Hypoxia serves as a physiological cue to drive angiogenic response via HIF-dependent mechanisms. Interestingly, minor elevation of lactate levels in the tissue produces the same effect under aerobic conditions. Aerobic glycolysis contributes to lactate accumulation in the presence of oxygen especially under inflammatory conditions. We have previously postulated that aerobic lactate accumulation, already known to stimulate collagen deposition, will also stimulate angiogenesis. If substantiated, this concept would advance understanding of wound healing and aerobic angiogenesis because lactate accumulation has many aerobic sources. In this study, Matrigel® plugs containing a powdered, hydrolysable lactate polymer were implanted into the subcutaneous space of mice. Lactate monomer concentrations in the implant were consistent with wound levels for over 11 days. They induced little inflammation but considerable VEGF production and were highly angiogenic as opposed to controls. Arterial hypoxia abrogated angiogenesis. Furthermore, inhibition of lactate dehydrogenase using oxamate also prevented the angiogenic effects of lactate. Lactate monomer, at concentrations found in cutaneous wounds, stabilized HIF-1α and increased VEGF levels in aerobically cultured human endothelial cells. Accumulated lactate, therefore, appears to convey the impression of "metabolic need" for vascularization even in well-oxygenated and pH-neutral conditions. Lactate and oxygen both stimulate angiogenesis and matrix deposition.

OBJECTIVE -Tissue oxygen supply is crucial for wound healing. Especially in diabetic foot lesions, the chances for healing are mainly dependent on the presence or absence of ischemia. This study investigates the impact of the tissue O2 analysis system "O2C" for noninvasive quantification of tissue oxygenation in diabetic foot ulcer patients.RESEARCH DESIGN AND METHODS -O2C assessed relative blood flow (flow), flow velocity (velo), and hemoglobin concentration (rHb) and hemoglobin oxygenation (SO 2 ) at 2 and 6 mm depth (means Ϯ SE). 1) Measurements were performed on intact skin of the forefoot and forearm of 20 healthy volunteers on 2 consecutive days. 2) Parameters were assessed on intact skin of the forefoot of diabetic foot ulcer patients (n ϭ 14). 3) Measurements were performed directly at the wound site in diabetic patients (n ϭ 14).RESULTS -1) Flow, velo, rHb, and SO 2 at 2 and 6 mm depth were not significantly different when measured at 2 consecutive days. 2) There were no significant differences between diabetic subjects and healthy volunteers. Only flow in 6 mm depth was significantly higher in diabetic subjects (75 Ϯ 13 vs. 51 Ϯ 0.4 arbitrary units [AU], P Ͻ 0.05). When diabetic foot ulcer patients were split into healers and nonhealers, initial readings of SO 2 at 2 mm (32 Ϯ 6 vs. 44 Ϯ 3%, P Ͻ 0.05) and flow in 6 mm (28 Ϯ 1 vs. 51 Ϯ 0.6 AU, P Ͻ 0.05) were significantly reduced in nonhealers compared with control subjects, whereas in healers flow in 6 mm (70 Ϯ 0.6 vs. 51 Ϯ 0.6 AU, P Ͻ 0.05) was significantly higher than that in control subjects. 3) Initial SO 2 , rHb, flow, and velo were significantly lower in nonhealing compared with healing wounds.CONCLUSIONS -O2C is a new reliable and valid method for noninvasive measurement of tissue oxygenation and microvascular blood flow in patients with diabetic foot ulcers. Diabetes Care 27:2863-2867, 2004F oot ulcers are severe long-term complications in diabetic patients. In addition to local wound therapy, adequate tissue oxygenation is crucial for healing since oxygen is necessary for collagen formation, bactericidal activity of neutrophils, and endothelial cell function. Prognosis of diabetic foot lesions is mainly dependent on the presence or absence of tissue ischemia. However, quantitative assessment of peripheral perfusion and microcirculation is still challenging. Different methods like Doppler ultrasound or angiography are able to evaluate macrocirculation, but a reliable, easy technique to assess microcirculation, i.e., tissue perfusion, is not available. Previous studies have shown that healing might be predictable by measurement of transcutaneous oxygen tension (TcPO 2 ) (1-3). If TcPO 2 is Ͻ30 mmHg, complete healing cannot be expected (4). However, TcPO 2 is only a qualitative, not a quantitative, approach for evaluating peripheral perfusion and has a main limitation due to the need for heating the skin before measurement. This affects the resistance of skin vasculature and attenuates reflex mechanisms.Lightguide tissue spectrophotometry (O2C), ...

The significance of the high lactate levels that characterize healing wounds is not fully understood. Lactate has been shown to enhance collagen synthesis by fibroblasts and vascular endothelial growth factor (VEGF) production by macrophages and endothelial cells. VEGF has been shown to induce endothelial cell migration. However, it has not been shown whether accumulated lactate correlates with the biological activity of VEGF. Therefore, we investigated the effect of lactate on migration of endothelial cells. Human umbilical vein endothelial cells and human microvascular endothelial cells were cultured to subconfluent monolayers in standard six-well tissue culture plates. Following a 24-hour serum starvation, cells were treated with the indicated concentrations of l-lactate. Cell migration was assessed using a modified Boyden chamber. VEGF protein in the cell culture supernatant was measured by enzyme-linked immunoassay. Lactate-enhanced VEGF protein synthesis in a time- and dose-dependent manner. Lactate added into the bottom well did not stimulate cellular migration from the upper well. However, lactate when added together with endothelial cells to the bottom well of the Boyden chamber increased cellular migration in a dose-dependent manner. This effect was blocked by anti-VEGF and by cycloheximide. Lactate enhances VEGF production in endothelial cells, although lactate, itself, is not a chemoattractant. We conclude that the lactate-mediated increase in cellular migration is regulated by VEGF.

OBJECTIVE—Several well-accepted classification systems are available for diabetic foot ulcers. However, there are only a few and scientifically not validated severity scores. The aim of this study was to establish a new wound-based clinical scoring system for diabetic foot ulcers suitable for daily clinical practice anticipating chances for healing and risk of amputation. RESEARCH DESIGN AND METHODS—Four clinically defined parameters, namely palpable pedal pulses, probing to bone, ulcer location, and presence of multiple ulcerations, were prospectively assessed in 1,000 consecutive patients. In the next step, a new diabetic ulcer severity score (DUSS) was created from these parameters. Palpable pedal pulses were categorized by the absence (scored as 1) or presence (scored as 0) of pedal pulses, while probing to bone was defined as yes (scored as 1) or no (scored as 0). The site of ulceration was defined as toe (scored as 0) or foot (scored as 1) ulcer. Patients with multiple ulcerations were graded as 1 compared with those with single ulcers (scored as 0). The DUSS was calculated by adding these separate gradings to a theoretical maximum of 4. Wounds were followed-up for 365 days or until healing or amputation if earlier. Probability of healing and risk of amputation were calculated by the Kaplan-Meier method. RESULTS—Uni- and multivariate analyses showed a significantly higher probability of healing for patients with palpable pulses, no probing to bone, toe ulcers, and absence of multiple ulcerations. When patients were divided into subgroups with the same DUSS, we found significantly different probabilities for healing. We showed a decreasing probability of healing for ulcers with a high DUSS, concurrent with increasing amputation rates. An increase in the DUSS by one score point reduced the chance for healing by 35%. Similarly, the higher the ulcer score, the larger the initial wound area, the longer the wound history, and the more likely the need for surgery or hospitalization. CONCLUSIONS—The DUSS categorizes different ulcers into subgroups with specific severity and similar clinical outcome. Using this score, the probabilities for healing, amputation, need for surgery, and hospitalization are predictable with high accuracy. This might be useful for the anticipation of health care costs and for comparison of subgroups of patients in clinical studies.