Gut-Targeted Immunonutrition Boosting Natural Killer Cell Activity Using Saccharomyces boulardii Lysates in Immuno-Compromised Healthy Elderly Subjects

Introduction

The gut microbiota represents a crucial check point of resistance to colonization by pathogens while modulating maturation and activity of both the innate and adaptive immune systems. ^1,2 In particular, the complex interaction between probiotic bacteria, resident flora, and mucosal surfaces is made possible because of the mucosal immune system and particularly the mucosa-associated lymphoid tissues. On the basis of the clinical evidence, it is suggested that the effects of probiotic bacteria over the mucosal immune response may be divided into local and systemic effects. Namely, this is recognition of bacteria that promote mucosal T cell function as the newly termed “immunobiotics” moves probiotic biology forward by focusing on a mechanism of outcome, i.e., immunomodulation at distant mucosal sites. ³ Indeed, several lactobacillus strains have been reported to exert stimulatory properties on the immune system cellular population either in vitro ^4,5 or in animal models. ^6,7

Moreover, human intervention studies have shown that probiotics enhance innate immunity, including natural killer (NK) cell activity, phagocytic activity, and respiratory burst. ⁸ In recent years, a number of Gram-positive lactic acid bacteria strains have been generated showing probiotic properties and immunomodulatory functions in healthy adults ^9,10 as well as elderly subjects. ^11,12 Recently, we have shown that KC-1317, a symbiotic mixture containing a microbial lysate (Saccharomyces boulardii lysate in a cranberry, colostrum-derived lactoferrin, fragaria, and lactose mixture, named, Italy) was able to counteract stress-induced gut hyperpermeability. ¹³ This may help reduce translocation of the antigenic burden into the bloodstream. The aim of the present study was to further probe the possible more direct influence of KC-1317 on immunocompetence in healthy subjects with decreased NK cell activity.

Subjects and Methods

The inclusion criteria complied with the admission criteria for immunogerontological studies (SENIEUR protocol), a World Health Organization (WHO) performance status (PS) of grade 1, 2, or 3, and informed consent. Subjects who exhibited NK cell activity <10% (bottom 30% of population) were selected for the trial (48 out of the of the initially 186 screened). Blood samples were always withdrawn in the morning from all the subjects to avoid diurnal variation in NK cell activity. It was seen that average NK cell activity of the entire population was 12.4±0.54%, whereas the average activity of selected volunteers was 6.4±0.41%. The study population consisted of sedentary, non-smoker patients without infectious or viral disease, steroid or immunosuppressive therapy, major debilitating diseases, and prior or ongoing cancer. Patients were instructed to refrain from physical exercise; subjects under overt psychological and physical distress were excluded at the time of selection. Moreover, the web-based version of the National Institutes of Health Diet History Questionnaire (NIH DHQ) was used to assess diet history over the past month and throughout the study period; patients were given written and verbal instructions by a registered dietitian. The study was designed for a 9-week randomized, double-blinded, placebo-controlled trial.

Subjects were randomly distributed in two groups that were matched as for baseline NK cell activity (6.5%–7.3%) and for dietary and lifestyle questionnaire answers. Group A received 100 mL of fruit juice as a placebo; group B received 90 mL of placebo that had 10 mL of KC-1317 added. The sealed drink bottles were number coded for each participant and provided on a weekly basis to the study subjects. There was no noticeable difference in taste between the placebo and the S. boulardii lysate-added samples. The subjects were asked to consume the supplement twice daily, in the morning and evening for 2 months while avoiding any other food supplements or vitamins. Peripheral blood samples were withdrawn at two different time points during the trial—at selection and after completion of trial.

Results

The subjects confirmed compliance with the dietary regimes. No significant differences were observed in routine biochemistry, body mass index, and white blood cell (WBC) count nor in daily dietary intake and energy expenditure between the two groups The baseline activity of NK cells of the volunteers in the two groups was comparable (6.2%–7.4%). On the basis of the questionnaire, it was also apparent that neither type of diet (vegetarian, western, mediterranean-like) nor the gender had any effect on NK cell activity. As compared to placebo-treated group, the KC-1317–treated group showed an overall significant increase of NK activity to 12.8±1.6% (data not shown, p<0.01). Only one subject (4.1%) responded poorly (<50% increase in NK cell activity; Fig. 1). In particular, 4 subjects (16.6%), 9 subjects (37.5%), and 10 subjects (41.6%) showed a mild (<100% increase in NK cell activity), moderate (100%–200% increase in NK cell activity), and intense (>200% increase in NK cell activity) response, respectively. The former and the latter two values were significantly different from placebo-treated group (p<0.01) (Fig. 2).

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FIG. 1.

Proportion of volunteers showing natural killer (NK) cell activity change: Effect of KC-1317 supplementation.

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FIG. 2.

The natural killer (NK) cell cytolytic activity of total and selected healthy elderly subjects.

Discussion

Aging is associated with impaired specific immune response. ¹⁴ The loss of the ability of T cells of the elderly people to generate an immune response equal to that of T cells of the young is unquestionably an age-related phenomenon, and this deficiency can expose to the increased susceptibility of elderly subjects to infections, cancers, and autoimmune diseases ¹⁵ as well as to the limitation incurred when immune therapy is envisaged in this population. ¹⁶ Several studies have suggested that the monitoring of cytolytic activity of the immune cells both in vivo and in vitro can be related to the overall immunity status of an individual. Although, other members of cell-mediated pathways play significant roles in the regulation of immunity, this variable has been used and successfully modulated with probiotic interventions, ^{6 –12,17,18} although controversial data exist even using the same strain. ¹⁹ Indeed, to date, a lack of consistency among some experimental models and different methods of preparation and administration of the bacteria represent factors yet to be fully explored.

Our present data suggest that KC-1317 is efficiently enhancing the immune system in healthy elderly and at a comparatively low dose. One cannot rule out the possibility of a synergistic action of the symbiotic milieu of KC-1337. ²⁰ Although these data need larger and longer-term studies together with correlations with several other health status markers, they offer a promising avenue to be pursued within a wider global health strategy by providing a safe dietary supplement enhancing innate cellular immune function.