Neuroimmune Communication in the Kidney

Inflammatory Determinants and Associated Morbidity in Hemodialysis Patients

Hemodialysis deteriorates patients' physical, metabolic, and mental status. Clinical outcomes derived from inflammation determine a worse status but are less frequently identified. The objective of the study was to identify inflammatory determinants and the effect of SNP-related serum IL-6 and IL-10 levels on associated morbidity in hemodialysis. A sample of hemodialysis patients at IMSS Regional Hospital No.46 in Guadalajara (n = 85) were tested using the Malnutrition Inflammation Score (MIS) and Patient Health Questionnaire-9 (PHQ-9) to assess the associated morbidity. Serum cytokine levels were quantified by enzyme-linked immunosorbent assay (ELISA). The restriction fragment length polymorphism (RFLP) technique was used for analysis of IL-6-572C/G and IL-10-1082A/G. Using data visualization methods, we identified relevant determinants of inflammation. A simple regression model was constructed between predictors and targets with genotypes as covariates. Results showed malnutrition in 85.9% of patients and depressive symptoms in 50.6%. IL-10 was the most relevant inflammatory determinant, with regression coefficients (R2) between 0.05 and 0.11. The GG genotype of IL-10-1082 A/G evinced small effect on both clinical outcomes (δ of 0.35 and 0.37, respectively). Hemodialysis increases the associated morbidity, cytokines act as inflammatory determinants, and genetic variability contributes to the severity of clinical outcomes. Further studies need to refine the causal relationship between inflammation and CKD.

Neuroimmune system-mediated renal protection mechanisms

The autonomic nervous system plays an important role in maintaining homeostasis in organisms. Recent studies have shown that it also controls inflammation by directly altering the function of the immune system. The cholinergic anti-inflammatory pathway (CAP) is one of the neural circuits operating through the vagus nerve. Acetylcholine released from the terminal of the vagus nerve, which is a parasympathetic nerve, acts on the α7 nicotinic acetylcholine receptor of macrophages and reduces inflammation in the body. Previous animal studies demonstrated that vagus nerve stimulation reduced renal ischemia-reperfusion injury. Furthermore, restraint stress and pulsed ultrasound had similar protective effects against kidney injury, which were mainly thought to be mediated by the CAP. Using optogenetics, which can stimulate specific nerves, it was also revealed that activation of the CAP by restraint stress was mediated by C1 neurons in the medulla oblongata. Nevertheless, there still remain many unclear points regarding the role of the nervous and immune systems in controlling renal diseases, and further research is needed.