Phosphodiesterase type 4 expression and anti-proliferative effects in human pulmonary artery smooth muscle cells

BACKGROUND: Pulmonary arterial hypertension is a proliferative vascular disease, characterized by aberrant regulation of smooth muscle cell proliferation and apoptosis in distal pulmonary arteries. Prostacyclin (PGI(2)) analogues have anti-proliferative effects on distal human pulmonary artery smooth muscle cells (PASMCs), which are dependent on intracellular cAMP stimulation. We therefore sought to investigate the involvement of the main cAMP-specific enzymes, phosphodiesterase type 4 (PDE4), responsible for cAMP hydrolysis. METHODS: Distal human PASMCs were derived from pulmonary arteries by explant culture (n = 14, passage 3–12). Responses to platelet-derived growth factor-BB (5–10 ng/ml), serum, PGI(2 )analogues (cicaprost, iloprost) and PDE4 inhibitors (roflumilast, rolipram, cilomilast) were determined by measuring cAMP phosphodiesterase activity, intracellular cAMP levels, DNA synthesis, apoptosis (as measured by DNA fragmentation and nuclear condensation) and matrix metalloproteinase-2 and -9 (MMP-2, MMP-9) production. RESULTS: Expression of all four PDE4A-D genes was detected in PASMC isolates. PDE4 contributed to the main proportion (35.9 ± 2.3%, n = 5) of cAMP-specific hydrolytic activity demonstrated in PASMCs, compared to PDE3 (21.5 ± 2.5%), PDE2 (15.8 ± 3.4%) or PDE1 activity (14.5 ± 4.2%). Intracellular cAMP levels were increased by PGI(2 )analogues and further elevated in cells co-treated with roflumilast, rolipram and cilomilast. DNA synthesis was attenuated by 1 μM roflumilast (49 ± 6% inhibition), rolipram (37 ± 6%) and cilomilast (30 ± 4%) and, in the presence of 5 nM cicaprost, these compounds exhibited EC(50 )values of 4.4 (2.6–6.1) nM (Mean and 95% confidence interval), 59 (36–83) nM and 97 (66–130) nM respectively. Roflumilast attenuated cell proliferation and gelatinase (MMP-2 and MMP-9) production and promoted the anti-proliferative effects of PGI(2 )analogues. The cAMP activators iloprost and forskolin also induced apoptosis, whereas roflumilast had no significant effect. CONCLUSION: PDE4 enzymes are expressed in distal human PASMCs and the effects of cAMP-stimulating agents on DNA synthesis, proliferation and MMP production is dependent, at least in part, on PDE4 activity. PDE4 inhibition may provide greater control of cAMP-mediated anti-proliferative effects in human PASMCs and therefore could prove useful as an additional therapy for pulmonary arterial hypertension

Trends in Market Demand for Internal Medicine 1999 to 2004: An Analysis of Physician Job Advertisements

BACKGROUND: The health care marketplace has changed substantially since the last assessment of demand for internal medicine physicians in 1996. METHODS: We reviewed internal medicine employment advertisements published in 4 major medical journals between 1996 and 2004. The number of positions, specialty, and other practice characteristics (e.g., location) were collected from each advertisement. RESULTS: Four thousand two hundred twenty-four advertisements posted 4,992 positions. Of these positions, jobs in the Northeast (31% of positions) or single specialty groups (36.8% of positions) were most common. The relative proportion of advertisements for nephrologists declined (P<.001), while the relative proportions of advertisements for critical care specialists (0.5% in 1996 to 1.7% in 2004, P = .004) and hospitalists (1.0% in 1996 to 12.1% in 2004, P<.001) increased. Advertisements for outpatient-based generalist positions (i.e., Primary Care and Internal Medicine) declined (−2.7% relative annual change, 95% confidence interval [95% CI] −4.1%, −1.2%) between 1996 and 2004, a decrease largely due to a substantial decline in advertisements noted between 1996 and 1998. However, over the entire time period, the combined proportion of advertisements for all generalists (hospitalists and outpatient-based generalists) did not change (0.5% relative annual change, 95% CI −0.8% to 2.0%). CONCLUSIONS: Since 1996, demand for the majority of medical subspecialties has remained constant while relative demand has decreased for primary care and increased for hospitalists and critical care. Increase in demand for generalist-trained hospitalists appears to have offset falling demand for outpatient generalists