Microangiopathy in human diabetic neuropathy: relationship between capillary abnormalities and the severity of neuropathy

Treatment of symptomatic diabetic peripheral neuropathy with the protein kinase C beta-inhibitor ruboxistaurin mesylate during a 1-year, randomized, placebo-controlled, double-blind clinical trial

OBJECTIVE

The aim of this study was to assess the effects of ruboxistaurin (RBX) mesylate on nerve function and sensory symptoms in patients with diabetes mellitus (DM) and diabetic peripheral neuropathy (DPN).

METHODS

Patients were enrolled in a multinational, randomized, Phase II, double-blind, placebo-controlled parallel-group trial comparing 32 mg/d or 64 mg/d RBX with placebo for 1 year. DPN was identified by abnormal measurable vibration detection threshold (VDT) and verified by abnormal neurologic examination and nerve electrophysiology measures. Baseline patient characteristics (eg, sex, type of DM, age, body mass index, glycosylated hemoglobin, and duration of DM and DPN) were measured. The primary end point was the change in VDT. Secondary end point measures included effects of RBX versus placebo on Neuropathy Total Symptom Score-6 (NTSS-6), neurologic examination, electrophysiologic nerve conduction studies, Neuropathy Impairment Score, Clinical Global Impressions, and safety. A post-hoc analysis was performed on patients with less severe DPN (sural sensory nerve action potential > or =0.5 microV and NTSS-6 total score >6).

RESULTS

Two hundred five patients were assessed: 66 were assigned to the RBX 32 mg/d group, 71 to the RBX 64 mg/d group, and 68 to the placebo group. The demographic and baseline characteristics of the treatment groups were well matched between the RBX 32 mg/d, RBX 64 mg/d, and placebo groups: mean (SD) age, 45.6 (8.41) years; 122 (60%) men, 83 (40%) women; 110 (54%) with type 1 DM, 95 (46%) with type 2 DM; mean (SD) duration of DPN, 3.4 (4.21) years. The RBX 32 mg/d group had slightly more patients with type 1 DM (P = 0.05). Eighty-three patients had clinically significant symptoms at baseline (defined as NTSS-6 total score >6: RBX 32 mg/d, n = 22; RBX 64 mg/d, n = 26; placebo, n = 35); 122 patients had NTSS-6 total scores < or =6. No treatment differences were observed for change in VDT. Among the 83 patients with significant symptoms at baseline, there was a reduction from baseline at 12 months in the NTSS-6 total score in the RBX 32 mg/d (P = NS) and RBX 64 mg/d (P = 0.015) groups compared with placebo. In a subgroup of patients with clinically significant symptoms and less severe DPN (n = 50), there was a significantly greater reduction in the NTSS-6 total score with RBX 64 mg/d (P = 0.006 vs placebo). Furthermore, in these patients, there was a statistically significant improvement in VDT for both RBX 32 mg/d (P = 0.012) and RBX 64 mg/d (P = 0.026) compared with placebo.

CONCLUSIONS

RBX appeared to be well tolerated in the patients with DPN who participated in this study. Overall, changes in VDT and NTSS-6 total scores did not differ among treatment groups at end point. However, RBX treatment appeared to be of benefit for the subgroup of patients with less severe symptomatic DPN by relieving sensory symptoms and improving nerve fiber function, as indicated by reductions in VDT and NTSS-6 total score.

Peripheral nerve functions may deteriorate parallel to the progression of microangiopathy in diabetic patients

Our aim was to obtain information to help in the early detection of impaired nerve function and to assess the severity of diabetic symmetric polyneuropathy (DPN). Various somatic and autonomic nerve functions in 40 diabetics and 20 age-matched healthy volunteers were evaluated using six objective examinations: nerve conduction study, quantitative vibratory perception threshold, heart rate variability, Valsalva test, head-up tilt and quantitative sudomotor axonal reflex test (QSART). The diabetics were divided into three groups according to the severity of their microangiopathy. The nerve function data and level of impairment were compared between a healthy control and three diabetic groups. The relationships between nerve function data and clinical background were also examined using multivariate analysis. Results were as follows: (1) all nerve dysfunctions seemed to develop parallel to the progression of microangiopathy, (2) reduced nerve conduction velocity and elevated vibratory perception thresholds in the feet might be early detectable signs of DPN, (3) vasomotor and sudomotor sympathetic functions and cardiovagal functions seemed to deteriorate with the appearance of microangiopathy, (4) lowered compound muscle action potential seemed to appear at the advanced microangiopathic condition, (5) hypohydrosis was closely related to diabetic foot ulcers. In conclusion, nerve dysfunction in diabetics might generally progress with microangiopathy from somatic sensory nerve dysfunction to autonomic nerve dysfunction and then to somatic motor nerve dysfunction. Sympathetic sudomotor dysfunction might be a sensitive predictor of diabetic foot ulcer.

Sural sensory action potential identifies diabetic peripheral neuropathy responders to therapy

Identifying patients with diabetic peripheral neuropathy (DPN) amenable to therapy is a challenge. To determine whether the amplitude of the sural sensory nerve action potential (sural SNAP) reflects the severity of DPN, an analysis was performed on 205 patients with DPN, identified by an abnormal vibration detection threshold (VDT), who were enrolled in a multinational clinical trial investigating ruboxistaurin (RBX) mesylate. Nerve conduction velocity and response amplitude and latency were measured and compared. VDT was significantly lower in those with preserved sural SNAPs (n = 128) than in those in whom they were absent (n = 77; 21.5 vs. 22.7 JND units, P = 0.002). Thus, preserved sural SNAP denoted less severe DPN. Logistic regression analyses evaluating baseline characteristics, HbA(1c), and baseline symptom scores identified only DPN duration as a factor that might contribute to the presence of sural SNAP (P = 0.004; OR = 0.896). For patients with abnormal VDT, preserved sural SNAP identifies a patient population with less severe DPN who may respond to therapeutic intervention in clinical trials.

The protein kinase C-β inhibitor, ruboxistaurin, for the treatment of diabetic microvascular complications

The potential for addressing the underlying biological abnormalities in diabetes has eluded most investigators because of the complex mechanisms underlying the effects of diabetes on the pathogenesis of the complications. Although macrovascular complications, such as myocardial infarction, stroke and gangrene, are only partially attributable to hyperglycaemia and its attendant effects, the microvascular complications including retinopathy, nephropathy and neuropathy are directly related to the degree of hyperglycaemia. In controlled trials, a 22-34% reduction in one of these side effects was achieved for every 1% reduction in glycosylated haemoglobin. Theoretically, it should be feasible to eliminate these complications in a perfect world. However, achieving euglycaemia is nearly impossible and there is increasing data to suggest that it may be an elusive target with ever lower levels being implicated in the pathogenesis of microvascular disease and there is a price to be paid of hypoglycaemia if further intensification is pursued. A logical argument would be to block pathways that are activated by hyperglycaemia. A major pathway implicated is the activation of protein kinase C-beta in all of the targeted tissues, and there is animal data to support the notion that blocking this pathway can reverse or abrogate the untoward effects of diabetes. The possible role of the protein kinase C-beta inhibitor, ruboxistaurin, in animal studies and the recently reported clinical studies to place in perspective a possible addition to the therapeutic armamentarium of the imperfect world of diabetes control will be reviewed.

Pulse pressure is independently associated with sensorimotor peripheral neuropathy in patients with type 2 diabetes

OBJECTIVES

The mechanisms responsible for the onset and progression of sensorimotor peripheral neuropathy (SMPN) in type 2 diabetes remain largely unknown. Although a link between hypertension and SMPN has been observed, it is not clear which blood pressure (BP) component (i.e. systolic, SBP; diastolic, DBP; or pulse pressure, PP) is primarily involved. We sought to determine the relationship between BP components and parameters of nerve function in type 2 diabetes.

DESIGN

Cross-sectional study.

SETTING

Academic medical centre.

SUBJECTS

A total of 55 consecutive ambulatory patients with type 2 diabetes (age 62.6 +/-8.0 years, mean +/- SD).

INTERVENTIONS

Measurement of clinic BP and 10 neurophysiological parameters: motor nerve conduction velocity (NCV; median, ulnar, posterior tibial and peroneal nerve), sensory amplitude (AMP) and latency (LAT; median, ulnar and sural nerve).

RESULTS

Univariate analysis showed that age, diabetes duration, SBP and PP were negatively correlated with nerve function. Regression analysis showed that, after correcting for age, duration of diabetes, glycated haemoglobin, body mass index, microalbuminuria and SBP, PP was independently and negatively associated with NCV (median, P =0.011; ulnar, P = 0.001; peroneal, P = 0.006 and posterior tibial, P = 0.005) and signal AMP (ulnar, P = 0.027; sural, P = 0.055), and positively associated with signal LAT (median, P = 0.083; sural, P = 0.021). SBP was negatively associated with signal AMP (median, P = 0.012) and positively associated with LAT (ulnar, P = 0.018). By contrast, DBP failed to show any significant correlation with nerve function.

CONCLUSIONS

The PP is strongly associated with neurophysiological parameters of nerve function in patients with type 2 diabetes. This relationship is independent of traditional risk factors and other BP components.

Sural nerve pathology in diabetic patients with minimal but progressive neuropathy

AIMS/HYPOTHESIS

The early pathological features of human diabetic neuropathy are not clearly defined. Therefore we quantified nerve fibre and microvascular pathology in sural nerve biopsies from diabetic patients with minimal neuropathy.

METHODS

Twelve diabetic patients underwent detailed assessment of neuropathy and fascicular sural nerve biopsy at baseline, with repeat assessment of neuropathy 8.7+/-0.6 years later.

RESULTS

At baseline, neuropathic symptoms, neurological deficits, quantitative sensory testing, cardiac autonomic function and peripheral nerve electrophysiology showed minimal abnormality, which deteriorated at follow-up. Myelinated fibre density, fibre and axonal area, and g-ratio were normal but teased fibre studies showed paranodal abnormalities (p<0.001), segmental demyelination (p<0.01) and remyelination (p<0.01) without axonal degeneration. Unassociated Schwann cell profile density (p<0.04) and unmyelinated axon density (p<0.001) were increased and axon diameter was decreased (p<0.007). Endoneurial capillaries demonstrated basement membrane thickening (p<0.006), endothelial cell hyperplasia (p<0.004) and a reduction in luminal area (p<0.007).

CONCLUSIONS/INTERPRETATION

The early pathological features of human diabetic neuropathy include an abnormality of the myelinated fibre Schwann cell and unmyelinated fibre degeneration with regeneration. These changes are accompanied by a significant endoneurial microangiopathy.

Peripheral nerve endoneurial microangiopathy and necrosis in rats with insulinoma

Peripheral nerve pathology related to chronic hyperinsulinemia and hypoglycemia has yet to be fully explored. Here we conducted a systematic quantitative analysis of morphological alterations in peripheral sensory and motor nerve fibers and endoneurial microvasculature in longstanding insulinoma-carrying rats (I-rats; n=12). Age-matched normal rats (n=6) served as controls. Over the 15-month observation period, two of I-rats developed paresis of the hind limbs when their blood glucose level fell below 1.7 mmol/l. These animals showed a massive myelinated fiber loss associated with active degeneration of residual myelinated fibers and multiple endoneurial microvascular occlusions at the sciatic nerve level. The rest of the non-paretic I-rats showed a decreased density of large myelinated fibers with axonal degeneration in the peroneal nerve and an increased density of small myelinated fibers with preserved morphology in the sural nerve. This was associated with endoneurial microangiopathic changes indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and an increase in endoneurial microvascular density in the sciatic and sural nerves. In conjunction with previous data, these findings suggest that the observed increase in endoneurial microvascular density may be a compensatory response to endoneurial ischemia/hypoxia induced by chronic hyperinsulinemia in I-rats without paresis. In conclusion, the present study showed characteristic morphological alterations in peripheral sensory and motor nerve fibers associated with microangiopathy indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and provides the first evidence for the occurrence of endoneurial necrosis in the sciatic nerve, to which the hind limb paresis can be ascribed in I-rats.

Diabetes Mellitus and the Sensory Neuron

Sensory neurons in diabetes may be primarily targeted by diabetes and their involvement may account for prominent sensory loss and pain in diabetic patients. Previous studies demonstrating evidence of excessive polyol flux, microangiopathy, and oxidative stress involving sensory axons and ganglia have been joined by more recent work demonstrating altered neuron phenotype, mitochondrial dysfunction, ion channel alterations, and abnormal growth factor signaling. As such, an interesting and unique panoply of molecular changes in primary sensory neurons has been identified in diabetic models. Insulin deficiency and subsequent changes in second messenger signaling may also play an important role in how sensory neurons respond to diabetes. Applying approaches to support sensory neurons in diabetes may be an important therapeutic direction in diabetic patients.

Perineurial cell basement membrane thickening and myelinated nerve fibre loss in diabetic and nondiabetic peripheral nerve

Diabetic neuropathy is associated with changes in the extracellular matrix of the perineurium, including thickening of the basement membrane of the perineurial cells. Peripheral vascular disease (PVD) is a common vascular condition that can occur in the absence or presence of diabetes. Thickening of the vascular basement membrane of the vasa nervorum is associated with both diabetes and nondiabetic peripheral vascular disease. However, perineurial cell basement membrane (PCBM) thickening in the nondiabetic PVD state has not, until now, been investigated. In this study, 36 nerve fascicles were examined from three patient groups: a diabetic group, a nondiabetic PVD group, and a group free of both PVD and diabetes (control group). PCBM thickness, fascicle size, and myelinated nerve fibre (MNF) density were measured in all three groups. Endoneurial blood vessels were also observed for evidence of morphological changes. The results showed that the thickness of the PCBM is significantly greater in the diabetic group in comparison with both the control and the nondiabetic PVD group, and this increase in thickness is linearly related to fascicle size. The thickness of the PCBM was not significantly different between the nondiabetic PVD and control groups. Although both the nondiabetic PVD and diabetic groups showed a loss of myelinated nerve fibres in comparison with the control group, this loss was statistically greater in the diabetic group. The endoneurial blood vessels of both the diabetic and nondiabetic PVD groups showed evidence of endothelial cell hyperplasia, hypertrophy, and basement membrane reduplication.

Diabetic neuropathy and microcirculation

The microcirculation in diabetic and neuropathic feet is subject to the same changes found in other end organs of diabetic patients, such as the retina or the kidney. Complications such as foot ulceration lead to further morbidity and hospitalizations. Research into the causes of microcirculatory dysfunction has revealed an interplay of numerous factors. The most prominent findings are impaired endothelium-dependent and -independent vasodilation and reduced or absent nerve-axon reflex-related vasodilation. This renders the diabetic foot unable to mount a vasodilatory response under conditions of stress, such as injury, and makes it functionally ischemic even in the presence of satisfactory blood flow under normal conditions.

New treatments for diabetic neuropathy: symptomatic treatments

Painful diabetic neuropathy is a common distressing and challenging condition. The mechanism or mechanisms involved in its pathogenesis continue to elude clinical scientists. As with other conditions of painful distal symmetrical neuropathic conditions, pain relief involves the use of a variety of analgesic and neuroleptic drugs, aimed at reducing either central responses to painful stimuli or at dampening spontaneous irritability of affected neurons. More recently, several therapies directed at putative pathologic mechanisms specific to painful diabetic neuropathy have evolved. These include vasodilators, protein kinase C beta inhibition, antioxidants, and novel aldose reductase inhibitors. Preliminary clinical studies of these therapies have at present involved small numbers of patients; however, the results have been encouraging. This article considers the clinical aspects of diagnosis and management of chronic painful diabetic neuropathy, focusing on existing and newer therapies.

Endoneurial capillary abnormalities presage deterioration of glucose tolerance and accompany peripheral neuropathy in man

To explore whether microangiopathy is associated with disturbed glucose tolerance and peripheral neuropathy, we assessed endoneurial capillary morphology in sural nerve biopsies from men with diabetes, impaired glucose tolerance (IGT), and normal glucose tolerance (NGT). Baseline morphology was related to glucose tolerance and neuropathy at baseline and at follow-up 6 years later. Capillary density (in number per millimeters squared) at baseline was higher in subjects with diabetes (n = 10) compared with those with NGT (n = 5) at follow-up (median [interquartile range]) (86.0 [24.3] vs. 54.9 [17.1]; P = 0.0200) and in those progressing from IGT to diabetes (n = 4) compared with those with persistent IGT (n = 4) (86.7 [25.2] vs. 54.1 [14.6]; P = 0.0433). The capillary luminal area (in micrometers squared) was lower in subjects with NGT progressing to IGT (n = 2) or subjects with IGT progressing to diabetes (n = 3) compared with subjects with constant NGT (n = 6) or constant IGT (n = 4) (11.9 [2.4] vs. 20.8 [7.8]; P = 0.0201). The capillary basement membrane area (in micrometers squared) was increased in patients with peripheral neuropathy (n = 10) compared with those without (n = 7) (114.6 [68.8] vs. 75.3 [28.7]; P = 0.0084). In conclusion, increased capillary density was associated with current or future diabetes, decreased capillary luminal area with future deterioration in glucose tolerance, and increased basement membrane area with peripheral neuropathy.

Peripheral neuropathy and microangiopathy in rats with insulinoma: association with chronic hyperinsulinemia

BACKGROUND

Hypoglycemia can precipitate or worsen peripheral neuropathy in patients with insulinoma or in diabetic patients on an intensive insulin regimen. It still remains unclear as to whether hyperinsulinemia itself is involved in neuropathic changes in these patients. We, therefore, explored the possible isolated effects of chronic hyperinsulinemia on neuropathic changes in insulinoma-bearing rats (I-rats).

METHODS

I-rats were generated by a combined treatment with nicotinamide and streptozotocin. At 15 months after the treatment, they showed a wide range of the plasma insulin (PI) level with or without a decrease in the blood glucose (BG) level and were divided into three groups on the basis of the presence of hypoglycemia (BG < 2.5 mmol/L) or hyperinsulinemia (PI > 100 mU/L): the first exhibited only hypoglycemia, the second exhibited only hyperinsulinemia, and the third exhibited neither. Peripheral nerve function and structure as well as microvasculature were evaluated among these groups in addition to age-matched untreated control rats (C-rats).

RESULTS

The first group of hypoglycemic I-rats showed a decrease (p < 0.05) in the axon/myelin ratio and an increase (p < 0.0001) in fibers undergoing axonal degeneration compared to C-rats, while the other two groups did not. On the other hand, the second group of hyperinsulinemic I-rats showed a decrease (p < 0.05) in the myelinated axonal size and an increase (all p < 0.05) in the F-wave latency and the densities of myelinated fibers and endoneurial microvessels exhibiting endothelial hyperplasia, vascular wall thickening, or pericytes debris compared to the third group of isoglycemic I-rats without hyperinsulinemia.

CONCLUSION

These results suggest that hypoglycemia is associated with increased myelinated axonal damage, while hyperinsulinemia is associated with increased densities of small myelinated axons and endoneurial microvessels with microangiopathic changes in I-rats. We, therefore, propose that the observed findings may be relevant to the complicated features of neuropathy in diabetic patients with chronic hyperinsulinemia.

Increased sural nerve epineurial blood flow in human subjects with painful diabetic neuropathy

AIMS/HYPOTHESIS

The pathogenesis of painful diabetic neuropathy remains unknown. As a consequence we still do not have any effective, rational treatments and a greater understanding of the mechanisms is urgently required. Previous studies have shown no consistent morphological differences in the nerves of patients with and without painful neuropathy. The aim of this study was to compare epineurial haemodynamics in patients with chronic painful and painless neuropathy.

METHODS

The techniques of microlightguide spectrophotometry and fluorescein angiography were used to measure epineurial intravascular oxygen saturation and blood flow respectively. Eleven patients with painful and eight with painless neuropathy were studied, with the groups matched carefully in terms of severity of neuropathy and diabetes control.

RESULTS

Intravascular oxygen saturation was higher in the painful neuropathy group compared to those without pain (median 73.8% vs 67.7%, respectively; p=0.021). Fluorescein rise time was also faster in those with painful symptoms (median 18.3 s vs 53.6 s; p=0.046) indicating higher epineurial blood flow in these subjects.

CONCLUSION/INTERPRETATION

These results indicate that there are distinct differences in haemodynamics within the epineurium of the sural nerve in subjects with painful and painless neuropathy. Haemodynamic factors could therefore have an important role in the pathogenesis of neuropathic pain and might offer further insight into potential treatments for this distressing condition.

Corneal confocal microscopy: a non-invasive surrogate of nerve fibre damage and repair in diabetic patients

AIMS/HYPOTHESIS

The accurate detection, characterization and quantification of human diabetic neuropathy are important to define at risk patients, anticipate deterioration, and assess new therapies. Corneal confocal microscopy is a reiterative, rapid, non-invasive in vivo clinical examination technique capable of imaging corneal nerve fibres. The aim of this study was to define the ability of this technique to quantify the extent of degeneration and regeneration of corneal nerve fibres in diabetic patients with increasing neuropathic severity.

METHODS

We scanned the cornea and collected images of Bowman's layer (containing a rich nerve plexus) from 18 diabetic patients and 18 age-matched control subjects.

RESULTS

Corneal nerve fibre density (F(3)=9.6, p<0.0001), length (F(3)=23.8, p<0.0001), and branch density (F(3)=13.9, p<0.0001) were reduced in diabetic patients compared with control subjects, with a tendency for greater reduction in these measures with increasing severity of neuropathy.

CONCLUSION/INTERPRETATION

Corneal confocal microscopy is a rapid, non-invasive in vivo clinical examination technique which accurately defines the extent of corneal nerve damage and repair and acts as a surrogate measure of somatic neuropathy in diabetic patients. It could represent an advance to define the severity of neuropathy and expedite assessment of therapeutic efficacy in clinical trials of human diabetic neuropathy.

Ultrastructural morphometry of capillary basement membrane thickness in normal and transgenic diabetic mice

Capillary basement membrane (CBM) thickening is an ultrastructural hallmark in diabetic patients and in animal models of diabetes. However, the wide variety of tissues sampled and diverse methods employed have made the interpretation of thickness data difficult. We showed previously that acellular glomerular BMs in OVE26 transgenic diabetic mice were thickened beyond normal age-related thickening, and in the current study we hypothesized that other microvascular BMs likewise would show increased widths relative to age-matched controls. Accordingly, a series of tissues, including skeletal and cardiac muscle, ocular retina and choriod, peripheral nerve, lung, pancreas, and renal glomerulus was collected from 300-350-day-old normal and transgenic mice. Transmission electron micrographs of cross sections through capillary walls were prepared, and CBM thickness (CBMT) was determined by the "orthogonal intercept" method. Morphometric analyses showed highly variable transgene-related BMT increases in the sampled tissues, with glomerular BM showing by far the greatest increase (+87%). Significant thickness increases were also seen in the retina, pulmonary alveolus, and thoracoabdominal diaphragm. BMT increases were not universal; however, most were modestly widened, and those that were thickest in controls generally showed the greatest increase. Although the pathogenesis of diabetes-related increases in CBM is poorly understood, data in the current study showed that in OVE26 transgenic mice increased BMT was a frequent concomitant of hyperglycemia. Accordingly, it seems likely that hyperglycemia-induced microvascular damage may be a contributing factor in diabetic BM disease, and that microvessel cellular and extracellular heterogeneity may limit the extent of CBM thickening in diverse tissues.

Enhanced angiogenesis and improvement of neuropathy by cotransfection of human hepatocyte growth factor and prostacyclin synthase gene

The current therapeutic angiogenesis strategy to treat ischemic disease by using angiogenic growth factors has been limited to use of a single gene. However, as vasodilator substances such as prostacyclin are widely used for the treatment of peripheral arterial disease, it might be useful to combine angiogenesis with vasodilation of new vessels. In a mouse hind limb ischemia model, cotransfection of the hepatocyte growth factor (HGF) gene with the prostacyclin synthase gene demonstrated a further increase in blood flow and capillary density compared with a single gene. Even in the rabbit ischemia model, cotransfection of HGF plasmid with the prostacyclin synthase gene demonstrated a further increase in angiogenic activity compared with HGF alone. Because peripheral neuropathy due to diabetes is common for significant morbidity, we examined the hypothesis that experimental diabetic neuropathy can be reversed by HGF and prostacyclin synthase genes. Severe peripheral neuropathy, characterized by significant slowing of nerve conduction velocity compared with nondiabetic control animals, was ameliorated. Overall, cotransfection of the prostacyclin synthase and HGF genes is more effective than single-gene transfection to stimulate angiogenesis, and it significantly improved neuropathy. These data provide important information relating to the clinical application of therapeutic angiogenesis to treat peripheral arterial disease.

Nerve and ganglion blood flow in diabetes: an appraisal

Vasa nervorum, the vascular supply to peripheral nerve trunks, and their associated cell bodies in ganglia have unique anatomical and physiological characteristics. Several different experimental approaches toward understanding the changes in vase nervorum following injury and disease have been used. Quantative techniques most widely employed have been microelectrode hydrogen clearance palarography and [14C]iodoantipyrine autoradiographic distribution, whereas estimates of red blood cell flux using a fiber-optic laser Doppler probe offer real time data at different sites along the nerve trunk. There are important caveats about the use of these techniques, their advantages, and their limitations. Reports of nerve blood flow require careful documentation of physiological variables, including mean arterial pressure and nerve temperature during the recordings. Several ischemic models of the peripheral nerve trunk have addressed the ischemic threshold below which axonal degeneration ensues (< 5ml/100 g/min). Following injury, rises in local blood flow reflect acitons of vasoactive peptides, nitric oxide, and the development of angiogenesis. In experimental diabetes, a large number of studies have documented reductions in nerve blood flow and tandem corrections of nerve blood flow and conduction slowing. A significant proportions, however, of the work can be criticized on the basis of methodology and interpretation. Similarly, not all work has confirmed that reductions of nerve blood flow are an invariable feature of experimental or human diabetic polyneuropathy. Therefore, while there is disagreement as to whether early declines in nerve blood flow "account" for diabetic polyneuropathy, there is unquestioned eveidence of early microangiopathy. Abnormalities of vase nervorum and micorvessels supplying ganglia at the very least develop parallel to and together with changes in neurons, Schwann cells, and axons.

Haemodynamics in microvascular complications in type 1 diabetes

Type 1 diabetes is commonly associated with microvascular complications. Most of the microvascular blood vessels are involved but those in the kidney, retina and large nerves exhibit the more significant pathology. Haemodynamic and metabolic factors both alone and through the activation of a common pathway contribute to the characteristic dysfunction observed in diabetic vasculopathy. The haemodynamic abnormalities in type 1 diabetes are characterized by increased systemic blood pressure and altered blood flow with subsequent activation of various vasoactive factors, which can contribute to the maintenance of the haemodynamic alterations and to the development and progression of the microvascular complications. These vasoactive factors include vasoconstrictors such as angiotensin II, and endothelin, as well as vasodilators such as nitric oxide (NO). Systemic hypertension and vasoactive factors independently and in interaction with the metabolic pathway activate intracellular second messengers, nuclear transcription factors and various growth factors which lead to the typical functional and structural alterations of diabetic microvascular complications. Therapeutic strategies involved in the management and prevention of diabetic complications currently include antihypertensive agents, particularly those that interrupt the renin-angiotensin system. Further understanding of the interactions among the vasoactive factors, the intracellular second messengers and the growth factors may help to identify novel strategies to influence the action of the vasoactive factors. These novel therapies, together with specific inhibitors of the metabolic pathway or the common pathway, may provide the possibility of preventing or even reversing the progression of diabetic microvascular complications.

Influence of experimental diabetes on the microcirculation of injured peripheral nerve: functional and morphological aspects

Regeneration of diabetic axons has delays in onset, rate, and maturation. It is possible that microangiopathy of vasa nervorum, the vascular supply of the peripheral nerve, may render an unfavorable local environment for nerve regeneration. We examined local nerve blood flow proximal and distal to sciatic nerve transection in rats with long-term (8 month) experimental streptozotocin diabetes using laser Doppler flowmetry and microelectrode hydrogen clearance polarography. We then correlated these findings, using in vivo perfusion of an India ink preparation, by outlining the lumens of microvessels from unfixed nerve sections. There were no differences in baseline nerve blood flow between diabetic and nondiabetic uninjured nerves, and vessel number, density, and area were unaltered. After transection, there were greater rises in blood flow in proximal stumps of nondiabetic nerves than in diabetic animals associated with a higher number, density, and caliber of epineurial vessels. Hyperemia also developed in distal stumps of nondiabetic nerves but did not develop in diabetic nerves. In these stumps, diabetic rats had reduced vessel numbers and smaller mean endoneurial vessel areas. Failed or delayed upregulation of nerve blood flow after peripheral nerve injury in diabetes may create a relatively ischemic regenerative microenvironment.

Evaluation of sensorimotor polyneuropathy in children and adolescents with type I diabetes: associations with microalbuminuria and retinopathy

To investigate diabetic polyneuropathy, we measured peroneal motor conduction velocity, sural sensory nerve conduction velocity and vibratory sense threshold (biothesiometry) in 28 children and adolescents with insulin-dependent diabetes (type 1), and in 28 age- and sex-matched, normal controls. Age varied from 8 to 19 yr (mean +/- SD = 13.04 +/- 2.61); age at the onset of diabetes from 9 months to 12 yr (4.53 +/- 2.42 yr); and the duration of diabetes from 5 to 16 yr (8.48 +/- 2.98). Eight patients (28%) fulfilled the minimal criteria for the diagnosis of polyneuropathy. Four of these patients showed symptoms while three had clinical signs of neuropathy. Eight patients had abnormal, sural sensory nerve conduction velocities. The presence of polyneuropathy did not correlate with the duration of diabetes or degree of metabolic control of diabetes. The prevalence of microvascular complications (microalbuminuria and retinopathy) was 32%. The presence of microvascular complications did not correlate with metabolic control but did with the duration of diabetes. The relationship between polyneuropathy and microvascular complications was 34%.

Retinopathy as a predictor of other diabetic complications

PURPOSE

Early predictors of diabetic complications may aid in the prevention and/or management of these complications. The aim of this cross-sectional study was to determine the predictive value of retinopathy for the presence of other diabetic complications.

METHODS

The population studied comprised 648 patients with diabetes mellitus assessed by our service. There were 210 patients (32.4%) with insulin-dependent diabetes mellitus (IDDM), and 438 patients (67.6%) with non-insulin-dependent diabetes mellitus (NIDDM).

RESULTS

Univariate analyses revealed that retinopathy significantly predicted the presence of neuropathy (odds ratio [OR] = 2.23; 95% confidence interval [CI] = 1.56-3.18; p < 0.001), nephropathy (OR = 5.68; 95% CI = 3.06-10.62; p < 0.001), and cerebrovascular disease (OR = 6.6; 95% CI = 1.16-67.21; p = 0.0239) in the total group. Similar associations were observed both in subjects with IDDM and NIDDM. The associations between retinopathy severity level and the prevalence rate of nephropathy were significant in the total group (p = 0.0001), in patients with IDDM (p = 0.0113), and in patients with NIDDM (p = 0.01). In patients with mild to moderate non-proliferative retinopathy (NPDR), nephropathy was present in 17.2% of patients with IDDM, and in 11.4% of patients with NIDDM. In patients with severe NPDR, nephropathy was present in 23.3% in patients with IDDM, and in 11.8% of patients with NIDDM. In patients with proliferative retinopathy (PDR), nephropathy was present in 50% in patients with IDDM, and in 45.5% in patients with NIDDM. In multivariate logistic regression analyses, nephropathy was the only significant complication to be independently associated with retinopathy in patients with IDDM (OR = 8.02; 95% CI = 1.95-33), and in patients with NIDDM (OR = 2.48; 95% CI = 1.02-6.03).

CONCLUSIONS

Retinopathy, especially the presence of PDR, is an independent predictor for nephropathy. The predictive value of retinopathy for nephropathy is stronger in patients with IDDM than in those with NIDDM. Ophthalmologists should refer patients with retinopathy for regular medical evaluations.

No correlation between impairment of cerebrovascular reserve capacity and electrophysiologically assessed severity of neuropathy in noninsulin-dependent diabetes mellitus

INTRODUCTION

Microvascular abnormalities have an important role in the most frequent neurological complications of diabetes mellitus: neuropathy and cerebrovascular disorders. Severity of neuropathy as well as of cerebral microvascular damage can be quantitatively evaluated by instrumental methods like nerve conduction studies and transcranial Doppler. In the present study, we investigated whether a correlation exists between the severity of peripheral neuropathy and the impairment of cerebrovascular reserve capacity (CRC) in 20 patients with Type 2 diabetes mellitus.

METHODS

CRC was measured by transcranial Doppler and defined as the maximal percentage increase in blood flow velocity in the middle cerebral artery within 20 min after an intravenous dose of 1000 mg of acetazolamide. Nerve conduction studies of the median, ulnar, peroneal, and sural nerves were performed. Severity of neuropathy was scored based on conduction velocities, amplitudes, and distal latencies.

RESULTS

There was no correlation between the neuropathic score and CRC (R= .003, P= .99). Neither CRC nor the neuropathic score correlated significantly with age, duration of diabetes, and serum values of HbA(1c), glucose, insulin, von Willebrand factor, and alpha(2) - macroglobulin. Severity of neuropathy but not CRC correlated with microalbuminuria (R= .47, P= .038 and R= .14, P= .54). Improper treatment reflected by HbA(1c) >10% was associated with significantly more severe albuminuria, higher actual blood glucose level, higher von Willebrand factor activity, and marginally higher neuropathic score (21 vs. 13, P=.096), but was not associated with CRC (44% vs. 42%, P= .81). When duration of diabetes was dichotomized to 15 years and less or over 15 years, CRC was significantly smaller (35% vs. 50%, P= .036) and neuropathy was more severe in the subgroup with longer diabetes duration (19 vs. 11.5 points, P= .07).

CONCLUSIONS

Although both CRC and peripheral nerve function are affected more severely in patients with long-lasting Type 2 diabetes mellitus, damage in the cerebrovascular system and in the long peripheral nerves occur independently. As in diabetes mellitus pathological changes in autonomic and large peripheral nerves develop simultaneously, decreased CRC in diabetic patients might be predominantly due to structural changes of resistance arteries or to metabolic than to neurogenic factors.

RheoSorb: a specific adsorber for fibrinogen elimination in clinical situations with impaired rheology

A functional microcirculation is crucial for the normal function of an organism. In many physiopathological situations, impaired microcirculation may contribute to the development or progress of diseases. Microcirculation is closely interrelated with blood and especially plasma rheology. Thus, improvement of plasma viscosity has beneficial effects on rheology, microcirculation, and the related tissue microenvironment. However, at best tools that only have a minor influence on plasma viscosity exist so far. Fibrinogen is known to be the major contributor to plasma viscosity, making it an interesting target for therapeutic intervention. An adsorber specific for fibrinogen was developed on the basis of the TheraSorb technology. The TheraSorb technology (PlasmaSelect AG, Teterow, Germany) allows the selective removal of components from human blood plasma by means of an affinity chromatography column. A ligand specific for a defined plasma component is coupled to a solid matrix (sepharose) thus binding and eliminating the target molecule from plasma. Using a fibrinogen specific pentapeptide as ligand, selective removal of fibrinogen, fibrin, and degradation products, containing the target sequence of these molecules, can be obtained. The LIFE-18, a state-of-the-art integrated plasma therapy instrument, is used to perform the treatment. The procedure improves plasma and whole blood viscosity in a dose dependent manner as shown in Phase 1 and 2 clinical trials. This article describes the first clinical experience in patients with diabetic foot syndrome and provides an outlook for further clinical and scientific investigations related to this promising new procedure.

Diabetes, peripheral neuropathy, and old age disability

The purpose of this study was to determine whether peripheral neuropathy explains the apparent association between diabetes and disability in old age, and to evaluate the utility of lower extremity function tests in older diabetic adults with and without neuropathy. We evaluated 39 adults, aged 70-79 years, for pressure sensation (log(10)g), vibration perception threshold (VPT; microns), and electrophysiologic function of the peroneal nerve. The subjects included patients with established diabetic neuropathy (DN; n = 14), diabetic controls without neuropathy (DC; n = 13), and nondiabetic controls (NDC; n = 12). Nonparametric statistical methods were used to relate neuropathy measures to performance in tests of walking speed, static and dynamic balance, coordination, and ankle strength (kilograms). Significant age-adjusted correlations were observed between measures of sensory neuropathy and a variety of performance measures, and electrophysiologic measures were related to static balance. DN subjects had significantly higher pressure sensation than NDC (5.17 vs 3.38g, P < 0.05), higher VPT (62.5 vs 21.7 microm, P < 0.05), and lower peroneal motor response amplitudes at multiple sites. Pressure sensation and nerve conduction measures did not differ between DC and NDC. Compared with NDC, DN subjects performed significantly worse on tests of walking speed (0.99 vs 1.34 m/s; P < 0.05), static balance (4.9 vs 20.4 s; P < 0.05), dynamic balance (9.23 vs 25.52 s; P < 0.05), and coordination (6.73 vs 4.76 s; P < 0.05). No differences were observed in these measures between DC and NDC. Observed differences in physical abilities between older diabetic and nondiabetic adults may have been due to the subset of diabetic individuals with peripheral neuropathy. Quantitative measures of sensory and motor nerve function have distinct effects on physical performance. Interventions aimed at reducing the impact of diabetes-associated disability in old age may have the greatest impact among people with peripheral neuropathy.

Measurement of somatic neuropathy for clinical practice and clinical trials

Distal sensory polyneuropathy is a common and unpleasant complication of diabetes mellitus. It is the main initiating factor for foot ulceration. The increasing prevalence of diabetes has important associated health implications, both in terms of morbidity and mortality, and results in the consumption of scarce medical resources. Identification of somatic neuropathy in clinical practice is therefore important for targeted educational and other interventions. In this article, we describe methods for detecting somatic neuropathy in clinical practice and highlight those tests that are proven to be predictors of foot ulceration. The approach for detecting and characterizing somatic neuropathy for clinical trials, however, differs significantly. These methods must ideally have high levels of reproducibility, sensitivity, and specificity. Currently, several neurophysiologic tests are employed in clinical trials in order to accurately characterize diabetic neuropathy. The recent introduction of the computer-assisted programs for the measurement of sensory modalities for clinical trials has been a major advance. Due to their invasive nature and associated morbidity, nerve biopsy studies are no longer used in clinical trials. Recently, using magnetic resonance imaging (MRI), significant spinal cord atrophy has been demonstrated in established neuropathy. If this observation proves to be an early feature, then a relatively rapid, noninvasive MRI technique may be used in the future to characterize diabetic neuropathy.

Reversal of experimental diabetic neuropathy by VEGF gene transfer

The pathogenetic basis for diabetic neuropathy has been enigmatic. Using two different animal models of diabetes, we have investigated the hypothesis that experimental diabetic neuropathy results from destruction of the vasa nervorum and can be reversed by administration of an angiogenic growth factor. Nerve blood flow, as measured by laser Doppler imaging or direct detection of a locally administered fluorescent lectin analogue, was markedly attenuated in rats with streptozotocin-induced diabetes, consistent with a profound reduction in the number of vessels observed. A severe peripheral neuropathy developed in parallel, characterized by significant slowing of motor and sensory nerve conduction velocities, compared with nondiabetic control animals. In contrast, 4 weeks after intramuscular gene transfer of plasmid DNA encoding VEGF-1 or VEGF-2, vascularity and blood flow in the nerves of treated animals were similar to those of nondiabetic control rats; constitutive overexpression of both transgenes resulted in restoration of large and small fiber peripheral nerve function. Similar experiments performed in a rabbit model of alloxan-induced diabetes produced comparable results. These findings support the notion that diabetic neuropathy results from microvascular ischemia involving the vasa nervorum and suggest the feasibility of a novel treatment strategy for patients in whom peripheral neuropathy constitutes a secondary complication of diabetes.

The role of protein kinase C in the development of the complications of diabetes

Diabetes mellitus produces a state of chronic hyperglycemia which in turn leads to the development of severe complications including retinopathy, nephropathy, neuropathy, and atherosclerosis. Many different mechanisms have been put forward to attempt to explain how glucose elevations can damage these various organ systems. Protein kinase C activation is one of the sequelae of hyperglycemia and is thought to play a role in the development of diabetic complications. There are multiple mechanisms for its activation in the diabetic state and multiple downstream effects attributable to that activation. The role of protein kinase C activation in the development of the above-mentioned complications of diabetes is discussed in this chapter. In addition, the potential use of isoform-specific inhibitors of protein kinase C for the treatment of diabetic complications is proposed.

Diabetic neuropathy--a continuing enigma

In this article we will review the clinical signs and symptoms of diabetic somatic polyneuropathy (DPN), its prevalence and clinical management. Staging and classification of DPN will be exemplified by various staging paradigms of varied sophistication. The results of therapeutic clinical trials will be summarized. The pathogenesis of diabetic neuropathy reviews an extremely complex issue that is still not fully understood. Various recent advances in the understanding of the disease will be discussed, particularly with respect to the differences between neuropathy in the two major types of diabetes. The neuropathology and natural history of diabetic neuropathy will be discussed pointing out the heterogeneities of the disease. Finally, the various prospective therapeutic avenues will be dealt with and discussed.

Ca(2+)-Mg(2+)-ATPase activity and ionized calcium in Type 2 diabetic patients with neuropathy

Ca(2+)-Mg(2+)-ATPase is an important regulator of intracellular calcium concentration and therefore, of erythrocyte deformability. We have investigated the possible relationship between Ca(2+)-Mg(2+)-ATPase activity (ATPase) and ionized calcium (Ca(2+)), in diabetic patients with peripheral neuropathy. A total of 104 Type 2 diabetic patients (57 neuropathic and 47 non-neuropathic) and 25 non-diabetic subjects were studied. After an overnight fast, blood was taken for Ca(2+)-Mg(2+)-ATPase activity, Ca(2+), Mg(2+), PTH and HbA(1c). The neuropathy study group had significantly lower levels of ATPase, 6.6 (95% CI, 5.6-7.7) nmol/mg/min compared to controls 7. 1 (6.2-8.3) nmol/mg/min, P<0.001 and to diabetic patients without neuropathy 7.0 (6.0-8.1) nmol/mg/min, P<0.001. The study group had also lower levels of Ca(2+) (0.89+/-0.18 mmol/l vs. control 1.08+/-0. 24 mmol/l, P<0.01 and non-neuropathic 0.98+/-0.27 mmol/l, P<0.05) and Mg(2+) (0.73+/-0.13 mmol/l vs. control 0.81+/-0.14 mmol/l, P<0. 05), despite similar PTH levels. In diabetic subjects, no correlation was found between ATPase or Ca(2+) with glucose, HbA(1c), age or duration of diabetes. We conclude that in patients with diabetic neuropathy there are abnormalities of Ca(2+)-Mg(2+)-ATPase activity and Ca(2+). This provides further support for the role of microangiopathy in the pathogenesis of neuropathy.

Can diabetic neuropathy be prevented by angiotensin-converting enzyme inhibitors?

The incidence of diabetes and its complications is increasing to staggering proportions. Presently the WHO estimates an overall prevalence of 130 million, but by 2025 there will be 300 million individuals with diabetes mellitus. The incidence of diabetic neuropathy approaches 50% in most diabetic populations; there is no treatment, and its consequences in the form of foot ulceration and amputation are financially punishing for health care providers. Attempts to develop treatments have faltered for want of an understanding of the aetiology of diabetic neuropathy. As a consequence, 1999 saw the demise of two further compounds: recombinant growth factor by Roche-Genentech and the aldose reductase inhibitor zopolrestat, by Pfizer, both had reached phase III clinical trials. They joined an impressive list of at least 30 other compounds which have reached phase III clinical trials and failed to establish efficacy. The need to establish a viable treatment for human diabetic neuropathy is absolutely paramount. To provide a rational answer as to whether angiotensin-converting enzyme (ACE) inhibitors can prevent human diabetic neuropathy, two major issues need addressing: 1) Does vascular dysfunction cause human diabetic neuropathy? 2) Can ACE inhibitors ameliorate diabetic vascular dysfunction and hence neuropathy? Epidemiological studies support a strong association between neuropathy, retinopathy and nephropathy. Microangiopathy is deemed as the root cause of both nephropathy, and retinopathy and mounting evidence provides support for a vascular basis of diabetic neuropathy. ACE inhibitors appear to correct many of the abnormalities associated with the vascular dysfunction found in diabetes. Thus effective ACE inhibition impacts very positively on cardiovascular outcomes in patients with ischaemic heart disease, particularly in diabetic patients. ACE inhibition also prevents the development and progression of incipient and established diabetic nephropathy and delays progression of background retinopathy. Quinapril improves measures of diabetic autonomic neuropathy. Our recent study has demonstrated a significant improvement in peripheral neuropathy following 12 months of treatment with the ACE inhibitor trandolapril.

Diabetic Neuropathies

There are currently no treatments available (beyond optimal control of hyperglycemia) that arrest or reverse progressive diabetic polyneuropathy. Consultation with a diabetologist is indicated for patients with poorly controlled disease and polyneuropathy. Immunotherapy for diabetic lumbosacral plexopathy has been advocated but is not supported to date by class 1 clinical trial evidence. Pharmacologic treatment for painful neuropathy may include topical anesthetics, capsaicin cream, anticonvulsants, tricyclic antidepressants, mexiletine, and opioids. Gabapentin, a newer anticonvulsant, has an attractive side-effect profile (a consideration in older patients) and has fewer interactions with other drugs. Amitriptyline may cause excessive sedation, postural hypotension, constipation, and urinary retention, but low evening doses (10 to 25 mg), slowly titrated upward, may offer relief from nocturnal pain. Opioids should not be withheld from patients with severe pain or with intolerance of or contraindications to other agents. A single physician should supervise their use.

Structural abnormalities do not explain the early functional abnormalities in the peripheral nerves of the streptozotocin diabetic rat

The streptozotocin (STZ)-diabetic rat, the most commonly employed model of experimental diabetic neuropathy, is characterised by a reduction in nerve conduction velocity, pain threshold and blood flow. Whether or not structural abnormalities underlie these functional abnormalities is unclear. 10 adult male Sprague-Dawley STZ-diabetic rats (diabetes duration 27 d) and 10 age-matched (23 wk) control animals were studied. Motor nerve conduction velocity (m s(-1)) was significantly reduced in diabetic (41.31 +/- 0.8) compared with control (46.15 +/- 1.5) animals (P < 0.001). The concentration of sciatic nerve glucose (P < 0.001), fructose (P < 0.001) and sorbitol (P < 0.001) was elevated, and myoinositol (P < 0.001) was reduced in diabetic compared with control animals. Detailed morphometric studies demonstrated no significant difference in fascicular area, myelinated fibre density, fibre and axon areas as well as unmyelinated fibre density and diameter. Endoneurial capillary density, basement membrane area and endothelial cell profile number did not differ between diabetic and control animals. However, luminal area (P < 0.03) was increased and endothelial cell area (P < 0.08) was decreased in the diabetic rats. We conclude there is no detectable structural basis for the reduction in nerve conduction velocity, pain threshold or blood flow, observed in the streptozotocin diabetic rat.

Skin perfusion in patients with erythromelalgia

BACKGROUND

Erythromelalgia (EM) is a chronic disorder characterized by intermittent pain, warmth and erythema of the extremities. Symptoms can be precipitated by increasing the temperature of the affected limb and can be partially relieved by direct cooling.

MATERIALS AND METHODS

Microvascular assessment was conducted under 'hot' (28 degrees C) environmental conditions in 61 EM (EMI) patients and 30 control subjects. Twenty patients with many of the symptoms of EM were enrolled as an active control group (EMII). Using laser Doppler flowmetry, basal skin erythrocyte flux (SkEF) and the hyperaemic response to local heating (44 degrees C) were measured.

RESULTS

Compared with control subjects, basal SkEF was reduced at the toe (P < 0.001), index finger (P < 0.05), dorsal and plantar aspects of the foot (P < 0.01) in both patient groups and at the medial mid-calf (P < 0.05) in EMI patients. Both EM groups also had a significantly reduced maximum SkEF at the dorsum of foot and medial mid-calf (all P < 0.001) compared with control values. In a subset of patients and control subjects, transcutaneous carbon dioxide levels were raised in EMI patients (P < 0.02) compared with levels in control subjects. Toe temperature was significantly reduced in both EM groups compared with control subjects (both P < 0. 001).

CONCLUSION

Our study indicates for the first time that there is a vasoconstrictor tendency in patients with EM, which may be related to functional or structural changes in skin microvessels. Thus, the previous hypothesis that the pathophysiology of EM relates to vasodilatation is not supported in our patients. We believe that, in EM, vasoconstriction precedes reactive hyperaemia, similar to that seen in Raynaud's phenomenon.

Increased peripheral nerve microvessels in early experimental diabetic neuropathy: quantitative studies of nerve and dorsal root ganglia

Microangiopathy is an important complication of diabetes mellitus and neovascularity is a feature of human diabetic retinopathy. The objective of this work was to evaluate numbers, areas and size distributions of whole nerve, endoneurial and dorsal root ganglia perfused microvessels in a detailed fashion using unfixed tissues from rats with experimental diabetes. Experimental neuropathy was studied in male Sprague-Dawley rats 12 weeks after streptozotocin or citrate buffer injection. Electrophysiological recordings of sciatic-tibial motor and caudal sensory fibers identified conduction slowing in diabetes indicating neuropathy. Diabetics had a rise in the numbers of whole nerve microvessels and endoneurial microvessels with associated rises in vessel densities and total vessel luminal areas. Increased vessel numbers in 15-30 microm diameter size ranges were particularly prominent. There was a rise in summed vascular areas in diabetics but the mean luminal area of vessels was not increased. Similar, but not significant trends were observed in a selective analysis of endoneurial vessels alone. In contrast, dorsal root ganglia microvessels were not increased in number. Early experimental diabetic neuropathy is associated with increased numbers of microvessels supplying the peripheral nerve trunk, likely representing neovascularity.

Diabetic neuropathies: features and mechanisms

Diabetic neuropathies include both focal neuropathies and diffuse polyneuropathy. Polyneuropathy, the most common of the diabetic neuropathies excluding focal entrapment, has not yet been explained by a single disease mechanism despite intensive investigation. A number of abnormalities appear to cascade into a 'vicious cycle' of progressive microvascular disease associated with motor, sensory and autonomic fiber loss. These abnormalities include excessive polyol (sugar alcohol) flux through the aldose reductase pathway, functional and structural alterations of nerve microvessels, nerve and ganglia hypoxia, oxidative stress, nonspecific glycosylation of axon and microvessel proteins, and impairment in the elaboration of trophic factors critical for peripheral nerves and their ganglia. While an initiating role for nerve ischemia in the development of polyneuropathy has been proposed, the evidence for it can be questioned. The role of sensory and autonomic ganglia in the development of polyneuropathy has had relatively less attention despite the possibility that they may be vulnerable to a variety of insults, particularly neurotrophin deficiency. Superimposed on the deficits of polyneuropathy is the failure of diabetic nerves to regenerate as effectively as nondiabetics. Polyneuropathy has not yet yielded to specific forms of treatment but a variety of new trials addressing plausible hypotheses have been initiated. This review will summarize some of the clinical, pathological and experimental work applied toward understanding human diabetic neuropathy and will emphasize ideas on pathogenesis.

Effect of angiotensin-converting-enzyme (ACE) inhibitor trandolapril on human diabetic neuropathy: randomised double-blind controlled trial

BACKGROUND

Diabetes is a common cause of polyneuropathy. The development and progression of nephropathy, retinopathy, and neuropathy are closely related. Angiotensin-converting enzyme (ACE) inhibitors delay progression of both nephropathy and retinopathy. We investigated the effect of ACE inhibition on diabetic neuropathy.

METHODS

We recruited 41 normotensive patients with type I or type II diabetes and mild neuropathy into a randomised double-blind placebo-controlled trial. Changes in the neuropathy symptom and deficit scores, vibration-perception threshold, peripheral-nerve electrophysiology, and cardiovascular autonomic function, were assessed at 6 and 12 months. The primary endpoint was the change in peroneal nerve motor conduction velocity.

FINDINGS

We found no significant difference at baseline for age, HbA1c, blood pressure, or severity of neuropathy between two groups. There was no change in HbA1c over the treatment period. Peroneal motor nerve conduction velocity (p=0.03) and M-wave amplitude (p=0.03) increased, and the F-wave latency (p=0.03) decreased and sural nerve action potential amplitude increased (p=0.04) significantly after 12 months of treatment with trandolapril compared with placebo. Vibration-perception threshold, autonomic function, and the neuropathy symptom and deficit score showed no improvement in either group.

INTERPRETATION

The ACE inhibitor trandolapril may improve peripheral neuropathy in normotensive patients with diabetes. Larger clinical trials are needed to confirm these data before changes to clinical practice can be advocated.

Diabetic neuropathy

Better clinical characteristics and a standardized approach to the definition of neuropathy has enabled us to define more precisely the natural history of diabetic neuropathy. Detailed studies on the pathology and pathogenesis have allowed dissection of important pathogenetic pathways. Effective treatment is currently limited, although a number of new and potentially important therapeutic interventions, including modification of the vascular supply and antioxidant status and growth factors, may prove to be of benefit in preventing damage and also promoting repair of peripheral nerves in human diabetic neuropathy.

Effects of cilostazol on the peripheral nerve function and structure in STZ-induced diabetic rats

We examined the effect of cilostazol (CZ), antiplatelet agent and potent vasoactive compound, which has an inhibitory effect on tissue phosphodiesterase, on peripheral nerve in streptozotocin-induced diabetic rats. Diabetic rats were fed for 12 weeks with a chow containing 0.01% or 0.03% CZ (w/w) and the results were compared with untreated diabetic rats. The 0.03% CZ treatment significantly improved motor nerve-conduction velocity and restored nerve Na+, K(+)-ATPase activity in diabetic rats without affecting body weight and glycated hemoglobin levels, but the effects of 0.01% CZ treatment did not reach statistical difference. Elevated sorbitol and reduced myo-inositol levels in diabetic nerve tissues were not influenced by CZ treatment. Structural analysis of the sural nerve demonstrated a partial but significant effect on decreased mean myelinated fiber area and atrophic changes of the axon in diabetic rats treated with 0.01% CZ. CZ treatment inhibited reduction of pericyte area of endoneurial microvessels in diabetic rats. Expansion of endoneurial microvessels and luminal area in relation to vascular area also tended to be inhibited by CZ treatment. Thus CZ treatment ameliorated, although not completely, functional and structural abnormalities in peripheral nerve of diabetic rats without effecting the polyol pathway. These results support the contention that vascular factors may play an important role in the etiology of experimental diabetic neuropathy and suggest that CZ may have a beneficial therapeutic effect on diabetic neuropathy.

Effects of aminoguanidine on structural alterations of microvessels in peripheral nerve of streptozotocin diabetic rats

This study was designed to explore the effect of aminoguanidine (AG) on the structural abnormalities of microvessels in the sural nerve of streptozotocin-induced diabetic rats. Diabetic rats were treated with AG (25 mg/ kg, sc) for 16 weeks, a dose high enough to prevent glycation but also inhibit inducible nitric oxide synthase. Non-treated diabetic rats and normal Wistar rats were used for comparison. Morphometric analysis disclosed an expansion of vascular and luminal areas of endoneurial microvessels in diabetic rats, particularly of large size, compared to control rats. These changes were partially but significantly corrected by AG treatment. There was no closure of microvessels in diabetic rats. The mean ratio of basement membrane area to vascular area was significantly smaller in diabetic rats than that in normal control rats and basement membrane was not thickened in diabetic rats. The mean ratio of endothelial cell area to vascular area was smaller in diabetic rats than that in nondiabetic control rats, and it was not influenced by AG treatment. Numbers of microvessels per unit endoneurial area in diabetic rats were not different from those of control rats. These findings in conjunction with previous reports suggest that alterations of nerve blood flow detected in diabetic peripheral nerve may be relevant to structural alterations of endoneurial microvessels, which may be an early sign of endoneurial microangiopathy. We also consider that AG treatment is beneficial for experimental diabetic neuropathy, partially through the correction of endoneurial microcirculation.

Diabetic peripheral neuropathy: effects of age, duration of diabetes, glycemic control, and vascular factors

The aim of this study was to determine the factors associated with diabetic peripheral neuropathy and more particularly its relation to precisely assessed microangiopathy. Peripheral neuropathy was assessed in 135 diabetic patients: 28 insulin-dependent diabetes mellitus (IDDM), 85 non-insulin-dependent diabetes mellitus (NIDDM), and 22 insulin-treated NIDDM patients, on the basis of both clinical findings and extensive electrophysiological testing (four motor nerves and four sensory nerves, and right and left Hoffmann's reflex), using a total of 20 parameters. The percentage of women with severe clinical neuropathy was significantly higher than that of men, and the clinical neurological stage correlated significantly with age and duration of diabetes. According to multivariate analysis the clinical stage correlated only with gender and duration of diabetes. Several electrophysiological parameters were significantly more abnormal in women and correlated with age, type and duration of diabetes, and recent glycemic control. The multivariate analysis showed that 17 electrophysiological parameters correlated with duration of diabetes, nine correlated with age, seven with glycemic control, and only one with gender. The presence of clinical neuropathy also correlated with presence of retinopathy, arterial hypertension, macroangiopathy, and biological signs of nephropathy. All the electrophysiological parameters were significantly more abnormal in patients with retinopathy or macroangiopathy than in patients without these complications. Separate parameter analysis showed that at least one abnormal electrophysiological parameter was almost always found in patients with retinopathy, macroangiopathy, or incipient nephropathy, but abnormalities were also found to a slightly lesser extent in patients without these complications. Multivariate analysis showed that when duration of diabetes, retinopathy, macroangiopathy, and biological signs of nephropathy were introduced into the model, 11 electrophysiological parameters correlated with duration of diabetes, 11 with retinopathy, seven with macroangiopathy, and five with a sign of nephropathy. This study demonstrates that age and glycemic control have an effect, and diabetes duration a major effect on peripheral nerve function. It suggests that vascular factors may participate in the development of nerve lesions.

Structure-function relationships within peripheral nerves in diabetic neuropathy: the hydration hypothesis

To define the quantitative relationship between peripheral nerve structure and function imposed by endoneurial oedema in the diabetic state, we determined values for sural nerve hydration structure as measured by magnetic resonance spectroscopy, and for neurological function with scores for nerve conduction properties (NCV-score), neuropathic symptoms (NS-score), and examination signs (NE-score). The coefficient of sural nerve hydration was elevated to 30 +/- 6% (p < 0.05) in 79 symptomatic neuropathic diabetic subjects with an average of 15 years of diabetes mellitus, compared to a value of 25 +/- 3% in 72 non-diabetic control subjects. In contrast, in 75 asymptomatic diabetic subjects with an average of 6 additional years of diabetes, the mean hydration coefficient was only 28 +/- 5% (p < 0.05). A nerve hyperhydration state was identified with a prevalence of 25% within the asymptomatic group characterized by nerve hydration greater than the 95th percentile, early changes in nerve electrophysiology and neurological examination, but with no symptomatology of neuropathy. Stratification of the symptomatic neuropathic group by worsening nerve electrophysiology, demonstrates a coincident deterioration in neurological examination (RR = 5.39 at maximum NCV-score), and neuropathy symptomatology (RR = 4.80 at maximum NE-score). The present data are consistent with the hypothesis that endoneurial oedema initiates deterioration sequentially in nerve electrophysiology, followed by abnormal findings on neurological examination, preceding the patient's final perception of symptomatic stocking glove peripheral diabetic neuropathy.

Microvessel basement membrane reduplication is not associated with repeated nerve fiber degeneration and regeneration

To determine whether repeated nerve fiber degeneration and regeneration can induce reduplication of endoneurial microvessel basement membranes (BMs), typical of such conditions as diabetic polyneuropathy, electronmicrographs of endoneurial microvessels of rat peroneal and tibial nerves were studied in repeatedly crushed (10 x) sciatic nerves and compared to microvessels of sham-operated uncrushed nerves. On average, crushed nerves had 2.6, SE +/- 0.1 BMs, whereas control nerves had 2.7, SE +/- 0.1 (P > 0.05). Microvessel cellular components were significantly increased in both number and size in the crushed nerves. These nerves also demonstrated a trend to increased vessel numbers and density. These results are not in keeping with the hypothesis that BM reduplication of endoneurial microvessels is simply due to repeated fiber degeneration and regeneration.

The impact of reversal of hypoxia by revascularization on the peripheral nerve function of diabetic patients

Hypoxia is considered to be one of the main aetiopathogenic factors of diabetic neuropathy. We have examined the effects of the reversal of hypoxia, achieved by revascularization, on peripheral nerve function in diabetic patients with or without clinical neuropathy. Fifty-six patients [mean age 62 (range 30-74) years, 44 (79%) males, 15 (27%) with insulin-dependent diabetes of 20 years (range 1-57) duration, and creatinine level 92.8 +/- 30.9 mumol/l (mean +/- SD)] were tested pre-operatively while 30 (54%) were reexamined at least 6 weeks post-operatively. At baseline the leg scheduled for operation showed worse measurements compared to the control leg when tested for Semmes-Weinstein monofilaments, peroneal motor conduction velocity (PMCV) (33.7 +/- 7.18 vs 35.7 +/- 6.09 m.s-1, p < 0.05) and transcutaneous oxygen tension (37.4 +/- 24.6 vs 52.0 +/- 21.5 mm Hg, p < 0.0001) while no differences were found in the vibration perception threshold and leg temperature. When baseline and post-operative measurements were later compared in the operated leg, no differences were noticed in the vibration perception threshold, PMCV and Semmes-Weinstein monofilaments but the transcutaneous oxygen tension increased significantly (32.7 +/- 27.1 vs 64.6 +/- 14.5 mm Hg, p < 0.001). No differences were noticed in any of the above parameters in the contralateral leg. No correlations were found between changes in transcutaneous oxygen tension and PMCV values measured at baseline and at the follow-up visit in either leg. Similar results were found when patients were stratified according to severity of neuropathy, ischaemia and the level of the bypass. We conclude that although there is greater impairment of nerve function in the more ischaemic leg, reversal of hypoxia does not result in any significant improvement of the nerve function measurements.

The endocrine pancreas of spontaneously diabetic db/db mice: microangiopathy as revealed by transmission electron microscopy

Abnormalities in ultrastructures of islet capillaries were detected in db/db mice, with the visual inspection and morphometry of electron micrographs. The observed changes are: (1) capillary scarcity; (2) increase in the mean and diversity of capillary size; (3) pericapillary edema and fibrosis; (4) hypertrophy of the pericyte and abundance therein of actin-like microfilaments; and (5) luminal irregularity. Changes (2), (3) and (4) are conceived to indicate hyperperfusion, capillary hypertension and secondary vascular response. In particular, such pericyte changes were found to be shared by other organs whose capillaries are susceptible to diabetic complications.