LT6 Beta-Cells as Therapeutic Target in Diabetes

Question 1

What is WHO diagnostic criteria for diabetes?

Answer 1

Fasting plasma glucose of above 7mM
OR
2h plasma glucose of above 11.1mM during a 75g oral glucose-tolerance test

Question 2

How can you test for diabetes?

Answer 2

Test for presence of glucose in urine

HbA1c test = better marker of long-term glycaemic control than fasting plasma glucose

6.5% (48mM) is the diagnostic threshold for HbA1c test

Question 3

What are the two core factors that cause T2D insulin deficiency?

Answer 3

Insulin resistance and beta-cell dysfunction

Results in insufficient insluin secretion to meet the demand of the body

Question 4

What is the relationship between insulin secretion and insulin sensitivity?

Answer 4

So long as insulin release meets the insulin sensitivity then glucose stays in homeostasis

If insulin sensitivity don’t need as much insulin release to lower glucose

If insulin resistant (near 0) then need more insulin release

Question 5

What feature causes T2D?

Answer 5

Inherent pancreatic beta-cell islet defect in insulin secretion

Both structural and functional

Question 6

What are islets?

Answer 6

Cluseters of ~1000 endocrine cells

Question 7

What % of pancreas do islets make up and what is the rest of the pancreas?

Answer 7

Islets make up ~1-2% of pancreatic volume

The remainder is mostly exocrine pancreas

Question 8

What do epsilon cell secrete?

Answer 8

Ghrelin

Question 9

Do beta-cells only sense glucose?

Answer 9

No

Question 10

What other molecules do beta-cells sense?

Answer 10

IL-6 from muscle

Leptin/Adiponectin from fat

Igf1 from liver

Glucagon from alpha-cells

GLP-1 and GIp form gut

Question 11

Why is T2D so heterogeneous?

Answer 11

Because could be caused by numerous different reasons in individuals

Insulin resistance or beta-cell dysfunction

Question 12

What are the 10 things needed to know to develop a target medicine profile?

Answer 12

Indications

Population = which patients/subtypes and where?

Mechanism of action = how does the drug work?

Clinical efficacy = how well will it need to work?

Safety/Tolerability = safety level and adverse events

Stabilitiy = transport, storage and delivery

Route of administration = how is it given to patients?

Dosing Frequency = how often and for how long?

Cost = will it be affordable to target populations?

Time to availability = how long will it take to develop?

Question 13

What would the ideal beta cell profile look like?

Answer 13

Target T2D with severe insulin deficient diabetes

Improve glycaemic control demonstrated by reduction in HbA1c less than 5.5%

Safe and well tolerated (esp by renally-impaired patients)

Taken orally at a low frequency

Stored at room temp for 12 months

Question 14

What categories would the chosen patients have to fall into for target profile?

Answer 14

Absence of autoAb (GADA, IAA and IA-2A)

Impaired glycaemic control

C-peptide and HOMA2-beta score

BMI

Question 15

What outcomes would need to be measured for a medicine profile?

Answer 15

HbA1c

Time in range of short term glycaemic control

Parient reported outcomes measure (PROMs)

Fasted ands timulated C-peptide secretion

HOMA-2beta (beta cell function)

Question 16

What is the HOMA2-beta score?

Answer 16

Homeostasis Model Assessment = a validated mathematical tool used to estimate beta-cell function based on fasting glucose and insulin levels

Question 17

What is the relationship between expenditure for diabetes and mortality?

Answer 17

Expenditure is inversely proportional to mortality

More money = less likely to die

Question 18

What is electrophysiology?

Answer 18

A measure of membrane voltage

Question 19

Give an example of a sulphonylurea

Answer 19

Tolbutamide

Question 20

What is the summary of SU treatment outcomes?

Answer 20

Good short-term but exhausts beta-cells long term

Risk of HYPOglycaemia and hyperinsulinaemia

Question 21

What are the 5 subgroups of polygenic diabetes?

Answer 21

SAID = severe autoimune diabetes (T1D)
SIDD = severe insulin-deficient diabetes
SIRD = severe insulin-resistant diabetes
MOD = mild obesity-related diabetes
MARD = mild age-related diabetes

Question 22

Why is there no control in drug trials for diabetes?

Answer 22

Unethical to have an uncontrolled diabetes group = allows the diabetes to get worse

Question 23

What typy of diabetes might SUs be best for?

Answer 23

Monogenic diabetes = Kir6.2 channel mutants

K_ATP channel is locked open, beta cell cannot depolarise in response to high glucose
SU override this defect and restore insulin secretion

Neonatal diabets = Kir6.2 mutation

Question 24

What new research tool was used with sulphonylurea?

Answer 24

Photo-activateable sulphonylurea

When blue light shines, the SU changes to active conformation (cis)

Can control Ca2+ influx in beta-cells with blue light alone

Question 25

Why are SUs good?

Answer 25

Oral, once daily dosing Stable at room temp and low cost

Question 26

What are gliptins?

Answer 26

DPP4 inhibitors

Question 27

What stimulates incretin release from gut?

Answer 27

Nutrients

Question 28

Where does glucose-loewring actions of GLP-1 occur?

Answer 28

In multiple organs Beta-cells Alpha-cells Brain = reduce appetite Gut = slow gastric emptying

Question 29

What is the bioactivity of GLP-1 like?

Answer 29

Glucagon (DNA/RNA) Pro-glucagon GLP1 (7-37) biologically activ Secreted extracelularly from L-cells DPP4 cleaves GLP1(7-37) into small peptides, which are inactive Small peptides converted into amino acids

Question 30

What is the issue for GLP-1 therapeutics?

Answer 30

GLP-1 has a very short SERUM half-life (minutes) = due to rapid degradation by DPP4 For incretin-like treatments need to either inhibit breakdown of GLP-1 (DPP4 inhibitors) or increase GLP-1 stability in serum

Question 31

What are the GLP-1RA?

Answer 31

Exenatide Liraglutide Semaglutide Duaglutide

Question 32

What are DPP4 inhibitors?

Answer 32

Small molecules (nonpeptides)

Question 33

What are the main 4 cellular receptor classes?

Answer 33

Ligand-gated ion channels GPCRs Kinase linked receptors Nuclear receptors

Question 34

What type of receptors is GLP1R?

Answer 34

G-protein coupled receptor

Question 35

What is the structure of GPCRs?

Answer 35

7 transmembrane structure Allows then to bind to a range of ligands

Question 36

What is the GPCR activation cycle?

Answer 36

When ligand binds, GEF displaces GDP with GTP Gby goes to downstream effectors Ga with GTP is then hydrolysed to GSP and rebinds Gby = when NO ligand

Question 37

What are the 3 different Ga proteins?

Answer 37

Gas = stimulates target enzyme adenylate cyclase Gai = inhibits target enzyme adenylate cyclase (cAMP) Gaq stimulates phospholipase C (IP3 and DAG)

Question 38

What is the mechanism of action of GLP-1R?***

Answer 38

GLP-1R is a Gas = stimulates cAMP production PKA activation

Question 39

What does action of GLP-1 do to beta cells?

Answer 39

POTENTIATES glucose-stimulated insulin secretion (GSIS) Does not STIMULATE insluin secreiton in absence of depolarising stimulus

Question 40

What is the secretion of insulin like?

Answer 40

BIPHASIC

Question 41

What is a sign of pre-diabetes?

Answer 41

Insulin secretion defects 1st phase of insulin secretion is lost first 2nd phase can be lost later in T2D

Question 42

What was the result of exenetide on biphasic phases of GSIS in T2D?

Answer 42

With i.v infusion = bypassing the gut There was an increase in BOTH 1st and 2nd phase GSIS in T2D = higher GSIS than healthy subjects even

Question 43

How did they test the incretin effect of GLP-1 on beta-cell GLP-1 receptors?

Answer 43

Produced different models WT mice KO GLP-1R everywhere Expressed GLP-1 only in pancreas Expressed GLP-1 everywhere except pancreas When no GLP-1R everywhere = no insulin secretion at all When GLP-1R ONLY in pancreas = restored insulin secretion but not fully

Question 44

How much does the beta-cell GLP-1R contribute to GSIS effect?

Answer 44

GSIS mostly POTENTIATED by beta-cell GLP-1R But not fully restored so other GLP-1R are also needed

Question 45

What are the two arms of cAMP signalling in the beta-cell in response to GLP1 binding its receptor?

Answer 45

cAMP activates EPAC or PKA EPAC = exchange protein directly activated by cAMP

Question 46

What is the mechanism of action caused by EPAC activation?

Answer 46

Causes insulin vesicle exocytosis

Question 47

What is the impact of EPAC and PKA on insulin secretion?

Answer 47

EPAC & PKA activation = highest potentiatation EPAC potentiates GSIS = medium PKA potentiates GSIS = low Incretin drugs do NOT increase Ca2+ = they increase cAMP signalling

Question 48

What is the mechanism of action of Glimins?

Answer 48

Regulating mitochondrial bioenergetics Improves insulin sensitivity in muscle and liver Improves insulin SECRETION from beta cells

Question 48

What are Glimins?

Answer 48

Oral glucose-lowering agents

Question 49

What needs to be improved for Glimin treatment?

Answer 49

Dose is quite a high conc 2 oral doses daily

Question 50

How do we know that Glimins increase insulin secretion?

Answer 50

We know insulin secretion has increase by looking at C-peptide rate This shows that it is not just a slower clearance of insulin

Question 51

What were the overall effects of Glimins?

Answer 51

Improved beta cell mitochondrial morphology, insulin granule density, and reduced beta cell apoptosis