Probiotics have been reported to exert beneficial effects along the gut-brain axis. This randomised, double-blind and placebo-controlled human study aimed to evaluate such properties of Lactobacillus plantarum DR7 and its accompanying mechanisms in stressed adults. One hundred and eleven (n=111; DR7 n=56, placebo n=55) stressed adults were recruited based on moderate stress levels using the PSS-10 questionnaire. The consumption of DR7 (1×10⁹ cfu/day) for 12 weeks reduced symptoms of stress (P=0.024), anxiety (P=0.001), and total psychological scores (P=0.022) as early as 8 weeks among stressed adults compared to the placebo group as assessed by the DASS-42 questionnaire. Plasma cortisol level was reduced among DR7 subjects as compared to the placebo, accompanied by reduced plasma pro-inflammatory cytokines, such as interferon-γ and transforming growth factor-α and increased plasma anti-inflammatory cytokines, such as interleukin 10 (P30 years old), such as basic attention, emotional cognition, and associate learning (P<0.05), as compared to the placebo and young adults (<30 years old). The administration of DR7 enhanced the serotonin pathway, as observed by lowered expressions of plasma dopamine β-hydroxylase (DBH), tyrosine hydroxylase (TH), indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase accompanied by increased expressions of tryptophan hydroxylase-2 and 5-hydroxytryptamine receptor-6, while stabilising the dopamine pathway as observed via stabilised expressions of TH and DBH over 12 weeks as compared to the placebo (P<0.05). Our results indicated that DR7 fulfil the requirement of a probiotic strain as per recommendation of FAO/WHO and could be applicable as a natural strategy to improve psychological functions, cognitive health and memory in stressed adults.

The aims of this study were to investigate the effects of Lactobacillus plantarum DR7 isolated from bovine milk against upper respiratory tract infections (URTI) and elucidate the possible mechanisms underlying immunomodulatory properties. The DR7 strain (9 log cfu/d) was administered for 12 wk in a randomized, double-blind, and placebo-controlled human study involving 109 adults (DR7, n = 56; placebo, n = 53). Subjects were assessed for health conditions monthly via questionnaires, and blood samples were evaluated for cytokine concentrations, peroxidation and oxidative stress, and gene expression in T cells and natural killer (NK) cells. The administration of DR7 reduced the duration of nasal symptoms (mean difference 5.09 d; 95% CI: 0.42-9.75) and the frequency of URTI (mean difference 0.32; 95% CI: 0.01-0.63) after 12 and 4 wk, respectively, compared with the placebo. The DR7 treatment suppressed plasma proinflammatory cytokines (IFN-γ, TNF-α) in middle-aged adults (30 to 60 yr old), while enhancing anti-inflammatory cytokines (IL-4, IL-10) in young adults (<30 yr old), accompanied by reduced plasma peroxidation and oxidative stress levels compared with the placebo. Young adults who received DR7 showed higher expression of plasma CD44 and CD117 by 4.50- and 2.22-fold, respectively, compared with the placebo. Meanwhile, middle-aged adults showed lower expression of plasma CD4 and CD8 by 11.26- and 1.80-fold, respectively, compared with the placebo, indicating less T-cell activation. In contrast, both young and middle-aged adults who received DR7 showed enhanced presence of nonresting and mature NK cells compared with those who received the placebo. We postulate that DR7 alleviated the symptoms of URTI by improving inflammatory parameters and enhancing immunomodulatory properties.

Probiotic microorganisms have been documented over the past two decades to play a role in cholesterol-lowering properties via various clinical trials. Several mechanisms have also been proposed and the ability of these microorganisms to deconjugate bile via production of bile salt hydrolase (BSH) has been widely associated with their cholesterol lowering potentials in prevention of hypercholesterolemia. Deconjugated bile salts are more hydrophobic than their conjugated counterparts, thus are less reabsorbed through the intestines resulting in higher excretion into the feces. Replacement of new bile salts from cholesterol as a precursor subsequently leads to decreased serum cholesterol levels. However, some controversies have risen attributed to the activities of deconjugated bile acids that repress the synthesis of bile acids from cholesterol. Deconjugated bile acids have higher binding affinity towards some orphan nuclear receptors namely the farsenoid X receptor (FXR), leading to a suppressed transcription of the enzyme cholesterol 7-alpha hydroxylase (7AH), which is responsible in bile acid synthesis from cholesterol. This notion was further corroborated by our current docking data, which indicated that deconjugated bile acids have higher propensities to bind with the FXR receptor as compared to conjugated bile acids. Bile acids-activated FXR also induces transcription of the IBABP gene, leading to enhanced recycling of bile acids from the intestine back to the liver, which subsequently reduces the need for new bile formation from cholesterol. Possible detrimental effects due to increased deconjugation of bile salts such as malabsorption of lipids, colon carcinogenesis, gallstones formation and altered gut microbial populations, which contribute to other varying gut diseases, were also included in this review. Our current findings and review substantiate the need to look beyond BSH deconjugation as a single factor/mechanism in strain selection for hypercholesterolemia, and/or as a sole mean to justify a cholesterol-lowering property of probiotic strains.