The Effect of Dietary Protein Level on Transaminase Activities and Fat Deposition in Vitamin B6-Depleted Rat Liver

Okada, Mitsuko; Ochi, Atsuko

doi:10.1093/oxfordjournals.jbchem.a129674

Cited by 64 publications

(33 citation statements)

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“…Of these isozymes, the cytosolic enzyme is thought to contribute to gluconeogenesis, as this enzyme is induced by the administration of a high-protein diet, starvation, and glucagon injection (20)(21)(22). We previously found an increase in cAST activity in the livers of alloxan-diabetic rats (22).…”

Section: Discussionmentioning

confidence: 99%

Glycation and Inactivation of Aspartate Aminotransferase in Diabetic Rat Tissues.

Okada

Murakami

Miyamoto

1997

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

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SummaryGlycated cytosolic aspartate aminotransferase was detected in the liver and kidney of streptozotocin diabetic rats using a boronate affinity column for adjacent cis-hydroxyl groups and an immunoblotting technique. The enzymatic activity and amount of immunoreactive sub stance were determined in the liver, kidney, and erythrocytes of diabetic and control rats. The ratio of enzymatic activity to the amount of enzyme was lower in diabetic rat tissue than in that in the control rats. It has been suggested that there is an inactive aspartate aminotransferase molecule in the tissues of diabetic rats. We therefore suggest that the cytosolic aspartate aminotransferase was inactivated in the diabetic rat tissues by a glycation reaction, accompanied by an impairment in glucose utilization. Key Words cytosolic aspartate aminotransferase (CAST), inactivation of cAST, glycation of cAST, diabetes, streptozotocin (stz) Non-enzymatic glucosylation (glycation) was first described by Maillard (1) who observed browning of amino acids when they were heated with sugars. The first protein demonstrated to be glycated in vivo was hemoglobin (2, 3). Levels of glycohemoglobin (HbAlc) are now used as an important marker in diabetics. Many other plasma and structural proteins have been shown to be glycated in vivo with increases in diabetes, and in some cases such glycated proteins are known to impair their function (4, 5). Accumulation of so called advanced glycation end-product is thought to contribute to the pathology of diabetes and aging (6).We (7,8) have studied the effects of various carbohydrates on the glycation of cytosolic aspartate aminotransferase (cAST) [EC 2.6.1.1] in an in vitro system. We found that fructose was very reactive with cAST, and that the enzymatic activity was decreased by the glycation.In this study, we detected a glycated cAST in the liver and kidney of streptozotocin (stz) diabetic rats, and its enzymatic and antigenic activities were examined.

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Section: Discussionmentioning

confidence: 99%

Glycation and Inactivation of Aspartate Aminotransferase in Diabetic Rat Tissues.

Okada

Murakami

Miyamoto

1997

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

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“…However, little information is available on the relationship between supplementation with BCAAs and the recommended daily allowance of vitamin B6. In addition, it is known that a high-protein diet (e.g., 70% casein diet) under vitamin B6 deficiency has a negative impact on several biochemical parameters and leads to fatty liver in rats (8)(9)(10).…”

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High Incidence of Lipid Deposition in the Liver of Rats Fed a Diet Supplemented with Branched-Chain Amino Acids under Vitamin B6 Deficiency

Kaimoto

Shibuya

Nishikawa

et al. 2013

J Nutr Sci Vitaminol

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73Branched-chain amino acids (BCAAs) composed of valine, leucine, and isoleucine are essential amino acids and account for about 40% of dietary essential amino acids in body protein and about 15% of total amino acids in muscle proteins (1). BCAAs play a role in delayed onset of muscle soreness and fatigue, and suppression of fatigue in the central nervous system (2, 3). BCAAs have been also used for the prevention of hepatic encephalopathy in patients with liver cirrhosis (4, 5). Recently, sport enthusiasts have created an increased demand for dietary supplements with BCAAs and have increased their consumption of BCAAs-enriched soft drinks.The first step in the catabolism of BCAAs involves branched-chain aminotransferase (BCAT; EC 2.6.1.42), a common enzyme. This enzyme requires vitamin B 6, which functions as a cofactor in many enzyme reactions of amino acid metabolism (6, 7). However, little information is available on the relationship between supplementation with BCAAs and the recommended daily allowance of vitamin B6. In addition, it is known that a high-protein diet (e.g., 70% casein diet) under vitamin B6 deficiency has a negative impact on several biochemical parameters and leads to fatty liver in rats (8-10).Our previous study showed that providing supplemented BCAAs under vitamin B6 deficiency and a 20% casein diet caused an accumulation of triacylglycerol in the liver, and individual differences in biological responses were observed (11). It is possible that a disorder of amino acid metabolism in the presence of vitamin B6 deficiency might influence the assembly of lipids and apolipoproteins and/or the secretion of lipoproteins. Among the serum lipoproteins, very low-density lipoprotein (VLDL) is present during endogenous lipogenesis in the liver and its major apolipoproteins are apolipoprotein (apo) B, apo C, and apo E (12). It is interesting to compare serum apo B and apo E levels, and hepatic apoE levels to evaluate lipid deposition, because apo B and apo E are key determinants responsible for cellular recognition and internalization of chylomicron remnants, VLDL, and high-density lipoprotein (HDL) (13,14). In this study, we investigated the possible mechanism of lipid deposition in the liver of rats fed with the supplementation of BCAA under vitamin B 6 deficiency and suggested the presence of impaired secretion of VLDL into the bloodstream from the liver. Materials and MethodsDiets and animals. Four diets composed of purified 20% vitamin-free casein diet with (1) or without (2) vitamin B6 (7.0 mg of pyridoxine HCl/kg of diet) and with (1) or without (2) Summary Male Wistar rats were fed four diets composed of purified 20% vitamin-free casein diet with (1) or without (2) vitamin B6 (7.0 mg of pyridoxine HCl/kg of diet) and with (1) or without (2) branched-chain amino acids (BCAAs) of valine, leucine, and isoleucine (4.75%): B6 (1)BCAA (2); B6(1)BCAA(1); B6 (2)BCAA (2); and B6 (2)BCAA (1) for 21 d. Among rats fed the B6(2)BCAA(1) diet, about a half showed lipid deposition in the liver. On the other...

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“…Wisteri strain male r&ts avera~ng 50 g body wt were fed on a ntamm B6-deficient diet for 4 weeks [9]. The control diet was supplemented with 30 mg pyridoxine/lOO g vrtamm B6-deficient diet.…”

Section: Methodsmentioning

confidence: 99%

Effect of vitamin B6 deficiency on the crosslink formation of collagen

1979

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Intr~uctjonWith the recent advances m collagen chemistry it became apparent that the mitial stage m the crosshnk formation of collagen 1s the enzymic syntheas of aldehydes by removal of e-amino groups of certam lysine and hydroxyiy~ne resrdues [ 1,2]. Tlus enzyme named Iysyl oxidase, one of the amine oxidases, has been purified to hrgh specriic activity and shown to be actrve upon both lysyl and hydroxylysyl groups in collagen and elastin [3,4]. It is well known that amine oxidases contain copper, and some of them require pyridoxal phosphate for their activity [5-73. It can be mferred therefore that vitamin B6 is also required for enzymic actrnty of lysyl oxidase. Thrs posstbrhty has been reinforced by the findings that partial purificatron of lysyl oxrdase from cartilage of chick embryos inJected wrth [G-3H]py~do~ne hydroc~onde revealed a smgle peak of ra&oactrvrty comadmg with a single peak of enzyme activity, and lysyl oxrdase actrvrty was mhrbrted after mcubatron wrth rsomcotmic acid hydrazide [8].In order to gam further mformatron on thus pos~b~ty, we have lnvestlgated aldehyde and crosshnk formation of skin and bone collagens from vitamm B6-deficient rats. Materials and methodsWisteri strain male r&ts avera~ng 50 g body wt were fed on a ntamm B6-deficient diet for 4 weeks [9]. The control diet was supplemented with 30 mg pyridoxine/lOO g vrtamm B6-deficient diet.Vitanun B6 content m the brain and skm was El~~~er~~orth-~oi~nd ~lomedlcal Pressdetermmed by an estab~~ed ~croblolo~cal method [lO,ll]. The skm and bone were cut into small pieces and powdered m hqurd nitrogen. Followmg demmerahzation with 0.8 M EDTA (PH 7.5) the powdered bone was sequentially extracted with 1 .O M NaCl m 0.05 M Trrs buffer (pH 7.4) and with 0.5 M acetic acrd. The powdered skin was extracted with 1 .O M NaCl and wrth 0.15 M sodium citrate (pH 3.4). The residue obtained after these extractions, which is primarily msoluble collagen, was washed with drstrlled water and then lyophrhzed.Following hydrolysis m 6 N HCl at 110°C for 24 h, hydroxyprohne was determined [ 121 for the estimation of the collagen content in each extract and m the insoluble fraction.Punfied neutral salt soluble collagen from skm was completely drssolved m potassium phosphate buffer, ~0.4 (pH 7.6) by stirrmg at 4% for 24 h. This collagen solutron and insoluble collagens from skm and bone were reduced wrth NaB3H4 [ 131, they were then dialyzed extensively agamst 0.1 M acetic acrd and lyophrlized. The tntrated proteins were hydrolyzed m 3 N HCl at 107OC for 48 h, and the hydrolysates were dried. A portion of each hydrolysate was measured for specriic radroactrvity, and the data were expressed in terms of the measured hydroxyproline content of the hydrolysates. Chromatographrc fracttonation of the radloactrve components of each hydrolysate was carried out on a 0.9 X 23 cm column of Ammex A-5 as in [ 14,153. Ahquots were counted for radroactivity, and values under each crosslink peak were expressed as cpm/mg hydroxyproline in the hydrolysate loaded on a column. 193

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The Effect of Dietary Protein Level on Transaminase Activities and Fat Deposition in Vitamin B6-Depleted Rat Liver

Cited by 64 publications

References 0 publications

Glycation and Inactivation of Aspartate Aminotransferase in Diabetic Rat Tissues.

Glycation and Inactivation of Aspartate Aminotransferase in Diabetic Rat Tissues.

High Incidence of Lipid Deposition in the Liver of Rats Fed a Diet Supplemented with Branched-Chain Amino Acids under Vitamin B6 Deficiency

Effect of vitamin B6 deficiency on the crosslink formation of collagen

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