Chemoattractant activity of tris-(hydroxymethyl)aminomethane for Brugia pahangi infective third-stage larvae

Abstract

Urocanic acid (UCA) is known as a major chemoattractant for Strongyloides stercoralis infective third-stage larvae (L3). Since Brugia pahangi is a skin-penetrating parasitic nematode similar to S. stercoralis, UCA was expected to be a chemoattractant for B. pahangi L3. Thus, the chemoattractant activity of UCA for B. pahangi L3 was assessed. The chemotactic responses of B. pahangi L3 to UCA or acetic acid (CH3COOH) dissolved in amine solutions were assessed using an agar-plate assay. A test solution of 200 mm UCA dissolved in aqueous 270 mm tris(hydroxymethyl)aminomethane (Tris) significantly attracted B. pahangi L3 compared with deionized water (DW), while neither a solution of 200 mm UCA dissolved in aqueous 230 mm ammonia (NH3) nor 290 mm triethylamine (TEA) significantly attracted L3. Similarly, a test solution of 200 mm CH3COOH dissolved with 200 mm Tris significantly attracted L3, but neither a test solution of 200 mm CH3COOH plus 200 mm NH3 nor 200 mm TEA attracted L3. Furthermore, L3 were significantly attracted to 200 mm Tris alone, compared with DW, but avoided 200 mm NH3 and 200 mm TEA. Moreover, the chemoattractant activity of Tris for L3 was observed even at a low concentration of 25 mm, and it was observed in a mild alkaline condition but not in an acidic condition. The present study reveals that Tris is a potential chemoattractant for B. pahangi L3 while UCA is not. This finding will contribute to an understanding of the mechanisms of skin-penetrating infection of filarial L3.

Chemotactic responses of Brugia pahangi infective third-stage larvae to tris(hydroxymethyl)aminomethane-related compounds and amino acids

“…Test solutions for the assays of chemotactic responses of B. pahangi L3 were prepared according to the test solutions used in previous studies (Mitsui et al, 2012(Mitsui et al, , 2018. For the assay for chemotactic response of filarial L3 to Tris-related compounds and amino acids, all Tris-related compounds were dissolved in deionized water (DW) at a concentration of 200 mM, while amino acids were dissolved in DW at concentrations of 50, 150 and 200 mM in view of the differences in solubility.…”

“…The assays of chemotactic responses of filarial L3 to test solutions were conducted by the modified method described previously by Mitsui et al (2018). Briefly, a 35 mm petri dish filled with 2 ml of 0.6% (w/v) agar (referred to as 'agar plate') was placed over a template transparent sheet (fig.…”

“…This suggests that filarial L3 use water-soluble chemicals as chemosensory cues to reach the wound. In fact, L3 of Brugia pahangi are attracted to water-soluble mammalian-serum, sodium ions and tris(hydroxymethyl)aminomethane (Tris), but are not attracted to volatile mammalian skin and sweat odorants such as urocanic acid and 3-methyl-1-butanol (Gunawardena et al, 2003;Kusaba et al, 2008;Mitsui et al, 2012Mitsui et al, , 2018Wheeler et al, 2020), even though the two odorants are attractants for S. stercoralis L3 (Safer et al, 2007;Castelletto et al, 2014;Gang & Hallem, 2016;Gang et al, 2020). On the other hand, L3 of Ancylostoma caninum are attracted to a host serum and dialysed host serum (Wauters et al, 1982;Vetter et al, 1985); Strongyloides ratti L3 are attracted to dialysed rat serum, mammalian serum and egg albumins, and sodium chloride Tobata-Kudo et al, 2000); and S. stercoralis L3 are attracted to sodium chloride (Forbes et al, 2003).…”

“…The chemical attractants for filarial L3 provide an indispensable foothold for the elucidation of the mechanism of filarial skinpenetrating behaviours. To date, only sodium ions and Tris have been identified as attractants for L3 of B. pahangi (Mitsui et al, 2012(Mitsui et al, , 2018. Sodium ions, a major component of mammalian blood, are easily acceptable as an attractant for filarial L3.…”

“…The objective of the present study was to assess the chemotactic responses of B. pahangi L3 for Tris-related compounds and amino acids and to identify endogenous attractants for L3 using the modified agar-plate assay of Mitsui et al (2018).…”