Binh Ngo

Manifestations of cutaneous diabetic microangiopathy.

The etiologies of a variety of skin conditions associated with diabetes have not been fully explained. One possible etiological factor is diabetic microangiopathy, which is known to affect the eyes and kidneys in patients with diabetes. There are many mechanisms by which diabetes may cause microangiopathy. These include excess sorbitol formation, increased glycation end products, oxidative damage, and protein kinase C overactivity. All of these processes occur in the skin, and the existence of a cutaneous diabetic microangiopathy has been well demonstrated. These microangiopathic changes are associated with abnormalities of skin perfusion. Because the skin plays a thermoregulatory role, there is significant capillary redundancy in normal skin. In diabetic patients, loss of capillaries is associated with a decrease in perfusion reserve. This lost reserve is demonstrable under stressed conditions, such as thermal stimulation. The associated failure of microvascular perfusion to meet the requirements of skin metabolism may result in diverse skin lesions in patients with diabetes.Many skin conditions peculiar to diabetes are fairly rare. Necrobiosis lipoidica diabeticorum (NLD) and diabetic bullae occur very infrequently as compared with diabetic retinopathy and nephropathy. Conversely, there is a correlation between diabetic microvascular disease and NLD. This correlation also exists with more common skin conditions, such as diabetic dermopathy. This relationship suggests that diabetic microangiopathy may contribute to these conditions even if it is not primarily causal.Clinically, the major significance of diabetic cutaneous microangiopathy is seen in skin ulceration which is very common and has a major impact on diabetic patients. Many factors contribute to the development of diabetic foot ulcers. Neuropathy, decreased large vessel perfusion, increased susceptibility to infection, and altered biomechanics all play a role, but there is no doubt that inadequate small blood vessel perfusion is a major cause of the inability to heal small wounds that eventually results in ulcer formation.The accessibility of skin capillaries makes cutaneous diabetic microangiopathy an attractive model for research on the evolution of microvascular disease in diabetic patients.

Skin blood flow in necrobiosis lipoidica diabeticorum

Background  Necrobiosis lipoidica diabeticorum (NLD) is a granulomatous skin reaction found in < 1% of diabetic patients. Our purpose was to determine if NLD represented areas of cutaneous ischemia.

Commentary on Almassalha Et Al., "the Greater Genomic Landscape: The Heterogeneous Evolution of Cancer"

In this issue of Cancer Research, Almassalha and colleagues have proposed a new concept of the development of malignancy, that of the greater genomic landscape. They propose a stressor-related exploration of intracellular genomic sites as a response mechanism. This process can express sites with beneficial or deleterious effects, among them those that promote cell proliferation. They point out that their conception is broader, although certainly inclusive, of the process of gene induction. The authors view the physical process of chromatin reorganization as central to the exploration of the genomic landscape. Accordingly, they advocate the development of agents to limit chromatin structural modification as a chemotherapeutic approach in cancer. We found their theory relevant to understand the phenotypic heterogeneity of malignancy, particularly in familial cancer syndromes. For example, the familial atypical multiple mole melanoma (FAMMM) syndrome, related to a gene mutation, is characterized by a diversity of melanocytic lesions, only some of which become malignant melanoma. This new conceptualization can do much to increase understanding of the diversity of malignancy in families with hereditary cancer. Cancer Res; 76(19); 5602-4. ©2016 AACR.

The effect of vasoactive agents on post-pressure hyperemia

The cutaneous hyperemic response following the release of direct pressure occlusion lasts much longer than the short-term hyperemia that occurs after proximal arterial occlusion. Post-pressure hyperemia may be an important mechanism to prevent pressure induced injury to the skin. The role of vasoactive mediators in modulating post-pressure hyperemia is unknown. In an effort to better understand this phenomenon, we performed an initial study using microdialysis infusion to measure the effect of several known mediators of vascular response on post-pressure hyperemia. A vise clamp was used to apply direct occlusive pressure to a laser Doppler sensor on the skin surface overlying the microdialysis fiber. Skin blood flow was measured continuously pre, during and post-occlusion while infusing the vasoactive substance or control phosphate buffer. Angiotensin II, Calcitonin gene related peptide and histamine had minimal effect on post pressure blood flow. Conversely, prostaglandin E1, prostaglandin E2, and L-NAME diminished the early phase of the post-occlusion hyperemic response. Perhaps the most profound effect we observed was the decrease in post-occlusive blood flow due to administration of epinephrine, dopamine and prostaglandin F2alpha. In contrast, adenosine and caffeine augmented blood flow post occlusion. In this initial survey study, we have demonstrated differential effects of various vascular mediators on the post-pressure hyperemic phenomenon. Our findings may lead to the development of agents to prevent pressure sores by augmenting the skin blood flow response to locally applied pressure.

Skin Blood Flow in Patients With Stage 5 Chronic Kidney Disease on Hemodialysis

We have shown previously that skin perfusion is reduced in patients with diabetes mellitus (DM). Patients with diabetes and with chronic kidney disease (CKD) stage 5 were having advanced microangiopathy. In this cross-sectional study, we measured skin blood flow in DM and non-DM patients on dialysis to assess whether any differences exist in skin perfusion in those 2 groups of patients. A total of 25 patients with DM (aged 59.9 +/- 2.2 years) and 24 patients with non-DM CKD stage 5 (44.6 +/- 2.9 years) on hemodialysis (HD) were studied. Ten healthy subjects (37 +/- 4.3 years) were used as a control group. Skin blood flow (SBF) was measured using Vasamedic Model 403B laser Doppler device (Vasamedics Inc., St. Paul, MN) in a standardized way at the plantar and dorsal surface of the finger and toe and at the pretibial surface of the leg at 2 different local skin temperatures of 35 degrees C and 44 degrees C. Laboratory biochemical data were collected at the time of SBF study. The SBF measured at 35 degrees C was lower in the patients with DM on dialysis as compared with healthy subjects and non-DM dialysis patients. The SBF response to the increase in temperature of the probe to 44 degrees C was 70% to 80% lower in DM patients as compared with healthy subjects and non-DM patients. However, non-DM subjects who displayed SBF similar to control subjects at 35 degrees C, had impaired response in SBF at 44 degrees C as well. Patients with lower serum albumin exhibited lower SBF even after adjustment for age. SBF is impaired in patients with stage 5 CKD on HD, particularly in those with DM as a cause of CKD. SBF negatively correlated with age and albumin (nutritional status) in DM and non-DM patients with stage 5 CKD on HD. Measurement of SBF can be useful in the evaluation of vasculopathy in CKD population and can potentially be used for assessment of vascular response during specific clinical intervention.