Dendrimer mediated targeted delivery of sinomenine for the treatment of acute neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a significant medical problem with limited treatment options and is one of the main causes of life-long disability. Neuroinflammation orchestrated by activated microglia/macrophages at the site of injury plays a critical role in the onset of many pathological events following TBI, leading to blood brain barrier (BBB) dysfunction, neuronal damage and long term neuronal and behavioral deficits. Current treatment involves intravenous administration of anti-inflammatory drugs which have limited clinical outcomes only when dosed within the early time window after injury. Hence there is an urgent need to develop improved drug delivery systems which have potential to cross impaired BBB, target and deliver drugs selectively to activated microglia/macrophages at the sites of injury, and suppress the detrimental effects of acute inflammation. In this study, we have used Sinomenine (Sino), a potent anti-inflammatory and antioxidant drug conjugated to hydroxyl terminated generation-4 PAMAM dendrimer (D-Sino) as a potential therapy for attenuating early inflammation in TBI. D-Sino conjugates were synthesized using highly robust copper-catalyzed click reaction with high purity. D-Sino conjugates enhanced the intracellular availability of Sino due to their rapid cellular uptake, significantly attenuated early/acute inflammation by suppressing pro-inflammatory cytokines (TNF-α, IL-1β, CCL-3 and IL-6), and reduced oxidative stress (iNOS and NO) in LPS activated murine macrophages (RAW 264.7) by inhibiting NF-κB activation and its nuclear translocation (the root cause for inflammation inception) significantly more as compared to the free drug. Upon systemic administration in a rabbit model of pediatric TBI, D-Sino conjugates specifically targeted activated microglia/macrophages at the site of injury in the brain. Single dose of D-Sino attenuated inflammation in the injured brain areas by suppressing inflammatory cytokines expression whereas free Sino treatment did not demonstrate a significant effect. Together, these results suggest that D-Sino conjugate may open up new avenues for increasing the therapeutic window in the treatment of early inflammation and for improving the efficacy of the drug in TBI. Moreover, this treatment can work in conjunction with current clinical practices such as therapeutic hypothermia and pharmacologically induced coma for many indications associated with TBI, where acute inflammation plays a critical role in disease progression.