Crohn's Strictures-Moving Away from the Knife

Crohn's disease (CD) is a lifelong inflammatory bowel disease with a rapidly rising incidence in the pediatric population. A common complication of CD is the development of fibrotic strictures, which may be present at initial diagnosis or develop many years later. Clinical presentation depends on stricture location and degree of obstruction, and strictures frequently contain a mixture of inflammatory and fibrotic tissue. Histological examination of Crohn's strictures shows thickening of the muscular layers and the submucosa, where increased collagen deposition by activated myofibroblasts is concentrated around islands of smooth muscle cells and at the superficial margin of the muscularis propria. No antifibrotic therapies for Crohn's strictures exist. Profibrotic transforming growth factor-β (TGFβ)/bone morphogenetic protein signaling stimulates myofibroblast differentiation and extracellular matrix deposition. Understanding and targeting TGFβ1 downstream signaling is the main focus of current research, raising the possibility of specific antifibrotic therapy in CD becoming available in the future.

Fulvene-5 potently inhibits NADPH oxidase 4 and blocks the growth of endothelial tumors in mice

Hemangiomas are the most common type of tumor in infants. As they are endothelial cell-derived neoplasias, their growth can be regulated by the autocrine-acting Tie2 ligand angiopoietin 2 (Ang2). Using an experimental model of human hemangiomas, in which polyoma middle T-transformed brain endothelial (bEnd) cells are grafted subcutaneously into nude mice, we compared hemangioma growth originating from bEnd cells derived from wild-type, Ang2+/-, and Ang2-/- mice. Surprisingly, Ang2-deficient bEnd cells formed endothelial tumors that grew rapidly and were devoid of the typical cavernous architecture of slow-growing Ang2-expressing hemangiomas, while Ang2+/- cells were greatly impaired in their in vivo growth. Gene array analysis identified a strong downregulation of NADPH oxidase 4 (Nox4) in Ang2+/- cells. Correspondingly, lentiviral silencing of Nox4 in an Ang2-sufficient bEnd cell line decreased Ang2 mRNA levels and greatly impaired hemangioma growth in vivo. Using a structure-based approach, we identified fulvenes as what we believe to be a novel class of Nox inhibitors. We therefore produced and began the initial characterization of fulvenes as potential Nox inhibitors, finding that fulvene-5 efficiently inhibited Nox activity in vitro and potently inhibited hemangioma growth in vivo. In conclusion, the present study establishes Nox4 as a critical regulator of hemangioma growth and identifies fulvenes as a potential class of candidate inhibitor to therapeutically interfere with Nox function.

Rac GTPase isoform-specific regulation of NADPH oxidase and chemotaxis in murine neutrophils in vivo. Role of the C-terminal polybasic domain

The Rho family GTPase Rac acts as a molecular switch for signal transduction to regulate various cellular functions. Mice deficient in the hematopoietic-specific Rac2 isoform exhibit agonist-specific defects in neutrophil chemotaxis and superoxide production, despite expression of the highly homologous Rac1 isoform. To examine whether functional defects in rac2(-/-) neutrophils reflect effects of an overall decrease in total cellular Rac or an isoform-specific role for Rac2, retroviral vectors were used to express exogenous Rac1 or Rac2 at levels similar to endogenous. In rac2(-/-) neutrophils differentiated from transduced myeloid progenitors in vitro, increasing cellular Rac levels by expression of either exogenous Rac1 or Rac2 increased formylmethionylleucylphenylalanine- or phorbol ester-stimulated NADPH oxidase activity. Of note, placement of an epitope tag on the N terminus of Rac1 or Rac2 blunted reconstitution of responses in rac2(-/-) neutrophils. In rac2(-/-) neutrophils isolated from mice transplanted with Rac-transduced bone marrow cells, superoxide production and chemotaxis were fully reconstituted by expression of exogenous Rac2, but not Rac1. A chimeric Rac1 protein in which the Rac1 C-terminal polybasic domain, which contains six lysines or arginines, was replaced with that of the human Rac2 polybasic domain containing only three basic residues, also reconstituted superoxide production and chemotaxis, whereas expression of a Rac2 derivative in which the polybasic domain was replaced with that of Rac1 did not and resulted in disoriented cell motility. Thus, the composition of the polybasic domain is sufficient for determining Rac isoform specificity in the production of superoxide and chemotaxis in murine neutrophils in vivo.

Rac1 in human breast cancer: overexpression, mutation analysis, and characterization of a new isoform, Rac1b

Rac1 is a member of the Ras superfamily of small guanosine triphosphatases (GTPases) that act as molecular switches to control cytoskeletal rearrangements and cell growth. Analogous to Ras, constitutively activating point mutations of Rac1 cause tumorigenic transformation of cell lines. However, there is no information about whether Rac1 is also mutated in vivo. After RT - PCR of Rac1, several clones of seven benign and 10 malignant breast cancer tissues as well as eight breast cancer cell lines were sequenced. Only single-nucleotide polymorphisms of Rac1 could be detected, and none of these corresponded to constitutively activating point mutations that have been used in cell lines for transformation. While sequencing Rac1 in breast tissues, a new Rac1 isoform with an insertion of 19 codons within the reading frame of Rac1 close to switch region II was identified and named Rac1b. The Rac1b protein acts like a fast cycling GTPase in GTP binding and hydrolysis assays. In Northern and Western blot experiments both Rac1 RNA and Rac1 protein had a significantly higher expression in breast cancer tissues compared to normal breast tissue samples. Immunohistochemical staining of Rac1 showed weak Rac1 expression in benign breast disease but high expression level in ductal carcinoma-in-situ, primary breast cancer, and lymph node metastases. In addition, breast tumor cells from patients with recurrent disease had Rac1 expression at the plasma membrane, suggesting activation of Rac1, in patients with aggressive breast cancer. Oncogene (2000).

Myosin I heavy chain kinase: cloning of the full-length gene and acidic lipid-dependent activation by Rac and Cdc42

Acanthamoeba myosin I heavy chain kinase (MIHCK) phosphorylates the heavy chains of amoeba myosins I, increasing their actin-activated ATPase activities. The activity of MIHCK is increased by binding to acidic phospholipids or membranes and by autophosphorylation at multiple sites. Phosphorylation at a single site is necessary and sufficient for full activation of the expressed catalytic domain. The rate of autophosphorylation of native MIHCK is controlled by a region N-terminal to the catalytic domain. By its substrate specificity and the sequence of its C-terminal catalytic domain, MIHCK was identified as a p21-activated kinase (PAK). We have now cloned the full-length genomic DNA and cDNA of MIHCK and have shown it to contain the conserved p21-binding site common to many members of the PAK family. Like some mammalian PAKs, MIHCK is activated by Rac and Cdc42, and this activation is GTP-dependent and accompanied by autophosphorylation. In contrast to mammalian PAKs, activation of MIHCK by Rac and Cdc42 requires the presence of acidic lipids. Also unlike mammalian PAK, MIHCK is not activated by sphingosine or other non-negatively charged lipids. The acidic lipid-binding site is near the N terminus followed by the p21-binding region. The N-terminal regulatory domain of MIHCK contains alternating strongly positive and strongly negative regions. and the extremely Pro-rich middle region of MIHCK has a strongly acidic N-terminal segment and a strongly basic C-terminal segment. We propose that autophosphorylation activates MIHCK by neutralizing the basic segment of the Pro-rich region, thus unfolding the regulatory domain and abolishing its inhibition of the catalytic domain.

[The clinical significance of ECG exercise testing at hospital discharge of patients with acute myocardial infarction]

330 patients were admitted to the intensive care unit of our hospital from January 1985 to December 1986. 141 of the 150 patients aged below 65 years underwent symptom-limited maximal exercise testing on a bicycle ergometer before discharge. No severe complications were noted. 61 of those tested showed a pathological reaction such as angina pectoris, ST-segment depression or ventricular ectopic activity (couplets, ventricular tachycardia). Coronary angiography was performed in 33 patients (23.4%). The outcome of this examination led to coronary bypass surgery in 15 cases and to PTCA in 2. For 9 of these 17 patients exercise testing soon after myocardial infarction was the essential investigation that led to angiography and surgery. Symptom-limited exercise testing before discharge is a safe method of distinguishing patients at risk, requiring further investigations for possible coronary bypass surgery, from those that do not need additional work-up. We conclude that every post-myocardial infarction patient should be exercise-tested before leaving hospital.

[Clinical significance of serum carnitine in the course and prognosis of dilated cardiomyopathy]

Serum carnitine is an essential cofactor for the transport of free fatty acids into the mitochondria. We determined the free and the total serum carnitine in 99 healthy blood donors and 58 patients with different forms of heart muscle disease. Thirty patients had dilated (DCM), 10 hypertrophic (HCM) and 8 alcoholic (ACM) cardiomyopathy and 10 patients had congestive heart failure of different etiology than cardiomyopathy (CHF). Free and total serum carnitine were determined by an enzymatic-spectrophotometric assay according to Pearson. Mean values for free and total serum carnitine were as follows: 47 and 74 mumol/l in controls (C; blood donors), 74 (P less than 0.01 vs. C) and 83 mumol/l in DCM, 66 (P less than 0.01 vs. C) and 89 mumol/l in HCM, 85 (P less than 0.01 vs. C) and 104 mumol/l (P less than 0.05 vs. C) in ACM and 86 (P less than 0.01 vs. C) and 129 mumol/l (P less than 0.01 vs. C) in CHF. Ten patients died during the mean observation time of 13 months, 8 patients with DCM and 2 with CHF; 9 of these 10 patients had initially a markedly increased serum carnitine. Patients with DCM were divided into two groups with normal (n = 15; 25-68 mumol/l) and increased (n = 15; greater than 68 mumol/l) free serum carnitine. Patients with increased serum carnitine showed a significantly higher mortality rate (47%) than patients with normal serum carnitine. It is concluded that free and total serum carnitine are elevated in patients with congestive heart failure, dilated and hypertrophic cardiomyopathy. The etiology of this carnitine metabolism disturbance is unclear but it is probably due to a secondary phenomenon in patients with congestive heart failure or primary myocardial hypertrophy. An increased serum carnitine is a poor prognostic sign in patients with dilated cardiomyopathy.