Ruihua Wang ¹ Changlian Gan ^2* Rui Mao ³ Yang Chen ⁴ Ru Yan ⁵ Geng Li ^6* Tianqin Xiong ^7* Jianwen Guo ^8*

• ¹ Research Team of Prevention and Treatment of Cerebral Hemorrhage Applying Chinese Medicine, The Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong Province, China
• ² School of Traditional Dai Medicine, West Yunnan University of Applied Sciences, Dali, Yunnan Province, China
• ³ Second Clinical Medical College, Guangzhou University of Traditional Chinese Medicine, Guangzhou, Guangdong Province, China
• ⁴ Department of Bioinformatics, State Key Laboratory of Dampness Syndrome of Chinese Medicine, The Second Affiliated Hospital, Guangdong Provincial Hospital of Chinese Medicine, Guangzhou, China
• ⁵ State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau, Taipa, Macau Region, China
• ⁶ Experimental Animal Center, Guangzhou University of Chinese Medicine, Guangzhou, China
• ⁷ School of Pharmaceutical Science, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong Province, China
• ⁸ State Key Laboratory of Traditional Chinese Medicine Syndrome, Department of Neurology, Guangdong Provincial Academy of Chinese Medical Sciences, Guangdong Provincial Hospital of Chinese Medicine, The Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong Province, China

Stroke-associated pneumonia (SAP) is the major complication that worsens the functional outcome. A stable and reproducible experimental bacterial pneumonia model postintracerebral hemorrhage (ICH) is necessary to help investigating the pathogenesis and novel treatments of SAP. In this study, we established a Gram-negative bacterial pneumonia-complicating ICH rat model and an acute lung injury (ALI)-complicating ICH rat model induced by nasal inoculation with Klebsiella pneumoniae (Kp) or intratracheal inoculation with lipopolysaccharide (LPS) 3 days after ICH. In Kp-induced bacterial pneumonia-complicating ICH rats, we demonstrated that Kp challenge caused more severe neurological deficits, brain damage, neuroinflammation, and aggravated pneumonia and lung injury. Disruptions of the intestinal structure and gut barrier and the reductions of the protective intestinal IL-17A-producing γδT cells were also observed. Kp challenge exacerbated the gut microbiota dysbiosis and fecal metabolic profile disorders, which were characterized by abnormal sphingolipid metabolism especially elevated ceramide levels; increased levels of neurotoxic quinolinic acid and an upregulation of tryptophan (Trp)–serotonin–melatonin pathway. Spearman’s correlation analyses further revealed that the reduction or depletion of some beneficial bacteria, such as Allobaculum and Faecalitalea, and the blooming of some opportunistic pathogens, such as Turicibacter, Dietzia, Corynebacterium and Clostridium_sensu_stricto_1 in Kp-induced SAP rats were associated with the disordered sphingolipid and Trp metabolism. Using an LPS-induced ALI complicating ICH model, we also characterized SAP-induced brain, lung and gut histopathology injuries, peripheral immune disorders and intense pulmonary inflammatory responses. These two models may be highly useful for investigating the pathogenesis and screening and optimizing potential treatments for SAP. Moreover, the differential genera and sphingolipid or Trp metabolites identified above seem to be promising therapeutic targets.