Inosine Treatment Attenuates White Matter Injury in Neonatal Rats Exposed to Maternal Inflammation

Abstract

Periventricular leukomalacia (PVL), a severe form of brain injury affecting premature infants, is characterized by damage to the cerebral white matter. Maternal inflammation has been identified as a critical etiological factor contributing to this condition. Microglia play a pivotal role in orchestrating the inflammatory response associated with PVL. To date, there are no established preventive or therapeutic interventions for this condition. Our prior research has indicated that inosine pretreatment during pregnancy notably mitigates maternal inflammation-induced hypomyelination in the offspring. However, it remains undetermined whether inosine administered following maternal inflammation offers protection against white matter injury of their offspring. In this investigation, Sprague-Dawley (SD) rats at embryonic day 17 (E17) were administered lipopolysaccharide (LPS) via intraperitoneal injection at a dosage of 350 µg/kg for two consecutive days, resulting in pups that served as PVL models. Following LPS injection, pregnant rats were treated with inosine at a dose of 100 mg/kg, twice daily for one day. Subsequently, the brains of their pups at postnatal day 7 were utilized for further analysis. The findings indicated that inosine treatment markedly diminished neuronal loss in newborn pups with PVL and enhanced myelination by encouraging the formation of myelin proteins and the differentiation of oligodendrocyte precursor cells (OPCs). This was evidenced by an increased number of CC-1 positive mature oligodendrocytes and a reduction in GPR17 levels, a negative regulator of OPCs differentiation. More significantly, inosine treatment not only decreased the quantity of Iba 1 positive microglial cells but also facilitated the shift of microglial phenotype from M1 to M2. This was characterized by a reduction in the expression of M1 microglial markers and pro-inflammatory factors (TNF-α, IL-6, IL-1β), along with an increase in M2 microglial markers and anti-inflammatory factors (IL-4, IL-10). Furthermore, the neuroprotective mechanism of inosine treatment on PVL may be linked to its suppression of TLR4-mediated inflammatory signaling molecules, specifically MyD88 and NF-κB expression, as inosine treatment reversed the elevated expression of TLR4, MyD88, and NF-κB proteins in the brains of PVL pups. In summary, the administration of inosine to pregnant rats exposed to LPS appears to have the potential to reduce brain damage in their PVL pups. The protective mechanism may be partly associated with the TLR4/MyD88/NF-κB signaling pathway.

Keywords: Inosine; Myelination; Neuroinflammation; Oligodendrocyte precursor cells; Periventricular leukomalacia.