Neuroprotection by Novel T Cell Enzyme Inhibitor

Research Summary: Granzyme B-inhibitor serpina3n induces neuroprotection in vitro and in vivo

The background

Previous studies have shown that immune cells, known as cytotoxic T cells, are critical in the development of multiple sclerosis (MS).  Although these cells are generally kept out of the brain, they are able to cross the blood-brain barrier in people with MS.  These T cells are found in large numbers around lesions and are thought to be responsible for the characteristic death of nerve cells observed in MS.  For this reason, most currently available therapies for MS are based on causing broad suppression of the immune system.  However, this approach can lead to significant side effects, which highlights the need for an alternative method that leaves the immune system more intact.

An enzyme, known as Granzyme B, has been shown to be released by cytotoxic T cells and cause neuronal death.  An inhibitor for this enzyme, called serpina3n, has been shown to have beneficial effects in models of other conditions, including diabetes and cardiac disease.  Therefore, it presents an attractive target for a novel therapy in MS.

The study

Researchers from the University of Alberta tested the ability to serpina3n to inhibit Granzyme B and act as a treatment for MS.  To achieve this, they used two different systems.  Firstly, they performed in vitro experiments using neuronal cell cultures.  These cells were incubated either with unactivated T cells, activated T cells or activated T cells and the inhibitor.  After incubation, the level of cell death was measured.

Secondly, the study tested the effects of the inhibitor in the EAE mouse model of MS.  The disease was induced in the mice and they then received serpina3n after either 7 days (when inflammation begins in the CNS), at the onset of disease or both.  The effect was measured by assessing disease severity and the amount of neuronal injury present.

The findings

For the cell experiments, incubating nerve cells with activated T cells led to the death of around 70% of the cells.  It was shown that inhibiting Granzyme B with serpina3n could decrease the amount of neuronal death caused by T cells to approximately 40%.

The results of the cell experiments were further confirmed by the in vivo experiments in the mouse model.  Treating the mice with serpina3n at day 7 led to both a delay in the onset of EAE and a decrease in the disease severity, when compared to mice that didn’t receive the inhibitor.  Similar results in the decrease in severity were observed if the mice received treatment at the onset of disease.  These benefits were short-lived, however, multiple doses of the inhibitor appeared to extend the length of time that improvements were observed.  The researchers then showed that while the amount of T cells present in the CNS did not change with serpina3n treatment, the amount of axonal injury was decreased.  It is likely that the reduction in disease severity observed was a result of this.

The outcomes

This study has provided evidence that serpina3n can inhibit Granzyme B, which leads to a neuroprotective effect in both in vitro and in vivo models of MS.  This suggests that inhibition of this enzyme may be a new treatment option for MS, with the added benefit of maintaining appropriate immune surveillance.  It is thought that this approach will help slow the progression of the disease.

As the lead researcher on the study, Dr Fabrizio Giuliani suggests, “In our models, we haven’t seen that the disease disappears.  The disease is still there, the inflammation is still there, but there’s not as much damage in the nerve cells that would induce a permanent disability”.

Learn More

The abstract for this article can be viewed here.