Dietary cystine essential in regulating mercaptalbumin levels

In this study, researchers from the Kyoto Prefectural University in Japan examined the amino composition of dietary protein to determine if it modulates the oxidized/reduced state of plasma albumin in rats. Their study, which demonstrated the effects of protein quality, was published in the journal Nutrition Research.

• The quantity of dietary protein influences the oxidized/reduced state of plasma albumin in rats.
• However, the effects of protein quality on the oxidized/reduced state of plasma albumin are not well-understood.
• The researchers hypothesized that the quality of dietary protein could modulate the oxidized/reduced state of plasma albumin.
• To test their hypothesis, they used male Sprague-Dawley rats and fed them low-protein diets containing 5 percent casein (CA), 5 percent egg white (EW), or 6 percent wheat gluten (WG) for two weeks.
• The researchers reported that plasma albumin concentration gradually decreased in rats fed each diet; however, they noticed no significant difference among the groups.
• They reported that in rats fed the 5 percent CA diet, the percentage of mercaptalbumin within the total plasma albumin was significantly lower than in those fed the EW or WG diet.
• Compared with EW or WG, CA contains lower amounts of glycine and cystine, so the researchers decided to supplement the diet with cystine and glycine.
• In rats fed a 5 percent CA diet supplemented with cystine, the percentage of mercaptalbumin was significantly higher than that in rats fed a 5 percent CA diet supplemented with glycine.
• The researchers also found that the expression of hepatic eukaryotic initiation factor 4E-binding protein 1 was significantly lower in rats fed the cystine-supplemented diet than in those fed the glycine-supplemented diet.

Based on their findings, the researchers concluded that dietary protein with a high cystine content maintains plasma mercaptalbumin levels in rats fed low-protein diets.

Journal Reference:

Kuwahata M, Kobayashi Y, Wada Y, Aoi W, Kido Y. DIETARY CYSTINE IS IMPORTANT TO MAINTAIN PLASMA MERCAPTALBUMIN LEVELS IN RATS FED LOW-PROTEIN DIETS. NUTRITION RESEARCH. August 2018;56:79–89. DOI: 10.1016/j.nutres.2018.04.019