Pyridoxamine: A novel treatment for schizophrenia with enhanced carbonyl stress.

AIM: The aim of this clinical trial was to obtain proof of concept for high-dose pyridoxamine as a novel treatment for schizophrenia with enhanced carbonyl stress. METHODS: Ten Japanese schizophrenia patients with high plasma pentosidine, which is a representative biomarker of enhanced carbonyl stress, were recruited in a 24-week, open trial in which high-dose pyridoxamine (ranging from 1200 to 2400 mg/day) was administered using a conventional antipsychotic regimen. Main outcomes were the total change in Positive and Negative Syndrome Scale score and the Brief Psychiatric Rating Scale score from baseline to end of treatment at week 24 (or at withdrawal). RESULTS: Decreased plasma pentosidine levels were observed in eight patients. Two patients showed marked improvement in their psychological symptoms. A patient who harbors a frameshift mutation in the Glyoxalase 1 gene also showed considerable reduction in psychosis accompanied with a moderate decrease in plasma pentosidine levels. A reduction of greater than 20% in the assessment scale of drug-induced Parkinsonism occurred in four patients. Although there was no severe suicide-related ideation or behavior, Wernicke's encephalopathy-like adverse drug reactions occurred in two patients and were completely suppressed by thiamine supplementation. CONCLUSION: High-dose pyridoxamine add-on treatment was, in part, effective for a subpopulation of schizophrenia patients with enhanced carbonyl stress. Further randomized, placebo-controlled trials with careful monitoring will be required to validate the efficacy of high-dose pyridoxamine for these patients.

Protective Effects of Pyridoxamine Supplementation in the Early Stages of Diet-Induced Kidney Dysfunction.

Pyridoxamine, a structural analog of vitamin B6 that exerts antiglycative effects, has been proposed as supplementary approach in patients with initial diabetic nephropathy. However, the molecular mechanism(s) underlying its protective role has been so far slightly examined. C57Bl/6J mice were fed with a standard diet (SD) or a diet enriched in fat and fructose (HD) for 12 weeks. After 3 weeks, two subgroups of SD and HD mice started pyridoxamine supplementation (150 mg/kg/day) in the drinking water. HD fed mice showed increased body weight and impaired glucose tolerance, whereas pyridoxamine administration significantly improved insulin sensitivity, but not body weight, and reduced diet-induced increase in serum creatinine and urine albumin. Kidney morphology of HD fed mice showed strong vacuolar degeneration and loss of tubule brush border, associated with a drastic increase in both advanced glycation end products (AGEs) and AGEs receptor (RAGE). These effects were significantly counteracted by pyridoxamine, with consequent reduction of the diet-induced overactivation of NF-kB and Rho/ROCK pathways. Overall, the present study demonstrates for the first time that the administration of the antiglycative compound pyridoxamine can reduce the early stages of diet-dependent kidney injury and dysfunction by interfering at many levels with the profibrotic signaling and inflammatory cascades.

The Sulforaphane and pyridoxamine supplementation normalize endothelial dysfunction associated with type 2 diabetes.

In this study we investigate pyridoxamine (PM) and/or sulforaphane (SFN) as therapeutic interventions to determine whether activators of NFE2-related factor 2 (Nrf2) can be used in addition with inhibitors of advanced glycation end products (AGE) formation to attenuate oxidative stress and improve endothelial dysfunction in type 2 diabetes. Goto-kakizaki (GK) rats, an animal model of non-obese type 2 diabetes, were treated with or without PM and/or SFN during 8 weeks and compared with age-matched Wistar rats. At the end of the treatment, nitric oxide (NO)-dependent and independent vasorelaxation in isolated aorta and mesenteric arteries were evaluated. Metabolic profile, NO bioavailability and vascular oxidative stress, AGE and Nrf2 levels were also assessed. Diabetic GK rats presented significantly lower levels of Nrf2 and concomitantly exhibited higher levels of oxidative stress and endothelial dysfunction. PM and SFN as monotherapy were capable of significantly improving endothelial dysfunction in aorta and mesenteric arteries decreasing vascular oxidative damage, AGE and HbA1c levels. Furthermore, SFN + PM proved more effective reducing systemic free fatty acids levels, normalizing endothelial function, NO bioavailability and glycation in GK rats. Activators of Nrf2 can be used therapeutically in association with inhibitors of AGE and cross-linking formation to normalize endothelial dysfunction in type 2 diabetes.

Effect of Scavenging Circulating Reactive Carbonyls by Oral Pyridoxamine in Uremic Rats on Peritoneal Dialysis.

Pyridoxamine, a reactive carbonyl (RCO) scavenger, can ameliorate peritoneal deterioration in uremic peritoneal dialysis (PD) rats when given via dialysate. We examined the effects of scavenging circulating RCOs by oral pyridoxamine. Rats underwent nephrectomy and 3 weeks of twice daily PD either alone or with once daily oral pyridoxamine. PD solution was supplemented with methylglyoxal, a major glucose-derived RCO, to quench intraperitoneal pyridoxamine. Oral pyridoxamine achieved comparable blood and dialysate pyridoxamine concentrations, suppressed pentosidine accumulation in the blood but not in the mesenterium or dialysate, and reduced the increases in small solute transport and mesenteric vessel densities, with no effects on submesothelial matrix layer thickening or serum creatinine. Thus, reducing circulating RCOs by giving oral pyridoxamine with PD provides limited peritoneal protection. However, orally given pyridoxamine efficiently reaches the peritoneal cavity and would eliminate intraperitoneal RCOs. Oral pyridoxamine is more clinically favorable and may be as protective as intraperitoneal administration.

Pyridoxamine and pyridoxal are more effective than pyridoxine in rescuing folding-defective variants of human alanine:glyoxylate aminotransferase causing primary hyperoxaluria type I.

Vitamin B6 in the form of pyridoxine (PN) is one of the most widespread pharmacological therapies for inherited diseases involving pyridoxal phosphate (PLP)-dependent enzymes, including primary hyperoxaluria type I (PH1). PH1 is caused by a deficiency of liver-peroxisomal alanine: glyoxylate aminotransferase (AGT), which allows glyoxylate oxidation to oxalate leading to the deposition of insoluble calcium oxalate in the kidney. Only a minority of PH1 patients, mostly bearing the F152I and G170R mutations, respond to PN, the only pharmacological treatment currently available. Moreover, excessive doses of PN reduce the specific activity of AGT in a PH1 cellular model. Nevertheless, the possible effect(s) of other B6 vitamers has not been investigated previously. Here, we compared the ability of PN in rescuing the effects of the F152I and G170R mutations with that of pyridoxamine (PM) and PL. We found that supplementation with PN raises the intracellular concentration of PN phosphate (PNP), which competes with PLP for apoenzyme binding leading to the formation of an inactive AGT-PNP complex. In contrast, PNP does not accumulate in the cell upon PM or PL supplementation, but higher levels of PLP and PM phosphate (PMP), the two active forms of the AGT coenzyme, are found. This leads to an increased ability of PM and PL to rescue the effects of the F152I and G170R mutations compared with PN. A similar effect was also observed for other folding-defective AGT variants. Thus, PM and PL should be investigated as matter of importance as therapeutics for PH1 patients bearing folding mutations.

Protective Effects of Pyridoxamine Against UVC-induced Programmed Cell Death in HaCaT Cells.

BACKGROUND: Exposure to ultraviolet (UV) light is closely related to human diseases, such as skin cancer, due to irreversible injuries to the skin cells. The UV-induced DNA damage and programmed cell death are important determinants for skin carcinogenesis. The aim of the present study was to investigate the anti-ultraviolet-C (UVC) effects of pyridoxamine in human keratinocyte HaCaT cells and its mechanisms of action. RESULTS: UVC-induced programmed cell death in HaCaT cells was abrogated by treated the cells immediately after UVC irradiation with 40, 80 and 160 µM of pyridoxamine. Monitoring the UVC-induced-specific reactive oxygen species, we found that 20, 40, 80 and 160 µM of pyridoxamine was also effective in suppressing the induction of reactive oxygen species by UVC. CONCLUSION: Overall, our results provided evidence showing that pyridoxamine was effective in protecting HaCaT cells from UVC-induced programmed cell death and may be a potential anti-UVC agent in life and clinical practice.

Amelioration of experimental autoimmune uveoretinitis by inhibition of glyceraldehyde-derived advanced glycation end-product formation.

AGEs are permanently modified macromolecule derivatives that form through nonenzymatic glycation of amino groups of proteins. Glycer-AGEs are highly toxic and play an important role in the pathogenesis of chronic inflammatory diseases. However, the contribution of glycer-AGEs to the pathogenesis of uveitis is unclear. In this study, we measured serum levels of glycer-AGEs in 100 patients with endogenous uveitis (22 with HLA-B27-associated uveitis, 20 with VKH disease, 14 with Behçet's disease, and 44 with sarcoidosis) and 33 healthy volunteers. We then examined the effect of the AGE inhibitor in a mouse model of human endogenous uveitis (EAU) by continuous oral administration of pyridoxamine at 200 or 400 mg/kg/day. Regardless of the etiology, serum glycer-AGE levels were significantly higher in patients with uveitis than in healthy subjects. Treatment with 400 mg/kg pyridoxamine significantly reduced the clinical and histological severity of EAU and was accompanied by a significant decrease in serum and retinal glycer-AGE levels and suppression of translocation of NF-κB p65 into the nucleus of retinal cells. Serum glycer-AGE levels may therefore serve as a biomarker of human uveitis, as well as systemic inflammation, and may contribute to the progression of uveitis, including diabetic iritis, via the activation of NF-κB.

Effects of methylglyoxal and pyridoxamine in rat brain mitochondria bioenergetics and oxidative status.

Advanced glycation end products (AGEs) and methylglyoxal (MG), an important intermediate in AGEs synthesis, are thought to contribute to protein aging and to the pathogenesis of age-and diabetes-associated complications. This study was intended to investigate brain mitochondria bioenergetics and oxidative status of rats previously exposed to chronic treatment with MG and/or with pyridoxamine (PM), a glycation inhibitor. Brain mitochondrial fractions were obtained and several parameters were analyzed: respiratory chain [states 3 and 4 of respiration, respiratory control ratio (RCR), and ADP/O index] and phosphorylation system [transmembrane potential (ΔΨm), ADP-induced depolarization, repolarization lag phase, and ATP levels]; hydrogen peroxide (H2O2) production levels, mitochondrial aconitase activity, and malondialdehyde levels as well as non-enzymatic antioxidant defenses (vitamin E and glutathione levels) and enzymatic antioxidant defenses (glutathione disulfide reductase (GR), glutathione peroxidase (GPx), and manganese superoxide dismutase (MnSOD) activities). MG treatment induced a statistical significant decrease in RCR, aconitase and GR activities, and an increase in H2O2 production levels. The administration of PM did not counteract MG-induced effects and caused a significant decrease in ΔΨm. In mitochondria from control animals, PM caused an adaptive mechanism characterized by a decrease in aconitase and GR activities as well as an increase in both α-tocopherol levels and GPx and MnSOD activities. Altogether our results show that high levels of MG promote brain mitochondrial impairment and PM is not able to reverse MG-induced effects.

Pleiotropic effect of pyridoxamine on diabetic complications via CD36 expression in KK-Ay/Ta mice.

AIM: Pyridoxamine inhibits the development of diabetic complications. CD36 is a receptor/transporter which binds fatty acids of lipoproteins. The objective of the present study was to examine the pleiotropic effects of pyridoxamine, especially CD36 expression in KK-A(y)/Ta mice with type 2 diabetic nephropathy. METHODS: KK-A(y)/Ta mice were divided into 2 groups as follows: pyridoxamine treatment group and a tap water group as controls. The urinary ACR, fasting serum insulin, TG and lipoprotein subclasses were measured as biochemical parameters. The renal expressions of malondialdehyde (MDA) were evaluated by immunohistochemistry. CD36 mRNA expressions in kidney and adipose tissue were also evaluated using real-time PCR. RESULTS: Pyridoxamine decreased levels of urinary ACR, serum TG, especially VLDL and fasting serum insulin. MDA accumulation in the pyridoxamine treated group was significantly lower than those in the non-treatment group. The CD36 accumulation and mRNA expressions in kidney and adipose tissue in the treatment group were significantly higher than those in the non-treatment group. CONCLUSIONS: It appears that pyridoxamine ameliorated lipid peroxidation and insulin resistance in KK-A(y)/Ta mice. This pleiotropic effect of pyridoxamine was related to CD36 expression in the kidney and adipose tissue.

Effect of pyridoxamine (K-163), an inhibitor of advanced glycation end products, on type 2 diabetic nephropathy in KK-A(y)/Ta mice.

Advanced glycation end products (AGEs) from the Maillard reaction contribute to the pathogenesis of diabetes-associated complications such as diabetic nephropathy. In therapeutic interventions for reducing AGEs, many compounds have been reported as AGE inhibitors. The objective of the present study was to examine the effect of pyridoxamine (K-163), an AGE inhibitor, in type 2 diabetic KK-A(y)/Ta mice. KK-A(y)/Ta mice were given pyridoxamine (200 or 400 mg/kg per day) starting at 8 weeks of age for 12 weeks. They were divided into 3 groups as follows: pyridoxamine 200 mg/kg per day treatment group (n = 10), pyridoxamine 400 mg/kg per day treatment group (n = 10), and a tap water group as the control group (n = 20). The urinary albumin/creatinine ratio (ACR), body weight (BW), levels of fasting and casual blood glucose, blood glycated hemoglobin (HbA(1c)), fasting serum insulin, triglyceride (TG), total cholesterol (T-Cho), and 3-deoxyglucosone (3DG), and systemic blood pressure were measured as biochemical parameters. N(epsilon)-(Carboxymethyl)lysine (CML) and nitrotyrosine accumulations in glomeruli were evaluated by immunohistochemical analyses. Transforming growth factor beta1 (TGF-beta1) and laminin-beta1 messenger RNA expressions in the kidneys were evaluated by real-time polymerase chain reaction. Pyridoxamine, especially at 400 mg/kg per day, improved the levels of urinary ACR, fasting serum TG, and 3DG. CML and nitrotyrosine accumulations in glomeruli were decreased. Furthermore, large doses of pyridoxamine prevented not only urinary ACR but also increases of BW, casual blood glucose, and HbA(1c). TGF-beta1 and laminin-beta1 messenger RNA expressions in kidneys were significantly lower than those in the controls. There were no significant changes in the levels of fasting blood glucose, serum T-Cho, and systemic blood pressure among all groups. It appears that pyridoxamine improved urinary ACR by its anti-AGE and anti-oxidant effects in the kidneys of KK-A(y)/Ta mice.

Effect of vitamin B6 on oxygen radicals, mitochondrial membrane potential, and lipid peroxidation in H2O2-treated U937 monocytes.

Vitamin B6 (Vit.B6) supplementation has been shown to be beneficial in reducing diabetic complications, cognitive aging, and in the prevention of coronary heart disease. It was hypothesized that Vit.B6 compounds may function as antioxidants and thus offer protection against oxidative stress under various pathophysiological and or experimental conditions. To test this hypothesis, U937 monocytes were cultured with pyridoxine (P), pyridoxal phosphate (PP) and pyridoxamine (PM) and H2O2, either alone or together for 2 h. Oxidative stress was determined by measuring superoxide radical production, lipid peroxidation, and mitochondrial transmembrane potential. Results demonstrate that Vit.B6 compounds can prevent the oxygen radical generation and lipid peroxidation caused by hydrogen peroxide in U937 monocytes, and that some of the protective effect of Vit.B6 may occur via modification of mitochondrial function.

Pyridoxine and pyridoxamine inhibits superoxide radicals and prevents lipid peroxidation, protein glycosylation, and (Na+ + K+)-ATPase activity reduction in high glucose-treated human erythrocytes.

Vitamin B(6) (pyridoxine) supplementation has been found beneficial in preventing diabetic neuropathy and retinopathy, and the glycosylation of proteins. Oxygen radicals and oxidative damage have been implicated in the cellular dysfunction and complications of diabetes. This study was undertaken to test the hypothesis that pyridoxine (P) and pyridoxamine (PM) inhibit superoxide radical production, reduce lipid peroxidation and glycosylation, and increase the (Na+ + K+)-ATPase activity in high glucose-exposed red blood cells (RBC). Superoxide radical production was assessed by the reduction of cytochrome C by glucose in the presence and absence of P or PM in a cell-free buffered solution. To examine cellular effects, washed normal human RBC were treated with control and high glucose concentrations with and without P or PM. Both P and PM significantly lowered lipid peroxidation and glycated hemoglobin (HbA(1)) formation in high glucose-exposed RBC. P and PM significantly prevented the reduction in (Na+ + K+)-ATPase activity in high glucose-treated RBC. Thus, P or PM can inhibit oxygen radical production, which in turn prevents the lipid peroxidation, protein glycosylation, and (Na+ + K+)-ATPase activity reduction induced by the hyperglycemia. This study describes a new biochemical mechanism by which P or PM supplementation may delay or inhibit the development of complications in diabetes.

Mechanism of reactions catalyzed by selenocysteine beta-lyase.

The reaction mechanism of selenocystine beta-lyase has been studied and it was found that elemental selenium is released enzymatically from selenocysteine, and reduced to H2Se nonenzymatically with dithiothreitol or some other reductants that are added to prepare selenocysteine from selenocystine in the anaerobic reaction system. 1H and 13C NMR spectra of L-alanine formed in 2H2O have shown that an equimolar amount of [beta-2H1]- and [beta-2H2]alanines are produced. The deuterium isotope effect at the alpha position was observed; kH/kD = 2.4. These results indicated that the alpha hydrogen of selenocysteine was removed by a base at the active site, and was incorporated into the alpha position of alanine, a product, without exchange of a solvent deuterium. When the enzyme was incubated with L-selenocysteine in the absence of added pyridoxal 5'-phosphate, the activity decreased with prolonged incubation time. However, the activity was recovered by addition of 5'-phosphate. The spectrophotometric study showed that the inactivated enzyme was the apo form. The apoenzyme was activated by a combination of pyridoxamine 5'-phosphate and various alpha-keto acids such as alpha-ketoglutarate and pyruvate. Thus, the enzyme is inactivated through transamination between selenocysteine and the bound pyridoxal 5'-phosphate to produce pyridoxamine 5'-phosphate and a keto acid derived from selenocysteine. The pyridoxal enzyme, an active form, is regenerated by addition of alpha-keto acids. This regulatory mechanism is analogous to those of aspartate beta-decarboxylase [EC 4.1.1.12], arginine racemase [EC 5.1.1.9], and kynureninase [EC 3.7.1.3] [K. Soda and K. Tanizawa (1979) Adv. Enzymol. 49, 1].

Vitamin B6 requirements of nutritionally variant Streptococcus mitior.

The growth rate of three vitamin B6-dependent Streptococcus mitior (B6DS) and two non-B6DS strains in Todd-Hewitt broth, with and without vitamin B6 supplementation, was examined. Even in optimally supplemented culture media, the growth rate of the three B6DS strains was much slower than that of comparable non-B6DS strains. Uptake studies with [3H] pyridoxine suggest that these B6DS strains cannot assimilate pyridoxine. Although not transported intracellularly, pyridoxine inhibited the growth of B6DS strains in media supplemented with other vitamin B6 analogs, probably by binding to the vitamin B6 transport system and inhibiting the uptake of the other vitamin B6 analogs.

[Effect of vitamin B6 group on cholesterol and fatty acid biosynthesis (author's transl)].

The effect of vitamin B6 groups, pyridoxine, pyridoxamine, pyridoxal (pyridoxal phosphate and pyridoxal phosphate Ca) on hepatic cholesterol and fatty acid biosynthesis in mice were studied. 1. Acetate-14C incorporation rate into cholesterol and fatty acid in pyridoxal phosphate supplement in vitro increased remarkably, relative to pyridoxine or pyridoxamine. 2. When daily subcutaneous injection of pyridoxal phosphate or pyridoxal phosphate Ca were given to normal mice, pyridoxal phosphate produced the decrease of liver cholesterol biosynthesis and cholesterol levell and the increase of fatty acid biosynthesis and fatty acid level, while pyridoxal phosphate Ca did not produce any significant changes, relative to the normal groups. 3. The dietary cholesterol supplement given pyridoxine fed mice did not produce any changes in liver cholesterol and fatty acid synthesis, and liver cholesterol level, while the increase of liver fatty acid and blood cholesterol biosynthesis were seen. Pyridoxal phosphate Ca plus cholesterol feeding did not produce any changes in liver cholesterol and fatty acid biosynthesis, and liver fatty acid levels and blood cholesterol biosynthesis, while the increase of liver cholesterol leve was seen, relative to the cholesterol fed group.