Peptides and Proteins Drug Delivery Flashcards
What are peptides and proteins?
Peptides & Proteins are built up of α-amino acids linked through amide bonds.
What are amide bonds?
Main bond forming the protein/peptide chain backbone.
Vulnerable to hydrolysis by proteases/peptidases.
What are disulphide bonds/bridges?
Formed between thiol (-SH) groups of 2 cysteines (Cys), by oxidative folding.
Stabilise protein folding e.g. Insulin chains.
Vulnerable to oxidation/reduction.
What are hydrogen bonds?
Form between protein/peptide chain back bone amides and responsible for stabilising secondary structures.
Can be formed between aa side chains.
Vulnerable to solvents e.g. DMSO.
What are ionic bonds?
Formed between positively charged (e.g. Glu, Asp) and negatively charged aa side chains through electrostatic interactions.
Stabilise protein folding.
Vulnerable to pH changes.
What are hydrophobic interactions?
Happens between hydrophobic aa side chains.
Important for driving and stabilising protein folding.
Folding shield hydrophobic areas from undesirable interactions with water.
Unfolding expose the hydrophobic regions to water and triggers protein aggregation to stabilise the system.
Unfolding is triggered by various factors e.g. pH, heat, salts, solvent, vigorous mechanical agitation…etc.
Considerations with formulation excipients and manufacturing process.
What are the challenges for peptides and proteins delivery?
Poor bioavailability.
Poor absorption & cellular uptake.
Metabolic liability.
Chemical and physical instability.
Formulation and storage issues.
Explain the physical instability of proteins:
Misfolding & Denaturation (extreme pH & high temperature).
Aggregation - adsorption to interface (air/water and container/water).
Drastic environmental conditions could be:
Elevated Temperature - protein denaturation.
Adsorption - protein aggregation.
Shaking & Shear Forces - protein aggregation.
Explain the chemical instability of proteins:
Deamidation (Asn & Gln).
Oxidation (Met, Cys, His, Trp & Tyr).
Isomerisation of the natural L configuration to the D-isomer (extreme pH & high temperature).
Degradation kinetics is dependent on pH, temperature and neighbouring amino acid.
Explain insulins chemical instability:
Acidic pH:
AsnA21 undergoes cyclisation to the anhydride, then react through two pathways, either:
Pathway A: react with water, leading to deamination to aspartate (Asp) AsnA21 –> AspA21.
Pathway B: react with the N-terminal PheB1 of another chain, leading to a cross-linked molecule.
Neutral pH:
AsnB3 undergoes deamidation to aspartate and isoaspartate-containing insulins, which are both equipotent to native insulin.
What excipients are used in protein formulations?
Antiadsorbent / aggregation blockers - Reduction of adsorption and aggregation prevention.
Buffer - Stabilising pH.
Preservatives - Inhibition of microbial growth in vials for multiple dosing.
Antioxidants - Prevent oxidation.
Storage conditions - low humidity & temperature.
What is limited oral absorption of peptides & proteins due to?
High molecular weights.
Low lipophilicity and charged functional.
Efflux of absorbed peptides & proteins by efflux pumps such as P-glycoprotein (P-gp).
What are some strategies to overcome poor absorption of peptides & proteins?
Absorption enhancers - Excipients that increases cell permeability to peptides & proteins.
Structural Modifications:
Modification with Vitamin B12 – receptor-mediated absorption of the vitamin B12 conjugate.
Lipidization – conjugation with fatty acid. Improved transport across biological membranes, higher stability and longer plasma half-lives.
Carrier Systems:
Mucoadhesive Polymers & Hydrogels – mucoadhesion in small intestine allows for a steeper concentration gradient across the epithelial barrier, which lead to increased passive drug uptake and a prolonged therapeutic effect.
Nano-carriers – Improved cellular uptake.
Define metabolic liability:
Limited oral bioavailability due to degradation via enzymes and hydrolysis in the acidic environment in the stomach.
To overcome the above drawbacks of oral route, most therapeutic proteins and peptides are administered through parenteral routes (mainly IV, IM & SC). Though, systemic proteases can still cause degradation.
What is PEGylation?
Protease Inhibitors.
Conjugation of PEG to the protein/peptide molecule. PEG is FDA approved & of low toxicity.
