Isomer-Dependent Escape Rate of Xenon from a Water-Soluble Cryptophane Cage Studied by Ab Initio Molecular Dynamics.

The escape of xenon from the anti and syn diastereomers of hexacarboxylic-cryptophane-222 in water has been studied by ab initio molecular dynamics simulations. The structures of both complexes, when the xenon atom is trapped inside their cages, have been compared and show no major differences. The free-energy profiles corresponding to the escape reaction have been calculated with the Blue Moon ensemble method using the distance between Xe and the center of mass of the cage as the reaction coordinate. The resulting free-energy barriers are very different; the escape rate is much faster in the case of the syn diastereomer, in agreement with experimental data obtained in hyperpolarized 129 Xe NMR. Our simulations reveal the mechanistic details for each diastereomer and provide an explanation for the different in-out xenon rates based on the solvation structure around the cages.

Photochemistry of glycolaldehyde in cryogenic matrices.

The photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization and fragmentation processes are found to compete. The hydrogen-bonded Cis-Cis form of GA is transformed mainly to the open Trans-Trans conformer and to CO and CH3OH fragments and their mixed complexes. Different photo-induced behaviours appear depending on the matrix. In nitrogen, small amounts of Trans-Gauche and Trans-Trans conformers are detected after deposition and grow together upon irradiation. The Trans-Gauche conformer is characterized for the first time. In para-hydrogen due to a weaker cage effect additional H2CO and HCO fragments are seen. Calculations of the potential energy surfaces of S0, S1, and T1 states--to analyse the torsional deformations which are involved in the isomerization process--and a kinetic analysis are presented to investigate the different relaxation pathways of GA. Fragmentation of GA under UV irradiation through the CO+CH3OH molecular channel is a minor process, as in the gas phase.

Gas-phase folding of a two-residue model peptide chain: on the importance of an interplay between experiment and theory.

In order to assess the ability of theory to describe properly the dispersive interactions that are ubiquitous in peptide and protein systems, an isolated short peptide chain has been studied using both gas-phase laser spectroscopy and quantum chemistry. The experimentally observed coexistence of an extended form and a folded form in the supersonic expansion was found to result from comparable Gibbs free energies for the two species under the high-temperature conditions (< or = 320 K) resulting from the laser desorption technique used to vaporize the molecules. These data have been compared to results obtained using a series of quantum chemistry methods, including DFT, DFT-D, and post-Hartree-Fock methods, which give rise to a wide range of relative stabilities predicted for these two forms. The experimental observation was best reproduced by an empirically dispersion-corrected functional (B97-D) and a hybrid functional with a significant Hartree-Fock exchange term (M06-2X). In contrast, the popular post-Hartree-Fock method MP2, which is often used for benchmarking these systems, had to be discarded because of a very large basis-set superposition error. The applicability of the atomic counterpoise correction (ACP) is also discussed. This work also introduces the mandatory theoretical examination of experimental abundances. DeltaH(0 K) predictions are clearly not sufficient for discussion of folding, as the conformation inversion temperature is crucial to the conformation determination and requires taking into account thermodynamical corrections (DeltaG) in order to computationally isolate the most stable conformation.

Evaluation of the persistent activity of moxidectin (10%) long-acting (LA) injectable formulation against Dictyocaulus viviparus, Haemonchus placei, Trichostrongylus axei and Oesophagostomum radiatum infections in cattle.

Two controlled studies were conducted to evaluate the persistent efficacy of moxidectin (10%) long-acting (LA) injectable formulation against Dictyocaulus viviparus, Haemonchus placei, Trichostrongylus axei and Oesophagostomum radiatum in cattle. The moxidectin LA injectable formulation was administered as a single subcutaneous injection into the proximal third of the ear at a dose rate of 0.01ml/kg BW to provide 1.0mg moxidectin/kg BW. The product had persistent efficacy of >90% against D. viviparus, H. placei and Oe. radiatum for at least 150 days post-treatment and against T. axei for at least 90 days post-treatment.

Molecular dynamics study of the hydration of lanthanum(III) and europium(III) including many-body effects.

Lanthanides complexes are widely used as contrast agents in magnetic resonance imaging (MRI) and are involved in many fields such as organic synthesis, catalysis, and nuclear waste management. The complexation of the ion by the solvent or an organic ligand and the resulting properties (for example the relaxivity in MRI) are mainly governed by the structure and dynamics of the coordination shells. All of the MD approaches already carried out for the lanthanide(III) hydration failed due to the lack of accurate representation of many-body effects. We present the first molecular dynamics simulation including these effects that accounts for the experimental results from a structural and dynamic (water exchange rate) point of view.

Pharmacokinetics of cefepime and comparison with those of ceftiofur in horses.

OBJECTIVE: To determine pharmacokinetics of i.v., i.m., and oral administration of cefepime in horses and to compare pharmacokinetics of i.m. administration of cefepime with those of ceftiofur sodium. ANIMALS: 6 clinically normal adult horses. PROCEDURE: Horses received 3 doses of cefepime (11 mg/kg of body weight, PO; 2.2 mg/kg, i.v.; and 2.2 mg/kg, i.m.) and 1 dose of ceftiofur (2.2 mg/kg, i.m.). Two horses also received L-arginine, p.o. and i.v., at doses identical to those contained in the cefepime dihydrochloride-L-arginine preparations previously administered. Blood samples were collected for 24 hours after administration of cefepime or ceftiofur and were assayed for cefepime and ceftiofur concentrations. RESULTS: Pharmacokinetic analysis of disposition data indicated that i.v. administration data were best described by a 2-compartment open model, whereas i.m. administration data were best described by a 1-compartment absorption model. Median elimination half-life and volume of distribution after i.v. administration of cefepime were 125.7 minutes and 225 ml/kg, respectively. After i.m. administration of cefepime, mean maximal plasma concentration of (8.13 microg/ml) was reached at a mean time of 80 minutes. Absorption of cefepime after i.m. administration was complete, with a median bioavailability of 1.11. Intramuscular administration of ceftiofur resulted in similar mean maximal plasma concentration (7.98 microg/ml) and mean time to this concentration (82 minutes). Cefepime was not detected in samples collected after oral administration. Adverse effects consisting principally of gastrointestinal disturbances were observed after oral and i.m. administration of cefepime and after 1 i.m. administration of ceftiofur. CONCLUSIONS AND CLINICAL RELEVANCE: Cefepime, administered i.v. or i.m. at a dosage of 2.2 mg/kg, every 8 hours is likely to provide effective antibacterial therapy for cefepime-sensitive organisms in horses. Further studies are needed to evaluate adverse effects on the gastrointestinal tract.

Regulation of glucose transport by pioglitazone in cultured muscle cells.

Recent evidence suggests that pioglitazone, a thiazolidinedione hypoglycemic agent, acts by increasing insulin responsiveness at the peripheral level. We studied the effect of pioglitazone (1 to 50 micrograms/mL) on the glucose transporter and glucose transport in BC3H-1 cells, a continuously cultured skeletal muscle cell line lacking the myoD transcription factor required for cell fusion. Glucose-fed cells (25 mmol/L) responded to insulin with a more than twofold increase in 2-deoxyglucose (2-DOG) uptake as compared with baseline. Treating these cells with pioglitazone alone for 24 hours resulted in a dose-dependent increase in hexose uptake, reaching twofold at 50 micrograms/mL. Combining long-term pioglitazone (10 micrograms/mL for 24 hours) and short-term insulin treatment resulted in an additive effect on 2-DOG uptake over a wide range of insulin concentrations (0.1 to 100 nmol/L) without the desensitization to 2-DOG uptake seen in other systems following long-term insulin administration. To determine the basis of the increased glucose uptake response, the level of specific mRNA and immunoreactive glucose transporter protein was determined. Northern and Western blot studies on glucose-treated cells (25 mmol/L) showed that glucose transporter mRNA and protein increased in parallel following treatment with either pioglitazone or insulin alone. The combination of insulin with pioglitazone resulted in an additive stimulation of glucose transporter mRNA and protein. In summary, pioglitazone stimulates hexose uptake both independently and in combination with insulin in BC3H-1 myocytes. These effects are largely accounted for by increases in glucose transporter mRNA and protein, indicating its potential efficacy in the treatment of non-insulin-dependent diabetes mellitus (NIDDM).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the GLUT1 glucose transporter in cultured myocytes: total number and subcellular distribution as determined by photoaffinity labelling.

We have used the impermeant photoaffinity label 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-[2-3H] 1,3-bis-(D-mannos-4-yloxy)-2-propylamine (ATB-[2-3H]BMPA) to identify and quantify the glucose transporters on the surface of BC3H-1 cells, a continuously cultured skeletal-muscle cell line lacking the MyoD transcription factor required for cell fusion. ATB-[2-3H]BMPA was used in combination with immunoprecipitation of the GLUT1 glucose transporter, the only isoform expressed in these cells. The total cellular GLUT1 content was also determined by photolabelling and immunoprecipitation after cell permeabilization with digitonin (0.025%). In glucose-starved cells, 85% of the glucose transporters were present at the cell surface in the basal state, with little change in response to insulin (200 nM), correlating with lack of additional 2-deoxyglucose uptake in response to insulin. Feeding the cells with glucose (25 mM) for 24 h resulted in an 80% decrease in the total GLUT1 content relative to starved cells, of which only 25% were present on the cell surface. This was associated with an 85% decrease in 2-deoxyglucose uptake. In addition, acute stimulation of the fed cells with insulin or phorbol 12-myristate 13-acetate (PMA) led to an increase in GLUT1 at the cell surface, and, in correspondence, an increase in 2-deoxyglucose uptake by approx. 2- and 4-fold respectively. We conclude that exofacial photoaffinity labelling of glucose transporters with ATB-[2-3H]BMPA in the presence and absence of digitonin, followed by specific immunoprecipitation, provides an accurate measure of total and cell-surface glucose transporters in differentiated BC3H-1 muscle cells. This technique demonstrates that glucose pre-feeding (1) decreases the total number of GLUT1 and (2) redistributes the majority of the remaining transporters to an intracellular site, where they can now be translocated to the cell surface in response to insulin and PMA.

Comparison of adverse effects of phenylbutazone, flunixin meglumine, and ketoprofen in horses.

The relative toxicity of phenylbutazone, flunixin meglumine, and ketoprofen was studied in healthy adult horses. Sixteen horses were randomly assigned to receive 10 ml of physiologic saline solution, or ketoprofen (2.2 mg/kg of body weight), flunixin meglumine (1.1 mg/kg), or phenylbutazone (4.4 mg/kg) IV, every 8 hours, for 12 days. Results of CBC, serum biochemical analyses, and fecal occult blood tests were monitored. On day 13, all horses were euthanatized and complete necropsy examinations were performed. Mean CBC values remained within normal limits for all groups. Phenylbutazone-treated horses had a significant (P < 0.05) decrease in serum total protein and albumin concentrations. Mean values of all other serum biochemical assays were not different from those of the saline-treated group. Results of all fecal occult blood tests were negative. At necropsy, the glandular portion of the stomach was the area of the gastrointestinal tract most severely affected by phenylbutazone, flunixin meglumine, and ketoprofen. In the phenylbutazone-treated group, but not in the other groups, edema of the small intestine and erosions and ulcers of the large colon were observed. None of the horses treated with saline solution had lesions in the glandular portion of the stomach or in the intestine. Four horses (1/5 and 3/3 in the flunixin- and phenylbutazone-treated groups, respectively) developed renal crest necrosis. Horses in the saline- and ketoprofen-treated groups did not develop renal lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of AHR-13268, an antiallergenic compound, in the management of pruritus caused by atopic disease in dogs.

Twenty-nine pruritic, atopic dogs were entered into a double-blind, placebo-controlled, crossover study to evaluate the efficacy of an investigational antiallergenic compound, AHR-13268. Fourteen dogs were evaluated by a veterinary dermatologist (at intervals) and the owner (daily). Fifteen dogs were evaluated only by the owner. The mean (+/- SE) owner scores for pruritus, erythema, and lesions with placebo treatment (higher score = worse signs) were 3.24 (+/- 0.12), 2.73 (+/- 0.12), and 2.61 (+/- 0.09), respectively. With drug treatment, the corresponding scores were 2.89 (+/- 0.12), 2.50 (+/- 0.12), and 2.25 (+/- 0.09). Scores for pruritus and lesions (but not erythema) were significantly better with drug treatment than with placebo treatment. Investigator scores showed similar trends, but the differences were not great enough to be statistically significant. Overall, 11/29 (38%) owners reported their dogs had moderate or better improvement from drug capsules, and 4/29 dogs (14%) improved on placebo capsules. A variety of adverse effects were reported following both drug (9/29 dogs) and placebo (8/29 dogs) capsule administration, but were mild and well tolerated. Results of this study indicate that AHR-13268 has potential for empiric treatment of allergic inhalant dermatitis in some dogs.

Protein kinase C inhibitors block insulin and PMA-stimulated hexose transport in isolated rat adipocytes and BC3H-1 myocytes.

Effects of protein kinase C (PKC) inhibitors and "down-regulation" on insulin and PMA-stimulated 2-deoxyglucose transport were determined in isolated rat adipocytes or BC3H-1 myocytes. In both model systems, H-7, sangivamycin, and staurosporine, inhibitors of the catalytic domain of PKC, each effectively blocked insulin and PMA-stimulated hexose uptake at similar concentrations. In the myocytes, staurosporine completely blocked the insulin effect retained post-chronic phorbol myristate acetate (PMA)-induced "down-regulation." These findings indicate (1) that chronic pretreatment with PMA may not lead to a complete loss of PKC activity in the myocyte, and (2) that PKC is involved in insulin-stimulated hexose transport in both isolated rat adipocytes and BC3H-1 myocytes.

Sulfonylurea-stimulated glucose transport association with diacylglycerollike activation of protein kinase C in BC3H1 myocytes.

The extrapancreatic effects of sulfonylurea drugs include increased glucose uptake by certain peripheral tissues. To study this effect, we used BC3H1 myocytes, which are reported to respond to these drugs. Within 30 min, tolbutamide and glyburide increased [3H]-2-deoxyglucose uptake in a dose-dependent manner. The inactive analogue carboxytolbutamide had no effect on glucose transport. Because increases in glucose transport may be mediated by activation of the diacylglycerol-protein kinase C signaling system, we examined the effects of these drugs on lipid metabolism and protein kinase C activity. Unlike insulin, tolbutamide and glyburide failed to increase [3H]glycerol labeling of diacylglycerol or labeling of phospholipids by 32P. After 30 min of treatment with tolbutamide or glyburide, however, membrane-associated and cytosolic protein kinase C activity were each increased. When cells were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 48 h to deplete certain isoforms of protein kinase C, glyburide, tolbutamide, and acute TPA treatment failed to increase glucose uptake, suggesting that TPA and sulfonylureas operate through activation of a common pathway. The effect of glyburide was additive to TPA in stimulating glucose uptake at low but not high TPA concentrations. As with insulin and TPA, extracellular Ca2+ was not essential for sulfonylurea-stimulated glucose uptake. Staurosporine, a protein kinase C inhibitor, blocked glyburide-, tolbutamide-, and insulin-stimulated glucose uptake. In intact cells, glyburide stimulated the phosphorylation of both 80,000-Mr and 40,000-Mr proteins, which are markers for protein kinase C activation. Addition of sulfonylureas directly to the protein kinase C assay system in vitro provoked dioleinlike effects, in that sensitivity of the enzyme to Ca2+ was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like effects of epidermal growth factor and insulin-like growth factor-I on [3H]2-deoxyglucose uptake, diacylglycerol generation and protein kinase C activation in BC3H-1 myocytes.

Epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I) were found to provoke increases in [3H]2-deoxyglucose uptake, diacylglycerol (DAG) generation and membrane-bound protein kinase C activity in BC3H-1 myocytes. These effects were similar to those provoked by insulin. The increases in DAG did not appear to be derived from hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) or phosphatidylinositol, but may have been derived from synthesis of phosphatidic acid de novo, and hydrolysis of phosphatidylcholine, as revealed by studies with [3H]glycerol and [3H]choline respectively. Accordingly, both EGF and IGF-I increased acute [3H]glycerol labelling of DAG (and other lipids) and [3H]choline labelling of phosphocholine. These labelling responses were similar in time course, suggesting that they are closely coupled. Our findings suggest that EGF and IGF-I, like insulin, increase DAG-protein kinase C signalling, apparently by activating co-ordinated lipid-synthesis and -hydrolysis responses, which are distinctly different from the PIP2-hydrolysis response.

Retention of specific protein kinase C isozymes following chronic phorbol ester treatment in BC3H-1 myocytes.

Since insulin effects on glucose transport persist in phorbol ester "desensitized" or "down-regulated" BC3H-1 myocytes, we reexamined the evidence for protein kinase C (PKC) depletion. After 24 hrs of 5 microM 12-0-tetradecanoyl phorbol-13-acetate (TPA) treatment, PKC-directed histone phosphorylation and acute TPA effects on glucose transport were lost, but PKC-dependent vinculin phosphorylation was still evident. Hydroxylapatite (HAP) chromatography revealed loss of a type III, but not a type II, PKC-dependent vinculin phosphorylation. Immunoblots of cytosolic preparations of PKC-"depleted" myocytes confirmed the retention of PKC. Our findings indicate that TPA "down-regulated" BC3H-1 myocytes contain immunoreactive and functionally active PKC. The latter may explain the continued effectiveness of both insulin and diacylglycerol (DiC8) for stimulating glucose transport in "down-regulated" cells.

Mechanisms whereby insulin increases diacylglycerol in BC3H-1 myocytes.

We previously suggested that insulin increases diacylglycerol (DAG) in BC3H-1 myocytes, both by increases in synthesis de novo of phosphatidic acid (PA) and by hydrolysis of non-inositol-containing phospholipids, such as phosphatidylcholine (PC) and phosphatidylethanolamine (PE). We have now evaluated these insulin effects more thoroughly, and several potential mechanisms for their induction. In studies of the effect on PA synthesis de novo, insulin stimulated [2-3H]glycerol incorporation into PA, DAG, PC/PE and total glycerolipids of BC3H-1 myocytes, regardless of whether insulin was added simultaneously with, or after 2 h or 3 or 10 days of prelabelling with, [2-3H]glycerol. In prelabelled cells, time-related changes in [2-3H]glycerol labelling of DAG correlated well with increases in DAG content: both were maximal in 30-60 s and persisted for 20-30 min. [2-3H]Glycerol labelling of glycerol 3-phosphate, on the other hand, was decreased by insulin, presumably reflecting increased utilization for PA synthesis. Glycerol 3-phosphate concentrations were 0.36 and 0.38 mM before and 1 min after insulin treatment, and insulin effects could not be explained by increases in glycerol 3-phosphate specific radioactivity. In addition to that of [2-3H]glycerol, insulin increased [U-14C]glucose and [1,2,3-3H]glycerol incorporation into DAG and other glycerolipids. Effects of insulin on [2-3H]glycerol incorporation into DAG and other glycerolipids were half-maximal and maximal at 2 nM- and 20 nM-insulin respectively, and were not dependent on glucose concentration in the medium, extracellular Ca2+ or protein synthesis. Despite good correlation between [3H]DAG and DAG content, calculated increases in DAG content from glycerol 3-phosphate specific radioactivity (i.e. via the pathway of PA synthesis de novo) could account for only 15-30% of the observed increases in DAG content. In addition to increases in [3H]glycerol labelling of PC/PE, insulin rapidly (within 30 s) increased PC/PE labelling by [3H]arachidonic acid, [3H]myristic acid, and [14C]choline. Phenylephrine, ionophore A23187 and phorbol esters did not increase [2-3H]glycerol incorporation into DAG or other glycerolipids in 2-h-prelabelling experiments; thus activation of the phospholipase C which hydrolyses phosphatidylinositol, its mono- and bis-phosphate, Ca2+ mobilization, and protein kinase C activation, appear to be ruled out as mechanisms to explain the insulin effect on synthesis de novo of PA, DAG and PC.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin provokes co-ordinated increases in the synthesis of phosphatidylinositol, phosphatidylinositol phosphates and the phosphatidylinositol-glycan in BC3H-1 myocytes.

BC3H-1 myocytes were cultured in the presence of [3H]inositol or [3H]glucosamine during their entire growth cycle to ensure that all lipids containing inositol and glucosamine were labelled to isotopic equilibrium or maximal specific radioactivity. After such labelling, a lipid (or group of lipids), which was labelled with both inositol and glucosamine, was observed to migrate between phosphatidylinositol 4-phosphate and phosphatidylinositol (PI) in two different t.l.c. systems. Insulin provoked rapid, sizeable, increases in the inositol-labelling of this lipid (presumably a PI-glycan), and these increases were similar to those observed in PI and PI phosphates. Our results indicate that insulin provokes co-ordinated increases in the net synthesis de novo of PI and its derivatives, PI phosphates and the PI-glycan, in BC3H-1 myocytes. This increase in synthesis of PI may serve as the mechanism for replenishing the PI-glycan during stimulation of its hydrolysis by insulin. Moreover, increases in the content of the PI-glycan may contribute to increases in the generation of head-group 'mediators' during insulin action.

Effects of insulin and phorbol esters on diacylglycerol generation and synthesis and hydrolysis of phosphatidylcholine in BC3H-1 myocytes.

Insulin was found to provoke simultaneous, rapid, biphasic increases in [3H]choline-labeling of phosphatidylcholine and phosphocholine in BC3H-1 myocytes. Phorbol esters increased [3H]choline-labeling of phosphocholine, but not phosphatidylcholine. Both agonists increased diacylglycerol production. These results suggest that: (a) insulin provokes coordinated increases in the synthesis and hydrolysis of PC; and, (b) insulin-induced activation of protein kinase C may activate a PC-specific phospholipase.

Insulin-induced glycerolipid mediators and the stimulation of glucose transport in BC3H-1 myocytes.

We have previously demonstrated that insulin stimulates glycerolipid synthesis and phospholipid hydrolysis in BC3H-1 myocytes, resulting in the generation of membrane diacylglycerol, a known cellular mediator. This led us to the original proposal that diacylglycerol may contribute to the mediation of insulin action, especially stimulation of glucose transport. The fact that agents such as phenylephrine and phorbol esters, which increase or act as membrane diacylglycerols, are fully active in stimulating glucose transport in this tissue lent further support to this proposal. In this paper, we demonstrate that the diacylglycerol analogues PMA (4 beta-phorbol 12-myristate 13-acetate) and mezerein (both possessing 12 beta- and 13 alpha-O-linked substituents as well as a 4 beta-hydroxyl group) each increase the Vmax of the glucose transporter as does insulin. Diacylglycerol generated by the addition of phospholipase C also stimulates glucose uptake to a maximum which is equal and nonadditive to that of insulin, while addition of the narrowly active phosphatidylinositol-specific phospholipase C which generates the putative phosphoinositol-glycan mediator of Saltiel et al. (Saltiel, A., Fox, J., She Lin, P., and Cutrecasas, P. (1986) Science 233, 967-972) stimulates pyruvate dehydrogenase in these cells without any effect on glucose uptake. Pretreatment of the myocytes with PMA resulted in desensitization of subsequent glucose uptake to stimulation by phenylephrine, but had no effect on stimulation of glucose uptake by phospholipase C or by insulin, indicating that PMA pretreatment primarily desensitizes agonist-induced polyphosphoinositide hydrolysis which, as we have previously shown, is not involved in the insulin-induced generation of diacylglycerol. This was confirmed by the absence of intracellular Ca2+ mobilization during insulin administration, as measured by the sensitive fluorescent probe fura-2 in attached monolayer BC3H-1 myocytes. Furthermore, we have shown that insulin-generated diacylglycerol satisfies several criteria for a mediator of insulin action, including the demonstration that insulin-stimulated endogenous diacylglycerol generation is antecedent to glucose transport and has an identical insulin dose-response curve and moreover that the magnitude and time course of subsequent stimulation of glucose transport is reproduced by the addition of the simple exogenous diacylglyerol, dioctanoylglycerol, in the complete absence of the hormone. These results establish a central role for insulin-induced glycerolipid metabolism in mediating insulin-stimulated glucose transport in BC3H-1 myocytes.

Insulin-glycerolipid mediators and gene expression.

Insulin is an anabolic polypeptide hormone with pleiotrophic effects. During the decades since the initial description by Banting and Best, the acute effects of insulin have been widely studied with particular focus on the mechanism or mechanisms of insulin activation of hexose transport and regulation of metabolic enzyme activity. However, recently there has been a major expansion of investigation to include insulin regulation of gene expression with multiple insulin-sensitive specific mRNAs now reported. In this review, we explore the involvement of insulin-induced changes in plasma membrane glycerolipid metabolism in the transmembrane signaling process required for insulin regulation of mRNA levels. Insulin increases diacylglycerol levels in insulin-responsive cells, and synthetic diacylglycerols or their phorbol ester diacylglycerol analogs, such as 4 beta,9 alpha,12 beta,13 alpha, 20-pentahydroxytiglia-1,6-dien-3-one 12 beta-myristate 13-acetate (TPA), mimic insulin regulation of ornithine decarboxylase mRNA, c-fos mRNA, and phosphoenolpyruvate carboxykinase mRNA levels. This suggests that insulin regulation of specific mRNA levels may be mediated by insulin-induced changes in phospholipid metabolism and that diacylglycerol may play a pivotal role in insulin regulation of gene expression.