Studies of sorbinil on axonal transport in streptozotocin-diabetic rats

Cilostazol prevents impairment of slow axonal transport in streptozotocin-diabetic rats

We studied the effects of cilostazol, an antiplatelet and vasodilating agent, on axonal transport patterns of cytoskeletal proteins in the motor fibers of sciatic nerve of streptozotocin-induced diabetic rats. Proteins labeled with L-[35S]methionine in 6-mm consecutive segments of the nerve were analyzed electrophoretically following fractionation into Triton-soluble and-insoluble subpopulations. Transport rates of proteins (particularly neurofilaments) in slow component a were reduced by 50% 2 weeks after labeling (4 weeks after streptozotocin). An apparent reduction of tubulin and actin was observed at later intervals after induction of diabetes. Actin transported in slow component b was also impaired, though to a lesser extent than in component a. Cilostazol prevented transport impairment of both slow components a and b without affecting hyperglycemia or reduction in body weight gain. These results suggest that in sciatic motor fibers early defects in slowly transported proteins are more marked in slow component a, and that impairment may be caused primarily by hemodynamic abnormalities.

The role of axonal cytoskeleton in diabetic neuropathy

The neuropathy associated with diabetes includes well documented impairment of axonal transport, a reduction in axon calibre and a reduced capacity for nerve regeneration. All of those aspects of nerve function rely on the integrity of the axonal cytoskeleton. Alterations in the axonal cytoskeleton in experimental diabetes include an insulin-dependent non-enzymatic glycation of actin that is reflected in increased glycation of platelet actin in the clinical situation. There is a reduced synthesis of mRNA for the isoforms of tubulin that are associated with nerve growth and regeneration and an elevated non-enzymatic glycation of peripheral nerve tubulin in both diabetic patients and diabetic animals. mRNAs for neurofilament proteins are selectively reduced in the diabetic rat and post-translational modification of at least one of the neurofilament proteins is altered. There is some evidence that altered expression of isoforms of protein kinases may contribute to these changes.

The effect of an aldose reductase inhibitor on cardiovascular performance in patients with diabetes mellitus

Because some aldose reductase inhibitor studies have demonstrated clinical improvement in scored neurological signs and symptoms of diabetic neuropathy, a prospective study of the effect on cardiovascular performance of sorbinil 250 mg/day for 12 months was conducted on patients with diabetic autonomic neuropathy who were free of atherosclerotic coronary artery disease and/or cardiomyopathy. After 1 year of treatment, the study group (n = 14) demonstrated significant improvement in both the resting cardiac output (P = 0.02), and the maximal cardiac output (P = 0.03). This observation suggests that the use of an aldose reductase inhibitor may be useful in treating suboptimal cardiovascular performance in patients with diabetic cardiac autonomic neuropathy.

Sensory nerves and urinary bladder function: effects of diabetes, capsaicin and acrylamide treatment

1. A comparison was made of the proposed neurotoxic effects of acrylamide, capsaicin, and diabetes on rat urinary bladder pressure responses elicited by infusion of buffer into the organ (distension). 2. Treatment with capsaicin or acrylamide completely abolished the bladder pressure responses. 3. After 4 weeks of diuresis equivalent to that of the diabetic model, the pressure response was markedly diminished compared to control. This response was greatly increased following L-DOPA, which augments the micturition reflex. 4. After 4 weeks of streptozoticin-induced diabetes, the pressure response was slightly diminished compared to control and most closely resembled the response from the diuretic group treated with L-DOPA.

Axonal transport of choline acetyltransferase and 6-phosphofructokinase activities in genetically diabetic mice

This study examined the anterograde axonal transport of activities of the cytoplasmic enzymes choline acetyltransferase and 6-phosphofructokinase in genetically diabetic C57BL/Ks (db/db) mice and their nondiabetic (+/?) littermates. Diabetic mice exhibited marked reductions in the accumulation of both choline acetyltransferase and 6-phosphofructokinase activity against a constriction of the left sciatic nerve (38% and 51% of nondiabetic values, respectively). Enzyme activities per unit length of unconstricted nerve were not different from those of nondiabetic mice. The nerves of diabetic mice did not accumulate measurable amounts of sorbitol or fructose and showed no myo-inositol depletion. Thus this study concludes that, in diabetic mice, the deficits in anterograde axonal transport of these two enzymes do not arise from the accumulation of sorbitol and fructose nor from depletion of nerve free myo-inositol.

Fast anterograde axonal transport of choline-containing lipids in rats with experimental diabetes

This study was designed to measure the velocity of axonal transport of choline-containing lipids in sensory and motoneurones of control rats and rats with streptozotocin-induced diabetes of 3 weeks duration. An additional experiment was performed in which nerves from control and diabetic rats were maintained in vitro during the period between injection of isotope in the nerve cell body region and arrest of transport. This was done to preclude the effects of temperature differences between controls and diabetics. None of these experiments revealed defects of velocity of fast orthograde transport of labelled lipids in the diabetic rats. The results indicate that short-term experimental diabetes has no effect on the velocity of fast anterograde axonal transport of choline-containing lipids. The findings are discussed in relation to similar studies on the fast anterograde axonal transport of proteins.

Treatment with an aldose reductase inhibitor can reduce the susceptibility of fast axonal transport following nerve compression in the streptozotocin-diabetic rat

The effect of treatment with an aldose reductase inhibitor on the susceptibility of peripheral nerves to compression was studied in rats made diabetic by the injection of streptozotocin (50 mg.kg-1). The response to nerve compression was determined in untreated diabetic rats after 22 days of diabetes and compared with the response in two similar groups of diabetic rats which had been treated with the aldose reductase inhibitor 'Statil' (ICI 128436; 25 mg.kg-1.day-1 orally) either from the induction of diabetes or for 7 days prior to nerve compression. Two groups of non-diabetic rats were treated with 'Statil' for either 22 days or 7 days to act as controls. Inhibition of fast axonally transported proteins was induced by local compression of the sciatic nerves 4 h after application of 3H-leucine to the motor neurone cell bodies in the spinal cord. The inhibition of fast axonal transport was quantified by calculation of a transport block ratio. Compression at 30 mmHg for 3 h induced a significantly greater (p less than 0.05) inhibition of axonal transport at the site of compression in nerves of untreated diabetic rats (transport block ratio 0.96 +/- 0.24, n = 8) than in nerves of control rats treated with the aldose reductase inhibitor for either the shorter time of 7 days (0.71 +/- 0.17, n = 10) or the longer time of 22 days (0.69 +/- 0.08, n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)