Dietary tryptophan deficiency and its supplementation compromises inflammatory mechanisms and disease resistance in a teleost fish

M. Machado,S. Fernandez-Boo,A. Domingues,R. Azeredo,L. E. C. Conceição,B. Costas,J. Dias

doi:10.1038/s41598-019-44205-3

Abstract

Tryptophan participates on several physiological mechanisms of the neuroendocrine-immune network and plays a critical role in macrophages and lymphocytes function. This study intended to evaluate the modulatory effects of dietary tryptophan on the European seabass (Dicentrarchus labrax) immune status, inflammatory response and disease resistance to Photobacterium damselae piscicida. A tryptophan deficient diet (NTRP); a control diet (CTRL); and two other diets supplemented with tryptophan at 0.13% (TRP13) and 0.17% (TRP17) of feed weight were formulated. Fish were sampled at 2 and 4 weeks of feeding and the remaining were i.p. injected with Phdp (3 × 106 cfu/fish) at 4 weeks and the inflammatory response (at 4, 24, 48 and 72 hours post-infection) as well as survival were evaluated. Results suggest that fish immune status was not altered in a tryptophan deficient scenario whereas in response to an inflammatory insult, plasma cortisol levels increased and the immune cell response was compromised, which translated in a lower disease resistance. When dietary tryptophan was offered 30% above its requirement level, plasma cortisol increased and, in response to bacterial infection, a decrease in lymphocytes, monocytes/macrophages and several immune-related genes was observed, also compromising at some degree fish disease resistance.

Highlights

Teleost requirements for amino acids (AA) are generally settled by means of optimal growth
In the present work no changes on growth performance, cell responses, cell-mediated mechanisms and gene expression were observed after a 4 weeks feeding period in fish fed the tryptophan deficient diet
Despite no differences were observed in the seabass immune status after 4 weeks of feeding, fish fed the NTRP diet presented a clear monocytopenia at 24 h post infection

Summary

Introduction

Teleost requirements for amino acids (AA) are generally settled by means of optimal growth. The interaction of neuroendocrine and immune machineries is a recognized phenomenon that allow animals to better cope with the disturbance of homeostasis as both share physiological pathways. Both immune and endocrine cells share common receptors while different hormones and cytokines are involved in the same mechanisms[11,12]. The ideal inflammatory response is rapid, specific and self-limiting[20] In this context, and knowing that tryptophan’s role during infection is mainly related to regulatory processes leading to anti-inflammatory signalling molecules, this AA presents itself as a tentative immunomodulator during the development of inflammation and its resolution. The present study aimed to evaluate the effects of dietary tryptophan deficiency and supplementation on the European seabass immune status, inflammatory response and disease resistance

Methods

Results

Conclusion