Residual NO modulates contractile responses and membrane potential in isolated rat mesenteric arteries

Acute kidney injury in patients with burns

Burn injury is associated with a high risk of acute kidney injury (AKI) with a prevalence of AKI among patients with burns of 9-50%. Despite an improvement in burn injury survival in the past decade, AKI in patients with burns is associated with an extremely poor short-term and long-term prognosis, with a mortality of >80% among those with severe AKI. Factors that contribute to the development of AKI in patients with burns include haemodynamic alterations, burn-induced systemic inflammation and apoptosis, haemolysis, rhabdomyolysis, smoke inhalation injury, drug nephrotoxicity and sepsis. Early and late AKI after burn injury differ in their aetiologies and outcomes. Sepsis is the main driver of late AKI in patients with burns and late AKI has been associated with higher mortality than early AKI. Prevention of early AKI involves correction of hypovolaemia and avoidance of nephrotoxic drugs (for example, hydroxocobalamin), whereas prevention of late AKI involves prevention and early recognition of sepsis as well as avoidance of nephrotoxins. Treatment of AKI in patients with burns remains supportive, including prevention of fluid overload, treatment of electrolyte disturbance and use of kidney replacement therapy when indicated.

Selective and sensitive fluorescence imaging reveals microenvironment-dependent behavior of NO modulators in the endothelial system

Nitric oxide (NO) is a second messenger playing crucial roles in the signaling of a variety of cellular functions. Due to its pathophysiological significance, various NO modulators have been developed to explore NO pathways and some have been used as therapies. These modulators are often used directly to observe pharmacological effects in cell lines, but their actual effect on intracellular NO level is seldom analyzed. Herein, facilitated by a selective and sensitive fluorescence probe, we observed that some NO modulators displayed unexpected behaviors with both NO scavenger carboxy-PTIO and endothelial nitric oxide synthase (eNOS) inhibitor N(ω)-nitro-l-arginine methyl ester (l-NAME) failing to decrease intracellular free NO level in EA. hy926 cells while NO donor diethylamine-NONOate (DEA·NONOate) and eNOS activator calcimycin (A23187) failing to increase free NO level in human umbilical vein endothelial cell line (HUV-EC-C), although the reagents were confirmed to work normally in the primary human umbilical vein endothelial cells (primary HUVECs) and RAW 264.7 macrophage cells. Further research suggested that these unusual behaviors might be attributed to the cellular microenvironments including both the NO synthase (NOS) level and the endogenous glutathione (GSH) level. Genetically manipulating eNOS level in both cells restores the expected response, while decreasing GSH level restores the ability of DEA·NONOate to increase NO level in HUV-EC-C. These results reveal that the cellular microenvironment has a profound impact on pharmacological effect. Our study suggests GSH as a reservoir for NO in live cells and highlights the value of chemical probes as valuable tools to reveal microenvironment-dependent pharmacological effects.

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An imaging based method for evaluating the efficacy of NO modulators in live cells was developed.

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Some NO modulators were observed yielding unexpected effects on cellular NO levels in some endothelial cell lines.

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Further study unveiled intracellular microenvironments have profound effects on the efficacy of NO modulators in live cells.

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This result highlights the pitfall of the specific cellular microenvironments on drug efficacy.

Sulodexide promotes arterial relaxation via endothelium-dependent nitric oxide-mediated pathway

Sulodexide (SDX) is a highly purified glycosaminoglycan with antithrombotic and profibrinolytic properties and reported benefits in thrombotic and atherosclerotic vascular disorders. However, the effects of SDX on vascular function are unclear. We tested whether SDX affects vascular relaxation and examined the potential underlying mechanisms. Isolated segments of male rat abdominal aorta and mesenteric artery were suspended in a tissue bath, and the changes in arterial contraction/relaxation were measured. The α-adrenergic receptor agonist phenylephrine (Phe) (10^-9-10^-5 M) caused concentration-dependent aortic and mesenteric artery contraction that was reduced in tissues pretreated with SDX (1 mg/ml). In aortic and mesenteric arterial segments precontracted with submaximal concentration of Phe (3 × 10^-7-6 × 10^-7 M), SDX (0.001-1 mg/ml) caused concentration-dependent relaxation. To test the role of endothelium, SDX-induced relaxation was compared with that of acetylcholine (ACh), a known activator of endothelium-dependent relaxation. In Phe precontracted aorta, ACh relaxation was abolished and SDX relaxation was significantly inhibited by endothelium removal or the nitric oxide synthase (NOS) inhibitor N_ω-nitro-l-arginine methyl ester (L-NAME), suggesting a role of NO. In mesenteric artery, ACh relaxation was abolished by endothelium removal, partially blocked by L-NAME, and completely blocked by a mixture of indomethacin, a cyclooxygenase inhibitor and blocker of the PGI₂-cAMP pathway, and tetraethylammonium, a blocker of K⁺ channels and EDHF-dependent hyperpolarization pathway. In comparison, SDX relaxation of mesenteric artery was almost completely inhibited by endothelium removal or NOS inhibitor L-NAME. SDX enhanced vascular relaxation and increased nitrate/nitrite production in response to all ACh concentrations in the aorta, but only to low ACh concentrations (<10^-7 M) in mesenteric artery. SDX did not affect aortic or mesenteric artery endothelium-independent relaxation to the NO donor sodium nitroprusside. Thus, SDX promotes arterial relaxation via a mechanism involving endothelium-dependent NO production; an effect that could enhance vasodilation and decrease vasoconstriction in vascular disorders.

Light-induced formation of NO in endothelial cells by photoactivatable NADPH analogues targeting nitric-oxide synthase

BACKGROUND

Nitric-oxide synthases (NOS) catalyze the formation of NO using NADPH as electron donor. We have recently designed and synthesized a new series of two-photon absorbing and photoactivatable NADPH analogues (NT). These compounds bear one or two carboxymethyl group(s) on the 2'- or/and 3'-position(s) of the ribose in the adenosine moiety, instead of a 2'-phosphate group, and differ by the nature of the electron donor in their photoactivatable chromophore (replacing the nicotinamide moiety). Here, we addressed the ability of NTs to photoinduce eNOS-dependent NO production in endothelial cells.

METHODS

The cellular fate of NTs and their photoinduced effects were studied using multiphoton fluorescence imaging, cell viability assays and a BODIPY-derived NO probe for NO measurements. The eNOS dependence of photoinduced NO production was addressed using two NOS inhibitors (NS1 and L-NAME) targeting the reductase and the oxygenase domains, respectively.

RESULTS

We found that, two compounds, those bearing a single carboxymethyl group on the 3'-position of the ribose, colocalize with the Golgi apparatus (the main intracellular location of eNOS) and display high intracellular two-photon brightness. Furthermore, a eNOS-dependent photooxidation was observed for these two compounds only, which is accompanied by a substantial intracellular NO production accounting for specific photocytotoxic effects.

CONCLUSIONS

We show for the first time that NT photoactivation efficiently triggers electron flow at the eNOS level and increases the basal production of NO by endothelial cells.

GENERAL SIGNIFICANCE

Efficient photoactivatable NADPH analogues targeting NOS could have important implications for generating apoptosis in tumor cells or modulating NO-dependent physiological processes.