A Toxicological Evaluation of Methylliberine (Dynamine®)

Abstract

Methylliberine (CAS 51168-26-4), a methoxiuric acid, is a caffeine metabolite present at low levels in various Coffea plants; however, very little has been published regarding this compound and we could find no toxicological data in the public domain. Therefore, we undertook the toxicological investigation of a pure, synthetic form of methylliberine in order to evaluate its potential health hazards as a food ingredient. A (1) bacterial reverse mutation test, (2) in vitro mammalian chromosomal aberration test, (3) in vivo mammalian micronucleus test, and (4) 90-day repeated-dose oral toxicity study in rats with a 28-day recovery period were conducted. No in vitro mutagenic or clastogenic activity was observed in the presence or absence of metabolic activation up to the maximum OECD recommended test concentrations. No genotoxicity was observed in the mammalian micronucleus study up to the highest dose tested of 700 mg/kg bw. In the 90-day study, methylliberine was administered to Han:WIST rats at doses of 0, 75, 112, 150, 187, and 225 mg/kg bw/day. No mortality or morbidity was observed and no toxicologically relevant clinical effects or effects on clinical pathology parameters were observed. In male animals, test item-related effects on body weight and sexual organs, which were not reversible after a 28-day recovery period without treatment, were observed in the high-dose group. Body weight development was also slightly and reversibly depressed in the 187 mg/kg bw/day male group. No toxicological effects were observed in females. The NOAEL for females was determined to be 225 mg/kg bw/day, the highest dose tested, while the NOAEL for males was determined to be 150 mg/kg bw/day. Future studies are encouraged to corroborate the safety, and assess efficacy, of methylliberine in humans.

Figure 1

Methylliberine.

Figure 2

Body weights in the 90-day study. (a) Male body weights. (b) Female body weights. ^∗p < 0.05, ^∗∗p < 0.01 (Duncan's multiple range test).

Figure 3

Recovery group body weights during the 90-day study recovery period. ^∗p < 0.05, ^∗∗p < 0.01 (T-test versus control).

Figure 4

Testes sections of male rats in the 90-day study (H&E, 200X). (a) Normal active spermatogenesis and mature spermatozoa (arrow) in a male control animal at termination of treatment. (b) Decreased intensity of spermatogenesis, degeneration of germ cells, multinucleated giant cell (arrow), and lack of mature spermatozoa in a male animal at 225 mg/kg bw/day at termination of treatment. (c) Normal active spermatogenesis and mature spermatozoa (arrow) in a male animal at 225 mg/kg bw/day at the end of the recovery period. (d) Decreased intensity of spermatogenesis, degeneration of germ cells, and lack of mature spermatozoa in a male animal at 225 mg/kg bw/day at the end of the recovery period.

Figure 5

Epididymis sections of male rats in the 90-day study (H&E, 200X). (a) Normal storage of mature spermatozoa in a male control animal at termination of treatment. (b) Lack of mature spermatozoa in a male animal at 225 mg/kg bw/day at termination of treatment. (c) Normal storage of mature spermatozoa in a male control animal at 225 mg/kg bw/day at the end of the recovery period. (d) Lack of mature spermatozoa in a male control animal at 225 mg/kg bw/day at the end of the recovery period.