Neutral Red Uptake, Cellular Growth and Lysosomal Function: In Vitro Effects of 24 Metals

Abstract

Specific toxic interference in lysosomal activity was evaluated by the relative uptake of neutral red by lysosomes. In this adaptation of the standard neutral red cytotoxicity assay, the results are expressed relative to cell culture protein content to avoid misinterpretation due to the influence on cell proliferation of the chemicals tested. Neuro-2a mouse neuroblastoma cells were exposed in vitro to 24 metal compounds and the lysosomal activity was quantified. Five different patterns of alterations were identified. Group A (ZnCl₂, NaAsO_2, Na2HAsO₄, CdCl₂, SnCl₂, HgCl₂, HgCH₃Cl and TlCOOCH₃) produced an inhibition of the relative uptake of the dye, in marked contrast to the greater inhibition shown by the neutral red uptake assay. Group B (MgCl₂, A1C1₃, KMnO₄₎ NiCl₂, BaCl₂ and Pb[NO₃]2) showed less inhibition with strong parallelism with the neutral red assay. In Group C (CrCl₃, Na₂Cr₂O₇, FeCl₃, CoCl₂, CuCl₂ and Sn[C₂H₅]₄), low-dose stimulation, and inhibition at higher concentrations were found. Group D (LiCl and CrCl₂) stimulated uptake, and Group E (MnCl₂ and Sr[NO₃]₂) produced no significant modifications. The relative uptake of neutral red can be a convenient tool for the study of specific toxic alterations of lysosomes.