Organs on Chips
In an effort to model the complex processes occurring in human bodies, Donald Ingber has pioneered the development of ‘organs-on-chips,’ reproducing the lung and the gut on microfluidic devices. These systems allow researchers to replicate and study organs without the use of human test subjects. While this is one of the best options, there are too many variables to control, understand, and more importantly, manipulate. At the other end of the spectrum is an in vitro study with a cell line and few variables that hardly resemble the real environment. Researchers in Switzerland have developed their own gut-on-a-chip that imitates a human gastrointestinal tract called the Nutrichip. They hope to use this microfluidic device to study the immune-modulatory function of food (with a strong focus on dairy food). This work is detailed in the article “NutriChip: Nutrition Analysis Meets Microfluidics,” which appears in Lab on a Chip.
The Nutrichip is primarily focused on analyzing the presence and kinetics of inflammatory biomarkers after a meal, which should shed insight on how certain foods impact our bodies. For example, milk products not only provide nutrients, but affect our physiological functions via bacteria, proteins and bioactive peptides. In particular these agents may modulate the fabrication of pro-inflammatory cytokines, which the Nutrichip aims to monitor. The Nutrichip mimics the thin layer of epithelial cells of the intestinal tract and the immune system it interacts with. In this system, the epithelial cells transport nutrients into circulation to be metabolized by the body, and the immune system controls responses to any trespassing pathogenic organisms. Not only do epithelial cells try to keep out pathogens, but they must filter what reaches the immune layer in order to maintain immunological tolerance to nutrients.
The device is composed of three distinct parts, an apical layer, a basolateral layer, and a membrane which separates them. The apical layer is populated with a culture of intestinal epithelial cells. In this model, the authors used Caco-2 cells to produce a confluent layer of the intestine. This cell line is derived from a human colorectal adenocarcinoma that demonstrates most of the morphological and functional traits of intestinal cells. The basolateral layer contains a culture of monocytic cell line differentiated into macrophages. A chamber downstream of the monocytes contains magnetic beads functionalized with antibodies against the targeted cytokines. These beads allow in situ capture and washing of the cytokines before fluorescent detection.
Experimental Procedure and Results
The researchers treated the apical layer with tumor necrosis alpha (TNFα) and lipopolysaccharide (LPS), which is found in the membrane of Gram-negative bacteria, for 24 hours. This resulted in a significant secretion of the cytokine Interleukin 6 (IL-6) in the basolateral media. However, the Caco-2 cells protected the macrophages very well, as the LPS concentration applied to the apical layer resulting in a response, was three orders of magnitude greater than that would be applied to the basolateral layer directly to produce the same cytokine response. When the macrophages were treated directly with LPS, there was a significant increase in IL-6 which indicates that they may be able to quantify the IL-6 with their proposed magnetic beads. These two experiments indicate that they can partially mimic the intestinal tract and monitor the effect that certain compounds or nutrients have on the body’s immune system.
Thoughts on Future Work
This is all very preliminary work, and the researchers hope to measure the pro-inflammatory activity of meals, anti-inflammatory activity of dairy products as well the bio-availability of nutrients in digested foods. To make that final component a reality, they also intend to include on-chip digestion capabilities. I am sure there are alternatives to a dynamic digestive tract moving bolus through the system, but I’d love to see it anyway. I think this work could be extremely beneficial in understanding food allergies. We seem to have more food allergies these days that may be due to changes in modern life or may have gone undetected previously (or is perhaps just over diagnosed).
Ramadan, Q., Jafarpoorchekab, H., Huang, C., Silacci, P., Carrara, S., Koklü, G., Ghaye, J., Ramsden, J., Ruffert, C., Vergeres, G., & Gijs, M. (2013). NutriChip: nutrition analysis meets microfluidics Lab on a Chip, 13 (2) DOI: 10.1039/c2lc40845g