Vascular risk: diabetes

Risk factors for repeated dexamethasone intravitreal implant therapy for macular edema due to treatment-naïve branch retinal vein occlusion

Background

This study evaluated the effects of dexamethasone intravitreal implant on treatment-naïve branch retinal vein occlusion (BRVO)-induced macular edema (ME), and the risk factors for earlier repeated treatment.

Methods

Patients treated from 2013 to 2016 were enrolled. The patients’ demographics, medical history, best-corrected visual acuity (BCVA), and central retinal thickness (CRT) were recorded. Risk factors for repeated treatment were identified using a Cox proportional hazard model and logistic regression.

Results

29 patients (mean age: 58.64 ± 13.3 years) were included; 44.8% received only one injection, while 55.2% received two or more. The mean initial CRT was 457.8 ± 167.1 μm; the peak CRT and final CRT improved significantly to 248.9 ± 57.9 μm and 329.2 ± 115.1 μm, respectively. The peak BCVA improvement and final improvement were 29.5 ± 23.5 approximate ETDRS letters and 19.8 ± 24.4 letters, respectively, with 62.1% of patients improving by more than 15 letters. Older age, higher initial CRT, and diabetes were the risk factors for multiple injections.

Conclusion

Dexamethasone intravitreal implant results in significant peak CRT and BCVA improvements, while older age, higher initial CRT, and diabetes are risk factors for repeated injections. The optimal retreatment schedule for these patients should be further explored.

Erythrocyte-derived ATP and perfusion distribution: role of intracellular and intercellular communication

In complex organisms, both intracellular and intercellular communication are critical for the appropriate regulation of the distribution of perfusion to assure optimal O(2) delivery and organ function. The mobile erythrocyte is in a unique position in the circulation as it both senses and responds to a reduction in O(2) tension in its environment. When erythrocytes enter a region of the microcirculation in which O(2) tension is reduced, they release both O(2) and the vasodilator, ATP, via activation of a specific and dedicated signaling pathway that requires increases in cAMP, which are regulated by PDE3B. The ATP released initiates a conducted vasodilation that results in alterations in the distribution of perfusion to meet the tissue's metabolic needs. This delivery mechanism is modulated by both positive and negative feedback regulators. Importantly, defects in low O(2) -induced ATP release from erythrocytes have been observed in several human disease states in which impaired vascular function is present. Understanding of the role of erythrocytes in controlling perfusion distribution and the signaling pathways that are responsible for ATP release from these cells makes the erythrocyte a novel therapeutic target for the development of new approaches for the treatment of vascular dysfunction.

Divergent effects of low-O(2) tension and iloprost on ATP release from erythrocytes of humans with type 2 diabetes: implications for O(2) supply to skeletal muscle

Erythrocytes release both O(2) and a vasodilator, ATP, when exposed to reduced O(2) tension. We investigated the hypothesis that ATP release is impaired in erythrocytes of humans with type 2 diabetes (DM2) and that this defect compromises the ability of these cells to stimulate dilation of resistance vessels. We also determined whether a general vasodilator, the prostacyclin analog iloprost (ILO), stimulates ATP release from healthy human (HH) and DM2 erythrocytes. Finally, we used a computational model to compare the effect on tissue O(2) levels of increases in blood flow directed to areas of increased O(2) demand (erythrocyte ATP release) with nondirected increases in flow (ILO). HH erythrocytes, but not DM2 cells, released increased amounts of ATP when exposed to reduced O(2) tension (Po(2) < 30 mmHg). In addition, isolated hamster skeletal muscle arterioles dilated in response to similar decreases in extraluminal O(2) when perfused with HH erythrocytes, but not when perfused with DM2 erythrocytes. In contrast, both HH and DM2 erythrocytes released ATP in response to ILO. In the case of DM2 erythrocytes, amounts of ATP released correlated inversely with glycemic control. Modeling revealed that a functional regulatory system that directs blood flow to areas of need (low O(2)-induced ATP release) provides appropriate levels of tissue oxygenation and that this level of the matching of O(2) delivery with demand in skeletal muscle cannot be achieved with a general vasodilator. These results suggest that the inability of erythrocytes to release ATP in response to exposure to low-O(2) tension could contribute to the peripheral vascular disease of DM2.