resistance to leptin action is the major determinant of hepatic triglycerides accumulation in vivo....
TRANSCRIPT
Resistance to Leptin Action is Resistance to Leptin Action is the Major Determinant of the Major Determinant of
Hepatic Triglycerides Hepatic Triglycerides Accumulation in vivo.Accumulation in vivo.
BySigal Fishman, MD
Insulin resistance/Syndrome X• Obesity/abdominal obesity• Diabetes (Type 2)• Hyperlipidemia (low HDL)• Hypertension (increased AGT)• Thrombosis (increased PAI-1)• Inflammation (Cytokines)• NAFLD• Leptin resistance (High leptin; develops with insulin resistance)
• Resistance to both, insulin and leptin action Resistance to both, insulin and leptin action may be implicated in accumulation of may be implicated in accumulation of hepatic TG hepatic TG
• Which one is the major determinant??Which one is the major determinant??
Leptin role:
Browning JD JCI 2004
Insulin action on glucose metabolism
Peripheral Hepatic
glycogenolysis Gluco-neogenesis
Glycogensynthesis
Glycolysis
Clamp studies
• Hyperinsulinemic clamp assesses peripheral insulin action and hepatic
• Insulin infused at a fixed rate (3mU/kg/min)
• In insulin sensitive states, glucose is driven into the cells, higher rate of glucose infusion required to maintain euglycemia
• In insulin resistant states, the amount of glucose required to maintain euglycemia is much lower.
• Glucose fluxes in to the peripheral tissues assessed by the use of tracers.
Clamp studies
• Blood glucose is a balance between Tissue glucose uptake (RD) and Hepatic glucose production (HGP)+ Glucose infusion rate (GIR).
• When hepatic glucose production goes down, glucose infusion rate should be increased to maintain euglycemia.
Liver
Muscle
25% glucose
Insulin action
++
__
Diet
a. Glycolysis
b. Glycogen syntase
a. Glycogenolysis
b. Gluconeogenesis
Insulin glucose isotopes infusion
Blood
Sample
VF- IV catheter
Day of the clampRecovery
Day -3
Day 0
Tritiated glucose infusion
Insulin 3mu/kg/min+glu
Somatostatin
H2O3
OldYoung
r=-0.57
p=0.01
Relationship between hepatic TG and hepatic insulin action
0
1
2
3
4
5
6
7
8
9
10
11
0 5 10
^ HGP (mg/kg/min)
He
pa
tic
TG
Co
nte
nt
(mg
/gr)
0
1
2
3
4
5
6
7
8
9
10
11
0 5 10
^ HGP (mg/kg/min)
He
pa
tic
TG
Co
nte
nt
(mg
/gr)
Leptin reduces hepatic TG and improves hepatic insulin
sensitivity in young lean rats
1
0
0.5
1
1.5
2
2.5
3
TG (mg/g liver)
YoungLeptinPair-fed
Effect of chronic leptin delivery on the hepatic TG
P<0.01 vs. all
*
0
1
2
3
4
5
6
7
HGP (mg/kg/min)
YoungLeptinPair-fed
Effect of chronic leptin delivery on the insulin-mediated suppression of HGP
P<0.001 vs. all
Role for SCD-1 in mediating leptin action:
Monounsaturated Fatty acid
Saturated Fatty Acyl CoA
Oxidation
TG
VLDL Storage
Acetyl-CoA Malonyl-CoA
CPT-1
SCD-1
ACC
Cohen P. J Nutr 2004
Effect of chronic leptin delivery on hepatic SCD-1 expression
p<0.001 vs. young
SCD-1
young
leptin
pair-fed
0
0.5
1
1.5
Effect of chronic leptin delivery on hepatic ACC-1 expression
p<0.001 vs. youngACC-1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
youngleptinpair-fed
Effect of chronic leptin delivery on hepatic ACC2 expression
P<0.05 vs. young
ACC2
0123
4567
youngleptinPair-fed
0
0.5
1
1.5
2
2.5
Malonyl Co-A ()
YoungLeptinPair-fed
Barzilai et al. JCI. 100:3105, 1997
Effect of chronic leptin delivery on hepatic Malonyl Co-A levels
P<0.01 vs. all
*
Jiang G. JCI 2005
Leptin:
• Improves hepatic insulin sensitivity.• Decreases hepatic TG stores
What happens in leptin resistant states?
Leptin’s effect on insulin suppression of glucose production in aging
-100
-80
-60
-40
-20
0
Young Old
% S
up
pre
ssio
n
Leptin vs. pair-fed
*
TG levels after leptin administration in aging rats
0
1
2
3
4
5
6
7
8
TG (mg/g liver)
Old LeptinOld Saline
Young– pair-fed
Young– leptin
Old– pair-fed
Old – leptin
0
1
2
3
4
5
6
7
8
9
0 2 4 6 8 10 12
HGP (mg/kg/min)
Hep
atic
TG
Co
nte
nt (
mg
/gr)
*
#
**
##
1A
1B
Improvement in hepatic insulin Improvement in hepatic insulin action by visceral fat removal action by visceral fat removal is associated with reduction in is associated with reduction in
hepatic TG content in old hepatic TG content in old obese rats…but also with obese rats…but also with
improvement in leptin improvement in leptin sensitivitysensitivity
2
Epidydimal fat removalEpidydimal fat removal
Visceral fat
• Associated with insulin resistance, abnormal glucose tolerance and diabetes across all ages.
• Labile fat depot.
• VF is associated with increased risk of hypertension, thrombosis and dyslipidemias.
• VF, in adolescents, correlates with insulin resistance.
• Increased visceral fat seen in aging.
Are the fat depots biologically distinct?• Sprague-Dawley rats were sacrificed after 12 hours fast.• RNA was isolated from perinephric (visceral fat) and
subcutaneous adipose tissues.• Experiments were performed using rat genomic microarrays
(RGU34A), a platform containing 9000 genes (Affymetrix, Santa Clara, CA).
• Results of gene array expression involving genes implicated in insulin resistance (PPAR-, leptin) or it’s syndrome (angiotensinogen and plasminogen activating inhibitor-1 {PAI-1}), were confirmed and quantified by real time PCR.
• Some of the genes that are involved in glucose metabolism but were not part of the gene array platform, such as Resistin and Acrp 30, were studied by real time PCR.
Out of approximately 8,000 full-length sequences and approximately 1,000 EST clusters
1660 were expressed
297 were up/down- regulated in each chip
Atzmon et. Al Horm Metab Res. 2002; 34:622
Beta 3-adrenergic receptor 5 -Phosphoenolpyruvate carboxykinase (GTP) PEPCK 4.3 -PPAR-gamma 4.1 -Hormone sensitive lipase 3.5 -Insulin-like growth factor I 3.2 -Fatty acid transporter 3.2 -Thioesterase II - 156Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase - 21.1Low molecular weight fatty acid binding protein - 10.1GLUT1 = glucose transporter 1 - 9.8Lipopolysaccharide binding protein - 9.7Lysosomal acid lipase = intracellular hydrolase - 4.6Fatty acid synthase - 3.9Type II cAMP-dependent protein kinase regulatory subunit 7.4 -Adipocyte hormone-sensitive cyclic AMP phosphodiesterase 5.7 -Potential-sensitive polyspecific organic cation transporter 5.6 -Retinol-binding protein (RBP) gene, exon 5 5.2 -Steroidogenic acute regulatory protein 5 -Growth hormone receptor 5 -
Chaperonin 60 (Hsp60) and chaperonin 10 (CPN10) genes, nuclear genes encoding mitochondrial proteins
4.8 -
Aquaporin 7 4.3 -Angiotensinogen 4.5 -Glutathione-dependent dehydroascorbate reductase 4 -MHC class II antigen RT1.B-1 beta-chain 3.6 -Tricarboxylate carrier 3.6 -Thyroid stimulating hormone receptor 3.6 -Phosphodiesterase I 3.5 -Water channel aquaporin 3 (AQP3) - 20.8Carbonic anhydrase II - 11.8Wistar-Kyoto (Heidelberg) angiotensin converting enzyme - 7.4GST - 6.1Na-K-Cl cotransporter (Nkcc1) - 5.7Alpha-2-u globulin - 5.3Glutathione S-transferase Yc1 subunit - 4.7Wistar transforming growth factor beta-3 - 4.7Liver glutathione S-transferase Yc subunit - 4.4Polymeric immunoglobulin receptor - 4Alkaline phosphatase - 3.9
Cellular metabolism and other
Glucose homeostasis Insulin action and lipid metabolism
Atzmon et. Al Horm Metab Res. 2002 34:622
Visceral and SC fat are biologically distinct
Visceral fat and subcutaneous fat are biologically distinct.
Some of the significant changes are in the expression of fat-derived peptides that may have a role in insulin resistance (PPAR, leptin, resistin, and adiponectin) or its syndrome (PAI-1 and AT) and in factors affecting body fat distribution (leptin, adrenergic receptors, PPAR, IGF-1, GH).
Factors affecting expression of FDP
• Is there a role for nutrients in the expression of FDP?
• How do nutrients affect the two fat depots?
• Is the effect of nutrients on the two depots different?
• How do adipocytes “sense” excess nutrients?
FFA
Hexosamine Biosynthetic Pathway
Glucose
Glucose-6-P
Glc-1-P
UDP- Glc
Glycogen
F -6-P
Triose -P
Glycolysis
GlcN-6-P
UDPGlcNAc
GFAT
1-3%FFA
Glucosamine
Glycosylationsp1
SC02468
10121416
SalineGlucoseInsulinGlcN+In
PAI-1
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VF
Nutrients, nutrient sensing, and induction of fat-derived peptides
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Resistin
0
10
20
30
40
50
60
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SC VF
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0
2
4
6
8
10
12
SC VF
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TNF-
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1
2
3
4
5
6
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ADA, 2003
What are the biological reasons for the risks determined by increased
VF?1) VF expresses higher harmful fat-derived peptides.
2) Nutrients induce the expression of fat-derived peptides more in VF than other fat depots.
The metabolic syndrome
Apo BApo B InsulinInsulin
GlucoseGlucose TGTG
Skeletal Muscle
IRIR LPLLPL
NEFAsNEFAs
Liver
HLHL
NEFAsNEFAs
Increased Visceral Fat
. . Thin fibrous cap
. Unstable plaque
. Impaired fibrinolysis
. Increased collagen
. Endothelial dysfunction
. . Thin fibrous cap
. Unstable plaque
. Impaired fibrinolysis
. Increased collagen
. Endothelial dysfunction
GlucoseFFA
Nutrient sensing (HBP?)
TNF-TNF-LeptinLeptin
PAI-1PAI-1
IL-6IL-6
adiponectinadiponectin
TNF-TNF-
AdiponectinAdiponectin
ResistinResistin
leptinleptin
TNF-TNF-
Insulin’s Suppression of Hepatic Glucose production After VF removal
0-
2-
4-
6-
8-
10-
12-
HGP (mg/kg/min)
*
P<0.01
Old AL Old VF-
Reduction in Hepatic TG After VF removal
0
TG (mg/g liver)
*
P<0.01 vs. VF-
Old AL Old VF- Old SC-
2-
4-
6-
8-
Plasma FFA levels in this model (old VF-) do not relate to changes in hepatic TG
FFA (mmol/l)
old VF- old AL
Basal: 1.06 ± 0.13 0.83 ± 0.6
clamp: 0.77 ± 0.11 0.65 ± 0.1
Removal of visceral fat in rats results in coordinated changes in leptin level and leptin gene expression of SC fat.
VF-
Leptin
ß-actin
VF+ VF-
Leptin (expression)-VF-
0
20
40
80
100
60 M SC*
E P M SC E P M SC E P M SC
0
2
3
4
5
6
Leptin (ng/ml)
*
Old AL VF-
1
Decrease levels of hormone may be an index for improvement in its action!
VF removal might improved leptin sensitivity:
• Hormone level decreased ,combined with reduction in SC gene expression
• No change in food intake!
• In this model we can not dissociate again, insulin action from leptin role
Improvement in hepatic insulin Improvement in hepatic insulin Does not improve hepatic TG Does not improve hepatic TG
content in leptin resistant ZDF content in leptin resistant ZDF ratsrats
33
Removal of visceral fat improves glucose tolerance in Zucker diabetic rats .
ZDVF+ ZDVF-
4
6
8
10
12
Glucose (mM)
*
4
6
8
10
12
14
16
EGP (mg/kg/min)
*
0
25
50
75
100
125
Insulin (µU/ml)
GIR 0 2.1 (mg/kg/min)
ZDVF+ ZDVF-
TG levels after VF extraction in ‘leptin resistance’ Zucker rats.
0
24
68
10
1214
1618
20
TG (mg/g liver)
VF+VF-
Hepatic TG stores improves by leptin independent of insulin sensitivity
Old – sham operationOld – VF-
17
22
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12
HGP (mg/kg/min)
Hep
atic
TG
Co
nte
nt
(mg
/gr)
ZDF– sham operationZDF – VF-
*
#
$
**
##
2A
2B
Summery• Leptin and insulin resistance occur together with
obesity and overfeeding.• Leptin decreases hepatic TG stores by decreasing
lipogenesis and increasing ß-oxidation.(leptin studies in young)
• With leptin resistance hepatic TG stores are not decreased (in old obese animals).
• Reversal of insulin resistance is associated with decreasing hepatic TG stores. (Visceral fat removal)
• It is the leptin action and not the insulin action that modulates hepatic TG stores (in Zucker NASHI rats).
Nir BarzilaiRadhika HumuzumdarGil Atzmon Xiao-Hui MaXiao-man YangHong qiang Liang
Thank you!!!