examples of peptide/protein delivery formulations Flashcards
(25 cards)
what is lyophilisation and why is it used
freeze drying, to preserve proteins that are unstable at room temperatures into lyophilised powders
steps of lyophilisation
- freezing aq sample to a vitreous state
-water molecules crystalise and trap amorphous components to interstices, cooling rate significantly influences properties of lyophilised protein
-ice crystals forming can generate temporary solid liquid interface - primary drying
-frozen water molecules removed by sublimation below glass transition temp (Tg) or collapse temperature (Tc) of protein
3.removal of remaining adsorbed water by diffusion and desorption at high temps
-residual water content in final freeze dried materials are 1-3%
-close association of protein molecules can lead to unwanted H bond interactions and disulfide exchange
-risks forming aggregates
-prevented by adding excipients that adsorb/bind water mc at inter protein sites
why is lyophilisation risky
brings protein molecules into close proximity of each other, increases risk of aggregation
how does protein size affect diffusion into solution/bloodstream, how do peptides and proteins cross membrane, diffusion of peptides and proteins in solution (bloodstream) depends on…
increasing size/charge=decrease diffusion
-peptides may cross membranes passively, most proteins dont cross, if need active transport
diffusion of peptides and proteins in solution (bloodstream) depends on: size, shape, interactions with solvents nad solutes, charge
what is the translational movement of proteins expressed in terms of
frictional coefficient (f)
f=kB T/D
kB=bolzmann contant
T=absolute temprature
D=diffusion coefficient
what is the frictional ratio of peptides
f/f0>1
f0=rate of diffusion of molecule of same size but spherical shape
protein shape can change depending on…
environment like pH and salt content
main role of insulin
manage uptake/use/storage of blood sugar
how does pancreas regulate blood glucose levels through insulin and glucagon
-specific islet cells in pancreas release insulin into blood in response to glucose
-cells remove glucose from blood and convert into energy or stored as glycogen/fatty acids
-when blood sugar levels drop, second pancreatic hormone, glucagon controls release of glucose from glycogen stores
when blood glucose level is high=insulin released and glucose taken up and stored as glycogen
when low=glucagon released and glycogen is converted intno glucose into bloodstream
why cant insulin be taken orally
gets degraded in transit, needs to be administered subcutaneously
3 main formulation types for insulin
short acting free insulin-peak activity at 2 hours
intermediate-suspension of zinc insulin amorphous particles (2um size) , peak at 4-8 hours
long acting-suspension of zinc insulin crystalline (10-40um size), peak at 8-12 hours
pharmacokinetic limitations for insulin
-very small protein so diffuses rapidly in blood
-liver degrades 50-60% of insulin released by pancreas into portal vein, elimination by kidney is 35-45% (normally)
-subcutaneous delivery for therapy
-different degradation profile for insulin injected exogenously as no longer delivered to portal vein
-kidney has greater role in insulin degradation (~60%) and liver (~30-40%) of subcutaneously delivered insulin
subcutaneously delivered and physiological insulin have different pharmacokinetics
yes
what is subcutaneous delivery and some limitations
injection into fatty/connective tissue beneath skin
-less well perfused than intramuscular, slower absorption, depot effect
-essential to avoid irritants in formulation bc there’s pain receptors in skin
-can inject solutions, suspensions, depot implants
-does need to be water miscible
-only can inject small volumes
name and describe the 2 types of fast acting insulin
insulin lispro
-proline at position 28 swapped with lysin at 29 on B chain
-resultant hexamer dissociates more rapidly to monomer than normal
insulin aspart
-proline 28 replaced with aspartate
-increases overall charge
-hexamer dissociates more rapidly to relieve charge to charge repulsion in associated state
problems with insulin pharmacokinetics
-peak absorption of regular insulin occurs 2-4 hours post injection
-persists for several hours
-doesnt provide early/quick rise in plasma insulin concentration
example of intermediate acting insulin
insulin glargine
-glycine added at A21 and 2 arginines added at B30
-changes isoelectric point from 5.4 to 6.7
-when injected to body with physiological pH of 7.4 it precipitates resulting in adsorption and prolonged action
intermediate and long acting insulin
what is insulin stabilised by, how do long acting formulations slow the release down, why is thorough agitation of container needed
-insulin normally stored as hexamer stabilised by zinc ions
-when injected the hexamers break apart to release active monomers
-long acting formulations need to slow this down^, achieved by preparing suspensions of insulin in crystallin/amorphous form
-thorough agitation of container needed before injection to ensure homogenous suspension and reproducible dosing
what are protamine zinc insulin formulations, how are thye prepared, what shape is formed, how is the formula modified, whats the duration
-salt like compounds formed bt acidic insulin and basic polypeptide protamine
-prepared by titration of acidic solution in insulin with buffered protamine solution at neutral pH
-isophane precipitation, no insulin or protamine in supernatant
-rod shaped crystals form
-formulation modified by carrying out precipitation in presence of zinc ions and other excipients
-duration 12-36 hours
what factors affect insulin activity after injection
insulin must be absorbed
-different pH/solubility for diff variants
injection site variations
-muscle movement and blood flow affects transport
-absorption faster from sc injection in arms than thigh
-short acting insulin can be injected intramuscularly since abs more rapid due to increased perfusion in muscles compared to sc
example of a formulation with proteins as carriers
paclitaxel (PTX)
-potent anticancer drug, almost insoluble in water
-conventional formulation of paclitaxel with polyoxyl castor oil and alcohol
-needs infusion 3< hours via in line filter
-hypersensitivity is common reaction due to surfactant
-carrier for drug is soluble well tolerated and safe
what is albumin
main protein in blood plasma
-made in liver, helps transport substances
how albumin in blood transports hydrophobic molecules
-repurpose plasma protein binding to use albumin as carrier for paclitaxel
-controlled protein aggregation as formulation tool
-albumin partially precipitated in presence of PTX
-nanoparticles of controlled size and albumin aggregation number can be formed under specific conditions
-exploits natural body mechanisms for albumin transport and processing
proposed mode of action of albumin assisted drug delivery to tumours
-albumin bound drugs leave bloodstream easier in tumours bc tumours have leaky blood vessels (EPR effect-enhanced permeability and retention) (leave through leaky tumour microvasculature)
-albumin actively transported into tumour, binds to gp60 and triggers caveolin-1 which forms caveolae (small transport bubbles that transport albumin drug complex across endothelial cells and into tumour interstitium)
-once inside tumour, albumin binds to SPARC (overexpressed tumour protein) which helps drug accumulate more in tumour
