Taurine Protects rat Bronchioles from Acute Ozone Exposure: A Freeze Fracture and Electron Microscopic Study

Abstract

Dietary taurine has been shown to protect rat and hamster lung epithelia from acute oxidant injury. One of the earliest morphologic criteria of oxidant injury is the alteration of tight junctions of the peripheral lung airways. In the present study, we have used this criteria to evaluate whether taurine was capable of protecting rat lungs from ozone exposure. Rats were treated for 10 days with 50% taurine in their drinking water, prior to exposure to 2 ppm of ozone for 3 hours. The lungs from rats pretreated with taurine and exposed to ozone were compared to untreated rats exposed to ozone and air-exposed controls. At 2, 6, 12, 24, 48, and 72 hours after exposure to air or ozone, rats were anesthetized and the lungs perfusion-fixed through the right side of the heart with a solution of glutaraldehyde and paraformaldehyde. Light microscopy revealed the typical, mild inflammatory cell infiltrate beginning at 6 hours after ozone exposure in bronchioles, alveolar ducts, and surrounding alveoli which was absent in the lungs of animals treated with taurine. Electron microscopic analysis of thin sections indicated alterations in tight junctions which was confirmed by tracer studies using ruthenium red and lanthanum. Alterations in airway epithelium tight junctions were seen 2 and 6 hours after ozone treatment and only in the 2-hour tissues from animals pretreated with taurine prior to ozone exposure. Freeze-fracture replicas from all exposure groups by electron microscopy revealed that only the 2- and 6-hour groups showed alterations in tight junctions. The alterations were characterized by decreased number of fibrils and breaks in the fibrils. Rats treated with taurine and exposed to ozone exhibited these alterations focally at 2 hours exposure and no changes were noted at 6 hours post ozone exposure. These data confirmed previous findings that injury induced by ozone is transient and that taurine protects the bronchioles from this form of oxidant injury