Marine Microalga Tisochrysis lutea F&M-M36 Modulates Gut Microbiota and Intestinal Cholesterol Transport Gene Expression in Association with Selected Early-Stage Metabolic Alterations Under High-Fat Feeding

Modulation of the gut microbiota represents a promising approach to counteract diet-induced metabolic alterations, with microalgae emerging as potential interventions. Building on our previous in vivo evidence that dietary supplementation with the marine microalga <i>Tisochrysis lutea</i> F&M-M36 (<i>T. lutea</i>) positively modulates selected metabolic alterations under high-fat feeding, the present study aimed to identify potential associations between these metabolic changes and coordinated modifications of the gut microbiota. Animals were fed normal-fat (NF), high-fat (HF), or HF supplemented with 5% <i>T. lutea</i> (HFTiso) diets for three months. Gut microbial profiles were analyzed by 16S rRNA sequencing and correlated with plasma lipids, glucose, blood pressure, fecal lipid excretion, and adiponectin levels. <i>T. lutea</i> supplementation was associated with significant modulation of selected metabolic parameters and coherent alterations in gut microbial communities. Multivariate analyses revealed treatment-dependent clustering of metabolic profiles, with HFTiso forming an intermediate group between HF and NF diets. Beta-diversity analyses showed marked treatment-specific shifts, while alpha-diversity remained stable. Linear discriminant analysis identified 31 discriminative genera, with the HFTiso group enriched in taxa associated with fermentative metabolism and lipid-related metabolic pathways including <i>Anaerotruncus</i>, <i>Marvinbryantia</i>, and <i>Eubacterium coprostanoligenes</i>, while the HF group was linked to <i>Clostridium sensu stricto 1</i> and <i>Terrisporobacter</i>. Positive correlations between HFTiso-associated taxa and adiponectin levels were consistent with microbiota-associated metabolic signatures. In parallel, <i>T. lutea</i> supplementation was associated with downregulation of colonic Niemann-Pick C1-like 1 (NPC1L1) mRNA expression, a key mediator of intestinal cholesterol uptake. The bioactivity of <i>T. lutea</i> likely reflects its content of polyunsaturated fatty acids, oleic acid, phytosterols, and fucoxanthin; however, whether these components act synergistically or whether specific bioactive compounds are primarily responsible remains to be clarified. Together, these findings indicate that <i>T. lutea</i> supplementation is associated with coordinated changes in gut microbiota composition and transcriptional modulation of the intestinal cholesterol transporter NPC1L1 in the context of selected early-stage metabolic alterations under high-fat feeding. While direct extrapolation to humans remains limited, these results suggest potential translational relevance of <i>T. lutea</i> as a nutraceutical approach targeting early-stage metabolic dysregulation. Future studies will be required to determine the mechanistic contribution of individual bioactive components and to assess whether microbiota- and gene expression-associated changes play a causal role in mediating the observed metabolic outcomes, thereby informing the rational development of <i>T. lutea</i>-derived interventions.