Biomedical subjects

Feng Chen

Publications and source records attributed to Feng Chen.

239 records · Page 14Linked to original sources

PubMedDate not supplied

Continuous cultivation of the diatom Nitzschia laevis for eicosapentaenoic acid production: physiological study and process optimization.

The continuous cultures of the diatom Nitzschia laevis were performed at different dilution rates (D) and feed glucose concentrations (S(0)) to investigate cellular physiological responses and its production potential of eicosapentaenoic acid (EPA). Steady-state cell dry weight, residual glucose concentration, cell growth yield, specific glucose consumption rate, and fatty acid profiles were investigated within the range of D from 0.1 to 1.0 day(-1) (S(0) fixed at 20 g/L) and the range of S(0) from 5 to 35 g/L (D fixed at 0.3 day(-1)), respectively. The highest EPA productivity of 73 mg L(-1) day(-1) was obtained at D = 0.5 day(-1) and S(0) = 20 g/L. However, when the continuous culture achieved high productivities of EPA at certain dilution rates and feed glucose concentrations, glucose in the feed could not be consumed completely. Accordingly, the continuous culture was evaluated in terms of both EPA productivity (P) and glucose assimilation efficiency (E). The parameter eta, defined as the product of P and E, was used as an overall performance index. Since eta is a function of the two independent variables D and S(0), we employed a central composite design to optimize D and S(0) for the highest eta value. Based on the experimental results of the design, a second-order polynomial equation was established to represent the relationship between eta and D and S(0). The optimal values of D and S(0) were subsequently determined as 0.481 day(-1) and 15.56 g/L, respectively by the empirical model. The verification experiment confirmed the validity of the model. Under the optimal conditions, eta value reached 46.5 mg L(-1) day(-1), suggesting a considerably high efficiency of the continuous culture of N. laevis in terms of EPA production and glucose utilization.

Bioreactors↗

PubMedDate not supplied

High-yield production of lutein by the green microalga Chlorella protothecoides in heterotrophic fed-batch culture.

The green microalga Chlorella protothecoides was grown heterotrophically in batch mode in a 3.7-L fermenter containing 40 g/L glucose and 3.6 g/L urea. In the late exponential phase, concentrated nutrients containing glucose and urea were fed into the culture, in which the nitrogen source was sufficient compared to carbon source. As a result, a maximum cell dry weight concentration of 48 g/L was achieved. This cell dry weight concentration was 28.4 g/L higher than that obtained in batch culture under the same growth conditions. In another cultivation run, the culture was provided with the same initial concentrations of glucose (40 g/L) and urea (3.6 g/L) as in the batch mode, followed by a relatively reduced supply of nitrogen source in the fed-batch mode to establish a nitrogen-limited culture. Such a modification resulted in an enhanced lutein production without significantly lowering biomass production. The cellular lutein content was 0.27 mg/g higher than that obtained in the N-sufficient culture. The improvements were also reflected by higher maximum lutein yield, lutein productivity, and lutein yield coefficient on glucose. This N-limited fed-batch culture was successfully scaled up from 3.7 L to 30 L, and a three-step cultivation process was developed for the high-yield production of lutein. The maximum cell dry weight concentration (45.8 g/L) achieved in the large fermenter (30 L) was comparable to that in the small one (3.7 L). The maintenance of the culture at a higher temperature (i.e., 32 degrees C) for 84 h resulted in a 19.9% increase in lutein content but a 13.6% decrease in cell dry weight concentration as compared to the fed-batch culture (30 L) without such a treatment. The enhancement of lutein production resulted from the combination of nitrogen limitation and high-temperature stress.

Biomass↗

PubMedDate not supplied

Study of apolipoprotein E genetic polymorphism in patients with atherosclerotic cerebral infarction.

OBJECTIVE: To explore the frequency and significance of ApoE gene polymorphisms in Chinese patients with atherosclerotic cerebral infarction (ACI). METHODS: Polymerase chain reaction and gene sequencing, single nucleotide polymorphisms of ApoE gene were used to analyze 33 cases of patients with ACI and 35 controls. RESULTS: The frequencies of ApoE gene single nucleotide polymorphisms 465C/G, 462C/G and 451delC in the ACI group were significantly higher than those in the control group (P<0.05). The prevalence of polymorphism 486G/T in the control group was significantly higher than that in the ACI group (P=0.011). CONCLUSIONS: 465C/G,462C/G and 451delC polymorphisms might be associated with ACI.486GT allele might have protective effect on the pathogenesis of ACI.

Aged↗

PubMedDate not supplied

Enhancement of antiangiogenic effects of human canstatin with a hypoxia-regulated transgene vector in lung cancer model.

UNLABELLED: Canstatin, a newly identified antiangiogenesis protein, has a potent inhibitory effect on the proliferation and growth of endothelial cells. To enhance the expression and antiangiogenic effects of canstatin in solid tumors, we constructed a eukaryotic expression vector that encodes human canstatin cDNA downstream from nine copies of the hypoxia-response element. METHODS: Canstatin complementary DNA from adult liver tissues was cloned into the mammalian expression vector pCMV-Script. Nine copies of the hypoxia-response element were ligated upstream from the canstatin gene near the cytomegalovirus promoter. The recombinant vector, pCMV9Cans, was transformed into A549 cells by cationic liposomes. The transformed cells were cultured under oxic and anoxic conditions. We detected canstatin messenger ribonucleic acid and protein expression in transformed cells by TaqMan polymerase chain reaction and Western blot analysis, respectively. Human umbilical vein endothelial cells were cocultured with recombinant vector transformed A549 cells using Transwell plates under oxic and anoxic conditions. The proliferation and apoptosis of the cocultured endothelial cells were evaluated with 3H-thymidine incorporation and terminal deoxynucleotidyl-mediated biotinylated deoxyuridine triphosphate nick end-labeling methods (TUNEL), respectively. A canstatin-encoding vector with no hypoxia-response element, pCMVCans, was used as the positive control, and naked plasmid-transformed and singly cultured parental cells were used as negative controls. The biologic activity of the vector in tumor tissues of lung cancer-bearing nude mice was evaluated by microvessel counts. Canstatin protein expression was assessed by Western blot analysis in tumor tissues. pCMVCans and empty vector were used as controls in the in vivo assays. RESULTS: Canstatin messenger RNA and protein were detected in both pCMV9Cans- and pCMVCans-transformed A549 clones. Under oxic conditions, canstatin expression was not significantly different in clones stably transformed with pCMV9Cans or pCMVCans. However, under anoxic conditions canstatin expression was significantly higher in pCMV9Cans-transformed cells than in pCMVCans-transformed cells. Moreover, the 3H-thymidine uptake rate of the human umbilical vein endothelial cells was markedly lower than that of the pCMVCans-transformed cells, and many endothelial cells underwent apoptosis when cocultured with pCMV9Cans-transformed A549 cells, especially under anoxic conditions. We detected canstatin expression in tumor tissues; the expression level in pCMV9Cans-transformed tumors was significantly higher than that in pCMVCans-transformed tumors. An in vivo assay showed that tumors transformed with pCMV9Cans remained small, and microvessels in those tumors were much fewer than those in pCMVCans-transformed tumors. CONCLUSION: The hypoxia-regulated vector pCMV9Cans increases the expression of canstatin, thereby enhancing its biological effects. We believe that the hypoxia-inducible canstatin-expressing vector is a promising gene therapy tool for antiangiogenesis research.

Angiogenesis Inhibitors↗

PubMedDate not supplied

Chemopreventive effects of Khaya senegalensis bark extract on human colorectal cancer.

An extract of the bark of Khaya senegalensis is commonly used in African traditional medicine for pain and inflammation. Khaya senegalensis bark extract (KSBE) was hypothesized to contain inhibitors of the cyclooxygenase-2 (COX-2) gene and to be useful in the prevention and treatment of colorectal cancer. The diphenyl-2-picrylhydrazyl (DPPH)- free radical activity and the total phenolic content of KSBE were measured, followed by an investigation of cell growth inhibition, COX and prostaglandin E 2 (PGE2) suppression, as well as apoptosis by Western blot analysis and ELISA. Our data clearly showed that KSBE displays anti-proliferative, antiinflammatory and pro-apoptotic effects on HT-29, HCT-15 and HCA-7 cells. Since all three cell lines, irrespective of COX-2 status (HCT-15 is COX-2-deficient), were affected by the treatment, it can be concluded that both COX-dependent and COX-independent pathways are activated by KSBE.

Antioxidants↗