Heat-Killed Lactobacillus brevis Enhances Phagocytic Activity and Generates Immune-Stimulatory Effects through Activating the TAK1 Pathway

Heat-killed Lactobacillus murinus confers neuroprotection against dopamine neuronal loss by targeting NLRP3 inflammasome

The intestinal flora has become very active in studies related to Parkinson's disease (PD) in recent years. The microbe-gut-brain axis is closely related to the maintenance of brain homeostasis as well as PD pathogenesis. Alterations in gut bacteria can contribute to neuroinflammation and dopamine (DA) neurodegeneration. Lactobacillus murinus, a gram-positive bacterium, is a commensal gut bacteria present in the mammalian gut and considered as a potential probiotic due to its beneficial effects, including anti-inflammatory and antibacterial actions. In this study, the effects of live L. murinus and heat-killed L. murinus on DA neuronal damage in rats and the underlying mechanisms were investigated. Data showed that heat-killed L. murinus ameliorated 6-hydroxydopamine-induced motor dysfunctions and loss of substantia nigra DA neurons, while no protection was shown in live L. murinus treatment. At the same time, heat-killed L. murinus reduced the activation of NLRP3 inflammasome in microglia and the secretion of pro-inflammatory factors, thus inhibiting the development of neuroinflammation. Furthermore, heat-killed L. murinus failed to display its original neuroprotective properties in NLRP3 inflammasome knockout mice. Together, heat-killed L. murinus conferred neuroprotection against DA neuronal loss via the inhibition of microglial NLRP3 inflammasome activation. These findings provide a promising potential for future applications of L. murinus, and also beneficial strategy for PD treatment.

Lactobacillus for the treatment and prevention of atopic dermatitis: Clinical and experimental evidence

Atopic dermatitis (AD) is a chronic inflammatory skin disease, accompanied by itching and swelling. The main pathological mechanism of AD is related to the imbalance between Type 2 helper cells (Th2 cells) and Type 1 helper cells (Th1 cells). Currently, no safe and effective means to treat and prevent AD are available; moreover, some treatments have side effects. Probiotics, such as some strains of Lactobacillus, can address these concerns via various pathways: i) facilitating high patient compliance; ii) regulating Th1/Th2 balance, increasing IL-10 secretion, and reducing inflammatory cytokines; iii) accelerating the maturation of the immune system, maintaining intestinal homeostasis, and improving gut microbiota; and iv) improving the symptoms of AD. This review describes the treatment and prevention of AD using 13 species of Lactobacillus. AD is commonly observed in children. Therefore, the review includes a higher proportion of studies on AD in children and fewer in adolescents and adults. However, there are also some strains that do not improve the symptoms of AD and even worsen allergies in children. In addition, a subset of the genus Lactobacillus that can prevent and relieve AD has been identified in vitro. Therefore, future studies should include more in vivo studies and randomized controlled clinical trials. Given the advantages and disadvantages mentioned above, further research in this area is urgently required.

Levilactobacillus brevis MG5311 Alleviates Ethanol-Induced Liver Injury by Suppressing Hepatic Oxidative Stress in C57BL/6 Mice

Alcoholic liver disease (ALD), caused by excessive alcohol consumption, leads to high mortality. We investigated the hepatoprotective effect of Levilactobacillus brevis MG5311 in C57BL/6 mice with liver injuries induced by chronic ethanol plus binge feeding. L. brevis MG5311 was administered orally at a dose of 1 × 10⁹ CFU/mouse once daily for 32 days. L. brevis MG5311 administration significantly reduced serum ALT, AST, and triglyceride (TG) levels in ethanol-fed mice. L. brevis MG5311 also decreased malondialdehyde levels and increased glutathione peroxidase (GPx) activity in liver tissues. In addition, hepatic TG content and histopathological scores were significantly reduced. L. brevis MG5311 increased the protein expression of SIRT1, PPARα, SOD1, CAT, and GPx 1/2 in liver tissue, while inhibiting CYP2E1 and SREBP-1c. These results indicated that L. brevis MG5311 alleviated ethanol-induced liver injury by inhibiting hepatic oxidative stress and promoting lipid metabolism. Therefore, L. brevis MG5311 may be a useful probiotic candidate for ameliorating or preventing ALD.

Immunostimulatory Activity of Lactic Acid Bacteria Cell-Free Supernatants through the Activation of NF-κB and MAPK Signaling Pathways in RAW 264.7 Cells

Lactic acid bacteria (LAB) can improve host health and has strong potential for use as a health functional food. Specific strains of LAB have been reported to exert immunostimulatory effects. The primary goal of this study was to evaluate the immunostimulatory activities of novel LAB strains isolated from humans and foods and to investigate the probiotic properties of these strains. Cell-free supernatants (CFS) obtained from selected LAB strains significantly increased phagocytosis and level of nitric oxide (NO) and pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 in RAW264.7 macrophage cells. The protein expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, which are immunomodulators, was also upregulated by CFS treatment. CFS markedly induced the phosphorylation of nuclear factor-κB (NF-κB) and MAPKs (ERK, JNK, and p38). In addition, the safety of the LAB strains used in this study was demonstrated by hemolysis and antibiotic resistance tests. Their stability was confirmed under simulated gastrointestinal conditions. Taken together, these results indicate that the LAB strains selected in this study could be useful as probiotic candidates with immune-stimulating activity.

Glycine max Fermented by a Novel Probiotic, Bifidobacterium animalis subsp. lactis LDTM 8102, Increases Immuno-Modulatory Function

Many probiotic species have been used as a fermentation starter for manufacturing functional food materials. We have isolated Bifidobacterium animalis subsp. lactis LDTM 8102 from the feces of infants as a novel strain for fermentation. While Glycine max has been known to display various bioactivities including anti-oxidant, anti-skin aging, and anti-cancer effects, the immune-modulatory effect of Glycine max has not been reported. In the current study, we have discovered that the extract of Glycine max fermented with B. animalis subsp. lactis LDTM 8102 (GFB 8102), could exert immuno-modulatory properties. GFB 8102 treatment increased the production of immune-stimulatory cytokines in RAW264.7 macrophages without any noticeable cytotoxicity. Analysis of the molecular mechanism revealed that GFB 8102 could upregulate MAPK2K and MAPK signaling pathways including ERK, p38, and JNK. GFB 8102 also increased the proliferation rate of splenocytes isolated from mice. In an animal study, administration of GFB 8102 partially recovered cyclophosphamide-mediated reduction in thymus and spleen weight. Moreover, splenocytes from the GFB 8102-treated group exhibited increased TNF-α, IL-6, and IL-1β production. Based on these findings, GFB 8102 could be a promising functional food material for enhancing immune function.

Heat-killed Limosilactobacillus reuteri PSC102 Ameliorates Impaired Immunity in Cyclophosphamide-induced Immunosuppressed Mice

The immune functions of heat-killed Limosilactobacillus reuteri PSC102 (hLR) were investigated in cyclophosphamide (CP)-treated immunosuppressed mice. BALB/c mice were randomly divided into five groups: normal control group, CP group, CP treated with levamisole (positive control group), and CP treated with low- and high-dose hLR. After receiving the samples for 21 days, mice were sacrificed, and different parameters, such as immune organ index, immune blood cells, splenocyte proliferation, lymphocyte subpopulations, cytokines, and immunoglobulins, were analyzed. Results showed that the immune organ (thymus and spleen) indices of hLR treatment groups were significantly increased compared to the CP group (p < 0.05). hLR administration prevented CP-induced reduction in the numbers of white blood cells, lymphocytes, midrange absolute, and granulocytes, providing supporting evidence for hematopoietic activities. Splenocyte proliferation and T-lymphocyte (CD4+ and CD8+) subpopulations were also significantly augmented in mice treated with hLR compared to the CP group (p < 0.05). Moreover, Th1-type [interferon-γ, interleukin (IL)-2, and tumor necrosis factor-α] and Th2-type (IL-4 and IL-10) immune factors and immunoglobulin (IgG) showed significant increasing trends (p < 0.05). Additionally, the other proinflammatory cytokines (IL-1β and IL-6) were also significantly elevated (p < 0.05). Taken together, this investigation suggested that orally administered hLR could recover immunosuppression caused by CP and be considered a potential immunostimulatory agent for the treatment of immunosuppressive disorders.

Immunostimulatory Effect of Heat-Killed Probiotics on RAW264.7 Macrophages

Probiotics modulate the gut microbiota, which in turn regulate immune responses to maintain balanced immune homeostasis in the host. However, it is unclear how probiotic bacteria regulate immune responses. In this study we investigated the immunomodulatory effects of heat-killed probiotics, including Lactiplantibacillus plantarum KC3 (LP3), Lactiplantibacillus plantarum CKDB008 (LP8), and Limosilactobacillus fermentum SRK414 (LF4), via phagocytosis, nitric oxide (NO), and pro-inflammatory cytokine production in macrophages. We thus found that heat-killed LP8 could promote the clearance of foreign pathogens by enhancing the phagocytosis of macrophages. Treatment with heat-killed LP8 induced the production of NO and pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β. In addition, heat-killed LP8 suppressed the production of NO and cytokines in LPS-induced RAW264.7 cells, suggesting that heat-killed LP8 exerts immunomodulatory effects depending on the host condition. In sum, these results indicate that heat-killed LP8 possesses the potential for immune modulation while providing a molecular basis for the development of functional probiotics prepared from inactivated bacterial cells.

Lactobacillus crispatus DSM25988 as novel bioactive agent to co-aggregate Streptococcus pyogenes and to exclude it by binding to human cells

Streptococcus pyogenes, a group A streptococcus, is the major bacterial pathogen responsible for acute bacterial infection of the human oropharynx and the causative agent of scarlet fever. Estimates of the global burden of S. pyogenes related diseases revealed 616 million cases of pharyngitis, and at least 517,000 deaths due to severe invasive diseases and sequelae. Here we describe Lactobacillus crispatus DSM25988 that was identified among hundreds of Lactobacillus strains (referring to all organisms that were classified as Lactobacillaceae until 2020) showing ability to prevent adhesion of S. pyogenes to Detroit 562 cells, and to exhibit a masking and co-aggregating effect on S. pyogenes in vitro. L. crispatus DSM25988 also inhibits invasion of cultured human epithelial pharyngeal cells by S. pyogenes. Competitive binding to fibronectin might be involved in the inhibition process. Antiviral activity of the L. crispatus DSM25988 cells were identified in an in vitro cell model demonstrating that L. crispatus effectively excludes viruses from epithelial cells using SARS-CoV2 proteins as a model. This finding points to the potential of DSM25988 to protect cells from virus infection. Biological activity is retained in heat treated cells. The heat-treated Lactobacillus strain was further developed into functional throat lozenges, wherein its biological activity is stably maintained in the formulation. Lozenges containing L. crispatus DSM25988 underwent testing in an uncontrolled, prospective user study in 44 subjects with symptoms of sore throat for a period of up to 14 days. The study data shows promising safety and efficacy of the medical device when used against symptoms of sore throat like scratchy feeling, hoarse voice and swallowing pain.

Immunomodulatory Properties of a γ-Aminobutyric Acid-Enriched Strawberry Juice Produced by Levilactobacillus brevis CRL 2013

Gamma-aminobutyric acid (GABA) plays a key role in mammals as the major inhibitory neurotransmitter of the central nervous system. Although GABA may not be able to cross the human blood-brain barrier, it was approved as a food ingredient because of its benefits to the host after oral administration including anti-hypertensive, anti-depressant and anti-inflammatory activities. Considering the current trend toward the development of new functional and natural products and that microbial fermentation is one of the most promising methods to produce this non-protein amino acid, the in situ production of GABA through fermentation of strawberry and blueberry juices by the efficient GABA producer strain, Levilactobacillus brevis (formerly known as Lactobacillus brevis) CRL 2013, was evaluated. A high GABA production (262 mM GABA) was obtained after fermenting strawberry juice supplemented with yeast extract for 168 h, being GABA yield significantly higher in strawberry juices than in the blueberry ones. Thus, GABA-enriched fermented strawberry juice (FSJ) was selected to carry out in vivo and in vitro studies. The in vitro functional analysis of the GABA-enriched FSJ demonstrated its ability to significantly decrease the expression of cox-2 gene in LPS stimulated RAW 264.7 macrophages. In addition, in vivo studies in mice demonstrated that both, L. brevis CRL 2013 and the GABA-enriched FSJ were capable of reducing the levels of peritoneal, intestinal and serum TNF-α, IL-6, and CXCL1, and increasing IL-10 and IFN-γ in mice exposed to an intraperitoneal challenge of LPS. Of note, the GABA-enriched FSJ was more efficient than the CRL 2013 strain to reduce the pro-inflammatory factors and enhance IL-10 production. These results indicated that the CRL 2013 strain exerts anti-inflammatory effects in the context of LPS stimulation and that this effect is potentiated by fermentation. Our results support the potential use of L. brevis CRL 2013 as an immunomodulatory starter culture and strawberry juice as a remarkable vegetable matrix for the manufacture of GABA-enriched fermented functional foods capable of differentially modulating the inflammatory response triggered by TLR4 activation.