Inhibition of phosphate transport by NAD⁺/NADH in brush border membrane vesicles

Abstract

Nicotinamide is an important regulator of Pi homeostasis after conversion into NAD+/NADH. In this work, we have studied the classical inhibition of Pi transport by these compounds in the brush border membrane vesicles (BBMV) of rat kidney and rat intestine, and we examined the effects in Opossum Kidney (OK) cells and in phosphate transporter-expressing Xenopus laevis oocytes. In BBMV, NAD+ required preincubation at either room temperature or on ice to inhibit Pi uptake in BBMV. However, no effects were observed in the known Slc34 or Slc20 Pi transporters expressed in Xenopus oocytes, in OK cells, or in isolated rat cortical nephron segments. In BBMV from jejunum or kidney cortex, the inhibition of Pi transport was specific, dose-related, and followed a competitive inhibition pattern, as shown by linear transformation and non-linear regression analyses. A Ki value of 538 µM NAD+ in kidney BBMV was obtained. Ribosylation inhibitors and ribosylation assays revealed no evidence that this reaction was responsible for inhibiting Pi transport. An analysis of the persistence of NAD+/NADH revealed a half-life of just 2 minutes during preincubation. Out of several metabolites of NAD degradation, only ADP-ribose was able to inhibit Pi uptake. Pi concentration also increased during 30 minutes of preincubation, up to 0.67mM, most likely as a metabolic end-product. In conclusion, the classical inhibition of Pi transport by NAD+/NADH in BBMV seems to be caused by the degradation metabolites of these compounds during the preincubation time.

Alterations in Intestinal Brush Border Membrane Functionality and Bacterial Populations Following Intra-Amniotic Administration (Gallus gallus) of Nicotinamide Riboside and Its Derivatives

“…Therefore, the administration of NRCl and its derivatives triggers altered expression of key BBM genes involved in digestion, and absorption, with additional effects on intestinal microbiota composition and function. Further and as was previously suggested, these functional changes, as demonstrated via gene expression of key BBM proteins (zinc transporter, inflammatory cytokines, absorptive proteins, and mucin), were previously associated with BBM tissue physiological and morphometric alterations, as increased villi size [ 24 , 50 , 93 , 94 , 95 , 96 , 97 ]. These alterations may potentially also be associated with increased proliferation of cellular populations that hold essential roles in BBM function, including, enterocytes, and therefore, increased villus surface area (the intestinal digestive and absorptive surface), and goblet cells (produce and secrete mucus), both number and diameter in intestinal villi and crypt [ 18 , 22 , 24 , 47 , 50 , 93 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ].…”

Mechanistic characterization of waterborne selenite uptake in the water flea, Daphnia magna, indicates water chemistry affects toxicity in coal mine-impacted waters

“…These inhibitors both target sodium–phosphate transporters such as those of the SLC34 family; however, they have distinct putative modes of action. It is suggested that PFA has a competitive effect directly blocking the uptake site, whereas NAD + acts non-competitively by indirectly effecting transporter function through transporter modification ( Loghman-Adham, 1996 ; Sorribas et al, 2019 ; Lucea et al, 2022 ). While evidence exists for sodium-dependent phosphate transporters in daphnids (e.g.…”

Understanding renal phosphate handling: unfinished business

“…Additional recently published findings include the demonstration that FGF23 decreases apical membrane NPT2A expression by stimulating endocytosis of NPT2A into an endolysosomal pathway [23], a mechanism that had been suspected but not explicitly demonstrated. Lucea et al [24] appear to have settled a longstanding debate about the inhibitory effects of NADþ on phosphate transport, demonstrating that only after degradation was NADþ able to inhibit phosphate transport in a cell culture model, and identifying the increase in local phosphate release and the breakdown product ADP-ribose as the responsible agents [24]. Finally, a recent manuscript showed that inhibition of the prorenin receptor blocked the inhibitory effect of high phosphate on renal phosphate transport through inhibition of FGF23 release [25].…”