Surfactant; emulsifier; solubilizer; Solutol HS15 acts as a mucosal absorption enhancer via interaction with cell membranes, affecting membrane fluidity, F-actin cytoskeleton organization, and tight junction structure. [1]

Molecules in Class 2 and Class 4 lipophilicity of the Biopharmaceutical Classification System (BCS) can become more soluble with the usage of solubol HS-15. It has been demonstrated that Solutol HS-15 increases the permeability of mid-sized biologic medications via epithelial cells [1].

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This work initially confirms surfactant-like behaviour of Solutol® HS15 in aqueous media, while subsequent experiments demonstrate that the effect of Solutol® HS15 on epithelial tight junctions is different from a 'classical' tight junction opening agent and illustrate the effect of Solutol® HS15 on the cell membrane (endocytosis rate) and F-actin cytoskeleton. Conclusion: Solutol® HS15 is the principle component of CriticalSorb™ that has shown an enhancement in permeability of medium sized biological drugs across epithelia. This study suggests that its mechanism of action arises primarily from effects on the cell membrane and consequent impacts on the cell cytoskeleton in terms of actin organisation and tight junction opening[1].

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- Solutol HS15 formed micelles in aqueous media with a critical micelle concentration (CMC) of 0.06–0.1 mM in deionized water, PBS, and HBSS:HEPES (25 mM, pH 7.4). The hydrodynamic diameter of micelles was 11–15 nm (typically 12–14 nm) across tested concentrations (0.1–104.0 mM) and temperatures (4–37°C). [1]
- In MTS cell viability assays, Solutol HS15 showed concentration-dependent reduction in metabolic activity in Calu-3, Caco-2, and A549 cells. EC50 values (concentration causing 50% reduction) were: Calu-3: 10.2 ± 1.2 mM, Caco-2: 6.5 ± 0.7 mM, A549: 8.7 ± 1.2 mM. [1]
- In LDH release assays (membrane integrity), Solutol HS15 showed concentration-dependent cytotoxicity. EC50 values for LDH release were: Calu-3: 7.2 ± 0.8 mM, Caco-2: 5.4 ± 0.5 mM, A549: 6.8 ± 0.9 mM. [1]
- Solutol HS15 (0.52–5.2 mM, 3 h, 37°C) significantly increased the apical-to-basolateral permeability of FITC-insulin (5.8 kDa) across polarized Calu-3 monolayers in a concentration-dependent manner: 0.52 mM (Papp = 3.01 ± 0.6 × 10⁻⁶ cm/s, P = 0.01), 1.0 mM (4.09 ± 1.21 × 10⁻⁶ cm/s, P = 0.0021), 5.2 mM (6.08 ± 1.93 × 10⁻⁶ cm/s, P = 0.0001), compared to control (2.27 ± 0.44 × 10⁻⁶ cm/s). Enhancement was absent at 4°C. [1]
- Solutol HS15 (5.2 mM, 37°C) increased permeability of human growth hormone (hGH, 22 kDa) from 1.81 ± 0.51 to 4.30 ± 1.26 × 10⁻⁶ cm/s (2.3-fold, P < 0.001), but had no significant effect on albumin (66 kDa) or IgG (150 kDa). [1]
- Solutol HS15 (0.01–5.2 mM) caused a gradual, concentration-dependent decrease in TEER over 3 h, which did not reverse after 24 h recovery. This profile differed from chitosan (0.003% w/v), which caused a steep initial TEER decrease that was reversible. [1]
- ZO-1 immunostaining showed that Solutol HS15 (1.0 and 5.2 mM, 3 h) caused faint distortion of the "chicken wire" pattern, unlike the dramatic redistribution seen with chitosan. [1]
- F-actin staining showed that Solutol HS15 at permeability-enhancing concentrations (≥0.52 mM) rearranged F-actin distribution from the cell periphery toward the cytosol. [1]
- In K562 cell suspensions, Solutol HS15 (0.01–5.2 mM) increased the endocytosis rate of the membrane probe FM2-10 in a concentration- and time-dependent manner. At 5.2 mM, endocytosis rate increased significantly after 35–40 min of incubation. [1]

- No direct in vivo data for Solutol HS15 are reported in the provided text. However, the authors reference previous studies showing that CriticalSorb (containing Solutol HS15 as principal component) enhanced nasal absorption of human growth hormone in rats (bioavailability 49.9% relative to subcutaneous injection) and was well tolerated in a 6-month repeat-dose toxicity study in rats at 10% w/v. [1]

- Critical micelle concentration (CMC) determination using pyrene fluorescence: Pyrene (2 μM final) was added to Solutol HS15 solutions (0.001–10.0 mM) in various media. Excitation at 337 nm, emission measured at 373 and 383 nm. The ratio of emission peaks 1:3 was plotted against concentration; the CMC was identified by the inflection point where the ratio dropped below 1, indicating a hydrophobic environment. [1]
- Dynamic light scattering (DLS) for micelle size: Solutol HS15 solutions (0.01–104.0 mM) in filtered 25 mM HEPES buffer (pH 7.4) were measured at 4, 25, and 37°C using a Viscotek 802 system. Hydrodynamic diameters were calculated. [1]

Micelle size and CMC of Solutol® HS15 were determined in biologically relevant media. Polarised airway Calu-3 cell layers were used to measure the permeability of a panel of biological drugs, and to assess changes in TEER, tight junction and F-actin morphology. The rate of cell endocytosis was measured in vitro in the presence of Solutol® HS15 using a membrane probe, FM 2-10[1].

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- MTS cell viability assay: Cells (1 × 10⁴/well) in 96-well plates were incubated with Solutol HS15 (0.01–20 mM in HBSS:HEPES) for 3 h at 37°C. MTS reagent was added, incubated for 3 h, and absorbance measured at 492 nm. Relative metabolic activity was calculated relative to negative (HBSS:HEPES) and positive (3 mM Triton X-100) controls. [1]
- LDH release assay: Following Solutol HS15 treatment, LDH working solution was added, incubated for 3 h, and absorbance measured at 492 nm. Relative LDH release was calculated as a percentage of negative control. [1]
- Permeability studies (Papp): Polarized Calu-3 monolayers on Transwell inserts (0.4 μm pore size, 12 mm diameter) with TEER > 500 Ω·cm² were used. Apical compartment received FITC-insulin (60 μg/mL) or other model proteins with or without Solutol HS15 (0.01–5.2 mM). Basolateral samples (100 μL) were collected every 30 min for 3 h and replaced with fresh buffer. Fluorescence was measured (ex/em 485/518 nm). Papp was calculated. [1]
- TEER measurement: TEER was measured using an epithelial voltammeter (EVOM) before, during (every 30 min for 3 h), and after (24 h recovery) Solutol HS15 application. Results expressed as percentage of baseline. [1]
- ZO-1 immunostaining: Cells were fixed with 4% paraformaldehyde, permeabilized with Triton X-100 (3.1 mM), blocked with 1% BSA, incubated with mouse anti-human ZO-1 primary antibody (10 μg/mL), then with FITC-labeled goat anti-mouse secondary antibody. Images were acquired by confocal microscopy. [1]
- F-actin staining: Cells were fixed and permeabilized as above, then incubated with Alexa Fluor 546-phalloidin (0.17 μM) for 20 min. Images acquired by confocal microscopy. [1]
- FM2-10 endocytosis assay: K562 cells (2.5 × 10⁶/mL) were suspended in PBS. Solutol HS15 (0.01–5.2 mM) and FM2-10 (200 nM) were added sequentially. Fluorescence (ex 530 nm, em 590 nm) was measured every 24 s for 1 h. Endocytosis rate (%/min) was calculated from the slope of fluorescence vs. time. [1]

The authors reference previous in vivo studies: nasal administration of 10% w/v Solutol HS15 in rats (Sprague Dawley) and non-human primates for human growth hormone delivery, and a 6-month repeat-dose toxicity study in rats. [1]

- In vitro cytotoxicity: Solutol HS15 showed concentration-dependent toxicity in Calu-3, Caco-2, and A549 cells with EC50 values of 6.5–10.2 mM (MTS assay) and 5.4–7.2 mM (LDH release assay). Calu-3 cells showed higher tolerance (EC50 = 10.2 mM) compared to Caco-2 (6.5 mM) and A549 (8.7 mM). [1]
- In vivo toxicity: The authors reference a previous 6-month repeat-dose toxicity study in rats showing that nasal administration of 10% w/v Solutol HS15 (the principal component of CriticalSorb) caused no treatment-related effects at the highest dose level. [1]

[1]. Mechanism of mucosal permeability enhancement of CriticalSorb (Solutol HS15) investigated in vitro in cell cultures. Pharm Res. 2015 Feb;32(2):516-27.

Solutol HS 15 is a polymer.

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Objective: CriticalSorb™ is a novel mucosal drug delivery system whose main component is Solutol® HS15, which has been shown to enhance the bioavailability of certain biotherapeutic drugs. This study aimed to elucidate the mechanism by which Solutol® HS15 enhances the mucosal absorption of biotherapeutic drugs.
Methods: The micelle size and critical micelle concentration (CMC) of Solutol® HS15 were determined in biorelevant media. The permeability of a range of biotherapeutic drugs was measured using a polarized airway Calu-3 cell layer, and changes in transepithelial electrical resistance (TEER), tight junctions, and F-actin morphology were assessed. The rate of endocytosis in the presence of Solutol® HS15 was determined in vitro using the membrane probe FM 2-10. Results: This study preliminarily confirmed that Solutol® HS15 has surfactant-like behavior in aqueous media. Subsequent experiments showed that the effect of Solutol® HS15 on epithelial cell tight junctions is different from that of "classic" tight junction openers, and elucidated the effects of Solutol® HS15 on cell membrane (endocytosis rate) and F-actin cytoskeleton. Conclusion: Solutol® HS15 is the main component of CriticalSorb™, which has been shown to enhance the permeability of medium-sized biological drugs across epithelial cells. This study shows that its mechanism of action mainly stems from its effect on the cell membrane, which in turn affects the cytoskeleton, specifically the organization of actin and the opening of tight junctions. [1]

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- Solutol HS15 (Macrogol 15 hydroxystearate) is a non-ionic surfactant composed of a mixture of polyglycol mono- and di-esters of 12-hydroxystearic acid. It is the principal component of CriticalSorb®, a novel mucosal drug delivery system. [1]
- The absorption-enhancing mechanism of Solutol HS15 is primarily transcellular, involving partitioning of surfactant monomers into the cell membrane at physiological temperature, increasing membrane fluidity, disrupting F-actin organization, and secondarily affecting tight junctions. Unlike classical tight junction openers (e.g., chitosan), Solutol HS15 does not cause rapid, reversible TEER decrease or dramatic ZO-1 redistribution. [1]
- The permeability-enhancing effect is temperature-dependent (absent at 4°C), size-selective (effective for molecules <60 kDa), and requires concentrations above the CMC. [1]
- Solutol HS15 increases fluid-phase endocytosis rate in a concentration- and time-dependent manner, with a lag period of 35–40 min, suggesting that membrane saturation is required before significant permeability enhancement occurs. [1]

C20H43NO4

361.559726953506

344.292

C, 69.72; H, 11.70; O, 18.57

61909-81-7

70142-34-6

124898

Colorless to off-white ointment

1.0±0.1 g/cm3

473.4±15.0 °C at 760 mmHg

153.2±13.9 °C

0.0±2.7 mmHg at 25°C

1.469

5.66

2

4

19

24

268

0

OC(CCCCCC)CCCCCCCCCCC(=O)OCCO.N

JVKUCNQGESRUCL-UHFFFAOYSA-N

InChI=1S/C20H40O4/c1-2-3-4-11-14-19(22)15-12-9-7-5-6-8-10-13-16-20(23)24-18-17-21/h19,21-22H,2-18H2,1H3

2-hydroxyethyl 12-hydroxyoctadecanoate

Solutol HS 15; Solutol HS-15; Solutol HS15; 2-hydroxyethyl 12-hydroxyoctadecanoate; 61909-81-7; 6284-41-9; 105109-85-1; SCHEMBL505106; CHEBI:9194; DTXSID90909336;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Ethanol : ~100 mg/mL
H2O : ~25 mg/mL

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)