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The effects of clofibrate ingestion on alveolar macrophage peroxisome content and oxygen metabolism
Abstract:
Respiratory burst activity in alveolar macrophages in response to particulate and soluble challenges, such as zymosan particles and phorbol myristate acetate (PMA), is not nearly as dependent upon membrane stimulation as in neutrophils. Microperoxisomes are subcellular organelles containing catalase and are present in lung macrophages and cells of other organs. Evidence from liver cells indicates that peroxisomes are intimately involved with hydrogen peroxide and lipid metabolism. Clofibrate (2-(p-chlorophenoxy)-2-methylpropionic acid ethyl, Atromid-S-), a hypolipidemic drug known to cause peroxisomal proliferation in liver cells, was studied with respect to its ability to cause increases in the microperoxisome content and to alter the cellular metabolism of alveolar macrophages. Liver weight increased over a 2-week drug treatment period while lung weight remained unchanged. Plasma triglyceride levels were decreased by the treatment, indicating the effectiveness of the drug. Unlike the effect on liver cells, however, clofibrate did not cause a proliferation of microperoxisomes, as determined by morphometric analysis. Oxygen consumption and hydrogen peroxide generation by alveolar macrophages in response to either stimulant (zymosan or PMA) was no greater in clofibrate-treated rats than in controls. Superoxide release, when expressed as the change in response to PMA, appeared elevated in the drug group; statistical significance, however, was not demonstrated. The hexose monophosphate shunt (HMP), which produces reducing equivalents for lipid biosynthesis, was elevated in macrophages from clofibrate-treated rats when expressed similarly. The significance of these results in relation to the known effects of the drug on liver cells.
Insights
Clofibrate, a lipid-lowering drug, did not increase microperoxisomes in rat alveolar macrophages. While it affected lipid metabolism, it did not significantly alter respiratory burst activity in these lung cells.
Area of Science:
- Cell Biology
- Pharmacology
- Pulmonary Medicine
Background:
- Microperoxisomes are organelles involved in hydrogen peroxide and lipid metabolism.
- Clofibrate induces peroxisome proliferation in liver cells.
- Alveolar macrophages play a role in lung immune responses.
Purpose of the Study:
- To investigate clofibrate's effect on microperoxisome content in alveolar macrophages.
- To assess clofibrate's impact on cellular metabolism and respiratory burst activity in alveolar macrophages.
- To compare clofibrate's effects on lung macrophages with its known effects on liver cells.
Main Methods:
- Rats were treated with clofibrate for 2 weeks.
- Morphometric analysis was used to quantify microperoxisome content.
- Oxygen consumption, hydrogen peroxide generation, and superoxide release were measured.
- Hexose monophosphate shunt activity was assessed.
Main Results:
- Clofibrate treatment increased liver weight and decreased plasma triglyceride levels but did not alter lung weight.
- Microperoxisome proliferation was not observed in alveolar macrophages from clofibrate-treated rats.
- Respiratory burst activity (oxygen consumption, hydrogen peroxide generation) remained unchanged.
- Hexose monophosphate shunt activity was elevated in macrophages from treated rats, but superoxide release did not reach statistical significance.
Conclusions:
- Clofibrate does not induce microperoxisome proliferation in rat alveolar macrophages, unlike its effect in liver cells.
- The drug did not significantly enhance the respiratory burst activity of alveolar macrophages.
- Elevated hexose monophosphate shunt activity suggests potential alterations in lipid metabolism within macrophages, warranting further investigation.