Valproic acid intoxication identified by 1H and 1H-(13)C correlated NMR spectroscopy of urine samples

Evidence of glucuronidation of the glycation product LW-1: tentative structure and implications for the long-term complications of diabetes

LW-1 is a collagen-linked blue fluorophore whose skin levels increase with age, diabetes and end-stage renal disease (ESRD), and correlate with the long-term progression of microvascular disease and indices of subclinical cardiovascular disease in type 1 diabetes. The chemical structure of LW-1 is still elusive, but earlier NMR analyses showed it has a lysine residue in an aromatic ring coupled to a sugar molecule reminiscent of advanced glycation end-products (AGEs). We hypothesized and demonstrate here that the unknown sugar is a N-linked glucuronic acid. LW-1 was extracted and highly purified from ~99 g insoluble skin collagen obtained at autopsy from patients with diabetes/ESRD using multiple rounds of proteolytic digestion and purification by liquid chromatography (LC). Advanced NMR techniques (¹H-NMR, ¹³C-NMR, ¹H-¹³C HSQC, ¹H-¹H TOCSY, ¹H-¹³C HMBC) together with LC-mass spectrometry (MS) revealed a loss of 176 amu (atomic mass unit) unequivocally point to the presence of a glucuronic acid moiety in LW-1. To confirm this data, LW-1 was incubated with β-glycosidases (glucosidase, galactosidase, glucuronidase) and products were analyzed by LC-MS. Only glucuronidase could cleave the sugar from the parent molecule. These results establish LW-1 as a glucuronide, now named glucuronidine, and for the first time raise the possible existence of a "glucuronidation pathway of diabetic complications". Future research is needed to rigorously probe this concept and elucidate the molecular origin and biological source of a circulating glucuronidine aglycone.

Valproate overdose: a comparative cohort study of self poisonings

AIMS

Based on individual case reports of massive overdoses, valproate is often regarded as having significant toxicity. This study aimed to describe the epidemiology of valproate poisoning and the spectrum of its clinical effects.

METHODS

Consecutive valproate poisonings were identified and compared with other anticonvulsant overdoses and all other poisonings, from a prospective database of poisoning admissions presenting to a regional toxicology service. National prescription data for the same period were obtained.

RESULTS

There were 79 patients with valproate poisoning from January 1991 to November 2001, 15 cases with valproate alone. Of the 15 cases, drowsiness occurred in two patients (both taking> 200 mg kg-1), vomiting occurred in four and tachycardia in five. In patients co-ingesting other medications, moderate to severe effects were consistent with the co-ingestants. There was one death not directly related to valproate. One patient had metabolic acidosis and thrombocytopaenia consistent with severe valproate toxicity. Comparison of valproate, carbamazepine, phenytoin and control groups showed that length of stay for both phenytoin and carbamazepine was significantly longer than for valproate (P < 0.0001), and there was a significantly increased risk of intensive care unit admission for carbamazepine vs valproate (OR 2.73; 95% CI 1.22, 6.28; P = 0.015). Although valproate prescriptions increased over the 10 years, there was relatively greater increase in the incidence of valproate poisoning. The odds of a valproate overdose in 1992 compared with carbamazepine were 0.29 (95% CI 0.07, 1.28; P = 0.141), but in 2001 were 2.73 (95% CI 1.38, 5.39; P = 0.004).

CONCLUSIONS

Valproate causes mild toxicity in the majority of cases. Massive overdoses of greater than 400 mg kg-1 can cause severe toxicity, but these are uncommon. The older anticonvulsants phenytoin and carbamazepine remain a greater problem than valproate in overdose.