Increased angiotensin II type 1 receptor expression in hypercholesterolemic atherosclerosis in rabbits

Angiotensin II (Ang II) promotes vascular smooth muscle growth and may be involved in the initiation and progression of atherosclerosis. To examine whether Ang II receptor expression in vascular tissues is altered in atherosclerosis, male New Zealand White rabbits were fed a high-cholesterol diet (1% cholesterol + 4% coconut oil mixed with regular chow; hypercholesterolemic group, n=12) or regular chow (control group, n=8) for 10 weeks. At the end of this period, the serum cholesterol level in the rabbits fed the high-cholesterol diet was higher than that in the control group (3616 +/- 144 versus 30 +/- 1 mg/dL, P<0.001). There was no atherosclerosis in the aortas of the control group, whereas 51 +/- 6% of the aorta was covered with atherosclerosis in the hypercholesterolemic group. Total Ang II receptor expression in the atherosclerotic aortic tissues was increased 5-fold in the hypercholesterolemic rabbits (292 +/- 28 versus 51 +/- 32 fmol/mg tissue, mean +/- SE, P<0.001), and the increased Ang II receptor expression was entirely due to enhanced Ang II type 1 (AT1) receptor expression (289 +/- 38 versus 38 +/- 18 fmol/mg, P<0.001), as Ang II type 2 receptor expression was unaltered (7 +/- 5 versus 3 +/- 2 fmol/mg, P=NS). AT1 receptors were localized primarily in the media and to some extent in the intima of the atherosclerotic aorta, as determined by immunohistochemistry with specific monoclonal and polyclonal AT1 receptor antibodies. Increased synthesis of AT1 receptor mRNA in atherosclerotic tissues was confirmed by reverse transcription-polymerase chain reaction. To evaluate the functional significance of increased AT1 receptor expression, the constrictor response of aortic rings to Ang II was examined and found to be markedly enhanced in atherosclerotic aortic rings (P<0.01 versus control aortic rings). The endothelium-dependent relaxation of aortic rings from hypercholesterolemic rabbits was markedly attenuated (P<0.001). This study shows that hypercholesterolemia in rabbits results in atherosclerosis, loss of endothelium-dependent relaxation, and increased Ang II receptor (entirely AT1 receptor) expression in aortic tissues, which may result in altered vasoreactivity.

Crowded little caves: structure and function of caveolae

Caveolae are small vesicular invaginations of the cell membrane. It is within this organelle that cells perform transcytosis, potocytosis and signal transduction. These "little caves" are composed of a mixture of lipids and proteins unlike those found in the plasma membrane proper. The chief structural proteins of caveolae are caveolins. To date, three caveolins (Cav-1, -2 and -3) with unique tissue distributions have been identified. Caveolins form a scaffold onto which many signalling molecules can assemble, to generate pre-assembled signalling complexes. In addition to concentrating these signal transducers within a distinct region of the plasma membrane, caveolin binding may functionally regulate the activation state of caveolae-associated signalling molecules.

Early diagnosis of mycotic keratitis: predictive value of potassium hydroxide preparation

Potassium hydroxide (KOH) preparation is an underutilized modality in the diagnosis of mycotic keratitis. We have earlier shown its utility in the diagnosis of Nocardia and Acanthamoeba keratitis. The aim of this study was (i) to evaluate the sensitivity, specificity and predictive value of KOH preparation, and (ii) to compare its efficacy with other methods of corneal scraping examination, for the diagnosis of mycotic keratitis. The study was conducted in two phases. In phase I, randomized corneal scrapings were examined by KOH, Gram's stain, and lactophenol cotton blue (LPCB) in 91 infectious keratitis subjects. In phase II, 53 corneal scrapings were stained with KOH and calcofluor white (CFW), and viewed with bright field (KOH) and fluorescence (CFW) microscopy. The KOH and CFW readings were recorded by an observer masked to the clinical findings and culture results. Nineteen scrapings were examined by two masked observers. In 22 culture positive fungal keratitis patients in phase I, the sensitivity of KOH, Gram's stain, and LPCB methods was 100%, 86.4%, and 77.3%, respectively. In phase II, the specificities of KOH and CFW were identical (83.8%), while the sensitivities were 81.2% and 93.7%, respectively (p = 0.59), in 16 culture positive mycotic keratitis patients. There was no significant difference between the negative and positive predictive values of KOH and CFW. Furthermore, no significant interobserver variability was found in the specificity and sensitivity. The KOH method compares well with other microscopy methods in the diagnosis of keratomycosis and has a definite place in the armamentarium of diagnostic techniques.

Aggregation of amyloid beta-protein as function of age and apolipoprotein E in normal and Alzheimer's serum

We compared the effect of serum from (a) 26 Alzheimer's disease (AD) patients and 22 age-matched non-demented controls (CO) with apolipoprotein E 4/4, 3/3 or 3/2 phenotypes, and (b) 17 normal young (aged 15-41 years) and 21 normal elderly (aged 64-83 years) people on in vitro aggregation of synthetic amyloid beta-protein (A beta) 1-40 by Thioflavin T fluorescence spectroscopy. A beta 1-40 aggregation in presence of serum from the normal elderly group was significantly higher as compared to the normal young group (correlation coefficient between age and A beta aggregation=0.73). However, no difference in A beta aggregation was observed in the presence of serum from AD patients and non-demented controls. There was a positive correlation between serum apo E concentrations and A beta aggregation, while there was no significant difference between different apo E phenotypes. The correlation coefficient in the AD 4/4 (0.65) was higher than the CO 4/4 group (0.04), while it was lower in the AD 3/3 group (-0.12) than in the CO 3/3 (0.39) group. These results suggest that the apo E4 allele alone may not be responsible for A beta fibril formation in AD; other factors may be involved in increasing risk for AD pathogenesis in those having the apo E4 allele. The severity of dementia and serum albumin levels also did not correlate with A beta aggregation. We propose that the age of an individual may be an important factor in determining the degree of A beta aggregation/fibrillization, and that mechanism of sequestration of A beta in serum may not be defective in AD.

Does sleep promote recovery after bone marrow transplantation?--A hypothesis

Bone marrow transplantation is increasingly being used for treatment of patients with malignant and hematologic disorders. The process requires 4-6 wk of waiting for recovery from conditioning regimens and for engraftment. Patients undergo intensive monitoring and supportive care, yet their requirements for deep uninterrupted sleep often go unrecognized. We suggest that deep sleep may promote recovery and stem cell proliferation through production of growth hormone and melatonin, and through other mechanisms. Growth hormone production occurs primarily during deep, rapid-eye-movement (REM) sleep. Growth hormone promotes nutritional recovery, mucosal healing, cellular uptake of amino acids, and promotes proliferation of bone marrow cell lines in animal models. Melatonin is also secreted during nighttime and during sleep. Melatonin increases immune response, inhibits tumor growth, counteracts stress-induced immunosuppression, protects against viral infections, stimulates GM-CSF, salivary IgA, antioxidant properties and enhances sleep. In our preliminary studies, we have found that most patients undergoing bone marrow transplantation complain of sleep disturbances related to laminar air flow noise-beepers, and lights. We recommend several simple methods of enhancing sleep and for more research in the pathophysiology of sleep and bone marrow transplantation.

Platelet-Mediated Cardioprotective Effect Against Ischemia-Reperfusion Injury in Isolated Rat Hearts: Role of Platelet Number and Contribution of Supernatant of Aggregated Platelets

BACKGROUND: Previous studies have documented cardioprotective effects of circulating platelets after reperfusion injury. The present study was designed to examine the role of platelet number and contribution of platelet-released mediators in the platelet supernatant in cardioprotection against ischemia-reperfusion-induced myocardial dysfunction. METHODS AND RESULTS: Isolated buffer-perfused (constant volume) Sprage-Dawley rat hearts were subjected to 25 minutes of global ischemia followed by 30 minutes of reperfusion. Ischemia-reperfusion resulted in myocardial dysfunction, indicated by an increase in coronary perfusion pressure and left ventricular end-diastolic pressure, and a decrease in developed left ventricular pressure. Perfusion of hearts with washed rat platelets (10(3)-2.2 x 10(7) cells/mL) significantly (P <.01) attenuated these indices of myocardial dysfunction upon ischemia-reperfusion in a concentration-dependent manner. A cardioprotective effect of platelets was observed at a concentration as low as 10(5) platelets/mL. Similar cardioprotection was seen in hearts perfused with the supernatant of aggregated platelets. CONCLUSIONS: These observations indicate that the platelet-mediated cardioprotective effect against ischemia-reperfusion in vitro is concentration dependent, and platelet-released mediators in the platelet supernatant are protective against ischemia-reperfusion injury.

Use of alternative therapies for children with cancer

OBJECTIVE

To compare the use of alternative therapy (AT) in families of children with cancer with its use in those with routine pediatric conditions.

BACKGROUND AND RATIONALE

AT refers to healing practices such as therapeutic massage, acupuncture, and use of medicinal herbs that have become increasingly popular with the general public, but are not widely accepted by the medical profession. Although studies have investigated the use of AT in the families of both healthy children and children with cancer, no comparison of the incidence of its use between these two populations has been published. We hypothesized that AT was used more frequently among the families of children with cancer.

METHODS

Using a prevalence survey design, we interviewed 81 parents of children with cancer attending a pediatric hematology/oncology clinic and 80 parents of children attending a continuity care clinic for routine check-ups and acute care. We explored the types of AT being used, the reasons for its use, and the frequency with which it was discussed with the patient's physician.

RESULTS

1) Overall, 65% of the cancer group were using AT, compared with 51% of the control group. This was not statistically significant. 2) Prayer, exercise, and spiritual healing were three AT practices most often used by the cancer group, and prayer, massage, and spiritual healing by the control group. 3) Discussion of AT with the physician varied according to group, with 53% of the cancer patients discussing its use; income level, with 59% of parents in the higher income group discussing its use; and ethnicity, with 47% of whites discussing its use.

CONCLUSION

Use of AT is not limited to the families of children with life-challenging illnesses, but is commonly used by those of children with routine pediatric problems. Pediatricians need to be aware that their patients may not tell them about AT practices they are using in addition to prescribed treatment.

Characterization of beta-amyloid peptide precursor processing by the yeast Yap3 and Mkc7 proteases

Two proteases, denoted beta- and gamma-secretase, process the beta-amyloid peptide precursor (APP) to yield the Abeta peptides involved in Alzheimer's disease. A third protein, alpha-secretase, cleaves APP near the middle of the Abeta sequence and thus prevents Abeta formation. These enzymes have defied identification. Because of its similarity to the systems of mammalian cells the yeast secretory system has provided important clues for finding mammalian processing enzymes. When expressed in Saccharomyces cerevisiae APP is processed by enzymes that possess the specificity of the alpha-secretases of multicellular organisms. APP processing by alpha-secretases occurred in sec1 and sec7 mutants, in which transport to the cell surface or to the vacuole is blocked, but not in sec17 or sec18 mutants, in which transport from the endoplasmic reticulum to the Golgi is blocked. Neutralization of the vacuole by NH4Cl did not block alpha-secretase action. The time course of processing of a pro-alpha-factor leader-APP chimera showed that processing by Kex2 protease, a Golgi protease that removes the leader, preceded processing by alpha-secretase. Deletions of the genes encoding the GPI-linked aspartyl proteases Yap3 and Mkc7 decreased alpha-secretase activity by 56 and 29%, respectively; whereas, the double deletion decreased the activity by 86%. An altered form of APP-695, in which glutamine replaced Lys-612 at the cleavage site, is cleaved by Yap3 at 5% the rate of the wild-type APP. Mkc7 protease cleaved APP (K612Q) at about 20% the rate of wild-type APP. The simplest interpretation of these results is that Yap3 and Mkc7 proteases are alpha-secretases which act on APP in the late Golgi. They suggest that GPI-linked aspartyl proteases should be investigated as candidate secretases in mammalian tissues.

Soluble monomeric P-selectin containing only the lectin and epidermal growth factor domains binds to P-selectin glycoprotein ligand-1 on leukocytes

Under shear stress, leukocytes use P-selectin glycoprotein ligand-1 (PSGL-1) to tether to and roll on P-selectin expressed on activated platelets or endothelial cells. P-selectin has an NH2-terminal lectin domain, an epidermal growth factor (EGF)-like motif, nine consensus repeats (CRs), a transmembrane domain, and a cytoplasmic tail. To determine whether the CRs are required for P-selectin to bind PSGL-1, we expressed a soluble protein (Lec-EGF) that contained only the lectin and EGF domains, plus a short C-terminal epitope tag. Electron microscopy and hydrodynamic analysis confirmed that Lec-EGF was monomeric, as previously shown for soluble P-selectin (sPS) that contained the lectin and EGF domains plus all nine CRs. Fluid-phase Lec-EGF or sPS inhibited binding of oligomeric125I-labeled membrane-derived P-selectin (mPS) to PSGL-1 on neutrophils and binding of 125I-PSGL-1 to immobilized mPS. The IC50 for inhibiting binding of mPS to neutrophils was fivefold greater for Lec-EGF than for sPS, whereas the IC50 for inhibiting binding of mPS to purified PSGL-1 was indistinguishable for Lec-EGF and sPS. Under static or shear conditions, neutrophils used PSGL-1 to tether to or roll on Lec-EGF that was captured by an immobilized monoclonal antibody to the C-terminal epitope. These data show that P-selectin requires only the lectin and EGF domains to bind to PSGL-1.

Keratinocyte growth factor expression in hormone insensitive prostate cancer

Cellular interactions between stroma and epithelium are important in the growth and proliferation of prostate cancer. Peptide growth factors may facilitate the progression of prostate cancer as autocrine and/or paracrine factors. Keratinocyte Growth Factor (KGF or FGF7) has a differentiative and proliferative effect on the epithelium of the developing rat prostate. We investigated if KGF may act as a paracrine agent in human prostate cancer and examined the expression of KGF and Fibroblast Growth Factor Receptors (FGFRs) (IIIb and IIIc isoforms of the FGFR1 and FGFR2 genes). Sixty-five percent (11 out of 17 informative cases) of prostate cancers (CaP) expressed KGF mRNA by RT-PCR, while KGF expression was not detected in benign prostatic hyperplasia (BPH) (n = 6). Upregulation of KGF expression was related to hormone insensitive tumours (P<0.05). Tumour grade and stage were not associated with KGF expression. The source of KGF expression was further characterised using an in vitro primary culture model, showing its restriction to the prostatic stroma. The FGFR1IIIb isoform was expressed in all cases of prostate cancer (n = 17), and FGFR1IIIc mRNA was not detected. In the BPH group, FGFR1IIIb transcripts were detected in four out of six cases. FGFR2IIIb expression was detected in five of six cases of BPH and twelve out of seventeen (71%) cases of prostate cancer. In CaP, though not reaching statistical significance, the persistence of FGFR2IIIb expression appeared to be associated with hormone insensitive tumours (P=0.052). FGFR2IIIc expression was present in eleven of seventeen tumours but was absent in all six cases of BPH. Functional assessment of recombinant KGF in a proliferation assay demonstrated a mitogenic effect of up to 100% on cultured prostatic epithelial cells.

Increase in angiotensin II type 1 receptor expression immediately after ischemia-reperfusion in isolated rat hearts

BACKGROUND

Myocardial ischemia is known to upregulate the systemic renin-angiotensin system, which influences myocardial ischemic events by affecting hemodynamics and hemostatic activity. This study was designed to examine whether angiotensin II (Ang II) receptor expression in the myocardium is altered immediately after ischemia-reperfusion.

METHODS AND RESULTS

Isolated buffer-perfused Sprague-Dawley rat hearts were subjected to continuous perfusion (control, n=5) or to 25 minutes of global ischemia followed by 30 minutes of reperfusion (n=10). Autoradiographic analysis for Ang II receptors of multiple myocardial sections was performed. Whereas continuous perfusion of hearts resulted in minor changes in coronary perfusion pressure (CPP), left ventricular end-diastolic pressure (LVEDP), and developed left ventricular pressure (dLVP=LVSP-LVEDP), ischemia-reperfusion caused a marked increase in CPP and LVEDP and a decrease in dLVP, indicating severe cardiac dysfunction. Concurrently, total myocardial Ang II receptor expression was greater (P<.05) in hearts subjected to ischemia-reperfusion than in the continuously perfused control hearts. Most of the increase in Ang II receptor expression was due to an increase in type 1 receptor (AT1) expression (34.6+/-6.5 versus 18.2+/-4.4 fmol/g, P<.05), because Ang II type 2 receptor expression was unaffected. To examine the importance of AT1 receptor expression, another group of isolated rat hearts (n=5) was perfused with buffer containing losartan (10(-5) mol/L) and subjected to ischemia followed by reperfusion. Perfusion of hearts with losartan attenuated the ischemia-reperfusion-induced cardiac dysfunction. Perfusion of hearts with losartan also blocked the ischemia-reperfusion-induced increase in myocardial AT1 binding.

CONCLUSIONS

These observations indicate that myocardial AT1 expression increases immediately after ischemia-reperfusion and contributes to cardiac dysfunction.

Psychometric properties of family members' reports of parental physical aggression toward clinic-referred children

This study examined (a) differences among mothers', fathers', and children's reports of parental physical aggression toward children; (b) the reliability and validity of family members' reports of aggression using confirmatory factor analysis; and (c) the discriminant validity of the constructs of mother-child and father-child aggression. Participants were 72 dual-parent families in which the parents were seeking clinical services for their children's (ages 7-9 years) conduct behavior problems. Each participant completed the parent-child version of the Conflict Tactics Scale (P-CTS). Results indicate that children reported lower levels of mother-child and father-child aggression than either mothers or fathers reported. Although the reliability (total systematic variance accounted for by observed variables) of family members' reports on the P-CTS ranged from moderate to high, convergent validity was generally low. The constructs of mother-child and father-child aggression were highly correlated but could be distinguished from each other when relationships among rater effects were considered.

Nitric Oxide Synthesis Inhibition and Role of P-selectin in Leukocyte Adhesion to Vascular Tissues

BACKGROUND: This study was designed to examine the role of P-selectin expression in leukocyte adhesion to endothelium caused by inhibition of nitric oxide synthesis. METHODS AND RESULTS: Rat aortic rings were treated with the nitric oxide synthesis inhibitor N(omicron)-nitro-l-arginine methyl ester (l-NAME) for 2 hours. Parallel sets of aortic rings were pretreated with the nitric oxide precursor l-arginine or posttreated with a specific monoclonal antibody against P-selectin. Some rings were used for determination of vasoreactivity in response to norepinephrine and acetylcholine, while other rings were incubated with autologous unlabeled leukocytes or Biotin-FITC labeled leukocytes for 30 minutes. Leukocyte adhesion to vascular endothelium was determined by scanning electron microscopy. l-NAME enhanced the contractile response in response to norepinephrine, suppressed the relaxant response to acetyleholine, promoted leukocyte adherence to the endothelium and resulted in P-selectin expression on the aortic endothelium. Pretreatment of aortic rings with l-arginine reversed the l-NAME-mediated changes in vasoreactivity in response to norepinephrine and acetyleholine and attenuated the l-NAME-enhanced leukocyte adhesion to endothelial intima. P-selectin treatment, on the other hand, had no effect on l-NAME-mediated changes. Intraperitoneal administration of l-NAME resulted in a significant decrease in plasma nitrite level, a small, but significant, increase in lung and spleen myeloperoxidase activity, and a significant increase in leukocyte deposition in lung and spleen. The l-NAME-mediated increase in myeloperoxidase activity and leukocyte deposition in the spleen, but not in the lungs, was abolished by treatment of rats with the P-selectin antagonist CY1503 administered 30 minutes prior to l-NAME. CONCLUSIONS: These observations indicate that a reduction in nitric oxide synthesis enhances leukocyte adhesion to aortic endothelium and in visceral tissues. While P-selectin expression is evident in some of the experimental models of leukocyte adhesion to endothelium under conditions of nitric oxide inhibition, the role of P-selectin expression remains unclear.

Psychometric properties of family members' reports of parental physical aggression toward clinic-referred children

This study examined (a) differences among mothers', fathers', and children's reports of parental physical aggression toward children; (b) the reliability and validity of family members' reports of aggression using confirmatory factor analysis; and (c) the discriminant validity of the constructs of mother-child and father-child aggression. Participants were 72 dual-parent families in which the parents were seeking clinical services for their children's (ages 7-9 years) conduct behavior problems. Each participant completed the parent-child version of the Conflict Tactics Scale (P-CTS). Results indicate that children reported lower levels of mother-child and father-child aggression than either mothers or fathers reported. Although the reliability (total systematic variance accounted for by observed variables) of family members' reports on the P-CTS ranged from moderate to high, convergent validity was generally low. The constructs of mother-child and father-child aggression were highly correlated but could be distinguished from each other when relationships among rater effects were considered.

Platelet inhibitory effect of nitroglycerin in platelet-rich plasma: relevance of glutathione-s-transferases in plasma

BACKGROUND

Nitroglycerin (NTG) is believed to exert its platelet inhibitory effect via its biotransformation to nitric oxide (NO). We examined the relevance of glutathione-s-transferases (GST) in plasma in the conversion of NTG to NO and the platelet inhibitory effect of NTG.

METHODS AND RESULTS

Nitroglycerin (1-100 micrograms/mL) was incubated with human platelet-rich plasma (PRP) for 10-60 minutes. Nitroglycerin caused a concentration-dependent inhibition of platelet aggregation in PRP with IC50 approximately 50 micrograms/mL. NTG also enhanced nitrite levels in PRP and stimulated cyclic GMP accumulation in platelets. In contrast, when NTG was incubated with washed platelets (WP) in concentrations as high as 100 micrograms/mL, there was no inhibition of platelet aggregation, formation of nitrite, or accumulation of cGMP. However, treatment of WP suspension with authentic NO exhibited diminished platelet aggregation, suggesting that NTG delivers NO in plasma that subsequently inhibits platelet aggregation. In keeping with this concept, the aggregation inhibitory effect of NTG in PRP was blocked by oxyhemoglobin. The platelet aggregation inhibition by NTG was potentiated by propylthiouracil (600 micrograms/mL), a GST inducer, and antagonized by ketoprofen (100 micrograms/mL), a GST inhibitor. Direct measurement indeed showed significant GST activity in plasma (24 +/- 3 mU/mL).

CONCLUSIONS

We suggest that NTG inhibits platelet aggregation in PRP by its biotransformation to NO in plasma. The presence of GST, and perhaps other cofactors, in plasma is relevant in the platelet inhibitory effects of NTG in PRP.

Effect of cerebrospinal fluid from normal and Alzheimer's patients with different apolipoprotein E phenotypes on in vitro aggregation of amyloid beta-protein

We examined the effect of cerebrospinal fluid (CSF) from 23 Alzheimer's disease (AD) patients and 22 age-matched non-demented controls with apolipoprotein E4/4, 3/3, or 3/2 phenotypes on in vitro aggregation of amyloid beta-protein (A beta) 1-40 by Thioflavin T fluorescence spectroscopy. CSF from both AD and control groups inhibited A beta aggregation, as compared to that of phosphate buffered saline, in agreement with an earlier report (Wisniewski et al., 1993). However, there was significantly less aggregation of A beta in presence of CSF from AD than that from non-demented controls. The presence of CSF from controls with apoE3/3 phenotype resulted in higher A beta aggregation as compared to other phenotypes. There was a positive correlation between CSF apoE concentrations and A beta aggregation; whereas age, CSF soluble A beta levels or severity of dementia did not correlate with A beta aggregation. These results suggest that mechanism of sequestration of A beta in CSF may not be defective in AD. Amyloid formation in AD may be impact of altered balance of other factors such as amyloid-associated proteins/extracellular matrix components that can immobilize A beta in the brain, and promote its fibrillogenesis in AD.

Studies of vascular tolerance to nitroglycerin: effects of N-acetylcysteine, NG-monomethyl L-arginine, and endothelin-1

Development of vascular tolerance to nitroglycerin (NTG) has been attributed to sulfhydryl (SH) depletion, guanylate cyclase desensitization, or both. Controversy regarding the precise contribution of these mechanisms may be due to variations in experimental design. To examine further the biochemical basis of NTG tolerance, norepinephrine (NE)-precontracted rat aortic rings were exposed to NTG (10(-5)M), which resulted in 84 +/- 6% relaxation. Other rings were first superfused with NTG (10(-6)M) and then contracted with NE. These rings showed a marked tolerance to the vasorelaxant effects of NTG (maximal relaxation 20 +/- 5%, n = 15, p < 0.001 vs. control rings). Similar tolerance to NTG was observed when the vascular rings were first superfused with acetylcholine (ACh 10(-6)M), indicating cross-tolerance between ACh and NTG. Treatment of NTG-tolerant rings with N-acetylcysteine (NAC) (10(-5)M) did not restore vascular smooth muscle (VSM) relaxation in response to NTG (maximal relaxation 23 +/- 5%, n = 8), suggesting that SH depletion may not be the basis of NTG tolerance in these experiments. Parallel sets of NTG-tolerant aortic rings were contracted with endothelin-1 (ET-1, n = 5) or the endothelium-derived relaxing factor (EDRF) synthase inhibitor NG-monomethyl L-arginine (L-NMMA, 10(-4)M, n = 8). In both ET-1- and L-NMMA-contracted rings, vascular relaxation in response to NTG was preserved (80 +/- 6 and 88 +/- 8% relaxation, respectively). Measurement of cyclic GMP in aortic rings showed marked accumulation on initial exposure of tissues to NTG (310 +/- 10 fmol/mg), whereas the NTG-tolerant rings showed much less cyclic GMP accumulation (48 +/- 29 fmol/mg). Rings contracted with L-NMMA or ET-1, but not NE, accumulated cyclic GMP when exposed to NTG (280 +/- 20 fmol/mg). These data indicate that NTG tolerance develops on exposure of vascular rings superfused with NTG or ACh and is probably not related to tissue SH depletion. Contraction of NTG-tolerant rings with ET-1 or L-NMMA restores NTG-mediated relaxation.

The design of agents to control DNA methylation adducts. Enhanced major groove methylation of DNA by an N-methyl-N-nitrosourea functionalized phenyl neutral red intercalator

An N-methyl-N-nitrosourea (MNU) moiety [CH3N(N=O)C(=O)NH-] linked to the C4'-position of the 5-substituted phenyl ring of phenyl neutral red (PNR), 2-methyl-3-amino-5-[p-[[2-[(N-nitroso-N-methylcarbamoyl)amino]ethy l] carbamoyl]phenyl]-7-(dimethylamino)phenazenium chloride (MNU-PNR), has been synthesized as an approach to design a molecule that will deliver alkylating agents with some preference to guanine (Gua) in the major groove of DNA. The PNR nucleus was chosen because previous studies suggested the following: (1) PNR binds with a slight preference for G/C rich sequences; and (2) PNR intercalates into DNA from the major groove with the 5-phenyl ring pointing out into the major groove (Müller, W., Bünemann, H., and Dattagupta, N. (1975) Eur. J. Biochem. 54, 279-291). It is demonstrated that MNU-PNR yields 2.6 and 6.0 times more N7-methylguanine (7-MeGua) than MNU at low salt (10 mM Tris buffer) and high salt (10 mM Tris buffer + 200 mM NaCl), respectively. It is also shown that the ratio of 7-MeGua (a major groove adduct) to N3-methyladenine (a minor groove adduct) is approximately 5 times higher for MNU-PNR than for MNU. The yield of the 7-MeGua adduct is decreased by the coaddition of a nonmethylating analogue of MNU-PNR or NaCl, but increased in the presence of the minor groove intercalator, ethidium bromide. Using a 32P-end-labeled restriction fragment, the enhanced methylation by MNU-PNR at 7-Gua is confirmed, and it is demonstrated that the sequence-dependent formation of 7-MeGua from MNU-PNR is the same as that seen with MNU. UV, circular dichrosism, and viscosity studies are consistent with MNU-PNR binding to DNA via an intercalation-based process.

Women and HIV infection

The pattern of the AIDS epidemic has recently changed with proportionately more women and children affected. Cases are becoming more widespread and heterosexual encounters are becoming an important means of spread of disease (presently 43% of all cases in the United States). Risks of contracting the virus depend upon sexual behaviors and the status of HIV disease in her partner. Manifestations of HIV infection are varied in women and include infections and cancer. Once the patient tests positive for HIV infection, she needs serial screening of blood counts, CD4 lymphocyte subsets and measurements of viral burdens. Antiretroviral therapy should be started when the CD4 count drops to under 500/d1, and prophylaxis against pneumocystis carinii and also for viral and mycobacterium avium infections when the CD4 count drops under 200/d1 and 100/d1 respectively. Pregnant women have a 25-33% risk of transmitting the disease to their fetus; this can be reduced through AZT treatment of the mother and of the baby after birth. Risk reduction through counseling about safer sex, e.g., abstinence, condom use, remains the best hope for protecting women against the HIV epidemic.

Oxidized LDL decreases L-arginine uptake and nitric oxide synthase protein expression in human platelets: relevance of the effect of oxidized LDL on platelet function

BACKGROUND

Oxidized LDL (ox-LDL) promotes vasoconstriction and platelet activation. The present study was undertaken to determine the involvement of the L-arginine-nitric oxide (NO) pathway in ox-LDL-mediated platelet activation.

METHODS AND RESULTS

Washed human platelets were incubated with native LDL or ox-LDL for 1 hour at 37 degrees C followed by measurement of platelet function and indexes of the L-arginine-NO pathway. Ox-LDL but not native LDL caused a concentration-dependent increase in thrombin-induced platelet aggregation and 14C-serotonin release. These effects of ox-LDL were inhibited by pretreatment of platelets with L-arginine, the precursor of NO. Ox-LDL also caused a concentration-dependent reduction in the uptake of 3H-L-arginine by platelets. In addition, NO synthase activity, measured as conversion of 3H-L-arginine to 3H-L-citrulline, decreased on incubation of platelet cytosol with ox-LDL. Nitrite production was also reduced by treatment of platelets with ox-LDL. These effects of ox-LDL on NO synthase activity and nitrite production were reversed by pretreatment of platelets with L-arginine. Concurrent with the decrease in NO production, cytosolic cGMP was inhibited in ox-LDL-treated platelets. The inhibitory effects of ox-LDL were dependent in part on the increase of cholesterol in the platelets. Western blot analysis demonstrated approximately 50% reduction in the expression of NO synthase protein in platelets treated with ox-LDL.

CONCLUSIONS

These observations indicate that the L-arginine-NO pathway is involved in the effects of ox-LDL on platelet function and that ox-LDL stimulates platelet function primarily by diminishing NO synthase expression as well as decreasing the uptake of L-arginine.