Fake brain

A doughnut created in a lab and made of silk on the outside and collagen gel where the jelly ought to be can mimic the basic function of brain tissue, scientists have found.

Bioengineers produced a kind of rudimentary grey matter and white matter in a dish, along with rat neurons that signalled one another across the doughnut’s centre. When the scientists dropped weights on the material to simulate traumatic injury, the neurons in the three-dimensional brain model emitted chemical and electrical signals similar to those in the brains of injured animals.

It is the first time scientists have been able to so closely imitate brain function in the laboratory, experts said. If researchers can replicate it with human neurons and enhance it to reflect other neurological functions, it could be used for studying how disease, trauma and medical treatments affect the brain —without the expense and ethical challenges of clinical trials on people.

“In terms of mechanical similarity to the brain, it’s a pretty good mimic,” said James J Hickman, a professor of nanoscience technology at the University of Central Florida, who was not involved in the research. “They’ve been able to repeat the highest level of function of neurons. It’s the best model I’ve seen.”

The research, led by David Kaplan, the chairman of the biomedical engineering department at Tufts University, and published in the journal PNAS, is the latest example of biomedical engineering being used to make realistic models of organs such as the heart, lungs and liver.

Most studies of human brain development rely on animals or on slices of brains taken after death; both are useful but have limitations.

Brain models have been mostly two-dimensional or made with neurons grown in a three-dimensional gel, said Rosemarie Hunziker, programme director of tissue engineering and biomaterial at the National Institute of Biomedical Imaging and Bioengineering, which funded Kaplan’s research.

None of those systems replicates the brain’s grey or white matter, or how neurons communicate, Hunziker said.

“Even if you get cells to live in there, they don’t do much,” she said. “It is spectacularly difficult to do this with the brain.”

Kaplan’s team found that a spongy silk material coated with a positively charged polymer could culture rat neurons, a stand-in for grey matter. By itself, though, the silk material did not encourage neurons to produce axons, branches that transmit electrical pulses to other neurons.

The researchers formed the silk material into a doughnut and added collagen gel to the centre. Axons grew from the ring through the gel — the white matter substitute — and sent signals to neurons across the circle.

They got “these neurons talking to each other,” Hunziker said. “No one’s really shown that before.”

Gordana Vunjak-Novakovic, a biomedical engineering professor at Columbia who has collaborated with Kaplan on other studies, described the model as a kind of “Lego approach”, a “modular structure” that can be expanded and made more complex.

“This is not normal tissue, but it is the first proof of a principle that something like this can be achieved outside ofthe body,” she said.

Hickman said future experiments would need to study human brain tissue, including other cells and regions in the brain.

“There are some limitations, but they seem to have gotten the mechanics right,” he said. “They’ve set up an architecture so some clever person in the future could then do it.”

Kaplan said his team was working on sustaining the brainlike tissue for six months — and with human neurons created from stem cells by other scientists. He plans to add a model of the brain’s vascular system, so researchers can study what happens when drugs cross the blood-brain barrier.

Ultimately, he hopes the bioengineered model can be used “to study everything from drugs to disease to surgical effects to electrode implants”, he said. “I mean, the list is endless.”

Molecular Event Mapping Opens Door to More Tests “In Silico”

Scientists report a new method for establishing whether chemical compounds are safe for human use without "in vivo" testing, based on so-called "molecular initiating events" at the boundary between chemistry and biology.

A new approach to mapping and predicting the impact of chemical compounds in the body, which it is hoped could eventually reduce the need for toxicity tests in animals, has been trialled by scientists.

Although still at an early stage, the process involves identifying “molecular initiating events” (MIEs) - the term given to the moment at which a molecule that has entered the body starts to interact with it, kick-starting a sequence of events which leads to a toxic outcome.

By identifying the specific features and properties within individual molecules that cause these events, the researchers argue that it should be possible to make accurate predictions about the effects of new and untested chemical compounds with similar characteristics.

In principle, that would reduce the need to test some chemicals contained within drugs, pesticides, food additives or other consumer products on animals. Instead, scientists would be able to screen a chemical’s molecular structure using customised computer software - a transition they characterize as one from testing “in vivo” (within the living) to “in silico” (on computers).

To prove the point, the new research, reported in the journal Chemical Research in Toxicology, mapped the pathways by which several well-known compounds, such as paracetamol, cause toxic outcomes. By tracing these back to the molecular initiating event, the team were able to identify chemical characteristics, that were present in other molecules exhibiting the same toxicities.

Tim Allen, a PhD researcher in chemistry at St John’s College, University of Cambridge, and the paper’s first author, said: “We are at the very early stages of building predictive tools for different molecules, and this work provides a proof-of-concept foundation for doing much more.”

“At the moment, there is sometimes no alternative to testing some new chemicals on animals to establish whether or not they are going to be safe for human use. Computer modelling is now finally starting to catch up. Eventually, if we can map the adverse outcome pathways of numerous molecules in the way that we have here, we will be able to develop models which mean you don’t have to administer products in vivo and then look for a reaction to establish whether or not they are safe.”

Ultimately, the researchers hope to develop a complete “MIE Atlas”, capturing data about a large number of molecules and their interactions with the body. Existing scientific knowledge of molecular initiating events is patchy and far from complete.

An initiating event can take on a number of forms. For example, a molecule from an ingested drug may bind to a certain protein within an organ, leading to a series of adverse effects. Equally, it may inhibit the production of a specific enzyme that the body would normally produce.

What each event has in common is that a link is established between a certain characteristic feature of the molecule in question - such as its size, shape, or acidity level - and a feature of human biology. “In many ways it represents the boundary between chemistry and biology,” Allen said. “If we can understand the chemistry of existing molecules and how they interact with the body, then we will be able to make predictions about new products and their likely toxicity based on similar characteristics.”

To test the theory, the Cambridge research team examined the pathway by which acetaminophen - better known as paracetamol - causes acute liver failure as a result of an overdose. From a survey of existing scientific literature on this subject, they were able to extrapolate the initiating event, its molecular basis, and accurately identify the likely toxicity of other molecules with a similar characteristic.

The molecular initiating event which leads to paracetamol becoming toxic is an oxidation process which happens when it enters the liver. This produces a toxic molecule called NAPQI, which is normally detoxified relatively quickly. When a person overdoses, however, too much NAPQI is produced, and this reduces the body’s normal defences and can ultimately result in liver failure.

The study identified that the key to this oxidation process is a feature of a paracetamol molecule’s structure known as the “para-aminophenol” fragment, a feature at the centre of the molecule without which this toxicity would not be observed.

Having established this, the researchers looked for similar structures in other substances, to see if they resulted in the same toxicity. The hypothesis proved to be correct in two cases - the compound Phenacetin, a now disused pain relief drug, and Amodiaquine, an anti-malarial agent. Both compounds had the same fragment within their structure, and because of this, both had the same toxic implications for the body when taken in certain quantities.

The research paper also speculates that better knowledge of Molecular Initiating Events could enable scientists to predict not only adverse, but also positive, outcomes which may emanate from the uptake of certain chemical compounds into the human body. The aim of the work, however, is firmly based in toxicology – to build on current in silico approaches, and increase understanding of what goes on during a toxic response.

“The approach seems strong and well-rooted in theory, and the aim of this paper is really to gain more feedback on the merits of widening out this type of research,” Allen said. “What we have done so far represents a tiny fraction of toxicological and chemical space. Further work will allow our approach to become a much more widely-used and valuable tool for toxicologists.”

Article adapted from a University of Cambridge news release. The original article is licensed under a Creative Commons Licence.

Publication: Defining Molecular Initiating Events in the Adverse Outcome Pathway Framework for Risk Assessment. Timothy E. H. Allen, Jonathan M. Goodman, Steve Gutsell, and Paul J. Russell. Chemical Research in Toxicology (2014): Click here to view.