Investigation of cardiotoxicity by dipeptidyl-peptidase-4 inhibitors in a human cardiomyocyte cell line as well as in samples from chronic heart failure patients

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): Horizon 2020 research and innovation programme, Ministry for Innovation and Technology

Background

Dipeptidyl-peptidase-4 (DPP4) inhibitors are relatively new therapeutic tools for type 2 diabetes. The SAVOR-TIMI-53 clinical trial has revealed an increased heart failure (HF)-associated hospitalization rate in saxagliptin treated patients. Although this critical side effect could limit the therapeutic use considerably, the mechanism by which DPP4 inhibitors damage the heart is still unclear.

Aims

We aimed to set up a relevant cellular platform to investigate mechanistically DPP4 inhibition, and the role of its potentially important neuropeptide substrates (e.g. Substance P and Neuropeptide Y). Moreover, we aim to determine the expression of DDP4 and its neuropeptide substrates in human and cellular samples.

Methods

Western blot, ELISA, and radioimmunoassay experiments were performed to investigate the expression of DPP4 and its neuropeptide substrates in human hearts and in AC16 cells. Viability measurements with calcein staining and scratch assay experiments were used to test the potentially toxic effect of DPP4 inhibitors. The localization of DPP4 mRNA was determined with RNA Scope in situ hybridization.

Results

Expression of DPP4 and NPY proteins decreased in interventricular septum samples of patients with HF compared to healthy controls. In human hearts DPP4 mRNA is detectable in cardiomyocytes, while other cell types (endothelial cells, fibroblasts, and macrophages) show negligible expression. AC16 human cardiomyocyte cell line expresses DPP4 enzyme.  Treatment with various DPP4 inhibitors administered alone or in combination with neuropeptides don’t affect cellular survival; although, in scratch assay experiments treatments with neuropeptides decreased cell migration speed in the isolated neonatal rat cardiomyocyte-fibroblast co-culture. The migration speed reducing effect of NPY was revered by the administration of saxagliptin at the highest concentration of NPY.

Conclusions

Decreased activity of DPP4 may play a role in the pathomechanism of end-stage congestive heart failure. The DPP4 enzyme could be important as a compensating mechanism against the elevated sympathetic activity in HF and for the altered neuropeptide tone. Inhibition of DPP4 could decrease this adaptive mechanism thereby exacerbating myocardial damage.

Mustard oil induces a transient receptor potential vanilloid 1 receptor-independent neurogenic inflammation and a non-neurogenic cellular inflammatory component in mice

A neurogenic component has been suggested to play a pivotal role in a range of inflammatory/immune diseases. Mustard oil (allyl-isothiocyanate) has been used in studies of inflammation to mediate neurogenic vasodilatation and oedema in rodent skin. The aim of the present study was to analyse mustard oil-induced oedema and neutrophil accumulation in the mouse ear focussing on the roles of neurokinin 1 (NK(1)) and vanilloid (TRPV1) receptors using normal (BALB/c, C57BL/6) as well as NK(1) and TRPV1 receptor knockout mice. A single or double treatment of 1% mustard oil on the BALB/c mouse ear induced ear oedema with responses diminished by 6 h. However a 25-30% increase in ear thickness was maintained by the hourly reapplication of mustard oil. Desensitisation of sensory nerves with capsaicin, or the NK(1) receptor antagonist SR140333, inhibited oedema but only in the first 3 h. Neutrophil accumulation in response to mustard oil was inhibited neither by SR140333 nor capsaicin pre-treatment. An activating dose of capsaicin (2.5%) induced a large oedema in C57BL/6 wild-type mice that was minimal in TRPV1 receptor knockout mice. By comparison, mustard oil generated ear swelling was inhibited by SR140333 in wild-type and TRPV1 knockout mice. Repeated administration of mustard oil maintained 35% oedema in TRPV1 knockout animals and the lack of TRPV1 receptors did not alter the leukocyte accumulation. In contrast repeated treatment caused about 20% ear oedema in Sv129+C57BL/6 wild-type mice but the absence of NK(1) receptors significantly decreased the response. Neutrophil accumulation showed similar values in both groups. This study has revealed that mustard oil can act via both neurogenic and non-neurogenic mechanisms to mediate inflammation in the mouse ear. Importantly, the activation of the sensory nerves was still observed in TRPV1 knockout mice indicating that the neurogenic inflammatory component occurs via a TRPV1 receptor independent process.

Substance P radioimmunoassay for quantitative characterization of sensory neurotransmitter release

In the present work we report the development of a new radioimmunoassay method for measuring the substance P content liberated from isolated rat tracheae in response to electrical or chemical (capsaicin, resiniferatoxin, piperine) stimulation. The amount of substance P released by electrical stimulation has been found to be dependent on the number of pulses and chemically elicited substance P release also proved to be dose-dependent. Our findings reinforce previous data that resiniferatoxin is approximately 100 times more potent than capsaicin and the potency ratio between piperine and capsaicin is 1/50.