Yaqub BA, Siddique A, Sulimani R.

Division of Neurology, King Khalid University Hospital, Riyadh, Saudi Arabia.

We studied the clinical and neurophysiological effects of methylcobalamin on patients with diabetic neuropathy. In a double-blind study, the active group showed statistical improvement in the somatic and autonomic symptoms with regression of signs of diabetic neuropathy. Motor and sensory nerve conduction studies showed no statistical improvement after 4 months. The drug was easily tolerated by the patients and no side effects were encountered.

Watanabe T Kaji R Oka N Bara W Kimura J, J Neurol Sci (1994 Apr) 122(2):140-3

Despite intensive searches for therapeutic agents, few substances have been convincingly shown to enhance nerve regeneration in patients with peripheral neuropathies. Recent biochemical evidence suggests that an ultra-high dose of methylcobalamin (methyl-B12) may up-regulate gene transcription and thereby protein synthesis. We examined the effects of ultra-high dose of methyl-B12 on the rate of nerve regeneration in rats with acrylamide neuropathy, using the amplitudes of compound muscle action potentials (CMAPs) after tibial nerve stimulation as an index of the number of regenerating motor fibers. After intoxication with acrylamide, all the rats showed equally decreased CMAP amplitudes. The animals were then divided into 3 groups; rats treated with ultra-high (500 micrograms/kg body weight, intraperitoneally) and low (50 micrograms/kg) doses of methyl- B12, and saline-treated control rats. Those treated with ultra-high dose showed significantly faster CMAP recovery than saline-treated control rats, whereas the low-dose group showed no difference from the control. Morphometric analysis revealed a similar difference in fiber density between these groups. Ultra-high doses of methyl-B12 may be of clinical use for patients with peripheral neuropathies.

Methylcobalamine (methyl-B12) Promotes Regeneration of Motor Nerve
Terminals Degenerating in anterior gracile muscle of
gracile axonal dystrophy (GAD) mutant mouse

Yamazaki K Oda K Endo C Kikuchi T Wakabayashi T, Neurosci Lett
(1994 Mar 28) 170(1):195-7

We examined the effects of methylcobalamin (methyl-B12, mecobalamin) on degeneration of motor nerve terminals in the anterior gracile muscle of gracile axonal dystrophy (GAD) mutant mice. GAD mice received orally methyl-B12 (1 mg/kg body wt/day) from the 40th day after birth for 25 days. In the distal endplate zone of the muscle, although most terminals were degenerated in both the untreated and methyl-B12-treated GAD mice, sprouts were more frequently observed in the latter. In the proximal endplate zone, where few degenerated terminals were seen in both groups of the mice, the perimeter of the terminals was increased and the area of the terminals was decreased significantly in the methyl-B12-treated GAD mice. These findings indicate that methyl-B12 promotes regeneration of degenerating nerve terminals in GAD mice.

Protective Effects of Methylcobalamine, A Vitamin B12 Analogue, Against Glutamate-induced Neurotoxicity in Retinal Cell Culture

Kikuchi M Kashii S Honda Y Tamura Y Kaneda K Akaike, Invest Ophthalmol Vis Sci (1997 Apr) 38(5):848-54

Purpose: To examine the effects of methylcobalamine on glutamate- induced neurotoxicity in the cultured retinal neurons. Methods: Primary cultures obtained from the fetal rat retina (gestation days 16 to 19) were used for the experiment. The neurotoxicity was assessed quantitatively using the trypan blue exclusion method. Results: Glutamate neurotoxicity was prevented by chronic exposure to methylcobalamine and S-adenosylmethionine (SAMe), which is formed in the metabolic pathway of methylcobalamin. Chronic exposure to methylcobalamine and SAMe also inhibited the neurotoxicity induced by sodium nitroprusside that release nitric oxide. By contrast, acute exposure to methylcobalamine did not protect retinal neurons against glutamate neurotoxicity. Conclusions: Chronic administration of methylcobalamine protects cultured retinal neurons against N-methyl-D- aspartate-receptor-mediated glutamate neurotoxicity, probably by altering the membrane properties through SAMe-mediated methylation.

Protective effects of a vitamin B12 analogue, methylcobalamin, against glutamate cytotoxicity in cultured cortical neurons

Akaike A Tamura Y Sato Y Yokota T, Eur J Pharmacol (1993 Sep 7) 241(1):1-6

The effects of methylcobalamin, a vitamin B12 analogue, on glutamate-induced neurotoxicity were examined using cultured rat cortical neurons. Cell viability was markedly reduced by a brief exposure to glutamate followed by incubation with glutamate-free medium for 1 h. Glutamate cytotoxicity was prevented when the cultures were maintained in methylcobalamin-containing medium. Glutamate cytotoxicity was also prevented by chronic exposure to S-adenosylmethionine, which is formed in the metabolic pathway of methylcobalamin. Chronic exposure to methylcobalamin and S- adenosylmethionine also inhibited the cytotoxicity induced by methyl-D-aspartate or sodium nitroprusside that releases nitric oxide. In cultures maintained in a standard medium, glutamate cytotoxicity was not affected by adding methylcobalamin to the glutamate-containing medium. In contrast, acute exposure to MK-801, a NMDA receptor antagonist, prevented glutamate cytotoxicity. These results indicate that chronic exposure to methylcobalamin protects cortical neurons against NMDA receptor-mediated glutamate cytotoxicity.

Pharmacokinetics of thiamine derivatives especially of benfotiamine.

Int J Clin Pharmacol Ther 1996 Feb; 34(2): 47-50. Loew D.

Pharmacokinetic data of orally administered lipid-soluble thiamine analogues like benfotiamine are reviewed and assessed. It is quite clear that benfotiamine is absorbed much better than water-soluble thiamine salts: maximum plasma levels of thiamine are about 5 times higher after benfotiamine, the bioavailability is at maximum about 3.6 times as high as that of thiamine hydrochloride and better than other lipophilic thiamine derivates. The physiological activity (alphaETK) increased only after benfotiamine was given. Due to its excellent pharmacokinetic profile benfotiamine should be preferred in treatment of relevant indications.

Exp Clin Endocrinol Diabetes 1996; 104(4): 311-6.
Stracke H, Lindemann A, Federlin K.

In a double-blind, randomized, controlled study, the effectiveness of treatment with a combination of Benfotiamine (an Allithiamine, a lipid-soluble derivative of vitamin B1 with high bioavailability) plus vitamin B6/B12 on objective parameters of neuropathy was studied over a period of 12 weeks on 24 diabetic patients with diabetic polyneuropathy. The results showed a significant improvement (p = 0.006) of nerve conduction velocity in the peroneal nerve and a statistical trend toward improvement of the vibration perception threshold. Long-term observation of 9 patients with verum over a period of 9 months support the results. Therapy-specific adverse effects were not seen. The results of this double-blind investigation, of the long-term observation and of the reports in the literature support the contention that the neurotropic benfotiamine-vitamin B combination represents a starting point in the treatment of diabetic polyneuropathy.

Benfotiamine inhibits intracellular formation of advanced Glycation end products in vivo

Diabetes. 2000 May; 49(Suppl1): A143(P583). Lin J, Alt A, Liersch J, Bretzel RG, Brownlee MA, Hammes HP.

We have demonstrated previously that intracellular formation of the advanced glycation end product (AGE) N-[Epsilon]-(carboxymethyl)lysine (CML) inversely correlates with diabetic vascular complications independently from glycemia (Diabetologia 42, 603, 1999). Here, we studied the effect of benfotiamine, a lipid-soluble thiamine derivative with known AGE-inhibiting properties in-vitro on the intracellular formation of (CML) and methylglyoxal-derived AGE in red blood cells. Blood was collected from 6 Type 1 diabetic patients (2m, 4f, age 31.8 ± 5.5 years; diabetes duration 15.3 ± 7.0 years) before and after treatment with 600 mg/day benfotiamine for 28 days. In addition to HbA1c (HPLC), CML and methylglyoxal were measured using specific antibodies and a quantitative blot technique. While treatment with benfotiamine did not affect HbA1c levels (at entry: 7.18 ± 0.86%; at conclusion 6.88 ± 0.88%; p not significant), levels of CML decreased by 40% (737 ± 51 arbitrary units/mg protein (AU) vs 470 ± 86 AU; p<0.01). The levels of intracellular methylglyoxal were reduced by almost 70% (1628 ± AU vs 500 ± 343 AU; p<0.01). The data indicate that thiamine derivatives are effective inhibitors of both intracellular glycoxidation and AGE formation.

Summary:Advanced glycation end product (AGE) has been linked to many age related illnesses such as cataract development, Alzheimer’s Disease, cardiovascular disease, strokes and reduced muscle function. In this study, benfotiamine was shown to inhibit (AGE) development which in turn leads to decresed risk for these diseases.

Diabetics are at risk for AGE formation beyond normal levels.

Benfotiamine blocks three major pathways of hyperglycemic damage and prevents experimental diabetic retinopathy.


Nat Med 2003 Mar; 9(3): 294-9. Hammes HP, Du X, Edelstein D, Taguchi T, Matsumura T, Ju Q, Lin J, Bierhaus A, Nawroth P, Hannak D, Neumaier M, Bergfeld R, Giardino I, Brownlee M.

Three of the major biochemical pathways implicated in the pathogenesis of hyperglycemia induced vascular damage (the hexosamine pathway, the advanced glycation end product (AGE) formation pathway and the diacylglycerol (DAG)-protein kinase C (PKC) pathway) are activated by increased availability of the glycolytic metabolites glyceraldehyde-3-phosphate and fructose-6-phosphate. We have discovered that the lipid-soluble thiamine derivative benfotiamine can inhibit these three pathways, as well as hyperglycemia-associated NF-kappaB activation, by activating the pentose phosphate pathway enzyme transketolase, which converts glyceraldehyde-3-phosphate and fructose-6-phosphate into pentose-5-phosphates and other sugars. In retinas of diabetic animals, benfotiamine treatment inhibited these three pathways and NF-kappaB activation by activating transketolase, and also prevented experimental diabetic retinopathy. The ability of benfotiamine to inhibit three major pathways simultaneously might be clinically useful in preventing the development and progression of diabetic complications.

Summary:Advanced glycation end product (AGE) has been linked to many age related illnesses such as cataract development, Alzheimer’s Disease, cardiovascular disease, strokes and reduced muscle function. In this study, benfotiamine was shown to inhibit (AGE) development which in turn leads to decresed risk for these diseases.

Diabetics are at risk for AGE formation beyond normal levels.

Prevention of cardiac autonomic neuropathy in dogs with Benfotiamine.

Koltai MZ. In Gries FA, Federlin K. Benfotiamin in the Therapy of Polyneuropathy.
New York: Georg Thieme Verlag, 1998; 45-9.

Experimentally-induced diabetes of the dog leads to disturbances in the autonomous neurological function of the heart after approximately 3 months of continuously- observed diabetes. As signs of autonomic cardiac neuropathy, the heart rate variability and Valsalva ratio clearly fell in the untreated diabetic animals. Oral benfotiamine, administered from the sixth day after diabetes-induction, prevented or at least delayed these changes. According to the results, treatment with fat-soluble benfotiamine can play an important role in the therapy and prevention of cardiac autonomic neuropathy, apart from any effect on diabetic metabolic disturbances.

Ziegler D, Gries FA. Diabetes. 1997;46 (suppl 2):S62–66.

http://www.ncbi.nlm.nih.gov/pubmed/9285502

Antioxidant treatment has been shown to prevent nerve dysfunction in experimental diabetes, providing a rationale for a potential therapeutic value in diabetic patients. The effects of the antioxidant alpha-lipoic acid (thioctic acid) were studied in two multicenter, randomized, double-blind placebo-controlled trials. In the Alpha-Lipoic Acid in Diabetic Neuropathy Study, 328 patients with NIDDM and symptomatic peripheral neuropathy were randomly assigned to treatment with intravenous infusion of alpha-lipoic acid using three doses (ALA 1,200 mg; 600 mg; 100 mg) or placebo (PLAC) over 3 weeks. The total symptom score (TSS) (pain, burning, paresthesia, and numbness) in the feet decreased significantly from baseline to day 19 in ALA 1,200 and ALA 600 vs. PLAC. Each of the four individual symptom scores was significantly lower in ALA 600 than in PLAC after 19 days (all P < 0.05). The total scale of the Hamburg Pain Adjective List (HPAL) was significantly reduced in ALA 1,200 and ALA 600 compared with PLAC after 19 days (both P < 0.05). In the Deutsche Kardiale Autonome Neuropathie Studie, patients with NIDDM and cardiac autonomic neuropathy diagnosed by reduced heart rate variability were randomly assigned to treatment with a daily oral dose of 800 mg alpha-lipoic acid (ALA) (n = 39) or placebo (n = 34) for 4 months. Two out of four parameters of heart rate variability at rest were significantly improved in ALA compared with placebo. A trend toward a favorable effect of ALA was noted for the remaining two indexes. In both studies, no significant adverse events were observed. In conclusion, intravenous treatment with alpha-lipoic acid (600 mg/day) over 3 weeks is safe and effective in reducing symptoms of diabetic peripheral neuropathy, and oral treatment with 800 mg/day for 4 months may improve cardiac autonomic dysfunction in NIDDM.

Nagamatsu M, Nickander KK, Schmelzer JD,et al. Lipoic acid improves nerve blood flow, reduces oxidative stress, and improves distal nerve conduction in experimental diabetic neuropathy. Diabetes Care. 1995;18:1160-1167.

http://care.diabetesjournals.org/content/18/8/1160.abstract

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.

Packer L, Kraemer K, Rimbach G. Nutrition. 2001;17(10):888-895.

http://www.ncbi.nlm.nih.gov/pubmed/11684397

Alpha-lipoic acid (LA) and its reduced form, dihydrolipoic acid, are powerful antioxidants. LA scavenges hydroxyl radicals, hypochlorous acid, peroxynitrite, and singlet oxygen. Dihydrolipoic acid also scavenges superoxide and peroxyl radicals and can regenerate thioredoxin, vitamin C, and glutathione, which in turn can recycle vitamin E. There are several possible sources of oxidative stress in diabetes including glycation reactions, decompartmentalization of transition metals, and a shift in the reduced-oxygen status of the diabetic cells. Diabetics have increased levels of lipid hydroperoxides, DNA adducts, and protein carbonyls. Available data strongly suggest that LA, because of its antioxidant properties, is particularly suited to the prevention and/or treatment of diabetic complications that arise from an overproduction of reactive oxygen and nitrogen species. In addition to its antioxidant properties, LA increases glucose uptake through recruitment of the glucose transporter-4 to plasma membranes, a mechanism that is shared with insulin-stimulated glucose uptake. Further, recent trials have demonstrated that LA improves glucose disposal in patients with type II diabetes. In experimental and clinical studies, LA markedly reduced the symptoms of diabetic pathologies, including cataract formation, vascular damage, and polyneuropathy. To develop a better understanding of the preventative and therapeutic potentials of LA, much of the current interest is focused on elucidating its molecular mechanisms in redox dependent gene expression.

Ziegler D, Reljanovic M, Mehnert H, Gries FA. Exp Clin Endocrinol Diabetes. 1999; 107:421-430.

http://www.ncbi.nlm.nih.gov/pubmed/10595592

Diabetic neuropathy represents a major health problem, as it is responsible for substantial morbidity, increased mortality, and impaired quality of life. Near-normoglycaemia is now generally accepted as the primary approach to prevention of diabetic neuropathy, but is not achievable in a considerable number of patients. In the past two decades several medical treatments that exert their effects despite hyperglycaemia have been derived from the experimental pathogenetic concepts of diabetic neuropathy. Such compounds have been designed to improve or slow the progression of the neuropathic process and are being evaluated in clinical trials, but with the exception of alpha-lipoic acid (thioctic acid) which is available in Germany, none of these drugs is currently available in clinical practice. Here we review the current evidence from the clinical trials that assessed the therapeutic efficacy and safety of thioctic acid in diabetic polyneuropathy. Thus far, 15 clinical trials have been completed using different study designs, durations of treatment, doses, sample sizes, and patient populations. Within this variety of clinical trials, those with beneficial effects of thioctic acid on either neuropathic symptoms and deficits due to polyneuropathy or reduced heart rate variability resulting from cardiac autonomic neuropathy used doses of at least 600 mg per day. The following conclusions can be drawn from the recent controlled clinical trials. 1.) Short-term treatment for 3 weeks using 600 mg of thioctic acid i.v. per day appears to reduce the chief symptoms of diabetic polyneuropathy. A 3-week pilot study of 1800 mg per day given orally indicates that the therapeutic effect may be independent of the route of administration, but this needs to be confirmed in a larger sample size. 2.) The effect on symptoms is accompanied by an improvement of neuropathic deficits. 3.) Oral treatment for 4-7 months tends to reduce neuropathic deficits and improves cardiac autonomic neuropathy. 4.) Preliminary data over 2 years indicate possible long-term improvement in motor and sensory nerve conduction in the lower limbs. 5.) Clinical and postmarketing surveillance studies have revealed a highly favourable safety profile of the drug. Based on these findings, a pivotal long-term multicenter trial of oral treatment with thioctic acid (NATHAN I Study) is being conducted in North America and Europe aimed at slowing the progression of diabetic polyneuropathy using a clinically meaningful and reliable primary outcome measure that combines clinical and neurophysiological assessment.

Melhem MF, Craven PA, Derubertis FR. Effects of dietary supplementation of alpha-lipoic acid on early glomerular injury in diabetes mellitus. J Am Soc Nephrol. 2001;12:124-133.

http://www.ncbi.nlm.nih.gov/pubmed/11134258

Antioxidants, in particular vitamin E (VE), have been reported to protect against diabetic renal injury. alpha-Lipoic acid (LA) has been found to attenuate diabetic peripheral neuropathy, but its effects on nephropathy have not been examined. In the present study, parameters of glomerular injury were examined in streptozotocin diabetic rats after 2 mo on unsupplemented diets and in diabetic rats that received the lowest daily dose of dietary LA (30 mg/kg body wt), VE (100 IU/kg body wt), or vitamin C (VC; 1 g/kg body wt), which detectably increased the renal cortical content of each antioxidant. Blood glucose values did not differ among the diabetic groups. At 2 mo, inulin clearance, urinary albumin excretion, fractional albumin clearance, glomerular volume, and glomerular content of immunoreactive transforming growth factor-beta (TGF-beta) and collagen alpha1 (IV) all were significantly increased in unsupplemented D compared with age-matched nondiabetic controls. With the exception of inulin clearance, LA prevented or significantly attenuated the increase in all of these glomerular parameters in D, as well as the increases in renal tubular cell TGF-beta seen in D. At the dose used, VE reduced inulin clearance in D to control levels but failed to alter any of the other indices of glomerular injury or to suppress renal tubular cell TGF-beta in D. VC suppressed urinary albumin excretion, fractional albumin clearance, and glomerular volume but not glomerular or tubular TGF-beta or glomerular collagen alpha1 (IV) content. LA but not VE or VC significantly increased renal cortical glutathione content in D. These data indicate that LA is effective in the prevention of early diabetic glomerular injury and suggest that this agent may have advantages over high doses of either VE or VC.

Lynch MA. Nutr Neurosci. 2001;4(6):419-438.

http://www.ncbi.nlm.nih.gov/pubmed/11843262

In the past decade or so, a convincing link between oxidative stress and degenerative conditions has been made and with the knowledge that oxidatiye changes may actually trigger deterioration in cell function, a great deal of energy has focussed on identifying agents which may have possible therapeutic value in combating oxidative changes. One agent which has received attention, because of its powerful antioxidative effects, particularly in neuronal tissue, is lipoic acid.

Melhem MF, Craven PA, Liachenko J, et al. Alpha-lipoic acid attenuates hyperglycemia and prevents glomerular mesangial matrix expansion in diabetes. J Am Soc Nephrol. 2002;13:108-116.

http://www.ncbi.nlm.nih.gov/pubmed/11752027

Previous studies demonstrated that 2 mo of dietary supplementation with alpha-lipoic acid (LA) prevented early glomerular injury in non-insulin-treated streptozotocin diabetic rats (D). The present study examined the effects of chronic LA supplementation (30 mg/kg body wt per d) on nephropathy in D after 7 mo of diabetes. Compared with control rats, D developed increased urinary excretion of albumin and transforming growth factor beta, renal insufficiency, glomerular mesangial matrix expansion, and glomerulosclerosis in association with depletion of glutathione and accumulation of malondialdehyde in renal cortex. LA prevented or ameliorated all of these changes in D. Because chronic LA supplementation also attenuated hyperglycemia in D after 3 mo, its effects on renal injury were compared with treatment of rats with sufficient insulin to maintain a level of glycemic control for the entire 7-mo period (D-INS) equivalent to that observed with LA during the final 4 mo. Despite superior longitudinal glycemic control in D-INS, urinary excretion of albumin and transforming growth factor beta, glomerular mesangial matrix expansion, the extent of glomerulosclerosis, and renal cortical malondialdehyde content were all significantly greater, whereas cortical glutathione content was lower than corresponding values in D given LA. Thus, the renoprotective effects of LA in D were not attributable to improved glycemic control alone but also likely reflected its antioxidant activity. The combined antioxidant and hypoglycemic actions of LA both may contribute to its utility in preventing renal injury and other complications of diabetes.

Androne L, Gavan NA, Veresiu IA, Orasan R. In vivo effect of lipoic acid on lipid peroxidation in patients with diabetic neuropathy. In Vivo. 2000;14(2):327-330

http://www.ncbi.nlm.nih.gov/pubmed/10836205

BACKGROUND: The diabetic state, in both humans and experimental animals, is associated with oxidative stress. Lipid peroxidation of nerve membranes has been suggested as a mechanism by which peripheral nerve ischemia and hypoxia could cause neuropathy. Lipoic acid (LA) is a powerful inhibitor of iron-dependent lipid peroxidation and reactive oxygen species. The treatment of diabetic peripheral and cardiac autonomic neuropathy with LA is based on good clinical and experimental evidence.

MATERIALS AND METHODS: To investigate the magnitude of the oxidative stress, serum ceruloplasmin (Cp) and lipid peroxide (Lp) levels were measured in 10 patients with diabetic neuropathy, before and 70 days after treatment with single dose of 600 mg LA/day. For other 12 healthy age- and sex-matched control subjects the serum Cp and Lp levels were evaluated.

RESULTS: Our results show that hyperglycemia is a factor for an increase in serum ceruloplasmin in patients with diabetic neuropathy compared to healthy subjects (p < 0.0001). High serum ceruloplasmin (Cp) level in patients with diabetes may be related to antioxidant defense. The treatment of diabetic neuropathy with LA does not affect significantly the serum Cp activity. The serum Lp levels after LA administration were significantly lower (p < 0.005) than those before treatment.

CONCLUSIONS: The antioxidant therapy with LA improves and may prevent diabetic neuropathy. This improvement is associated with a reduction in the indexes of lipid peroxidation. Oxidative stress appears to be primarily due to the processes of nerve ischemia and hyperglycemia autooxidation.