Quantitative inference of cellular parameters from microfluidic cell culture systems

Microfluidic cell culture systems offer a convenient way to measure cell biophysical parameters in conditions close to the physiological environment. We demonstrate the application of a mathematical model describing the spatial distribution of nutrient and growth factor concentrations in inferring cellular oxygen uptake rates from experimental measurements. We use experimental measurements of oxygen concentrations in a poly(dimethylsiloxane) (PDMS) microreactor culturing human hepatocellular liver carcinoma cells (HepG2) to infer quantitative information on cellular oxygen uptake rates. We use a novel microchannel design to avoid the parameter correlation problem associated with simultaneous cellular uptake and diffusion of oxygen through the PDMS surface. We find that the cellular uptake of oxygen is dependent on the cell density and can be modeled using a logistic term in the Michaelis–Menten equation. Our results are significant not only for the development of novel assays to quantitatively infer cell response to stimuli, but also for the development, design, and optimization of novel in vitro systems for drug discovery and tissue engineering. Biotechnol. Bioeng. 2009;103: 966–974. © 2009 Wiley Periodicals, Inc.     

Sequential activation of caspases and synergistic beta-cell cytotoxicity by palmitate and anti-Fas antibodies

To assess the mechanism of beta-cell lipotoxicity in comparison with Fas-mediated cell death, we used a mouse beta-cell clone stably transfected with human Fas. Palmitate induced beta-cell death in correlation with medium glucose levels between 5 and 20 mmol/l, while Fas-mediated cytotoxicity was observed irrespective of glucose concentration. At the glucose level of 10 mmol/l, palmitate induced caspase-6 activity within 3 h, and caspase-3 activity after a lag period of 6 h. The activities of caspases were correlated with glucose concentration. A caspase-6 inhibitor attenuated caspase-3 activation and cell death induced by palmitate. Oxfenicine, an inhibitor of carnitine palmitoyltransferase-1, attenuated both palmitate-induced cytotoxicity and activation of caspases. Finally, beta-cell cytotoxicity caused by the combination of anti-Fas and palmitate at 25 mmol/l of glucose was greater than the sum of those induced by each. These observations suggest that palmitate induces sequential activation of caspase-6 and caspase-3 through a mitochondrial signal(s), and caspase-6 plays a primary role in the mechanism. Fas-mediated beta-cell death and lipotoxicity may share common mechanisms involving caspase activation, and thereby synergistically inducing beta-cell death, although upstream signaling pathways are distinct.     

Modification at the acidic domain of RXR agonists has little effect on permissive RXR-heterodimer activation

Retinoid X receptors (RXRs) function as homo- or heterodimers with other nuclear receptors, such as peroxisome proliferator-activated receptors (PPARs), which are targets for treatment of hyperlipidemia and type 2 diabetes, or liver X receptors (LXRs), which are involved in glucose/lipid metabolism. PPAR/RXR or LXR/RXR are known as permissive RXR-heterodimers because they are activated by RXR agonists alone. Interestingly, the pattern of RXR-heterodimer activation is different depending on the RXR agonist structure, but the structure–activity relationship has not been reported. Here we show that modification or replacement of the carboxyl group in the acidic domain of RXR agonists has little or no effect on permissive RXR-heterodimer activation. Phosphonic acid (9), tetrazole (10), and hydroxamic acid (12) analogues were synthesized from the common bromo intermediate 7. Except for 9, these compounds showed RXR full-agonistic activities in the concentration range of 1–10 μM. The order of agonistic activity toward both PPARγ/RXRα and LXRα/RXRα was the same as it was for RXR, that is, 11 > 10 > 12. These results should be useful for the development of RXR agonists with improved bioavailability.     

Lipase inhibitors for the treatment of acne

Propionibacterium acnes lipase is an important factor in the pathogenesis of acne, because free fatty acids formed as a result of the effect of P. acnes lipase on sebaceous triglycerides induce severe inflammation. Tetracyclines have been the most common systemic therapy for acne due to their beneficial clinical effects, their inhibition of lipase activity of P. acnes as well as their inhibition of P. acnes chemotaxis. Erythromycin and Jumi-haidoku-to also inhibit the lipase activity of P. acnes. Among P. acnes biotypes and serotypes, stronger P. acnes lipase activities were seen in P. acnes biotype III and serotype II. Conversely, Propionibacterium granulosum is also isolated in acne lesions but has only a faint lipase activity, which might not be of significance. In the future, the degree of P. acnes lipase activity in acne, identified by genetic techniques, needs to be compared to the condition of acne rash.     

Performance Evaluation of Flexible Manufacturing Systems with Finite Local Buffers: Fixed and Dynamic Routings

This article evaluates the performance of flexible manufacturing systems with finite local buffers and fixed or dynamic routing rules, and addresses the optimal design or system configuration problem of maximizing the system throughput. The costs include machine cost, part (or pallet) cost, and local buffers cost. First, the system throughputs and their behaviors are considered with both queueing network analysis and simulation, and it is shown for a fixed routing model that the system throughput in the case of finite local buffers is greater than in the case of infinite local buffers. For a fixed versus dynamic routing rule, it is also found that the throughput in the former case can be close to the one in the latter case by changing the setting parameters. Next, the design problems of maximizing the system throughput are considered numerically for fixed and dynamic routing cases. Then, it is seen that better combination of design variables is a class of the monotonicity in local buffers, service rates, and routing probabilities.     

Loss of mRor1 Enhances the Heart and Skeletal Abnormalities in mRor2-Deficient Mice: Redundant and Pleiotropic Functions of mRor1 and mRor2 Receptor Tyrosine Kinases

The mammalian Ror family of receptor tyrosine kinases consists of two structurally related proteins, Ror1 and Ror2. We have shown that mRor2-deficient mice exhibit widespread skeletal abnormalities, ventricular septal defects in the heart, and respiratory dysfunction, leading to neonatal lethality (S. Takeuchi, K. Takeda, I. Oishi, M. Nomi, M. Ikeya, K. Itoh, S. Tamura, T. Ueda, T. Hatta, H. Otani, T. Terashima, S. Takada, H. Yamamura, S. Akira, and Y. Minami, Genes Cells 5:71-78, 2000). Here we show that mRor1-deficient mice have no apparent skeletal or cardiac abnormalities, yet they also die soon after birth due to respiratory dysfunction. Interestingly, mRor1/mRor2 double mutant mice show markedly enhanced skeletal abnormalities compared with mRor2 mutant mice. Furthermore, double mutant mice also exhibit defects not observed in mRor2 mutant mice, including a sternal defect, dysplasia of the symphysis of the pubic bone, and complete transposition of the great arteries. These results indicate that mRor1 and mRor2 interact genetically in skeletal and cardiac development.     

Abstracts from the Japanese Journal of Limnology

The Japanese Journal of Limnology is another official publication of the Japanese Society of Limnology. The original papers in the journal were peer-reviewed by a few authorized referees, and appeared in Japanese with English abstracts.An erratum to this article can be found at     

Fecal microbiota of a dugong (Dugong dugong) in captivity at Toba Aquarium

A captive female dugong at Toba Aquarium (Japan) was examined to describe the microbiota of its lower digestive tracts using the molecular-biological technique, a culture-independent method. The phylogenetic analysis of bacterial 16S rRNA genes was conducted for fecal samples, which were taken at 3 different periods. Based on phylogenetic analysis of these sequences, the representatives of six bacterial phyla could be identified: Actinobacteria (0.7%), Bacteroidetes (15%), Firmicutes (83.1%), Lentisphaerae (0.1%), Proteobacteria (0.1%), and Verrucomicrobia (1.0%), suggesting the existence of bacterial species newly found not only in the digestive tract but also in natural field.