The effect of 3-methylindole on the uptake and incorporation of 14C-choline into phospholipids in lung tissue slices

Role of thyroid hormone in de novo synthesis of cholinephosphotransferase in guinea pig lung mitochondria and microsomes

It is known that thyroid hormone enhances the biosynthesis of phosphatidylcholine in the lung. The purpose of the present study was to investigate the effects of thyroid hormone on the activity of cholinephosphotransferase, the terminal enzyme in the CDP-choline pathway, in guinea pig lung mitochondria and microsomes. Intramuscular injection of triiodothyronine (T3, 0.25-4 mg/kg body wt) stimulated the activities of both mitochondrial and microsomal enzymes in a dose-dependent manner. However, the stimulation was much more pronounced in the microsomes than in the mitochondria. The stimulatory effect of T3 was blocked by the intraperitoneal injection of both actinomycin D and cycloheximide in the microsomes, whereas in the mitochondria, the hormonal effect was blocked only by cycloheximide. Thus, it is suggested that T3 stimulates not only the nucleocytoplasmic system for the de novo synthesis of the enzyme, but possibly also the regulation of the transport of the synthesized protein into the mitochondria. Furthermore, administration of T3 produced an increase in the uptake and incorporation of [14C]choline into phospholipids of lung slices in vitro. However, this effect was blocked by intraperitoneal injection of both actinomycin D and cycloheximide. Thus, the change in CPT activity by T3 in mitochondria is not reflected by enhanced incorporation of choline into phosphatidylcholine.

The effect of bleomycin on the uptake and incorporation of [14C]choline into phospholipids in hamster lung tissue slices

Intratracheal administration of the anticancer drug bleomycin to hamsters produced an increase in the uptake and incorporation of [14C]choline into phospholipids of lung slices in vitro. The stimulatory effect is opposite to the results obtained previously using [14C]acetate and would appear to occur distal to cytidine diphosphocholine. Although alternate explanations are possible, the results are consistent with morphological evidence, published by others, indicating an increase in lung phospholipid following bleomycin treatment, and illustrate the significance of precursor selection when evaluating the effects of xenobiotics on phospholipid synthesis.

The metabolic basis of 3-methylindole-induced pneumotoxicity

3-Methylindole (3MI), an abnormal metabolite of tryptophan, causes acute pulmonary edema and emphysema. 3MI toxicity is species-, tissue- and cell-specific and is an excellent model for understanding the processes of chemically-induced lung injury. Experimental evidence showed that 3MI is metabolically activated by both microsomal cytochrome P-450-dependent mixed function oxidase (MFO) and prostaglandin H synthase (PHS) systems in the lung. Formation of a free radical intermediate during 3MI metabolism is the initial chemical event which is responsible for the pneumotoxicity. 3MI free radicals bind covalently to microsomal protein and induce lipid peroxidation. Microsomal enzymes which regulate the glycogen and phospholipid biosynthesis in the lung are altered during the cellular repair processes after 3MI-induced lung injury. Inhibition of cellular differentiation from Type II to Type I cells and impaired surfactant function may be crucial to the disease process.

Impaired surfactant function in 3-methylindole-induced lung injury in goats

1. This study was designed to monitor the changes in surfactant quantity and function in the 72 hr following 3-methylindole (3MI) infusion in goats. 2. 3MI, at 35 mg/kg body wt, caused an increase in surfactant phospholipid isolated from lamellar bodies and lavage fluid. 3. The function of surfactant isolated from lavage fluid was tested using the pulsating bubble surfactometer. The results indicated a serious impairment in the ability to lower surface tension in vitro. 4. Results suggested 3MI caused an impaired surfactant function rather than surfactant synthesis in response to epithelial damage.