In vitro activity of dried extracts of Nepeta cataria against Helicobacter pylori strains

Abstract

Introduction Nepeta cataria L. has been used for the treatment of colds, colic, antispasmodic in folk medicine. H. pylori can induce peptic ulcers and gastric adenocarcinoma. The triple therapy for the eradication of H. pylori induce side-effects and fails to eliminate infection. The use of herbs provides a therapeutic alternative. Spray drying and freeze-drying present several pharmaceutical advantages over the conventional fluid form. In addition, spray-drying is the most commonly used method in the herbal processing industries. With the aim of achieving more stable solids with improved technological properties for pharmaceutical use, spray drying (SDE) and freeze-drying procedures (FDE) were applied to N. cataria aqueous extracts. Also, the evaluation of the obtained products activities against H. pylori was carried out. Methods Drying processes: infusions of two concentration levels (10 and 15% w/v) were subject to two different drying methods: SDE and FDE. SDEs were prepared using a BÜCHI 290 Mini-spray Dryer under the following operating conditions: pump setting 10% (3.2 ml min-1), airflow rate of 670 Nl h-1 (5 mm) and aspirator rate between 50-100%. The inlet temperature was set at 140°C±2 and 100°C±2; the outlet temperature at 83°C ± 2 and 75°C ± 2. Infusions were spray-dried in the presence of 15 and 30% (w/w) of colloidal silicon dioxide; 15% (w/w) of dibasic calcium phosphate; 15% (w/w) of fumed silica and 30% (w/w) of maltodextrin. For FDEs preparation, the infusions were placed on stainless steel trays and freeze-dried using a lyophilizer at -70 ºC at 0.025 mmHg of pressure. The temperature conditions were: condensate temperature -45ºC, the initial product temperature -35ºC. Antibacterial activity: The MICs of Nepeta FDE10% and Nepeta FDE15% were determined by the microplate method in tripticase soy broth supplemented with 5 % fetal calf serum and 0.01% (W/V) of 2,3,5-triphenyltetrazolium chloride as visual indicator of bacterial growth. The inoculum of each strain of H. pylori (NCTC 11638 and two clinical isolates) were tested (107CFU/ml). The FDEs were dissolved in distilled water and tested in a concentration range of 10 mg/ml to 0.310 mg/ml. After 72h incubation at 37ºC under the microaerophilic condition, the inhibition of antibacterial activity was defined as absence of red colour. The wells that showed no bacterial growth were confirmed by agar plating and determined the minimum bactericidal concentration (MBC). Results and discussion/conclusion The FDEs (10% and 15%) were active and inhibited H. pylori at concentration of 10 mg/ml and 0.310 mg/ml respectively. The MIC was coincident with MBC for all strains assayed. SDEs did not show antimicrobial activity in the investigated concentration. This study show that the lyophilized extract of N. cataria can inhibit the growth of H. pylori and can reduce the colonization of gastric mucosa. Further studies about antioxidant and citotoxicity activity must be conducted to evaluate the possible use of these extracts on anti-Helicobacter pylori therapy.