Brain imaging correlates of mild cognitive impairment and early dementia in patients with type 2 diabetes mellitus

BACKGROUND AND AIMS

The risk of mild cognitive impairment and dementia is increased in type 2 diabetes mellitus (T2DM). We aimed to identify the neuroanatomical correlates of mild cognitive impairment (MCI) and early dementia in patients with T2DM, using advanced multimodal MRI.

METHODS AND RESULTS

Twenty-five patients (≥70 years) with T2DM and MCI (n = 22) or early dementia (n = 3) were included. The reference group consisted of 23 patients with T2DM with intact cognition. All patients underwent a 3 T MRI. Brain volumes and white matter hyperintensity volumes were obtained with automated segmentation methods. White matter connectivity was assessed with diffusion tensor imaging and fiber tractography. Infarcts and microbleeds were rated visually. Compared to patients without cognitive impairment, those with impairment had a lower grey matter volume (effect size: -0.58, p=0.042), especially in the right temporal lobe and subcortical brain regions (effect sizes: -0.45 to -0.91, false discovery rate corrected p < 0.05). White matter volume (effect size: -0.47, p = 0.11) and white matter connectivity (effect size: 0.55, p = 0.054) were also reduced in patients with versus without cognitive impairment, albeit not statistically significant. White matter hyperintensity volumes and occurrence of other vascular lesions did not differ between the two patient groups.

CONCLUSION

In patients with T2DM, grey matter atrophy rather than vascular brain injury appears to be the primary imaging correlate of MCI and early dementia.

The calcium hypothesis of brain aging and neurodegenerative disorders: significance in diabetic neuropathy

In this paper we discuss the possible role of disturbed neuronal calcium homeostasis in brain aging and diabetic neuropathy. Disturbances in the homeostasis of cytosolic calcium concentration have been implicated in the pathogenesis of various acute and chronic neurodegenerative disorders and in brain aging. Obviously, these disorders do not all share the same pathogenetic mechanisms. However, a number of the pathogenetic mechanisms involved have in common that they may ultimately cause loss of calcium homeostasis, leading to neuronal damage. By identifying the possible role of calcium, treatment strategies can be developed that may be effective in a variety of neurodegenerative disorders, despite differences in their pathogenesis. Our aim is to explore some of the similarities that exist between a number of processes that have been implicated in the pathogenesis of brain aging and diabetic neuropathy, including ischemia, oxidative stress and non-enzymatic protein glycosylation. Each of these factors might impair neuronal calcium homeostasis, and ultimately lead to neurodegenerative changes. By discussing the putative role of these specific factors in two apparently dissimilar disorders, such as brain aging and diabetic neuropathy, we obviously do not intend to suggest that their pathogenesis is one and the same. Instead, by examining the relative role of these factors in two different types of neurodegenerative disorders we would like to emphasize the importance of disturbances in cellular calcium homeostasis as a final common pathway in neuronal damage resulting from various noxious events.

Beneficial effect of the Ca2+ antagonist, nimodipine, on existing diabetic neuropathy in the BB/Wor rat

1. Neuropathy is a frequently diagnosed complication of diabetes mellitus. Effective pharmacotherapy is not available. 2. The spontaneously diabetic BB/Wor rats develop secondary complications like neuropathy as do human diabetic patients. 3. BB/Wor rats treated with insulin via a subcutaneous implant show a significant impairment of sensory and motor nerve conduction velocity 6 weeks after the onset of diabetes mellitus. 4. Intraperitoneal treatment of diabetic BB/Wor rats with the Ca2+ antagonist, nimodipine (20 mg kg-1), from week 6 onwards every 48 h for a period of 6 weeks resulted in a significant increase of sensory and motor nerve conduction velocity. 5. Twelve weeks after the onset of diabetes mellitus BB/Wor rats show a 40% impairment of sciatic nerve blood flow as compared to the non-diabetic age-matched controls. Treatment with nimodipine (20 mg kg-1) from week 6 onwards significantly increased the sciatic nerve blood flow as compared to placebo-treated diabetic BB/Wor rats. 6. The adrenergic responsiveness of the vasa nervorum of the sciatic nerve to tyramine and phenylephrine was investigated as a parameter for autonomic neuropathy. 7. The fact that nimodipine treatment restored the reduced response to tyramine independently of the reduced postsynaptic phenylephrine responsiveness indicates that nimodipine improves adrenergic responsiveness mainly at the presynaptic level.

Influence of dihydropyridines on the recovery of sensory function after a caudal nerve crush in the rat

Nimodipine, a Ca2+ antagonist of the dihydropyridine type, is known to display a variety of neuropharmacological effects including facilitation of functional recovery following a crush of the sciatic nerve in the rat. In the present study, we investigated the effect of nimodipine, nifedipine (another Ca2+ antagonist with a lesser penetration in neural parenchyma) and Bay K 8644 (a Ca2+ agonist) treatment following a crush of the major caudal nerve. The caudal nerve crush model was used because this model provided the opportunity for longitudinal evaluation of nerve repair. Recovery of sensory function was tested by vocal reaction following local stimulation with a small electric current. The results suggest that nimodipine (20 mg/kg) both enhances the initial sprouting response and exerts an effect on the outgrowth rate of newly developed sprouts. Neither nifedipine (20 mg/kg) nor Bay K 8644 (0.5 mg/kg) had any influence on the recovery of nerve function. Furthermore, it was demonstrated that nimodipine, nifedipine and Bay K 8644 had no influence on nerve conduction velocity of the non-injured sciatic nerve indicating that there was no general beneficial effect of these agents on the peripheral nerve.