Evaluating the quality of randomized controlled trials that examine the efficacy of natural health products: a systematic review of critical appraisal instruments

Approaches by the US National Institutes of Health to support rigorous scientific research on dietary supplements and natural products

Mechanistic, clinical, and epidemiological research relevant to dietary supplements (DS) is supported by the U.S. National Institutes of Health. The Office of Dietary Supplements and the National Center for Complementary and Integrative Health promote the development and appropriate use of rigorous and comprehensive DS analyses which are critical for research reproducibility, particularly when the investigational DS include chemically complex natural products with unclear mechanisms of action.

Gastroprotective effects of thymol on acute and chronic ulcers in rats: The role of prostaglandins, ATP-sensitive K(+) channels, and gastric mucus secretion

Thymol, a monoterpene phenol derivative of cymene, is found in abundance in the essential oils of Thymus, Origanum, and Lippia species. The present study investigated the gastroprotective actions of thymol (10, 30, and 100 mg/kg, p.o.) in the acute (ethanol- and nonsteroidal anti-inflammatory drug-induced ulcers) and chronic (acetic acid-induced ulcers) ulcer models in rats. Some of the mechanisms underlying to the gastroprotective effect of thymol were investigated in the ethanol-induced ulcer model. Gastric secretion parameters (volume, pH, and total acidity) were also evaluated by the pylorus ligature model, and the mucus in the gastric content was determined. The anti-Helicobacter pylori activity of thymol was performed using the agar-well diffusion method. Thymol (10, 30, and 100 mg/kg) produced dose dependent reduction (P < 0.01) on the total lesion area in the ethanol-induced ulcer model. The gastroprotective response caused by thymol (30 mg/kg) was significantly attenuated (P < 0.001) by intraperitoneal treatment of rats with indomethacin (a non-selective inhibitor of cyclo-oxygenase, 10 mg/kg) and glibenclamide (ATP-sensitive K(+) channel blocker, 10 mg/kg), but not by DL-Propargylglycine (PAG, a cystathionine-γ-lyase inhibitor, 25 mg/kg) and Nw-nitro-L-arginine methyl ester hydrochloride (L-NAME, a non-selective inhibitor of nitric oxide synthase, 70 mg/kg). Thymol (30 and 100 mg/kg) also reduced the ulcer index (P < 0.05) and the total lesion area (P < 0.001) in the indomethacin- and acetic-acid-induced ulcer models, respectively. In the model pylorus ligature, the treatment with thymol failed to significantly change the gastric secretion parameters. However, after treatment with thymol (30 and 100 mg/kg), there was a significant increase (P < 0.01) in mucus production. Thymol no showed anti-H. pylori activity in vitro. Collectively, the present results provide convincing evidence that thymol displays gastroprotective actions on the acute and chronic ulcer models through mechanisms that involve increased in the amount of mucus, prostaglandins, and ATP-sensitive K(+) channels.

Involvement of glutathione, sulfhydryl compounds, nitric oxide, vasoactive intestinal peptide, and heat-shock protein-70 in the gastroprotective mechanism of Croton cajucara Benth. (Euphorbiaceae) essential oil

This study aimed to evaluate the gastroprotective mechanism of action of the essential oil of Croton cajucara Benth. (Euphorbiaceae) stem bark in ethanol-induced gastric ulcers and its in vitro anti-Helicobacter pylori activity. The involvement of heat-shock protein-70, vasoactive intestinal peptide, glutathione, nitric oxide, and nonprotein sulfhydryl compounds in the gastroprotective effect was determined in male Wistar rats. The minimum inhibitory concentration against H. pylori was determined in vitro. The results were analyzed by analysis of variance followed by the Dunnett test, and a P value less than 0.05 was considered to represent a statistically significant difference. C. cajucara decreased ethanol-induced ulcer area in 100% of ulcers and decreased the histologic lesions. In the C. cajucara group, the area marked by heat-shock protein-70 was significantly higher than the area in the control group; this finding was not seen for vasoactive intestinal peptide. C. cajucara could not maintain glutathione levels close to those in the sham group. The gastric ulcer area of rats treated with the sulfhydryl compound blocker was decreased, but the ulcer area of rats treated with nitric oxide synthase inhibitor showed no alteration. The minimum inhibitory concentration obtained for C. cajucara was 125 μg/mL. These findings suggest that sulfhydryl compounds and heat-shock protein-70, but not nitric oxide, glutathione, or vasoactive intestinal peptide, are involved in the C. cajucara gastroprotective effect against ethanol-induced gastric ulcers.

Reporting experiments in homeopathic basic research-description of the checklist development

The objective of this study was to develop a criteria catalogue serving as a guideline for authors to improve quality of reporting experiments in basic research in homeopathy. A Delphi Process was initiated including three rounds of adjusting and phrasing plus two consensus conferences. European researchers who published experimental work within the last 5 years were involved. A checklist for authors provide a catalogue with 23 criteria. The “Introduction” should focus on underlying hypotheses, the homeopathic principle investigated and state if experiments are exploratory or confirmatory. “Materials and methods” should comprise information on object of investigation, experimental setup, parameters, intervention and statistical methods. A more detailed description on the homeopathic substances, for example, manufacture, dilution method, starting point of dilution is required. A further result of the Delphi process is to raise scientists' awareness of reporting blinding, allocation, replication, quality control and system performance controls. The part “Results” should provide the exact number of treated units per setting which were included in each analysis and state missing samples and drop outs. Results presented in tables and figures are as important as appropriate measures of effect size, uncertainty and probability. “Discussion” in a report should depict more than a general interpretation of results in the context of current evidence but also limitations and an appraisal of aptitude for the chosen experimental model. Authors of homeopathic basic research publications are encouraged to apply our checklist when preparing their manuscripts. Feedback is encouraged on applicability, strength and limitations of the list to enable future revisions.

Development and evaluation of an instrument for the critical appraisal of randomized controlled trials of natural products

BACKGROUND

The efficacy of natural products (NPs) is being evaluated using randomized controlled trials (RCTs) with increasing frequency, yet a search of the literature did not identify a widely accepted critical appraisal instrument developed specifically for use with NPs. The purpose of this project was to develop and evaluate a critical appraisal instrument that is sufficiently rigorous to be used in evaluating RCTs of conventional medicines, and also has a section specific for use with single entity NPs, including herbs and natural sourced chemicals.

METHODS

Three phases of the project included: 1) using experts and a Delphi process to reach consensus on a list of items essential in describing the identity of an NP; 2) compiling a list of non-NP items important for evaluating the quality of an RCT using systematic review methodology to identify published instruments and then compiling item categories that were part of a validated instrument and/or had empirical evidence to support their inclusion and 3) conducting a field test to compare the new instrument to a published instrument for usefulness in evaluating the quality of 3 RCTs of a NP and in applying results to practice.

RESULTS

Two Delphi rounds resulted in a list of 15 items essential in describing NPs. Seventeen item categories fitting inclusion criteria were identified from published instruments for conventional medicines. The new assessment instrument was assembled based on content of the two lists and the addition of a Reviewer's Conclusion section. The field test of the new instrument showed good criterion validity. Participants found it useful in translating evidence from RCTs to practice.

CONCLUSION

A new instrument for the critical appraisal of RCTs of NPs was developed and tested. The instrument is distinct from other available assessment instruments for RCTs of NPs in its systematic development and validation. The instrument is ready to be used by pharmacy students, health care practitioners and academics and will continue to be refined as required.