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Effects of particulate and soluble cadmium species on biochemical and functional parameters in cultured murine
P L Goering1, R K Kuester, A R Neale
1Center for Devices and Radiological Health, Office of Science and Technology, Division of Life Sciences, Food and Drug Administration, Rockville, Maryland 20852, USA. plg@cdrh.fda.gov
Abstract:
Cultured murine macrophages (RAW 264.7) were used to evaluate the temporal relationships between cytotoxicity, phagocytosis, tumor necrosis factor-alpha (TNF-alpha), and nitric oxide (NO) production, and alterations in expression of stress proteins after exposure to cadmium oxide (CdO) or cadmium chloride (CdCl(2)), particulate and soluble forms of cadmium, respectively. Macrophages were exposed in vitro to CdO (25 or 50 microg) or CdCl(2) (30 or 40 microM) for 2 to 72 h. Cytotoxicity was not evident until 18 h when exposed to 30 microM CdCl(2) or 25 microg CdO, but occurred as early as 12 h after exposure to 40 microM CdCl(2) or 50 microg CdO. Relative to untreated controls, phagocytic activity decreased progressively from 2 to 24 h after exposure to both forms of cadmium. TNF-alpha levels increased to 2- to 3-fold after 4 h and remained elevated until 24 h after exposure to 25 and 50 microg CdO and 30 microM CdCl(2), but decreased by 18-24 h at 40 microM CdCl(2). CdCl(2) or CdO alone did not induce NO; however, both cadmium species reduced lipopolysaccharide (LPS)-stimulated NO production in a dose-dependent manner. Enhanced de novo synthesis of 70- and 90-kD heat shock, or stress, proteins was observed 2 to 8 h after exposure to both CdCl(2) and CdO; however, synthesis of these proteins returned to control levels by 24 h. Stress protein synthesis was enhanced by CdCl(2) or CdO prior to cytotoxicity, but coincided with a decrease in phagocytic capacity and an increase in TNF-a levels. The data suggest that cultured macrophages respond similarly in vitro to a particulate form and a soluble form of cadmium in a cell type that plays a pivotal role in inflammatory and immune responses.
Insights
Both cadmium forms (CdO and CdCl2) similarly affected cultured macrophages, impacting stress protein synthesis, phagocytosis, and TNF-alpha levels before causing cytotoxicity. Nitric oxide production was reduced by cadmium exposure.
Area of Science:
- Immunotoxicology
- Cellular Biology
- Environmental Health
Background:
- Macrophages play a critical role in immune and inflammatory responses.
- Cadmium exposure, through various forms, can induce cellular toxicity and modulate immune functions.
- Understanding the differential effects of particulate versus soluble cadmium is crucial for risk assessment.
Purpose of the Study:
- To investigate the temporal relationships between cadmium-induced cytotoxicity, phagocytosis, tumor necrosis factor-alpha (TNF-alpha), nitric oxide (NO) production, and stress protein expression in murine macrophages.
- To compare the in vitro effects of particulate cadmium oxide (CdO) and soluble cadmium chloride (CdCl2) on macrophage function and response.
Main Methods:
- Cultured murine macrophages (RAW 264.7) were exposed to varying concentrations of CdO or CdCl2 for 2 to 72 hours.
- Assessed cytotoxicity, phagocytic activity, TNF-alpha and NO production, and de novo synthesis of stress proteins (70- and 90-kD).
Main Results:
- Cytotoxicity was observed after 12-18 hours, depending on cadmium form and concentration.
- Phagocytic activity decreased progressively from 2 to 24 hours post-exposure.
- TNF-alpha levels increased early and remained elevated, while NO production was suppressed in a dose-dependent manner.
- Enhanced synthesis of stress proteins occurred within 2-8 hours, preceding cytotoxicity but coinciding with reduced phagocytosis and increased TNF-alpha.
Conclusions:
- Both particulate CdO and soluble CdCl2 elicit similar temporal responses in macrophages in vitro.
- Stress protein induction, altered phagocytosis, and TNF-alpha modulation occur before overt cytotoxicity.
- Macrophages, central to immune responses, exhibit significant functional changes upon cadmium exposure, highlighting potential immunotoxicological risks.
