Background/Purpose: Acyclic nucleoside phosphonates are a key class of antivirals commonly used in the treatment of both DNA and retroviral infections.  Adefovir and tenofovir are AMP analogues that resemble substrates of CD73.  We have previously reported that adenosine, generated by the CD73-mediated dephosphorylation of AMP, acting at A_2Areceptors, plays a critical role in development of both hepatic and dermal fibrosis in murine models of cirrhosis and scleroderma, respectively. A recent clinical trial demonstrated that tenofovir, but not other antiviral agents, reverses hepatic fibrosis/cirrhosis in patients with hepatitis B.  We therefore proposed the hypothesis that tenofovir’s antifibrotic effects are mediated by inhibition of adenosine production by CD73-mediated dephosphorylation of AMP.Methods:  In silico modeling and docking studies were performed using an ICM-Browser www.molsoft.com. CD73 enzyme activity was quantitated by malachite green. Alkaline Phosphatase activity (Abcam) was performed. Thioacetamide(TAA,100 mg/kg IP)-treated mice were treated with vehicle, Adefovir, or Tenofovir (75mg/kg, SubQ) [n=5-10 per group].  Bleomycin (0.25 U, SubQ)-treated mice were treated with vehicle, Adefovir, or Tenofovir (75mg/kg, IP) [n=5-10 per group].  Adenosine levels were determined by HPLC. Skin breaking strength was via tensiometer. H&E or picrosirus red-stained slides were imaged, and pixel quantification was performed with SigmaScan software.   Scar index was determined as the ratio of red/green pixels representing compact/filamentous fibers; higher numbers indicate more fibrosis. Results: In silico modeling data suggested that both adefovir and tenofovir bound to the enzymatic pocket of CD73.  Tenofovir (Sequoia), but not adefovir (Sequoia), inhibited CD73 activity of 293T cells overexpressing CD73 (38+7.4%, at 10 uM) and of recombinant enzyme (72+1.0%, at 10uM). Yet, the inhibition of CD73 by Tenofovir (Gilead) was not pharmacologically relevant with an IC50>100uM.  Alkaline phosphatase activity wasn’t modulated by Adefovir or Tenofovir. Adefovir decreased adenosine levels in the skin of bleomycin-challenged mice though this trend was not significant.  Tenofovir significantly decreased adenosine levels in the skin of bleomycin-challenged mice (273.95+8.41 vs. 432.58+24.34nM adenosine/12mm punch biopsy, n=8-10, [p<0.05]). Tenofovir (75mg/kg), but not Adefovir (75mg/kg), diminished hepatic fibrosis in thioacetamide-treated mice (fibrotic area/hepatic slide area 1.00+0.04% vs 4.45+0.37%) Tenofovir (75mg/kg), but not Adefovir (75mg/kg), diminished bleomycin-induced dermal fibrosis in bleomycin-treated mice (73.7+3.1% reduction of hydroxyproline content [p<0.05]; 33.5+3.8% reduction of dermal thickness [p<0.06] and reduction of breaking tension by 66.8+1.4% [p<0.05]). Picrosirius red staining showed dramatic altering of dermal collagen quality (scar index of 1.2+0.1 vs 22.2+0.7 [p<0.001], normal skin is 2.5) in Tenofovir-treated mice. Conclusion: Tenofovir reduces fibrosis via inhibition of adenosine production.  Tenofovir may have therapeutic potential in treating fibrosis in patients suffering from non-viral fibrosing diseases such as scleroderma.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/tenofovir-but-not-adefovir-prevents-liver-and-skin-fibrosis-in-two-models-of-adenosine-mediated-injury/