Our results demonstrated that cultured LE cells produce IL-6 at increasing levels, even without any external stimulus, reaching high values after 12 hours. IL-8 was also produced by LE cells, but at lower levels than with IL-6. When exposed to triamcinolone, these cells showed a significant reduction in IL-6 and IL-8 production, compared to unexposed controls and PRP. We also observed that the PRP significantly increased the levels of IL-8 at 96 hours time point, compared to controls.
The present study aimed to compare the traditional treatment, based on corticosteroids, with PRP. Intralesional steroid injection has the advantage of a low cost, is easily acquirable and has practically no side effects [19, 20], except the inherent risks related to the injection, which are the same as those for PRP.
PRP is a relatively recent treatment, with high cure rates [13, 21]. However, the response to PRP occurs only after the sixth month of application, the cost is higher than triamcinolone due to processing [13, 22] and it requires a -80oC freezer for storage, if not immediately used .
The current study found high IL-6 levels produced by the LE cells, possibly related to the development and progression of this condition, as it is a cytokine involved in tendinopathy in humans [23–25]. IL-6 can influence several cell types, with multiple biological actions through its unique receptor system. It usually acts as a pro-inflammatory cytokine, involved in the positive regulation of inflammatory reactions and in the pain process, but IL-6 can also act as an anti-inflammatory cytokine depending on the circumstance, through the activation of its soluble receptors. IL-6 is produced by T-cells, B-cells, monocytes, fibroblasts, keratinocytes, endothelial, mesangial cells, adipocytes, some tumour cells and also by tenocytes .
LE cells also secreted IL-8, a potent chemokine, also with proven inflammatory involvement in tendinopathies. IL-8 plays a key role in neutrophil-mediated inflammation, which leads to cartilage destruction and bone damage .
PRP led to an increase in IL-8 levels compared to controls at 96 hours time point, suggesting a pro-inflammatory effect. Thus, triamcinolone can be considered more effective than PRP in reducing inflammation in the first 96 hours of treatment. The use of triamcinolone was effective at the three studied concentrations, also leading to a reduction in IL-8 levels, when compared to controls and PRP.
IL-10 showed a significant time-dependent punctual increase by 48 hours with 100 µM triamcinolone; concomitantly, there was also an increase in IL1-β at this time point, which could explain the elevation of IL-10, since it is an anti-inflammatory cytokine that regulates the intensity of inflammation . It may have been produced in order to control the rising levels of IL1-β. After this time point (48 hours), IL-1-β levels gradually decreased. Although this increase in IL1-β was not statistically significant, it was probably able to stimulate the IL-10 production by LE cells.
Despite the superior results of corticosteroids on PRP in reducing the inflammatory cytokines of LE, they are not exempt from undesirable effects. It has been shown that triamcinolone 0.1 mg/mL leads to a decrease in the viability of rotator cuff cells when exposed for 7, 14 and 21 days, due to apoptosis . Therefore, treatment with corticosteroids requires caution, and it is not recommended to use it with repetitions in short time intervals.
The PRP used in the present study was processed according to the protocol for the obtaining leukocyte-poor PRP [16, 17], since leukocytes, despite having important functions in tissue repair and providing protection against infectious agents, also have pro-inflammatory actions and immunological effects that can result in undesirable and opposing effects in healing, leading to increased inflammation due to pro-inflammatory cytokines [16, 29]. However, even this PRP preparation caused intense and significant production of IL-8 when compared to controls.
It is known that PRP has in its composition IL-6, IL-8, IL1-β and TNF-α [30, 31]. The development of a PRP free of pro-inflammatory factors, especially VEGF, could have provided better results . Clinical studies comparing the use of PRP with triamcinolone confirm our results, with an initial advantage for the corticosteroid group and gradual improvement for the PRP group, with significant improvement in the PRP group only after six months . However, according to the natural history of LE, it can evolutes with spontaneous improvement in six months. Another difficult that we found was the lack of standardization for the PRP production, which makes it difficult to compare with studies in the literature, as PRPs are very heterogeneous and qualitatively very different, with no strong evidence regarding the ideal preparation, dosage and efficacy [31, 33, 34].
The late effect of PRP in the treatment of LE, which can be up to six months, also limits the assessment of the PRP effectiveness, both in in vitro and in vivo studies. In in vitro studies, the maintenance of the cells in culture after exposure to PRP for up to six months is not feasible, since the cells will lose their phenotypic characteristics and the senescence of the cultures will invariably result in the loss of proliferation capacity, followed by apoptosis. In vivo studies also have limitations, due to the possibility of spontaneous remission of LE in most cases, not allowing for an assessment of whether the cases that were resolved resulted from the late effect of PRP or if resolution resulted from the natural course of the disease.