INSULIN RESISTANCE CAUSES AND
DR .KAPIL DEV
Decreased biological response to normal concentration of
Insulin (endogenous) or administered (exogenous).
Beta cells in the pancreas subsequently increase their
production of insulin, further contributing to
INSULIN RESISTANCE IS OFTEN SEEN
WITH THE FOLLOWING CONDITIONS
Infection or severe illness,
Inactivity and excess weight.
SIGNS AND SYMPTOMS
Inability to focus.
Intestinal bloating (cannot digest and absorb).
Sleepiness (after meals).
Weight gain, difficulty losing weight ( around abdominal
organs in both males and females).
Increased blood pressure
Increased blood triglyceride levels.
brown to black, poorly defined, velvety
hyperpigmentation of the skin.
found in body folds
↑insulin activates keratinocyte insulin-like growth
factor receptors, particularly IGF-1.
At high concentrations, insulin may also displace
IGF-1 from IGFBP.
Increased circulating IGF may lead to keratinocyte
and dermal fibroblast proliferation
CAUSES AND CONSEQUENCES
Mutation in IRS
Increased in serine phosporylation of IRS protein
PI3 Kinase Activity
Type 2 Diabetes mellites.
Obesity/ Inactivity and excess weight
Protein Kinase B
The serine/threonine kinase Akt (also called PKB), triggers insulin
effects on the liver
Akt1 --inhibiting apoptotic processes, induce protein synthesis
pathways, key signaling protein in cellular that lead to skeletal
muscle hypertrophy, general tissue growth
Akt2 is required for the insulin-induced translocation of glucose
transporter 4 (GLUT4) to the plasma membrane
Phosphorylation of the serine stimulates Akt phosphorylation at a
Glycogen synthase kinase 3 (GSK-3) inhibited upon
phosphorylation by Akt, which results in increase of glycogen
Suppression of hepatic glucose , PEPCK inhibition.
Glycogen synthase kinase
Insulin receptor substrate 1
MUTATION IN IRS
Most of the metabolic and antiapoptotic effects of insulin
are mediated by the signaling pathway involving the
phosphorylation of the insulin receptor substrate (IRS)
proteins, IRS-1, IRS- 2
Mutation of IRS 1 results in IR in muscles and adipose
Mutation of IRS 2 results in IR in liver.
INCREASED IN SERINE PHOSPORYLATION
OF IRS PROTEINS
Serine phosphorylation of IRS proteins can reduce the ability of IRS
proteins to attract PI3-kinase, minimizing its activation.
Serine phosphorylation in turn ↓ IRS-1 tyrosine phosphorylation,
impairing downstream effectors.
serine phosphorylation may lead to dissociation between insulin
receptor/IRS-1 &/or IRS-1/PI3-kinase, preventing PI3-kinase
activation or increased degradation of IRS-1
circulating FFA & adipokine tumour necrosis factor (TNF) may ↑
serine phosphorylation of IRS proteins, causing impaired insulin
CAUSES OF SERINE PHOSPHORYLATION
OF IRS-1 PROTEINS ARE
PI3 KINASE ACTIVITY
Consisting of a regulatory subunit p85, tightly associated with a
catalytic subunit, p110.
p85 monomer & p85-p110 heterodimer compete for same binding
sites on tyrosine-phosphorylated IRS proteins, Imbalance could
cause either ↑ or ↓PI3kinase activity
Human placental growth hormone causes severe insulin resistance
by specifically ↑ expression of p85α subunit
Subsequently affecting the ability of insulin to stimulate the
association of the p85-p110 heterodimer with IRS-1
Reducing the PI3-kinase insulin signaling resistant states induced
by obesity, type 2 diabetes
(α, βⅠ, βⅡ,
(δ, ε, θ, η)
FATTY ACID INDUCED IR
defective insulin-stimulated glucose transport activity
↑intramyocellular lipid metabolites (fatty acyl CoAs & diacylglycerol)
activate a serine/threonine kinase cascade
Defect insulin signaling through the Ser/Thr phosphorylation IRS-1
Reduced IRS 1 associated PI3K activity
Defective regulation of GLUT4
The primary defects in insulin action appear to be in muscle
cells and adipocytes, with impaired GLUT 4 translocation
resulting in impaired insulin-mediated glucose transport.
β cells fail to compensate for the prevailing insulin resistance
leading impaired glucose tolerance.
As glucose levels rise, β cell function deteriorates further, with
diminishing sensitivity to glucose and worsening
hyperglycemia and diabetes develops.
Due to the combined effects of human placental lactogen,
progesterone, oestradiol and cortisol, which act as counterregulatory hormones to insulin mainly in 3rd trimester of
Exaggeration of the insulin resistance normally seen in
pregnancy is associated with gestational diabetes mellitus and
In 2003 Rotterdam- indicated PCOS
excess androgen activity
Oligoovulation &/or anovulation
polycystic ovaries (ultrasound)
The ovarian dysfunction relates to the effects of compensatory
hyperinsulinaemia increasing pituitary LH secretion & androgen
production by the theca cells of the ovary.
Aromatization of androgens in setting of obesity ↑production of oestrogens,
further impairing function of the HPA axis.
Hyperinsulinaemia also suppresses SHBG production by liver, ↑ free
androgens. Elevated androgens in turn further aggravate insulin resistance.
INSULIN RESISTANCE SYNDROME
Constellation of associated clinical and laboratory findings
consisting of Insulin resistance, Hyperinsulinemia
dyslipidemia (↓HDL,↑ TG), Hypertension
Clinical syndromes associated with insulin resistance
include type 2 diabetes, cardiovascular disease, essential
hypertension, polycystic ovary syndrome, non-alcoholic
fatty liver disease, certain forms of cancer and sleep
Insulin is a vasodilator with secondary effects on Na+2
Hyperinsulinemia may result in enhanced sodium
reabsorption and increased sympathetic nervous system
(SNS) activity and contribute to the hypertension.
INSULIN RESISTANCE ROLE IN DEVELOPMENT OF
ATHEROSCLEROSIS AND HYPERTENSION
Compensatory hyperinsulinaemia is associated higher levels of
plasminogen activator inhibitor-1 (PAI-1) and ↑ fibrinogen levels
Dyslipidaemia with ↑ LDL, ↓ HDL are also found in insulin
Again, lower levels of testosterone in men have been associated
with a proatherogenic lipid profile (high total and LDL cholesterol)
Testosterone is an L-channel calcium blocker acting directly at the
level of the ion pore serve as systemic vasodilator improve cardiac
index and functional capacity.
Endothelin 1, a potent vasoconstrictor also inhibits insulin
signalling via PIP-3 kinase & competes with NO resulting in
Mitogenic properties, mediated via MAP (mitogen activated
protein) kinase pathway, remain intact.
These mitogenic effects of insulin on endothelial smooth muscle cell
proliferation probably contribute to atherosclerosis.
MEASUREMENT OF INSULIN RESISTANCE
= Fasting Glucose(mmol/L) x Fasting Insulin(mU/L)
= 1 / [log(fasting insulin µU/mL) + log(FBG mg/dL)]
Functional Measures of Insulin Resistance
McLoughlin et al were able to identify insulin resistant individuals
from an overweight-obese cohort
plasma triglyceride concentration,
ratio of triglyceride to high-density lipoprotein
Using cut points of
1.47 mmol/L for TG,
1.8 mmol/L for the TG-HDL - cholesterol ratio
109 pmol/L (16 mIU/L) for insulin
Review Article -Insulin and Insulin Resistance-Gisela WilcoxMelbourne Pathology, Collingwood, VIC 3066, Monash
University Department of MUnit, C/- Body Composition
Laboratory, Monash Medical Centre, Clayton, VIC 316
Willams Endocrinology12TH EDN
Teitz Clinical Chemistry 5TH EDN
Text book of biochemistry 3rd EDN lby dr.dinesh puri