Historical epidemiology of hepatitis C virus in select countries-volume 4

Due to the introduction of newer, more efficacious treatment options, there is a pressing need for policy makers and public health officials to develop or adapt national hepatitis C virus (HCV) control strategies to the changing epidemiological landscape. To do so, detailed, country-specific data are needed to characterize the burden of chronic HCV infection. In this study of 17 countries, a literature review of published and unpublished data on HCV prevalence, viraemia, genotype, age and gender distribution, liver transplants and diagnosis and treatment rates was conducted, and inputs were validated by expert consensus in each country. Viraemic prevalence in this study ranged from 0.2% in Hong Kong to 2.4% in Taiwan, while the largest viraemic populations were in Nigeria (2 597 000 cases) and Taiwan (569 000 cases). Diagnosis, treatment and liver transplant rates varied widely across the countries included in this analysis, as did the availability of reliable data. Addressing data gaps will be critical for the development of future strategies to manage and minimize the disease burden of hepatitis C.

The present and future disease burden of hepatitis C virus infections with today's treatment paradigm: Volume 4

Factors influencing the morbidity and mortality associated with viremic hepatitis C virus (HCV) infection change over time and place, making it difficult to compare reported estimates. Models were developed for 17 countries (Bahrain, Bulgaria, Cameroon, Colombia, Croatia, Dominican Republic, Ethiopia, Ghana, Hong Kong, Jordan, Kazakhstan, Malaysia, Morocco, Nigeria, Qatar and Taiwan) to quantify and characterize the viremic population as well as forecast the changes in the infected population and the corresponding disease burden from 2015 to 2030. Model inputs were agreed upon through expert consensus, and a standardized methodology was followed to allow for comparison across countries. The viremic prevalence is expected to remain constant or decline in all but four countries (Ethiopia, Ghana, Jordan and Oman); however, HCV-related morbidity and mortality will increase in all countries except Qatar and Taiwan. In Qatar, the high-treatment rate will contribute to a reduction in total cases and HCV-related morbidity by 2030. In the remaining countries, however, the current treatment paradigm will be insufficient to achieve large reductions in HCV-related morbidity and mortality.

Strategies to manage hepatitis C virus infection disease burden-Volume 4

The hepatitis C virus (HCV) epidemic was forecasted through 2030 for 17 countries in Africa, Asia, Europe, Latin America and the Middle East, and interventions for achieving the Global Health Sector Strategy on viral hepatitis targets-"WHO Targets" (65% reduction in HCV-related deaths, 90% reduction in new infections and 90% of infections diagnosed by 2030) were considered. Scaling up treatment and diagnosis rates over time would be required to achieve these targets in all but one country, even with the introduction of high SVR therapies. The scenarios developed to achieve the WHO Targets in all countries studied assumed the implementation of national policies to prevent new infections and to diagnose current infections through screening.

The present and future disease burden of hepatitis C virus infections with today's treatment paradigm - volume 3

The total number, morbidity and mortality attributed to viraemic hepatitis C virus (HCV) infections change over time making it difficult to compare reported estimates from different years. Models were developed for 15 countries to quantify and characterize the viraemic population and forecast the changes in the infected population and the corresponding disease burden from 2014 to 2030. With the exception of Iceland, Iran, Latvia and Pakistan, the total number of viraemic HCV infections is expected to decline from 2014 to 2030, but the associated morbidity and mortality are expected to increase in all countries except for Japan and South Korea. In the latter two countries, mortality due to an ageing population will drive down prevalence, morbidity and mortality. On the other hand, both countries have already experienced a rapid increase in HCV-related mortality and morbidity. HCV-related morbidity and mortality are projected to increase between 2014 and 2030 in all other countries as result of an ageing HCV-infected population. Thus, although the total number of HCV countries is expected to decline in most countries studied, the associated disease burden is expected to increase. The current treatment paradigm is inadequate if large reductions in HCV-related morbidity and mortality are to be achieved.

Strategies to manage hepatitis C virus infection disease burden - volume 3

The hepatitis C virus (HCV) epidemic was forecasted through 2030 for 15 countries in Europe, the Middle East and Asia, and the relative impact of two scenarios was considered: increased treatment efficacy while holding the annual number of treated patients constant and increased treatment efficacy and an increased annual number of treated patients. Increasing levels of diagnosis and treatment, in combination with improved treatment efficacy, were critical for achieving substantial reductions in disease burden. A 90% reduction in total HCV infections within 15 years is feasible in most countries studied, but it required a coordinated effort to introduce harm reduction programmes to reduce new infections, screening to identify those already infected and treatment with high cure rate therapies. This suggests that increased capacity for screening and treatment will be critical in many countries. Birth cohort screening is a helpful tool for maximizing resources. Among European countries, the majority of patients were born between 1940 and 1985. A wider range of birth cohorts was seen in the Middle East and Asia (between 1925 and 1995).

Historical epidemiology of hepatitis C virus (HCV) in select countries - volume 3

Detailed, country-specific epidemiological data are needed to characterize the burden of chronic hepatitis C virus (HCV) infection around the world. With new treatment options available, policy makers and public health officials must reconsider national strategies for infection control. In this study of 15 countries, published and unpublished data on HCV prevalence, viraemia, genotype, age and gender distribution, liver transplants and diagnosis and treatment rates were gathered from the literature and validated by expert consensus in each country. Viraemic prevalence in this study ranged from 0.2% in Iran and Lebanon to 4.2% in Pakistan. The largest viraemic populations were in Pakistan (7 001 000 cases) and Indonesia (3 187 000 cases). Injection drug use (IDU) and a historically unsafe blood supply were major risk factors in most countries. Diagnosis, treatment and liver transplant rates varied widely between countries. However, comparison across countries was difficult as the number of cases changes over time. Access to reliable data on measures such as these is critical for the development of future strategies to manage the disease burden.

A small dose of the immunosuppressive agent FK506 (tacrolimus) protects peripheral nerve from ischemic fiber degeneration

The immunosuppressant agent FK506 (tacrolimus) has proven to be neuroprotective against brain ischemia, but there are no data on potential neuroprotective effects of FK506 in peripheral nerve ischemia. We examined the potential effects of two doses of FK506 in protecting peripheral nerve from ischemic fiber degeneration. Ischemia in the left sciatic nerve of the rat was produced by injecting 2 x 10(6) microspheres (14 microm) into the left femoral, hypogastric, and superior gluteal arteries in proportions of 47%, 37%, and 17%, respectively. After embolization, FK506 was injected into the left femoral, hypogastric, and superior gluteal arteries in doses of 9.4, 7.4, and 3.4 microg, respectively, for the high-dose group and 4.7, 3.7, and 1.7 microg, respectively, for the low-dose group. The control rats were injected with saline. FK506 treatment resulted in dramatic behavioral improvement in nerve function, in the number of functioning nerve fibers, and in the salvage of a majority of nerve fibers from ischemic fiber degeneration in a dose-dependent fashion. These results suggest that a small dose of FK506 protects peripheral nerve from ischemic fiber degeneration and that it may have potential in the treatment of ischemic neuropathy.

Pro- and Anti-inflammatory Cytokine Gene Expression in Rat Sciatic Nerve Chronic Constriction Injury Model of Neuropathic Pain

Cytokines may be pathophysiologically involved in hyperalgesia. Uncertainty exists about the types of cytokines and their site of action. To study the role of key pro- and anti-inflammatory cytokines in a chronic constriction model of neuropathic pain, mRNA expression of TNF, IL-1beta, IL-6, and IL-10 was quantified using competitive RT-PCR. Each cytokine mRNA in rat sciatic nerve was examined at days 3, 7, 14, and 45 after chronic constriction injury (CCI). We also undertook behavioral testing of these rats. Thermal warming and touch thresholds were significantly reduced at days 3, 7, and 14 in the CCI group, compared with the sham-operated group. Cytokine gene expression in sciatic nerve was significantly increased at day 7 for IL-1beta and IL-6 and at day 14 for TNF. Expression of IL-10 underwent a gradual and progressive increase, reaching statistical significance at day 45.

Gene expression of antioxidant enzymes in experimental diabetic neuropathy

Chronic hyperglycemia results in a large deficit in nerve blood flow. Both autoxidative- and ischemia-induced lipid peroxidation occurs, with resultant peripheral sensory neuropathy in streptozotocin-induced diabetes in the rat. Free radical defenses, especially involving antioxidant enzymes, have been suggested to be reduced, but scant information is available on chronic hyperglycemia. We evaluated the gene expression of glutathione peroxidase, catalase, and superoxide dismutase (cuprozinc and manganese separately) in L4,5 dorsal root ganglion (DRG) and superior cervical ganglion, as well as enzyme activity of glutathione peroxidase in DRG and sciatic nerve in experimental diabetic neuropathy of 3 months and 12 months durations. We also evaluated nerve electrophysiology of caudal, sciatic-tibial, and digital nerves. A nerve conduction deficit was seen in all nerves in experimental diabetic neuropathy at both 3 and 12 months. Gene expression of glutathione peroxidase, catalase, cuprozinc superoxide dismutase, and manganese superoxide dismutase were not reduced in experimental diabetic neuropathy at either 3 or 12 months. Catalase mRNA was significantly increased in experimental diabetic neuropathy at 12 months. Glutathione peroxidase enzyme activity was normal in sciatic nerve. We conclude that gene expression is not reduced in peripheral nerve tissues in very chronic experimental diabetic neuropathy. Changes in enzyme activity may be related to duration of diabetes or due to post-translational modifications.

Aging differentially modifies sensitivity of nerve blood flow to vasocontractile agents (endothelin-1, noradrenaline and angiotensin II) in sciatic nerve

This study examined the influence of the vaso-constricting agents (noradrenaline, endothelin-1 and angiotensin II) in Sprague-Dawley rats aged 2, 6 and 24 months by evaluating epineurial arteriolar vasoreactivity in response to superfused teat agents. Nerve blood flow (NBF) was measured using microelectrode H2 polarography. In 24-month-old rats, NBF was decreased and vascular resistance (VR) was increased compared with 2- and 6-month-old rats. All of the constricting agents reduced NBF in the 2-, 6- and 24-month groups, however, the effects of the constricting agents reduced significantly with age. These results suggest that during aging, there is a decline of vasoconstrictive responses to noradrenaline, endothelin-1 and angiotensin II in peripheral nerve and that these changes may be due to altered function of receptors.

The expression of proinflammatory cytokine mRNA in the sciatic-tibial nerve of ischemia-reperfusion injury

We evaluated the proinflammatory cytokines, TNF-alpha and IL-1beta, mRNA expression in the rat sciatic and tibial nerves following ischemia-reperfusion (IR) injury, using competitive RT-PCR, to explore the role of cytokines in IR injury. The expressions of both TNF-alpha and IL-1beta mRNA were related to severity of ischemia and occurred with reperfusion rather than ischemia alone. TNF-alpha gene expression peaked at 24 h of reperfusion, while that of IL-1beta peaked at 12 h. These data support the notion that the proinflammatory cytokines TNF-alpha and IL-1beta are involved in the inflammatory response of IR injury to the peripheral nervous system and may be involved in the pathophysiology of ischemic fiber degeneration.

Alpha-lipoic acid: effect on glucose uptake, sorbitol pathway, and energy metabolism in experimental diabetic neuropathy

The peripheral nerve of experimental diabetic neuropathy (EDN) is reported to be ischemic and hypoxic, with an increased dependence on anaerobic metabolism, requiring increased energy substrate stores. When glucose stores become reduced, fiber degeneration has been reported. We evaluated glucose uptake, nerve energy metabolism, the polyol pathway, and protein kinase C (PKC) activity in EDN induced by streptozotocin. Control and diabetic rats received lipoic acid (0, 10, 25, 50, 100 mg/kg). Duration of diabetes was 1 month, and alpha-lipoic acid was administered intraperitoneally 5 times per week for the final week of the experiment. Nerve glucose uptake was reduced to 60, s 37, and 30% of control values in the sciatic nerve, L5 dorsal root ganglion, and superior cervical ganglion (SCG), respectively, in rats with EDN. Alpha-lipoic acid supplementation had no effect on glucose uptake in normal nerves at any dose, but reversed the deficit in EDN, with a threshold between 10 and 25 mg/kg. Endoneurial glucose, fructose, sorbitol, and myo-inositol were measured in sciatic nerve. Alpha-lipoic acid had no significant effect on either energy metabolism or polyol pathway of normal nerves. In EDN, endoneurial glucose, fructose, and sorbitol were significantly increased, while myo-inositol was significantly reduced. Alpha-lipoic acid had a biphasic effect: it dose-dependently increased fructose, glucose, and sorbitol, peaking at 25 mg/kg, and then fell beyond that dose, and it dose-dependently increased myo-inositol. Sciatic nerve cytosolic PKC was increased in EDN. ATP, creatine phosphate, and lactate were measured in sciatic nerve and SCG. Alpha-lipoic acid prevented the reduction in SCG creatine phosphate. We conclude that glucose uptake is reduced in EDN and that this deficit is dose-dependently reversed by alpha-lipoic acid, a change associated with an improvement in peripheral nerve function.

Altered vasoreactivity to angiotensin II in experimental diabetic neuropathy: role of nitric oxide

We evaluated the effects of angiotensin II and an angiotensin-converting enzyme inhibitor (cilazapril) on nerve blood flow (NBF) and electrophysiology in control and diabetic rats. When applied locally to the sciatic nerve, the dose-response curve of angiotensin II was more potent in experimental diabetic neuropathy (EDN) than control rats. No difference existed in plasma angiotensin II levels between EDN and controls. The rats were given typical rat pellets or pellets treated with 10 mg/kg per day cilazapril for 4 weeks. Diabetes caused a significant reduction in NBF, nerve conduction velocity, and compound muscle action potential (CMAP) amplitudes. NBF was significantly increased in diabetic rats supplemented with cilazapril diet, and nerve conduction velocity and amplitudes of the CMAP were also improved after 4 weeks on this diet. Direct application 10(-3) mol/L cilazapril on sciatic nerve did not increase NBF in normal and EDN rats. We topically applied the nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine, on sciatic nerve and observed reduced inhibition of NBF in EDN, which was correctable with a cilazapril diet. These results suggest that diabetic neuropathy may have an increasing vasopressor action with angiotensin II and this is likely to be the mechanism of NOS inhibition. Angiotensin II-converting enzyme inhibitors may have potential in the treatment of diabetic neuropathy.

Hypothermic neuroprotection of peripheral nerve of rats from ischemia-reperfusion injury: intraischemic vs. reperfusion hypothermia

The pathophysiology of ischemic fiber degeneration (IFD) is not known, but mechanisms involved during nerve ischemia differ from those during reperfusion. We have previously demonstrated hypothermic neuroprotection of peripheral nerve from IFD. We now evaluate the efficacy of hypothermia in the intraischemic vs. the reperfusion period, using our established model of ischemia-reperfusion injury. Intraischemic hypothermia resulted in significant recovery of all indices (behavior score, electrophysiology and histology, P<0.01 or 0.05) while hypothermia during reperfusion period showed less improvement, significant only for the histological score compared to normothermia group (IFD index, P<0.05). Once hypothermia was applied in the ischemic period, the resultant neuroprotection continued into the reperfusion period, even if nerve temperature was then raised during the reperfusion period. These results indicate that hypothermic neuroprotection is more efficacious during the intraischemic period than during reperfusion, when a lesser degree of neuroprotection ensued.

Alpha-lipoic acid provides neuroprotection from ischemia-reperfusion injury of peripheral nerve

BACKGROUND

Reperfusion aggravates nerve ischemic fiber degeneration, likely by the generation of reduced oxygen species. We therefore evaluated if racemic alpha-lipoic acid (LA), a potent antioxidant, will protect peripheral nerve from reperfusion injury, using our established model of ischemia-reperfusion injury.

METHODS

We used male SD rats, 300+/-5 g. Ischemia was produced by the ligature of each of the supplying arteries to the sciatic-tibial nerve of the right hind-limb for predetermined periods of time (either 3 or 5 h), followed by the release of the ligatures, resulting in reperfusion. LA was given intraperitoneally daily for 3 days for both pre- and post-surgery. Animals received either LA, 100 mg/kg/day, or the same volume of saline intraperitoneally. Clinical behavioral score and electrophysiology of motor and sensory nerves were obtained at 1 week after ischemia-reperfusion. After electrophysiological examination, the sciatic-tibial nerve was fixed in situ and embedded in epon. We evaluated for ischemic fiber degeneration (IFD) and edema, as we described previously.

RESULTS

Distal sensory conduction (amplitude of sensory action potential and sensory conduction velocity (SCV) of digital nerve) was significantly improved in the 3-h ischemia group, treated with LA (P<0.05). LA also improved IFD of the mid tibial nerve (P=0.0522). LA failed to show favorable effects if the duration of ischemia was longer (5-h ischemia).

CONCLUSION

These results suggest that alpha-lipoic acid is efficacious for moderate ischemia-reperfusion, especially on distal sensory nerves.

Hypothermic neuroprotection of peripheral nerve of rats from ischaemia-reperfusion injury

Although there is much information on experimental ischaemic neuropathy, there are only scant data on neuroprotection. We evaluated the effectiveness of hypothermia in protecting peripheral nerve from ischaemia-reperfusion injury using the model of experimental nerve ischaemia. Forty-eight male Sprague-Dawley rats were divided into six groups. We used a ligation-reperfusion model of nerve ischaemia where each of the supplying arteries to the sciatic-tibial nerves of the right hind limb was ligated and the ligatures were released after a predetermined period of ischaemia. The right hind limbs of one group (24 rats) were made ischaemic for 5 h and those of the other group (24 rats) for 3 h. Each group was further divided into three and the limbs were maintained at 37 degrees C (36 degrees C for 5 h of ischaemia) in one, 32 degrees C in the second and 28 degrees C in the third of these groups for the final 2 h of the ischaemic period and an additional 2 h of the reperfusion period. A behavioural score was recorded and nerve electrophysiology of motor and sensory nerves was undertaken 1 week after surgical procedures. At that time, entire sciatic-tibial nerves were harvested and fixed in situ. Four portions of each nerve were examined: proximal sciatic nerve, distal sciatic nerve, mid-tibial nerve and distal tibial nerve. To determine the degree of fibre degeneration, each section was studied by light microscopy, and we estimated an oedema index and a fibre degeneration index. The groups treated at 36-37 degrees C underwent marked fibre degeneration, associated with a reduction in action potential and impairment in behavioural score. The groups treated at 28 degrees C (for both 3 and 5 h) showed significantly less (P < 0.01; ANOVA, Bonferoni post hoc test) reperfusion injury for all indices (behavioural score, electrophysiology and neuropathology), and the groups treated at 32 degrees C had scores intermediate between the groups treated at 36-37 degrees C and 28 degrees C. Our results showed that cooling the limbs dramatically protects the peripheral nerve from ischaemia-reperfusion injury.

Blood flow and autoregulation in somatic and autonomic ganglia. Comparison with sciatic nerve

We studied blood flow rates along the sciatic nerve and in the superior cervical and L-5 dorsal root ganglia of rats at rest and during reductions and increases in mean arterial pressure induced by partial exsanguination or blood transfusion. Blood flow was measured by the tissue distribution of [14C]iodoantipyrine and autoradiography. At rest, blood flow did not vary along the peripheral nerve, but was two to three times greater in dorsal root and superior cervical ganglia. In peripheral nerve, blood flow increased with increases in blood pressure. In contrast, blood flow in dorsal root and sympathetic ganglia did not vary with changes in pressure. Thus, peripheral nerve cell bodies have greater blood flow than their axons; ganglion blood flow is autoregulated within the range of blood pressure tested. Nerve ganglia appear to be protected against ischaemic stress by autoregulation rather than by a blood flow "safety margin', as in peripheral nerve.

Neuropathology and blood flow of nerve, spinal roots and dorsal root ganglia in longstanding diabetic rats

Vascular perfusion and neuropathologic evaluation of the lumbar spinal roots and dorsal root ganglia (DRG) were studied in rats with longstanding (duration 12-15 months) streptozotocin-induced diabetes and age- and sex-matched control rats. We also undertook nerve conduction studies including F-wave recordings and measured blood flow in sciatic nerve, DRG, and superior cervical ganglion (SCG). Light microscopically, changes of the myelin sheath in the dorsal and ventral roots and vacuolated cells in the DRG were the major findings, being significantly higher in diabetic rats than in control rats. The effects of the diabetic state on myelin splitting were greater in the dorsal than ventral roots. Electron microscopic studies revealed a gradation of changes in myelin from mild separation to severe ballooning of myelin with relative axonal sparing. DRG cells showed vacuoles of all sizes with cristae-like residues, suggestive of mitochondria. These findings suggest that diabetes mellitus has a dual effect: it accelerates the normal age-related degenerative changes in the spinal roots and DRG, and it also has a selective effect on the sensory neuron. Nerve conduction studies showed markedly reduced conduction velocities in the distal nerve segments and prolonged F-wave latency and proximal conduction time despite the shorter conduction pathway in diabetic rats. Blood flow, which was measured using iodo[14C]antipyrine autoradiography, was significantly reduced in the sciatic nerves, DRG, and SCG of diabetic rats. We suggest that the combination of hyperglycemia and ischemia results in oxidative-stress and a predominantly sensory neuropathy.

Chronic constriction model of rat sciatic nerve: nerve blood flow, morphologic and biochemical alterations

We evaluated the nerve blood flow (NBF), light and electron microscopy, and adrenergic innervation of rat sciatic nerve at 2-45 days after the application of four loose ligatures. Ischemia developed at the lesion edge, creating an endoneurial dam. Calcitonin gene-related peptide, norepinephrine and NBF were increased within the lesion. Morphologic alterations consisted of early endoneurial edema, followed by myelinated fiber degeneration, with relative sparing of small myelinated and unmyelinated nerve fibers, and leukocyte adhesion to microvessels. Axonal degeneration predominated over demyelination. At 45 days, profuse regeneration of small myelinated fibers was seen. The mechanism of lesional sensitization is discussed.

Efficacy of limb cooling on the salvage of peripheral nerve from ischemic fiber degeneration

Since peripheral nerve has a large ischemic safety factor, hypothermia, by reducing metabolic demands, is potentially an efficacious technique to rescue nerve from ischemic fiber degeneration (IFD). We therefore evaluated the influence of temperature on the severity of IFD resulting from a standard ischemic stress. Ischemia to the left sciatic nerve in the rat was produced by embolization of 2 x 10(6) microspheres (14 microns) into its supplying arteries. The limb was embolized at three temperatures, 37 degrees C, 32 degrees C, and 28 degrees C and was maintained at each temperature for an additional 4 h. End points, evaluated 7 days after embolization, for the embolized limb were: (1) behavioral scores, 0-11 in increasing limb function; (2) compound nerve action potential of sciatic-tibial nerve; (3) sciatic nerve blood flow (NBF, in mL/100 g/min); and (4) histologic grade, expressed as percentage of fibers undergoing IFD (0 = < 5%; 1 = 5-25%; 2 = 26-50%; 3 = 51-75%; 4 = > 75%). NBF was reduced in all groups, varying with temperature, and all indices of nerve structure and function were significantly improved with hypothermia. We conclude that hypothermia, easily achievable in a limb nerve, is highly efficacious in the rescue of nerve from IFD. These findings are of clinical relevance.

Ischemic reperfusion causes lipid peroxidation and fiber degeneration

Although the neuropathology of ischemic fiber degeneration (IFD) is relatively well known, its pathogenesis is poorly understood. One putative mechanism of IFD is oxidative stress, causing a breakdown of the blood-nerve barrier (BNB) and lipid peroxidation. We evaluated the effect of ischemic reperfusion of rat sciatic-tibial nerve seeking biochemical and pathologic evidence of BNB disruption and lipid peroxidation. Ischemia, caused by the ligation of the supplying arteries to sciatic-tibial nerve, was maintained for 3 h, followed by reperfusion. Reperfusion resulted in an increase in nerve lipid hydroperoxides, greatest at 3 h, followed by a gradual decline over the next month. Nerve edema and IFD consistently became more severe with reperfusion, indicating that oxidative stress impairs the BNB (edema) and causes IFD. Reduced reperfusion was greatest over distal sciatic nerve and midtibial nerve at day 7. The most ischemic segment (midtibial), of nonreperfused ischemic nerves (duration 3 h), underwent both edema and IFD that was as pronounced as those of other segments after reperfusion, and underwent a smaller increase with reperfusion, suggesting that ischemia alone can also cause IFD and edema. The type of fiber degeneration was that of axonal degeneration.

Effect of cilostazol on experimental diabetic neuropathy in the rat

Two proposed mechanisms of diabetic neuropathy are microvascular ischaemia and a reduction in Na,K-ATPase activity. We evaluated the effect of cilostazol, a drug that is both a potent phosphodiesterase inhibitor that normalizes nerve Na,K-AT-Pase and a vasodilator, on nerve blood flow (NBF) to determine whether it would improve experimental diabetic neuropathy. We examined whether epineurally applied cilostazol acted as a vasodilator on the peripheral nerve of normal and diabetic rats, and whether feeding the rats a cilostazol-supplemented diet could improve diabetic neuropathy. Cilostazol increased nerve blood flow (NBF) in a dose-dependent fashion with an EC50 of 10(-5.74) mol/l. Cilostazol also normalized NBF in experimental diabetic neuropathy with a 10(-4) mol/l local application on the sciatic nerve. In diabetic neuropathy, a cilostazol-supplemented diet improved both NBF and nerve conduction in a dose- and time-dependent fashion. Potential mechanisms of action of cilostazol on the nerve include its effect on NBF, Na, K-ATPase, and restoration of the thromboxane:prostacyclin ratio. Cilostazol may have potential in the treatment of diabetic neuropathy.

Lipoic acid improves nerve blood flow, reduces oxidative stress, and improves distal nerve conduction in experimental diabetic neuropathy

OBJECTIVE

To determine whether lipoic acid (LA) will reduce oxidative stress in diabetic peripheral nerves and improve neuropathy.

RESEARCH DESIGN AND METHODS

We used the model of streptozotocin-induced diabetic neuropathy (SDN) and evaluated the efficacy of LA supplementation in improving nerve blood flow (NBF), electrophysiology, and indexes of oxidative stress in peripheral nerves affected by SDN, at 1 month after onset of diabetes and in age-matched control rats. LA, in doses of 20, 50, and 100 mg/kg, was administered intraperitoneally five times per week after onset of diabetes.

RESULTS

NBF in SDN was reduced by 50%; LA did not affect the NBF of normal nerves but improved that of SDN in a dose-dependent manner. After 1 month of treatment, LA-supplemented rats (100 mg/kg) exhibited normal NBF. The most sensitive and reliable indicator of oxidative stress was reduction in reduced glutathione, which was significantly reduced in streptozotocin-induced diabetic and alpha-tocopherol-deficient nerves; it was improved in a dose-dependent manner in LA-supplemented rats. The conduction velocity of the digital nerve was reduced in SDN and was significantly improved by LA.

CONCLUSIONS

These studies suggest that LA improves SDN, in significant part by reducing the effects of oxidative stress. The drug may have potential in the treatment of human diabetic neuropathy.

Experimental ischemic neuropathy: salvage with hyperbaric oxygenation

Hyperbaric oxygenation is effective in augmenting the delivery of oxygen to tissue, but also causes oxidative stress. As part of our focus on improving peripheral nerve salvage from ischemic fiber degeneration, we evaluated whether hyperbaric oxygenation rescues peripheral nerve, rendered ischemic by microembolization, from ischemic fiber degeneration. The supplying arteries of rat sciatic nerve were embolized with microspheres of 14 microns diameter at moderate (2 x 10(6)) and high (5.6 x 10(6)) doses. Rats were randomized to receive hyperbaric oxygenation treatment (2.5 atm 100% oxygen for 2 hours/day for 7 days beginning within 30 minutes of ischemia), or room air. End points for the embolized limb were (1) behavioral scores (0-11 in increasing levels of limb function), (2) nerve action potential of sciatic-tibial nerve, (3) nerve blood flow, and (4) histological grade as percentage of fibers undergoing ischemic fiber degeneration (0 = < 5%; 1 = 5-25%; 2 = 26-50%; 3 = 51-75%; 4 = > 76%). Nerve blood flow and nerve action potential were uniformly absent and more than 90% of fibers had degenerated in both control and treatment groups receiving high doses. Control and treatment groups receiving moderate doses were well matched by level of ischemia (8.5 +/- 0.3 [N = 18] vs 7.7 +/- 0.4 ml/100 gm/min [N = 18], p > 0.05) but were significantly different by behavior score (5.6 +/- 0.7 vs 9.2 +/- 0.5 [N = 19], p < 0.001), nerve action potential (1.4 +/- 1.0 vs 3.9 +/- 0.5 [N = 6], p < 0.05), and histology (2.4 +/- 0.4 [N = 5] vs 0.8 +/- 0.5 [N = 4], p < 0.05). On single teased fiber evaluation, the predominant abnormality was E (axonal degeneration). We conclude that hyperbaric oxygenation will effectively rescue fibers from ischemic fiber degeneration, providing the ischemia is not extreme.

Effect of alpha-tocopherol deficiency on indices of oxidative stress in normal and diabetic peripheral nerve

We tested the hypothesis that oxidative stress can cause neuropathy by evaluating the effect of alpha-tocopherol depletion in normal and streptozotocin (STZ) diabetic peripheral nerve (known to be subject to oxidative stress). The end points were nerve electrophysiology and indices of oxidative stress. Studies were done on 6 groups of rats at 1 and 3 months: (1) Controls, normal alpha-tocopherol (Con[N]). (2) Controls, alpha-tocopherol-deficient (Con[-]) (3) Controls, alpha-tocopherol supplemented (Con[+]); (4) Diabetic, normal alpha-tocopherol (STZ[N]); (5) Diabetic, alpha-tocopherol-deficient (STZ[-]) (6) Diabetic, alpha-tocopherol supplemented (STZ[+]). An alpha-tocopherol-deficient diet resulted in a rapid depletion of the vitamin in plasma and sympathetic neurones (superior cervical ganglion), and a slower depletion in sensory neurones (dorsal root ganglion) and nerve. The depletion was associated with a reduction in reduced glutathione and an increase in conjugated dienes and hydroperoxides in normal rats, and resulted in similar changes, or accentuated the abnormalities, in diabetic nerves. Changes were more pronounced at 1 than 3 months and alpha-tocopherol supplementation, for the most part, did not prevent the abnormalities. alpha-Tocopherol depletion induced or worsened nerve conduction abnormalities in both sciatic-tibial and caudal nerves. Sensory fibers were more affected than motor fibers and the changes were more pronounced at 3 than 1 month. These findings support the notion that oxidative stress may cause neuropathy and that it might be mechanistically implicated in experimental diabetic neuropathy (STZ-EDN).

Different reinnervation patterns in the celiac/mesenteric and superior cervical ganglia following guanethidine sympathectomy in adult rats

We sought to determine whether chronic guanethidine (Gu) treatment in adult rats produces depletion of sympathetic neurons and hyperinnervation by sensory neuropeptides in the celiac/superior mesenteric (C/SMG) ganglion. Rats received Gu 40 mg/kg per day i.p or saline for 5 weeks. Upon completion of treatment, the C/SMG and the superior cervical ganglion (SCG) were examined for neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP), both by immunocytochemistry (ICC) and radioimmunoassay (RIA). Gu produced marked depletion of NPY-containing neurons and NPY content in the C/SMG, similar to that in the SCG (-89 +/- 2 vs. -92 +/- 4%, respectively). SP and CGRP immunoreactivities were significantly higher in control C/SMG as compared with SCG; after Gu treatment, there was no significant increase in either SP or CGRP in the C/SMG, however, both increased in the SCG. In contrast, VIP levels were similar in the SCG and C/SMG in controls and increased in the C/SMG but not in the SCG after Gu treatment. Thus, in adult rats, the C/SMG is as susceptible as the SCG to Gu treatment; the different pattern of hyperinnervation by SP, CGRP and VIP of the C/SMG as compared with the SCG may reflect the different sources for these neuropeptides in prevertebral as compared with paravertebral ganglia.

Motor and somatosensory evoked potentials in mice infected with Theiler's murine encephalomyelitis virus

We used an in vivo technique to record spinal motor and somatosensory evoked potentials in SJL/J and B10 mice chronically (4-10 months) infected with Daniel's strain of Theiler's murine encephalomyelitis virus (TMEV). SJL/J mice demonstrated primary spinal cord demyelination with chronic TMEV infection, whereas B10 mice were resistant to TMEV induced demyelination. Analysis based on the velocity of the initial peak of evoked responses demonstrated significantly slower conduction velocities in infected SJL/J mice as compared to age-matched uninfected SJL/J controls (p < 0.01) and infected B10 mice (p < 0.01). We noted no significant differences in conduction velocities of spinal evoked potentials recorded between uninfected SJL/J mice, uninfected B10 mice and infected B10 mice. Chronic infection with TMEV in susceptible SJL/J mice is associated with slowed conduction of spinal motor and somatosensory evoked potentials. This sensitive electrophysiologic assay will provide an in vivo method to test therapeutic regimens to inhibit demyelination or promote remyelination.

The influence of dose of microspheres on nerve blood flow, electrophysiology, and fiber degeneration of rat peripheral nerve

Microsphere embolization of peripheral nerve results in a variable degree of ischemic fiber degeneration. To enhance the utility of the model, we evaluated the relationship between dose of microspheres to the supplying arteries of the sciatic-tibial nerve to nerve blood flow (NBF), electrophysiology, morphology, and behavioral changes. There was considerable variability in the effect of embolization on nerve pathology in individual nerves. However, the dose of microspheres regressed with the degree of hindlimb paresis, reduction in NBF, degree of fiber pathology, and ischemic conduction failure of the tibial nerve, evaluated at day 7. All nerves with severe (grade 4) fiber degeneration had flows of < 3 mL x 100 g-1 x min-1. We conclude that it is possible to predict with a high degree of accuracy the severity of fiber degeneration by the degree of NBF reduction and by the electrophysiologic abnormalities.

Guanethidine sympathectomy increases substance P concentration in the superior sympathetic ganglion of adult rats

Adult rats received intraperitoneal injections of guanethidine or saline for 5 weeks. Six to 8 weeks following completion of treatment, concentrations of substance P and neuropeptide Y (NPY) were measured by radioimmunoassay in the superior cervical ganglion (SCG) and thoracic spinal cord. The SCG was also immunostained for NPY and substance P. No differences were observed in thoracic spinal cord content of either NPY or substance P. We observed depletion of NPY immunoreactive neurons and NPY levels in the SCG, and pharmacologic evidence of postganglionic denervation in guanethidine-treated rats. In guanethidine-treated rats, there was a marked increase of substance P levels in the SCG, where substance P was localized in fibers, but not cell bodies. Thus, sprouting of substance P-containing sensory fibers in the sympathetic ganglia occurs following postganglionic sympathectomy in adult rats.

Effect of ischemia and reperfusion in vivo on energy metabolism of rat sciatic-tibial and caudal nerves

Our model of severe nerve ischemia consistently results in extinction of the compound nerve and muscle action potentials (NAP; CMAP) within 30 min. Since impulse transmission may depend on nerve energy metabolism (NEM), we studied the effects of ischemia with reperfusion on sciatic-tibial nerve NEM in vivo and compared these results with NEM of this nerve in deoxygenated Ringer's solution in vitro and postmortem. Ischemia for 30 min postmortem or in deoxygenated Ringer's solution resulted in marked depletion of adenosine triphosphate (ATP) and creatine phosphate (CP) and an increase in lactate (LAC) of sciatic-tibial nerve of adult male Sprague-Dawley rats. In vivo ischemia for up to 3 h to sciatic-tibial nerve was sufficient to extinguish CMAP but not NAP and did not deplete ATP, CP, or GLU nor did it increase LAC. Ischemia sufficient to extinguish NAP resulted in reduction of energy substrates to about 50% of resting. Muscle fails to conduct impulses before nerve and in vivo reductions of energy substrates are milder than in vitro changes. These changes are explainable in terms of energy requirements and supply. These findings support an energetic basis of ischemic conduction failure.

Aminoguanidine effects on nerve blood flow, vascular permeability, electrophysiology, and oxygen free radicals

Since advanced glycosylation end products have been suggested to mediate hyperglycemia-induced microvascular atherogenesis and because aminoguanidine (AG) prevents their generation, we examined whether AG could prevent or ameliorate the physiologic and biochemical indices of streptozotocin (STZ)-induced experimental diabetic neuropathy. Four groups of adult Sprague-Dawley rats were studied: group I received STZ plus AG (25 mg.kg-1.day-1), group II received STZ plus AG (50 mg.kg-1.day-1), group III received STZ alone, and group IV was a control. We monitored conduction and action potential amplitudes serially in sciatic-tibial and caudal nerves, nerve blood flow, oxygen free radical activity (conjugated dienes and hydroperoxides), and the product of the permeability coefficient and surface area to 125I-labeled albumin. STZ-induced diabetes (group III) caused a 57% reduction in nerve blood flow and in abnormal nerve conduction and amplitudes and a 60% increase in conjugated dienes. Nerve blood flow was normalized by 8 weeks with AG (groups I and II) and conduction was significantly improved, in a dose-dependent manner, by 16 and 24 weeks in sciatic-tibial and caudal nerves, respectively. The permeability coefficient was not impaired, suggesting a normal blood-nerve barrier function for albumin, and the oxygen free-radical indices were not ameliorated by AG. We suggest that AG reverses nerve ischemia and more gradually improves their electrophysiology by an action on nerve microvessels. AG may have potential in the treatment of diabetic neuropathy.

Noradrenergic and neuropeptide Y mechanisms in guanethidine-sympathectomized rats

The cardiovascular responses to sympathomimetic agents, the norepinephrine (NE) content in peripheral tissues, and the tissue content and cardiovascular effects of neuropeptide Y (NPY) were examined in anesthetized adult rats with guanethidine-induced sympathectomy (GuSx). We observed blunted pressor responses to tyramine, exaggerated pressor responses to phenylephrine, and markedly reduced NE contents in the atrium, femoral artery, superior cervical ganglion (SCG), and sciatic and vagus nerves. When tyramine responses were corrected for the NE content in the SCG, GuSx rats were similar to controls. A depletion of NPY levels in tissue resulted in an increased sensitivity to the pressor effects of intravenous NPY administration. GuSx, therefore, reproduces findings of postganglionic adrenergic failure in humans. Responses to the administration of sympathomimetic agents may reflect the degree of noradrenergic denervation. NPY may be a potential marker of chronic postganglionic sympathetic denervation in cardiovascular tissue.

Comparison of nerve regeneration in vascularized and conventional grafts: nerve electrophysiology, norepinephrine, prostacyclin, malondialdehyde, and the blood-nerve barrier

We compared the efficacy of vascularized (VASC) and conventional (CONV) sciatic nerve grafts in restoring nerve blood flow (NBF), conduction, the blood-nerve barrier, norepinephrine (NE), and 6-keto prostaglandin F1 alpha (6-KPGF; the stable prostacyclin metabolite) in the sciatic nerve of the rat. We also measured malondialdehyde (MDA) content. NBF was much greater in VASC grafts, but the increase was confined to non-nutritive flow. There was a statistically non-significant increase in nerve action potential amplitude in the grafted segments of VASC nerves at 1 and 2 months post graft. The [14C]sucrose permeability surface area (PA) product was increased in both CONV and VASC at 1 and 3 months and was not different to each other. NE and 6-KPGF, the major vasoconstrictor and dilator of nerve microvessels were better restored in VASC than CONV reaching statistically significance for 6-KPGF (P less than 0.001). MDA used as an index of oxygen free radical generation was not significantly different in the 3 groups. The better restoration of 6-KPGF and perhaps NE suggest that VASC grafts may be more effective in restoring vasoreactivity of peripheral nerve following graft.

Ischemic and reperfusion injury of rat peripheral nerve

A rat model of severe nerve ischemia was used to study the effects of ischemia and reperfusion on nerve conduction, blood flow, and the integrity of the blood-nerve barrier. Conduction failure was consistently found in the sciatic-tibial nerve during 1- and 3-hr ischemic periods. Recovery of the compound muscle action potential was prompt and complete upon reperfusion following 1 hr of ischemia. However, after 3 hr of ischemia, recovery in the proximal portion of the sciatic nerve was less than 10%, and conduction block occurred in the distal portion of the nerve. Nerve blood flow was restored to only 55% and 45% of resting values following 1 and 3 hr, respectively, of ischemia and did not recover even after 2 hr of reperfusion. The blood-nerve barrier was not statistically impaired to the passage of [14C]sucrose following 1 hr of ischemia but was significantly impaired after 3 hr of ischemia. The permeability-surface area product was consistently greater following 1 hr of reperfusion than during the immediate reperfusion period. These data indicate that severe ischemia of peripheral nerve results in reperfusion injury, conduction block, and blood-nerve barrier disruption. Microvascular events, which may occur during reperfusion, may be important in amplifying the nerve fiber damage that began during ischemia.

Aortic occlusion and reperfusion and conduction, blood flow, and the blood-nerve barrier of rat sciatic nerve

We studied the effect of ischemia and reperfusion on blood flow, electrophysiology, and the blood-nerve barrier of the sciatic nerve of the rat. Ischemia for 10 to 60 min, with up to 3 h of reperfusion, was produced by closure and then release of a noose around the abdominal aorta. Nerve blood flow and function were measured serially using microelectrode-hydrogen polarography and electrophysiologic recordings, respectively. The integrity of the blood-nerve barrier was assessed using the permeability surface area product to [14C]sucrose. Ischemia of up to 30 min did not impair reperfusion. One hour of ischemia resulted in reperfusion abnormalities that affected about half of the nerves. The ischemic and reperfusion stresses did not disrupt the blood-nerve barrier to [14C]sucrose nor produce conduction block. Possible mechanisms for this resistance to ischemic and reperfusion injury are discussed.

Prostacyclin and noradrenaline in peripheral nerve of chronic experimental diabetes in rats

Noradrenaline levels in the superior cervical ganglion and sciatic nerve were significantly reduced in chronic streptozotocin-induced diabetes in rats. Sciatic nerve sheath in vitro biosynthesis of 6-keto prostaglandin F1 alpha (6KPGF1 alpha; the stable metabolite of prostacyclin) was significantly reduced but not in acute experimental diabetes. Nerves with reduced 6KPGF1 alpha had an excessive response to arachidonic acid stimulation. We suggest that the reduced endogenous biosynthesis of prostacyclin is due to reduced substrate availability, possibly due to the reduced noradrenaline. The implications of these findings on the pathogenesis of diabetic neuropathy are discussed. Neuropathy was found to involve all fibre populations studied (motor, sensory and sympathetic) and progressed with duration of diabetes.

The effect of hyperbaric oxygenation and hypoxia on the blood-nerve barrier

We measured the permeability coefficient--surface area product (PA) of peripheral nerve to [14C]sucrose in rat sciatic nerve in experimental chronic hypoxic hypoxia of up to 8 weeks and following hyperbaric oxygenation for 1 to 4 weeks. Chronic hypoxia caused an increase in PA presumably indicating impairment of the blood-nerve barrier at 4 weeks with restoration to normal by 8 weeks. Hyperbaric oxygenation (100% oxygen at 2.5 ata for 120 min/day 5 days per week) caused a mild but time dependent increase in PA reaching statistical significance by 4 weeks.

Effect of hyperbaric oxygenation on normal and chronic streptozotocin diabetic peripheral nerves

Hyperbaric oxygenation is known to affect energy metabolism and endothelial cell structure and function, but its effects on peripheral nerve have not been reported. We investigated whether it would (i) reverse established streptozotocin-induced diabetic neuropathy, a condition in which endoneurial hypoxia exists; (ii) affect energy metabolism in nerve; and (iii) alter the blood-nerve barrier. Sprague-Dawley rats that had been diabetic for 3 months and age-matched controls were used in these studies. One diabetic group and one control group were treated with hyperbaric oxygenation (2 atm for 2 h, 5 days/week) for 4 weeks. Identical groups remained in room air. Sciatic nerve adenosine triphosphate (ATP), creatine phosphate, lactate, and glucose concentrations showed similar changes at rest in both room air and after hyperbaric oxygenation. Nerves of control and diabetic groups exhibited increased lactate production and increased utilization of glucose, ATP, and creatine phosphate after 15 min of anoxia. The albumin blood-nerve barrier index was increased in control and diabetic nerves after hyperbaric treatment. Nerve conduction velocity was reduced in the diabetic-room air group and not improved by hyperbaric oxygenation. Caudal nerve action potential, which was significantly reduced in this group, was normalized after hyperbaric treatment. Resistance to ischemic conduction failure was increased in untreated diabetic nerve but not significantly different from controls after hyperbaric exposure. These findings indicate that treatment with hyperbaric oxygenation will partially reverse the neuropathy encountered in chronic diabetes. The biochemical changes are suggestive of enhanced nerve energy metabolism induced by hyperbaric oxygenation. The altered albumin blood-nerve barrier index presumably results from the action of free radicals on endothelial cells.

Slow axonal transport in experimental hypoxia and in neuropathy induced by p-bromophenylacetylurea

The slow axonal transport of proteins radiolabeled by incorporation of [35S]methionine was studied in motor nerves of rats subjected to chronic hypoxia. The conditions involved exposure to an atmosphere of 8-10% oxygen for periods of 3, 5, or 10 weeks. An experimentally verified computer model predicted a drop in mean endoneurial oxygen tension from 30.5 to 19 mm Hg, despite a measured increase in circulating hemoglobin from 16 to 22 g%. Nerve conduction velocity was unaffected during the early stages of hypoxia. After 10 weeks of hypoxia, conduction velocity still appeared normal in the sciatic nerve but was reduced in the caudal nerve by 2.5-4.5 m/s. At no time, however, was there evidence of impaired slow axonal transport, which proceeded with a mean velocity between 1 and 2 mm/day. Another set of experiments was performed to evaluate slow axonal transport in motor nerves of rats with peripheral neuropathy induced by the toxicant, p-bromophenylacetylurea. The results suggested a lower transport velocity in rats showing total hind-limb paralysis as compared with rats showing only mild to moderate motor dysfunction. The difference, however, could have reflected accelerated transport in mild neuropathy. In our view, the observations in experimental hypoxia- and toxicant-induced neuropathy are noteworthy for the resistance of slow transport to perturbation of the neuronal environment.

Electrophysiological studies on the effect of age on caudal nerve of the rat

The effect of age on electrophysiologic parameters was studied on the caudal nerve of 374 male Sprague-Dawley rats (age 24 to 630 days) and on 83 Fischer 344 rats (age 29 to 900 days). For Sprague-Dawley rats nerve conduction velocity and nerve action potential amplitude were both a parabolic function of age, increasing to 1 year and then declining. For Fischer 344 rats the same parameters increased progressively to 1.5 years and then declined. In contrast, for both Sprague-Dawley and Fischer 344 rats, resistance to ischemic conduction failure was a hyperbolic function of age reaching an asymptote at 1.5 to 2 years of age. These age-related changes in caudal nerve parallel the electrophysiologic alterations with age in human peripheral nerve more closely than previous reports in rodent limb nerves.

The effect of age on energy metabolism and resistance to ischaemic conduction failure in rat peripheral nerve

Caudal nerve conduction velocity and amplitude of nerve action potential increased progressively with age to 8 months after which time no further increases were demonstrated. Rat peripheral nerve was progressively more resistant to ischaemic-anoxic conduction failure with increasing age. This resistance to ischaemic conduction failure was paralleled by a progressive age-related decline in endoneurial O2 consumption. Endoneurial adenosine triphosphate and creatine phosphate values were also progressively reduced with age. 15 min of anoxia resulted in progressively smaller reductions in these nucleotide phosphates with increasing age to 8 months after which time little further change occurred. Nerve lactate response to anoxia was higher in young rats (1 and 2 months) than in older animals (8 and 21 months). High energy phosphate expenditure progressively declined with age to 8 months, then stabilized. These findings indicate that the major mechanism of resistance to ischaemic conduction failure is a progressive decline in energy requirements.

Experimental chronic hypoxic neuropathy: relevance to diabetic neuropathy

The cardinal electrophysiological abnormalities in experimental diabetic (EDN) and experimental galactose (EGN) neuropathy, models in which endoneurial hypoxia has been demonstrated, are a slowing in nerve conduction velocity (NCV) and a resistance to ischemic conduction block (RICB). These electrophysiological abnormalities are also present in human diabetic neuropathy, where microangiopathy has been demonstrated to be more severe than in EDN so that endoneurial hypoxia is also likely to be present. We examined the effects of endoneurial hypoxia per se on normal nerves. In rats subjected to chronic hypoxia (10% O2) for up to 10 wk, the two electrophysiological abnormalities had developed by 4 wk and were very similar in degree to those seen in EDN and EGN. These abnormalities occurred in the absence of hyperglycemia, nerve sorbitol accumulation, or myoinositol reduction. Resting O2 consumption was reduced, the percent increase in nerve lactate under anoxic stress was increased, and nerve free sugars were normal. Hexokinase and phosphofructokinase activities were not altered substantially when studied under conditions of O2 excess. These findings indicate that hypoxia per se will cause conduction slowing and suggest that the hypoxic nerve develops RICB because of a reduced energy requirement and an increased efficiency of anaerobic glycolysis, but without major changes in the activity of its controlling glycolytic enzymes.

Pyridoxine neuropathy in rats: specific degeneration of sensory axons

When rats received pyridoxine in doses large enough to cause neuropathy in humans, the animals developed gait ataxia that subsided after the toxin was withdrawn. By using quantitative histologic techniques, we found axonal degeneration of sensory system fibers and that the fibers derived from the ventral root were spared. Although the degeneration approached the dorsal root ganglion, neurons in the ganglion did not degenerate. We found no early decrease in oxygen consumption of nerve, suggesting that impaired oxidative metabolism was not the primary event.

Endoneurial oxygen tension and radial topography in nerve edema

Endoneurial edema occurs in numerous human and experimental neuropathies. We tested the hypothesis that the resultant increase in intercapillary distance (ICD) may result in endoneurial hypoxia. Experimental galactose neuropathy (EGN) was chosen since in this model, edema is due to the accumulation of galactitol, which does not directly damage nerve fibers, so that it was possible to study the role of endoneurial edema alone. We measured endoneurial oxygen tensions (PnO2) using oxygen-sensitive microelectrodes and related PnO2 radial topography to ICD. We also determined local oxygen consumption (VLO2) and critical PnO2(PcritO2). EGN and age-matched controls were studied at 4 months. (1) Caudal nerve conduction velocity was reduced in EGN. (2) The PnO2 values were reduced in EGN and the PnO2 histogram was shifted into the hypoxic range. These changes were paralleled by a significant increase in ICD in EGN. (3) The radial topography of PnO2 in EGN differed from the relatively uniform distribution in control nerves. In EGN the subperineurial PnO2 was significantly lower than the PnO2 at the center of the fascicle. These changes were paralleled by a significantly greater increase in ICD in the periphery. (4) That the PnO2 reduction in EGN was significant is suggested by the marked reduction in VLO2 and the large percentage (greater than 75%) of intrafascicular regions that fell below PcritO2 in EGN.

Ischemic conduction failure and energy metabolism in experimental diabetic neuropathy

We examined the effect of ischemia on nerve conduction in experimental diabetic neuropathy (EDN) and related electrophysiological changes to nerve adenosine triphosphate (ATP), creatine phosphate (CP), and lactate under anoxic conditions. Rats rendered diabetic with streptozotocin had a resistance to ischemic conduction block (RICB). Caudal nerve action potential (NAP) was well maintained for 10 min in controls and for 15 min in EDN, after which time NAP declined in both groups but more rapidly in normal rats. Time to 50% reduction in nerve ATP and CP was 10 and 3 min, respectively, in controls and delayed to 20 and 8 min in EDN. Rate of utilization of high-energy phosphate (approximately P) was linear for 5 min in controls to be followed by a progressive decline. In EDN rate of utilization of approximately P was linear to 15 min to be followed by a more gradual decline than in normal nerves. These findings suggest that the maintenance of nerve transmission in anoxic-ischemic states depends on anaerobic metabolism and that RICB in EDN is due in part to the ability of diabetic nerves to maintain a higher level of anaerobic glycolysis and for a longer time than normal nerves.

Prevention of some electrophysiologic and biochemical abnormalities with oxygen supplementation in experimental diabetic neuropathy

Endoneurial hypoxia has been suggested as a mechanism of human and experimental diabetic neuropathy (EDN). We found that rats rendered diabetic for 4 months had reduced nerve blood flow (NBF) and nerve oxygen tension (PnO2). The NBF was reduced by at least 33% in EDN and 60% of the oxygen tensions in the endoneurial O2 histogram were less than 25 mm Hg (3.3 kPa) in EDN compared with only 19% in the controls. To test the hypothesis that EDN may in part be due to hypoxia, we studied the effectiveness of oxygen supplementation in preventing some electrophysiologic and biochemical abnormalities. Rats with EDN had reduced caudal nerve conduction velocity and had a resistance to ischemic conduction block. When a matched groups of rats with EDN were O2 supplemented for 4 weeks, the time to 50% block of nerve conduction and nerve conduction velocity was no longer statistically different from controls. Endoneurial free sugars (glucose, fructose, sorbitol) were markedly increased in EDN. Oxygen supplementation resulted in no change in plasma glucose; by contrast, these increased endoneurial free sugars were significantly reduced (towards normal) by 60%, 33%, and 34%, respectively. myo-Inositol, however, was further decreased by oxygen supplementation. These findings of a partial prevention of electrophysiologic and biochemical abnormalities support a role of hypoxia in the pathogenesis of EDN.

Endoneurial blood flow and oxygen tension in the sciatic nerves of rats with experimental diabetic neuropathy

Endoneurial hypoxia has been postulated to be important in the pathogenesis of diabetic peripheral neuropathy and may be due to reduced nerve blood flow. Neither blood flow nor oxygen tension have previously been measured in peripheral nerve in diabetic neuropathy. We have therefore measured both nerve blood flow and endoneurial oxygen tension in the sciatic nerves of 8 rats with streptozotocin-induced diabetes for four months, and in 8 age-matched controls. In 7 of the diabetic animals mean nerve blood flow was 8.7 +/- 1.3 ml X min-1 X 100 g-1 which is significantly less than mean nerve blood flow in the controls (13.08 +/- 0.8 ml X min-1 X 100 g-1; P less than 0.01). In one diabetic animal, nerve blood flow was too low to be accurately measured. The reduction in nerve blood flow in diabetic neuropathy is due to an increase in resistance to flow which may be due to microangiopathy and to blood hyperviscosity. Endoneurial oxygen tension was also significantly reduced in experimental diabetic neuropathy in which 60 per cent of the oxygen measurements were less than 25 mmHg, compared with 19 per cent in the controls. Nerve blood flow was also measured in rats with experimental galactose neuropathy in which there is more marked sugar-alcohol accumulation, endoneurial oedema and elevation of endoneurial fluid pressure than in experimental diabetic neuropathy. The results obtained in this neuropathy suggest that the reduction in nerve blood flow which occurs in experimental diabetic neuropathy is due largely to factors other than sugar-alcohol accumulation in nerve. We postulate that endoneurial hypoxia may produce many of the observed morphological and biochemical changes in experimental diabetic neuropathy.

Structural specificity in demyelination induced by lysophospholipids

The demyelinating activity of lysophosphatidylcholine (lysoPC) and various structural analogs in rat sciatic nerve was evaluated by following electrophysiologic changes within the first hour and 1 week after intraneural injection. The lysophospholipids tested included 1-O-hexadecanoyl-sn-glycero-3-phosphocholine (1-acyl-GPC), 3-O-hexadecanoyl-sn-glycero-1-phosphocholine (3-acyl-GPC), 1-O-hexadecanoylpropanediol-3-phosphocholine (acyl-PPC), 1-O-hexadecylpropanediol-3-phosphocholine (alkyl-PPC) and 1-acyl-sn-glycero-3-phosphoethanolamine (1-acyl-GPE). Changes in conduction velocity, width, amplitude and time integral percentage were measured. Within 1 hour, the highest demyelinating activity was observed for alkyl-PPC, followed by 3-acyl-GPC, 1-acyl-GPC and acyl-PPC. Hydrolysis products of lysoPC (glycerophosphocholine, fatty acid), lysophosphatidylethanolamine (1-acyl-GPE), biradyl choline phospholipids (1,2-di-O-alkyl-rac-glycero-3-phosphocholine, dialkyl-GPC) or sodium deoxycholate proved ineffective in these short-term experiments. One week after intraneural injection, all lysophospholipids tested caused severe electrophysiologic changes, although dialkyl-GPC and sodium deoxycholate did not. Our data suggest (i) that differences in early demyelinating activity by the choline lysophospholipids are related to their rate of turnover, as highest activity was associated with the agents that are not metabolized by lysophospholipase (e.g., alkyl-PPC) or lysolecithin acyltransferase (e.g., 3-acyl-GPC), (ii) that the lysoPC molecule as such and not its products of catabolism causes demyelination, and (iii) that demyelinating activity is not due to the general detergent action of lysoPC, but rather that specific interactions appear to trigger the processes of demyelination induced by lysophospholipids.

Peripheral nerve conduction studies in galactose-poisoned rats. Demonstration of increased resistance to ischemic conduction associated with endoneurial edema due to sugar alcohol accumulation

Edematous nerves of galactose-poisoned rats had an increased resistance to ischemic conduction block when compared with control animals. Ischemia was caused by cardiac arrest due to intracardiac air embolism in 1 group and by occlusion of the abdominal aorta in another. In these 2 groups of galactose-fed rats, time to 50% conduction block was increased by 27 and 42%, respectively and the difference between control and galactose rats was significant (P less than 0.01 and P less than 0.001).