A factor in the serum of diabetic patients inhibits microtubule formation.

The effect of serum from non-diabetic patients, diabetics without neuropathy and diabetics with significant neuropathy on the ability of pig brain microtubule proteins to polymerize in vitro to microtubules was observed. The extent of polymerisation on the second and third cycles of polymerisation was significantly reduced in the presence of diabetics' serum compared with non-diabetics' serum. No significant difference between the serum samples from diabetics with and without neuropathy could be found. The finding suggests the presence of a factor in the serum of diabetics, whether or not they have neuropathy, which will impair microtubule formation in vitro.

Diabetic rat serum has an increased capacity to inhibit brain microtubule formation in vitro.

The assembly of pig brain microtubule proteins was measured in vitro in the presence of serum from control rats and rats that had been rendered diabetic with 50 mg/kg streptozotocin 14 d previously. Control serum inhibited total microtubule assembly and increased the lag time before assembly commenced. Serum from diabetic animals was significantly more potent in both respects. The effect on lag time was reproduced in a predominantly albumin-containing fraction of serum that had been fractionated by affinity chromatography. Glycosylation of rat albumin in vitro led to an increase in its ability to increase polymerization lag time, but the concentration of albumin required was greater than that found in the serum fractions. The results indicate that diabetic serum contains factors that can adversely affect microtubule formation and that part of this effect may be caused by the presence of glycosylated albumin. This phenomenon may underlie some of the complications associated with diabetes.