Nathalie Neveux

Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study.

Previous experimental studies have highlighted that citrulline (CIT) could be a promising pharmaconutrient. However, its pharmacokinetic characteristics and tolerance to loading have not been studied to date. The objective was to characterise the plasma kinetics of CIT in a multiple-dosing study design and to assess the effect of CIT intake on the concentrations of other plasma amino acids (AA). The effects of CIT loading on anabolic hormones were also determined. Eight fasting healthy males underwent four separate oral loading tests (2, 5, 10 or 15 g CIT) in random order. Blood was drawn ten times over an 8 h period for measurement of plasma AA, insulin and growth hormone (Gh). Urine samples were collected before CIT administration and over the next 24 h. None of the subjects experienced side effects whatever the CIT dose. Concerning AA, only CIT, ornithine (ORN) and arginine (ARG) plasma concentrations were affected (maximum concentration 146 (sem 8) to 303 (sem 11) micromol/l (ARG) and 81 (sem 4) to 179 (sem 10) micromol/l (ORN); time to reach maximum concentration 1.17 (sem 0.26) to 2.29 (sem 0.20) h (ARG) and 1.38 (sem 0.25) to 1.79 (sem 0.11) h (ORN) according to CIT dose). Even at high doses, urinary excretion of CIT remained low ( < 5 %). Plasma insulin and Gh were not affected by CIT administration. Short-term CIT administration is safe and well-tolerated. CIT is a potent precursor of ARG. However, at the highest doses, CIT accumulated in plasma while plasma ARG levels increased less than expected. This may be due to saturation of the renal conversion of CIT into ARG.

Plasma citrulline is a biomarker of enterocyte mass and an indicator of parenteral nutrition in HIV-infected patients

BACKGROUND Plasma citrulline is a biomarker of enterocyte mass and function in humans. OBJECTIVE We evaluated citrulline in the reemerging context of diarrhea in HIV-infected patients receiving highly active antiretroviral therapy. DESIGN This study prospectively measured citrulline in 6 groups of HIV-1 patients (n = 115): 1) undetectable viral load without chronic diarrhea (a; n = 40) and with protease inhibitor-associated toxic chronic diarrhea (b; n = 26), 2) detectable viral load and CD4 > 200/mm(3) without (a; n = 6) and with (b; n = 11) chronic diarrhea, and 3) detectable viral load and CD4 <200/mm(3) without chronic diarrhea (a; n = 7) and with opportunistic intestinal infections or HIV enteropathy (b; n = 25). The influence of diarrhea on citrulline was assessed by comparing the a and b subgroups with healthy control subjects (n = 100). RESULTS Citrulline was slightly decreased (22-30 micromol/L) in groups 1b and 2b and was <22 micromol/L in 19 of 25 patients in group 3b. In group 3b, a citrulline concentration <10 micromol/L was associated with a clinical indication for parenteral nutrition (n = 6 of 8 compared with 2 of 17 if the citrulline concentration was >10 micromol/L; P < 0.05). Citrulline correlated positively with albumin (P < 0.01) and BMI (P < 0.05) and negatively with C-reactive protein (P < 0.01). When antiinfectious and nutritional therapies were successful (n = 18 of 25), citrulline normalized in 2-12 wk. Neither chronic hepatic or pancreatic disease nor lipodystrophy and the metabolic syndrome affected citrulline. Compared with control subjects (38 +/- 8 micromol/L), patients without chronic diarrhea (groups 1a, 2a, and 3a) had normal citrulline concentrations (36 +/- 6 micromol/L). CONCLUSIONS Plasma citrulline is a reliable biomarker of enterocyte functional mass in HIV patients. Citrulline does not allow the etiologic diagnosis of enteropathy, but it can discriminate between protease inhibitor toxic diarrhea and infectious enteropathy and quantify the functional consequences, which makes it an objective tool for indicating the need for parenteral nutrition.

Impairment of arginine metabolism in rats after massive intestinal resection: effect of parenteral nutrition supplemented with citrulline compared with arginine.

Arginine homoeostasis is impaired in short bowel syndrome, but its supplementation in short bowel syndrome patients remains controversial. Recently, we demonstrated the benefits of citrulline supplementation by the enteral route in resected rats. Since the first step in managing short bowel syndrome is to initiate total parenteral nutrition, we hypothesized that parenteral citrulline supplementation would be more appropriate in this situation than arginine supplementation. In the present study, 24 rats were assigned to four groups. The sham group underwent transection whereas the three other groups underwent resection (R) of 80% of the small intestine. All rats were then fed exclusively by total parenteral nutrition as follows: supplementation with citrulline (R+CIT), with arginine (R+ARG) or no supplementation (R). All of the rats received isocaloric and isonitrogenous nutrition for 4 days. Nitrogen balance was measured daily. Rats were then killed and the blood was collected and the intestinal mucosa and extensor digitorum longus muscle were removed for amino acid and protein analysis. Citrulline and arginine increased mucosal protein content in the ileum (compared with sham and R, P<0.05). However, only citrulline prevented extensor digitorum longus atrophy (R+CIT, 130+/-3 mg compared with R, 100+/-6 mg and R+ARG, 110+/-2 mg, P<0.05). In addition, arginine worsened nitrogen balance (R+ARG, 104+/-46 mg/72 h compared with R, 249+/-69 mg/72 h, P<0.05). Only citrulline was able to prevent muscle atrophy and it was achieved independently from any noticeable effect on the gut in particular because citrulline and arginine share the same effect on mucosal ileal protein content. These results suggest that citrulline should be considered as a potential supplement for total parenteral nutrition of short bowel syndrome patients.

Taurine: The comeback of a neutraceutical in the prevention of retinal degenerations

Taurine is the most abundant amino acid in the retina. In the 1970s, it was thought to be involved in retinal diseases with photoreceptor degeneration, because cats on a taurine-free diet presented photoreceptor loss. However, with the exception of its introduction into baby milk and parenteral nutrition, taurine has not yet been incorporated into any commercial treatment with the aim of slowing photoreceptor degeneration. Our recent discovery that taurine depletion is involved in the retinal toxicity of the antiepileptic drug vigabatrin has returned taurine to the limelight in the field of neuroprotection. However, although the retinal toxicity of vigabatrin principally involves a deleterious effect on photoreceptors, retinal ganglion cells (RGCs) are also affected. These findings led us to investigate the possible role of taurine depletion in retinal diseases with RGC degeneration, such as glaucoma and diabetic retinopathy. The major antioxidant properties of taurine may influence disease processes. In addition, the efficacy of taurine is dependent on its uptake into retinal cells, microvascular endothelial cells and the retinal pigment epithelium. Disturbances of retinal vascular perfusion in these retinal diseases may therefore affect the retinal uptake of taurine, resulting in local depletion. The low plasma taurine concentrations observed in diabetic patients may further enhance such local decreases in taurine concentration. We here review the evidence for a role of taurine in retinal ganglion cell survival and studies suggesting that this compound may be involved in the pathophysiology of glaucoma or diabetic retinopathy. Along with other antioxidant molecules, taurine should therefore be seriously reconsidered as a potential treatment for such retinal diseases.

Evaluation of a newly available biochemical analyzer : the Olympus AU 600

Abstract The performance of the Olympus AU 600, a newly available open multiparametric analyzer, available for routine biochemical analysis of biological samples, was evaluated. The analytical and technical performance of the apparatus and the quality of the Olympus reagents were both examined in a single site study. Electrolyte concentrations were determined with patented ion-selective electrodes; substrate concentrations and enzyme activities were determined by spectrophotometric measurement after coloured reaction or UV detection-based-reactions. The protocol of the evaluation and the acceptability criteria were those recommended by the French Society for Clinical Biology. For the parameters studied, the upper limits of linearity were equal to or higher than those claimed by the manufacturer. The CV values for within-run and between-run precision were lower than the target values with few exceptions. The comparison study gave satisfactory results for most of the parameters. Only expected interferences occurred. In summary, the results obtained for the 25 parameters studied and the characteristics of the apparatus were satisfactory. The analyzer is rapid (800 to 1200 tests per hour) and easy to use. In addition, the analyzer complies with good analytical practice and its flexibility enables users to plan work according to local laboratory constraints.

Autoimmune lymphoproliferative syndrome caused by a homozygous null FAS ligand (FASLG) mutation

BACKGROUND Autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic nonmalignant lymphoproliferation, accumulation of double-negative T cells, hypergammaglobulinemia G and A, and autoimmune cytopenia. OBJECTIVES Although mostly associated with FAS mutations, different genetic defects leading to impaired apoptosis have been described in patients with ALPS, including the FAS ligand gene (FASLG) in rare cases. Here we report on the first case of complete FAS ligand deficiency caused by a homozygous null mutant. METHODS Double-negative T-cell counts and plasma IL-10 and FAS ligand concentrations were determined as ALPS markers. The FASLG gene was sequenced, and its expression was analyzed by means of Western blotting. FAS ligand function was assessed based on reactivation-induced cell death. RESULTS We describe a patient born to consanguineous parents who presented with a severe form of ALPS caused by FASLG deficiency. Although the clinical presentation was compatible with a homozygous FAS mutation, FAS-induced apoptosis was normal, and plasma FAS ligand levels were not detectable. This patient carries a homozygous, germline, single-base-pair deletion in FASLG exon 1, leading to a premature stop codon (F87fs x95) and a complete defect in FASLG expression. The healthy parents were each heterozygous for the mutation, confirming its recessive trait. CONCLUSION FAS ligand deficiency should be screened in patients presenting with ALPS features but lacking the usual markers, including plasma soluble FAS ligand and an in vitro apoptotic defect. An activation-induced cell death test could help in discrimination.

Increasing plasma glutamine in postoperative patients fed an arginine-rich immune-enhancing diet - a pharmacokinetic randomized controlled study.

Objective:Immune-enhancing diets (IEDs) rich in arginine (ARG) reduce morbi-mortality in trauma and surgical patients. Among the pharmaconutrients inducing these effects, ARG may be involved by generating active metabolites such as glutamine (GLN). However, the ability of an ARG-enriched diet to normalize GLN plasma levels in intensive care unit (ICU) patients has never been documented. To analyze plasma GLN and related amino acid (AA) kinetics in response to an ARG-enriched IED in ICU surgical patients. Design:This prospective, randomized, single-blind, comparative study was performed on 22 patients randomized to receive total enteral nutrition for 7 days with either an ARG-enriched IED or a standard formula (rendered isonitrogenous to the IED, S group, n = 11), providing 30 kcal/kg/day and 0.3 g N/kg/day. Measurements:Plasma AA concentrations were measured on day 5 after a 3-hour washout period (basal values = T0) and after 30, 60, 90, 120, 180, and 360 minutes of enteral nutrition. The primary end point was the variation in plasma GLN from T0 to T90. Results:Only the IED-fed patients showed an increase in plasma levels of GLN (differences [T90 − T0]: +40 ± 6 vs. −35 ± 18 &mgr;mol/L, mean ± sem, p < 0.05, two-way analysis of variance), ARG (+35 ± 5 vs.+1 ± 4 &mgr;mol/L, p < 0.05), ornithine (+23 ± 6 vs. −2 ± 2 &mgr;mol/L, p < 0.05), and proline (+36 ± 10 vs. −6 ± 11 &mgr;mol/L, p < 0.05). Conclusion:To our knowledge, this is the first reported pharmacokinetic study on an IED even though these products have been on the market for 20 years. Our main result is that administering an ARG-enriched IED causes a significant increase in plasma GLN probably from de novo GLN synthesis from ARG. This suggests that the ARG present in IED can serve to supply GLN to ICU patients, who are usually depleted in this conditionally essential AA during injury.

Endotoxemia affects citrulline, arginine and glutamine bioavailability

Eur J Clin Invest 2012; 42 (3): 282–289

Citrulline Supplementation Induces Changes in Body Composition and Limits Age-Related Metabolic Changes in Healthy Male Rats

BACKGROUND Aging is associated with profound metabolic disturbances, and citrulline may be of use to limit them. OBJECTIVE The aim of this work was to evaluate the long-term effect of citrulline supplementation on metabolism in healthy aged rats. METHODS Twenty-month-old male rats were randomly assigned to be fed (ad libitum) for 12 wk with either a citrulline-enriched diet (1 g ⋅ kg(-1) ⋅  d(-1)) or a standard diet [rendered isonitrogenous by addition of nonessential amino acids (NEAAs)]. Motor activity and muscle strength were measured, body composition was assessed, and muscle metabolism (protein structure, mitochondrial exploration, and transductional factors) and lipid metabolism (lipoprotein composition and sensitivity to oxidative stress) were explored. RESULTS Compared with the NEAA-treated group, citrulline supplementation was associated with lower mortality (0% vs. 20%; P = 0.05), 9% higher lean body mass (P < 0.05), and 13% lower fat mass (P < 0.05). Compared with the NEAA-treated group, citrulline-treated rats had greater muscle mass (+14-48% depending on type of muscle; P < 0.05 for tibialis, gastrocnemius, and plantaris). Susceptibility to oxidation of lipoproteins, as measured by the maximal concentration of 7-ketocholesterol after copper-induced VLDL and LDL oxidation, was lower in citrulline-treated rats than in NEAA-treated rats (187 ± 8 μmol/L vs. 243 ± 7 μmol/L; P = 0.0005). CONCLUSIONS Citrulline treatment in male aged rats favorably modulates body composition and protects against lipid oxidation and, thus, emerges as an interesting candidate to help prevent the aging process.

Disturbed intestinal nitrogen homeostasis in a mouse model of high-fat diet-induced obesity and glucose intolerance

The oligopeptide transporter peptide cotransporter-1 Slc15a1 (PEPT1) plays a major role in the regulation of nitrogen supply, since it is responsible for 70% of the dietary nitrogen absorption. Previous studies demonstrated that PEPT1 expression and function in jejunum are reduced in diabetes and obesity, suggesting a nitrogen malabsorption from the diet. Surprisingly, we reported here a decrease in gut nitrogen excretion in high-fat diet (HFD)-fed mice and further investigated the mechanisms that could explain this apparent contradiction. Upon HFD, mice exhibited an increased concentration of free amino acids (AAs) in the portal vein (60%) along with a selective increase in the expression of two AA transporters (Slc6a20a, Slc36a1), pointing to a specific and adaptive absorption of some AAs. A delayed transit time (+40%) and an increased intestinal permeability (+80%) also contribute to the increase in nitrogen absorption. Besides, HFD mice exhibited a 2.2-fold decrease in fecal DNA resulting from a reduction in nitrogen catabolism from cell desquamation and/or in the intestinal microbiota. Indeed, major quantitative (2.5-fold reduction) and qualitative alterations of intestinal microbiota were observed in feces of HFD mice. Collectively, our results strongly suggest that both increased AA transporters, intestinal permeability and transit time, and changes in gut microbiota are involved in the increased circulating AA levels. Modifications in nitrogen homeostasis provide a new insight in HFD-induced obesity and glucose intolerance; however, whether these modifications are beneficial or detrimental for the HFD-associated metabolic complications remains an open issue.