Dietary d-Lactate Intake Facilitates Inflammatory Resolution by Modulating M1 Macrophage Polarization

Lactate: A New Target for Brain Disorders

Lactate in the brain is produced endogenously and exogenously. The primary functional cells that produce lactate in the brain are astrocytes. Astrocytes release lactate to act on neurons, thereby affecting neuronal function, through a process known as the astrocyte-neuron shuttle. Lactate affects microglial function as well and inhibits microglia-mediated neuroinflammation. Lactate also provides energy, acts as a signaling molecule, and promotes neurogenesis. This article summarizes the role of lactate in cells, animals, and humans. Lactate is a protective molecule against stress in healthy organisms and in the early stages of brain disorders. Thus, lactate may be a potential therapeutic target for brain disorders. Further research on the role of lactate in microglia may have great prospects. This article provides a new perspective and research direction for the study of lacate in brain disorders.

Lactate and lactylation in macrophage metabolic reprogramming: current progress and outstanding issues

It is commonly known that different macrophage phenotypes play specific roles in different pathophysiological processes. In recent years, many studies have linked the phenotypes of macrophages to their characteristics in different metabolic pathways, suggesting that macrophages can perform different functions through metabolic reprogramming. It is now gradually recognized that lactate, previously overlooked as a byproduct of glycolytic metabolism, acts as a signaling molecule in regulating multiple biological processes, including immunological responses and metabolism. Recently, lactate has been found to mediate epigenetic changes in macrophages through a newfound lactylation modification, thereby regulating their phenotypic transformation. This novel finding highlights the significant role of lactate metabolism in macrophage function. In this review, we summarize the features of relevant metabolic reprogramming in macrophages and the role of lactate metabolism therein. We also review the progress of research on the regulation of macrophage metabolic reprogramming by lactylation through epigenetic mechanisms.

Yogurt Alleviates Cyclophosphamide-Induced Immunosuppression in Mice through D-Lactate

Numerous studies have investigated the immunomodulatory effects of yogurt, but the underlying mechanism remained elusive. This study aimed to elucidate the alleviating properties of yogurt on immunosuppression and proposed the underlying mechanism was related to the metabolite D-lactate. In the healthy mice, we validated the safety of daily yogurt consumption (600 μL) or D-lactate (300 mg/kg). In immunosuppressed mice induced by cyclophosphamide (CTX), we evaluated the immune regulation of yogurt and D-lactate. The result showed that yogurt restored body weight, boosted immune organ index, repaired splenic tissue, recovered the severity of delayed-type hypersensitivity reactions and increased serum cytokines (IgA, IgG, IL-6, IFN-γ). Additionally, yogurt enhanced intestinal immune function by restoring the intestinal barrier and upregulating the abundance of Bifidobacterium and Lactobacillus. Further studies showed that D-lactate alleviated immunosuppression in mice mainly by promoting cellular immunity. D-lactate recovered body weight and organ development, elevated serum cytokines (IgA, IgG, IL-6, IFN-γ), enhanced splenic lymphocyte proliferation and increased the mRNA level of T-bet in splenic lymphocyte to bolster Th1 differentiation. Finally, CTX is a chemotherapeutic drug, thus, the application of yogurt and D-lactate in the tumor-bearing mouse model was initially explored. The results showed that both yogurt (600 μL) and D-lactate (300 mg/kg) reduced cyclophosphamide-induced immunosuppression without promoting tumor growth. Overall, this study evaluated the safety, immune efficacy and applicability of yogurt and D-lactate in regulating immunosuppression. It emphasized the potential of yogurt as a functional food for immune regulation, with D-lactate playing a crucial role in its immunomodulatory effects.

Yogurt Prevents Colorectal Tumorigenesis in ApcMin/+ Mice

SCOPE

Yogurt consumption is related to a decreased risk of colorectal cancer (CRC), but whether such association is causal remains unclear. Patients with familial adenomatous polyposis (FAP) are at increased risk of CRC development. Here, the study investigates the efficacy of yogurt for intestinal polyposis chemoprevention in ApcMin/+ mice, a preclinical model for human FAP.

METHODS AND RESULTS

A 10-week yogurt supplementation (15 g kg-1) in ApcMin/+ mice significantly reduces the intestinal polyp number (6.50 ± 0.97 versus 1.80 ± 0.49; p < 0.001) compared to controls. 16S rRNA gene-based microbiota analysis suggests that yogurt supplementation may greatly modulate the gut microbiome composition, especially in the relative abundance of Lactobacillus and Bifidobacterium. Importantly, the fecal concentration of d-lactate (d-Lac, 0.39 ± 0.04 µmol g-1 versus 8.14 ± 0.62 µmol g-1; p < 0.001) is boosted by yogurt, while oral administration with d-Lac (125 or 250 mg kg-1) reduces the polyp number by 71.43% or 77.14% (p < 0.001), respectively. The study also observes that d-Lac does not affect cell viability and anchorage-independence in CRC cells, but it greatly suppresses epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced cell transformation in preneoplastic cells. Mechanistically, it demonstrates that d-Lac may attenuate epithelial cell transformation by targeting PI3K/AKT/β-catenin axis.

CONCLUSION

Yogurt protects against intestinal polyposis in ApcMin/+ mice, and d-Lac may partially account for the chemopreventive effects above.

Lactic acid induces transcriptional repression of macrophage inflammatory response via histone acetylation

Lactic acid has emerged as an important modulator of immune cell function. It can be produced by both gut microbiota and the host metabolism at homeostasis and during disease states. The production of lactic acid in the gut microenvironment is vital for tissue homeostasis. In the present study, we examined how lactic acid integrates cellular metabolism to shape the epigenome of macrophages during pro-inflammatory response. We found that lactic acid serves as a primary fuel source to promote histone H3K27 acetylation, which allows the expression of immunosuppressive gene program including Nr4a1. Consequently, macrophage pro-inflammatory function was transcriptionally repressed. Furthermore, the histone acetylation induced by lactic acid promotes a form of long-term immunosuppression ("trained immunosuppression"). Pre-exposure to lactic acid induces lipopolysaccharide tolerance. These findings thus indicate that lactic acid sensing and its effect on chromatin remodeling in macrophages represent a key homeostatic mechanism that can provide a tolerogenic tissue microenvironment.

Yogurt Alleviates Imiquimod-Induced Psoriasis by Activating the Lactate/GPR81 Signaling Axis in Mice

In addition to colorectal cancer and metabolic syndrome, regular yogurt consumption has shown promise in improving skin inflammation. In this study, we investigated the effects and possible mechanisms of yogurt on imiquimod-induced psoriasis-like inflammation in mice. After oral administration with yogurt (18 or 36 g/kg) and/or its main metabolite lactate (250 or 500 mg/kg) for 3 days, the mice were treated with a topical dose of 62.5 mg of imiquimod (IMQ) cream for seven consecutive days. Data showed that yogurt and lactate treatment significantly reduced the severity of psoriasis-like skin lesions, excessive keratinocyte proliferation, and immune cell infiltration. Mechanistically, we found that the genetic deficiency of the lactate receptor GPR81 aggravated psoriasis-like features in mice. Activation of the lactate/GPR81 axis inhibited the degradation of IκBα, prevented the nuclear translocation of histone deacetylase 3 (HDAC3) in macrophages, and thus constrained skin inflammation. Overall, these findings suggest that yogurt consumption effectively protects against experimental psoriasis and targeting the lactate/GPR81 signaling axis could be a promising approach for psoriasis inflammation management.

Versatile lactate signaling via HCAR1: a multifaceted GPCR involved in many biological processes

G-coupled protein receptors (GPCRs) are the ultimate refuge of pharmacology and medicine as more than 40% of all marketed drugs are directly targeting these receptors. Through cell surface expression, they are at the forefront of cellular communication with the outside world. Metabolites among the conveyors of this communication are becoming more prominent with the recognition of them as ligands for GPCRs. HCAR1 is a GPCR conveyor of lactate. It is a class A GPCR coupled to Gαi which reduces cellular cAMP along with the downstream Gβγ signaling. It was first found to inhibit lipolysis, and lately has been implicated in diverse cellular processes, including neural activities, angiogenesis, inflammation, vision, cardiovascular function, stem cell proliferation, and involved in promoting pathogenesis for different conditions, such as cancer. Other than signaling from the plasma membrane, HCAR1 shows nuclear localization with different location-biased activities therein. Although different functions for HCAR1 are being discovered, its cell and molecular mechanisms are yet ill understood. Here, we provide a comprehensive review on HCAR1, which covers the literature on the subject, and discusses its importance and relevance in various biological phenomena.

Yogurt Prevents Colitis-Associated Colorectal Cancer in Mice

SCOPE

Epidemiological studies indicate an inverse correlation between yogurt consumption and colorectal cancer (CRC), but whether there is a cause-and-effect relationship has not yet been validated. This study aims to investigate the effects and possible mechanisms of yogurt on colitis-associated colorectal cancer (CAC) in mice.

METHODS AND RESULTS

Experimental CAC is induced by azoxymethane (AOM, 10 mg kg-1 , ip) followed by three cycles of dextran sulfate sodium (DSS, 3%) treatment. Colitis is induced by adding DSS (3%) in drinking water for 5 days. Primary mouse macrophages are isolated for mechanistic studies. Data clearly show that yogurt (15 g kg-1 body weight) significantly reduces the multiplicity of colonic neoplasms by 38.83% in mice. Yogurt protects mice from colitis dependent on lactate receptor GPR81. The deficiency of Gpr81 exacerbates colitis and CAC in mice. Further investigation reveals that GPR81 may be dispensable for gut barrier function but essential for colonic mucosal repair. d-lactate in yogurt can activate GPR81 to suppress proinflammatory macrophage polarization, thereby facilitating inflammatory resolution after colonic injury and consequently suppressing CAC progression.

CONCLUSION

Yogurt effectively protects against colitis-associated colorectal tumorigenesis in mice, and this study provides a rationale for introducing yogurt supplementation to patients with chronic inflammatory bowel diseases.