Myo-inositol Treatment Research Articles

Effect of myo-inositol supplementation on the development of renal pathological changes in the Cohen diabetic (type 2) rat

A lower concentration of intracellular myo-inositol has been implicated in the development of diabetic nephropathy. This was based on short-term studies showing that early administration of aldose reductase inhibitors or myo-inositol supplementation reduces increased glomerular filtration rate and partly reduces increased urinary albumin excretion in streptozotocin diabetic rats. We studied the effect of long-term (4 months) administration of 1% myo-inositol supplement to the Cohen diabetic (type 2) rat on the development of nephropathy and renal Na+-K+-ATPase. This treatment reduced the increased renal Na+-K+-ATPase activity but had no effect on blood glucose levels, body weight, increased kidney weight, or creatinine clearance and did not prevent or reduce the development of renal glomerular pathology. There was no correlation between the level of Na+-K+-ATPase activity and the degree of nephropathy. It is possible that the renal pathological changes are due to metabolic and humoral factors resulting from hyperglycaemia, other than myo-inositol depletion. The fact that myo-inositol treatment had no effect on the development of renal pathological changes but was shown to have a beneficial effect on restoring impaired conduction velocity and on the disruption of structural elements in the nerve indicates that the effect of the biological changes ensuing from hyperglycaemia vary in different tissues depending on local conditions.

Aldose reductase inhibition, nerve perfusion, oxygenation and function in streptozotocin-diabetic rats: Dose-response considerations and independence from a myo-inositol mechanism

We examined the effects of aldose reductase inhibition on nerve biochemistry and function, blood flow and endoneurial oxygenation in experimental diabetes mellitus. After 1 month untreated diabetes in rats, treatment with the novel sulphonylnitromethane aldose reductase inhibitor, ZENECA ZD5522, prevented a progressive increase in sciatic nerve resistance to hypoxic conduction failure (p < 0.05). Motor conduction velocity deficits after 4 months untreated diabetes were rapidly returned to normal within 12 days (p < 0.0001) by ZD5522 treatment. Following 2-months untreated diabetes, examination of 1 month ZD5522 treatment dose-response relationships for correction of nerve sorbitol and fructose accumulations and reduction in myo-inositol concentration, sciatic motor and saphenous sensory conduction velocity and sciatic blood flow by laser-Doppler flowmetry revealed poor agreement between nerve function and biochemical indices. In addition, polyol accumulation differed between sciatic and saphenous nerves, the latter showing ten-fold lower sorbitol concentrations. Laser-Doppler blood flow was 60% decreased by untreated diabetes (p < 0.001) and there was a strong correlation between ZD5522-mediated increases in blood flow and conduction velocity (p < 0.0001). Measurement of nutritive endoneurial blood flow by microelectrode polarography and hydrogen clearance showed 44% and 45% deficits for 1 and 2 months untreated diabetes (p < 0.001) that were prevented by ponalrestat and ZD5522 treatments, respectively. In contrast, 2 months myo-inositol treatment from diabetes induction did not prevent reduction in blood flow or sciatic motor conduction velocity. A 37% reduction in endoneurial oxygen tension after 2 months diabetes (p < 0.001) was completely prevented by ZD5522 treatment (p < 0.001). The data show that a very high degree of polyol pathway blockade is necessary to correct nerve functional deficits and that aldose reductase inhibitors have a neurovascular action that does not depend on restoration of nerve myo-inositol.

The effect of myo-inositol treatment on basement membrane thickening in the [formula omitted] retina

A polyol-pathway related perturbation of myo-inositol metabolism has been invoked in the pathogenesis of diabetic complications, including retinal microvasculopathy. Previous studies have demonstrated a beneficiary effect of aldose reductase inhibition on basement membrane thickening of retinal microvessels in diabetic animals. In the present study we demonstrate a significant but partial effect on basement membrane thickening following myo-inositol supplementation. Qualitative structural changes, such as nodular swellings, fibrillar changes and basement membrane projections were not effected by myo-inositol supplementation, suggesting that although abnormal myo-inositol tissue levels may play a role in basement membrane thickening, other factors may be of primary pathogenetic importance.

Effect of Insulin and Dietary Myoinositol on Muscarinic Receptor Alterations in Diabetic Rat Bladder

Previous studies from our laboratory demonstrated that there is an up-regulation of muscarinic receptor density in the bladder dome of the 8-wks diabetic rat compared to control. To determine whether the changes observed in receptor density can be corrected by insulin or dietary myoinositol, five groups of rats were maintained for eight weeks: control (C), diabetic (D), diabetic insulin-treated (DI), diabetic myoinositol-treated (DMI), and control myoinositol-treated (CMI). Diabetes was induced by i.v. injection of 65mg./kg. of streptozotocin. D and DMI animals were smaller, had higher serum glucose and lower serum insulin levels, higher water intakes and urine outputs, and larger bladder domes than the other groups. The density of the muscarinic receptors measured by radioligand receptor binding assays using [3H]quinuclidinyl benzilate were (in fmol./mg. protein): C, 88 ± 13; D, 176 ± 19; DI, 94 ± 5; DMI, 158 ± 8; CMI, 112 ± 10. These data indicate that insulin, but not myoinositol treatment normalized diabetes induced abnormalities observed in the general features of streptozotocin-injected rats and prevented the diabetic-induced upregulation of bladder dome muscarinic receptors.

Effects of Sorbinil, Dietary myo-Inositol Supplementation, and Insulin on Resolution of Neuroaxonal Dystrophy in Mesenteric Nerves of Streptozocin-Induced Diabetic Rats

Previous studies indicate that experimental diabetic autonomic neuropathy can be largely prevented by initiating therapy at the onset of diabetes. More clinically relevant, however, is the ability of therapy to reverse established neuropathy produced by long-standing diabetes. We have examined the effect of selected therapies on established neuroaxonal dystrophy (NAD) in ileal mesenteric nerves, a rat model of diabetic autonomic neuropathy. Groups of 3-mo-old rats were made diabetic with streptozocin (STZ-D) and allowed to survive untreated for 5 mo, at which time they were begun on sorbinil, dietary myo-inositol, and daily insulin therapies or left untreated for an additional 2 or 4 mo. Ultrastructural evidence of NAD was demonstrated in ileal mesenteric nerves of rats with untreated 5-mo STZ-D and increased with the duration of diabetes. No lesions were demonstrated in control rats of any age. myo-Inositol or sorbinil administration failed to alter the severity of diabetes as measured by its metabolic indices. Institution of sorbinil or insulin treatment at 5 mo of diabetes prevented the increase in, but did not normalize, NAD at 7 or 9 mo. Dietary myo-inositol failed to significantly reverse established NAD or prevent its initial development. Morphometric examination of ileal mesenteric nerves demonstrated a decrease in the number of axons comprising each diabetic Schwann cell unit, suggestive of chronic cycles of axonal degeneration and regeneration. This parameter, clearly abnormal by 5 mo of diabetes, was not normalized by 2 or 4 mo of insulin, sorbinil, or myo-inositol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta adrenergic receptor alterations in diabetic rat prostate: Effects of insulin and dietary myoinositol

As sexual dysfunction is a well-recognized manifestation of diabetes mellitus and as the function of the prostate, a major accessory organ in the male reproductive system, is regulated by the autonomic nervous system, we studied beta adrenergic receptors in the prostate of streptozotocin-induced diabetic rats, using radioligand receptor binding techniques. Four groups of rats were maintained for 8 weeks: controls, diabetics, insulin-treated diabetics, and myoinisitol-treated diabetics. The diabetic and myoinisitol-treated diabetic animals were smaller, had higher blood glucose levels, higher water intake and urine output, smaller prostates, and lower serum insulin levels than the other groups. Saturation experiments with [3H]dihydroalprenolol showed that the induction of diabetes decreased the density of beta adrenergic receptors in prostatic membrane particulates. Inhibition studies with selective beta adrenergic antagonists demonstrated that these receptors were of the beta 2 subtype. Furthermore, insulin but not myoinositol treatment normalized blood glucose and insulin levels, maintained normal prostate and body weight-gain, and prevented the decrease in the density, i.e., down-regulation, of the prostatic beta adrenergic receptors.

Calcium uptake activity of cardiac sarcoplasmic reticulum in myo-inositol-treated diabetic rats

1. 1. Cardiac function of STZ-diabetic rats has been shown to be partially improved by myo-inositol treatment. We studied the effect of myo-inositol on Ca 2+-uptake activity in sarcoplasmic reticulum in diabetic animals. 2. 2. Cardiac sarcoplasmic reticulum Ca 2+-uptake activity was significantly depressed in 8-week diabetic rats. 3. 3. Myo-inositol treatment could not improve Ca 2+-uptake activity in diabetic rats. 4. 4. The data suggest that the cardiac dysfunction in diabetic rats is due to factors other than the decreased Ca 2+-uptake activity in sarcoplasmic reticulum.

THE EFFECT OF ALDOSE REDUCTASE INHIBITION ON THE PATTERN OF NERVE CONDUCTION DEFICITS IN DIABETIC RATS

Conduction deficits caused by 2-4 months diabetes were examined in one sensory and six motor nerve branches of mature rats. The effect of aldose reductase inhibitor (ponalrestat) treatment was assessed in preventative and reversal studies. The efficacy of 1% dietary myoinositol supplementation was also examined in a 2 month preventative group. Diabetes suppressed a maturation-related increase in conduction velocity in the interosseus nerve supplying foot muscles. This was unaffected by any treatment. Large conduction velocity reductions (22-29%) seen for fast nerves supplying four calf muscles and sensory saphenous nerves were prevented by ponalrestat treatment. In a reversal group, which had 2 months of diabetes followed by 2 months of treatment, restoration of conduction varied between nerves, ranging from 100% in sensory saphenous to 25% in soleus motor branches. Myo-inositol supplementation had little effect. Sciatic nerves accumulated the sugar alcohol sorbitol with diabetes. This was markedly reduced by treatment, and correlated with the conduction velocity improvement. There was a 40% reduction in nerve free myo-inositol levels after 2 months diabetes. Ponalrestat normalized myo-inositol in the short term but failed to do so in 4 month preventative and reversal groups. Myo-inositol treatment did not affect nerve levels. The data implicate the polyol pathway in the diabetic conduction velocity deficits seen in normally fast conducting motor and sensory nerves and suggest that aldose reductase inhibitor action does not depend on restoration of nerve myo-inositol levels.

Tissue noradrenaline and the polyol pathway in experimentally diabetic rats

1. The effects of a six week period of streptozotocin-induced diabetes on tissue catecholamines and on in vivo noradrenaline turnover were assessed in rats. 2. Noradrenaline concentrations measured in heart ventricle, terminal ileum, vas deferens, spleen and adrenal tissue from the diabetic rats were all found to be elevated compared to those found in control rat tissues. The adrenaline contents of the adrenal glands were also raised in these animals. 3. Noradrenaline turnover in heart ventricle, terminal ileum and vas deferens was estimated from the decline in tissue content of the amine following inhibition of its synthesis with alpha-methyl-p-tyrosine. Turnover was found to be increased in all three tissues. 4. The involvement of the polyol pathway in the above changes was investigated by examining the effects of continuous treatment with an aldose reductase inhibitor, Statil (ICI 128436) or dietary myo-inositol supplementation. Either treatment was found to prevent or reduce the increases in tissue noradrenaline and in its turnover. Myo-inositol treatment also partially prevented the rise in adrenal adrenaline. 5. It is concluded that the elevation of tissue catecholamines and of noradrenaline turnover by diabetes was related to myo-inositol depletion secondary to excessive sorbitol synthesis. Possible mechanisms for the observed increase in noradrenaline turnover could involve Na+, K+-ATPase depression.

Myo-inositol normalizes decreased sodium permeability of the blood-brain barrier in streptozotocin diabetes

The effect of a dietary supplement of an aldose reductase inhibitor (ponalrestat) or of myo-inositol on sodium transport into the rat brain and on concentrations of saccharide and polyols in cortical brain tissue and sciatic nerve was investigated in control rats and in streptozotocin-diabetic rats after a diabetes duration of 2 weeks. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 28% ( 3.4 ± 0.4 vs 4.7 ±1.6 × 10 −5ml/s g,mean±SD ) as compared to controls. Levels of glucose, sorbitol and fructose increased in brain as well as in nerve tissues, whereas myo-inositol depletion was not demonstrable. Ponalrestat treatment of diabetic animals had no effect upon the decreased neocortical blood-brain barrier permeability to sodium ( 3.5 ±0.9 vs 4.7 ± 1.1 × 10 −5ml/s g ) despite normalization of brain and nerve content of sorbitol and fructose. Myo-inositol supplementation of diabetic rats normalized sodium passage into the brain ( 4.2 ± 1.1 vs 4.4 ±0.5 × 10 −5ml/s g ). Brain concentrations of monosaccharides and polyols were normalized as compared to the myo-inositol treated control group and nerve concentrations of glucose, sorbitol, and fructose were significantly increased. Myo-inositol treatment leads to a normalization of blood-brain barrier permeability; it is suggested that myo-inositol exerts a restituting effect upon Na +/K +-ATPase activity of the cerebral endothelial cells.

Effect of myo-inositol and T3 on myocardial lipids and cardiac function in streptozocin-induced diabetic rats.

Numerous experimental studies have implied a link between diabetes-induced abnormal lipid buildup in the myocardium and the development of cardiomyopathy. Because the diabetic state in rats is associated with lowered T3 (triiodothyronine) and T4 levels and because diabetic patients excrete large amounts of myo-inositol, a lipotropic agent, we investigated the effects of myo-inositol and T3 on the elevated myocardial lipid levels and depressed cardiac performance of streptozocin (55 mg/kg i.v.)-induced diabetic (STZ-D) rats. myo-inositol (2.5 g.kg-1.day-1 in the drinking water) and T3 (30 micrograms.kg-1.day-1 s.c.) were given for an 8-wk period 3 days after diabetes induction. Untreated diabetic rats were characterized by a decreased rate of body weight gain, hyperglycemia, and hypoinsulinemia, which were not altered after myo-inositol and/or T3 treatment. Thyroid status of diabetic animals was normalized by T3 alone or in combination with myo-inositol but not by myo-inositol alone. The elevations in plasma and myocardial lipids associated with the diabetic state were prevented by myo-inositol treatment. However, the plasma lipid and myocardial cholesterol levels in diabetic rats remained elevated or were further increased with treatment with T3 or myo-inositol plus T3. myo-inositol treatment partially improved cardiac performance in STZ-D rats. T3 treatment alone did not prevent cardiac dysfunction in diabetic rats. There was, however, some improvement in heart function in the groups treated with both myo-inositol and T3, coinciding with a significant decrease in the myocardial triacylglycerol level. The data indicate that a possible correlation may exist between elevated myocardial triacylglycerol levels and cardiac dysfunction in diabetic rats.

Structure and function of phosphatidylglycerol-deficient lung surfactant.

The structure and properties of phosphatidylglycerol-deficient lung surfactant were examined using the myoinositol-treated rat as an experimental model. Hyperinositolemia was produced in pregnant rats (and their fetuses) by the administration of myoinositol throughout the final 5 days of gestation. Weight gain by pregnant rats during this period was reduced significantly as a result of myoinositol treatment. On day 21 of gestation, the number of type II cells in sections of lungs from fetuses of myoinositol-treated rats was not significantly different from that of fetuses of saline-treated rats. The profile area occupied by lamellar bodies, however, was significantly decreased in type II cells of fetuses from myoinositol-treated rats. There also was an apparent decrease in the size of lamellar bodies in the lungs of hyperinositolemic fetuses, but this was not accompanied by alterations in the structure of the tubular myelin form of surfactant present in fetal alveoli. Nonpregnant adult rats treated with myoinositol exhibited no gross respiratory impairment, and the recovery of total phospholipid in their alveolar lavage fluid was indistinguishable from that of saline-treated rats. In contrast, the phosphatidylglycerol content of the lavage fluid was decreased and the phosphatidylinositol content was increased as a result of myoinositol treatment. Furthermore, the molar ratio of palmitate to stearate esterified in phosphatidylglycerol was decreased (from 6.2 to 1.4) after myoinositol treatment. The palmitate/stearate ratio for phosphatidylinositol, however, tended to increase after myoinositol treatment. Pressure-volume relationships for freshly excised lungs of myoinositol-treated rats were not significantly different from those for lungs of saline-treated rats. Similarly, the surface-active properties of phosphatidylglycerol-deficient surfactant, measured in vitro by use of a surface balance, were not different from those of normal surfactant. These data indicate that phosphatidylglycerol-deficient surfactant has normal surface activity, and that the apparent requirement for phosphatidyglycerol for normal respiration in the neonate is likely not related directly to surface activity.

Reversal of deficits in axonal transport and nerve conduction velocity by treatment of streptozotocin-diabetic rats with myo-inositol

This study examined the effects of myo-inositol treatment on the deficits of motor nerve conduction velocity and of axonal transport of choline acetyltransferase in rats with streptozotocin-induced diabetes. Motor nerve conduction velocity was measured in seven groups of male rats. Two groups formed nondiabetic controls; one survived for 3 and the other for 6 weeks, then motor nerve conduction velocity was again measured and the accumulation of choline acetyltransferase activity proximal to a 24-h sciatic nerve constriction was estimated. The other five groups were rendered diabetic and subjected to similar measurements. Two diabetic groups were untreated and survived 3 or 6 weeks. The other three groups received myo-inositol for 1, 2, and 3 weeks, respectively, commencing 21 days after induction of diabetes. These groups survived for 4, 5, or 6 weeks, respectively. In all groups surviving for longer than 3 weeks an interim measurement of motor nerve conduction velocity was made 21 days after the start of the experiment (immediately before onset of treatment in the treated groups). In these groups a third measurement was made on the day before death. At death, choline acetyltransferase accumulation was measured and the remainder of the sciatic nerves was assayed for sorbitol and myo-inositol. In the two untreated diabetic groups we found reduced motor nerve conduction velocity, a deficit in the accumulation of choline acetyltransferase proximal to the sciatic nerve constriction, and a marked build-up of nerve sorbitol and a depletion of nerve myo-inositol. All three treated groups showed a reversal of this myo-inositol depletion without a reduction in the nerve sorbitol content. One week of treatment was without effect on nerve conduction velocity or axonal transport. In the 2-week treatment group axonal transport of choline acetyltransferase was similar to controls but the nerve conduction deficit was not reversed. After 3 weeks of treatment choline acetyltransferase accumulation was slightly greater than controls and the motor nerve conduction velocity had increased significantly from the pretreatment value (after 3 weeks' diabetes) and was not significantly less than the prediabetic value.

Composition and surface activity of normal and phosphatidylglycerol-deficient lung surfactant.

The possibility that pulmonary surfactant, characterized by a phosphatidylglycerol deficiency, as in early fetal life, might have inferior surface properties was evaluated. We obtained this specific surfactant from adult rabbits by withholding glucose and giving them an excess of myoinositol by mouth and intravenously. Controls were given a similar quantity of glucose. The myoinositol resulted in a drastic reduction of surfactant phosphatidylglycerol, from 7.2 to 0.3% of phospholipids, and a corresponding increase in phosphatidylinositol from 4.8 to 11.3%. In addition, the myoinositol treatment increased the myoinositol that was disaturated from 18.5 to 27.3% (p less than 0.05). The corresponding figures for disaturated phosphatidyl-choline were 56.0 and 60.5%, respectively (NS). The myoinositol treatment for 4 days increased the pool size of alveolar surfactant by 32% (p less than 0.01). The surface activity was studied with modified Wilhelmy balance and the pulsating bubble surfactometer. Surfactant containing phosphatidylinositol rather than phosphatidylglycerol was not inferior, as compared to surfactant that contained phosphatidylglycerol (minimum surface tension: 2.0 versus 2.2 mN X m-1; collapse rate at 10 nM X m-1: 1.85 versus 1.95 min-1; rate of adsorption from subphase to surface: 32 versus 35 mN X m-1 X 30 s-1), nor was there a difference in the ability of the two surfactants to improve lung stability of 27-day-old rabbit fetuses (air retention at 35 cm H2O: 1.8 versus 1.8 ml/30 g; air retention at 0 cm H20: 0.8 versus 0.9 ml/30 g). We conclude that phosphatidylinositol surfactant does not have inferior surface properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Myo-inositol and sorbitol metabolism in relation to peripheral nerve function in experimental diabetes in the rat: the effect of aldose reductase inhibition.

A possible relationship between increased sorbitol concentration and decreased myo-inositol concentration in peripheral nerves of diabetic rats has been examined. To this end, sorbinil, an aldose reductase inhibitor, was used either to prevent or reverse elevation of nerve sorbitol concentration in diabetic rats. Sorbinil treatment at 20 mg . kg-1 . day-1 prevented elevation of nerve sorbitol levels in early diabetes and reduced sorbitol concentration from 2.38 to 0.51 mumol/g in rats diabetic for 10 weeks. This treatment reduced the increase in nerve fructose concentration and prevented the reduced myo-inositol concentration found in diabetic rat nerve (control 3.63, diabetic 2.40, diabetic/sorbinil, 3.56 mumol/g). Sorbinil treatment did not prevent a significant slowing of motor-nerve conduction velocity at 10 weeks although treatment reduced the extent of slowing. Sorbinil treatment at 25 mg . kg-1 . day-1 reduced elevated sorbitol and fructose concentrations in diabetic in diabetic rat nerve and normalised myo-inositol concentration. Myo-Inositol treatment at 650 mg . kg-1 . day-1 did not affect the elevated concentrations of sorbitol, fructose or glucose in peripheral nerves of diabetic rats, but it did restore reduced myo-inositol concentration. Both sorbinil and myo-inositol treatment partially reversed the slowing of motor-nerve conduction velocity in diabetic rats. These results are discussed in relation to the involvement of sorbitol and myo-inositol metabolism in the aetiology of diabetic neuropathy.

Analysis of labeling and clearance of lung surfactant phospholipids in rabbit. Evidence of bidirectional surfactant flux between lamellar bodies and alveolar lavage.

Turnover and clearance of lung surfactant phospholipids were studied with particular reference to myoinositol-induced perturbation in the acidic phospholipids. Administration of myoinositol decreased [(3)H]palmitate and [(32)P]phosphate incorporation into phosphatidylglycerol by 80-90% in whole lung, and by 94-99% in lamellar bodies and in alveolar lavage. The increased incorporation of radioactive isotopes into phosphatidylinositol following myoinositol, was inverse to the decrease in phosphatidyl-glycerol incorporation. Myoinositol treatment affected neither content nor labeling of phosphatidylcholine or disaturated phosphatidylcholine as studied within 50 h of administration. Phosphatidylglycerol was pulse labeled by intravenous [(32)P]phosphate and [(3)H]palmitate, followed by myoinositol. The biological half-lives of phosphatidylglycerol in the microsomal fraction, lamellar bodies, and alveolar lavage were 1.6, 4.6, 5.4 h (with (3)H), and 2.8, 6.5, 7.0 h (with (32)P), respectively.(32)P-labeled lung surfactant tracer was applied to the airways in saline suspension and the clearance of phospholipid radioactivity was measured in alveolar lavage, alveolar macrophages, lamellar bodies and lung homogenates. The clearance rates of phosphatidylcholine, disaturated phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol as studied in whole lung over 6 h were 3.4-5.8% h. Only a small amount of phospholipid radioactivity was recovered in the alveolar macrophage fraction (including bis-[monoacylglycerol]phosphate). Phospholipid radioactivity in alveolar lavage fell to 40-70% of the maximum during the 1st h, and to 5-18% over the next 6 h. During 2 h after the application of phospholipids, the radioactivity in the lamellar body fraction increased, and the specific radioactivities approached those in alveolar lavage. The association of phosphatidylglycerol with lamellar bodies was unaffected by myoinositol. Phosphatidylinositol entered more slowly than did phosphatidylglycerol from microsomes to the alveolar lavage fraction, and from alveolar lavage to lamellar bodies. These differences may be of importance regarding the poor performance of phosphatidylinositol-containing surfactant at birth. Further investigations are needed to clarify the possible role for the postulated bidirectional surfactant flux between the lamellar body and alveolar lavage fractions in maintaining the activity of surfactant.