Central and Peripheral Nervous System Changes as Markers of Disease Progression in Multiple Sclerosis

Central and Peripheral Nervous System Changes as Markers of Disease Progression in Multiple Sclerosis

OBJECTIVE To investigate neurodegeneration and demyelination in the central and peripheral nervous system in multiple sclerosis linked to disease progression and mechanisms that can explain different responses to Fampridine treatment in MS patients with walking disability.

METHOD The study is a prospective cohort follow-up study with 98 participants with MS and walking disability. Participants are identified as responders or non-responders to Fampridine treatment prior to the study. Participants will undergo MRI of the cerebrum with lesion load quantification, neurophysiological tests comprised of motor evoked potentials and electroneurographic examination, blood samples examining KIR4.1 antibodies, brain derived neurotrophic factor (BDNF), myelin protein zero (MPZ), peripheral myelin protein 22 (PMP22), p75-nerve growth factor receptor (p75NGFR) and anti-myelin associated glycoprotein (anti-MAG). The presence of SORCS-3 gene mutation will also be examined, as will cerebrospinal fluid levels of myelin basic protein, neurofilament heavy and light chains. Functional test of Timed 25-foot walk test (T25FW) will identify response to Fampridine treatment. A functional test battery will further detail function of upper extremities and cognition.

CONCLUSION This study will add to the understanding of neurodegeneration and demyelination in CNS and PNS in patients with MS having walking disability. This will impact clinical decision-making by improving organization of immunomodulatory treatment, identifying biomarkers thus facilitating earlier treatment and improving patient control, information and education.

BACKGROUND Multiple Sclerosis (MS) is an autoimmune, inflammatory demyelinating disease targeting myelinated axons in the Central Nervous System (CNS). It is the most common nontraumatic cause of disability in young people. Most MS patients are diagnosed between the ages of 20 and 40 years. Denmark has a prevalence of approximately 155 MS patients per 100,000 inhabitants, which is among the highest in the world. The etiology of MS is not known, however, a combination of genetic and environmental factors is likely to be involved in triggering the disease.

CLINICAL PRESENTATION MS damages the CNS and causes progressive disability. Clinical symptoms of the patient depend on the location of the lesions that can occur anywhere in the CNS. Consequently the neurological impairments are very variable and consist of sensory, motor, visual, urinary, coordination and cognitive deficits. MS is divided into several categories based on disease progression: relapse-remitting multiple sclerosis (RRMS), secondary progressive multiple sclerosis (SPMS) and primary progressive multiple sclerosis (PPMS). Clinically isolated syndrome (CIS) is a single relapse compatible with MS accompanied by paraclinical evidence of demyelination with more than 80 percent of patients with CIS developing MS at a later stage.

WORKUP

McDonald criteria are used for diagnosing MS. They are based on clinical findings supported by paraclinical tests mentioned below. The aim is to demonstrate neurological impairments disseminated in time (lesions in the CNS are of different age) and localization in the CNS, while excluding other conditions:

1. Magnetic Resonance Imaging (MRI) of the brain and spinal cord is used to demonstrate lesions in the CNS.

2. Lumbar puncture is performed in order to demonstrate inflammation in the CNS. Analysis of the CSF can also exclude infection in the CNS.

3. Blood Samples are drawn to assess IgG, glucose and albumin in order to assess levels on both sides of the blood brain barrier (BBB) and to exclude other conditions.

4. Evoked Potentials are useful at identifying subclinical lesions.

   • Visual Evoked Potentials (VEP) assess the anterior visual pathways where delays in latencies indicates demyelination.
   • Somatosensory Evoked Potentials (SSEP) assess the posterior column of the spinal cord, brainstem and somatosensory cortex.

OTHER ASPECTS OF CURRENT WORKUP

The other aspects of the workup that are mentioned below, are not a part of the established workup on diagnosing or monitoring MS:

Blood Samples: Currently, there are no established peripheral blood biomarkers for MS. A study has demonstrated the SORCS3-gene as a potential MS risk gene. It has not been evaluated as a peripheral blood biomarker for MS as of yet, despite being potentially important in the pathogenesis of MS.

Furthermore a study has screened serum samples aiming to identify CNS-specific antibodies in MS.

Antibodies to the glial potassium channel KIR4.1 (Inward-rectifier potassium ion channel) was present in a subgroup of MS patients while being absent among patients with other neurological conditions and healthy controls.

Brain Derived Neurotrophic Factor (BDNF) is suggested to play a neuroprotective role in MS. BDNF concentrations has been shown to be lower in patients with RRMS compared to healthy controls.

There are currently biomarkers being indicative of demyelination in the PNS. Myelin protein zero (MPZ) is a cell surface component of myelin, which decreases in the tissue when demyelination occurs in the PNS. Peripheral myelin protein 22 (PMP22) is a glycoprotein component of myelin only found in the PNS, where it accounts for 2-5% of the myelin protein content.

The P75 nerve growth factor receptor (p75 NGFR) also known as P75 neurotrophin receptor (p75NTR) or low-affinity nerve growth factor receptor (LNGFR) is a ligand, which plays a role in Schwann cell migration and myelination during development, apoptosis and axonal regeneration. Anti-myelin associated glycoprotein (Anti-MAG) is a myelin marker that is rather specific for the PNS.

Neurophysiological tests: Motor Evoked Potentials (MEP) assess the motor pathways by stimulating the precentral gyrus. It is valuable in evaluating descending motor pathways, PNS and muscles. Electroneurographic examination (ENG) assesses the nerve conduction speed in the PNS and is not usually applied for patients with MS. Few studies that have evaluated examining nerve conduction speeds in the PNS among MS patients show that deficits in the PNS may be common among MS patients.

TREATMENT

There are three aspects of MS-treatment:

1. Immunomodulatory treatment with the aim of reducing/preventing relapses and slowing disease progression. Patients who are initiated in immunomodulatory treatment can be classified into two groups: responders or non-responders. The former profits from treatment while the latter does not respond or has marginal response to treatment. Responders can become non-responders after a while. Currently, the aim of immunomodulatory treatment among MS patients with RRMS, is no evidence of disease activity (NEDA), where the patient has no relapses, no increase in disability and no new active lesions on MRI.
2. Symptomatic treatment of walking disabilities, urinary tract problems, pain, depression, sexual problems, spasticity and fatigue. Neurorehabilitation is also an important part of the symptomatic treatment.
3. Treatment of relapses using high dose corticosteroids.

FAMPRIDINE Fampridine (Ampyra/Dalfampridine/4-aminopyridine) is the first oral agent approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) for the treatment of walking disability in MS. It was approved in 2011 in Denmark for treatment of MS patients with walking disability.

Fampridine is a potassiumchannel blocker with a primary mechanism of action of blocking voltage-gated potassium channels. It blocks potassium from entering the channel, which leads to smoother nerve conduction and a subsequent improved amplitude and duration of the action potential. Fampridine acts at both the CNS and PNS and enhances nerve conduction in demyelinated axons and improves walking ability in a subset of MS patients. Furthermore a study has demonstrated improvement in cognition and upper extremity functioning, as a result of Fampridine treatment. Patients who do not profit from Fampridine treatment, are classified as non-responders. Currently, the mechanism behind non-response to Fampridine and conversion from response to non-response has not been studied. The functional test of T25FW is widely used to discriminate patients as responders or non-responders as well as to monitor response to treatment with Fampridine. When Fampridine treatment is indicated, patients will undergo a short-term treatment period while undergoing the T25FW in order to establish if there is response to treatment or non-response. If patients are classified as the latter, treatment will be stopped. During long-term treatment with Fampridine, the initial responders are yearly evaluated as to whether they are continuous responders.

SUMMARY OF STUDY RATIONALE Walking impairment is one of the most common symptoms of MS and has been reported as one of the most impactful symptoms on quality of life. MS patients with walking impairments receive the potassium-channel blocker, Fampridine, if they respond to this treatment. It has been established that approximately 35% of MS patients with walking disabilities are responders to this treatment, and thus have improvements in their walking speed and acceleration. The response status is established using the functional test T25FW. The presence of a specific potassiumchannel antibody (KIR 4.1) has been demonstrated in a subtype of MS patients while being absent in healthy controls. Antibodies affecting the PNS and thus aggravating walking abilities have been studied, but their links to MS remain to be investigated.

MS patients undergo neurodegeneration in the CNS with progressive neurological disability associated with axonal and neuronal damage, which is a major contributor to walking impairment. The involvement of the PNS in the dysfunction of the lower extremities as well as the role of the PNS as a potential marker of disease progression in MS remains to be fully elucidated. The effect of Fampridine in relation to the PNS has also not been examined and the mechanism behind non-response to Fampridine treatment and conversion from response to non-response remains to be elucidated.

Consequently, the overall research question of the present study proposal is to further clarify disease mechanisms involved in MS. Moreover, the overall aim of this project is to expand the knowledge on 1) neurodegeneration and demyelination in the central and peripheral nervous system in MS linked to disease progression over time and 2) to examine mechanisms that can explain the different responses to Fampridine treatment. Below, the specific study aims and hypotheses are outlined.

STUDY AIMS

Overall one main study is conducted, which has three inherent sub-studies. The aims of the main study Central and Peripheral Nervous System Changes as Markers of Disease Progression in Multiple Sclerosis are therefore:

1. to investigate the progression-rate and the corresponding changes, in patients with MS undertaking Fampridine treatment, in regards to a) magnetic resonance imaging-verified lesions in the central nervous system and b) neurophysiologic examinations of the peripheral nervous system. (Study I).
2. to investigate the response of potential peripheral blood biomarkers to Fampridine treatment in patients with MS. (Study II).
3. to compare motor pathways in the central nervous system and peripheral nervous system in patients with MS who are responders to non-responders of Fampridine treatment.

Null hypotheses are:

• Over time, among MS patients, there is neurodegeneration in the central nervous system while there is no neurodegeneration in the peripheral nervous system.
• There is no difference in biomarkers of the CNS and the PNS in MS patients.
• There are no differences in the motor pathways of the central and peripheral nervous system in patients with MS who respond and do not respond to treatment with Fampridine.
• Responders to Fampridine treatment do not convert to non-responders over time.

Participants will undergo MRI, blood samples, neurophysiologic examinations and the functional testing, as described in the trial outline section, in order to evaluate response to treatment with Fampridine and markers of disease progression. In addition to the widely used T25FW, additional functional tests will also be performed to have a more detailed overview of the function of the lower and upper extremities while also examining cognition over time. The T25FW test will also be used for identification of responders to treatment with Fampridine.

Inclusion Criteria:

• Participants are diagnosed with MS according to the McDonald criteria.
• Categorized as responder or non-responder to Fampridine treatment.
• Age in the range of 18-65 years.
• Extended Disability Status Scale (EDSS) 4-7 points.
• Pyramidal Functions Score ≥ 2 in the Kurtzke Functional Systems Scores (FSS).

Exclusion Criteria:

• MS-attack and/or change in immunomodulatory treatment within 60 days before inclusion.
• Simultaneous use of medications that inhibit the organic cation transporter (OCT2).
• History of epileptic seizures.
• Clinically manifest heart-, liver-, kidney- (glomerular filtration rate < 80 ml/min), pulmonary disease, diabetes, alcohol intake exceeding the National Institute of Health's recommendations and pregnancy.