Dipeptidyl peptidase IV beyond glucose homeostasis. A focus on substrates
2 March 2016
UAntwerp - Campus Drie Eiken - Building Q - Promotiezaal - Universiteitplein 1 - 2610 Antwerp (Wilrijk)
5:00 PM - 7:00 PM
Ingrid De Meester
PhD defence Lesley Baerts - Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, Department Pharmaceutical Sciences
DPPIV is an exopeptidase able to split off Xaa-Pro or Xaa-Ala dipeptides from the N-terminus of peptide substrates. This process modulates the biological activity of cytokines and (neuro)hormones, resulting in an altered interaction with their receptor. DPPIV inhibitors are routinely used as a second-line therapy, after metformin, in the treatment of type 2 diabetes. The knowledge about these inhibitors has progressed immensely since the development of the first generation of inhibitors (vildagliptin and sitagliptin). DPPIV inhibitors may prove useful in the treatment and prevention of the micro- and macrovascular complications in diabetes, such as stroke, myocardial infarction and nephropathy. This doctoral thesis aimed to shed a light on the mechanisms underlying these glucose-independent mechanisms.
First of all, a sampling protocol was optimized for the collection of blood when DPPIV substrates are to be analysed. We found that enzymatic conversion of SDF1α by DPPIV lowers its immunoreactivity in vitro and ex vivo. Even under optimal pre-analytical conditions, ex vivo truncation results in the underestimation of SDF1α concentrations. The collection of blood in tubes containing DPPIV inhibitors, and a general cocktail of protease inhibitors, effectively blocks this cleavage. In the absence of a specific DPPIV inhibitor a loss in immunoreactivity could not be prevented. Therefore, it is highly recommended to collect all samples in tubes containing at least a DPPIV inhibitor to block ex vivo cleaving.
Secondly, nesfatin-1 was shown to be a novel substrate of DPPIV. Analysis of the main circulating forms revealed that not nesfatin-1 but its precursor molecule, NUCB2, is the predominant protein in the circulation. Further investigation revealed the presence of another, higher molecular weight form.
Thirdly, the effect of sitagliptin on the activities of four key enzymes involved in collagen breakdown (DPPIV, matrix metalloproteinase 2 and 9 and prolidase) and the levels of collagen-derived dipeptides was investigated in diabetic and non-diabetic rats. We found three-fold higher MMP9 activities in vehicle treated diabetic rats compared to controls. In contrast, sitagliptin-treatment of the diabetic animals attenuated this rise. In addition, two-fold higher Ala-Pro and Pro-Pro levels were observed in diabetic rats (sitagliptin- or vehicle-treated) compared to controls, while Pro-Hyp concentrations were lower in diabetes (sitagliptin- or vehicle-treated).
Lastly, DPPIV activities were analyzed in the serum of 50 hyperacute stroke patients at admission, 1 day, 3 days and 7 days after stroke onset. Patients with a higher DPPIV activity at admission and stronger decrease in the activity during the first week after stroke onset had a more severe stroke and worse short-term and long-term outcomes.
In conclusion we can state that DPPIV inhibitors are promising molecules for the treatment of micro- and macrovascular complications of diabetes. They offer additional benefits in type 2 diabetes besides their effect on blood glucose, suggesting them as a logical choice when add-on therapy is needed.