Thalidomide, a sedative originally used to treat morning sickness and now used to treat leprosy and multiple myeloma, is also a teratogen that induces birth defects in humans such as limb truncations and microphthalmia. However, the teratogenic mechanism of action of this drug remains obscure. Thalidomide induces limb and eye defects in the chicken embryo at an EC ₅₀ of 50 μg/kg egg wt and apoptosis in primary human embryonic fibroblasts (HEFs) at an EC ₅₀ of 8.9 μM. Using these model systems, we demonstrate by semiquantitative reverse transcriptase‐polymerase chain reaction and whole‐mount in situ hybridization that thalidomide‐induced oxidative stress enhances signaling through bone morphogenetic proteins (Bmps). This leads to up‐regulation of the Bmp target gene and Wnt antagonist Dickkopfl (Dkkl) with subsequent inhibition of canonical Wnt/β‐catenin signaling and increased cell death as shown by trypan blue and terminal deoxynucleotidyl transferase‐mediated nick end labeling staining. Thalidomide‐induced cell death was dra‐matically reduced in HEFs and in embryonic limb buds by the use of inhibitors against Bmps, Dkkl, and Gsk3β,a β‐catenin antagonist acting downstream of Dkkl in the Wnt pathway. Most interestingly, blocking of Dkkl or Gsk3β dramatically counteracts thalido‐mide‐induced limb truncations and microphthalmia. From this, we conclude that perturbing of Bmp/Dkkl/ Wnt signaling is central to the teratogenic effects of thalidomide.—Knobloch, J., Shaughnessy, Jr., J. D., Rüther, U. Thalidomide induces limb deformities by perturbing the Bmp/Dkkl/Wnt signaling pathway FASEB J. 21, 1410–1421 (2007)

Many hypotheses have been proposed to explain the molecular mechanism of thalidomide teratogenicity, in particular regarding to limb defects. Most experimental evidence in vivo has been provided for a model that suggests the generation of oxidative stress by thalidomide with subsequent down-regulation of Wnt and Akt survival pathways. As a consequence apoptosis is induced during early embryonic limb development resulting in limb truncations. Here we summarize and discuss the relevant data supporting this hypothesis. We extend this model by presenting new data demonstrating an involvement of the transcription factors Tbx5 and Sall4 in thalidomide-induced molecular pathology. Finally, we discuss a possible participation of other stress-responsive and/or pro-apoptotic transcription factors in the mechanism of thalidomide teratogenicity.

Chronic obstructive pulmonary disease (COPD) therapy is complicated by corticosteroid resistance of the interleukin 8 (IL-8)-dependent and granulocyte macrophage-colony stimulating factor (GM-CSF)-dependent chronic airway inflammation, for whose establishment human airway smooth muscle cells (HASMCs) might be crucial. It is unclear whether the release of inflammatory mediators from HASMCs is modulated by cigarette smoking and is refractory to corticosteroids in COPD. Resveratrol, an antiaging drug with protective effects against lung cancer, might be an alternative to corticosteroids in COPD therapy. Vascular endothelial growth factor (VEGF) might offer protection from developing emphysema. We tested the following hypotheses for HASMCs: 1) smoking with or without airway obstruction modulates IL-8, GM-CSF, and VEGF release; and 2) corticosteroids, but not resveratrol, fail to inhibit cytokine release in COPD. Cytokine release from HASMCs exposed to tumor necrosis factor α (TNFα), dexamethasone, and/or resveratrol was measured via enzyme-linked immunosorbent assay and compared between nonsmokers (NS), smokers without COPD (S), and smokers with COPD (all n = 10). In response to TNFα, IL-8 release was increased, but GM-CSF and VEGF release was decreased in S and COPD compared with NS. Dexamethasone and resveratrol inhibited concentration-dependently TNFα-induced IL-8, GM-CSF, and VEGF release. For IL-8 and GM-CSF efficiency of dexamethasone was NS > S > COPD. That of resveratrol was NS = S = COPD for IL-8 and NS = S < COPD for GM-CSF. For VEGF the efficiency of dexamethasone was NS = S = COPD, and that of resveratrol was NS = S > COPD. All resveratrol effects were partially based on p38 mitogen-activated protein kinase blockade. In conclusion, smoking modulates cytokine release from HASMCs. Corticosteroid refractoriness of HASMCs in COPD is cytokine-dependent. Resveratrol might be superior to corticosteroids in COPD therapy, because it more efficiently reduces the release of inflammatory mediators and has limited effects on VEGF in COPD.

Rationale: The increased susceptibility to bacterial infections in chronic obstructive pulmonary disease (COPD) is critical for exacerbations. Toll-like receptor-4 (TLR4) detects bacteria via LPS and induces IFN-γ–based immune responses. The direct responsiveness of Th1 lymphocytes to LPS is disputed because they lack surface expression of the TLR4 coreceptor CD14. Objectives: We hypothesized that the Th1-mediated adaptive immune response to bacterial infections is impaired in COPD. Methods: LPS-induced TLR4 expression and IFN-γ release in and from ex vivo–generated Th1 cells was compared among nonsmokers (n = 14), smokers without COPD (n = 13), and smokers with COPD (n = 25) via quantitative reverse transcription polymerase chain reaction, Western blot, and ELISA. TLR4 transfection experiments were performed to functionally link receptor to IFN-γ dysregulation in COPD. Measurements and Main Results: Short-chain LPS from Salmonella species and nontypeable Haemophilus influenzae and nontypeable Haemophilus influenzae whole-cell extract all induced TLR4 expression via TLR4/MyD88/IRAK/mitogen-activated protein–kinase signaling and IFN-γ release via TLR4/TRIF/IKKε/TBK1 signaling in Th1 cells of nonsmokers. These effects were all impaired in smokers with and without COPD. The LPS responses were partially dependent on soluble CD14 and correlated positively to lung-function parameters but negatively to cigarette smoking (pack-years). Endogenous MyD88/IRAK signaling antagonists were up-regulated in Th1 cells of smokers and COPD, and TLR4 overexpression in Th1 cells of COPD restored LPS-dependent IFN-γ release. Conclusions: Th1 cells directly respond to short-chain LPS. Cigarette smoking suppresses Th1-mediated immune responses to gram-negative bacterial infections by interfering with MyD88/IRAK signaling thereby reducing LPS-induced TLR4 expression. This can explain the increased susceptibility to bacterial infections in COPD. Targeting TLR signaling might be useful to reduce exacerbation rates.