Oxalate is a divalent organic anion that affects many biological and commercial processes. It is derived from plant sources, such as spinach, rhubarb, tea, cacao, nuts, and beans, and therefore is commonly found in raw or processed food products. Oxalate can also be made endogenously by humans and other mammals as a byproduct of hepatic enzymatic reactions. It is theorized that plants use oxalate to store calcium and protect against herbivory. Clinically, oxalate is best known to be a major component of kidney stones, which commonly contain calcium oxalate crystals. Oxalate can induce an inflammatory response that decreases the immune system’s ability to remove renal crystals. When formulated with platinum as oxaliplatin (an anticancer drug), oxalate has been proposed to cause neurotoxicity and nerve pain. There are many sectors of industry that are hampered by oxalate, and others that depend on it. For example, calcium oxalate is troublesome in the pulp industry and the alumina industry as it deposits on machinery. On the other hand, oxalate is a common active component of rust removal and cleaning products. Due to its ubiquity, there is interest in developing efficient methods to quantify oxalate. Over the past four decades, many diverse methods have been reported. These approaches include electrochemical detection, liquid chromatography or gas chromatography coupled with mass spectrometry, enzymatic degradation of oxalate with oxalate oxidase and detection of hydrogen peroxide produced, and indicator displacement-based methods employing fluorescent or UV light-absorbing compounds. Enhancements in sensitivity have been reported for both electrochemical and mass-spectrometry-based methods as recently as this year. Indicator-based methods have realized a surge in interest that continues to date. The diversity of these approaches, in terms of instrumentation, sample preparation, and sensitivity, has made it clear that no single method will work best for every purpose. This review describes the strengths and limitations of each method, and may serve as a reference for investigators to decide which approach is most suitable for their work.

Fluorescence sensing of oxalate has garnered some attention in the past two decades as a result of this anion’s prominence and impact on society. Previous work on oxalate sensors and other divalent anion sensors has led to the conclusion that the sensors are selective for the anion under investigation. However, sensor selectivity is often determined by testing against a relatively small array of “guest” molecules or analytes and studies often exclude potentially interfering compounds. For example, studies on oxalate sensors have excluded compounds such as citrate and urate, which are anions in the biological matrices where oxalate is measured (e.g., urine, blood, and bacterial lysate). In the present study, we reassessed the selectivity of a dinuclear copper(II) macrocycle (Cu₂L) in an eosin Y displacement assay using biologically relevant anions. Although previously reported as selective for oxalate, we found greater indicator displacement (fluorescence response) for urate and oxaloacetate and a significant response to citrate. These anions are larger than oxalate and do not appear to fit into the putative binding pocket of Cu₂L. Consistent with previous reports, Cu₂L did not release eosin Y in the presence of several other dicarboxylates, including adipate, glutarate, malate (except at 10 mM), fumarate, succinate, or malonate (except at 10 mM), and the monocarboxylate acetate. This was demonstrated by the failure of the anions to reverse eosin Y quenching by Cu₂L. We also assessed, for the first time, other monocarboxylates, including butyrate, pyruvate, lactate, propionate, and formate. None of these anions were able to displace eosin Y, indicating no interaction with Cu₂L that interfered with the eosin Y binding site. Single-crystal X-ray crystallography revealed that nonselective binding of the anions is likely partly caused by readily accessible copper(II) ions on the external surface of Cu₂L. In addition, π–π stacking of urate with the aromatic groups of Cu₂L cannot be ruled out as a contributor to binding. We conclude that Cu₂L is not suitable for oxalate sensing in a biological matrix unless interfering compounds are selectively removed or masked.

Objective: Gamma-hydroxybutyrate (GHB) has been an abused and illicit substance for decades, but the antinarcoleptic medication Xyrem (sodium oxybate), the sodium salt of GHB, was approved just in 2002 for increasing wakefulness. We present a case of coma induced by co-ingestion of prescription GHB and ethanol and describe the response to naloxone treatment, by first responders, without evidence of opiate exposure. The purpose of this report is to bridge updated knowledge on GHB and ethanol pharmacology with the clinical sequence of events in a patient co-ingesting these compounds and to theorize on a potentially better pharmacological approach to narcolepsy. Case Summary: The patient was a 25-year-old woman with a history of narcolepsy. She suddenly collapsed at home but became transiently responsive after being administered naloxone in the ambulance. She presented to the emergency department with apnea, poor responsiveness with a Glasgow Coma Score of 7, and urinary incontinence. While undergoing intubation, the patient spontaneously and abruptly awoke. Labs were unremarkable except a blood alcohol concentration of 0.123%. The dosage of, and adherence to, GHB was unknown in this case. Discussion: The case is described in light of the most recent pharmacological advancements on these co-ingestants. A conceptual dose–response curve is shown to facilitate understanding of the complex pharmacology of GHB. Conclusions: Approved and potential alternatives to GHB, for achieving wakefulness, are discussed. Potential new strategies should bear low to no risk of coma with accidental overdose or co-ingestion of ethanol. In addition, promising antidotes for future consideration are discussed.

ClopHensor, a fluorescent fusion protein, is a dual function biosensor that has been utilized as a tool for the simultaneous measurement of intracellular chloride and pH in cells. ClopHensor has traditionally been used in conjunction with fluorescence microscopy for single cell measurements. Here, we present a promising multi-well format advancement for the use of ClopHensor as a potential high-throughput method capable of measuring fluorescence signal intensity across a well of confluent cells with highly reproducible results. Using this system, we gained mechanistic insight into an endogenous oxalate transporter in Chinese hamster ovary (CHO) cells expressing ClopHensor and the human chloride transporter, SLC26A3. SLC26A3, a known anion exchanger, has been proposed to play a role in colonic oxalate absorption in humans. Our attempt to study the role of SLC26A3 in oxalate transport revealed the presence of an endogenous oxalate transporter in CHO cells. This transporter was strongly inhibited by niflumate, and exhibited clear saturability. Use of ClopHensor in a multi-well cell assay allowed us to quickly demonstrate that the endogenous oxalate transporter was unable to exchange chloride for bicarbonate, unlike SLC26A3.

Oxalate is a divalent organic anion that has implications across many biological and commercial processes. It is derived from plant sources, such as spinach, rhubarb, tea, cacao, nuts, and beans, and therefore is commonly found in raw or processed food products. Oxalate can also be made endogenously by humans and other mammals as a byproduct of hepatic enzymatic reactions. It is theorized that oxalate is useful for plants to store calcium and protect against herbivory. Clinically, oxalate is best known to be a major component of kidney stones, which commonly contain calcium oxalate crystals. Oxalate can induce an inflammatory response that decreases the immune system’s ability to remove renal crystals. When formulated with platinum as oxaliplatin (an anticancer drug), oxalate has been proposed to cause neurotoxicity and nerve pain. There are many sectors of industry that are hampered by oxalate, and some that depend on it. For example, calcium oxalate is troublesome in the pulp industry and the alumina industry as it deposits on machinery. On the other hand, oxalate is a common active component of rust removal and cleaning products. Due to its ubiquity, there is interest in developing efficient methods to quantify oxalate. Over the past four decades several diverse methods have been reported. These approaches include electrode-based detection, liquid chromatography or gas chromatography coupled with mass spectrometry, enzymatic degradation of oxalate with oxalate oxidase and detection of hydrogen peroxide as a product, and indicator displacement-based methods employing fluorescent or UV light-absorbing compounds. It has become clear that no single method will work best for every purpose. This review describes the strengths and limitations of each method, and may serve as a reference for investigators to decide which approach is most suitable for their work.