Stability of ascorbic acid in human aqueous humor.

OBJECTIVE: The stability of ascorbic acid (AA) in the human aqueous humor (AqH) remains unclear. This study aimed to investigate the stability of AqH AA under varying conditions (27, 4, - 20, and - 80 °C) without acidification. RESULTS: Rapid AA degradation occurred at 27 °C. At 4 °C, a significant 12.2% degradation was observed after 24 h. Storage at - 20 °C resulted in a notable 37.5% degradation after 28 days, whereas storage at - 80 °C resulted in 10.7% degradation after 28 days. Unacidified AqH samples recorded early decomposition at 27 °C and 4 °C. In conclusion, it is recommended to conduct measurements within 28 days for samples stored at - 80 °C.

Molecular diversity of the two sugar-binding sites of the ß-trefoil lectin HA33/C (HA1) from Clostridium botulinum type C neurotoxin.

A critical role in internalizing the Clostridium botulinum neurotoxin into gastrointestinal cells is played by nontoxic components complexed with the toxin. One of the components, a ß-trefoil lectin has been known as HA33 or HA1. The HA33 from C. botulinum type A (HA33/A) has been predicted to have a single sugar-binding site, while type C HA33 (HA33/C) has two sites. Here we constructed HA33/C mutants and evaluated the binding capacities of the individual sites through mucin-assay and isothermal titration calorimetry. The mutant W176A (site I knockout) had a K(d) value of 31.5mM for galactose (Gal) and 61.3mM for N-acetylgalactosamine (GalNAc), while the K(d) value for N-acetylneuraminic acid (Neu5Ac) was too high to be determined. In contrast, the double mutant N278A/Q279A (site II knockout) had a K(d) value of 11.8mM for Neu5Ac. We also determined the crystal structures of wild-type and the F179I mutant in complex with GalNAc at site II. The results suggest that site I of HA33/C is quite unique in that it mainly recognizes Neu5Ac, and site II seems less important for the lectin specificity. The architectures and the properties of the sugar-binding sites of HA33/C and HA33/A were shown to be drastically different.

Reduced aqueous humour ascorbic-acid concentration in women with smaller anterior chamber depth.

Short anterior chamber depth (ACD) is considered a risk factor of endothelial-cell loss after phacoemulsification. However, whether it is an independent risk factor or not remains controversial. We investigated the relationship between ascorbic acid (AA) concentrations in the aqueous humour (AqH) and ACD. We analysed 165 AqH samples of 97 patients (42 men and 55 women) who underwent small incision cataract surgery. AqH and plasma AA concentrations were measured using a high-performance liquid chromatography - electrochemical detection method. Patient characteristics were compared between and within the sexes. As a result, age and ACD were significantly correlated with AqH AA concentrations (r = -0.206, P = 0.045; r = 0.339, P < 0.001) only in women. Moreover, plasma AA concentrations were significantly correlated with AqH AA concentrations (r = 0.420, P < 0.001; r = 0.316, P = 0.002) both in men and women. After adjusting for confounding factors (age and plasma AA concentrations), ACD was significantly and positively correlated with AqH AA concentrations (partial.r = 0.275, P = 0.009) only in women. In conclusion, AqH AA concentrations were reduced in women with smaller ACD. This may suggest that women with short ACD could be more susceptible to oxidative damage.