Induction of hemeoxygenase-1 expression after inhibition of hemeoxygenase activity promotes inflammation and worsens ischemic brain damage in mice.

Hemeoxygenase (HO) is an enzymatic system that degrades heme. HO-1 is an inducible isoform whereas HO-2 is constitutive. Stroke strongly induces HO-1 expression but the underlying mechanisms are not fully elucidated. Cytokines that are up-regulated after ischemia, like interleukin (IL)-10, can induce HO-1 gene expression, which is positively regulated by the transcriptional activator nuclear factor erythroid 2-related factor 2 (Nrf2) and negatively regulated by the transcriptional repressor breast cancer type 1 susceptibility protein (BRCA1) associated C-terminal helicase 1 (Bach-1). While Nrf2 is activated after ischemia and drugs promoting Nrf2 activation increase HO-1 and are beneficial, the involvement of Bach-1 is unknown. Here we investigated mechanisms involved in HO-1 induction and evaluated the effects of HO activity inhibition in mouse permanent middle cerebral artery occlusion (pMCAO). HO-1 was induced after ischemia in IL-10-deficient mice suggesting that post-ischemic HO-1 induction was IL-10-independent. Attenuation of Bach-1 gene repression after ischemia was associated to enhanced HO-1 induction. Administration of the HO activity inhibitor zinc proto-porphyrin IX (ZnPP) i.p. 24h before pMCAO exacerbated ischemia-induced tumor necrosis factor-α (TNF-α) and IL-1ß, nitro-oxidative stress, and the presence of neutrophils at 8h, and increased infarct volume at day 4. However, ZnPP did not worsen ischemic damage when given 30min before pMCAO. ZnPP induced HO-1 expression in the cerebral vasculature at 24h, when it was still detected by high-performance liquid chromatography (HPLC) in plasma. While ZnPP was not found in brain tissue extracts of controls, it could be detected after ischemia, supporting that a small fraction of the injected drug can reach the tissue following blood-brain barrier breakdown. The deleterious effect of inhibiting HO activity in ischemia became apparent in the presence of ZnPP-induced HO-1, which is known to exert effects independent of its enzymatic activity. In conclusion, HO-1 induction after ischemia was associated to down-regulation of transcriptional repressor Bach-1, and induction of HO-1 when HO enzymatic activity was inhibited was related to worst outcome after brain ischemia.

Chondroitin sulfate inhibits lipopolysaccharide-induced inflammation in rat astrocytes by preventing nuclear factor kappa B activation.

Chondroitin sulfate (CS) is a glucosaminoglycan (GAG) currently used for the treatment of osteoarthritis because of its antiinflammatory and antiapoptotic actions. Recent evidence has revealed that those peripheral effects of CS may also have therapeutic interest in diseases of the CNS. Since neuroinflammation has been implicated in different neuronal pathologies, this study was planned to investigate how CS could modulate the inflammatory response in the CNS by using rat astrocyte cultures stimulated with lipopolysaccharide (LPS). We have evaluated different proteins implicated in the nuclear factor kappa B (NFkappaB) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways employing RT-PCR, western blot and immunofluorescence techniques. At 10 microM, CS prevented translocation of p65 to the nucleus, reduced tumour necrosis factor alpha (TNF-alpha) mRNA and mitigated cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) induction by LPS. However, it did not modify LPS-induced IP-10 and SOCS-1 mRNA, proteins that participate in the JAK/STAT pathway. The results of this study indicate that CS can potentially reduce neuroinflammation by inhibition of NFkappaB. Therefore endogenous GAGs could afford neuroimmunomodulatory actions under neurotoxic conditions.

Signalling pathways mediating inflammatory responses in brain ischaemia.

Stroke causes neuronal necrosis and generates inflammation. Pro-inflammatory molecules intervene in this process by triggering glial cell activation and leucocyte infiltration to the injured tissue. Cytokines are major mediators of the inflammatory response. Pro-inflammatory and anti-inflammatory cytokines are released in the ischaemic brain. Anti-inflammatory cytokines, such as interleukin-10, promote cell survival, whereas pro-inflammatory cytokines, such as TNFalpha (tumour necrosis factor alpha), can induce cell death. However, deleterious effects of certain cytokines can turn to beneficial actions, depending on particular features such as the concentration, time point and the very intricate network of intracellular signals that become activated and interact. A key player in the intracellular response to cytokines is the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway that induces alterations in the pattern of gene transcription. These changes are associated either with cell death or survival depending, among other things, on the specific proteins involved. STAT1 activation is related to cell death, whereas STAT3 activation is often associated with survival. Yet, it is clear that STAT activation must be tightly controlled, and for this reason the function of JAK/STAT modulators, such as SOCS (suppressors of cytokine signalling) and PIAS (protein inhibitor of activated STAT), and phosphatases is most relevant. Besides local effects in the ischaemic brain, cytokines are released to the circulation and affect the immune system. Unbalanced pro-inflammatory and anti-inflammatory plasma cytokine concentrations favouring an 'anti-inflammatory' state can decrease the immune response. Robust evidence now supports that stroke can induce an immunodepression syndrome, increasing the risk of infection. The contribution of individual cytokines and their intracellular signalling pathways to this response needs to be further investigated.