Dietary sphingolipids and milk fat globule membrane: emerging roles in cardiometabolic health and muscle function

Abstract

Sphingolipids (SPLs) are bioactive lipids that play a critical role in metabolic health. Milk fat globule membrane (MFGM) is a rich source of SPLs, and emerging evidence suggests that dietary SPLs and MFGM contribute to cardiometabolic health. Dietary SPLs, including MFGM, have been shown to reduce intestinal lipid absorption, improve hepatic lipid metabolism, and modulate cholesterol transport. The ceramide (Cer)/sphingosine-1-phosphate (S1P) ratio, rather than total plasma Cer levels, appears to be a key determinant of their effects on insulin resistance, atherosclerosis. myogenesis, and neuromuscular function. Although dietary SPLs, particularly MFGM-derived lipids, offer promising cardiometabolic and muscle health benefits, variations in SPL source, structure, acyl chain length, and phosphorylation state influence their effects. Further research is needed to elucidate the molecular mechanisms, optimize dosage, and establish long-term efficacy.

Introduction

Cardiometabolic diseases pose a significant global health threat, with obesity and type 2 diabetes being major contributing factors (Nelson, 2013). These diseases are intricately linked, involving complex interactions between genetic predispositions and environmental factors (Kang et al., 2022). In light of these growing health concerns, dietary modifications have gained increasing attention as a viable strategy to combat cardiometabolic diseases.

Sarcopenia is a physical condition characterized by decreased muscle mass, strength, and mobility. This natural aging phenomenon compounds the health challenges associated with aging populations (Thornton et al., 2024). Sarcopenia significantly elevates the risk of falls, fractures, and mortality (Yeung et al., 2019) and affects an estimated 10–16% of older adults aged 60 years worldwide (Petermann-Rocha et al., 2022). The pathogenesis of sarcopenia is multifaceted, involving oxidative stress, hormonal imbalances, and chronic inflammation and it has close association with cardiometabolic diseases (Offord and Witham, 2017). While regular exercise is a well-established method to enhance muscle strength (Cruz-Jentoft et al., 2014), it remains a challenge for many older individuals. Thus, nutritional interventions including protein supplementation, are often recommended as complementary approaches.

Sphingolipids (SPLs) have gained interest for their potential health benefits. These substances can be synthesized endogenously or obtained from dietary sources, such as dairy products, meat, fish, eggs and soybeans (Yang and Chen, 2022). Emerging evidence suggests that dietary SPLs and their metabolites may play a role in preventing or managing adverse health conditions. In this review, we explore how milk SPLs can may influence cardiometabolic health and muscle function, offering novel perspectives on their potential as functional ingredients.

Structure, metabolism, and functional diversity of SPLs

SPLs are a complex and diverse class of lipids characterized by a sphingoid backbone such as sphingosine (SP). SP can undergo esterification with fatty acids to form ceramides (Cer) or phosphorylated to produce sphingosine-1-phosphate (S1P). Cer can further react with phosphocholine or sugar residues to produce sphingomyelin (SM) or glycosphingolipids, respectively (Fig. 1). Cers can be broken down into SP by ceramidase. Additionally, Cers are converted into glycosphingolipids via glycosylation mediated by glycosylceramide synthase (GluCerS) (Hannun and Obeid, 2018). Among glycosphingolipids, gangliosides (GAs) are a specific subset that includes sialic acid in their structure (Quinville et al., 2021). The synthesis of SPLs is tightly regulated by various enzymes, and their composition varies depending on the organs, reflecting their distinct functional roles.

Fig. 1.

Metabolism of dietary SPLs. SPLs sphingolipids, SP sphingosine, S1P sphingosine-1-phosphate, Cer ceramide, SM sphingomyelin, CB cerebroside, GA ganglioside, S1Pase sphingosine-1-phosphatase, SK sphingosine kinase, CerS ceramide synthase, CDase ceramidase, SMS sphingomyelin synthase, SMase sphingomyelinase, GluCerS glucosylceramide synthase, GalCerS galactosylceramide synthase, GBA glucocerebrosidase, GALC galactosylceramidase, GT glycosyltransferase, ST sialyltransferase, Neu neuraminidase

Neurons contain high levels of GAs, which are critical for neuronal development and the stability of myelin, the protective sheath surrounding neurons. Glycosphingolipids and GAs regulate various cell functions, including cell recognition, adhesion, movement, and growth, through specialized regions known as glycosynaptic microdomains (Todeschini and Hakomori, 2008). In this regard, SM-rich diets or SM supplementation have been proposed to enhance neurogenesis and neuronal communication (Alashmail, 2024). SPLs are predominantly localized in the apical membrane of intestinal epithelial cells, where they play critical roles in supporting nutrient absorption and cell development (Rohrhofer et al., 2021). GAs, found on the surface of intestinal cells, provide protection by shielding the intestinal lining from bile salt-induced damage. Furthermore, GAs act as ligands for bacteria, viruses, and toxins preventing their entry into the body. This protective mechanism reduces gut inflammation and alleviates symptoms such as nausea, vomiting, diarrhea, and abdominal pain (Kurek et al., 2013).

Dietary sources and metabolism of SPLs

SPLs are distributed across various food resources including, animal products, plants, and aquatic products (Table 1). The type and amounts of SPLs vary significantly depending on their source. Animal-based foods, such as milk and eggs, are rich source of SPLs compared to fruits and vegetables, which generally contain relatively lower amounts. Plant-derived SPLs are typically simpler in structure, with cerebrosides being a predominant type, compared to the more complex SPLs found in animal-based foods (Vesper et al., 1999; Yang and Chen, 2022). Aquatic products, particularly microalgae are excellent sources of SPLs.

Table 1.

Sphingolipids contents in foods

SM is a major SPL in eggs and dairy products. Dairy products contain higher SM levels than raw milk due to their higher lipid content. Milk-derived SM typically features longer fatty acid chains compared to egg-derived SM (Sanchez Juanes et al., 2009). These structural differences may lead to different nutritional impacts which will be discussed in more detail later. Cers are present in various foods, including soybeans, rice bran, and marine organisms. In contrast, SP and S1P, which are breakdown products of Cers, are less commonly found in foods (Li et al., 2021). GAs are glycosphingolipids containing acidic carbohydrate moieties, such as sialic acid. Milk fat globule membrane (MFGM) of mammalian milk is the major source of GAs and contain 0.9 – 36.9 mg GAs/L (Ali et al., 2022).

SM is a major phospholipid (PL) in human milk; breast milk contains 2.5 – 17.7 mg SM/100 mL (Zheng et al., 2019). In adults, the estimated daily intake of total SPLs in the United States ranges from 300 to 400 mg, and milk, egg, and fish are major sources of SM (Nilsson and Duan (2006a, b). The total intake of SPLs in the typical Japanese diet was about 128 ~ 292 mg/3000 kcal and SM was the major SPL in the diet (Yunoki et al., 2008). In Western diets, dairy products and eggs are the primary sources of dietary SPLs. Conversely, Asian diets generally contain lower levels of SPLs compared to Western diets (Norris and Blesso, 2017a). Currently, no recommended daily intake (RDI) for SPLs, including cerebrosides and GAs is available as SPLs are not classified as essential nutrients by health authorities, such as the Food and Drug Administration in the United States (FDA) or the World Health Organization (WHO). Further studies are needed to better understand their nutritional significance and potential health benefits.

Dietary SPLs, such as SM, are barely digested in the mouth and stomach; their primary digestion begins in the small intestine (Wang et al., 2021). As shown in Fig. 2, dietary SM is hydrolyzed predominantly in the jejunum by alkaline sphingomyelinase (SMase) into Cer and phosphocholine (Duan, 2006). Whereas Cer can be directly absorbed, phosphocholine is broken down by phosphatases and absorbed as choline. Subsequently, Cer is hydrolyzed by neutral ceramidase at the brush border of the intestine into SP and a fatty acid. Once absorbed into enterocytes, SP can be metabolized into hexadecenal, which is subsequently converted into palmitic acid (Li et al., 2021). The palmitic acid is then incorporated into chylomicrons and transported through the lymphatic system. The remaining SP is resynthesized into Cer or converted into more complex SPLs. SP can also be phosphorylated to S1P by sphingosine kinase (SK) or dephosphorylated back to SP by S1P phosphatase (S1PP). This regenerated SP can be further metabolized into Cer or other complex SPLs, such as SM and glycosphingolipids (Yang and Chen, 2022). Additionally, the intestine contains enzymes such as glucosidase, glucosylceramidase, and galactosylceramidase, which degrade various glycosphingolipids substrates (Duan, 2011).

Fig. 2.

The metabolic fate of dietary SPLs in small intestine. SPLs sphingolipids, SM sphingomyelin, Cer ceramide, SP sphingosine, S1P sphingosine-1-phosphate, SMase sphingomyelinase, CDase ceramidase, PA palmitic acid

Effect of dietary SPLs on cardiometabolic health

Intestinal lipids absorption

Excessive intake of triglycerides (TG) and cholesterol is a major risk factor for cardiometabolic diseases, including obesity, diabetes, and cardiovascular diseases (CVDs), and controlling lipid absorption in the intestinal tract is considered an effective strategy to reduce the risk of cardiometabolic diseases (Ros, 2000). One approach to inhibiting lipid absorption involves targeting key enzymes, such as pancreatic lipase, cholesterol esterase, and phospholipase A₂ (PLA₂), which play key roles in the emulsification and hydrolysis of lipids, facilitating their absorption. Additionally, disrupting the action of bile acids, which aid in the formation of water-soluble micelles necessary for lipid digestion and absorption, can be another potential strategy (Shi and Burn, 2004). Orlistat, a widely used weight management drug, functions by inhibiting gastric and pancreatic lipases, thereby reducing fat absorption (Henness and Perry, 2006).

Dietary SM has been shown to reduce the intestinal absorption of lipids in numerous rodent and human studies (Norris et al., 2016). This suggests that SM actively modulates intestinal lipid absorption, and three plausible mechanisms have been proposed (Fig. 3). One theory is that SM can form complexes with cholesterol in the intestinal lumen, reducing its solubility and availability for absorption. SM-enriched micelles significantly decrease cholesterol solubility compared to PL-enriched micelles (Ramprasath et al., 2013). Milk-derived SM, which contains longer saturated acyl chains, has demonstrated a greater inhibitory effect on intestinal cholesterol absorption in rats compared to egg-derived SM (Noh and Koo, 2004). The second mechanism posits that SM delays fat digestion by inhibiting lipase-colipase and PLA₂, both of which are involved in fat and cholesterol absorption. This inhibition reduces lysophospholipid generation, thereby decreasing the formation of chylomicrons and their transport (Noh & Koo, 2004). A third possible mechanism is that SPLs may regulate cholesterol uptake and metabolism within intestinal cells. Niemann-Pick C1-Like 1 (NPC1L1), a protein located on the apical membrane of enterocytes, is an essential transporter for dietary and biliary cholesterol uptake. Administration of milk SM significantly increases NPC1L1 mRNA levels in the small intestine, likely as a compensatory response to decreased cellular cholesterol entry (Norris et al., 2016). Additionally, the improved gut barrier function may contribute to reduced cholesterol uptake by minimizing paracellular leakage in the gut (Brun et al., 2007). SM-containing milk polar lipids (MPL) significantly promote the expression of tight junction proteins both in Caco-2/TC7 cells and C57BL/6 mice (Milard et al., 2019). This suggests that MPL and its active constituent SM hold significant potential for mitigating disorders associated with increased gut permeability.

Fig. 3.

Mechanism of dietary SPLs on inhibition of lipid absorption in small intestine. SPLs sphingolipids, PLA₂ phospholipase A₂, NPC1L1 Niemann-Pick C1-Like 1

SM was metabolized into Cers (30–90%) and free SP (2–6%) in the intestinal tract of rats, and approximately 25% of SM was excreted as its intact form in feces (Nilsson, 1968). Cers also showed a strong inhibitory effect on cholesterol absorption in the Caco-2 cell model (Feng et al., 2010). In our study, Cers with a longer acyl chain length (C16 and C24) exhibited a more pronounced inhibitory effect on micellar cholesterol solubility than short-chain Cer (C2). (unpublished data; Fig. 4(A)). In addition, long-chain Cers demonstrated greater inhibition of pancreatic lipase and cholesterol esterase activity (unpublished data; Fig. 4(B, C)). Cers with longer acyl chain length displayed greater bile acid binding capacity than short-chain Cer (unpublished data; Fig. 4(D)). These findings suggest that Cers can modulate cholesterol absorption at multiple stages, including micelle solubilization and cholesterol mobilization, in an acyl chain length-dependent manner.

Fig. 4.

Effects of Cers with various acyl chain lengths on micellar cholesterol solubility (A), pancreatic lipase inhibition (B), pancreatic cholesterol esterase inhibition (C), and bile acid binding capacity (D). Con, control; C2/C16/C24-cer, C2/C16/C24-ceramide

Garmy et al. (2005) demonstrated that a specific interaction between cholesterol and the amide head group of SP was responsible for molecular binding. The strong bile acid binding affinity of C24-Cer might hinder enterohepatic bile circulation and promote bile acid excretion via feces. Increased cholesterol displacement is expected in micelle formations due to the significant influence of van der Waals interaction between cholesterol and Cer, given their strong hydrophobic nature. This mutual displacement between cholesterol and Cer has been observed under various conditions, the extent of which is dependent on Cer concentration and chain length (Garcia-Arribas et al., 2016). The reduced cholesterol incorporation into micelles in the presence of C16- and C24-Cer may contribute to increased fecal cholesterol excretion.

Regulatory effects of SPL and MFGM on hepatic lipids metabolism

The liver is the primary organ for Cer generation and contains higher levels of Cer and SM than other body tissues (Holland and Summers, 2008). Consequently, SPLs play a significant role in the liver, from homeostasis to metabolic liver diseases (Regnier et al., 2019). Among SPL metabolites, Cers and S1P are key regulators in the development of non-alcoholic fatty liver diseases (NAFLD), the most prevalent chronic liver disease in Western countries. NAFLD is closely linked to metabolic disorders, including obesity, dyslipidemia, hypertension, and hyperglycemia (Nojima et al., 2024). Given this, dietary SPL may serve as potential strategy for NAFLD management.

Dietary SPLs reduce hepatic lipids accumulation in a high-fat diet- or high-cholesterol-induced steatosis mice model. Egg or milk SM lowered macrophage infiltration in adipose tissue and TG in muscle tissues. This effect was associated with the downregulation of stearoyl-CoA desaturase-1 (SCD-1) and peroxisome proliferator-activated receptor gamma 2 (PPARγ2) in the liver (Norris et al., 2017). Wat et al. (2009) demonstrated that supplementation of PL-rich milk extract positively affected hepatic steatosis and plasma lipid metabolism in mice fed a high-fat diet. The observed lipid-lowering effect was attributed to the decreased expression of key enzymes involved in fatty acid synthesis (acetyl-CoA carboxylase [ACC], elongation of very-long-chain fatty acids protein 5 [ELOVL5], fatty acid synthase [FAS], malic enzyme 1 [ME1], and SCD-1). These findings suggest that PL-rich milk extract may inhibit hepatic fatty acid synthesis, thereby contributing to regulation of lipid metabolism.

In a study on Zucker fatty rats, supplementation with pure SM of animal origin and glucosylceramide (GC) of plant origin resulted in significant reductions in hepatic lipid content and plasma non-HDL cholesterol levels after 45 days. Hepatic gene expression analysis revealed an upregulation of adiponectin receptor 2, PPARα, and pyruvate dehydrogenase kinase 4 (PDK4), and a significant downregulation of the expression of SCD-1. Dietary SM significantly lowered hepatic cholesterol and TG levels by regulating liver X receptor alpha (LXRα)-mediated cholesterol efflux (Chung et al., 2013). Reduced LXRα activity led to the downregulation of sterol regulatory element-binding protein-1c (SREBP-1c) and FAS, both of which are responsible for fatty acid synthesis (Repa et al., 2000). Norris and Blesso (2017b) reported that the hepatic Cer profile is closely associated with liver function. A reduction in hepatic very- long-chain (C22-C24) Cers was observed in mice fed a high-fed diet (Cinar et al., 2014). Recently, dietary supplementation with MFGM (20%, w/w) and extracellular vesicles rich whey concentrate (MFGM/EV) alleviated hepatic dysfunction by increasing hepatoprotective Cer species (Cer 18:1;2/24:0) in plasma (Sprenger et al., 2024). This finding suggests that an MFGM/EV-enriched diet may modulate hepatic steatosis by regulating the balance of SPL species involved in lipid metabolism and turnover. In addition, S1P has been shown to stimulate vascular endothelial growth factor (VEGF) production in liver sinusoidal endothelial cells, exerting proliferative effects by activating S1P receptors (S1PR) on hepatocytes (Nowatari et al., 2015).

In contrast, adverse effects of SPLs on NAFLD have also been reported. Elevated Cer levels promote the production of proinflammatory cytokines, such as interleukin-6 (IL-6), and causes endothelial dysfunction, which further stimulates hepatocyte NAFLD (Zhu et al., 2023). S1P acts as a ligand of G-protein coupled receptors (GPRs) and serves as a key messenger of various complex cellular processes. S1P has been implicated in liver fibrosis by activating hepatic stellate cells, leading to the formation of fibrotic tissue. S1P promotes cancer progression by facilitating epithelial-to-mesenchymal transition, a process that enhances cancer metastasis (Regnier et al., 2019). The conflicting findings regarding SPLs in liver disease may be attributed, in part, to differences in experimental conditions and models, as different responses have been observed between wild-type and transgenic mouse strains. Modulating the levels of Cers and S1P may provide a balanced approach to support liver repair and regeneration while mitigating fibrosis and oncogenesis (Nojima et al., 2024).

The effects of SPLs and MFGM on the advanced stages of liver disease, such as Nonalcoholic Steatohepatitis (NASH), beyond NAFLD remain largely unexplored. However, findings from liver injury animal models suggest that MFGM may offer potential hepaprotective benefits. Dietary MFGM has been shown to inhibit liver injury in a short-bowel syndrome-associated liver injury rat model by suppressing autophagy and NLRP3 inflammasome activation (Yu et al., 2022). Additionally, MFGM supplementation exerted protective effects against DSS-induced colitis and secondary liver injury by reducing oxidative stress in the liver (Wu et al., 2022). Since NLRP3 inflammasome activation and oxidative stress are recognized as key drivers of NASH progression and other liver damage (Mridha et al., 2017; Rolo et al., 2012), MFGM may have a potential therapeutic role in NASH management. However, the impact of autophagy on NASH remains complex, as it may play either a protective or aggravating role in disease progression (Cui et al., 2024; Yu et al., 2022). Therefore, further research is needed to elucidate the precise effects of MFGM on NASH.

Regulatory effects of SPL and MFGM on insulin resistance

Increased endogenous Cers have been implicated in insulin resistance in peripheral tissues, including adipose tissue and muscle (Bandet et al., 2019). Cer is present in the plasma membrane in the form of microdomains and influences permeability and apoptosis (Colombini, 2010). C2-Cer has been shown to induce insulin resistance by reducing Akt phosphorylation, a key step in glucose uptake (Hassan et al., 2016). Clinical studies further support this link as elevated Cer levels in muscle have been associated with increased insulin resistance and a higher incidence of type II diabetes (Adams et al., 2004; Perreault et al., 2018).

Cer levels are regulated by de novo synthesis and the salvage pathway, which involves SMase. Inhibition of serine palmitoyl transferase (SPT), the rate-limiting enzyme in de novo Cer synthesis, by intraperitoneal injection of myriocin (SPT inhibitor) significantly alleviated high-fat diet-induced insulin resistance in Wister rats (Blachnio-Zabielska et al., 2016). Similarly, inhibition of the SMase-mediated Cer salvage pathway significantly reduced palmitate-mediated lipotoxicity and insulin resistance in C2C12 myotubes (Verma et al., 2014). Furthermore, the degradation of Cer to S1P improved insulin resistance and β-cell dysfunction (Bellini et al., 2015). These findings suggest that modulating SPL metabolism, particularly Cer generation and the balance between Cer and S1P, may provide a therapeutic option for treating type II diabetes.

Oral administration of phytosphingosine (PS), the major SPL in yeast, improved high-fat diet-induced insulin resistance in mice, and this effect was mediated by stimulating PPARγ (Murakami et al., 2013). In a clinical study, dietary PS administration (1 g/day, 4 weeks) lowered plasma cholesterol levels and improved insulin sensitivity in men with metabolic syndrome (Snel et al., 2010). Although the sample size was relatively small (12 men), the study demonstrated that dietary PS, even over a short duration, has a positive effect on plasma glucose management. These results indicate that the effects of SPLs on insulin resistance may depend on the specific type of SPL.

Milk SM supplementation significantly inhibited lipid absorption in the gut and reduced total fatty acid accumulation in the liver of obese/diabetic KK-Ay mice (Yamauchi et al., 2016). In their study, wild type mice did not show a significant difference in lipid metabolism, suggesting that the primary mechanism underlying the observed metabolic benefits was the milk SM-mediated reduction in intestinal lipid absorption. Additionally, dietary supplementation with sea cucumber-derived GCs and Cer improved hepatic carbohydrate metabolism and reduced inflammation in Sprague–Dawley rats fed a high-fructose diet. These GCs and Cer stimulated the IRS/PI3K/Akt signaling pathway, an insulin-dependent glucose uptake pathway, thereby alleviating insulin resistance (Yang et al., 2021). These findings suggest that dietary SPL may affect insulin resistance that differs from endogenous SPLs. The influence of SPL source on insulin resistance warrants further investigation.

Regulatory effects of SPL and MFGM on atherosclerosis

SPLs are closely associated with lipoproteins and elevated plasma SM levels have been linked to an increased risk of atherosclerosis (Iqbal et al., 2017). The conversion of SM to Cer promotes atherosclerotic plaque inflammation and acts as a metabolic switch that contributes to CVD (Edsfeldt et al., 2016). Consequently, various enzymes that regulate Cer production are implicated in the development of hypertension, obesity, diabetes, and CVD (Choi et al., 2021).

Recent studies suggest that SPL metabolites, including Cer, dihydroCer, glucosylCer, lactosylCer, SM, and S1P, can exert protective or detrimental effects on endothelial cells and atherosclerosis, depending on their specific structure and metabolic context (Lai et al., 2022; Peters et al., 2022). Hammerschmidt and Bruning (2022) reported that variations in Cer acyl chain length result in different physiological outcomes by altering biophysical properties of membrane structure and protein-Cer interactions that affect cell signaling. Additionally, an inverse relationship has been observed between the cellular cholesterol level and the synthesis of very-long-chain acyl SPLs (Kim et al., 2023). Evidence suggests that detrimental cardiometabolic effects of Cer are primarily driven by alterations in Cer acyl chain composition rather than total Cer levels (Peterson et al., 2018; Tarasov et al., 2014).

Daily consumption of MPL-enriched cream cheese has been shown to improve CVD risk factors by reducing serum atherogenic SM and Cer species in postmenopausal women (Michalski et al., 2021). This finding suggests that the nutritional effects of dietary SPL consumption are dependent on the molecular structure, including the type of polar head group and the chain length/desaturation of fatty acids. MPL and their metabolites, such as SM and Cer, were reported to reduce cholesterol absorption in postmenopausal women, likely through mechanisms involving decreased chylomicron and cholesterol absorption. Moreover, MPL administration did not alter gut microbiota composition and short-chain fatty acid production (Vors et al., 2020). Their study suggests that milk SM and its metabolites may help to reduce the risk of metabolic diseases by modifying the serum SM and Cer species. Piccoli et al. (2023) proposed that the plasma Cer/S1P ratio may serve as a more critical biomarker for assessing atherosclerosis risk than the traditional LDL/HDL ratio.

The Cer/S1P ratio is influenced by dietary fat composition. Reducing saturated fat intake while increasing polyunsaturated fats intake promotes Cer degradation and increased S1P synthesis in Wister rats. A lower Cer/S1P ratio reduces hepatocyte sensitivity to inflammation (Zabielski et al., 2010). Additionally, Mediterranean diet-rich in monounsaturated fatty acids has been associated with a decreased risk of CVD by lowering plasma Cer level (Estruch et al., 2018).

Effect of dietary SPLs and MFGM on muscle function

Regulatory effects of SPLs on muscle health

Cer and S1P are two dominant SPL metabolites and exert opposite effects on myogenesis, intercellular oxidation, cell survival, insulin signaling, and muscle protein synthesis (Nikolova-Karakashian and Reid, 2011). Cers have detrimental effects on insulin sensitivity and inhibit myogenic differentiation in muscle cells (Meadows et al., 2000). Cicilicot and Schiaffino (2010) reported that S1P contributes to muscle regeneration by promoting the myogenesis of satellite cells and upregulating myogenic factor 5 (Myf5)—a key myogenic marker—through the activation of S1PR-1 (Fig. 5(A)). S1P also facilitates recovery from myotoxic injuries, such as those induced by intramuscular bupivacaine injection, by binding to GTP-binding protein-coupled S1PRs, which are essential for muscle regeneration and atrophy prevention (Danieli-Betto et al., 2010; Tan-Chen et al., 2020). Pharmacological approaches targeting S1P metabolism, including the use of 2-acetyl-5-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, improved muscular dystrophy by reducing muscle fibrosis and fat deposition (Leronimakis et al., 2013). Moreover, research indicates that SK1, which regulates S1P production, is downregulated in C2C12 myotubes following dexamethasone exposure, suggesting its vital role in maintaining muscle health (Pierucci et al., 2018).

Fig. 5.

Metabolic fate of SPLs in muscle (A), and effects of MGFM supplementation on neuromuscular junction and muscle type shift (B). C1P ceramide-1-phosphate, PI3K phosphoinositide 3-kinase, Akt protein kinase B, mTOR mammalian target of rapamycin, Myf5 myogenic factor 5, MyoG myogenin, MyoD myogenic differentiation 1, Cer ceramide, SK sphingosine kinase, S1P sphingosine-1-phosphate, S1PR sphingosine-1-phosphate receptor. SPLs sphingolipids, MFGM milk fat globule membrane, AChR acetylcholine receptor, Dock-7 dedicator of cytokinesis 7, MuSK muscle-specific kinase

The balance between S1P and Cers, known as the "Ceramide/S1P rheostat," is a critical determinant of muscle health and regeneration (Tan-Chen et al., 2020). For instance, tumor necrosis factor-alpha (TNF-α)-induced Cers, particularly C2-Cer, inhibit differentiation in C2C12 muscle cells and reduce the expression of key myogenic markers, such as myogenin (MyoG) and myogenic differentiation factor 1 (MyoD) (Strle et al., 2004). In contrast, ceramide 1-phosphate (C1P) promotes myoblast proliferation by activating the PI3K/Akt/mTOR signaling pathway, reflecting the complex role of SPLs in muscle biology (Bernacchioni et al., 2018; Gangoiti et al., 2012). Although the exact molecular mechanisms remain to be fully understood, phosphorylated SPLs, such as S1P and C1P, generally stimulate myogenesis and muscle regeneration, and unphosphorylated forms, like Cers, tend to have inhibitory effects. Understanding these pathways will provide valuable insights into potential therapeutic strategies for treating muscle-related dysfunctions.

Regulatory effects of MFGM on physical performance

MFGM is a biological membrane that surrounds fat droplets in milk, forming a protective barrier. It is composed of a unique combination of proteins, lipids, and glycoproteins. The MFGM has gained much interest as a potential nutraceutical, due to its high PL, SPLs, and protein contents (Raza et al., 2021). Dietary supplementation of MFGM in combination with habitual exercise, mitigated age-associated muscle mass loss in senescence-accelerated mice (Haramizu et al., 2014). In their in vitro study, mechanical stretching of C2C12 myotubes, which mimicked the adaptive response of skeletal muscle, did not improve muscle differentiation alone. However, treatment with MFGM, its SPL fraction or purified SM treatment with mechanical stretching significantly promoted the expression of MyoG, muscle associated receptor tyrosine kinase (MuSK), and docking protein 7 (Dock-7), which are key markers of synapse formation (Fig. 5). These findings suggest that the combined effect of exercise and MFGM/SPL supplementation enhances muscle function through neuromuscular development.

In addition, physical exercise may stimulate SPL metabolism, and increase S1P production, which is known to stimulate neuromuscular signaling in motor units (Brailoiu et al., 2002). Neuromuscular development relies on the integrity and plasticity at the neuromuscular junction (NMJ) (Lyer et al., 2021), a critical structure that enables motor neurons to transmit signals ensuring proper muscle contraction (Hughes et al., 2005). Thus, muscle strength is influenced by factors such as the number and size of muscle fibers, NMJ integrity, and neural activation. Physical exercise strengthens the NMJ and promotes recovery from nerve damage (Nishimune et al., 2014). Yano et al. (2017) demonstrated that MFGM supplementation combined with voluntary running exercise attenuated age-related motor dysfunction by suppressing NMJ abnormalities in mice. They found that MFGM intake upregulated the expression of agrin (AGRN). This protein plays a crucial role in NMJ maintenance and has a negative correlation with age-related NMJ degradation in skeletal muscle. Aging is associated with decreased AGRN secretion from motor neurons, leading to weakened acetylcholine receptor (AChR) clustering and NMJ destabilization (Bao et al., 2020).

Dietary supplementation with MFGM or MPLs to growing rats (from 7 days after birth to 70 days) significantly increased the number and concentration of fast twitch Type IIa muscle fibers (Markworth et al., 2017). Fast-twitch fibers are preferentially lost during aging, contributing to sarcopenia (Thompson, 2009). This shift from slow- to fast-twitch muscle fibers was associated with the upregulation of genes involved in myogenesis, muscle fiber type specialization, and neuromuscular development (Markworth et al., 2017). Based on this study, MFGM or its lipid components (SM, glycerophospholipids, and GAs) play a role in neuromuscular development.

The combined effects of MFGM and exercise on physical performance have been investigated in clinical studies. In a randomized controlled trial of middle-aged adults (men: 22, women 22), daily MFGM intake (1 g/day) combined with biweekly exercise significantly improved physical performance parameters, including sidestep score and muscle cross-sectional area, compared to the placebo group (Ota et al., 2015). In another study focusing on older individuals, either exercise or MFGM supplementation (1 g/day) improved walking speed and foot progression angle in Japanese women over 79 with impaired walking ability. However, no synergistic effect was observed between exercise and MFGM supplementation (Kim et al., 2019).

In addition, a study involving healthy adults over 60 years old (10 men and 12 women) examined the effect of MFGM supplementation (1 g/day) combined with low- intensity and light exercise (Minegishi et al., 2017). After 10 weeks, MFGM supplementation alone improved muscle function and strength, whereas no significant improvement was observed in the placebo group. These results suggest that dietary MFGM supplementation, even with minimal physical activity, may offer a practical approach for individuals who have difficulty engaging in regular exercise.

In conclusion, dietary SPLs, such as MFGM, have shown potential benefits for cardiometabolic health by reducing intestinal lipid absorption and improving hepatic lipid profiles. Recent scientific evidence suggests that the effects of dietary SPLs on insulin resistance and atherosclerosis are primarily determined by the balance of key SPL metabolites, the Cer/S1P ratio, rather than the total plasma Cer levels. Variations in SPL sources, specific molecular structure, acyl chain length, and phosphorylation type may lead to different effects on cardiometabolic health. Since SPL and MFGM metabolites can interact with gut microbiome, influencing lipid absorption, inflammation, and metabolic function, long-term clinical trials are essential to evaluate their role in gut-liver axis, a key regulator in metabolic diseases.

Although several clinical trials have demonstrated the potential benefits of MFGM for physical performance, the underlying molecular mechanisms remain unclear. Further studies are needed to identify specific bioactive components, determine optimal dosage, and evaluate the long-term efficacy of MFGM supplementation in promoting muscle health and neuromuscular function. In addition, personalized nutrition approaches incorporating multi-omics technologies could help optimize the benefits of SPL/MFGM supplementation, enabling tailored dietary strategies for individual metabolic responses.

Funding

This research was funded by the Ministry of Science, ICT and Future Planning (2020R1A2C1011548).

Declarations

Conflict of interest

The authors declare no conflicts of interest.