The impact of l-arginine supplementation on the enteral phase of experimental Trichinella spiralis infection in treated and untreated mice

Abstract

The role of nitric oxide (NO) in the immunopathological response during Trichinella spiralis (T. spiralis) infection remains controversial. The amino acid, l-arginine is a NO precursor commonly used by athletes and bodybuilders as a protein supplement. As to our knowledge, there are no published studies which have tested the effect of l-arginine on the intestinal phase of experimental trichinellosis. The present work aims to investigate the effect of l-arginine on the enteral phase of experimental T. spiralis infection in albendazole-treated and untreated mice. Forty BALB/C mice infected orally with T. spiralis larvae were divided into 4 groups as follows: Group A were infected and untreated (control) mice, Group B received albendazole alone, Group C received l-arginine alone, and Group D received both l-arginine and albendazole. Compared to the control group, l-arginine supplementation showed; a significant increase in the intestinal adult worm burden, a significantly high inducible NO synthase (iNOS) expression, elevated immune markers; tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), and enhanced apoptosis. Albendazole treated-group had a significant reduction in the adult worm number (90.9%), while combined albendazole-arginine regimen showed a lower percentage of worm reduction (72.7%). During the enteral phase of T. spiralis infection, l-arginine supplementation should be taken cautiously, as it may modulate the proinflammatory immune response and subsequently affect the outcome of the infection and/or treatment.

Keywords: Apoptosis; IFN-γ; TNF-α; Trichinella spiralis; iNOS; l-arginine.

Fig. 1

a–e Cut sections of (H&E) stained intestinal samples. a infected- untreated control group showed marked inflammatory cellular infiltrate (*), and goblet cell proliferation [red arrow] (mag. 400), b albendazole-treated group showed minimal inflammatory cellular infiltrate, reduction of goblet cell proliferation (mag. 200), c–d l-arginine-tested group showed moderate inflammatory cellular infiltrate (*) with cut sections of the adult worms [red arrows] embedded within the intestinal villi in (c) (mag. 200), and e combined (AL + AR) tested group showed mild inflammatory cellular infiltrate (mag. 200)

Fig. 2

Immunohistochemical expression of iNOS in intestinal sections of T. spiralis infected mice (a–d). a control group, b albendazole group (AL), c l-arginine group (AR), d albendazole and l-arginine group (AL + AR) (scale bar 50 µm). e Area percentage of intestinal iNOS immunoreactivity in the different groups. (n = 6). * Statistically significant compared to control group. # Statistically significant compared to albendazole group. @ Statistically significant compared to l-arginine group. & Statistically significant compared to albendazole and l-arginine group

Fig. 3

Immunohistochemical expression of Bax and Bcl2 in intestinal sections of T spiralis infected mice. a–d Bax immunohistochemical expression in a control group, b albendazole group (AL), c l-arginine group (AR), d albendazole and l-arginine group (AL + AR). e–h Bcl2 immunohistochemical expression in e control group, f albendazole group (AL), g l-arginine group (AR), h albendazole and l-arginine group (AL + AR) (scale bar 50 µm). i Area percentage of Bax immunoreactivity in the different groups, j Area percent of Bcl2 immunoreactivity in the different groups, k Bax/Bcl2 ratio in the different groups (n = 6). * Statistically significant compared to control group. # Statistically significant compared to albendazole group. @ Statistically significant compared to l-arginine group. & Statistically significant compared to albendazole and arginine group