Synthetic Mucin Gels with Self-Healing Properties Augment Lubricity and Inhibit HIV-1 and HSV-2 Transmission

Abstract

Mucus is a self-healing gel that lubricates the moist epithelium and provides protection against viruses by binding to viruses smaller than the gel's mesh size and removing them from the mucosal surface by active mucus turnover. As the primary nonaqueous components of mucus (≈0.2%-5%, wt/v), mucins are critical to this function because the dense arrangement of mucin glycans allows multivalence of binding. Following nature's example, bovine submaxillary mucins (BSMs) are assembled into "mucus-like" gels (5%, wt/v) by dynamic covalent crosslinking reactions. The gels exhibit transient liquefaction under high shear strain and immediate self-healing behavior. This study shows that these material properties are essential to provide lubricity. The gels efficiently reduce human immunodeficiency virus type 1 (HIV-1) and genital herpes virus type 2 (HSV-2) infectivity for various types of cells. In contrast, simple mucin solutions, which lack the structural makeup, inhibit HIV-1 significantly less and do not inhibit HSV-2. Mechanistically, the prophylaxis of HIV-1 infection by BSM gels is found to be that the gels trap HIV-1 by binding to the envelope glycoprotein gp120 and suppress cytokine production during viral exposure. Therefore, the authors believe the gels are promising for further development as personal lubricants that can limit viral transmission.

Keywords: HIV-1; HSV-2; immune suppression; lubricant; mucin hydrogels; self-healing; strain-weakening.

Figure 1

Schematic illustration of the dynamic covalent hydrazone bonds forming BSM gels.

Figure 2

Rheological, strain‐weakening, and self‐healing properties of BSM gels. A) Time‐dependent sweep analyses (linear material response) and strained‐controlled time‐dependent sweep analyses with an increase in oscillatory shear strain from 0.1% to 1000% and a constant oscillation frequency of 1 Hz (nonlinear material response) were performed for three cycles. Each test of the time‐dependent sweep was repeated 5 s after the BSM gels were ruptured by high oscillatory shear strain. B) Frequency‐dependent sweep analyses (linear material response) were performed. C,D) The injectability and self‐healing properties of BSM gels were tested. E–G) The hydrolytic and enzymatic stability of the BSM gels by swelling/disintegration studies. Error bars indicate the standard deviation obtained from n = 3 independent measurements.

Figure 3

Tribological properties of BSM gels were studied using a commercial shear rheometer equipped with a tribology unit (T‐PTD 200, Anton Paar) with a steel ball‐on‐PDMS cylinder, as reported previously.^{[ 57 ]} The better lubricity was indicated by the lower friction coefficient of BSM gels (5% wt/v) compared to BSM solutions (5% wt/v). All tribological experiments were conducted at 21 °C and using a solvent trap. A paper towel soaked with water was used in a closed chamber to prevent evaporation of the sample during the experiments. Error bars indicate the standard deviation determined from n = 3 independent measurements.

Figure 4

Prophylactic efficacy against HIV‐1 and HSV‐2 infections of BSM gels (5% wt/v), BSM solutions (5% wt/v) and HEC gels (2% wt/v) compared to the control (no protection). The gels or solutions were added to the cells before they were exposed to the viruses and removed after 1 h of virus exposure. BSM gels were the most effective prophylaxis, inhibiting infection of TZM.bl and PHA‐activated hPBMC cells by HIV‐1 (R5‐HIV‐1NL (AD8) isolate) as well as VERO cells by HSV‐2. BSM solutions inhibited only HIV‐1 but not HSV‐2 infection. HIV‐1 infection of hPBMCs was measured indirectly by transferring the supernatant containing newly produced HIV‐1 from hPBMCs after 48 h to TZM.b1 cells. HIV‐1 infection of TZM.b1 cells was measured by luciferase assay. HSV‐2 infection of VERO cells (0.1 MOI, multiplicity of infection) was determined by quantifying the number of viral plaques at 48 h post‐infection. The error bars denote the standard deviation as obtained from n = 3 independent experiments. Differences were determined using ordinary one‐way ANOVA tests.

Figure 5

BSM binds to HIV‐1 gp120. Association and dissociation curves showing real‐time binding of BSM to gp120 were obtained using biolayer interferometry (BLI). Concentration‐dependent (0, 1, 2, 3 mg mL⁻¹) responsive shifts were observed. The black dotted line indicates the separation of the association and dissociation phases. The results are an average of three independent measurements.

Figure 6

Cytokine secretion from hPBMCs after HIV‐1 exposure with and without protection by BSM gels. Cells were protected with or without BSM gels and then exposed to HIV‐1 viruses for 1 h. Cytokine secretion after 24 h of incubation was quantified using U‐PLEX Inflammatory Panel 1 Human Kits. Data show the mean from n = 9 samples from three independent experiments. Differences were determined using ordinary one‐way ANOVA tests.