Maternal Tryptophan Supplementation Protects Adult Rat Offspring against Hypertension Programmed by Maternal Chronic Kidney Disease: Implication of Tryptophan-Metabolizing Microbiome and Aryl Hydrocarbon Receptor

Abstract

Hypertension and chronic kidney disease (CKD) can originate during early-life. Tryptophan metabolites generated by different pathways have both detrimental and beneficial effects. In CKD, uremic toxins from the tryptophan-generating metabolites are endogenous ligands of the aryl hydrocarbon receptor (AHR). The interplay between AHR, nitric oxide (NO), the renin-angiotensin system (RAS), and gut microbiota is involved in the development of hypertension. We examined whether tryptophan supplementation in pregnancy can prevent hypertension and kidney disease programmed by maternal CKD in adult offspring via the aforementioned mechanisms. Sprague-Dawley (SD) female rats received regular chow or chow supplemented with 0.5% adenine for 3 weeks to induce CKD before pregnancy. Pregnant controls or CKD rats received vehicle or tryptophan 200 mg/kg per day via oral gavage during pregnancy. Male offspring were divided into four groups (n = 8/group): control, CKD, tryptophan supplementation (Trp), and CKD plus tryptophan supplementation (CKDTrp). All rats were sacrificed at the age of 12 weeks. We found maternal CKD induced hypertension in adult offspring, which tryptophan supplementation prevented. Maternal CKD-induced hypertension is related to impaired NO bioavailability and non-classical RAS axis. Maternal CKD and tryptophan supplementation differentially shaped distinct gut microbiota profile in adult offspring. The protective effect of tryptophan supplementation against maternal CKD-induced programmed hypertension is relevant to alterations to several tryptophan-metabolizing microbes and AHR signaling pathway. Our findings support interplay among tryptophan-metabolizing microbiome, AHR, NO, and the RAS in hypertension of developmental origins. Furthermore, tryptophan supplementation in pregnancy could be a potential approach to prevent hypertension programmed by maternal CKD.

Keywords: aryl hydrocarbon receptor; chronic kidney disease; developmental origins of health and disease (DOHaD); gut microbiota; hypertension; nitric oxide; pregnancy; renin–angiotensin system; tryptophan.

Figure 1

Effects of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on systolic blood pressure measured in male offspring at 4, 6, 8, 10, and 12 weeks of age. Data are shown as means ± S.E.M. A two-way ANOVA was performed for statistical analysis. CKD × Trp = interaction of CKD and Trp. n = 8/group.

Figure 2

Effects of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on aryl hydrocarbon receptor (AHR) pathway in offspring kidneys at 12 weeks of age. Data are shown as means ± S.E.M. A two-way ANOVA with a Tukey’s post hoc test was performed for statistical analysis. CKD × Trp = interaction of CKD and Trp. * p < 0.05 vs. CN. # p < 0.05 vs. CKD. n = 8/group.

Figure 3

Effects of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on the renin-angiotensin system in offspring kidneys at 12 weeks of age. Data are shown as means ± S.E.M. A two-way ANOVA with a Tukey’s post hoc test was performed for statistical analysis. CKD × Trp = interaction of CKD and Trp. * p < 0.05 vs. CN. # p < 0.05 vs. CKD. n = 8/group.

Figure 4

Effects of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on the gut microbiota in offspring at 12 weeks of age. (A) Variation in fecal bacterial α-diversity represented by the Shannon’s diversity indexes. (B) β-diversity changes in gut microbiota across groups by the Partial Least Squares Discriminant Analysis (PLS-DA). (C) Relative abundance of top 10 phyla of the gut microbiota among the four groups. (D) Relative abundances of the phylum Firmicutes. (E) Relative abundances of the phylum Bacteroidetes. (F) The Firmicutes to Bacteroidetes ratio. * p < 0.05. ** p < 0.01. *** p < 0.001.

Figure 5

Effects of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on the gut microbiota at the genus level in 12-week-old offspring. (A) Relative abundance of top 10 genera of the gut microbiota among the four groups. Relative abundances of the genus (B) Lactobacillus, (C) Ruminiclostridium_9, (D) Ruminococcus_1, (E) Intestinimonas, (F) Turicibacter, and (G) Clostridium. * p < 0.05. ** p < 0.01. *** p < 0.001.

Figure 6

Effect of maternal adenine-induced chronic kidney disease (CKD) and tryptophan supplementation (Trp) on the gut microbiota at 12 weeks of age. Linear discriminant analysis effect size (LEfSe) was applied to identify enriched bacterial species. The threshold of the linear discriminant was set to 3. Most enriched and depleted species in the (A) CKD (red) versus CN group (green) and (B) CKD (red) versus CKDTrp group (green).

Figure 7

Schematic illustration of study design to establish a maternal adenine-induced chronic kidney disease (CKD) rat model to evaluate male offspring outcome at 12 weeks of age.