Ikuo Hatanaka

Effect of Prostaglandin E1 Analogue TFC 612 on Diabetic Neuropathy in Streptozocin-Induced Diabetic Rats Comparison With Aldose Reductase Inhibitor ONO 2235

The effect of a newly developed oral agent, prostaglandin E1 (PGE1) analogue TFC 612, on diabetic neuropathy was studied by giving it for 6 wk to streptozocin-induced diabetic rats that had been diabetic for 3 mo and was compared with the effects of aldose reductase inhibitor ONO 2235. Although both compounds improved decreased motor nerve conduction velocity, the effect of TFC 612 continued during the 6 wk of treatment, whereas that of ONO 2235 became weaker from wk 4. The abnormality in sciatic nerve sorbitol and myo-inositol levels was reversed with ONO 2235, whereas it was unchanged with TFC 612. With the laser Doppler flowmetry technique, a decrease in the sciatic nerve blood flow in diabetic rats was shown to improve with both compounds, but TFC 612 had a greater effect than ONO 2235, and the increased lactate level of the diabetic nerve was corrected with both compounds, suggesting that both may be associated with the amelioration of ischemia in the diabetic endoneurium. Both TFC 612 and ONO 2235 partially but significantly normalized decreased fiber size in diabetic rats. On the other hand, TFC 612 completely normalized the dilated lumen area in diabetic rats, whereas ONO 2235 did not. These results suggest that the PGE, analogue TFC 612 has a significant effect on diabetic neuropathy, possibly via vasotropic action, and may be a potent compound for the treatment of diabetic neuropathy.

Effect of a new aldose reductase inhibitor, (E)-3-carboxymethyl-5-[(2E)-methyl-3-phenylpropenylidene]rhodanine (ONO-2235) on peripheral nerve disorders in streptozotocin-diabetic rats.

SummaryA new aldose reductase inhibitor, (E)-3-carboxy-methyl-5-[(2E-methyl-3-phenylpropenylidene]rhodanine (ONO-2235) was administered orally to streptozotocin-diabetic rats (60 mg/kg IV) for 14 days and its effect on motor nerve conduction velocity studied. The compound significantly improved motor nerve conduction velocity of diabetic rats at a minimal dose of 10 mg · kg-1 · day-1 (treated 28.8±0.5 versus untreated 23.2±4.7 m/s, p < 0.01). The sorbitol content of the sciatic nerve and red blood cells measured after 2 weeks was concomitantly reduced in ONO-2235-treated rats (sciatic nerve: 120±13 versus 595±146 nmol/g wet weight; red blood cell: 91±21 versus 165±39 nmol/g haemoglobin; p < 0.01 in both 20 mg · kg-1 · day-1-treated versus untreated animals). These results suggest that sorbitol accumulation might contribute to the development of peripheral nerve dysfunction in acutely diabetic animals and the new aldose reductase inhibitor could be a potential drug for therapy of diabetic neuropathy.

Prevention of peripheral nerve dysfunction by an aldose reductase inhibitor in streptozotocin-diabetic rats.

A potent inhibitor of aldose reductase, (E)-3-carboxy-methyl-5-[(2E)-methyl-3-phenylpropenylidene]rhodanin e (ONO-2235), was orally administered at a dose of 20 mg X kg-1 X d-1 for 2 weeks to streptozotocin-diabetic rats from the beginning of the diabetic state, ie, 24 hours after streptozotocin injection. The impairment of motor nerve conduction velocity (MNCV) of the tail nerve found in nontreated diabetic rats was apparently prevented by the treatment with the aldose reductase inhibitor (24.5 +/- 0.4 v 29.0 +/- 1.4 m/s on day 14, P less than 0.005). Those diabetic rats treated with the compound actually showed an age-dependent increase in MNCV similar to that of normal control rats (25.5 +/- 1.5 v 26.4 +/- 1.0 m/s on day 7, 29.0 +/- 1.4 v 29.4 +/- 1.3 m/s on day 14, treated v normal, not statistically significant on both days). The sorbitol content of the sciatic nerve excised from ONO-2235-treated diabetic rats (0.067 +/- 0.018 nmol/g wet weight) was significantly lower than that of the nontreated diabetic rats (1.309 +/- 0.080 nmol/g wet weight, P less than 0.001) but significantly higher than that of normal control rats (0.229 +/- 0.015 nmol/g wet weight, P less than 0.001). These results suggest that the reduction in MNCV noted in the experimental diabetic animals is not the result of retarded maturation of peripheral nerves but of metabolic derangement caused by the diabetic state, which can be prevented by suppressing sorbitol accumulation in nerve tissue. It also appears that there may be a threshold level of sorbitol accumulation that causes the impairment of nerve conduction velocity.

A new prostaglandin E1 analogue (TFC-612) prevents a decrease in motor nerve conduction velocity in streptozocin-diabetic rats.

A new prostaglandin E1 analogue (TFC-612) was orally given to streptozocin-diabetic rats for 4 weeks after the induction of diabetes and its effects on motor nerve conduction velocity were studied. The compound significantly prevented a decrease of the velocity but did not reverse abnormal sorbitol and myo-inositol contents of the sciatic nerve. The results suggest that TFC-612 has a potent effect on diabetic nerve dysfunction via other mechanism than the correction of sorbitol and myo-inositol metabolisms and could be a potential compound for therapy of diabetic polyneuropathy.

SKIN BIOPSY AS A BENEFICIAL PROCEDURE FOR MORPHOLOGICAL EVALUATION OF DIABETIC NEUROPATHY

In an attempt to evaluate the morphological abnormalities of dermal non‐myelinated nerve fibers of diabetics and elucidate the pathogenesis of diabetic peripheral neuropathy, the terminal part of peripheral nerve in the upper dermis was observed on electron microscopy using skin samples biopsied in 10 diabetics with symptomatic neuropathy and 6 age‐matched controls. In diabetics, the density of nerve fibers was significantly lower than in controls. In addition, swelling, lytic change and vacuolation in the axon, multiplication of basement membrane of the Schwann cell and Schwann cell cluster devoid of axon were more frequently observed in diabetics. The Schwann cell did not show significant structural alterations. These findings suggest that the axon is primarily involved, at least in the terminal region of nerve fiber, in diabetic peripheral neuropathy. It is also concluded that the skin biopsy technique is unharmful, cosmetically not troublesome and might be beneficial for studying peripheral neuropathies including diabetic neuropathy.

Chronically streptozocin-diabetic monkey does not closely mimic human diabetic neuropathy.

In order to evaluate the value of diabetic Japanese monkeys (Macaca fuscatus) as an animal model for studying the pathogenesis of diabetic neuropathy, morphological examinations were performed on myelinated nerve fibers and endoneurial microvessels at three levels of the lower limb nerve in eight streptozocin (STZ)-diabetic monkeys with the duration of diabetes up to 36 months and in four roughly age-matched control monkeys using a computer-assisted image analyzer. Nerve fiber loss was not found, although a tendency for nerve fiber atrophy was found in diabetic monkeys. Endoneurial microvessels did not show either endothelial or pericyte proliferation or basement membrane thickening. The results suggest that chronically STZ-diabetic Japanese monkeys with the duration of diabetes up to 36 months might be useful for studying diabetic axonopathy, but do not closely mimic the nerve pathology found in human diabetic neuropathy.

Thyrotropin-releasing hormone reduces myo-inositol content in rat cerebellum pretreated with lithium.

Abstract: The effect of thyrotropin‐releasing hormone (TRH) and lithium on myo‐inositol metabolism has been assessed in rat cerebral cortex, cerebellar cortex, and sciatic nerves. Sprague‐Dawley male rats were injected subcutane‐ously with 10 mEq/kg of LiCl and intraperitoneally with 10 mg/kg of TRH‐tartrate, alone or in combination. Either lithium or TRH alone had little effect on the myo‐inositol concentration in cerebellar cortex, whereas the combination of lithium and TRH significantly lowered the level. The myo‐inositol level of cerebellar cortex reached its nadir (70% of values in untreated control rats) 30 min after addition of TRH and then returned to the control level at 90 min. In cerebral cortex, both lithium alone and lithium plus TRH significantly reduced the myo‐inositol level. No effect was seen on the myo‐inositol concentration in sciatic nerves with these regimens. These results suggested that the pharmacological dose of TRH activated phosphatidylinositol turnover in rat cerebellar cortex and subsequently reduced the myo‐inositol level in the presence of lithium.

Morphological characteristics of dermal diabetic microangiopathy

In an attempt to characterize dermal diabetic microangiopathy, dermal microvessels were qualitatively and quantitatively assessed in 26 healthy control subjects and 47 non-insulin-dependent diabetic patients. Basement membrane thickness (BMT) was significantly greater and the homogeneous BM more frequent in diabetic than in control microvessels. BMT did not change with duration of diabetes but significantly decreased with age and onset age of diabetes, suggesting either a different process of BM thickening with respect to age in diabetic dermal microvessels or the implication of genetic influence on the pathogenesis of dermal diabetic microangiopathy. Endothelial cell hyperplasia was not noted in dermal diabetic microvessels. In view of the fact that the hyperplasia has been reported in other tissues and is closely associated with diabetic microangiopathy, the nature of dermal microvessels or endothelial cells or the milieu around dermal microvessels might be different from other organs.