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 Tisochrysis lutea F&M-M36 (T. lutea) 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% T. lutea (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. T. lutea 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 Anaerotruncus, Marvinbryantia, and Eubacterium coprostanoligenes, while the HF group was linked to Clostridium sensu stricto 1 and Terrisporobacter. Positive correlations between HFTiso-associated taxa and adiponectin levels were consistent with microbiota-associated metabolic signatures. In parallel, T. lutea 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 T. lutea 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 T. lutea 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 T. lutea 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 T. lutea-derived interventions.