[Analysis of the types and functions of CD34+ cells in full-thickness skin defect wounds of normal mice and diabetic mice by single-cell RNA sequencing]

Objective: To analyze the types and functions of CD34+ cells in full-thickness skin defect wounds of normal mice and diabetic mice by single-cell RNA sequencing. Methods: This study was an experimental study. The CD34+ cell lineage tracing mouse was produced, and the visualization of CD34+ cells under the fluorescent condition was realized. Six male CD34+ cell lineage tracing mice aged 7-8 weeks (designated as diabetic group) were intraperitoneally injected with streptozotocin to establish a diabetic model, and full-thickness skin defect wounds were prepared on their backs when they reached 13 weeks old. Another 6 male CD34+ cell lineage tracing mice aged 13 weeks (designated as control group) were also subjected to full-thickness skin defect wounds on their backs. On post-injury day (PID) 4, wound tissue was collected from 3 mice in control group and 2 mice in diabetic group, and digested to prepare single-cell suspensions. CD34+ cells were screened using fluorescence-activated cell sorting, followed by single-cell RNA sequencing. The Seurat 4.0.2 program in the R programming language was utilized for dimensionality reduction, visualization, and cell clustering analysis of CD34+ cell types, and to screen and annotate the marker genes for each CD34+ cell subpopulation. Kyoto encyclopedia of genes and genomes (KEGG) and gene ontology (GO) enrichment analysis was performed to analyze the differentially expressed genes (DEGs) of CD34+ fibroblasts (Fbs), smooth muscle cells (SMCs), keratinocytes (KCs), and chondrocyte-like cells (CLCs) in the wound tissue of two groups of mice for exploring cellular functions. Results: On PID 4, CD34+ cells in the wound tissue of both groups of mice were consisted of 7 cell types, specifically endothelial cells, Fbs, KCs, macrophages, T cells, SMCs, and CLCs. Among these, Fbs were further classified into 5 subpopulations. Compared with those in control group, the proportions of CD34+ endothelial cells, Fbs subpopulation 1, Fbs subpopulation 4, KCs, and CLCs in the wound tissue of mice were increased in diabetic group, while the proportions of CD34+ Fbs subpopulation 2, Fbs subpopulation 3, and SMCs were decreased. The marker genes for annotating CD34+ CLCs, endothelial cells, Fbs subpopulation 1, Fbs subpopulation 2, Fbs subpopulation 3, Fbs subpopulation 4, Fbs subpopulation 5, KCs, macrophages, SMCs, and T cells were respectively metastasis-associated lung adenocarcinoma transcript 1, fatty acid binding protein 4, Gremlin 1, complement component 4B, H19 imprinted maternally expressed transcript, Dickkopf Wnt signaling pathway inhibitor 2, fibromodulin, keratin 5, CD74 molecule, regulator of G protein signaling 5, and inducible T-cell co-stimulator molecule. KEGG and GO enrichment analysis revealed that, compared with those in control group, DEGs with significant differential expression (SDE) in CD34+ Fbs from the wound tissue of mice in diabetic group on PID 4 were significantly enriched in terms related to inflammatory response, extracellular matrix (ECM) organization, regulation of cell proliferation, and aging (with Pvalues all <0.05), DEGs with SDE in CD34+ SMCs were significantly enriched in terms related to cell migration, apoptotic process, positive regulation of transcription, and phagosome (with P values all <0.05), DEGs with SDE in CD34+ KCs were significantly enriched in terms related to mitochondrial function, transcription, and neurodegenerative diseases (with P values all <0.05), and DEGs with SDE in CD34+ CLCs were significantly enriched in terms related to rhythm regulation, ECM, and viral infection (with P values all <0.05). Conclusions: CD34+ cells display high heterogeneity in the healing process of full-thickness skin defect wounds in both normal mice and diabetic mice. The significantly enriched functions of DEGs with SDE in CD34+ cell subpopulations in the wound tissue of the two mouse groups are closely related to the wound healing process.

Lactobacillus rhamnosus GG ameliorates hyperuricemia in a novel model

Hyperuricemia (HUA) is a metabolic syndrome caused by abnormal purine metabolism. Although recent studies have noted a relationship between the gut microbiota and gout, whether the microbiota could ameliorate HUA-associated systemic purine metabolism remains unclear. In this study, we constructed a novel model of HUA in geese and investigated the mechanism by which Lactobacillus rhamnosus GG (LGG) could have beneficial effects on HUA. The administration of antibiotics and fecal microbiota transplantation (FMT) experiments were used in this HUA goose model. The effects of LGG and its metabolites on HUA were evaluated in vivo and in vitro. Heterogeneous expression and gene knockout of LGG revealed the mechanism of LGG. Multi-omics analysis revealed that the Lactobacillus genus is associated with changes in purine metabolism in HUA. This study showed that LGG and its metabolites could alleviate HUA through the gut-liver-kidney axis. Whole-genome analysis, heterogeneous expression, and gene knockout of LGG enzymes ABC-type multidrug transport system (ABCT), inosine-uridine nucleoside N-ribohydrolase (iunH), and xanthine permease (pbuX) demonstrated the function of nucleoside degradation in LGG. Multi-omics and a correlation analysis in HUA patients and this goose model revealed that a serum proline deficiency, as well as changes in Collinsella and Lactobacillus, may be associated with the occurrence of HUA. Our findings demonstrated the potential of a goose model of diet-induced HUA, and LGG and proline could be promising therapies for HUA.

Clinical efficacy of targeted therapy, immunotherapy combined with hepatic artery infusion chemotherapy (FOLFOX), and lipiodol embolization in the treatment of unresectable hepatocarcinoma

To evaluate the clinical efficacy of targeted therapy and immunotherapy combined with hepatic arterial infusion chemotherapy (HAIC) of FOLFOX and lipiodol embolization in the treatment of unresectable hepatocellular carcinoma. Patients included in the study were those who received targeted therapy and immunotherapy combined with HAIC of FOLFOX and lipiodol embolization in Zhongshan People's Hospital from December 2020 to June 2021 for unresectable hepatocellular carcinoma. Evaluation indicators included objective response rate (ORR), median progression-free survival (mPFS), median duration of response (mDOR), 1-year overall survival rate (OS), surgical conversion rate, and adverse events. Treatment response was assessed using Response Evaluation Criteria in Solid Tumors (mRECIST and RECIST v1.1). A total of 35 patients were included in this study, 30 of whom completed treatment evaluation. According to mRECIST evaluation criteria, the objective response rate (ORR) was 83.3% (25/30); the complete response (CR) was 60% (18/30); the partial response (PR) was 23.3% (7/30), and stable disease (SD) was 16.7% (5/30). The mDOR was 10.3 months (95% Cl: 8.27-NE), and the mPFS was 13.2 months (95% CI: 10.3-NE); the surgical conversion rate was 30.0% (9/30). The 1-year OS was 96.7%. There were no serious surgical complications and grade 4 or 5 adverse events of targeted therapy, immunotherapy and HAIC. Some patients had grade 3 adverse reactions in gastrointestinal toxicity or hepatotoxicity, and the adverse reactions were improved after corresponding symptomatic treatment. We concluded that HAIC of FOLFOX and lipiodol embolization combined with targeted therapy and immunotherapy had a significant curative effect in the treatment of unresectable hepatocellular carcinoma, with no serious adverse reactions and a high rate of surgical conversion rate.

[Comparison of the curative effect of transjugular intrahepatic portosystemic shunt with expanded polytetrafluoroethylene-covered stent and drug combined with gastroscopy as the secondary prevention of esophageal -gastric variceal bleeding in portal hypertension]

Objective: To compare the clinical efficacy of transjugular intrahepatic portosystemic shunt (TIPS) with expanded polytetrafluoroethylene (ePTFE)-covered stent and drug combined with gastroscopy as the secondary prevention of esophageal-gastric variceal bleeding in portal hypertension. Methods: Patients with esophageal-gastric variceal bleeding who received TIPS treatment (ePTFE covered stent) or gastroscopy for the first time as the secondary prevention for portal hypertension at Nanfang Hospital of Southern Medical University through March to July 2017 were selected. One year after the operation, liver function changes, ascites remission rates, incidence of hepatic encephalopathy, re-bleeding rate, average hospitalization frequency and expenses, survival time, as well as the TIPS patency conditions were analyzed in the two groups of patients. 2 test, Kaplan-Meier method and Mann-Whitney U test were used to analyze the data. Results: There were 74 and 66 cases in the TIPS and the drug combined gastroscopy group and the follow-up duration (14.57 ± 0.79) was 12-16 months. One year after surgery, the remission rate of ascites in the TIPS group was higher 57.1% (32/56) than that of the drug combined gastroscopy group (0), and the difference was statistically significant (χ(2) = 2 = 36.73, P < 0.01). The cumulative incidence of hepatic encephalopathy at 1, 3, 6, and 12 months after surgery in the TIPS group was 32.4% (24/74), 37.8% (28/74), 40.5% (30/74), and 40.5% (30/74), respectively. The cumulative incidence of hepatic encephalopathy in the drug combined gastroscopy group was 3.0% (2/66), 3.0% (2/66), 3.0% (2/66), and 6.1% (4/66), respectively. Kaplan-Meier analysis showed that the cumulative incidence of hepatic encephalopathy in the TIPS group was higher than that of the drug combined gastroscopy group (χ(2) = 11.29, P < 0.01). The incidence of severe hepatic encephalopathy ( grade III to IV) at 1, 3, 6, and 12 months after surgery in the TIPS group was 2.7% (2/74), 0, 0, and 0, respectively. The incidence of severe hepatic encephalopathy in drug combined gastroscopy group was 0, and there was no statistically significant difference in development of hepatic encephalopathy between the two groups (P > 0.05). The re-bleeding rates of TIPS group and drug combined gastroscopy group were 0 and 27.3% (18/66), respectively, and the difference was statistically significant (χ(2) = 22.42, P < 0.01). There was no death reported during the follow-up period between both groups. The hospitalization frequency times (1.45 ± 0.80) in TIPS group was lower than that of the drug combined gastroscopy group times (3.24 ± 1.80), and the difference was statistically significant (U = -4.52, P < 0.01). Conclusion: In the prevention of esophageal-gastric variceal bleeding, TIPS (ePTFE-covered stent) treatment has the advantages of reducing re-bleeding rate, high ascites remission rate and hospitalizations frequency. In addition, patients treated with TIPS have a higher incidence of hepatic encephalopathy than that of drugs combined with gastroscopy. However, TIPS did not exacerbate the incidence of hepatic encephalopathy, and there was no significant difference in the 1-year survival rate after TIPS and drugs combined with gastroscopy treatment.

[Therapeutic effect of low-temperature radiofrequency coblation on early-stage laryngeal cancer]

Objective: To evaluate the safety,efficacy and prognosis of low-temperature plasma radiofrequency coblation for early-stage laryngeal cancer(Tis, T1 and T2). Method: A retrospective analysis of 202 patients with early-stage laryngeal cancer who underwent the low-temperature radiofrequency coblation surgery, including 34 cases of Tis(16.83%), 49 cases of stage T1aN0M0(24.26%), 50 cases of stage T1bN0M0(24.75%) and 69 cases of stage T2N0M0(34.16%). Surgical patients were followed up closely for 6 to 60 months, with a median follow-up of 29 months. Result: Of the 202 patients,165(81.68%) had no recurrence and achieved good surgical results. None of them suffered severe complications such as post-operative hemorrhage and asphyxia. 37 cases(18.32%) had recurrence, including 1 case(0.50%) in stage Tis, 7 cases(3.47%) in stage T1a,7 cases(3.47%) in stage T1b, and 22 cases(10.89%) in stage T2. Thirteen patients who had recurrence underwent total laryngectomy(5 of which had a recurrence of T3 and 8 of which progressed to T4), including 1 in the stage T1a,2 in the stage T1b, and 10 in the stage T2. Vertical hemilaryngectomy were performed in 4 cases, 3 cases of stage T1a and 1 case of stage T2; 5 cases underwent plasma radiofrequency coblation again, including 3 cases of stage T1b and 2 cases of stage T2,no recurrence was found in all the patients; 1 patient had no obvious recurrence in the larynx but had cervical lymph node metastasis, radical neck dissection was performed; 1 patient with stage T2 recurrence was treated with a tracheotomy to relieve laryngeal obstruction without further treatment;3 cases showed improvement by radiotherapy and chemotherapy treatment after recurrence; 9 death cases,5 patients died after radiotherapy and chemotherapy, and 4 patients stopped getting treatment after recurrence.Conclusion: Low-temperature radiofrequency coblation surgery for patients with early-stage laryngeal cancer has great advantages in the preservation of laryngeal function and reduction of surgical trauma after surgery compared with traditional surgical method, and can obtain satisfactory results, but the selection of surgical indications for some patients with clinical stage T2 is still need to be carefully considered..

Droplet optofluidic imaging for λ-bacteriophage detection via co-culture with host cell Escherichia coli

Bacteriophages are considered as attractive indicators for determining drinking water quality since its concentration is strongly correlated with virus concentrations in water samples. Previously, bacteriophage detection was based on a plague assay that required a complicated labelling technique and a time-consuming culture assay. Here, for the first time, a label-free bacteriophage detection is reported by using droplet optofluidic imaging, which uses host-cell-containing microdroplets as reaction carriers for bacteriophage infection due to a higher contact ratio. The optofluidic imaging is based on the effective refractive index changes in the microdroplet correlated with the growth rate of the infected host cells, which is highly sensitive, i.e. can detect one E. coli cell. The droplet optofluidic system is not only used in drinking water quality monitoring, but also has high potential applications for pathogenic bacteria detection in clinical diagnosis and food industry.

Bisoprolol improved endothelial function and myocardium survival of hypertension with stable angina: a randomized double-blinded trial

AIM

This study was designed to determine the effect of bisoprolol on endothelial function of brachial artery and the myocardium survival in hypertensive patients with stable angina.

PATIENTS AND METHODS

222 subjects with hypertension who had received coronary angiography examination were involved in the study, 162 in bisoprolol therapy group (96 men, 59%) and 60 in non-bisoprolol group (39 men, 65%). In accordance with results of angiography (coronary stenosis ≥ 50%), the patients in bisoprolol group were divided into three sub-groups: (1) single-vessel coronary disease group (n=42); (2) double-vessel coronary disease group (n=44); (3) multi-vessel coronary disease group (n=39) and hypertension-only group (n=37). All the subjects were treated with conventional drugs plus bisoprolol and followed up for 12 months. Parameters of clinical features, echocardiography, radionuclide ventriculographic and laboratory findings were measured and analyzed.

RESULTS

After 12 months bisoprolol treatment, the flow-mediated vasodilatation (FMD) and 99Tcm-sestamibi (99Tcm-MIBI) uptake fraction which reflects the survival of myocardium were improved markedly in bisoprolol group (all p < 0.05). Interestingly, a more significant improvement in FMD and 99Tcm-MIBI uptake fraction were observed in severe coronary disease sub-groups (double-vessel group and multi-vessel group) when compared with single-vessel sub-group (p < 0.05).

CONCLUSIONS

Hypertensive subjects with stable angina might get benefit from the treatment of bisoprolol in improving endothelial function and the survival of myocardium.

Prostaglandin A1 inhibits stress-induced NF-kappaB activation and reverses resistance to topoisomerase II inhibitors

Stress conditions associated with solid tumors lead to the formation of heterogeneous tumor cell subpopulations and insensitivity to cancer chemotherapeutics. In this report, we show that EMT6 mouse mammary tumor cells treated with the chemical stress, brefeldin A (BFA), or the physiological stress, hypoxia, develop resistance to the topoisomerase II (topoII) inhibitors teniposide and etoposide. BFA and hypoxia treatment did not alter intracellular drug concentrations, topoll protein levels, or inhibit topoII activity. BFA and hypoxia did cause the activation of the nuclear transcription factor NF-kappaB. We demonstrate that pretreatment with the synthetic cyclopentenone prostaglandin A1 (PGA1) inhibits stress-induced NF-kappaB activation and reverses BFA- and hypoxia-induced resistance. The reversal of BFA-induced resistance can occur when PGA1 is administered either before or several hours after the induction of stress. Taken together, these data support the involvement of NF-kappaB in stress-induced drug resistance, show that pharmacologic inhibitors of NF-kappaB can disrupt the biological consequences of stress, and imply that inhibitors of NF-kappaB may be useful agents to enhance the clinical efficacy of topoII-directed chemotherapeutics.

Reversal of physiological stress-induced resistance to topoisomerase II inhibitors using an inducible phosphorylation site-deficient mutant of I kappa B alpha

Physiological stress conditions associated with the tumor microenvironment play a role in resistance to anticancer therapy. In this study, treatment of EMT6 mouse mammary tumor cells with hypoxia or the chemical stress agents brefeldin A (BFA) or okadaic acid (OA) causes the development of resistance to the topoisomerase II inhibitor etoposide. The mechanism of physiological stress-induced drug resistance may involve the activation of stress-responsive proteins and transcription factors. Our previous work shows that treatment with BFA or OA causes activation of the nuclear transcription factor NF-kappa B. Pretreatment with the proteasome inhibitor carbobenzyoxyl-leucinyl-leucinyl-leucinal inhibits stress-induced NF-kappa B activation and reverses BFA-induced drug resistance. To test whether NF-kappa B specifically mediates stress-induced drug resistance, an inducible phosphorylation site-deficient mutant of I kappa B alpha (I kappa B alpha M, S32/36A) was introduced into EMT6 cells. In this study, we show that I kappa B alpha M expression inhibits stress-induced NF-kappa B activation and prevents BFA-, hypoxia-, and OA-induced resistance to etoposide. These results indicate that NF-kappa B activation mediates both chemical and physiological drug resistance to etoposide. Furthermore, they imply that coadministration of agents that inhibit NF-kappa B may enhance the efficacy of topoisomerase II inhibitors in clinical cancer chemotherapy.

The pharmacological phenotype of combined multidrug-resistance mdr1a/1b- and mrp1-deficient mice

Two major classes of plasma membrane proteins that actively extrude a wide range of structurally diverse hydrophobic amphipathic antineoplastic agents from cells, with different mechanisms of action, lead to multidrug resistance. To study the importance of these ATP-binding cassette transporters to the toxicity of cancer chemotherapy agents, we have used mice genetically deficient in both the mdr1a and mdr1b genes [mdr1a/1b(-/-) mice], the mrp1 gene [mrp1(-/-) mice], and the combined genes mdr1a/1b and mrp1 [mdr1a/1b(-/-), mrp1(-/-) mice] and embryonic fibroblasts derived from wild-type mice and from the three gene knockout animals. The consequences of export pump deficiencies were evaluated primarily using vincristine and etoposide. Mice deficient in the three genes, mdr1a/1b and mrp1, exhibited a 128-fold increase in toxicity to vincristine and a 3-5-fold increase in toxicity to etoposide; increased toxicity to embryonic fibroblast cells from triple knockout mice also occurred with vincristine and etoposide. Vincristine, which normally does not express toxicity to the bone marrow and to the gastrointestinal mucosa when used at therapeutic doses, caused extensive damage to these tissues in mdr1a/1b(-/-), mrp1(-/-) mice. The findings indicate that the P-glycoprotein and mrpl are compensatory transporters for vincristine and etoposide in the bone marrow and the gastrointestinal mucosa and emphasize the potential for increased toxicities by the combined inhibition of these efflux pumps.

Quenching and enhancement of aroyl luminescence in excited nitrogen

This study investigates both decreases and increases of aromatic carbonyl phosphorescence in excited nitrogen, i.e., in a gas-chromatographic device called the aroyl luminescence detector (ALD). The ALD responds, with nigh specificity, to subpicogram amounts of strongly phosphorescing aroyls. Aroyl response may, however, be quenched by coeluting peaks or gaseous impurities. This deleterious effect has been investigated with O2, H2, CH4, and C3H8 as model quenchers. Aroyl phosphorescence is more severely quenched than the nitrogen background, i.e., the so-called second-positive system, N2 (C 3 pi u)-->N2 (B 3 pi g). Oxygen, while being the strongest among the tested quenchers of aroyl phosphorescence, is the weakest quencher of nitrogen emission. The efficiency of various quenchers is similar for aroyl compounds of similar structure. It differs, however--though not by more than a factor of 2--among aroyls of different chemical types. In contrast to these intensity-reducing effects, aroyl phosphorescence is significantly enhanced by the addition of argon to (the carrier and excitation gas) nitrogen. It is proposed that the reaction sequence Ar*(3P0,2) + N2-->N2(C)*-->N2(B)* + hv-->N2(A)* + hv results in an increased yield of the metastable N2(A 3 sigma u+) state (this state being considered responsible for the n-->pi* excitation of aroyl compounds via an efficient triplet-triplet energy-transfer process).

Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase

Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.

Gas chromatographic determination of primary alcohols as their formylbenzoic esters by gas-phase luminescence detection

A new and convenient method is described for the derivatization of primary alcohols with p-formylbenzoyl chloride, and the sensitive photometric detection of the resulting formylbenzoic ester derivatives based on their gas-phase luminescence in excited nitrogen. The coupling reaction proceeds rapidly and quantitatively, and the formylbenzoic esters show good GC properties. The minimum detectable amounts of the derivatized alcohols, at a signal three-times the peak-to-peak noise, lie between 10 and 100 pg per injection, and their linear ranges cover approximately three-orders of magnitude.

Prevention of brefeldin A-induced resistance to teniposide by the proteasome inhibitor MG-132: involvement of NF-kappaB activation in drug resistance

Brefeldin A, an agent that disrupts protein transport from the endoplasmic reticulum to the Golgi, induces the expression of GRP78 and the activation of nuclear factor (NF)-kappaB in cells. Treatment of cells with brefeldin A causes the development of resistance to topoisomerase II-directed agents, such as etoposide and doxorubicin. In this study, we show that treatment of EMT6 mouse mammary tumor cells with brefeldin A strongly induces GRP78 mRNA (8.5-fold) and resistance to teniposide (VM26). Treatment with okadaic acid causes a minor increase in GRP78 mRNA (2.1-fold) yet still induces resistance to VM26 as effectively as brefeldin A. In contrast, cells treated with castanospermine show a moderate increase in GRP78 mRNA (3.9-fold) but no resistance to VM26. These data imply that GRP78 induction does not mediate the development of drug resistance. An alternative mechanism of drug resistance may involve activation of the transcription factor, NF-kappaB, and we show that both brefeldin A and okadaic acid activate NF-kappaB in EMT6 cells. Furthermore, we demonstrate that treatment with the proteasome inhibitor MG-132 blocks the activation of NF-kappaB and prevents the development of resistance to VM26 induced by brefeldin A. Collectively, these results suggest that the resistance to VM26 in EMT6 cells treated with brefeldin A is mediated by the activation of NF-kappaB rather than the induction of GRP78. Our results also suggest that inhibition of NF-kappaB activation in tumor cells may increase the efficacy of topoisomerase II-directed agents in chemotherapy.

Hormonal regulation of glutamine metabolism by OK cells

The precise mechanism(s) of action of PTH, insulin or glucagon in the regulation of renal glutamine and ammonia metabolism is unknown. Our aim was to delineate the effects and the site(s) of action of these hormones on renal glutamine metabolism. Experiments were carried out using OK cells as a model system. Cell cultures were incubated for three hours in a bicarbonate buffer of pH 7.4 supplemented with either 1 mM [2-15N] or [5-15N] glutamine and 10(-7) M PTH, insulin or glucagon. Comparative studies were performed at pH 6.8, 7.4 or 7.6 without hormone. PTH and acute acidosis significantly stimulated glutamine metabolism via both the phosphate-dependent glutaminase (PDG) and glutamate dehydrogenase (GLDH) pathways. The opposite was observed at pH 7.6. Insulin augmented flux via PDG with little effect on the GLDH pathway. Glucagon had insignificant effects on either PDG or GLDH pathways. Intracellular [15N] glutamate formed from [2-15N] glutamine was removed partially by transamination to alanine, aspartate and serine and partially by translocation to an extracellular compartment. Acidosis, PTH and insulin enhanced the formation of [15N] alanine with little effect on [15N] aspartate. PTH, insulin and glucagon significantly stimulated the production of [15N]serine, whereas acidosis had little effect. The translocation of intracellular glutamate was significantly increased by acidosis, PTH and insulin and decreased by acute alkalosis. The data indicate that: (a) PTH mimicks the effect of acute acidosis on renal glutamine metabolism, that is, augmented glutamine metabolism through both PDG and GLDH pathways and stimulated the output of intracellular glutamate. This effect might be mediated via decreased activity of the Na(+)-H+ exchanger associated with cellular acidification and/or through a second messenger; (b) insulin, but not glucagon, increased glutamine uptake and metabolism, and simultaneously enhanced output of intracellular glutamate sufficiently to stimulate the PDG pathway; and (c) overall, glucagon had little effect on glutamine metabolism by OK cells compared with either PTH or insulin.

Interrelationships of leucine and glutamate metabolism in cultured astrocytes

The aim was to study the extent to which leucine furnishes alpha-NH2 groups for glutamate synthesis via branched-chain amino acid aminotransferase. The transfer of N from leucine to glutamate was determined by incubating astrocytes in a medium containing [15N]leucine and 15 unlabeled amino acids; isotopic abundance was measured with gas chromatography-mass spectrometry. The ratio of labeling in both [15N]glutamate/[15N]leucine and [2-15N]glutamine/[15N]leucine suggested that at least one-fifth of all glutamate N had been derived from leucine nitrogen. At the same time, enrichment in [15N]leucine declined, reflecting dilution of the 15N label by the unlabeled amino acids that were in the medium. Isotopic abundance in [15N]isoleucine increased very quickly, suggesting the rapidity of transamination between these amino acids. The appearance of 15N in valine was more gradual. Measurement of branched-chain amino acid transaminase showed that the reaction from leucine to glutamate was approximately six times more active than from glutamate to leucine (8.72 vs. 1.46 nmol/min/mg of protein). However, when the medium was supplemented with alpha-ketoisocaproate (1 mM), the ketoacid of leucine, the reaction readily ran in the "reverse" direction and intraastrocytic [glutamate] was reduced by approximately 50% in only 5 min. Extracellular concentrations of alpha-ketoisocaproate as low as 0.05 mM significantly lowered intracellular [glutamate]. The relative efficiency of branched-chain amino acid transamination was studied by incubating astrocytes with 15 unlabeled amino acids (0.1 mM each) and [15N]glutamate. After 45 min, the most highly labeled amino acid was [15N]alanine, which was closely followed by [15N]leucine and [15N]isoleucine. Relatively little 15N was detected in any other amino acids, except for [15N]serine. The transamination of leucine was approximately 17 times greater than the rate of [1-14C]leucine oxidation. These data indicate that leucine is a major source of glutamate nitrogen. Conversely, reamination of alpha-ketoisocaproate, the ketoacid of leucine, affords a mechanism for the temporary "buffering" of intracellular glutamate.

Brain glutamate metabolism: neuronal-astroglial relationships

The concentration of glutamate in the brain extracellular fluid must be kept low (approximately 3 microM) in order to maximize the signal-to-noise ratio upon the release of glutamate from neurons. In addition, the nerve endings require a supply of glutamate precursors that will not cause depolarization. The major precursor to neuronal glutamate is glutamine, which is synthesized in astrocytes and converted to glutamate in neurons. However, glutamine is not the sole source. Alanine also might serve as a precursor to glutamate via transamination, although this reaction is relatively inactive in synaptosomes. Finally, the branched-chain amino acids, and in particular leucine, appear to be very important precursors to glutamate and glutamine in astrocytes. By providing alpha-NH2 groups for the synthesis of glutamine, leucine also abets the uptake into brain of neutral amino acids, which are transported in exchange for brain glutamine. In addition, the branched-chain ketoacids are readily reaminated to the cognate amino acids, in the process consuming glutamate. Intraneuronal consumption of glutamate via ketoacid reamination might serve to buffer internal [glutamate] and to modulate the releasable pool.

Glutamate dehydrogenase reaction as a source of glutamic acid in synaptosomes

The role of the glutamate dehydrogenase reaction as a pathway of glutamate synthesis was studied by incubating synaptosomes with 5 mM 15NH4Cl and then utilizing gas chromatography-mass spectrometry to measure isotopic enrichment in glutamate and aspartate. The rate of formation of [15N]glutamate and [15N]aspartate from 5 mM 15NH4Cl was approximately 0.2 nmol/min/mg of protein, a value much less than flux through glutaminase (4.8 nmol/min/mg of protein) but greater than flux through glutamine synthetase (0.045 nmol/min/mg of protein). Addition of 1 mM 2-oxoglutarate to the medium did not affect the rate of [15N]glutamate formation. O2 consumption and lactate formation were increased in the presence of 5 mM NH3, whereas the intrasynaptosomal concentrations of glutamate and aspartate were unaffected. Treatment of synaptosomes with veratridine stimulated reductive amination of 2-oxoglutarate during the early time points. The production of ([15N]glutamate + [15N]aspartate) was enhanced about twofold in the presence of 5 mM beta-(+/-)-2-aminobicyclo [2.2.1]heptane-2-carboxylic acid, a known effector of glutamate dehydrogenase. Supplementation of the incubation medium with a mixture of unlabelled amino acids at concentrations similar to those present in the extracellular fluid of the brain had little effect on the intrasynaptosomal [glutamate] and [aspartate]. However, the enrichment in these amino acids was consistently greater in the presence of supplementary amino acids, which appeared to stimulate modestly the reductive amination of 2-oxoglutarate. It is concluded: (a) compared with the phosphate-dependent glutaminase reaction, reductive amination is a relatively minor pathway of synaptosomal glutamate synthesis in both the basal state and during depolarization; (b) NH3 toxicity, at least in synaptosomes, is not referable to energy failure caused by a depletion of 2-oxoglutarate in the glutamate dehydrogenase reaction; and (c) transamination is not a major mechanism of glutamate nitrogen production in nerve endings.

Glutathione turnover in cultured astrocytes: studies with [15N]glutamate

The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids.