The lathyrus toxin, beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (ODAP), and homocysteic acid sensitize CA1 pyramidal neurons to cystine and L-2-amino-6-phosphonohexanoic acid

A brief exposure of hippocampal slices to L-quisqualic acid (QUIS) sensitizes CA1 pyramidal neurons 30- to 250-fold to depolarization by certain excitatory amino acids analogues, e.g., L-2-amino-6-phosphonohexanoic acid (L-AP6), and by the endogenous compound, L-cystine. This phenomenon has been termed QUIS sensitization. A mechanism similar to that previously described for QUIS neurotoxicity has been proposed to describe QUIS sensitization. Specifically, QUIS has been shown to be sequestered into GABAergic interneurons by the System x(c)(-) and subsequently released by heteroexchange with cystine or L-AP6, resulting in activation of non-NMDA receptors. We now report two additional neurotoxins, the Lathyrus excitotoxin, beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (ODAP), and the endogenous compound, L-homocysteic acid (HCA), sensitize CA1 hippocampal neurons >50-fold to L-AP6 and >10-fold to cystine in a manner similar to QUIS. While the cystine- or L-AP6-mediated depolarization can be inhibited by the non-NMDA receptor antagonist CNQX in ODAP- or QUIS-sensitized slices, the NMDA antagonist D-AP5 inhibits depolarization by cystine or L-AP6 in HCA-sensitized slices. Thus, HCA is the first identified NMDA agonist that induces phosphonate or cystine sensitization. Like QUIS sensitization, the sensitization evoked by either ODAP or HCA can be reversed by a subsequent exposure to 2 mM alpha-aminoadipic acid. Finally, we have demonstrated that there is a correlation between the potency of inducers for triggering phosphonate or cystine sensitivity and their affinities for System x(c)(-) and either the non-NMDA or NMDA receptor. Thus, the results of this study support our previous model of QUIS sensitization and have important implications for the mechanisms of neurotoxicity, neurolathyrism and hyperhomocystinemia.     

N-acetyl-L-cysteine suppresses TGF-beta signaling at distinct molecular steps: the biochemical and biological efficacy of a multifunctional, antifibrotic drug

The interrelated signaling via TGF-beta1 and reactive oxygen species has a profound impact on fibrogenesis and is therefore selected as target for antifibrotic therapies. This prompted us to investigate the influence of the antioxidant N-acetyl-L-cysteine on TGF-beta signaling in culture-activated hepatic stellate cells, the most relevant pro-fibrogenic cell type in liver. Dissection of the molecular steps involved in TGF-beta signaling revealed that N-acetyl-L-cysteine dose-dependently abrogated the induction of the TGF-beta1 signaling reporter gene activation, the phosphorylation of Smad2 and Smad3, and the up-regulation of Smad7 mRNA. By means of Western blot analysis and cross-linking experiments, it was demonstrated that these effects are based on disintegration of TGF-beta1 and the TGF-beta receptor endoglin, as well as a reduced ligand binding capacity of betaglycan. We conclude that N-acetyl-L-cysteine is a specific inhibitor of TGF-beta signaling targeting different components of the TGF-beta signaling machinery. In conclusion, these findings suggest that this non-toxic aminothiol downregulates TGF-beta signal transduction thereby mediating beneficial effects on experimental liver fibrosis characterized by TGF-beta hyperactivity.     

Curcumin induces the degradation of cyclin E expression through ubiquitin-dependent pathway and up-regulates cyclin-dependent kinase inhibitors p21 and p27 in multiple human tumor cell lines

Curcumin, a well-known chemopreventive agent, has been shown to suppress the proliferation of a wide variety of tumor cells through a mechanism that is not fully understood. Cyclin E, a proto-oncogene that is overexpressed in many human cancers, mediates the G(1) to S transition, is a potential target of curcumin. We demonstrate in this report a dose- and time-dependent down-regulation of expression of cyclin E by curcumin that correlates with the decrease in the proliferation of human prostate and breast cancer cells. The suppression of cyclin E expression was not cell type dependent as down-regulation occurred in estrogen-positive and -negative breast cancer cells, androgen-dependent and -independent prostate cancer cells, leukemia and lymphoma cells, head and neck carcinoma cells, and lung cancer cells. Curcumin-induced down-regulation of cyclin E was reversed by proteasome inhibitors, lactacystin and N-acetyl-L-leucyl-L-leucyl-L-norleucinal, suggesting the role of ubiquitin-dependent proteasomal pathway. We found that curcumin enhanced the expression of tumor cyclin-dependent kinase (CDK) inhibitors p21 and p27 as well as tumor suppressor protein p53 but suppressed the expression of retinoblastoma protein. Curcumin also induced the accumulation of the cells in G1 phase of the cell cycle. Overall, our results suggest that proteasome-mediated down-regulation of cyclin E and up-regulation of CDK inhibitors may contribute to the antiproliferative effects of curcumin against various tumors.     

The L-3,4-dihydroxyphenylalanine transporter in human and rat epithelial intestinal cells is a type 2 hetero amino acid exchanger

Information on the intestinal transport of L-3,4-dihydroxyphenylalanine (L-DOPA) is scarce. We present here the functional characteristics and regulation of the apical inward L-DOPA transport in two intestinal epithelial cell lines (human Caco-2 and rat IEC-6). The inward transfer of L-DOPA and L-leucine was promoted through an energy-driven system but with different sensitivity to extracellular Na(+) concentration: a minor component of L-leucine uptake (approximately 25%) was found to require extracellular Na(+) in comparison with L-DOPA transport which was Na(+)-independent. L-DOPA and L-leucine uptake was insensitive to N-(methylamino)-isobutyric acid, but competitively inhibited by 2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid (BCH). L- and D-neutral amino acids, but not acidic and basic amino acids, markedly inhibited L-DOPA and [(14)C]L-leucine accumulation in both cell lines. The [(14)C]L-DOPA and [14C]L-leucine outward were markedly increased by L-leucine and BCH present in extracellular medium, but not by L-arginine. In both cell lines, L-DOPA transport was stimulated by acidic pH in comparison with [(14)C]L-leucine inward which was pH-independent. In conclusion, it is likely that system B(0) might be responsible for the Na(+)-dependent uptake of L-leucine in Caco-2 and IEC-6 cells, whereas sodium-independent uptake of L-leucine and L-DOPA may include system type 1 and type 2 L-amino acid transporter (LAT1 and LAT2), the activation of which results in trans-stimulation of substrates outward transfer.     

Synergism between staurosporine and drugs inducing endoplasmic reticulum stress

Drugs causing endoplasmic reticulum or mitochondrial dysfunction may trigger apoptosis in eukaryotic cells. The thiol reagent dithiothreitol (DTT) belongs to the first group whereas the protein kinases inhibitor staurosporine acts on mitochondria. Since the endoplasmic reticulum and the mitochondrial pathways of apoptosis may converge in common steps, we examined the possibility of synergism between these two drugs. Using the activation of caspase-3 as indicator of apoptosis, we found that in two cell lines, Jurkat and Mono-Mac 6, staurosporine and DTT elicited apoptosis with a different pattern: staurosporine acted rapidly and at nanomolar concentrations while DTT acted slowly and at higher concentrations (1mM). When staurosporine and DTT were combined, the proapoptotic action was increased. This was confirmed examining late apoptotic events such as the translocation of phosphatidylserine across the plasma membrane and the cleavage of the antiapoptotic protein Mcl-1. The use of subthreshold DTT concentrations and isobologram analysis demonstrated the synergic nature of the interaction. Tunicamycin, a drug that, like DTT, inhibits protein folding in the endoplasmic reticulum also increased the proapoptotic effect of staurosporine. In agreement with the interplay between the mitochondrial and the endoplasmic reticulum pathways it was found that both staurosporine and DTT induced cytochrome c release. Furthermore, 90min incubation with DTT did not induce caspase-4 activation while staurosporine alone or in combination with DTT stimulated caspase-4 activity. We conclude that staurosporine is more active in cells undergoing endoplasmic reticulum stress. This synergism may warrant evaluation to establish whether the anticancer activity of staurosporine is also enhanced.     

Biochemical characterization of the binding of cyclic RGDyK to hepatic stellate cells

Activated hepatic stellate cells (HSCs) play a crucial role in the development of liver fibrosis. Noninvasive monitoring of the activation of HSCs has been challenging due to the lack of specific receptors or motifs on the cells. The present study provides the evidence that integrin αvβ3 expressed on HSCs is a biomarker reflecting the activation of HSCs. Solid-phase synthesis of cRGDyK (Arg-Gly-Asp-_DTyr-Lys) peptide and FAM-conjugated peptide were employed for binding to integrin αvβ3. The increased expression of integrin αv and β3 at mRNA and protein levels was detected during HSC activation. The affinity of cRGDyK to integrin αvβ3 was examined by both radioligand binding assay and FAM-conjugated peptide binding measurements. Quantitative RT-PCR and Western blotting showed a less dramatic, but significant increase in αv and β3 integrin mRNA and protein expression following activation of rat HSCs. Radioiodinated cRGDyK binds to both purified and membrane-bound integrin αvβ3 with high affinity in a dissociable manner. FAM-conjugated cRGDyK was coupled to activated HSCs in a time- and dose-dependent, receptor-mediated manner. Activated HSCs express sufficient number of integrin αvβ3 receptor. cRGDyK peptide binds to both purified and membrane-bound integrin αvβ3 with high affinity in a reversible fashion. Thus, the cRGDyK peptide represented a new agent potentially useful for the diagnosis of liver fibrosis.     

Pepstatin A attenuates the inhibitory effect of N-acetyl-L-cysteine on proliferation of hepatic myofibroblasts (stellate cells)

The pharmacological interaction between pepstatin A, a specific inhibitor of cathepsin D, and N-acetyl-L-cysteine was analyzed using hepatic stellate cells in primary culture. Isolated rat stellate cells were cultured on plastic dishes in Dulbecco's modified Eagle's medium (DMEM). Proteins and phospho-proteins were detected by Western blot. DNA synthesis was determined by [3H]thymidine uptake. Pepstatin A restored DNA synthesis of stellate cells stimulated by either platelet-derived growth factor-BB (PDGF-BB) or insulin-like growth factor-I (IGF-I), an effect that was attenuated by N-acetyl-L-cysteine. This agent induced the recovery of both the expression of PDGF receptor beta and IGF-I receptor beta and the phosphorylation of p42/44 mitogen-activated protein kinase (MAPK) and Akt under stimulation with either PDGF-BB or IGF-I, which were downregulated by N-acetyl-L-cysteine. Expression of cathepsin D was induced in activated stellate cells. These results indicate that pepstatin A hampers the inhibitory effect of N-acetyl-L-cysteine on stellate cell growth by ameliorating growth factor receptor downregulation.     

Neuroprotectant effects of iso-osmolar D-mannitol to prevent Pacific ciguatoxin-1 induced alterations in neuronal excitability: a comparison with other osmotic agents and free radical scavengers

The basis for the neuroprotectant effect of D-mannitol in reducing the sensory neurological disturbances seen in ciguatera poisoning, is unclear. Pacific ciguatoxin-1 (P-CTX-1), at a concentration 10 nM, caused a statistically significant swelling of rat sensory dorsal root ganglia (DRG) neurons that was reversed by hyperosmolar 50 mM D-mannitol. However, using electron paramagnetic resonance (EPR) spectroscopy, it was found that P-CTX-1 failed to generate hydroxyl free radicals at concentrations of toxin that caused profound effects on neuronal excitability. Whole-cell patch-clamp recordings from DRG neurons revealed that both hyper- and iso-osmolar 50 mM D-mannitol prevented the membrane depolarisation and repetitive firing of action potentials induced by P-CTX-1. In addition, both hyper- and iso-osmolar 50 mM D-mannitol prevented the hyperpolarising shift in steady-state inactivation and the rise in leakage current through tetrodotoxin (TTX)-sensitive Na(v) channels, as well as the increased rate of recovery from inactivation of TTX-resistant Na(v) channels induced by P-CTX-1. D-Mannitol also reduced, but did not prevent, the inhibition of peak TTX-sensitive and TTX-resistant I(Na) amplitude by P-CTX-1. Additional experiments using hyper- and iso-osmolar D-sorbitol, hyperosmolar sucrose and the free radical scavenging agents Trolox and L-ascorbic acid showed that these agents, unlike D-mannitol, failed to prevent the effects of P-CTX-1 on spike electrogenesis and Na(v) channel gating. These selective actions of D-mannitol indicate that it does not act purely as an osmotic agent to reduce swelling of nerves, but involves a more complex action dependent on the Na(v) channel subtype, possibly to alter or reduce toxin association.     

The role of osteopontin in d-galactosamine-induced liver injury in genetically obese mice

Various epidemiological studies have shown that obesity increases the risk of liver disease, but the precise mechanisms through which this occurs are poorly understood. In the present study, we hypothesized that osteopontin (OPN), an extracellular matrix and proinflammatory cytokine, has an important role in making obese mice more susceptible to inflammatory liver injury. After exposure of genetically obese ob/ob and db/db mice to a single dose of d-galactosamine (GalN), the plasma liver enzyme levels, histology and expression levels of cytokines and OPN were evaluated. The ob/ob and db/db mice, which were more sensitive to GalN-induced inflammatory liver injury compared with wild-type mice, had significantly higher plasma and hepatic OPN expression levels. Increased OPN expression was mainly found in hepatocytes and inflammatory cells and was correlated with markedly up-regulated interleukin (IL)-12 and IL-18 levels. Furthermore, pretreatment with a neutralizing OPN (nOPN) antibody attenuated the GalN-induced inflammatory liver injury in ob/ob and db/db mice, which was accompanied by significantly reduced macrophages recruitment and IL-12 and IL-18 productions. Taken together, these results suggest that up-regulated OPN expression is a contributing factor to increased susceptibility of genetically obese mice to GalN-induced liver injury by promoting inflammation and modulating immune response.     

Recombinant arginine deiminase as a differential modulator of inducible (iNOS) and endothelial (eNOS) nitric oxide synthetase activity in cultured endothelial cells

Modulation of the extracellular level of arginine, substrate for nitric oxide synthetases, is a promising modality to alleviate certain pathological conditions where excess nitric oxide (NO) is produced. However, complications arise, as only preferential inhibition of the inducible nitric oxide synthetase (iNOS), but not endothelial nitric oxide synthetase (eNOS), is desired for the treatment of NO over-production. We investigated the effect of arginine deprivation mediated by a recombinant arginine deiminase (rADI) on the activity of iNOS and eNOS in an endothelial cell line, TR-BBB. Our results demonstrated that cytokine-induced NO production depends on the extracellular arginine as substrate. However, if sufficient citrulline is present in the medium, A23187-activated NO production by eNOS does not rely on extracellular arginine. Treatment with rADI can markedly inhibit cytokine-induced NO production via iNOS, but not A23187-activated NO production via eNOS. Our results also showed that the decrease of NO production by iNOS could be achieved by depleting arginine from the medium even under the conditions that would up-regulate iNOS expression. Thus, rADI appears to be a novel selective modulator of iNOS activity that may be a used as a tool in the study of pathological disorders where NO over-production plays a key role.     

Granulocyte colony-stimulating factor treatment ameliorates liver injury and improves survival in rats with D-galactosamine-induced acute liver failure

Only liver transplantation is currently available therapy for the patients with acute liver failure (ALF). This study was designed to determine whether administration of granulocyte colony-stimulating factor (G-CSF) has therapeutic efficacy in animals with ALF. Female Sprague-Dawley (SD) rats were intraperitoneally injected with a single dose of d-galactosamine (d-GalN, 1.4 g/kg) to induce ALF. After 2 h, the rats were randomized to receive G-CSF (50 μg/kg/day), or saline vehicle injection for 5 days. Rats were observed for survival and assessed for liver injury by serum alanine transaminase (ALT) measurement and histological analysis. CD34+ cells in bone marrow were assessed by flow cytometry. CD34+ cells and Ki-67+ hepatocytes in liver tissue were evaluated by immunohistochemistry. In the ALF model, 5-day survival after d-GalN injection was 33.3% (10/30), while G-CSF administration following d-GalN resulted in 53.3% (16/30) survival (p = 0.027). G-CSF treated rats had lower ALT level and less hepatic injury compared with saline vehicle rats. The increases of CD34+ cells in bone marrow and liver tissue and Ki-67+ cells in liver tissue in G-CSF treated rats were higher than those in saline rats. No correlation was observed between CD34+ cells and Ki-67+ hepatocytes in liver tissue in both G-CSF and vehicle rats. It is suggested that G-CSF increases survival rate, decreases liver injury and enhances hepatocyte proliferation in rats with d-GalN-induced ALF possibly through actions including but not limiting to CD34+ cell mobilization, and that G-CSF may be of potential value in treating ALF.     

Improvement of high-fat diet-induced obesity by a mixture of red grape extract, soy isoflavone and l-carnitine: Implications in cardiovascular and non-alcoholic fatty liver diseases

In the present study, we examined the effect of a mixture of dietary components, including red grape extract, soy isoflavone and l-carnitine (RISC), on obesity. RISC substantially inhibited high-fat diet (HFD)-induced increase in body weight in a dose-dependent manner in C57BL/6 mice. The amount of subcutaneous and mesenteric fat was also significantly decreased by RISC treatment in HFD-fed C57BL/6 mice, whereas epididymal fat was not affected. Moreover, HFD-induced plasma leptin levels were down-regulated by RISC treatment. In these mice, RISC treatment significantly increased the plasma level of high density lipoprotein cholesterol without affecting the level of low density lipoprotein cholesterol and triglycerides. In addition, HFD-induced increase in liver weight and lipid accumulation in liver was significantly suppressed by RISC treatment in C57BL/6 mice. Plasma level of glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase was also inhibited by RISC treatment. These results demonstrate that RISC suppresses HFD-induced obesity and suggest that RISC supplementation might be a promising adjuvant therapy for the treatment of obesity and its complications, such as cardiovascular and non-alcoholic fatty liver diseases.     

肝星状细胞激活与增殖相关信号转导通路在肝纤维化中的作用及机制

肝星状细胞激活和增殖在肝纤维化的发生过程中占有重要的地位。控制肝星状细胞的激活和增殖并逆肝纤维化的进程是抗肝纤维化研究的重点之一。本综述以肝星状细胞激活与增殖相关信号转导通路为中心,探讨其在肝纤维化发病作用方面的作用机制。通过干预细胞外信号传导通路,为研究肝纤维化的发病机制和药物治疗提供新的途径。     

Temporal study of acetaminophen (APAP) and S-adenosyl-l-methionine (SAMe) effects on subcellular hepatic SAMe levels and methionine adenosyltransferase (MAT) expression and activity

Acetaminophen (APAP) is the leading cause of drug induced liver failure in the United States. Previous studies in our laboratory have shown that S-adenosyl methionine (SAMe) is protective for APAP hepatic toxicity. SAMe is critical for glutathione synthesis and transmethylation of nucleic acids, proteins and phospholipids which would facilitate recovery from APAP toxicity. SAMe is synthesized in cells through the action of methionine adenosyltransferase (MAT). This study tested the hypothesis that total hepatic and subcellular SAMe levels are decreased by APAP toxicity. Studies further examined MAT expression and activity in response to APAP toxicity. Male C57BL/6 mice (16-22 g) were treated with vehicle (Veh; water 15 ml/kg ip injections), 250 mg/kg APAP (15 ml/kg, ip), SAMe (1.25 mmol/kg) or SAMe administered 1 h after APAP injection (SAMe and SAMe + APAP). Hepatic tissue was collected 2, 4, and 6 h after APAP administration. Levels of SAMe and its metabolite S-adenosylhomocysteine (SAH) were determined by HPLC analysis. MAT expression was examined by Western blot. MAT activity was determined by fluorescence assay. Total liver SAMe levels were depressed at 4 h by APAP overdose, but not at 2 or 6 h. APAP depressed mitochondrial SAMe levels at 4 and 6 h relative to the Veh group. In the nucleus, levels of SAMe were depressed below detectable limits 4 h following APAP administration. SAMe administration following APAP (SAMe + APAP) prevented APAP associated decline in mitochondrial and nuclear SAMe levels. In conclusion, the maintenance of SAMe may provide benefit in preventing damage associated with APAP toxicity.     

Anticholesterolemic effect of 3,4-di(OH)-phenylpropionic amides in high-cholesterol fed rats

Two amide synthetic derivatives of 3,4-di(OH)-hydrocinnamate (HC), 3,4-dihydroxyphenylpropionic (l-serine methyl ester) amide (E030) and 3,4-dihydroxyphenylpropionic (l-aspartic acid) amide (E076), were investigated to compare their lipid-lowering efficacy with HC. Male rats were fed a 1 g/100 g high-cholesterol diet for 6 weeks with supplements of either clofibrate (0.02%, w/w), HC (0.025%, w/w), E030 (0.039%, w/w) or E076 (0.041%, w/w). The clofibrate supplement was used as a positive control for the lipid-lowering efficacy. The food intakes and body weight gains were not significantly different among the groups. The plasma and hepatic cholesterol and triglyceride levels were lower in clofibrate, HC, E030, and E076-supplemented groups compared to the control group. The supplementation of HC and its amide derivatives was as effective as clofibrate in increasing the ratio of HDL-cholesterol to total plasma cholesterol and reducing the atherogenic index (AI). The hepatic cholesterol level in the HC and E076 groups was significantly lower than that in the clofibrate group. The hepatic 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA reductase) and acyl-CoA:cholesterol acyltransferase (ACAT) activities were significantly lower in the all test groups than in the control group. The excretion of neutral sterol was significantly higher in the HC, E030, and E076-supplemented groups compared to the control group. The plasma AST and ALT activities, indirect indexes of hepatic toxicity, were significantly lower in the HC, E030, and E076-supplemented groups than in the control group. Accordingly, the current results suggest that E030 and E076, two amide synthetic derivatives of HC, are effective in lowering lipid activity.     

Chlorogenic acid protects d-galactose-induced liver and kidney injury via antioxidation and anti-inflammation effects in mice

Context Oxidative stress and inflammation are implicated in the aging process and its related hepatic and renal function decline. Chlorogenic acid (CGA) is one of the most abundant polyphenol compounds in the human diet. Recently, CGA has shown in vivo and in vitro antioxidant properties.

Objective The current study investigates the effects of protective effects of chlorogenic acid (CGA) on d-galactose-induced liver and kidney injury.

Materials and methods Hepatic and renal injuries were induced in a mouse model by subcutaneously injection of d-galactose (d-gal; 100?mg/kg) once a day for 8 consecutive weeks and orally administered simultaneously with CGA included in the food (200?mg/kg of diet). The liver and renal functions were examined. Histological analyses of liver and kidney were done by haematoxylin and eosin staining. The oxidative stress markers and pro-inflammatory cytokines in the liver and the kidney were measured.

Results CGA significantly reduced the serum aminotransferase, serum creatinine (SCr) and blood urea nitrogen (BUN) levels in d-gal mice (p?<0.05). CGA also restored superoxide dismutase, catalase, and malondialdehyde levels and decreased glutathione content in the liver and kidney in d-gal mice (p?<0.05). Improvements in liver and kidney were also noted in histopathological studies. CGA reduced tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) protein levels in the liver and kidney in d-gal mice (p?<0.05).

Discussion and conclusion These findings suggest that CGA attenuates d-gal-induced chronic liver and kidney injury and that this protection may be due to its antioxidative and anti-inflammatory activities.     

Accessibility of endothelial and inducible nitric oxide synthase to the intracellular citrulline-arginine regeneration pathway

This study investigates our hypothesis that argininosuccinate synthase (AS), the rate-limiting enzyme for arginine (L-arg) regeneration from citrulline (L-cit), plays a pivotal role in supplying L-arg to endothelial (eNOS), but not inducible (iNOS) nitric oxide synthase, for nitric oxide (NO) production. Transgenic rat blood-brain barrier (TR-BBB) endothelial cells were used as a model to elucidate the accessibility of the L-arg compartments for NOS isozymes. NO production via eNOS or iNOS, with or without alpha-methyl-DL-aspartic acid (MDLA), an AS inhibitor, was measured by a fluorometric method. NO production via eNOS was activated by the calcium ionophore A23187, while via iNOS was induced by cytokines. AS activity was assayed by the amount of argininosuccinate regenerated from radioactive aspartic acid from cell extracts. Upon increased AS activity (5.9-fold) in cells grown in L-arg-free/L-cit-supplemented medium, A23187-activated NO production also significantly increased, however cytokine-induced NO production was not detected. A23187-activated NO production was observed not only in L-arg containing medium, but also L-arg-free and L-arg-free/L-cit-supplemented medium, and was abolished by MDLA regardless of medium type. Cytokine-induced NO production was only observed in L-arg containing medium, not in L-arg-free or L-arg-free/L-cit-supplemented medium, and it was not inhibited by MDLA in the L-arg containing medium. Our results indicate that extracellular L-arg was the only L-arg pool for cytokine-induced NO production and intracellular L-arg regenerated from L-cit via AS pathway was the major L-arg pool for A23187-activated NO production in TR-BBB endothelial cells. Therefore, modulation of AS activity could be a promising strategy to selectively alter NO production via eNOS, but not iNOS.     

Effect of propionyl-l-carnitine,l-arginine and nicotinic acid on the efficacy of vardenafil in the treatment of erectile dysfunction in diabetes

ABSTRACT

Objective: The association of diabetes-related vascular damage and the role of metabolic factors in erectile dysfunction are well known in the literature. The compounds propionyl-l-carnitine (PLC), l-arginine (l-Arg) and nicotinic acid have numerous metabolic actions which have been reported to improve endothelial function. This study investigated the administration of the combination of these three compounds alone and in association with an inhibitor of 5-phosphodiesterase (5PDE), vardenafil, on endothelial function in diabetic patients with erectile dysfunction.

Methods: A total of 40 patients aged between 50 and 60 years with insulin-dependent diabetes (IDDM) for 3–4 years were selected from 509 patients presenting with erectile dysfunction. The patients were randomly subdivided into four groups of ten to be treated for 12 weeks. Group A was administered one sachet each day of test formulation containing PLC, l-Arg and nicotinic acid (Ezerex); group B with one 20 mg capsule of vardenafil (Levitra) twice a week; group C was treated with one sachet each day of the test formulation plus vardenafil 20 mg twice a week. Group D was administered placebo capsules twice weekly. Endothelial function was evaluated by examining flow-mediated dilation (FMD) and erectile function was estimated with the International Index of Erectile Function (IIEF5) questionnaire in all subjects.

Results: At the end of treatment group A showed an increment of 2 points in the IIEF5; group B showed an increment of 4 points; group C, the group which was administered all the treatments, showed an increment of 5 points, and group D, treated with placebo, showed no increment in the IIEF5.

Conclusion: Although there was a small number of subjects in this study the data suggest that the test formulation may improve the endothelial situation in diabetes. The test formulation together with vardenafil was better than the 5PDE inhibitor alone, but further studies are needed to confirm these findings.     

Role of nitric oxide in systemic effect of theophylline on mouse body temperature

In the present study, the interaction of nitric oxide synthase (NOS) inhibitors, L-NAME (N(G)-nitro-L-arginine methyl ester HCl) and L-NA (N(omega)-nitro-L-arginine), and its precursor, L-arginine (2-(S)-2-amino-5-[(aminoiminomethyl)amino] pentatonic acid), with theophylline on mouse body temperature was studied. Intraperitoneal (i.p.) injection of different doses of theophylline altered body temperature. Lower doses of theophylline (12.5 and 25 mg/kg) increased, but a higher dose (100 mg/kg) reduced, the animals' body temperature. The combination of L-arginine (20 and 40 mg/kg) with the highest dose of theophylline potentiated the hypothermic effect induced by the latter drug, while L-arginine by itself did not alter body temperature. L-NAME (10-80 mg/kg) or L-NA (10 mg/kg) plus a lower dose of theophylline (12.5 mg/kg) reduced the theophylline-induced hyperthermic response. L-NA (1, 5, and 10 mg/kg) in combination with the high dose of theophylline (100 mg/kg) also induced greater hypothermia. Both L-NAME and L-NA by themselves reduced body temperature. It is concluded that nitric oxide (NO) may be involved in the effects of theophylline on body temperature in mice.     

l-Arginine and l-glutamine as immunonutrients and modulating agents for oxidative stress and toxicity induced by sodium nitrite in rats

Sodium nitrite (NaNO₂) is a flavoring, coloring and preservative agent in meat and fish products. The study aimed to evaluate the efficacy of l-arginine and l-glutamine supplementation as a potentially novel and useful strategy for the modulation of oxidative stress and toxicity induced by NaNO₂ in male rats. Rats were divided into six groups each of 10 rats and treated for 6 weeks: group 1 as normal control; group 2 fed standard diet containing 0.2% NaNO₂; group 3 and 4 fed the previous diet supplemented with 1% and 2% arginine, respectively; group 5 and 6 fed NaNO₂ diet supplemented with 1% and 2% glutamine, respectively. NaNO₂ treatment induced a significant increase in serum malondialdehyde, nitric oxide, arginase, glutathione-S-transferase activities, urea and creatinine as well as differential leucocytes%. However, a significant decrease was recorded in reduced glutathione, catalase activity, total protein, albumin and some hematological parameters as well as immunoglobulin G. On the other hand, arginine or glutamine showed a remarkable modulation of these abnormalities as indicated by reduction of malondialdehyde and improvement of the investigated antioxidant and hematological parameters. It can be concluded that arginine or glutamine supplementation may reduce oxidative stress and improve the hazard effects of NaNO₂.