Effect of aldonic acids on the uptake of ascorbic acid by 3T3 mouse fibroblasts and human T lymphoma cells

Determination of plasma and leukocyte vitamin C concentrations in a randomized, double-blind, placebo-controlled trial with Ester-C(®)

Background

Rapid uptake of vitamin C into blood and retention in tissues are important indicators of the efficacy of vitamin C supplementation and its immune-supporting role. The objective of this study was to evaluate the bioavailability of vitamin C in plasma (reflective of recent intake) and leukocytes (reflective of tissue stores and influences on immune function) from a novel vitamin C formulation, Ester-C^®.

Methods

The study was a double-blind, placebo-controlled, crossover trial. Thirty-six subjects, 18–60 years of age, were randomized to receive placebo (PL, 0 mg vitamin C), ascorbic acid (AA, 1000 mg vitamin C), and Ester-C^® (EC, 1000 mg vitamin C). Plasma and leukocyte vitamin C were measured baseline and at 2, 4, 8 and 24 h postdose.

Results

The concentration and percent change from baseline in plasma were significantly higher with EC at all time points when compared to PL. No significant differences between EC and AA were observed in plasma concentration. Maximum plasma concentration was higher for EC compared to AA (P = 0.039) and PL (P < 0.001). Plasma area under the curve (AUC_0–24h) was higher for EC (P < 0.001) compared to PL. The concentration change from baseline in leukocyte vitamin C was increased with EC at 24 h post-dose (P = 0.036) while no significant within-group changes were observed in AA or PL at any time point. The percent change in leukocyte vitamin C concentration was higher for EC at 8 and 24 h compared to AA (P = 0.028 and P = 0.034, respectively) and PL (P = 0.042 and P = 0.036, respectively).

Conclusions

A single dose of EC resulted in favorable percent change in leukocyte vitamin C concentration compared to AA and PL, indicating EC is retained longer within leukocytes.

Trial registration ClinicalTrials.gov Identifier NCT01852903

Pharmacokinetics and safety of calcium L-threonate in healthy volunteers after single and multiple oral administrations

AIM

To evaluate the pharmacokinetics of L-threonate after single or multiple oral administrations and its safety profile in healthy Chinese volunteers.

METHODS

This was an open-label, single- and multiple-dose study. The subjects were assigned to receive a single dose, 675, 2025, or 4050 mg, of calcium L-threonate (n=12) or repeated doses of 2025 mg twice daily for 4 d (n=12). Serial plasma and urine samples were analyzed with HPLC-MS/MS. Pharmacokinetic parameters of L-threonate were calculated using non-compartmental analysis with WinNonlin software.

RESULTS

In the single dose group, C(max) reached at 2.0 h and the mean t(1/2) was approximately 2.5 h. Area under curve (AUC) and C(max) increased with dose escalation, but dose proportionality was not observed over the range of 675 to 4050 mg. AUC and C(max) in the fasted subjects were lower compared with those in the non-fasted subjects. Cumulative urinary excretion of L-threonate over 24 h represented 5.9% of the administered dose with a mean Cl/r of 0.8 L/h. In the multiple-dose study, no accumulation appeared upon repeated doses of 2025 mg twice daily for 4 d. There were no serious adverse events that occurred during this study.

CONCLUSION

Calcium L-threonate was well tolerated in healthy Chinese subjects, with no pattern of dose-related adverse events. Plasma exposure increased with dose escalation, but linear pharmacokinetics were not observed over the studied doses. L-threonate was absorbed rapidly, and its absorption was enhanced by food intake. No systemic accumulation appeared after repeated administrations.

Safety and tolerance of ester-C compared with regular ascorbic acid

The goal of this randomized, double-blind crossover clinical trial in 50 healthy volunteers sensitive to acidic foods was to evaluate whether Ester-C calcium ascorbate causes fewer epigastric adverse effects than are produced by regular ascorbic acid (AA). Volunteers were randomly separated into 2 groups of 25. The study comprised an observation period of 9 days (phase 1 medication for 3 consecutive days, washout phase for 3 consecutive days, phase 2 medication for 3 consecutive days). Participants took 1000 mg vitamin C as Ester-C during phase 1 of the study followed by 1000 mg of vitamin C as AA during phase 2, or vice versa. During the course of the study, 3 examinations for the evaluation of epigastric adverse effects were performed (on days 0, 3, and 9). Participants used a diary to record epigastric adverse effects on a daily basis. In total, 28 (56%) of 50 participants reported 88 epigastric adverse effects of mild to moderate intensity. Of these 88 adverse effects, 33 (37.5%) occurred after intake of Ester-C and 55 (62.5%) were noted after intake of AA. The tolerability of Ester-C was rated "very good" by 72% of participants, whereas AA was rated "very good" by only 54%. This difference is statistically significant (P<.05). Investigators concluded that Ester-C compared with AA caused significantly fewer epigastric adverse effects in participants sensitive to acidic foods and that Ester-C is much better tolerated.

Pharmacokinetics in dogs after oral administration of two different forms of ascorbic acid

The dog is able to synthesise ascorbic acid (AA), but is frequently given the vitamin in an attempt to improve health and performance. The pharmacokinetics of AA in this species, however, are not well studied. Using a selective analytical method and careful stability control, the pharmacokinetics of orally given AA was studied in 20 dogs, at two dosage levels (15 and 50 mg kg(-1)) and with two forms of supplement [crystalline AA and the vitamin C product Ester-C(Inter-Cal Corp., Prescott, AZ, USA)]. After oral administration, a rapid increase was found in the plasma level of AA, indicating a possible intestinal active transport mechanism in this species. The obtained C(max)and AUC values were found to increase in a non-linear fashion when the dose of AA was increased. The pharmacokinetic modeling of the elimination of AA was made difficult by a pronounced secondary peak appearing after about 9 hours. The comparison of crystalline AA and Ester-C did not indicate any significant differences in pharmacokinetic parameters between the two preparations of the vitamin.

Enhanced production of mineralized nodules and collagenous proteins in vitro by calcium ascorbate supplemented with vitamin C metabolites

BACKGROUND

Vitamin C or ascorbate is important in wound healing due to its essential role in collagen synthesis. To study wound healing in the periodontium, cells adherent to expanded polytetrafluoroethylene (ePTFE) augmentation membranes, recovered from edentulous ridge augmentation procedures, have been established in culture in our laboratories. The objective of this study was to determine whether treatment of these cells with a calcium ascorbate, which contains vitamin C metabolites (metabolite-supplemented ascorbate), would increase the production of collagenous protein and mineralized tissue in vitro, as compared to unsupplemented calcium ascorbate (ascorbate).

METHODS

Cells derived from ePTFE membranes were cultured with beta-glycerophosphate and the test agents for 2 to 5 weeks, and the surface areas of the cell cultures occupied by mineralized nodules were measured using computerized image analysis. One experiment tested the effects of calcium threonate, one of the vitamin C metabolites in metabolite-supplemented ascorbate. Incorporation of radioactive proline and glycine was used as a measure of total protein (radioactivity precipitated by trichloracetic acid) and collagenase-digestible protein (radioactivity released by collagenase digestion.) Co-localization of collagen and fibronectin was examined by immunofluorescence.

RESULTS

In vitro treatment of these cells with metabolite-supplemented ascorbate increased the area of the cell cultures occupied by mineralized nodules after 5 weeks. Cell cultures treated with metabolite-supplemented ascorbate also exhibited significant increases in total protein. The increase in collagenous proteins in these cultures accounted for 85% of the increase in total protein. The greatest difference between treatment groups was observed in the cell-associated fraction containing the extracellular matrix. The additional collagen exhibited normal co-distribution with fibronectin. In cultures treated with ascorbate spiked with calcium threonate, the area of mineralized tissue was significantly greater than in ascorbate-treated cultures, but was less than that observed in cultures treated with metabolite-supplemented ascorbate.

CONCLUSIONS

In vitro treatment with ascorbate containing vitamin C metabolites enhanced the formation of mineralized nodules and collagenous proteins. Calcium threonate may be one of the metabolites influencing the mineralization process. Identifying factors which facilitate the formation of mineralized tissue has significant clinical ramifications in terms of wound healing and bone regeneration.