Desferal Administration to Improve the Impaired Reaction to Hypoxia in Diabetes

Background Complications of diabetes represent the main concern for modern diabetes therapy, and it has become a priority to further characterize the pathophysiological mechanisms of these complications to ensure the development of novel rational therapeutic strategies.

Although the prolonged exposure of tissues to hyperglycemia is the primary causative factor for chronic diabetes complications, it has recently become increasingly evident that hypoxia also plays an important role in all diabetes complication. A low tissue concentration of oxygen in diabetes is the consequence of several mechanisms (e.g., deficient blood supply secondarily to micro- and macro-vascular disease, poor local oxygen diffusion secondarily to local edema or as a result of increased oxygen consumption).

Adaptive responses of the cells to hypoxia are mediated by Hypoxia-Inducible Factor 1 (HIF), which is a heterodimeric transcription factor, composed of two subunits (alfa and beta subunit) both constitutively expressed in mammalian cells. In normoxia, HIF-1α is continually degraded by the ubiquitin-proteasome system as a consequence of the oxygen-dependent hydroxylation of two key proline residues catalyzed by a group of enzymes called prolyl-hydroxylases (PHDs). Under hypoxia when the degradation pathway is suppressed and HIF-1α is stabilized, it translocates in the nucleus where it induces more than 800 genes that are

involved in angiogenesis, glycolytic energy metabolism, cell proliferation and survival that enable the cells to adapt to reduced oxygen availability. HIF-1 is central for expression of several angiogenic growth factors (ex. as Vascular Endothelial Growth Factor (VEGF), erythropoietin (EPO), and stromal cell-derived factor-1α (SDF-1α) and for endothelial progenitor cells (EPC) recruitment. Recently, it has been proposed that microRNAs (ex. mir210) also mediate a part of the HIF-1 functions.

PHDs that control the HIF 1 α stability and function are Fe 2+ and/or O2 -dependent enzymes and their activity could be inhibited by depleting the iron. Deferoxamine (DFO), which is an iron chelator induces therefore HIF-1α accumulation and hypoxia-response genes in normoxia both in vitro and in vivo being able to restore the repressed adaptative reaction to hypoxia different animal models of diabetes. DFO has been in clinical use for decades for treating excessive iron deposition secondary to different pathologies (thalassemia, myelosclerosis etc) and was used as pharmacological tool to induce HIF dependent responses.

In the last decade several pieces of evidence have gathered, point out that in diabetes there is a defective cellular response to hypoxia. An impaired hypoxia response is present in all tissues that develop complications both in animal models for diabetes and in patients with diabetes as a consequence of a defective HIF signaling. It is a direct effect of hyperglycemia that directly represses HIF stability and function at multiple levels.

The recently described impaired reaction to hypoxia in diabetes have potentially important consequences in acute hypoxic challenges as acute heart infarction, stroke, limb ischemia (known to have a worse prognosis in diabetes) but also in subtle regulation of cardiovascular and respiratory system as a consequence of autonomic neuropathy with potential severe prognostic effect on late cardiovascular events. Different studies have addressed the cardiovascular responses to intermittent hypoxia (IH) compared with normoxia exposure in patients with diabetes. In order to establish the appropriateness of the cardiovascular reaction to hypoxia in diabetes the cardiorespiratory and angiogenetic responses towards IH in patients with diabetes compared with matched non- diabetic control subjects has recently been investigated(HYKRAND ethical approval number 2015/1182-31/4). The preliminary results (not published) showed several defects in both acute and delayed reaction of the patients with diabetes compared with controls. The baroreflex sensitivity (BRS) which is a marker of cardiovascular risk and survival prognosis after cardiovascular events was decreased in patients with diabetes after IH compared with non-diabetic subjects. Both the Endothelial Precursors Cells (EPC) number and the levels of their main stimulator Stromal derived factor (SDF-1α) were decreased in in response to IH in diabetics compared with non- diabetic subjects confirming the worse capacity to repair ischemic lesions in diabetes.

The project proposed here investigate the potential of DFO (known to improve the HIF dependent hypoxic signaling) to reverse the impaired cardiorespiratory and angiogenetic response in diabetic patients.

Research design. It is a blinded randomized cross-over study that investigates the efficacy of DFO (50mg/kg) vs isotonic saline given i.v before intermittent hypoxia (IH) to improve the cardiorespiratory and angiogenetic response in patients with diabetes. IH will consist in five hypoxic periods (13% O2 inspired fraction of oxygen) each lasting 6 min, with five normoxic intervals of same duration (as used in HYKRAND study) in 30 patients with type 1 diabetes without clinical signs of any complication. The study will be performed during 4 days with minimum 2 months separation between the 2 admissions to ensure sufficient wash-out and to restore iron deposits.

Methods Study design This is a randomized, double blind study conducted in patients with diabetes type 1 without chronic complications.

Patients will be randomized (by block randomization) (httpps://www.sealedenvelope.com/ simple-randomiser/v1/lists) to (A) Desferal (DFO) treatment or (B) isotonic saline treatment.

Both the patients and the personnel will be blinded to the patient's treatment group.

Subjects will be advised to abstain from caffeinated beverages for 12 h and from alcohol for 36h prior to testing

Day 1: Baseline blood samples will be collected in the morning and afterwards the patients will receive Desferal (50 mg/kg) / Saline infusion s.c during 6hs. During the last hour of infusion the subjects will be exposed to intermittent hypoxia (IH). Blood samples and cardiovascular and respiratory (CR) measurements will be performed (as detailed below) immediately before and at several time points after IH.

Day 2: Blood samples will be collected in the morning. IH exposure consists of five hypoxic periods (13% O2 inspired fraction of oxygen) each lasting 6 min, with five normoxic intervals of same duration (totally 1 hour).

Day 1: blood pressure, heart rate and arterial oxygen saturation are continuously measured. In case of a decrease in oxygen saturation 80% or the occurrence of symptoms, hypoxia is discontinued until oxygen levels reached at least 80%. A technician regulates and control the breathing periods under supervision of a medical doctor in a way that the intervention could not be observed by the patient. Thereafter, three measurement sessions will be performed: immediately after (t2), after 3 h (t3), and after 6 h (t4). After t2, each patient obtained an individual meal according to diet requirement.

Cardiovascular and respiratory testing.

Assessment of baroreflex sensitivity. All patients will be tested in the supine position in a silent room at comfortable temperature. Before participants will be connected to a rebreathing circuit through a mouthpiece with an antibacterial filter, spontaneous breathing of room air at rest will be performed for 4 min in order to obtain baseline data.

During each condition, continuous measurement of oxygen saturation (SaO2) by a pulse oximeter and end-tidal CO2 (CO2-et) using a capnograph connected to a mouthpiece will be performed. Recordings of electrocardiogram will be performed by chest leads, and continuous noninvasive blood pressure will be recorded using the cuff method. Two belts (positioned around the chest and the abdomen) will monitor respiratory movements of the chest. A pneumotachograph will be connected to a differential pressure transducer and inserted in series to the expiratory component of the rebreathing system to measure airway flow.

The baroreflex sensitivity (BRS) will be measured during spontaneous breathing at each measurement session. Since previous studies did not document a better performance of one method over the others, the average of seven different methods: positive and negative sequences, the a-coefficient in the low- and high-frequency bands and its average, the transfer function technique, and the ratio of SDs of R-R interval and systolic blood pressure variabilities will be calculated. Besides BRS, SD of the R-R interval (SDNN) was applied to determine a global index of heart rate variability. This selection is done based on the fact that normal distribution is more pronounced in this variable compared with other indices of variability (e.g., variance).

Hypoxic ventilatory response (HVR) and hypercapnic ventilatory response (HCVR) will be evaluated to determine respiratory system activity.

Cardiovascular autonomic function will be determined performing four tests according to recent guidelines: deep-breathing, 30:15 ratio, Valsalva maneuver and systolic blood pressure response to standing. Cardiovascular autonomic neuropathy will be defined as the "presence of two or more abnormal tests".

The baroreflex sensitivity (BRS) will be evaluated before (t1), immediately after (t2), 3 h (t3), and 6 h (t4) after IH.

The angiogenetic potential will be evaluated at the same endpoints and after 24 H (Day N3) by measuring in serum relevant cytokines that are gene targets for HIF-1 (i.e. Vascular endothelial growth factor (AVEGFA), stromal cell-derived factor 1a (SDF-1a), erythropoietin etc.). The direct response of HIF signaling will be evaluated by the serum levels of mir210 which exclusively regulated by HIF.

The EPC response will be evaluated at the same time points by Fluorescence-activated Cell Sorting (FACS) analysis of the number of Hematopoietic progenitor cell antigen (CD34+)/ CD133 antigen/Kinase insert domain receptor (KDR +)