Impairment of cysteine synthesis from methionine in rats exposed to surgical stress

Amino Acid Availability of a Dairy and Vegetable Protein Blend Compared to Single Casein, Whey, Soy, and Pea Proteins: A Double-Blind, Cross-Over Trial

Protein quality is important for patients needing medical nutrition, especially those dependent on tube feeding. A blend of dairy and vegetable proteins (35% whey, 25% casein, 20% soy, 20% pea; P4) developed to obtain a more balanced amino acid profile with higher chemical scores, was compared to its constituent single proteins. Fourteen healthy elderly subjects received P4, whey, casein, soy, and pea (18 g/360 mL bolus) on five separate visits. Blood samples were collected at baseline until 240 min after intake. Amino acid availability was calculated using incremental maximal concentration (iCmax) and area under the curve (iAUC). Availability for P4 as a sum of all amino acids was similar to casein (iCmax and iAUC) and whey (iCmax) and higher vs. soy (iCmax and iAUC) and pea (iCmax). Individual amino acid availability (iCmax and iAUC) showed different profiles reflecting the composition of the protein sources: availability of leucine and methionine was higher for P4 vs. soy and pea; availability of arginine was higher for P4 vs. casein and whey. Conclusions: The P4 amino acid profile was reflected in post-prandial plasma levels and may be regarded as more balanced compared to the constituent single proteins.

Metabolism in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a poorly understood condition that presents as long-term physical and mental fatigue with associated symptoms of pain and sensitivity across a broad range of systems in the body. The poor understanding of the disorder comes from the varying clinical diagnostic definitions as well as the broad array of body systems from which its symptoms present. Studies on metabolism and CFS suggest irregularities in energy metabolism, amino acid metabolism, nucleotide metabolism, nitrogen metabolism, hormone metabolism, and oxidative stress metabolism. The overwhelming body of evidence suggests an oxidative environment with the minimal utilization of mitochondria for efficient energy production. This is coupled with a reduced excretion of amino acids and nitrogen in general. Metabolomics is a developing field that studies metabolism within a living system under varying conditions of stimuli. Through its development, there has been the optimisation of techniques to do large-scale hypothesis-generating untargeted studies as well as hypothesis-testing targeted studies. These techniques are introduced and show an important future direction for research into complex illnesses such as CFS.

Cystine and theanine: amino acids as oral immunomodulative nutrients

The decreases in the glutathione (GSH) level in the mouse spleen and liver after immune stimulation are suppressed by the oral administration of cystine and theanine (CT). GSH is considered to be important for the control of immune responses. Antibody production in mice after infection is enhanced by the oral administration of CT. In humans, also, the oral administration of CT has been confirmed to enhance antibody production after vaccination against Flu and also reduce the incidence of cold. However, the GSH level is reduced by intense exercise and surgery. In clinical studies of body-builders and long-distance runners, the intake of CT suppressed excessive inflammatory reactions and a decline in immune functions after intense training. Surgery as well as intense exercise induces excessive inflammatory reactions. In mice, the preoperative administration of CT suppressed excessive inflammatory reactions associated with surgery and promoted the postoperative recovery. Moreover, in clinical studies of gastrectomized patients, CT intake suppressed excessive postoperative inflammatory reactions and induced early recovery. If infection is regarded as invasive stress, CT intake is considered to exhibit an immunomodulatory effect by suppressing the decrease in GSH due to invasive stress. The clarification of their detailed action mechanisms and their application as medical or function foods is anticipated.

Enhancement of postoperative recovery by preoperative oral co-administration of the amino acids, cystine and theanine, in a mouse surgical model

BACKGROUND & AIMS

Glutathione (GSH) is important in the control of immune responses, and its levels decline following trauma. We previously reported that the oral administration of cystine/theanine (CT) increased GSH synthesis and that CT intake inhibited intense exercise-induced inflammation. Based on these results, we hypothesised that CT inhibits surgically induced inflammation and promotes postoperative recovery. Our aim was to confirm this hypothesis using a mouse surgical model.

METHODS

CT or a vehicle (V) was administered orally to mice once a day for 5 days, until the day of surgery. On the day of surgery, a sham operation or an intestinal manipulation was performed 2 h after the oral administration of CT or V. Levels of IL-6 in the blood and GSH in the intestine were analysed 2 h after surgery. Behavioural analysis was also undertaken after surgery.

RESULTS

Treatment with CT inhibited the manipulation-induced increase in IL-6 in the blood and decrease in GSH in the intestine. There was a significant negative correlation between IL-6 in the blood and GSH in the intestine. In addition, behavioural analysis revealed that CT administration improved locomotor activity and food intake after surgery.

CONCLUSION

These results suggest that CT suppresses inflammatory responses by inhibiting the surgically induced decrease in GSH in the small intestine and promotes postoperative recovery.

Cystathionine gamma-Lyase-deficient mice require dietary cysteine to protect against acute lethal myopathy and oxidative injury

Cysteine is considered a nonessential amino acid in mammals as it is synthesized from methionine via trans-sulfuration. However, premature infants or patients with hepatic failure may require dietary cysteine due to a lack of cystathionine gamma-lyase (CTH), a key trans-sulfuration enzyme. Here, we generated CTH-deficient (Cth(-/-)) mice as an animal model of cystathioninemia/cystathioninuria. Cth(-/-) mice developed normally in general but displayed hypercystathioninemia/hyperhomocysteinemia though not hypermethioninemia. When fed a low cyst(e)ine diet, Cth(-/-) mice showed acute skeletal muscle atrophy (myopathy) accompanied by enhanced gene expression of asparagine synthetase and reduced contents of glutathione in livers and skeletal muscles, and intracellular accumulation of LC3 and p62 in skeletal myofibers; they finally died of severe paralysis of the extremities. Cth(-/-) hepatocytes required cystine in a culture medium and showed greater sensitivity to oxidative stress. Cth(-/-) mice exhibited systemic vulnerability to oxidative injury, which became more prominent when they were fed the low cyst(e)ine diet. These results reveal novel roles of trans-sulfuration previously unrecognized in mice lacking another trans-sulfuration enzyme cystathionine beta-synthase (Cbs(-/-)). Because Cbs(-/-) mice display hyperhomocysteinemia and hypermethioninemia, our results raise questions against the homocysteine-based etiology of CBS deficiency and the current newborn screening for homocysteinemia using Guthrie's method, which detects hypermethioninemia.

Transsulfuration pathway defects and increased glutathione degradation in severe acute pancreatitis

Glutathione depletion is a consistent feature of the progression of mild to severe acute pancreatitis. In this study, we examined the temporal relationship between cysteine, homocysteine, and cysteinyl-glycine levels; total reduced erythrocyte glutathione; gamma-glutamyl transpeptidase activity; and disease severity. Initially, cysteine concentration was low, at levels similar to those of healthy controls. However, glutathione was reduced whilst cysteinyl glycine and gamma-glutamyl transpeptidase activity were increased in both mild and severe attacks. As the disease progressed, glutathione and cysteinyl glycine were further increased in mild attacks and cysteine levels correlated with homocysteine (r = 0.8, P < 0.001) and gamma-glutamyl transpeptidase activity (r = 0.75, P < 0.001). The progress of severe attacks was associated with glutathione depletion, reduced gamma-glutamyl transpeptidase activity, and increased cysteinyl glycine that correlated with glutathione depletion (r = 0.99, P = 0.01). These results show that glutathione depletion associated with severe acute pancreatitis occurs despite an adequate cysteine supply and could be attributed to heightened oxidative stress coupled to impaired downstream biosynthesis.

The essentiality of sulfur is closely related to nitrogen metabolism: a clue to hyperhomocysteinaemia

N and S metabolisms are closely interwoven throughout both the plant and animal kingdoms. The essentiality of S relates to its participation in the structure of S-containing amino acids (SAA), to its inclusion in many sulfonated molecules, and to a myriad of metabolic and catalytic reactions of vital importance. Methionine (Met) is the indispensable SAA supplied by food proteins and its plasma homeostasis is achieved via a number of highly efficient regulatory mechanisms. In all conditions characterised by a negative body protein balance such as in dietary restriction or cytokine-induced hypercatabolic losses, N and S endogenous pools manifest parallel tissue depletion rates. Adaptive conservation of N and S body stores is reached by a functional restraint of the trans-sulfuration cascade, through the depression of cystathionine β-synthase activity. As a result, upstream accumulation of homocysteine favours its re-methylation conversion to Met which helps maintain metabolic pathways of survival value. In addition to the measurement of vitamin indices, that of plasma transthyretin, a sensitive marker of protein nutritional status, is proposed to identify the fluctuations of the total body N component accountable for the alterations of homocysteine concentrations in body fluids.

Depletion of glutathione by buthionine sulfoximine decreases random-pattern skin flap viability in rats

BACKGROUND

Glutathione (GSH) is one of the most highly concentrated intracellular antioxidants. Exogenous GSH has been shown to increase random-pattern skin flap survival. However, the effects of endogenous GSH depletion on random-pattern skin flap viability have never been studied.

MATERIALS AND METHODS

To evaluate the effects of systemic glutathione depletion on random-pattern skin flap survival in rats, 28 Wistar albino rats were divided into control, sham, and BSO (buthionine sulfoximide, a selective inhibitor for gamma-glutamylcysteine synthetase) groups. Dorsal, cranial-based random-pattern skin-flaps were elevated and the percentage of flap necrosis was measured in all rats at the postoperative day 7.

RESULTS

BSO-treated rats showed increased skin flap necrosis when compared with untreated animals (P < 0.001). High-dose BSO treatment group had more clinically evident necrosis than low dose group (P < 0.05).

CONCLUSIONS

This study reveals the importance of endogenous GSH for random skin-flap viability.

Inhibition of betaine-homocysteine S-methyltransferase causes hyperhomocysteinemia in mice

Inhibitors and methyl donor substrates for betaine-homocysteine S-methyltransferase (BHMT) were used to study the role of this enzyme in the regulation of plasma total homocysteine (tHcy). Mice were administered an i.p. injection of S-(delta-carboxybutyl)-dl-homocysteine (CBHcy; 1 mg), a specific and potent inhibitor of BHMT, and tHcy and hepatic BHMT protein and activity levels were monitored over a 24-h period. Compared with saline-injected control mice, at 2 h postinjection, the CBHcy-treated mice had 87% lower BHMT activity and a 2.7-fold increase (11.1 vs. 3.0 micromol/L) in tHcy, effects that lasted nearly 8 h but returned to normal by 24 h. The level of BHMT protein remained constant over the 24-h period. After 6 CBHcy (1 mg) injections (one every 12 h), the mice had 7-fold higher tHcy, a 65% reduction in the liver S-adenosylmethionine:S-adenosylhomocysteine ratio, and a marked upregulation of BHMT protein expression. At 2 h after injection of the sulfoxide derivative of CBHcy (10 mg) into mice, there was a modest reduction in BHMT activity and a 90% increase in tHcy. When given an injection of Met (3 mg) or Met plus CBHcy (1 mg), post-Met load tHcy levels were 2.2-fold higher (128 vs. 40 micromol/L) at 2 h postinjection in the mice given CBHcy. Like betaine, dimethylsulfoniopropionate was an effective tHcy-lowering agent when given with a Met load. These studies are the first to show that transient inhibition of BHMT in vivo causes transient hyperhomocysteinemia, and that dimethylsulfoniopropionate can reduce a post-Met load rise in tHcy.

Hydrogen sulfide as an endogenous modulator of biliary bicarbonate excretion in the rat liver

Cystathionine gamma-lyase (CSE) is an enzyme catalyzing cystathionine and cysteine to yield cysteine and hydrogen sulfide (H(2)S), respectively. This study aimed to examine if H(2)S generated from the enzyme could serve as an endogenous regulator of hepatobiliary function. Gas chromatographic analyses indicated that, among rat organs herein examined, liver constituted one of the greatest components of H(2)S generation in the body, at 100 mumol/g of tissue, comparable to that in kidney and 1.5-fold greater than that in brain, where roles of the gas in the regulation of neurotransmission were reported previously. At least half of the gas amount in the liver appeared to be derived from CSE, because blockade of the enzyme by propargylglycine suppressed it by 50%. Immunohistochemistry revealed that CSE occurs not only in hepatocytes, but also in bile duct. In livers in vivo, as well as in those perfused ex vivo, treatment with the CSE inhibitor induced choleresis by stimulating the basal excretion of bicarbonate in bile samples. Transportal supplementation of NaHS at 30 mumol/L, but not that of N-acetylcysteine as a cysteine donor, abolished these changes elicited by the CSE inhibitor in the perfused liver. The changes elicited by the CSE blockade did not coincide with alterations in hepatic vascular resistance, showing little involvement of vasodilatory effects of the gas in these events, if any. These results first provided evidence that H(2)S generated through CSE modulates biliary bicarbonate excretion and is thus a determinant of bile salt-independent bile formation in the rat liver.

Age-associated oxidative damage leads to absence of gamma-cystathionase in over 50% of rat lenses: relevance in cataractogenesis

Oxidative damage to lens proteins and glutathione depletion play a major role in the development of senile cataract. We previously found that a deficiency in gamma-cystathionase activity may be responsible for glutathione depletion in old lenses. The aims of this study were: (1) to investigate the mechanism that causes the age-related deficiency in gamma-cystathionase activity in the eye lens, and (2) to determine the role of gamma-cystathionase deficiency in cataractogenesis. Two populations of old rats were found, one (56%) whose lenses lacked gamma-cystathionase activity and the rest that exhibited detectable enzyme activity. gamma-Cystathionase protein was absent in lenses from old rats without gamma-cystathionase activity. Oxidative stress targeted gamma-cystathionase in the eye lens upon aging, since the enzyme contained more carbonyl groups in old lenses than in young ones. gamma-Cystathionase mRNA was also markedly reduced in old lenses, thus contributing to the age-associated deficiency in gamma-cystathionase. Inhibition of gamma-cystathionase activity caused glutathione depletion in lenses and led to cataractogenesis in vitro. In conclusion, the lack of gamma-cystathionase activity in over 50% of old lenses is due to decreased gene expression and proteolytic degradation of the oxidized enzyme. This results in a high risk for the development of senile cataract.

Murine cystathionine gamma-lyase: complete cDNA and genomic sequences, promoter activity, tissue distribution and developmental expression

Cystathionine gamma-lyase (CSE) is the last key enzyme in the trans-sulphuration pathway for biosynthesis of cysteine from methionine. Cysteine could be provided through diet; however, CSE has been shown to be important for the adequate supply of cysteine to synthesize glutathione, a major intracellular antioxidant. With a view to determining physiological roles of CSE in mice, we report the sequence of a complete mouse CSE cDNA along with its associated genomic structure, generation of specific polyclonal antibodies, and the tissue distribution and developmental expression patterns of CSE in mice. A 1.8 kb full-length cDNA containing an open reading frame of 1197 bp, which encodes a 43.6 kDa protein, was isolated from adult mouse kidney. A 35 kb mouse genomic fragment was obtained by lambda genomic library screening. It contained promoter regions, 12 exons, ranging in size from 53 to 579 bp, spanning over 30 kb, and exon/intron boundaries that were conserved with rat and human CSE. The GC-rich core promoter contained canonical TATA and CAAT motifs, and several transcription factor-binding consensus sequences. The CSE transcript, protein and enzymic activity were detected in liver, kidney, and, at much lower levels, in small intestine and stomach of both rats and mice. In developing mouse liver and kidney, the expression levels of CSE protein and activity gradually increased with age until reaching their peak value at 3 weeks of age, following which the expression levels in liver remained constant, whereas those in kidney decreased significantly. Immunohistochemical analyses revealed predominant CSE expression in hepatocytes and kidney cortical tubuli. These results suggest important physiological roles for CSE in mice.

Cysteine is the metabolic signal responsible for dietary regulation of hepatic cysteine dioxygenase and glutamate cysteine ligase in intact rats

Cysteine, rather than a precursor or metabolite of cysteine, appears to mediate the upregulation of cysteine dioxygenase (CDO) and the downregulation of glutamate cysteine ligase (GCL) in cultured primary rat hepatocytes. However, similar experiments in intact rats have not been performed to confirm in vivo that changes in hepatic cysteine levels are associated with the regulation of CDO or GCL activity. Therefore, rats were fed a low protein basal diet (100 g casein/kg diet) with or without supplemental sulfur amino acids (8 g cystine, 9 g homocystine or 10 g methionine/kg diet) and with or without propargylglycine (PPG, 1 mmol/kg), an irreversible inhibitor of cystathionine gamma-lyase. Rats were fed the assigned diet for 2 full days and up until the mid-point of the dark cycle on d 3, at which time they were killed for collection of liver. Rats fed the PPG-containing diets had hepatic cystathionine gamma-lyase activities that were approximately 16% of the uninhibited level. PPG treatment reduced CDO activity by 50 and 54%, increased GCL activity by 41 and 61% and lowered total cysteine concentration by 33 and 64% in liver of the homocystine and methionine-supplemented groups, respectively, but not in the cystine-supplemented groups or unsupplemented groups. Glutathione levels were not affected by PPG treatment in any groups. These experiments are consistent with a role for cysteine, rather than a precursor or metabolite of cysteine, in the metabolic signaling responsible for diet-induced regulation of CDO and GCL.

Plasma L-5-oxoproline kinetics and whole blood glutathione synthesis rates in severely burned adult humans

Compromised glutathione homeostasis is associated with increased morbidity in various disease states. We evaluated the kinetics of L-5-oxoproline, an intermediate in the gamma-glutamyl cycle of glutathione production, in fourteen severely burned adults by use of a primed, constant intravenous infusion of L-5-[1-(13)C]oxoproline. In nine of these patients, whole blood glutathione synthesis and plasma kinetics of glycine and leucine were also measured with [(15)N]glycine and L-[(2)H(3)]leucine tracers. Patients were studied under a "basal" condition that provided a low dose of glucose and total parenteral nutrition. For comparison with control subjects, whole blood glutathione synthesis was estimated in six healthy adults. Burn patients in a basal condition showed significantly higher rates of plasma oxoproline clearance and urinary D- and L-oxoproline excretion compared with fasting healthy control subjects. Whole blood glutathione concentration and absolute synthesis rate in the basal state were lower than for control subjects. Total parenteral feeding without cysteine but with generous methionine did not affect oxoproline kinetics or whole blood glutathione synthesis. The estimated rate of glycine de novo synthesis was also lower in burn patients, suggesting a possible change in glycine availability for glutathione synthesis. The roles of precursor amino acid availability, as well as alterations in metabolic capacity, in modulating whole blood glutathione production in burns now require investigation.

Effects of surgical stress and nitrous oxide anaesthesia on peri-operative plasma levels of total homocysteine. A randomised, controlled study in general surgery

Previous studies of patients have shown that anaesthesia with nitrous oxide (N2O) increases the plasma levels of total homocysteine. In a randomised, controlled trial we measured the plasma total homocysteine levels in patients undergoing general surgery before and after anaesthesia with and without N2O. Plasma total homocysteine levels were measured before anaesthesia and 1, 3-5 and 24 h after incision in 24 patients randomly allocated to anaesthesia with N2O (n = 12) and without N2O (n = 12). Total homocysteine levels significantly decreased from 10.4 +/- 2.7 to 8.2 +/- 2.9 micromol x l(-1) in the non-N2O group 24 h after incision (p < 0.02), while they tended to increase slightly in the N2O group from 10.5 +/- 4.5 to 10.9 +/- 4.3 micromol x l(-1) (p > 0.05). Our randomised controlled study indicates that total homocysteine decreases after general surgery in patients in whom anaesthesia is maintained without N2O, but not in patients in whom anaesthesia is maintained with N2O.

Blood sulfur-amino acid concentration reflects an impairment of liver transsulfuration pathway in patients with acute abdominal inflammatory processes

Whole-blood free amino acids were measured in a control group made up of eight healthy women fasted for 12 h and also in eight patients with acute pancreatitis, five patients with acute cholecystitis and seven patients with acute appendicitis. Blood was withdrawn immediately on admission to hospital and again 3 d later following a controlled peripheral parenteral nutrition diet; this is with the exception of the appendicitis group. l-Cystathionine and l-methionine concentrations were significantly higher in pancreatitis and appendicitis patients when compared with controls. In the pancreatitis and cholecystitis patients, l-serine concentration was also significantly higher when compared with controls. The l-homocysteine concentration was significantly higher only in the appendicitis group when compared with the control group. l-Cystine concentration was unchanged in all the patients studied when compared with control subjects. The l-methionine : l-cystine ratio was significantly higher and the l-glutamine : l-cystine ratio was significantly lower in all the patients when compared with controls. The blood S-amino acid pattern reflects an impairment in liver transsulfuration pathway during acute abdominal processes. This work supports the idea that the l-methionine : l-cystine and l-glutamine : l-cystine ratios can be taken as good markers to evaluate the S-amino acid metabolism and suggests the importance of using N-acetylcysteine as a required nutrient in these situations.

Effects of parenteral cysteine and glutathione feeding in a baboon model of severe prematurity

BACKGROUND

The availability of cysteine for glutathione synthesis is low in premature infants with respiratory distress.

OBJECTIVE

The effects of gestational age, oxygen delivery, and cysteine infusion or glutathione infusion, or both, on plasma total cysteine and other methionine metabolites were studied in a baboon model of severe premature birth with respiratory distress.

DESIGN

Premature baboons were studied as part of the multiinvestigator National Institutes of Health Collaborative Project on Bronchopulmonary Dysplasia. Premature baboons, 125 d (69% of term) or 140 d (78% of term) of gestational age, were maintained in neonatal intensive care units for </=14 d. Parenteral feeding with or without supplemental cysteine and glutathione infusions was given. Plasma total cysteine, methionine, N:-methylglycine, cystathionine, and the other methionine metabolites were monitored by capillary gas chromatography-mass spectrometry.

RESULTS

Cord blood plasma total cysteine was the lowest in the 125-d-old premature baboons. Plasma total cysteine decreased in the first 3 d after delivery in the 125-d-old (but not in the 140-d-old) premature baboons even when cysteine was infused. Supplementation with glutathione from the first day of life raised plasma total cysteine markedly. Plasma cystathionine increased in all animals after birth but increased 4-fold in 125-d-old animals with glutathione infusion. At 6 and 10 d postdelivery, the arterial-alveolar oxygen gradient was significantly higher in the 125-d-old animals that received glutathione infusions.

CONCLUSIONS

Glutathione, but not supplemental cysteine, infusions prevented the postdelivery decline in plasma cysteine concentrations in premature baboons. Glutathione infusions resulted in marked elevations of plasma cystathionine concentration.

Methionine transsulfuration is increased during sepsis in rats

Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsis in rats. Rats were infected with an intravenous injection of live Escherichia coli, and control pair-fed rats were injected with saline. Two days after injection, the rats were infused for 6 h with [(35)S]methionine and [(15)N]cysteine. Transsulfuration was measured from the transfer rate of (35)S from methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P < 0.05) the contribution of transsulfuration to cysteine flux in both plasma and liver (by 80%) and the contribution of transsulfuration to plasma methionine flux (by 133%). Transsulfuration measured in plasma was significantly (P < 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 micromol. h(-1). 100 g(-1), respectively). However, liver cystathionase specific activity was decreased by 17% by infection (P < 0.05). Infection increased methionine flux (16%, P < 0.05) less than cysteine flux (38%, P < 0.05). Therefore, the plasma cysteine flux was higher than that predicted from estimates of protein turnover based on methionine data, probably because of enhanced glutathione turnover. Taken together, these results suggest an increased cysteine requirement in infection.

1999 Jonathan E. Rhoads lecture. Isotopic metaprobes, nutrition, and the roads ahead

The 1999 Jonathan E. Rhoads lecture, delivered by Vernon R. Young at the annual meeting of American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.), San Diego, February 2, 1999, with the printed version coauthored with Alfred M. Ajami, is concerned with the application of isotopic probes and how, in particular, they may be used as diagnostic tools to enhance the role of nutrition in the comprehensive medical management of the patient. Following a brief review of the early uses of stable isotopes in metabolic research we consider the present and possible future application of stable isotope probes. The concept of a "gateway" enzyme in a discrete biochemical pathway and how the flow of substrate through this step might be assessed by giving a "metaprobe" is developed. The specific and desirable structural requirements of the metaprobe are considered. A number of examples are given that further exploit the concepts of "underground" metabolism and of metabolic "hijackers." It is our view that we are on the verge of a new era where, for the many pragmatic and exciting reasons discussed, stable isotope probes will find and increasing use in the practice of clinical medicine and in the preventive and public health areas.

Early and prolonged widespread increase in brain protein synthesis following a single electroconvulsive shock in free-moving rats

The autoradiographic method with l-[35S] methionine ([35S]Met) was used to determine the effect of a single electroconvulsive shock (ECS) on local rates of protein synthesis in the adult rat brain in free-moving conditions. We have estimated the relative contribution of methionine derived from protein breakdown to the intracellular precursor amino acid pool (tRNA pool) for protein synthesis. In steady-state conditions, we showed a large contribution (around 60%) of Met recycling into the precursor pool (lambda=0.37+/-0.11), after a single ECS. In all the 36 brain regions examined, apparent rates of protein synthesis were greatly increased (21-50%) 3 h after a single ECS indicating a generalized effect in rat brain. This ECS-induced activation of the overall rate of brain protein synthesis persisted for at least 24 h after cessation of ECS. This is consistent with the hypothesis that electroconvulsive therapy is associated with long-term molecular changes in neuronal activity.

Nutrient antioxidants in gastrointestinal diseases

Oxidative stress appears to play a role in the pathogenesis of a number of gastrointestinal disease states, including pancreatitis; gastric and duodenal ulcer disease; IBD; gastric, esophageal, and colon cancers; and hepatic injury secondary to alcohol, metal storage disorders, hepatitis, and ischemia/reperfusion injury. The nutritional antioxidants are attractive potential therapeutic and chemopreventive agents because they are inexpensive and have a relatively low toxicity profile. A word of caution should be noted: Some antioxidants, such as vitamin C, can be prooxidant under certain conditions, and systemically altering the redox state may have untoward effects on the inflammatory response in certain disease states. Thus, at the current time, antioxidant therapy should be restricted to randomized, controlled clinical trials, in which treatment effects can be closely monitored, and therapeutic efficacy can be determined with scientific accuracy.

Liver intracellular L-cysteine concentration is maintained after inhibition of the trans-sulfuration pathway by propargylglycine in rats

To study the fate of L-cysteine and amino acid homeostasis in liver after the inhibition of the trans-sulfuration pathway, rats were treated with propargylglycine (PPG). At 4 h after the administration of PPG, liver cystathionase (EC 4.4.1.1) activity was undetectable, L-cystathionine levels were significantly higher, L-cysteine was unchanged and GSH concentration was significantly lower than values found in livers from control rats injected intraperitoneally with 0.15 M-NaCl. The hepatic levels of amino acids that are intermediates of the urea cycle, L-ornithine, L-citrulline and L-arginine and blood urea were significantly greater. Ura excretion was also higher in PPG-treated rats when compared with control rats. These data suggest a stimulation of ureagenesis in PPG-treated rats. The inhibition of gamma-cystathionase was reflected in the blood levels of amino acids, because the L-methionine: L-cyst(e)ine ratio was significantly higher in PPG-treated rats than in control rats; blood concentration of cystathionine was also greater. Histological examination of liver and kidney showed no changes in PPG-treated rats when compared with controls. The administration of N-acetylcysteine (NAC) to PPG-treated rats reversed the changes in blood urea and in liver GSH. These data suggest that when liver L-cysteine production was impaired by the blockage of the trans-sulfuration pathway, the concentration of this amino acid was maintained mainly by an increase in protein degradation and by a depletion in GSH concentration that may spare L-cysteine.

Effect of nitrous oxide and propofol on amino acid metabolism in neoplasic patients

In a randomized controlled clinical trial, 14 patients requiring resection of tumors were divided in two groups: one group was anesthetized with nitrous oxide [67% N2O-33% O2 (vol/vol)] and the other with propofol. Two other groups of subjects were studied: a group of patients that was undergoing orthopedic procedures and was anesthetized with nitrous oxide [67% N2O-33% O2 (vol/vol)] and a control group (fasted for 10 hrs and no anesthesia). In patients requiring resection of tumors, the blood L-methionine concentration was significantly lower and the blood amino acid pattern was significantly affected after the administration of nitrous oxide (120-310 mins) compared with values after the induction of anesthesia and before surgery. The administration of propofol (120-240 mins) did not produce any of these changes. No patients required blood transfusion during surgery, and the patients had not previously been treated with cancer chemotherapeutic agents. The administration of nitrous oxide (60-150 mins) to patients undergoing orthopedic procedures did not affect blood L-methionine. It is concluded that the administration of nitrous oxide to cancer-bearing patients, but not to those undergoing orthopedic surgery, produced major changes in amino acid metabolism; therefore, consideration should be given to the avoidance of exposure of cancer patients to nitrous oxide.

Microsomal function in biliary obstructed rats: effects of S-adenosylmethionine

BACKGROUND/AIMS

S-adenosylmethionine has been reported to have beneficial effects in the treatment of different chronic liver diseases and to protect against different hepatotoxic agents. The aim of this study was to investigate whether S-adenosylmethionine treatment might contribute to improved microsomal function in chronically biliary obstructed rats.

METHODS

Secondary biliary cirrhosis was induced by 28 days of bile duct obstruction. Groups of control and cirrhotic animals received S-adenosylmethionine (10 mg/kg per day) through the experimental period.

RESULTS

Bile duct obstruction resulted in a marked increase in lipid peroxidation levels and decreases in glutathione concentration, microsomal membrane fluidity, microsomal cytochrome P-450 content, NADPH-cytochrome P-450 reductase activity and the activities of the aniline hydroxylase, aminopyrine demethylase and ethoxycoumarin deethylase. Reductions in glutathione and cytochrome P-450 concentration were not corrected by S-adenosylmethionine, but lipid peroxidation, the decrease in the activities of the various microsomal monooxygenases and the reduction in microsomal membrane fluidity were partially prevented. A significant relationship was found between membrane fluidity and aniline hydroxylase, aminopyrine demethylase or ethoxycoumarin deethylase activities.

CONCLUSIONS

S-adenosylmethionine administration partially preserves microsomal function. This effect could be associated to the protection of membrane function by restoring transmethylation reactions.

Triiodothyronine does not affect the average incorporation of L-[35S]methionine in rat brain structures

The autoradiographic method with L-[35S]methionine was used to examine the effect of acute administration of L-triiodothyronine on local rates of brain protein synthesis in free-moving adult rats. Triiodothyronine was given intraperitoneally at doses of 12.5 or 25 micrograms kg-1. It did not modify the rate of plasma methionine incorporation in the 40 brain regions examined, despite a 4- to 8-fold increase of plasma free triiodothyronine levels. Biochemical analysis confirmed that triiodothyronine (25 micrograms kg-1) had no apparent effect on the overall rate of protein synthesis in the brain as a whole. These results suggest that changes in the circulating levels of thyroid hormones do not exert a general and direct metabolic effect in brain of intact adult rats.