Jean François Huneau

Proton Nuclear Magnetic Resonance Spectroscopy of Urine and Plasma in Renal Transplantation Follow-Up

Urine and plasma samples from 39 patients who underwent renal transplantation were analyzed by proton nuclear magnetic resonance (NMR) spectroscopy. The most relevant resonances for evaluating renal function after transplantation were those arising from citrate, trimethylamine-N-oxide (TMAO), alanine, and lactate when compared to creatinine. A resonance at 3.7 ppm was related to cyclosporine toxicity when associated with elevated levels of TMAO. The respective variations in these metabolites in urine could contribute to prognosis and diagnosis of renal function impairment related to cyclosporine toxicity or overdosage, or to rejection. Thus, NMR spectroscopy should improve the follow-up and management of renal transplantation patients.

Metabolism of enterostatin in rat intestine, brain membranes, and serum: differential involvement of proline-specific peptidases.

The degradation of enterostatin (VPDPR), a potent inhibitor of food intake, by intestinal brush-border membranes, brain membranes, and rat serum has been investigated in the presence of specific inhibitors. Hydrolysis by intestinal membranes was found to be 10 and 100 times faster than in serum and brain membranes, respectively. Enterostatin hydrolysis by intestinal and brain membranes involves the removal of C-terminal arginine by carboxypeptidase P, leading to the production of des-Arg-enterostatin, and the splitting of the Pro2-Asp3 bond by dipeptidyl aminopeptidase IV (DPP IV). A small amount of the potent anorectic peptide Pro2-Asp3-Pro4 was released during hydrolysis of des-Arg-enterostatin by brain membranes and rat serum. In rat serum, enterostatin degradation was mainly due to DPP IV.

Early postprandial low-grade inflammation after high-fat meal in healthy rats: possible involvement of visceral adipose tissue ☆

In the postprandial period, low-grade inflammation may contribute to vascular endothelial dysfunction, a hallmark of atherogenesis. Little is known about the involvement of the adipose tissue in the initiation of the postprandial inflammatory response such as obtained after a high-saturated fat meal (HFM). In the present study, we first studied the time course of appearance of systemic inflammation after a HFM in healthy rats, and then we investigated whether a HFM activates the inflammatory signaling in the visceral adipose tissue, with a focus on the key component, nuclear factor-kappaB (NF-kappaB). Two hours after the HFM, plasma IL-6 and PAI-1, but not plasma C-reactive protein and soluble intracellular adhesion molecule-1, showed a marked, transient increase. These changes were specific to the postprandial state as not observed after a control water load. Neutrophils count and activation markers CD11B and CD62L, assessed by flow cytometry, also rose significantly 2 h after the HFM, while remaining steady after the control. At the same time, the HFM decreased significantly B-cell count and expression of the activation marker CD62L. Interestingly, at the same early time after the HFM, in the visceral adipose tissue, there was a 2.2-fold increase in the activation of NF-kappaB (p65) in nuclear extract and an increase in IL-6 mRNA. As far as we know, this is the first study evidencing an acute, postprandial activation of inflammation in visceral adipose tissue. This early activation of NF-kappaB pathway after a HFM may play a triggering role in the initiation of the complex postprandial proatherogenic phenotype.

Potential pitfalls of health claims from a public health nutrition perspective

The European Union is implementing a new regulatory framework for nutrition and health claims (HCs) that will greatly impact the communication of health messages on foodstuffs. In particular, approved HCs will be included in a positive register of generic claims. In the currently available literature, assessment of the relevance of HCs has mainly been related to scientific substantiation, and the issue of relevance in terms of public health has tended to be overlooked. Interestingly, the new regulation states that claims must be well understood by the average consumer. This article delves beyond the issue of scientific substantiation of claims and reviews possible discrepancies between consumer perception/understanding of HCs and the public health nutrition reality, which can confuse or mislead the consumer and ultimately impact public health nutrition. Six pitfalls are described herein and a comprehensive overview of the critical examination of any HC is proposed.

Rapeseed protein inhibits the initiation of insulin resistance by a high-saturated fat, high-sucrose diet in rats.

In contrast to the quality of carbohydrates and lipids, little is known on the influence of the type of dietary protein on the development of the metabolic or insulin resistance syndrome. Cysteine intake has been recently documented to impact insulin sensitivity. The aim of this study was to determine whether rapeseed protein, an emergent cysteine-rich protein, could inhibit the onset of the metabolic syndrome. For 9 weeks, rats were fed a diet rich in saturated fats and sucrose, which also included 20 % protein either as milk protein (Induction diet I) or rapeseed protein (diet R). A third, control group received an isoenergetic diet containing milk protein but polyunsaturated fats and starch (Prudent diet P). Plasma glucose, insulin, TAG and cholesterol, and blood pressure were monitored during the study, glucose tolerance was tested at week 7 and body composition determined at week 9. Plasma glucose, insulin and TAG increased during the experiment and, at week 9, plasma insulin was significantly 34 % lower in the R group and 56 % lower in P group as compared with the I group. The insulin peak after the glucose load was significantly 28-30 % lower in R and P than in I and the insulin sensitivity index was significantly higher in R than in I. Unexpectedly, peripheral fat deposition was slightly higher in R than in I. In this model, substituting rapeseed protein for milk protein had preventive effects on the early onset of insulin resistance, similar to those achieved by manipulating the types of dietary fat and carbohydrates.

Peptide fragments released from Phe-caseinomacropeptide in vivo in the rat

The aim of this study was to investigate the pharmacokinetics of bovine Phe-caseinomacropeptide (Phe-CMP) in the rat after oral administration. This polypeptide was monophosphorylated and mainly nonglycosylated: Phe-CMP-1P. During gastrointestinal digestion and absorption, Phe-CMP-1P was degraded. Intact Phe-CMP-1P and CMP-1P were rapidly released from the stomach. In contrast, partial hydrolysis by pancreatic enzymes was observed. In vitro hydrolysis by brush-border membrane vesicles also indicated that the peptide was degraded. In the blood, CMP-immunoreactive material appeared rapidly, reaching a maximum level of 5.5 microg/ml at 60 min.

Whole-body basal nitric oxide production is impaired in postprandial endothelial dysfunction in healthy rats.

In healthy humans, a high-saturated-fat/high-sucrose meal induces vascular endothelial dysfunction, a hallmark of atherogenesis. This transient dysfunction indicates a loss in nitric oxide (NO) production and/or bioactivity in the vasculature but it remains unknown if this is the local manifestation of a general impairment in NO pathway in the postprandial state. Here, we studied whole-body NO production and systemic NO bioactivity in postprandial endothelial dysfunction, as induced by a high-saturated-fat, high-sucrose meal. We first developed a physiological test of endothelial function on conscious rats, based on the transient fall in blood pressure after iv acetylcholine, and showed that this response was NO-dependent. As assessed with this method in healthy rats, endothelial function decreased during the postprandial state, being 60+/-7% lower than baseline at 6h after the meal challenge, associated with important elevations in plasma triglycerides and hydroperoxides. Aortic superoxide anion production, as assessed by oxidative fluorescent detection, was higher 6h after the meal challenge than after the nutrients vehicle (water). During the postprandial period, plasma cGMP, but not plasma ANP, markedly decreased, indicating a general decrease in NO bioavailability, which was numerically maximal 4h after the meal challenge. As determined 4h after ingestion by a tracer-based method using iv [(15)N(2)-(guanido)]-arginine, the whole-body NO production fell by 27+/-9% postprandially. This is the first study evidencing that a meal challenge that impairs the stimulated, NO-mediated, vascular response also reduces whole-body basal NO production and bioavailability. Postprandial pathophysiology may build on this general, fundamental alteration in NO production.

Cryptosporidiosis-Induced Impairment of Ion Transport and Na/-Glucose Absorption in Adult Immunocompromised Mice

Electrolyte transport was investigated during chronic cryptosporidiosis in adult anti-interferon-gamma-treated SCID mice by means of Ussing chamber techniques. In basal conditions, infection of immunocompromised mice with Cryptosporidium parvum resulted in a 30% reduction (P < .05) in the ileal short-circuit (Isc) current related to a 28% reduction (P < .05) in tissue conductance compared with controls. The rises in Isc and transepithelial potential difference induced by glucose (10 mM) were significantly reduced by Cryptosporidium infection (P < .01) compared with controls. In contrast, responses to mucosal glutamine were marginally affected. Electrical parameters of the ileum were not affected by the addition of indomethacin or furosemide, in either control or Cryptosporidium-infected mice. Thus, long-term cryptosporidiosis in immunocompromised animals leads to a reduction in net ion exchanges, decreased paracellular shunting, and impaired Na+-glucose cotransport in the ileum, without prostanoid- or enterotoxin-mediated electrogenic Cl- secretion.

Effects of chronic oral l -arginine administration on the l -arginine/NO pathway in patients with peripheral arterial occlusive disease or coronary artery disease: l -Arginine prevents renal loss of nitrite, the major NO reservoir

Despite saturation of nitric oxide (NO) synthase (NOS) by its substrate l-arginine (Arg), oral and intravenous supplementation of Arg may enhance NO synthesis, a phenomenon known as “The l-arginine paradox”. Yet, Arg is not only a source of NO, but is also a source for guanidine-methylated (NG) arginine derivatives which are all inhibitors of NOS activity. Therefore, Arg supplementation may not always result in enhanced NO synthesis. Concomitant synthesis of NG-monomethyl arginine (MMA), NG,NG-dimethylarginine (asymmetric dimethylarginine, ADMA) and NG,NG´-dimethylarginine (symmetric dimethylarginine, SDMA) from supplemented Arg may outweigh and even outbalance the positive effects of Arg on NO. Another possible, yet little investigated effect of Arg supplementation may be alteration of renal function, notably the influence on the excretion of nitrite in the urine. Nitrite is the autoxidation product of NO and the major reservoir of NO in the circulation. Nitrite and Arg are reabsorbed in the proximal tubule of the nephron and this reabsorption is coupled, at least in part, to the renal carbonic anhydrase (CA) activity. In the present placebo-controlled studies, we investigated the effect of chronic oral Arg supplementation of 10xa0g/day for 3 or 6xa0months in patients suffering from peripheral arterial occlusive disease (PAOD) or coronary artery disease (CAD) on the urinary excretion of nitrite relative to nitrate. We determined the urinary nitrate-to-nitrite molar ratio (UNOxR), which is a measure of nitrite-dependent renal CA activity before and after oral intake of Arg or placebo by the patients. The UNOxR was also determined in 6 children who underwent the Arg test, i.e., intravenous infusion of Arg (0.5xa0g Arg/kg bodyweight) for 30xa0min. Arg was well tolerated by the patients of the three studies. Oral Arg supplementation increased Arg (plasma and urine) and ADMA (urine) concentrations. No appreciable changes were seen in NO (in PAOD and CAD) and prostacyclin and thromboxane synthesis (in PAOD). In the PAOD study, UNOxR did not change in the Arginine group (480xa0±xa051 vs 486xa0±xa050), but fell in the Placebo group (422xa0±xa067 vs 332xa0±xa042, Pxa0=xa00.025). In the CAD study, UNOxR did not change significantly in the Arginine group (518xa0±xa077 at start vs 422xa0±xa040 after 3xa0months vs 399xa0±xa066 after 6xa0months), but fell in the Placebo group (524xa0±xa069 vs 302xa0±xa036 vs 285xa0±xa031; Pxa0=xa00.025 for 0 vs 3xa0months). Infusion of Arg tended to decrease the UNOxR in the children (317xa0±xa041 vs 208xa0±xa016, Pxa0=xa00.06). We propose that oral long-term Arg supplementation prevents loss of NO bioactivity by saving nitrite. The optimum Arg dose needs to be elaborated and is likely to be less than 10xa0g per day in adults. Orally and intravenously administered arginine was well tolerated by the elderly patients and young children, respectively.

Biosynthesis of homoarginine (hArg) and asymmetric dimethylarginine (ADMA) from acutely and chronically administered free L-arginine in humans.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis, whereas l-arginine (Arg) and l-homoarginine (hArg) serve as substrates for NO synthesis. ADMA and other methylated arginines are generally believed to exclusively derive from guanidine (NG)-methylated arginine residues in proteins by protein arginine methyltransferases (PRMTs) that use S-adenosylmethionine (SAM) as the methyl donor. l-Lysine is known for decades as a precursor for hArg, but only recent studies indicate that arginine:glycine amidinotransferase (AGAT) is responsible for the synthesis of hArg. AGAT catalyzes the formation of guanidinoacetate (GAA) that is methylated to creatine by guanidinoacetate methyltransferase (GAMT) which also uses SAM. The aim of the present study was to learn more about the mechanisms of ADMA and hArg formation in humans. Especially, we hypothesized that ADMA is produced by NG-methylation of free Arg in addition to the known PRMTs-involving mechanism. In knockout mouse models of AGAT- and GAMT-deficiency, we investigated the contribution of these enzymes to hArg synthesis. Arg infusion (0.5xa0g/kg, 30xa0min) in children (nxa0=xa011) and ingestion of high-fat protein meals by overweight men (nxa0=xa010) were used to study acute effects on ADMA and hArg synthesis. Daily Arg ingestion (10xa0g) or placebo for 3 or 6xa0months by patients suffering from peripheral arterial occlusive disease (PAOD, nxa0=xa020) or coronary artery disease (CAD, nxa0=xa030) was used to study chronic effects of Arg on ADMA synthesis. Mass spectrometric methods were used to measure all biochemical parameters in plasma and urine samples. In mice, AGAT but not GAMT was found to contribute to plasma hArg, while ADMA synthesis was independent of AGAT and GAMT. Arg infusion acutely increased plasma Arg, hArg and ADMA concentrations, but decreased the plasma hArg/ADMA ratio. High-fat protein meals acutely increased plasma Arg, hArg, ADMA concentrations, as well as the plasma hArg/ADMA ratio. In the PAOD and CAD studies, plasma Arg concentration increased in the verum compared to the placebo groups. Plasma ADMA concentration increased only in the PAOD patients who received Arg. Our study suggests that in humans a minor fraction of free Arg is rapidly metabolized to ADMA and hArg. In mice, GAMT and NG-methyltransferases contribute to ADMA and hArg synthesis from Arg, whereas AGAT is involved in the synthesis of hArg but not of ADMA. The underlying biochemical mechanisms remain still elusive.