August 9, 2023 | The liver carries out a variety of complex roles ranging from secretion and storage to metabolism and detoxification, and researchers across the globe see the potential of using liver-on-a-chip and liver organoid technologies to improve our understanding of this organ and find better ways of diagnosing and treating the diseases and conditions that hinder its normal operation.
Organ-on-a-Chip Studies Explore COVID, NAFLD & Diabetes
Recent research utilizing organ-on-a-chip technology has led to new insights into issues such as the liver processes of COVID-19 patients, non-alcoholic fatty liver disease (NAFLD), and diabetes.
For example, researchers at Kyoto University in Japan have explored the liver processes of COVID-19 patients. Junior Associate Professor Kazuo Takayama and colleagues developed a liver-on-a-chip that included a bile duct (ibd-LoC) and another with a blood vessel (bv-LoC). They then infected these chips with SARS-CoV-2 to learn more about the liver pathology of patients with COVID-19 and better understand the impact of COVID-19 therapeutics.
“Interestingly, despite observing viral clearance after two weeks, increased hepatotoxicity and lipid droplet accumulation continued in the infected bv-LoCs, but not in the infected ibd-LoCs,” a news release explained. The findings suggest that vascularized areas of the liver are more susceptible to damage caused by SARS-CoV-2 infection, which can lead to liver dysfunction.
After exploring the impact of several COVID-19 drugs, the group found that anti-viral and immunosuppressive treatments helped infected bv-LoCs recover hepatic functions. As they noted in their study, published in PNAS Nexus (DOI: 10.1093/pnasnexus/pgad029), this suggests the combination of remdesivir and baricitinib “is effective at treating organ dysfunctions in COVID-19 patients.” However, more research using models of different organs is needed to test this hypothesis.
Takayama indicated that he and colleagues do intend to build upon this research. “To generate a liver model that more faithfully reproduces the living body, it is necessary to develop a liver-on-a-chip that includes immune cells,” he told Diagnostics World, which he and colleagues are now pursuing.
Kyoto University researchers have also developed a two-organ chip to help explore how gut and liver cells interact. The integrated-gut-liver-on-a-chip (iGLC) platform was developed by scientists at the university’s Institute for Integrated Cell-Material Sciences (iCeMS) to arrive at a better understanding of non-alcoholic fatty liver disease (NAFLD) in particular.
“NAFLD affects a significant percentage of the population, but no effective treatments have been established,” iCeMS bioengineer Ken-ichiro Kamei said in a news release. This complex condition involves a wide range of interactions between the gut and liver, and for the time being, transplantation is the only way to treat severe cases. The researchers see a need for improved approaches for studying the condition so that better treatment options can be discovered.
Kamei and colleagues tested their iGLC platform by putting cells from a liver cancer cell line and a gut cancer cell line into separate chambers connected by fluidic channels with valves that can be opened and closed. The platform includes a pump for moving fluid between the chambers while keeping the cells separate, which is intended to resemble the interaction between the gut and liver.
Their findings, published in Communications Biology (DOI: 10.1038/s42003-023-04710-8), revealed changes in gene expression in gut and liver cells cultured in the iGLC platform compared to the same cells cultured on their own. The researchers also noted cell changes when free fatty acids were introduced for either one day or seven days. One day sparked the start of DNA damage, and seven days led to cell death, similar to what occurs in severe cases of NAFLD. The platform could serve as an alternative to animal experiments for exploring the mechanisms underlying NAFLD for the development of new treatments and diagnostic tools. Next steps include plans to use liver and gut organoids to explore NAFLD under conditions that more closely resemble those found in humans.
In another line of research, a group of South Korean scientists have developed a multi-organ on-a-chip that utilizes 3D cell printing technology to replicate the environment of type 2 diabetes. To mimic the features of this disease and its impact, they created bioinks derived from the liver, pancreas, and adipose tissue.
They then used 3D cell printing to develop a chip intended to simulate characteristics of type 2 diabetes and the cellular interactions that take place within the human body. Findings published in Advanced Functional Materials (DOI: 10.1002/adfm.202213649) detail their exploration of the relationship between fatty tissues and type 2 diabetes. The study results also reveal that a retina compartment in the chip led to impaired retina cell function, suggesting the chip could be used to study disease complications in addition to simulating key features of type 2 diabetes.
Organ-on-a-Chip & Organoid Study Digs Deeper into DILI
A study conducted by University of Michigan researchers and published in the Journal of Hepatology (DOI: 10.1016/j.jhep.2023.01.019) used an organ-on-a-chip system and liver organoids to explore drug-induced liver injury (DILI). The researchers pointed out that the platforms explored in their study show promise as predictive models for novel drugs and as a potential diagnostic tool.
Although it may be an infrequent occurrence, the researchers noted that DILI is a crucial cause of acute and chronic liver disease. Many cases of DILI are deemed “idiosyncratic” because they are not tied to drug dose or duration—and because they emerge in just a small proportion of treated patients for reasons that aren’t yet well understood.
Whether intrinsic or idiosyncratic, this condition is difficult to study because existing models are either expensive or not great at modeling human biology, said Charles Zhang, a PhD candidate at the University of Michigan, Ann Arbor, and first author of the study. And idiosyncratic DILI is especially challenging to study because it occurs within such a niche patient population, he told Diagnostics World.
In their research, he and colleagues explored the use of a human liver organoid screening platform focused on DILI risk prediction as well as an organ-on-a-chip system. Zhang said the findings that have emerged from this research have both economic and scientific significance. From a financial perspective, “the current standard use of primary human hepatocytes is very expensive,” he said, and at least in theory, their method could be used to produce hepatocyte-like cells infinitely. From a scientific vantage point, their organoids consist of not only hepatocyte-like cells but also other cell types found in the liver, which makes it possible to model DILI with better physiology than previous approaches.
“There’s more and more evidence showing that for drug-induced liver injury specifically, but also for other diseases, this kind of activity between cell types is very important in properly modeling the disease,” he explained.
Organoid Research Offers Insights into Cancer, NAFLD, and More
Meanwhile, researchers are pursuing a 3D bioprinting approach and harnessing liver organoids to explore issues like liver cancer and NAFLD.
The liver performs a variety of complicated bodily functions, noted researchers at the University of Chinese Academy of Sciences in Beijing, yet “unfortunately, orthotopic liver transplantation (OLT) is still the only effective treatment for end-stage liver disease.” And issues such as donor organ shortages and immune rejection have limited its application. For these reasons and more, 3D liver models that can mimic both the structure and function of liver tissue are in demand.
Still, the complexities of liver tissue make it extremely difficult to build liver models in vitro. In a study published in Cell Proliferation (DOI: 10.1111/cpr.13465), the researchers detail a droplet-based, layer-by-layer 3D bioprinting method for the creation of organoids. They say it offers “meaningful insights” in terms in relation to disease modeling, tissue regeneration, and the pursuit of new drugs.
Elsewhere, researchers in South Korea have developed multilineage liver organoids (mLOs) with vasculature and bile ducts through the combination of hepatic endoderm, endothelial cells, and hepatic stellate cell-like cells (HscLCs) derived from human pluripotent stem cells (hPSCs). Their study, published in Stem Cell Research & Therapy (DOI: 10.1186/s13287-023-03235-5), reveals that HscLCs play a critical role in vessel formation in this type of organoid. The group called their mLOs “a promising tool for the modeling of liver diseases mediated by parenchymal and non-parenchymal interplay.”
In a Q&A published by the Minderoo Foundation, Benjamin Dwyer called the liver “an extraordinary organ,” highlighting its ability to perform roughly 500 different functions. And notably, it is the only human organ capable of regenerating itself.
Dwyer leads the patient-derived organoid platform for the Liver Cancer Collaborative, a group of over 50 multidisciplinary experts in Australia and Asia that is building a biorepository and dataset with clinical and genomics data from diagnosis to late-stage disease. He and colleagues grow organoid models using patient tumors and surrounding liver tissue. They characterize the cells by their genetic makeup, marker expression, and RNA expression. They then match it back to the original tumor to learn how well their models resemble the tissue from which they were derived.
“Doing this allows us to be more confident when we test patient-specific responses to drug treatments,” Dwyer explained. Using the drug screening results, he and colleagues hope to repurpose therapies and come up with new ones that are matched back to patient subtypes.
They are testing 1,600 drugs already approved for patient use, which is expected to provide a benchmark to help test new therapies. They are also carrying out “in-depth image-based phenotypic analysis” of their organoids to create a library of images that other researchers can use to spark additional insights.
A research group from the Netherlands is also exploring liver cancer with the help of organoids, pursuing a deeper understanding of fibrolamellar carcinoma (FLC)—a rare, deadly form of cancer that affects adolescents and young adults. “Molecular understanding of FLC tumorigenesis is limited, partly due to the scarcity of experimental models,” the authors noted in a paper published in Nature Communications (DOI: 10.1038/s41467-023-37951-6). Although earlier work has helped reveal the molecular characteristics of tumor tissues, “mechanistic studies into how FLC mutations affect healthy liver cells and how different genetic backgrounds collectively drive FLC remains unknown.”
To learn more, the group CRISPR-engineered human hepatocyte organoids to determine how the introduction of different FLC genetic backgrounds affected the behavior of human hepatocytes and discovered the appearance of two molecular subgroups—one driven by a PKA-related mutation and another by a BAP1 mutation.
Several of the same researchers from the Netherlands have also conducted research that digs into NAFLD. Despite its prevalence, they point out that effective therapies for this disease are lacking, and recent clinical trial failures have only underscored the complexity involved in battling this condition.
Although efforts are often geared toward addressing more advanced stages of the disease, they see promise in working to identify biomarkers of early NAFLD to help reduce liver damage and disease progression. Findings published in Nature Biotechnology (DOI: 10.1038/s41587-023-01680-4) reveal their use of human fetal hepatocyte organoids to model steatosis—the first stage of NAFLD. They modeled and studied several different triggers: free fatty acid loading (to mimic a Western diet), genetic risk (using variant PNPLA3 I148M), and monogenic lipid disorders (using APOB and MTTP mutations). The researchers screened various candidates, hoping to pinpoint drugs capable of tackling steatosis across these models. They also established a screening platform called FatTracer, a tool designed to identify steatosis modulators and targets. After screening 35 candidates, it found fatty acid desaturase 2 (FADS2) to be a crucial factor in hepatic steatosis, suggesting it could be a potential novel therapeutic target.
The researchers hope to learn more about the genetic risks associated with the development of fatty liver and discover which factors impact disease progression, according to a news release, and the ultimate goal is to use these fatty liver organoid models to define personalized drug treatments capable of curing the liver.
Paul Nicolaus is a freelance writer specializing in science, nature, and health. Learn more at www.nicolauswriting.com.