Ontogeny of serine hydroxymethyltransferase isoenzymes in fetal sheep liver, kidney, and placenta

Serine is an amino acid that is not transported from the placenta to the ovine fetus. Thus, fetal plasma serine levels may be controlled by flux through their relevant biosynthetic pathways. This study was designed to determine, in fetal sheep tissues, the ontogeny of the three key enzymes in the biosynthetic pathway for serine, the cytosolic (c) and mitochondrial (m) isoforms of serine hydroxymethyltransferase (SHMT), phosphoglycerate dehydrogenase (PGD), and phosphoserine aminotransferase (PSAT). PGD and PSAT activity did not vary during gestation in either liver (PSAT, 9.4 +/- 1.3 nmol/min/mg cytosolic protein; and PGD, 76 +/- 10 mU/mg protein) or placenta (PGD, 8.0 +/- 3.6 mU/mg protein). In the liver, cSHMT activity was low early in gestation (0.6 +/- 0.5 nmol/min/mg protein at 45 days), rose in the last one-third of gestation, and peaked in the newborn period (25 +/- 3 nmol/min/mg protein at 1 week of age). Hepatic cSHMT RNA levels parallel the activity pattern. Mitochondrial SHMT was stable throughout gestation and with low constant mSHMT RNA levels. In contrast, the kidney and placenta had high mSHMT and steady low cSHMT activity throughout gestation. These data support the possible role of SHMT in the fetal control of plasma serine levels. While cSHMT may contribute to fetal hepatic serine production, its activity pattern does not support a primary role in the control of fetal hepatic serine biosynthesis. In the placenta, mSHMT may be important for glycine production from serine.     

不平衡支链氨基酸对胃癌细胞体外增殖和化疗敏感性的影响

在不含缬氨酸（ Ｌ Ｖａｌ）的 Ｍ Ｅ Ｍ 培养基基础上,以普通 Ｍ Ｅ Ｍ 培养基 Ｌ Ｖａｌ（４６ｍ ｇ／ Ｌ）和亮氨酸（ Ｌ Ｌｅｕ）含量（５２ｍ ｇ／ Ｌ）为准,配制 １２ 种限制 Ｌ Ｖａｌ、增加 Ｌ Ｌｅｕ 的不平衡支链氨基酸培养基,用 Ｍ Ｔ Ｔ法观察其对胃癌细胞株 Ｓ Ｇ Ｃ７９０１ 体外增殖的影响和对该细胞株化疗药物敏感性的影响。结果表明,限制 Ｌ Ｖａｌ至正常的 １／４ 对 Ｓ Ｇ Ｃ７９０１ 细胞即有明显的抑制作用（ Ｐ＜ ０．０１）,随着 Ｌ Ｖａｌ浓度的继续降低,抑制作用更加显著。增加 Ｌ Ｌｅｕ 至正常的４ 倍,显著增强了 Ｌ Ｖａｌ缺乏对 Ｓ Ｇ Ｃ７９０１ 细胞的抑制作用。不平衡支链氨基酸与抗癌药物５ Ｆ Ｕ、 Ｍ Ｍ Ｃ 和 Ｍ Ｔ Ｘ 有协同作用。提示在氨基酸疗法中,不仅要调整某种氨基酸的绝对量,而且应调整该氨基酸与其他氨基酸的比例。     

血浆内皮素和非酯化脂肪酸改变与糖尿病视网膜病变的关系

目的：为探讨血浆内皮素（ＥＴ）和非酯化脂肪酸（ＮＥＦＡ）水平与糖尿病视网膜病变（ＤＲ）Ｒ 关系。方法：分组分析了５６例伴和不伴ＤＲ的２型糖尿病（ＤＭ）人血浆ＥＴ和ＮＥＥＡ水平,并与正常人进行了比较。结果：２型ＤＭ病人血浆ＥＴ水平明显高于正常人,伴有ＤＲ组病人又明显高于无ＤＲ的病人。     

Effects of intraoperative glucose administration on circulating metabolites and nitrogen balance during prolonged surgery

Study Objectives: To compare the effects of intraoperative administration of 2.5% glucose or Ringer’s solution on metabolism during prolonged surgery.

Design: Prospective, randomized study.

Setting: Teaching hospital.

Patients: 20 ASA physical status I and II adults patients scheduled for thoracic or abdominal surgery lasting at least 3 hours.

Interventions: Patients received Ringer’s solution (Group R) or 2.5% glucose solution (Group G) 10 ml · kg⁻¹ · h⁻¹ during surgery and 2 ml · kg.⁻¹ · h⁻¹ during the first two postoperative hours (Ringer’s or glucose), then 40 ml · kg.⁻¹ · day⁻¹ of 5% intravenous (IV) glucose postoperatively.

Measurements and Main Results: Plasma glucose, free fatty acids, ketone bodies, lactate, insulin, glucagon, cortisol, and growth hormone concentrations were determined after an overnight fast (T₀), on induction of anesthesia (T₁), at the end of surgery (T₂), 2 hours thereafter (T₃), and on the following morning (T₄). Capillary blood glucose was determined every 30 minutes from T₁ to T₂. Urinary nitrogen and 3-methylhistidine were measured every day for 5 days. There were no differences between groups in demographic data, anesthesia, or surgical procedures. All data were comparable at baseline and on the following morning. In Group R, no patient experienced hypoglycemia, but plasma fatty acids and ketone bodies increased during surgery. In Group G, glycemia rose to very high levels, with a significant increase in insulin during surgery. Other hormones were the same within the two groups. Urinary nitrogen and 3-methylhistidine were similar in both groups.

Conclusion: The absence of glucose infusion in prolonged surgery did not cause hypoglycemia, and no increase in protein catabolism was observed.     

Stabilization of rat serum proteins following oral administration of fish oil

The mechanism of action of fish oil (FO), currently used in different chronic inflammatory conditions such as rheumatoid arthritis (RA), is not completely understood, although it is thought that it could alter the metabolism of endogenous autacoids. In addition, we hypothesized that the known capability of fatty acids (FA) of stabilizing serum albumin and perhaps other proteins, may be of pharmacological relevance considering that it is shared by other anti-rheumatic agents (e.g. nonsteroidal antiinflammatory drugs). Thus, we studied the effect of oral administration of FO and corn oil (CO), a vegetable oil with a different composition, on the stability of rat serum proteins, evaluated by a classical in vitro method based on heat-induced protein denaturation. FO, and, to a lower extent, CO inhibited heat-induced denaturation of rat serum (RS): based on the inhibitory activity (EC50) of the major fatty acids against heat-induced denaturation of RS in vitro, it was possible to speculate that in vivo effects of palmitic acid (C16:0) and eicosapentaenoic acid (EPA, C20:5, n-3) may be more relevant than that of linolenic acid (C18:2). To better investigate this phenomenon, we extracted albumin from the serum of animals treated or not with FO with a one-step affinity chromatography technique, obtaining high purity rat serum albumin preparations (RSA-CTRL and RSA-FO), as judged by SDS-PAGE with Coomassie blue staining. When these RSA preparations were heated at 70 degrees C for 30 min, it was noted that RSA-FO was much more stable than RSA-CTRL, presumably due to higher number of long chain fatty acids (FA) such as palmitic acid or EPA. In conclusion, we provided evidences that oral administration of FO in the rat stabilizes serum albumin, due to an increase in the number of protein bound long chain fatty acids (e.g. palmitic acid and EPA). We speculate that the stabilization of serum albumin and perhaps other proteins could prevent changes of antigenicity due to protein denaturation and glycosylation, which may trigger pathological autoimmune responses, suggesting that this action may be involved in the mode of action of FO in RA and other chronic inflammatory diseases.     

Uptake of iodine-123-α-methyl tyrosine by gliomas and non-neoplastic brain lesions

Using single-photon emission tomography (SPET), the radiopharmaceuticall,-3-iodine-123--methyl tyrosine (IMT) has been applied to the imaging of amino acid transport into brain tumours. It was the aim of this study to investigate whether IMT SPET is capable of differentiating between high-grade gliomas, low-grade gliomas and non-neoplastic brain lesions. To this end, IMT uptake was determined in 53 patients using the triple-headed SPET camera MULTISPECT 3. Twenty-eight of these subjects suffered from high-grade gliomas (WHO grade III or IV), 12 from low-grade gliomas (WHO grade II), and 13 from non-neoplastic brain lesions, including lesions after effective therapy of a glioma (five cases), infarctions (four cases), inflammatory lesions (three cases) and traumatic haematoma (one case). IMT uptake was significantly higher in high-grade gliomas than in low-grade gliomas and non-neoplastic lesions. IMT uptake by low-grade gliomas was not significantly different from that by non-neoplastic lesions. Diagnostic sensitivity and specificity were 71% and 83% for differentiating high-grade from low-grade gliomas, 82% and 100% for distinguishing high-grade gliomas from non-neoplastic lesions, and 50% and 100% for discriminating low-grade gliomas from non-neoplastic lesions. Analogously to positron emission tomography with radioactively labelled amino acids and fluorine-18 deoxyglucose, IMT SPET may aid in differentiating high-grade gliomas from histologically benign brain tumours and non-neoplastic brain lesions; it is of only limited value in differentiating between non-neoplastic lesions and histologically benign brain tumours.     

Dependence of 5-HT and catecholamine synthesis on concentrations of precursor amino-acids in rat brain

Summary The short-term influence of varying concentrations of the precursors tryptophan and tyrosine on the formation of 5-hydroxytryptophan and Dopa, respectively, in three different rat-brain regions was investigated. The concentrations of the precursors were either increased by the intraperitoneal administration of the respective precursor or decreased by loading with large neutral amino acids competing with the precursors for the same carrier mechanisms.The formation of 5-hydroxytryptophan was found to depend on the level of tryptophan in the brain in a manner predicted from published kinetic data, except when large doses of non-precursor amino acids had been given (>300 mg/kg). In the latter case the hydroxylation of tryptophan was less rapid than expected. The apparent K _m of tryptophan hydroxylase calculated from these data was about 25 M, which is in reasonably good agreement with earlier published in-vitro and in-vivo data.The formation of Dopa likewise depended on the level of the precursor tyrosine in a predictable manner, in this case without any anomalous results after large doses of non-precursor amino acids. The apparent K _m of tyrosine hydroxylase was calculated from these invivo observations to be about 25 M, which is in fairly close agreement with published in-vitro data.It is concluded that under normal conditions tryptophan hydroxylase in the rat brain is about half-saturated with its amino-acid substrate, whereas tyrosine hydroxylase appears to be about 75% saturated.     

Competitive inhibition of the uptake of demethylphalloin by cholic acid in isolated hepatocytes

Summary Cholic acid inhibits the uptake of demethylphalloin (DMP), in a competitive manner. The bile acid increases the Michaelis constant but not V _max of the inward transport. The inhibition constant K _i for cholate was found to be 8 M. Cholate competes for the transport system but not for intracellular binding of phallotoxins. Various experimental data presented in this paper exclude an accumulation of phallotoxins in hepatocytes by intracellular binding only.Preincubation of hepatocytes with small concentrations of either (³H)-demethylphalloin or (¹⁴C)-cholate and subsequent treatment with high concentrations of the nonlabelled compounds reduces the intracellular concentration of both radioactive substrates. In accordance with earlier findings the above results suggest a common component needed for the transport of both phallotoxins and cholic acid.This work was supported by the Deutsche Forschungsgemeinschaft     

Free amino acid pool in the brain of mice homozygous for the gene "dilute lethal"

The neurologic mutant "dilute lethal" (dl) mice, which reveal several neurologic and biochemical disturbances similar to human phenylketonuria, were used to investigate some aspects of amino acid disorder. We have studied the free amino pool in the brain of "dl" mice and of their control littermates as well as phenylalanine and tyrosine levels in brain and liver as a function of age and after phenylalamine overload. The tyrosine level decreased in brain and liver of affected mice whereas the phenylalanine/tyrosine ratio increased as a function of age. The significantly higher phenylalanine level and phenylalanine/tyrosine ratio in the liver of 20-day-old "dl" mice suggest a lower liver phenylalanine hydroxylase activity. After phenylalanine overload, the impairment of phenylalanine metabolism is predominant in the brain of "dl" mice, suggesting a disturbance in phenylalanine hydroxylation. A decrease in the level of several amino acids occurs in the brains of "dl" mice without or after phenylalanine overload; these facts might correspond to a disturbance in the transfer of amino acids to the brain and may lead to impairment in protein synthesis.     

Rectal Mucosa Damage in Rabbits After Subchronical Application of Suppository Bases

The effect of suppository bases on rabbit rectal mucosa was investigated using six triglyceride bases, polyethylene glycol, and a triglyceride base combined with monoglycerides or fatty acids and methyl esters of those acids. Rectal irritation was evaluated and scored according to defined pathological features. Pure triglycerides and a triglyceride to which a nonionic surfactant was added caused severe mucosal damage with ulceration and inflammation. Hyperemia was characteristic for irritation by polyethylene glycol suppositories. Mucosal damage by a pure triglyceride combined with monoglycerides or fatty acids and methyl esters of those acids was similar but statistically less pronounced than with all other bases.