A facile method for monitoring sphingomyelin synthase activity in HeLa cells using liquid chromatography/mass spectrometry.

Sphingomyelin synthase (SMS) is a sphingolipid-metabolizing enzyme involved in the de novo synthesis of sphingomyelin (SM) from ceramide (Cer). Recent studies have indicated that SMS is a key therapeutic target for metabolic diseases such as fatty liver, type 2 diabetes, atherosclerosis, and colorectal cancer. However, very few SMS inhibitors have been identified because of the limited sensitivity and selectivity of the current fluorescence-based screening assay. In this study, we developed a simple cell-based assay coupled with liquid chromatography/tandem mass spectrometry (LC-MS/MS) to screen for SMS inhibitors. HeLa cells stably expressing SMS1 or SMS2 were used for the screening. A non-fluorescent unnatural C6-Cer was used as a substrate for SMS to produce C6-SM. C6-Cer and C6-SM levels in the cells were monitored and quantified using LC-MS/MS. The activity of ginkgolic acid C15:1 (GA), a known SMS inhibitor, was measured. GA had half-maximal inhibitory concentrations of 5.5 µM and 3.6 µM for SMS1 and SMS2, respectively. To validate these findings, hSMS1 and hSMS2 proteins were optimized for molecular docking studies. In silico analyses were conducted to assess the interaction of GA with SMS1 and SMS2, and its binding affinity. This study offers an analytical approach for screening novel SMS inhibitors and provides in silico support for the experimental findings.

Dissimilar social cognition signatures in remitted schizophrenia and bipolar disorder.

In the light of shared genetic underpinnings of schizophrenia and bipolar disorder, their comparative profile of social cognition (SC) performance - an intermittent phenotype and determinant of functional outcome - is poorly understood. Using data from 160 individuals, we identify unique patterns of composite and domain-specific SC-abilities between these groups after controlling for their neurocognition. Individuals with schizophrenia and not bipolar disorder demonstrated deficits in composite SC-measures, which were not associated with their functional status. While patients with bipolar disorder had significantly lower scores on emotion recognition, they outperformed the healthy and schizophrenia groups on the second-order theory of mind.