The role of lipoxygenases in epidermis.

Lipoxygenases (LOX) are key enzymes in the biosynthesis of a variety of highly active oxylipins which act as signaling molecules involved in the regulation of many biological processes. LOX are also able to oxidize complex lipids and modify membrane structures leading to structural changes that play a role in the maturation and terminal differentiation of various cell types. The mammalian skin represents a tissue with highly abundant and diverse LOX metabolism. Individual LOX isozymes are thought to play a role in the modulation of epithelial proliferation and/or differentiation as well as in inflammation, wound healing, inflammatory skin diseases and cancer. Emerging evidence indicates a structural function of a particular LOX pathway in the maintenance of skin permeability barrier. Loss-of-function mutations in the LOX genes ALOX12B and ALOXE3 have been found to represent the second most common cause of autosomal recessive congenital ichthyosis and targeted disruption of the corresponding LOX genes in mice resulted in neonatal death due to a severely impaired permeability barrier function. Recent data indicate that LOX action in barrier function can be traced back to the oxygenation of linoleate-containing ceramides which constitutes an important step in the formation of the corneocyte lipid envelope. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

A European training system in cardiothoracic surgery: is it time?

OBJECTIVE: Training in cardiothoracic surgery across Europe remains diverse and variable despite the ever closer integration of European countries at all levels and in all areas of life. Coupled with the increasing ease of movement across Europe, the need for uniform training programmes has arisen to allow for equivalent accreditation and certification. METHODS: We review the current training paradigms within the specialty across the world and in Europe and also explore the concept of competence. RESULTS: There are diverse training systems across the world and in Europe in particular. Competence-based training is the new model of training; however, competence remains difficult to define and measure. We propose a European Training Programme in Cardiothoracic Surgery that aims to standardize training across the European countries. CONCLUSIONS: The difficulties in unifying training across Europe are numerous, but it is time to implement a European Training System in Cardiothoracic Surgery that will deliver a competence-based curriculum.

Long-term results and prognostic factors after resection of hepatic and pulmonary metastases of colorectal cancer.

BACKGROUND: Resection of colorectal liver or lung metastases is an established therapeutical concept at present. However, an affection of both these organs is frequently still regarded as incurable. METHODS: All cancer patients are documented in our prospective cancer registry since 1995. Data of patients who underwent liver and lung resection for colorectal metastases were extracted and analysed. RESULTS: Sixty-five patients underwent surgery for liver and lung metastases. In 33 cases, the first distant metastasis was diagnosed synchronously to the primary tumour. For the remaining patients, median time interval between primary tumour and first distant metastasis was 18 months (5-69 months). Complete resection was achieved in 51 patients (79 %) and was less likely in patients with synchronous disease (p = 0.017). Negative margins (p = 0.002), the absence of pulmonary involvement in synchronous metastases (p = 0.0003) and single metastases in both organs (p = 0.036) were associated with a better prognosis. Five- and 10-year survival rates for all patients are 57 and 15 % from diagnosis of the primary tumour, 37 and 14 % from resection of the first metastasis and 20 and 15 % from resection of the second metastasis. After complete resection, 5- and 10-year survival rates increased to 61 and 18 %, 43 and 17 % as well as 25 and 19 %, respectively. Long-term survivors (≥10 years) were seen only after complete resection of both metastases. CONCLUSIONS: Patients with resectable liver and lung metastases of the colorectal primary should be considered for surgery after multidisciplinary evaluation regardless of the number or size of the metastases or the disease-free intervals. Clear resection margins are the strongest prognostic parameter.

Epidermis-type lipoxygenase 3 regulates adipocyte differentiation and peroxisome proliferator-activated receptor gamma activity.

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) is essential for adipogenesis. Although several fatty acids and their derivatives are known to bind and activate PPAR gamma, the nature of the endogenous ligand(s) promoting the early stages of adipocyte differentiation has remained enigmatic. Previously, we showed that lipoxygenase (LOX) activity is involved in activation of PPAR gamma during the early stages of adipocyte differentiation. Of the seven known murine LOXs, only the unconventional LOX epidermis-type lipoxygenase 3 (eLOX3) is expressed in 3T3-L1 preadipocytes. Here, we show that forced expression of eLOX3 or addition of eLOX3 products stimulated adipogenesis under conditions that normally require an exogenous PPAR gamma ligand for differentiation. Hepoxilins, a group of oxidized arachidonic acid derivatives produced by eLOX3, bound to and activated PPAR gamma. Production of hepoxilins was increased transiently during the initial stages of adipogenesis. Furthermore, small interfering RNA-mediated or retroviral short hairpin RNA-mediated knockdown of eLOX3 expression abolished differentiation of 3T3-L1 preadipocytes. Finally, we demonstrate that xanthine oxidoreductase (XOR) and eLOX3 synergistically enhanced PPAR gamma-mediated transactivation. Collectively, our results indicate that hepoxilins produced by the concerted action of XOR and eLOX3 may function as PPAR gamma activators capable of promoting the early PPAR gamma-dependent steps in the conversion of preadipocytes into adipocytes.

15-lipoxygenase-1 production is lost in pancreatic cancer and overexpression of the gene inhibits tumor cell growth.

Pancreatic cancer patients have an abysmal prognosis because of late diagnosis and lack of therapeutic options. Pancreatic intraepithelial neoplasias (PanINs), the precursor lesions, are a potential target for chemoprevention. Targeting eicosanoid pathways is an obvious choice because 5-lipoxygenase (5-LOX) has been suggested as a tumor promoter in pancreatic carcinogenesis. Here we provide evidence that 15-lipoxygenase-1 (15-LOX-1) expression and activity may exert antitumorigenic effects in pancreatic cancer. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed absence or very weak expression of 15-LOX-1 in all pancreatic cancer cell lines tested. 15-LOX-1 was strongly stained in normal ductal cells, tubular complexes, and centroacinar cells, but no staining was seen in islets, cancer cells, PanIN lesions, or in tumor cells in lymph node metastases, indicating that 15-LOX-1 expression is lost during tumor development in human pancreas. Overexpression of 15-LOX-1 in pancreatic tumor cells or treatment with its arachidonic acid-derived metabolite resulted in decreased cell growth. These findings provide evidence that loss of 15-LOX-1 may play an important role in pancreatic carcinogenesis, possibly as a tumor suppressor gene. Thus, induction of 15-LOX-1 expression may be an attractive option for the prevention and treatment of pancreatic cancer.

Removal of a left atrial thrombus adherent to a patent foramen ovale occluder.

A 62-year-old man presented with bilateral thromboembolic occlusion of the lower leg arteries 8 months after closure of a patent foramen ovale with an Amplatzer patent-foramen-ovale occluder (AGA Medical Corporation, Plymouth, MN). Then he developed an acute myocardial ischemia. A left heart catheter revealed thromboembolic occlusion of the right coronary artery, and echocardiography demonstrated a thrombus attached to the device within the left atrium. Cerebral computer tomography showed a new ischemic lesion. In an emergency procedure, the device and the left atrial thrombus were removed, the septal defect was closed, and a coronary artery bypass grafting was performed. The patient was discharged from the hospital in stable condition.

Inducible expression of 15-lipoxygenase-2 and 8-lipoxygenase inhibits cell growth via common signaling pathways.

Human 15-lipoxygenase (LOX)-2 and mouse 8-LOX represent orthologous members of the LOX family but display different positional specificities and tissue distribution. To study the functional role of 15-LOX-2 and 8-LOX in keratinocytes, an inducible Tet-On gene expression system was established in the premalignant mouse keratinocyte cell line 308. Doxycycline (dox)-induced expression of enzymatically active 15-LOX-2 and 8-LOX led to an inhibition of cell growth that was associated with an inhibition of DNA synthesis, as shown by a 15-46% reduction of 5-bromo-2-deoxy-uridine (BrdU) incorporation. The inhibitory effects were increased in the presence of exogenous arachidonic acid. In contrast, addition of linoleic acid or the LOX inhibitor baicalein reversed the growth-inhibitory effects. Treatment of the cells with 15-hydroxyeicosatetraenoic acid (HETE) or 8-HETE resulted in a similar inhibition of BrdU incorporation, whereas 13-hydroxyoctadecadienoic acid (HODE) and 9-HODE, in contrast, had no effects. Dox-induced keratinocytes showed increased levels of reactive oxygen species (ROS). The antioxidant N-acetyl-L-cysteine and a specific inhibitor of p38 mitogen-activated protein kinase, but not of extracellular signal-regulated kinase 1/2 or c-Jun N-terminal kinase/stress-activated kinases, completely abolished the LOX-induced growth inhibition, indicating a critical role of ROS and p38. Our data suggest that 15-LOX-2 and 8-LOX, although displaying different positional specificity, may use common signaling pathways to induce growth inhibition in premalignant epithelial cells.

Arachidonate 8(S)-lipoxygenase.

The recently identified mouse 8(S)-lipoxygenase almost exclusively directs oxygen insertion into the 8(S) position of arachidonic acid and, with lower efficiency, into the 9(S) position of linoleic acid. The protein of 677 amino acids displays 78% sequence identity to human 15(S)-lipoxygenase-2 which is considered to be its human orthologue. The 8(S)-lipoxygenase gene, Alox15b, consisting of 14 exons and spanning 14.5 kb is located within a gene cluster of related epidermis-type lipoxygenases at the central region of mouse chromosome 11. 8(S)-Lipoxygenase is predominantly expressed in stratifying epithelia of mice, constitutively in the hair follicle, forestomach, and foot-sole and inducible in the back skin with strain-dependent variations. The expression is restricted to terminally differentiating keratinocytes, in particular the stratum granulosum and 8(S)-lipoxygenase activity seems to be involved in terminal differentiation of mouse epidermis. Tumor-specific up-regulation of 8(S)-lipoxygenase expression and activity indicate a critical role of this enzyme in malignant progression during tumor development in mouse skin.

Modulation of epidermal tumor development caused by targeted overexpression of epidermis-type 12S-lipoxygenase.

In contrast to other 12S-lipoxygenase (LOX) isoforms expressed in the skin of mice, epidermis-type (e) 12S-LOX was found to be transcriptionally down-regulated in the course of epidermal tumor development in NMRI mice. This may indicate that this enzyme is related to antitumorigenic rather than protumorigenic effects. To test this hypothesis, two transgenic mouse lines were generated that differentially expressed e12S-LOX under the control of the bovine keratin 6 promoter known to be constitutively up-regulated in mouse skin tumors. As compared with the wild-type, low transgene expression correlated with a decreased skin tumor response paralleled by an up-regulation of leukocyte-type 12S-LOX and an accumulation of the linoleic acid derivative 13S-hydroxyoctadecadienoic acid. In contrast, high transgene expression coincided with an increased tumor response paralleled by a strong keratin 6 promoter-driven up-regulation of the transgenic e12S-LOX and an accumulation of the arachidonic acid derivative 12S-hydroxyeicosatetraenoic acid as the predominant LOX product. These results indicate a complex interaction between different LOX isoforms and an opposite role of arachidonic acid and linoleic acid products in the modulation of skin carcinogenesis.