Effects of orange juice and proline betaine on glycine betaine and homocysteine in healthy male subjects
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Proline betaine (PB), a glycine betaine (GB) analogue found in citrus foods, increases urinary GB loss and plasma total homocysteine (tHcy) concentrations in rats. Its presence in human plasma is associated with increased GB excretion.
To compare the effects of dietary levels of PB on GB excretion, and on plasma tHcy and GB concentrations in healthy volunteers.
In a randomized crossover study, eight healthy males (18–50 years) ingested either 750 mL orange juice (containing 0.545 g PB), a PB supplement (0.545 g PB dissolved in 750 mL apple juice), or 750 mL apple juice (control). Plasma PB, GB and tHcy, and urine PB, GB and creatinine concentrations were measured hourly for 6 h and at 24 h post-treatment.
Plasma tHcy concentrations were not increased (relative to control) following ingestion of either orange juice or PB supplement. Both treatments produced a significant increase in plasma PB concentrations (P < 0.001), this effect being greater following orange juice compared with PB supplement (P < 0.05, 1–2 h). Urinary excretion of PB was greater than the control following both orange juice (P < 0.001) and PB supplement (P < 0.001), from 2 to 24 h post-treatment. This increase in PB excretion was significantly greater following orange juice compared with PB supplement with higher peak excretion (C max difference, P = 0.008). GB excretion was significantly greater following ingestion of orange juice compared with PB in apple juice (P = 0.007) and apple juice control (P < 0.001) in the first 2 h post-ingestion.
PB administered in dietary doses had little effect on plasma tHcy concentrations in healthy humans. Ingestion of PB in orange juice compared with PB alone resulted in greater increases in the urinary excretion of PB and GB.
Key wordsproline betaine (PB) glycine betaine (GB) total homocysteine (tHcy) orange juice methionine load test
We thank Chris McEntyre for synthesizing the proline betaine and assisting with HPLC analysis, Linda Pike for tHcy analysis, Professor Richard Robson for the use of the Christchurch Clinical Studies Trust facilities and the volunteers for their participation in the study. This study was supported by a grant from the National Heart Foundation of New Zealand, and used equipment funded by the Lottery Grants Board of New Zealand.
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