Intensive exercise and immunity: effect of diets enriched in fibre and/or flavonoids in rats

Abstract

[eng] The influence of exercise on immune system has gained increasing attention from researchers lately, mainly due to the growing participation of the general population in sport competitions. Whereas moderate intensity exercise enhances immune function, high intensity exercise can have a deleterious effect on the immune system, which, in addition to increase the risk of infections, is associated with a decline in exercise performance and an impaired recovery. Furthermore, intensive exercise can disrupt the gastrointestinal integrity and function, which results in the appearance of symptoms of varying severities. Nevertheless, the mechanisms underlying these gastrointestinal effects remain unclear. It seems that splanchnic ischaemia, altered motility, malabsorption and neuroendocrine factors may be involved, although the exercise-induced immune alterations may also play an important role. Nutritional strategies aimed at counteracting these effects are needed. Previous studies have shown the immunomodulatory, antioxidant and anti-inflammatory properties of polyphenols, especially of those found in cocoa and oranges. Considering this background, the main goals of the current thesis were to establish the immune alterations induced by intensive exercise on the gut microbiota composition and the mucosal immune system and to evaluate the possible preventive properties of cocoa, cocoa fibre and hesperidin on such alterations, focusing on the changes induced in mucosal immunity as well as those induced in systemic immunity.

To achieve the first goal, two different training protocols were used. First, to assess changes in caecal microbiota composition, male and female Wistar rats performed two 30-min running sessions per day for 15 days followed by a final exhaustion test (ET). Although these training programme slightly modified the gut microbiota composition in both male and female Wistar rats, most of the alterations depended on the rats’ sex. After this first approach, a more intense exercise model was used in Wistar rats for assessing the exercise-induced alterations in mucosal immunity; the model included three trainings and two exhaustion tests per week, for 5 weeks. This longer training programme was able to disrupt the mucosal immunity, by reducing salivary IgA and altering the composition and function of mesenteric lymph nodes lymphocytes, as well as the intestinal epithelial barrier integrity, by altering the gene expression of tight junction proteins.

To accomplish the second part of the objective, female Wistar rats were fed either a standard diet, a diet containing 10% cocoa providing 5% fibre, or a diet containing only 5% cocoa fibre. After 25 days of dietary intervention, half of the rats of each diet performed an exhaustion test without prior training, given that acute exercise also impairs immune system. Both cocoa- and cocoa fibre-enriched diets protected against the oxidative stress induced by a single session of exhausting exercise, although they differently modulated the mucosal immunity.

We next established the effects of supplementation with a pure flavonoid, hesperidin, in the immune alterations induced by the 5-week training programme. Hesperidin enhanced the exercise performance and prevented the increase in circulating leukocytes induced by the final exhaustion test, as well as the higher secretion of IFN-γ by peritoneal macrophages induced by training. After observing these

promising results, a dietary intervention with both cocoa and hesperidin was also evaluated. In this case, Lewis rats undertook a 6-week intensive training programme in an uphill treadmill. Although some preventing effects after the dietary interventions were found, such as avoiding the plasma cortisol increase and some of the immune alterations induced by exercise, such effects were mainly associated with cocoa.

Overall, different models of intensive exercise have been applied and evidenced some immune impairments. Dietary interventions with cocoa, cocoa fibre and hesperidin have partially prevented these changes, without affecting exercise performance, except for the ergogenic effects induced by oral supplementation with hesperidin.

[cat] La influència de l’exercici físic intens sobre el sistema immunitari ha guanyat molt d’interès durant els darrers anys. La pràctica d’activitat física moderada potencia la funció immunitària, mentre que la pràctica d’exercici físic intens pot alterar-la, augmentant el risc de patir infeccions. A més, l’exercici físic intens s’ha relacionat amb l’aparició de molèsties gastrointestinals de diversa gravetat que requereixen un tractament ràpid i eficaç. Tanmateix, s’ha suggerit que una dieta rica en components bioactius, com els polifenols i la fibra, poden tenir un paper clau en la prevenció d’aquests efectes negatius de l’exercici físic intens. En aquest sentit, els objectius d’aquesta tesi doctoral han consistit en establir les alteracions que provoca l’exercici físic intens sobre el sistema immunitari mucosal i la microbiota de rata, i avaluar les possibles propietats preventives del cacau, la fibra de cacau i l’hesperidina sobre aquestes alteracions.

Per tal d’assolir aquests objectius, s’han emprat diferents models d’exercici físic intens: un model agut i tres models crònics finalitzats amb una prova d’extenuació final (un de 2 setmanes de durada amb 2 sessions d’entrenament diàries, un de 5 setmanes de durada amb 2 proves d’extenuació i 3 entrenaments regulars setmanals, i un de 6 setmanes de durada amb les mateixes proves d’extenuació i entrenaments).

Els resultats mostren que, mentre que l’entrenament de 2 setmanes pràcticament no modifica la composició de la microbiota intestinal, l’entrenament més llarg altera el sistema immunitari mucosal i la integritat de la barrera epitelial intestinal. D’altra banda, dietes riques en cacau i fibra de cacau van prevenir l’estrès oxidatiu per part dels macròfags peritoneals induït per l’exercici agut. En animals entrenats, la suplementació oral amb hesperidina va millorar el rendiment esportiu dels animals i va prevenir la leucocitosi provocada per l’extenuació final, mentre que la ingesta d’una dieta rica en cacau va evitar l’augment de cortisol en plasma i la disminució de la proporció de les cèl·lules T CD4+ en melsa induïdes per l’extenuació final.

En conclusió, aquesta tesi doctoral demostra com diferents models d’exercici físic intens en rata modifiquen el sistema immunitari i com intervencions dietètiques amb cacau, fibra de cacau i hesperidina poden evitar parcialment aquestes alteracions.