Validation of “sasLM,” an R package for linear models with type III sum of squares

The general linear model (GLM) describes the dependent variable as a linear combination of independent variables and an error term. The GLM procedure of SAS® and the “car” package in R calculate the type I, II, or III ANOVA (analysis of variance) tables. In this study, we validated the newly-developed R package, “sasLM,” which is compatible with the GLM procedure of SAS®. The “sasLM” package was validated by comparing the output with SAS®, which is the current gold standard for statistical programming. Data from ten books and articles were used for validation. The results of the “sasLM” and “car” packages were compared with those in SAS® using 194 models. All of the results in “sasLM” were identical to those of SAS®, whereas more than 20 models in “car” showed different results from those of SAS®. As the results of the “sasLM” package were similar to those in SAS® PROC GLM, the “sasLM” package could be a viable alternative method for calculating the type II and III sum of squares. The newly-developed “sasLM” package is free and open-source, therefore it can be used to develop other useful packages as well. We hope that the “sasLM” package will enable researchers to conveniently analyze linear models.

Downregulation of IL-18 Expression in the Gut by Metformin-induced Gut Microbiota Modulation

IL-18 is a crucial pro-inflammatory cytokine that mediates chronic intestinal inflammation. Metformin, an anti-diabetic drug, was reported to have ameliorative effects on inflammatory bowel disease. Recently, the mechanism of action of metformin was explained as a modulation of gut microbiota. In this study, fecal microbiota transplantation (FMT) using fecal material from metformin-treated mice was found to upregulate the expression of GLP-1 and pattern-recognition receptors TLR1 and TLR4 for the improvement in hyperglycemia caused by a high-fat diet. Further, FMT downregulated the expression of the inflammatory cytokine IL-18. Within the genera Akkermansia, Bacteroides, and Butyricimonas, which were promoted by metformin therapy, Butyricimonas was found to be consistently abundant following FMT. Our findings suggest that modulation of gut microbiota is a key factor for the anti-inflammatory effects of metformin which is used for the treatment of hyperglycemia.