The use of recently described ionisation techniques for the rapid analysis of some common drugs and samples of biological origin

Three ionisation techniques that require no sample preparation or extraction prior to mass analysis have been used for the rapid analysis of pharmaceutical tablets and ointments. These methods were (i) the novel direct analysis in real time (DART), (ii) desorption electrospray ionisation (DESI), and (iii) desorption atmospheric pressure chemical ionisation (DAPCI). The performance of the three techniques was investigated for a number of common drugs. Significant differences between these approaches were observed. For compounds of moderate to low polarity DAPCI produced more effective ionisation. Accurate DESI and DAPCI tandem mass spectra were obtained and these greatly enhance the selectivity and information content of the experiment. The detection from human skin of the active ingredients from ointments is reported together with the detection of ibuprofen metabolites in human urine.

Impairment of sustained attention after major gynaecological surgery *

BACKGROUND AND OBJECTIVES

The sustained attention to response task (SART) test is a sensitive indicator of deficits in sustained attention and is simple to perform. Sustained attention is impaired for a short period after minor surgery under general anaesthesia but the magnitude and duration of this effect after major surgery is unknown. We used the SART test to investigate deficits in sustained attention in patients undergoing major surgery under general anaesthesia.

METHODS

The SART test was completed before surgery and at 24, 48 and 72 h postoperatively by 20 ASA I-II female patients (mean age 48.6 yr) undergoing total abdominal hysterectomy under general anaesthesia. It was also completed by 20 age-matched female controls at similar time intervals to evaluate the effect of repeated test performance.

RESULTS

There was a significant (P < 0.05) interaction between the groups in number of errors made (a measure of sustained attention deficit). The number of errors decreased in control subjects on repeated performance of the SART test but remained unchanged in patients undergoing total abdominal hysterectomy. The differences between groups remained significant after 72 h (P < 0.05). Patients' overall response times slowed significantly at 24-48 h (P < 0.05), but this recovered by 72 h after surgery. In contrast, overall response times in the control group tended to accelerate on repeated performance of the SART.

CONCLUSIONS

The results of this study suggest that 72 h following major surgery patients have deficits in sustained attention compared with controls. Control subjects demonstrated a marked learning effect on repeated test performance compared with patients.

Noncovalent Shiga-like Toxin Assemblies: Characterization by Means of Mass Spectrometry and Tandem Mass Spectrometry

Shiga-like toxin 1 (SLTx), produced by enterohemorrhagic strains of Escherichia coli (EHEC), belongs to a family of structurally and functionally related AB(5) protein toxins that are associated with human disease. EHEC infection often gives rise to hemolytic colitis, while toxin-induced kidney damage is one of the major causes of hemolytic uremic syndrome (HUS) and acute renal failure in children. As such, an understanding and analysis of the noncovalent interactions that maintain the quaternary structure of this toxin are fundamentally important since such interactions have significant biochemical and medical implications. This paper reports on the analysis of the noncovalent homopentameric complex of Shiga-like toxin B chain (SLTx-B(5)) using electrospray ionization (ESI) triple-quadrupole (QqQ) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) and the analysis of the noncovalent hexameric holotoxin (SLTx-AB(5)) using ESI time-of-flight (TOF) MS. The triple-quadrupole analysis revealed highly charged monomer ions dissociate from the multiprotein complex to form dimer, trimer, and tetramer product ions, which were also seen to further dissociate. The ESI-TOFMS analysis of SLTx-AB(5) revealed the complex remained intact and was observed in the gas phase over a range of pHs. Theses findings demonstrate that the gas-phase structure observed for both the holotoxin and the isoloated B chains correlates well with the structures reported to exist in the solution phase for these proteins. Such analysis provides a rapid screening technique for assessing the noncovalent structure of this family of proteins and other structurally related toxins.

Rapid accurate mass desorption electrospray ionisation tandem mass spectrometry of pharmaceutical samples

Desorption electrospray ionisation (DESI) has been successfully combined with a hybrid quadrupole time-of-flight mass spectrometer to provide mass spectra and product ion mass spectra of active ingredients formulated in pharmaceutical tablets, gels and ointments. Accurate mass data has been obtained from the DESI mass spectra and of the product ion fragments of selected ions, greatly enhancing the selectivity and information content of the experiment. This accurate mass information only takes seconds to acquire since the DESI technique does not require any sample preparation or extraction prior to mass analysis.

Differential effects of calmodulin and protein kinase C antagonists on bone resorption and acid transport activity

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the PKC inhibitor, bis indolylmaleimide II (bIM), on bone resorption and acid transport activity in isolated membrane vesicles. Bis indolylmaleimide inhibited bone resorption 50% with an IC50 approximately 3 microM, as well as acid transport activity in a concentration -dependent manner with an IC50 of approximately 0.4 IM. The IC50 of bIM for inhibiting acid transport activity was similar to that of calmodulin antagonists. The potassium ionophore, valinomycin, failed to restore bIM or tamoxifen-dependent inhibition of acid transport, suggesting that bIM and tamoxifen both inhibit H(+)-ATPase activity. Half maximal inhibitory concentrations of tamoxifen and bIM were not additive in acid transport assays, suggesting different sites of action. Furthermore, exogenous calmodulin blocked tamoxifen, but not bIM, -dependent inhibition of acid transport. We also compared the effects of tamoxifen and bIM on phosphorylation of proteins in isolated membrane fractions as determined by 32P incorporation and autoradiography. Tamoxifen had no effect on protein phosphorylation in contrast to bIM, which inhibited phosphorylation of eight proteins with different apparent kinetics. The data suggest that, while tamoxifen and bIM both affect H(+)-ATPase activity, the mechanisms of action are different.

Increasing Plasmodium falciparum malaria in southwest London: a 25 year observational study

AIMS

To identify changes in the presenting number and species of imported malaria in children in southwest London.

METHODS

A prospective single observer study over 25 years (1975-99) of all cases of paediatric malaria seen at St George's Hospital.

RESULTS

A confirmed diagnosis was made in 249 children (56% boys; 44% girls; median age 8.0 years). Of these, 53% were UK residents and 44% were children travelling to the UK. A significant increase was noted in the number of cases over the 25 years (1975-79: mean 4.8 cases/year; 1990-99: mean 13.7 cases/year). Over the 25 years Plasmodium falciparum was seen in 77%, P vivax in 14%, P ovale in 6%, and P malariae in 3% of cases. P falciparum had increased in frequency (1975-79: P falciparum 50%, P vivax 50%; 1990-99: P falciparum 82%, P vivax 6%), associated with an increase in the proportion of children acquiring their infection in sub-Saharan Africa. Median time between arrival in the UK to the onset of fever was: P falciparum, 5 days; P ovale, 25 days; P malariae, 37 days; and P vivax, 62 days. Median time interval between the onset of fever to commencement of treatment was 4 days. This had not improved over the 25 year period. Only 41% of UK resident children presenting to hospital had taken prophylaxis and the overall number of symptomatic children taking no prophylaxis was increasing.

CONCLUSION

Imported childhood P falciparum malaria is increasing in southwest London associated with increasing travel from sub-Saharan Africa. Over the 25 year period there has been no improvement in chemoprophylaxis rates or time to diagnosis.

Minimally invasive direct coronary artery bypass surgery under high thoracic epidural

IMPLICATIONS

This report describes the use of high-thoracic epidural anesthesia for a patient undergoing minimally invasive direct coronary artery bypass.

Dielectrophoretic assembly of electrically functional microwires from nanoparticle suspensions

A new class of microwires can be assembled by dielectrophoresis from suspensions of metallic nanoparticles. The wires are formed in the gaps between planar electrodes and can grow faster than 50 micrometers per second to lengths exceeding 5 millimeters. They have good ohmic conductance and automatically form electrical connections to conductive islands or particles. The thickness and the fractal dimension of the wires can be controlled, and composite wires with a metallic core surrounded by a latex shell can be assembled. The simple assembly process and their high surface-to-volume ratio make these structures promising for wet electronic and bioelectronic circuits.

Engineering salt-tolerant Brassica plants: characterization of yield and seed oil quality in transgenic plants with increased vacuolar sodium accumulation

Transgenic Brassica napus plants overexpressing AtNHX1, a vacuolar Na(+)/H(+) antiport from Arabidopsis thaliana, were able to grow, flower, and produce seeds in the presence of 200 mM sodium chloride. Although the transgenic plants grown in high salinity accumulated sodium up to 6% of their dry weight, growth of the these plants was only marginally affected by the high salt concentration. Moreover, seed yields and the seed oil quality were not affected by the high salinity of the soil. Our results demonstrate the potential use of these transgenic plants for agricultural use in saline soils. Our findings, showing that the modification of a single trait significantly improved the salinity tolerance of this crop plant, suggest that with a combination of breeding and transgenic plants it could be possible to produce salt-tolerant crops with far fewer target traits than had been anticipated.

Minimally invasive coronary bypass without general endotracheal anesthesia

This report describes the case of a 51-year-old man with myocardial ischemia resulting from in-stent restenosis of the left anterior descending coronary artery who underwent a minimally invasive direct coronary artery bypass using thoracic epidural analgesia while awake, without general endotracheal anesthesia.

External beam irradiation for inhibition of intimal hyperplasia following prosthetic bypass: preliminary results

To determine whether external beam irradiation delivered immediately after graft implantation can inhibit anastomotic intimal hyperplasia (IH) 1 month following polytetrafluoroethylene (PTFE) bypass in a sheep carotid artery model, 23 sheep underwent bilateral bypass of the ligated common carotid artery with 8-mm PTFE immediately followed by a single dose of irradiation (15, 21, or 30 Gy) to one side. The 15 animals with bilaterally patent grafts were euthanized at 1 month and graft-arterial anastomoses harvested. Using computer-aided image analysis, IH areas and thicknesses were measured. Graft patency in this model was 83% at 1 month and did not differ according to treatment administered. In the control animals, IH was greatest at mid-anastomosis, but minimal within the native vessel. All three radiation doses markedly inhibited mid-anastomotic IH area and thickness. At the proximal anastomosis, 30 Gy reduced the IH area 20-fold, from 2.06 to 0.14 mm2 (p < 0.0001 by ANOVA), and IH thickness 70-fold, from 29.0 to 0.4 micron (p < 0.0002); similar effects were seen at the distal anastomosis. No adverse effects of radiation treatment were observed. External beam irradiation in doses of 15 to 30 Gy delivered in a single fraction immediately after operation markedly inhibits development of intimal hyperplasia 1 month following end-to-side anastomosis with PTFE in sheep.

The nitric oxide-induced reduction in cardiac energy supply is not due to inhibition of creatine kinase

OBJECTIVES

While nitric oxide (NO) is a potent vasodilator already in the nM range, a cGMP-independent negative inotropic effect is observed at higher concentrations. Since inhibition of creatine kinase (CK) by NO-induced nitrosylation has been proposed as a possible mechanism of action, we measured the flux through CK in the intact heart.

METHODS

In saline perfused, paced guinea pig hearts 31P NMR spectroscopy was employed to directly assess the cardiac energy status, i.e. free energy of ATP hydrolysis (DeltaG(ATP)) and flux through CK using magnetization transfer in absence and presence of NO.

RESULTS

NO (50 microM) doubled coronary flow and induced a rapid drop in left ventricular developed pressure (39+/-10 vs. 81+/-10 mmHg) and MVO(2) (1.3+/-0.8 vs. 3.7+/-0.5 micromol/min/g) (n=7). This effect was associated with an immediate decrease in phosphocreatine (PCr) (-69%) and DeltaG(ATP). During the subsequent 35 min of NO infusion cardiac function and MVO(2) remained depressed, while PCr partially recovered. NO had no effect on the unidirectional forward flux through CK (98 +/- 21 vs. 99 +/- 20 micromol/min/g, n=7) which was 5- to 10-fold greater than the rate of ATP turnover. Upon cessation of NO infusion both cardiac function and PCr rapidly returned to baseline values. The NO-induced fall in the myocardial energy status was associated with an increase in mitochondrial NADH (n=7) as assessed by surface fluorescence. The observed change in fluorescence was similar to that observed with short term ischemia.

CONCLUSION

The NO-mediated depression of myocardial function, MVO(2) and energy status is not mediated by changes in CK flux. Most likely a partial blockade of mitochondrial oxidative phosphorylation at the level of cytochrome c oxidase is responsible for this effect.

Effect of energy restriction and exercise on vitamin B-6 status of women during lactation

PURPOSE

Lactation increases vitamin B-6 requirements because its concentration in breast milk is related to maternal intake and it is essential for infants. Exercise may also increase the requirement because it increases utilization and excretion of vitamin B-6. Therefore, the purpose of this study was to determine whether energy restriction and exercise affected vitamin B-6 status of lactating women.

METHODS

Breastfeeding women with a body mass index > or = 25 and < or = 30 kg x m(-2) were randomly assigned at 4 wk postpartum to either restrict energy intake by 500 kcal x d(-1) and exercise for 45 min x d(-1), 4 d x wk(-1) (weight loss group, WG) or maintain usual diet and not exercise (control group, CG) for 10 wk. Women were given a supplement containing 2.0 mg of vitamin B-6. Measurements included vitamin B-6 concentrations in breast milk and plasma, plasma pyridoxal 5'-phosphate, and erythrocyte alanine aminotransferase activity.

RESULTS

The WG lost more weight (-4.4 +/- 0.4 vs -0.9 +/- 0.5 kg, P < 0.01) than the CG. Cardiovascular fitness increased by 12% in the WG, compared to 3% in the CG (P = 0.09). Milk vitamin B-6 concentrations increased in both groups (161 +/- 107 and 191 +/- 85 nmol x L(-1), WG and CG, respectively, P = 0.05). There were no significant differences in other vitamin B-6 parameters. Weight and length gain (2.06 +/- 0.21 and 1.83 +/- 0.17 kg; 8.6 +/- 0.6 and 7.2 +/- 0.5 cm; WG and CG, respectively) of infants was not significantly different between groups.

CONCLUSIONS

Energy restriction and exercise from 4 to 14 wk postpartum in overweight, breastfeeding women consuming adequate dietary intakes and 2.0 mg of supplemental vitamin B-6 does not adversely affect vitamin B-6 status or infant growth.

Tamoxifen inhibits phorbol ester stimulated osteoclastic bone resorption: an effect mediated by calmodulin

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the phorbol ester, phorbol myristate acetate, on osteoclast activity. Phorbol esters stimulate bone resorption and calmodulin levels four-fold (k0.5 = 0.1-0.3 microM). In contrast, tamoxifen inhibited osteoclast activity approximately 60% with an IC50 of 1.5 microM, had no apparent effect on protein kinase C activity in whole-cell lysates, and reduced protein kinase C alpha recovered by immunoprecipitation 75%. Phorbol esters stimulated resorption in a time-dependent manner that was closely correlated with a similar-fold increase in calmodulin. Protein kinase C alpha, beta, delta, epsilon, and zeta were all down-regulated in response to phorbol ester treatment. Tamoxifen and trifluoperazine inhibited PMA-dependent increases in bone resorption and calmodulin by 85 +/- 10%. Down-regulation of protein kinase C isoforms by phorbol esters suggests that the observed increases in bone resorption and calmodulin levels are most likely due to a mechanism independent of protein kinase C and dependent on calmodulin. In conclusion, the data suggest that protein kinase C negatively regulates calmodulin expression and support the hypothesis that the effects of both phorbol esters and tamoxifen on osteoclast activity is mediated by calmodulin.

Osteoclasts secrete the chemotactic cytokine mim-1

Osteoclasts are terminally differentiated, multinucleated cells of monocytic origin. In this study, we report that osteoclasts secrete a 35 kD protein and that phorbol myristate acetate treatment stimulates secretion dramatically. Peptide digests of the protein were analyzed by mass spectroscopy. The protein was identified as myb induced myeloid protein-1 precursor (mim-1 protein). Mim-1 is expressed specifically by hematopoietic cells and has no known function. It is homologous with the neutrophil chemokine, chondromodulin II, which stimulates proliferation of osteoblasts and chondrocytes. Western analysis showed that osteoclasts secrete mim-1 into culture media. Immunofluorescence studies demonstrated a cytoplasmic and perinuclear distribution of mim-1 in both avian osteoclasts and human osteoclast-like cells. Expression and secretion of a chemokine-like protein by osteoclasts suggests a novel signaling pathway in the bone microenvironment that may be involved in coordinating bone remodeling.

Effect of a neuronal sodium channel blocker on magnetic resonance derived indices of brain water content during global cerebral ischemia

Diffusion-weighted magnetic resonance imaging (DWI) with calculation of the apparent diffusion coefficient (ADC) of water is a widely used noninvasive method to measure movement of water from the extracellular to the intracellular compartment during cerebral ischemia. Lamotrigine, a neuronal Na(+) channel blocker, has been shown to attenuate the increase in extracellular concentrations of excitatory amino acids (EAA) during ischemia and to improve neurological and histological outcome. Because of its proven ability to reduce EAA levels during ischemia, lamotrigine should also minimize excitotoxic-induced increases in intracellular water content and therefore attenuate changes in the ADC. In this study, we sought to determine the effect of lamotrigine on intra- and extracellular water shifts during transient global cerebral ischemia. Fifteen New Zealand white rabbits were anesthetized and randomized to one of three groups: a control group, a lamotrigine-treated group, or a sham group. After being positioned in the bore of the magnet, a 12-min 50-s period of global cerebral ischemia was induced by inflating a neck tourniquet. During ischemia and early reperfusion there was a similar and significant decrease of the ADC in both the lamotrigine and control group. The ADC in the sham ischemia group remained at baseline throughout the experiment. Lamotrigine-mediated blockade of voltage-gated sodium channels did not prevent the intracellular movement of water during 12 min 50 s of global ischemia, as measured by the ADC, suggesting that the ADC decline may not be mediated by voltage-gated sodium influx and glutamate release.

Calmodulin and HIV type 1: interactions with Gag and Gag products

The level of calmodulin increases in cells expressing HIV-1 envelope glycoprotein. Although a calmodulin increase is bound to alter many cellular metabolic and signaling pathways, the benefits to the virus of these alterations must be indirect. However, the possibility exists that increased cellular calmodulin benefits the virus by directly associating with nonenvelope viral proteins. We have, therefore, investigated whether calmodulin can interact with HIV structural proteins Gag, p17, and p24. Calmodulin binds Gag and p17 but not p24 in (125)I-labeled calmodulin overlays of SDS-polyacrylamide gels. Removal of calcium by addition of EGTA eliminates this binding. A computer algorithm for predicting helical regions that should bind calmodulin predicts that there are two calmodulin-binding regions near the N terminus of p17. Intrinsic tryptophan fluorimetry shows that two peptides, each of which includes one of the predicted regions, bind calmodulin: p17(11-25) binds calmodulin with a 2-to-1 stoichiometry and dissociation constant of approximately 10(-9) M(2), and p17(31-46) also binds calmodulin with a dissociation constant of about 10(-9) M. These binding sites are nearly contiguous, forming an extended calmodulin-binding domain p17(11-46). In H-9 cells, Gag and calmodulin colocalize within the resolution of confocal light microscopy.

Antibody-targeted chemotherapy for the treatment of relapsed acute myeloid leukemia

A promising new development in cancer treatment is antibody-targeted chemotherapy (ATC), a strategy that allows antineoplastic drugs to be delivered to malignant cells but not most normal ones, possibly resulting in fewer side effects. A new drug, gemtuzumab ozogamicin (Mylotarg), employs the ATC strategy and has been approved by the Food and Drug Administration for the treatment of CD33+ acute myeloid leukemia (AML) in patients who are 60 years of age and older, are in their first relapse, and are not considered candidates for cytotoxic chemotherapy. AML is the second most frequent type of leukemia in adults and is associated with a poor prognosis. If untreated, death usually occurs within a few months of diagnosis.

Process analysis in outpatient knee surgery: effects of regional and general anesthesia on anesthesia-controlled time

BACKGROUND

The performance of anesthetic procedures before operating room entry (e.g., with either general or regional anesthesia [RA] induction rooms) should decrease anesthesia-controlled time in the operating room. The authors retrospectively studied the associations between anesthesia techniques and anesthesia-controlled time, evaluating one surgeon performing a single procedure over a 3-yr period. The authors hypothesized that, using the anesthesia care team model, RA would be associated with reduced anesthesia-controlled time compared with general anesthesia (GA) alone or combined general-regional anesthesia (GA-RA).

METHODS

The authors queried an institutional database for 369 consecutive patients undergoing the same procedure (anterior cruciate ligament reconstruction) performed by one surgeon over a 3-yr period (July 1995 through June 1998). Throughout the period of study, anesthesia staffing consisted of an attending anesthesiologist medically directing two nurse anesthetists in two operating rooms. Anesthesia-controlled time values were compared based on anesthesia techniques (GA, RA, or GA-RA) using one-way analysis of variance, general linear modeling using time-series and seasonal adjustments, and chi-square tests when appropriate. P < 0. 05 was considered significant.

RESULTS

RA was associated with the lowest anesthesia-controlled time (11.4 +/- 1.3 min, mean +/- 2 SEM). GA-RA (15.7 +/- 1.0 min) was associated with lower anesthesia-controlled time than GA used alone (20.3 +/- 1.2 min).

CONCLUSIONS

When compared with GA without an induction room for outpatients undergoing anterior cruciate ligament reconstruction, RA with an induction room was associated with the lowest anesthesia- controlled time. Managers must weigh the costs and time required for anesthesiologists and additional personnel to place nerve blocks or induce GA preoperatively in such a staffing model.

The role of phosphatidylcholine in fatty acid exchange and desaturation in Brassica napus L. leaves

The role of phosphatidylcholine (PC) in fatty acid exchange and desaturation was examined and compared with that of monogalactosyldiacylglycerol (MGDG) in Brassica napus leaves using (14)C-labelling in vivo. Data are presented which indicate that in the chloroplast newly formed saturated (palmitic acid, 16:0) and monounsaturated (oleic acid, 18:1) fatty acid is incorporated into MGDG and desaturated in situ. In the non-plastidic compartments, however, newly formed fatty acid is exchanged with polyunsaturated fatty acid in PC, the probable major site of subsequent desaturation. The unsaturated fatty acid is released to the acyl-CoA pool, which is then used to synthesize diacylglycerol (DAG) containing a high level of unsaturated fatty acid. This highly unsaturated DAG may be the source for the biosynthesis of other cellular glycerolipids. The generally accepted pathway in which PC is synthesized from molecular species of DAG containing 16:0 and 18:1 followed by desaturation of the 18:1 to linoleic (18:2) and linolenic (18:3) acids is questioned.

Photosynthetic acclimation of the filamentous cyanobacterium, Plectonema boryanum UTEX 485, to temperature and light

Photosynthetic acclimation to temperature and irradiance was studied in the filamentous, non-heterocystous cyanobacterium Plectonema boryanum UTEX 485. Growth rates of this cyanobacterium measured at ambient CO2 were primarily influenced by temperature with minimal effects of irradiance. Both growth temperature and irradiance affected linolenic (18:3) and linoleic acid (18:2) levels in the four major lipid classes in an independent but additive manner. In contrast, photosynthetic acclimation was not due to either growth temperature or irradiance per se, but rather, due to the interaction of these environmental factors. P. boryanum grown at low temperature and moderate irradiance mimicked cells grown at high light. Compared to cells grown at either 29 degrees C/150 micromol m(-2) s(-1) (29/150) or 15/10, P. boryanum grown at either 15/150 or 29/750 exhibited: (1) reduced cellular levels of Chl a and phycobilisomes (PBS), and concomitantly higher content of an orange-red carotenoid, myxoxanthophyll; (2) higher light saturated rates (Pmax) when expressed on a Chl a basis but lower apparent quantum yields of oxygen evolution and (3) enhanced resistance to high light stress. P. boryanum grown at 15/150 regained normal blue-green pigmentation within 16 h after a temperature shift to 29 degrees C at a constant irradiance of 150 micromol m(-2) s(-1). DBMIB and KCN but not DCMU and atrazine partially inhibited the change in myxoxanthophyll/Chl a ratio following the shift from 15 to 29 degrees C. We conclude that P. boryanum responds to either varying growth temperature or varying growth irradiance by adjusting the ability to absorb light through decreasing the cellular contents of Chl a and light-harvesting pigments and screening of excessive light by myxoxanthophyll predominantly localized in the cell wall/cell membrane to protect PSII from over-excitation. The possible role of redox sensing/signalling for photosynthetic acclimation of cyanobacteria to either temperature or irradiance is discussed.

Phosphatase activity in rat adipocytes: effects of insulin and insulin resistance

Insulin regulates the activity of both protein kinases and phosphatases. Little is known concerning the subcellular effects of insulin on phosphatase activity and how it is affected by insulin resistance. The purpose of this study was to determine insulin-stimulated subcellular changes in phosphatase activity and how they are affected by insulin resistance. We used an in vitro fatty acid (palmitate) induced insulin resistance model, differential centrifugation to fractionate rat adipocytes, and a malachite green phosphatase assay using peptide substrates to measure enzyme activity. Overall, insulin alone had no effect on adipocyte tyrosine phosphatase activity; however, subcellularly, insulin increased plasma membrane adipocyte tyrosine phosphatase activity 78 +/- 26% (n = 4, P < 0.007), and decreased high-density microsome adipocyte tyrosine phosphatase activity 42 +/- 13% (n = 4, P < 0.005). Although insulin resistance induced specific changes in basal tyrosine phosphatase activity, insulin-stimulated changes were not significantly altered by insulin resistance. Insulin-stimulated overall serine/threonine phosphatase activity by 16 +/- 5% (n = 4, P < 0.005), which was blocked in insulin resistance. Subcellularly, insulin increased plasma membrane and crude nuclear fraction serine/threonine phosphatase activities by 59 +/- 19% (n = 4, P < 0. 005) and 21 +/- 7% (n = 4, P < 0.007), respectively. This increase in plasma membrane fractions was inhibited 23 +/- 7% (n = 4, P < 0. 05) by palmitate. Furthermore, insulin increased cytosolic protein phosphatase-1 (PP-1) activity 160 +/- 50% (n = 3, P < 0.015), and palmitate did not significantly reduce this activity. However, palmitate did reduce insulin-treated low-density microsome protein phosphatase-1 activity by 28 +/- 6% (n = 3, P < 0.04). Insulin completely inhibited protein phosphatase-2A activity in the cytosol and increased crude nuclear fraction protein phosphatase-2A activity 70 +/- 29% (n = 3, P < 0.038). Thus, the major effects of insulin on phosphatase activity in adipocytes are to increase plasma membrane tyrosine and serine/threonine phosphatase, crude nuclear fraction protein phosphatase-2A, and cytosolic protein phosphatase-1 activities, while inhibiting cytosolic protein phosphatase-2A. Insulin resistance was characterized by reduced insulin-stimulated serine/threonine phosphatase activity in the plasma membrane and low-density microsomes. Specific changes in phosphatase activity may be related to the development of insulin resistance.

The effect of weight loss in overweight, lactating women on the growth of their infants

BACKGROUND

The retention of weight gained during pregnancy may contribute to obesity. Lactation should promote weight loss, but weight loss is highly variable among lactating women. The risks associated with the restriction of energy intake during lactation have not been adequately evaluated. The purpose of this study was to determine whether weight loss by women during lactation affects the growth of their infants.

METHODS

We randomly assigned 40 breast-feeding women who were overweight (defined as a body-mass index [the weight in kilograms divided by the square of the height in meters] of 25 to 30) at 4 weeks post partum either to restrict their energy intake by 500 kcal per day and to exercise for 45 minutes per day for 4 days per week (the diet-and-exercise group) or to maintain their usual dietary intake and not exercise more than once per week for 10 weeks (the control group). We measured the weight and fat mass of the women and the weight and length of the infants before, during, and at the end of the study period.

RESULTS

The mean (+/-SD) energy intake decreased by 544+/-471 kcal per day in the diet-and-exercise group. As compared with the control group, the women in the diet-and-exercise group lost more weight (4.8+/-1.7 kg vs. 0.8+/-2.3 kg, P<0.001) and fat mass (4.0+/-2.0 kg vs. 0.3+/-1.8 kg, P<0.001). The gains in weight and length of the infants whose mothers were in the diet-and-exercise group (1925+/-500 g and 7.8+/-2.0 cm, respectively) were not significantly different from those of the infants whose mothers were in the control group (1861+/-576 g and 7.3+/-1.7 cm).

CONCLUSIONS

Weight loss of approximately 0.5 kg per week between 4 and 14 weeks post partum in overweight women who are exclusively breast-feeding does not affect the growth of their infants.