Kryptopyrrole and other monopyrroles in molecular neurobiology

Sixty years of conjecture over a urinary biomarker: a step closer to understanding the proposed link between anxiety and urinary pyrroles

OBJECTIVE

For over 60 years there has been conjecture about the identity of an Ehrlich's test positive pyrrole (Mauve Factor) reputed to be a biomarker for psychological disorders, including anxiety. We reviewed studies that attempt to identify Mauve Factor and subjected authentic standards of the 2 main candidates, kryptopyrrole and hydroxypyrrole, to the Ehrlich's reaction.

METHODS

Modified Ehrlich's test for kryptopyrrole and hydroxypyrrole were applied to urine samples from 10 volunteers, anxious and nonanxious.

RESULTS

Based on the mechanistic chemistry of Ehrlich's reaction and reactions of the 2 compounds, Mauve Factor cannot be hydroxypyrrole. Analyses of urine samples from volunteers, identified by the Generalized Anxiety Disorder - 7 item scale (GAD-7 ≥10; n = 5) and control urine samples (GAD-7 <10; n = 5) using a kryptopyrrole calibration graph, show that concentrations are similar in both groups.

CONCLUSION

Kryptopyrrole may be the elusive Mauve Factor. Its possible origin from stercobilin via gut microbiome-mediated metabolism, its link to gut-mediated neurological effects via γ-aminobutyric acid (GABA) receptors, and its predicted interaction with Zn2+ and consequent impact on zinc homeostasis are discussed. The GAD-7 scale does not differentiate between state and trait anxiety and as such, the minimal difference in pyrrole levels between volunteer groups requires further study.

Pyroluria: Fact or Fiction?

Objective: The term "Mauve factor" (pyrroluria) dates back to 1958 when Dr. Abram Hoffer defined the condition as elevated levels of pyrroles in the urine, currently called hydroxyhemepyrrolin-2-one (HPL). It was suggested that the raised pyrrole levels lead to depletions in zinc and vitamin B₆, which, in turn, were hypothesized to result in a range of psychiatric disorders, such as schizophrenia, anxiety, and depression. Treatment implications are supplementation with zinc and B₆. This article aimed to review the scientific literature associating pyrroluria with psychiatric symptoms, explore the validity of HPL testing, explore the role of nutrients as treatment options for pyrroluria, and discuss future research directions. Methods: A PRISMA review was conducted using search results from electronic databases PubMed, MEDLINE, PsycINFO, EMBASE from inception to February 2020 using the following keywords: hydroxyhemepyryrrolin (HPL), kryptopyrrole (KP), mauve factor, pyroluria, pyrroluria, monopyrroles. Article reference lists were also scanned and included where relevant. Results: Seventy-three articles were identified of which only three studies identified significantly higher HPL levels in a psychiatric population compared with controls, and there were no placebo-controlled treatment trials directed at pyrroluria. The other 13 clinical studies either showed no association or did not provide adequate data to show group differences in HPL levels. Despite an extensive history of practitioners diagnosing and treating a wide variety of mental health conditions associated with pyrroluria as well as clinical observations of elevated HPL being associated with psychiatric disorders, there was no clear research that showed the following: (1) elevated HPL is robustly associated with increased mental health symptoms, (2) elevated HPL in urine is associated with increased urine excretion of zinc and B₆, and (3) high-dose zinc and B₆ are an efficacious treatment for mental health problems associated with elevated HPL. Conclusions: Elevated HPL is a clinically observed, but poorly researched biomarker with unclear associations with mental disorders. Based on current evidence, HPL testing is not recommended as a screening or treatment tool. Further research is required in the following areas: establishment of which specific clinical populations exhibit elevated HPL, validation of the chemistry and validity of testing, and controlled trials to establish efficacy of high-dose zinc and B₆ as treatment of elevated pyrroles.

Quantitative determination of 3-ethyl-5-hydroxy-4,5-dimethyl-delta3-pyrrolin-2-one in urine using gas-liquid chromatography

A method is presented for the quantitation in urine of 3-ethyl-5-hydroxy-4,5-dimethyl-delta3-pyrrolin-2-one, a substance associated with hepatic porphyria and psychiatric disorders. The method involves gas-liquid chromatography following solvent extraction using one of two other heterocyclic compounds as internal standards. Quantitation of this substance in the urine of a group of normal subjects is also reported.

Hyperprolinemia type II: identification of the glycine conjugate of pyrrole-2-carboxylic acid in urine

The urinary organic acids were studied in two cases of hyperprolinemia Type II, using various combinations of chromatographic, electrophoretic and mass spectrometric techniques. In both cases N-(pyrrole-2-carboxylic acid) was idenfitied as a major urinary metabolite. While there was evidence for an additional conjugate of this pyrrolic acid, no free pyrrole-carboxylate could be detected in the urine from either case.

Autotransfer chromatography in the characterization of pyrroles. Chemistry of multiple-spot phenomena

A characteristic pattern of five interconverting "component" zones is obtained on autotransfer chromatography when pure kryptopyrrole (KP) is adsorbed from aqueous solution onto charcoal and then eluted with methanol. Specific oxidation products (lactams) derived from synthetic KP matched four of the five zones. Zone 1 was obtained directly from the a'-hydroxy-a-lactam. Zone 3 was produced directly by the a'-methoxy-a-lactam, while zones 2 and 5 were formed as a consequence of its acid hydrolysis during equilibration and chromatographic development. The formation of the methoxy lactam itself depended upon the presence of added methanol in the extraction process. In the absence of methanol during extraction only zone 1 (sometimes accompanied by zone 4) was formed.