3′-Sialyllactose curbs atherosclerosis via gut-immune-cardiovascular axis in mice

A sugar found in human breast milk may hold the key to preventing one of the world’s leading causes of death, according to a new preclinical study published in Food Science & Nutrition. Researchers report that 3′-sialyllactose (3′-SL), a sialylated oligosaccharide abundant in human milk, significantly reduced atherosclerotic plaque formation in mice fed a high-cholesterol diet—and that the protection appears to travel along an unexpected route: from the gut, through the immune system, and into the blood vessels themselves.

Atherosclerosis, the gradual buildup of cholesterol-laden plaques inside artery walls, has long been understood as a disease of lipids. But cardiologists increasingly recognize chronic inflammation as its silent engine. Inflammatory markers predict cardiovascular risk independently of LDL cholesterol levels, and landmark trials of anti-inflammatory drugs have shown that taming the immune response can reduce cardiac events even when cholesterol is already controlled. The new study taps directly into this shift, asking whether a dietary compound could achieve what drugs have only partially delivered: suppressing the chronic, low-grade inflammation that drives plaque development before it starts.

The research team, led by scientists affiliated with Xiamen University, turned to low-density lipoprotein receptor knockout (LDLR−/−) mice, a classic model of human atherosclerosis in which the absence of the LDL receptor causes rapid accumulation of plasma LDL cholesterol and accelerated deposition in the arterial wall. Forty male mice, seven weeks old at arrival, were randomized into five groups after a week of adaptive feeding. Eight animals received a normal diet, while the remaining thirty-two were placed on a high-cholesterol diet containing just over 20% fat and 1.25% cholesterol. Three of these groups also received daily oral doses of 3′-SL at 40.5, 81.0, or 162.0 milligrams per kilogram of body weight, a range selected by allometric scaling from an established effective dose of free sialic acid and well below the compound’s reported no-observed-adverse-effect level of more than 2,000 milligrams per kilogram per day. The intervention continued for twelve weeks.

The results were striking and dose-dependent. Mice receiving 3′-SL showed significantly reduced lipid deposition in the aorta, visualized by Oil Red O staining of the full length of the vessel from the ascending arch to the iliac bifurcation. Blood chemistry told a parallel story: triglycerides fell in all intervention groups, LDL cholesterol declined in a clear dose–response relationship, and HDL—the “good” cholesterol—rose significantly. In the highest-dose group, total cholesterol also dropped. Meanwhile, oral glucose tolerance improved across the treatment groups, suggesting the compound’s benefits extended beyond lipid handling alone.

The inflammatory signature changed just as dramatically. High-cholesterol feeding elevated serum levels of pro-inflammatory cytokines including interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α). Supplementation with 3′-SL reversed this pattern, significantly lowering IL-6 and IL-1β across intervention groups, reducing TNF-α at medium and high doses, and boosting the anti-inflammatory cytokine IL-10. Because IL-6 and IL-1β are independently associated with elevated cardiovascular risk in human studies, this cytokine shift represents a potentially meaningful cardioprotective change, not merely a biochemical curiosity.

To understand how a milk sugar could accomplish all this, the investigators deployed a multi-omics arsenal: 16S rDNA sequencing of colon contents to map the gut microbiota, RNA sequencing of colonic tissue to capture transcriptional changes, and ultra-high-performance liquid chromatography–tandem mass spectrometry to profile the colonic metabolome. Using the medium-dose group as the representative cohort for mechanistic analysis, they found that 3′-SL substantially reshaped the microbial ecosystem. The abundance of Firmicutes—a phylum that expanded under the high-cholesterol diet—fell, while Verrucomicrobiota and Bacteroidetes rose, correcting the Firmicutes-to-Bacteroidetes ratio that has been repeatedly linked to obesity, metabolic disease, and atherosclerosis. At the genus level, the beneficial microbe Akkermansia expanded notably.

Akkermansia muciniphila has earned a reputation as an “intestinal guardian” in the microbiome literature. It feeds on the mucus layer lining the gut, stimulates the expression of tight junction proteins such as Occludin and Claudin-1, and releases outer membrane vesicles that reinforce the epithelial barrier. A sturdier barrier means fewer microbial endotoxins leaking into the bloodstream—an important source of the systemic inflammation that stokes arterial damage. Akkermansia also promotes short-chain fatty acid production, which dampens inflammatory signaling through G protein-coupled receptors on macrophages and intestinal epithelial cells, inhibiting the NF-κB pathway and reducing IL-6 secretion. Consistent with these mechanisms, the researchers observed that microbial correlations with serum IL-1β weakened after intervention while correlations with anti-inflammatory IL-10 strengthened, and the gut microbial structure of treated mice shifted toward that of the normal-diet controls.

The transcriptomic and metabolomic data added a deeper layer of mechanistic detail. Colonic tissue from treated mice showed differential expression of genes involved in immune regulation and lipid metabolism, including Ccl2, Il2ra, Kng1, and the complement component gene C6. Differential metabolites—ranging from lipid species to vitamin D derivatives and amino acid compounds—showed significant correlations with these immune- and cardiovascular-related genes. Among the findings, one molecule stands out as the linchpin of the study: Ccl2, better known as monocyte chemoattractant protein-1 (MCP-1). This chemokine recruits monocytes and macrophages into the subendothelial space of artery walls, the critical initiating step in foam cell formation and plaque development. The researchers found that 3′-SL suppressed Ccl2 expression, suggesting that gut-derived, anti-inflammatory metabolites entering the circulation may directly throttle the recruitment of inflammatory cells into the vasculature. Changes in Kng1 hint at additional benefits through the kinin system—potentially improving vascular tone and endothelial function—while effects on C6 suggest reduced complement-mediated damage to the endothelium via the membrane attack complex.

Taken together, the data sketch a coherent causal chain the authors call the “gut-immune-cardiovascular axis.” A high-cholesterol diet disrupts the gut microbiome, weakening the intestinal barrier and activating mucosal immune cells that seed systemic inflammation. 3′-SL, arriving intact in the colon after passing through the small intestine, feeds beneficial bacteria, restores microbial balance, strengthens the barrier, and recalibrates the metabolite pool. Those metabolites and immune signals then converge on the vascular wall, where reduced MCP-1 expression means fewer monocytes infiltrating the artery lining and fewer plaques taking root. The study’s integrated pathway analysis showed that the top enriched KEGG pathways among differential genes and metabolites involved immune regulation, inflammatory response, energy metabolism, lipid metabolism, and hormone synthesis—all processes implicated in the transition from metabolic stress to arterial disease.

The findings arrive amid growing enthusiasm for human milk oligosaccharides as functional food ingredients. 3′-SL is already recognized as safe by the U.S. FDA and approved as a novel food in the European Union, and a clinical trial in dyspeptic patients with Helicobacter pylori infection found doses up to 20 grams per day for four weeks to be well tolerated. Previous work has suggested the sugar can promote the growth of anti-inflammatory bacteria such as Faecalibacterium prausnitzii and Blautia in fecal communities from pediatric Crohn’s disease patients, and that it synergizes with Bifidobacterium infantis to alleviate intestinal inflammation through cross-feeding mechanisms that generate short-chain fatty acids. The current study extends this portfolio into cardiovascular territory, providing what the authors describe as robust preclinical evidence for gut-microbiota-targeted nutritional intervention against atherosclerosis.

Still, the researchers are careful about the limits of their work. The experiment used only male mice, leaving open whether hormonal cycles in females might alter the response, since estrogen and progesterone influence lipid metabolism, inflammation, and microbiome composition. The multi-omics analysis revealed correlations, not proven causation; future experiments such as fecal microbiota transplantation would be needed to establish that the reshaped microbiome itself drives the cardioprotection. Dosing also remains unresolved for humans—the mouse doses used translate to roughly 6.5 to 26 grams per day for a 60-kilogram adult by allometric scaling, and no clinical trials have yet tested 3′-SL for cardiovascular prevention. Patients with inflammatory bowel disease, whose permeable and inflamed guts may respond differently, warrant particular caution and dedicated trials before supplementation could be recommended.

Even with those caveats, the study marks a compelling proof of concept: a molecule designed by evolution to nourish infant guts may also defend adult arteries. As the global burden of atherosclerotic cardiovascular disease continues to climb, and as statins leave a residual inflammatory risk untouched in millions of patients, the idea that a prebiotic sugar could intercept the disease at its immunological source—via the gut—is precisely the kind of accessible, food-based strategy that prevention medicine has been searching for. The next step, translating the gut-immune-cardiovascular axis from mouse models to human trials, will determine whether breast milk’s lesser-known sugar becomes a genuine weapon against heart disease.