Eric Ah-Sing

Characterization of a Novel Glucose-Responsive Insulin-Secreting Cell Line, BRIN-BD11, Produced by Electrofusion

A novel insulin-secreting cell line (BRIN-BD11) was established after electrofusion of RINm5F cells with New England Deaconess Hospital rat pancreatic islet cells. Wells of cell fusion mixture with insulin output 5–10 times greater than parent RINm5F cells were subcultured with eventual establishment of clones, including BRIN-BD11. Morphological studies established that these cells grow as monolayers with epithelioid characteristics, maintaining stability in tissue culture for >50 passages. Culture of these cells for 24 h at 5.6–33.3 mmol/l glucose revealed a 1.8- to 2.0-fold increase of insulin output compared with 1.4 mmol/l glucose. Dynamic insulin release was recorded in response to 16.7 mmol/l glucose, resulting in a rapid threefold insulin secretory peak followed by a sustained output slightly above basal. In acute 20-min tests, 4.2–16.7 mmol/l glucose evoked a stepwise twoto threefold stimulation of insulin release. 3-Isobutyl-1-methylxanthine (1 mmol/l) served to increase basal and glucose-stimulated insulin release, shifting the threshold from 4.4 to 1.1 mmol/l glucose. Stimulation of insulin secretion with 16.7 mmol/l glucose was abolished by mannoheptulose or diazoxide (15 or 0.5 mmol/l). In contrast, glyceraldehyde (10 mmol/l) and 25 mmol/l K+ evoked 1.7- to 9.0-fold insulin responses. l-Alanine (10 mmol/l) evoked a twofold secretory response, which was potentiated 1.4-fold by increasing the Ca2+ concentration from 1.28 to 7.68 mmol/l. Forskolin (25 εmol/l) and phorbol 12-myristate 13-acetate (10 nmol/1) both increased insulin secretion in the presence of l-alanine (1.4- and 1.8-fold, respectively). Western blotting confirmed that BRIN-BD11 cells expressed the GLUT2 glucose transporter. This, coupled with a high glucokinase/hexokinase ratio in the cells, confirms an intact glucose sensing mechanism. High-performance liquid chromatography analysis demonstrated that insulin was the major product secreted under stimulatory conditions. Collectively, these data indicate that the BRIN-BD11 cell line represents an important stable glucose-responsive insulinsecreting β-cell line for future studies.

Long-chain conversion of [13C]linoleic acid and α-linolenic acid in response to marked changes in their dietary intake in men

We studied the long-chain conversion of [U-13C]α-linolenic acid (ALA) and linoleic acid (LA) and responses of erythrocyte phospholipid composition to variation in the dietary ratios of 18:3n-3 (ALA) and 18:2n-6 (LA) for 12 weeks in 38 moderately hyperlipidemic men. Diets were enriched with either flaxseed oil (FXO; 17 g/day ALA, n = 21) or sunflower oil (SO; 17 g/day LA, n = 17). The FXO diet induced increases in phospholipid ALA (>3-fold), 20:5n-3 [eicosapentaenoic acid (EPA), >2-fold], and 22:5n-3 [docosapentaenoic acid (DPA), 50%] but no change in 22:6n-3 [docosahexanoic acid (DHA)], LA, or 20:4n-6 [arachidonic acid (AA)]. The increases in EPA and DPA but not DHA were similar to those in subjects given the SO diet enriched with 3 g of EPA plus DHA from fish oil (n = 19). The SO diet induced a small increase in LA but no change in AA. Long-chain conversion of [U-13C]ALA and [U-13C]LA, calculated from peak plasma 13C concentrations after simple modeling for tracer dilution in subsets from the FXO (n = 6) and SO (n = 5) diets, was similar but low for the two tracers (i.e., AA, 0.2%; EPA, 0.3%; and DPA, 0.02%) and varied directly with precursor concentrations and inversely with concentrations of fatty acids of the alternative series. [13C]DHA formation was very low (<0.01%) with no dietary influences.

Antioxidant defenses in the bile duct-ligated rat

Changes in pro-oxidant and antioxidant balance in the serum and liver were studied in an experimental model of obstructive jaundice in the rat. The results showed a decrease in plasma vitamin E concentration (P < 0.01) and a threefold reduction in liver vitamin E concentration (P < 0.001). There was also a threefold reduction in levels of the liver enzymes glutathione peroxidase (P < 0.01) and glutathione transferase (P < 0.001), together with a six-fold reduction in catalase activity (P < 0.001). The serum selenium level decreased by 35% in the jaundiced rats (P < 0.05). The total liver glutathione level decreased to half the control value (P < 0.01). The malonyldialdehyde level, the measure of lipid peroxidation used in this study, doubled (P < 0.01). The results suggest a shift in the pro-oxidant/antioxidant balance in favor of lipid peroxidation. The possible etiology of this change and its relationship to human cholestasis are discussed.

Caffeoyltyrosine from green robusta coffee beans

Abstract A component found in commercial green robusta coffee beans from many origins, but particularly characteristic of those from Angola, has been characterised as N -caffeoyltyrosine.

Mechanism of the ketoconazole-cyclosporin interaction.

Study of influence of ketonazole ou cyclosporin blood concentrations after it had reached steady-state levels in rats. The possibilities that the site of interaction is during metabolism or during absorption were investigated

Heats of solution of electrolytes in ethanol and derived enthalpies of transfer from water

Heats of solution of 12 1 : 1 electrolytes in ethanol have been determined calorimetrically, and have been extrapolated to zero electrolyte concentration to give ΔH°s values for these electrolytes. Together with literature data for 9 other 1 : 1 electrolytes, these measurements yield a set of single ion enthalpies of transfer from water to ethanol for 11 univalent cations and 6 univalent anions. Using the assumption that ΔH°t(Ph4As+)=ΔH°t(Ph4B–), it is shown that small univalent cations are enthalpically more stable in ethanol than in water, but that the larger tetra-alkylammonium ions are less stable in ethanol. With the same assumption, it is also shown that all the univalent cations and anions studied are of almost the same enthalpy (within about ± 0.5 kcal mol–1) in the three alcohols methanol, ethanol and 1-propanol.

Enterohepatic circulation of IgA does not occur in rats

The concentration of IgA in rat bile falls with time after cannulation. This effect is particularly marked in germ-free animals, in which the initial level of IgA is markedly subnormal anyway. The fall suggests that the cannula is draining to the exterior IgA, which would normally be recirculated. However, when germ-free or normal rats were supplied intraduodenally with bile whose IgA carried 125I, no transfer of this labelled IgA from the gut lumen back to the bile could be detected.

Thermodynamics of solution of two forms of DL-α-amino-n-butyric acid in water

Two crystalline polymorphic forms of DL-α-amino-n-butyric acid have been obtained and have been shown to be identical to the A-form and B-form previously described by Iitaka and coworkers. The two forms differ in heat of solution and in their solubility in water. We find that for the A-form at 298 K, ΔH°s= 374 cal mol–1, ΔG°s= 1772 cal mol–1 and ΔS°s=–4.7 cal K–1 mol–1 and for the B-form ΔH°s= 1653 cal mol–1, ΔG°s= 1883 cal mol–1 and ΔS°s=–0.8 cal K–1 mol–1. Although the B-form is the stable form at 298 K, it is predicted from the above measurements that the A-form should be the stable form above ∼ 326 K.