Plasma Cystine Levels Research Articles

SAR of L-ABBA analogs for GGT1 inhibitory activity and L-ABBA's effect on plasma cysteine and GSH species

Gamma-glutamyl transferase 1 (GGT1) is a critical enzyme involved in the hydrolysis and/or transfer of gamma-glutamyl groups of glutathione, which helps maintain cysteine levels in plasma. In this study, we synthesized L-ABBA analogs to investigate their inhibitory effect on GGT1 hydrolysis and transpeptidase activity, with the goal of defining the pharmacophore of L-ABBA. Our structure–activity relationship (SAR) study revealed that an α-COO- and α-NH3+ group, as well as a two-CH2 unit distance between α-C and boronic acid, are essential for the activity. The addition of an R (alkyl) group at the α-C reduced the activity of GGT1 inhibition, with L-ABBA being the most potent inhibitor among the analogs. Next, we investigated the impact of L-ABBA on plasma levels of cysteine and GSH species, with the expectation of observing reduced cysteine levels and enhanced GSH levels due to its GGT1 inhibition. We administered L-ABBA intraperitoneally and determined the plasma levels of cysteine, cystine, GSH, and GSSG using LCMS. Our results showed time- and dose-dependent L-ABBA changes in total plasma cysteine and GSH levels. This study is the first to demonstrate the regulation of plasma thiol species upon GGT1 inhibition, with plasma cystine levels reduced by up to ∼ 75 % with L-ABBA (0.3 mg/dose). Cancer cells are highly dependent on the uptake of cysteine from plasma for maintaining high levels of intracellular glutathione. Thus, our findings suggest that GGT1 inhibitors, such as L-ABBA, have the potential to be used in GSH reduction thereby inducing oxidative stress in cancer cells and reducing their resistance to many chemotherapeutic agents.

High Plasma Cystine Levels Are Associated with Blood Pressure and Reversed by CPAP in Patients with Obstructive Sleep Apnea.

Obstructive sleep apnea (OSA) independent of obesity (OBS) imposes severe cardiovascular risk. To what extent plasma cystine concentration (CySS), a novel pro-oxidative vascular risk factor, is increased in OSA with or without OBS is presently unknown. We therefore studied CySS together with the redox state and precursor amino acids of glutathione (GSH) in peripheral blood mononuclear cells (PBMC) in untreated male patients with OSA (apnea-hypopnea-index (AHI) > 15 h−1, n = 28) compared to healthy male controls (n = 25) stratifying for BMI ≥ or < 30 kg m−2. Fifteen OSA patients were reassessed after 3–5-months CPAP. CySS correlated with cumulative time at an O2-saturation <90% (Tu90%) (r = 0.34, p < 0.05) beside BMI (r = 0.58, p < 0.001) and was higher in subjects with “hypoxic stress” (59.4 ± 2.0 vs. 50.1 ± 2.7 µM, p < 0.01) defined as Tu90% ≥ 15.2 min (corresponding to AHI ≥ 15 h−1). Moreover, CySS significantly correlated with systolic (r = 0.32, p < 0.05) and diastolic (r = 0.31, p < 0.05) blood pressure. CPAP significantly lowered CySS along with blood pressure at unchanged BMI. Unexpectedly, GSH antioxidant capacity in PBMC was increased with OSA and reversed with CPAP. Plasma CySS levels are increased with OSA-related hypoxic stress and associated with higher blood pressure. CPAP decreases both CySS and blood pressure. The role of CySS in OSA-related vascular endpoints and their prevention by CPAP warrants further studies.

MP43-05 ENZYMATIC LOWERING OF PLASMA CYSTINE PREVENTS FORMATION AND GROWTH OF STONES IN A MOUSE MODEL OF CYSTINURIA UNDER DEHYDRATION CHALLENGE

You have accessJournal of UrologyStone Disease: Medical & Dietary Therapy (MP43)1 Apr 2020MP43-05 ENZYMATIC LOWERING OF PLASMA CYSTINE PREVENTS FORMATION AND GROWTH OF STONES IN A MOUSE MODEL OF CYSTINURIA UNDER DEHYDRATION CHALLENGE Giulia Agnello, Jason Wiggins, Silvia Ferrati, Anthony Quinn, Scott Rowlinson, and J Stuart Wolf* Giulia AgnelloGiulia Agnello More articles by this author , Jason WigginsJason Wiggins More articles by this author , Silvia FerratiSilvia Ferrati More articles by this author , Anthony QuinnAnthony Quinn More articles by this author , Scott RowlinsonScott Rowlinson More articles by this author , and J Stuart Wolf*J Stuart Wolf* More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000898.05AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Cystinuria is an autosomal recessive disease caused by mutations in the SLC3A1 and/or SLC7A9 dibasic amino acid transporter genes. The defective reabsorption of dibasic amino acids filtered by the glomerulus leads to high urine cystine content, subsequent cystine crystallization and the formation of upper tract urinary calculi, with recurrent stone passages and/or need for multiple procedural interventions. Symptomatic stone events include severe abdominal pain, hydronephrosis, hematuria, infective syndromes and chronic pain. Although high fluid intake remains a cornerstone of therapy, this regimen is inadequate at reaching the target cystine urine concentration owing to poor compliance, periods of increased fluid loss (fever, diarrhea/vomiting, high ambient temperature; PMID:16001591, 7996811) or impact on quality of life (e.g. nocturia and increased day time micturition frequency). We are developing a highly novel approach for the treatment of cystinuria patients that works by reducing cystine delivery into the kidney tubules through enzymatic lowering of plasma cystine. Herein, we investigated the therapeutic potential of this approach to prevent cystine stone formation in dehydration prone environments. METHODS: We used a murine model of cystinuria (SLC3A1-/-) that develops cystine stones in the kidneys and bladder (PMID:28165480) and rationed water to 65% to model dehydration conditions. During water rationing, mice were dosed with a human enzyme with novel activity for cystine. Stone burden in the kidneys and bladder was assessed by microcomputed tomography, and plasma and urine cystine concentration was monitored over time. RESULTS: Enzymatic reduction of plasma cystine prevented stone formation and growth in the kidneys and bladder, even under dehydration challenge. Lowering of plasma cystine resulted in reduction of cystine concentration in urine despite temporary dehydration. CONCLUSIONS: This study provides proof of concept that enzymatic lowering of plasma cystine levels is effective at reducing the cystine concentration in the urine in a mouse model of cystinuria in temporary dehydration conditions, and prevents formation and growth of cystine stones. Enzymatic lowering of plasma cystine warrants further investigation as a new potential approach for disease management of cystinuric patients unresponsive or intolerant to current treatment, or facing quality of life factors that impact the ability to comply with current treatment approaches. Source of Funding: This study was funded by Aeglea BioTherapeutics, Inc. © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e648-e649 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Giulia Agnello More articles by this author Jason Wiggins More articles by this author Silvia Ferrati More articles by this author Anthony Quinn More articles by this author Scott Rowlinson More articles by this author J Stuart Wolf* More articles by this author Expand All Advertisement PDF downloadLoading ...

P3648Plasma glutamate are increased in non-smoker patients with vasospastic angina pectoris and associated with plasma cystine and antioxidant capacity

Abstract Background Endothelial dysfunction of the coronary arteries caused by oxidative stress plays an important role in the pathogenesis of vasospastic angina pectoris (VSAP). Glutamate, a non-essential amino acid, exerts endothelial dysfunction by oxidative stress production through N-methyl-D-aspartate receptor activation. Besides oxidative stress, decrease of antioxidant may be responsible for endothelial dysfunction. Glutathione (GSH), an important antioxidant, is synthesized from imported cystine through the cystine/glutamate antiporter system (XC-) in association with the export of glutamate. Glutamate also competitively inhibits cystine import into the endothelial cells through the XC-leading to GSH depletion. Thus the extracellular glutamate and cystine are crucial for the intracellular redox status. However, it remains unclear whether glutamate and/or cystine are implicated in the pathogenesis of VSAP. As smoking induces powerful oxidant stresses in the whole body, we investigated plasma glutamate, cystine, oxidative stress markers and antioxidant capacity in non-smoker patients with VSAP. Methods and results Sixty-two consecutive non-smoker patients suspected having VSAP were performed coronary angiograms (CAG). Forty-nine patients who did not show any significant coronary stenosis (&lt;50%) were performed the intracoronary acetylcholine provocation test. Patients were categorized into the VSAP-positive group (n=27) and the VSAP-negative group (n=22) on the basis of test results. Blood samples were collected from the femoral sheath before the CAG. Plasma glutamate, cystine, nitrotyrosine (NT), reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP) were measured. The levels of plasma glutamate and cystine in the VSAP-positive group were significantly higher than those in the VSAP-negative group (59.8±25.7 vs 43.5±18.7 nmol/L, p=0.0054, and 35.3±14.2 nmol/L vs 25.2±9.1 nmol/L, p=0.0018, respectively). The levels of plasma glutamate showed significant and positive association with the levels of plasma cystine (r=0.40, p=0.005). There were no significant differences in the levels of NT and d-ROMs as oxidative stress markers, and BAP as an antioxidant capacity between the two groups, respectively. However, the levels of plasma glutamate showed significant and negative association with BAP values (r=−0.3, p=0.038). Conclusions Plasma levels of glutamate were increased in non-smoker patients with VSAP and positively associated with plasma cystine levels and negatively associated with antioxidant capacity, suggesting that plasma glutamate modulate plasma cystine levels and antioxidant capacity through the XC- inhibition, and could be a novel risk factor of VSAP.

Plasma Cystine and Nitrite Levels are Synergistic Determinants of Arterial Stiffness and Mortality in Heart Failure

Background Endothelial dysfunction plays a key role in heart failure with reduced ejection fraction (HFrEF) pathogenesis, and is determined via the balance between oxidative stress (OS) and nitric oxide (NO) bioavailability. Higher cystine levels indicate increased OS. Nitrite is a major oxidative metabolite of NO. We sought to examine the relationship between OS, NO metabolism and vascular function, and their association with clinical outcomes in HFrEF patients. Methods Cystine, nitrite and vascular function were measured in 130 HFrEF patients (mean age: 54.6 ± 12.7 yrs, 59.2% black, 48.5% female). Plasma cystine was quantified by high performance liquid chromatography. Plasma nitrite was determined by ion chromatography (ENO20 Analyzer, Eicom). Arterial stiffness was assessed as Augmentation index (Aix) using pulse wave analysis (SphygmoCor, AtCor Medical). Patients were categorized by median cystine (97.39 μM) and nitrite (0.26 μM) values. Linear regression was used to determine the association between cystine, nitrite and Aix, adjusting for age, gender, race, height, weight and mean arterial pressure. Cox regression was used to estimate the association of cystine, nitrite and Aix, with all-cause mortality, adjusting for age, gender, race, BNP and history of MI. Results: Cystine, nitrite and Aix Patients with higher levels of both cystine and nitrite (>median, n=31) had higher Aix (adjusted β =5.7, p=0.006, mean Aix= 27.6 ± 10.3) than those that had either elevated cystine (n=33) (p=0.1, mean Aix= 21.4 ± 7.9) or nitrite (n=33) (p=0.5, mean Aix= 18.9 ± 10.3), or neither (n=33) (P=0.9, mean Aix=22.1 ± 1.0). Cystine, nitrite and mortality There were 14 deaths during a median follow up of 375 (IQR 188.5, 696) days. Patients with higher levels of both cystine and nitrite (>median) had a higher mortality (adjusted HR=15.2, 95% CI: 1.8-129.7, p=0.01) than those with elevation of either cystine or nitrite, or neither (Figure 1). Cystine did not correlate with BNP (p=0.2), while nitrite had a weak positive correlation with BNP (r=0.21, p=0.04). Aix and mortality Higher Aix tended to be associated with mortality (adjusted HR: 1.2, 95% CI: 1.0-1.3, p=0.06), but was not a significant predictor when cystine and nitrite were added to the model (adjusted HR: 1.1, 95% CI: 0.9-1.2, p=0.5). Conclusions Higher levels of OS and NO metabolites are synergistic determinants of arterial stiffness, and are independent determinants of mortality in HFrEF even after adjusting for BNP.

Plasma Cystine Levels and Cardiovascular and All-Cause Mortality in Hemodialysis Patients.

Oxidative stress accelerates the development of cardiovascular disease. Plasma cystine, a thiol oxidative stress marker, is related to several established factors for cardiovascular disease risk and prognosis. Although a comprehensive oxidative stress index is clinically required for hemodialysis patients with high oxidative stress, there are few reports concerning thiol oxidative stress markers predicting their prognosis. We investigated the relationship between plasma amino acids including cystine levels and cardiovascular disease-related and all-cause mortality in 132 maintenance hemodialysis patients. Higher cystine levels were associated with old age, longer hemodialysis duration, hemodialysis-associated hypotension, higher cardiothoracic ratio, higher blood urea nitrogen, and lower ankle-brachial index. Multivariate Cox regression analysis revealed that high plasma cystine was independently related with both cardiovascular disease mortality and all-cause mortality. Thus, high plasma cystine levels predict the prognosis of hemodialysis patients. High cystine levels necessitate a careful investigation for the cause of oxidative stress and comorbidities like vascular injury.

Cystinosis as a lysosomal storage disease with multiple mutant alleles: Phenotypic-genotypic correlations.

Cystinosis is an autosomal recessive lysosomal storage disease with an unclear enzymatic defect causing lysosomal cystine accumulation with no corresponding elevation of plasma cystine levels leading to multisystemic dysfunction. The systemic manifestations include a proximal renal tubular defect (Fanconi-like), endocrinal disturbances, eye involvements, with corneal, conjunctival and retinal depositions, and neurological manifestations in the form of brain and muscle dysfunction. Most of the long-term ill effects of cystinosis are observed particularly in patients with long survival as a result of a renal transplant. Its responsible CTNS gene that encodes the lysosomal cystine carrier protein (cystinosin) has been mapped on the short arm of chromosome 17 (Ch17 p13). There are three clinical forms based on the onset of main symptoms: nephropathic infantile form, nephropathic juvenile form and non-nephropathic adult form with predominant ocular manifestations. Avoidance of eye damage from sun exposure, use of cystine chelators (cysteamine) and finally renal transplantation are the main treatment lines. Pre-implantation genetic diagnosis for carrier parents is pivotal in the prevention of recurrence.

Preclinical antitumor activity, pharmacokinetics and pharmacodynamics of imexon in mice

Imexon, a novel pro-oxidant, thiol-binding agent, is currently in phase I/II clinical trials in patients with advanced solid tumors. The aim of this study was to characterize the preclinical pharmacology of imexon in vivo. We investigated the anticancer activity of imexon in several cancer cell lines grown as xenografts in severe combined immunodeficient mice. Imexon was active against both hematologic and solid tumor types. The maximally tolerated dose, at the selected dosing schedule, was 150 mg/kg. Using the maximally tolerated dose of imexon, we sought to identify a potential pharmacodynamic biomarker to monitor the mechanistic effect systemically. As imexon binds cellular thiols in vitro, thiol depletion by imexon in vivo was evaluated as a potential biomarker. Following a single 150 mg/kg dose of imexon by intraperitoneal injection, glutathione levels decreased by 40% at 3 h in mouse erythrocytes. In mouse plasma, imexon treatment led to a significant decrease in cystine levels 2-4 h after drug administration. Notably, by this time, free imexon plasma levels were nondetectable. By investigating the pharmacokinetics of imexon, we also found that imexon undergoes rapid clearance from plasma in a dose-independent fashion with a half-life of 12-15 min. In summary, imexon is active against several cancer types in vivo. Imexon also decreases circulating thiols and exhibits dose-independent pharmacokinetics in mice. Plasma cystine levels may represent a biomarker of imexon activity in vivo.

Lipoic Acid and Ascorbic Acid Affect Plasma Free Amino Acids Selectively in the Teleost Fish Pacu (Piaractus mesopotamicus)

Most studies on the antioxidants, lipoic acid (LA) and ascorbic acid (AA), focused on species that, unlike teleost fish, are not scurvy-prone, and are able to synthesize AA. The antioxidant properties of LA may make it useful in aquaculture nutrition, but several effects must first be investigated, and we address here plasma free amino acids (FAA). In mammals, LA and AA in high doses were claimed to alter plasma FAA profile; to our knowledge, however, no data are available in fish. We therefore studied the effects of dietary LA and AA on plasma FAA in the South American teleost fish pacu, which is being used increasingly in aquaculture. LA treatment decreased concentrations of 18 of 23 individual FAA; specifically, dispensable and total FAA were significantly affected. Ornithine was elevated (+26%) in LA-treated fish and significantly decreased ratios of plasma [Arg]/[Orn] and other individual [FAA]/[Orn] were observed. LA and AA both affected sulfur FAA concentrations. Plasma cystine levels were significantly increased in the LA-supplemented groups. AA had little effect on most amino acids, and no interaction with LA was detected. AA supplementation did, however, significantly lower taurine (-42%) and cystathionine (-31%) levels in plasma. No effect on the branched chain:aromatic amino acid ratios was observed. The data indicate that at the dietary level studied, LA and AA independently affect selected plasma FAA in pacu, and suggest that any use of LA in particular as a dietary supplement should take into account an altered plasma FAA profile.

Amino acids and asthma: a case-control study

Amino acids contribute to various anti-oxidant and immunological activities relevant to asthma pathogenesis, raising the possibility that differences in amino acids may be involved in asthma aetiology. The authors hypothesised that cystine reduces the risk of asthma via glutathione metabolism. Methionine, glutamine, glutamic acid and glycine may have potential protective effects, whilst arginine, phenylalanine and tryptophan may have adverse effects in asthma. Fasting plasma levels of amino acids were compared in a case-control study. A total of 89 adults, aged 18-65 yrs, with asthma controlled by inhaled corticosteroids, were recruited from a volunteer database and local primary care registers, and compared with 89 controls individually matched for age, sex and primary care centre. Contrary to the primary hypothesis, cases had higher fasting plasma cystine levels than controls, and there was no difference between cases and controls in any of the other amino acids tested, with the exception of plasma glycine, which was associated with a strongly reduced risk of asthma (odds ratio for the highest tertile compared to lowest 0.30 (95% confidence interval (0.11-0.82)). This study negates the hypothesis that higher fasting plasma cystine levels have a protective effect on the risk of asthma, although the inverse correlation with plasma glycine deserves further investigation.

Glutathione and immune function.

The immune system works best if the lymphoid cells have a delicately balanced intermediate level of glutathione. Even moderate changes in the intracellular glutathione level have profound effects on lymphocyte functions. Certain functions, such as the DNA synthetic response, are exquisitely sensitive to reactive oxygen intermediates and, therefore, are favoured by high levels of the antioxidant glutathione. Certain signal pathways, in contrast, are enhanced by oxidative conditions and favoured by low intracellular glutathione levels. The available evidence suggests that the lymphocytes from healthy human subjects have, on average, an optimal glutathione level. There is no indication that immunological functions such as resistance to infection or the response to vaccination may be enhanced in healthy human subjects by administration of glutathione or its precursor amino acid cysteine. However, immunological functions in diseases that are associated with a cysteine and glutathione deficiency may be significantly enhanced and potentially restored by cysteine supplementation. This factor has been studied most extensively in the case of human immunodeficiency virus (HIV)-infected patients who were found to experience, on average, a massive loss of S equivalent to a net loss of approximately 4 g cysteine/d. Two randomized placebo-controlled trials have shown that treatment of HIV-infected patients with N-acetyl-cysteine caused in both cases a significant increase in all immunological functions under test, including an almost complete restoration of natural killer cell activity. It remains to be tested whether cysteine supplementation may be useful also in other diseases and conditions that are associated with a low mean plasma cystine level and impaired immunological functions.

Hepatic export of glutathione and uptake of constituent amino acids, glutamate and cysteine, in broilers in vivo

This study was conducted to document the glutathione (GSH) cycle (interorgan circulation of GSH) in broilers in vivo. Two experiments were conducted on 36 anesthetized male broilers (n = 6 per treatment) implanted with cannulae in the carotid artery, hepatic portal, and hepatic veins. Plasma GSH, glutamate, cysteine, cystine, and cysteinylglycine levels in each vessel were monitored following a bolus injection [Experiment (Exp.) 1] or 30 min continuous infusion (Exp. 2) of GSH, or a gamma-glutamyltranspeptidase inhibitor (AT125) into the hepatic portal vein. Controls received saline alone. The GSH and AT125 treatments were used to determine the effect of increasing the prehepatic GSH load and of inhibiting systemic GSH degradation, respectively, on the GSH cycle. Hepatic export of GSH was clearly evident in all three treatment groups in both experiments (Exp.). The GSH and AT125 treatments raised amino acid levels in some or all of the vessels, whereas cysteinylglycine was elevated by AT125 and depressed by the GSH treatment compared to Controls. Hepatic uptake of glutamate, cysteine, and/or cystine was observed in Controls and GSH-treated birds, but not in birds given AT125 (Exp. 2). Neither hepatic export nor uptake of cysteinylglycine was observed in any treatment group. The results clearly demonstrate the ability of the avian liver to export GSH into the general circulation despite alterations that might arise from changes in extra-hepatic ability to utilize GSH or its constituent amino acids.

Role of cysteine and glutathione in signal transduction, immunopathology and cachexia.

Abnormally low plasma cystine levels have been found in the late asymptomatic stage of HIV infection and several other diseases associated with progressive loss of skeletal muscle mass. The phenomenon is commonly associated with a low NK cell activity, skeletal muscle wasting or muscle fatigue and increased rates of urea production. In its extreme form, the negative nitrogen balance leads to overt cachexia and is associated with severe debilitation and psychological stress. The low NK cell activity is in most cases not life-threatening but may be disasterous in HIV infection, because it may compromise the initially stable balance between immune system and virus and trigger disease progression. This review summarizes briefly (i) the role of cysteine in the physiological regulation of body cell mass and the development of skeletal muscle wasting, and (ii) the role of glutathione in the immune system.

Role of cysteine and glutathione in HIV infection and other diseases associated with muscle wasting and immunological dysfunction.

The combination of abnormally low plasma cystine and glutamine levels, low natural killer (NK) cell activity, skeletal muscle wasting or muscle fatigue, and increased rates of urea production defines a complex of abnormalities that is tentatively called "low CG syndrome." These symptoms are found in patients with HIV infection, cancer, major injuries, sepsis, Crohn's disease, ulcerative colitis, chronic fatigue syndrome, and to some extent in overtrained athletes. The coincidence of these symptoms in diseases of different etiological origin suggests a causal relationship. The low NK cell activity in most cases is not life-threatening, but may be disastrous in HIV infection because it may compromise the initially stable balance between the immune system and virus, and trigger disease progression. This hypothesis is supported by the coincidence observed between the decrease of CD4+ T cells and a decrease in the plasma cystine level. In addition, recent studies revealed important clues about the role of cysteine and glutathione in the development of skeletal muscle wasting. Evidence suggests that 1) the cystine level is regulated primarily by the normal postabsorptive skeletal muscle protein catabolism, 2) the cystine level itself is a physiological regulator of nitrogen balance and body cell mass, 3) the cyst(e)ine-mediated regulatory circuit is compromised in various catabolic conditions, including old age, and 4) cysteine supplementation may be a useful therapy if combined with disease-specific treatments such as antiviral therapy in HIV infection.

Cystine levels, cystine flux, and protein catabolism in cancer cachexia, HIV/SIV infection, and senescence.

Patients with skeletal muscle catabolism (cachexia) fail to conserve the skeletal muscle protein and release large amounts of nitrogen as urea. Previous studies suggest that the threshold for the conversion of amino acids into other forms of chemical energy and the concomitant production of urea are regulated by the plasma cystine level and hepatic cysteine catabolism. Studies of plasma amino acid exchange rates in the lower extremities now show that healthy young subjects regulate their plasma cystine level in a process that may be described as controlled constructive catabolism. The term controlled describes the fact that the release of cystine and other amino acids from the peripheral tissue is negatively correlated with (certain) plasma amino acid levels. The term constructive describes the fact that the release of cystine is correlated with an increase of the plasma cystine level. The regulation of the plasma cystine level is disturbed in conditions with progressive skeletal muscle catabolism including cancer, HIV infection, and old age. These conditions show also a low plasma glutamine:cystine ratio indicative of an impaired hepatic cystine catabolism. In HIV+ patients and SIV-infected macaques, a decrease of the plasma cystine level was found to coincide with the decrease of CD4+ T cells.

Role of Cysteine and Glutathione in HIV Infection and Cancer Cachexia: Therapeutic Intervention with N-Acetylcysteine

Publisher Summary Massive loss of skeletal muscle mass (cachexia) is sign of HIV infection, sepsis, and trauma, and a cause of death among cancer patients. In HIV infection, the immunological dysfunction develops progressively into a severe condition called acquired immunodeficiency syndrome. Increasing evidence suggests that an abnormal cysteine and glutathione metabolism plays a decisive role in the development of catabolic conditions and associated immunological dysfunctions. This chapter gives a conceptual overview; the chances for a therapeutic intervention with cysteine derivatives such as N-acetylcysteine (NAC) and the methodological aspects. The agenda is to identify abnormal biochemical patterns in different catabolic diseases and conditions, abnormal biochemical parameters that are significantly correlated with mortality, disease progression, and weight loss, to prove cause-and-effect relationships by experimental intervention, to develop and optimize interventive strategies that may be suitable for clinical therapy, and to test new therapeutic strategies in clinical trials. Discussed are the elevated venous plasma glutamate levels as universal marker for catabolic and precatabolic conditions—evidences for an impairment of muscular membrane transport activities, abnormal cysteine catabolism and glutathione level in skeletal muscle tissue, and the pathological significance of decreased membrane transport activity and elevated venous plasma glutamate levels. There is discussion on “Push” and “Pull” mechanisms in catabolic and precatabolic processes, decreased plasma cystine levels and evidence for “Push” and “Pull” mechanisms in sepsis, HIV Infection, and other malignant diseases, abnormally low plasma cystine and glutamine levels in patients with chronic fatigue syndrome (CFS), and the hypothetical mechanism of the “pull” condition—evidence for an abnormal cysteine and glutathione metabolism in liver. Noted are the immunological implications—cysteine deficiency and immunological dysfunction, abnormal glutathione levels in HIV Infection, and redox regulation by glutathione and glutathione disulfide. Also, there are details on the therapeutic intervention with a cysteine derivative: effects of long-term treatment with N-acetylcysteine.

Influence of betaine on blood metabolites of Alpine and Angora kids

Five Angora and five Alpine kids (average BW = 12.1 ± 1.6 kg and age = 120 ± 5 days) were fitted with indwelling jugular catheters to study the effect of betaine on plasma methionine and related metabolites. Betaine (0, 0.1, 0.2, 0.5 g kg −1 BW) was administered as a single injection. Blood samples were taken −30, 0, 10, 30, 50, 70 and 90 min post-injection. Alpine kids had higher initial levels of plasma methionine than Angora kids (29.0 vs. 21.3 μM; P < 0.05). There were differences in utilization of betaine between the two goat breeds. Plasma methionine of Alpine kids increased 10 min after injection of 0.1 or 0.2 g betaine kg −1 BW (34.7 μM; P < 0.05) whereas 0.2 g betaine kg −1 BW was required to increase plasma methionine in Angora kids (23.2 μM; P < 0.10). Betaine did not affect plasma cystine or cystathionine levels although cystine was higher in Alpine kids than in Angora kids (44.4 vs. 22.9 μM; P < 0.05). Plasma s-adenosylhomocysteine and glycine were increased 30 min after injection of 0.2 g betaine kg −1 BW in both breeds (2.9 vs. 6.0 and 659 vs. 821 μM; P < 0.05 for Alpine, 2.1 vs. 5.1 and 846 vs. 920 μM; P < 0.05 for Angora, respectively). The only other amino acid that was affected was serine, which increased 70 min after betaine injection. There were no differences in plasma triglycerides between breeds (17.5 mg dl −1), and injection of betaine (0.2 g kg −1 BW) did not change its level. An overloading effect was observed with 0.5 g betaine kg −1 BW in both breeds, that led to lack of changes in methionine level. This study indicated that increased plasma methionine level may not only be due to remethylation of homocysteine, but betaine may also spare methionine by substituting for it in some metabolic processes. Betaine supplementation may have positive effects on animal production by increasing amount of methionine available for fiber, milk or meat protein synthesis; however, this needs to be further investigated.

Nutritional responses in wool growth by four Merino genotypes of differing wool growth performance

Sheep from four Merino flocks, different in annual clean fleece production when grazed together, were offered a range of nutritional treatments to compare their ability to digest dietary organic matter (experiment 1) and to compare the relationships of wool growth and fibre diameter with nutrient intake (experiment 2). The sheep were selected from a finewool (Fl), a strong wool (S), and two medium-Peppin (MP6 and MP10) flocks. The nutritional treatments varied intakes of two pelleted diets-B and F. Diet B consisted of oat grain, lucerne chaff, and oaten straw, while diet F was as for B but fortified with fishmeal. The digestibility of both diets was negatively related to the level of intake, and there were some differences between the flocks in their ability to digest organic matter. Clean wool growth per unit area of skin was curvilinearly related (P &lt; 0.001) to N intake, but was not influenced by diet per se. The regression coefficient for the relationship of clean wool growth with N intake and the estimated maximum wool growth rate of flock F1 were less than the other flocks. However, flock MP10 grew less wool than flocks S and MP6 at any given intake. Variation in (fibre diameter)2 accounted for 0.6 of the variation in wool growth, with responses in fibre diameter to intake being similar to those observed in wool growth. The responses in plasma cystine of the flocks to N intake differed, with the relationship for flock F1 being curvilinear and reaching a maximum at an intake of 27 g N day-1, while the responses of the other flocks were essentially linear. The relationships between plasma cystine level and wool growth differed between the flocks such that wool growth of sheep from flocks S and MP6 was more responsive to increased plasma concentration of cystine.

Plasma Amino Acid Dysregulation after Lentiviral Infection

The absence of AIDS-like symptoms in HIV-infected chimpanzees and SIV-infected African Green monkeys (AGMs) may provide important clues about the pathogenic mechanism of AIDS and about mechanisms of resistance. HIV-infected persons and SIV-infected rhesus macaques have, on the average, markedly decreased cysteine, cystine, and glutathione levels and elevated plasma glutamate concentrations. Glutamate inhibits the membrane transport of cystine and a combination of low plasma glutamate and high cystine levels was found to be correlated with high CD4+ T cell numbers even in HIV-negative healthy human individuals. We have now found that glutamate and cystine levels are also correlated with CD4+ T cell numbers in chimpanzees. But infection of chimpanzees, AGMs, and goats with HIV-1, SIV, and caprine arthritis encephalitis virus (CAEV), respectively, does not induce significant changes in plasma cystine or glutamate levels, although infected AGMs and goats have, on the average, significantly elevated plasma levels of the biochemically related amino acid proline.

Effect of modulators of glutathione synthesis on the hepatotoxicity of 2-methylfuran

Treatment of male Sprague-Dawley rats with buthionine sulfoximine (BSO), prior to administration of carbon-14( 14C)-labelled 2-methylfuran (2MF) caused a marked decrease in the covalent binding of 14C-labelled 2MF metabolites to both DNA and protein, although there was no apparent change in the distribution of the labelled parent 2MF. BSO pretreatment also protected against hepatotoxicity of 2MF, as indicated by lower serum glutamic pyruvic transaminase (GPT) levels. Pretreatment with BSO offered protection only if administered 1.5 hr before 2MF dosage. Administration of 2MF, 4 and 6 hr after BSO resulted in manifestation of the hepatotoxicity of 2MF. Prior treatment with diethylmaleate (DEM), increased covalent binding of [ 14C]2MF to liver proteins and also elevated serum GPT levels. Thus, depletion of tissue glutathione (GSH) by two different chemicals acting by different mechanisms produced opposite effects on the covalent binding and toxicity of 2MF. Pretreatment with L-2-oxothiazolidine-4-carboxylate (OTZ), a promoter of GSH biosynthesis, increased the hepatic covalent binding of [ 14C]2MF and potentiated hepatotoxicity. However, administration of OTZ and BSO prior to an i.p. dose of 100 mg/kg of 2MF, decreased the hepatic covalent binding of [ 14C]2MF and decreased the hepatotoxicity. The marked instability of the GSH conjugate of the reactive metabolite of 2MF may account for the potentiation of hepatotoxicity of 2MF by OTZ. A single s.c. dose of BSO, caused a transient increase in plasma cystine levels concurrent with the depletion of liver GSH. Administration of 2MF, 1.5 hr after BSO, significantly decreased plasma cystine levels as compared to control animals that received vehicle alone. Pretreatment with BSO also resulted in increased excretion of urinary metabolites in 2MF treated animals as compared to animals receiving 2MF alone. Thus, BSO probably protects against hepatoxicity of 2MF by indirectly causing more detoxification of the reactive metabolite of 2MF, as it does not alter the distribution of unmetabolized 2MF and does not have any apparent effect on the microsomal mixed-function oxidase which mediates the activation of 2MF. The enhanced detoxification of 2MF in BSO treated animals appears independent of the depleted GSH levels; it may result from increased availability of a better alternative nucleophile (i.e. cysteine), capable of conjugating with acetyl acrolein. Acetyl acrolein (AA) appears to be the principal reactive metabolite of 2MF which binds covalently to tissues. Previous in vitro studies have shown that cysteine is a better trapping agent of AA than GSH or N-acetyl cysteine.