Lecture 24; Type One diabetes

Question 1

What is diabetes?

Answer 1

Diabetes is a spectrum of diseases which manifest themselves as an inability of insulin to properly regulate glucose metabolism either because insulin is not being produced or because insulin is being produced but is unable to function properly.

• Faulty signalling pathways
• Low insulin production

Question 2

What are the clinical features of untreated diabetes?

Answer 2

• No insulin (type one)
• Hyperglycmeia
• Glucose cannot be taken into the muscle, fat, liver, so lack of fuel stores
  = Tired and hungry (polyphagia)
• Above 20mM BG (normally 4-5mM) glucose spills over into the urine. (diabetes mallitus)
• Urine = hyperosmolar thus polyuria (excessive urination) and polydipsia.
• Fatty acids remain high (not supressed), partially oxidised into ketone bodies (alternative energy source). High levels of these can lead to kteoacidosis and coma.
• Wasting ot tissues (AA and FA compensate for no glucose) (therefore weightloss)

Question 3

What does a prediabetic state mean?

Answer 3

Increase risk of an early death.

Question 4

What happens to glucose re-uptake in the kidney?

Answer 4

SGLT kinetics are saturated and cannot re-uptake the all glucose so some is lost in the urine.

Question 5

What does insulin do?

Answer 5

• In healthy people insulin stimulates storage of glucose in liver and stops the breakdown of the lipids stored in adipose tissue after a meal.
• In healthy people the stored glucose is released from the liver in between meals so the brain can use this for its energy needs.

Question 6

What happens in diabetics?

Answer 6

Gluconeogenesis keeps blood levels at homeostatic levels between meals, as no glucose stores to release.

= body weight loss in diabetics as substances like glycerol and amino acids are used by gluconeogenesis.

Gluconeogenesis isnt enough glucose production to keep the brain going so the body switches to lipids coming from fat cells.

Lipids are mainly triglycerides and these are broken down to glycerol and fatty acids. Insulin stops this from happening which means diabetics will have very high levels of fatty acids in their circulation and helps contribute to weight loss in untreated diabetics.

Question 7

Can the brain use fatty acids directly?

Answer 7

No, so ketone bodies must be produced for the brain uto use.

Question 8

What are the typical ketone bodies?

Answer 8

Two such ketone bodies are acetoacetic acid and betahydroxy butyrate

Question 9

What can ketone bodies do?

Answer 9

• Ketoacidosis (blood buffering system doesnt cope)
• Sometimes on breath
• Ketones in the urine make it hyperosmolar, therefore leads to polyuria and dehydration

Question 10

Why is type one diabetes still dangerous today?

Answer 10

Now that Type-1 diabetes can be controlled with insulin the major problem with diabetes is that inappropriately high circulating levels of glucose are dangerous and is a direct cause of major pathological complications of diabetes.

Glucose is a reactive sugar therefore attatches to cells and damage their function

Question 11

What are the diabetic complications of high blood glucose?

Answer 11

High blood glucose has damaging effects on proteins and if levels remain high for long times this causes serious damage to tissues, especially small blood vessels

Damage to small blood vessels that resulting in damage to retina (retinopathy) which leads to blindness.

Damage to small blood vessels also causes problems with peripheral circulation so persistent infections and gangrene can set in. Also b/c blood vessels;

• Neuropathy
• Nephropathy (dialysis)
• An increased rate of development of coronary artery disease (atherosclerosis) – heart attacks are a major killer of diabetics.

Question 12

What are the causes of diabetic complications? (high blood glucose)

Answer 12

1. Dysregulation of osmolarity caused by high glucose

2. Non-enzymatic glycosylation of proteins

Question 13

How does high blood glucose leak to dysregulation of osmolarity?

Answer 13

High glucose leads to Aldose Reductase activation which then produces High sorbitol.

This can’t get out of cells easily so causes osmolar imbalance, water accumulates and cells can swell/die.

This particularly affects tissues where aldose reductase is expressed such as nerves, retina and kidneys.

Question 14

How does high blood glucose lead to non-enzymatic glycosylation of proteins?

Answer 14

More glucose in the blood in diabetes means more sugar added to proteins, especially those that are exposed to blood supply (non-enzymatically)

Amadori products

Question 15

What can be used to measure the non-enzymatic glycosylation of proteins?

Answer 15

Hemoglobin is very abundant in the blood and becomes glycated at a rate that is dependent on glucose concentration in blood.

Hemoglobin has a 8-12 week half life in the blood so monitoring glycated forms of Hemoglobin (e.g. HbA1C) allows an estimate of longer term exposure to glucose

Question 16

What did a study of HbA1C reveal in terms of relative risk?

Answer 16

This study of thousands of type-1 diabetics (called DCCT) demonstrated correlation between high blood glucose (as measure by HBA1C) and increased risk of a wide range of diabetic complications.

• Genetic variability
• Tight regulation of BG reduces risk

Question 17

What else did the DCCT study show?

Answer 17

This showed that in DCCT trial that if you treat diabetes aggressively to control blood glucose that you can reduce the risk of retinopathy

Question 18

How does lowering blood glucose over time reduce your risk of developing diabetic complications?

Answer 18

DCCT and (UKPDS)(type 2) showed that lowering blood glucose levels over time (10% reduction) (measured here by HBA1C) resulted in much lower risk of patients developing a

• Retinopathy (35% reduction - DCCT and 21% UKPDS)
• Nephropathy (36% and 33%
• Neuropathy 30% reduction

Question 19

What are the types of diabetes?

Answer 19

• Type-1 (Juvenile Diabetes or Insulin Dependent Diabetes Mellitus)
• Type-2 (Adult Onset or Non-insulin Dependent Diabetes Mellitus)

Minor causes;
•MODY (Maturity Onset Diabetes of the Young)
•Other type of monogenic diabetes causing earlier onset
•Maternally Inherited Diabetes and Deafness (MIDD)

•Gestational Diabetes•Other Causes e.g. Cystic fibrosis, cancer, autoantibodies to insulin etc

Question 20

What is MODY?

Answer 20

Post adolescence to middle age (2% diabetes)

• no islet cell antibodies
• low numbers of beta cells-later onset than type-1 diabetes but earlier than type-2
• no association with obesity
• autosomal dominant pattern of inheritance (so sometimes also called monogenic diabetes)

Question 21

What are a couple of the many MODY genes?

Answer 21

MODY1 Caused by mutations in Hepatic Nuclear Factor 4a(HNF-4a). Estimated to cause 1% of MODY. Insulin secretion normal at birth but decreases dramatically with age.

MODY2 Caused by mutations in glucokinase thus affecting glucose sensing in pancreas. Estimated to cause 15% of MODY. Insulin secretion impaired at birth but remains relatively stable.

Basically mostly caused by mutations of transcription factors that regulate the development of the pancreas.

Question 22

What sort of diabetes is similar to MODY?

Answer 22

Neonatal diabetes

• Obvious at or soon after birth but not type one.
• Many mutations in genes that compromise Beta cell function
• Parents have no phenotype.

Question 23

What is Mitochondiral diabetes (MIDD)?

Answer 23

Mutations in mitochondria (e.g in leu-tRNA gene) and is maternally (inherit mito from mum) transmitted as the oocyte contributes all the functional mitochondria to the embryo.

When mutant mitochondria predominate then cells oxidative capacity greatly reduced.

penetrance is variable

2% diabetes

Question 24

What does MIDD cause in the beta cells?

Answer 24

In cells this results in reduced capacity to secrete insulin in response to glucose as insulin secretion is linked to glycolysis. Can also produce symptoms e.g. muscle weakness, deafness, neurological problems and lactic acidosis as a result of inefficient glucose metabolism.

Question 25

What is gestational diabetes?

Answer 25

·Severe insulin resistance bought on by hormonal changes and metabolic stress of pregnancy. In women with low insulin secretory capacity this can result in a form of diabetes.
·Affects 2% of pregnancies of non diabetic women.
·Symptoms normally disappear after birth but 60% of these women go on to develop diabetes in later life which suggests these women had an underlying pre-disposition.

Question 26

What is the cause of type one diabetes?

Answer 26

No insulin due to loss of functional beta-cells

·Usually in younger subjects

Affects around 0.3% of the population in the western world although lower in other parts of the world.

·Most common cause is immune system attack on insulin producing beta-cells of pancreas and this leaves tell tale sign in the form of auto antibodies against beta-cell proteins.

Question 27

Does diabetes type one exist as a non-autoimmune disease?

Answer 27

·A smaller number of people found to have type-1 diabetes with no immune involvement. This can be via genetic defects that directly affect beta-cells (e.g. mutations in insulin gene that cause insulin to aggregate in beta cells and so kill them) and also include some indirect genetic disease (e.g. cystic fibrosis), some viral infections that damage beta-cells, some forms of cancer (e.g. pancreatic), some drug induced conditions.

Question 28

Whats happened to diabetes worldwide?

Answer 28

Type one diabetes is rising globally and this is unknown why it is happening.

Question 29

What are the predominant autoantibodies?

Answer 29

• Insulin,
• GAD65 (Glutamic acid decarboxylase) then later
• IAP2 (a protein phosphatase)
• Zinc transporter (ZnT8).

Question 30

What is rate of onset related to?

Answer 30

The speed of onset of the disease correlates well with the number of different islet cell antibodies an individual has

Question 31

What happens to the beta cells over time?

Answer 31

Beta cell mass slowly decreases and for long period there is still enough insulin and patients are asymptomatic (see figure). When beta cells almost depleted then a glycemic crisis can be precipitated and disease will be notice . Eventually all beta cells totally destroyed.

Question 32

To what degree can the beta cells be lost before symtpoms onset?

Answer 32

Can loose up to 50% of beta cells before symptoms onset.

Question 33

What can be used to predict the development of type one diabetes?

Answer 33

The Presence of Islet Cell Antibodies Predicts the development of Type-1 Diabetes

Can predict who is at risk based on autoantibodies

Question 34

Whats the evidence for a genetic link of type one diabetes?

Answer 34

There is evidence of a genetic link but no single gene has been identified that definitely causes diabetes. However, in identical twins if one twin gets type-1 diabetes there is a 30% chance the other twin will get type 1 and a 70% lifetime expectancy of diabetes (vs 5% for all forms of diabetes in general population)

Question 35

How is MHC believed to be linked to type one diabetes?

Answer 35

It is estimated that between 20 and 50% of all type-I diabetes can be explained by variants of the MHC-class 2 locus.

Some alleles increase risk some are protective

Some forms of MHC class-2 protein somehow make individuals susceptible to autoimmune destruction of the pancreas although the mechanism for this is poorly understood.

Question 36

What are some important variants of MHC locus in type one diabetes?

Answer 36

Type 1 diabetes is higher in individuals with a copy of the DQA301 allele or DRB1401 allele

33% of diabetics have copies of both alleles (called a 3/4 genotype) whereas 57 % of non diabetics don’t have either of these alleles

Question 37

Describe the structural role of MHC in T1D?

Answer 37

Every different alpha-beta MHC class-2 dimer creates a different shape binding pocket

This means every different MHC class-2 alpha-beta dimer will be suited to presenting only certain peptides to the immune system. These are called ”dominant” peptides

Question 38

What are some other causes of type one diabetes?

Answer 38

• IDDM-2 locus – polymorphism in non-coding region that seems to regulate insulin gene expression in thymus and so modulate immune response against insulin.
• Lymphoid specific phosphatase – mutation in a phosphatase that controls T-cell function

(CTLA-4) gene mutation = reduced expression

• Up to 40 other genes implicated
• Probably environmental triggers that initiate disease in some people with genetic predisposition.

Question 39

What was used to treat T1DM?

Answer 39

Insulin replacement therapy has been the only effective treatment since the 1920’s

Previously purified from animal pancreas, now human insulin produced as recombinant protein (i.e it is genetically engineered)

Question 40

What are some problems with insulin treatment?

Answer 40

Injected insulin is not at entering the body via the normal route

Problems with tissue damage at site of injection

Problem with insulin needing to dissociate from crystalline form- takes time to work

Possibility of hypoglycemia if to much insulin is given

Problem of maintaining insulin levels overnight

Question 41

What happens if excess insulin is given?

Answer 41

Hypoglycemia

If blood glucose gets much below 2 mM then the brain won’t work properly as the nerve cells won’t be getting enough glucose to make ATP. This can be fatal.

•It can be rapidly treated by eating or drinking stuff that has lots of glucose in it

Question 42

Whats the diabetic tight rope?

Answer 42

Too much insulin = hypoglycemia and potential death

No insulin = diabetic ketoacidosis = coma death

Question 43

Describe the structure of the given insulin;

Answer 43

Insulin crystals are a hexamer of Insulin molecules co-ordinated to Zinc via the end of the Insulin B-chains

Insulin Crystals Break Down Relatively Slowly- First To Dimers Then To Monomers

Question 44

What has been used to make insulin act far quicker so it doesnt have to break down to work?

Answer 44

Use of recombinant DNA technology to improve its pharmacodynamic properties

They altered the AA sequence to be more like IGF1 so it doesnt dimerise or Hexamerise

Question 45

What else has been done to engineered insulin?

Answer 45

Use of recombinant DNA technology to make a longer acting form of insulin

Question 46

Whats an example of long lasting insulin?

Answer 46

Detemir (Levemir) - An Engineered Long Acting Insulin

Question 47

Whats cab be done to monitor blood glucose?

Answer 47

• Originally blood glucose could only be detected in lab so required a doctors visit.
• Urine glucose measurement methods allow home detection but glucose only in urine when blood glucose very high so not optimal.
• Miniature glucose monitoring devices are now available for home use so make control of blood glucose easier

Question 48

What are some new treatments for type one diabetes?

Answer 48

• Immunosuppressive therapy to stop further loss. This has some effect but has very serious side effects and effects are not long lasting

·Islet transplantation – some success but limited by availability of islets and need for immunosuppressive therapy·

Artificial islets – some way off·

Islet neogenesis e.g using EGF and GLP

·Xenotransplantation - being pioneered here in Auckland

·iPS (induced pluripotent stem cells) cells to generate human beta-cells matched specifically to a person

Question 49

What could be done to prevent diabetes type one?

Answer 49

·As it is possible to use the predictive antibodies to determine those at risk of developing type-1 diabetes is it possible to prevent it ?

·Prophylactic insulin or GAD65 orally in those at risk of diabetes has been trialled in an attempt to induce immune tolerance and so perhaps delay onset of diabetes.

·Resetting the immune system using anti-CD3 antibodies is also be tried to try an restore immune tolerance towards autoantigens