Hepatic Arginase Research Articles

Quercetin and l-Arginine Ameliorated the Deleterious Effects of Copper Oxide Nanoparticles on the Liver of Mice Through Anti-inflammatory and Anti-apoptotic Pathways

The widespread use and applications of copper oxide nanoparticles (CuO NPs) in daily life make human exposure to these particles inevitable. This study was carried out to investigate the deteriorations in hepatic and serum biochemical parameters induced by CuO NPs in adult male mice and the potential ameliorative effect of l-arginine and quercetin, either alone or in combination. Seventy adult male mice were equally allocated into seven groups: untreated group, l-arginine, quercetin, CuO NPs, arginine + CuO NPs, quercetin + CuO NPs, and quercetin + arginine + CuO NPs. Treating mice with CuO NPs resulted in bioaccumulation of copper in the liver and consequent liver injury as typified by elevation of serum ALT activity, reduction in the synthetic ability of the liver indicated by a decrease in the hepatic arginase activity, and serum total protein content. This copper accumulation increased oxidative stress, lipid peroxidation, inflammation, and apoptosis as manifested by elevation in malondialdehyde, nitric oxide, tumor necrosis factor-α, the expression level of caspase-3 and bax quantified by qPCR, and the activity of caspase-3, in addition to the reduction of superoxide dismutase activity. It also resulted in severe DNA fragmentation as assessed by Comet assay and significant pathological changes in the liver architecture. The study proved the efficiency of quercetin and l-arginine in mitigating CuO NPs-induced sub-chronic liver toxicity due to their antioxidant, anti-inflammatory, and anti-apoptotic properties; ability to inhibit DNA damage; and the potential as good metal chelators. The results of histopathological analysis confirmed the biochemical and molecular studies.

Galectin-3 is a key hepatoprotective molecule against the deleterious effect of cisplatin

AimsEvaluate the role of galectin-3 in the liver using an acute model of cisplatin-induced toxicity. Material and methodsModified citrus pectin (MCP) treatment was used to inhibit galectin-3. Rats were distributed into four groups: SHAM, CIS, MCP and MCP + CIS. On days 1–7, animals were treated by oral gavage with 100 mg/kg/day of MCP (MCP and MCP + CIS groups). On days 8, 9 and 10, animals received intraperitoneal injection of 10 mg/kg/day of cisplatin (CIS and MCP + CIS groups) or saline (SHAM and MCP groups). Key findingsCisplatin administration caused a marked increase in hepatic leukocyte influx and liver degeneration, and promoted reactive oxygen species production and STAT3 activation in hepatocytes. Plasma levels of cytokines (IL-6, IL-10), and hepatic toxicity biomarkers (hepatic arginase 1, α-glutathione S-transferase, sorbitol dehydrogenase) were also elevated. Decreased galectin-3 levels in the livers of animals in the MCP + CIS group were also associated with increased hepatic levels of malondialdehyde and mitochondrial respiratory complex I. Animals in the MCP + CIS group also exhibited increased plasma levels of IL-1β, TNF-α, and aspartate transaminase 1. Furthermore, MCP therapy efficiently antagonized hepatic galectin-9 in liver, but not galectin-1, the latter of which was increased. SignificanceReduction of the endogenous levels of galectin-3 in hepatocytes favors the process of cell death and increases oxidative stress in the acute model of cisplatin-induced toxicity.

EFFECT OF VIBRATION STRESS BOTH ON THE SHIFTS OF SOLUBLE PROTEIN FRACTIONS FROM RAT LIVER AND ON THE ARGINASE I ACTIVITY

Vibration pathology is in the second place among diseases connected to the profession. The vibration effect both on the protein fraction shifts and on the activities of I type arginase (Arg) IA and IB from white rat liver has been studied in the conditions of 5-, 10- and 15-day vibration state. In the initial state of vibration some decrease of Arg IA and Arg IB activities was revealed as compared to the control without general protein spectrum change of liver extract. Along with vibration effect, the expression level of Arg IA was increased with duration enhancement, which possibly is due to hyperammonemia, in the result of which ureagenesis is stimulated. Stimulation of easy available adaptation reserves were described due to protein catabolism. Analysis of shifts of general and enzyme protein fractions in the conditions of vibration effect allows to reveal their qualitative and quantitative changes and to make important the organism adaptation reactions that result from anabolic and catabolic process relations. It is possible that the revealed changes in the activity of arginase IA and IB are a biologically expedient mechanism for regulating the activity of hepatic arginase during vibration stress.

Semen Cuscutae Administration Improves Hepatic Lipid Metabolism and Adiposity in High Fat Diet-Induced Obese Mice.

Since arginase has been shown to compete with nitric oxide (NO) synthase, emerging evidence has reported that arginase inhibition improves obesity by increasing NO production. Semen cuscutae (SC), which is a well-known Chinese medicine, has multiple biological functions such as anti-oxidant function and immune regulation. In this study, we investigated whether the SC as a natural arginase inhibitor influences hepatic lipid abnormalities and whole-body adiposity in high-fat diet (HFD)-induced obese mice. The lipid accumulation was significantly reduced by SC treatment in oleic acid-induced hepatic steatosis in vitro. Additionally, SC supplementation substantially lowered HFD-induced increases in arginase activity and weights of liver and visceral fat tissue, while increasing hepatic NO. Furthermore, elevated mRNA expressions of sterol regulatory element-binding transcription factor 1 (SREBP-1c), fatty-acid synthase (FAS), peroxisome proliferator-activated receptor-gamma (PPAR-γ)1, and PPAR-γ2 in HFD-fed mice were significantly attenuated by SC supplementation. Taken together, SC, as a novel natural arginase inhibitor, showed anti-obesity properties by modulating hepatic arginase and NO production and metabolic pathways related to hepatic triglyceride (TG) metabolism.

Hepatic arginase deficiency fosters dysmyelination during postnatal CNS development.

Deficiency of arginase is associated with hyperargininemia, and prominent features include spastic diplegia/tetraplegia, clonus, and hyperreflexia; loss of ambulation, intellectual disability and progressive neurological decline are other signs. To gain greater insight into the unique neuromotor features, we performed gene expression profiling of the motor cortex of a murine model of the disorder. Coexpression network analysis suggested an abnormality with myelination, which was supported by limited existing human data. Utilizing electron microscopy, marked dysmyelination was detected in 2-week-old homozygous Arg1-KO mice. The corticospinal tract was found to be adversely affected, supporting dysmyelination as the cause of the unique neuromotor features and implicating oligodendrocyte impairment in a deficiency of hepatic Arg1. Following neonatal hepatic gene therapy to express Arg1, the subcortical white matter, pyramidal tract, and corticospinal tract all showed a remarkable recovery in terms of myelinated axon density and ultrastructural integrity with active wrapping of axons by nearby oligodendrocyte processes. These findings support the following conclusions: arginase deficiency is a leukodystrophy affecting the brain and spinal cord while sparing the peripheral nervous system, and neonatal AAV hepatic gene therapy can rescue the defects associated with myelinated axons, strongly implicating the functional recovery of oligodendrocytes after restoration of hepatic arginase activity.

Hepatic arginase 2 (Arg2) is sufficient to convey the therapeutic metabolic effects of fasting

Caloric restriction and intermittent fasting are emerging therapeutic strategies against obesity, insulin resistance and their complications. However, the effectors that drive this response are not completely defined. Here we identify arginase 2 (Arg2) as a fasting-induced hepatocyte factor that protects against hepatic and peripheral fat accumulation, hepatic inflammatory responses, and insulin and glucose intolerance in obese murine models. Arg2 is upregulated in fasting conditions and upon treatment with the hepatocyte glucose transporter inhibitor trehalose. Hepatocyte-specific Arg2 overexpression enhances basal thermogenesis, and protects from weight gain, insulin resistance, glucose intolerance, hepatic steatosis and hepatic inflammation in diabetic mouse models. Arg2 suppresses expression of the regulator of G-protein signalling (RGS) 16, and genetic RGS16 reconstitution reverses the effects of Arg2 overexpression. We conclude that hepatocyte Arg2 is a critical effector of the hepatic glucose fasting response and define a therapeutic target to mitigate the complications of obesity and non-alcoholic fatty liver disease.

Recurrent hepatic failure and status epilepticus: an uncommon presentation of hyperargininemia

Argininemia is a rare hereditary disease due to a deficiency of hepatic arginase, which is the last enzyme of the urea cycle and hydrolyzes arginine to ornithine and urea. Herein we report a patient with arginase I (ARG1) deficiency who presented with recurrent nonconvulsive status epilepticus and liver failure. A novel homozygous frameshift mutation c.703_707delGGACTinsAGACTGGACC (p.G235Rfs*20) was detected.

Human hepatocyte transplantation corrects the inherited metabolic liver disorder arginase deficiency in mice

The transplantation, engraftment, and expansion of primary hepatocytes have the potential to be an effective therapy for metabolic disorders of the liver including those of nitrogen metabolism. To date, such methods for the treatment of urea cycle disorders in murine models has only been minimally explored. Arginase deficiency, an inherited disorder of nitrogen metabolism that presents in the first two years of life, has the potential to be treated by such methods. To explore the potential of this approach, we mated the conditional arginase deficient mouse with a mouse model deficient in fumarylacetoacetate hydrolase (FAH) and with Rag2 and IL2-Rγ mutations to give a selective advantage to transplanted (normal) human hepatocytes. On day −1, a uroplasminogen-expressing adenoviral vector was administered intravenously followed the next day with the transplantation of 1 × 106 human hepatocytes (or vehicle alone) by intrasplenic injection. As the initial number of administered hepatocytes would be too low to prevent hepatotoxicity-induced mortality, NTBC cycling was performed to allow for hepatocyte expansion and repopulation. While all control mice died, all except one human hepatocyte transplanted mice survived. Four months after hepatocyte transplantation, 2 × 1011 genome copies of AAV-TBG-Cre recombinase was administered IV to disrupt endogenous hepatic arginase expression. While all control mice died within the first month, human hepatocyte transplanted mice did well. Ammonia and amino acids, analyzed in both groups before and after disruption of endogenous arginase expression, while well-controlled in the transplanted group, were markedly abnormal in the controls. Ammonium challenging further demonstrated the durability and functionality of the human repopulated liver. In conclusion, these studies demonstrate that human hepatocyte repopulation in the murine liver can result in effective treatment of arginase deficiency.

Metabolic and immune effects of orange-spotted grouper, Epinephelus coioides induced by dietary arginine

Arginine (Arg) as an important substrate for protein metabolism and endocrine influences on fish health directly. To evaluate the effect of dietary Arg on these endocrine and immunity of juvenile orange-spotted grouper (Epinephelus coioides), an experiment adding Arg with 0.00, 0.30, 0.60, 0.90, 1.20, 1.50, and 1.80% in seven diets was conducted. Dietary Arg levels reached 2.13 (Diet 1), 2.42 (Diet 2), 2.71 (Diet 3), 2.95 (Diet 4), 3.20 (Diet 5), 3.48 (Diet 6) and 3.74% (Diet 7), respectively. Each treatment was randomly assigned to triplicate groups of 30 fish (7.52 ± 0.02 g) each tank. The present results indicated that different Arg levels of diets were no significant effects on the fish survival rate of each groups (P > 0.05) after 8 weeks feeding experiment. The highest weight gain and specific growth rate were found in Diet 4, and significantly higher than the other groups (P < 0.05). Hepatic arginase activities were significantly higher in fish fed Diet 6 and Diet 7 compared to the activities of the fish fed first three Diets (P < 0.05). Hepatic ornithine decarboxylase activities of fish fed Diet 1 and Diet 2 were significantly decreased compared to the fish fed Diet 4–Diet 7 (P < 0.05). With ascending dietary Arg, the serum Insulin (INS) and insulin-like growth factor I (IGF-I) levels significantly increased. Gene expression of tissue toll-like receptors 22 in the three tissues were found first up-regulated and then down-regulated with the Arg increasing. Gene expression of major histocompatibility complex II in liver and kidney significantly increased in fish fed Diet 4 and Diet 6, and decreased thereafter. However, gene expression of hepcidin decreased with dietary Arg increased. The present study showed alterations in serum INS and IGF-I levels in response to Arg-induced growth activation. Additionally, the results indicate that Arg has beneficial effects on regulating mRNA expression of immune-associated genes and improving humoral and cellular immunity of fish.

Early obesity leads to increases in hepatic arginase I and related systemic changes in nitric oxide and L-arginine metabolism in mice.

Obesity is a risk factor for vascular endothelial cell dysfunction characterized by low-grade, chronic inflammation. Increased levels of arginase I and concomitant decreases in L-arginine bioavailability are known to play a role in the pathogenesis of vascular endothelial cell dysfunction. In the present study, we focused on changes in the systemic expression of arginase I as well as L-arginine metabolism in the pre-disease state of early obesity prior to the onset of atherosclerosis. C57BL/6 mice were fed a control diet (CD; 10% fat) or high-fat diet (HFD; 60% fat) for 8weeks. The mRNA expression of arginase I in the liver, adipose tissue, aorta, and muscle; protein expression of arginase I in the liver and plasma; and systemic levels of L-arginine bioavailability and NO2- were assessed. HFD-fed mice showed early obesity without severe disease symptoms. Arginase I mRNA and protein expression levels in the liver were significantly higher in HFD-fed obese mice than in CD-fed mice. Arginase I levels were slightly increased, whereas L-arginine levels were significantly reduced, and these changes were followed by reductions in NO2- levels. Furthermore, hepatic arginase I levels positively correlated with plasma arginase I levels and negatively correlated with L-arginine bioavailability in plasma. These results suggested that increases in the expression of hepatic arginase I and reductions in plasma L-arginine and NO2- levels might lead to vascular endothelial dysfunction in the pre-disease state of early obesity.

Hepatic Arginase - Nitric oxide imbalance: Impact of carcinogenesis and therapeutic effect of sodium channel blockage in an in vivo rat model

Abstract Objective: Nitric oxide synthase and arginase are frequently antagonistic and interactive, although both use L-arginine as common substrate. Their balance is of potential functional importance. How the balance changes in cancer is unknown. Increasing evidence suggests that progression of carcinomas involves functional voltage-gated sodium channel (VGSC) activity. Methods: The present study extended this study to liver and aimed to determine whether (i) DMBA carcinogenesis would affect the activities of arginase and NOS and (ii) treatment with Na-channel blocker RS100642 would ameliorate the impact of the carcinogen on the arginase-NOS balance. Results: DMBA application significantly increased arginase activity and, correspondingly, the level of L-ornithine by 25-33%. In contrast, NOS activity decreased by 11%. Importantly, RS100642 treatment completely suppressed the effect on arginase. Conclusion: It is concluded (i) that DMBA carcinogenesis changes the hepatic arginase-NOS balance, increasing the overall dominance of arginase and (ii) that VGSC inhibition has a protective effect on liver.

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy.

Arginase 1 deficiency is a urea cycle disorder associated with hyperargininemia, spastic diplegia, loss of ambulation, intellectual disability, and seizures. To gain insight on how loss of arginase expression affects the excitability and synaptic connectivity of the cortical neurons in the developing brain, we used anatomical, ultrastructural, and electrophysiological techniques to determine how single-copy and double-copy arginase deletion affects cortical circuits in mice. We find that the loss of arginase 1 expression results in decreased dendritic complexity, decreased excitatory and inhibitory synapse numbers, decreased intrinsic excitability, and altered synaptic transmission in layer 5 motor cortical neurons. Hepatic arginase 1 gene therapy using adeno-associated virus rescued nearly all these abnormalities when administered to neonatal homozygous knock-out animals. Therefore, gene therapeutic strategies can reverse physiological and anatomical markers of arginase 1 deficiency and therefore may be of therapeutic benefit for the neurological disabilities in this syndrome. These studies are one of the few investigations to try to understand the underlying neurological dysfunction that occurs in urea cycle disorders and the only to examine arginase deficiency. We have demonstrated by multiple modalities that, in murine layer 5 cortical neurons, a gradation of abnormalities exists based on the functional copy number of arginase: intrinsic excitability is altered, there is decreased density in asymmetrical and perisomatic synapses, and analysis of the dendritic complexity is lowest in the homozygous knock-out. With neonatal administration of adeno-associated virus expressing arginase, there is near-total recovery of the abnormalities in neurons and cortical circuits, supporting the concept that neonatal gene therapy may prevent the functional abnormalities that occur in arginase deficiency.

Pharmacological PPARα activation markedly alters plasma turnover of the amino acids glycine, serine and arginine in the rat.

The current study extends previously reported PPARα agonist WY 14,643 (30 µmol/kg/day for 4 weeks) effects on circulating amino acid concentrations in rats fed a 48% saturated fat diet. Steady-state tracer experiments were used to examine in vivo kinetic mechanisms underlying altered plasma serine, glycine and arginine levels. Urinary urea and creatinine excretion were measured to assess whole-body amino acid catabolism. WY 14,643 treated animals demonstrated reduced efficiency to convert food consumed to body weight gain while liver weight was increased compared to controls. WY 14,643 raised total amino acid concentration (38%), largely explained by glycine, serine and threonine increases. 3H-glycine, 14C-serine and 14C-arginine tracer studies revealed elevated rates of appearance (Ra) for glycine (45.5±5.8 versus 17.4±2.7 µmol/kg/min) and serine (21.0±1.4 versus 12.0±1.0) in WY 14,643 versus control. Arginine was substantially decreased (−62%) in plasma with estimated Ra reduced from 3.1±0.3 to 1.2±0.2 µmol/kg/min in control versus WY 14,643. Nitrogen excretion over 24 hours was unaltered. Hepatic arginase activity was substantially decreased by WY 14,643 treatment. In conclusion, PPARα agonism potently alters metabolism of several specific amino acids in the rat. The changes in circulating levels of serine, glycine and arginine reflected altered fluxes into the plasma rather than changes in clearance or catabolism. This suggests that PPARα has an important role in modulating serine, glycine and arginine de novo synthesis.

Minimal ureagenesis is necessary for survival in the murine model of hyperargininemia treated by AAV-based gene therapy.

Hyperammonemia is less severe in arginase 1 deficiency compared with other urea cycle defects. Affected patients manifest hyperargininemia and infrequent episodes of hyperammonemia. Patients typically suffer from neurological impairment with cortical and pyramidal tract deterioration, spasticity, loss of ambulation, seizures, and intellectual disability; death is less common than with other urea cycle disorders. In a mouse model of arginase I deficiency, the onset of symptoms begins with weight loss and gait instability which progresses to development of tail tremor with seizure-like activity; death typically occurs at about two weeks of life. Adeno-associated viral vector gene replacement strategies result in long-term survival of mice with this disorder. With neonatal administration of vector, the viral copy number in the liver greatly declines with hepatocyte proliferation in the first 5 weeks of life. While the animals do survive, it is not known from a functional standpoint how well the urea cycle is functioning in the adult animals that receive adeno-associated virus. In these studies we administered [1-13C] acetate to both littermate controls and adeno-associated virus-treated arginase 1 knockout animals and examined flux through the urea cycle. Circulating ammonia levels were mildly elevated in treated animals. Arginine and glutamine also had perturbations. Assessment thirty minutes after acetate administration demonstrated that ureagenesis was present in the treated knockout liver at levels as low at 3.3% of control animals. These studies demonstrate that only minimal levels of hepatic arginase activity are necessary for survival and ureagenesis in arginase deficient mice and that this level of activity results in control of circulating ammonia. These results may have implications for potential therapy in humans with arginase deficiency.

Myocyte-mediated Arginase Expression Controls Hyperargininemia but not Hyperammonemia in Arginase-deficient Mice

Human arginase deficiency is characterized by hyperargininemia and infrequent episodes of hyperammonemia that cause neurological impairment and growth retardation. We previously developed a neonatal mouse adeno-associated viral vector (AAV) rh10-mediated therapeutic approach with arginase expressed by a chicken β-actin promoter that controlled plasma ammonia and arginine, but hepatic arginase declined rapidly. This study tested a codon-optimized arginase cDNA and compared the chicken β-actin promoter to liver- and muscle-specific promoters. ARG1(-/-) mice treated with AAVrh10 carrying the liver-specific promoter also exhibited long-term survival and declining hepatic arginase accompanied by the loss of AAV episomes during subsequent liver growth. Although arginase expression in striated muscle was not expected to counteract hyperammonemia, due to muscle's lack of other urea cycle enzymes, we hypothesized that the postmitotic phenotype in muscle would allow vector genomes to persist, and hence contribute to decreased plasma arginine. As anticipated, ARG1(-/-) neonatal mice treated with AAVrh10 carrying a modified creatine kinase-based muscle-specific promoter did not survive longer than controls; however, their plasma arginine levels remained normal when animals were hyperammonemic. These data imply that plasma arginine can be controlled in arginase deficiency by muscle-specific expression, thus suggesting an alternative approach to utilizing the liver for treating hyperargininemia.

Single- and multiple-dose pharmacokinetics of arginase inhibitor Nω-hydroxy-nor-L-arginine, and its effect on plasma amino acids concentrations in Wistar rats

Arginase inhibitor Nω-hydroxy-nor-L-arginine (nor-NOHA) augments synthesis of nitric oxide (NO) exerting therapeutic effects in rodent models for cardiovascular and airway diseases. This study examined single- and multiple-dose pharmacokinetics and effects of nor-NOHA on plasma amino acids in Wistar rats. Animals were administered 30 mg/kg nor-NOHA in a single bolus intravenous (i.v.) or intraperitoneal (i.p.) injection, or five once-daily i.p. injections at the same dose, or vehicle. Nor-NOHA and amino acids were assayed in blood plasma by high-performance liquid chromatography. After a bolus i.v. injection, the elimination of nor-NOHA was rapid (the mean residence time was 12.5 min). The area under the concentration-time curve and maximum concentration were higher by 17% and 31%, respectively, after the fifth as compared to the first i.p. injection. A shift in arginine utilization towards the synthesis of NO was indicated by elevated citrulline-to-ornithine and citrulline-to-arginine ratios. No changes in plasma arginine were observed. Increased glutamine concentrations might indicate an alternative detoxification pathway for ammonia due to inhibition of hepatic arginase. In conclusion, pharmacokinetic data of the present study can guide rational dosing of nor-NOHA in future studies. Limitations of the strategy of NO modulation via arginase inhibition should be further explored.

Oleuropein supplementation increases urinary noradrenaline and testicular testosterone levels and decreases plasma corticosterone level in rats fed high-protein diet

The effects of oleuropein, a phenolic compound in extra virgin olive oil, on protein metabolism were investigated by measuring testicular testosterone and plasma corticosterone levels in rats fed diets with different protein levels. In Experiment 1, rats were fed experimental diets with different protein levels (40, 25 and 10 g/100 g casein) with or without 0.1 g/100 g oleuropein. After 28 days of feeding, the testosterone level in the testis was significantly higher and the plasma corticosterone level was significantly lower in rats fed the 40% casein diet with oleuropein than in those fed the same diet without oleuropein. The urinary noradrenaline level, nitrogen balance and hepatic arginase activity were significantly higher in rats fed the 40% casein diet with oleuropein supplementation than in those fed the 40% casein diet without oleuropein supplementation. In Experiment 2, the effects of oleuropein aglycone (a major phenolic compound in extra virgin olive oil and the absorbed form of oleuropein ingested in the gastrointestinal tracts) on the secretion of luteinizing hormone (LH) from the pituitary gland, which regulates testosterone production in the testis, were investigated in anesthetized rats. Plasma LH level increased dose dependently after the administration of oleuropein aglycone (P<.001, r=0.691). These findings suggest that dietary supplementation with 0.1 g/100 g oleuropein alters the levels of hormones associated with protein anabolism by increasing urinary noradrenaline and testicular testosterone levels and decreasing plasma corticosterone level in rats fed a high-protein diet.

Effects of dietary arginine and lysine levels on growth performance, nutrient utilization and tissue biochemical profile of black sea bream, Acanthopagrus schlegelii, fingerlings

An 8-week feeding trial was conducted to determine the effects of imbalanced levels of arginine and lysine in the diets of black sea bream, Acanthopagrus schlegelii, fingerlings. Eight isonitrogenous diets were formulated using a combination of intact protein and crystalline amino acids to contain different arginine/lysine levels: 2.83/3.25, 3.46/4.06, 2.27/4.09, 3.51/2.70, 2.31/2.74, 2.87/4.03, 2.91/4.68 and 2.85/5.24, % dry diet (analysis values), respectively. Each diet was fed to triplicate groups of 25 fish (mean weight, 10.0 ± 0.1 g) twice a day to apparent satiation. Fish fed diets with disproportionate levels of arginine and lysine showed significant ( P < 0.05) growth reduction compared to fish fed the control diet. The lower growth rates observed were due in part to lower feed intake, reduced nutrient availability (arginine and lysine), and increased catabolism of absorbed amino acids. Supplementing additional arginine to the diet was able to partially ameliorate the reduced growth, feed utilization and hepatic arginase activity observed in fish fed with excess dietary lysine, suggesting the possibility that there exists an antagonistic relationship between dietary lysine and arginine in black sea bream. Fish fed diets with excess lysine had lower whole-body protein content compared to fish fed the control diet. The significant increase in plasma ammonia levels as well as enzymes related to amino acid deamination and transamination reactions were found in the present study. To ensure optimal growth of black sea bream, the dietary levels of both arginine and lysine should be considered together when formulating feeds for this commercially farmed marine fish.

Reduction of arginase I activity and manganese levels in the liver during exposure of rats to methylmercury: a possible mechanism

The toxicity of methylmercury (MeHg) is, in part, thought to be due to its interaction with thiol groups in a variety of enzymes, but the molecular targets of MeHg are poorly understood. Arginase I, an abundant manganese (Mn)-binding protein in the liver, requires Mn as an essential element to exhibit maximal enzyme activity. In the present study, we examined the effect of MeHg on hepatic arginase I in vivo and in vitro. Subcutaneous administration of MeHg (10 mg/kg) for 8 days to rats resulted in marked suppression of arginase I activity. With purified arginase I, we found that interaction of MeHg with arginase I caused the aggregation of arginase I as evaluated by centrifugation and subsequent precipitation, and then the reduction of catalytic activity. Experiments with organomercury column confirmed that arginase I has reactive thiols that are covalently bound to organomercury. While MeHg inhibited arginase I activity, Mn ions were released from this enzyme. These results suggest that MeHg-mediated suppression of hepatic arginase I activity in vivo is, at least in part, attributable to covalent modification of MeHg or substantial leakage of Mn ions from the active site.

Synergistic Therapeutic Potential of Dexamethasone and l-arginine in Lipopolysaccharide-Induced Septic Shock

Dexamethasone (DEX) is demonstrated to have anti-inflammatory properties and known to induce hemodynamic improvement in sepsis and septic shock. L-arginine (L-arg), a semi-essential amino acid, depending on its metabolic pathway, becomes very essential in stress situations such as heatstroke, burns, sepsis, trauma, and wound healing. The aim of this study was to evaluate the synergistic therapeutic effect of DEX and L-arg in rescuing the mice from experimental septic shock induced by bacterial lipopolysaccharide (LPS). The experiments were designed to delineate the molecular mechanisms responsible for the increased therapeutic benefit of the combination therapy (CT) in LPS-induced septic shock. Acute endotoxemia was induced in Swiss male mice by i.p. injection of LPS (18 mg kg(-1)) at 0 h. LPS-treated mice were divided into four groups. The first group (DEX group) received DEX (2 mg kg(-1)) i.p. at +2 h of LPS. The second group (L-arg group) received L-arg i.p. at a dose of 120 mg/kg at +6 h of LPS injection. The third group (CT group) received DEX (2 mg kg(-1)) at +2 h LPS followed by L-arg at +6 h of LPS injection. The fourth group received saline in place of L-arg or DEX (LPS group). A sham group was also included, where normal mice received saline in place of LPS or L-arg or DEX. At +6 h, mice from sham group, LPS group, and DEX group were sacrificed at +24 h. Mice from sham group, DEX group, L-arg group, and CT group were sacrificed to examine various parameters associated with LPS endotoxemia. The CT with DEX followed by L-arg significantly increased the survival of mice injected with a lethal dose of LPS. Monotherapy with either DEX or L-arg given at the same dose and time did not increase the survival of the mice injected with LPS. DEX administration could significantly reduce the levels of serum TNF-alpha, IL-1beta, IFN-gamma, aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT), and nitrite. DEX also down-regulated the expression of liver-inducible nitric oxide synthase (iNOS), and up-regulated the levels of serum anti-inflammatory cytokines like TGF-beta1 and IL-4, hepatic and splenic arginase, in LPS-injected mice. The enhanced therapeutic effect of CT correlated with reduced pathological symptoms, decreased Th1 cytokines, increased TGF-beta1 and arginase levels compared to the mice administered with either of the monotherapies. The CT group had significantly increased expression of hepatic Hsp 70 and reduced septic shock associated histopathology, in lung and liver, compared to the mice treated with either DEX or L-arg. The therapeutic combination therapy with DEX and L-arg, at the appropriate dose, time, and sequence of administration, changed the cytokine profile, in favor of reducing the inflammatory response. The significantly enhanced survival observed in the CT group was accompanied by an increased hepatic Hsp 70, hepatic arginase, splenic arginase, and decreased organ injury. This novel concept of combined therapy could form the basis of an effective therapeutic approach in the treatment of sepsis and septic shock.