A resin cyanoacrylate nanoparticle as an acute cell death inducer to broad spectrum of microalgae

Highlights

• Poly (isobutyl-cyanoacrylate) nanoparticles induced cell death in non-green algae.

• Enlarged mitochondria was frequently detected by transmission electron microscopy.

• Cell covering structure acts as a barrier against cell mortality induction.

• Reactive oxygen species (ROS) scavenger treatment reduced cell mortality.

Abstract

We examined the potency of resin nanoparticles (NPs) to induce cell mortality in diverse non-green algal species (e.g., species in SAR and Hacrobia clades) and the difference in sensitivity to NPs among the species. In total, 18 non-green algal species were co-incubated with laboratory-prepared NPs (mean diameter, 180 nm) composed of poly (isobutylcyanoacrylate) resin NPs (iBCA-NPs).

Exposure to 100 mg L⁻¹ iBCA-NPs for 24 h induced cell death in two of three Bacillariophyceae species, all three Cryptophyceae species, four of six Dinophyta species, three of four Haptophyta strains, and all three Raphidophyceae species. However, exposure at an increased concentration of 1 g L⁻¹ induced cell death in all the examined species. Observation of NP trails showed that they occasionally collided with the cells and bounced off but did not adhere to the cell surface. The reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine substantially delayed cell death induction. This finding strongly suggests that ROS generation is a direct cause of induced cell death.

The cells of Raphidophyceae species that lack covering structures and a Haptophyta strain bearing no coccoliths were more sensitive than species bearing covering structures. Moreover, iBCA-NPs pre-coated with bovine serum albumin or skim milk had severely reduced cell death-inducing potency. We propose a hypothetical mechanism of cell death induction by iBCA-NPs in a wide range of algal species, focusing on cell covering structures and ROS generation.

Introduction

The use and number of engineered resin nanoparticles (NPs), e.g., poly(alkyl)-cyanoacrylate NPs, polystyrene NPs, and polypropylene NPs, have been rapidly increasing. Their physical and chemical properties render them suitable for use in industrial and medical applications, such as in cosmetics, pigmented inks, and crack-resistant paints. However, the potential adverse effects of residual resin NPs on ecosystems are currently a serious concern [1,2].

Historically, studies on the effects of metal oxide NPs such as TiO₂ preceded those on resin NPs [3]. To date, in vitro experiments have shown that metal oxide NPs, carbon NPs, quantum dots, and dendrimers can induce growth inhibition and photosynthesis reduction in various green algal species [[4], [5], [6], [7], [8]]; however, they do not induce acute cell death.

Polycyanoacrylate NPs (PCA-NPs) are resin NPs that are promising for use in medical industries as drug delivery systems owing to their biocompatibility, biodegradability, and ability to adsorb active biological compounds such as antibiotics, antibodies, and enzymes [9,10].

Recently, we reported that poly (isobutylcyanoacrylate) resin NPs (iBCA-NPs) with a mean diameter of 25 nm possess the ability to rapidly induce cell mortality in green microalgae at a concentration of 100 mg L⁻¹. For example, cell mortality was induced in 19 of 25 investigated Volvocales species [11].

Algae are primary producers in aquatic ecosystems. They form the basis of the aquatic food web by providing oxygen to other organisms as well as absorbing trace metals and synthesizing nutrients [12]. Therefore, the harmful effects of algae will eventually affect the function and structure of aquatic ecosystems [13]. Thus, it is essential to analyze the fundamental mechanism of how resin NPs induce algal cell mortality and determine how widely distributed algal species differ in their sensitivity. In this study, we evaluated the effects of iBCA-NP exposure on 18 widely distributed non-green algal species (i.e., 19 strains belonging to SAR and Hacrobia clades). Detailed analyses were performed using Prymnesium parvum (Haptophyta) and Rhodomonas atrorosea (Cryptophyta).