticpatients. In the same way, GLP-1 increased in both groups
at the same levels of the meal. Duringthe clamps, in both the
control subjects and the diabetic patients, a significant increase
in nitro-tyrosine and 8-iso-PGF2a and a decrease in FMD were
observed, effects that were significantlyreduced by GLP-1. After
improved glycemic control, hyperglycemia during the clamps was
lesseffective in producing oxidative stress and endothelial
dysfunction and the GLP-1 administrationwas most effective in
reducing these effects.
CONCLUSIONS—Our data suggest that during the meal GLP-1 can
simultaneously exert anincretin effect on insulin secretion and a
protective effect on endothelial function, reasonablycontrolling
oxidative stress generation. The ability of GLP-1 in protecting
endothelial functionseems to depend on the level of glycemia, a
phenomenon already described for insulin secretion.
Diabetes Care 34:697–702, 2011
O ral administration of glucose is amore potent secretory
stimulus forinsulin than its intravenous infu-sion (1). This
observation gave rise to the“incretin effect” concept, i.e.,
stimulationof insulin secretion as a response to foodbefore an
increase in blood glucose levels.An incretin hormone is the
glucagon-likepeptide 1 (GLP-1).
Type 2 diabetes mellitus is increasingall over the world.
Patients with diabetes
have an increased risk of cardiovasculardisease. Recently, much
attention hasbeen paid to evidence that abnormalitiesof the
postprandial state are importantcontributing factors to the
developmentof atherosclerosis, even in diabetes (2). Indiabetic
subjects, the combination ofpostprandial hyperglycemia and
post-prandial hypertriglyceridemia has beenrecently proposed as an
independentrisk factor for cardiovascular disease (2).
The response-to-injury hypothesisof atherosclerosis states that
the initialdamage affects the arterial endothelium,leading to
endothelial dysfunction (3). In-deed, endothelial dysfunction has
beendemonstrated in patients with diabetes,and hyperglycemia has
been implicatedas a cause of endothelial dysfunction innormal and
diabetic subjects (2). It hasbeen suggested that hyperglycemia
indu-ces an endothelial dysfunction throughthe production of an
oxidative stress (2).
GLP-1 is now being used in clinics toenhance insulin secretion
and reducebody weight in patients with type 2 di-abetes mellitus
(4), in whom a defect ofGLP-1 secretion/action in response to
themeal has often been reported (5). GLP-1has been shown to lower
postprandialand fasting glucose and HbA1c, to sup-press the
elevated glucagon level, and tostimulate glucose-dependent insulin
syn-thesis and secretion (4).
Apart from the well-documented in-cretin effect of GLP-1, its
role in thecardiovascular system also arouses inter-est. GLP-1
effects on the cardiovascularsystem may include a direct action on
theendothelium, where the presence of spe-cific receptors for GLP-1
has been demon-strated (6). GLP-1 has been demonstratedto improve
endothelial function in diabe-tes (7). However, the explanation of
whyGLP-1 may have such a relevant physio-logic role on
cardiovascular system stillremains unknown. A possible
explanationwould be to consider GLP-1 as an endog-enous protective
factor for the vascularsystem when this protection is
especiallyneeded: during a meal. As pointed out byZilversmit (8)
many years ago, atheroscle-rosis could be considered to be a
prandialphenomenon. Therefore, it is clearly plau-sible that GLP-1,
on the one hand, canhelp during a meal (glucose
homeostasis,appetite control, fat metabolism), and onthe other, can
protect the endotheliumagainst the possible damaging effect ofthe
meal. This protective effect should be
c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c
c c c c c c c c c c c c c c c c c
From the 1Insititut d’Investigacions Biomèdiques August Pi i
Sunyer, Barcelona, Spain; the 2Division ofMetabolic Diseases,
Center of Excellence for Cardiovascular Diseases, Second University
of Naples, Naples,Italy; and the 3Metabolic and Nutrition Research
Centre on Diabetes, INRCA, Ancona, Italy.
Corresponding author: Antonio Ceriello,
[email protected] 14 October 2010 and accepted 21
December 2010.DOI: 10.2337/dc10-1949© 2011 by the American Diabetes
Association. Readers may use this article as long as the work is
properly
cited, the use is educational and not for profit, and thework is
not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/
for details.
care.diabetesjournals.org DIABETES CARE, VOLUME 34, MARCH 2011
697
P a t h o p h y s i o l o g y / C o m p l i c a t i o n sO R I G
I N A L A R T I C L E
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exerted improving the antioxidant defen-ses of the endothelium
(9), thereby pro-tecting the vascular system against theoxidative
stress that increases afteringesting a meal (2).
The aim of this study is to prove thatGLP-1 physiologically
protects the endothe-lial function during a meal and,
morespecifically, protects the endothelial func-tion from the
hyperglycemia-induced alter-ations, and that this effect is
mediated bylowering oxidative stress. Moreover, a fur-ther aim is
to explore this aspect in diabetes.
RESEARCH DESIGN ANDMETHODS—Sixteen type 2 diabeticpatients and
12 matched healthy controlsubjects participated in the study.
Base-line characteristics of the study groups areshown in Table
1.
The study was approved by the ethicscommittee of Institut
d’Investigacions Bio-mèdiques August Pi i Sunyer (IDIBAPS),and
written consent from the study sub-jects was obtained.
Ten patients were on diet alone, andthe other six patients were
on metformin,which was discontinued at least 4 weeksbefore the
study. None of the type 2 di-abetic patients had retinopathy,
nephropa-thy, or neuropathy. Five patients hadhypertension treated
with an angiotensin-converting enzyme inhibitor, which waswithheld
on the study days. None of thesubjects were receiving statin or
antioxi-dant supplementation.
Synthetic GLP-1 (7–36) amide waspurchased from PolyPeptide
Laboratories
(Wolfenbuttel, Germany), and the samelot number was used in all
studies.
Study designBoth healthy control subjects and type 2diabetic
patients underwent the followingstudies: a standard meal according
toVollmer et al. (10) and an oral glucosetolerance test (OGTT; 75 g
glucose in300 mL water) in randomized order, ondifferent days.
These tests were followedin a randomized order and on differentdays
by two hyperglycemic clamps (11)with or without GLP-1. GLP-1 was
in-fused at a rate aiming to have the sameplasma concentration
reached duringthe OGTT (0.4 pmol z kg21 z min21) ac-cording to
Nauck et al. (12). During thehyperglycemic clamp, the level of
glyce-mia was settled at the same level as thatof mean glycemia
reached at 1 h (controlsubjects 8.5 mmol/L; diabetic patients15
mmol/L) and 2 h (control subjects5 mmol/L; diabetic patients 12.8
mmol/L)during the OGTT.
At the end of these studies, diabeticpatients were treated
intensively with in-sulin for 2 months to improve glycemiccontrol.
The clamp studies were thenrepeated randomly with the same levelsof
glycemia and GLP-1 infusion rate.
At baseline and at 1 and 2 h, duringthe meal test and the OGTT,
and duringeach clamp, glycemia, insulin, endothelialfunction
(flow-mediated vasodilation[FMD]), plasma nitrotyrosine and
plasma8-iso prostaglandin F2a (8-iso-PGF2a)(both markers of
oxidative stress), and
GLP-1 (active 7–36) plasma levels weremeasured.
Biochemical measurementsCholesterol and triglycerides were
mea-sured enzymatically (Roche Diagnostics,Basel, Switzerland). HDL
cholesterol wasestimated after the precipitation of apoli-poprotein
B with phosphotungstate/magnesium (13). LDL cholesterol was
cal-culated after lipoprotein separation (13).Plasma glucose was
measured by theglucose-oxidase method, HbA1c wasmeasured by
high-performance liquidchromatography, and insulin was mea-sured by
microparticle enzyme immuno-assay (Abbott Laboratories,
Wiesbaden,Germany). Nitrotyrosine plasma concen-tration was assayed
by enzyme-linkedimmunosorbent assay, recently validatedby our
laboratory (13).
A commercially available kit was usedto measure 8-iso-PGF2a
(Cayman Chem-ical, Ann Arbor, MI). GLP-1 (active 7–36)was measured
by a radioimmunoassay kit(Peninsula Laboratories, Belmont, CA).The
detection limit is 10 pg/mL, and theintra- and interassay
coefficient of varia-tion are 8 and 18% at 50 pg/mL and 5 and13% at
300 pg/mL, respectively.
Endothelial functionFMD was evaluated (14). At the end ofeach
test, sublingual nitroglycerin (0.3 mg)was administered, and 3 min
later the lastmeasurements were performed to mea-sure
endothelium-independent vasodila-tion.
Statistical analysisData are expressed as mean 6 SE. Thesample
size was selected according to pre-vious studies (7,10). The
Kolmogorov–Smirnov algorithmwas used to determinewhether each
variable had a normal dis-tribution. Comparisons of baseline
dataamong the groups were performed usingunpaired Student t test or
Mann-WhitneyU test, where indicated. The changes invariables during
the tests were assessedby two-way ANOVA with repeated meas-ures or
Kolmogorov–Smirnov test, whereindicated. If differences reached
statisticalsignificance, post hoc analyses withpaired, two-tailed t
test or Wilcoxonsigned rank test for paired comparisonswere used to
assess differences at individ-ual time periods in the study.
Statisticalsignificance was defined as P , 0.05.
RESULTS—As expected, basal glyce-mia, insulin, HbA1c,
nitrotyrosine, and
Table 1—Baseline characteristics of the control and type 2
diabetic subjects
Control subjects (n 5 12)Type 2 diabeticsubjects (n 5 16)
Sex 6M/6F 9M/7FAge, years 50.5 6 2.5 51.3 6 2.6BMI, kg/m2 28.5 6
3.1 29.5 6 3.3Duration of diabetes, years 5.5 6 1.3Fasting plasma
glucose, mmol/L 4.5 6 0.3 7.8 6 2.2*HbA1c, % 4.8 6 0.2 8.4 6
0.3*Resting systolic blood pressure, mmHg 117.3 6 5.5 123.4 6
6.4Resting diastolic blood pressure, mmHg 77.5 6 2.2 80.2 6
3.6Total cholesterol, mmol/L 4.5 6 0.6 5.1 6 0.8Triglycerides,
mmol/L 0.9 6 0.2 1.2 6 0.4HDL cholesterol, mmol/L 1.4 6 0.2 1.2 6
0.3LDL cholesterol, mmol/L 2.5 6 0.3 2.6 6 0.4FMD, % 11.7 6 0.7 5.9
6 0.6*Nitrotyrosine, mmol/L 0.24 6 0.05 0.52 6 0.03*8-iso-PGF2a,
pg/mL 32.6 6 4.6 65.0 6 4.5*Fasting insulin, pmol/L 73.3 6 4.4
107.3 6 15.2*Data are expressed as means 6 SE. *P , 0.001 vs.
control subjects.
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8-iso-PGF2a were increased in diabetes,and FMD was decreased
(Table 1). Basal,fasting level of GLP-1 was not differentbetween
control subjects and diabeticpatients (Table 1).
During the meal, all test parameters,except those for GLP-1 and
insulin, re-mained unchanged in the control sub-jects, whereas a
significant increase at 1and 2 h of glycemia, insulin,
nitrotyro-sine, and 8-iso-PGF2a and a decrease inFMD were observed
in type 2 diabeticpatients compared with their basal values.In both
control subjects and diabeticpatients, GLP-1 increased at 1 and 2
hin a similar manner (Fig. 1).
In the control subjects, during theOGTT, an increase of
glycemia, insulin,nitrotyrosine, and 8-iso-PGF2a and a de-crease of
FMD were observed at 1 h,whereas at 2 h all the parameters
returnedto the basal values (Fig. 1). In the diabeticpatients, at
both 1 and 2 h, a significant
increase of glycemia, insulin, nitrotyro-sine, and 8-iso-PGF2a
and a decrease ofFMD were observed compared with thebasal values
(Fig. 1). In both control sub-jects and diabetic patients, during
theOGTT, GLP-1 increased at 1 and 2 hin a similar manner (Fig. 1),
and the val-ues were not different from those reachedduring the
meal test (Fig. 1).
In diabetic patients, at both 1 and2 h, a significant increase
in glycemia (P,0.01), insulin (P , 0.01), nitrotyrosine(P , 0.05),
and 8-iso-PGF2a (P , 0.05),and a decrease in FMD (P , 0.05)
wereobserved compared with the valuesreached during theOGTT,
whereas no dif-ference was found for GLP-1 (Fig. 1).
According to the values observedduring the OGTT, during the
clamps gly-cemia was maintained for the first hourat 8.5 mmol/L in
control subjects and at15 mmol/L 1 h in diabetic patients,whereas
for the second hour glycemia
was maintained at 5 mmol/L in controlsubjects and at 13 mmol/L
in diabeticpatients. During the clamps, performedwith placebo,
GLP-1 concentration re-mained unchanged during the study pe-riod in
both control subjects and diabeticpatients, whereas its
concentration wasalmost equivalent to that observed duringthe meal
test and the OGTT when it wasconstantly infused (Fig. 2). Insulin
con-centration increased in both control sub-jects and diabetic
patients during thehyperglycemic clamp, and its increasewas
significantly higher during GLP-1 in-fusion (Fig. 2). During both
the clamps,with or without GLP-1, in the control sub-jects, an
increase in nitrotyrosine and8-iso-PGF2a and a decrease in FMDwere
observed at 1 h, whereas at 2 h, allthe parameters returned to
their basal val-ues (Fig. 2). Similarly, in diabetic patients,at
both 1 and 2 h during both the clamps,a significant increase in
nitrotyrosine and8-iso-PGF2a and a decrease in FMD wereobserved
compared with the basal values(Fig. 2). However, in the control
subjects,at 1 h, the values of nitrotyrosine and8-iso-PGF2a
significantly increased, andthe values of FMD significantly
decreasedin the clamp with placebo compared withthe values observed
during the clamp withGLP-1 (Fig. 2). Similarly, in diabetic
pa-tients at both 1 and 2 h, the values of nitro-tyrosine and
8-iso-PGF2a significantlyincreased, and the values of FMD
signifi-cantly decreased in the clamp with pla-cebo compared with
the values observedduring the clamp with GLP-1 (Fig. 2).
Two months of insulin treatment re-sulted in a significant
decrease in HbA1c(8.46 0.3 vs. 7.26 0.4%, P, 0.01) andan
improvement of fasting glycemia(8.2 6 2.0 vs. 6.4 6 1.8 mmol/L, P
,0.01), insulin (110.3 6 17.2 vs. 86.2 613.2 pmol/L, P , 0.01),
nitrotyrosine(0.52 6 0.03 vs. 0.39 6 0.06 mmol/L,P , 0.05),
8-iso-PGF2a (65.0 6 4.5 vs.44.2 6 2.5 pg/mL, P , 0.05), and FMD(5.9
6 0.6 vs. 7.8 6 0.7%, P , 0.05) indiabetic patients.
During the two clamps, in diabeticpatients, at 1 and 2 h, a
significant in-crease in nitrotyrosine and 8-iso-PGF2aand a
decrease in FMD (P , 0.01) wereobserved compared with the basal
values(Fig. 3). As before the improvement ofglycemic control, at
both 1 and 2 h, thevalues of nitrotyrosine and
8-iso-PGF2asignificantly increased and the values ofFMD
significantly decreased in the clampwith placebo compared with the
valuesobserved during the clamp with GLP-1
Figure 1—Changes of glycemia, GLP-1, FMD, plasma nitrotyrosine,
8-iso-PGF2a, and insulinduring the meal and the OGTT in normal
healthy control subjects and type 2 diabetic patients.Data are
expressed as mean6 SE;△, meal test controls;▲, OGTT controls;○,
meal test type 2diabetes;●, OGTT type 2 diabetes; *P, 0.001 vs.
basal; †P, 0.01 vs. basal; ‡P, 0.05 vs. basal;§P , 0.01 vs. OGTT;
||P , 0.05 vs. OGTT.
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(Fig. 3). However, the same values of gly-cemia were less
effective in producing ox-idative stress and endothelial
dysfunctionafter 2 months of improved glycemic con-trol. Because
the basal values before andafter tight glycemic control were
signifi-cantly different, we have compared the Dbetween the basal
value and the value at 1and 2 h, during each clamp,
respectively:Dnitrotyrosine 1 h 0.426 0.04 vs. 0.2060.05, P,
0.01;Dnitrotyrosine 2 h 0.3260.03 vs. 0.15 6 0.05, P , 0.01; D
8-iso-PGF2a 1 h 68.96 4.1 vs. 30.36 3.2, P,0.05; D 8-iso-PGF2a 2 h
50.5 6 3.1 vs.20.3 6 1.2, P , 0.01; D FMD 1 h 4.1 60.5 vs. 2.36
0.2, FMD, P, 0.05; D FMD2 h 3.7 6 0.5 vs. 2.2 6 0.2, FMD, P ,0.05
in the study performed with pla-cebo, compared with that in the
previousclamp. Of particular interest is that GLP-1administration
was most effective in
this condition of improved metaboliccontrol than in previous
experiments:Dnitrotyrosine 1 h 0.21 6 0.02 vs.0.08 6 0.02, P ,
0.01; Dnitrotyrosine2 h 0.15 6 0.04 vs. 0.03 6 0.02, P ,0.01; D
8-iso-PGF2a 1 h 31.5 6 4.1 vs.15.36 3.7, P, 0.05; D 8-iso-PGF2a 2
h20.3 6 2.1 vs. 10.2 6 1.5, P , 0.05; DFMD 1 h 1.5 6 0.4 vs. 0.6 6
0.2, FMD,P, 0.05; D FMD 2 h 2.16 0.3 vs. 0.360.2, FMD, P, 0.05 in
the study performedwith placebo, compared with the previousclamp.
GLP-1 infusion after optimized gly-cemic control was accompanied by
a sig-nificant increase in insulin secretion at both1 and 2 h (Fig.
3). No difference was foundin endothelium-independent
vasodilata-tion in all the studies.
CONCLUSIONS—This study dem-onstrated that the presence of
GLP-1
during hyperglycemia significantly pro-tects endothelial
function and decreaseshyperglycemia-induced oxidative
stressgeneration. This evidence clearly emergeswhen we compare the
effect of hypergly-cemia during the clamps in both normaland
diabetic patients. In the absence ofGLP-1, hyperglycemia induces
endothe-lial dysfunction and oxidative stress,whereas the
concomitant infusion ofGLP-1 significantly prevents this effect.It
has already been largely demonstratedthat hyperglycemia induces
endothelialdysfunction through the generation of anoxidative stress
(2) and that GLP-1 canreduce oxidative stress (9). GLP-1
alsoimproves endothelial dysfunction in dia-betes (7). Therefore,
our data suggest thatGLP-1 may protect endothelia functionduring
hyperglycemia, reducing oxida-tive stress generation.
Our data also support a possiblephysiologic protective role of
GLP-1 onendothelial function. However, the effectof GLP-1 on
endothelial function seemsto be dependent on the level of
hypergly-cemia. The same plasma levels of GLP-1have a different
effect on the endothelialfunction and oxidative stress in
normalsubjects during the test meal and theOGTT. Consistent with a
previous study,in normal control subjects the levels ofGLP-1 are
almost superimposable duringthe meal and the OGTT (9).
However,during the meal test, when glycemia re-mains constantly in
the normal range, en-dothelial function and oxidative stressremain
unaltered. However, at 1 h, duringthe OGTT, as already reported
(15), whenhyperglycemia appears, endothelial func-tion and
oxidative stress also appear.These data suggest that in the
presenceof hyperglycemia, GLP-1 partly loses itsprotective effect
on endothelial functionand oxidative stress.
This finding is also supported by thedata in diabetic patients.
As previouslyreported (10), the plasma levels of GLP-1were not
different between the meal testand the OGTT. As expected, the
levels ofglycemia were significantly different be-tween the meal
test and the OGTT, andthis was accompanied by a parallel wors-ening
of both oxidative stress and endo-thelial function.
The possibility that hyperglycemiamay condition the protective
effects ofGLP-1 on endothelial function and oxi-dative stress is
also supported by the datawith clamps in type 2 diabetic
patientsafter a period of improved glycemic con-trol.
Figure 2—Changes of glycemia, GLP-1, FMD, plasma nitrotyrosine,
8-iso-PGF2a, and insulinduring the hyperglycemic clamp with or
without GLP-1 infusion in normal healthy control sub-jects and type
2 diabetic patients. Data are expressed as mean6 SE;△,
hyperglycemic clamp +placebo control subjects; ▲, hyperglycemic
clamp + GLP-1 control subjects; ○, hyperglycemicclamp + placebo
type 2 diabetes;●, hyperglycemic clamp + GLP-1 type 2 diabetes; *P,
0.001 vs.basal; †P , 0.01 vs. basal; ‡P , 0.05 vs. basal; §P , 0.01
vs. placebo; ||P , 0.05 vs. placebo.
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As previously reported, improvingglycemic control partly
restored basalendothelial function and oxidative stress(16), as
well as the response to the samelevel of glycemia during the clamp
interms of oxidative stress and endothelialfunction. However, the
protective effectof infused GLP-1 was more pronouncedin this
situation of improved glycemiccontrol compared with the
previousstudy.
These data together support the hy-pothesis that the endothelium
becameless sensitive to GLP-1 in hyperglycemia,more than GLP-1
itself loses its activity.
This concept has already been pro-posed for insulin secretion,
where evi-dence suggests that the impaired GLP-1incretin effect is
mostly related to animpairment of b-cell function than to an
impairment of incretin secretion (5).Højberg et al. (17)
reported that a near-normalization of blood glucose has no ef-fect
on postprandial GLP-1 secretion, butit augments b-cell
responsiveness, similarto our data for endothelial function.
A possible direct influence of insulinconcentration on our
results cannot beexcluded. Insulin by itself has antioxidantand
vasodilatory effects (18), and GLP-1infusion during any clamp was
accompa-nied by a significant increase of insulinconcentration
compared with the pla-cebo. However, it has been reported thatacute
hyperglycemia during a clamp, as inour case, blunts the
vasodilatory effect ofinsulin (19). Moreover, at 2 h during
theclamps the effect of GLP-1 on FMD wasalmost similar to that at 1
h; even at 2 h,insulin concentration was significantly
reduced compared with 1 h (Fig. 3). Inaddition, insulin can
induce an endothe-lial dysfunction (20,21), evidence thatsupports
the possibility that GLP-1 has adirect beneficial effect on
endothelialfunction.
In conclusion, our data suggest thatduring the meal, GLP-1 can
simulta-neously exert an incretin effect on insulinsecretion and
have a protective effect onthe endothelial function, reasonably
con-trolling oxidative stress generation. As forinsulin secretion,
the ability of GLP-1 inprotecting endothelial function seems tobe
dependent on the level of glycemia (5).Hyperglycemia may induce at
the endo-thelial level, as well as at the level of theb-cells, a
resistance to the GLP-1 action.
Acknowledgments—No potential conflicts ofinterest relevant to
this article were reported.A.C. and K.E. researched data, wrote
the
article, and researched and reviewed the arti-cle. R.T.
researched and reviewed the article.A.R.B. and M.M. reviewed the
article. D.G.researched data, wrote the article, and re-searched
and reviewed the article.
References1. Drucker DJ. Minireview: the glucagon-
like peptides. Endocrinology 2001;142:521–527
2. Ceriello A. Postprandial hyperglycemiaand diabetes
complications: is it time totreat? Diabetes 2005;54:1–7
3. Ross R. The pathogenesis of atheroscle-rosis: a perspective
for the 1990s. Nature1993;362:801–809
4. Peters A. Incretin-based therapies: reviewof current clinical
trial data. Am J Med2010;123(Suppl.):S28–S37
5. Meier JJ, Nauck MA. Is the diminishedincretin effect in type
2 diabetes just anepi-phenomenon of impaired beta-cellfunction?
Diabetes 2010;59:1117–1125
6. Mudaliar S, Henry RR. Effects of incretinhormones on
beta-cell mass and function,body weight, and hepatic and
myocardialfunction. Am J Med 2010;123(Suppl.):S19–S27
7. Nyström T, Gutniak MK, Zhang Q, et al.Effects of
glucagon-like peptide-1 on en-dothelial function in type 2 diabetes
pa-tients with stable coronary artery disease.Am J Physiol
EndocrinolMetab 2004;287:E1209–E1215
8. Zilversmit DB. Atherogenesis: a post-prandial phenomenon.
Circulation 1979;60:473–485
9. Oeseburg H, de Boer RA, Buikema H, vander Harst P, van Gilst
WH, Silljé HH.Glucagon-like peptide 1 prevents reactiveoxygen
species-induced endothelial cellsenescence through the activation
of
Figure 3—Changes of glycemia, GLP-1, FMD, plasma nitrotyrosine,
8-iso-PGF2a, and insulinduring the hyperglycemic clamp with or
without GLP-1 infusion in normal healthy controlsubjects and type 2
diabetic patients at baseline and after 2 months of optimized
glycemic control.For the comparisons between baseline and after 2
months of optimized glycemic control, see theRESULTS section. Data
are expressed as mean 6 SE; △, hyperglycemic clamp + placebo; ○,
hy-perglycemic clamp + placebo after 2 months of optimized glycemic
control; ▲, hyperglycemicclamp + GLP-1;●, hyperglycemic clamp +
GLP-1 after 2 months of optimized glycemic control;*P , 0.001 vs.
basal; †P , 0.01 vs. basal; ‡P , 0.05 vs. basal.
care.diabetesjournals.org DIABETES CARE, VOLUME 34, MARCH 2011
701
Ceriello and Associates
-
protein kinase A. Arterioscler ThrombVasc Biol
2010;30:1407–1414
10. Vollmer K, Holst JJ, Baller B, et al. Pre-dictors of
incretin concentrations in sub-jects with normal, impaired, and
diabeticglucose tolerance. Diabetes 2008;57:678–687
11. DeFronzo RA, Tobin JD, Andres R.Glucose clamp technique: a
method forquantifying insulin secretion and resis-tance. Am J
Physiol 1979;237:E214–E223
12. Nauck MA, Heimesaat MM, Orskov C,Holst JJ, Ebert R,
Creutzfeldt W. Pre-served incretin activity of glucagon-likepeptide
1 [7-36 amide] but not of syn-thetic human gastric inhibitory
polypeptidein patients with type-2 diabetes mellitus.J Clin Invest
1993;91:301–307
13. Ceriello A, Mercuri F, Quagliaro L, et al.Detection of
nitrotyrosine in the diabeticplasma: evidence of oxidative stress.
Dia-betologia 2001;44:834–838
14. Corretti MC, Anderson TJ, Benjamin EJ,et al.; International
Brachial Artery Re-activity Task Force. Guidelines for
theultrasound assessment of endothelial-dependent flow-mediated
vasodilation ofthe brachial artery: a report of the In-ternational
Brachial Artery Reactivity TaskForce. J AmColl Cardiol
2002;39:257–265
15. Kawano H, Motoyama T, Hirashima O,et al. Hyperglycemia
rapidly suppressesflow-mediated endothelium-dependent va-sodilation
of brachial artery. J Am CollCardiol 1999;34:146–154
16. Ceriello A, Kumar S, Piconi L, Esposito K,Giugliano D.
Simultaneous control ofhyperglycemia and oxidative stress
nor-malizes endothelial function in type 1 di-abetes. Diabetes Care
2007;30:649–654
17. Højberg PV, Vilsbøll T, Zander M, et al.Four weeks of
near-normalization of bloodglucose has no effect on postprandial
GLP-1and GIP secretion, but augments pancreatic
B-cell responsiveness to a meal in patientswith type 2 diabetes.
Diabet Med 2008;25:1268–1275
18. Dandona P, Chaudhuri A, Ghanim H,Mohanty P. Insulin as an
anti-inflammatoryand antiatherogenic modulator. J Am CollCardiol
2009;53(Suppl.):S14–S20
19. Srinivasan M, Herrero P, McGill JB, et al.The effects of
plasma insulin and glucoseon myocardial blood flow in patients
withtype 1 diabetesmellitus. J AmColl Cardiol2005;46:42–48
20. Arcaro G, Cretti A, Balzano S, et al. Insulincauses
endothelial dysfunction in hu-mans: sites and mechanisms.
Circulation2002;105:576–582
21. Campia U, Sullivan G, Bryant MB,Waclawiw MA, Quon MJ, Panza
JA.Insulin impairs endothelium-dependentvasodilation independent of
insulin sen-sitivity or lipid profile. Am J Physiol HeartCirc
Physiol 2004;286:H76–H82
702 DIABETES CARE, VOLUME 34, MARCH 2011
care.diabetesjournals.org
Endothelial resistance to GLP-1 in diabetes