Role of isoflavones in multiple sclerosis

Abstract

Myelin degeneration is a hallmark of multiple sclerosis, a chronic, autoimmune neurological condition that alters Central Nervous System communication. Despite the fact that the pathophysiology of multiple sclerosis is multifactorial and not fully understood, new research indicates that reducing oxidative stress and inflammation may have therapeutic advantages. A class of phytoestrogens called isoflavones, which are mostly present in soy and other legumes, have drawn interest because of their possible anti-inflammatory and neuroprotective properties. A comprehensive literature review was performed covering the period from 2000 to 2024, utilizing various databases such as PubMed, Scopus, ScienceDirect, and Google Scholar. This process involved the use of specific search terms and Boolean operators, including “isoflavones” AND “multiple sclerosis,” “phytoestrogens” AND “neuroprotection,” and “soy isoflavones” AND “autoimmune diseases,” to locate relevant articles. The function of isoflavones in multiple sclerosis is examined in this review, with particular attention paid to their mechanisms of action, which include immune response modulation, antioxidant effects, and possible influence on neurodegenerative processes. This review discusses the preclinical data that currently supports isoflavones' capacity to lower inflammation, enhance myelin repair, and slow the progression in MS models. Future research directions are proposed, highlighting the challenges and limitations in implementing these findings in clinical practice. Even though isoflavones are still being studied, their promising role in MS treatment highlights the need for more research to assess their potential as supplemental therapies in managing MS symptoms and progression.

1. Introduction

Multiple sclerosis (MS) is a neurological disorder affecting the central nervous system that is characterized by inflammation and autoimmunity. The main targets in MS pathology are myelinated axons in the brain and spinal cord. In the pathology, partial or complete damage to the myelin and axons is observed, along with ongoing neurodegeneration (Goldenberg, 2012). Multiple sclerosis (MS) is the leading cause of nontraumatic neurological impairment in young adults between the ages of 20 and 40 (Hauser and Cree, 2020, Sospedra and Martin, 2005, Adamu et al., 2024). Multiple sclerosis is characterized by two invasive processes: inflammation linked to demyelination and the proliferation of astroglial cells (gliosis), along with neurodegeneration. The incidence of multiple sclerosis ranges from 60 to 300 cases per 100,000 individuals, exhibiting latitude gradients and a higher prevalence among females, as evidenced by comprehensive epidemiological studies conducted in high-income and high-risk regions such as Western Europe and North America (Zhang et al., 2024). MS is a complex and multifactorial disease, characterized by an autoimmune response against the central nervous system (CNS), triggered by a complex interplay of genetic predisposition, environmental factors such as smoking, geographic latitude, vitamin D deficiency, and Epstein-Barr virus (EBV) infection, as well as epigenetic influences (Dolcetti et al., 2020, Ramagopalan et al., 2010, Adamczyk-Sowa et al., 2020)

Demyelinating lesions found in both white and gray matter are characteristic features of multiple sclerosis (MS) and lead to a range of neurological symptoms, both typical and atypical. These symptoms may include ataxia resulting from extensive cerebellar damage, sensory loss and muscle weakness due to transverse myelitis, cranial nerve issues stemming from brainstem dysfunction, monocular vision loss associated with optic neuritis, as well as depression and cognitive difficulties (Dolcetti et al., 2020, Lassmann, 2018). The fundamental pathophysiology of multiple sclerosis (MS) is characterized by a persistent inflammatory condition that engages immune cells reacting to myelin antigens, such as CD4 + T-cells, CD8 + T-cells, and B-cells (Wu and Alvarez, 2011). As a result, damage to the myelin sheaths covering the axons occurs first, followed by axonal destruction. A significant and intentionally orchestrated event that initiates multiple sclerosis (MS) is the breakdown of the blood-brain barrier (BBB). This protective barrier becomes compromised as a result of the action of pro-inflammatory cytokines, including interferon-γ (INF-γ) and tumor necrosis factor-α (TNF-α) (Maciak et al., 2021a). The most common type of multiple sclerosis is referred to as relapsing-remitting multiple sclerosis (RRMS), which features cycles of remission interspersed with flare-ups. Typically, secondary progressive multiple sclerosis (SPMS) develops as a consequence of accumulating neurological damage, leading to the absence of noticeable recovery phases. Primary progressive multiple sclerosis (PPMS) is marked by a gradual worsening of neurological symptoms, along with occasional periods of stability or remission. When there are frequent acute exacerbations and the disease advances steadily, it is classified as progressive-relapsing multiple sclerosis (Maciak et al., 2021a, Schreiner and Genes, 2021).

Plant-based polyphenols, referred to as phytoestrogens, exhibit structural resemblances to both human estrogens and corticosteroids. Similar to corticosteroids, phytoestrogens feature a polycyclic structure with hydroxyl (-OH) groups, enabling them to engage with cellular receptors and modulate gene expression. These compounds are categorized into several chemical families, including isoflavones (found in soy), lignans (located in flaxseeds and whole grains), coumestans (rich in clover and alfalfa), and stilbenes (such as resveratrol found in grapes and berries) (Branca and Lorenzetti, 2005, Lecomte et al., 2017a). Therefore, isoflavones act as partial agonists for estrogen receptors and can exert either estrogenic or antiestrogenic effects depending on the body's estrogen levels (Ko, 2014). Natural estrogenic substances called phytoestrogens are present in the seeds and leaves of many different types of plants (Canivenc-Lavier and Bennetau-Pelissero, 2023). The estrogen receptors ERα and ERβ can interact with phytoestrogens and their metabolites, such as daidzein, genistein, and equol. These receptors are expressed in immunogenic cells in both humans and mice, including dendritic cells (DCs), B cells, T cells, natural killer (NK) cells, and macrophages (Canivenc-Lavier and Bennetau-Pelissero, 2023, Kovats, 2015). The main providers of isoflavones are products derived from soy, beans, chickpeas, and other crops like fruits, vegetables, nuts, dairy products, red clover products (Křížová et al., 2019). Isoflavones have been linked to a serve of possible health advantages, including the prevention and treatment of cancer (Andres et al., 2011), the alleviation of menopausal symptoms (Laudani et al., 2024), the preservation of cognitive abilities (Cheng et al., 2015) a lower risk of cardiovascular ailments, and the enhancement of bone health (Contador et al., 2024). Soy isoflavones affect steroid metabolism by regulating essential enzymes that play a role in the synthesis and breakdown of hormones, including 17β-hydroxysteroid dehydrogenase and aromatase. Furthermore, they may engage with mineralocorticoid (MR) and glucocorticoid (GR) receptors, which could influence the body's response to stress, immune function, and the balance of electrolytes (Swart et al., 2019).The main objective of the review discusses the benefits of isoflavones on multiple sclerosis and the potential processes that underlie these outcomes.

2. Pathophysiology of multiple sclerosis

Multiple sclerosis (MS) is a multifaceted autoimmune disease of the CNS that is characterized by chronic inflammation, demyelination, and neurodegeneration. The pathophysiology encompasses an interplay of immune dysregulation, inflammation, demyelination, and neurodegeneration, resulting in progressive neurological impairment (Ten Bosch et al., 2021).

The activation and proliferation of such autoreactive cells have potentially a complex interaction between genetic and environmental risk factors, which could ultimately lead to the disease. Such an interaction provides a background for the immune dysregulation that occurs in MS, where autoreactive T-cells and B-cells are activated and orchestrate inflammatory and neurodegenerative mechanisms. Both innate and adaptive immune cells have important roles in MS pathogenesis (Farzan et al., 2025, Satarker et al., 2022).CD^8 + T-cells are generally observed at the edges of the lesions and predominate within acute lesions (Adamu et al., 2024), whereas CD⁴⁺ T-cells are more internally located in the lesions (Gold and Wolinsky, 2011). Autoreactive CD⁴⁺ T cells, especially Th17 cells, characterized by their production of cytokines like IL-17A, IL-21, and IL-17F, further intensify inflammation. Cytokines such as TGF-β, IL-6, IL-1β, and IL-23 induce the differentiation and upkeep of Th17 cells. Hyperactivated Th1 cells secrete pro-inflammatory cytokines that result in chronic inflammation and tissue damage (Dobson and Giovannoni, 2019). These cells recognize CNS antigens, which induces an inflammatory cascade that results in demyelination and neuronal damage (Fig. 1) (Maciak et al., 2021b).

Fig. 1.

Role of immune cells in neurodegeneration in multiple sclerosis.

The newer research has identified that CD⁸⁺ T cells also show large-scale clonal expansions throughout the CNS in MS, implying their contribution to pathogenesis (Kunkl et al., 2020). Moreover, B cells are also involved in MS pathogenesis by antibody-dependent and -independent mechanisms, such as acting as antigen-presenting cells and cytokine-producing cells. The existence of germinal centre-like ectopic lymphoid follicles within the meninges of MS patients is another supporting evidence for the role of B cells in perpetuating the autoimmune process (Haki et al., 2024).

Concurrently, these immune attacks destroy oligodendrocytes that produce myelin and result in direct damage of the myelin sheath, both of which contribute to progressive CNS injury in MS (Papiri et al., 2023). Myelin plaque development, inflammation, and damage to the neuronal myelin sheath are hallmarks of MS neuropathology. Inflammation, myelin degradation, astrogliosis, oligodendrocyte damage, neurodegeneration, and axonal loss and remyelination are all grouped as myelin plaque. Cell-mediated immunity is triggered by an abnormal immune response in genetically predisposed patients to certain environmental stimuli, leading to the development of demyelination (Abulaban et al., 2024).

2.1. Immune system dysfunction in MS

MS immunopathology actually proposes a dysfunctional regulatory immune cell pool in the peripheral immune system and a distribution imbalance of pro-inflammatory immune cells. This condition is associated with immune cells' ability to change their phenotype, which impairs regulatory cells' ability to block a response and increases the invasion of autoreactive adaptive immune cells into the central nervous system (Balasa et al., 2021).

The first stage of MS pathology is the entrance of autoreactive CD⁴⁺ T cells into the CNS, which sets off inflammatory responses. CD⁴⁺ T lymphocytes are reactivated in their original environment by myelin antigens, HLA class II molecules, and accessory molecules on the surface of Antigen Presenting cells and subsequently neurodegenerative processes and subsequently neurodegenerative processes (Wang et al., 2024). Accessory molecules play a crucial role in driving MS by facilitating T cell activation and CNS invasion. Costimulatory signals (CD28-B7) enhance autoreactive T cells against myelin, and adhesion molecules (VLA-4/VCAM-1, LFA-1/ICAM-1) facilitate blood-brain barrier violation and immune cell migration. Lesional Antigen Presenting Cells reactivate T cells through HLA class II, perpetuating inflammation (Chastain et al., 2011). Indeed, MS patients' cerebrospinal fluid (CSF) and CNS lesions contain CD4 + T lymphocytes (Broux et al., 2012). It is thought that CD4 + T cells that secrete interferon-gamma (IFNγ) and interleukin-17 (IL-17) are the pathogenic initiators of MS. B cell lineage cells play a role in adaptive immunological inflammation in the central nervous system of MS patients (Chitnis, 2007). MS can be influenced by B cells in multiple ways: by creating ectopic lymphoid follicles in the central nervous system, presenting antigens to T cells, secreting cytokines and chemokines, and producing autoantibodies in the central nervous system which compromises the blood–brain barrier (BBB), promotes chemotaxis, and causes a greater number of inflammatory cells to enter that can cause demyelination and neurodegeneration (Pegoretti et al., 2020).

2.2. Neuroinflammation and neurodegeneration

It has been proposed that four key characteristics serve as distinguishing markers for neuroinflammation: increased production of cytokines, activation of microglial cells, peripheral immune cell migration, and localized tissue injury. Microglia, astrocytes, and immune cells (monocytes, neutrophils, lymphocytes) release inflammatory mediators such as histamines, cytokines, and reactive oxygen species (ROS) to initiate the reaction (Sanabria-Castro et al., 2024, Liu et al., 2020).

Microglia: Microglia, the primary immune cells of the central nervous system, may present two different phenotypes: M1 and M2, representing opposing functional states. M1 microglia are classically activated, releasing pro-inflammatory cytokines and contributing to neuroinflammation, while M2 microglia are alternatively activated, releasing anti-inflammatory cytokines and promoting neuroprotection and tissue repair. When microglia become hyperactive in pathological situations (M1), they play a substantial role in neuroinflammation and the development of CNS illnesses, including acute injuries like haemorrhage and head trauma, as well as chronic conditions such as Alzheimer’s disease, Parkinson’s disease, and chronic traumatic encephalopathy (Gao et al., 2023, Khodadadei et al., 2022, Dhaiban et al., 2021, Guerrero and Sicotte, 2020). In MS, microglia are primarily activated in regions of demyelination in the brain and spinal cord. These activated microglia release ROS, pro-inflammatory cytokines, and neurotoxic substances, aggravating tissue damage and promoting lesion growth. Gray matter atrophy, seen on MRI, is linked with persistent degeneration of demyelinated axons and neurons even in early stages. Neurodegeneration may be a consequence of demyelination but can also be triggered directly by inflammation, leading to permanent neuronal loss and synaptic dysfunction. Dysregulation of the MAPK/ERK signaling pathway in microglia is associated with persistent neuronal damage even after immunomodulatory treatment (Tsouki and Williams, 2021, Ramos-González et al., 2024). Triggering receptors expressed on myeloid cells (TREM) also influence microglial activity and modulate the inflammatory response in MS (Ten Bosch et al., 2021, Farzan et al., 2025)

Astrocytes: Astrocytes, as well, can exhibit two distinct reactive phenotypes: A1 and A2. A1 astrocytes are considered harmful—promoting inflammation, inducing neuronal death, and inhibiting regeneration—whereas A2 astrocytes are neuroprotective, supporting neuronal survival, promoting tissue repair, and modulating inflammation. Astrocytic dysfunction can worsen neuronal loss and cognitive decline by impairing synaptic function, reducing glutamate absorption and thereby increasing excitotoxicity, and disrupting the metabolic support of neurons (Satarker et al., 2022). Additionally, astrocytes interact with microglia and other glial cells to intensify neuroinflammatory responses and influence disease progression (Gold and Wolinsky, 2011, Dobson and Giovannoni, 2019). In MS lesions, characteristic perivascular infiltration of CD4 + , CD8 + , and Th1 T cells, monocytes, and occasionally B and plasma cells is observed (Adamu et al., 2024). These autoreactive T cells produce inflammatory cytokines and granulocyte-macrophage colony-stimulating factors that exacerbate the autoimmune response (Kunkl et al., 2020). Th1 cells promote inflammation, while Th2 cells mediate anti-inflammatory effects through cytokine secretion targeting microglia and macrophages (Haki et al., 2024). Myelin autoantibodies are generated when autoreactive T-cells stimulate B-cell activation. These antibodies cross the damaged blood–brain barrier, initiate the complement cascade, and lead to further demyelination and relapse events. Additional features of MS pathology include iron accumulation, mitochondrial abnormalities, and alterations in synaptic structure and density (Papiri et al., 2023).

2.3. Role of oxidative stress in MS

Oxidative stress contributes importantly to pathogenesis and development of MS. An imbalance between the formation of free radicals and the antioxidant defence system leads to oxidative stress. Lipid and protein damages can result from peroxidation and nitration processes caused by an increase in free radicals, which include reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), hydroxyl radicals (•OH), and superoxide anion (O₂⁻), reactive chlorine species and Reactive Nitrogen Species (Bizoń et al., 2023, Jiménez-Jiménez et al., 2024). These alterations are responsible for many aspects of MS pathology, such as inflammation, demyelination, and neurodegeneration. There has been evidence of elevation of indicators of oxidative stress and reduction of antioxidant compounds in the case of MS patients, with cerebrospinal fluid and serum/plasma malonyl- dialdehyde being the most consistent indicators (Liu et al., 2020, Rottoli et al., 2017). Since oxidative stress has become a crucial factor in demyelination, it may have an impact on the development of MS. The relationship between inflammation and oxidative state is close because the stress may be triggered by TLR and inflammasome signalling. Inflammation may contribute to the production of ROS and Reactive Nitrogen Species, and vice versa. High levels of ROS may act on mitochondria, impeding the production of ATP required for neurons and glia to function regularly. Additionally, Reactive Nitrogen Species may induce excitotoxicity through glutamate release and compromise its uptake system (Bizoń et al., 2023, Jiménez-Jiménez et al., 2024, Rajda et al., 2017).

In addition to causing a decrease in ATP synthesis and an impairment in Ca_2 + concentration, mitochondrial dysfunction also causes an increase in ROS and Reactive Nitrogen Species and alters several signalling pathways, and induces autoimmune reactions (Liu et al., 2020). The development of MS has been demonstrated to be significantly influenced by mitochondrial damage (Buga et al., 2023). The gut microbiota has also been suggested to be an inducing factor for oxidative damage in MS, enhancing mitochondrial dysfunction, neuroinflammation, and neurodegeneration through the gut-brain axis (Dziedzic et al., 2024). This underscores the multifactorial origins in MS pathogenesis. Moreover, oxidative stress could be closely associated with vascular changes, leading to blood-brain barrier breakdown, which can predispose MS patients to added cardiovascular threats. In summary, oxidative stress is a pivotal mechanism in MS pathology that leads to a triad of vascular injury, chronic inflammation, and oxidative imbalance that mutually enhance one another (Zha et al., 2022). Targeting the oxidative stress-associated processes could prove to be a promising preventive as well as therapeutic approach for MS (Javanbakht et al., 2023). Several interventions, including antioxidant treatments like Quercetin (Tobore, 2021) lifestyle changes like a Mediterranean-style diet and stress-reducing activities (Vitale et al., 2013) have been found to have potential against oxidative stress in MS. Fig. 1 illustrates the role of immune cells in neurodegeneration in multiple sclerosis.

3. Isoflavones

Isoflavones such as genistein, daidzein and glycitein can be found in soybeans at levels as high as 1–3 mg/g (Barnes, 2010). Many levels (up to 8 mg/g) of the genistein derivative 7-O-glucosyl glucoside are found in the tuber of the American peanut, Apios americana. The biosynthesis pathway of isoflavones is the same as the biosynthesis of flavonoids production, phenylpropanoid pathway (Yang and Wang, 2024). A typical isoflavone's carbon skeleton is C6-C3-C6, which consists of two 6-carbon benzene rings (A and C) and one 3-carbon heterocyclic ring (B) in Fig. 2.

Fig. 2.

Structure of isoflavone.

The chemical structure of legume isoflavonoids consist of glycosides such as acetyl glucosides, malonyl glucosides, and glucosides as well as aglycones in Fig. 3 (Gaya et al., 2020).

Fig. 3.

The chemical structure of the legume isoflavones.

These glycosides are: Glucosides: The general glycoside structure where a glucose molecule is bonded to the isoflavone aglycone via a β-glycosidic bond (Wang et al., 2022). Malonyl glucosides: Glucosides that have a malonyl group bonded to the 6 carbons of the glucose molecule. They tend to be the most predominant in soybeans. Acetyl glucosides: The same as malonyl glucosides, except that an acetyl group is bonded to the 6 carbons of the glucose molecule in place of a malonyl group (Macedo et al., 2023).

Aglycones are the non-carbohydrate parts of glycosides. Common aglycones in isoflavones are daidzein, genistein, and glycitein. Interestingly, glycosidic forms are normally less bioavailable than the aglycone forms. Enzymatic or microbial hydrolysis may convert glycosides into aglycones, thus increasing their bioavailability (Sirotkin and Harrath, 2014). Malonyl- and acetyl-isoflavones are a pair of highly unstable glycosides. Due to their hydrophilicity and larger molecular weight, glycoside forms are poorly absorbed in the small intestine. Phytoestrogen cannot be digested by humans, but some gut bacteria (Fig. 4) can, and they can create metabolites like S-equol from isoflavones (Lecomte et al., 2017b).However, the bioconversion of isoflavones is significantly influenced by gut microbiota. In the gastrointestinal system, bacteria, primarily strains of Lactobacillus and Bifidobacterium, hydrolyze isoflavones to produce their corresponding bioactive aglycone forms (Das et al., 2018, Varytė et al., 2020).

Fig. 4.

Gut bacteria metabolised daidzein into Daidzein (Biologically active) and further metabolised into Equol (biologically active).

Isoflavones interact with estrogen receptors, functioning as partial agonists that can produce either estrogenic or anti-estrogenic effects based on the hormonal environment. Multiple sclerosis flare-ups typically decrease during pregnancy because of the partial agonist action of elevated estrogen levels. Isoflavones may replicate this protective mechanism by influencing immune responses and lowering inflammation. Their efficacy is additionally amplified by gut microbiota, which transform them into a more powerful estrogen-like substance known as equol. More evidence is needed to justify their impact on the management of MS (Shrode et al., 2022, Kim, 2021a).

They are believed to have an inflammatory agent and sterol-lowering qualities. Because of their steroidal effects, they can modulate hormone dependent processes, which is most helpful for symptoms in menopause, osteoporotic conditions, and heart disease (Messina et al., 2022). Even with their activities similar to estrogen, studies suggest that isoflavones do not disrupt endocrine activity significantly in the case of the thyroid and other hormones. All in all, while further scrutiny is required to elucidate their lasting impacts, there most definitely is potential health benefits these individuals who are going through menopause (Essawy et al., 2019).

As well as to have a beneficial impact on hormone-related tumors, including dementia (Grade B) (Naghshi et al., 2024), heart failure (Grade B) (Zhao et al., 2019), and breast (Grade B) (Pollard and Wolter, 2000) and prostate cancer (Grade B) (Sugiyama, 2019). Beyond their positive effects on human health, isoflavonoids play a critical role in the interactions between plants and microbes (Natale et al., 2024, Guo, 2023). The chemical structure of the major isoflavones, their sources, and the potential benefits are listed in Table 1 below.

Table 1.

Chemical structure of the major isoflavones, their sources, and the potential benefits.

ISOFLAVONES & IUPAC name	SOURCE	CHEMICAL STRUCTURE	STUDY TYPE	Natural Standard Evidence-based Validating Grading	Biological activity	Reference
Genistein (7,4′-dihydroxy−6-methoxyisoflavone)	Legumes, Including Kudzu,Beans,Fava Beans And Kudine (Lupinus albus L.).		Preclinical	B	Improved Blood Insulin Levels (Invitro)	(Huang et al., 2015)
				C	Antibacterial And Anti-Inflammatory Effects (In Vivo)	(Huang et al., 2015)
				C	Antiviral (Invitro)	(Li et al., 2023)
				C	Osteoporosis	(Elsayed et al., 2022)
				C	Estrogenic Activity, Regulation of VEGF Expression and Modulation of Oestrous Cycle (Invivo)	(Zhang and Kowsalya, 2023)
Daidzein (7,4′-dihydroxyisoflavone),	Soybean and mung bean		Preclinical	C	Anti-Inflammatory Activity, Neuroprotective Effect, Antioxidant Action and Modulation of Apoptosis (Invivo)	(Kato et al., 2000)
				C	Prostate Cancer (Invivo)	(Wu et al., 2022)
				C	Neuro Protective (Invitro)	(Yang et al., 2023)
				B	Hepatoprotective Effects, Anti-Inflammatory and Antioxidant Properties (Invivo)	(Dong and Yang, 2022)
Glycitein (7,4′-dihydroxy−6-methoxyisoflavone	Soyabean		Preclinical	C	Neuro Protective, Anti-Oxidant (Invitro)	(Pan et al., 2001)
				B	Anti-Diabetic (Invivo)	(Zhang et al., 2015)
				C	Breast Cancer (Invitro)	(Hakimi Naeini et al., 2025)
				B	Neuroprotective Properties, Anti-Oxidant, Anti Inflammatory and Modulating Inflammatory Responses.	(Diksha and Singh, 2024)
				B	Managing Depression and Memory (Invivo)	(Yamada et al., 2025)
S- Equol ((3S)−3-(4-hydroxyphenyl)−3,4-dihydro-2H−1-benzopyran−7-ol)	Soybeans and soy products		Preclinical	A	Cardioprotective (Invivo)	(Lund et al., 2004)
				D	Anti-Androgenic (Invivo)	(Hwang et al., 2003)
				D	Anti-Oxidant (Invitro)	(Choi and Kim, 2011)
				D	Anti-Tumour, Hepatoprotective (Invivo)	(Moriyama et al., 2018)
				D	Neuro Protective and Anti Inflammatory (Invivo)	(Xu et al., 2022)
				D	Anti-Osteoporosis Effects (Invivo)	(Widyarini, 2006)
				D	Reduces Skin Damage, Anti-Ageing (Invivo)	(Magnet et al., 2017)
			Clinical	B	Reduces Skin Damage, Anti-Ageing, Skin Barrier Protection (RCT)	(Tanaka et al., 2009)
				B	Anti-Androgenic Activity (RCT)	(Usui et al., 2013)
				B	Cardioprotective, Obesity, Metabolic Disease (RCT)	(Wilkins et al., 2017)
				C	Neuroprotective and Cognitive Function (RCT)	(Breikaa et al., 2013)
Biochanin A (5,7-dihydroxy−4′-methoxyisoflavone)	chickpea, red clover and soybean		Preclinical	D	Hepatoprotective, Anti Oxidative, Anti Inflammatory (Invivo)	(Li et al., 2024)
				D	Anti-Oxidant, Anti Inflammatory, Neuro Protective (Invivo)	(Zhang et al., 2020)
				D	Anti-inflammatory, Osteoprotective Effects, Bone Regeneration (Invivo)	(Amri et al., 2022)
				D	Antidiabetic, Antihyperlipidemic, and Antioxidant Effects (Invivo)	(Lueangarun and Panchaprateep, 2020)
				B	Androgenetic Alopecia (Invivo)	(Sun et al., 2011)
Formononetin (7-hydroxy−3-(4-methoxyphenyl) chromen−4-one)	Beans and Legumes, Asparagus Astragalus membranaceus (Fisch),Reddish clover species Trifolium pratense L, Monosperma butea		Preclinical	D	Vasorelaxant and Antihypertensive Effects (Invivo)	(Aladaileh et al., 2019)
				D	Anti-Oxidant, Anti Inflammatory and Nephroprotective (Invivo)	(Jin et al., 2014)
				D	Anti-Cancer Agent (Invitro &Invivo)	(Liang et al., 2014)
				D	Neuroprotective (Invivo)	(Wang et al., 2012)
				D	Anti-Inflammatory, Anti-Apoptotic and Diabetes Management (Invitro)	(Liu et al., 2021)
				D	Hepatoprotective, Anti-Inflammatory, Anti-Apoptotic (Invivo)	(Yang et al., 2020)
Sophoricoside (5,7-dihydroxy−3-(4-(((2 R,3S,4 R,5 R,6S)−3,4,5-trihydroxy−6-(hydroxymethyl)tetrahydro-2H-pyran−2-yl)oxy)phenyl)-4H-chromen−4-one).	Fruits of the Ginseng tree L. and Sophora japonica L.		Preclinical	D	Neuro Protective, Anti Inflammatory, Cognitive Function (Invivo)	(Gaya et al., 2020)
				D	Hepatoprotective Effects, Regulate Lipid Metabolism, Anti-Oxidant and Anti Inflammatory (Invivo)	(Li and Lu, 2018)
				D	Anti-Lipogenic and Glucose-Regulating Effects (In Vitro)	(Wu et al., 2013)
				D	Managing Osteoporosis, Estrogenic Activity (Invitro & Invivo)	(Abdallah et al., 2014)
				D	Anti-Allergic and Anti-Inflammatory Action (Invitro & Invivo)	(Kim et al., 2013)
				D	Anti-Inflammatory and Immunosuppressive Activity (Invivo)	(Liu et al., 2024)
Millewanin-F (3-(3-hydroxyphenyl)−5-hydroxy−6-(3-methylbut−2-enyl)−7-methoxy−8-(3-methylbut−2-enyl)chromen−4-one	Millettia taiwaniana		Preclinical	C	Induces Apoptosis in Leukaemia HL−60 Cells (In vitro)	(Ito et al., 2006)

3.1. Metabolism and bioavailability of isoflavones

The isoflavones' limited bioavailability is explained by their considerable first-pass metabolism following initial absorption. Phase II biotransformation occurs when glucuronosyl-transferases and sulfotransferases in the liver and gut use the hydroxyl molecules of the isoflavones as sites for glucose metabolism and sulfation. The conjugates of glucuronide and sulfate are either released in bile and then returned to the intestine, or they can be carried by circulation throughout the body to tissues, from hence they will finally be eliminated by the kidneys (Shelnutt et al., 2002, Heinonen et al., 2003, Larkin et al., 2008). Main isoflavones such as glycitein, genistein, and daidzein are found in soy enhanced as β-D-glycosides of glycitin, daidzein, and genistein. After consumption, the intestinal wall's β-glucosidases hydrolyze the glycosides, converting them into the corresponding bioactive aglycones, daidzein, and genistein. Daidzein is further broken down into equol and O-demethyangolensin, and genistein into p-ethyl phenol (Yoon and Park, 2014, Sonee et al., 2004). Parent substances daidzein and genistein are metabolized from biochanin A and formononetin and sophoricoside, their plant ancestors (Sakai and Kogiso, 2008) which is further transformed into daidzein and equol (Yin et al., 2019, Yu et al., 2019) is quickly absorbed and broken down in the liver, kidneys, and feces (Zhi et al., 2014). The amount of these molecules that become available for tissue distribution, where they can have physiological effects, is measured as isoflavone bioavailability. Therefore, evaluating the possible health advantages of isoflavones and knowing bioavailability may help interpret the significant degree of diversity in clinical trial findings (Larkin et al., 2008). Fig. 5 metabolism and bioavailability of isoflavone.

Fig. 5.

Metabolism and bioavailability of isoflavones.

4. Mechanisms of action

4.1. Potential mechanisms of isoflavones

Soy products are rich in phytoestrogens which may offer neuroprotective and immunomodulatory benefits for individuals with multiple sclerosis. These compounds have the ability to suppress pro-inflammatory cytokines, function as antioxidants, and enhance immune system activity.

Genistein has only modest inhibitory impacts on astrocyte and microglia activation.

Sudeep Ghimire et al., conducted research on the gut microbiota of mice that were given a phyto free diet in contrast to those on an isoflavone-rich diet. Their findings indicated that an isoflavone-rich diet enhances microbial diversity and promotes gut health in mice. Additionally, the study demonstrated that this diet stimulates the production of anti-inflammatory cytokines within the gut microbiota, resulting in alterations in Lipopolysaccharide biosynthesis and an increase in the pathways for O-antigen and UDP-N-acetyl-D-glucosamine biosynthesis. These results imply that an isoflavone-rich diet may mitigate the severity of EAE disease and decrease overall mortality associated with the condition (Ghimire et al., 2022).

Kim IS examined soybeans, which are rich in protein and lipids and contain isoflavones that influence estrogen activity, potentially reducing the risk of breast, endometrial, and prostate cancers. The popularity of soybeans has increased in Western countries, leading to investigations into the biological efficacy of isoflavones. Genistein, a plant-derived natural antioxidant, has been found to enhance cognitive abilities in postmenopausal women by elevating protein kinase C levels and activating the cyclic AMP/CREB signalling pathway. Isoflavones may improve cognitive function and emotional well-being in menopausal women by preventing alterations to Tau proteins associated with Alzheimer's disease and enhancing serotonin activity in the brain. However, long-term intake of isoflavones could potentially hinder cognitive performance. Furthermore, isoflavones may offer neuroprotection and bolster the immune response in individuals with multiple sclerosis (MS) by binding to estrogen receptors, mitigating inflammation, and functioning as antioxidants. Animal studies involving MS have indicated that isoflavone supplementation can help preserve myelin integrity and promote the survival of oligodendrocytes, which may aid in maintaining or repairing myelin sheaths (Kim, 2021a).

Jahromi SR et al., conducted a research study to evaluate the impact of genistein on the severity of experimental autoimmune encephalomyelitis (EAE) during both early and late phases in female C57Bl/6 mice. The mice were induced with EAE by immunized with MOG 35–55 and pertussis toxin. Mice received genistein (300 mg/kg) or DMSO every day through a tube in their stomach (6 mice in each group), and their brains and spleens were checked for immune cell growth and loss of myelin. The results indicated that genistein has positive effects in the early stages of EAE by influencing enzymes, cytokines, cell growth, and programmed cell death. However, its efficacy diminishes in later stages (Jahromi et al., 2014).

Sandra Gredel et al., focused on exploring how phytoestrogens (PE) and their metabolites influence human leukocyte functions invitro. This study assessed the effects of genistein, daidzein, matairesinol, secoisolariciresinol, and equol on the activity of natural killer cells, their proliferation, cytokine production, as well as rates of apoptosis and necrosis in fasting blood from healthy male volunteers. Peripheral blood mononuclear cells (PBMC) containing 15–30 % Natural killer cells were incubated with 50 ll of phytoestrogen (PE) for 24 h at 37 C. Cell proliferation was assessed by cultured PBMC for 5 days with PE. The most effective modulators of immune functions, according to a study on PE's effects on immune function markers, were genistein (GEN), daidzein (DAI), and equol (EQ). Parent compounds were more potent than their metabolites, and isoflavones had greater immunomodulatory potential than lignans. With the exception of GEN's low-dose effect in promoting TNF-a production, PE continuously inhibited immunological activities. The metric most susceptible to PE exposure was mitogen-stimulated cytokine secretion. According to the study, PE may have an impact on immunological functioning in vivo, with the most susceptible parameter being mitogen-stimulated cytokine release. It is still unknown how various substances affect human immune cells (Gredel et al., 2008).

Corina Danciu et al., conducted a review on isoflavones, which are also referred to as phytoestrogens. These natural compounds possess a 3-phenyl chromen-4-one structure and exhibit a range of therapeutic properties, including antioxidant, chemo preventive, anti-inflammatory, antiallergic, antibacterial, and cardioprotective effects. Genistein and daidzein are particularly noted for their anti-inflammatory properties and are employed in clinical practice to promote neurological recovery and reduce the risk of neurodegenerative diseases, such as Alzheimer's disease. These compounds enhance the expression of PPAR, which plays a role in preventing the accumulation of beta-amyloid and the proliferation of astrocytes, thus contributing to the overall health of the nervous system. Including these isoflavones in one's diet is an essential strategy for preserving nervous system health (Danciu et al., 2018).

Jurga Bernatoniene et al., conducted a review on the role of estrogen receptors in the central nervous system, emphasizing their involvement in learning and memory functions. Their findings suggest that isoflavones may have a beneficial impact on cognitive abilities. Studies have demonstrated that soy isoflavones possess neuroprotective effects in animal models, including mice and rats, with genistein potentially alleviating inflammation and lessening the impact of Alzheimer's disease. However, clinical trials in humans have yielded inconsistent results, underscoring the need for additional research to clarify the possible benefits of isoflavones in relation to neurodegenerative diseases (Bernatoniene et al., 2021).

Jie Yu et al., conducted a review on Isoflavones, which are antioxidants, provide advantages for individuals suffering from cardiovascular diseases, cancer, osteoporosis, and conditions related to menopause. They possess anti-inflammatory properties that influence granulocytes, monocytes, and lymphocytes. Diets rich in isoflavones help to prevent the inflammation-related activation of metallothionein and manganese superoxide dismutase. These compounds effectively neutralize reactive species and demonstrate resistance to oxidation. Additionally, isoflavones inhibit the activity of pro-inflammatory cytokines, chemokines, arachidonic acid metabolism, and various enzymes (Yu et al., 2016).

Jenkins DJ et al., conducted a clinical trial involving 41 men and postmenopausal women with elevated cholesterol levels. The findings suggested that the consumption of high-isoflavone soy protein foods could increase serum levels of interleukin-6 (IL-6), potentially heightening the risk of autoimmune diseases and cardiovascular issues. Notably, the study revealed that women exhibited significantly higher IL-6 levels after following a high-isoflavone soy diet, implying that soy isoflavones may enhance immune function due to their estrogen-like properties. Additionally, the research indicated that high-isoflavone soy foods might prepare the immune system to better manage infections and improve natural defenses against tumor formation. Nevertheless, the effect of soy consumption was relatively minor when compared to the control group, highlighting the need for further investigation into the influence of soy phytoestrogens on IL-6 and their potential role in mitigating growth factors (Jenkins et al., 2002).

Xu SZ et al., conducted an invitro study focusing on the isolation and culture of Human Umbilical Vein Endothelial Cells (HUVECs). They transfected Bcl-2 siRNA into the HUVECs and assessed gene expression through real-time PCR. Additionally, they performed assays to evaluate cell death and proliferation, along with Western blot analysis. The findings indicate that soy-derived isoflavones, specifically genistein and daidzein, offer protection to vascular endothelial cells against oxidative stress damage induced by high glucose levels and H2O2. This protective effect is attributed to the modulation of Bcl-2/Bax expression, as well as the PI3K and Rho/ROCK signalling pathways, and the expression of ERβ. The study proposes that supplementation with soy isoflavones may provide a beneficial impact on oxidative stress-related endothelial cell damage in diabetic patients, with the protective mechanisms of genistein and daidzein likely operating through ERβ (Xu et al., 2009).

Davis JN et al., conducted a clinical trial on six healthy males at the Barbara Ann Karmanos Cancer Institute revealed no notable differences in the levels of NF-kB oligonucleotides and p50 NF-kB antibodies among the groups. This indicates that Novasoy tablets are both safe and effective for cancer patients. Additionally, the research demonstrated that genistein, a soy isoflavone, effectively inhibits the activation of NF-kB in human lymphocytes (Davis et al., 2001).

Myelin-specific CD⁴ T lymphocytes are essential for promoting inflammation and demyelination because they infiltrate the central nervous system (CNS) and produce interferon (IFN), interleukin-17A (IL-17A), and/or granulocyte-macrophage colony-stimulating factor (GM-CSF) (Jensen et al., 2021). The number of lymphatic CD⁴ T cells, CD⁸ T cells and double-positive CD⁴, CD⁸ lymphocytes decreased in mice given genistein, suggesting that genistein may have an impact on the maturation of CD⁴, CD⁸ helper T cells and early thymocyte maturation (Sakai and Kogiso, 2008).

In reaction to damage, infection, or inflammation, microglia are easily activated. The degeneration of dopaminergic neurons is facilitated by the proinflammatory substances secreted by activated microglia (Gao et al., 2002).These factors include free radicals like superoxide and nitric oxide (NO) and cytokines like tumor necrosis factor-α (TNF-α). Genistein prevented microglial activation, hence shielding dopaminergic neurons (Chen et al., 2008).Toll-like receptor 4 (TLR4) and downstream signalling molecules like MyD88, TRAF6, phosphorylated TAK1, p38, ERK, IκBα, and NF-κB are all downregulated by genistein. By preventing microglia from activating and polarizing into the M1 phenotype, this inhibition lowers neuroinflammation (Jahromi et al., 2014).

5. Preclinical studies

This preclinical study induced experimental autoimmune encephalomyelitis (EAE) in female C57Bl/6 mice aged 8–12 weeks to model multiple sclerosis. The research indicated that the production of experimental autoimmune encephalomyelitis (EAE) using myelin oligodendrocyte glycoprotein 35–55 peptide (MOG35–55) demonstrated that genistein administration markedly improved clinical symptoms via regulating pro- inflammatory and anti-inflammatory cytokines. One group of mice received no therapy, whereas the other group received 200 mg/kg body weight of genistein in DMSO 4 % every day. It also mitigates disease severity by regulating cytokine production, lymphocyte proliferation, and CD8 + cytotoxicity. Treatment with genistein was observed to reduce clinical symptoms and alter pro- and anti-inflammatory cytokines in the central nervous system. By blocking enzymes that up-regulate adhesion proteins and integrins and down-regulating inflammatory cytokines, the study also discovered that genistein indirectly influences cell-endothelium interaction in the brain microvasculature. Alternative treatments for MS may result from this (De Paula et al., 2008).

In this research study female C57BL/6 J and SJL/J mice, as well as HLA-DR15 transgenic mice, were used. Mice were given either an isoflavone-rich diet containing genistein (0.24 g/kg of food) and daidzein (0.22 g/kg of diet) or an isoflavone-free diet for six weeks. The standard group is given regular food. In order to induce and assess EAE studies, mice were given 100 μg of MOG35–55 (for C57BL/6 J and DR2) or 50 μg of PLP139–151 (for SJL/J) emulsified in 200 μg of CFA subcutaneously on the left and right flank on day 0 and 80 ng of pertussis toxin (PTX) intraperitoneally on days 0 and 2 (PTX was administered only to C57BL/6 and DR2 mice). The severity of each disease was assessed, and all operations were conducted in accordance with university of lowa protocols. The study reveals that an isoflavone diet can enhance the severity of autoimmune encephalopathy (AE) in mouse models. The diet can decrease the number of gut bacteria that can metabolize isoflavones, potentially reducing inflammation and demyelination. Researchers suggested that a diet rich in isoflavones could protect against autoimmune inflammation in the CNS, potentially altering the course of EAE. After EAE, cellular infiltration into the CNS decreases, leading to decreased activation and proliferation of MOG-specific CD4 + T cells. The presence of gut bacteria that metabolism isoflavone is crucial for isoflavone diet-mediated protection (Jensen et al., 2021).

This research study examined the impact of flavonoids and related substances from eight groups on activated macrophages' generation of NO and iNOS expression. The substance including luteolin, luteolin-7-glucoside, vitexin, daidzein, genistein, genistin, rhamnetin, isorhamnetin, kaempferol, myricetin, taxifolin, naringin, ferulic acid, pelargonidin, and procyanidin B2, were investigated for their actions on murine J774 macrophages. STAT-1 was unaffected by the four substances flavone, isorhamnetin, naringenin, and pelargonidin. LPS-induced iNOS expression and NO generation were dose-dependently reduced by the isoflavones genistein and daidzein. Quercetin inhibited macrophage STAT-1 activation brought on by LPS. LPS-induced iNOS expression and NO generation were dose-dependently reduced by the isoflavones genistein and daidzein. Quercetin inhibited macrophage STAT-1 activation brought on by LPS. To sum up, flavonoids that prevent NF-κB and/or STAT-1 from activating are probably going to suppress the synthesis of a variety of inflammatory mediators in addition to iNOS. This research suggests that it partly elucidates the pharmacological activity of flavonoids as anti-inflammatory agents (Hämäläinen et al., 2007).

6. Future directions

Due to their anti-inflammatory, antioxidant, and neuroprotective properties, isoflavones—plant-derived compounds found in soy and other legumes—have shown promise in the treatment and management of multiple sclerosis (MS) (Kim, 2021a). Isoflavones, especially the soy-based genistein and daidzein, can influence immune cells through their interactions with cell signalling pathways. They decrease pro-inflammatory signals by binding to estrogen receptors and altering gene expression. Consequently, this lowers inflammation and may lessen MS-related nervous system damage. Additionally, isoflavones affect T-cell differentiation by increasing TGF-β and IL-10 for the generation of regulatory T-cells and decreasing IL-6 and IL-23 for Th17 cell development. Additionally, they might alter dendritic cells, which would support a more robust T-cell profile (Sharifi-Rad et al., 2021, Kim, 2021). Combining isoflavones with conventional MS therapies, such as disease-modifying treatments, may offer synergistic effects that enhance treatment efficacy; however, these combinations may not necessarily reduce adverse effects (Lambert et al., 2017). Isoflavones may stimulate estrogen receptors in people with hormone-sensitive diseases, including uterine fibroids, endometriosis, and breast cancer, which could accelerate the course of the disease (Messina and Wood, 2008). Isoflavones' anti-inflammatory and neuroprotective qualities, as well as our increasing knowledge of how each person reacts to these substances, make them potentially useful in the treatment of multiple sclerosis (MS). By customizing isoflavone-based treatments to a patient's genetic and metabolic profile, personalized medicine techniques may greatly improve therapy results (De Jager, 2009). Indeed, isoflavones have been shown to improve fatigue and general quality of life, especially in populations going through menopausal symptoms (Khapre et al., 2022). The possibility of these compounds as a useful, supplemental treatment for MS management is highlighted by these directions (Table 2).

Table 2.

Effect of isoflavones on experimental multiple sclerosis: animal models, mechanisms, and outcomes.

S.no	Animal used	Isoflavones studied	Exposure	Concentration of isoflavones	Formulation	Mechanism assessed	Conclusion	Reference
1.	Female C57Bl/6 mice (n = 6)	Genistein	300 µg of Myelin oligodendrocyte glycoprotein peptide (MOG) 35–55	300 mg/kg	Genistein was dissolved in DMSO administered daily by oral gavage for 10 days.	IL−12 is one of the key proinflammatory cytokines that is changed in EAE/MS; an increase in its secretion causes an increase in demyelination. Furthermore, blocking IL−12 secretion or signalling prevents the pathological and clinical manifestations of EAE.	Genistein reduces the severity of the disease by controlling cytokine production, lymphocyte proliferation, and CD8 +cytotoxicity when taken orally at the beginning of clinical symptoms, but not in the late phase of EAE.	(Jahromi et al., 2014)
2.	Female C57Bl/6 mice (n = 6)	Genistein	100 μg of MOG 35–55 peptide	200 mg/kg	Genistein was dissolved in DMSO administered daily by s. c. on daily basis for 7 days.	In addition to its molecular action, genistein also inhibits the activity of ATP-using enzymes, such as tyrosine-specific protein kinases, at the cellular level, where it causes apoptosis, suppresses the functions of osteoclasts and lymphocytes, and has antioxidant properties.	Genistein significantly reduced the severity of EAE by influencing leukocyte trafficking into the central nervous system in addition to downregulating inflammatory cytokines.	(De Paula et al., 2008)
3.	C57BL/6 J, SJL/J female mice	Isoflavones diet	100 μg of MOG 35–55 (for C57BL/6 J and DR2) or 50 μg of PLP 139–151 (for SJL/J emulsified in 200 μg of CFA	Isoflavone diet [Genistein (0.24 g/kg of diet) and daidzein (0.22 g/kg of diet)]	Isoflavone diet [Genistein (0.24 g/kg of diet) and daidzein (0.22 g/kg of diet)].	Specifically, mice on an isoflavone diet exhibit a lower frequency of activated myelin-specific CD4 + T cells following induction of disease.	The study state that state that illness prevention with an isoflavone diet is reliant on the existence of bacteria that metabolize isoflavones and their metabolites.	(Jensen et al., 2021)
4.	Female C57Bl/6 mice 4–6 weeks old (n = 17)	7-O-tetradecanoyl-genistein (TDG)	100 μg of Myelin oligodendrocyte glycoprotein peptide (MOG)35–55	200 mg/kg	TDG administered s.c daily for a total of seven doses.	Furthermore, the study's findings provide support to the theory that the influx of cells in the brain and spinal cord, which raises the number of cells generating IL−17 and IFN-γ, is linked to the deterioration of EAE's clinical symptoms.	Finally, these findings imply that the clinical manifestations of EAE are ameliorated by administration of TDG, a more lipophilic homologue of genistein.	(Castro et al., 2012)
5.	Male C57BL/6 mice	Icariin	250 μg of MOG35–55 (myelin oligodendrocyte glycoprotein, MOG)	25 mg/kg	Icariin (25 mg/kg) was dissolved in 0.5 % CMC solution and orally administered daily from day 5 to day 15 after immunization.	Treatment with Icariin results in less inflammatory infiltration and less paracellular tracer blood–brain barrier leakage.	Icariin reduces EAE, which has been linked to decreased Th1 and Th17 cell differentiation.	(Shen et al., 2015)

7. Conclusion

Isoflavones possess antioxidant, anti-inflammatory, and neuroprotective properties, making them a promising candidate for the adjunct treatment of multiple sclerosis, particularly when derived from soy. One of the main contributors to MS progression, neuroinflammation, may be mitigated by isoflavones through immune response modulation and reduction of oxidative stress. Isoflavones, especially genistein, have demonstrated protective effects on the blood-brain barrier (BBB) in various preclinical studies. These compounds may lower BBB permeability by influencing inflammatory cytokines, mitigating oxidative stress, and increasing the expression of tight junction proteins. By stabilizing the function of endothelial cells and decreasing neuroinflammation, isoflavones contribute to preserving both the structural and functional integrity of the BBB, which is frequently impaired in neurodegenerative and autoimmune disorders, including multiple sclerosis. Additionally, isoflavones effects on gut microbiota may support immune regulation. Despite these promising findings, clinical research is necessary to fully understand and enhance the efficacy of isoflavones in the treatment of multiple sclerosis. This includes identifying optimal dosages, which would typically be addressed in Phase II clinical trials, evaluating efficacy in Phase III trials, and assessing long-term safety during Phase IV, across diverse patient populations.

CRediT authorship contribution statement

A MONISHA: Writing – review & editing, Resources, Project administration, Conceptualization. R Divya: Writing – review & editing, Validation. S Sowmiya: Writing – review & editing, Methodology. V Anushya vardhini: Writing – original draft. R Sakthi: Visualization, Investigation. Sameer S Abdul: Formal analysis, Data curation.

Funding

The authors acknowledge the support of Dr. MGR Educational and Research Institute for providing the resources and facilities necessary to conduct this work.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.