Milk fermented with the probiotic candidate Lactobacillus paracasei FT700 induces differentiation of monocytes toward macrophages in vitro

Highlights

• FT700 tolerated simulated gastric conditions.

• The strain hydrolyzed milk proteins during milk fermentation.

• Fermented milk stimulated in vitro differentiation of monocytes in macrophages.

• FT700 has potential to be used as a probiotic in functional fermented milk products.

Abstract

Lactobacillus paracasei FT700 was tested for its survival in simulated gastrointestinal conditions (in vitro) and for its sensitivity to antibiotics. The strain was used to produce fermented milk and the cell-free supernatant was freeze-dried and applied in cell cultures (monocytes and macrophages) to evaluate its cytotoxicity and immunomodulatory effects. After 180 min at pH 2.0 or in simulated gastric juice, L. paracasei FT700 concentrations were reduced by 4 and 3 log cfu/mL, respectively. Moreover, the strain was susceptible to the majority of antibiotics tested. Freeze dried cell-free fermented milk supernatant (FMS) was toxic to monocytes after 72 h of exposure at 10 mg/mL inducing their apoptosis. However, at concentrations below toxic level, FMS stimulated the differentiation of monocytes into macrophages, as observed by the increased expression of CD71 marker. This immune stimulation was not inflammatory since low production of TNF-α was observed. Overall, L. paracasei FT700 has potential to be used as probiotic in functional fermented milk.

Introduction

The World Health Organization (WHO) and the Food and Agriculture Organization (FAO) define probiotics as “live microorganisms that when administered in adequate amounts confer health benefits to the host” (Food and Agriculture Organization & World Health Organization, 2002). In this context, some authors have studied the role of probiotics in the modulation of the immune system aiming to alleviate symptoms of inflammatory intestinal diseases (Saad et al, 2013, Walsh et al, 2014). Certain probiotic strains may increase the production of interleukin-10 (IL-10), an anti-inflammatory cytokine that down-regulates the expression of Th1 pro-inflammatory cytokines (e.g. INF-γ) and decreases the production of the pro-inflammatory cytokines TNF and IL-8 (Bai et al, 2006, Fernandez et al, 2011). TNF-α and INF-γ play a key role in the pathogenesis of inflammatory bowel diseases (IBD) and other gastrointestinal disorders. Therefore specific probiotic strains could be an additional strategy to alleviate symptoms of such pathologies (Chiba et al, 2006, Reiff, Kelly, 2010, Singh, Pardi, 2014). Moreover, during milk fermentation, bioactive peptides with immunomodulatory activities may be released from milk proteolysis by lactic acid bacteria (LAB) (Beermann, Hartung, 2013, Hayes et al, 2007, Korhonen, 2009, Nagpal et al, 2011, Zagato et al, 2014). Thus, concerning industrial applications, these peptides may be considered as health enhancing nutraceuticals for food or for pharmaceutical applications (Kanwar et al., 2009).

In this study the goat cheese isolate Lactobacillus paracasei FT700 (with proteolytic activity on milk proteins) was evaluated for probiotics traits, and the fermented milk supernatant obtained with this strain was evaluated for in vitro cytotoxicity and immunomodulatory effects on monocytes with the aim of being used in a functional fermented milk with immunomodulatory and probiotic health benefits.