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The middle molecule hypothesis in perspective
Abstract:
The middle molecule (MM) hypothesis states that molecules in the molecular weight range of 500 to 2000 daltons/molecule accumulate in uremia and are one cause of peripheral neuropathy. Evidence for and against this hypothesis is reviewed and evaluated. The course of events in the core of early hemodialysis patients who developed neuropathy provides important support ofr the hypothesis. Failure of early peritoneal dialysis patients to develop neuropathy suggested that the peritoneum is more permeable to MM's than early hemodialysis membranes, a fact that was later hemodialysis membranes, a fact that was later confirmed by appropriate investigations. Several investigators have demonstrated that MM's actually do accumulate in uremia and disappear rapidly following a renal transplant, which suggests a high clearance by the human kidney. Retrospective and prospective studies have demonstrated a protective effect of residual renal function against MM intoxication. Our prospective studies to produce MM intoxication are reviewed and their strengths and weaknesses delineated. Similarly, the investigations of others that are cited as evidence against the MM hypothesis are reviewed. It is the opinion of hte authors that the weight of evidence supports the validity of the MM hypothesis; but that final proof still is lacking. A protocol for more definitive studies is discussed.
Insights
The middle molecule (MM) hypothesis suggests that accumulating MM in uremia causes neuropathy. Evidence supports this, showing MM clearance by kidneys and dialysis, but definitive proof is still needed.
Area of Science:
- Nephrology
- Uremia Pathophysiology
- Neurology
Background:
- The middle molecule (MM) hypothesis proposes that molecules of 500-2000 daltons/molecule accumulate in uremia, causing peripheral neuropathy.
- Evidence for and against the MM hypothesis has been reviewed and evaluated.
- Uremic neuropathy is a significant complication in patients with kidney failure.
Purpose of the Study:
- To review and evaluate the evidence supporting and refuting the middle molecule (MM) hypothesis of uremic neuropathy.
- To assess the role of MM accumulation in the pathogenesis of peripheral neuropathy in uremia.
- To discuss the implications of MM levels in relation to dialysis efficacy and residual renal function.
Main Methods:
- Review of existing literature and clinical observations.
- Evaluation of early hemodialysis and peritoneal dialysis patient data regarding neuropathy development.
- Analysis of studies investigating MM accumulation and clearance in uremia, post-renal transplant, and with residual renal function.
Main Results:
- Early hemodialysis patients developing neuropathy provided support for the MM hypothesis.
- Peritoneal dialysis patients' lack of neuropathy suggested higher peritoneal membrane permeability to MM compared to early hemodialysis membranes.
- MM accumulation in uremia was demonstrated, with rapid disappearance post-renal transplant, indicating high renal clearance.
Conclusions:
- The weight of evidence supports the validity of the middle molecule (MM) hypothesis in uremic neuropathy.
- Residual renal function appears to have a protective effect against MM intoxication.
- Further definitive studies are required to conclusively prove the MM hypothesis, and a protocol for such studies is discussed.