Inhibition of acid sphingomyelinase (ASM), a lysosomal enzyme that catalyzes the hydrolysis of sphingomyelin into ceramide and phosphorylcholine, may serve as an investigational tool or a therapeutic intervention to control many diseases. Specific ASM inhibitors are currently not sufficiently characterized. Here, we found that 1-aminodecylidene bis-phosphonic acid (ARC39) specifically and efficiently (>90%) inhibits both lysosomal and secretory ASM in vitro. Results from investigating sphingomyelin phosphodiesterase 1 (SMPD1/Smpd1) mRNA and ASM protein levels suggested that ARC39 directly inhibits ASM’s catalytic activity in cultured cells, a mechanism that differs from that of functional inhibitors of ASM. We further provide evidence that ARC39 dose- and time-dependently inhibits lysosomal ASM in intact cells, and we show that ARC39 also reduces platelet- and ASM-promoted adhesion of tumor cells. The observed toxicity of ARC39 is low at concentrations relevant for ASM inhibition in vitro, and it does not strongly alter the lysosomal compartment or induce phospholipidosis in vitro. When applied intraperitoneally in vivo, even subtoxic high doses administered short-term induced sphingomyelin accumulation only locally in the peritoneal lavage without significant accumulation in plasma, liver, spleen, or brain. These findings require further investigation with other possible chemical modifications. In conclusion, our results indicate that ARC39 potently and selectively inhibits ASM in vitro and highlight the need for developing compounds that can reach tissue concentrations sufficient for ASM inhibition in vivo.

Objective To study the impact of time to diagnosis on cardiac Mayo stages, treatment outcome, and overall survival. Methods We retrospectively analyzed 77 consecutive patients diagnosed between 2015 and 2020 with AL amyloidosis and cardiac involvement. Medical history was recorded in standardized form with the help of a questionnaire. Results Time from onset of symptoms of cardiac failure to diagnosis was correlated with the severity of cardiac involvement in modified Mayo 2004 and revised Mayo 2012 staging systems (rs = 0.30, 95% CI: 0.07‐0.50, P = .007 and rs = 0.25, 95% CI: 0.01‐0.45, P = .03). Patients with advanced Mayo 2004 stages received reduced‐intensity regimens and had a lower probability to achieve adequate hematologic‐ and cardiac response after first‐line treatment than patients with early stages (rs = 0.28, 95% CI: 0.04‐0.48, P = .01 and rs = 0.72, 95% CI: 0.55‐0.82, P < .0001) and poorer overall survival (P = .0004). Compared with patients diagnosed within the first year, patients diagnosed after 13‐18 or ≥19 months from first symptoms had a 3‐ to 5 times higher risk of dying. Our data indicate that there is a 12‐month window within which the diagnosis of AL amyloidosis needs to be established to avoid early deterioration and death. Conclusions Sensitizing physicians and raising awareness for the disease are crucial for timely diagnosis and may improve the outcome of the disease.

Highlights d Infection with cytopathic virus, such as VSV, leads to innate anergy d Innate anergy is associated with apoptotic cells, which activate TAM receptor Mertk d Mertk signaling induces higher levels of IL-10 and TGF-b and enhances virus replication d Dexamethasone treatment upregulates Mertk, thereby enhancing innate anergy

Acid sphingomyelinase (Asm) and acid ceramidase (Ac) are parts of the sphingolipid metabolism. Asm hydrolyzes sphingomyelin to ceramide, which is further metabolized to sphingosine by Ac. Ceramide generates ceramide-enriched platforms that are involved in receptor clustering within cellular membranes. However, the impact of cell-intrinsic ceramide on T cell function is not well characterized. By using T cell-specific Asm- or Ac-deficient mice, with reduced or elevated ceramide levels in T cells, we identified ceramide to play a crucial role in T cell function in vitro and in vivo. T cell-specific ablation of Asm in Smpd1fl/fl/Cd4cre/+ (Asm/CD4cre) mice resulted in enhanced tumor progression associated with impaired T cell responses, whereas Asah1fl/fl/Cd4cre/+ (Ac/CD4cre) mice showed reduced tumor growth rates and elevated T cell activation compared to the respective controls upon tumor transplantation. Further in vitro analysis revealed that decreased ceramide content supports CD4+ regulatory T cell differentiation and interferes with cytotoxic activity of CD8+ T cells. In contrast, elevated ceramide concentration in CD8+ T cells from Ac/CD4cre mice was associated with enhanced cytotoxic activity. Strikingly, ceramide co-localized with the T cell receptor (TCR) and CD3 in the membrane of stimulated T cells and phosphorylation of TCR signaling molecules was elevated in Ac-deficient T cells. Hence, our results indicate that modulation of ceramide levels, by interfering with the Asm or Ac activity has an effect on T cell differentiation and function and might therefore represent a novel therapeutic strategy for the treatment of T cell-dependent diseases such as tumorigenesis.