Metabolism of valine and 3-methyl-2-oxobutanoate by the isolated perfused rat kidney

Unraveling metabolism during kidney perfusion using tracer studies, a systematic review

BACKGROUND

Understanding kidney metabolism during perfusion is vital to further develop the technology as a preservation, viability assessment, and resuscitation platform. We reviewed the evidence on the use of labeled metabolites (tracers) to understand "on-pump" kidney behavior.

METHODS

PubMed, Embase, Web of Science, and Cochrane databases were systematically searched for studies evaluating metabolism of (non)radioactively labeled endogenous compounds during kidney perfusion.

RESULTS

Of 5899 articles, 30 were included. All were animal studies [rat (70%), dog (13%), pig (10%), rabbit (7%)] perfusing but not transplanting kidneys. Perfusion took place at hypothermic (4-12°C) (20%), normothermic (35-40°C) (77%), or undefined temperatures (3%). Hypothermic perfusion used albumin or a clinical kidney preservation solution, mostly in the presence of oxygen. Normothermic perfusion was mostly performed with oxygenated crystalloids often containing glucose and amino acids with unclear partial oxygen tensions. Active metabolism of carbohydrate, amino acid, lipids, and large molecules was shown in hypothermic and normothermic perfusion. Production of macromolecules, such as prostaglandin, thromboxane, and vitamin D, takes place during normothermic perfusion. No experiments compared differences in metabolic activity between hypothermic and normothermic perfusion. One conference abstract showed increased anaerobic metabolism in kidneys donated after circulatory death by adding labeled glucose to hypothermically perfused human kidneys.

CONCLUSIONS

Tracer studies during kidney perfusion contribute to unraveling kidney metabolic behavior in pre-clinical models. Whether findings are truly translational needs further investigation in large animal models of human kidneys. Furthermore, it is essential to better understand how ischemia changes this metabolic behavior.

Integrated omics analysis: the relationship between significantly increased Klebsiella post-hepatectomy and decreased hub-metabolite 3-methyl-2-oxobutanoic acid is associated with induced liver failure

BACKGROUND

This study sought to evaluate the association between intestinal Klebsiella and post-hepatectomy liver failure (PHLF) in patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (B-HCC), and identify the inner relationship.

METHODS

Patients with B-HCC were divided into Groups A and B based on the presence or absence of PHLF. 16S ribosomal ribonucleic acid surveys were used to identify gut microbiome alterations. PICRUST2 was used to examine the metagenomic data in PHLF patients. Fecal and serum samples were processed by chromatography-mass spectrometry based non-targeted metabonomics, then comprehensively analyzed to obtain hub metabolites. A Spearman correlation analysis was then conducted to find any associations between fecal differential metabolites and the relative abundance of differential microbes.

RESULTS

Hepatectomies were significantly associated with a gut microbial imbalance in B-HCC patients, and a significant elevation of Klebsiella abundance was observed in PHLF patients. Klebsiella appears to act on 13 amino acid-related pathways, especially significantly observed in branched-chain amino acid (BCAA) metabolic pathways. Additionally, Klebsiella was found to be highly correlated with 3-methyl-2-oxobutanoic acid shared by feces and serum in the BCAA metabolic pathway.

CONCLUSIONS

Hepatectomy can lead to an imbalance of intestinal microflora in B-HCC patients. Due to its potential connections with 3-methyl-2-oxobutanoic acid in the BCAA pathway, significantly increased Klebsiella has the potential to be an evaluation indicator of PHLF in B-HCC patients. Moreover, 3-methyl-2-oxobutanoic acid has research value in PHLF-targeted treatments.

Human branched-chain L-amino acid aminotransferase: Activity and subcellular localization in cultured skin fibroblasts

Assay conditions for measurement of human skin fibroblast branched-chain L-amino acid aminotransferase activity were established and applied to studies on subcellular distribution and kinetic properties of the enzyme. Digitonin fractionation of cultured cells revealed that the aminotransferase activity was mainly (at least about 95%) associated with mitochondrial citrate synthase activity. As tested with L-leucine, activity of the enzyme against amino group acceptors (forward reaction) was in the order 2-oxoglutarate [Symbol: see text] branched-chain > straight-chain 2-oxo acids (C3-C8). With 4-methyl-2-oxopentanoate, activity against amino group donors (reverse reaction) was in the order L-glutamate [Symbol: see text] branched-chain > straight-chain (C2-C6) and other L-amino acids. The data suggest that, in human fibroblasts, isoenzyme type I resides within the mitochondrial space. Possible implications for the metabolism of branched-chain compounds are discussed.

Phylogenetic comparisons of the branched-chain alpha-ketoacid dehydrogenase complex

1. Antibodies against the E1b and E2b components of bovine branched-chain alpha-ketoacid (BCKA) dehydrogenase (BCKAD) complex completely inhibited BCKA oxidation in mammalian and avian mitochondria. BCKA oxidation by salmonid mitochondria was less affected and the enzyme from Pseudomonas putida was unaffected. 2. In rodents, anti-E1b E2b IgG inhibited oxidation of all three BCKA in a similar dose-dependent manner: oxidation of alpha-ketobutyrate and alpha-keto-y-methiolbutyrate was also partially inhibited. 3. Except for the salmonid BCKAD, a similar Mr for the E2b and E1b alpha proteins was observed in these species. 4. After digestion with V-8 protease similar immunoreactive peptides were observed for the human and rodent complex.

Transamination and oxidative decarboxylation of L-isoleucine, L-alloisoleucine and related 2-oxo acids in perfused rat hind limb muscle

Metabolism of L-isoleucine, L-alloisoleucine and corresponding 2-oxo acids in rat hind limb muscle was comparatively studied under steady-state perfusion conditions. At 0.5 mM L-[1-14C]isoleucine, apparent transamination and 2-oxo acid decarboxylation rates amounted to about 17 and 4 nmol/min per g of muscle, respectively. With L-allo[1-14C]isoleucine, the corresponding rates were about 5- and 10-fold lower, respectively. After addition of dichloroacetate (1-5 mM), the portion of (S)- and (R)-methyl-2-oxopentanoate undergoing further oxidative decarboxylation within the tissue was similarly increased by over 40%. In perfusions with 0.5 mM (R,S)-3-methyl-2-oxopentanoate and tracer doses of 1-14C-labeled (S)- or (R)-enantiomer, the 14CO2 production was comparable (about 0.5 nmol/min per g of muscle). Dichloroacetate caused a several-fold increase in 14CO2 release from either enantiomer, apparent 2-oxo acid transamination rates remaining unaffected. Indications for a racemization of 2-oxo acid were not obtained in the experiments. The results are discussed with respect to the appearance/disappearance of L-alloisoleucine in vivo and to the fact that (R)-3-methyl-2-oxopentanoate, but not L-alloisoleucine, can support growth of rats on a diet deficient in L-isoleucine.

Formation and excretion of branched-chain acylcarnitines and branched-chain hydroxy acids in the perfused rat kidney

alpha-Keto[U-14C]isovalerate, alpha-keto[U-14C]isocaproate and alpha-keto[U-14C]beta-methylvalerate are metabolized in the perfused kidney. Labelled 3-hydroxyisobutyrate, 3-hydroxyisovalerate, 2-methyl-3-hydroxybutyrate, branched-chain amino acids, branched-chain acylcarnitines and lactate are formed. Hydroxy acids and acylcarnitines are excreted preferentially in the urine, whereas the branched-chain amino acids are preferentially excreted in the perfusate. There is no accumulation of (U-14C)-labelled alpha-keto acids or labelled metabolites in the kidney during perfusion. (-)-Carnitine accumulates rapidly in the kidney when it is added to the perfusate. A high kidney carnitine level enhances the excretion of carnitine esters in the urine.

Lack of glomerular hemodynamic stimulation after infusion of branched-chain amino acids

Renal hemodynamics (Inutest. CPAH) were studied in five adult volunteers infused on separate occasions with branched-chain amino acids (BCAA), a mixture of nonessential and essential amino acids of the same volume, osmolality and nitrogen content, and 0.9% saline solution. BCAA infusion caused moderate renal vasoconstriction, a slight increase of GFR and a progressive rise of the filtration fraction (FF), whereas the amino acids mixture induced a significantly higher increase of GFR and a state of renal vasodilatation without altering the FF. The volume expansion with 0.9% saline did not cause any notable hemodynamic modification except for reduced FF. This study demonstrates that whereas a state of hyperfiltration and hyperemia is specifically induced by an amino acid mixture independently of volume expansion and osmolar load, the administration of BCAA provides nitrogen without renal hemodynamic stimulation.

The occurrence of 4-methylthio-2-hydroxybutyrate in human urine

A method for determination of 4-methylthio-2-hydroxybutyrate and 4-methylthio-2-oxobutyrate in human urine has been devised, based on metoxime formation of the keto acid and a clean-up procedure using a strong anion-exchange resin AG 2 X 8 and ethyl acetate extraction. After alkylation, the compounds were quantified by GC, using a flame photometric sulfur-selective detector. A normal urinary excretion of 0.14 to 0.25 mmol/mol creatinine and 0.07 to 0.22 mmol/mol creatinine of the alpha-hydroxy and alpha-keto acid, respectively, was found, whereas a markedly elevated excretion of the hydroxy acid was noted in subjects with hypermethioninemia. The enzymatic reduction of 4-methylthio-2-oxobutyric acid by lactate dehydrogenase: NAD+ oxidoreductase (EC 1.1.1.17) was also studied. The Km and Kequil values for 4-methylthio-2-oxobutyrate were 1.41 mM and 0.92 X 10(8) M-1. The Vmax value of the enzyme at infinite concentrations of the two substrates was 7.2 mumol/s/mumol enzyme, which indicates low affinity and reduced catalytic activity compared to other known substrates of lactate dehydrogenase. The reaction product 4-methylthio-2-hydroxybutyrate was not inhibitory on the reaction. The M4 isoenzyme of lactate dehydrogenase (rabbit and pig muscle) possessed approximately 20% of the activity of the H4 isoenzyme (pig heart) for the substrate.