case 9: diabetes type 2 mellitus

Question 1

The Endocrine Pancreas

Answer 1

• Islets of Langerhans
  – β cells - 60%, secrete insulin & amylin
  – α cells - 25%, secrete glucagon
  – δ cells - 10%, somatostatin
  – F cells – pancreatic polypeptide
• The insulin/IGF/relaxin superfamily
  – Insulin – metabolism, growth
  – IGF-I & IGF-II – growth, differentiation
  – Relaxin – parturition
  – Insulin-like protein – reproduction
  – Others
• Close proximity of islet cells
  – Cell-cell communication
  – Insulin inhibits glucagon secretion
  – Somatostatin inhibits insulin & glucagon secretion

Question 2

About Amylin

Answer 2

• Amylin (islet amyloid polypeptide,
  IAPP), a 37-residue peptide
  hormone
• Co-secreted with insulin from the
  pancreatic β-cells in the ratio of
  ~100:1 (insulin:amylin)
• Amylin plays a role in glycemic
  regulation by
  – Slowing gastric emptying
  – Promoting satiety
  – -> Preventing post-prandial spikes
  in blood glucose levels

β cells produce a lot of insulin to control or lower glucose level

Question 3

Insulin – Synthesis

Answer 3

• Preproinsulin – insulin mRNA is translated as preproinsulin
• Proinsulin – removal of signal peptide during insertion into ER
• Insulin – in ER, proinsulin exposed endopeptidases to excise the C
  peptide -> the mature form of insulin
  – Secretion of insulin & C peptide in equi-molar. Important clinical
  indication. Why? patients are injected with recombinant insulin clinically is difficult to differentiate from insulin secreted by patient. measure c peptide from blood to know how much insulin that is self producing insulin

A- & B-chains must be
linked by disulfide bonds
to be bioactive

Question 4

Excitable Cells

Answer 4

• Excitable cells – electrically
  excitable to change Vm from
  resting MP (RMP, or Vr) to
  action potential
  – e.g neurons, muscle cells
  (skeletal, cardiac, & smooth),
  and pancreatic β cells
  – RMP ~ -60 - -80 mV
• The fluctuation of Vm is due to
  changes in membrane’s
  permeability to specific ions

Question 5

Insulin – Control of Secretion

Answer 5

• increase Blood glucose -> entry of
  glucose into β cells through
  GLUT-2 (facilitated diffusion), more ATP/ADP production
• Glycolysis (glucose -> G-6-P
  -> pyruvate), Kreb’s cycle
  (pyruvate -> acetyl CoA),
  oxidative phosphorylation -> increase
  ATP -> increase ATP/ADP ratio
• ATP binds to ATP-sensitive
  K+ channel -> close K+
  channel -> no efflux of K+ -> increase
  membrane potential
• Depolarization -> open
  voltage-dependent Ca2+
  channel -> Ca2+ influx ->
  insulin secretion

Question 6

Oral Hypoglycemic Drugs

Answer 6

• At rest, ADP binds to ATP-sensitive K+ channel -> K+ channel remains open
• Glucose-stimulated state -> increase ATP -> ATP-sensitive K+ channel closed
• Oral hypoglycemic drugs (sulfonylureas, meglitinides) -> close K+ channels
  -> depolarization -> … -> increase insulin secretion -> hypoglycemic effects

Question 7

Insulin – Actions

Answer 7

• When blood glucose level is
  high -> increase insulin secretion ->
  insulin-R’ activation at target
  tissues -> signal pathway
  – 1. -> increase insertion of glucose
  transporters 4 (recruitment
  of GLUT4) to cell
  membrane of insulin-
  sensitive cells (cardiac,
  skeletal muscles &
  adipocytes)
  – GLUT4 – determinant of
  glucose homeostasis
  – 2. Anabolic effects (growth,
  metabolism of
  carbohydrates, lipids &
  proteins)
• T1/2 = 6 min in plasma, mostly
  gone in 10-15 min
  – Degraded by proteases in
  kidneys, liver & muscle

the more GLUT4 inserted onto membrane of cells the easier it is for glucose to enter into target cell, decreasing blood glucose level

Question 8

Insulin Stimulates Insertion of GLUT4

Answer 8

• GLUT4 is rapidly translocated to the cell surface in response to insulin, exercise (more GLUT4 inserted onto membrane) or hypoxia

when insulin action disappear, GLUT 4 packed into cytosol

Question 9

Insulin – Effects by Time

Answer 9

• Fast effects (seconds to min)
  – Glucose uptake (insulin -> increase GLUT-4 insertion onto membrane)
• Mainly in muscle (skeletal & cardiac) cells , adipose cells
• Facilitates glucose uptake in 80% of body tissues (exceptions – brain neurons, pancreatic β cells, intestinal mucosa, kidney
  tubules, red blood cells)
• GLUT-4 separated from cell membrane 3-5 min after insulin degradation
  – Insulin -> increase membrane permeability to amino acids, K+ & PO42- into cells
• Intermediate effects (10-15 min)
  – Changes in cellular enzyme activities by phosphorylation
• Slow effects (hrs to days) – formation of new proteins (growth effects)

Question 10

Insulin – Metabolic Functions

Answer 10

• Insulin is the hormone of abundance -> purely anabolic functions
• Carbohydrate metabolism
  – increase Cellular uptake of glucose -> decrease blood glucose
  – increase Glycogenesis – increase entry of glucose into liver & skeletal muscle cells
  (15x faster with insulin) -> increase glycogen storage (5% of liver mass)
• Lipid metabolism – increase lipogenesis, decrease lipolysis by decrease hormone-sensitive lipase on hydrolysis of triglycerides
• Protein metabolism – increase cellular uptake of amino acids -> increase proteins
  synthesis (anabolic), decrease protein degradation
• Insulin on liver
  – increase Glycogenesis by increase glucokinase & glycogen synthase
  – decrease Glycogenolysis by decrease glycogen phosphorylase
  – increase Conversion of glucose into fatty acids (after glycogen storage
  mechanisms are saturated) -> increase VLDL -> transport to adipose cells
  – decrease Gluconeogenesis

Question 11

Insulin – Other Functions

Answer 11

• The growth-promoting activities of insulin
  – Insulin is a member of a family of structurally and functionally
  similar molecules (IGF-1, IGF-2 & relaxin)
  – The family members have growth-promoting activities
  (modulates transcription, stimulates protein translocation, cell
  growth, DNA synthesis and cell replication)
• Insulin and endothelial cell functions
  – Insulin exerts vasodilator action in the vascular endothelium as
  a result of increased nitric oxide (NO) production
• Uptake of amino acids and potassium into the cells that
  cannot take place in the absence of insulin
• Manage excretion of sodium and fluid volume in the urine
• Enhance learning and memory of the brain functions

Question 12

Regulation of Insulin Secretion

Answer 12

• increase Blood glucose level -> increase insulin secretion (most potent)
• Amino acids – -> increase insulin secretion (arginine & lysine most potent)
• Effect of autonomic nerves
  – Sympathetic – “fight or flight”, stress hyperglycemia -> decrease insulin
  secretion
  – Parasympathetic– “rest and repair” (anabolic) -> increase insulin secretion
• Effect of incretin hormones (hormones -> increase insulin secretion)
  – Glucose in gut -> increase GIP (glucose-dep. insulinotropic peptide, or gastric
  inhibitory peptide) secretion -> increase insulin secretion, decrease gastric motility
  – Cholecystokinin (CCK), gastrin, secretin -> increase insulin secretion
  – increase Blood glucose, amino acids, fatty acids -> increase GLP-1 (glucagon-like
  protein) -> major increase insulin (potent antihyperglycemic)

Question 13

GLP-1 and Insulin Release

Answer 13

• GLP-1 – glucagon-like peptide-1 from proglucagon gene
• Secreted by intestinal L cells as a gut hormone
• Potent antihyperglycemic – increase insulin & decrease glucagon
• Short half-life (2 min), inactivated by DPP-4 enzyme

Question 14

Effects of Glucagon

Answer 14

• Effects of glucagon – catabolic
  – increase Glycogenolysis
  – increase Lipolysis
  – increase Protein degradation
  – increase Gluconeogenesis – formation of glc from non-carbohydrate
  sources
  – increase Ketogenesis – formation of ketone bodies
  – decrease Storage of triglycerides in the liver

Question 15

Questions

Answer 15

• Why store glycogen rather than just glucose?
  – Osmotic pressure problem (remember glucose trapping?) so glucose can continue to enter from blood circulation into liver
• Why store glycogen rather than just fat?
  – Metabolism of fat requires oxygen (could be a problem for muscle)
  – Trouble making glucose (for brain) from fat (fat cannot be reconverted to glucose)
  – Fat is stored, but it cannot be mobilized as quickly as glycogen (fewer steps to convert to glucose)
• Glycogenenesis – requires glycogen synthase (regulatory enzyme, insulin-sensitive)

Question 16

Pathogenesis of Type 2 DM

Answer 16

• a.k.a. Non-insulin-dependent diabetes (NIDDM). Why? B cells can still secrete insulin
• 2 Metabolic defects
  – Insulin resistance – decrease ability of peripheral tissue’s response
  – (Later stage) β-cell dysfunction – impaired insulin secretion
• Environmental factors play a large role (lifestyle, diet etc.)

Question 17

Development of Type 2 DM

Answer 17

• Insulin secretion rises as insulin sensitivity falls when an individual goes
  from a state of exercise training/being physically active (point A) to
  inactivity/sedentary (point B).
• When insulin secretion fails to compensate for a fall in insulin sensitivity,
  the person will progress to IGT (Point C). If no changes are made at this
  point, the disease will progress from point C to Point D (type 2DM).
• NGT – normal glucose
  tolerance
• IGT (impaired glucose
  tolerance) – a
  transition phase
  between normal GT
  and DM

Question 18

Prediabetes – IFG and IGT

Answer 18

• Prediabetes – a term used to distinguish people who are at
  increased risk of developing diabetes.
• People with prediabetes have impaired fasting glucose (IFG)
  or impaired glucose tolerance (IGT), or both.
  – IFG – the fasting blood sugar level is elevated (100 to 125
  mg/dL)
  – IGT is a condition in which the blood sugar level is elevated
  (140 to 199 mg/dL after a 2-hour OGTT), but is not high
  enough to be classified as diabetes

Question 19

From Prediabetes to Type 2 DM

Answer 19

• Progression to diabetes from prediabetes is not inevitable.
  Weight loss and increased physical activity may prevent or
  delay diabetes and may return blood glucose levels to
  normal
  – People with insulin-resistant does not necessarily have type 2
  DM unless there is some impairment of insulin secretion
• The more a person is insulin-resistant, the less impairment is
  required to induce.
• Over the years 10-20, there is progressive decline of insulin
  secretion, but does not decline to 0 level

Question 20

Obesity

Answer 20

• Definition – having an excessive amount of body fat
• Obesity has become an epidemic in USA
• Defined by body mass index (BMI)
• Metric system – BMI = w (kg) / h (m2)
• w = weight in kilograms; h = height in meters
• BMI classification
• BMI < 18.5 – underweight
• BMI between 18.5 and 25 – healthy weight
• BMI between 25 and 29.9 – overweight
• Obesity defined as BMI > 30

Question 21

Complications of Diabetes – Acute

Answer 21

• Acute complications due to hyperglycemia
• Hyperosmolar hyperglycemic state (HHS)
  – Hyperglycemia -> severe dehydration -> increase in osmolality -> higher
  risk of complications -> hyperosmolar non-ketotic
  – The presence of some insulin in type 2 DM -> inhibit hormone-
  sensitive lipase -> no ketone formation, similar to but different
  from DKA
• Effect of insulin -> increase uptake of K+ by cells
  – In the absence of insulin action -> increase K+ exit from cells into plasma
  -> increase plasma [K+] -> hyperkalemia
  – The consequences hyperkalemia – changes in cell membrane
  potential (depolarization) -> cardiac arrhythmia

Question 22

Complications of Diabetes – Chronic

Answer 22

• Chronic complications due to vascular damage
• Macrovascular complications
  – Large and medium vessel disease due to accelerated
  atherosclerosis -> coronary artery disease, peripheral vascular
  disease, stroke
  – Main cause of mortality
• Microvascular complications
  – Capillary dysfunction in target organs -> neuropathy,
  nephropathy, retinopathy
  – Significant source disability and decrease in quality of life

Question 23

Proposed Mechanisms

Answer 23

• What makes DM people sick and die?
  – DM patients do not die from hyperglycemia directly, but die from heart attack, stroke, atherosclerosis, renal damage, eye damage
• Proposed mechanisms of vascular damage from hyperglycemia
  – Aldose reductase pathway and reactive oxygen species
  – Advanced glycation end products theory
  – Protein kinase theory

Question 24

The Polyol Pathway

Answer 24

• In euglycemic state,
  – Glucose -> ATP production (glycolysis & Krebs cycle)
  – Glucose -> hexose monophosphate shunt
  (pentose phosphate pathway) to make NADPH & ribose
• In hyperglycemic state, ~30%
  of glucose -> the polyol pathway
  – increase Glucose -> increase aldose
  reductase activity -> increase sorbitol
  -> increase fructose in cells
  – NADPH -> NADP+

Question 25

Reactive Oxygen Species

Answer 25

• Free radicals – chemical compounds with odd number of electrons, extremely unstable and reactive
  – Tend to acquire an electron from other substance -> “attack” proteins, lipids, carbohydrates or DNA in its vicinity
  – The “attacked” molecules become unstable -> chain reaction -> disruption of a living cell -> cell mutation or death -> tissue damage
• also kill bacteria
• Reactive oxygen species (ROS) are reactive chemical
  species containing oxygen, many of them are free radicals

Question 26

Antioxidants as Defenses against ROS

Answer 26

• The ‘glutathione system’ – present in every animal cells, exert antioxidant effects
  – Glutathione – a tripeptide (glutamic acid-cysteine-glycine)
  – Glutathione reductase and peroxidase
• Oxidized glutathione (G-S-S-G) and reduced glutathione (G-SH)
• NADPH indirectly provides electrons for the reduction of H2O2, thus decrease the reactive oxygen species

Question 27

NADPH, ROS and DM

Answer 27

• The glucose uptake in cells of retina, kidney and nervous tissues are insulin-independent
• increase Blood glucose -> depletion of NADPH by aldose reductase -> inability to regenerate reduced glutathione (G-SH) -> increase oxidative stress reactions -> cell death
• increase [Sorbitol] -> decrease nitric oxide -> vasoconstriction in neuronal tissue and eventually ischemia

Question 28

Diabetic Cataract

Answer 28

• Sorbitol does not diffuse through cell membranes easily
• -> increase accumulation of sorbitol -> increase osmotic pressure
• -> increase water retention -> cell swelling -> damage -> cataract formation

too much glucose

Question 29

NADH, ROS and DM

Answer 29

• Glycolysis requires NAD+
  – Glycolysis occurs in the
  cytoplasm and it generates
  NADH (gains 1 e-) from NAD+
  – If NAD+ is not regenerated,
  glycolysis will halt
  – With O2 in mitochondria NADH
  -> NAD+
  – If production of NADH exceeds
  mitochondrial oxidation of NADH
  -> cytoplasmic NAD+ will
  become depleted
  – The cell regenerate NAD+ from
  NADH by making lactate from
  pyruvate (anaerobic respiration)
  – Cori cycle…
• In mitochondria electrons (e-) donated from NADH & FADH2 pass through
  the electron transport chain and ultimately reduce O2 to form H2O
• ROS are produced from e- leakage to form superoxide (O2.-)
• Normally O2.- -> H2O2 by superoxide dismutase (SOD); H2O2 -> H2O by
  glutathione peroxidase (GPX)
• In DM patients, the polyol pathway -> increase NADH -> NADH/NAD+ redox
  imbalance (more e- leakage) -> increase ROS -> oxidative stress

NAD+ needed to continue glycolysis in cell
refer to pic

Question 30

DM and Free Radicals

Answer 30

• Question – which cellular organelle is the major source of
  reactive oxygen species, why?
• Answer – mitochondria, due to its central role in the energetic metabolism to generate ATP through oxidative phosphorylation (oxidation of electron donors NADH &
  FADH2) & electron transfer chain (complex proteins I-V)

Question 31

DM and Free Radicals

Answer 31

• Question – NADH & FADH2 are generated during glycolysis/TCA cycle. What is the effect of hyperglycemia on the production of NADH & FADH2?
• Answer – hyperglycemia would increase the cellular glycolytic reactions, thus increase the production of NADH & FADH2 (excess of electron donors)

Question 32

DM and Free Radicals

Answer 32

• Question – What is the consequence of an electron donor excess?
• Answer – an excess of electron donors would result in
  increased electron delivery and subsequently leading to
  more electron leaking.

Question 33

DM and Free Radicals

Answer 33

• Question – What is the consequence of an increased
  electron leaking?
• Answer – an increased electron leaking in the mitochondria
  would lead to more anion superoxide generation, thus the
  oxidative stress

Question 34

DM and Free Radicals

Answer 34

• Question – Does hyperglycemia cause increased free
  radical production (and oxidative stress) in other intracellular
  structures?
• Answer – Yes, hyperglycemia causes oxidative stress in
  structures such as endoplasmic reticulum (ER stress) or
  plasma membrane (lipids peroxidation)

Question 35

The polyol pathway
activation leads to

Answer 35

– decrease NADPH/NADP+ ratio
– decrease Nitric oxide production
– increase Sorbitol -> increase osmotic
stress
– increase NADH/NAD+ -> increase ROS
production -> oxidative
stress
– increase Fructose -> increase non‐
alcoholic fatty liver
disease (NAFLD)
– increase Fructose -> increase glycation
– -> diabetic complications
including retinopathy,
nephropathy, and
neuropathy

refer to pic

Question 36

Dietary Fructose and the Metabolic Syndrome

Answer 36

• Over-consumption of fructose:
  – In small intestine, fructose -> increase production of uric acid, fatty acids & glucose
  – In liver, fructose -> increase production of glucose, VLDL & ApoC -> increase lipogenesis -> non alcoholic‐ fatty liver disease

Question 37

Microvascular Complications

Answer 37

• Diabetes is the most common cause of blindness in the US
• Retinopathy has the highest correlation with severity and duration of diabetes (due to microvascular complications)
• Hyperglycemia is the primary cause of diabetic retinopathy
  – Vascular endothelium growth factor (VEGF) may be involved in the development of proliferative retinopathy

refer to pic

Question 38

DM-Induced Macrovascular Disease

Answer 38

• In contrast to diabetic microvascular disease, hyperglycemia is not the
  major determinant of diabetic macrovascular disease
• Insulin resistance -> increase lipolysis -> increase free fatty acid (FFA) flux from
  adipocytes -> plaque deposition in arterial endothelial cells
• In macrovascular endothelial cells, but not in microvascular
  endothelial cells, increase free fatty acid (FFA) flux -> increase FFA oxidation by the
  mitochondria -> increase ROS -> macrovascular inflammation

Question 39

Intramyocellular Lipid Accumulation

Answer 39

• Skeletal muscle – accounts for ~ 80% of glucose uptake in absorptive state
• Insulin resistance would increase total intramyocellular lipid content

Question 40

Through which metabolic mechanism does the intramyocellular lipid accumulation occur?

Answer 40

insulin resistance increases lipolysis in fat tissue, so ffa circulating in blood from fat tissue and ffa into muscle cells, so muscle becomes weak and can’t function well

Question 41

Diabetes Mellitus & AGE Theory

Answer 41

• Intracellular – high [glucose] -> increase formation of advanced glycation end products (AGEs) from nonenzymatic reactions -> defects in the metabolism pathways
• Extracellular – high [glucose] -> increase AGE’s effect on extracellular matrix -> crosslinking between polypeptides -> abnormal matrix -> interrupts normal cell interactions

refer to pic

Question 42

Protein Kinase Theory

Answer 42

• Ca2+ activation of protein kinase C (PKC) & diacylglycerol (DAG) pathways is an important intracellular signaling pathway
• Hyperglycemia -> increase de novo synthesis of DAG -> unregulated activation of PKC

originally pkc stimulated by activation of hormones or cytokines, but without it the cells automatically produce DAG

refer to pic

Question 43

Management of DM – Life Style

Answer 43

• Research studies have found that
  lifestyle changes can prevent or
  delay the onset of type 2 DM among
  high-risk adults
• Lifestyle interventions included diet
  and moderate-intensity physical activity
• Diet – nutritional requirements with
  weight control
• Exercise
  – Physical activity -> decrease body weight
  and increase insulin sensitivity -> decrease blood glucose levels

vegetables have vitamin c that is an antioxidant and fiber which increases motility of gi tract

insulin binding to receptors cause entry of glucose through GLUT, without insulin stimulation and high exercise it doesnt need insulin there will be increase of GLUT in absence of insulin by exercise

Question 44

Aerobic Exercise & Insulin Sensitivity

Answer 44

• Aerobic exercise
  – Physical activity that increases the heart rate and the body’s use of O2
  – The use of O2 to adequately meet energy demands during exercise via aerobic metabolism
• Aerobic exercise leads to:
  – increase Use of FFA -> decrease adipokine production, decrease inflammation -> increase insulin sensitivity
  – Improvement of the redox state & reducing oxidative stress induced insulin‐ resistance
  – Up regulation of GLUT 4‐ in cell membrane of insulin dependent cells‐
  – Reduction of plasma levels of ceramide -> prevention of ceramide induced‐ insulin resistance
  – increase Phosphorylation of insulin receptor substrate-1 (IRS 1)‐ -> improvement of insulin signal transduction
  – Improving β cell function & prevention of β cell apoptosis
  – Induction of angiogenesis in skeletal muscle -> increase glucose uptake by myocytes

Question 45

Medication of DM

Answer 45

• Oral hypoglycemic therapy
  – Glucophage (metformin) – decrease glycogenolysis, decrease
  gluconeogenesis, increase insulin sensitivity, decrease glucose release into
  the blood
  – Sulfonylureas – target to close K+ channels -> depolarization
  of β cells -> increase insulin release
  – GLP-1 agonists – increase insulin release
  – DPP-4 inhibitors – DPP metabolizes GLP-1, extend glp1 half life
  – Thiazolidindiones (TZD) – PPARγ agonists
• Insulin therapy – in severe cases when insulin major decrease

Question 46

Major Targeted Sites of Drug Classes

Answer 46

refer to picture

Question 47

Oral Hypoglycaemic Medications

Answer 47

refer to picture

Question 48

Insulin Therapy

Answer 48

refer to picture

Question 49

Issues Remain

Answer 49

• Can insulin treatment or stimulation of insulin secretion by sulfonylureas, GLP-1 agonists or DPP-4 inhibitors solve the problem of insulin resistance? they are used to stimulate more insulin, but if B cells already depleted, then
• What would be your suggestions as a clinician?
  – Diet
  – Physical activities