Development of a continuous fermentation process for the production of recombinant uricase enzyme by Pichia pastoris

Recent studies in the biopharmaceutical industry have shown an increase in the productivity and production efficiency of recombinant proteins by continuous culture. In this research, a new upstream fermentation process was developed for the production of recombinant uricase in the methylotrophic yeast Pichia pastoris. Expression of recombinant protein in this system is under the control of the AOX1 promoter and therefore requires methanol as an inducing agent and carbon/energy source. Considering the biphasic growth characteristics of conventional fed-batch fermentation, physical separation of the growth and induction stages for better control of the continuous fermentation process resulted in higher dry-cell weight (DCW) and enhanced recombinant urate oxidase activity. The DCW and recombinant uricase activity enzyme for fed-batch fermentation were 79 g/L and 6.8 u/mL. During the continuous process, in the growth fermenter at a constant dilution rate of 0.025 h-1 , DCW increased to 88.39 g/L. In the induction fermenter, at methanol feeding rates of 30, 60, and 80 mL/h, a recombinant uricase activity was 4.13, 7.2, and 0 u/mL, respectively. The optimum methanol feeding regime in continuous fermentation resulted in a 4.5-fold improvement in productivity compared with fed-batch fermentation from 0.04 u/mL/h (0.0017 mg/mL/h) to 0.18 u/mL/h (0.0078 mg/mL/h).

High yield expression and purification of Aspergillus flavus uricase cloned in Pichia pink™ expression system

In this research, for the first time, A. flavus uricase gene was cloned in pPink-UOX plasmid under strong alcohol oxidase promoter of Pichia pink expression system after codon optimization. After selecting the best uricase producing clone with an activity of 0.7 U/ml at the Flask level, a 5-L fermenter was used to increase the expression of the enzyme. Within 60 h, the fermentation process produced 1500 g of biomass from 4 L of semi defined culture media and expressed 2.5 g/L of the enzyme. The purity of recombinant uricase production using three consecutive DEAE Sepharose, CM Sepharose and Phenyl Sepharose columns was above 99%, which was confirmed by SDS-PAGE and RP-HPLC analyses. Size exclusion chromatography analysis showed that the purified enzyme has comparable heterogeneity to the Rasburicase. The yield of recombinant uricase production in this study was 63% and its specific activity was 24 U/mg. The high expression of recombinant uricase in the Pichia pink strain and the increased enzyme activity compared to the standard sample indicate the potential of therapeutic and diagnostic applications of recombinant uricase in the present study.

Real-time ocular artifact suppression using recurrent neural network for electro-encephalogram based brain-computer interface

The paper presents an adaptive noise canceller (ANC) filter using an artificial neural network for real-time removal of electro-oculogram (EOG) interference from electro-encephalogram (EEG) signals. Conventional ANC filters are based on linear models of interference. Such linear models provide poorer prediction for biomedical signals. In this work, a recurrent neural network was employed for modelling the interference signals. The eye movement and eye blink artifacts were recorded by the placing of an electrode on the forehead above the left eye and an electrode on the left temple. The reference signal was then generated by the data collected from the forehead electrode being added to data recorded from the temple electrode. The reference signal was also contaminated by the EEG. To reduce the EEG interference, the reference signal was first low-pass filtered by a moving averaged filter and then applied to the ANC. Matlab Simulink was used for real-time data acquisition, filtering and ocular artifact suppression. Simulation results show the validity and effectiveness of the technique with different signal-to-noise ratios (SNRs) of the primary signal. On average, a significant improvement in SNR up to 27 dB was achieved with the recurrent neural network. The results from real data demonstrate that the proposed scheme removes ocular artifacts from contaminated EEG signals and is suitable for real-time and short-time EEG recordings.

[Hereditary chondrocalcinosis in Tunisia. Apropos of 3 families]

Hereditary chondrocalcinosis was reported in three Tunisian families. The clinical manifestations appeared early in life and extensive radiologic involvement was apparent. The mode of inheritance seemed to be autosomal with incomplete penetrance. In one family HLA typing revealed that all affected subjects had the haplotype A1 B12 DR3.