Acute cyclosporine A nephrotoxicity in a renal allograft recipient with hypothyroidism

Molecular Basis of Na, K-ATPase Regulation of Diseases: Hormone and FXYD2 Interactions

The Na, K-ATPase generates an asymmetric ion gradient that supports multiple cellular functions, including the control of cellular volume, neuronal excitability, secondary ionic transport, and the movement of molecules like amino acids and glucose. The intracellular and extracellular levels of Na+ and K+ ions are the classical local regulators of the enzyme's activity. Additionally, the regulation of Na, K-ATPase is a complex process that occurs at multiple levels, encompassing its total cellular content, subcellular distribution, and intrinsic activity. In this context, the enzyme serves as a regulatory target for hormones, either through direct actions or via signaling cascades triggered by hormone receptors. Notably, FXYDs small transmembrane proteins regulators of Na, K-ATPase serve as intermediaries linking hormonal signaling to enzymatic regulation at various levels. Specifically, members of the FXYD family, particularly FXYD1 and FXYD2, are that undergo phosphorylation by kinases activated through hormone receptor signaling, which subsequently influences their modulation of Na, K-ATPase activity. This review describes the effects of FXYD2, cardiotonic steroid signaling, and hormones such as angiotensin II, dopamine, insulin, and catecholamines on the regulation of Na, K-ATPase. Furthermore, this review highlights the implications of Na, K-ATPase in diseases such as hypertension, renal hypomagnesemia, and cancer.

Impact of severe hypothyroidism on cyclophosphamide disposition and routes of metabolism and transport in a patient with treatment-resistant lupus nephritis

OBJECTIVE

To report what we believe to be the first case of severe hypothyroidism with reduced drug metabolism and transport activity.

CASE SUMMARY

A 32-year-old African American woman with a history of treatment-resistant lupus nephritis and concurrent hypothyroidism was participating in a clinical study to evaluate cyclophosphamide pharmacokinetics in patients with glomerulonephritis due to lupus nephritis and small-vessel vasculitis. Thyroid-stimulating hormone levels ranged from 60 to 300 μIU/mL, despite high doses of thyroid replacement hormone (levothyroxine 400 μg twice weekly). The pharmacokinetics of the probe drug cocktail (flurbiprofen/fexofenadine) were altered, with formation clearance of flurbiprofen (CYP2C9 function) lower in our patient versus the average value in our study cohort, suggesting a reduction in activity. The area under the concentration-time curve from 0 to 24 hours for fexofenadine (transporter function) was 2-fold higher in our patient compared to that of other study patients. Pharmacokinetic data showed markedly decreased cyclophosphamide clearance and exposure to 4-hydroxycyclophosphamide, as well as a reduced metabolic ratio of 4-hydroxycyclophosphamide to cyclophosphamide.

DISCUSSION

Previous cases of altered pharmacokinetics and toxicity of medications in patients with mild to moderate thyroid dysfunction have been published. Our case evaluated the impact of a severe form of hypothyroidism on cyclophosphamide pharmacokinetics and probe drug metabolism and transport. If changes were not demonstrated at the extreme spectrum of hypothyroidism, there would be little concern for changes in patients with less severe disease. Profound hypothyroidism likely contributed to the patient's poor response to cyclophosphamide treatment through its influence on CYP isoenzymes responsible for the activation to 4-hydroxycyclophosphamide and possibly through reduced transport function.

CONCLUSIONS

Clinicians should monitor for significant hypothyroidism in patients who are prescribed drugs (eg, cyclophosphamide) that require metabolic conversion to form active therapeutic moieties.

Lithium toxicity precipitated by profound hypothyroidism

Many patients who have undergone surgical treatment for thyroid cancer are treated with postoperative radioactive iodine ablation. Thyroid hormone is generally stopped for several weeks prior to treatment. We report the case of a woman on long-standing treatment with lithium for bipolar disorder who, after 3 weeks of withdrawal from thyroid hormone, presented to the hospital with severe lithium toxicity. She required admission to the intensive care unit and was treated with hemodialysis and supportive care with resolution of her illness. In this patient, renal dysfunction associated with her hypothyroid state was likely the precipitating event leading to the lithium toxicity. We review the effect of hypothyroidism on renal function and the association of hypothyroidism with drug toxicities. This case illustrates the potential for hypothyroid-induced renal dysfunction to lead to adverse clinical consequences in patients taking medications cleared by the kidneys.

Thyroid hormone administration to hypothyroid rats restores the mitochondrial membrane permeability properties

We have investigated the effect of thyroid hormone on the mitochondrial membrane permeability properties in a hypothyroid rat model. The role played by calcium in affecting these properties has been also examined. Cyclosporin A-sensitive mitochondrial calcium efflux, swelling, and external release of matrix proteins are events that occur normally during the permeability transition process induced by calcium loading of mitochondria. We demonstrate that these events are impaired in mitochondria isolated from the liver of hypothyroid rats, even in the presence of high calcium content. However, after thyroid hormone administration to hypothyroid rats, the mitochondrial permeability transition process in response to calcium loading is restored. Consequently, mitochondrial calcium efflux, swelling, and release of matrix proteins, like glutamate dehydrogenase, malate dehydrogenase, and aspartate aminotransferase occur. These effects are abrogated by the concomitant administration of cyclosporin A. The results of the present study suggest that hypothyroidism may be a potential source of adverse effects in patients receiving cyclosporin A.

Changes in thyroxine requirements in patients with hypothyroidism undergoing renal transplantation

Hypothyroidism is common in the renal failure population and is both influenced by the onset of renal failure and its correction with renal transplantation. We report a series of 20 consecutive patients on oral thyroxine, in which restoration of renal function following transplantation resulted in reduced thyroxine requirements. We speculate that iodide excess, reduced bioavailability, and drug interactions may have contributed both to their hypothyroidism and the increased requirements for thyroxine in these patients while on dialysis. Failure to recognize the changes following renal transplantation may result in significant morbidity.

Changes in trough levels of whole blood cyclosporine and graft function of a kidney transplant recipient with onset of hypothyroidism after transplantation

The immunosuppressive and toxic effects of cyclosporine (CsA) are affected by many factors. We present the first case of a kidney transplant patient who had an onset of hypothyroidism about two months after the transplantation. In this case, trough levels of whole blood CsA and total serum cholesterol levels increased at the same time. But the decrease in renal function was not as severe as expected from the very high trough levels of whole blood CsA. Elevation of the trough level of whole blood CsA may be due to a decrease in CsA clearance resulting from the decreased cytochrome P-450 activity in hypothyroidism. Furthermore, a decrease in thyroid hormone level and increase in plasma lipoprotein level might have affected the distribution of CsA, and this change might have influenced the toxic effect of CsA In conclusion, our case suggests that thyroid function and plasma lipoprotein level should be considered important factors that affect the pharmacokinetics and action of CsA.