To our knowledge, this study is the first meta-analysis to examine the association of psoriasis with hepatitis C. The high risk of bias in the study is mainly related to the failure to consider many confounding factors that affect the results of the trial, but these confounding factors will not affect the positive correlation between the two diseases. We found that patients with psoriasis were prone to have comorbid hepatitis C. The evidence from case control/ cross-sectional studies indicates that patients with psoriasis had 1.72-fold increased odds of developing hepatitis C when compared with controls. However, the exact pathway leading to concurrence of both psoriasis and hepatitis C remains unclear, in the present study, we use an integrative system bioinformatics approach to clarify the relationship between psoriasis and hepatitis C, and elucidate a more exact mechanism that links these two conditions.
The results showed that 398 overlapping gene targets were obtained through PPI analysis, such as IL6, TNF, IL10 and other immune-related inflammatory factors. Many previous studies have shown that psoriasis is an immune-related disease based on T lymphocytes, which is mainly manifested in the imbalance of the balance between different cytokines and the imbalance of complex interactions in tissue disease [33]. It is well known that the inflammatory state associated with hepatitis C virus infection not only affects the liver, but also affects the entire complicated body system [34].
There are many typical pathways and molecular expressions upregulated in the skin of psoriatic lesions, including TNF/IL23/IL17A pathway, TNF, IL1A, IL1B, IL6, IL12B, IL17C, IL23A, IL36A, IL36B, IL36G, CXCL1, CXCL2, CXCL8, CXCL9, CXCL10, Cathelicidin (CAMP) and Interferon-β (IFNB) [35–45]. The occurrence, development and chronic recurrence of psoriasis are mainly due to the fact that these cells/chemokines and antimicrobial peptides promote the proliferation of keratinocytes and recruit pathogenic T cells and neutrophils [35–45].
Cytokines play a key role in the immune response to mediate disease progression and viral infection [46]. Infection with hepatitis C virus can lead to a systemic increase in the production of a variety of inflammatory cytokines, especially interleukin-6 (IL6) and tumor necrosis factor-a (TNF-α). Tumor necrosis factor is a key member of the tumor necrosis factor receptor superfamily (TNFSF), which is produced by the activation of macrophages caused by tissue damage [47–48].
As a new type of therapy for psoriasis, biological therapy is more effective than traditional drugs, and it is safer and can significantly improve the quality of life of patients with psoriasis [49]. But the use of TNF-α inhibitors and other biological agents in patients with hepatitis C virus infection may activate viral replication and aggravate the condition of hepatitis C patients. However, some cases report and small retrospective cohort studies have found TNF-α inhibitors, especially etanercept. Generally speaking, there is no or very little risk of HCV activation. However, some guidelines suggest that dermatologists should cooperate with hepatologists to comprehensively manage patients with psoriasis associated with hepatitis C virus infection, and when using TNF-α inhibitors, it is necessary to use HCV-DNA and alanine aminotransferase (ALT) detection methods to monitor the hepatitis C status [49–51].
Toll-like receptors (TLR) are a group of evolutionary conserved pattern recognition receptors, which are found on innate immune cells in a variety of organisms [52]. TLR is the initiator of inflammation and can promote host defense, trigger signal transduction pathways, activate transcription, and synthesize pro-inflammatory cytokines and other proteins. There are 11 types of TLRs that have been discovered so far [53–55]. These cytokines recruit neutrophils and macrophages to the injury site, which activates the inflammatory cascade in turn [56–57]. Hepatitis C virus can evade innate immune response by blocking the Toll-like receptor 3 (TLR3)-mediated interferon signaling via NS4B-induced TRIF degradation [58]. Toll-like receptor 4 (TLR4) can induce innate immune response in chronic inflammation in patients chronically infected with HCV [59]. Sobia et al. provided the foundation and proposed the use of TLR4 inhibitors in patients, who were previously resistant to INF-α ribavirin combinational therapy and treatment-naive patients, along with direct acting antivirals (DAAs), to reduce liver tissue damage [59].
The expression of Toll-like receptor 2(TLR2) and TLR4 in the outer keratinocytes and peripheral blood mononuclear cells of patients with psoriasis is increased [60–61]. There is also an association between chronic plaque psoriasis and psoriatic arthritis with polymorphisms in TLR4 [62]. A recent study found that epidermal infiltration of neutrophils drives the inflammatory response in the skin by activating epidermal TLR4-IL36R crosstalk in a psoriasis-like mouse model induced by imiquimod [63].
Glycyrrhizic acid (GA), a triterpene isolated from the roots and rhizomes of licorice, named GA, is the principal bioactive ingredient of anti-viral, anti-inflammatory and hepatoprotective effects, and can also strongly attenuate the inflammatory response induced by TLR3 and TLR4 ligands [64]. Compound glycyrrhizin can be used to treat psoriasis [65]. Ashfaq et al. [66] illuminated that GA can inhibits HCV core gene expression or function and has a cooperative effect with INF. GA can reduce the level of transaminase in patients with hepatitis C, and the cancer rate of chronic hepatitis C patients with long-term formulation treatment is significantly reduced [67].
Since there is no cohort study, it is difficult to explore the causal relationship between hepatitis C and psoriasis. Therefore, the quality of evidence may be limited. In addition, as mentioned earlier, although hepatitis C and psoriasis may have a similar pathogenesis, it is difficult to determine whether there is a direct relationship between the two. In addition, we did not include subtypes of psoriasis because our goal is to reduce the heterogeneity of the data. In addition, these studies did not provide information to describe the risks of different ages, genders, or disease severity.
Our research suggests a relationship between hepatitis C and psoriasis. In order to further study this finding and establish stronger results, more large-scale prospective studies are needed to provide more detailed information about the link between hepatitis C and psoriasis. The prevalence of hepatitis C is increased in patients with psoriasis, and clinicians should be aware of this possibility. Targeted TLRs therapy may be helpful for the clinical treatment of psoriasis complicated by hepatitis C.