Modulating effect of keratinocyte growth factor on cellular kinetics of murine lung(I)

Keratinocyte growth factor (KGF) causes the proliferation of type II pneumocytes in the lungs and confers protection against many external stimulation in the lung. Historically, the kinetic parameters, especially of slowly proliferating normal tissues, such as the lung, were difficult to measure. However, recently developed techniques made it possible to measure accurately the cellular kinetics in normal tissues. Flow cytometric techniques following bromodeoxyuridine (BrdUrd) incorporation into DNA of cells allow the accurate measurement of cellular proliferation. The purpose of this study was to measure the changes of the dynamic kinetics of normal lung tissue after treatment with KGF so as to build up the basis to prevent the occurrence of radiation-induced pneumonitis.

C3Hf/Kam mice were treated intratracheally (i.t.) with KGF (5 mg/kg) or the control (saline) and were sacrificed at 0, 1, 2, 3, 4, 5, and 7 days. The mice were labeled intraperitoneally (i.p.) with BrdUrd (60 mg/kg) at 20 minutes or 6 hours before sacrifice. Lungs were excised, fixed in 60% ethanol, digested to produce nuclei; and BrdUrd as well the total DNA content were labeled for flow cytometric analysis. The kinetic parameters including the labeling index (LI), duration of S-phase (T(S)), and potential doubling time (T(pot)) were measured by novel analytical methodology. Immunofluorescence staining was used to identify the specific cell type that was proliferating.

(1)An optimum route for the administration (i.t.), dose (5 mg/kg), and time course of KGF to stimulate proliferation of type II pneumocytes in the lungs was established. (2)Lung LI control values (0.5%) rose to a maximum (5.5%) at 3 days after KGF treatment and returned to normal level on the 7(th) day. (3)Of the lung tissue, there is a dramatic reduction in T(pot) from 75.5 days to 4.7 days in the KGF-treated mice, while the saline-treated control mice exhibited no change in proliferative parameter values.

KGF caused the proliferation of type II pneumocytes, followed with the elevated LI and reduced T(pot). This proliferative effect was transient and levels returned to normal level by the 7(th) day. The data obtained from this study would lay the groundwork for future investigation of KGF as a possible radioprotector of the lung in the field of radiation oncology.