Modulation of ingestive behavior and gastrointestinal motility by ghrelin in diabetic animals and humans.
ABSTRACT Acyl ghrelin, a 28-amino acid peptide hormone, is the endogenous cognate ligand for the growth hormone secretagogue receptor. Ghrelin is involved in stimulating growth hormone release, eliciting feeding behavior, inducing adiposity and stimulating gastrointestinal motility. Ghrelin is unique for its post-translational modification of O-n-octanoylation at serine 3 through ghrelin O-acyltransferase, and is the only peripheral signal to enhance food intake. Plasma ghrelin levels manifest "biphasic changes" in diabetes mellitus (DM). In the early stage of DM, the stomach significantly increases the secretion of ghrelin into the plasma, and elevated plasma ghrelin levels are correlated with diabetic hyperphagic feeding and accelerated gastrointestinal motility. In the late stage of DM, plasma ghrelin levels may be lower, which might be linked with anorexia/muscle wasting, delayed gastrointestinal transit, and even gastroparesis. Therefore, the unique ghrelin system may be the most important player compared to the other hindgut hormones participating in the "entero-insular axis". Further studies using either knockdown or knockout of ghrelin gene products and ghrelin O-acyltransferase may unravel the pathogenesis of DM, and show benefits in combating this disease and metabolic syndrome.
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ABSTRACT: Narcolepsy-cataplexy is characterised by orexin deficiency, sleep disturbance, obesity and dysautonomia. Ghrelin and obestatin affect both energy intake and sleep. Our aim was to investigate ghrelin, obestatin and metabolic/autonomic function in narcolepsy-cataplexy. Eight narcolepsy-cataplexy patients (seven CSF orexin-deficient) and eight matched controls were studied. The subjects had a fixed energy meal with serial blood samples and measurement of heart rate variability (HRV). Fasting plasma obestatin was more than threefold higher in narcolepsy subjects (narcolepsy 89.6 ± 16 pg/ml vs. control 24.9 ± 3 pg/ml, p < 0.001). There was no change in HRV total power, but post-prandial low-frequency (LF) power and high-frequency (HF) power were lower in the narcolepsy group [area under the curve (AUC): HF power narcolepsy 1.4 × 10(5) ± 0.2 × 10(5) vs. control 3.3 × 10(5) ± 0.6 × 10(5 )ms(2)/h, p < 0.001]. On multiple regression analyses, the only significant predictor of plasma obestatin was HF power, which was inversely correlated with obestatin (β = -0.65 R (2) = 38 %, p = 0.009). Fasting and post-prandial plasma ghrelin were similar in both groups (narcolepsy 589.5 ± 88 pg/ml vs. control 686.9 ± 81 pg/ml, p = 0.5; post-prandial AUC-narcolepsy 161.3 ± 22 ng/ml/min vs. control 188.6 ± 62 ng/ml/min, p = 0.4). Only the narcolepsy group had significant suppression of plasma ghrelin after the meal (ANOVA, p = 0.004). In orexin-deficient narcolepsy, fasting plasma ghrelin is unaltered, and post-prandial suppression is preserved. Fasting plasma obestatin is increased and correlates with autonomic dysfunction. As obestatin affects NREM sleep, we suggest that increased plasma levels contribute to the disrupted sleep-state control in narcolepsy.Endocrine 11/2012; · 1.42 Impact Factor
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ABSTRACT: Growth hormone (GH)-releasing peptides (GHRPs) are synthetic peptides that strongly induce GH release. GHRPs act via a specific receptor, the GHRP receptor (GHSR), of which ghrelin is a natural ligand. GHRPs also induce adrenocorticotropic hormone (ACTH) release in healthy subjects. GHRPs or ghrelin stimulate ACTH release via corticotropin-releasing factor (CRF) and arginin vasopressin in the hypothalamus. Stress-activated CRF neurons are suppressed by glucocorticoids in the hypothalamic paraventricular nucleus (PVN), while CRF gene is up-regulated by glucocorticoids in the PVN cells without the influence of input neurons. However, little is known about the regulation of ghrelin and GHSR type 1a (GHSR1a) genes by glucocorticoids in PVN cells. To elucidate the regulation of ghrelin and GHSR gene expression by glucocorticoids in PVN cells, here we used a homologous PVN neuronal cell line, hypothalamic 4B, because these cells show characteristics of the parvocellular neurons of the PVN. These cells also express ghrelin and GHSR1a mRNA. Dexamethasone increased ghrelin mRNA levels. A potent glucocorticoid receptor antagonist, RU-486, significantly blocked dexamethasone-induced increases in ghrelin mRNA levels. Dexamethasone also significantly stimulated GHSR1a mRNA and protein levels. Finally, ghrelin increased CRF mRNA levels, as did dexamethasone. Incubation with both dexamethasone and ghrelin had an additive effect on CRF and ghrelin mRNA levels. The ghrelin-GHSR1a system is activated by glucocorticoids in the hypothalamic cells.Regulatory Peptides 11/2011; 174(1-3):12-7. · 2.06 Impact Factor
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ABSTRACT: Few investigations reported the reductive effect of preload consuming on energy intake. The objective of the study was to compare the effects of consuming a mix of low glycaemic index foods such as vegetable salad, yogurt and water before or with meal on anthropometric measures and cardio vascular diseases (CVD) risks. In this randomized controlled clinical trial, 25 men and 35 women were recruited to consume similar amounts of macronutrients within a hypocaloric diet for 3 months. Although subjects in the preload group consumed preload 15 min before the main meal, subjects in the control group consumed them with meal. The results showed that body weight, waist circumference, triglyceride, total cholesterol and systolic blood pressure decreased in more amount in the preload group ( - 7.8 ± 0.5%, - 2.7 ± 0.2%, - 5.7 ± 1.1%, - 3.1 ± 0.53% and - 4.4 ± 0.4%, respectively; p < 0.05 for all). Fasting blood sugar and low density lipoprotein (LDL)-cholesterol decreased significantly only in the preload group. Consuming vegetable salad, yogurt and water as preload leads to greater changes in anthropometric measures and CVD risks.International Journal of Food Sciences and Nutrition 12/2012; · 1.26 Impact Factor
J Chin Med Assoc • May 2010 • Vol 73 • No 5
© 2010 Elsevier Taiwan LLC and the Chinese Medical Association. All rights reserved.
Acyl ghrelin, a 28-amino acid peptide hormone, has
been identified as the endogenous cognate ligand for
the growth hormone secretagogue receptor (GHS-R).1
It was discovered by “reverse pharmacology”.1,2After
acyl ghrelin binds to GHS-R, it induces the release of
growth hormone.3Ghrelin is mainly synthesized in
specific endocrine cells, designated X/A-like cells, in the
gastric oxyntic glands.1,4Des-acyl ghrelin, the major
form of ghrelin in plasma,2may be acylated into acyl
ghrelin through ghrelin O-acyltransferase (GOAT) in
the stomach.5In addition to inducing growth hor-
mone release, acyl ghrelin enhances food intake, and
it is the only peripheral signal to increase meal size.6
Acyl ghrelin also stimulates adiposity, which is inde-
pendent of its hyperphagic effects.7Therefore, ghrelin
is an interesting molecule of high clinical relevance to
human obesity and metabolic syndrome.8With regard
to the gastrointestinal tract, acyl ghrelin accelerates gas-
tric emptying9and elicits gastroduodenal phase III-
like contractions10in rats.
Diabetes mellitus (DM) is a common clinical prob-
lem with increasing prevalence in the world. There
are 2 main types of DM. Both types are caused by
derangement of insulin’s function and activity in the
body.11Type 1 DM most often develops in childhood
or adolescence and causes hyperglycemia due to
insufficient production of insulin, while over 90% of
all DM cases are type 2 DM. DM may manifest many
Modulation of Ingestive Behavior and
Gastrointestinal Motility by Ghrelin in Diabetic
Animals and Humans
Chih-Yen Chen1,2*, Mineko Fujimiya3, Alessandro Laviano4, Full-Young Chang1,2,
Han-Chieh Lin1,2, Shou-Dong Lee1,2
1Division of Gastroenterology, Department of Medicine, Taipei Veterans General Hospital and
2Faculty of Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan, R.O.C.;
3Department of Anatomy, Sapporo Medical University School of Medicine, Sapporo, Japan; and
4Department of Clinical Medicine, Sapienza University of Rome, Italy.
Acyl ghrelin, a 28-amino acid peptide hormone, is the endogenous cognate ligand for the growth hormone secretagogue
receptor. Ghrelin is involved in stimulating growth hormone release, eliciting feeding behavior, inducing adiposity and
stimulating gastrointestinal motility. Ghrelin is unique for its post-translational modification of O-n-octanoylation at serine
3 through ghrelin O-acyltransferase, and is the only peripheral signal to enhance food intake. Plasma ghrelin levels man-
ifest “biphasic changes” in diabetes mellitus (DM). In the early stage of DM, the stomach significantly increases the
secretion of ghrelin into the plasma, and elevated plasma ghrelin levels are correlated with diabetic hyperphagic feeding
and accelerated gastrointestinal motility. In the late stage of DM, plasma ghrelin levels may be lower, which might be
linked with anorexia/muscle wasting, delayed gastrointestinal transit, and even gastroparesis. Therefore, the unique
ghrelin system may be the most important player compared to the other hindgut hormones participating in the “entero-
insular axis”. Further studies using either knockdown or knockout of ghrelin gene products and ghrelin O-acyltransferase
may unravel the pathogenesis of DM, and show benefits in combating this disease and metabolic syndrome. [J Chin Med
Key Words: acyl ghrelin, diabetes mellitus, feeding, gastrointestinal motility, ghrelin O-acyltransferase
*Correspondence to: Dr Chih-Yen Chen, Division of Gastroenterology, Department of Medicine,
Taipei Veterans General Hospital, 201, Section 2, Shih-Pai Road, Taipei 112, Taiwan, R.O.C.
● Received: February 3, 2010
● Accepted: April 16, 2010
gastrointestinal symptoms such as nausea, vomiting,
diarrhea, constipation, abdominal pain,12and even
hyperphagia.13,14Some symptoms can be attributed
to gastrointestinal dysmotility. Acyl ghrelin dose-
dependently inhibits insulin secretion in mice,15and
the relationship between ghrelin and glucose metabo-
lism has been previously discussed in our review.8A
recent study revealed that MK-677, an acyl ghrelin
mimetic, increases blood glucose and HbA1c levels in
healthy aged volunteers after 1 year of administration.16
Mice lacking acyl ghrelin demonstrate lower fasting
blood glucose, a better insulin-induced blood-glucose-
lowering effect, as well as higher plasma insulin and
lower blood glucose levels after intraperitoneal glucose
injection.17These acyl ghrelin knockout mice are pro-
tected against hyperinsulinemia and hyperglycemia
induced by a high-fat diet.18,19GHS-R knockout mice
exhibit lower blood glucose and serum insulin lev-
els,20,21and greater “metabolic flexibility” under diet-
induced metabolic stress.22Furthermore, acyl ghrelin
and GHS-R double knockout mice show a greater
blood glucose drop during 50% caloric restriction.21
Inhibition of GOAT8and GOAT knockout23is pro-
posed to have potential for anti-diabetic therapeutics.
Since acyl ghrelin plays an important role in inducing
food intake, eliciting gastroduodenal phase III-like
contractions, accelerating gastric emptying, and glucose
homeostasis, the present mini-review will focus on
the influence of ghrelin on ingestive behavior and gut
motility in diabetic animals and humans.
Regulation of Ghrelin Secretion and the
Influence of Ghrelin on Ingestive
Behavior in Diabetes
Ghrelin-immunoreactive cell density was found to be
reduced in type 1 non-obese and type 2 obese dia-
betic mice.24This observation could explain the slow
gastric emptying and slow intestinal transit encoun-
tered in human diabetic gastroenteropathy, based on
the fact that ghrelin has gastrointestinal prokinetic
effects. However, the correlation between ghrelin lev-
els and diabetic gastrointestinal dysmotility needs to
be further investigated before drawing a definite con-
clusion. In streptozotocin-induced diabetic rats, the
number of ghrelin-immunoreactive cells in the gastric
fundus is consistently found to be decreased, whereas
insulin treatment reversed this finding, implying that
a decrease in ghrelin-immunoreactive cells reflects a
decrease in ghrelin content in X/A-like cells but not a
decrease of ghrelin-producing cells.25Body weight and
serum insulin levels in the streptozotocin-induced
rats was decreased, whereas plasma acyl ghrelin and
total ghrelin levels and gastric preproghrelin mRNA
expression levels were significantly increased.25When
considered together, these results indicate that DM, a
negative energy balance condition, may enhance pre-
proghrelin mRNA expression in the stomach and
ghrelin secretion into the bloodstream. Acyl ghrelin
and des-acyl ghrelin have been demonstrated to inhibit
apoptosis and stimulate proliferation of pancreatic β
cell lines and human islets of Langerhans.26This finding
indicates that acyl ghrelin, as well as des-acyl ghrelin,
might protect β cells against apoptosis and increase β
cell survival. A subsequent study revealed that acyl
ghrelin treatment for 21 days increases pancreatic
insulin, pancreatic and duodenal homeobox 1 gene
(Pdx1) mRNA and the number of replicating cells in
streptozotocin-treated neonatal rats.27This finding
showed that acyl ghrelin and des-acyl ghrelin promote
regeneration of β cells in streptozotocin-treated ani-
mals. Collectively, in addition to the effects compen-
satory for the loss of body weight and serum insulin
levels in streptozotocin-induced rats, the increases in
plasma acyl ghrelin and total ghrelin levels and gastric
preproghrelin mRNA expression levels could prevent
further β cell damage and facilitate β cell regeneration.
Therefore, early administration of acyl ghrelin might
prevent or ameliorate the development of DM in
disease-prone subjects after β cell destruction.27
Uncontrolled DM is characterized by marked
behavioral perturbations, such as severe hyperphagia
and increased circulating ghrelin levels could cause
the development of diabetic hyperphagia.12,13In
streptozotocin-induced rats, plasma total ghrelin levels
are increased well before the onset of hyperphagic feed-
ing, supporting the hypothesis that increased ghrelin
signaling contributes to the stimulatory effect on food
intake in the early stage of DM.13A subthreshold dose
of intracerebroventricular administration of acyl ghrelin
was found to increase food intake by 357% in diabetic
rats compared with that in controls, indicating in-
creased behavioral sensitivity to acyl ghrelin in the
absence of the opposing effects of leptin and insulin in
DM.13Similarly, plasma fasting acyl ghrelin levels are
increased, whereas des-acyl ghrelin levels are decreased
in patients with obesity-related type 2 DM compared
with lean subjects.28Metformin therapy was found to
prolong the postprandial fall in total plasma ghrelin
levels, and thus had concomitant effects on appetite
in type 2 DM, contributing to its actions in promoting
weight loss and attenuating weight gain in these
patients.29A recent study demonstrated that barley
intake dose-dependently decreases plasma glucose and
insulin levels, whereas postprandial reduction of plasma
J Chin Med Assoc • May 2010 • Vol 73 • No 5
C.Y. Chen, et al
des-acyl ghrelin is suppressed by barley intake in a
dose-dependent manner, compared with glucose and
white rice.30Since des-acyl ghrelin might have anorex-
igenic31,32and insulin-mimetic33effects, either through
binding to an additional as-yet unidentified receptor8
or buffering33of acyl ghrelin’s actions, it has been
advocated that a combination of white rice and barley
may play a beneficial role in preventing and treating
human type 2 DM.30However, total plasma ghrelin
levels are negatively correlated with HbA1c in diabetic
patients, suggesting that long-term poor glycemic
control might impair ghrelin secretion,34and that
plasma ghrelin levels could be lower in the late stage
of DM. Consistently, fasting total plasma ghrelin levels
are decreased in insulin-resistant obese adults compared
with those in equally obese insulin-sensitive controls,
implying that insulin resistance and compensatory
hyperinsulinemia are independently associated with
suppression of ghrelin.35In addition, salivary levels of
acyl ghrelin and des-acyl ghrelin are similarly decreased
in obese diabetic subjects in comparison with non-
obese diabetic and healthy controls.36These alterations
may have a causal role in the development and severity
Impacts of Ghrelin on Gastrointestinal
Motility in Diabetes
Circulating acyl ghrelin levels fluctuate and the peaks
are associated with the gastric migrating motor complex
cycle,37indicating the indispensable role of endogenous
acyl ghrelin in modulating gastrointestinal motility.
Experiments with a streptozotocin-induced DM rat
model showed elevated plasma acyl ghrelin levels in
diabetic rats, and the elevated levels were accompanied
with accelerated solid gastric emptying and enhanced
postprandial antro-pyloric coordination.38Treatment
with anti-acyl ghrelin antibodies suppressed the accel-
erated gastric emptying and stimulated antro-pyloric
coordination. An elevated plasma acyl ghrelin level-
induced accelerated gastric emptying could predispose
to overeating, which would, in turn, exacerbate DM
in the diabetic early stage. In contrast, gastric emptying
becomes slow in the late stage of DM, and severe gas-
troparesis sometimes occurs. These findings have clini-
cal implications in the prevention for the development
of complications in DM, such as diabetic gastroparesis,
as in the late stage of DM. Sham feeding is characterized
by an increase in pancreatic polypeptide and ghrelin
in normal healthy humans, whereas changes in pan-
creatic polypeptide and ghrelin levels in diabetic gas-
troparesis are significantly less than those in normal
subjects.39Ghrelin subsequent to lunch significantly
decreases in patients without gastroparesis, but not in
gastroparetic patients.40Taken together, these findings
suggest that decreased plasma ghrelin levels are linked
with a slow gastrointestinal transit in the late stage of
DM. Loss of rhythmicity in ghrelin levels of diabetic
gastroparesis highlights the importance of integrity of
the neurohumoral-intestinal axis.32Patients with dia-
betic gastroparesis show no decrease of plasma acyl
ghrelin after glucose loading, unlike patients without
gastroparesis or healthy controls,41indicating that dia-
betic gastroparesis might be related to ghrelin-associated
neurohormonal abnormalities. Conceivably, intravenous
infusion of acyl ghrelin improves impaired gastric emp-
tying in patients with diabetic gastroparesis, and this
effect is independent of vagal tone.42Therefore, we
propose that analogs of acyl ghrelin may represent a
new class of prokinetic agents in future treatment for
patients with diabetic gastroparesis.
Conclusions and Future Perspectives
Obesity has replaced cigarette smoking as a severe new
burden on public health.43Obesity-related metabolic
syndrome, and DM, which negatively affects quality
of life and life expectancy, also cannot be overlooked.
Ghrelin is an exceptionally intriguing gastric hormone,
and actively participates in the modulation of ingestive
behavior and gastrointestinal motility. Plasma ghrelin
levels are elevated in the early stage of DM, which
correlates with hyperphagic feeding and accelerated
gastrointestinal motility. In contrast, plasma ghrelin
levels can be decreased in the late stages of DM, which
may be linked with poor appetite, body weight loss
and gastroparesis. The “entero-insular axis” has clinical
implications for the treatment of human DM.44Hind-
gut hormones, such as glucose-dependent insulin-
otropic polypeptide and glucagon-like peptide 1, hold
great promise. However, a recent study indicated that
selective bypass of the proximal intestine by an endo-
luminal sleeve, mimicking human Roux-en-Y gastric
bypass (the only way to resolve DM), reduces body
weight and food intake, and improves fasting hy-
perglycemia and glucose tolerance in rats with diet-
induced obesity.45These results suggest that the
“foregut theory” may be preferable to the “hindgut
theory”. Therefore, ghrelin deserves more attention in
the pathogenesis of DM. Two recent studies showed
that measurement of total ghrelin did not adequately
reflect acyl ghrelin and des-acyl ghrelin levels.46,47
Therefore, in contrast to the original concept, levels
of total ghrelin are not an ideal surrogate for those of
J Chin Med Assoc • May 2010 • Vol 73 • No 5
Ghrelin in diabetic food intake & GI motility
acyl ghrelin.8Further studies, particularly using state-
of-the-art techniques to separately measure acyl ghrelin,
des-acyl ghrelin, and obestatin, are necessary to clarify
the differential roles of ghrelin gene products in the
pathogenesis of DM. Ghrelin manifests “biphasically”
in DM. GOAT enhancers, acyl ghrelin and/or des-acyl
ghrelin, and GHS-R agonists, may rescue damaged β
cells and even endothelial progenitor cell function in
individuals with type 2 DM,48while GOAT inhibitors,
immunization against acyl ghrelin/acyl ghrelin anti-
bodies, des-acyl ghrelin, and GHS-R antagonists, may
be useful in the treatment of hyperphagic feeding and
accelerated gastrointestinal motility in the early stage
of DM. Conversely, GOAT enhancers, acyl ghrelin, as
well as its mimetics and GHS-R agonists, may provide
therapeutic targets in the treatment of diabetic anorexia-
cachexia and gastroparesis in the late stage of DM. In
conclusion, manipulating the unique GOAT/ghrelin/
GHS-R system may provide relevant approaches to
prevent, ameliorate and treat disturbance of ingestive
behavior and gastrointestinal motility in human DM.
This work was supported by intramural grants from
Taipei Veterans General Hospital (V95C1-096 and
V96C1-112), Taiwan and a grant from Sapporo
Medical University for the Promotion of Medical
Science in 2009, Japan. The authors also appreciate
the kind help of Chi Chin-Wen, PhD, Hung Mei-Whey,
MS, and the Clinical Research Core Laboratory,
Taipei Veterans General Hospital.
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J Chin Med Assoc • May 2010 • Vol 73 • No 5
Ghrelin in diabetic food intake & GI motility