Sophorolipid produced from the new yeast strain Wickerhamiella domercqiae induces apoptosis in H7402 human liver cancer cells

Sophorolipids as anticancer agents: progress and challenges

Sophorolipids (SLs) are considered effective biosurfactant for cancer treatment, which can efficiently inhibit the viability of various cancer types including breast, lung, liver, cervical and colon cancers. Their mechanism of action targets apoptosis and operates at the level of caspase enzymes, upregulation and downregulation of the B-cell lymphoma (Bcl)-family proteins, and changes in mitochondrial membrane permeability. The binding of SLs to the cancer cell receptors modulates the expression of Bax, APAF1, Bcl-2 and Bcl-x, and triggers the release of cytochrome c into the cytosol which further activates caspase-3/9 pathways leading to apoptosis. SLs also increase intracellular reactive oxygen species (ROS) level in cancer cells that activates pro-apoptotic JNK and p38 MAPK signaling pathways and induce apoptosis through the activation of caspase (3, 6 and 7) pathways. Recently, the integration of anticancer drugs like doxorubicin hydrochloride into SL based nanoparticles (SLNPs) enhanced stability, biocompatibility, bioavailability, pharmacokinetics and therapeutic efficacy. Besides, doxorubicin and resveratrol conjugated NPs induced apoptosis in resistant breast cancer cells by down-regulating the expression of Bcl-2, NF-kB and efflux transporters. However, several challenges exist regarding the stability of SLs under physiological conditions, targeting specific cancer cells, and their clinical applications. This study provides updated concepts on the formulations and properties of different types of SLs, their mechanism of anticancer action and applications in nanotechnology for targeted drug delivery system.

Production and characterization of novel/chimeric sophorose-rhamnose biosurfactants by introducing heterologous rhamnosyltransferase genes into Starmerella bombicola

Glycolipid biosurfactant, sophorolipids (SLs) and rhamnolipids (RLs) can be widely used in agriculture, food and chemical industries. The different physicochemical properties of SLs and RLs, such as hydrophilic lipophilic value (HLB) and critical micelle concentration (CMC), determine they have different application focus. Researchers are still hoping to obtain new glycolipid surfactants with unique surface activities. In this study, we successfully transformed two rhamnosyltransferase genes rhlA and rhlB from Pseudomonas aeruginosa to the sophorolipid-producing Starmerella bombicola CGMGG 1576 to obtain a recombinant strain was SbrhlAB. Two novel components with molecular weight of 554 (C26H50O12) and 536 (C26H48O11) were identified with the ASB C18 column from the fermentation broth of SbrhlAB, the former was a non-acetylated acidic C14:0 glycolipid containing one glucose and one rhamnose, and the latter was an acidic C14:1 glycolipid containing two rhamnoses. With the Venusil MP C18 column, one new glycolipid component was identified as an acidic C18:3 glycolipid with one rhamnose (C24H40O7), which has not been reported before. Our present study demonstrated that novel glycolipids can be synthesized in vivo by reasonable genetic engineering. The results will be helpful to engineer sophorolipid-producing yeast to produce some specific SLs or their derivatives in more rational and controllable way.

Microbial Biosurfactants: Antimicrobial Activity and Potential Biomedical and Therapeutic Exploits

The rapid emergence of multidrug-resistant pathogens worldwide has raised concerns regarding the effectiveness of conventional antibiotics. This can be observed in ESKAPE pathogens, among others, whose multiple resistance mechanisms have led to a reduction in effective treatment options. Innovative strategies aimed at mitigating the incidence of antibiotic-resistant pathogens encompass the potential use of biosurfactants. These surface-active agents comprise a group of unique amphiphilic molecules of microbial origin that are capable of interacting with the lipidic components of microorganisms. Biosurfactant interactions with different surfaces can affect their hydrophobic properties and as a result, their ability to alter microorganisms' adhesion abilities and consequent biofilm formation. Unlike synthetic surfactants, biosurfactants present low toxicity and high biodegradability and remain stable under temperature and pH extremes, making them potentially suitable for targeted use in medical and pharmaceutical applications. This review discusses the development of biosurfactants in biomedical and therapeutic uses as antimicrobial and antibiofilm agents, in addition to considering the potential synergistic effect of biosurfactants in combination with antibiotics. Furthermore, the anti-cancer and anti-viral potential of biosurfactants in relation to COVID-19 is also discussed.

A comprehensive review of biosurfactant production and its uses in the pharmaceutical industry

Biosurfactants are naturally occurring, surface-active chemicals generated by microorganisms and have attracted interest recently because of their numerous industrial uses. Compared to their chemical equivalents, they exhibit qualities that include lower toxic levels, increased biodegradable properties, and unique physiochemical properties. Due to these traits, biosurfactants have become attractive substitutes for synthetic surfactants in the pharmaceutical industry. In-depth research has been done in the last few decades, demonstrating their vast use in various industries. This review article includes a thorough description of the various types of biosurfactants and their production processes. The production process discussed here is from oil-contaminated waste, agro-industrial waste, dairy, and sugar industry waste, and also how biosurfactants can be produced from animal fat. Various purification methods such as ultrafiltration, liquid-liquid extraction, acid precipitation, foam fraction, and adsorption are required to acquire a purified product, which is necessary in the pharmaceutical industry, are also discussed here. Alternative ways for large-scale production of biosurfactants using different statistical experimental designs such as CCD, ANN, and RSM are described here. Several uses of biosurfactants, including drug delivery systems, antibacterial and antifungal agents, wound healing, and cancer therapy, are discussed. Additionally, in this review, the future challenges and aspects of biosurfactant utilization in the pharmaceutical industry and how to overcome them are also discussed.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

Sophorolipids: A comprehensive review on properties and applications

Sophorolipids are surface-active glycolipids produced by several non-pathogenic yeast species and are widely used as biosurfactants in several industrial applications. Sophorolipids provide a plethora of benefits over chemically synthesized surfactants for certain applications like bioremediation, oil recovery, and pharmaceuticals. They are, for instance less toxic, more benign and environment friendly in nature, biodegradable, freely adsorb to different surfaces, self-assembly in hydrated solutions, robustness for industrial applications etc. These miraculous properties result in valuable physicochemical attributes such as low critical micelle concentrations (CMCs), reduced interfacial surface tension, and capacity to dissolve non-polar components. Moreover, they exhibit a diverse range of physicochemical, functional, and biological attributes due to their unique molecular composition and structure. In this article, we highlight the physico-chemical properties of sophorolipids, how these properties are exploited by the human community for extensive benefits and the conditions which lead to their unique tailor-made structures and how they entail their interfacial behavior. Besides, we discuss the advantages and disadvantages associated with the use of these sophorolipids. We also review their physiological and functional attributes, along with their potential commercial applications, in real-world scenario. Biosurfactants are compared to their man-made equivalents to show the variations in structure-property correlations and possible benefits. Those attempting to manufacture purported natural or green surfactant with innovative and valuable qualities can benefit from an understanding of biosurfactant features structured along the same principles. The uniqueness of this review article is the detailed physico-chemical study of the sophorolipid biosurfactant and how these properties helps in their usage and detailed explicit study of their applications in the current scenario and also covering their pros and cons.

Draft Genome Sequence of the Sophorolipid-Producing Yeast Pseudohyphozyma bogoriensis ATCC 18809

Pseudohyphozyma bogoriensis is gaining attention as a microbial source of high-value sophorolipids. We report here on its genomic sequence, which will improve our understanding of its metabolic pathways and allow the development of genome manipulation systems. PacBio sequencing was performed, yielding a 26-Mbp genome with 57% GC content and encoding 7,847 predicted proteins.

Mono-Rhamnolipid Biosurfactants Synthesized by Pseudomonas aeruginosa Detrimentally Affect Colorectal Cancer Cells

Over the past 15 years, glycolipid-type biosurfactant compounds have been postulated as novel, naturally synthesized anticancer agents. This study utilized a recombinant strain of Pseudomonas aeruginosa to biosynthesize a preparation of mono-rhamnolipids that were purified via both liquid and solid-phase extraction, characterized by HPLC-MS, and utilized to treat two colorectal cancer cell lines (HCT-116 and Caco2) and a healthy colonic epithelial cell line CCD-841-CoN. Additionally, the anticancer activity of these mono-rhamnolipids was compared to an alternative naturally derived anticancer agent, Piceatannol. XTT cell viability assays showed that treatment with mono-rhamnolipid significantly reduced the viability of both colorectal cancer cell lines whilst having little effect on the healthy colonic epithelial cell line. At the concentrations tested mono-rhamnolipids were also shown to be more cytotoxic to the colorectal cancer cells than Piceatannol. Staining of mono-rhamnolipid-treated cells with propidium iodine and acridine orange appeared to show that these compounds induced necrosis in both colorectal cancer cell lines. These data provide an early in vitro proof-of-principle for utilizing these compounds either as active pharmaceutical ingredient for the treatment of colorectal cancer or incorporations into nutraceutical formulations to potentially prevent gastrointestinal tract cancer.

Optimization of the primary purification process of extracting sphorolipid from the fermentation broth to achieve a higher yield and purity

Sophorolipid (SL) is a surface-active glycolipid biosurfactant with promising industrial applications. It is synthesised by fermentation of hydrophobic and hydrophilic substrates using selected non-pathogenic yeasts. However, its applications are limited by high production costs and ineffective product recovery in downstream purification stages. Natural sophorolipids are produced in six to nine different hydrophobic sophorosides, where the carboxyl end of the fatty acid is either free, which is known as the acidic or open form, or it can be esterified internally to produce the lactonic form. The present study deals with the screening and selection of suitable solvents for the extraction of acidic and lactonic SL from fermentation broth. The optimisation study involves exhaustive extraction with the six different immiscible solvents ethyl acetate, butyl acetate, methylene dichloride, methyl tert.-butyl ether, methyl iso-butyl ketone and methyl ethyl ketone. The partition coefficient (Kd), which is the ratio of the solute concentration in the organic layer compared to the aqueous layer, determines the performance measurement of the extraction process in terms of yield and purity of the desired solute. The factors that influence exhaustive extraction were the broth to solvent ratio and the extraction stages. The optimal extraction conditions for the highest possible yield were a broth to solvent ratio of 1:1 and a number of extraction steps of 2. Methylene dichloride showed better results in terms of yield and selectivity in the extraction of acidic and lactonic SL from the fermentation broth compared to the other solvents investigated. For lactonic SL, the highest Kd value determined was 36.6 and for acidic SL the highest Kd value was 1.14.

Microbial sophorolipids inhibit colorectal tumour cell growth in vitro and restore haematocrit in Apcmin+/- mice

Abstract

Sophorolipids are glycolipid biosurfactants consisting of a carbohydrate sophorose head with a fatty acid tail and exist in either an acidic or lactonic form. Sophorolipids are gaining interest as potential cancer chemotherapeutics due to their inhibitory effects on a range of tumour cell lines. Currently, most anti-cancer studies reporting the effects of sophorolipids have focused on lactonic preparations with the effects of acidic sophorolipids yet to be elucidated. We produced a 94% pure acidic sophorolipid preparation which proved to be non-toxic to normal human colonic and lung cells. In contrast, we observed a dose-dependent reduction in viability of colorectal cancer lines treated with the same preparation. Acidic sophorolipids induced apoptosis and necrosis, reduced migration, and inhibited colony formation in all cancer cell lines tested. Furthermore, oral administration of 50 mg kg⁻¹ acidic sophorolipids over 70 days to Apc^min+/− mice was well tolerated and resulted in an increased haematocrit, as well as reducing splenic size and red pulp area. Oral feeding did not affect tumour numbers or sizes in this model. This is the first study to show that acidic sophorolipids dose-dependently and specifically reduces colon cancer cell viability in addition to reducing tumour-associated bleeding in the Apc^min+/− mouse model.

Key points

• Acidic sophorolipids are produced by yeast species such as Starmerella bombicola.

• Acidic sophorolipids selectively killed colorectal cells with no effect on healthy gut epithelia.

• Acidic sophorolipids reduced tumour-associated gut bleed in a colorectal mouse model.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12115-6.

Sophorolipids: Anti-cancer activities and mechanisms

Sophorolipids (SLs) are biosurfactants synthesized as secondary metabolites by non-pathogenic yeasts and other microorganisms. They are members of glycolipid microbial surfactant family that consists of a sophorose polar head group and, most often, an ω-1 hydroxylated fatty acid glycosidically linked to the sophorose moiety. Since the fermentative production of SLs is high (>200 g/L), SLs have the potential to provide low-cost therapeutics. Natural and modified SLs possess anti-cancer activity against a wide range of cancer cell lines such as those derived from breast, cervical, colon, liver, brain, and the pancreas. Corresponding data on their cytotoxicity against noncancerous cell lines including human embryo kidney, umbilical vein, and mouse fibroblasts is also discussed. These results are compiled to elucidate trends in SL-structures that lead to higher efficacy against cancer cell lines and lower cytotoxicity for normal cell lines. While extrapolation of these results provides some insights into the design of SLs with optimal therapeutic indices, we also provide a critical assessment of gaps and inconsistencies in the literature as well as the lack of data connecting structure-to-anticancer and cytotoxicity on normal cells. Furthermore, SL-mechanism of action against cancer cell lines, that includes proliferation inhibition, induction of apoptosis, membrane disruption and mitochondria mediated pathways are discussed. Perspectives on future research to develop SL anticancer therapeutics is discussed.

Moesziomyces spp. cultivation using cheese whey: new yeast extract-free media, β-galactosidase biosynthesis and mannosylerythritol lipids production

Mannosylerythritol lipids (MELs) are biosurfactants with excellent biochemical properties and a wide range of potential applications. However, high production costs, low productivity and unsatisfactory scale-up production have hampered commercial adoption. Herein, we report for the first time the β-galactosidase production by Moesziomyces spp. from different sugars (D-galactose, D-glucose and D-lactose), with D-galactose being the best β-galactosidase inducer, with 11.2 and 63.1 IU/mgbiomass, for Moesziomyces aphidis 5535 T and Moesziomyces antarcticus 5048 T, respectively. The production of this enzyme allows to break down D-lactose and thus to produce MEL directly from D-lactose or cheese whey (a cheese industry by-product). Remarkably, when CW was used as sole media component (carbon and mineral source), in combination with waste frying oil, MEL productivities were very close (1.40 and 1.31 gMEL/L/day) to the ones obtained with optimized medium containing yeast extract (1.92 and 1.50 gMEL/gsusbtrate), both for M. antarcticus and M. aphidis. The low-cost, facile and efficient process which generates large amounts of MELs potentiates its industrialization.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02837-y.

Serum Exosomal lncRNA AC007099.1 Regulates the Expression of Neuropeptide-Related FAP, as a Potential Biomarker for Hepatocarcinogenesis

Neuropeptide-associated fibroblast activation protein (FAP) may be an important risk factor for neurovascular metastasis in hepatocellular carcinoma. Analysis of The Cancer Genome Atlas (TCGA) database showed that FAP mRNA was highly expressed in most human tumor tissues. The HPA database then verified that FAP was highly expressed in tumor tissues following protein translation. Survival analysis then showed that the level of FAP expression significantly affected the overall survival (OS), progress free interval (PFI), and disease specific survival (DSS) of patients with hepatocellular carcinoma. A high expression of FAP in tumor tissue is associated with poor patient prognosis. According to the results of spearman correlation, AC009099 and FAP were negatively correlated with miR-7152 expression, while AC009099 and FAP expression were positively correlated. The lncRNA AC007099.1, which may serve as a potential target for the treatment of hepatocellular carcinoma, was associated with liver cancer. AC007099.1/miR-7152/FAP was found to be associated with immune infiltration in patients with hepatocellular carcinoma. Enrichment analysis suggests that the AC009099/miR-7152/FAP ceRNA regulatory network is associated with neuropeptide functional pathways. In conclusion, a neuropeptide-related AC009099/miR-7152/FAP ceRNA regulatory network was constructed in this study.

Biosurfactants as Anticancer Agents: Glycolipids Affect Skin Cells in a Differential Manner Dependent on Chemical Structure

Melanomas account for 80% of skin cancer deaths. Due to the strong relationship between melanomas and U.V. radiation, sunscreens have been recommended for use as a primary preventative measure. However, there is a need for targeted, less invasive treatment strategies. Glycolipids such as sophorolipids and rhamnolipids are microbially derived biosurfactants possessing bioactive properties such as antimicrobial, immunomodulatory and anticancer effects. This study aimed to ascertain the differing effects of glycolipids on skin cells. Highly purified and fully characterized preparations of sophorolipids and rhamnolipids were used to treat spontaneously transformed human keratinocyte (HaCaT) and the human malignant melanocyte (SK-MEL-28) cell lines. Cell viability and morphological analyses revealed that glycolipids have differential effects on the skin cells dependent on their chemical structure. Lactonic sophorolipids and mono-rhamnolipids were shown to have a significantly detrimental effect on melanoma cell viability compared to healthy human keratinocytes. These glycolipids were shown to induce cell death via necrosis. Additionally, sophorolipids were shown to significantly inhibit SK-MEL-28 cell migration. These findings suggest that glycolipids could be used as bioactive agents with selective inhibitory effects. As such, glycolipids could be a substitute for synthetically derived surfactants in sunscreens to provide additional benefit and have the potential as novel anti-skin-cancer therapies.

Sophorolipid: a glycolipid biosurfactant as a potential therapeutic agent against COVID-19

Biosurfactants are natural surfactants produced by a variety of microorganisms. In recent years, biosurfactants have garnered a lot of interest due to their biomedical and pharmaceutical applications. Sophorolipids are glycolipid types of biosurfactants produced by selected nonpathogenic yeasts. In addition to the detergent activity (reduction in surface and interfacial tension), which is commonly utilized by biomedical applications, sophorolipids have shown some unique properties such as, antiviral activity against enveloped viruses, immunomodulation, and anticancer activity. Considering their antiviral activity, the potential of sophorolipids as an antiviral therapy for the treatment of COVID-19 is discussed in this review. Being a surfactant molecule, sophorolipid could solubilize the lipid envelope of SARS-CoV-2 and inactivate it. As an immunomodulator, sophorolipid could attenuate the cytokine storm caused by the SARS-CoV-2 upon infection, and inhibit the progression of COVID-19 in patients. Sophorolipids could also be used as an effective treatment strategy for COVID-19 patients suffering from cancer. However, there is limited research on the use of sophorolipid as a therapeutic agent for the treatment of cancer and viral diseases, and to modulate the immune response. Nevertheless, the multitasking capabilities of sophorolipids make them potential therapeutic candidates for the bench-to-bedside research for the treatment of COVID-19.

Biosurfactants: Potential Agents for Controlling Cellular Communication, Motility, and Antagonism

Biosurfactants are surface-active molecules produced by microorganisms, either on the cell surface or secreted extracellularly. They form a thin film on the surface of microorganisms and help in their detachment or attachment to other cell surfaces. They are involved in regulating the motility of bacteria and quorum sensing. Here, we describe the various types of biosurfactants produced by microorganisms and their role in controlling motility, antagonism, virulence, and cellular communication.

From bumblebee to bioeconomy: Recent developments and perspectives for sophorolipid biosynthesis

Sophorolipids are biobased compounds produced by the genera Starmerella and Pseudohyphozyma that gain exponential interest from academic and industrial stakeholders due to their mild and environmental friendly characteristics. Currently, industrially relevant sophorolipid volumetric productivities are reached up to 3.7 g∙L^-1∙h^-1 and sophorolipids are used in the personal care and cleaning industry at small scale. Moreover, applications in crop protection, food, biohydrometallurgy and medical fields are being extensively researched. The research and development of sophorolipids is at a crucial stage. Therefore, this work presents an overview of the state-of-the-art on sophorolipid research and their applications, while providing a critical assessment of scientific techniques and standardisation in reporting. In this review, the genuine sophorolipid producing organisms and the natural role of sophorolipids are discussed. Subsequently, an evaluation is made of innovations in production processes and the relevance of in-situ product recovery for process performance is discussed. Furthermore, a critical assessment of application research and its future perspectives are portrayed with a focus on the self-assembly of sophorolipid molecules. Following, genetic engineering strategies that affect the sophorolipid physiochemical properties are summarised. Finally, the impact of sophorolipids on the bioeconomy are uncovered, along with relevant future perspectives.

ROS-Mediated Necrosis by Glycolipid Biosurfactants on Lung, Breast, and Skin Melanoma Cells

Cancer is one of the major leading causes of death worldwide. Designing the new anticancer drugs is remained a challenging task due to ensure complexicity of cancer etiology and continuosly emerging drug resistance. Glycolipid biosurfactants are known to possess various biological activities including antimicrobial, anticancer and antiviral properties. In the present study, we sought to decipher the mechanism of action of the glycolipids (lactonic-sophorolipd, acidic-sophorolipid, glucolipid, and bolalipid) against cancer cells using lung cancer cell line (A549), breast cancer cell line (MDA-MB 231), and mouse skin melanoma cell line (B16F10). Scratch assay and fluorescence microscopy revealed that glycolipids inhibit tumorous cell migration possibly by inhibiting actin filaments. Fluorescence activated cell sorter (FACS) analysis exhibited that lactonic sophorolipid and glucolipid both induced the reactive oxygen species, altered the mitochondrial membrane potential (ΔΨ) and finally led to the cell death by necrosis. Furthermore, combinatorial effect of lactonic-sophorolipd and glucolipid demonstrated synergistic interaction on A549 cell line whereas additive effect on MDA-MB 231 and B16F10 cell lines. Our study has highlighted that lactonic-sophorolipd and glucolipid could be useful for developing new anticancer drugs either alone or in combination.

Lactonic sophorolipid-induced apoptosis in human HepG2 cells through the Caspase-3 pathway

Liver cancer, one of the most common types of cancer in the world, is the second leading cause of death for cancer patients. For liver cancer, there is an urgent need for an effective treatment with no or less toxic side effects. Lactonic sophorolipids (LSL), as a potential anticancer drug, has attracted wide attention of pharmaceutical researchers with its good biological activities. The effects of LSL and cell death inhibitors were measured by MTT test on HepG2 cells. Meanwhile, the morphology of the cells was observed under a microscope. The apoptosis rate was detected by flow cytometry, and the expression levels of enzyme activity of Caspase-3 and Caspase-9 were measured by detection kits. Meanwhile, mRNA levels of Apaf-1, Caspase-3, Bax, and Bcl-2 were measured by quantitative real-time RT-PCR; protein levels of Caspase-3, Cleaved Caspase-3, Bax, and Bcl-2 were measured by western blot. LSL can inhibit the proliferation of cells, and it is possible to induce apoptosis in cells. The HepG2 cells with LSL co-culture exhibited typical apoptotic morphology, and the expression levels of enzyme activity of Caspase-3 and Caspase-9 increased (P< 0.05). We also found that LSL increases cell apoptosis rate and regulates the expression of genes and proteins associated with apoptosis through the Caspase-3 pathway. These results indicate that LSL may be one of the potential drug candidates to inhibit the proliferation and induce apoptosis in HepG2 cells.Key points• LSL, which is of good biological activities such as anti-bacterium, virus elimination, and inflammatory response elimination, has been firstly used to intervene in vitro to investigate its effect on HepG2 cell proliferation.• LSL can inhibit the proliferation of cells, and it is possible to induce apoptosis in HepG2 cells through the Caspase-3 pathway.• The mechanism of LSL action on HepG2 cell proliferation was firstly also discussed, which provides a certain experimental reference for the clinical treatment of liver cancer.

Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development

The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science.

Advances in sophorolipid-producing strain performance improvement and fermentation optimization technology

Sophorolipids (SLs), currently one of the most promising biosurfactants, are secondary metabolites produced by many non-pathogenic yeasts, among which Candida bombicola ATCC 22214 is the main sophorolipid-producing strain. SLs have gained much attention since they exhibit anti-tumor, anti-bacterial, anti-inflammatory, and other beneficial biological activities. In addition, as biosurfactants, SLs have a low toxicity level and are easily degradable without polluting the environment. However, the production cost of SLs remains high, which hinders the industrialization process of SL production. This paper describes SL structure and the metabolic pathway of SL synthesis firstly. Furthermore, we analyze factors that contribute to the higher production cost of SLs and summarize current research status on the advancement of SL production based on two aspects: (1) the improvement of strain performance and (2) the optimization of fermentation process. Further prospects of lowering the cost of SL production are also discussed in order to achieve larger-scale SL production with a high yield at a low cost. KEY POINTS: • Review of advances in strain performance improvement and fermentation optimization. • High-throughput screening and metabolic engineering for high-performance strains. • Low-cost substrates and semi-continuous strategies for efficient SL production.

Biosurfactants as a Novel Additive in Pharmaceutical Formulations: Current Trends and Future Implications

BACKGROUND

Surfactants are an important category of additives that are used widely in most of the formulations as solubilizers, stabilizers, and emulsifiers. Current drug delivery systems comprise of numerous synthetic surfactants (such as Cremophor EL, polysorbate 80, Transcutol-P), which are associated with several side effects though used in many formulations. Therefore, to attenuate the problems associated with conventional surfactants, a new generation of surface-active agents is obtained from the metabolites of fungi, yeast, and bacteria, which are termed as biosurfactants.

OBJECTIVES

In this article, we critically analyze the different types of biosurfactants, their origin along with their chemical and physical properties, advantages, drawbacks, regulatory status, and detailed pharmaceutical applications.

METHODS

243 papers were reviewed and included in this review.

RESULTS

Briefly, Biosurfactants are classified as glycolipids, rhamnolipids, sophorolipids, trehalolipids, surfactin, lipopeptides & lipoproteins, lichenysin, fatty acids, phospholipids, and polymeric biosurfactants. These are amphiphilic biomolecules with lipophilic and hydrophilic ends and are used as drug delivery vehicles (foaming, solubilizer, detergent, and emulsifier) in the pharmaceutical industry. Despite additives, they have some biological activity as well (anti-cancer, anti-viral, anti-microbial, P-gp inhibition, etc.). These biomolecules possess better safety profiles and are biocompatible, biodegradable, and specific at different temperatures.

CONCLUSION

Biosurfactants exhibit good biomedicine and additive properties that can be used in developing novel drug delivery systems. However, more research should be driven due to the lack of comprehensive toxicity testing and high production cost which limits their use.

Direct Observation of Sophorolipid Micelle Docking in Model Membranes and Cells by Single Particle Studies Reveals Optimal Fusion Conditions

Sophorolipids (SLs) are naturally produced glycolipids that acts as drug delivery for a spectrum of biomedical applications, including as an antibacterial antifungal and anticancer agent, where they induce apoptosis selectively in cancerous cells. Despite their utility, the mechanisms underlying their membrane interactions, and consequently cell entry, remains unknown. Here, we combined a single liposome assay to observe directly and quantify the kinetics of interaction of SL micelles with model membrane systems, and single particle studies on live cells to record their interaction with cell membranes and their cytotoxicity. Our single particle readouts revealed several repetitive docking events on individual liposomes and quantified how pH and membrane charges, which are known to vary in cancer cells, affect the docking of SL micelles on model membranes. Docking of sophorolipids micelles was found to be optimal at pH 6.5 and for membranes with -5% negatively charge lipids. Single particle studies on mammalian cells reveled a two-fold increased interaction on Hela cells as compared to HEK-293 cells. This is in line with our cell viability readouts recording an approximate two-fold increased cytotoxicity by SLs interactions for Hela cells as compared to HEK-293 cells. The combined in vitro and cell assays thus support the increased cytotoxicity of SLs on cancer cells to originate from optimal charge and pH interactions between membranes and SL assemblies. We anticipate studies combining quantitative single particle studies on model membranes and live cell may reveal hitherto unknown molecular insights on the interactions of sophorolipid and additional nanocarriers mechanism.

Effects of sophorolipids on fungal and oomycete pathogens in relation to pH solubility

AIMS

The objective of this study was to determine the effects of sophorolipids on several fungal and oomycete plant pathogens and the relationship between sophorolipids at different pH and antimicrobial activities.

METHODS AND RESULTS

Sophorolipids had different solubility at different pH with a dramatic increase in solubility when pH was 6 or higher. Inhibition of mycelial growth of Phytophthora infestans by sophorolipids was affected by pH values, showing that when the pH value was higher, the inhibition rate was lower. Sophorolipids inhibited spore germination and mycelial growth of several fungal and oomycete pathogens in vitro including Fusarium sp., F. oxysporum, F. concentricum, Pythium ultimum, Pyricularia oryzae, Rhizoctorzia solani, Alternaria kikuchiana, Gaeumannomyces graminis var. tritici and P. infestans and caused morphological changes in hyphae by microscope observation. Sophorolipids reduced β-1,3-glucanase activity in mycelia of P. infestans. In greenhouse studies, foliar application of sophorolipids at 3 mg ml^-1 reduced severity of late blight of potato caused by P. infestans significantly.

CONCLUSION

Sophorolipids influenced spore germination and hyphal tip growth of several plant pathogens and pH solubility of sophorolipids had an effect on their efficacy. Application of sophorolipids reduced late blight disease on potato under greenhouse conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings indicated that sophorolipids have the potential to be developed as a convenient and easy-to-use formulation for managing plant diseases.

Microbial biosurfactants: current trends and applications in agricultural and biomedical industries

Synthetic surfactants are becoming increasingly unpopular in many applications due to previously disregarded effects on biological systems and this has led to a new focus on replacing such products with biosurfactants that are biodegradable and produced from renewal resources. Microbially derived biosurfactants have been investigated in numerous studies in areas including: increasing feed digestibility in an agricultural context, improving seed protection and fertility, plant pathogen control, antimicrobial activity, antibiofilm activity, wound healing and dermatological care, improved oral cavity care, drug delivery systems and anticancer treatments. The development of the potential of biosurfactants has been hindered somewhat by the myriad of approaches taken in their investigations, the focus on pathogens as source species and the costs associated with large-scale production. Here, we focus on various microbial sources of biosurfactants and the current trends in terms of agricultural and biomedical applications.

Triacylglycerols accumulation and glycolipids secretion by the oleaginous yeast Rhodotorula babjevae Y-SL7: Structural identification and biotechnological applications

The newly isolated oleaginous yeast, Rhodotorula babjevae Y-SL7, was shown to accumulate high intracellular content of microbial oil (mainly triacylglycerols) and to secret, under the same culture conditions, an atypical glycolipid. This unusual behavior was induced when the strain was subjected to nitrogen limitation and high amount of carbon. A series of analytical methods was adopted in order to structurally characterize the secreted glycolipid. The latter consists of a mixture of 9 molecules formed by a polyol head group, bound through the carboxyl end of an acetylated 3-hydroxy fatty acid with C18 or C16 chain length. In addition of their physicochemical properties such as emulsifying activity on hydrophobic substrates, Y-SL7 glycolipids have shown a therapeutically promising cytotoxic effect against different cancer cell lines. In fact, Y-SL7 strain can be used for the production of triacylglycerols as energetic molecules and for the secretion of a biosurfactant of therapeutic and environmental interest.

Sophorolipid exhibits antifungal activity by ROS mediated endoplasmic reticulum stress and mitochondrial dysfunction pathways in Candida albicans

In the present study, we investigated the mechanism of cell death in C. albicans due to treatment with sophorolipid (SL). SL is an extracellular glycolipid biosurfactant produced by various species of non-pathogenic yeasts and is known to inhibit the growth and biofilm formation of C. albicans. This study revealed that treatment of C. albicans cells with SL increases the ROS production and expression of oxidative stress-related genes significantly (SOD1, CAT1). Increased ROS level within the cells causes ER stress and release of Ca²⁺ in the cytoplasm and alteration of the mitochondrial membrane potential (MMP). Quantitative real time-polymerase chain reaction (qRT-PCR) data showed that SL also upregulates the Endoplasmic Reticulum (ER) stress marker HAC1. Flow cytometric analysis (AnnexinV/PI) indicated that the cell death may have occurred due to necrosis which was further confirmed by LDH release assay and transmission electron microscopy (TEM). Further experiments with the null mutant Δ hog1 strain of C. albicans SC5314 indicated the activation of the osmotic stress response pathway (HOG-MAPK) and SAP9. This study gave an insight into the mechanism of cell death initiation by glycolipids and indicated that further modification of these molecules can lead to the development of new therapeutic agent against C. albicans.

Sophorolipid induces ROS generation in C. albicans leading to mitochondrial dysfunction and ER stress followed by the release of Ca²⁺ ions (from the ER lumen) that enter mitochondria and further magnify ROS generation leading to cell death.

Amphiphilic glycoconjugates as potential anti-cancer chemotherapeutics

Amphiphilicity is one of the desirable features in the process of drug development which improves the biological as well as the pharmacokinetics profile of bioactive molecule. Carbohydrate moieties present in anti-cancer natural products and synthetic molecules influence the amphiphilicity and hence their bioactivity. This review focuses on natural and synthetic amphiphilic anti-cancer glycoconjugates. Different classes of molecules with varying degree of amphiphilicity are covered with discussions on their structure-activity relationship and mechanism of action.

Anti-proliferative effect of novel primary cetyl alcohol derived sophorolipids against human cervical cancer cells HeLa

Sophorolipids (SLs) are glycolipid biosurfactants that have been shown to display anticancer activity. In the present study, we report anti-proliferative studies on purified forms of novel SLs synthesized using cetyl alcohol as the substrate (referred as SLCA) and their anticancer mechanism in human cervical cancer cells. Antiproliferative effect of column purified SLCA fractions (A, B, C, D, E and F) was examined in panel of human cancer cell lines as well as primary cells. Among these fractions, SLCA B and C significantly inhibited the survival of HeLa and HCT 116 cells without affecting the viability of normal human umbilical vein endothelial cells (HUVEC). The two fractions were identified as cetyl alcohol sophorolipids with non-hydroxylated tail differing in the degree of acetylation on sophorose head group. At an IC₅₀ concentration SLCA B (16.32 μg ml^-1) and SLCA C (14.14 μg ml^-1) blocked the cell cycle progression of HeLa cells at G1/S phase in time-dependent manner. Moreover, SLCA B and SLCA C induced apoptosis in HeLa cells through an increase in intracellular Ca²⁺ leading to depolarization of mitochondrial membrane potential and increase in the caspase-3, -8 and -9 activity. All these findings suggest that these SLCAs could be explored for their chemopreventive potential in cervical cancer.

Sophorolipids production from rice straw via SO3 micro-thermal explosion by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576

A novel lignocellulose material, holocellulose from rice straw via the pretreatment of SO3 micro-thermal explosion, was developed to produce sophorolipids (SLs) with Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The influence factors of inoculum dose, yeast extract concentration and pH regulators (chemical regents used for adjusting/influencing pH) was investigated and discussed. Results showed that W. domercqiae can grow in the rice straw holocellulose hydrolysate, and acquire relative high SL yield of 53.70 ± 2.61 g/L in shake flask culture. Inoculum dose, yeast extract concentration and pH regulator made obvious influence on fermentation parameters, especially on final broth pH and SLs production. Furthermore, there is a strong negative linear correlation existing between final broth pH and lactonic SL or ratio of lac SL/tot SL. Additionally, comparison between SL production and non-glucose carbon sources, culture methods, microbes in previous reports was carried out. These results will be benefit for acquiring SL mixture with suitable lac SL/tot SL ratio for specific purpose and scope economically.

Current status in biotechnological production and applications of glycolipid biosurfactants

Biosurfactants are natural compounds with surface activity and emulsifying properties produced by several types of microorganisms and have been considered an interesting alternative to synthetic surfactants. Glycolipids are promising biosurfactants, due to low toxicity, biodegradability, and chemical stability in different conditions and also because they have many biological activities, allowing wide applications in different fields. In this review, we addressed general information about families of glycolipids, rhamnolipids, sophorolipids, mannosylerythritol lipids, and trehalose lipids, describing their chemical and surface characteristics, recent studies using alternative substrates, and new strategies to improve of production, beyond their specificities. We focus in providing recent developments and trends in biotechnological process and medical and industrial applications.

Lactonic Sophorolipids Increase Tumor Burden in Apcmin+/- Mice

Sophorolipids (SL) are amphiphilic biosurfactant molecules consisting of a disaccharide sophorose with one fatty acid at the C1 position and optional acetylation at the C6’and C6” positions. They exist in a closed ring lactonic (LSL) or open acidic (ASL) structure Sophorolipids are produced in crude mixtures in economically viable amounts by the yeast Starmerella bombicola and used in a variety of consumer products. Varying levels of anti- proliferative and anti-cancer activity of crude sophorolipid mixtures are described in a number of tumor cell lines in vitro. However, significant inter-study variation exists in the composition of sophorolipid species as well as other biologically active compounds in these mixtures, which makes interpretation of in vitro and in vivo studies difficult. We produced a 96% pure C18:1 lactonic sophorolipid that dose-dependently reduces the viability of colorectal cancer, as well as normal human colonic and lung cell lines in vitro. Oral administration of vehicle-only; or lactonic sophorolipids (50 mg/kg for 70 days), to Apc^min+/- mice resulted in an increase in the number (55.5 ± 3.3 vs 70.50 ± 7.8: p < 0.05) and size (modal size 2mm vs 4mm) of intestinal polyps. Lactonic administration resulted in a systematic effect via reduced hematocrit (49.5 ± 1.0 vs 28.2 ± 2.0 vs: p<0.03) and splenomegaly (0.56 ± 0.03g vs 0.71 ± 0.04g; p<0.01) confirming exacerbation of disease progression in this model.

Production and Biomedical Applications of Probiotic Biosurfactants

Biosurfactants have been widely used for environmental and industrial applications. However, their use in medical field is still limited. Probiotic biosurfactants possess an immense antimicrobial, anti-adhesive, antitumor, and antibiofilm potential. Moreover, they have an additional advantage over conventional microbial surfactants because probiotics are an integral part of normal human microflora and their biosurfactants are innocuous to human. So, they can be effectively exploited for medicinal use. Present review is aimed to discourse the production and biomedical applications of probiotic biosurfactants.

Evaluation of the transfection efficacies of quaternary ammonium salts prepared from sophorolipids

Two quaternary ammonium sophorolipids proved to be suitable as transfection vectors for gene delivery.

Glycolipid biosurfactants: Potential related biomedical and biotechnological applications

Glycolipids, consisting of a carbohydrate moiety linked to fatty acids, are microbial surface active compounds produced by various microorganisms. They are characterized by highly structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface respectively. Rhamnolipids, trehalolipids, mannosylerythritol-lipids and cellobiose lipids are among the most popular glycolipids. Moreover, their ability to form pores and destabilize biological membrane permits their use in biomedicine as antibacterial, antifungal and hemolytic agents. Their antiviral and antitumor effects enable their use in pharmaceutic as therapeutic agents. Also, glycolipids can inhibit the bioadhesion of pathogenic bacteria enabling their use as anti-adhesive agents and for disruption of biofilm formation and can be used in cosmetic industry. Moreover, they have great potential application in industry as detergents, wetting agents and for flotation. Furthermore, glycolipids can act at the surface and can modulate enzyme activity permitting the enhancement or the inhibition of the activity of certain enzymes.

Development of novel sophorolipids with improved cytotoxic activity toward MDA-MB-231 breast cancer cells

Sophorolipids (SLs) are glycolipid biosurfactants, produced as a mixture of several compounds by some nonpathogenic yeast. In the current study, separation of individual SLs from mixtures with further evaluation of their surface properties and biologic activity on MDA-MB-321 breast cancer cell line were investigated. SLs were biosynthesized by Starmerella bombicola in a culture media supplemented with borage oil. A reverse-phase flash chromatography method with an automated system coupled with a prepacked cartridge was used to separate and purify the main SLs. Compositional analysis of SLs was performed by high-performance liquid chromatography with electrospray ionization mass spectrometry and tandem mass spectrometry. The following diacetylated lactonic SLs were isolated and purified: C18:0, C18:1, C18:2, and C18:3. The critical micelle concentration (CMC) and surface tension at CMC (γCMC ) of the purified SLs showed an increase with the number of double bonds. High cytotoxic effect against MDA-MB-231 cells was observed with C18:0 and C18:1 lactonic SLs. The cytotoxic effects of C18:3 lactonic SL on cancerous cells were for the first time studied. This cytotoxic effect was considerably higher than the promoted by acidic SLs; however, it induced a lower effect than the previously mentioned SLs, C18:0 and C18:1. To our knowledge, for the first time, C18:1 lactonic SL, in selected concentrations, proved to be able to inhibit MDA-MB-231 cell migration without compromising cell viability and to increase intracellular reactive oxygen species.