Mucosal drug delivery Flashcards
What are mucosal membranes?
epithelial membranes with a layer of mucus
What surfaces do mucosal membranes line? Give some examples.
hollow organs/body cavities exposed to external environment
eg digestive, respiratory, reproductive system
What are the functions of mucosal membranes?
- provide hydration, lubrication
- protective barrier
What is the composition of mucus?
viscoelastic hydrogel composed of:
- cross-linked mucin fibres
- cell/cell debris
- microbiota and secretions
- DNA, proteins, Ig, lysozyme, lactoferrin
- lipids, polysaccharides
whys it hard to deliver NPs through or across mucosal memb?
its a protective barrier function
Generic structure of mucin monomer
oligonucleotides stuck to repeat structure and cysteine residues between
What is an example of microbiota and secretions found within mucus?
microbes in the vagina secrete lactic acid
What can impact the mucus composition and properties? 2
anatomical site and disease state
What are the two properties of mucus that can vary?
pH
layer thickness
pH of resp tract?
neutral
What is the pH of mucus in the ocular, distal colonic and endo-cervical membranes?
slightly basic
What is the pH of mucus in the vagina?
slightly acidic
What is the pH of mucus across the gastric lumen to epithelium?
transitions from acidic in lumen to neutral in epithelium
gradient
What is the thickness of mucus in the nasal cavity?
thin
What is the thickness of mucus in the stomach and colon?
thick, but can vary depending on digestive activity
What example shows that mucus thickness can vary in disease states?
cystic fibrosis - thick, sticky mucus in the lungs
Why is mucus a difficult barrier to cross for drug delivery?
- dynamic properties: high turnover rates
- composition: strong adhesive forces
What thickness of mucus has the fastest turnover rate?
thin:
- nasal cavity and respiratory tract replenished every 10-20min
- eyes turnover rate of 13-20% every minute
What is the implication of mucus turnover on the nanomedicine?
nanomedicine residence time is shortened as it can be turned over with the mucus
What are the 2 types of strong adhesive forces that mucus can form with nanomedicines and why?
- electrostatic: due to negative charge on mucus
- hydrophobic: presence of hydrophobic domains (originally to minimise transport of bacteria)
Why do we delivery nanomedicine to mucosal surfaces?
same reasons we use nanomedicines in general:
- sustained/controlled drug release
- protect drug from degradation (mucus also has enzymes)
What is the goal of mucoadhesive nanomedicines?
want to adhere to mucus
to prolong its residence time in memb, maybe to facilitate enhanced absorption of drug
What is the goal of mucopenetrating nanomedicines?
penetrate mucus to reach epithelial cells
What are two approaches to achieving mucoadhesion with nanomedicines?
non-specific and specific binding
What is the non-specific binding used to achieve mucoadhesion?
electrostatic forces or H bonds
this is targeting the natural property of the mucus rather than a specific mucus component
How can mucoadhesion be achieved through electrostatic attractions?
coat NPs with either:
- positively charged polymer so it can interact w negative charge of mucus
- negatively charged/neutral polymer to get H bonding in components of mucus
What is an example of a cationic polymer used to achieve mucoadhesion through electrostatic forces?
chitosan
What is an example of a neutral polymer used to achieve mucoadhesion through H bonds?
cellulose + derivatives
What are examples of anionic polymers used to achieve mucoadhesion through H bonds?
- poly(acrylic acid) + derivatives
- sodium alginate
Sodium alginate combinations to achieve mucoadhesion through H bonds
gellan gum
xanthan gum
carrageenan (sulfate)
Poly(acrylic acid) + derivatives to achieve mucoadhesion through H bonds
polycarbopol
carbomer
carmellose
carbopols
What is the specific binding used to achieve mucoadhesion?
- covalent bonds
- lectins
What covalent bonds are used to achieve mucoadhesion?
- disulphide bridges
- interact thiolated polymers (R-SH) and cysteine residues
and Cysteine found in mucin fibres
How do lectins work to achieve mucoadhesion? (what are they?)
they’re carbohydrate-binding glycoproteins
attach to NM surface to allow active targeting of NPs
What is the disadvantage of lectins?
- can permeate through mucus and enter cell
- immunogenicity?
- toxicity?
- therefore need to consider lectin choice carefully
Particles of what size cannot penetrate the mucus and are cleared away quickly? Why?
> 1000nm - too big to squeeze through pores of mucus meshwork created by mucin fibres
Particles of what size are the best for mucopenetration? Why?
mid range - 200-500nm
any smaller means they become stuck in ‘dead-end’ structures
What are the ideal characteristics of mucopenetrating particles?
- small enough to fit through mucus pores
- inert/ non-adhesive to avoid binding to mucus
whats the ultimate fate of bigger particles not able to penetrate mucus memb?
mucus memb turned over at some point and big particles taken out
Mucus-penetrating particles must overcome what 2 things?
adhesive and steric
(size and trafficking through pores) barriers…
What are strategies we can use to create mucopenetrating particles?
- mask surface charge and hydrophobicity w polymers
- add mucolytic agents
What polymers can be used to mask surface charge and hydrophobicity for mucopenetration?
- PEG
- Pluronic F-127
- Poly(vinyl alcohol)
What are the issues with PEG to help mucopenetration?
- people could have anti-PEG antibodies due to prior exposure in personal care products
- masking surface properties hinders cell uptake
- can also be mucoadhesive if high MW
high MW PEG has low Dm/Dw value (particle coating) what does this mean?
not good surface penetration
promotes mucoadhesion instead.
Long chain PEGs may get tangled up and create a steric barrier… making particles stick in mucus/formation of interpenetrating polymer networks: long chain PEGs intercalate with mucin fibres in mucus -> stick
what is Dm/Dw? and what values are desirable?
relative diffusion of these particles in mucus relative to diffusion in water
System that penetrates well through mucus has high Dm/Dw. Want as close to 1 = better penetration.
if you have 2 2kDas PEGs (essentially same PEG coating but diff weights), whats the reason for difference in surface penetration/ Dm/Dw?
Not having good coverage of surface, not masking fully and well = not getting best mucopenetration possible.
what sort of NPs: hydrophobic or hydrophilic have low Dm/Dw ?
hydrophobic NPs with no coating = very low Dm/Dw. Not good penetration. Getting hydrophobic interactions between surface and hydrophobic pockets
Number increase with coating with PEG and high coverage
What must be correct about PEG to achieve mucopenetration?
- needs low MW
- needs high density (higher coverage w no exposed parts)
pluronic F-127 is an alternative to PEG.
its a triblock copolymer working similar to PEG, but requires a poly(propylene oxide) PPO segment that’s >3kDa for MoA
name 2 benefits of using it over PEG
can pre-make nanomedicine and pluronic F-127 will physically adsorb to NP surface
What are the issues with pluronic F-127?
- stability of coverage
- masking surface properties hinders cell uptake
What is an alternative to PEG and pluronic F-127?
poly(vinyl alcohol)
has hydroxyl group (hydrophilic)
acetate group (hydrophobic)
mucolytic agents aid mucopenetration by disrupting the mucus layer. how can they do this?
- enzymatic degradation of proteins
- degradation of entangled DNA
- reduction of disulfide bonds
What is an example of a mucolytic agent that works by degrading entangled DNA in the mucus?
recombinant human DNAse
What is an example of a mucolytic agent that works by reducing disulfide bonds?
N-acetyl-L-cysteine (NAC)
Formed between thiol groups. Lots of cysteine residues in mucus. Form disulphoide bridges with thiol groups on NM, but also with each other! Lots of cross links in mucus. NAC opens up mucus structure by reducing these = easier for NM to get through
size modulation: what size particles
- increase mucoadhesion
- decrease mucoadhesion
- 100nm
- 200-500nm
???
what 3 surface chemistry changes will increase mucoadhesion.
what 1 will decrease it?
+ve charge
mucoadhesive polymers
hydrophobic surface
dense PEGylation :(
Part 2: Mucosal delivery applications……
pulmonary delivery: why target the lung for local admin?
treat lung diseases
potential targets: epithelial cells and alveolar macrophages
pulmonary delivery: why target the lung for systemic admin?
- Large SA for absorption
- Low thickness of epithelial barrier (mucosal membrane quite thin too)
- Low enzyme activity
- Extensive vascularisation: blood supply
where do the smallest size (0-1um) NPs deposit in lungs?
alveolar region
some in airways
where do the mid size (1-5um) NPs deposit in lungs?
highest % in alveolar region
where do the largest size (5um+) NPs deposit in pulmonary system?
mouth and throat, airways
smaller NPs given IV, dont even reach lungs, but more accumulate where?
liver and spleen
problem with admin larger particles IV for pulmonary delivery?
block smaller capillaries and cause embolism :(
thus non inhalatory admin of NMs not best way to get to lung
assessing how hydrophobic surface of NP and found high HIC index associated with?
adverse effects/ tox in lung
whats a good HIC index score for NPs to have (hydrophobicity) to exhibit no adverse effects?
low
< 0.7
What is the main risk of using nanoparticles for pulmonary drug delivery?
High nanoparticle hydrophobicity increases toxic side effects.
What characteristics can be manipulated for PASSIVE targeting pulmonary drug delivery?
(exploiting natural physiology of lung)
Size
Charge
Surface proteins
Active targeting in pulmonary delivery involves sticking targeting moiety to NP surface: antibody/ protein that will interact with particular receptor.
What can be targeted in ACTIVE targeting in pulmonary drug delivery?
Alveolar macrophages
Bronchial epithelial targets
How can alveolar macrophages be actively targeted?
(first line of immune defence)
By targeting mannose receptors
give examples of diseases that use Alveolar macrophages as a target
TB
CF
AIDS
targeting macrophages may not be best for specific delivery why?
Non-specific target (Kupffer cells in liver, peritoneal macrophages), as have macrophages in other sites of body, may be affected too.
Consider ROA
when passively targeting alveolar macrophages, as particles increase in size, how is uptake affected?
increases too
Makes sense: if want to target alveolar macrophages, make bigger particles. Job of alveolar macrophages: recognise and clear up foreign particles). If make higher nm particles, approximatimating size of bacteria, exploiting natural function of alveolar macrophages through making specific size particles and encouraging uptake/ passive targeting
Why are mannose receptors a good target to target alveolar macrophages?
They are exclusive to alveolar macrophages within the lung.
BUT still have some elsewhere: peritoneal, kupffer cells (liver)
If you put drug in gelatin parts, what affect does this have on residence time in plasma regardless of mannose?
(experiment)
increases.
NM via non-inhalational route dont go to lungs, most to liver
What is lactoferrin? and its use
iron binding glycopritein
for Active targeting of epithelial cells (bronchial epithelial…)
lactoferrin has Ubiquitous distribution.
what does this mean?
its everywhere in body
- secreted by epithelial cells into most exocrine fluids e.g. tears, sweat, milk
So have to be careful if using as active targeting
lactoferrin is used for active targeting of bronchial epithelial cells why?
as receptors are overexpressed on apicalside of those cells
lactoferrin has a role in many processes including:
- Antimicrobial, immunomodulatory, antiviral, and anti-metastasis activity
- Bacterial defense within the respiratory tract
What are potential limitations to using lactoferrin to target epithelial cells?
May not be applicable to every disease.
Degradation by proteases, as it is itself a protein
What are the benefits of mucosal administration?
Route of entry for pathogens.
Ease of administration
Local and systemic immunity.
why would you want to initiate immune response at mucosal memb/ site?
Route of entry for pathogens. An interphase between inside and outside world.
give some examples of mucosal vaccines used on the market?
polio
cholera
flu
mucosal immune system composed of what 2 sites?
inductive
effector
What are inductive sites in the mucosal immune system?
where immune responses are initiated
What are effector sites in the mucosal immune system?
where effector cells get involved and mediate the immune response
What are the 3 types of Mucosae-associated lymphoid tissue (MALT)?
Gut
Broncheal
Nasal
GALT, BALT, NALT
how many types of Mucosal immune system (MALT) are there and what are the differences?
2
type I: IgA
typeII: IgG, no M cells
What effector molecule mediates response for Type 1 MALT?
IgA
What effector molecule mediates response for Type 2 MALT?
IgG
name of the cells involved in MALT..
characteristic: interspersed in cell layer of a mucosal membrane.
Really different in function to epithelial cell. Key part of immune system.
Tend to mediate transport of antigens/ pathogens from lumen across mucosal membrane to other immune structures.
Microfold (M) cells
involved in MALT Type II are Specific types of antigen presenting cells e.g. ?
dendritic Langerhans cells
4 characteristics of good ideal vaccine dleivery system?
Protective (of antigen inside)
Targeted delivery
Effective
Safe and (not immunogenic) in itself
what should ideal vaccines protect?
antigen inside and prevent degradation of vaccine
why should ideal vaccines provide targeted delivery?
Increased accumulation at inductive sites (MALT…)- where mucosal immune response kicks off
Avoid entrapment in mucus layer. How to avoid mucoadhesion… from before
how would vaccines be termed effective? if they are able to do what?
Able to stimulate immune response to pathogen
How can adjuvants improve mucosal vaccines efficacy?
Can help reduce the dose and enhance immune response. (by alerting immune response to danger)
common parenteral adjuvants used?
o Aluminium salts
o Emulsions
What is immune stimulating complex (ISCOM)?
particle based vaccine adjuvant
3D, open cage-like structures (30-70 nm)
What is immune stimulating complex (ISCOM)?
particle based vaccine adjuvant
3D, open cage-like structures (30-70 nm)
what is ISCOM a mixture of?
o Phospholipids
o Cholesterol
o Quil A (soap bark tree extract) some detergent activity,– punch holes in membranes - immunoadjuvant
Antigen incorporation into lipid network
can improve mucosal vaccines by targeting M cells in type I.
2 ways to do this
passively or actively
Why would you target M cells in mucosal vaccines?
M cells are where the immune response starts
what parameters are of importance for passive targeting of mucosal vaccines to M cells
size (internalisation, drug loading)
surface chem
-charge
-hydrophobicity
-adhesion to M cells
All things BAD and cause premature clearing of NPs loaded w drug from blood by MPS, are GOOD for targeting vaccines to M cells
what does active targeting of mucosal vacicnes – targeting M cells (in Type I) involve?
attaching moeity to surface
2 examples of active targeting of mucosal vacicnes – targeting M cells (in Type I) involve?
Cholera toxin B
-Adjuvant properties (2 in 1, with active targ)
-Risk of CNS inflammation – in brain. Very careful especially if using for nasal, as clear pathway to brain
UEA (Ulex europaeus agglutinin I)
-Selective binding to M cells in Peyer’s patches
-Clinical relevance?
Why does the innate immune system need to be triggered in mucosal vaccine delivery?
active targeting is not enough and good efficacy is difficult to achieve.
(inborn defense system) fairly general and non specific immunity
Adaptive immune system forms exposure and vaccinations over life.
role/ use of:
- adjuvants
- hydrophobic surface
- DAMPs
- alert immune system to danger
- to trigger IS
- release effector mols and start immune response
What else can be targeted to improve mucosal vaccines?
why?
dendritic cells
- Typical cell type in type II mucosa
- Antigen presenting cells.
Lectin ligand (Active targeting), antibodies, mannose receptors (on macrophages + dendritic)
Impact on:
- Intracellular routing
- Antigen presentation
maybe improving uptake of DDS by antigen presenting cell -> help immune response kick off and start
Mucosal vaccines and formulation: 2 ways to improve?
- Incorporate vaccine into NP to offer protection
- Employ targeting strategy
Describe the ways in which nanoparticles can act with antigens is vaccine delivery? 4
Conjugation
Encapsulation
Adsorption
Mix
What are the challenges for using mucosal vaccines?
Dosing
Frequency
Tolerance (not always bad- allegens)
infection/inflamm
May be induced by prolonged release of low doses (loss of adjuvant effect)…
… but also by burst release of high antigen doses
