Endoplasmic reticulum stress in the peripheral nervous system is a significant driver of neuropathic pain.

Despite intensive effort and resulting gains in understanding the mechanisms underlying neuropathic pain, limited success in therapeutic approaches have been attained. A recently identified, nonchannel, nonneurotransmitter therapeutic target for pain is the enzyme soluble epoxide hydrolase (sEH). The sEH degrades natural analgesic lipid mediators, epoxy fatty acids (EpFAs), therefore its inhibition stabilizes these bioactive mediators. Here we demonstrate the effects of EpFAs on diabetes induced neuropathic pain and define a previously unknown mechanism of pain, regulated by endoplasmic reticulum (ER) stress. The activation of ER stress is first quantified in the peripheral nervous system of type I diabetic rats. We demonstrate that both pain and markers of ER stress are reversed by a chemical chaperone. Next, we identify the EpFAs as upstream modulators of ER stress pathways. Chemical inducers of ER stress invariably lead to pain behavior that is reversed by a chemical chaperone and an inhibitor of sEH. The rapid occurrence of pain behavior with inducers, equally rapid reversal by blockers and natural incidence of ER stress in diabetic peripheral nervous system (PNS) argue for a major role of the ER stress pathways in regulating the excitability of the nociceptive system. Understanding the role of ER stress in generation and maintenance of pain opens routes to exploit this system for therapeutic purposes.

Soluble CD163 levels are elevated in cerebrospinal fluid and serum in people with Type 2 diabetes mellitus and are associated with impaired peripheral nerve function.

AIMS: To measure soluble CD163 levels in the cerebrospinal fluid and serum of people with Type 2 diabetes, with and without polyneuropathy, and to relate the findings to peripheral nerve function. METHODS: A total of 22 people with Type 2 diabetes and 12 control subjects without diabetes were included in this case-control study. Participants with diabetes were divided into those with neuropathy (n = 8) and those without neuropathy (n = 14) based on clinical examination, vibratory perception thresholds and nerve conduction studies. Serum and cerebrospinal fluid soluble CD163 levels were analysed using an enzyme-linked immunosorbent assay. RESULTS: Soluble CD163 levels were significantly higher in the cerebrospinal fluid and serum of the participants with Type 2 diabetes compared with the control participants [cerebrospinal fluid: median (range) 107 (70-190) vs 84 (54-115) µg/l, P < 0.01 and serum: 2305 (920-7060) vs 1420 (780-2740) µg/l, P < 0.01). Cerebrospinal fluid soluble CD163 was positively related to impaired peripheral nerve conduction (nerve conduction study rank score: r = 0.42; P = 0.0497) and there was a trend for higher levels of soluble CD163 in the cerebrospinal fluid and serum in participants with neuropathy than in those without neuropathy [cerebrospinal fluid: median (range) 131 (86-173) vs 101 (70-190) µg/l, P = 0.08 and serum: 3725 (920-7060) vs 2220 (1130-4780), P = 0.06). CONCLUSIONS: Cerebrospinal fluid soluble CD163 level is associated with impaired peripheral nerve function. Higher levels of soluble CD163 in people with diabetic polyneuropathy suggest that inflammation plays a role in the development of neural impairment. The relationship between cerebrospinal fluid soluble CD163 level and peripheral nerve conduction indicates that soluble CD163 may be a potential biomarker for the severity of diabetic polyneuropathy.

PAPP-A activity is increased in cerebrospinal fluid from patients with diabetic polyneuropathy and correlates with peripheral nerve impairment.

OBJECTIVE: Insulin-like growth factors (IGFs) have neuroprotective effects. IGF activity is partly controlled by pregnancy-associated plasma protein-A (PAPP-A), an enzyme which enhances IGF-action by cleavage of IGF-binding protein-4 (IGFBP-4). To study the role of PAPP-A and the IGF system in diabetic polyneuropathy (DPN), we measured immunoreactive (total) concentrations of IGF-I and IGF-II, bioactive IGF by cell-based bioassay, PAPP-A, as well as intact and PAPP-A-cleaved IGFBP-4 in cerebrospinal fluid (CSF) and serum from patients with type 2 diabetes (T2D) with and without DPN. DESIGN: Twenty-three patients with T2D were included. Based on clinical examination, vibratory perception thresholds and nerve conduction studies, patients were diagnosed with (n = 9) or without (n = 14) DPN. RESULTS: In CSF, PAPP-A activity, as estimated by IGFBP-4 fragment levels, was higher in patients with than without DPN (34.57 vs 13.79 µg/L, p = .003) and concentrations correlated with peripheral nerve impairment measures (r = 0.73, p < .01). Furthermore, serum bioactive IGF was lower in patients with than without DPN (0.8 vs 1.3 µg/L, p = .006) and correlated inversely to the severity of DPN (r = -0.67, p < .01). CONCLUSIONS: In both CSF and serum, members of the IGF system correlated with measures of peripheral nerve impairment in patients with T2D. This supports a relationship between the IGF system and the development of DPN. Further studies are needed to clarify if these changes are causally linked to the pathogenesis of DPN.

Spinal orexin-1 receptors mediate anti-hyperalgesic effects of intrathecally-administered orexins in diabetic neuropathic pain model rats.

Orexin-A and orexin-B are endogenous ligands of orexin receptors that contain orexin-1 and orexin-2. Activation of the orexinergic system can produce antinociceptive effects in acute inflammatory, mono-neuropathic, and postoperative pain animal models, though the effects of orexins on diabetic neuropathic pain have not been previously investigated. In this study, we studied the anti-hyperalgesic effects of intrathecally administered orexins in a streptozotocin-induced diabetic rat. First, dose-dependent effects were investigated by measuring hind paw withdrawal thresholds in response to noxious-heat and punctate stimuli, after which orexin levels in the cerebrospinal fluid of diabetic rats were measured and compared with those of normal rats using a radioimmunoassay method. The functional role of spinal orexin-1 receptors with the anti-hyperalgesic effects of orexins was also investigated using intrathecal pretreatment with SB-334867, a selective orexin-1 receptor antagonist. Intrathecally administered orexins produced an antinociceptive effect in diabetic rats, however, not in normal rats, though the orexin levels in the cerebrospinal fluid of diabetic rats were similar to those in normal rats. In addition, the anti-hyperalgesic effects of orexins were significantly inhibited by pretreatment with SB-334867. These findings demonstrate that the anti-hyperalgesic effects of orexins in diabetic rats are unlikely due to any direct effect by the supplement on decreased endogenous orexins in the cerebrospinal fluid and that orexin-1 receptors in the spinal cord may be involved in the modulation of nociceptive transmission in diabetic neuropathy. We conclude that the spinal orexinergic system may be a possible target for elucidating the mechanisms of diabetes-induced hyperalgesia.

CSF enkephalins in diabetic neuropathy.

CSF methionine and leucine enkephalins were measured by high performance liquid chromatography and radioimmunoassay in diabetic patients with painful neuropathy (n = 22) and painless neuropathy (n = 5), and non-diabetic subjects with low back pain (n = 11). Wide variations in CSF enkephalin levels were found and they were often below the limit of detection (less than 0.1 pmol/l) in the diabetic and non-diabetic groups. The origin of CSF enkephalins is unknown and CSF levels may not reflect tissue concentrations. In conclusion, CSF enkephalin levels are difficult to interpret and do not provide useful information on the function of enkephalinergic pathways.

Cerebrospinal fluid levels of beta endorphin in painful and painless diabetic polyneuropathy.

beta endorphin (beta-EP) is an important modulator of central pain pathways. To examine whether changes in central production of beta-EP contribute to the pathogenesis of diabetic neuropathic pain, we compared the cerebrospinal fluid (CSF) levels of beta-EP and its precursor proopiomelanocortin (POMC) between 15 diabetic patients with chronic painful diabetic polyneuropathy, eight patients with severe painless diabetic neuropathy, and ten nondiabetic controls. Both peptides were measured by specific monoclonal antibody-based two-site immunoradiometric assays (IRMAs). In the diabetic patients with painful neuropathy, mean +/- SD CSF beta-EP concentrations (5.7 +/- 2.2 pmol/L) were comparable to those of the diabetic patients with painless neuropathy (6.0 +/- 2.3 pmol/L) and did not correlate with the severity of neuropathic pain. CSF beta-EP, but not POMC, concentrations were lower in the diabetic neuropathic patients overall (5.8 +/- 1.9 pmol/L) compared to the control subjects (7.6 +/- 2.2 pmol/L) (p < 0.05). CSF POMC showed no intergroup differences. However, POMC levels were 80-fold higher than those of beta-EP and should always be considered when interpreting immunoreactive beta-EP or other derivative peptide levels in CSF. We conclude that CSF beta-EP levels appear to be reduced in diabetic polyneuropathy but they do not relate to the presence of neuropathic pain. This might explain why opioid analgesics are of little, if any, help in alleviating diabetic neuropathic pain.

[Fibrin fibrinogen degradation products in the cerebrospinal fluid of neurological patients]. / Produkty degradacji fibryny-fibrynogenu w plynie mózgowo-rdzeniowym chorych neurologicznie.

The authors determined FDP levels in the cerebrospinal fluid by the method of Merskey in 214 neurological patients and found raised levels in 58.6% of cases (from 0.1 to 8.0 ug/ml, with normal value range 0-0.5 ug/ml). In the control group the FDP levels in the CSF were normal. No correlation was noted between the FDP levels in the CSF and in blood. Raised CSF FDP level was observed in exacerbations of multiple sclerosis, strokes especially of embolic origin, syringomyelia, bulbar form of amyotrophic lateral sclerosis, epilepsy, migraine, lumbar disc lesions, polyneuropathy, parkinsonism, brain atrophy, after craniocerebral trauma, in Kleine-Levin syndrome. The authors are studying now the course of FDP changes in the CSF in various cases in the aspect of clinical-laboratory correlations.

Cerebrospinal fluid lactate in patients with diabetes mellitus and hypoglycaemic coma.

Cerebrospinal fluid (CSF) lactate and pyruvate concentrations were determined in 20 patients with diabetes mellitus but without disturbance of consciousness and five who recovered from hypoglycaemic coma. CSF lactate was slightly but significantly higher in diabetes mellitus (1.78, SEM 0.04 m mol/l) than that in 15 control subjects (1.40, SEM 0.05 m mol/l). In those who recovered from hypoglycaemic coma, CSF lactate was markedly elevated to 2.45-4.43 m mol/l. CSF glucose concentrations, however, were substantially the same between treated hypoglycaemic and diabetes mellitus groups. These findings indicate that CSF lactate levels increase with glycaemic levels in diabetes mellitus owing to enhanced glucose influx into glycolytic pathway of the brain, and also increases in treated hypoglycaemic coma probably due to mitochondrial dysfunction or damage.

Cerebrospinal fluid levels of substance P and calcitonin-gene-related peptide: correlation with sural nerve levels and neuropathic signs in sensory diabetic polyneuropathy.

1. Lumbar spinal substance P and calcitonin-gene-related peptide derive from spillage out of the dorsal horns associated with activity of small primary sensory afferents (C- and A delta-fibres). Cerebrospinal fluid and sural nerve levels of substance P and calcitonin-gene-related peptide have been measured in patients with diabetic polyneuropathy to determine whether differences in small primary sensory afferent activity are related to the presence or absence of painful symptoms. 2. Calcitonin-gene-related peptide was undetectable in the cerebrospinal fluid of the majority of diabetic patients (14 out of 22); it was lower overall in diabetic patients as compared with control subjects (P < 0.01), it was lower in those diabetic patients with painless neuropathy (100% undetectable) as compared with those with painful neuropathy (50% undetectable; P < 0.05) and it correlated conversely with warming threshold (r = 0.50; P < 0.01). 3. Substance P showed no overall numerical intergroup differences or correlation with other measured variables, but six diabetic patients as compared with one control subject had undetectable cerebrospinal fluid levels and the proportion of patients with undetectable levels was higher in the group with painless neuropathy than in the group with painful neuropathy (P < 0.05). 4. The levels of each peptide in cerebrospinal fluid correlated with its equivalent in sural nerve (P < 0.01 for calcitonin-gene-related peptide and P < 0.03 for substance P). Calcitonin-gene-related peptide correlated with substance P in the sural nerve (r = 0.84; P < 0.002) and in the cerebrospinal fluid (r = 0.30; P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrospinal fluid sorbitol and myoinositol in diabetic polyneuropathy.

Changes in cerebrospinal fluid (CSF) concentrations of sorbitol and myoinositol in 21 patients with diabetic polyneuropathy were studied with gas-liquid chromatography. The sorbitol concentration was significantly increased in diabetic patients with elevated plasma glucose. Myoinositol concentration was significantly decreased in patients with polyneuropathy compared with the controls. Both alterations in polyol concentrations of the CSF were present already two months from onset of symptoms of diabetes. Patients with peripheral polyneuropathy receiving oral hypoglycemic drugs did not have elevated plasma glucose and CSF sorbitol levels, but showed significantly decreased CSF myoinositol concentrations compared with the controls. These observations suggest that myoinositol concentration may be decreased in the central nervous system in adult onset mild diabetes with normal plasma glucose and that the decrease in the myoinositol in CSF possibly is connected with the development of neuropathy.

Lysozyme activity in cerebrospinal fluid.

The concentration of lysozyme (LZM) in cerebrospinal fluid (CSF) has been studied in 148 patients to evaluate its possible significance in the differential diagnosis of various diseases affecting the central nervous system (CNS). In the control group only 3 of 45 patients had detectable LZM in their CSF, the highest value being 1.3 mug/ml. The diabetic and epileptic groups did not differ from the control group. Of 8 patients with primary intracranial tumours, 4 had raised CSF-LZM levels. Twenty of 23 uraemic patients had elevated CSF-LZM, the highest value being 3.3 mug/ml. The highest values were found in patients with bacterial meningitis, tuberculous meningitis and leptomeningitis due to Aspergillus. A positive correlation was found between CSF-LZM and protein concentrations. The measurement of LZM may be of value in the diagnosis of inflammatory processes affecting the CNS and in the diagnosis of certain intracranial tumours.