Reverse transcription polymerase chain reaction (RT-PCR) analysis of proteolytic enzymes in cultures of human respiratory epithelial cells

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

ACE2 and COVID-19: using antihypertensive medications and pharmacogenetic considerations

COVID-19 utilizes the ACE2 pathway as a means of infection. Early data on COVID-19 suggest heterogeneity in the severity of symptoms during transmission and infection ranging from no symptoms to death. The source of this heterogeneity is likely multifaceted and may have a genetic component. Demographic and clinical comorbidities associated with the severity of infection suggest that possible variants known to influence the renin–angiotensin–aldosterone (RAAS) system pathway (particularly those that influence ACE2) may contribute to the heterogenous infection response. ACE2 and Ang(1–7) (the product of ACE2) seem to have a protective effect on the pulmonary and cardiac systems. Hypertension medication modulation, may alter ACE2 and Ang(1–7), particularly in variants that have been shown to influence RAAS system function, which could be clinically useful in patients with COVID-19.

Development of new in vitro models of lung protease activity for investigating stability of inhaled biological therapies and drug delivery systems

Proteases play a vital role in lung health and are critically important to the metabolic clearance of inhaled protein-based therapeutics after inhalation. Surprisingly little is known about lung fluid protease composition and there is a consequent lack of biorelevant experimental models, which limits research and development in the burgeoning field of inhaled biologics. The aim of this study was to quantify proteases in human lung fluid and to use this data to design novel in vitro experimental models of lung lining fluid possessing biorelevant lung protease activity for use in biopharmaceutical stability studies. As a proof of concept, these novel models were used to investigate the effect of proteolytic activity on the stability of albumin nanoparticles, a biologic nanoparticle formulation widely investigated as a pulmonary drug delivery system. Bronchoalveolar lavage fluid was collected from healthy human volunteers and proteomic analysis was used to quantify the predominant proteases. Based on these data, four new lung protease models were constructed based on: (i) trypsin as a sole protease, (ii) dipeptidyl peptidase IV, cathepsin D, cathepsin H, and angiotensin converting enzyme in ratio and concentration to mimic the protease concentration in healthy lungs. Neutrophil elastase was used to model protease activity in inflammation. Albumin nanoparticles of 100 nm diameter remained intact over 48 h in phosphate buffered saline, but were degraded more rapidly in trypsin (50% reduction in 10 min) compared to the healthy lung protease model (50% reduction in 150 min). The addition of neutrophil elastase to the healthy lung protease model resulted in a similar, but more variable degradation profile. Nanoparticle degradation was associated with concomitant appearance of small fragments and aggregates. In conclusion, we have characterised the protease concentration in the lungs of healthy humans, designed models of lung protease activity and demonstrated their utility in studying albumin nanoparticle degradation. These methods and models have wide application to study the influence of proteases in lung disease, expression of proteases in respiratory cell culture models, stability of peptide and protein-based drugs and inhaled drug delivery systems.

Oligopeptide Transport in Rat Lung Alveolar Epithelial Cells is Mediated by Pept2

PURPOSE

Studies were conducted in primary cultured rat alveolar epithelial cell monolayers to characterize peptide transporter expression and function.

METHODS

Freshly isolated rat lung alveolar epithelial cells were purified and cultured on permeable support with and without keratinocyte growth factor (KGF). Messenger RNA and protein expression of Pept1 and Pept2 in alveolar epithelial type I- and type II-like cell monolayers (±KGF, resp.) were examined by RT-PCR and Western blotting. ³H-Glycyl-sarcosine (³H-gly-sar) transmonolayer flux and intracellular accumulation were evaluated in both cell types.

RESULTS

RT-PCR showed expression of Pept2, but not Pept1, mRNA in both cell types. Western blot analysis revealed presence of Pept2 protein in type II-like cells, and less in type I-like cells. Bi-directional transmonolayer ³H-gly-sar flux lacked asymmetry in transport in both types of cells. Uptake of ³H-gly-sar from apical fluid of type II-like cells was 7-fold greater than that from basolateral fluid, while no significant differences were observed from apical vs. basolateral fluid of type I-like cells.

CONCLUSIONS

This study confirms the absence of Pept1 from rat lung alveolar epithelium in vitro. Functional Pept2 expression in type II-like cell monolayers suggests its involvement in oligopeptide lung disposition, and offers rationale for therapeutic development of di/tripeptides, peptidomimetics employing pulmonary drug delivery.

The expression of proline-specific enzymes in the human lung

The pathophysiology of lung diseases is very complex and proteolytic enzymes may play a role or could be used as biomarkers. In this review, the literature was searched to make an overview of what is known on the expression of the proline-specific peptidases dipeptidyl peptidase (DPP) 4, 8, 9, prolyl oligopeptidase (PREP) and fibroblast activation protein α (FAP) in the healthy and diseased lung. Search terms included asthma, chronic obstructive pulmonary disease (COPD), lung cancer, fibrosis, ischemia reperfusion injury and pneumonia. Knowledge on the loss or gain of protein expression and activity during disease might tie these enzymes to certain cell types, substrates or interaction partners that are involved in the pathophysiology of the disease, ultimately leading to the elucidation of their functional roles and a potential therapeutic target. Most data could be found on DPP4, while the other enzymes are less explored. Published data however often appear to be conflicting, the applied methods divers and the specificity of the assays used questionable. In conclusion, information on the expression of the proline-specific peptidases in the healthy and diseased lung is lacking, begging for further well-designed research.

Generation of tailored aerosols for inhalative drug delivery employing recent vibrating-mesh nebulizer systems

Direct drug delivery to the lungs is considered the gold standard for the treatment of a variety of respiratory diseases, owing to the increased therapeutic selectivity of the inhalative approach. Airborne formulations with defined size characteristics are required to improve the deposition pattern within the airways. In this respect, different nebulizer systems have been conceived, which has enabled the generation of respirable medicament mists. Here, vibrating-mesh technology revealed significant potential to overcome the main shortcomings associated with ‘traditional’ devices. Tailored orifice dimensions and defined formulation characteristics are of special interest for the generation of suitable aerosol droplets for inhalative purposes. Ongoing developments in device and formulation design will optimize the clinical outcome of inhalative drug delivery under application of vibrating-mesh technology.

DPP4 inhibitors increase differentially the expression of surfactant proteins in Fischer 344 rats

AIM

Intact surface active agent (surfactant) composed of surfactant-associated proteins (SPs) and lipids is necessary for respiration and prevents alveoli from collapsing. CD26, a transmembrane glycoprotein exerting dipeptidyl peptidase activity (DPP4), highly expressed in lung parenchyma, is involved in inflammatory processes. A pharmacological inhibition of DPP4 influenced not only the inflammation but also elevated the SPs. Thus, DPP4 inhibitors may be a novel drug for treatment of diseases with surfactant deficiency. Therefore, we tested firstly the hypothesis that DPP4 inhibitors increase the expression of SPs in healthy rats.

METHODS

SP mRNA and protein expression were determined different times after nebulization of aerosolized DPP4 inhibitors [L-isoleucine-thiazolidide (L-Ile-Thia), L-valine-pyrrolidide (L-Val-Pyrr)], budesonide, saline or stereoisomers.

RESULTS

Compared with negative controls (1) L-Ile-Thia as well as budesonide led to a significant higher and L-Val-Pyrr had the tendency to a significant higher expression of SP-A mRNA 6 h after nebulization, (2) the expression of SP-D mRNA increased significantly 6 h after nebulization with L-Ile-Thia and 3 and 6 h after nebulization with Val-pyrr, (3) SP-B mRNA levels showed significantly higher values 3 and 6 h after nebulization with L-Val-Pyrr, (4) protein levels of SP-A, SP-B and SP-C were elevated significantly 6 h after nebulization with L-Val-Pyrr as well as with budesonide, and (5) phospholipids were also increased in response to DPP4 inhibition; the minimal surface tension was comparable.

CONCLUSION

DPP4 inhibition influence differently the expression of surfactant proteins in healthy rats and may be suitable to elevate surfactant synthesis in different diseases accompanied with surfactant deficiencies.

Delivery strategies for sustained drug release in the lungs

Drug delivery to the lungs by inhalation offers a targeted drug therapy for respiratory diseases. However, the therapeutic efficacy of inhaled drugs is limited by their rapid clearance in the lungs. Carriers providing sustained drug release in the lungs can improve therapeutic outcomes of inhaled medicines because they can retain the drug load within the lungs and progressively release the drug locally at therapeutic levels. This review presents the different formulation strategies developed to control drug release in the lungs including microparticles and the wide array of nanomedicines. Large and porous microparticles offer excellent aerodynamic properties. Their large geometric size reduces their uptake by alveolar macrophages, making them a suitable carrier for sustained drug release in the lungs. Similarly, nanocarriers present significant potential for prolonged drug release in the lungs because they largely escape uptake by lung-surface macrophages and can remain in the pulmonary tissue for weeks. They can be embedded in large and porous microparticles in order to facilitate their delivery to the lungs. Conjugation of drugs to polymers as polyethylene glycol can be particularly beneficial to sustain the release of proteins in the lungs as it allows high protein loading. Drug conjugates can be readily delivered to respiratory airways by any current nebulizer device. Nonetheless, liposomes represent the formulation most advanced in clinical development. Liposomes can be prepared with lipids endogenous to the lungs and are particularly safe. Their composition can be adjusted to modulate drug release and they can encapsulate both hydrophilic and lipophilic compounds with high drug loading.

Human GGT2 does not autocleave into a functional enzyme: A cautionary tale for interpretation of microarray data on redox signaling

AIMS

Human γ-glutamyltranspeptidase 1 (hGGT1) is a cell-surface enzyme that is a regulator of redox adaptation and drug resistance due to its glutathionase activity. The human GGT2 gene encodes a protein that is 94% identical to the amino-acid sequence of hGGT1. Transcriptional profiling analyses in a series of recent publications have implicated the hGGT2 enzyme as a modulator of disease processes. However, hGGT2 has never been shown to encode a protein with enzymatic activity. The aim of this study was to express the protein encoded by hGGT2 and each of its known variants and to assess their stability, cellular localization, and enzymatic activity.

RESULTS

We discovered that the proteins encoded by hGGT2 and its variants are inactive propeptides. We show that hGGT2 cDNAs are transcribed with a similar efficiency to hGGT1, and the expressed propeptides are N-glycosylated. However, they do not autocleave into heterodimers, fail to localize to the plasma membrane, and do not metabolize γ-glutamyl substrates. Substituting the coding sequence of hGGT1 to conform to alterations in a CX3C motif encoded by hGGT2 mRNAs disrupted autocleavage of the hGGT1 propeptide into a heterodimer, resulting in loss of plasma membrane localization and catalytic activity.

INNOVATION AND CONCLUSIONS

This is the first study to evaluate hGGT2 protein. The data show that hGGT2 does not encode a functional enzyme. Microarray data which have reported induction of hGGT2 mRNA should not be interpreted as induction of a protein that has a role in the metabolism of extracellular glutathione and in maintaining the redox status of the cell.

New cardiovascular and pulmonary therapeutic strategies based on the Angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor axis

Angiotensin (Ang)-(1–7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). The discovery of the angiotensin-converting enzyme homologue ACE2 revealed important metabolic pathways involved in the Ang-(1–7) synthesis. This enzyme can form Ang-(1–7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1–9) with subsequent Ang-(1–7) formation. Additionally, it is well established that the G protein-coupled receptor Mas is a functional ligand site for Ang-(1–7). The axis formed by ACE2/Ang-(1–7)/Mas represents an endogenous counter regulatory pathway within the RAS whose actions are opposite to the vasoconstrictor/proliferative arm of the RAS constituted by ACE/Ang II/AT₁ receptor. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1–7)/Mas arm in the cardiovascular and pulmonary system. Also, we will highlight the initiatives to develop potential therapeutic strategies based on this axis.

Comparison of the activity levels and localization of dipeptidyl peptidase IV in normal and tumor human lung cells

Dipeptidyl peptidase IV (DPPIV) was studied in three human lung cells - P (fetal lung-derived cells), A549 (lung adenocarcinoma) and SK-MES-1 (squamous cell carcinoma) using a fluorescent cytochemical procedure developed on the basis of the substrate 4-(glycyl-L-prolyl hydrazido)-N-hexyl-1,8-naphthalimide. The observed differences in the enzyme expression were confirmed by measuring the enzyme hydrolysis of glycyl-L-prolyl-para-nitroanilide. The surface and total dipeptidyl peptidase activities of P cells were correspondingly 7-8 and 3-10 times higher than those of SK-MES-1 and A549 cells. The ratio surface per total activity showed that in P (95%) and A549 (93%) cells the enzyme is associated with the plasmalemma while in SK-MES-1 cells (35%) it is bound to intracellular membranes. In order to compare the results from cell cultures with those in human tumor, the enzyme activity was investigated in cryo-sections of three cases of diagnosed squamous lung carcinoma. DPPIV activity was restricted to the connective tissue stroma surrounding the DPPIV-negative tumor foci.

Evaluation of HPβCD-PEG microparticles for salmon calcitonin administration via pulmonary delivery

For therapeutic peptides, the lung represents an attractive, noninvasive route into the bloodstream. To achieve optimal bioavailability and control their fast rate of absorption, peptides can be protected by coprocessing with polymers such as polyethylene glycol (PEG). Here, we formulated and characterized salmon calcitonin (sCT)-loaded microparticles using linear or branched PEG (L-PEG or B-PEG) and hydroxypropyl-beta-cyclodextrin (HPβCD) for pulmonary administration. Mixtures of sCT, L-PEG or B-PEG and HPβCD were co-spray dried. Based on the particle properties, the best PEG:HPβCD ratio was 1:1 w:w for both PEGs. In the sCT-loaded particles, the L-PEG was more crystalline than B-PEG. Thus, L-PEG-based particles had lower surface free energy and better aerodynamic behavior than B-PEG-based particles. However, B-PEG-based particles provided better protection against chemical degradation of sCT. A decrease in sCT permeability, measured across Calu-3 bronchial epithelial monolayers, occurred when the PEG and HPβCD concentrations were both 1.6 wt %. This was attributed to an increase in buffer viscosity, caused by the two excipients. sCT pharmacokinetic profiles in Wistar rats were evaluated using a 2-compartment model after iv injection or lung insufflation. The maximal sCT plasma concentration was reached within 3 min following nebulization of sCT solution. L-PEG and B-PEG-based microparticles were able to increase T(max) to 20 ± 1 min and 18 ± 8 min, respectively. Furthermore, sCT absolute bioavailability after L-PEG-based microparticle aerosolization at 100 μg/kg was 2.3 times greater than for the nebulized sCT solution.