Cerebrospinal fluid sorbitol and myoinositol in diabetic polyneuropathy

Gene expression in the dorsal root ganglion and the cerebrospinal fluid metabolome in polyneuropathy and opioid tolerance in rats

First-line pharmacotherapy for peripheral neuropathic pain (NP) of diverse pathophysiology consists of antidepressants and gabapentinoids, but only a minority achieve sufficient analgesia with these drugs. Opioids are considered third-line analgesics in NP due to potential severe and unpredictable adverse effects in long-term use. Also, opioid tolerance and NP may have shared mechanisms, raising further concerns about opioid use in NP. We set out to further elucidate possible shared and separate mechanisms after chronic morphine treatment and oxaliplatin-induced and diabetic polyneuropathies, and to identify potential diagnostic markers and therapeutic targets. We analysed thermal nociceptive behaviour, the transcriptome of dorsal root ganglia (DRG) and the metabolome of cerebrospinal fluid (CSF) in these three conditions, in rats. Several genes were differentially expressed, most following oxaliplatin and least after chronic morphine treatment, compared with saline-treated rats. A few genes were differentially expressed in the DRGs in all three models (e.g. Csf3r and Fkbp5). Some, e.g. Alox15 and Slc12a5, were differentially expressed in both diabetic and oxaliplatin models. Other differentially expressed genes were associated with nociception, inflammation, and glial cells. The CSF metabolome was most significantly affected in the diabetic rats. Interestingly, we saw changes in nicotinamide metabolism, which has been associated with opioid addiction and withdrawal, in the CSF of morphine-tolerant rats. Our results offer new hypotheses for the pathophysiology and treatment of NP and opioid tolerance. In particular, the role of nicotinamide metabolism in opioid addiction deserves further study.

Major depressive disorder viewed as a dysfunction in astroglial bioenergetics

For many years scientists and physicians have pondered upon the apparent connection between depressive disorder and diabetes mellitus. Several epidemiologic studies confirm that diabetics have increased incidence of depression, and vice versa. In addition: depressive, non-diabetic patients have several insulin- and glucose-metabolism disturbances, probably exerting a compensatory reaction to the malfunction in the depressed brain as these disturbances are normalised in remission. After the discovery of PET-scanning, such studies have shown that patients with depressive disorder have reduced glucose metabolism in frontal parts of the brain. The present hypothesis regards the PET findings as observations of the primary pathophysiology of depression. Furthermore: two studies of post mortem samples from depressed patients show reduced numbers of astroglia. This is in accordance to the mentioned insulin disturbances, as only astroglia, not neurons, have insulin-sensitive glucose metabolism. Hence: the astroglia, not necessarily the neurons, are proposed to be the type of cells in which the disease resides. Most probably depressive disorder is a multitude of diseases, explaining the apparent multitude of symptoms, and the fact that different patients do respond to different drugs. Therefore: one can only formulate the hypothesis by mentioning a common denominator to these specific malfunctions, namely: disturbed glucose metabolism in the depressed brain. The present paper reviews several findings and proposes that attenuated cerebral glucose metabolism in frontal parts of the brain, in the astroglia, is the cause of depressive disorder.

Elevated sorbitol concentration in the cerebrospinal fluid of patients with mood disorders

This study was undertaken to test the hypothesis that a specific pathophysiological mechanism of diabetic neuropathy, namely increased polyol pathway flux, could be operative in patients with bipolar and unipolar mood disorders. Numerous studies have shown abnormalities of carbohydrate metabolism, including high rates of diabetes mellitus, in patients with mood disorders. Several studies have found that peripheral neuropathy is a risk factor for depression in diabetics. Furthermore, increased polyol pathway flux results in elevated sorbitol concentrations in peripheral tissues and cerebrospinal fluid (CSF) of diabetics with neuropathy. The purpose of this study was to determine whether sorbitol concentration is elevated in the CSF of non-medically ill patients with mood disorders. Lumbar punctures were performed on 30 subjects - 10 with bipolar mood disorder, 10 with unipolar mood disorder, and 10 age-matched normal controls, and CSF sorbitol concentrations were measured, using a gas chromatographic-mass spectroscopic technique. The mean+/-standard deviation of CSF sorbitol concentrations differed among the three groups as follows: bipolar (22.9+/-4.6 micromoles/l) > unipolar (19.0+/-2.8 micromoles/l)>normal control (15. 6+/-1.9 micromoles/l). One-way ANOVA showed significant (P=0.0002) differences among the three groups. Post-hoc tests indicated a significant (P<0.05) difference between bipolars and normal controls, bipolars and unipolars, and unipolars and normal controls. Further investigation is needed to determine the pathophysiological significance of this novel finding of elevated sorbitol concentration in the CSF of patients with mood disorders.

Leukoencephalopathy associated with a disturbance in the metabolism of polyols

In vivo proton magnetic resonance spectroscopy of the brain demonstrated highly elevated levels of arabitol and ribitol in a 14-year-old boy with a white matter disorder and neuropathy of unknown origin. These polyols also were shown to be elevated in body fluids, suggesting an inborn error in polyol metabolism. The strong plasma/ cerebrospinal fluid/brain gradient, with concentrations increasing in that order, suggests a primary neurometabolic disorder. Thus far, a basic enzyme defect has not been identified.

Polyol profiles in Down syndrome. myo-Inositol, specifically, is elevated in the cerebrospinal fluid

Polyols are reduction products of aldoses and ketoses; their concentrations in tissues can reflect carbohydrate metabolism. Several polyol species were quantitated in cerebrospinal fluid (CSF) and plasma from 10 Down Syndrome (trisomy 21) subjects between the ages of 22 and 63 years (3 of whom were demented) and from 10 healthy age-matched controls, using a gas chromatographic/mass spectrometric technique. The mean CSF concentration and the mean CSF/plasma concentration ratio of myo-inositol were significantly elevated in Down syndrome compared with controls, but were not correlated with the presence of dementia in the Down subjects. Plasma myo-inositol was not significantly altered in these subjects. No significant difference between Down syndrome and controls was found for CSF concentrations of mannitol, sorbitol, galactitol, ribitol, arabitol, or 1,5-anhydrosorbitol, but plasma mannitol, ribitol and arabitol were elevated in Down syndrome. The present observation provides new impetus for studying synthesis and transport of myo-inositol as well as phosphatidylinositol cycle in trisomy 21 disorder.

Oral supplementation of myoinositol: effects on peripheral nerve function in human diabetics and on the concentration in plasma, erythrocytes, urine and muscle tissue in human diabetics and normals

28 young diabetics with short disease duration participated in a double-blind study by taking 6 g of myoinositol or placebo daily for 2 months. The aim was to demonstrate a possible beneficial effect of this compound on subclinical diabetic neuropathy. Measurement of vibratory perception threshold, motor and sensory conduction velocity and amplitude of nerve potential did not disclose any effect of the myoinositol given. In accordance with this, no indication for a lack of myoinositol in human diabetic blood or tissue could be found. The concentration of myoinositol in the plasma and erythrocyte of 4 human diabetics was normal or high, even though the loss of urinary myoinositol was greater than in the case of 4 normals. Further, an analysis of the content of free and lipid-bound myoinositol in muscle biopsies taken from the 4 diabetics did not give any indication of deficiency. The content of myoinositol in their muscle tissue remained uninfluenced by oral supplementation of myoinositol.

Myoinositol and function of peripheral nerves in human diabetics. A controlled clinical trial

Fifty-nine diabetic patients participated in a double-blind study in order to evaluate the efficiency of myoinositol to improve the function of peripheral nerves. Myoinositol in the amounts given was not able to change motor conduction velocity or vibratory perception threshold. No change in retinopathy and several biochemical parameters was observed.