Studies of the toxicological potential of tripeptides (L-valyl-L-prolyl-L-proline and L-isoleucyl-L-prolyI-L-proline): II. Introduction.

The consumption of fermented milk to maintain good health, including the maintance of normal blood pressure, is an ancient tradition in a number of areas of the world (e.g., East Asia, France). Recent studies have suggested that fermented milk has a normotensive effect in hypertensive rats and humans, but no effect on blood pressure in normotensive rats and humans. Two tripeptides, L-valyl-L-prolyl-L-proline (VPP) and L-isoleucyl-L-prolyl-L-proline (IPP), have been identified as possessing significant angiotensin-converting enzyme inhibitory activity and are therefore believed to be the source of the normotensive effects. This document, the second of nine chapters, provides information on these two tripeptides, including physical/chemical properties, molecular weights, chemical structures, normal consumption in the diet, manufacturing information, regulatory approval in Japan, and Japanese consumption of food containing enhanced levels of VPP plus IPP. In addition, the results of studies in rats and humans conducted to evaluate the effect of these substances on blood pressure are presented. The research suggests that in adult normotensive volunteers, consumption of up to 7.92 mg of VPP and 4.52 mg IPP daily for 2 weeks causes neither clinical signs nor biologically meaningful effects on systolic or diastolic blood pressure, pulse rate, or clinical pathology (serum chemistry or hematology). However, when a similar study was performed using mildly and moderately hypertensive adults as subjects and they consumed 2.52 mg of VPP and 1.64 mg of IPP per day, a significant drop in systolic blood pressure was detected for a prolonged time interval. This chapter also introduces the issue of safety testing for these substances and describes the information to be found in the subsequent seven chapters.

Studies of the toxicological potential of tripeptides (L-valyl-L-prolyl-L-proline and L-isoleucyl-L-prolyl-L-proline): IV. Assessment of the repeated-dose toxicological potential of synthesized L-valyl-L-prolyl-L-proline in male and female rats and dogs.

The objective of these repeated-dose, 8-week studies was to assess the toxicological potential of a synthetic tripeptide, L-valyl-L-prolyl-L-proline (VPP), when administered to Charles River rats and Beagle dogs. Groups of 20 male and 20 female rats were fed powdered diets containing sufficient VPP to afford daily doses of 0, 2, 8, or 16 mg/kg body weight (BW)/day. Groups of five male and five female dogs were administered 0, 2, 8, or 16 mg/kg BW/day in hard gelatin capsules. Antemortem evaluative parameters for both species included grossly observable clinical signs, body weight and food consumption, clinical pathology (hematology, clinical chemistry, urinalysis), and ophthalmological examinations. Dogs also received electrocardiographic examinations. Postmortem evaluations in both species included complete necropsy, determination of major organ weights, and histopathological examination of specimens from approximately 50 organs and tissues. All rats and dogs survived to the scheduled termination of the studies and neither species exhibited evidence of VPP effects on appetite or body weight gain/maintenance. Ophthalmic examinations revealed occasional lens clouding in rats, but this occurred in all groups and was not attributable to VPP. Some clinical pathology parameters in both species were occasionally altered, but there was no evidence that this was dose-related. Electrocardiographic examinations in dogs revealed no VPP-associated changes. Mid- and high-dose male rats (but not females) had slightly reduced mean pituitary and kidney weight parameters, whereas mid- and high-dose females had slightly increased mean uterus:body weight ratios. There were no microscopic correlates for these minor changes. Ten percent to 20% of all female rats (but not males) exhibited corticomedullary mineralization of the kidney and gliosis of the optic nerve, and 10% to 20% of males (but not females) had thymic hemorrhage. Postmortem evaluations of dogs revealed no VPP-related effects on organ weights or either macro- or microscopic appearances of organs. The results of these studies provided no evidence of either local or systemic toxicity. Similarly, there was no evidence of neurotoxicity that might have been detected by the appearance of physical or behavioral changes during gross observations of animals. Although these results do not identify target organs for VPP toxicity, the no-observable-effect level and maximally tolerated dose are both greater than 16 mg/kg/day when administered to male and female rats and dogs for 8 consecutive weeks. Based upon food enhancement levels of VPP currently being evaluated, the resultant margin of safety (160) is substantial.