Diabetic neuropathy in the rat: 1. Alcar augments the reduced levels and axoplasmic transport of substance P

Constipation in DM are associated with both poor glycemic control and diabetic complications: Current status and future directions

Constipation is a major complications of diabetes mellitus. With the accelerating prevalence of diabetes worldwide and an aging population, there is considerable research interest regarding the altered function and structure of the gastrointestinal tract in diabetic patients. Despite current advances in hyperglycemic treatment strategies, the specific pathogenesis of diabetic constipation remains unknown. Patients with constipation, may be reluctant to eat regularly, which may worsen glycemic control and thus worsen symptoms associated with underlying diabetic bowel disease. This paper presents a review of the complex relationship between diabetes and constipation, exploring the morphological alterations and biomechanical remodeling associated with intestinal motility dysfunction, as well as alterations in intestinal neurons, cellular signaling pathways, and oxidative stress. Further studies focusing on new targets that may play a role in the pathogenesis of diabetic constipation may, provide new ideas for the development of novel therapies to treat or even prevent diabetic constipation.

Sensitized peripheral nociception in experimental diabetes of the rat

Painful neuropathy is a common complication of diabetes. Particularly in the early stage of diabetic neuropathy, patients are characterized by burning feet, hyperalgesia to heat, and mechanical stimuli, as if residual nociceptors were sensitized. Such symptoms are barely explained by common pathophysiological concepts of diabetic neuropathy. Diabetes was induced in Wistar rats by streptozotocin (STZ). After 4 weeks behavioral testing (Plantar test, Randall-Selitto) was conducted. Basal and stimulated release of calcitonin gene-related peptide (CGRP), Substance P (SP) and prostaglandin E(2) (PGE(2)) from isolated skin and sciatic nerve were assessed by enzyme immunoassays. Electrophysiological properties of identified nociceptors under hyperglycemic, hypoxic, and acidotic conditions were investigated using the skin-nerve preparation. The diabetic rats showed hyperalgesia to heat and pressure stimulation. The basal CGRP/SP release was reduced, but chemical stimulation with bradykinin induced greater release of SP, CGRP and PGE(2) than in control animals. In contrast, capsaicin-stimulated CGRP release was reduced in sciatic nerves. Hypoxia per se lowered von Frey thresholds of most C-nociceptors to half. Hyperglycemic hypoxia induced ongoing discharge in all diabetic but not control C-fibers which was further enhanced under acidosis. Sensory and neurosecretory nociceptor functions are sensitized in diabetes. Diabetic C-fibers show exaggerated sensitivity to hyperglycemic hypoxia with and without additional acidosis, conditions that are thought to mimic ischemic episodes in diabetic nerves. Ongoing C-fiber discharge is known to induce spinal sensitization. Together with altered receptor and ion channel expressions this may contribute to painful episodes in diabetic neuropathy.

Protective effects of acetyl-L-carnitine on cisplatin cytotoxicity and oxidative stress in neuroblastoma

The most widely used platinum-derived drug is cisplatin in neuroblastoma (NB) chemotherapy, which is severely neurotoxic. Acetyl-L-Carnitine (ALC) is a natural occurring compound with a neuroprotective activity in several experimental paradigms. The aim of this study was to determine the effects of ALC on cisplatin induced cytotoxicity and oxidative stress in NB cells. SH-SY5Y (N-Myc negative) and KELLY (N-Myc positive) human NB cell lines were used. Cisplatin induced apoptosis was assessed by using a Cell Death Detection ELISA(PLUS) kit. Lipid peroxidation levels were determined by HPLC analysis. Glutathione levels were determined spectrophotometrically. ALC was used prophylactic or after cisplatin application. The level of cisplatin doses were determined in both type of NB cells at which 50% cell death occurred along with synchronized apoptosis induced. Prophylactic 10 and 50 micromol of ALC concentrations were decreased cisplatin induced lipid peroxidation compared to controls that normally exhibited apoptosis especially in SH-SY5Y cells. Cisplatin caused oxidative stress through decreasing glutathione levels in both cell types. ALC were effectively inhibited the increase in cisplatin induced oxidized glutathione and lipid peroxidation formation in NB cells. We suggested that prophylactic ALC would be a useful agent for cisplatin induced toxicity in NB cells.

Role of acetyl-L-carnitine in the treatment of diabetic peripheral neuropathy

OBJECTIVE

To examine the role of acetyl-L-carnitine (ALC) in the treatment of diabetic peripheral neuropathy (DPN).

DATA SOURCES

A MEDLINE search (1966-April 2008) of the English-language literature was performed using the search terms carnitine, diabetes, nerve, and neuropathy. Studies identified were then cross-referenced for their citations.

STUDY SELECTION AND DATA EXTRACTION

The search was limited to clinical trials, meta-analyses, and reviews addressing the use of ALC for the treatment of DPN. Studies that included other disease states that could cause peripheral neuropathy were excluded. Two large clinical studies that used ALC for the treatment of DPN were identified. No case studies were identified.

DATA SYNTHESIS

The results from 2 published clinical trials involving 1679 subjects were included. Subjects who received at least 2 g daily of ALC showed decreases in pain scores. One study showed improvements in electrophysiologic factors such as nerve conduction velocities, while the other did not. Patients who had neuropathic pain reported reductions in pain using a visual analog scale. Nerve regeneration was documented in one trial. The supplement was well tolerated. A proprietary form of ALC was used in both studies.

CONCLUSIONS

Data on treatment of DPN with ALC support its use. It should be recommended to patients early in the disease process to provide maximal benefit. Further studies should be conducted to determine the effectiveness of ALC in the treatment and prevention of the worsening symptoms of DPN.

Depletion of peptidergic innervation in the gastric mucosa of streptozotocin-induced diabetic rats

Autonomic neuropathy affecting the gastrointestinal system is a major presentation of diabetic neuropathy. Changes in the innervation of gastric mucosa or muscle layers can contribute to gastrointestinal symptoms. The present study investigated this issue by quantitatively analyzing the immunohistochemical patterns of the gastric innervation in rats with streptozotocin (STZ)-induced diabetes. In control rats, calcitonin gene-related peptide (CGRP) and substance P (SP) (+) nerve fibers appeared in the gastric mucosa and muscle layers. Double immunohistochemical staining showed that immunoreactivities for SP and CGRP were co-localized with a pan-neuronal marker protein gene product 9.5. Both SP (+) nerve fibers (p<0.001) and CGRP (+) nerve fibers (p<0.005) were decreased in the gastric mucosa within 4 weeks of diabetes; the reduction persisted throughout 24 weeks. Diabetic rats treated with insulin did not show decrease of SP or CGRP (+) fibers in the mucosa 4 weeks after STZ injection (p>0.05). There was no significant change in SP (+) nerve fibers (p>0.05) or CGRP (+) nerve fibers (p>0.05) of the gastric muscle layers. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression levels of SP and CGRP mRNA in the thoracic dorsal root ganglia were similar between diabetic and control animals (p>0.05). Qualitative and quantitative ultrastructural examinations on the gastric mucosa documented unmyelinated nerve degeneration. These results suggest the existence of gastric sensory neuropathy in STZ-induced diabetes, and this pathology provides a foundation for understanding diabetic gastropathy.

Acetyl-L-carnitine in diabetic polyneuropathy: experimental and clinical data

Diabetic polyneuropathy (DPN) is the most common late complication of diabetes mellitus. The underlying pathogenesis is multifaceted, with partly interrelated mechanisms that display a dynamic course. The mechanisms underlying DPN in type 1 and type 2 diabetes mellitus show overlaps or may differ. The differences are mainly due to insulin deficiency in type 1 diabetes which exacerbates the abnormalities caused by hyperglycaemia. Experimental DPN in rat models have identified early metabolic abnormalities with consequences for nerve conduction velocities and endoneurial blood flow. When corrected, the early functional deficits are usually normalised. On the other hand, if not corrected, they lead to abnormalities in lipid peroxidation and expression of neurotrophic factors which in turn result in axonal, nodal and paranodal degenerative changes with worsening of nerve function. As the structural changes progress, they become increasingly less amendable to metabolic interventions. In the past several years, experimental drugs--such as aldose reductase inhibitors, antioxidants and protein kinase C inhibitors--have undergone clinical trials, with disappointing outcomes. These drugs, targeting a single underlying pathogenetic factor, have in most cases been initiated at the advanced stage of DPN. In contrast, substitution of acetyl-L-carnitine (ALC) or C-peptide in type 1 DPN target a multitude of underlying mechanisms and are therefore more likely to be effective on a broader spectrum of the underlying pathogenesis. Clinical trials utilising ALC have shown beneficial effects on nerve conduction slowing, neuropathic pain, axonal degenerative changes and nerve fibre regeneration, despite relatively late initiation in the natural history of DPN. Owing to the good safety profile of ALC, early initiation of ALC therapy would be justified, with potentially greater benefits.

Upper gastrointestinal sensory-motor dysfunction in diabetes mellitus

Gastrointestinal (GI) sensory-motor abnormalities are common in patients with diabetes mellitus and may involve any part of the GI tract. Abnormalities are frequently sub-clinical, and fortunately only rarely do severe and life-threatening problems occur. The pathogenesis of abnormal upper GI sensory-motor function in diabetes is incompletely understood and is most likely multi-factorial of origin. Diabetic autonomic neuropathy as well as acute suboptimal control of diabetes has been shown to impair GI motor and sensory function. Morphological and biomechanical remodeling of the GI wall develops during the duration of diabetes, and may contribute to motor and sensory dysfunction. In this review sensory and motility disorders of the upper GI tract in diabetes is discussed; and the morphological changes and biomechanical remodeling related to the sensory-motor dysfunction is also addressed.

HSV-1-mediated NGF delivery delays nociceptive deficits in a genetic model of diabetic neuropathy

A previous phase III clinical trial failed to show significant therapeutic benefit of repeated subcutaneous nerve growth factor (NGF) administration in the treatment of diabetic neuropathy. Animal studies have since shown that site-specific viral-mediated expression of NGF in the lumbar dorsal root ganglia prevents peripheral nerve dysfunction associated with chemically induced neuropathy. Using a Herpes simplex virus expression vector, we have investigated the effect of localized NGF expression in a genetic mouse model of progressive diabetic neuropathy, the +/+ Leprdb mouse. We found that site-specific delivery of NGF initially delayed the appearance of hypoalgesia, assessed by the Hargreaves test, by 1 month and effectively attenuated this deficit for 2 months over the approximately 10 months normal life-span of these animals. Once the disease progressed into its more severe stages, NGF, although still capable of altering the electrophysiological profile of the sensory A- and C-fibers and influencing the expression of p75 and substance P in the dorsal root ganglia, could no longer maintain normal nociception. These data suggest that maximal therapeutic benefit in future NGF-based gene therapy trials will be gained from early applications of such viral-mediated neurotrophin delivery.

Effects of ALCAR on the fast axoplasmic transport in cultured sensory neurons of streptozotocin-induced diabetic rats

The effects of acetyl-L-carnitine (ALCAR) on fast axoplasmic transport were studied in cultured dorsal root ganglion (DRG) neurons of diabetic rats. Three-month-old male rats were used 7 days after streptozotocin injection. Neurons obtained from ganglia were cultured with a high concentration of glucose. The amount and the mean velocity of retrogradely transported particles, reduced in the diabetic animal, were transiently recovered by 1 mM ALCAR. The number of particles moving at 0.8-1.2 microm/s, considered to be lysosomes, increased in the velocity distribution. ALCAR did not modify the amount and mean velocity of anterograde particles which were unaffected by diabetes, or of bidirectional particles in neurons of control rats. This study suggests that diabetic neuropathy may be relieved by ALCAR via recovering retrograde axoplasmic transport.

Alterations of protein mono-ADP-ribosylation and diabetic neuropathy: a novel pharmacological approach

This study monitored the extranuclear endogenous mono ADP-ribosylation of proteins. At least 10 proteins were ADP-ribosylated in a crude extract from control superior cervical ganglia, and 7 were labeled in control dorsal root ganglia; whereas in the diabetic rat the extent of labeling was reduced. These data suggest that proteins of peripheral ganglia are excessively ADP-ribosylated in vivo. Treatment of diabetic animals with silybin, a flavonoid with ADP-ribosyltransferase inhibitory activity, did not affect hyperglycemia, but prevented the alterations in the extent of mono-ADP-ribosylation of proteins. This effect was associated with the prevention of substance P-like immunoreactivity loss in the sciatic nerve. In the membrane fraction of sciatic nerve Schwann cells, at least 9 proteins were ADP-ribosylated, in diabetic rats the extent of labeling was increased. A comparable increase involving the same proteins was triggered by chronic nerve injury and by corticosteroid treatment. Silybin treatment of diabetic rats prevented such an increase. We propose that the inhibition of excessive protein mono-ADP-ribosylation by silybin prevented the onset of diabetic neuropathy, while the silybin effect on mono-ADP-ribosylation of Schwann cells is likely indirect and secondary to the improvement of diabetic axonopathy.

Diabetes and the nervous system

Hyperglycemia and its vascular complications affect the entire nervous system, contributing to increased morbidity and mortality. Chronic hyperglycemia is not only a known and major risk factor for cerebral vascular diseases but also the presence of hyperglycemia at the time of a cerebrovascular event may adversely influence the outcome. It also affects the treatment of some neurodegenerative disorders, and there are suggestions that diabetes may in fact suffer from a "chronic diabetic encephalopathy." Its varied effects on the peripheral nervous system result in several forms of diabetic neuropathies, the exact pathogenesis of which is still obscure. There is, however, some new information that may link metabolic and vascular hypotheses.

Nitric oxide-sensitive protein ADP-ribosylation is altered in rat diabetic neuropathy

Endogenous ADP-ribosylation of proteins was studied in retina crude extract, membrane and cytosolic fractions of control and diabetic rats. ADP-ribosyltransferase activity is present in all cellular fractions, but protein ADP-ribosylation is reduced in diabetic rat retina. At least 6 proteins are labelled in the crude extract fraction and a similar number in the membrane preparation of control animals. In these preparations from diabetic retina, only two bands were labelled, the 85 K and 36 K for the crude extract, and the 97 K and 39 K for membranes. Labelling of 36 K and 39 K proteins was much less than in controls. In the cytosolic preparations of controls, two proteins of 85 K and 39 K are ADP-ribosylated, while in diabetic rat retina cytosol, only the 85 K is labelled. Treatment of diabetic rats with insulin normalized plasma glucose levels and prevented the alterations of the extent of ADP-ribosylation for the 38 K cytosolic, 39 K membrane and 36 K crude extracts proteins, but it failed to affect the other bands. These results suggest a hyperactivity of endogenous ADP-ribosylases in diabetic rat retina, so that the protein sites for ADP-ribosylation are no longer available. Since insulin treatment prevents the onset of neuropathy and of retinal G protein impairment (Abbracchio et al., J Neurosci Res 29:196-220, 1991) in diabetic rats and, in this study, normalizes ADP-ribosylation of 39 K, 38 K and 36 K proteins, we suggest that the abnormal endogenous ADP-ribosylation of these proteins might play a role in the onset of diabetic neuropathy.