Marshall, I. | bioRxiv Science

bioRxiv2025

Loratadine decreases virulence of methicillin-resistant Staphylococcus aureus by widespread disruption of hemolysis in both Stk1-dependent and -independent fashions

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial pathogen that relies on expression of a wide range of virulence factors. Hemolysins are a diverse collection of cytolytic toxins that promote virulence by being excreted and lysing host blood cells. We previously reported on novel anti-virulence compounds that modulate hemolysis in vitro, including a brominated carbazole (compound 8) and the active ingredient in Claritin (loratadine). We analyzed expression and activity of MRSA hemolysins in two hospital-acquired strains. Even with the same staphylococcal cassette chromosome mec (SCCmec) type, the strains displayed unique responses to loratadine where both repression and elevation of hemolysis occurred. These compounds are potentially binding and regulating the master regulatory protein, Stk1, which has known ties to hemolysis in S. aureus. We hypothesized that modulation of hemolysis by these putative Stk1 inhibitors would extend to community-acquired strains of MRSA. Furthermore, we wanted to determine if Stk1 was the only hemolysis regulatory protein being engaged by these compounds. To test this, we examined compound 8 and loratadines effects on two different USA300 strains, in addition to transposon mutants for a range of hemolysis regulatory genes. We observed strain-specific regulation of hemolysis by Stk1. Loratadine continued to downregulate both alpha and beta hemolytic activity in USA300 JE2 in both Stk1-dependent and independent pathways. Additionally, we report that this anti-virulence compound effectively disrupts hemolysis by modulating both agr and vraSR global regulators, contributing to widespread cytotoxin repression. Both alpha hemolysin (hla) and RNAIII/delta hemolysin (hld) mRNA reductions occurred in vitro and in a human cell line model of MRSA infection. Together, these results expand our knowledge of loratadines mode of action as a virulence modulator.

microbiology↗

bioRxiv2019

Intracranial functional haemodynamic relationships in patients with cerebral small vessel disease

BackgroundCerebral small vessel disease (SVD) is a major cause of stroke and dementia. The underlying cerebrovascular dysfunction is poorly understood. We investigated cerebrovascular reactivity, blood flow, vascular and cerebrospinal fluid (CSF) pulsatility, and their independent relationship to SVD features, in patients with minor ischaemic stroke and MRI evidence of SVD.\n\nMethodsWe recruited patients with minor ischaemic stroke and assessed CVR using Blood Oxygen Level Dependent (BOLD) MRI during a hypercapnic challenge, cerebral blood flow, vascular and CSF pulsatility using phase contrast MRI, and structural MR brain imaging to quantify white matter hyperintensities (WMH) and perivascular spaces (PVS). We quantified CVR in seven white matter and six subcortical grey matter regions, measured blood flow in carotid and vertebral arteries, intracranial venous sinuses, internal jugular veins and CSF flow at the aqueduct and foramen magnum. We used multiple regression to identify SVD features, blood flow and pulsatility parameters associated with CVR, controlling for patient characteristics.\n\nResultsIn 53 of 60 patients with complete data (age 68.0{+/-}8.8, 74% male, 75% hypertensive), CVR in grey and white matter decreased with increasing blood pressure (BP, respectively -0.001%/mmHg, p=0.01 and -0.006%/mmHg, p=0.01, per mmHg increase in BP). After controlling for age, gender and systolic BP, white matter CVR decreased with increasing WMF volume (-0.01%/mmHg per log10 increase in WMH volume, p=0.02) and basal ganglia PVS (-0.01%/mmHg per point increase in PVS score, p=0.02). White matter CVR decreased with increasing venous pulsatility (superior sagittal sinus -0.03%/mmHg, p=0.02, per unit increase in pulsatility index) but not with cerebral blood flow (p=0.58). Lower foramen magnum CSF stroke volume was associated with worse white matter CVR (0.04%/mmHg per ml increase in stroke volume, p=0.04) and increased basal ganglia PVS.\n\nConclusionsContemporaneous assessment of CVR, intracranial vascular and CSF pulsatility demonstrates important interrelationships of these vascular functions in humans. Decreased CVR, increased venous pulsatility and reduced foramen magnum CSF stroke volume suggests that dynamic vascular dysfunctions underpin PVS dysfunction and WMH development. Improved understanding of microvascular dysfunction and CSF dynamics offers new intervention targets to reduce SVD lesion development and their impact on cognitive dysfunction and stroke.

neuroscience↗