Electrospray ionization mass spectrometric analyses of phospholipids from INS-1 insulinoma cells: comparison to pancreatic islets and effects of fatty acid supplementation on phospholipid composition and insulin secretion

Insulin secretion by pancreatic islet beta-cells is impaired in diabetes mellitus, and normal beta-cells are enriched in phospholipids with arachidonate as sn-2 substituent. Such molecules may play structural roles in exocytotic membrane fusion or serve as substrates for phospholipases activated by insulin secretagogues. INS-1 insulinoma cells respond to secretagogues and permit the study of effects of culture with free fatty acids on phospholipid composition and secretion. INS-1 cell glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) lipids are demonstrated here by electrospray ionization mass spectrometry to contain a lower fraction of molecules with arachidonate and a higher fraction with oleate as sn-2 substituent than native islets. Palmitic acid supplementation induces little change in these INS-1 cell lipids, but supplementation with linoleate or arachidonate induces a large rise in the fraction of INS-1 cell GPC species with polyunsaturated sn-2 substituents and a fall in oleate-containing species to yield a GPC profile similar to native islets. The fraction of GPE lipids comprised of plasmenylethanolamine species with polyunsaturated sn-2 substituents in early-passage INS-1 cells is similar to that of islets, but declines on serial passage. Such molecules might participate in exocytotic membrane fusion, and late-passage INS-1 cells have reduced insulin secretory responses. Arachidonate supplementation induces a rise in the fraction of INS-1 cell GPE lipids with polyunsaturated sn-2 substituents and partially restores responses to insulin secretagogues by late-passage INS-1 cells, but does not further amplify secretion by early-passage cells. Effects of extracellular free fatty acids on beta-cell phospholipid composition and secretory responses could be involved in changes in beta-cell function during the period of hyper-free fatty acidemia that precedes diabetes mellitus.

Subdural empyema complicating cerebrospinal fluid shunt infection

Subdural empyema has not been reported previously as a complication of cerebrospinal fluid (CSF) shunt surgery. An infant submitted to CSF shunt insertion for congenital hydrocephalus developed subdural empyema after a failed attempt to treat a superficial scalp wound infection with oral antibiotics. Enterobacter cloacae was isolated from the empyema. Temporizing management of the preceding superficial wound infection with oral antibiotics probably was the cause of this exotic pathogen. The treatment of infected scalp wounds contiguous with shunt hardware must be surgical.

Intrarenal insulin-like growth factor-1 axis after unilateral nephrectomy in rat

It has been suggested that insulin-like growth factor-1 (IGF-1) may play a role in early compensatory renal growth. Since IGF-1 action is influenced by IGF binding proteins (IGFBP), this study was conducted to characterize the changes in gene expression not only of IGF-1 and its receptor, but also of IGFBP in the hypertrophying kidney of adult and weanling rats 1 wk after removal of the other kidney. At this time, there were distinct age-dependent changes in the renal IGF-1 axis. In the mature kidney, IGF-1 mRNA levels fell without a change in kidney IGF-1 peptide content. Likewise, although IGFBP-2, -3, and -5 mRNA levels fell, membrane-associated IGFBP did not change. IGF-1 receptor mRNA levels and IGF-1 receptor number both fell. In the weanling kidneys, IGF-1 mRNA and peptide levels and IGF-1 receptor binding were unaltered. However, IGFBP-3, -4, and -5 mRNA levels were increased, as were plasma membrane-associated IGFBP. Although these changes in the intrarenal IGF-1 axis were distinct, it is difficult to conceive how in either the mature or immature rat they could contribute to the ongoing compensatory renal growth that occurs 1 wk after loss of kidney mass unless IGF-1 were acting in a synergistic manner with other growth promoters.

Effects of changes in three catalytic residues on the relative stabilities of some of the intermediates and transition states in the citrate synthase reaction

This work reports the relative importance of the interactions provided by three catalytic residues to individual steps in the mechanism of citrate synthase. When the side chains of any of the residues (H320, D375, and H274) are mutated, the data indicate that they are involved in the stabilization of one or more of the transition/intermediate states in the multistep citrate synthase reaction. H320 forms a hydrogen bond with the carbonyl of oxaloacetate and the alcohols of the citryl-coenzyme A and citrate products. Enzymes substituted at H320 (Q, G, N, and R) have reaction profiles for which the condensation reaction is cleanly rate determining. None of these mutants can activate the carbonyl of oxaloacetate by polarization. All these mutants catalyze the necessary proton transfer from the methyl group of acetyl-coenzyme A only poorly, a process which occurs in a structurally separate site. Furthermore, all H320 mutants hydrolyze the citryl-coenzyme A intermediate significantly more slowly than does the wild-type. D375 is the base removing the proton of acetyl-coenzyme A. D375E and D375G have greatly diminished ability to catalyze proton transfer from acetyl-CoA. The D375 mutants polarize the oxaloacetate carbonyl as well as wild-type. For D375E, the hydrolysis of citryl-CoA is rate determining. D375G, having no side chain capable of acid-base chemistry in either the condensation or hydrolysis reactions is nearly completely devoid of activity in any of the reactions catalyzed by the wild-type. H274 hydrogen bonds to the carbonyl of acetyl-coenzyme A but also forms the back wall of the oxaloacetate-binding site. H274G cannot properly activate either oxaloacetate or acetyl-coenzyme A, and the condensation reaction is overwhelmingly rate determining. Nonetheless, hydrolysis of the intermediate is impaired. All the enzymes except H320R and H274G show kinetic cooperativity with CitCoA as substrate, indicating changes in the subunit interactions with these latter two mutants. The energetics of citrate synthase are surprisingly tightly coupled. All changes affect more than one step in the catalytic cycle. Within the condensation reaction, the intermediate of proton transfer must occupy a shallow well between transition states close in free energy so that perturbations of one have substantial effects on that of the other.

The insulin-like growth factor-I axis in acute renal failure

We have examined the response of the renal insulin-like growth factor (IGF-I) axis to acute ischemic injury in the rat Key findings included a decrease in IGF-I mRNA and peptide levels, a decrease in GH receptor gene plus protein expression and a decrease in the IGF binding proteins except for IGF binding protein I. Administration of GH to compensate for the reduced GH receptor binding corrected the IGF-I mRNA levels suggesting a relative GH deficiency. Interestingly, IGF-I receptor mRNA levels were unchanged while plasma membrane IGF-I receptor number increased two fold. This appeared to be due to a redistribution of receptors to a membrane location. IGF-I receptor autophosphorylation and tyrosine kinase activity were intact despite severe uremia for up to 6 days. We propose that this increase of functional IGF-I receptors following acute tubular necrosis will sensitize the kidney to the administration of exogenous IGF-I.

Urinary mutagenicity as a biomarker in workers exposed to benzidine: correlation with urinary metabolites and urothelial DNA adducts

Urinary mutagenicity has been used in occupational and epidemiological studies for over two decades as a cost-effective, general biomarker of exposure to genotoxic agents. However, few studies have compared urinary mutagenicity to additional biomarkers determined among low- and high-exposed groups. To address this issue, we evaluated the relationship between urinary mutagenicity and other types of biomarkers in a cross-sectional study involving 15 workers exposed to the urinary bladder carcinogen benzidine (BZ, high exposure), 15 workers exposed to BZ-dyes (low exposure), and 13 unexposed controls in Ahmedabad, India. Urinary organics were extracted by C18/methanol and evaluated for mutagenicity in the presence of S9 in the Salmonella strain YG1024, which is a frameshift strain that overproduces acetyltransferase. The results were compared to biomarker data reported recently from the same urine samples (Rothman et al., Proc. Natl Acad. Sci. USA, 93, 5084-5089, 1996) that included a metabolite biomarker (the sum of the urinary levels of BZ + N-acetylbenzidine + N,N'-diacetylbenzidine) and a DNA adduct biomarker [a presumptive N-(3'-phosphodeoxyguanosin-8-yl)-N'-acetylbenzidine (C8dG-ABZ) DNA adduct in exfoliated urothelial cells]. The mean +/- SE urinary mutagenicity (revertants/micromol of creatinine) of the low-exposure (BZ-dye) workers was 8.2 +/- 2.4, which was significantly different from the mean of the controls (2.8 +/- 0.7, P = 0.04) as was that of the mean of the high-exposure (BZ) workers (123.2 +/- 26.1, P < 0.0001). Urinary mutagenicity showed strong, positive correlations with urinary metabolites (r = 0.88, P < 0.0001) and the level of the presumptive C8dG-ABZ urothelial DNA adduct (r = 0.59, P = 0.0006). A strong association was found between tobacco use (bidi smoking) and urinary mutagenicity among the controls (r = 0.68, P = 0.01) but not among the exposed workers (r = 0.18, P = 0.11). This study confirms the ability of a biomarker such as urinary mutagenicity to detect low-dose exposures, identify additional genotoxic exposures among the controls, and correlate strongly with urinary metabolites and DNA adducts in the target tissue (urinary bladder epithelia) in humans.

Linkage of the locus for cerebral cavernous hemangiomas to human chromosome 7q in four families of Mexican-American descent

OBJECTIVE

To determine with greater precision the map location of the locus associated with familial cavernous hemangiomas.

BACKGROUND

Cavernous malformations of the brain are a significant cause of seizures, progressive or apoplectic neurologic deficit, and headache. Prevalence estimates from autopsy series vary from 0.39 to 0.9%. This disorder (OMIM #116860) can be inherited as an autosomal dominant trait with variable penetrance. Linkage to markers on the long arm of chromosome 7 was recently reported in separate reports in three apparently unrelated Hispanic kindreds as well as in two kindreds of non-Hispanic descent.

DESIGN/METHODS

We examined clinically, by MRI scanning, and by pathologic examination of surgical specimens, members of four large Mexican-American families segregating cavernous hemangiomas of the brain. Linkage analysis was performed with use of blood specimens from morphologically proven cases. Two-point linkage analysis was performed with the MLINK program of the LINKAGE package. Multipoint analysis was performed between two markers and the disease locus with LINKMAP in the FASTLINKAGE package. Allele frequencies were set as described by the Genome Database (GDB). Maximum penetrance for the disease allele was set to 0.75.

RESULTS

The highest lod score was observed for marker D7S652 with Zmax = 6.66 at theta(max) = 0.00. Multipoint LOD score analysis placed the disease locus in the 11 cM interval between markers D7S630 and D7S527 with Zmax = 9.19. Haplotype analysis is in agreement with the placement of the disease gene between D7S630 and D7S527 and further shows a minimal shared region within this interval, indicating a founder effect in the establishment of the mutation in these families.

CONCLUSIONS

We confirmed the linkage of cavernous hemangioma to markers on the long arm of chromosome 7q, and the estimate of the map location has been refined to a region of shared haplotype between markers D7S630 and D7S527 in four Mexican-American families who may be descended from a common ancestor in Sonora County, Mexico.

The impact of interindividual variation in NAT2 activity on benzidine urinary metabolites and urothelial DNA adducts in exposed workers

Several epidemiologic studies indicate that NAT2-related slow N-acetylation increases bladder cancer risk among workers exposed to aromatic amines, presumably because N-acetylation is important for the detoxification of these compounds. Previously, we showed that NAT2 polymorphisms did not influence bladder cancer risk among Chinese workers exposed exclusively to benzidine (BZ), suggesting that NAT2 N-acetylation is not a critical detoxifying pathway for this aromatic amine. To evaluate the biologic plausibility of this finding, we carried out a cross-sectional study of 33 workers exposed to BZ and 15 unexposed controls in Ahmedabad, India, to evaluate the presence of BZ-related DNA adducts in exfoliated urothelial cells, the excretion pattern of BZ metabolites, and the impact of NAT2 activity on these outcomes. Four DNA adducts were significantly elevated in exposed workers compared to controls; of these, the predominant adduct cochromatographed with a synthetic N-(3'- phosphodeoxyguanosin-8-yl)-N'-acetylbenzidine standard and was the only adduct that was significantly associated with total BZ urinary metabolites (r = 0.68, P < 0.0001). To our knowledge this is the first report to show that BZ forms DNA adducts in exfoliated urothelial cells of exposed humans and that the predominant adduct formed is N-acetylated, supporting the concept that monofunctional acetylation is an activation, rather than a detoxification, step for BZ. However, because almost all BZ-related metabolites measured in the urine of exposed workers were acetylated among slow, as well as rapid, acetylators (mean +/- SD 95 +/- 1.9% vs. 97 +/- 1.6%, respectively) and NAT2 activity did not affect the levels of any DNA adduct measured, it is unlikely that interindividual variation in NAT2 function is relevant for BZ-associated bladder carcinogenesis.

Pharmacokinetics of computer-controlled alfentanil administration in children undergoing cardiac surgery

BACKGROUND

Cardiopulmonary bypass (CPB) induces changes in the pharmacokinetics of drugs. The purpose of this study was to model the pharmacokinetics of alfentanil in children undergoing cardiac surgery to provide accurate dosage titration intraoperatively as well as in the postoperative period.

METHODS

Fourteen children (aged 3 months to 8 yr) undergoing cardiac surgery with CPB were administered alfentanil via a computer-controlled infusion pump. During surgery, the computer-controlled infusion pump was set to target plasma alfentanil concentrations of 500-2500 micrograms/ml. After surgery, the computer-controlled infusion pump was set to target plasma concentrations of 200-500 micrograms/ml. Parameters for children previously published by Goresky et al. were programmed into the device. Arterial blood samples were taken throughout the infusion. Plasma samples were assayed by radioimmunoassay. Alfentanil pharmacokinetics were estimated using a pooled-data approach with a simple weight-proportional, three-compartment mamillary model with parameters expressed in volumes and clearances as well as a CPB-adjusted, three-compartment model in which the parameters were allowed to change before, during, and after CPB. The accuracy of the three models was compared using cross-validation.

RESULTS

Plasma alfentanil concentrations during computer-controlled infusion pump administration exceeded target concentrations for the first 10 min of drug administration, and from 300 min to the end of the study. The median absolute performance error was 33%. Pharmacokinetic modeling estimated a set of parameters for a simple three-compartment model with a median absolute weighted residual of 18.4%. A CPB-adjusted model nominally decreased the median absolute weighted residual to 17.0%. The performance of these models as measured by cross-validation performance was 18.9% median absolute performance error for the simple model and 18.4% median absolute performance error for the CPB-adjusted model. Parameters for the simple three-compartment model are: V1 = 19.2 ml.kg-1; V2 = 99 ml.kg-1; V3 = 2344 ml.kg-1; Cl1 = 2.5 ml.kg-1.min-1; Cl2 = 38 ml.kg-1.min-1; and Cl3 = 15 ml.kg-1.min-1. In the CPB-adjusted model V1, V2, and Cl2 changed with the onset of CPB. After CPB, V1 and Cl2 returned to the initial values, while V2 was described by a third value.

CONCLUSIONS

The population pharmacokinetics of alfentanil in children undergoing cardiac surgery were well described by both a simple weight-proportional, three-compartment model and a weight-proportional, CPB-adjusted three-compartment model. Cross-validation estimated an expected median inaccuracy of approximately 18-20% with the estimated models in identical experimental circumstances. The flexible CPB-adjusted pharmacokinetic model could be used for modeling any drug with linear pharmacokinetics given in the context of CPB.

Structure-activity studies of new imidazolines on adrenoceptors of rat aorta and human platelets

Potencies of new aromatic substituted fluoro or iodo analogues of catecholimidazolines on functional responses in rat aorta (alpha 1) and platelets (alpha 2) were quantified. (1) When compared either on the basis of EC50 or the dissociation constant (KA), 5-fluorocatecholimidazoline was as potent as the reference alpha 1-adrenoceptor agonist, phenylephrine in the vascular tissue. The maximum contraction of aorta produced by the fluoro analogue was, however, 17% higher than that of phenylephrine. The time required for 1/2 relaxation of the tissue after 5-fluoro hydroxy imidazoline was at least twice as long as that of the phenylephrine. The catechol moiety as well as fluorine substitution at the critical 5-position of the aromatic ring is essential for higher alpha 1 adrenoceptor-mediated potency. (2) As compared to the fluoro analogues, the adrenoceptor-mediated potencies of iodo-analogues were relatively weak on vascular tissue. Naphazoline and its analogues were partial agonists on vascular tissue with dissociation constants which ranged from 110 to 2600 nmol/l. (3) Imidazole analogues were generally less potent agonist than the imidazolines by one order of magnitude. (4) The vacular effects of all agonists were competitively blocked by prazosin with KB values which ranged from 0.04 to 0.48 nmol/l. Since the variation in KB values were within normal limits, the action of new imidazolines on rat aorta appears to be mediated mainly by the activation of the alpha 1-adrenoceptor. Prazosin 10 nmol/l abolished the vascular response of some partial agonists. This indicates a slightly different mode of interaction of agonists with the transduction process. (5) Carbon 4-substituted imidazolines produced little or no alpha 1 adrenoceptor-mediated intrinsic activity, but competitive receptor blocking potency was comparable to that of phentolamine. (6) Medetomidine was a partial agonist on the rat aorta with a KA of 260 nmol/l. When investigated as a blocker, the KB of medetomidine against phenylephrine was approximately 5600 nmol/l. The variation in the latter value was high. (7) In acetylsalicylic acid-treated human platelets, the alpha 2-adrenoceptor-mediated aggregatory effect of all fluoro analogues was weak. Iodo or naphazoline analogues did not initiate platelet aggregation but blocked the aggregation induced by epinephrine. The affinity of naphazoline for the alpha 2-adrenoceptor was 1100 nmol/l. The IC50 of medetomidine for platelet anti-aggregatory effect was 3300 nmol/l, which compares favorably with other imidazoline type of blockers of platelet aggregation. (8) Sympathomimetic vasoconstrictor actions and platelet aggregation effects of these compounds can be dissociated.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning and expression of a gamma-interferon-inducible gene in monocytes: a new member of a cytokine gene family

To define activation-specific sequences in human peripheral blood lymphocytes (PBL), a cDNA library was constructed by subtractive hybridization using resting and stimulated PBL pairs. Stimulation of PBL was achieved by triggering with mitogenic anti-CD2 (T11) monoclonal antibodies. Differential library screening with cDNA probes derived from stimulated versus resting PBL led to identification of two novel sequences, termed HC11 and HC14. The predicted primary and secondary structure of HC11 deduced from the translated nucleotide sequence suggests that the gene encodes a secreted protein of 99 amino acids (aa), including a 23 aa residue leader sequence. Surprisingly, Northern blot analysis demonstrated that HC11 mRNA is induced predominantly in peripheral blood non-T cells. Subsequently, we observed that the HC11 mRNA is induced in macrophages and the monocytic line U-937 by gamma-IFN, raising the possibility that T cell-derived gamma-IFN induced upon anti-CD2 stimulation activated monocytes to express HC11 RNA. In support of this notion, neutralizing anti-gamma-IFN monoclonal antibody inhibits the induction of HC11 mRNA in PBL activated through anti-CD2 antibodies. These findings suggest that there is a molecular cascade involving T cell-produced lymphokines and monokines which serve as a means for intercellular communication. Transient expression of HC11 cDNA results in a readily detectable specific set of protein bands in SDS-PAGE analysis of supernatants from radio-labeled COS cells, consistent with HC11 encoding a secreted product(s). Protein sequence comparison reveals homology with other members of a recently described inducible cytokine family whose functions are yet to be defined.

The determination of sucrose in molasses by high-performance thin-layer chromatography

A method is described for the determination of sucrose in molasses by high-performance thin-layer chromatography. A baseline separation of sucrose is achieved in about 40 min using acetone--water (90:10) as developing solvent. The relative standard deviation of determinations by this method is about 2.2%. Results agree with those obtained by isotope dilution analysis of the same molasses samples.

High-performance thin-layer chromatographic determination of psychopharmacologic agents in blood serum

High-performance thin-layer chromatography affords a rapid, sensitive method for determination of psychopharmacologic agents in blood serum samples. Quantitation of the representative drugs chlorpromazine, amitriptyline, nortriptyline, imipramine, and desipramine at levels as low as 5 ng/ml is demonstrated by scanning the developed thin-layer plates with a chromatographic spectrophotometer in the ultraviolet absorption mode. Neither derivatization prior to, nor color development after chromatographic separation is required to achieve sensitivity and reproducibility of determinations.

Dynamics of the human eyeblink

High-speed photography of eyeblinks in 4 subjects provided displacement and velocity time functions. The results from dynamic measurements made with a mechanical transducer connected physically to the upper eyelid gave estimates of the passive spring constant (Kp = 1.5 gmf/mm) and the passive viscosity (Bp = 0.09 gmf - sec/mm) of the eyelid. Noting the similarity between the reciprocal-innervation mechanisms in the eyelid and the eye-movement systems, a mathematical eyelid model was derived based on the well-known eye-movement model and using similar ideal mechanical-element representations. The model-simulation time course shows the essential characteristics of an eyeblink and suggests that the force program consists of reciprocally acting pulse forces during the downblink, and pulse-step forces during the upblink. When 1 mm of lid displacement is equated with 5 deg of eyeball rotation and when the main sequences for lid movements and for time-optimal saccadic eye movements are compared, the eyeblinks are not found to be time optimal for their various amplitudes.