Cause and effect of ischaemia in chronic experimental diabetic neuropathy

Gait characteristics in people with type 2 diabetes mellitus

Sixteen control subjects and 15 subjects with type 2 diabetes were examined to compare gait characteristics during walking in a linear path and in turns of 0.33 and 0.66 m diameter. Subjects were excluded if there was diminished sensation in the feet or impairment of strength in the legs. This was done to isolate the effect of diabetes gait independent of loss of sensation. Gait was assessed through contact sensors on the foot, video, and two axis accelerometers mounted bilaterally on the head, shoulders, hips, knees and ankles. The results of these experiments showed that subjects with diabetes walked significantly slower (P<0.05) than control subjects and with a wider stance (P<0.01), both for walking in a linear path (velocity of subjects with diabetes was 62.2% that of controls and stance was 134.9% wider than controls) and when making turns (velocity 50.6% of controls and stance 120.1% wider than that of controls). Accelerometry showed increased flexion/extension and lateral movement of the major joints in subjects with diabetes during both walking in a linear path and turns compared to control subjects. Part of the increased movement at the joints in the subjects with diabetes was due to tremor in both the 8 Hz and 16 Hz bands. These findings suggest that at least some of the increased joint movement during walking in people with diabetes is likely neurological in origin and not related to muscle weakness or loss of sensation in the feet.

Effect of aldose reductase inhibition on cardiovascular reflex tests in patients with definite diabetic autonomic neuropathy over a period of 2 years

The potential of the aldose reductase inhibitor tolrestat to ameliorate definite diabetic autonomic neuropathy (DAN), as defined by standard cardiovascular autonomic function tests, was evaluated in 35 patients over a period of 2 years, with repeated measurements at 3-month intervals. The effect of tolrestat (200 mg a day) was compared with that of placebo on 35 controls with diabetes mellitus, of similar age, gender, and glycemic control. In the placebo group, a significant deterioration of the indices, with the exception of Valsalva ratio, was recorded, while tolrestat induced a significant beneficial change in the values of most standard cardiovascular reflex tests, in comparison to baseline and placebo. The deep breathing tests (expiration-inspiration ratio, standard deviation, and mean circular resultant of R-R intervals), postural index, and postural hypotension were favorably affected. Three of 35 patients on tolrestat (8.6%) developed high transaminases levels (more than threefold the upper normal limit) and were withdrawn from the study. In conclusion, tolrestat improved autonomic nervous system function in patients with definite DAN, in comparison to baseline and placebo. The clinical importance of this finding needs further investigation.

Improvement in blood flow and diabetic neuropathy by thromboxane A2 dual blocker KDI-792

We studied the effect of a thromboxane A2 (TXA2) dual blocker KDI-792 on skin blood flow as well as on the peripheral nerve function of nine diabetics with neuropathy. After administration of KDI-792, there was no change in urinary TXB2; however, urinary 6-keto-prostaglandin (PG) F1 alpha increased significantly. Nerve conduction velocity (NCV) and vibration perception threshold (VT) in the four extremities improved significantly, as did deep skin temperature and skin blood flow. The degree of improvement in sensory NCV in the lower extremities correlated significantly with that of deep skin temperature in the toes and the degree of improvement of VT in the lower extremities correlated well with that of deep skin temperature in the soles and of skin blood flow in the toes. Based on these findings, treatment of diabetic neuropathy with a TXA2 dual blocker appears to increase PGI2 production, improving blood flow, and resulting in improvement of nerve functions.

Vascular factors in diabetic neuropathy

Despite considerable research we still do not have a comprehensive explanation for the pathogenesis of diabetic neuropathy. Although chronic hyperglycaemia is almost certainly involved, it is not known whether the primary pathology is metabolic, microvascular, or an interaction between the two. Hyperglycaemia-induced polyol pathway hyperactivity associated with nerve sorbitol accumulation and myo-inositol depletion may play a part in the genesis of diabetic neuropathy. The case for microvascular disease in diabetic neuropathy is now strong. Fibre loss in human sural nerve is multifocal, suggesting ischaemia. The degree of vessel disease has been related to the severity of neuropathy. People with chronic obstructive pulmonary disease develop the so called "hypoxic neuropathy" in which similar microvascular changes occur as in diabetic neuropathy. In rats with experimental diabetic neuropathy nerve blood flow is reduced and oxygen supplementation or vasodilator treatment improved the deterioration in conduction velocity and nerve blood flow. Similarly, in human diabetic neuropathy, there is impaired nerve blood flow, epineurial arterio-venous shunting and a reduction in sural nerve oxygen tension. At what stage during the development of nerve damage these changes occur is yet to be determined.