Risk assessment of free hydroquinone derived from Arctostaphylos Uva-ursi folium herbal preparations.

Uva-ursi folium (bearberry leaf) has been traditionally used to treat symptoms of lower urinary tract infections. The most representative constituent of this herbal drug is arbutin that is rapidly absorbed in the small intestine and undergoes hepatic conjugation to form hydroquinone (HQ) conjugates. As free HQ is crucial for the safety of the herbal preparation, we reviewed published and unpublished experimental and human studies to clarify some outdated assumptions and to support the safety of therapeutic daily doses of Uva-ursi folium extract. Specifically, data on pharmacokinetics and the human exposure of arbutin and HQ were reviewed. A therapeutic recommended human daily dose of bearberry leaf extract (420 mg hydroquinone derivatives calculated as anhydrous arbutin) liberates free HQ in urine at a maximum exposure level of 11 µg/kg body weight (bw)/d. By means of an experimental no observed effect level value, a permitted daily exposure dose below which there is a negligible risk to human health was estimated for free HQ (100 µg/kg bw/d). Dietary sources of arbutin/HQ that are regularly consumed long term by humans generate comparable free HQ exposure levels. There is no direct evidence, regarding human data, supporting the fact that free HQ causes convulsion, hepatotoxicity, nephrotoxicity, or promotion of tumors in humans. Free HQ had no activity promoting pancreatic, bladder, stomach, or liver carcinogenesis. In conclusion, under the recommended use conditions Uva-ursi folium is a safe therapeutic option for treating lower urinary tract infections.

Suspected black cohosh hepatotoxicity: no evidence by meta-analysis of randomized controlled clinical trials for isopropanolic black cohosh extract.

OBJECTIVE: Black cohosh, a popular herbal treatment for menopausal symptoms, has been implicated in a number of hepatotoxicity case reports. The purpose of this investigation was to analyze data gained from clinical trials on the effect of black cohosh on liver function. METHODS: A meta-analysis of randomized, double-blind, and controlled clinical trials was conducted. These studies primarily evaluated the efficacy and safety of the isopropanolic black cohosh extract (iCR) in perimenopausal and postmenopausal women. Raw data on liver function values of aspartate aminotransferase, alanine aminotransferase, and γ-glutamyltranspeptidase were considered in this analysis, if these data at baseline and after 3 to 6 months of treatment were available. Standard methods of descriptive statistics were used in this analysis. RESULTS: Five studies involving a total of 1,117 women were included in the meta-analyses. A total of 1,020 women (test population=517 and reference population=503) completed the studies. Perimenopausal and postmenopausal women (40-60 y) were treated daily with iCR (corresponding to 40-128 mg drug) for 3 to 6 months. The meta-analyses of the standardized mean differences in the "test" versus "reference" showed no significant effects and no differences between double-blind, placebo-controlled and other trials. The overall fixed effect ± SEM was 0.055 ± 0.062 (P=0.37) for aspartate aminotransferase and 0.063 ± 0.062 (P=0.31) for alanine aminotransferase. The nonsignificant effects concerned the overall analyses of all included studies as well as the proportion of placebo-controlled studies. CONCLUSIONS: The results of this meta-analysis of five randomized, double-blind, and controlled clinical trials showed no evidence that iCR has any adverse effect on liver function.

Methylglyoxal impairs glucose metabolism and leads to energy depletion in neuronal cells--protection by carbonyl scavengers.

Advanced glycation end products (AGEs) are found in various intraneuronal protein deposits such as neurofibrillary tangles in Alzheimer's disease and Lewy bodies in Parkinson's disease. Among the many reactive carbonyl compounds and AGE precursors, methylglyoxal is most likely to contribute to intracellular AGE formation, since it is extremely reactive and constantly produced by degradation of triosephosphates. Furthermore, methylglyoxal levels increase under pathophysiological conditions, for example, when trisosephosphate levels are elevated, the expression or activity of glyoxalase I is decreased, as is the case when the concentration of reduced glutathione, the rate-determining co-factor of glyoxalase I, is low. However, the effects of methylglyoxal on mitochondrial function and energy levels have not been studied in detail. In this study, we show that methylglyoxal increases the formation of intracellular reactive oxygen species and lactate in SH-SY5Y neuroblastoma cells. Methylglyoxal also decreases mitochondrial membrane potential and intracellular ATP levels, suggesting that carbonyl stress-induced loss of mitochondrial integrity could contribute to the cytotoxicity of methylglyoxal. The methylglyoxal-induced effects such as ATP depletion and mitochondrial dysfunction can be prevented by pre-incubation of the cells with the carbonyl scavengers aminoguanidine and tenilsetam. In a clinical context, these compounds could not only offer a promising therapeutic strategy to reduce intracellular AGE-accumulation, but also to decrease the dicarbonyl-induced impairment of energy production in aging and neurodegeneration.

Carbonyl stress and NMDA receptor activation contribute to methylglyoxal neurotoxicity.

Methylglyoxal (MG) is a reactive alpha-ketoaldehyde physiologically generated as a by-product of glycolysis. MG that is able to form protein adducts resulting in advanced glycation end products accumulates under conditions associated with neurodegeneration such as impaired glucose metabolism or oxidative stress. In the present study, short-term exposure of human neuroblastoma SH-SY5Y cells to MG was associated with an early depolarization of the plasma membrane, glutamate release, and formation of reactive oxygen species. In addition, long-term exposure (24 h) of SH-SY5Y cells to MG caused a decrease in cell viability, intracellular ATP, and rhodamine 123 (Rh-123) fluorescence. ATP depletion and the decrease in Rh-123 fluorescence were prevented by carbonyl scavengers, the nitric oxide synthase inhibitor L-NAME, and N-methyl-d-aspartate (NMDA) receptor antagonists. Furthermore, the MG-induced glutamate release and the loss in cell viability were prevented by NMDA receptor antagonists. Therefore, MG renders cells more vulnerable to excitotoxicity. In conclusion, carbonyl scavengers as well as NMDA receptor antagonists may represent effective therapeutic tools to reduce the risk of pathophysiological changes associated with carbonyl stress in neurodegenerative diseases.

The carbonyl scavengers aminoguanidine and tenilsetam protect against the neurotoxic effects of methylglyoxal.

Advanced glycation end products (AGEs) have been identified in age-related intracellular protein deposits of Alzheimer's disease (amyloid plaques and neurofibrillary tangles) and Parkinson disease (Lewy bodies), suggesting that these protein deposits have been exposed to AGE precursors such as the reactive dicarbonyl compound methylglyoxal. In ageing tissue and under diabetic pseudohypoxia, intracellular methylglyoxal levels rise through an impairment of triosephosphate utilization. Furthermore, methylglyoxal detoxification is impaired when reduced glutathione levels are low, conditions, which have all been described in Alzheimer's disease. However, there is less known about the toxicity of methylglyoxal, particularly about therapeutic strategies to scavenge such dicarbonyl compounds and attenuate their toxicity. In our study, extracellularly applied methylglyoxal was shown to be toxic to human neuroblastoma cells in a dose-dependent manner above concentrations of 150 microM with a LD50 of approximately 1.25 mM. Pre-incubation of methylglyoxal with a variety of carbonyl scavengers such as aminoguanidine or tenilsetam and the thiol antioxidant lipoic acid significantly reduced its toxicity. In summary, carbonyl scavengers might offer a promising therapeutic strategy to reduce the neurotoxicity of reactive carbonyl compounds, providing a potential benefit for patients with age-related neurodegenerative diseases.

Advanced glycation endproducts induce changes in glucose consumption, lactate production, and ATP levels in SH-SY5Y neuroblastoma cells by a redox-sensitive mechanism.

Advanced glycation endproducts (AGEs) accumulate on long-lived proteins, including beta-amyloid plaques in Alzheimer's disease, and are suggested to contribute to neuronal dysfunction and cell death. We have investigated the effects of a model AGE upon glucose metabolism and energy production in a neuroblastoma cell line. AGEs decrease cellular ATP levels and increase glucose consumption and lactate production. All of the AGE-induced metabolic changes can be attenuated by antioxidants such as (R+)-alpha-lipoic acid and 17beta-estradiol. These antioxidants may become useful drugs against (AGE-mediated) effects in neurodegeneration through their positive effects on cellular energy metabolism.