The metabolic syndrome (MetS) is a chronic disorder of glucose and lipid metabolism, including abdominal obesity, hyperglycemia, hypercholesterolemia and hyperlipidemias [1]. With changes in lifestyle and diet, MetS has emerged as a worldwide issue in public health [2]. Approximately, 25% of the global populace is afflicted with MetS [3]. Obesity is considered to be a key factor in MetS [4], it stimulates the attraction of macrophages to adipose tissue and plays an important role in the course of metabolic abnormalities and diseases associated with obesity in these patients [5, 6]. Current therapies (e.g., lifestyle interventions and anti-obesity drugs) face limitations due to side effects, necessitating safer alternatives.

Modern dietary shifts, particularly increased intake of high-purine foods, alcohol, and fructose-sweetened beverages, elevate serum uric acid (UA) levels, driving hyperuricemia, a condition linked to cardiometabolic disorders (e.g., hypertension, obesity-related complications, insulin resistance) [7, 8, 9] and multi-organ damage including chronic kidney disease [9]. Although not included in World Health Organization (WHO) MetS criteria, hyperuricemia serves as a clinical marker of MetS [10]. In MetS patients, systemic inflammation and renal microcirculation dysfunction exacerbate renal impairment, evidenced by declining glomerular filtration, albuminuria, and accelerated progression to end-stage disease. Mechanistically, fructose metabolism depletes hepatic ATP via fructokinase activation, promoting purine catabolism and UA overproduction, thereby sustaining hyperuricemia [11].

Lactiplantibacillus plantarum (formerly known as Lactobacillus plantarum) YDJ-03 (YDJ-03) is derived from kimchi, and is highly adaptable in high salt, acidic and low temperature environments, secreting natural antibiotics—bacteriocins, which can hinder the proliferation of detrimental microorganisms. This strain also has good intestinal cell adhesion, which helps it to colonise the intestines and maintain the balance of intestinal microorganisms, as well as synthesizing an array of digestive enzymes, facilitating improved nutrient uptake from dietary sources [12, 13, 14]. Limosilactobacillus fermentum (formerly known as Lactobacillus fermentum) YDJ-6 (YDJ-6) originates from the healthy human intestinal tract and is a common intestinal probiotic with good acid and bile salt resistance, capable of surviving in the environment of gastric acid and bile. It can generate a range of beneficial metabolites, such as organic acids, vitamins and antioxidants, which can improve the intestinal environment, strengthen the functionality of the intestinal barrier, thereby impeding the entry of detrimental substances and pathogens [15].

Although there are a wide variety of probiotics used in the food industry, the functions of most probiotic products lack sufficient scientific support. Consequently, this study investigated the effects of orally administered probiotics YDJ-03 and YDJ-6 in mice with MetS to determine a scientific rationale for the clinical application of probiotic products.

Compared to prior probiotic studies using a disease model which predominantly focused on a single metabolic abnormality, such as obesity and diabetes, we used a combination of chronic metabolic disorders and acute hyperuricemia to establish a dual metabolic stress model in mice, which more closely resembles the development of MetS in humans, where chronic metabolic disorders are coupled with an acute causative factor. We also conducted combined histopathological evaluation of both the liver and kidneys, revealing the systemic damage inherent to MetS. We validated and compared the differential therapeutic effects of two ecologically distinct probiotics in this composite model. By elucidating niche-specific regulatory mechanisms, our findings provide direct evidence for precise strain functional profiling and personalized clinical applications targeting multifactorial metabolic dyshomeostasis.

Over the past two decades, study has shown that the intestinal microbiota is a significant factor in the onset of obesity and associated metabolic disorders [22]. It has been demonstrated that supplementation with the probiotics Lactobacillus and Bifidobacterium improves anthropometric parameters in mice and rats fed high fat diet (HFD) [23, 24]. For instance, the provision of Lactobacillus plantarum K21 notably decreased the accumulation of epididymal fat and liver mass in mice that were on a 8-week high-fat diet [25]. Among probiotics, the Lactobacillus species and Bifidobacterium species play an important role in the management of MetS, by regulating body weight gain, improving glycemic and lipid metabolism, and demonstrate significant anti-obesity properties in human study, while also lowering insulin resistance [26]. The favorable impacts of these probiotics may be attributed to various mechanisms, such as enhanced synthesis of short-chain fatty acids, alteration of bile acid metabolism, safeguarding the host against metabolic endotoxemia, and the orchestration of the composition of the intestinal microbiota [27]. The number of studies on Lactobacillus plantarum with probiotic health benefits is increasing. In accordance with the change in the international taxonomic status of the strains, Lactobacillus plantarum and Lactobacillus fermentum were renamed in 2022 as Lactiplantibacillus plantarum and Limosilactobacillus fermentum.

This study focuses on the role of Lactiplantibacillus plantarum YDJ-03 and Limosilactobacillus fermentum YDJ-6 in the HFFC diet-induced MetS model in mice. A high-fructose diet leads to elevated fasting blood glucose levels, which are considered to be a key marker in the diagnosis of MetS [28]. Probiotics reduce HFD-induced hyperglycemia, which is consistent with prior research indicating a decrease in blood glucose levels in rats fed a high-fructose diet following an 8-week period of oral treatment with probiotic dahi enriched with Lactobacillus acidophilus and Lactobacillus casei [29]. However, in our experiments we observed no marked decrease in body weight and blood glucose in mice consuming YDJ-03 and YDJ-6 for 28 days compared to HFFC diet-fed mice. One possible reason for this is our probiotics intervention of 28 days was too short compared to the 8 weeks of probiotic intervention in their study. In addition, hypertriglyceridemia is a key component of MetS and is closely related to insulin resistance [30]. Therefore, we examined the impact of YDJ-03 and YDJ-6 on hyperlipidemia and hypercholesterolemia, and found that the probiotic preparations reduced serum TC levels, but not significantly, while YDJ-6 significantly down-regulated serum TG, and fasting LDL-C levels, another MetS factor. This is consistent with study reporting that the combined use of Lactobacillus plantarum KY1032 and Lactobacillus curvatus HY7601 reduces triglyceride levels and LDL levels in a high-fat diet-induced hypertriglyceridemia rat model [31]. This suggests that a longer treatment period with probiotics might be required to have a significant effect on hyperglycemia and obesity.

Hepatic biomarkers of liver function, specifically ALT and AST, were also evaluated. Animals that received probiotic supplementation exhibited marked reductions in liver function markers, suggesting a reduction in liver damage and a return to normal liver function [32]. Consistent with previous study [33], supplementation with YDJ-03 and YDJ-6 both reduced hepatic ALT and AST levels in HFFC diet-fed mice, along with reduced hepatocellular fat deposition and globular degeneration with YDJ-6.

In individuals with MetS, there is often an increase in oxidative stress and inflammation, which can lead to lipid peroxidation in the liver [8]. Increasing evidence indicates that oxidative stress acts as a catalyst triggering a low-grade inflammatory reaction, which plays an important role in the onset of obesity and MetS [34, 35]. MDA, a key indicator of oxidative stress, represents the terminal byproduct of free radical-induced lipid peroxidation. In contrast, the antioxidant enzymes SOD and GSH function to neutralize superoxide radicals and eliminate reactive oxygen species. The ptgs2 gene has been associated with the pathogenesis of steatosis and MetS [36]. Study has shown that increased expression of Ptgs2 gene in the liver is linked to inflammation and oxidative stress, which are crucial elements in the progression of fatty livers [37]. In contrast, F4/80 is a cell surface glycoprotein that is commonly used as a marker for macrophages, such as kupffer cells in the liver. In conditions such as MetS, the upregulation of Adgre1 (F4/80 gene) in the liver may suggest immune cell infiltration [38]. Animals administered with probiotics exhibit elevated antioxidant levels and reduced oxidative agents, which may suppress the generation of reactive oxygen species, including peroxyl radicals, superoxide anions, and hydroxyl radicals, thus diminishing inflammatory responses [39]. Therefore, we measured hepatic MDA and SOD, as well as Ptgs2 gene expression and found that oral administration of both YDJ-03 and YDJ-6 significantly decreased hepatic MDA levels and Ptgs2 expression and slightly increased SOD levels, suggesting an improvement in hepatic oxidative stress. This data suggests that inhibition of Ptgs2 and Adgre1 by YDJ-03 and YDJ-6 might be one of the mechanisms to reduce hepatic inflammation and attenuate liver damage in the HFFC diet-induced MetS model.

The preservation of a standard serum uric acid level is crucial in clinical practice, since it not only averts hyperuricemia and gout but also serves as a preventive measure against the onset of type 2 diabetes, as well as renal, cerebrovascular, and cardiovascular pathologies [40, 41]. The HFFC diet also mimics the high fructose diet structure of humans. Serum UA levels in mice fed the HFFC diet for 90 days were approximately 3-fold higher than those in mice fed the regular diet. Our results showed that supplementation with YDJ-03 and YDJ-6 effectively reduced serum uric acid levels in MetS mice, especially by YDJ-03. We also evaluated the protective effects of YDJ-03 and YDJ-6 on the functional integrity of the kidneys, since MetS and hyperuricemia may affect kidney function through common physiological and metabolic pathways, such as persistent inflammation, oxidative stress, and endothelial dysfunction. The results showed that YDJ-03 significantly reduced renal inflammatory cell infiltration as well as the expression level of the immune cell infiltration-related gene Adgre1 in HFFC diet-fed mice and restored the structural integrity of renal tubular cells, in addition to a marked decrease in the concentrations of serum CREA and UA, both of which are biomarkers of renal function. This demonstrated that YDJ-03 had a significant nephroprotective effect in HFFC diet-induced MetS mice.

A study reported that oral intake of the probiotic strain Bifidobacterium longum 51A (BL) mitigated inflammation triggered by monosodium urate crystals (MSU) in a murine model of gout [42]. We examined the expression levels of genes associated with the activated renal TLR2/NF-$\kappa$B signaling pathway. The RT-qPCR results showed that YDJ-03 and YDJ-6 suppressed the activation of this pathway, and that YDJ-03 significantly down-regulated the expression levels of Tlr2, Traf6, and Nfkb1 genes. This suggests that YDJ-03 may exert anti-inflammatory properties by modulating the TLR2-mediated NF-$\kappa$B signaling pathway.

In this study we combined a HFFC diet with intraperitoneal hypoxanthine injections to induce both MetS and acute hyperuricemia. This dual metabolic stress model effectively simulates the interplay between chronic metabolic dysfunction and acute triggers observed in human disease progression, thereby enhancing its translational relevance. Furthermore, we systematically compared the organ-specific protective effects of two functionally distinct probiotics. Notably, YDJ-03 exhibited superior renoprotective efficacy, while YDJ-6 showed stronger hepatoprotective activity, suggesting strain- and tissue-specific therapeutic potentials. However, several limitations should be acknowledged in this study. First, additional studies are necessary to elucidate the precise mechanism of action behind these observed effects. Second, extended study periods are necessary to evaluate whether probiotic effects on metabolic markers are sustained and can be translatable to chronic human disease management. Third, it is also necessary to investigate the impact of probiotics on daily blood pressure in mice with MetS.

In this study, an animal model of concurrent hyperuricemia, hyperlipidemia and hyperglycemia was successfully established by combining an HFFC fed diet and intraperitoneal injection of hypoxanthine. The model innovatively linked high uric acid levels to MetS simulating elevated uric acid level and liver and kidney damage in MetS patients. The results of this study demonstrate the promising capabilities of the two bacilli from the Lactobacillaceae family, YDJ-03 and YDJ-6, in modulating key metabolic parameters in MetS as well as hyperuricemia. Both YDJ-03 and YDJ-6 alleviated the development of MetS and hyperuricaemia. YDJ-03 was more advantageous in kidney protection, while YDJ-6 was more capable of protecting the liver. Taken together, this study provides solid evidence for the potential of probiotics as a biotherapeutic approach to modulate MetS.

MetS, metabolic syndrome; HFFC, high-fat, high-fructose, high-cholesterol; TG, triglycerides; TC, total cholesterol; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; GLU, glucose; AST, aspartate aminotransferase; ALT, alanine aminotransferase; UA, uric acid; CREA, creatinine.

All core datasets supporting the findings of the study have been presented in the text as tables and figures.

JH designed the study. SC, MS, XC and QL conducted the research and investigation process. SC analyzed the data and drafted the manuscript. JH revised the manuscript. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

All animals received humane care according to Guide for the Care and Use of Laboratory Animals (National Research Council, USA). The protocols were approved by the Institutional Committee on the Care and Use of Animals of the Third Institute of Oceanography, Ministry of Natural Resources (TIO-IACUC-04-2022-03-01).

This research was funded by the Scientific Research Foundation of Third Institute of Oceanography, Ministry of Natural Resources, grant number 2023009; Xiamen Natural Science Foundation, grant number 3502Z20227247.

The authors declare no conflict of interest.