Genetic susceptibility to nickel-induced acute lung injury

Abstract

Human exposure to insoluble and soluble nickel compounds is extensive. Besides wide usage in many industries, nickel compounds are contained in cigarette smoke and, in low levels, in ambient particulate matter. Soluble nickel particulate, especially nickel sulfate (NiSO₄), has been associated with acute lung injury. To begin identifying genes controlling susceptibility to NiSO₄, mean survival times (MSTs) of eight inbred mouse strains were determined after aerosol exposure. Whereas A/J (A) mice were sensitive, C57BL/6J (B6) mice survived nearly twice as long (resistant). Their offspring were similarly resistant, demonstrating heritability as a dominant trait. Quantitative trait locus (QTL) analysis of backcross mice generated from these strains identified a region on chromosome 6 significantly linked to survival time. Regions on chromosomes 1 and 12 were suggestive of linkage and regions on chromosomes 8, 9, and 16 contributed to the response. Haplotype analysis demonstrated that QTLs on chromosomes 6, 9, 12, and 16 could explain the MST difference between the parental strains. To complement QTL analysis results, cDNA microarray analysis was assessed following NiSO₄ exposure of A and B6 mice. Significant expression changes were identified in one or both strains for >100 known genes. Closer evaluation of these changes revealed a temporal pattern of increased cell proliferation, extracellular matrix repair, hypoxia, and oxidative stress, followed by diminished surfactant proteins. Certain expressed sequence tags clustered with known genes, suggesting possible co-regulation and novel roles in pulmonary injury. Together, results from QTL and microarray analyses of nickel-induced acute lung injury survival allowed us to generate a short list of candidate genes.

Introduction

Particulate matter (PM) levels associated with respiratory morbidity and mortality are low compared to the existing scientific literature, suggesting that individual susceptibility differences may play a role in response. Clinical studies demonstrated that individuals vary in bronchoconstriction induced by ozone (O₃), a common respiratory irritant (McDonnell et al., 1985). Inbred mouse strains also vary in sensitivity to O₃-induced respiratory effects, including acute lung injury (Stokinger, 1957; Goldstein et al., 1973; Ichinose et al., 1982; Prows et al., 1997, Prows et al., 1999) and O₃-induced increases in neutrophils or total proteins retrieved from bronchoalveolar lavage (BAL) fluid (Kleeberger et al., 1990, Kleeberger et al., 1993a, Kleeberger et al., 1993b, Kleeberger et al., 1997a). These studies indicated not only that survival of O₃-induced acute lung injury is controlled by multiple genetic loci (i.e. polygenic), but also that the major genes controlling susceptibility to acute lung injury survival differ from those controlling neutrophil influx or BAL total proteins.

Besides O₃, other environmental and surrogate environmental pollutants have been shown to induce differential responses in mice and rats. For example, inbred mice show susceptibility differences to NO₂-induced pulmonary inflammation (Holroyd et al., 1997; Kleeberger et al., 1997b) and to acid-coated particle-induced macrophage phagocytosis (Ohtsuka et al., 2000). Recent studies of residual oil fly ash (ROFA), a PM surrogate, demonstrated that the water-soluble metals (e.g., vanadium, chromium, nickel, and iron) contained in ROFA may be responsible for the observed acute lung injury (Costa and Dreher, 1997; Dreher et al., 1997; Dye et al., 1997). In vitro studies reported that the active components of ROFA were vanadium, chromium, and nickel; vanadium was the most active (Pritchard et al., 1996; Kodavanti et al., 1998a, Kodavanti et al., 1998b). On the other hand, in vivo studies demonstrated that nickel was the most biologically active of the metals found in ROFA (Pritchard et al., 1996; Costa and Dreher, 1997; Kodavanti et al., 1998a, Kodavanti et al., 1998b). Additional in vivo studies with intratracheal instillation of ROFA found differences in rat strain sensitivity, suggesting genetic susceptibility may play a role in individual responsiveness to inhaled PM (Kodavanti et al., 1997).

Acute lung injury is characterized by a deficit in gas exchange, owing to macrophage activation, epithelial and endothelial disruption, and surfactant protein (SP) dysfunction (Lewis and Jobe, 1993; Levy et al., 1995). Because numerous insults can induce acute lung injury, studying additional agonists could reveal common mechanisms likely to involve pathways that control macrophage activation, epithelial or endothelial injury, and oxidative stress (Pryor et al., 1990; Stohs and Bagchi, 1995; Pritchard et al., 1996). For example, insoluble ultrafine particulate, such as those generated from polytetrafluoroethylene (PTFE), can induce acute lung injury (Pryor et al., 1990; Johnston et al., 1996; Oberdörster et al., 1998). In fact, we found a similar strain phenotype pattern for acute lung injury survival in mice following exposure to PTFE (Wesselkamper et al., 2000) as seen with O₃ (Prows et al., 1997). In both cases, A/J (A) mice were sensitive and C57BL/6J (B6) mice were relatively resistant to the induced acute lung injury.

Certain transition metals also can induce acute lung injury. Of the transition metals enriched in the fine fraction of ambient PM and the workplace, nickel compounds can be especially harmful (NIOSH, 1977; IARC, 1990; NTP, 1996). Nickel occurs primarily in soluble (e.g., sulfate, chloride and acetate) and insoluble (e.g., oxide and elemental nickel) forms. Nickel enters the environment via many sources (Table 1), primarily through high temperature combustion, electroplating, and smelting processes (Senior and Flagan, 1982; Milford and Davidson, 1987; IARC, 1990; NTP, 1996). The fraction of the population exposed to nickel in the environment is significant (Table 2), and still others are exposed in the workplace (Table 3). Besides ambient and occupational exposures, nickel (0.2–0.51 μg/m³) is a component of mainstream cigarette smoke in concentrations greater than other metal ions, such as copper, cadmium, and iron (0.19, 0.07–0.350, and 0.042 μg/cigarette, respectively) (IARC, 1986).

Previous inhalation exposures of rats and mice to NiSO₄ (Benson et al., 1988; Dunnick et al., 1988; Benson et al., 1995; Dunnick et al., 1995; NTP, 1996) noted acute and chronic respiratory effects. Because of the prevalence of nickel exposures and the link to respiratory morbidity and mortality in laboratory animals, we initiated studies using nickel concentrations at or near the current occupational standard (i.e. TLV=100 μg Ni/m³) to determine the effects of NiSO₄ on different strains of inbred mice. At these concentrations, NiSO₄ produced an acute lung injury in inbred strains of mice, ultimately resulting in death due to endothelial disruption and hemorrhagic pulmonary edema (Wesselkamper et al., 2000). This acute lung injury was similar to that seen with O₃- and PTFE-induced lung injuries. An important distinction, however, was that the NiSO₄-induced lung injury progressed much slower than that caused by O₃ or PTFE (Wesselkamper et al., 2000)––a timeframe that more closely resembles the human condition. Given that (1) little is known currently about susceptibility differences to fine PM; (2) NiSO₄ can be a frequent component of environmental and occupation air; and (3) NiSO₄ can induce an acute lung injury with a progression approximating that seen clinically, we sought to determine a mouse model to identify the genetic factors controlling survival differences to nickel-induced acute lung injury. Once established, this mouse model was utilized in quantitative trait locus (QTL), haplotype, and cDNA microarray analyses to investigate the genetic determinants of NiSO₄-induced acute lung injury.