Peripheral arterial disease (PAD) usually results from atherosclerosis and associated thrombosis and limits blood supply to the lower limbs. Common presenting symptoms include intermittent claudication (IC), rest pain and tissue loss. When limb viability is threatened, known as critical limb ischaemia (CLI), surgical and endovascular interventions are frequently undertaken; however, these are not always successful and ultimately major amputation may be required. There is significant interest in developing new therapeutic approaches to manage PAD which can be applied to patients unlikely to benefit from interventional approaches. Many of the therapeutic agents successful in inducing angiogenesis and arteriogenesis in pre-clinical animal models of PAD have failed to have efficacy in human randomized control trials. One possible reason for this inability to translate findings to patients could be the type of pre-clinical animal models used. In the present review, we describe currently available pre-clinical models of PAD and discuss the advantages and disadvantages of the available models. A detailed assessment of the currently available pre-clinical animal models shows major limitations such as variability in the surgical procedure used to induce limb ischaemia, variability in the strains of rodents used, lack of risk factors incorporated into the model and lack of standardized functional outcomes. The most commonly used outcome assessments in studies within pre-clinical models differ from those employed in clinical trials within PAD patients. Most current pre-clinical models are designed to produce acute ischaemia which leads to muscle necrosis and inflammation. Patients, however, most commonly present with chronic ischaemia suggesting that more representative models are needed to evaluate therapeutic modalities that can be potentially translated to clinical practice.

Athero-thrombosis of the arteries supplying the brain and lower limb are the main causes of stroke and limb loss. New therapies are needed to improve the outcomes of athero-thrombosis. Recent evidence suggests a role for epigenetic changes in the development and progression of ischaemic injury due to atherosclerotic occlusion of peripheral arteries. DNA hypermethylation have been associated with cardiovascular diseases. Histone post-translational modifications have also been implicated in atherosclerosis. Oxidized low-density lipoprotein regulated pro-inflammatory gene expression within endothelial cells is controlled by phosphorylation/acetylation of histone H3 and acetylation of histone H4 for example. There are a number of challenges in translating the growing evidence implicating epigenetics in atherosclerosis to improved therapies for patients. These include the small therapeutic window in conditions such as acute stroke and critical limb ischaemia, since interventions introduced in such patients need to act rapidly and be safe in elderly patients with many co-morbidities. Pre-clinical animal experiments have also reported conflicting effects of some novel epigenetic drugs, which suggest that further in-depth studies are required to better understand their efficacy in resolving ischaemic injury. Effective ways of dealing with these challenges are needed before epigenetic approaches to therapy can be introduced into practice.

Patients suffering from both diabetes and PAD (peripheral arterial disease) are at risk of developing critical limb ischaemia and ulceration, and potentially requiring limb amputation. In addition, diabetes complicates surgical treatment of PAD and impairs arteriogenesis. Arteriogenesis is defined as the remodelling of pre-existing arterioles into conductance vessels to restore the perfusion distal to the occluded artery. Several strategies to promote arteriogenesis in the peripheral circulation have been devised, but the mechanisms through which diabetes impairs arteriogenesis are poorly understood. The present review provides an overview of the current literature on the deteriorating effects of diabetes on the key players in the arteriogenesis process. Diabetes affects arteriogenesis at a number of levels. First, it elevates vasomotor tone and attenuates sensing of shear stress and the response to vasodilatory stimuli, reducing the recruitment and dilatation of collateral arteries. Secondly, diabetes impairs the downstream signalling of monocytes, without decreasing monocyte attraction. In addition, EPC (endothelial progenitor cell) function is attenuated in diabetes. There is ample evidence that growth factor signalling is impaired in diabetic arteriogenesis. Although these defects could be restored in animal experiments, clinical results have been disappointing. Furthermore, the diabetes-induced impairment of eNOS (endothelial NO synthase) strongly affects outward remodelling, as NO signalling plays a key role in several remodelling processes. Finally, in the structural phase of arteriogenesis, diabetes impairs matrix turnover, smooth muscle cell proliferation and fibroblast migration. The review concludes with suggestions for new and more sophisticated therapeutic approaches for the diabetic population.

Arm cranking is a useful alternative exercise modality for improving walking performance in patients with intermittent claudication; however, the mechanisms of such an improvement are poorly understood. The main aim of the present study was to investigate the effects of arm-crank exercise training on lower-limb O 2 delivery in patients with intermittent claudication. A total of 57 patients with intermittent claudication (age, 70±8 years; mean±S.D.) were randomized to an arm-crank exercise group or a non-exercise control group. The exercise group trained twice weekly for 12 weeks. At baseline and 12 weeks, patients completed incremental tests to maximum exercise tolerance on both an arm-crank ergometer and a treadmill. Respiratory variables were measured breath-by-breath to determine peak V ̇ O 2 (O 2 uptake) and ventilatory threshold. Near-IR spectroscopy was used in the treadmill test to determine changes in calf muscle S t O 2 (tissue O 2 saturation). Patients also completed a square-wave treadmill-walking protocol to determine V ̇ O 2 kinetics. A total of 51 patients completed the study. In the exercise group, higher maximum walking distances (from 496±250 to 661±324 m) and peak V ̇ O 2 values (from 17.2±2.7 to 18.2±3.4 ml·kg −1 of body mass·min −1 ) were recorded in the incremental treadmill test ( P <0.05). After training, there was also an increase in time to minimum S t O 2 (from 268±305 s to 410±366 s), a speeding of V ̇ O 2 kinetics (from 44.7±10.4 to 41.3±14.4 s) and an increase in submaximal S t O 2 during treadmill walking ( P <0.05). There were no significant changes in the control group. The results suggest that the improvement in walking performance after arm-crank exercise training in patients with intermittent claudication is attributable, at least in part, to improved lower-limb O 2 delivery.

Expansion of the capillary network, or angiogenesis, occurs following endurance training. This process, which is reliant on the presence of VEGF (vascular endothelial growth factor), is an adaptation to a chronic mismatch between oxygen demand and supply. Patients with IC (intermittent claudication) experience pain during exercise associated with an inadequate oxygen delivery to the muscles. Therefore the aims of the present study were to examine the plasma VEGF response to acute exercise, and to establish whether exercise training alters this response in patients with IC. In Part A, blood was collected from patients with IC ( n =18) before and after (+20 and +60 min post-exercise) a maximal walking test to determine the plasma VEGF response to acute exercise. VEGF was present in the plasma of patients (45.11±29.96 pg/ml) and was unchanged in response to acute exercise. Part B was a training study to determine whether exercise training altered the VEGF response to acute exercise. Patients were randomly assigned to a treatment group (TMT; n =7) that completed 6 weeks of high-intensity treadmill training, or to a control group (CON; n =6). All patients completed a maximal walking test before and after the intervention, with blood samples drawn as for Part A. Training had no effect on plasma VEGF at rest or in response to acute exercise, despite a significant increase in maximal walking time in the TMT group (915±533 to 1206±500 s; P =0.009) following the intervention. The absence of a change in plasma VEGF may reflect altered VEGF binding at the endothelium, although this cannot be confirmed by the present data.

1. We have determined the frequency of DNA polymorphisms of the human apolipoprotein AI-CIII-AIV gene cluster, detected with Xmn I, Pst I, and Pvu II, in a group of patients with peripheral arterial disease. 2. Of the patients, 81 had no evidence of disease in the coronary and carotid arteries, 73 had coronary artery disease but no evidence of carotid artery disease, 25 patients had carotid artery disease but no evidence of coronary artery disease, and 38 had both coronary and carotid artery disease. 3. Levels of triacylglycerol, cholesterol, apolipoprotein B and apolipoprotein AI were not significantly different between the four patient groups. 4. The frequencies of the alleles for the apolipoprotein AI-CIII-AIV polymorphisms, detected with Xmn I, Pst I and Pvu II, did not differ significantly in the patient groups when compared with a sample of clinically well normolipidaemic individuals also from a London population. 5. All five patients with the Xmn I genotype we designate X2X2 had high levels of cholesterol, apolipoprotein B and apolipoprotein AI. 6. Patients with the rare VB2 allele of the apolipoprotein CIII-AIV restriction fragment length polymorphism had lower levels of cholesterol, acylglycerol and significantly lower levels of serum apolipoprotein. 7. Our observations suggest that variation in the apolipoprotein AI-CIII-AIV gene cluster may not be contributing significantly to the development of peripheral arterial disease, but variation associated with some of the restriction fragment length polymorphisms may be involved in determining levels of cholesterol- and apolipoprotein-B-containing lipoproteins.