The main lesion in Parkinson disease (PD) is loss of substantia nigra dopaminergic neurons. Levodopa (l-DOPA) is the most widely used therapy, but it does not arrest disease progression. Some possible contributing factors to the continuing neuronal loss are oxidative stress, including oxidation of l-DOPA, and neurotoxins generated by locally activated microglia and astrocytes. A possible method of reducing these factors is to produce l-DOPA hybrid compounds that have antioxidant and antiinflammatory properties. Here we demonstrate the properties of four such l-DOPA hybrids based on coupling l-DOPA to four different hydrogen sulfide-donating compounds. The donors themselves were shown to be capable of conversion by isolated mitochondria to H₂S or equivalent SH⁻ ions. This capability was confirmed by in vivo results, showing a large increase in intracerebral dopamine and glutathione after iv administration in rats. When human microglia, astrocytes, and SH-SY5Y neuroblastoma cells were treated with these donating agents, they all accumulated H₂S intracellularly as did their derivatives coupled to l-DOPA. The donating agents and the l-DOPA hybrids reduced the release of tumor necrosis factor-α, interleukin-6, and nitric oxide from stimulated microglia, astrocytes as well as the THP-1 and U373 cell lines. They also demonstrated a neuroprotective effect by reducing the toxicity of supernatants from these stimulated cells to SH-SY5Y cells. l-DOPA itself was without effect in any of these assays. The H₂S-releasing l-DOPA hybrid molecules also inhibited MAO B activity. They may be useful for the treatment of PD because of their significant antiinflammatory, antioxidant, and neuroprotective properties.

The activity of NADPH oxidase (NOX) is blocked by nitric oxide (NO). Hydrogen sulfide (H₂S) is also produced by blood vessels. It is reasonable to suggest that H₂S may have similar actions to NO on NOX. In order to test this hypothesis, the effect of sodium hydrosulfide (NaHS) on O₂^– formation, the expression of NOX-1 (a catalytic subunit of NOX) and Rac₁ activity (essential for full NOX activity) in isolated vascular smooth muscle cells (hVSMCs) was investigated. hVSMCs were incubated with the thromboxane A₂ analogue U46619 ± NaHS for 1 or 16 h, and O₂^– formation, NOX-1 expression and Rac₁ activity were assessed. The possible interaction between H₂S and NO was also studied by using an NO synthase inhibitor, L-NAME, and an NO donor, DETA-NONOate. The role of K_ATP channels was studied by using glibenclamide. NaHS inhibited O₂^– formation following incubation of 1 h (IC₅₀, 30 nM) and 16 h (IC₅₀, 20 nM), blocked NOX-1 expression and inhibited Rac₁ activity. These inhibitory effects of NaHS were mediated by the cAMP-protein-kinase-A axis. Exogenous H₂S prevents NOX-driven intravascular oxidative stress through an a priori inhibition of Rac₁ and downregulation of NOX-1 protein expression, an effect mediated by activation of the adenylylcyclase-cAMP-protein-kinase-G system by H₂S.

Background and purpose: Superoxide (O₂^•−), derived from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, is associated with acute respiratory distress syndrome (ARDS). NADPH oxidase activity and expression are blocked by nitric oxide (NO) and sildenafil. As another gas, hydrogen sulphide (H₂S) is formed by blood vessels, the effect of sodium hydrosulphide (NaHS) and the H₂S‐donating derivative of sildenafil, ACS6, on O₂^•− formation and the expression of gp91^phox (a catalytic subunit of NADPH oxidase) in porcine pulmonary arterial endothelial cells (PAECs) was investigated.Experimental approach: PAECs were incubated with 10 ng mL⁻¹ tumour necrosis factor‐α (TNFα) (±NaHS or ACS6), both of which released H₂S, for 2 h or 16 h. O₂^•− was measured. Expression of gp91^phox was measured by western blotting and the role of cyclic AMP (cAMP) and/or cyclic GMP was assessed using protein kinase inhibitors.Key results: After either 2‐ or 16‐h incubations, O₂^•− formation by PAECs was inhibited by NaHS or ACS6, with IC₅₀ values of about 10 nM and less than 1 nM, respectively. Both 100 nM NaHS and 1 nM ACS6 completely inhibited gp91^phox expression induced by TNFα. The effects of NaHS were blocked by the inhibition of protein kinase A (PKA), but not PKG, and not by the inhibition of guanylyl cyclase. Effects of ACS6 were blocked by inhibition of both PKA and PKG. Both NaHS and ACS6 augmented cAMP formation.Conclusion and implications: H₂S inhibited O₂^•− formation and upregulation of NADPH oxidase in PAECs through the adenylyl cyclase‐PKA pathway. ACS6 may be effective in treating ARDS through both elevation of cAMP and inhibition of phosphodiesterase type 5 activity.British Journal of Pharmacology (2008) 155, 984–994; doi:10.1038/bjp.2008.326; published online 1 September 2008