Normalization of urinary oxalate by taurine in glycolate-fed rats

Final Report On the Safety Assessment of Glycolic Acid, Ammonium, Calcium, Potassium, and Sodium Glycolates, Methyl, Ethyl, Propyl, and Butyl Glycolates, and Lactic Acid, Ammonium, Calcium, Potassium, Sodium, and Tea-Lactates, Methyl, Ethyl, Isopropyl, and Butyl Lactates, and Lauryl, Myristyl, and Cetyl Lactates

This report provides a review of the safety of Glycolic Acid, Ammonium, Calcium, Potassium, and Sodium Glycolates, Methyl, Ethyl, Propyl, and Butyl Glycolates, Lactic Acid, Ammonium, Calcium, Potassium, Sodium, and TEA-Lactates, and Lauryl, Myristyl, and Cetyl Lactates. These ingredients belong to a group known as alpha-hydroxy acids (AHAs). Products containing these ingredients may be for consumer use, salon use, or medical use. This report does not address the medical use. In consumer and salon use, AHAs can function as mild exfoliants, but are also used as pH adjusters and skin-conditioning agents. AHAs are absorbed by the skin; the lower the pH, the greater the absorption. Metabolism and distribution studies show expected pathways and distribution. Consistent with these data, acute oral animal studies show oxalate-induced renal calculi, an increase in renal oxalate, and nephrotoxic effects. No systemic effects in animals were seen with dermal application, but irritation at the sight of application was produced. While many animal studies were performed to evaluate AHA-induced skin irritation, it was common for either the AHA concentration or the pH of the formulation to be omitted, limiting the usefulness of the data. Clinical testing using AHA formulations of known concentration and pH was done to address the issue of skin irritation as a function of concentration and pH. Skin irritation increased with AHA concentration at a given pH. Skin irritation increased when the pH of a given AHA concentration was lowered. Repeat insult patch tests using lotions and creams containing up to 10% Glycolic or Lactic Acid were negative. Glycolic Acid at concentrations up to 10% was not comedogenic and Lactic Acid at the same concentrations did not cause immediate urticarial reactions. Glycolic Acid was found to be nonirritating to minimally irritating in animal ocular tests, while Lactic Acid was found to be nonirritating to moderately irritating. In vitro testing to predict ocular irritation suggested Glycolic Acid would be a minimal to moderate-severe ocular irritant, and that Lactic Acid would be a minimal to moderate ocular irritant. Developmental and maternal toxicity were reported in rats dosed by gavage at the highest dose level used in a study that exposed the animals on days 7-21 of gestation. No developmental toxicity was reported at levels that were not maternally toxic. AHAs were almost uniformly negative in genotoxicity tests and were not carcinogenic in rabbits or rats. Clinical reports suggested that AHAs would enhance the penetration of hydroquinone and lidocaine. Animal and clinical tests were done to further evaluate the potential ofAHAs to enhance the skin penetration of other chemical agents. Pretreatment of guinea pig skin with Glycolic Acid did not affect the absorption of hydroquinone or musk xylol. Clinical tests results indicated no increase in penetration of hydrocortisone or glycerin with Glycolic Acid pretreatment. Because AHAs can act to remove a portion of the stratum corneum, concern was expressed about the potential that pretreatment with AHAs could increase skin damage produced by UV radiation. Clinical testing was done to determine the number of sunburn cells (cells damaged by UV radiation that show distinct morphologic changes) produced by 1 MED of UV radiation in skin pretreated with AHAs. A statistically significant increase in the number of sunburn cells was seen in skin pretreated with AHAs compared to controls. These increases, however, were less than those seen when the UV dose was increased from 1 MED to 1.56 MED. The increase in UV radiation damage associated with AHA pretreatment, therefore, was of such a magnitude that it is easily conceivable that aspects of product formulation could eliminate the effect. Based on the available information included in this report, the CIR Expert Panel concluded that Glycolic and Lactic Acid, their common salts and their simple esters, are safe for use in cosmetic products at concentrations ≤10%, at final formulation pH≥3.5, when formulated to avoid increasing sun sensitivity or when directions for use include the daily use of sun protection. These ingredients are safe for use in salon products at concentrations ≤30%, at final formulation pH ≥3.0, in products designed for brief, discontinuous use followed by thorough rinsing from the skin, when applied by trained professionals, and when application is accompanied by directions for the daily use of sun protection.

Clofibrate feeding to Sprague-Dawley rats increases endogenous biosynthesis of oxalate and causes hyperoxaluria

The effects of clofibrate feeding (5 g/kg diet) on oxalate metabolism were investigated in male and female rats. Following clofibrate feeding, 24-hour urinary excretion of oxalate increased until 4 days and then reached a plateau. Whereas the contribution of dietary oxalate (1.4 g/kg diet, as potassium salt) to urinary oxalate was less than 5% in both control and clofibrate-treated male rats, the contribution of dietary glycolate (1.0 g/kg diet, as sodium salt) to urinary oxalate was six times higher in clofibrate-treated male rats compared with controls, indicating that the clofibrate-induced hyperoxaluria is due to increased endogenous biosynthesis of oxalate. This was supported by the increased lactate dehydrogenase (LDH) activity observed in liver supernatants of clofibrate-treated rats compared with controls, and the increased rate of conversion of glycolate and glyoxylate to oxalate by clofibrate-treated male rat liver supernatants. Female rats had lower excretion of urinary oxalate and lower levels of liver glycolic acid oxidase (GAO) as compared with males. Clofibrate-treated female rat liver supernatants had higher LDH levels and produced more oxalate from glyoxylate. Thus, it can be concluded that the increase in LDH activity may be the cause of the increased endogenous biosynthesis of oxalate leading to increased urinary excretion of oxalate in male and female rats treated with clofibrate.

Idiopathic calcium oxalate urolithiasis and endogenous oxalate production

Despite the great effort that has gone into investigating urolithiasis, this condition still persists as one of the major ailments of the urinary tract. Calcium oxalate urolithiasis is the most common form, accounting for some 60 to 80% of total stones. This review examines the elements (i.e., urine volume and pH and urinary excretion of calcium, oxalate, citrate, urate, magnesium, pyrophosphate, and glycosaminoglycans) that give rise to idiopathic calcium oxalate urolithiasis. Treatment strategies for idiopathic calcium oxalate urolithiasis, including lithotripsy, also are discussed. Urinary oxalate excretion is a major risk factor for calcium oxalate urolithiasis, with 85 to 95% of the urinary load derived endogenously. The factors controlling endogenous oxalate production are reviewed, including pathways for the diversion of glyoxylate from oxalate production. The use of beta-aminothiols and other substances to reduce endogenous oxalate production in subjects with idiopathic calcium oxalate urolithiasis is also discussed. A review of current methodologies for the determination of urinary oxalate is also included.