Elsevier

Toxicology Letters

Volume 197, Issue 1, 1 August 2010, Pages 19-28
Toxicology Letters

Skin toxicology of lead species evaluated by their permeability and proteomic profiles: A comparison of organic and inorganic lead

https://doi.org/10.1016/j.toxlet.2010.04.019Get rights and content

Abstract

Lead compounds are known to cause cytotoxicity and genotoxicity. Lead absorption by the skin is an important route through which this metal enters the body. The purpose of this work was to evaluate the skin permeability and toxicological profiles of two lead species, lead acetate and lead nitrate. This study assessed lead-induced toxicity mechanisms by focusing on the histopathology, proteomics, cell growth, and cellular ATP. In vitro skin permeation assays showed that there was no significant difference of lead accumulation within and across the skin between the two lead species. The presence of simulated sweat reduced the skin uptake of lead. The skin deposition of lead acetate was greater than that of lead nitrate with in vivo topical application. On the other hand, lead nitrate produced greater changes in the skin's histology and proteomic profiles compared to lead acetate. Four protein spots which showed significant changes were identified and are discussed in this study. These included glucose-related protein precursor (GRP) 78, K14, α-actin, and Rho GDP-dissociation inhibitor 2 (RhoGDI2). These proteins are respectively associated with oxidative stress, apoptosis, wound healing, and proliferation. Lead presented a biphasic pattern on cell growth and intracellular ATP content, with a stimulating effect at low concentrations and an inhibitory effect on cell proliferation at higher concentrations.

Introduction

Both environmental and occupational exposures to hazardous metals, such as arsenic, cadmium, chromium, and lead, are significant toxicological concerns. In the fields of environmental health and medicine, lead exposure remains one of the most important problems in terms of the prevalence of exposure and public health impacts (Hu et al., 2007). Lead poisoning is a problem in some developing countries where exposure may be high due to continued use of leaded gasoline, hyperurbanization, and industrial pollution (Kwong et al., 2004). Lead is used in the production of a wide range of products including lead-acid batteries, leaded crystal ware, printing dyes, hair coloring dyes, and cosmetics (Woźniak and Blasiak, 2003). Occupational exposure to lead occurs in mines, smelters, and battery plants, as well as the welding of lead-painted metal (Järup, 2003). Exposure to lead is detrimental to the central nervous system and learning abilities. Recent data indicate that there may be neurotoxic effects of lead at lower levels of exposure than previously anticipated (Domínguez et al., 2002, Järup, 2003).

Lead can cause adverse health effects through three routes: inhalation, ingestion, and skin contact. The skin is the largest organ of the body, and provides a protective barrier between the body and the environment. This organ is a critical target for lead-mediated pathological effects (Bae et al., 2001, Hostýnek, 2003). Although the clinical features of lead intoxication are well documented, the mechanisms by which lead compounds produce their deleterious effects prior to the onset of clinical symptoms are not fully understood. The permeation of lead species via the skin has not been systematically evaluated. The aim of this work was to establish profiles of the permeability characteristics of lead compounds into and across the skin. Both in vitro and in vivo skin absorption experiments were performed in this study. This investigation was also designed to clarify and compare the possible mechanisms through which different lead species act on the skin. The two types of lead compounds used in this work included organic lead (lead acetate, Pb(CH3COO)2) and inorganic lead (lead nitrate, Pb(NO3)2).

The skin can react to stresses from environmental stimuli. Each of these stresses may result in any combination of alterations in DNA conformation, levels of messenger (m)RNA, and protein expressions. The stresses can also contribute to post-translational modifications of proteins specific to each stressor (Huang et al., 2005). The electrophilic nature of many metals determines their protein reactivity. Such protein-metal binding typically occurs with lead (Hostýnek, 2003, Thier et al., 2003). Functional proteomics has fostered a novel and deeper understanding of cell systems and pathway properties. Some proteomics might also be suitable as diagnostic or prognostic markers. A proteomic analysis was performed on the skin after topical lead delivery in this study. Possible mechanisms involved in the toxicity of lead species were thus explored.

Section snippets

Animals

The animal experimental protocol was reviewed and approved by the Institutional Animal Care and Use Committee of Chang Gung University. The committee confirmed that the animal experiment followed the guidelines set forth by the Guide for Laboratory Factlines and Care. Female nude mice (ICR-Foxn1nu strain) aged 8 weeks were obtained from the National Laboratory Animal Center (Taipei, Taiwan). The nude mice were sacrificed, and full-thickness skin was excised from the dorsal region in the in

In vitro skin permeation

To better understand the bioavailability of lead, which is important in skin toxicity, the skin permeation characteristics of the two lead compounds after contact with skin were evaluated through an in vitro Franz cell system using nude mouse skin. For topical delivery via the skin, the skin deposition of the permeant is considered to be an important parameter. Lead accumulation within the skin was determined at the end of the in vitro experiment as shown in Fig. 1. Uptake values of 11.10 and

Discussion

In the fields of environmental and occupational health and safety, percutaneous absorption is particularly important when assessing the risk of exposure to toxic substances. Permeation studies can be used to define the diffusion characteristics of xenobiotics as a way of documenting their bioavailability (Tanojo et al., 2001). Proteomics can provide information on the effects of toxic substances on skin irritation and damage. Both techniques were used in this study to elucidate lead's toxicity

Conclusions

We systematically examined and compared the skin permeation and proteomic profiles of two topically applied lead species. The in vitro deposition extents in the skin of lead acetate and lead nitrate were approximately the same. This may have been due to saturation of the compounds within the skin reservoir. In vivo topical application showed that lead acetate had a greater skin deposition compared to lead nitrate. A higher skin uptake of lead species did not guarantee greater skin damage or

Conflict of interest statement

The authors declare that there are no conflicts of interest.

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