Serum and brain purine levels in an experimental systemic infection of mice by Cryptococcus neoformans : Purinergic immunomodulatory effects

Purinergic signaling in infectious diseases of the central nervous system

The incidence of infectious diseases affecting the central nervous system (CNS) has been increasing over the last several years. Among the reasons for the expansion of these diseases and the appearance of new neuropathogens are globalization, global warming, and the increased proximity between humans and wild animals due to human activities such as deforestation. Neurotropism affecting normal brain function is shared by organisms such as viruses, bacteria, fungi, and parasites. Neuroinfections caused by these agents activate immune responses, inducing neuroinflammation, excitotoxicity, and neurodegeneration. Purinergic signaling is an evolutionarily conserved signaling pathway associated with these neuropathologies. During neuroinfections, host cells release ATP as an extracellular danger signal with pro-inflammatory activities. ATP is metabolized to its derivatives by ectonucleotidases such as CD39 and CD73; ATP and its metabolites modulate neuronal and immune mechanisms through P1 and P2 purinergic receptors that are involved in pathophysiological mechanisms of neuroinfections. In this review we discuss the beneficial or deleterious effects of various components of the purinergic signaling pathway in infectious diseases that affect the CNS, including human immunodeficiency virus (HIV-1) infection, herpes simplex virus type 1 (HSV-1) infection, bacterial meningitis, sepsis, cryptococcosis, toxoplasmosis, and malaria. We also provide a description of this signaling pathway in emerging viral infections with neurological implications such as Zika and SARS-CoV-2.

Theacrine protects against nonalcoholic fatty liver disease by regulating acylcarnitine metabolism

OBJECTIVE

Acylcarnitine metabolism disorder contributes significantly to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). There are, however, few ideal medications for NAFLD, which work by targeting acylcarnitine metabolism. The aim of this study was to investigate the protective effects of theacrine, a rare purine alkaloid isolated from Camellia assamica var. kucha, against acylcarnitine metabolism disorder in NAFLD.

METHODS

The pharmacological activities of theacrine were studied using high-fat diet (HFD)-fed ApoE-/- and C57BL/6J mice models. Oleate-treated HepG2 and L-02 cells were used to investigate the molecular mechanism of theacrine on acylcarnitine metabolism. The target of theacrine was confirmed in vitro as the blockade of sirtuin 3 (SIRT3) and protein kinase A.

RESULTS

Theacrine inhibits hepatic steatosis and liver inflammation and improves energy expenditure in HFD-fed mice. Theacrine ameliorates acylcarnitine metabolism disorder in HFD-fed mice and oleate-treated hepatocytes by improving fatty acid oxidation. The underlying mechanism involves theacrine's activation of the mitochondrial deacetylase SIRT3 and consequently, the increased activity of long-chain acyl coenzyme A dehydrogenase (LCAD) through deacetylation.

CONCLUSION

Theacrine promotes acylcarnitine metabolism in NAFLD through the SIRT3/LCAD signaling pathway. The target of theacrine's activities on NAFLD is identified as SIRT3.