Carnosine synthase deficiency is compatible with normal skeletal muscle and olfactory function but causes reduced olfactory sensitivity in aging mice

Carnosine (β-alanyl-l-histidine) and anserine (β-alanyl-3-methyl-l-histidine) are abundant peptides in the nervous system and skeletal muscle of many vertebrates. Many in vitro and in vivo studies demonstrated that exogenously added carnosine can improve muscle contraction, has antioxidant activity, and can quench various reactive aldehydes. Some of these functions likely contribute to the proposed anti-aging activity of carnosine. However, the physiological role of carnosine and related histidine-containing dipeptides (HCDs) is not clear. In this study, we generated a mouse line deficient in carnosine synthase (Carns1). HCDs were undetectable in the primary olfactory system and skeletal muscle of Carns1-deficient mice. Skeletal muscle contraction in these mice, however, was unaltered, and there was no evidence for reduced pH-buffering capacity in the skeletal muscle. Olfactory tests did not reveal any deterioration in 8-month-old mice lacking carnosine. In contrast, aging (18-24-month-old) Carns1-deficient mice exhibited olfactory sensitivity impairments that correlated with an age-dependent reduction in the number of olfactory receptor neurons. Whereas we found no evidence for elevated levels of lipoxidation and glycation end products in the primary olfactory system, protein carbonylation was increased in the olfactory bulb of aged Carns1-deficient mice. Taken together, these results suggest that carnosine in the olfactory system is not essential for information processing in the olfactory signaling pathway but does have a role in the long-term protection of olfactory receptor neurons, possibly through its antioxidant activity.

Impaired mucociliary motility enhances antigen-specific nasal IgA immune responses to a cholera toxin-based nasal vaccine

Nasal mucosal tissues are equipped with physical barriers, mucus and cilia, on their surface. The mucus layer captures inhaled materials, and the cilia remove the inhaled materials from the epithelial layer by asymmetrical beating. The effect of nasal physical barriers on the vaccine efficacy remains to be investigated. Tubulin tyrosine ligase-like family, member 1 (Ttll1) is an essential enzyme for appropriate movement of the cilia on respiratory epithelium, and its deficiency (Ttll1-KO) leads to mucus accumulation in the nasal cavity. Here, when mice were intra-nasally immunized with pneumococcal surface protein A (PspA, as vaccine antigen) together with cholera toxin (CT, as mucosal adjuvant), Ttll1-KO mice showed higher levels of PspA-specific IgA in the nasal wash and increased numbers of PspA-specific IgA-producing plasma cells in the nasal passages when compared with Ttll1 hetero (He) mice. Mucus removal by N-acetylcysteine did not affect the enhanced immune responses in Ttll1-KO mice versus Ttll1-He mice. Immunohistological and flow cytometry analyses revealed that retention time of PspA in the nasal cavity in Ttll1-KO mice was longer than that in Ttll1-He mice. Consistently, uptake of PspA by dendritic cells was higher in the nasopharynx-associated lymphoid tissue (NALT) of Ttll1-KO mice than that of Ttll1-He mice. These results indicate that the ciliary function of removing vaccine antigen from the NALT epithelial layer is a critical determinant of the efficacy of nasal vaccine.

Characterization of a Bacillus subtilis surfactin synthetase knockout and antimicrobial activity analysis

Gene knockout is an important approach to improve the production of antimicrobial compounds. B. subtilis PB2-LS10, derived from B. subtilis PB2-L by a surfactin synthetase (srf) genes knockout, exhibits stronger inhibitory action than its parental strain against all tested pathogenic bacteria and fungi. The antimicrobial extracts produced by B. subtilis PB2-L and B. subtilis PB2-LS10 respectively were characterized by the high-resolution LC-ESI-MS. To provide further insight into the distinct antimicrobial activities, we investigated the impact of the srf genes deletion on the growth and gene transcriptional profile of the strains. The mutant strain grew quickly and reached stationary phase 2h earlier than the wild-type. Prominent expression changes in the modified strain involved genes that were essential to metabolic pathways and processes. Genes related to amino acid transport, ATP-binding cassette (ABC) transporters and protein export were up-regulated in strain PB2-LS10. However, amino acid metabolism, carbohydrate metabolism and fatty acid metabolism were repressed. Because of its excellent antimicrobial activity, strain PB2-LS10 has potential for use in food preservation.

Thymidine and hypoxanthine protection patterns of the folic acid-enhanced synergies for combinations of trimetrexate plus a polyglutamylatable inhibitor of purine or thymidylate synthesis against human ileocecal HCT-8 cells

In order to examine the intracellular locus of the folic acid (PteGlu)-enhanced synergies of trimetrexate (TMQ) plus the thymidylate synthase (TS) inhibitor, raltitrexed (RTX), and TMQ plus the glycinamide ribonucleotide formyltransferase (GARFT) inhibitor, AG2034, comprehensive protection studies with thymidine (dThd) and hypoxanthine (HX) were conducted in a 96-well plate cell growth inhibition (sulforhodamine B) assay. Current modeling techniques were extended to characterize these protection patterns involving multiple-agent interaction. Wild-type human ileocecal HCT-8 cells and DW2, a subline deficient in folylpoly-gamma-glutamate synthetase (FPGS) were individually treated for 96 h with TMQ, AG2034 and a 1:1 mixture of TMQ:AG2034 or with TMQ, RTX, and a 1:1 mixture of TMQ:RTX in the presence of PteGlu (2.3 or 40 micro M) and the protection agents (10 micro M dThd and/or 100 micro M HX). Drug treatments were randomly assigned to wells. Both isobols and 3-dimensional concentration-effect surfaces were used to assess the nature and the intensity of drug interactions. The structural Hill model was fitted to data with weighted non-linear regression for most cases. A so-called 'double Hill' model was sometimes more appropriate when a plateau in the middle of the concentration-effect curve was found. In HCT-8 and DW2 cells at 2.3 and 40 micro M PteGlu, inhibition of DHFR by TMQ induced antithymidylate and antipurine effects; AG2034 and RTX selectively inhibited de novo purine or thymidine synthesis, respectively. dThd protection increased the PteGlu-enhancement of the TMQ + AG2034 synergy, whereas HX protection increased the PteGlu-enhancement of the TMQ + RTX synergy. The PteGlu-enhanced synergies of TMQ + AG2034 and TMQ + RTX occur primarily through inhibition of purine synthesis and inhibition of thymidylate synthesis, respectively. These results further substantiate the hypothesis that the nonpolyglutamylatable DHFR inhibitor, TMQ, acts as a modulator by decreasing the protection by PteGlu of cells against the polyglutamylatable AG2034 and RTX.

Identification of ubiquitin ligases required for skeletal muscle atrophy

Skeletal muscle adapts to decreases in activity and load by undergoing atrophy. To identify candidate molecular mediators of muscle atrophy, we performed transcript profiling. Although many genes were up-regulated in a single rat model of atrophy, only a small subset was universal in all atrophy models. Two of these genes encode ubiquitin ligases: Muscle RING Finger 1 (MuRF1), and a gene we designate Muscle Atrophy F-box (MAFbx), the latter being a member of the SCF family of E3 ubiquitin ligases. Overexpression of MAFbx in myotubes produced atrophy, whereas mice deficient in either MAFbx or MuRF1 were found to be resistant to atrophy. These proteins are potential drug targets for the treatment of muscle atrophy.

The salicylate-derived mycobactin siderophores of Mycobacterium tuberculosis are essential for growth in macrophages

Mycobacterium tuberculosis is an important pathogen of mammals that relies on 2-hydroxyphenyloxazoline-containing siderophore molecules called mycobactins for the acquisition of iron in the restrictive environment of the mammalian macrophage. These compounds have been proposed to be biosynthesized through the action of a cluster of genes that include both nonribosomal peptide synthase and polyketide synthase components. One of these genes encodes a protein, MbtB, that putatively couples activated salicylic acid with serine or threonine and then cyclizes this precursor to the phenyloxazoline ring system. We have used gene replacement through homologous recombination to delete the mbtB gene and replace this with a hygromycin-resistance cassette in the virulent strain of M. tuberculosis H37Rv. The resulting mutant is restricted for growth in iron-limited media but grows normally in iron-replete media. Analysis of siderophore production by this organism revealed that the biosynthesis of all salicylate-derived siderophores was interrupted. The mutant was found to be impaired for growth in macrophage-like THP-1 cells, suggesting that siderophore production is required for virulence of M. tuberculosis. These results provide conclusive evidence linking this genetic locus to siderophore production.

Cross-resistance studies of folylpolyglutamate synthetase-deficient, methotrexate-resistant CCRF-CEM human leukemia sublines

CCRF-CEM human leukemia sublines resistant to short-term methotrexate (MTX) exposure as a result of decreased folylpolyglutamate synthetase (FPGS) activity were examined for their response to other cytotoxic agents. The R3/7 and R30dm sublines display 25 and 1%, respectively, of the FPGS activity of CCRF-CEM cells as measured with MTX in vitro. Response to agents in outgrowth experiments was examined under both continuous exposure (120 h, where MTX resistance is not observed) and short-term (6-14.5 h) exposure. During continuous exposure to various classes of agents, cross-resistance of R3/7 and R30dm that correlated with FPGS level was not observed, although some minor (< or = 3-fold) stochastic variations in sensitivity were noted. These agents included actinomycin D, Adriamycin, etoposide, vincristine, cisplatin, cytosine arabinoside, 5-fluorouracil, and some other antifolates. Cross-resistance during continuous exposure that did correlate with FPGS level was noted, however, to glutamate-containing thymidylate synthase inhibitors (including ICI D1694) and, to a minor extent, to 6-mercaptopurine and 5-fluorodeoxyuridine. Slight collateral sensitivity during continuous exposure that apparently correlated with FPGS level was noted to the lipid-soluble antifolate trimetrexate and to 5,8-dideazapteroyl-L-ornithine, an FPGS-specific inhibitor. In short-term exposures (where MTX resistance of the sublines is observed), the resistant sublines displayed sensitivity or cross-resistance to each agent that was qualitatively similar to that observed for the same agent in continuous exposure. Because of the requirement for reduced folates in the anti-DNA mechanism of action of fluoropyrimidines and the current clinical use of leucovorin (LV) to enhance their effects, the interaction of LV and fluoropyrimidines was examined. The results suggest that even highly FPGS-deficient cells are as sensitive to the effects of LV modulation as are wild-type cells even at fluoropyrimidine exposure times as short as 4 h.

Gamma-glutamylcysteine synthetase deficiency and hemolytic anemia

gamma-Glutamylcysteine synthetase is one of the enzymes of glutathione (GSH) synthesis. A deficiency of this enzyme has been found only once previously in humans: it was associated with spinocerebellar degeneration and hemolytic anemia. We report the case of a woman, daughter of fifth cousins, who was gamma-glutamylcysteine-synthetase-deficient. Modest decreases in the amount of GSH in cultured lymphoblasts and fibroblasts could be documented. The amount of residual enzyme was insufficient to permit detailed studies of the characteristics of the mutant enzymes, but no major abnormality in its Km for cysteine and glutamic acid or in its heat stability were found. In contrast to the earlier report, the only manifestation of the enzyme deficiency was hemolytic anemia. This leads us to conclude that either the occurrence of neurologic symptoms in the other reported family was a chance association or that the clinical expression of this rare defect is pleomorphic.

A therapeutic trial with N-acetylcysteine in subjects with hereditary glutathione synthetase deficiency (5-oxoprolinuria)

In a therapeutic trial, the effect of short-term low-dosage N-acetylcysteine supplementation on glutathione metabolism was investigated in two patients with hereditary glutathione deficiency (5-oxoprolinuria). Clinical and neurophysiological examinations of the patients indicated progressive neurological damage. The pretreatment concentrations of total and free glutathione in leukocytes were 15-20% of normal, whereas the corresponding gamma-glutamylcysteine levels were increased. In plasma, the glutathione concentrations were similarly decreased, but no gamma-glutamylcysteine was detected. Total glutathione in erythrocytes was markedly decreased. Low urinary excretion of cysteinylglycine, cyst(e)ine, taurine, N-acetylcysteine, mercaptolactate and mercaptoacetate and reduced leukocyte taurine levels constituted additional evidence of decreased intracellular availability of cysteine, i.e. glutathione. Oral supplementation with N-acetylcysteine (5 mg/kg x 3/day) had no effect on acid-base balance, erythrocyte glutathione levels or 5-oxoproline concentrations in plasma and urine. In leukocytes, the glutathione concentrations were increased by 20-30%, whereas the gamma-glutamylcysteine levels were essentially unaltered. In parallel, the urinary excretion of cysteinylglycine was increased and the leukocyte levels and urinary outputs of sulphur amino acids were restored. No side-effects of the treatment were noted. The results indicate that N-acetylcysteine may be of value in increasing the low intracellular glutathione concentrations and cysteine availability in patients with hereditary glutathione synthetase deficiency.

Low molecular weight thiol content in glutathione synthetase-deficient human fibroblasts

The activity and the kinetic properties of glutathione synthetase and the concentrations of non-protein bound thiols of the gamma-glutamyl cycle were measured in 11 human fibroblast cell strains. Six of these strains were derived from patients suffering from 5-oxoprolinuria, a recessive genetic disease characterized by a deficiency in glutathione synthetase; the other cell strains were derived from healthy heterozygous or homozygous relatives of the patients. The glutathione synthetase activities of homozygous deficient strains were 1/3 of control values while those of heterozygous strains were 2/3 of control values. The total thiol concentration was lower in only 3 of the 6 deficient homozygotes and that of glutathione (GSH) was lower in only 4 of the 6 deficient homozygotes. This lower GSH level was at least partly offset by an accumulation of gamma-glutamylcysteine, a precursor of GSH, which is almost completely absent from control cells. The total quantities of thiols and GSH in plateau phase cells were about 50% and 30% respectively of the levels in growth phase cells. Approximately 80% of the GSH was in the reduced form in both quiescent and growing cells.

Reduced repair of potentially lethal radiation damage in glutathione synthetase-deficient human fibroblasts after X-irradiation

Using a human fibroblast strain deficient in glutathione synthetase and a related proficient control strain, the role of glutathione (GSH) in repair of potentially lethal damage (PLD) has been investigated in determining survival by plating cells immediately or 24 h after irradiation. After oxic or hypoxic irradiation, both cell strains repair radiation-induced damage. However, under hypoxic conditions, the proficient cells repair PLD as well as under oxic conditions while the deficient cells repair less PLD after irradiation under hypoxic than under oxic conditions. Therefore, the oxygen enhancement ratio (o.e.r.) for proficient cells is similar whether the cells are plated immediately or 24 h later (2.0 and 2.13, respectively). In contrast, the o.e.r. for deficient cells is lower when the cells are plated 24 h after irradiation than when they are plated immediately thereafter (1.16 as compared to 1.55). The results indicate that GSH is involved in PLD repair and, in particular, in the repair of damage induced by radiation delivered under hypoxic conditions.

Erythrocyte glutathione synthetase deficiency leads not only to glutathione but also to glutathione-S-transferase deficiency

Glutathione synthetase (GSH-S) is one of the two known hereditary causes of glutathione deficiency. We describe a family whose two children have hemolytic anemia. The children's erythrocytes lack GSH and are severely deficient in GSH-S activity. No neurologic findings or 5-oxoprolinuria were present. A concurrent deficiency of glutathione-S-transferase (GST) was also detected in the erythrocytes. Residual glutathione could be detected in the erythrocytes using a sensitive cycling assay. The deficiency was found to be most severe in reticulocyte-depleted preparations. The GSH-S activity of the erythrocytes of the parents was one-half normal, while the glutathione S-transferase activity was normal. We conclude that the primary defect is one of GSH-S. Glutathione stabilizes GST in vitro, and it is assumed that the deficiency of GST in the erythrocytes of the patients is due to the instability of this enzyme in the absence of adequate intracellular GSH levels.

Radioprotective effect of cysteamine in glutathione synthetase-deficient cells

The radioprotective role of endogenous and exogenous thiols was investigated, with survival as the end-point, after radiation exposure of cells under oxic and hypoxic conditions. Human cell strains originating from a 5-oxoprolinuria patient and from a related control were used. Due to a genetic deficiency in glutathione synthetase, the level of free SH groups, and in particular that of glutathione, is decreased in 5-oxoprolinuria cells. The glutathione synthetase deficient cells have a reduced oxygen enhancement ratio (1.5) compared to control cells (2.7). The radiosensitivity was assessed for both cell strains in the presence of different concentrations of an exogenous radioprotector:cysteamine. At concentrations varying between 0.1 and 20 mM, cysteamine protected the two cell strains to the same extent when irradiated under oxic and hypoxic conditions. The protective effect of cysteamine was lower under hypoxia than under oxic conditions for both cell strains. Consequently, the oxygen enhancement ratio decreased for both cell strains when cysteamine concentration increased. These results suggest that cysteamine cannot replace endogenous thiols as far as they are implicated in the radiobiological oxygen effect.

Sulphur amino-acid degradation in subjects with hereditary glutathione synthetase deficiency (5-oxoprolinuria)

The role of a low intracellular glutathione concentration in sulphur amino-acid degradation was investigated in two sisters (10 and 13 years old) with glutathione-synthetase deficiency, by determination of the urinary excretion of sulphur amino-acids and their main degradation products. The urinary excretion of total sulphur and inorganic sulphate was normal, indicating adequate dietary intake of sulphur amino-acids and normal oxidation to inorganic sulfate. Decreased excretion of N-acetylcysteine was found in the younger sister, which could be due to a reduced intracellular availability of cyst(e)ine. Increased excretion of mercaptolactate was found in the older sister, probably featuring a more catabolic condition in this subject. She also had an increased excretion of thiosulphate. Low excretion of thiocyanate was observed in both subjects, probably a consequence of a reduced dietary intake of thiocyanate or its precursors. Neither glutathione nor gamma-glutamylcysteine were detectable in urine. The excretion of cysteinylglycine was clearly reduced, reflecting that this dipeptide mainly is a degradation product of glutathione.

Survival curves of glutathione synthetase deficient human fibroblasts: correlation between radiosensitivity in hypoxia and glutathione synthetase activity

The role of intracellular non-protein bound sulphydryl compounds (NPSH), and in particular that of glutathione (GSH), in the response of cells to ionizing radiation under different O2 concentrations has been assessed using cell strains deficient in glutathione synthetase and exhibiting different NPSH levels. The cell strains used originated from patients with 5-oxoprolinuria and from their relatives (heterozygotes and proficient homozygotes). No correlation has been found between NPSH and GSH concentrations and radiosensitivity under oxic, aerobic and hypoxic conditions. However, a highly significant correlation has been observed between radiosensitivity under hypoxic conditions (and therefore the oxygen enhancement ratio) and the glutathione synthetase activity, suggesting that synthesis of GSH is required after irradiation. In order to explain our results we postulated, beside radical processes, the existence of a GSH-dependent enzymatic repair mechanism for N2 type damage. Hypoxic radio-sensitivity measured with survival curves would result from the interaction of both competition and biochemical repair processes.

Radiosensitizing and cytotoxic properties of misonidazole on glutathione synthetase deficient human fibroblasts

The cytotoxic and radiosensitizing effects of misonidazole have been studied on glutathione synthetase deficient fibroblasts and on their controls. At any concentration from 0.1 to 4 mM, deficient cells are more sensitive to the cytotoxic effect of misonidazole than the control cells. The differential effect between the two cell strain concerns both the shoulder and the slope of the survival curve, thus suggesting that NPSH play a role in the determination of misonidazole cytotoxicity. Like oxygen, misonidazole clearly sensitizes deficient cells to a lesser extent than control cells. For both cell strains, the maximum sensitizing effect of misonidazole is very close to that of oxygen (1.5 and 1.5 for deficient cells, 2.8 and 2.9 for control cells, respectively). The sensitizing effect of misonidazole appears in the same concentration range for both cell strains, with a maximal effect at lower concentrations for deficient cells.

Ophthalmological, psychometric and therapeutic investigation in two sisters with hereditary glutathione synthetase deficiency (5-oxoprolinuria)

Two sisters with hereditary glutathione synthetase deficiency (5-oxoprolinuria) were investigated. Assays of erythrocyte enzyme levels in relatives revealed additional clinically healthy carriers. The girls had chronic metabolic acidosis, which was corrected by substitution with bicarbonate. They had an increased rate of hemolysis which was well compensated. Their granulocyte function was normal when tested in vitro. In both girls mental retardation developed progressively without additional clinical neurological symptoms. Their electroretinograms were abnormal indicating disturbed retinal electrophysiological function. Therapeutic trials were performed with oral administration of glutathione (Tathion), mercaptopropionylglycine (Thiola) and vitamin E. None of these compounds had an effect on the urinary excretion of 5-oxoproline, acid-base balance, pathological electroretinograms or the clinical condition. Initially, Thiola therapy increased the low levels of glutathione in patient erythrocytes but after several months of treatment the concentration of glutathione declined to pretreatment levels. There was no indication that orally administered glutathione, mercaptopropionylglycine or vitamin E had a beneficial effect in the doses used. Nevertheless, vitamin E administration has been continued in addition to the correction of acidosis with sodium bicarbonate.

Acetaminophen toxicity in lymphocytes heterozygous for glutathione synthetase deficiency

We have studied the effects of acetaminophen metabolites generated by a murine hepatic microsomal system on lymphocytes from two subjects heterozygous for glutathione synthetase deficiency. Heterozygous cells exhibited greater dose-related toxicity than controls. Following a 2-h incubation with acetaminophen and the microsomal system, cells were washed and incubated for 16 h in the presence or absence of N-acetylcysteine, the standard antidote for acetaminophen toxicity. In control cells, glutathione content was replenished to nearly base-line values and toxicity was prevented. N-Acetylcysteine thus prevented toxicity even after covalent binding of acetaminophen metabolites had occurred. Heterozygous cells failed to use N-acetylcysteine as efficiently to resynthesize glutathione, and the cells were not protected from acetaminophen toxicity. Heterozygotes may be at increased risk of toxicity from drugs whose metabolites are detoxified by glutathione conjugation.

Glutathione synthetase deficient human fibroblasts in culture

Cultured skin fibroblasts from patients with 5-oxoprolinuria caused by hereditary deficiency of glutathione synthetase have decreased levels of the corresponding enzyme as well as of glutathione. Fibroblasts from the same patients accumulated gamma-glutamyl cysteine, but the levels were lower than those of glutathione in control fibroblasts. The uptake of [35S]cystine was equally rapid in control and patient fibroblasts. In the acid-soluble fraction gamma-glutamyl-[35S]cysteine accumulated in fibroblasts from patients but not from controls. Appreciable turnover of gamma-glutamyl cysteine and glutathione in the respective cell strains was observed, the half-lives of these pools being approximately 5 hours. The growth rate of mutant fibroblasts in culture was significantly slower than that of control fibroblasts. There was no significant accumulation of 5-oxoproline in the culture medium.

Hemolytic anemia, recurrent metabolic acidosis, and incomplete albinism associated with glutathione synthetase deficiency

The clinical and laboratory features of a 3-mo-old black male infant with glutathione (GSH) synthetase deficiency of the generalized type was evaluated. Partial albinism, brisk hemolytic anemia, recurrent febrile episodes, and mental retardation were noted. Also, severe recurrent metabolic acidosis and marked oxoprolinemia and oxoprolinuria were found in the proband but not in his first-degree relatives. The relationship of these disease manifestations to the underlying metabolic defect is discussed.

Reduced oxygen enhancement of the radiosensitivity of glutathione-deficient fibroblasts

Following the demonstration of the radioprotective role of artificial aminothiols, the question logically arose concerning the role of aminothiols present naturally in cells: non-protein bound sulfhydryls (NPSH), especially glutathione (GSH). The latter is the most abundant NPSH and would be a likely candidate for a radioprotector.

Induction and repair of single-strand DNA breaks after X-irradiation of human fibroblasts deficient in glutathione

Using the unwinding technique in weak alkali, the induction and repair of DNA single-strand breaks was determined after aerobic and anerobic X-irradiation of human fibroblasts, obtained from a patient suffering from 5-oxoprolinuria, and from a clinically healthy control. The metabolic disorder associated with 5-oxprolinuria is a deficiency in glutathione synthetase activity resulting in a greatly reduced glutathione content in the cells. A small dose-modifying effect of oxygen (o.e.r. = 1.1) was found for these cells in comparison to an o.e.r. of 2.5 for control cells with normal glutathione content. No significant difference was found between the repair capacity of cells with normal and deficient glutathione content, and repair was nearly completed within 60 min of anoxic irradiation in each case. In contrast, after aerobic irradiation of glutathione-deficient cells repaired less than 70 per cent of the breaks during the same period. When the glutathione-deficient cells were incubated with either dithiothreitol or mercaptopropionylglycine directly after aerobic irradiation, almost complete repair was obtained within 60 Min. The data are interpreted as indicating that the repair mechanism for oxically and anoxically induced single-strand breaks is qualitatively different, and requires glutathione in the former case.

Disulphide reduction in glutathione-deficient erythrocytes from a patient with pyroglutamic acidemia

Erythrocytes from a patient with pyroglutamic acidemia, containing about 5% of the normal content of glutathione, were able to reduce cystamine at a relatively high rate (about 50% that of normal cells) at low concentrations of the disulphide. Compared to normal cells, the reduction of disulphide by the patient's cells were highly sensitive to inhibition by high concentrations of the disulphide. This inhibition was noted whether glucose or inosine were used as carbohydrate substrate, and was also present when hemolysates were used and NADPH was added directly to the reaction mixture. The "disulphide poisoning" is assumed to be due to the formation of mixed disulphides at the expense of oxidized glutathione available for reduction by glutathione reductase. The glutathione/glutathione reductase system is probably the only disulphide reducing system of importance in human erythrocytes.

Glutathione synthetase-deficient lymphocytes and acetaminophen toxicity

Toxic electrophilic metabolites of acetaminophen are detoxified by conjugation with glutathione. Cellular glutathione content of patients with glutathione synthetase deficiency (5-oxoprolinuria) is 10% to 20% of normal. These patients might be at increased risk for acetaminophen toxicity. The hypothesis was tested by challenging lymphocytes from normals and a patient with glutathione synthetase deficiency in vitro with acetaminophen metabolites generated by a mouse hepatic microsomal drug-metabolizing system. For toxicity to be manifested in normal cells, glutathione content had to be depleted to less than 20% of control values at high acetaminophen concentrations (500 and 1,500 micrograms/ml), concentrations similar to blood levels in massive overdose and associated with hepatotoxicity in vivo. The patient's cells had only 14% of normal glutathione content, and exhibited more toxicity at 12.5 micrograms/ml acetaminophen (within the therapeutic range) as normals at maximum concentrations. The in vitro system may be of value in screening drugs potentially hazardous for glutathione synthetase-deficient patients, for exploring the role of glutathione in the detoxification of xenobiotics, and for examining glutathione protective mechanisms in patients with idiosyncratic cytotoxic drug reactions.

Protection of granulocytes by vitamin E in glutathione synthetase deficiency

The administration of vitamin E (alpha-tocopherol) was found to improve polymorphonuclear leukocyte function in an infant with congenital deficiency of glutathione synthetase activity. Before therapy with vitamin E the abnormal leukocytes exposed to phagocytic challenge showed oxidant damage. They released 60 per cent more hydrogen peroxide than did normal leukocytes, iodinated only 20 to 25 per cent of the normal number of particles, and were unable to kill bacteria as effectively as normal leukocytes although the rates of phagocytosis were normal. These functional abnormalities disappeared when the patient was placed on 400 IU of alpha-tocopherol daily for three months. Associated with the functional improvement was a normalization of microtubule assembly during phagocytic challenge.

Oxidative damage to neutrophils in glutathione synthetase deficiency

Several episodes of neutropenia were observed in a child with glutathione synthetase deficiency (5-oxoprolinuria). Studies of the patient's glutathione-deficient neutrophils were undertaken to examine the responses of the cells to oxidative stress associated with phagocytosis. The patient's neutrophils contained 10--20% of normal glutathione content. Circulating neutrophils in infection-free periods appeared less mature than normal by morphologic criteria, suggesting increased cell turnover. The cells ingested particles, responded to chemotactic stimuli, and oxidized 1-14C glucose normally. However, following ingestion of particles, the cells accumulated excess hydrogen peroxide compared with normal cells, and showed impaired protein iodination and bacterial killing. Electron micrographs revealed damage to microtubules and membranous structures in the patient's neutrophils during phagocytosis. The level of glutathione in the cells appears inadequate to protect against peroxide generated during normal cell function, and the cells are thus damaged and rendered less effective in bacterial killing. The data provide evidence for a protective role of glutathione in normal neutrophil function.

Biochemical heterogeneity in glutathione synthetase deficiency

Two different clinical syndromes are associated with glutathione synthetase deficiency, one presenting with hemolytic anemia and 5-oxoprolinuria, the other with isolated hemolysis. We have differentiated these disorders on an enzymatic basis. In 5-oxoprolinuria, all cell types examined have grossly deficient enzyme activity and glutathione content. In contrast, in the nonoxoprolinuric variant, erythrocytes have decreased enzyme activity and glutathione content, whereas nucleated cells maintain substantial levels of both. The enzyme in this disorder is unstable in vitro and has shortened survival in intact erythrocytes. Nucleated cells appear able to maintain sufficient enzyme activity and concentrations of glutathione to suppress overproduction of 5-oxoproline.

5-oxoprolinuria: biochemical observations and case report

We have studied a patient with 5-oxoprolinuria who presented with hemolysis and metabolic acidosis as a neonate; he has had normal growth and development to one year of age. Compensated hemolytic anemia persists, and he requires alkalinizing agents for correction of acidosis. Biochemical studies have confirmed that a deficiency of glutathione synthetase is responsible for the 5-oxoprolinuria. Genetic heterogeneity was apparent on comparative study of glutathione synthetase kinetics in cells from two patients with this disorder. The consequences of the deficiency of glutathione synthetase, decreased intracellular glutathione, and overproduction of 5-oxoproline are discussed with reference to the possible cellular roles of these compounds.

Nutritional requirements for folate compounds and some enzyme activities involved in the folate biosynthesis

Dihydrofolate synthetase activity is widely distributed in various microorganisms and mushrooms. Animals and microorganisms i.e., rat and chicken (in the liver), L. casei and P. cerevisiae, which require essentially pteroylglutamic acid as a nutrient for growth showed no detectable dihydrofolate synthetase activity. S. faecalis R, which can replace pteroylglutamic acid with pteroic acid as a nutrient for growth, had little dihydropteroate synthetase activity but showed normal dihydrofolate synthetase activity. This suggests that the nutritional requirements for folate compounds shown in vivo is in good agreement with the results obtained with dihydropteroate and dihydrofolate synthetase activities in vitro, and that the pathway through dihydropteroic acid as an intermediate is the main route in folate biosynthesis in nature.

Erythrocyte glutathione synthetase in 5-oxoprolinuria: kinetic studies of the mutant enzyme and detection of heterozygotes

The primary metabolic defect in 5-oxoprolinuria is a generalized deficiency of glutathione synthetase. The activity of this enzyme was determined in cell-free extracts of erythrocytes from patients with 5-oxoprolinuria, their parents and a sibling as well as from normal control individuals. The following activities (pkat/mg of hemoglobin) for glutathione synthetase were obtained: homozygotes mean 0.10 (range 0.07-0.12), heterozygotes mean 3.1 (range 2.8-3.7) and control individuals mean 6.1 (range 5.4-6.7). These results indicate that 5-oxoprolinuria, i.e. the defective gluthione synthetase gene(s), is transmitted by autosomal recessive inheritance. Studies of the kinetics of the low remaining activity of erythrocyte glutathione synthetase in patients with 5-oxoprolinuria failed to reveal defective affinity for glycine, gamma-glutamyl-alpha-aminobutyrate, ATP and Mg2+ ions. Furthermore, the pH optimum, time curves and temperature dependence for the mutant enzyme activity did not significantly differ from the corresponding parameters observed with normal enzyme.

Cystine metabolism in human fibroblasts. Comparison of normal, cystinotic, and gamma-glutamylcysteine synethetase-deficient cells

Incubation of normal human skin fibroblasts or fibroblasts derived from patients with erythrocyte deficiency of gamma-glutamylcysteine synthetase (gamma-glutamylcysteine synthetase-deficient) in culture medium containing L-[35S]cystine resulted in incorporation of radioactivity into protein, cysteine, and glutathione, gamma-Glutamylcysteine synthetase-deficient fibroblasts synthesized glutathione from [35S]cystine at 30% the rate of normal cells and contained 30% the normal amount of glutathione. Cystinotic fibroblasts incorporated [35S]cystine into the large intracellular cystine pool not found in normal or gamma-glutamylcysteine synthetase-deficient cells and also appeared to synthesize glutathione more slowly than normal cells. However, the radioactivity recovered as cystine was reduced greatly and the rate of [35S]cystine incorporation into glutathione increased if cystinotic cells were first depleted of their intracellular cystine pool before incubation in [35S]cystine. This suggests that the apparent reduced rate of glutathione synthesis observed in untreated cystinotic cells was a secondary effect caused by dilution of the [35S]cystine by the large pool of nonradioactive cystine. Cystinotic cells depleted of cystine by treatment with mercaptoethylamine reaccumulate 30 to 50% of their initial cystine in 24 hours in the absence of extracellular cystine. Both normal and cystinotic cells lose more than 90% of their intracellular glutathione in 24 hours in cystine-free medium. Both cell types can reutilize cysteine from glutathione for protein synthesis.

On the mechanism of 5-oxoproline overproduction in 5-oxoprolinuria

The primary metabolic defect in 5-oxoprolinuria (pyroglutamic aciduria) is the lack of glutathione synthetase. The mechanism of the concomitant overproduction of 5-oxoproline was studied using cell-free extracts of erythrocytes from control individuals and from patients with 5-oxoprolinuria. Such extracts catalyzed the synthesis of 5-oxoproline from L-glutamate. Addition of ATP, Mg ions and alpha-aminobutyrate was needed for optimal activity. The conversion of glutamate to 5-oxoproline occurred in two steps, catalyzed by gamma-glutamyl-cysteine synthetase and gamma-glutamyl cyclotransferase, respectively. Extracts of erythrocytes from control subjects and patients with 5-oxoprolinuria had identical capacity to synthesize 5-oxoproline. The conversion of glutamate to 5-oxoproline was markedly inhibited by reduced glutathione, which exerted its effect on the gamma-glutamyl-cysteine synthetase step. The following mechanism is postulated for the overproduction of 5-oxoproline in 5-oxoprolinuria: the deficiency of glutathione synthetase causes a lack of glutathione which is an essential feed-back inhibitor in the initial step of its biosynthesis. Therefore gamma-glutamyl-cysteine is produced in excessive amounts and it is subsequently converted to 5-oxoproline (and cysteine) by gamma-glutamyl cyclotransferase. This overproduction of 5-oxoproline exceeds the capacity of the 5-oxoprolinase and 5-oxoproline accumulates in body fluids.