Polysialic acid production using Escherichia coli K1 in a disposable bag reactor

Low molecular weight polysialic acid binds to properdin and reduces the activity of the alternative complement pathway

Sialic acids as the terminal caps of the cellular glycocalyx play an essential role in self-recognition and were shown to modulate complement processes via interaction between α2,3-linked sialic acids and complement factor H. Previously, it was suggested that low molecular weight α2,8-linked polysialic acid (polySia avDP20) interferes with complement activation, but the exact molecular mechanism is still unclear. Here, we show that soluble polySia avDP20 (molecular weight of ~ 6 kDa) reduced the binding of serum-derived alternative pathway complement activator properdin to the cell surface of lesioned Hepa-1c1c7 and PC-12 neuroblastoma cells. Furthermore, polySia avDP20 added to human serum blocked the alternative complement pathway triggered by plate-bound lipopolysaccharides. Interestingly, no inhibitory effect was observed with monosialic acid or oligosialic acid with a chain length of DP3 and DP5. In addition, polySia avDP20 directly bound properdin, but not complement factor H. These data show that soluble polySia avDP20 binds properdin and reduces the alternative complement pathway activity. Results strengthen the previously described concept of self-recognition of sialylation as check-point control of complement activation in innate immunity.

Low molecular weight polysialic acid prevents lipopolysaccharide-induced inflammatory dopaminergic neurodegeneration in humanized SIGLEC11 transgenic mice

Parkinson's disease is one of the most common neurodegenerative diseases in the elderly population, with a pathophysiology linked to neuroinflammation, complement activation, and oxidative damage. Soluble polysialic acid with an average degree of polymerization 20 (polySia avDP20) prevents inflammation and oxidative burst in human macrophages via sialic acid-binding immunoglobulin like lectin-11 (SIGLEC11) receptor and interferes with alternative complement activation. Here, we confirmed the anti-inflammatory capacity of polySia avDP20 on cultured murine embryonic stem cell-derived microglia and analyzed the effect of polySia avDP20 in a lipopolysaccharide-triggered animal model of Parkinson's disease. We demonstrated a neuroprotective effect of intraperitoneally applied polySia avDP20 in humanized SIGLEC11 transgenic mice after repeated systemic challenge with lipopolysaccharide. Pathway enrichment analysis of the brain transcriptome on day 19 after disease initiation showed that intraperitoneal application of 10 μg/g body weight polySia avDP20 prevented excessive inflammation. In line with these data, polySia avDP20 attenuated the lipopolysaccharide-triggered increase in mRNA levels of immune-related genes (Il1b, Cd14, Myd88, Fcer1g, Itgam, C4, Cybb, Iba1 and Cd68) and cell death-related genes (Casp8, Ripk1 and Ripk3) in the brains of SIGLEC11 transgenic mice on day 19, but not on day 5. Moreover, immunohistochemistry demonstrated that polySia avDP20 reduced the lipopolysaccharide-induced increase in immunoreactivity of IBA1 and CD68 in the substantia nigra pars reticulata in SIGLEC11 transgenic and wild type mice on day 19. Furthermore, treatment with polySia avDP20 prevented the loss of dopaminergic neurons in the substantia nigra pars compacta induced by lipopolysaccharide challenge in both SIGLEC11 transgenic and wild type mice on day 19. Thus, our data demonstrate that polySia avDP20 ameliorates inflammatory dopaminergic neurodegeneration and therefore is a promising drug candidate to prevent Parkinson's disease-related inflammation and neurodegeneration.

An overview and future prospects of sialic acids

Sialic acids (Sias) are negatively charged functional monosaccharides present in a wide variety of natural sources (plants, animals and microorganisms). Sias play an important role in many life processes, which are widely applied in the medical and food industries as intestinal antibacterials, antivirals, anti-oxidative agents, food ingredients, and detoxification agents. Most Sias are composed of N-acetylneuraminic acid (Neu5Ac, >99%), and Sia is its most commonly used name. In this article, we review Sias in terms of their structures, applications, determination methods, metabolism, and production strategies. In particular, we summarise and compare different production strategies, including extraction from natural sources, chemical synthesis, polymer decomposition, enzymatic synthesis, whole-cell catalysis, and de novo biosynthesis via microorganism fermentation. We also discuss research on their physiological functions and applications, barriers to efficient production, and strategies for overcoming these challenges. We focus on efficient de novo biosynthesis strategies for Neu5Ac via microbial fermentation using novel synthetic biology tools and methods that may be applied in future. This work provides a comprehensive overview of recent advances on Sias, and addresses future challenges regarding their functions, applications, and production.

Accelerated production of α2,8- and α2,9-linked polysialic acid in recombinant Escherichia coli using high cell density cultivation

Polysialic acid (polySia) are α2,8- and/or α2,9-linked homopolymers with interesting properties for meningococcal vaccine development or the cure of human neurodegenerative disorders. With the goal to avoid large scale production of pathogenic bacteria, we compare in the current study the efficacy of conventional polySia production to recombinant approaches using the engineered laboratory safety strain E. coli BL21. High cell density cultivation (HCDC) experiments were performed in two different bioreactor systems. Increased cell densities of up to 11.3 (±0.4) g/L and polySia concentrations of up to 774 (±18) mg/L were reached in E. coli K1. However, cultivation of engineered E. coli BL21 strains delivered comparable cell densities but a maximum of only 133 mg/L polySia. Using established downstream procedures, host cell DNA and proteins were removed. All recombinant polySia products showed an identical degree of polymerization >90. Polymers with different glycosidic linkages could be successfully differentiated by nuclear magnetic resonance spectroscopy.

Determination of the Structural Integrity and Stability of Polysialic Acid during Alkaline and Thermal Treatment

Polysialic acid (polySia) is a linear homopolymer of varying chain lengths that exists mostly on the outer cell membrane surface of certain bacteria, such as Escherichia coli (E. coli) K1. PolySia, with an average degree of polymerization of 20 (polySia avDP20), possesses material properties that can be used for therapeutic applications to treat inflammatory neurodegenerative diseases. The fermentation of E. coli K1 enables the large-scale production of endogenous long-chain polySia (DP ≈ 130) (LC polySia), from which polySia avDP20 can be manufactured using thermal hydrolysis. To ensure adequate biopharmaceutical quality of the product, the removal of byproducts and contaminants, such as endotoxins, is essential. Recent studies have revealed that the long-term incubation in alkaline sodium hydroxide (NaOH) solutions reduces the endotoxin content down to 3 EU (endotoxin units) per mg, which is in the range of pharmaceutical applications. In this study, we analyzed interferences in the intramolecular structure of polySia caused by harsh NaOH treatment or thermal hydrolysis. Nuclear magnetic resonance (NMR) spectroscopy revealed that neither the incubation in an alkaline solution nor the thermal hydrolysis induced any chemical modification. In addition, HPLC analysis with a preceding 1,2-diamino-4,5-methylenedioxybenzene (DMB) derivatization demonstrated that the alkaline treatment did not induce any hydrolytic effects to reduce the maximum polymer length and that the controlled thermal hydrolysis reduced the maximum chain length effectively, while cost-effective incubation in alkaline solutions had no adverse effects on LC polySia. Therefore, both methods guarantee the production of high-purity, low-molecular-weight polySia without alterations in the structure, which is a prerequisite for the submission of a marketing authorization application as a medicinal product. However, a specific synthesis of low-molecular-weight polySia with defined chain lengths is only possible to a limited extent.

Single-use membrane adsorbers for endotoxin removal and purification of endogenous polysialic acid from Escherichia coli K1

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Production process for highly pure polysialic acid is shown.

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Single-use elements are used during cultivation and downstream processing.

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Maturation process led to increased polysialic acid release from the cell surface.

Polysialic acid (polySia) is a promising molecule for various medical applications (e.g., treatment of inflammatory neurodegenerative diseases).

In this study a complete production process for human-identical α-(2,8)-linked polySia was developed using a disposable bioreactor for cultivation of Escherichia coli K1 and single-use membrane adsorbers for downstream processing (DSP). The cultivation process was optimized to minimize complex media components and a maturation process after cultivation was established. The maturation led to further product release from the cell surface into the supernatant. Afterwards DSP was established using sodium hydroxide treatment combined with anion exchange membrane adsorbers for endotoxin and DNA depletion.

After downstream processing the final product had neither detectable protein nor DNA contamination. Endotoxin content was below 3 EU mg⁻¹. Investigation of the maximal chain length showed no effect of the harsh sodium hydroxide treatment during DSP on the stability of the polySia. Maximal chain length was ∼98 degree of polymerization.

Sensors for disposable bioreactors

Modern bioprocess monitoring demands sensors that provide on-line information about the process state. In particular, sensors for monitoring bioprocesses carried out in single-use bioreactors are needed because disposable systems are becoming increasingly important for biotechnological applications. Requirements for the sensors used in these single-use bioreactors are different than those used in classical reusable bioreactors. For example, long lifetime or resistance to steam and cleaning procedures are less crucial factors, while a requirement of sensors for disposable bioreactors is a cost that is reasonable on a per-use basis. Here, we present an overview of current and emerging sensors for single-use bioreactors, organized by the type of interface of the sensor systems to the bioreactor. A major focus is on non-invasive, in-situ sensors that are based on electromagnetic, semiconducting, optical, or ultrasonic measurements. In addition, new technologies like radio-frequency identification sensors or free-floating sensor spheres are presented. Notably, at this time there is no standard interface between single-use bioreactors and the sensors discussed here. In the future, manufacturers should address this shortcoming to promote single-use bioprocess monitoring and control.

Additive manufactured customizable labware for biotechnological purposes

Yet already developed in the 1980s, the rise of 3D printing technology did not start until the beginning of this millennium as important patents expired, which opened the technology to a whole new group of potential users. One of the first who used this manufacturing tool in biotechnology was Lücking et al. in 2012, demonstrating potential uses 1, 2. This study shows applications of custom-built 3D-printed parts for biotechnological experiments. It gives an overview about the objects' computer-aided design (CAD) followed by its manufacturing process and basic studies on the used printing material in terms of biocompatibility and manageability. Using the stereolithographic (SLA) 3D-printing technology, a customizable shake flask lid was developed, which was successfully used to perform a bacterial fed-batch shake flask cultivation. The lid provides Luer connectors and tube adapters, allowing both sampling and feeding without interrupting the process. In addition, the digital blueprint the lid is based on, is designed for a modular use and can be modified to fit specific needs. All connectors can be changed and substituted in this CAD software-based file. Hence, the lid can be used for other applications, as well. The used printing material was tested for biocompatibility and showed no toxic effects neither on mammalian, nor on bacteria cells. Furthermore an SDS-PAGE-comb was drawn and printed and its usability evaluated to demonstrate the usefulness of 3D printing for everyday labware. The used manufacturing technique for the comb (multi jet printing, MJP) generates highly smooth surfaces, allowing this application.