Meal cysteine improves postprandial glucose control in rats fed a high-sucrose meal

J Nutr Biochem. 2007 Aug;18(8):519-24. doi: 10.1016/j.jnutbio.2006.10.002. Epub 2006 Dec 4.

Abstract

Whey protein, particularly the alpha-lactalbumin fraction, are rich in cysteine (cys) and could therefore favor postprandial glucose homeostasis by a glutathione-mediated effect. This work investigates the effects of the ingestion of an alpha-lactalbumin-rich whey concentrate (alpha-LAC) during a high-sucrose (HS) meal on postprandial glucose homeostasis in healthy rats. In the first experiment, rats received an HS meal containing 14% protein, in which the protein source was either alpha-LAC (HS(a)) or total milk proteins, alone (HS(0)) or supplemented with 17 mg (HS(1)) or 59 mg (HS(2)) of N-acetylcysteine (NAC). This resulted in a total cys content 3.6-fold higher in the HS(1) and HS(a) meals and 12-fold higher in the HS(2) meal, when compared to the HS(0) meal. Postprandial parameters were monitored for 3 h after ingestion of the meal. The same measurements were performed on rats injected with 4 mmol/kg of buthionine sulfoximine (BSO), a specific inhibitor of glutathione synthesis. Increasing the meal's cys content dose-dependently reduced both postprandial glucose and insulin (P<.05). The inhibition of glutathione synthesis with BSO injection abrogated the beneficial effects of NAC supplementation on postprandial glucose response but did not affect those of alpha-LAC. These results show that (1) the substitution of alpha-LAC for total milk protein reduces glucose response, as does the addition of a cys donor to the meal, (2) but contrary to those of a simple cys donor, the beneficial effects of alpha-LAC are not entirely mediated by glutathione synthesis, suggesting additional mechanisms.

MeSH terms

  • Animals
  • Area Under Curve
  • Blood Glucose / drug effects
  • Blood Glucose / metabolism*
  • Buthionine Sulfoximine / blood
  • Buthionine Sulfoximine / pharmacology
  • Cysteine / administration & dosage
  • Cysteine / pharmacology*
  • Dietary Carbohydrates*
  • Insulin / blood
  • Kinetics
  • Liver / metabolism
  • Male
  • Postprandial Period
  • Rats
  • Rats, Wistar
  • Sucrose / pharmacology*

Substances

  • Blood Glucose
  • Dietary Carbohydrates
  • Insulin
  • Buthionine Sulfoximine
  • Sucrose
  • Cysteine