A Study on CYP2C19 and CYP2D6 Polymorphic Effects on Pharmacokinetics and Pharmacodynamics of Amitriptyline in Healthy Koreans.

We performed a double-blinded, genotype-based stratification study to explore the pharmacokinetics and pharmacodynamics of amitriptyline according to CYP2C19 and CYP2D6 genotype in Korean subjects. Twenty-four healthy adults were grouped by genotype of CYP2C19 and CYP2D6. After a single dose of 25 mg of amitriptyline, blood samples were collected and anticholinergic effects were measured. The extent of N-demethylation of amitriptyline significantly decreased in subjects carrying two nonfunctional alleles of CYP2C19. The extent of hydroxylation of amitriptyline or nortriptyline was significantly reduced in subjects carrying two CYP2D6 decreased functional alleles compared with those with no or one decreased functional allele. The overall metabolic pathway of amitriptyline was more likely to be dominated by CYP2C19 than CYP2D6. The gene variations of CYP2C19 and CYP2D6 did not change the pharmacodynamic effect. The findings of this study will provide useful information on individualized drug treatment with amitriptyline considering both CYP2D6 and CYP2C19 gene variations.

Foxp3 is a key downstream regulator of p53-mediated cellular senescence.

The downstream events and target genes of p53 in the process of senescence are not fully understood. Here, we report a novel function of the forkhead transcription factor Foxp3, which is a key player in mediating T-cell inhibitory functions, in p53-mediated cellular senescence. The overexpression of Foxp3 in mouse embryonic fibroblasts (MEFs) accelerates senescence, whereas Foxp3 knockdown leads to escape from p53-mediated senescence in p53-expressing MEFs. Consistent with these results, Foxp3 expression resulted in the induction of senescence in epithelial cancer cells, including MCF7 and HCT116 cells. Foxp3 overexpression also increased the intracellular levels of reactive oxygen species (ROS). The ROS inhibitor N-acetyl-l-cysteine rescued cells from Foxp3-expression-induced senescence. Furthermore, the elevated ROS levels that accompanied Foxp3 overexpression were paralleled by an increase in p21 expression. Knockdown of p21 in Foxp3-expressing MEFs abrogated the Foxp3-dependent increase in ROS levels, indicating that Foxp3 acts through the induction of p21 and the subsequent ROS elevation to trigger senescence. Collectively, these results suggest that Foxp3 is a downstream target of p53 that is sufficient to induce p21 expression, ROS production and p53-mediated senescence.

Proteolytic degradation and potential role of onconeural protein cdr2 in neurodegeneration.

Cerebellar degeneration-related protein 2 (cdr2) is expressed in the central nervous system, and its ectopic expression in tumor cells of patients with gynecological malignancies elicits immune responses by cdr2-specific autoantibodies and T lymphocytes, leading to neurological symptoms. However, little is known about the regulation and function of cdr2 in neurodegenerative diseases. Because we found that cdr2 is highly expressed in the midbrain, we investigated the role of cdr2 in experimental models of Parkinson's disease (PD). We found that cdr2 levels were significantly reduced after stereotaxic injection of 1-methyl-4-phenylpyridinium (MPP(+)) into the striatum. cdr2 levels were also decreased in the brains of post-mortem PD patients. Using primary cultures of mesencephalic neurons and MN9D cells, we confirmed that MPP(+) reduces cdr2 in tyrosine hydroxylase-positive dopaminergic neuronal cells. The MPP(+)-induced decrease of cdr2 was primarily caused by calpain- and ubiquitin proteasome system-mediated degradation, and cotreatment with pharmacological inhibitors of these enzymes or overexpression of calcium-binding protein rendered cells less vulnerable to MPP(+)-mediated cytotoxicity. Consequently, overexpression of cdr2 rescued cells from MPP(+)-induced cytotoxicity, whereas knockdown of cdr2 accelerated toxicity. Collectively, our findings provide insights into the novel regulatory mechanism and potentially protective role of onconeural protein during dopaminergic neurodegeneration.

Prevalence, awareness, treatment and control of hypertension in adults with diagnosed diabetes: the Fourth Korea National Health and Nutrition Examination Survey (KNHANES IV).

We evaluated the prevalence, awareness, treatment and control of hypertension in Korean adults with diagnosed diabetes using nationally representative data. Among subjects aged ≥30 years who participated in the Fourth Korea National Health and Nutrition Examination Survey in 2007 and 2008, a total of 745 subjects (336 men and 409 women) with a previous diagnosis of diabetes mellitus were analyzed. The prevalence of hypertension in adults with diagnosed diabetes was 55.5%. The rates of awareness, treatment and control were 88.0, 94.2, and 30.8%, respectively. Compared with the general population, the prevalence of hypertension in adults with diagnosed diabetes was higher in all age groups in both genders. Factors independently associated with a high prevalence of hypertension included being male, increasing age, single, <9 years of education, the presence of chronic kidney disease risk, hypercholesterolemia (≥240 mg dl(-1)) and high body mass index (≥25 kg m(-2)). Regular medical screening was positively associated with hypertension control, whereas a high triglyceride level (≥150 mg dl(-1)) was inversely associated. A high prevalence and a low control rate of hypertension in adults with diagnosed diabetes suggest that stringent efforts are needed to control blood pressure in diabetic patients.

von Hippel-Lindau protein promotes Skp2 destabilization on DNA damage.

Germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene cause VHL disease, a rare and autosomal-dominant genetic syndrome. Because VHL protein (pVHL) is the master regulator of hypoxia-inducible factor alpha (HIFα), the most prominent feature of VHL disease is the deregulation of HIFα proteins. However, the precise mechanism by which the loss of pVHL function contributes to tumorigenesis is not fully understood. Here, we show that pVHL destabilizes the F-box protein Skp2, a chief component of Skp, Cullin, F-box-containing complex that promotes DNA synthesis in the S phase. The ß-domain of pVHL interacts with Skp2, stimulating proteasome-dependent Skp2 degradation, but the destabilization of Skp2 does not depend on the E3 ubiquitin ligase activity of pVHL. Notably, the generation of DNA damage induces Skp2 degradation, which is attenuated by the suppression of endogenous pVHL expression. One possible mechanism of pVHL-dependent Skp2 degradation entails the antagonizing of Akt-mediated Skp2 phosphorylation, which maintains Skp2 stability. Reintroduction of VHL into VHL-null renal cell carcinoma (RCC) cells decreased Skp2 levels and restored DNA damage-dependent Skp2 degradation. These results identify the tumor suppressor function of pVHL in delaying the S-phase progression to inhibit cell proliferation on DNA damage. Clinically, this report explains as to why Skp2 accumulates abnormally in RCC tissues.

Variations in Gnai2 and Rgs1 expression affect chemokine receptor signaling and the organization of secondary lymphoid organs.

Ligand bound chemoattractant receptors activate the heterotrimeric G-protein G(i) to stimulate downstream signaling pathways to properly position lymphocytes in lymphoid organs. Here, we show how variations in the expression of a chemokine receptor and in two components in the signaling pathway, Galpha(i2) and RGS1, affect the output fidelity of the signaling pathway. Examination of B cells from mice with varying numbers of intact alleles of Ccr7, Rgs1, Gnai2, and Gnai3 provided the basis for these results. Loss of a single allele of either Gnai2 or Rgs1 affected CCL19 triggered chemotaxis, whereas the loss of a single allele of Ccr7, which encodes the cognate CCL19 receptor, had little effect. Emphasizing the importance of Gnai2, B cells lacking Gnai3 expression responded to chemokines better than did wild-type B cells. At an organismal level, variations in Rgs1 and Gnai2 expression affected marginal zone B-cell development, splenic architecture, lymphoid follicle size, and germinal center morphology. Gnai2 expression was also needed for the proper alignment of MOMA-1(+) macrophages and MAdCAM-1(+) endothelial cells along marginal zone sinuses in the spleen. These data indicate that chemoattractant receptors, heterotrimeric G-proteins, and RGS protein expression levels have a complex interrelationship that affects the responses to chemoattractant exposure.

Distribution of streptogramin resistance genes and genetic relatedness among quinupristin/dalfopristin-resistant Enterococcus faecium recovered from pigs and chickens in Korea.

Fifty-four quinupristin/dalfopristin-resistant Enterococcus faecium (QDREF) isolated from chickens and pigs during 2002-2003 in Korea were screened by PCR for the presence of streptogramin resistance genes vatD, vatE, and vgbA, and macrolide resistance gene ermB. None of the QDREF isolates carried vgbA and vatD genes, while vatE and ermB were detected in 9.2% and 74% of the isolates, respectively. Twenty-six percent (14/54) of the QDREF isolates contained none of the resistance determinants tested. Pulsed-field gel electrophoresis (PFGE) patterns revealed high heterogeneity: 47 different patterns for 54 QDREF evaluated. Identical PFGE types were observed in two pairs of chicken isolates and a pair of pig isolates, respectively, but chicken isolates did not share PFGE pattern with pig isolates, suggesting clonal spread of QDREF strain between the same species of animals but not between different species of animals. This is the first report, to our knowledge, of vatE-positive E. faecium isolates and also the first evidence of clonal spread of QDREF strain between animals in Korea.

Outbreak of brucellosis in domestic elk in Korea.

Seven of 18 elk on a deer farm were found by the official Rose-Bengal agglutination test (RBT) and tube agglutination test to be brucellosis reactors/suspects. Evaluation with the competitive ELISA (C-ELISA) and the fluorescence polarization assay (FPA) tests revealed that six and five sera were positive respectively. The seven reactors/ suspects were slaughtered and their blood and tissues were collected. Brucella species could be isolated from three of the slaughtered animals, with nine isolates being obtained from the popliteal, supramammary and submandibular lymph nodes, vaginal discharge, mammary tissue and spleen. Brucella genus-specific PCR based on 16S rRNA and AMOS-PCR, which is specific for differential Brucella species, revealed that all nine isolates were Brucella abortus. These nine were further confirmed to be B. abortus biovar 1 by classical biotyping scheme assays. This is the first report of an outbreak of brucellosis in domestic elk in Korea. Our observations suggest that deer should be included in the routine Brucella surveillance programme for the effective control and prevention of brucellosis in Korea.

Pseudo-Kaposi's sarcoma associated with acquired arteriovenous fistula.

Pseudo-Kaposi's sarcoma or acroangiodermatitis usually has underlying conditions of increased venous pressure or circulatory abnormality. We experienced two cases of pseudo-Kaposi's sarcoma in patients with acquired iatrogenic arteriovenous fistula from hemodialysis on their forearms. The patients complained of painful swollen crusted vesicles and purple or erythematous patches or plaques on their hands and fingers. Histologic findings included features of pseudo-Kaposi's sarcoma such as proliferations of small vascular spaces with narrow vascular channels lined by spindle cells, extravasated erythrocytes, and hemosiderin deposits. Percutaneous arteriography performed in Case one excluded the possible coexistence of arteriovenous malformation. In both cases, venous pressure and skin surface temperature were increased around the lesions; these may have played important roles in the development of the lesions. Both cases improved after oral erythromycin treatment, which seemed to be safe and effective for pseudo-Kaposi's sarcoma.

Effects of pH, temperature, and chemical structure on the stability of S-(purin-6-yl)-L-cysteine: evidence for a novel molecular rearrangement mechanism to yield N-(purin-6-yl)-L-cysteine.

The stability of S-(purin-6-yl)-L-cysteine (SPC), a kidney-selective prodrug of 6-mercaptopurine and a putative metabolite of 6-chloropurine, was investigated under various pH and temperature conditions. At room temperature, the half-life (t 1/2) of SPC at either highly acidic (pH 3.6) or basic conditions (pH 9.6) was longer than at neutral or slightly acidic or basic conditions (pH 5.7-8.75). The primary degradation product, N-(purin-6-yl)-L-cysteine (NPC), was isolated using Sephadex LH-20 chromatography and characterized by 1H NMR and FAB/MS after derivatization with 2-iodoacetic acid. These results reveal novel stability requirements and implicate the cysteinyl amino group and the purinyl N-1 nitrogen in the mechanism of SPC rearrangement to NPC. Further evidence for this hypothesis was provided by the findings that the stability of SPC in phosphate buffer (pH 7.4) at 37 degrees C was similar to that of S-(guanin-6-yl)-L-cysteine, whereas S-(purin-6-yl)-N-acetyl-L-cysteine and S-(purin-6-yl)glutathione which have their cysteine amino groups blocked were much more stable than SPC. S-(Purin-6-yl)-L-homocysteine (SPHC) was also more stable than SPC, possibly because the formation of a 6-membered ring transition state as would be expected with SPHC is kinetically less favored than the formation of a 5-membered ring transition state as would be expected with SPC. These results may explain previous in vivo metabolism results of SPC and its analogs and may contribute to a better understanding of stability of structurally related cysteine S-conjugates.

A gas-liquid system for enzyme kinetic studies of volatile organic chemicals. Determination of enzyme kinetic constants and partition coefficients of trichloroethylene.

A gas-liquid system was developed for enzyme kinetic study with volatile organic chemicals (VOCs) by modification of the gas uptake method for the in vivo physiologically based pharmacokinetic experiment. This gas-liquid system, designed in our laboratory, is composed of: 1) a diffusion chamber for adjusting initial vapor concentration by mixing ambient air and the VOCs; 2) a condenser for maintaining the liquid level in the incubation chamber; 3) a stainless-steel metal bellows pump for recirculating vapor in this system; 4) a gas chromatograph equipped with an autosampler and a flame ionization detector; and 5) a computer for controlling automation and data processing. Trichloroethylene (TCE) was used as a model chemical, and enzyme kinetics were studied by measuring the depletion of TCE in the gas phase of the system. TCE-at initial concentrations of 56, 620, and 1240 ppm-was incubated with rat liver microsomes and a NADPH regenerating system in a 100-ml round-bottom flask. Based on parallel enzyme assays using p-nitrophenol as a substrate, cytochrome P450IIE1, activity remained stable up to 3 hr under the incubation conditions (37 degrees C and pH 7.4) whereas addition of glutathione into the incubation mixture did not affect TCE metabolism. Kinetic constants were analyzed using a two-compartment pharmacokinetic model and the computer software SimuSolv. Statistical optimization using the maximum-likelihood method produced apparent in vitro Vmax and KM values of 0.55 nmol/mg protein/min and 0.9 microM, respectively. In addition, this newly developed methodology has a number of advantages over those reported in the literature, including the potential utility of determining tissue partition coefficients of VOCs for physiologically based pharmacokinetic modeling. We conclude that this gas-liquid system is suitable for determination of kinetic constants near realistic environmental concentrations of VOCs including TCE.

Targeting 6-thioguanine to the kidney with S-(guanin-6-yl)-L-cysteine.

Recently, S-(purin-6-yl)-L-cysteine (GC) was shown to be a kidney-selective prodrug of 6-mercaptopurine. In the present study, for further development of kidney-selective chemotherapeutic agents, GC was synthesized, and its metabolism was examined in the rat by cysteine conjugate beta-lyase (beta-lyase) to yield the antitumor and immunosuppressant drug, 6-thioguanine (6-TG). The apparent Km values obtained with renal mitochondrial and cytosolic beta-lyases were similar, but the Vmax value obtained with renal mitochondrial beta-lyase was approximately 45-fold higher than the Vmax value obtained with renal cytosolic beta-lyase. After rats were administered GC (400 mumol/kg), the concentrations of GC in the kidney, liver and plasma at 30 min were higher than the corresponding values at 15 or 60 min. GC concentrations in plasma and kidney were, however, 3- and 5-fold higher than that in liver, respectively. Although GC metabolites were not detected in plasma, they were detectable in liver and kidney; metabolite concentrations at 30 min were higher than those at 15 or 60 min. Renal 6-TG concentration at 30 min was nearly 4-fold higher than hepatic 6-TG concentration; hepatic and renal 6-thioxanthine and 6-thiouric acid concentrations were similar. The amount of GC metabolites excreted in urine within 24 hr was linearly proportional to the administered GC dose. Rats administered GC (400 mumol/kg) excreted nearly 5-fold the amount of metabolites as rats given an equimolar dose of 6-chloroguanine, a GC precursor. These results and the finding that renal 6-TG concentrations after GC treatments were in excess of the ED50 of 6-TG (0.5-1.0 microM) in two human renal carcinoma cell lines (A-498 and CAKI-1) suggest that GC may have clinical usefulness as a prodrug of 6-TG.

Targeting of 6-mercaptopurine to the kidneys. Metabolism and kidney-selectivity of S-(6-purinyl)-L-cysteine analogs in rats.

Previously, we have shown that 30 min after S-(6-purinyl)-L-cysteine (PC; 0.13 or 0.4 mmol/kg, ip) treatment of rats, kidney concentrations of 6-mercaptopurine (6-MP) and its further metabolites, 6-methylmercaptopurine and 6-thiouric acid, were nearly 2.4-fold higher than those in liver, and were nearly 90-fold higher than those in plasma. 6-MP was also detected in the urine of rats given the PC analogs, S-(6-purinyl)-N-acetyl-L-cysteine (NAPC), S-(6-purinyl)glutathione (PG), and S-(6-purinyl)-L-homocysteine (PHC). In this study, the kidney-selectivity of the PC analogs was investigated by determining the concentrations of 6-MP and its further metabolites in the kidney, liver, and plasma of rats given the analogs. After NAPC, PG, and PHC (0.8 mmol/kg, ip) treatments, kidney concentrations of total metabolites at 30 min were nearly 17.6-, 6.5-, and 2.9-fold higher than those in liver, respectively. Only trace amounts of metabolites were detected in plasma with any analog. After NAPC treatment (0.8 mmol/kg, ip) total metabolite concentrations in the kidney at 30 min were higher than those detected at 60 or 90 min. When the PC analogs were given at a lower dose (0.4 mmol/kg), only trace amounts of metabolites were detected in the kidney, and no metabolites were detected in liver or plasma. Rates of in vitro metabolism of PHC, PG, and NAPC to 6-MP by kidney homogenates were nearly 10.0, 6.7, and 0.3% of that measured with PC, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection and mechanisms of formation of S-(6-purinyl)glutathione and 6-mercaptopurine in rats given 6-chloropurine.

6-Chloropurine (CP) has antitumor activity against animal and human neoplasms, but the mechanism is unclear. Recently, we have shown that S-(6-purinyl)glutathione (PG), a putative metabolite of CP, is metabolized in vivo to yield the antitumor drug, 6-mercaptopurine (6-MP). In this study, CP metabolism to PG and 6-MP was investigated in an effort to provide further insights into the mechanism of CP antitumor activity. Rat hepatic and renal glutathione S-transferases metabolized CP to PG; Vmax values for liver and kidney cytosol were 166 and 24 nmol/mg of protein/min, respectively. PG was isolated and characterized by fast atom bombardment mass spectrometry from the bile of rats given CP. When rats were given CP (14 mumol/kg), PG excretion was linear with time for up to 1 hr; nearly 80% of the PG excreted at 2 hr was excreted at 1 hr. Rats given CP (10-1200 mumol/kg) excreted at 1 hr into bile nearly 18% of the dose as PG; rats given CP (400-1200 mumol/kg) excreted at 24 hr into urine nearly 4% of the dose as 6-MP and its further metabolites, 6-methylthiopurine and 6-thiouric acid. CP, PG, 6-MP, 6-methylthiopurine and 6-thiouric acid were also detected in plasma, liver and kidney of rats given CP (1200 mumol/kg); in these tissues, maximum CP concentrations were observed at 30 min, as compared to 60 to 180 min, and plasma CP concentrations were higher than those detected in liver or kidney. Liver or kidney CP metabolite concentrations at 30 to 120 min were, however, higher than those detected in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Kidney-selective prodrugs of 6-mercaptopurine: biochemical basis of the kidney selectivity of S-(6-purinyl)-L-cysteine and metabolism of new analogs in rats.

Recently, we have reported that S-(6-purinyl)-L-cysteine (PC) is a kidney-selective prodrug of 6-mercaptopurine. In the present study, the in vivo metabolism of PC and the biochemical basis of its renal selectivity were further investigated. In addition, several PC analogs were synthesized and evaluated as prodrugs of 6-mercaptopurine by determining the concentrations of 6-mercaptopurine and its metabolites, 6-methylmercaptopurine and 6-thiouric acid, in urine after rats were given the analogs. At 30 min after PC treatments, kidney metabolite concentrations were dependent on the PC dose at 40 to 130 mumol/kg and were not increased when a 400 mumol PC/kg dose was given. At the 400 mumol PC/kg dose, metabolite concentrations in the kidneys were higher at 30 min than at 1 or 3 hr, and were nearly 2.5- and 100-fold higher than those in liver and plasma, respectively. Rates of PC in vitro metabolism by liver and kidney cytosolic cysteine conjugate beta-lyases (beta-lyases) were similar, but metabolism by renal mitochondrial beta-lyase occurred at a 3-fold higher rate than the rate obtained with hepatic mitochondrial beta-lyase. When rats were given aminooxyacetic acid (500 mumol/kg) or probenecid (270 mumol/kg) before PC (130 mumol/kg), total kidney metabolite concentrations were reduced by 55 and 36%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo metabolites of S-(2-benzothiazolyl)-L-cysteine as markers of in vivo cysteine conjugate beta-lyase and thiol glucuronosyl transferase activities.

Cysteine conjugate beta-lyases (beta-lyase), enzymes that are present in mammalian liver, kidneys, and intestinal microflora, were exploited recently for site-selective delivery of 6-mercaptopurine to the kidneys. In this study, in vivo beta-lyase activity was assessed using S-(2-benzothiazolyl)-L-cysteine (BTC). 2-Mercaptobenzothiazole and 2-mercaptobenzothiazole S-glucuronic acid were major metabolites of BTC in rat liver, kidney, plasma, and urine. Total metabolite concentrations in liver, kidney, or plasma at 30 min were similar and were higher than that detected at 3 hr; metabolites were mostly in the glucuronide form. The portions of metabolites excreted in urine at 8 and 24 hr were nearly 93 and 99% of that excreted at 40 hr, respectively. Pretreatment of rats with aminooxyacetic acid did not alter kidney, liver, plasma, or urinary metabolite concentrations. The portion of the BTC dose excreted as metabolites at 24 hr was independent of the BTC dose (100-400 mumol/kg), age (5-12 weeks), or sex of the rats. The rates of in vitro BTC metabolism by guinea pig hepatic and renal beta-lyases were slower than those of rats, but the portion of the BTC dose recovered as metabolites in guinea pig urine at 24 hr was nearly 60%, which was nearly 2-fold higher than that recovered in urine of rats, mice, or hamsters. The amounts of total metabolites excreted into urine by mice or hamsters were similar, but the portion of metabolites that was in the glucuronide form in hamster urine was higher than that in mouse urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Cysteine S-conjugates may act as kidney-selective prodrugs: formation of 6-mercaptopurine by the renal metabolism of S-(6-purinyl)-L-cysteine.

The recent reports that cysteine S-conjugates of several halogenated hydrocarbons are metabolized selectively in the kidney by cysteine conjugate beta-lyase (beta-lyase) to generate thiols suggest that renal beta-lyase might be exploited for site selective delivery of sulfhydryl drugs to the kidney. In this study, the in vitro and in vivo metabolism of S-(6-purinyl)-L-cysteine, the potential precursor of the antitumor and immunosuppressant drug, 6-mercaptopurine, was examined. With renal subcellular fractions, 6-mercaptopurine was identified as a metabolite of S-(6-purinyl)-L-cysteine by its electronic absorption spectrum and by high-performance liquid chromatography. The rate of enzymatic 6-mercaptopurine formation was dependent upon incubation time, substrate and protein concentrations. Aminooxyacetic acid, an inhibitor of renal beta-lyase, inhibited the reaction. The total renal beta-lyase activity with S-(6-purinyl)-L-cysteine as substrate was distributed equally between the cytosolic and mitochondrial fractions and constituted nearly 54% of the activity measured with the prototype substrate, S-(2-benzothiazolyl)-L-cysteine. The apparent Vmax value for the mitochondrial beta-lyase-dependent metabolism of S-(6-purinyl)-L-cysteine to yield 6-mercaptopurine was 4-fold greater than the rate measured with cytosol, whereas the rates of metabolism of S-(2-benzothiazolyl)-L-cysteine by the cytosolic and mitochondrial beta-lyase were similar. When rats were given S-(6-purinyl)-L-cysteine (31.2 mg/kg i.p.) and were sacrificed at 30 min after treatments, 6-mercaptopurine, 6-methyl-mercaptopurine and 6-thiouric acid were detected in the kidney, liver or plasma.(ABSTRACT TRUNCATED AT 250 WORDS)