Many authors believe that amino acids such as ectoine and hydroxyectoine provide much more effective protection against the effects of osmotic or temperature stress than other osmolytes known to date. These amino acids have a strong protective effect for enzymes and proteins. Their accumulation in the cell occurs through
Ectoine belongs to the so-called compensating substances meaning that it protects against changes in the cell resulting from osmotic stress. This molecule is also referred to as a kosmotropic substance. Salt ions may have a kosmotropic effect on water, causing stabilization of the quasi-crystalline water structure or a chaotropic effect, affecting the disorganization of this structure, disturbing the polar structure of water. This is due to the interaction of a free pair of electrons with the cation and hydrogen atoms with the anion, which creates electrostatically stabilized hydration shells around the ions. Such immobilized water molecules are inaccessible to macromolecules exhibiting a hydrophobic character (e.g. proteins), because the polar solvent (water) is more strongly held by the electric field of ions with a higher charge-to-radius ratio [46]. Ectoine as a kosmotropic substance has the properties of stabilizing water molecules. The kosmotropic effect is manifested as a reduction in contact surface between water molecules and phospholipids of cell membranes. Derived from Greek κόσμος, it denotes order and refers to the ability to create orderly structures by strengthening the structure of water [31]. This phenomenon is explained by model tests carried out by Graf
Compounds having compensatory character are removed outside the hydration layer of proteins (the so-called preferential exclusion model), which explains the stabilising effect of proteins, resulting from the reduction of the surface of interaction (a phenomenon being more beneficial from the point of view of entropy) [86]. The “preferential exclusion model” is a hypothesis explaining the biophysical mechanism of the impact of ectoine on macromolecules, according to which osmoprotectants in aqueous solutions do not interact directly with macromolecules but increase the hydration of the molecule, preventing its denaturation [14, 45]. Hahn
It turned out that the influence of ectoine and hydroxyectoine on macromolecules and cells in some aspects is mutually antagonistic [86].
The properties of ectoine cause this amino acid to be multifunctional and have a wide spectrum of applications in many industries, mainly in medicine, pharmacy, cosmetology or biotechnology. The industrial use of ectoine is based primarily on the possibility of protecting the skin and relieving inflammation (Table I), stabilizing enzymes; protection of cells and macromolecules against osmotic and temperature stress, UV radiation, desiccation (Table II, Table IV). The protective effect of ectoine described on the example of microorganisms capable of its synthesis can be also used in relation to higher organisms: human, animal and also plants.
Potential possibilities of practical use of ectoine in skin protection
Effect | References |
Anti-aging effect ( | [41] |
Skin protection against desiccation ( | [35] |
Anti-aging activity ( | [17] |
Inducing thermal shock proteins and mediation in the proinflammatory response of human epidermal keratinocytes | [19] |
Photoprotection against visible light ( | [13] |
Moisturising factor ( | [71] |
UV protection of Langerhans cells ( | [10] |
Blocking the release of ceramides in human epidermal keratinocytes under the influence of UVA | [36] |
Skin protection against dehydration caused by surfactants | [18] |
Inhibition of melanogenesis | [96] |
Author’s own modification following [74].
The use of ectoine in cosmetics is based on its protective effect on the skin. It is used as a component of anti-wrinkle and moisturizing cosmetics. Human skin is a barrier between the body and the environment, so it is exposed to many external factors. The stratum corneum of the epidermis is particularly important in this regard. It has a double function in maintaining skin hydration. First, keratinized cells of the stratum corneum form a hydrophobic barrier that prevents water from entering the body through skin. Secondly, with respect to the internal environment, it maintains hydration thanks to its Natural Moisturizing Factor (NMF). It keeps water in the skin and protects it from evaporation [79]. Many environmental factors can have a destructive effect on this natural barrier, causing the skin to lose water. Skin desiccation may result, among others, from exposure to extreme temperatures, dry air, solar radiation, wind or frequent use of detergents. All this causes the skin to dry out and accelerates its aging. There are many examples in the literature confirming the anti-aging and moisturizing effect of ectoine on the skin (Table I). The first commercial use of ectoine for skin protection was related to protection against solar radiation and anti-aging activity [18]. Also, now, ectoine is widely used for this purpose [3, 4, 35]. It has been proved that ectoine protects Langerhans cells from UV radiation [10] and is responsible for blocking the release of ceramides in human epidermal keratinocytes under the influence of UVA [36]. Exposure of keratinocytes to UVA radiation, especially in humans, results in elevated levels of ceramides, and consequently activates the intracellular signalling cascade, leading to the expression of intercellular adhesion molecules. These negative effects can be effectively prevented by using ectoine, which is capable of “extinguishing” singlet oxygen [17, 36]. Büenger and Driller exposed human keratinocytes to 1 mM ectoine and UV radiation (30 J/cm2) for 24 hours. Then, they examined the release of inflammatory agents such as AP-2, ICAM-1, ceramides and showed that the initial effect of ectoine on keratinocytes leads to a decrease in the release of AP-2 inflammatory factor and increased expression of ICAM-1 adhesion molecules [17].
The cosmetics industry also uses the fact that ectoine has a stronger moisturizing effect than glycerol and ensures longer skin hydration [35]. It has been proven that the addition of 2% ectoine improves the care properties of products, causes better skin hydration, significant improvement of its elasticity and regeneration of the structure [41, 56]. Clinical studies ordered by Langsteiner LEK-Pharmaceutical company producing ectoine confirm that after 3–4 weeks of treatment, the preparation based on ectoine reduces skin dryness by up to 86% and skin desquamation by up to 70%.
The use of ectoine in pharmacy, medicine and biotechnology was influenced by its ability to protect macromolecules (Table II). Numerous studies have shown that ectoine, by forming a complex with water molecules, increases the stability of enzymes and thus reduces the susceptibility of protein to denaturation [97]. It was also shown that ectoine, like other compatible solutes, strengthens the intramolecular interactions important for protein stability [80]. Ectoine reduces the denaturation of enzymes induced by elevated temperature. It prolongs the activity of enzymes sensitive to freezing-defrosting, heating and freeze-drying, such as: lactate dehydrogenase (LDH) and phosphofructokinase [62]. In addition, it increases the stability of phytase, ribonuclease-A and DNA polymerase at elevated temperature [100]. In addition, it has been shown that an ectoine derivative – hydroxyectoine – has a better ability to protect proteins in the conditions of raised temperature [29, 90] (Table III). Ectoine can also protect macromolecules from proteolytic factors. For example, zymogen, trypsinogen and chymotrypsinogen become resistant to enteropeptidase [54]. In addition, it has been shown that ectoine and some polyols can inhibit HIV replication [58] and stabilize retrovirus vectors in gene therapy [26].
Potential possibilities of the practical use of ectoine and hydroxyectoine for protecting macromolecules
Effect | References |
Ensuring thermostability of cyanophycin synthetase | [39] |
Ensuring the thermostability of the phytase (90° C) | [100] |
Antibodies protection against proteolytic degradation | [9] |
Lowering the melting temperature of DNA | [58] |
Limiting the formation of infectious prions (PrP106–126) causing encephalopathy ( | [47] |
Activation of proinflammatory reactions in the lung epithelium by stabilizing the membrane signalling platform ( | [93] |
Neutrophil apoptosis restoration during pneumonia | [88, 89] |
Limiting the penetration of neutrophils into the muscle layer of the intestine after transplantation ( | [75] |
Macromolecule protection against proteolytic factors ( | [54] |
Inhibition of HIV replication | [58] |
Stabilization of retrovirus vectors in gene therapy | [26] |
Recombinant proteins protection against degradation, aggregation, change of conformation and freezing | [6] |
Protection of immunotoxins against stress related to freezing and defrosting | [6] |
Increasing the melting temperature of DNA | [57] |
Improving the quality of DNA microarrays | [68] |
Lowering AST level after liver reperfusion (as an ingredient of organ storage solution), (ex vivo) | [11] |
Increase in bile production after reperfusion (as an ingredient of organ storage solution), (ex vivo) | [11] |
Pressure reduction in the portal vein after reperfusion (as an ingredient of the organ storage solution), (ex vivo) | [11] |
Reduction of cellular apoptosis after liver transplantation (as an ingredient of organ storage solution), (ex vivo) | [11] |
Enzymes protection against high temperature, freezing and desiccation | [62] |
Reduction of protein fibrillation (Aß42) in Alzheimer’s disease ( | [47, 53, 81] |
Cryoprotection of umbilical cord blood cells ( | [12] |
Reduction of ulcerative areas and inflammatory mediators during colitis due to the ability to stabilize macromolecules ( | [1] |
Author’s own modification following [74].
Proteins protected under stress conditions by ectoine and hydroxyectoine
Protein | Stress | Protein concentration | Concentration of osmolytes | Activity of protein (%) |
Lactate dehydrogenase | fast freezing/slow defrosting (4x) | 52 μ/ml | 1.0 M hydroxyectoine | 100 |
Phosphofructokinase | 75 μ/ml | 1.0 M ectoine | 100 | |
Enolase | 50 μ/ml | 0.4 M ectoine | 100 | |
Glutamate dehydrogenase | 350 μ/ml | 0.5 M hydroxyectoine | 85 | |
Carboxylesterase | 200 μ/ml | 0.5 M hydroxyectoine | 100 | |
Binding protein CD30 | 1 μ/ml | 1.0 M hydroxyectoine | 89 | |
Lactate dehydrogenase | incubation at elevated temperature: | 52 μ/ml | 0.5 M hydroxyectoine | 90 |
Phosphofructokinase | 75 μ/ml | 1.0 M hydroxyectoine | 100 | |
Enolase | 50 μ/ml | 0.1 M hydroxyectoine | 88 | |
Carboxylesterase | 200 μ/ml | 2.0 M hydroxyectoine | 65 | |
20 IU/ml | 1.0 M hydroxyectoine | 45 | ||
Monoclonal antibody | – | 0.5 M hydroxyectoine | active | |
RNase A | melting | 1 mg/ml | 3.0 M hydroxyectoine | increase in Tm by 12 K |
Lactate dehydrogenase | freeze-drying | 52 μ/ml | 1.0 M ectoine | 61 |
Phosphofructokinase | 75 μ/ml | 1.0 M hydroxyectoine | 68 | |
Enolase | 50 μ/ml | 0.4 M hydroxyectoine | 97 | |
Lactate dehydrogenase | H2O2 oxidation | 200 μ/ml | 0.5 M hydroxyectoine | 95 |
Author’s own modification following [29].
Other applications of ectoine are associated with its ability to relieve inflammation. Its protective properties have been demonstrated in the case of neutrophilic pneumonia in humans [88, 89, 93] and experimentally induced colitis in rats [1]. The administration of ectoine inhibits signalling caused by the presence of nanoparticles, which is known to be responsible for proinflammatory reactions in the epithelial cells of rat lungs. The animals which were administered the ectoine solution intrathecally prior to the introduction of carbon nanoparticles exhibited lower IL-8 expression, lower neutrophil counts in the lung, modulation of the cytokine profile, and reduced MAP kinase activation. These observations have been supported and extended by experiments on cultured human bronchial cells in which ectoine inhibited cell signalling triggered by nanoparticles and limited IL-8 induction [88, 89, 93].
Ectoine can also be used to protect the small intestine from ischaemia and reperfusion in transplantology [1]. Alleviation of the inflammatory reaction is associated with the stabilization of the intestinal barrier and the reduction of cytokine production [75]. In 2015 Bilstain
Some pathological processes, such as the formation and aggregation of amyloid, trigger neurodegenerativa diseases. It was found that both ectoine and hydroxyectoine prevent the formation of amyloid (Aß42) and delay the progression of Alzheimer’s disease [48, 53, 81].
Preparations containing ectoine ensure adequate long-term moisturization of mucous membranes. Ectoine is also a natural substance performing a cell-protective function and inhibits immune reactions, including allergic reactions. Among other things, it has been investigated whether intra-tracheal administration of ectoine exerts protective effect on allergic asthma based on early allergic response (EAR), airway hyperresponsiveness (AHR) and inflammation experimentally induced in rats. The results of the study are promising, because they prove that ectoine has a significant therapeutic effect on EAR, AHR and inflammatory response in the animal model of asthma [43]. This aspect supports potential preventive and therapeutic utility of inhaling ectoine in cases of allergy and/or asthma.
It has also been demonstrated that ectoine can protect entire cells (Table IV). It increases the fluidity of cell membranes under extreme conditions [40] and increases the distance between lipid molecules, which improves membrane fluidity [28]. Other researchers report that ectoine may affect the synthesis of chaperone proteins such as heat shock proteins (Hsp), and it is also assumed that the ectoine itself may act as a chaperone molecule [7, 19]. Ectoine and some polyols make human erythrocytes more resistant to damage caused by surfactants [18]. It has been shown that this effect is stronger than in the case of lecithin (phosphatidylcholine), whose stabilizing properties are already well understood. Graf
Potential possibilities of practical use of ectoine and hydroxyectoine to protect cells
Effect | References |
Supporting the ethanol fermentation process by | [99] |
[69] | |
Maintenance of | [72] |
Osmoprotective effect on lactic acid bacteria | [5] |
Tolerance to the salinity of transformed tobacco plants | [70] |
Increase in the fluidity of cell membranes under extreme conditions | [40] |
Increases the distance between lipid molecules and improves the membrane fluidity | [28] |
Effect on the synthesis of chaperone proteins ( | [7, 19] |
Enterocytes protection against alpha haemolysin of | [15] |
Protection of | [65] |
Protection of | [66, 67] |
Induction of thermotolerance in | [64] |
Stabilization of | [63] |
Author’s own modification following [74].
The current annual world production of L-amino acids significantly exceeds 2 million tons. In the industry microbiological synthesis with the participation of production strains, as well as the enzymatic and chemical synthesis method are used for production of amino acids.
The chemical synthesis of ectoine consists of the thermal cyclization of
A combination method based on the biological isomerization of a chemically obtained product may also be used for the synthesis of amino acids. Enzymatic synthesis is also possible, which has found application in industry in the production of aspartic acid, tryptophan and serine [61]. Due to the limitations of the abovementioned methods, manufacturers are searching for other, more economical methods of biotechnological production of amino acids, including ectoine [92].
The most commonly used method of obtaining amino acids is their microbiological synthesis. The largest share on the amino acid market is currently accounted for by the bioproduction of L-glutamic acid (1.5 million tonnes per year) and L-lysine (850 thousand tonnes per year) [34]. Currently, there is also a growing demand for other amino acids, including ectoine and hydroxyectoine. Biotechnological production of these amino acids is based on the use of the possibility of their synthesis by microorganisms. It is believed that ectoine is currently one of the most valuable products synthesized by microorganisms. The global consumption of ectoine is 15,000 tons per year and retail sales, only in the pharmaceutical industry, are estimated at 1,000 USD per kg [25, 87]. The mechanism of the biosynthesis of ectoine and hydroxyectoine is similar to that of other amino acids such as: L-lysine, L-methionine, L-threonine (Fig. 1). The first stage of the synthesis is the phosphorylation of L-aspartate and its conversion to 4-phospho-L-aspartate by aspartate kinase (Ask enzyme). Then, from 4-phospho-L-aspartate, L-aspartic acid 4-semialdehyde is formed. This reaction is catalysed by L-aspartate-β-semialdehyde dehydrogenase (Asd enzyme). In turn, L-aspartic acid 4-semialdehyde is converted to L-2,4-diaminobutyrate by diaminobutyric acid aminotransferase (enzyme EctB). The next stage is the transformation of the resulting acid by diaminobutyric acid acetyltransferase (EctA enzyme) to
Biotechnological production of ectoine on an industrial scale consists of several stages. The stage of preparing the inoculum, usually it is a laboratory phase, in which the production strain is revived, and the culture is prepared in a volume of a few litres in small laboratory fermenters. The second stage is the main biosynthesis process. At each of these stages monitoring of the growth of microorganisms and control of physicochemical parameters of the culture is required. The proper biosynthesis process includes: the upstream stage, i.e. fermentation and production of the substance and the downstream stage, in which the desired substance is isolated, purified and analysed [74, 86].
The first process developed for the biotechnological production of ectoine, the so-called “bacterial milking”, was developed by Sauer and Galinski in 1998 and is currently used on an industrial scale. It allows release of synthesized osmolytes outside the cell, without degradation of the bacterial biomass. The water solubility of ectoine at 25°C is 6.5 mol/kg and it is collected in the cytoplasm of bacterial cells at a concentration up to 1 M [42]. Halophilic bacteria (e.g.
Biosynthesis of ectoine on an industrial scale is currently done mainly by the German company Bitop (Witten, Germany) which uses
In addition to the
Within the genus
In addition, as proved by Bursy
Ectoine producers known in the literature are also methanotrophic microorganisms. Current literature reports concern mainly halotolerant methanotrophs, i.e.:
Khmelenina and Reshetnikov together with their team focused on the genetic aspect by identifying the organisation of genes responsible for the synthesis of ectoine [52, 76, 77]. However, little attention was given to process optimization and refinement of the synthesis and extraction conditions of this compound. Recently, this topic has gained increasing interest on the part of Spanish scientists. Papers published in 2017 include the technological aspects of ectoine production by
Methanotrophic bacteria in addition to the possibility of providing an amino acid like ectoine, being valuable to the medicine, the pharmaceutical and cosmetics industry, show many environmental benefits. In this case the process of producing ectoine can be combined with the simultaneous production of other compounds, among others, biopolymers, phospholipids, sucrose, metal chelating proteins and many other ones. The use of methanotrophs on an industrial scale is also supported by the fact of simultaneous utilization of waste compounds, such as methane, which is a source of coal and energy for them [25, 87].
Halophiles are microorganisms with a high biotechnological potential associated with the production of enzymes, β-carotene or osmolytes. In order to maintain the osmotic balance between the cytoplasm and the substrate in high salinity conditions, these microorganisms developed two basic strategies. The first mechanism concerns the maintenance of high concentration of potassium ions inside the cell. The second strategy involves the biosynthesis of organic osmotic solutes such as sugars (e.g. trehalose), amino acids (e.g. glycine, betaine, glutamic acid, L-proline, ectoine, hydroxyectoine) and polyols (e.g., glycerol). The protective effect of compatible compounds described on the example of microorganisms capable of synthesizing them may also be used in relation to other organisms: human, animals or plants. In recent years, a rapid increase in the demand for ectoine has been observed, mainly due to its properties related to the health protection, and especially that of skin and mucous membranes. Pharmaceutical companies are increasingly willing to test and introduce products in which ectoine is the active substance.