insulin treatment

Question 1

conversion of pre-pro-insulin to insulin

Answer 1

• the signal sequence (pre) targets the protein to the endoplasmic reticulum and it is packaged into secretory vesicles
• pre is cleaved off by a protease in the endoplasmic reticulum generating pro-insulin
• disulphide bonds form between chain A and B of pro-insulin
• proteases cleave at either end of chain C
• giving insulin chain A and B joined by disulphide bonds and C peptide

Question 2

insulin hexamer

Answer 2

• insulin is stored as an inactive hexamer in secretory vesicles
• hexamer is stabilised by Zn2+ ions
• upon release into bloodstream hexamers disassemble

Question 3

three groups of insulin

Answer 3

animal: not widely used but some people find it works better for them
human: synthetically made via recombinant DNA technology
analogues: human insulin is altered to make it work quicker or last longer

Question 4

three types of insulin preparations

Answer 4

• short duration with a relatively rapid onset of action; soluble insulin, insulin aspart, insulin glulisine, insulin lispro
• intermediate action; isophane insulin
• slow onset and lasts for long periods; insulin detemir, insulin glargine

Question 5

biphasic insulin

Answer 5

pre-mixed insulin preparations containing various combinations of short-acting insulin or rapid-acting insulin analogue together with an intermediate-acting insulin

Question 6

uptake of insulin

Answer 6

• injected insulin has to diffuse across capillary walls to enter circulation
• diffusion is limited by size of insulin
• monomer > dimer > hexamer/aggregates

Question 7

humulin S

Answer 7

• soluble
• short-acting

Question 8

humulin I

Answer 8

• isophane
• medium-acting
• contains protamine

Question 9

protamine

Answer 9

• basic protein (positively charged) that binds to negatively charged insulin and clusters insulin hexamers
• causes clustering of insulin, limiting diffusion through capillary walls

Question 10

insulin aspart (novorapid)

Answer 10

has proline to aspartate substitution in the B chain which reduces the tendency to form hexamers as a result it is more rapidly transferred from the sub-cutaneous injection site to the bloodstream

Question 11

insulin lispro (humalog)

Answer 11

• has two substitutions in the B chain which also diminish the tendency of insulin molecules to self-associate

Question 12

insulin glulisine

Answer 12

has two substitutions in the B chain
asparagine replaced with a lysine and a lysine replaced with a glutamic acid these changes also reduce insulin self association

Question 13

insulin glargine (lantus)

Answer 13

contains an asparagine to glycine substitution in A chain and also has two arginines added to the carboxyl terminal end of the B chain
these changes make the insulin analogue less soluble at physiological pH which limits absorption from the site of injection

Question 14

insulin detemir (levemir)

Answer 14

• covalently attached fatty acid (myristic acid) that causes the molecule to bind to albumin in the blood serum
• albumin with the insulin receptor for binding to insulin detemir prolonging its action
• albumin binding also protects insulin detemir from circulating peptidases increasing its stability

Question 15

insulin degludec (tresiba)

Answer 15

• has a hexadecanedioic acid group added to B chain this mediates albumin binding but also causes formation of multi-hexamers when injected
• monomers are slowly released from these multi-hexamers extending duration of action beyond 40 hours

Question 16

injection of insulin

Answer 16

• injection is necessary as orally-administered insulin would be degraded by proteases in the stomach and small intestine
• injection is sub-cutaneous
• once injected, insulin diffuses into small blood vessels and enters bloodstream
• injection site: stomach, buttocks, thighs
• injection sites are rotated to avoid lipohypertrophy, accumulation of lumps under skin
• all insulin should be stored below 25 degrees in fridge

Question 17

insulin treatment of type 2

Answer 17

• insulin used in combination with oral antidiabetic drugs
• basal insulin is usually a suitable first step with once/twice daily intermediate or long acting insulin
• biphasic insulin can be used if diabetic control is particularly poor
• basal-bolus regimen can be introduced if blood glucose remains inadequate

Question 18

insulin pumps

Answer 18

• alternative to injections
• size of small mobile
• delivers varied dose of rapid acting insulin continually during day/night
• when food is eaten can give an additional bolus dose of insulin by pressing specific buttons

Question 19

islet cell transplantation

Answer 19

• implanting islet cells from deceased donor
• simple procedure cells injected through catheter in the upper abdomen into the liver
• recipients need to take immunosuppressive drugs to prevent rejection
• lack of suitable organ donors

Question 20

stem cell-derived beta cells

Answer 20

• produced from pluripotent stem cells
• the cells form islet-like clusters and made insulin when transplanted into mice
• overcomes limitation of acquiring donors

Question 21

re-purposing of cells in patient

Answer 21

• switching off a single gene GI cells allowed them to produce insulin
• gut endocrine progenitor cells could be differentiated into glucose-responsive insulin-producing cells by ablation of the transcription factor Fox01

Question 22

insulin sprays

Answer 22

• attaching insulin to carriers that protect from degradation and allow oral delivery
• non-protein insulin substitutes that are able to bind to the insulin receptor and activate intracellular signalling pathways