Kuldeep R. Dhariwal

Determination of optimal vitamin C requirements in humans.

Although the recommended dietary allowance provides an estimate for vitamin C ingestion in humans, optimal vitamin C requirements are unknown. We define optimal vitamin C requirements operationally based on the following: dose-function relations, availability in the food supply, steady state concentrations in plasma and tissues achieved at each dose of vitamin C, urinary excretion, bioavailability, toxicity, and epidemiologic observations. Optimal vitamin C requirements can be estimated when information is available for at least some of these criteria.

A parkinsonian syndrome induced in the goldfish by the neurotoxin MPTP.

Parkinsons disease has been modeled in humans, lower primates, and to a lesser extent in some other vertebrates by administration of the potent neurotoxin MPTP (1‐methyl‐4‐phenyl‐1,2,3,6 tetrahydropyridine). The MPTP model has thus drawn considerable attention as a system to search for anti‐Parkinsons disease drugs, although the cost and scarcity of primates has limited extensive applications. We now report that a parkinsonian syndrome can be elicited in the common goldfish (Carassius auratus) by a single dose of MPTP. The syndrome is characterized by profound bradykinesia (slow movement), the full extent of which is reached 3 days after MPTP administration. The reduction in movement is paralleled by loss of dopamine and norepinephrine from the forebrain and midbrain and in other brain regions as well. The toxic oxidative product of MPTP, MPP+, is also accumulated predominantly in forebrain and midbrain, and pretreatment with the monoamine oxidase blocker tranylcypromine substantially reduces accumulation of the toxic metabolite. A barely perceptible coarseness in balance adjustment also occurs in treated animals. The MPTP‐treated goldfish recover normal movement and normal brain monoamine levels within 10–13 days after administration of the drug. We interpret these and other data to indicate that MPTP can induce a Parkinsons disease‐like syndrome in the goldfish that is similar in many aspects to the syndrome induced by MPTP in humans and other primates. This remarkable parallel may permit the goldfish to supplement expensive and scarce primates for the purpose of searching and screening neuroprotective drugs with specific relevance to Parkinsons disease.— Pollard, H. B., Dhariwal, K., Adeyemo, O. M., Markey, C. J., Caohuy, H., Levine, M., Markey, S., Youdim, M. B. H. A parkinsonian syndrome induced in the goldfish by the neurotoxin MPTP. FASEB J. 6: 3108‐3116; 1992.

Determination of dehydroascorbic acid using high-performance liquid chromatography with coulometric electrochemical detection

A method for the detection of dehydroascorbic acid using high-performance liquid chromatography with coulometric electrochemical detection is described. Samples were first assayed for ascorbic acid, then reduced with 2,3-dimercapto-1-propanol to convert dehydroascorbic acid in the sample to ascorbic acid, and subsequently reassayed for total ascorbic acid. The dehydroascorbic acid content was the difference between the two measurements. The dehydroascorbic acid assay provides complete recovery of dehydroascorbic acid, without affecting the ascorbic acid content present prior to reduction. The assay is highly sensitive and reproducible with both standards and biological samples, and was used for routine detection of less than or equal to 1 pmol per sample injection of dehydroascorbic acid. Prior to reduction, dehydroascorbic acid standards frozen at -80 degrees C were stable for at least 1 month; after reduction, stability was limited to 3 days. Dehydroascorbic acid was added to human neutrophil samples; the samples were reduced and ascorbic acid was measured. Ascorbic acid in these samples was stable for greater than or equal to 12 h in a refrigerated autosampler (0-2 degrees C). With a run time for each sample of only 4 min, multiple samples can be prepared and placed in the autosampler for unattended assaying.

Ascorbic acid and in situ kinetics: a new approach to vitamin requirements

Ascorbic acid requirements are based on preventing the deficiency disease scurvy and on urinary excretion of vitamin C. We proposed the first quantitative approach to determining optimal requirements for ascorbic acid and other vitamins, called in situ kinetics. In situ kinetics biochemically is based on the application of Michaelis-Menten reaction kinetics to ascorbic acid-dependent reactions in situ. Clinically in situ kinetics is based on determining vitamin availability to tissues so that cell-specific reactions can occur. The biochemical concepts of in situ kinetics are verified for the first time through studying ascorbic acid regulation of norepinephrine biosynthesis. The principles of in situ kinetics can now be applied to humans and human cells and for determining optimal requirements for ascorbic acid and for other vitamins.