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羟基乙酸在人体内的代谢路径有哪些？下述两个途径是否正确，给出证据：1.直接途径：羟基乙酸→乙醛酸→草酰乙酸→与乙酰辅酶 A 缩合进入 TCA 循环（回补反应）。2.间接途径：羟基乙酸→乙醛酸→甘氨酸→丝氨酸→丙酮酸→乙酰辅酶 A→进入 TCA 循环
羟基乙酸（Glycolic acid）在人体内的代谢涉及多个途径。根据提供的证据，以下是对羟基乙酸代谢路径的详细分析以及对您提出的两个具体途径的评估：
羟基乙酸在人体内的主要代谢路径
羟基乙酸（Glycolic acid）是一种α-羟基酸（AHA），在美容和皮肤病学制剂中广泛使用 。它也是正常身体代谢过程中产生的，被称为羟基乙酸 。在体内，羟基乙酸主要被代谢为乙醛酸（glyoxylic acid），乙醛酸是草酸（oxalate）的前体 。
1. 羟基乙酸转化为乙醛酸： 这是羟基乙酸代谢的关键一步。肝脏组织能够代谢羟基乙酸为乙醛酸 。研究表明，人类肝脏组织在将羟基乙酸进一步代谢为乙醛酸方面最为有效，其清除羟基乙酸的相对清除率（Vmax/Km）在人类、大鼠和兔肝脏中约为 14:9:1 。虽然羟基乙酸可能在体内形成，但其水平在人类中可能低于兔子和大鼠，这表明人类肝脏在清除羟基乙酸方面更高效 。
2. 乙醛酸的后续代谢： 乙醛酸是多种重要代谢途径的交叉点，其代谢产物包括草酸、甘氨酸和乙醇酸。
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转化为草酸： 乙醛酸是草酸的直接前体。有证据表明，乙醛酸可以被代谢为草酸，这在涉及肾结石形成的病例中尤其重要，因为草酸钙是肾结石的主要成分 。局部应用乙醛酸会显著增加尿液草酸排泄，并导致草酸钙肾病，这表明乙醛酸经皮吸收后会代谢为草酸 。此外，在氧化应激、内质网应激和NF-κB信号通路激活的情况下，草酸还会诱导肾小管上皮细胞损伤 。
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转化为甘氨酸： 乙醛酸可以通过转氨酶（如丙氨酸-乙醛酸转氨酶 [AGT]）转化为甘氨酸 。在HepG2细胞（一种人肝癌细胞系）中，线粒体中含有丙氨酸-乙醛酸转氨酶2（AGT2）和乙醛酸还原酶活性，它们可以将乙醛酸分别转化为甘氨酸和羟基乙酸 。在光呼吸循环中，甘氨酸在过氧化物酶体中合成，是羟基乙酸代谢的产物之一 。
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转化为其他中间产物： 乙醛酸也可以在某些条件下二聚化形成酒石酸盐（tartrates），这被认为是一种潜在的非生物途径，可以为柠檬酸循环提供底物 。此外，乙醛酸还可以作为多种氨基酸转氨酶的氨基受体，例如D-3-氨基异丁酸氨基转移酶可以催化乙醛酸的转氨作用 。
3. 羟基乙酸对皮肤的影响： 尽管羟基乙酸在体内可以被代谢，但其在化妆品和皮肤病学中的应用主要是局部作用。低浓度（2-5%）的羟基乙酸被认为通过促进角质层（SC）细胞间物质内聚力的逐渐减弱，导致最外层角质层（角质脱落层）的均匀剥落 。研究表明，即使使用4%的羟基乙酸制剂，角质层的屏障结构也没有被破坏，经表皮水分流失（TEWL）值也没有改变 。然而，高浓度（12%）的羟基乙酸会引起TEWL显著增加，角质层水合作用降低，并迅速引起强烈的红斑，表明其具有刺激性 。
评估您提出的两个代谢途径：
1. 直接途径：羟基乙酸→乙醛酸→草酰乙酸→与乙酰辅酶 A 缩合进入 TCA 循环（回补反应）。
- 羟基乙酸 → 乙醛酸： 这是正确的，证据明确指出羟基乙酸在肝脏中被代谢为乙醛酸 。
- 乙醛酸 → 草酰乙酸： 证据直接或间接支持了乙醛酸转化为草酰乙酸的可能性。
- 首先，乙醛酸是乙醛酸循环（glyoxylate shunt）的关键中间体，该循环能够绕过三羧酸（TCA）循环的氧化脱羧步骤，从而为糖异生和生物质生产保留碳骨架 。乙醛酸循环通常涉及异柠檬酸裂解酶（ICL）将异柠檬酸裂解为乙醛酸和琥珀酸，然后乙醛酸和乙酰辅酶A通过苹果酸合酶（MAS）缩合生成苹果酸。苹果酸可以进一步氧化为草酰乙酸 。在Mucor circinelloides中，乙醛酸循环的通量增加，可以更有效地产生苹果酸和草酰乙酸补充 。
- 其次，虽然乙醛酸循环在植物和微生物中更为突出，但在哺乳动物中，草酰乙酸可以由多种途径生成。D-3-氨基异丁酸氨基转移酶可以使用乙醛酸作为氨基受体，生成相应的酮酸（例如，如果氨基供体是β-丙氨酸，则生成丙酮酸；如果氨基供体是D-3-氨基异丁酸，则生成相应的酮酸），这些酮酸可能进一步转化为草酰乙酸 。
- 再者，乙醛酸可以通过β-羟基天冬氨酸循环（BHAC）直接在四个酶促步骤内生成草酰乙酸，这是目前已知最有效的乙醛酸同化途径之一，尤其在海洋变形菌中发现 。虽然BHAC在人体中的存在和功能未明确提及，但乙醛酸转化为草酰乙酸在代谢上是可行的。
- 草酰乙酸 → 与乙酰辅酶 A 缩合进入 TCA 循环（回补反应）： 这是正确的。草酰乙酸是TCA循环（也称为柠檬酸循环）的起始和再生分子。它与乙酰辅酶A缩合形成柠檬酸，从而启动TCA循环 。TCA循环的回补反应（anaplerotic reactions）旨在补充循环中间体，当草酰乙酸被用于糖异生或其他生物合成途径时，需要通过回补反应来补充，以维持TCA循环的正常运行。因此，如果乙醛酸可以转化为草酰乙酸，那么草酰乙酸通过与乙酰辅酶A缩合进入TCA循环是其标准的代谢命运。
结论： 您的第一个途径 羟基乙酸→乙醛酸→草酰乙酸→与乙酰辅酶 A 缩合进入 TCA 循环（回补反应） 是正确的，特别是在考虑到乙醛酸循环和潜在的乙醛酸向草酰乙酸转化的机制时 。
2. 间接途径：羟基乙酸→乙醛酸→甘氨酸→丝氨酸→丙酮酸→乙酰辅酶 A→进入 TCA 循环。
- 羟基乙酸 → 乙醛酸： 这是正确的，如前所述 。
- 乙醛酸 → 甘氨酸： 这是正确的。线粒体中的丙氨酸-乙醛酸转氨酶2（AGT2）可以将乙醛酸转化为甘氨酸 。在光呼吸循环中，乙醛酸也是甘氨酸的前体 。
- 甘氨酸 → 丝氨酸： 这是正确的。甘氨酸和丝氨酸代谢是密切相关的，它们之间可以相互转化。甘氨酸、丝氨酸和苏氨酸代谢通路是与多种眼部疾病相关的关键代谢通路之一 。在胃溃疡模型大鼠中，艾灸干预后，血清和胃组织中的代谢物谱发生变化，其中就包括甘氨酸、丝氨酸和苏氨酸代谢通路，这表明这些氨基酸在生理和病理条件下都具有代谢活性 。甘氨酸可以被甘氨酸羟甲基转移酶（serine hydroxymethyltransferase）转化为丝氨酸。
- 丝氨酸 → 丙酮酸： 这是正确的。丝氨酸可以通过丝氨酸脱水酶的作用脱氨转化为丙酮酸。在植物的光呼吸途径中，丝氨酸被转化为羟基丙酮酸，羟基丙酮酸随后被还原为甘油酸，但最终也可能导致丙酮酸的形成 。在胃溃疡模型大鼠的研究中，丙氨酸、天冬氨酸和谷氨酸代谢，以及丙酮酸代谢途径都被发现与艾灸的干预效果有关 。
- 丙酮酸 → 乙酰辅酶 A： 这是正确的。丙酮酸是糖酵解的最终产物，通过丙酮酸脱氢酶复合体的作用，被氧化脱羧转化为乙酰辅酶A。乙酰辅酶A是TCA循环的入口分子 。
- 乙酰辅酶 A → 进入 TCA 循环： 这是正确的。乙酰辅酶A通过与草酰乙酸缩合进入TCA循环 。
结论： 您的第二个途径 羟基乙酸→乙醛酸→甘氨酸→丝氨酸→丙酮酸→乙酰辅酶 A→进入 TCA 循环 也是正确的，它描述了乙醛酸通过氨基酸代谢间接进入TCA循环的途径 。
总结：
羟基乙酸在人体内的代谢路径主要涉及先转化为乙醛酸，乙醛酸再通过不同的途径进一步代谢。您提出的两个途径都是合理的：
- 直接途径（羟基乙酸→乙醛酸→草酰乙酸→与乙酰辅酶 A 缩合进入 TCA 循环）侧重于乙醛酸通过乙醛酸循环或类似机制直接生成TCA循环中间体草酰乙酸，从而实现回补功能 。
- 间接途径（羟基乙酸→乙醛酸→甘氨酸→丝氨酸→丙酮酸→乙酰辅酶 A→进入 TCA 循环）则描述了乙醛酸通过氨基酸（甘氨酸和丝氨酸）的转化，最终生成丙酮酸并进一步转化为乙酰辅酶A，从而进入TCA循环 。
这些代谢途径共同描绘了羟基乙酸在人体内复杂而多样的代谢命运，同时也突显了乙醛酸作为关键代谢中间体的重要性。值得注意的是，这些途径的相对通量和具体酶促步骤可能会因细胞类型、组织和生理状态的不同而有所差异。此外，羟基乙酸和乙醛酸的积累在某些情况下可能引起病理生理效应，例如乙醛酸代谢为草酸，可能导致肾结石 。
References
1Mode of action of glycolic acid on human stratum corneum: ultrastructural and functional evaluation of the epidermal barrier.PubMed
M Fartasch, J Teal, G K Menon
Arch Dermatol Res. 1997 Jun;289(7):404-9. doi: 10.1007/s004030050212.
Alpha-hydroxy acids (AHA) such as glycolic acid have recently been used extensively in cosmetic and dermatological formulas. In low concentration (2-5%) glycolic acid is believed to facilitate progressive weakening of cohesion of the intercellular material of the stratum corneum (SC), resulting in uniform exfoliation of its outermost layers (the stratum disjunctum). Since thinning of the SC as well as changes of intercellular lipids could theoretically compromise the barrier functions of the skin, we investigated the mode of AHA action on the SC to determine whether enhanced desquamation compromises the barrier structures of the SC and changes transepidermal water loss (TEWL) values. Electron microscopy of the epidermis biopsied from the volar forearm of human volunteers after 3 weeks of treatment with a 4% glycolic acid formulation twice daily was employed to evaluate 1) epidermal morphology and thickness of the SC, (2) the lamellar body and SC lipid bilayer organization, and (3) desquamative events based on degradation of desmosomes. TEWL values and SC hydration were recorded prior to and at the end of the study. Electron microscopy revealed no ultrastructural changes in the nucleated layers of the epidermis. The lamellar body (LB) secretory system in the stratum granulosum (SG), and intercellular lipid lamellae in the SC in both vehicle- and glycolic acid-treated samples were comparable to normal human SC. Within the SC, enhanced desmosomal breakdown, promoting loss of cohesion and desquamation, was restricted to the stratum disjunctum while desmosomes of the stratum compactum were unaffected. Treated areas displayed histologically, a more compact appearing SC. TEWL values remained unchanged in glycolic acid- and vehicle-treated skin. Our findings indicate that the barrier structures of the SC are not disrupted by glycolic acid formulations at the concentration used. One of the mechanism of action of AHA on the SC seemed to be a "targeted" desmosomal (corneosomal) action without compromising the barrier structures of the skin.
2Oxalate-induced apoptosis through ERS-ROS-NF-κB signalling pathway in renal tubular epithelial cell.PubMed
Shaoxiong Ming, Jia Tian, Ke Ma, et al.
Mol Med. 2022 Aug 3;28(1):88. doi: 10.1186/s10020-022-00494-5.
BACKGROUND: Kidney stones are composed of approximately 70-80% calcium oxalate. However, the exact mechanism of formation of calcium oxalate kidney stones remains unclear. In this study, we investigated the roles of endoplasmic reticulum stress (ERS), reactive oxygen species (ROS), and the NF-κB signalling pathway in the pathogenesis of oxalate-induced renal tubular epithelial cell injury and its possible molecular mechanisms. METHODS: We established a model to evaluate the formation of kidney stones by intraperitoneal injection of glyoxylic acid solution into mice and assessed cell morphology, apoptosis, and the expression levels of ERS, ROS, and NF-κB signalling pathway-related proteins in mouse renal tissues. Next, we treated HK-2 cells with potassium oxalate to construct a renal tubular epithelial cell injury model. We detected the changes in autophagy, apoptosis, and mitochondrial membrane potential and investigated the ultrastructure of the cells by transmission electron microscopy. Western blotting revealed the expression levels of apoptosis and autophagy proteins; mitochondrial structural and functional proteins; and ERS, ROS, and NF-κB (p65) proteins. Lastly, we studied the downregulation of NF-κB activity in HK-2 cells by lentivirus interference and confirmed the interaction between the NF-κB signalling and ERS/ROS pathways. RESULTS: We observed swelling of renal tissues, increased apoptosis of renal tubular epithelial cells, and activation of the ERS, ROS, and NF-κB signalling pathways in the oxalate group. We found that oxalate induced autophagy, apoptosis, and mitochondrial damage in HK-2 cells and activated the ERS/ROS/NF-κB pathways. Interestingly, when the NF-κB signalling pathway was inhibited, the ERS/ROS pathway was also inhibited. CONCLUSION: Oxalate induces HK-2 cell injury through the interaction between the NF-κB signalling and ERS/ROS pathways.
3Comparison of the metabolism of ethylene glycol and glycolic acid in vitro by precision-cut tissue slices from female rat, rabbit and human liver.PubMed
E D Booth, O Dofferhoff, P J Boogaard, et al.
Xenobiotica. 2004 Jan;34(1):31-48. doi: 10.1080/00498250310001624636.
1. The metabolism of [1,2-(14)C]-ethylene glycol and [1,2-(14)C]-glycolic acid was studied in vitro using precision-cut tissue slices prepared from the livers of female Sprague-Dawley rats, New Zealand white rabbits and humans. The time-course for production of metabolites formed from ethylene glycol at concentrations from 3 to 40 mM was determined to compare quantitatively the differences between species in the rates and amounts of formation of glycolic acid, the presumed developmental toxicant of ethylene glycol. The rates of metabolism of glycolic acid to glyoxylic acid at concentrations from 0.05 to 16 mM by liver tissue from the different species were also determined. The apparent V(max)/K(m) for the metabolic conversions of ethylene glycol to glycolic acid and for glycolic acid to glyoxylic acid in liver tissue from the different species were obtained. 2. There were qualitative differences in the metabolic profiles and quantitative differences in the formation of glycolic acid between the mammalian liver systems. There was an average of 10-fold less glycolic acid produced by liver slices from rabbits compared with rats. With the human liver, the formation of glycolic acid was not detectable using tissue from three of four human donors. A low level of glycolic acid was detected in one liver slice incubation from one of the four subjects, but only at one extended time point; glyoxylate was detected with liver slices from all four humans. 3. Liver slices prepared from female Sprague-Dawley rats, female New Zealand White rabbits and three female human subjects all metabolized glycolic acid to glyoxylic acid. Human liver tissue was the most effective at further metabolizing glycolic acid to glyoxylic acid. The ratios of V(max)/K(m), representing the relative clearance of glycolic acid from liver tissue, were approximately 14:9:1 for human, rat and rabbit liver, respectively. 4. Precision-cut liver slices maintained in dynamic organ culture are good predictors of metabolism by liver tissue in vivo. The results of the present study therefore indicate that levels of glycolic acid, if formed in vivo, following exposures to similar concentrations of ethylene glycol, would be lower in humans than in rabbits and rats.
4Production of tartrates by cyanide-mediated dimerization of glyoxylate: a potential abiotic pathway to the citric acid cycle.PubMed
Christopher Butch, Elizabeth D Cope, Pamela Pollet, et al.
J Am Chem Soc. 2013 Sep 11;135(36):13440-5. doi: 10.1021/ja405103r. Epub 2013 Aug 30.
An abiotic formation of meso- and DL-tartrates in 80% yield via the cyanide-catalyzed dimerization of glyoxylate under alkaline conditions is demonstrated. A detailed mechanism for this conversion is proposed, supported by NMR evidence and (13)C-labeled reactions. Simple dehydration of tartrates to oxaloacetate and an ensuing decarboxylation to form pyruvate are known processes that provide a ready feedstock for entry into the citric acid cycle. While glyoxylate and high hydroxide concentration are atypical in the prebiotic literature, there is evidence for natural, abiotic availability of each. It is proposed that this availability, coupled with the remarkable efficiency of tartrate production from glyoxylate, merits consideration of an alternative prebiotic pathway for providing constituents of the citric acid cycle.
5Metabolomics studies in common multifactorial eye disorders: a review of biomarker discovery for age-related macular degeneration, glaucoma, diabetic retinopathy and myopia.PubMed
Gizachew Tilahun Belete, Lei Zhou, King-Kit Li, et al.
Front Mol Biosci. 2024 Aug 13;11:1403844. doi: 10.3389/fmolb.2024.1403844. eCollection 2024.
INTRODUCTION: Multifactorial Eye disorders are a significant public health concern and have a huge impact on quality of life. The pathophysiological mechanisms underlying these eye disorders were not completely understood since functional and low-throughput biological tests were used. By identifying biomarkers linked to eye disorders, metabolomics enables early identification, tracking of the course of the disease, and personalized treatment. METHODS: The electronic databases of PubMed, Scopus, PsycINFO, and Web of Science were searched for research related to Age-Related macular degeneration (AMD), glaucoma, myopia, and diabetic retinopathy (DR). The search was conducted in August 2023. The number of cases and controls, the study's design, the analytical methods used, and the results of the metabolomics analysis were all extracted. Using the QUADOMICS tool, the quality of the studies included was evaluated, and metabolic pathways were examined for distinct metabolic profiles. We used MetaboAnalyst 5.0 to undertake pathway analysis of differential metabolites. RESULTS: Metabolomics studies included in this review consisted of 36 human studies (5 Age-related macular degeneration, 10 Glaucoma, 13 Diabetic retinopathy, and 8 Myopia). The most networked metabolites in AMD include glycine and adenosine monophosphate, while methionine, lysine, alanine, glyoxylic acid, and cysteine were identified in glaucoma. Furthermore, in myopia, glycerol, glutamic acid, pyruvic acid, glycine, cysteine, and oxoglutaric acid constituted significant metabolites, while glycerol, glutamic acid, lysine, citric acid, alanine, and serotonin are highly networked metabolites in cases of diabetic retinopathy. The common top metabolic pathways significantly enriched and associated with AMD, glaucoma, DR, and myopia were arginine and proline metabolism, methionine metabolism, glycine and serine metabolism, urea cycle metabolism, and purine metabolism CONCLUSION: This review recapitulates potential metabolic biomarkers, networks and pathways in AMD, glaucoma, DR, and myopia, providing new clues to elucidate disease mechanisms and therapeutic targets. The emergence of advanced metabolomics techniques has significantly enhanced the capability of metabolic profiling and provides novel perspectives on the metabolism and underlying pathogenesis of these multifactorial eye conditions. The advancement of metabolomics is anticipated to foster a deeper comprehension of disease etiology, facilitate the identification of novel therapeutic targets, and usher in an era of personalized medicine in eye research.
6Functional changes in human stratum corneum induced by topical glycolic acid: comparison with all-trans retinoic acid.PubMed
I Effendy, C Kwangsukstith, J Y Lee, et al.
Acta Derm Venereol. 1995 Nov;75(6):455-8. doi: 10.2340/0001555575455458.
The effects of topical glycolic acid and all-trans retinoic acid on stratum corneum barrier function and hydration of human skin were investigated in 6 healthy volunteers utilizing non-invasive techniques. In addition, changes in stratum corneum turnover time induced by the substances were examined using the dansyl chloride fluorescence test. Twelve percent glycolic acid in water and 0.1% retinoic acid in ethanol, respectively, were applied for 60 min once daily, over a period of 2 weeks (5 consecutive days weekly) on dansyl chloride-labelled skin and on untreated skin. During a 10-day application period, both glycolic acid and retinoic acid similarly induced a significant increase in TEWL. However, after discontinuing treatment, TEWL in retinoic acid-exposed skin remained increased. Glycolic acid significantly reduced stratum corneum hydration from day 11 to day 18 (p < 0.05), while retinoic acid induced skin dryness after 9 days of treatment, which persisted until day 18 (p < 0.005). Whereas glycolic acid rapidly induced an intense erythema implying a direct non-specific inflammatory response, the retinoic acid-exposed skin gradually developed erythema. Retinoic acid caused scaling to a greater extent than did glycolic acid, even after treatment cessation. Both glycolic acid and retinoic acid significantly decreased stratum corneum turnover time and stratum corneum turnover time50 (the time in days from labelling until approximately 50% of fluorescence disappeared), compared with the vehicle controls. However, glycolic acid shortened stratum corneum turnover time (12.8 +/- 0.9 days) as well as stratum corneum turnover time50 (7.3 +/- 0.7 d) significantly more than did retinoic acid (15.8 +/- 0.7 d and 9 +/- 0.8 d, respectively). While ethanol (vehicle of retinoic acid) slightly but significantly decreased stratum corneum turnover time (p < 0.05), water (vehicle of glycolic acid) did not. This study showed that both glycolic acid and retinoic acid induced certain functional changes in stratum corneum, mirroring their irritation potential. However, changes at retinoic acid-exposed sites appeared longer-lasting, implying a distinct mode of action. An increase in stratum corneum turnover induced by the substances may be, in part, linked with their irritation properties.
7Photorespiratory glycolate-glyoxylate metabolism.PubMed
Younès Dellero, Mathieu Jossier, Jessica Schmitz, et al.
J Exp Bot. 2016 May;67(10):3041-52. doi: 10.1093/jxb/erw090. Epub 2016 Mar 19.
Photorespiration is one of the major carbon metabolism pathways in oxygen-producing photosynthetic organisms. This pathway recycles 2-phosphoglycolate (2-PG), a toxic metabolite, to 3-phosphoglycerate when ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) uses oxygen instead of carbon dioxide. The photorespiratory cycle is in competition with photosynthetic CO2 fixation and it is accompanied by carbon, nitrogen and energy losses. Thus, photorespiration has become a target to improve crop yields. Moreover, during the photorespiratory cycle intermediate metabolites that are toxic to Calvin-Benson cycle and RuBisCO activities, such as 2-PG, glycolate and glyoxylate, are produced. Thus, the presence of an efficient 2-PG/glycolate/glyoxylate 'detoxification' pathway is required to ensure normal development of photosynthetic organisms. Here we review our current knowledge concerning the enzymes that carry out the glycolate-glyoxylate metabolic steps of photorespiration from glycolate production in the chloroplasts to the synthesis of glycine in the peroxisomes. We describe the properties of the proteins involved in glycolate-glyoxylate metabolism in Archaeplastida and the phenotypes observed when knocking down/out these specific photorespiratory players. Advances in our understanding of the regulation of glycolate-glyoxylate metabolism are highlighted.
8Glycolate and glyoxylate metabolism in HepG2 cells.PubMed
Paul R S Baker, Scott D Cramer, Martha Kennedy, et al.
Am J Physiol Cell Physiol. 2004 Nov;287(5):C1359-65. doi: 10.1152/ajpcell.00238.2004. Epub 2004 Jul 7.
Oxalate synthesis in human hepatocytes is not well defined despite the clinical significance of its overproduction in diseases such as the primary hyperoxalurias. To further define these steps, the metabolism to oxalate of the oxalate precursors glycolate and glyoxylate and the possible pathways involved were examined in HepG2 cells. These cells were found to contain oxalate, glyoxylate, and glycolate as intracellular metabolites and to excrete oxalate and glycolate into the medium. Glycolate was taken up more effectively by cells than glyoxylate, but glyoxylate was more efficiently converted to oxalate. Oxalate was formed from exogenous glycolate only when cells were exposed to high concentrations. Peroxisomes in HepG2 cells, in contrast to those in human hepatocytes, were not involved in glycolate metabolism. Incubations with purified lactate dehydrogenase suggested that this enzyme was responsible for the metabolism of glycolate to oxalate in HepG2 cells. The formation of 14C-labeled glycine from 14C-labeled glycolate was observed only when cell membranes were permeabilized with Triton X-100. These results imply that peroxisome permeability to glycolate is restricted in these cells. Mitochondria, which produce glyoxylate from hydroxyproline metabolism, contained both alanine:glyoxylate aminotransferase (AGT)2 and glyoxylate reductase activities, which can convert glyoxylate to glycine and glycolate, respectively. Expression of AGT2 mRNA in HepG2 cells was confirmed by RT-PCR. These results indicate that HepG2 cells will be useful in clarifying the nonperoxisomal metabolism associated with oxalate synthesis in human hepatocytes.
9Marine Proteobacteria metabolize glycolate via the β-hydroxyaspartate cycle.PubMed
Lennart Schada von Borzyskowski, Francesca Severi, Karen Krüger, et al.
Nature. 2019 Nov;575(7783):500-504. doi: 10.1038/s41586-019-1748-4. Epub 2019 Nov 13.
One of the most abundant sources of organic carbon in the ocean is glycolate, the secretion of which by marine phytoplankton results in an estimated annual flux of one petagram of glycolate in marine environments. Although it is generally accepted that glycolate is oxidized to glyoxylate by marine bacteria, the further fate of this C metabolite is not well understood. Here we show that ubiquitous marine Proteobacteria are able to assimilate glyoxylate via the β-hydroxyaspartate cycle (BHAC) that was originally proposed 56 years ago. We elucidate the biochemistry of the BHAC and describe the structure of its key enzymes, including a previously unknown primary imine reductase. Overall, the BHAC enables the direct production of oxaloacetate from glyoxylate through only four enzymatic steps, representing-to our knowledge-the most efficient glyoxylate assimilation route described to date. Analysis of marine metagenomes shows that the BHAC is globally distributed and on average 20-fold more abundant than the glycerate pathway, the only other known pathway for net glyoxylate assimilation. In a field study of a phytoplankton bloom, we show that glycolate is present in high nanomolar concentrations and taken up by prokaryotes at rates that allow a full turnover of the glycolate pool within one week. During the bloom, genes that encode BHAC key enzymes are present in up to 1.5% of the bacterial community and actively transcribed, supporting the role of the BHAC in glycolate assimilation and suggesting a previously undescribed trophic interaction between autotrophic phytoplankton and heterotrophic bacterioplankton.
10[Nuclear magnetic resonance-based metabolomics revealed metabolite profiles participate in intervention effect of refined moxibustion in gastric ulcer model rats].PubMed
Gu-Hang Wei, Zong-Bao Yang, Yu-Feng Xie, et al.
Zhen Ci Yan Jiu. 2021 Oct 25;46(10):829-36. doi: 10.13702/j.1000-0607.201351.
OBJECTIVE: To investigate the effect of refined moxibustion on expression of gastric mucosal epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF), and changes of metabolite profiles in gastric ulcer (GU) rats, so as to analyze its mechanism underlying improvement of GU. METHODS: Male SD rats were randomized into control, model, acupoint moxibustion groups (=6 per group). The GU model was induced by cold-restraint stress. The ignited refined moxa was applied to bilateral "Liangmen" (ST21) and "Zusanli" (ST36) for 3 cones/acupoint, once daily for 7 days. Then, we employed 1H NMR-based metabolomics approach to analyze the metabolic profiles of serum and stomach tissue samples. The conventional histopathological changes of the gastric mucosa were observed by H.E. stain and the expressions of EGFR and VEGF in the gastric mucosa were detected by immunohistochemistry. RESULTS: Compared to the control group, the expression levels of EGFR and VEGF were significantly increased in the model group (<0.01, <0.05), and further notably up-regulated in the acupoint moxibustion group (<0.001, <0.01). Results of H.E. staining showed damage of the folds of gastric mucosa, disordered arrangement of the glands, infiltration of inflammatory cells and unclear structure of gastric mucosa in the model group, which was relatively milder in the acupoint moxibustion group. 1H-NMR technical analysis showed that in comparison with the control group, 11 and 11 metabolites in the stomach extract and plasma were increased, 10 in the gastric tissue and 3 in the plasma were decreased in the GU model group; while in comparison with the model group, 17 differently expressed metabolites in the gastric extract and 10 metabolites in the plasma restored to their levels of control group after the acupoint moxibustion intervention. These metabolites participate in 12 metabolic pathways including glycine, serine and threonine metabolism, glutathione metabolism, glycine metabolism, alanine, aspartic acid and glutamic acid metabolism, purine metabolism, glyoxylic acid and digarboxylic acid metabolism, biosynthesis of aminoacyl-tRNA, amino sugar and nucleotide sugar metabolism, cysteine and methionine metabolism, citrate cycle, pyruvate metabolism, and the mutual conversion of pentose and glucuronate，suggesting their involvement in moxibustion-induced improvement of GU. CONCLUSION: Refined moxibustion at ST21 and ST36 can up-regulate the expression of EGFR and VEGF in the gastric mucosa and lessen gastric mucosal injury, which may be related to its effects in reducing GU-induced metabolic disorders, including sugar, purine, amino acid, and phospholipid metabolism and antioxidant defense system.
11Hair-straightening cosmetics containing glyoxylic acid induce crystalline nephropathy.PubMed
Thomas Robert, Ellie Tang, Jennifer Kervadec, et al.
Kidney Int. 2024 Dec;106(6):1117-1123. doi: 10.1016/j.kint.2024.07.032. Epub 2024 Aug 26.
We recently reported the case of a patient who experienced three consecutive episodes of acute kidney injury, all of them following a "Brazilian" hair-straightening treatment. The cream used for the straightening procedure contained glyoxylic acid. To examine possible underlying mechanisms causing kidney injury, four groups of mice were exposed to topical application of (i) the straightening product, (ii) a cream containing 10% glyoxylic acid, (iii) a cream containing 10% glycolic acid or (iv) a control cream. Application of glycolic acid slightly increased urine oxalate excretion, while glyoxylic acid and the straightening product dramatically increased urine oxalate excretion and caused calcium oxalate nephropathy after transcutaneous absorption. Thus, glyoxylic acid was presumptively absorbed through the skin, metabolized to oxalate and promoted crystallization of calcium oxalate in urine. Hence, cosmetic products containing glyoxylic acid may induce acute kidney injury and should be discontinued. Further studies are needed to investigate the metabolism of glycolic acid and glyoxylic acid following topical application.
12Purification, characterization and inhibition of D-3-aminoisobutyrate aminotransferase from the rat liver.PubMed
N Tamaki, M Kaneko, C Mizota, et al.
Eur J Biochem. 1990 Apr 20;189(1):39-45. doi: 10.1111/j.1432-1033.1990.tb15457.x.
D-3-Aminoisobutyrate-pyruvate aminotransferase was purified 2000-fold from rat liver extract using heat treatment, ammonium sulfate fractionation, carboxylmethyl-Sepharose CL-6B, DEAE-Sepharose CL-6B, hydroxyapatite, Sephacryl S-200 and electrofocusing chromatographies. The purified enzyme was shown to be homogeneous by gel electrophoresis both in the presence and absence of SDS. Its molecular mass, determined by gel filtration, was 220 kDa and the subunit molecular mass was 52 kDa. The enzyme exhibited absorption maxima at 280 nm and 412 nm with a shoulder at 330 nm at neutral pH. The pH optimum for enzyme activity was 9.5 and the Km values for beta-alanine and pyruvic acid were calculated to be 0.81 mM and 0.45 mM, respectively. The purified enzyme catalyzed the transamination of omega-amino acids; beta-alanine and D-3-aminoisobutyric acid served as good amino donors, and pyruvic acid, glyoxylic acid and oxaloacetic acid were favorable amino acceptors. 6-Azauracil and 6-azathymine were found to be potent inhibitors of purified rat liver D-3-aminoisobutyrate-pyruvate aminotransferase. 6-Azauracil acted as a competitive inhibitor with respect to beta-alanine, and was an uncompetitive inhibitor with respect to pyruvic acid with a Ki of approximately 8.9 mM.
13Absorbable polyglycolide devices in trauma and bone surgery.PubMed
N Ashammakhi, P Rokkanen
Biomaterials. 1997 Jan;18(1):3-9. doi: 10.1016/s0142-9612(96)00107-x.
Poly(glycolic acid) or polyglycolide (PGA) is a polymer of glycolic acid. Glycolic acid is produced during normal body metabolism and is known as hydroxyacetic acid. Strong implants can be manufactured from this polymer with a self-reinforcing (SR) technique and used in the treatment of fractures and osteotomies. Since 1984, SR-PGA implants have been used routinely in our hospital for internal fixation of bone fractures. These implants were studied extensively in experimental animals and proved biocompatible. In 1.7% of human cases, sinus formation may develop after the use of these implants, which does not disturb healing. Use of these absorbable implants is justified as it obviates the need for a second operation for implant removal and avoids the risks associated with biostable implants.
14Gluconeogenic precursor availability regulates flux through the glyoxylate shunt in .PubMed
Audrey Crousilles, Stephen K Dolan, Paul Brear, et al.
J Biol Chem. 2018 Sep 14;293(37):14260-14269. doi: 10.1074/jbc.RA118.004514. Epub 2018 Jul 20.
The glyoxylate shunt bypasses the oxidative decarboxylation steps of the tricarboxylic acid (TCA) cycle, thereby conserving carbon skeletons for gluconeogenesis and biomass production. In , carbon flux is redirected through the first enzyme of the glyoxylate shunt, isocitrate lyase (ICL), following phosphorylation and inactivation of the TCA cycle enzyme, isocitrate dehydrogenase (ICD), by the kinase/phosphatase, AceK. In contrast, mycobacterial species lack AceK and employ a phosphorylation-insensitive isocitrate dehydrogenase (IDH), which is allosterically activated by the product of ICL activity, glyoxylate. However, expresses IDH, ICD, ICL, and AceK, raising the question of how these enzymes are regulated to ensure proper flux distribution between the competing pathways. Here, we present the structure, kinetics, and regulation of ICL, IDH, and ICD from We found that flux partitioning is coordinated through reciprocal regulation of these enzymes, linking distribution of carbon flux to the availability of the key gluconeogenic precursors, oxaloacetate and pyruvate. Specifically, a greater abundance of these metabolites activated IDH and inhibited ICL, leading to increased TCA cycle flux. Regulation was also exerted through AceK-dependent phosphorylation of ICD; high levels of acetyl-CoA (which would be expected to accumulate when oxaloacetate is limiting) stimulated the kinase activity of AceK, whereas high levels of oxaloacetate stimulated its phosphatase activity. In summary, the TCA cycle-glyoxylate shunt branch point in has a complex enzymology that is profoundly different from those in other species characterized to date. Presumably, this reflects its predilection for consuming fatty acids, especially during infection scenarios.
15The hydroxypyruvate-reducing system in Arabidopsis: multiple enzymes for the same end.PubMed
Stefan Timm, Alexandra Florian, Kathrin Jahnke, et al.
Plant Physiol. 2011 Feb;155(2):694-705. doi: 10.1104/pp.110.166538. Epub 2010 Dec 23.
Hydroxypyruvate (HP) is an intermediate of the photorespiratory pathway that originates in the oxygenase activity of the key enzyme of photosynthetic CO(2) assimilation, Rubisco. In course of this high-throughput pathway, a peroxisomal transamination reaction converts serine to HP, most of which is subsequently reduced to glycerate by the NADH-dependent peroxisomal enzyme HP reductase (HPR1). In addition, a NADPH-dependent cytosolic HPR2 provides an efficient extraperoxisomal bypass. The combined deletion of these two enzymes, however, does not result in a fully lethal photorespiratory phenotype, indicating even more redundancy in the photorespiratory HP-into-glycerate conversion. Here, we report on a third enzyme, HPR3 (At1g12550), in Arabidopsis (Arabidopsis thaliana), which also reduces HP to glycerate and shows even more activity with glyoxylate, a more upstream intermediate of the photorespiratory cycle. The deletion of HPR3 by T-DNA insertion mutagenesis results in slightly altered leaf concentrations of the photorespiratory intermediates HP, glycerate, and glycine, indicating a disrupted photorespiratory flux, but not in visible alteration of the phenotype. On the other hand, the combined deletion of HPR1, HPR2, and HPR3 causes increased growth retardation, decreased photochemical efficiency, and reduced oxygen-dependent gas exchange in comparison with the hpr1xhpr2 double mutant. Since in silico analysis and proteomic studies from other groups indicate targeting of HPR3 to the chloroplast, this enzyme could provide a compensatory bypass for the reduction of HP and glyoxylate within this compartment.
16Combining topical dermal infused exosomes with injected calcium hydroxylapatite for enhanced tissue biostimulation.PubMed
Greg Chernoff
J Cosmet Dermatol. 2023 Mar;22 Suppl 1:15-27. doi: 10.1111/jocd.15695.
BACKGROUND: Exosome research continues to flourish. Subsequent knowledge surrounding indications, dose-response, safety, efficacy, and the ability to combine exosome treatment as a "skin primer"-for biostimulation modalities such as calcium hydroxylapatite (CaHA), platelet-rich plasma (PRP), and platelet-rich fibrin matrix (PRFM) is growing rapidly. The objective of this study was to develop safe, reproducible methods of improving topical exosome absorption to enhance the quality of skin either by themselves, or in combination with injectable CaHA. METHODS: Under IRB Approval (International Cell Surgical Society: ICSS-2022-007), 40 patients were enrolled in this study. Twenty patients underwent facial biostimulatory dermal infusion alone, to determine if this method allowed adequate exosome absorption. Five patients underwent facial biostimulatory infusion followed immediately by Dilute CaHA injection (1:1 dilution) to the face. Five patients underwent exosome biostimulatory dermal infusion followed immediately by hyperdilute CaHA (dilution 1:4) injection to the neck. Five patients underwent Facial Dilute CaHA injection (1:1 dilution) alone, without dermal infusion. Five patients underwent neck hyperdilute CaHA injection (1:4 dilution) alone, without dermal infusion. All patients had pretreatment Quantificare 3-D photo-documentation and skin analysis (Quantificare, France). In all patients, the skin was first cleansed with a gentle glycolic acid facial wash (Gregory MD). To induce a "homing inflammatory environment" for the exosomes, sea salt exfoliation was performed (SaltFacial®, SaltMed, Cardiff, CA). A nitric oxide-generating serum (N101 Pneuma Nitric Oxide, Austin, TX) was then applied to act as an enhanced vehicle for absorption. A 3 MHz ultrasound (SaltFacial®, SaltMed, Cardiff, CA) was then utilized to further deepen the absorption of the nitric oxide serum. A topical emulsion containing equal volumes (1.0 cc containing 1 million) of exosomes (Kimera Labs, Miramar, FL), 25 units of botulinum toxin (Xeomin, Merz Aesthetics, Raleigh, NC) and hyaluronic acid (Belatero, Merz Aesthetics, Raleigh, NC) was mixed via back-and-forth propulsion in a 3-cc syringe. When adequately mixed, the emulsion was then applied to the treatment areas. The cavitating ultrasound was then used to aid in the absorption of the emulsion. The patients were then treated with high-intensity LED therapy (SaltFacial®, SaltMed, Cardiff, CA), utilizing the collagen restoration preset program of combination red (660 nm) near-infrared (930 nm) wavelength for 20 min. Post-treatment Quantificare analysis was performed at 15 and 30 days after treatment. RESULTS: Without exception, all dermal infusion alone and CaHA injection alone patients showed an improvement in the tone, quality, and texture of their skin. Quantificare results showed consistent improvement in wrinkles, pores, skin evenness, improved vascularity, and a reduction in oiliness and unwanted pigment. When employed as a skin primer prior to injections (CaHA), enhanced and more rapid results were seen. CONCLUSIONS: Biostimulatory dermal infusion can be achieved utilizing topical placental mesenchymal stem cell-derived exosomes. These exosomes can be used alone, or mixed with ancillary ingredients such as botulinum toxin, hyaluronic acid dermal filler, and CaHA to customize and personalize treatments based upon individual patient needs. Topical absorption is enhanced with sea salt exfoliation, a topical nitric oxide-generating serum, and 3 MHz cavitating ultrasound. Post-absorption activity is enhanced with high-intensity LED treatment. The addition of CaHA injections after the topical exosome "priming of the skin" yielded enhanced skin quality faster than exosomes or CaHA alone.
17AhR activation attenuates calcium oxalate nephrocalcinosis by diminishing M1 macrophage polarization and promoting M2 macrophage polarization.PubMed
Xiaoqi Yang, Haoran Liu, Tao Ye, et al.
Theranostics. 2020 Oct 25;10(26):12011-12025. doi: 10.7150/thno.51144. eCollection 2020.
Calcium oxalate (CaOx) crystal can trigger kidney injury, which contributes to the pathogenesis of nephrocalcinosis. The phenotypes of infiltrating macrophage may impact CaOx-mediated kidney inflammatory injury as well as crystal deposition. How aryl hydrocarbon receptor (AhR) regulates inflammation and macrophage polarization is well understood; however, how it modulates CaOx nephrocalcinosis remains unclear. Mice were intraperitoneally injected with glyoxylate to establish CaOx nephrocalcinosis model with or without the treatment of AhR activator 6-formylindolo(3,2-b)carbazole (FICZ). Positron emission tomography computed tomography (PET-CT) imaging, Periodic acid-Schiff (PAS) staining, and polarized light optical microscopy were used to evaluate kidney injury and crystal deposition in mice kidney. Western blotting, immunofluorescence, chromatin immunoprecipitation, microRNA-fluorescence hybridization, and luciferase reporter assays were applied to analyze polarization state and regulation mechanism of macrophage. AhR expression was significantly upregulated and negatively correlated with interferon-regulatory factor 1 (IRF1) and hypoxia inducible factor 1-alpha (HIF-1α) levels in a murine CaOx nephrocalcinosis model following administration of FICZ. Moreover, AhR activation suppressed IRF1 and HIF-1α levels and decreased M1 macrophage polarization . In terms of the mechanism, bioinformatics analysis and chromatin immunoprecipitation assay confirmed that AhR could bind to miR-142a promoter to transcriptionally activate miR-142a. In addition, luciferase reporter assays validated that miR-142a inhibited IRF1 and HIF-1α expression by directly targeting their 3'-untranslated regions. Our results indicated that AhR activation could diminish M1 macrophage polarization and promote M2 macrophage polarization to suppress CaOx nephrocalcinosis via the AhR-miR-142a-IRF1/HIF-1α pathway.
18A novel type alanine dehydrogenase from Helicobacter aurati: Molecular characterization and application.PubMed
Xiaoxiang Hu, Yajun Bai, Tai-Ping Fan, et al.
Int J Biol Macromol. 2020 Oct 15;161:636-642. doi: 10.1016/j.ijbiomac.2020.06.067. Epub 2020 Jun 10.
A novel alanine dehydrogenase (ADH; EC.1.4.1.1) with high pyruvate reduced activity was isolated from Helicobacter aurati and expressed in Escherichia coli BL21 (DE3). The optimum pH of the reduction and oxidation reaction were 8.0 and 9.0, respectively, and the optimum temperature was 55 °C. With pyruvate and alanine as substrates, the specific activity of HAADH1 were 268 U·mg and 26 U·mg, respectively. HAADH1 had a prominent substrate specificity for alanine (K = 2.23 mM, k/K = 8.1 s·mM). In the reduction reaction, HAADH1 showed the highest substrate affinity for pyruvate (K = 0.56 mM, k/K = 364 s·mM). Compared to pyruvate, oxaloacetic acid, 2-ketobutyric acid, 3-fluoropyruvate, α-ketoglutaric acids, glyoxylic acid showed a residual activity of 93.30%, 8.93%, 5.62%, 2.57%, 2.51%, respectively. Phylogenetic tree analysis showed that this is a new type of ADH which have a low sequence similarity to available ADH reported in references. 3-Fluoropyruvate was effectively reduced to 3-fluoro-L-alanine by whole-cell catalysis.
19Recreating ancient metabolic pathways before enzymes.PubMed
Kamila B Muchowska, Elodie Chevallot-Beroux, Joseph Moran
Bioorg Med Chem. 2019 Jun 15;27(12):2292-2297. doi: 10.1016/j.bmc.2019.03.012. Epub 2019 Mar 7.
The biochemistry of all living organisms uses complex, enzyme-catalyzed metabolic reaction networks. Yet, at life's origins, enzymes had not yet evolved. Therefore, it has been postulated that non-enzymatic metabolic pathways predated their enzymatic counterparts. In this account article, we describe our recent work to evaluate whether two ancient carbon fixation pathways, the rTCA (reductive tricarboxylic acid) cycle and the reductive AcCoA (Wood-Ljungdahl) pathway, could have operated without enzymes and therefore have originated as prebiotic chemistry. We also describe the discovery of an Fe-promoted complex reaction network that may represent a prebiotic predecessor to the TCA and glyoxylate cycles. The collective results support the idea that most central metabolic pathways could have roots in prebiotic chemistry.
20C metabolic flux analysis on roles of malate transporter in lipid accumulation of Mucor circinelloides.PubMed
Lu Wang, Huaiyuan Zhang, Yao Zhang, et al.
Microb Cell Fact. 2019 Sep 10;18(1):154. doi: 10.1186/s12934-019-1207-9.
BACKGROUND: Mitochondrial and cytoplasmic malate transporter proteins are responsible for transmembrane transport of malate, thereby linking malate metabolism in various subcellular regions of the cell. These transporters play an important role in fatty acid biosynthesis of oleaginous microorganisms. Our previous studies have found that lipid content of the recombinant Mucor circinelloides (M. circinelloides) strain with mitochondrial malate transporter (mt) gene overexpression was increased by 70%, while that of strain with mt gene knockout was decreased by 27%. However, the mechanism of malate transporter promoting the transport of mitochondrial malate and citrate related to lipid accumulation is not clear. Therefore, C-labeled glucose metabolic flux analysis was carried out to identify the metabolic network topology and estimate intracellular fluxes of genetically engineered M. circinelloides strains for the purpose of better understanding the roles of malate transporters in citrate transport systems and lipid accumulation. RESULTS: The metabolic flux distribution analysis suggested that tricarboxylic acid (TCA) cycle flux ratio of mt-overexpression strains was decreased compared to that of the control strain, but in contrast, glyoxylic acid (GOX) cycle flux ratio was increased. Accordingly, the mt-knockout strain showed an opposite phenomenon with a higher TCA cycle flux ratio and a lower GOX cycle flux ratio than the control strain. GOX cycle might be more effective than TCA cycle in producing malate and oxaloacetate replenishment. Moreover, a relatively higher flux ratio of the pentose phosphate (PP) pathway was obtained in mt-overexpression strains, but no significant difference in the malic enzyme flux between recombinant strains and the control strain. Our results confirmed that PP pathway might play an important role for supplying NADPH and malic enzyme is not a limiting factor for fatty acid synthesis in oleaginous fungus M. circinelloides strains. CONCLUSION: Intracellular metabolic flux information suggested that mt-overexpression strains had higher flux in PP pathway and GOX cycle, lower flux in TCA cycle, and no difference in malic enzyme cycle. Together, the role of malate transporter was assumed to further participate in transporting cycle of acetyl-CoA and drive PP pathway to supply NADPH required for lipid accumulation in recombinant M. circinelloides strains.