Martin Berghoff

Vascular and neural mechanisms of ACh-mediated vasodilation in the forearm cutaneous microcirculation

The relative contribution of endothelial vasodilating factors to acetylcholine (ACh)-mediated vasodilation in the forearm cutaneous microcirculation is unclear. The aims of this study were to investigate the contributions of prostanoids and cutaneous C fibers to basal cutaneous blood flow (CuBF) and ACh-mediated vasodilation. ACh was iontophoresed into the forearm, and cutaneous perfusion was measured by laser-Doppler flowmetry. To inhibit the production of prostanoids, four doses of acetylsalicylic acid (ASA; 81, 648, 972, and 1,944 mg) were administered orally. Cutaneous nerve fibers were blocked with topical anesthesia. Cyclooxygenase inhibition did not change basal CuBF or endothelium-mediated vasodilation to ACh. In contrast, ASA (972 and 1,944 mg) significantly reduced the C-fiber-mediated axon reflex in a dose-dependent fashion. Blockade of C-fiber function significantly reduced axon reflex-mediated vasodilation but did not affect basal CuBF or endothelium-dependent vasodilation. The findings suggest that prostanoids do not contribute significantly to basal CuBF or endothelium-dependent vasodilation in the forearm microcirculation. In contrast, prostanoids are mediators of the ACh-provoked axon reflex.

Neural and endothelial control of the microcirculation in diabetic peripheral neuropathy

Objective: To examine the role played by endothelium-dependent and endothelium-independent vasodilation of the cutaneous microcirculation and their relationship to neural microcirculatory control in type 1 and type 2 diabetic patients. Methods: Acetylcholine and sodium nitroprusside were iontophoresed using a dose–response technique. Endothelium-dependent, endothelium-independent, and C-fiber–mediated vasodilation were measured with a laser Doppler device. Results: Endothelium-dependent vasodilation of the forearm cutaneous microcirculation was attenuated in diabetic subjects. The response was less in type 2 diabetic subjects than in controls (p < 0.005). In contrast, there was no significant difference between type 1 diabetic subjects and controls. There was no significant abnormality in endothelium-independent vasodilation in either diabetic group. The C-fiber–mediated axon reflex in the forearm was impaired in both type 1 and type 2 diabetics, which is consistent with a small-fiber neuropathy (p < 0.005). The duration of diabetes in type 2 diabetics was a significant predictor of the maximum endothelium-mediated vasodilation. Conclusion: Changes in cutaneous blood flow are seen relatively early in the course of diabetic peripheral neuropathy and are characterized by endothelial and neural but not smooth muscle dysfunction. The presence of significant C-fiber impairment in both diabetic groups, together with significantly greater dysfunction in endothelium-dependent vasodilation in type 2 diabetics, suggests that the endothelial function and nitric oxide may play a greater role in the pathogenesis of diabetic peripheral neuropathy in type 2 diabetic patients.

Identification of the variant Ala335Val of MED25 as responsible for CMT2B2: molecular data, functional studies of the SH3 recognition motif and correlation between wild-type MED25 and PMP22 RNA levels in CMT1A animal models

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous disorder. All mendelian patterns of inheritance have been described. We identified a homozygous p.A335V mutation in the MED25 gene in an extended Costa Rican family with autosomal recessively inherited Charcot-Marie-Tooth neuropathy linked to the CMT2B2 locus in chromosome 19q13.3. MED25, also known as ARC92 and ACID1, is a subunit of the human activator-recruited cofactor (ARC), a family of large transcriptional coactivator complexes related to the yeast Mediator. MED25 was identified by virtue of functional association with the activator domains of multiple cellular and viral transcriptional activators. Its exact physiological function in transcriptional regulation remains obscure. The CMT2B2-associated missense amino acid substitution p.A335V is located in a proline-rich region with high affinity for SH3 domains of the Abelson type. The mutation causes a decrease in binding specificity leading to the recognition of a broader range of SH3 domain proteins. Furthermore, Med25 is coordinately expressed with Pmp22 gene dosage and expression in transgenic mice and rats. These results suggest a potential role of this protein in the molecular etiology of CMT2B2 and suggest a potential, more general role of MED25 in gene dosage sensitive peripheral neuropathy pathogenesis.Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous disorder. All mendelian patterns of inheritance have been described. We identified a homozygous p.A335V mutation in the MED25 gene in an extended Costa Rican family with autosomal recessively inherited Charcot-Marie-Tooth neuropathy linked to the CMT2B2 locus in chromosome 19q13.3. MED25, also known as ARC92 and ACID1, is a subunit of the human activator-recruited cofactor (ARC), a family of large transcriptional coactivator complexes related to the yeast Mediator. MED25 was identified by virtue of functional association with the activator domains of multiple cellular and viral transcriptional activators. Its exact physiological function in transcriptional regulation remains obscure. The CMT2B2-associated missense amino acid substitution p.A335V is located in a proline-rich region with high affinity for SH3 domains of the Abelson type. The mutation causes a decrease in binding specificity leading to the recognition of a broader range of SH3 domain proteins. Furthermore, Med25 is coordinately expressed with Pmp22 gene dosage and expression in transgenic mice and rats. These results suggest a potential role of this protein in the molecular etiology of CMT2B2 and suggest a potential, more general role of MED25 in gene dosage sensitive peripheral neuropathy pathogenesis.

Role of immune cells in animal models for inherited neuropathies: facts and visions

Mice heterozygously deficient in the peripheral myelin adhesion molecule P0 (P0+/− mice) are models for some forms of Charcot–Marie–Tooth (CMT) neuropathies. In addition to the characteristic hallmarks of demyelination, elevated numbers of CD8‐positive T‐lymphocytes and F4/80‐positive macrophages are striking features in the nerves of these mice. These immune cells increase in number with age and progress of demyelination, suggesting that they might be functionally related to myelin damage. In order to investigate the pathogenetic role of lymphocytes, the myelin mutants were cross‐bred with recombination activating gene 1 (RAG‐1)‐deficient mice, which lack mature T‐ and B‐lymphocytes. The immunodeficient myelin mutants showed a less severe myelin degeneration. The beneficial effect of lymphocyte‐deficiency was reversible, since demyelination worsened in immunodeficient myelin‐mutants when reconstituted with bone marrow from wild‐type mice. Ultrastructural analysis revealed macrophages in close apposition to myelin and demyelinated axons. We therefore cross‐bred the P0+/− mice with spontaneous osteopetrotic (op) mutants deficient in the macrophage colony‐stimulating factor (M‐CSF), hence displaying impaired macrophage activation. In the corresponding double mutants the numbers of macrophages were not elevated in the peripheral nerves, and the demyelinating phenotype was less severe than in the genuine P0+/− mice, demonstrating that macrophages are also functionally involved in the pathogenesis of genetically mediated demyelination. We also examined other models for inherited neuropathies for a possible involvement of immune cells. We chose mice deficient in the gap junction component connexin 32, a model for the X‐linked form of CMT. Similar to P0‐deficient mice, T‐lymphocytes and macrophages were elevated and macrophages showed a close apposition to degenerating myelin. We conclude that the involvement of T‐lymphocytes and macrophages is a common pathogenetic feature in various forms of slowly progressive inherited neuropathies.

Evidence-based patient information programme in early multiple sclerosis: a randomised controlled trial

Objective To evaluate the efficacy of an evidence-based patient information programme aiming to increase informed choice in patients with early multiple sclerosis (MS). Background Patients with early MS face a number of uncertainties concerning diagnosis, prognosis and effectiveness of immunotherapy. Prior studies suggest that evidence-based patient information combined with group education can promote informed choice in MS patients. Methods A 12-month, six-centre, double-blind randomised controlled clinical trial with 192 patients with a diagnosis of confirmed relapsing-remitting MS or clinical isolated syndrome in Germany. A 4-h interactive evidence-based educational programme was compared with a 4-h MS-specific stress management programme. The primary endpoint was informed choice after 6 months comprising risk knowledge and congruency between attitude towards immunotherapy and actual immunotherapy uptake. Secondary endpoints included autonomy preference, decision autonomy, decisional conflict and satisfaction, anxiety and depression, and number of immunotherapies. Results For the primary endpoint, a significant difference was shown with 50 of 85 (59%) participants in the intervention group achieving informed choice after 6 months compared with 18 of 89 (20%) in the control group (OR 0.2 (95% CI 0.1 to 0.4), p<0.001). Four weeks after the intervention, more participants in the intervention group showed good risk knowledge (difference between groups 39% (95% CI 26% to 53%), p<0.001). There were no significant differences between groups for attitude towards immunotherapy and for immunotherapy uptake. There were trends towards increased autonomy preference after the intervention and increased adherence to immunotherapies in the intervention group. Conclusions The intervention significantly increased informed choice and relevant risk knowledge without negative side effects.

Neuroprotective effect of the immune system in a mouse model of severe dysmyelinating hereditary neuropathy: enhanced axonal degeneration following disruption of the RAG-1 gene

In mouse models of later onset forms of human hereditary demyelinating neuropathies, the immune system plays a crucial pathogenic role. Here, we investigated the influence of immune cells on early onset dysmyelination in mice homozygously deficient of the myelin component P0. In peripheral nerves of P0(-/-) mice, CD8+ T-lymphocytes increased with age. Macrophages peaked at 3 months followed by a substantial decline. They were mainly of hematogenous origin. To evaluate the functional role of immune cells, we cross-bred P0(-/-) mutants with RAG-1-deficient mice. At 3 months, the number of endoneurial macrophages did not differ from the macrophage number of immunocompetent myelin mutants, but the later decline of macrophages was not observed. Quantitative electron microscopy revealed that in plantar nerves of 6-month-old double mutants, significantly more axons had degenerated than in immunocompetent littermates. These data suggest a neuroprotective net effect of T-lymphocytes on axon survival in inherited, early onset dysmyelination.

Role of immune cells in animal models for inherited peripheral neuropathies

Mice expressing half of the normal dose of protein zero (P0+/− mice) or completely deficient gap-junction protein connexin 32−/− micemimic demyelinating forms of inherited neuropathies, such as Charcot-Marie-Tooth (CMT) neuropathies type 1B and CMT type 1X, respectively. In both models, an almost normal myelin formation is observed during the first months of life, followed by a slowly progressing demyelinating neuropathy. In both models, there is a substantial increase of CD8+ T-lymphocytes and macrophages within the demyelinating nerves. Recently, this has also been observed in mice mildly overexpressing human peripheral myelin protein 22 kD mimicking the most common form of CMT, CMT type 1A. In all demyelinating models, the macrophages show close contacts with intact myelin sheaths or demyelinated axons, suggesting an active role of these cells in myelin degeneration. Additionally, fibroblast-like cells contact macrophages, suggesting a functional role of fibroblast-like cells in macrophage activation. By cross-breeding P0+/− and gap-junction protein connexin 32−/− mice with immunodeficient recombination activating gene-1-deficient mutants, a substantial alleviation of the demyelinating phenotype was observed. Similarly, cross-breeding of P0+/− mice with mutants with a defect in macrophage activation led to an alleviated phenotype as well. These findings demonstrate that the immune system is involved in the pathogenesis of demyelinating neuropathies. In contrast, in P0−/− mice, which display a compromised myelin compaction and axonal loss from onset, immune cells appear to have a neuroprotective effect because cross-breeding with recombination activating gene-1 mutants leads to an aggravation of axonopathic changes. In the present review, we discuss the influence of the immune system on inherited de- and dysmyelination regarding disease mechanisms and possible clinical implications.

Endothelial dysfunction precedes C-fiber abnormalities in primary (AL) amyloidosis.

Primary (AL; immunoglobulin light‐chain associated) amyloidosis is characterized by the deposition of pathological proteins in the extracellular matrix of tissues and organs. Autonomic and sensory peripheral neuropathy is a common feature of this disorder. The pathogenesis of the neuropathy is poorly defined. The aims of this study were to investigate vascular and neural function in the cutaneous microcirculation of AL amyloidosis patients. Seven patients with AL amyloidosis and controls were studied. Acetylcholine and sodium nitroprusside were iontophoresed into the forearm skin. Endothelial, smooth muscle, and C‐fiber–mediated cutaneous blood flow (CuBF) were recorded by laser Doppler flowmetry. Endothelial vasodilation in the forearm skin was attenuated in AL amyloidosis patients (p = 0.007). Maximum endothelium‐mediated CuBF in the patient group was reduced (p = 0.047). No group differences could be detected in the C‐fiber response or smooth muscle vasodilation (p value not significant). Maximum C‐fiber and endothelium‐independent CuBF did not differ between the two groups (p value not significant). Early in the disease, AL amyloidosis patients present with impaired endothelial function. At this stage, C‐fiber and smooth muscle function are still preserved. These data suggest that endothelial abnormalities precede and may contribute to the pathogenesis of the neuropathy associated with AL amyloidosis. Ann Neurol 2003;53:725–730

Differential impairment of the sudomotor and nociceptor axon-reflex in diabetic peripheral neuropathy

It is not known whether C‐fiber functional subclasses are differentially affected by diabetes mellitus or whether the patterns of C‐fiber dysfunction are different between type 1 and type 2 diabetes. We therefore examined efferent sympathetic sudomotor and primary afferent nociceptor C‐fiber function in diabetic patients. Acetylcholine (10%) was used to evoke C‐fiber (axon‐reflex)–mediated responses. The nociceptor (flare) response was measured using a laser Doppler device. The sudomotor response was quantified with silastic imprints. The nociceptor C‐fiber–mediated flare response was reduced in type 2 diabetic patients (P < 0.008) but was similar to controls in type 1 diabetic patients. The sympathetic C‐fiber–mediated responses, including sweat volume (P < 0.05) and the number of activated sweat glands (P = 0.003), were increased in patients with type 1 diabetes. There also was a trend toward a larger axon‐reflex sweat area in patients with type 1 diabetes (P = 0.09). No differences in these sweat responses were found in patients with type 2 diabetes compared to controls. These findings suggest that the functional abnormalities in diabetic peripheral neuropathy are not homogeneous and that C‐fiber subclasses are differentially affected in type 1 and 2 diabetes mellitus. Muscle Nerve, 2006

Abnormal vasoreaction to arousal stimuli--an early sign of diabetic sympathetic neuropathy demonstrated by laser Doppler flowmetry.

Summary Early diagnosis of diabetic autonomic neuropathy contributes to the prevention of serious complications and improves the prognosis of patients with diabetes. Common tests of peripheral autonomic function are the quantitative sudomotor axon reflex test or the sympathetic skin response (SSR). Quantitative sudomotor axon reflex test is quantifiable but technically demanding. Sympathetic skin response cannot be quantified easily. To study whether measurement of skin vasomotion is suited to assess early sympathetic peripheral neuropathy, we monitored skin blood flow at the index finger pulp using laser Doppler flowmetry before and after electrical stimulation. We assured that the stimulus was sufficient to elicit an efferent sympathetic response by monitoring palmar SSR ipsilateral to the flow measurement. In 21 diabetic patients with at least stage one polyneuropathy and 21 age-matched controls, SSR was recorded from one palm and sole following electrical stimulation at the contralateral wrist. Sympathetic skin response was present at the palms in all patients and controls and absent at the sole of two patients only. Eight patients (38.9%) had abnormal SSR, with absent plantar responses in two patients, prolonged plantar latencies in six patients, and prolonged volar SSR latencies in two patients. Skin blood flow responses were more often abnormal (46.1%) than SSR (P < 0.05), responses were delayed in two patients and absent in another 8 patients. Skin blood flow retest reliability was high with a repeatability coefficient of 10.64% in controls and 12.34 % in patients. Skin blood flow monitoring after sympathetic stimulation provides a reproducible parameter of sympathetic vasomotor control and complements the diagnostic value of SSR testing.