Nutrients 2023 , 15 , 3466
12of 16
Dejection, and Confusion–Bewilderment. Similar results were obtained in a study with a probiotic blend given to healthy individuals, where significant within-group differences were observed only for the above-mentioned sub-scores related to the “negative” sub- scales of mood [23]. Another study investigating the impact of a dual-strain probiotic on healthy subjects with a non-pathological mood disturbance showed a close to significant improvement in the overall POMS level, as well as within-group improvements in the negative aspects of mood only for the probiotic group [24]. Decreased levels of the negative subscales of POMS are interpreted as an improved mood. In the present study, the subjects were challenged using cognition tests before and after treatment. Generally, many cognition tests are used to evaluate if the subject has cognitive impairment, but in a study with healthy and relatively young subjects, as in the present case, it may not be surprising that some cognition tests were too easy (four choice reaction time and Corsi blocks). But the more difficult tests (numeric working memory, rapid visual information processing, paired associate learning, and word recall) were found to be applicable to evaluate differences due to treatment. One of the most significant results in the present study is that intake of LPHEAL9 improved working memory compared to the placebo group in the word recall test. The effect of LPHEAL9 on working memory agrees with a similar study that tested the effect of L. plantarum DR7 on subjects with moderate stress for 12 weeks [9], and a study investigating the intake of a probiotic mixture showing an increased stress-induced working memory in the probiotic group but not in the placebo group [10]. A positive effect on memory after consumption of LPHEAL9 was also seen in the numeric working memory test, where there was a significantly larger reduction in the reaction time for the LPHEAL9 group compared to the placebo group. Learning and visuospatial memory were studied in the paired associate learning test, where LPHEAL9 treatment caused a significant reduction in the mean errors to success compared to the placebo group. A trend for a difference in total errors was also observed in the PP population ( p = 0.068, between groups) in favor of LPHEAL9, which agrees with an earlier study that observed a larger reduction in PAL total errors after intake of Bifidobacterium longum 1714 compared to placebo [8]. Different mechanisms can explain the effects of LPHEAL9 on cognition. It is known that LPHEAL9 survives the passage through the gastrointestinal tract [25–27] and has the ability to adhere to human mucosa cells that is dependent on a mannose-binding mecha- nism [28,29]. Thus, LPHEAL9 has the possibility to affect factors that influence cognition. The cognitive function can be influenced by components derived from the metabolism of tryptophan such as kynurenine, as shown in a study with L. plantarum 299v, where intake of this probiotic strain decreased kynurenine levels and improved cognitive function in subjects with depression [6]. However, in the present study on subjects with moderate stress, no changes in the tryptophan and kynurenine levels were found in the LPHEAL9 group, while both parameters increased significantly in the placebo group. The increase in tryptophan level was significantly higher in the placebo group compared to the LPHEAL9 group. In agreement with these results, an earlier 8-week study with L. casei Shirota YIT 9029 or placebo administered to fifty-one healthy medical students under academic examination stress showed a significant increase in tryptophan from baseline to one day before the exam in the placebo group compared to the probiotic group ( p < 0.05). Likewise, the kynurenine value also increased at the same time ( p = 0.07), while no significant changes were observed in the probiotic group [30]. It is difficult to explain the results of increased levels in the placebo group, while no differences were detected in the probiotic group, but one factor that may lower the tryptophan and kynurenine levels in plasma could be that gut bacteria metabolize tryptophan into indole and indolic compounds [31]. Indoles have several health benefits and can enhance barrier function, regulate intestinal immune tolerance, and act as neuroprotective compounds [31]. The potential ability of LPHEAL9 to metabolize tryptophan to indoles is currently unknown, but other lactobacilli strains have been shown to carry this capability [31,32]. In the paper by Kato-Kataoka et al. [30], it was
Powered by FlippingBook