Effects of aldose reductase inhibitor treatment in diabetic polyneuropathy - a clinical and neurophysiological study

Strategies in synthetic design and structure-activity relationship studies of novel heterocyclic scaffolds as aldose reductase-2 inhibitors

Heterocyclic scaffolds of natural as well as synthetic origin provide almost all categories of drugs exhibiting a wide range of pharmacological activities, such as antibiotics, antidiabetic and anticancer agents, and so on. Under normal homeostasis, aldose reductase 2 (ALR2) regulates vital metabolic functions; however, in pathological conditions like diabetes, ALR2 is unable to function and leads to secondary diabetic complications. ALR2 inhibitors are a novel target for the treatment of retinopathy (cataract) influenced by diabetes. Epalrestat (stat), an ALR2 inhibitor, is the only drug candidate that was approved in the last four decades; the other drugs from the stat class were retracted after clinical trial studies due to untoward iatrogenic effects. The present study summarizes the recent development (2014 and onwards) of this pharmacologically active ALR2 heterocyclic scaffold and illustrates the rationale behind the design, structure-activity relationships, and biological studies performed on these molecules. The aim of the current review is to pave a straight path for medicinal chemists and chemical biologists, and, in general, to the drug discovery scientists to facilitate the synthesis and development of novel ALR2 inhibitors that may serve as lead molecules for the treatment of diseases related to the ALR2 enzyme.

Crystal structure of methyl 3-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)propanoate, C16H13NO4

C16H13NO4, monoclinic, P21/c (no. 14), a = 9.930(3) Å, b = 6.9807(18) Å, c = 18.954(5) Å, β = 93.080(4)°, V = 1311.9(6) Å3, Z = 4, R gt (F) = 0.0400, wR ref (F 2) = 0.1142, T = 296 (2) K.

Crystal structure of methyl 2-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)acetate, C15H11NO4

C15H11NO4, monoclinic, P21/n (no. 14), a = 8.0909(6) Å, b = 24.4463(18) Å, c = 12.6980(10) Å, β = 96.6020(10)°, V = 2494.9(3) Å3, Z = 8, R gt (F) = 0.0470, wR ref (F 2) = 0.1273, T = 296 (2) K.

Aldose reductase inhibitors for the treatment of diabetic polyneuropathy

BACKGROUND

Polyneuropathy, a common complication of diabetes mellitus, causes pain and sensory and motor deficits in the limbs, and is also an important independent predictor of foot ulceration. Inhibiting the metabolism of glucose by the polyol pathway using aldose reductase inhibitors is a potential mechanism to slow or reverse the neuropathy's progression.

OBJECTIVES

To assess the effects of aldose reductase inhibitors on the progression of symptoms, signs or functional disability in diabetic polyneuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (from January 1966 to May 2007), EMBASE (from January 1980 to May 2007) and LILACS (from 1982 to May 2007). We reviewed bibliographies of randomized trials identified, and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomized controlled trials comparing an aldose reductase inhibitor with control, and lasting at least six months. The primary outcome measure was change in neurological function, measured in various ways, including strength testing, sensory examination, and composite scores of neurological examination. Secondary outcome measures were nerve conduction studies, neuropathic symptoms, quality of life, occurrence of foot ulcers and adverse effects.

DATA COLLECTION AND ANALYSIS

Trials included in the review were selected and assessed independently by at least two of us. Methodological criteria and study results were recorded on data extraction forms.

MAIN RESULTS

Thirty-two randomized controlled trials meeting the inclusion criteria were identified. Many had significant methodological flaws. Change in neurological function, our primary outcome measure, was assessed in 29 trials, but sufficient data for meta-analysis were only available in 13 studies, involving 879 treated participants and 909 controls. There was no overall significant difference between the treated and control groups (SMD -0.25, 95% CI -0.56 to 0.05), although one subgroup analysis (four trials using tolrestat) favored treatment. A benefit for neuropathic symptoms was suggested by a group of trials using a dichotomized endpoint (improvement or not), but this was contradicted by another group of trials which measured symptoms on a continuous scale. There was no overall benefit on nerve conduction parameters (27 studies) or foot ulceration (one study). Quality of life was not assessed in any of the studies. While most adverse events were infrequent and minor, three compounds had dose limiting adverse events that lead to their withdrawal from human use: severe hypersensitivity reactions with sorbinil, elevation of creatinine with zenarestat, and alteration of liver function with tolrestat.

AUTHORS' CONCLUSIONS

We found no statistically significant difference between aldose reductase inhibitors and placebo in the treatment of diabetic polyneuropathy. Any future clinical trials of aldose reductase inhibitors should be restricted to compounds proven to have substantial biological or preclinical advantages over previously tested agents.

Systemic and ocular pharmacokinetics of N-4-benzoylaminophenylsulfonylglycine (BAPSG), a novel aldose reductase inhibitor

To better develop N-[4-(benzoylamino)phenylsulfonyl]glycine (BAPSG), a potent and selective aldose reductase inhibitor capable of delaying the progression of ocular diabetic complications, the objective of this study was to assess its pharmacokinetics. The plasma pharmacokinetics of BASPG was assessed in male Sprague-Dawley rats following intravenous, intraperitoneal and oral routes of administration and its distribution to various tissues including those of the eye was studied following intraperitoneal administration. In addition, rat plasma protein binding of BAPSG was studied using ultracentrifugation method and its ocular tissue disposition was assessed following topical administration in rabbits. Plasma and tissue levels of BAPSG were analysed using an HPLC assay. BAPSG exhibited dose-proportionate AUC0 --> infinity (area under the plasma concentration-time curve) following both intravenous and intraperitoneal administration over the dose range (5-50 mg kg(-1)) studied and an erratic oral absorption profile with low oral bioavailability. The fraction bioavailability following oral and intraperitoneal administration was 0.06 and 0.7-1, respectively. BAPSG exhibited short plasma elimination half-lives in the range 0.5-1.5 h. BAPSG was bound to rat plasma proteins and the percent protein binding ranged from 83 to 99.8%. BAPSG was better distributed to cornea, lens and retina than to brain, following intraperitoneal administration in rats. However, the distribution was lower compared with kidney and liver. Following topical administration in rabbits, BAPSG delivery to the surface ocular tissues, cornea and conjunctiva was higher compared with intraocular tissues, aqueous humour, iris-ciliary body and lens. Thus, BAPSG was distributed to ocular tissues following systemic and topical modes of administration.

Diabetic neuropathy in children and adolescents

Diabetic neuropathy (DN) represents a major complication of type 1 diabetes mellitus (T1DM) but there is considerable uncertainty as to its incidence, prevalence, diagnosis and prognosis in pediatric population. Generally, DN is classified as polyneuropathy, focal neuropathy and autonomic neuropathy. The latter seems to be detectable even in asymptomatic children and adolescents with diabetes and is associated with the most serious consequences, such as hypoglycemia unawareness and cardiovascular dysfunction. A near-normal control of blood glucose in the early years after onset of diabetes may delay the development of clinically significant nerve impairment and, therefore, children and adolescents with diabetes represent a critical target for primary prevention of this complication. The aim of this review is to focus on the main clinical, epidemiological and prognostic aspects of DN in children and adolescents with T1DM. Etiopathogenetic theories and diagnostic tools are also reviewed from in a pediatric perspective.

Clinical Potential of Aldose Reductase Inhibitors in Diabetic Neuropathy

A number of aldose reductase inhibitors (ARIs) have been developed over the past few decades with the expectation of therapeutic effects for diabetic complications. Neuropathy is the complication that has been most intensively studied as a potential target for ARIs. Most ARIs have shown satisfactory effects in animal models. However, the clinical potential of ARIs in diabetic patients has been controversial due to the lack of conclusive evidence. The safety of this category of drugs is also uncertain. This article summarizes the results of clinical trials of ARIs for patients with diabetic neuropathy that have been performed to date. The efficacy and toxicity of each ARI will be briefly assessed by the clinical data. The theoretical background along with major issues in the evaluation of drug efficacy will also be discussed. Overall the observed efficacy varied among the compounds. A few ARIs showed favorable effects in multiple endpoints in the majority of trials, while the results from many ARIs seemed ambivalent. One drug barely exhibited positive effects on any endpoint. This discrepancy may be attributable at least in part to the different degree of inhibition of the polyol pathway in nerve tissues, which is determined not only by the pharmacokinetic properties of the drug but also by its penetration into nerve tissues. In addition to the uncertain potential of each ARI, the issues of design and analytical methods used for clinical trials may underlie the ambivalent outcomes. The power of analysis and the duration of trials were apparently inadequate in a large number of the studies. Various indices selected as endpoints are not necessarily sensitive or reproducible. Studies of longer duration, large-scale trials, better methods to assess neuropathy, and the selection of patients with a homogenous background would provide more conclusive evidence. The risk of serious adverse reactions, for example, hypersensitivity reactions and hepatic damage, has led to some ARIs being withdrawn from the market or from further development. These adverse effects, however, do not appear to result from the inhibition of aldose reductase activity per se but from specific reactions to each compound. In conclusion, sufficient inhibition of the nerve aldose reductase activity seems likely to prevent or ameliorate diabetic neuropathy, and further development of more potent and safe ARIs is necessary before extensive clinical application.

Pharmacotherapy of painful diabetic neuropathy

The scope of this review is to describe the epidemiology, physiology, symptomatology, and treatment of diabetic painful neuropathy, which is a common complication of diabetes with significant morbidity. This article focuses on treatment options. Various clinical trials of several classes of medications (eg, antidepressants, anticonvulsants, and topical medications) and alternative treatments (eg, acupuncture, electrostimulation, magnets) are reviewed. Physicians have a large panel of medications that can be used effectively solely or in combination at their disposal. However, a number of these treatments have significant side effects, which are noted, that limit their use. As the understanding of the pathophysiologic mechanisms of diabetic neuropathy improves, new medications are under investigation, which are reviewed in this article. There is great hope that the future may hold treatments that would prevent nerve damage.

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.

Aldose reductase inhibitors for the prevention and treatment of diabetic peripheral neuropathy

OBJECTIVES

To assess the efficacy of aldose reductase inhibitors in the prevention, reversal or delay in the progression of diabetic peripheral neuropathy.

SEARCH STRATEGY

The Cochrane Diabetes Group's database was searched and the citation lists of identified trials and previous reviews checked. Investigators identified as active in the field were approached for overlooked studies.

SELECTION CRITERIA

Randomised controlled trials of aldose reductase inhibitors versus placebo, no treatment or other treatment in diabetic patients with or without clinical neuropathy.

DATA COLLECTION AND ANALYSIS

Nerve conduction velocity was the only end point measured in all trials. Treatment effect was evaluated in terms of nerve conduction velocity mean difference in median and peroneal motor and median and sural sensory nerves.

MAIN RESULTS

19 trials, testing 4 different aldose reductase inhibitors for between 4 to 208 weeks duration (median 24 weeks), met the inclusion criteria for the meta-analysis. A small but statistically significant reduction in decline of median and peroneal motor nerve conduction velocities was present in the treated group when compared to the control group (weighted mean 0.66 m/s 95% CI 0.18-1.14 m/s and 0.53 m/s 95% CI 0.02-1.04m/s respectively). No clear benefit of aldose reductase inhibitor treatment was observed in either of the sensory nerves.

REVIEWER'S CONCLUSIONS

Although aldose reductase inhibitor treatment has been demonstrated to diminsh the reduction in motor nerve conduction velocity, the clinical relevance of such a change in this outcome measure is uncertain. There was no effect in terms of this outcome measure in the smaller sensory fibres, degeneration of which is primarily responsible for the most common neuropathic syndrome associated with diabetes, that of severe pain and loss of sensation in the extremity leading in some cases to ulceration and eventual amputation.

Diabetic neuropathy: pathogenesis and therapy

Diabetic neuropathies are complex, heterogeneous disorders that encompass a wide range of abnormalities affecting both peripheral and autonomic nervous systems, causing considerable morbidity and mortality. Treatment should be based upon the underlying etiology and not symptoms alone, although symptomatic therapy is needed. Neuropathies may be focal or diffuse, proximal or distal, and involve somatic and autonomic nerves. Focal syndromes are classified as (1) entrapment syndromes or (2) mononeuropathies. Entrapment syndromes are treated by means of relieving compression within confined spaces. Mononeuropathies are due to a vascular insult and resolve spontaneously. They are best treated by supportive therapy. Proximal neuropathies are usually due to an inflammatory, vasculitic, or autoimmune condition and are best treated with specific therapies for the underlying disorder based on biopsy findings. Therapies for distal polyneuropathies include metabolic treatments (e.g., aldose reductase inhibitors, aminoguanidine, gamma-linolenic acid), autoimmune therapies, and nerve growth factors. No definitive treatment is available for painful diabetic neuropathy. Several medications have been used, among them tricyclic antidepressants, antiepileptic drugs, phenothiazines, calcitonin, local anesthetics, nonsteroidal anti-inflammatory drugs, and dextromethorphan. Nonpharmacologic therapies include surgical sympathectomy, spinal cord blockade, electrical spinal cord stimulation, and prostaglandin.

Impairment, disability, or handicap in peripheral neuropathy: analysis of the use of outcome measures in clinical trials in patients with peripheral neuropathies

Outcome measures can be classified into measures of impairment, disability, and handicap. To investigate the biological effect of treatment, measures of impairment are appropriate. Studies investigating whether patients benefit from treatment in terms of improvement of functional health, however, require disability or handicap measures. In a review of the medical literature between 1978 and 1993, 73 controlled intervention studies in patients with peripheral neuropathies were found. Disability or handicap measures were used in two of 54 studies in patients with diabetic neuropathy, in two of six studies in patients with chronic inflammatory demyelinating polyneuropathy, in none of five studies in a mixed group of patients, and in all eight studies in patients with Guillain-Barré syndrome. The limited use of disability and handicap measures in patients with diabetic and mixed neuropathies can be explained by the experimental nature of most studies. In four of six studies, however, in patients with chronic inflammatory demyelinating polyneuropathy or neuropathy associated with monoclonal gammopathy that were designed to assess effectiveness of treatment, the choice of outcome measures was not appropriate. It is concluded that in the design of intervention studies in patients with peripheral neuropathy more attention should be paid to a proper choice of suitable outcome measures to assess the effectiveness of treatment.

Effects of fructose on D-[6-3H]-glucose uptake and sorbitol metabolism of bovine retina in vitro

In order to study the influence of fructose on sorbitol formation, bovine retinal tissue was incubated with different concentrations of glucose and fructose, and supplemented with tracer amounts of D-[6-3H]-glucose. Combining high-performance liquid chromatography (HPLC) with radioactivity determinations allowed detection of sorbitol and fructose derived from glucose in the incubation medium. In addition, the total amount of sorbitol was measured with a sensitive bioluminescence method. In this way, it was possible to distinguish between sorbitol formation from glucose and fructose. High concentrations of glucose in the medium increased the formation of sorbitol and fructose from glucose. Addition of fructose to the incubation medium diminished the sorbitol and fructose formation from glucose although the total amount of sorbitol increased significantly. Incubating retinal tissue with an aldose reductase inhibitor decreased sorbitol formation from glucose but did not influence the formation of sorbitol from fructose. Thus, the present findings clearly demonstrate the important influence exerted by fructose on sorbitol formation. The possible significance of the present finding is discussed with respect to diabetes retinopathy and retinal osmoregulation.

Composite autonomic scoring scale for laboratory quantification of generalized autonomic failure

An autonomic reflex screen, which consisted of a quantitative sudomotor axon reflex test, orthostatic blood pressure and heart rate response to tilt, heart rate response to deep breathing, the Valsalva ratio, and beat-to-beat blood pressure measurements during phases II and IV of the Valsalva maneuver, tilt, and deep breathing, was used to develop a 10-point composite autonomic scoring scale of autonomic function. The scheme allots 4 points for adrenergic and 3 points each for sudomotor and cardiovagal failure. Each score is normalized for the compounding effects of age and sex. Patients with a score of 3 or less on the composite autonomic scoring scale have only mild autonomic failure, those with scores of 7 to 10 have severe failure, and those with scores between these two ranges have moderate autonomic failure. The sensitivity and specificity of the method were assessed by evaluating the composite autonomic scoring scale in four groups of patients with known degrees of autonomic failure: 18 with multisystem atrophy, 20 with autonomic neuropathy, 20 with Parkinson's disease, and 20 with peripheral neuropathy but no autonomic symptoms. The composite scores (means +/- SD) for these four groups, respectively, were as follows: 8.5 +/- 1.3, 8.6 +/- 1.2, 1.5 +/- 1.1, and 1.7 +/- 1.3. Patients with symptomatic autonomic failure had scores of 5 or more, those without symptomatic autonomic failure had scores of 4 or less, and no overlap existed in these groups. Thus, autonomic laboratory tests should be useful in grading the degree of autonomic failure.

Withdrawal of the aldose reductase inhibitor tolrestat in patients with diabetic neuropathy: effect on nerve function. The Tolrestat Study Group

A double-blind, placebo-controlled clinical trial was conducted to study the effects of discontinuing tolrestat, an aldose reductase inhibitor, on peripheral sensorimotor diabetic neuropathy. After an average of 4.2 years of continuous tolrestat use, 372 patients were randomly assigned to either placebo or continued tolrestat therapy and were followed for 52 weeks. After 3 months, patients who perceived worsening of symptoms of neuropathy were allowed to switch once to the alternate treatment group while maintaining the double-blind. Patients assigned to placebo had significant deterioration in motor nerve conduction velocity (MNCV) while those maintained on tolrestat did not (p < 0.05). The 28 patients who were randomly assigned to tolrestat and elected to switch to placebo had a significant deterioration in MNCV while the 36 assigned to placebo who switched to tolrestat had a significant improvement (p < 0.05). Treatment differences in favor of tolrestat were observed for sensation in the toes as well as for pain (p < 0.05). These data indicate that withdrawal from long-term treatment with tolrestat has a detrimental effect on several measures of diabetic neuropathy, whereas continuation of treatment is associated with stabilization of these measures, suggesting a continued role for polyol pathway activity in late neuropathy.

Treatment of diabetic autonomic neuropathy with an aldose reductase inhibitor

To evaluate the effects of the aldose reductase inhibitor Ponalrestat (Statil) on diabetic autonomic neuropathy, a double-blind placebo controlled trial was carried out on a group of 34 diabetic patients with documented cardiac autonomic neuropathy. After a 4-week, placebo run-in period, patients were randomised for treatment with 600 mg Statil or placebo for another 24 weeks. Moreover, the reliability of the autonomic nerve function tests was investigated by comparing the results at onset and at week 4. Fifteen patients treated with Statil and 12 with placebo completed the study. Neither symptom scores nor cardiovascular reflexes, pupil reflexes and skin vasomotor reflexes improved after Statil therapy, which led us to conclude that Statil is not effective in the treatment of diabetic autonomic neuropathy. Reliability coefficients for cardiovascular reflexes and pupil reflex showed high values, ranging from 60% to 80%. Therefore these methods are recommended in future therapy trials.

[Role of polyols in the development of diabetic complications. Value of aldose-reductase inhibitors]

The evidence of sorbitol excess in the crystalline lens of alloxan-diabetic rats has led to anticipate the role of the enzyme aldose-reductase in the pathogenesis of the diabetic cataract. In addition, a number of experimental works have more recently shown the involvement of myoinositol deficiency, which probably results from the sorbitol accumulation. These metabolic pathways are most likely implicated in the pathogenesis of diabetic neuropathy and perhaps additionally in that of microangiopathy. The synthesis of several aldose-reductase inhibitors (AR inhibitors) confirmed experimentally these hypothesis. By reducing the activity of the enzyme aldose-reductase, these substances suppress the adverse metabolic consequences of polyol accumulation, myositol deficiency and dysfunction of the Na+/K+ ATPase dependent sodium activity. Although different experimentations showed that the AR inhibitors could prevent in animals the development of experimental cataract as well as the early functional or later anatomic abnormalities of the diabetic retinopathy and nephropathy, the clinical trials did not clearly support these experimental results in humans. On the other hand, the AR inhibitors were proved to exhibit some efficacy in the early stage of diabetic neuropathy and in incipient nephropathy where they delay the development of albustix positive proteinuria. However, the benefit of an early treatment with AR inhibitors should be confirmed by long term prospective studies, which could also assess the safety of these drugs in chronic administration.

Recent clinical experience with aldose reductase inhibitors

Since 1981 a number of aldose reductase inhibitors (ARIs) have been extensively investigated in clinical trials for the treatment or prevention of diabetic complications. In general, the results from these trials have varied from no effect to improvement. In part, the inconclusive results are due to differences in the study designs. Investigation of some ARIs has been discontinued because of lack of efficacy (ponalrestat) or major toxicity (sorbinil). Of the ARIs that have been evaluated, only tolrestat is currently undergoing clinical investigation. Although the most recent studies have shown promising results, the role of ARIs in the treatment or prevention of secondary complications of diabetic neuropathy will be determined in ongoing or future clinical trials.

Aldose reductase inhibitors as pathobiochemical probes

In tissues susceptible to damage from chronic diabetes, excess glucose is metabolized by aldose reductase (AR) to sorbitol. Originally, AR-catalyzed sorbitol formation (and accumulation) was found in the diabetic lens; the cataractogenicity of this process was proven by preventing cataract formation with an AR inhibitor (ARI). These findings were extended to the hypothesis that, in diabetic tissues, excessive intracellular sorbitol formation initiates a cascade of metabolic abnormalities which gradually progress to loss of functional and structural integrity. The pivotal role of AR as a trigger for such abnormalities was established by preventing their occurrence in diabetic animals treated with an ARI. By inference, this led to the concept that inhibition of AR should prevent, arrest, and, possibly, reverse the development of late diabetic sequelae. In addition to motivating drug-oriented research, the ARI concept provided a rationale for the use of ARIs as experimental tools to probe the pathogenesis of diabetic complications. By helping to elucidate the metabolic, functional, and structural ramifications of the AR-catalyzed disposal of excess glucose in diabetic schemes, and in addition, by helping to define the applicability of animal models for the study of early functional pathogenic alterations occurring in diabetic subjects, ARIs may enable the discrimination in diabetic tissue of arrestible and reversible from the irreversible abnormalities.

Effects of aldose reductase inhibitors on the progression of nerve fiber damage in diabetic neuropathy

Aldose reductase inhibitors improve nerve biochemistry, function, and structure in diabetic animals and increase nerve conduction in diabetic patients. Nevertheless, it has been difficult to demonstrate a benefit from these agents in patients with clinically overt diabetic neuropathy. Direct measurement of the nerve tissue penetration and biochemical and biological potency of these compounds is essential to fully understand and evaluate their effectiveness. Human sural nerve biopsies obtained from diabetic neuropathic patients undergoing treatment with an aldose reductase inhibitor revealed a reduction in intermediates of the polyol pathway. Specific morphologic lesions that correlate with the degree of clinical and electrophysiologic impairment also were identified. Morphologic evaluation of sural nerve biopsies obtained after aldose reductase inhibitor treatment suggests that these biochemically effective compounds ameliorate clinically relevant structural lesions in patients with diabetic neuropathy.

The selective serotonin reuptake inhibitor paroxetine is effective in the treatment of diabetic neuropathy symptoms

The effect of the selective serotonin reuptake inhibitor paroxetine on diabetic neuropathy symptoms was examined in comparison to imipramine and placebo in a randomised, double-blind, cross-over study. Paroxetine was given as a fixed dose of 40 mg/day, while the dose of imipramine was adjusted to yield optimal plasma levels of imipramine plus desipramine of 400-600 nM. Paroxetine significantly reduced the symptoms of neuropathy as measured by both observer- and self-rating, but was somewhat less effective than imipramine. However, patients showing a weaker response to paroxetine than to imipramine had lower plasma concentrations of paroxetine than patients with similar response to the 2 drugs. On imipramine 5 patients dropped out because of intolerable side effects and 4 of 19 patients completing the study reported withdrawal symptoms after discontinuing imipramine. On paroxetine no patients dropped out due to side effects and no withdrawal symptoms were reported. Self-rating showed no depressive symptoms at baseline, and no changes during the study. Neither paroxetine nor imipramine caused changes in objective measures of peripheral nerve function. In conclusion, 40 mg paroxetine/day significantly reduced the symptoms in peripheral diabetic neuropathy, and it was suggested that by dose adjustment on the basis of drug level monitoring, paroxetine may become as effective as imipramine. Paroxetine was devoid of the often disturbing autonomic side effects limiting the use of imipramine in several patients.

Peripheral sympathetic neuropathy evaluated by recording the evoked electrodermal response using an impedance reactometer

Autonomic nervous dysfunction was indirectly evaluated on the basis of the skin electrical resistance relative variation (SERV), recorded by our recently developed system, with two pairs of surface electrodes placed on the palm and on the sole of the foot, after the application to the subject of a sensory stimulus (sound 60 dB, 860 Hz, 0.5 s duration) or in the course of a Valsalva manoeuvre. The results were digitally measured and recorded on thermosensitive millimetric paper analysing the following parameters: latency (LT), i.e. the time interval(s) between application of the stimulus and onset of SERV, both at palm (LTh) and foot (LTf); amplitude of the response (mm) recorded and evaluated in the form of SERV; velocity of the response as rate of time change (Vr) and autonomic conduction velocity, -ACV (m/s), calculated by the height/LT ratio. The present study refers to a group of 60 diabetic patients: 32 F/28 M; mean age +/- SD 46.8 +/- 11.8 years; 29 insulin-dependent, 21 non-insulin-dependent; duration of diabetes 8.6 +/- 4.6 years. The data were compared to those recorded in a group of 50 nondiabetics (22 F/28 M; mean age 47.5 +/- 14.1 years) who were apparently healthy. A significant statistical difference (P less than 0.001) was found between diabetic patients and controls for all studied parameters: LTh (s) 2.65 +/- 1.2 vs. 1.91 +/- 0.6; LTf(s) 3.6 +/- 1.4 vs. 2.6 +/- 0.7; SERV (mm) 7.5 +/- 4.8 vs. 18.5 +/- 6.6; Vr (mm) 4.4 +/- 2.1 vs. 13.5 +/- 5.3; ACT (m/s) 0.41 +/- 0.23 vs. 0.97 +/- 0.18.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved technique for testing autonomic dysfunction: evaluation of transient behaviour of the autonomic response

The transient behaviour of the autonomic response has been studied by means of a reactometer incorporating self-balancing of the electrodermal impedance. This instrument has been used for the indirect measurement of certain parameters associated with the autonomic response detected as skin electrical resistance relative variation (SERV) and capacitance (SECV). Transient signals of the electrodermal impedance response were obtained online by differentiating the analogue output of the impedance reactometer: d(SERV)/dt and d(SECV)/dt. We describe here how the use of the transient signals of the electrodermal impedance response can improve the accuracy and reduce variability and dispersion of the results and how autonomic conduction velocities (ACV) can be indirectly measured.

Aldose reductase inhibitors in the treatment of diabetic neuropathy. A review of the rationale and clinical evidence

This review considers the definition of clinical diabetic neuropathy and the theoretical basis for the use of aldose reductase inhibitors in the treatment of distal sensorimotor neuropathy, the most common clinical problem. Myoinositol depletion is related to hyperglycaemia-induced polyol activity, changes which are associated with early functional deficits in acute experimental diabetes. These changes are reversible by the administration of aldose reductase inhibitors, and this provides the rationale for the treatment of human diabetic neuropathy with these agents. Many early trials of these drugs have produced some evidence of clinical benefit in patients with diabetic neuropathy, but interpretation of data is difficult as patient selection and neuropathy definition are not yet standardised. In addition, it is possible that once the neuropathic process is initiated, there is a point where it becomes irreversible, and treatment with aldose reductase inhibitors may therefore be of more relevance in early neuropathy. Long term double-blind multicentre trials are in progress, and preliminary data from some of these are reasonably encouraging. In conclusion, the results from clinical trials of the aldose reductase inhibitors in this difficult area are sufficiently encouraging to lead us to be optimistic about their future development, and continuing work should clarify their potential role with respect to the prophylaxis and treatment of diabetic neuropathy.

Sorbitol metabolism in the retina, optic nerve, and sural nerve of diabetic rats treated with an aldose reductase inhibitor

Sorbitol concentration has been measured in retina, optic, and sural nerve of normal, diabetic, and aldose reductase inhibitor-treated diabetic rats. The sural nerve displayed significantly higher sorbitol content than the retina and the optic nerve both in control animals and in diabetic animals. In the sural nerve the response to treatment with an aldose reductase inhibitor was more marked than in the two other tissues. The activities of aldose reductase and sorbitol dehydrogenase were not influenced by diabetes. It is suggested that aldose reductase inhibition may be of greater use for alleviating peripheral nervous system accumulation of sorbitol than for hindering CNS accumulation of the polyol.

Peripheral diabetic neuropathy

Diabetic neuropathy is a common complication of diabetes mellitus with significant morbidity and mortality. Hyperglycemia with its secondary metabolic, vascular, and enzymatic consequences is most likely to be the predominant cause. The clinical manifestations includes a wide range of somatic and autonomic syndromes. Painful diabetic neuropathy may require symptomatic treatment. The precise role of therapies such as continuous subcutaneous insulin therapy and aldose reductase inhibitors remains to be clarified.

Regeneration and repair of myelinated fibers in sural-nerve biopsy specimens from patients with diabetic neuropathy treated with sorbinil

There is reason to believe that diabetic neuropathy may be related to the accumulation of sorbitol in nerve tissue through an aldose reductase pathway from glucose. Short-term treatment with aldose reductase inhibitors improves nerve conduction in subjects with diabetes, but the effects of long-term treatment on the neuropathologic changes of diabetic neuropathy are unknown. To determine whether more prolonged aldose reductase inhibition reverses the underlying lesions that accompany symptomatic diabetic peripheral polyneuropathy, we performed a randomized, placebo-controlled, double-blind trial of the investigational aldose reductase inhibitor sorbinil (250 mg per day). Sural-nerve biopsy specimens obtained at base line and after one year from 16 diabetic patients with neuropathy were analyzed morphometrically in detail and compared with selected electrophysiologic and clinical indexes. In contrast to patients who received placebo, the 10 sorbinil-treated patients had a decrease of 41.8 +/- 8.0 percent in nerve sorbitol content (P less than 0.01) and a 3.8-fold increase in the percentage of regenerating myelinated nerve fibers (P less than 0.001), reflected by a 33 percent increase in the number of myelinated fibers per unit of cross-sectional area of nerve (P = 0.04). They also had quantitative improvement in terms of the degree of paranodal demyelination, segmental demyelination, and myelin wrinkling. The increase in the number of fibers was accompanied by electrophysiologic and clinical evidence of improved nerve function. We conclude that sorbinil, as a metabolic intervention targeted against a specific biochemical consequence of hyperglycemia, can improve the neuropathologic lesions of diabetic neuropathy.

Red blood cell sorbitol lowering effects and tolerance of single doses of AL 1576 (HOE 843) in diabetic patients

The safety and biochemical effects of AL 1576 (HOE 483), a recently developed aldose reductase inhibitor, were evaluated. In a double-blind, placebo-controlled, clinical trial, AL 1576 (HOE 483) was administered to diabetic patients for the first time. Four single, orally administered dose levels were tested, (2, 5, 10, and 20 mg). No clinically important adverse effects were seen in any of the patients. AL 1576 (HOE 483) suppressed red blood cell (RBC) sorbitol concentrations in a dose-related fashion. Also found were statistically significant inverse correlations between the plasma drug concentration and both RBC sorbitol concentrations as well as RBC sorbitol/serum glucose ratios. In single doses up to 20 mg, AL 1576 (HOE 483) is well tolerated and decreases RBC sorbitol, a biochemical marker of pharmacologic activity, in diabetic patients.

Clinical aspects of diabetic neuropathies

Diabetic neuropathy is a common complication of diabetes that may be associated both with considerable morbidity (painful polyneuropathy, neuropathic ulceration) and mortality (autonomic neuropathy). The epidemiology and natural history of diabetic neuropathy is clouded with uncertainty, largely due to confusion in the definition and measurement of this disorder. We have reviewed a variety of the clinical manifestations associated with somatic and autonomic neuropathy and discussed current views related to the management of the different abnormalities. Although unproven, the best evidence suggests that near normal control of blood glucose in the early years following onset of diabetes may help delay the development of clinically significant nerve impairment. Intensive therapy to achieve normalization of blood glucose may also lead to reversibility of early diabetic neuropathy, but again this is unproven. Our ability to manage successfully the many different manifestations of diabetic neuropathy depends ultimately on our success in uncovering the pathogenic processes underlying this disorder. The recent resurgence of interest in the vascular hypothesis, for example, has opened up new avenues of investigation for therapeutic intervention. Paralleling our increased understanding of the pathogenesis of diabetic neuropathy, there must be refinements in our ability to measure quantitatively the different types of defects that occur in this disorder. These tests must be validated and standardized to allow comparability between studies and more meaningful interpretation of study results.

Pathogenesis and prevention of diabetic neuropathy

Diabetic neuropathy, long-recognized as an important but complex and poorly understood clinical complication of diabetes, is finally yielding to more than a decade of intense clinical and laboratory investigation. At least one basic biochemical mechanism involving sorbitol and MI metabolism, phosphoinositides, protein kinase C, and the (Na,K)-ATPase has been identified that can rationally account for the neurotoxicity of glucose. This biochemical sequence has been examined in some detail in vitro, but some of its elements, such as the link between abnormal sorbitol and MI metabolism, and between protein kinase C and the (Na,K)-ATPase, remain the subject of ongoing investigation. Through its effect on the (Na,K)-ATPase, this metabolic sequence can explain both the rapidly-reversible functional impairment and the early structural lesions of nerve fibers, such as paranodal swelling in acute diabetes. Extrapolation of early paranodal swelling to the more advanced stages of nerve fiber damage remains somewhat speculative, although axo-glial dysjunction is a likely intermediate step. Impaired axonal transport or microvascular dysfunction may be additional contributing factors, possibly also related to abnormal sorbitol and MI metabolism. Blunted phosphoinositide-mediated signal transduction could potentially explain a putative insensitivity to neurotrophic factors and a diminished regenerative response in diabetic neuropathy. Human morphometric studies and ARI trials support the relevance of these pathogenetic processes to human diabetic neuropathy, and suggest that specific metabolic therapy with agents such as ARIs hold promise as important new elements in the treatment and possibly prevention of diabetic neuropathy.

Diabetic neuropathy in the upper limb and the effect of twelve months sorbinil treatment

Clinical and neurophysiological studies were undertaken, with particular reference to the arms, in 39 patients with diabetic neuropathy. The effects of an aldose reductase inhibitor, sorbinil, on neuropathy in these patients were studied in a 12 month double blind placebo controlled trial. Neurophysiological measurements, particularly of sensory amplitude, were considerably more sensitive than measurements of temperature and vibration sensation and remain of fundamental importance in measuring diabetic neuropathy at an early and potentially reversible stage. There was no significantly beneficial effect of sorbinil on clinical or neurophysiological measurements of nerve function in patients with established diabetic neuropathy. These results indicate that neurophysiological techniques are necessary, in conjunction with clinical measurements, for the assessment of 'early' diabetic neuropathy and that aldose reductase inhibitors are not effective in the treatment of established diabetic neuropathy.

Intravenous lidocaine infusion--a new treatment of chronic painful diabetic neuropathy?

In a randomized double-blind, cross-over study the effect of intravenous lidocaine (5 mg/kg body weight) on the symptoms and signs of painful diabetic neuropathy of more than 6 months duration has been evaluated. Using a clinical symptom scale, there was significant beneficial effect 1 and 8 days after lidocaine infusion compared to after saline infusion (P less than 0.05 and P less than 0.02, respectively). The duration of the individual effect ranged from 3 to 21 days. Lidocaine infusion had no effect on the objective measurements of neuropathy. Intravenous lidocaine infusion seems to be a new alternative treatment of chronic painful diabetic neuropathy.

The effect of sorbinil treatment on red cell sorbitol levels and clinical and electrophysiological parameters of diabetic neuropathy

A randomized placebo-controlled double-blind cross-over study was conducted in order to examine the effect of an aldose reductase inhibitor, sorbinil (100 mg daily for 4 weeks), on red cell sorbitol concentration and clinical and electrophysiological parameters of diabetic neuropathy. A total of 31 diabetic patients with either clinically or electrophysiologically verified diabetic neuropathy were studied. Red cell sorbitol levels decreased significantly to the levels reported in non-diabetic subjects, but there were no significant changes in symptoms, signs, vibration perception thresholds or nerve conduction variables. One patient had transient skin rash, fever, myalgia and leucopenia, but no other significant adverse effects were found.