Exploring ALI Exposures:
From Cell Lines to Endpoints

Air liquid interface (ALI) exposure of lung cells is a biological technique used to study the effects of airborne pollutants on the cells of the human lung. It involves growing cells in an atmosphere of air and liquid, so that the cells are exposed to the same type of environment that they would experience in the lungs of a human being. This type of exposure allows researchers to better understand the effects of different pollutants on lung cells, and to develop new treatments and therapies for diseases such as asthma, chronic obstructive pulmonary disease, and lung cancer. 

Cell Lines vs Primary Cells

With ALI, both cell lines and primary cells can be used. Cell lines are cells that have been grown in a laboratory setting and can be frozen and stored for long periods of time. They are derived from a single cell, and are typically immortalized by a virus or another type of genetic manipulation. Cell lines are often used in research because they are easier to manipulate than primary cells. Primary cells, on the other hand, are isolated directly from a living organism, therefore they are often considered more relevant. However, they cannot be frozen or stored for long periods of time. They are more difficult to work with, but provide more accurate results due to the fact that they are not subject to the same genetic manipulation as cell lines.

ALI Important Endpoints

The typical end points for ALI exposure are the size distribution and concentration of particles, the concentration and size of droplets, and the chemical composition of the aerosol. Other end points may include the physical characteristics of the aerosol such as particle shape, surface tension, and volatility.

Below are a couple examples of common ALI endpoints

• Trans-Epithelial Electrical Resistance (TEER) can be used as a quality control to ensure healthy cultures. It is a measure of the electrical resistance across a monolayer of cells, such as those found in the air-liquid interface (ALI). TEER is used as a measure of cell health and cell-cell interaction at the ALI, and is therefore commonly used as an endpoint for ALI exposure studies.
• Lactate dehydrogenase (LDH) assay: LDH is an important endpoint for ALI cultures because it provides an indication of cell death. LDH is a marker of cell membrane integrity, so increased LDH levels in the culture medium indicate that the cells have been damaged and are releasing their intracellular contents. This assay is useful for monitoring the health of ALI cultures, as it can be used to detect even subtle changes in the cell population that may be indicative of toxicity or other pathological processes. Additionally, the LDH assay can be used to monitor the progress of a treatment over time, as it can detect changes in the cell population that may be due to the treatment.
•  MTT (methylthiazolyldiphenyl-tetrazolium bromide) is an important endpoint for air liquid interface endpoints as it provides a way to measure the metabolic activity of cells in a culture. The MTT assay is based on the ability of living cells to reduce a yellow tetrazolium salt to a purple-colored formazan product which can be easily detected and quantified. This assay is often used to assess the cytotoxic effects of a compound on a cell line or to measure cell viability. It is a rapid, simple, and cost-effective method for measuring cell viability.
• Cilia beating can also be an endpoint and quality control.

The expoCube: efficient, reproducible and translational ALI exposure system

The expoCube allows scientists to precisely expose cells and tissue explants (e.g. Precision-Cut Lung Slices) to airborne particulates in a physiologically relevant ALI environment. The innovative design of the expoCube permits aerosol deposition profiles that are efficient, reproducible, and translational. The expoCube is engineered to create an efficient, uniform, and precise exposure of particulates onto target cells and tissues. Its flow paths were designed and optimized using advanced computational fluid dynamics (CFD) modelling. They allow a uniform deposition of airborne particles on the target cells, regardless of the particle size. The expoCube’s patented use of thermophoresis increases the deposition efficiency of small particles without imparting unnatural electrostatic charges onto the aerosols.

ALI exposure of pulmonary cells is an important factor in understanding the effects of airborne pollutants on lung health. It allows us to understand how pollutants interact with cells at the air-liquid interface, which is the most important site for pollutant-host interaction. Air-liquid interface exposure of pulmonary cells provides an invaluable tool for understanding the mechanisms of pulmonary toxicology, and for developing strategies to protect pulmonary health.