Regenerating Airway Epithelium

J. Thomas Pierce MBBS PhDInternational University of Health Sciences

Airway epithelium is in the line of fire…

• Continuously exposed to microorganisms, dust, tobacco smoke, among hundreds of entries;

• Natural regeneration depends upon cell migration, proliferation and differentiation;

• (Histology) Microcirculation determines degree of fibrin-fibronectin (Fn-Fbn) covering;

Suggested Regenerative Components

• Regenerative components includes cytoskeleton proteins, integrins receptors, matrix metalloproteinases (MMPs), cytokines (IL-series) and growth factors (Puchelle et al. 2006).

• Pro-inflammatory cytokines of interest include• (IL-8) and MMPs (-9 and -7 in particular) - barometers of

dysregulation and remodeling of airway mucosa;

• Airway epithelium literature is vast - solutions will likely span molecular scaffolds, adapted stem cells, small molecules and newer biologic therapies.

Glutathione Synthesis, Distribution & Homeostasis Critical to Regeneration

• Glutathione is the body’s major antioxidant and detoxifier, reducing both upper airway and lung inflammation (Ziem 2013);

• Synthetic derivatives such as L-γ-glutamyl-2-methyl-L-cysteinyl-glycine disulfide preferred in terms of inhibiting glutathione reductase activity (Kedrowski and Gutow 2013).

They all smell bad…

• Glutathione can be used to form a molecular hydrogel based on glutathione (GSH) reduction (Lv et al. 2013);

• Another possibility is that of a nanoparticle delivery vehicle for S-nitroso-N-acetyl cysteine (Nacharaju et al. 2012).;

• We don’t know whether glutathione or N-acetyl cysteine or might be best suited;

Biomarker possibilities…

• Underlying airway dysfunction somewhat mirrored by disturbances in transcription of nuclear factor (erythroid-derived 2)-like 2 (Nrf2);

• Disturbances result in both Nrf2 mRNA and protein

increasing with increased thiol oxidation, yet the Nrf2 is dysfunctional (Fitzgerald et al. 2012);

• Noted primarily in children c severe asthma (Fitzgerald 2011, 2012).

No heuristic ever tells you all you need to know, but…

• We like the MLP (multiple lipophilicity potential) because…

• It relates to individual features of candidate molecules (‘drug seeds’) as opposed to;

• A single logP value the provides a sort of grand average, neglecting individual contributions.

MLP

• • MLPk = Σfi fct (dik)• Sum over i = 1 to N• • MLP = Multiple lipophilicity potential• k = label for a point on the molecular surface• i = fragment label• N = total no. of fragments• fi = lipophilicity constant for fragment• fct = distance function• d ik = distance between fragment i and space point f

Thinking about several things at once – they are all important…

----------------Lipophilicity-----------

log P < 0 log P > 0

<-------------Hydrophobicity------------

-Philic -Phobic

<------------------------Polarity------------------------------ -

Polar Non polar

• Recent work by Vallianatou et al. (2015) suggest an adaptation of ADME-T in favor of what they term "drug-likeness;"

• They posit that special attention should be paid to lipophilicity and molecular weight;

• NB: Excessive lipophilicity itself can be associated with undesired effects.

NAC has a History of Poor Acceptance – Odor and Taste Issues

• Cysteine levels can be WNL when glutathione concentrations ar, in fact, low (Ziem 2014), suggesting local effects and differences;

• Oral availability of glutathione (tripeptide) is low, perhaps suggesting nebulizer use;

• Bishop et al. (2005) pioneered use of inhaled buffered reduced glutathione for cystic fibrosis patients.

Which one is it...?

• Clinical practice in treating airway irritation sometimes uses a cocktail approach inclusive of a reduced sulfur entity plus methyl cobalamine (B12) and tocopherol (Vitamin E);

• In its role as an anti-oxidant, glutathione must be protected from its own photo- or heat-based oxidation;

• For neurologic diseases glutathione (and analogues) have been injected and given intravenously.;

Continuous, lifelong irritation – Prophylaxis or Curative Rx?

• In an older paper, Duan et al. (1996) considered regional differences in the ability to supply glutathione;

• How would a drug candidate address the continuous, progressive nature of injury and even changes initiated before a therapeutic regimen commences (Ganesan and Sajjan 2013).