LT6 Beta-Cells as Therapeutic Target in Diabetes Flashcards
What is WHO diagnostic criteria for diabetes?
Fasting plasma glucose of above 7mM
OR
2h plasma glucose of above 11.1mM during a 75g oral glucose-tolerance test
How can you test for diabetes?
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
What are the two core factors that cause T2D insulin deficiency?
Insulin resistance and beta-cell dysfunction
Results in insufficient insluin secretion to meet the demand of the body
What is the relationship between insulin secretion and insulin sensitivity?
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
What feature causes T2D?
Inherent pancreatic beta-cell islet defect in insulin secretion
Both structural and functional
What are islets?
Cluseters of ~1000 endocrine cells
What % of pancreas do islets make up and what is the rest of the pancreas?
Islets make up ~1-2% of pancreatic volume
The remainder is mostly exocrine pancreas
What do epsilon cell secrete?
Ghrelin
Do beta-cells only sense glucose?
No
What other molecules do beta-cells sense?
IL-6 from muscle
Leptin/Adiponectin from fat
Igf1 from liver
Glucagon from alpha-cells
GLP-1 and GIp form gut
Why is T2D so heterogeneous?
Because could be caused by numerous different reasons in individuals
Insulin resistance or beta-cell dysfunction
What are the 10 things needed to know to develop a target medicine profile?
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?
What would the ideal beta cell profile look like?
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
What categories would the chosen patients have to fall into for target profile?
Absence of autoAb (GADA, IAA and IA-2A)
Impaired glycaemic control
C-peptide and HOMA2-beta score
BMI
What outcomes would need to be measured for a medicine profile?
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)
What is the HOMA2-beta score?
Homeostasis Model Assessment = a validated mathematical tool used to estimate beta-cell function based on fasting glucose and insulin levels
What is the relationship between expenditure for diabetes and mortality?
Expenditure is inversely proportional to mortality
More money = less likely to die
What is electrophysiology?
A measure of membrane voltage
Give an example of a sulphonylurea
Tolbutamide
What is the summary of SU treatment outcomes?
Good short-term but exhausts beta-cells long term
Risk of HYPOglycaemia and hyperinsulinaemia
What are the 5 subgroups of polygenic diabetes?
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
Why is there no control in drug trials for diabetes?
Unethical to have an uncontrolled diabetes group = allows the diabetes to get worse
What typy of diabetes might SUs be best for?
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
What new research tool was used with sulphonylurea?
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
Why are SUs good?
Oral, once daily dosing
Stable at room temp and low cost
What are gliptins?
DPP4 inhibitors
What stimulates incretin release from gut?
Nutrients
Where does glucose-loewring actions of GLP-1 occur?
In multiple organs
Beta-cells
Alpha-cells
Brain = reduce appetite
Gut = slow gastric emptying
What is the bioactivity of GLP-1 like?
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
What is the issue for GLP-1 therapeutics?
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
What are the GLP-1RA?
Exenatide
Liraglutide
Semaglutide
Duaglutide
What are DPP4 inhibitors?
Small molecules (nonpeptides)
What are the main 4 cellular receptor classes?
Ligand-gated ion channels
GPCRs
Kinase linked receptors
Nuclear receptors
What type of receptors is GLP1R?
G-protein coupled receptor
What is the structure of GPCRs?
7 transmembrane structure
Allows then to bind to a range of ligands
What is the GPCR activation cycle?
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
What are the 3 different Ga proteins?
Gas = stimulates target enzyme adenylate cyclase
Gai = inhibits target enzyme adenylate cyclase (cAMP)
Gaq stimulates phospholipase C (IP3 and DAG)
What is the mechanism of action of GLP-1R?***
GLP-1R is a Gas = stimulates cAMP production
PKA activation
What does action of GLP-1 do to beta cells?
POTENTIATES glucose-stimulated insulin secretion (GSIS)
Does not STIMULATE insluin secreiton in absence of depolarising stimulus
What is the secretion of insulin like?
BIPHASIC
What is a sign of pre-diabetes?
Insulin secretion defects
1st phase of insulin secretion is lost first
2nd phase can be lost later in T2D
What was the result of exenetide on biphasic phases of GSIS in T2D?
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
How did they test the incretin effect of GLP-1 on beta-cell GLP-1 receptors?
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
How much does the beta-cell GLP-1R contribute to GSIS effect?
GSIS mostly POTENTIATED by beta-cell GLP-1R
But not fully restored so other GLP-1R are also needed
What are the two arms of cAMP signalling in the beta-cell in response to GLP1 binding its receptor?
cAMP activates EPAC or PKA
EPAC = exchange protein directly activated by cAMP
What is the mechanism of action caused by EPAC activation?
Causes insulin vesicle exocytosis
What is the impact of EPAC and PKA on insulin secretion?
EPAC & PKA activation = highest potentiatation
EPAC potentiates GSIS = medium
PKA potentiates GSIS = low
Incretin drugs do NOT increase Ca2+ = they increase cAMP signalling
What is the mechanism of action of Glimins?
Regulating mitochondrial bioenergetics
Improves insulin sensitivity in muscle and liver
Improves insulin SECRETION from beta cells
What are Glimins?
Oral glucose-lowering agents
What needs to be improved for Glimin treatment?
Dose is quite a high conc
2 oral doses daily
How do we know that Glimins increase insulin secretion?
We know insulin secretion has increase by looking at C-peptide rate
This shows that it is not just a slower clearance of insulin
What were the overall effects of Glimins?
Improved beta cell mitochondrial morphology, insulin granule density, and reduced beta cell apoptosis
