Background: In CKD the biochemical milieu of gastrointestinal tract (GI) is altered by several mechanisms, affecting gut microbiota composition and function. Beyond exerting metabolic functions, microbiota influences the general healthy status. It digests food mainly through saccharolytic or proteolytic catabolism, with a prevalence of the former in healthy status. On the contrary, in CKD, dysbiosis with the prevalence of the latter is observed.
In this setting, reduction in glomerular filtration rate and increase in urea levels result in its heavy influx into the GI. Here urea is hydrolyzed spontaneously and/or by microbial urease, releasing ammonia, readily converted into ammonium hydroxide. The latter raises GI pH, causing mucosa irritation, enterocolitis and changes in microbiota composition. This contributes to worsening of inflammation and disease progression: indeed, microbiota has been identified as the primary source of several well known and yet unidentified volatile organic compounds (VOC), including some of the main uremic toxins.
Some beneficial effects observed from studies with low-protein diet supplemented with ketoacids in CKD cannot be solely explained by the reduced protein intake. Investigators' hypothesis is that ketoacids may have direct protective effects on renal damage progression, through induced modifications in gut biochemical milieu and in microbiota composition.
Similarly, the Mediterranean Diet with its fibers supply can contribute to restore gut microbiota balance.
Hypothesis:
The first hypothesis foresees a beneficial effect of KD on microbiota balancing and microbial-derived uremic toxins decrease in CKD patients, through KD-induced urea reduction. The second envisages MD direct effects on gut microbiota composition with an increase in protective species and a decrease in uremic toxins production.
The study will evaluate the effects of three different dietary regimens, composed as follows:
FD contains 1 g/bw/day of protein, plant protein 15-20 g/day;
* MD contains 0.7-0.8 g/bw/day of protein, plant protein 40-50 g/day;
* KD contains 0.3-0.5 g/bw/day of protein, animal protein zero g/day, plant protein 30-40 g/day, plus ketoacids of 0.05 g/bw/day.
Specific aim:
1. To evaluate the effects of Mediterranean diet (MD) and low-protein diet supplemented with ketoacids (KD) on microbiota composition
2. To evaluate the effects of KD and MD on microbial-derived VOC (already identified and yet unidentified uremic toxins) levels by metabolomics
3. To evaluate the effects of KD or MD on renal function parameters, uremia, inflammatory and nutritional status
Experimental Design Aim 1:
The designed study will be experimental, randomized, cross-over. It will be carried out according to the Declaration of Helsinki (IV Adaptation) and will be submitted to the approval of the local Ethics Committee; written consent will be obtained from all subjects. 60 patients with CKD stages 3b-4 (MDRD formula) will be enrolled, according to the inclusion and exclusion criteria (see below).
Experimental Design Aim 2:
Untarget metabolomic analysis will be carried out on fecal and urine samples collected at the same time points described in Experimental design aim 1 for VOC (GC-MS/MS) and non-VOC profiling (LC-MS/MS). Sera collected at the same time points will be also analyzed by untarget metabolomic for non-VOC profiling and by target metabolomic to quantify the already known uremic toxins, namely indoxyl sulfate and p-cresyl sulfate, and potential metabolite biomarkers found by the untarget experiment.
Experimental Design Aim 3:
Additionally, each patient will undergo medical examination every three months, with evaluation of: blood pressure and nutritional status. Moreover, at the same time points of aim 1 (T0, T3, T9, T12 and T18 months from the beginning of the study) each patient will provide blood and urine samples, both for routine and experimental analysis.
