No abstract

Hepatocyte function on 3-D microfabricated polymer scaffolds realised with the pressure-activated microsyringe was tested under static and dynamic conditions. The dynamic cell culture was obtained using the multicompartment modular bioreactor system. Hepatocyte cell density, glucose consumption, and albumin secretion rate were measured daily over a week. Cells seeded on scaffolds showed an increase in cell density compared with monolayer controls. Moreover, in dynamic culture, cell metabolic function increased three times in comparison with static monolayer cultures. These results suggest that cell density and cell-cell interactions are mediated by the architecture of the substrate, while the endogenous biochemical functions are regulated by a sustainable supply of nutrients and interstitial-like flow. Thus, a combination of 3-D scaffolds and dynamic flow conditions are both important for the development of a hepatic tissue model for applications in drug testing and regenerative medicine.

Permeability studies across epithelial barriers are of primary importance in drug delivery as well as in toxicology. However, traditional in vitro models do not adequately mimic the dynamic environment of physiological barriers. Here, we describe a novel two-chamber modular bioreactor for dynamic in vitro studies of epithelial cells. The fluid dynamic environment of the bioreactor was characterized using computational fluid dynamic models and measurements of pressure gradients for different combinations of flow rates in the apical and basal chambers. Cell culture experiments were then performed with fully differentiated Caco-2 cells as a model of the intestinal epithelium, comparing the effect of media flow applied in the bioreactor with traditional static transwells. The flow increases barrier integrity and tight junction expression of Caco-2 cells with respect to the static controls. Fluorescein permeability increased threefold in the dynamic system, indicating that the stimulus induced by flow increases transport across the barrier, closely mimicking the in vivo situation. The results are of interest for studying the influence of mechanical stimuli on cells, and underline the importance of developing more physiologically relevant in vitro tissue models. The bioreactor can be used to study drug delivery, chemical, or nanomaterial toxicity and to engineer barrier tissues.

In the present study we assessed the effect of physical training on Laser Doppler skin flux (LDF) and nitric oxide (NO) release, before and after 3 min of brachial artery occlusion. To this end we performed laser Doppler measurements and the venous plasma assay of nitrite/nitrate (NOx) on 10 sedentary healthy subjects and 10 endurance athletes. The sedentary control subjects had lower basal and post reperfusion levels of NOx as compared to athletes (mean +/- SE: 27.8 +/- 3.5 vs. 33.2 +/- 3.4, 48.6 +/- 7.9 vs. 60.1 +/- 10.1 micromol/L; p < 0.05). LDF at baseline was not significantly different in the two groups (157.5 +/- 7.9 and 176.64 +/- 26.7 PU for sedentary subjects and athletes, respectively) while post ischemic LDF was significantly lower in nonathletic subjects than in athletes (209.9 +/- 13 and 343.8 +/- 21.3 PU, p < 0.001). In both groups the hyperaemic stimulus significantly increased LDF and NOx levels (p < 0.01 and p < 0.05, respectively). The flow reserve, estimated as peak/basal LDF, was significantly lower in control subjects than in athletes (1.34 +/- 0.2 and 2.32 +/- 0.9, respectively, p < 0.01). In athletes, as opposed to sedentary subjects, a direct correlation was found between plasma NOx concentration and LDF both in basal conditions (r = 0.92; p < 0.001), and during hyperaemia (r = 0.84; p < 0.01). In conclusion, compared to sedentary subjects, athletes had an enhanced nitric oxide release. Hyperaemia increased LDF and nitric oxide levels both in sedentary subjects and in athletes.