Peyronie’s disease (PD) is a debilitating condition characterized by the formation of collagen-rich and fibrous plaques within the penile tunica albuginea. This condition affects approximately 8% of adult men and is often associated with penile curvature, painful erections, and/or erectile dysfunction.^1,2 The potential inability to engage in penetrative intercourse can increase the risk of depression, lower self-esteem, and significantly impact both patient and partner quality of life.³ Research has highlighted the important role of collagen in the pathogenesis of PD.^2-4 The availability of intralesional injections of collagenase from Clostridium histolyticum, the conventional treatment option for PD, has been withdrawn from markets in Canada and Europe due to its significant cost, and demand for the product is unsustainably low.⁵

Actinidin is a natural enzyme derived from the kiwifruit (Actinidia deliciosa) that has been shown to possess proteolytic activities to hydrolyze various types of collagen and fibrinogen.^6-8 The collagenolytic properties of actinidin suggest a potential in modulating collagen remodeling in pathological conditions of PD. However, despite its potential as a collagenase substitute, there have been no studies evaluating the application of actinidin on in vitro cellular models of PD. Our aim was to determine the effectiveness of the actinidin enzyme in reducing cell-bound collagen in a 2D model of PD.

We cultured human PD (HPD) tissues obtained during penile prosthesis implantation and isolated for primary fibroblast cells to create a stable 2D model. We divided the models into 1 of 4 treatment groups: media, saline, and low- and high-concentration actinidin treatment (0.5 to 37.5 mg/mL). The actinidin treatments were prepared by dissolving freeze-dried kiwi powder in saline and then filtered; the low concentration was further diluted with saline. The PD cells had a significantly higher amount of cellular collagen compared to the human control group cells (P = .0074; Figure 1, A), confirming our clinical theory that HPD cells have more collagen, validating our cellular model. In addition, the cell treated with high levels of actinidin (1 mg/mL) had a significantly lower level of cellular collagen when compared to the control groups (P = .0003; Figure 1, B). This shows that actinidin has possible proteolytic properties and potential to reduce collagen.

Figure 1. A, Average amount of collagen (±SE) for human Peyronie’s disease (HPD) cells and human control cells (HC). **P = .0074. B, Average amount of collagen (±SE) for HPD cells treated cells after actinidin treatment. ***P = .0003.

An MTT assay kit was used to assess the viability of PD cells treated with various levels of actinidin. Results revealed that at high concentrations of actinidin, the cell viability is significantly reduced (P < .0001; Figure 2, A), revealing that actinidin has the potential to degrade PD cells at high concentrations.

Figure 2. a, Percent viability for human Peyronie’s disease cells treated with 10, 25, or 50 mg/mL purified actinidin. ****P < .0001. b, Time-lapse of normalized actin levels of human Peyronie’s disease cells treated with saline, high actinidin (37.5 mg/mL), or low actinidin (10 mg/mL). ****P < .0001.

We conducted a time-lapse of PD cells treated with various concentrations of actinidin stained for the nucleus and actin filaments (using DAPI and impermeable phalloidin-conjugated FITC, respectively). The high-concentration actinidin treatment group had a significantly higher normalized actin signal than other treatment groups (P < .0001; Figure 2, B). An increased level of normalized actin in the high-concentration kiwifruit extract group acts as an indicator of permeated plasma membrane as the fluorescent dye was able to enter the cell and stain the nucleus. Our results and emerging research both suggest that actinin has mechanisms to disrupt not only the extracellular matrix, but also the plasma membrane.⁹

This preliminary study suggests that the natural collagenase actinidin can break down PD cells by reducing the extracellular collagen content and compromising the cellular membrane. Further studies are underway to investigate treatment of actinidin in 3D cellular PD models and animal models, as well as to determine the optimal actinidin concentration of purified actinidin that can further reduce the collagen composition in HPD cell models. Actinidin has the potential to be a novel treatment option for patients suffering from PD. In the absence of durable Food and Drug Administration–approved treatments for PD in Canada and worldwide, this novel option could offer future treatment potential.