INSULIN RESISTANCE Flashcards
What four organs contribute to hyperglycaemia?
Pancreas - decreased insulin output
Muscle - decreased glucose uptake
Fat - decreased glucose uptake and lipolysis
Liver - gluconeogenesis not inhibited
What are the two different fat types?
android fat is harmful – fat above the waist – linked to metabolic syndrome . fat bellow the waist – gynoid fat is harmless – insulin sensitive
What pathway occurs for beta cells?
Increased output and beta cell compensation, alterations in beta cell expression and genetic alterations, beta cell failure
What is the link between diabetes and cancer in terms of risk?
Diabetics are 5% more likely to develop cancer than non-diabetics (treating with insulin and sulphonylureas can increase risk)
What treatment in diabetics increases the risk of cancer?
Sulphonylureas and insulin
What happens in an insulin receptor knock out mouse?
Insulin receptor knock out mice: born at term with slight growth impairment but then get progressively high glucose levels. Then get beta cell failure (excessive degranulation) and death within 48-72 hours from hyperglycaemia and ketoacidosis
What happens in muscle specific knock out mice?
70-90% of an oral glucose load is taken up in skeletal muscle and this is one of the first defective sites in T2DM. But muscle specific IR KO mice have normal glucose and insulin tolerance tests. 75% less insulin stimulated glucose transport,78% less glycogen synthesis. Decrease in protein muscle mass. There is a redistribution of glucose to adipose tissue and increased body fat. 16% increase in free fatty acids 48% increase in serum TG
Liver specific insulin receptor knock out mice?
LIVER specific insulin receptor knock out mice are massively glucose intolerant and insulin resistant. Islet cell hypertrophy. Only 20% of an oral glucose load is taken up by adipose tissue which normally impairs lipolysis.
What happened in a glut 4 ko mouse?
Glut4 translocation to the plasma membrane: in the absence of insulin its in the nucleus but when insulin is present it goes to the membrane allowing glucose to enter the cell muscle specific glut4 knockout mouse: had higher levels of glucose after glucose injection
What happens in beta cell IRKO mice?
you get a progressive deterioration of glucose tolerance. Loss of the first phase response to glucose ( which is important as stops hepatic gluconeogenesis, comes from a stored pool of insulin).
What has been found concerning glut 4?
It has been found that there are 2 types of GLUT 4 receptors – one which is responsive to exercise (insulin independent via PKC and AMPK) and the other which is responsive to insulin (via the PI3K pathway – Akt stimulates the GLUT4 vesicles in the cytoplasm to move to the membrane)
What is AMPK’s role?
It was also shown that inactivation of AMPK in muscle cells causes mild glucose intolerance
When glucose is transported into the muscles via insulin or excerise if it is not used it gets stored as glycogen, if glycogen stores are high then this has negative feedback on the AMPK preventing more glucose entering – but if you exercise then this improves glucose tolerance as there is less glucogen negative feedback
What does AMPK do in the pancreas?
Decreased insulin levels
What does AMPK do in the muscle?
Increased glucose uptake, lipid oxidation and mitochondrial biogenesis
What does AMPK do in the liver?
Decreased hepatogluconeogenesis and increased lipid oxidation and decreased lipid synthesis
What does AMPK do in the fat?
Decreased lipogenesis and lipolysis meaning decreased circulating insulin and increased insulin sensitivity
What are AMPK’s roles concerning exercise?
decreases insulin secretion, increases exercise induced muscle glucose transport
When is AMPK activated?
When AMPK is activated (in starvation) it will inhibit pathways which use energy – stops fatty acid and protein synthesis, and stimulates pathways for energy production – fatty acid oxidation and glucose transport
metformin activates AMPK which causes decreased glucose and lipid synthesis – by blocking insulin secretion from the pancreas and increasing insulin sensitivity which appears to have beneficial effects on the B cells
What happens in adipose tissue knock out mice?
Adipose tissue insulin receptor knockout mice: found that knockout mice had improved glucose tolerance and insulin sensitivity, protection against hyperphagia induced obesity and inc longevity
Overall what happens in IRKO for liver, muscle and fat?
So: Muslce insulin knockout = no effect Liver = negative effect Adipose = positive effect
What happens in neuron specific IRKO?
Neuron specific insulin receptor knockout mouse: lots of insulin receptors are in the brain, but the brain metabolises glucose in an insulin independent manner however insulin receptor knockout mice were still: hyperphagic, obese, hyperleptinemic, insulin resistance, high TG reduced fertility 2ndry to hypothalamic hypogonadism (females mostly effected) – role in limiting reproduction in times of food deprivation?
What happens in BAT IRKO?
Brown adipocyte insulin receptor knockout mouse: progressive deterioration of glucose tolerance, progressive loss of BC mass and function –still unsure if the BAT is an endocrine organ and there is an adipokine which promotes B cell growth?
What activates AMPK?
. It is activated by increases in the cellular AMP:ATP ratio caused by metabolic stresses that either interfere with ATP production (eg, deprivation for glucose or oxygen) or that accelerate ATP consumption (eg, muscle contraction).
Why is Metformin good in cancer?
Activates AMPK. Once activated, AMPK switches on catabolic pathways that generate ATP, while switching off ATP-consuming processes such as biosynthesis and cell growth and proliferation.
In obesity and diabetes, what contributes to insulin resistance?
Subclinical inflammation
What is another reason there is increased inflammation in obesity?
Decreased production of the anti-inflammatory ADIPONECTIN
How does obesity and inflammation cause insulin resistance?
Inflammatory cytokines and stress lead to JNK and TNF alpha that lead to serine phosphorylation of IRS
What way does stress contribute to insulin resistance?
Cortisol causes gluconeogenesis
What is another way that inflammation is linked to T2DM?
Inflammatory markers help to predict t2dm
What was a study looking at inflammation and T2DM?
Salicylate for prevention of t2dm/inflammation. Low dose inhibits COX, thrombosis and platelet aggregation.
High dose is an inhibitor of NFkB kinase that inhibits NfkB promoting deactivation and suppression of pro inflammatory signalling.
ANAKINRA: blocks interleukin 1b action that improves glycaemic control and pro insulin to insulin ratio
What is the general pathway of interleukins and TNF being produced?
Macrophages and monocytes produce TNFalpha and interleukins
Describe subclinical inflammation as a risk factor/
It does vary between those who do and do not have the disease (study looked at risk factors for metabolic syndrome and CRP), there is a biologically plausible mechanism. Sub clinical inflammation can be used to predict the outcome of DM. Does improvement of subclinical inflammation lead to an improvement in DM
How can subclinical inflammation be improved?
exercise reduces CRP
weight loss reduces CRP
weight loss in the obese reduces TNF-alpha, interleukin-6, P-selectin, ICAM-1 and VCAM-1
What study is there for improvement in inflammation leading to an improvement in DM?
The use of statins that decrease the risk of developping T2DM
What are causes of insulin resistance and how is inflammation linked?
Oxidative stress, endoplasmic reticulum stress (ER stress), amyloid deposition in the pancreas, ectopic lipid deposition in the muscle, liver and pancreas, and lipotoxicity and glucotoxicity ALL OF WHICH ARE ASSOCIATED/EXACERBATED BY OBESITY
What is predictive of T2DM?
Furthermore, elevated levels of interleukin-1β (IL-1β), IL-6 and CRP are predictive of T2D
What is particularly of note concerning CRP?
increased CRP level, which is currently the best epidemiological biomarker for T2D-associated cardiovascular disease
What is one counter-intuitive study for inflammation in T2DM?
Some animal studies and several clinical trials using TNF blockade have failed to demonstrate beneficial effects on glucose metabolism. However, a few small studies conducted with obese individuals suggest that TNF blockers may alter insulin sensitivity or glycaemic parameters, indicating that further prospective studies may be warranted
What is the association between macrophages and obesity?
The increase in the number of macrophages in adipose tissue largely correlates with the degree of obesity. Proposed hypothesis that adipose tissue is associated with a phenotypic switch in macrophages from a M2 to a M1 phenotype and that these M1-type macrophages contribute to the development of insulin resistance
Is there inflammation seen in the islets?
Tissue inflammation has also been detected in the islets of patients with T2D, along with increased levels of cytokines and chemokines. Of note, patients with T2D and every animal model of T2D investigated to date display immune cell infiltration of the islet. slet tissue sections from patients with T2D also show fibrosis, which is found in conjunction with amyloid deposits, and this also argues for an inflammatory response in islets, as fibrosis is a hallmark of chronic inflammation.
What is the role of NfKB?
Indeed, IKKβ activates the transcription factor nuclear factor-κB (NF-κB), and obesity induces the expression of NF-κB target genes, such as pro-inflammatory cytokines, in the liver and adipose tissue1, 66, 67. These cytokines, including TNF, IL-6, and IL-1β, may promote insulin resistance in the tissues where they are produced, such as the liver and adipose tissue, and may also be transported through the circulation to affect more distant sites, including the vessel walls, skeletal and cardiac muscle, the kidneys and circulating leukocytes
How is the beta cell affected?
glucose concentrations induce the expression of the pro-apoptotic receptor FAS (also known as CD95) on β-cells82, which is further upregulated by glucose-induced IL-1β production by β-cells55. Therefore, IL-1β and FAS contribute to both the glucose-induced impairment of β-cell secretory function and apoptosis
What does high glucose do?
HIGH GLUCOSE PROMOTES IL1 SECRETION IN BETA CELLS that inhibits beta cell function and promotes apoptosis
What do salicyclates do?
Salicyclates inhibit the NfKB pathway
How can fatty acids be used in metabolism?
• Fatty acids can be oxidized and generate ATP by beta oxidation in the mitochondria.
What are fatty acids the primary energy source for
They are the primary oxidative fuel for the liver, resting skeletal muscle, renal cortex and myocardium, but not the CNS which relies on glucose
• Fasting→ adipose main energy source, can account for 70% sparing glucose
How can fatty acids be converted and how is this beneficial?
Can convert from saturated fat to unsaturated through DELTA 9 DESATURASE. If you treat diabetes with delta 9 desaturase then you get re-instatement of delta 6 desaturase nRNA and an improvement in microvascular complications
How can fatty acids lead to insulin resistance?
- Compete with glucose as a metabolic fuel to cause insulin resistance and affect insulin sensitivity according to diet. HIGH FATTY ACID LEVELS INCREASE INSULIN RESISTANCE BY OPPOSING OXIDATION OF GLUCOSE
- Affect insulin sensitivity via direct
How can fatty acids affect insulin resistance?
insulin sensitivity insulin secretion VLDL synthesis LDL receptor levels PPAR, HNF, RXR and LXR nuclear receptors SREBP-1c activity inflammation
What do fatty acids do in the short term versus long term to insulin secretion?
Short term they stimulate, long term they inhibit
How do fatty acids influence insulin sensitivity?
• Affect insulin sensitivity via direct signaling effects and via membrane composition
Name how obesity leads to DM?
SUbclinical inflammation, fatty acids, exercise and glut 4, AMPK’s beneficial effects though activated in starvation
What are the three states of fatty acids in the circulation?
- NEFAs (non esterified fatty acids) which are carried in the blood stream, primarily on albumin. In the serum it is mainl
- Esterified to form a cholesterol ester
- Triglyceride
What evidence is there for the risk of fatty acids in the diet
Epidemiological data showing the diabetes risk for the amount of saturated versus unsaturated fat, even taking into account BMI
What does high glucose lead to?
high glucose drives triglyceride accumulation, because high glucose means high G3P which causes TG accumulation. High glucose result in high TG formation so this prevents fatty acid release from adipocytes as they are needed to make the TG
What does low glucose drive?
low glucose drives fatty acyl CoA accumulation because TG don’t accumulate so get a shift towards TG break down and FA formation which results in fatty acyl CoA being made and this drives fatty acid oxidation
What happens in continuous lipid infusion?
1st glucose oxidation is suppressed, then glycogen synthesis is suppressed and then glucose uptake into cells is suppressed so all these things together cause high fatty acids to result in insulin resistance
How do fatty acids lead to insulin resistance?
They up regulate JNK and IKKB cause increase serine phosphylation of IRS which prevents insulin signalling
What clinical evidence is there concerning IKKB?
it has been shown that if you give salicylate (inhibitor of IKKB) this suppresses NFKB activation – if you give people fatty acids their insulin sensitivity decreasing, adding salicylate improves their insulin sensitivity
What is the mechanism by which fatty acids cause insulin resistance?
increased plasma FA causes inc fatty acyl coA and DAG (diacylglycerois) which results in activation of PKC- theta leadings to increased IRS-1 serine phosphorylation
What does omega 3 do? Evidence
Anti-inflammatory and insulin sensitising effects of omega-3 fatty acids: G protein coupled receptor (GPR120) specific for omega 3 has been shown to supress the inflammatory pathway in macrophages of NFKB and JNK – . so not all fatty acids cause insulin resistance some have opposing effects (improved insulin sensitivity in adipocytes)
rats fed diets containing 1% or 19% omega 3 ffatty acids and then insulin stimulated musce glucose uptake was measured – higher omega 3 diet was associated with improved insulin sensitivity in both healthy and diabetic rats
What clinical evidence is there for polyunsaturated fats and insulin resistance.
27 patiens underwent coronary artery surgery this showed that reduced fasting insulin was associated with having high % of polyunsaturated fatty acids – high insulin levels were associated with less polyunsaturated fats in the membrane
What happens to pancreatic islets in the long term with fatty acids?
FFA can cause decreased insulin gene expression and decreased proinsulin processing prolonged exposure to FFA can cause B cell death
What is the role of malonyl COa?
at high glucose concs malonyl CoA levels increase which inhibits carnitine palmitoyl transferase 1 activity and therefore prevents B oxidation of fatty acid – fatty acids are diverted from oxidation towards acylation. Diacyl glycerols and phospholipids accumulate and act to amplify insulin secretion
What evidence is there for the short and long term effects of fatty acids on insulin?
Fatty acids and insulin secretion: short and long term - 12 healthy volunteers given infusion of FA shown 6 hours after infusion their acute insulin response to glucose improved showing in short term FA stimulate insulin secretion, however 24 horus after their AIRg decreased showing FA suppressed IS in long term
What did pancreatic cells exposed to FFA have?
Fatty acids and B cell apoptosis: Panc islet cells exposed to FFA had a higher apoptotic index, if you inhibit the enzymes involved in apoptosis such as VAD-FMK (caspases inhibition) and put this inhibitor with the FAA the apoptotic index decreased – this shows how long term prolonged fatty acid exposure promotes apoptosis
What happens in glucolipotoxicity?
at high glucose concentrations and high FA concs, long chain fatty acyl coAs accumulate in the cytoplasm complex lipids accumulate in the cytoplasm including diacyl glycerols, TG, phsopholipids and sphingolipids, they accumulate in excess of signalling requirements long chain fatty acyl-CoAs promote reactive oxygen species formation, they undergo peroxidation and induce inflammatory response and B cell apoptosis – in early stages of daibetes B cells can overcome the peroxidases and regrow if damage is not extreme. so it is important to intervene in diabetes early. high glucose levels alone appear to be insufience to cause B cell apoptosis, fatty acids must be present
What proportion of white adipose tissue is lipid?
60-85%, with 90-99% lipid
What is the difference between lipogenesis and lipolysis
Lipogenesis (esterification)
FA+ glycerol————————————————–> triglyceride
←———————————————–
Lipolysis
How does adipocyte lipogenesis occur?
Lipoprotein lipase makes glycerol and fatty acids from lipoprotein such as VLDL in vascular endothelium. And the free fatty acid can go into TG
What makes fatty acids unsaturated?
SCD ( stearoyl coA desaturase) make fatty acids unsaturated and its gene expression is the rate limiting step in triglyceride synthesis in adipocytes and hepatocytes. Over expression associated with increase in triglyceride levels.
What are the two genes promoting glycolysis, FA synthesis and TG synthesis?
ChREBP: carbohydrate response element binding protein
SREBP1c is sterol regulatory binding protein Ic, stimulates LIPOGENESIS (fatty acid synthesis and acetyl coa carboxylase)
These are transcription genes promoting glycolysis, fatty acid synthesis and TG synthesis.
What is SREBP?
s sterol regulatory binding protein Ic, stimulates LIPOGENESIS (fatty acid synthesis and acetyl coa carboxylase)
What affect does insulin have on fa synthesis?
Insulin binding to IR activates SREBPIc through the RAF/MEK/ERK pathway and via the PHOSPHORYLATION AND EXCLUSION OF FOXO1 FOR HEPATIC TRIGLYCERIDE SYNTHESIS meaning decreased enzymes of gluconeogenisis and glycogenolysis and PHOSOPHORYLATION AND EXCLUSION OF FOXA2: decreased transcription of enzymes of fatty acid oxidation, ketogenesis and VLDL export / increased enzymes of fatty acid synthesis
How does insulin stimulate SREBPic action?
insulin stimulates SREBP-1c action via nuclear exclusion of Foxo1
What does SREBP1c action do?
insulin stimulates SREBP-1c action via nuclear exclusion of Foxo1
•stimulation of SREBP-1c increases heptocyte and adipocyte lipogenesis
•insulin suppresses hepatic fatty acid oxidation and VLDL export via Foxa2
What action does Foxa2 have
•insulin suppresses hepatic fatty acid oxidation and VLDL export via Foxa2
What action does insulin have to Foxa2?
. Insulin suppresses hepatic FA oxidation and VLDL export via foxa2 that helps to increase fatty acid storage
Overall what does insulin do?
Promotes lipid storage
What actions do the catecholamines and glucagon have?
Glucagon and catecholamines stimulate HSL activity that increases lipolysis.
Glucagon stimulates fatty acid oxidation.
What happens in insulin deficiency?
- Lipolysis no longer inhibited
- Diminishes glycerol phosphate provision, reducing LPL Activity
- Glucagon stimulates hepatic fatty acid oxidation and lack of insulin lifts suppression of this
- Ketones, acetoacetate and beta hydroxybutyrate accumulate
What happens in insulin resistance?
- IRS2 inhibited that promotes dephophorylation and nuclear Translocation of foxo1 that increases hepatic gluconeogenesis
- Increased glut 4 signalling, enhanced nuclear exclusion of foxa2 and augments fatty acid and lipid retention+ synthesis in liver
- Augments SREBPIc via mapk pathway.
What is the difference between upper and lower body fat?
- LOWER BODY FAT small adipocytes resistant to lipolytic stimuli
- UPPERBODY (central, android visceral fat) sensitive to lipolytic stimuli such as catecholamines (act pI3K/AKT Pathway) and pro inflammatory cytokines
What is the difference between visceral and subcutaneous fat?
• Muscle sympathetic nerve activity increases more with visceral fat than subcutaneous. • Visceral fat drains into hepatic portal blood supply exposing liver to increased fatty acid flux meaning increased hepatic TG production and VLDL secretion
What overall effect does insulin have?
• Increasing the uptake of glucose in the adipose cell via recruitment of glucose transporters to the plasma membrane, as well as activating lipogenic and glycolytic enzymes
Generally what happens in lipolysis?
- Lipolysis is the breakdown of lipids and involves hydrolysis of triglycerides into glycerol and free fatty acids.
- Induced by catecholamines and glucagon
- Until recently, Hormone sensitive lipase was believed to be the primary enzyme responsible for virtually all TAG and DAG hydrolase activity in adipocytes, as well as neutral cholesteryl ester hydrolase (NCEH) activity
- HSL is activated by glucagon and catecholamines
- HSL is suppressed by insulin
What things cause beta cell failure?
Glucolipotoxicity, amyloid deposition, ER stress, mitochondrial dysfunction with ROS. (Also drugs, developmental and idiopathic)
What do you look for in T1DM? What HLA?
T1DM is associated with other monogenic immune conditions such as autoimmune poly endocrine system. AIRE gene meaning harmful immune cells to self are not deleting. Look for auto islet cell antibodies, glutamate acid decarboxylase (GAD)
• T cell mediated inflammation of the pancreas, insulinitis
• Associated with Hla dr3/4
• Virus molecular mimicry that triggers environmental response
What happens in glucolipotoxicity? Rat models. What do fatty acids to?
High levels of glucose/lipids accumulate that are toxic. In obese rats get increased expression of enzymes responsible for lipogenesis and lipid esterification. There is increased steatosis.
• At high glucose and fatty acid concentrations, long chain fatty acyl coa accumulate in the cytoplasm in excess of signaling requirements
• They promote formation of ROS, promote inflammatory signalling and beta cell apoptosis
What happens in amyloid deposition?
formed from aggregates of beta cell amyloid polypeptide that is toxic to beta cells inducing dysfunction and apoptosis, as well as mitochondrial dysfunction.
Increased mitochondrial oxidation, increased ROS, increased uncoupling protein 2 ( leads to increased heat dissipation as oppose to ATP synthesis) →BETA CELL APOPTOSIS
How is it known that insulin resistance has an auto-immune component?
Associated with other Autoimmune diseases
• E.g. hypothyroidism, viKligo, Addison’s disease • Feature of mono-geneKc autoimmune
syndromes
– APS (Autoimmune Polyendocrine syndrome)
– IPEX (Immune dysregulaKon, polyendocrinopathy, enteropathy, X-linked syndrome)
Also AUTO-ANTIBODIES Islet-cell
• Glutamic acid
decarboxylase-65
• Islet anKgen 2 (IA-2)
• Proinsulin (INS)
• Insulin (IAA)
• Zinc Transporter 8 (ZnT8)
What evidence is there that T1DM genetic
Cytotoxic T cell mediated Insulitis and HLA DR3/4
– Selective inflammation of β-cell of pancreas in >70% of recent onset T1DM cases
What other link is there for T1DM?
- Viral infecKons – enterovirus, cocsackie, rubella
- Early childhood diet – cow’s milk
- Toxins?
- Hygeine theory?
What evidence is there for glucolipotoxicity?
- Evidence from ZDF rats for islet steatosis – Increased accumulation of intracellular
- triglycerides
- – Increased expression of enzymes responsible for lipogenesis and lipid esterification
- – Increased islet steatosis
What does increased ROS lead to?
↑ UCP2 activationà→↑dissipation of energy as heat (at expense of ATP synthesis)à→Impaired insulin-secretory capacity
II. β-cell damage and apoptosis
What does persistent ER stress lead to?
Apoptosis and a decreased ability to make insulin
Evidence 1 that IR. Think families
- Regular pulsatility of insulin secretion is disrupted in those at risk of DM. Beta cell mass increase in insulin resistant states such as obesity and pregnancy, and beta cell responsiveness also increases. Insulin output from the pancreas adapts to prevailing insulin sensitivity.
Evidence 2 that IR. Think physiology
Beta cell mass increases in insulin resistant states (e.g. obesity, pregnancy) Beta cell responsiveness increases in insulin resistant states (e.g. nicotinic acid administration) (how much insulin B cell release in response to a given glucose stimulus). HYPERBOLIC NORMAL RELATIONSHIP
Evidence 3 that IR. Think compensation
for a given level of insulin resistance, compensatory hyperinsulinaemia is reduced in those at risk of diabetes. Give OGTT to IGT patients
Evidence 4 ID. Think post meal
The initial response to glucose is reduced. Draw graph of what happens post meal
Evidence 5 ID think insulin processing
5.processing of insulin for secretion is disrupted in diabetes Phase 1 insulin, proinsulin and incident diabetes: If you follow up patients and see what predicts their development of diabetes. 27 yr follow up, measured glucose, insulin sensitivity etc the only independent predictor of T2DM was the acute insulin response to glucose and proinsulin levels. The more proinsulin the higher your risk of diabetes and the less you AIR is the higher your risk of diabetes. So these two things which are related to impaired insulin secretion caused diabetes. 5.processing of insulin for secretion is disrupted in diabetes Phase 1 insulin, proinsulin and incident diabetes: If you follow up patients and see what predicts their development of diabetes. 27 yr follow up, measured glucose, insulin sensitivity etc the only independent predictor of T2DM was the acute insulin response to glucose and proinsulin levels. The more proinsulin the higher your risk of diabetes and the less you AIR is the higher your risk of diabetes. So these two things which are related to impaired insulin secretion caused diabetes.
Evidence 6 ID think predictors
Very difficult as insulin produced in very inaccessible area of the body, the hepatic portal vein, also because of the closed loop system between insulin and glucose. Between the pancreas and the periphery there is a complex pathway of distribution. 50% is uptaken on first pass metabolism through the liver . Then some goes into extra cellular fluid, some into plasma and then some is renally excreted. Phasic/ pulsatile production.
Is influenced by many factors:
1) INCRETIN hormones increase the sensitivity of insulin release
2) INCREASED SNS/INFLAMMATORY TONE suppresses insulin production
Another factor that could be coming in?
GLP1
