Reproductive toxicity in rats with crystal nephropathy following high doses of oral melamine or cyanuric acid

Abstract

The industrial chemical melamine was used in 2007 and 2008 to raise the apparent protein content in pet feed and watered down milk, respectively. Because humans may be exposed to melamine via several different routes into the human diet as well as deliberate contamination, this study was designed to characterize the effect of high dose melamine or cyanuric acid oral exposure on the pregnant animal and developing fetus, including placental transfer. Clear rectangular crystals formed following a single triazine exposure which is a different morphology from the golden spherulites caused by combined exposure or the calculi formed when melamine combines with endogenous uric acid. Crystal nephropathy, regardless of cause, induces renal failure which in turn has reproductive sequelae. Specifically, melamine alone-treated dams had increased numbers of early and late fetal deaths compared to controls or cyanuric acid-treated dams. As melamine was found in the amniotic fluid, this study confirms transfer of melamine from mammalian mother to fetus and our study provides evidence that cyanuric acid also appears in the amniotic fluid if mothers are exposed to high doses.

Melamine–cyanurate complexes and oxidative stress markers in trout kidney following melamine and cyanuric acid long-term co-exposure and withdrawal

“…Recently, Stine et al (2014) demonstrated that rats fed high concentrations of only MEL formed rectangular crystals and in shape different from the MELcyanurate ones. The MEL only crystals dissolve very rapidly in formalin, and this outcome may explain findings reported by other studies which did not include wet-mount analysis on fresh specimens.…”

Use of urinary renal biomarkers to evaluate the nephrotoxic effects of melamine or cyanuric acid in non-pregnant and pregnant rats

“…Note: Although pregnant melamine-treated animals displayed markedly altered changes in most of the endpoints that were measured, it is likely that the statistical comparisons would have been improved if more animals in this group had survived the duration of the study. Table 1 summarizes the effects of repeated doses of 1000 mg/ kg bw/day of melamine or cyanuric acid on rat body and kidney weights and the formation of crystals in renal tubules in a subset of non-pregnant and pregnant animals that were part of a larger cohort reported in Stine et al (2014). Compared to controls, nonpregnant melamine-treated rats displayed altered behavior (i.e., listlessness, anorexia, and reluctance to groom) and experienced adverse health effects, including dehydration, an 8% decrease in body weight, a 54% increase in kidney weight, and a moderate number of elongated rectangular-shaped crystals (not consistent with melamine-cyanurate crystals) in the lumen of renal tubules, which were composed exclusively of melamine.…”

“…These rats represented a subset (36 out of 66) of animals from a larger cohort that was recently reported in Stine et al (2014). Animals in each treatment group received the test article daily (via gavage) for 10 consecutive days.…”

“…Non-pregnant and pregnant Cesarean-derived CD IGS VAF/ + rats 8-10 weeks of age were purchased from Charles River (Frederick, MD, USA) and maintained according to Stine et al (2014). Briefly, rats were individually housed in micro isolator cages and provided feed (Harlan Tekland Global 2018CM rodent diet) and water (Hydro-Pico Systems, Inc., Research Triangle Park, NC, USA) ad libitum throughout the study.…”

“…Following the 10-day exposure period, animals were euthanized by carbon dioxide inhalation and portions of kidneys were fixed in formalin for histopathology and portions were frozen for subsequent wet mount analyses as described in detail in Stine et al (2014). Blood was collected by cardiac puncture for blood chemistry analyses [i.e., serum creatinine (SCr), blood urea nitrogen (BUN), and uric acid] using a VetTest™ Chemistry Analyzer (IDEXX Laboratories, Inc., Westbrook, ME, USA).…”