Ribavirin inhibits angiogenesis by tetrahydrobiopterin depletion

Abstract

Ribavirin is a broad-spectrum antiviral drug that is used to treat hepatitis C virus (HCV)-infected patients. The virological response after ribavirin treatment appears to be insufficient to fully explain ribavirin-induced beneficial effects. Angiogenesis plays a pathogenic role in HCV-induced liver damage. Here, we investigated the influence of therapeutic ribavirin concentrations on angiogenesis. Ribavirin inhibited endothelial cell tube formation in vitro and vessel formation in the chick chorioallantoic membrane assay in vivo. Ribavirin inhibits inosine monophosphate dehydrogenase, which causes depletion of cellular GTP and in turn reduction of cellular tetrahydrobiopterin levels. The availability of tetrahydrobiopterin limits NO production by endothelial NO synthase. Ribavirin reduced levels of tetrahydrobiopterin (as revealed by HPLC), NO (as revealed by electron spin resonance spectroscopy), and cGMP (as revealed by RIA) in endothelial cells. Addition of tetrahydrobiopterin or NO prevented ribavirin-induced tube formation inhibition. In conclusion, angiogenesis inhibition by ribavirin has not been described before. This inhibition may contribute to ribavirin-induced pharmacological effects including adverse events.

A novel immunomodulatory mechanism of ribavirin in suppressing natural killer cell function

“…In an attempt to identify the possible mechanism by which ribavirin inhibits cytotoxicity of IL-15-activated NK cells, we investigated a mode of action that has been ascribed to ribavirin -the inhibition of tetrahydrobiopterin syntheis and hence NO synthesis inhibition [25,28]. NO is a highly reactive free radical synthesized in vessel endothelium, immune cells, brain, and other tissues.…”

“…We previously demonstrated that ribavirin neither induced a block in the cell cycle progression nor exerted cytotoxic effects in primary HUVEC at concentrations up to 20 µg/ml and 100 µg/ml respectively [25]. We therefore studied effects of ribavirin at concentrations ranging from 5 µg/ml to 80 µg/ml on viability of IL-15-activated NK cells.…”

“…Previous studies indicated that ribavirin acts by inhibition of tetrahydrobiopterin, a cofactor of NO synthase enzymes, thereby leading to suppression of NO synthesis [25,28]. We therefore investigated whether ribavirin suppressed IL-15-activated NK cell cytotoxicity by tetrahydrobiopterin inhibition.…”

Roles of Tetrahydrobiopterin in Promoting Tumor Angiogenesis

“…18 Conversely, indirectly decreasing BH4 levels by depleting intracellular GTP, a substrate for de novo BH4 synthesis, reduces NO production and inhibits both endothelial cell proliferation and tubule formation in vitro. 19 However, a rigorous study of the molecular mechanisms by which BH4 promotes angiogenesis in in vitro and in vivo models remains unavailable. The present study clearly showed that BH4 enhances NO production in endothelial cells through the effects on wild-type Ras activation and the downstream PI3K/Akt signaling response.…”

“…[17][18][19] BH4 is synthesized via either the de novo pathway-GTP cyclohydrolase I (GCH; EC 3.5.4.16) is the rate-limiting enzyme, converting GTP to dihydroneopterin triphosphate before final generation of BH4 by sepiapterin (Sep) reductase; or the pterin salvage pathway-sepipaterin is a substrate. 20 Essentially BH4 synthesis has been directly associated with activation of Akt and eNOS phosphorylation for NO production.…”