After behavioral testing, adult offspring were sacrificed to confirm that inhibition of Stat3 phosphorylation by diosmin attenuates IL-6/Stat3 induced behavioral abnormalities. At sacrifice, brain homogenates were prepared from control mice and mice exposed prenatally to IL-6, IL-6/S31-201, and IL-6/Diosmin. Pro-inflammatory cytokine ELISA showed significant increases in TNF-α and IL-1β levels in the homogenates of IL-6 adult offspring. Maternal co-treatment with S31-201 or diosmin significantly reduced TNF-α and IL-1β cytokine levels, with diosmin showing slightly more significant reductions as shown in Fig. 4.8.
Western blot analysis of phospho- and total Stat3 showed that prenatal IL-6 treatment increased Stat3 phosphorylation in the brain homogenates of adult offspring while co-treatment with either S31-201 or diosmin lead to a significant reduction of STAT3 phosphorylation. This data suggest that activation of the Stat3 pathway following prenatal infection is a plays a major role in the resultant pathologies including behavioral deficits. Inhibition of Stat3 activation, by diosmin reduces these behavioral deficits and may be a key therapeutic intervention strategy.
Fig. 4.8
Diosmin reduces pro-inflammatory cytokine expression in the brain homogenates of prenatally exposed animals. Pro-inflammatory cytokine analysis by ELISA revealed a significant reduction of TNFα and IL-1β cytokines in brain homogenates from IL-6/31-201 and IL-6/Diosmin adult offspring when compared to offspring prenatally exposed to IL-6 only.(**P < 0.05).
Fig. 4.9
Diosmin attenuates Stat3 phosphorylation in the brain homogenates of prenatally exposed animals. Western blot analysis showed a significant reduction of STAT3 phosphorylation in brain homogenates from IL-6/S31-201 and IL-6/Diosmin/adult offspring when compared to offspring of IL-6 offspring. These reductions were further showed by densitometric analysis (**P < 0.005).
4.3 Discussion
Epidemiological data, clinical findings from pregnancy disorders and observations from murine models of prenatal infection have supported a role for activation of the maternal immune system, and subsequent maternal cytokine expression as a key component of their pathological mechanism (Hwang and Chen, Brown et al., 2000, Brown and Susser, 2002, Li et al., 2009, Atladottir et al., 2010).
Furthermore, IL-6 has been shown to be an important mediator of these pathological events through its dysregulation of the Stat3 pathway. This chapter shows how flavonoids luteolin and diosmin not only attenuate IL-6 mediated Stat3 activity but more importantly the adverse maternal and fetal outcomes stemming from prenatal infection.
To confirm the ability of luteolin to attenuate maternal immune responses during prenatal infection, cytokine production from the spleen was examined following an immunological challenge. The spleen is an important mediator during immune activation and a reservoir of pro-inflammatory cytokines. In splenocytes challenged with LPS or conA luteolin co-treatment significantly inhibited IL-6 and TNF-α expression.
Immunological disruption including increased IL-6 expression has been shown to be a consistent feature in adverse perinatal outcomes precipitated by prenatal bacterial or viral infections or instances of chronic immunological dysregulation. Increased plasma levels of IL-6 for example has been observed in FIRS precipitated by bacterial infections as well as in preeclampsia, thought to be connected to immunological disruptions (Gomez et al., 1998, Chaiworapongsa et al., 2002, Tosun et al., 2010, Zhou et al., 2011). The ability of luteolin to inhibit inflammatory response to both LPS and conA
1β, were reduced by luteolin in co-treatment. TNF-α and IL-1β have both been shown to indirectly induce IL-6 expression and Stat3 activity (Mori et al., 2011). As increased Stat3 activity is a known consequence of IL-6 expression, this was also examined. Stat3 phosphorylation was significantly reduction by luteolin co-treatment in prenatally challenged animals. The attenuation of maternal immunological disruptions and cytokine expression by luteolin also reduced fetal pathological outcomes, particularly growth restrictions, as mice exposed prenatally to LPS or IL-6 had significantly lower birth weights than control offspring, a pathology not seen in the offspring of mice that received luteolin co-treatment.
It is clear that maternal immunological disruptions following prenatal infection play an important role in adverse perinatal outcomes, however fetal immunological responses have also been observed to play an equally important role in pathologies, particularly the neurological abnormalities observed in prenatally exposed offspring (Dammann and Leviton, 2000, Chaiworapongsa et al., 2002). To examine the ability of flavonoids to attenuate fetal immune responses, fetal cytokine expression and Stat3 activity were examined in newborn and adult offspring, while abnormal behaviors were analyzed in the adult offspring of prenatally exposed animals. A more chronic administration route of flavonoid treatment was also examined. Diosmin dietary intervention was utilized to examine prenatal supplementation of flavonoids and their effects on fetal outcomes. Similar to maternal outcomes, there was an increase in inflammatory cytokines and Stat3 phosphorylation in the brains of prenatally exposed animals which was attenuated by diosmin co-treatment. Additionally, behavioral deficits observed in these animals were also attenuated following diosmin co-treatment. It is therefore evident that flavonoid co-treatment is a beneficial therapeutic intervention in prenatal infection, as it can reduce the neuropathological and abnormal behavioral outcomes seen in prenatally exposed offspring.
CHAPTER 5 CONCLUSION
Clinical observations in disorders such as preeclampsia, schizophrenia and ASD have highlighted the role of maternal immune activation and subsequent IL-6 expression, often a consequence of prenatal infection, in the pathological features observed in these disorders. Similarly, murine models replicating these disorders have identified this immune reaction and IL-6 expression as a central component of the pathological mechanism. Studies have also shown that IL-6 may be a measurable indicator of pathology and target of therapeutic intervention as inhibition of IL6 has been shown to reduce associated disease pathology (Smith et al., 2007, Zhou et al., 2011). In disorders such as preeclampsia for example, elevations in IL-6 have been implicated as an observable and measurable mediator of hypertension through its regulation of vasoconstrictive proteins and its inhibition has been shown to reduce this pathology (Zhou et al., 2011). Similarly, in models of prenatal infection meant to recapitulate neurodevelopmental disorders such as ASD, IL-6 has been shown to induce not only the neuropathologies such as abnormal cellular morphology, but also abnormal behaviors such as impaired social interactions, outcomes all attenuated by inhibition of IL-6 (Smith et al., 2007).
This study further explores how prenatal infection can lead to adverse perinatal
Stat3 pathway in these pathologies and how attenuation of this pathway, by flavonoids can reduce the pathological outcomes associated with prenatal infection. Chapter three explores this relationship by utilizing an in vitro model of pathological IL-6 expression to examine the neuropathologies that may occur following prenatal infection and subsequent exposure to IL-6. Treatment of neural stem cells with IL-6 revealed significant pathologies including increases in proliferation, and aberrant patterns of differentiation. Most notably, and possibly most relevant to clinical observations in disorders such as ASD were findings of increased astroglial differentiation following IL-6 treatment, an effect inhibited by luteolin co-treatment. Astrocyte pathologies have been implicated in neurological disorders such as epilepsy due largely to their role in regulating synaptic transmission, and their supportive role in maintaining optimal neuronal function and integrity in the CNS (Brunello et al., 2000, Dutuit et al., 2000, Brenner et al., 2001). These types of pathologies may be particularly relevant in disorder such as ASD as increased expression of astroglial markers such as GFAP and aquaporin 4 have been observed in post mortem autistic brain samples (Fatemi et al., 2004, Laurence and Fatemi, 2005, Fatemi et al., 2008a). When NSC cultures were co-treated with IL-6 and luteolin, astroglial differentiation, a Stat3 mediated event was significantly reduced. An examination of Stat3 phosphorylation showed that this was also significantly reduced following luteolin co-treatment suggesting prenatal luteolin treatment has the potential to attenuate IL-6/Stat3 mediated pathologies.
To expand on these findings, luteolin’s effects were investigated in vivo. The effects of chronic prenatal administration were also examined using diosmin. The experiments outlined in chapter four looked at the ability of luteolin and diosmin to inhibit activation of the maternal immune system as well as adverse fetal outcomes such as low birth weight, indicative of in utero growth restriction and abnormal behaviors. To look at maternal immune reactions, luteolin activity was examined in splenocyte cultures as well
as the spleens of recently delivered prenatally exposed animals. Luteolin treatment was able to attenuate inflammatory response following prenatal infection, an event mediated by attenuation of Stat3 phosphorylation, which was also inhibited by luteolin co-treatment. Specifically, luteolin inhibited expression of IL-6 and TNF-α in splenocytes challenged with LPS or conA, confirming the ability of luteolin to attenuate maternal immune responses independent of the pathogenic stimuli. In spleen tissue, luteolin inhibited TNF-α and IL-1β expression in the spleens of mice challenged with IL-6 or LPS.
Like IL-6, these cytokines have been shown to be elevated following prenatal infection and during other instances of immune dysregulation and can indirectly induce IL-6 expression and resultant activation of Stat3 (Mori et al., 2011).
The inhibition of maternal immune activation following prenatal infection by luteolin suggests fetal pathologies resulting from prenatal infection can also be attenuated by prenatal flavonoid treatment. To confirm this, several fetal outcomes were examined, including birth weight, as decreased birth weight is a known consequence of prenatal infection. As expected, prenatal infection not only activated the maternal immune system but also led to decreased birth weight in exposed offspring a feature often correlated to subsequent neurological deficits. These effects were significantly inhibited by luteolin co-treatment. The neurological consequences of prenatal infection were examined next. Although maternal cytokine expression has been noted as central to the pathologies attributed to prenatal infection, fetal immune activation has also been observed and are considered a key mediator of the neuropathologies and resultant neurological deficits observed in exposed offspring. Chronic flavonoid administration as
enriched diet from the time of prenatal challenge until birth, these pathologies were inhibited. To confirm the role of Stat3 activity in the neurological deficits following prental infection, behavioral outcomes were examined in prenatally exposed adult offspring.
The efficacy of flavonoids and inhibition of IL-6/Stat3 activity in reducing these abnormal behavioral outcomes were also examined. In mice prenatally exposed to IL-6, there were significant behavioral abnormalities observed including deficits in social interaction, a prominent feature in ASD and schizophrenia. In animals co-treated with diosmin, this deficit was significantly attenuated. More importantly, analysis of brain homogenates following behavioral assessment showed an attenuation of pro-inflammatory cytokine production and Stat3 phosphorylation.
Currently there is no cure for ASD and therapeutic interventions focus primarily on the management of symptoms, utilizing behavioral therapy to control the abnormal behaviors and pharmacological intervention to manage comorbid conditions. The role of prenatal infection in precipitating adverse pregnancy and fetal outcomes has not only provided a potential mechanism but a focus for therapeutic intervention as targeted inhibition of IL6 and Stat3 activation has been shown to attenuate, and in many cases completely ameliorate pathological outcomes. In addition to neurological disorders attributed to prenatal infection, disorders of pregnancy such as preeclampsia and recurrent spontaneous abortions share a similar pathology to those precipitated by prenatal infection due to the involvement of maternal immune dysregulation. This overlap in pathological features suggests that modulation of the maternal immune system may also be beneficial in these disorders and may be a potential therapeutic alternative. While some of these disorders such as recurrent miscarriages seem to be characterized by a persistent dysregulation of the maternal immune system and may require more aggressive and chronic treatments, others such as preeclampsia often appear more transient with a sudden onset of pathological symptoms and may benefit
from short term interventions. The results of this study show the potential for both chronic and one time flavonoid intervention to yield significant therapeutic effects.
Additionally, the relative safety of many of these flavonoid compounds make their application during pregnancy for chronic or transient treatment feasible as compounds such as diosmin have already been shown to be safe when administered during pregnancy (Buckshee et al., 1997). Although there is room for more research in this area, the potential application of flavonoid compounds, particularly diosmin and luteolin, is evident in light of their therapeutic efficacy in attenuating both maternal and fetal adverse outcomes during periods of maternal immune activation, or dysregulation.
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