Control of pathological immunity in multiple sclerosis may be accomplished (at least in part) by antigen-specific vaccination, by administration of immune modulators such as Interferon Beta, or by depletion of activated effector T cells using antibodies. 

Immune modulation by hormones offers a new method of addressing multiple sclerosis.  For example, it is known that mesenchymal stem cells have therapeutic effects in animal models of multiple sclerosis, and that these effects seem to be mediated both by immune modulaton but also by stimulation of regeneration.  Interestingly, hormones such as progesterone have been demonstrated to stimulate immune modulatory activities of mesenchymal stem cells.

A recent paper (Theil et al. Suppression of Experimental Autoimmune Encephalomyelitis by Ghrelin. J Immunol 2009 Jul 20) described the ability of the “hunger hormone” ghrelin to inhibit the mouse model of multiple sclerosis, experimental allergic encephalomyelitis (EAE).

Ghrelin is a hormone made by the pancreas and stomach cells that stimulates the feeling of hunger.  It is also known to stimulate growth hormone release.  Some have compared ghrelin as the opposite of leptin, a hormone known to inhibit hunger.  Interestingly leptin has been associated with induction of inflammation of autoimmunity.  For example, administration of leptin has been demonstrated to augment mouse multiple sclerosis (Matarese et al. Leptin potentiates experimental autoimmune encephalomyelitis in SJL female mice and confers susceptibility to males. Eur J Immunol. 2001 May;31(5):1324-32).

In the paper we are discussing, EAE was induced in B6 mice by administration of MOG peptide (myelin oligodendrocyte glycoprotein 35-55) and treated groups were administered ghrelin after immunization with the autoantigen.  As compared to vehicle-controls, the treated groups had a profound inhibition of EAE induction as assessed by the disease severity index.  Additionally, suppression of the inflammatory triad of TNF, IL-1, and IL-6 was observed at the mRNA level in cells that have infiltrated the spinal cord, as well as resident microglial cells.  In vitro treatment of microglial cells by ghrelin resulted in suppressed ability to produce inflammatory trial cytokines after stimulation with lps.

These data suggest that ghrelin itself may be useful for the treatment of multiple sclerosis, as well as the possibility of using it in combination with other agents that block microglial activation.  For example, the endocannabinoid anandamide has previously been demonstrated to inhibit microglial inflammatory activity.

Suppression of microglial-based inflammation is important because the microglia are activated by cytokine producing T cells and are critical components of multiple sclerosis neurodegeneration, not only by inflammatory mediators, but also by glutamate excitotoxicity.

A recent study (Rossi et al. Exercise attenuates the clinical, synaptic and dendritic abnormalities of experimental autoimmune encephalomyelitis. Neurobiol Dis 2009 Jul 7) seems to suggest that exercise may be beneficial in slowing progression of multiple sclerosis. 

The investigators induced a multiple sclerosis-like disease in mice by administration of peptides derived from the myelin protein called myelin oligodendrocyte glycoprotein (MOG) and induced the mice to undergo voluntary running in a wheel.

Voluntary exercise decreased progression of disease, and overall severity, as compared to control animals.  Furthermore, the inflammation-associated suppression of GABA synapse stimulation by cannabinoid CB1 receptors, that is associated with the animal model of multiple sclerosis was inhibited as a result of exercise.  Additionally, exercise effectively reduced dendritic spine loss induced by by the multiple sclerosis-like disease in striatal neurons.

Exercise has been demonstrated to induce insulin like growth factor (IGF)-1 expression in certain cell types in response to mechanical motion, as well as growth hormone administration.  It is interesting to note that IGF-1 stimulates production of new myelin, as well protects the animal model of multiple sclerosis from disease (Yao et al. Insulin-like growth factor-I given subcutaneously reduces clinical deficits, decreases lesion severity and upregulates synthesis of myelin proteins in experimental autoimmune encephalomyelitis. Life Sci 1996;58(16):1301-6).  So it would be interesting to see if exercise, along with vitamins and stem cells may be syngergistic in treatment of multiple sclerosis.

Stem cell therapy of multiple sclerosis is associated with immune modulation, as well as the possibility of inducing regeneration of damaged neural tissue.  In the quest to figure out novel agents that may be useful in combination with stem cell therapy, scientists assess various drugs.  One class of interesting drugs to evaluate are drugs that are already on the market for different diseases.  For example, erythropoietin was previously demonstrated to inhibit multiple sclerosis in animal models.  Erythropoietin is a hormone made by the kidneys that normally stimulates red blood cell production from the bone marrow hematpoietic stem cell.  Erythropoietin is administered as a drug in patients with anemia to increase red blood cells.  Interestingly, erythropoietin is also associated with suppression of inflammatory Th1 and Th17 responses, upregulation of antiinflammatory Th2 responses, and stimulation of endogenous stem cells, including stem cells in the brain. 

The video above describes the effects of lithium on the animal model of multiple sclerosis called experimental allergic encephalomyelitis (EAE).  It demonstrates that administration of lithium suppresses autoreactive T cells but not overall T cell responses.  Furthermore, the paper demonstrated that lithium administration not only suppressed disease onset, but also reversed established disease. 

It appears that lithium mediates its effects through the suppression of the GSK-3 enzyme, which is involved not only in inflammation but also self-renewal of stem cells. 

The above video is provided for educational purposes only and is not suggesting the use of lithium in treatment of multiple sclerosis patients, it is only providing some scientific information that may be useful in future clinical trials and scientific experiments.

We have discuss previously that numerous nervous system molecules have immune modulatory effects.  For example, the endocannabinoid anandamide is capable of converting microglial cells from secreting inflammatory compounds to producing antiinflammatory cytokines such as interleukin-10.  Microglial cells generally cause pathology in multiple sclerosis through production of glutamate, as well as release of inflammatory agents.  By inducing microglial cells to produce interleukin-10, mechanisms similar to those that mesenchymal stem cells use to control inflammation may be activated.  Neurologically-associated molecules also may play a role in homing of stem cells.  For example, the neurotransmitter Substance P has recently been shown to act as attractant of stem cells. 

Here we discuss an interesting new way of modulating T cells so as to prevent onset and progression of an animal model of multiple sclerosis.  The publication (Bittner et al. TASK1 modulates inflammation and neurodegeneration in autoimmune inflammation of the central nervous system.  Brain 2009 Jul 1) discusses the role of TASK1 in T cell activity in the experimental allergic encephalomyelitis model. 

What is TASK1?

TASK1 stands for “TWIK-related acid-sensitive potassium channel 1″, which is a the two-pore domain potassium channel family that is important for maintaining resting membrane potential and balancing neuronal excitability.  TASK1 activity is inhibited by low pH and is activated by certain anesthetics… and It is also known as OAT1; TASK; TBAK1; K2p3.1; and KCNK3, with the official name being KCNK3 potassium channel, subfamily K, member 3. 

In the publication it was demonstrated that mice made genetically deficient for the TASK1 gene were substantially resistant to induction of experimental allergic encephalomyelitis.  Interestingly, T cells from the TASK1 knockout mice had an inhibited proliferative and cytokine response in vitro, suggesting the resistance to EAE may be associated with alterations on the T cell side and not just on the neuronal side.  Conceptually, one may expect neurons from TASK deficient animals to be more resistant to damage due to possible role of TASK1 in induction of apoptosis.  Indeed, the authors did demonstrate using in vitro isolated neurons from TASK1 deficient and wild-type neurons that a protective effect was observed associated with TASK1 deficiency.

Anandamide, which we previously described as having potentially beneficial effects on the mouse model of multiple sclerosis (EAE) by virtue of its ability to alter microglial production of inflammatory agents was demonstrated to inhibit TASK1 activity.  In vitro administration of anandamide was shown to inhibit T cell production of inflammatory cytokines.

Perhaps most exciting from the pubication was that administration of anandamide was capable of inhibiting progression of EAE after disease onset was initiated. 

It will be interesting in the future to try to tease out the effects of anandamide between activities on the T cells and activities on the microglia, which do not necessarily need to be exclusive.  For example, one could envision a system where T regulatory cells may be selectively “reprogramming” microglia to reduce inflammatory activities.  Or conversely, T regulatory cells may be generated in the central nervous system as a result of microglial presentation of self-antigen in the presence of interleukin-10 generated by the anandamide-reprogrammed microglia.

In conclusion, the current work supports further investigation into the TASK1 channel as a possible target for drug development in multiple sclerosis.  Given that mesenchymal stem cells already have demonstrated therapeutic effects in multiple sclerosis but in mice and man, it will be interesting to see if co-administration of anandamide may enhance mesenchymal stem cell regenerative activity by modulating the local microenvironment.

Microglia, the macrophages that reside in the brain, are believed to be involved in the process of neuronal degeneration in multiple sclerosis and animal models of the disease.  What are the mechanisms by which microglia may be pathological?  A recent report (Shijie et al. Blockade of glutamate release from microglia attenuates experimental autoimmune encephalomyelitis in mice. Tohuko J Exp Med 2009 Feb;217(2):87-92) suggests that microglial production of glutamate may be a cause of toxicity.

How can glutamate kill neurons?  Glutamate is used by neurons to communicate with each other.  The concentration of glutamate in the brain is tightly controlled by the blood brain barrier, which has specific glutamate transporters to only allow as much glutamate as is needed.  Additionally, when neurons communicate with each other, mechanisms exist to clear up the glutamate very rapidly after the signal is transmitted.  Too much glutamate causes what is called excitotoxicity, that is, death of the neurons from over stimulation.

In the current study the investigators demonstrated that in vitro activated microglial cells produced high concentrations of glutamate, which induced killing of neurons.  Microglial cells were demonstrated to have high concentrations of glutaminase, which generates glutamate.  When glutaminase was inhibited in vitro by addition of a small molecule inhibitor, the ability of the activated microglial cells to make glutamate, and subsequently to kill neurons was decreased. 

Furthermore, it was found that administration of the glutaminase inhibitor to mice suffering from experimental allergic encephalomyelitis (mouse multiple sclerosis) resulted in functional improvement.

These data suggest that microglial toxicity of neurons may be not only related to immunological means, but also through direct production of mediators that kill neurons.

It should be noted that Riluzole, the first drug approved for treatment of ALS works in part through suppressing interacton of glumate with its receptor, as well as upregulating activity of glutamate transporters that clear glutamate.  In fact, Riluzole has actually been demonstrated to inhibit MS-like disease in the EAE model (Gilgun-Sherki et al. Riluzole suppresses experimental autoimmune encephalomyelitis: implications for the treatment of multiple sclerosis. Brain Res 2003 Nov 7;989(2):196-204).

Stem cells may be attracted to the injured central nervous system of patients with multiple sclerosis by virtue of the molecule known as SDF-1, which is expressed at the onset of disease.  Indeed, we do know that stem cells selectively home to the central nervous system, at least from animal studies, in which adult mesenchymal stem cells are selectively found associated with areas of injury.  But could there be other injury signals that attract stem cells? 

We discussed previously that receptors associated with pain-related peptides, such as the kinin receptor B1, have the ability to make the disease worse or better depending on inhibition or activation, respectively.  An interesting molecule called Substance P, is a peptide neurotransmitter that is released in various situations of tissue injury.  We will discuss a recent paper (Hong et al. A new role of substance P as an injury-inducible messenger for mobilization of CD29(+) stromal-like cells. Nat Med. 2009 Apr;15(4):425-35)  demonstrating that Substance P is associated with homing of stem cells.

The investigators describe a model system in which injury induces mobilization of a mesenchymal stem cell-like population that expresses CD29 and is involved in acceleration of wound healing.

They  demonstrate that administration of Substance P in absence of injury in either mice, rabbits, or rats, induces mobilization of the CD29 cells from out of the bone marrow and into systemic circulation.  

To demonstrate that the mobilized CD29 cells actually had regenerative activity, they harvested CD29 cells that were mobilized, and injected mobilized cells, together with substance P in a rabbit wound model, in which the wound is induced by alkaline injury. Engraftment of the transplanted cells, as well as acceleration of healing, was observed. 

In order to make the case for clinical relevance of these observations, the investigators performed a series of experiments using human bone marrow mesenchymal stem cells as a model system for in vitro study.  It was observed that Substance P augmented the rate of transmigration, induced nuclear translocation of beta-catenin, triggered cell proliferation, and stimulated the activation of ERK1 and ERK2 pathways.

The authors conclude with the statement that: “This finding highlights a previously undescribed function of substance P as a systemically acting messenger of injury and a mobilizer of CD29(+) stromal-like cells to participate in wound healing”

If indeed new stem cell mobilizers can be identified in addition to G-CSF and the Anormed compound, perhaps one day it may be possible to simply redistribute your stem cells between body compartments so as to not need to take stem cells from outside of the body.

When I started my training, if you wanted to know whether one gene goes up or down, it would take at least a week to figure out for every gene.  Now, in one afternoon a scientist in one shot take a look at level of expression of all known genes (about 30,000) of the human body!  This revolution in science has allowed for the discovery of new molecular pathways without having to know what one is looking for.  So in conditions such as multiple sclerosis, many scientists basically “go fishing” to try to find new genes whose expression correlates with disease.  People have even taken it further by being able to assess not only all genes, but also proteins made by the genes (called proteomics), and more recently, like my friend Gabriela Cezar at Stemina does, look for all small molecules (called metabolomics).

These very powerful techniques are beginning to bear their fruits.  A recent paper (Schulze-Topphoff et al.  Activation of kinin receptor B1 limits encephalitogenic T lymphocyte recruitment tothe central nervous system.  Nature Medicine.  June 28, 2009) identified that patients with multiple sclerosis, as well as in animals bearing a disease similar to multiple sclerosis (experimental allergic encephalomyelitis) have increased expression of the kinin receptor B1.  This receptor is activated by components of the kinin-kallikrein system, which are a group of proteins involved in pain, inflammation, and coagulation of blood.

The investigators found that giving mice developing experimental allergic encephalomyelitis (mouse model of multiple sclerosis) activators of the kinin receptor resulted in less disease, whereas administration of inhibitors of this receptor resulted in acceleration of disease onset.  This was demonstrated when the compounds were given before disease onset, but in other experiments even after disease onset. 

Manipulation of receptors using small molecules can be tricky business.  In other words, it may be that the small molecule receptor activator/inhibitors may have been working through other biological pathways to alter disease course.  Therefore, in order to know conclusively whether the kinin receptor B1 is responsible or not for alteration in disease process, the investigators used mice lacking the kinin receptor B1.  These mice suffered from accelerated disease, thus suggesting that the receptor is normally involved in controlling the disease. 

Expression of the receptor had to be on the T cells in order to mediate protection from disease.  It was demonstrated that activation of the kinin receptor B1 selectively suppressed the infiltration of Th17 cells into the central nervous system.  Most interestingly suppression of infiltration was limited to Th17, with Th1 cells still infiltrating.  One intersting question is whether there is selective expression of the kinin receptor B1 associated with various TCR clonotypes that are expanded in multiple sclerosis progression, as seen in this video describing a paper by Eli Sercarz.

These data suggest a brand new molecule that can be targetted in multiple sclerosis.  It also illustrates the power of using “discovery based” approaches.  If indeed selective inhibition of Th17 entry into the CNS can be achieved in humans, this may be useful as a synergistic agent with bone marrow or fat stem cell approaches to multiple sclerosis.

Finding new uses of existing medications is a field of great interest to biotechnology and pharmaceutical companies since it saves all the money needed for performing pharmacological and safety studies.  A recent example of a “new use for an old drug” comes to us from a study recently published from the Medical University of South Carolina. 

In the study (Nath et al. Metformin attenuated the autoimmune disease of the central nervous system in animal models of multiple sclerosis. J Immunol 2009 Jun 15;182(12):8005-14) the investigators treated mice bearing an MS-like disease called experimental allergic encephalomyelitis (EAE) with the drug metformin. 

Metformin is the most widely used drug to treat type 2 diabetics in the US.  It originates from the plant called the French Liliac, which was used for centuries in traditional medicine to treat diabetes associated with obesity.

Mechanistically Metformin works through inhibiting sugar production from the liver, a process called gluconeogenesis, which is much higher in type 2 diabetics as compared to non-diabetic patients.  It does this by activating an enzyme called AMPK

In the study it was found that administration of metformin suppresses symptoms of the MS-like mouse disease through decreasing entry of T cells and monocytes into the central nervous system of the animals.  Additionally, a suppression of inflammatory products such as TNF-alpha, IL-17, IFN-gamma was also observed.

The same enzyme, AMPK, which metformin activates in the liver, when activated in macrophages results in their loss of ability to cause substantial inflammation.

Obviously more research needs to be performed to see if the concentrations achievable in animals can be achieved at a stable enough level in humans without causing adverse effects.  However, besides practical implications of the study, the study is important because it teaches that activation of AMPK can lead to suppression of macrophage inflammatory mediator production.  This could lead to development of new classes of AMPK activators that are selectively designed for macrophage suppress.