Terry H. Walker

Long-chain polyunsaturated fatty acids promote paclitaxel cytotoxicity via inhibition of the MDR1 gene in the human colon cancer Caco-2 cell line.

Objective: Accumulating evidence in both humans and animal models indicates that dietary intake of long-chain polyunsaturated fatty acids (PUFAs) can improve response to chemotherapy. The intent of this study was to determine the mechanisms by which PUFAs affect the response to anticancer chemotherapy. Methods: Human colorectal cancer cell line Caco-2 was used as a model system in this study. Caco-2 cells were treated with different concentrations of three PUFAs: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA). Real-time polymerase chain reaction was used to determine mdr1 gene (codes for P-glycoprotein [P-gp]) expression. Western blotting and calcein-acetoxymethylester efflux assay were used for P-gp expression and functional evaluation, respectively. Furthermore, apoptosis assay was conducted by adding PUFAs with paclitaxel to confirm the synergetic effect. Finally, gene expression of nuclear receptors CAR and PXR were estimated to evaluate the possible mechanisms. Results: Both classes of PUFAs, omega-3 (ω-3) and omega-6 (ω-6), can cause a modest but very reproducible reduction of gene expression, protein production, and pump activity of MDR1. Incubation of cells with PUFAs greatly enhanced the cytotoxicity of the anticancer drug paclitaxel, manifested mainly through enhanced paclitaxel-induced apoptosis. Furthermore, PUFAs increased the messenger RNA (mRNA) levels of the nuclear receptors CAR and PXR, thus implicating these two transcription factors as cellular targets of PUFAs in cells but not directly affecting MDR1 regulation. Conclusions: Our results suggest that inhibition of the multidrug resistance MDR1/P-gp is one mechanism through which dietary polyunsaturated fatty acids exert a synergetic effect on the response of tumor cells to anticancer drugs.

Fed-batch fermentation and supercritical fluid extraction of heterotrophic microalgal Chlorella protothecoides lipids

Lipids obtained from Chlorella protothecoides in heterotrophic cultivation are considered a suitable feedstock for biodiesel production. In this study, glucose fed-batch fermentation was performed to increase final biomass and lipid production. The biomass productivity and lipid productivity were 6.28 and 2.06 g/L day, respectively. Biomass/glucose conversion and the lipid/glucose conversion were 43.3% and 14.2%, respectively. Extraction of lipids from algae has been identified as a key bottleneck in bioprocessing operations. Supercritical carbon dioxide (SC-CO(2)) was applied for neutral lipids extraction and the SC-CO(2) kinetics was investigated by the Goto et al. model. The modeling showed a good fit with experimental data. Additionally, neutral lipids extracted by SC-CO(2) displayed a suitable fatty acid profile for biodiesel [mainly C18:1 (60.0%), C18:2 (18.7%) and C16:0 (11.5%)]. Our study demonstrated the ability to produce high levels of neutral lipids through heterotrophic algal culture and subsequent extraction of lipids with SC-CO(2) method developed.

Biomass and lipid production of Chlorella protothecoides under heterotrophic cultivation on a mixed waste substrate of brewer fermentation and crude glycerol

Biomass and lipid accumulation of heterotrophic microalgae Chlorella protothecoides by supplying mixed waste substrate of brewer fermentation and crude glycerol were investigated. The biomass concentrations of the old and the new C. protothecoides strains on day 6 reached 14.07 and 12.73 g/L, respectively, which were comparable to those in basal medium with supplement of glucose and yeast extract (BM-GY) (14.47 g/L for old strains and 11.43 g/L for new strains) (P>0.05). Approximately 81.5% of total organic carbon and 65.1% of total nitrogen in the mixed waste were effectively removed. The accumulated lipid productivities of the old and the new C. protothecoides strains in BM-GY were 2.07 and 1.61 g/L/day, respectively, whereas in the mixed waste, lipid productivities could reach 2.12 and 1.81 g/L/day, respectively. Our result highlights a new approach of mixing carbon-rich and nitrogen-rich wastes as economical and practical alternative substrates for biofuel production.

Production and recovery of polyunsaturated fatty acids-added lipids from fermented canola.

Canola flake was investigated as a potential substrate for fungal conversion to produce polyunsaturated fatty acids (PUFAs)-added oil in a 7l fermenter. The results showed that yields of total oil were reduced 9-22% compared to initial oil in the canola flake, but as high as 445mg/l arachidonic acid (ARA, C20:4n6) and 67mg/l eicosapentaenoic acid (EPA, C20:5n3) were produced. The percentages of ARA and EPA of total fatty acids in this fermented oil were 15.5% and 2.3%, respectively. Supercritical CO2 extraction was then investigated for the lipid recovery from fermented canola flake, and extraction kinetics were modeled. The feasibility was demonstrated for production of PUFAs in a laboratory-scale fermentor using canola flake as a single nutrient, and for lipid extraction using supercritical CO2.

Improved oxidative stability of biodiesel via alternative processing methods using cottonseed oil

Abstract Biodiesel from waste cooking oil (WCO) requires antioxidants to meet oxidation stability specifications set forth in ASTM D6751 or EN 14214. In contrast, unrefined cottonseed oil (CSO), containing tocopherols and gossypol, produces biodiesel of higher oxidation stability. However, only a portion of these CSO endogenous antioxidants are suspected to be retained in biodiesel. Because the economics of biodiesel manufacturing rely upon inexpensive sources of triglycerides, emphasis was placed on developing improved alternative processing methods where WCO was the main source of methyl esters (WCOME) and CSO was used as a supplemental source of triglycerides and antioxidants in a 4:1 ratio. This study compared four processing methods for their ability to produce biodiesel of increased oxidative stability prepared from a 4:1 ratio of WCO:CSO. Two novel processing methods developed for this study utilise solvent properties of fatty acid methyl esters and glycerol to avoid additional chemical inventory for biodiesel processors. This study concludes that the two new processing methods resulted in biodiesel that had statistically significant improved oxidation stability when compared to two common industrial processing methods. Another significant finding is that high-shear homogenisation during transesterification reduced reaction time from the published one hour to 16 minutes.