Lipid acetylation reactions and the metabolism of platelet-activating factor

X-Linked Immunodeficient Mice With No Functional Bruton's Tyrosine Kinase Are Protected From Sepsis-Induced Multiple Organ Failure

We previously reported the Bruton's tyrosine kinase (BTK) inhibitors ibrutinib and acalabrutinib improve outcomes in a mouse model of polymicrobial sepsis. Now we show that genetic deficiency of the BTK gene alone in Xid mice confers protection against cardiac, renal, and liver injury in polymicrobial sepsis and reduces hyperimmune stimulation (“cytokine storm”) induced by an overwhelming bacterial infection. Protection is due in part to enhanced bacterial phagocytosis in vivo, changes in lipid metabolism and decreased activation of NF-κB and the NLRP3 inflammasome. The inactivation of BTK leads to reduced innate immune cell recruitment and a phenotypic switch from M1 to M2 macrophages, aiding in the resolution of sepsis. We have also found that BTK expression in humans is increased in the blood of septic non-survivors, while lower expression is associated with survival from sepsis. Importantly no further reduction in organ damage, cytokine production, or changes in plasma metabolites is seen in Xid mice treated with the BTK inhibitor ibrutinib, demonstrating that the protective effects of BTK inhibitors in polymicrobial sepsis are mediated solely by inhibition of BTK and not by off-target effects of this class of drugs.

Application of a TCA-precipitation method for the determination of 1-alkyl-sn-glycero-3-phosphate: Acetyl-CoA acetyltransferase in human renal tissue

The activity of 1-alkyl-sn-glycero-3-phosphate:Acetyl-CoA acetyltransferase, which catalyses the first step of the de novo biosynthesis of PAF, was determined and characterised in cortical and medullary human renal tissues. A novel thin-layer chromatographic system as well as a trichloroacetic acid precipitation method, were utilised in order to determine the enzyme's activity. The acetyltransferase activity was associated with the membranous fractions of the renal tissue, it showed an optimum pH of 8.4 and it had a bell-shaped dependence on BSA concentration. One or more disulphide bonds were necessary for the action of acetyltransferase while the enzyme seemed to be independent from divalent cations. Two assay products were extracted from the incubation mixture namely alkylacetylphosphatidic acid, produced by the acetylating action of the acetyltransferase on alkyllyso-phosphatidic acid and alkylacetyl-glycerol, which is produced by the action of a phosphohydrolase on alkylacetylphosphatidic acid. The presence of NaF in the assay mixture resulted to a decreased degradation of alkylacetylphosphatidic acid, as well as to an increased overall product formation. Cortical and medullary acetyltransferases share similar biochemical properties and there is no statistical difference between the two activities.

Acetylation suppresses the proapoptotic activity of GD3 ganglioside

GD3 synthase is rapidly activated in different cell types after specific apoptotic stimuli. De novo synthesized GD3 accumulates and contributes to the apoptotic program by relocating to mitochondrial membranes and inducing the release of apoptogenic factors. We found that sialic acid acetylation suppresses the proapoptotic activity of GD3. In fact, unlike GD3, 9-O-acetyl-GD3 is completely ineffective in inducing cytochrome c release and caspase-9 activation on isolated mitochondria and fails to induce the collapse of mitochondrial transmembrane potential and cellular apoptosis. Moreover, cells which are resistant to the overexpression of the GD3 synthase, actively convert de novo synthesized GD3 to 9-O-acetyl-GD3. The coexpression of GD3 synthase with a viral 9-O-acetyl esterase, which prevents 9-O-acetyl-GD3 accumulation, reconstitutes GD3 responsiveness and apoptosis. Finally, the expression of the 9-O-acetyl esterase is sufficient to induce apoptosis of glioblastomas which express high levels of 9-O-acetyl-GD3. Thus, sialic acid acetylation critically controls the proapoptotic activity of GD3.