No abstract

Fascicles of the sural nerve from each of 20 diabetic patients, mostly with maturity-onset diabetes, were studied by biochemical and pathological techniques, and results were compared to values found in nerve specimens from 15 healthy persons. The sorbitol and fructose content was much more variable in diabetic than in healthy nerves. More than one-third of the diabetic nerves had sorbitol and fructose values above the highest levels for controls. myo-Inositol and scyllo-inositol content was not reduced in diabetic nerves. The sorbitol, fructose, and inositol concentrations could not be related to clinical, neurophysiological, or pathological severity of neuropathy. A comparison of scored symptoms and signs and clinical neurophysiological studies against morphometric and teased fiber studies of sural nerve demonstrated that the former three provide sensitive and reliable measures of severity of neuropathy that can be used for controlled clinical trials of diabetic neuropathy. The presence and type of teased fiber abnormalities could be related to the duration of diabetes and to symptoms of neuropathy. In untreated diabetics without symptoms of neuropathy, a higher than normal frequency of teased fibers showing segmental demyelination and remyelination was found. Untreated diabetics with symptomatic neuropathy showed two kinds of abnormalities: fibers with segmental demyelination and remyelination and fibers undergoing axonal degeneration. In treated diabetics, who often had longstanding neuropathy, the most common abnormalities were fibers undergoing axonal degeneration.

Administration of pilocarpine or physostigmine to rats treated with lithium chloride produced sustained limbic seizures, widespread brain damage, and increased concentrations of D-myo-inositol-1-phosphate (a metabolite of the phosphoinositides, lipids involved in membrane receptor function) in the brain. The syndrome was preventable with atropine. The physostigmine doses and concentrations of blood lithium that caused the syndrome are similar to those considered appropriate for psychiatric chemotherapy.

D-chiro-Inositol is a rare inositol isomer present in inositol phosphoglycans which are proposed mediators of insulin action. To study D-chiro-inositol metabolism in diabetes mellitus, a sensitive and specific assay was developed using negative-ion chemical ionization gas chromatography/mass spectrometry. Median urinary D-chiro-inositol excretion, which was 2.1 ,umol/day in nondiabetics, was substantially increased to 12 ,umol/day in non-insulin-dependent diabetes (P < 0.0001) and to 74 j,mol/day in insulin-dependent diabetes (P < 0.0001). Urinary D-chiro-inositol was strongly correlated with fasting plasma glucose (r = 0.568, P < 0.0001), glycated hemoglobin (r = 0.529, P < 0.0001), and urinary glucose (r = 0.368, P = 0.01). The renal clearance of D-chiro-inositol was selectively elevated in both non-insulin-dependent and insulindependent diabetes when compared with the clearances of L-chiro-inositol or myo-inositol and exceeded the glomerular filtration rate in 71% of the diabetics but in none of the nondiabetics. In poorly controlled diabetic patients insulin treatment reduced urinary D-chiro-inositol losses by 63% and increased plasma levels by 8.8-fold. The metabolism of D-chiroinositol is abnormal in diabetes and appears to be influenced by short-and long-term metabolic control.One of the most important problems in endocrinology is the rigorous description of the mechanism of insulin action. Previous work suggests that some (but not all) of the actions of insulin may be mediated through inositol phosphoglycan molecules released from cell membranes (1-4). When such putative mediators were hydrolyzed and analyzed chemically it was found unexpectedly that in some preparations much or all of the inositol present was not myo-inositol (which is, by far, the most common mammalian inositol) but rather the rare epimer D-chiro-inositol (5, 6). Kennington et al. (7) reported abnormally low or unmeasurable levels of D-chiro-inositol in urine and muscle from patients with non-insulin-dependent diabetes mellitus (NIDDM) and suggested that D-chiroinositol deficiency might be related to the insulin resistance observed in NIDDM.However (9) and urinary albumin (Diagnostic Products, Los Angeles) were determined by radioimmunoassay, and glycated hemoglobin was determined by affinity chromatography (Pierce; normal range 4.4-6.3%).Inositol Analysis. Twenty-four-hour urine specimens were collected with cooling but without preservatives and aliquots were stored frozen at -20°C. D-chiro-Inositol levels changed <3% after incubation of nonsterile urine from two poorly controlled diabetics and two normal subjects for 24 hr at 25°C, indicating that urinary D-chiro-inositol levels are stable during collection. To 0.25 ml of urine were added 10 nmol of deuterated DL-chiro-inositol and 20 nmol of deuterated myoinositol as internal standards. The samples were then purified by a modification of a procedure (7) in which the sample was first passed over a 0.6-ml column of water-washed Amberlite IR-120(+) (Aldrich) and then over a 0....

The present experiments were undertaken to examine the hypothesis that glucose-induced increased de novo synthesis of 1,2-diacyl-sn-glycerol (which has been observed in a number of different tissues, including retinal capillary endothelial cells exposed to elevated glucose levels in vitro) and associated activation of protein kinase C may play a role in mediating glucoseinduced vascular functional changes. We report here that twice daily instillation of 30 mM glucose over 10 -d in a rat skin chamber granulation tissue model induces approximately a 2.7-fold increase in diacylglycerol (DAG) levels (versus tissues exposed to 5 mM glucose) in association with marked increases in vascular clearance of albumin and blood flow. The glucose-induced increase in DAG levels as well as the vascular functional changes are prevented by addition of 3 mM pyruvate. Pharmacological activation of protein kinase C with the phorbol ester TPA in the presence of 5 mM glucose increases microvascular albumin clearance and blood flow, and similar effects are observed with 1-monoolein (MOG), a pharmacological inhibitor of the catabolism of endogenous DAG. A pharmacological inhibitor of protein kinase C (staurosporine) greatly attenuates the rise in microvascular albumin clearance (but not the rise in blood flow) induced by glucose or by MOG. These findings are compatible with the hypothesis that elevated concentrations of glucose increase tissue DAG content via de novo synthesis, resuIting in protein kinase C activation, and that these biochemical events are among the factors that generate the increased microvascular albumin clearance. (J. Clin. Invest. 1991.