Administration of L-citrulline prevents Plasmodium growth by inhibiting/ modulating T-regulatory cells during malaria pathogenesis

Background & objectives: Malaria affects around 228 million people all over the globe. Malaria causing parasite Plasmodium infection leads to activation of immune responses. The growth of parasite and immune activation requires semi essential amino acids like L-arginine. Malaria infection leads to condition of hyperargininemia and low availability of nitric oxide. However, the effect of L-arginine supplementation in malaria infected mice has not been explored in in-vivo studies. In this study we have compared the effect of oral supplementation of nitric oxide donor, L-arginine and L-citrulline, in malaria infected mice Methods: To examine the effect of oral supplementation of L-arginine and L-citrulline, Plasmodium berghei infected mice were divided in different groups and respective groups were fed with L- arginine and L-citrulline, parasitemia was measured on different days. Mice was sacrificed and immunophenotyping was done on 10 days post infection. Results: our results show that supplementation of L-arginine induces conducive environment for Plasmodium growth due to which the infected mice dies earlier than control wild type infected mice whereas L-citrulline supplementation inhibits parasite growth and mice survives for longer period of time. Flow cytometric analysis shows that supplementation of L-arginine increases cTLA-4 on T cell population, increases Treg cells leading to immunosuppression while supplementation of L-citrulline does not have effect on T cells population and number of Treg cell decrease compared to P. berghei infected mice. Interpretation & conclusion: our results show that L-citrulline can be a better alternative than L-arginine because of lower expression of inhibitory molecules and lower parasitemia as well as increased survival of infected mice.

Risk Assessment of "Other Substances" – L-Citrulline

The Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen for mattrygghet, VKM) has, at the request of the Norwegian Food Safety Authority (Mattilsynet; NFSA), assessed the risk of "other substances" in food supplements and energy drinks sold in Norway. VKM has assessed the risk of doses in food supplements and concentrations in energy drinks given by NFSA. These risk assessments will provide NFSA with the scientific basis while regulating the addition of “other substances” to food supplements and other foods. "Other substances" are described in the food supplement directive 2002/46/EC as substances other than vitamins or minerals that have a nutritional and/or physiological effect. It is added mainly to food supplements, but also to energy drinks and other foods. VKM has not in this series of risk assessments of "other substances" evaluated any claimed beneficial effects from these substances, only possible adverse effects. The present report is a risk assessment of L-citrulline, and it is based on a previous risk assessment and articles retrieved from a literature search. According to information from NFSA, L-citrulline is an ingredient in food supplements sold in Norway. NFSA has requested a risk assessment of 1000, 1500 and 2000 mg/day of L-citrulline in food supplements. The intake of L-citrulline was estimated for the age groups children (10 to <14 years), adolescents (14 to <18 years) and adults (≥18 years). Other sources of L-citrulline, such as foods and cosmetics, have not been included in the present risk assessment. The natural isoform of citrulline is the L-form. In mammals, it is found in all organisms and tissues. L-Citrulline is not part of the amino acids that are incorporated into proteins by the standard genetic code; therefore it is classified as a non-protein amino acid. Thus, its presence in a protein always results from a post-translational modification of the protein. L-citrulline is found in high levels in certain Cucurbitacea, including watermelon, cucumber, pumpkin and courgette, and in certain algae such as Grateloupia vulgaris. It is also present in fish, meat, pulses and milk, and in vegetables such as onions and garlic. Following oral intake of L-citrulline, plasma L-citrulline concentration increases rapidly but returns to baseline values within 5-8 hours post-exposure. There are three interconnected metabolic pathways for L-citrulline: 1) arginine biosynthesis, 2) nitric oxide (NO) cycle, and 3) the complete urea cycle. Renal L-citrulline reabsorption appears very efficient because urinary loss is very low even at high (up to 15 g) L-citrulline intake. No adverse health effects of L-citrulline were observed in six human studies covering the ages 12 months to 56 years, with L-citrulline exposure lengths varying from less than one day (acute doses) to 2 years. The doses varied from 2.1-179 mg/kg bw per day for children. (<14 years), 1.5-175 mg/kg bw per day for adolescents (14 to <18 years) and 21-214 mg/kg bw per day in adults. The human studies available had low number of participants and, with exception of one study, included non-healthy populations. In a 2-year study by Rajantie et al. (1980), 19 patients with lysinuric protein intolerance, ages 1.9-32.7 years, were included. No adverse effects were reported from daily intakes of 65 mg/kg bw in children (10 to <14 years), 46 mg/kg bw in adolescents (14 to <18 years) and 40 mg/kg bw in adults (highest doses applied). These age-specific reference points were used for comparisons with the estimated exposures in the risk characterization. For children, from a daily intake of 1000, 1500 and 2000 mg the estimated exposures are 23.0, 34.6 and 46.1 mg/kg bw per day, respectively. These intake values are below 65 mg/kg bw per day. VKM therefore considers it unlikely that a daily intake of 1000, 1500 or 2000 mg L-citrullline from food supplements causes adverse health effects in children (10 to <14 years). For adolescents, from a daily intake of 1000, 1500 and 2000 mg the estimated exposures are 16.3, 24.5 and 32.6 mg/kg bw per day, respectively. These intake values are below 46 mg/kg bw per day. VKM therefore considers it unlikely that a daily intake of 1000, 1500 or 2000 mg L-citrullline from food supplements causes adverse health effects adolescents (14 to <18 years). For adults, from a daily intake of 1000, 1500 and 2000 mg the estimated exposures are 14.3, 21.4 and 28.6 mg/kg bw per day, respectively. These intake values are below 40 mg/kg bw per day. VKM therefore considers it unlikely that a daily intake of 1000, 1500 or 2000 mg L-citrullline from food supplements causes adverse health effects in adults (≥18 years). Since LPI patients have a different intestinal absorption, renal reabsorption and reduced intracellular efflux of cationic amino acids compared to healthy individuals, it is uncertain whether doses given to LPI patients can be directly extrapolated to healthy individuals. Persons with citrullinemia caused by mutations in enzymes involved in citrulline metabolism are potentially vulnerable to intake of additional L-citrulline from supplements. In addition, humans with chronic renal failure and/or mutations in renal citrulline transporters are potentially vulnerable to supplementation of L-citrulline.

Effect of incubation with L-citrulline ex vivo on relaxation dysfunction of corpus cavernosum from type 2 diabetic rats / 中国医师杂志

Objective To explore the role of the changes in endogenous L-citrulline levels and arginases expression in erectile dysfunction of diabetic rats,and investigate the effect of L-citrulline incubation ex vivo on the erectile dysfunction.Methods Type 2 diabetic rats were induced by high fat diet plus a single intraperitoneal injection of small dose streptozotocin (30 mg/kg),followed by high fat diet for 8 weeks.The erectile function of rats was reflected by the relaxation response to acetylcholine (ACh) of corpus cavernosum detected by isometric tension measurement.Levels of endogenous nitric oxide inhibitor asymmetric dimethylarginine (ADMA) and cyclic guanosine monophosphate (cGMP) were measured by enzyme-linked immunosorbent assay (ELISA).The content of L-citrulline,nitric oxide (NO) and the activity of nitric oxide synthase (NOS) were determined with colorimetric method.Western blotting was applied to detect the protein expression of NOS,arginases and phosphodiesterase 5 (PEDS).Results The relaxation response to ACh of corpus cavernosum from diabetic rats was significantly lower than that of control rats (P ＜ 0.01),indicating the erectile dysfunction of diabetic rats.This erectile dysfunction was companied by the decreases of L-citrulline levels in serum and corpus cavernosum as well as up-regulation of arginaseⅠ & Ⅱ expression in the corpus cavernosum of diabetic rats.Incubation with L-citrulline (3 mmol/L) for 45 min ex vivo improved the relaxation function of corpus cavernosum from diabetic rats (P ＜ 0.05),while incubation with PED5 inhibitor silaenafil (3 μmoL/L) had no significant effect.Furthermore,the ADMA level was increased,while the NOS activity,cGMP and NO contents were decreased in corpus cavernosum of diabetic rats compared to control rats.Down-regulation of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) protein expression as well as up-regulation of inducible nitric oxide synthase (iNOS) and PDE5 protein expression were also observed in the corpus cavernosum of diabetic rats.Conclusions The decreased endogenous L-citrulline levels and upregulated arginases expression was closely related to erectile dysfunction of diabetic rats,and the mechanism is associated to the up-regulation of arginase activity and decrease of NO synthesis in corpus cavernosum.L-citrulline incubation ex vivo exerted therapeutic effect on the relaxation dysfunction of corpus cavernosum from diabetic rats.

Production of L-citrulline by a recombinant Corynebacterium crenatum SYPA 5-5 whole-cell biocatalyst / 生物工程学报

Arginine deiminase (ADI) was first high-efficient expressed in Corynebacterium crenatum SYPA 5-5. The ADI was purified by Ni-NTA affinity chromatography and SDS-PAGE analysis showed the molecular weight (MW) was 46.8 kDa. The optimal temperature and pH of ADI were 37 ℃ and 6.5 respectively. The Michaelis constant was 12.18 mmol/L and the maximum velocity was 0.36 μmol/(min·mL). Under optimal conditions, 300 g/L of arginine was transformed and the productivity reach 8 g/(L·h). The recombinant strain was cultivated in a 5-L fermentor and used for whole-cell transformation of 300 g/L arginine, under repeated-batch bioconversion, the cumulative production reached 1 900 g/L.

Establishment and Clinical Application of the Analytical Method for Plasma L-citrulline and L-arginine Concentration / 现代检验医学杂志

Objective To establish a method for simultaneously measuring L-citrulline and L-arginine concentration in plasma using reversed-phase high performance liquid chromatography (RP-HPLC)with ultraviolet detection,and the novel method is applied to the patients with digestive system tumor.Methods Plasma samples were deproteinized by trichloroacetic acid with heating method.Phenylisothiocyanate (PITC)was used as derivatization reagent and a gradient elution was adopted. The feasibility verification of method was carried out by detecting plasma L-citrulline and L-arginine acid concentration in 21 cases of advanced digestive tract malignant tumor patients,21 cases of non malignant tumor patients and 39 cases of healthy people.Results The linearity for L-citrulline and L-arginine ranged from 0 to at least 1 000 μmol/L.r=0.999 95 for both. The lower limits of quantification for L-citrulline and L-arginine were 0.240 μmol/L and 0.448 μmol/L respectively.The in-traday and interday coefficients of variation (CVs)were less than 3.4% and 7.2%,respectively.The average recovery rate was from 95.2% to 104.1%.The ratio of plasma L-citrulline/L-arginine in patients with digestive cancar was significantly higher than that in the healthy control group,t-test,P =0.009.The sensitivity and specificity of plasma L-citrulline/L-argi-nine ratio in the malignant tumor of digestive system were 81% and 71.4% respectively.Conclusion This method can pro-vide a reliable and efficient method for the clinical determination of the L-citrulline and L-arginine concentration in plasma. The ratio of plasma citrulline/arginine increased obviously in patients with digestive cancer,suggesting that this ratio is a more sensitive index than single concentration of L-citrulline or L-arginine when evaluating patients with digestive tumor.