ß-Aminoisobutyric Acid Suppresses Atherosclerosis in Apolipoprotein E-Knockout Mice.

Endurance exercise training has been shown to induce peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression in skeletal muscle. We recently reported that skeletal muscle-specific PGC-1α overexpression suppressed atherosclerosis in apolipoprotein E-knockout (ApoE-/-) mice. ß-Aminoisobutyric acid (BAIBA) is a PGC-1α-dependent myokine secreted from myocytes that affects multiple organs. We have also reported that BAIBA suppresses tumor necrosis factor-alpha-induced vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) gene expression in endothelial cells. In the present study, we hypothesized that BAIBA suppresses atherosclerosis progression, and tested that hypothesis with ApoE-/- mice. The mice were administered water containing BAIBA for 14 weeks, and were then sacrificed at 20 weeks of age. Atherosclerotic plaque area, plasma BAIBA concentration, and plasma lipoprotein profiles were assessed. Immunohistochemical analyses of the plaque were performed to assess VCAM-1 and MCP-1 protein expression levels and macrophage infiltration. The results showed that BAIBA administration decreased atherosclerosis plaque area by 30%, concomitant with the elevation of plasma BAIBA levels. On the other hand, plasma lipoprotein profiles were not changed by the administration. Immunohistochemical analyses indicated reductions in VCAM-1, MCP-1, and Mac-2 protein expression levels in the plaque. These results suggest that BAIBA administration suppresses atherosclerosis progression without changing plasma lipoprotein profiles. We propose that the mechanisms of this suppression are reductions in both VCAM-1 and MCP-1 expression as well as macrophage infiltration into the plaque.

Metabolomic profiles and development of metabolic risk during the pubertal transition: a prospective study in the ELEMENT Project.

OBJECTIVES: (1) Examine associations of a branched-chain amino acid (BCAA) metabolite pattern with metabolic risk across adolescence; (2) use Least Absolute Shrinkage and Selection Operator (LASSO) to identify novel metabolites of metabolic risk. METHODS: We used linear regression to examine associations of a BCAA score with change (∆) in metabolic biomarkers over 5-year follow-up in 179 adolescents 8-14 years at baseline. Next, we applied LASSO, a regularized regression technique well suited for reduction of high-dimensional data, to identify metabolite predictors of ∆biomarkers. RESULTS: In boys, the BCAA score corresponded with decreasing C-peptide, C-peptide-based insulin resistance (CP-IR), total cholesterol (TC), and low-density-lipoprotein cholesterol (LDL). In pubertal girls, the BCAA pattern corresponded with increasing C-peptide and leptin. LASSO identified asparagine as a predictor of decreasing C-peptide (ß = -0.33) and CP-IR (ß = -0.012), and acetyl-carnitine (ß = 2.098), 4-hydroxyproline (ß = -0.050), ornithine (ß = -0.353), and α-aminoisobutyric acid (ß = -0.793) as determinants of TC in boys. In girls, histidine was a negative determinant of TC (ß = -0.033). CONCLUSIONS: The BCAA pattern was associated with ∆glycemia and ∆lipids in a sex-specific manner. LASSO identified asparagine, which influences growth hormone secretion, as a determinant of decreasing C-peptide and CP-IR in boys, and metabolites on lipid metabolism pathways as determinants of decreasing cholesterol in both sexes.

ß-ureidopropionase deficiency: phenotype, genotype and protein structural consequences in 16 patients.

ß-ureidopropionase is the third enzyme of the pyrimidine degradation pathway and catalyzes the conversion of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid to ß-alanine and ß-aminoisobutyric acid, ammonia and CO(2). To date, only five genetically confirmed patients with a complete ß-ureidopropionase deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 11 newly identified ß-ureidopropionase deficient patients as well as the analysis of the mutations in a three-dimensional framework. Patients presented mainly with neurological abnormalities (intellectual disabilities, seizures, abnormal tonus regulation, microcephaly, and malformations on neuro-imaging) and markedly elevated levels of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid in urine and plasma. Analysis of UPB1, encoding ß-ureidopropionase, showed 6 novel missense mutations and one novel splice-site mutation. Heterologous expression of the 6 mutant enzymes in Escherichia coli showed that all mutations yielded mutant ß-ureidopropionase proteins with significantly decreased activity. Analysis of a homology model of human ß-ureidopropionase generated using the crystal structure of the enzyme from Drosophila melanogaster indicated that the point mutations p.G235R, p.R236W and p.S264R lead to amino acid exchanges in the active site and therefore affect substrate binding and catalysis. The mutations L13S, R326Q and T359M resulted most likely in folding defects and oligomer assembly impairment. Two mutations were identified in several unrelated ß-ureidopropionase patients, indicating that ß-ureidopropionase deficiency may be more common than anticipated.

A Thorough QT Study of the Combination Glecaprevir + Pibrentasvir on Cardiac Repolarization in Healthy Subjects.

PURPOSE: Fixed-dose combination glecaprevir (GLE) 300 mg + pibrentasvir (PIB) 120 mg is an orally administered once daily antiviral regimen approved for the treatment of hepatitis C virus (HCV) infection. The objective of this study was to evaluate the potential for cardiac repolarization following GLE + PIB administration in healthy adults. METHODS: This placebo- and active-controlled, randomized, single-dose, 4-period, 4-sequence crossover study enrolled 48 healthy subjects. The doses of GLE 400 mg + PIB 120 mg were selected to provide exposures comparable to those with the doses that are therapeutic in the HCV-infected population, GLE 300 mg + PIB 120 mg. The doses of GLE 600 mg + PIB 240 mg were selected to provide supratherapeutic exposures without exceeding the exposures of the GLE + PIB maximal tolerated doses. Moxifloxacin 400 mg (active control/open label) was used for confirming the sensitivity of the ECG assay in detecting QTc prolongation. Time-matched plasma concentrations and triplicate ECGs were obtained on treatment days -1 and 1. The primary end point was time-matched, placebo-corrected, baseline-adjusted Fridericia-corrected QT interval (ΔΔQTcF). Pharmacokinetic-pharmacodynamic analyses characterized the relationship between GLE and PIB plasma concentrations and ΔΔQTcF using a linear regression model and linear mixed-effects model. Findings from categorical analyses of ECG-interval data were also summarized. Tolerability was evaluated through adverse-events monitoring, physical examination including vital sign measurements, ECGs, and laboratory tests. FINDINGS: A total of 48 subjects (22 women [46%], 26 men [54%]), were enrolled in the study, and 47 subjects completed all 4 periods. None of the subjects had a change from baseline in QTcF interval of >30 msec or an absolute QTcF interval of >450 msec. Peak ΔΔQTcF values observed at 5 h postdose (Tmax) were 2.9 msec (upper 95% confidence limit, 4.9 msec) with the therapeutic dose and 3.1 msec (upper 95% confidence limit, 5.1 msec) with the supratherapeutic dose, with both upper 95% confidence limits well below the 10-msec threshold. Assay sensitivity was confirmed by peak ΔΔQTcF in the positive control (12.8 ms at 2 h postdose). No statistically significant GLE or PIB concentration-dependent effects on ΔΔQTcF were observed. Headache and skin irritation from ECG electrodes were the most commonly reported AEs. No clinically significant vital sign measurements, ECG findings, or laboratory measurements were observed. There were no patterns of T- and U-wave morphologic abnormalities. IMPLICATIONS: The fixed-dose combination regimen of GLE/PIB does not prolong the QTc interval. ClinicalTrials.gov identifier.

Maternal malnutrition and placental transfer of alpha-aminoisobutyric acid in the rat.

In the pregnant rat, dietary protein restriction reduces the transfer of 14C-labeled alpha-aminoisobutyric acid from the maternal blood into the fetus. One of the causes of this phenomenon is a reduced capacity of the placenta to release into the fetus alpha-aminoisobutyric acid taken up from the maternal blood.

Maternal insulin-like growth factor-II promotes placental functional development via the type 2 IGF receptor in the guinea pig.

In guinea pigs, maternal insulin-like growth factor (IGF) infusion in early-pregnancy enhances placental transport near-term, increasing fetal growth and survival. The effects of IGF-II, but not IGF-I, appear due to enhanced placental labyrinthine (exchange) development. To determine if the type-2 IGF receptor (IGF2R) mediates these distinct actions of exogenous IGF-II in the mother, we compared the impact of IGF-II with an IGF-II analogue, Leu(27)-IGF-II, which only binds the IGF2R. IGF-II, Leu(27)-IGF-II (1mg/kg per day.sc) or vehicle were infused from days 20-38 of pregnancy (term = 67 days) and placental structure and uptake and transfer of [(3)H]-methyl-D-glucose (MG) and [(14)C]-amino-isobutyric acid (AIB) and fetal growth and plasma metabolites, were measured on day 62. Both IGF-II and Leu(27)-IGF-II increased the volume of placental labyrinth, trophoblast and maternal blood space within the labyrinth and total surface area of trophoblast for exchange, compared to vehicle. Leu(27)-IGF-II also reduced the barrier to diffusion (trophoblast thickness) compared to vehicle and IGF-II. Both IGF-II and Leu(27)-IGF-II increased fetal plasma amino acid concentrations and placental transfer of MG to the fetus compared to vehicle, with Leu(27)-IGF-II also increasing AIB transport compared with vehicle and IGF-II. In addition, Leu(27)-IGF-II increased fetal weight compared to vehicle. In conclusion, maternal treatment with IGF-II or Leu(27)-IGF-II in early gestation, induce similar placental and fetal outcomes near term. This suggests that maternal IGF-II in early gestation acts in part via the IGF2R to persistently enhance placental functional development and nutrient delivery and promote fetal growth.

Phorbol ester restores L-system amino acid transport of B lymphocytes in chronic lymphocytic leukemia.

L (leucine-favoring)-system amino acid transport is uniquely and selectively diminished in chronic lymphocytic leukemia B lymphocytes: the maximal velocity of transport is 10% of normal B lymphocytes. We examined L-system transport in chronic leukemic B lymphocytes after incubation with tetradecanoyl phorbol acetate to determine if the transport abnormality can be corrected by the apparent cell maturation induced by this agent. Amino acid uptake was measured using 2-amino-2-carboxy-bicycloheptane, an L-system specific synthetic amino acid. Marked enhancement of L-system transport occurred in each of 12 leukemic cell populations; the initial velocity of transport in phorbol ester-treated cells increased 8-fold and 14-fold at 16 and 40 h, respectively, compared with untreated cells. The Vmax of the L-system in phorbol ester-treated leukemic cells was similar to that of phorbol ester-treated normal B lymphocytes. The L-system enhancement of the leukemic cells paralleled the development of plasmacytoid features at 40 h. Uptake of leucine, a naturally occurring L-system amino acid, was also increased by tetradecanoyl phorbol acetate. Cycloheximide, 100 micrograms/ml, which inhibited over 90% of protein synthesis in phorbol ester-treated chronic leukemic cells, blocked completely the phorbol ester-induced L-system enhancement. Phorbol ester treatment restores the selective L-system transport defect in chronic lymphocytic leukemia B lymphocytes, and this process coincides with in vitro maturation of the leukemic cells.

The metabolite beta-aminoisobutyric acid and physical inactivity among hemodialysis patients.

OBJECTIVE: Physical inactivity is frequent in patients on hemodialysis (HD), and represents a reliable predictor of morbidity and mortality. Beta-aminoisobutyric acid (BAIBA) is a contraction-induced myokine, the plasma levels of which increase with exercise and are inversely associated with metabolic risk factors. The aim of this study was to ascertain whether physical inactivity and clinical parameters relate to plasma BAIBA levels in this patient population. METHODS: Adult patients on HD were included, and the presence of physical inactivity was assessed. BAIBA levels were measured in these patients and in healthy individuals. We assessed barriers to physical activity, including 23 items regarding psychophysical and financial barriers. Body composition was assessed by bioimpedance and muscle strength by handgrip dynamometer. Nonparametric tests and logistic regression analyses were performed. RESULTS: Forty-nine patients on HD were studied; 49% were physically active and 51% were inactive. Of the patients, 43 reported barriers to physical activity and 61% of inactive patients reported three or more barriers. BAIBA levels were lower in patients on HD with respect to controls (P < 0.001). Stratifying HD patients as active and inactive, both groups showed significantly lower BAIBA levels versus controls (P = 0.0005, P < 0.001, respectively). Nondiabetic patients on HD showed increased BAIBA levels compared with diabetic patients (P < 0.001). Patients on HD endorsing the two most frequent barriers showed lower BAIBA levels than those not reporting these barriers (P = 0.006). Active patients showed higher intracellular water (%) (P = 0.008), and active and inactive patients showed significant correlation between total body muscle mass and handgrip strength (P = 0.04, P = 0.005, respectively). CONCLUSIONS: Physical inactivity is highly prevalent among patients on HD and BAIBA correlates with barriers to physical activity reported by inactive patients.

Insulin binding and response in erythroblastic leukemic cells.

Mammalian erythrocytes have been shown to bind, but not to respond to, physiologic doses of insulin. Insulin binding was studied in normal rat erythrocytes and erythroblastic leukemic (EBL) cells by standard 125I-insulin competitive binding assays. EBL cells exhibited marked insulin degradation, which was time, temperature, and concentration dependent and was mediated by both cell-bound and soluble enzymes. Bacitracin or bovine serum albumin was used to inhibit such degradation in a dose-dependent fashion to allow meaningful data analysis. Insulin binding studies showed a greater than 10-fold increase of specific binding to EBL cells compared with erythrocytes. Scatchard analysis was consistent with increases predominantly in the number of receptors on EBL cells. Concordant with increased insulin binding, EBL cells demonstrated increased transport of alpha-aminolsobutyric acid and increased incorporation of uridine into ribonucleic acid in response to physiologic doses of insulin (100 microunits/ml). It can be concluded that EBL cells may serve as useful models of erythroblasts to explore the relationships between insulin binding, response, and cell maturation.

Differential permeability of a human brain tumor xenograft in the nude rat: impact of tumor size and method of administration on optimizing delivery of biologically diverse agents.

To assess how to maximize drug delivery to intracerebral tumors and surrounding brain, this study examined the effects of route and method of administration and tumor size on the distribution of three agents in a nude rat intracerebral tumor xenograft model. Aminoisobutyric acid (M(r) 103), methotrexate (M(r) 454), and dextran 70 (M(r) 70,000) were administered i.v. or intra-arterially (i.a.) with or without osmotic blood-brain barrier disruption (BBBD) at 8, 12, or 16 days after tumor cell inoculation (n = 72). A 2.2- to 2.5-fold increase in delivery to tumor and surrounding brain was observed when i.a. was compared with i.v., and a 2.5- to 7.6-fold increase was observed when BBBD was compared with the saline control. The combined effect of i.a. administration and BBBD was to increase delivery 6.3-16.7-fold. The greatest benefit of BBBD was seen in animals with 8-day tumors, whereas BBBD had less benefit in improving delivery to intracerebral tumor and brain around tumor as the tumors grew larger. Regional delivery decreased as the molecular weight of the agent increased. Based on these results, we suggest that i.a. administration of antitumor agents may be adequate to obtain initial responses in large, very permeable, intracerebral tumors. However, in smaller, less permeable tumors or after an initial response to treatment, there may be a significant therapeutic advantage to i.a. agent administration and BBBD.

New insights in dihydropyrimidine dehydrogenase deficiency: a pivotal role for beta-aminoisobutyric acid?

DPD (dihydropyrimidine dehydrogenase) constitutes the first step of the pyrimidine degradation pathway, in which the pyrimidine bases uracil and thymine are catabolized to beta-alanine and the R-enantiomer of beta-AIB (beta-aminoisobutyric acid) respectively. The S-enantiomer of beta-AIB is predominantly derived from the catabolism of valine. It has been suggested that an altered homoeostasis of beta-alanine underlies some of the clinical abnormalities encountered in patients with a DPD deficiency. In the present study, we demonstrated that only a slightly decreased concentration of beta-alanine was present in the urine and plasma, whereas normal levels of beta-alanine were present in the cerebrospinal fluid of patients with a DPD deficiency. Therefore the metabolism of beta-alanine-containing peptides, such as carnosine, may be an important factor involved in the homoeostasis of beta-alanine in patients with DPD deficiency. The mean concentration of beta-AIB was approx. 2-3-fold lower in cerebrospinal fluid and urine of patients with a DPD deficiency, when compared with controls. In contrast, strongly decreased levels (10-fold) of beta-AIB were present in the plasma of DPD patients. Our results demonstrate that, under pathological conditions, the catabolism of valine can result in the production of significant amounts of beta-AIB. Furthermore, the observation that the R-enantiomer of beta-AIB is abundantly present in the urine of DPD patients suggests that significant cross-over exists between the thymine and valine catabolic pathways.

In-vivo imaging of blood-brain barrier permeability using positron emission tomography with 2-amino-[3-11C]isobutyric acid.

OBJECTIVE: The blood-brain barrier (BBB) limits the entry of some therapeutics into the brain, resulting in reduced efficacy. BBB-opening techniques have been developed to enhance the entry into the brain. However, a noninvasive, highly sensitive and quantitative method for evaluating the changes in BBB permeability induced by such techniques is needed to optimize treatment protocols. We evaluated 2-amino-[3-C]isobutyric acid ([3-C]AIB) as a PET probe to quantify BBB permeability in model rats. METHODS: BBB opening was induced by a lipopolysaccharide injection or focused ultrasound (FUS) sonication. [3-C]AIB distribution in the brain was evaluated by autoradiography and PET and compared with that of Evans blue, a traditional BBB permeability marker. Kinetics of [3-C]AIB was compared with that of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)-enhanced MRI. The unidirectional blood-brain transfer constant (Ki) of [3-C]AIB was estimated using the Patlak plot. RESULTS: [3-C]AIB uptake in the lesion area was significantly higher than that in the control area and radioactivity colocalized with Evans blue in both models. [3-C]AIB uptake in the FUS-sonicated region decreased over time after sonication. The ratio of [3-C]AIB accumulation in the FUS-treated to the contralateral side increased during the experimental period, whereas that of the Gd-DTPA intensity reached a maximum at 10 min after injection and decreased thereafter. The [3-C]AIB Ki values were significantly higher in the lesion area than the control area. CONCLUSION: [3-C]AIB PET is a promising, highly sensitive and quantitative imaging method for assessment of BBB permeability.

Effects of zidovudine, stavudine and beta-aminoisobutyric acid on lipid homeostasis in mice: possible role in human fat wasting.

OBJECTIVE: Although mitochondrial DNA (mtDNA) depletion could play a role in nucleoside reverse transcriptase inhibitor-induced lipoatrophy, poor correlations between fat mtDNA levels and lipoatrophy suggest additional mechanism(s). Stavudine (d4T), zidovudine (AZT) and the thymine catabolite, beta-aminoisobutyric acid (BAIBA), but not zalcitabine (ddC) or didanosine (ddI), can increase fatty acid oxidation in liver mitochondria and plasma ketone bodies in mice. Since fat oxidation in non-adipose tissue can influence body adiposity, we sought to determine whether d4T, AZT and BAIBA can cause lipoatrophy in mice by this catabolic mechanism. METHODS: Lean or obese ob/ob mice were treated for 6 weeks with d4T, AZT or BAIBA, and lean mice with ddC or ddI. Body fat mass was assessed by dual energy X-ray absorptiometry, and mtDNA by Slot blot hybridization in epididymal fat. RESULTS: Whereas ddC or ddI did not change plasma beta-hydroxybutyrate and body fat mass, d4T, AZT and BAIBA increased plasma beta-hydroxybutyrate in lean mice suggesting increased hepatic fatty acid oxidation and ketogenesis. Despite unchanged food consumption, a supra-pharmacological dose of d4T tended to decrease, whilst AZT and BAIBA decreased body fat mass. Fat mtDNA and plasma triglycerides, cholesterol, glucose, insulin, leptin and adiponectin levels were unchanged. In obese mice, d4T, AZT and BAIBA did not increase plasma beta-hydroxybutyrate, and only AZT decreased body fat mass without reducing fat mtDNA. CONCLUSIONS: d4T and AZT can enhance hepatic fat oxidation and cause fat wasting, without decreasing adipose tissue mtDNA and without causing insulin resistance in mice. BAIBA, a thymine catabolite, reproduces these effects. These catabolic effects could play a role in the lipoatrophy, which can occur in AZT- or d4T-treated patients.

Effect of inhibitors of arachidonic acid metabolism on alpha-aminoisobutyric acid transport in human lymphocytes.

The role of arachidonic acid metabolism (or metabolites) in the modulation of alpha-aminoisobutyric acid transport in resting and concanavalin A-stimulated human peripheral blood lymphocytes was evaluated using previously characterized inhibitors of arachidonic acid metabolism. Nordihydroguairetic acid (a nonselective antioxidant), 5,8,11,14-eicosatetraynoic acid (an inhibitor of lipoxygenase and cyclooxygenase activities), indomethacin and acetylsalicylic acid (selective cyclooxygenase inhibitors), and 1-benzylimidazole, Ro-22-3581 and Ro-22-3582 (thromboxane synthetase inhibitors) proved to be potent inhibitors of amino acid transport activity in normal resting and lectin-activated lymphocytes at concentrations known to decrease thromboxane A2 production. The rank order of effectiveness of these various inhibitors compared favorably with their relative potencies as inhibitors of thromboxane B2 synthesis under the same conditions, as determined by radioimmunoassay. Inhibitory effects noted were not due to overt cytotoxicity and seemed to involve changes primarily in the Vmax and not the Km of the transport process. Drug-induced alterations in the magnitude of concanavalin A binding were not observed. These results suggest that the activity of amino acid transport systems can be influenced by certain arachidonic acid metabolites, probably thromboxanes, in both stimulated and unstimulated lymphocytes. In addition, these findings may provide a partial explanation for the observation that inhibitors of thromboxane formation prevent lymphocyte mitogenesis.

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep.

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

The effects of neonatal androgenization on the in vivo transport of alpha-aminoisobutyric acid into specific regions of the rat brain.

The purpose of the present study was to determine if the administration of testosterone propionate (TP) to neonatal rats is followed in vivo by alterations in the transport of the non-metabolizable amino acid, alpha-aminoisobutyric acid (AIB), into specific regions of the brain. Forty-eigh hours after birth, male and female rats were injected s.c. with either 1,25 mg TP or an equivalent volume of vehicle. Five, 10 and 17 days after birth, control and TP-treated rats were decapitated at intervals of 2, 5, 60 and 300 min after the i.p. injection of 0.25 muCi [1-14C]alpha-aminoisobutyric acid/g body weight. Twelve brain regions, i.e., amygdala, cerebellum, corpora quadrigemina, frontal cortex, hypothalamus, medulla, occipital cortex, olfactory bulbs, olfactory tubercles, parietal cortex, pons, pyriform cortex and samples of serum were analyzed in terms of disint./min/mg tissue and as tissue/serum (T/S) ratios. At the end of 300 min there was a significant increase in the active transport of AIB in all brain regions of the 5-days-old TP-treated rats. Similarly, by 300 min, the active transport of AIB was significantly increased in all brain regions sxcept cerebellum and pons of the 10-day-old TP-treated rats. The administration of TP to neonatal rats did not alter the accumulation and/or active transport of AIB in brain regions of the 17-day-old rat at any of the tested intervals. These data indicate that (1) neonatally administered TP enhanced (either directly or indirectly) the transport and/or accumuation of AIB in specific brain regions of 5- and 10-day-old rats and (2) the effectiveness of the steroid decreased with the age of the rat.

Oleic acid reversibly opens the blood-brain barrier.

This study examined the effect of intracarotid oleic acid infusion on blood-brain barrier permeability. Oleic acid was infused for 30 s at a rate of 6 ml/min into the right internal carotid artery at concentrations of 10(-6), 10(-5), 2 x 10(-5) and 5 10(-5) M. Extensive Evans blue-albumin extravasation was observed 15 min after the administration of 2 x 10(-5) M oleic acid. The permeability surface area product for alpha-aminoisobutyric acid (AIB), determined 1-11 min following the infusion of oleic acid was increased 10-fold following infusion of 10(-5) M oleic acid and 20-fold following the administration of 5 x 10(-5) M oleate. The blood-brain barrier opening to AIB proved to be reversible 80-90 min after the infusion of 2 x 10(-5) M oleic acid. The possible mechanisms of the oleic acid effect are discussed.

Identification of beta-aminoisobutyric acid in uremic serum.

An unidentified ninhydrin-positive substance found in uremic sera but not found in normal sera was isolated by gel-filtration through Sephadex G-75 followed by high voltage paper electrophoresis (pH 3.5), and identified as beta-aminoisobutyric acid using paper chromatography and automated amino acid analyzer. The quantitative determination of beta-aminoisobutyric acid in serum revealed that the level of beta-aminoisobutyric acid in uremic sera was much higher than that of normal sera. Gas chromatographic determination of the enantiomorphs of beta-aminoisobutyric acid showed that uremic sera contain R- and S-isomers of the amino acid, but with the R-isomer as the dominating form.

Middle cerebral artery occlusion increases cerebral capillary permeability.

One hour after middle cerebral artery occlusion, the regional blood to brain transfer coefficient of alpha-aminoisobutyric acid was determined in eight barbiturate anaesthetized rats. The transfer coefficient (microliter/min-1/g-1) was significantly higher in the ischaemic cortex (10.6 +/- 2.3) than in the contralateral cortex (6.5 +/- 1.0). Cerebral regional capillary surface area was determined in another group of twelve rats using an alkaline phosphatase stain for the total capillary bed and fluorescein isothiocyanate-dextran to visualize the perfused capillaries. Perfused capillary surface area (cm2/cm3) was lower in the ischaemic cortex (141 +/- 31) than in the contralateral cortex (426 +/- 32). Using these values for the transfer coefficient, surface area and our previously published data of regional cerebral blood flow after middle cerebral artery occlusion, we calculated the extraction fraction of alpha-aminoisobutyric acid, the permeability-surface area product and the permeability of cerebral regional capillary beds. Although, there are numerous reports of permeability-surface area product of brain capillaries, to our knowledge, the permeability has never been determined before. The calculated extraction fraction ratio for alpha-aminoisobutyric acid for ischaemic cortex/contralateral cortex was 3.1. Similar ratios for permeability-surface area product and capillary permeability were 1.6 and 4.4, respectively. Thus, there was a more than four fold increase in capillary permeability to small molecules in the ischaemic cortex one hour after middle cerebral artery occlusion.

Elevation of serum levels of beta-aminoisobutyric acid in uremic patients and the toxicity of the amino acid.

A reliable method for the determination of beta-aminoisobutyric acid in serum was developed utilizing an automated amino acid analyzer. The serum concentrations of beta-aminoisobutyric acid were determined in 20 normal subjects and in 71 uremic patients. The mean serum level of beta-aminoisobutyric acid was markedly increased in the uremic patients to 0.856 +/- 0.910 (mean +/- SD) mg/100 ml as compared with a normal value of 0.026 +/- 0.027 mg/100 ml. The distribution of serum beta-aminoisobutyric acid level in uremic patients was wide-spread, and there was no correlation between the serum levels of the amino acid and those of urea nitrogen, creatinine and uric acid. The toxicity of beta-aminoisobutyric acid on mice with acute renal failure induced by uranyl acetate was investigated and compared with that of alpha-amino-n-butyric acid and gamma-amino-n-butyric acid. All mice given more than 4 g/kg body wt of beta-aminoisobutyric acid showed twitching and cramps, and some of them died. However, the control mice given an equivalent dose of alpha-amino-n-butyric acid or gamma-amino-n-butyric acid showed no change. These results suggest that beta-aminoisobutyric acid might be a factor influencing the development and progression of uremic toxemia.