Biomedical subjects

D R Tomlinson

Publications and source records attributed to D R Tomlinson.

At least 19 recordsLinked to original sources

PubMed2003

Enhanced activation of axonally transported stress-activated protein kinases in peripheral nerve in diabetic neuropathy is prevented by neurotrophin-3.

The objective was to determine whether stress-activated protein kinases (SAPKs) mediated the transfer of diabetes-induced stress signals from the periphery to somata of sensory neurons. Thus, we characterized axonal transport of SAPKs in peripheral nerve, studied any alteration in streptozotocin (STZ)-diabetic rats and examined effects of neurotrophin-3 (NT-3) on diabetes-induced events. We demonstrate that c-jun N-terminal kinase (JNK) and p38 are bidirectionally axonally transported at fast rates in sciatic nerve. In STZ-diabetic rats the relative levels of retrograde axonal transport of phosphorylated (activated) JNK and p38 were raised compared with age-matched controls (all data are in arbitrary units and expressed as fold increase over control: JNK 54-56 kDa isoforms, control 1.0 +/- 0.19, diabetic 2.5 +/- 0.26; p38, control 1.0 +/- 0.09, diabetic 2.9 +/- 0.52; both P < 0.05). Transport of total enzyme levels of JNK and p38 and phosphorylated extracellular signal-regulated kinase (ERK) was not significantly altered and anterograde axonal transport of phosphorylated JNK and p38 was unaffected by diabetes. The transcription factor ATF-2, which is phosphorylated and activated by JNK and p38, also exhibited elevated retrograde axonal transport in STZ-diabetic animals (control 1.0 +/- 0.07, diabetic 3.0 +/- 0.41; P < 0.05). Treatment of STZ-diabetic animals with 5 mg/kg human recombinant NT-3 prevented activation of JNK and p38 in sciatic nerve (phosphorylated JNK, control 1.0 +/- 0.09, diabetic 1.95 +/- 0.35, diabetic + NT-3 1.09 +/- 0.12; P < 0.05 diabetic versus others; phosphorylated p38, control 1.0 +/- 0.16, diabetic 4.7 +/- 0.9, diabetic + NT-3 1.19 +/- 0.18; P < 0.05 diabetic versus others). The results show that JNK and p38 are transported axonally and may mediate the transfer of diabetes-related stress signals, possibly triggered by loss of neurotrophic support, from the periphery to the neuronal soma.

Animals↗

PubMed2001

Effects of experimental diabetes on axonal and Schwann cell changes in sciatic nerve isografts.

A reduced ability to regenerate peripheral axons may be partly responsible for diabetic neuropathy. The source of the impairment has not been narrowed down to axonal or Schwann cell failure. We used nerve grafts from control or diabetic donor rats transplanted into control or diabetic hosts to pursue this differential diagnosis. An isograft between the left sciatic nerves of inbred Lewis rats was performed 8 weeks after STZ treatment and on age-matched controls. The nerve exchanges were control-control, control-diabetic, diabetic-control and diabetic-diabetic. At postsurgical day 14, nerves were excised and analysed for levels of axonal markers, total and phosphorylated neurofilament, and Schwann cell receptors, ErbB2 and p75(NTR), using immunohistochemistry and Western blotting. The aim was to measure ingress of axonal markers into the graft and judge the appropriateness of Schwann cell phenotype changes. Transfer of nerve from diabetic to control rats resulted in a doubling in neurofilament, both phosphorylated and nonphosphorylated (both P<0.05). ErbB2 was decreased in grafts from diabetic rats (53% of control, P<0.05) and p75(NTR) levels were increased in both types of graft in diabetic rats (to 300-400% of controls, P<0.05). Schwann cells in diabetic nerve grafts showed receptor levels more similar to controls when placed into a normal environment and the converse also appeared to hold. TUNEL staining revealed increased apoptosis in diabetic nerve distal to the graft. The data show that alterations in Schwann cell phenotype in diabetes are reversed by transfer to control rats and develop in normal nerve after transfer to a diabetic host.

Animals↗

PubMed2001

Nerve growth factor modulates the activation status and fast axonal transport of ERK 1/2 in adult nociceptive neurones.

Mature dorsal root ganglion cells respond to neurotrophins, and the intracellular signalling pathways activated by neurotrophins have been characterized in vitro. We have now used immunocytochemistry and Western blots to examine the expression and activation of extracellular signal-regulated protein kinase-1/2 (ERK) in rat dorsal root ganglion cells in vivo, using antisera to total (tERK) and phosphorylated (pERK) forms. This has revealed a number of novel findings. tERK immunoreactivity is present in most dorsal root ganglion cells but is expressed most strongly in small (nociceptive) cells and, surprisingly, is absent in a population of large cells that expressed trkB or trkC but mainly lack p75(NTR) immunoreactivity. In contrast pERK is prominent in a few trkA cells and in satellite glial cells, and is further increased by NGF treatment. tERK and pERK both undergo fast anterograde and retrograde axonal transport, indicated by accumulation at a sciatic nerve ligature, and NGF reduces the level of retrograde pERK transport.

Aging↗

PubMed2001

Oxidative stress participates in the breakdown of neuronal phenotype in experimental diabetic neuropathy.

AIMS/HYPOTHESIS: This study compared the effects of streptozotocin-induced diabetes in rats with those of two pro-oxidant interventions; a diet deficient in vitamin E and treatment with primaquine. METHODS: Measurements were made by the classic motor and sensory conduction velocity deficits and by indicators of the breakdown of small fibre phenotype i.e., sciatic nerve content of nerve growth factor and the neuropeptides, substance P and neuropeptide Y. RESULTS: As with diabetes, the pro-oxidant interventions decreased conduction velocities (though the effect of vitamin E deficiency was not significant), the sciatic nerve content of nerve growth factor and the neuropeptides (all percentages refer to the mean value for the appropriate control groups). In diabetes, nerve growth factor was depleted to 50% in the control rats (p < 0.05); oxidative stress depleted nerve growth factor to 64% (primaquine; p < 0.05) and 81% (vitamin E deficient; not significant) of controls. Substance P was depleted to 51% in the control rats (p < 0.01) with depletions to 74% and 72% (both p < 0.01) by oxidative stress; equivalent depletions for neuropeptide Y were 38% controls in diabetes (p < 0.001) and 67% (primaquine; p < 0.001) and 74% (vitamin E deficient; p < 0.05) for oxidative stress. CONCLUSION/INTERPRETATION: The relative magnitudes of these changes suggest an effect in diabetes of oxidative stress, coupled with some other cellular event(s). This is supported by the effects of a diester of gamma-linolenic acid and alpha-lipoic acid, which completely prevented the effects on the pro-oxidant interventions on conduction velocity, nerve growth factor and neuropeptide contents, but was only partially preventative in diabetes.

Animals↗

PubMed2001

Effects of nerve growth factor on expression of GAP-43 in right atria after sympathectomy in diabetic rats.

AIM: The present study investigated the role of nerve growth factor (NGF) in the regeneration of noradrenergic nerves of right atria (following 6-hydroxydopamine; 6-OHDA, 100 mg/kg, i.p.) from non-diabetic and 8-week diabetic rats. RESULTS: In cryostat sections of the right atria, GAP-43 immunoreactivity was concentrated in nerve terminals, preterminal axons of the endocardium, epicardium and myocardium, as well as in nerve fibres innervating the blood vessels and ganglionic cells. In serial sections, all positive staining for GAP-43 showed immunoreactivity for the neuronal marker PGP-9.5. In untreated non-diabetic rats, the total GAP-43 immunoreactivity was reduced to 60% relative to pretreatment levels, at day 14 after 6-OHDA, as quantified by Western blotting. In diabetic rats, 6-OHDA treatment produced a marked increase in the levels of total GAP-43 at days 28 and 49. NGF treatment (1 mg/kg, s.c., 3 times/week, for 2 weeks) had no effect on the level of total GAP-43 in right atria from non-diabetic and diabetic rats before treatment with 6-OHDA. However, it normalized the reduced GAP-43 immunoreactivity observed in 6-OHDA-treated non-diabetic rats. Interestingly, NGF treatment alone produced an increase in GAP-43 phosphorylation relative to total GAP-43 in right atria from both non-diabetic (44%) and diabetic groups (42%). CONCLUSIONS: These findings suggest that nerve terminals of the right atria retain, in the mature adult, the capacity for structural and functional plasticity. The expression of GAP-43 in right atria of control and diabetic rats was differentially affected by 6-OHDA treatment. In injured noradrenergic neurones of the right atria, NGF modified the expression of GAP-43 only in non-diabetic rats and not in diabetic rats.

Administration, Oral↗

PubMed2001

A role for mitogen-activated protein kinases in the etiology of diabetic neuropathy.

The onset of diabetic neuropathy, a complication of diabetes mellitus, has been linked to poor glycemic control. We tested the hypothesis that the mitogen-activated protein kinases (MAPK) form transducers for the damaging effects of high glucose. In cultures of adult rat sensory neurons, high glucose activated JNK and p38 MAPK but did not result in cell damage. However, oxidative stress activated ERK and p38 MAPKs and resulted in cellular damage. In the dorsal root ganglia of streptozotocin-induced diabetic rats (a model of type I diabetes), ERK and p38 were activated at 8 wk duration, followed by activation of JNK at 12 wk duration. We report activation of JNK and increases in total levels of p38 and JNK in sural nerve of type I and II diabetic patients. These data implicate MAPKs in the etiology of diabetic neuropathy both via direct effects of glucose and via glucose-induced oxidative stress.

Animals↗

PubMed2000

Pharmacological modulation of nerve growth factor synthesis: a mechanistic comparison of vitamin D receptor and beta(2)-adrenoceptor agonists.

Increasing nerve growth factor (NGF) in the PNS is a rational strategy for treating certain neurodegenerative disorders. The present studies were undertaken to compare two compounds, a vitamin D(3) analogue (CB1093) with minimal calcaemic effects, and clenbuterol, a long-acting beta(2)-adrenoceptor agonist, both of which induce NGF synthesis in vivo. Clenbuterol caused significant increases in both NGF mRNA and protein in 3T3 cells; with maxima at 10 nM and at 8-12 h exposure. Effects of clenbuterol on NGF mRNA were antagonized by propranolol. Mobility shift assays on whole cell extracts showed that clenbuterol increased AP1 binding in 3T3 cells prior to increasing NGF synthesis. Clenbuterol was without effect on NGF mRNA levels in L929 cells, whereas CB1093 caused significant increases in both NGF mRNA and protein levels in both 3T3 and L929 cells. Stimulation was almost maximal at 24 h exposure and was sustained for at least 72 h. The magnitude of the increase was much greater in L929 (700% increase) than in 3T3 cells (80%). Binding to the vitamin D nuclear receptor (VDR), which acts as a transcription factor itself, was increased as early as 30 min after exposure to of CB1093 and maintained up to 24 h. Increased VDR binding preceded increased NGF mRNA. A 150% increase in AP-1 binding was also evident. This study demonstrates that CB1093 and clenbuterol stimulate NGF levels in vitro and that AP-1 binding could be a commonality between the mechanism of NGF induction of these two compounds.

3T3 Cells↗

PubMed2000

Effect of streptozotocin-induced diabetes on NGF, P75(NTR) and TrkA content of prevertebral and paravertebral rat sympathetic ganglia.

Diabetic autonomic neuropathy results in significant morbidity and mortality. Both diabetic humans and experimental animals show neuroaxonal dystrophy of autonomic nerve terminals, particularly in the prevertebral superior mesenteric ganglia (SMG) and celiac ganglia (CG) which innervate the hyperplastic/hypertrophic diabetic small intestine. Previously, investigators suggested that disturbances in ganglionic nerve growth factor (NGF) content or transport might play a pathogenetic role in diabetic autonomic pathology. To test this hypothesis, we measured NGF content and NGF receptor expression, p75(NTR) (low affinity neurotrophin receptor) and trkA (high affinity NGF receptor), in control and diabetic rat SMG, CG and superior cervical ganglia (SCG). Surprisingly, rather than a decrease, we observed an approximate doubling of NGF content in the diabetic SMG and CG, a result which reflects increased NGF content in the hyperplastic diabetic alimentary tract. No change in NGF content was detected in the diabetic SCG which is relatively spared in experimental diabetic autonomic neuropathy. NGF receptor expression was not consistently altered in any of the autonomic ganglia. These observations suggest that increased NGF content in sympathetic ganglia innervating the diabetic alimentary tract coupled with intact receptor expression may produce aberrant axonal sprouting and neuroaxonal dystrophy.

Animals↗

PubMed2000

Alternative splicing of the neurotrophin-3 gene gives rise to different transcripts in a number of human and rat tissues.

The mouse neurotrophin-3 (NT-3) gene has been shown to contain two exons (exon 1A and exon 1B) upstream of the single coding exon (exon 2). These upstream exons are alternatively spliced to the coding exon, generating two different NT-3 transcripts. We investigated whether alternative splicing of two upstream exons also occurs in the human and rat NT-3 gene. It was found that the human and rat NT-3 gene also contains two exons upstream of the main coding exon and that alternative splicing of these upstream exons generates two different NT-3 transcripts : transcript 1A and transcript 1B (TR1B). These two transcripts were widely expressed in several human and rat tissues. Also, a third transcript, transcript 1A1C, derived from splicing of exon 1A to exon 1B before splicing to the coding exon was seen in a small number of rat tissues. Previous quantification of neurotrophin-3 mRNA has not been transcript-specific. Here we describe a transcript-specific semiquantitative RT-PCR method allowing the quantification of TR1B in human tissues. We show that this is the major NT-3 transcript and that expression of this transcript was much higher in the adult when compared with the corresponding fetal tissues.

Adult↗

PubMed2000

Primary care involvement in human immune deficiency virus infection-a pan-European view. The Eurosupport Study Group.

OBJECTIVE: The aim of this study was to compare the primary care experiences of human immunodeficiency virus (HIV)-positive individuals across Europe. METHODS: An anonymous self-administered questionnaire study was carried out between August 1996 and August 1997. A total of 15 HIV/AIDS treatment centres and 14 HIV support organizations in 11 European countries participated in the distribution of questionnaires. Overall, 1366 completed questionnaires were included in the analysis from a total of 2751 distributed (50% response rate). The majority of respondents were homosexual men (53.6%), and 54.2% had AIDS or symptomatic HIV disease. The main outcome measures were use of GP services in the preceding 6 months, GP involvement in HIV care provision, satisfaction with current service provision and reasons for non-involvement of the primary care services. RESULTS: Most patients (64.8%) had visited their GP at least once in the preceding 6 months, but 53.9% of respondents reported that their GP was not involved in their HIV care. Of these patients, 53.4% would like their GP to be involved. Patients from central European countries were more likely to have seen their GP than their counterparts from northern and southern countries (P < 0.005), and were less worried that the GP would not have enough knowledge about HIV (P = 0.002) or would not be sympathetic (P = 0.052). CONCLUSIONS: There are clear differences in GP utilization by HIV-positive individuals across Europe, reflecting in part local service provision but primarily patients' attitudes and beliefs. Strategies to promote the involvement of primary health care services need to address patients' core beliefs, if these are to be changed.

Adult↗

PubMed2000

STI prevention and the male sex industry in London: evaluating a pilot peer education programme.

OBJECTIVE: To evaluate the effectiveness of a pilot peer education STI prevention programme with male sex workers. DESIGN: A process and outcome evaluation of the pilot programme undertaken in three London male escort agencies, using a quasi-experimental design. SUBJECTS: Workers in three London escort agencies, including 88 who completed a questionnaire, five peer educators, and a further 16 men (including management) working in two of these agencies. METHODS: A peer education STI prevention programme run by the Working Men Project (WMP), a specialist sexual health service for male sex workers, was piloted in two London escort agencies. Five male sex workers participated in a 2 day peer education training programme. They then returned to their respective agencies to disseminate information and condoms, in an attempt to influence norms of behaviour. An outcome evaluation aimed to assess changes in STI related knowledge, high risk sexual behaviour, and attendance at a sexual health service. A pre-intervention questionnaire assessing variables such as STI related knowledge, sexual behaviour, and demographic information was administered in both agency A and agency B and a third agency, C, which acted as a control. Ten weeks after the peer educators returned to their agencies, the same questionnaire was administered in the same agencies. Peer educator referrals to the WMP were also recorded over this time period. The process evaluation involved interviews and focus groups with peer educators, and the completion of diaries about their experiences in the role. A further 16 men working in the agencies (including managers and an owner) were interviewed about their experience of the programme. Participant observation was also undertaken through regular outreach work to the agencies. RESULTS: 57 men completed the questionnaire at time 1 and 44 at time 2. Unfortunately, only 13 of these were matched, precluding any meaningful analysis of change in STI related knowledge and sexual behaviour. The questionnaire provided a profile of the men working in the agencies. Of the 88 men who completed the questionnaire at least once, the majority were homosexual, and in their late teens/early 20s. Most were of a "white" ethnic group, though there was some range within these categories. Most preferred to speak English and education levels were high. Relative STI knowledge revealed a high understanding of HIV and hepatitis B, moderate understanding of gonorrhoea, syphilis, genital warts and herpes, and little knowledge of non-specific urethritis (NSU) or chlamydia. Sexual behaviour suggested a highly sexually active population with both male and female paying and non-paying partners. Condom use was highest for paying partners, particularly for anal sex. Condom use for oral sex with all partners was less consistent, and condom use for all types of sex with regular partners was lower than with other partners. The small number of men engaging in vaginal sex with paying and regular partners were less likely to use condoms. 26 new patients registered at the WMP as a result of peer educator referrals, representing 65% of all new contacts over the study period. The process evaluation revealed that while the training programme was considered adequate and while peer educators felt the programme and their roles to be a success, their experience of the role was difficult. The role of management support was crucial in supporting the programme. The assumption that "peers" are particularly effective educators was not borne out by the results. While peers were considered suitable to discuss some aspects of the industry, many preferred to consult "professionals" about health related matters. The concept of "peers" was problematic with most of the men drawing "peers" from subgroups within the agencies. Other constraints on behaviour such as a lack of power, particularly with regard to a lack of management support, or poverty, had a substantial impact on behaviour which were not influenced by the peer educators. CONCLUSIONS: The study illustrated the difficulties of utilising quasi-experimental evaluation methodology with this client group. It also demonstrated the limitations of peer education based on information provision health education models which focus on individual behaviour change. Suggestions are given for future interventions.

Adolescent↗

PubMed1999

Axonal transport of activating transcription factor-2 is modulated by nerve growth factor in nociceptive neurons.

The aim of this study was to determine whether axonal transport of activating transcription factor-2 (ATF2) occurs in adult sensory neurons, and whether this process is under neurotrophin control. Antisera to both total ATF2 and to the activated (i.e., phosphorylated) form were used for immunocytochemistry and Western blotting. ATF2 was localized to predominantly nociceptive dorsal root ganglion cells in adult rats and shown to accumulate proximal and distal to a sciatic nerve ligature as a result of axonal transport. Subcutaneous injection of nerve growth factor (NGF) decreased the levels of fast retrograde axonal transport of activated ATF2 by 97% (p < 0.05) and elevated levels of retrograde axonal transport of total ATF2 by twofold (p < 0.02). In contrast, blocking endogenous NGF using an anti-NGF antibody induced an elevation in retrograde axonal transport of activated ATF2 of 4. 5-fold (p < 0.05) and decreased retrograde axonal transport of total ATF2 by 72% (p < 0.05). NGF or anti-NGF treatment had no effect on the anterograde transport levels of total or activated ATF2. This study shows that signaling by target-derived NGF to the cell bodies of sensory neurons consists, in part, of the modulation of levels and activation status of a retrogradely transported transcription factor, ATF2.

Activating Transcription Factor 2↗

PubMed1999

Transforming growth factor-beta1 and glial growth factor 2 reduce neurotrophin-3 mRNA expression in cultured Schwann cells via a cAMP-dependent pathway.

The aim of the study was to determine which factors regulated the expression of neurotrophin-3 (NT-3) mRNA in cultured primary Schwann cells derived from sciatic nerve of neonatal rats. Treatment of primary Schwann cells with the adenylate cyclase activator, forskolin, or the cAMP agonist, 8-Br-cAMP, induced a significant reduction in NT-3 transcript levels. Transforming growth factor-beta1 (TGF-beta1) and glial growth factor 2 (GGF(2)) also reduced the levels of NT-3 mRNA in a dose and time-dependent manner. Treatment with nerve growth factor, brain-derived neurotrophic factor, NT-3, ciliary neurotrophic factor or interleukin-1beta was without effect. The TGF-beta1, GGF(2) and forskolin dependent reduction in NT-3 mRNA levels involved a destabilization of transcripts which was antagonised by co-treatment with cycloheximide. The cAMP-dependent protein kinase A (PKA) inhibitor, H-89, blocked the reduction in levels of NT-3 mRNA induced by TGF-beta1, GGF(2) and forskolin. The data show that the effects of TGF-beta1, GGF(2) and forskolin on the downregulation of NT-3 mRNA, at least in part, were due to a post-transcriptional event involving a labile protein intermediate under the control of PKA. The results suggest that the down-regulation of NT-3 mRNA in Schwann cells at a site of peripheral nerve damage may be mediated via a cAMP-dependent pathway and possibly involve neuroma-related elevations in TGF-beta1 and GGF(2).

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1999

Elevated expression of neurotrophin-3 mRNA in sensory nerve of streptozotocin-diabetic rats.

Decreased expression of NT-3 mRNA in the sciatic nerve and leg muscles of streptozotocin (STZ)-diabetic rats has been associated with the pathogenesis of diabetic neuropathy. The aim of this study was to determine whether STZ-induced diabetes also affects the expression of NT-3 mRNA in the central and peripheral projections of sensory nerves. Competitive reverse transcription-polymerase chain reaction (cRT-PCR) was used to quantify the levels of NT-3 mRNA in the dorsal root, sural nerve, sciatic nerve and foot skin of age-matched and 12-week STZ-diabetic rats. Diabetes increased by 52% (P < 0.05) the expression of NT-3 mRNA in the dorsal root and sural nerve. It is proposed that diabetes-induced sensory nerve damage may elevate NT-3 mRNA production which may act as a source of neurotrophic support for sensory axons whose target-derived supply of NT-3 may be impaired.

Animals↗

PubMed1999

Nerve conduction impairment in experimental diabetes-proximodistal gradient of severity.

We compared a conventional method of measurement of sciatic motor and sensory nerve conduction velocity, with a novel procedure that measures conduction in an 8-mm segment of the rat sural nerve. Conventional procedures gave reductions in velocity of 20% and 14% for motor and sensory fibers, respectively, whereas sural sensory fibers showed a 40% reduction (P <0.05). Changes were attenuated by treatment with either an aldose reductase inhibitor or a gamma-linolenic acid-alpha-lipoic acid conjugate, such that values from conventional procedures were not significantly different from controls and the sural sensory deficit halved. Putative motor fibers of the sural nerve showed no conduction velocity deficit in diabetic rats. Measurement of chronaxie and rheobase in sural sensory fibers revealed mild reductions in excitability in diabetics, with prevention of the chronaxie change by the treatments. Thus, measurement of sensory conduction in distal nerve segments show more profound defects in diabetic rats and may give a truer picture of preventive drug efficacy.

Animals↗

PubMed1999

The regeneration of peripheral noradrenergic nerves after chemical sympathectomy in diabetic rats: effects of nerve growth factor.

The study investigated the role of nerve growth factor (NGF) in the regeneration of noradrenergic nerves of the right atria from control and 8-week diabetic rats, after lesion caused by a single injection of 6-hydroxydopamine (6-OHDA, 100 mg/kg ip). This treatment caused a profound depletion of tissue noradrenaline (NA) of the right atria from both control and diabetic groups, followed by a progressive repletion that was not complete at 49 days. Immunoreactivity for the NGF receptors trkA and p75(NTR) was decreased and increased, respectively, between days 3 and 28 in right atria from diabetic rats and returned to pretreatment levels at day 49. Receptor levels were not significantly altered in controls. In contrast to tissue NA, at day 14 functional responses to electrical nerve stimulation of the right atria had completely returned to the pretreatment state in diabetic rats and were very close to normal in nondiabetic rats. NGF treatment (1 mg/kg, three times/week, for 2 weeks) increased tissue NA only in control rats; the pattern was similar after 6-OHDA. These findings are consistent with the hypothesis that NGF normally plays a role in the regulation of autonomic sympathetic nerves in the adult rat atrium and that mature and uninjured sympathetic neurons remain responsive to NGF. In injured noradrenergic neurons, NGF promotes regeneration in nondiabetic rats. The ability of NGF to promote regeneration of noradrenergic nerves is lost in diabetes and this may relate to the loss of trkA receptor on prejunctional nerve terminals after denervation.

Animals↗

PubMed1999

Mitogen-activated protein kinases as glucose transducers for diabetic complications.

The damaging effects of glucose on the cells which contribute to the development of diabetic complications are ill-understood. There are three major hypotheses - the sorbitol pathway, non-enzymatic glycation of proteins and increased oxidative stress - and many examples illustrate inter-connections between the three. It is suggested that these pathways, together with other biochemical anomalies arising from hyperglycaemia, can synergise by sharing the capacity to activate mitogen-activated protein kinases (MAP kinases) and that these enzymes in actual fact form glucose transducers. The more recent hypothesis, namely that activation of a specific isoform of protein kinase C (PKC) underpin damaging changes in retinopathy and neuropathy, can also be related because protein kinase C is an effective activator of mitogen-activated protein kinases. These latter kinases phosphorylate transcription factors, which in turn alter the balance of gene expression. In this way they can alter cellular phenotype, promote division or increase production of extracellular material. In short, mitogen-activated protein kinases have the capacity to trigger all the cellular events necessary for the development of diabetic nephropathy, retinopathy and neuropathy and it is suggested that their pharmacological modulation might provide therapeutic control of these conditions. [Diabetologia (1999) 42: 1271-1281]

Animals↗

PubMed1999

A vitamin D(3) derivative (CB1093) induces nerve growth factor and prevents neurotrophic deficits in streptozotocin-diabetic rats.

AIMS/HYPOTHESIS: Streptozotocin-diabetic rats show impaired neurotrophic support by deficient nerve growth factor (NGF) in muscle and skin. We, therefore, examined a novel agent (CB1093; 1(S), 3(R)-Dihydroxy-20(R)-(1-ethoxy-5-ethyl-5-hydroxy-2-heptyn-1-yl)-9, 10-seco-pregna-5(Z),7(E),10(19)-triene), which induces expression of endogenous nerve growth factor. METHODS: We gave CB1093 orally followed by measurements of mechanical nociception, nerve growth factor, neuropeptides (immunoassay) and nerve growth factor receptors (western blots). RESULTS: In non-diabetic rats CB1093 caused dose-dependent increases in nerve growth factor production (140 % in soleus muscle and 190 % in sciatic nerve) and a mechanical hyperalgesia in the foot. There was also increased sciatic nerve expression of neuronal NGF target gene products, substance P (16 %) and calcitonin gene-related peptide (CGRP; 52 %). Depletions of nerve growth factor, substance P and CGRP in sciatic nerves of diabetic rats were prevented by CB1093, which also increased soleus nerve growth factor concentrations to 30 % over those seen in non-diabetic rats and increased its mRNA expression in skin. The CB1093 did not affect expression of nerve growth factor receptors (trkA and p75(NTR)) in dorsal root ganglia in control or diabetic rats, though the p75(NTR) expression was reduced by diabetes. The mechanical hyperalgesia seen in diabetic rats treated with vehicle was not exacerbated by CB1093. CONCLUSION/INTERPRETATION: These findings show that in animal models of diabetes it is possible to prevent depletions of nerve growth factor and the products of its neuronal target genes by oral treatment of a highly potent inducer of NGF gene expression. Pain is a possible side-effect, though this was a function of dose and was manifest more in controls than in diabetic rats. [Diabetologia (1999) 42: 1308-1313]

Animals↗