Metformin-induced encephalopathy: the role of thiamine

Evaluation of whole blood thiamine pyrophosphate concentrations in critically ill patients receiving chronic diuretic therapy prior to admission to Turkish intensive care units: A pragmatic, multicenter, prospective study

BACKGROUND/OBJECTIVES

Thiamine plays a pivotal role in energy metabolism. The aim of the study was to determine serial whole blood TPP concentrations in critically ill patients receiving chronic diuretic treatment before ICU admission and to correlate TPP levels with clinically determined serum phosphorus concentrations.

SUBJECTS/METHODS

This observational study was performed in 15 medical ICUs. Serial whole blood TPP concentrations were measured by HPLC at baseline and at days 2, 5 and 10 after ICU admission.

RESULTS

A total of 221 participants were included. Of these, 18% demonstrated low TPP concentrations upon admission to the ICU, while 26% of participants demonstrated low levels at some point during the 10-day study period. Hypophosphatemia was detected in 30% of participants at some point during the 10-day period of observation. TPP levels were significantly and positively correlated with serum phosphorus levels at each time point (P < 0.05 for all).

CONCLUSIONS

Our results show that 18% of these critically ill patients exhibited low whole blood TPP concentrations on ICU admission and 26% had low levels during the initial 10 ICU days, respectively. The modest correlation between TPP and phosphorus concentrations suggests a possible association due to a refeeding effect in ICU patients requiring chronic diuretic therapy.

Extrapyramidal syndromes of chronic kidney disease and dialysis (diabetic uremic syndrome) with reversible parkinsonism and lentiform fork sign: A case report and literature review including metformin-induced encephalopathy

Diabetic uremic syndrome has been rarely reported in patients on maintenance dialysis for diabetic nephropathy who present subacutely with neurological symptoms and bilateral basal ganglia lesions. There are also a few reports on metformin-induced encephalopathy, which is clinically similar to diabetic uremic syndrome. Because some patients with each of these diseases also have metabolic acidosis, it is speculated that these two diseases may have the same pathology. Recently, the term "extrapyramidal syndromes of chronic kidney disease and dialysis" (EPS-CKDD), with associated diagnostic criteria, has been proposed to describe these conditions, and metformin use is considered a risk factor for developing these syndromes. We report a case of a patient on maintenance hemodialysis for diabetic nephropathy who was taking metformin and developed subacute parkinsonism and bilateral basal ganglia lesions that rapidly improved after discontinuation of metformin with continued maintenance hemodialysis. We should ascertain whether patients with EPS-CKDD are taking metformin because it may be inappropriately prescribed for end-stage renal disease. If metformin has been prescribed, it should be discontinued immediately; its discontinuation may lead to rapid symptom recovery and improved prognosis.

The extrapyramidal syndromes of chronic kidney disease and dialysis (EPS-CKDD): diagnostic criteria, risk factors and prognosis

BACKGROUND

Acute extrapyramidal movement disorders in dialysis patients are rare, inconsistently defined and have uncertain aetiology and prognosis.

AIM

Define diagnostic criteria, prognosis and risk factors.

DESIGN AND METHODS

Retrospective case series review of 20 patients (14 female, mean age 62 years) receiving dialysis for a median of 15 (interquartile range 4-35) months who presented with acute parkinsonism (AP = 11) or chorea/athetosis (CA = 9).

RESULTS

All patients had type 2 diabetes (HbA1c 6.8 ± 1.0) and had received metformin. Lactic acidosis was present in 2 patients at presentation and serum lactate was elevated in 7/15 patients tested. No patient had abnormal copper or thyroid metabolism and 5/8 patients tested returned marginal abnormalities in heavy metal screening. Magnetic resonance imaging (MRI) revealed characteristic bilateral symmetric T2 hyperintensity of the basal ganglia (BG), predominantly putamen and globus pallidus (the lentiform nucleus) and more extensive involvement of the external and internal capsules in patients with AP presentation. Post-mortem demonstrated cytotoxic necrosis of the BG. Therapy included thiamine, intensive dialysis and cessation of metformin. Two patients died acutely, nine recovered and nine had residual symptoms. Median survival did not differ by presentation: AP 24 [95% confidence interval (CI) 21-27] and CA 33 (95% CI 32-35) months, P = 0.21.

CONCLUSIONS

There are two distinct clinical extrapyramidal movement disorders associated with specific diagnostic MRI imaging that support the diagnosis of the extrapyramidal syndromes of chronic kidney disease and dialysis. The associations with diabetes, metformin and metabolic acidosis suggest a common pathogenic mechanism but require additional study. Early recognition and treatment may improve outcomes.

Focal brain lactate accumulation in metformin-induced encephalopathy without systemic lactic acidosis: A case report suggesting mitochondrial vulnerability in lentiform fork sign

Metformin causes metabolic encephalopathy in some patients with end-stage chronic kidney disease, resulting in impaired consciousness and parkinsonism. This encephalopathy has a very characteristic magnetic resonance imaging feature in lentiform nuclei known as the “lentiform fork sign”. However, the mechanism is unknown. Here, we report a case of metformin-induced encephalopathy with a novel observation of lactate accumulation in the lentiform nuclei on magnetic resonance spectroscopy without systemic lactic acidosis. Since metformin is an inhibitor of mitochondrial complex-I, this focal brain lactate accumulation implies that a part of the pathogenesis of metformin-induced encephalopathy is the focal vulnerability of mitochondria to metformin in the lentiform nuclei. When metformin causes encephalopathy, not only testing for serum lactic acidosis and performing routine magnetic resonance imaging but also evaluation of brain lactate accumulation by magnetic resonance spectroscopy should be required to elucidate the etiology.

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Metformin-induced encephalopathy with lactate accumulation in lentiform fork sign was reported.

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Lentiform nuclei might be more vulnerable to metformin than other organs.

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This case suggested an etiology for the lentiform fork sign because metformin is a mitochondrial inhibitor.

Case Report: A Case of Encephalopathy Presenting the Lentiform Fork Sign on MRI in a Diabetic Dialysis Patient

Basal ganglia lesions showing an expansile high signal intensity on T2-weighted MRI are termed the lentiform fork sign. This specific finding is mainly observed in diabetic patients with uremic encephalopathy with metabolic acidosis, although there are also reports in patients with ketoacidosis, dialysis disequilibrium syndrome, intoxication, and following drug treatment (e.g., metformin). A 57-year-old Japanese man on chronic hemodialysis for 4 years because of diabetic nephropathy was admitted to our hospital for relatively rapid-onset gait disturbance, severe dysarthria, and consciousness disturbance. Brain T2-weighted MRI showed the lentiform fork sign. Hemodialysis was performed the day before admission, and laboratory tests showed mild metabolic (lactic) acidosis, but no uremia. Surprisingly, metformin, which is contraindicated for patients with end-stage kidney disease, had been prescribed for 6 months in his medication record, and his sluggish speaking and dysarthria appeared gradually after metformin treatment was started. Thus, the encephalopathy was considered to be related to metformin treatment. He received hemodialysis treatment for 6 consecutive days, and his consciousness disturbance and dysarthria improved in 1 week. At the 8-month follow-up, the size of the hyperintensity area on MRI had decreased, while the mild gait disturbance remained. Considering the rapid onset of gait and consciousness disturbance immediately before admission, diabetic uremic syndrome may also have occurred with metformin-related encephalopathy, and resulted in the lentiform fork sign, despite the patient showing no evidence of severe uremia on laboratory data.

Case Report: A Case of Encephalopathy Presenting the Lentiform Fork Sign on MRI in a Diabetic Dialysis Patient

Basal ganglia lesions showing an expansile high signal intensity on T2-weighted MRI are termed the lentiform fork sign. This specific finding is mainly observed in diabetic patients with uremic encephalopathy with metabolic acidosis, although there are also reports in patients with ketoacidosis, dialysis disequilibrium syndrome, intoxication, and following drug treatment (e.g., metformin). A 57-year-old Japanese man on chronic hemodialysis for 4 years because of diabetic nephropathy was admitted to our hospital for relatively rapid-onset gait disturbance, severe dysarthria, and consciousness disturbance. Brain T2-weighted MRI showed the lentiform fork sign. Hemodialysis was performed the day before admission, and laboratory tests showed mild metabolic (lactic) acidosis, but no uremia. Surprisingly, metformin, which is contraindicated for patients with end-stage kidney disease, had been prescribed for 6 months in his medication record, and his sluggish speaking and dysarthria appeared gradually after metformin treatment was started. Thus, the encephalopathy was considered to be related to metformin treatment. He received hemodialysis treatment for 6 consecutive days, and his consciousness disturbance and dysarthria improved in 1 week. At the 8-month follow-up, the size of the hyperintensity area on MRI had decreased, while the mild gait disturbance remained. Considering the rapid onset of gait and consciousness disturbance immediately before admission, diabetic uremic syndrome may also have occurred with metformin-related encephalopathy, and resulted in the lentiform fork sign, despite the patient showing no evidence of severe uremia on laboratory data.

Movement Disorders and Renal Diseases

Movement disorders often emerge from the interplay of complex pathophysiological processes involving the kidneys and the nervous system. Tremor, myoclonus, ataxia, chorea, and parkinsonism can occur in the context of renal dysfunction (azotemia and electrolyte abnormalities) or they can be part of complications of its management (dialysis and renal transplantation). On the other hand, myoglobinuria from rhabdomyolysis in status dystonicus and certain drugs used in the management of movement disorders can cause nephrotoxicity. Distinct from these well-recognized associations, it is important to appreciate that there are several inherited and acquired disorders in which movement abnormalities do not occur as a consequence of renal dysfunction or vice versa but are manifestations of common pathophysiological processes affecting the nervous system and the kidneys. These disorders are the emphasis of this review. Increasing awareness of these conditions among neurologists may help them to identify renal involvement earlier, take timely intervention by anticipating complications and focus on therapies targeting common mechanisms in addition to symptomatic management of movement disorders. Recognition of renal impairment in a patient with complex neurological presentation may narrow down the differentials and aid in reaching a definite diagnosis.

Drug-nutrient interactions: discovering prescription drug inhibitors of the thiamine transporter ThTR-2 (SLC19A3)

BACKGROUND

Transporter-mediated drug-nutrient interactions have the potential to cause serious adverse events. However, unlike drug-drug interactions, these drug-nutrient interactions receive little attention during drug development. The clinical importance of drug-nutrient interactions was highlighted when a phase III clinical trial was terminated due to severe adverse events resulting from potent inhibition of thiamine transporter 2 (ThTR-2; SLC19A3).

OBJECTIVE

In this study, we tested the hypothesis that therapeutic drugs inhibit the intestinal thiamine transporter ThTR-2, which may lead to thiamine deficiency.

METHODS

For this exploration, we took a multifaceted approach, starting with a high-throughput in vitro primary screen to identify inhibitors, building in silico models to characterize inhibitors, and leveraging real-world data from electronic health records to begin to understand the clinical relevance of these inhibitors.

RESULTS

Our high-throughput screen of 1360 compounds, including many clinically used drugs, identified 146 potential inhibitors at 200 μM. Inhibition kinetics were determined for 28 drugs with half-maximal inhibitory concentration (IC50) values ranging from 1.03 μM to >1 mM. Several oral drugs, including metformin, were predicted to have intestinal concentrations that may result in ThTR-2-mediated drug-nutrient interactions. Complementary analysis using electronic health records suggested that thiamine laboratory values are reduced in individuals receiving prescription drugs found to significantly inhibit ThTR-2, particularly in vulnerable populations (e.g., individuals with alcoholism).

CONCLUSIONS

Our comprehensive analysis of prescription drugs suggests that several marketed drugs inhibit ThTR-2, which may contribute to thiamine deficiency, especially in at-risk populations.

Mechanisms of Non-coenzyme Action of Thiamine: Protein Targets and Medical Significance

Thiamine (vitamin B1) is a precursor of the well-known coenzyme of central metabolic pathways thiamine diphosphate (ThDP). Highly intense glucose oxidation in the brain requires ThDP-dependent enzymes, which determines the critical significance of thiamine for neuronal functions. However, thiamine can also act through the non-coenzyme mechanisms. The well-known facilitation of acetylcholinergic neurotransmission upon the thiamine and acetylcholine co-release into the synaptic cleft has been supported by the discovery of thiamine triphosphate (ThTP)-dependent phosphorylation of the acetylcholine receptor-associated protein rapsyn, and thiamine interaction with the TAS2R1 receptor, resulting in the activation of synaptic ion currents. The non-coenzyme regulatory binding of thiamine compounds has been demonstrated for the transcriptional regulator p53, poly(ADP-ribose) polymerase, prion protein PRNP, and a number of key metabolic enzymes that do not use ThDP as a coenzyme. The accumulated data indicate that the molecular mechanisms of the neurotropic action of thiamine are far broader than it has been originally believed, and closely linked to the metabolism of thiamine and its derivatives in animals. The significance of this topic has been illustrated by the recently established competition between thiamine and the antidiabetic drug metformin for common transporters, which can be the reason for the thiamine deficiency underlying metformin side effects. Here, we also discuss the medical implications of the research on thiamine, including the role of thiaminases in thiamine reutilization and biosynthesis of thiamine antagonists; molecular mechanisms of action of natural and synthetic thiamine antagonists, and biotransformation of pharmacological forms of thiamine. Given the wide medical application of thiamine and its synthetic forms, these aspects are of high importance for medicine and pharmacology, including the therapy of neurodegenerative diseases.