Metabolic profile and impact of diet in patients with primary hyperoxaluria.

PURPOSE: The primary goal of this pilot study was to evaluate metabolic characteristics and to examine the impact of diet in patients with primary hyperoxaluria (PH) under controlled, standardized conditions. METHODS: Four patients with genetically confirmed PH collected 24 h urines on their habitual, self-selected diets and on day 1, 6, 7, 8, and 11 under controlled, standardized conditions. The [13C2]oxalate absorption, calcium, and ammonium chloride loading tests were performed. RESULTS: While none of the patients had abnormal findings from the calcium loading test, incomplete distal renal tubular acidosis (RTA) was diagnosed in each of the four patients. Dietary intervention resulted in a significant decrease in urinary oxalate expressed as molar creatinine ratio (mmol/mol) between 30 and 40% in two of four patients. The evaluation of dietary records revealed a high daily intake of oxalate-rich foods as well as gelatin-containing sweets and meat products, rich sources of hydroxyproline, under the habitual, self-selected diets of the two responders. Intestinal oxalate hyperabsorption of 12.4% in one of the two patients may have additionally contributed to the increased urinary oxalate excretion under the individual diet. CONCLUSIONS: Our pilot data indicate that patients with PH may benefit from a restriction of dietary oxalate and hydroxyproline intake. Further research is needed to define the role of distal RTA in PH and to evaluate the hypothesis of an acquired acidification defect.

The effect of dietary hydroxyproline and dietary oxalate on urinary oxalate excretion in cats.

In humans and rodents, dietary hydroxyproline (hyp) and oxalate intake affect urinary oxalate (Uox) excretion. Whether Uox excretion occurs in cats was tested by feeding diets containing low oxalate (13 mg/100 g DM) with high (Hhyp-Lox), moderate (Mhyp-Lox), and low hyp (Lhyp-Lox) concentrations (3.8, 2.0, and 0.2 g/100 g DM, respectively) and low hyp with high oxalate (93 mg/100 g DM; Lhyp-Hox) to 8 adult female cats in a 48-d study using a Latin square design. Cats were randomly allocated to one of the four 12-d treatment periods and fed according to individual energy needs. Feces and urine were collected quantitatively using modified litter boxes during the final 5 d of each period. Feces were analyzed for oxalate and Ca, and urine was analyzed for specific density, pH, oxalate, Ca, P, Mg, Na, K, ammonia, citrate, urate, sulfate, and creatinine. Increasing hyp intake (0.2, 2.0, and 3.8 g/100 g DM) resulted in increased Uox excretion (Lhyp-Lox vs. Mhyp-Lox vs. Hhyp-Lox; P < 0.05), and the linear dose-response equation was Uox (mg/d) = 5.62 + 2.10 × g hyp intake/d (r(2) = 0.56; P < 0.001). Increasing oxalate intake from 13 to 93 mg/100 g DM did not affect Uox excretion but resulted in an increase in fecal oxalate output (P < 0.001) and positive oxalate balance (32.20 ± 2.06 mg/d). The results indicate that the intestinal absorption of the supplemental oxalate, and thereby its contribution to Uox, was low (5.90% ± 5.24%). Relevant increases in endogenous Uox excretion were achieved by increasing dietary hyp intake. The hyp-containing protein sources should be minimized in Ca oxalate urolith preventative diets until their effect on Uox excretion is tested. The oxalate content (up to 93 mg/100 g DM) in a diet with moderate Ca content does not contribute to Uox content.

Improved methodology to induce hyperoxaluria without treatment using hydroxyproline.

The use of hydroxyproline (HP) to generate hyperoxaluria in the rat is a problem because it is impossible to separate the effect of oxalate on renal injury from the effects of HP and the large array of metabolic intermediates formed when HP is converted to oxalate. Previously, the Dahl salt-sensitive (SS) and Brown Norway (BN) rat strains were studied to determine genetic control of resistance or susceptibility to HP-induced renal injury and crystal deposition. To develop a better model to induce hyperoxaluria without causing injury from HP metabolites, animals were fed a diet containing various levels of added oxalate (0, 1, 2, 3, or 5%). After 5 weeks rats were killed and the kidneys were removed for microscopic evaluation of tubule changes and crystal deposition. The 3 and 5% oxalate-fed groups had a substantial increase in urine oxalate, about 50 and 140 µmol/g body weight over controls, respectively. Both the SS and BN 3% oxalate-fed animals showed only slightly elevated tubule area and no crystal deposition. However, BN animals fed 5% oxalate had a dramatic increase in their percent tubule areas compared to control BN rats and treated SS rats. Crystal deposition in the kidneys was only observed in the 5% oxalate-fed groups. The BN kidneys demonstrated a threefold higher crystal deposition compared to oxalate-fed SS rats. We conclude that oxalate-supplemented food is a better method of producing hyperoxaluria in the rat than using HP which may introduce metabolic intermediates injurious to the kidney.

Liposome encapsulation improves the effect of antifibrotic agent in rat lung fibrosis.

We studied whether the therapeutic efficacy of the antifibrotic agent cis-4-hydroxy-L-proline (cHyp) in preventing bleomycin-induced pulmonary fibrosis in rats is enhanced by intratracheal delivery in liposomes. Dual-radiolabeled liposomes were used to study the distribution and stability of liposomes after intratracheal instillation. Lung retention was > 20% 1 wk after intratracheal instillation of 9 mumol phospholipid, and liposomes were intact as indicated by the ratio of the lipid and aqueous-phase markers remaining unchanged. For the fibrosis study, groups of rats were instilled with 1.2 U bleomycin (Bleo) and treated 1 and 2 wk later by single intratracheal instillation of test compounds. The control group received 0.3 ml saline (Bleo/sal). The treated groups received 9 mumol phospholipid in 0.3 ml of the following liposome preparations: empty liposomes (Bleo/lip), liposomes and 100 mg/kg of free unencapsulated cHyp (Bleo/lip/cHyp), and 100 mg/kg of liposome-encapsulated cHyp (Bleo/lip-cHyp). At 3 wk, fibrosis (mg hydroxyproline/g weight lung) by groups was as follows: control, 2.6 +/- 0.1 (SEM); Bleo/sal, 3.2 +/- 0.1, Bleo/lip, 3.2 +/- 0.1, and Bleo/lip/cHyp, 3.1 +/- 0.1, p < 0.05 compared with control; Bleo/lip-cHyp, 2.6 +/- 0.1, p < 0.05 compared with Bleo/sal, n = 3 to 6. Histologic grading of fibrosis did not show decreased fibrosis in the Bleo/lip-cHyp group, probably because of the focal nature of the fibrotic lesions. We conclude that cHyp encapsulated in liposomes prevents bleomycin-induced fibrosis by biochemical measurements. Delivery of antifibrotic agents to the lung in carrier vehicles promotes retention and may enhance their efficacy in treating bleomycin-induced pulmonary fibrosis.