Jan C. Becker

Heme oxygenase-1 induction may explain the antioxidant profile of aspirin

Aspirin is known to exert antioxidant effects by as yet unidentified mechanisms. In cultured endothelial cells derived from human umbilical vein, aspirin (30-300 microM) increased heme oxygenase-1 (HO-1) protein levels in a concentration-dependent fashion up to fivefold over basal levels. HO-1 induction was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of both carbon monoxide and bilirubin. Pretreatment with aspirin or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by aspirin were not mimicked by indomethacin, another inhibitor of cyclooxygenase. The nitric oxide (NO) synthase blocker L-NAME prevented aspirin-dependent HO-1 induction. These findings demonstrate that aspirin targets HO-1, presumably via NO-dependent pathways. Induction of HO-1 expression and activity may be a novel mechanism by which aspirin prevents cellular injury under inflammatory conditions and in cardiovascular disease.

Colonic expression of heme oxygenase-1 is associated with a better long-term survival in patients with colorectal cancer

Objective. Heme oxygenase-1 (HO-1) has emerged as a crucial mediator of mucosal defense in the gastrointestinal tract. Its metabolic pathway products, biliverdin/bilirubin and carbon monoxide, can reduce oxidative stress and inflammation, and promote resistance to apoptosis. The role of HO-1 in gastrointestinal malignancies, however, remains to be elucidated. The purpose of this study was to analyze HO-1 expression in human colon adenoma and cancer samples. Material and methods. Fifty-five paraffin-embedded surgical specimens of colorectal cancer and 19 colonic adenoma samples were stained immunhistochemically for HO-1 expression using an anti-HO-1 monoclonal antibody. HO-1 expression was evaluated independently by two different investigators and subsequently correlated to clinical data and patients’ life expectancy. Results. Focal HO-1 expression could be documented in 41.8% (23/55) of patients with colorectal cancer. HO-1 expression in colonic adenoma was detectable in 36.8% (7/19) of cases. The rate of lymphatic tumor invasion was significantly lower in colorectal cancer samples expressing HO-1 (p=0.048). Additionally, fewer lymph node metastases were found in colorectal cancer samples with HO-1 expression, but these differences did not reach statistical significance. Mean observation period was 65.87±3.96 months. Kaplan-Meier analysis showed a significantly better survival for colorectal cancer patients with colonic HO-1 expression (p=0.018). Conclusions. This study demonstrates that colonic HO-1 may be a prognostic marker of colorectal-cancer outcome.

Biological in vitro effects of fibrin glue: fibroblast proliferation, expression and binding of growth factors

Background: Fibrin glue is used in the endoscopic therapy of bleeding ulcerations. Accelerated closure of ulcers has been documented for this treatment in comparison with other injection techniques; the biological reason, however, remains unclear. Methods: In an in vitro model the effects of fibrin glue on the expression and secretion of growth factors by gastric epithelial (AGS, KATO III) and mesenchymal cells (fibroblasts) as well as their proliferative response and their interaction were compared with those of other matrices. Results: Native fibrin glue does not release vascular endothelial growth factor (VEGF) but is able to bind this growth factor in biologically relevant concentrations of 152.6 pg/mL. The addition of fibrin glue to a collagen type I matrix led to an increased proliferation rate of gastric wall fibroblasts. The transcription of VEGF and platelet‐derived growth factor (PDGF) mRNA was significantly increased in epithelial cells. Co‐culture of fibroblasts grown on fibrin glue containing matrix and epithelial cells resulted in an increased secretion of VEGF by both cell lines. Conclusions: Fibrin glue leads to increased proliferation of fibroblasts and local accumulation of VEGF. These findings might at least partly explain the accelerated closure of bleeding ulcers treated by fibrin glue injection.

Teaching ultrasound in a curricular course according to certified EFSUMB standards during undergraduate medical education: a prospective study

BackgroundAs a non-invasive and readily available diagnostic tool, ultrasound is one of the most important imaging techniques in medicine. Ultrasound is usually trained during residency preferable according to German Society of Ultrasound in Medicine (DEGUM) standards. Our curriculum calls for undergraduate training in ultrasound of medical students in their 4th year of undergraduate education. An explorative pilot study evaluated the acceptance of this teaching method, and compared it to other practical activities in medical education at Muenster University.Methods240 medical students in their 4th year of undergraduate medical education participated in the training and completed a pre- and post-questionnaire for self-assessment of technical knowledge, self-assurance of the procedure, and motivation in performing ultrasound using a Likert scale. Moreover, students were asked about their interest in pursuing a career in internal medicine. To compare this training to other educational activities a standardized online evaluation tool was used. A direct observation of procedural skills assessment (DOPS) for the first time applied on ultrasound aimed to independently assess the success of our teaching method.ResultsThere was a significant increase in technical knowledge and self-assurance (p < 0.001) of the students’ self-assessments. The clinical relevance and self-motivation of the teaching were evaluated positively. The students’ DOPS results demonstrated proficiency in the understanding of anatomic structures shown in ultrasonographic images, including terminology, machine settings, and transducer frequencies.ConclusionsTraining ultrasound according to certified DEGUM standards was successful and should be offered in undergraduate medical education. The evaluation of the course affirmed the necessity, quality and clinical relevance of the course with a top ranking score of hands-on training courses within the educational activities of the Medical Faculty of Muenster.

Fibrin glue, healing of gastric mucosal injury, and expression of growth factors: results from a human in vivo study

BACKGROUND Fibrin glue is used in the endoscopic therapy of bleeding ulcerations. Accelerated closure of ulcers has been attributed to this treatment; the biologic reason, however, remains unclear. METHODS Two artificial gastric lesions were induced in healthy, Helicobacter pylori negative volunteers and were treated by injection of either saline solution or fibrin glue. After 72 hours, resulting ulcers were measured and biopsy specimens were taken for immunohistochemistry (to identify proliferating cells and small vessels) and assessment of growth factor messenger RNA (mRNA) expression (platelet derived growth factor, vascular endothelial growth factor, fibroblast growth factor 2 [FGF-2]) by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS After 72 hours, most lesions exposed to fibrin glue were smaller than the corresponding ones treated with saline solution. The ulcer rim was more pronounced; immunohistochemistry revealed more proliferating cells (p < 0.02 compared with saline solution). The number of microvessels also increased, though this difference did not reach statistical significance (p = 0.10). FGF-2 mRNA expression markedly increased (about 7-fold compared with the control [ p < 0.001], and about 5-fold compared with saline solution [ p < 0.015]); whereas, with respect to platelet derived growth factor and vascular endothelial growth factor mRNAs, only small changes occurred. CONCLUSIONS Fibrin glue positively modulates gastric ulcer healing by causing an increase in the number of proliferating cells in the ulcer margin and also possibly enhances the density of microvessels. These changes are accompanied by an enhanced expression of FGF-2, which is known to exert beneficial effects on ulcer healing.

Collagen matrix‐bound clotting factors (CMBCF) promote healing‐associated events independent of factor XIII in an in vitro model

We have previously explored in vitro as well as in vivo models of the biological effects of liquid fibrin glue (FG) containing factor XIII. The fixed combination of a collagen matrix and coagulation factors I and IIa (TachoSil®, Nycomed, Linz, Austria) is void of factor XIII. We aimed to determine whether (1) this preparation exerts similar effects to liquid FG on cells in an in vitro system, or (2) this effect is modulated by factor XIII. In an in vitro model, the effect of the fixed combination of collagen matrix and coagulation factors I and IIa (collagen matrix‐bound clotting factor [CMBCF]) on the expression and secretion of growth factors (vascular endothelial growth factor, platelet‐derived growth factor, fibroblast growth factor‐2) by gastric epithelial (AGS) and mesenchymal cells (fibroblasts), as well as their proliferative response (WST‐test), was compared in the presence and absence of factor XIII. The use of CMBCF compared with collagen type I matrix resulted in an increased proliferation rate of fibroblasts; there was an increased secretion of fibroblast growth factor‐2. Gastric epithelial cells secreted more vascular endothelial growth factor and platelet‐derived growth factor into the culture supernatant in the presence of CMBCF. All responses remained unaltered by the addition of factor XIII in different concentrations. In conclusion, CMBCF exerted effects similar to liquid FG in an in vitro model of healing. The addition of factor XIII did not alter the response of mesenchymal or epithelial cells, with respect to proliferation and growth factor secretion.

Facilitators of high-quality teaching in medical school: findings from a nation-wide survey among clinical teachers

BackgroundClinical teachers in medical schools are faced with the challenging task of delivering high-quality patient care, producing high-impact research and contributing to undergraduate medical education all at the same time. Little is known on the gap between an ‘ideal’ environment supporting clinical teachers to provide high quality teaching for their students and the reality of clinical teaching during worktime in the clinical environment. Most quantitative research published so far was done in a wide range of medical educators and did not consider individual academic qualifications. In this study, we wanted to survey clinical teachers in particular and assess the potential impact of individual academic qualification on their perceptions.MethodsBased on qualitative data of focus group discussions, we developed a questionnaire which was piloted among 189 clinical teachers. The final web-based questionnaire was completed by clinical teachers at nine German medical schools.ResultsA total of 833 clinical teachers (569 junior physicians, 264 assistant professors) participated in the online survey. According to participants, the most important indicator of high quality teaching was “sustained student learning outcome” followed by “stimulation of interest in the subject matter”. Lack of time was the main factor impeding effective teaching (78%). Among the factors facilitating high-quality teaching, protected preparation time during working hours (48%) and more recognition of high-quality teaching within medical schools (21%) were perceived as most helpful. Three out of four teachers (76%) were interested in faculty development programmes directed at teaching skills, but 60% stated they had no time to engage in such activities. With regard to evaluation, teachers preferred individual feedback (75%) over global ratings (21%). Differences between assistant professors and junior physicians were found in that the latter group perceived their teaching conditions as more difficult.ConclusionsLack of time is a major barrier against planning and delivering good clinical teaching in medical schools. According to our findings, the situation at German medical schools is particularly challenging for junior physicians. Creating an institutional culture in which teaching is regarded as highly as patient care and research is a prerequisite for overcoming the barriers identified in this study.

Gastroprotection by vitamin C — a heme-oxygenase 1 dependent mechanism?

Free oxygen radicals contribute to gastric mucosal damage induced by acetylic-salicylic acid (ASA). Vitamin C has been shown to reduce gastric toxicity of ASA in humans. We intended to assess the role of heme oxygenase-1 (HO-1) in this process by application of these substances to AGS and KATO III cells. HO-1 expression was monitored by real-time RT-PCR, Western blot, and HO activity measurement. HO-1 mRNA was significantly elevated by either ASA or vitamin C in gastric epithelial cells, combination of both substances further increased expression. HO-1 protein and enzyme activity rose in cells exposed to vitamin C alone or combined with ASA, but not after stimulation with ASA alone. In contrast to endothelia, in which ASA simultaneously induces HO-1 mRNA and protein expression, gastric epithelial cells require vitamin C to translate HO-1 mRNA into active protein, which then may exert gastroprotection by its antioxidant and vasodilative properties.

Role od reactive oxygen metabolites in aspirin-induced gastric damage in humans. gastroprotection by vitamin C

BACKGROUND The roles of active oxygen metabolites and anti-oxidative defenses in aspirin (ASA)-induced gastric damage have been little studied. AIM We determined the effects of aspirin (400 mg b.d.) with or without vitamin C (480 mg b.d.) for 3 days on gastric mucosa in human volunteers. METHODS Gastric injury was assessed endoscopically; gastric blood flow, reactive oxygen release (quantified by chemiluminescence), lipid peroxidation, myeloperoxidase, superoxide dismutase and glutathione peroxidase activity and intragastric vitamin C content were measured. Expression of superoxide dismutase and glutathione peroxidase mRNAs was assayed semi-quantitatively. RESULTS ASA produced erosions, a marked increase in chemiluminescence, lipid peroxidation, and myeloperoxidase activity. It also resulted in a suppression of gastric blood flow, intragastric vitamin C levels, superoxide dismutase and glutathione peroxidase activities. The addition of vitamin C significantly attenuated gastric damage and reversed the effects of ASA on these parameters. Superoxide dismutase and glutathione peroxidase mRNAs were decreased in ASA-treated subjects; the addition of vitamin C restored their regular levels. CONCLUSIONS (i) free radical-induced lipid peroxidation and suppression of antioxidizing enzymes play an important role in gastric damage induced by aspirin; (ii) increased myeloperoxidase activity suggests activated neutrophils to be the major source of these radicals; (iii) vitamin C protects against ASA-induced damage due to its anti-oxidizing activity.