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In cells from patients with the autoinflammatory disorder mevalonate kinase (MK) deficiency, which includes the hyperimmunoglobulin D with periodic fever syndrome, MK becomes the rate‐limiting enzyme in the isoprenoid biosynthesis pathway. This suggests that up‐regulation of residual MK activity in these patients could be a way in which to prevent or alleviate the associated symptoms. We studied the effect of 2 specific inhibitors of isoprenoid biosynthetic enzymes on the residual activity of MK in cells from patients with MK deficiency.Skin fibroblasts from MK‐deficient patients and from controls were cultured for 7 days with either simvastatin, an inhibitor of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase, or zaragozic acid A, an inhibitor of squalene synthase. Following culture, MK activity, MK protein levels, MVK messenger RNA levels, and the effect on the pathway flux toward nonsterol isoprenoid biosynthesis were determined.Treatment of the fibroblasts with either of the inhibitors led to a marked increase in residual MK enzyme activity, which was largely attributable to increased MVK gene transcription. This effect was even more pronounced when the cells were cultured in lipoprotein‐depleted medium. The flux toward nonsterol isoprenoid end‐product synthesis was reduced when cells were treated with simvastatin but was partly restored by concomitant treatment with zaragozic acid A.Our results indicate that manipulations of the isoprenoid biosynthesis pathway that promote the synthesis of nonsterol isoprenoids may provide an interesting therapeutic option for the treatment of MK deficiency. [ABSTRACT FROM AUTHOR]

Ganciclovir exhibits broad-spectrum activity against DNA viruses such as cytomegaloviruses, herpes simplex viruses, varicella-zoster virus, Epstein-Barr virus and human herpes virus-6. Ganciclovir is widely applied for anti-herpetic treatment, cytomegalovirus prophylaxis after organ transplantation, and, more recently, in experimental gene therapy to eradicate cycling cells that express the herpes simplex virus thymidine kinase gene. Although ganciclovir supposedly acts as a chain terminator, there is compelling evidence demonstrating the presence of ganciclovir, but not of acyclovir, incorporated internally into DNA, leaving the precise mechanism by which ganciclovir inhibits DNA synthesis enigmatic. To study the potential involvement of mitochondria in the ganciclovir nucleotide cytotoxicity, we used adenovirus-mediated gene transfer to express herpes simplex virus thymidine kinase in rat liver and administered ganciclovir 2 days post-infection. The integrity and function of mitochondria in the rat liver cells were evaluated by several techniques. In addition, we analyzed the nucleotide pools in cellular extracts and in isolated mitochondria. We show that ganciclovir nucleotides are abundantly present in the mitochondria of rat livers that express the HSVtk gene. Already 48 h after administration, 10–30% of the total mitochondrial nucleotide pool consists of ganciclovir nucleotides. Their presence is correlated with a lower amount of mitochondrial DNA, a reduced mitochondrial-membrane potential, morphological abnormalities, and liver dysfunction. These data provide evidence for the involvement of mitochondria in the hepatotoxicity of the HStk/ganciclovir combination. This may explain the toxicity of the HSVtk/gancilovir combination in some metabolically active but non-proliferating cells, such as liver cells. This toxicity limits the applicability of this enzyme/prodrug combination. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]