Doctor of Philosophy
A new pathobiologic hypothesis has recently emerged that the alveolar structural destruction and loss in emphysema are caused by the deficiency of vascular endothelial growth factor (VEGF). Therefore, this project hypothesized that such pathobiologic VEGF deficiency of emphysematous lungs can be recovered with a natural caffeic acid tetramer, salvianolic acid B (SalB), through activation of signal transducer and activator of transcription 3 (STAT3), so that emphysema can be reversed as a result of inhibition of induced cell death, stimulation of cell proliferation and migration, and promotion of stem cell recruitment to the lungs.
SalB was first shown to be potently anti-oxidative (IC50 = 3.7 μM), but devoid of anti-elastase activity. SalB was then administered to the lungs of healthy rats at 0.2 mg/kg for two weeks, verifying ~1.7-fold increased lung tissue expressions of phosphorylated STAT3 (pSTAT3; an activated form of STAT3) and VEGF. Subsequently, SalB was examined in the anti-cell death assay, cell proliferation and migration assays, and trans-
endothelial stem cell recruitment assay in the in vitro lung epithelial (A549) and endothelial (HMVEC-L) cell systems. SalB at 25 μM exerted significant 48-88 % inhibitory activities against cell death induced with oxidative stress and VEGF receptor blockade (with SU5416) in both cell systems, measured by the trypan blue exclusion and propidium iodide-based flow cytometry assays. SalB at 25 μM also stimulated A549 and HMVEC-L cell proliferation by ~1.4-fold and promoted cell migration by ~1.6-fold, while recovering stem cell recruitment impaired with SU5416 by 60 %. The anti-cell death, and proliferation and migration stimulatory activities of SalB were significantly opposed by pharmacological inhibitors of JAK2 (Janus kinase 2; an upper signal of STAT3), STAT3 and VEGF.
SalB was then examined for its in vivo reversal activities in emphysema induced with porcine pancreatic elastase (PPE) and cigarette smoke extract (CSE) in rats. Upon establishment of emphysema on day 21, SalB was administered to the lungs three times weekly over three weeks. SalB at 0.2 mg/kg significantly recovered ~85 %-impaired treadmill exercise endurance by 57-82 %; and reduced abnormal airspace enlargement by 59-75 %. In the PPE-induced emphysematous rats, SalB also reduced the 4-fold greater alveolar destruction index by 61 %. The lung tissue protein expression by Western blot analysis found that cleaved caspase 3 (cell apoptotic marker) was induced by 13-fold, and VEGF was reduced by 60 % in the PPE -induced emphysematous rats. However, pulmonary treatment with SalB at 0.2 mg/kg normalized these proteins, and also significantly increased the expression of a cell proliferation marker, proliferative cell nuclear antigen (PCNA) by 2.6-fold. Note however that SalB treatment did not reduce the neutrophilic myeloperoxidase activity in the lungs induced in the PPE-induced rats. Taken all together, this study has demonstrated that SalB potently inhibited lung cell death, stimulates lung cell proliferation and migration, and restores stem cell migration with its mechanism of STAT3 activation and VEGF elevation and reversed established emphysema in rat models.
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