Using Human Stem Cells to Predict the Efficacy of Alzheimer’s Drugs

Scientists who work in the pharmaceutical industry have seen this time and time again: A candidate drug that works brilliantly in laboratory animals fails to work in human trials. So what’s up with this?

Now a research consortium from the University of Bonn and the biomedical company Life & Brain GmbH has shown that animal models of Alzheimer’s disease fail to recapitulate the results observed with cultured human nerve cells made from stem cells. Thus, they conclude that candidate Alzheimer’s disease drugs should be tested in human nerve cells rather than laboratory animals.

In the brains of patients with Alzheimer’s disease beta-amyloid protein deposits form that are deleterious to nerve cells. Scientists who work for drug companies are trying to find compounds that prevent the formation of these deposits. In laboratory mice that have a form of Alzheimer’s disease, over-the-counter drugs called NSAIDs (non-steroidal anti-inflammatory drugs), which include such population agents as aspirin, Tylenol, Advil, Nuprin and so on prevent the formation of beta-amyloid deposits. However in clinical trials, the NSAIDs royally flopped (see Jaturapatporn DIsaac MGMcCleery JTabet N. Cochrane Database Syst Rev. 2012 Feb 15;2:CD006378).

Professor Oliver Brüstle, the director of the Institute for Reconstructive Neurobiology at the University of Bonn and Chief Executive Officer of Life and Brain GmbH, said, “The reasons for these negative results have remained unclear for a long time.”

Jerome Mertens, a former member of Professor Brüstle’s research, and the lead author on this work, said, “Remarkably, these compounds were never tested directly on the actual target cells – the human neuron.”

The reason for this disparity is not difficult to understand because purified human neurons were very difficult to acquire. However, advances in stem cell biology have largely solved this problem, since patient-specific induced pluripotent stem cells can be grow in large numbers and differentiated into neurons in large numbers.

Using this technology, Brüstle and his collaborators from the University of Leuven in Belgium have made nerve cells from human patients. These cells were then used to test the ability of NSAIDs to prevent the formation of beta-amyloid deposits.

According to Philipp Koch, who led this study, “To predict the efficacy of Alzheimer drugs, such tests have to be performed directly on the affected human nerve cells.”

Nerve cells made from human induced pluripotent stem cells were completely resistant to NSAIDs. These drugs showed no ability to alter the biochemical mechanisms in these cells that eventually lead to the production of beta-amyloid.

Why then did they work in laboratory animals? Koch and his colleagues think that biochemical differences between laboratory mice and human cells allow the drugs to work in one but not in the other. In Koch’s words, “The results are simply not transferable.”

In the future, scientists hope to screen potential Alzheimer’s disease drugs with human cells made from the patient’s own cells.

“The development of a single drug takes an average of ten years,” said Brüstle. “By using patient-specific nerve cells as a test system, investments by pharmaceutical companies and the tedious search for urgently needed Alzheimer’s medications could be greatly streamlined.”

Induced Pluripotent Stem Cells Lead Neuroscientists to the Cause of Neuron Loss in Parkinson’s Disease

Salk Institute scientists have made induced pluripotent stem cells (iPSCs) from patients with early-onset Parkinson’s disease (PD) in order to study precisely what goes wrong in the brains of PD patients. Their findings may lead to new ways to diagnose and even treat PD.

At the Salk Institute for Biological Studies in La Jolla, CA, Juan Carlos Izpisua Belmonte and his colleagues have examined the effects of mutations in a gene that encodes the leucine-rich repeat kinase 2 (LRRK2) protein on cultured neurons. LRRK2 mutations are responsible for approximately 2% of all inherited and sporadic cases of PD in North American Caucasian populations and up to 20% of all PD cases in Ashkenazi Jewish patients and approximately 40% of all PD cases in patients of North African Berber Arab ancestry. Therefore, the LRRK2 gene product plays a central role in PD pathology.

When iPSCs derived from PD patients who carry LRRK2 mutations, they were differentiated into neurons that were cultured in the laboratory. Cultured neurons from PD patients show profound disruption of the nuclear membrane and this undoes all nuclear architecture, which leads to cell death.

According to Dr. Izpisua Belmonte, “This discovery helps explain how PD, which had traditionally been associated with loss of neurons that produce dopamine and subsequent motor impairment, could lead to locomotor dysfunction and other common non-motor manifestations, such as depression and anxiety. Similarly, current clinical trials explore the possibility of neural stem cell transplantations to compensate for dopamine deficits. Our work provides the platform for similar trials by using patient-specific corrected cells. It identifies degeneration of the nucleus as a previously unknown player in PD.”

Izpisua Belmonte and his colleagues were also able to confirm that these disruptions of the nuclear membrane also occur in brain tissue from deceased PD patients. While it is still unclear if these disruptions to the nuclear membrane are the result of PD or are a cause of PD, Izpisua Belmonte’s lab used gene replacement techniques that were initially developed and perfected in work with mouse ESCs to fix the mutation in the PD patient-derived iPSCs. When they fixed the mutation, the disruptions to the nuclear membrane failed to form. Belmonte thinks that this could open the door for drug treatments of PD patients, although he did speculate as to how a pharmacological agent might mitigate abnormal nuclear architecture.

These results underscore the power of using iPSCs to model genetic diseases. As Belmonte noted, “We can model disease using these cells in ways that are not possible using traditional research methods, such as established cell lines, primary cultures and animal models.”

Another finding that nicely comports with data from clinical observations of PD patients is the tendency for patients to become progressively worse as they age. Likewise, in their cultured neurons differentiated from that were iPSCs derived from PD patients, Belmonte and his group observed progressively greater deformities in the nuclear membranes of the cells as they aged.

“This means that, over time, the LRRK2 mutation affects the nucleus of neural stem cells, hampering [sic] both their survival and their ability to produce neurons. It is the first time to our knowledge that human neural stem cells have been shown to be affected during Parkinson’s pathology due to aberrant LRRK2. Before development of these reprogramming technologies, studies on human neural stem cells were elusive because they needed to be isolated directly from the brain,” said Belmonte.

Belmonte further opined that dysfunctional neural stem cell populations that are afflicted with LRRK2 mutations might also contribute to other health issues associated with this particular form of PD, which includes depression, anxiety, and the inability to smell.

Modeling diseases with iPSCs also has an added bonus, since this model system can effectively recapitulate the effects of aging. Since unique dysfunctions result from aging, there are very few ways to model such events. However, using cultured cells made from iPSCs can bypass this problem, since the age-related pathologies will typically show up in culture.