Effects of salient factors on the pursuit of higher education among multicultural youth in Hong Kong

This study presents novel and compelling evidence of the disparities in factors influencing the beliefs and aspirations for higher education among mainstream and immigrant youth in Hong Kong, particularly those who are underprivileged. We developed and validated a psychometric questionnaire, known as the Post-Secondary Education Pursuit Instrument (PSEPi), which was administered to 4,850 students aged between 15 and 18 years old from 23 secondary schools. The objective of this study was to explore the factors that impact students' choices and plans for higher education. The results of the one-way Multivariate Analysis of Variance (MANOVA) analysis deepen our understanding of the differential effects of success and obstacle factors on students' higher education pursuits across various cultural groups. The underprivileged mainstream, Chinese immigrant, and ethnic minority South Asian youth reported a perceived glass ceiling effect associated with their ethnic backgrounds, as well as financial aid barriers, while pursuing higher education, in contrast to their average Hong Kong mainstream counterparts (mean Cohen's d = 0.40). The direct effects and multiple mediation analyses demonstrated that significant others' influence, particularly the influence of parents, and locus of control are prime determinants of the perceived usefulness of higher education for all student groups. The implications are that educational policies should be implemented to level the playing field in higher education admissions for both privileged and underprivileged youth in Hong Kong and other international countries. Overall, this study provides robust empirical evidence that can be utilized to enhance educational policies and practices to bridge the gap between mainstream and underprivileged immigrant youth in their pursuit of higher education.

Re-examine the transfusion transmitted risk of SARS-CoV-2 virus during a major COVID-19 outbreak in 2022

INTRODUCTION

Although no case of COVID-19 transmission through transfusion has been reported, blood transfusion service (BTS) continues to implement pre-donation and post-donation measures to minimise the risk. In year 2022, when local healthcare system was badly impacted by a major outbreak, it opened an opportunity to re-examine the viraemia risk in these asymptomatic donors.

MATERIALS AND METHODS

Records were retrieved from blood donors who reported COVID-19 after donation and follow-up was also made for recipients who received their blood. Blood samples at donation were tested for SARS-CoV-2 viraemia by single-tube nested real-time RT-PCR assay designed to detect most SARS-CoV-2 variants including the prevailing delta and omicron variants.

RESULTS

From 1 January to 15 August 2022, the city with 7.4 M inhabitants recorded 1 187 844 COVID-19 positive cases and 125 936 successful blood donations were received. 781 donors reported to the BTS after donation with 701 being COVID-19 related (including close contact and symptoms respiratory tract infection). 525 COVID-19 were positive at the time of call back or follow-up. Of the 701 donations, they were processed into 1480 components with 1073 discarded upon donors' call back. For remaining 407 components, no recipient was found to have adverse event or COVID-19 positive. 510 samples from the above 525 COVID-19 positive donors were available and all tested negative for SARS-CoV-2 RNA.

DISCUSSION

With the negative SARS-CoV-2 RNA in blood donation samples and follow up data in transfusion recipients, the risk of transfusion transmitted COVID-19 appears negligible. However, current measures remains important in securing blood safety with ongoing surveillance of their effectiveness.

Transition Strength Measurements to Guide Magic Wavelength Selection in Optically Trapped Molecules

Optical trapping of molecules with long coherence times is crucial for many protocols in quantum information and metrology. However, the factors that limit the lifetimes of the trapped molecules remain elusive and require improved understanding of the underlying molecular structure. Here we show that measurements of vibronic line strengths in weakly and deeply bound ^{88}Sr_{2} molecules, combined with ab initio calculations, allow for unambiguous identification of vibrational quantum numbers. This, in turn, enables the construction of refined excited potential energy curves, informing the selection of magic wavelengths that facilitate long vibrational coherence. We demonstrate Rabi oscillations between far-separated vibrational states that persist for nearly 100 ms.

Preoperative radiography versus computed tomography for surgical planning for ankle fractures

PURPOSE

To review preoperative radiography and computed tomography (CT) of the ankle in 69 patients who underwent surgery for ankle fractures to determine the value of CT in diagnosis and surgical planning.

METHODS

Preoperative radiography and CT of the ankle of 46 women and 23 men aged 17 to 90 (mean, 48.8) years were reviewed. CT was deemed necessary when radiographs showed the following features: (1) comminuted fracture of the medial malleolus involving the tibial plafond, (2) comminuted fracture of the posterior malleolus, (3) presence of loose bodies, and/or (4) suspected Chaput or Volkman fracture fragment. Two orthopaedic surgeons independently reviewed the radiographs to look for any of the above features for which CT was indicated. In patients whose radiographs did not show any of the above features, each surgeon formulated a surgical plan based on radiographs alone and decided if any modification was needed after reviewing the CT scan.

RESULTS

Based on radiographs of the 69 patients, 19 (28%) patients had features of posterior malleolar comminution (n=7), medial malleolar comminution (n=7), suspected Chaput fracture fragment (n=1), suspected Volkman fracture fragment (n=1), and combination of 2 lesions (n=3), and were deemed to require CT. In 10 (20%) of the remaining 50 patients, the surgical plan was modified after review of the CT scan. The intra- and inter-observer agreement was good to excellent.

CONCLUSION

Radiography alone is not adequate for surgical planning for ankle fractures. More accurate imaging tools such as CT are needed to enable a more accurate diagnosis and surgical planning.

Review article: Venous thromboembolism after total joint replacement

Venous thromboembolism can occur in up to 84% of cases following total joint replacement. It can result in pain, swelling, chronic post-thrombotic syndrome, and pulmonary embolism. Its prevention is vital to the success of the surgery. To achieve a safe and effective prophylaxis, a combination of mechanical and pharmacologic agents should be used. New generation of thromboprophylactic agents target different factors of the coagulation pathway.

Dysmenorrhoea among Hong Kong university students: prevalence, impact, and management

OBJECTIVE. To evaluate the prevalence of dysmenorrhoea, its impact, and management approaches in Hong Kong university students, and to compare between medical and non-medical students for any potential differences in coping strategies. DESIGN. Cross-sectional questionnaire survey. SETTING. The University of Hong Kong, Hong Kong. PARTICIPANTS. A total of 240 undergraduate (128 medical and 112 non-medical) students. MAIN OUTCOME MEASURES. Data on the presence and severity of dysmenorrhoea, its impact on daily life, management approaches, specific strategies, and their self-perceived effectiveness were obtained and analysed. RESULTS. In these subjects, the prevalence of dysmenorrhoea was 80% (95% confidence interval, 75-85%) with a mean (standard deviation) pain score of 5.0 (1.7). The most common impacts on daily life included reduced ability to concentrate and/or disturbance with study (75%) and changes in normal physical activity (60%). Only 6% sought medical advice, while 70% practised self-management. Pain scores and pain affecting normal physical activities were important predictive factors for self-management and for management based on pharmacological or non-pharmacological means. The commonest specific strategies used were a warm beverage (62%), paracetamol (57%), and sleeping (45%), while the most effective strategies were non-steroidal anti-inflammatory drugs (100%), traditional Chinese medicine (93%), and dietary/nutritional supplements (92%). Regarding the comparison of medical and non-medical students, the former used fewer pharmacological strategies among the various management approaches investigated. CONCLUSION. With data showing dysmenorrhoea as a very common condition having a significant impact in the Hong Kong community, primary care doctors should reassure young women with dysmenorrhoea that it is a common experience in the same age-group. Health education on the existence of effective treatment from medical practitioners could help women whose dysmenorrhoea was not controlled by self-management.

Common polymorphisms in TLR4 gene associated with susceptibility to pulmonary tuberculosis in the Sudanese

SETTING

Host genetic risk factors influence susceptibility to tuberculosis (TB). There is ample evidence supporting the involvement of toll-like receptor 4 (TLR4) in mycobacterial infection.

OBJECTIVE

To study the relationship between the TLR4 gene and TB susceptibility in the Sudanese population.

DESIGN

A case-control study was conducted among 207 patients with pulmonary TB and 395 healthy controls. Ten tag single nucleotide polymorphisms (SNPs) of the TLR4 gene were genotyped using restriction digestion or hybridisation assays, and analysed.

RESULTS

The genotypes were in Hardy-Weinberg equilibrium. After controlling for sex using the Mantel-Haenszel test, four SNPs showed significant differences between cases and controls, even after correction of multiple comparisons by Bonferroni procedure. The Mantel-Haenszel estimates of allelic odds ratios for the high-risk alleles were 1.67 for rs1927911 (P = 0.0001), 1.85 for rs5030725 (P = 0.0008), 2.14 for rs7869402 (P = 1.87e-07) and 2.31 for rs1927906 (P = 1.23e-10). Haplotype analysis showed that rs1927911 and rs5030725 were in one haplotype block, and rs7869402 and rs1927906 were in another haplotype block. Conditional haplotype analysis suggested the presence of one causal variant downstream of a recombination hot spot at the 3' region of the TLR4 gene.

CONCLUSION

This is the first study to show that common TLR4 polymorphisms are associated with TB susceptibility in the Sudanese population.

Case report: Spinal anesthesia by mini-laminotomy for a patient with ankylosing spondylitis who was difficult to anesthetize

BACKGROUND

Orthopaedic surgeons frequently encounter patients with ankylosing spondylitis who would benefit from various types of lower limb operations; however, some of these patients present challenges for anesthesiologists.

CASE DESCRIPTION

We report the case of a 65-year-old patient with a fractured femoral component 30 years after a cemented THA. The patient had severe tracheal stenosis and ankylosing spondylitis making general endotracheal and conventional neuraxial anesthesia nearly impossible.

LITERATURE REVIEW

Possible alternative anesthetic approaches described in the literature include awake fiberoptic bronchoscopic guided intubation, laryngeal mask airway, and caudal anesthesia.

PURPOSES AND CLINICAL RELEVANCE

We achieved successful anesthesia using spinal laminotomy with the patient under local anesthesia followed by insertion of a spinal catheter and injection of an anesthetic agent. The loosened component was revised to a cementless THA.

Extent and distribution of linkage disequilibrium around the SLC11A1 locus

The SLC11A1 (or NRAMP1) locus on human chromosome 2q35 encodes for the protein solute carrier family 11, member 1. It is expressed in macrophages and involved in the early stages of macrophage priming and activation. Different association studies have shown that the SLC11A1 gene affects susceptibility to infectious diseases and autoimmune inflammatory diseases. Although functional SLC11A1 polymorphisms may account for its role in affecting the susceptibility to these diseases, the positive association can also be because of flanking polymorphisms showing linkage disequilibrium (LD) with this locus. This is the first systematic study to investigate the LD pattern within and around the gene. LD was investigated by genotyping 17 genetic markers in a Chinese population (n=360). The results indicate that LD is maintained at least 110 kb both upstream and downstream of the locus. The complex LD pattern demands that association studies with SLC11A1 should be carried out with both 5' and 3' markers. The strong LD between IL8RB and the 5' SLC11A1 markers also dictates that IL8RB be tested for association with these diseases. Thus, positive association with SLC11A1 should be interpreted cautiously, and IL8RB should also be considered as a potential candidate susceptibility gene unless proven otherwise.

Transient-resonance Raman and density functional theory investigation of 4-biphenylylnitrenium, 2-fluorenylnitrenium, and diphenylnitrenium ions

We present transient-resonance Raman spectra for the 4-biphenylylnitrenium, diphenylnitrenium, and 2-fluorenylnitrenium ions. These spectra display a number of fundamental vibrational bands whose frequencies exhibit good agreement with those computed using BPW91/cc-PVDZ density functional theory calculations for the singlet ground states of the 4-biphenylylnitrenium, diphenylnitrenium, and 2-fluorenylnitrenium ions. Comparison of these arylnitrenium ions with each other and with previous results for structurally similar biphenyl radical cations indicates that the degree of iminocyclohexadienyl character observed in these arylnitrenium ions depends on the relative orientation of the two phenyl rings, the nature of the nitrenium ion moiety, and the ability of the biphenyl-like group to accommodate positive charge through formation of a more planar-like structure with quinoidal-like character.

Transient resonance Raman and density functional theory investigation of the 2-fluorenylnitrenium ion

We report a transient resonance Raman spectrum for the 2-fluorenylnitrenium ion obtained after photolysis of 2-azidofluorene. The 10 experimental Raman band frequencies of the transient spectrum show very good agreement with the computed frequencies from BPW91/cc-PVDZ density functional theory calculations for the 2-fluorenylnitrenium ion. Our results confirm the assignment of the approximately 460 nm transient absorption band formed after photolysis of 2-azidofluorene in water/acetonitrile or water solution to the singlet ground electronic state 2-fluorenylnitrenium ion. Our study indicates the 2-fluorenylnitrenium has a large degree of iminocyclohexadienyl cation character with significant delocalization of the charge over both phenyl rings of the fluorene moiety. We compare our results for the 2-fluoreneylnitrenium ion to those previously reported for several other arylnitrenium ions.

Tissue-specific expression and long-term deposition of human collagen VII in the skin of transgenic mice: implications for gene therapy

We report the isolation of a cosmid clone containing the entire human COL7A1 gene in one piece. The ability of the genomic sequences within this clone to direct tissue-specific expression of human collagen VII in transgenic mice was tested. The data show that the gene construct is capable of directing expression of collagen VII in the skin of fetal and neonatal transgenic mice. Expression of COL7A1 in these mice was widespread, in a pattern consistent with that found in human tissues and was in parallel with that of the endogenous mouse gene. Immunostaining, using human-specific antibodies, showed that human collagen VII protein was present at the skin basement membrane zone of the transgenic mice. Dermal extracts from 19-month-old transgenic mice contained mature human collagen VII protein, and fibroblasts derived from skin biopsies of these mice actively synthesized human collagen VII. The demonstration of successful and stable expression of human collagen VII in in vivo gene transfer is the first step towards the future development of therapeutic protocols for the rescue of keratinocyte function in severe blistering diseases such as dystrophic epidermolysis bullosa.

Electronic and resonance Raman spectra of [Au2(CS3)2]2-. Spectroscopic properties of a "short" Au(I)-Au(I) bond

The anion [Au2(CS3)2]2- has an unusually short Au-Au distance (2.80 A) for a binuclear Au(I) complex. We report detailed Raman studies of the nBu4N+ salt of this complex, including FT-Raman of the solid and UV/vis resonance Raman of dimethyl sulfoxide solutions. All five totally symmetric vibrations of the anion have been located and assigned. A band at delta nu = 125 cm-1 is assigned to nu (Au2). The visible-region electronic absorption bands (384 (epsilon 30,680) and 472 nm (epsilon 610 M-1 cm-1)) are attributable to CS3(2-) localized transitions, as confirmed by the dominance of nu sym(C-Sexo) (delta nu = 951 cm-1) in RR spectra measured in this region. An absorption band at 314 nm (22,250 M-1 cm-1) is assigned as the metal-metal 1(d sigma*-->p sigma) transition, largely because nu sym(C-Sexo) is not strongly enhanced in RR involving this band. Observation of the expected strong resonance enhancement of nu (Au2) was precluded as a result of masking by intense solvent Rayleigh scattering in the UV.

Determination of in vitro permeability of drug candidates through a caco-2 cell monolayer by liquid chromatography/tandem mass spectrometry

Studying the permeability of compounds across a Caco-2 cell monolayer is an established in vitro model to screen for oral absorption and to evaluate the mechanism of transport. This assay can also be used to evaluate compounds as potential P-glycoprotein substrates and/or inhibitors. The traditional methods of sample analysis (high-performance liquid chromatography (HPLC) with a UV or fluorescence detector) limit the throughput and sensitivity of this assay. Data are presented here describing the use of liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the analysis of samples derived from the Caco-2 cell studies. During the analysis an automatic switching valve was used to divert the flow from the HPLC column to waste for the first minute, preventing the early eluting salts from entering and contaminating the LC/MS interface. This approach allows the rapid and accurate determination of drug transport across the Caco-2 cell monolayer. The high sensitivity and specificity of LC/MS/MS make this technique an ideal candidate for the low concentration and high throughput routine analysis of Caco-2 cell solutions, especially if multiple compounds are administered and analyzed simultaneously. Thus, the use of LC/MS/MS will increase the value of the Caco-2 cell assay as an in vitro screening tool.

Release of soluble ICAM-1 from human lung fibroblasts, aortic smooth muscle cells, dermal microvascular endothelial cells, bronchial epithelial cells, and keratinocytes

We determined effects of IL-1alpha, TNFalpha and IFNgamma on sICAM-1 release in culture media from human aortic smooth muscle cells (AOSMC), dermal microvascular endothelial cells (DMEC), keratinocytes (KC), bronchial epithelial cells (BEC) and lung fibroblasts (LF) as determined by ELISA. Under basal conditions of cultures for 20 h, low concentrations of sICAM-1 were only detected in the culture media of two (DMEC and BEC) of these cell types. IL-1alpha, TNFalpha and IFNgamma stimulated sICAM-1 from these cells. IFNgamma stimulated more shedding from AOSMC, BEC and KC than IL-1alpha or TNFalpha. TNFalpha enhanced more sICAM-1 release from DEMC than from AOSMC, BEC and LF. IL-1alpha and IFNgamma or TNFalpha and IFNgamma acted synergistically to enhance shedding of sICAM-1 from these cells. The levels sICAM-1 in pathophysiological conditions may influence leukocyte-vascular cell interactions to block leukocyte transmigration to tissue injury sites as a negative feedback mechanism.

Studies on cytochrome P-450-mediated bioactivation of diclofenac in rats and in human hepatocytes: identification of glutathione conjugated metabolites

The nonsteroidal anti-inflammatory drug diclofenac causes a rare but potentially fatal hepatotoxicity that may be associated with the formation of reactive metabolites. In this study, three glutathione (GSH) adducts, namely 5-hydroxy-4-(glutathion-S-yl)diclofenac (M1), 4'-hydroxy-3'-(glutathion-S-yl)diclofenac (M2), and 5-hydroxy-6-(glutathion-S-yl)diclofenac (M3), were identified by liquid chromatography-tandem mass spectrometry analysis of bile from Sprague-Dawley rats injected i.p. with a single dose of diclofenac (200 mg/kg). These adducts presumably were formed via hepatic cytochrome P-450 (CYP)-catalyzed oxidation of diclofenac to reactive benzoquinone imines that were trapped by GSH conjugation. In support of this hypothesis, M1, M2, and M3 were generated from diclofenac in incubations with rat liver microsomes in the presence of NADPH and GSH. Increases in adduct formation were observed when incubations were performed with liver microsomes from phenobarbital- or dexamethasone-treated rats. Adduct formation was inhibited by polyclonal antibodies against CYP2B, CYP2C, and CYP3A (40-50% inhibition at 5 mg of IgG/nmol of CYP) but not by an antibody against CYP1A. Maximal inhibition was obtained when the three inhibitory antibodies were used in a cocktail fashion (70-80% inhibition at 2.5 mg of each IgG/nmol of CYP). These data suggest that diclofenac undergoes biotransformation to reactive metabolites in rats and that CYP isoforms of the 2B, 2C, and 3A subfamilies are involved in this bioactivation process. With respect to CYP2C isoforms, rat hepatic CYP2C7 and CYP2C11 were implicated as mediators of the bioactivation based on immunoinhibition studies using antibodies specific to CYP2C7 and CYP2C11. Screening for GSH adducts also was carried out in human hepatocyte cultures containing diclofenac, and M1, M2, and M3 again were detected. It is possible, therefore, that reactive benzoquinone imines may be formed in vivo in humans and contribute to diclofenac-mediated hepatic injury.

Parenting and preschooler attachment among low-income urban African American families

This study examined the parental correlates of child attachment in a preschool-aged, economically disadvantaged, urban, African American sample. Sixty-nine 4- to 5-year-olds and their primary caregivers participated in the Strange Situation assessment procedure. Based on Cassidy and Marvin's classification system for preschoolers, 61% of the children were classified as securely attached, with girls being significantly more likely to be securely attached than boys (74% versus 45%). The majority of the insecure attachments were of the avoidant variety. Consistent with attachment theory, parents of securely attached children were rated as significantly more warm and accepting and less controlling with their children than were parents of insecurely attached preschoolers. Relative to parents of securely attached preschoolers, parents of children judged to be insecurely attached reported being more likely to use corporal punishment and less likely to use verbal reminders when their children misbehaved. Parenting was associated with attachment over and above the effects of child sex.

Functional effects of FGF-13 on human lung fibroblasts, dermal microvascular endothelial cells, and aortic smooth muscle cells

We studied the effects of FGF-13 and FGF-2 on human lung fibroblasts, dermal microvascular endothelial cells, and aortic smooth muscle cells. FGF-13 induced cell growth of lung fibroblasts and aortic smooth muscle cells but had no effect on dermal vascular endothelial cells. FGF-2 induced cell growth in all the three cell types. FGF-13 and FGF-2 had little effect on IL-6 production by lung fibroblasts and aortic smooth muscle cells and substantially enhanced that induced by IL-1alpha. In contrast, FGF-13 and FGF-2 had little effect on IL-6 production by dermal vascular endothelial cells, either alone or in synergy with IL-1alpha.

Evidence for a novel heme adduct generated by the in vitro reaction of 2,4,6-trinitrotoluene with human hemoglobin using electrospray ionization mass spectrometry

The bioactivation of nitroaromatic compounds to highly reactive intermediates is responsible for the genotoxic and cytotoxic effects by reaction with DNA and proteins. Due to its continued use as a secondary explosive and its prevalence at contaminated sites, the mechanism of covalent binding of 2,4,6-trinitrotoluene (TNT), or its metabolites, to critical cellular proteins has been of interest. Herein, we report the in vitro reaction of TNT with human hemoglobin under anaerobic and reductive (using sodium hydrosulfite) conditions, yielding a novel adduct between a putative nitrosodinitrotoluene (MW = 211 Da) and the prosthetic heme group (iron protoporphyrin-IX or heme b). While the covalent modification of hemoglobin polypeptide chains by TNT has been established, to our knowledge, this is the first example of a heme-TNT related adduct. This finding could be of relevance in investigation of biotransformation of TNT in subjects exposed to TNT via skin exposure or inhalation.

Pharmacokinetics and disposition of L-692,429. A novel nonpeptidyl growth hormone secretagogue in preclinical species

L-692,429 is a novel nonpeptidyl growth hormone secretagogue that has been demonstrated to stimulate growth hormone secretion in rats, dogs, and humans after intravenous administration. We have examined the pharmacokinetics and disposition of L-692,429 in male Sprague-Dawley rats, beagle dogs, and chimpanzees. Plasma clearance (CLp) of L-692,429 in dogs after intravenous dosing was approximately 18 ml/min/kg and was constant between the doses of 0.1 and 0.9 mg/kg. In rats, CLp after intravenous dosing increased from 3 to 12 ml/min/kg in a dose-dependent manner between 0.1 and 5 mg/kg. In chimpanzees, CLp after an intravenous dose of L-692,429 at 0.5 mg/kg was 5.7 ml/min/kg. In vitro binding of L-692,429 to plasma proteins of dogs, chimpanzees, and humans was approximately 87%, 94%, and 93.5%, respectively, and was independent of concentration. In contrast, plasma binding of L-692,429 was concentration-dependent in rats and decreased from 98.5% to 90.6% between 0.01 and 10 micrograms/ml. Metabolism of L-692,429 was minimal in rats, but moderate in dogs, with the major metabolite being a derivative monohydroxylated at the benzolactam moiety. Thus, the faster clearance of L-692,429 in dogs likely is caused by less extensive plasma protein binding and higher metabolic clearance. The nonlinear pharmacokinetics in rats probably is the result of concentration-dependence in plasma binding. The results of these studies suggest that plasma protein binding plays a major role in determining the values of CLp of L-692,429 among the species. After an intravenous dose of [3H]L-692,429 to rats, liver, kidney, lung, and heart had the highest levels of radioactivity at the early time points, but the gastrointestinal tract had increasing concentrations at later time points. Most of the radioactivity was cleared from all tissues by 24 hr, indicating that L-692,429 did not accumulate in tissues. After intravenous dosing of [3H]L-692,429 to rats and dogs, recoveries of total radioactivity in urine and feces corresponded to approximately 10% and 90%, respectively. Greater than 70% of radioactivity was recovered in bile of rats within 24 hr after intravenous dosing of [3H]L-692,429, indicating that biliary excretion was the primary route of elimination. Based on the combined recoveries of the radioactive dose in bile and urine after an oral dose of L-692,429, oral absorption in rats was approximately 3%. The poor absorption may be the result of the zwitterionic nature of this compound.

Mechanism of bioactivation and covalent binding of 2,4,6-trinitrotoluene

Studies were undertaken to investigate the mechanism of bioactivation and covalent binding of TNT. Incubation of [14C]TNT with rat liver microsomes in the presence of an NADPH generating system resulted in metabolism and covalent binding to microsomal proteins. Time-dependence studies showed that TNT was rapidly reduced to yield 4-hydroxylamino-2,6-dinitrotoluene (4HA), 4-amino-2,6-dinitrotoluene (4A) and 2-amino-4,6-dinitrotoluene (2A) as intermediates which were further metabolized to form 2,4-diamino-6-nitrotoluene (2,4DA) and 2,6-diamino-4-nitrotoluene (2,6DA). In contrast to the rapid disappearance of TNT, formation of covalent protein adducts increased with time, suggesting that the reactive intermediate was likely to be formed not directly from TNT but from proximal intermediates such as 4HA. The hypothesis that 4HA was more readily converted to the reactive intermediate than TNT was further supported by the increased levels of covalent adduct formation when [14C]4HA was incubated directly with liver microsomes. Covalent binding of TNT and 4HA was dependent on oxygen concentration. Higher levels of covalent adducts were formed when TNT was incubated aerobically (up to 50% oxygen concentration) than under anaerobic conditions. Covalent binding of [14C]4HA also increased with increasing oxygen concentrations. These results suggest that the reactive intermediate is likely to be an oxidized metabolite of 4HA, e.g. 4-nitroso-2,6-dinitrotoluene. Compounds containing a free sulfhydryl group (cysteine, N-acetylcysteine, GSH or 3,4-dichlorobenzenethiol) decreased the amount of covalent binding to various degrees, suggesting the involvement of the sulfhydryl group in adduct formation with TNT following bioactivation. Metabolic activation of TNT by liver microsomes required NADPH but not NADH as the cofactor. Incubation of [14C]TNT with purified rat liver NADPH cytochrome P450 reductase under either aerobic or anaerobic conditions yielded exclusively 4HA. In contrast, 2A and 4A were formed following incubation of TNT with the reconstituted system containing cytochrome P450, NADPH cytochrome P450, reductase and dilauroyl phosphatidylcholine. These observations suggest that the initial reduction of the nitro group can be catalyzed by NADPH cytochrome P450 reductase alone but cytochrome P450 is needed in the reduction of the hydroxylamine to the amine.

Characterization of biochemical responses of angiotensin II (AT2) binding sites in the rat pheochromocytoma PC12W cells

Rat pheochromocytoma PC12W cell membranes have previously been shown to exclusively contain the AT2 receptor subtype. The present study extended these binding data and explored the functional expression of these binding sites. Our binding competition studies show a potency series of Ang II = Ang III greater than saralasin greater than Ang I = PD123177 much greater than Ang II(1-7) much much greater than losartan. PD123177 (1 microM) completely eliminated [125I]Ang II binding to PC12W cells. Competitive displacement of [125I]Ang II with Ang II shows a dissociation equilibrium constant (Kd) of 1.79 nM and a binding site maximum (Bmax) of 3.97 fmol/mg protein. Investigating several Ang II signal transduction pathways on these cells, we found that Ang II (10(-8) to 10(-6) M) does not affect basal cAMP, cGMP, arachidonic acid release, prostacyclin release, intracellular Ca2+ mobilization or thymidine incorporation in the PC12W cells. Nerve growth factor, cAMP, 5-fluorouridine deoxyriboside modulation of the number of AT2 receptor sites in PC12W cells failed to unmask any Ang II effects on basal cAMP, cGMP and intracellular Ca2+ mobilization. In conclusion, the present study confirms the exclusive presence of AT2 binding sites in the PC12W cells. However, these binding sites are not functionally coupled to common signal transduction pathways.

AT1 receptors mediate the release of prostaglandins in porcine smooth muscle cells and rat astrocytes

Angiotensin II (AII) can release arachidonic acid metabolites such as prostacyclin (PGI2) and PGE2 from cells in cultures. It has recently been reported that the AT1 selective nonpeptide AII receptor antagonist losartan had similar effects. The present study was undertaken to further evaluate the effects of AII and losartan on cells which synthesize prostaglandins, including vascular smooth muscle, endothelial, and glial cells. Inhibition of specific [125I]AII binding was demonstrated in porcine smooth muscle cell (PSMC) suspensions with unlabeled AII and losartan. The IC50 values were 1.3 x 10(-9) mol/L and 7.7 x 10(-9) mol/L, respectively. PD123177 (an AT2 selective antagonist) had no effect on binding. AII produced a concentration-related increase in calcium mobilization (fura-2 fluorescence) which was blocked by losartan (IC50 = 8.4 x 10(-8) mol/L) but not by PD123177 (10(-6) mol/L). AII (10(-7) to 10(-5) mol/L) stimulated the basal release of PGI2 by 100%. This response was blocked by losartan (10(-6) to 10(-5) mol/L) but not by PD123177 (10(-6) to 10(-5) mol/L) and neither agent stimulated basal release in PSMC. Similar effects of AII and antagonists were observed upon receptor binding and PGE2 release in primary rat astrocyte (RA) cultures. AII did not release PGI2 from porcine endothelial cells, bovine pulmonary arterial endothelial cells, or rat C6 glioma cells. Losartan had no significant effect at 10(-5) mol/L. By contrast, bradykinin or the calcium ionophore A23187 dramatically increased PGI2 release in each of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

DuP 532: a second generation of nonpeptide angiotensin II receptor antagonists

DuP 532 is a novel nonpeptide angiotensin II (AII) receptor antagonist under development for the treatment of hypertension. DuP 532 is a more potent antihypertensive agent in renal hypertensive rats (ED30 = 0.042 mg/kg, i.v.) and displays a similar or longer duration of action than the previously described AII antagonist, DuP 753. DuP 532, in contrast to DuP 753, is a noncompetitive antagonist of AII-induced contractions of rabbit aortic strips (KB = 1.1 x 10(-10) M). However, the inhibition of AII binding by DuP 532 in rat adrenal cortex does not correlate with either the aortic contractile response or with the hypotensive response. Assay conditions were evaluated and the presence or absence of BSA was shown to markedly affect the apparent binding affinity of DuP 532 and other 5-carboxylic acid derivatives. DuP 753 and other compounds were much less affected. The IC50 for DuP 532 was 4.7 x 10(-6) M with and 3 x 10(-9) M without BSA. The IC50s for DuP 753 were 1.7 x 10(-8) M with and 5 x -9 M without BSA. Both compounds with or without BSA did not completely inhibit AII binding which is characteristic of AT1 selectivity. BSA also reduced the effect of DuP 532 on the AII-induced contractions of rat main pulmonary artery preparations and the AII-induced Ca2+ mobilization in rat aortic smooth muscle cells. DuP 532 was very specific for AT1 receptors and did not interfere with receptors associated with neurotensin, prazosin, bradykinin, nitrendipine, or vasopressin. It is concluded that DuP 532 represents a new class of specific, but noncompetitive. AII receptor antagonists whose binding characteristics may provide new insight into AII receptor function.

Regional distribution of the two subtypes of angiotensin II receptor in rat brain using selective nonpeptide antagonists

We have demonstrated the existence and localization of two angiotensin II (AII) receptor subtypes in different regions of the rat brain using competitive radioligand binding technique. The identification of the subtypes was made by the reciprocal selectivity of DuP 753 and PD123177 for the AII-1 and AII-2 receptors, respectively. In the pituitary gland, DuP 753 inhibited 95% of the specific AII binding with a Ki value of 1.85 x 10(-9) M while PD123177 had little effect. In the whole brain, thalamus-septum and midbrain, PD123177 inhibited 90% of the specific binding with Ki value of 7.77 x 10(-8) M, 8.21 x 10(-8) M and 4.93 x 10(-8) M, respectively while DuP 753 had little effect. In the hypothalamus, DuP 753 and PD123177 had Ki values of 5.67 x 10(-8) M and 1.60 x 10(-7) M, respectively, for their respective receptor subtypes. In the cerebellum and cerebral cortex, the AII specific binding was low. The data suggest there are at least two subtypes of AII receptor in the rat brain and that they are not uniformly distributed.

Human lymphokine-activated killer (LAK) cells--II. Studies of various L-amino acid methyl esters on LAK generation at high cell density

Nineteen L-amino acid methyl esters were studied for their cytotoxic activity on human monocytes, NK activity, and LAK activation by IL-2 at high cell density (5 x 10(6) cells/ml). Phenylalanine, Met, Trp, Cys, Tyr, Asp and Glu methyl esters depleted monocytes from PBMC, caused inhibition of NK activity, and allowed LAK activation at high cell density. Alanine, Val and Pro methyl esters were marginal. Glycine, Ser, Thr, Lys, His and Arg were not active. Leucine, Ile and cystine methyl esters depleted monocytes and also NK activity; LAK activation was suppressed. The D series of the active L-amino acid (Met, Tyr and Trp) methyl esters were not active. The position of the methyl ester is important as shown by 5-Glu methyl ester which was not active as Glu(OMe)2. Phenylalanine T-butyl ester was not as active as the methyl or the ethyl ester. This indicates that the breakage of the ester bond is the rate-limiting step for the actions of the Phe alkyl esters. Seven L-amino acid amides (Ile, Leu, Phe, Val, Glu, Asp and Tyr) were studied and only Ile, Leu and Phe were found to be active. Isoleucine and Leu amides depleted monocytes with little inhibitory effect on NK activity and thus allowed LAK activation. In summary, depletion of monocytes by the amino acid methyl esters and the amides allowed LAK activation at high cell density.

Human lymphokine-activated killer (LAK) cells: III. Effect of L-phenylalanine methyl ester on LAK cell activation from human peripheral blood mononuclear cells: possible protease involvement of monocytes, natural killer cells and LAK cells

We have shown that depletion of monocytes from human peripheral blood mononuclear cells (PBMC) by L-phenylalanine methyl ester (PheOMe) enhanced lymphokine-activated killer cell (LAK) generation by recombinant interleukin-2 (rIL-2) at high cell density. In this study, we have investigated the mechanism of action of PheOMe on LAK activation by using trypsin, chymotrypsin, tosylphenylalaninechloromethanol (TPCK, a chymotrypsin inhibitor), tosyl-L-lysinechloromethane (TLCK, a trypsin inhibitor), phenylalaninol (PheOH), and benzamidine. PBMC were treated with 1-5 mM PheOMe for 40 min at room temperature in combination with the various agents, washed and assessed for their effects on natural killer (NK) activity against K562 cells and monocyte depletion. The treated cells were then cultured with or without rIL-2 for 3 days. LAK cytotoxicity was assayed against 51Cr-labeled K562 and Raji tumor target cells. TPCK at 10 micrograms/ml partially inhibited depletion of monocytes by PheOMe. TLCK did not prevent depletion of monocytes nor inhibition of NK activity induced by PheOMe. TPCK and TLCK inhibited NK activity by themselves. TPCK but not TLCK inhibited rIL-2 induction of LAK cells. On the other hand, PheOH and benzamidine (analogs of PheOMe) lacked any effect on monocyte depletion but abrogated the inhibitory effect of PheOMe on NK activity. They had no effect on rIL-2 activation of LAK activity enhanced by PheOMe. Trypsin potentiated the inhibitory effect of PheOMe on NK activity and monocyte depletion. Trypsin partially inhibited IL-2 activation of LAK activity enhanced by PheOMe. Chymotrypsin had little effect on NK activity but prevented the inhibitory effect of PheOMe on NK activity. It had little effect on monocyte depletion induced by PheOMe. PheOMe was hydrolysed by monocytes and chymotrypsin to Phe and methanol as determined by HPLC. TPCK inhibited hydrolysis of PheOMe by monocytes. Our data suggest that the effects of PheOMe on monocytes, NK cells and LAK activation involve protease activities of monocytes.

Inhibition of human NK cell and LAK cell cytotoxicity and differentiation by PGE2

Activation of natural killer (NK) activity K562 target cells from nonadherent (NA) lymphocytes by interleukin 2 (IL-2) was inhibited marginally PGE2 (30-3000 nM). PGE2 did not effectively suppress the NK activity of IL-2-activated cells. The NK activation and acquisition of resistance to PGE2-mediated suppression of NK activity were dependent on protein synthesis. When NA cells were incubated with IL-2 for 3 or more days to generate lymphokine-activated killer (LAK) activity against Raji target cells, PGE2 only partially inhibited the activation of NK/LAK activity by an optimal dose of IL-2 (10 U/ml). The activation of NK/LAK activity by a suboptimal dose of IL-2 (0.1 U/ml) was inhibited by PGE2. When the NK/LAK activity of IL-2-activated cells was assessed in the presence or absence of PGE2, the LAK activity was more sensitive than the NK activity to PGE2-mediated suppression.

Inhibition of human natural killer cell and lymphokine-activated killer cell cytotoxicity and differentiation by vitamin D3

Recent data suggest that vitamin D3 may be capable of immunoregulation after it is converted to an active metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). The effect of vitamin D3 and 1,25(OH)2D3 on human natural killer (NK) cells and their activation by interferon (IFN) and interleukin 2 (IL-2) was investigated. Vitamin D3 and 1,25(OH)2D3 inhibited NK cytotoxicity in a dose-dependent manner. Pretreatment of non-adherent (NA) cells at 37 degrees C for 18 h with the vitamins also led to inhibition of NK activity. Both the inhibition of NK lysis and pretreatment of NA cells were dependent on the concentrations of fetal calf serum (FCS) in the medium. The inhibition of NK activity was less effective in the presence of 10% FCS than with 1% FCS. Vitamin D3 inhibited both IFN and IL-2 activation of NK activity. However, increasing doses of IL-2 were able to abrogate the inhibition caused by vitamin D3. Vitamin D3 was able to inhibit NK activity of phytohaemagglutinin and IL-2-activated cells, and also inhibit the proliferation and lymphokine-activated killer activity induced by IL-2. NA cells pretreated with vitamin D3 did not respond well to IL-2. NA cells pretreated with low doses of IL-2 were sensitive to inhibition by vitamin D3 while those pretreated with high doses of IL-2 were not. The data presented suggest that vitamin D3 and 1,25(OH)2D3 inhibit NK activity and LAK cellular differentiation.

Effect of sulfite on the covalent reaction of benzo[a]pyrene metabolites with DNA

Sulfur dioxide (SO2) potentiates the carcinogenicity of polycyclic aromatic hydrocarbons. To investigate the mechanism of SO2 cocarcinogenesis, the effect of sulfite, the hydrated form of SO2, on the covalent reaction of benzo[a]pyrene (BaP) metabolites with DNA in vitro was measured. [14C]BaP was incubated with rat lung or liver post-mitochondrial supernatant (S9), an NADPH generating system, calf thymus DNA and sodium sulfite (0-20 mM). In the presence of lung S9, covalent reaction increased linearly from 0.66 to 1.20 pmol BaP metabolites per mg DNA with increasing sulfite concentrations. Addition of sulfite to rat liver S9 also increased BaP-DNA adduct formation with BaP-DNA adducts increasing from 80 to 120 pmol per mg DNA. Sulfite altered the amount and pattern of BaP metabolites formed by either lung or liver enzyme preparations. BaP was metabolized more extensively and the amount of water soluble BaP metabolites formed increased significantly with sulfite present. With lung S9, the amount of BaP-tetrols, diols, and phenols increased slightly. With liver S9, diol and phenol formation was significantly lower while tetrol formation was unchanged. Incubation of rat lung S9 with sulfite resulted in formation of glutathione S-sulfonate (GSSO3H), a known inhibitor of glutathione S-transferases mediating the conjugation of glutathione (GSH) and BaP epoxides. Our results suggest that sulfite may, by altering the overall metabolic activation and detoxication of BaP, or by reacting directly with DNA, subsequently affect the covalent reaction of BaP metabolites with DNA. These are offered as possible mechanisms to explain the cocarcinogenic effect of SO2.

Human lymphokine-activated killer (LAK) cells. I. Depletion of monocytes from peripheral blood mononuclear cells by L-phenylalanine methyl ester: an optimization of LAK cell generation at high cell density

Pretreatment of peripheral blood mononuclear cells (PBMC) with 5 mM L-phenylalanine methyl ester (PheOMe) provides an efficient means to deplete monocytes. PheOMe does not affect the number of large granular lymphocytes after the pretreatment, but does inhibit natural killer cell cytotoxicity temporarily after the pretreatment. However, depletion of monocytes by PheOMe allows lymphokine-activated killer (LAK) cell generation with recombinant interleukin-2 (rIL-2) at high cell density (greater than 5 x 10(6) cells/ml). The time of the PheOMe pretreatment is 40-60 min, though some effect could be observed within 15 min, and the pretreatment could be performed at room temperature. Pretreatment density of PBMC with 5 mM PheOMe could be achieved at cell density up to 3 x 10(7) cells/ml. PheOMe-pretreated cells could be activated by rIL-2 in serumless media at high cell density. Pretreatment of PBMC with 5 mM PheOMe provides an efficient means to deplete monocytes, as compared to plastic and nylon-wool adherence. LAK cell generation is similar in both methods of monocyte depletion; therefore, depletion of monocytes allows, LAK cell generation at high cell density. The PheOMe procedure provides an improved and convenient process for preparing LAK cells for adoptive immunotherapy.

Selective inhibition of leukotriene C4 synthesis and natural killer activity by ethacrynic acid

We have investigated the role of arachidonic acid (AA) metabolism in natural killer (NK) cell activity. Human nonadherent (NA) peripheral blood lymphocytes were used as effector cells against 51Cr-labeled K562 target cells. Synthesis of leukotriene C4 (LTC4) is dependent on glutathione S-transferase (GST). We have chosen to study three putative GST inhibitors, namely, ethacrynic acid (ET), caffeic acid (CA), and ferulic acid (FA), with regard to NK activity and with regard to their effect on AA metabolism. The GST inhibitors inhibited NK lysis when added directly to the NK assay. The GST inhibitors inhibited LTC4 synthesis as induced by calcium ionophore A23187 in a dose-dependent manner similar to their inhibition of NK activity. However, only ET was selective, for it had little effect on LTB4, 5-hydroxyeicosatetraenoic acid, and prostaglandin E2 synthesis. LTC4 synthesis was associated with the NK-enriched fractions obtained from discontinuous Percoll gradients. NK-specific anti-Leu-11b antibody and C treatment could abrogate NK activity and LTC4 synthesis. ET was also inhibitory when NA cells were cultured at 37 degrees C for 18 hr. In this case, LTC4 could reverse the inhibitory effect of ET. Our data suggest that LTC4 plays an important role in NK activity.

Regulation of human natural killing. IV. Role of lipoxygenase in regulation of natural killing activity

In this study we demonstrated that natural killer (NK) cell lysis by human peripheral blood nonadherent (NA) cells against K562 target cells was rapidly inhibited by four agents that inhibit the lipoxygenase pathway of arachidonic acid metabolism, nordihydroguaiaretic acid (NDGA), U-60257, alpha-phenanthroline, and esculetin. However, human NK cells activated by interferons (IFN) or poly I:C were partially resistant to suppression by NDGA and U-60257. Pretreatment of the NA cells with the four lipoxygenase inhibitors at 37 degrees C for 18 h led to suppression of NK activity. The inhibition of NK activity by NDGA was not reversed by aspirin at a concentration that inhibits PGE2 synthesis. Thus, suppression of NK activity by NDGA was not mediated by the effects on PGE2 synthesis. However, the inhibition of endogenous NK activity by NDGA, U-60257, alpha-phenanthroline, or esculetin was partially reversed by IFN or poly I:C. These results suggest that products of lipoxygenation are required for maintenance of human NK activity.

Analysis of the immunoadjuvant octadecyl tyrosine hydrochloride

A simple, rapid, high performance liquid chromatographic (HPLC) method for the analysis of the immunoadjuvant octadecyl tyrosine hydrochloride is described. The HPLC procedure can be applied to the direct determination of amino acid reactants present as contaminants in the adjuvant (tyrosine, ethyl tyrosine) and from this information the content of octadecanol reactant can be estimated. Further, these same determinations provide a means of monitoring immunoadjuvant stability in any vaccine preparation.

Regulation of rat natural killing. II. Inhibition of cytolysis and activation by inhibitors of lipoxygenase: possible role of leukotrienes

Rat splenic natural killer (NK) cell activity against 51Cr-labeled YAC-1 or TMT-081 tumor cells can be augmented by culturing at 37 degrees C for 18 hr. Inhibitors of the lipoxygenase pathway of arachidonic acid metabolism, NDGA, alpha-phenanthroline, quercetin, ETYA, BW755C, esculetin, and timegadine, inhibited this NK activation and also inhibited NK cytotoxicity when added directly to the NK assay. However, there was a partial loss of sensitivity of activated NK cells to suppression by NDGA, BW755C, and esculetin. Indomethacin failed to reverse the inhibition of NK activation caused by NDGA. However, LTB4 and LTC4 (0.01 microgram/ml) were able to reverse the inhibitory effect of NDGA on NK activation. Furthermore, spleen cells cultured for 18 hr synthesized detectable amount of LTC4 in their supernatants. NDGA inhibited the LTC4 synthesis in a dose-dependent manner. These data therefore suggest that leukotrienes are responsible for NK activation, and lipoxygenase activity is essential for NK cytolytic activity.

Selective inhibition of leukotriene C4 synthesis in human neutrophils by ethacrynic acid

Addition of glutathione S-transferase inhibitors, ethyacrynic acid (ET), caffeic acid (CA), and ferulic acid (FA) to human neutrophils led to inhibition of leukotriene C4 (LTC4) synthesis induced by calcium ionophore A23187. ET is the most specific of these inhibitors for it had little effect on LTB4, PGE2 and 5-HETE synthesis. The inhibition of LTC4 was irreversible and time dependent. ET also had little effect on 3H-AA release from A23187-stimulated neutrophils.

Covalent reactions in the toxicity of SO2 and sulfite

Toxic effects of SO2 and sulfite such as bronchitis and bronchoconstriction have been well documented. SO2 has also been suggested to potentiate carcinogenic effects of PAH. However, the molecular basis of these toxic effects is unclear. We have examined the covalent reaction of SO2 and sulfite with cellular proteinacious and nonproteinaceous sulfhydryl compounds using rat liver, and lung and human lung derived A549 cells. Reactions of sulfite and protein in rat and human lung cells reveals at least three proteins with sulfite-reactive disulfide bonds. Besides fibronectin and serum albumin, which had been reported to contain sulfonated products following exposure to sulfite, we have found one other protein with sulfite-binding capabilities. Since the integrity of disulfide bonds is crucial to the tertiary structure and thus protein function, the disruption of protein structure by sulfitolysis may result in altered cellular activities leading to biochemical lesions. Using carefully controlled conditions, reproducible GSH contents can be found in cultured cells and used as an experimental basis for studying alterations in the GSH and GSSG content of cells. Sulfitolysis of GSSG results in the formation of GSSO3H in A549 cells, and possibly in the lung. GSSO3H can be reduced enzymatically by GSSG reductase. However, the Km of GSSO3H is high compared to that of GSSG, suggesting the existence of a transient concentration of GSSO3H once it is formed. Cysteine S-sulfonate is, however, not reduced by cytosolic extracts in the presence of NADPH and would have to be eliminated from the cell by other means. GSSO3H is a strong competitive inhibitor of GST in rat liver and lung and A549 cells, using 1-chloro-2,4-dinitrobenzene as a substrate. It also inhibits the formation of GSH conjugates of BP 4,5-oxide, anti and syn BPDE, but to a lesser extent. These results suggest that SO2 may affect the detoxification of xenobiotic compounds by inhibiting, via formation of GSSO3H, the enzymatic conjugation of GSH and reactive electrophiles. Since GSH conjugation represents the major pathway of elimination of BP epoxides in the lung, our results offer a possible explanation for the cocarcinogenicity of SO2 with PAHs. These data suggest that the sulfitolysis reaction of sulfite is the common reaction mechanism mediating the underlying biochemical reactions leading to both the toxic and cocarcinogenic properties of SO2. Quantitation of sulfitolysis products and their interaction with cellular processes should provide a coherent scheme relating SO2 and sulfite toxicity among animal species and humans.

Effect of dietary polyunsaturated fat and 7,12-dimethylbenz(a)-anthracene on rat splenic natural killer cells and prostaglandin E synthesis

Dietary polyunsaturated fat has been shown to stimulate mammary tumorigenesis induced in rats by 7,12-dimethylbenz(a)anthracene (DMBA). Studies were undertaken to investigate the effect of polyunsaturated fat and DMBA on splenic natural killer (NK) activity and prostaglandin E (PGE) synthesis. In a first experiment, splenic NK activity at 33, 55, 75, and 110 days of age was measured in Sprague-Dawley rats fed 0.5% low fat (LF), 5% normal fat (NF), or 20% high fat (HF) corn oil diets from 23 days of age. At 55 days of age, half of the rats from the 75 and 110 day age groups were given 5 mg DMBA. Ten days after the initiation of the diets splenic NK activity against YAC-1 lymphoma was decreased from 50% cytotoxicity in rats fed NF diet to 21% cytotoxicity in rats fed HF diet, but was not affected by LF feeding. No difference in NK activity was observed among the groups at the later time periods. DMBA had no effect on NK activity at 20 or 55 days after its administration. In a second experiment, where DMBA (15 mg/rat) was given to half of the rats at 50 days of age and NF or HF diets were started 3 days later, NK activity was 35% in rats fed NF diet and 21% in rats fed HF diet, 5 days after the diets were started. No difference in NK activity in rats fed either diet was observed at later time periods. DMBA decreased both NK activity and spleen cellularity transiently. In both experiments, PGE synthesis by spleen cells cultured for 18 h was not affected by dietary fat intake, but was slightly increased 3 days after DMBA administration. Results from these experiments suggest that the stimulation of DMBA-induced mammary tumorigenesis by polyunsaturated fat and by DMBA itself may possibly be mediated by a transient decrease in splenic NK cell activity.

Glutathione S-sulfonate, a sulfur dioxide metabolite, as a competitive inhibitor of glutathione S-transferase, and its reduction by glutathione reductase

Glutathione S-sulfonate (GSSO3H) is a reaction product of glutathione disulfide (GSSG) and sulfite, the hydrated form of sulfur dioxide. In the present study, GSSO3H was found to be a potent competitive inhibitor of the glutathione S-transferases (GST) in the rat liver (Ki = 14 microM) and lung (Ki = 9 microM), and in human lung tumor-derived A549 cells (Ki = 4 microM). GSSO3H was also reduced by a cytosolic enzyme in the rat liver (Km = 313 microM) and lung (Km = 200 microM), and human lung A549 cells (Km = 400 microM). These results suggest that SO2 may affect the detoxification of xenobiotic compounds by inhibiting, via formation of GSSO3H, the enzymatic conjugation of glutathione (GSH) and reactive electrophiles. Although GSSO3H can be enzymatically degraded, the high substrate Km value suggests that this compound may not be readily reduced at low concentrations.

Mechanism of DNA methylation by N-nitroso(2-oxopropyl)propylamine

Using an in vitro assay system for measuring 7-methylguanine formation in DNA, it was demonstrated that N-nitroso(2-oxopropyl)propylamine (NOPPA) is converted into a methylating agent by a microsomal, cytochrome P-450 dependent mixed function oxidase from rat liver. Formation of propionaldehyde, but not formaldehyde, in this assay system, indicated that a single alpha-oxidation reaction on the propyl side chain of NOPPA leads to the formation of a methylating agent. A mechanism for this reaction is proposed.

Regulation of rat natural killing. I. Inhibition of cytolysis and activation by protein synthesis inhibitors

Rat splenic natural killer (NK) cell activity against 51Cr-labeled YAC-1 or TMT-081 tumor cells can be augmented by culturing at 37 degrees C for 18 h. The protein synthesis inhibitors, cycloheximide and emetine, inhibited such NK activation and also inhibited NK lysis when added directly to the NK assay. Both drugs also inhibited conjugation of effector cells to target cells. The inhibitory effect of cycloheximide on both the NK lysis and NK activation was reversible while that of emetine was irreversible. Both agents were able to inhibit 3H-amino acid incorporation at the concentrations that inhibited NK activity and activation. Culture-activated NK cells were found to be less susceptible to inhibition by cycloheximide and emetine.

Regulation of human natural killing. III. Mechanism for interferon induction of loss of susceptibility to suppression by cyclic AMP elevating agents

In this study we demonstrated that human NK cells activated by IFN or poly I:C were partially resistant to suppression by PGE2, PGD2, PGA2, PGI2, dibutyryl cAMP, isoproterenol, and theophylline. This partial loss of inhibition was not due to endogenous PG production because the addition of indomethacin to cultures stimulated with IFN or poly I:C did not prevent the partial loss of sensitivity to PGE2. NK cells incubated in the presence of PGE2 overnight, however, were not sensitive to inhibition. IFN or poly I:C did not stimulate PG synthesis nor elevate intracellular cAMP levels of NK cells. On the other hand, IFN or poly I:C diminished the accumulation of intracellular cAMP levels in NK cells in response to PGE2 stimulation. Dibutyryl cAMP and theophylline suppressed the cytolytic activity of the unstimulated cells more than that of the activated cells. A possible mechanism for the IFN-induced unresponsiveness to PGE2 may be a compartmentalized loss of cAMP responsiveness. Cycloheximide, puromycin, emetine, and actinomycin D blocked NK activation by IFN and poly I:C as well as the acquisition of resistance to PGE2-mediated suppression.

Regulation of human natural killing. III. Mechanism for interferon induction of loss of susceptibility to suppression by cyclic AMP elevating agents

In this study we demonstrated that human NK cells activated by IFN or poly I:C were partially resistant to suppression by PGE2, PGD2, PGA2, PGI2, dibutyryl cAMP, isoproterenol, and theophylline. This partial loss of inhibition was not due to endogenous PG production because the addition of indomethacin to cultures stimulated with IFN or poly I:C did not prevent the partial loss of sensitivity to PGE2. NK cells incubated in the presence of PGE2 overnight, however, were not sensitive to inhibition. IFN or poly I:C did not stimulate PG synthesis nor elevate intracellular cAMP levels of NK cells. On the other hand, IFN or poly I:C diminished the accumulation of intracellular cAMP levels in NK cells in response to PGE2 stimulation. Dibutyryl cAMP and theophylline suppressed the cytolytic activity of the unstimulated cells more than that of the activated cells. A possible mechanism for the IFN-induced unresponsiveness to PGE2 may be a compartmentalized loss of cAMP responsiveness. Cycloheximide, puromycin, emetine, and actinomycin D blocked NK activation by IFN and poly I:C as well as the acquisition of resistance to PGE2-mediated suppression.

Studies on the metabolic activation of beta-keto nitrosamines: mechanisms of DNA methylation by N-(2-oxopropyl)-N-nitrosourea and N-nitroso-N-acetoxymethyl-N-2-oxopropylamine

At pH 7.35, N-(2-oxopropyl)-N-nitrosourea (OPNU) reacted with calf thymus DNA to yield O6-methylguanine, 7-methylguanine and 3-methyladenine. Kinetic measurements of the base catalyzed decomposition of OPNU and the extent of methylation of DNA by OPNU suggested that methylnitrosourea is not formed as an intermediate product. Diazoacetone, acetic acid and methanol were identified as products of decomposition of OPNU at pH 7.35. Reaction of OPNU with N-methylmaleimide yielded the product resulting from 1,3-dipolar cycloaddition of diazomethane. Hydrolysis of N-nitroso-N-acetoxymethyl-N-2-oxopropylamine (NAMOPA) in the presence of hog liver esterase also produced diazoacetone, acetic acid and methanol. Enzymatic hydrolysis of NAMOPA in the presence of DNA produced O6-methylguanine, 7-methylguanine and 3-methyladenine. These results suggest that OPNU undergoes base-catalyzed decomposition and NAMOPA undergoes enzymatic hydrolysis to yield the same intermediate, 2-oxopropyldiazotate. This diazotate then reacts either by protonation followed by loss of water to form diazoacetone, or by internal nucleophilic attack by the diazotate oxygen on the carbonyl carbon to form an oxadiazoline intermediate which then collapses to form acetate and the methylating agent diazomethane. These reaction schemes are used to suggest the mechanism by which N-nitroso-2-oxopropylpropylamine methylates hepatic DNA in vivo.

Enzymatic reduction of beta-ketonitrosamines

The reduction of N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-oxopropyl)propylamine (NOPPA) by hepatic and pancreatic cytosol and microsomes from Syrian golden hamsters and Sprague-Dawley rats has been examined. All hepatic fractions reduced both substrates, although the activity depended on the fraction tested and the cofactor employed (NADH or NADPH). Generally, hamster hepatic fractions contained higher activity than the rat hepatic fractions and BOP was a better substrate than NOPPA. Of the pancreatic fractions, only cytosol exhibited reductase activity. The hamster cytosol was able to utilise both cofactors, but the rat fraction exhibited activity only when NADPH was present. BOP was the better substrate for the pancreatic enzymes and in the presence of NADPH, the rat and hamster activities were about equal. These results suggest that the pancreatic reduction of BOP to HPOP is unlikely to be a significant factor in the species-specific induction of pancreatic cancer by BOP.

Erythromyeloid tumor cells (K562) induce PGE synthesis in human peripheral blood monocytes

Human peripheral blood monocytes were found to spontaneously produce prostaglandin of the E series (PGE) in culture medium (0.5 ng to 3.0 ng/7.5 X 10(5) cells), and the addition of K562 tumor cells enhanced the production by five- to 15-fold after 18 hr of incubation. PGE2 (10(-6) M) inhibited the cytolytic activity of freshly isolated peripheral blood monocytes against K562 target cells by 50%. The PGE production was inhibited by inhibitors of cyclo-oxygenase (indomethacin, aspirin, and ETYA) when present during the incubation. However, pretreatment of monocytes with these cyclo-oxygenase inhibitors was ineffective in preventing PGE production. Kinetic experiments showed that appreciable stimulation of PGE production occurred only after 6 hr of co-culture. Other human tumor cell lines (HSB, SB, and CEM) enhanced PGE production upon co-culture with monocytes but to a lesser extent (twofold to threefold). Monocytes treated with 0.4% formaldehyde or heat (56 degrees C) were not capable of producing PGE when cultured alone or with K526 tumor cells. In contrast, formaldehyde-treated, but not heat-treated, K562 tumor cells were able to induce monocytes to produce PGE. By using a single cell conjugation assay, K562 tumor cells were found to bind equally well to treated or untreated monocytes. In contrast, the lytic activity of treated monocytes against K562 target cells was abolished. The presence of protein synthesis inhibitor, cycloheximide, was found to inhibit PGE production by monocytes cultured alone or with K562 tumor cells. Supernatants from K562 tumor cell cultures were also capable of inducing monocytes to produce PGE, and their effect on PGE production from monocytes was suppressed by cycloheximide. In addition, pretreatment of either K562 tumor cells or monocytes with an irreversible protein synthesis inhibitor, emetine, also suppressed the production of PGE upon co-culture with the untreated counterpart. The production of PGE by monocytes in response to exposure to tumor cells may represent a mechanism whereby tumor cells subvert host immune defense against them.

Erythromyeloid tumor cells (K562) induce PGE synthesis in human peripheral blood monocytes

Human peripheral blood monocytes were found to spontaneously produce prostaglandin of the E series (PGE) in culture medium (0.5 ng to 3.0 ng/7.5 X 10(5) cells), and the addition of K562 tumor cells enhanced the production by five- to 15-fold after 18 hr of incubation. PGE2 (10(-6) M) inhibited the cytolytic activity of freshly isolated peripheral blood monocytes against K562 target cells by 50%. The PGE production was inhibited by inhibitors of cyclo-oxygenase (indomethacin, aspirin, and ETYA) when present during the incubation. However, pretreatment of monocytes with these cyclo-oxygenase inhibitors was ineffective in preventing PGE production. Kinetic experiments showed that appreciable stimulation of PGE production occurred only after 6 hr of co-culture. Other human tumor cell lines (HSB, SB, and CEM) enhanced PGE production upon co-culture with monocytes but to a lesser extent (twofold to threefold). Monocytes treated with 0.4% formaldehyde or heat (56 degrees C) were not capable of producing PGE when cultured alone or with K526 tumor cells. In contrast, formaldehyde-treated, but not heat-treated, K562 tumor cells were able to induce monocytes to produce PGE. By using a single cell conjugation assay, K562 tumor cells were found to bind equally well to treated or untreated monocytes. In contrast, the lytic activity of treated monocytes against K562 target cells was abolished. The presence of protein synthesis inhibitor, cycloheximide, was found to inhibit PGE production by monocytes cultured alone or with K562 tumor cells. Supernatants from K562 tumor cell cultures were also capable of inducing monocytes to produce PGE, and their effect on PGE production from monocytes was suppressed by cycloheximide. In addition, pretreatment of either K562 tumor cells or monocytes with an irreversible protein synthesis inhibitor, emetine, also suppressed the production of PGE upon co-culture with the untreated counterpart. The production of PGE by monocytes in response to exposure to tumor cells may represent a mechanism whereby tumor cells subvert host immune defense against them.