Red cell aspartate aminotransferase saturation with oral pyridoxine intake

Pyridoxine deficiency modulates benzene inhalation-induced hematotoxicity associated with hepatic CYP2E1 activity in B6C3F1 mice

•

Modifying effects of pyridoxine deficiency on benzene toxicity were assessed in B6C3F1 mice.

•

The mice were fed either a pyridoxine-deficient diet or control diet.

•

Pyridoxine deficiency was combined with nose-only benzene inhalation exposure (100 ppm).

•

Pyridoxine deficiency and benzene inhalation led to lower body, thymus and spleen weights.

•

The treatment combination also led to higher hepatic CYP2E1 protein expression and activity.

Pyridoxine is a co-factor in many enzymatic reactions and impacts of deficiency have been observed in affected populations. A possible modifying effect of pyridoxine deficiency on benzene toxicity was assessed in male B₆C₃F₁ mice fed either a pyridoxine-deficient diet or a control diet. This treatment was combined with benzene inhalation exposure (100 ppm) or no benzene treatment. Pyridoxine-deficient mice exposed to 100 ppm benzene had significantly lower body, thymus and spleen weights. While total white blood cell counts, percentage of lymphocytes, hematocrit and hemoglobin levels were lower, the percentage of neutrophils was significantly higher in deficient and benzene-exposed mice compared to non-exposed controls. Hepatic CYP2E1 protein expression and activity in the deficient and exposed mice were also significantly higher compared to the non-exposed controls. A significant correlation between CYP2E1 activity and several hematological parameters was observed. These results demonstrated that pyridoxine deficiency significantly impacted benzene-induced hematotoxicity. Moreover, the observed agonistic effect of pyridoxinedeficiency and benzene inhalation exposure on CYP2E1 would seem to indicate an involvement of metabolism, but this needs to be further assessed.

Methionine tumor starvation by erythrocyte-encapsulated methionine gamma-lyase activity controlled with per os vitamin B6

Erymet is a new therapy resulting from the encapsulation of a methionine gamma-lyase (MGL; EC number 4.4.1.11) in red blood cells (RBC). The aim of this study was to evaluate erymet potential efficacy in methionine (Met)-dependent cancers. We produced a highly purified MGL using a cGMP process, determined the pharmacokinetics/pharmacodynamics (PK/PD) properties of erymet in mice, and assessed its efficacy on tumor growth prevention. Cytotoxicity of purified MGL was tested in six cancer cell lines. CD1 mice were injected with single erymet product supplemented or not with vitamin B6 vitamer pyridoxine (PN; a precursor of PLP cofactor). NMRI nude mice were xenografted in the flank with U-87 MG-luc2 glioblastoma cells for tumor growth study following five intravenous (IV) injections of erymet with daily PN oral administration. Endpoints included efficacy and event-free survival (EFS). Finally, a repeated dose toxicity study of erymet combined with PN cofactor was conducted in CD1 mice. Recombinant MGL was cytotoxic on 4/6 cell lines tested. MGL half-life was increased from <24 h to 9-12 days when encapsulated in RBC. Conversion of PN into PLP by RBC was demonstrated. Combined erymet + PN treatment led to a sustained Met depletion in plasma for several days with a 85% reduction of tumor volume after 45 days following cells implantation, and a significant EFS prolongation for treated mice. Repeated injections in mice exhibited a very good tolerability with only minor impact on clinical state (piloerection, lean aspect) and a slight decrease in hemoglobin and triglyceride concentrations. This study demonstrated that encapsulation of methioninase inside erythrocyte greatly enhanced pharmacokinetics properties of the enzyme and is efficacy against tumor growth. The perspective on these results is the clinical evaluation of the erymet product in patients with Met starvation-sensitive tumors.