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Uridine supplementation enhances hepatic mitochondrial function in thymidine-analogue treated HIV-infected patients
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AIDS: Volume 20(11) 13 July 2006 p 1554-1556
Banasch, Matthiasa; Goetze, Oliverb; Knyhala, Kathya; Potthoff, Anjac; Schlottmann, Renatea; Kwiatek, Monika Ab; Bulut, Kerema; Schmitz, Franka; Schmidt, Wolfgang Ea; Brockmeyer, Norbert Hc
aDepartment of Internal Medicine, St. Josef-Hospital, University of Bochum, Germany
bDivision of Gastroenterology and Hepatology, University of Zurich, Switzerland
cDepartment of Dermatology, University of Bochum, Germany.
Abstract
Supplementation with uridine offers the possibility of a new and promising approach to nucleoside analogue reverse transcriptase inhibitor-associated mitochondrial toxicity. We investigated the metabolic effects of short-course treatment with the uridine-enriched food supplement NucleomaxX on hepatic mitochondrial function in thymidine-analogue treated HIV-infected patients. Mitochondrial function was assessed by a recently introduced non-invasive 13C-methionine breath test. NucleomaxX supplementation enhanced mitochondrial decarboxylation function reversibly but reproducibly in all patients. Repeated administration in shorter treatment intervals may maintain this effect.
Hepatic mitochondrial damage by nucleoside reverse transcriptase inhibitors (NRTI) may play a role in the increasing incidence of liver-related disease particularly among HIV-infected patients [1]. Inhibition of DNA-polymerase-ƒÁ and cumulative mitochondrial DNA depletion could help explain the toxicity of NRTI to mitochondria. Decreased mitochondrial DNA content has been found in subcutaneous adipose tissue of HIV-positive lipoatrophic patients as well as in muscle and liver tissue of NRTI-treated individuals with evidence of mitochondrial dysfunction [2,3].
Recently, supplementation of the pyrimidine precursor uridine has been proposed to abrogate mitochondrial adverse effects of thymidine analogues and to reverse cellular mitochondrial DNA depletion in vitro [4,5]. Exogenous uridine supplementation might prevent uridine depletion at the cellular level, as the key enzyme of endogenous pyrimidine synthesis is also encoded by mitochondrial DNA and therefore might be affected by mitochondrial DNA depletion.
NucleomaxX, a food supplement based on sugarcane extract with a high content of nucleosides (17%), has been shown to effectively increase serum uridine levels in vivo [6]. In the present study we sought to investigate the potential metabolic effects of uridine (NucleomaxX) on hepatic mitochondrial function in thymidine analogue-treated HIV-infected patients with clinical evidence of lipoatrophy as a marker of chronic mitochondrial toxicity.
14 lipoatrophic HIV-infected men who were using thymidine analogues as part of their regimens (stavudine, n = 10, zidovudine, n = 4) with a mean treatment duration of 59 months (range, 21-113 months) and two HIV-negative controls participated in this prospective interventional study which was approved by the local ethical board of the Ruhr-University of Bochum. All patients had suppressed HIV-viral load (< 50 copies/ml) and CD4 cell count > 350 cells/ƒÊl at time of randomization. Patients with concurrent liver diseases such as viral hepatitis or excessive alcohol consumption (> 50 g ethanol/day) were excluded from this study.
Uridine supplementation was performed according to the manufacturer's recommendations with 36 g of NucleomaxX three times daily on 3 consecutive days taken orally. Five randomly selected patients received a second treatment directly after week 8 of the first cycle.
Hepatic mitochondrial decarboxylation function was assessed by a recently introduced 13C-methionine breath test (MeBT) pre-treatment and at week 2, 4 and 8 after treatment [7,8]. The detailed test procedure is described elsewhere [8]. Briefly, each patient received 2 mg/kg body weight [methyl-13C]-labelled methionine (Cambridge Isotope, Andover, Massachusetts, USA) dissolved in 100 ml water. Breath samples were obtained before substrate administration and at 10-min intervals for 90 min. The 13C/12C isotope ratio of the breath samples were analysed by non-dispersive isotope selective infrared spectroscopy. To measure the proportion of the substrate given by mouth that is metabolized, the results were expressed as percentage dose of 13C recovered (PDR) over time for each time interval from which the cumulative PDR (cPDR) for each time interval was calculated. Effects of drug treatment and cycles of treatment were compared using a mixed effect model ANOVA [9]. Data were considered to be significant at P < 0.05. Bonferroni correction was applied for three pair-wise comparisons of each treatment period. Data are presented as mean ± SEM.
NucleomaxX supplementation induced a significant increase of 13CO2-exhalation during week 2 and 4, illustrated by the 13CO2 exhalation curves at pre-treatment and at week 2, 4 and 8 after uridine administration (Fig. 1a). The cumulative 13CO2 excretion increased following treatment (cPDR1.5h, 3.1 ± 0.4% pre-treatment versus 5.1 ± 0.6% week 2 and 5.5 ± 0.6% week 4, P < 0.0001). There was no difference between week 2 and 4 (P = 0.6). The increase was followed by a decay to pre-treatment value at week 8 (cPDR1.5h, 3.6 ± 0.4%, P = 0.08). In five patients, after the second treatment cycle metabolic improvement was reproducible (Fig. 1b) with a similar 13CO2-recovery (cPDR1.5h: cycle 1, 2.3 ± 0.8% versus 4.2 ± 0.4% and 4.8 ± 0.4%; cycle 2, 2.7 ± 0.8% versus 4.6 ± 0.3% versus 5.1 ± 0.3 pre-treatment, week 2 and week 4 respectively, P < 0.0001; P = 0.3 for the difference between the cycles). 13CO2-exhalation was not induced by NucleomaxX in HIV negative controls (cPDR1.5h: 5.70 ± 0.31 pre-treatment versus 5.69 ± 0.27, 5.96 ± 0.45 and 5.04 ± 0.45 at week 2, 4 and week 8 respectively).
Supplementation with uridine offers the possibility of a new and promising approach to NRTI-associated mitochondrial toxicity In the present study we investigated the metabolic effects of NucleomaxX on hepatic mitochondrial function. We demonstrated for the first time that NucleomaxX supplement in standard dosage confers a significant and reproducible increase of hepatic metabolic mitochondrial function in thymidine analogue-treated patients. The observed 'wash-out' effect at week 8 might be prevented by administration of NucleomaxX in shorter treatment intervals-the distribution volume of uridine and the short half-life in vivo further supports this concept.
It is noteworthy that in previously published clinical trials, the administered dosage of NucleomaxX was five- to sixfold higher than recommended by the manufacturer [10,11]. The optimized dosage for preventing or treating mitochondrial toxicity is not yet clear and might be tissue specific. Note that the effectiveness of uridine in absence of thymidine analogues remains unclear and is not supported by in vitro data.
In summary, NucleomaxX appears to be a promising agent in the treatment of NRTI-related mitochondrial toxicity, but many questions need to be answered before recommending NucleomaxX as a safe and effective adjuvant therapy in clinical practice. Specific issues that need to be addressed include the mode and specificity of action, possible interference with NRTI-antiretroviral activity, the optimal schedule and dosage for clinical use. The data from our research may contribute to the design and initiation of further clinical trials, particularly with focus on hepatic mitochondrial function, and illustrates a potential application for 13C-methionine breath test diagnostic in clinical practice.
References
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