Introduction
Relapsing-remitting multiple sclerosis (RRMS) is characterised by the development of inflammatory lesions in the central nervous system (CNS), resulting in demyelination and axonal loss.
Many different dynamic processes are involved and simultaneously coordinated for MS pathogenesis. Oligodendrocytes, the myelin-forming cells of the CNS, are target cells in the pathogenesis of MS, but the exact aetiology is unknown. Pathological mechanisms that seem to be involved in MS include immune-mediated inflammation, oxidative stress and excitotoxicity.1 These mechanisms can potentially contribute to oligodendrocyte and neuronal damage and cell death, leading to disease progression.
Polyunsaturated fatty acids (PUFAs), such as the omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are the most abundant structural components of the neural tissue and play a fundamental role in the development and the proper functioning of the nervous system. The PUFA composition of membrane phospholipids are involved in a variety of cellular and multicellular processes, including inflammation and immunity, with implications to diseases such as MS. The fatty acid composition of phospholipids determines the biophysical and functional characteristics of the cellular membranes such as ‘fluidity’, transport, polarity and plays an important role in cellular integrity and intracellular and intercellular communication.2
PUFA and antioxidant deficiencies have been reported in patients with MS.3 Both antioxidants, vitamin E and γ-tocopherol are efficiently implicated in trapping reactive oxygen and nitrogen oxide radicals,4 respectively, and both exert non-antioxidant properties, including modulation of cell signalling, regulation of specific gene transcription, modulation of immune function and induction of apoptosis.5 6
In vitro, in vivo and ex vivo studies have demonstrated that diet EPA/DHA omega-3 and omega-6 linoleic acid (LA)/γ-linolenic acid (GLA) may be implicated and modulate many of the known complex pathways in MS pathophysiology. Anti-inflammatory properties of omega-3 and omega-6 PUFAs include competitive inhibition of arachidonic acid (AA) and its metabolites that can be involved in promoting inflammation7; they promote production of anti-inflammatory prostaglandins, thromboxanes and can inhibit production of proinflammatory cytokines8; they promote reduction of the level of the proinflammatory interleukin-1, interleukin-1-α and tumour necrosis factor.9 10 They have also been reported to produce lipoxins and modify the cytoskeletal components, thereby inhibiting the ability of leucocytes for migration.11 12 Omega-3 PUFAs inhibit the expression of the nuclear transcription factor, κ-B that is involved in the production of inflammatory cytokines, chemokines and various adhesion molecules with crucial roles in MS.13–15 Resolvins and protectins are derived from omega-3 PUFAs through lipooxygenase-mediated mechanisms16 17 and promote control of inflammation in neural tissues by activating G-protein-coupled receptors,18 inhibition of neutrophil, reduction of tumour necrosis factor expression, interferon (IFN)-α production and T-cell apoptosis.17 In vitro, T-cell proliferation in acute and chronic inflammation can be reduced by supplementation with either omega-6 or omega-3 PUFA.19 Furthermore, DHA prevented dendritic cell maturation and CD4+ T cell stimulation and differentiation, in an animal model of MS.20
Culture cell-line experimental studies report that cyclooxigenase-2 participates in the formation of electrophilic fatty acid derivatives of the omega-3 fatty acids in activated macrophages21 which in turn are implicated in the activation of the nuclear respiratory factor 2 that induces the transcription of a number of protective genes. Τhe electrophilic fatty acids activate the peroxisome proliferator-activated receptor (PPAR)γ for anti-inflammatory response. Omega-3 PUFAs and their eicosanoid derivatives are thought to possess strong PPAR-α-agonist properties on T cells in humans. This event has been shown to be neuroprotective in experimental animal models.22–24
Animal studies report that retinol X receptor (RXR)γ is a positive regulator of the endogenous oligodendrocyte precursor cell differentiation and remyelination.25 EPA and DHA have neuroprotective effects, are endogenous ligands of RXRs and PPAR and have been found to increase neurogenesis in old rats.26 27 DHA may block depolarisation-induced increased glutamate efflux and the activation of glutamate receptors leading to excitotoxicity, partly through inhibition of voltage-sensitive Na+ and Ca2+ channels.28 In vitro, omega-3 PUFAs have been shown to prevent neuronal accumulations of Ca2+, which can trigger a destructive cellular cascade of events that leads to neuronal damage and death.28 In vitro, omega-6 PUFAs can alter the function of oligodendrocytes by affecting their membrane composition.29 Membrane depolarisation affects protein phosphorylation of myelin basic protein in oligodendrocytes, an important event in myelination.30 DHA is reported as neuroprotective against excitotoxicity, inflammation and oxidative stress.28 Recent data report that dietary intake of a preformed DHA supplement is more effective in reaching the brain and achieving neuroprotection in an animal model of PD.31 PUFAs might also interfere with the production of certain matrix metalloproteinases that can be the cause of disruption of the brain–blood barrier,32 but they can also stimulate the production of molecules involved in myelinogenesis.33 Thus, the action mechanisms of the omega-3 PUFAs may most likely be considered as holistic, multifactorial and may be related to a number of cellular and molecular effects in CNS.
At present, agents used in MS seem to be partially effective and lack remyelinating and significant neuroprotective properties. Moreover, severe side effects have been reported to be associated with current RRMS treatments.34
The increasing incidence and prevalence of MS and the long-term sequelae of the disease urges the need for the development of new treatments to prevent activity and disability progression in patients with this condition. Based on the above research findings, the afore-mentioned specific dietary antioxidants and specific omega-3 and omega-6 PUFA fulfil the biological criteria and have the potential to affect disease activity and progression.1 35 36 The inconsistent data available from clinical trials performed to date on PUFA dietary interventions as complementary therapies for MS are the result of several notable limitations including supplement optimal dosing, design and selection of outcome measures.37 38
In 2013, we have published the results of a proof-of-concept clinical trial39 based on a dietary cocktail formula preparation using the exact same ingredients, formulation and dosing as now named ‘Neuroaspis plp10’ dietary intervention, with promising outcome and statistically significant; reducing the annual relapse rate (ARR) and the risk of sustained disability progression. With this study, we are reporting the results of a phase III, multicentre, double-blind, randomised, placebo-controlled clinical trial of efficacy and safety, the MINERAL Study, using the Neuroaspis plp10 dietary supplement.