ADME of macromolecules Flashcards
significance of protein degradation
1) normal protein turnover = proper regulation of cell signalling pathway
2) remove misfolded/damaged protein -> normal cellular activities
processes for uptake of extracellular proteins
1) phagocytosis
- large solid particles phagocytosed by phagocytes -> cell debris, protein aggregate
2) pinocytosis
- take in extracellular fluid & solute dissolved in fluid by budding of small vesicles from cell membrane
- non specific
3) receptor-mediated endocytosis
- ligands on cell surface receptors take up specific molecules
- internalised coated vesicles fused w endosome -> send to lysosome/recycled
what are the types of proteasomal degradation methods
1) 26s proteasoe
2) ubiquitin
26s proteasome function
specific for degradation of regulatory proteins & removal of damaged proteins
structure of 26s proteasome
20s core particle capped by 19s regulatory particle at one or both ends
20s core particle for 26s proteasome
- 4 hepatameric ring in cylindrical structure
- 2 outer ring = 2 alpha subunit
- 2 inner ring = 2 beta subunit
- central cavity = proteolytic active site
19s regulatory particle for 26s proteasome
- arranged into lid & base
- ATPase subunits (energy consuming)
- function:
1) recognise substrate w polyubiquitin chain
2) unfolded protein
3) translocation into 20s core particle
ubiquitin
- small protein
- a lot of 7 glycine molecules
- attached to protein substrate through isopeptide bond between C-terminal of Gly of Ub and amino group of Lys of substrate
- monoubiquitination
** post translational mod
proteasomal degradation process
1) delivery of susbtrates to proteasome
- substrate interact w 19s regulatory particle subunit -> bind directly
- adaptor protein bind proteasome & polyubiquitin chain on substrate -> deliver for degradation
- degraded wo ubiquitination
2) substrate recognition by 19s regulatory particle (only polyubiquitin chain)
- remove uniquitin tag by deubiquitinating enzyme (DUBs) into monomers (leave proteasome & recycled)
- degradation of remaining protein substrate
3) entering degradation chamber
- narrow entrance prevent any random protein from entering
- folded proteins enter -> unfold -> translocate -> hydrolysed to short peptides -> released from opp ends of channel
traditional vs biologic/biopharmaceutical products
1) molecular weight
- traditional: smaller
- new: larger
2) source
- traditional: chemically synthesised & purified to homogenity
- new: derived from living source, refined to high degree of purity
3) predictability
- old: less predictable, off target effecets
- new: more predictable, lesser SE
macromolecule oral absorption
poor oral systemic absorption & poor bioavailability
1) poor protein stability
- acid gastric juice, digestive enzyme
2) poor permeability
- mucous layer lining GIT (immune cells recognise foreign particles)
- intestinal epithelium carry -ve charge
- tight junctions
how is macromolecules absorbed after SC administration
1) protein delivered to hypodermis
- hypodermis (subcu tissue): adipose tissue, ECM network, nerve, blood capillaries
2) proteins move through ECM -> blood/lymphatic nerves
- diffusion
- conovestion
factors affecting type of transport & system for macromolecules after SC administration
1) larger proteins (> 16 - 20 kDa)
- slow movement across capillary membrane
- most absorption via lymphatic system -> drain into lymph nodes & larger lymphatic vessels -> circulatory system
2) smaller proteins (< 16-20 kDa)
- absorption via both circulatory & lymphatic system
- perfusion affect capillary absorption
what are the rate limiting factors that affect macromolecule absorption after SC administration
1) interstitial fluid transport rate
2) lymphatic transport rate
advantages of protein binding in circulation
1) improve circulation half life
2) more efficient delivery to target tissue
3) protect foreign proteins from identification by immune cells
location of macromolecule metabolism via proteolysis
interstitial fluid (ECF), cell surface, intracellular once protein drug taken into cell
what is neonatal Fc receptor (FcRn)
IgG binding site, serum albumin binding site
significance of IgG homeostasis & albumin recycling for endothelial cells
allow intracellular trafficking of Ab & albumin -> Ab & albumin escape degradation in lysosome -> recycling -> increase half life
process of IgG homeostasis & albumin recycling
1) IgG & albumin taken up by endothelial cells (pinocytosis) -> early endosome
2) acidic endosome w internalised FcRn fuse w early endosome -> binding of substrate to receptor at pH 5-6 -> FcRn IgG complex or FcRn-albumin complex
3) complex recycled to cell surface -> exocytosis
4) neutral pH of blood -> IgG/albumin dissociate from complex -> IgG/albumin back to blood, FcRn re-expressed onto cell surface
5) proteins not bound to Fc -> degradation
sides of cells
1) apical: outside
2) basolateral: inside
methods of macromolecule elimination
1) extra & intracellular proteolytic degradation
2) glomerular filtration
factors affecting macromolecule elimination
1) MW
- X filter if too big
2) charges
- +ve charge = higher renal filtration (-ve charge on glomerular basement membrane)
3) shape & rigidity of protein
4) tubular reabsorption
- tubular epithelial net negative charge -> positively charged more reabsorbed
protein glycosylation - general
- add glycan to specific amino acid
- different glycosylation pattern - different amino acid (straight vs branched)
- affect activity (enhance receptor binding), increase t1/2
process of protein glycosylation
N-linked glycosylation of proteins -> increase size of protein/modify binding to glycoprotein receptor -> increase circulation half time
polyethylene glycol (PEG)
- a lot of hydroxyl groups make PEG water compatible
- conjugation w macromolecule increases half life
1) increase size = lower glomerular filtration
2) PEG protective layer on protein so protein X recognised by proteolytic enzyme/immune cells = lesser proteolysis & immunogenesis
