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PubMed2003

Anomalous distance dependence of electron transfer across peptide bridges.

The first investigation on the distance dependence of a dissociative electron transfer process across peptide bridges is reported. This study was carried out by using a series of donor-peptide-acceptor systems in which the donor is a phthalimido moiety, the peptide bridges are provided by alpha-aminoisobutyric acid (Aib) homooligomers, and the acceptor is a peroxide functional group. The intramolecular electron transfer from the electrogenerated phthalimido radical anion to the peroxide was studied in comparison with the thermodynamic and kinetic information obtained with models of the acceptor and the donor. The intramolecular rate constants were determined in N,N-dimethylformamide by taking into account the corresponding intermolecular values. The experimental results point to an unusual non-exponential dependence of the intramolecular electron transfer rate on the number of bridge units. The same trend could be verified also by taking into account the actual donor-acceptor edge-to-edge distance. The peculiar distance dependence that was observed for the intramolecular electron transfer rate is attributed to the mediating effect of the intramolecular C=O...H-N hydrogen bonds.

Aminoisobutyric Acids↗
PubMed1989

Spermidine uptake by type II pulmonary epithelial cells in primary culture.

The transport pathway for the polyamine spermidine (SPD) was characterized in primary isolates of type II pulmonary epithelial cells from rat lungs. [14C]spermidine was accumulated by type II cells via a temperature-, sodium-, and concentration-dependent saturable pathway, with an apparent Km of 0.48 microM and a maximum velocity (V max) of 0.32 pmol.microgram DNA-1.min-1. SPD uptake was inhibited by gramicidin and by reduced extracellular sodium but was unaffected by alpha-aminoisobutyric acid (AIB), which entered the cells by a similar saturable pathway. Uptake of SPD also was inhibited by the exogenous polyamines putrescine (PUTR) and spermine (SPM), as well as by the methylglyoxal bis(guanylhydrazone) (MGBG) and by paraquat (PQ). The order of potency of these inhibitors was SPM greater than PUTR = MGBG much greater than PQ. The absence of serum reduced the Vmax of the system slightly but had no effect on the apparent Km. In contrast, after 3 days in primary cell culture, the kinetics of SPD transport were altered by decreases in both the Km and Vmax of the uptake process. These observations indicate that type II pulmonary epithelial cells exhibit a pathway of polyamine uptake with general characteristics similar to those observed previously in intact lung tissue and other cell types.

Aminoisobutyric Acids↗
PubMed1987

The absence of gamma-glutamyltransferase activity in transport-dependent methotrexate-resistant hepatoma cells.

A cell line derived from H35 hepatoma cells resistant to methotrexate (MTX) as a result of a defective transport system for MTX has been examined to determine how closely the variant resembles the parent cells with regard to other biochemical properties. The capacity of extracts of resistant cells to catalyze the poly-gamma-glutamylation of MTX was approximately twice as great as that of wild-type cell extracts. Evidence of similarity between wild-type and H35 R0.3 cells was derived from the equitoxic activity to both cell lines of nonclassical antifolates and other miscellaneous antineoplastics which act by a variety of mechanisms. Two phenotypic markers of hepatic cell function, alpha-aminoisobutyric acid (AIB) transport and tyrosine aminotransferase (TAT) activity inducibility, were present in both cell types, demonstrating the maintenance of these phenotypic properties in the H35 R0.3 cells. gamma-Glutamyltransferase (GGT, EC 2.3.2.2) activity differed in that it was present in wild-type cells and barely detectable in H35 R0.3 cells. The GGT activity reappeared in the H35 cells when they regained MTX sensitivity after incubation for 14-20 weeks in MTX-free media. Although defective MTX transport appeared to be correlated with the disappearance of GGT activity in an H35 variant cell line, no functional relationship between them is apparent at this time. It is possible that a lack of GGT activity may be evidence of a more differentiated phenotype in the transport-resistant cell line.

Aminoisobutyric Acids↗
PubMed1995

In vitro effects of fentanyl, methohexital, and thiopental on brain endothelial permeability.

BACKGROUND: The use of anesthetics can lead to changes of the permeability of the blood-brain barrier (BBB). To eliminate those factors, such as varying hemodynamic effects that are associated with anesthesia, an in vitro model of the BBB consisting of brain microvascular endothelial cells (BMEC) was used to study the direct effects of the opiate, fentanyl, and the barbiturates methohexital and thiopental, which are widely used in the clinical setting, on the permeability of confluent monolayers. METHODS: BMEC isolated from porcine brains were grown to confluence on collagen-coated polycarbonate membranes, which were placed into 24 well dishes, thus forming a two-compartment chamber. The permeability of the BMEC monolayer to ions--determined by measurements of the transendothelial resistance (TER)--the passage of sucrose, Evans Blue albumin (EBA), and alpha-aminoisobutyric acid (AIB) across the BMEC monolayer were assessed in the presence and absence of fentanyl (25-100 ng/ml), methohexital (10-50 micrograms/ml), and thiopental (25-100 micrograms/ml). RESULTS: The permeability of cultured BMEC to the tracers used increased significantly after exposure of the monolayer to arabinose and after removal of calcium ions. Fentanyl, methohexital, and thiopental did not change the permeability of the cell monolayer to ions, sucrose, albumin, and AIB. Only thiopental at the concentration of 100 micrograms/ml increased the flux of AIB. CONCLUSIONS: At the concentrations tested, there is little evidence of changes in the permeability of the in vitro BBB caused by fentanyl, methohexital, and thiopental regarding the para- and transcellular route of ions, sucrose, and albumin. Only thiopental at a concentration of 100 micrograms/ml increased the passage of AIB across the BMEC monolayer.

Albumins↗
PubMed1990

Effect of steroid therapy on ischaemic brain oedema and blood to brain sodium transport.

Dexamethasone has been shown in some studies to reduce ischaemic brain oedema, however, the mechanism is unknown. One possible mechanism is through inhibition of active transport of sodium across the blood-brain barrier (BBB) since some steroids, especially progesterone, inhibit sodium transport in isolated brain capillaries. Therefore, we measured brain oedema and BBB permeability to sodium and a passive permeability tracer, alpha-aminoisobutyric acid (AIB), 4 hr after middle cerebral artery occlusion (MCAO) in rats that had been treated 1 hr before MCAO with vehicle (control) or 2 mg/kg of either dexamethasone or progesterone. In controls, the water content of tissue in the center of the ischaemic zone was 82.4 +/- 0.2%. Brain oedema was significantly reduced following pretreatment with either dexamethasone (80.6 +/- 0.1, p less than 0.001) or progesterone (81.5 +/- 0.3, p less than 0.05). Both steroids also reduced BBB permeability to AIB by about 40% in normal brain but to a lesser extent in ischaemic brain. In contrast, steroid treatment had no effect on BBB permeability to sodium in either normal or ischaemic brain. We conclude that pretreatment with dexamethasone and progesterone reduces brain oedema accumulation during the early stages of ischaemia, however, this effect does not result from a reduction in BBB permeability to sodium.

Aminoisobutyric Acids↗
PubMedDate not supplied

Tumor and organ biochemical profiles determined in vivo following uptake of a combination of radiolabeled substrates: potential applications for PET.

This paper describes a method which generates an in vivo metabolic profile of tumors and organ tissues derived from the tissue uptake of a combination of radiotracers. Metabolic substrates labeled with carbon-11, a positron-emitting radionuclide (T1/2 = 20.4 min) have been used to probe tumor metabolism in vivo using positron emission tomography (PET). Carbon-11 labeled radiotracers which have been used include alpha-aminoisobutyric acid (AIB), 2-deoxy-D-glucose (2-DG), and thymidine (TdR). This paper reports data on the tissue distribution of carbon-14 labeled analogues of AIB, 2-DG, and TdR. Tissue distribution studies were carried out in normal male Copenhagen rats, in rats bearing Dunning R3327G or R3327H prostatic adenocarcinomas, and in tumor rats that have been treated with difluoromethylornithine and methylglyoxal-bisguanylhydrazone, or with diethylstilbestrol. A combination of the tissue distribution data of these radiolabeled agents is used to provide a metabolic description of the state of a tumor or tissue in vivo. This approach to defining a tissue's biochemical profile may be useful for the assessment and prediction of a therapeutic response, even at low tracer concentrations in a tumor, and may be useful in relating the biochemical characteristics of one tissue to that of another.

Adenocarcinoma↗
PubMed1995

Blood-brain barrier taurine transport during osmotic stress and in focal cerebral ischemia.

Little is known about blood to brain taurine transport despite substantial evidence suggesting a role of taurine in brain volume regulation during osmotic stress or conditions inducing cell swelling, such as ischemia. We have made measurements of the taurine influx rate constant (K1) with [3H]taurine in three conditions: raised plasma taurine concentrations induced by infusion with 50 mM taurine (10 microliters/100 g/min); osmotic stress induced by i.p. injections of 1.5 M NaCl (2 ml/100 g) or distilled water (10 ml/100 g); and 4 h of middle cerebral artery occlusion (MCAo). In rats with MCAo, additional determinations were made of tissue water and taurine contents, and blood-brain barrier passive permeability with [3H]alpha-aminoisobutyric acid. Taurine infusion increased plasma taurine from 110 +/- 63 microM (SD) to 407 +/- 63 (p < 0.001) and decreased taurine K1 at the blood-brain barrier by 70% (p < 0.001), signifying saturable uptake that maintained unidirectional influx constant. Similarly, although hypo- and hyperosmolality increased and decreased plasma taurine concentration, respectively, a reciprocal relationship between K1 and plasma taurine in these experiments ensured that unidirectional fluxes of taurine into brain were unchanged by osmotic stress. During MCAo, the taurine K1 was reduced 80% in the ipsilateral ischemic tissue compared with the contralateral nonischemic tissue (p < 0.001). This decline may be due to a release of taurine into the brain circulation, because there was a concomitant loss of tissue taurine of 7.4 +/- 2.4 mmol/g dry weight (p < 0.05). Alternately, if taurine uptake is sodium dependent, the decline might reflect a disruption of the endothelial sodium gradient.

Aminoisobutyric Acids↗
PubMedDate not supplied

Placental blood flow and transfer of nutrient analogues during normal gestation in the guinea pig.

Simultaneous measurements of placental transfer of 14C-alpha-aminoisobutyric acid (AIB), 3H-methyl glucose (MG) and placental blood flow were performed in anaesthetized guinea pigs at various gestational ages. The results were correlated with the growth of the conceptus. The placenta increased its weight at a maximal rate (g/day) between days 31 and 40 of gestation while maximal fetal increments in weight occurred between days 51 and 60. Total net transfer of AIB and MG per gram of placenta increased progressively during pregnancy while net transfer per gram of fetus decreased approaching term. Placental blood flow in the maternal side increased linearly near term. The quantities of AIB and MG transferred by the placenta per ml of blood was maximal between 51 and 60 days of gestation. These data suggest that a relatively smaller placenta in relationship with fetal size limits the quantity of nutrients transferred to the fetus near term, and reduces the rate of fetal growth.

Acidosis↗
PubMed1985

Regional blood-brain barrier permeability changes after restoration of blood flow in postischemic gerbil brains: a quantitative study.

A quantitative technique utilising [14C]alpha-aminoisobutyric acid as a tracer was used to study cerebrovascular permeability in 22 Mongolian gerbils. Seven other animals were used to measure cerebral blood volumes. Global cerebral ischaemia was produced by temporary bilateral carotid artery occlusion (60 min) in 16 gerbils that were sacrificed at 1, 2, and 3 h following reperfusion. The blood-to-brain transfer constant was significantly increased after 2 h of reperfusion in the ischaemic zones and also in structures, like the cerebellum, not supplied by the carotid artery and not ischaemic during the vessel occlusion. The blood-brain barrier (BBB) alterations were coincident with the onset of ischaemia--induced seizures that were accompanied by sudden "spikes" of systemic blood pressure. Epilepsy may play an important role in the development of BBB damage in this ischaemic model, and this factor must be considered in the interpretation of BBB damage data in gerbils.

Aminoisobutyric Acids↗
PubMed1992

Increased opening of blood-tumour barrier by leukotriene C4 is dependent on size of molecules.

Intracarotid injections of leukotriene C4 (LTC4) will increase blood-tumour barrier (BTB) permeability for 14C aminoisobutyric acid (AIB) in RG-2 tumours in rats. In this study, rats with RG-2 tumours were given 15 minute intracarotid infusions of LTC4 (5 micrograms total dose). Blood-tumour and BBB permeability were determined by quantitative autoradiography using different sized 14C tracers; AIB (103.1 daltons, radius = 2.8 A), Sucrose (342 daltons, radius = 5 A), Inulin (5000 daltons, radius = 15 A) and Dextran (70,000 daltons, radius = 60 A), respectively (n = 7 in each group). Permeability (Ki) within tumours for AIB, Sucrose and Inulin increased significantly after LTC4 infusion (92.7 +/- 15.0 vs 39.4 +/- 6.5, 47.8 +/- 5.2 vs 29.1 +/- 8.8, and 46.4 +/- 8.4 vs 26.4 +/- 4.8 microliters/gm/min, respectively, p < 0.01) (mean +/- SD). No significant change in Ki for 14C Dextran was observed. Increased permeability within tumours after LTC4 infusion is dependent on molecular size. This suggests that LTC4 opens tight junctions rather than increases vesicular transport through endothelial cells.

Aminoisobutyric Acids↗
PubMed1997

Effect of transient focal ischemia on blood-brain barrier permeability in the rat: correlation to cell injury.

Prolonged ischemia is known to damage the blood-brain barrier, causing an increase in vascular permeability to proteins. We studied the time course of extravasation of endogenous albumin in rats after 1 and 2 h of middle cerebral artery (MCA) occlusion followed by 6, 12, and 24 h of recirculation. In a separate group of rats that had undergone 1 h of MCA occlusion and 6 h of recirculation, influx of [14C]aminoisobutyric acid (AIB) from blood to brain was also measured. After 1 h of occlusion followed by 6 h of recirculation, neuronal damage was evident in caudoputamen, but there were no signs of blood-brain barrier leakage to either AIB or albumin. At 12 h, the caudoputamen contained extravasated albumin, and at 24 h extravasation was extended to the somatosensory cortex. Animals subjected to 2 h of MCA occlusion showed albumin extravasation in caudoputamen already at 6 h of recirculation, and at 12 and 24 h albumin was abundant in the major part of the right hemisphere. This study suggests that damage to neurons precedes leakage of the blood-brain barrier. Even a relatively short period of ischemia such as 1 h will result in markedly increased vascular permeability. However, a longer transient ischemic insult disrupts the blood-brain barrier earlier than a shorter one.

Albumins↗
PubMed1985

Recirculation model following MCA occlusion in rats. Cerebral blood flow, cerebrovascular permeability, and brain edema.

A new model for establishing a successful and consistent arterial recirculation has been devised following middle cerebral artery (MCA) occlusion in the rat. A snare ligature was introduced at the stem of the MCA just distal to the lenticulostriate branches, and occlusion and recirculation were performed by pulling and releasing the thread. This method had an advantage over the use of a small clip which caused damage to the artery without good recirculation. Study of local cerebral blood flow using carbon-14 (14C)-iodoantipyrine, of cerebrovascular permeability using 14C-aminoisobutyric acid, and of brain-water content using the microgravimetric technique was performed upon recirculation following various periods of occlusion and compared with the results in permanent ischemia. A reactive hyperemia was noted within the previously ischemic area immediately upon recirculation following either a 30-minute or a 2-hour ischemic period. One or 2 hours later, delayed hypoperfusion developed in this region, but the circulation over the periphery of the ischemic area recovered well. Cerebrovascular permeability was not, however, altered during the time courses studied. Topographic changes in tissue specific gravity were compared between permanent and transient ischemia in the corresponding time-courses. Although there was a greater decrease in tissue specific gravity following recirculation when the ischemic period was maintained longer, edema formation was resolved by recirculation. Further study is required to determine thresholds of ischemic brain damage and edema formation at recirculation following focal cerebral ischemia.

Aminoisobutyric Acids↗
PubMed1984

Local blood-to-tissue transport in Walker 256 metastatic brain tumors.

Local blood-to-tissue transfer constants (K) in metastatic Walker 256 (WL-256) brain tumors produced by the intracarotid artery injection of WL-256 tumor cells in rats were measured using 14C-alpha-aminoisobutyric acid and quantitative autoradiography. Small compact and diffuse infiltrative intraparenchymal tumors had values of K similar to that of contralateral nontumorous brain tissue. Medium and large tumors, meningeal metastases and intraventricular tumors had higher K values (5 to 30 fold) than contralateral nontumorous brain tissue indicating that intraparenchymal tumor size and location in meningeal and choroidal tissue influence the permeability of tumor capillaries. The local intratumor values of K varied considerably in these tumors and this variability of K correlated to only a few specific histopathologic features of the tumors. The value of K abruptly decreased at the tumor-brain interface when this interface was sharply defined, indicating that the metastatic tumors have only a small effect on the permeability of adjacent brain capillaries. Low blood-to-tumor transport of water soluble drugs will significantly affect drug concentrations in the tumor and the tumor-drug exposure.

Aminoisobutyric Acids↗
PubMed1982

Cerebrovascular permeability following MCA occlusion in the rat. The effect of halothane-induced hypotension.

A quantitative autoradiographic technique that utilizes carbon-14-aminoisobutyric acid (14C-AIB) as a tracer was used to study alterations in cerebral microvascular permeability in 15 rats. Five were "sham-operated" controls and 10 underwent microsurgical, unilateral occlusion of the proximal middle cerebral artery (MCA). Histological changes indicative of focal cerebral ischemia were observed in only the latter 10 animals. These changes were confined to tissue normally perfused by the occluded MCA. After MCA occlusion, five animals were also subjected to transient halothane-induced hypotension (mean arterial blood pressure 50 mm Hg) for 20 to 30 minutes. Only in these five animals were blood-to-brain transfer constants (ki) significantly increased (by approximately 100%) at 4 hours after MCA occlusion. The topographical distribution of this alteration in cerebral microvascular permeability corresponded closely with the histological changes. Neither proximal MCA occlusion nor halothane-induced hypotension alone was associated with any focal or diffuse increase in ki after 4 hours.

Aminoisobutyric Acids↗
PubMed1989

[Effects of dehydration of the pituitary microcirculation in rats].

The contiguous three lobe of the pituitary gland have different endocrine functions and vascular bed. This study was designed to investigate the effects of dehydration, which stimulates the secretion of vasopressin, on the pituitary microcirculation. Male Sprague-Dawley rats, weighing 300-380 g, were divided into two groups. Twenty three rats were allowed free access to food and water, and 24 rats had free access to food but were deprived of water for 5 days. Capillary solute transfer (K), plasma volume (Vp) and erythrocyte volume (Ve) in each pituitary lobe were determined for both control and dehydrated rats. Quantitative autoradiographic techniques were used to measure the K with 14C-alpha-aminoisobutyric acid (AIB, a small neutral amino acid), the Vp with 125I-albumin and the Ve with 51Cr-erythrocytes. Body weight was lower (-23%) and the arterial hematocrit was higher (+22%) in the dehydrated rats. In the lobes of the control pituitary gland, the order of K from the highest to the lowest was posterior much greater than anterior greater than intermediate lobe. K was increased by several folds only in the posterior lobe in dehydrated rats (p less than 0.05). Even under normal hydrated conditions, K for AIB in the posterior lobe was several hundreds times greater than in cerebral gray matter structures. The rank of Vp and Ve in each lobe of normal animals was about the same order and anterior greater than posterior much greater than intermediate. Normal microvascular Vp in the anterior and posterior lobes was 5-10 times larger than in cerebral gray matter.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoisobutyric Acids↗
PubMed2003

Prevention of peptide fibril formation in an aqueous environment by mutation of a single residue to Aib.

The behavior of a number of 16 residue polypeptides with a sequence Acetyl-EACARXZAACEAAARQ-amide, where X = V or A and Z = A or Aib, is studied under aqueous conditions. It is shown that the substitution of a single alanine residue by alpha-aminoisobutyric acid (Aib) completely alters both the conformation and the aggregation properties of the peptides. The Ala-Ala (X,Z = A,A) peptide is shown by circular dichroism and FTIR methods to adopt a predominately beta-sheet conformation. Furthermore, the peptide has limited solubility and is shown to form fibrils by electron microscopy and thioflavin T binding assays. In contrast, a single substitution at the center of peptide of alanine to Aib (X,Z = A,Aib) completely abolishes fibril formation and alters the conformation to a mixture of random coil and alpha-helix. The results show that Aib is a strong beta-sheet disrupter that is also able to adopt a helical conformation. This is linked to its role in peptaibol antibiotics. Aib provides an attractive alternative to proline and other substitutions in producing peptide variants with a lower tendency to produce fibril aggregates.

Aminoisobutyric Acids↗
PubMed1990

Human malignant gliomas secrete a factor that increases brain capillary permeability: role in peritumoural brain oedema.

The effect of conditioned media obtained from two human malignant gliomas and normal human glia on rat brain capillary permeability was investigated by measuring the entry of 14C-aminoisobutyric acid by a quantitative autoradiographic method. Conditioned media were concentrated 50-fold to create SUP-C. The SUP-C contained proteins with a molecular weight greater than 10 kD. The SUP-C from glioma cells markedly increased brain capillary permeability, whereas that from normal glial cells did not. The activity of capillary permeability factor in the SUP-C was significantly inhibited by pretreatment of animals with dexamethasone or BW755C (lipoxygenase inhibitor), but not with indomethacin. On the other hand, coincubation of glioma cells with dexamethasone produced SUP-C whose capillary permeability activity was about one and a half times greater than that without dexamethasone. These results indicate that human malignant glioma cells secrete a protein factor that increases brain capillary permeability. Glucocorticoids inhibit the effect of the factor by directly acting on capillary endothelial cells, possibly through the inhibition of phospholipase A2 activity, resulting in a decrease of lipoxygenase rather than cyclo-oxygenase products.

Aminoisobutyric Acids↗
PubMed2006

Early treatment of the pregnant guinea pig with IGFs promotes placental transport and nutrient partitioning near term.

Appropriate partitioning of nutrients between the mother and conceptus is a major determinant of pregnancy success, with placental transfer playing a key role. Insulin-like growth factors (IGFs) increase in the maternal circulation during early pregnancy and are predictive of fetal and placental growth. We have previously shown in the guinea pig that increasing maternal IGF abundance in early to midpregnancy enhances fetal growth and viability near term. We now show that this treatment promotes placental transport to the fetus, fetal substrate utilization, and nutrient partitioning near term. Pregnant guinea pigs were infused with IGF-I, IGF-II (both 1 mg.kg-1.day-1) or vehicle subcutaneously from days 20-38 of pregnancy (term=69 days). Tissue uptake and placental transfer of the nonmetabolizable radio analogs [3H]methyl-D-glucose (MG) and [14C]aminoisobutyric acid (AIB) in vivo was measured on day 62. Early pregnancy exposure to elevated maternal IGF-I increased placental MG uptake by>70% (P=0.004), whereas each IGF increased fetal plasma MG concentrations by 40-50% (P<0.012). Both IGFs increased fetal tissue MG uptake (P<0.048), whereas IGF-I also increased AIB uptake by visceral organs (P=0.046). In the mother, earlier exposure to either IGF increased AIB uptake by visceral organs (P<0.014), whereas IGF-I also enhanced uptake of AIB by muscle (P=0.044) and MG uptake by visceral organs (P=0.016) and muscle (P=0.046). In conclusion, exogenous maternal IGFs in early pregnancy sustainedly increase maternal substrate utilization, placental transport of MG to the fetus, and fetal utilization of substrates near term. This was consistent with the previously observed increase in fetal growth and survival following IGF treatment.

Aminoisobutyric Acids↗