Biochemical reactivity of melatonin with reactive oxygen and nitrogen species: a review of the evidence

Melatonin (N-acetyl-5-methoxytryptamine), an endogenously produced indole found throughout the animal kingdom, was recently reported, using a variety of techniques, to be a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. Initially, melatonin was discovered to directly scavenge the high toxic hydroxyl radical (*OH). The methods used to prove the interaction of melatonin with the *OH included the generation of the radical using Fenton reagents or the ultraviolet photolysis of hydrogen peroxide (H202) with the use of spin-trapping agents, followed by electron spin resonance (ESR) spectroscopy, pulse radiolysis followed by ESR, and several spectrofluorometric and chemical (salicylate trapping in vivo) methodologies. One product of the reaction of melatonin with the *OH was identified as cyclic 3-hydroxymelatonin (3-OHM) using high-performance liquid chromatography with electrochemical (HPLC-EC) detection, electron ionization mass spectrometry (EIMS), proton nuclear magnetic resonance (1H NMR) and COSY 1H NMR. Cyclic 3-OHM appears in the urine of humans and other mammals and in rat urine its concentration increases when melatonin is given exogenously or after an imposed oxidative stress (exposure to ionizing radiation). Urinary cyclic 3-OHM levels are believed to be a biomarker (footprint molecule) of in vivo *OH production and its scavenging by melatonin. Although the data are less complete, besides the *OH, melatonin in cell-free systems has been shown to directly scavenge H2O2, singlet oxygen (1O2) and nitric oxide (NO*), with little or no ability to scavenge the superoxide anion radical (O2*-) In vitro, melatonin also directly detoxifies the peroxynitrite anion (ONOO-) and/or peroxynitrous acid (ONOOH), or the activated form of this molecule, ONOOH*; the product of the latter interaction is proposed to be 6-OHM. How these in vitro findings relate to the in vivo antioxidant actions of melatonin remains to be established. The ability of melatonin to scavenge the lipid peroxyl radical (LOO*) is debated. The weight of the evidence is that melatonin is probably not a classic chain-breaking antioxidant, since its ability to scavenge the LOO* seems weak. Its ability to reduce lipid peroxidation may stem from its function as a preventive antioxidant (scavenging initiating radicals), or yet unidentified actions. In sum, in vitro melatonin acts as a direct free radical scavenger with the ability to detoxify both reactive oxygen and reactive nitrogen species; in vivo, it is an effective pharmacological agent in reducing oxidative damage under conditions in which excessive free radical generation is believed to be involved.

Melatonin directly scavenges hydrogen peroxide: a potentially new metabolic pathway of melatonin biotransformation

A potential new metabolic pathway of melatonin biotransformation is described in this investigation. Melatonin was found to directly scavenge hydrogen peroxide (H(2)O(2)) to form N(1)-acetyl-N(2)-formyl-5-methoxykynuramine and, thereafter this compound could be enzymatically converted to N(1)-acetyl-5-methoxykynuramine by catalase. The structures of these kynuramines were identified using proton nuclear magnetic resonance, carbon nuclear magnetic resonance, and mass spectrometry. This is the first report to reveal a possible physiological association between melatonin, H(2)O(2), catalase, and kynuramines. Melatonin scavenges H(2)O(2) in a concentration-dependent manner. This reaction appears to exhibit two distinguishable phases. In the rapid reaction phase, the interaction between melatonin and H(2)O(2) reaches equilibrium rapidly (within 5 s). The rate constant for this phase was calculated to be 2.3 x 10(6) M(-1)s(-1). Thereafter, the relative equilibrium of melatonin and H(2)O(2) was sustained for roughly 1 h, at which time the content of H(2)O(2) decreased gradually over a several hour period, identified as the slow reaction phase. These observations suggest that melatonin, a ubiquitously distributed small nonenzymatic molecule, might serve to directly detoxify H(2)O(2) in living organisms. H(2)O(2) and melatonin are present in all subcellular compartments; thus, presumably, one important function of melatonin may be complementary in function to catalase and glutathione peroxidase in keeping intracellular H(2)O(2) concentrations at steady-state levels.

Melatonin and its relation to the immune system and inflammation

Melatonin (N-acetyl-5-methoxytryptamine) was initially thought to be produced exclusively in the pineal gland. Subsequently its synthesis was demonstrated in other organs, for example, the retinas, and very high concentrations of melatonin are found at other sites, for example, bone marrow cells and bile. The origin of the high level of melatonin in these locations has not been definitively established, but it is likely not exclusively of pineal origin. Melatonin has been shown to possess anti-inflammatory effects, among a number of actions. Melatonin reduces tissue destruction during inflammatory reactions by a number of means. Thus melatonin, by virtue of its ability to directly scavenge toxic free radicals, reduces macromolecular damage in all organs. The free radicals and reactive oxygen and nitrogen species known to be scavenged by melatonin include the highly toxic hydroxyl radical (.OH), peroxynitrite anion (ONOO-), and hypochlorous acid (HOCl), among others. These agents all contribute to the inflammatory response and associated tissue destruction. Additionally, melatonin has other means to lower the damage resulting from inflammation. Thus, it prevents the translocation of nuclear factor-kappa B (NF-kappa B) to the nucleus and its binding to DNA, thereby reducing the upregulation of a variety of proinflammatory cytokines, for example, interleukins and tumor neurosis factor-alpha. Finally, there is indirect evidence that melatonin inhibits the production of adhesion molecules that promote the sticking of leukocytes to endothelial cells. By this means melatonin attenuates transendothelial cell migration and edema, which contribute to tissue damage.

High levels of melatonin in the seeds of edible plants: possible function in germ tissue protection

The seeds of plants represent the anlage of the next generation and are vital to their existence. Melatonin has been identified in the leaves and flowers of plants but not in seeds. In this study, we examined the seeds of 15 edible plants for the presence of melatonin which was extracted using cold ethanol. Melatonin was initially identified by radioimmunoassay and subsequently quantified and confirmed using high performance liquid chromatography. The physiological concentrations of melatonin in the 15 seeds studied ranged from 2 to 200 ng/g dry weight. The highest concentrations of melatonin were observed in white and black mustard seeds. This level of melatonin is much higher than the known physiological concentrations in the blood of many vertebrates. Since the seed, particularly its germ tissue, is highly vulnerable to oxidative stress and damage, we surmise that melatonin, a free radical scavenger, might be present as an important component of its antioxidant defense system. Thus, melatonin in seeds may be essential in protecting germ and reproductive tissues of plants from oxidative damage due to ultraviolet light, drought, extremes in temperature, and environmental chemical pollutants.

Pharmacology and physiology of melatonin in the reduction of oxidative stress in vivo

This brief resume summarizes the evidence which shows that melatonin is a significant free radical scavenger and antioxidant at both physiological and pharmacological concentrations in vivo. Surgical removal of the pineal gland, a procedure which lowers endogenous melatonin levels in the blood, exaggerates molecular damage due to free radicals during an oxidative challenge. Likewise, providing supplemental melatonin during periods of massive free radical production greatly lowers the resulting tissue damage and dysfunction. In the current review, these findings are considered in terms of neurodegenerative diseases, cancer, ischemia/reperfusion injury and aging. Besides being a highly effective direct free radical scavenger and indirect antioxidant, melatonin has several features that make it of clinical interest. Thus, melatonin is readily absorbed when it is administered via any route, it crosses all morphophysiological barriers, e.g., blood-brain barrier and placenta, with ease, it seems to enter all parts of every cell where it prevents oxidative damage, it preserves mitochondrial function, and it has low toxicity. While blood melatonin levels are normally low, tissue levels of the indoleamine can be considerably higher and at some sites, e.g., in bone marrow cells and bile, melatonin concentrations exceed those in the blood by several orders of magnitude. What constitutes a physiological level of melatonin must be redefined in terms of the bodily fluid, tissue and subcellular compartment being examined.

Downregulation of miR-181a upregulates sirtuin-1 (SIRT1) and improves hepatic insulin sensitivity

AIMS/HYPOTHESIS

Sirtuin-1 (SIRT1) is a potential therapeutic target to combat insulin resistance and type 2 diabetes. This study aims to identify a microRNA (miRNA) targeting SIRT1 to regulate hepatic insulin sensitivity.

METHODS

Luciferase assay combined with mutation and immunoblotting was used to screen and verify the bioinformatically predicted miRNAs. miRNA and mRNA levels were measured by real-time PCR. Insulin signalling was detected by immunoblotting and glycogen synthesis. Involvement of SIRT1 was studied with adenovirus, inhibitor and SIRT1-deficient hepatocytes. The role of miR-181a in vivo was explored with adenovirus and locked nucleic acid antisense oligonucleotides.

RESULTS

miR-181a targets the 3' untranslated region (3'UTR) of Sirt1 mRNA through a miR-181a binding site, and downregulates SIRT1 protein abundance at the translational level. miR-181a is increased in insulin-resistant cultured hepatocytes and liver, and in the serum of diabetic patients. Overexpression of miR-181a decreases SIRT1 protein levels and activity, and causes insulin resistance in hepatic cells. Inhibition of miR-181a by antisense oligonucleotides increases SIRT1 protein levels and activity, and improves insulin sensitivity in hepatocytes. Ectopic expression of SIRT1 abrogates the effect of miR-181a on insulin sensitivity, and inhibition of SIRT1 activity or SIRT1 deficiency markedly attenuated the improvement in insulin sensitivity induced by antisense miR-181a. In addition, overexpression of miR-181a by adenovirus impairs hepatic insulin signalling, and intraperitoneal injection of locked nucleic acid antisense oligonucleotides for miR-181a improves glucose homeostasis in diet-induced obesity mice.

CONCLUSIONS/INTERPRETATION

miR-181a regulates SIRT1 and improves hepatic insulin sensitivity. Inhibition of miR-181a might be a potential new strategy for treating insulin resistance and type 2 diabetes.

High physiological levels of melatonin in the bile of mammals

Bile is an important physiological bodily fluid which functions in the regulation of cholesterol metabolism, promotes the absorption of lipid and fat-soluble vitamins by the gut and serves in the excretion of toxic substances from the liver. Conversely, due to autooxidative processes bile is highly toxic to the hepatocyte and gastrointestinal epithelium. In this investigation, extremely high day time physiological levels of the endogenous antioxidant, melatonin, were measured in the bile of several mammals including rat, guinea pig, rabbit, pig, monkey and humans. Melatonin concentrations in the bile samples ranged from 2,000 to 11,000 pg/ml when measured by radioimmunoassay (RIA). These melatonin levels in bile are 2 to 3 orders of magnitude higher than those in day time serum. The presence of melatonin in bile was confirmed by HPLC with an electrochemical detector. This method, like the RIA, also documented very high levels of melatonin in bile. The presence of high levels of melatonin in bile may be essential to prevent oxidative damage to biliary and small intestinal epithelium induced by bile acids and oxidized cholesterol derivatives.

Ischemia/reperfusion-induced arrhythmias in the isolated rat heart: prevention by melatonin

Cardiac arrhythmias during ischemia/reperfusion are believed to be related to free radicals generated in the heart especially during the period of reperfusion. Since melatonin functions as a free radical scavenger and antioxidant, the ability of this molecule to influence cardiac arrhythmias was investigated. The pineal secretory product, melatonin, reduced the incidence and severity of arrhythmias induced by ischemia/reperfusion due to ligation of the anterior descending coronary artery in the isolated rat heart. Melatonin was either infused during both the ischemia and reperfusion periods or only late in the ischemia period and throughout reperfusion. The percentage of hearts that developed cardiac arrhythmias during reperfusion as indicated by the incidence of premature ventricular contraction (PVC) and ventricular fibrillation (VF) were recorded. Melatonin either infused during both the ischemia and reperfusion periods or during essentially the period of reperfusion greatly reduced PVC and VF due to occlusion and reopening the anterior descending coronary artery. Presumably melatonin's beneficial effect in reducing cardiac arrhythmias was due in part to its free radical scavenging activity, which is greatly assisted by the rapidity with which it is taken up into cells. Previous studies have shown that vitamin C is effective in reducing the severity of cardiac arrhythmias induced by ischemia/reperfusion; thus, we also compared the efficacy of melatonin with this well-known antioxidant. Melatonin was more potent than vitamin C in protecting against arrhythmias induced by ischemia/reperfusion. Besides melatonin's function as a broad spectrum free radical scavenger, melatonin may have also reduced cardiac arrhythmias due to its regulation of intracellular calcium levels, i.e., by preventing calcium overloading, or due to its ability to suppress sympathetic nerve function and reduce adrenergic receptor function in the myocardium. Additional studies into the mechanisms of melatonin's action in reducing cardiac arrhythmias due to ischemia/reperfusion or other causes are warranted because of the possible application of this information to humans with heart disease.

Augmentation of indices of oxidative damage in life-long melatonin-deficient rats

The chief pineal secretory product, melatonin, is an efficient free radical scavenger and antioxidant. The current study tested whether the life-long reduction of endogenous melatonin levels due to pinealectomy would influence the accumulation of oxidatively damaged products as the animals aged. Rats were either pinealectomized or sham operated when they were 2-months-old. At 25 months of age these animals were killed along with 2-month-old controls. Aging in the pineal-intact animals was associated with increased levels of lipid peroxidation products (malondialdehyde and 4-hydroxyalkenals in the lung, kidney and skin), rises in an oxidatively damaged DNA product (8-hydroxy-deoxyguanosine in liver, kidney and pancreas), and in the levels of protein carbonyls (in the liver). Likewise, advanced age was associated with a significant decrease in membrane fluidity (increased membrane rigidity) of hepatic microsomes in pineal-intact rats. For all of these parameters and in a number of organs, pinealectomy caused further increases in the indices of oxidative damage. Consistent with previous suggestions, the implications of these findings is that aging is associated with the augmented accumulation of oxidatively damaged macromolecules and that these increases are exaggerated when a relative melatonin deficiency is induced by pinealectomy. The findings are consistent with the idea that the accelerated accumulation of oxidatively damaged products after pinealectomy was due to reduction in melatonin since it functions as a free radical scavenger and antioxidant. On the other hand, other pineal secretory products that were reduced as a consequence of pineal removal may have also been responsible for some of the observed changes.

Development of secondary mutations in wild-type and mutant EZH2 alleles cooperates to confer resistance to EZH2 inhibitors

The histone methyltransferase Enhancer of Zeste Homolog 2 (EZH2) is frequently dysregulated in cancers, and gain-of-function (GOF) EZH2 mutations have been identified in non-Hodgkin lymphomas. Small-molecule inhibitors against EZH2 demonstrated anti-tumor activity in EZH2-mutated lymphomas and entered clinical trials. Here, we developed models of acquired resistance to EZH2 inhibitor EI1 with EZH2-mutated lymphoma cells. Resistance was generated by secondary mutations in both wild-type (WT) and GOF Y641N EZH2 alleles. These EZH2 mutants retained the substrate specificity of their predecessor complexes but became refractory to biochemical inhibition by EZH2 inhibitors. Resistant cells were able to maintain a high level of H3K27Me3 in the presence of inhibitors. Interestingly, mutation of EZH2 WT alone generated an intermediate resistance phenotype, which is consistent with a previously proposed model of cooperation between EZH2 WT and Y641N mutants to promote tumorigenesis. In addition, the findings presented here have implications for the clinical translation of EZH2 inhibitors and underscore the need to develop novel EZH2 inhibitors to target potential resistance emerging in clinical settings.

Natriuretic peptides in patients with aortic stenosis

BACKGROUND

Whereas atrial natriuretic peptide (ANP) is secreted mainly from cardiac atria, brain natriuretic peptide (BNP) is produced to a larger extent in ventricles. Their relative importance as markers of cardiac function and myocardial hypertrophy is not yet clarified. This study evaluated circulating BNP and ANP and the N-terminal part of their propeptides (NT-proBNP and NT-proANP) as markers of left ventricular hypertrophy and atrial pressure increase in patients with aortic stenosis.

METHODS

The plasma concentrations of BNP, NT-proBNP, ANP, and NT-proANP were measured by radioimmunoassay in 67 patients with aortic stenosis. Peptide plasma concentrations were related to measurements obtained by cardiac catheterization and echocardiography.

RESULTS

Receiver operating characteristic curves indicated that BNP and NT-proBNP performed best in the detection of increased left ventricular mass and NT-proANP in the detection of increased left atrial pressure. NT-proBNP was significantly increased in mild left ventricular hypertrophy (left ventricular mass index, 78 to 139 g/m(2)), whereas NT-proANP was not increased until left ventricular mass index was 141 to 180 g/m(2).

CONCLUSIONS

Plasma BNP and NT-proBNP may serve as early markers of left ventricular hypertrophy, whereas ANP and NT-proANP reflect left atrial pressure increase. The repeated and combined measurements of natriuretic peptides might provide diagnostic information relevant to the evaluation of the stage of aortic stenosis.

Intermittent high glucose enhances cell growth and collagen synthesis in cultured human tubulointerstitial cells

AIMS/HYPOTHESIS

We investigated the effects of constant and intermittently increased glucose concentrations on human proximal tubule cells and cortical fibroblasts in primary culture.

METHODS

Cells were grown to confluence and then exposed for 4 days to 6.1 mmol/l D-glucose (normal), 25 mmol/l D-glucose (high), or 6.1 mmol/l alternating with 25 mmol/l D-glucose on a daily basis.

RESULTS

In proximal tubular cells, exposure to high glucose caused an 11 % increase in thymidine uptake (p < 0.05), a 230 % increase in secretion of transforming growth factor beta 1 (TGF-beta1; p < 0.05) and a 393 % increase in platelet derived growth factor. Intermittent exposure to high glucose caused thymidine uptake to further increase by 42 % (p < 0.01) and TGF-beta1 secretion by 352 % (p < 0.01) but no additional increase in platelet-derived growth factor secretion was observed. Cellular protein content increased by 27 % (p < 0.05) and collagen synthesis by 29 % (p < 0.05), changes that were not observed in cells constantly exposed to high glucose. In cortical fibroblasts constant exposure to high glucose caused a 35 % increase in thymidine uptake (p < 0.01). Intermittently high glucose increased thymidine incorporation a further 58 % (p < 0.001), collagen synthesis by 65 % (p < 0.01) and insulin-like growth factor binding protein 3 secretion by 216 % (p < 0.01).

CONCLUSION/INTERPRETATION

In cultured human tubulointerstitial cells, increased glucose concentrations change cell growth, collagen synthesis and cytokine secretion. These effects are enhanced following intermittent exposure to high glucose, indicating that short lived excursions in glycaemic control have important pathological effects on the human tubulointerstitium.

Gum arabic glycoprotein is a twisted hairy rope : a new model based on o-galactosylhydroxyproline as the polysaccharide attachment site

Separation of the wound exudate from Acacia senegal (L.) Willd., "gum arabic," on a preparative Superose-6 column gave two major fractions: a high molecular weight gum arabic glycoprotein (GAGP) containing about 90% carbohydrate and a lower molecular weight heterogenous gum arabic polysaccharide fraction. Hydrogen fluoride-deglycosylation of GAGP gave a large ( approximately 400 residue) hydroxyproline-rich polypeptide backbone (dGAGP). Alkaline hydrolysis of GAGP showed that most of the carbohydrate was attached to the polypeptide backbone as small ( approximately 30 residue) hydroxyproline (Hyp)-polysaccharide substituents. After partial acid hydrolysis of the Hyp-polysaccharide fraction we identified O-galactosylhydroxyproline as the glycopeptide linkage, identical with that of hydroxyproline-rich arabinogalactan-proteins (AGPs). However, unlike the acidic alanine-rich AGPs, GAGP is basic and notably deficient in alanine. Thus, while the GAGP polypeptide backbone more closely resembles that of the Hyp-rich cell wall protein extensin, the GAGP polysaccharide sidechains resemble AGPs. Possibly all three proteins comprise a phylogenetically related extensin superfamily of extended rod-like macromolecules. The "wattle-blossom" model for AGP and gum arabic predicts a few large polysaccharide substituents along the polypeptide backbone of a spheroidal macromolecule. On the contrary, our data imply a rodlike molecule with numerous small polysaccharide substituents (attached to 24% of the Hyp residues), regularly arranged along a highly periodic polypeptide backbone based, hypothetically, on a 10 to 12 residue repetitive peptide motif. Thus, a simple statistical model of the gum arabic glycoprotein predicts a repeating polysaccharide-peptide subunit of about 7 kilodaltons. The small polysaccharide substituents will maximize intramolecular hydrogen bonding if aligned along the long axis of the molecule, forming in effect a twisted hairy rope. Electron micrographs of rotary shadowed GAGP molecules support that prediction and may also explain how such apparently large molecules can exit the cell by endwise reptation through the small pores of the primary cell wall.

Phase I pharmacokinetic and pharmacodynamic study of the pan-PI3K/mTORC vascular targeted pro-drug SF1126 in patients with advanced solid tumours and B-cell malignancies

BACKGROUND

SF1126 is a peptidic pro-drug inhibitor of pan-PI3K/mTORC. A first-in-human study evaluated safety, dose limiting toxicities (DLT), maximum tolerated dose (MTD), pharmacokinetics (PK), pharmacodynamics (PD) and efficacy of SF1126, in patients with advanced solid and B-cell malignancies.

PATIENTS AND METHODS

SF1126 was administered IV days 1 and 4, weekly in 28day-cycles. Dose escalation utilised modified Fibonacci 3+3. Samples to monitor PK and PD were obtained.

RESULTS

Forty four patients were treated at 9 dose levels (90-1110 mg/m(2)/day). Most toxicity was grade 1 and 2 with a single DLT at180 mg/m(2) (diarrhoea). Exposure measured by peak concentration (C(max)) and area under the time-concentration curve (AUC(0-)(t)) was dose proportional. Stable disease (SD) was the best response in 19 of 33 (58%) evaluable patients. MTD was not reached but the maximum administered dose (MAD) was 1110 mg/m(2). The protocol was amended to enrol patients with CD20+ B-cell malignancies at 1110 mg/m(2). A CLL patient who progressed on rituximab [R] achieved SD after 2 months on SF1126 alone but in combination with R achieved a 55% decrease in absolute lymphocyte count and a lymph node response. PD studies of CLL cells demonstrated SF1126 reduced p-AKT and increased apoptosis indicating inhibition of activated PI3K signalling.

CONCLUSION

SF1126 is well tolerated with SD as the best response in patients with advanced malignancies.

Increased levels of oxidatively damaged DNA induced by chromium(III) and H2O2: protection by melatonin and related molecules

Chromium (Cr) compounds are known occupational and environmental carcinogens. This trace element is found in the workplace primarily in the valence forms Cr(III) and Cr(VI). Cr(III), which was thought originally to be relatively nontoxic, was recently found to be more reactive toward purified DNA than was chromium(VI). Herein, we examined the ability of Cr(III) to induce oxidative DNA damage by measuring the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in purified calf thymus DNA incubated with CrCl3 plus H2O2. In this system we observed that the Cr(III)-induced formation of 8-OH-dG in isolated DNA was both dose- and time-dependent. When melatonin and related molecules, including 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (pinoline), N-acetylserotonin, 6-hydroxymelatonin and indole-3-propionic acid, were co-incubated with CrCl3 plus H2O2, the accumulations of 8-OH-dG in DNA samples were markedly inhibited in a concentration-dependent manner. The concentrations of each indole required to reduce DNA damage by 50%, i.e. the IC50 values, were 0.48, 0.51, 0.88, 1.00 and 3.08 microM for pinoline, melatonin, N-acetylserotonin, 6-hydroxymelatonin and indole-3-propionic acid, respectively. These results suggest that one of the mechanisms by which Cr(III) may induce cancer is via Fenton-type reactions which generate the hydroxyl radical (*OH). The findings also indicate that the protective effects of melatonin and related molecules against Cr(III)-induced carcinogenesis relate to their direct *OH scavenging ability which thereby reduces the formation of the damaged DNA product, 8-OH-dG.

Integrated actions of transforming growth factor-beta1 and connective tissue growth factor in renal fibrosis

Matrix accumulation in the renal tubulointerstitium is predictive of a progressive decline in renal function. Transforming growth factor-beta(1) (TGF-beta(1)) and, more recently, connective tissue growth factor (CTGF) are recognized to play key roles in mediating the fibrogenic response, independently of the primary renal insult. Further definition of the independent and interrelated effects of CTGF and TGF-beta(1) is critical for the development of effective antifibrotic strategies. CTGF (20 ng/ml) induced fibronectin and collagen IV secretion in primary cultures of human proximal tubule cells (PTC) and cortical fibroblasts (CF) compared with control values (P < 0.005 in all cases). This effect was inhibited by neutralizing antibodies to either TGF-beta or to the TGF-beta type II receptor (TbetaRII). TGF-beta(1) induced a greater increase in fibronectin and collagen IV secretion in both PTC (P < 0.01) and CF (P < 0.01) compared with that observed with CTGF alone. The combination of TGF-beta(1) and CTGF was additive in their effects on both PTC and CF fibronectin and collagen IV secretion. TGF-beta(1) (2 ng/ml) stimulated CTGF mRNA expression within 30 min, which was sustained for up to 24 h, with a consequent increase in CTGF protein (P < 0.05), whereas CTGF had no effect on TGF-beta(1) mRNA or protein expression. TGF-beta(1) (2 ng/ml) induced phosphorylated (p)Smad-2 within 15 min, which was sustained for up to 24 h. CTGF had a delayed effect on increasing pSmad-2 expression, which was evident at 24 h. In conclusion, this study has demonstrated the key dependence of the fibrogenic actions of CTGF on TGF-beta. It has further uniquely demonstrated that CTGF requires TGF-beta, signaling through the TbetaRII in both PTCs and CFs, to exert its fibrogenic response in this in vitro model.

Melatonin protects hippocampal neurons in vivo against kainic acid-induced damage in mice

In this investigation, 40 mg/kg of the excitatory neurotoxin kainic acid (KA) was subcutaneously administered to CD2-F1 mice. In this mouse strain morphological damage induced by KA in the hippocampus was markedly concentrated in the CA3 pyramidal neurons. Neuronal injury was accompanied by several pathological neurobehavioral activities including arching of tail, tremors and seizures, and by certain biochemical changes, i.e., increased lipid peroxidation products (LPO) in the brain. When melatonin was injected intraperitoneally at a single dose of 5 mg/kg 10 min before KA administration, it significantly reduced these pathological neurobehavioral changes and almost completely attenuated the increase in LPO and morphological damage induced by KA. The neuroprotective effect of melatonin against KA-induced brain damage in mice is believed to be in part related to its oxygen radical scavenging properties as well as its antiepileptic and GABA receptor regulatory actions. Considering melatonin's relative lack of toxicity and ability to enter the brain, these results along with previous evidence suggest that melatonin, which is a natural substance, may be useful in combating free radical-induced neuronal injury in acute situations such as stroke and brain trauma as well as neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease that have free radicals as causative factors.

Melatonin reduces oxidative neurotoxicity due to quinolinic acid: in vitro and in vivo findings

The in vivo and in vitro effects of melatonin on quinolinic acid-induced oxidative damage in rat brain were determined. The concentrations of malonaldehyde and 4-hydroxyalkenals were assayed as an index of oxidatively damaged lipid. In in vitro experiments, the increase in malonaldehyde and 4-hydroxyalkenals concentrations induced by quinolinic acid were concentration-dependent and time-dependent. The accumulation of products of lipid peroxidation induced by quinolinic acid were very significantly reduced by melatonin in a concentration-dependent manner. Additionally, at the highest concentrations of melatonin used in quinolinic acid treated homogenates, it reduced the levels of oxidatively damaged lipid products below those measured in control homogenates (no quinolinic acid or melatonin). When quinolinic acid (200 mg/kg) was intraperitonally injected into 11-day-old rats, lipid peroxidation in the brain was significantly increased 24 hours later compared to levels in control rats. When melatonin (10 mg/kg) was injected i.p. 30 min before and 4 and 20 hours after the administration of quinolinic acid, the increased lipid peroxidation induced by quinolinic acid was significantly reduced. Likewise, neurobehavioral signs associated with quinolinate administration were attenuated by melatonin. These results show that both in vitro and in vivo pharmacological levels of melatonin confer protection against quinolinic acid-induced oxidative toxicity in the brain. The findings also indicate that melatonin may be pharmacologically useful in combatting quinolinic neurotoxicity which is associated with several acute and chronic neurodegenerative neurological diseases.

Prospective observational study of acute coronary syndromes in China: practice patterns and outcomes

OBJECTIVE

To describe the investigation and management of patients admitted to hospitals in China with suspected acute coronary syndromes (ACS) and to identify potential areas for improvement in practice.

DESIGN

A multicentre prospective survey of sociodemographic characteristics, medical history, clinical features, in-hospital investigations, treatment practices and major events among patients with suspected ACS.

SETTING

Large urban public hospitals.

PATIENTS

Consecutive patients admitted to in-patient facilities with a diagnosis of suspected acute myocardial infarction (MI) or unstable angina pectoris.

MAIN OUTCOME MEASURES

Myocardial infarction/re-infarction, heart failure, death.

RESULTS

Between September 2004 and May 2005, data were collected prospectively from 2973 patients admitted to 51 hospitals in 18 provinces of China. An initial diagnosis of ST elevation MI, non-ST elevation MI and unstable angina was made in 43%, 11% and 46% of patients, respectively. Diagnosis was inconsistent with objective measures in up to 20% of cases. At both tertiary and non-tertiary centres, there was little evidence that clinical risk stratification was used to determine the intensity of investigation and management. The mortality rate during hospitalisation was 5% overall and similar in tertiary and non-tertiary centres, but reported in-hospital re-infarction rates (8%) and heart failure rates (16%) were substantially higher at non-tertiary centres.

CONCLUSION

This study has identified a number of areas in the management of ACS patients, including diagnosis and risk stratification, which deviate from current guidelines. These findings will help inform the introduction of widely used quality improvement initiatives such as clinical pathways.

Deoxycholic acid suppresses p53 by stimulating proteasome-mediated p53 protein degradation

Bile acids, principally deoxycholic acid (DCA), have been implicated in the promotion of colon tumorigenesis in both animals and humans. Increasing evidence suggests that bile acids may exert their tumor promoting activity by modulating intracellular signaling and altering gene expression. In this study we have investigated the effect of bile acids on the tumor suppressor p53 using the human colon tumor cell line HCT116, which retains the wild-type p53 gene and functional p53 signaling in response to DNA damage. We found that exposure of the cells to elevated concentrations of DCA suppressed accumulation of p53 protein as well as p53 transactivation and impaired the p53 response of the cells to DNA damaging agents, such as ionizing radiation. Neither ursodeoxycholic acid, a putative chemopreventive agent, nor cholic acid, which is biologically inert, had any effect on p53 protein level and transactivation activity. Further examination revealed that instead of inhibition, DCA induced p53 mRNA in a dose-dependent manner, indicating that the inhibitory effect of DCA on p53 protein is mediated by a post-transcriptional mechanism. Both lactacystin, a specific inhibitor of the 26S proteasome, and leptomycin B, a specific inhibitor of the nuclear export protein CRM1, could block the effect that DCA had on p53 protein levels, suggesting that DCA suppressed p53 by stimulating the process of proteasome-mediated degradation of p53. Significantly, blocking extracellular signal-regulated kinase (ERK) signaling, but not protein kinase C (PKC), blunted suppression by DCA of p53 protein levels and transactivation activity, suggesting that DCA suppressed p53, in part, by stimulating the ERK signaling pathway. Both ERK and PKC signaling have been previously demonstrated to be stimulated by DCA. These results suggest a novel signaling mechanism of bile acids that may play an important role in colon tumor promotion mediated by bile acids.

Bone morphogenetic protein-2 blocks MDA MB 231 human breast cancer cell proliferation by inhibiting cyclin-dependent kinase-mediated retinoblastoma protein phosphorylation

Bone morphogenetic protein-2 (BMP-2) has been shown to act as an antiproliferative agent for a number of different cell types. We show that BMP-2 dose-dependently inhibits growth of MDA MB 231 human breast cancer cells. Epidermal growth factor (EGF) stimulates DNA synthesis and entry of these cells into the S-phase. BMP-2 inhibits EGF-induced DNA synthesis by arresting them in G1 phase of the cell cycle. BMP-2 increases the level of cyclin kinase inhibitor p21. Furthermore, we show that exposure of MDA MB 231 cells to BMP-2 stimulates association of p21 with cyclin D1 and with cyclin E resulting in the inhibition of their associated kinase activities. Finally, BMP-2 treatment is found to cause hypophosphorylation of the retinoblastoma protein (pRb), a key regulator of cell cycle progression. Our data provide a mechanism for the antiproliferative effect of BMP-2 in the breast cancer cells.

Genesis of the novel human-infecting influenza A(H10N8) virus and potential genetic diversity of the virus in poultry, China

Human infection with a novel influenza A(H10N8) virus was first described in China in December 2013. However, the origin and genetic diversity of this virus is still poorly understood. We performed a phylogenetic analysis and coalescent analysis of two viruses from the first case of influenza A(H10N8) (A/Jiangxi-Donghu/346-1/2013 and A/Jiangxi-Donghu/346-2/2013 and a novel A(H10N8) virus (A/chicken/Jiangxi/102/2013) isolated from a live poultry market that the patient had visited. The haemagglutinin (HA), neuraminidase (NA), PA subunit of the virus polymerase complex, nucleoprotein (NP), M and nonstructural protein (NS) genes of the three virus strains shared the same genetic origins. The origins of their HA and NA genes were similar: originally from wild birds to ducks, and then to chickens. The PA, NP, M, and NS genes were similar to those of chicken influenza A(H9N2) viruses. Coalescent analyses showed that the reassortment of these genes from A(H9N2) to A(H10N8) might have occurred at least twice. However, the PB1 and PB2 genes of the chicken A(H10N8) virus most likely originated from H7-like viruses of ducks, while those of the viruses from the case most likely stemmed from A(H9N2) viruses circulating in chickens. The oseltamivir-resistance mutation, R292K (R291K in A(H10N8) numbering) in the NA protein, occurred after four days of oseltamivir treatment. It seems that A(H10N8) viruses might have become established among poultry and their genetic diversity might be much higher than what we have observed.

Multiple roles of the p75 neurotrophin receptor in the nervous system

The p75 neurotrophin receptor (p75NTR) is a transmembrane protein that binds nerve growth factor (NGF) and has multiple functions in the nervous system where it is expressed widely during the developmental stages of life, although expression decreases dramatically by adulthood. Expression of p75NTR can increase in pathological states related to neural cell death. p75NTR is a member of the tumour necrosis factor (TNF) receptor family and it consists of intracellular, transmembrane and extracellular domains which are different from other TNF receptors. Either by interacting with tropomyosin receptor kinase (Trk) receptors or via the independent binding of neurotrophin, p75NTR can induce neurite outgrowth and cellular survival or cell apoptosis through several complicated signal transduction pathways. Most of these signalling pathways remain to be elucidated. By interacting with different cellular factors, p75NTR can induce neuron growth cone collapse or regrowth. p75NTR is also expressed in a variety of glial populations. The many functions of p75NTR require further study.

Effect of the Pl(A2) alloantigen on the function of beta(3)-integrins in platelets

The polymorphism responsible for the Pl(A2) alloantigen on the beta(3)-component of beta(3)-containing integrins is reported to be a risk factor for coronary thrombosis. This study examined the effect of Pl(A2) on the function of beta(3)-integrins using platelets from subjects homozygous and heterozygous for Pl(A1) and Pl(A2). There was overlap in the distribution of the dissociation constant (K(d)) and maximum fibrinogen binding (B(max)) values for fibrinogen binding to alpha(IIb)beta(3) on platelets from Pl(A1) and Pl(A2) homozygotes and Pl(A1)/Pl(A2) heterozygotes. However, whereas there was no statistical difference in these values for the Pl(A1) homozygotes and Pl(A2) heterozygotes, the K(d) for the Pl(A2) homozygotes was significantly lower than that for the Pl(A1)/Pl(A2) heterozygotes, but was not statistically different from that for the Pl(A1) homozygotes. No differences were detected in ADP sensitivity between platelets from Pl(A1) homozygotes and Pl(A1)/Pl(A2) heterozygotes, in the IC(50) for RGDS inhibition of fibrinogen binding to alpha(IIb)beta(3), in the alpha(v)beta(3)-mediated adhesion of platelets to osteopontin and vitronectin, and in the phorbol ester-stimulated adhesion to fibrinogen of B lymphocytes expressing alpha(IIb)beta(3) containing either the Pl(A1) or the Pl(A2) polymorphism. Finally, no differential effects of Pl(A2) on turbidometric platelet aggregation, platelet secretion, or platelet thrombus formation were found as measured in the PFA-100. Because no differences were detected in the ability of beta(3)-integrins to interact with ligands based on the presence or absence of the Pl(A2) polymorphism, the results suggest that factors unrelated to beta(3)-integrin function may account for the reported association of the Pl(A2) allele with coronary thrombosis.

Chromium(III)-induced 8-hydroxydeoxyguanosine in DNA and its reduction by antioxidants: comparative effects of melatonin, ascorbate, and vitamin E

Chromium compounds are well documented carcinogens. Cr(III) is more reactive than Cr(VI) toward DNA under in vitro conditions. In the present study, we investigated the ability of Cr(III) to induce oxidative DNA damage by examining the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in calf thymus DNA incubated with CrCl(3) plus H(2)O(2). We measured 8-OH-dG using HPLC with electrochemical detection. In the presence of H(2)O(2), we observed that Cr(III)-induced formation of 8-OH-dG in isolated DNA was dose and time dependent. Melatonin, ascorbate, and vitamin E (Trolox), all of which are free radical scavengers, markedly inhibited the formation of 8-OH-dG in a concentration-dependent manner. The concentration that reduced DNA damage by 50% was 0.51, 30.4, and 36.2 microM for melatonin, ascorbate, and Trolox, respectively. The results show that melatonin is 60- and 70-fold more effective than ascorbate or vitamin E, respectively, in reducing oxidative DNA damage in this in vitro model. These findings also are consistent with the conclusion that the carcinogenic mechanism of Cr(III) is possibly due to Cr(III)-mediated Fenton-type reactions and that melatonin's highly protective effects against Cr(III) relate, at least in part, to its direct hydroxyl radical scavenging ability.