Intra-specific kin recognition contributes to inter-specific allelopathy: A case study of allelopathic rice interference with paddy weeds.

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter-specific and intra-specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly.

[Assessment of Antimalarial Activity of Choline Derivatives against Plasmodium falciparum Growth in vitro by SYBR Green I Method].

OBJECTIVE: To investigate the antimalarial activity of four choline derivatives against Plasmodium falciparum 3D7 strain growth in vitro. METHODS: Four choline derivatives MD [N-dodecyl-N-(2-hydroxyethyl)-N,N- dimethyl ammonium bromide], ED [N-dodecyl-N-(2-hydroxyethyl)-N,N-diethyl ammonium bromide], MT [N-tetradecyl-N- (2-hydroxyethyl)-N,N-dimethyl ammonium bromide], and ET [N-tetradecyl-N-(2-hydroxyethyl)-N,N-diethyl ammonium bromide] were dissolved separately in DMSO at serial concentrations (1-10(5) µmol/L). The solutions were diluted by 1,000-fold with RPMI 1640 medium. 20 µl drug-containing medium and 80 µl P. falciparum-infected erythrocyte suspension (2% final hematocrit and 0.3%-0.5% parasitemia) were added to each well of microtiter plates. Drug effect on the in vitro growth of P. falciparum was measured by SYBR Green I method. The half maximal inhibitory concentration (IC50) was calculated from dose-response curves. Artemisinine served as positive control. RESULTS: Artemisinine, MD, ED, MT, and ET showed different degrees of dose-dependent inhibition on P. falciparum growth. When the MD concentration was above 10 nmol/L, the inhibition rate increased significantly. Both ED and ET showed significant inhibitory effects at high concentrations, with inhibition rate of > 95% when their doses were > 10(4) nmol/L. The IC50 values of MD, ED, MT, and ET were 1 620, 33.9, 116, and 68.9 nmol/L, respectively, all significantly higher than that of artemisinine (5.7 nmol/L) (P < 0.05). CONCLUSION: The four choline derivatives show certain antimalarial activity, which is lower than that of artemisinine. Among the four derivatives, ED has the strongest antimalarial activity against P. falciparum 3D7 strain.

Pseudocapacitive mechanism of manganese oxide in 1-ethyl-3-methylimidazolium thiocyanate ionic liquid electrolyte studied using X-ray photoelectron spectroscopy.

The electrochemical behavior of anodically deposited manganese oxide was studied in pyrrolidinium formate (P-HCOO), 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), and 1-ethyl-3-methylimidazolium thiocyanate (EMI-SCN) ionic liquids (ILs). The experimental data indicate that the Mn oxide electrode showed ideal pseudocapacitive performance in aprotic EMI-SCN IL. In a potential window of approximately 1.5 V, the oxide specific capacitance, evaluated using cyclic voltammetry and chronopotentiometry, was about 55 F/g. The electrochemical energy storage reaction was examined using X-ray photoelectron spectroscopy (XPS). It was confirmed that the SCN- anions, instead of the EMI+ cations, were the primary working species that can become incorporated into the oxide and thus compensate the Mn3+/Mn4+ valent state variation upon the charge-discharge process. According to the analytical results, a pseudocapacitive mechanism of Mn oxide in the SCN- based aprotic IL was proposed.

Nitric oxide stimulates cyclooxygenase-2 in cultured cTAL cells through a p38-dependent pathway.

To examine the interaction of nitric oxide (NO) and cyclooxygenase (COX-2) and the signaling pathway involved, primary cultured rabbit cortical thick ascending limb (cTAL) were used. In these cells, immunoreactive COX-2 and vasodilatory prostaglandins were increased by a NO donor, S-nitros-N-acetylpenicillamine (SNAP; 2.5 +/- 0.3-fold control, n = 6, P < 0.01). SNAP increased expression of phosphorylated p38 (pp38; 2.4 +/- 0.3-fold control; n = 5; P < 0.01), which was inhibited by the p38 inhibitor SB-203580 (1.3 +/- 0.1-fold control, n = 5, P < 0.01). SB-203580 inhibited SNAP-induced COX-2 expression [1.4 +/- 0.2-fold control, n = 6, not significant (NS) vs. control] and levels of PGE2 significantly. In cTAL cells transfected with a luciferase reporter driven by the wild-type mouse COX-2 promoter, SNAP stimulated luciferase activity, which was reversed by SB-203580 (control vs. SNAP vs. SNAP + SB-203580: 1.4 +/- 0.2-, 8.3 +/- 1.4-, and 0.4 +/- 0.1-fold control, respectively, n = 4, P < 0.01). Electrophoretic mobility shift assay indicated that SNAP stimulated nuclear factor (NF)-kappaB binding activity in cTAL that was also inhibited by the p38 inhibitor. SNAP was not able to stimulate a mutant COX-2 promoter construct that is not activated by NF-kappaB (0.9 +/- 0.1, 1.2 +/- 0.1, and 1.0 +/- 0.2 respectively, n = 4, NS). Low chloride increased COX-2 expression (2.7 +/- 0.4-fold control, n = 6, P < 0.01) and pp38 expression (2.8 +/- 0.3-fold; n = 5, P < 0.01), which were reversed by the specific NO synthase (NOS) inhibitor 7-nitroindazole. Administration of a low-salt diet increased immunoreactive COX-2 and neuronal NOS (nNOS) in the macula densa and surrounding cTAL of kidneys of wild-type mice but did not significantly elevate COX-2 expression in nNOS-/- mice. In summary, these studies indicate that, in cTAL, NO can increase COX-2 expression in cTAL and macula densa through p38-dependent signaling pathways via activation of NF-kappaB.

Renal cortical cyclooxygenase 2 expression is differentially regulated by angiotensin II AT(1) and AT(2) receptors.

Macula densa cyclooxygenase 2 (COX-2)-derived prostaglandins serve as important modulators of the renin-angiotensin system, and cross-talk exists between these two systems. Cortical COX-2 induction by angiotensin-converting enzyme (ACE) inhibitors or AT(1) receptor blockers (ARBs) suggests that angiotensin II may inhibit cortical COX-2 by stimulating the AT(1) receptor pathway. In the present studies we determined that chronic infusion of either hypertensive or nonhypertensive concentrations of angiotensin II attenuated cortical COX-2. Angiotensin II infusion reversed cortical COX-2 elevation induced by ACE inhibitors. However, we found that angiotensin II infusion further stimulated cortical COX-2 elevation induced by ARBs, suggesting a potential role for an AT(2) receptor-mediated pathway when the AT(1) receptor was inhibited. Both WT and AT(2) receptor knockout mice were treated for 7 days with either ACE inhibitors or ARBs. Cortical COX-2 increased to similar levels in response to ACE inhibition in both knockout and WT mice. In WT mice ARBs increased cortical COX-2 more than ACE inhibitors, and this stimulation was attenuated by the AT(2) receptor antagonist PD123319. In the knockout mice ARBs led to significantly less cortical COX-2 elevation, which was not attenuated by PD123319. PCR confirmed AT(1a) and AT(2) receptor expression in the cultured macula densa cell line MMDD1. Angiotensin II inhibited MMDD1 COX-2, and CGP42112A, an AT(2) receptor agonist, stimulated MMDD1 COX-2. In summary, these results demonstrate that macula densa COX-2 expression is oppositely regulated by AT(1) and AT(2) receptors and suggest that AT(2) receptor-mediated cortical COX-2 elevation may mediate physiologic effects that modulate AT(1)-mediated responses.

Does cyclooxygenase-2 affect blood pressure?

With the development and clinical implementation of the new cyclooxygenase (COX)-2 inhibitors, their safety, including the effects on renal function and blood pressure, is attracting increasing attention. In the kidney, COX-2 is constitutively expressed and is highly regulated in response to alterations in intravascular volume. COX-2 metabolites have been implicated in mediation of renin release, regulation of sodium excretion, and maintenance of renal blood flow. Similar to conventional nonsteroidal anti-inflammatory drugs, inhibition of COX-2 may cause modest elevations in blood pressure in a minority of subjects. COX-2 inhibitors may also exacerbate pre-existing hypertension or interfere with other antihypertensive drugs. Special caution should be taken in patients with volume depletion or decreased organ perfusion.

Cyclooxygenases, the kidney, and hypertension.

Selective cyclooxygenase (COX)-2 inhibitors that are in widespread clinical use were developed to avoid side effects of conventional NSAIDs, including gastrointestinal and renal toxicity. However, COX-2 is constitutively expressed in the kidney and is highly regulated in response to alterations in intravascular volume. COX-2 metabolites have been implicated in maintenance of renal blood flow, mediation of renin release, and regulation of sodium excretion. COX-2 inhibition may transiently decrease urine sodium excretion in some subjects and induce mild to moderate elevation of blood pressure. Furthermore, in conditions of relative intravascular volume depletion and/or renal hypoperfusion, interference with COX-2 activity can have deleterious effects on maintenance of renal blood flow and glomerular filtration rate. In addition to physiological regulation of COX-2 expression in the kidney, increased renal cortical COX-2 expression is seen in experimental models associated with altered renal hemodynamics and progressive renal injury (decreased renal mass, poorly controlled diabetes), and long-term treatment with selective COX-2 inhibitors ameliorates functional and structural renal damage in these conditions.

Cyclooxygenase-2 expression in cultured cortical thick ascending limb of Henle increases in response to decreased extracellular ionic content by both transcriptional and post-transcriptional mechanisms. Role of p38-mediated pathways.

We showed previously that decreased extracellular salt or chloride up-regulates the cortical thick ascending limb of Henle (cTALH) COX-2 expression via a p38-dependent pathway. The present studies determined that low salt medium increased COX-2 mRNA expression 3.9-fold control by 6 h in cultured cTALH, which was blocked by actinomycin D pretreatment, suggesting transcriptional regulation. Luciferase activity (normalized to beta-galactosidase activity) of the full-length (-3400) COX-2 promoter in cTALH increased from 1.8 +/- 0.3 in control media to 5.8 +/- 0.7 in low salt (n = 9; p < 0.01). Low chloride medium had similar effects as low salt has on COX-2 promoter activity. Deletion constructs -815, -512, and -410 were similarly stimulated, but -385 could not be stimulated significantly by low salt (1.8 +/- 0.3 versus 2.4 +/- 0.5, n = 10). This suggested involvement of an NF-kappaB cis-element located in this region, which was confirmed by utilizing a construct with a point mutation of this NF-kappaB-binding site that was not stimulated by low salt medium. Co-incubation of the specific p38 inhibitor, SB203580 or PD169316, inhibited a low salt-induced increase in luciferase activity of the intact COX-2 promoter (5.8 +/- 0.7 versus 1.1 +/- 0.2, n = 8 and 1.4 +/- 0.4, n = 4 respectively, p < 0.01). Mobility shift assays indicated that the low salt medium stimulated NF-kappaB binding activity, and this stimulation was inhibited by p38 inhibitors. To test whether p38 also increased COX-2 expression by increasing mRNA stability, cTALH were incubated in low salt for 2 h, and actinomycin was then added with or without SB203580. p38 inhibition led to a decreased half-life of COX-2 mRNA (from 68 to 18 min, n = 4-7, p < 0.05). Therefore, these studies indicate that p38 stimulates COX-2 expression in cTALH and macula densa by transcriptional regulation predominantly via a NF-kappaB-dependent pathway and by post-transcriptional increases in mRNA stability.

The type 1 angiotensin II receptor tail affects receptor targeting, internalization, and membrane fusion properties.

Endocytosis modulates cell responses by removing and recycling receptors from the cell surface. Type I angiotensin II receptors (AT1R) are somewhat unique in that they are expressed at apical (AP) and basolateral (BL) membranes in proximal tubule cells and both receptor sites undergo endocytosis. We analyzed AT1R cytoplasmic (-COOH) tail deletion mutants to determine whether classic AT1R endocytosis motifs functioned similarly in polarized cells and simultaneously altered receptor properties. Serially truncating the AT1R tail had little effect on AP/BL AT1R distribution as determined by 125I-angiotensin II binding in LLCPK(Cl4) cells transfected with an AT1R transcript. AP AT1R expression required the proximal 12 amino acids in the AT1R-COOH tail. Deleting all but the proximal 12 aa of the AT1R-COOH tail (T316L mutant) decreased AP AT1R internalization at 20 min (17 +/- 6%; p < 0.05 versus full-length; n = 5) and inhibited AP AT1R-stimulated arachidonic acid release (counts released per milligram of protein at 20 min: full-length, 18,762 +/- 4018; T316L, 2430 +/- 1711; n = 4; p < 0.02). Endosomal fusion assays were performed using peptide sequences of regions in the AT1R tail involved in endocytosis (YFLQLLKYIPP [LL] and LSTKMSTLSY [STL]). Peptide STL significantly inhibited endosomal fusion (22 +/- 10% of control; n = 5; p < 0.05 versus positive control). Peptide LL had no significant inhibitory effect. AT(1)R in polarized cells contain dominant endocytosis signals but these motifs do not correlate with AP or BL AT1R expression. Moreover, peptide sequences within the AT1R-COOH tail necessary for endocytosis also modulate endosomal fusion properties.

Cyclooxygenase-2 inhibitor blocks expression of mediators of renal injury in a model of diabetes and hypertension.

BACKGROUND: We previously reported that renal cortical cyclooxygenase (COX-2) expression increased following subtotal nephrectomy, and chronic treatment with a selective COX-2 inhibitor, SC58236, reduced proteinuria and retarded the development of glomerulosclerosis. The present studies were designed to examine the effects of COX-2 inhibition in a model of diabetic nephropathy. METHODS: Rats were divided into three groups: control, diabetic (streptozotocin-induced diabetic animals with superimposed DOCA/salt hypertension; right nephrectomy and DOCA treatment), and treated (administration of the selective COX-2 inhibitor, SC58236, to a subset of diabetic/DOCA/salt rats). Insulin was administered to maintain blood glucose in the 200 to 300 mg/dL range. RESULTS: Systolic blood pressure in the two diabetic groups was elevated within one week and remained elevated until sacrifice at six weeks (control, 108 +/- 2 mm Hg; diabetic, 158 +/- 4 mm Hg; treated, 156 +/- 7 mm Hg). When measured at six weeks, immunoreactive COX-2 expression in the renal cortex of the diabetic rats was 2.5 +/- 0.3-fold of control animals (N = 7). Immunohistochemical localization indicated increased expression in macula densa and surrounding cortical thick ascending limb of Henle (cTALH). The COX-2 inhibitor decreased COX-2 expression in diabetic rats to 1.3 +/- 0.1-fold control. In addition, SC58236 decreased expression of PAI-1 (diabetic vs. treated, 3.2 +/- 0.5 vs. 1.7 +/- 0.2-fold control, N = 7, P < 0.05), vascular endothelial growth factor (VEGF; 2.0 +/- 0.2 vs. 1.2 +/- 0.2; N = 7, P < 0.05), fibronectin (2.4 +/- 0.3 to 1.3 +/- 0.1; N = 7, P < 0.05) and transforming growth factor-beta (TGF-beta; 2.1 +/- 0.2 vs. 1.3 +/- 0.2; N = 7, P < 0.05). Proteinuria at six weeks was decreased in the SC58236-treated rats (149 +/- 8 vs. 92 +/- 8 mg/24 h; N = 7, P < 0.01). The mesangial sclerosis index, defined as increases in extracellular matrix within the mesangial space, was determined at six weeks; the control group had an index of 0.06 +/- 0.01, the diabetic group was 2.7 +/- 0.04 and the treated group was 0.6 +/- 0.03 (P < 0.0001 compared to the diabetic group). CONCLUSIONS: These results suggest that in an experimental model of diabetes and hypertension, inhibition of COX-2 expression decreases potential mediators of glomerular and tubulointerstitial injury and also decreases biochemical, functional and structural markers of renal injury.

Prostaglandins that increase renin production in response to ACE inhibition are not derived from cyclooxygenase-1.

It is well known that nonselective, nonsteroidal anti-inflammatory drugs inhibit renal renin production. Our previous studies indicated that angiotensin-converting enzyme inhibitor (ACEI)-mediated renin increases were absent in rats treated with a cyclooxygenase (COX)-2-selective inhibitor and in COX-2 -/- mice. The current study examined further whether COX-1 is also involved in mediating ACEI-induced renin production. Because renin increases are mediated by cAMP, we also examined whether increased renin is mediated by the prostaglandin E(2) receptor EP(2) subtype, which is coupled to G(s) and increases cAMP. Therefore, we investigated if genetic deletion of COX-1 or EP(2) prevents increased ACEI-induced renin expression. Age- and gender-matched wild-type (+/+) and homozygous null mice (-/-) were administered captopril for 7 days, and plasma and renal renin levels and renal renin mRNA expression were measured. There were no significant differences in the basal level of renal renin activity from plasma or renal tissue in COX-1 +/+ and -/- mice. Captopril administration increased renin equally [plasma renin activity (PRA): +/+ 9.3 +/- 2.2 vs. 50.1 +/- 10.9; -/- 13.7 +/- 1.5 vs. 43.9 +/- 6.6 ng ANG I x ml(-1) x h(-1); renal renin concentration: +/+ 11.8 +/- 1.7 vs. 35.3 +/- 3.9; -/- 13.0 +/- 3.0 vs. 27.8 +/- 2.7 ng ANG I x mg protein(-1) x h(-1); n = 6; P < 0.05 with or without captopril]. ACEI also increased renin mRNA expression (+/+ 2.4 +/- 0.2; -/- 2.1 +/- 0.2 fold control; n = 6-10; P < 0.05). Captopril led to similar increases in EP(2) -/- compared with +/+. The COX-2 inhibitor SC-58236 blocked ACEI-induced elevation in renal renin concentration in EP(2) null mice (+/+ 24.7 +/- 1.7 vs. 9.8 +/- 0.4; -/- 21.1 +/- 3.2 vs. 9.3 +/- 0.4 ng ANG I x mg protein(-1) x h(-1); n = 5) as well as in COX-1 -/- mice (SC-58236-treated PRA: +/+ 7.3 +/- 0.6; -/- 8.0 +/- 0.9 ng ANG I x ml(-1) x h(-1); renal renin: +/+ 9.1 +/- 0.9; -/- 9.6 +/- 0.5 ng ANG I x mg protein(-1) x h(-1); n = 6-7; P < 0.05 compared with no treatment). Immunohistochemical analysis of renin expression confirmed the above results. This study provides definitive evidence that metabolites of COX-2 rather than COX-1 mediate ACEI-induced renin increases. The persistent response in EP(2) nulls suggests involvement of prostaglandin E(2) receptor subtype 4 and/or prostacyclin receptor (IP).