The isoprenoid pathway produces three key metabolites: endogenous digoxin (membrane sodium-potassium ATPase inhibitor, immunomodulator and regulator of neurotransmitter/amino acid transport), dolichol (regulates N-glycosylation of proteins) and ubiquinone (free radical scavenger). The role of the isoprenoid pathway in the pathogenesis of sarcoidosis in relation to hemispheric dominance was studied.

The isoprenoid pathway-related cascade was assessed in patients with systemic sarcoidosis with pulmonary involvement. The pathway was also assessed in patients with right hemispheric, left hemispheric and bihemispheric dominance for comparison to find out the role of hemispheric dominance in the pathogenesis of sarcoidosis.

In patients with sarcoidosis there was elevated digoxin synthesis, increased dolichol and glycoconjugate levels and low ubiquinone and elevated free radical levels. There was also an increase in tryptophan catabolites and a reduction in tyrosine catabolites. There was an increase in the cholesterol:phospholipid ratio and a reduction in the glycoconjugate level of red blood cell (RBC) membrane in this group of patients. The same biochemical patterns were obtained in individuals with right hemispheric dominance. In individuals with left hemispheric dominance the patterns were reversed.

Endogenous digoxin, by activating the calcineurin signal transduction pathway of T cells, can contribute to immune activation in sarcoidosis. An altered glycoconjugate metabolism can lead to the generation of endogenous self-glycoprotein antigens in the lung as well as other tissues. Increased free radical generation can also lead to immune activation. The role of a dysfunctional isoprenoid pathway and endogenous digoxin in the pathogenesis of sarcoidosis in relation to right hemispheric chemical dominance is discussed. All the patients with sarcoidosis were right-handed/left hemispheric dominant according to the dichotic listening test, but their biochemical patterns were suggestive of right hemispheric chemical dominance. Hemispheric chemical dominance has no correlation with handedness or the dichotic listening test.

This study assessed the changes in the isoprenoid pathway and its metabolites in seizure disorder (ILAE classification – I generalized – idiopathic generalized epilepsy with age-related onset – epilepsy with generalized tonic clonic seizures on awakening) and the metabolic cascade produced by isoprenoid pathway dysregulation.

The following parameters were assessed in seizure disorder: isoprenoid pathway metabolites, tyrosine and tryptophan catabolites, glycoconjugates metabolism and red blood cell (RBC) membrane composition.

There was elevation in plasma HMG-CoA reductase activity, serum digoxin and dolichol and a reduction in RBC membrane Na-K+ ATPase activity, serum magnesium and ubiquinone levels. Serum tryptophan, serotonin, strychnine, nicotine and quinolinic acid were elevated while tyrosine, dopamine, morphine and norepinephrine were decreased. The total serum glycosaminoglycans and glycosaminoglycan fractions (except dermatan sulfate), the activity of glycosaminoglycans (GAG) degrading enzymes and glycohydrolases, carbohydrate residues of glycoproteins and serum glycolipids were elevated. Total serum cholesterol, LDL cholesterol and free fatty acids were increased while HDL cholesterol and triglycerides were unaltered. The concentration of membrane hexose, fucose, cholesterol and phospholipids in the RBC membrane decreased significantly but the total RBC membrane GAG was unaltered.

Epileptogenesis could be due to a dysfunctional isoprenoidal pathway and paroxysmal hypothalamic digoxin hypersecretion.

The isoprenoid pathway was assessed in 15 patients with chronic fatigue syndrome (CFS). The pathway was also assessed in individuals with differing hemispheric dominance to assess whether hemispheric dominance has any correlation with these disease states.

The isoprenoid metabolites – digoxin, dolichol and ubiquinone – RBC membrane Na+-K+ ATPase activity, serum magnesium and tyrosine/tryptophan catabolic patterns were assessed. The free radical metabolism, glycoconjugate metabolism and RBC membrane composition were also assessed.

Membrane Na+-K+ ATPase activity and serum magnesium levels were decreased while HMG-CoA reductase activity and serum digoxin levels were increased in CFS. There were increased levels of tryptophan catabolites – nicotine, strychnine, quinolinic acid and serotonin – and decreased levels of tyrosine catabolites –dopamine, norepinephrine and morphine – in CFS. There was an increase in dolichol levels, carbohydrate residues of glycoproteins, glycolipids, total/individual glycosaminoglycans (GAG) fractions and lysosomal enzymes in CFS. Reduced levels of ubiquinone, reduced glutathione and free radical scavenging enzymes as well as increased lipid peroxidation products and nitric oxide were noticed in CFS. The biochemical patterns in CFS correlated with those obtained in right hemispheric dominance.

The role of hypothalamic digoxin and neurotransmitter-induced immune activation, altered glycoconjugate metabolism and resultant defective viral antigen presentation, NMDA excitotoxicity and cognitive and mitochondrial dysfunction in the pathogenesis of CFS is stressed. CFS occurs in individuals with right hemispheric dominance.