Saffron extract attenuates neuroinflammation in rmTBI mouse model by suppressing NLRP3 inflammasome activation via SIRT1

Abstract

Traumatic brain injury (TBI) remains a major cause of morbidity and disability worldwide and a healthcare burden. TBI is an important risk factor for neurodegenerative diseases hallmarked by exacerbated neuroinflammation. Neuroinflammation in the cerebral cortex plays a critical role in secondary injury progression following TBI. The NOD-like receptors (NLR) family pyrin domain containing 3 (NLRP3) inflammasome is a key player in initiating the inflammatory response in various central nervous system disorders entailing TBI. This current study aims to investigate the role of NLRP3 in repetitive mild traumatic brain injury (rmTBI) and identify the potential neuroprotective effect of saffron extract in regulating the NLRP3 inflammasome. 24 hours following the final injury, rmTBI causes an upregulation in mRNA levels of NLRP3, caspase-1, the apoptosis-associated speck-like protein containing a CARD (ASC), nuclear factor kappa B (NF-κB), interleukin-1Beta (IL-1β), interleukin 18 (IL-18), nuclear factor erythroid 2–related factor 2 (NRF2) and heme oxygenase 1 (HMOX1). Protein levels of NLRP3, sirtuin 1 (SIRT1), glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1), and neuronal nuclei (Neu N) also increased after rmTBI. Administration of saffron alleviated the degree of TBI, as evidenced by reducing the neuronal damage, astrocyte, and microglial activation. Pretreatment with saffron inhibited the activation of NLRP3, caspase-1, and ASC concurrent to reduced production of the inflammatory cytokines IL-1β and IL-18. Additionally, saffron extract enhanced SIRT1 expression, NRF2, and HMOX1 upregulation. These results suggest that NLRP3 inflammasome activation and the subsequent inflammatory response in the mice cortex are involved in the process of rmTBI. Saffron blocked the inflammatory response and relieved TBI by activating detoxifying genes and inhibiting NLRP3 activation. The effect of saffron on the NLRP3 inflammasome may be SIRT1 and NF-κB dependent in the rmTBI model. Thus, brain injury biomarkers will help in identifying a potential therapeutic target in treating TBI-induced neurodegenerative diseases.

Saffron extract and crocin exert anti-inflammatory and anti-oxidative effects in a repetitive mild traumatic brain injury mouse model

“…Glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1) are major markers of astrocyte and microglial activity respectively 40 , 41 and neuronal nuclei (Neu N) acts as a neuronal damage marker 42 . In our recent study 43 , the expression levels of these markers were measured to assess the head injury and an increase in their expression levels was observed in the TBI group confirming induction of astrocyte, microglial activation, and neuronal injury.…”

“…Sirtuin 1 (SIRT1) is also an essential element for normal cognitive function and synaptic plasticity 67 and proved to enhance cognitive dysfunction in many studies 68 , 69 . The measured SIRT1 levels were also suppressed post TBI 43 . In alignment with our data, inhibition of NLRP3 inflammasome has shown to play a crucial part in ameliorating the cognitive deficits induced in diabetic rats following ischemia 70 , encephalomyelitis 71 , AD models 68 , and TBI models 72 .…”

“…Overactivation of inflammatory mediators such as cytokines and inflammasomes may lead to detrimental neurological consequences that can be improved using anti-inflammatory interventions 62 . To assess saffron and crocin anti-inflammatory efficacy following repetitive injury, we measured the levels of brain cytokines TNF-α and IFNγ 24 h after the last brain hit, and in our recent study 43 we assessed the expression levels of NF-κB, NLRP3, and its related gene caspase-1, the apoptosis-associated speck-like protein containing a CARD (ASC), IL-1β, and IL-18. The obtained data reasonably explains the emergence of cognitive and motor deficits in our model, as inflammation is associated with such elicited acute disturbances following TBI 63 – 66 .…”

“…The levels of pro-inflammatory cytokines TNF alpha (TNF-α) and interferon-gamma (IFN-γ) were measured using commercially available kits (Elabscience, United States, catalog number: E-EL-M0049 for the TNF-α and E-EL-M0048 for IFN-γ) according to the manufacturer’s instructions. The experiments were conducted as described in our previous work 43 . In brief, standards and supernatants of homogenates were added to the 96-well plates coated with the specific murine monoclonal antibodies raised against TNF-α or IFN-γ.…”

SIRT1 Promotes M2 Microglia Polarization via Reducing ROS-Mediated NLRP3 Inflammasome Signaling After Subarachnoid Hemorrhage

“…Shaheen et al. reported that saffron attenuated neuroinflammation in TBI mouse model by suppressing NLRP3 inflammasome via SIRT1 activation ( 49 ). Li et al.…”